Progress in Ion Exchange: Advances and Applications

Progress in Ion Exchange Advances and Applications

Progress in Ion Exchange Advances and Applications

Edited by

A. Dyer University of Savord, UK M. J. Hudson University of Reading, UK

P.A. Williams North East Wales Institute, Wrexham, UK

CHEMISTRY Information Services

The proceedings of the Ion-Ex '95 Conference, held at the North East Wales Institute in Wrexham, UK, September, 1995.

Special Publication No. 196 ISBN 0-85404-791-3 A catalogue record for this book is available from the British Library.

0 The Royal Society of Chemistry 1997

All rights reserved. Apart from anyfair dealingfor the purposes of research or private study, or criticism or review as permitted under rhe terms of rhe UK Copyrights,Designs and Patents Acr, 1988, this publication may nor be reproduced,stored or rransmirred, in anyform or by any means, withour the prior permission in writing of The Royal Society of Chemistry, or in rhe case of reprographic reproductiononly in accordance wirh rhe renns of rhe licences issued by rhe CopyrightLicensing Agency in the UK,or in accordance wirh the rems of rhe licences issued by rhe appropriate Reproduction Righrs Organization outside rhe UK.Enquiries concerning reproductionourside rhe renns stated here should be sent to The Royat Society of Chemistry at the address printed on this page.

Published by The Royal Society of Chemistry, Thomas Graham House, Science Park,Milton Road, Cambridge CB4 4°F. UK Printed by Great Britain by Hartnolls Ltd, Bodmin, UK

Preface This book is a record of a conference which is the fourth in the series held at NEW Wrexham. It brought together scientists with interests in the broadly based subject of ion exchange, with the aim to cover aspects of its application as well as advances in the theory of ion exchange. Professor David Shemngton opened the Conference with a special paper on ‘Polymer resins - synthesis and structure’. The other plenary speakers presented topical reviews on the areas relating to ion exchange in the context of the pharmaceutical industry and its use of macroreticular resins (C. Robinson, Glaxo), the use of ion exchange in environmentalclean-up (H. Eccles, BNF plc), ion exchange routes to novel nanoporous materials (D. J. Jones, University of Montpellier, France), ion chromatographyand capillary electrophoresis for the determination of inorganic ions (P. Haddad, University of Tasmania) and ion exchange in zeolites, detergency and catalytic systems (L. V. C. Rees, University of Edinburgh). The contributed papers expanded on these general themes. The conference also contained a Workshop on the nomenclature of ion exchange led by J. Lehto and R. Harjula (University of Helsinki) who found that the diversity of interests shown by the participants helped to promote progress in this area. The Organising Committee is grateful for the support of its sponsors and both The Society of Chemical Industry and The Royal Society of Chemistry Analytical Division as well as the host institution for its much appreciated help. Dr Alan Dyer: Chairman, Ion Ex ’95

MEMBERS OF THE ORCANlSlNG COMMITTEE *Prof M Abe

Tsurouoka National College of Technology, Japan

Mr E R Adlard

RSC (N W Region), UK

Dr C Bainbridge

Dow Chemicals, UK

*Prof U Costantino

University of Perugia, Italy

Dr A Dyer (Chairman)

University of Salford, UK

Dr H Eccles

BNFL Ltd, UK

Mr J Greene

Consultanf UK

Dr H Greenwood (Treasurer)

BNFL Ltd, UK

*Prof P Haddad

University of Tasmania, Australia

Dr M J Hudson

University of Reading, UK

Mr H Hughes (Secretariat)

Newtech, UK

'Mr T Itagaki

Mitsubishi Kasei Corporation, Japan

Dr P Jones

University of Plymouth, UK

Mr T Jones

Waters Ltd, UK

Dr W Jones

University of Cambridge, UK

*Mr B Joyce

Dionex Corporation, UK

M r B WKing

Phase Separations Ltd, UK

*Dr J Lehto

University of Helsinki, Finland

Dr P Lcvison

Whatman International, UK

*Dr A Marton

University of Veszprem, Hungary

Mr D Naden

Purolite International Ltd

Mr M Parker

Beckman Instruments (WK) Ltd

Mr D Ryder

FMC Process Additives, UK

*Dr G K Saldadze

Research Institute for Plastics, Russia

Dr K Tittle

Consultant, UK

Dr N Truslove

Zeneca Specialities,UK

MrKWhitC

Merck Ltd, UK

Dr P A Williams (Secretariat)

North East Wales Institute, UK

Supported by the Royal Society of Chemistry, North West Region (Analytical Division) and the Society of Chemical Industry. ('Denotes corresponding member)

Contents PREFACE

V

-

PART 1 Novel Materials and Novel Applications

Polymer Resins - Synthesis and Structure D C Sherrington

3

Ion Exchange Routes to Novel Nanocomposite materials D J Jones and J Rozibre

16

Synthesis of layered Titanium (I V) Phosphates and Phosphonates by Direct Precipitation from Titanium (111) Solutions M A Villa-Garcia, E Jaimez, A Bortun, C Trobajo, M Sudrez, R Llavona, J R Garcia and J Rodriguez

30

The removal and Solidification of Iodide Ion using a new Inorganic Anion Exchanger H Kodama

39

The Utilisation of Hydrothermal Altered Power Plant Ashes in the Ion Exchange Processes D Kalousek, H Kusa, I Svetlik, F Kovanda, E Prochazkova and J Hrazdira

48

Polyelecfrolyte Complexes Between a Weak Polyanion and a Strong Polycation with Cationic Groups in the Main Chain

53

S Dragan, M Cristea, C Luca and B C Simonescu

Counterion Binding on Cationic Polyelectrolyfes with Cationic Groups in the Main Chain S Dragan, L Ghimici and F Popescu

62

An Unconventional Synthesis of Strongly Basic Anion Exchangers C Luca, V Neagu, G Grigoriu and B C Simionescu

70

Amphoteric Polyelectrolytes with Carboxybetainic Groups C Luca, E Streba and V Barbiou

78

Anionic Ion Exchangers as Phase Transfer Catalysts in Alkylation Reactions F Varona, F Mijangos, J I Lombrana and M Diaz

87

...

Progress in Ion Exchange: Advances and Applications

Vlll

Reagentless Separation of Electrolyte Mixtures using Ion Exchange Resins NB Ferapontov, H T Trobov, V I Gorshkov, L R Parbuzina, N L Strusovskaya and 0 T Gavlina

96

Analytical Selectivity of Membrane Electrode Based on Salicylaldoxime Formaldehyde Resin H Vardham and L P Singh

104

PART 2

- Ion Chromatoaraphv and Electrophoresis

Ion Chromatography and Capillary Electrophoresis for the Determination of lnorganic Anions - Current Status and Relative Merits P Haddad

115

Ions in Ink Jet Dyes by Capillary Electrophoresis and Ion Chromatography S C Stephen and N J Truslove

124

The Determination of Tetraphenyl Phosphonium in the EARP MAC Permeate Stream by Ion Chromatography S Aitken

133

Separating the Sample from the Matrix. An Insight into New Column Design: A Review of Cation Exchange Columns 1975 to present S L Somerset

137

Ionization Control of Metal-Chelate Separation in Ion Chromatography P Hajos, 0 Horvath, G Revesz, J Peear and C Sarzanini

144

Water-Eluent Based Ion Chromatography on Silica Bonded Molecular Baskets J Glennon, B Lynch, K Hall, S J Harris and P O'Sullivan

153

Potential Uses of Capillary Ion Electrophoresis In the Nuclear Power lndustry N J Drew

160

Improved Separation and Detection of lnorganic Ions by Capillary Electrophoresis K Divan

176

ix

Contents

Decontamination of Arsenic-Containing Aqueous Solutions Using Inorganic Solvents. lnvestigation of the Arsenic Species in Solution by Means of Capillary Electrophoresis J M Galer, R Delmas and C Loos-Neskovic

187

-

PART 3 Resins as Biosorbents Applications of Non-Functional Macroreticular Resins C Robinson

199

Desalination of Specific Immunoglobulins by Microporous Neosepta Membranes: Role of lonogenic Groups M Bleha, G Tishchenko, Y Mizutani and N Ohmura

211

Chromatographic Strategy in Bioprcduct Purification J H Creedy

219

lodinated Resin and Its Use in Water Disinfection L E Osterhoudt

227

Removal of Metals from Dilute Aqueous Solutions by Biosorbents K A Matis, A I Zouboulis, LV Ekateriniadou, I C Hancock, T Butter and A N Philipson

235

-

PART 4 Ion Exchanae for Environmental Clean-UP

lor?Exchange - Future ChallengedOppotfunitiesin Environmental Clean-Up H Eccles

245

Uptake of Radioisotopes onto Cerium Phosphate A Dyer and A K J Jasem

260

Utilization of Hydrous Crysfalline Silico-Titanates (CSTSs) for Removing Cs+from Nuclear Aqueous Waste R G Anthony, 2 Zheng, D Gu and C V Philip

267

The Determination of Curium - 242, 243 and 244 in

275

Process Waste Streams using Extraction Chromatography G Cunningham

Fixation of Radioactive Caesium on Copper Hexacyanoferrates S Ayrault, C Loos-Neskovic, M Federoff, E Garnier and D J Jones

279

X

Progress in Ion E-xchange: Advances and Applications

Isolation of Caesium from Fission Product Waste Solution on a New Granular Inorganic Exchanger - Titanium Phosphate-Ammonium Phosphomolybdate (TIP-AMP) G S Murthy, V N Reddy and J Satyanarayana

289

Preparative Separation of Caesium and Rubidium from Alkali Metal Mixtures using Phenol-Formadehyde Ion Exchange Resins V A Ivanov, V I Gorshkov and I V Staina

298

The Role of Temperature in Ion Exchange Process of Separation and Purification V A Ivanov, N V Drozdova, V I Gorshkov and V D Tirnofeevskaya

307

Equilibrium Studies of the Application of Polymeric Resins Aggregated with Calcium Alginate F Mijangos and Y Jodra

31 4

Oxidative Regeneration of Sulphonic Resins for the Prevention of Chromium(ll1) Accumulation F Mijangos, M P Elizalde and M K Kebdani

323

Adsorption of Phenolic Compounds from Multicomponent Solutions onto Polymeric Resins F Mijangos, A Navarro and M Martin

332

Application of Microanalytical Techniques to Ion Exchange Processes of Heavy Metals Involving Chelating Resins F Mijangos and L Bilbao

341

Reagentless Concentration of Copper from Acidic Mine Waters by the Dual-Temperature /on Exchange Technique D Muraviev, J Noguerol and M Valiente

349

Treatment of Silver-bearing Waste-Waters using Ion Exchange Celluloses P R Levison, N D Pathirana and M Streater

357

STDS Study of some Commercial Anion Exchange Resins A Marton, G Mascolo, G Petruuelli and G Tiravanti

365

Separation of Chromium with a Fibrous Ion Exchanger J Lehto, T Laurila, H Leinonen and R Koivula

372

Adsorption-Elution Behaviours of Lightly Crosslinked Porous Amidoxime Resins for Uranium Recovery from Seawater N Kabay and H Egawa

378

xi

Contents

Selective Ion Exchange Separation Processes without Reagent Regeneration A A Zagorodni and M Muhammed

383

-

PART 5 Ion Exchanae in lnoraanic Materials and its Theory

Ion Exchange in Zeolites: Detergency and Catalytic Systems

393

1 V C Rees Anion Exchange in Cooper Hydroxy Double Salts C S Bruschini and M J Hudson

403

The Extraction of the Hexamminecobalt(l1l) Cation by Kanemite (NaH[Si,O,(OH)J. 2H20):Enhanced Extraction in the Presence of a Cationic Surfactant M T J Keene, J A Knowles and M J Hudson

412

Uptake of Rh(ll1) by PZimnium Phosphate and its Intercalation Compounds with Heterocyclic Bases C Ferragina, P Cafarelli and R di R o w

421

Application of NMR for Interpretation of Ion Exchange Selectivities M Abe, Y Kanzaki and R Chitrakar

430

Harmonisation of Ion Exchange Formulations and Nomenclature: What can be done? R Harjula and J Lehto

439

The Significance of the Term Ideal in the Thermodynamics of Electrolyte Solutions and Ion Exchangers D G Hall

448

The Natural Convection in the Dynamics of Ion Exchange and Sorption from Solutions V I Gorshkov and N B Ferapontov

457

Simulation of Multicomponent Ion Exchange Dynamics in the Case of Dissimilar Diffusivities N A Tikhonov, R Kh Khamizov and D A Sokolsky

463

Non-Ion Exchangeable Interaction of Electrolytes and Ion Exchange Resins V I Gorshkov, N 8 Ferapontov, L R Parbuzina, H T Trobov, N L Strusovskaya and 0 T Gavlina

470

xii

Progress in Ion Exchange: Advances and Applications

Influence of the Nature of the Co-Ion on the Equilibrium Distribution of Eiectrolyfes Between the Solution and Ion Exchanger L R Parbuzina, H T Trobov, N B Ferapontov, V I Gorshkov, N L Strusovskaya and 0 T Gavlina

479

Multi-component Counter-Current Ion Exchange Chromatography N P Nikolaev, V A lvanov and V I Gorshkov

486

Subject Index

495

Part 1 Novel Materials and Novel Applications

POLYMER RESINS - SYNTHESIS AND STRUCTURJ2

D.C. Sherrington Department of Pure and Applied Chemistry University of Strathclyde 295 Cathedral Street Glasgow G1 lXL 1 INTRODUCI’ION

Although styrene-divinylbenzene resins, and pamcularly the ion exchangers derived from them, have been readily and widely available for over thirty years, their further development,characterisation and exploitation continues unabated’ in an incnaSing number of fields. This has been stimulated in particular by the drive to produce cleaner processes and hence meet inCreesingly strict mvhnmcntal demands. The present paper will describe work primarily from the author’s own l a h a t m y and will cover results lbm the mimscopic characterisation of conventional resins in the “wet” state, data from a state-of-the-art solid state I3C NMR study of chlmethylated resins, recent developments of reactive resins containing epoxide, thiirane and phenolic functions,data fromwork on improving the capacity of chelakg ion exchange resins via the use of a functionalcomonomer, and a progress report on the development of resins with extnmely high thmmo-oxidative stability. Time limitarim will p v e n t any details of applications being given, but an indication of areas of exploitationwill be included as appropriate.

1.1

Macroporous PdystyrendDivinylbenzeneResins

These sphexical particulate materials typicaUy 100-1OOO pm in diameter are prepared by suspension polymerizaton methodologies? A great deal of work has been carried out to try and quantify the detailed morphology of these porous species, and to relate this to the conditions employed in polymerization. Seminal miem have been published by Albrigh? and Guyot‘ and a generally accepted model is shown in Figure 1. Despite this it has proved very difficult to relate ab inirio the pc&mmce of a resin (e.g. as a hydraphobic sorbent’) to the conditions used in resin synthesis, and indeed to resin parameters such as surface area, pore size,pore volume, etc. Undoubtedly one of the problems has been that resin morphology is generally characterised using “dry‘‘ resins, whereas in practice resins are used in the “wet” state. As a result there has always been a suspicion that morphological changes might occur, even when a “rigid hydrophobic” sorbent is hyhted., and hence the “wet” performance correlation with “dry“ parameters might be expected to break down. Manufacturersof resins have known for some time that solvent tnatment can influence morphology even after polymerization is complete, and now this “rearrangement”of the porous structure has been quantified6

4

Progress in Ion Exchange: Advances and Applications

Eigugl

Schematic representationof the structure of a macroporous resin.

We have recently used state-of-the-art electron mimscopic and image analysis techniques to evaluate resin ultrastructures in both the ‘‘dry” and “wet” state? Table 1 shows a matrix of styrenedivinylbemne resins prepared with high levels of crosslinker and a “good” solvating porogen, toluene, in order to produce high surface area resins. . . electron mimgraphs (TEM) were obtained on unstained mimtomed lkammum sections (70nm) using contrast enhanced procedures on a Zeiss 902 electron mimscope at 80 kV.

3h!kI

Feed Composition and Surface Areas of Resin Sorbents”’

Solvent

PS55X

PS8OX

0.5T 1T

Divinyl benzene (vol%)

Volume ratio m-. p-Ethylvinylbenzene (~01%) toluene porogen to comonomers

p-.m-

55

45

p-,m-

80

20

2T 3T 0.5T

1T 2T 3T PSl00X 0.5T

1T PS2OX

2T 3T 1ET

0

P-, m100 p-,m-

20

0.5 1 2 3 0.5 1

2 3 0.5 1 2

1Sb’

a) From Nzsorption,BET method,b) styrene 64 ~01%;c) 2ethylhexanol

Surface area of resin (mz g-’)

103 609 655 759 561 587 738 870 530 370 450 487 68

Novel Materials and Novel Applications

5

Specimens were prepared in three ways: a) vacuum-dried and embedded, b) freeze-dried from the wet frozen state and embetide4 and c) sectioned directly in the wet frozen state with no embedding. These samples are designated “dry”, “freeze-dried” and “frozen”, respectively (see reference 7 for more details). Images for pore s t r u m analysis were collected at 20,OOO magnification on a video camera and then subjected to non-sophisticated image analysisprocedures. Figure 2 shows the pore -parameters

Resin sorbent pore profile cross-sectioMlparameters: A=area; d=marimwn diameter; w=marinuunwidth;p=perimeter.

used to characterise quantitatively each pore examined. The pore profile cross-stctional area A, should correlate most closely with conventionally determined pore volume data; the pore profile perimeter parameter, p, with conventionally determined pore surface m and the pore profile diameter, d, with conventionalpore diameter. Figure 3 shows a histogram in which the sum of pore profile areas (pm2) (5 pore volume) is correlated with resin composition data. From this it is clear that the pore volume, seen to inmase in the photomicrographs (see reference 7), does indeed do so as the volume of porogen is inmased 0.5 + 3 in the 55 and 80% crosslinked series. This agrees with earlier findings.’ However, the -100% crosslinked series is quite anomalous with the pore volume frryine as the level of porogen is inThis is rather difficult to explain. Clearly in the 55X and 8OX series the morphology stems to evolve according to the model detailed by Guyot i.e. crosslinked nuclei are formed at low conversion and interbonding occurs between these as polymerization continues. As the proportion of solvating pomgen is increased interbonding is progressively reduced and the final sorbent possesses a larger total pore volume. A similar trend is seen in the average pore diameter and the morphology in the 55X and 8OX series might be regarded as forming under thennodynamic control. The situation with the lOOX series (Figure 3) is quite different, however, and with the lowest level of porogen (0.5 toluene) it seems that the very high level of divinylbenzene gives rise to the very rapid generation of a highly rigid, stmined and dense matrix of crosslinked polymer chains even at low conversion, which quickly “locks-in” a well defined pore structure. Indeed, the situation probably corresponds quite closely to the case when a precipitating porogen is used, and the pore structure arises h m kineric rather than thennodynamic conaol. As the proportion of toluene porogen is increased the whole process of pore fonnation is probably increasingly delayed by more extensive solvation, and as a result a more u n i f m evolution of nuclei and interbonding occurs, with a closer adherence to the Guyot model: In many respects therefore the matrix formed with 100% pdivinylbewne and volume ratio of toluene porogen of 0.5 has similaritieswith Davankov’s hypemosslinked resins?

Progress in Ion Exchange: Advances and Applications

6 W

0 Dry resin Freeze-dried (decreow) Freeze-dried (increosel

”

@me 3

051 I01 2 0 1 301

051 I01 201 301

0 5 T I01 201 301

PS55X

PS80X

PSIOOX

Total pore profile areasfor dry and freeze-dried resin samples.

Figures 3 also show the changes in pore volume determined for the “freeze-dried” resins and in most cases there is clear evidence for these “hydmphobic” resins swelling significantly when wet. The effect is largest for the species with the larger “dry” pore volumes, and in the extreme cases total pore volume increases by -40%. Almost certainly therefore hydration allows considerable internal adjustment to the morphology, probably via plasticization of polymer chains and, in particular, the relief of steric suain. Again the effects are probably related closely to those seen on hydration of hypercrosslinked resins, when swellingis readily observed as a macroscopic change? With such changes occunkg therefore, it is not surprising that correlation of e.g. sorbent performance with dry resin parameters has been poor, but now there is an opportunity to make such correlation with more appropriate data from hydrated resins. Photomicrographsfrom three “frozen” resins examined without embedding procedures (PS55XIT,PSlOOXIT and PSZOXIET) (see reference 7) show even larger swelling effects for the fist two resins but only minor changes for the latter. This negative result with PSZOXIETtends to confirm the validity of the technique since this highly rigid and entangled matrix prepared under precipitating conditions would be expected to react least to be hydrated. The results from “frozen” resins suggest that the quantitative data produced for the “freeze-dried” samples probably represent lllinimal swelling values, and that in the real wet state pore volumes and diameters are even larger. Note that the validity of our TEM technique has also been confirmed by detailed correlation of the derived porosity data (dry state) with that obtained from mercury porosimeny data on the same samples.’o Note also that ‘‘apparent” bulk morphological information obtained from Scanning elecmn micrographs (SEM)can be misleading because this technique images primarily surfaces, and the resolution it offers is usually too low to probe ultrastructure.””* 1.2

Chloromethylationof Polystyrene Resins and Methylene Bridging

Chloromethylationof polystyrene resins is of course a key chemical modification in the synthesis of anion exchange resins.13 For almost as long as this reaction has been

7

Novel Materials and Novel Applications

exploited the imparuint side mction of methylene bridging has been known to occur. It has, however, proved very difficult to make a qu&&g structural analysis of this reaction. Instead manufacturers have tended to use bulk physical paramem, such as swelling and water content, to specify their resins. Control of the initial divinyl benzene content of resins and of the chlmmethylation reaction is then used to meet specifications consistently. We have now been able to use state-of-the-art solid state 13C nuclear magnetic resonance (NMR) specmscopic techniques to Quantifv the level of methylene bridging typicaUy occurring in resins analogous to those produced by ion exchange man~facturers.'~care^ analysis of the aromatic carbon resonances in the strong base form of the exchangers produced by amination (using NMe3) of the c h l d y l a t c d precursors shows a much higher level of quaternary (fully substituted - no H substituents) carbons than expected from the monomer feed composition and the -CH2Cl content. These additional quaternary carbons can arise only from the presence of mthylene bridges (orrelated additional msslinks). Quantitative evaluation of the data indicates that -50-6096 of pendent aromatic groups are subject to methylene bridging with the lower levels arising with use of a weaker Lewis acid in the chlmmethylation naction. These levels seem very high, CeRainly much higher than previously anticipated. However, the data Seems very robust and it is difficult to interpret the spectra in any other way. It stems therefore that our view of the chemical structure (and possibly the uluastructure) of ion exchangers, particularly anion ion exchange resins, may need to be radically altered. This work14 also allowed the reaction of residual double bonds (from the crosslinker) which occurs concurrently with chlmmethylation to be probed. Overall the carbon resonancesobserved suggest the side reaction shown in Figure 4 to be operative.

Q

Q, 7

+,cH3 1

Eigud

Reaction of residual double bonds during chloromethylationof polystyrene resins

This picture differs in detail from that proposed earlier" but conceptually the views are similar.

1.3

Resins containing oxirane (epoxide)", thiirane (episulfide)" and phenol1a functions

Epoxide containing resins based on glycidyl methacrylate (GMA) crosslinked with ethylene pycol dimethaaylate (EGDMA) are well known and have been widely y? some * exploited, indeed it seems that some materials are now available oamma~lall applications are favoured by resins with a high surface area, and to generate the latter usually requires high levels of msslinker with a solvating porogen. This then automatically limits the maximum GMA content that can be used. We have explored the use of uimcthylolpropane trimethacrylate (TRIM) as a mfunctional crosslinker to rtplace

Progress in Ion Exchange: Advances and Applications

8

EGDMA, in an effort to achieve high surface areas resins with simultaneously a high GMA content.16 Table 2 summarises the resins synthesised. It can be seen from these results that the copolymerization of GMA and TRIM with different porogens yields a wide variety of polymers. Some of the resins i.e. those made in octan-2-one, n-butyl acetate, p-xylene, toluene and cyclohexanol-dodecan-1-01 9/1 v h , show high porosity, while the beads made in benzonitrile and cyclohexanone were found to be non-porous. Both the B.E.T. surface area and the pore volume were found to decrease with increasing GMA:TRIM ratio in the monomer mixture when the cyclohexanol-dodecan-1-01mixture was used as the porogen. The pore volume also decreases with increasing monomer:porogen ratio in the organic phase. The B.E.T. surface area is a maximum at monomer:porogen = 1:2. Perhaps most importantly of all using n-butyl acetate and octan-Zone as the porogen, resins with substantial surface areas are indeed achievable (170-175 rn'g-') while maintaining a GMA content of 50%. Chemical modification and exploitation of GMA resins is usually via ring o p h g of the epoxide yielding an hydroxyl group on the p carbon atom (Figure 5). This generates some hydrophilicity in the resin. It occurred to us that the sulfur analogue of a GMA resin would offer great potential for producing novel resin structures, and indeed Kalal ef a?' remarked on this earlier. The organic chemistry literature indicates that epoxides can be converted directly to thiiranes by treatment with thiourea or thiocyanate.22This also turns out to be so with GMA based resins (Table 3).17 Table 2

Physical and structural parameters of the GMAITRIM polymers

-

GMA:TRIM M:P

~~

solvent

pore vovcm3g-'

CyCl-dod 9/1 CyCl-dod 9/1 CyCl-dod 9/1 CyCl-dod 9/1 CyCl-dod 9/1 cctan-1-one octan-2-one octan-2-one octan-2-one n-butyl acetate p xylene p xylene toluene ethyl acetate bermnitrile cyclohexanone dodecan- 1-01

0.38 1.28 1.13 0.57 1.12 0.65 1.31 0.97 1.86 1.27 1.50 1.47 1.02 0.66 0.07 0.16

1:l 1 :2 1 :2: 1:2 1:3 1:l 1:2 1:2 1:3 1:2 1:2 1:2 1 :2 1 :2 1 :2 1 :2 1 :2

surface area' mz -1

P

_=3

1:l 1:3 1:l 3: 1 1:l 1:l 1:l 3: 1 1:l 1:l 1:l 3: 1 1:l 1:l 1:l 1:l 1:l

surface area" rnz -1

d

121 339 140 41 128 127 174 39 149 170 139 2 145 110 <1 0.2 d

144 267 223 130 120 173 245 73 225 199 266 51 192 176 44 82 d

=_/

M:P = monomer:porogen; b determined by NZ adsorption according to the B.E.T. method, determined by mercury porosimetry; not determined, very fine powder. a

9

Novel Materials and Novel Applications

Table 3 Influence of solvent on the conversion of GMA resin into its thiirane analogue"

furan waterdioxane (1/1 volhol)

8.3

2.6

68

--

-_

--

--

(8.5

2.7 3.3

71) 87)

90

7.5

2.4

63

( 10.7b

60% G W G D M A resin; [reagent] = 1 mol dm-3;reagentlepoxy groups = lO/l; 24 h; 90°C of thiourea in The most favourable procedure involves reaction water catalysed by dilute sulfuric acid. Resins containing up to 3 mmol g" of thiitane groups are readily prepared. The resultant thiirane resins are very reactive, and in particular a range of simple aliphatic amines and moles have been immobilised via ringopening of the thiirane ring. (Figure 5). Toluene has been shown to be the best solvent of those examined, and in this case the reaction is clean, generating 1 mol of thiol group for every azole attached (Table 4), in keeping with the simple mechanisticpicture.

QMI

,x

CO2CH2CH-CH2

-

x=o,s

Immobilisation of azole ligands on GMA and thiirane resins The recent commercial availability of p-acetoxystyreneZ now makes the synthesis and exploitation of phenolic-based resins an attractive proposition, and such species might provide a versatile alternative precursor to chloromethylatedpolystyrene resins. Ledwith et a P utilised this monomer some time ago but the resins were resmcted to a nominal phenol content of -10% and crosslinking to -1.5%. We have now shown that a range of macropomus and gel-type species are readily accessible with an acetoxy group content of -1540% and levels of crosslinking -2-20% (Figure 6)(Table 3.''

10

Progress in Ion Exchange: Advances and Applications

& +

0

6 4 6 p

NBr

Br

\

N A N

AAcl

c1

Figure 6

Synthesis and Chemical Modijication of p-Acetoxystyrene Resins

i) AIBN, 80°C, 6h; ii) NH2NH21.5H20,50"C,24k iii) Cl&OCVpyridine, 80°C, 12h; iv) Brz/Bu,N, 5OoC, 12 h; v) NaOH, cyanuric chloride, O"C, 2 days; vi) 2-(aminomethyl)pyridine,50°C, 3 days.

Novel Materials and Novel Applications

11

WJd Immobilisation of azole groups on GMA and thiirane resin.4’

a. Using optimised procedure in text; b. based on azole introduced.

nlm

Synthesis of Resins Based on pdcetoxystyrene (AS)

a) AS = p-acetoxystyrene; S = styrene; DVB = technical divinylbenzene(mol%); b) 2-ethylhexanol porogen; c) toluene porogen Hydrazinolysis of the acetoxy resins offers a facile and high conversion hydrolysis route to the free phenolic function independently of overall functional group loading, with phenol contents of up to -3 mmol g-* being readily achieved. Further chemical modification of the phenol function has also been examined. Reaction with bromine is essentially quantitative, and attachment of dichlorotriazineresidues occurs specifically by a single linkage even for heavily loaded resins. Subsequent displacementof chloride from the triazine residues by 2-aminomethylpyridine is again essentially quantitative (Figm 6).

Progress in Ion Exchange: Advances and Applications

12

These reactions demonstrate the ease and cleanliness of chemical modification of these msins, and illustrate the potential for their exploitation. 1.4

Ligand-modified monomer

The introduction of a specific chemical group e.g. a ligand onto a resin can be achieved by a series of reactions m m g a precursor resin or alternatively via synthesis of the resin using a comonomer already derivatised with the group of interest. The "pros and cons" of these approaches have been discussed before." Suffice to say that the use of functionalised comonomen is costly and inconvenient, and as a result is generally poorly exploited in practical terms. Recently we synthesised a chelating resin containing the pyrazole ligand, 3,5-dimethyl-l-pyrazole,which was attached via an ethoxy link to a GMA-based resin.26The latter had an epoxy content of -4.2 mmol g-I. Despite a number of attempts the ligand content achieved never exceeded -0.25 mmol g-I. Non-quantitative conversion of epoxy groups is generally observed but the efficiency in this case was particularly low, and not well understood. For comparison monomer, I, (Figure 7) was synthesised and then used to prepare a resin. Employing the same level of I replacing GMA and the same level of crosslinker and porogen as in the GMA resin preparation, an analogous resin with ligand loading of -2.0 mmol g-' was obtained, i.e. approaching an order of magnitude higher. Interestingly this resin shows a very unusual and s i m c a n t selectivity for the complexation of Ni2+in competition with a'+, Cuz+and Co2+at pH >2. At p H 4 it shows selectivity for Cd2+(probably as CdCli and Cdm").The low capacity of the conventionally prepared resin does not allow this selectivity to be clearly developed.

GMA

Figure 7

1.5

Synthesis of ligand-containingmonomer I

Thermo-oxidatively Stable Resins

One potentially very important area where considerable scope remains for the technological exploitation of polymer resins is in the supporting of homogeneous transition metal complex catalysts?' The advantages such systems might provide have been well documented,' but perhaps the most important features are: i) efficient metal retention and hence high purity in product streams; ii) flexibility for use in gas and liquid phase reactions; and iii) opportunities for simpllfylng plant requirement (e.g. continuous reactive separation processes in a single column reactor) and hence sigdicant cost

Novel Materials and Novel Applications

13

reduction. Although there is broad interest in the types of catalyst which might be i m m o w there is a particular drive towards developing selective oxidation catalysts where the substrate might be an alkene, alkane or arene. For application in highly oxidising environments conventional resins based on polystyxnes and polymethacrylates will be of limited use since they are stable only up to -200°C. In contrast polymers such as polybenzimidamles2' and polyimides29 are stable to -500°C in air and -700°C in nitrogen. These therefore represent attractive candidates for exploitation as resin catalyst supports in oxidation reactions. For practical application such polymers should be in the form of porous particulates. We have now prepared polybenzimida~oles~~ in this form by carrying out the polycondensation of an aromatic tetraamine with an aromatic diacid, catalysed by polyphosphoric acid, in suspension in paraffin oil at -230°C. The suspension was stabilised using an oil soluble p o l p e r such as the copolymer of maleic anhydride with octadec-1-ene to provide steric stabilisation. Typically the surface atea of the product is rather low eventually solid particulates are formed. These can be collected, washed and dried in the usual way. Materials prepared by this method have higher porosity and a surface 8 c t ~of -30 m'g'. The resins have been used to immobilise Pd(II) complexes as higher alkcne Wacker oxidation catalysts where air is the and also to immobilise Mow) complexes as alkene epoxidation catalysts where t-b~tylhydroperoxide~~' is the oxidant. In the latter case a polymer-supported catalyst with high activity and selectivity in propylene epoxidation has been developed. This is also exmmely stable with essentially no metal leaching and as a result is attracting industrial interest In the case of polybenzimidam> le particulates the precursor chemicals are, however, rather costly and the dispersion polycondensation reaction inconvenient (e.g. temp. -230°C) and difficult to control repducibly. In contrast the synthesis of particulate polyimides involves much lower cost precursors, and a dispersion polycondensation which runs at -60°C. and is relatively robust and +dble?' A wide range of particulate polyimides have now been produced and some control of morphology has been possible. Porous species with surface areas up to -90 m2g-l have been achieved3' Direct exploitation of polyimide particulates as catalyst supports is unfortunately not possible because the simple mmatic polyimides, unlike the polybenzimidrur> les, have no inherent structural unit that can function as an electron donor or a ligand, We have therefore been actively pursuing the synthesis of functionpolyimides, the immobilisation of metal complexes on these resins, and their use as oxidation catalysts?' We hope to report on these in due course.

Summary The area of resin synthesis and development remains a very active one, with extensive work being pursued on conventional resins as well as entirely novel systems. While

14

Progress in Ion Exchange: Advances and Applications

manufacturers continue to make important developmental improvements to existing resins, the number of lower volume speciality species continues to increase as well. With the number of application of resins expanding the area of resin development promises to remain a key one for the foreseeable future. Deciding exactly where the technology ‘‘prizes’’ will be won is very Micult to predict, but that “prizes” will be won is assured!

Acknowledgement The author would like to thank the Organising Committee of ION-FX95 for the opportunity to present this lecture, and his hardworking co-workers cited in the various refemces for their efforts in making it all possible.

References 1. 2. 3. 4. 5.

6.

7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

D.C. Sherrington, “Polymer-supported Synthesis” in “Chemistry of Waste Minimisation”,Ed, J.M. Clark, Blackie Publishers, Glasgow, U.K.. 1995 in press. See Appendix, Eds. P. Hodge and D.C. Sherrington, in “Polymer-supported Reactions in Organic Synthesis”,p.469, J. Wiley and Sons, Chichester, 1980. R.L. Albright, React. Polym., 1986,4, 155. A. Guyot in “Syntheses and Separations Using Functional Polymers”, Eds. D.C. Sherrington and P.Hodge. Chap. 1, p.1, J. Wiley and Sons, Chichester, 1988. B. Rowatt and D.C. Shenington “Synthesis and charactexisation of resin sorbents for cephalosphorin C recovery” in “Ion Exchange Advances”, Ed. M.J. Shter, Elsevier App. Sci., London, 1992,p.128. J. Hradil, F. Svec, E. VotavovB, M. Bleha, Z. Pelzbauer and J. Brych, Polymer, 1992,33,1731. I.M. Huxham, B. Rowatt, D.C. Shemngton and L. Tetley, Polymer, 1992, 33, 2769. J.R. Millar, D.G. Smith, W.E. Man and T.R.E. Kressman, J. Chem. Soc., 1963, 128. V.A. Davankov and M.P. Tsyurupa,React. Poiym., 1990,13,27. I.M. Huxham, L. Tetley, B. Rowatt and D.C. Sherrington,J . Marer. Chem., 1994, 4,253. F.M.B. Coutinho and D. Rabelo, Europ. Polym. J., 1992,28,1553. LM. Huxham, L. Tetley and D.C. Sherrington,Europ. Poiym. J., 1994,30,67. K. Dorfner, Ed. “Ion Exchangers”. Walter de Gruyter. Berlin, 1991. R.V. Law, D.C. Sherrington, C.E. Snape, I. Ando and H. Korosu, Ind. and Eng. Chem. Res., 1995, in press. J.P.C. Bootsma, B. Eling and G. Challa, React. Polym., 1984,3, 17. P.D. Verweij and D.C. Sherrington,J. Marer. Chem., 1991,1,37 1. B.D. Moore, D.C. Sherrington and A. Zitsmanis, J. Muter. Chem., 1992,2,1231. H. Deleuze and D.C. Shemngton, J. Chem.Soc., Perkin ZI, 1995, in press. See refs. 1 and 2 in ref. 16. Macro Prep (MP) from Biorad, Richmond, California, USA. J. Kalal, F. Svec and V. Marousek, J. Polym. Sci., Polym. Symp., 1974,47, 155. D.D. Reynolds and D.L. Fields in “HeterocyclicCompounds with Three and Fourmembered Rings”. Part 1 of “The Chemistry of Heterocyclic Compounds” ed. A. Weissberger, Wiley, New York, 1964, Chap. 111, p.576.

Novel Materials and Novel Applications

23. 24.

15

p-Acetoxystyrene Monomer Product Bulletin, Hoechst-Celanese, Dallas, Texas, USA. R. Arshady, G.W. Kenner and A. Ledwith, J. Polym. Sci.. Polym. Chem., 1974,

12,2017. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.

D.C. Sherrington in ‘mghValue Polymers”, Ed. A.H. Fawcett, Roy. Soc. Chem, London 1990,p.1. P.M. van Berkel and D.C. Sherrington,Polymer, 1995,in press. F.R.Hartley, “Supported Metal Complexes”, Reidel Pubs., Dordrecht, 1985. A. Buckley, D.E. Stuetz and G.A. Serad in “Encyclopedia of Polymer Science and E n g i n e g ” , Eds. H.F. Mark, N.M. Bikales, C.C. Overberger, G. Menges and J.I. Kroschwitz, Vol. 11, p.522,J. Wiley and Sons, New York, 1988. M.I. Bessonov, M.M. Koton, V.V. Krudrgavtser and L.A. Laius, “Polyimides Thermally Stable Polymers”, Plenum Press, New York,1987. T. Brock and D.C. Sherrington,Polymer, 1992.33.1773. H.G.Tang and D.C.Shenington, Polymer, 1993,34,2821. H.G.Tang and D.C.Sherrington,J. Cuzul., 1993,142,540. H.G.Tang and D.C. Shenington, J. Molec. Cutul., 1994,94,7. M.M. Miller and D.C. Sherrington, J. Chem.SOC.,Perkin 2,1994,2091. M.M. Miller and D.C. Sherrington, J. Cotal., 1995,152,368and 377. T. Brock and D.C. Sherrington,J. Muter. Chem., 1991,1,151. T. Brock D.C. Sherrington and J. Swindell,J. Muter. Chem., 1994.4,229. J.H. Ahn, J.C. Kim and D.C. Sherrington, unpublished results.

-

ION EXCHANGE ROUTES TO NOVEL NANOCOMPOSITE MATERIALS

Deborah 3. Jones and Jacques Rozikre Laboratoire des AgrCgats MolCculaires et MatCriaux Inorganiques, URA CNRS 79, UniversitC Montpellier 2, 34095 Montpellier cedex 5 , France

1 INTRODUCTION

The modification of open-structured two- or three-dimensional hosts by ion exchange is an increasingly powerful route to the synthesis of (mu1ti)functional bidimensional or entrapment-type nanocomposite solids. The functionality enhanced or induced ranges from electrical (ionic or electronic) properties to the introduction of significant accessible porosity in a layered system. In many cases, the porous material then defines a new three-dimensional arrangement modifiable in turn by ion-exchange or intercalation. Clearly the nature of the ion-exchanged species influences the ultimate properties of the resulting nanocomposite and we will concentrate here on the derivatization of bidimensional systems: the development of organic polymer and inorganic gel intercalates and associated protonic conduction properties; the use of redox intercalation with electron donor molecules (aniline, TTF) as a route to electronically conducting organic-inorganic materials; the use of ion exchange and intercalation in the synthesis of precursor solids to pillared layered structures. In general terms, layer structured crystals may be classified into those molecular solids where the layers carry no charge, as in TaS,, MOO,, MPS, etc., and those having charged (positive or negative) layers, with which are associated anion and cation exchange properties respectively, Figure 1. The best known anion exchangers are the layered double hydroxides [Mr~,~xM~1(OH)2]X+[~-x,.nH,0]X~ and hydroxy double salts M"M'"(OH),X, where X is an exchangeable anion: C1, NO,, OAc etc. Smectite clays, layered titanates and niobates, metal(1V) hydrogen phosphates and silicic acids are typical cation exchangers, which are also solid acids when the exchangeable cation is the proton. Indeed, ion exchange with inorganic layered materials can be perceived in the more general framework of ionic mobility and ion transferhransport. Layered compounds often display high, water-assisted, protonic conductivity. Ion exchange or intercalation in solid acids can be accompanied also by a charge transfer process ('redox intercalation'), which is the dominant mechanism operative in the case of insertion into an neutral matrix.

-

17

Novel Materials and Novel Applications

neutral layers: molecular solids

ion-exchangeablesolids anionic layer

-

-

M”+

-

-

M”+

-

-

-

M”+

-

M”+

-

cation exchanger

cationic layer

r+

+ + I 0 0 0

I+ +

+I

0 0 0

I + +

+I

anion exchanger

Figure 1 Schematic representationof molecular and ion-exchangeables o l a 2 BULK ION EXCHANGERS

Before describing the synthesis, characterisation and properties of a number of bidimensional nanocomposites, we briefly turn our attention to two bulk ion exchangers. These examples have been chosen because they reflect the association referred to above between ion exchange properties arising from high ionic mobility or charge transfer characteristics and functional materials. Layered zirconium hydrogen phosphate is a typical inorganic ion exchanger, the proton being exchanged for monoand di-valent ions as well as more complex polynuclear species. It is also known to be a proton conductor, both in its crystalline and amorphous forms. Spinel lithium manganate, as its lithium-extracted derivative known as “2.-MnO,”, is a highly selective sieve for Li+. Both direct ion-exchange and electron transfer processes are involved in the lithium extraction/reinsertion reactions and lithium manganate is finding use as a lithium insertion electrode material in rocking chair batteries. In addition, the X-ray absorption study on spinel lithium manganate described below illustrates particularly well the detailed information that can be obtained by the use of probe spectroscopic techniques on inserted transition metal oxide phases. 2.1 Zirconium hydrogen phosphate

Zirconium hydrogen phosphate, ZrP, is the starting point for all of the intercalates subsequently considered. It crystallises in two modifications known as a and 1). The structure of a-ZrP was determined by Clearfield in 1969.’ The inorganic layers are formed by a plane of octahedral Zr atoms which are linked together alternately above and below via phosphate groups. Three oxygen atoms of the phosphate group are coordinated in this way, and the fourth bears the hydrogen atom. Subsequent refinements of the structure? as well as spectroscopic3 studies, enabled the location of hydrogen to be described with certainty as being covalently bonded to the phosphate

Progress in Ion Exchange: Advances and Applications

18

groups and not transferred to the interlayer water molecule. In the absence of dominant steric effects, all the protons are exchangeable. The interlayer distance is 7.6 A. The ion exchange properties of a-ZrP have been studied in great detail by Clearfield4and Alberti? whilst its intercalation chemistry was developed from the mid-seventies onwards by Costantino.6 The structure of y-ZrP is formed by two planes of zirconium atoms each linked to a central layer of PO, groups and outer layer of dihydrogen phosphate groups.'** Two important consequences arise from this difference with respect to the a-structure, firstly, that yZrP has a rigid layer arrangement and, secondly, that its ion-exchange properties are usually limited to 50% of the cation exchange capacity. Ion exchange or intercalation lead to an increase in basal spacing, and the judicious use of aliphatic amines or alcohols of various carbon chain lengths provides a means of controlling the degree of expansion in a precursor phase. On intercalation, the guest molecule will adopt a parallel or perpendicular orientation depending both on its degree of loading and the nature and extent of its interaction with the layers above and below. 2.2 Lithium manganate The chemical extraction of lithium from spinel lithium manganates gives manganese dioxide phases which retain the spinel structures of the parent materials and which are highly selective as sorbentsfor lithium in aqueous environments.'The mechanisms involved in the extraction and insertion processes - ion exchange andlor electron transfer reactions involving oxidation and reduction of manganese - have been under discussion for some years.'O Recent studies suggest that different processes operate depending on the stoichiometry of the lithium manganate phase. Lithium extraction in aqueous acid from the mixed valence stoichiometric LiMn20, is believed to occur mainly by the redox reaction: 4LiMn111Mn1V0,+ 8H+->

3Mr1'~,0, + 4Li+ + 2MnZ++ 4H,O

(1)

but in the case of the compound Li4/3Mn5n04,which contains no Mn"', a mechanism has been proposed in which lithium ions exchange with protons:

The manganese oxide phases obtained fix aqueous lithium ions by reinsertion into the spinel lattice, which behaves as a selective sieve. The reverse processes may be formulated: Mn1V204 + n LiOH -> Li, Mnl*',,Mn" 2-n 04 + n/2 H 2 0 + n/40, 3H4/3Mn1V5,04 + n Li+-> 3H4/3~,nLi,,Mn'V5/304 + n H+

(3)

19

Novel Materials and Novel Applications

Determining the oxidation state of manganese before and after lithium extraction/ reinsertion is essential for the identification of the dominant mechanism. Few techniques are adapted, X-ray photoelectron spectroscopy has been used to provide information on the oxidation state of manganese atoms at the surface." For the bulk, the recent use of X-ray absorption near-edge spectroscopy (XANES)has given definitive evidence that cation-cation ion exchange dominates when Li4nMn,n04 is acid washed (lithium extraction) and when A-MnO, is treated with LiOH (lithium insertion) but that electron transfer occurs when LiMn"'MnNO4 is used as a precursor.

t

t

I

0

10

20

30

40

!

E-E,, (ev)

Figure 2 X M E S spectra andfirst derivativesfor (a) LiMn204 and (b) L&l3Mns1304: parent compounds (dots),lithium-extractedsamples (opencircles),and lithium-reinserted samples (crosses).Spectra of a-MnzO3 (dashed line) and /I-MnOz (solid line) are also shown. Figure 2 shows the XANES region of the parent spinel phases and acid washed and lithium reinserted samples of Li,nMnSnO, and LiMnlllMnlVO,.No shift in the main edge structurecan be seen in the spectra of the formerwhich indicates that the processes of lithium extraction and reinsertion are not accompanied by changes in the oxidation state of MnN. However, the reversible shift of 3 eV observed in the position of the rising absorption edge in the spectraof LiMn"'Mn'"0, is compatiblewith an oxidation/ reduction process on extractionlreinsertion respectively. In addition, the average oxidation state for manganese in LiM%O, can be estimated as 3.5 from the shape and intensity of the pre-peak labelled A in Figure 2a, in agreement with the presence of equimolar Mn"' and MnIV.Further details are given elsewhere.I2

Progress in Ion Exchange: Advances and Applications

20

3 FUNCTIONAL INTERCALATION NANOCOMPOSITES

3.1 Nanocomposites with electrical properties

3.Z.I Polymer intercalation compounds, High conductivity can be induced in polyethers, polyimines and polyamides by doping with protons13or alkali metal ions,14 but the utility of these polymer electrolytes is restricted by their water solubility. Inclusion of the polymers in a layered host matrix provides a means of recourse by protecting the polymer from the environment. Different strategies have been devised using a-ZrP, including intercalation of the polymer from aqueous s o l ~ t i o n , ~either ~.'~ directly or into a pre-expanded host phase, interlayer polymerisation of ion-exchanged monomer^,'^ and a one-step reaction involving the grafting of polymer chains during synthesis of the layered host.I7 Interlayer polymerisation provides an excellent example of the degree of structural control which becomes possible in intercalation chemistry. The surface properties of the inorganic host are decisive in determining the orientation and positioning of the guest. E-aminocaproic acid is a 6-carbon atom aminoacid bearing the two functional groups at positions a and 0. Refluxing an aqueous solution with a - Z r P suffices to give a well-crystallised intercalate of interlayer spacing 16.5 A, in which a fully protonated monomer HO,C(CH,),NH,+ can be identified using infrared (IR) spectroscopy. The expansion of almost 10 A and chemical analysis showing ca. 0.8 mole insertearnole a-ZrP suggest that a monomer of inserted aminoacid is formed, having a tilted orientation with respect to the layers. On heating, several plateaux were observed in the thermogravimetric trace, and the material was recovered after heating at various temperatures in order to identify any new phases formed. Interlayer water is lost up to 12OoC, which leads to a dehydrated phase of interlayer spacing 15.2 A. Loss of organic matter between 210 and 26OOC reduces the organic content to 0.5 mole/mole a-ZrP, and is accompanied by an interlayer reorientation, since the basal spacing determined from X-ray diffraction drops to 10.6 A, a value characteristic of organic molecules lying parallel to the layers. The most significant reaction occurs at 27OOC however; above this temperature bands in the IR spectrum identifying the C0,H and -NH, groups are replaced by amide I and amide I1 bands, indicating

t

16.5

m 2

J Figure 3 Schematic representationof aaminocaproic acid-a-ZrP intercalate and the occluded nylon-6phaseformed in situ on heating

Novel Materials and Novel Applications

21

polyamide formation, in this case, interlayer nylon-6. The head-to-tail orientation of protonated aminocaproic monomers in the precursor phase can be considered to be conducive to the polymerisation process by placing in proximity -q and HO,Cgroups which undergo condensation under appropriate conditions of temperature, Figure 3. The IR spectra of the phases before and after thermal treatment, and that of the materials recovered after destruction of the inorganic matrix with HF are shown in Figure 4. It is of interest to note the coalescence of the amide I and I1 bands (1600, 1545 cm-I) in the nanocomposite and their separation in the extracted polymer, and to compare the spectra with those of a bulk nylon/phosphoric acid blend.18Thus, whereas bulk pristine nylon shows well separated amide I and I1 absorptions, those given by a blend of nylod0.67 %PO, form a broad massif. We conclude that hydrogen bonding interactions between the amide group and the dissociated protons in H,PO, are a close model for those in nylodzirconium hydrogen phosphate nanocomposites. This is supported also by comparison of the proton conduction properties of the bulk and nanocomposite phases. Nylond-umvrnmbma (an-') ZrP has a conductivity at 7O0C/10O0Cof 1200 2600 2800 3600 2.lO-, Scm-', comparable to that of the bulk system.18 Figure 4 IR spectra of

(4~ ~ - i ~ ~ ~ ~ ~ ~ , ~ 5 ~ ~ J I , ,

3.1.2 Interlayer 'gels'. The ion- (b)ZrP-[(-CH,)5CONH-)aJ exchange of [A1',04(OH),,. 12H,0I7+, (c)polymerexnocredfrom(b)by destrucprepared by basic hydrolysis of AlCl,, with tion of the phosphate matrix

pre-inserted butylammonium in a-ZrP was first described by Clearfield and Roberts,l9 who used the intercalate obtained as a precursor to an alumina pillared layered phosphate. The proton conduction properties of both the intercalation and pillared phases, prepared according to the published method, have been investigated in our laboratory. The conductivity of the 'All,' intercalate increases as a function of temperature but is, in particular, a function of the relative humidity, showing a sigmoidal dependence. The conductivity measured at 100 % RH and 8OoC, cu. lo-, Scm-l?o is amongst the highest reported for inorganic protonic conductors. Here, the

22

Progress in Ion Exchange: Advances and Applications

hydroxyaluminium species can be considered to form a highly hydrated gel-like interlayer network, which may be continuous with traces of surface aluminium oxyhydroxide which would play a binding role and reduce grain boundary resistance.

3.1.3 In situ polymerisation of electroactive polymers. Aniline, pyrrole, thiophene and acetylene have been polymerised over the past 5 years in situ in two- and threedimensional host matrices, amongst which may be cited iron oxychloride?' divanadium pentoxide?2 mordenite and ~eolite-Y?~, MoSY. MCM41u etc. This formation of hybrid organic-inorganic systems represents a new development in research on conducting polymers. Different methods have been used to induce polymerisation of pre-inserted monomers: uv or thermal treatment e.g. on acetylenic guest molecules, electron transfer reaction, either with the host matrix or with an exchanged redox centre, or by use of an external oxidant, e.g. ammonium persulfate. The last two methods were used in attempts to polymerise aniline C,H,NH, in a and y-zirconium phosphate. Aniline readily intercalates into these substrates, and spectroscopic characterisation using IR, Raman and inelastic neutron scattering techniques have allowed a detailed description of the interlayer anilinium ion.% However, when these aniline-ZrPphases are treated with (NH4),(S,0,), ion exchange occurs with ammonium ion and surface polymerisation of aniline occurs. Greater success is achieved by using a partially Cu(I1)-exchanged phase, ZrCu,H,,(P04),.4H,0, in which Cu(II) serves as an oxidant." Redox intercalation of aniline with Cu(I1) derivatives of a and y-ZrP gives rise to blue and green coloured materials respectively. The interlayer distance is increased with respect to that in the ZrCu,H,~,(P04),.4H20 precursors and, in some experiments, copper particles were observed to be expelled. Figure 5 shows the IR spectra of the materials prepared. Bulk polyaniline typically shows characteristic absorption bands at 1302, 1496 and 1578 cm-'. Absorption at these wavenumbers can be seen also in the spectrum of y-ZrPCu(I1)-aniline, Figure 5(a). The band at ca. 1300 cm-' is of particular utility in characterising the polymer since its position is senstive to the degree of electron

I

1200

1400

1600

I

1800 1200 1400 wavenumber (cm-I)

I

I

1600

Figure 5 IR spectra of (a)yZrP-Cd'-Cp$fH, (b)a-ZrP-Ctc"-CppH2

I

I

1800

I

Novel Materials and Novel Applications

23

delocalisation at the C-N bond, and it reflects, therefore, the chain length of the polymer.28In the spectrum of the nanocomposite prepared using a-ZrP,this band is very weak, and is replaced by one at 1396cm-', associated with the presence of radical cations of 3-4units. Evidence for the formation of shorter chain oligomers is seen also in the y-ZrP composite, from the co-presence of absorption at 1401 cm-'. Diffuse reflectance spectra in the visible region also support the conclusion that oligomerisation occurs both in a-and y-ZrP, but that it is only in the latter that an electron delocalised system is formed, compatible with the presence of polymeric aniline. The conductivity measured on disks of compacted powder is ca. lo-' Scm-l, far below the values obtained on bulk doped polyaniline. Several reasons contribute, the most important of which include the limited polymer conjugation and the absence of percolation effects. High electronic conductivity has been demonstratedin e.g. FeOCV polyaniline, where the partial reduction of Fen*in the layers provides a mixed valence host lattice, and in fluorohectorite/polypyrrolefilms?9 where the conductivity in directions parallel and perpendicular to the layers was shown to differ by a factor l@. 3.1.4 Assembly of ITF in ZrP. We have recently explored the use of layered inorganic hosts as macroionic electronic acceptors to provide a matrix that imposes a segregated stack structure upon organic Ic-donors such as those derived from tetrathiafulvalene, "F.30 Such segregation is known to be crucial in determining the properties of lowdimensional conductors. Our first attempts made use of the mixed valence salt ("F)3(BF,)2, which undergoes ion exchange with y-ZrP to give a well-crystallised phase of interlayer spacing 19.7 A. Confirmation that the inserted TTF is completely ionised was obtained from Raman spectroscopy,where the position of the line arising from central (C=C) stretching is known to be sensitive to the extent of charge transfer from TTF (1415cm-' in TTF+and 1515 cm-' in the neutral molecule)?l In a second stage,precursorphases containing Cun (0.035- 0.50 mole/mole y-ZrP) were used in reaction with neutral TTF, a strategy which proved to enable the synthesis of a series of redox intercalates, the TTF content of which c increases with the degree of Cundoping E in the precursor. Furthermore,the extent of charge transfer as determined from Raman spectroscopy was also seen to depend upon the initial Cu" concentration. The spectra of two 1470 1450 1430 1410 1390 1370 samples prepared from precursors wavmurnber (an-') containing 0.035 and 0.21 mole Cu"/ Figure 6 Rmnan spectra of (a)TTF' and redox mole y-ZrP are shown in Figure 6 and intercalatespreparedfrom(b) ZrPdoped with compared with that of TTF+. For the 0.21 ??Wk cu"/??Wh? ZrP ( C ) 0.035 m O k Cd'I former, of maximum at 1439 cm-', the mole ZrP charge is estimated as 0.77+. For the

-E

24

Progress in Ion Exchange: Advances and Applications

latter, more than one partial oxidation state is stabilised, since a maximum at 1422 cm-' and a shoulder at 1439cm-' are simultaneouslyobserved, corresponding to charges of 0.93+ (dominant) and 0.77+ (minor). Most interestingly, the conduction properties of the nanocomposites are also seen to be a function of the extent of copper doping. At room temperature, ZrHl,(PO4),.(TTF),,.2~O (prepared by ion-exchange, charge +1 on TTF) has a conductivity of lo"." Scm-'. For samples prepared by redox intercalation, the conductivity is higher by up to two orders of magnitude, and increases with decreasing degree of charge transfer. ZrH,~92(P04)2(TTF0~77+)o,l.0.9H20 has the highest conductivity, Scm-'. These values are in the semiconductor range, but it is significant that the conductivity is higher for compounds containing little intercalated organic electron donor suggesting that the conductivity conferred on the (insulating matrix + conducting guest) composite by is particularly high. Pre-insertion of varying amounts of Cu" is therefore a route to the modulation of the extent of charge transfer within a certain range, and is directly responsible for the electrical properties of the intercalates. This is the first time that such a relation has been shown for an intercalation compound and provides a good example of how materials manipulation can give functional nanocomposites.

m.77+

3.2 Porous Solids Layered compounds potentially have a very high surface area which is not, however, generally accessible unless the layers are propped open by permanent spacers. For aZrP, nitrogen BET measurements reveal an accessible surface area of cu. 5 m2g-' only, although the calculated value is 960 m2g-'. Intercalation or ion exchange is a necessary first step in the synthesis of porous solids from layered compounds. The expanded phase obtained is subsequently treated thermally or chemically to remove specific groups (organic, hydroxyl) and graft the core of the intercalated species to the layers to form a pillared layered structure (PLS). scheme 1: layered solid ion exchange

intercalation

J

grafting process

pillared &rnpound

expansion

partial contraction open-structured solid

Scheme 1 PLS materials are finding application as heterogeneous and supportedhomogeneous

25

Novel Materials and Novel Applications

catalysts, for sorptionlseparation processes and environmental and solid state applications, in particular as sensors. The extent of intercalation or ion-exchange in the first stage in scheme 1, predetermined by the charge density characteristics of the layered host, is a key factor which dictates whether or not the ultimate PLS solid will be porous or simply crosslinked. Scheme 2 summarises the consequences of low (as in smectite clays) and high (as in metal(1V) phosphates) layer charge density: non-clay substmes

mectlte clays

low layer charge density

high layer charge density

swell in water

not possible

pillaring by direct reaction

no direct intercalation

with aqueous solution of inorganic crosslinking

---> must pre-expand e.g. butylamine/Al,,'* competition 7 pH ?

species

crowded interlayer

inserted species are well-spaced

Scheme 2 3.2 .I Synthesis of silica-pillared zirconium phosphate. An example is provided by the synthesis of silica-pillared phosphates using aminopropylmethoxysilane. Under appropriate conditions of hydrolysis in waterlethanol, condensation of the silanol groups occurs to give octameric aminopropylsiloxane species32in which the basic hnctionalities serve to enable intercalation into the solid acid mamx, and the siliconoxygen framework plays the role of inorganic pillar.33 Each -POH group in a-ZrP occupies a surface area of 24 A2. The approximate lateral dimension of the cubic octamer is 11.2 A, and a cube face carrying four organic side-arms occupies a surface area of approximately 125 A2. A covering effect is therefore expected to limit the uptake of the guest siloxane to (4 x 24J125) x 100 = 77% of the total cation exchange capacity. Indeed, a ratio of intercalated silicon to layer phosphorus atoms of 0.8 is observed experimentally. The interlayer distance of 17.7 A determined from powder X-ray diffraction agrees with the insertion of a single octamer layer. After calcination above 5OOoCin air, organic functions are removed, and the interlayer spacing falls to 12 - 13 A. However, although cross-linked through Si-0-P bonds?' silica-pillared ZrP formed in this way is non-porous, due to complete filling of the interlayer region at the intercalation stage.33 Synthesis of porous solids from a-ZrP therefore requires the development of a strategy which spaces the pillars laterally in the interlayer region. Imposing greater steric crowding (e.g. co-intercalation of a bulky, expendable organic molecule) is one

26

Progress in lon Exchange: Advances and Applications

possibility; another is reduction of the layer charge density by post-synthetic treatment of a-ZrP with m e t h ~ l a m i n e This . ~ ~ method allows replacement of HPO, by OH groups giving a modified ZrP of lower cation exchange capacity: Z r ~ 0 , ) , , ( 0 H ) , , . n ~ 0 . The reduction of the layer charge density has two effects, both of which are favourable to the formation of porous solids, viz. (i) lower uptake of octa(aminopropy1)-siloxane and (ii) a tendency for the guest molecules to arrange themselves i n a bilayer, so potentially increasing the internal surface area, Figure 7. Porous solids of BET surface area more than Q P-OH 300 m2g1can be prepared using Zr(HPO,), octa(aminopropy1)siloxane x(OH)2x.n%0with x = 0.4 - 1.0. Furthermore, T Zr-OH variation of the degree of reduction in CEC would seem to provide a route to the Figure 7 Schematic representation of modulation of interlayer micro- and meso- layered Zr(HPO,),.x(OH),x and porosity, with more mesoporous materials flocculation from a colloidal suspenbeing prepared as the degree of reduction in sion i n the presence of CEC is increased towards 50%.36 aminopropylsiloxane.

3x

3.2.2 Characterisation of chromia-pillared ZrP using X-ray absorption spectroscopy. In common with other ion-exchanged or intercalation compounds, pillared layered solids are difficult to characterise structurally. Despite the dimension ‘added to the layered structure brought about by permanent pillaring, powder XRD patterns are still those characteristic of two-dimensional solids with direct information limited to the interlayer spacing. In this context, the use of a probe spectroscopic technique capable of providing structural information concerning the environment of specific elements is of particular value. Intercalation from chromium acetate solutions into colloidal a-ZrP leads to a series of precursor phases of interlayer spacing dependent on the [Cr3+]concentration in sol~tion.~’The hypothesis that the hydroxyoligomers inserted vary with regard both to their nuclearity and charge was confirmed using EXAFS spectroscopy at the chromium edge.38 The Fourier transformed EXAFS spectra of two phases having interlayer distances 17 A and 34 A are shown in Figure 8(a). For the former, the result from curve fitting: 6 oxygen atoms at 1.97 A and 2 chromium atoms at 3.06 A is compatible with a cyclic mmer structure, Figure 8(b).For the more expanded phase formed at higher [Cr3+]concentration- in solution, two chromium atom shells of different Cr---Cr distance are included in the second peak in the Fourier transform, in agreement with the presence in this phase of a more complex tetramer, Figure 8(c).

27

Novel Materials and Novel Applications

c Figure 8 (a) Fourier transformed EXAFS spectra of two precursor phases to chrom'a pillmdphosphates (b)hydroxychromiwn trimer ( I 7 Aphase) (c)hydroxychromiwn open tetramer (34 A phase)

Porous materials are formed by calcination of the precursors above 400°C, but crystallinity is progressively lost such that at 800°C the compound is amorphous to X-rays. For the pillared solid formed at 400°C, EXAFS was able to provide evidence for a pillar to layer Cr-0-P interaction, and showed that the local structure around chromium closely resembles that in chromium oxide, suggesting that the pillars are formed of 'chromia nanoparticles'.The local structure around chromium is substantially modified by calcination at 800°C, with dominant Cr---P interactions at distances close to those in a-CrPO, suggesting some degradation of the zirconium phosphate mamx.

4 CONCLUSIONS

Ion-exchange and intercalation are increasingly useful routes to functional twodimensional nanocomposites. Depending on the intercalant molecule used, various properties can be induced either directly or after further chemical modification (grafting, polymerisation). Non-exhaustively,these include conductivity,high internal surface area and porosity, molecular sieving, catalysis, chiral recognitiod9 and photosensitivity. Combination of the 'porous solids' and 'insertion/formation of polymers' aspects leads to the concept of nano/nanocomposite solids and a new form of controlled reactivity at the nanometer scale.

28

Progress in Ion Exchange: Advances and Applications

References 1. 2. 3. 4. 5. 6.

7. 8.

9. 10.

11. 12.

13.

14. 15. 16. 17.

18. 19. 20. 21.

22. 23.

A. Clearfield and G. D. Smith, Znorg. Chem. 1969,8,431. J. M. Troup and A. Clearfield, Znorg. Chem., 1977, 16, 33 11; J. Albertsson, A. Oskarsson, R. Tellgren and J. 0. Thomas, J. Phys. Chem..1977,81, 1574. D. J. Jones, J. Penfold, J. Tomkinson and J. Rozitre, J. Mot. Struct., 1989,197, 113. A. Clearfield, in 'Inorganic Ion Exchange Materials', ed. A. Clearfield, CRC Press, Boca Raton, 1982, Ch. 1. G. Alberti, Acc. Chem. Res., 1978, 11, 163; U. Costantino in ref 4. Ch. 3; G. Alberti and U. Costantino, in 'Intercalation Chemistry', ed. M. S. Whittingham and A. J. Jacobson, Academic Press, 1982, pp. 147 - 180; G. Alberti and U. Costantino, in 'Inclusion Compounds', ed. J. L. Atwood, J. E. D. Davies and D. D. MacNicol, Vol. 5, 1991, 136 - 176. A. N. Christiansen, E. Krogh Andersen, I. G. Krogh Andersen, G. Alberti, M. Nielsen and M. S. Lehmann, Acta Chem. Scand. 1990,44,865. D. M. Poojary, B. Shpeizer and A. Clearfield, J. Chem. SOC.Dalton Trans., 1995,111. Q. Feng, Y.Miyai, H. Kanoh and K. Ooi, Langmuir, 1992.8, 1861. X.-M. Shen and A. Clearfield, J. Solid State Chem., 1986,64,270; J. C. Hunter, J. Solid State Chem., 1981,39, 142; K Ooi, Y. Miyai, S. Katoh, H. Maeda and M. Abe, Langmuir, 1990,6,289. G. R. Bums, private communication. B. Ammundsen, D. J. Jones, J. Rozi5re and G. R. Burns, Proceedings of the International Conference on Ion Exchange, Takamatsu, Japan, December 4 - 6, 1995. J.-C. Lasstgues, in 'Protonic Conductors, Solids Membranes and Gels - Materials and Devices', ed. Ph. Colomban, Cambridge University Press, 1992, Ch. 20, pp. 311 - 328. T.Wong, M. Brodwin, B. L. Papke and D. F. Shriver, Solid State Zonics, 1981, 5,689. Y.Ding, D. J. Jones, P. Maireles-Torres and J. Rozi&re,Chem. Muter., 1995,7, 562. U. Costantino and E Marmottini, Materials Chemistry and Physics, 1993,35, 193. A. Clearfield and C. Y. Ortiz-Avila, in 'SupramolecularArchictecture: Synthetic Control in Thin Films and Solids', ed. T. Bein, A. C. S. Symp. Ser. 499, 1992, Ch. 14, pp. 178 - 193. J. Grondin, D. Rodriguez and J. C. Lasstgues, Solid State Zonics, 1995,77,70. A. Clearfield and B. D. Roberts, Znorg. Chem., 1988, 27,3237. D. I. Jones, J. M. Leloup, Y.Ding and J. Rozitre, Solid State Zonics, 1993,61, 117. M. G. Kanatzidis, C.-G. Wu,H. 0. Marcy, C. R. Kannewurf, A. Kostikas and V. Papafthymiou, Adv. Muter. 1990,2, 364. Y. I. Liu, D.C. DeGroot, J. L. Schindler, C. R. Kannewurf and M. G. Kanatzidis, J. Chem. SOC.Chem. Commun. 1993,593. P. Enzel and T. Bein, J . Phys. Chem., 1989,93, 6270; T. Bein and P. Enzel,

Novel Materials and Novel Applications

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Angew. Chem. Int. Ed. Engl. 1989,28, 1692.

24. 25. 26. 27. 28.

M. G. Kanatzidis, R. Bissessur, D. C. DeGroot, J. L. Schindler and C. R. Kannewurf, Chem. Muter., 1993,5,595; L. Wang, J. Schindler, J. A. Thomas, C. R. Kannewurf and M. G. Kanatzidis, Chem. Muter., 1995.7, 1753. C.-G. Wu and T. Bein, Science, 1994,264,1757. M.-H. Herzog-Cance, D. J. Jones, R. El Mejjad, J. Rozibre and J. Tomkinson, J. Chem. SOC.Faraday Trans., 1992,88,2275. D. J. Jones, R. El Mejjad and J. Rozi&e, in ref. 17, Ch. 16, pp. 220 - 230. F. Ueda, K. Mukai, I. Harada, T. Nakajima and T. Kawagoe. Macromolecules,

1990,23,4925. 29. V. Mehotra and E. P. Giannelis, Solid State lonics, 1992,51, 115. 30. R. Backov, D. J. Jones and J. Rozibre, J. Chem. SOC. Chem. Commun. 1995, in 31.

press. S. Matsuzkai, T. Moriyama and K. Toyoda, Solid State Communications, 1980,

34,857. 32. T. Cassagneau, D. J. Jones and J. Rozibre, J. Phys. Chem., 1993.97.8678. 33. J. Rozibre, D. J. Jones and T. Cassagneau, J. Muter. Chem., 1991, 1, 1081. 34. D. J. Jones, T. Cassagneau and J. Rozibre, in 'Multifunctional Mesoporous

35. 36.

37. 38. 39.

Inorganic Solids', ed. C. A. C. Sequeira and M. J. Hudson, Kluwer Academic, Dordrecht, NATO AS1 Ser. (2,1993, Vol. 400, pp. 289 - 302. G. Alberti and F. Marmottini, J. Colloid Interface Sci., 1993,157,513. T. Cassagneau, D. J. Jones, P. Maireles-Torres and J. Rozihre, in 'Synthesis of Microporous Materials: Zeolites, Clays and Nanostructures', ed. M.L. Occelli and H. Kessler, Marcel Dekker, New Yorlc, in press P. Maireles-Toms, P. Olivera-Pastor, E. Rodriguez-CastelMn, A. Jimdnez-Lt5pez and A. A. G . Tomlinson, J. Muter. Chem. 1991,1,739. D . J. Jones, J. Rozibre, P. Maireles-Torres, A. Jimbnez-Upez, P. Olivera-Pastor, E. Rodrfguez-Castell6n and A. A. G. Tomlinson, Inorg. Chem., 1995,34,4611. M. E. Garcia, J. L. Naffin, N. Deng and T. E.Mallouk, Chem. Muter. 1995.7, 1968.

SYNTHESIS OF LAYERED TITANIUM(1V) PHOSPHATES AND PHOSPHONATES BY DIRECT PRECIPITATION FROM TITANIUM(II1) SOLUTIONS M.A. Villa-Garcia, E. Jaimez, A. Bortun,’ C. Trobajo, M. SuArez, R. Llavona, J.R.Garcia, and J. Rodriguez* Departamento de Quimica Orghica e Inorghica, Universidad De Oviedo, 33071 Oviedo, Spain ‘Institute for Sorption and Problems of Endoecology of the Ukrainian Academy of Sciences, 32/34 Palladina Prosp., 252142 Kiev, Ukraine

1 INTRODUCTION Crystalline inorganic ion exchangers based on layered acid phosphates of polyvalent metals are known as high resistant and selective adsorbents for some radionuclides and heavy metal ions.’” In the last years it was found that layered phosphates of Group IV elements are able to form pillared structure^,'^ which arise now as promising materials for selective catalysis’ and, also, as multifunctional solids exhibiting a broad spectrum of physical and chemical Usually, layered acid titanium(1V) phosphates are formed by refluxing an amorphous titanium phosphate with H3P04,or by treating it with H3P04under hydrothermal condition^."^^ These compounds have also been obtained by slow decomposition of titanium-fluoro complexes in the presence of H3PO4.’* Using the latter procedure different titanium phosphates can be obtained, depending on the experimental conditions employed. The main inconveniences of this way of synthesis are the low rate of the process due to the stability of the fluorocomplexes, and the problems derived from the use of HF.” It is also known that crystalline titanium phosphates can be prepared by direct precipitation, using solutions obtained by dissolving metallic titanium in phosphoric acid.20In this case water soluble titanium(II1) phosphates are formed which, by oxidation in air, are converted into titanium(1V)phosphates, but this method requires the use of a large excess of concentrated H3P04, in addition, the process of titanium dissolution (without addition of catalysts) is very slow. Layered phosphonates of polyvalent metals have received a considerable attention for the last several years as new promising materials for ion exchange, shape selective catalysis, protonic conductors, selective adsorbents, etc?l-zs All these applications are possible due to their special properties which are based, mainly, on the existence of a well defined layered structure. There are two traditional methods of preparation of tetravalent metal phosphonates: a) slow decomposition of fluoro-complexes of Group IV elements in the presence of phosphonic acidz6and b) treatment of layered phosphates of Group IV elements with phosphonic acid.”” These methods were initially developed for the zirconium

Novel Materials and Novel Applications

31

compounds and latter applied in the synthesis of other metal phosphonates. It is clear now that both of them have some disadvantages, the main among them are the low crystallinity of the materials obtained, the large duration of the synthesis and the need to use HF. We have approached the preparation of layered titanium (IV) phosphates and phosphonates using a novel method of synthesis: direct precipitation from titanium(III) solutions. 2 EXPERIMENTAL

2.1 Reagents and Analytical Procedures

All chemical used were of reagent grade. The analysis of the concentration of phosphorus and titanium was carried out gravimetrically. Microanalytical data (C, H and N) were obtained with a Perkin-Elmer 240B elemental analyzer. Thermal analysis was performed in a Mettler TA 4OOO (TG50). The diffractometer used was a Phillips PV 1050/23 with CuKa radiation. The NMR spectra combined with magic angle spinning (abbreviated 31P-MASNMR)were obtained at 121.5 MHZ on a Brucker MSL-300 spectrometer. Rspectra were obtained on a Perkin-Elmer 1720-XFI' spectrometer. Nitrogen adsorption-desorption isotherms at 77 K were obtained using a Micrometics ASAP 2000 instrument with a turbomolecular Pump. 2.2 Preparation of Titanium(IV) Phosphates a-Titanium(1V) phosphate, a-Ti(HPO,),-H,O (a-TiP), was synthesized as follows: to 13 mL of 13% TiCl, placed in a plastic bottle were added 10.4 mL of 5 M H,P04 solution (PJTi4). The bottle was sealed and put an the oil bath with regulated temperature (60°C) for 2 days. To favour the oxidation of Ti(II1) the mixture was periodically stirred under air. Then, the solution was evaporated practically to dryness at the same temperature. The precipitate obtained was thoroughly washed with distilled water from the excess of reagents till pH = 3.54.0, and then dried at 50 OC. y-Titanium(IV) phosphate, y-Ti(H2P04)(P04).2H20(y-Tip), was synthesized as follows: to 13 mL of 13% TiC1, in a glass bottle were added 15.3 mL of 17 M H,P04 solution (P/Ti=17). The reaction mixture was refluxed 18 hours. The solid obtained was thoroughly washed with -distilledwater from the excess of reagents till pH = 3.5-4.0, and then dried at 50 "C. a-Titanium(1V) hydroxophosphate, a-Ti(OH),(HPO,)-H,O (a-Ti(OH)P), was synthesized as follows: to 13 mL of 13% TiCl, in plastic bottle was added 52 mL of 1 M H3P04solution (P/Ti=4). Then the bottle was sealed and put into the oil bath with regulated temperature for 5 days. To favour the oxidation of Ti(II1) the mixture was periodically stirred under air.The solution was evaporated practically to dryness at the same temperature. The precipitate obtained was thoroughly

32

Progress in Ion Exchange: Advances and Applications

washed with distilled water from the excess of reagents till pH = 3.5-4.0, and then dried at 50°C. 2.3 Preparation of Titanium(IV) Phosphonates a-Titanium(N) phenylphosphonate,a-Ti(03PC6H5)2 (a-TiPPh), was synthesized by reaction of phenylphosphonic acid with TiCl,. 60 mL of 1 M solution of phenylphosphonic acid were added to a solution containing 13 mL of 13% TiCI, and 12 mL of distilled water placed in a plastic bottle (PRi4.6). Then the bottle was sealed and the reaction mixture was treated at 80°C for 7 days. To favour the oxidation of Ti3' the reaction mixture was periodically stirred under air. The solution was evaporated at the same temperature (18 hours), the precipitate obtained was washed with distilled water from the excess of reagents, until the pH of the rinse was 4. The precipitate was air dried at 50°C. a-Titanium(1V) 2-~arboxyethylphosphonate, a-Ti(O,PGH4COOH), (aTiPCOOH), was synthesized by reaction of 2-carboxyethylphosphonicacid with TiCI,. 90 mL of 1 M solution of 2-carboxyethylphosphonicacid were added to a solution containing 26 mL of 13% TiC1, and 26 mL of distilled water placed in a plastic bottle (P/Ti=3.5). The reaction mixture was treated at 80°C for 7 days. The bottle remained open, and the evaporating water was periodically replaced. The precipitate obtained was centrifugated and washed with distilled water until the pH of the rinse was 3.5. The precipitate was air dried at 75°C. 3 RESULTS AND DISCUSSION

Table 1 shows the chemical analysis data of the compounds whose synthesis is described in Experimental Section. As it can be seen, there is a good agreement between the experimental values and the theoretical ones obtained from the formulas proposed. Table 1

Analytical Data and Experimental Weight Loss in Air at 800°C of the Titanium(1V) Phosphates and Phosphonates Experimental

Calculated

Compound

PI% YTioIp032.~20 y-Ti(H,P04)(P0,).2H,0 u-Ti(OH),(HP04) .H,O a-Ti(03P&H5), a-Ti(03PGH4COOH),

24.00 22.08 15.68 16.93 16.95

Ti/%

Cl% w.I.l% PI%

18.21 --- 14.32 17.57 --- 20.22 24.07 --- 23.71 13.45 38.98 39.77 13.48 19.25 36.80

24.04 22.47 15.82 17.23 17.62

Ti/%

CI% w.lJ%

18.57 --13.95 17.36 --- 19.57 24.45 --- 22.97 13.31 40.01 38.34 13.61 20.46 36.94

33

Novel Materials and Novel Applications

3.1 TitaniumgV) Phosphates Figures l a and l b show the X-ray patterns of the a and yTiP phases obtained by direct precipitation from titanium(III) solutions. The angular positions of the diffraction lines concur with the earlier described for these compounds,B being their crystallinity similar to that of the materials obtained by refluxing amorphous titanium(1V) phosphate in concentrated phosphoric acid. Figures 2a and 2b show the 31Psp&trum of these samples. The a-TiP shows an unique peak (-18.1 ppm from H,PO,) due to the hydrogenphosphate groups. In

Angle. 28 I deg

Figure 1

X-Ray d@iractionpatter& ofi a) a-Tip, b) ?-Tip, c) a-Ti(OH)P, d ) a-TiPPh, and e) a-TiPCOOH

I

I

L

a

I

I b

A

d

A

-

d

d

&

I

-

C

c

1-

8

J 1

~~

I

i

L I

I

I

I

1

1

1

I

L

I

1-

I

I

~~

c) a-Ti(OH)P,

Progress in ton Exchange: Advances and Applications

34

Table 2

31PNMR Shifts (in ppm) in Layered Metal(1V) Phosphates

Compound a-M(HPO,),*W y-MaPOJ(P0.J -2HZO

M = Ti

M = Zr

-18.1 , -18' -10.6, -10.5' -32.5 , -32.5'

-18.7b, -16.6" -9.4b, -12.6' -27.4b, -25.0"

a) ref. 30, b) ref. 31, c) ref. 32.

contrast the y-Tip does show two 31Presonances of equal integrated intensity, due to the dihydrogenphosphate groups (-10.6 ppm) and orthophosphate (-32.5ppm). These results are in agreement with those reported by other authors:' and are similar to that described for the a & y varieties of the zirconium ph~sphate"~' (Table 2). Figure l c shows the X-ray patterns of a-Ti(0H)P. It is a semicrystallinelamellar compound (interlayer distance 10.1 A) whose formation is favoured by reacting This phase Ti(II1) solutions with low concentrated H3P0, at low tem~eratures.3~ had been previously described." 31Pspectrum presents an unique band at -6.4 ppm. This implies that the material has only one type of phosphate groups in an

Figure 3

Infrared spectra of: a ) a-Tip, b) a-TiPPh, and c) a-TiPCOOH

35

Novel Materials and Novel Applications

P/P'

Figure 4

N477 K adoption-desorption isotherms ofi

a ) a-TiPPh, and

b) a-TiPCOOH

environment different from that of the crystalline varieties of the titanium(1V) phosphate. The band width must be associated to the local structural disorders as might be expected from a compound of low crystallinity.

3.2 Titanium(IV) Phosphonates Titanium(IV) phenylphosphonate is a layered compound with a basal spacing of 15.0 A (Fig. Id). Its crystallinity is higher than that observed in compounds obtained by direct precipitation from complexed titanium(IV).' Only one resonance at -4.1 ppm is seen for the 31Pspectrum (Fig. 2d), proving the existence of an unique arrangement for the phosphorus, Titanium(IV) 2-carboxyethylphosphonatepresents a lower interlayer distance (13.1 A) and a higher crystallinity than the a-TiPPh (Fig. le). 31P-MASNMR spectrum (Fig. 2e) shows two peaks at 11.6 and 12.5 ppm. This is probably due to the presence of chemically similar but crystallographically inequivalent phosphorus atoms. Figure 3 shows the infrared spectra of two a-titanium(1V) phosphonates, and also that of the a-titanium(1V)phosphate obtained as described before. The spectra of both phosphonates are similar to that previously described for the a-TiP?' but they show two new bands: at 1438 cm-' (very sharp) characteristic of phosphonic acids, and at 1145 cm", also observed in in amorphous titanium(1V) phenylphosphonates,g6between 600-800 cm-' appear the bands corresponding to the C-H vibrations of the aromatic group. The spectrum of a-TiPCOOH also shows new bands, that characteristic of the phosphonates at 1434 cm-', and two bands at 1694 cm-' and 1262 cm-' corresponding to the vibrations of the carboxilic group. Thermal stability in air of the a-TiPPh is higher than that of the a-TiPCOOH.

36

Progress in Ion Exchange: Advances and Applications

Table 3

Specific Surface Area Calculated by BET and t-plot Methods

Sample

a-Ti(O,PGH,), a-Ti(O,P~H.,COOH),

61 21

62 20

76 59

In both cases, the decomposition of the material begins at 300-400°C. Figure 4 shows the nitrogen adsorption-desorption isotherms of the samples outgassed at 140°C. The shape of the a-TiPPh isotherm corresponds with type IV of the BDDT clas~ification~~ and the hysteresis loop is of type H-l.38This type of isotherms is characteristic of non-microporous solids. a-TPCOOH presents an isotherm of type I1 without noticeable hysteresis loop, which means that these materials behave as non-porous or macroporous adsorbents. Table 3 shows the textural parameters of the samples. The specific surface areas were calculated with the BET equation3' and the t-plot method." In the application of the latter method we have used as standard the isotherm corresponding to a titanium phosphate furthermore whose t-plot is a straight line over all the relative pressures range>1742 the value of the C, parameter of this sample is similar to those of our samples. The porous texture of the samples was analyzed using the method of Bmet, Joyner and Halenda43applied to the adsorption branch of the isotherms. The multilayer thickness was calculated using the equation of Halsey.& The t-plot of the samples presents a straight section at low relative pressures intercepting the coordinate origin, which indicates the absence of microporosity. The absence of mensurable microporosity is also confirmed by the good agreement between the BET areas and the surface areas obtained by the t-plot method. 4 CONCLUSIONS Crystalline and semicrystalline phases of titanium(1V) phosphates have been obtained from titanium(II1) chloride in phosphoric acid solutions. The synthesis of a-titanium(1V) phosphate is possible at low temperature and low phosphoric acid concentration. y-Titanium(1V)phosphate is obtained by refluxing a Ti(II1) solution with very concentred phosphoric acid during very short times. The formation of a-titanium(1V) hydroxophosphate is favoured by low phosphoric acid concentrations and low temperatures. a-Titanium(1V) phosphonates also can be obtained by direct precipitation from titanium(II1) solutions. The chemical composition of the compounds obtained by reaction of Ti(II1) solutions with different phosphonic acids is independent of the synthesis conditions (phosphonic acid concentration, P/Ti molar ratio, temperature, reaction time), and only were observed differences in the degree of crystallinity and in the textural parameters. This behaviour is different from that observed in titanium(1V) phosphates, where the synthesis conditions have influence on the composition and structure of the obtained solids.

Novel Materials and Novel Applications

37

Acknowledgements We wish to gratefully acknowledge .the financial support of CICYT (Spain), Research Project no. MAT94-0428. A.B. would like to thank the Central European University, Soros Scientific Foundation for a research fellowship in the Oviedo University. M.A.V.G. thanks Du Pont Chemicals for financial support. References 1. A. Clearfield,G.H. Nancollas and R.H. Blessing, in "Ion Exchange and Solvent Extraction", vol. 4., Eds. J.A. Marinsky and Y. Marcus, Marcel Dekker, New Yok, 1973. 2. "Inorganic Ion Exchange Materials", Ed. A. Clearfield, CRC Press, Boca Raton, FL, 1982. 3. J.R. Garcia, R. Llavona, M. Suikz, and J. Rodrfguez, Tre& Inorg. Chem., 1993, 3, 209. 4. A. Clearfield and B.D. Roberts, Inorg. Chem.. 1988,27, 3237. 5. P. Oliveira-Pastor, A. Jimenez-Upez. P. Maireles-Torres, E. Rodriguez-Castell6r1, A.A.G. Tomlinson, andL. Alagna. J. Chem. SOC.C o r n . , 1989,751. 6. P. Maireles-Torres, P. Oliveira-Pastor, E. Rodriguez-Castell6n, A. Jimenez-Upez, L. Alagna, and A.A.G. Tomlinson, J. Muter. Chem.. 1991. 1, 319. 7. A. Espina, J.B. Pam, J.R. Garcla. J.A. Pajares and J. Rodrfguez, Muter. Chem. Phys., 1993. 35, 250. 8. P. Maireles-Torres, A. Jimt?nez-Upez, P. Oliveira-Pastor, I. Rodriguez-Ramos, A. Guerrero-Ruiz, and J.L. Garcla-Fiem, J:Catal., 1992. 92, 81. 9. "Catalysis Today, Pillared Clays", Ed. R. Burch, Elsevier, Amsterdam. 1988. 10. "Pillared Layered Structures, Current Trends and Applications", Ed. I.V. Mitchell, Elsevier, London, 1990. 11. A. Clearfield, Eur. J. Solid State Inorg. Chem., 1991, 28, 37. 12. "Multifunctional Mesoporous Inorganic Solids", Eds. C.A.C. Sequeira and M.J. Hudson, Kluwer, Amsterdam, 1993. 13. G. Alberti. P. Cardini-Galli, U. Costantino, and E. Towcca, J. Inorg. Nucl. Chem.. 1967.29. 571. 14. S . Auulli, C. Ferragina, A. La Ginestra, M.A. Massucci, and N. Tomassini, J. Inorg. Nucl. Chem., 1977, 39, 1043. 15. G. Alberti, M.G. Bemasconi, M. Casciola, and U. Costantino, J. Inorg. Nucl. Chem., 1980, 42, 1637. 16. E. Kobayashi and S. Yamazaki,Bull. Chem. SOC.Jpn.. 1983.56, 1632. 17. R. Llavona, J.R. Garcia, M. Suirez, and J. Rodriguez, Thermochim. Actu, 1985.86.281. 18. G. Alberti, U. Costantino, and M.L.L. Giovagnotti, J . Inorg. Nucl. Chem., 1979, 41, 643. 19. R. Llavona, PhD Thesis, University of Oviedo, 1985. 20. P.-E. Tegehall, Acta Chem. Scad., 1986, 40,507. 21. G. Cao, H-G. Hong, and T.E. Mallouk, Acc. Chem. Res.. 1992, 25,420. 22. "2nd Int. Summer School on Supramolecular Chemistry", Eds. J.L. Atwood, A.W. Coleman, W. Hosseini, J. Lipkowski, and G. Tsoucaris, Strasbourg, 1992. 23. K. Segawa, A. Kihara, and H. Yamamoto. J. Mol. Catal., 1992,74,213. 24. G. Alberti, M. Casciola, U. Costantino,A. Peraio, and E. Montoneri, Solid State Ionics, 1992, 50, 318. 25. G. Alberti, S. Murcia-Mascar6s, and R. Vivani, Muter. Chem. Phys., 1993.35, 187. 26. M.B. Dines and P.M. DiGiacomo, Inorg. Chem.. 1981.20.92. 27. A. Clearfield, Eur. J. Solid State Znorg. Chem., 1991, 28, 37. 28. G. Alberti, R. Vivani, R.K. Biswas, and S . Murcia-Mascar6s. React. Polym., 1993,19, 1.

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Progress in Ion Exchange: Advances and Applications

29. A.N. Christensen, E.K. Andersen, I.G.K. Andersen, G. Alberti, M. Nielsen, and M.S. Lehmann, Acta Chem. Scad., 1990,44,865. 30. Y.J. Li and M.S. Whittingham, Solid State lonics, 1993,63,391. 31. N.J. Clayden, J. Chem. SOC.,Dalton Trans., 1987, 1877. 32. K. Segawa, S. Nakata, and S. Asoka, Muter. Chem. Phys., 1987,17, 181. 33. A. Bortun, E. Jaimez, R. Llavona, J.R. Garcia, and J. Rodrfguez, Muter. Res. Bull., 1995.30, 413. 34. M.A. Via-Garcia, E. Jaimez, A. Bortun; J.R. Garcia, and I. Rodrfguez. J. Porous Muter., 1995,2,293. 35. E.D. Dzyuba, V.V.Pechkovskii, and G.I. Salonets, UI. Prikl. Spectrosk., 1974,21,127. 36. A. Bortun, V.V. Strelko, E. Jaimez, J.R. Garcia, and J. Rodrfguez, Chem. Muter., 1995.7. 249. 37. S . Brunauer, L.S. Deming, W.S. Deming, and E. Teller, J. Am. Chem. SOC., 1940,62,1723. 38. K.S.W. Sing, D.H. Everet, R.A.W. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol, and T. Siemieniewska, Pure Applied Chem., 1985,57,603. 39. S.Brunauer, P.H. Emmett, and E. Teller, J. Am. Chem. SOC.,1938,60,309. 40. B.C. Lippens and J.H. DeBoer, J. Catal., 1965,4,319. 41. A. Espina, J.B. Parra, J.R. Garcia, J.A. Pajares, and J. Rodrfguez, Muter. Chem. Phys., 1993, 35, 250. 42. J.B. Parra, A. Espina, J.R. Garcia, J. Rodrfguez, and J.J. Pis, in "Studies in Surface Sciences and Catalysis", vol. 87, Eds. J. Rouquerol, F. Rodriguez-Reinoso, K.S.W. Sing, and K.K. Unger, Elsevier. Amsterdam, 1994,p 467. 43. E.P. Barret, L.G. Joyner, and P. Halenda, J. Am. Chem. Soc., 1951,73,373. 44. G.Hasley, J. Chem. Phys., 1948.16, 931.

THE REMOVAL AND SOLIDIFICATION OF IODIDE ION USING A NEW INORGANIC ANION EXCHANGER

Hiroshi Kodama National Institute for Research in Inorganic Materials Namiki 1- 1, Tsukuba, Ibaraki, 305 Japan

1 INTRODUCTION

Various radioactive elements are produced in a nuclear reactor and their removal and solidification are very important. The present paper discusses a method for removing radioactive iodide ions by fixing them onto an inorganic compound by use of a new anion exchanger. From the viewpoint of the immobilization of radioactive iodide, various inorganic compounds such as Bi203,l-3 Ag compound? Bi507N035-7 etc. have been studied. The present paper reports a new inorganic compound to remove and solidify the radioactive iodide from solution. The synthesis of a new inorganic compound, BiPbO2NO3, its structure, and its ion exchange properties with iodide ion are studied in detail. The compounds which contain NO3 have the high possibility to remove and solidify iodide ion in solution. Therefore, we expect BiPb02N03 to be a new material for removing and for immobilizing radioactive iodide. 2 SYNTHESIS OF A NEW ANION EXCHANGER

2.1 Synthesis of

B1Pb02N03

The preparation of BiPbO2NOg was carried out by solid state reaction. Mixed powder of Bi2O3, PbO and Bi(N03)-5H20 was used as a starting material. The reaction can be written as follows: Biz03 + 3PbO + Bi(N03)3-5H20-+ 3BiPb02N03 + 5H20 (1) This reaction did not proceed at room temperature but proceeded at the temperature higher than it. The starting material was charged in a platinum capsule. The platinum capsule was sealed by welding and set in a high pressure reaction vessel. The vessel was

. ..

Table 1 The experimental conditions and results of the synthesis of BiPbOzNOjr. Heating Temperature1“c 100 150 200 250

350 450

Reaction Products

BiPbOzN03 BiPbO2N03 BiPbO2NOs BiPbO2NOg BiPbOaNO3 BiPbOzNO3

+ impure compounds + impure compounds

Progress in Ion Exchange: Advances and Applications

40

set within an electrically heated furnace and heated. The high pressure reaction vessel was used for protecting the platinum capsule from its explosion by the increasing pressure in it on heating. After a heating run, the reaction products were quenched and identified by their Xray diffraction (XRD) patterns. Table 1 shows a experimental condition (heating temperature) and results, where heating time was 24 hours. These results show that the temperature near or above 200 "C is necessary for the synthesis of pure BiPbOzNO3 under the present conditions. The produced BiPbOzNO3 was white powder and well crystallized. A scanning electron micrograph of the crystal is shown in Figure 7. The crystal is platelet and its surfaces are very smooth. 2.2 Structureof BiPbOzNOj

A XRD pattern of BiPbOzN03 is shown in Figure 1 with the patterns of BiPbO2I and Bi202C03. These three patterns are very similar and the patterns of BiPb02N03 and Bi2OzC03 are especially similar. That is, BiPbOzN03 is expected to be isostructural with BiPbOzI* or Bi202C03.9 The former belongs to the space group, I4/mmm with a tetragonal cell of the lattice parameters a = 4.0533 A, c = 13.520 8, and the latter has a tetragonal cell of the lattice parameters, a = 3.870 A, b = 13.697 A. With the reference of the XR D data for Bi202C03, the diffraction peaks of

Table 2 X-ray difraction data for BiPbO2NO3 (h

0 1 0 1 1 1 0 1 1 2 2 1 1 0 2 2 2 2 1 2 1 2 2 2 3 3 2 3 I 3

k

1 )

0 2 0 1 0 4 0 3 1 0 1 2 0 6 0 5 1 4 0 0 0 2 0 7 1 6 0 8 1 1 0 4 1 3 0 6 1 8 1 5 0 9 2 0 2 2 1 7 0 3 1 0 2 6 0 5 1 12 1 6

d C d iJ

dobs(A)

7.410 3.836 3.705 3.095 2.808 2.626 2.470 2.375 2.238 1.986 1.918 1.868 1.855 1.852 1.763 1.750 1.671 1.548 1.546 1.523 1.521 1.404 1.380 1.361 1.279 1.256 1.221 1.209 1.130 1.1 19

7.412 3.837 3.702 3.094 2.808 2.626 2.468 2.374 2.237 1.986 1.918 1.867 1.853

60 20 5 100 32 9 16 13 11 15 6 5 22

1.763 1.749 1.671 1.546

7 3 24 10

1.520

10

1.404 1.379 1.360 1.278 1.256 1.220 1.207 1.129 1.119

Iobs(%J

41

Novel Materials and Novel Applications

BiPbOzNO3, were indexed on the basis of a tetragonal cell of a = 3.9710 A, c = 14.819 A. The XRD data are listed in Table 2 and all the observed peaks are well indexed on the above cell. These data prove that the synthesized compound is very pure.

10

20

30

40

50

60

2 0 (deg)

10

20

30 40 2 0 (deg)

50

60

10

20

30 40 2 0 (deg)

50

60

Figure 1The XRD patterns of BiPbOzN03, BiPb02I and Bi202C03.

Progress in lon Exchange: Advances and Applications

42

3 REACTION WITH IODIDE ION Well ground BiPb02N03 was equilibrated with NaI solution. The reaction was carried out with shaking in a plastic test tube stopped tightly with a lid and placed in a thermostatic container. The test tube was confirmed to be airtight by measuring its mass both before and after the reaction. After the reaction, solid was separated from solution and identified by their XRD patterns. The iodide ion concentration was determined by means of ion chromatography, using a DIONEX 4500 i instrument.

3.1 Extent of Ion Exchange Reaction The extent of the ion exchange reaction of BiPbO2NO3 with aqueous iodide was examined as a function of time at 25 "C and 50 "C. The experiments were carried out in the solutions previously adjusted pH to 1 and 13. The experimental conditions were as follows: mass of BiPbO2NO3, 102 mg; concentration of NaI solution, 0.1 mol dm-3 ; volume of NaI solution; 0.1 ml. The results are given in Figures 2 and 3, They show the results with the solutions of pH =1 and 13 respectively and the curves 1 and 2 in each figure show the results measured at 25 "C and 50 "C. The curves in Figures 2 show the reactions in the solution of pH = 1. They come to an end in very short time. Within 15 minutes from the beginning of the reaction, the concentration of iodide ion remained in solution became almost constant but it is not so small in comparison with the values shown in Figure 3. The presence of NO3- at high concentration in acidic solution may disturb removing iodide (or iodate) ion . The curves in Figures 3 show the reactions in the solution of pH = 13. When they comes to an end, the percentage of remained iodide ion was below 1 %. In the case of former, it was 5 6 %. In the case of the reaction in the solution of pH = 13, the reaction at 25 "C is slow in the comparison with the reaction at 50 "C, but this is still considerably faster as compared with the reaction with the previously reported material (Bi507N03).5.7

-

0

1

2 3 4 Reaction Time / h

5

Figure 2 Extent of reaction in solution adjusted p H to 1 by using HNO3, iodide remained vs. reaction time

6

43

Novel Materials and Novel Applications

When compared Figures 1 and 2, they show the very different patterns of concentration change. This suggests that the ion exchange reaction proceeds by different mechanisms in the two solutions. The mechanisms of the ion exchange reaction will be discussed in the later section in more detail. 100

80

60 40

20

0 0

2

4

6

8

10

12

Reaction Time / h Figure 3 Extent of reaction in solution adjustedpH to 13 by using NaOH, iodide remained vs. reaction time

before reaction in solution of pH = 1

after reaction I in solution of pH = I3

I

6.537 x lo4 ( 82.95 ppm) 5x103 ( 634.5 ppm)

I

m :;;;::ip

I

2.85 x 10 -6 (0.36ppm)

Progress in Ion Exchange: Advances and Applications

44

3.3 Ion Exchange Capacity

-

Accurately weighted BiPb02N03 ( 97 103 mg ) was reacted with 0.2 mol dm-3 NaI solution ( 1 ml ) for 24 hours at 25 "C, 50 "C and 75 "C. The ion exchange capacity was measured with the solution of various pH values. The results are shown in Figure 4, where the curves 1 , 2 and 3 are corresponding to the measurements at 25 "C, 50 "Cand 75 "C. The curves 1 and 2 shows almost the same change but curve 3 shows a different pattern. That is, curves 1 and 2 show that the ion exchange capacity at 25 'C and 50 "C has large values at pH = 1 and 13 but at the other pH values, especially at the pH between 3 and 10, it has a small value. Curve 3 shows, however, that the ion exchange capacity at 75 "C has large values at almost the all pH values without pH = 2 and 3. If the ion exchange reaction proceeds according with only following equation; BiPbO2NO3 + I- j BiPb02I + N03- .................... (2) The calculated maximum value of the ion exchange capacity is 1.96 meqe / g. The large values observed at pH = 1 and 13 are close to the calculated maximum value.

-

'M

. ._

2

1.5

h

c)

%a

9

1

0.5

0

0

2 ( HNO,

4

1

6

8

PH

10

12

14

( NaOH )

Figure 4 Ion exchange capacity in solution adjusted pH to various values 3.4 Reaction Mechanism 3.4.1 The Reaction in Solution of pH = 13. After the ion exchange reaction, solid was separated from solution and identified by their XRD patterns. The observed patterns are shown in Figure 5. It shows that they are mixed patterns of the starting material, BiPbO2N03 and a reaction product, BiPb02I. Hence, in this reaction BiPbOzI is the sole product and this means that the ion exchange reaction is represented only by the equation (2). The reaction product was yellow powder and well crystallized. Their scanning electron micrograph is shown in Figure 6. A scanning electron micrograph of starting material, BiPb02N03 is also shown in Figure 7. When both crystals are compared, their habits are not so different but the crystal surfaces of the reaction product seem to be considerably etched.

45

Novel Materials and Novel Applications

........... ..............

10

20

30 40 2 0 (deg)

50

60

Figure 5 The XRD patterns of reaction product in solution adjusted pH to 13

Figure 6 Scanning electron micrograph of reactionproducts in solution adjusted pH to 13

Figure 7 Scanning electron micrograph of BiPbO2NO3

46

Progress in Ion Exchange: Advances and Applications

3.4.2 The Reaction in Solution of pH = I, Figure 8 shows the XRPD pattern of the solids after reaction. It consists of a mixed pattern of starting material BiPb02N03 and several new peaks. The new peaks are very small and were not identified. The peaks of BiPb02I were not observed. These results are very strange but very interesting. Because, in these experimental conditions, the ion exchange capacity is about 1.7 meqe/g. This value means that more than 80 % of NO3 site must be exchanged with I-. However, the majority of solid after reaction was not BiPb021, but BiPb02N03. These results suggest that the exchange reaction in solution adjusted pH to 1 proceeds not by the equation (l), but by another reaction. As the another reaction, we propose an adsorption of iodide ion on BiPb02N03. That is, iodide ions are removed by adsorption on the surfaces of BiPb02N03 crystals from the solution. To prove this assumption, the reacted solid was observed by a thermobalance. Figure 9 shows TG curves, where the weight of the sample decreases through two steps. After this experiment, the XRD pattern of the final products was examined. It was different from that of BiPb02N03 or BiPb021, but not identified.

10

30 40 2 0 (deg)

20

50

60

Figure 8 The XRD pattern of solid produced in solution adjusted pH to I

0 -2 h

F v

F

-4 -6

-8 -10 -12

100

200

300

400

500

600

700

Temperature / C

Figure 9 TG-DTAcurves of solid produced in solution adjusted pH to 1

Novel Materials and Novel Applications

47

In order to get the more information, another TG-DTA was carried out. The sample was quenched to room temperature just after the first weight decrease (at 435 'C) and its XRD pattern was observed. The XRD pattern was almost same as the one before heating. That is, it consists of a mixed pattern of unreacted BiPbO2NO3 and several new peaks. These experimental results can be well explained by that the first weight decreases was caused by desorption of iodine from crystal surfaces and the second weight decrease was caused by thermal decomposition of unreacted BiPbOzNO3. A SEM of the reaction products in the solution of pH = 1 was shown in Figure 10. When the crystals in this figure are compared with the one in Figure 7, a big difference is observed on surfaces of crystals. Many fine products are observed on the surfaces. This may be also the another proof to the adsorption of iodide.

Figure 10 Scanning electron micrograph of reaction products in solution adjusted pH to 1

5 ACKNOWLEDGMENT

The author wishes to express thanks to Mr. Masayuki Tsutumi of the National Institute for Research in Inorganic Materials, for obtaining a scanning electron micrograph.

References 1) P.Taylor, AECL-1990,AECL-10163 2) P.Taylor, D.D.Wood and V.J.Lopata, AECL-1988,AECL-9554 3) HKodama, Bull. Chem. SOC.Jpn., 1992,65,3011 4) K.Funabashi, T.Fukasawa, M.Kikuchi, F.Kawamura and Y.Kondo, Proceeding of the 23rd DOE/NRC Nuclear Air Cleaning and Treatment Conference, 10-3 5 ) H.Kodama, Proceeding of the Ion Ex'93 Conference, 1993, p-55 6) H.Kodama, J. Solid State Chem., 1994,112,27 7) H.Kodama, Bull. Chem. SOC.Jpn., 1994,67, 1788 8 ) J.Ketterer and V.Kr&ner, Mat. Res. Bull., 1985,20, 1031 9) TShama and M.Lehtinen, Bull. Geol. SocFinland, 1968,40,145

THE UTILIZATION OF HYDROTHERMAL ALTERED POWER PLANT ASHES IN THE ION EXCHANGE PROCESSES D. KoloGek, H. Kusi, I. SviWk*), F. Kovanda, E. Prochizkova and J. Hrazdira Department of Solid State Chemistry Institute of Chemical Technology Technicki 5, 166 28 Prague 6, Czech Republic *)Water Research Institute Podbabski 30, 160 62 Prague 6, Czech Republic

1 INTRODUCTION

Power plant fly ash is an amorphous solid with a favourable silicon and aluminium content making its alteration to crystalline zeolitic materiais possible. Zeolites may be easily synthetized fiom such precursors even at low temperatures (e.g. synthetic forms faujasites X and Y at 90OC). Fly ash also may be converted to phillipsite under special reaction conditions. The knowledge of precursor chemical composition is the most important condition of a successful synthesis and must be followed by a proper selection of hydrothennal alteration parameters (i.e. liquid/solid ratio, temperature, N a K ratio, and concentrationsof correspondinghydroxides). Trace elements migrate from ash to the liquid phase during synthesis. Increased concentrations of elements in anionic forms (arsenates, vanadates, molybdates) arise in final stages in the liquid phase dependmg on the kind of starting ash and the combustion temperature of coal used. These extracts generally create problems. We propose in our technological scheme that these problems will be solved either by selective sorption on sorbents prepared especially for this purpose or by building in the extracts into construction mat* (e.g. concrete) as liquids.

2 E,XPER.IMENTAL

The application field of fly ash alteration products may be determined by the choice of grantdometry for the starting ashes. Heat and power stations produce all grantdometric fractions from the finest fly ashes (fiom electrostaticfdtm) to coarse slag. Two samples of fly ash were selected for the experimental measurements. The first one was the product from electrostaticfilters of a Czech power plant Viesovi. The second one was also product from electrostaticfilters but of the Dutch power plant in St. Geertruidenberg. Hydrothermal alterations of fly ashes from the two sources were realized with the pilot plant equipment in the Kaubk p h t in Kralupy. The phillipsite synthesis conditions have been published in a patent application by KolouSek et. al. (1). Solid products were cenmfuged, washed with water after synthesis, and dried. Ion-exchange properties of the zeolite prepared from the Czech fly ash were studied at the isothermal conditions by the batch method. 1 g of washed and dried zeolite was stirred in 1000 ml of aqueous solution at the laboratoq temperature. Initial concentrations of metah in solutions were (in mg L-'): Cd 77, Pb 97, Sr 100, Ba 98 and .4g 105. The solution

49

Novel Materials and Novel Applications 120

Concentration[mg/l1

1

1

0

0.5

1

2

1.6

2.5

3

Time [hrs]

Figure 1 ; The time dependence of residual concentrations of metaI cations in the solution (phillrpsiteprepuredfiom the& ash of Vfesovapower plant) samples were taken m evtry 30 minutes. The metal concentrations were determined by AAS.

The comparison between sorption characteristics of a MWclinoptilolite (Nw Hrabovec, East Slovakia) and phillipsite (altered fly-ash Erom the Slovak power plant Novaiky) for selected types of radiotoxic isotopes was based on the following experiment: 16 g of the adsorbent (clinoptilolite or fly ash altered to phillipsite) were added to 1 L of an IS I37 aqueous solution containing Sr, or Cs and stirred mtensiveiy for 2 hours. A sample was taken after that time, filtered and the filtrate was submitted to the activity measurement. The w solutions. A CANBERRA 80 gamma samples activity were compared with those of o spectrometer with a NaI(T1) scintillation detector was used for the detennination of activities, the counting time was 2oooS. The rest of the suspension was sedimented and the activity of the clear liquid above the sediment measured after 24 hrs, without any previous filtration. Sorption properties of adsorbents were characterized by residual activity and decontamidon efficiency as follows: residual activity; (Yo)

=

--

finalactivity .loo Yo original activity

decontamination efficiency

= 1009.6

- residual activity.

Au sorption experiments were repeated I times and the resuls were averaged. The ion-exchange equilibrium isotherm was measured with synthetic Na-phillipsite preparcd fiom Dutch power plant fly ash. First the zeolite was washed with HCl solution having pH at least 3 (due to the remahing atkalinity removal) to filtrate pH = 6 and then with distilled water. After filtration the zeolite was dried at the room temperature for 5 days.

Progress in Ion Exchange: Advances and Applications

50

0

0.2

0.8

0.4

Pb

0.8

1

(1)

Figure 2 : Ion-exchange isotherm f o r PbAra exchange in synthetic phillipsite prepared from t h e h ash of St. Geertruidenberg p a v e r plant. Measured at 2 r C and 0.05M PbflOJ,solution. Ion-exchange equilibriumbetween zeolite and solution was measured with the batch method at 25°C. Solutions were prepared from pure Pb(NO& and redistilled water. The metal concentration in the initial solution was 0.05 M. The exchange reaction was carried out for 8 days. It is the necessary time for equilibrium reaching between phillipsite and bivalent cation in the solution. The ratio of reactant phases (solidlliquid) was in the interval of 15 200.

-

3 DISCUSSION

Phillipsite has one of the highest known ion-exchange capacities among ~ t u r azeolites. l It reaches the value of 5 meq.gl, whereas the one of a natural clinoptilolite is 2.6 meq.g', the highest ion-exchange capacity has been found at the synthetic zeolite .4 (7.16meq g'). The rare natural zeolite merlinoite approachs the same value of the ion-exchange capacity. The afsnity of synthetic phillipsite toward Pb", Ag', S?, Cdz+,B? is showed in fig.1. The best results were obtained with Pb" and Ag+ ions sorption. The advantage in using synthetic phillipsite in comparison with clinoptilolite show in the 137 results of radioisotopes Cs and "Sr sorption. The values obtained show that altered fly 85 ashes have better sorption characteristics than clinoptilolite for Sr and '"Cs. Residual acthities of altered fly ash measured after 24 hrs sedimentation were 0.03 and 0.14 % for 85 Sr and '37Csrespectively whereas those of the M ~ L U clinoptilolite ~I were 16.9 and 1.3 96 (see Tables 1 and 2).

Novel Materials and Novel Applications

51

Table 1 Decontamination eficiency (averaged values-filtered)

snatactivity (%) philripsite

isotope clinoptilolite 8S

Sr

137

cs

78.58 93.80

-

94.22 93.65

Table 2 Decontamination eficiency (averaged values, 24 hours sedimentation withoutfiltration)

finalactivity (%) isotope 8S

Sr cs

137

clinoptilolite phillijxite 83.08 98.70

99.97 99.86

The ion-exchange Pb-Na equilibrium isothm was also measured for synthetic phillipsite (see Fig. 2). It is obvious that the zeolite used is (at temperature 25OC, initial concentration 0.05 M) selecthe toward entering cation. The highest exchange degree was reached with the ratio of reactants (solution mentioned above and zeolite) L [d]/ S [g] = 100). The lead content in the zeolite was 1.636 meq/g equivalent to 96.4% of ion-exchange positions. The cation-exchange capacities (CEC) for monovalent cations are considered to be at the maximum, because for these cations the total exchange is realized m comparison with bivalent cations which n e w m h e s the maximumvalue (2). In spite of this nearly total removal of Pb2+from solution was already reached at US = 22.2 and initial concentration of Pb2+was decreased to 0.5%

4 CONCLUSION

Hydrothermallytreated tly ash is a useful zeolite raw material. It is possible to use it for the sorption of metal ions, e.g. for waste and radioactive water treatment. Hydrothermal alteration results confhmed that tly ashes with proper ratio SilAl can be utilized for the zeolite and sorption processes.

Progress in Ion Exchange: Advances and Applications

52

References

1. D. KolouSek, E. Prochhzkovi, V. Seidl and M. Smejkalovi, Patent application 04530-90.R.,1992

-

2. N. F. Chelishtchev, B. G. Berenshtein and V. F. Volodin, 'Zeolites The New Type of Raw Minerals', Moscow, 1987.

POLYELECTROLYTE COMPLEXES BETWEEN A WEAK POLYANION AND A STRONG POLYCATION WITH CATIONIC GROUPS IN THE MAIN CHAIN

Stela Dragan*, Mariana Cistea*, Cornelia Luca* and B.C. Simionescu**

* Institute of MacromolecularChemistry “Petru Pod’,** Technical University “Gh. Asachi”, 6600Iasi, Romania

1 INTRODUCTION There are many reasons for the intensive study of the interpolymer complexes as well as of the complexes between polyions and ionic surfactants or dyes. Starting with the systematic research promoted by Michaels the formation of polyelectmlyte complexes has been widely studied 3-7 and the application of this process, and of the products thus obtained, is very often met in industrialg’* and biomedical field^.'"'^ The synthetic polyelectrolytes, by their huge variety of structuns and ways of combination, offer a very attractive field for detailed studies of the multiple interactions that take place between biopolymers, such as electrostatic interactions, hydrogen bonds, hydrophobic interactionsas well as selective complexations. This is another reason for the various studies on the parameters involved in the synthesis and the properties of the polyania-plycation complexes, recently reviewed by B. Philipp” and E. Ts~ichida.’~ These parameters are mainly related to the cbaracteristics of complementary polyelectrolytes and to the properties of the solvent used as reaction medium. The cationic polyelectrolytes of integral type, with quaternary ammonium salt groups in the main chain and pendent hydroxyl groups, could constitute a complementary polymer in the synthesis of some less studied interpolyelectmlytecomplexes. The aim of this paper is the study of the synthesis conditions of some water insoluble polyelectrolytecomplexes (PEC) when the cationic polyelectrolyte is a poly(N,Ndimethyl2-hydroxypropyl ammonium chloride) with different degrees of branching, achieved by and the anionic using a polyfunctional amhe such as N,Ndimethyl-l,3diaminopropane polyelectrolyte is the sodium salt of poly(acrylic acid), poly(acrylic acid-co-itaconic acid) or poly(acrylic acidco-maleic acid), with different molecular weights. 2 EXPERIMENTAL 2.1 Materials Poly(acrylic acid) and copolymers of acrylic acid with itacOnic acid or maleic acid were synthesized with S O , as radical initiator in aqueous solution. These polymers

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Progress in Ion Exchange: Advances and Applications

were converted into their sodium salt by 10M NaOH aqueous solution. AAer two purifications with waterketone system, the sodium salts were recovered from aqueous solutions by atomizing. The molecular weight of the sodium salts of poly(acrylic acid) (PANa) was viscometrically determined in 2M NaOH aqueous solution, at 25OC, according to the following relationship :I7 [ q 3 ~ 4 . 2 2x 104x M?@

(1)

The following values for M, of PANa were found: PANal 14,200; PANaz 51,400 and PANa3 217,600. PANal was also characterized by GPC: M, = 15,900 and M a = 1.13. The sodium salts of poly(acrylic acidco-itaconic acid) (97.17:2.83 % moYmol) (PAINa) and poly(acrylic acidco-maleic acid) (90: 10 % mol/mol) (PAMNa) were characterized by GPC md the following values for molecular weights and polydispersity degres were obtained: PAINa: M, = 17,500 and MJM. = 1.11; PAMNa: M, = 16,900 and M& = 1.13. The molecular weight and the polydispmity degree of PANal are comparablewith those of PAINa and PAMNa. The cationic polyelectrolytes with N,Ndimethyl-2-hydmxypmpylammonium chloride units in the main chain were synthesized by condensative polymerization of epichlorohydrinwith dimethylamine and a polyfunctional mine such as N,Ndimethyl-1,3diaminopropane, according to the method previously presented." The samples were carefully purified by dialysis against distilled water until the absence of C1- ions in the external water; the diluted aqueous solutions were concentrated by gentle heating in vacuum and then recovered by atomizing. The cationic polymer samples were kept for days in vacuum on PzOS,at room temperature. The intrinsic Viscosities of these polymers in 1M ~ 0.420; NaCl aqueous solution at 25°C were determined: [ ~ ] P C I . I = 0.680; [ ~ ] P c I . = [ d p n = O,355(dVg). The theoretical structures of the cationic polyelectrolytes used in this work are presented in Scheme I:

CH3 I +c1N-CHTCH-CH,

I

CH3

I

OH

HCl

~ ~ ~ P ; E C H ~ ~ I-pE Cn H + ~ (CH2h OH I N:

/ \

H3C CH3 where: p = 0.95, PC1 polycation p = 0.80, PCZpolycation Scheme I 2.2 Methods

In order to study the complex formation, the aqueous solution of polyanion (or polycation), with a concentration of lo-' unit mol.&., was slowly dropped into 50 ml aqueous solution of polycation (or polyanion) having a concentration of unit mo1.n

Novel Materials and Novel Applications

55

under magnetic stimng, at room temperature, in a range of unit molar ratio h m 0 to 3

[PAy[PC]. The mixing was continued for 2 hours; after this time the precipitate8 were removed by centrifbgation at 2000 r.p.m. or by filtration. The reaction betweea polyrnioo and polycation was checked by compuison of the supematant mixture chamcteristicr (specific viscosity and conductivity) with those of a control solution prepared taking into account the composition expected for a stoichiometric d o n and a complete release of NaCl. Viscometric measurements were performed with an Ubbelohde viscometer with internal dilution, at 25°C. Conductivities were measured in a specific cell with platinum/platinum electrodes (Radiometer copenbrgen,type CDM 2d). GPC analyses were performed in the following conditions: a G75 Sephadex column (200 x 6 mm) equipped with a 308 Wdetector and a 250 nm filter.

3 RESULTS AND DISCUSSION The interaction of a strong polycation with the sodium d t of poly(rcrylic acid) should result in a polyanion-polycationcomplex whose structure will depend mainly on the

Progress in Ion Exchange: Advances and Applications

56

following parameters, related to the complementary polymers: the molecular weight, the charge density, the degree of branching, the concentration of both solutions, the mixing order and the unit molar ratio. Depending on these parameters, soluble (nonstoichiometric), or insoluble (stoichiometric) complexes can be obtained. The influence of the branching degree and of the charge density of the cationic polyelectrolytes on the complex formation has been little studied. The cationic polyelectrolytes used in this work have the peculiarity to offer both different branching degrees and different kinds of charges (strong and weak) provided by the presence of the polyhctional amine (Scheme I). They have also different molecular weights, as proved by the [q] values and different flexibilitia of the chain emphasized by their viscometric behaviour in water solution.18 Firstly, we followed the influence of the molecular weight of the PANa on the complex formation when the cationic polyelectrolyte was PCI . The variation of the qSpof the reaction mixture vs. the unit molar ratio emphasized a significant influence of the polyanion molecular weight upon the moment when qv is about 0 (Figs. la, lb, 2). The unit molar ratio corresponding to the endpoint is about 1.1 for PANa, and 1.05 for PANa2,,

TSP

0.2

0.15

0.I

0.0:

0

Figure 1b Depenaknce of the spcflc viscosi& (qSJ on the unit molar ratio [PA]/[pc] for P A N ~ ~ ~ / P( C4 Imtd . ~ PANa2 /PCI.2 (9systems

Novel Materials and Novel Applications

51

when the cationic polyelectrolyte is Pc1.1and about 1.26 for PANal, 1.16 for PANa2 and 0.95 for PANa3, when the cationic polyelectrolyteis PC13.The magnitude of the deviation of the endpoint h m 1:1 unit molar ratio seems to be influenced by the molecular weight of the complementary polymers and by their mixing way. When the polycation is host and a guest polyanion is added to it, the higher polycation molecular weight the grenter is theunit molar ratio corresponding to the endpoint ( Figs. la, l b ). When a host polyanion (PANa3) is added to a guest polycation ( PC13 ) the endpoint is better emphasized and it is slightly before the 1:1 unit molar ratio. Af€erthe endpoint, qlp values are determined by the polyanion excess, increasing along with the rise of the polyanion moleculu weight. The continuous increase of q,,, after the endpoint is a p m f for the absence of interaction between polyanion in excescr and PEC. The qw values higher than that of the umtrol solution, at the same unit molar ratio (Fig.la).could be explained by the incomplete microion release and could represent a measure of the deviation h m stoichiometry. After minimum, qlp values less than those of the control solution suggest a less amount of the polyanion in excess, that meaning a higher polyanion amount included in PEC structure. The conductivity values increase linearly with the increasing of the unit molar ntio [PAI/[PC], until the endpoint when a break is evident, this meam the end of microion release and the increase of the conductivityonly due to the polyanion excess (Figs. 2,3 ).

FigUte 2 D e p d n c e of the Jpecijc viscosity (qz$ and ofthe COnductiviQfi) on the unit moku ratio [PAJ/[X’ fbr PANaj /PC,.2system: qsp(a); k (0)

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Progress in Ion Exchange: Advances and Applications

As one can observe from Figs. 2,3 the conductivity values are influenced mainly by the polycation before the endpoint, and by the polyanion after that. When PCI.1 was used as polycation the conductivity values, both for PANSl and PANa 2, are very close before the endpoint, but significantlyhigher for PANa, than for PANa2 after this moment (Fig. 3).The same situation arose in the case of PCll (Figs. 2,3). The conductivity values measured as being less than those of the control solution also confirm incomplete microion release (Fig. 3). The deviation from stoichiometry could be induced by a polycation structure which was different fkom the polyaaion one, both by the distance between charged sites and by a slight branching degree d e t d n e d by the presence of the polyfunctional amine (SChemeI). It should be emphasized that, for all polymions irrespective of molecular weight, the endpoint is accompanied by the separation of the insoluble PEC. The polyanion molecular weight is important especially to define the endpoint. The higher molecular weight, the clearer the endpoint. To obtain some information about the importance of the polyanion structure on the complexation by electmstatic interactionswe also followed the complexation between PC1.2 and PAINa OT PAMNa (Fig. 4). Little difference between these copolymers,both from q,,, and conductivity point of view, was observed though the q,,,values were slightly higher for PAINa before the endpoint and smaller after that than for PAMNa The conductivity values were very close with each other until the endpoint and higher for PAMNa than for PAINa after this moment. This behaviour could be explained by structural differences that can induce a great ability of PAMNa to bound to polycation comparative with PAINa.

Figure 3 Depemknce of the conductivity (&)on the unit molar ratio [PA]/fPC] for PANal /PCI.I(O), PANat /PC1.](4,PANal /PCI.Z(@and PANa2/PC1..2(L&ystems; (0) and (9control samplesfor PANal /PCI.Iand PANadPCI.1 respectively

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Novel Materials and Novel Applications

By comparison with PANal, before the endpoint, we can note higher values of q9 and smaller values of conductivity fot both copolymers, although their molecular weights and polydispersity degrees are near to those of PANal. This means a smaller amount of polycation included into PEC at the m e molar ratio. The conductivity values, very close for these three polymers after the endpoint, could be explained by a similar mobility of polyioas with similar molecular weights. Takiag into lccount the results presented above the small influence of the molecular weight of the guest polyioo (PANal and PANb) on the complex formation with PCI as polycation is evident. The greater efficiency of PANaz in the complex formation is proved W y by the wit molar ratio [PAl/[PC] at the endpoint that is higher for PANal thrn for (Fig. la) and PCll (Fig. lb). The lower efficiency of PAINa PANa2, both in the case of and PAMNa in the complex formation is a further proof of the negative influence of the increase of structural differences betweeo the complementilly polymers. For PCll (IS host polyioa we can suggest the following order for the pref-e in the complex formation:

Related to the influence of the molecular weight of host polyion, the increase of the

120 VO fOO$

90

eo 70

60 u) 40

30 20

60

Progress in Ion Exchange: Advances and Applications

ability in complex formation along with the increase of host molecular weight is evident. The conductivity values found in the case of PC1.2 as host polymer were much higher than those obtained in the case of PCI.I (Fig. 3) and closer to those of the control samples. Concerning the unit molar ratio [PA]/[PC] at the endpoint, an increase of the amount of polyanion needed to achieve the phase separation was observed, along with the increase of polycation molecular weight (Figs. 1a, 1b). When the host polycation was dropped into the guest polyanion a shifting of the phase Also, separation moment to a unit molar ratio [PC]/[PA] less than 1:l was emphasi~ed.'~ when a host polyanion (PANa3) was dropped into the guest polycation (PC1.2) the phase separation took place at about 0.95 unit molar ratio (Fig. 2). Though the cationic polyelectrolytes used in this work are of integral type we did not obtain soluble complexes either when the unit molar ratio [PA]/[PC] was very high (8:1), as reported by T ~ c h i d aor , ~when the host polymer was dropped upon the guest polymer, as reported by Kabanov.6 This behaviour could be a p m f for the greater stability of the PECs obtained in these conditions and also an argument for a tight structure that could be most probably achieved by a ladder mechanism of formation. The situation could be different in the case of a strong polyanion. A similar situation was met for the complex formation between chitosan and carboxymethylcellulose? the complex being insoluble irrespectiveof mixing way and of the excess of complementary polymers.

TSP

t

0.I

0.05

0

Figure 5 Dependence of the spec@ viscosiy (qsJ and of the conductivi@fi) on the unit molar ratio [PA]/[PCJfor PANa2 /PC2 system: (e) qspand (4 k c o m p k fonnation;(o) qs,, and (9k control samples

61

Novel Materials and Novel Applications

The influence of the polycation structure upon the complex formation was studied for PANa2RC2 system (Fig. 5). Because the branching degree of PC2 was higher than that of PC,(according to the content in polyfunctional amine, Scheme l), the structural differences between PANa and plycation were stronger in the PANadPC, system. The presence of more branches determines more loops of the plyanion chain and a poorer cornpeasation of the charges even tiom the starting of the process. This situation was reflected in the variation of the viscosity and of the conductivity vs. the unit molar ratio [PAl/[PC].Thw, the conductivity increase seems to be slower in this system than in the PANa2/PCI system at the unit molar ratio [PA]/[FC] less than about 0.4 and becomes linearly after that. The unit molar ratio [PAl/[PC] at the endpoint was higher in the last system as reflected also in the viscosity curve; furthermore, another difference was the intermediary aspect of the complex between a precipitate and a coacervate. References

1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11.

12. 13. 14. 15. 16. 17. 18. 19. 20.

a

A. S. Michaels and R G. Miekka, J. Phys. Chem., 1961, 1765 1447 A. S.Michaels, L. Mir and N. S. Schneider, J. Phys. Chem., 1965, E. Tsuchida, J. Osada and K. Sanada, J. Poiym.Sci.. P o h . Chem. Ed,1972, & 3397 583 E. Tsuchida, Y.Osada and K. Abe, Mukromol Chem., 1974, J. KO& B. Philipp, V.Sigitov, S. Kudaibergenov and E. A. BeLturov, Coll. P o w . Sci., 1988,26?4,906 V.A. Kabanov, A. B. Zezin, M. I.. Mwtafaev and V.A. Kasaikin, “Polyme& Amines and Ammonium Salts’’, Ghent, Belgium, 1979, p. 173. B. Philipp, J. Katz, K-J. Linow and H. Dnutzenberg,P o w . News, 1991, fi 106 H. H. Schwartz,K. Richau and D. Paul, Poiym.Bull., 1991, 95 H. H. Schwartz, R Apostel, K. Richau and D. Paul, “Sixth InternationalConference on Perevaporation Prucesses in the Chemical Industry” Ottawa, Canada, 1992, p.233 167 C. K. Trinh and W.Sclmabel,Angew . M h o l . Chem.,1993, Xang Yu and P. Somasundaran,COILSur$ A. Physiicohem. Eng. Aspects, 1993, sl, 17 J. Katz and S. Kosmella, J. Coll. Inter$ Sci., 1994, laa.SO2 Y.Kikuchi and T.Koda, Bull. Chem.SOC. Jpn., 1979, 880 K. Kataoka, T.Tsmta, T. Akaike and Y.Sahwi,Mukromol. Chem., 1980, 1363 B. Philipp, H. Dautzenberg, K. J. Linow, J. Kiitz and W.DawydofE, Progr. Poiym. Sci., 1989, && 91 E. Tsuchida, J. MaRromol. Sci.-Pure Appl. Ckm., 1994, I A. Takahashi, Hayashy and I. Kagawa, Kogvo figah Zasshi, 1957, @, 1059 S. Dragan and L. Ghimici, Angew. Mdromol. Chem., 1991, && 199 S.Dragan and M.Cristea, unpublished data W.Arguelles-Monai, M. Garciga and C. Peniche-Covas, Polym.Bull., 1990, 307

a

a

a

COUNTERION BINDING ON CATIONIC POLYELETROLYTESWITH CATIONIC GROUPS IN THE MAIN CHAIN

Stela Dragan, Luminita Ghimici and Florin Popescu Institute of MacromolecularChemistry “Petru Poni” RO-6600 Jassy, Romania

1 INTRODUCTION

An extensive literature deals with the counterion binding in polyelectrolyte solutions from both theoretical and experimental points of view because a good knowledge of the nature of these interactions is a prerequisite for the understanding of the polyelectrolyte solutions properties. It is known that, in aqueous solution, polyelectrolytes are dissociated into polyions and a great number of counterions. The high charge density on the macroion backbone produces a high electrostatic potential around it and consequently a fraction of the counterions are bound to the charged groups of the macroion. The measurements both of the thermodynamic equilibrium and nonequilibrium properties of the aqueous polyelectrolyte solutions have shown that the counterion size, its polarizability and valence, water structure around the macroion and counterion, the charge density of the polyion are factors which play an important role in the counterion binding. This important feature of polyelectrolyte solutions has not been so intensively investigated for cationic polyelectrolytes as for anionic polyelectrolytes. In this context, we have investigated the interaction of several mono-, bi- and trivalent anions with some cationic polyelectrolytes by two methods usually used in the study of the counterion binding: viscometric and conductometric methods.

’-*

2 EXPERIMENTAL

2.1 Materials

Polyelectrolytes used in this study were cationic polymers with quaternary N-atoms and / or tertiary amine N-atoms in the main chain. They were prepared, either by condensation polymerization of epichlorohydrin (ECH) with dimethylamine (DMA) and N,Ndimethyl-l,3-diaminopropane (DMAPA) polymer type A, or by polyaddition of PEG diglycidyletherswith N,Ndimethyl-l,3diaminopropane polymer type PEGA. The structures of these polymers are presented in Scheme 1. Details about the synthesis of these polymers have been reported earlier. ’J’ The samples of cationicpolyelectrolytetype A were carefully purified by dialysis against distilled water until the absence of Cl- in the

-

-

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Novel Materials and Novel Applications

external water; the diluted solution were concentrated by gentle heat in vacuum to about 50 % wlw and then precipitated with acetone p.a. The sample were dried in vacuum over CH3 HC1 I +Cl' ff=HTCH-cH2+JfyTyK-CH&& I 1 (7H2h OH CH3 OH N: H3C CH3 / \

cationic polyelectrolyte A

cationic polyelectrolyte PEGA Scheme 1 P205, at mom temperature and were characterized by: [q]nm.c1=0.680 for A33 and [q]-1 =0.550 for & . Salts wed f NaCl, NaBr, Nd.2H20, Na2S04' NsPO+12H20) were analyticalgrade products and were used without further purification. 2.2 Mtthoda

Vimmetric measurements of the polyelectrolyte solutions were determined at 2 9 C using an Ubbelohde vismneter with internal dilution. Conductometric meururements were carried out with a Radiometer Copenhagen Model CFM 2d, using a CDC 114 conductivitycell. The water used had a specific conducti~tyof 162.4 pS. 3 RESULTS AND DISCUSSION

Studying the dependence of the reduced viscosity on the added salt nature and concentration, we have shown the different affinity of these polymers for mono-, bi- and trivalent counterims. The polymer concentration was kept constant 1.0 &/lo0mL. The reduced viscosity ( q d )vs. salt ~ t u r and e concentration is plotted in Figure8 14 Ib, Ic. The reduced viscosity decreases rapidly as expected, with the increase of the concentration. This suggests the association of a part of counterions to the charged groups

Progress in Ion Exchange: Advances and Applications

64

0' 0

1

I

0.5

I

b

I

1.0

Figure l a Variation of the reduced viscosity ( q / C ) of A5.3 vs. salt concenrration (Cs) : (X) NaCl, ( 0 ) NdO5 (0) N d r , (V)Nal@) Na.804, (4 N a 3 0 4 .

on the chain. An increase in salt concentration, enhances considerably the counterion binding reducing, at the same time, the hydrodynamic dimension of the coil. For As.3 and AS polyelectrolytes, at the same salt concentration, the reduced viscosity decreases in the following order: C1- > NO; > Br- > I' > PO:- > SO:- . The counterion binding increases in opposite order. As one can observe, the binding order increases in the halide series from Cl- to r, in line with the decrease of hydrated counterion radius. Following the curves which plot the viscometric behaviour of these polymers in the presence of SO4 and PO? anions, one can observe a more pronounced decrease of the viscosity in the low salt concentration regions. This indicates a remarkable binding of these counterions to the charged groups of the polyions. The SO? and PO?- anions can also associate with two and three, respectively adjacent ionic groups on the macroion, to f o m intrachain bridges leading to an additional folding of the polyion and hence to a more decreased viscosity. Nevertheless, the viscosity decrease is less pronounced at greater salt concentrations. In the case of SO: - ,the reduced viscosity of the solution passes through a minimum at about Cs = YlO-'M and then increases again at higher Cs. This phenomenon could be explained by an intermolecularassociation of the polymeric chains via binding of two nitrogen atoms. The plyelectrolyte type PEGA can bind both the cations and anions due to the presence of the PEG chains in the main chain. Some authors" studying the binding of

'-

65

Novel Materials and Novel Applications

electrolytes to poly(ethy1ene oxide) in 4ueous solutions have established that the anions are actually bound with the polyether through an iondipole interactions (the association has been attributed to the polarizability of the anion), whereas the other ones 12*13 have shown the binding is mainly determined by the cations. As we have alredy mentioned we have studied in this work the interactions of PEGA with salts containing an alkali metal cation ma’) and a series of different anions. . As one may see in Figure lc, a different interaction between anions and PEGA is indicated by the changes in the viscosity of the PEGA solutions. For the same salt concentration, the viscosity decreases in the following order: CT > NO; > Bf > r > SO? > PO’:. However, the interaction between PEGA and salts is less pronounced because this polymer has a low charge density. The electrical tnmpoxt properties of the polyelectrolyte solutions in the presence of low molecular weight salts vuy with the counterion type suggesting the difference in the strength of the interaction of these polymers with counterions. In our work we pursued the polyelectrolyte conductivity variation versus both the salt and polyelectrolyte concentrations. The specific conductivity (k) includes the contributions of wunterions, coions and polyions at the current tmwport and depends both on the number of ions per unit volume and on their mobilities.

0

0.5 CS ( m o V L 1

1.0

Figure 1b Variation of the reduced viscosig(qsp/C) of A 9 vs. salt concentration (cs): (X) N d l , (0) N d O s (0) NaBr,(q N d , (Q NaSOh (4 NaSO4..

Progress in Ion Exchange: Advances and Applications

66

The dependence of k versus polyelectrolyte concentration (Cp) has been used for obtaining the molar conductivity values. The molar conductivity of polyelectrolyte in a simple salt solution, & may be expressed by the equation 2: ''~1s

A = 10 '(k-t) I C,

(2)

where k and k, are the specific conductivitiesof the salt solution with and without added polyelectrolyte and C is the polyelectrolyte concentration, expressed in terms of mom. The molar conductivity of the polyelectrolyte solutions in the presence of uni-univalent low molecular salts increases slowly with decreasing of Cp (Figures 2 4 2b). At concentrations below 1.104 unit movL, where k differs only slightly 6om k,, the molar conductivityrises much faster with the decreasing of Cp. It is worth remarking that in the O : - counterions, the &-f i plots exhibit a pronounced minimum case of the SO:- and P between l.10'3 unit mom and 3.10" unit mom; the minimum that appears in these cases could be explained by maximum counterion interactions due to the increased intramacromolecular bridges, as we have already mentioned in the viscometric study. At concentrations less than l.10-3unit mom the expansion degree as well as the distance between two polyions increase enough to prevent the formation of these bridges. Similar minima in the conductanceplots were also observed for several salts of

0.050

0

Figure lc Varibtionof the reduced viscosity ( w / C ) of PEGA vs. salt concentration (Cs):(X)Ndl, (0) N d O s (a) NaBr, (V NaI, (0NaSO, (4NajpoC

r

Novel Materials and Novel Applications

67

polystyrene sulphonate with monovalent counterions and several divalent counterions.’ Concentration effects are not yet clear. From Figures24 2b, one can see that at the same polymer concentration the molar conductivitydecreases in the followingorder Cl-> NO3 > Br- > r > PO4 3- > SO,‘- for and Ap,this means the counterion binding increkrles in opposite order. This order of counterion interactions is in agreement with that obtained by viscOmetric measurements, as follows: the degree of interaction is higher for tri- and bithan for monovalent counterions and increases with the decreasing size of the hydrated ions. The molar conductivity values obtained in the case of & are lower than t h e obtained for A5.3 indicating the binding is stronger in the former case. This m y be due to the increased branching of the polyions which creates regions with higher numbers of

‘4 10

Figure 2a Vmation of the m o b comhctivity (Am), of A3.3 vs. po&lecmlyte concentration (Cp) in salt aqueous solutim: ( X ) N d l , (0) N&OA (9N d , (0) N ~ S O C(A) , Nap04

(0) NaBr,

Progress in Ion Exchange: Advances and Applications

68

2010-

Figure 2b Variation of the molar conductivity (h) of As vs. plyelectrolyte concentration (Cp) in salt aqueous solutions: (X)NaCl, (0) NaNOz (pl NaI, (0) Na2so4, (1)NaSO,.

(0)

NaBr,

charged groups, even at high dilution, and consequently an increased number of counterions is associatted to them. Tbe conductometric measurements have also confirmed the lower interaction between PEGA and the low molecular weight salts.

References 1. G. S. Manning, JChem. Phys., 1969,&924 2. F. Oosawa, “Polyelectrolytes”, Marcel Dekker, New York 1971. 3. G. S. Manning, Ann. Rev. Phys. Chem., 1972, 117 4. M. Mandel, “Polyelectrolytes”, Em. Polym. Sci. Eng.,m(Sec. Ed.), 1988

a

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Novel Materials and Novel Applications

5. D. G. Peiffer and R D. Lundberg, J. Polym. Sci., P o w . Chem. Ed., 1 9 8 4 , a 1757 133 6. A. Ikegami and Imai, J. Polym. Sci., 1%2, 1537 7. E. Pmkopova and J. Stejskd, J. Polym. Sci., Polym. Phys Ed., 1974, 8. B. Boussouir8, A. R i c d and R Audebert, J. Pdym. Sci., Polym. Phys. M.1 9 8 8 , a 649 9. S. Dragan and L. Ghiaici, A q w . M h o l , Chem. 1 9 9 1 , m 199 107 10. S. Dragan and L. Ghimici, Angw. Mdmnol. Chem., 1994, 11. R D. Lundberg, F. E. Bailey and R W. Callard, ,J. P o w Sci., Part A1,1966, &1563 1715 12. H. Awm,K Ono and K MuraLuni, Bull. Chem. Soc. Jpn.,1983, 13. R Sartori, L. Sepulveda,F. Quina, E.Lissi and E. Albiun, Mucmmolecules, 1990,23, 3878 14. U. P. Stmuss and S. Bluestone ,J Am. Chem. Soc. 1959, fi 5295 15. K T d and Horiuchi, Bull. Chem. Soc. Jjm, 1970, 2367

s

a

s

AN UNCONVENTIONAL SYNTHESIS OF STRONGLY BASIC ANION EXCWNGEBS

*,

Cornelia Luca **Violeta Neagu B.C. Simionescu

* **

* , G.

Grigoriu

*

and

"Petru Poni" Institute of Macromolecular Chemistry "Gh. Asachi" Technical University, 6600, Iagi, Romania

1 INTRODUCTION The most common method for the synthesis of strongly .basic anion exchangers is the chloromethylation of 3tyrene:divinylbenzene copolymers, followed by ainination, with trimethylamine or N,N-dimethyl-2-hydroxyethylamine, of chloromethylated copolymers. Our previous studies analysed the possibility of obtaining strongly basic anion exchangers by an unconventional method, namely chloruration of vinylto1uene:divinylbenzene copolymers, followed by amination of chlorurated copolymers with the above-mentioned amines. 1 9 2 The present paper analyses another unconventional method for the synthesis of strongly basic anion exchangers, involving the addition reaction of the protonated 4-viny1pyridine:divinylbenzene copolymer to ethylenic electrophilic compounds such as, acrylamide (AM), acrylonitrile (AN) and methylvinylketone (MVK); the same 3 reaction has been applied to linear poly(4-vinylpyridine). The objective of the paper was, on one hand, to

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Novel Materials and Novel Applications

observe whether the reactions really take place, and on the other, to determine some characteristics of the structures obtained, i.e.: exchange capacity, Fe(II1) ion sorption capacity and chemical stability in aqueous HC1 solutions. 2 EXPERIHENTAL

2.1.

Materials

4-vinylpyridine (4-VP) was purified by vacuum distillation immediately before use. Divinylbenzene (DVB) (57.45 wt. X DVB and 38.97 wt. X as ethylstyrene by G.C.) was freed of inhibitor by distillation. 2.2.

Methods

The starting 4-VP:DVB copolymer was obtained by suspension copolymerization of 4-VP with DVB using 1.5 wt. % Ba202 as initiator. The aqueous phase consisted of 3 wt. % NaC1, 0.12 wt. X gelatine and 0.5 wt. X ammonium salt of poly(styrene-comaleic acid). The organic:aqueous phase ratio was 1:3 v/v. The copolymerization reaction was allowed to proceed for 10 hours at 8OoC and 2 hours at 90°C. After copolymerization, the copolymer beads were separated by filtration washed with warm water and then extracted with methanol, in a Soxhlet apparatus, to remove traces of residual monomers and linear oligomers of 4-VP, and finally vacuum dried at 5OoC for 48 hours. The copolymer was characterized by its nitrogen content as determined by elemental analysis. The addition reactions were performed at 5OoC in a glass round bottomed f1as.k equipped with stirrer, reflux condenser and thennometer. The following method was applied: the copolymer preswollen in methanol was poured into the flask, 1 M aqueous HCl solution and an ethylenic compound being added. A nitrogen:HCl:cthylenic compound molar ratio of 1 :1 . 2 : 1 . 2 was used. After stirring for 24 hours at 50°C, the beads were isolated by filtration, washed with warm distilled water. They were then extracted w i t h either water, dimethylfodde, or acetone,

,

72

Progress in Ion Exchange: Advances and Applications

to remove respectively, the homopolymers, of AM, A N , or MVK (if any). Finally, the chemically modified copolymers were washed with methanol and dried under vaccuum at 5OoC for 48 hours. To observe whether the addition reactions had taken place, the samples yielded after these reactions were characterized by IR spectroscopy and as to their strongly basic exchange capacities. The IR spectra were recorded on a Perkin-Elmer 5 7 7 spectrophotometer (KBr pellets). The strongly basic anion exchange capacity was determined by C1- $-, S042- ion exchange. The Fe(II1) ion sorption capacity was determined a s fol1ows:chemically modified copolymer samples of 0.2 g, prepared as described, were contacted with 200 ml solution of 0.01 M Fe2(S04)3 for 7 days. The pH of the sample solution system was maintained at 2.0 by use of a solution of either H2S04 or KOH. After contact, the samples were filtered, washed with distilled water and air-dried. The Fe content of the samples was determined photocolorimetrically by use of M,d'-dipyridine, after its desorption with a solution of 1-1.5 M HC1. Several desorptions were performed, until no traces of Fe were found in the eluent. follows: The chemical stability was determined as chemically modified copolymer samples with determined ion exchange capacities were contacted with HC1 aqueous solutions of different concentrations for various contact times. An HC1:ion exchange capacity ratio of 20:l was applied. After contact, the samples were filtered, washed with distilled water until the absence of C1- in the eluent water was achieved. The ion exchange capacities were determined.

-

3 RESULTS AND DISCUSSION

The syntheses of chemically modified 4-VP:DVB copoly-

Novel Materials and Novel Applications

73

mers were performed according to Scheme 1.

Scheme 1

IR spectra of the structures obtained from the addition reactions given in Scheme 1, present the bands characteristic for -CONH2 to the Z groups, as follows: at 1670 cm" at 2250 cm" for -C=N and at 1715 cm" for C=O. These spectra also show a band at 1460-1470 cm", attributed to the deformation vibrations of the C-H bonds in the -CH2-CHZ- groups situated between the quaternary nitrogen atom and the Z group. The results of characterization, by exchange capacity, of the 4-VP:DVB samples chemically modified by the addition reactions given in Scheme 1, are listed in Table 1. The data provided by Table 1, and also by IR spectra, show that the products resulted from protonated 4-VP:DVB copolymer addition to the electrophilic ethylenic compounds (Scheme 1) possess strongly basic exchange capacities. They are strongly basic anion exchangers containing, in addition to quaternary nitrogen atoms, other functional groups with electron donating atoms such as nitrogen and/or oxygen, namely amide, nitrile and ketone groups. The exchange

,

Progress in Ion Exchange: Advances and Applications

74

capacities of the anion exchangers synthetized according to Scheme 1 lie within those of the classical strongly basic exchangers. Table 1

Characteristics of the products resulted from the addition reaction of 4-VP:gX DVB gel type copoly* mer to electrophilic ethylenic compounds.

Electrophilic e thylenic compound

Sample Code

4-VP:DVB 4-VP:DVB 4-VP:DVB

*

+ AM + AN + MVK

AM AN

Strongly basic anion exchange capacity meq/g meq/ml dried resin 2.20 3.98 2.23

MVK

1.34 1.78 1.30

Nitrogen content of starting 4-VP:DVB copolymer was 10.00 % (calculated 11.47 %).

It is known4 that strongly basic anion exchangers retain Fe(II1) ions from aqueous Fe2(S04)3 solution in the 7-14 mg Fe/g anion exchanger range, as R4N+(Fe3( S04)2(OH)6 7 , The anion exchangers synthesized in the present study, in also retain the Fe(II1) ions from Fe2(SOG)3, as shown Table 2.

-.

Table 2

Fe amounts retained by the synthesized anion exchangers.

Sample Code

4-VP:DVB + AM 4-VP:DVB + AN 4-VP:DVB + M V K

Amount of retained Fe (mg Fe/g dried anion exchanger) 57.15 40.58 63.76

75

Novel Materials and Novel Applications

The data listed in Table 2 show that the new ionic crosslinked structures containing quaternary nitrogen atoms retain much higher amounts of Fe than the crosslinked ionic structures with benzyltrimethylammonium chloride or benzyldimethyl-2-hydroxyammonium chloride groups corresponding to classical strongly basic anion exchanger of types I or 11, respectively. The retention of Fe might be induced by the ionic exchange in the R4Ni[Fe3(S04)2(OH)dform or by the complexing of Fe(II1) with amide, nitrile or ketone groups. The IR spectra of the chemically modified copolymers containing Fe(II1) ions display absorption bands at 1100, 870 and 620 cm", belonging to the free S042- ions, whereas the absorption bands at 1200 and 1300-1130 cm" belong to S042- coordinated with 3 metallic ions. The absorption band at about 480 cm" can be assigned to the 9 (M-0) metal 5 oxygen bond from S042-, OH-, H20. Another aspect worth mentioning in characterizing the IR spectra of the ionic polymer -Fe(III) complexes refers to the fact that the band characteristic of the amide, nitrile and ketone functional groups are not subjected to any shift. They may be found at the following valuer: 9 (CN) = 2250 cm", 9 (CO) 1710 cm" and $(CONHZ) 1670 crn-lshilarly to the situation in ionic polymers without Fe. All these observations promote the conclusion that the Fe(X1X) ions are retained by the new synthesized ionic polymers only through ion exchange. It was also observed that, although containing atoms that form donor-acceptor bonds, the functional groups do not participate in complexation. The presence of the nitrogen quaternary atom with an inductive effect (-I) probably reduces the electron density from the donor atoms of the functional groups, thus preven% complexation with metallic ions. It is possible that these functional groups can manifest only a catalytic effect in the retention of Fe, inducing higher retention values than the classical strongly basic anion exchangers.

-

-

-

76

Progress in Ion Exchange: Advances and Applications

Table 3 list the results for the chemical stability of strongly basic anion exchangers synthesized. The data in Table 3 show that, under the experimental conditions used in the present study, the anion exchangers possess a good chemical stability in acid medium. Influence of t h e concentration of aqueous HCL * solution on strongly basic anion exchange CEpeCity.

Table 3

Sample Code

Concentration of HCl

4-VP:DVB + AM

0 In 2n 3n

2.20 2.10 1.90 1.88

1.34 1.30 1.28 1.27

0 ln 2n 3n

3.98 4.00 3.70 3.86

1.78 1.77 1.75 1.73

0 In 2n 3n

2.23 2.15 2.10 2.00

1.30 1.28 1.27 1.28

4-VP:DVB

~-

+

AN

Strongly basic anion exchange capacity meq/g meq/ml dried resin

~

4-VP:DVB + MVK

~~

*

All experiments were made at room hours.

temperature for 24

4 CONCLUSIONS The addition reaction of protonated 4-VP:DVB copolymers to electrophilic ethylenic compounds such as: acrylamide,

77

Novel Materials and Novel Applications

acrylonitrile, methylvinylketone, leads to the synthesis of crosslinked quaternary ammonium compounds containing other functional groups, in addition to the quaternary nitrogen atom, These quaternary ammonium compounds possess strongly basic anion exchanger capacities, hence, the addition reactions presented may constitute a new, unconventional method for the synthesis of strongly basic anion exchangers.

REFERENCES

1.

C. Luca, V. Neagu, B.C. Simionescu in "Ion Exchange Processes: Advances and Applications", A. Dyer, H.J. Hudson, P.A. Williams (Eds), The Royal Society of Chemistry, Cambridge 1993, p. 337.

2.

C. Luca, V. Neagu, Ig. Poinescu, B.C. Angew.Macromol.Chem,, 1994, 222, 1.

3.

C. Luca, V. Birboiu, I . Petrariu and M. Dima, J,Polym.Sci.:Polym.Chem.Ed., 1980, 18, 2347.

4.

V.L. Gutsanu, K.I. Turta, V.A. Gofuchuk and N.V. Shafanskii, Zhurn.Fiz.Khimii, 1988, 62, 2415

5.

M.M. Shakarev, E.V. Margulis, F.I. Verahinina, Zhurn.NeorRan Khimii, 1972, 17, 2474.

Simionescu

AMPHOTERIC POLYELECTROLYTES WITH CARBOXYBETAINIC GROUPS

Cornelia Luca, Emilia Streba and Virgil Bgrboiu "Petru Poni" Institute of Macromolecular Chemistry 6600, Iagi, Romania

1 INTRODUCTION

Amphoteric polyelectrolytes contain both acidic and basic functional groups. Another type of polyampholyte, the so-called "polybetaines", as polycarboxybetaines or polysulphobetaines have oppositely charged functional groups pendant to the same structural unit. 1 One of the main features of these polymers is the presence of a permanent dipole which is due to the covalent chemical bonds between the ionic functions. 2 The polysulphobetaines can be prepared by alkylation of monomers containting tertiary arnine groups using 1,4-butanesultone (or propanesultone) as well as by addition of the monomers to alkenylsulphonylchloride, followed by the polymerization of zwitterionic monomers. 3-6 Interestingly, polysulphobetaines show "antipolyelece lyte" behaviour, that is low solubility in water which increases, with chain expansion, in the presence of increasing salt concentrations. 6 9 7

Novel Materials and Novel Applications

79

Poly(carboxybetaine)s with one, two or three methylene groups between the opposite charges were synthesized by the alkylation of N-vinyl imidazole with halocarboxylic acids, followed by polymerization of the yielded betaine monomers. The solubility behaviour of these poly(carboxybetaine)s depends on the number of methylene groups between the opposite charges. a A poly(carboxybetaine) with one methylene group between the opposite charges, based on poly(4-vinylpyridine), was obtained by the alkylation of this polymer with chloroacetic acid. This zwitterionic polymer displays polyelectrolyte behaviour in aqueous solutions. 9,lO The synthesis of poly(carboxybetaine)s, based on poly(4-vinylpyridine), with a spacer between the opposite charges containing two methylene groups, with or without side The groups, was reported in a previous study of ours. l1 method applied involved the addition reaction of poly-unsaturated carboxylic (4-vinylpyridine) to several d acids such as: acrylic (AA), methacrylic (MeA), crotonic ( C r A ) , itaconic (IA), fumaric (FA) and maleic (MA) acid. The present paper discusses the results obtained using new experimental conditions for some of the above mentioned reactions. For the sake of comparison, our previous results are presented. The paper also analyzes briefly the solu*ty and viocosimetric behaviour of the synthesized poly(carboxybetaine)s.

,p

The starting poly(4-vinylpyridine) (P4VP) was prepared, purified and characterized, as reported. 11 The preparation, purification and characterization of the above poly(carboxybetaine)s used were the same as in mentioned literature. Vicosimetric determinations were performed using a Ubbelohde viscometer with internal dilution in a constant

Progress in lon Exchange: Advances and Applications

80

temperature bath (25.00

2 0.OS"C).

3 RESULTS AND DISCUSSION As expected, the reaction between a pyridine compound and an d , -unsaturated carboxylic acid can take place with neutralization and/or addition, the products obtained being either a salt (S) and/or a carboxybetaine (B), as indicated by eqs. (1) and (2):

/8

\

-

N+

0

7 \N

+

-0oc

/"

fl

C-C-COOH

/

-H

i

R2

1

1/. N+-

- ?1c - c'\ H

(1)

R2

(s)

' t y 1

C

I

-

CH

-

COO-

(2)

R2

where:

R1 Rp

-

-

H;

CH3;

CH2COOH

H;

CH3;

COOH

The reaction conditions and the molar transformation degrees, fg and fS (fraction of betaine units and salt for some reactions of P4VP with units, respectively), 4,p -unsaturated carboxylic acids are listed in Table 1. The data given in Table 1 show that the reactions of P4VP with d , -unsaturated carboxylic acids lead to polymers with only betaine structural units in the case of AA, MeA, CrA, IA and FA (which can be considered as

P

81

Novel Materials and Novel Applications

weak acids), and to polymers with betaine and salt itructural units in the case of M A (which is a stronger acid than the former ones). The f g fraction is strongly dependent on the reaction conditions. Thus, the addition rate increases with solvent polarity, very long reaction times being necessary in the case of CrA and MeA. Table 1

Characteristics of the polymeric products resulted in reactions of P4VP w i t h d,p-unsaturated carboxylic acids under different conditions.

Resultant Polymer

Reaction Time

Methanol fB

~~

P4VP P4VP P4VP P4VP P4VP P4VP P4VP P4VP P4VP P4VP P4VP P4VP

fS

Methano1:Water (1:l v/v) fB

fS

< 0.10

-

~

+ AA-1

+ AA-2 +. AA-3 + AA-4 + AA-5 + CrA-1

+ CrA-2 + MeA-1 + MeA-2 + IA-1

+ FA-1 + MA-1 ~

8 24 48 72 140 24 240 24 240 24 24 24

0.37 0.60 0.80 0.86 0.98 < 0.10 0.27 < 0.10 0.25 < 0.10 <,0.10 0.33

0.25

0.87

< 0.10 0.85 0.87 0.63 0.54

0.46

~

All reactions were performed at 50°C, and with a pyridine structural unit:acid molar ratio of 1:l. The poly(carb0xybetaine) derived from AA dissolves readily in water, and in aqueous solutions of the alkali metal salts, when their fg values are higher than 0.3.

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Progress in Ion Exchange: Advances and Applications

As known, the poly(su1phobetaine) with two methylenic groups between the opposite charges and without side groups, based on P4VP, was insoluble in water but dissolved readily in aqueous solutions of NaC1.6 This behaviour has been interpreted as being due to the presence of a collapsed coil in water as a result of intra-salt and intra-chain htew3hs. These interactions are broken in the presence of an electrolyte like NaC1, leading to dissolution of the polymer. 4,12 We suggest that the difference in the solubility in water of poly(su1phobetaine) and poly(carb0xybetaine) could be caused by the stronger Coulombic interactions of N+- SO; + COO-. in comparison to those of N derived from CrA and MeA with fg Poly(carboxybetaine)s 0.87 and 0.85, respectively have the s ~ m e solubility behaviour

-

as the poly(carb0xybetaine) from AA. Comparison of literature data with the present ones shows that both poly( su1phobetaine)s and poly(carboxybetaine)s, with side methyl group at the spacer between the opposite charges, are soluble in water. All poly(carboxybetaine)s derived from the monocarboxylic acids (AA, CrA and MeA) show typical polyelectrolyte aqueous behaviour, because the reduced viscosity of their solutions increases with decreasing polymer concentration. Viscosity also decreases by addition of a simple salt i.e., NaCl (Fig. 1).

i Figure 1. Reduced viscosity against polymer concentration for P4vp + AA-5 i n water and NaCl aqueous solutions of various concentrations. Cs molar concentration of salt. 5

0.0 1 0.0 0.2 0.4 I

I

I

I

0.6 0.8 1.0 1.2 1.4 c(g/dL)

Novel Materials and Novel Applications

83

Behaviour of the intrinsic viscosity as a function of NaCl concentration was examined for polymer P4VP + AA-5 (Fig. 2).

0.01 0.01 1

Figure 2.

I

0.05

I

1.0

I

1.5

I

u)

Intrinsic viscosity against molar salt (NaCl) concentration for P4VP + AA-5

This polymer exhibits the usual decrease of the intrinsic viscosity with increasing NaCl concentration in the 0.01 0.05 M range. A t higher malt concentrations, intrinsic viscosity has little response to charga in the range 0 . 0 5 4 2.0 M NaC1. Figure 3 shows the viscosimetric behaviour of P4VP + AA-5 solutions in the presence of several salts. For poly(acrylates), the following binding sequence of alkali metal ions has been observed: ti+ > Na' > K+ > Cs+ 13 The same binding sequence exists in the case of the poly(carboxybetaine) P4VP + AA-5 (lines 1 and. 3, Fig. 3). It

-

.

Progress in Ion Exchange: Advances and Applications was also observed that the binding sequence between SO4 2- and

84

C1- is S042- > Cl-,which is known for quaternary ammonium compounds. Such observations show that, in poly(carboxybetaine) P4VP + AA-5, the carboxylate and quaternary ammonium groups maintain their identity; no reciprocal influence being observed.

0.8}

-0 v

0 \

0.4 -

n

a

so.2-u

Figure 3.

n

u

"

n

n

U

n

v

n U

U

n 2 " 3

Reduced viscosity against polymer concentration of for P4VP *. AA-5 in 0.1 M aqueous solutions different salts. 1

- KC1;

2

- NapS04;

3

- NaCl

Poly(carboxybetaine)s derived from IA, FA, and MA (i.e., dicarboxylic acids) are insoluble in water. Addition of simple salts such as NaC1, LiC1, KC1 etc., leads to opalescent solutions, while addition of HCl gives clear solutions. In the latter case, the transformation from carboxybetaine units into quaternary ammonium salt units takes place, according to equation (3):

85

Novel Materials and Novel Applications

\ . +- C yN

' - CH - C O O - + HCl 42."I

I

- COOH, Cl-

(3)

This solubility behaviour of P4VP + IA, P 4 V P + FA and P4VP + MA mnybe caused by the presence of intra- and intermolecular hydrogen bonds between the carboxylate and the carboxyl groups. These interactions are broken up in the presence of HC1.

4 CONCLUSIONS The reaction of P 4 V P with d,~-unsaturated carboxylic acids such as: AA, CrA, MeA, IA, FA and MA leads to polymers with carboxybetaine structural unit. The carboxybetaine structural unit content, namely fg, is controlled by the reaction conditions. From these reactions, two types of polymer appear: polymers with only carboxybetaine structural units derived from the acids having pKa > 2, namely AA, CrA, MeA, IA and FA; polymer with mixture of carboxybetaine and salt structural units, derived from the acid with pKa C 2 i.e., MA. The poly(carboxybetaine)s derived from P4VP and monocarboxylic acids are soluble both in water and aqueous solution of alkali mataf salts. In water, these poly(carboxybetaine)s display a polytype behaviour. electrolyte The insolubility in water is typical for the poly(carboxybetaine)s derived from P4VP and dicarboxylic acids.

-

-

Progress in Ion Exchange: Advances and Applications

86

REFERENCES 1.

E.A. Bekturov, S.E. Kudaibergenov and S.R. Rafikov J.M.S.-Rev.Macromol.Chem.Phys., 1990, C 30(2), 233

2.

T. Hamaide, M. Gnambodoe and A. Guyot, Polymer, 1990, 31, 286

3.

R. Hart and D. Timmerman, J.Polym.Sci., 638

4.

J.C. Salamone, W. Valksen, S.C. Israel, A.P. Olson and D.C. Raia, Polymer, 1977, 18, 1058

5.

V.M. Monroy Sato and J.C. Galin, Polymer, 1984, 25, 121

6.

T.A. Wielema and J.B.F.N. 1987, 23, 947

7.

J.C. Salamone, C.C. Tsai, A.P. Olson and A.C. Watterson, Polymer Prepr., 1978, 1 9 ( 2 ) , 261

8.

T.W. Wielema and J.B.F.N. 1990, 2 6 ( 4 ) , 415

9.

H. Ladenheim and H. Morawetz, J.Polym.Sci., 251

1958, 28,

Engberts, Eur.Polym.J.,

Engberts, Eur.Polym.J., 1957, 2 6 ,

10.

T.K. Dzumadilov, Z.Kh. Bakanova and E.A. Eur.Polym.J., 1986, 22, 413

11.

V.

12.

D.N. Schultz, D.G. Peiffer, P.K. Agarwal, J. Larabec, J.J. Kaladas, L. Soni, H. Handwerker and R.T. Gardner, Polymer, 1986, 27, 1734

13.

R.W. Armstrong and U.P. Strauss. In Encyclopedia of Polymer Science and Technology, vol. 10, p. 804 Interscience, New York (1969)

Bekturov,

Bllrboiu, E. Streba, C. Luca and Cr.1. Simionescu, J.Polym.Sci. Part A: Polym.Chem., 1995, 33, 389

ANIONIC ION EXCHANGERS AS PHASE TRANSFER CATALYSTS IN ALKYLATION REACTIONS

Fernando Vmna, Federico Mijangos, Jose 1. LombraRa and Mario Dhz* Lkparment of Chemical Engineering University of the Basque Country (*) University of Oviedo Apdo 644 Bilbao. Spain.

1 ABsTRAa

The application of commercial anionic resins as Phase Transfer Catalysts m) has been studied in an alkylation reaction. The akylation of phenylacetonitrile with 1-bromobutane using excess of aqueous sodium hydroxide (50% wlw) was carried out catalyzed by insoluble polystyrene-bond ammonium ions in a triphasic system. A commercial polystyrenic anionic resin of type II (Lewatit MP-600 by Bayer) was selected because of its better performance. Reaction rate increases when: (1) stirring speed increases within 500-1600 rpm, (2) particle size decreases within 0.902 to 0.402 mm and (3) higher hydroxyl ion concentrations in the aqueous phase. The presence of halides such as bromide or iodide in aqueous phase decreases the reaction rate. 2 INTRODUCTION The alkylation of molecules containing -CH2 groups, classified as weak acids, belong to a kind of reaction that presents a great difficulty to carry out. Conventional methods need to use a solvent (i.e. dimethylformamide) and chemicals (sodium amidure) which are difficult to handle, recover after reaction, and also require very strict reaction requirements (anhydrous). The employment of soluble catalysts (ammonium quaternary salts) enables the reaction to be carried out using as neutralizing agent. Concentrated NaOH solutions has been suggested to perform these alkylations. The employment of solvent is avoided with this technique which is called phase transfer catalysis (PTC).The use of these catalysts permits very good -lation yields with a higher selectivity for the monoalkylation than for the diakylation The utilization of solids that bond active groups (quaternary ammonium cations) over a polymeric structure has been proposed some years ago*. The employment of these catalysts has the advantage of their easy recovery after the reaction and obtaining reaction products without impurities. Catalysts could be recycled for a new alkylation process. This study analyzes the possibility of applying commercial resins as alkylation catalysts. These resins have a relative low cost and easy availability, and can be directly applied at the industrial scale. In this work, the reaction selected for alkylation was phenylacetonitrile (PAN)plus 1bromobutane to lead to 2-phenylhexanonitrile (monoalkylated product) and 2-butyl 2phenylhexanonitrile in presence of concentrated sodium hydroxide solution.

88

Progress in Ion Exchange: Advances and Applications

CdyCH2-CN

+ Br-CqHg ->

C&-CH-CqHg CN

+ C&IyC-(Cflg)2 CN

The alkylation of very weak acids, like PAN, with phase transfer catalysts takes place in two steps: (1) the formation of the carbanion, according to: [catalyst] CdyCH2-CN + OH- -> C6HyCH-- CN + H20

(neutralization)

and (2) the reaction of the anion formed with the alkylating agent (l-bromobutane). C&Ig-CH-- CN + Br-CqHg ->

CgHyCH-CqHg CN

(aylation)

It has been generally accepted that the first step take place at the aqueous/organic interface and the second in the bulk of the organic phase. The role of the catalyst would be to stabilize the carbanion formed at the interface and to introduce it in the bulk organic phase, in conditions of high reactivity2. Since the reactions of carbanions with the alkylating agent are usually very fast, it is likely that the formation of carbanion is rate limiting, whenever mass transfer or interparticle diffusion does not control the reaction. 3 EXPERIMENTAL METHODS The alkylations of PAN with l-bromobutane were carried out in a 750-mL batch stirred reactor equipped with a condenser and temperature controller. The reaction temperature was kept constant within f l ° C by a thermostated bath. In a standard run the reactor is charged with 102 cm3 of aqueous sodium hydroxide (50% w/w). 28.91 cm3 (0.248 mols) of PAN and 34.05 cm3 (0.310 mols) of l-bromobutane. The mixture was heated to reaction temperature and then wet resin were added (2.5 g dried). Reaction mixture was stirred up to 1,600 rpm. The samples were analyzed by Gas Chromatography with a 5 ft x 1/4 in. column of 20% SAE-30 on 60/80 mesh Chromosorb W at 200OC. 4. ANALYSIS OF THE ALKYLATION KINETICS 4.1 Catalyst selection

Several commercial anion ion exchangers (Lewatit, from Bayer) were tested as FTC for alkylation of phenylacetonitrile with l-bromobutane. The studied characteristics were: anion exchange center (type I and 11, with different functinal group), matrix structure (macroporous or microporous) and chemical composition of matrix (polystyrenic and acrylic). The anionic exchangers bound ammonium ions used are shown in Table I. Type I resins have a tetramethyl ammonium cation, while type I1 have a ethyl trimethyl ammonium cation as functional group. In all cases studied, slower kinetics than those obtained for the alkylation catalyzed with soluble catalyst (triethyl benzyl ammonium cloride, TEBA) were found. The results achieved with these resins are shown in Figure 1. A higher reaction rate was obtained with the resin MP-600 whose characteristics are: type 11, macroporous and polystyrene.

89

Novel Materials and Novel Applications

Experimental results indicate that the more porous is the matrix structure is the greater is catalytic activity. This is due to the high accessibility to the active centers for the molecule of PAN. Moreover, the larger ammonium quaternary functional groups also increase reaction rate, which confers great lipphicity to the active centers of anion exchanger.

Table 1.- Commercial resins (Lewatit, BayerA.G.1 used as catalyst. Anion exchanger

Type

Structure

Matrix

MP-600 MP-500 M-500

II

macroporous macroporous microporous microporous

polystyrene polystyrene polystyrene acrylic

I I I

AP-246

0

20

40

60

80

100

TIME (min) Figure 1.- Alkylation kineticsfor commercial anionic exchangers.

4.2 Inert solid phase

The catalytic activity of the anionic resins that support ions of quaternary ammonium could be explained in the same way as that of ammonium quaternary soluble salts. These active centres participate either in the step of removing the proton (neutralization), or in the alkylation reaction by stabilization of the carbanion formed. Nevertheless, it is also possible that the increase of reaction rate observed in relation with the non-catalyzed reaction could be due to an improvement in the contact between the organic and aqueous phase. The presence of solids causes an increment of the interfacial area, favouring the reaction rate of the phenylacetonitrile with the hydroxyl anions at the aqueous /organic interface.

Progress in Ion Exchange: Advances and Applications

90

An experiment with a cationic exchanger (Lewatit SP-112) was carried out to check the role the resin functional group. Lewatit SP-112 does not contain ammonium quaternary groups and can not be considered a phase transfer catalyst but this resin has similar characteristics, structure and particle size, as the anion exchangers selected as alkylation catalysts.

Conversion shows time profiles similar to that obtained when the alkylation reaction is carried out in absence of catalyst, yielding very low conversions up to 90 min reaction time. These results confirm that the reaction rate increment with the employment of anionic resins with is fundamentally due to the participation of ammonium quaternary groups in the alkylation mechanism.

4.3 Catalyst Selectivity

An important aspect concerning the utility of any phase-transfer catalyst for phenylacetonitrile alkylation is the selectivity for monoalkylation versus dialkylation. Figure 2 shows the conversion attained for both produts. Monobutyl product had yields of 88% and dibutyl product was limited to 6%. Since the reaction of monoalkylation takes place to a more intensive degree than dialkylation, in this work, only the first alkylation of the phenylacetonitrile was considered, and formation of dialkylated product was assumed negligible. C&IS-CH~-CN+Br-CqHg -> C&-CH-C4Hg CN

100 89

MONOALKYLATION

60 40 DIALKYLATION

20

0 0

20

40

60 80 100 TIME (rnin)

Figure 2.- Kinetics of monoalkylation and dialkylation of phenylacetonitrile with 1 bromobutane with the ion exchange MP-600as catalyst.

91

Novel Materials and Novel Applications

4.4 Stirring Speed Alkylation experimentswere carried out at different stiring speeds beween 500 - 1,600 rpm in standard conditions. The reaction rates of alkylation catalyzed by anionic exchangers increases with agitation within the tested range. This indicates an important effect of the diffusion processes in the reaction rate or the existence of a interfacial mechanism in the alkylations in presence of concentrated solution of caustic soda. According to this last mechanism, the deprotonation of PAN occurs only at the aqueous/organic interface while the ammonium cation acts as a carrier of the organic anion from the interface to the bulk organic phase.

(-w+)

A kinetic equation of fust order respect to the two reagents: phenylacetonitrileand 1bromobutane,was considered to study the influence of different parameters in the reaction rate. This equation fits accurately to the experimental results, where,

-rpm= kobs [PANJ [ l-bromobutane]

- rpm = mol / cm3 s [PAN] = mol / cm3

[l-bromobutane]= mol / cm3

bs = cm3 s-1 mol-1. The kinetic constant,( shown in Figure 3). has been calculated by the correlation of the experimental data. The Figure 3 show how the reaction rate increases with the interfacial surface within the tested range. In previous studies on soluble catalyst akylation has been obserbed that the constant k,,bs does not change at stirring speeds higher than 1,300 rpm, approximately3. The solid phase improve interfacial contact, either L L or S-L (aqueous or organic), enhancing kinetics. These results agree with those cited by several authod.5 who also have observed an increment in the reaction rate in reactions such as nitriles formation, displacementreactions or in others where there is halogen exchange and new alkyl halides are formed.

4.5 Catalyst Particle Size The effect of particle size on alkylation kinetics was studied. Different samples of catalyst with mean particle diameters : 0.92 mm, 0.47 mm and 0.40 mm were used. The rate of the triphasic reactions was dependent on the catalyst particle size. Small particle sizes increase L-L interfacial area. Moreover, the effect of particle size could be due to the intraparticular diffusion control. In this case, an incrementin the reaction rate was oberved when the catalyst particle size decI.eased (Figure 4). When mass transfer is rate limiting, reaction rates are directly proportional to catalyst surface area and inversely proportional to the sphericalcatalyst particle radius6. If reactants must be transported into the catalyst particle for reaction to occur, the rate depends upon some combination of the intrinsic reaction rate at an active site and the intraparticle diffusivity of the reactant. The dependence of kinetic constants with the size of particle is show in Figure 4, in which is observed that constant decreases with the particle size. This effect is justified by greater external area of the catalyst solid and higher accessibility of the reagents to the active centers inside the resin. The high value of the slope observed indicates that this effect is not solely due to a larger area of solid, but principally to the minor particle diameter that favours the intraparticlediffusion p'ocess.

92

Progress in Ion Exchange: Advances and Applications 1.2

* 1.1 w

L I

8 ? v)

E

1

0.9

0.8

" 0.7 v)

$ Y

0.6 0.5

0.4 400

600

800 1000 1200 1400 1600 1800

=Pm Figure 3.- Stirring speed eflect on kinetic constant kobs within 500-1,600rpm range.

3

2.5 n v1

I

Eo2

;?

5

v

1.5

%

M 1

0.5

1

2

3

4

5

6

l / r (mm-1)

Figure 4.- Effect of catalyst particle size on reaction rate.

7

93

Novel Materials and Novel Applications

This agrees with the improved results achieved with the macroporous resins compared with the microporous ones. Moreover, this effect also agrees with the higher reaction rate observed for the dialkylation which is relatively more favoured in their access to the active centers due to the greater volume of the molecules. Table 2 shows the kinetic constant ratios of both alkylation reactions. Table 2.- Reaction ratesfor mono and dia&l.arion at diferent catalystparticle sizes. Particle size (mm)

h'k2 (a)

0.920 0,47 1 0,402

20.50 9,60 7,OO

(a) Kinetics constants of monoalkylation and dialkylation ratio. 4.6 Catalyst concentration

The dependence of the reaction rate with the catalysts concentration was studied in the 5 3 meq C1- /L to 88 meq C1- /L range, refenred to the organic phase volume. The results show a proportional dependence of the reaction rate with the catalyst concentration. So, the plot of In k vs In [catalyst] show a linear dependence whose slope is approximately equal to one, so; - rpm oc [Catalyst] consequently, the kinetic model of phenylacetonitrilealkylation can be rewriten, -rpm= h b s [ P W [ 1-bomobutane] [Catalyst] where, [catalyst] = meq cl-/cm3 bs = cm6 s-1 mol-1 meq CI- -1 .

4.7 Temperature Effects

The monoalkylation reaction rate was determined from experiments at temperatures within the 60 to 80 O C range. A strongly dependence of the reaction rate to the temperawas observed.Table 3 shows the calculated values &&,& for the three temperatures. Table 3.- Temperature dependence of reaction rate. Temperature "C

kobs x lo2 (cm3 s-1 mol-lmq CI--1)

80 70 60

2.42 1.70 0.468

94

Progress in Ion Exchange: Advances and Applications

The apparent activation energy was calculated, 80,25 kJ mol-l, from the slope of In b b s vs lm. This Arrhenius energy is relatively high for strongly limited by diffusion or ion exchange reactions (< 10 kcal mol-I) and seems to indicate a reaction control in the

alkylation. 4.8 Hydroxyl concentration The effect of sodium hydroxide concentration in the aqueous phase has been analyzed within the 8 to 19 mom range. Table 4 shows kinetic constants kobs for these concentration range. The plot of In b b s vs In [NaOH] shows a dependence of order 4 with respect to hydroxyl concentration in aqueous phase (- rpm Dc [NaOHI4). Higher kinetic orders for sodium hydroxide have been obtained by other authors7. This dependence of sodium hydroxide concentration is not justified by effect of ionic equilibria, but the increase of basicity (greater activity) of the ions OH- at p t e r concentrations. Table 4.- Hydroxyl concentrationdependence of reaction rate. NaOH concentration (moliL)

kobs (cm3 s-1 mol-1)

19 12 8

1,068 0.147 0,0106

4.9 Others ions in aqueous solution 4.9.1 Bromide The catalytic activity in the reactions catalyzed by resins with cationic groups must be related with the ionic equilibria between the resin exchanger and the anions present in the reaction medium. An functional group is only a catalyticaly active centre when in the hydroxyl form or bonded to the carbanion formed. During the reaction, ions B r are produced in the medium and this reduces the catalytic activity of the exchanger, because some centres will be blocked by bromide. Bromide ions (1.96 mol/L) were introduced into the aqueous phase to analyze its effect in the alkylation kinetics. The kinetics are analyzed to check the "poisoning effect" produced by the association of this anion with the active centers of the exchanger. Figure 5 shows that reaction rate decrease in the presence of significant amounts of B r . This effect is due to the occupation of active centres of the resin by bromide ions ("poisoning"). These groups in the resin taken by anions other than OH- or PhCH-CN would lose activity. This negative effect would be different depending on the type of anion present (I- > Br- > Cl-) in the aqueous phase. This "poisoning" is more important when the ion halide affinity for the resin catalyst is greater.

95

Novel Materials and Novel Applications 4.9.2 Iodide. Alkylation with l-iodobutane

Alkyl bromides, as alkylating agents, have often been used in biphasic (aqueousorganic) PTC systems for alkylation reactions. In these systems, the use of alkyl iodides not employed because of the great lipophicity of I- and its great affimity for the catalysts.The alkyl iodides, however are good alkylating agents when the reaction is carried out without catalyst 2. A similar behavior can be expected in the reactions catalyzed by strong anionic exchangers due to the occupation of higher number of active c e n m by iodide anion ("poisoning"). The alkylation of phenylacetonitrile with l-iodobutane was carried out using the exchanger Lewatit MP-600 as catalyst, in similar conditions to those employed with l-bromobutane. 100

80

n

# W

60

2

s

*

40 20

0

u

0 0

20

40

60

80 100 TIME (min)

Figure 5.- Effect of aqueous bromide ion on reaction rate. A similar initial reaction rate was observed in both cases, since at the beginning of the reaction the amount of I- in the medium is very low. However, when the alkylation takes place, the amount of iodide anion in the aqueous phase becomes appreciable and, consequently, the reaction rate decreases because of catalyst poisoning by I-. Then, values of 1.068 (cm3 s-1 mol-l) for alkylation with 1-bromobutane and 0.398 (cm3 smol-1) for alkylation with 1-iodobutane were obtained.

9

References

1.- S.L. Regen, J. A m Chem Soc., 1976.98, 6270. M.Dim, F. Varona, J. Gondlez, A$nidad, 1990.47.105. 3.- M.Makosza and E. Bialwka, TetraedronLer~1977.183 4.- H. Molinari, F. Montanari, S. Quici and P. Tundo, J. Org. Chem., 1979.43, 156 5.- M.S.Chiles, D.J. Jackson and P.C. Reeves, Org. Chem. , 1980,45, 2915 6.- F. Helfferich, "Ion Exchange", (chapter 1l),MacGraw-Hill, New York ,1962 7.- R. Solaro, S. D'Antone. E. Chiellini, J. Org. Chem., 1980,45,4179. 2.-

REAGENTLESS SEPARATION OF ELECTROLYTE MIXTURES USING ION EXCHANGE RESINS

N.B. Ferapontov, H.T. Trobov, V.I. Gorshkov, L.R Parbuzina, N.L. Strusovskaya and O.T. Gavlina Department of Chemistry Lomonosov Moscow State University Moscow 119899 Russia

1 INTRODUCTION

Usually m ion exchange separation methods auxiliary ions and reagents are used for @lacing the mixture bemg separated from the ion exchanger. Application of auxiliary reagents entails some additionaloperations such as ion exchange resin and auxiliary reagent regeneration. These additional operations require expenditure of other reagents and result m a large amount of waste. Moreover, the efficiency of ion exchange separation decreases with increasing of solution concentration, due to the reduction m equilibrium separation coefficient, and to the sorption fiont m the column swelling [ 1,2]. These drawbacks can be considered as the factors hampering the wider application of large-scale ion exchange separationprocess. The method described below is free from these disadvantages [2]. It is based on the differences in molecular absorbabllrty of electrolytes by ion exchangers. As it is known [3], an ion exchanger grain placed in an electrolyte solution absorbs water and electrolyte m proportion to their ratio m the solution. If electrolyte and ion exchanger have the same counter-ion, then ion exchange is absent m this case, and only molecular absorption takes place. During the authors' research an experimental procedure was developed [4], founded on the fact of the relation between electrolytes concentrations inside and outside the grain being always different. Using these differences high separation efficiencies can be achieved. Because the ion exchanger does not change its ionic form during separation, ion exchanger regeneration is not necessary. This is possible if the substances being separated and ion exchanger have the same ion. For example, NaCl is easily separated from CaClz admixture with the use of C1-form anion exchanger, while KNO3 and KC1 separation proves to be good with the use of the K-form cation exchanger. As it follows from the above, m this method cations are separated on an anion exchanger, and anions on a cation exchanger. The proposed method of electrolyte solution separation makes it possible to treat efficiently moderate and high concentration solutions, in d c h it differs from the existing ion exchange methods. Moreover, the method productivity goes up as long as the solution concentration also increases.

97

Novel Materials and Novel Applications

2 EXPERIMENTAL The AX and BX electrolyte mixed solution to be separated is passed through a column containing water-washed X-form RX ion exchanger. Obviously, no ion exchange will take place after ion exchanger and the solution are contacted, due to their possessing the same X- ion. At the same time, the unequal adsorbabdity of the electrolytes by the ion exchanger results m one of the electrolytes accumulating m the ion exchanger grains by comparison with the initial solution. If AX electrolyte enjoys a higher affitutv than BX electrolyte to the ion exchanger, then the former (AX) will be e x c e e l y accumulatjng, due to which the solution getting poor m that substance, and its total concentrationm the solution decreasing. If the columu is high enough, therein wiU appear a zone containing BX electrolyte only, and which can be separately collected (Figure 1 a,b). The concentration of BX m such a case is close to its concentrationin the initial solution. After the c o b reaches equilihium with AX + BX, the initialcomposition solution can be recovered (Figure lc). AX electrolyte recovery is accomplished by water-washing of the column (Figure Id). In the course of the initial mixed solution being driven out, the pure AX electrolyte mne is accruing m the columu, the solution of which electrolyte is easily recovered after removal of the initial solution. The refined AX electrolyte concentration is obviously higher than that of the initial solution. If the initial solution has a small &action of AX, the latter can be concentrated at least tenfold. After the c o h washing to remove AX is finished, it is m equiliirium with water and is ready for the next cycle. Figure 2 shows the breakthrough curves of component concentrationsand m a t e composition, as function of the quantity of the solution passed. The electrolytes separation by the proposed method can be run m continuous mode as well. The flowsheet of thisprocess is shown on Figure 3. The process is carried out m two AX+BX

AF+BX

AX+BX

++++++ ++++++ :AX: +****+ ++++++ ++++++ ++++++ ++++++ ++++++ ++++++ +---++

++++++I

+++---+

++++++ ++++++ ++++++ ++++++ ++++++ ++++++

++++++

++++++ ++++++ ++++++ ++++++ ++++++

a

b

Figure 1 The SeparationProcess Scheme

C

d

98

Progress in Ion Exchange: Advances and Applications

counter-current columns. The BX electrolyte is being extracted and accumulated in the first column, and the AX in the second one. The water-washed ion exchanger &om the column 11is fed into the column I (Figure 3), and fiom the column I a suspension of ion exchanger m the state of e q u i l i i d with the initial solution is supplied into the cohunn II. The solution of inhial composition coming out of the column II, is joined to the feeding solution and re enters column I. Counter-current technique usage provides not only a marked gain m productivity [5]. The continuous presence of the sorption fionts inside the columns allow economy of the washing water, whilst enjoying the production of more concentrated solutions, as a result of the process two electrolyte solutions, AX and BX are withdram. The unseparated mixed solution is sent back to be reprocessed. 3 RESULTS and DISCUSSION

The efficiency of separation, besides the integral concentration of the solution, is subject to the nature of the electrolytes being separated, and to the ion exchanger properties. The quantity of the absorbed electrolyte depends on the nature of the ion exchange group and increaseswith decrease of ion exchanger cross-linking. The ion exchanger regeneration stage is absent in the operating cycle. It results in no a u x h r y reagents expenditure, no waste water, a simpler technological flow sheet of the separation process, less equipment, and a lower energy consumption. Changing the column size does not S e c t the method efficiency, hence, no scale-effect exists. These advantages provide the economic efficiency of the method and make it environmentallysafe. The following are the systems investigated by the authors. It should be noted than none of them were beyond the method. HC1- LiC1; HC1- NaCl; HC1- KCl; HC1- CaCh; HC1- HN03; KC1 - NaC1; KC1 - KBr; KCl CaC12;KC1 K N 0 3 ; KC1 - KClO,; NaCl - NaC103; NaCl Na2S04;NaCl CaC12; NaCl NaOH, KCl - KOH; KI - KOH; CuCh - NiC12. The integral concentrations of these mixed solutions were always above 1 g.equiv.il, which does not exclude the possibihty that more dilute solutions can be separated. However, the method efficiency does increase at higher concentrations. The ratio of electrolytesin these mixtures was not always the same. To illustratethe efficiency of this method, examplesof separation of some mixtures are in Table I. As it shows, subject to the electrolyte nature, in the range of 0.1 - 0.5 m3 of mixture per cycle can be separated m a 1 m3 column.

-

-

-

-

Table I The Investigated Systems

Fig.

A-B System

Integral concentration

4 5 6 7 8

KC1 -HC1 KC1 -HC1 NaCl- CaClz KC1 -KNO3 NiC12-CuCb

4.20 4.00

Concentration ratio CA:CB 1:20

2.45

9: 1 10: 1 1: 1

3.50

1: 2

3.50

Separated volume, 1 0.30 0.50 0.25 0.20 0.12

Figare 2 The Breakthrough Curves of Axand BXSepration (Scheme)

ition

Ion exchangerRX in water

Figure 3 The Flawsheet for the Mixture Separation in Counter-currentColumns

Progress in Ion Exchange: Advances and Applications

100

I

b

I

0”

Figure 4 Pur$cution of HClpom KCI .admix:&re

0.4

0.5

Figure 5 Purrfication of KClfrom HCl admixture

0.3

-

0.5

0.7 V,l

101

Novel Materials and Novel Applications

0”

0.6

0.8

v,1

Figure 6 Purijkation of NaCIfiom CaC12 admixture

Figure 7 Separation of KCI-KNOj mixture

Progress in Ion Exchange: Advances and Applications

102

Figure 8 Separation of NiClrCuC12 mixture

Figures 4-8 provides the results obtained in the course of experimental separation of some of the above listed mixtures. About one liter either of a strong acid, or of a strong base ion exchanger was used.. Choosing the optimum conditions for separation of various electrolyte mixtures, and calculation of efficiency, are based on the results of electrolyte sorption equilibrium investigations. The authors have created a data bank to support work in this field. 4 CONCLUSION

As the results of the investigations show, a new application of ion exchange resins has been developed. Its main difference as compared with the existing ones consists in its being free of any reagents for regeneration. That, and other advantages of the method herein described, makes us hopefid that it is going to h d a wide range of application in chemical technology. This work was carried out with the hancial support of the Russian Foundation for Fundamental Research. References 1. F. Hemerich, ‘Ion Exchange’, McGraw HiU, New York, 1962, part 5.3.

2. B.Tremillon, ‘Les separations par les resines echangeuses d’ions’, Gauthier - Villars,

Paris, 1965. 3. C.W.Davies and G,D. Geoman, Tram. Farad. Soc., 1953,42,968

Novel Materials and Novel Applications

103

N.B.Ferapontov, V.I.Gorshkov, HT.Trobov and L.R Parbuzina, Zh Fiz. a i m . , 1994, 68,N6,1002 5. V.I.Gorshkov,M.S.Safonovand N.M.Voskresenskiy, 'Ion exchange m c0mtm-t columns', Nauka, Moscow. 1981 4.

ANALYTICAL SELECTIVITY OF MEMBRANE ELECTRODE BASED ON SALICYLALDOXIME FORMALDEHYDE RESIN Harsh Vardhan and Lok P. Singh. Biomolecular Electronics and Conducting Polymer Research Group National Physical Laboratory, Dr. K.S. Krishanan Road, New Delhi - 110 012 (India) *Department of Chemistry University of Roorkee, Roorkee - 247 667 (India)

1 INTRODUCTION The electrochemical properties and preparation of the lead(l1) ion-selective membrane electrodes have been studied by using active materials, one of which is the solid-state membranes made by sulfide, oxide, selenide and other salts of lead together with silver sulfide and the other are liquid ion exchange and crown ether membranes (1-12). Recently an ion exchanger salicylaldoxime formaldehyde resin (13) has been reported t o possess promising selectivities for some heavy metal ions. The product provides a highly suitable electroactive phase for sensing lead ions and the present paper deals with the performance for this electrode system which, in certain respects, may be better than the one reported so far.

2 EXPERIMENTAL 2.1 Reagents All the reagents used were of analytical-reagent grade. Salicylaldoxime (Glindia, India) and formaldehyde (Glindia, India) were used. The metal solutions were prepared in doubly distilled water and were standardized by appropriate methods. 2.2 Synthesis of Salicylaldoxime-Formaldehyde Resin

Salicylaldoxime and formaldehyde solutions were mixed in the molar ratio 1:1.1 and 3% m / m of 40% sodium hydroxide was added as a catalyst. The mixture was heated under reflux in an oil bath at 110 f 1 OC for 6 hours. The resinous mass was

Navel Materials and Navel Applications

105

poured into a container and dried at 50k 1 OC for t w o hours. The resin was finally powdered and sieved through a 100 BSS (British Standard Size) sieve.

2.3 Preparation of Membranes (a) Master membrane was prepared by dissolving and thoroughly mixing the resin and PVC in 1:1.5 ratio in tetrahydrofuran and spreading the solution into a glass cast ring with an end ground t o give flush contact with the glass plate, and the solvent was left t o evaporate naturally. An elastic membrane of 0.6 mm thickness was obtained. The discs o f membranes of required size were cut out. (b) The resin was ground with 12% polystyrene and the membranes were prepared by using a Mount Press at 62 OC and the pressure was maintained 450-480 bar. The required amounts of binders were obtained after a good deal of experimentation. The membranes were conditioned by immersing in 1.O M lead nitrate solutions for 5 days.

2.4 EMF Measurements The EMF measurements were made at 30* l0C against a saturated calomel reference electrode. 0.1 M Pb(N03)2 solution was taken as the reference and potentials were measured from lower t o higher concentrations (12). If the measurements were made from higher to lower concentrations, erratic results were obtained owing t o a "memory" effect and to the difficulty of removing adsorbed ions from the surface of membrane electrode.

3 RESULTS AND DISCUSSION The composition of the membrane, i.e., the ratio of the electroactive phase and the binder material, influences the properties o f ion-selective electrodes and the amount which yields optimal electrode characteristic (resin vs polystyrene 25:3 & resin vs PVC 1:1.5) was arrived at after exhaustive preliminary investigations. Response time, life time, adsorption effects, chemical resistance and extent of dynamic change also depend o n the membrane composition. The membrane supported agreement

water content was taken as the difference of wet membrane and dried divided by the weight of wet membrane. The values for polystyrene and PVC matrix membranes are 17.52 and 20.32 respectively, in with the lo w degree o f swelling.

The response time for polystyrene supported membrane is less than 10 seconds for all concentrations but for PVC matrix membrane, the static potential is obtained within 15 seconds at higher concentrations while at lower concentrations the response time is 40-50 seconds. The potentials

Progress in Ion Exchange: Advances andApplications

I06

remains constant for more then 15 minutes and are quite reproducible (Standard deviation = 0.2 mV) in both the cases. The working concentration range of the membrane electrodes using polystyrene - ~ with a slope of 21 mV/decade of and PVC as binders are 1.OOxlO-' t o 1. O O X ~ O M concentration and l.OOxlO-' to 2 . 5 1 ~ 1 0M~with ~ higher slope of 48 mV/decade of concentration respectively (Figure 1). The sensitivity of the membrane electrodes using polystyrene as a binder is higher while slope is lower as compared t o PVC matrix membranes. The useful pH range for both the membranes i.e. polystyrene supported and PVC matrix membranes is 3 to 6 (Figure 2).A sharp change at l o w pH values probably accounts for the competition due to H+ ions under these circumstances.

tion

7

6

5

4

3

2

1

0

-tug Concentrotion/activily (Pb2

'J

Fig.1 Plots between cell potential and Pb2+ ion concentration.

Polyrtymno bosrd - 4

membmnr

w

'

60

PVC borrd membraw I

*

.

.

1

2

3

4

5

I

6

Fig.2 Effect of pH of) cell potential; polystyrene and PVC based membranes at 7.00~ 1O2M Pb2+ ion concentration.

107

Novel Materials and Novel Applications

10

20 OI

W

I

50

-bg cpb2+1 Fig.3 Effect of monovalent concentration on variation of cell potential with Pb2+ ion concentration.

11 0 .

, 4

1

1

,

~

'

,

1

a ,

4 .

*

B

''

e

2

~

'

~ *

Pb2* o

I

l

a

'

N t I N.* o

A' 4 1+' ' -be [Pb 1 l*

.

I

,

~

l l'

P'

l'

1

4

+

I+ J'1*

O

re O

Fig.4 Effect of monovalent concentration on variation of cell potential with ?b2 ion concentration.

'

108

Progress in Ion Exchange: Advances and Applications

Table-1 Selectivity o f the electrode system for lead ions in the presence of 1.00xfCT’ M concentration of interfering ions (as calculated by the expression for fixed interference method using expression with and without superscripts)

...........................................................................................................

interfering ion

Selectivity coefficient PVC based membrane Expression Expression Expression without with without superscript superscript superscript

Polysr yrene based membrane Expression with superscript

-----_-_-________---________________

Na

19.00

1.9ox10’

25.10

2.51~10-’

K+

19.95

2.00xlO’

28.10

2.81~10-’

TI+

19.95

2 .oox 10‘’

22.38

2.241 ~0-’

Li

10.00

1.oox1 o 1

19.95

2.00x10-’

Ag +

17.78

1.79x10’

25.1 1

2.51x l 0 - l

NH4+

19.00

1.9OX1O1

28.10

2.8 1x lo-’

Mn2+

1.99x101

1.99x10-1

2.23~10-’ 2.23~10.’

Cd2+

3.16~10~’

3.16~10-’

4.46~10-’ 4 . 4 6 ~ 1 0 - ’

Zn2

3.16~10-’

3.1 6x10”

3.54~ 10-’ 3.54~10-’

Ba2+

3.1 6x10-’

3.1 6x10’

3.98~10”

Sr2

2.8 1x 10”

2.81~10”

3.1 6x1 0-’ 3.16x10-’

2.5 1x lo-’

2.51 x l 0 ’

2.81~10”

2.8 1x 10-’

2.8 1x 10”

3.54~10~’ 3 . 5 41 ~0-’

Mg2+

3.16xlO-’

3.1 6x10-’

3.54~10-’ 3 . 5 4 lo-’ ~

A I ~

5.41~10-~

2.25~10”

7.64~10”

o.oox1o-’

~a~

4.291 ~O 2

0.00x10-’

5.42x10-‘

2.25~ lo-’

7.64~ 1O-‘

0.00x10-’

8.51xlb’

o.oox1o-‘

+

+

+

+

co2 cu2

+

+

+

+

~e~+

3 . 9 8 10.’ ~

2.8 1x l 0 - l

Novel Materials and Novel Applications

109

Both the membrane sensors can be used in partially non-aqueous media, but the working concentration range decreases with an increase in the slope and the response time having non-aqueous contents up to 25%.

In order t o investigate the selectivity of this sensor, its response was examined in the presence of various foreign ions. Normally such membranes generate potentials due t o selective uptake of determinand ions and EMFs measured are the composite values of Donnan and Henderson potentials. Since the electroactive phase is not ideally permselective the co-ions transfer does take place which consequently reduces and disturbs the selectivity of membrane material. Potentiometric selectivity M coefficients were obtained by a fixed interference method (14)at concentration of interfering ions. The selectivity data for polystyrene as well as PVC-based membranes (Table 1) reflect that the selectivity coefficient values are generally low for bivalent and trivalent ions as compared to those for monovalent ones. When the same are obtained by using the expression without superscripts, the monovalent ions do not seem t o interfere (Table 1). The pattern of bivalent ions remains the same whereas higher selectivity coefficient values are recorded for trivalent cations. The trivial nature of the methodology used t o assess the selectivity and the controversy involved in representing these values (1 2,15-22)make it imperative t o have an actual idea of the level of interferences caused by various ions when the same are present in varying concentrations. Some mixed runs (15-171, in the presence of primary as well as interfering monovalent cations were obtained (Figure 3 & 4). Upto 1 .00x104 M interference level absolutely no adverse effect is observed on the working o f both the electrodes for lead despite the high selectivity coefficient values but above this level the mono valent cations start showing some interference. The tolerance o f the electrodes for bivalent as well as trivalent ions, for which the selectivity coefficient values are less, is also upto 1.00x104 M.This further raises doubts regarding the applicability of fixed interference method. Selectivity coefficient values were also calculated (fixed interference method) at different sodium ion concentrations and it was quite interesting to observe that selectivity coefficient values increase with decreasing concentration o f interfering ion (1 5,17,18).For polystyrene supported membrane the values are 871 2.50, 210.87 and 19.00 and for l o 3 and PVC matrix membrane the values are 8901.78,226.24 and 25.62 at l o 2 M respectively. The selectivity coefficient value for sodium ions at M is M Na' concentration overwhelmed the lowest despite the observation that a lead ions response. On the other hand, at l o 4 M Na' Concentration, which shows almost no actual interference, the selectivity coefficient value is very high. This is the consequence of the power term used in the expression for the calculation of selectivity coefficient by the conventional method. Resulting coefficients are either deceptively large or small depending on whether the ion of higher charge is considered as the primary or interfering species. This amply shows the necessity of observing the mixed runs simulating the real practical situations. Data given above shows that the expression used here for the calculation of selectivity coefficients (without superscripts) gives a more reliable picture about the behaviour o f the electrode in the presence of interfering ions(l7). The method used

110

Progress in Ion Exchange: Advances and Applications

is the one presently recommended by IUPAC, though, because of many problems, the methodology is under review. The working concentration range and selectivity coefficient pattern by both methods clearly indicates the superiority of polystyrene supported membrane electrodes over PVC matrix membrane electrodes for lead ions, since the former is less subject t o interference. The practical utility of both of the membrane electrodes has been observed by using them as indicator electrodes in the potentiometric titrations. The titrations of 5xlO”M Pb+* with lO-*M EDTA are shown in Figure-5. The potentials fall gradually with the addition of EDTA. Although the shape of the curves are not the same as are normally observed in potentiometric titrations but the break in the curve (End point) corresponds to the stoichiometric ratio.

Wumc of EDTAoddedW ) Fig.5 fitration curve o f 5 . 0 0 ~ 1 0 - ~Pb2+ M ion with l . 0 0 x 1 0 - 2 M EDTA.

Novel Materials and Novel Applications

REFERENCES 1. 2. 3. 4.

5. 6.

7. 8. 9. 10. 11. 12. 13. 14.

15. 16. 17. 18.

H. Hirata and K. Higashiyama, Anal. Chim. Acta, 1971, 54,415. H. Hirata and K. Higashiyama, Anal. Chim. Acta, 1971, 57, 476. A.V. Gordievskii, V.S. Shterman, A. Ya. Syrchenkov, N.I. Savvin, A.F. Zhukov and Yu.1. Urusov, Zh. Anal. Khim., 1972, 27, 2170. H. Hirata and K. Higashiyama, Talanta, 1972, 19, 391. J.W. Ross and M.S. Frant, Anal. Chem., 1969, 41, 967. P. Kivalo, R. Virtanen, K. Wickstroen, M. Wilson, E. Pungor, G. Horvai and K. Toth, Anal, Chim. Acta, 1976, 87, 401. P.S. Thind, H. Singh and T.K. Bindal, lnd. J. Chem., 1982, 21A, 295. S.K. Srivastava, S. Kumar, C.K. Jain and Surender Kurnar, Talanta, 1986, 33, 717. A.K. Jain and V. Tyagi, lnd. J. Chem.. 1990, 29A. 608. M. Sharp, Anal. Chim. Acta. 1972, 59, 137. A.M.Y. Jaber, G.J. Moody and J.D.R. Thomas, Analyst, 1988, 113, 1409. S.K. Srivastava, V.K. Gupta and S. Jain, Analyst. 1995, 120, 495. S. Srivastava and G.N. Rao, Analyst, 1990, 115 , 1607. G.G. Guilbault, R.A. Durst, M.S. Frant, H. Freiser, E.H. Hansen, T.S. Light, E. Pungor, G.A. Rechnitz, N.M. Rice, T.J. Rohm, W. Simon and J.D.R. Thomas, (Recommendations 1975). PureAppl. Chem., 1976,48, 127. S.K. Srivastava, V.K. Tewari & Harsh Vardhan, Sensors and Actuators, 6, 1995, 28, 21. L.P. Singh & Harsh Vardhan, Anal. Proc. Comms., 1995, 32, 193. S.K. Srivastava, V.K. Tewari & Harsh Vardhan. Indian J. Chem. A, 1995, 34, 625. G.J. Moody and J.D.R. Thomas, lon-Selective Electrode Rev., 1979, 1,

3. 19. 20. 21. 22.

J.B. Harrell. A.D. Jones and G.R. Choppin, Anal. Chem., 1969, 41, 1459. L. Ebdon, A.T. Ellis and G.C. Corfield, Analyst, 1982, 107, 288. Y. Umezawa, M. Kataoka, W. Takami, E. Kimura, T. Koike and H. Nada, Anal. Chem., 1988, 60, 2392. S.K. Srivastava, V. Sahgal and H. Vardhan, Sens.,Actuators, 6,1993, 13-14, 391.

111

Part 2 Ion Chromatography and Electrophoresis

ION CHROMATOGRAPHYAND CAPILLARY ELECTROPHORESISFOR THE DETERMINATION OF INORGANIC ANIONS - CURRENT STATUS AND RELATIVE MERITS

Paul R. Haddad Department of Chemistry University of Tasmania GPO Box 252C Hobart Tasmania, Australia

1 INTRODUCTION

Ion chromatography (IC), first introduced in 1975, can now be considered to be a mature analytical technique and this maturity is reflected in a more sedate rate of new research output than was evident even as recently as five years ago. The emphasis in modem IC is no longer the development of new hardware and column technology since the existing technology has already been refined to a high degree. In particular, a very wide range of chromatographic columns now exists and these columns provide high efficiency and a wide choice of separation selectivities. The current trend in IC is the more sophisticated use of existing technology for very demanding applications. That is, applications have taken precedence over fundamentals. In particular, sample treatment is now emerging as a major field of study as researchers seek to apply IC to difficult sample matrices, such as strongly alkaline samples, highly saline solutions containing traces of analyte, and solid samples. Approaches to two of these sample types will be discussed in order to illustrate the scope of modem IC. The first example is the direct determination of iodide in seawater by matrix-elimination IC with post-column reaction, whilst the second concerns on-line pretreatment of alkaline samples using a flow-through electrodialysis device. In contrast to IC, capillary zone electrophoresis (CZE) is undergoing a phase of extremely rapid development, especially with regard to its use in inorganic analysis. The emphasis in CZE is currently on fundamental studies concerned with improvement of our understanding of the factors governing the separation and detection processes. Two projects in these areas will be discussed in order to illustrate the type of studies being undertaken. The first concerns the manipulation of separation selectivity in CZE of inorganic anions, whilst the second concerns optimisation of the sensitivity of indirect detection in CZE. 2 DETERMINATIONOF IODIDE IN SEAWATER BY IC

Iodine is an essential micronutrient for many organisms - both terrestrial and marine. The total dissolved concentration of iodine in ocean waters, apart b m the surface layer, is relatively constant at about 60 pg iodine/L. Iodine is also a multi-oxidation state element; the important species in seawater are iodate and

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Progress in ion Exchange: Advances and Applications

iodide (the former is usually predominant), but there are also minor amounts of organo-iodine compounds. The requirement to determine iodine concentration and speciation in seawater is not solely because of its biological importance. There are also the chemical characteristics of iodine that make it a valuable indicator of a number of important processes in the marine environment. There are very few analytical methods that allow iodide to be determined directly in seawater with adequate sensitivity. The voltammetric method of Luther et al.* with a detection limit of 0.01-0.03 pg/L is more than sensitive enough but is not suited to shipboard analysis. IC seems to offer advantages for the determination of iodide since this species is usually well separated from interferences. There have been two problems for seawater analysis: (i) deterioration of chromatographic efficiency with injection of the high-chloride matrix, and (i) lack of sensitivity. The first has been solved by using the matrix elimination technique, where chloride is added to the mobile p h a ~ e , ~but .~ sensitivity remains an obstacle. Both problems for determining iodide in seawater by IC can be addressed by combining the matrix-elimination technique with a sensitive and selective postcolumn reaction (PCR) for iodide. The PCR is derived from the reaction of iodide with 4,4'-bis(dimethyl-amino)diphenylmethane ("tetrabase") in the presence of chloramine T.

2.1 Optimisation of the Post-Column Reaction Iodide catalyses the reaction between tetrabase and hypochlorite (generated by the hydrolysis of chloramine 7) yielding a quinoidal product of intense blue colour which gradually turns into green. These reagents have been used successfully in IC and PCR detection for iodide: although the stability of chloramine T solutions as a source of hypochlorite was not completely satisfactory. Therefore, substitution of chloramine T by N-chlorosuccinimidesuccinimide was examined. It should be remembered that one of the reagents, namely the tetrabase, was a component of the mobile phase so that only one post-column reagent pump was necessary for the addition of the N-chlorosuccinimide/succinimide reagent. The practicable pH for the reaction was limited to a range below 4.5 because the tetrabase was not soluble at higher pH values. Generally, sensitivity decreased with decreasing pH. In practice, a pH not higher than 4.0 was chosen in order to avoid precipitation in the reaction coil under all circumstances. Increasing the tetrabase concentration from 0.4 g/L to 0.8 g/Lresulted in a four-fold increase in sensitivity. The temperature effect was investigated and up to 55"C, the sensitivity increased linearly and was roughly doubled for each 10°C. A temperature of 45°C yielded a satisfactory signal-to-noise ratio. Finally, the sensitivity depended on the concentration of the N-chlorosuccinimide. An increase in its concentration from 1g/L to 1.5 g/L yielded an increase in sensitivity of approximately 50%. 2.2 Analysis of Seawater Samples Generally, samples of high ionic strength such as seawater cannot be injected directly onto the separation column because of severe peak broadening as a result of self-elution by the sample matrix itself and loss of band-compression effects. Special techniques such as on-column matrix elimination can overcome these problems. In this case, the matrix ion was used as a component of the

Ion Chromatographyand Electrophoresis

117

eluent in a concentration close to, or even higher than, the sample matrix. A concentration of 0.6 M sodium chloride (approximately the ionic strength of sea water samples) yielded satisfactory results and symmetrical peaks for an injection volume of 150 pL. The only potential interference also reacting in the tetrabaseN-chlorosuccinimide system would be bromide, but it eluted near the void volume and was well separated b m iodide. Thiocyanate showed no interference up to 10 ppm. The response of the PCR detector was found to be linear in a range up to 100 ppb for an injection volume of 150 pL. The detection limit (given as signal-to-noise ratio of 3) was approximately 0.8 ppb (injection volume of 150 pL) corresponding to an absolute amount of 120 pg injected. This detection limit was adequate for the desired application. Fig. 1 shows a typical chromatogram for the determination of iodide in seawater. The reproducibility was checked by injecting a seawater sample 6 times which yielded a relative standard deviation of 3.2% for a 5 ppb iodide sample.

0

2

4

6

8

RETENTION TIME (min)

Figure 1 Typical chromatogramfor the a'etermination of iodide in seawater. Injection volume: 150 jd;wavelength: 605 nm; 0.01 AUFS , iodide concentration:5ppb.

The method was successfully used for seawater sample analysis. The samples were collected in the Southern Ocean on board the RSV Aurora Australis during February 1995. They were partially analysed on board, and the remainder analysed back in the laboratory after the cruise. The method proved to be suitable for shipboard analysis, and was sensitive enough to analyse surface water samples, with concentrationsvarying from 1 to 5 ppb. 3 ON-LINE IC ANALYSIS OF ALKALINE SAMPLES USING A FLOWTHROUGH ELECI'RODIALYSISDEVICE

Donnan dialysis, in which ions of a specified charge pass selectively through an ion-exchange membrane, has been used for matrix normalization, sample preconcentration and sample clean-up6in IC. Electrodialysis, wherein an electric field is applied to enhance the performance of a conventional Donnan dialysis experiment, has also recently found use in IC7v8and in high-performance liquid chromatography with the electrodialysis being performed off-line. An important application of dialytic methods in IC is the treatment of alkaline samples, chiefly because of the importance of alkaline fusion as a sample dissolution method. In

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Progress in Ion Exchange: Advances and Applications

the present work, a flow-through electrodialysis cell which permits on-line treatment of the sample, followed by direct injection onto the IC, has been developed. 3.1 Flow-through electrodialysis device The flow-through electrodialysis cell was constructed as a series of perspex blocks held together with longitudinal screws to form a three-compartment cell separated by cation-exchange membranes, as depicted in Fig. 2. The sample chamber was designed to allow the sample to flow during the electrodialysis process. Electrodes were constructed from stainless steel plates (60 x 25 x 0.7 mm), inserted into the electrode compartments and connected to the power supply. The membranes were supported with a perspex sheet attached to each electrode solution compartment, through which had been drilled numerous closely spaced holes, 2 mtn in diameter. The volume of both the anode and cathode compartments was 15 ml,whilst the sample compartment contained 300 pl. A BioRad microprocessor-controlled electrophoresis power supply (Model 3000 Xi)was used in the fixed power and fixed current modes. The sodium hydroxide sample solution was passed through the sample compartment of the cell at a constant flow-rate of 0.1 d m i n using a syringe pump, whilst a DC potential was applied at constant power (2 W) to the electrodes at the two ends of the cell. The outlet of the sample compartment was connected to a six-port switching valve fitted with a standard 20 pl sample loop so that direct injection of the neutralized sample solution onto the IC system was possible.

*

Cathode (-) Cathode

/

=Yon J

Sam le w&t

Anode (+)

Sample inlet Anode

solution

/

/ .... ..,.

...

..... ..... ..... ..... ..... .,.... \*.. ..... ,.... .....

, . % . .

. . % . .

% . . .

0

0

.... ..,. .... .... .... .... .... .... ..,. .... .... .... .... ... ...

% \

/

Cation-exchange membrane

Figure 2 Flow-through electrodialysis cell.

1

Ion Chromatography and Electrophoresis

119

3.2 Selection of the membrane The permselectivities of the membranes, assessed by determining the recoveries of a range of inorganic anions initially added to NaOH solution before the samples were subjected to electrodialysis,played an important role in ensuring the success of the process. Recovery experiments using three different types of membranes (Neosepta CM-2, Neosepta CMS and Asahi CMV) were undertaken using a constant power of 2 W (which correlated to a current of 120 mA). Suitable recoveries were obtained for all ions except for nitrite, with the Neosepta CM-2 membrane giving the best overall performance. Chromatograms showing a mixture of inorganic anions in Milli-Q water and in 1 M NaOH after electrodialytic treatment using the Neosepta CM-2 membrane are given in Fig. 3. The two chromatograms are virtually identical, except for the low recoveries of fluoride and nitrite in the treated sample.

F'

NO,'

(b)

I

(a)

SO,'.

SO,'.

NO,'

Y

7

n

Y

5

>

i

10

I5

Time (nin)

Figure 3 Chromatogramsof inorganic anions (3-10p g h l ) in (a)Milli-Q water and (b) 1 M NaOH @er electrcdialytic treatment using Neosepta CM-2 membranes. Injection volume: 20 pl. Eluent: 2.0 mM Na,CO, - 2.0 mM NaHCO, Column: Dionex HPICAS4A with AG4A Guard Column and AMMS Suppressor.

3.3 Determination of fluoride in forage vegetation samples Fluoride is a major environmentalpollutant from an aluminium smelter and can be absorbed and accumulated in the tissues of plants which grow in the vicinity of the smelter. Whilst there is no standardised method yet for sample preparation prior to fluoride analysis, acid leaching and hydroxide fusion are the most commonly employed techniques. Vegetation samples obtained from the vicinity of an aluminium smelter, and two standard reference plant materials, were prepared by hydroxide fusion and the sample solution then neutralized using the flow-through electrodialysis cell connected to a suppressed IC system. Excellent agreement of results with the standard distillation-colorimetric method for fluoride' were obtained.

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Progress in Ion Exchange: Advances and Applications

4 MANIPULATION OF SEPARATION SELECTIVITY IN CZE OF ANIONS

High speed, minute sample requirement, minimal sample pre-treatment, minimal reagent (electrolyte) consumption, and high separation efficiency are some of the advantages that make CZE attractive for the separation of inorganic anions. The application of CZE to samples with simple matrices is straightforward but separation is likely to be problematic with complex and difficult samples of high ionic strength, low pH, high pH and high disparity of solute concentrations. The factors influencing anion selectivity in CZE can be divided into three main groups involving (i) chemical, (ii) instrumental and (iii) miscellaneous effects. For these effects to be exploited, effective sizes and effective charges are the fundamental propertes of anions which need to be manipulated. Such manipulation is possible using electrolyte parameters such as pH, organic modifer content, type and concentration of surfactant, etc. The effects of two of these parameters are discussed below. 4.1 Effect of electrolyte pH

Fig. 4 shows the effect of variation of the electrolyte pH. Here the relative migration time with respect to bromide (RMT)of each anion is plotted against pH.

-

1.5 1.4

c-c

- 1

-

- 3

9.5

1.3

- 4

5 1.2

- 5

1.1

1.2 -

7.5

- 2

- 2

2 1.3 1.1

- 1

1.4

11.5

PH

Figure 4 Effect of electrolyte pH on selectivity. Key: I fluoride, 2 iodide, 3 nitrate, 4 phosphate, 5 carbonate. The electrolyte had 5 mM chromate as probe and 2.5 mM TTAB at pH 8.

- 3 - 4

- 5

1.o

no - ,

~

;~~g~T!~~ O

?

Z ?

1 0 1 0 d

mM TTAB:mM DTAB Figure 5 Effect of TTAB and DTAB surfactant mixtures on selectivity. Key: as for Fig 4. All electrolytes had 5 mM chromate and pH 9.

Pronounced changes in migration order occur for weak acid anions (e.g. carbonate and phosphate) at pH values close to their pKa values. These changes can be attributted to changes in the charge to mass ratio brought about by changes in the effective charge on the anion. Increased anion charge results in a faster migration speed and thus reduced migration time. For practical purposes, it should be noted that electrolytes containing chromate and tetradecyltrimethyl ammonium bromide (lTAE3) are limited to pH27.5 to avoid precipitation. For studies at lower pH, probes like benzoate are suitable.

lon Chromatography and Electrophoresis

121

4.2 Effect of binary surfactant mixtures

Cationic surfactants such as 'ITAB and dodecyltrimethylammonium bromide (DTAB) are usually added to the electrolyte to alter the capillary surface charge. This has the effect of reversing the electroosmotic flow (EOF)to migrate in the same direction as anions, i.e. from the cathode to anode and has the net result of reducing anion migration lime. Most inorganic anion separations by CZE have used electrolytes with a single cationic surfactant. In this study, electrolytes containing binary mixtures of lTAB and DTAB were examined. The effect on selectivity is shown in Fig. 5. The selectivity depends on both the total surfactant concentration and the ratio of the two surfactants." The likely mechanism is ion-pair formation (e.g. iodide migration time has been observed to be high at high surfactant concentration). The increased migration rate is due to a high zeta potential at the capillary-electrolyteinterface resulting from a high surfactant concentration (and charge). Consequently the EOF velocity is high. The ability to manipulate selectivity in this way has been used to advantage in the analysis of Bayer Liquor from an aluminium refining process." Full resolution of 11 anions has been obtained, as shown in Fig. 6.

.

3

II

I

2.4

I

2.6

10

I

2.0

I 3.0

I 3.2

I 3.4

Migration Time (min.)

Figure 6 Separation of diluted Bayer liquor using Optima 2 conditions. Ekctroly&: 5.5 mA4 chromate, 5 mM lTAB and 1 mM DTAB atpH 9.1. Key: 1 = chloride, 2 = nitrite, 3 = nitrate, 4 =fluoride and 5 = hydrogen phosphate. 5 OpTIMlSATION OF S E N S m OF LNDIRECT DEXECl'ION IN CZE

OF INORGANIC ANIONS

Adequate detection is a particularly difficult problem in CZE. Many inorganic ions have negligible absorbance at useful wavelengths and this necessitates the use of direct absorption detection. In this form of detection, a W absorbing species (or "probe") having the same charge as the sample ion is used as carrier electrolyte. Displacement of the probe by the migrating sample creates a region of decreased concentration of the probe, so that the sample ions are monitored as a decrease in the background absorbance. Sensitivity in indirect UV detection is governed by the molar absorptivity of the carrier electrolyte and its charge. The displacement of the probe ion by the migrating sample ion might be expected to occur on an equivalent-per-equivalent

122

Progress in Ion Exchange: Advances and Applications

basis, but this is true only if the sample ion has the same electrophoretic mobility as the background ion. When this is not the case, the number of moles of probe ions displaced by one mole of sample ions (which here will be referred to as the transfer ratio, TR) will be affected to some extent. The detection sensitivity can also be expected to vary under these conditions. The factors which should be considered in selecting an appropriate carrier electrolyte in order to optimise the sensitivity of indirect UV detection in CZE will be discussed here.

5.1 Determinationof transfer ratios The measurement of transfer ratios can be carried out according to the following sequence of The first step involves the injection of the probe ion (for example, chromate) into a UV transparent electrolyte (for example, a phosphate buffer at the pH of the carrier electrolyte under investigation) using direct UV detection at an appropriate wavelength (for example 254 nm). A calibration plot (peak areas versus molar concentration) is established for the probe and in order to account for the influence of different migration velocities on the peak area monitored by the detector, the peak areas should be multiplied by the apparent velocities of the ions. The slope of this calibration plot provides a quantitative value for the detector signal (normally expressed as area counts) per mole of the probe. The next step involves the injection of sample ions using the probe as carrier electrolyte and indirect UV detection at the same wavelength as in the first step. Again, a calibration plot of peak area of sample ion versus molar concentration is established for each sample ion and the slope calculated. In the final step, transfer ratios are obtained for each sample ion by calculating the quotient of the slope of the sample calibration plot and the slope of the probe calibration plot. Experimentally determined transfer ratios (multiplied by the charge of the probe in order to normalise variation in transfer ratios arising from the different charges of the probes) of several sample ions using different probes are plotted against the relative mobilities of the probes in Fig. 7. At the electrolyte pH used (8.0),all of the probes were fully ionised, so that the charge varied between -1 for benzoate and -4for pyromellitate. Considering the two univalent ions chloride and fluoride, it can be seen that the observed transfer ratios, corrected for the charge on the probe, were less than unity for benzoate and phthalate (probes 1 and 2 in Fig. 7), close to unity for trimellitate (probe 3) and greater than unity for pyromellitate and chromate (probes 4 and 5, respectively). A similar pattern was evident for the remaining sample ions (sulfate, phosphate and citrate).

5.2 Evaluation of carrier electrolytes for practical applications A quick estimate of the suitability of a probe for a certain separation can be performed on the basis of the product of the transfer ratio and the molar absorptivity, E, of the probe. The higher the value of this product, the higher the sensitivity of indirect UV detection. It must also be remembered that the average mobility of the sample ions should roughly match the mobility of the probe ion (in order to avoid distorted peaks) and in any case should not be considerably higher than that of the probe in order to avoid decreased transfer ratios. The results showed that the transfer ratios of trimellitate, pyromellitate and chromate exceeded the equivalent-per-equivalent values, and combined with their high molar absorptivities, suggested that these probes should be preferred to benzoate and phthalate.

123

Ion Chromatography and Electrophoresis 1

- - 5- . Legend: -0- Fluoride

B

12:-

-

0.5

1 Benmate

2 phthdate sulfate 3 Trimellitate phosphate 4 PyrOmeUitatc t- Citrate 5 ammate ---t Chloride

---

--cT

- - Equivalent-to-cquivdent 0.6

0.7

0.8

0.9

1.0

exchange

1.1

~ d r t t v e ~ ~ g ~ ~ o n ~ i m c d h ~ l

Figure 7 Dependence of framfer retios (multiplied by the charge on the probe) upon the relative mobility of the probe (chromate = I ) . The broken lines show the values expected on the basis of an equivalent-to-equivalentexchangefor Malytes having a single, double and triple charge.

6 A

C K " T S

Contributions to the above research by Wolfgang Buchberger, Sarah Cousins, Tony Harakuwe, Ana Brandao, Ed Butler, Peter Fagan and Soehendra Laksana are gratefully acknowledged. AU figures except Fig. 4 are reproduced with permission of Elsevier Scientific Publishers. 7 REFERENCES 1. 2. 3. 4. 5. 6. 7.

G.T.F. Wong, Rev.Aquut. Sci., 1991,4,45. G.W. Luther, C.Branson-Swartz and W.J.Ullman, Anal. Chem., 1988,60,1721. K.It0 and H. Sunahara, J.Chromatogr., 1990,502, 121. Marheni, P.R. Haddad and A. McTaggart, J. Chromtogr., 1991,546,22 1. W. Buchberger, J.Chromatogr., 1988,439, 129. S. Laksana and P. R. Haddad, J. Chromutogr., 1992,602 57. Y.Okamoto, N. Sakamoto, M. Yamamoto and T.Kumamaru, J. Chromutogr.,

1991,539,221. 8. P. R. Haddad, S.Laksana and R. G. Simons, J. Chromutogr., 1993,640,135. 9. official Methods of Analysis, Association of Official Analytical Chemists, 15th ed. (1990) p. 52. 10. A.H. Harakuwe, P.R. Haddad and W. Buchberger, J. Chromutogr. A, 1994, 685,161. 11. P.R. Haddad, A.H. Harakuwe and W. Buchberger, J. Chromutogr. A, 1995, 706,57 1. 12. S.M. Cousins, P.R. Haddad and W. Buchberger, J. Chromtogr. A, 1994, 671, 397. 13. W. Buchberger, S.M. Cousins and P.R. Haddad, Trends in Analytical Chemistry, 1994,13,313.

IONS IN INK JET DYES BY CAPILLARY ELECTROPHORESIS AND ION CHROMATOGRAPHY

S.C. Stephen and N.J. Truslove ZENECA Specialties Hexagon House Blackley Manchester 'M9 8ZS INTRODUCTION ZENECA Specialties manufacture a range of ink jet colorants for use in desk top and industrial printers. Such dyes are typically acid dyes with sulphonic acid and carboxylic acid groups present in the salt form. A typical dye is shown in Figure 1. The method in which the dyes are applied to the substrate necessitates control of inorganic impurities. Ion Chromatography (IC) is the current technique employed to measure the anions in the final product although other techniques have been assessed. This paper outlines the progress of anion analysis in ink jet dyes and presents a comparison of chloride and sulphate analysis by IC and Capillary Electrophoresis (CE), using both indirect UV and conductivity detection.

ION CHROMATOGRAPHY IC is a well established technique for the determination of chloride and sulphate in aqueous solutions. However, in the early stages of method development for dye applications, it was discovered that the dyes are irreversibly absorbed onto anion exchange columns. Hence column efficiency was rapidly lost. Removal of the dyes was not possible without destroying the columns. A number of options have since been investigated including precolumn cleanup of the samples using various adsorbents and ion exchange resins. This has been largely unsuccessful due to the poor capacity for the dyes at the concentrations required for the analysis. Ion pairing HPLC using indirect UV to detect the ions was also investigated using an octadecyl silane (ODS) column and an eluent consisting of tetrabutyl ammonium phthalate. This seldom used technique involves the addition of a chromophore to the eluent to provide a background absorbance. The eluting ions are detected as decreases in the background

Ion Chromatography and Electrophoresis

125

Typical Ink Jet Dye Structure

R R = H, SGH. COOH

Ion Chromatographof Common Anions using Reverse UV Detection

absorbance and give excellent chromatograms (Figure 2). However, the chromatography is adversely affected by co-eluting absorbing species in the sample. In addition, cations in the

126

Progress in Ion Exchange: Advances and Applications

sample can dislodge tetrabutyl ammonium ions used as the ion-pairing reagent and result in large peaks appearing near the elution position of fluoride/chloride. Although some reasonable results were obtained, this technique was not robust enough for routine use. At that stage ion chromatography was further investigated. The addition of an ion-pair reagent to the normal IC eluent (sodium carbonate/sodium bicarbonate) was proposed by Dionex Ltd. Tetrapropyl ammonium hydroxide forms an ion pair with the dyes which can be absorbed onto a non-polar polymeric precolumn. This approach was successful for many textile dyes, however break-through onto the analytical column was encountered for the ink jet dyes. The current method employed at ZENECA uses a 5 x 0.42 cm ID ODS precolumn to trap the dye and has resulted in a considerable reduction in the cost and frequency of column replacement due to fouling of the analytical column by the dye. Methanol is used to wash the dye from the precolumn after approximately ten injections of dye or on completion of the analysis.

CAPILLARY ELECTROPHORESIS CE would seem to offer many advantages over IC in terms of speed but more importantly the ease of column clean up and the significantly reduced costs. Moreover, the ability to inject organic substances onto the capillary offers the possibility of the direct analysis of dyes dissolved in solvents. A specific example is a black ink jet dye in a ketone matrix manufactured at Grangemouth Works. The current methodology uses IC and necessitates evaporation of the solvent followed by dissolution in water prior to analysis. The application of CE to ZENECA Specialties products has been investigated by Evans and Beaumont’ and has included some preliminary studies for anions in dyes. Further work, including comparative studies was required to assess fully the technique for chloride and sulphate in ink jet dyes.

COLLABORATIVE STUDIES Within ZENECA, several sites are involved in ink jet development and manufacture and employ different instrumentation to perform anion analysis to monitor product quality. In summary these include Dionex and Waters IC systems and both Grangemouth and Blackley have Waters Quanta 4000 CE instruments. Cross comparison of results from the sites using IC is paramount and ongoing. To date, CE is not used routinely for ink jets analysis and an appraisal of the feasibility of its use for quality control (QC) testing was assessed by means of a collaborative study. This study involved analysis using Dionex 21 1Oi IC, Waters IC and Waters Quanta 4000 CE at both sites. The instrument conditions are shown in Table 1.

Ion Chromatography and Electrophoresis

127

Instruments and Experimental Conditions used in Collaborative Studies

Precolumn: Guard Column: Analytical Column: Mobile Phase:

Flowrate: Injection Volume:

ODS Hypersil(5 cm x 0.45 mm ID) AG4A AS4A 1.8 mm sodium carbonate, 1.7 mM sodium hydrogen carbonate, 0.5 mM tetrapropyi ammonium hydroxide 2 mumin 100 pl

(43 1 Conductivity Detector) Column: Buffer: Flowrate: Injection Volume:

Injector: Detector: Capillary: Buffer: Applied Potential: Capillary Current: Sample loading:

Detection: Capillary: Buffer: Potential: Injection: Temperature:

Hamilton PRP xl00 Anion Column, 25 x 0.45 cm ID 4 mM sodium benzoate in water 2.0 ml/min 100 p1

Crystal 3 10 Crystal 1000 Conductivity Detector 60 cm x 50 pm ID ConCap and ConTip 1 mM CTAB (cetyltrimethylammoniumbromide), 100 mM CHES/ 40 mM LiOWO.2% Triton XlOO -25 kV, Conductivity Detector Cell Voltage: 1.3 V -26 PA 39 mBar for 0.2 minutes (equivalent to 1% plug length)

Reverse UV at 254 nm Fused silica, 60 cm x 75 pm ID 5 mM chromate containing tetradecytrimethylammoniumhydroxide at pH 8. Caustic wash 1 minute, water wash 1 minute 20 kV Hydrostatic 10 c d 3 0 secs Ambient

128

Progress in Ion Exchange: Advances and Applications

The results from the initial study were poor and were attributed to sample preparation discrepancies between sites. To obtain a valid assessment of the techniques, a second study which involved the circulation of prepared samples was performed. The results are shown in Table 2. Ten samples were prepared in duplicate to contain 0.2% w/v of the dyes and each reported analysis result was based on the mean of two injections. The results shown in Table 2 have been rounded to the nearest 10 pg/g. In addition to chromatographic analysis, samples containing higher levels of chloride were analysed by titrimetry.

RESULTS Statistical analysis of the data has been carried out using the paired “t” test and based on a 95% confidence limit. The following trends were deduced:-

Chloride The IC results between sites are significantly different although the calculated t value is close to the critical value. The results obtained on the Waters IC generally show a positive bias which may indicate contamination problems, possibly attributed to filtration of the samples. Similarly, the CE results produced by each site are significantly different although the calculated t value is identical to the critical value. The variation is more apparent for results 2800 pg/g. The IC and CE data generated within each of the two sites was compared and was found to agree. Better correlation of results was found for Site 1. Closer scrutiny of the CE data from Site 2 shows that the results at 5800 pg/g are significantly different to the results obtained by IC on Site 2 and also CE on Site 1. This may be indicative of integration problems rather than the lack of sensitivity as the CE results from Site 1 shows better agreement with both the Waters IC and the Dionex IC data. Sulphate Results In general, the results show better agreement both between techniques and sites, although due to the poor duplication of results obtained on the Waters IC system, statistical analysis of all results was not possible. There was no significant differences on comparison of the between site IC results, CE results or intersite comparison of the IC/CE results based on the data examined.

3.

Further Statistical Treatment of Results

In addition to the chloride and sulphate quantitative data, statistical calculations have been carried out on the duplicate injections by each technique to obtain precision data. This was carried out by calculating the cumulative % RSD of all duplicate injections. The data is

129

Ion Chromatography and Electrophoresis

Collaborative Results for Chloride and Sulphate in Ink Jet Dyes, pg/g 2.1

Chloride Results Sample Ref

-J-& Dionex

Titration

Waters CE Site 2

Site 2

1026 1032 1037 1051 1056 1055 1073 1074

1730 1650 1440

1400 1580 1270

1210

1230

1101 1107 2.2

640 2000 1790 1420 1050 1370

520 1300* 1600 1760* 1000 1390

520 610 600 560 790 1720 1730 1700 950 1290

Sulphate Results, pglg Sample Ref

Dionex IC Site 1

Waters IC Site 2

Waters CE Site 1

Waters IC Site 2

1026 1032 1037 1051 1055 1056 1073 1074 1101 1107

490 350 540 510 1580 560 1540 1390 910 1180

860 8001<500 640/<500 7401<500 1390 GOO 1520 6401<500 940/<500 920

540

410 450 770 590 1510 670 1660 1680 940 1120

Analyte

Dionex IC

Waters IC

Waters CE Site 1

Waters CE Site 2

Chloride Sulphate

3.1 2.4

10.3 7.1

6.1 9.9

9.2 8.5

450 550 1300 650 1570 1750 1000 1100

shown in Table 3. The precision of replicates obtained by Dionex IC is considerably better than the other three techniques.

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Progress in Ion Exchange: Advances and Applications

CE WITH CONDUCTIVITY DETECTION AT1 Unicam have recently introduced conductivity detection for CE. The potential increase in sensitivity and robustness compared with indirect UV detection offers lower limits of detection and permits the analysis of a wide range of analyte species. To assess CE with conductivity detection, two samples were prepared in duplicate and analysed by both Dionex IC and CE using the AT1 Unicam Crystal 1000 conductivity detector. The results are presented in Table 4. Statistical analysis of the results confirms good agreement of the results based on the two sets of data. Typical electrophorograms of an ink jet injection and a solution containing 20 ng/ml chloride and sulphate are shown in Figures 3 and 4 respectively. Excellent resolution and baseline stability are demonstrated and a proven detection limit of 20 ng/ml.

lmd

Comparison of Chloride and Sulphate Results by IC and CE with Conductivity Detection, pglg

Chloride,pg/g Sample Ref Black MEK Lampranol Black

Dionex IC 825 5410

AT1 Unicam CE 825 5140

Sample Ref Black MEK Lampranol Black

Dionex IC 595 3750

AT1 Unicam CE 505 3200

-

Sulphate,pg/g

CONCLUSIONS The determination of chloride and sulphate in ink jet dyes has been assessed using different IC and CE systems. In general, agreement of IC/CE results has been found within sites. However, poorer correlation is obtained between sites, particularly for chloride analysis. Based on the data from this study and our experiences, lead us to conclude that Dionex IC offers the most precise and reliable results. Whilst CE offers several advantages in terms of speed and cost, from the evaluation carried out, the Waters CE system is not considered suitably reliable for this particular application in a QC environment. This is due to a combination of the concentration of sample solution prepared for analysis (0.2% w/v) and the specification levels for the ink jet dyes. Higher concentrations have been investigated for CE analysis to improve sensitivity however these were found to overload the capillary. This lack of sensitivity could account for the poor precision obtained for replicate analysis. The results

Ion Chromatography and Electrophoresis

131

provided by ATI Unicam using conductivity detection were promising, particularly the improvement in sensitivity compared to W detection and worthy of further investigation. As a result of this study, we have a greater appreciation of the errors associated with the

various instruments and techniques. Ion chromatography using Dionex technology is now employed at all Sites and consistent results are now achieved for this complex analysis. Electrophorogram of a 0.2% w N Injection of Ink Jet Dye on AT1 Unicam Crystal CE using Conductivity Detection

E@&

uk

Peak

I

Name CI

2

SO,

Type RT(Mins) 3.637 BB 4.273 BB

Area

8.737 4.503

Height 5.254 3.331

RTBtir)

I

3.637

2

4.273

Base Conc 25.572 2.083 25.638 1.330

Electrophorogram of 20 n g h l Chloride and Sulphate Standards using AT1 Unicam CE with Conductivity Detection

Progress in Ion Exchange: Advances and Applications

132 ACKNOWLEDGEMENTS

The authors wish to thank Dionex UK Ltd, Waters Chromatography UK and AT1 Unicam and ZENECA Grangemouth Works for their assistance in our evaluations.

REFERENCES 1.

K.P. Evans and G.L. Beaumont, JChromatog., 636 (1993) 153.

THE DETERMINATION OF TETRAPHENYL PHOSPHONIUM IN THE EARP MAC PERMEATE STREAM BY ION CHROMATOGRAPHY

S. Aitken Research and Development Department British Nuclear Fuels plc Sellafield Cumbria CA20 IPG

1 INTRODUCTION 1.1 Plant and Process

The Enhanced Actinide Removal Plant (EARP)at Sellafield is a new E600M plant which is currently undergoing its final commissioning stages before coming into routine operations. During commissioning it has been shown to be a very effective treatment for the removal of much of the activity from low active and medium active liquid streams prior to their controlled discharge to sea. This project deals only with the medium active (MAC) streams. On a simplified level the plant process involves the neutralisation of the acidic waste streams, which causes the precipitation of insoluble metal hydroxides. Most of the acidity associated with these streams co-precipitates with, or is absorbed onto this floccular precipitation, which is then removed by a series of ultrafiltration units. The floc is sent for encapsulation, with the permeate being sampled and analysed prior to discharge. 1.2 Project Origin

One species present in the MAC which is not removed by this process however is technetium. This remains in solution throughout the process. It is not absorbed onto the ferric floc and hence passes through the ultrafiltration units with the rest of the permeate. This makes a significant contribution to the plants p activity discharges. In the sample matrix the technetium is present as the stable pertechnetate ion (TcOl'). Tetraphenyl phosphonium (TPP) is well known to co-ordinate with the pertechnetate ion on a 1:1 basis to form an insoliible precipitate. Investigations are taking place at Sellafield into the feasibility of batchwise dosing of the MAC feed with tetraphenyl phosphonium bromide to improve the removal of technetium by the plant. At the levels which would be added to the plant all the TPP would be expected to precipitate out, and be removed by the ultrafilters for encapsulation with the rest of the floc. As such there is no expectation for any TPP to be present in the permeate. However the results of toxicity testing carried out independently for BNFL have shown that TPPB can be quite toxic to some forms of marine life, even in quite small doses. Hence before any discharge authorisation may be granted the permeate will need to be tested for TPP.

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Progress in Ion Exchange: Advances and Applications

2 ANALYTICAL DEVELOPMENT 2.1 Sample Matrix

The EARP MAC permeate is quite a complex matrix, and may contain a range of species including several transition metals as well as organic molecules. As such any method developed would have to be very specific for TPP. 2.2 Development

The technique would also have to be sensitive, to meet anticipated discharge limits, and reliable enough to be used on a routine basis. No method was currently available within our analytical services department. A literature search carried out found little on the topic of TPP in any of the common literature, and analytically this amounted to one paper on a polarographic method. The method in the paper was reproduced, and a detection limit of about 50pg/ml of TPP was suggested. This would be no good for the levels we would be trying to determine, and well above the level we would expect to receive a discharge authorisation for. FT-IR was ruled out due to the high solubility of TPPB in aqueous solution, making quantitative extraction into a suitable solvent almost impossible, and gas chromatography was ruled out due to the high boiling point. TPP absorbed strongly in the UV region of the spectrum, but simple UV spectrometry was unable to cope with the very complex EARP MAC permeate simulate matrix, even when the matrix is diluted 100 times. The TPP also fluoresces very strongly, showing the potential for a very sensitive technique, but despite working well on standards, again it could not cope with the simulated sample matrix.

3 METHOD

In aqueous solution the TPPB molecule dissociates to give the TPP cation, and the bromide anion. As such a cation exchange column seemed like a good starting point to try to separate the TPP from the matrix. The only other organic species expected to be present in the EARP MAC feed are mono and dibutyl phosphates, which would be anionic and pass straight through the column. Interferences from any of the metal cations present in the sample was uncertain. 3.1 Equipment

The system used was a Dionex 4000i, and the column chosen was their IonPac CS12, chosen for its high capacity, as the sample is of notable ionic strength, and quite short elution times for multivalent cations. Using the recommended eluent for the column and suppressor, methane sulphonic acid, proved to be ineffective for eluting TPP from the column, probably due to the high hydrophobicity of the column, and the expected hydrophobicity of the TPP. It was only

Ion Chromatographyand Electrophoresis

135

when a proportion of a 90% acetonitrile solution was used that elution of the TPP could be seen. Initially both suppressed conductivity, and a UV detector were used, to help in the identification of the peak, and also to discern which of the two detectors would provide the greater sensitivity for TPP analysis. It was expected to be the UV detector from the size, and the nature of the analyte, and this proved to be the case.

3.2 Method The TPP peak was identified and the W detector was seen to be far more sensitive than the conductivity cell. This also had the benefit that no suppression was required, and none of the cations in the EARP matrix were expected to exhibit a UV absorbance at the 226nm wavelength at which the TPP was measured. The method was optimised manually to achieve the best possible separation of the TPP from the EARP MAC permeate simulate matrix using an HCVacetonitrile eluent whilst keeping the run time as short as possible, and without running a gradient eluent program, as our Analytical Services instrument only has an isocratic pump and would therefor be unable to run any gradient application developed. It was found that the optimum analysis was carried out using the 4 x 50mm guard column only with the UV detector measuring at 226nm. Analysis on the analytical column resulted in lengthy elution times, and a broad, flat peak which reduced the sensitivity of the method. 4 RESULTS

Analysis of the TPP was carried out on a Dionex CG12 guard column using an eluent containing 58.5% acetonitrile and 40mM HCl. Running this eluent isocratically the TPP was completely eluted in less than seven minutes, and was well separated from the huge peak coming off with the solvent front, containing all the possible interferences to the TPP UV absorbance. Although detection was made at 226nm, detection at 202nm would give about a 2 fold increase in sensitivity. This however approaches the W cut offlimits of the eluents and was not deemed as suitable for routine operation. Using a 50pl injection loop, the standard deviation of the method was found to be about 1% (lo) on a lOpgiml TPP standard, and about 2%(1o) on a lOpg/ml TPP spiked sample of the EARP MAC permeate simulate. The standard deviation rose to only 5%( lo) at the 1pgiml TPP level in the simulate. The discrimination level of the method, calculated as 4 times the standard deviation of the blank added to the mean of the blanks was 0.4pglml TPP, giving a sensitivity expected to cover any discharge limits agreed with the regulatory bodies. Run times were reproducible, the standard deviation over 11 runs was less than 1.5%(10). Ideally it would be nice to quote cost, or time savings over previous techniques used for TPP analysis, but as no suitable analysis was available at Sellafield, this is not possible.

136

Progress in Ion Exchange: Advances and Applications

5 CONCLUSIONS AND FUTURE WORK

The conclusions which may be drawn from this work are quite clear. Ion chromatography can be used to analyse for TPP accurately, sensitively, and precisely, even in this complex matrix. Further work will need to be carried out on actual plant samples if the proposed TPPB dosing of the EARP MAC feed commences. Further work in this area is dependent upon the discharge limits agreed with the regulatory bodies after reviewing the results of the toxicology testing on aquatic samples which will set the detection levels required. I believe that a more sensitive method may be possible by measuring the absorbance at 202nm, which will require higher quality reazents, or by using a fluorescence detector on the ion chromatograph. Unfortunately we do not own one at present and due to the infrequency of the analysis expected to be carried out there is little justification in purchasing one solely for this application.

SEPARATING THE SAMPLE FROM THE MATRIX. AN INSIGHT INTO NEW COLUMN DESIGN: A REVIEW OF CATION EXCHANGE COLUMNS 1975 TO PRESENT.

S L Somerset

Dionex (UK) Limited Albany Court Camberley Surrey GU15 2PL 1 INTRODUCTION 1975 launched the first commercially available ion chromatograph and in 1981 the first cation exchange column, the CS1 (cation separator 1). This was a surface sulphonated column which was used with a packed bed suppressor, then came the fibre suppressor in 1982. These were low efficiency systems which led to the introduction of the CMMS (cation micromembrane suppressor) in 1985 and the CSRS (cation self regenerating suppressor) in 1992, which offered gradient capabilities due to suppression of high eluent concentrations, not previously possible. The most recent columns developed, include the IonPac CS12, CS14 and most recently the CSl2A. All are cahoxylic acid hntionalised cation exchange columns. The CS12A can be used isocratically for the separation of alkali and alkaline earth metals. Sulphuric acid or methane sulphonic acid are used as eluents in conjunctionwith the CSRS, operated in Autosuppressionmode.

Table 1 Comparison of CationExchange Columns Column

Particle Substrate Diam. (pm) (% X-Link)

OmniPac@ PCX-100 IonPacQCS10 IonPac CS12 IonPac CS14 IonPac CS12A

8.5 8.5 8.0

8.0 8.0

55 55 55 55 55

Capacity

Functional

Surface Area

(peqlcolumn)

Group

(m$)

120 80 2800 1300 2800

Sulfonic acid Sulfonic acid Carboxylic acid Carboxylic acid Carboxylic acid Phosphoric acid

(1 c1 300

300 300

The PCXlOO and CSlO are sulphonic acid cationic exchangers with capacities typical of conventional ion chromatography resins. The CS12, CS14 and CSl2A are carboxylic acid cationic exchangers with much higher capacity than the sulphonic acid types. The CS12 and CSl2A have identical capacities, with one major difference, the CSl2A has a substrate hctionalised with a mixed hydrophilic carboxylidphosphonic

Progress in Ion Exchange: Advances and Applications

138

acid layer which results in a column capable of separating a wide range of amines together with inorganic cations. The construction of the PCXlOO/CSlO cation exchange resin is shown in Figure 1. The resin consists of 3 regions, a central spherical core, which comprises approximately 99% of the total phase volume and is an inert, highly cross-linked, ethylvinylbenzene divinylbenzene copolymer coated with an adhesive layer (anion exchange latex) allowing attachment of the active stationary phase on the outer layer. The second and third layers comprise a colloidal dispersion, attachment is electrostatic. Figure 2 shows the 8 pm diameter macroporous particle consisting of ethylvinylbenzene cross-linked with 55% divinylbenzene. Carboxytic acid phases are used in a weakly ionised form and only a small number of available ion exchange sites are actually available for retention of cations hence the need for macroporous particles. The entire surface is covered in a thin am, 5-10 A thickness, of polymer containing carboxylic or carboxylidphosphonic acid groups. With macroporous resins nearly 99% of the available surface area is in the interior of the support particle.

Mia0 Anm ExchangeLatex

Microporous Polymeric Subslrale 8.5 pm 55% x-Link

Figure 1 Lutex Coated Pellicular Cation Exchangers co; co;

Sudace Area = 300 m*/g

Figure 2 Weak Acid Cation Exchanger

Ion Chromatography and Electrophoresis

139

The monomer ratio used in the CS12A is in the order of 4 5 , phosphonate: carboxylate. Adding phosphonate as a co-monomer in the stationary phase for the CS12A was one improvement over the CS12. Another was to change the way the phase was attached to ensure inner core penetration of the polymer stationary phase and support particle was not possible. The result (Figure 3) was a column with improved peak shape and efficiency. 2 RESULTS AND DISCUSSION

When comparing sulphuric acid versus methane sulphonic acid (MSA) as eluent (Figure 4), the MSA separation is good but when u s i g an equivalent strength of sulphuricacid an inferior manganese/magnesium separation is observed. This is due to sulphate forming a weak complex with the divalent cations, calcium, magnesium and manganese resulting in magnesium and calcium, plus manganese and magnesium, eluting more closely, MSA is the better eluent to choose for such a separation. 22 mN Suilunc acid

I

I

I

1 0 mumin 25 pL suppressed wnductlvlly CSRSAuloSuppression 1 Lilhium 0 5 mglL (ppm) 2 Scdium 20 3 Ammanium 25 4 Wassium 50 5 Magnesium 25 6 Calcium 50

I

lonPacCS12

141

Ynules

Figure 3 Cornpison of IonPac CSl2A and CSI2 14 -

22 mN H$O,

14 -

Peaks

,

1

4

Column Flav Rate In1 Volume Deleclmn

1

m mM MSA

IJS

0-

0

hnPaO CSlZA (noguard) 1 0 mUmin 25 pL Suppressedconduclivily CSRSAuloSuppressioil " 1 Lithium 0 5 mglL Ippilll 2 Sodium 20 3 Ammonium 25 4 Polassium 50 5 DRlhylamine 100 6 Magnesium 25 7 Manganese 25 8 Calcium 100

I

10

15

klnUlSl

Figure 4 Detenninaiion of Manganese, Alkali and Alkaline Earth Metals using IonPac CSI2A

140

Progress in Ion Exchange: Advances and Applications

When manganese is not present, sulphuric acid is a good eluent to choose, as it is less expensive in high purity form than MSA and, as it forms a complex with divalent cations, it causes them to elute earlier, this effectively allows shorter analysis time for the overall run. Retention times for the monovalent cations are unchanged, which means when using the CSl2A with 3 1 mM sulphuric acid eluent at a flowrate of 1 d m i n the 6 common cations elute in a little over 6 minutes (Figure 5 ) Figure 6 gives a complete separation of alkali metals, alkaline earth metals and ammonia. The efficiency is essentially the Same for all the metals although slightly higher for the alkali metals as, being monovalent, their mass transport kinetics are improved in comparison with alkaline earth metals at ambient temperature.

90

1

Column: Eluent, Flow Rate: Inj. Volume: Detection:

4

Peaks:

-

00 I I

I

I

I

I

I

0

2

4

6

8

10

IonPac” CS12A (no guard) 31 mN Sulfuric acid 1.0 mLlmin 25 pL Suppressed conductivity, CSRS AutoSuppression’” 0.5 mglL (ppm) 1.Lithium 2.0 2.Sodium 3.Ammonium 2.5 4.Potassium 5 0 5.Magnesium 2.5 6.Calcium 50

Minutes

Figure 5 Fast Separation of Alkali and Alkaline h r t h Metals and Ammonium 4

20

ColumnEluent: Flow Rate: Inj. Volume: Detection:

IJs

0

Peaks:

1

0

I

5

I

I

10 15 Minutes

I

I

20

25

lonPac@CS12A (no guard) 18 mN Methanesullonic acid 1 .O mLlmin 25 pL Suppressed conductivity, CSRS AutoSuppression” 1. Lithium 1.0 mg/L (ppm) 2.Sodiurn 4.0 3. Ammonium 5.0 4. Potassium 10.0 5. Rubidium 10 0 6. Cesium 10.0 7.Magnesium 5.0 8. Calcium 10.0 9. Strontium 10.0 10. Barium 10.0

Figure 6 Separation of Expamkd Alkali and Alkaline Eurth Metals and Ammonium

Ion Chromatography and Electrophoresis

141

A formation water run with 20 mM MSA (Figure 7) shows how the improved resin enables much lower detection limits for strontium and barium can be achieved.

Sodium and ammonia at a 1OOO:l ratio are easily resolved with a step gradient. Morpholine, ammonia and the 6 common inorganic cations are separated on a CS12 or CS14 by addition of solvent to the eluent. The CSl2A allows the same separation, with improved peak symmetry on morpholine with a totally aqueous eluent system (Figure 8) By raising the temperature to 50°C the efficiency for all cations is SigniScantly increased using a CS12A. Monodents elute earlier and divalents elute later. Divalents are most affected by stationary phase mass transport and hence the effect of raising the temperature is largest. Elevated temperature improves the separation of methylamine and ammonium which are only partially separated under ambient conditions. 4

l0nP.C cG12. cs12 2OmM MSA 1mUmln 25uL

s

u

m eondudlvny,CSRS Aulosuppntrlocl

I. Sodium 2. Poturim 3. M8gmhlm 4. Caldum 5. StrorXium 0. B8llWl

I'

7

Mwl:

5 28

6

2

Figure 7 Isocratic Separation of Fonnation Water Column: Eluent: Flow Rate: Inj,Volume: Detection:

Peaks:

0

10

5

15

lonPa9CS12A (no guard) 20 mN Sulfuric acid 1.OmUmin 25 pL Suppressedconductivity, CSRS AutoSuppression" 1. Lithium 0.5 mgll (ppm) 2. Sodium 2.0 3. Ammonium 2.5 4. Potassium 5.0 5. Morpholine 25.0 6. Magnesium 2.5 7. Calcium 5.0

Minutes

Figure 8 Isocratic Spuation of MorphIine, AIMi and AIkaIine Earlh Metals on IonPac CS12A

noOomf9L 500

so0

2800 0

P

Progress in Ion Exchange: Advances and Applications

142

The retention of hydrophobic analytes is decreased significantly by the addition of solvent (Figure 9) as is shown in separation of common inorganic cations plus a range of aliphatic diamines. The separation is achieved at ambient temperature using a gradient of sulphuric acid and acetonitrile. An acetonitrile gradient can be used to separate a variety of quaternary ammonium compounds (Figure 10) IonPac CS12A performance does not deteriorate with injection of acidic samples of upto 50 mM hydronium ion which enables acid digested or acid preserved samples to be injected without pH adjustment.

Column Eluent

Flow Rale In1 Volume Deleclion Temp Peaks

0

5

10

15 Minutes

20

25

I o n P f l CSlZA (no guard) 22 mN Sulfunc acidlZ% acelonilnle lo 44 mN sullunc acid115 6% acelonilrile in 10 min lo 50 mN sulluiic acid 130% acelonilfilein 14 min 10 mUmn 25 pL Suppressedconduclivily CSRS AuloSuppression 40 "C 1 Lilhium 0 2 mglL (ppm) 2 Sodium 08 3 Ammonium 10 4 Polassium 20 5 Magnesium 10 6 Calclum 20 7 1 2-Pmpanediamine 8 0 80 8 1 6 Heranediamine 9 1 7-Heplanediamine 8 0 10 1.8 Octanediamine 80 11 1 9 Nonanediamme 80 12 1.10 Decanediamine 8 0 13 1.l2-Dodecanediamine 8 0 1,191

Figure 9 G r d e n t Elution of Diamines on the IonPac CSiM Column Eluent

6 13

0

IonPaCCSIZA (noguard) 22 mN Sulfuric acidll0I acelonilrile lo 22 mN sulfuric acidBO% acelonilrile In 15 min Flow Rale 1.0 mUmin in) Volume 25 pL Deleclwn Suppressedconductivity, CSRS AuloSuppression" 1. Sodium Peaks 0 3 wlL (ppm) 2. Ammonium 2 3 Potassium 5 4. Telramelhylamnmnium 5 5. Calcium 8 6 Telraelhylamnmnium 20 7 TelsprcQylammonium 25 8. Tributy(melhylammonium 50 9. Heptyllrielhylammonium 10. Tetrabutylammonium 11. Lkvllrimethvlammonium 50 12 Tel&ntylamnmnium 50 13 DodeeylMmethylammonium 100 20 14 Tetrahexylammonium 1W 15 Telraheptylammium 100 I6 Hexadecyllnmelhylammonium 1W

I 0

5

10 Minutes

15

Figure 10 Gradient Elution of QuarternaryAmmonium Ions

Ion Chromatographyand Electrophoresis

143

3 CONCLUSION

The IonPac CSl2A column is useful in determining the common alkali metals, alkaline earth metals and ammonium, achievable in just over 6 minutes. It gives excellent peak symmetry and allows determination of a variety of amines, diamines and quarternary ammonium compounds. Typical applications include determination of inorganic cations and amines in drinking water, waste water, power plant waters, soil extracts, acid digests, chemical additives, chemical process solutions, scrubber solutions, plating baths and solvents. The CSl2A can be operated at elevated temperatures between 30°C and 80°C to improve peak &ciency and solvent compatibility allows for the use of solvent control for cation exchange selectivity to resolve more hydrophobic amines, to enhance sample solubility and for easy column cleanup after analysis of complex matrices. The CS 12A is a versatile cation exchange column. References 1.

H Small, JChrom, 1991,546,3

2.

D Jensen, J Weiss, M A Rey & C H Pohl,JChrom, 1993,640,65

3.

S.Rabh, J Stillian, V Baretto,K Friedman & M Toofan, J Chrom, 1993, 640,97

4.

A Siriraks & J Stillian, JChrom, 1993,640,371

5.

S Rabin & J Stillian, JChrom, 1994,671,63

IONIZATION CONTROL OF METAGCHELATE SEPARATION I N ION CHROMATOGRAPHY

PCter Hajhs,” Ott6 Horvith,b Gabriella R ~ v ~ s zJayne ,’ Peear,‘ Corrado Sananinid aDepartment of Analytical Chemistry, University of Veszprdm, P.O. Box 158, 8201 Veszprdm,Hungary bDepartment of General and Inorganic Chemistry, University of Veszprem ‘The Nottingham Trent University, Nottingham, NGllaNS, England dDepartment of Analytical Chemise, UniversiQ of Turin, 10125 Turin, Italy

1 INTRODUCTION

Complexing eluents have been used to improve the selectivity of the chromatographic separation of metal ions.’. 2 When a basic solution contains an excess of a strong complexing anion of high charge such as ethylenediaminetetraacetate(EDTA) ion, most metal ions will occur as anionic complexes. The metal EDTA complexes (MEDTA2-, MHEDTA-) are anions and can be separated by anion exchange. Hence this method provides simultaneous metal and anion separation.34 The principle of ionization control is the control of the affinity of ionic species in a solvent through the manipulation of the charge. Not only does pH control retention, but the complexation of the species also plays an important role. The aim of this work was to extend the ion-exchange retention modeF9 by predicting the retention of Cu, Pb and Zn EDTA complexes, in simultaneous analysis with inorganic anions (CI-, NO*-, Br‘, NO3-) and hence demonstrate further, the reliability of the ionization model, when complexing effects are present in the analyte. The study takes into consideration all possible analyte species using carbonate buffer as the most widely used eluent system for suppressed IC. The unknown values for the ion exchange equilibrium constants, required in the model, are determined by repetitive minimization using a nonlinear regression algorithm. These values are then used to compare observed and predicted retention data. Good comparison was shown for all metal EDTA complexes studied. Practical application of the retention model, in determining the elution behaviour of the species, proved successhl and demonstrates the reliability of the model. 2 THEORY

The model involves strict consideration of all equilibrium opportunities within and between the eluent and analyte. We shall consider the equilibrium distribution and separation of anionic metal EDTA complexes of Pb, Zn and Cu, in simultaneous separation with inorganic anions (C1-, NOz’, Br- and NOj). We shall also assume that distribution equilibrium between the mobile and stationary phase is maintained constant as the solute migrates through the separation column. The separation is performed using carbonate, a multiple species eluent. The theory is based on the extension of ion-exchange equilibrium by protonation and complex formation equilibria.

Ion Chromatography and Electrophoresis

145

In general, the ion exchange equilibrium, in which a solute anion (AY-) competes with a prebound eluent anion Q for a position on the stationary phase (R), may be defined as yRx-E

+

xAY-

KAIE

a

xRy-A

+

yEX-

In terms of molar concentration of species present in each phase, the ion exchange equilibrium constant is expressed as:

where the square and parenthesesbrackets represent the molar concentration of the species in the mobile and stationary phase, respectively. At any point in which an equilibrium is established,the ratio ofthe analyte concentration in the stationary phase with respect to the concentration of analyte in the mobile phase may be expressed as the distribution co&cient, which in turn may be defined in terms of KAm.

The total ion exchange capacity is expressed as the number of eluent anions able to take up position on the stationary phase. At any one point in the separation process, it is assumed that the eluent anion (Ex-)occupies x number of sites, out of a total of Q,on the stationary phase. (EX-) = -

e X

(4)

Substituting this into the second part of Eq 3 enables the distribution coefficient to be expressed as:

2.1 Complexation and Ion Exchange Equilibria of Metal Ions.

To enable the simultaneous separation with inorganic anions, the metal cations are complexed with EDTA to form anionic metal EDTA complexes. The nature of the complexes formed is dependent upon the pH of the mobile phase. In the pH range of 8-12 the formation of protonated EDTA complexes and hydroxo complexes can occure. Thus, in the systems studied the following species were taken into account: PbEDTA2-, PbHEDTA-, Pb(OH)3-, ZnEDTA2-, ZnHEDTA-, Zn(OH)3-, Zn(OH)4'-, CuEDTA2-, and CuHEDTA-.

Progress in Ion Exchange: Advances and Applications

146

The ion exchange equilibrium for the anionic metal EDTA complexes may be expressed as: KMEDTAIE

2 R-E + M E D T A ~ R-E

+ MHEDTA‘

a

KMHEDTAIE Q

where E- represents the eluent species HCOf and 7 respectively,may be given as:

R2 -MEDTA + 2 E- (6) R-HEDTA

+ E-

(7)

The equilibrium constants for equations 6

(M E D T A ~ - ) [ E - ] ~ KMEDTAIE =

I2

[ M E D T A](E~-

(MHEDTA-)[,-] KMHEDTAIE =

(9)

In the case of the species considered in this study, the formation of hydroxo complexes must also be taken into consideration. The distribution coefficient @d in this instance is considered as the sum of the distribution coefficient of the individual species containing M:

(MEDTAZ-)+( MHEDTA-)+( M(oH);) DM =

1

[M2+]+[MHEDTA-

(10)

Substitution of Eqs 8 and 9 into Eq 10 gives:

DM

=

[

[MHEDTA- E M(OH&](E) +KMHEDTAIE [El )+KM(OH)~IE [El

[MEDTA KMEDTAI E

[El2

[M 2 ++[] MHEDTA -1 +[MEDTA2-

I(

(1 1)

which can be rewritten as:

(12)

where +MEDTA and ~

D

T

and A Q M ~ H )are ~ the actual values for the molar f i a ~ t i o n s . ~ * ’ ~

147

Ion Chromatography and Electrophoresis

2.2 Ion Exchange Equilibria of Eluent Ions.

The carbonate eluent is a multiple species eluent which contains 3 competing anions (CO3’- HC03; Om.With competing anions, in simultaneous ion exchange, the ion exchange capacity of the column is best described by:

Q = 2( CQ2-) + ( H C Q - ) +(OH-)

(13)

The series of ion exchange equilibrium processes for the eluent species may be given by:

C032-

+

QO3IHCQ

2 R-HC03

e mH/HCOjl

R2-C03

OH- + R-HCOJ ts R-OH where each equilibrium constant may be expressed as:

+

2 HC03- (14)

+ HCO3- (IS)

By rearrangement of equations 16 and 17, the concentration of C0-: and OIF in the stationary phase may be expressed in terms of (HCO,?. Substituting these expressions for (C03’-) and (OK)into Eq 13 gives rise to the ion exchange capacity (Q) in a quadratic form.

(18)

By solving Eq 18 for (HCO3-), a value for (HCO3-) can be substituted into Eq 12 in place of Q. After the calculation of the molar fractions for the complex anions, one of the final forms of the model may be obtained. Finally, in order to eliminate the instrument-specific void volume (Vo), the distribution coefficient @A), can be expressed by the capacity factor &’),

where Vsis the volume of the stationaryphase, which can also be easily determined.

Progress in Ion Exchange: Advances and Applications

148

3 EXPERLMENTAL SECTION 3.1 Reagents and Solution.

The anion eluent mixtures of Na2CO3, NaHC03 and NaOH were prepared by dissolving analytical grade salts (Fluka, Switzerland). High purity water was obtained using a Milli-Q-system (Mdlipore, Bedford, Mass., USA). All eluents were treated with an ultrasonic bath and ultrafiltrationto remove air and particles. The pH was measured using a Radelkis (Budapest) pH-meter as a last operation. Standard solutions of metals, P b O , Z n O and Cu(II), were prepared by the dilution of concentrated stock solutions of analytical grade salts (Fluka, Switzerland). Standard solutions of simple anions were prepared by the dilution of concentrated stock solutions of analytical grade salts (Fluka, Switzerland). The chelating agent, EDTA, was prepared by the dilution of a concentrated stock solution of an analytical grade sodium salt (Carlo Erba, Mlan, Italy). Unless otherwise stated, all sample injections(50 pl volume) contained [Pb] = 0.124 mmol, [Zn] = 0.055 mmol, [Cu] = 0.085 mmol and [EDTA] = 0.532 mmol. The sample pH was adjusted to the appropriatevalue using NaOH. 3.2 Instrumentation

A Dionex series 2010i ion chromatograph was used with a conductivity detector equipped with an AMMS anionic membrane suppressor (Dionex, Sunnyvale, CA, USA). The chromatograms were recorded on a Dionex SP4270 module integrator. The separation column (Dionex, AS9, 250 x 4mm) was based on a 15pm polystyrene divinylbenzene substrate, agglomerated with an anion exchange latex which had been completely aminated. The latex had a polyacrylate backbone which carried the actual ion exchange sites. The ion exchange capacity was determined empirically (20pequiv per column). AU chromatogramswere obtained at room temperature. The flow rate was fixed at 1.6dmin. All retention times obtained were the result of triplicate injections of a sample containing all analytes. 4 RESULTS AND DISCUSSION

The retention behaviour for three anionic metal EDTA complexes (Cu, Pb, Zn) and four inorganic anions were considered. A typical chromatogram is shown in Figure 1. All experimental retention data, obtained from various eluent compositions and pHs, was suitably evaluated. The evaluated data was used to determine the unknown values for the analyte-eluent and inter-eluent ion exchange equilibrium constants, required in the model, by repetitive minimization. The non-linear regression algorithm (Nelder and Mead simplex method), used in the repetitive minimization, was then used successfklly to compare the observed and predicted retention data. A comparison was obtained for each analyte at the varying eluent compositions and pHs. The protonation and complex formation constants required in the calculations were taken from the literature.", l2 The activity coefficients were calculated using the Davies extension of the Debye-Huckel equation.

149

Ion Chromatography and Electrophoresis

b" z

Figure 1. Chromatogram of anionic metal EDTA complexes and simple anions obtained by using carbonate eluent ( Ce~l,e~~=lHC03-Jf(CO~2-]=4.5 mM, C032-/HCO3-=2.5/2.0, pH=10.28,sample volime 5 0 4 , conductivity detection). The calculated values of the ion exchange equilibrium constants are summarized in Tables 1. From this table, it can be seen that the inter-eluent ion exchange equilibrium constant is independent of the analyte present and the eluent concentration. The analyteeluent ion exchange equilibrium constants are also independent of the eluent concentration. These values are of particular importance when considering simultaneous separation.

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150

Table I. Ion-Specific and Intereluent Chromatographic Ion-Exchange Selectivity Constantsfor Complex Forms of Cu2', Pb2', and Zn2'

Eluent concentration (C032-+ HC03-)(mM)

Ion-exchange Constant

2.5

5.0

6.5

Mean f Gn-1

8.0

GUHEDTARICO3 %uEDTA/HC03 kHRIC03 &!03/HCO3

0.765 8.796 1.228 13.559

0.854 8.161 1.098 13.857

0.792 7.812 1.391 13.503

0.732 0.786f 0.05 7.591 8.090f 0.53 1.357 1.269f 0.13 13.659 13.645f 0.16

KPbHEDTAEiC03 KPbEDTA/HCO3 kHMC03 &03/HC03 KPb(OH)3/HCO3

0.743 3.206 1.499 13.567 10.985

0.762 3.187 1.496 13.728 10.925

0.808 3.174 1.496 13.614 10.483

0.757 0.768f 0.03 3.293 3.215f 0.05 1.409 1.475f 0.04 13.993 13.726f 0.19 10.231 10.656f 0.36

KZnHEDTARICO3 KZnEDTARICO3 kHRIC03

0.799 6.776 1.379 13.743 3.746 8.388

0.820 6.480 1.379 13.902 3.676 8.358

0.942 6.390 1.386 13.721 3.726 8.376

0.727 6.337 1.441 13.867 3.963 8.776

&03/HC03

KZn(OH)3/HC03 KZn(OH)4MC03

0.822f 0.09 6.496f 0.20 1.396f 0.03 13.808f 0.09 3.778f 0.13 8.475f 0.20

The comparison of observed and predicted retention volumes for metal EDTA complexes are shown in Figure 2. These results unambiguously show that good correlation between the observed and predicted retention volume was obtained for all analytes. CuEDTA2-

+

PbEDTA2-

*t

ZnEDTA2-

1.4

1.2 1.o

0.8

0.6 Ju

0.4

0.2 0 -0.2

0

0.2

0.4

0.6

0.8

1.O

1.2

LOG k' MEASURED

Figure 2. Relationship of measwed and calculated capacity factors for anionic metal ED TA complexes eluted with carbonate bidfir (slope: 1.085kO.022; correlatori coefjcietil: 0.987for 63 dala pairs).

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The calculated ion exchange equilibrium constants were used in the preparation of a retention surface diagram for the metal complexes studied. Figure 3. shows a typical example. These kind of retention surfaces give a clear picture of the relationship between the value of log k', eluent concentration and pH.

3.5 3.O 2.5 h 0 2.0 1.5

s

1.o 0.5

.l.O

0.0

'

m

Z

.0.8 0 '

U

.0.4

2 2

.

4

.0.6

L

I

.0.2 0 2 0

CWDTq2-

I, 12

Figure 3. Calciilaled releiition slrrface for the anionic Cii-EDTA complex eluted with HC03--C032- b1rffL.r (C=[HCO3-]+[CO32-]). Partial molar fractions of HCO3- and C032(together with the O H concentration) it1 HCO3--CO32- biflir are also illuslrated as firnctiotis of pH.

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Progress in Ion Exchange: Advances and Applications

Since the selectivity constant of C o t - is significantly higher than that of HC03-, increasing pH results in decreasing value of log k’, which as decreasing retention time was experienced practically. All the retention surfaces obtained show a slight break at about pH 10.1. This phenomenon can be attributed to the inflexion point on the molar fraction plot of C032; which is the determiningeluent ion. The retention model was used successfilly in predicting the retention of the analytes prior to their simultaneous separation, using new eluent compositions. ACKNOWLEDGMENTS We would sincerely like to acknowledgethe financial support from Hungarian National Science Foundation (OTKA TO 17342). The authors wish to thank F. Montandon diploma student (Swiss Federal Institute of Technology, Lausanne) for his assistance in experimental work. J. P. (The Nottingham Trent University, England) would like to acknowledge the financial support for a BSc thesis from the Tempus Joint European Project. References G. J. Sevenich and J. S . Fritz, Anal. Chem., 1983,55, 12. J. Inczedy, Analytical Applications of ComplexEquilibria, Ellis Horwood, Chichester and Akademiai Kiado, Budapest, 1976, p. 22. 3. S . Matsushita, J. Chromatogr., 1984,312, 327. 4. G. Schwedt and B. Kondratjonok, Fresenius’ 2.Anal. Chem., 1989,332, 855. 5 . C. Sarzanini, 0. Abollino, E. Mentasti and V.Porta, Chromatographia, 1990,30,293. 6 . C. Sarzanini, G. Sacchero, E. Mentasti and P. Hajos, J. Chromatogr., 1995, 706, 141. 7. P. Hajos, G. Revesz, C. Sarzanini, G. Sacchero and E. Mentasti, J. Chromatogr., 1993,640, 15. 8 . P. Hajos, 0. Homith and V.Denke, Anal. Chem., 1995,67,434. 9. D. Jenke, Anal. Chem., 1994,66,4466 10. G. Anderegg, Critical Survey of Stability Constants of EDTA Complexes;IUPAC Chemical Data series, No. 14, Pergamon Press, Oxford, 1977. 1 1. G. Foti, P. Hajos and E. sz. Kovats, Talanta, 1994, 41, 1073. 12. L. G. Sillen, Stability Constants of Metal Ion Complexes, The Chemical Society, London, 1971. 1. 2.

Water-eluent based Ion Chromatography on Silica Bonded Molecular Baskets

J. D. Glennon*, B. Lynch, K. Hall, S.J. Hanis and P. O'Sullivan.

DEPARTMENT OF CHEMISTRY.

UNIVERSITY COLLEGE CORK, CORK, IRELAND.

1 ABSTRACT

The retention behaviour of alkali and alkaline earth metal ions on a novel silica bonded macrocyclic calix[4larene tetradiethylamidephase is reported using water-eluent based ion chromatography. Using.a shofl column and water as the mobile phase, the silica bonded phase displays enhanced chromatographicselectivitiesfor Ca2' and S?' over and Ba2' and for Na' over K , Cs' and Li' in line with known complexation selectivity ' from stability constant and extraction data. Selected ternary mixrureS of alkali and alkaline earths can be separated with the elution order Ca2'/Na' >> K ' >' ! g M using water modified with methanol or acetonitde as the mobile phase.

M2'

2 INTRODUCTION

Synthetic macrocyclic compounds known as calixarenes, have the ability, when suitably functionalised. to act as molecular baskets for binding ionic guests. The hostguest interactions of free calix[nlarenes with a variety of neutral and ionic species have been widely reported. While analogies could be drawn with crown ethers or cyclodextxins, the calixarenes are chemically quite unique. Calix[n]arenes are cyclic oligomers composed of phenolic units linked by methylene bridges at positions ortho to the hydmxyl groups. These compounds may contain four to eight aryl moieties arranged in a macrocyclic array with a central cavity.' Derivatisation of the phenolic groups has produced a variety of functionalised calixarenes which show selective ionophoric pmpetties towards selected guest species. The host-guest complexation is determined by the overall macrocyclic structure, most importantly by the cavity size but also by the nature of the functional groups which act as the binding sites. The ionophoric properties of functionalised calixarenes have been clearly demonstrated using NMR spectroscopy and by liquid-liquid extraction studies. Specifically, the conversion of p-ferf-butylcalix[4larene and p-ferf-butylcalix[6lareneinto acetic esters, ketones and amides results in ionophoric activity.2 The phase transfer

154

Progress in Ion Exchange: Advances and Applications

activity of these functionalised calixarenes has been demonstrated for the extraction of metal picrates from water into di~hloromethane.~ Tetrameric calixarene esters, ketones and amides show a selective ability to extract Na+ while the hexameric c a l h n e s have higher efficiencies for Cs+ ions. As with crown ethers, the selective complexation properties of calixarenes have been successfully exploited in the construction of ion selective electrodes4*5and in the development of chemically modified voltammetric sensors.6 However, only recently have applications in chromatography appeared in the literature. Specifically, water soluble calixarenes have been shown to be effective as selectivity modifiers in chromatography and capillary electrophoresis. In particular, the water soluble calix[6]arenepsulphonate has been used in the modification of selectivity for substituted phenols in capillary electrophoresis' and reversed phase liquid chromatography.' Our laboratory has concentrated on the development of novel solid phase materials incorporating functionalised calixarenes, with applications in ion separation and analysis. Solid phase extraction cartridges. incorporating chelating molecular baskets immobilised onto XAD or silica, have been used to sequester metal ions from aqueous s o l ~ t i o n .The ~ quantitative trace enrichment of Cu2+, Zn2+, and Mn2+ from water samples prior to ion chromatographic analysis has been demontrated using immobilised calix[4]arene tetrahydmxamate. The separation of alkali and alkaline earth ions on chemically bonded crown ether stationary phases, using simple water-methanol mobile phases, has previously been r e p ~ r t e d . ~ OThe - ~ ~application of silica bonded calixarene phases in watereluent based ion Chromatography offers exciting possibilities, in view of the established tailoring of selectivity for these ions that is possible through lower rim functionalisation. A silica bonded calix[4]arene tetraester phase has been shown to have e n h a n d chromatographic selectivity for Na+ over other alkali metal ions.l3 In this paper, the use of the silica bonded tetrameric calixarene tetradiethylamide phase for water-eluent based ion chromatographic separation of alkali and alkaline earth metal ions is reported.

3 EXPERIMENTAL Chemicals and reagents.

Silica (Nucleosil, 5pm particle size) was purchased from Macherey-Nagel (Diiren, Germany). HPLC grade methanol and acetonitrile and AnalaR grade toluene were purchased from Merck, (Darmstadt, Germany). All alkali metal salts were AnalaR grade from BDH (Poole. UK). Instrumentation.

For water-eluent based ion chromatography, the system consisted of a Dionex series 4000i metal free pump and injection system, plumbed with PTFE tubing. The injection was pneumatically driven, with a loop volume of 25 pl, unless otherwise stated. The conductivity detector used was a Dionex CDM I1 utilising a Dionex conductivity cell (8 pl volume) and incorporating temperature compensation facilities. Empty stainless steel columns ( 4.5 cm x 4.6 mm i.d.) were slurry packed with the silica bonded calix[4]arene tetraamide phase. An Elgastat water purification system provided water for ion

Ion Chromtography and Electrophoresis

155

chromatography with a resistivity greater than 15Mohm cm. Synthesis of the silica bonded calixI4larene tetradiethylamide phase p-Allylcalix[4]arene was prepared according to the reported procedure' and was converted into its ethyl acetate derivative by refluxing with ethyl bromoacetate in acetone in the presence of anhydrous potassium carbonate as described p r e v i o ~ l y . ~p Allylcalix[4larene tetraacid was treated with oxalyl chloride to afford pallylcalix[4]arene tetraacid chloride, which on treatment with N.Ndiethylamine in tetrahydrofuran was converted to the diethylamide. This pallylcalix[4larene derivative was treated with mercaptopropyl-triethoxysilane at 7OoC for one hour in the presence of cumene hydroperoxide (free radical source for thiolene addition) to yield the triethoxysilane derivative. The silica immobilised caliix[4]arene tetradiethylamide shown in Figure 1, was prepared by refluxing ca. 0.32 g of the triethoxysilyl derivative of the calix[4]arene in 30 ml toluene with 2.0 g of activated Nucleosil for 24 hr. The silica bonded phase was filtered, washed with ca. 100 ml toluene and yielded 6.7% C on elemental analysis. Water-eluent based Ion Chromatography The chromatographic selectivity for alkali metal and alkaline earth metal ions was examined at mom temperature by injection of standard aqueous solutions, prepared in the concentration range from O.lmM - lOmM, onto the calix[rl]arene tetradiethylamide phase with water as the mobile phase. Injections of methanol were used to determine the value. Methanol or acetonitrile in different concentrations was added to the mobile phase and its influence on the retention determined. 4 RESULTS AND DISCUSSION The use of water or other polar solvents as the sole component of the mobile phase in ion chromatography, can eliminate the need for electrolytes, precise mobile phase make-up and ion suppression as part of conductivity detection. This water-eluent based ion chromatography is possible with electrolyte sorbing phases such as ionophoric crown ether phases. While the earliest results with crown ether phases gave broad peaks, excellent alkali metal ion separations were subsequently obtained in a matter of minutes with water as eluent.'0." In the present work, some of the first results obtained with silica bonded molecular baskets, constructed using functionalised calixarenes. are presented. Distinct features of these macrocyclic compounds, apart from their shape, is that very high ion selectivities are possible and that this selectivity can be modulated by suitable functionalisation of the lower rim of the calixarene. In earlier work, with silica bonded tetraethyl calix[4]arene tetraacetate, it has been shown that its Na' selectivity is transferable to silica bonded phases. From extraction and stability constant work, it has been shown that a similar tetrameric calixarene functionalised instead with diethylamide, exhibit, substantial complexation of alkaline earths in addition to Na'. It has the highest reported complexation selectivity for Ca2+ over Mg2+ for a neutral camer ionophore. l4 The structure of this silica bonded calix[4larene diethylamide, prepared from the triethoxysilane derivative, is given in Figure 1. Details of the characterisation of this

156

Progress in Ion Exchange: Advances and Applications

silica bonded phase by solid state NMR are to be presented elsewhere.

-Si-

I 0 --O-~i-O-CH~-CH3 I

Figure 1 Structure of the silica bonded calix[4larene diethylamide phase. In the present work using conductivity detection and with water only as the mobile phase, sodium ions are retained significantly longer than all the other alkali metal ions. While sharp peaks very close to the to are obtained on injections of LiCl, KCl and CsCl, NaCl has a different chromatographic behaviour, is retained and shows fronting. A mivtUre of 5mM NaCl and 5mM KC1 on injection yields close-to-baseliie resolution and a selectivity factor of 5. For alkaline earths, Ca2' and S?' are selectively retained, like Na', while M g ' and Ba2' elute close to to. Again close-to-baselime resolution is obtained on injection of a mixture of Ca2' and M g ' and while the quality of the separation obtained is reduced by broadening of the Ca2' peak, a selectivity factor of 14 is observed. If watedorganic modifier mixtures are utilised instead of pure water as the mobile phase, the retention times obtained for alkali and alkaline earths increase significantlywith the rise of organic fraction in the eluent. These increases are in proportion to the extent of complexation of the ion in the molecular basket. The most noticable feature is how little the retention of ~ g 2 ' varies, staying close to the to. These results are illustrated in Figure 2, where the capacity factors obtained for selected metal ions are plotted against % methanol and % acetonitrile. Acetonitrile is seen to be more effective than methanol at increasing ion retention. In Figure 3, a chromatogram obtained for a mixture of Ca?' and M 8 ' is given to illustrate the type of separation achieved.

157

Ion Chromatography and Electrophoresis

4.5 4

3.5 3

L 2.5 2 1.5 1 0.5 0

0

5

1

0

1

5

2

0

2

5

3

KM

0

5

1

0

1

5

2

0

2

5

0

3

5

4

0

4

0

a

3

0

3

6

K ACN

M2'

Figure 2 Variation of capacity factors for chloride salts of Na+, K+,Ca2+, and as a function of percentage organic modifier in the mobile phase. (concentration: 1mM)

Progress in Ion Exchange: Advances and Applications

158

,

'

.

.

.

L

0 1 2 3 4 5

TIME I MIN

figure 3 Chromatogram obtained on injectionof 5mM CaCl, and 5mM MgCl, on a silica bonded calix[4]arene diethylamide column (20% aqueous MeOH eluent, 1.0 mumin., conductivity detection). A typical chromatogram obtained on injection of a mixture of NaCl, KCl and MgCl, is given in Figure 4, using 20% aqueous acetonitrile.

Mg

K

0

5 10 15

TIME / MIN

Figure 4 Chromatogram obtained on injection of 1mM NaCl, 1mM KCl and 1mM MgCl,. (20% aqueous ACN eluent, 1.0 ml/min., conductivity detection.) 5 CONCLUSIONS Silica bonded calix[4]arene diethylamide stationary phases show selective retention of Na+ , S?+ and Ca2' ions over other alkali and alkaline earth ions injected, with pure

Ion Chromatography and Electrophoresis

159

water mobile phases. These new molecular recognition phases based on macrocyclic calixarenes show enormous potential for the tailoring of chromatographic selectivity thmugh calixarene functionalisation and the use of mobile phase additives. Further work is in progress on these versatile molecular basket sorbent phases for ion Separation and analysis.

ACKNOWLEDGEMENTS The authors wish to gratefully acknowledge the help and advice given by Professor M.A. McKervey, School of Chemistry, Queens University, Belfast. Thanks also to Ms. G. Flynn for work in the laboratory.

(1) C.D. Gutsche, 'Calixarenes', Vol 1 inMonographs in Supramolecular Chemktry, ed. J.F. Stoddart, Royal Society of Chemistry. 1989. (2) M.J. Schwing-Weill and M.A. McKervey in 'Topics in Inclusion Phenomena, Calixarenes, A Versatile Class of Macrocyclic Compounds' eds V. Bohmer and J. V i m . Kluwer Academic Publishers, pp. 149-172, 1990. (3) F. Amaud-Neu. E. M. CoIliins, M. Deasy, G. Ferguson, S.J. Harris, B. Kaitnef, A. J. hugh, M. A. McKervey, E. Marques, B. L. Ruhl, M.J. Schwing-Weill and E. M. Seward, J. Am. Chem. Soc.,1989, 111.8681. (4) D. Diamond, G. Svehla. E. Sewad and M.A. McKervey, Anal. Chim. Acta. ,1988, 204, 223. (5) K. Kimura,T. Miura, M. Matsuo and T. Shono. Anal. Chem.,1990, 62, 1510. (6) D.W.M. Anigan, G. Svehla, S.J. Harris and M.A. McKervey, Electrr;Mnalysk,l994, 6, 97-106. (7) D. Shohat and E. Grushka, Anal. Chem., 1994, 66,747-750. (8)J.H. Park, Y.K. Lee, N.Y. Cheong and M.D. Jang, Chromatographiu, 1993,37(3/4), 221-223. (9) S . Hutchinson, G.A. Kearney, E. Home, B. Lynch, J.D. Glennon, M.A. McKervey and S.J. Harris, Anahtica Chimica Acta, 1994, 291, 269. (10) E. Blasius, K.P. Janzen, W. Klein, H. Kloa, T. Nguyen-Tien, R. Pfeiffer, G. Scholten, H. Simon, H. Stockemer and A. Oouissant, J. ChrOmatogr.,l980, 201, 147166. (1 1) K. Kimura, H. Harino, E. Hayata and T. Shono. Anal. Chem. ,1986,58,2233-2237. (12) J.S. Bradshaw, R.M. Izatt.J.J. christensen, K.E. Krakowiak, B.J. Tarbet, R.L. Bruening and S.Lifson, J. Inclusion Phenomena and Molecular Recognitwn in Chemktry, 1989, 7, 127-136. (13) J. D. Glennon, K. O'Connor. S. Srijaranai, K. Manley, S. J. Harris and M. A. McKervey, Anal. Left., 1993, 26(1), 153. (14) F. Amaud-Neu, M.J. Schwing-Weill, K. Ziat, S. Cremin, S.J. Harris and M.A. McKervey, New J. Chem., 1991, 15, 33-37 (15) H. Small, 'Ion Chromatography' in Modem Analytiical Chemktry Series (D. Hercules, 4 . ) . Plenum Press, New York, 1989.

POTENTIAL USES OF CAPILLARY ION ELECTROPHORESIS IN THE NUCLEAR POWER INDUSTRY.

N J Drew BSc PhD, Plant Engineering, Nuclear Electric, Berkeley Technology Centre, Berkeley, Gloucs., GL13 9PB.

1 INTRODUCTION Two sets of Capillary Ion Electrophoresis (CE) equipment were examined in 1994 to ascertain potential uses to Nuclear Electric for the analysis of anions and cations. Analysis ranges required for applications on large power generation boilers are below lopgkg-', with the main emphasis being measurements below Ipgkg-'. Ion chromatography is currently used at these low concentrations, the application of electrophoresis to these analyses is relatively new. The buffer systems used were those currently recommended by literature sources or recommended by the manufacturer's. No optimisation of the recommended systems was attempted. The systems both used indirect UV detection. This paper examines the strengths and weaknesses of this analysis technique in the following applications: Species Identification (by migration times) Quantitative Cation Analysis Quantitative Anion Analysis Practical Considerations such as ease of sampling, ease of servicing and changing between anion & cation analyses

2 EQUIPMENT AND METHODS The principle of the technique is illustrated in Figure 1. A fine, silica capillary is filled with a conductive buffer solution. A small volume of sample is loaded at one end of the capillary, both ends of the capillary are then immersed in identical buffer solutions. Applying a high voltage across the capillary induces an electro-osmotic flow (EOF). The direction of this flow is selected by the applied polarity and the charge sign on the capillary walls which is adjustableby pH and addition of cationic surfactant. These factors are chosen to induce an EOF which modifies the ionic mobility of species to be analysed. For example in analysis of cations the ions migrate to the cathode, separation is caused by

161

Ion Chromatographyand Electrophoresis

""n -

Capillary Electrophoresis Basic Schematic

e 8

e

0

0

Figure 1. hinciples of capihty ion electrophoresis

the differing magnitude of ionic mobiities in the presence of a complexing agent in the buffer, all ions moving within the osmotic flow of the buffer. Near the receiving end of the capillary a method of detecting the passage of the ions is required. Currently this is by indirect W absorption, where the concentration of ions displace a W active species. There is potential for use of more sensitive methods such as conductivitydetection which is currently being developed. For useful analysis of any type the choice of the appropriate 'Buffer' ranga is essential. These contain constituents to control three factors: 0

Osmotic flow modifiers:

0

pH: W absorbing species:

Reduce or reverse osmotic flow, (generated by interaction of the electrolyte with silanol groups) affects the ionisation of electrolytes and silica wall silanol groups. for indirect W detection.

The composition of these buffers is the subject of exhaustive research by instrument suppliers and users, both sources being helpful in making an appropriate choice for the user's application. The buffers employed for obtaining the results listed here are described in the following table, with the details of capillaries and analysis conditions. The reagents were mostly as recommended by the manufacturers, with the exception of cation analysis by the Dionex CES 1. For cation analysis Dionex would now recommend an electrolyte containing dimethyldiphenylphosphonium, but the reagents reported to give the best sensitivity at that time were as listed'. It must be recognised that research into optimising

162

Progress in Ion Exchange: Advances and Applications

electromigration conditions is continuing and improved buffer systems may already be in use or about to become available. Changes in sensitivity and other properties of the CIE are unlikely to be of an order of magnitude from such variations. But a change in detection method does have such a potential. ~

BUFFERS AND CONDITIONS FOR ANALYSIS BY WATERS CIE EQUIPMENT

Anion Analysis: 5 mM sodium chromate & 5cc in 2OOcc of CIA-PAK osmotic flow modifier, anion, converted to hydroxide form. Capillary: 52cm of 75pm , 20kV applied. Detection: indirect uv 254nm Elcctro injection was at Skv, with 75fiMole OSA added, for 45s. Electrodgrotion at 20kV Cation Analysis: 6.5 mM a-bydroxy iso butyric acid & 5 mM 4 methyl beazyl amine Capillary: as above with 25kV applied aftex hydrostatic loading (lOOmm/6Os), or lSkV applied after electro-injection (5kV for 45s) Detection: indirect uv detection at 185nm

~~

BUFFERS AND CONDITIONS FOR ANALYSIS BY DIONEX CIE EQUIPMENT

Anion Analysis: 2.25 mM 1.2,3,4 benzenetetracarboxylic acid 1.6 mM triethanolamine 6.4 mM sodium hydroxide 0.75 mM hexamethonium bromide converted to the hydroxide form. Capillary: 6Ocm of 75pm Detection: indirect uv at 25Onm. Electro injection was at SkV, with 75pMole OSA added, for 45s. Eiectromigration at 2OkV. Cation Analysis: 8 mM a-hydroxy isobutyric acid 3mM 18 crown 6 ether 10 mM imidazole made to pH 3.5 With acetic acid Capillary of 55cm of 75pm Detection: indirect uv at 220ma. Hydrostatic loading was lOOmm for 6Os, migration at 18kV. Electro injection was 5kV for 5s. migration at l5kV

The results reported here are of two types. Examples of electropherogramsare given to illustrateparticular features, eg. peak heights, baselineproperties, distortions or splitting of peaks and resolution. To establish the quantitativebehaviour of CE systems for anions and cations repeated applications of mixed standards were applied. The mean response of the CE system and spread of results (indicated by error bars) are then plotted against concentration and linear regression analysis applied to generate a "calibration line". The actual instruments used illustrated in Figures 2 and 3.

Figure 2 Illustmiion of the Dionex CES 1 instrument

Ion Chromatographyand Electrophoresis

163

3 RESULTS

3.1 GeneralDetaii The analytid equipment was quite easy to set up and use. The analysis time for anions or cations was relatively short. When using equipment from either Waters or Dionex, the carousel could be loaded with a Series of samples for investigationand left for automatic analysis. That would be the case even if analysis uNts were used with just a simple chart recorder, because the sequence of samples and conditions for analysis arc internally controlled. The two systems investigated were, however, also supplied complete with PC based, complex and sophisticated integration software.

3.2 Species Identification The first example electrophemgrams (Figures 4 and 5) show that the peaks obtained during analysis are sharp and well defined. The suppliers (Dionex and Waters) give good theoretical reasons why peaks will always appear in a set order for anions and cations (except possibly I-). No evidence was found too contradict that theory. The electropherograms showed that them could be s e v d unlcnown/impurity peaks which are 'unexpected'. So for a sample to be chamterised requires a knowledge of migration times for the species to be found. Unfortunately migration times for a given species can vary according to several factors. Some of these!factors can be easily 'fixed' by adopting standard conditions for sample loading into the capillary and migration potential. There still remains a variability from day to day, probably caused by temperature and most importantly that caused by the sample matrix. The concentration of all ionic species within the sample have an effect on its conductivity, this affects species migration time as can be seen in Tables 1 to 4. It

Progress in Ion Exchange: Advances and Applications

164

would not be possible from these examples to say the migration time of say Mg2+ is exactly 4.5 minutes (Table 1) or exactly 2.85 minutes (Table 2).

File: C2oo(nllDO4 Sample: CIMZMlo

Con(%ntrations Of bglkg) Na' Mg2' Lit

Ca2'

Pk. No. 1

2 3 4 5 6 7

0.005

Name

unlrnown

0.004

250

Calcium Sodium Magnesium .UO.WJ UllkUOWll

Lithium

copper

0.002

I'"'I'"'I""l"''1""~""~""~ 3 4 5 6 7

0

8

9

10

M i i S

Figure 4 Example electropherogramfor cations after hydrostanc loading

-

2

Time

Npme

Concentrations of (&kg)

CI' 1.85 Chloride suiphate 1.90 l.%N i h k Fluoride 2.28

4.6

00

SO," 4.6

NO; F 4.6

4.6

I

2.00

1.00

"

"

'

Hinuto.

Figure 5 Example electropherogramfor anions @er electro-injection

In the following Table values are given in minutes with standard deviation in parentheses. Samples were of mixed cations at concentrations of: X = lOOOpg/kg Lithium, 1OOOpglkg Copper, lOOOpg/kg Magnesium, 2OOOpg/kg Sodium, 2OOOpglkg Calcium. These used hydrostatic loading with analysis using 18kV. Y = S.llpg/kg Lithium, 10.22pglkg Sodium, 10.22c(g/kg Calcium, 3.21pglkg Magnesium. This analysis used electro-injectionwith subsequentanalysisat 15kV.

Ion Chromatography and Electrophoresis

165

' From I

Electroisjection

0 3.77(0.O2) 3.93(0.O2) 4.12(0.03) 4.91(0.04)

Broad, duration lmin. between 3 & 5 Broad, duration lmin. >4.8

Table 1 Migration timesfor cations using Dionex CES 1

In Table 2 (see two pages forward) times are in minutes with standard deviation in parentheses. Results to the left of the double line were obtained with electromigration at +25kV, results to the right under electromigration of 15kV. Samples were of mixed cations at concentrations of

+

V=

16Opg/kg Lithium, J6Opglkg Copper, 160pg/kg Magnesium, 32Opglkg Sodium, 32Opg/kg Calcium.

W = 9.12pg/kg Lithium, 18.24pgIkg Sodium, 18.24pg/kg Calcium, 5.74pg/kg Magnesium Z =

10.67pglkg Lithium, 21.34pg/kg Sodium, 21.34pg/kg Calcium, 6.71pg/kg Magnesium

166

Progress in Ion Exchange: Advances and Applications

For each species to be identified it would always be necessary to run a series of samples 'spiked' with the relevant species. The same procedures are required to identify anions, note that in Figure 5 and Table 3 the peaks are only 0.05 mins apart but very well resolved .

3.3 Quantitative Cation Analysis

3.3.1 Hydrostatic Loading. For this procedure the sample, is loaded into the capillary by a siphon action prior to electromigration. Typically the sample vial and end of the capillary is elevated by l00mm for 45 to 60s. Subsequent analysis (eg. Figure 4) indicated large peaks for cation concentrations greater than approximately 100 pgkg" and up to ranges of mgkg-I the same analysis conditions were still useful. Identifiable peaks can still be found = 50 pgkg-' (eg. Figure 6). Examples of linear regression analysis of peak areas with applied concentration for a single system @ionex) in Figs. 7 A to E show that analysis by peak area provides a linear relationship over this wide concentration range. Analysis by peak heights indicated a much smaller linear range for the response, although at the lowest concentrations where the response was linear, the standard deviation of concentration as determined from peak height was generally slightly smaller. Results given for calcium, sodium, magnesium, lithium and copper are given indicating similar linear characteristics, differing in the magnitude of sensitivity. Very similar results were obtained with the Waters system. Comparison of the standard deviation with the response factor indicated that the standard deviation was equivalent to 10% in concentration terms. Using peak heights provided slightly lower repeatabilityfor analyses, but only usefully for lower concentration values where a linear response to concentration is seen. When using hydrostatic loading there was little effect from ammonia or morpholine in the sample on all the cation species except copper where that peak was eliminated. There were strong additional peaks for ammonia or morpholine, which did not overlap other cation peaks.

At

At 40pccglkg

At 15pg/kg

1.864 (0.017)

1.791 (0.007)

1.868 (0.006)

(0.Ow

SO,"

1.899 (0.014)

1.829 (0.007)

1.912 (0.006)

1.923 (0.

NO;

1.957 (0.032)

1.882 (0.007)

1.970 (0.006)

F

2.192 (0.021)

2.145 (0.021)

2.248 (0.011)

1~CrgJkg

c1-

At 15pglkg with "€I3

At 15 with Morpholine

1.875

1.980 (0.010)

1.791 (0.007) 1.829 (0.007) 1.892 (0.007)

2.102 (0.038)

2.145 (0.021)

167

Ion Chromatographyand Electrophoresis =

At

At V120

At Vl10

V120 with Morph.

with

Conc.

NH3

caz+

2.71 (0.098)

2.578 (0.005)

2.78 (0.062)

Na+

2.80 (0.10)

2.660

2.86

(0.009

(0.066)

2.85 (0.11)

2.730 (0.011)

2.95 (0.069)

Li+

3.32 (0.091)

3.09 (0.025)

cu2+

4.49 (0.088)

4.16. (0.084)

-

-

I

At W using El&+ injection

-

' 4.25 (0.040)

4.81 (0.035)

4.44

(0.044)

4.99 (0.033)

-

4.60 (0.030)

5.16 (0.040)

3.33 (0.084)

-

5.46 (0.020)

6.15 (0.053)

-

-

2.33 (0.043)

-

-

- I broad pk, 3.1 4.4

MOVholine

'(0.03)

Table 2 Migration timesfor cclrions with Waters Quanta 4cKx)

Peak

cd+

Npms

25 1

2 3 4

Calcium Sodium Magnesium Lithium

, , ,,

0.0013 4

, , , , 5

w , , , ,

6

, , , ,

7

, , , , 6

, , , , 0

10

uhu(a

IFFgure 6 &le electropherogram: low concentration of cations @er hydrostatic loading.

At 160pglkg

At 7.79pglkg

c1-

3.63 (0.008)

3.67 (0.015)

so:-

3.81 (0.008)

3.82 (0.011)

NOi

3.98 (0.008)

4.00 (0.012)

F

5.62 (0.023)

5.88 (0.039)

Table 4 Anion migration times using the Dionex CES I

A 800000

-

700000

-

e 600000

-

R a

-

500000

Y

-

254.3629 +364.895SX

400000 S

-

300000

0

200

400

600

.a00

lo00

1200

1400

1600

1800

2000

1200

1400

1600

1800

2000

B

-

9ooooo

700000 800000

600000

-

500000

-

P n e

X

-

-4223.925 U 2 5 . 4 0 3 3 X

400000

-

300000 A

r 200000 e a 100000

~

-

0 0

Figure 7 A, B

200

400

600

800

1000

cow. PPb

Analysis of all results for cations aftcr hydrostatic loading, using lincar regression

169

Ion Chromatography and Electrophoresis

C

nssmnsE m ruciresron

-

700000

600000 S

-

500000

-

n 400000

-

P 0

r

I

; A

r

-

100oOOk 300000

200000

-

0 0

100

200

300

'

400

500

800

700

600

lo00

900

Cone. ppb

Lrruron

RBSPONSS TO

D

180000

160000

n 100o00 1 ) m

600000

r

4oooOO

2ooooo 0

100

0

200

300

400

500

600

700

800

900

lo00

B n c . ppb

RESPCUSL

0

100

200

300

4W

m COPPER

500 600 B n c . ppb

700

800

900

1000

ETgure 7 C to E Analysis of all resultsfor cations @er hydrostatic loading, using linear regression

170

Progress in Ion Exchange: Advances and Applications

30 to 45s. All initial results (ie. for both instruments) from electro-injection gave very variable results for peak heightskireas. The cause was found to be matrix interference from the nitric acid contained in the SpectrosoL standards used to prepare known samples. For CIE work the suppliers recommend the use of Neutral Salts to prepare standards. The results indicated that the cause of the matrix interference problem lay with the technique of electro-injection for sample loading, because samples analysed successfully using hydrostatic loading (Section 3.3.1) had been prepared from the same SpectrosoLstandards. Figure 8 A and B gives example electropherograms at the extreme of sensitivity for both sets of apparatus examined. Even minor improvements in the technique would bring routine cation sensitivity into the 0 to 0.5 Fg kg-' range most useful to large power generation boilers. However, it would be wise to duplicate 3 to 5 analyses in the light of the repeatability results, which would still give 18-30 minutes analysis time, comparable to 1 or 2 determinations by ion chromatography.

In Figures 8A, 8B, (below) the concentration of cations is given in the same order as the peaks identified by number or migration time. File: NJLMOcUYDO9 Sample: CB327E.3 4

I

0.m

Concentrations Of @gfi& Na+ Mg'+ Li+ 1.054 1.054 0.278 0.527

Ca*'

0.oOy

0.0032 0.0031

W

0.m

1-00

Concentrations of (pgnCg) Ca*+ Na+ Mg2+ Li+

0.80

2.93

3

2.93 0.93

1.47

from neutral saIu

0.60

0.40

0.20 0.00

0.00

2.00

4.00

MiImteS

Figure 8 Elcctropherogrm for low concentralions of catiom using electro-injection.

Ion Chromatography and Electrophoresis

ai f I8 f I I

\

171

172

Progress in Ion Exchange: Advances and Applications

The analysis of samples prepared from neutral salts gave results summarised graphically in Figure 9 A to D. Applying linear regression to peak heights indicated that useful sensitivity was being maintained down to below lopgkg". These electro - injection results still gave higher values for reproducibility than results from hydrostatic loading, and typically gave standard deviation values of up to 30%with Na' and Ca2'. However, results for Mg2+ and Li+ were considerably better, with a repeatability of less than 10% at 0.6 to 0.9 pgkg-' from the Dionex equipment.

3.3 ANION ANALYSIS Clear peaks for anions could be obtained at mgkg-' levels using hydrostatic loading, but work was concentrated on lower ranges, for which electro - injection was found to be essential. The sensitivity to anions is exemplified in Figures 5 and 10 A and B. The current buffer solutions are not providing the same sensitivity as for cations, but peaks corresponding to 5 pg kg" would be clearly identified.

Peak

Name

o.m81

C1-

2

7.79

I

: O S

N0i

7.79

7.79

F 7.79

6

Chloride Sulphate

I

unlrnown Nitrate

unknown Fluoride

Peak

0.0020

2

Name

1.89

1.89 1.89

1.89

I

0 0021

Chloride

1 2

Sulphate

5 63 4

Fluoride unknown Nitrate

I

00019 Om

0 0018

0 0017

y,,$14y;h

30

35

40

45

50

55

60

65

70

Ion Chromatography and Electrophoresis

174

Progress in ion Exchange: Advances and Applications

In this instance one of the buffer systems was giving extra peaks which could not be identified. These appeared relatively stable in height (ie. not varying with sample composition or addition of octane sulphonic acid), such that at low (1.9 pgkg-') concentrationsthe electropherogram became dominated by the false peaks and peak species assignment became difficult. The results are presented graphically in Figures 11 A to D. Useful analysis was being obtained to below 20 pgkg-' for each instrument. At higher concentrations the standard deviation for chloride and sulphate response was in the order of 8 td 10%. At lower concentrations the results were either a poor fit to the regression line and/or gave high values for standard deviation. With both manufacturers' buffer and analysis systems, matrix effects dominated behaviour once morpholiie or ammonia were introduced. There is the possibility of using calibration with similar matrices, but the peak shapes become split and distorted with one of the buffer systems. The other buffer gave useable peaks, but the sensitivity changed significantly for all the anions when 60mgkg-' of morpholine or 2mgkg-' of ammonia were present. 4 PRACTICAL CONSIDERATIONS

4.1 Sampling

Currently the equipment relies upon the manual loading of samples into a carousel. This has disadvantages when handling pgkg-' concentration samples. The larger Waters' vials were much easier to handle and fill. The 0.6 cm3 conical type of vial was 'fiddly' to de-gas and rinse. For cation analysis the standard method of soaking and rinsing apparatus were found essential. This was: 10 96 nitric acid Rinses

de-ionised water

-

soak overnight

-

soak for at least 12 hours. Store in de-ionised water.

All vials were Msed with de-ionised water six times prior to rinsing with sample (twice) and loading. This is why a convenient form of vial is a major advantage. 4.2 Ease of Servicing

Both analysis units require a short period of training for competent use. But all the procedures required were relatively simple. Each system had particular advantages but the following resum6 is not intended to indicate that one was overall better than the other. CIE instruments require the power supply polarity to be changed between aniodation analysis. This was a simple procedure on both instruments examined, changing a plug position on the System 1 and exchanging the plug-in supply on the Quanta. The buffer will also have to be changed and usually the measuring wavelength, the ease of accomplishing these simple procedures are discussed below. The Quanta analyser was the easiest for a novice user. The sequence of events was immediately understandable being the more manually operated machine. Operator intervention (for runs failing) was also easier for this reason. There is a requirement to manually change buffers which was not onerous. But when changing between anion and

Ion Chromatography and Electrophoresis

175

cation analysis it would be easy to overlook the changing of the optical filter in the source and detector heads. The Quanta machine was also easy to decontaminate after use with active samples. The CES 1 analyser was more complex in that all buffering and rinsing was carried out automaticallyfrom reservoirs. This required close day to day control of buffer quality (ie knowledge of what was in the reservoirs and its age). It required longer period of study to ensure the user was familiar with the sequence of procedures and the methods for control. However, in a carefully structured I to 1 tutorial it should be possible to convey this information in 2-4 hours and in the long term would yield more rapid and convenient set up of analyses by the experienced user. In this analyser the wavelength was continuously selectablefrom the front panel, so it is more difficult to make any error with that parameter providing the operator has a checklist of actions. Cleaning out the buffer reservoirs when changing between anion to cation analysis was the most time consuming task. 5 CONCLUSIONS

Using hydrostatic sample loading both instruments with their recommended buffer solutions were found to be capable of analysis at concentrations in the order of 5Opgkg-* for cations, but only at significantly higher concentrations for anions. Elecbo-injection allowed analysis at much lower concentrations with the sacrifice of increasing the sensitivity to matrix interference. Using electro-injection, analysis was possible for anion concentrationsjust below 1Opgkg-"and for cation concentrations down to lpglcg-'. It is concluded that the technique is already extremely useful for ranges where hydrostatic loading can be used, but that most applications pertaining to large boilers await an increase in the sensitivity of the detection method by a factor of 100, such that hydrostatic loading can be used for concentration ranges below lpgkg-I.

6 ACKNOWLEDGEMENTS The author thanks both Dionex (UK) and Waters Ltd. for their assistance with this project. References 1. W Beck, H Englehart: Chromatographia 33, 313 (1992).

IMPROVED SEPARATION AND DETECTION OF INORGANIC IONS BY CAPILLARY ELECTROPHORESIS

K Divan Dionex (UK) Limited 4 Albany Court Camberley Surrey GUI 5 2PL

1 INTRODUCTION

The determination of small ions using capillary electrophoresis (CE) has generated a great deal of interest over the last few years. The technique offers high resolution, efficiencies and fast run times for the analysis of these small inorganic anions and cations. Ions are separated according to their relative ionic mobilities in an electric field and detected using indirect photometric detection which allows the detection of these ions many of which have no optical absorbances. This paper will discuss the parameters influencing the selectivity and mobility of inorganic anions and cations and the technique of sample stacking will be illustrated to show the improved detection of these ions. Finally the use of suppressed conductivity with CE will be presented for the detection of these non-chromophoricions. 2 INORGANIC ANION ANALYSIS

Electrolyte composition is critical in optimising separation of inorganic anions by CE. Some of the important parameters which must be considered when designing a electrolyte system for CE include: 2.1 Carrier Ion :Mobility

The anion in the greatest quantity in the electrolyte is termed the carrier ion. One of the important requirements of the carrier ion is that the electrophoreticmobility is closely matched to the electrophoretic mobility of the analytes of interest.’” The matching of the mobilities of carrier and analyte ions govern the peak shapes observed in CE. If the electrophoretic mobility of the analyte is faster than the carrier ion the peak fionts. Conversely, the slower the analyte peak compared to the carrier ion, the analyte peak tails. The closer the match, the better the peak symmetry.

Ion Chromatography and Electrophoresis

177

2.2 Carrier Ion :W Character The majority of common inorganic anions are W transparent or absorb only in the low W. For the detection of these ions the technique of indirect UV detection is employed. The capillary is filled with a highly mobile chromophoric ion. This produces a high background absorbance. A decrease in absorbance occurs when an analyte ion displaces a chromophoric ion resulting in a negative peak. Since indirect UV detection relies on displacement of a chromophore the carrier ion should have a large extinction &cient to maximise the decrease in signal resulting from its displacement. The wavelength at which the chromophore absorbs should be well away &om any wavelength at which analyte ions may absorb. This prevents an analytes direct U V absorbance from counteracting the indirect absorption mechanism. The use of pyromeliitic acid is well suited as an electrolyte because its electrophoretic mobility when fidly ionised is closely matched to many of the common inorganic anions. In addition, pyromeliitic acid has the required spectral properties, including a high extinction d c i e n t and a strong UV absorbance at 250 nm, well away from the low UV wavelength at which several inorganic anions absorb. 2.3 ElectroosmoticFlow Modifier

The natural direction of the electroosmotic flow @OF) in an uncoated silica capillary is opposite to the direction of the migration of anions. @OF is from anode to cathode). This is detrimental in terms of analysis speed. In order to minimise the analysis time, the EOF should be in the same direction as the d y t e of interest (for anions EOF should be 60m cathode to anode). The use of hexamethonium bromide is very effective in reversing the EOF. The bromide salt is converted to the hydroxide form to remove the bromide ion that can compromise detection. By the addition of this alkyl ammonium salt to make the detector side anodic very fast analysis times for inorganic anions are possible. An example of the analysis of inorganic anions is shown in Figure 1. The highly mobile pyromellitate ion is used as the background absorbiig ion. Hexamethonium hydroxide is added as the EOF modifer. The electrolyte solution is also buffered with triethanobine at pH 7.7 to ensure reproducibility between runs.'

2.4 Ionic Strength of Electrolyte

The ionic strength of the electrolyte is important for two reasons. Firstly as the ionic strength is increased the current increases. This leads to heating effects resulting from the inability to dissipitate heat. The effects manifest as noise and baseline disturbances. For this reason the ionic strength should be minimised to prevent noise resulting from high currents. Secondly, efficiency is proportional to electrolyte ionic strength. As the ionic strength decreases, electromigrative dispersion increases resulting in lowered peak efficiencies. This is shown in Figure 2. In both electropherograms, the voltage and pH of the electrolyte are identical, only the ionic

Progress in Ion Exchange: Advances and Applications

178

strength is different. Clearly there is an increase in peak efficiency as the ionic strength is increased. The optimum ionic strength of an electrolyte must be a balance which will produce low current to minimise noise while maintaining good peak efficiencies. Caprtlaq

I

In]. Volume

50 pn I 50 Cm 2 25 mM P~romelt~l~c nd 6.5 mM Sodium hydrosde 0.75 mM HexameIhONYmhydroxide 1 6 mM TneIhanclamine.pH 7 7 Gravily, 100 mm lo( 30 rec

Polanly'

I-),detector a r d u

Control M d e

lndiiecl UV. 250 nm

BuIIer:

Peaks

mAU

D8Iluonale

2 Tinosullele

3m@ 5

3 Brom~de

8

Chloride

3 3 3

I

4

5 Sulfate 6 Nilitte

7 Nllrale S. Md)tdate 9. bad0 io.mmyanate t i Chbms 12. F I w d s 13. Eamate 14. Fwmale I 5 Phorphale

0 5

-

1

Minutes

16

Phihatale

I 5 4 3 3 0.5

3 2 3 I0

Figure 1 CE anabsis of inorganic anion standard.

-

-4.0 Eleclrolyte Ionic Strength = 7.25 m M

2

5

I

Ill I

11

mAU1 mAU

0

-4.0-

1

4

13

Capillary:

50 pm x 50 cm

Buller

Pyromelliticacid Hexamelhoniumhydroxide Tiiethanolamine, pH 7 8

Injection

Gravity 100 mm lo: 20 seconds

Peak:

1 . Bromide 2 Chloride 3. Sullate

I

1

Electrolyte Ionic Strength = 11.10

rnM

f;iq mAU

0'

1

1

I

I

J,,

4.Nilrite 5. Nitrate

I

I

SmgR

5 5 5 5

-

Figure 2 Eflect of ionic strength on peak .yrnrnetry. 2.5 pH of Electrolyte

The pH of the electrolyte solution can have a great effect on the separation of anions in CE. pH changes can change migration times of weak acid analytes by modifjmg the charge of the analyte. The majority of inorganic anions are unaffected

Zon Chromatography and Electrophoresis

179

by pH in the range 3 to 9 but ions such as phosphate, carbonateand acetate can display large changes in mobility. Optimisation of the pH can help in maximising resolution of closely eluting weak acid anions. The pH of the electrolytealso controls the ionisation of the pyromellitic acid and therefore controls the electrophoretic mobility of the carrier ion. Separation of lower mobility ions can be optimised by decreasing the pH Figure 3. As the pH is decreased the carrier ion becomes more protonated decreasing its charge and its electrophoretic mobility. At this low pH the mobility of the pyromellitate ion is well matched to the mobility of the akyl sulphonates resulting in symmetrical peak shapes. Alkyl sulphonates run at the higher pH would show peak hiling, characteristicof the condition when d y t e peak is travelling much slower than the carrier ion. Capillary: Euller:

50 pin x 50 Cm 2.5 mM Pyromelliticacid, 0.75 mM Hexamethoniurn hydroxide, pH 3.5

Injection: Polarity:

gravity, 100 mm for 30 seconds

-1.o

3

1

mAU

0.1

I

3jo

i

(-), detector anodic

Control Mode: constant voltage, 20 kV

I

Detection: Peaks :

Indirect UV @ 250 nrn 1. Methanesullonate 2. Elhanesullonale 3. Propanesullonate 4. Bulanesullonale 5. Pentanesullonate 6. Hexanesullonate 7. Heolanesullonale

2 rngR 2 2 2 2 2

8. aianesuilonate

2

I

I

I

I

I

I

3.5

4.0

4.5

5.0

5.5

6.0

2

Minutes

Figure 3 Sepmation of alkyl sulphonic mi& at pH 3.5 2.6 Addition of Solvent

Figure 4 shows the effect of methanol on the separation of ions with identical mobilities. Under the standard conditions used iodide and chloride coelute as do perchlorate and azide. With the addition of 15% methanol all four ions are separated. It is possible that resolution of the ions in 15% methanol results &oma combination of changes in pKa and the hydration spheres around the ions

Progress in Ion Exchange: Advances and Applications

180

standard conditions

: l .Am 0

2

Capillary: Buffer:

2.5

3

3.5

4 4.5 Minutes

5

5.5

6 Injection:

15% methanol

Polarity: Conlrol Mode: Detection: Peaks:

2

mAU0 2

2.5

3

3.5 Minutes 4 4.5

5

5.5

50 pm x 50 cm 2.25 mM Pyromellilicacid 6.5 mM Sodium hydroxide 0.75 mM Hexamethonium hydroxide 1.6 mM Triethanolamine pH 7.7 Gravity, 100 mm for 30 sec. (-), detector anodic -30 kV Indirect UV, 250 nm 1 . Iodide 5.0 mg/L 2. Chloride 2.5 3. Perchlorate 2.5 4. Azide 2.5

6

Figure 4 Eflect of methanol on anion separation. 3 INORGANIC CATION ANALYSIS

In selecting an electrolyte system for cation analysis, majority of the considerations stated for anion analysis also apply. The carrier ion is now a chromophoric cation which should have an electrophoretic mobility similar to the analytes of interest to maintain good peak symmetry. Indirect photometric detection is again chosen since inorganic cations are W inactive. The natural direction of the EOF in an unwated capillary is in the same direction as the inorganic cations so EOF modifers are not required for the fast separation of these species. Figure 5 shows an example of the separation of group I and 11 metals using copper sulphate as the U V background component of the electrolyte. 18-Crown-6 ether was also included to aid the separation of ammonium and potassium. Formic acid was added to lower the pH and improve se1ectivity.s Detection is indirect W at 210 nm. The concentration of the analytes ranges from 0.7ppm for lithium to 27ppm for barium. As is apparent from the electropherogram some of the peaks are fronting while others are tailing, thus the mobility of this electrolyte is not optimum and sensitivity is compromised. Improved detection limits are observed when using dimethyldiphenylphosphonium (DDP) ion as the W absorbing carrier ion6 DDP is an excellent alternative to the copper carrier ion Figure 6. DDP exhibits strong absorbance in the W, a requirement for indirect detection. The electrophoretic mobility of DDP is also well matched to the mobilities of the cations of interest resulting in highly efficient peaks and enhanced sensitivity.

lon Chromatography and Electrophoresis Capillary: -4

Buffer:

7

1

Control Mode.

5

mAU

0

1

-I

0

I

I

I

I

1

2

3

4

I

5

Minutes

181 50 cm x 50 pm 1.D fused silica.

55 cm total length 4mM Copper sulfate 4mM Formic acid 4mM 18-crown-6ether. pH3 Constant voltage. 20 kV (+), Detectorcathodic Ambient Indirect UV (210 nm) Hydrostalii, 10 cm lor 30 s 1. Ammonium 3.6 mg/L 2. Potassium 7.0 3. Sodium 46 4.0 4. Calcium 5. Magnesium 2.4 6. Strontium 15.0 7. Lilhium 0.69 8. Barium 27.0

Figure S Sepation of alkali and alkaline earth metals using copper as the electrolyte. Capillary: Buffer: Control Mode:

0

1

2

3 Minules

4

5

6

50 cm x 50 ID. fused silica, 55 cm total length IonPhor" DDP Constant voltage, 20 kV (+), Detector cathodic Ambient Indirect UV (210 nm) Hydrostatic, 10 cm for 30 s 1. Ammonium 1 .O mg/L 2. Potassium 2.0 3. Calcium 2.0 4. Sodium 2.0 5. Magnesium 1.0 6. Strontium 2.0 7. Barium 4.0 0.25 8. Lilhium

Figure 6 Sepation of alkali andalkaline earth metals using DDP as the electrolyte 4 TRACE ION ANALYSIS

CE using indirect W detection with electrostackingcan achieve pg/L detection limits for inorganic anions and cations. To perform electrostacking, sample is introduced into the capillary using an applied voltage (electromigration injection). Analyte ions migrate into the capillary based on their individual electrophoreticmobilities. During the electromigration injection,the field strength along the length of the capillary is not constant. The local field strength in the sample zone is significantly higher than in the operating buffer region of the capillary because the lower ionic strength sample has a lower specific conductance and a higher resisitivity. As the effective field strength in the sample zone increases, the velocity of the analytes which is proportional to field strength, increases. When the analytes reach the concentration boundary between the higher ionic strength operating buffer and the lower ionic strength sample zone, they

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experience a lower field strength and slow down. This causes "stacking" or "focusing" into zones, hence the term electrostacking. To normalise the specific conductances of sample and standards, a terminating ion, typically at low ph4 concentrations is added to both. With similar specific conductance for both sample and standards, accurate quantificationof analyte in low ionic strength matrices is possible. The terminating ion must be the same charge as the analytes of interest and migrate slower as not to interfere with the stacking of analytes during injection or their separation during electrophoresis.7 Figure 7 shows the trace level determination of anions and cations. For anion analysis 50pM octanesulphonic acid is added to the sample as the terminating ion. For cation analysis 50pM tetrabutylammonium hydroxide (TBAOH) was added as a terminating ion. The cations are in the range of 10-20 pg/L except for lithium whch is present at 2.5 pg/L and we are still not at the detection limits* Bufler: PMNHMOH Eleclromigralion. 5000 V, 45 S Injection: Terminating Ion: Oclanesullonale (50 PM) ,7 Peaks: 1. Bromide 5 pg/L 2. Chloride 5 3. Sullate 5 4.Nitrite 5 5. Nitrale 5 6 . Fluoride 5 7. Formale 5

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Figure 7 (A) Trace anions in high purity water with electrostacking. (23), Trace cation analysis with electrostacking.

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Ion Chromatographyand Electrophoresis 4.1 Effect of Operating Buffer pH on efliciency

To observe the effect of operating buffer pH on efficiency we can compare the electropherograms obtained with the copper electrolyte at pH 3 and pH 4.8 Figure 8. In both cases the standard contained 50pM TBAOH as the terminating ion and identical electromigration conditions were used, 5000V for 45 seconds. Because of the increased EOF at pH 4.8 strontium and lithium are no longer baseline resolved. Better efficiencies are observed for the later eluting peaks at the lower pH and baseline resolution of strontium and lithium is maintained. It is important when attempting trace analysis to optimise the operating buffer pH such that the best efllicicncies are achieved for the d y t e s of interest? 5

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Figure 8 Eflect of operating buffer pH on eflciency. 4.2 Effect of Water ProInjection on Efliciency

Another way to improve efficiencyis to hydrodynamically inject water prior to the electromigration injection Figure 9. In both electropherograms, the concatration of the analytes is at or near the detection limits. For electropherogmm A, electrostackhg with a SOOOV electromigration injection for 90 seconds was used. In B a gravity injection employing a 100 mm height for 20 seconds was used to first inject a plug of water, then the electrostackinginjection was done using the same conditions as in A. Improved efficiencies for calcium through to barium are observed in B. The improved efficiencies results &om the larger low ionic strength sample mne. That results in a higher field strength permitting more stacking. No apparent improvement in ammonium, potassium and sodium is observed because these d y t e s are present at or below their detection limits.

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Buffer: Cu IonPhor Electrolyte Injection: A) Elecfromigrafion,5000 V, 90 s 8)Wafer Pre-injection,gravity, 100 mm, 20 s Elecfromigration,5000 V, 90 s Peaks: 1.Ammonium 5 pg/L 2. Potassium 5 3. Sodium 5 4. Calcium 5 5. Magnesium 5 6. Strontium 5 7. Lithium 1 8. Barium 7.5

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Figure 9 EfJecr of waterpre-injectionon eflciency 5 SUPPRESSED CONDUCTIVITY DETECTION FOR

CAPILLARY ELECTROPHORESIS Since most of the low molecular weight ions that can be separated by CE are generally W inactive, indirect W methods have been developed for the detection of these small ions as discussed. However a more appropriate detection mode for these ions would be conductivity. Direct conductivity suffers fiom high backgrounds and lower sensitivities and offers no great advantage over indirect W detection. The development of suppressed conductivity detection for CE would overcome the limitations of direct conductivity. Chemical suppression for CE is completely analagous to suppression for Ion Chromatography. An ion exchange membrane is used to exchange buffer cations for hydronium ions. This results in a greatly reduced background signal through neutralisation of the buffer, as well as an increase in analyte response because the anion is detected with the hydronium counter ion which is more conductive. Overall, a 25 to lOOx improvement in detection limits are achiveable compared to indirect U V . There are some significant challenges in adapting suppressed conductivity detection to CE. First, one must design a capillary scale conductivity cell. Second, an appropriate suppressor ion exchange membrane must be designed, both in terms of the appropriate ion exchange transport rate to facilitiate the suppressionreaction and the physical dimensions must be compatiblewith the capillary scale of CE. Finally, the suppressor must be coupled to the capillary so a reliable joint must be designed that couples a polymeric ion exchange membrane to a rigid silica capillary. An example of the performance scan of such a system developed by Avdalovic10 et al is shown in Figure 10. The separation is performed in 2.0 mM sodium tetraborate at pH 9.2. Under these conditions, the anions are migrating in the opposite direction of the EOF. The EOF at this pH and ionic strength is sufficiently fast to pull all of the anions past the detector in less than 15 minutes. Although running the separation with the migration of anions opposite to the EOF slightly increases the run time, it is

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counteracted by the greatly increased resolution of the analytes. Also note that the ion concentraiions are in the low ppm to mid ppb range and there is essentially no noise noticeable on the baseline indicating detection limits in the low ppb range without any preconcentration.

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Capillary: Fused silica, 75 pm i.d. x 60 cm Electrolyte: 2' mM Sodium tetraborate '24 kV (detector negative) Voltage: Injection: Gravity, 3 mm, 3 s Regenerant: 10 mN Sulfuric acid Detection: Suppressedconductivity Peaks: 1. Chlorite 0.4 mglL 0.1 2. Fluoride 3, Phosphate 0.6 0.5 4. Chlorate 5. Perchlorate 0.6 6. Nitrate 0.4 0.3 7. Nitrite 8. Sulfate 0.6 9. Chloride 0.2 10. Bromide 0.5 0.7 11. Chromate

Figure 10 Sepmation of inorganic anions using CE with suppressed cormbctivity. 6 CONCLUSION

Variation of the electrolyte system parameters can provide flexibility in optimising the separation and detection of inorganic ions. Ions can be separated by CE with high eflliciency and resolution by matching the electrophoretic mobility of the carrier ion to the analytes of interest. Thus leading to sharp symmetrical peaks and improved detection limits. pH changes can change migration times of weak acid analytes by modifing the charge on the analytes and pH can be used to modify the electrophoretic mobility of the carrier ion if carrier ion is a weak acid or base. The addition of solvent to the electrolyte was found to be u&id for the resolution of some co-migratingpeaks. Electrostacking can be used to achieve low p g L detection limits. Optirnisationof the electrolyte pH gives better eflliciencies and enhancementof the stackingprocess can be obtained by pre-injecting water to create a larger high field zone. Further improvement in detection of ions was shown by the use of suppressed conductivitydetection for CE. Low pg/L detection can easily be achieved without any electrostacking.

References. 1

F.E.P Mikkers, F.M. Everats, Th. P.E.M.Verheggen,JChrom, 1979,169, 1

2

S. Hjerten, Chromatog. Rev. 1%7,9,122

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3

M.P. Harrold. M. Jo Wojtusik, J. Riviello, P. Henson, JChrom, 1993, 640, 463

4

Dionex Application Note 68, 1992

5.

Dionex Application Note 84, 1993

6.

Dionex Application Note 9 1, 1994

7.

Dionex Technical Note 34, 1994

8.

Dionex Technical Note 35,1994

9.

M. Jo Wojtus&, M.P.Harrold, JChrom, 1994,671,411

10.

N.Avdalovic, C.Pohl, R.RocWin, J.Stillian, Anal. Chem, 1993,65, 1470

DECONTAMINATION OF ARSENIC-CONTAINING AQUEOUS SOLUTIONS USING INORGANIC SORBENTS. INVESTIGATION OF THE ARSENIC SPECIES IN SOLUTION BY MEANS OF CAPILLARY ELECTROPHORESIS

J. M. Galer. R. Delmas and C. Loos-Neskovic Laboratoire Pierre Siie Centre d'Uudes de Saclay 91191 Gif-sur-Yvette France

ABSTRACT Direct removal of both As(II1) and As(V) from strongly acidic industrial liquid wastes is possible using several oxides. We have studied hydrated antimony pentoxide (HAP) and manganese dioxide (MDO) in detail. The kinetics and capacity of the As sorption were determined radiochemically, the exchange balance of the elements in solution by ICPIAES and quantitative analysis of the As species in the solutions using capillary zone Sb or Mn release was low and not related to the As sorption, electrophoresis except for As(II1) on MDO. Manganese dioxide rapidly oxidised As(II1) to As(V) and Mn(I1) was simultaneously released into solution. HAP had the highest capacity and selectivity for As(II1). A single layer of As oxycomplexes could be formed on the surface of both solids.

(a).

1 INTRODUCTlON

Arsenic is used as a dopant in electronics industry and needs to be eliminated from the acidic liquid wastes. Since the toxicity of arsenic greatly increases when it is nduced from the +5 to the +3 oxidation state, it is necessary to analyse both the concentration and the nature of the arsenic species in solution. Currently known methods for As extraction present several problems: prior neutralisation of the liquid wastes 1; hindrance by competing ions such that specialised products are required 2-4; several processing stages are necessary 5. Natural and synthetic Al-, Fe- or Mn-rich minerals exhibit an affinity for As 6-8. However, the oxides of iron and aluminium are soluble in acidic solution. Arsenic sorption studies on MDO have generally been limited to the oxidative extraction of arsenite from neutral aqueous solutions 7-8.However, this sorbent has also been shown to sorb arsenate from more acidic solutions and to be similar to natural minerals 6. As(II1) forms oxycations in very acidic media and neutral oxycomplexes in the pH range 1-8. As(V) oxycomplexes are slightly negatively charged in this pH range 9. Metal oxides can be characterised by an isoelectric point, pH&, at which the net charge on the surface is zero 10. For the sorption of As(V) oxyanions, it may be advisable to work at a pH below the pH& of the oxide, such that the surface of the sorbent is positively charged and offers the possibility of ion exchange of the hydroxyl groups. The p H b for MDO is within the range 1.5 - 5, depending upon the structure of the oxide 10. Although HAP has

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a very low pH&, it has been shown to sorb As in acidic media 11. The main advantage of synthetic HAP is its granular form which alIows its use in columns even in concentrated acidic media. The aim of this study was to investigate the sorption of As species on MDO and HAP, with emphasis on following the oxidation state of the As species. Oxidation of As(1II) by MDO has previously been reported by Oscarson et af. 7 3 at neutral pH, but the kinetics of the reaction have not been investigated. We used several methods such as radiochemistry, inductively coupled plasmdatomic emission spectroscopy (ICP/AES) and CZE. The separation of arsenic species in water by CZE has been previously studied 9,12J3, but quantitative analysis of As( 111) was scarcely reproducible. Since real industrial liquid wastes have high salt contents, we have adopted a new protocol to analyse As(II1) and As(V) in acidic solutions containing NaCl.

2 EXPERIMENTAL

2.1 Materials The sorbents used were hydrated antimony pentoxide, HAP (Car10 Erba) and manganese dioxide, MDO (SociBtB des Techniques en Milieu Ionisant). They were analysed by neutron activation analysis and their compositions found to be 67.5 % Sb, < 0.2 % alkaline metals and 65 % Mn, < 0.05 % Na, respectively. The specific surfaces of HAP, MDO, As-modified HAP and MDO were determined by the BET (Brunauer, Emmett, Teller) method and the surface arsenic coverages were subsequently calculated. HAP and MDO had specific surfaces (BET) of 27 m2/g and 79 m2/g, respectively. Radioactive isotopes, 76As(III) and 76As(V) (half-life : 26.3 h), were prepared by neutron activation of As203 (Fluka) or AsHNa?O4.7H20 (Fluka). The radioactive compounds were dissolved in 1 M NaOH and deionised water, respectively.

22 Fixation of Arsenic The kinetic and capacity studies were performed by batch experiments 14 in 0.01 M HCI and 0.15 M NaCI. The sorption of arsenic was determined radiochemically for short agitation times and by (ICP/AES, Atomscan 25 Thermo Jarrell Ash Spectrometer) for long agitation times. The effects of Na, pH dependence (pH adjusted by addition of NaOH or HCI) and anion competition on the fixation of As(II1) and As(V) on HAP and MDO were investigated by determining the distribution coefficients, Kd, after 24 h agitation in aqueous solutions containing different concentrations of sodium chloride, nitrate, sulphate and orthophosphate anions (0.01 - 3 M acids). The Kd is defined as the ratio of sorbed element per g of solid to the quantity of the same element per cm3 of the solution. The mass balance of the arsenic sorption was studied by measuring the concentrations of antimony and manganese by ICP/AES, as well as any variation in pH in the filtrates, after the decay of the radioisotope.

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2.3 Determination of Arsenic Species The species present in the aqueous solutions before and after the sorption were studied by capillary zone electrophoresis (CZE).A Beckman PfACE System 5510 CE apparatus equiped with a UV diode array detector and a 3/57cm x 75 mm i.d. fused silica capillary was employed. Linear calibration curves for As(II1) and As(V) were obtained using phosphate buffer solutions containing known concentrations of both

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As(II1) and As(V). Arsenic was detected at 195 nm (bandwidth 10 nm) with substraction of a reference signal at 210 nm (bandwidth 10 nm). The capillary was carefully rinsed between runs with 0.1 M NaOH and buffer solution (10 mins each). The capillary was washed with 1 M HCI, 0.1 M NaOH, water, methanol, dried and left clean and dry over night. 3 RESULTS AND DISCUSSION

3.1 Choice of Experimental Conditions for CZE Experiments Lopez-Sanchez et al. 13 have separated arsenic species in water by CZE, using a 25 mM sodium phosphate buffer with a pH between 5.6 and 6.8.Quantitative analysis of As(II1) was scarcely reproducible because the As(II1) peak was preceeded by-a negative peak, which leads to integration errors. This peak may be due to a lower Na concentration in the samples than in the buffer solution. We chose a working buffer pH of 8, because As(II1) is a neutral species at pH 7 9 and is subject to sodium interference. A higher working buffer pH would further separate the Na and As(II1) peaks, but precipitation of dissolved MDO is undesirable. 0.01 M acidic solutions which contained arsenic concentrations of 5 - 70 pg/mL were analysed. The calibration curves for As(II1) and As(V) deviated from linearity at As concentrations of 5 pg/rnL. We took 150 pg As to be the limit of detection of the system with an injection of 30 nl of solution. Between 5 and 40 pg/rnL As, the standard deviation (sd) of the measured As(V) concentration was 3 %. The reproducibility (sd) was 3.6 % for As(II1) at 50 pg/mL, but only 28 % at 5 pg/mL As(II1) owing to the interference of Na at these low As(II1) concentrations. 3.2 Sodium Influence, pH Dependence and Anion Competition

Extraction of As(II1) and As(V) by HAP and MDO at pH 2 was found to be hardly affected by altering the quantity of sodium in the experimental solutions from zero to 0.2 M NaCI. The pH dependence of As sorption on MDO is shown in Figure 1. In acidic media, As(1II) and As(V) were readily extracted (Kd > 20000 and > 2500, respectively). In alkaline media, there was a decrease in As retention with increasing pH. The Mn release appears to be related to the pH of the solution rather than the sorption of As. Anionic exchange with hydroxyl groups is not suspected since the pH tended to remain approximately constant during the fixation of arsenic. The similar pH dependencies of As(II1) and As(V) possibly result from the oxidation of As(II1) to As(V) by MDO. The corresponding plot for HAP shows a similar trend of decrease in As rekntion with increasing pH. The final pH was slightly lower for HAP than for MDO owing to the inherent acidity of HAP. Maximum extraction occurred at pH < 3 and there was a preference for As(II1) over As(V) in alkaline conditions. HAP has a greater affmity for the neutral As(II1) than for the negatively charged As(V). The release of antimony into solution is < 1 % over most of the pH range and is not related to the sorption of arsenic on HAP. The release of Sb in strongly acidic media may be due to partial dissolution and the formation of colloidal particles during surface modification of the solid.

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190 1,00E-02

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Fiare 1 : Atomic ratios of As(ll1) or As( V )fixed on MDO and Mn found in the solution per Mn atom initiallv present in the solid against pH. Experimental conditions :MDO : 100 mg ;volume of solution :28 mL ;As introduced :0.15 mg ;agitation time :24 h.

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Figure 2 : QuantiQ of As(f1f)and As( V )sorbed on HAP and Sb found in the solution per Sb atom initiallv present in the solid against agitation time in 0.01 M HCl solution . Experimental conditions :HAP :100 mg ;volume of solution :28 mL ;As introduced : 2 mg ;Nu (asNaCl) :100 mg.

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2'00E-02 1,60E-02

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F'igure 3 :Quantity of As(ZZZ) and As( VJsorbed on MDO and Mnjbund in the solution p n Mn atom initially present in the solid against agitation time in 0.01 M HCI solution. Erperimental conditions :MDO :100 mg ;volume of solution :28 mL ;As introduced : 2 mg ;Na (asNaCl) :I00 mg. The presence of C1- and N03- had little influence on As soxption. Increasing the concentration of SO$- or €043- greatly reduced As(V) sorption on both HAP and MDO and As(II1) extraction by MDO, which may be due to the oxidation of As(II1) to As(V). Competition between arsenate and sulphate has been reported 15. Strong competition between arsenate and phosphate may be explained by similarity between H2As04- and H2P04-16.

a. in mg/g dry sorbent b. RC :radiochemistry ;NAA : neutron activation analysis ;ICP : ICPIAES c. HAP agitated one day in 0.01 N HCl prior to addition of the As. d. in days (d) or weeks (w) e. Average distance between oxyarsenic species

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192 10

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Figure 4 : Electrophoregrarn of arsenite and arsenate ions. Phosphate buffer :pH 8. Electrolyte :25 rnM.L-' ;V = 30 kV ;T= 25 "C ;UV detection at 195 nm.

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Figure 5 : Rate of oxidation ($As ([It) to As(V) bv MDO .

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3.3 Capacity and Kinetics of Sorption The quantity of As sorbed as a function of time is given in Figure 2 for HAP and Figure 3 for MDO.The radiochemical and ICP results are in good agreement. Table 1 summarises the capacities of HAP and MDO for As(II1) and As(V), together with the results of calculations performed on the BET specific surface areas of the sorbents. The oxyarsenic species on sorbent were estimated to occupy 21 Az, assuming a square-planar geometry. As(II1) is rapidly extracted during the first hours of agitation with HAP and is then sorbed more slowly, Apparent equilibrium was reached in less than 2 weeks for As(V) at lower As retention. Much more As is extracted than Sb released (10-5 m o l ) . When HAP was agitated one day in 0.01 M HCI prior to addition of the As, an increase in the capacity was observed. No similar increase was obtained with the finely divided MDO. A change in surface area of the aggregated HAP particles is postulated probably owing to the formation of smaller particles 14. MDO extracts As(II1) faster than HAP (quasi-equilibrium approached after 5 h), but does not have such a high capacity. The extraction of As(V) by MDO is similar to that of As(III), but equilibrium is reached slower, within 2 days. The amount of arsenic fixed in the As(V) experiment is about 10 times that of manganese released into solution (5 x 10-5 moUL). Although the same quantity of arsenic is fixed in the A@) experiment, more manganese is released into solution. Both the HAP and MDO products investigated in the present study have capacities in acidic media which are at least as high as those (8 mg/g) reported for As@) on amberlite anionic resin at pH 8 2. For initial concentrations of arsenic similar to those employed in the present experiments, but at neutral pH, aluminium hydroxide is reported to extract 12 mg/g of As(II1) in 8 h and a manganese dioxide 12 mg/g of arsenic in 30 minutes 8. However, iron hydroxide has a higher affinity for As(1II) of 60 mg/g after 9 h 8. It is unfortunate that this product is not suitable for use in acidic media. 3.4 Oxidation of As(III) to As(V) by MDO

An example of an analytical electrophoregram of As species is shown in Figure 4. The more negatively charged As(V) species are retained longer in the capillary and are detected later than the more neutral A@) species. CZE experiments showed that agitation of HAP for 2-3days in 0.01 M HN@ or HCI solutions containing either As(1II) or A$V) resulted in no change in oxidation state of the arsenic, although A@) could be oxidised slowly in acidic media. CZE experiments showed that As(II1) was oxidised to As(V) when agitated with MDO. The rate of oxidation of As(II1) by MDO is shown in Figure 5. The As(II1) concentration decreases rapidly with increasing time of contact and is below the detection limit (150 pg) after 10 minutes. The decrease in As@) was accompanied by an increase of As(V), indicating that the AdIII) is oxidised to As(V). The total As in solution was not constant owing to fixation of As(V) on MDO. The time dependence of the Mn(I1) released during the agitation of As(II1) with MDO indicated that the Mn(I1) release occurred more slowly (Figure 3) than the oxidation of As(II1) (Figure 5). The extraction of As(II1) by MDO is believed to involve sorption of arsenite onto MDO, oxidation of arsenite to arsenate by oxygen transfer, release of Mn(I1) 7.8.The oxidation is believed to occur in the presence of the strongly electric potential at the MDO/solution interface 17. The oxidation capacity of MDO towards As(1II) is likely to be related to the number of accessible Mn surface sites. Reduction of the surface Mn creates a potential barrier, thus preventing the reduction of bulk or structural Mn 7. The sorption is believed to be rate limited by the presence of sorbed As(V) and by Mn(I1) diffusion. This may infer faster kinetics for the

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direct extraction of As(V), as less Mn(I1) is released. The sorption of As after a 10 min contact time is expected to be similar whether As(II1) or As(V) is introduced, since the As(II1) in solution would be oxidised to As(V). This is not the case. The increased sorption when A s W ) is initially contacted with the MDO is believed to be a result of surface redox catalysis 18.

3.5 Reversibility of the Sorption After rinsing As-loaded products in 0.01 M HCI, the As release during a one day agitation in solutions of pH 5 8 or 10 was < 10 % from MDO and < 5 % from HAP. If the sorption were entirely electrostatic, it would be expected to be more reversible. Since basic solutions were employed in the reversibility experiments, it is very unlikely that the sorption is due to ion exchange with hydroxyl groups. 3.6 Possible Sorption Mechanisms

It has been shown that the fixation of arsenic on HAP and MDO is not an exchange with hydroxyl groups, antimony or manganese. Arsenic sorption on oxides seems to be mainly a surface phenomenon. A molecular sorption mechanism for the extraction of As(V) on titanium dioxide which involves no pH change, but the loss of water, has been suggested 19. This mechanism may be considered for arsenious acid (H3AsO3) which remains undissociated up to pH 7,or below pH 2 - 3 where there is an appreciable proportion of undissociated arsenic acid (H3AsO4.). In the pH range 2 - 7,H2AsO4- is the predominant species and an alternative mechanism must be considered. A mechanism involving no pH change has also been proposed for the sorption of mono-anions 20. However, this requires the presence of a positively charged surface site to facilitate loss of water by ligand exchange. Since only a small proportion of the avaiIable sites are charged, this prerequisite is less likely to be fulfilled at pHs above or approaching the PHiso. The sorption of ions on a surface of the same charge is possible if there is sufficient energy to overcome the electrostatic repulsion, but renders subsequent sorption more difficult 21. Precipitation at the surface or in the cavities of the solid could be possible with As(V) which easily forms insoluble salts. X-ray powder diffraction studies showed no change in the diffraction peaks of HAP after As sorption. No significant increase in background noise, indicative of an amorphous phase, was observed. No crystalline phase other than HAP was detected. It is possible that the sorption of As was too low to enable detection of the As-containing phase by XRD. 4 CONCLUSION

We have shown that CZE can be used for the determination of As species in aqueous solution down to concentrations as low as 5 pglmL, even in the presence of sodium. The quantitative detection of As(V) is less difficult than that of As(II1) under these conditions. CZE experiments have shown that MDO is able to oxidise As(II1) to As(V) within a few minutes of contact. The sorption of arsenic by MDO is much faster than that by HAP. Maximum extraction of both As(II1) and As(V) by HAP occurs at pH 0 - 3, pH-2 appears to be best for the extraction by MDO. Sulphate and phosphate interfer with the fixation of As(V). HAP is selective towards As(III), but fixes similar quantities of As(V) to MDO.

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195

The sorption of arsenic on HAP and MDO is not an exchange with antimony or manganese and is unlikely to be an exchange with hydroxyl groups as it is not reversible in alkaline media. The release of Sb or Mn is limited and related to the pH of the solution rather than to the sorption of As, except in the case of As(II1) on MDO where redox catalysed sorption of As(V) is believed to occur resulting in the release of more Mn(I1). Calculations indicate that almost a monolayer of arsenic species is present in As(II1)modified HAP. The sorption of As(II1) seems to be surface limited. The precipitation of an insoluble mixed oxide could be possible. Further studies are in progress.

5 ACKNOWLEDGEMENTS We would like to thank the following people for their assistance in this research: J.C. Rouchaud (use of ICPIAES equipment), J. Jeanjean and M. Fedoroff (XRDstudies) of the Centre d'audes de Chimie Metallurgique, Vitry-sur-Seine; D. Jones of the Universid de Montpellier and B. Rasner from the DTA-CEREM-DTM-SERC Service of the Centre d'Etudes de Saclay (BET measurements). We would also like to thank the BRITE-EURAM I1 program for funding.

6 REFERENCES

.(

a

1. T.R. Harper and N.W. Kingham, 1992, 200. L.Jubinka, V. Rajakovic and M.M. Mitmvic, .(1992,z 279. 3. M. Chanda, K.F. ODriscoll and G.L Rempel, 1W,Z251. 4. A. Ramanu and A.K. Sengupta, Ukig&&g . ,1992,1l&755. 5. R.P. Poncha, U.S.Patent US 5 137640,llAug. 1992. : 257523~. 6. T. Takamatsu, M. Kawashima and M. Koyama. Wat..,1985, 1029. 7. D.W. Oscarson, P.M. Huang, C. Defosse and A. Herbillon, .1981.m . 50. 8. D.W. Oscarson, P.M. Huang U.T.Hammer and W.K. Liaw, 1983,24,233. 9. P.Morin, M.B. Amran, S. Favier, R. Heimburger and M. Leroy, &&J&L&& I992,3&z 357. 10. J.W.Mumy ,1974,a357. 11. F. Girardi, R.Pietra and E. Sabbioni, J.Radioanal.chem., 1970,z141. 12. M. Albert, C. Demesmay, M. Porthault and J.L.Rocca, A&&, 1992, 24,383. 13. J.F. Lopez-Sanchez, M.B. Amran, M.D. Lakkis, F. Lagarde, G. Rauret and MJ.F. Leroy, , 1994, 810. 14. S.Zouad, J. Jeanjean, C. Loos-Neskovic, M. Fedoroff, 1992,s1. 15. F.F. Peng and P. D i m . , 1994, 922. 16. B.F. Shchegolev and A.N. Lazarez, * ,1992,&184. 17. J. Murray and J.G. Dillard, ,1979,gL781. 18. A. Manceau, L. Charlet, M.C. Boisset, B. Didier and L. Spadini, 1992,2201. 19. S.A. Onorin. M.B. Khodyashev, T.A. Denisova, V.V. Vol'khin and N.D. Zakharov, 1992, 612. * ,1992, 20. M.M. Bhutani, A.K. Mitra and R. Kumari. 75. ,1973, 21. J.W. Bowden, M.D.A. Boliand, A.M. Posner and J.P. Quirk, 2.

a w.,

m,

m.,

.

a

w.,

a,

v., a 242 81.

-.

Part 3 Resins as Biosorbents

Applications of Non-Functional Macroreticular Resins

C Robinson Glaxo Wellcome Operations Limited North Lonsdale Road Uhrerston Cumbria LA12 9DR

1 INTRODUCTION

A wide variety of organic molecules are adsorbed on non-functional macro-reticular resins which are based on styrene-divinylbenzene@VB) copolymers. These adsorbents have a high degree of physical and chemical stability which allows regeneration and reuse over a large number of cycles. Although such resins are used in extraction from fermentation broth, decolourisation and scavenging organic molecules from waste streams, their use can be demonstrated in recovery, separation and purification from chemical reaction mixtures. Choice of a suitable resin with appropriate conditions for adsorption and elution can achieve significant chromatographic separation. Conditions and separations which apply in the laboratory are capable of direct scale-up by factors of up to 50,000. Using this technique, industrial scale chromatographic separation and purification of a wide range of organic species may be achieved, using solid adsorbents in simple column operations.

1.1 Non-functional Macroreticular Resins

This group of resins refers to polymers derived from styrene cross-linked with divinylbenzene (eg XAD-2, XAD-4, XAD-1180, XAD-16, HP-20,HP-21), or those based on acrylic esters (eg XAD-7, XAD-8). The former are relatively non-polar (aromatic) resins whilst the latter are of intermediate polarity (aliphatic). Polar resins are of course represented by the incorporation of ionic functional groups onto the resin matrix which results in an ion exchange resin. This matrix is a rigid structure and each resin bead consists of a collection of microspheres such that the structure gives the appearance of a sponge. The resin is thus described as being macroporous or macroreticular.

200

2

Progress in Ion Exchange: Advances and Applications

PHYSICAL PROPERTIES OF STYRENE-DVB RESINS

Physical characteristics have a significant effect on the performance of the resin. These properties include: surface area, pore size and shape, and pore size distribution. They are dependent on the degree of cross-linking and specific polymerisation conditions, eg type of initiator, temperature, etc, and are therefore controlled by the manufacturing process. The degree of swelling of the resin bead in solvent is also important in design of columns to cater for the hydraulic properties of the resin. On a laboratory scale it should be noted that the lateral pressure exerted on glass columns during resin swelling may be sufficient to lock the resin bed and cause the column to shatter. Swelling during solvent treatment will obviously change pore size compared to the hydrated form (which may be as much as 20 - 30%).

3 MECHANISM OF ADSORPTION AND ELUTION

3.1 Resin Factors A variety of chemical and physical factors affect the performance of the resin in any particular application. Absorption is based on surface binding by van der Waals forces, where hydrophobic bonding, dipole-dipole interaction and hydrogen bonding are important2. The internal porous structure of the resin beads comprises both macropores and micropores. The function of the macropores is transfer of the solute through the absorbant primarily for adsorption or desorption purposes. The micropores may be envisaged as capillaries which involve the major area of surface sites available for adsorption. In general, fine control of the distribution of pores during manufacture is not strictly possible. From a resin point of view, a degree of adsorption selectivity may be obtained by attempting to optimise pore size and distribution, pore shape and active surface polarity, during manufacture. There will be an inverse relationship between pore size and surface area. The need to consider these points when choosing the appropriate resin is illustrated by the following observation. For a small molecule such as phenol, XAD-4 (SA 760 m2 g-’) has a greater capacity than XAD-2 (SA 350 m2 g”) whereas for a larger molecule, such as an alkylbenzene sulfonate, XAD-2 has a higher capacity than XAD-4’. Several factors arising from the polymerisation process may affect surface polarity. These include type of monomer, cross-linker, phase extender, initiator, etc. A range of mathematical expressions and equations have been derived which describe the mechanism of adso tion and the effect of the physical characteristics of the resin but are not discussed here3 f g. 3.2 Solution Factors Adsorption. For ideal extraction and subsequent chromatographic separation the polarity of the required compound should be closely matched to that of the resin surface,

Resins as Biosorbents

20 1

with all other physical parameters optimised. Practically, information regarding comparative polarity may be obtained from adsorption isotherms. However, the polarity of the required compound may be significantly affected by pH. For example, at pH 2.5 cephalosporin C5p6 is significantly less ionised than at pH 5, thus increasing its "hydrophobic" nature at lower pH. Since the resin contains both macropores and micropores which exist over a range of sizes, different components of a mixture may absorb at different parts of the resin, ie different binding sites. A degree of molecular exclusion must exist due to the structure of the resin. Thus large molecules in the macropores are likely to be less tightly bound and may be removed by washing. For complex mixtures, such as fermentation broth, where there may be a number of compounds present with similar properties, competition for binding sites will occur. Here the concentration of the required product is important together with the extent to which the resin is loaded. For example, loading cephalosporin C to -1180 at ca20g/L results in the less strongly bound deacetyl cephalosporin C and other impurities being expelled from the resin column by direct competition. At the two ends of the adsorption spectrum, inorganic salts pass through the resin without adsorption, whereas fermentation oils and antifoam agents have a high affinity for the resin and are retained, even under normal elution conditions. In practice, column operations are carried out at less than equilibrium loadings. The solvent used for adsorption must of course be one in which the material to be adsorbed is soluble. Water would generally be the solvent of choice but many other combinationsare possible and this may affect the choice of resin. Basic compounds are best adsorbed from basic solvents and acids from acidic media, ie ionic material is more strongly bound in the non-ionised form. Rate of loading of the resin is also important. This is usually referred to as the number of Bed Volumes per hour (BVhour), where 1 BV refers to the volume of resin used. The time to reach an equilibrium during adsorption varies with the different resins, such that if the resin is loaded at too high a rate, leakage of the required component from the resin will occur. Temperature has relatively little effect on the equilibrium, but generally adsorption under cool conditions with warm elution is preferred to achieve optimum conditions for improved chromatographic separation and increased concentration of eluate. Although it is not possible to describe the micro-environment at the surface of the resin, the affinity of the resin for molecules is not simple hydrophobic binding. Hydrogen bonding may have a significant effect on the selectivity in binding of like molecules. 3.3 Elution Whilst a degree of selectivity can be achieved by choice of resin and selection of adsorption conditions, the degree of chromatographic separation may be W e r enhanced by choice of eluant and rate of elution. In general, adsorption takes place from a predominantly aqueous solution. Conversely elution may be effected using a mixture of solvent and water with 10% 40% v/v of the solvent.

202

Progress in Ion Exchange: Advances and Applications

Organic solvents which are not miscible with water may also be used. Variation in solvation affecting the nature of the bonding at the surface of the resin may also occur. Acids, bases or buffer solutions which affect the polarity of the sorbate are useful eluants. Compounds which require a low pH for optimal adsorption may be effectively eluted at higher pH. Inorganic salts of higher molecular weight organic acids or bases (eg surfactants) may be used for elution of the desired product by ion-pair interactions. For weaker binding affinities, perhaps where hydrogen bonding is important, water may be used as an effective eluant. Steam may also be used in this context where volatile components are involved. When a number of similar compounds are adsorbed to the resin, significant improvements in chromatographic separation have been achieved by gradient elution'. An important requirement in assessing the above factors when choosing the preferred operating conditions is analysis of the various streams arising from resin column operations. HPLC analysis of profiles is useful for successful monitoring of these operations. Optical activity, conductivity and refractive index measurements have also been useful in this context. 3.4

Regeneration

New resin may require conditioning before use, and in most cases this can be conveniently achieved using a regeneration cycle'. When adsorption occurs fiom complex mixtures, such as fermentation broth, it is inevitable (and to some extent desirable) that a number of strongly bound impurities will remain adsorbed to the resin at the end of elution. Such impurities must be removed before reuse. The nature and the composition of the regenerant will depend on the impurity, its solubility and affinity for the resin. In general, the resins have a high degree of chemical stability and it is important to maximise regeneration and achieve an extended lifetime for the resin. Efficient regenerants include alkaline or acidic aqueous solutions of acetone, methanol or isopropanol. The treatment may be carried out at ambient temperature or up to ca 80 O C with isopropanol. These regenerants may be used in combination with a neat solvent treatment and water wash. Such treatments may be advantageously carried out each cycle. For the more intractable foulant, the occasional use of an oxidising agent may be necessary. An aqueous solution of sodium hypochlorite may be suitable for this duty. In practice, regular capacity checks are required to ensure that progressive fouling of the resin is not occurring due to incomplete regeneration. Regular treatment to maintain a high capacity of the resin is preferable to occasional treatments in an attempt to obtain a significant improvement. It is difficult to measure accurately the effect on resin capacity since in the majority of cases any reduction is within the experimental error of individual results, and therefore trend analysis should be used.

Resins as Biosorbents

203

3.5 Resin Fouling In general, the assumption is made that reductions in resin capacity is due to fouling, particularly when used for extraction from fermentation broth. We have used many different techniquesto discover the nature of foulants which cause irreversible reduction of capacity. However, no significant levels of organic or inorganic material have been detected in resin beads or change in porosity which would explain reductions of up to 60% resin capacity over many cycles of use.

4

APPLICATIONS OF NON-FUNCTIONAL MACRORETICULAR RESINS

Macroporous styrene-DVB resins have been used in purification and isolation of a wide variety of organic compounds from complex natural, fermentation or chemical reaction media. In many cases the resins have been used in conjunction with other separation techniques, but occasionally are used as the specific means of purification. There are many examples which illustrate the range of chemical structures which may be adsorbed, washed and eluted from macroporous styrene-DVB resins, thus allowing a possible means of purification and isolation. The importance of this technique may be judged by the fact that many of the subsequent references are obtained from patent literature rather than published papers. The following rough classification of organic compounds has been attempted to demonstrate the versatility of the resins as absorbents used in separation and purification.

4.1 Polycyclic Sulphonic Acids, Alkanolamines, Carboxylic Acids, etc Scroggins and Miller describe the separation of a variety of mono and disulphonic acids using XAD-Z9. Separation of terephthalate and benzoate is also reported", together with phenols, aromatic amines, carboxylic acids'' and a number of all
P-Lactam Antibiotics

Penicillins. Separation of semi-synthetic penicillins from precursors have been rep~rted'~. In particular, the purification of a sulphobenzyl penicillin using XAD-2 has been described. Partial separation of penicillin V and p-hydroxy penicillin V, both as acids and sulphoxides, is also possible. Cephalosporins. There are many references to the use of macroporous styrene-DVB resins for purification of cephalosporin corn pound^^^^^^^'^. One of the fvst usages of XAD-2 in the fermentation extraction area was the separation of cephalosporin C from broth. This particular example has become a reference point for much of the work which has been carried out on the mechanism of adsorption or organic molecules to such polymers. Cephamycins A and B have also been purified and separated in a similar manner on ~ ~ 2 0 ~ ' .

204

Progress in Ion Exchange: Advances and Applications

XAD 1180 and 16 resins are in use at Glaxo Wellcome Operations, Ulverston on processes involving ce halosporins. Separation of oxime isomers is also described for various cephalosporinsf2.23 . Other P-Lactams. Japanese workersz4 describe the separation and isolation of Nocardicins from fermentation broth using HP20 resin. Separation of other P-lactams have also been decribed'8'25,26.

4.3 Vitamins Work carried out at Ulverston has shown that XAD-2, ,XAD1180 and XAD16 are u s e l l for the purification of vitamin B12. References to other work canied out using XAD-2 in the corrinoid field have been A Japanese patent" describes the purification of Vitamins E and K on HP20 as part of work carried out on the isoprene family of compounds: Vitamins K, and K2 were purified after synthesis and a crude suspension of natural vitamin E (a-tocopherol) also purified using HP20 resin. Solanol is also reported to be isolated as a pure compound from a paste obtained from tobacco extract by this technique. A further patent describes the separation of various tocopherol derivatives3'. Zsoprenes. Apart from vitamin K, HP20 has also been used in the purification of a variety of other isoprene derivatives including solanol, carotene, geraniol, linalool, coenzyme Q, etc29,30.One patent29claims that compounds containing a substituent side chain of more than 3 isoprene units are easily separated compared with difficult separations for less than 3 units. It is suggested that cyclic isoprenes will also be difficult to separate, ie Vitamins K, K,, carotene, tocopherols, coenzyme Q and chain alcohols can be separated. 4.4 Aminoglycosides A US patent3, claims processes for extraction of members of the lincomycin family from broth using macroporous styrene-DVB resins. These include isolation of lincomycin, streptomycin, neomycin. Purification and separation of acylkanamycins have also been described using ~~~-232~33

4.5 Condensed Ring Systems and Macrolides Separation and purification of multi-component basic macrolide antibiotics using HP20 resin has been Fermentations often contain many similar derivatives of the same base compound, eg Leucomycins. Examples include Leucomycins, spiramycins, marbomycin, pikromycin, cirramycin, oleandomycin and also vancomycin3.'. 6-N-acylkanamycinhas three free amino groups, which on reaction with amino-a-hydroxybutric acid gives 1-, 3- or 3"-acylkanamycin derivatives. Complete separation of all three resultant isomers is reported after adsorption on HP20 resin, by elution with 5%, 10% and 20% aqueous methanol. The order of elution was 1-,3"- followed by the 3-N-acylated isomer respectively.

Resins as Biosorbents

205

4.6 Aminoacids, Purines and Pyrimidines Although styrene-DVB resins are successful in purification and separation of macrocyclic structures, separation of small organic molecules is also possible. Aminoacids may be separated into two groups using XAD-2. Those possessing longer alkyl chains (eg leucine) or aromatic groups (tyrosine, phenylalanine) as expected bind more strongly to the resin because of increased hydrophobicity and are retarded36. Also reported is the fractionation of nucleic acids with resolution of base-nucleoside pairs. Pyrimidine nucleosides (eg uracil, uridine) may be separated from purines (eg inosine, guanosine, adenosine), with pyrimidines being less readily adsorbed to the resin36. 4.7 Proteins/Enzymes

A Japanese Patent3' describes a method for purifications of a protease enzyme from culture media using HF' resins. Purification of cellulase and amylase enzymes are also described. Croteau et a13*reports the purification of a cyclase enzyme from plant tissues using XAD-4.

4.8 Flavanoids

H ~ r describes i ~ ~ the chromatographic separation and purification of many different flavanoids from crude methanol extracts of plants, using XAD-2 and gradient elution. The elution profile is in the order of: Sugar esters + Glycosides + Aglycones 4.9 Steroids ~ ~ r i 4 0 , 4 has 1 also demonstrated albeit on a small scale, the separation and purification of a number of insect-moulting steroids from plant extracts.

5

MODE OF ACTION

The simple classification by virtue of the structures of molecules exemplified in Section 4 can lead to predictions of compounds which should adsorb to macroporous resins allowing possible purification and separation. However, the action of the resin may also be categorised as follows: a Extraction from fermentation broth and plant tissue. b Purification. c Separationof isomers or closely related compounds. d Desalting. e Decolourisation and scavenging from waste streams. Examination of the data presented in Section 4 by both molecular structure and mode of action of the resin gives a fiuther insight into the mechanism of binding and allows fiuther predictions to be made with respect to future uses of the resin.

206

Progress in Ion Exchange: Advances and Applications

5.1 Extraction from Fermentation Broth and Plant Tissue

Resin extraction is often the method of choice where a dilute aqueous solution of the desired compound. In most cases this describes the problem of extraction from fermentation broth, where the dificulty is compounded by the presence of a large number of impurities including precursor, metabolites, proteins, salts, etc. Selectivity is therefore a critical requirement for any successful extraction process. 5.2

Purification

Examples of purification of p-lactam antibiotics, vitamins E and K, kanamycins and enzymes have been demonstrated. Examination of the different processes involved indicate the versatility of the resins for this type of operation. In the past, removal of impurities from pharmaceutical intermediates has been a severe problem on a large scale. Generally, this has resulted in significant (and often expensive) modifications to the chemical synthesis to prevent formation of certain impurities in the absence of inexpensive large scale chromatographictechniques. 5.3

Separation of Isomers and Closely Related Compounds

Geometrical Isomers. Work carried out at Glaxo Wellcome Operations has led to a simple process for separating syn and anti oxime isomers of cefuroxime using XADl180 resin23. Separation of the two isomers was also achieved for the side chain ammonium salt and a number of other cephalosporin oxime compounds including ceftazidime, the corresponding cyclopropyl methyloxime derivative, cefotaxime and cefiizoxime, etc. This reaction is important from a production point of view, since the anti isomer is pharmacologically inactive and cannot be converted to the syn isomer. Nocardicin A and B (syn and anti oxime isomers) have also been separated by a similar technique in which Nocardicin A was eluted from resin using a salt solution, followed by elution of B using aqueous solvent24. Separation of the pairs of olivanic acid isomers is also reported using HP20. The isomers arise from the cis and trans stereochemistry at the p-lactam ring25. Consideration of these cases suggest that molecular shape andor hydrogen bonding are particularly important with regard to binding affinity with the surface of the resin. In all cases examined the syn isomer is less strongly bound to the resin than the anti isomer. In these examples the polarity of the syn isomer is possibly greater than the anti isomer due to interaction of the oxime group with the p-lactam carbonyl which would be in the same plane. In the case of the side chain acid this interaction would presumably be with the carboxylate group. In a mixture of tocopherols, a-tocopherol (5,7,8-trimethyltocol) has been successfully separated from 5,8-dimethyltocol 7,8-dimethyltocol and 8-methyltocol derivatives. In this case, a-tocopherol is more strongly bound than the other derivatives to the resin. In this particular example, molecular shape is likely to have relatively little effect on binding and the effect of the alkyl side chain remains the same in all cases. It is tempting to suggest that the difference is associated with the effect of the methyl groups on the aromatic ring which may play a major role in hydrophobic binding to the

Resins as Biosorbents

207

surface of the resin. An example of such effects on polarity can be seen from the dipole moments of toluene, o- andp-xylene which are 0.36,0.62 and 0.00 respectively. Closely Related Compounh. Fermentation of macrolide antibiotics often gives rise to multi-component mixtures of closely related structures. Non-functional macroreticular resins appear to be surprisingly successful in separating the components. For example, as shown previously, the hydroxybutyric acid isomers of 6-N-acylkanamycin can be separated and Spiramycin I has also been successfully separated from Spiramycin I1 and Spiramycin 111 using HP20 resin. Selective elution was achieved using dilute sodium acetate buffer containing 7% vlv n-butanol. In a similar manner, eight different Leucomycins are reported to have been separated from a mixture in a single resin column operation. The order of elution was: A9 -# A8 +A7 + A6 + A5 + A4 + A1 + A3 This series is remarkable for two effects. The eight Leucomycins may be arranged by virtue of changes in group -R2.

-COCH3 -COCH2 CH, -COCH2 CH2CH3 -COCH&H(CH3)2

A8,A9 A6, A7 A4, A5 A3, A1

Figure 1 Leucomycin Thus increasing the length of the alkyl side chain at R2 increases the binding strength to the surface of the resin. Furthermore, examination of these pairs of Leucomycins with respect to R, on the main ring reveals that A9, A7, AS, and A1 have a hydroxyl group at R,,whilst A8, A6, A4 and A3 have an acetate group at R,.For each pair the hydroxy compound is eluted from the resin first and therefore is less tightly bound than when an acetate group is present. This analagous to the separation of the spiramycins in with spiramycin I (-hydroxyl) is eluted first, followed by I1 (-acetate) and I11 (propionate). Separation of pikromycin (>C,,-OH) from narbom cin (>C,,-H) shows the same effect which is repeated in various other rna~rolides~'~~. It is difficult to envisage the apparently dramatic effect on resin binding affinity, of comparatively small changes in a large structure unless strong

208

Progress in Ion Exchange: Advances and Applications

internal hydrogen bonding occurs which affects polarity, or the molecules are in someway ordered or structured on the surface of the resin. In perhaps a similar manner, cephalosporin C can be separated from deacetyl cephalosporin C (acetate versus hydroxyl at C-3), whilst separation from the corresponding desacetoxy compound is extremely difficult”. Examination of the work carried out on the range of Flavanoid compounds (4.9) indicates the aglycones with a greater number of hydroxyl groups are eluted preferentially compared to similar compounds with fewer hydroxyl groups. It is also suggested that the position of the hydroxyl group affects the position of the aglycone in the elution series. The relative binding affinity of the glycosides also appears to vary considerably with the position where the sugar moiety is attached. The effect of hydroxyl groups, therefore, appears to be considerable in the context of chromatographic separation, which is perhaps surprising in view of the hydrophobic nature of the adsorbant surface, unless a layer of structured water is associated with the surface of the resin. This series of examples indicates that introduction of hydroxyl groups weakens binding whilst increasing the length of alkyl sidechains strengthens binding.

6 SCALE OF OPERATIONS The parameters used to achieve separation on a laboratory scale are the same as those employed on a plant scale. Adsorption, washing and elution profiles are almost independent of scale provided column operations have been adequately designed. For example, if purification is achieved using 500 ml of resin in the laboratory by adsorbing from 5 BV of solution, washing with 0.75 BV of water and eluting with 2 BV of 15% vlv acetonelwater, then exactly the same profile can be obtained using 15,000 L of resin. A variety of different types of columns are in operation at Glaxo Wellcome Operations, ranging from tall, slim columns with a height to diameter ratio of >2 : 1, to short, squat columns (WD <2 : 1). The basic design requirements have been discussed by Vose?’. Important parameters include the critical design of the distributors to achieve plug flow throughout the column. Resin-bed dimensions of 3 - 4 m diameter and 1 - 2 m height are of the order required to achieve optimum chromatography and minimise the effects of resin swelling. The following scale of operations have been demonstrated for various processes at Glaxo Wellcome Operations using XADll80 and XADl6 resins:

SGik

Amount of sorbate

Laboratory Pilot Plant Plant

2-15g

1 - 10kg 20 - 400 kg

0.1 - 0.5 L 100 L - 600 L 2500 - 16000 L

Chromatographic separation, efficiency of adsorption and elution profiles on a plant scale are generally as predicted from small scale laboratory experiments.

Resins as Biosorbents

209

7 RESIN DEVELOPMENT Future development of resins may be associated with variation in pore size and surface area but mainly with varying the polarity of the polymer surface by attaching non-ionic functional groups to the matrix. Since selective adsorption and elution, which is required for separatiodpurification may depend on matching the polarity of the desired component to the polarity of the polymer surface, attachment of non-functional groups could enhance chromatographic separation. Examination of styrene-DVB polymers containing 421, -Br, and NO2 groups has demonstrated such effects are possible. Attachment of -NO2 to the styrene ring appears to deactivate the polymer surface to the extent that various cephalosporins are no longer adsorbed under normal operating conditions. Bromination of the free vinyl groups at the ends of polymer chains (SP 207, Mitsubishi) results in a macroporous resin containing ca 34% wlw of -Br. Adsorption of cephalosporins to this resin results in a two-fold increase in capacity compared to XAD 1 180 resin. An increased strength of adsorption is demonstrated by a requirement for solvent elution to remove cephalosporin C compared to an aqueous salt solution for XADI180. The chlorinated versions of -1180 show a similar capacity for cephalosporin C adsorption to -1180 but show an increased tendency towards solvent elution to achieve a comparable elution profile.

8 CONCLUSIONS Non-functional macroreticular resins may be used for a wide variety of applications. Because of the high level of physical and chemical stability of such resins, reuse will minimise the operating costs. Efficiency over the resin stage is generally high (ca 90% recovery) and product stability under column operating conditions appears to be extremely high for products examined to date. There are, therefore, many advantages in pursuing further background development work into macroporous resin systems which would allow rapid process development for new products and take full advantage of their versatility.

9 REFERENCES 1 R M Simpson, 3rd Symposium of the Institute of Advanced Sanitation Research, 1972. 2 M Pirotta, Die Angew Makramol Chem 1091110, page 197,1982. 3 K H Weisenberger, Thesis, Cambridge University, 1985. 4 N F Kirby, Thesis, University of Surrey, 1985. 5 Mitsubishi Diaion Technical Data Sheet, HP Series. 6 D Sacco and E Dellacherie, Anal Chem, Vol56, page 1521, 1984. 7 M Hori, Bull Chem SOCJapan, Vol42, page 2333,1969. 8 Rohm and Haas Amberlite XAD-1180 Technical Bulletin. 9 M W Scroggins and J W Miller, Anal Chem, Vol40, No 7, page 1155, 1968. 10 M W Scroggins, Anal Chem, Vol44, page 1285,1972.

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Progress in Ion Exchange: Advances and Applications

11 M D Grieser and D J Pietrzyk, Anal Chem, Vol45, No 8, page 1348,1973. 12 British Patent No 1, 155,924, 1967. 13 Japanese Patent No 50,799,1977, Takeda. 14 W Voser (Ciba), US Patent No 3,725,400. 15 W Voser and K Weiss, J Chromatag, Vol201, page 287,1980. 16 Japanese Patent Application No 32791, 1976, Meiji Seika. 17 Japanese Laid Open Patent No 53,597, 1975. 18 British Patent No 1,472,966, 1977, SKF. 19 Japanese Laid Open Patent No 117,990,1977, Banyu. 20 Japanese Laid Open Patent No 110,587,1976, Nippon Kayaku 21 W Voser, J Chem Tech and Biotech 32, page 109,1982. 22 UK Patent No, 2,157,682. 23 US Patent No 4,876,35 1. 24 M Kurita et al, J Antibiot, Vol29, No 11, page 1243, 1976. 25 S J Box et al, J Antibiot, Vol32, No 12, page 1239, 1979. 26 K Okamura et al, J Antibiot, Vo13 1, No 5, page 480, 1978. 27 UK Patent No 2088 - 383,1980, Nippon Oil KK. 28 T Kamikubo and H Narahara, Vitamins, Vol37, No 3, page 225,1968. 29 Japanese Laid Open Patent No 51,305,1977. 30 Japanese Laid Open Patent No 75,074,1976. 31 US Patent No 3,515,717, 1970. 32 Japanese Laid Open Patent No 127,950,1974. 33 Japanese Laid Open Patent No 127,951,1974. 34 Japenese Laid Open Patent No 76,880,1973. 35 US Patent No 4,440,753, 1984, Eli Lilly. 36 L L Zaika, J Chromatog, Vol49, page 222,1970. 37 Japanese Laid Open Patent No 15,884,1977. 38 R Croteau et al, Biochem Biophys Res Comm, Vol50, No 4, page 1006, 1973. 39 M Hori, Bull Chem SOCJapan, Vol42, page 2333,2336,1969. 40 M Hori, Steroids, Vol 14, page 33, 1969. 41 D A Schooley et al, Steroids, page 377, 1972.

DESALINATION OF SPECIFIC IMMUNOGLOBULINS BY MICROPOROUS NEOSEPTA MEMBRANES: ROLF! OF IONOGENIC GROUPS

M. Bleha, G. Tishchenko, Y. Mizutani*, N. Ohmura* Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague, Czech Republic ‘Tokuyama Corp., Tokuyama City 745, Japan

1 INTRODUCTION

We reported earlier on the effective application of microporous membranes, both neutral (Synpore, Sartorius) and of the ion-exchange type (Neosepta) in the dialysis desalination of protein fractions of ascitic fluids containing immunoglobulins (Igs) of various specificity”. Replacing traditional dense dialysis membranes by neutral microfiltration membranes having pore sizes 0.05-0.1 pm we not only reduced considerably the duration of dialysis (from 5 days to 5-6 hours), but also were able to separate up to 2530% of the accompanying low-molecular-weight components, thus improving the conditions of further chromatographic isolation of specific Igs from the protein solution undergoing desalination. The universal character of such an approach, based theoretically on a considerable difference between the rate of diffusion of small and large molecules3reaching 2-3 orders of magnitude in porous polymeric carriers, was experimentally confirmed for microporous membranes of both types used in the isolation of various types of Igs, such as Ig GI specific to the heavy chain of human Ig M, Ig G, specific to hepatitis viruses B or horse-radish peroxidase. At the same time, a strict regularity could be observed in all these cases, namely, that the retention of high-molecular-weight Igs (M.w. 180 OOO) in the retentate and the selectivity of their separation from low-molecular-weight proteins were always higher if microporous ion-exchange Neosepta membranes were used. It was quite natural to assume, therefore, that their higher transport and sorption selectivity values were determined both by their morphological featuxes and by the presence of ionogenic groups. Research carried out in the chromatographic analysis of proteins using high-porous ion-exchange membranes4 has proved that the steric order of membrane has a great, though not always decisive, effect on their transport selectivity, due to the tendency of organic molecules to enter into polyfunctional interactions (electrostatic, hydrophobic, hydrogen bonds) with functional groups of the membranes and with the pore surface. A change in the nature and charge of the ionogenic groups may bring about a change in the transport selectivity of the membranes in a very wide range. The role of ionogenic groups is similarly distinct in filtration membrane processes. In particular, in the ultrafiltration of p-casein hydrolysis product through membranes bearing charged groups on the pore surfaces, bioactive peptides can be successfully separated5.

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In this study we try to analyze the effect of the nature and volume concentration of ionogenic groups in Neosepta membranes of various porosity in the dialysis desalination of high-concentrated salt protein solution containing Ig G, specific to horse-radish peroxidase. 2 EXPERIMENTAL PART Membranes The experiments were carried out using microporous cation- and anion-exchangeNeosepta membranes (Fig.1) (TokuyamaCorp., Japan) containing sulfonic acid and trimethylbenzylammoniumgroups, respectively. The membranes differed in the volume concentration of ionogenic groups, porosity and pore size distribution6. Ion -exchange capacity, meq/g

M t e r sorption capocity,cm3Jg

dry membrane

Figure 1 Characteristics of microporous ion-exchange Neosepta membranes 0 cation-exchange membranes C-1 - C-10; A anion-exchange membranes A-1 -A - I 0 Solution containing Ig G, spectjic to horse-radish peroxidase. In the dialysis desalination and equilibrium sorption a solution of protein fraction containing Ig GI specific to horse-radish peroxidase was used, obtained after the ammonium sulfate precipitation of mouse ascitic fluid (Sevac, Czech Republic) (Table 1). Along with specific Ig GI,the solution contained serum albumin and other serum proteins, transfemn, natural mouse immunoglobulins and a large amount of ammonium sulfate (0.53 moM). Equilibrium sorption of ascitic proteins in porous membranes. The sorption of proteins in cation- and anion-exchange membranes in the Na' and C r form, respectively, proceeded from a solution of the protein fraction of ascitic fluid. Membrane discs 3.5 cm in diameter were kept in contact with the protein solution (3 ml) for one week at 5°C. The protein content in the membranes was calculated from the difference between their concentrations in the starting and equilibrium solution determined spectrophotometrically at the wavelengths 260 and 280 nm7. The proteins were desorbed from the membranes with 0.4M NaCl in 0.02 M tris-HC1, pH = 7.8 (buffer B).

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Table 1 Characteristics of the used solution of Ig G, specific to horse-radish peroxidase Electric conductivity mS/cm

PH

14.2

5.87

PI of

Ammonium

Organic

Proteins

Ig GI

sulfate

substances

(Ig G I )

m€m

mg/ml

mg/ml

70.29

14.44

13.1(2.5)

5.95-6.3

Dialysis desalination of proteinfraction of asciticfluid. In the dialysis experiments, a three-compartment flat membrane cell (membrane diameter 2.6 cm, distance between the membranes 3 mm) and a three-compartmentspiral membrane module’ (membrane area 160 cm’, distance between the membranes 1 mm) were used. The protein solution was pumped through a central compartment formed between two membranes, with water circulating on the other side of the membranes. The respective volumes used in the membrane cell and spiral module were 8 and 50 ml of dialysate (protein solution) and 10 and 100 ml of diffusate (water). The circulation rate of the solutions was 8 d m i n . The determination of the concentration of proteins (spectrophotometrically) and ammonium sulfate (conductometrically)in the diffusate was carried out after 30 min, and water was replaced by a fresh volume. On reaching the maximum electric conductivity of the protein solution 6 mS/cm, the desalinated protein solution was subjected to ion-exchange chromatography on a column packed with DEAE cellulose DE 52 (Whatman, U.S.A.) in a NaCl linear gradient obtained by mixing buffer A (0.02 M tris-HC1, pH = 7.8) and buffer B. The concentration of specific immunoglobulin in eluate fractions and in diffusate was determined by sandwich ELISA titration with standards9. 3 RESULTS AND DISCUSSION As can be seen in Fig.1, relative porosity ( E ) , and volume concentration of ionogenic groups (ZJ in the membranes varied in a wide range. Due to the fact that both steric inaccessibility of pores and nature of ionogenic groups may influence the sorption and transport permeability of the membranes, it is very difficult to define the contribution of each factor to the membrane transport characteristics. Therefore, we consider here their effect on the membrane transport not separately, but as a whole. Structure research of the membranes performed by mercury porosimetry, gas adsorption and electron microscopy showed that they have a polymodal pore size distribution6given by the conditions of their preparation’. Along with large entrance pores (200-300 and 400-600 nm), they also contain macropores (50-80 and 80-150 nm), mesopores (22-27,30-37 and 40-42 nm) and micropores (7-9, 11-14 and 14-16 nm) which occupy the basic part of the free membrane volume. The ionogenic groups are connected with the styrene-divinylbenzenecopolymer distributed in the poly(viny1 chloride) matrix. The volume concentration of ionogenic groups in both types of the membranes decreases steeply with increasing porosity, which is reflected in the obvious increase of the specific volume of membranes.

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Progress in Ion Exchange: Advances and Applications Rotan sorption Water sorption

nl pores. 04

capacity

"/

0

1

Figure 2 Water and protein sorption with microporous ion-exchange Neosepta membranes. Dashed lines - specific sugace of pores of the membranes The specific volume of swollen polymer determined as the difference between the specific volume of membrane and the water content in membrane characterizes the packing of polymer globules in the hydrated membrane. This membrane-characteristicdata defines the geometry of membrane structure better than the relative membrane porosity determined as the relation between the water sorption in membrane and the specific volume of membrane. This assumption is in full agreement with the data on the equilibrium sorption of proteins in the membranes given below, as well as with the dependences of transport fluxes of ammonium sulfate and proteins in the dialysis desalination of the protein fraction solution on the membrane characteristic mentioned above. The dependences of water and protein sorption capacity and specific pore surface on the specific volume of swollen polymer in membrane (Fig.2) are governed by the same laws for both types of membranes. The water and protein sorption capacity increases with increasing E and decreasing &. Membranes possessing the highest Z, (2.45 and 1.73 meq/cm3 of hydrated membrane for cation-exchange membranes C-1, C-2 and 0.96 meq/cm3 for the anion-exchange membrane A-1) were permeable to low-molecularweight components only. A comparison between these results and the specific pore surface leads to a conclusion that the free volume of membranes lying on the left-hand side of the curves is due to pores of a smaller diameter compared with membranes of the right-hand side. Thus, the anion-exchange membrane A-2 having an approximately same Z, as the membrane A-6 (0.42and 0.45 meq/cm3, respectively) shows a considerably smaller E (49 and 59%, respectively). The same trend can be seen also in their sorption of water and proteins. It should be noted that the high sorption capacity of high-porous membranes of both types (A-5, A-8, A-9, A-10 and C-6, C-7, C-8, C-9, C-10) having a low Z, (0.03-0.13 meq/cm3)with respect to proteins is due to the hydrophobic binding of protein molecules on the pore surface. In this case only 50% of the sorbed proteins could be desorbed. Only membranes with a high charge density (A-1, A-2, and C-1, C-2) showed full reversibility of protein sorption.

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0.2 -

Figure 3 Dependence of distribution coefficientof proteins within microporous ionexchange Neosepta membranes on their volume concentration of ionogenic groups The difference in protein sorption in cation- and anion- exchange membranes depending on Z,is illustrated in Fig.3. The distribution coefficient K,, defined as the ratio between the equilibrium protein concentrations in the membrane and in solution characterizes the sorption selectivity of the membrane. One can see that for both types of membranes with a volume charge density up to 0.45 meq/cm3,log K,, varies linearly. The large slope of the linear part of the curve observed with anionexchange membranes in contrast with cation-exchange membranes seems to indicate a higher binding selectivity of proteins with trimethylbenzylammoniumgroups compared with sulfonic acid groups. For both types of membranes in the range of a low Z,and high E (more than 0.59-0.60), the distribution coefficients approach a limiting value which for the anionexchange membranes A-8, A-9, A-10 is approximately by 25% higher than that for the cationexchange membranes of a comparable porosity C-8, C-9, C-10. The increase in Z, values in the membranes (A-I, A-2 and C-1, C-2) leads to a steep drop in the distribution coefficients of proteins due to the steric inaccessibility of the larger part of membrane pores. The anomalous increase in the distribution coefficients of proteins with decreasing concentration of ionogenic groups may be explained by an increase in the nonspecific sorption of proteins on the pore surface at the expense of hydrophobic and hydrogen bonds. Since the proteins are sorbed from a solution of high-concentrated ammonium sulfate, the role of just this type of sorption binding with the pore surface must become increasingly important. This role appeared to be stronger for the anionexchange membranes. The only exception was membrane A-1 with its E of only 25%. Figs 3 -5 show the effect of ionogenic groups and steric structure of the membranes on the diffusion of proteins and salt molecules. The flux of ammonium sulfate through the membranes observed in the dialysis desalination of the solution of protein fraction is considerably lower compared with the salt flux determined in model experiments using 0.5 M of ammonium sulfate as a dialysate. This occurs owing to the competitive protein transport and to the narrowing of pore sizes during their sorption in the transport

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5-

b -

3 -

2-

1-

0

8 0.7 0.8 OQ q.0 11 sp.c,iic vo\urn.o~ s*nl\en po\ymrr. ern%

Figure 4 Transport of ammonium sulfate through the microporous ion-exchange Neosepta membranes in dialysis desalination of the solution of protein fraction of ascitic fluid and 0.5 M solution of ammonium sulfate (dashed lines)

Flux of serum proteins a l~-’mg/cm~.s

A A

6t 2

01

A ’

I

I

0.7 0.8 0.9 1.0 1.1 Specific volume of s w o ~ mpokymer. cm’/g

Figure 5 Transport of proteins through the microporous ion-exchange Neosepta membranes in dialysis desalination of the solution of protein fraction of ascitic fluid

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217

channels of the membranes. The effect of ionogenic groups on the transport of salt and protein molecules was distinctly seen only in the case of membranes with high Z,values. The permeability of membranes C-1, C-2 and A-1 (E = 0.48, 0.50, 0.25 and Z,= 2.45, 1.73,0.96) for salt molecules was so low, due to the Donnan ion exclusion, that their use in the dialysis desalination became impossible. The role of the Donnan ion exclusion can be analyzed by comparing the transport fluxes of ammonium sulfate through the membranes C-2 (Z,1.73, E 0.50) and A-2 (Z,0.42, E 0.49), C-3 (Z,0.27, E 0.56) and A-7 (Z,0.37, e 0.59). The much stronger salt flux through the membranes A-2 and A-7 because of the weaker Donnan ion exclusion agrees with Helfferich's conclusions about the more prefened utilization of anionexchange membranes in the separation of salts consisting of univalent cations and bivalent anions. The protein flux through both types of membranes is almost by two orders of magnitude lower compared with the salt flux (FigS).Moreover, it should be noted, that the rate of diffusion transport of the proteins is more dependent on membrane porosity and pore size distribution than the rate of transport of the salt. One can see this by comparing the salt and protein fluxes through membranes A-3 (Z,0.23, E 0.53) and A-6 (Z,0.45, E 0.59).If the salt flux through the membrane A-6 is considerably higher than that through the membrane A-3, an opposite dependence is observed for the protein flux. This finding confirms the earlier assumption regarding the more microporous structure of A-6. Due to the considerable difference in the rate of diffusion transport of proteins and ammonium sulfate, 8590% of salt could be separated with minimum losses of specific Ig G, (1-3%). The amount of low-molecular-weight proteins which passed into the diffusate varied in the range 7-25% depending on the structure characteristics of the membranes and value of Z,,. 4 CONCLUSIONS

The effect of the nature and volume concentration of ionogenic groups of membranes on their sorption of, and transport permeability to, components of the protein fraction of ascitic fluid was reflected in the higher selectivity of binding of proteins with trimethylbenzylammoniumthan with sulfonic acid groups. Due to the unique morphology of microporous ionexchange Neosepta membranes consisting in the polymodal pore size distribution, it was possible to perform an effective dialysis procedure of protein mixture containing Ig G, specific to horse-radish peroxidase.

References 1. 2. 3.

4. 5.

G. Tishchenko, M. Bleha, J. Skvor, L. BureS, Bioseparations, 1995, 5, 19. G. Tishchenko, M. Bleha, J. Skvor, L. BureS, Y.Mizutani, N. Ohmura, J. Membr. Sci., in press. A.N. Cherkasov, V.A. Pasechnik, "Membranesand Sorbents in Biotechnology" (in Russian), Khimiya, Leningrad, 1991. T.B. Tennikova, M. Nahdnek, F. Svec, J. Liq. Chromatogr., 1991,14, 2621. F. Nau, F.L. Kerherve, G. Daufin, J. Uonil, Biotechnol. Bioeng., 1995, 46,246.

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Progress in Ion Exchange: Advances and Applications

G. Tishchenko, M. Bleha, J. Skvor, L. BureS, Y. Mizutani, N. Ohmura, J. Appl. Polym. Sci. 1995, 58, 1341. 7. C. Warburg, W. Christian, Biochem. Z., 1941,310, 384. 8. M. Bleha, G. Tishchenko, J. Membr. Sci., 1992, 73, 305. 9. R.H.Yolken, J. Biol. Med., 1980, 53, 85. 10. Y. Mizutani, J. Membr. Sci., 1990, 49, 121. 1 1 . F. Helfferich, "IonExchange", McGraw-Hill, New York, 1959. 6.

CHROMATOGRAPHIC STRATEGY IN BIOPRODUCT PURIFICATION

J H Creedy

TosoHaas GmbH Zettachring 6 D-70567

Stuttgart GERMANY

1 INTRODUCTION

The isolation of natural products, especially proteins, peptiides, and other macromolecular species from biological source material presents a number of unique problems to the purification chemist. Such material is characteristically complex and many contaminants are similar in nature to the target product. A number of well-established purification modes are available, including Ion Exchange, Hydrophobic Interaction and Size Exclusion chromatography. together with an array of alternative resins representing each mode. It is common for several sequential stages and complementary modes to be required for effective purification of a protein product. Selection of the most suitable resin, however, and its implementation within a purification strategy can be a daunting proposition. Difficulties in determining the most effective strategy and conditions for a purification can be minimised by developing a structured approach and by working with a system of convenient tools designed to provide quick and economical answers to the key questions posed at each stage of methods development, This paper describes the use of a novel and practical solution, a "Resin Library" system, consisting of both process resins and dedicated tools designed to meet the unique needs of the protein purification chemist. 2 A RATIONAL APPROACH TO PURIFICATION STRATEGY

To achieve a valid purification system for a product, one must attempt to establish the operational constraints . These are dictated by the nature of the source material, the specification required for the final product, and the economics of proceeding from one to the other. It helps to tabulate the details of these at the outset. This data then assists the method development process, and helps to avoid illogical or counterproductive sequences. A detailed list should be drawn up to charaderise the volume and complexity of the source material with respect to both the product and the contaminants. A specification should be drawn up for the purified product, and these two lists will provide the basis for developing the purification strategy. The design of the process, both the strategic sequence of chromatographic steps and the optimisation of method within each step, must aim for a robust process capable of routine and longterm operation within a defined specification. Resin resilience and lifetime is a major element in the development of such a system, together with documentary support and continuity of supply by the manufacturer.

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Progress in Ion Exchange: Advances and Applications

The detailed economics of process method development relate in principle to the capacity, stability and productivity of the design. In general, biological products require multistage strategic approach involving a logically adapted sequence of complementary steps. An economically sound process will avoid those elements which require intervening conditioning steps, and will as a rule keep the number of individual operations to a minimum. It will also exploit the complementary nature of the available modes, such as ion exchange, hydrophobic interaction and other chromatographic modes, utilising the strengths of each whilst avoiding the weaknesses. 2.1 Purification Priorities and How They Influence the Process

Each operator will have definable priorities which will influence and modify decisions in the development of an optimised protocol. As a result there exists, arguably, no ideal protocol for any particular separation, but a number of potential tailored approaches, each combining a differing set of compromises. The guiding principles for achieving an optimal strategy are, however, the same for all operators. Some examples of differing priorities may be offered: 1 2

3 4 5 6

Level of purification required (defined specification) Product recovery (loss of material to be tolerated) Need to retain bioactivity (absolute or specific activity) Throughput (capacity of system per unit time) Final presentation of product (dry, bufferedlnonbuffered solution) Special objectives (eg. sterility)

Depending upon the presentation of the source material, there may be need for sample pretreatment of some description, eg. cell disruption and clarification. Following this treatment, there remain a wide variety of chromatographic techniques and conditions each of which may offer different advantages. The order of implementation, in particular, can influence the end result as much as the choice of technique. For this reason, a good understandingof the strengths and weaknesses of each approach is worth developing. A rational choice can then be made to avoid counterproductive procedures, such as an intervening conditioning step.

2.2 Stages of Process Design and the Working Tools One can define five operations within the design and development of an effective bioprocess purification scheme. Each operation presents a number of challenges which must be addressed with a unique approach and a different working tool. 1. 2. 3. 4. 5.

Define and understandthe characteristics of the source material. Explore the alternative chromatographic modes and resin options. Propose and develop the strategy and chromatographic methods. Validate the method and determine the operational envelope. Scale the system via pilot scale to full scale production, and validate the installation.

2.2.1 Define and Understandthe Characteristicsof the Source Material.

Biological source material such as a fermentation broth, cell extract or plant derived material is characteristically highly complex. It is also often presented in large aqueous volumes. The overriding need is often to reduce the material to manageable volumes whilst maintaining product integrity and bioactivity. Destructive components such as proteolytic enzymes and other bulk contaminants are oflen similar in nature to the target protein product. As a result, it is Often impractical to provide the data required for confident determination of the most effective separation mode or sequence of modes. It is left to the experience and skill of the operator to select a strategy. Such experience is often based on source materials of a significantly different nature, and will thus normally demand an empirical approach.

Resins as Biosorbents

22 1

If it is possible to quickly investigate the behaviour of a sample with analytical or high

performance resins of similar selectivity to the available process resins, then any data which results may be used with confidence to predict selectivity of the process resin. High performance columns of similar selectivity thus offer a convenient and practical tool for speedy and detailed investigations. As a consequence, the behaviour of complex source material is easily characterised with such high definition columns. Their cost, however, mediates against their use as a general purpose resin screening tool. They are better reserved for problem solving during the method development phase. 2.2.2 Explore the Ahmatiw Chromatogaphic Modes and Resin Options.

Initial resin screening need not involve high resolution work. The objective here is to quickly determine whether a number of resins will bind either the target molecule or its essential contaminants and elute the target molecule in useable condition. A wide range of resins and separation modes should be screened in a quick and conveniently low cost format. Chromatographic conditions applied need not be optimised, as this will be achieved during the subsequent method development phase, using a purpose designed working tool. The results, however, will indicate the resins best suited to in depth evaluation using a more appropriate column format. 2.2.3 Propose and Develop the Strategy and Chromatogmphic Methods Using an Understending of the strengths and Complement@ of the Attematiw ChmmatogaphicModes.

The presentation of the source material will often suggest the initial purification strategy. It is likely that source material volume reduction will be required, and a number of other objectives may be met at the same time such as target product concentration and protease removal in order to conserve bioactivity. It is always a good principle to follow to keep volumes low on the ground of ease of handling. This also helps to minimise capital plant costs. If the feedstock salt concentration is sufficiently low, then an ion exchange step is indicated, but the mode (cation or anion exchange) will depend upon the isoelectric points of the target protein relative to the major contaminants. 2.2.3.1 /on Exchange Chromatogaphy (EC). Ion exchange may be employed in adsorptive or non-adsorptive mode of operation. The greatest concentration of target product is achieved in adsorptive mode, where load conditions are chosen to bind the target molecule selectively. pH is normally contrived to maximise taw adsorption at the expense of unbound contaminant material. Subsequent elution achieves the twofold objective of product concentration and purification. Careful attention to ion exchange conditions (mode, pH, salt load concentration) and adoption of stepwise elution conditions where possible, will pay major dividends in process economics and reliability.

The power of Ion Exchange resides in the extensive range of conditions that can be exploited to achieve selective isolation of a target molecule. Both cation and anion exchange resins, adsorptive or non-adsorptive modes of operation, combine with the ability to use pH and salt strength under either gradient or where possible stepwise elution conditions to provide an unparallelled range of purification opportunities. Elution conditions can be selected to enhance bioactivity retention, binding capacity or selectivity. It is this ability to match objectives of the separation step with the priorities of the purification that determines the sequence within a multistage separation strategy. whilst Ion Exchange as a technique exploits differences between sample components on the basis of overall molecular charge, Hydrophobic Interaction exploits differences based on the principle of surface hydrophobicity. The two techniques are thus complementary, working on different principles. They offer, in sequential combination, powerful opportunities for high purity product isolation.

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Progress in Ion Exchange: Advances and Applications

2.2.3.2 Hydrophobic Interaction Chromatography (HIC). Hydrophobic Interaction is a rational technique to follow an Ion Exchange step, since the salt present in the eluted IEC material does not normally adversely affect product binding to the HIC resin. If the source material has a high salt concentration, then HIC may be indicated to precede any ion exchange step, and has been used for initial product capture under such conditions. It is easier to add salt to the load material than to remove salt from it, but it is better to avoid any such conditioning steps where possible. Judicious selection of resin from a range of HIC resin hydrophobicities permits the convenient matching of feedstock salt concentration to target product loading conditions. In this way, the need for salt addition or desalting can sometimes be avoided. 2.2.3.3 Size Exclusion or Gel Fitfration Chromatogaphy (GFC). Aqueous size exclusion, or Gel Filtration, is normally less suited to the early stages of purification for a number of reasons. It is impractical to process large volumes of source material, as large columns are required relative to sample volume, compared to IEC or HIC columns. This is uneconomical use of both resin and column hardware. GFC is also a diluting technique and product is recovered in a larger volume than it was applied. This is contrary to the overall objectives of a normal purification. Selectivity is characteristically less than that offered by adsorption techniques. Gel filtration is thus best resewed for either terminal polishing stages in which polymeric forms or aggregates of product are isolated when the volumes have already been reduced substantially, or for when desalting or buffer exchange may be required. In many cases, careful selection of the mode sequence can avoid the need for such conditioning steps. 2.2.3.4 AtYinity Chromatography (AFC). Possibly the greatest selectivity of any chromatographic mode is offered by Affinity Chromatography (AFC), in which a biospecific adsorbent is used to selectively capture a target molecule, which is subsequently recovered by desorption in a small volume. Whilst AFC is in theory ideally suited to selective capture of target molecule from low concentration, large volume source material, adsorbents are frequently high cost media, and most frequently resewed for isolation of higher value products. Sensitivity of ligands to repetitive reconditioning steps can reduce resin lifetime and additional problems associated with validation of the removal of leached biospecific ligand also exist. Such problems can be in practice insuperable. 2.2.3.5 Reverse Phase Chromafosaphv (RPC). Only a restricted number of proteins retain activity following solvent exposure during reverse phase purification. The technique is becoming the method of choice for smaller molecules such as peptides, antibiotics and oligonucleotides. For such products RPC offers high recovery, and high resolutionwithin a concentration step. 2.2.4 Validate the Method and Determine the Operational Envelope.

Before proceeding to implement the refined method and sequential purification strategy at large scale, it is important to determine the most economic particle size and column geometry for the process. In general, large particles offer the advantage of lower cost and lower flow resistance. which can result in more efficient system throughput. Small particles offer high resolution and possible savings in eluent volume compared with large particles. Column capacity will depend upon resin binding capacity for the load material together with the effective load capacity with a given column geometry and flow rate. Considerable work may be needed in order to achieve an fully optimised step, and it is impractical to work at this stage with full size columns. It is, however, essential to be working with the resin proposed for the final full scale system. In this way, scale-up data may be used with confidence to predict the proposed full-scale system performance and processing costs. The degree of accuracy of this data depends largely upon work with small scale versions of the proposed system at laboratory or pilot scale.

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223

Particle size has a direct effect upon the resolution performance of a column, particularly in isocratic (non-gradient) and linear gredient elution mode. If a method can be established in stepwise elution mode (IEC or HIC) then this effect is minimised, and method transfer to a large particle resin provides the benefb of enhanced throughput with fewer of the disadvanlages. A gradient method may be transferred to a larger particle resin as long as acceptable resolution is maintained. For this reason, there is a compelling reason to work, where possible, towards developing a stepwise elution method. Stepwise elution of bound components is in general easier to operate reliably. pH may be used in such a system to control recovery, whereas gradient pH elution is to be avoided due to difficulties in reproduction of conditions from run to run. Having determined the method on the particle size of choice, it is necessary to establish the "operational envelope" of the system. These are the limits of conditions within which an operation may be performed reliably. For example, recovery of the product from an ion exchanger may occur at pH 6.5. It is important to establish the limits of pH control within which the spedfied purification may be achieved, say between pH 6.40 and pH 6.53. A full discussion on this subjed is beyond the scope of this artide, however the objective of this method validation is to document the robust nature of the system. A highly sensitive step condition could mean that it may be inappropriate within a manufacturing situation. A robust system is one which operates reliably within defined and practicable limits of, for example, pH control, salt concentration, operational temperature etc. Finally it will be necessary to calculate step processing capacity for both feedstock volume and mass. This enables a valid calculation of system throughput under a number of alternative configurations, such as single pass or multiple pass column operation. It may be economically expedient to divide the load material, processing it in a number of passes, and pooling the resultant material for onward processing. This decision will have a major

implication on plant design and process economics. Capital installation, labour and variable and fixed running costs will vary considerably dependant upon the adoption or otherwise of batch processing methods. Column size, resin volume, and lifetime of the resin under controlled operational conditions will affect process operational cost calculations in a manufacturing situation probably to a far greater extent than the price of resin per litre of kilogram. In the final analysis, a good process is reliably robust in operation, and will deliver a known processing throughput at economically acceptable costs.The ease with which such a process may be developed depends to a large extent upon following rational process design principles, and the a b i l i to work with accredited process resins at all stages of this development. 2.2.5 Scab the System via Riot Scale to Full Sale Frvdudion, and Validate the Installation.

The sequence and relative scale of each step within the strategy will have been optimised during the previous stages of method development. Having worked throughout with process resins and their selectivity equivalents, it is now possible to employ standard principles to scale the system to full production scale. Throughput calculations based on resin capacity, cycle time and batch process cycle numbers will now define the column volume required. An allowance should be made for operational downtime and the anticipated schedule for system operation (number of hourr operational during a 24 hour period. weekend operation, vacationlpublic holiday downtime etC.). The column cycle load capacity will be scaled directly to column volume, but certain factors should remain constant. Column bed height, load and eluent linear velocity, source material mass concentration, and load and elution volumes (measured in column volumes) must all remain constant. Column volume is thus increased on the basis of column diameter alone. Throughput may be scaled at any step by either increase in column volume, number of load cydes or number of parallel column operations.

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By observing such principles, the previously defined operating conditions may be directly tranSfemd from laboratory, via pilot scale to production installation. Validation of the system may then primarily be confined to system hardware operation.

2.3 Source Material and its Chromatographic Behaviour The source material containing the product of interest is the single most variable element relevant to any discussion on biopurification. It is critical to development of a well-conceived scheme that as much information on both the product and its contaminants should be brought to bear upon the strategic decisions required to define a separation protocol. The following elements will impact strongly upon this decision-making process: 1

2 3 4 5 6 7

Physicochemicalcharacteristicsof the product and, where possible, contaminants (Molecular Weight, lsoelectric Point, hydrophobicity, solubility) Heterogeneityof the starting material (many or few contaminants) Concentration of Product (both absolute and relative to Total Mass) Mass of Product Volume to be processed (Total, batch, pooled batches) Lability/stability to pH, temperature, protease activity etc. Other relevant data ( Viscosity, toxicity, value, intended use eg. therapeutic)

Some of this data can be obtained from non-chromatographic sources, such as electrophoretic titration curves. documented reference literature etc. The behaviour of sample material with a high resolution resin of identical selectivity, however, can provide information of practical use in subsequent transfer of the method to a similar process resin at large scale. The ability to work throughout with a system which offers direct, or seamless, scaleability is a significant advantage in a methods development situation. Characterisationof the source material is thus a prerequisite of efficient strategy determination, that is to say the selection and sequence of separation mode. A rational sequence can help to avoid unnecessary conditioning steps, and is normally dictated by the source material and the final product specification. 2.4 Resin Determination

In principle, a number of options may exist for each stage of product purification. both chromatographic mode and individual resin selectivity or chemistry. Initial selection can be simplified by screening a number of resins with the proposed sample material with the purpose of obtaining fundamental information such as whether the product can be bound and recovered under certain conditions. The intention here is not to obtain detailed performance data, but merely the likelihood of such a resin being worth further detailed investigation. The tool required for such a screening study should be quick simple and inexpensive, but available across the full spectrum of resin products. Such a tool is central to the concept of a "Resin Library" system. Ideally such resins should then be available, appropriately packed, as dedicated method development columns for use on a range of alternative instrumentation. The fundamental requirement of a useable and practical "Resin Library" system is that the resins employed at every stage should be consistent throughout in their selectivity. In this way the predictive scaleability of the system is conserved. Only thus can the methods developed be transferred to larger scale with confidence.

Resins as Biosorbents

225

3 THE RESIN LIBRARY SYSTEM TosoHaas have developed a system of products which permit convenient and rational evaluation of a wide range of Ion Exchange and Hydrophobic Interaction process resins. Each resin offers a difference in selectivity, and is available in a number of alternative product confgurations suited to the different stages of process design. 3.1 Sample Characterisationwith High F+edonnance Columns

Since the TSK-Gel@ 5PW 10 p resins provide similar selectivity to many of the Toyopearl@ process resins due to their identical chemical nature, these high performance columns are ideally suited to analytical evaluation of the resinlsample interactions that will occur when using process Toyopearl resins. Data obtained from such columns may be extrapolated to the process resins with confidence. Fine detail of method characterisation and troubleshooting is easily accomplished with a high performance column of this type.

3.2 Resin Screening for Primary Strategy Proposal Primary resin selection is better investigated with a low cost resin screening tool. Coarse grade process resins (loop) are packed into 5 ml gravity operated cartridges for this purpose. and kits of alternative resin selectivities are used to establish fundamental resin/sample loading and recovery data without the need for more expensive columns. In this way, a comprehensive preliminary resin screening may be economically performed in either cation I anion exchange or hydrophobic interaction mode.

3.3 Strategy I Method Developmentwith purpose designed MDN Series Columns Strategy design and methods development is predictive of large scale operation only if the resin is identical to the final process resin in terms of selectivity. Using the superfine grade of Toyopearl process resins (35p), the Toyopearl MDWP series column provides a convenient and economic working tool for methods development. It too is available in a number of ion exchange and hydrophobic resin formats. By working a method up with the final process resin in a column designed to tolerate crude soum material, data obtained may be transferred to process scale easily and with confidence. Much of the process development will be accomplished with this purpose designed working tool, and the hardware configuration is modified for this purpose. Toyopeall MPSeries columns have been developed for d i m method development work using a range of process resins. The bulk resins are available in three particle sizes, 35p (S grade), 65p (M grade) and loop (C grade) diameter. MD columns are packed with S grade superfine resin in a 7.5 mm x 8.5 mm column geometry (3.8 ml column volume). They may be used with a special adapter fming on the full range of method development instrumentation including low pressure chromatography systems. lntemal modifications and frit porosity permits use of this column with CNde samples normally encounteredwith biological source material. As the MD column resin is identical in selectivity to the bulk resins, methods developed with these columns may be transferred to large scale operation with confidence. Particle sizes larger than S grade resin will retain similar selectivity, but offer faster throughput at the expense of a reduction in column efficiency. Small particles. however, offer higher resolution.

Changes to a process foiiowing registration are not easy and are very expensive to implement. The resin library system was developed to ensure that the best resin is selected and optimal conditions are developed, thus avoiding the need for any subsequent changes to the process.

226

Progress in Ion Exchange: Advances and Applications

3.4 Method Validation and Process Economics Design at Laboratory Pilot Scale Method validation and process economics can only be determined with accuracy using identical bulk resin to that intended for final produdion. Small laboratory scale columns should be packed with economically available samples of alternative resin particle sizes. The Toyopearl LabPak Samplers offer a convenient and economic supply, prior to committing a system to full-scale operation. 3.5 Process Validation and Large Scale Implementation with Bulk Resin Large scale produdion requires the availability of batch resin in quantities in the order of hundreds of litres. Product registration increasingly demands resin support and documentation to acceptable standards such as FDA Drug Master File status. Furthermore, the reliability of resin supply is critical to the longterm operation of the process. The TosoHaas Resin Library fulfills all of the above criteria for process resin supply.

IODINATED RESIN AND ITS USE I N WATER DISINFECTION

L. E. Osterhoudt General Manager The Purolite C Company 150 Monument Road Bala Cynwyd, PA USA 19004

1 INTRODUCTION Our bodies are about 70% water, all of which is replaced every five to ten days. We need to ingest about six quarts of water daily from all sources, and without water we could die in three days. During our lifetime w e will consume about 16.000 gallons of water, so the quality of the water we drink will have a direct impact on the health of our bodies. So how is the quality of our water? Contaminated water is by far the largest health problem on the planet. According to the World Health Organization, an estimated 50,000 people die each day due to waterborne disease. Four out of five people in hospitals around the world are there because of waterborne disease. According to UNICEF, 1.2 billion people in the developing world are denied access to safe drinking water. I n many areas from 80 98 % of the population has no ability to get safe drinking water. Even in many areas where there is central treatment, a lack of control and contaminated delivery systems can render such treatment unreliable and ineffective. The problem is not limited to under-developed countries, however.

-

In the U.S. there has been increasing awareness that our water quality is questionable in many areas. The most dramatic illustration of this was the largest recorded outbreak of a waterborne disease in U.S. history. I’m referring to the recent epidemic in Milwaukee that was caused by the cryptosporidium cyst which made an estimated 400,000 people sick. 41,000 were treated for abdominal cramps and diarrhea and more than 4.000 were hospitalized, and 104 people died. This means that this water epidemic killed more people than the recent Los Angeles earthquake. The Centers for Disease Control estimate that in the U.S. almost 1,000,000 people get sick each year from microbiologically contaminated water, and that almost 1,000 people may die as a result. Up until this outbreak, the Giardia cyst was the major focus, but Cryptosporidium has now become the major health concern, as it is somewhat smaller than Giardia (4-5 pM), and more resistant to disinfection. One study showed that Crypto is 30 times more resistant to ozone than Giardia, and.is unaffected by exposure to 3% chlorine as sodium hypochlorite for 18 hours.

228

Progress in Ion Exchange: Advances and Applications

Other microorganisms that cause health problems include coliform bacteria, which has been monitored in the U.S. for most of the twentieth century as an indicator as to the contamination of a water supply. The most prevalent and dangerous of the coliforms is E Coli which is frequently found as a result of fecal contamination. E Coli is probably the most widespread problem in the world as a whole, although other bacteria such as cholera receive much publicity. In addition to bacteria and the giardia and cryptosporidium cysts, viruses such as polio and rotavirus also cause major problems as waterborne diseases. 2 TREATMENT TECHNOLOGIES The use of home water filtration and treatment has existed for many years in the U.S..where tap water has been assumed to be microbiologically safe to drink. Most people have used filters when they have had a problem with high sediment i n the water or unpleasant tastes or odors that rendered the water undrinkable. More recently, however, people are relying on these devices as well as more sophisticated technologies to protect their health. Problems and controversy have arisen because of occasional misrepresentation of what some of these products could do. Consumer misunderstanding and improper use and maintenance could cause some of these devices to actually worsen the quality of the water. Outside of many of the developed countries, most people rely on bottled water for drinking and would never consider trying to drink the water from the tap. I n developing countries, untreated surface waters and hand pumped shallow wells are the major source of drinking water. Local authorities advise boiling water to reduce the chance of illness, however this becomes impractical in many areas where firewood is a scarce and precious commodity. I t is in these developing countries where the need for safe drinking water is the greatest. I t is also in these countries where the level of personal income is the lowest and where people typically pay up to 30% of their income for drinking water. Several technologies have been developed for disinfecting water, most of which involve treatment at a central source with distribution networks. Chlorine is used most frequently in central treatment because of its relatively low cost, although ozone with a small chlorine dioxide residual is gaining acceptance as well. However, the distribution networks that follow the central treatment are often old, and have dead ends or areas with very low flow. A s a result, residual chlorine levels can become ineffective at preventing the growth of microorganisms, and recontamination of the treated water is possible. Treating the water at the point where i t is used - or Point of Use (POU) treatment - presents an opportunity to treat only the water that will be ingested. I n addition, the water is treated immediately before it is consumed, so the chance of recontamination is minimized. Many of these POU devices are based on reverse osmosis or ultra-violet light to reduce bacteriologicals. Not only are these devices expensive to purchase, they also require either high water pressure or a steady supply of electricity to ensure continuous treatment. Since neither of these requirements are available in most developing countries, the use of these POU devices has been limited.

Resins as Biosorbents

229

3 HALOGENATED RESIN

Several alternative technologies involving ion exchange resins have been in use for many years for the disinfection of potable water. Ion exchange resin provides a unique method of storing and dispensing iodine into the water that is both safe and reliable. Ion exchange resin has been used as a bromine carrier by the U.S. Navy for many years. Cartridges loaded with brominated resin are used on board ship in order to provide residual disinfection of drinking water that is produced by distillation and reverse osmosis systems. The sealed brominated resin cartridge is much more stable and less corrosive than either liquid or dry chlorine, both of which are considered hazardous on board ship. Bromine is still quite volatile. however, and care must be taken in the loading of the cartridges into the systems. Iodine is preferred in small POU systems due to its lower volatility and greater storage stability. NASA has used iodinated resin on board shuttle missions to disinfect the water created in the fuel cells. Iodine’s higher cost is not a great problem due to the extremely large treatment capacity of the iodinated resin. In properly designed devices incorporating this resin, over 3,000 liters of water can be disinfected by only 20 cc. of resin. Relatively simple devices can introduce the iodine into the water, hold the treated water within the device for a period of time to allow the halogen to work, and remove all traces of iodine before the water is consumed. In some countries where goiter is a problem, iodinated resin can also be used to introduce a low level of iodine into the water as a dietary supplement. At these low levels. disinfection may take several minutes, but the level is below the objectionable taste level. In areas where water jugs are filled from a central well and carried home for the day’s water supply, this residual will disinfect the water, prevent recontamination, and will provide a dietary supplement to prevent goiter. A properly designed and manufactured ion exchange resin will elute iodine at a controlled, predictable level for a long period of time. The alternatives to using resin involve using motorized feed pumps with monitoring and control equipment to adjust the amount of iodine in the water. Problems have arisen with some iodinated resins that have been developed because inconsistent iodine elution levels result in either too high or too low a level of residual iodine. Excess iodine will overwhelm the media that is used to remove it and will create a burning in the mouth with a strong metallic iodine taste. Insufficient iodine will not provide adequate disinfection which will make the device ineffective at providing safe drinking water. 4 PATENT REVIEW

The first mention of putting a halogen on an ion exchange resin appeared in U.S. Patent No. 3,316,173. Mills et al. in 1967. Since then there have been around a dozen patents issued with variations on this technology. Perhaps the first patent that describes the current technology of putting iodineliodide complexes onto a strong base anion exchange resin is 3,817,860, Lambert and Fina dated 1974. This patent talks about a “triiodide ion” in which the iodine ion (I-) combines with molecular iodine (12) to form the triiodide ion (I3-).

Progress in Ion Exchange: Advances and Applications

230

Adding more elemental iodine t o the solution will f o r m higher polyiodide ions such as Is- and 17-. etc. In these patents, i t was considered undesirable to form these compounds as excess iodine would elute off of the resin and would have t o be washed off before the resin was used. I t was thought that only having the triiodides on the resin would cause the resin to release iodine “on demand” and would avoid a residual of iodine in the water passing through the resin. T h e essential reaction was illustrated in the patent as shown in Figure 1 below: I ”

c

C H3

I

I I

C

H2-N+-

I

C

I C

CH3Cl-

+ K+I3- d

C H3

I

C

I

c c I

CH3

CH3

‘CH3

T h e patent states that “in the above equation, t h e quaternary ammonium anion exchange resin is represented with three methyl groups bonded t o the basic nitrogen, which is also bonded to the styrene polymer, and the resin is shown as being originally in the chloride form. I t will be understood, however, that other short chain aliphatic groups can be bonded t o the nitrogen, such as ethyl or hydroxyethyl groups. In the resin-triiodide compound, as indicated, the triiodide becomes closely bound t o the fixed quaternary ammonium group, o r other strongly basic group, and i s thereby insolubilized.” ( 15) Subsequent patents have focused on producing higher polyiodide compounds on the resin. Patent 4,999,190. Lambert and Fina, 1991 describes a method of using heat in a closed system t o produce a concentrated iodine solution that can be loaded onto the resin. Care must be taken in this process that the resin does not become encrusted with iodine which will prevent absorption of the iodine throughout the resin bead, and will wash off as the resin is initially used. An encrusted resin will yield a higher than desired initial iodine level followed by a rapid reduction in iodine t o a very low level. There have been several recorded instances in the marketplace where users of devices containing resin that was apparently encrusted became ill due t o excess iodine which had overwhelmed the removal media and was present in high concentrations (excess of 10 ppm) in the treated water.

Resins as Biosorbents

23 1

5 RECENT DEVELOPMENTS

After examining all of the existing technologies, our researchers attempted to produce an iodinated resin that would elute a more consistent amount of iodine with a much reduced chance of encrustation. These efforts have resulted in our current line of iodinated resins which is trademarked Purodine””. These resins are based on utilizing a tightly controlled base anion resin. We found that if the base resin is the least bit inconsistent in it’s physical and chemical properties, the post iodinated product will perform inconsistently. We also found that by loading the iodine onto the resin using a totally different methodology produced a resin that had iodine loaded throughout the structure of the bead with no encrustation. We also found that we could control the elution level of this resin quite precisely (for a given set of operating conditions), and could produce resins that begin eluting at a range of iodine levels. We chose to retain the exact methodology as proprietary information, as proving infringement against a potential patent would be difficult. The relative performance of these resins is illustrated in the chart shown in Figure 2. A typical resin made with the patented methodology previously described can typically produce the type of curve shown as “encrustation.” Several different grades of Purodine are shown as examples of what we are calling “diffusion” technology. A s you can see, the encrustation will product a high initial elution with a rapid reduction to a low level. The diffusion technology produces a resin that will elute at a lower, more controllable level to start, and since the iodine has penetrated throughout the bead, the reduction in elution level is much slower, and stabilizes at a higher level. This will produce more predictable and more uniform disinfection which will retain it’s effectiveness for a longer period of time.

Liters of Water Figure 2.

232

Progress in Ion Exchange: Advances and Applications 6 FACTORS EFFECTING PERFORMANCE

Two water conditions will effect the amount of iodine that is eluted from an iodinated resin: pH and temperature, w i t h pH having the most dramatic effect. The relationship between pH and iodine elution was tested in our laboratory; the results are shown graphically in Figure 3. The equation generated by this data has a correlation coefficient of 0.97,confirming its accuracy. This formula can only predict performance above pH 4 however. Further testing at pH values below 4 is required to predict iodine elution levels at those lower pH values. Given the dramatic change in iodine elution at varying pH levels, it is recommended that devices incorporating iodinated resin include a pretreatment cartridge to adjust the pH of the water before it reaches the iodinated resin. This will help to ensure that the resin does not exhaust prematurely, nor w i l l it elute at a level that is too low to be microbiologically effective. Elution Level vs. pH of lodinated Resin

Figure 3

T o illustrate a specific example from this graph we find that the same resin that elutes 1.8 ppm of Iodine at a pH of 5 will elute 5.3 ppm of Iodine at a pH of 9. This is why the U.S. Environmental Protection Agency in it’s Guide Standard and Protocol for Testing Microbiological Water Purifiers requires testing of these units at a pH of 5 and 9. There are also temperature considerations which must be taken into account when designing devices containing iodinated resin. The abovementioned EPA Guide Standard addresses this situation by requiring testing at 4 deg. C.

Resins as Biosorbents

233

Temperature of the water being treated will effect the elution level of iodinated resin to a lesser extent than pH, but still must be taken into account in the design of devices containing these resins. The graph shown in Figure 4 shows the relationship between temperature and iodine elution level with water of varying temperatures. The resultant formula (with a correlation coefficient of 0.99) predicts that for every 10 degrees C increase in temperature, the resin will have an increased elution of approximately 0.5 PPm. Elution Level vs. Temperature 1.7 1.6 1.5

1.4 1.3 1.2

1.1 1.o

Figure 4

7 SUMMARY Iodinated resin represents a technology that provides the potential for producing water treatment devices which can be effective in removing and/or killing the majority of waterborne pathogens in the world. These devices can be designed so that they require no electricity or water pressure to operate, and can provide potable water from virtually any source at an extremely low cost. This technology can be applied in small point of use devices to treat water for an individual, or can be scaled up to provide potable water for a small village or commercial establishment. Devices incorporating these resins must be thoroughly tested to ensure their microbiological effectiveness under the range of conditions specified in the EPA protocol. I t is also recommended that pretreatment be applied in areas with extremes in either pH or temperature to help to ensure the resin will elute iodine at a consistent and predictable level. If these precautions are taken into consideration, iodinated resin represents the most universally applicable method for disinfecting water that is currently available.

Progress in Ion Exchange: Advances and Applications

234 8 REFERENCES

1. “Living Water”. Water Conditioning & Purification, November, 1994 2. Steven G. Singer, “Facing World Water Disinfection Challenges”, Water Technology, November, 1994. 3. United States Environmental Protection Agency, The Safe Drinking Water Act, June, 1993 4. Anthony A. Rutkowski, PhD, “Cryptosporidium, A Versatile, Complex Organism”, Water Conditioning & Purification, June, 1993. 5 . EPA, Safe Drinking Water Act Reauthorization Overview, February, 1994 6. “Around the Industry”, Water TechnoEogy, June, 1994 7. EPA, Home Water Treatment Units, September, 1990

8 . Lykins, Clark & Goodrich, Point-of-uselpoint-of-entry f o r Drinking Water Treatment. Lewis Publishers, Inc. 1992 9. F. Jerome Tone, “Compliance Testing Vs. Informational Testing”, Water Conditioning & Purification, March, 1994 10. United States Patent No. 3,316,173, Mills et al. Process For Treating Water with Bromine. 11. U.S. Patent 3,425,790, Sloan, Process for Obtaining Equilibrium Controlled Amounts of Halogen andlor Interhalogen in a Fluid Medium 12. U.S. Patent 3,436.345, Goodenough e t al, Water Treatment with Polybromide Resin Packets. 13. U.S. Patent 3,462,363, Mills, Control of Microorganisms with Pol yhali d e Resins. 14. U.S. Patent 3,772,189, Kreusch e t al, Iodine Treated Activated Carbon and Process of Treating Contaminated Water Therewith. 15. U.S. Patent 3,817,860, Lambert & Fina, Method of Disinfecting Water and Demand Bactericide for use Therein 16. U.S. Patent 3,923,665, Lambert & Fina, Demand Bactericide f o r Disinfecting Water and Process of Preparation 17. U.S. Patent 4,187,183, Hatch, Mixed-Form Polyhalide Resins f o r Disinfecting Water 18. U.S. Patent 4,190,529. Hatch, Mixed-Form Polyhalide Resins f o r Disinfecting Water 19. U.S. Patent 4,238,477, Lambert & Fina, Process of Preparing Homogeneous Resin-Polyiodide Disinfectants 20. U.S. Patent 4,420,590, Gartner, Bacteriocidal Resins and Disinfection of Water Therewith 21. U.S. Patent 4,594,392. Hatch, Synergistically Stabilized Mixed Form Halogenated andlor Interhalogenated Resins for Disinfecting Water. 22. U.S. Patent 4,999,190, Fina e t al., Preparation of Is Polyiodide Disinfectant Resins. 23. U.S. EPA - Report of Task Force on Guide Standard and Protocol for Testing Microbiological Water Purifiers, April, 1986

REMOVAL OF METALS FROM DILUTE AQUEOUS SOLUTIONS BY BIOSORBENTS

K.A. Matis, A. I. Zouboulis, L. V. Ekateriniadou Chemistry Dept., Aristotle Univ. (Box 116), GR-540 06 Thessaloniki, Greece

I. C. Hancock, T. Butter and A. N. Philipson Microbiology Dept., The Medical School, Framlington Place, Univ. Newcastle, Newcastle upon Tyne NE2 4HH, U.K.

1 INTRODUCTION

Process waste streams from mining operations, metal plating facilities, electronic device manufacturingoperations, etc., contain dilute concentrationsof heavy metals. The ground water surrounding many manufacturing sites, nuclear fuel processing and military bases is also often contaminated with low levels of toxic metal ions (such as cadmium). Several materials were suggested in the literature as suitable sorbend or even biosorbentsz. Biosorption constitutes today a potential alternativeto existing removal technologies. After metal loading the biomass must be separated from solution using for instance filtration, sedimentation,or centrifugation.It was advocated3that such a process scheme is not efficient. For this reason, immobilization technology was used4, to convert biomass into a form whereby it can be employed in modes similar to that of ion exchange resins. Further, magnetite was added to chitosan beads, during the casting process, to incorporate the magnetic component and facilitate separation5. A multi-stage process has been proposed for the removal of aqueous cadmium, at low concentrations, from industrial effluents and other metal contaminated water&. Such a process would contain the following steps: i) Contacting biomass of microbial origin with the metal containing waste stream so that biosorption of the metal ions can occur; a stirred tank contactor was applied for surface binding, where the biosorbent was suspended in the liquid. ii) Separation by flotation of the biomass from the aqueous phase, which can then be discharged; flotation is a known separation technique, primarily from mineral processing7. No loss of ultrafine biomass particles was foreseen, in this way. iii) Elution of the biosorbed cadmium ions from the biomass, at a high concentrationand recovery of cadmium, in the form of metal (end product). iv) Recycling of biomass and eluant, wherever possible. The biomass selected for this project consisted of dead actinomycetebacteria of the genus Sfreptomyces; the used bacteria grow as a branched, filamentous, flocculent biomass. Gram-positivebacteria, such as the actinomycetes,exhibit several features that make them of potential value for metal biosorption8. Contacting mobile, fine particulate sorbents (such as zeolites, activated carbon, mineral fines, etc.) in suspension with ionic metallic species in solution using a CSTR type equipment is an effective method for sorption (or ion exchange), due to the high surface area for sorption sites. Foam flotation has been investigated as a successful S L

236

Progress in Ion Exchange: Advances and Applications

separation method downstream9.10 and the combined process was termed biosorptive flotation2. The problem of fine particles and their separation have been recently overviewed, as well as the various available flotation techniques, as dispersed-air or dissolved-air flotation7.The surface-basedconcentration methods offer many advantages.

2 EXPERIMENTAL Commercially used streptomycetes (a by-product of an antibiotic process) and strains from the Newcastle collection were examined. Streptomyces clavuligerus, a waste product of industrial fermentation producing clavulanic acid was mostly tested as sorbent (kindly supplied by SmithKline Beecham, UK). The application of a flotation technique to accomplish the separation of cadmiumloaded biomass, following metal sorption, was proposed after preliminary tests. The use of a sedimentation step instead would give much lower rates, as showed (biomass is a light material). Microfiltrationwas also problematic. Experimental details have been earlier given elsewhere219.An around 11 mg/L Cd2+ (10-4 M) solution was the feed to be treated and biomass was added at a concentration of 1 g/L, with a low-speed mixing for 900 s. The joint pilot testwork was gratefully carried out in the Environmetal Engineering Laboratories of the Civil Engineering Department, University of Newcastle upon Tyne.

3 RESULTS AND DISCUSSION Dead biomass was used as the sorbent material for cadmium removal, offering simplicity in its use (due, for example, to the toxicity of effluents, maintenance and nutrient supply problems, etc.), but also higher sorption ability than similar alive bacteria, as proved. Biosorption of cadmium is a quite fast process, starting at pH values over 4 approximately;attention should be paid to metal speciation in dilute aqueous solutions. A comparison was attempted, as far as loading was concerned, with other metal sorbents and biosorbents'O. The behaviour of (un-cross-linked) chitosan powder and 1 mm prepared beads did not have any advantagesover the immobilized one$. It was shown that most of actinomycetesbivalent metal cation-bindingcapacity can be attributed to anionic groups in the cell wall. S. clavuligerus biomass is a cheap byproduct, which exhibits a high loading capacity and high affinity for cadmium; thousand of tons of residual biomass are produced each year from industries. A study of c-potential measurement of streptomycetes was also reportedlo. An isoelectric point around pH 2 was found. It has been already published2 that dissolved-air flotation was a possible separation technique of metal-loaded biomass, following cadmium biosorption. Figure 1 presents typical laboratory, first-cycle results; it is shown that particularly over the solution pH of about 6 a frother, like ethanol, was necessary for efficient recovery by dissolved-air flotation. Table 1 presents respective continuous flow laboratory work. A 30% recycle ratio was found necessary, in presence also of a cationic surfactant, cetyl trimethyl ammonium bromide, applied as collector. Increasing the biomass concentration in the suspension, required a parallel increase of the used collector, for effective biomass recovery. Some problems appeared with separation at low cadmium presence]1. Except the pH above examined, ionic strength varied with the addition of salts, like sodium chloride (and sulphate1O) was another parameter quite critical to flotation and also biosorption, needing careful control. The application of a surfactant improved flotation

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231

recoveries under certain conditions, as presented in Figures 2 and 3. It is noted that the shown pH value applied of 3.9 was the lower limit for sorption; however, at pH 10.1 also tried (not shown in the figures), the ionic strength was not found to influence Cd biosorption. Figure 4 shows the also good results with a laboratory grown actinomyces (A825). New isolates from cadmiumcontaminated soil showed no advantage, in terms of binding capacity, but some strains exhibited a much higher affinity for Cd. The correlation of high cell wall content of particular types of phosphate-containing polymers with high Cd binding capacity and affinity provided a method for rationally searching for improved strain&. This time (in the figure) the dispersed-air flotation technique was effectively used. More results with dispersed-air flotation have been publishedgil0. It was apparent that both techniques were applicable in this system. Often, a filter aid of diatomaceousearth type, celite was also present in the suspension treated, as it was used by the industry; no metal sorption on the filter aid was found. However, celite could be also separated by flotation. From the point of view of the possible elution of cadmium from floated biomass, many successful alternativeshave been realised, for instance a complexing agent. The use of EDTA as eluant was observed to create problems in the next cycles, for both biosorption and flotationlo. A simple salt, sodium sulphate was further applied. The effectivenessof the latter was due to the fact that biosorption seemed actually to follow an ion exchange mechanism, between cadmium and sodium in this case. An equilibrium stage was reached between the concentration of metal ions in solution and the amount bound on (or eluted from) the biomass solid phase. Recycled biomass, from which cadmium had been desorbed, exhibited excellent performance in a subsequent biosorption cycle. Recovery of cadmium from the eluate has been also investigated at the end of the conceptual process, by the use of a rotatingcathode electrolyticcell. Table 2 presents some of the results from pilot testwork with five consecutive cycles comprising biosorption, flotation and elution each. All the biomass floatability recoveries obtained were considered very acceptable (all were >96%). Nevertheless, a decrease of cadmium sorption can be noticed (down to 25%), possibly due to the use in each cycle (as required) of the surfactant; hence, a concentration in excess of a quaternary ammonium compound on biomass surface, which was possibly stereochemically preventing and depressing Cd sorption. During elution, the collector was found to mostly remain on biomass. It is noted that many interfacial processes are quite sensitive to surface coverage and the presence of various modifiers’. Different alternatives have been recently investigated for the forementioned. Among them, the application of a primary amine (i.e. dodecylamine) instead of CTMA-Br, as presented in Figure 5. The flotation results were good up to a pH value of 6 approximately. In the same figure, a comparison is shown with the case of no biomass present, which illustrates the advantages of applying the biosorbent; cadmium removal was found to follow a precipitate flotation mechanism, as described in detail previously12. Meanwhile, the possible effects of dodecylamineused in consecutive cycles on Cd sorption was examined (see Table 3), showing possibly a solution to the problem. The application of a common coagulant, such as aluminium sulphate, is another alternative. Satisfactoryflotation recoveries have been obtained and without the use of a surfactant, as presented in Figure 6. Cadmium removal was again not affected. Concluding, the waste biomass from the antibiotic fermentation industry, which was studied as a sorbent in the present, had considerablepotential in cadmium biosorption; it exhibited substantial capacity and affinity for the heavy metal. The actinomycetes generally have a high surface area with a large fixed anionic charge within their thick. porous cell walls. They are also very diverse in their cell-surface chemistry, offering the possibility of some selectivity of metal binding.

Progress in Ion Exchange: Advances and Applications

238 Re% 100

80

60

40

20 __ -8- Biomass

0 2

*

I

I

I

I

I

3

4

5

8

7

-& Elom.-no ethanol

Cd 1

8 PH

I

I

I

9

10

11

1

I

1 2 1 3

Fispre 1 Influence of solutionpH on the obtained resultsfor cadmium removal and biomass recovery by dissolved-airflotation: application of S. clavuligerus, with and without ethanol (aspother).

1.000E-05

1.000E-04

1.000E-03

0.01

0.1

1

INaCII, M

Fispre 2 Effect of ionic strength, adjusted byforeign salt addition,at pH 3.9, on Cd biosorption on S. clavuligerusand dispersed-airflotation (without any SU~&rnt).

Resins as Biosorbents

239

Table 1 Laboratory dissolved-airflotation experiments of metal-loaded biomass in continuousflow (unwashed Streptomyces chuligerus, 41 % solubility; CTM-Br 1xlH

M & ethanol 0.5%; initially 5 L feed alpH 7;retention time 600 s).

Table 3 Applicationof dodecylumine asfrotationcollector: effect on mylticycle biosorption-elutionof cadmium ( I x 10-4 M Cd initially,and I x 10-4 M of surfactant added each time).

No. of cycle

Cd sorbed

Cd desorbed

(%)

(%I

1

97.9

87.0

2

99.6

90.2

3

100.0

100.0

4

89.3

86.0

5

100.0

97.7

BIOSORFTNE FLOTATION 5th cycle

BIOSORFTIVE FLOTATION 3rd cycle

BIOSORFTIVE FLOTATION 1st cycle

ELUTION

ELUTION

BIOSORF'TIVE FLOTATION 4th cycle

BIOSORPTIVE FLOTATION 2 n d cycle

shown below: Biomass I glL dry (0.71 g + 0.29jlter aid), treated with eluant and unloaded.

ELLITION

ELUTION

natural): the flowrate and the amount of surfactant were the parameters examined, and the resulted Cd removal and biomass recovery are

Table 2 Continuouspilot testwork of biosorption-potation (cadmium sorption in a 40 L clarger, dispersed-air flotation cell 1.6 L; p H

F

0

Resins as Biosorbents

24 1

4 SUMMARY Biosorption of heavy metals such as Cd2+ by dead biomass has been recognised as a potential alternative to existing removal technologies applied to wastewater treatment. Bacterial strains and industrial by-products, belonging to actinomycetes were studied for this in the laboratory. Foam flotation was proposed as the solidfliquid separation stage following biosorption and various parameters affecting the former were investigated. The results were promising. 5 ACKNOWLEDGEMENTS

This paper was a part of a European Community Environment programme (contract no. EVWA-CT92-0003). Thanks are due for their help in many ways to Dr. N. K. Lazaridis and Prof. D. A. Kyriakidis (Chemistry Dept., Aristotle Univ.), and also to Ms. L. Evisson (Civil Eng. Dept., Univ. Newcastle upon Tyne). References 1. S. Mandjiny, A.I. Zouboulis and K.A. Matis, Sep. Sci. Technol., 1995, 30, 2963. 2. K.A. Matis, A.I. Zouboulis and I.C. Hancock, ibid., 1994, 29, 1055. 3. C.L. Brierley, J.A. Brierley and M.S. Davidson, "Metal Ions & Bacteria", T.J. Beveridge and R. Doyle (eds.), Wiley, Chishester, 1989, p. 359. 4. T.H. Jeffers, C.R. Ferguson and P.G. Bennett, "Mineral Bioprocessing", R.W. Smith and M. Misra (eds.), TMS, Warrendale, 1991, p. 289. 5. G.L. Rorrer, T.-Y. Hsien and J.D. Way, I d . Eng. Chem. Res., 1993.32. 2170. 6. European Commission, 2nd Europ. Recycling Workshop, Report EUR 16155 EN, Brussels 1994, p. 33. 7. K.A. Matis (ed.), "Flotation Science and Engineering", Marcel Dekker, N. Yolk, 1994. 8. I.C. Hancock, "Trace Metal Removal from Aqueous Solution", R. Thomson (ed.), RSC, London, 1986, p. 25. 9. K.A. Matis, A.I. Zouboulis and I.C. Hancock, Bioresource Technol.,1994,49, 253. 10. K.A. Matis and A.I. Zouboulis, Biotechnol. Bioeng., 1994, 44, 354. 11. K.A. Matis, A.I. Zouboulis and I.C. Hancock, "Biotechnology '94", Envir. Biotech., IChemE, Brighton, 1994. p. 86. 12. A.I. Zouboulis and K.A. Matis, IAWQ-IWSA-AWWA Joint Specialist Conf. "Flotation Processes in Water and Sludge Treatment", Orlando, Florida, 1994, p. 271.

Part 4 Ion Exchange for Environmental Clean-Up

ION EXCHANGE - FUTURE CHALLENGES/OPPORTUNITIESIN ENVIRONMENTAL CLEAN-UP

H Eccles British Nuclear Fuels plc SpringfieldsWorks Salwick PRESTON Lancashire PR4 OW UK ABSTRACT The ion exchange industry which has developed significantly over the last five decades, is now a worldwide billion pound industry. The application of ion exchange materials varies from the treatment of liquid effluentsto the purification of chiral molecules.

This paper will address a specific area of application, namely environmental clean-up. As society becomes ever more increasingly aware of environmental issues, pressures on governments to legislate for more stringent environmental controls, will demand that industries employ cleaner technologies and, for the moment, end-of-pipe solutions. An abundance of EU environmental directives has been adopted by the UK and more will have to be adopted before the end of the millennium. Could this mean further growth for the ion exchange industry? This may not be so, because competing separation technologies are now finding favour. These technologies will be described with specific reference to the potential for industrial applications. 1. INTRODUCTION

The estimated world market for ion exchange resins (organic polymeric materials) is of the order 550 million dollars, with the US accounting for approximately half this value. For the last couple of years, however, the market has been flat and manufacturers in the US and in Europe are struggling to compete against government subsidised imports from Asia and Eastern Europe. Furthermore, the biggest market for resins - water treatment - is shrinking as reverse osmosis membranes (ROM’s) are increasingly capturing a greater market share. Prior to the mid-l980s, the market for ion exchange resins was growing 8 to 10 per cent annually, a decade later this figure is nearer 2 to 3 per cent a year.

246

Progress in Ion Exchange: Advances and Applications

Despite this prospect, ion exchange manufacturing capacity is increasing and will continue to do so for the foreseeable fbture. So, what are the prospects for ion exchange resins and what could be the competing technologies in the fbture ? This paper will briefly explain how ion exchange resin manufacturers are attempting to meet this challenge; describe the developing environmental technology market, and review the competing technologies for metal removal from aqueous streams and liquid effluents.

2.

CURRENT DEVELOPMENTS IN ION EXCHANGE RESIN TECHNOLOGY

The following examples of the more recent developments of ion exchange resins are by no means exhaustive, but they are seen by those representing the industry (mainly marketing/product managers) as being the major ones. Few developments, if any, address the manufacture of truly new and novel ion exchange resins. US ion exchange resin manufacturers are, however, exploring creative ways to add value to their products. About two years ago, Sybron Chemicals Co introduced Impact Ion Exchange Resins for semi-conductor manufacture and other applications where high strength resins are required. A few years ago, it seemed the market was highly receptive to uniform particlesize resins; a technology Dow Chemical Co invented about thirty years ago. Since then, some of the euphoria has waned. Developed for ultra-pure water processing in the electronics, pharmaceutical and biotechnology industries, uniform particle resins have had an insignificant impact on the profits of their manufacturers. To stem the tide of defection from ion exchange resins, some manufacturers are trying to persuade US operators to switch to counter-current processes, which most agree, is more cost effective and environmentally sound than the co-current method that most of them use. Counter-current ion exchange is a method of operating a column in one flow direction during the service cycle and in the opposite direction during the regeneration cycle. The sequence can be either downflow service with upflow regeneration or upflow service with downflow regeneration. In co-current operation both service and regeneration flows are in the same direction, usually downward. The problem is that during regeneration, hydrogen ions displace calcium, magnesium and sodium ions from the top to the lower regions of the bed. Excessive amounts of regenerants are needed to eradicate the hydrogen ions otherwise they accumulate towards the bottom of the bed. In the subsequent service cycle, the hydrogen ions re-exchange with residual metal ions, eg. sodium, to cause sodium leakage.

Ion Exchangefor Environmental Clean-Up

247

In the counter-current process, the residual ions are at the top of the bed, with hydrogen ion at the bottom. There is little or no contact or opportunity for leakage to occur. In the US, unlike Europe, operators have shunned counter-current systems because they appear to be more expensive and require more technical labour. This reluctance is being addressed by resin manufactwen such as Rohm and Haas in collaboration with equipment manufacturers, (Guelph, Ontario, Canada), by optimising contactors so that a smaller counter-current system has the process capability and cost efficiency of a larger co-current unit. For example, 300 gallons per minute of watex can be processed in a co-current system, with an eight inch diameter vessel filled sixty per cent with resin. A comparablejob could be done with a packed-bed counter-current unit fitted with a five inch diameter vessel. Counter-current systems will reduce the amount of sulphuric acid and hydrofluoric acid needed to regenerate ion exchange resins, but other companies are looking for ways to eliminate the hazardous chemicals altogether. Safer chemicals is but one option. Methane sulphuric acid (MSA) is proving to be a safe and cost-effective alternative for some applications. In electroplating,semi-conductor and film o p t i o n s that use MSA, non-ferrous metal can be removed from the process stream, reclaimed and recycled. No chemicals are used in the continuous de-ionisation process patented by US FilterAon pure (Lowell, Mass.).Instead, it uses a combination of ion exchange resins, ion exchange membranes and electricity to produce high-purity water. Throughout the process, ion exchange resins are regenerated by an applied electric potential. Despite these developments, ion exchange resin technology se has changed little during the last twenty or so years. Are new opportunities needed to spur more novel developments, and if these opportunities arise will alternative emergent technologiesbe more favoured ? The demand for environmental technology is on the rise around the world, could this market opportunity be the stimulusfor the ion exchange resin industry ?

3. ENVIRONMENTAL TECHNOLOGY By definition, environmental technology covers a broad spectrum of activity, ranging from services to products that reduce or prevent damage to the environment. Demand for these services or goods heads only upwards; developing nations want improved quality of life, whilst developed nations are ever fussier about pollution and waste.

248

Progress in Ion Exchange: Advances and Applications

More companies are realising that cleaner production can mean savings on energy and raw materials - a theme which will be considered later. The exact market value of environmental technology (ET) is difficult to predict, but the Organisation for Economic Cooperation and Development (OECD) has estimated a 200 billion dollar world market value in 1990. It projected a value of 300 billion dollars by the year 2000, equivalent to a 5.5 per cent per annum growth rate (Table 1). Other estimates by the Environmental Business International (EBI) and Ecotec have indicated figures of 295 billion dollars in 1992, reaching 426 billion dollars by 1997, and 2 10 billion dollars in 1992, and 570 billion dollars by 20 10 respectively. However crude, the sums suggest that the global ET market is about the size of the aerospace products business, or half as big as the chemicals industry. The ET market for Western Europe was about 60 billion dollars in 1992, and should grow at a rate of roughly five per cent annually, reaching almost 80 billion dollars by 2000, according to the OECD. Four major market sectors, as illustrated in Table 2, account for nearly ninety per cent of the total ET market.

Table 1

us Canada Germany France UK Netherlands , IMY Japan OECD Non-OECD TOTAL

Environmental Technology Markets ($ billion)

lpeQ

2QQQ

Growth % Demnum

78 7 17 10 7 3 5 24 164 36

113 12 23 15 11 4 8 39 245 55

5.4 5.0 4.0 5.5 6.3 4.1 6.0 6.7 5.5 5.9

200

300

5.5 (average)

The annual growth rate is largely influenced by the environmental standards adopted by respective European countries. Denmark, Germany (West), the Netherlands, and Finland, for example, with more strictly enforced standards, are seeking “cutting edge” environmental technologies, rather than basic equipment or incremental improvements to existing technology. Consequently, the markets are comparatively small (less than 3 billion dollars, except for Germany), with slow annual growth rates (3 to 5 per cent).

Ion Exchangefor Environmental Clean-Up

Table 2

249

Environmental Market Sectors in Western Europe ($ billion)

On the other hand, the UK, Belgium, France, northern Italy and Ireland are now striving to meet EU standards and markets are now, after the recession, starting to grow; typical growth rates are about 6 per cent per annum. The final group, comprising Greece, Portugal, southern Italy and Spain are using EU aid programmes to upgrade environmental infra-structure and markets which exist for all types of ET. Waste water treatment is a pressing problem, but other opportunitiesexist in waste management sg. Annual growth rates are around 8%. The fastest growing environmental sector in Western Europe is contaminated land remediation; over 60,000 sites need clean up. Another growth area is waste treatment. As landfUs become scarce and controls more strict, this market is estimated to triple by 2000 to around 7.5 billion dollars.

By far the largest producer and consumer of ET is the US, accounting for about two fifths of the global market. Pollution abatement spending has risen, according to the Environmental Protection Agency (EPA) estimates, from 52 billion dollars in 1972 to 108 billion dollars in 1990 (1.95 % GDP). Further growth is being driven by new regulations like the 1990 amendments to the Clean Air Act, and by decommissioning of old military sites. More recently, however, the US White House announced “that it was committed to promoting a new generation of innovative environmental technologies that will give a healthier environment, a greater market share for US companies and more jobs for American workers”.The plan, described in a report “Bridge to a Sustainable Future” aims to move from an era of waste management to one of pollution prevention. Whether industry is seeking end-of-pipe solutions to tackle the legacy of environmental mis-management or, with foresight, is developing cledcleaner process technologies, then in both cases the market potential is enormous. Separation, purification and concentration technologies are needed in either case. Ion exchange being a well proven and accepted technique should be capable of capturing a significant share of this developing market.

250

Progress in Ion Exchange: Advances and Applications

4. COMPETING TECHNOLOGIES Although ion exchangeladsorption techniques have been used for more than 5,000 years, they have, in the last twenty years or so, come under significant pressure from other separation technologies. Some of these competitors will be described in this section, with reference to the more recent publications. The pursuit of more novel ion exchange resin systems has not been totally abandoned, and some noticeable developments within the last five years or so will be initially described for completeness. 4.1

Ion exchange resin systems

The quest to prepare and characterise new chelate ion-exchange resins remains undeterred. Preparation of materials which have greater selectivity and more rapid exchange kinetics compared with the current commercially available chelate ionexchange resins is judged by numerous workers as paramount. A cellulose based material containing diethylenetriamine tetra-acetic acid, Ostsorb DTTA, has been prepared and evaluated by a group of Czech workers (1). The characteristics of the spherical cellulose beads were compared with the vintage chelate ion-exchanger Dowex A-I (imminodiacetic acid resin). The workers concentrated their comparative studies on lead sorption from acid solutions, in particular those of pH value 6. Although their resin has a significant faster lead equilibration rate (15-30 minutes to achieve saturation) compared with Dowex A-I (70-90 minutes), Ostsorb DTTA had an inferior lead capacity (210 mg g-') compared with the Dowex A-I value of 1100 mg g-' . Furthermore, except for the alkaline earth metals, other heavy metals, when present in solution at concentrations higher than that of lead by a factor of 100, significantly decreased the lead sorption efficiency. The alternative preparative approach to chelate ion exchange resins, namely impregnates using an available, preferably commercial, chelating agent, is still being pursued some twenty years after the first publication describing these materials. In this period, numerous chelates have been studied, with more recent attention devoted to elaborate extractants such as crown ethers. Workers at Oak Ridge National Laboratory have incorporated the tetradentate macrocyclic ionophore tetrathia-14-crown-4 (TT14C4) into strong acid poly(styrene-divinyl benzene) cation exchange beads (2). Although the workers demonstrated several advantages of this approach, not least, the synergistic effect of the polymer host matrix for copper extraction, the problem of extractant leakage was still noticeable.

25 1

Ion Exchangefor Environmental Clean-Up

The workers concluded that further work is required to improve cycle lifetimes, to optimise preparative techniques and determine the best combination of macrocycle and host polymer matrix. Some recent work has concentrated on the synthesis of new types of microporous adsorbents selective for transition metals. One group of workers have synthesised a porous polymer containing ally1 acetylacetone (3). Unfortunately, the polymeric material (in sheet form) had a low copper capaciy (8.9 mg g-') which is significantly less than conventional resins of typically 60 mg g' . A second, similar type of material developed out of the NASA space battery programme was an ion exchange material (IEM) which was highly effective for Pb, Cu, Hg, Cd, Ag, Cr (111), Ni, Zn, Y (4). The IEM is composed of a cross-linked polyvinyl alcohol and polyacrylic acid and Figure 1 illustrates some of the metal profiles of this polymer.

Figure 1

Precipitation of Metals with Caustic Soda

4 -X-Zn

2

6

4

8

lo

pl

4.2

Precipitation and Filtration

Heavy metal bearing liquid effluents have traditionally been treated by the adjustment of the pH with lime or caustic soda to precipitate hydrated metal oxides. The process technology required is simple but not selective as Figure 2 illustrates. Sometimes a sulphide compound or other materials are added which cause the production of heavy metal compounds with lower solubility products (Table 3).

Progress in [on Exchange: Advances and Applications

252

Removal of the heavy metal precipitate is then accomplished, usually by settlement, occasionally followed by a polishing technique such as sand filtration. With the advent of more stringent environmental legislation regarding the quality of the final disposal stream, and the need to intensify the solid-liquid separation process, the use of cross-flow filtration is becoming attractive.

Figure 2

Metal Adsorption by the new IEM as a function of the solution pH 100 90 80 70 60 50 40 30 20 10 0

pH 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 Hg

Table 3

Cdr Cur

Znx

Metal Cation Solubilities : Ks at 25 ‘1c (5)

METAL

HYDROXIDE

SULPHIDE

Ag

2x

1.6 8.5 x lo4’

cu

Zn Ni co Fe Cd

1x 1020 1 10’’’ 1 10‘‘~

1 x 1Ol5 1 1

1014

1.2

10 2 3

1.4 3.0 x loz6 3.7 1 0 - l ~ 3.6 1019

An Anglo-Australian group (6) demonstrated the efficiency of cross-flow filtration compared with clarificationusing gravity settling (Table 4).

253

Ion Exchange for Environmental Clean-Up

Table 4

Cd Cr Ca Pb Hg Ni Zn

Comparison of metal removal by cross-flow micro--1trationand clarifierpilot tests

2.44 7.24 9.98 4.88 8.00 13.00 71.20

0.06 0.10 2.14 0.62 0.15 1.62 5.46

0.04 <0.08 1.48 0.42 0.08 1.16 1.63

Following extensive pilot-plant and full scale studies using a variety of metal precipitants such as lime, sulphide and diethyl dithiocarbonate (DTC), the group concluded that cross-flow microfiltration offers a very efficient method of treating mixed heavy metal containing effluents, where a high degree of treatment is necessary. It requires the minimum of civil engineering, operates at low hydraulic residence time, carries a high solids concentration, and is not affected by wide variations in feed eMuent quality. Cross-flow filtration is a more expensive technology than conventional clarification techniques and is, therefore, only a practical method of removing heavy metals in those situations where very high quality discharge is sought. 4.3

Solvent Extraction

Liquid-liquid extraction, or as more commonly referred to these days as solvent extraction, has found favour in several process industries for treating metal containing solutions of relatively high metal values. Since metal selectivity of the separation process can be engineered by the judicious selection of the extractant it offers some unique advantages over other separation processes. In recent times solvent extraction has been evaluated for liquid effluent treatment. Although the technology is relatively rarely applied in the Czech Republic, its potential for treating cadmium and lead and zinc rinse waters has been evaluated (7). Using a battery of mixer-settlers and 20% by volume trisoctylamine, for cadmium chloride extraction and a 0.8M di-2-ethylhexyl phosphoric acid in an aliphatic industrial solvent for lead and zinc, metal values of a 27 mg I-' cadmium solution and 212 mg I-' lead and 1970 mg I-' zinc solution could be reduced to lOpg I-', 21pg I-' and 42pg K' respectively.

Progress in Ion Exchange: Advances and Applications

254 4.4

Membranes

Membrane technology can be categorised into three groups, namely i) filtration ii) supported liquid membranes (SLM) iii) emulsion liquid membranes (ELM). Filtration membranes are essentially microporous barriers of polymeric, ceramic or metallic materials which are used to separate dissolved materials (solutes), colloids, or fine particulate from solutions. Pressure-driven membrane processes are generally further classified into four categories based on the mean pore size of membranes :

-

-

hyperfiltration (HF) or reverse osmosis (RO), which typically separates materials less than 0.001 pm in size such as the separation of monovalent salts from water, as practised in the desalinationof seawater and brackish water. nanofiltration(NF), which separates larger size molecules such as sugars and divalent salts while allowing passage of monovalent salts ultrdiltration (UF), which is used to separate materials in the 0.001 to 0.1 pm range, such as proteins or colloids and finally microfiltration (MF), which is used for sterilisationby removing insoluble particulate materials (microbes) ranging in size from 0.1 to 10.0 pm.

RO units (8) have been used to treat :

i) ii) iii) iv) v) vi) vii)

acid mine drainage (AMD) flotation water copper smelting and refining wastewater mill waste waters uranium waste waters dilute gold cyanide solutions ammonium and nitrate bearing effluents.

In SLM’s the organic liquid membrane is present in the pores of a polymeric support iembrane where metal is extracted into the pore liquid at the feed solutionmembrane interface. SLM’s have suffered in the past from instability, resulting from the loss of membrane by solubility, osmotic flow of water across the membrane, progressive wetting of the support pores and the pressure differential across the membrane. Ways to eradicate these problems have been extensively researched with some noticeable successes (9).

255

Ion Exchange for Environmental Clean-Up

SLM preparations have involved a variety of metal extractants and solid support materials, as illustrated in Table 5.

Table 5

SLM Preparations

hollow fibre a-alumina/silica polypropylene

EXTRACTANTI

METALSREFERENCE

DILUENT

REMOVED

LIX 84* in heptane Tri-n-octylamine

cu Cr Hg cu cu Cd Zn

LIX 84* in kerosene Bathocuproine, Bathophenanthroline Neocuproine

10 11 12

Pb

* LIX 84 is 2 hydroxy-5-nonylacetophenoneoxime

co

ELM'S first invented by Li (13) are made by forming an emulsion between two immiscible phases. Usually stabilised by surfactants,the water in-oil emulsion contains the extractant in the oil phase and the stripping reagent in the aqueous receiving phase. The emulsion is then dispersed by mechanical agitation into a feed phase containing the metal to be extracted. Combining the extraction and stripping processes removes equilibrium limitations and reduces metal concentrations in the feed to very low levels. De-emulsification by the application of a high voltage electric field has proven to be most efficient.

This technology has been successfully applied to several and diverse situations, two such applicationsare briefly reviewed in Table 6. Table 6

ELM Composition

tetradecane

D2EHPA

ECA5025

Isopar L

P5100

Paranox 100

Pb(ii) Cd(ii) Cu(ii)

14

15

256

4.5

Progress in Ion Exchange: Advances and Applications

Microorganisms and Biomaterials

Over the last twenty five years or so, the evaluation of microorganisms and biomaterials for removal of metals from aqueous streams has progressed from curiosity via fimdamental understanding to, more recently, applications. The number and type of materials studied appears to be exhaustive ranging from waste biomass (yeast) from the brewing industry, to microorganisms isolated from natural environments such as soil and water. In general, workers have isolated microorganisms from numerous environments which have expressed on them some unique capability, be it tolerance to toxic heavy metals or metal selectivity. Alternatively, waste biomasses which are discarded in significant quantities from a variety of industries have been considered as good metal adsorbents, largely owing to their cheapness. In general these materials lack metal selectivity and hence attempts to improve this characteristichave been reported (16). Microbial cell walls tend to have an overall negative charge. The surface charge is caused by dissociation of chemical groups, such as carbonyl groups, on the cell wall. Negatively charged groups found on the polymers, that constitute the cell wall, allow for cation exchange while other chemical groups allow coordination of metal cations. Biomass contains many “softer” metal binding sites and, therefore, has greater heavy metal binding affinity than for alkali and alkaline-earth metals. Typical metal capacities for a variety of recently studied materials are reported in Table 7. Numerous studies have concentrated on the biochemical engineering of contacting liquid with microorganisms. Encapsulation, immobilisation techniques as well as various bioreactor designs have all been considered. One such approach involves the use of granular activated carbon as an inert support for biofilms. Workers at the University of Bath (19) showed that a biofilm of Pseudomonus sp on GAC was not only capable of adsorbing copper, zinc and nickel (respective metal uptakes (mg g-’ GAC) 0.85,0.78 and 0.4), but also atrazine (a common herbicide for controllingweeds). One of the more obscure biomaterials recently evaluated is hen egg shell membrane. Japanese researchers (20) have demonstrated that this material has high affinities for a variety of metal ions (Table 8). They proposed that HESM may contain high proportion of sulphydryl and disulphide groups which may be responsible for precious metal binding.

Ion Exchangefor Environmental Clean-Up

Table I

257

Metal Capacities of a Variety of Biological Materials

BIOLOGICAL METAL MATERIAL

ISIY

Saccharomyces Cerevisiae

cu Cd co Ag Cd co Cr cu Ni Pb Zn Cr

Streptomyces noursei

Sawdust Sugar cane bagasse Sugar beet pulp Maize cob

CAPACITY

&my

REFERENCE

materinn

6.2

25.4 19.1 6.5 38.6 3.4 1.2 10.6

6.0 6.5 5.8 5.5 5.5 5.9 6.1 5.8 6.0 2.0

16

17

9.0 0.8 36.5 1.6 3.3 13.4

2.0 1.5

18

17.2 13.8

Table 8

Metal Capacities of Hen Egg Shell Membrane mg g-' (HESM)

Metal ion pHvalue Capacity

Fe(ous) Cu 4.0 6.0 4.0 9.5

Zn

Ca

2.0 12.5

6.0 6.5

6.0 2.5

Metalion pHValue Capacity

Ag

Cd

co

Au

Pt

Pd

6.0 15.0

6.0 15.0

6.0 8.0

4.0 550

4.0 280

4.0 250

5.

Fe(ic)

SUMMARY

More stringent legislation and maintainance of industrial competitiveness is predicted to be demanding appreciable growth in environmental technology worldwide. This is unquestionable. Which separation technology will be favoured by industry (the customer) in the future is less clear. Precipitation followed by solid-liquid separation and ion-exchange have dominated the preferred technologies for treating heavy metal bearing liquid effluents.

258

Progress in Ion Exchange: Advances and Applications

Ion exchange is now a mature technology and, although well established, other separation technologies have over the past ten years challenged its supremacy. Some alternative technologies such as those involving membranes have been selected because they are capable of offering some unique features for particular applications. There are several other techniques which still reside in the laboratory, but with a more focused approach to their development could come of age in the next decade, thus further diminishing the opportunities for ion exchange resins.

6.

REFERENCES

1.

L. Svoboda, J. Chutny, and M. Tomek, ‘Collect. Czech. Chem. Commun.’ 59, 106-1 18, 1994

2.

B. A. Moyer, G. N. Case, S. D. Alexandratos and A. A. Kriger, ‘AnaLChem.’, 65,3389-3395, 1993.

3.

J. H-K. Yang, J. H. Burban and E. L. Cussler, AZchE Journal, 41, No 5 , 11651170, May 1995.

4.

W. H. Phillipp Jr and K. W. Street Jr, ‘Technology 2003,4th National Technology Transfer Conference and Exposition, Vol 1,266-272, Dec 1993.

5.

C. Fabiani, ‘Recovery of Metal Ions from Waters and Sludges’. ENEA, ISSN/1120-5555, 1992.

6.

G. P. Broom, R. C. Squires, M. P. J. Simpson, and I. Martin, J Membrane Sci. 87,2 19-230, 1994.

7.

M. Cerna, ‘Environ. Monitoring and Assessment’, 34, 151-162, 1995.

8.

F. T. Awadalla, and A. Kumar, ‘Sep.Sci and Tech.’, 29(10) 1231-1249,1994.

9.

0. C. Keller, S. Poitry, and J. Buffle, J.EZectroanaZ.Chem,378,165175,1994

10.

A. K. Guha, C. H. Yun, R. Basu, and K. K. Sirkar, AZChem Journal, 40, No 7, 1223-1228, July 1994.

11.

J. Yi, and L. L. Tavlarides, AZChem Journal, 38, No 12,1957-1968, Dec 1992.

12.

T. Saito, ‘Sep. Sci. and Tech.’, 29(10), 1335-146, 1994.

ton Exchangefor Environmental Clean-Up 13.

N. N. Li, ‘Separating Hydrocarbons with Liquid Membranes’, US Pat 3,410, 794 12 Nov 1968.

14.

B. J. Raghurarnan, N. P.Tirmizi, B-S. Kim, and J. M. Wiencek, ‘Environ Sci Technol.’, 29,979-984, 1995.

15.

J. B., Wright, D. N. Nilsen, G. Hundley, and G. J. Galvan, ‘Min.Eng.’, 8, No 415,549-556, 1995.

16.

D. Brady, and J. R. Duncan, ‘Enzyme Microb. Technol.’, 16,633-638, July

259

1994. 17.

B. Mattuschka, and G. Straube, J.Chem.Tech.Biotechnol.,58,57-63,1993.

18.

D. C. Shams, and C. F. Forster, ‘Bioresource Tech.’, 47,257-264,1994.

19.

J. A. Scott, A. M. Karanjkar, and D. L. Rowe, ‘Min. Eng.’, 8, Nos 1/2,221-230, 1995.

20.

K. Suyama, Y.Fukazawa, and Y.Umetsu, ‘App.Biochem and Biotech.’, 45/46, 871-879, 1994.

Uptake of radioisotopes onto Cerium Phosphate

A. Dyer* and A K J Jasem Department of Chemistry & Applied Chemistry University of Salford Salford, M5 4WT U.K.

Introduction Ion exchange media are widely used both for radioisotope separation and the removal of hazardous fission products from aqueous waste prior to discharge to the environment. The choice of an inorganic exchanger is advised because of their resistance to radiolytic damage and likely high selectivity for specific fission products. Additionally the use of organic resin exchangers creates problems for their safe containment and disposal - even their cement encapsulation should be viewed as a short term alternative. Many inorganic ion-exchanger materials have been investigated and the phosphates of zirconium and titanium are good examples of this interest1. Although several exchangers show promise their utility is often hampered by the physical form in which they can be prepared. Often they are synthesised by simple precipitation from solution, resulting in powders inappropriate for column use. Exceptions to this come in the use of natural zeolites, such as clinoptilolite, in the BNF plc SIXEP process2, and the early use of amorphous zirconium phosphate3. An earlier paper reports the production of various forms of cerium phophate (CeP) appropriate for column use4. This paper decribes a series of experiments designed to test the column efficiency of these forms of CeP for the uptake of caesium and strontium radioisotopes. They include estimates of hydrolysis - a common problem with amorphous phosphates, and also containmenb'leaching studies.

1.1 Experimental and Results The synthesis and characterisation of the forms of CeP studied have been described elsewhere4. This earlier work demonstrated that preparation of CeP in the presence of various inorganic salts gave robust materials (density 3.0 kg dm-3) having maximum cation exchange capacities in the range 4-5 meq g-l . The materials chosen for these studies were those orginating from a synthesis based on sodium chloride (CePNa) and its hydrogen form (CePH), which were used in the ion-exchange investigations, and the ammonium form (CePNH4) chosen for the encapsulatiodleachingexperiments.

-

26 1

Ion Exchange for Environmental Clean- Up

Their compositionsare in Table 1. Table 1 Composition of CeP Form

Formula

CePNI-Q CePH

Prepared from CePNa by elution with 0.5MHCl

Ion-exchange Distribution coefficient (Qml g-1) measurements for 137-Cs showed that CePH was more effective than CePNa in both carrier-free conditions and moderate Cs+ concentrations (Fig 1). Similar results were observed for 89-Sr uptake. Anion capacities were also measured, determined from specific ion electrode measurements, as shown in Table 2. Because of the use of zirconium phosphate for haemodialysis checks of NHq capacity for CePNa were made. This was much lower (0.01 meq g-1) than a synthesised disodium form of zirconium phosphate (3.05 meq g-9. Table 2 Anion capacities of CeP (meq gl) ion

c1-

FNO3-

CePH 0.5 0.2 nil

CePNH4 0.2 0.1 nil

Column experiments 3g aliquots were placed in a column (0.55 cm 0.D)and eluted with 0.15 M NaCYNaOH solution at flow-rates in the range 5-12 ml min-1. The materials tested were CePH and exchangers produced from this form of CeP by re-exchange with Na (CePHNa), Sr (CePHSr) and two samples derived from CePH by exhaustive treatment with 0.5M CsCl (CePHCs) and 0.5M NHqCl (Ce PHNI-Q). The observed breakthrough capacities are listed in Table 3.

Progress in Ion Exchange: Advances and Applications

262

-

-

l

-

6

7

'

.

meqn

Fig. 1 Kdas a function of Cs concentrationfor the uptake of 137-Cs onto CePH(x) and CePNa(V)

-E

2n

12000

-

loo00

-

A

8OOO6Ooo-

0

4Mx)-

2000

-

0

I

,

I

.

I

.

T

.

4 . .

Throughput, mi

Fig. 2 Elution of 137-Cs from CePHNa with 1M NaCl

0

100

200

300

400

Throughput, ml

Fig. 3 Elution of 89-Sr from CePHNa with 0.5M HCI

500

263

lon Exchange for Environmental Clean-Up

Table 3

Breakthrough capacities for 1374s and 89-Sr on various CeP based ion-exchangers for camer free solutions in eluant of 0.15M NaCUNaOH Exchanger

Breakthrough cs 700 325 414 8400 9070

CePH CePHNa CePHSr CePHCs C e P m

(BV) Sr 1614 404 403

-

Results from tests for bed capacities using uptake from deionised water onto the parent materials (CePNdCePH) are listed in Table 4.

Table 4

Bed capacities of CePNa & CePH for Cs+ & Sr2+ Material

ion

meq g1

CePNa

cs Sr cs Sr

0.50 0.35 0.63 0.22

CePH

Some improvement in Sr capacity can be obtained by drying CePH at 14OOC (rather

than the normal 80OC). Elution Experiments Elution experiments were commenced to study (a) acid hydrolysis and (b) for regeneration purposes. Fig 2 shows the effect of 0.5M HCl elution. Regeneration with 0.5M HCl proved better than that by 1M NaCl (see Fig 3) and the regenerated beds had reproducible breakthrough and pH profiles even after 3 regeneration cycles. Batch measurements to determine alkaline hydrolysis showed loss of PO43- in the range pH 811 with a maximum of 4% at pH11, hydrolysis in column studies reached 14% in a 0.1M N Q O WN Q C l eluant.

Leaching Tests Leach tests were made using C e P w preloaded with either 137-Cs or 89-Sr. These labelled materials (AS) were encapsulated into cylindrical moulds (1.2 cm long, 2.0 cm diameter) as mixtures with Portland Cement (PC) Blast Furnance Slag (BFS) and Concreting Sand (CS). The materials were obtained from the following suppliers;

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Progress in Ion Exchange: Advances and Applications

PC - Ribblesdale Cement Ltd, BFS - Frodingham Cement Works, CS - BMSS Ltd UK. The weight proportions used were 1: 0.5:0.5:1; as PC/BFS/CS/AS. Water was added in the ratio 1/2 watedsolid and the resulting mixture fully homogenised. After 24 hrs in the cylinder the composite was removed, immersed in deionised water, and left to cure. The cured composites were leached with deionised water (DW), synthetic ground water (SGWS,and synthetic sea water (SSW6. Analysis of leach profiles followed the method previously used in other work7 whereby diffusion coefficients are generated from the leach curves which express the rates of release of the appropriate radioisotopes from the composite. This method includes the ability to input different geometries and the results in Table 5 reflect this. Data can be produced based upon the assumption that (a) the rate-controlling process is release from the CePNH4 particles or (b) ratecontrolled by the geometry of the composite. This means that comparisons can be made to other data making this latter assumption. Table 5

Diffusion coefficients (m2 s-l) for the leaching processes of 137-Cs and 89- Sr from CePNH4 composites (at 40°C) Leachant

DW SGW

ssw

Particle Composite Controlled Controlled cs Sr cs Sr 2x10-13 2x10-10 7xio-15 2x10-10 6x10-15 1 ~ l O - l ~ 1 ~ 1 0 - l ~ 1xlO-ll 2x1042 2x1012 iX10-15 3xio-15

Conclusions The 'acid' form of CeP shows promise as a material for the scavenging of both 137-Cs and 89-Sr from effluent solutions. It functions over a wide range of pH but suffers from hydrolysis in high alkaline media when used as an ion-exchange column. Acid hydrolysis is much less and CePH can be regenerated by 0.5M HCI. The small anion exchange capacity reflects this. It should be noted that the mode of action of the exchanger (both cation and anion) still remains to be completely resolved. As with all phosphate materials the synergistic relationship between "ion-exchange'' and hydrolytic damage has not yet been clarified. In this context, it is important to record that the CePH material is a bright yellow colour which fades as the ion-exchange capacity is exhausted (but returns on regeneration). This, of course, is a useful property but it implies that the Ce2+/Ce3+ couple is involved in the "exchange" reactions on CePH. Clearly the material in its ammonium form (CePNH4) is compatible with cement encapsulation. Study of Table 5 demonstrates the insensitivity of the approach using the geometry of the composite to analyse leach data. This, to some extent, merely reflects the lack of good fits to experimental data but this is, of course, an example of the inappropriateness of the approach based only on use of the geometries of the composites. Correct use of computed data and fitting procedures can be used to suggest the rate-controlling step to a leaching process, as seen here, and also to indicate if the

Ion Exchangefor Environmental Clean-Up

265

process is controlled by a chemical process rather than that of diffision - demonstrated by lack of fit to either geometrics. The leach rates in Table 5 compare favourably with those from other encapsulates as can be seen from Table 6. The only deviation from this is the relatively high removal of 89-Sr from CePNH4 by deionized water which is surprising.

Table 6

Diffusion coefficients 0). For leaching of 137-Cs and 90 S r N from inorganic ion-exchangedcement composites. Calculations based on the assumption that release of radioisotope from the exchanger is rate-controlling. Exchanger Clinoptilolite (Californian) Clinoptilolite (Indonesian)

Leachant DW SGW

Isotope 137-cs 137-CS 137-CS

Reference 8 8 8

DW SGW

137-CS 137-CS 137-Cs

8 8 8

DW SGW

137-CS 137-CS 137-CS 90-SrN 90-SrN 90-SrN

6 6 6 6 6 6

ssw

ssw

Amorphous Zirconium Phosphate

ssw

DW SGW

ssw

Acknowledgements Both authors are grateful for the free supply of the composite materials from the companies mentioned. One of us (AKJ.9 thanks the Higher Education Ministry of Iraq for financial support.

References 1.

A. Cledield, "InorganicIon Exchange Materials", CRC Press, Boca Raton, Florida, 1982.

2.

M. Howden and J. Pilot, in "IonExchange Technology", D. Naden and M. Streat (Eds.), Ellis Horwood, Chichester, 1984, pg 66.

3.

C.B. Amphlett, L.A. MacDonald, and M.J. Redman, J. Inorg. Nucl. Chem., 1958, 6,220.

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Progress in Ion Exchange: Advances and Applications

4.

A. Dyer and A.K.J. Jasem in Yon Exchange Processes -Advances and Applications", A. Dyer, M.J. Hudson and P.A. Williams (Eds.) Royal Society of Chemistry, Cambridge, 1993, pg. 215.

5.

B. Allard, J. Rydberg, H. Kipatsi, and B. Torstenfelt in "Radioactive Waste in Geologic Storage''. S . Fried (Ed.) ACS Symp. Ser. 100, Washington DC, 1979, pg 47.

6.

H.A. Taylor and A. Kawari, Cement Concrete Res., 1978,8,491.

7.

M. Zamin, Ph.D. Thesis, Univ of Salford 1991 (see also M. Zamin, T. Shaheen and A. Dyer, J.Radioanalytical and Nucl. Chem. Articles, 1984, 182,335).

8,

T. Las, Ph.D. Thesis, Univ. of Salford, 1989.

UTILIZATION OF HYDROUS CRYSTALLINE SILICO-TITANATES (CSTS) FOR REMOVING Cs' FROM NUCLEAR AQUEOUS WASTE

R G. Anthony, Z. Zheng, D. Gu, and C. V. Philip Kinetics, Catalysis and Reaction Engineering Laboratory Department of Chemical Engineering Texas A&M University College Station, TX 77843-3122

1 INTRODUCTION

For the past forty years,' research has been conducted on methods of removing cesium from dilute aqueous nuclear waste. While several materials performed this function, they all had a variety of problems, such as instability to radiation and in highly basic alkaline solutions, which resulted in decomposition to undesirable and hazardous products. A new hydrous crystalline sodium silicotitanate,an inorganic ion exchanger material, was synthesized by Anthony, Dosch and Philip' that was highly selective for cesium relative to sodium, potassium, rubidium and the proton, and it did not have undesirable decomposition products. This new inorganic ion exchanger, labelled TAM4 or CST, was stable to radiation and performed well in acidic, neutral, and basic ~astes~9'~~94'9~*~ with sodium concentrationsup to 7 M. Because of these unique properties, TAM9 has considerable potential for use in the treatment of nuclear wastes. Consequently, TAM4 is currently manufactured and marketed by UOP as IONSW ion exchange powder TYPE IE-910. Treatment of nuclear waste solutions will result in two economic benefits. The first is the removal of the radionuclides from aqueous waste so that the other components of the wastes can be treated as conventional chemical or low activity wastes. This step alone results in a siBnificant cost savings. The second major advantage is the reduction of the volume of radioactivewaste that will have to be stored and monitored for centuries. Zheng et 81." presented a method for estimating the distribution coefficients for cesium in basic, neutral and acidic wastes by using a Langmuir isotherm developed from data in simple simulated waste solutions, i.e., a simulant. The simple basic simulant was 5.1 M NaN03 0.6 M NaOH, and Cs', as CsN03or CsC1. For neutral or acidic simulants, solutions of NaN03 and NaNO with HN03 were used, and in each case the simulant contained 5.7M Na'. Even though good results were obtained for a variety of solutions, the method su€€eredby not including the competitive ion exchange of cesium and sodium with potassium, rubidium and hydrogen. Even though this deficiency could be overcome by developing Langmuir isotherms for each type of simulant, the purpose of a thermodynamic equilibrium model, which is to estimate the performance of the CST for any solution, was not satisfied. Therefore, a model was developed to calculate the

268

Progress in Ion Exchange: Advances and Applications

equilibrium distribution coefficients for different solutions. Data used in developing the model and the results of the model will be presented in this paper.

2 EXPERIMENTAL Equilibrium ion exchange experiments are conducted in simple simulants by using a volume of simulant per gram of CST equal to 100, i.e., in many cases 10 cc of simulant and 0.1 g of CST. The simple simulant consists of 5.7 M Na', 5.1 M NO< and 0.6 M OH. The complex simulants were used to evaluate the predictive capabilities of the model. Compositions of the complex simulants are listed in Table 1.

Table 1. Compositionof Complex Simulants, mole L-I.

**

In addition to these C1- = 0.06, P O: = 0.016. Nitrate is used to complete the charge balance.

Initial caesium concentrations are varied as desired. The NCAW 3 M Na' and 1 M Na' simulants are simply dilutions of the 5 M NB NCAW solution. (3 concentrations were varied over a wide range to obtain Na:Cs molar ratios of lo3 to 1 6 . Since the variation of the Na:Cs ratio was obtained by varying the caesium concentrations, the K:Cs and Rb:Cs ratios were also changing over a wide range even though the molar ratio of Na:K:Rb remained constant at 41.7 for Na:K and lo5for Na:Rb. The desired mixture is charged to a vial, which is placed on a shaker for a period of 18 to 24 hours. Afterwards the contents of the vial are allowed to settle, and an analysis of the supernatefor caesium is performed by atomic absorption or ICP-MS. Experiments conducted at locations other than Texas A&M University or Sandia National Laboratories used radiotracers to determine the distribution coefficient for caesium. This coefficient is defined as follows:

K,

=

(co-ceJ-V- ceg

W

Conc. on the Solid Conc. of solution

The distribution coefficient is widely used in industry and is a measure of the removal of a cation from solution. The assumption, based on a material balance, is that all of the cations removed from solution sorb onto the solid. We have checked this assumption for our experiments and fmd that the vessels used in the experiments do not adsorb or

lon Exchange for Environmental Clean- Up

269

remove the cations from the solution. Therefore, the distribution coefficient for a given cation is the amount of cation ion exchanged onto the solid divided by the concentration of the cation in solution at equilibrium. 3 THEORY

For a multicomponent system at equilibrium Equation (2) can be written:

v,A? +

-

)A ;,.(

+

(VIAI'I)

where, the overline= the ion exchanger phase, i = 1, c: j = 1, c: i z j, and c = number of ion exchange components and sites that are being considered. A, and A, = cations on the solid and in solution, u = stoichiometriccoefficient, and z = valence. For monovalent cations, u=z=l. The equilibrium constants are given by:

A series of experiments were designed to allow the evaluation of the equilibrium constants. The necessary equations were then used along with the equations for the charge balances, the site balances and the ion (K, Cs, Na, Rb) balances to calculate the equilibrium concentrationsfor the proton and cations, caesium, sodium, potassium, and rubidium. Activity coefficients in the solution phase were calculated by use of Bromley's equations." For the solid phase, we will present data that strongly suggest the solid phase can be treated as an ideal surface. Ideal solid behavior has been reported, also, for ion exchange with zeolites.'2 Two methods are used to evaluate the validity of the assumption of an ideal surface for the CST. Methodl is a Mass Action Plot for a simple ion exchange reaction, i.e., Equation (2) written for Al = Cs,and Az = Na, and the overline representing the solid phase, and is shown as follows:

Ne' + C S +

--

C S + + Ne'

(4)

Although ion exchange of radioactive waste with the CST is not so simple, this simplification is justified for a fixed pH for solutions without other cations. The equilibrium constant for a simple ion exchange process is as follows:

270

Progress in Ion Exchange: Advances and Applications

where Q, and G,= concentrations of caesium and sodium in the CST. C, and CN, = concentrations in solutions, and y = activity coefficients with the overline representing the solid. By using logarithms, the following equation is obtained:

During an isothermal experiment of Cs exchange, the anion composition in the liquid does not change much; therefore, the activity coefficientsfor the solution and their ratio are constant. If we plot log(C&,.) vs. log(Q,/&.) an obtain a straight line with slope of 1, we can conclude that the activity coefficient ratio in the solid phase is a constant over the entire range of the isotherm. If the ratio is constant over the entire range, we can conclude that each one of the activity coefficients is 1, since the individual activity coefficients should not vary in the same manner as the change of the caesium and sodium concentrations in the solid. &thod 2. I(ielland's Plot: Equation (5) can be rewritten in terms of a partial equilibrium term, called the rational selectivity, bA, and the ratio of the activity coefficients on the solid as shown in Equation (7).

Rearrangement yields Equation (8).

If the solid phase is not ideal, activity coefficients will be functions of solid composition, i.e.,

Ion Exchange for Environmental Clean- Up

K:

=

Ki

27 1

(Q,)

(10)

If a plot for &A vs. Qc.for the entire isotherm is a straight line with a slope of 0, we can conclude that bA is not a function of solid phase composition over the entire range and hence the solid phase is ideal.

4 RESULTS AND DISCUSSION Mass Action and Kielland Plots, illustrated in Figures 1 and 2, indicate the CST solid phase can be treated as an ideal phase.

Figure 1.

Mass Action Plot illustrating an ideal solid TAM-5 = CST = UOP IONSIP IE-9IO.

Figure 2.

Kielland Plot illustrating an ideal solid. TAM5 = CST = UOP IONSIP IE910.

The equilibrium isotherm for K' ion exchanged onto UOP IONSIV IE-910 powder in a solution with 1.5 M NaOH was obtained. Figure 3 shows the potassium isothem obtained after 24 hours of shaking. For this experiment, 0.5 g UOP powder in a 50 ml solution was used, and potassium nitrite was used as the potassium source. The solid was dissolved and analyzed for K, and the solution concentrations were obtained by material balance. The Rb ion exchange isotherm presented in Figure 4 was determined for a 3.42M NaOH solution. CST (TAM-5) batch DG141 was used for this experiment. The isotherm was measured by mixing 0.2g solid in 20ml liquid. Rb was added as RbNO,. Liquid concatrations were analyzed, and solid concentrationswere calculated by material balance. A step change was observed in the Rb isotherm at Rb concentrations greater than 65.33 mg/g. On a milliequivalentbasis this is 0.76meq, which is approximately equal to the number of meq of cesium obtained in the simple simulant for TAM-5. The effect of K on Cs ion exchange was measured by using a solution with concentrations close to those in the standard solution. The solution matrix consisted of 4.96MNaN03and 0.6M NaOH with 150ppm initial Cs. Different amounts of KNO, were

272

Progress in Ion Exchange: Advances and Applications K Ion Exchange Isotherm

Rb*/Cs'lon Exchange Isotherm by TAM6 Solution: 3.42 M NaOH

Solution: 1.5 M NaOH

0

2

1

3

4

C. (M)

Figure 3.

Potassium isotherm at 25 "C in 1.5 M NaOH and KNO2.

Figure4.

Rb isotherm in 3.42 M NaOH and RbNO, at 23 O

C.

added, and Gs were measured for IONSIV IE-910powder. The change in density caused by adding KNO, was also measured. The addition of potassium nitrate resulted in an increase in the liquid volume, which resulted in dilution and change of solution density. To obtain more accurate information from the experiment, solution densities for each experiment were determined. Figure 5 illustrates a comparison between the equilibrium model developed by using Bromley's model" for calculating activity coefficients and data from Figures 3 and 4, other experiments, and the experimental data obtained for different initial concentrations of potassium. The model is obviously over predicting the negative effect of potassium on the caesium distribution coefficient. K effect on Cs Solution: 4.06 M NaNO,. 0.699 M NaOH

~

-JE

;

Effect of K Concentration on Cs Kd

' r ; F l r4

1wo

Solution: DSSF5

25w

C.lcub1.d

m 4M)

m 0 0

02

04

06

08

1

bnoentntlon ol K (MI

Figure 5.

A comparison of predicted and experimental caesium distribution coefficients.

Figure 6.

EfSect of potassium on caesium distribution coejficients in DSSF5. Potassium concentrations are initial concentrations.

Ion Exchange for Environmental Clean-Up

213

The K.,'s for Cs were measured by using IONSIV IE-910 ion exchange powder in DSSF5 solutions with various K' concentrations. The potassium concentrations were adjusted by adding a 1.04 M KN03-3.96M KOH solution. The initial caesium concentration was 100 ppm. The percent potassium on the solid was determined by using AA, the r d t s are presented in Figure 6. The curves presented in Figure 6 were calculated by using the equilibrium model that was developed by using data presented in Figures 3 and 4. Apparently, some of the potassium is in direct competition with caesium and some replaces sodium that is inaccessible to the caesium. Hence, the fmt addition of potassium competes directly for the same sites that caesium can access, but as the potassium concentration is increased, additional Na sites in the ion exchanger are accessed. The approach of an asymptote for the concentration of potassium on solid also correlates with the rate of decrease of the caesium distribution coefficient. We have also evaluated the effect of the addition of aluminum to the solutions. In the base solutions the aluminum is assumed to be present as AI(0H)i. The caesium distribution coefficients were measured for CST batch DG141 in DSSF with 4.5 M Na (DSSF4.5) without and with Al, and the values were 1872 and 1242 mug without and with Al,respectively. The calculated values were 2408 and 1211, respectively. Additional refinement of the model is needed to account for error in the estimation of K,, for the DSSF4.5 without Al. Figure 7 shows a comparison between the experimental and calculated values obtained for solutions of DSSF5, NCAW, and lO1AW-DSSF. As is evident from Figure 7, the calculated values are in good agreement with the experimental data

1E+5

n

m

=E

1E+3

v

1E+l 1E+O

-

1

I

I

I

In

Simulants

Figure 7.

Comparison of calculated and experimental valuesfor simulated wastes, DSSFS, NCA Wand 10IA W. Compositions are presented in Table I .

274

Progress in Ion Exchange: Advances and Applications 5 CONCLUSIONS

We have shown that UOP IONSIP ion exchange powder Type IE-910, i.e., TAM-5 or CST, is an effective ion exchanger for removing caesium from wastes containing high concentrations of sodium that are basic, neutral or acidic. We have also illustrated the use of an equilibrium model for calculating the distribution coefficients for Cs and other cations. The experimental data and the equilibrium model illustrate the effect of the waste solution composition on the performance and selectivity of TAM-5.

6 ACKNOWLEDGEMENT The work presented herein was performed at Texas A&M University, and was funded by Sandia National Laboratories under Texas A&M Research Foundation contract number RF8880. Sandia National Laboratories is supported by the U.S. Department of Energy under contract number DE-AC04-94AL85000.

1. 2. 3.

4. 5.

6.

7. 8.

References L. A. Emelity, "Technical Reports Series No. 78," International Atomic Energy Agency, Vienna, 1967, R. G. Anthony, R. G. Dosch and C. V. Philip, U.S. Patent Application Serial No. 081023,696, filed February 25, 1993. R. G. Anthony, C. V. Philip and R G. Dosch, Presented at the "Gulf Coast Hazardous Research Center's 5th Annual Symposium on Emerging Technologies: Metals, Oxidation and Separations," 1993, Lamar University, Beaumont, Texas; also in WasteMmgement, 1993, 13, 503-512. R. G. Anthony, R G. Dosch, D. Gu and C. V. Philip, Ind Eng. Chem. Rex, 1994, 33,2702-2705. L. A. Bray, K. J. Carson and R. J. Elovich, Prepared for Westinghouse Hanford Company, October 1993, PNL-8847, UC-5 10. R. G. Dosch, R. G. Anthony, N. E. Brown, J. L. Sprung and H. P. Stephens, Presented at the "Symposium on Chemical Pretreatment of Nuclear Wastes for Disposal - Revisited at the 204th National American Chemical Society," August 1992, Washington, D.C. R. G. Dosch, N. E. Brown, H. P. Stephens and R. G. Anthony, Presented at the '93 Waste Management Symposia," 1993, Tucson, Arizona. E. Klavetter, N. E. Brown, D. Trudell, D. Gu, C. Thibaud-Erkey and R. G. Anthony, Presented at the '94 Waste Management Symposia,," 1994, Tucson, Arizona. D. E. Kurath, W. G. Richmond, L. A. Bray, B. C. Bunker and E. 0. Jones, Presented at the "AIChE Spring National Meeting," March 28-31, 1993, Preprint 28b, Houston, Texas. Z. Zheng, D. Gu,E. Klavetter and R. G. Anthony, Ind fig. Chem. Rex, 1995,34, 2142-2147. L. A. Bromley, AIChEJ., 1973,19,313-320. R. M. Barrer and J. Falconer, Proc. Roy. SOC.,1956, A236, 227, London. 'I

'I

9.

10. 11. 12.

THE DETERMINATION OF CURIUM-242,243 AND 244 IN PROCESS WASTE STREAMS USING EXTRACTION CHROMATOGRAPHY

G. Cunningham British Nuclear Fuels plc Sellafield Seascale Cumbria CA20 1PG

1 INTRODUCTION

Increased environmental awareness has made accurate and reliable methods for the determination of actinides in various samples increasingly important. Curium isotopes are specifically important to BNFL because they are bi-products of the nuclear &el industry. Monitoring of these isotopes enables plant performance to be checked on a regular basis as well as reporting to the regulatory bodies governing site discharge authorisations. 1.1 Method Requirements

As indicated in the title the method is used for process waste streams. Routine analysis of these streams is carried out by Analytical Services Department at Sellafield who analyse a wide range of streams for a large number of analytes. The method was therefore required to be simple, accurate and as short as possible. 1.2 Sample Description

The process streams analysed in this work were those associated with our Enhanced Actinide Removal Plant (EARP). EARP is currently undergoing active commissioning. The process involved is relatively simple with an initial neutalisation of the streams, resulting in the precipitation of insoluble metal hydroxides and coprecipitation of activity. SolidAiquid separation is accomplished by cross flow ultrafiltration through tubular membranes. After concentration the flocs are washed and encapsulated in cement. The permeates are sentenced prior to discharge. As a result of conditioning and previous process conditions the streams analysed are relatively high in sodium nitrate and iron which have caused problems with analysis in the past. The method therefore had to cope with this specific matrix. 1.3 Previous Work

1.3.I Lntilhnnimi Carrier. Initial work was carried out using a lanthanum carrier as a means of separation. In the final clean up stages the curium was separated from the carrier

Progress in Ion Exchange: Advances and Applications

276

using a methanol/thiocyanate mixture. Unfortunately, it was found that the lanthanum began to drop out of solution on cooling. Since curium isotopes are determined by alpha pulse height analysis, which requires alpha trays containing very little solid the method proved to be unsuitable. 1.3.2Lirtetiirni Hydroxide. Further work was undertaken using a lutetium hydroxide precipitation stage. This involved the formation of insoluble fluorides and hydroxides with actinide co-precipitation with the lutetium. The lutetium and americium, curium fraction were then separated on a column (DZEHPA). This was again found to be unsuitable as the precipitation stage lost anything from 0 to 60 % of the curium. It was at this stage that it was decided to look into the use of extraction chromatography. 1.4 Extraction Chromatography

Work undertaken by E.P. Honvitz et al.’ using a chromatographic resin consisting of Amberchrom CG-7 1 impregnated with 0.75M solution of octyl(pheny1)-N,N-diisobutylcarbamoylrnethyl phosphine oxide (CMPO), (Figure 1) in tri-butyl phosphate or TBP concluded that the resin provided an effective method for the separation and preconcentration of actinides.

‘P

Ph’

Figure I

Slriicirirr

‘

CH2

\ Bu

of CMPO

The resin is commercially available. This seemed relevant to our needs so trials were undertaken. The extraction chromatographic system is comprised of three main components namely an inert support, in this case the Amberchrom CG-71. An organic phase, the CMPO and a mobile phase which is the load solution containing the analytes under study in the sample matrix. The organic phase selectively co-ordinates with ions in various mobile phases. The metal and anion, in this case nitrate, coordinate with the organic phase resulting in the extraction from the solution of the mixed ions. This process is reversible so the extracted ion can then be eluted from the column. Depending upon the acid strength used separation of specific ions can be achieved.

2 METHOD PROCEDURE All trials were carried out using curium standards with americium-243 used as a tracer. The volume of sample used was 50 ml.

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211

2.1 Coltinin Conditioning

The resin was conditioned with 2M nitric acid to take advantage of the high selectivity of the resin for actinides over most matrix constituents in nitrate media. The 2M nitric acid provided greatest retention for the americium and curium. 2.2 Sample Pre-treatment As mentioned previously, the effect of iron on the retention of the curium was especially important. Iron(lI1) will also be retained by the column in 2M nitric acid. Unfortunately this has a considerable negative effect on the retention of the americium and curium. Fortunately however iron I1 does not effect the retention so an initial treatment stage was carried out before putting the solution down the column. This initial pre-treatment of the sample consisted of adding lml of a solution of ammonium iron(I1) sulphate and sodium formaldehyde sulphoxylate and allowing to stand for one hour. This reduced the iron(II1) to iron(I1). It also ensured the reduction of neptunium(\/) to neptunium(1V). Neptunium (IV) is highly retained on the resin whereas the neptunium (V)is not. Converting the neptunium(V) to neptunium(1V) therefore allows the separation of this ion from the americium and curium. The sample solution was then evaporated to dryness and taken up in 50ml of 2M nitric acid and then loaded onto the column.

2.3 Wash and Elution Procedure

10 ml of 1M nitric acid was used to wash the column. This provided a good separation of the curium isotopes from other matrix constituents such as strontium, ruthenium and yttrium. This wash is sufficient to elute the afore mentioned elements whilst leaving the americium and curium untouched. Americium and curium have a low retention at 4M hydrochloric acid on the column. So once the wash with 1M nitric acid had passed through the column lml of9M hydrochloric acid was used to convert the column to the chloride form. The americium and curium fraction was then eluted with 20ml of 4M hydrochloric acid. This eluted the Am and Cm whilst leaving uranium(VI) and tetravalents such as plutonium(IV), neptunium(1V) and thorium(IV), essentially untouched. The americium and curium fraction was then evaporated to dryness and taken up in 5 mls of 0.5M nitric acid to provide optimum conditions for the extraction. Since the curium isotopes are determined by alpha pulse height analysis, which requires very little solid, a solvent extraction was carried out. This procedure consisted of an extraction into TTNxylene and backwashing into 0.5Mnitric acid. The aqueous phase was then trayed out onto an alpha tray and analysed for total alpha and alpha pulse height analysis. The columns can be used more than once provided that care is taken to ensure that all traces of sorbed ions are removed prior to reuse. This is achieved by washing the column with 10 mlO.1M ammonium bioxalate which strips off any actinides remaining on the column.

278

Progress in Ion Exchange: Advances and Applications

3 RESULTS 3.1 Standard Trials

For the curium 242 the level examined was 5 Bq The overall results gave an average recovery of 98.6% 2 5.398.0. The curium 243 and 244 level examined was 5.02 Bq. This gave an average recovery of 100.23%i 4.35%.

3.2 Roiitiiir Samples

The method has an overall precision of 100.23%5 4.5%.There have been no problems encountered with the sample matrix as before so the method seems to be both accurate and reliable and suitable for the desired matrix. From the description of the method procedure it can be seen that the method is also simple and relatively short which enables report times to be met quite easily.

4 CONCLUSIONS

The method was required for routine analysis for the determination of curium isotopes in process waste streams. The chosen technique was that of extraction chromatography using a commercially available extraction chromatographic resin. The resin can cope with substantial load volumes in a given run. Also, the resin could be used more than once if the column is washed with lOml of 0.1Mammonium bioxalate prior to reuse. The ability of the system to operate under gravity flow and room temperature is also very convenient. The developed method is simple, accurate, precise and relatively short and is used successfully for routine analysis.

References 1. E.P. Horwitz et al., Anal. Chim. Acta., 281 (1993) 361-372.

FIXATION OF RADIOACTIVE CAESIUM ON COPPER HEXACYANOFERRA'I'ES

S. Ayrault *, C. LoosNeskovic

*. M. Fedoroff f, E. Gamier

and D. J. Jones @

* Laboratoire P. Sue, C. E. N. Saclay. 91191 Gif-sur-Yvette. France E Centre &Etudes de Chimie MBtallurgique, 15, rue Georges Urbain, 94407 Vitry-surSeine, France Laboratoire de Chimie Thbrique, 40,Avenue du Recteur Pineau. 86022 Poitiers, France @ Laboratoire des Agdgats Molkulaires et MatBriaux Inorganiques, Universie Montpellier II, Place Eughe Bataillon, 34095 Montpellier, France 1 INTRODUCTION

Caesium sorption has been studied on copper hexacyanoferratesl-g. These compounds exhibit not only a strong affinity for caesiumlo, but they present also a potential interest for the fixaton of palladium and other precious metalsll. The industrial applications of such products are closely connected to the isolation of compounds with reproducible properties. Before undertaking a systematic study of their exchange properties, we first examined various synthesis methods, with the aim of defining reproducible preparative methods which give pure compounds12*13.The aim of this study was to assess the 'efficiency of different products and to improve our understanding on the fixation mechanisms. Sorption kinetics and isotherms were therefore studied by batch experiments and related to the chemical composition and crystal structure of the products. The results of these experiments were then applied to separations on columns. After decontamination of a liquid effluent by an insoluble hexacyanoferrate, the solid product will be saturated by the solution and long contact ,timesare expected. Depending on the medium, the femyanide anion is more or less protonated and may be oxidized, with formation of iron hexacyanoferrate whose blue color is characteristic (Prussian blue). Decomposition of such sorbents have been suspected to be responsible for gazeous evolution at Hanfordlq We have correlated the sorption experiments with the study of the stability of the solids in the reacting solutions over several months. 2 MATERIALS AND METHODS

2.1 Preparation of copper hexacyanoferrates. New synthetic procedures have been developed and compared with published methods. We used three preparation modes which can be classified as : precipitation13 and local growth16-17 for the preparation of powders and growth in a gel for the preparation of single crystals. The products obtained were analysed for their composition by instrumental neutron activation analysis (INAA) for powders, and Emission Disperse X-ray Spectrometry coupled to a Scanning Electron Microscope (EDXVSEM) for single crystals. Their

280

Progress in Ion Exchange: Advances and Applications

structures were determined by X-ray diffraction studies. Four stoichiometric compounds were obtained. In the cases when the mixed alkaline copper hexacyanoferrates had no s of several phases could be detected. definite compositions, the s i m u l ~ uexistence 2.1.1 CuI$FeII(CN)g This compound was easily prepared by precipitation from a 0.125 M lithium or sodium hexacyanoferrate(1l) solution and a 0.375 M copper(II) nitrate solution with the reagent ratio Cu/Fe = 3. The slurries were washed with de-ionised water by decantation at least 8 times. The precipitate was allowed to dry in air. 200, 100 and 25 pm sieves were then used and the various fractions dried in air at room temperature. 2.1.2 CuIIj[FeIlI(CN)6]2. This compound was prepared by precipitationl9 by mixing a 0.125 M potassium hexacyanoferrate(III) solution and a 0.375 M copper(I1) nitrate solution with the reagent ratio Cu/Fe = 3. The slurries were washed by decantation and centrifugation. For preparation by local growth, 200 g potassium hexacyanofernte(m) were placed in one litre of a 1.4 M copper(I1) sulphate solution maintained at 45OC for 45 hours. The granular product was washed thorougly with water. The majority of the particles have dimensions greater than 100 p. 2.1.3 K2CulIFeIf(CN)6 This compound could not be obtained by precipitation and was prepared by local growth. 15 g of cupric sulphate crystals were placed in 750 ml of 0.5 M potassium hexacyanoferrate(I1) solution and allowed to stand for 24 h. The particles were washed with de-ionised water on a 25 pm sift. They were dried in air at room temperature. 2.1.4 Na2CuIIFeI1(cN)6. 10 H 2 0 . This compound could not be obtained in large quantities as a powder. In experiments where the resulting precipitate includes sodium, this is always eliminated during the washing operation. Single crystals of this compound could however be prepared by growth in a gel. Copper m a t e crystals were placed at the bottom of a test tube and covered with a sodium metasilicate solution neutralized by 1 M acetic acid solution to pH<10. After setting of the metasilicate gel. a sodium hexacyanoferrate(I1) solution was introduced and allowed to diffuse slowly (at least one month). The crystals obtained were individually separated from the gel using a binocular magnifier and glass capillaries and washed several times in a drop of water (Fig. 1). 2.2. Batch sorption experiments We chose to study caesium sorption mechanisms on CuII2FeIX(CN)6. x H 2 0 and K@1Fe"(CN)6. Radioactive 1342s was obtained by irradiating caesium nitrate in the neutron flux of the Orphee reactor using the facilities of the Pierre Sue Laboratory of Saclay. A known amount of sorbent was shaken with a solution (either de-ionised water, HNO3 (0.1 M) or 7 g/L LiB@ solution at pH=8) containing caesium labelled with the radioactive tracer. The atomic ratio Cs(in solution)/Fe(in solid) was initially equal to 2. After a known time, the solid was separated from the liquid by filtration. The quantity of caesium sorbed in the solid was determined by measuring the radioactivity of an aliquot of the solution. The kinetics of the fixation were determined by varying the time of shaking. The release of cations from the solid into the solution was also monitored by analysis for Cu, Fe, Cs and K by Inductively Coupled Plasma / Atomic Emission Spectrometry (ICP/AES). The powders were washed with de-ionised water and air-dried at room temperature. X-ray diffraction patterns were then recordered. Cu, K and Cs were analysed in the solid by INAA.For complementary results, we used ICP/AES (after dissolution of powders) for Cu, Fe and K, and Li, B and NO3- were determined at the Service Central

-

ion Exchangefor Environmental Clean-Up

28 1

,H20

single crystal

@ Cul cu2

0 Fe ,--\ 1 ‘-r

Fe4(a) 0 Cul 4(h) 1/2 Cu2 8(c) 1/4

) missing Fe

site occupancy 0 Y3

0 0

0

1

1/3

1/4

0.1667

282

Progress in Ion Exchange: Advances and Applications

d'halyses (SCA) of the CNRS. In parallel to the sorption studies, a control experiment applied the same methods to examine any evolution of the 2 products in the same media over several months.

2.3. Column experiments Sorption was studied by passing a solution containing 137Cs without caesium camer through a column containing 5 g of sorbent and by measuring the radioactivity of the solution as a function of the eluted volumem. The waste solution was obtained by an acid washing of used organic resins from the Osiris reactor of Saclay and further neutralization with a LiOH solution. The main radioactivities were due to 137Cs, 134Cs and 6oCo (respectively 36,77 and 7 Bq.mL-l).The decontamination factor was defined as the ratio of the radioactivity in the same volume of solution before and after passing through the column.

3 RESULTS AND DISCUSSIONS 3.1 Composition and structures 3.1.1. Cull2Fell(CN)6. x H 2 0 . Powders with chemical compositions close to this formula were obtained. The yield of the precipitate was close to 100 % using lithium hexacyanoferrate and 50 % with sodium hexacyanoferrate. The difference is probably due to the co-precipitation of a colloidal sodium-copper hexacyanoferrate which is eliminated during the washing step. The powder obtained is mainly composed of black particles of dimensions > 200 pm.(yield > 95%). The crystal structure analysis showed that Cu%Fe1I(CN)6. x H20 is cubic, space group Fm3m19. The site occupancy of the iron atoms is 2/3. There are two kinds of site for copper atoms in the crystal.(Fig.2). Copper atoms Cul are linked to the iron atoms through cyanide bridges. The Cu2 atoms, with fractional coordinates 1/4,1/4,1/4, are not linked to the Fe-C-N-Cul network and are much more mobile than the Cul. Among the various products, some powders were cation deficient with the same XRD patterns. For example, the composition of the powder used for short time sorption experiments was Cu1.83~.&e(CN)6.8.5 H20. This could be due to the substitution of Cul atoms by protons during the precipitation reaction with acidic copper(II) nitrate solution (pH-3). The water content of these powders was high : 7 to 10 H20 molecules per Fe atom. The specific surface area of a powder dried at 60°C for 17 hours under vacuum was 1010 m2.g-1 with a microporous volume of 0.391 cm2.g-l. The drying step probably removed a part of the water molecules contained in the zeolitic cavities.

-

3.1.2 Cul1j[Fel1l(CN)6]2. x H20. The atomic ratio Cu/Fe was 1.51fo.03 for the powder prepared by local growth. The powder prepared by precipitation and used for ) 6 Both sorption experiments had the composition ~ . 0 3 6 ~ . ~ C u l . 3 ~ . 0 3 F e ( .c5NH20. products had similar X-ray diffraction patterns. Cun3[FeIn(CN)& . x H20 is cubic Fm3m 17920. The structure is close to that of Cu1I2FeI1(CN)6 . x H20. but only C u l sites are occupied, suggesting less exchange possibilities.

-

3.1.3 K2Cu11Fe11(CN), The overall yield of the preparation is 40 %.We obtained a series of powders whose chemical compositions slightly differed. For example, the composition of the powder used for sorption experiments was

Ion Exchange for Environmental Clean-Up

283

Kl.gl~.oaCul.0~~.03Fe(CN)6.3.4 H20. A careful analysis of the XRD patterns showed traces of the compound Cun2Fen(CN)6, except in the case when the composition was K1.g7~.03Cu1.00f0.01Fe(CN)6.0.3 H2O. Analysing the chemical composition of the product at successive washing steps, we observed that the decrease of the W e ratio and the increase of the Cu/Fe and H 2 W e ratio were correlated to the volume of water used. The diffraction pattern of pure K$unFen(CN)a has only few lines and hence k difficult to index. However, intensities and reflections do not correspond to the reported cubic structure21 and are somewhat different also from those published by Gellings (ICDD 20.0875) corresponding to a tetragonal s t r u c d 2 . TGA measurements showed a water content less than one water mole per mole of iron in the solid. The specific area was 46 m2.g-1. This solid is mesoporous. A better knowledge of this complex crystalline structure would be obtained from X-ray analysis of single crystals. 3.1.4. Na2CullFell(CN)6.10H 2 0 . A complete determination on a single crystal showed the presence of a new structural arrangementld. Na2CuIIFeII(CN)6 . 10 H20 crystallises in the monoclinic system, with space group W m (tab. 5a). The Fe(CN)a and Cu(CN)q units are linked into layers, parallel to the ab plane, through cyanide bridges. Chains of hydrated Na ions -(H20)2-Na-(HzO)2-Na- run parallel to the hexacyanoferrateJtetracyanocupratesheets, and water molecules above and below the plane of these chains serve to complete the coodination spheres both of sodium and copper, and to link the cyanometallate layers together. Na2CuIIFeII(CN)6. 10 H 2 0 dehydrates spontaneouslyin air with a concomitantloss of its single crystal character. This phase was not detected in any of the prepared products.

3.2. Stability in solution The structure of CuI%Fen(CN)ais not modified even after several months of contact in various solutions. No iron could be detected in the liquids. In 0.1 M HN03 ,a certain amount of Cu was released, equilibrium being reached after a few hours of contact with a final ratio Cu/Fe 1.8. This ratio remains unchanged even after a contact time of six months. The compound K2CuI1FeI1(CN)6 is less stable. In all the solutions studied, Fe was detected. In an acidic medium, Prussian blue was visible and the X-ray diffractionpatterns showed the emergence of other phases, such as cU1%Fen(cN)6.The intermediate phase H2CunFeqCN)tj which could be formed is not stable and evolves rapidly to M a n blue.

-

Table 1 Atomic ratios (per iron atom) in dte so& a fir a contact time of 6 months

n.d. :Not determined

Progress in Ion Exchange: Advances and Applications

284

3.3. Sorption of caesium The kinetics of sorption of caesium on C U ~ F $ ( C N )and ~ K2CunFdr(CN)6were followed for periods up to several months (Fig.3). We give in Tab.1 the compositions of the resulting solids assumed to be close to equilibrium.

Table 2 Maximum uptake of caesium on various copper hemcymferrates (II)in Cs atom per Fe atom

e

pH<4 1.34

Cu%.01Fen(CN).9.5H20

lxemarks

I

Reference

0.1 M HNO

0.99

-

0.1 M HNO3

OUT

L i B a solution pH 2.25 pH 0.43 3MHN03 pH 4.5 pH 1.2

results

1.01

0.57

0.43 -

1

1.4 1.13 1.02c

28

29 30

a : water content not given

b :Duodenal juice c :Gasmc juice d :precipitationin-situ e : Na = 2% weight 3.3.1. Cuf12Fe11(CN)6. x H 2 0 . Exchange of protons present in the solid (see above) explains the caesium fixation over the initial period (Fig.4). For longer contact times. copper ions appear in solution only in acidic medium. In lithium borate solution, no copper is found in solution because of the precipitation of insoluble copper borate on the solid (Tab.1). After one day of contact, a mean uptake of 0.4 Cs/Fe was measured. This value is close to the capacities reported in the literature. The uptake continues to increase for longer times of contact and does not reach an equilibriumvalue. In all media, the fixation of caesium on CuII2FeIX(CN)6. x H20 causes the formation of a crystallographically different phase whose structure remains unknown. In the same media, but without caesium in solution, the crystalline structure of C U ~ ~ ~ F ~ ~ Ix (H20 C Nis) ~not. modified, although 0.2 CdFe could be replaced by protons in HN@.

3.3.2. K2Cu1IFeII(CN)6. The elimination of potassium in solution explains the caesium fixation (Tab.1 and FigS), although the initial potassium content is never fully replaced by caesium. The maximum uptakes are lower than for CuII2FeII(CN),j. Exchange

285

Ion Exchange for Environmental Clean- Up I

I I

0 '

0

-. 0

I

50

100

150

200

T (days)

Figure 3 : Sorption kinetics of caesium on Cu1l2Fel1(CN)6and K2Cul1Fel1(CN)6in 0.1 M HNO3 and at pH 8 in Li B02 solution.

Figure 4 : Exchange balance of Cu1l2Fel1(CN)6in 0.1 M HNO3, Released protons and total equivalents in h e solution as a fwtction of Csjked on the solid

286

Progress in Ion Exchange: Advances and Applications

9 aJ

5J

0

4

Cs/Fe 00

0 00 Cu/Fe WFe

't 10 A

T (min)

H/Fe

Figure 5 Fixation of caesium on K2Cul1FeI1(CN)6in 0.1 M HNO3. Evolution of the composition of the solid as a function of time during the sorption of caesium

10000

I

I

1000

137Cs E

n

100

0

-

#

10

60cO min

max

1 0

500

1000

v (ml) Figure 6 :Decontamination factor of a waste solution at pH Cu1l2Fel1(CN)6

.

- 8 an a column of

Ion Exchange for Environmental Clean- U p

287

for copper ions does not contributeto the furation of caesium. Traces of iron were found in the filtrates. The sum of cation equivalents is less than 4 in all the studied media. The oxidation state of the hexacyanoferrate complex also requires verification No modification of the X-ray diffractogram is observed after contact with water and L i B a during the fixation of caesium. It seems that the incorporationof caesium stabilises the K2CuFe(O& phase. However, in acidic medium, the initial structure disappeared after fiiation of caesium. The crystallographic structure of the new phase has not yet been detemined. 3.3.3. Cull3[Felll(CN)& .x H20. A fmation of 0.06 to 0.08 Cs/Fe is reached after 10 minutes and remains constant after a contact time of several hours. Copper(II)

hexacyanofemte(m) has less affinity for caesium than copper hexacyanofemtes (n).The mechanism of the caesium fuation on this compound could be a surface sorption. 3.4. Applications to liquid radioactive wastes Owing to its good mechanical and chemical stability, CuI12FeI1(CN)6 was chosen for column experiments. The decontaminationfactor D as a function of the eluted volume of waste solution is shown in Fig.6. We observed high D values (> 500) for caesium during the fmt day of experiment. For security reasons, the experiments were stopped overnight and when the solution was poured again on the column, D dropped slightly, but no breakthrough was observed and after the passage of 100 bed volumes on the column, D was still > 200.The efficiency of the column is poor for 6oco with a decontaminationfactor less than 10. 4. CONCLUSION

Powders of CUI12Fe1I(CN)6 and CuII3[FeIII(CN)& are easily prepared by precipitation and by local growth. They a~ cubic Fm3m and present disordered spuctures. In C ~ n ~ F e n ( c Ntwo ) ~ different , sites for copper are possible :the Cul positions are linked to the network, and the Cu2 at the interstitial sites are more mobile and exchangeable by protons. The second type of site is not occupied in Cun3[Fem(CN)&. This could explain its low sorption of caesium, much lower than on Cu%Fen(CN)& The only stable product seems to be cUu2Fer1(cN)6:its Structure is not modified even after standing several months in various solutions. It presents also the highest observed uptakes. The kinetics of caesium sorption shows two steps. In the fmt, caesium is rapidly exchanged with protons with no change in the crystal structure. After several months of contact with caesium ion solutions, the emergence of another phase can be detected. The characterisation of mixed caesium-copper hexacyanoferrates was not possible, due to the lack of reference spectra. The preparation of the corresponding single crystals is in progress. The sorption of caesium on K2CunFe11(CN)6 is the most rapid during the first minutes of contact. However, for longer contact times, the performances of this compound a~ always inferior. In addition, its chemical stability is poor in solution and its mechanical stability is unsatisf;bctory. CU2Fe(CN)6. x H20 seems to be the most promising compound and is easy to prepare by precipitation. The composition and the performances of the product are reproducible. The first step of exchange allows its use for the decontamination of radioactive liquid wastes.

288

Progress in Ion Exchange: Advances and Applications

5. REFERENCES

-

1. G. B. Barton, J. L. Helpworth, E. D. McClanahan Jr, R. L. Moore, H. H. Van Tuyl, 212 1958, 2. H. Loewenschuss,Radioactive-W 1982,2,327 3. P. A. Haas, ce Te1998,2& 2479 4. E. F.T.-=eL e , 1 9 8 3 . m . 333 5. J. Doled, V. Kourim, 1969.1.295 6. M.T. Ganzerli Valentini, R. Stella, L. Maggy. G. Ciceri, 1 9 8 6 , U . 99 7. E. F. T. Lee. M. Streat, , 1983, 80; 87 . . 8. R. Pfrepper, G. Pfrepper, M. Siiss, Zfi-Mlttelluneen, 1 9 8 6 , ~43 . 9. P. Nielsen, B. Dresow, H. C. Heinrich, 7. Naturforsch., 1987,42h, 1451 1989,Z. 131 10. C. Loos-Neskovic, M. Fedoroff,,11. C. Loos-Neskovic, M. H. Dierkes, E. Jackwerth, M. Fedoroff, E. Gamier, HvdrometallurpvL1993929345 12. S. Ayrault, C. Loos-Neskovic, M. Fedoroff, E. Gamier1994, 1435 1995, in 13. S. Ayrault, C. Loos-Neskovic, M. Fedoroff, E. Gamier, D.J. Jones, Press 14. M. Fedoroff, C. Loos-Neskovic, 8 4 - 1 2 m, 1984 * , 1990,2,677 15. C. Loos-Neskovic, S. Abousahl, M. Fedoroff, 16. S. Abousahl, C. Loos-Neeskovic, M. Fedoroff, E. Gamier, U&& Growth, 1994. U ,569 17. B. Ayers,,1971, S, 721 1989. 347 18. C.Loos-Neskovic. M. Fedoroff, 19. M. L. Beasley, Ph. D. Milligan, W. 0. Milligan, New York A c 'a, 1969, U,261 * 1 9 3 8 ,s. 1259 20. A. K. Van Bever, Rec. 21. R. Rigamonti, , 1937,fl, 146 22. P. J. Gelling, 3 Phys. C a , 1967,54, 296

a,

m,

-. a, u,

ISOLAIION OF CAESIUM FROM FISSION PRODUCT WASTE SOLUlION ON A NEW GRANULAR INORGANIC BXCHANGER TIlANIUM PHOSPHATE-AMMONIUM PHOSPHOMOLYBDAls ( llP-AMP)

G.S.

Murthy, V.N.

Reddy and J. Satyanarayam

Nuclear Chemistry Section School of Chemistry Andhra Univeraity, India-530 008

1. IN'IRODUCIION

In recent years a great nunber of synthetic inorganic ion exchangers have been developed for processing nuclear waste eolutions. The high sslectivity and resistance towards heat and ionizing radiation 111 make these ion exchangers attractive altmnatives to Organic resins. Much attention was paid to develop methods to isolate Cs-137 when compared to other fission products due to i t s wide range of applications as radiation sources in the fields of medicine and industry [2]. Several workers studied the separation of Cs. from using ammoniun acidic fission product waste solutions, molybdophosphate (which is micro crystalline in nature) mixing with different inert binding materials [3-71 to improve the flow We present here the investigations charcterlstics of the colunn. carrled out on TIP-AMP (prepared in a different method to that of Zhoxiang et al. [Sl) which offared better flow rates (seven bed lhe stability of the exchanger was studied tp to volumes per hour). five cycles of colunn operations. 2. EXPERIMENTAL 2.1 Reagents and Chemicals: A l l magents used w e r e of E.Merck o r BDH (AnalaR) grade. lhe radio isotopes used. w e r e supplied by

Board of Radiation and Isotope 'IBchnology, Department of Atomic Energy, Bombay. 2.2 Preparation of TIP-AMP: Tltaniun phosphate (TIP) was precipitated by mixing 5 0 b l of 0.3M Tl@, in 2M HC1 and equal amomt of 1.5M H PO with constant stirring. Ammoniun 3 4 molybdophosphate ( A M P ) was precipitated by mixing 5 0 b 1 of ammonirrm molybdate 5OQnl of 0.1M NH4N03 and 5oQll of 0.25M H PO and the final solution was made to 67M with respect t o HNO 3 4 3' The above two precipitates w e r e mixed thoroughly w i t h themother solutions and digested a t 5CPC f o r three hours with constant stirring. The precipitate was allowed to settle, filtered and washed with distilled water severe1 timea until the p~ of the wash maches about 3 to 4 and then.air d6ied for two days.

290

Progress in Ion Exchange: Advances and Applications

2.3 Camiun e mkanf$ Capacity * Caesium exchange capacities w e r e determined radiomet cally following the procedure reported earlier [91*

2.4 'IAermal studies: lhermo analytical determinations w e r e carried out using a Sink0 Rico (ULVAC) balance model n; D-7000) thermal analyzer, a - A 1 0 was used a s the reference material with a heating 2 3 rate of 10K/min. lhe DTA curves w e r e simNltaneomly mcorded. 2.5 XRD Studies : ?he X-ray studies wem carded out ming a Diano XRD-Z8O model instrunent. lhe intensities of diffracted X-rays a s a

fmction of diffractionangle 2 8 has been recorded. Distribution ratios: Distribution ratios of variom elements wem determined radiometrically ming suitable radio tracers following the pmcedure reported earlier [lo]. 2.7 Colunn Studies: Breakthrough experiments w e r e carried out on a 2g exchanger column (bed volme=Zml) with the f e e d solutions 2.6

containing 0.5 W/ml Of cS+ tagged with -1pci of the Cs-137 tracer. 'he flow rate conditions are: seven bed volrrmes/hour i n absorption studies and three bed volunes/hour in elution studies. 2.8 Irradiation studies: Y -ray irradiation of the exchanger was carried out in a 5950 curie G.C-40W gamma chamber and electmn irradiation in the ILU-6 electmn accelerator at the Isotope division. 2.9 Gamma ray spectra: me Y-spectra w e r e obtained on a high purhty germanium detector coupled to a PC based 4k multi channel analyzer.

3. RBSULlS AND DISCUSSION

In the mcent past considereble interest has been shown in improving the physical characteristics of the insoluble ammoniun salts of heteropolyacids to exploit the ion exchange properties suitable for colunn operations [4-71. lhe exchanger TIP-AMP (28b Tip and 74% AMP), is obtained in granular form and the fraction-50- +lo0 mesh size offered better flow rates when compared to earlier reports 181. 3.1

Caesiun Rxchange Capacity

lhe caesium exchange capacity of TIP-AMP was determined in (able-1). which is relevant for C s removal fmm fission prodmt waste solutions. The capacity obtained (0.82 meq/gl, corresponding to 1.1 meq/g of AMP, is in agreement with the value reported by earlier workem [11,12] suggesting that two ammoniun ions a r e being replaced from AMP. A l b e r t i e t al. [131 reported that the C s uptake on crystalline Tip is negligible in acid solution. The TIP prepared under OUT experimental condition is fomd to p ~ s - 8 a~ considerable degree of crystallinity a s obsenred from crystallographic studies ( a b l e - 2 ) , and exhibit no Cs uptake in 2 M HNO ThW nf' 3' plays the role of inert binder mder the exparlmental conditions studied. The C s exchange capacities (in 2 M HNO ) Of this 3 exchanger w e r e fomd to be almost same even after subjecting to thermal trsatment a t diffewnt temperatures ranging fmm 100-400% (mble-1). which indicate that this exchanger can be med at elevated temperatures for C s exchange. 2M HN03

29 1

Ion Exchange for Environmental Clean-Up

Ihble 1 Cs exchange capacity of IlP-AMP a t different drying temperatums. Room 'IBmp.

Dryine

2WC

lOOOC

400%

3WC

lbmperatum

Ce exchang~ Capcity( mewe 1 3.2

0.82

0.84

0.79

0.81

0.78

Thelma1 Studios

lhe thermolysfs curve O f 'IIF-AMP is shorn In Fig-1. The8-p weight lose up to l W C may be dm to the loss of interstitial water to the stmng endothermic peak at 9BC. lhe which correspondg continwue weight loss in the region 200-4OOOC may be due to the condensation of phosphate gmws into pymphosphate gruups [13,141. A small weight loss In the temperatrange 430-5WC followed by an exothermic peak a t 46CPC Indicate8 the decomposition of the molybdate ion pregcnt i n AMP [15]. 'Lhe compound formed (molybdic oxide) In the decomposition was foud to be stable In the temperature range 500-720%. Further the continwue weight loss above 720% followed by a stmng endothermic peak a t 76CPC is due to the sublimation of molybdfc oxide ( M o o 3 ) which is in agreement with the earlier work 1151.

-

n

:

>

a

% 4

t

x

2 00

Fig

,

,

401

-

400

. 600

,

800

1-25 1000

Tcmperoturc ('C) 8

Thermogram

of T ~ P- A MP

3.3 X-Ray M f f r a c t h Studiem

lhe Intensities of diffracted x-ray and d-valres for pure compomds TlP and AMP and that of Tip-AMP (before and after

292

Progress in Ion Exchange: Advances and Applications

X-Ray Diffraction data of TIP, AMP and TIP-AMP

'IBble 2

....................................................................... Tip

AMP

Tip-AMP

Tip-AMP (irrad)

....................................................................... d 1/10 d 1/10 d 1/10 d 1/10 ....................................................................... 11.45 7.85 4.29 r3.45 a2.50 *l.64

*

82 79 56 100 50 22

8.40 6.75 5.85 4.80 4.14 3.70 3.37 3.13 2.92 2.75 2.48 2.30 2.10 1.94 1.90 1.80 1.76 1.65 1.48 1.43

69 10 27 15 37 11 100 11 32 14 23 14 17 7 11 10 8 17 14 11

8.34 5.87 4.79 4.14 3.71 3.38 2.93 2.76 2.49 2.29 2.07 1.95 1.89 1.80 1.76 1.65 1.48 1.44

61 27 15 30 11 100 31 13 27 17 13 8 15 10 10 18 18 12

8.33 5.87 4.80 4.14 3.69 3.38 2.39 2.76 2.49 2.29 2.07 1.95 1.90 1.80 1.76 1.65 1.48 1.44

52 28 16 31 14 100 30 12 25 15 13 8 13 10 9 8 19 18

....................................................................... irradiation) a r e presented in 'Igble-2. me values show that TIP is a semicrystalline material'showing 4 X-ray reflectiorwWith the same dvalues a s that in the crystalline TIP [131. AMP is foInd to be a micm crystalline substance [16].lhese results suggest that TIP-AMP is a physical mixture consisting of AMP and TIP. I t was also observed that the x-ray diffractogm taken for Tip-AMP after subjecting to a gamma radiation dose of 108 rads remained almost the sameshowfagthat the exchanger i s stable to intense gamma radiation. 3.4 Infrared spectra Studies

me infrared spectra of TIP-AMP (Fig-2) w e r e obtained f o r alsample dried a t room temp. b ) sample dried a t 400k c ) sample irradiated to a ga a dose of rads and d ) sample irradiated to an electron dose of 1 rads. A broad band fomd in the region 2800-3600 -1

7

108

cm may be due to the 0-H stretching vibration of interstitial water present in the exchanger.A sharp peak in the region 1 Q O cm" indicates 0-H bending mode and a strong band a t 1400 cm" may be due to tby presence of ammoniun ion [17]. Frequencies in the region of 400-900 cm are due to the Mo-0 stretching vibration mode [18]. A broad band in the m i o n 940-1140 Cm" may be due to the Ti-0-P stmtching present in the

293

lon Exchange for Environmental Clean- Up

'RP-AMP. It is interesting to note that the chamcterlstic absorption bands mnalned same in all the samples.

Wave nunber (cm-1 1

---

Sample dried-at mom temp.:

3.5

MatdbutLm mtios

gamma irradlated sample:

--Sample at 4 W C ..-_---Electron irradiated sample dried

From the Kd values obtained (lbble-3) i t is observed that Cs, R b and Zr a m the only elements which a m taken w by the exchanger

at all the acidities. C8 1s plef8IWlthlly taken up by the exchangers a t all acidities, the elements R b and Zr compete to a gmater extent even In 2M nitric acid. It Is found that the ram earth elements and Ru compete considerably at lower acidities, but the uptake of these elements a m reduced to pmctically migligible velum beyond 1 M HNO3. I t is also observed that the uptake of Na is negligible in the acid concentration studied while practically no uptake f o r Sr and Ba-occurs 'beyand 0.5M HNC3 a b l e 3 Distribution coefficients of several tmcer cations ----o-------------_-___I________________--------------------------

Element

Nitric acid concentration --------------------u_u_________________---~---------

0.1

0.2

0.5

1.0

4.0

2. 0

6.0

8.0

10.0

-------------------u_______I____________--------------

Na cs Rb

Sr Ba

Y

ce Bu Nd

Ru Zr

18320 7277 27 96 103 2572 2221 1267 77 1286

7960 5M5 15 34 54 20lO 579 483 56 1285

7000 4108

6420 3240

a75 2250

9 18 108 48 80 26 1282

9 13 12 16 11 1231

808

No uptake 5080 4440 No No No No No No No

1545

1225

3880 744

2980 520

738

643

505

432

uptake uptake uptake uptake uptake uptake uptake

294 3.6

Progress in Ion Exchange: Advances and Applications

Absorption and Elution studies

Breakthrough capacities for C s determined in different concentrations of nitric acid and in different types of simulated fission pmduct waste solutions 1161 are given in Table-4. The results indicate that the breakthrough capacity for caeduu is not affected much by the presence of macm concentrations of electrolytes and other fission pmduct elements. This proves the specificity of the exchanger TIP-AMP towan38 the element caesiun under these conditions. The 5ab breakthrough capacities for caesiun on this exchanger a r e measumd for five cycles, and the results a r e given in Table-5. It is observed that the breakthrough capacity slightly decreased after each cycle and almost 15-2ab loss of capacity was observed after fifth cycle. This may be due to the slow dissolution of AMP 1191. The elution studies ( l h b l e - 6 1 shows that 9ab of caesium was eluted in 15 bed volmes Further increase in concentration of NH NO and with IN NH4N03. 4 3 the presence of 2 M HNO in the eluting agent has little effect on the 3 elution pattern. Breakthrough capacities of Caesim on TIP-AMP

Table 4

2. 3. 4.

0.31

0.36

HN03-2M

0.23

0.27

HN03-4M

0.27

0.33

-

vpe-I 2M HN03 wpe-II-4M HN03

0.29

0.34

6.

0.28

0.33

7.

vpe-III-O.3M

0.32

0.3 6

8. 9.

vpe-I V-2M HN03 Wpe-V-ZM HN03

0.24 0.29

0.2 6 0.34

5.

mble 5

HN03

Effect of cycle n m b e r on the capacity of TIP-AMP

Cycle No. 5ab Bmakthmugh capacity ( me q/g 1

I

I1

111

IV

V

0.35

0.34

0.32

0.30

0.29

295

Ion Exchangefor Environmental Clean-Up 'hble 6

Elution of Caesiun from TIP-AMP colunns Eluent composition

~.NO.

4.

88 91

5.

1(M

6.

ZM H N O ~+-ZM N H ~ N O ~ 2M HN03 + 4M NH4N03

7.

3.7

8M NHpN03 NH4N03

sepa~tlonof

Percentage eluted in 15 colunn volunea

66 80

ceseiun

A selective method for the removal and recovery of Cs-137 from fission products waste solution has been finalized on the basis of information available [3,201 and on the results obtained in our laboratory. In the present separation scheme 10.0 m l of the simulated fission product waste type-I solution [161 containing the fission products Q , Ba, Sr, Cs and Zr-Nb, was mixed with adequate quantities of tracers Ce-141 (representing the ram earths), Be-133, Sr-85, Cs-137 and 2 ~ 9 5 respectively. The feed solution was passed through tlie calumn andathe effluent was collected. The colunn was then washed with 2M HNO till 3 the effluent was f r e e of activity. 'he absorbed caesiun was eluted with 6M ammoniun nitrate.

The spectrun of the feed solution (Fig-3) exhibit the peaks corresponding to Ce-141 ( 146 Kev) , Ce-139 ( 165 Kev ) , Be-133 (355 Kev 1 ,

CIIANNEL NUMDER

Fig-3: Gamma ray spectrun of feed

Progress in Ion Exchange: Advances and Applications

296

u> Y

-

W 1'

20000 -

2 0'

u>

0

u>

Y

Y

I n

In

-

In

>

I I

1

,

Y c

In

1 0

400

8bO

I

1200

1600

Channel Number

P i g - 4 : Gamma ray spectrum of effluent 1000

> Y FI u)

In

U v)

C

3

0

0

0 401)

Fi g - 5 : G-a

800

1200

1600

Channel Number ray spectrum of eluted Cs-137

Channel N u m b e r Fig-6: Gamma ray spectrum of eluteU Zr-95

Ion Exchange for Environmental Clean-Up

297

S ~ 8 5(514 Kev), Cs-137 ( 6 Q Kev) and Z ~ 9 5(757 Kevl respectively. lhe absence of peaks corresponding to Cs-137 and Zr-95, in the effluent spectrun (Fig-4) indicates the absorption of these elements by the 'be spectrun of (3-137 (Fig-5). eluted f r o m the colmn, exchanger. shows only the peak corresponding to Cs-137 ( 6 Q Kev) indicating the purity of the final caesiun pmduct. However Z r , which forms an oxobridge complex with the exchange matrix, is not eluted with 6M NH4N03. 'be spectrun of Z ~ 9 5which is eluted with 0.5M oxalic acid

is shown in Fig-6. ACKNOWLEDGWdENlS

lhe authors would like to thank the Board of Research in Nuclear Science, Department of Atomic Bnergy, for the financial support given to carry out this work. REFERBNCBS

1. 2.

3. 4. 5. 6. 7. 8.

9. 10.

11. 12. 13. 14. 15. 16. 17.

18. 19. 2 0.

C.B. Amphlett, Pmc. Conf. on peaceful -8 of Atomic Isneqy, Geneva 1968, 28. A. Clearfield, Inorganic Ion Exchange Materials. CRC Press, Boca RatonFlorida 1982. J. Van R. Smit, W. Robb and J.J. Jacobs, J. Inow. Nml. Chem., 1959, la, 104. T.S. Murthy, et al. Rep. BARC-893, 1977. J. Stejskar J. Soukup J. Dolezal and V. Kourim, J. Radioanal. Nucl. Chem., 1974, 21(2), 371. H.T. Matstrla, A. Abrao 1PEN.Pub-13 Jm. 1980. F. Sebesta, V. Stefula, J. Radioanal. Nuc. Chem. Art., 1990, 15, 140. S. Zhaoxiang, et al. IAEA. lbc OOc-337 July 1985. V.N. Reddy, J. Satyanaravana, G.S. Murthy and A. Dash Sep. Sci. P c h . (in press). V.N. Reddy, J. Satyanamyana, G.S. Murthy and A. Dash J. Radioenal. Nucl. Chem. Articles, 1994, 183(2), 371. J. Van R. Smit, AERE-R3884, 1961. M. Suss and G. Pfrepper, Radiochim. Acta. 1981, 29, 33. G. Albert1 et al. J. Inorg. Nucl. Chem. 1967, 29, 571. V. Wsely, V. Pekarek, Tblanta, 1972, 19, 219. S.F. West and L.F. Andrieth, J. Phys. Chem., 1955, 59, 1068. J.W. Illingworth and J.F. Keggin, J. Chem, Soc., 1935, 575. Kazw Nakamoto "IR spectra of Inorganic and Coordination Compoundst1, John Wiley 8 Sons,Inc. 2nd ed, 1970, p.108. J.S. G i l l , S. N. 'hndon, J.Radioana1. Nuc.Chem.Art. 1979,3 6,345. J. K r t i l andVKourim, J. Inorg. Nuc. Chem., 1959, 12, 367. S.Dutta Roy and M.Sankaradas, Anal.Chim. Acta. 1970, 51, 509.

PREPARATIVE SEPARATION OF CAESIUM AND RUBIDIUM FROM ALKALI METAL MIXTURES USING PHENOL-FORMALDEHYDE ION EXCHANGE RESINS

V.A.Ivanov, V.I.Gorshkov, 1.V.Staina Department of Chemistry Lomonosov Moscow State University Moscow 119899 Russia 1 INTRODUCTION

Caesium and rubidium occur always in mixtures with other alkali metals in nature. Their separation from each other and from other alkali metals, according to the traditional technologies is achieved by rather tedious operations such as repeated extraction and recrystallisation [l]. In a short previous communication of one of us [21 it has been shown that phenol-formaldehyde resin (PhFR) possessed the greatest selectivity towards caesium and rubidium, when compared to other organic ion exchangers. This resin has been supposed to be very promising for the separation of caesium and rubidium from each other and from other alkali metals. Later [3] the resorcinol-formaldehyde resin has been found to be very selective for the 137Cs removal from high-activity solutions. At the same time we have demostrated [41 an ion exchange method for preparative separations of caesium and rubidium from mixtures containing alkali metal ions on PhFR using both the fixed bed and counter-current techniques; some equilibrium characteristics have been presented [ 5 , 6 ] . Our present report explains the main peculiarity of the last method. In the first place, the counter-current technique is under consideration while it can provide the continuous production and can be easily fit in technology of the complex processing of natural waters with aim of recovery of the valuable components. The main objects are the rubidium and potassium mixture containing the first cation as microcomponent, and the caesium and rubidium mixture. These metals are very similar in chemical properties and their mixtures are difficult to separate. 2 EQUILIBRIUM

The chemically stable macroporous PhFR resin which have been produced as products of the acidic condensation reaction of phenol and formaldehyde (with molar relation of formaldehyde to phenol in the reaction mixture equal to 1.4) were studied. For comparison some equilibrium data were obtained by us for the pirocathechin-formaldehyde resin

Ion Exchangefor Environmental Clean-Up

299

PirFR, the commercial sulphonated phenol-formaldehyde resin KU-1, the commercial phosphorylated phenol-formaldehyde resin

RF with the methylen- phosphonic groups -CH2PO(OH), the commercial polymethacrylic resin KB-4 cross-linked by 6% divinylbenzene, and the macroporous nitrated sulphonic styrene-divinylbenzene cation exchanger KRS-20t(202N) (nitrogen content 2.31%). Experimental methods for determining the equilibrium characteristics were the same as before [ 5 , 6 1 . Figure 1 shows that the ion exchange groups of the PhFR are substantially dissociated only at pHs higher than 9 . The increase of the sorption capacity does not stop for pH increase up 12.4. This may be due both to the different pK values of phenolic groups above 10, and to the significant molecular sorption of electrolyte by the macroporous phenolic resin.

2

1

0 6

8

10

12

PH

Figure 1 Dependence of the ion exchange capacity of PhFR versus pH. Due to the macroporosity of PhFR the sorption capacity increases (Figure 2) at higher alkali concentration as well: more strongly - up to the concentration 0.1 M and some weaker almost linearly - at higher concentrations. + The conversion of PhFR from the H ionic form (in acidic or neutral solutions) to the alkali metal ionic form (in the alkaline solutions) is accompanied by considerable resin swelling (Figure 2B) and by a resin color change from the sand-yellow to the bright violet-brown. A most remarkable peculiarity of the phenolic resin is its high selectivity towards Cs+and Rb+ ions compared to the sulphonic, carboxylic, phosphonic and nitrated sulphonic resins (Table 1). The phenolformaldehyde resin is more selective than PirFR. The selectivity of PhFR increases significantly by decrease of the equivalent content of component which is sorbed by resin more strongly (Figure 3 ) .

300

Progress in Ion Exchange: Advances and Applications A

0

A

q D

rn!m!iv

0 0

3

0

*

*

0

g

0

0

0

0 0

0

0 *

0

0

0

6

. A'

4

0 0 00

.

0 0

-8 I I

I

2

-

0

>

0.5 'ao

equiv/i

Figure 2 Dependencies of the sorption capacities of the PhFR q ( A ) and of the specific volume of resin v (B) versus the K+ concentration in the equilibrium solution containing KOH ( 0 ) ; 0.1 H KOH and K C l at different concentrations (0).

30 1

Ion Exchangefor Environmental Clean-U p Table. Equilibrium Coefficients

$=

‘A

*A

of Resins by B ‘B are the Exchange in the 0.1 M Solutions (y and x Equivalen Fractions of the Exchangeable Ions in Resin and Solution Respectively; xA= 3= 0.5).

.-_-_------

(--)/(:-)

____-------

Ic

----c--

Solution

It

--_----

KOH+NaOH LiOH+NaOH RbOH+KOH CsOH+RbOH CsOH+NaOH

1.43 1.24 1.60 2.44 3.57

CsOH+RbOH

1.71

-------

RbN03 +KN03

1.12 1.11

RbN03+KN03

1.35

0.96 RbOH+KOH CsOH+RbOH 1.01 CSCl+RbCl 1.64 RbCl +KC1 1.30 CsOH+RbOH 1.80 ----_ _RbOH - - - - _+KOH - - - - - - -_1.30

(B) values Figure 3 Dependencies of the -. (A) and versus the ionic compositions of the equilibrium 0.1 M solutions of alkalis of the ions tested for PhFR and for the KU-1 resin.

302

Progress in Ion Exchange: Advances and Applications

2 SEPARATION PROCESS FLOW SHEET

Separation of the binary alkali metal mixture A+ and B+ can be carried out in two stages according to+the usual frontal chromatography technique: the component B , which is sorbed by resin more weakly, is separated by passing of the alkalies AOH and BOH mixture through a column with PhFR in the H+ ionic form; then, by passing of the acid solution through the same column with PhFR in the mixed A+-B+ ionic form the component A+ is separated. After the second stage the resin is in the H+ - ionic form and can be used in the first stage without any additional processing. Separation can be carried out both in a fixed bed column and in a countercurrent one. This mode of separation has a drawback: for complete separation of components of the initial solution the mixture of alkali metal salts AX and BX, which are eluted from resin in the second stage, must be converted in alkalis AOH and BOH completely in order to use this mixture for fitting in the first stage. Such an operation is difficult. This drawback is diminished significantly in the second mode of separation. Described below and shown in Figure 4 is the ion exchanger closed-circuit scheme of the continuous separation process in columns with counter-current movement of liquid and solid phases. The process consists of two main separation stages I and I1 and of an auxiliary stage I11 for a solution composition correction.

1 I

., I I

R-0 (A,B)

AX+BX

(AOH+BOH)

yw

I

I1

"; R-oH

I

Figure 4 Continuous separation process f l o w sheet.

HX

Ion Exchangefor Environmental Clean-Up

303

Stage I. The cation exchange resin ROH in H++form an9 an initial solution containing alkali metal ions A and B as mixture of alkalis (AOH and BOH) and salts (AX and BX) are fed into a counter-current column I. The extremely low acidic phenolic groups react with alkalis only according to reaction R-OH + (A+, B+)OH = R-o(A+, B+) + H ~ O (1) and do not react with salts. At the same time both alkalis and salts are sorbed molecularly by resin to some extent (A', B+)OHl = (A+, B+)OH] (2) (A+,B+)XIS = [(A', B+)XIR (3) (the subscripts S and R refer to the solution and resin phases, respectively). The flow rates of phases are maintained so that the sorption fronts of alkalis do not move along column (fixed in the upper part of column). The neutral solution of salts leaves the column. The main peculiarity of the discussed process is that the solution feeding the column I contains a mixture of alkalis (AOH and BOH) and salts (AX and BX) at a definite ratio. This ratio can be determined according to relation (K - 1) x 'alk, F

>

(4)

'salt,F (K - 1) (1 - x )F If the ratio of alkalis and salts in the appropriate solution is chosen correctly, the solution of only salt BX leaves the column I or with the minimal admixture of salt AX. Stage 11. The cation exchange resin in the mixed A+ - B+ ionic form leaving the column I is fed into a counter-current column 11. In this column the ion exchange resip is trfated by a solution of acid HX and the sorbed ions A and B are displaced from resin completely according to reaction R-o(A+,B+) + HX = R-OH + (A+, B+)X (5) and to the reactions which are reverse to the ones ( 2 ) and ( 3 ) . Due to the extremely low acidity of the phenolic groups both strong acids (like hydrochloric or sulphuric ones) and weak acids (like acetic one) can be used. In column I1 above the ion exchange front, the hydrolysis of the (A', B+) ionic form of resin takes place as well (6) R-o(A+, B+) + H ~ O = R-OH + (A+,B+)OH The continuous separation of the A+ and B+ ions, as in reverse frontal chromatography, in the+ fixed bed column technique takes place in column 11; the A ion is accumulated and concentrated in a zone adjusting to the desorption f5ont. After the formation of an extended zone where the A is separated from the B+ - component (x; =l), the solution containing the first one is periodifally withdrawn from this zone. Ion exchange resin in the H ionic form leaving the column I1 is fed into the column I without any additional treatment.

304

Progress in Ion Exchange: Advances and Applications

Stage 111. The solution withdrawn fray coluT I1 contains both alkalis and salts of the separated A and B ions. It is expedient to return this solution via siage I+ of the separation process because the ratio of the A and B ions is the same as in the initial solution. At the same time the alkali concentration in this solution is less than that in the solution feeding the column I. The correction of the composition of this solution in the stage I11 (meaning some increase of the alkalis concentration) can be accomplished by the electrolysis or by the well known anion exchange technique. 3 EXPERIMENTAL

Experimental breakthrough curves for separation of the caesium and rubidium ions in the fixed bed column are shown in Figure 5 and demonstrate the high effectivity of PhFR. C,

0.

0.

v, 1 Figure 5 Breakthrough curves for separation of the cesium and rubidium ions in the fixed bed column (ion exchanger bed height 70 cm, solution flow rate 2 ml/min). A counter-current setup for continuous separation of the alkali metal ions on PhFR has been designed (Figure 6 ) . The setup consisted of two main sections I and I1 (connected altogether in the bottoms as the u shaped loop) for simultaneous accomplishment of both main stages I and 11. In the section I the solution is passed through the compact resin bed from the bottom upwards and in the section I1 the solution is passed from the top downwards; periodically the compact resin bed is transferred along column in direction which is opposite to the solution moving direction. 7 shows the experimental profiles of Figure concentrations of components in solution along the sect+ion I. It demonstrates effective purification of K from Rb . The

Ion Exchange for Environmental Clean- Up

305

0.15 M KC1 solution with no more than 0.0001 M Rb+ admixture was leaving continuously section I.

H

-

Figure 6 Schematic diagram of the separation setup: 1,2 the main sections, 3,4 - auxiliary sections, 5,6 filters, 7-14 - valves, 1 5 , 1 6 pumps, 17 vessel.

-

-

Figure 8 shows the experimental profiles of concentrations of components in solution along the section II+ The extending zone in which+the solution contained 0.3 M Rb with minimal admixture of K was gradually formed in the middle part of section 11. As this zone extended enough, the solution of the purified RbCl with RbOH was+ withdrawn periodically. It contained no more then 0.001 M K . From the bottom of section I1 the mixed solution of KC1 and RbCl with total concentration 0.22 M and of KOH and RbOH with total concentration -011 M +was collected; the ratio of the separated ions R b and K was the same 1:19 as in the initial solution. The total concentration of that solution (-0.32 M) was some higher than the concentration of the eluting HC1 solution (0.3 M) . That increase was explained by higher molecular sorption of electrolytes from alkaline solution in comparison the molecular sorption of HC1 on resin in H ionic form.

306

Progress in Ion Exchange: Advances and Applications A

A

K'

equi v equiv 1---1 1---

t

0 7 0 - 0o-o- 0 0 7

0-

0-

0

O-O\

0

O0 .m22

&-

OH-

6-a-A-&-

A

Rb' \

t y t

Figure

'

0

A

gqui Y 1---

.o. 02

0.1.

0

cRb' &-&-

-0.01

7 Distribution of ions along the section I after passing 3.75 1 of the initial solution 0.150 M KOH + 0.135 M K C l + 0.015 M R b C l .

Figure 8 Distribution of ions along the section 11 after passing 12.75 1 of the initial solution 0,3 I HCl. 1.

2. 3. 4.

5.

6.

References R.E.Davis, in Kirk-Othmer Encyclopedia of Chemical Technology, Interscience, New York, 2nd ed., Vo1.17, 1968, P.684. V.I.Gorshkov, I.Sh.Sverdlov, Zh.Fiz.Khim., 1975, 4 9 , 2724. J.P.Bibler, R.M.Wallace, L.A.Bray, in 'Proceedings of Symposium on Waste Management (waste Management'90)', HLW&LLW Technology, Vol.11, 1990, P.745. V.A.Ivanov, V.I.Gorshkov, I.V.Staina, Russian Patent No 1781313, Priority August 15, 1990, Patented August 15, 1992. V.A.Ivanov, V.I.Gorshkov, I.V.Staina, V.A.Vakulenko, V.N.Tarasov, Zh.Fiz.Khim., 1991, 65, 1962. V.A.Ivanov, V.I.Gorshkov, I.V.Staina, V.A.Vakulenko, V.N.Tarasov, Zh.Fiz.Khim., 1991, 65, 2184.

THE ROLE OF TEMPERATURE IN ION EXCHANGE PROCESSES OF SEPARATION AND PURIFICATION

V.A.Ivanov, N.V.Drozdova, V.I.Gorshkov, V.D.Timofeevskaya Department of Chemistry Lomonosov Moscow State University MOSCOW, Russia, 119899

Most ion exchange separations are traditionally carried out as isothermal ones. In particular, this concerns the ion exchange processes for removal or concentration of alkaliearth and transition metals from natural, technological, or waste solutions. Applying temperature to influence the equilibrium and dynamic properties of certain ion exchange resins allows a significant improvement to the separations, to diminish reagent consumption and quantities of wastes. Consequently, environmentally non-hazardous reagent-less ion exchange separation methods can be developed. 1 EQUILIBRIUM

The influence of temperature on the equilibrium properties has been extensively studied since the pioneering work of researchers on the strongly acidic sulphonic ion exchange resins. Based on those results, the influence of temperature on equilibria of most ion exchange systems is considered insignificant [ 1, P .166; 2, Ch.31 . Our studies of the exchange of mono- and divalent ions on weak acid resins have indicated more significant temperature effects than observed for sulphonic resins. Partially, these results have been published earlier [3-63. Herein, we present mainly new results, which allowed to significantly formulate the conclusions regarding the relationship between temperature effects and chemical structure of resins. The experimental methods of determining the equilibrium parameters were the same as earlier 13-61. Experimental results for some of the resins studied are shown in Fig.1 as plots of the equilibrium constant versus xII at two temperatures (here y and x are the equivalent fractions of the ions in resin and solution phases respectively; the subscripts I1 and I mean the divalent and monovalent components). Similar results for transition metals

308

Progress in Ion Exchange: Advances and Applications

are presented in Table.

D

C

Figure 1 Plots of the equilibrium constant K versus the ionic composition of solution xII for Ca2+- Na+ exchange from 2.5 N solution at 2OoC (1) and 82OC (2). Resins: A - polymethacrylic KB-4; B - phosphonic polystyrene KFtPh; C -d-polyvynilpyridene carboxylic iminodiacetic ANKB-50. VPK; D

-

These results show, that for cation exchangers (sulphonic, carboxylic, phosphonic) without the donor nitrogen containing groups, the selectivity towards divalent ions of the alkaliearth and transition metals increases with temperature. The temperature effects in the case of polyacrylic and

Ion Exchange for Environmental Clean-Up

309

Table Equilibrium characteristics of resins by ion exchange in solution of 2.5 N NaCl and 0.01N transition metal Resin

KB-4

I Ionic system

I I

--------t°C

r ----------

Zn2+-Na+ Ni2+-Na+ 13 39

polymethacrylic resins have been found to be significantly stronger than that in the case of resins with a polystyrene matrix. The equilibrium constants for chelating polyampholytic resins depend on temperature quite insignificantly in the case of exchange of alkali-earth and alkali metals ions and obviously decrease with temperature in the case of transition and alkali metals ion exchange. Due to the non-uniform effects of temperature, for some solution compositions at high temperature, cation exchangers become more selective than chelating resins (Figure 1). This fact erodes, to some extent, the traditional opinion about the chelating resins as being more promising than cation exchangers for separation of divalent ions due to their higher selectivity. Temperature affects the capacity of cation exchange resins (Figure 2). At high temperature polymethacrylic resin has about 20% more volumetric capacity (per 1 ml of the volume proper of resin) than at room temperature. Polymethacrylic cation exchange resins have significantly more ion exchange capacity than chelating resins. 2 DYNAMIC PROPERTIES

The effect of temperature on the shape and length of the ion exchange sorption front is rather complex due to the temperature dependencies of the mass transfer or diffusion coefficients, the selectivity coefficients and resin swelling (Figure 3) . Experimental studies have demonstrated that the equilibrium properties depend on temperature in many cases more significantly than the dynamic ones, in spite of most

310

Progress in Ion Exchange: Advances and Applications

monographs [l, P.166, 285; 2 , Ch.3, 41 emphasizing the temperature dependencies of the dynamic properties in the first place.

G

4 2 C

0.5

Yb

d

Figure 2 Volumetric capacity of resins (per lml of2fesin) versus the ionic composition of resin for Ca - Na exchange from 2.5 N solution. Resins: 1,:' polymethacrylic KB-4; 2 - A-polyvynilpyridene carboxylic chelating VPK; 3 - imgnodiacetic ANKB-50. Tegperature: empty points - 20 C; black points 90 c . 3 ION EXCHANGE SEPARATION AND PURIFICATION

Experimental results on the equilibrium properties have caused us to look critically at the role of temperature in the ion exchange processes of separation and purification. 1. Consider the relationship to the traditional methods of ion exchange softening and purification of the alkali metal salts solutions from the alkali-earth or transition metals. These methods consist in filtration of the being purified solution through a column with a cation exchange resin or with a chelating one in the same alkali metal ionic form. Divalent ions are sorbed by resin; the purified solution of the alkali metal salt is withdrawn from the column. The exhausted resin is regenerated either by the consecutive treatment by acid and alkali or by an alkali metal salt solution more concentrated than the initial one. Obviously, the application of cation exchange resins at a high temperature can increase the volume of the purified solution due to both the significant increase of the ion

Ion Exchange for Environmental Clean-Up

311

A 0.04 0.02

0

6

8

v,e

Figure 3 The self-sharpening fronts by sorption of Ca2+ from mixed solution of 2.5 N NaCl and 0 . 0 7 N CaC120n (A)+ and polymethacrylic cation exchanger polyvinilpyridene carboxylic resin (B) in Na ionic form: initial resin bed 185 cm; solution flow rate 2.6 cm/min - 2.9 cm/min. exchange selectivity and capacity in respect to divalent metals as compare the process at low temperature. The most significant increase of productivity up to 2,5 times is achieved in the case of polyacrylic and polyrnethacrylic resins (see Figure 3 ) . Moreover, if the initial ion exchanger has not been completely regenerated, a better purification is achieved at high temperature than at low temperature. The elution of the divalent ions from the exhausted resin by the

312

Progress in Ion Exchange: Advances and Applications

concentrated alkali metal salt solution is facilitated at low temperature due to lower selectivity of resin. The only positive effect of temperature by sorption of elements of the second group on polyampholyte is the sharpening of the sorption front. If the transition metals admixture is sorbed by a chelating resin from concentrated alkali metal salts solutions, then the productivity of process must decrease due to the decrease of selectivity of polyampholytes. 2. A significant influence of temperature on the ion exchange selectivity of some weak acid cation exchange resins allowed us to propose a dual-temperature reagentless cyclic process for partial purification of the concentrated alkali metal salts solutions from alkali-earth and transition metal admixtures. It consists in filtration of the initial solution through the same column with the polyacrylic, polymethacrylic, or some other resin at periodically alternating high and low temperatures. During the rrhotrr stage of filtration a partial purification of solution is accomplished as the result of higher selectivity at a higher temperature. At the rrcoldrr stage the ion exchanger is regenerated and the concentrated solution of the divalent ion salt is eluted from resin. The experimental breakthrough curves for purification of 2.5 N solution of sodium chloride from calcium admixture on polymethacrylic resin are shown in Figure 4 . It is seen that during the llhotrl stage a tenfold purification of the solution have been achieved. After cooling of the column during filtration of the same initial solution, a significant increase of the impurity-ion in the effluent was observed. After regeneration of resin the purification stage was repeated. The cyclic process described has been theoretically and experimentally found very convenient and successful in the continuous mode, using counter- current columns. Hence, in both modes of the proposed method the initial solution is divided into two parts: the first one - with a smaller concentration of the divalent ions as compare to the initial solution and the second one - with a higher concentration. 3 . Polyacrylic, polymethacrylic and some other resins have been found to be exclusively effective for reagentless dual temperature softening and deep purification of concentrated alkali metal salt solutions from alkali earth and transition metal ion admixtures with application of a cascade of single separation units (such as above described), the parametric pumping technique, or the countercurrent technique. For instance, parametric pumping achieves a decrease in concentration of divalent ions by 3-4 orders magnitude in only 5 stages. So, weak acid polymethacrylic resins can be considered as very useful ion exchangers for thorough purification of concentrated alkali metal salts solutions without any auxiliary reagents.

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Figure 4 Concentration of Ca2+-ions versus the volume of eluted solution under py.ification (1,3) of 2.5 N NaCl solution from Ca impurity (0.02 N) and regeneration (2) of cation exchanger KB-4. The column 60x0.8 cm, the flowrate 2 ml/min.

References 1. F.Helfferich, ’Ion Exchange’, McGraw-Hill, New York, 1962.

2. 3. 4. 5.

6.

W.Rieman, H.Walton, ‘Ion exchange in analytical chemistry’, Pergamon Press, New York, 1970. V.D.Timofeevskaya, V.A.Ivanov, V.I.Gorshkov, Zh. Fiz. Khim., 1988, 62, 2531. V.A.Ivanov, V.D.Timofeevskaya, V.I.Gorshkov, S.N.Grishenina, Zh. Fiz. Khim., 1989, 63, 1867. V.A.Ivanov, V.D.Timofeevskaya, V.I.Gorshkov, T.V.Eliseeva, Zh. Fiz. Khim., 1991, 65, 2455. V.A.Ivanov, V.D.Timofeevskaya, V.I.Gorshkov, Reactive Polymers, 1992, 17, 101.

EQUILIBRIUM STUDIES OF THE APPLICATION OF POLYMERIC RESINS AGGREGATED WITH CALCIUM ALGINATE

Federico Mijangos and Yolanda Jodra. Department of Chemical Engineering. University of Pals Vasco. Apdo. 644. Bilbao 48080. Spain.

ABSTRACT Calcium alginate gels have been applied for agglutinating Lewatit TP207 ion exchange resin for the recovery of copper from synthetic solutions. The biopolymer acts as a membrane support, physically separating the polymeric resin from the aqueous phase. In this way, the ion exchanger is protected, by a coating effect, against suspended solids, coldoids, etc. The sorption on spherical composite particles improved mass transfer in relation with calcium alginate gels. Distribution coefficients were also modified at the same time that abrasion and poisoning were drastically reduced. Solute distribution makes us to conclude that the system behaves basically as ion exchanger but the amount of the free water in the gel modified quantitatively the amount of retained solute. 1 INTRODUCTION

Many biopolymers derived from microorganisms and plants are known to strongly bind heavy metals1. Due to the excelent selectivity for multivalent metal ions and their low production cost, such biopolymers offer an alternative to convencional methods of metal recovery. Alginate is known to have a high metal-binding capacity and a favorable selectivity specially for copper. The gel-forming property of alginic acid, by ionexchange of alkali-metal ions such as calcium, suggests its use as a metal sorbent. Lin2 characterized the gelation of sodium alginate with calcium ions by a moving gel front and applied a physical diffusion model to predict the speed of the front and estimate the physical parameters. Potter3 studied this process by magnetic resonance imaging to track the reaction front during the gelation. The ion-exchange properties of alginates were reported by Smidsrod et a1.4,5 and Kohn6. They determined the ion-exchange selectivity coefficients of a number of alginates and alginate fragments. These authors observed that the affinity of alginate for divalent cation and the selectivity coefficients increased with increasing content of guluronic acid in the polymer, and that alginate in solution presented a lower selectivity than alginate in the gel form. Ion-exchange properties of other polyanions were compared by Haug et aL7. Cozzi et al.8 observed that the affinity of alginic acid for homologous ions of the periodic table can be correlated to the size of the hydrated ionic radius. He also reported that the ion-exchange is not the only mechanism, but that the influence of the two vicinal hydroxyl groups on the retention capacity of alginic acid is also important. Jang et al. carried out experiments concerning the sorption equilibrium of copper by sodium alginate directly dispersed into a loop fluidized bed reactor9 and also by calcium alginate gels previously

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315

formedlo. They used a modified Langmuir model to correlate the experimental data. Alginate gels were also used to recover cobalt and copper from a cobalt ore leachatell. Konishi et al.12 found that gel particles of alginic acid were useful to recover zinc, cadmium, and lanthanum from aqueous solutions and determined the distribution equilibrium constants. Mongar and Wassermannl3 showed that fully-swollen alginate fibers are also cation-exchange materials. Alginic acid, sodium alginate and calcium alginate have been extensively employed as ionexchangers in colummn chromatographic separations of different elements14. Cozzi et al.15v16v17 proposed alginic acid as a new stationary phase for thin layer chromatography for organic and inorganic ions because of its chemical and physical favourable properties. The alginate of propylene glycol is used as a component of paper and paperboard, a deforming agent, an inert pesticide adjutant and an emulsifier/stabilizer. The sodium alginate is used as a food emulsifier, stabilizer and thickener, and as a potential substitute for natural foods. It has also been used as a coagulant aid for water treatment. Fanel* reported that ultrafiltration coupled with ion-complexing polymers as alginate or ionexchange resins provided efficient metal recovery from electroplating industry. Biomaterials has been applied to the recovery of heavy metal from mine drainages and industrial waste waters. The gel forming property of alginic acid has also led to its extensive use in biomedicine and the biotechnology industry to immobilize or encapsulate enzymes, subcellular organelles, and living cell@. For instance, ethanol fermentation using alginate immobilized yeast cells is well known. This method of cell immobilization in calcium alginate has several advantages: it is possible to establish dense cell cultures and, therefore, obtain faster overall reaction rates; the methods retains the cells in the reactor, so the cells can be used for a longer period of time and the need for a new biomass synthesis is reduced; a high percentage of the cells remains viable during calcium alginate immobilization; and the processing is simplified because the product is free of cells. However, in this entrapped systems mass transfer limitation exists since the gel introduces an additional mass transfer resistance. The technique of immobilization has also been applied to metal recovery. Jang et al.20 added a trace amount of EDTA to the algin solution in order to enhance the capacity of copper absorption. The alginate gel provided a matrix for holding the water-soluble EDTA. In the same way, Yong-Xiang Gu21 observed that alginate bead containing activated carbon increased the mass transfer rate of pentachlorophenol. Therefore, the alginate properties allow the preparation of gel beads with physical-chemical characteristics to be adapted to the process requeriments. These system could be used for the recovery of solutes from aqueous solutions. This paper reports the experimental results obtained using calcium alginate beads, with and without iminodiacetic type Lewatit TP207 ionexchange min in the gel phase, as ion-exchangers for the retention of copper from synthetic solutions. The equilibrium data were then analyzed to determine the stoichiometry ratio, the distribution coefficients and the equilibrium constant. The maximum retention capacities of sodium alginate and synthetic resin powder were also determined.

2 EXPERIMENTAL Calcium alginate spheres were prepared by dripping 3.0 %J w/v sodium alginate solution into a stirred 0.05 M calcium nitrate solution at room temperature2'). As soon as the sodium alginate sol came into contact with the calcium solution, spherical gel particles were formed2. The drops gelled into approximate 3 mm diameter spheres. After an overnight, gel particles became rigid and turned opaque white colour. They were separated from the calcium solution to be used later in the recovery of copper from

Progress in Ion Exchange: Advances and Applications

316

Table 1 Experimental conditions of copper retention Dry ion No-spheres Calcium alginate beads Alginate beads with resin particles Alginate beads with resin Dowder

Initial

Average initial diameter of beads

Dry,sodium alglnate (g)

exchanger resin

500

0.4093

0.0

116.0

0.309

500

0.4644

0.5276

108.5

0.288

346

0.2807

0.1737

105.0

0.309

(ppm Cu2+)

@)

(Bn)

Table 2 Summary of conditions in equilibrium experiments NO.spheres

Calcium alginate beads Alginate beads with resin powder

Dry alginate (g)

Dry ion Average initial exchanger resin diameter of beads @)

(cm)

100

0.0924

0.0568

0.326

I0

0.0

0.0351

0.309

synthetic solutions. The same procedure was used to prepare alginate beads containing the ion-exchange resin. An appropiate amount of resin was aggregated to the sodium alginate solution and, then, the mixture was pumped into the calcium solution. Previous to the equilibrium analysis, the kinetics of polymer-metal binding was investigated in order to find the time required to achieve equilibrium. The experiments were carried out by a batchwise method. Alginate gel particles were added to a stirred flask containing 400 mL of CuS04.5H20 solution at 25 "C. The ionic strength was adjusted by adding 0.1 mole NaNO3 to each litre of the reactor fluid and solution pH was adjusted about 4.0 with HC1 during the experiments. The initial conditions of each experiment are listed in Table 1. Equilibrium data were determined by contacting calcium alginate beads and 100 mL of copper sulfate solutions with different initial concentrations. Experiments were camed out using alginate beads with and without ion exchanger powder (particle diameter lower than 0.21 mm). Experiments were run at room temperature, at constant ionic strength and at pH around 4.0 to avoid precipitation reactions during experiments. Table 2 shows the experimental conditions for equilibrium runs. Concentrations of copper and calcium in samples were determined by atomic absorption spectrophotometry. The concentration of copper uptaken and the calcium displaced from the gel at equilibrium was determined from the mass balance. At the end of each run, the spheres were collected, external water removed and the total volume of the alginate spheres was measured. The equilibrium pH of the solutions was measured by using a pH meter. The total cationic exchange capacity of sodium alginate Qa was evaluated as 3.93 moll kg dry sodium alginate by acid-base titration, so that the concentration of avaible carboxilic groups was estimated. Therefore, divalent ion exchange capacity should be 1.96 molkg. The metal-equilibrium behaviour and characteristics of the comercial ion exchanger, Lewatit TP207 from Bayer AG, are described in literaturez2. The acid-base capacity of the ion exchanger is Qr = 5.68 moll kg dry resin. 3 DISTRLBUTION EQUILIBRIUM OF COPPER Alginate is known to bind both calcium and copper strongly, with the selectivity for copper being several times more favorable than for calcium4~5~6~7. When the gel particles of calcium alginate gel are in contact with the liquid phase, the metal ions exchange with

317

Ion Exchange for Environmental Clean- Up

the calcium ions in the gel phase until the equilibrium is reachedlo. The ion-exchange reaction can be expressed as follows: R2Ca + Cu2' + R2Cu + Ca" (1) The equilibrium constant for the reaction should be - qcucca K cu a -(2) qcaccu where qcu and qCa are the amount of copper and calcium bound to the gel in mol per unit of dry mass of sodium alginate, and Ccu and CCa are the concentrations of copper and calcium, respectively, in the bulk solution. The distribution ratio DM of any metal between the gel and the liquid phase is defied as

So, the equilibnb constant (2) can be rewritten as Kca CU =% (4) Dca However, the gel particles contain an important amount of water, higher than 95%. Then, the metal fraction -rMenclosed or soaked up in the gel matrix should be considered and distinguised from the total amount of metal content, but not bound to the alginate groups. Therefore, the fraction of metal enclosed in the gel matrix can be estimated by taking into account the metal distribution between both phases using a Donnan distribution coefficient a.This fraction is define as:

where v is the volume of gel and ma the weight of dry sodium a l g i ~ t dispersed. e 'de mass balances of species involved in equilibrium are:

GuV"= qcuma + rcuma + C ~ u v

(6)

6 a v o =qNama+rNama+cNav

(7)

c"M

where is the initial concentration of metal. VO is the initial volume of liquid, V is the final volume of liquid, and r$ is the initial metal concentrationenclosed defied as:

Then, the conc&tration of binding copper qc,, and calcium q h will be calculated by rearrangement of the mass balance on copper and on calcium into the Q. (1 1) and Eq. (12), respectively. (11) 4cu = (4cu)eXp - r cu (12) q a = G - (qca)dis + G a - rca where Qa is the initial concentration of functional groups in the gel phase, that is the maximum ion-exchange capacity of alginate, (qcJeXp is the copper concentration in the gel phase given by Q. (13) and ( q d a is the concentration of calcium displaced from the gel given by Eq. (14).

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Progress in Ion Exchange: Advances and Applications

On the other hand, when alginate includes ion exchanger resin powder in the gel matrix, the contribution of the ion exchanger to metal retention is necessary take into account. Then, the material balances of copper and calcium can be rewritten into the following form: (16) f & + r&)ma + Qrmr = qcom, + rcama + CcuV where Q is the concentration of functinal groups in the ion exchanger, mr is the amount of dry ion exchanger dispersed within the alginate, mt = ma+mr and Xa = ma I mt. The concentration of binding copper and calcium will be given by Eqs. (17) and (18), respectively.

Finally, substituting the values of metal concentration in the bulk solution and the amount of metal bound to the alginate into Eq. (3), the distribution ratio for both calcium and copper are calculated ( DcU and Dca, respectively). If the equilibrium data are consistent with the above mentioned equations, the equilibrium constants will be evaluated from the slope of a straight line of the plot of Dcu vs D a . 4 RESULTS AND DISCUSSION

Figure 1 shows the variation in Cu2+ ion concentration in solutions vs time for calcium alginate beads with and without the ion exchanger in the gel matrix. 24 hours were considered as sufficient time to attain equilibrium state. Equilibrium isotherms for copper and calcium alginate beads with, and without, the resin powder are shown in Figure 2. For calcium alginate beads, the amount of copper uptake (qculeXpis calculated by Eq.(13) and the amount of calcium displaced from the gel (qCa)dis by Eq. (14). These expressions are similar for composite alginate beads; the weight of dry sodium alginate ma is changed by mt. The composite spheres show a higher capacity for copper. In fact, there is a stoichiometric relationship between the mole of calcium displaced and the mole of copper uptake (Figure 3). Therefore, an equilibrium model based on Cu2+/Ca2+ion-exchange process has been proposed. At equilibrium, the pH of solutions ranges from 5.58 for the lower metal concentration to 3.64 for the higher when composite alginate beads were used; but, when calcium alginate gels were used the pH ranges from 4.59 to 4.06. In all the cases, a fixed amount of calcium is displaced from the gel phase for any amount of metal exchange because of the calcium enclosed in the gel matrix during the gelation. As calcium is released from the gel matrix, the spheres swelled significantly in runs which the lower initial copper concentration, so that the volume of the gel vg is different in each experiment. Any increase in copper concentration in solution reduces the osmotic pressure difference, thus the solvent uptake is smaller z3. Therefore, due to the swelling of the gel beads, the value of the distribution coefficient a is also different in

319

Ion Exchangefor Environmental Clean-Up

0

100

300

200

400

500

Time, min Figure 1Kinetic of copper retention onto alginate gels using dfferent amounts of ion exchanger included (whv 96)

0

2

4

6

a

Conc. of copper in solution, m M Figure 2 E uilibrium isothermfor copper solution and alginate spheres: (0) Copper uptaken (0) Calcium disphcedfrom calcium alginate beads; ( 0 )Copper uptaken and (m) Calciumdisplacedfrom alginate be& with ion exchangerpowder

M%

Progress in Ion Exchange: Advances and Applications

320

each run as Figure 4 shows. The swelling is more important for composite alginate beads than calcium alginatebeads because of a higher osmotic effect in the later system. The values of the distribution coefficient for both systems have been calculated combinating the total material balance with copper and calcium balances. A fixed amount of sodium concentration of 0.65 moY kg dry sodium alginate in the gel phase has been considered, while qH is negligiblein respect to the concentration of the other metals.

I

31

0

1

0

0

I

1

1

2

3

Conc. of copper in the gel phase, moYkg Figure 3 Relationship between copper ion uptake and calcium ion release

In a Figure 4 Relationship between swelling per cent and the distribution coeficient

32 1

Ion Exchange for Environmental Clean-Up 5

4 -

3-

0.0

0.5

1.o

3 Distribution ratio of calcium x 10 ,L / kg Figure 5 Correlationfor observed dism*butwnratio of copper and calcium

1.5

Taking into account the values of the different parameters, the concentration of copper and calcium bound was calculated by Eqs.( 11) and (12) for calcium alginate beads, and Eqs.(l7) and (18) for the composite system. Then, the distribution ratio of each metal was determined substituting the metal concentration in the bulk solution and the concentration of metal bound in Eq.(3). It is verified from Figure 5 that experimental data are well correlated to the equilibrium model proposed in Eq.(4) for the ion-exchange reaction (1). The slope of the straight tine yields the equilibrium constant as Kg:= 2.81 for calcium alginate beads and 3.54 for alginate beads with ion exchanger. 5 REFERENCES

1. W. Hartmeier, R. Schumacher. W. Gloy, R. Lass&, Med. Fac. Lundbouww. Univ. Gent., 1992, 57, 1713. 2. S.H. Lin, Chemical Engineering Science, 1991.46.651. 3. K. Potter, B. J. Balcom, A. Carpenter, L. D. Hall, Carbohydrate Research, 1994, 257, 130. 4. 0. Srnidsrod and A. Haug, Acta Chem. Scand, 1968.22, 1989. 5. 0. Smidsrod and A. Haug, Acta Chem. Scand.. 1972.26.2063. 6. R. Kohn. Pure and Appl. Chem. 1975.42.371. 7. A. Haug and 0. Smidsrod,Acta Chem Scand., 1970.24, 843. 8. D. Cozzi, P. G. Desideri, L. Lepri, J. Chromatog., 1969.40, 130. 9. L. K. Jang, G. G. Geesey, S. L. L6pez. S.L. Eastman, P.L. Wichlacz, Water Research, 1990,24,889. 10. L. K. Jang, G.G. Geesey. S. L. Lbpez, S.L. Eastman, P.L. Wichlacz, Chem Eng. Comm.. 1990.94, 63. 11. L. K . Jang, G.G.Geesey, S. L. L6pez, S.L. Eastman, P. Pryfogle, Biotechnology and Bioengineering, 1991,37,266.

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Progress in Ion Exchange: Advances and Applications

12. Y. Konishi, A. Satoru, Y. Midoh, M Oku, Separation Science and Technology, 1993, 28, 1691. 13. I. L. Mongar, A. Wassermann, J. Chem SOC., 1952,492. 14. L. K. Jang, W. Brand, M. Resong, W. Marinieri, G. G. Geesey, Environmental Progress, 1990,9,269. 15. D. Cozzi, P. G. Desideri, L. Lepri, G. Ciantelli, J. Chromatog., 1968, 35, 396. 16. D. Cozzi, P. G. Desideri, L. Lepri, G. Ciantelli, J. Chromatog., 1968,35405. 17. D. Cozzi, P. G. Desideri, L. Lepri, G. Ciantelli, J. Chromatog., 1969, 40, 138. 18. A. G. Fane, A. R. Awang, M. Bolko, R. Macoum, R. Schofield, Y. R. Shen, F. Zha, Wat. Sci. Tech., 1992, 25, 5 . 19. R. M. Hassan, S. A. El-Shatoury, T. H. Makhlouf, High Peryormance Polymers, 1992. 4, 49. 20. M. Kierstan, J. Reilly, Bioechnalogy and Bioengineering, 1982, XXIV,1507. 21. Yong-xiang Gu, Zhong-cheng Hu, R. A. Korus, The Chemical Engineering Journal, 1994, 54, B1. 22. F. Mijangos and M. Diaz, Ind Eng. Chem Res., 1992,31, 2524. 23. F. Helfferich, "Ion Exchange", McGraw Hill, New York, 1962.

OXIDATIVE REGENERATION OF SULPHONIC RESINS FOR THE PREVENTION OF CHROMIUM(III) ACCUMULATION Federico Mijangos, Maria Puy Elizalde and Moufdi Kame1 Kebdani. Department of Chemical Engineering and Analitical Chemistry. Universidad del Pais Vasco. Apdo. 644.Bilbao. Spain.

ABSTRACT Chromium(II1) retention from 0.5 M NaNO3 solution by the sulphonic resin Lewatit SlOO has been studied and proved to be an almost irreversible process using conventional acidic elution. An oxidative regeneration of the resin by hydrogen peroxide has been also studied. For this purpose, thekinetics of chromium (111) oxidation by H202 was analyzed. Optimal conditions for total elution and the effect of the oxidative method in the matrix structure are reported. Analysis of the ion-exchange process by SEM-EDX (Scanning Electron Microphotographs- Energy Dispersive Spectrometry X)has been also carried out. 1 INTRODUCTION

Some heavy metals such as chromium, cadmium and mercury present great interest in environmental control owing to their high toxicity. Therefore, their presence in waste waters is the object of legislation, leading to the total elimination of the polluter. In particular, waste waters from tannery industries contain large amounts of chromium (III) (2-5% on dry weight) as well as Fe(II1) and A l O ' . There are different processes to recover these metals, which in general involve a step of retention of the metals based on ion-exchange resins. However, the high affinity for chromium (III) of cationic resins gives rise to difficulties in the acidic elution. A similar problem appears also in waste waters from electroplating and hydrometallurgy since a decrease of the efficiency of the ion exchanger due to the irreversible retention of chromium (In)and other trivalent ions has been reportedz. Under these conditions, an alternative oxidation stripping-elution using hydrogen peroxide in alkaline medium has been reported to be very promising3 . Cation exchangers of the sulphonated polystyrene (i.e., Lewatit S100, S112) and iminodiacetate (i.e., Lewatit TP207)types have been frequently used for the uptake of heavy metals4, from weakly acidic to weakly basic solutions. In particular chromium(1n) can tie selectively recovered with resins mentioned above4. In this work, the use of a cationic ion exchanger to recover chromium(II1) from NaN03 aqueous solution has been studied. Conventional acidic elution by HC1 has been compared with oxidative regeneration of the loaded resin by hydrogen peroxide The processes of retention and elution have been examined by scanning electron microphotographs and microanalysis since these techniques, through the analysis of the mamx structure, has been proved to be very useful to study ion exchange phenomena.

Progress in Ion Exchange: Advances and Applications

324

2 EXPERIMENTAL The characteristics of the polystyrene gel sulphonic resin (Lewatit S100) used for chromium recovery are described in Table 1, and referred to the resin as supplied (Lewatit Handbook).

Table 1 Product datafor Lewatit SIOO

Prior to the experiments, the resin was conditioned by three successive washings with 1M HCl and 0.1M NaOH (lObv/h). To convert the resin into the sodium form a treatment with 1M NaOH was carried out. The last stage was used for capacity measurements. All the chemicals used were of analytical reagent grade. The ionic strength was adjusted to 0.5M NaN03 and maintained constant in all the experiments, which were performed at room temperature. The experiments in homogeneous phase were carried out in a 200 ml stirred tank using 9.6mM Cr(II1) in 0.5M NaN03 and several concentrations of H,O,. The experiments in the heterogeneous Cr(II1)-Lewatit S 100 system were carried out either in batch (100 ml of 19.2 mM Cr(II1) and 2.5 g of dry resin) or using a laboratory column of 3 cm diameter and 25 cm length containing conditioned resin was saturated with lo00 ppm Cr(II1) at 9.6 bv/h. Total metal concentration in the liquid-phase was determined by atomic absorption spectroscopy on a Perkin-Elmer Model 1100B. UV spectrophotometry (PYE UNICAM PU 8600) was used to determine the concentrationof the chromate ion at 370 nm. On the other hand, hydrogen peroxide concentration was determined by a iodometric methods. Scannig electron microphotographs and microanalysis were obtained using a JEOL-6400 microscope. The time used to obtain the spectra was 500 seconds, and a high limit energy of 20 Kev was applied. 3 ANALYSIS IN HOMOGENEOUS PHASE

3. 1 Speciation Equilibria Literature data on the protolytic and redox reactions of chromium in aqueous media617 have been used to construct the predominance diagram pE=f@H)of chromuim (1mM total concentration) using the PREDOM program8 , as seen in Figure 1. It can be appreciated that the trivalent ion is dominant in acidic conditions, whereas when increasing the pH value the hydrocomplexes Cr(OH),' and Cr(OH$ dominate until

325

Ion Exchange for Environmental Clean-Up

the formation of the solid chromium (111) hydroxide which, at the most alkaline conditions, redissolves to give the chromite anion Cr(OH&. Concerning the speciation of WVI) in aqueous solution, the sequenceof species H2CrO4, HCrOT, and CrO;- is dominant depending on pH, whereas the contribution of Cr2& is only important at concentrationsof chromium (VI) higher than 0.01M. 3.2 Homogeneous Oxidation of Cr(III) in aqueous Phase According to the speciation data on Figure 1, chmmium(III) exists as Cr(OH& in alkaline solution (pH>11). Therefore, the oxidation reaction by hydrogen could be described as: 2Cr(OH)i + 3H2@ + 20H- t)2C& + 8H20 (1) The required amount of H202 to produce complete oxidation of Cr(III) was determined by batch experiments of a 9.6 mM WIII) solution in 0.5 NaNOd 0.95 M NaOH aqueous medium and varying the total concentration of H 2 0 2 . An optimum ratio C ~ 2 0 2 : of 4: 1 was deduced. Figure 2 shows the effect of hydrogen peroxide on the oxidation of chromium(1II) and the formation of chromate versus reaction time, as well as the remaining hydrogen peroxide. The total oxidation reaction requires a reaction time of, approximately, 90 min in these conditions.

" V

0

5

10

Figure 1p E vs pH diagram at 1 mM chromium concentration

326

Progress in ion Exchange: Advances and Applications 4 ION EXCHANGE EQUILIBRIUM AND OXIDATIVE ELUTION

4.1 Ion-exchange Equilibrium in the Cr(II1)-Lewatit SlOO System

The ion-exchange reaction of Cr(lI1) by Lewatit SlOO Na+Rdescribed by the following equation: u Cr3" + Nu+R-

could be

--

Cr, R iNu+

The equilibrium constant for this reaction, KO ,can be expressed as

where qCr is the amount of chromium in the resin, qR is the amount of fixed groups of the ion exchanger and Ca is the concentration of chromium in the solution. The total capacity of the resin, Q,can be described as 1 (4) Q ' q R + q H + Fqcr

qH being the amount of H+ in the solid phase. On the other hand, the acidic constant of the protonated resin can be defined as:

a++]

0

ka =

qH Substituting Eqs. (4) and (5) into Eq. (3). an apparent constant kapcan be defined as follows:

V-~I 50

100

n

I

I

150

200

n

"

250

Time. min Figure 2 Homogeneous oxidation of Cr(tt1) (CH202=0.038M, C G =9.6 m M in 0.5 M N d O 3 . 0.95NaOH aqueous medium :(0) Total H202. ( A ) Free H202. (0 ) Chromate,(0)Cr(ttt)

321

Ion Exchange for Environmental Clean-Up

Figure 3 shows the results of the ion exchange process in the system Cr(ll1)Lewatit SlOO at different pH values (Lower than 4 to avoid metal precipitates). Equilibrium data were fitted to an ion exchange model according to Eq. (6) and the values of the parameters calculated have been summarized in Table 2. It can be appreciated that the apparent constant, as well as the resin uptake, increase with pH. From the best fit the values of Q--.405 moVkg dry resin and a4.5 were obtained. At the same time values of the equilibrium constants kc,=2.75 (Umol)l/2 and ka=1.15 10-2(moVL)

Table 2 Effect of pH on equilibriumparameters

4.2 Elution of Cr(II1) born the Lewatit SlOO

As a first step, a conventional regeneration of the loaded resin was camed out using a 1M HCI. The results obtained are shown in Figure 4, from which it can be derived that the elution of Cr(II1) is only partial.

A

A

a

A

0

10

A

%A

A

CIA

A

A

0

0 0

20 30 40 Ct(111) in soIution, mmol/L

0

50

Figure 3 Effect ofpH on the ion-exchange equilibrium in Crflll)-L.ewatitSloO system: ( o ) p H = 2.0. ( a) pH= 2.5. ( A ) p H = 3.0, ( A ) ~ H =4.0

In order to confirm these deductions a sample of the resulting resin was analyzed by EDX ( Energy Dispersive Spectrometry X).In Figure 5 the microanalysis of an X-

Progress in Ion Exchange: Advances and Applications

328

Ray microanalysis of the regenerated resin is illustrated. It can be appreciated the presence of chromium fixed onto the ion exchanger structure. The peaks correspond to the chromium transitions jointly with the sulphur from sulphonic groups and other trace metal such as iron. From these results it can be confirmed that the total elution of Cr(II1) by 1M HCI is not possible, probably due to the strong bond between the structure of the resin and the metal ion. So, it is necessary to think of complementary methods to achieve the regeneration of the resin. For this purpose, acid regeneration (1MHCI) followed by an oxidative step using 0.08 M H202 was tried. Although chromium(II1) is selectively recovered onto the sulphonic resin, it has been proved that there is not a quantitative retention of chromate. Probably this anion is excluded from the polyanionic matrix by the Donnan effect9Prior to the experiments, some scanning electron microphotographs were taken for samples of the resin, either conditioned, and unused (Fig. 6a) and treated with H202 (Fig. 6b). The effect of the oxidant on the structure of &heresin exchanger can be deduced if compared both microphotographs. It is probable that the formation of oxygen inside the resin could modify and even break the resin bead producing a resin with a lower operation life. Finally, Figure 7 shows the results of the oxidative elution, and prove that H 2 0 2 is able to elute the amounts of Cr(II1) quasi-irreversibly loaded into the resin.

40

30

20

10

ob

I

I

I

0

10

20

30

Bed Volume Figure 4 Elution of Crflll)using HCI IM

-

--, 0 40

,

50

329

Ion Exchange for Environmental Clean-Up Counts ( x ~ o * )

0

2

4

6

8

10

Range ( k e V )

Fcgnre SScanning electron microanalysis of a particle regenerated with 1M HCl

Figure 6a Scanning electron microphotographof unusedparticle

Progress in Ion Exchange: Advances and Applications

330

Figure 6b Scanning electron microphotograph of a particle regenerated with HCl followed by H 2 0 2

0

10

20

30

Bed Volume Figure 7 Oxiahtive stripping of Cr(ll1)

40

50

60

Ion Exchange for Environmental Clean-Up

33 1

Acknowledgements Thanks to Domenico Petruuelli and Giovani Trivanti from the Istituto di Ricerca sulle Acque, whom introduced us in this topic. 5 REFERENCES 1. D. Petruzzelli. R. Passino. M. Santori. G. Tiravanti. Heaw Metal in the Environmentv1989,2,337. 2. K.Dorfner. Ion Exchange", Walter de Gruyter, Berlin, 1990, p. 845. 3. D. Pemzzelli, L. Alberga, R. Passino, M. Santori, G. Tiravanti, Reactive Polymers , 1992,18,95. 4. K. Dorfner, Ion Exchange", Walter de GNyter, New York. 1991, Chapter 2, p. 1384. 5. I. M. Kolthoff, E. B. Sandell, E. J. Meehan, S. Bruckenstein, " Anflisis Qufmico Cuantitativo", Nigar S.R. L., Buenos Aires, 1972, Chapter 5, p. 871. 6. C. F. Baes and R. E.Mesmer, "The Hydrolysis of Cations", Wiley and Sons, New York,1976,Chap 10,p. 211. 7. L. G. Sillen, Stability Constants of Metal Complexes, Section 1, Inorganic Ligands". The Chemical Society, London, 1964, Section 1, p. 50. 8. I. Puigdomenech, "INPUT, SED and PREDOM: Computer Programs Drawing Equilibrium Diagrams", TRITA-00K-3010, Dept. hog. Chem. The Royal Inst. Technolog. (KTH), Stokholm, 1983. 9. F. Helfferich, " Ion Exchange", Mc Gmw-Hill, New York, 1962, Chapter 3, p. 134. It

I'

ADSORPTION OF PHENOLIC COMPOUNDS FROM MULTICOMPONENT SOLUTIONS ONTO POLYMERIC RESINS.

Federico Mijangos, Ana Navarro and Marta Martin. Department of Chemical Engineering. University of Basque Country A p h 644. Bilbao

Spain.

1.- ABSTRACT Adsorption with polymeric material is a competitive operation that contributes effectively to the removal of pollutants in waste water treatments. In general, waste waters contain more than one component, so that is necessary to study the adsorption equilibrium from solutions containing more than one solute. First of all, distribution equilibrium have been investigated for the adsorption of single component solutions: ortho, meta, para-cresol and phenol on Amberlite XAD-4resin. The experiments were done using a batch technique. A new model based on the Langmuir equation was selected to analysed the effect of pH, temperature and ionic strength on the equilibrium. Finally, adsorption isotherms were obtained experimentally for multicomponent solutions of phenol, ortho and meta-cresol, finding basically the same relationship between simple and multicomponent systems. A general equation has been used for multicomponent systems, this includes molecular interaction in the adsorbed phase and the adsorbent surface heterogeneity.

2.- INTRODUCTION The potential impacts of hazardous organic pollutants in industrial and municipal water constitute a matter of steadily expanding concern for water quality specialist. Control of toxic pollutants is gaining increased emphasis in both water and waste water treatment. This interest in removing organic pollutants from waste waters has stimulated investigations of various possible processes of water purification, Treatment methodologies such as biological degradation, adsorption, ion exchange, chemical oxidation, membrane separation, incineration and stream stripping have been applied for a long time'. Adsorption has been demonstrated to be a wide spectrum treatment for removal of dissolved organic substances. Over the last decade, the use of synthetic polymeric adsorbents in the separation and recovery of organic compounds from waste waters in the chemical and pharmaceutical industries has increased rapidly. These adsorbents solve industrial-waste-treatment problems, whilst meeting two needs not usually attainable with activated carbon: non destructive adsorption, which peimits recovery of costly or short supply products (organic compounds that have been recovered effectively from waste streams using synthetic adsorbents include phenols, chlorinated phenols, aromatic and aliphatic nitro-compounds and chlorinated pesticides.); and non-thermal regeneration, which reduces fuel bills.

Ion Exchange for Environmental Clean-Up

333

Capital costs of synthetic adsorbents systems and those of activated carbon are Comparable. However operating costs indicate that polymeric adsorbent methods are more economical than carbon systems when the level of dissolved organic adsorbate is high2. Industrial and municipal wastes usually contain several substances, which compete for available adsorption sites on the surface of the adsorbent The design of equipment for the adsorption process requires equilibrium data for each of the organic pollutants involved and their mixtures. In case of mixtures, competitive adsorption is most likely to occur since the available surface area of the adsorbent will be occupied, to varying degrees, by all the adsorbate components. ASa result, the uptake of a single solute will be reduced when compared to the load that can be reached in the absence of other competing components. Hence, proper modelling of the adsorption process requires a reliable technique for simulating the concentrations of the mixture in equilibrium from pure solute data. For this purpose, several models have been proposed, including the Langmuir competitive adsorption model3, the Polanyi competitive adsorption model4, and models developed by Fritz and Schlunder5and Minka and Myers6. However, the model with the most thermodynamically accepted foundation is the ideal adsorbed solution theory (IAST) propose by Myers and Praunitz7 for gas mixtures and later developed by Radke and Praunsnitzs for dilute liquid solutions.

3.- ADSORPTION FROM SINGLE SOLUTION Figure 1 shows experimental results from single solute equilibrium adsorption studies of phenol, ortho, meta and para-cresols on XAD-4 resin. Here, the experimental relationships between the equilibrium liquid phase concentration and the amount adsorbed were fitted to three equations: Langmuir, Freundlich and BET. Langmuir equation does not fit well the experimental data at high concentrations, however Freundlich and BET equations, give satisfactory results. These two equations were not selected because their parameters cannot be modified to take into account the effect of pH and ionic strength on the equilibrium. A new model based on the multilayer adsorption has been developed. The mechanism of adsorption from aqueous solution of organic substances is based on the differences between adsorption surface sites and on the basis of the Langmuir equation. The isotherm equation can be written as follows:

s = Q

K,c'

zm

where q is the amount adsorbed in the solid phase (moVkg dry resin), C is the molality of phenolic compound (mollkg water), q is the m a x i q m adsorption capacity (mol/kg dry resin) and K are the equilibrium constants (kg/mol)l. Values of parameters Ki and Q, listed in Table 1, have been calculated by comparison of the equation 1 against experimental results. The adsorption capacity for cresols was higher than phenol. This was due to the activation of the aromatic ring by the methyl group, which favours the formation of donor-acceptor interaction between the phenolic compound and the group on the resin surface. To evaluate the effect of temperature on the constants, measurements were made over the range from 20 to 8OoC,using the staggered procedure described by Mijangos and Navarro9. The adsorption enthalpies, AH, and the pre-exponential constants derived from the Arrhenius relation are summarised in Table 1.

Progress in Ion Exchange: Advances and Applications

334

' I 0 0 0. 0

0 0.

0 0

0-cresol p-cresol

A A m-cresol 0 Phenol Phenol50'C 0

50

100

150

C (mmoVL) Figure 1.- Adsorption isotherms of phenol, 0-cresol, m-cresol and p-cresol at pH=5.73 and T=3OOC 4.- ANALYSIS OF THE ADSORPTION PARAMETERS

4.1.-

Solution pH

Phenolic compounds are weak acids, and their non-ionic and dissociated forms show different adsorption behaviour. The pH of the bulk solution can affect phenol speciation as well as the resin structure. For adsorbents resins, there is no detailed description of the effect on surface area, pore size distribution or surface polarity. One derives from the results summarised in Figure 2, that the adsorption is high in acid solutions of phenolic compounds where the non-ionic or neutral form predominate, and low in basic solution. Hence, if adsorption is conducted at several pH units below pKa value of the compound to be retained, good efficiencies in separation processes can be achieved, but the stripping of sorbates can be done using alkaline solutions. The concentration of the undissociated form,c, can be calculated from the concentration of the phenolic compound measured analytically by HPLC, co (molkg of water) by equation 2. c = ac" (2) where a i s a dissociation parameter which is a function of the pH and Ka the dissociation constant of the compounds;

335

Ion Exchange for Environmental Clean-Up

a =

1

-

(3)

+

1

cH+

Then, introducing this factor into equation 1, an apparenhadsorption constant, K'. can be derived (4)

To check the speciation approach of model (eq. 1). the apparent adsorption constants was compared to the parameter a The pKa values were estimated from Eauation 4. The pKa values are grouped in Table 1.

0

0.0 '-6

I

I

8

10

.

12

A

0 0

m-cresol 0-cresol Phenol

14

PH Figure 2.- Effect of the pH on the adrorption of phenol (c"=2.5, US=20.78 u k g , T= 22oC), 0-cresol (c"=2.14, US=31.17 U k g , T= 22OC) and m-cresol (c0=2.14, US=14.63 U k g , T= 22OC). 4.2.- Sodium sulphate concentration. Although strong electrolytes are not adsorbed, and do not modify the adsorbent, the presence of an electrolyte. such as sodium sulphate in an aqueous system enhances phenolic adsorption 2.10.11. This is probably due to a "salting oul" effect in the aqueous

Progress in Ion Exchange: Advances and Applications

336

phase. The fraction of free water in solution decreases with the salt content as a consequence of the ion solvating, causing an effective increase in solution concentration that can be estimated from Equation 5. c

no c-

=

1 -

PXS

Here c, is the molal concentration of the undissociated form of the phenolic compound. This equation has been derived by considering the solvation water. using the term p, which is the averaged amount of water bound to sodium sulphate.

1000 IL

. 800 600

0

A A

A

0-cresol m-cresol p-cresol

I3

Phenol 0

-

A

B 400

-

B A61

A

A

A

u

0

20

40

60

80

xs*1000 Figure 3.- Effect of the ionic strength on the adsorption of phenol (co=2.13, U S = 2 0 U k g , T= 22OC), o-cresol (c0=2.14, US=14.6 U k g , T= 22OC), m-cresol (co=2.14, US=16.1 U k g , T= 22OC) US=16.2 U k g , T= 22OC) andp-cresol((~"=2.14, The distribution coefficient of phenol between phases is shown in Figure 3. Experimental and fitted values are given as a function of the sodium sulphate concentration. This improvement of adsorption is a solution effectg. So the concentration of phenol, c, can be described as a function of the solvation factor (kg of associated watedmol of salt) and the molar ratio of sodium sulphate in the solution, xs (mol of Na2SOq/mol of water). Thcn , introducing Equation 5 into Equation 1 , an alternative form of the basic equation is deiived where the apparent equilibrium constant K", given by Equation 6 .

331

Ion Exchangefor Environmental Clean-Up

Figure 4 shows that the average number of water molecules associated to the electrolyte depends on it's electrolyteconcentration. As the electrolyteconcentration increases. the average number of water molecules surrounding the electrolyte decreases. The relationship between the solvation water, 0, and the salt concentration, xs, we have established using the empirical Equation 7;

P = P . . + - l +P,x *

(7)

The solvation factor at high concentration, ,p and the solvation factor at low concentrations, Po. are derived from the regression of the experimental results. These values are reported in Table 1.

2

-2

n

-0-

c)

--t

o-cresol m-cresol

1.5

0

0.5

1

1.5

2

2.5

3

3.5

Xs (mol salt/mol water) Figure 4.- Average solvation factor srimaredfrorn Equation 7 4.3.- General Equation.

On the basis of these measurements a modified equation (eq. 8) is proposed to predict equilibrium results in systems where the pH,salinity and temperature can change. Two of these variables are exclusively related to the sorbate concentration, and the constants are linear in the temperature term. If one considers that the only species

338

Progress in Ion Exchange: Advances and Applications

adsorbed is the neutral or undissociated form, the Equation 8 can be derived from Equations 4 and 6.

4 =

Q

z 1

K,~"c' Kyc'

+

where the constants are:

--I

a' (1 -&)'

(9)

5.- MULTICOMPONENT ADSORPTlON EQUILIBFULJM STUDDES

Experimental data for competitive adsorption of multicomponent system, phenol, ortho and m-cresol, are shown in Figure 5. It was not possible to obtain adsorption data of the system with p-cresol because its ultraviolet spectra overlapped with m-cresol, making it impossible to determine experimentally adsorption uptake and bulk concentration of individual solutes. For multicomponent studies a suitable model was needed to predict equilibrium adsorption uptakes. One common approach for estimating competitive equilibrium adsorption is to use empirical equations based on extensions of adsorption isotherms for the single solutes. Myers and Buyton12 extended the basic equation (eq. 1) to another form by incorporating the competition and interactions between different adsorbates to occupy the limited number of adsorption sites.

On the other hand, it is usual to find isotherms equations where the solute-solute and the solute-solvent interactions are quantified by a dimensionless interaction coefficient,qj, which modifies the value of the constants for pure components. In this case, an average factor which modifies the Myer's equation (eq. 10) is considered because experimental results and predicted values from single solutions derivedparameters show a linear dependence, as it can be seen in Figure 6.

339

Ion Exchangefor Environmental Clean-Up

C Phenol (mmol/L) Figure 5.- Adsorption isotherms of multicomponentsolutions of phenol, 0-cresol, mcresol and p-cresol at pH=6.00 and T=300C. Equation 11 shows this modification.

,

where qj is the dimensionlessinteraction factor. Table 2.-Average Interaction Factors applying for Myer's

l w ~ h ~*~~m olute

0-cresol m-cresol

0.83 0.77

Then equilibrium constants in Equation 11 are those calculated for pure components. The chemical interactions are considered by the interaction factor. These factors are shown in Table 2. From the results summarised in Table 2, it can be derived that the adsorption of weakly adsorbing solutes (lower constants) in monocomponent systems increase when they are in multicomponent one, while those which are taken up strongly show the

Progress in Ion Exchange: Advances and Applications

340

opposite behaviour. This means that all phenolic compounds show a homogeneous behaviour when they are adsorbed simultaneously. Consequently, the values of thermodynamic parameters are similar. This could be because this resin has no a high selectivity. 290 U

I

A

1

0

0-cresol m-cresol

0

0

A

0

Phenol

A

0

=

0,o'

u,O

I

0,l

q

*

0,2

-

predicted

A

I

0,3

.

I

0.4

(mol/kg

dry

I

0,5

.

'

0,6

resin)

Figure 6.- Dependence between experimental and predicted values. Acknowledges: Partial support for this research was provided by "Secretaria del plan Nacional de I+D "( AMB95-0760)and by the Education Ministry in the form of predoctoral fellowship to AM N a m . The work was further supported, in part, by Bilbafna de Alquitranes S.A.

6.- REFERENCES I.-Mulligan, T.J. and Fox, R.D., Chem Eng., 1976, 18, 49. 2.-Stevens, B.W. and Kerner, J.W., Chem Eng., 1975,3, 84. 3.-Mc Ketta. J.J.; Kobe, K.A., Advances in Petroleum Chemistry and Refining", WilleyInterscience: New York, 1960. 4.-Fritz, W. and Schlunder, E.U., Chem Eng. Sci., 1974, 29(5), 1279. 4.-Rosene, M.R. and Manes, M., J. Phys. Chem., 1976, 80(9), 953. S.-Fritz, W. and Schlunder, E.U., Chem. Eng. Sci., 1981, 36(4), 721. 6.-Minka, C. and Myers, A.L., AIChE J. ,1973, 19(3),453. 7.-Myers, A.L. and Praunsitz, J.M.,Amer. Inst. Chem Eng. J., 1965,11(1), 121. 8.-Radke, C.J. and Praunitz, J.M., Amer. Inst. Chem Eng. J., 1972, 18(4),761. 9.-Mijangos, F. and Navarro, A., J. Chem. Eng. Data, August 1995, in press. 10.-Crook, E. H.; McDonnell, R. P.; McNulty,J. T., Ind Eng. Chem Prod. Res. Dev., (1975), 14(2),113. 11.-Fox, C. H., Hydrocarbon Processing, (1978), 57( 1l), 269. 12.-Myers, A.L. and Buyton, S., "Ion-Exchange: Science and Technology." Rodrigues, A., 1986.

APPLICATION OF MICROANALYTICAL TECHNIQUES TO ION EXCHANGE PROCESSES OF HEAVY METALS INVOLVING CHELATING RESINS

Fedenco Mijangos and Lourdes Bilbao. Department of Chemical Engineering. University of the Basque Country. Apdo 644. Bilbao. Spain.

1 ABSTRACT Ion exchange accompanied by a chemical reaction has been studied for heavy metal retention onto chelating resins. In this kind of system the metals are reacting with the chelating groups of the ion exchanger at the same time that intraparticular diffusion takes place. Different coloured layers can be distinguished by microscopy corresponding to the qualitative concentration profiles. These observations can be used for kinetic data analysis.The study of interactions of copper and cobalt during retention onto iminodiacetic resins has been considered in this report. Here, two different coloured layers and a central core, were observed. Scanning Electronic Microscopy generates topographic and compositional images which can be used to distinguish and measure the different metallic layers, in addition to internal structure. Sample preparation involved dehydration of the bead, in order to expose the internal surface and farly coating with carbon or gold. The emission of electrons of a determined wavelength restricted to X-Ray emission allowed to be determined the composition of the layers and local concentration, for the mathematical treatment to build up models for the simultaneous uptake of copper and cobalt 11.

2 INTRODUCTION

Ion exchange processes have been applied for treating residual industrial waters and, in particular, to recover heavy metals from these effluents’. However, the industrial viability of these processes of recovery is determined fundamentally for its operative selectivityz. The real capacity to separate cations of the same family, i.e., copper, cobalt, nickel, zinc, is determined by the affinity for the functional group of the ion exchanger and, fundamentally, the kinetic behavior of the system. The grades of separation estimated from thermodynamic considerationsare rarely attained in industrial conditions because the cations diffuse slowly, and with similar velocities, within the particle affected by, is determined by the internal structure of the exchangers Research work on ion exchange kinetics, structural modifications and intraparticular interactions are relatively scarce3.4. In this sense, the work by Helfferich and Hwang is remarkable, having succeeded in developing a general model of multicomponent ion exchange that applies for systems with a simultaneouschemical reaction5. The application of Scanning Electron Microscopy -SEM- to the study of the ion exchange is rare apart from some structural photographs. Bayer AG show a series of microphotographsof great quality that reflect the effect of several solvents on the internal

Progress in Ion Exchange: Advances and Applications

342

Figure 1. Diagram of a cut bead and its characteristic dimensions. porosity and the microspheres6. However, frequently it is required to get reliable information on the mechanism that controls the process and consequently studies on ion diffusion in the solid phase are required. These kinetic studies, using SEM can be supplemented by X-ray microanalysis in order to get internal maps and levels of concentration’. These techniques are expensive and difficult and have not been used extensively8. Here has been considered a case of ion exchange accompanied by chemical reaction: the retention of heavy metals onto chelating resins. The ion exchange reaction between the solution and solid, with a chelation reaction is found when the absorbed metallic cation forms a chelate with the functional group. Moreover, another neutralization reaction occurs because chelating groups are usually Bronsted bases. A classification and a comprehensive discussion on this type of kinetics has been published by Helfferich9. The analysis of kinetic experimental results for this kind of reaction, via the pseudosteady state approximation has been considered, which has been supported by the observation of sharp concentration profiles under the microscope because of the very clear reaction fronts. These fronts divide the unreacted core and the external shell that usually have a different colour as a consequence of the chelate. Dana and Weelocklo have observed these moving boundaries or fronts and measured their size for determination of kinetics parameters . Dealiig with iminodiacetic-type ion exchangers, Nativ and Goldsteinll were among the first to apply mathematical models with the pseudosteady state approach and HOll and Sontheimerlz reported different microphotographs. In this work, microscopic methods were used in order to obtain internal concentration profiles. This has been done using optical and electron microscopes and also X-ray microanalysis. These methods have not been previously used, as far as we know, in ion exchange microkinetics analysis and specially for bimetallic reactions. Mijangos and Diaz4 derived from this observation that cobalt load should show a maximum level for an intermediate reaction time. Here in order to check this assertion, the real internal concentration profiles have been measured by X-ray microanalysis and the overall solid phase concentrations have been chemically measured. 3MATERIALANDMETHODS The general procedure followed in these experiments and the resin characteristics (Lewatit TP207) have been previously described3~~. After the reaction starts, at a certain t h e one particle is taken out of the reactor; this bead is washed with distilled water and then cut The bead is then dried. This procedure is required because resin beads are opaque so otherwise it would be impossible to observe the internal reaction fronts or different coloured

Ion Exchangefor Environmental Clean-Up

343

layers. Its characteristic dimensions, shown in Figure 1, are then measured under the microscope so that the particle size does not change by drying. Some microphotographs were taken at the beginning of the reaction. Thw show the appearance of the cut surface and relative dimensions of the mcted layers (Figure 2). Sample preparation is an important step for correct observation and characterization, especially to see if materials alter their composition or microstructure during handling. In the case of the ion exchange resins, the preparation procedure of specimens require care because the measurements or observations should correspond to beads in the "as used" state. Otherwise, the observed structure or analysis will lack physical meaning even though they had been correctly done. The procedure starts by recognizing and selecting a group of beads under a magnifying glass, on the basis of their sphericity, absence of deformations or fractures. Subsequently, they are conditioned through several cycles "acid-washing-base", prior to ion exchange with the metallic solution. Finally, the resin is dried, at 60 OC, in a vacuum oven. Alternately to this drying method, water could be displaced from the ionic matrix using a series of solvents in order to keep the same structure as that in the hydrated state. In order to bring out the reacted layers, in the way depicted in the Figure 1, it is necessary to cut under a magnifying glass the spherical particles by means of a scalpel or other cutting tool (trying to make two equal parts). The examination of microstructural morphology on the cut surface has been carried out without using any etching procedure. Microstructure of the specimens without etching has been made apparent using secondary electrons and also backscatterer images as a result of the atomic number contrast. that Samples for X-Ray microanalysis do not require any special preparation, except the region of interest must be on a flat surface. The conductive coating has been ma& using a thin layer of carbon in order to reduce the absorption effects Here, specimens have been attached to the specimen stub (12,3 mm) with carbon glue and then coated with a layer of gold or carbon depending if the samples were for microscopy or microanalysis. A diode sputter coating device, CEA 035, has been used for this purpose. This equipment was used as high vacuum evaporative technique for carbon coat at a distance of 35 mm. The microanalysis and examinations were carried out in a microscope JEOL 6400 coupled with Energy and Wavelength-Dispersive X-ray Spectrophotometer, EDX Link EXL and WDX JEOL. 4 OPTICAL AND SCANNING ELECTRON MICROSCOPY

Using the microscopic techniques described above, the internal concentration profiles for copper and cobalt uptake were observed. The optical appearance of these concentration layers are shown in the microphotograph (Figure 2). Two different coloured fronts, or layers, surrounding the central core can be clearly distinguished: an external blue one that corresponds to a resin that mainly contains the copper chelate, and another internal pink one that is a zone where cobalt chelate is the main species. These reaction fronts have been clearly shown by Backscatter Electron Images. A partially reacted bead is shown in Figure 3 where the three above-mentioned zones can be distinguished. In this microphotograph, the softer-gray tones belong to those elements with higher atomic number. Figure 3 shows that the copper is concentrated in the periphery of the particle and cobalt fills the intermediate ring. Only elements of low atomic number are within the central core (such as sodium). No compositional differences occur within a zone, otherwise this should appear as a progressive radial gray tone. Sharp boundaries characterized the interfaces as it happens with optic microscopy (Figure 2). Nevertheless, some microstructural differences could be observed in these mnes by means of the secondary electrons images. Microphotographs, at medium magnification (40000x), can show the microstructure of each one of the three characterized zones.

344

Progress in Ion Exchange: Advances and Applications

Figure 2.Microphotograph of a partially reacted bead using an optical microscope.

Figure 3. Microphotgraph of a partially reacted bead using a Scanning Electron Microscopy (BSE).

I6

16

I4

14

12

12

10

10

B 8

8

'

6

6

4

4

2

2

A

m

2

J

0

0

0

. I

o w

9 3

d

10

0 -0

0

Figure 4. X-ray spectra collected from the three direrent layers.

Ion Exchange for Environmental Clean- Up

345

No important structural differences are revealed even though the ion exchanger beads conditioned in the sodium, copper and cobalt forms have different values of some macroscopic magnitudes such as density and internal porosity. Microbeads and macropom with their disDosition and size are roughly distinguished. Microbeads are grouped like rolling stones their size beingaround 150 nm. Internal pores have a wide size distribution ranging from a few nanometers to more than 300 nm. 5 ELECTRON PROBE X-RAY MICROANALYZER

X-ray microanalysis, Energy Dispersive Spectrometry, has been used to verify the presence of majority elements within the three zones. The three corresponding spectra are shown together in the Figure 4 where each analysis zone is point out. Copper, cobalt, sulphur, chlorine, silicon and sodium appear everywhere tested, but copper and cobalt concentrations change drastically between zones. On the other hand, other elements concentrations appear to be of the same magnitude order. Chlorine and silicon are present as traces homogeneously distributed as a result from the polymerization, synthesis or preparation stages. From the previous results, above mentioned, one could derive that the layers are characterized by the amounts of heavy metals which they contain. The external blue layer, contains mainly copper and little amounts of cobalt both surrounded by a sodium sulphate ionic medium. In the pink layer, the only heavy metal was cobalt. And finally, no heavy metal would have achieved the core of the bead so no trace of cobalt nor copper was found here. Nevertheless, the collected spectra show that the previous assertion is only an approach because all the metals are found in any part of the bead. A linear X-ray scan is useful for quantitative analysis since relative changes in concentration along a line are recorded as the measured characteristic x-ray intensity for that element. The determination of radial distribution of the majority element is an important step to discriminate kinetic models based on intraparticular evidences. In the Figure 5, a linear scan is shown where radial concentrations of the most important elements detected in the spectra, i.e., copper, cobalt and sulphur are depicted. Other trace elements have not been included (sodium, chlorine or silicon), because their radial distribution is unchanging. In order to collect this scan, highenergy peaks, Ka, have been selected. The energy of the X-ray peaks associated with those elements and their low concentration, cause peak overlap and can be confused with background noise. It is difficult to conclude anything about their distribution, except that noticeable differences in concentration between radial positions do not exist. In the Figure 5 , the X-ray intensity of the emission has been represented, and named as the relative solid phase concentration using an arbitrary scale, versus the radial position. This is possible because the intensity of the X-ray emission is proportional to the concentration of the element for a given condition. In this way, the changes in radial concentration of majority elements are recorded. Sulphur is associated to the co-ion, the sulphate species. So, sulphate concentration shows a decreasing radial profile. This means that the anions penetrate from the external solution together with metallic ions. As is derived from optic and electron microscope, copper ion is virtually constrained to the outer layer which is characterized by its blue colour. Although this zone is apparently saturated, copper shows a clearly decreasing profile. Very fine line scan has been obtained for cobalt. Three welLdistinguished zones are shown in Figure 5: Finally, the cobalt appears in three zones clearly differentiated by its composition: (a) external layer, cobalt solid phase concentration is relatively high and constant, (b) intermediate ring (pink), its concentration abruptly goes up to very high values where the concentration of copper decreases and finally, deeper in the particle, cobalt decreases to reach an almost negligible concentration, (c) central core of the particle, beige coloured, here only traces of cobalt are found, so other cations should be the predominant species.

Progress in Ion Exchange: Advances and Applications

346 100

80 .?,...

I

I I

~

t-

I

40 -

I I I I

20.

!.

.

0

I I

I .:..;'.~~~...~,,'.C;Y..~~,~..

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it:

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. .:: .: i. .

.

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These concentration profiles are roughly coincident with those shown in the Figure 5. The zones of predominance measured here are coincident with the layers observed by microscopy. In order to accomplish a more accurate estimation of the internal profiles or solid phase concentrations, a high resolution line scan has been carried out along half the sphere. In this way, the concentration profiles, shown in Figure 6, have been obtained for the main elements. Now, sodium profile has been also included, but its signal is noisy so it can be concluded only that it appears that sodium concentration is higher in the central core. In Figure 6, it is noted that copper concentration in the intermediate zone is higher than in the central core where both, cobalt and copper concentrations, are very low but meaningful. On the outer layer, the gradient of copper concentration decreases almost linearly up to, r/R= 0.71, where the boundary between the predominance zones Cu KOis located. Cobalt profile shows a very characteristic peak, this is asymmetric which indicates that mainly diffusion is only toward the centre of the particle, mainly or exclusively through the intraparticular solution. Otherwise, cobalt ions would spread and this peak would be progressively smoother and finally disappear. In other words here motion of the cations is exclusively promoted by the liquid phase gradients and independent of the solid phase concentration. An interesting aspect of the radial distribution of sulphate ion is that higher values of concentration are confine to outer layer. This means that its presence within the particle is associated with the total amount of heavy metals loaded despite sodium migration. No differences a~ noted

347

Ion Exchange for Environmental Clean-Up

of equilibrium can be estimated at different radial positions. These concentration profiles can be compared with those estimated on the basis local equilibrium assumption from the observations with the optic microscope4. 6. KINETICS OF METAL UPTAKE

The ion exchange kinetics of cobalt and copper for the sodium cation has been investigated using conventional chemical methods for analysis. After acid elution of the metal, total amount of metals loaded onto the resin were estimated by measuring metal concentrations in eluate by Atomic Absorption Spectrophotometry. This experiment was carried out using a metallic solution that contained both cobalt and copper, 0.1 M in saline medium of sodium nitrate 0.669 M and pH 3.28. The commercial resin was prepared as described above but particles were selected by sizing, between 1.0 and 1.2 mm in diameter. Cobalt, the cation with less affinity for the functional group shows a behaviour that is in line with the internal profiles measured by X-ray microanalysis. That is, after a few minutes *is metal is displaced from the resin. The maximum amount of loaded metal is four times higher than the final equilibrium value at around 40 minutes. On the other hand, copper diffuses “normally” to the resin, and when the reaction has finished, metal uptake achieves the equilibrium value which is the maximum load. Using the experimental results shown in Figure 7, one can conclude by comparing the load rates for both metal that at the beginning of the reaction that they diffuse in parallel but finally copper is displacing cobalt from the central core so the process is merely a copper/cobalt ion exchange reaction. 100 Sulphur 80-

60-

0

..O,O

. 42

0,4

0,6

0,8

Dhedo de s s radius, r/R

1,0

0,O

42

0,4

0,6

0,s

Dimenaionlaes radid, r/R

Figure 6. Radial concentration profiles of the main components.

1,0

Progress in Ion Exchange: Advances and Applications

5

0

100

200

300

400

Time (min) Figure 7 Kinetic of cobalt and copper uptake onto the chelating ion exchange resin. Solid phase concentration chemically analyzed 7 REFERENCES

1 . F. Mijangos, J.I. Lombralia, F. Varona and M. Diaz, I. Chem E. Sym Ser., 1990, 119, 61. 2. F. Mijangos, I. Galarza, P. Apezteguia and M. Diaz, Afinidad, 1991,436, 367. 3. F. Mijangos and M. Diaz, Can. J. Chem. Eng., 1994,72, 1028. 4. F. Mijangos and M. Diaz, J. Colloid Zntelface Sci., 1994, 164,215 5. Y.L. Hwang and F.Helfferich, React. Polymers, 1986.5, 237. 6. Bayer AG, ‘Structure and Properties of Levextrel Resins’, W/I 20356e, 10,1983 7 . Liberti et al., React. Polymers, 1984,2, 1 1 1 8. K. Dorfner, Laboratory Experiments and Education in Ion Exchange, in ‘Ion K. Dorfner (ed.), de Gruyter, Berlin, 1990. Exchange’, 409-440, 9 . F. Helfferich, Ion Exchange Kinetics, in ‘Ion Exchange and Solvent Extraction’, Vol.1, Chap. 2, .65-100, J.A. Marinsky (ed.), Marcel Decker, New York, 1966. 10. P.R. Dana and P.R. Weelock, Ind Engng Chem Fundam,1974,13 ,20. 1 1 . M. Nativ, S. Goldstein and G. Schmuckler, J. Inorg. Nucl. Chem , 1975,37(9), 1951. 12. W. HOll and H. Sontheimer, Chem.-Ing-Technick , 1975, 47,615.

REAGENTLESS CONCENTRATION OF COPPER FROM ACIDIC MINE WATERS BY THE DUAL-TEMPERATURE ION-EXCHANGE TECHNIQUE.

D. Muraviev, J. Noguerol and M. Valiente. Unitat de Quimica Analitica, Departament de Quimica E-08193 Bellaterra (Barcelona), Spain

1 INTRODUCTION

lon-exchange (IX) treatment of metal-bearing effluents is a well-established process for metal removal and recovery that dates back to the 1950s’. The main disadvantage of IX relates to the resin regeneration step known to be the main source of wastes in IX technology, hence IX separation methods which exclude this step are of particular interest. Parametric pumping‘” and allied dual-parametric IX tiactionation techniques4’ are such methods. Despite the obvious advantages, the practical application of these IX methods is still very limited, which can be attributed to the lack of information about real systems (effluents, waste waters, etc) which can be effectively treated by applying such separation methods, e.g. dual-temperature IX separation technique. The present study was undertaken (a) to investigate the IX equilibrium of acidic mine water metal ions on carboxylic and iminodiacetic resins at different temperatures and (b) to develop the reagentless IX method for concentration of copper from acidic mine waters based upon a dual-temperature technique. 2 EXPERIMENTAL The work was performed using samples of acidic mine waters from the Rio Tinto area (Huelva, Spain). A preliminary treatment of Rio Tinto water (RTW) samples was carried out as described elsewhere’. The composition of RTW samples, before and after treatment, and that of artificial RTW, are shown in Table 1. lminodiacetic ion exchanger, Lewatit TP-207 (LTP) and polyacrylic resin, Lewatit R 250-K (LRK), w r e kindly supplied by Bayer Hispania industrial, S.A. (Barcelona). The source, and qualtty, of all chemicals used in this work, as well as the analytical methods w e identical to those described in our previous paperso8. The techniques used to study IX equilibrium and to carry out thermostripping and thermosorption experiments are given, in detail, elsewhere”.

Progress in Ion Exchange: Advances and Applications

350

Table 1. Composhon of RTW (natural and artificial) samples (C, ppm) before and a8er treatment. ~

SG-

C(ppm) S1” Slb S2b S3”

Cu

Fe

16,450 5,050 3 16,300 0.3 17,350 17,250 0

Zn

239 912 235 890 115 1,275 120 4,700

~

Al

Mn

Mg

Ca

399 386 530 530

75 73 90 0

751 735 950 0

326 19 319 4,175 475 3,550 0 3,500

Na

(a) before treatment; (b) after treatment; (c) artificial 3 RESULTS AND DISCUSSION 3.1 Resin Capacities

The relative capacities of LTP and LRK (% of the total capacity of the amount of resin used) toward RTW metal ions after equilibration with S2 (see Table 1) at 20C are shown in Table 2. As follows from Table 2, the capacities of the resins studied towards Zn,Fe, Mn, Mg, Ca and Na do not differ markedly from each other (cf.LTP-S1 and LRK-S1 systems). The main difference in resin capacities can be noticed in respect to Al and Cu: LTP is selective towards Cu2+whereas LRK demonstrates a remarkable preference to AI* over the rest of the RTW metal ions. The influence of RTW composition on the capacity of LTP becomes clear after the comparison of LTP-Sl and LTP-S2 systems shown in Table 2, from which it follows that LTP is most sensitive to the Al” content in the equilibrium solution. Thus the 20% decrease of A19 concentration in the feed leads to a drop in its relative sorbability from 15.3 to 8.4%. As a consequence, the further elimination of A” content in the resin phase will increase the resin capacity towards the more valuable RTW components, such as Cu2+,and so improve the efficiency of their recovery from RTW. The relative capacities of LTP and LRK towards RTW metal ions at different temperatures are collected in Table 3.

Table 2. Relative capacities (equiv.%) of Lewatit TP-207 and Lewatif R 250-K towards RTW metal ions at 20 C.

System

Fe

Cu

Zn

Al

Mn

Mg

LTP-S2 LTP-S1 LRK-S2

0.31 3.62 0.45

68.27 69.99 3.91

5.03 3.38 5.52

15.33 8.43 81.64

0.23 0.20 0.22

2.87 2.80 2.06

Ca

Na

1.54 6.44 1.18 10.40 1.24 4.97

351

Ion Exchange for Environmental Clean-Up

Table 3. Relative capacities (equiv.%) of LTP and LRK towards RTW metal ions at different temperatures: ' LTP S1; ( )b LRK - S2 (see Table1).

-

T( C)

Al

cu

20 40 60 80

8.4' (81.6)b 11.6' (89.1)b 15.V (90.9)b 21.I(91 ' .8)b

69.9.(3.9)b 67.3* (2.4)b 65.6' (1.8)b 60.7' (1.2)b

Zn 3.6' 2.7. 2.5' 2.5'

(5.5)b (1.6)b (1.4)b (1.4)b

MQ 2.8' (2.1)b 2.6. (1.5)b 2.2. (1.3)b 2.V (1.2)b

The relative sorbabilities of Mn", Ca2+and Na' at elevated temperatures are not given in Table 3 since they remain essentially constant for both resins within the temperature interval studied (with a value show in Table 2 for the respective RTW samples). The data presented in Table 3 may be used for predictingthe behaviour of different ionic species in dual-temperature concentration. The degree of concentration for a given ion in thermostripping solution obtained under "ideal displacement" conditions (i.e. when the ion under displacement is concentrated in the first portion of the eluate) can be expressed as follows:

where Aq=q(Tl)qv2) and is the difference in the resin bed capacity at the loading (TI) and stripping (T2)temperatures; Vi is the volume of the feed solution passed through the column at T., Parameter b is directly proportionalto the difference in distribution coefficients (D)of the ion under consideration at T, and T2.Thus, an alternative expression for b can be written as: A

vhere m is the mass of the resin portion used. Corresponding values of Aq, C, and b for LTP and LRK at T,=20C and T2=80Care collected in Table 4. The sing of b in fact determines the direction of the interphase mass-transfer for a given ionic species during the thermostripping cycle, i.e. negative b values testii to the accumulation ofthe ion in the resin phase whereas positive b values indicate that the ion is concentrated in the solution. As seen from the b values given in Table 4, CU" is the on$ ionic species which can be expected to be concentrated by the dual-temperature IX technique using both LTP and LRK resins. The opposite behaviour can be anticipatedfor AI* which is characterized by negative b values. This results in the expected remarkable decrease of Alp concentration in the eluate obtained by thermostripping of both the resins studied.

352

Progress in Ion Exchange: Advances and Applications

Table 4. Aq, C, and b values for RTW metal ions sorbed by LTP and LRK at T1=20Cy T,=80C: " LTP - S1; ( )b LRK - S2 (see Table 1).

Me Al cu Zn Mg Aq'( mequiv.) -0.398'( -3.4 13)b 0.057"(0.29)b 0.016"(0.45)b0.017"(0.068)b Co"(mequiv/dm3) 47.90.(58.80)b 8.60.(3.90)b 34.00.(29.66)b 74.40.(70.78)b bx103"" -8.31a(-58.04)b 6.63a(74.36)b 0.47a(15.17)b 0.23a(0.96)b

3.2 Resins Selectivity Separation factors a : ; defined as:

(&re X and Y denote the equivalent fractions of metal ions in solution and resin phases, respectively) were determined at different temperatures in the experiments with RTW sample S1 on LTP and with S2 on LRK. The values obtained, shown in Table 5, demonstrate a strong temperature dependence of resin selectivities towards the Cu2'-AIs couple. Moreover all ion couples involving AV3 are : than characterized by a far stronger influence of temperature on the respective a that determined for the rest RTW ion couples.8-'1 This feature of a$=f(T) dependencies can be clearly understood. Indeed, the ratio of two a values, a, determined for a given ion couple (Me,and Me,) at two different temperature (T, and T,) from the equilibrium solution of the same composition (the same RTW sample) can be written as follows:

If T, and T, are chosen so that a z l and AY= ,Y(,T),-Y(,T), (4) in the following form:

one can rewrite eq.

The sign of AY is determined by the type of ,Y vs T dependency (positive or negative). The a value becomes a maximum for a given temperature interval if AY <,O , and AY > ,O, i.e. when the relative sorbabilities of Me, and Me, depend on temperature in an opposite manner. As follows from Table 3, AIs is only the RTW cation which is characterized by the rise of its relative sorbability on both resins studied when the temperature increases, hence strong a$ vs T dependencies are observed for both LTP and LRK.

Ion Exchange for Environmental Clean- Up

Table 5.

353

& vs temperature (K) for LTP and LRK resins.

Resin I T (K) Lewatit TP-207 Lewatit R 250-K

293

313

333

353

45.5 0.69

33.3 0.43

24.4 0.33

16.9 0.20

3.3 Thermostripping and Thermosorption

Typical concentration-volume histories obtained in thermostripping at 353 K using S l sample on LTP and S2 on LRK resins equilibrated at 293 K with the same RTW samples are shovm in Figure 1, a and b, respectively. The total capacities of the resin beds used were 2.63 and 11.58 mequiv for LTP and LRK, respectively. Hot RTW was passed at 0.34 cm3/minof flow rate through LTP and at 1.6 cm3/minthrough LRK resin beds. The thermostripping breakthrough curve shown in Figure 1b was obtained after a repetitive loading of LRK resin with RTW sample S2 at 293 K followed the first thermostripping cycle. The first cycle was camed out after equilibration of the resin in the initial seawater ions form* (mixed Na', Ca" and Mg" form) with the same RTW sample and resulted in the rise of Cuz* concentration in the eluate obtained by a factor approximately equal to 3. As seen in figure Ithermostripping from both resins leads to a selective concentration of Cu2' and to a significant drop of AI* content in the eluate

I

1.4

I

I

1.2 1 .I

.

4 1.0 \

v0.9 0.8

1.0

16

0.8

0.6

0.7

0.00

0.25

0.50

0.75

1.00

l/\ (

/IA

I 0.00

0.25

4 0.50

i'

'

0.75

1.oo

"qua

Figure 1. Thermostripping breakthrough curves for RTW from Lewatit TP-207 (a) and Lewatit R 250-K (b) resin; Zn (open circles), Mn (open squares), Cu (open triangles), A1 (inverted triangles), Ca (filled circles), Mg (filled squares) and Na (filled triangles).

Progress in Ion Exchange: Advances and Applications

354 1.3

1.2

1.2

1.1

1.1

0" 1.o

0

2

\

1.0

ci-

O- 0.9

0.9 0.8

0.8

0.7

0.7 0

25

50

Volume (mi)

75

100

0

10 20 30 40 50 Volume (mi)

60

Figure 2. Thermostripping (a) and thermosorption (b) breakthrough curves for RTW from Lewatit TP-207 at different temperatures; 40C (circles), 60C (squares) and 80C (triangles). obtained whereas the concentration of the rest RTW metal ions remain essentially at the feed level. This testifies to the correctness of the predictions made (see Table 4 and comments). The thermostripping efficiency can be influenced (either positively or negatively) by two different parameters which can be described within the system under study in terms of the maximum Cu2+degree of concentration and the minimum degree of depletion for AI* achieved. The increase of the height of the resin bed increases the zone where the maximum separation of Cuz+and AI* occursB9". An opposite trend is observed by narrowing the range of warking temperatures (T, -Tl). This is clearly seen in Figure 2a where the thermostripping breakthrough curves obtained on LTP resin at different temperatures are shown. The decrease of the stripping temperature leads to a remarkable drop of thermostripping efficiency. Consequently, data presented in Figure 2b demonstrate that the effectiveness of the thermosorption process also depends on the temperature of the previous thermostripping cycle. As follows from the results s h m in Figure 2 after thermostripping the resin phase appears "unloaded" with Cuz* and becomes able to sorb it again from cold RTW without any additional treatment (regeneration). The solution collected during the first thermostripping cycle (with increased Cuz+concentration and decreased AI* content) can be repeatedly subjected to thermosorption-thermostripping cycles whereby further Cu* concentrates are yielded. Separate experiments on consecutive thermo-sorption-stripping cycling were carried out with LRK resin (11.6 mequiv. of the total resin bed capacity) and artificial RTW samples. The primary composition of artificial RTW (see S3 in Table 1) has been shown to model adequately the behaviour of the native RTW components in dual-temperature IX concentration. The results of 4 cycles carried

355

Ion Exchange for Environmental Clean-Up

37 2

. 4

0-

1

I

0 0

1

2 N cycles

3

4

Figure 3. Concentrations of Cu2+ (circles) and AI” (squares) obtained in consecutive themKFsorption-stripping cycles vs number of cycle with artificial RTW on LRK resin. out are show in Figure 3. As follows from Figure 3, the CJC. value for C 3 ’ obtained, after the 4th cycle, was -2.7 whereas the value for Al” reached 0.10. The last concentrate contained 324 ppm C P and 51 ppm AI” (cf.S3 in Table 1). The concentrations of Zn” and Na’ remained essentially constant and did not change from cycle to cycle (seeTable 1). The final recovery of C 3 ‘ from this concentrate was carried out on LTP resin by loading the resin bed followd by rinsingwith H,O and stripping with 1 M H,SO,

100

100

3

75

-

0”

z

75

’0z

50

50

0-

3

25

25

0

0 0

5 10 Volume (mi)

15

0

5 10 Volume (mi)

15

Figure 4 (a) Relative concentrations of Zn2*(open circles), Cu” (open triangles), AI” (inverted triangles) and Na’ (filled triangles) obtained in stripping with 1M H30, from Levvatit TP-207 loaded with artificial RTW. (b) Copper purity (% mass) obtained in different samples during the process of reversal separation.

356

Progress in Ion Exchange: Advances and Applications

The concentration-volume history obtained in the stripping of Cu" from LTP is presented in Figure 4a, where CJC, vs volume is plotted. The elution curve shown in Figure 4a may be reproduced in terms of the purity of CuSO, obtained in different eluate portions as shown in Figure 4b. As seen in Figure 4a, the stripping leads to the significant concentration of Cuz+in the eluate. Although an average purity of CuSO, obtained (for the total eluate volume collected) has been estimated to be more than 86%, this value can be significantly improved by the differential collecting the product, as can be clearly seen in Figure 4b.

Acknowledgement The present w r k has been carried out with the financial support of the Programme Environment (European Union), contract NOEV5V-CT94-556.

References 1. R. K. Khamizov, D. Muraviev and A. Warshawsky in: "Ion Exchange and Solvent Extraction", J. Marinsky and Y. Marcus, eds., Marcel Dekker, New York, 1995, v.12, ch.3, p. 93. 2. H. T. Chen in: "Handbook of Separation Techniques for Chemical Engineers", P.A. Schweitzev, ed., McGraw-Hill, NewYork, 1979, p. 467. 3. D. Tondeur and G. Grevillot in: "Ion Exchange: Science and Technology" , A.E. Rodriguez, ed, NATO ASI, 11.197, Martinus Nijhoff, Dordvecht, 1986, p.369. 4. B. M. Andreev, G.K. Boreskov and S.G. Katalnikov Khim. Prom-st, 1961, 6, 369 (Russian). 5. V. 1. Gorshkov, A. M. Kurbanov and N. V. Apolonnik. Zh. Fiz. Khim, 1971, 45, 2969 (Russian). 6. V. I.Gorshkov, M. V. Ivanova, A. M. Kurbanov and V. I. Ivanov. Vecth. Mosk. Univ. Chem. Bull. (Engl Transl), 1977, 32, 23. 7. P.C. Wankat in: "Percolation Processes Theory and Applications", A.E. Rodrigues and D. Tondeur, eds. ; Sijthoff and Noordhoff: Alphen aan den Rijm, 1978, p. 443. 8. D. Muraviev, J. Noguerol and M. Valiente. Hydrometell.,submitted, 1996. 9. D. Muraviev, J. Noguerol and M. Valiente. React. Polym., 1996, 28, 111. 10. D. Muraviev, A. Gonzalo and M. Valiente. Anal. Chem., 1995, 67(17), 3028. 11. D. Muraviev, J. Noguerol and M. Valiente. Environmental Science 8, Technology,submitted, 1996.

TREATMENT OF SILVER-BEARING WASTE-WATERS USING ION-EXCHANGE CELLULOSES

Peter R. Levison. Navin D. Pathirana and Michael Streater Whatman International Ltd, Springfield Mill Maidstone Kent ME14 2LE UK

1 INTRODUCTION

Cellulose-based ion-exchange media have been comercially available since the late 1950's. They are currently used predominantly in the industrial bioprocessing market for large-scale protein purification'*'. Ion-exchange celluloses can be used in the treatment of waste-waters and cellulose phosphate, for example, has been demonstrated to bind thorium from monazite leach liquors3 and also to selectively remove certain metal ions from aqueous solution, for example Pe(II1) from Cr(II1) in a process application4. The photographic industry generates silver-bearing wastes, both in the manufacture and use of both colour and black and white photosensitive paper. The liquid wastes are mainly spent fixing and bleach solutions and dilute wash liquors from film manufacturing and processing units. In addition to silver, such solutions also contain ferrocyanide. ferric-EDTA and dichromate, sodium sulphate and thi~sulphate~'~. Silver-bearing wastes of concentrations up to 2 0 0 mg/l can be effectively treated with ionexchange resins to reduce levels to 4-6 mg/l'. Silver is a toxic metal and discharge consent limits are typically S lmg/l. Furthermore studies using resins8 and algal biomersg are also effective at silver removal. It has been reported" that silver may be precipitated inside a resin particle using sulphuric acid as a method of column regeneration. In the present study we have investigated the treatment of silverbearing waste-waters with the DEAE-substituted fibrous anion-exchange cellulose Whatman Cellect-Ion'" Exchanger DT-1 and report the removal of silver species to levels of < 1 mg/l using this ion-exchanger. 2

MATERIALS AND METHODS

2.1 Batch Studion

Cellect-Ion DT-1 (Whatman International Ltd., Maidstone. Kent, VK) was added to 95.50 mg/l silver solution (100 m l ) obtained from a photoprocessing facility, over the range 0.374-18.70 g (0.10-5.00 dry g) and stirred for 3h. Silver concentrations were determined by atomic absorption spectrometry. A Langmuir isotherm was plotted and values of Qm and Kd computed (Simulus Software, BioSep. Harwell, UK). Cellect-Ion DT-1 (5.61 g; 1.5 dry g) was added to 95.50 mg/l silver solution (500 ml) and stirred for 150 mins. Samples (3 ml) were taken

358

Progress in ion Exchange: Advances and Applications

1

.e-.

I

C

E

-0 0 0 c

Figure 1 Equipment c o n f i g u r a t i o n f o r t h e p r o c e s s - s c a l e treatment of silver- bearing p h o t o p r o c e s s i n g waste- wa t er

Ion Exchangefor Environmental Clean-Up

359

periodically during the study and analysed for silver by atomic absorption spectrometry. From the kinetic adsorption curve, a value of K1 was computed using Simulus software. 2.2 Procerr Scale Study

Cellect-Ion DT-1 (12 kg; 3.80 dry kg) was packed into two columns (30 cm i.d. x 24.5 cm) connected in series giving an effective bed height of 49 cm. A silver-bearing photoprocessing waste-water (30000 1) adjusted to pH 5 . 0 f 1.0 and filtered through 10 pm cartridges was pumped through the Cellect-Ion DT-1 column at a flow rate of 170-250 cm/h. The silver concentration of the feed ranged from 1.6-9.4 mg/l (mean 4.55 mg/l). Silver levels in the column effluent were determined by atomic absorption spectrometry. The equipment was configured as shown in Figure 1.

2.4 Media Regeneration Study Cellect-Ion DT-1 (13.25 g; 4.21 dry g) was packed into a column (2.5 cm i.d. x 6.1 cm; 30 ml) and silver-bearing waste-water ( 5 0 0 0 ml) containing 23 mg/l silver, adjusted to pH 6 . 0 pumped onto the column at a flow rate of 5 0 0 cm/h. Pooled column effluent was analysed for silver. 2% H$04 (30 ml) was pumped onto the column at a flow rate of 50 cm/h, collecting the column effluent, then stood for lh. 2% H,S04 (30 ml) was pumped onto the column at a flow rate of 50 cm/h, collecting the effluent, then stood for lh. 2% HzS04 (120 m l ) was pumped through the column at a flow rate of 50 cm/h collecting the effluent. The column was washed with tap water ( - 1000 ml) at a flow rate of 500 cmfh until the pH of the Silver levels were effluent was > 3.0. collecting the effluents. determined for each effluent. The complete silver loading-H2S04 regeneration cycle WRS repeated a further 4 times.

-

3 RESULTS AND DISCUSSION The results of the batch isotherm study are represented in Figure 2. The data demonstrate that the fitted values of q* and c* give a good fit to the experimental values for a Langmuir isotherm and the Simulus software calculated a value for Qm of 29.50 mg/dry g Cellect-Ion DT-1 and a & of 0.00948 mg/ml. The kinetics of adsorption of silver by Cellect-Ion DT-1 were very fast and the data are summarized in Figure 3. By use of the Simulus programe. a curve fitting algorithmwas employed which calculated the rate constant K1 as 5.51 ml/mg/min. The results of the process-scale breakthrough study for silver are represented in Figure 4. The data demonstrate that significant silver breakthrough occurred after - 25000 1 of feed had passed through the column, i.e. after 114 g silver had passed through the column. This equates to a loading of 30 mg silver per dry g Cellect-Ion DT-1 a level similar to the Qm value determined above. During the loading the level of silver in the column effluent was less than 0.1 mg/l for the first 17000 1 of feed loaded. At the completion of the study we determined an operating capacity of 31.5 mg silverldry g Cellect-Ion DT-1, close t o its Qm and indicative of the efficiency of the adsorptive process reinforcing the rapid kinetic rates determined previously. The column regeneration data is summarised in Table 1. It is clear that the Cellect-Ion DT-1 adsorbs silver during run 1. and negligible silver is released during column regeneration. During the regeneration procedure the column packing turned black indicative of sulphide

Progress in Ion Exchange: Advances and Applications

360

+ .

Figure 2

Langmuir Isotherm plot for s i l v e r adsorption t o C e l l e c t - I o n DT-1

Silver concentat ion (mg/l) --L

0

CT,

0

0

Iu

0

P

0

r!

cn 0

3 CD

A

0 0

Iu

0

A

P

0

19E

o

'T

cx, 0

0 0

Progress in Ion Exchange: Advances and Applications

362

I

0

I

I

I

co

I

I

I

I

I

I

I

d

I

I

I

I

I

cu

T-

Figure 4 Breakthrough c u r v e f o r t h e p r o c e s s - s c a l e treatment o f a s i l v e r - b e a r i n g p h o t o p r o c e s s i n g w a s t e - w a t e r using C e l l e c t - Ion D T - 1

- 0 0

adsorbed

0%)

in effluent (mg1

10.00

26.90

Passed (mg)

114.57 116.84 1 15. 9 6 101.00 101.00

1 2 3 4

5

Ag adsorbed

adsorbed (mg)

removed by the regenerant (mg)

413.26

70.27 3.73

342.99

73.80 1.70 75.50

25.50

74.00

269.19

81.38 0.95

82.33 33.63

27.00

1137.81

85.54

102.27 102.27 4.40

2.30

(mg)

T o t a l mass of

Mass of Ag Mass of Ag

89.94

104.57

Mass of Ag

Mass of Ag

Mass of Ag

Cycle No.

8

w

Progress in Ion Exchange: Advances and Applications

364

formation. In the second and subsequent runs, further silver was adsorbed by the column. This implies that the AgzS produced in situ is dissociated from the functional group of the exchanger, thereby enabling subsequent adsorption to occur. The initial silver capacity for the Cellect-Ion DT-1 was 24.3 %/dry g similar to the Qm value (29.50 mgldry g ) determined earlier. However. after 5 cycles the cumulative capacity of the medium for silver was 98.2 mgldry g. These data demonstrate the effectiveness of column regeneration using HzSO4'O and provides a means to increase the cost effectiveness of such a process. 4 CONCLUSIONS

The results of the present study demonstrate that silver can be removed from silver-bearing waste-waters to sub-ppm levels using the anionexchange cellulose Cellect-Ion DT-1. The high capacity and fast adsorption kinetics of this medium facilitate its use in industrial applications. An in situ, silver precipitation approach can be used during column regeneration, to improve the cost-effectiveness of the process.

References 1. P. R. Levison "Cellulosics : Materials for Selective Separation and Other Technologies" (J. F . Kennedy, G. 0. Phillips and P. A. Williams eds.) Ellis-Horwood Ltd, Chichester, 1993, p. 25. 2. P. R. Levison "Process-Scale Liquid Chromatography" (G. Subramanian, ed.) VCH, Weinheim, 1995, p. 131. A. J. Head, N. F. Kember, R. P. Miller and R. A. Wells, J. A p p l . 3.

Chem., 1959,

2, 599.

4. P. R. Levison, N. D. Pathirana and M. Streater "Cellulosics : Materials for Selective Separations and Other Technologies", (J. F. Kennedy, G. 0. Phillips and P. A. Williams, eds.) Ellis-Horwood, Chichester, 1993, p. 77. P. B. Linkson, S u r v . Ind. W a s t e w a t e r T r e a t . , 1987, 2, 65. 5. 6. N. Saithaiyan, P. Adaikkalam, J. A. M. Abdul Kader and S . Visvanathan, J. M e t a l s , 1990, m, 38. T. N. Henrickson and G. A . Lorenzo. Proceedings of the International 7. Precious Metals Institute Symposium, California, 1981. F. M. Chen, G. Cote and D. Bauer "Recent Developments in Ion-Exchange 8. 2." (P. A. Williams and M. J. Hudson eds.) Elsevier, London, 1990, p. 287. D. W. Darnall, B. Greene, M. Hosea, R. A. McPherson, M. Henzl and M. 9. D. Alexander "Trace Metal Removal from Aqueous Solution" (R. Thompson, ed.) Royal Society of Chemistry, London, 1986, p. 1. 10. H. W. Chou, R e s . D i s c l . , 1980, 194,200.

STDS Study of Some Commercial Anion Exchange Resins

Marton, A'. Mascolo, G. Petmzzel.h, D. Tiravanti, G. Istituto di Ricerca Sulle Acque, National Research Cound, 70123 Bmi, Italy; 'Department of Analytical Chemistry, University of V e s q r h , P.O.Box 158 H-8201 V e s q r h , Hungary

1. INTRODUCTION

Physical and chemical stabhty of ion exchange resins (and generally polymeric sorbents) has recentlybecome the main concern for both manufacturers and users. In most countries governments are gradually enactiug regulations for the use of ion exchangers m water treatment, food and beverage processiag, m the treatment of pharmaceutical products and for the use of ion exchangers as medicines and medical devices'. Smce these applications may directly affect the well-being of an animal or a human being the treated product should be fkee of any toxic compounds released by the ion exchange resin. For the Bssessment of the physical and chemical stability of the resins various laboratory tests have been developed2.A recent review on the standardisationof test methods for ion exchange resins has been compiled by Kiihne3. The effect of the osmotic and hydromechanicalstress associated with the operation of the resin has been widely studied by investigating the breakage and fiagmentation of the resin beads?. The adopted techniques usually include visual microscopy and the study of particle size distriiution. The action of heats-8, oxidantssll, organic solvents12 and ionising radiation13-ls on the stab* of the ion exchange polymers have been the subject of several publications. For these investigationseither the determination of total (or operational) exchange capacity, or simultaneous TG and DTA mvestigations, or the measurement of the resin water content and density have been adopted as major experimentaltechniques. As a consequence of the above mentioned physical and/or chemical effects all ion exchange resins release certain compounds which are leached out during their use. F h e r sohble components may also be generated by the action of oxygen, W light and trace metals a h g as catalyst. Numerous tests have therefore been developed for the measuring of the level of leachable contaminants1618.These tests, m general, specify heating the resin m water m a sealed bottle for a set period of time, separatingthe water fiom the resin, then measuring the total organic carbon (TOC)level of the solution and/or the total residue fiom the evaporated solution. Ahhough these mvestigations provide quantitative measures for the total concentration of resin released components m a closed environment m a short

366

Progress in Ion Exchange: Advances and Applications

period of time they do not provide information about the types of the extracted compounds. A rather systematic determination and identification of the high and low molecular mass components of the TOC content has been made by Stahlbush et aL using size e x c ~ o n and reversed phase ion pair chromatography18. The wide variation m the types and amounts of leachables of the studied gel and macroporous resins led the authors to the conclusion that the resin manufacturing conditions play a decisive role which can dramatically affect the amount and types of the resin released components. As can be seen from the above short review of literature relatively little attention has been paid so far to the separation and identification of the individual components conmhting to the TOC content. The purpose of our current investigationwas to mtroduce a recently available highly sophisticated technique, the System for Thermal Diagnostic Studies commercialised by Hewlett Packard, into the rather traditional arsenal of the ion exchange resin characterisation I qualification techniques. The recommended technique is specifically designed to carry out thermal decomposition experiments m a quartz reactor under well defined, reproducible circumstances and to separate and subsequently id e n w the generated components by temperature programmed gas chromatographic method and quadrupole mass spectrometry. 2. EXPERIMENTAL

Thermal degradation studies of resin were carried out with the System for Thermal Diagnostic Studies (STDS). The system19 consists of a modified pyromjector (SGE Australia) connected by a 1/8' silicosteel tube (Restec Bellefonte PA, USA) to the h d silica tubular reactor that is connected to a 5890 Series II gas chromatograph interfaced to a 5971 quadrupole mass spectrometer (Hewlett Packard, Palo Alto, CA, USA) equipped with an electron impact ion source. The pyromjector was modified m order to allow a quartz probe to be manually inserted m it through its silicon septa. The water content of the ion exchangers were removed before the STDS experiment by drymg the resins overtllght m a vacuum oven at 30 "C. Resin samples (about 10 mg) were placed mto small quartz tubes (1.5 mm id. 15 mm length, Vitro Dynamics Inc. Rochaway, NJ. USA) and held m Table 1 characteristicparameters of the studied resins

*G

=

Gel type, MP = Macroporous resin

Ion Exchange for Environmental Clean-Up

367

place by quartz wool inserted fiom both ends. The quartz tube was then inserted mto the pyroprobe for thermal experiments. The conditions for the thermal experiments were as follows: the sample was held for 10 min at 130 C then for 10 min at 200 C then for 10 min 250 C and finally for 10 min at 300 C.During the thermal experiments mert helium gas was flowing through the quartz probe (7 d m i n ) inserted into the pyromjector, while both silicosteel and the fhed silica tubular reactor were heated to 250 C to allow the transportation of the resin released products to the gas chromatographic column without any fiuther thermal side reaction. The GC analyhcal column connected to the end of the fused silica tubular reactor, was kept at -60 C during the time of the thermal experiment m order to cyrofocus the developed organic compounds mto a small band. The other end of the GC column was interfaced to the ion source of the quadrupole mass spectrometer through a t r d e r line heated to 280 C. After completion of the thermal experiment the organics trapped at the top of the GC column were analyzed by raising the oven temperature to 280 C at a rate of 5 C/min, then that temperature was held for 5 min. Electron impact mass spectra were recorded by scanning the quadrupole fiom mass 35 to 550 dalton at 1.4 scads at an electron energy of 70 eV. In order to see the effect of the thermal stress on the ion exchange capacity the resins were thermally treated m a separate experiment m the pyroprobe as described earlier. For example the resin was first treated at 130 C for 10 min then at 200 C for 10 min and fimalh, at 250 C for 10 min and the exchange capacity of the resin samples were determined after each thermal experiment. Ion exchange capacity of the resin samples was determined after displacement of the chloride counter ions fiom a known amount of resin by 0.1 moL/dd NaN03 solution and by the subsequent ion chromatographicdetermination of the concentration of the displaced chloride ions. The calculated resin capacities together with some fiuther important properties of the studied resins are shown m Table 1. 3. RESULTS AND DISCUSSION

Figure 1. shows a typical example of the TPGC-MSD outputs obtained for the A1 resin after a 10 min exposure of the sample to a 300 C thermal shock. An almost complete list of the separated and identified compounds (with their mass spectrometry hirary qualay match figure) is also included. As it became clear fiom the description of the STDS experiments the applied circumstances did not mean to .simulate conditions of any actual application of the ion exchange resins. Instead, our purpose was here to develop a characterisation method whereby the resins are c h a r a c t e d by a set of compounds which are released when the ion exchange polymer is exposed to a thermal shock m an oxygen fiee atmosphere. The released components may eventually be identical to those which are leached out during the usual applicationsm aqueous solutionsor m various hydro-organic solvent mixtures. As compared to the thermal stab@ of the crosslinked covalent polymers the applied thermal exposure is rather mild (10 min, 300 C) therefore sigdicant degradation of the matrix can not be expected to occur. The thermal stab* of the pendant functional groups is, of course, much weaker and their cleavage may take place on the effect of the thermalstress. A typical although not complete list of the resin released compounds originating fiom the thermal cleavage of the hctional groups (resulting m the development of the various amine derivatives)or fiom the subsequent rearrangements of the aromatic rings

368

Progress in Ion Exchange: Advances and Applications

LGiaXsE 1. 6-07

1.4-07

l.lW7

1 . + 0 7

3

1:

11

.oooooo L000000

4000000

2000000

Figure 1. Gas chromatogramshowing the separated components released by the A1 resin aJer the 300 T (I0min) thermal e x p u r e in the STDS experiment. The idenhped components (with their MS libmty quality match number) are as follows: I . Methanoamine, N,N-dimethyl (53); 2.Ethanamine, N,Ndimethyl (64); 3. I.jl-Propanediamine, N,N,N'N'-tehurmethyl (12); 4. 1,2-EthanediamineN,Ndimethyl (72); 5. Methanediamine N,N,N'N'-tetrarnethyl (80); 6. Propanenitrile, 3-(dimethylamino) (64); 7. 2-Propanamine, N-(I-methylethylidene) (53); 8. I-Propanamine, n-

prowl (80); 9. I-Butanamine, N.Ndimethy1 (56); 10. findine, 3-methyl (96); 11. Pyridine, 3-methyl (96); 12. 1,3F'ropnediamine, N,N,N: N'-tehumethyl (40); 13. Pyridine, 2,5dimethyl (93); 14. Pyridine, 3-ethyl (95); 15. Pyridine 2,S-dirnetJyl (87); 16. 3-(chloromethyl)pridine (42); 17. &+dines 3-ethy1-5-methyl (94); 18. Benzenemethanamine, N,N, 4-trimethyl (87); 19. &?dine. 3-metJyl-5-propl (94); 20. Acetamide, N-(2-methylphenyf) (76); 21. Quinoline, 1,2,3,4-tetrahydro (42); 22. 1.2-Propnediol, 3-(dimethylamino) (38).

(leading to the formation of the various pyridine derivatives) is shown in Tables 2. and 3. The emerging of these decomposition products is, of course, accompanied by the decrease of the resin capacity as it is indicated by the capacity vs. temperature curves shown in Figure 2. As can be seen from the curves, the rate of capacity loss does not follow a uniformly decreasing tendency. Certain resins sufFer less dramatic rate of capacity loss in certain temperature ranges: A2 (130 - 250 C), A3 (130 - 250 C), P1 (130 200 C), P1 and P3 (25 - 130 C) as it is also confirmed by the missing of any detected components m the STDS experiments (Tables 2. and 3.). In the case of the A2 and A3 resins Table 2. indicates no components in up to 250 C despite of the decrease m the resin capacities. These (weak base) resins certainly loose ammonia due to the applied thermal shock which is, however, not seen by the MS due to the higher starting limit of the mass scan (28 dalton). Although the released set of components are highly characteristic for the resins the comparison of the sets of the compounds obtained fiom the individual resins seems to be rather difficult and inconclsrve, at least, on the ground of the currently available data base. The released compounds or temperature data can not be unanimously related to the type of the matrix, to the degree of crosslinking or to the type of the hctional groups. Our conclusion, in fact, corroborates the observation of Stahlbush et a1.18 who pointed out that the type of the released compounds is practically determined by the technological parameters of the resin synthesis.

-

369

Ion Exchangefor Environmental Clean-Up

"\ A1 3.6

f

-

3 2.6

.-s. 2

," 1.5 ._ v1 rr

1 0.5

130

260

250

3d0

Temperature. 'C

Figure 2 Change of the resin capcity rn afinction of the applied (10 min) thermal shock

*

Table 2 Some major identfled components OriginatingfPom the acrylic polymer matrix ued resins at various temperatures * Resin

I

Pyrolysis temperature

component

200 "C No dekctable component

250 "C 300 "C 13.8:Methanamine 13.8:MethauamineN,NN,Ndimethyl (60) dimethyl (53) 15.3:Ethanamine N,Ndimethyl (64) 16.7:1,3-Propandamine N,N.N,W-tetramethyl (12) 16.9-18.5:Amine derivs. 20.4-23:Pyridine derivs.

component

No detectable wmponent

No detectable component

component

Nodetectable component

130 "C

I

1

1 Nodetectable

I

I

component

I

8.9:Methanamine N,Ndimethyl (53) 15.1:EthanamineN,Ndimethyl (64) 18.7-23 Fyndine dem. 19.8:Pyrimidine.2mthyl(72) 21.1:Pyndinamine,Smethyl 22-23:Pyrazine derivts.

I

GC retention time, min: 1 me of compound (MS library quality match figure)

According to our opinion, the unique flexibiltty of the experimental circumstances of the STDS tests (temperature program, gas atmosphere, pressure, flow rate etc.), their low material consumption (approximately 10 mg), and time demand (depending on the program five to ten complete tests can be made eady m 8 hours), the specificity and the good reproducibility of the results make these investigations extremely usefid m the QC and QA programs implemented m the field of the resin manufacturingand development. the fact that the circumstances of the STDS experiments are quite Despite different fiom the usual conditionsof the resin applications it is felt that this technique

Progress in Ion Exchange: Advances and Applications

370

Table 3. Some major identijied components originatingfiom the polystyrene - D K3! * $ t & ?-eratures Resin

Pyrolysis tempemre

VO

130

P1

P2

P3

200

c

250 C

300 C

C

No detect. comp.

No detectable component

13.3:MethanamineN,N&methyl (53)

No detect. comp.

17.9:Methanediamine N,N,N"'tetramethyl(78) 23.9:Methanamine N.Ndimethyl(56)

6.8: 1,3-Butadyine(38)

No detect. comp.

5.8:Methanamine N,N< 15:Methanoamine, dimethyl (50) N,N dimethyl (50) 17.9:Methanediamine N,N,NNtetramethyl(78)

E E

3.5: 1,3-Butadyme (59)

7.4:Methanamine N,Ndimethyl (47) 17.9:Methanediamine N,N,NN -tetramethyl(72) 19.0:l-PrOpanOl,3dimethylamino (72) 20.8:Benzene ethenyl(58) 22.2:Benzene 1-propenyl(87) 26.5:Methanamine, N,Ndimethyl(59) No detectable comp.

20.8:Cyclooctatetrene(91) 24.8:Benzene (3-chloro-1 ProPenYl) (93) 28.5:Benzene 1. I'(l.3proanediyl) bis (91)'

GC retention ime, min: Name of compound (MS library quality match figure) provides a fast and reliable screening test for the selection of the most suitable type of exchanger for certain types of advanced applications in the field of food- and biotechnology or m the water treatment for human consumption. Due to the nonspecific nature of the applicabilay of the STDS techniques its application for the characterisation of other polymeric sorbents or for the very delicate and expensive HPLC stationary phases can eady be made. ACKNOWLEDGEMENT

Support of this work by the Consiglio Nazionale d e b Ricerche, Italy (under the grant No. 53585) and by the National Fund for Scientific Research, Hungary (under the grant No. OTKA T-014173) is hereby gratefully acknowledged. REFERENCES 1. R Kunin, Reactive Polymers, 1995,24,79. 2. G. Neuman, Testing of Ion Exchangers, in: Theory and Practice of Ion Exchange (ed.: M.Streat) Society of Chemical Industry. London, 1976, p.5.1. 3. G. Kiihne, Standardisation of Test Methods for Ion Exchange Resins, in: Ion

Ion Exchangefor Environmental Clean-Up

37 1

Exchangers(ed.: K.Dorher) Walter de Gruyter, Berlin, 1991, p.397. 4. K. Hochmiiller, Shock Test for the Determination of the Resistance of Ion Exchange Resins to Osmotic and Hydromechrnical Stress, m Ion Exchange Technology (ed.: D.Naden and M.Streat), Ellis Horwood Ltd.,Chich&er, 1984, p.472. 5. G.R Hall et aL, Intem.Conference on Ion Exchange m the Process Indus&ies,London, 1969, p.62. 6. L.S. Golden, J.IrvingChemhd. (London) 1972,21,837. 7. S.I. Laptev et al., Plast. Massy, 1976,1,52. 8. J.P. Aittolla, J.Chyder, Hkgberg, Thennal Stability of Ion Exchange Resins, 1982,

Studsvik Energiteknik AB Report, Sweden 9. W.J. Bleadel, E.D.0haLChem., 1961,33,531. 10. L.F.Wirth et aL, Ind.Eng.Chem.,l961, S3,638. 11. M. Falk, et al., Phannazie, 1982,37,387. 12. M A &to, G.J.Moody, J.D.RThomas, Lab. Practice, 1973,21,797. 13. G.R Ha& M.Streat, J.Chem.Soc., 1963,5205. 14. E.D. Kiseleva et aL, Zh.FizKhim., 1982,56,369. 15. K.K.S. PiIlay, J.RadioanalNucLChem., 1986,97,135. 16. Westinghouse Specification 53141, Pittsburgh,Pa.,1951. 17. S.A Fisher, G.Chten,45th Int.Water C o d , 1984, lWC-84-70,402-406. 18. J.R Stahlbush et al, Identification, Prediction and Consequence of the, Decomposition

Products from Cation Exchange Resins m Ion Exchange for Industry (ed.: M.Streat), Ellis Horwood Ltd.,Chichester, 1988. p.22. 19. V.ARubey, RACames, Rev.SciInstnun.,1985,56,1795.

SEPARATION OF CHROMIUM WITH A FIBROUS ION EXCHANGER

Jukka Lehto, Tiina Laurila, Heikki Leinonen and Risto Koivula Laboratory of Radiochernistry, Department of Chemistry University of Helsinki, Helsinki, Finland

1 ABSTRACT

For the separation of chromium from solutions sixteen commercially available ion exchanger were tested. Best performance was shown by a fibrous ion exchanger FIBAN AK-22, which has both carboxylic and imidazole functionalities on lypropylene fibres. It takes u very efficiently all forms of chromium, Cr3' and Crz0,'at pH range of 3-4 and C a p - at pH range of 6-9. Na+, Mg2+ and Ca2+ ions interfere with the chromium separation at concentrations higher than 0.1M and Fez+ and Fe3+ ions at concentrations higher than 0.001M. From waste solutions from a metal plating plant FIBAN AK-22 removed chromium rather efficiently.

2 INTRODUCTION Many metal plating plants discharge their waste waters to sewerage or to open water systems without proper purification. Increasing and stricter regulations against releases of metal-containing effluents require more effective purification methods. The primary purpose of this study was to develop highly effective ion exchange methods for the separation of chromium, and other harmful metals', from waste waters of the metal plating industry in order to diminish their releases inro the environment. Special attention has been paid to chelating ion exchange resins since they have shown better performance with respect to transition metal ions compared to ordinary organic ion exchangers. In addition, when they are used in packed bed columns, a more effective and straightforward purification system can be obtained compared to purification by precipitation, which is the most commonly used method at present for this purpose. Another purpose in our development of separation methods was to minimize the amounts of waste to be disposed of, which may result in a considerable reduction in waste disposal costs.

3 EXPERIMENTAL The ion exchangers used in this work are listed in Table 1 and they were used as supplied. The screening tests with these exchangers were carried out using a batch method with a solution volume to wet exchanger weight ratio (batch factor) of 100 ml/g. All

373

Ion Exchange for Environmental Clean-Up

distribution coefficient (KD) determinations for FIBAN AK-22 were also done using the batch method with a batch factor of 109 ml/g based on the dry weight of the exchanger. Samples of the exchangers were shaken in buffer solutions havin 0.1 mM of chromium. Cr3+ and Cr,O?- were in sodium citrate buffers and CrOf in sodiudpotassium phosphate buffer. After at least three days' 'shaking time the exchanger samples were separated by centrifugation. Chromium concentrations were measured with an atomic absorption spectrophotometer having a zeeman furnace. K, valugs were calculated with the following formula, in which Ci is initial chromium concentration, C chromium concentration in equilibrium and BF is the batch factor.

The applicability of FIBAN AK-22 for the decontamination of industrial waste solutions was tested by carrying out column experiments with actual waste effluents from a metal plating plant. These effluents were from rinsing baths and had chromium concentrations 1 mM and 28 mM. The initial pH values were 6.1 and 1.3, respectively.

Exchanger

Manufacturer

Functional group (exchangeable ion)

Amberlite IRC718

Rohm and Haas

iminodiacetic acid (Na?

1 Chelite C

I Serva

I iminodiacetic acid

Diaion CR20

Mitsubishi

polyamine (OH3

Duolite C467

Rohm and Haas

aminophosphonate (Na')

Imac GT73

Rohm and Haas

unknown

Lewatit TP214

Baver

contains S and N

1 Spheron Oxin

I Lachema

I 8-hydroqyquinoline

1 Varion BTKM

I Nike

I tiocarbamate (Na')

Chelex 20

Bio-Rad

iminodiacetic acid (Na+)

Amberlite IRCSO

Rohm and Haas

H') oxalic acid (

1 AG 50Wx8 FIBAN AK-22

I Bio-Rad reference 2

I sulphonic acid (H*) imidazole, carboxylic

374

Progress in Ion Exchange: Advances and Applications

4 RESULTS AND DISCUSSION

4.1 Selection of Ion Exchanger From the sixteen ion exchangers tested in the buffer solutions at two pH values, the best behavior to all three forms of chromium was shown by the fibrous ion exchanger FIBAN AK-22 (Table 2). At pH 3.1 FIBAN AK-22 could remove 97.6 % of C?' and 99.6 % of Cr 0 2- and at pH 7.4 the removal of Cr0:was 99.7 %. Since no other 2 .7 exchanger exhibited such a good efficiency FIBAN AK-22 was chosen for further studies.

Table 2

Percentages of chromium (Cr3', Cr20:and CrO:-) separation by various ion exchangers determined in two different buffer solutions, sodium citrate buffer at pH 2.0 and sodium/potassium phosphate buffer at pH 7.0. Initial chromium concentration 0.1 mM. Solution volume to wet exchanger weight ratio 100 mUg. CrO,2.

C?' EXCHANGER log KD p H q ~

~~

1. Amberlite IRC 718

1.83

2.43

--

7.30

1.86

2.87

2. Chelite C

2.40

3.32

0.70

7.35

1.91

3.24

3. Diaion CR20

1.40

2.48

2.93

7.22

2.78

2.49

4. Duolite C 467

3.07

2.67

0.04

7.24

2.72

2.66

5. Imac GT 73

2.01

1.96

2.98

6.90

1.68

1.97

-__ --

2.00

3.20

6.99

1.45

2.01

2.05

1.52

6.99

2.61

2.06

2.98

--

6.90

1.45

1.99

7.00

0.85

2.00

6. Lewatit TP 214 7. Spheron OXIN 8. Spheron SALICYL 9. Spheron THIOL

--

1.98

--

10. Varion BSM

--

1.94

1.37

6.95

0.84

1.94

11. Varion BTAM

0.98

2.39

2.65

7.15

--

2.38

12. Varion BTKM

1.28

2.05

3.82

6.86

1.56

2.05

13. Chelex 2 0

2.21

3.19

7.46

1.96

3.14

14. AG 50Wx8

3.01

1.51

---

4.92

1.95

1.52

--

1.99

0.4

6.43

1.08

2.01

3.64

3.10

4.55

7.44

4.40

3.04

15. AMBERLITE IRC5O 16. AK-22 FIBAN

-- = no sorption

375

Ion Exchangefor Environmental Clean-Up

FIBAN AK-22 has been developed at the Institute of Physical Organic Chemistry in Minsk, Belorussia'. It contains two kinds of functionalities, carboxylic and imidazole groups on polypropylene fibres:

\

COOH Since there are carboxylic groups this exchanger works as a cation exchanger and due to protonation of the imidazole groups it can work as an anion exchanger as well. In addition, the nitrogen atoms in the imidazole group also forms chelates with transition metal ions. 4.2 Effect of pH on the Uptake of Chromium by FIBAN AK-22

FIBAN AK-22 takes u very efficiently anionic chromium species, the distribution coefficient (KD) for Cr20:being about 40,000ml/g at pH range of 3-4and for (21-0:25,000-80,000 ml/g at pH range of 6.3-8.6. The uptake of C?' is somewhat lower, the KD being between 4.000 and 15,000 at pH range of 3-4(Fig. 1).

I

0

8

3

9

pH eg Figure 1 Distribution coefficient (KD) of C?', Cr,O?- and CrO': on FIBAN AK-22 as a function of pH determined in sodium citrate (C?+. Cr,O?-) and sodium/potassium phosphate buffers ( C r o p ) . Initial chromium concentration 0.1 mM. Solution volume to dry exchanger weight ratio 109 ml/g. Since the solutions used in these experiments were sodium citrate and sodiudpotassium phosphate solutions, the behavior of distribution coefficient is not solely determined by the solution pH. Changing sodiudptassium concentration due to different ratios of Na2HP04 to KH,P04 in phosphate buffers and Na2HC,HS0, to HCI in citrate buffers at different pH values may have had a minor effect as well. In the phosphate buffer the total concentration of alkali metals increases from 0.067M at pH 5.0 to 0.13M

376

Progress in Ion Exchange: Advances and Applications

at pH 8.0. In the citrate buffer the corresponding increase was from 0.01M at pH 1.1 to 0.2M at pH 5.0. As can be seen from Figure 2, the latter increase of alkali metal concentration from 0.01M to 0.2M may have had an essential effect on the distribution coefficient. Another important effect on the distribution coefficient may have arised from the higher dissociation degrees of citrate and phosphate at higher pH values. Part of the decrease in KD may have been caused by increasing competition of chromium phosphate/citrate complexes with ion exchange process. 4.3 Effect of Interfering Cations on the Uptake of Cr3+ by FIBAN AK-22

Alkali and alkaline earth metal cations, Na', Mg2+ and Ca2+, have no effect on the uptake of Cr3' by FIBAN AK-22 at concentrations below 0.1M. However, both divalent and trivalent iron ions start to interfere with chromium exchange already at concentration above 0.001M (Fig. 2). This is as expected since as a transition metal iron competes with the complex formation of chromium with the exchanger. As a trivalent ion Fe3+ has a stronger interfering effect than Fe2+.

I

5 t

0.001

0.01

0.1

1

log C mol/l Figure 2 Distribution coefficient (K ) of C ?' on FIBAN AK-22 as 3 function of Na', Mg2+, Ca2+, Fe2+ and Fe3P concentration determined in sodium citrate buffer at pH 3. Initial chromium concentration 0.1 mM. Solution volume to dry exchanger weight ratio 109 ml/g.

The pH of the solution remained in the Na solutions constant at 3.0-3.1, but in the Mg and Ca solutions the pH dropped from 3.1 at the concentration of 0.0001M to 2.7-2.8 at 1M concentration. This may have had a slight effect on the KD (see Fig. 1). However, it is only a minor effect, compared to the influence of increasing metal ion concentration. For example, at pH 2.7 the K, in Fig. 1 is 5,100, but in 1M Mg and Ca solutions at the same pH value only 32 and 200, respectively. In 0.1M Fe2+ and Fe3' solutions the pH drop was even more dramatic, the pH being 2.3 and 2.4, respectively, after equilibrations. Even this rather large drop cannot explain the decrease of K, at high iron ion concentration. For example, at pH 2.3 the K, in Fig. 1 was 1,600, but in 0.1M Fe2+ solution at the same pH value only 79.

311

Ion Exchange for Environmental Clean-Up 4.4 Removal of Chromium from Waste EMuents by FIBAN AK-22Columns

FIBAN AK-22 column removed chromium from a 1 mM waste solution (pH 6.1) rather efficiently (Fig. 3). The level of Cr in the effluent prior to breakthrough was very low, only 0.01% and the chromium loading was 0.47 mmol/g, calculated from the 50% breakthrough value. The pH of effluent remained constant at pH 6.8-7.0, which indicates that chromiun in this solution was probably as chromate. The behavior of the more acidic solution with pH 1.3 was rather complicated. In the beginning of the elution the exchanger took up Cr rather efficiently, the breakhtrough percentage being 0.2%, but as the equilibrium pH went down from 8.4 to 5 and below the performance of the FIBAN AK22 column was very poor. In addition a1 pH values of about 3-4 Cr was also precipitated as a hydroxide. The loading, calculated from the 50% breakthrough, was, however, reasonable, about 0.8 mmol/g. In this solution chromium was probably present as several forms of chromium.

100

s

10

.c

CD =

z

1

za

0.1

D

0.01

L

0.001 100

200

300

bed volumes Figure 3 Separation of chromium from a waste solution from a metal plating plant with a FIBAN AK-22 column. Initial Cr concentration 1 mM and pH 6.1.

References 1. H.L.einonen. J.Lehto and A.Makela, React. Polymers, 1994, 23, 221. 2. V.S.Soldatov, A.A.Shunkevich and GLSergeev, React. Polymers, 1988, 7, 159.

ADSORPTION-ELUTION BEHAVIOURS OF LIGHTLY CROSSLINKED POROUS AMIDOXIME RESINS FOR URANIUM RECOVERY FROM SEAWATER

N.Kabay

* and H.Egawa **

* Ege University, Department of Chemical Engineering, 35100 Izmir, Turkey **Kumamoto Institute of Technology, Kumamoto 860,Japan

1 INTRODUCTION The chelating resins containing amidoxime groups have found wide application in the recovery of uranium from seawater.1 The modification of polymer networks by a porogenic agent has long been known to produce significant changes in their properties.2.3 The relationship between the physical structure and the performance of chelating resins containing amidoxime groups has been reported b e f ~ r e The . ~ purpose of this study is to investigate the adsorption characteristics of highly porous amidoxime resins in kinetic terms for uranium recovery from seawater. 2 EXPERIMENTAL 2.1 Resin Preparations The chelating resins (RNH) were derived from poly(acrylonitri1e-co-divinylbenzene) beads via NH20H treatment at 8OOC for 2 h. The precursor copolymers (RN) were synthesized by suspension copolymerization using divinylbenzene (5 mol%) as a crosslinker and chloroform (CH) or dichloroethane (DCE) (60-120 ~ 0 1 % as ) a porogen. The alkaline treatment was performed with 1 M NaOH at 3W for 72 h.

2.2 Uranium Extraction from U-Spiked Seawater A 0.1 g of resin and 25ml of natural seawater spiked with U@(NQ)26H20 (uranium concentration 10 mg/L) were contacted at 300C for 1 h using a shaking water bath (GFL-1083 Model). A recording spectrophotometer, Shimadzu 260, was used for the determination of uranium in the filtrate by the Arsenazo method at 665 nm.

379

Ion Exchangefor Environmental Clean-Up 3 RESULTS AND DISCUSSION

The chelating resins (RNH) were derived from poly(acrylonitri1e-co-divinylbenwne) beads with NH2OH treatment. The precursor copolymers were synthesized by suspension polymerization using divinylbenzene (5 mol%) as a crosslinker and varying the proportion of dichloroethane and chloroform as porogenic agents from 60 to 120 ~01%.All the resins prepared using various monomer/progen ratios were tested in the standard batch extracton process using uranium-spiked seawater. The extraction profiles were obtained in order to compare the relative performance of each resin in kinetic terms. Figure 1 shows comparable extraction curves. The resins prepared using 80 to 120 vol% of dichloroethane or chloroform exhibited high uranium extraction significantly more quickly than the ones prepared 60 vol% of pomgen. 100

1uu

80

80

.2 60 c

60

2

40

0

40

c

@

n

? 20

DCE-100

20

D

0

" 0

50 100 150 Extraction period (min.)

0

50 100 Extraction period (min.)

150

Figure 1 Uranium extraction isotherms of cheluting resins 100

100

80

80

60

60

2 40

40

W

a

2 c 0

c

n

20 0

0

0

50 100 Extraction period (min.)

150

0

50 100 Extraction period(min.)

Fcgnre 2 Effect of alkaline treatmenton kinetic behaviow of cheluting resins

150

Progress in Ion Exchange: Advances and Applications

380

The effect of alkaline treatment on the adsorption rate of uranium from seawater was investigated before. As shown in Figure 2, the alkali-treated resins achieved equilibrium uptake with faster exchange due to the increased hydrophilicity based on the high swelling by alkaline treatment (NT:nontreated; AT :alkali-treated resin). The effect of resin amount on the uptake of uranium from uranium-spiked seawater was investigated, increasing the amount of resin from 10 to 200 mg during the batch extraction process. The dependence of uranium recovery on the amount of resin is shown in Figure 3. The data obtained for the nontreated resins showed that as the amount of resin increased from 10 to 100 mg, the increase in uranium recovery was sufficiently fast. However, as illustrated in Figure 3, the adsorption isotherm of the alkali-treated resins reached almost equilibrium uptake with 50 mg of resin because of the enhanced diffusion rate of uranium by alkaline treatment.

100 h

5

80

a

.f 60 U U

a

5 40

g

20 0 0

50

100

150

200

250

Amount of resin tmg) Figure 3 Adsorption isotherms as a function of the amount of resin 100 h

& SO v a

2 U

60

2

40

0

U

bt

w

3

20 0 0

50

100

150

Extraction periodtmin.)

Figure 4 Effect of temperature on adsorption isotherms

381

Ion Exchange for Environmental Clean-Up

The effect of seawater temperature on the adsorption of uranium from seawater was reported before. The temperature-dependencestudies with respect to the kinetic behaviour of resins have been examined by using the standard batch adsorption process with uranium-spiked seawater at 17,25, and 3 9 C . Figure 4 shows the effect of temperature on the uranium recovery versus time. It is clear that the temperature significantlyinfluenced the equilibrium over the temperature range examined.The equilibrium uptake is reached within 40 or 60 min at 3 9 C and needs more than 2 hours at 17OC. The temperature-dependence studies performed in this study generally show reasonable correlation with the results reported before. The dependence of percent elution on eluting agent concentrationsis shown in Figure 5. It is clearly illustrated that the quantitative elution of uranium was achieved by acid as low as 0.5 N in concentration. Elution was shown to be achieved by bicarbonate eluants. The data in Figure 5 confirm that bicarbonate eluants were less effective for achieving a high elution eficiency. It is clearly shown that bicarbonate solution of at least 1 M was required for high efficiency in elution. 100 a

0-

0-

3

80 60

40

L

2o0 0.0

0.5 1.0 1.5 2.0 2.5 Concentration of eluant

(N) Figure 5 Concentration-&pendence of percent elution by acid and bicarbonate eluants

* R N H (CH-12O)AT I

0

2

4 6 Cycle Number

Figure 6 Recycle use of chelating resin

.

8

382

Progress in Ion Exchange: Advances and Applications

The recycling of both nontreated and alkali-treated resins in terms of batch uranium extraction from uranium-spiked seawater was performed with high efficiency (Figure 6). The percent recovery of uranium remained stable after seven adsorption-elution cycles using 0.5 M HCI as an eluting agent.

Acknowledgements This work was supported by Ege University Research Foundation (Research Roject No. NBE 93-003). The financial support offered by the British Council for N.K to attend ION-EW95 conference is gratefully acknowledged.

References 1. N.Kabay and H.Egawa, Sep.Sci.Technol., 1994,29, 135. 2. J.R.Millar, D.G.Smith, W.E.Marr, and T.R.E.Kressman, J.Chem.Soc., 1%3, 218. 3. W.L.Sedere1 and G.J.de Jong, J.Appl.Polym.Sci., 1973, 17, 2835. 4. H.Egawa, N.Kabay, T.Shuto, and A.Jyo, J.Appl.Polym.Sci., 1992, 46, 129.

SELECTIVE ION-EXCHANGE SEPARATION PROCESSES WITHOUT REAGENT REGENERATION

A. A. Zagorodni and M. Muhammed

Department of Inorganic Chemistry, Royal Institute of Technology 100 44 Stockholm, Sweden

1 INTRODUCTION

Ion exchange is a widely used technique for selective separation of ions from different solutions. A highly selective ion exchange process is required for the treatment of waste effluents as, in most of the cases, the toxic ion to be removed, exists at very low concentrationtogether with other ions that exist at much higher concentration. However, its application to processes for treating solutions with large volume is complicated because conventional processes requires large quantities of acid or alkali for resin elution and regeneration. A less known method for the selective separationof dissolved ion is based on the use of t e m v variation. Some ion exchange resins show temperature depeadent ailhities for the binding of different metal ions. Several studies are reported for the use of distinct temperatwe dependence of some strong cation exchange resins for the selective 1-3 separation of metal ions . In these studies examples of the possibility of separating some alkali and transition metal ions ( e.g. CdK, AglCu, FelCu) are demonstrated. However, these resins show weak selectivity dependence on temperature. Carboxylic ion exchangers are found to have more temperature dependent selectivity. Ivanov et al 415 have shown a fairly good temperature dependent selectivity for alkali earth metal ions using weak cationic resin containing mboxylic groups. ~ o l t et o a16 reported a process for the partial demineralion of solutions by thermal regeneration of the resins. The main drawback of these mins is that they lack the selectivity for transition metals against e.g. alkali metals that are commonly present in waste effluents. Hence, they cannot be used for the effective removal of these metals from mdticomponent solutions. Chelating ion exchangers, on the other hand, may have a high selectivity towards different metal ions. In the current work, we studied the temperature dependence of several chelating ion exchange resins for the binding of some heavy metal ions. In this communication we present some p r e l i i results for the separation of copper fiom zinc by the dual temperature method using some chelating ion exchangeresins.

384

Progress in Ion Exchange: Advances and Applications

2 EXPERIMENTAL

2.1 Chemicals and Solutions The following ion exchange resins were used: Amberlite IRC-718 (Rohm & Haas, USA), iminodiacetic resin. VPC-1 (Institute of Chemical Technology, Moscow, Russia), picolinic resin, three different thiourea-based resins, BTUO-1, BTUL-1 and BTUL-2, were synthesized in this laboratory as described in Reference All resins were washed by HCl then NaOH solutions three times to remove organic matter present. C d O C 5 H z 0 and ZFISO~ 7Hz0 (Kebo Lab, Sweden) and H$04 (Merk) of p.a. quality were used as received. All solutions were prepared using de-ionised water. The composition of the stock solution was: 102 mmoVl Zn, 12 mmoyl Cu, 140 mmoyl SO:-. CdO, solution with Ccu = 120 mmolA, was chosen for correction coefficient (only for Amberlite IRC-718 resin) determination.

'.

2.2 Analysis The concentrations of Cu and Zn in the aqueous phase were determined by AAS (Perkin Elmer, AAS 603). The uncertainty of analysis was less then 1 % for Cu and 2 % for Zn. The solution pH was measured using a combined glass electrode.

2.3 Ion Exchange Equilibria The ion exchange equilibria were studied under dynamic conditions in thermostated glass columns providing the heating / cooling of both resin and solution phases. Each column was loaded with a certain amount of air dried resin of around 2 g (&-form). The amount of water in the resin had been determined separately by drying the resin in vacuum over PzOs (until the constant weight). The feed solution was passed through each column up to achieving the equilibriumat a constant flow rate of 0.5 ml/min., correspondingto a linear velocity 0.37 m/h in the column. The experiments were w o r m e d at a temperature range 15-75 'C. Ion-exchange equilibriumwas considered to be establishedwhen the concentration of each cationic species in the feed solution and in the effluent were equal. Then all resins (except Amberlite IRC-718) were washed with 10 ml HzO for the removal of the stock solution from the interbed space. In the case of the IRC-718 resin, different methods were applied for the removal of residual solution h m the resin bed. The elution of the loaded resin was carried out using 1 M H$04. 2 M H$04 solution was used for the removal of Cu residues from the gel-type sorbents. The analysis of Cu and Zn in the acidic eluate obtained was carried out.

3 THE METHODOLOGY DEVELOPMENT

The investigation of exchange equilibria is done by passing a solution through the ion exchange column until it is l l l y loaded. Excess solution is then removed ftom the column by washing, e.g., with water. A complete phase separation is a key point for the correct results. The column is then eluted by a suitable solution. In this case, the amount of ions

Ion Exchangefor Environmental Clean-Up

385

sorbed on the ion exchanger bed can not be accurately determined for resins which undergo hydrolysis reactions ,as shown by equation (1) during the resin wadung: R; M" + zH, 0 = zR- H' + M" + zOH(1), (where R is a ion exchange resin, M is a metal ion of charge z) Such reactions may occur during washing the chelating resins. A practical way to avoid this problem is to apply vacuum to the resin bed to remove excess solution4instead of the washing. However, the vacuum procedure does not completely remove solution from the resin, which results in higher values for the amount the sorbed ions. A comtion term should be taken into accounf for the correct debmination of the sorbed ion amount. Test experiments showed that the speed of the ion exchange process is different for different resins. The slow kinetics of VPC-1 and BTU resins does not allow any hydrolysis reactions during the washing stage. Meantime, the IRC-718 resin has fast kinetics. The reaction R&-,,,Znz+ + 2 H , O = R&-,,,H; + Znz+ +2OH(2) occurs during the displacement of stock solution. 3.1 A Correction Term for Exchange Capacity Determination

The experiments with IRC-718resin were carried out. After loading the resin, excess solution was then removed from the resin bed by three differentmethods: a: washing with 10 ml of H S O , solution at pH = 1.8 (equal to the pH of the stock solution); b: washing with 10 ml HZO;and c: applying suction without washing. The results are summanzed * in Table 1 for 5 replicate measurements of each sample. The confidence limit, 90 %, is calculated by standard student t-test. As seen, the repraducibility in the determinationof copper on the resin phase is satisfactory for the method of washing with pH 1.8 solution (2.6% confidence limit) while that of the Zn is much lower (with 24 % confidence limit). The determination of the concentration of Cu wasperformedat 6 different tempemtures. The results are summatlzed * in Figure 1 and show a linear relationship between RCu and T, while in the Zn case the results are scattered.This may be explained by the hydrolysis of zinc attached to the iminodiaceticgroup during the washing step. Table 1

Determination of the concentration of sorbed ions on the resin IRC-718 at 45 "C Method

RCu

Rzn

mmoUg of dry resin

mmoUg of dry resin

Washing withpH 1.8 solution Washing with HZO

1.525 f 0.040

0.048 f 0.012

1.574 f 0.051

0.098 f 0.024

Vacuum suction

1.561f 0.045

0.220f 0.013

z:I I

Progress in Ion Exchange: Advances and Applications

386

0.3

0.22

d

0

x

U

0

Figure 1

I

v

0.lE

The Cu and Zn sorption, determinated by two different methoak

A second set of the experiments was performed by washing with water instead of

HgO,solution of pH=1.8. It appears that both methods produce the same results for RCu however, the results seems to be different for RZn. The amount of RZn determined by the second method is twice as large as that obtained by the first one. It shows that hydrolysis of the zinc - functional group complexes (reaction (2)) decreases as the pH increasing. The large confidence limit obtained for RZn indicatesthat H 2 0 causes hydrolysis too. A third series of experiments was carried out by applying suction to remove the solution from the resin. The results show that this method gives a smaller confidence limit for zinc adsorption. Temperature dependence has a linear relationship on both RCu and RZn (see Figure 1). It should be mentioned that the vacuum procedure can not completely remove solution from the ion exchange resin bed. Hence, the values of ion adsorption are higher than the real values. The copper forms of iminodiacetic resins are not liable to hydrolysis, because they have a high selectivity for Cu” ‘-lo. The same conclusion follows f h m Table 1 and Figure 1. Hence, it is possible to estimate the residual volume of the stock solution after the suction by comparing RCu determined by the two different methods. A solution containing only C d 0 4(Ccu= 120 mmoVL), was chosen for this investigation.Two sets of experiments were carried out: one including washing with H 2 0 and one including suction to remove the residual stock solution. The experimental results are shown in Figure 2. The RCu = f(T) dependence can be fitted by straight lines. From Figure 2 it appears that,in our case, we can ignore the dependence RCu(S) - RCu( W)= (7‘). The coefficient (u3 shows the water washing method, the coefficient(s)shows the vacuum suction method. Hence, we can describe the experimental results by two parallel straight lines:

f

387

Ion Exchangefor Environmental Clean-Up

Figure 2

The Cu sorption, determinated by two methodr

R C u m = a.T + bm (3). RCu(S) = a.T + b(S) We have used the least square method for calculation of the coefficients a, bm and bp). From these calculationswe obtained: a = 2.Ol.lO"; b(W) = 2.38; b(W) = 2.51 (4). Assuming that the amount of copper per 1 g of dry resin inside the column after washing with water is R C u m = RCu, (5)s where RCu, is the amount of Cu sorbed by ion exchange reaction accordingto the (6): Cu" -+ R H 2 = RCU -+ 2 f l (6). For vacuum suction method, the following mass balance is valid RCu(S) = R C U ~-+ C C ~* V r (3, where: Ccu is the copper concentration in the stock solution; v, is stock solution residual volume (ml per g of dry resin). The equation for determination of residual volume after the vacuum procedure ensues from ( 5 ) and (7): RCu(S) - RCu(R3 vr =

cr.

(8).

For our case (we ignore dependence of v, on temperature>

- bm = 1.I6 (mL / g dty resin) (9). CC" The amount of ion sorbed by ion exchange can be calculatedh m the equation: vr = b'B)

where C, and V, are the concentration and the volume of the eluate, m is the mass of ion exchange resin, and C, is the ion concentration in the test solution. This correction was applied for IRC-718resin experimental results.

388

Progress in Ion Exchange: Advances and Applications

Cu-IRc718

A

h-IRc718

C u- v pc l

0

Figure 3

20

60

80

The temperature dependence of resin capacity toward copper and zinc

4 RESULTS OF CdZn EQUILIBRIA

The sorption parameters of the resins studied towards Cu and Zn at different temperature are shown in Figure 3 and Figure 4. Here a is the separation factor for the Zn-Cu exchange reaction (1 1): RZn + Cu" = RCu iZn2' (1 1). It was calculated as follows:

where C,, is the total concentrationof the metal in the solution phase. As follows fiom these figures, IRC-718 and VPC-1 resins demonstrate a far higher selectivity towards Cu than BTU resins. a values for IRC-718 depend slightly on temperature, while those for VPC-1 increase remarkably when temperature rises. The selectivity parameters of the BTU resins also depend on the temperature, but low ion-exchange capacities of these resins towards Cu and Zn (see Figure 3) limit their practical use.

Ion Exchange for Environmental Clean-Up

389

7

ii'i m

im

Figure 4

Temperature dependence of the separation factor for direrent resins

5 DISCUSSION

The dependence of sorptionparameters on temperature may be used for the Separation of the Cu-Zn mixtures. A solution containing Cu and Zn is passed continuously through the resin bed. No regeneration solution is used. The temperature of the column may be changed between 15 and 75 'C ("low" and "high"temperature), for example. Two eluate fractions are collected at different temperatures. The concentrationof Cu in the effluent increases during contact with VPC-1 at the "low" temperatureand decreasesat the I t h i g h " temperature. The Cu-Zn separation factor of Amberlite IRC-718 resin has a weak dependence on temperature.However the temperature dependence of IRC-7 18 exchange capacity toward Cu and Zn and high selectivity of this resin to Cu allow one to use this resin for separation by this method. The total concentration of Cu and Zn (Ccu + C& in the treated solution increases at the "low" temperature and decreases at the "high". The ratio Cc,/Ca in the concentratedsolution is expected to be several time more that in feed solution.

Progress in Ion Exchange: Advances and Applications

390

6 CONCLUSIONS The preliminary experimental results reported above clearly demonstrates the possibility of separating CdZn using temperature dependent chelating ion exchange resins. Equilibrium results give a better Cu and Zn separation by using VPC-1 resin. However, IRC-718 resin has better kinetic properties and may be used for the separation and I or concentration of this ionic mixture. In such mode of operation described above, there is no need for the use of regeneration chemicals which may ultimately pollute the environment or either product. 7 ACKNOWLEDGMENT The work was funded by TFR (Swedish Research Council for Engineering Sciences). One of us (AZ)are indebted to the Swedish Institute for their support. We would like to thank Dr. G. Zuo for the BTU resins, and to Dr. N. Nikolaev and Dr. D. Muraviev for discussions.

References 1.

2. 3. 4.

5. 6. 7. 8. 9. 10.

V. I. Gorshkov, A. M. Kurbanov and N. B. Apolonnik, Russian Journal of Physical Chemistty, 1971,45,1686. G. Grevillot, J. A. Dodds and S. Marques, J. Chromatogr.,1980,201,329. M. Bailly and D. Tondeur, J Chromutogr.,1980,201,343. V. A. Ivanov, V. D. Timofeevskaya, V. I. Gorshkov and T. V. Eliseeva, Russian Journal ofphysical Chemistty, 1991,65,1296. V. A. Ivanov, V. D. Timofeevskaya and V. I. Gorshkov, Reactive Polymers, 1992, 17, 101. B. A. Bolto, K. H. Eppinger, P. S. K. Ho, M. B. Jackson, N. H. Pilkington and R. V. Siudak, Desalination, 1978,25,45. G. Zuo and M. Muhammed, Reactive Polymers, 1995,24,165. Rohm and Haas datasheet for Amberlite IRC-718 resin. D. Voutsa, C. Samara, K. Fytianos and Th. Kouimtzis, Fresenius Z. Anal. Chem., 1988,330,596. W. H. Holl, J. Horst and M. Wemet, Reactive Polymers, 1991,14,251.

Part 5 Ion Exchange in Inorganic Materials and its Theory

ION EXCHANGE IN ZEOLITES: Detergency and Catalytic Systems

Lovat V.C. Rees Department of Chemistry The University of Edinburgh West Mains Road Edinburgh EH9 3JJ

1 INTRODUCTION:Detergency

For a number of years zeolite A (4A) has been used in extensive tonnages throughout the world as a builder in detergentsto replace phosphates which are banned, or whose concentrations are severely limited, in many countries. Zeolite A exchangesthe Ca2' and Mg2' ions present in hard waters with the Na' ions resident in the zeolite on synthesis. The selectivity of Na-A towards the ingoing divalent ion is very large as can be seen in the exchange isotherms in Figure 1 where Ca,and Mg,and Ca, and Mg, represent the respective equivalent cation fractions of the ingoing divalent ions in the zeolite phase, z,and the solution phase, s. The corrected selectivity coefficient,%, can be expressed in a convenient form for use with the isotherm data by Equation 1

where N is the total normality of the solution phase and y* is the activity coefficient of the indicated salt in the mixed salt solution phase. The correction introduced by the last two terms in Equation 1 removes the selectivity of the exchange introduced by the solution phase. The corrected selectivitycoefficient is a quantitative representation of the selectivity of the exchange associated with the zeolite phase only. Equation 1 quantifies the concentrationvalency effect which is clearly demonstrated in Figure 1 . Q2 Q.4 Q.6 0.8 Decreasing solution phase 0.2 a4 a6 ae normality results in increasing Caz Mgz selectivity in the exchange Figure 1 NdCa and N&g Isotherms reaction towards the ingoing divalent ion. 0 0.2N; X 0.1N; 0 O.05N; 0 0.01N; 0.005N

394

Progress in Ion Exchange: Advances and Applications

2 RESULTS

The corrected selectivity coefficients,%, were calculated from the isotherm data in Figure 1 using Equation 1 and from these the logl& vs Ca, or Mgz plots in Figure 2 and 3 respectively were constructed. As indicated above these plots indicate the selectivity of the zeolite phase for the respective ingoing divalent ion as a finction of loading. Log& values greater than zero indicate preference for the divalent ion over the Na’ ion by the zeolite phase. Figures 2 and 3 show that Na-A prefers Ca” ions up to loadings greater than 90% and Mg” ions up to 40%. Thus Na-A is a better builder towards Ca2+than Mg*+. These figures show, also, the enhancement in selectivity for both divalent ions as the temperature increases because of the endothermicnature of the exchange reaction. The experimentalpoints in Figures 2 and 3 were fitted to a polynomial equation of the form lOgl&

=

C, + CIA, + CxA,Z + C3A;

(2)

(where A, = Ca, or Mg, ). The resulting polynomials are listed in Table 1 and the isotherms calculated from these polynomials are drawn as continuous lines in Figure 1 which shows the goodness-of-fit of the polynomials in representing the experimentalisotherms.

2.0

1.5

LoeKc 1.c

0. r

0

-a!

,

0.2

QC

I

0.6 0.8

Figure 2 Log,& vs Ca,

Figure 3 LogiOKcvsMgz

(Symbols as in Fig. 1)

(Symbols as in Fig. 1)

395

Ion Exchange in Inorganic Materials and its Theory Table 1 PolynomialEquations Exchange Reaction Temp("C) Na+Ca Na+Mg

25 65 25 65

PolynomialEquation

-

logl&=2.83 6.03Ca, + 1lSCa,' - 9.11Ca,3 =3.41 - 5.28Ca, + 6.32Ca,'- 4 . 0 1 C ~ ~ log1&=1.46 - 2.66Mgz - 6.34Mgz2+5.08Mgs3 =2.61 - 7.74Mgr + 3 . 5 7 M ~ ~

From these polynomials the corrected selectivities,K, are 676 and 2570 for Ca,= 0 and 28.8 and 407 for ME= 0 at 25 and 65°C respectively. These values indicate the very high initial selectivitiesfor Ca2' at 25 and 65°C respectively. From these log& plots or the polynomials in Table 1 it is possible to calculate the standard free energies, enthalpies and entropies of these exchange reactions. The quantities so obtained are listed in Table 2. Table 2 Standard Thermodynamic Quantities (kJ/g.equiv)

Exchange Reaction Na+Ca Na+Mg

Temp("C) 25 65 25 65

AG' -2.68 -4.69 3.26 1.20

AH@

12.2 18.6

TAP 14.9 16.9 15.5 17.4

The TAS' values are very similar for all four exchanges. The negative AG' values for the Ca2+exchange and the correspondingpositive values for the Mg" exchange arise, therefore from the larger endothermicenthalpiesfor the Mg" exchange. The divalent ions have to shed some of their hydration shell before they can enter the channels of zeolite A whose size is controlled by the free diameter of rings of 8-framework oxygens (theoretically 4.2A). The endothermic dehydration energy must be some 50% greater for Mg2+ions than for Ca2' ions and it is this increase in dehydration enthalpy which produces the positive free energy to the Mg" exchange reaction'. When zeolite A is used as a builder in detergency, at its simplest concept, one is dealing with a ternary exchange reaction. All such ternary reactions behave in a manner similar to that shown in Figure 4. Ternary isotherms display a high selectivityfor both divalent ions at low Mgr and Ca, loadings and in this region of the isotherm few divalent ions remain in the solution phase at equilibrium. All divalent ions, initially in the solution phase are exchanged into the zeolite which results in a straight line zeolite phase composition curve, as seen in Figure 4, at low divalent ion loadings. When this line is extrapolated to Na,= 0 it intersects the Ca-Mg axis at a value equal to the Ca:Mg ratio in the initial solution phase. The concentration of divalent ions in the solution phase gradually builds up with increasing divalent ion loading of the zeolite phase until, finally, the Na. value approaches zero and the CaJMg. ratio approaches that of the initial solution phase. The Mg. value attains its starting solution phase value long before the Ca. value attains its starting value. Mgr passes through a maximum in all ternary isotherms measured in our laboratories. The magnitude of Mgr at the maximum depends on the Ca/Mg ratio of the initial solution phase but the maximum always occurs at a Na, value of -0.33. The value of Mg, is found to increase from -0.19 for a CdMg ratio of 2:l to -0.38 for a ratio of 1 2 . It is also interesting to note that Mgz never increases above a value of -0.4, the maximum found in

396

Progress in Ion Exchange: Advances and Applications co

Figure 4 NdCalMg ternay isotherms at 6PC and 0.05N CalMgratios (a) 2 : l ; (b) 1:l; (c) 1:2. Continuouslines- zeolite phase. Dashed lines-solutionphase

the binary exchange of Ca-A with Mg2‘ ions confirming the great difficulty of loading zeolite A with more than 2Mg2’ ions per unit cell when there are Ca2’ions available to the zeolite’ (N.B. There are 12 Na’ ionsl6 divalent ions per U.C.in pure cationic forms) The rates of exchange of the Na’ ions in Na-A by Ca2’, Mg” and binary mixtures of these ions at 25°C have been determined2. The diffusion coefficients calculated fiom these rates are given in Table 3. This table shows that the rate of pure Ca” exchange is 10 fold faster than the corresponding Mg2’ exchange rate. The presence of Mg” ions in the binary mixtures does not decrease the rate of exchange found with pure Ca2’ solutions when the solution phase contains an initial CdMg ratio of 2: 1. However, when this ratio decreases to 1:2 the rate of divalent exchange is considerablyreduced. Mg2’ ions, in this latter case, must block the eight-membered oxygen windows controlling access to the channel network of zeolite A and slow down the ingress of the more rapidly diffusing Ca2’ ions. From these rate measurements the time constants for 50% exchange of Na-A crystals, which have a radius of lpm (the size of crystals used in detergent formulations), by Ca” and Mg” ions could be calculated. They were found to be 9s and 250s respectively at 25°C. The slowness of the Mg2’ exchange must be ascribed, once again, to the need to strip water molecules from the hydration shell of the Mg” ions before they can enter the channel network of zeolite A. The slowness of the exchange reaction allows Mg” ions to react with other species present in the detergent formulation.

397

Ion Exchange in Inorganic Materials and its Theory

Table 3 Kinetics of Ion Exchange in Zeolite A at 2% Initial Solution Phase

PureCa Ca:Mg 2: I

Diffusion Coefficient @Ao - * ~ ~ * s - * )

1.67

Ca:Mg 1:I

Ca:Mg

1.38

0.62

1.70

PureMg

1:2

0.18

Recently Unilever has introduced zeolite P (MAP), which is a synthetic gismondine, as a builder in their detergents. In Figure 5 a comparison of the calcium exchange capacity of MAP and Na-A (4A) as a hnction of temperature can be seen. In this figure the capacity is defined as the amount of CaO in mg removed after 15 minutes per g of zeolite (dehydrated). Both of these zeolites have SVAl ratios of 1:1 and have, therefore, the same theoretical, maximum exchange capacity of 197 mg/g of zeolite. The difference in performance of MAP and 4A is due to a) an enhanced selectivityof MAP over 4A at high loadings in the presence of reasonable concentrations of Na' ions in the solution phase and b) enhanced kinetics of exchange of MAP over 4A because of differencesin the crystallite sizes involved. Although MAP has a particle size of 1pm the particles are aggregates of 500/600A crystallites. Zeolite 4A tends to be non-aggregated crystallites of 1-2 pm diameter. The rate of exchange is dependent on l/? where r is the crystallite radius and this size difference is the main reason for the enhanced performance of MAP after a 15 minute contact time. Figure 5 demonstrates, also, that at (say) 40"C, which is a reasonable wash temperature, the difference in effective capacity is still maintained. In Figure 6 the effect of temperature on the kinetics of exchange can be observed. Although at 5°C there is a very large difference in the Ca uptake rate, which is deiined as the time in seconds to reduce the Ca*+concentration in the solution phase from ~ x ~ O to -~M 105M,the difference at 40°C is still large but not critical for detergency purposes. However, it is interesting to note the very fast kinetics of MAP resulting from the small crystallite size. The defined reduction in Ca concentration occurs at 40°C in a time scale of -1 sec compared with times of 25-30 sec for 4A zeolite3.

- 011

0

1

0

2

0

3

0

4

0

5

Tempe nlunCC)

Figure 5 Calcium exchange capacities of zeolites MAP and 4A

0

01 0

1

0

2

0

3

0

4

0

5

0

Tempen!ureCC)

Figuie 6 Calcium uptake rates of zeolites MAP and 4A

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Progress in Ion Exchange: Advances and Applications

3 INTRODUCTION:Catalytic Systems

Although ion exchange in zeolites containing high concentrationsof framework Al has been studied in depth because of their high exchange capacities (there is one equivalent of cation sites associated with each mole of framework Al) and ease of followingthe exchange reaction little work has been carried out on zeolites with high SilAl ratios. We have recently studied ion exchange in ZSM-5‘ and EU-15zeolites with SdAl ratios in the range of 20-100 ; i.e. with frameworks which have only 1 to 4 Al atoms per unit cell (u.c.). These samples have exchange capacities of 0.1-0.5 m.equiv. per g of dehydrated zeolite and require very accurate analyses to establish the exchange isotherms with any degree of accuracy. These zeolites are interesting as novel ion exchangers since their exchange sites are, on average, far removed from each other. However, it is, also, of interest to study the thermodynamics of their exchange reaction and compare the values obtained with those for zeolites with maximum exchange capacities (i.e. 7 m.equiv./g of zeolite) where the exchange sites are only -4A apart. Divalent ion exchange of the Na forms of these high silica zeolites has been shown to be able to be used to describe the Al-Al separation distance distributions in these zeolites. Thus ion exchange is, therefore, a useful method of characterisingthe separation distances between catalytic centres in these important catalysts since a Bronsted acid site is located near to each Al atom in the framework. 4 RESULTS

In Figure 7 the isotherms for the exchange of Na’ by K’, H‘ and Cs’ at 25 and 65°C are shown for EU-1 zeolite with 3.8 Al atoms per U.C. 0.8 These isotherms all show complete 0.4 reversibility and complete exchange of Na by the ingoing cation as & AS 0.0 approached 1.O. 0.8 The corresponding isotherms for the exchange of the Na’ ions in 0.4 EU-1 with 2.1 Al per U.C. with Ca”, Sr2’ and Ba” are shown in Figure 8. 0.0 This figure shows that “cut-offs” 0.0 0.4 0.8 0 0.4 0.8 0 0.4 0.8 AZ occurred at higher degrees of exchange and that these “cut-off’ Figure 7 Uni-univalentexchange in EU-1 values increased as the temperature with 3.8 A1 atoms per U.C. increased. All isotherms were 0 forward and 0 reverse points reversible within the experimental error. These isotherms clearly demonstrate that divalent exchange in these zeolite samples is completely different in character from that found for uni-univalent exchange in two respects; a) 100% exchange of Na’ ions is never obtained and b) sigmoidal isotherms are always found. The maximum divalent exchange values, Asrmxobtained from these isotherms are listed in Table 4.

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Ion Exchange in Inorganic Materials and its Theory

AS

Table 4 Isotherm cut-ojfsfor EU-I

TempCC) 25

65

Zeolite

Si/Al

23.8 22.1 21.2 23.8 22.1

28.9 52.0 95.8 28.9 52.0

Ca 0.86 0.62 0.54 0.96 0.85

Sr 0.93 0.67 0.56 0.97 0.89

Ba 0.93 0.67 0.56 0.97 0.89

The "cut-offs" found in these divalent exchanges are not due to any kinetic effect. Sampleswere exchanged with fresh solutions over several weeks but the maximum exchange levels remained constant. Secondly, as stated above, the exchanges were found to be reversible. The limited exchange levels were not due to inaccessible exchange sites because a large cation, such as Cs', showed 100% exchange and, finally, the &values increased as the size of the divalent cation increased; i.e. Ba*'>SrZ'>Ca*'. Similar results were obtained when corresponding studies were carried out with another high silica zeolite, ZSMJ. The standard thermodynamic parameters for the Na/K exchange in three high silica ZSM-5 samples at 298 and 338K are given in Table 5 .

Table 5 StanHard lIermaJnmnic Quantitiesfor N d K Exchange in ZSM-5

Sample 21.1 22.0 24.2

AGmK AG~K AH (kJ/g equiv) (kJ/g equiv) (kJ/g equiv) -7.8 -8.8 -9.0

-4.2 -7.8 -8.2

-19 -16 -15

AS~K JK(g equiv) -3 8 -24 -20

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Progress in Ion Exchange: Advances and Applications

Values of similar magnitude were reported previously6for a number of univalent ions to give a thermodynamic affinity series of Cs>RbzNH&I3O>K>Na>Li. In all cases @ was exothermic with values less than -20 kT1g.equiv. and ASe was, also, always negative with values in all cases around -20 JK-' g.equiv-'. Thus, the thermodynamics of uni-univalent exchange in these high silica zeolites was not very different from that found with aluminous zeolites with much greater exchange capacities4. Qualitatively uni-univalent ion exchange in zeolites does not change significantly as the negative framework charge density increase. Changing the SUAl ratio of high silica zeolites had little effect on the respective isotherms, presumably, because of the large separation distances, on average, between the cation sites in all cases. When divalent exchange in ZSM-5 was studied "cut-offs" were once again observed. These "cut-off values were, however, smaller in the case of ZSM-5 than found with EU-1 as can be seen in Tables 4 and 6 Table 6 Isotherm cut-03s for ZSM-5

25

65

24.2 22.0 Zl.1 24.2 22.0 Zl.1

21.9 47.0 86.3 21.9 47.0 86.3

Ca 0.37 0.3 1 0.28 0 62 0.54 0.50

Sr 0.42 0.36 0.3 1 0.85 0.64 0.51

Ba 0.90 0.56 0.36 0.93 0.76 0.52

The occurrence of isotherm cut-offs can be explained in terms of the Al-Al distance a divalent ion can bridge as first suggested by McAleer et a1 '. The charge on each divalent ion is balanced by the negative charge on the framework associated with 2 Al atoms. If the pair of Al atoms are close together the interaction energy is stronger ( i e . more negative) than twice that between a Na' ion and an Al atom. As the distance between Al atoms increases the interaction energy decreases ( i e . becomes less negative), and eventually it will become unfavourable for a divalent ion to sit between 2 Al atoms and hence the isotherm cuts off. At higher temperatures the divalent cation can bridge greater distances from Boltzmann energy considerations. Thus cut-offs increase with increasing temperature. As the zeolite becomes more aluminous, the Al atoms are, on average, closer together and hence there are more sites with lower energy and fewer sites with higher energy. i.e. there are more pairs of Al atoms which a divalent cation can bridge. Hence, the cut-offs increase in value as the Al content increases. Changing the divalent ion will not affect the energies of the sites; the interaction energy is determined by the separation of the Al atoms and not the cation radius. However, changing the cation does affect the free energy of the solution phase. The smaller the cation, the more negative its free energy of hydration and the greater the preference of the ion for the solution phase relative to the zeolite, resulting in a smaller cut-off. The cut-offs for ZSM-5 follow the same trends as EU- 1, but with values which are much smaller. This suggests the Al atoms are closer on average in EU-1 than in ZSM-5.

Ion Exchange in Inorganic Materials and its Theory

401

5 MONTE CARLO SIMULATIONS OF Al-Al DISTRIBUTIONS

To test the A-Al bridging model, the distribution of AI-AI distances has been calculated using a Monte Carlo simulation described previously' . This calculates the percentage of AI 60 atoms closer than a given ?Lo distance, such that each Al atom is a member of one pair only. The atomic coordinates of 20Briscoe et a17for EU- 1 were used. 0 5 10 15 20 Al-AIdistance distributions AI-AI DistancelA for Al atoms capable of occupying all T sites (see Figure 9) Figure 9 Distribution of Al-A1 separation distances in EU-I (all Tsites available) and for AI occupying sites T1 and T6 only have been calculated. Sites T1 and T6 correspond to the 4 rings situated at the bottom of, and opposite, the mouth of the side pockets . X-ray diffraction studies indicate that the cationic ends of the hexamethonium template molecules in as-synthesized EU-1 are located near these 4 rings, and it is possible that the Al atoms are located there5. It should be noted that T1 and T6 refer to the labelling used by Briscoe et d 7and not that in the Structure Atlas'. As expected the higher the Al content the greater the proportion of pairs of Al atoms closer than a given distance and the shorter the distance at which the distribution curve reaches a 100%. The fraction of Al atoms within a certain distance increases in a series of steps, with larger steps for Al occupying T1 and T6 only, reflecting the smaller number of possible Al-AI distances. The critical bridging distances given in Figure 10 have been determined from the Al-Al distance distributions by reading off the Al-Al distance for the appropriate Si/N ratio correspondingto the percentage AI-AI '5 exchange cut-off The maximum bridging distances for EU-1 are -10125A for Al atoms in all sites and -11-13.5A for AI in T1 and T6 only. 5 So the choice of Al sites makes relatively little difference to the n critical bridging distance. It is difficuit 1.2 2.1 3.8 therefore to decide which, if either, of AlNC the AI distributions is correct. In comparison, the maximum bridging Figure 10 Maximum bridging distancesfor EU-I distances for ZSM-5 varied from (all T sites available) -6-12A4. The larger range of distances

r,", Y

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Progress in Ion Exchange: Advances and Applications

with ZSM-5 reflects the greater range of cut-off values obtained. As with the isotherm cutoffs, and for the same reasons, the maximum bridging distances increase with the cation in order Ca<Sr
ANION EXCHANGE IN COPPER HYDROXY DOUBLE SALTS Catherine S. Bruschini and Michael J. Hudson

Department of Chemistry, University of Reading, P.O. Box 224, Reading, UK RG6 2AD

INTRODUCTION

Many studies have been carried out on inorganic cation exchangers, but only recently have inorganic anion exchangers received attention. These compounds may have positively-charged layers charged balanced by the interlayer anions. This study concerns the hydroxy double salts (HDS) which are formed by (h4',M''))(OH), cation layers charged-balanced with organic and/or inorganic anions. There are several methods by which the HDSs may be synthesised. One method starts from a mixture of a metal oxide MO and an aqueous solution of a metal salt (M2'Xnxlb,) in which n equals 1 or 2.'-3The solid MO is transformed into the basic metal salt. Another method consists o f a slow addition of sodium hydroxide into the solution of the metal salt until the basic metal salt is precipitated."" The metal(II) salts may be hydrolysed using urea'.'' or by controlled hydrolysis of metal complexes such as copper nitrite amine.I2 Corrosion of the metal itself may lead to HDS.'7'3 The general formula of HDSs is [(MnlI,,M'n~+x)(OH)~~I.~,]'X",l+~,.,, zHzO in which M and M correspond to a divalent metal such as Cu,l-17 Co,1,2.".y Ni,l.z.J My:'.'.' Zn,'.'Cd.' Fe or Mn.' X is an anion situated between the cationic layers of [(MnlI.,,MUI+~)(OH)~(I-\.)]+, and can be either monovalent, Cr,'*475*'0 ~0,-,2.3,5.9-l7 ~~:,-t..'.lO 1-,J.S.I1.10 C10;,5,10 Mn04.,','0 NO;," or divalent, S04","7.'0 CO?." It is possible to intercalate organic anions such as acetate,"'" long chain carboxylates,' long chain alkylsulfates,' or even a bulky anion such as phthalocyanine tetrasulfonate.'8 The alkyl sulfateexchanged H D S intercalates neutral species such as alcohols or ion-pairs in the interlayer space.* The crystal structure of Cuz(OH)3NO;, which is shown in Figure I , has been extensively studied.',""' The layered structure consists of [Cu2(0H)30]' units linked together by hydrogen bonds through NO;' ions. Each copper atom is octahedrally coordinated. Cu(1) atoms are surrounded by four hydroxides and two oxygen atoms of the N 0 i ions. Cu(2) atoms are coordinated by four OH, a fifth OH- at a greater distance, and one oxygen atom of the

404

Progress in Ion Exchange: Advances and Applications

NO<. For the Cu( l)Oo polyhedron, four equatorial distances range from I .87(2) to 2.1 l(2) A and axial distances are equivalent to 2.54(2)and 2.35(2) A. For the Cu(2)Oe polyhedron, the variation of distances is lower; four equatorial distances range from 1.96(2) to 2.04(2) A and axial distances are equivalent to 2.44( I )and 2.29( 1) A.3 The surface properties of HDSs have not been examined except in the work of Hayashi and Hudson on exchanged copper acetate HDS with copper(l1) phthalocyanine tetrasulfonate anion which gave a compound of low surface area (1 tn2y“).” In the present study, anion exchange with organic as well as inorganic anions was carried out on copper HDS compound. The dodecylsulfate ion (DS)and dodecylbenzenesulfonate (DBS)were used as well as the carboxylate anions such as benzoate (BZ), sebacate (SEB), (CPL) and caprate (CAP).The inorganic anions used for the anion . . caprylate . . exchange were nitrate, chloride and sulfate Thermal, structural and surface properties of the compounds were studied.

in tlic h projection Figure 1. Ccstal srnic1iire of CII~(OH)~NO,

EXPERIMENTAL The methods for the synthesis of C U ~ ( O H ) ~ Nand O ~the anion exchange with the different anions were described in a recent study.” The reversibility of the exchange to the nitrate form was examined in the case of dodecylsulfate, acetate. benzoate, caprylate, chloride and sulfate exchanged HDS with a ratio X:NO3 equal to 120. The exchange between C12H250S& and C7H&0; has been studied The dodecylsulfate and the caprylate HDS were added into a solution of sodium caprylate and sodium dodecylsulfate (0.1 mol L’)respectively. The mixture was allowed to stay for four days at 65°C. The ratio between the interlayer HDS anion and the anion in solution was I : 10. The anion exchange selectivity among the surfactant anions C ~ ~ H ~ S O C,H&Oi S O ~ , and (-02C(CH2)&0;) was examined. An aqueous solution (0.1 mol L-’)containing two ofthe surfactant sodium salts with a ratio 1: 1 was prepared. CU~(OH)JNO, was put into this solution for four days at 65°C.The ratio NOi:(surfactant)*l,n was 1.2. The composition of the sample obtained was estimated using thermal analysis as shown in Table 1.

405

Ion Exchange in Inorganic Materials and its Theory

Table 1. Composition of anion-exchanged HDS materials determined by thermal analysis (lOO/minin air). The percentage of interlayer water was estimated from the mass loss between 100 and 200°C. The values in brackets correspond to the theoretical residual mass in the case of a complete exchange. Interlayer

anion NO; NO; NO; NO; NO;

NO; NO; NOi DS CPL BZ CPL CI'

so," CPL DS

Anion in solution DS BZ CPL CAP SEB CI-

so,"

DBS

NOT' NO;

NO; NO; N0i NO' DS CPL

%water

% CuO loss at 900°C 0 (0) 37.5 (35.9) 0 (0) 53.7 (53.2) 2.5 (2.7) 54.0 (48.2) 2.2 (2.5) 47.2 (44.4) 0 (0) 59.8 (57.2) 0 (0) 76.8 (74.5) 0 (0) 71.5 (70.4) 0 (0) 45.9 (3 I .6) 0 (0) 48.2 (66.2) 0 (0) 72.6 (66.2) 0 (0) 54.8 (66.2) 2.2 (0) 47.2 (66.2) 0 (0) 69.2 (66.2) 0 (0) 70.1 (66.2) 0.8 (0) 45.4 (35.9) 2.8 (2.7) 49.9 (48.2)

Compound formula CudOHMDS) CuA0H)dBZ) Cu~(0H)3(NOp)o.~(CPL)o.~.(H20~,4 CU:(OH)~(NO~)~ I(CAP)oP.(H20)~.J CUAOHMNOI)OI (SWo4s CU~(OH)~(CI) cu2(0H)3(s04)0~ ~ ~ ~ ( ~ H ) ~ ( N ~ ~ ) o . ~ ( ~

C~~(OH)I(NO~)~&WO~ CU~OH)~(NO~).(CUO)O~

CU~(OH)~(NOJ)O,~(BZ)O.P.(CUO)~ CU~(OH)~(CPL).(H~O)~~.(CUO)~ cu2~0H)3~c~)0.4(N03~06 cu2~0H)3(s04)0~

CU~(OH)~(NO~)~~(CPL)~~(DS)~J.(H~O) CU~(OH)~(CPL).(H~O)O~

RESULTS AND DISCUSSION Thermal Properties By 900°C all samples are decomposed to CuO, as deduced from the XRD patterns, enabling the composition of the materials to be estimated (Table 1). The TG analysis of CUZ(OH)~NOO showed only one large mass loss with an endothermic transformation around 244°C corresponding to the loss of water and nitric acid. The residue of 65.8% (theory, 66.2%) corresponds to a complete decomposition in copper(I1) oxide, which was subsequently confirmed by X-ray powder diffraction analysis. In CUZ(OH)~CI, the thermal decomposition occurred in two steps corresponding to two endothermic peaks. The first stage between 240 and 270°C is associated with the loss of one water molecule. The intermediate compound is CuOCu(0H)CI which decomposed to CuO and HCI between 390 and 520°C. The TG analysis of Cu2(0H)3(SO& showed two endothermic peaks associated with the mass loss in the ranges 365-470°C and 625-750T which corresponded to the loss of 1.5 water molecules and 0.5 SO3 molecule respectively. The exothermic peak at 540°C was due to the recrystallisation of the mixture of CuO and C U O C U O S O ~Cuz(OH)3(DS) .~ contained no interlayer water. Above 300°C a mixture of CuO and CuOSO3 was obtained. There was no recrystallisation of these compounds as in the thermal decomposition of CU~(OH)~(SOJ)I/~. The endothermic peak at 730°C corresponded to the transformation of CuOSO3 into CuO. As Cu2(0Hh(DS), the dodecylbenzenesulfonate-exchanged HDS contained no interlayer water. Above 400°C a mixture of

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Progress in Ion Exchange: Advances and Applications

Cu20 and CuOSO; was obtained. Copper(1) oxide was then completely transformed into copper(I1) oxide above 500°C. Above 600°C occured the decomposition of the oxysulfate in CuO. In the Cu:(OH)2(RCOO).nH2O series, water molecules were intercalated between the OH)?’ layers in caprylate- and caprate-exchanged HDS, with one copper hydroxide CUZ( molecule of water for two unit cells. The mass loss occurred around 150°C suggesting that the No water molecules interact strongly in the interlayer region as in CU~(OH)~(CH~COO).H~O.~ molecules of water were present in the structure of the benzoate and the sebacate HDS which means the packing of the interlayer anions does not allow the intercalation of molecules of water. A mixture of copper(l1) and copper(1) oxides was obtained in the range of 250-340°C as deduced from the XRD patterns. This mixture was due to the oxido-reduction reaction between copper(l1) and the carboxylate group.2u

X-Ray Powder Diffractioo Results The X-ray powder diffraction patterns of the HDS are typical of layered compounds (Figure 2). The peaks move according to the size of the intercalated anion which modifies the interlayer space. In the case of the sulfate-exchanged H D S , the compound was coincident with that of brochantite, CU,(OH)G(SO,).with a c dimension of 6.03 A.?’ The diffraction pattern of Cu2(0H);CI suggested a botallackite-type structure as reported by H.R. Oswald et a/. with a c dimension of 5.72 A.‘ The c dimensions of alkyl-anion exchanged H D S are reported in Figure 3 together with the length of the anion. Comparing the sebacate (dicarboxylate in CS) basic copper salt with the caprylate basic copper salt (C,), a difference of 10 A between their interlayer distances was observed even though the numbers of carbon atoms are close. A large interlayer space is also observed in the dodecylsulfate basic copper salt with 27.1 A. These observations enable us to propose a double layered structure for the HDS with long alkyl chain anions as suggested by Lagaly el LII for similar compounds.2 The crystal structure of this double layer structure has been studied in copper(I1) dodecylsulfate tetrahydrate with a c dimension of 25.1 A.22 The layers containing the copper atoms are very similar in CU~(OH)~(CL~H~~OSO:) and C U ( C ~ ~ H ~ ~ O S OThe ~ ) ~layer ~H~ formed O . by the copper atoms bridged by hydroxide anions is comparable to the layer formed by the [Cu.4H20] units bridged by hydrogen bonds. In both structures the dodecylsulfate chains are organized in a double layered structure with a comparable space around the chains of 36A2 (plane xy). The c dimensions observed in the copper HDS form and in the copper(I1) complex form of the caprylate anion are also similar with 24.4 and 22.0 A respectively. Caprate- and dodecylsulfate-exchanged HDS have a similar interlayer space although the number of the carbons in the alkyl chain is very different (7 and 12 respectively). This similarity is explained by the fact that alkylcarboxylate chains are standing more perpendicular between the layers of the [CUZ(OH)Z]+ units than the dodecylsulfate chains. In the case of the benzoate HDS, it seems that the aryl groups form also a bilayer, the interlayer distance being twice as large as the anion length. It is important to note that. in the case of interlayer long-chain alkyl anion, the gallery height may vary slightly owing to modifications in the chain packing.”

407

Ion Exchange in Inorganic Materials and its Theory

L 6.39 A

0

10

0

20

10

20

30

30

40

50

20

20

0

60

20

10

40

30

SO

60

0

20

40

50

0

60

10

20

30

20

40

50

60

10

0

10

20

20

30

30

40

50

60

20

28

40

50

60

Figure 2. X-ray powder diffraction patterns of Copper HDS with different interlayer anions. (+) Copper nitrate HDS phase remaining after anion exchange.

50

(C 12H25C6H4S03)

5

40

8

3 v)

30

--

(C9HlYC02) --

(C7H15C02)

5 .I

-5k 20 c

--

(C6H5C02)

10 --

(C12H250S03) (02C-C4H8-C02)

(CH3C02)

08 0

10

Anion length / A

15

20

Figure 3. c dimensions of copper HDS with different interlayer organic anions related to the appropriate anion length (calculated distance using the most separated atoms).

Progress in Ion Exchange: Advances and Applications

408 Nitrogen adsorptioii isotherms results

The samples exhibit type4 isotherms and the surface areas range from 2 to 57 m2 g-' as shown in Table 2. The surface area decreases for the series nitrate, sulfate and chloride. This observation suggests that the packing of the anions in the interlayer region increases within this series. Only alkylmonocarboxylates-, dodecylsulfate- and dodecylbenzenesulfonate-exchangedHDS showed a type-I1 isotherm with a type-H3 desorption hysteresis according to the KJPAC ~lassification.~~ The volumes of mesopores were in the range of 36 to 55 pL g'. The presence of porosity in these samples can be related to the double layered structure of the alkyl chains discussed in the previous paragraph. Since there is no interdigitation between the alkyl chains of two adjacent layers, as in the structure of copper (II) dodecylsulfate tetrah~drate,'~ pores may be present in the structure.

Table 2 Surface area data oft he copper HDS compounds for different interlayer anions Interla! er :man

SHbd Ill2 I:

c1-

c6Hscoo-

NO?

2 4 7 IX

(-C4HIlCo0')2 C-HisCW

31 22

S04?'

c9H19co0-

Ci:H:
'

10

4 17

H! steresis type2 No No No No No H3 H3 H3 H3

Pores Volume / p~ g-'

50 36 Y

55

Reversibility of the illlion excliaiige The reversibility to nitrate exchange was examined in the case of chloride, sulfate, dodecylsulfate, acetate, benzoate and caprylate HDS. Table 3 gives the powder diffraction data of the samples Cu2(0H)>X after their immersion in a solution of sodium nitrate. The compositions deduced from the thermal analyses are shown in Table 1. For the acetate HDS, the exchange with the nitrates was complete as Yamanaka e/ a/.suggested;' a small quantity of copper oxide could be observed in the compound. The chloride anions were partly replaced by the nitrate anions (see Table I), this result is different from the irreversibility of the exchange back to acetate anions.' The sulfate interlayer anions were not replaced by the nitrate anions which suggests that they are strongly bonded in the structure as expected from a divalent anion. In the rest of the organic anion-exchanged HDS, three phases could be observed in the diffraction patterns: Cu2(0H),(X); C U ~ ( O H ) ~ Nand O ~CuO. The presence of copper oxide in the samples could be explained by the removal of weakly bound anions on the external surface.8The examination of the thermal analyses (Table I ) showed that only a very small quantity of the interlayer anions has been exchanged with the nitrate ions. An explanation of these results could be the effect of steric hindrance. When these large anions begin to be replaced by the nitrates at the surface of the sample, the interlayer space is considerably reduced which could prevent the remaining bulky anions from going out of the structure. Another explanation would be that the

409

ton Exchange in Inorganic Materials and its Theory

hydrogen bond network is too different in the two structures to allow the nitrate anions to replace the large organic anions. The above results suggest that only ions of Similar Sizes can be exchanged, probably owing to the rigidity of the HDS. Therefore, owing to the Similaritybetween the interlayer space of the captylate and the dodecylsulfate HDS (24.4 and 27.1 A respectively), the rwersibility between these two forms was examined. XRD (Figure 4) and thermal analyses (Table 1) showed that in each case,the anions were readily exchanged. The exchange of the dodecylsulfite ion by the caprylate ion was complete but not for the opposite exchange. In this case,two different interlayer distances were observed in the deaction pattern related to the presence of both caprylate and dodeqlsulfate ions in the interlayer spaces. The peaks are broader which means a dispersion of the interlayer distances, this may be explained by different packing of the mixed interlayer anions. Table 3. X-ray powder data for chloride, sulfate, acetate, benzoate, caprylate and dodecylsulfate copper H D S exchanged with nitrate. Initial interlayer anion Chloride Sulfate Acetate Benzoate Caprylate Dodecylsulf. d/A I dlA 1 dIA I dIA I d/A I d/A I 6.90(a) 81 6.38 71 6.92 (a) 100 14.81 100 24.33 100 34.2 100 5.70 100 5.35 80 7.01 21 12.08 17 8.42 7 3.45 (a) 30 3.89 99 3.46(a) 43 8.03 9 58 6.93 (a) 46 6.92 (c) 27 6.73 (a) 4 2.85 9 3.19 2.69 9 2.92 17 3.46(a) 23 3.45 (c) 10 2.67 (a) 20 2.68 73 2.67 (a) 3 2.67 (a) 9 2.67 (c) 6 16 2.46 (a) 7 2.46(c) 5 2.58 21 2.60 2.46(a) 19 2.52 100 2.46(a) 5 2.53 (b) 4 2.52 (b) 2 14 2.53 (b) 6 2.32 (b) 6 2.32(b) 3 2.41 30 2.38 2.07 I I 2.32 (b) 5 2.32 (b) 5 (a) for Cu2(OH),NOj phase: (b) for CuO phase: (c) nitrate HDS impurity in the starting material.

0

10

20

30

40

28

50

60

0

10

20

30

20

40

50

60

Figure 4. X-ray powder digraction patterns of (a) dodecylsulfate- and (b) caprylate-exchanged HDS in which the interlayer anion has been exchanged with caprylate and dodecylsulfate ions respectively. (+) CU?(OH)~(C~HISCO~)* 1I2H20; ( 0 ) C U ~ ( O H ) ~ ( C I ~ H ~ ~ O S O ~ ) .

Progress in Ion Exchange: Advances and Applications

410

Selectivity of the anion exc1i:inge with :ilhyl-containing anions In order to examine the selectivity of alkyl-containing anions by Cu2(OI-Q3NO3,three solutions were prepared by mixing equal volumes of two of the anion sodium salt solutions (0.1M).The resulting compounds are shown in Table 4. The nitrate HDS phase is present in a very small quantity in each product although it is clearly visible on the X-ray difitaction patterns in Figure 5 . Thermal decomposition between 100 and 200°C showed that interlayer water molecules are present in the three exchanged HDS. The results showed that the selectivity increases in the series DS-SEBCPL. In the case of the mixture CPL/SEB, the thermal decomposition of the product showed a mass loss much bigger (69.2%) than the one expected in the case of complete exchange with CPL i.e. (51 8%). This result probably indicates that some sebacate anions may be present in the interlayer space with one of its carboxylate functional groups free that is not coordinated to a copper ion. This situation may lead to the intercalation of alkylcarboxylate salts in the interlayer space. Table 4. Cu2(0H)~(N03) exchanged with a mixture of organic anions. CPL=caprylate; DS=dodecylsulfate; SEB=sebacate. X-ray data of C U ~ ( O H ) ~ ( Nhave O ~ ) been omitted. X-ray data I A

Product YOwater YOCuO CPLlDS C U ~ ( O H(CPL)hI(DS),;xH20 )~ 2.2 47.7 DS/SEB Cuz(0H)~(DS),,(SEB)u%HzO 30 54.1 CPUSEB &(OH); (SEB),(CPL)UXH~O 1 . j 30.8 M = major. m = minor

Anion mixture

28. I*, 14.0** 28.9*, 24.2*, 15.6*, 12.4** 24. I*, 12.0**

*=(OOl). **=(002)

i'.

100

0

0

10

20

30

ze

40

50

60

0

10

20

30

40

10

50

60

0

10

20

40

30

50

60

20

Fig. 5 . X-ray diffraction patterns of Cu2(OH);(N03) after anion exchange with a mixture of alkyl-containing anions. Mixture: (a)CPL/DS; (b)DS/SEB; (c)CPL/SEB. (+)=CUZ(OH)~(NO~). CONCLUSIONS The copper nitrate hydroxy double salt readily exchanges its interlayer anions with inorganic and organic anions. Alkyl- and aiyl-containing monoanions are arranged in bilayers between

Ion Exchange in Inorganic Materials and its Theory

41 1

the positively charsed copper hydroxy layers. Mesopores are present in the long alkyl chain anion-exchanged HDS. In the case of bulky anion-exchanged H D S such as caprylate- or dodecylsulfate-exchanged HDS, the process is nearly irreversible to nitrate, because the large difference of size between the t w o anions prevents a complete exchange. This limitation of exchange is not the case when the anions are of a similar size, as for the exchange between caprylate and dodecylsulfiite ion The exchangeability towards alkyl-containing anions is Rmonocarboxylate>R-dicnrbox),late>R-sulfate. Intercalating R-monocarboxylate and Rdicarboxylate anions encourages the extraction of R-carboxylate salts.

Acknowledgment

W e gratefully acknowledge the financial support of the EU with respect t o a postdoctorate tbr

C.S.B. in connection with the Brite Euram (grant BRE2.CT92.01.98). REFERENCES 1

2 3 4 5 6 7 8 9 10

II 12 13 14 I5 16 17 18 19 20 21 22 23 24

W. Feitknecht and K. hlaget. He/\>.('hem. Ada. 1949,32(5),1653 M. Mqn, K.k k e and G . Lagal!. fnorg. Chem., 1993.32, 1209. N.Guillou. M.Louer and D. Louer. J. .So/idS/are Chem., 1994,109.307. H.R. O s n d d and W. Feitknecht. Hdv. ('hem. Acfa, 1964,47,272. S.Yamanaka T. Sako. K. Seh and M.Hnttori, C'hem. Left., 1989. 1869. H. TanakaandN. K o p , J. Chna. Ed. 1990,67(7),612. S.Ymanaka, T. Sako. K. Seki aid M. Hattori, .%/id State Zonic.s, 1992,5346:527. A. Jimenez-Lopez. E. Rdiguer-C3steIlon. P. Oliven-Pastor, P.Maueles-Tom, A.A.G. Tomlinson. D.J. Jones Yul J. Rozi6re.J Mar. Chem., 1993,3(3), 303. M.Atanasov. N.Zotov. C. Fri&l. K. Petrov and D. Reinen,J S l i d State Chem.. 1994,108,37. S. Yanumka. Zeolires andMicropclroia Cry.s/al.s,Ed. Kodansha Ltd. 1994. R.J. Candal. A.E. Regazzoni and M.A. Blesa. J. Muter. Chem.. 1992,2(6).657. A. Riou. K. Rochdi. Y. cud em^. Y. GLmult and A. Lecerf, Europ. 1 SOlidSrare Inorg. Chem, 1993, 30,1143. W.Nowvacki aid R. Sheidegger,Acfa Cryst.. 1950.3,472.Exprrientia, 195I, 7,454. H.Effenberger. Z. Krisrdlogr., 1983. 165. 127. W.Feitknecht, A. Kummer and J.W. Feitknecht. C'ongr. Inf. de Chim. Pure et Appliq.,1957,243. B. Bovio and S. Locchi. J C'qsr. Spec/ro.sc. Research, 1982,12,507. M. Schmidt, H.Mwllcr and H.D. Lutz. Z. Anorg. Allgem. Chem., 1993.619,1287. H.Hayashi and M.J. Hudson. J.Mm.Chem.. 1995,5(5),781. C.S. Bruschiiii and M.J. Hudson. to be published in Accefs In Nanoporoits Materials, FtindmnenfaiMureriiif Hcscarch Series, 2 . R.A. Sheldon and J.K. Kochi. Mefal-(iifoljred0xydation.s of Organic Compounds, Academic Press, 1981,p. 140. File ASTM 13-398. C.S. Bruschini. M.G.B. Drew. M.J. Hudson and K. Lyssenko, Polyhedron, accepted. R.A. Vaia, R.K. Teukolsky and E.P. Gimelis, Chenz. Mafer., 1994,6,1017. K.S.W. Sing. D.H. Everett. R.A.W. Haul. L. Moscou. R.A. Pierotti, J. Rouquerol and T.Siemienieswska. Pirre Appl. Chem. 1985.57. 603.

The Extraction of the Hexamminecobalt(II1) Cation by

Kanemite

(NaH[Si20~(0&].2H20): Enhanced Extraction in the Presence of a Cationic Surfactant Matthew T. J. Keene, James A. Knowles and Michael J. Hudson”. Department of Chemistty, Universiw of Reading? IVhileknights, P.O.Box 224, Reading, Berksltire. OK, RG6 2AD.

Introduction

It has been reported previously that inorganic ion exchangers with layered structures, such as aZr(I-lP0~)z.HzO’(aZrP) and aSn(HPO4)2.HzO2(aSnP), cannot directly intercalate metal complex cations such as hexamminecobalt(III) ([co(NH3)6I3+) and hexammineruthenium(III) ([Ru(NH&]~’). In a previous study we have shown that aSnP is able to intercalate [Ru(NH&]” by a self-catalysed intercalation mechanism involving labile ammonia Ligands tiom the Ru(II) complex whereas the unreactive complex ruthenium(III) cation is not so intercalated.’ For aZrP to extract [cO(NH3)6l3+and to overcome the effects of stenc hindrance attributable to the high charge density;’ heating4 or the addition of a catalyst’ is needed. Previously,6 we have shown that kanemite, which is formulated as NaH[Siz04(OH)2].2H207,is able to extract metal cations from basic aqueous solutions but the extent of the extraction is reduced at low pH. Whereas aZrP and aSnP have rather inflexible layered structures, kanemite consists of s i d e flexible layers of SiO4

tetrahedra (the interlayer spacing being 10.23 A) and has a theoretical exchange capacity of 4.67 mmol g-’ for a monovalent ion’. Lagaly and Benekeg showed that the sodium ions between the

layers are easily exchangeable by large organic cations giving an innercrystalline reactivity. There have been no previous reports that kanemite is able to extract complex cations. In order to investigate the ion exchange properties of kanemite, to a complex metal cation, the model cation, hexamminecobalt(II1) was used. This cation is approximately spherical with a diameter of ca. 7 6 The use of the metal-ammine complex is suitable, since the ammonia molecule is small and can be easily removed by heating.” The resulting silicate loaded with the transition metal ion, cobalt, could be promising as a catalyst. (It has been shown that a method of reducing the

Ion Exchange in Inorganic Materials and its Theory

413

activation energy of ion exchange is to add a little amount of a small cation such as NaT.'z'3) Additions of a small amount of the quaternary ammonium salt, hexadecyltrimethylammonium chloride or cetyltrimethylammonium chloride (CMA)were used in order to ascertain whether the extraction of the complex metal cation could be e n h a n d by a catalytic process in which the monovalent CMA cation facilitated the separation of the layers to allow the intercalation of the polyvalent complex cation. To establish that the hexamminedalt(rII) cation had been exchanged by the kanemite and to determine if the cobalt ions in the hexamminecobalt(III) loaded material could be eluted fiom between the layers, the loaded material was treated with solutions of HCI and NaCi, all solutions being of constant ionic strength. It was anticipated that the flexible nature of the kanemite layers may have an important role to play with respect to the ion exchange properties.

Results and Discussion Ion Exchange Eqmitnents The extraction of the hexamminecobalt(III) cation from an aqueous solution (2.8 x lo" mol dm-3), as a fhction of time is shown in fig 1. Line A shows that kanemite can extract hexamminecobah(II1) cations directly h m aqueous solution and at ambient temperatures. The time for half of the equilibrium amount to be extracted was ca 11 min. Equilibrium was reached after 450 min when the uptake was 0.18 mmol Co g-' dry kanemite (1 1.6% of the CEC for a trivalent

ion). As indicated earlier, other layered compounds, like CrZrP, have been shown to need either the addition of a catalyst5 or an increase from ambient temperatures in order to be able to extract the complex metal cation hexammine~obalt(III).~ Once the kanemite had been allowed to extract the hexamminecobalt(III) cation for the required amount of time, a small aliquot of the supemate was removed fbr analysis. To the solution chloride (0.5 an3,7.6

x lo"

WBS

immediitely added hexadecyltrimethylammonium

mol dm'3) and the extraction was allowed to proceed for a Wer

period of t i e . The addition of the CMA can be seen in line B to enhance the overall uptake of the cobalt species by kanemite. After 500 min the uptake had reached about 0.20 mmol Co g' kanemite (12 8% of CEC of kanemite), but then the rate of uptake slowed considerably although the kanemite still continued to extract the cobalt species. Clearly the CMA enhances the overall extraction of the cobalt. However, the extraction rate was found to be enhanced krther by the

414

Progress in Ion Exchange: Advances and Applications

presence of the CMA at the onset of the extraction. Figure 1 line C shows that the extraction had reached equilibrium after 500 min when an uptake of 0.22 mmol Co g-' kanemite (14.1% of CEC ofkanemite) had been reached. However, the kanemite still extracted hexamminecobalt(III) slowly, finally reaching a maximum after about 1400 min for a total uptake of 0.26 mmol Co g-' kanernite

(16.7% of the CEC). After 2000 min the extraction decreased slightly, either because hydrolysis is breaking the kanemite down and releasing the cobalt back into the solution or the extracted cobalt species is being replaced by the CMA cation. It can be seen by comparison of lines A and C, that the addition of the CMA enhances the rate and capacity of the uptake of the cobalt species relative to the solution with no CMA present. Comparison of the initial sections of lines B and C shows that the intermittent addition of CMA leads to the greatest rate of extradon of hexamminecobalt@I) in the first hour, with the overall extraction being enhanced fiom 0.18 mmol Co g-' h e m i t e (12.8%

of CEC of kanemite) for the extraction without the use of CMACl (line A) to 0.26 mmol Co g-' kanernite (16.7% of CEC of kanemite) with the addition of CMACl to the solution at the onset of the extraction (line C). As will be discussed later, the slight enhancement in the extraction could be the result of the alkyl chains of the cetyltrimethylammonium penetrating the layers of the kanemlte. Once the concentration of CMACl increases above a certain level, the alkyl chains are believed to reorientate within the layers so that they become inclined to the layers, thereby increasing the intdayer spacing"

Figure 1

Extraction of Hexamminecobalt(II1) by Kanemite Showing the Influence of CMA

-

0.25

1.

) 1IS % of CEC

-

0.20

3% of CM:

0.1s

0.10

-8- CMA ADDED AT ONSET -BNOQUAT

h ec Line A

+QUAIADDED

Line B

5% of CEC

Ion Exchange in Inorganic Materials and its Theory

415

EIution The elution of the cobalt fiom the kanemite loaded with the hexamminecobalt(m)cation with and without the Ch4A is shown in figure 2. The ionic strength of the solutions was kept consmt throughout. It can be seen that solutions containing only NaCl or HCI can be used to elute 10?/0

and 25% of the cobah species present respectively Erom the loaded kanemite. There was little or no

elution when the ratio of HCVNaCl was between 0.2 and 0.4 suggesting that the cobalt species are strongly bound betweenthe layers of the kanemite. The presence of the CMA cation is seen to have little effect on the amount of cobalt released back into the aqueous phase. The greatestelution, as in the case when no CMA was present, was obtained when the solution only contains HCI.The highest rdease of 0.045 mmol Co 8' was fiom ma!erial that had originally been loaded to 0.239 mmd Co g-' of kanemite. Therefore, by increasing the acid concentration relative to the concentration of NaCl above 0.4 HCVNaCl in solution it can be seen that the dalt(m) ions are increasinglyeluted into the aqueous phase. Figure 2

Elution of Hexamminecobalt(II1)fiom Partially Loaded Kanemite as a Function of the HClMaCl Concentration 0.05 J -

0

0.2

0.4

0.6

[HCI] 1 Wac11 ratio

0.8

1

416

Progress in Ion Exchange: Advances and Applications

X-ray Poivrler Dflraction Charactehation X-ray powder diffraction patterns (XRD) of the hlly loaded kanemite, Fig. 3(b), has much fewer

peaks than that of the synthetic kanemite, Fig. 3(a), suggesting that the extraction is non-topotactic. There is also a sharp reduction in the intensity of the peaks suggesting that the loaded hemite is more amorphous. Comparison of the powder patterns of the kanemite partidy loaded with heXamminocobalt(III) in the absence, Fig. 3(c), and the presence of CMA, Fig. 3(d) gives some

indication that CMA assists in the ordering of the kanemite as evidenced by the retention of the intensities of the [020/ and 10401 peaks. Figure 3a

24000'

"

'

The XRD Pattern of Kanemite ' ' I ' ' ' " ' I '

'

I ' 111

I

'

I J

19000

-

14000

-

9000

-

220

040

4000

0

20

40

60 2 8

80

100

Ion Exchange in Inorganic Materials and its Theory

417

Figure 3b

The XRD Pattern of Fully Exchanged Kanemite

0

20

60

40

80

100

2 8

1 1

2750.0 7 2250.0

200

-

Progress in Ion Exchange: Advances and Applications

418

Figure 3d The XRD Pattern of Kanemite Partially Loaded with Hexamminecobalt(1II)in the Presence of CMA

0

20

60

40

80

100

2 8

Mechanism of Enhanced &&action

At the low concentrations used it is probable that the alkyl chain of the quaternary ammonium salt

lies parallel to the layers (fig. 4).IJ The hydrophobic cation of the quaternary ammonium salt interacts with the hydroxyl anion to reduce the interlayer forces particularly at the edges of the

layers. The reduction of the interlayer forces enables the hexamminecobalt(III) cation to exchange the Na' cations of kanemite. The hexamminembalt(III) cations are subsequently able to diffirse through the layers. In this way the hexammineobaltQII) cations are able to penetrate deeper into

the layers, thereby providing a higher exchange capacity for the kanemite than for the surface and edge exchange

Ion Exchange in Inorganic Materials and its Theory

F b e 4a Schematic Viw of the Wraction ofHexanrmnrecob *ah@I) cation by Kanemite

10.16 A

F&e 4b Schematic View of the Enhanced Edraction of Hexarmninecobah@I) by Kanemite m the Presence ofCh4A

I

T 10.25 A

OH’

Figre 4c Interlayer View of the Enhanced Extraction of HexamminecObak(III) by Kanemite in the Presence ofCMA

Key:

Hexadecylbimethylmnm~ni~~~~ chloride chain

0 Hexamminecobalt0 chloride

419

Progress in Ion Exchange: Advances and Applications

420

Conclusions Kanemite, unlike other inorganic layered materials, can extract the complex metal(III) cation, hexamminecobalt(1II) directly fiom aqueous solution. The process of extraction seems to involve the intercalation at the edges of the flexible silicate layers, followed by the absorption of the complex metal ions into the kanemite. The resulting material might prove usehi, once the ammonia is calcined out for catalytic reactions.The enhanced extraction in the presence of CMA could be a result of the alkyl chains lying parallel to the kanemite layers, across the hydroxyl anions,thereby reducing the effective interlayer forces. This is thought to allow the hexamminecob&@I) cations to penetrate deeper into the layers in order to interact with fiee hydroxyl anions. This process increases the exchange capacity of kanemite above the surface and edge exchange that occurs in the absence of the quaternary ammonium salt.

References 1. A. Clearfield, G. H. Nancollas and R. H. Blessing, in "Ion Exchange and Solvent Extraction", J. A. Marinsky and Y.Marcus, a s . , Marcel Dekker, New York, Vol. 5, ( 1 973), Ch. 1. A. Workman, PhD Thesis University of Reading 1992 2. 3. Y. Hasegawa and S. I(lzalu, Chem. Sot. Jpn. ChemistiyLetters, ( 1980), 24 1-244 4. Y. Hasegawa, S.Kizaki and H Amekura, Bull. Chem. Soc. Jpn, 56, (1983), 734-737 A. Clearfield and R. M. Tindwa, Imq. Nucl. Chem. Letters, 15, (1979), 251-254 5. D. J. Apperley, M. J. Hudson, M. T. J. Keene and J. A. Knowles, J. Muter. C'hem. 5(4), 6. 7. 8. 9. 10. 11. 12.

13. 14. 15.

(1999, 577-582 M. T. Le Bihan, A. Kalt and R. Wey, Bull. Chem. Soc.Jpn, 95, (1972), 371-382 S.Ingaki, Y. Fukushima and K. Kuroda, . I Chem. h. Chem. Comm., (1993), 680-682 G. Lagaly, K. Beneke and A. Weiss, AmericanMineruIogist, 60, (1979,642-649 Y. Hasegawa and G. Yamamine, Bull. Chem. Soc.Jpn., 56, (1983), 3765-3768 M. Iwata and Y.Saito, Acrcl Crystallog.,Sect B, 29, (1973), 822 G. Alberti and U. Costantino, in "Inclusion Compounds Volume 5 Inorganic and Physical Aspects of Inclusion", J. L. Atwood, J. E. D. Davies and D. D. MacNicol, W o r d University Press, New York, (1991), Ch. 5. M. Abe, Denki Kugaku, 48, (1980), 344 F. G. Lagaly, K. Beneke and A. Weiss, Am. Miner., 60, (1973,642-649 U. Costantino, Intercalation Behavior of Group IV Layered Phosphates in "Inorganic Ion Exchange Materials", A. Clearfield, CRC Press, Florida, (1 982)

UPTAKE OF RIIO BY r-zIRcoNIuM PHOSPHATE AND INTERCALATION COMPOUNDS WlTH HETEROCYCLICBASES.

ITS

C. Ferragina, P.Cafarelli and R. Di R o w

-

1.M.A.I .- CNR via Salaria Km 29.300 Monterotondo (Rome) ITALY.

ABSTRACT Rh3+/H+ion-exchangeon y-zirconium phosphate and on its intercalation cornpounds with organic diamine (2,2'-bipyridyl, 1,lO-phenanthroline and 2,9-dimethyl-l, 10phenanthroline) has been investigated. Fully exchanged Rh3++zirconium phosphate has composition y - Z r ( P 0 4 ~ . ~ . ~ ~ P O 4 ) . 2 . 3 and H 2 0interlayer distance 15.2A. The exchange of Rh3+ on intercalation compounds leads to phases in which the molar ratio Rh 3+/diamine within the layers is about one. In some cases a partial leaching of organic ligand during the Rh3+/H+exchange has been observed. All the materials produced were characterised for their chemical composition, X-ray powder diftiaction patterns and coupled TGDTA analysis. In the presence of Rh3+ ion, the temperature of thermal d a intercalation of diamine is lower than that observed in the pure intercalation compounds. 1 INTRODUCTION In recent years layered acid phosphates of tetravalent metals (Zr, Ti, Sn) have been a subject of many investigation for their peculiar abiity both to exchange transition metal ions (t.rn.i.)lJ and to intercalate organic ligands with basic centre$. These latter intercalation compounds may exchange t.m.i. that are co-ordinated by the ligands giving rise to "in-situ" formed complexed~5~6.This phenomenon provides an alternative route to heterogenise, on an inorganic support, complexes ofien used in homogeneous catalysis. This research group has already studied compounds obtained by Rh3+/H+ionexchange on a-zirconium phosphate (a-Zr(HPO4)2-H2O. a-ZrP) as such or previously intercalated with heterocyclic diamines (2,2'-bipyridyl (bipy), 1,lO-phenanthroline@hen) and 2,9-dimethyl-l,lO-phenanthroline(dmp)), and these compounds have been tested in the heterogeneous catalysis7. In continuing the work, this paper describes the preparation, and the chemical and thermal characterization of compounds obtained after ion exchange of Rh3+ on y-zirconium phosphate (y-Zr(P04)(H,PO4).2H20, y-ZrP) and on its intercalation compounds with the above mentioned heterocyclic diaminess. It is now well established that the y-ZrP has a crystal structure9J0 different &om that of the a-phase, and the different disposition of the 02P(OH)2 groups in the interlayer region could induce a different orientation of the ligands and different ability to form "insitu" complexes.

422

Progress in ion Exchange: Advances and Applications

2 EXPERlMENTAL

2.1 Chemicals. Rhodium(III) nitrate, bipy, phen and dmp were Fluka purissi. p.a. All other chemicals were of the highest purity available commercially and were used as received. 2.2 Materials. The compound y-ZrP was prepared, characterised and stored as described in the literaturell. The pre-swelled ethanolic form of y-ZrP (y-ZrPEtOH) was flesh prepared before each reaction. The intercalation compounds y-Zr(PO4)(H2PO4) biPYo.26'1.64H2o(*I-zrpbiPYo.26), ~-Z~(PO~)(H,PO~>~~~YO.~.O. 3H20( y-ZrPbipyo.44), r-zr(Po4>~2p04>phet.~2.04H20(y-2rPphen0.44), ~-zr(Po4)(H,p04)dmP0.26 ,73 H20(y-ZrPdmp0.26) and y-Zr(P04)(H2P04)dmp,,,44.2.98H20(y-ZrPdmp~.44)were prepared as previously describedl2. The compounds obtained 2.3 Physical Measuremenis and Chemical Analysis. were characterised by X-ray difiactometry by using a Philips dfiactometer (Ni-filtered Cuka radiation), 28 angles are estimated to be accurate to 0.05'. The amine and the water contents and the thermal behaviour of various materials were determined by simultaneous apparatus TGDTA Stanton Model 750 Redcroft (ignition up to 1l0O'C to reach a constant weight, in an air flow), heating rate10'Wmin. Rh3+ uptake was monitored by following concentration changes in the supernatant solutions before and after contact with the exchanger. The measurements were carried out on a G.B.C.903 apparatus atomic adsorption. The rhodium uptake, either by y-ZrP or y-ZrP2.4 Rh3+ Exchange Procedure. diamine intercalation compounds, was carried out by the batch procedure. The suspensions were thermostated at 45'C for different set times. The solids were then filtered off and washed with distilled water. The supernatant solutions were analysed for their Rh3+ content and for their pH value. 3 RESULTS AND DISCUSSIONS 3.1 Uptake of Rh3+ by y-ZrPEtOH.

The experiments were carried out by equilibrating the y-ZrP phase previously preswelled with EtOH (h2=16.6A) with increasing volumes of Rh(N03)3 solutions 3.10-3 mol dm-3 in order to obtain compounds with different rhodium content. We did not obtain a filly exchanged compound even by increasing the volume of the contact solution so as to have 150% of theoretic exchange or by prolonging the time of contact between the exchanger and the rhodium solution (two weeks). The compound with maximum rhodium content has a composition of y-Zr(P04)&,86%,38P04).2.3H20(y-ZrPRh()38) and interlayer distance &2= 15.22Agreater than that showed by y-ZrP (&2=12.26&). AU the obtained materials are yellow coloured, and from X-ray difiaction patterns, we observe that there is one y-ZrP-rhodium-phase present if the rhodium uptake is 2 0.2moVmol y-ZrPEtOH. Below this rhodium content value there are two phases present (&2= 12.26Aand d0,-,2,15.22A), the former referring to the starting material (not in the ethanolic phase which quickly loses EtOH in the air and turns back in y-ZrP) and the latter referring to the y-ZrP-rhodium phase. If the rhodium content is less than 0.2moI/mol exchanger, only the y-ZrP phase is present. We also used as starting material

Ion Exchange in Inorganic Materials and its Theory

423

exchanger not pre-swelled and we obtained materials with the same rhodium content obtained starting fiom the ethanolic phase, but X-ray dfiaction patterns indicated always two phases even ifthe rhodium content was >0.2moVmol exchanger. 3.2 Uptake of Rh3+ by y-ZrPphen0.a and y-ZrPdmp0.U The intercalated materials y-ZrPpherb4 and y-ZrPdmpo.a behave in the same way when they exchange rhodium ions, the uptake value differsvery little (see Tablel). The experiments were performed in batch, at 45OC to improve the exchange, and for several set times, by utilising a molar ratio[intercalated diamine]:Rh3+=l:l so as to obtain complex species in the exchanger with equal molar composition. Figure 1 shows the percentage of the moles of rhodium exchanged with respect to those of the exchanger considered according to contact time. Table 1 reports the chemical composition of obtained materials with their interlayer distance &2. For y-ZrPpheQ.44 it has been observed that after 24 hours of batch contact, there is maximum uptake and, even with prolonged times, the exchange does not increase markedly. During the process of the rhodium uptake we note the partial elution of the phen, which could be the result of a competition between the diamine and the incoming Rh3+ ions towards the interlayer region. The elution increases with the increase in rhodium uptake. From the X-ray difE-action patterns it is evident that, whatever the rhodium uptake, the patterns of the various materials obtained are similar to that of the starting y-ZrPphq.44. There is only a small reduction of h2 of y-ZrPphen-Rh (18.78A) compared to y-ZrPphq.44 (19.19A) and the increasing elution of diamine, with rhodium uptake, causes a decrease in the intensity of the reflections of these phases in the dfiaction patterns. For the materials obtained fiom y-ZrPdmp0.M we have results similar to those obtained with y-ZrPphq.a: the maximum uptake is obtained practically after 24 hours of batch contact, but there is a more enhanced elution of diamine. The X-ray diffraction patterns show a decrease of &2 value compared to that observed for the precursor. This decrease is more evident than that observed in the case of phen (17.31A vs. 19.62A). The rhodium uptake and the possible co-ordination to the dmp does not occur simultaneously for some materials. In fact the X-ray dfiaction patterns of the wet materials, immediately after filtering, obtained at set times of 0.5 and 1, 3, 6 hours of batch contact, show either one phase of 19.62A (similar to that of the precursor y-ZrPdmp) or two phases: one of 19.62A (Similar to the precursor ) and one of 17.31A (relative to the y-ZrPdmp-Rh phase) respectively. The same materials, left in the air for two weeks, show only the y-ZrPdmp-Rh phase. When the experiments are performed for longer times, we immediately obtain the dmp-rhodium phase if the rhodium content in the material is more than O.15moles of ~h3+/moieexchanger. We could ascribe this behaviour to the larger steric hindrance of dmp. 3.3 Uptake of Rh3+by y-ZrPdmpga26,y-ZrPbipyo.z6 and y-ZrPbipy0.m

Figure 2 shows the rhodium uptake by y-ZrPdrnp0.~6and y-ZrPbipy0.26 as a finction of time. For the two intercalation compounds, the uptake speed is very similar, but it takes more batch contact time between the rhodium solution and the solid exchanger to

Progress in Ion Exchange: Advances and Applications

424 50

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Ion Exchange in Inorganic Materials and its Theory 20

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Table 2 Chemical composition and interlayer distance of the obtained compounds

426

Progress in Ion Exchange: Advances and Applications

reach to maximum of rhodium exchange (one week): either the lower content of the ligand (in the case of dmp 0.26moles/mole exchanger, vs. 0.44moles/mole exchanger ) or the lower interlayer distance of the precursor (h2=16.661( vs. &2=19.62A) seem to hinder the ion exchange. None of the obtained materials shows a marked diamine elution, perhaps because the rhodium content does not "disturb" the less crowded materials. The X-ray dfiaction patterns of the materials are practically identical to those of the precur9or5. In Figure 2 the uptake value of rhodium by y - Z r P b i p ~is~also . ~ ~reported. As it can be seen, this intercalated material exchanges less rhodium compared to the other intercalation compounds and even less than that found for y-ZrPbipy0.26 which has a lower content of bipy. A similar behaviour has been observed in the a-zirconium phosphate-bipy, the ion rhodium uptake was less in comparison with that observed with the other diamines intercalated in the exchanger'. So we can suppose that the different behaviour of y - Z r P b i p ~ and ~ . ~ y-ZrPbipy~,~~ ~ regarding the rhodium uptake can be attributed to the different interlayer distance (h2=14.251( vs. &2=15.221( respectively) and to the different structural arrangement of bipy between the layers of the exchangers. 4 T H E W BEHAVIOUR

The thermal behaviour of the materials containing rhodium is very similar to each other, the decrease in temperature of the ligand decomposition being the common result. Figures 3 and 4 show the simultaneous TG/DTA curves of rhodium phases derived from y-ZrPdmpoM, y-ZrPphen0.44 and y-ZrPdm~~.~6, y-ZrPbipyo.26 (all materials with maximum rhodium content ) in comparison with those of the precursors. The DTA curve of y-ZrPdmpO.qq-rhodiumphase shows a clear exothermic peak at 370°C corresponding to the dmp decomposition; in the phase y-ZrPdmpo.44 this decomposition happens in two steps, at temperatures of 420 and 5OOOC. This suggest the formation of an unusual rhodium-dmp species between the layers of the y-ZrP in the rhodium material and the ion presence catalyses the ligand temperature decomposition lowering it by-100°C on average. The same occurs for y-ZrPphen~~~-rhodium phase: the decomposition temperature of phen at 570°C is lowered to 370°C. We can also note this catalytic effect of the rhodium ion from the TG curves.The materials containing rhodium lose their hydration water continually until 250°C and the decomposition of the organic ligand suddenly overlaps. The dmp and phen materials lose their hydration water until 280°C, then there is a step (plateau) before the ligand decomposition occurs. In the same materials containing rhodium, the loss of water, due to hydrogen-phosphate condensation, ceases at 8OO0C, whereas in their precursors that loss is slower and terminates at 1000°C. The rhodium-materials obtained by y-ZfPdmpo.26 and y-ZrPbipy0.26 behave in the same way: both the TG and DTA curves show the lowering of decomposition temperature compared to their precursors, but to a lesser degree. In the TG/DTA curves of the materials derived from y-ZrPbipyo,44there is a slight difference compared to its precursor because, as we have already seen, the rhodium ion uptake is very small. The thermal behaviour of y-ZrPRh0.38 is slightly different from the y-ZrP: in the TG curve the hydration water loss of the material containing rhodium continues up to 250"C, when

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the loss of the water of hydrogen phosphate groups starts immediately. Moreover in the y-ZrP there is a step of 100°C between 250 and 350°C: at this latter temperature the condensation into pyrophosphates starts. At 320°C the DTA curve of y-ZrPRh038 shows small, broad exothermic peak and this thermal effect could be due to the formation of Rhz03.

5 CONCLUSION

The Rh3+ ion can be exchanged in y-ZrP, both intercalated with organic diamines and pre-swelled with EtOH. The rhodium uptake in y-ZrPEtOH does not involve all hydrogens of the phosphate group probably for steric reasons. Nevertheless we obtain a single material whose interlayer distance is bigger than that of the starting material. The rhodium uptake in the intercalation compounds differs depending on the diamine present in interlayer region. In the case of y-ZrPdmpo.4 and y-ZrPpheno.4 the rhodium uptake comes close to a maximum after 24hrs of batch contact (exchangerhhodium solution) even though 6 days are need to obtain the equilibrium. The yellow materials obtained contain less diamine than their precursors, the ligand elution increases with the increase in rhodium content. In the case of y-ZrPdmpo.4-rhodium materials we note a variation in the X-ray dfiaction patterns compared to y-ZrPdrnp0.4~.The TGDTA curves show a lowering of ligand decomposition temperature. In the case of y-ZrPdmp0.26 and y-ZrPbipyo.26 we again obtain the maximum uptake after 24hrs of batch contact: these rhodium materials have neither diamine eluted nor variation in X-ray diffraction patterns. The thermal behaviour is similar to that of previous materials: the decomposition temperature of the ligands is lower than that of the precursors. In the case of y-ZrPbipyo.4-rhodiummaterials, the rhodium uptake is much less than that observed for the other intercalation compounds. This could be due to a particular orientation of bipy between the layers of y-ZrP that hinders the ion uptake and to the value of the interlayer distance lesser than that of the other materials studied. ACKNOWLEDGEmNTS Thanks are expressed to L. Mattioli and M.Vinci for their fruitfultechnical assistance.

References 1. 2. 3. 4. 5.

A.Clearfield and J.M.Kalnins, J.Znorg. Nucl. Chem., 1976,38,849 S.AUulli, C.Ferragina, A.La Ginestra, M.A.Massucci, N.Tomassini, J. Chem. SocDalton Trans., 1977, 1879. G.Alberti and U.Costantino, "Inclusion Compounds", J.L.Atwood, J.E.D.Davies, D.D.MacNico1,Eds., 1991,5, 136. CFerragina, A.La Ginestra, M.A.Massucci, P.Patrono and A.A.G.Tomlinson, J.Phys.Chem., 1985, 89, 4762. C.Ferragina, A.La Ginestra, M.A.Massucci,P.Patrono and A.A.G.TomIinson, J.Chem.Soc.DaltonTrans.,1986,265.

Ion Exchange in Inorganic Materials and its Theory

6. 7. 8.

9. 10. 11. 12.

429

C.Ferra@, A.La Ginestra, M.A.Massucci, P.Patrono and A.A.G.Tomlinson, J.Chem.Soc.DaltonTrans. 1988,851. P.Giannoccaro, C.F.Nobde, C.Ferragina,A.La Ginestra, M.A.Massucciand P.Patrono,J.Mo1. Gatal., 1989,53,349. G.Mattogno, C.Femgh, A.La Ginestra, M.A.Massucci and P.Patrono, J.Ekcmn Specmsc, Relat. Phen., 1988,46,285. A.N.Chrinstensg E.K.Andersen,I.G.K.Andersen,G.Alberti, M.Nielsen and M.S.Lehmann,AcoCiemca ScandiMvca ,1990,44,865. D.M.Poojary,B.Shpeizer,A.Clearfield,J. chem. SocDalton lYans, 1995,111. A.La Ginestra, M.A.Massucci, C.Ferraginaand N.Tomsini, "Thermal Analysis" Proceedings 4th ICTA, 1974,1,63 1. C.Ferragina, M.A.Massucci and A.A.G.Tomlinson, J. chem. SocDalton lYans. 1990,1191.

APPLICATION OF NMR FOR INTERPRETATION OF ION EXCHANGE SELECI'IVITlEs

Mitsuo ABE*1, Yasusi KANZAKI*2, and Ramesh CHITRAKAR*3 Department of Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152 JAPAN

1 INTRODUCTION Inorganic ion exchange materials are known to exhibit good thermal and radiation stabilityl. In addition, some of them were found to have excellent high selectivities for certain metal ions compared to organic ion-exchange resinszd. Various types of antimonic acids and antimonates have been developed by one of the authors4-26. Titanium antimonate (TiSbA) and tin antimonate(SnSbA) showed an unusual selectivity sequence for micro amounts of alkali metal ions; Na+
ZEXPERIMENTALS 2.1 Materials

TiSbA and SnSbA were synthesized by the addition of various ratios of 4M(M=mol/l) antimony(V) chloride solution to titaniurn(1V) chloride and tin(1V) chloride solutions at room temperature, respectively4.5.7. The precipitate obtained was washed with water and then air dried. Two samples, giving high lithium selectivity, 0.67 molar ratio(Sb/ri) for 1.76(SnSbA) for SnSbA, were selected from various preparations. The XRD patterns showed the tetragonal system described by earlier papers. M-SbA was prepared by Li+/H+exchange reaction with a concentrated nimc acid solution

* 1 :present address; Tsuruoka National college of Technology, Inooka, Tsuruoka,997 Japan '2 :present address; Showa College of Pharmaceutical Science, Machida, Tokyo, 192, Japan *3 : present address; Dept Mines and Geology, Lainchour, Katmandu, Nepal

I

Ion Exchange in Inorganic Materials and its Theory

43 1

from LiSbOjl6. The LiSbO3 was obtained by heating Lisb(0H)a at 900°C. The LiSb(OH)6 synthesized by the addition of LiOH solution to a Sb(V) chloride solution at 60°C. M-SbA was characterized by XRD, IR and thermal analysis. The results obtained showed a good agmment with the previous resultsl6. Chemicd Analysis. The apples used for the N M R spectra were analyzed for lithium, sodium and antimony contents by dissolving in concentrated sulfuric acid and then by flame or atomic absorption photometry. NMR Spectra. The following four types of NMR spectrometers were used in this study: (a) 270-MHz FT-NMR spectrometer(JEOL GX-270; 900 pulse 15p) far ordinary Xi measurement, the temperaturerange being room temperature to -1OOOC; (b) 20-MHz pulse NMR spectrometer (Bruker Minispec PC-20) for TZmeasurement of IH; (c) 270MHz CP/MAS m-NMRspectrometer (JEOL GSX-270; 90' pulse 2ps) to eliminate the dipolar-dipolar coupling of 7Li ; (d) high-power and wide-band (2 MHz) sptcwmeter (EOL GSX-270; 90"pulse 2ps) for ordinary measurement. Determination of relaxation time was carried out by Inversion Recovery method of Ti and Carr-Purcell MeiboonGill method for T2, as usual. NMR samples were prepared by mechanical mixing to avoid the effect of dielectricloss as follows. Since each sample had a different loading content (see Figure 2), they wert weighed out so as to make the amount of lithium in each sample constant;0.02mequiv. for TiSbA and 0.07 mequiv. for SnSbA. The samples were then mixed with the H+form of TiSbA or SnSbA to make the net amount of sample, 0.4g for TiSbA and 0.5g for SnSbA. Due to the procedure each sample contained a constant amount of lithium and had a constant weight. Sodium samples were prepared in a same manner. Li+ Uptakes A study of the ion-exchangeisotherms for alkali metal ion*+ systems on TiSbA, SnSbA and M-SbA was determined as follows; a 1.00 g sample was immersed in 100 ml of a mixed solution of (MNQ + HNQ) or ( M N Q+ MOH)(M = alkali metal), at different pH (ionic srrength was kept at 0.1) with intermittentshaking at 30,45 and 60 OSOC, respectively. After attainment of equilibrium, the concentration of H+ and alkali metal ions were determined by pH measurement and atomic absorption spectrometry, respectively.

*

3 RESULTS AND DISCUSSIONS 3.1 Ion Exchange Isotherms of Alkali Metal ions/H+ on TiSbA and SnSbA. Ion exchange isotherms for Li+/H+systems showed sigmoidal curves on both of TiSbA and SnSbA(Fig. 1). This indicates that the Li+exchangereaction is favorable for the initial stage and then progressively unfavorable with increasingconcentration of Li+in the solution. The isotherms for other alkali metal ions/H+ systems show anti-Langmur type-the selectivity for the leaving cations over the entire range of exchangercomposition (Fig.la and lb). The pmcess was found to be reversible. The plot of (ln KZ) vs. XN, ,Kielland plot, was almost linear, indicating that the ion exchange sites for both TiSbA and SnSbA were homogeneous over the entire range studied(Fig. 2). However, the Kielland plot for Li+ showed a break point at about XLi = 0.04 far both TiSbA and SnSbA, indicating the presence of different exchange sites ( r e f e d to as Site A for low loading and site B for high loading) in the exchangers. When an exchanger (solid phase) is equilibrated with an electrolyte solution, the ion exchange reaction of the mono-valent metal ions/H+exchange system on an exchangerin the H+-form - can be repmented -by the following expression, H+ + M+ 2 M+ + H+ 1)

43 2

Progress in Ion Exchange: Advances and Applications

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Fig. 3. Temperaturedependence of 7Li and lH NMR spectra Sample 8 (in Figure 2a) is selected for this measurement

433

Ion Exchange in Inorganic Materials and its Theory

As shown by Sheny and Walton, the ion exchange reaction can be separated into the following two reactions27. H+(gas)+ M+(aq) 2 H+(aq)+ M+(gas) -AXyd 2) M+-) + H+ 2 M+ + H+-) 3) where Y represents thermodynamic functions such as G. H, and S. The numerical values of AYo contribute to the difference in the thermodynamic function of hydration (AY%yd)of the ions in aqueous solution and that (AY'cx) of the exchanged cations. The values of A y h y d can be found from the Rosseinsky tablea. Thermodynamic data on the zero loading of lithium ions on SnSbA showed a large numerical value for the increase of exchange enmpy(ASoex) in the exchange reaction for lithium ions. The entropy producing process may be due to the net transfer, to some extent, of water molecules from exchanger to the solution phase. When the less hydrated lithium ions were adsorbed on site A, a high electrostatic force between the lithium ion and the exchange site. As a result the motion of lithium may be resaicted in a narrow cage in the exchanger.

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3. 2 NMR Measurements Table 1 shows the isotopes used for determination of NMR study with their nuclear spin resonance frequency. Table 1 shows isotopes used and their nuclear spin resonance frequency Isotopes Nuclear spin Resonance frequency (MHz: at 6.34 2 n 1H 1/2 270 7Li 3/2 104.9 23~a 312 71.72 3.2.1. NMR Spectra of 7Li and IH on TiSbA and SnSbA According to the above considerations, one can postulate that Li+ can be adsorbed very tightly, presumably like that in the dehydrated state of lithium compounds. Figure 3 shows the temperature dependence of the 7Li and 1H spectra for Li-TiSbA(samp1e 8 in Figure 2). At room temperam both were simple Lorentzan cwes. The chemical shifts were almost negligible compared with the reference samples, 1M LiCl solution for 7Li and pure water for 1H. Line widths were about 0.4 and 1.2 KHz for 7Li and 'H, respectively, at room temperature. At a temperature below -8OOC. the l H spectrum broadened abruptly and showed that the adsorbed water molecules in TiSbA were frozen. At the same temperam the 7Li spectrum disappeared suddenly. On other hand, the intensity (area of peak) of 1H spectrum decreased gradually (line width became narrower and the intensity became high at 120OC) as the temperature became higher and showed that the number of water molecules increased with temperature as expected from the thermal analysis data. In the 7Li spectrum, the intensity decreased gradually, corresponding to decrease in the 1H spectrum. In the sample heated at 24OoC, at which water molecules adsorbed, no signal was observed in either 1H and 7Li on the TiSbA and SnSbA. Concentration Dependence of Ahorbed Metal Ions on NMR Spectra. F i p 4 shows the intensity of the NMR spectra of 7Li and BNa vs. the equivalent fraction of alkali metal ions in each of TiSbA and SnSbA exchangers, which can be correlated to Fig 2. From the above qualitative observation, we have concluded that the Li+adsorbed in the hydrated form gave a sharp NMR spectrum( site B), while that adsorbed tightly, presumably adsorbed in less hydrated form, gave a very broad NMR spectrum. As described in the experimental section, the total amount of metal ions in a sample used for NMR and its total weight were adjusted by adding exchanger in the H+ form to the exchangers with different loadings of Li+ and Na+.

Progress in Ion Exchange: Advances and Applications

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Ion Exchange in Inorganic Materials and its Theory

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The ZNa NMR intensities observed are almost independentof the equivalent fraction of exchanged Na+ in both TiSbA and SnSbA, indicating a homogeneous state of adsorption over the entire range of loading studied. This suggested that the adsorbed Na+ in these exchangers is in a hydrated form similar to that in aqueous solution. On other hand, NMR intensities increased markedly with equivalent fraction of adsorbed Li+ upto the inflection point of Kielland plot. This indicates that in the case of a low equivalent fraction, the Li+ in the exchanger is exchanged preferentially on site A with littIe or no hydration and low contribution of Li+ on site B. In the case of a high equivalent fraction, the Xi NMR signal increases as a result of increased contribution of adsorbed Li+on the site B. These finding arc in good agreement with the entropy producing proccss of Li+ exchange with a low loading on SnSbA11. Theoretical Analysisfor thesite A and site B. The Kieland's equation on site i: log (ln K:)(i) = 2C(i) M+ +log K(i) - (a) 4) where (In K:)(i) is the observed selectivity coefficient on site i, C(i) the Kielland the equivalent fraction of ion adsorbed on site i. and K(i) the coefficient for site i, thermodynamic equilibrium constant on site i. To account for the result of the NMR experiment, the following assumptions am postulated13. (1) The Li+ in the solution can be exchanged with H+ on site A and on site B independently. (2) The equilibrium state can be established with Li+ in solution and exchanged Li+on site A and site B simultaneously. obeys the Kielland equation(eq.3) on site A and site B (3) The relation (ln Kg) vs. independently. According to a computer analysis, using Newton's approximation, the observed Kielland plots in the exchangers can be represented by two separate equations for site A and site B on TiSbA and SnSbA by using a trial-error method. These approximations indicate that the theoretical plots can be reproduced well by the experimental plots (Figure 5), which suggests the validity of our assumptions. Table 2. Parameters for Kielland's equation on site i = A and B A\ C(A\ 1 C(B\ D TiSbA -24.4 -26.0 -3.6 -2.55 0.35 15.1 18.6 2.7 2.2 0.28 where p indicates the fraction of the site number of site A to the total number of (site A + site B) =l.

3. 3 N M R Spectra of 'Li and 'H on M-SbA 3. 3. 1 . Ion exchange isotherm of alkali metal ionslH+ on M-SbA Figure 6(left) shows the pH titration curve of M-SbA for lithium ion at different temperatures. A large jump on LiOH addition indicates that M-SbA behaves as a smng monobasic acid type ion exchanger. The Li+ uptakes at different pH values are shown in Figure 6(right). Uptakes of Li+increase markedly at pH higher than 2. The maximum uptake of Li+at 6OOC was found to be 5.4 meq/g which was close to the theoretical capacity of 5.7 meq/g. The samples for X i and lH NMR measurement were selected from Figure 6(right). 3 . 3 . 2 . Iff NMR spectra The lH NMR spectra measured by a high-power wideband m-NMR spectrometer with 90' pulse of 1.0 ps are shown in Figure 7 (numerical values of A-E correspond to meq/g of Li+ uptake). M-SbA and the samples exchanged at relatively low lithium uptakes showed two peaks in the NMR spectra with different widths. Computer graphic simulation showed that the chemical shifts for both spectra were similar, and the half-widths were found to be 1.5 kHz for the narrower one and 17.6 kHz for widtr

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a

-15

(f-f,)/kHz

(f-fo)/kHz

2

1

1

-40

O

0

2

4

6

Li+ exchanged/ meg g-’

Fig. 8. l H NMR signal intensity of -OH and H20 vs. uptake of Li+.on M-SbA

Ion Exchange in Inorganic Materials and its Theory

437

one, respectively. The change in peak m a was plotted against the lithium uptake in Figure 8. The areas of both absorption lines decreased monotonously with increasing uptake of lithium ions. The area reached almost zero in sample E for the wider spectrum, where as lithium ionexchange almost reached the theattical capacity of 5.7 m a g . On other hand, the narrow one did not reach zero and about 3096 of the water originally in M-SbA still remained. These results indicated that the narrow peak was due to water of hydration of lithium ions adsorbed on the surface and the wider one the exchangeable proton in the exchanger. Most of the exchanged lithium ions in the lattice were in the unhydrated state plus a small amount of lithium ions on the surface. 3 . 3 . 3 . 7Li NMR spectra The ordinary 7Li NMR spectrum of LiSbO3 showed a doublet with splitting constant of about 7 kHz,while the M A S spectrum of LiSb0-J s h o d a single Lorentzian shape, half-width being 0.5 kHz. Since 'Li has a nuclear magnetic moment of 3/2, the doublet is attributable to the second order quadrupole interaction29.30 which is revealed when such nuclear spin is located at the position with a 3-fold symmetrical electric field Thus it is concluded that the lithium ions in LiSb0-J are located at homogeneous sites through they had a less Symmetrical coordination, e. g. ,tetrahedral and/or distorted o c t a h a coodinations as stated later. F i m 9 showed ordinary 7Li N M R spectra of the samples A-E at different uptakes of Li+. The absorption lines were simple at low uptakes of lithium ions and the curve was almost Gaussian indicating that the line broading was governed mainly by the dipoledipole interaction. The line width increased with incrtasing uptake of lithium ions (A-C) keeping their Gaussian nature. Since the simple Gaussian nature indicates the absence of the second-order quadruple interaction within this range, the lithium ions must have a Cfold symmetrical coordination. The uptake of Li+ was almost independent of temperature within the range of A-C for uptake of lithium ions. At higher uptakes @, E), the singlet peak was split into a doublet and an additional sharp peak appeared at the centre of the doublet. The ratio of the area for the doublet to the centre singlet in sample E was estimated to be about 955. The doublet spectrum in sample E was similar to that in LiSb0-J. Thus the transformation from the singlet spectrum to the doublet indicates that the lithium ions were transferred from Cfold symmetrical site to a less symmetrical site. The lithium ions producing the centre singlet must be exchanged at a relatively mobile site. The transverse relaxation time, TI,for the centre peak measured by the inversion recovery method was about 83 ms. On other hand the TIfor the doublet was over 1 s as estimated by the pulse interval change measurement. The central peak of sample E disappeared completely at -1OOOC. Similar behaviour was observed for the *HNMR for H20(central peak in Figure 7) of the same sample and suggested that the motional nature was similar between 7Li and 1H. Lithium ions thus adsorbed can be more mobile than those exchanged without hydration water. 3 . 3 . 4 Lithium Ion-Exchange Mechanism Considering the results on 7Li and 1H NMR experiments, it may be concluded that lithium ions were exchanged at 4-fold symmetrical sites by shedding the hydration shell of lithium ions in the solution and by expelling the co-absorbed water molecules up to half of the theoretical capacity. They then changed their positions to those with Zfold symmetrical electrostatic field when the uptake of lithium ion exceeded half of the theoretical capacity because of the electrostatic repulsion between the ions. At a later stage, other lithium ions were also adsorbed, keeping their hydrated state, and showed relatively free motion on the surface of the matrix. 4 CONCLUSIONS The solid state NMR technique is very useful for interpretation of lithium selectivities on the inorganic ion exchangers, such as tin antimonate (SnSbA), titanium antimonate(IiSbA) and monoclinic antimonic acid(M-SbA) cation exchangers. This paper describes lH-, 7Li- and BNa-NMR spectra of these materials exchanged with different loadings of Li+ and Na+. These NMR studies on the SnSbA and TiSbA showed two types of ion exchange sites, one favourable for lithium ions and other has a poor

438

Progress in Ion Exchange: Advances and Applications

selectivity for lithium and sodium ions. In the former site, the lithium ions exchanged ax! present .in the anhydrous state and the latter site both with hydrated state. The 1H- and 'Li-NMR spectra on the M-SbA showed two different spectras; very sharp and broad. The former indicates hydrated water of lithium ions adsorbed on the surface and the latter the exchangeable proton in the exchanger. This indicates that most of the lithium ions in the lattice are unhydrated and small amount of lithium ions are on the surface.

4 REFERENCES 1.A. Clearfield " Inorganic Ion Exchange Materials" CRC Press Inc., Boca Raton, Fl. USA,1982. 2.M. Abe, Chap. 6 in Ref. 1. 3.M. Abe, " Ion Exchange Selectivitiesof Inorganic Ion Exchangers" in J. A. Marinsky and Y. Marcus Eds. " Ion Exchange and Solvent Extraction" Vol. 12,Marcel Dekker, Inc., 1995 Chap. 9. 4.M. Abe and T. Ito, Nippon Kagaku Zasshi, 1967,70,291. 5. M. Abe and T. Ito, Nippon Kagaku Zasshi, 1967,70,440 6.M. Abe, M. Tsuji and K. Hayashi, Chern. Lett., 1983, 1561. 7.M. Abe and K. Hayasi,Solvent Extr. Ion Exch., 1983,1,97. 8. M. Abe and K. Hayashi, Hydrometallurgy, 1984,12,83. 9. M. Abe and N. Furuki, Bull. Chem. Soc. Jpn, 1985,58,1812. 10.M. Abe, R.Chitrakar, M.Tsuji and K.Fukumoto,Solvent Extr.Ion Exch., 1985,3,149. 11.M. Abe and N. Furuki, Solvent Extr. Ion Exch., 1986,4,547. 12. R. Chitrakar and M. Abe, Analyst, 1986,111,339. 13. M. Abe, Y. Kanzaki and R. Chitrakar, J. Phys. Chem., 1987,91,2997. 14.M. Abe and R. Chitrakar, Hydrometallurgy, 1987,19,117. 15. R. Chitrakar and M. Abe, Bull. Chem. Soc. Jpn. , 1987,60,2274. 16. R. Chitrakar and M. Abe, Mat. Res. Bull., 1988,23,1231. 17.R. Chitrakar and M. Abe, Solvent Extr. Ion Exch., 1989,7,721. 18.Y. Kanzaki, R. Chitrakar and M. Abe, J. Phys. Chem., 1990,94,2206. 19.R. Chitrakar M. Tsuji M. Abe, and K. Hayashi, Bull. Soc. Sea Water Sci.Jpn., 1990,44, 267. 20.H. Kaneko, M. Tsuji, M.Abe, Y.Morita and M.Kubota, J. Nucl. Sci. Technol., 1992, 29, 988. 21. Y.Kanzaki, RChitrakar, T.Ohsaka, and M. Abe, J. Chem. Soc. Jpn., Chem. Ind., 1993,1299. 22.M. Abe,"Lithium Separation by Ion Exchange" in "Lithium; Current Applications in Science,Medicine and Technology"$d.R.O.Bach,1985, John Wiley & Sons,Inc., p 1. 23.M. Abe, R. Chitrakar and K. Hayashi, "Selective Separation of Lithium from Seawater and Hydrothermal Water by Titanium (IV) or Tin(IV) Antimonate Cation Exchanger" "Chemical Separations Vol. l.Principles", Eds. C. J. King and J. D. Navratil, Litarvan Literature, Denver, 1986,p.187. 24.M. Abe, " Ion Exchange Selectivities of Crystalline Antimonic Acid Eds. P. A. Williams and M. J. Hudson, Elsevier Appl. Sci. Publ., N. Y. USA, 1987,p. 277. 25.M. Abe, R. Chitrakar, M.Tsuji and Y. Kanzaki, "Synthesis and Ion Exchange Propemes of Lithium Ion Selective Inorganic Ion Exchangers by Applying Ion Memory Effect" in "Recent Developments in Ion Exchange 2"Eds. P. A. Williams and M. J. Hudson, Elsevier Appl. Sci. Publ., N. Y. USA, 1990, p. 57. 26.M. Abe, Ion Exchamge Selectivitiesof Inorganic Ion Exchangers, in "Recent Developments in Ion Exchange 3" Eds. A. Dyer, M. J. Hudson and P. A. Williams, Appl. Sci. Publ., N. Y.USA, 1993,p.199. 27.H. S. Sherry and H. F. Walton, J. Phys. Chem., 1967,71,1457 28. D. H. Rosseinsky, Chern. Rev., 1965,469 29. J. F. Baugher, P. C. Taylor, andT. Oja, J. Chem. Phys., 1969,50,4914. 30.P. J. Bray, A. E. Geissberger, F. Bocholtz, I. A. Harris, J. Non-Cryst. Solids 1982, 52,45.

HARMONISATION OF ION EXCHANGE FORMULATIONS AND NOMENCLATURE: WHAT CAN BE DONE?

R. Harjula and J. Lehto Laboratory of Radiochemistry Department of Chemistry P.O.Box 55 FIN-00014 HELSINKI UNIVERSITY Finland 1 INTRODUCTION

Historically, the research and developmentwork involving different types of ion exchange materials (ie. organic resins, zeolites and other minerals) has been carried out in parallel and separate ways. As a consequence quite a number of different formulations and nomenclature are being used for ion exchange today. The situation is such that considerablevariation in definitions and formulations can be seen also in research papers dealing with same type of exchange materials. Serious misuse and misunderstanding is involved in the use of many basic deftnitions. This situation is creating major obstacles for the progress of ion exchange.' It is making it difficult for the scientists to communicate with each other and with those who make use of their work, e.g. materials manufacturers and end-users. Different types of ion exchange materials have different theories relating to their function. For instance, the behaviour of chelating resins can be often rationalized by considering appropriate "complexation constants" of metal ions and "acid dissociation constants" of the resin. For another type of exchanger, e.g. for a strong-acid resin, such an approach may completely fail and consequently the ion exchange equilibria is decscribed in dimerent terms. Thus, in fundamental studies it may be sometimes necessary that formulations vary from case to case. However, for applications of ion exchangers it is very important to have common basic parameters to use to measure their performance, such as capacity and selectivity, since in many fields today different types of ion exchangers compete in the same markets. Recommendations for ion exchange nomenclature were issued by IUPAC in 1972. Practically no updating of these recommendationshas taken place in more recent IUPAC publications. 3*4 This may be one major reason why these recommendations are so often ignored in present literature. In the previous ion exchange conference in Wrexham (Ion-Ex '93) barriers to the progress of ion exchange were discussed', including the confusion involved in the ion exchange formulations. This led to the organisation of workshop in Helsinki titled "Uniform and Reliable Nomenclature, Formulations and Experimentation for Ion Exchange" in 1994.5 There were in total nineteen participants in this workshop from Japan, China, Russia, Belorussia, Hungary, Finland, Germany, UK and USA. In this workshop, formulations, nomenclature and experimentation were discussed. It was

440

Progress in Ion Exchange: Advances and Applications

concluded that updated recommendations for ion exchange nomenclature should be prepared and suggestions were made on how to start such a process. In addition, some tentative suggestionswere made to update some of the most essential nomenclature, such as "ion exchanger'' and "selectivity coefficient". It was understood in the Helsinki workshop that, to be successful, the process of updating ion exchange nomenclature should have support and guidance from the ion exchange community at large and that any new recommendations should have widespread acceptance prior to publication. This paper is aimed to be a base for the discussion of the subject in the workshop in Ion Ex '95 and it is hoped that it will initiate further discussion after publication.

2 CONVENTIONAL NOMENCLATURE AND RECOMMENDATIONS IUPAC recommendations from 19722 cover a large number of essential terms for ion exchange and it is obvious that the situation in the ion exchange literature would be much less confusing if these recommendations had been or were even now followed. However, many terms in these recommendations are so broadly defined that a large number of interpretations are possible, or a wide variety of numerical values can be obtained for a given parameter, such as selectivity coefficient. In the following, conventions and recommendations for some of the most essential terms, eg. selectivity coefficient, ion exchange, and ion exchange capacity, are discussed to demonstrate the confusion that arises from the diverse conventions. 2.1 Ion exchange and ion exchanger

The IUPAC recommendation for ion exchanger, '2 solid or liquid inorganic or organic, containing ions, exchangeable with others of the same sign of charge present in a solution in which the exchanger is considered to be insoluble" is probably an appropriate definition for organic ion exchange resins. However, for inorganic ion exchangers this definition is rather ambigious and confusion arises eg. between substitution reactions and true ion exchange reactions. For instance, when a solution of CoC1, is contacted with manganese sulphide, transfer of ions (Mn2' and Co2') between solution and solid takes place and two distinctive solid phases (MnS,CoS) will be present in the system. This is a conventional substitution reaction, which can be written as

Mns + co2+ r.c o s + Mn2+ The equilibrium of this reaction can be easily rationalized by using the solubility products of the two metal sulphides. When a zeolite in sodium form is contacted with a solution of KC1, a true ion exchange reaction takes place. At equilibrium, usually both potassium and sodium ions will be present in the zeolite framework but usually, no separate solid compounds co-exist (there are some rare exceptions to this). The situation would be similar in a ion exchange resin. Considering the rapid development of inorganic ion exchange materials during the past decades, it is desirable that a more unambigious definition would be found for "ion exchanger".

Ion Exchange in Inorganic Materials and its Theory

441

2.2 Ion exchange capacities Three distinctive static capacities are recommended by IUPAC. Theoretical smcific caDacity and volume caDacity are quantities based on the number of milliequivalents of "ionogenic groups" per gramme of dry ion exchanger or per gramme of swollen ion exchanger, respectively. Practical smific caDacitv is a quantity based on the number of millimoles of ions taken up per gramme of dry ion exchanger under spesified conditions. Theoretical sDecific caDacity is constant for a given ion and varies only slightly for different ions, depending how much a given mass contributes to the total weight of the exchanger. Practical specific caoacitr, on the other hand, depends strongly on the the experimental conditions (especially on the ion concentrations and amount of ion exchanger in contact with the solution) for a given ion and can have values ranging fiom zero to the value of the theoretical capacity. The IUPAC terms are, however, very seldom used. Instead, terms like ''ion exchange capacity", "cation exchange capacity", "total weight capacity", "apparent capacity" and effective capacity" are used. Furthermore, varying definitions are used for these terms and various experimental conditions are used to determine the values of these quantities. In addition to these terms, it is often necessary to use term "maximum capacity", "maximum ion uptake" or l'saturation capacity". In several types of exchangers a proportion of ionogenic groups or exchange sites are unavailable for ion exchange, eg. due to steric and ion-sieve effects. The proportion of these inactive sites depends on the size and chemical nature of the in-going ion. If properly determined, these maximum capacities are constant for a given ion and given exchanger. It is obvious that the existence of so many "capacities" creates confusion in the ion exchange literature. This confusion is likely to a have harmful effect on the utility of the basic ion exchange data.

2.3 Reaction equation Various formulationshave been developed for the reaction equation of ion exchange. Considering binary exchange reaction between ions A (charge zA)and B (charge %) two types of basic formulations are in common use: zABZB+z$lzA

e-+

zABzB+

z2

(1)

and

In addition to overbars, various other symbols are used to denote the ion in the exchanger (eg. AR, A, A(r)). No recommendations have been given on how to write an ion reaction. However, the IUPAC definition of selectivity coefficient is only consistent with reaction equation (1) above (see later 2.5).

2.4 Ion exchange equilibria IUPAC recommendations for equilibrium parameters include selectivitv coefficient, corrected selectivitv coefficient and various distribution ratios or coefficients. Only the first two terms will be discussed here. In general (IUPAC recommendations were given

442

Progress in Ion Exchange: Advances and Applications

as examples) the recommendation for the selectivitv coefficient has the following form:

Also subscript letter lor''can be used to designate ion concentrationsin the exchanger. It is also noted that "for exchanges involving counter-ions differing in their charges, the numerical value of km depends on the choice of the concentration in the ion exchanger and the solution (molar scale, mold scale, mole fraction scale etc.). The concentration units must be clearly stated in exchange of ions of differing charges". Corrected selectivitv coefficient is obtained when "concentrations of external solution are replaced by activities". A lot of freedom is given for the measurement of ion exchange selectivity and this has resulted in a multitude of selectivity coeffients with differing numerical values. Most commonly, molar or mold concentration scales are used. When the mold scale (m) is used, a mold selectivity coefficient kmABis obtained:

Also formulations that involve mixed concentration scales, mold (or molar) scale for solution and rational scales for exchanger are very popular. Mole fractions were introduced eg. by Hogfeldt et a1.6 and the corresponding selectivity coefficient can be written as

--

Equivalent fractions E (EA = zAGA/ C qGi) are used in the formulation introduced by Gaines and T h ~ r n a sie. ,~

Equations 5 and 6 are not complete original formulations6*',which defined so called "corrected selectivity coefficients" (i. e. activities were used instead of concentrations for the solution phase). However, selectivity coefficients of Eqs. 5 and 6 have become popular and they serve here the purpose of demonstrating the variance in the numerical values of the different coefficients arising from the different exchanger phase concentration scales. In Figure 1 values are shown of k'",,, k", and kEm for Ca2'/Na' in a hypothetical ion exchanger (capacity for Ca" 3 meq/g), which has been given a constant value of 10 for kmwn. It can be seen that there can be considerable variation in the numerical values of the selectivity coefficents. The relationships between the different selectivity coefficients are:

Ion Exchange in Inorganic Materials and its Theory

443 (71

Rational selectivity coefficients of Eqs. 5 and 6 (mole or equivalent fraction) thus depend on the exchange capacity Q of the exchanger (or vice versa). Equations 7 and 8 are valid also for the corresponding corrected selectivity coefficents, since the solution phase activity correction is the same in each case. In addition to the above se!ectivity coefficients, a rational selectivity coefficient may be used:’

100

* : .

-

‘ X

*0a

-

10

:

1 .

1

-

E (Ca2+)

Figure 1 Selectivity coefficients PIMB KME and R“,, for Ca”/Na’ exchange in a hypothetical ion exchager for which PNEis constant at 10. Capacity of exchanger for Ca” 3.0 meq/g , total ion concentration in solution: 0.1 eqn.

444

Progress in Ion Exchange: Advances and Applications

This rational selectivity coefficient depends on the exchange capacity Q of the exchanger and total ion concentration (Naeqll) in solution, reflecting the electroselectivity effect, i.e. k$,=k,m/,Q ( z A - z B ' ( N , )

(zB-zA)

(10)

In ion exchange experiments, total ion concentration may be varied at will and the numerical value of kN, can become very large in dilute solutions although the selectivity, as measured by the other selectivity coeffcients, is low. For instance, in the example of Fig. 1, the value of kNAm would be constant at 300. For application oriented research in ion exchange, it is obvious that it would be very useful if agreement could be reached on the recommended concentration scale. This would make the comparison of different exchange materials much more straightforward. People who are involved in the development and employment of new ion exchange materials are not all specialists of ion exchange. For instance, a synthetic chemist would appreciate a common measure that could be used to compare the new materials that are under developed to the older ones prepared by other chemists. A salesperson would be happy to advertise the new materials with selectivity data that are comparable with the competitors' products, without carrying out "suspicious" conversions between the different selectivity measures.

3 TENTATIVE SUGGESTIONS FOR UPDATED NOMENCLATURE The following tentative suggestions were made in the Helsinki Workshop' for the definitions of some of the most essential terms of ion exchange.

3.1 Ion exchange and ion exchanger "Ion exchange is the equivalent exchange of ions between two or more ionized species located in different phases, at least one of which is an ion exchanger, without the formation of new types of chemical bonds." "Ion exchanger is a phase containing an osmotically inactive insoluble carrier of the electrical charge (matrix)." Osmotically inactive means that the carrier cannot migrate from the phase where it is located to another phase. For example, sulphonic acid groups (-S0,H) cannot migrate from polystyrene(PS)-divinylbenzene(DVB) framework into the solution phase. Thus PSDVB-SO,H is an ion exchanger, but BaSO., is not, since SO,= can migrate into the solution phase due to dissolution. 3.2 Static ion exchange capacities "Ion exchange caDacity is the number of millimoles, or milliequivalents, of ionizable groups, or exchange sites of unit charge, per gram of dry exchanger." Ion exchange capacity can be determined unambiguously by determining analytically the composition of the ion exchanger. This way the number of ionizable groups, such as SO,H in sulphonic acid resins, or the exchange sites, such as hypothetical A10; sites in

Ion Exchange in Inorganic Materials and its Theory

445

zeolites, can be obtained. In most inorganic ion exchangers there are no distinctive ionizable groups. For example, in zeolites the negative charge created by isomorphous A13' for Si4+ substitutions is uniformly distributed to the oxygen atoms of the aluminisilicate framework. The term "exchange site" was chosen to describe this kind of case, even though it is not unambiguous. The ionic form, to which the ion exchange capacity refers, should be given, since it affects the numerical capacity value. "Loading is the total amount of ions expressed in milliequivalentsor millimoles taken up per unit mass or unit volume of the exchanger under the specified conditions, which should be always given." Loading refers always to the specific experimental conditions under which the ion uptake value was determined. Loading can of course be equal to the ion exchange capacity. For example, with strongly acidic and basic ion exchange resins maximum loading most probably equals the ion exchange capacity. Maximum loading can exceed ion exchange capacity, for example, due to electrolyte sorption, or it can be lower than the ion exchange capacity due to steric and ion sieve effects. As an example zeolite Y in sodium-form, N~6(A102),,(Si02),3,-237H,0, might be discussed as follows: The "molecular weight" of the anhydrous Y is 12013 g/mol and thus the ion exchange caDacitv is 56 equivalentdmol x 1/(12013 g/mol) = 4.66 mea/q. Typically, ten out of fifty six sodium ions may be inaccessible to calcium ions and, therefore, the maximum loading in calcium exchange in sodium-form zeolite Y is 46/56 x 4.66 meq/g = 3.83 mealq. In any other ion exchange experiment the loading is between 0 and 3.83 meq/g, and in when is electrolyte sorption, even higher values can be obtained. 3.3 Reaction equation

In the discussions it was concluded that both common formulations of Eq. 1 and Eq 2 are appropriate. It was noted however, that there is a clear distinction between the formulations. Equation 1 (section 2.2) refers to the exchange of z,z, equivalents of ions whereas Eq. 2 always refers to the exchange of one equivalent of ions. 3.4 Ion exchange equilibria

In the tentative suggestions, the terms describing ion exchange equilibriumparameters were divided in two groups: 3.4.1 Equilibrium parameters

Thermodynamic eauilibrium constant: -x

Y

-Y

x

addB K=-

(11)

a Bad

where a's are ion activities and the exponent x is either z, (Eq. 1) or l/z, (Eq. 2) and y either z, (Eq. 1) or l/z, (Eq. 2).

Progress in Ion Exchange: Advances and Applications

446 Corrected eauilibnum coefficient:

c,

where and E, are exchanger phase concentrations. Molarity, molality or full mole fiactions were the preferred concentration units. Full mole fractions means that also water content of the exchanger, and eg. the sorbed electrolyte, should be considered. Eauilibrium coefficient: -x

Y

C*CB

-yc*

‘8

A

where C, and C, are solution phase concentrations. Molality, molarity and mole fractions were the preferred concentration units.

3.4.2 Selectivity parameters SeDaration factor:

Selectivity coefficient:

There is a clear distinction between the two groups of parameters. Separation factor (Eq. 14) and selectivity coefficient (Eq. 15) depend strongly on the total concentration of the exchanging ions in the solution, at given C, or EA,in case that their charges are not equal (electroselectivityeffect). Equilibrium parameters of Eqs. 12-13 do not reflect this effect and are almost independent of the total solution concentration. 4 WHAT CAN BE DONE

The harmonisation process of ion exchange nomenclature will require guidance and support from the ion exchange community at large. It was suggested in the Helsinki Workshop that further workshops for discussions need to be arranged as part of international ion exchange conferences. A working committee could be established at a later stage if appropriate. Sponsoring industrial or academic organisations would be needed for the harmonisation process. It is hoped that this paper will stimulate discussion on ion exchange nomenclature. The authors welcome any comments and suggestions that the readers may have.

Ion Exchange in Inorganic Materials and its Theory

447

5 REFERENCES 1. R.P. Townsend, in "Ion Exchange Processes: Advances and Applications", Eds., A.

Dyer, M.J. Hudson and P.A. Williams, Royal Society of Chemistry, Cambridge, 1993, p. 3. 2. Recommendations on Ion Exchange Nomenclature, Pure Appl. Chem., 1972, 29, 619. 3. V. Gold, K.L. Loening, A.D. McNaught and P. Sehmi, "Compendium of Chemical

Terminology, IUPAC Recommendations", Blackwell Scientific Publications, Oxford, 1987. 4. Nomenclature for Chromatography, IUPAC Recommendations, Pure Appl. Chem., 1993, 65, 819. 5. Proceedings of the International Workshop on "Uniform and Reliable Nomenclature, Formulations and Experimentation for Ion Exchange", Helsinki, 30.5.-1.6.1994, Special Issue of Reactive and Functional Polymers, 1996, 27, 93-153. 6. E. Hbgfeldt, E. Ekedahl and L.G. Sillen, Actu Chim. Scand., 1950, 4, 404. 7. G.L. Gaines and H.C. Thomas, J Chem. Phys., 1953,21, 714. 8. F. Helfferich, "Ion Exchange", McGraw-Hill, New York, 1962, p. 154.

THE? SIGNIFICANCE OF THE TERM IDEAL IN THE? THERMODYNAMICSOF ELECTROLYTE SOLUTIONS AND ION EXCHANGERS

BY DENVER G HALL N.E.W.I., Mold Road, Wrexham, Clwyd, LL11 2AW U.K.

ABSTRACT. Ideal behaviour in an electrolyte solution is defined as that whereby the chemical potentials p, of the ionic species i conform to the expression

pj = p8(T,po) + kTlnn, 0.

------

(Al)

where pi is a standard chemical potential, 0 refers to solvent, and n denotes number density. Kirkwood - Buff Solution Theory is used to identify the physical conditions which must be met for equation A1 to hold for the various complex species in an electrolyte solution when all deviations from ideality of the components attributable to association equilibria. A method is then developed for describing the effect of solution composition on the phase boundary potential between an electrolyte solution and a liquid ion exchanger, when the latter behaves as an ideal associated solution. Two novel features of ion exchangers with fixed charges arranged on a lattice are that the fixed charges do not contribute to the ionic strength and need not appear in the equations describing thermodynamic properties. In general species which bind to the fixed charges are unlikely to behave ideally. Finally it is shown that when the mobile species in the ion exchanger conform to equation 1 charge fractions rather than ion fractions are the appropriate concentration units for defining ideal exchange behaviour.

Ion Exchange in Inorganic Materials and its Theory

449

INTRODUCTION Thermodynamicallyideal behaviour may be defined in different ways. In each case the chemical potentials depend on the solution composition in a particularly simple way. For dilute solutions the definitions most commonly employed are those based on mole fractions, or volume fractions ,or number densities. All three become equivalent in the limit that the solute concentration----> 0, in which case the solute chemical potentials take the form 8 (1 )

p, = pi

______

+ RTlnc,

8. where c denotes concentration and p; is a standard chemical potential. The dependence of chemical potentials on composition is important, not only for understandingthe equilibrium aspects of ion exchange, but also for describingthe kinetics. For example, when the Nernst - Planck equations(')are employed to describe ion transport processes in ion exchange membranes it is assumed that equation 1 applies where the q are number densities. The aim of this paper is to identify the physical conditions which must be met for ideal behaviour to occur in solutions of electrolytesand in ion exchangers. The structure of the paper follows the outline given in the abstract.

I1 SOLUTIONS OF NON ELECTROLYTES

Kirkwood - Buff solution theory (2s3) provides general and exact relationshipsbetween the dependence of chemical potentials on solution composition and molecular distribution functions. The key equation is

kTdlnnk = C(Ni, +Sk,)dpi

--_-__(2)

i

where n and p respectively denote number density and chemical potential S, =1 when i=k,=O,wheni f k W

Nii = n; I (gkj(r) - 1)4xr2dr

____(3)

0

and gki (r)is the pair distribution function of i molecules with respect to k molecules. For a binary solution of non-electrolytes consisting of a solute 1 and solute 0 equation 2 gives

kTd Innl = (1 + N;,)dpl

+ N;odpo

------ (4)

When the solute molecules are randomly distributed gll(r) =1 and it follows fiom equation 4 that

p1 = p!(T,po) + kTlnn1

(5)

_ I _ _ _

8. where the standard chemical potential p1 IS a function of T and po . For very dilute 8 8 8 solutions po = po (T, p) consequently, as nl --->o p1 = p1 ( T ,p )

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Progress in Ion Exchange: Advances and Applications

When there are several solutes present, and all are dilute,

lvli reflects the associationof

i and k molecules and N ; reflects the self association of k. Moreover in the situation where we have a series of aggregate species r which are randomly distributed so that

______ ( 6 )

p, = p:(T,po)+ kTlnn, = C N ; p j i

where

N;

is the number of i molecules in a member of species r ,it can be shown that

------ (7a,b)

r A solution which conforms to equation 6 is known as an ideal associated solution. The

various quantities T i ,NiNk etc may, if so wished be related to the various association equilibria that occur in the system and may be calculated from the total concentrations and a complete set of association constants. Thus the theory of ideal associated solutions provides a general way of handling a series of complex equilibria in solution.

(2) SOLUTIONS OF ELECTROLYTES The measurable macroscopic thermodynamic properties of electrolyte solutions can be described completely in terms of the behaviour of electricallyneutral components. When there are c independent species present, the number of independent electrically components is c - 1. These may be chosen in a variety of ways. That adopted here is to choose one species, say species c, as a reference species and to define the components as the electrically neutral combinations of each of the other species with species c. Thus a unit of component i consists of one ion of i plus sufficient c to neutralise its charge. hence if i is Na'and c is CI -then the chemical potential of component i, 8; is given in this case by 8,+ = pNa+ ,p = chemical potential of electrically neutral

+

NaCI. On the other hand if i is Br- and c is CI- then

8,_ = pB,- - pcI-

and is

the change in free energy accompanyingthe replacement of a CI ion by a Br ion. In general

Species c may be chosen in any way that is convenient.

45 1

Ion Exchange in Inorganic Materials and its Theory

This method of defining components has several advantages. In particular components are never present in negative amounts. Equation 2 is equally applicableto electrolyte and non electrolytesolutions. However a consequence of the electrical neutrality condition is that

0=

c (Nii + 6ki)Vi

------ (9)

i

where V , denotes ionic valency (including sign). It follows from this equation that the

*

Nki do not

---->

Oas all Q -----> 0 and it may be shown that if

ei = 8 8 ( T , p o ) + k T l n n i--kkTlnnc Vi

----(10)

VC

for all ionic components ,we must also have

-----

(1 1)

i

and vice-versa. Equations 7 and 8 represent ideal behaviour of the electricallyneutral components but it does not follow necessarily therefiom that the individual p, are given by

pi = pie (T,po)+ kTlnni

---

(12) For this latter result to hold as well it is also necessary that, in the presence of an applied electric field such as that adjacent to a charged surface;

=-vie

k ( 2 )

----- (13)

T,Oi

where I ) denotes electrical potential relative to bulk homogeneous solution. Quatiom 10 and 13 describe the physical conditionsthat must be met for ideal behaviour to occur. #

For non-ideal systems equations 10 -13 do not apply. We may define the quantity V i as

---

(14)

Thus defined the V: describe the response of the electrolyte solution to an applied electric field. We may also define the quantities N g by

Progress in Ion Exchange: Advances and Applications

452

------ ( 15)

Moreover it follows from the material in refs 4-6 that

_-____ ( 16)

kTdlnnk = x ( N g + 6 k ; ) d p ; i

and that V z = C ( N E

+6 k ; ) V ;

#

Hence for equation 12 to apply all N,, are zero

i #

and V , = V i Since, for ideal electrolyte solutions, there is no association as usually understood yet the

N;,

are non zero it is clear that these quantities are not related to binding i association

in the same way as the N ; , in solutions of non-electrolytes. It is instead the N which appear to fill this role. According to this viewpoint equation 15 splits the

#

,

Nii

into two contributions, one from ion association,the other from the ion atmosphere of the k i ~ n ' ~ * ~ ) . This viewpoint receives further confirmationwhen an ideal associated ionic solution is considerd. For aggregate species r in such a solution

pr = p : ( ~ , p ~ ) + kTlnnr =

c~ i

Hence

r

where V, =

C N:vi i

Also it may be shown that

and that

: p ~

------ ( 17)

453

Ion Exchange in Inorganic Materials and its Theory #

In this case the correspondence between the Nli for non-electrolytes and the Nki for electrolytes is complete and unequivocal, and the same equations which describe the effects of association on the p, in non-electrolyte solutions apply as they stand to electrolyte solutions. For future reference it is noted that

Cnivrdpi= 0

------ (22)

I

and c-

1

C niviv’ (23)

I -

3) LIOUID ION EXCHANGERS Liquid ion exchangers are used in the development of membrane electrodes which in their simplest form consist of a hydrophobic solvent base and dissolved ions. Of these, at least one species should be sufficiently hydrophobicthat it is effectively confined to the liquid ion exchanger. The other species may exchange with ionic species in solution. In addition, to manipulate selectivity, neutral ionophores are often present. Since the solvent base of the exchanger phase has a lowish dielectric coefficient considerable ion association is to be expected. The theory described above provides a general framework for treating such association in cases where a large number of equilibria occur. In particular it provides a means of calculating changes in phase boundary potentials when the composition of the aqueous solution is varied. Let a denote the species which is confined to the membrane. According to equation (16)

kTd Inna = 0 = (1 + Nza)dpa +

C Nzidpi

-----

(24)

i#a

This equation enables dpa to be expressed in terms of the other dpi . Now at equilibrium p: = fiz where p denotes electrochemicalpotential and where s and e respectively denote solution and exchanger phases. Hence

_____(25)

dP: - dP: = vced(4, - 4 s ) where e denotes the charge of a proton

Equations 22,23, and 24 enable dp: and dp: to be expressed in terms of the Hence an expression for d

(4 - 4 x)

in terms of the

di.

& may be obtained where the #

coefficients of the latter are given by combinations of the various N values for the two coexistant phases. Although the concept of phase boundary potentials is not strictly necessary for describing electrochemicalequilibria between coexistant phases in thermodynamicterms it can be useful in modelling membrane behaviour.

454

Progress in Ion Exchange: Advances and Applications

(4) ION EXCHANGERS WITH FD(ED SITES The question of interest in this section is “How to deal with fixed charges?” at a molecular level. Let 2 denote the fixed charges. One method is to regard them as uniformally distributed with a charge density p by treating them as a very large concentrationof mobile particles each having a very small charge v. In the limit that v ---->0 such particles do not contribute to the ionic strength of the system and their distribution is unchanged by the application of an electric field. A second more realistic method is to regard the fixed charges as occupying a rigid lattice In this situation it is clear that

N;1 = - 1 and that V1# = 0. Consequently, again species 1 does not

contribute to the ionic strength of the system also By writing

# N11 = -1

c

k ~ Ind nl = o = (1+ N ; )dpl + N & ~

____-_ (26)

i #

it turns out that all N,; = 0 even though there may be specific binding of some species by the fixed sites. It follows that thermodynamic properties can be discussed without explicit reference to the fixed charges. Despite this, binding of ions to the fixed sites will, in general, lead to non-ideality because of the influence of site binding on the

Ni;

#

and the Nki.In particular, equation 13 cannot be expected to apply. For the homoionic form of a fixed charge exchanger, when 2 denotes the counterion,

N2fi = N;1 = 0.Consequently N;2 = -1

*

and NT2 = N2,

+ -.v;

It follows

V., L

#

that the counterionsbehave ideally if V 2 = V 2 . Also if each fixed site is neutralised by #

a bound counterion, and all counterions are bound, then V 2 = 0 because some free counterionsmust be present if an applied field is to lead to a charge density distribution. This indicates that the Nernst - Planck equations are unlikely to apply to species which are bound to the fixed charges. (el IDEAL ION EXCHANGE BEHAVIOUR Consider an ion exchange material which contains but two counterion species, 2 and 3 and no coion species. Let No ,N2 and N3 be the amounts of solvent,species 2 and species 3 in a given amount of exchanger. At constant T and p these variables are suacient to determine the extensive state of the system including the Gibbs free energy. Hence (27) dG = podNo h2dN2 h3dN3

+

+

______

where h2 and h3are defined as the appropriate derivativesof G. It follows from equation 27 that at constant T,pand h,h2 and A3 are determined by the ratio n2ln3 in the ion exchanger.

455

Zon Exchange in Inorganic Materials and its Theory

It is this dependence that is of interest in studies of ion exchange equilibria. Let (33 be defined by 8 3

v3 =( 1 3 -p2 )

______ (28)

v2 v 3 h2 ) . At equilibrium it can be shown that 83 = (h 3 - v2 At constant T and p, the Gibbs - Duhem equation for the exchanger phase may be written as --- (29) 0 = Qdpo n 2 d 2 n 3 d 3 Since

+

&3 = d h 3

+

v3

(30)

I -

V?L

it follows that at constant T, p and

When n2v2+n3v3 does not depend on n2h3 and p2 and ~3 are given by p 2 = P!(T,P,PO)+

kTlnn2

-----

(32 a,b)

p 3 = p!(T,p,pO)+kTlnn3 we may integrate equation 3 1 to obtain

h2 =

+ kTln

--___-(33)

0 . where h2 is the value of h2for which n34.The corresponding equation for h3 is obtained by interchanging 2 and 3 in equation 33. Equation 33 is identical in form to the equations for the chemical potentials of athermal mixtures given by Flory-Huggins theory. In particular, the vi of the ions play the Same role as partial molar volumes. If equation 33 is not obeyed then neither also are equations 32a,b, in which case it is unlikely that the Nemst-Planck equations will give an adequate description of ion transport phenomena. This considerationin particular constitutes a strong case for regarding equation 33 as defining ideal exchange behaviour and suggests that charge fractions as used by Gaines and Thomas are preferable to ion fractions as concentrationunits.

456

Progress in Ion Exchange: Advances and Applications

REFERENCES 1) W.E Morf, The principles of ion selective electrodes and of membrane transport, Elsevier, Amsterdam, Oxford. 198 1. 2) J.G.Kirkwoodand F.P.Buff, J. Chem. Phys. 195 1,u.774. 3) D.G.Hall,Trans.Faraday SOC. 1971,67,2516. 4) D.G.Hal1,J.Chem. SOC.Faraday Transactions 2 1973,@, 1391. 5) D.G.Hal1,Advances in Colloid and Interface Sci., 1991,34,89. 6) D.G.Hal1,J.Chem. SOC.Faraday Transactions, 1991,87,3523. 7) G.L.Gainesand H.C.Thomas,J.Chem.Phys. 1953,2l, 7 14.

THE NATURAL CONVECTION IN THE DYNAMICS OF ION EXCHANGE AND SORPTION FROM SOLUTIONS.

V.I.Gorshkov and N.B.Ferapontov Department of Chemistry Lomonosov Moscow State University Moscow 119899 Russia

In the processes of ion exchange, sorption and desorption of electrolytes by ion exchangers, as well as any other processes of sorption and desorption from solutions m cohunns run under dynamic conditions, the densities of the solutions above and below the sorption fionts are Werent. These difFerences are more prominent in concentrated solutions and induce a natural convection (i.e. a spontaneous relocation of some portions of the solution due to gravitation). This phenomenon has never been taken into account m the analysis of sorption and ion exchange dynamics. Meanwhile, a number of facts revealed due to investigations of ion exchange from concentrated s o h t i m under dynamic conditions, of ion exchangers washing, of electrolytes sorption, as well as observations of the sorption boundaries' deformation under mtmption of the above processes have shown that, if the denser solution is above the sorption or ion exchange fronts m the column, this causes an additional spreading of the boundary [l]. The opposite relation of the densities is a factor stabilizing the sorption front. These facts will now be considered. Characteristics of the systems under discussion are given m Table 1, wherein: U*B - -y(l-x) y and x m the system 1-3 - are the equivalent fractions of A m ion x(1- Y) ' exchanger and solution respectively, c is the concentration, Ap is the Werence of the densities of the solutions above and below the front, v is the h e a r flow rate of the solution, R denotes the matrix with fixed ions. First consider the ion exchange processes. As a rule, ion exchangers have a substantial exchange capacity due to which the ion concentration m the ion exchanger grains isusually higher than that m the solution. This results m stabilization ofthe sorption boundary, moderation of the effects of various hydrodynamic k e g h i t i e s m the solution and usually allows the mtmption of the ion exchange processes for extended periods with no appreciable deformation of the sorption zones' boundaries [2]. The followingtwo examples are that of systems with convex equiliirium isotherms of exchange of the ion entering mto the column for the ions of the ion exchanger.

458

Progress in Ion Exchange: Advances and Applications

Table 1 7he Characteristics of the investigated Systems (I, 2,3 -Ion Exchange,&Ion Exchanger washing, 5 - Displacement of one Electrolyte by another). Characteristic Process l.KCI+NH&+ m c 1 + KR 2, BaC12+ CaRz + BaR2 + CaCh 3. CaCh + 2HR + CaR2 + 2HC1 4. H20 + KR,KCI-+ KC1 + KR, H20 5. KNO3 + KR,KCl+ KCI + KR,KNo3

a

AP

V

g,equiv/l 3.5

1.3

gicm-' 0.10

cm/min 5 + 30

0.5

4.0

0.15

6.5

4.0

XH <0.4;a= 1 x ~ > 0 . 4 ;a > 1

0.35

0.3

3.0

0.15

5 +40

3.0

0.06

7 + 32

C

During the ion exchange synthesis of KN03 [3-51 on the sulphonic cation exchanger KU-2x8, the K-form of the cation exchanger was obtained by the treatment NH,,-form with 3,6 N KC1 solution. This process was inibally investigated on laboratory columns with a fixed ion exchanger bed and in counter-current columns with alternating movement ofthe solution through a packed bed of ion exchanger and with relocation of the ion exchanger bed during short interruption of the sobtion supply. The treatment was carried out under natural direction of the solution flow i.e. fiom above downward, with the rate of 5-30 cm/min. In all cases the exchange was talcing place in theregimeof parallel transition of the self-Sharpeningsorptionfiont. During long continuoustests on a pilot unit with counter-current columns (d = 150 mm, H = 3,75 M), the characteristics of the process were the same as on laboratory columns. Nevertheless, during a 5 hour interruption of the process the boundary K' NI-L,' was spread to such extent that any further testing was meaningless. At the same time, when the KC1 solution was fed fiom the bottom of the column, no spreading of the boundary between K'and ions during one or two day process breaks was taking place. Moreover, as it appeared, extension of the sorption fiont in such a case decreased (in 1.4 +1.5 times for the rate of 14 cm/min) as compared to the solution moving fiom above downwards. A similar development was observed in the dqlacement of Ca2'-ions fiom KU2x8 ion exchanger wtth 0.5 N BaClz solution, fed from above in a column 4.0 cm in diameter and 166 cm high. Atter a 12 hour, the boundary between Ba2' and Caw spreaded considerably.On the other hand, when the BaCl2 solution was fed fiom below to a column containing the Ca-form of ion exchanger, there was no spreading of the boundary during interruption of the process. In both cases (K' and Ba2' - Ca2'), with convex exchange equilibrium isotherms, and reasonably high flow rates, the influence of natural convection was si@cant only during interruption of the processes, and not during the process with a high flow rate of the solution. Later, this phenomenon was specially investigated on the examples of exchange CaZ'H'and H'-Ca" on the K u - 2 ~ 8fiom 4 N solutions [13. The equilibrium of the exchange

m'

m'

459

ton Exchange in Inorganic Materials and its Theory

Ca2'- H'fiom 4 N chloride solutions with equivalent fiaction of H' fiom 0 + 0.4 was characterized by a linear isotherm and the separation coefficient a was close to 1.0, the Ca z+ ions being absorbed more intensively at higher H' equivalent fiactions. The results for a column with approximately 50 d of the KU-2x8 ion exchanger with a solution flow rate of 0.3 d m i n are presented m Figure 1. In the experiments 'la'' and "bb"Ca-form of ion exchanger was being regenerated with a HC1 solution, fed fiom above. The difference was only m the mtergrain space being filled initielh/ with CaC12 solution m the test "a", and with water m the test %". Comparingthe breakthrough curves shows that while m the first case the breakthrough curves are typical for the regenerationprocesses with isothenns of the descriied type, m the second case, as the result of natural convection a significant mixing leading to spreading of sorption boundary takes place immediately m the stage of displacement of water &om mtergrain space by the solution. Figures "lc" and "Id" show the breakthrough curves of the reversal process, 4 N HCI solution being present between the grains m the initialstate. When a denser 4 N CaC12 sohtion is fed m the column fiom above, the sorption fiont

-

C,NI

4l

a

4-

22

b

IyHC CaC1,

0

40

I

0

0

80

I

C

40

40

80

120

0

80

d

40

80

V,ml

Figure 1 Breakthrough curves of the ion exchangefrom 4 N solution on cation exchanger Ku-2~8.llre diameter of a grains are 0.25-0.50mm, the column's diameter is 20 mm. a - HCI + C d 2 (in 4 N CaCl2 solution); b - HCl + CaCI, (in water); c,d. - CaC12+HR (in 4 N HCC solution). Direction of the solution movement: a,b,c - from above downward; d - from below upward.

460

Progress in Ion Exchange: Advances and Applications

spread considerably, but when it was fed fiom below ("ld") a sharp sorption fiont is formed ( see back). These data show that, with nearly linear equiliirium isotherms and low solution flow rates, natural convection can have both negative or positive inthences. Considering now the processes of electrolyte sorption and desorption by ion exchangers and of %lacement of one electrolyte by another with no ion exchange (the counter-ions of ion exchanger and of electrolytes being the same). In such systems the concentration of sorbed electrolyte is usually lower than its concentration in the solution and consequently the stabilizing effect of the sorbent bed here is sigdicantly less than that of ion exchange processes, while the influence of natural convection is more sigdicant. Therefore, with sorption of an electrolyte having the same counter-ion by an ion exchanger which was initiallyin water, it is necessary to supply solution into the column fiom below, and when washing the ion exchanger to remove electrolyte, water must be supplied fiom above. As an example, Figure 2 shows the desorption fionts for KU-2x8 ion exchanger for water washing of 3,6 N KCl solution [ 5 ] . It is seen that, whde moving along the ion exchanger bed the fionts preserve their shapes as well as dimensions, their extension depending on the solution flow rate less than during the ion exchange process. Under alternate counter-current phase movement the fronts had practically the same shapesandextension as on the fixed bed.

Figure 2. The distribution of KCl concentratiom along the column height (d = 17 mm) during washing K-form KU-2x8 cation exchanger to remove 3.6 N KCl solution. a - 50 ml water passed (I - 8.2 ml/min; 2 - 40.3 ml/min), b - 120 ml water passed (I - 6.9 ml/min; 2 - 3 I . 0 ml/min), c - 190 mi water passed (1 - 6.6 m l/min; 2 - 43.5 ml/min), d. - 260 ml water passed (I - 7.8 ml/min; 2 - 27.7 mlmin).

Ion Exchange in Inorganic Materials and its Theory

46 1

From the practical application of ion exchanger pomt of view the formation of the self-sharpening fronts of electrolyte sorption and of ion exchanger washing is very important, as these processes can be carried out with minimum expenditure of solutions and a minimal waste outflow for the fjxed ion exchanger bed columns. A practically wasteless regime can be achieved when counter-mment COW are applied. Natural convection can facilitate organizing m continuous mode such rather subtle processes as replacing the electrolyte m contact with ion exchanger with another one of the same counter-ion. For example, m the work cited above [4], the K'-form of an ion exchanger was obtainedmKC1 solution, while for KN03 synthesis the ion exchanger must be m exchange problem that contact with KN03 solution. It was the KCI for - 0 3 appeared. This problem was solved m two stages: first, the ion exchanger was washed to remove KCI, and then the water was dqlaced by - 0 3 solution. This problem can be solved m a simpler way. A better absorbabihy of KN03,as compared to KCl, and a higher density of KNG solution with the same concentration provided the grounds to suppose, that when the K N 0 3 solution was moving fiom the below and through the K' -form bed of the KU2x8 cation exchanger filled with the KC1 solution, the formation of the self-sharpening fiont became possiile to a minor extent. Figure 3 provides an example of the displacement fionts m a counter-current column (2,3 cm m diameter) with alternate movement of KN03 solution fiom below, and of a packed bed of ion exchanger with KCl intergrain solution fiom above. In an experiment of several days, which was run with mterruptions and with changes of the solution flow rate, more than 1,s litres of KN03 solution were obtained. Under all conditions the fionts preserved their shape and dimensions slightly increasing with increase of flow rate. They were being slightly deformed during the ion exchanger's movement but were quickly recoveringunder renewal of the solution's movement [4]. Theoretical explanation of these results can be done using a onedimensional nonequiliirium diffusion model taking mto account the longitudinal mixing (axial dqersion) m the solution [6]. The longitudinal mixing coefficient m this model additively takes mto account various sources of deviation fiom the ideal displacement model such as a d diffusion, transverse heterogeneity, packing irreguhties, wall effects etc. If it is assumed that natural convection is one of this sources, then, under unfavorable r a t i o o f d d e s o f the enteringand the resulting solutions, itcontributes additionally to dspersion and acts m the same direction as the other fiont spreading factors. If the heavier solution is below the fiont, then natural convection stabilizesthe fiont and the correspondingcontributionto dtspersion becomes negative. Summary. If the densities of the solution being fed m the column, and of that imtdly filling the column (or of the resulting solutions), are dSerent, then natural convection arises. This results either m additional spreading of the sorption fiont (if the solution above it has a higher density than the solution below), or m self-sharpening of the sorption front (if the density ratio is inverse). The influence of natural convection increases with increases m the density dSerence of the solutions above and below the fiont,decreasing of the solution flow rate, decreasingof affmitv of ion exchanger to the substance entering mto the column, decreasing of the ratio of the total concentrationsof the being exchanged substancesm the solution and m ion exchanger, and increasing of the column diameter.

462

!

CsN

Progress in Ion Exchange: Advances and Applications

1

1

100

150

200 z,cm

Figure 3. 7%edistribution of C t -concentration along the height of the counter-current column (d = 23 mm, H = 2. 25 m) during the treatment of the packed bed Kform KU-2x8 in 3.O N KCl by 3.O N Kl?Oj solution beingf e d j - o m below: a. aster the movement of ion exchanger; b. after 80 ml KNO3 solution parsed. The rate is 22.4 ml/min. Apparently, increase of ion exchanger grain size, decrease of the solution viscosity and deviation of the column from vertical position will have influences in the same direction. For practical work, especdly with concentrated solutions, the process is to be organized m such a way, that heavier solution m the column were below the sorption fkont.

References 1..I.Gorshkov, N.B.Ferapontov, O.T.Gavlina, A.I.Novoselov, Ju.A.Kovalenko, 7th

USSR Cod. 'Use of Ion Exchangers m Industry and A n w c a l Chemistry', October 1-4, 1991, Voronezh, Abstracts, p.7. 2. V.LGorshkov, Teor.0snovy Khim.Tekhnol., 1970,4, p. 168. 3. V.I. Gorshkov, O.T. Gavlina, A.I. Novoselov et al., 'Theory and Practice of Sorption Processes', Voronezh, 1989,20,72. 4. V.LGorshkov, O.T.Gavlina, A.1.Novoselov et al., Khim.Prom., 1989, N 2, 35. 5. O.T.Gavlina, PhD Thesis, Lomonosov Moscow State University, 1990. 6. V.V.Rachb&i, 'Introduction in general theoryof sorption dynamics and chromatography',Nauka,Moscow, 1964,Chapter 3.5.

S W A T I O N OF MULTI-COMPONENT ION EXCHANGE DYNAMICS IN THE CASE OF DISSIMILAR DIFRJSMTIES.

N.A.Tikhonov, R.Kh. Khamizov, D.A. Sokolsky Department of Physics, Moscow State University V.1.Vernadsky Institute of Russian Academy of Sciences

1 INTRODUCTION Research on ion exchange between components with dissimilar diffusivities has led to the conclusion that a local electric field arises in the sorbent to equalize the incoming and outcoming ion fluxes 111. The models describing this phenomenon have been developed [ 1,2,3] and kinetic simulations carried out for a single sorbent particle or a shallow bed. These studies have succeeded in explaining the extreme shape of some kinetic curves. At the same time the effects caused by the electric field can be accumulated in long sorbent beds. The investigation of multi-ion exchange dynamics seems to be more interesting and promising than that of kinetics. This paper presents results of dynamic simulation. The particle diffusion model is analyzed and the simulation results compared with the experimental ones. New phenomena observed in simulations are discussed. Some experimental results are explained by means of simulations. 2 MATHEMATICAL MODEL Suppose an ion exchange column is loaded by a granulated sorbent and a mixture of dissolved substances passes through it. This model describes the sorbent grain as a homogeneous medium whereby diffusion, as well as sorption, takes place. In the presence of the electric field the flux of the i-th component can be described [l] by the Nernst-Planck equation:

dx'

RT

If we neglect the electric field the kinetics may be described by the well known equation:

where the mass-transfer coefficient pi is proportional to the diffusion one. If we supplement the model by the electric field we will have to take the last term in (1) into consideration and add a one more term into the kinetics equation (2) equal to aj(aj+~j)3ni where

Progress in Ion Exchange: Advances and Applications

464

‘r 3=

]E dx.

0.5 RT

0

Finally, the following model can be derived: aCi aCi aai E-+q-+-=O i = 1 , ...,N dt & a t

Using this model we have studied the ion exchange process in the systems with various parameter values, boundary and initial conditions.

3 SIMULATION RESULTS Since a number of parameters for the model are to be given we will omit their dimensions in the following text for the sake of brevity. In all instances the parameters are measured as: concentrations ai and ci in e v/l, time in min, geometric coordinates in cm, flow rate in cdmin, pi in min.-4. Parameters k, n, E are dimensionless. The parameters Pi, q, 1 may be combined in the equations into dimensionless groups PiYq, consequently the values of pi can be varied without any effect upon the simulation result so long as the value of q is varied proportionately. Thus the breakthrough curve depends, not on the values of pi coefficients, but on the ratios of the values. The values of other parameters in the simulation experiments were chosen in accordance with actual characteristics of some processes and sorbents. Simulating ion-exchange process, we mainly examined the impact of the electric field E on the micro component dynamics and the possibilities of application of the effects for solution enrichment. The electric field arising in an ion-exchanger is such, that the incoming and the outcoming fluxes are balanced by it. Consider the ternary system with two macro components and one micro component. If the value of the P-parameter of the incoming component is less than the one of the component being replaced, the field arises so as to increase the inward directed fluxes and the micro component is “drawn in” the sorbent. If an intensive exchange of macro components takes place in a narrow micro component zone of the sorbent bed, in comparison with the column’s length, then the concentration of the micro component within this zone will fall. It looks so as if a barrier appears that the micro component can not penetrate through and consequently accumulates in front of it. If the value of the p parameter is the largest one for the incoming macrocomponent a field arises to “push out” the micro component and its desorption increases. The authors believe the effects described above can be the cause of interesting processes. Let us demonstrate the effects by the results of several simulation experiments.

Ion Exchange in Inorganic Materials and its Theory

465

Let us consider a process which is proposed to enrich the solution with the target component (TC) by means of concentrating it within narrow zones of break-through curves. The process consists of two stages. During the first stage sorption of the TC takes place and the micro component is accumulated in front of the barrier. At the second stage the micro component is desorbed and powerfully forced out of the sorbent. As a result the break-through curve has a sharp peak. We chose the simulation pxameters as follows: 1=100; q=2; A,=2; ni = 1, 1, 2; ki=l, 2 1; p.-0.3, 0.01, 0.2; c/"'~= 1, 0, 0. The boun ary conditions at the first stage were C i b o u n d = ~ 1, 0.01 and at the second stage Cil""'~1, 0, 0 (ki=l, 2, 1 is the short form for kl=l, k2=2, k3=l. The same form is used for other indexed parameters). Figure 1 depicts the calculated results. The upper part of figure 1 presents the curves of concentrations ci and 3 value versus z at the moment t=100. The micro component is being accumulated in front of the barrier. The lower part of figure 1 presents the same curves but now referring to the desorption stage, at the moment t=160. The electric field has now the opposite direction compared with the fist stage and pushes the micro component out of the sorbent. On the c3 concentration profile two waves can be seen. The fist one, on the right hand side, of the plot is the same wave as on the first plot. Being driven by the electric field, the second one, which is in the centre of the graph, moves at a higher rate along the column. Before leaving the ion exchanger these two waves coalesce and form onelarge concentration peak. CJC,""

c3-

I .o 0.8 0.6

0.4

o.2f*/j. 0

0

25

50

?5

100

ciGrn= 1.0 0.8

0.6

0.4 0.2 0.0

- 0.2 - 0.4 - 0.6 - 0.8 - 1.0

0

Figure 1 Sorption and regeneration in the case when barrier appears

0

200

400

800

Figure 2 Two enrichment cycles

Thereafter the process of desorption can be continued and the initial conditions in the column can be restored. Thus a cyclic process can be organized. Figure 2 shows the curves ci(1,t) versus t for two repeated cycles such as described above.

466

Progress in Ion Exchange: Advances and Applications

The enriched solution of the TC can be extracted from the eluates corresponding to zones with peak concentration c3. The placements of these zones are fixed to the moments when sorption starts. Consider the process of TC accumulation in front of the barrier (this is the first stage of the process discussed above) described by the model (3). Suppose two univalent macro components (i=l,2) and a bivalent micro component (i=3) participate in the exchange. Let us denote the transfer rate of the TC concentration front in the absence of the electric field V3, the transfer rate of the incoming macro component V1 and of the outcoming V2 correspondingly. The system behaviour depends on the relationship between the transfer rates. In the first case to be considered V2V1. As the quantity of the accumulated TC increases the micro component increases its facility to penetrate through the barrier formed by the electric field. When the field can no longer hold the micro component the wave runs forward along the exchange column. Having let through a large portion of the accumulated mass, the field barrier stops the rest. The accumulation process continues. The break-through curve c3(l,t) has two peaks as a result.

c 3 0.05

0.04

0.03

0.02

0.01

0.00 80

120

I

Figure 3 Dissimilar curves obtained for the different relationships between the phase rates.

Figure 4 Experimental break-through curves and corresponding simulation curves

In figure 3 there are two simulation break-through curves illustrating this effect. The simulations correspond to the following sets of parameters: 1=100; q=3; Ac=2; ki=l, 4, 1; ni = 1, 1, 2; p, = 0.6, 0.03, 0.6; cYit= 1, 0, 0; c P d = O , 1, 0.01 in the first case when V2V1. The curves are

Ion Exchange in Inorganic Materials and its Theory

467

qualitatively different. The curve corresponding to the second set of parameters has two peaks whereas the curve corresponding to the fnst set is commonly observed.

4 COMPARISON WITH THE EXPERIMENTAL,RESULTS. The electric field strongly affects the ion-exchange process only under several conditions. In the first place the difference between the components' diffusivities should be large enough and the ratio of the phase rates should have an appropriate value. We have experimental results of desorption in the cation-exchanger. It is a Russian made inorganic cation exchanger based on mixed oxides of manganese and aluminum, which is similar to the well known exchanger y-MnOz (Japan) [ 5 ] . The sorption was carried out from sea water. The desorption was effected by nitric acid. The sorbent volume was equal to 20L. The sorbent was highly selective towards Li. The main cations contained in sea water are - in the order of diminishing concentrations - Na, Mg and Ca. We consider the dynamics desorption of these ions by nitric acid. In figure 4 the experimental results of desorption are demonstrated. The dashed lines correspond to the break-through curves observed for Mg, Ca and Li. The Na distribution coefficient is the smallest one and consequently this element is the first to come out of the column. For the sake of simplicity Na curves are not shown in the figure. The curves for Mg and Ca each have two peaks. That is unusual and cannot be explained by the usual ion exchange model. The special feature of the sorbent is it's large selectivity towards Li and especially towards H. The sorbent is two-phase . Bv.this term we denote a sorbent the grain of which consists of solid particles and channels between them. Inside the sorbent grain the diffusion takes place partly by internal solution in the channels. In this case, if the internal solution diffusivities di have a value of one and of the same order, the kinetic coefficients pi in the model (3) are significantly different, because the distribution coefficients are different (Piedi/ k?). The initial and boundary conditions, equilibrium constants of component phases, the column size, the flow rate, the sorbent exchange capacity and other parameters were chosen in accordance with the experimental data. The model parameter values were as follows: 1=100; 1~0.4;q=1; A,=0.27; ni = 1,2,2,1,1; ki= 1010:5, 1.85010". 3.5010" 1. 100; pi = 5010-~,3.3010-~,3.3010'~,1.16010-~,7.1010-~;aii"lt= 0.02, 0.1, 0.1, 0.05, 0. The concentration of components in sea water is: Ci= 0.4, 0.12. 0.016, 20lO-~.The index value 1 corresponds to Na, 2 to Mg, 3 to Ca, 4 to Li. 5 to H. To achieve more precise results the simulations were performed for the model (3) d2Ci supplemented by the term A in the transfer equation to provide for the

ax2

longitudinal convective diffusion in the solution. We have also taken into account the fact that some solution was poured off after the sorption stage. The boundary conditions for the nitric acid were taken in accordance with the experimental breakthrough curve shown in figure 4. In figure 4 the solid lines depict simulation results. We can a f f m that a satisfactory level of correlation between the simulation and experiment has been achieved especially if the system complexity is taken into consideration. This result allows us to explain the unusual character of the curves via the field influence. The fist peaks of the Mg and Ca curves are those common for desorption; the electric field arises to equalize the fluxes. Otherwise the incoming flux would be smaller, for the H kinetic parameter is sufficiently smaller than the other ones. The electric field influence upon bivalent ions is stronger than upon monovalent ones. As a result the concentrations of Mg and Ca in solution and their phase transfer rates fall. On the Li

468

Progress in Ion Exchange: Advances and Applications

break-through curves the peaks coincide with the minimums in the bivalent element curves. The partial blocking of these elements continues until Li is desorbed to a large degree. The field value then diminishes and the second peaks of the Mg and Ca curves appear. This qualitative analysis is based on the results of simulation. 5 CONCLUSION

The results discussed demonstrate that the electric field should be taken into account in some cases to describe the actual exchange systems adequately. The provision for an electric field in a model may quantitatively change the simulation results and allows one to explain such effects as the unusual and the two-peak break-through curves which were observed in experiments. The results show that the selection of components with appropriate values of kinetic parameters is a way to control the ion-exchange dynamics. Processes based upon the considered phenomena can be developed with the goal of enriching solutions with the target micro components.

Acknowledgments. This investigation was p e q r m e d with the financial support of the International Science Foundation ( grants N ND 2000 and ND 2300 ) and with the support of Russian Foundation of Fundamental Researchs ( project code 93-012-17 ).

Nomenclature t - time z - longitudinal coordinate in the column i - component number q(z,t) - concentration in solution ail - component local concentration in sorbent grain ai(z,t) - component content in sorbent per bed volume unit pi(z,t) -component content in equilibrium with solution per bed volume unit cFt - initial conditions CiboUnd - boundary conditions ni - ion charge ki - equlibrium constant in the mass action law Di - diffusivity pi - mass transfer coefficient q - solution flow rate A, - exchange capacity E - sorbent porosity E - value of electric field F - Faraday constant R - universal gas constant T - temperature

Ion Exchange in Inorganic Materials and its Theory

469

References 1. F. Helfferich ‘Ion Exchange’ McGraw Hill, New York, 1962. 2. Y.-L. Hwang. F. Helfferich. React. Polym., 1978, 5 , 237. 3. R. K. Bajpai, A. K. Gupta, M. G. Rao, AIChE J.. 1974, 20, 989. 4. R. Khamizov, D. Muraviev, A. Warshawsky, Zon Exchange and Solvent Extraction, ed. J.Marinsky and Y. Marcus, Marcel Dekker, Inc., New York-Basel-Hong Kong, 1995, 12, 3, 93. 5. K.Ooi, Y.Miyai, Sep. Sci. Technol., 1986, 21, 8, 755.

NON - ION EXCHANGABLE INTERACTION OF ELECTROLYTES AND ION EXCHANGE RESINS

V.I. Gorshkov, N.B. Ferapontov, L.R Parbuzina, HT. Trobov, N.L. Strusovskaya and O.T. Gavlina Department of Chemistry Lomonosov Moscow State Univemty Moscow 119899 RUSSia The concept of the sorption of water and simple electrolytes by ion exchangers now current m literature, is based on the concept of the quasi-homogeneity of a swelled ion exchanger gram and applies the Donnan model of the electrolyte distribution, m which the grain boundary is considered as a semipermeable membrane [1,2]. At the same time a number of experimental facts provide grounds for perceiving the distribution of componentswithin the ion exchanger grains as non-homogeneous. These are first the facts which confirm the existence of “free” and “bound” water (the results of mvestigations of the freezing temperatures of the water in ion exchangers [3], thermoanalytical [4] and thermogravimetrical [5] data, temperature dependencies of the heat capacity [6] and dielectric perrmttnay [7] of swelled ionits ), as well as calculations which show that distances between adjacent fixed ions along a polymer chain have less sigmficance than those between ions which are connected to Werent chains [ 81. We suggested [9,10] that an ion exchanger grain in equilibrium with electrolyte solution consists of two parts. One is an electrolyte solution identical to the external one, and the other is a polyelectrolyte solution. In an older work of Tye [111 the idea of two zones within the ion exchanger grain has been used to explain the unusual concentration dependenciesof the activity coefficient of an electrolyte adsorbed by the ion exchanger. The structure of the model that we suggest is shown m Figure 1. For convenience sake, m writing the equations of material balance the polyelectrolyte solution is considered to be composed of the following integral parts: a matrix with fixed ions, counter-ions, water and electrolyte. The inner volume of the ion exchanger column is divided into five parts: 1 - the ion exchanger matrix with fixed ions; 2 the counter-ions which compensate the polyion charge; 3 - the molecules of water and electrolyte adsorbed by polyelectrolyte; 4 - the electrolyte solution inside the ion exchanger gram and 5 the external electrolyte solution. The masses of these parts are respectively ml ,mz, m3, m and m5. The experimental determination of the model’s parameters was carried out at room temperature as follows. Frustums of cone shaped graduated columns with the top angle of 3” were used. In columns of this type the ion exchanger undergoes less destruction when swelling changes than in cylinder shaped columns. The design of the capillariesfor e n t b g and exitiag solutions allowed the easy disconnection and weighmg of the c o b , as well the complete replacement of the air from the space above and below the ion exchanger bed by the solution.

-

-

Ion Exchange in Inorganic Materials and its Theory

47 1

Figure 1 The model of ion exchanger grains in equilibrium with solution: I -polymer matrix with$xed ions; 2 - counter-ions; 3 - water and low molecular electrolyte in polyelectrolyte solution; 4 - electrolyte solution inside grains; 5 - external electrolyte solution.

Previous to the experiment, the mass M and the inner volume V of the empty column were determined. Then a sample amount, mm, of AR form ion exchanger ( A counterion, R matrix)with known exchange capacity E (mg.equiv.) dried to a waterless state by the proceeding provided m [12, p.861 was placed inside. It is clear that ~ A =R ml + mz. The ion exchanger was covered with distilled water and water was periodically run through up to the total swelliug of the ion exchanger. All the following operations were carried out at a constant volume of the system: ion exchanger solution. After equiliixium was achieved, the column was reweighed and the mass of the water calculated. In similar experimentswith electrolyte solutions the same method was applied to find the sum of m3 + m + m5 = m345. Then the ion exchanger was alternately taken to the equiliirium either with water or AX electrolytes solutions, changiug for each experiment the concentration and type of the electrolyte (X).In each experiment after the system was taken to the equilibrium the column was weighed and the solution @laced fiom the c o h was analyzed to calculate the quantity of electrolyte (Q, mg.equiv) m the column. Having completed the experiments with the AR-form ion exchanger, it underwent transformation m the c o b mto another ionic fonn, BR, and experiments with the BXelectrolytes solutions were carried out. Simultaneously, the same experiments with an independently prepared dehydrated BR-form ion exchanger were being carried out m another column. The coincidence of the produced results confirmed the thoroughness of the ion exchangers dehydration, as well as immutability of their properties after a Series of experiments. For each experiment the effective volume V* = Qlc was calculated which the electrolyte would occupy if its concentrationwere equal to the concentration c of the external solution. The volume V’ is the similitude of the “retention volume” m the liquid chromatography.

-

-

-

472

Progress in Ion Exchange: Advances and Applications

Figure 2 Plots of v“ versus equilibrium solution concentration. Anion exchanger A V-I7x8 in Cl-fom For all systems the volumes V* were always bigger than those of the fiee intergrain space (to be exact bigger than V,) and in some cases exceeded that accessible for liquid volume (V345 ) in the column (the inner volume of the column without dry polyelectrolyte) (Figure 2). The effective redundant amount of water in ion exchanger (nmo) was calculated (moles per one g.equiv exchange groups);

pi - the density of electrolyte solution with concentration c.

To evaluate possible changes of the partial molar volume of water with its interaction with ion exchanger, simultaneously the calculation of nHzowas carried out based on the volumes:

VJ = v - v,

- v’ ;

and

nHzOv = pmo VJ/ 0.018E

(2)

The asterisks (m or V) in (1) and (2) are used to denote the method of calculation of nmo. For the overwhelming majonty of the investigated systems in a wide range of concentrations( fiom 0.01 N up to 6 N) the Werences between m o r n and nmov (pmo = 1.0 g/cm3)were within the error of method (i.e. 9-1 1%). Only in the equilibrium of H-form sulphonic cation exchangers with acid solutions with the concentrations above 2 N, were these differences (nJV< nJrn) beyond the limits indicated. This was due to the decrease of partial molal volumes (and increase of the “apparent” densities) of the first and the second molecules of water bonded by the -S03H exchange group. The calculation of the average density of the first two molecules of water based upon our data (the differences n3 rn and n3’) provided plz = 1.5 g/cm3, which was not far fiom earlier data [13], providing pl = 1.8 g/cm3 and pz= 1.4 g/cm3. The values obtained horn the mass balance are used in further calculations.

473

Ion Exchange in Inorganic Materials and its Theory

‘5:

m on’ llequi

0- NH,NO,

A-

NaCl

I-

Figure 3 Dependencies nHm =f(c) for A V-17x8 anion exchanger

The dependencies of nmo upon the concentration c of an equilibrium solution for C1and NO3 forms of strong base AV-17x8 anion exchanger are presented m Figure 3. For each ion form, a set of uniformly down sloping curves starting fiom the same initial pomt have been obtained. Some of the systems have curves passing, to some extent., through the area of negative nHzovalues. This reflects the fact that, for certain concentrations, the ratio of the mole quantities of the electrolyte and water m the ion exchanger grain is above that of an equiliirium solution (ie. the concentration of electrolyte m the grain is higher than that m the solution). These results, as well as those for other systems [14] show that the propensity to penetrate mto the ion exchanger grains varies for Merent electrolytes. The quantity of water m the polyelectrolyte solution changes as well. Of special import is the fact that the higher is the concentrationthe stronger are the distinctions. The analysis of the results obtained at equiliirium with sulphonic cation exchangeas shows that, unlike the dependencies nmo = qc), the dependencies nmo = flaw) for different co-ions, where a,., is the activity of water m equiliirium solution, m many cases are the same as those for the same ionic form (Figure.4). Moreover, they perfectly coincide (within experimentalerror) with the nmo = qP/p.) dependencies for water sorption fiom the vapour phase, obtained by the isopiedc technique (p is the vapour pressure ,p. is saturated vapour pressure at the same temperature). Something similar has been pointed out for several systems [8]. This results mean that the quantity of water bound by the given ionic form of ion exchanger depends only upon the activity of water m an equiliirhm solution or in vapour, also supporting the suitability of the heterogeneousmodel. Unlike the results obtained for cation exchangers, the investigation of equiliirium with anion exchangers shows that, m most cases, the molecules of electrolyte penetrate fiom equiliirium solution mto polyelectrolyte solution (mto the volume VIz3).In such cases the calculationbased on equation (1) gives low values as compared to the isopidc, or even negative values of nmo. To directly determine the quantity of the adsorbed electrolyte, ie. that passed into polyelectrolyte solution, as well as that of water m this solution, the followingtechnique

-

-

-

474

Progress in Ion Exchange: Advances and Applications

1.00

0.95

0.90

0.85

a

w

Figure 4 Isotherm of water sorption by K-form of sulphonic cation exchanger KU-2x8. Points - sorptionfiom solution; lines - isopiestic data: I - of f15J 2 - of [16] has been developed. A large amount of ion exchanger (approximately 1000 ml ) was used in these experiments. Through the column with AR ion exchanger in equilibrium with sorbing electrolyte AX of known concentration, a solution of the AY electrolyte unable to penetrate in the polyelectrolyte sohtion is mered. The breakthrough curves obtained are similar to the ones shown on Figure 5. Their unusual shape can be explained as follows: being displaced by the AY solution, the AX solution of the initial concentration in the volume V45 is the first to leave the column. The adsorbed electrolyte's molecules (or ionic pairs) being present in the volume V3 , and at equilibrium with the AX solution, can pass into the volume V45 only when the latter's composition is changing. Such a process begins upon substitutionm the volume V45 of the initial solution for the AY solution. If the activity of water in the AY solution is less than in the AX solution, it also results in a partial desorption of water fiom the volume V3. Both processes take place simultaneously.

Figure 5 Breakthrough curves of 2.5 N HCI solution displacementporn the column with anion exchanger AV-I 7x8 in CI-form by 3.4 N solution KCI. E =I670 mg.equiv, solutionjlow rate I mUmin

Ion Exchange in Inorganic Materials and its Theory

475

Consequently, the total concentration of the solution m the transitional mne increases (due to desorption of the AX), and the concentration of the displacing AY solution within this zone becomes lower than that of the entering solution, due to its dilution with the water desorbed &om the volume V3. Finally, the ion exchanger attains equilibrium with the AY solution. The second plateau of the breakthrough curve is evidence of the existence of two zones m ion exchanger with difFerent concentrations of electrolyte. This confirms, once more, the substantiahy of the heterogeneousmodeL The position of the V1 boundary gives a clue to finding Vq5for the equiliirium of ion exchanger with the AX solution, as well as the amount of the AX m polyelectrolyte solution. Knowing the volume V45 (found as above), the total volume of ion exchanger, and that of the solution m the column, it is possible to find V3 v3 =

v - VAR - v45

(3)

There are water and electrolyte present m this volume, the amount of the latter can be calculated either as the function of the space under the second plateau of the breakthrough curve, or as that of the remainder 93 = Q cv45 (4)

-

Then, using the “apparent” molar volumes of electrolytes 1171, it is possible to h d the volume VC1occupied with the electrolyte, and afterwardsthe volume of water; v3mo =

v3

- V3d

(5)

The latter being found, it is possiile to find nmo as:

From these data the quantity of the molecules (or equivalents) of electrolyte per one exchange group of polyelectrolytem can be found as:

n” = q 3 ~

(7)

and M e r the concentration of electrolyte m polyelectrolyte solution m any concentration scale calculated. The error of the method is within 10% for nmo, and within 15%for ncl. Some of the results obtained m the study of water and HCl sorption by the C1-form of AV-17x8 anion exchanger with the exchange capacity of 1670 mFequiv, the above technique being applied, are presented m the Table 1. As the data of Table 1 shows, the vah~esof nmo are close to the isopiestic ones. Therefore the sorption of electrolyte does not affect the amount of water m polyelectrolyte solution. Firstly, this result conkns that nmo for the given AR depends only on the activity of water m an equiliirium solution. Secondly, it provides a way of calculating the electrolytesorption 43 and the concentration of electrolyte m polyelectrolyte solution fiom results obtained by applymg the technique described m earlier parts of this paper, and upon the dependenciesnmo = 4aw which are found for the equiliirium with an unadsorbable electrolyte solution, or by the hpiestic method. )7

Progress in Ion Exchange: Advances and Applications

476

Table 1 The results of equilibrium investigation of HCI-solutions with Clform of anion exchanger A V-I 7x8 (E = 1670 mgequiv)

q45, mg.equiv

~HZO,

mg.equiv

exp.

nH200, isop.[l5]

q3, mg. equiv

n"', exp.

202 5 15 710 963 1261 1282 1476 1488

180 391 500 686 827 867 992 995

7.5 7.4 6.6 6.6 6.8 6.7 6.6 6.7

8.2 7.8 7.2 6.9 6.7 6.5 6.3 6.3

21.6 124 210 277 403 414 484 493

0.01 0.07 0.13 0.17 0.23 0.25 0.29 0.30

Q, 1 2 3 4 5 6 7 8

0.48 1.04 1.50 1.72 2.10 2.18 2.48 2.50

0.97 1.05 1.50 2.44 2.10 2.44 3.04 2.52

The formulae for these calculations, as well as the results of investigation of the influence of various factors on the sorption of electrolyte have been previously pubhhed

I.

Only some general patterns will be further described.

Anion exchangers adsorb electrolytesto a higher degree than cation exchangers. This is due to the larger size of fixed ions of strong base anion exchangers when compared to the

sulphonic groups of cation exchangers. More exactly the positive charge on nitrogen happens to be screened by methyl groups in contrast to the negative charge of oxygen in sulphonic group. Therefore the electrostaticinteractionbetween fixed ions and counter-ions is characterized by a lesser energy in case of the anion exchangers, the counter-ions of anion exchanger thus having more possibility to interact with co-ions. In this case the larger the size of counter-ion, the greater the corresponding ionic form's ability to adsorb electrolyte. Thus for different ionic form of anion exchangers this abhty to adsorb electrolytes increases in the next sequence: RCl < RBr < RI < N O 3 ; for cation exchangers the similar sequence is: HR < NaR < KR. The co-ion has one of the most influential factors in the sorption of the electrolyte, the lesser is its size and bigger its charge, the greater is the energy of its interaction with the noncompensated charge of the counter ion of polyelectrolyte. Thus for the same ionic form of anion exchanger, for example C1-form, the sorption changesin sequence: HC1 >CaClz mMgClz > LiCl>NaCl>KCl. With the increase of solution concentration the sorption of electrolyte always increases, because the amount of water in V3 which hydrates the exchange group decreases, and interaction between counter ion of ion exchanger and co-ion is facilitated. The differences m amounts of water and electrolyte m polyelectrolyte solution have a great influence on the form of the breakthrough curves in processes of @lacement of one electrolyte by another one. If ion exchanger was in equilibrium with the more adsorbed electrolyte, than the +lacing one, the zones of these electrolytes overlap and there happens to be a part of the breakthrough curve with increased summary electrolyte concentration (Figure 5).

Ion Exchange in Inorganic Materials and its Theoy

477

In the reverse process, when the less adsorbed electrolyte is being cllsplaced by the more adsorbed one, the summaq concentration m the mixture mne is less than the concentration of @lacing solution (see Figure 6). If the ion exchanger bed is sufficiently h&, the mne of the @lacing and the being @laced electrolytes will separate and an mterlayer of water will appear between them.

Figure 6 Breakthrough curves of I . 0 N CaCl, solution displacementfrom the column with anion exchanger AV-17x8 in Cl-fonn by 1.0 N HCl solution.

Figure 7 Breakthrough curves of 3.5 N solution of HCl and CaCl, mixture separation in the column with A V-17x8 in Cl#orm. &change capaciv 1270 mg.equiv. a j?onial separation, b - displacementseparation

478

Progress in Ion Exchange: Advances and Applications

The considerable distinctions m the amounts of the adsorbed electrolytes create a startiug point for developing a new method of electrolyte mixture separation. Unlike the ion exchange methods, this method does not require awalllLIy reagents and needs no special expenditures for the ion exchanger regeneration. The higher is the concentration of electrolyte m the solution being processed, the higher is the productivity. The breakthrough curves for the separation of 4N mixture solution of CaClz and HCl (m 1:l proportion) are presented on fig. 7. A more detailed description is provided m reference [19].

This work have been carried out with the financial support of the Russian Foundation for Fundamental Research. References

1. F. HeHerich, ‘Ion Exchange’, McGraw HiU, New York, 1962,part 5.3. 2. ‘Ion Exchangers’, ed. Konrad Dorher, De Gruyter, Berlin, New York, 1992,parts 1.1.3; 1.2.3. 3. E.A. Krilov, E.N. Tarasova, ’Thermodynamicof organic compounds’, Gorkq 1982, 88 (m Russian). 4. J. Inczedy, J. Thermal. Anal,, 1978,13,257. 5. Ju. M. Marchevskaya,O.D. Kurilenko, Zh.Phis. Khim.,1965,39,2849. 6. I.B. Rabmovich, E.A. Krilov, E.Ju, Ovchinnikov, C.C. Zarudneva, ’Thermodynamic of organic compounds’, Gorku, 1979,N 8,88 (in Russian). 7. G. Dickel, K.Bunzl,Z. Phys. Chem., N.F., 1966,51,13. 8. L.K. Arhangelsky, ‘Ion exchange and Ionometric’, ed. B.N. Nikolskii, Leningrad, 1976, issue 1,89. 9. N.B. Ferapontov, V.I. Gorshkov, 7th USSR Cod. ‘Use of the Ion Exchangers m Industry and A n w c a l Chemistry’, October 14,1991,Voronezh, Abstracts, 155. 10. N.B. Ferapontov, V.I. Gorshkov, H.T. Trobov, L.R Parbuzina, Zh. Phis. Khim.,1994, 68,1109. 11. F.L. Tye, J. Chem. Soc.,1961,4784. 12. N.G. Pohmky, G.V. Gorbunov, N.L. Polianskaya, ‘Methodsof investigationof ion exchangers’, Chemistry, Moscow, 1976. 13. G.E. Myers, G.E. Boyd,J. Phys. Chem., 1956,60,521. 14. I-LT. Trobov, PhD Thesis, Department of Chemistry, Moscow State University, 1994. 15. G.E. Boyd, B.A. Soldano, 2. Elektrochem., 1953,57,N 3,162. 16. L.V. Kustova, PhTl Thesis, Department of Chemistry, Moscow State University, 1969. 17.H.S. b e d , B.B. Owen, ‘The physical chemistry of electrolytk solutions’, second edition, revised and enlarged, N.Y., 1950, part 8.5. 18. L.R Parbuzina, H.T. Trobov, N.B. Ferapontov, V.I. Gorshkov, N.L. Strusovskaya, O.T.Gavha. This volume. 19. N.B. Ferapontov, H.T. Trobov, V.I. Gorshkov, L.R Parbuzina, N.L. Strusovskaya, O.T. Gavha. This volume.

INFLUENCE OF THE NATURE OF THE CO-ION ON THE EQUILIBRIUM DISTRJBUTION OF ELECTROLYTES BETWEEN THE SOLUTION AND ION EXCHANGER

L.RParbuzha, H.T.Trobov, N.B.Ferapontov, V.I.Gorshkov, N.L.Strusovskaya, 0.T.Gavlina Department of Chemistry Moscow State University Russia 1INTRODUCTION

Results concerning experimental study of molecuIar sorption of low molecular electrolytes by ion exchangers are presented. The term “sorption of electrolyte” will be defhed as the penetration of electrolyte mto polyelectrolyte solution. Unlike the wen known mvestigations m the field, we use the formerly mtroduced heterogeneous model of the resin grain (for more detail see the earlier communication [1,2]; Figure 1.) We suppose, that there are two phases which compose the resin grain m equilibrium state with electrolyte solution: 1) a low molecular electrolyte solution identical to the external equilibrium solution, and 2) a polyelectrolyte solution with polyelectrolyte, water and electrolyte as its components. 2 EXPEIUMENTAL

Having studied a large number of the ion exchange resin - solution systems, we may split them now mto two groups, the first one embracing the systems wherein a low molecular electrolyte does not penetrate into polyelectrolyte solution, and the second one, where penetration does occur. For the 1st group, the mole quantity of water m polyelectrolyte solution per one gram equivalent polyelectrolyte exchange groups (nm) was found to be equal to that at equiliirium with the vapour phase at p/p. = aw (aw is the water activity of equilibrium solution). The 2nd group systems, as the results of sorbed electrolyte content direct dehition experiments (see [1,2] for description of procedure) showed, have the same quantity nmo of water m polyelectrolytesolution. In all the cases, n m for a particular ionic form is subject to the water activity m e q u i l i i d solution or vapour. This made it p o s i l e to work out a procedure of determiniug electrolyte content m polyelectrolyte solution. Unfortunately, we cannot use the literary data &om early work about electrolyte sorption for dehition of the heterogeneous model parameters, because this data includesinformation only about general water or electrolyte content and average concentrationsm ion exchanger. Our calculation of electrolyte content q3is based on the following equations: mu5

M - m ~ ; mSm0 = m345 m3m0 QI&,,; 43 = Q - 445 ; 445 = cV45; =

-

-

m3Hzo = 0.018E nmo; /(pi c h z , /1000) ; v45 = m45 n”’ = q 3 ~ ; m = q31m3~.

-

480

Progress in Ion Exchange: Advances and Applications

Figure 1 The model of ion exchanger grains in equilibrium with solution: I -polymer matrix withfixed ions; 2 - counter-ions; 3 - water and low molecular electrolyte in polyelectrolyte solution; 4 - electrolyte solution inside grains; 5 - external electrolyte solution. Herein: c is the concentration of the equilibrium solution, g.equiv.il; Q is the quantity of electrolyte in the column under equilibrium with the solution, mg.equiv.; M is the mass of ion exchanger and of equilibrium solution in the column, mm is the mass of dry ion exchanger m A form; E - the ion exchange capacity of resin in the column, mg.equiv; miH2' and qi are the mass of water and the electrolyte content in the volume Vi ;n m and n"' are the mole quantity of water and the number of electrolyte equivalents in polyelectrolyte solution per gram equivalent exchange groups under the given concentration of the equilibrium solution; Muly is the mass of the electrolyte equivalent; pi is the density of equilibrium solution; m is the electrolyte molality in polyelectrolyte solution. The composition of polyelectrolyte solution (n") can be found by determining the following : 1) the mass of the column with an ion exchange resin at equilibrium with electrolyte solution of given concentration and mass of the ion exchanger present; 2) the content of electrolyte in the column at equilibrium, 3) the ion exchange capacity of resin in the column. The nmo value can be taken from a water sorption isotherm for the ionic form of resin, obtained either from equilibrium with solution of unadsorbed electrolyte or from isopiestic data. Experimentalerror for n"' value is 10-15%. Presence of electrolyte sorption is shown in Table 1. We have investigated a large number of systems containing solutions (0.1 6.0 M) of various electrolytes and polyelectrolytes (cation and anion exchangers of various ionic forms and varying in degree of cross-link as well). Below, the experimental results of the investigation of electrolyte sorption by KU-2 and KRS polystyrene sulphonic cation exchangers with 2,4,5,8,12 and 20% content of cross-linking agent (DVB)in H and K forms and by strong base AR4 and AV-17 anion exchangers, contiking ternary ammonium base as fixed group, with 4,8,12 and 20% DVB in NO3 - and C1- forms are

-

-

given.

48 1

Ion Exchange in Inorganic Materials and its Theory

Table 1 Presence (+) or Absence 6) of Electrolyte in Polyelectrolyte solution Cation exchangers KRS or KU-2, % DVB Electrolyte KOH KCl KBr

Ionic form

K+

KI

mo3

&so4

H+

HCl mo3

2

4

5

8

+

-

+

+

+ + +

+

+

+

-

+ + + +

+

+

-

-

+

+ +

+

+

Anion exchangers ARA or AV-17, % DVB Ionic 4 8 12 form

NHaN4

NOi

+ +

+

Cl-

+ + + +

+

KC1 CaCh m c 1 HCl

+

-

+

+

-

+ +

-

Electrolyte

mo3

12

+ +

+ +

+

20

-

+

+

3 DISCUSSION

As the experimentaldata provides, the electrolyte sorption depends on: a) the concentrationof solution m contact with the exchanger; b) the nature of polyelectrolyte(either cation or anion exchanger, the cross-linking degree); c) the nature of counter-ion; d) the nature of co-ion. In all cases studied, the sorption of electrolyte increases as the solution concentration increases (see Figures 2-5). In the course of the equiliirium between electrolyte solutions and strong base anion exchangers study, a sigdcant sorption of electrolytesby polyelectrolyteshas been n o t i d This is the main distingukhmg feature of the sorption properties of the anion exchangem being studied fiom those for cation exchangers (see Figure 2). This phenomenon m a y be explained by the anion exchanger having positive charged fixed ions of huge size m the comparison with the sulphonic groups of a cation exchanger. Hence, the pure ion-ion mteractions between fixed ions and counter-ions have a lesser energy. Consequently, counter-ions of anion exchangers are more apt to interact with electrolyte ion pairs m solutions. As far as the degree of cross-linking& concerned, the electrolyte sorption is subject to the lesser energy case . At low cross linking (I 4% DVB), all the

Progress in Ion Exchange: Advances and Applications

482

I:

)$ HCI

I 0.02

I

/

n v

1

2

3

C,N

0

2

4

6

C,N

Figure 2 Isotherms of electrolyte sorption by K- form of K R s - 1 2 ~(a) and CI -form of A R t t - 1 2 ~@) (C,N - concentraion:Normalityl low-molecular electrolytes studied were sorbed by anion exchangers, whereas at high cross-link (20% DBV) thisproved to be true only for acids. Let us consider the influence of the nature of the counter-ion. So far as cation exchangers are concerned, a considerable sorption is noted for the K- form, whereas for anion exchangersthe same is true for NO; -form (see Figure 4). We suggest that the NO3 ions have greater uncompensated charge in comparison with CT because of their greater size and consequently have less interactions with a fixed ion. The electrolyte sowtion by cation exchangers of various ionic forms is as presented below (see Figure 4).

0.041

Y

J

Figure 3 Isotherm of electrolyte sorption by KU-2x8 (a) and A V-I 7x8 (b)

ton Exchange in Inorganic Materials and its Theory

Figure 4 Isotherms of eIectro&te sorption by K -fonn of KU-2x4 (a) and CI -form Of M - 4 p (b) a 1.0

AV-17x8

0.8

0.6

0.4

AQA-20P

0.04.

0.2

0

Figure 5 Isotherms of sorption of HN03 by anion exchangers (a) and cation exchangers (b)

483

484

Progress in Ion Exchange: Advances and Applications

a6

4

2-

0

2

4

m

Figure 6 Isotherms of acid sorption by A V-17x8

The influence of the nature of the co-ion on electrolyte sorption is much more pronounced (see Figure 5). Among the anions studied (sorption by cation exchange resin), the nitrates have the best sorption properties ,the next in order are iodides, bromides and chlorides. Among the cations (sorption by anion exchange resin) the proton is most prominent for its sorption properties. This is most probably due lo the small size of proton. The ion with the least absorbability is K'. The other cations f d into the following order: K'
<m'

-

Ion Exchange in Inorganic Materials and its Theory

485

This work have been carried out with the financial support of the Russian Foundation for Fundamental Research. References 1.

V.I.Gorshkov, N.B. Ferapontov, L.R Parbuzina, HT.Trobov, N.L. Strusovskaya,

0.T.Gavha (this volume). .2. N.B. Ferapontov, V.I. Gorshkov, RT. Trobov, L.R Parbuzina, Zh Phis. Khim., 1994,68,1109. 2. K.A Kraus and G.E. Moore, J. Am. Chem. Soc., 1953,75, 1457. 3. F. NelsonandKA Kraus, J. Am. Chem.Soc., 1958,80,4154. 4. N.B.Ferapontov, HT.Trobov, V.I. Gorshkov, L.R Parbuzina, N.L. Strusovskaya, 0.T.Gavlina(thisvolume).

MULTICOMPONENT COUNTER-CURRENT ION-EXCHANGE CHROMATOGRAPHY

N. P.Nikolaev, V.k Ivanov and V.I. Gorshkov Department of Physical Chemishy Moscow State University 119899 Vorobievy Gory Moscow, RUSSIA

1. INTRODUCTION

Theory of multicomponent chromatography has been successfuyr advanced since 1943 when DeVault' descnied the behaviour of species being separated m a fixed-bed column by using dif€erentialbalance equations. One of the most progressed models of thistheory is the equiliirium model with plug flows. The model is based on the assumptions both of a local equilibrium between components m the phases (at any time at all pomt of the column) and the absence of axial diffusion (dlspersion) m the column. The most comprehensive presentation of the theory was by Helfferich and Kleh?. The equiliirium theory allows the description of the species distriiution mto the chromatographic column as well as m the ef€luent. By this approach it is possile to estimate some characteristics of the fractionation process and to avoid numerous experiments. Rare attempts of such estimations have been reported3, they have shown the high accuracy of these predictions. The multicomponent chromatography theory is mamly advanced for the fixed-bed column while it is known that the use of counter-current contactors offer few advantages over the fixed-bed columns4. The counter-current chromatography technique allows continuous separation, and so diminkh the size of ion-exchange columns and auxiliary equipment. The resin, and solution escaping fkom the column, have constant composition which decreases the amount of waste produced and, m certain cases, makes the process completely wasteless. We will consider estimation of the separation process characteristics by the example of strontium recovery from high-concentrated sodium chloride solutions (like natural brines) containing calcium. Experimental realisation of this task by using counter-current columns has been recently reported5. A three-stage process (fiontal separation of strontium,calcium, and sodium ions- elution strontium from the resin- regeneration of the ion-exchanger) operating m continuous mode has been performed by using carboxylic type cation-exchange resins. It has been shown that the frontal separation stage occurs with the formation of steady-state sorption fronts m the column. Strontium has been enriched up to 4 times in the column and has been separated from calcium. Product solution has been removed from a wide zone with purified and concentrated strontium which has been formed m the column.

lon Exchange in Inorganic Materials and its Theory

487

The influence of both the species concentration m initial solution and initial resin compositions as well as of the s e l w coefficients on the characteridcs of the fiontal separation stage will be outlinedhere. 2. THEORETICAL BACKGROUND

Features of the fiontal separation process of a multicomponent solution m a column have been described m the literature, e.g2. When percolating solution through an ionexchange resin bed the species are redidbuted (separated) m the column and the plateau (equilibrium) as well as the transition (sorption fiont) zones appear. The fractionation process m the counter-ament column can be carried out as long as wished if the flows of the solid and the liquid phases are held such that the first (related to solution d e t pomt) sorption front stays stationary about the c o b walls. For the process under consideration strontium concentration mcreases and that of calcium decreases (m certaia cases to zero) m this t r d o n m e . Strontium accumulates m the column due to propagation of the second sorption fiont along the column co currently with solution (see Figure 1). The accumulation flow (flow density) of the product species (strontium), PA,is defined as:

where L E p c o and S I (1 - x)wmo - flows of total concentrations with liquid and solid phases m the pomt of solution iulet (z = 0); co and mo - total species concentrations m liquid and solid phases per unit of the phase volume; v and w-linear velocities of solution and resin; x- void fraction; Xsr,o and ysr,o equi.alent fractions of strontium in the initial solution and treated resin at the pomt of solution iulet (z = 0), respectively; z- coordinate along the cohlmn. After a wide zone of purified and concentrated strontium was fomed,the solution enriched by strontium was collected from the middle part of the column (Figure Ic). The product flow has to be such that both Sorption fionts stay stationary relative to the cohunn WaIls. The equations for the sum of two-charged ions and of strontium at these steady-state conditions are following:

-

where P-product flow; subscripts 0 and P refer to the inlet solutions and product collection points. In equation (2) it is assumed that the product beiug collected contains no calcium (Xsr,,p>> xc4p). From equations (1) and (3) it can be seen that limited output of strontium (pXSr,p) is equal to the accumulation flow (PA) m the non-collection mode. The relationship between the species concentrations m the phases at the solution inlet pomt can be described by an isotherm equation, e.g:

488

where a:;

Progress in Ion Exchange: Advances and Applications

- separation factor. The equations set (2)-(4) can be rearranged as:

It has been that when recovering strontium from h&-concentrated solutions of sodium chloride (1-2.5 M) on the carboxylic cation-exchanger KB-4 the separation factor uca= 2.5 and the limited degree of strontium recovery (r=0.6) was independent of Sr strontium and calcium ion concentrations in the inaialsolution. The balance equation for the column section surrounding the first steady-state soqtion fiont can be written as:

which can be reduced, by using the (l), (3) and (5) equations, to the following:

where q , = xsr,

/ xsr,o and qy

= ysr,

/ ysr,o the degrees enrichment

the liquid and the solid phases, respectively. Sincea;:

of strontium in

>1, it is seen fiom equation (7) the qy

value is larger than qx. This means that strontium is concentrated in the resin phase rather than the solution. Moreover, considering that ysr,o > xSr,O it can be said that strontium bemg collected by the resin phase should be more concentrated than that collected in solution. Nevertheless, resin collection operation is more complicated than solution withdrawing. It has been shown7 that effective fiontal separation can be made when the initial solution is treated by the resin m mixed Na,Ca-form (uncompleted regeneration condition). This allows the reduction of the amount of NaCl used in the regeneration stage. In this case the calcium impurity will appear in the zone of concentrated strontium ( X C ~ , ~on ) the frontal separation stage. Nevertheless, strontium can be both enriched and completely removed from the solution being treated7. The equation for sum of the two-charged ions in this case is more complicated than (2) and can be written as:

where subscript H refers to the point of the resin inlet into the column. The expression for

Ion Exchange in Inorganic Materials and its Theory

489

H

0

I

'Sr

.

- -> I

C

0

Z

a,

H

Figure 1. Distribution (according to the equilibrium model) of strontium and calcium ions along the counter-current column at drfferent times: t = 0 (a); t > 0 (b) and (c).

limited degree of strontium recovery can be obtained by transformation of the equations set (3)s (4) and (8):

490

Progress in Ion Exchange: Advances and Applications

It can be show that, when increasing the Y C ~ H value, the denominator increases faster than the numerator and r decreases with the rise of calcium concentration m the initial resin. It is seen that consideration of the muhicomponent chromatography problems by using only integral balance equations gives limited information about the characteristics of the technological process. A more effective approach is to discuss the problem by using differential balance equations together whh the above considerations. For steady-state sorption fronts (which are considered m the equilibrium model as abrupt) the task can be formulated in terms of balance equations m finite mcrements (integral) form2". Taking mto account the coherence condition2(ie. the synchonisation of the concentration profiles of all components) the balance equation can be written:

where L,g = dv - ukk+l)co and sc = (l-xxw + ukk+l)mo - flows of total concentrations with liquid and solid phases m coordinate system related to the sorption front4;ukk+l- velocity of the sorption fiont propagation along column walls; T- throughput parameter used when subscxipts i and j considering multicomponent chromatography in the fked-bed refer to the components, k and k-el to the plateau zones, double subscript k,k+l refers to the sorption front between k and k+ 1 equiliirium zones. To descriie the species distribution m the counter-current column the equation (10) should be supplemented by an isotherm equation, e.g.:

and conservation equations in the phases:

where Kfi

- selectivity coefficient; - charge of the ith ion; subscript n refers to the least Zj

sorbable ion. It is possible to calculate the concentrations of both species m all plateau zones and flow ratios

(L6

'

' g ) k , k + 1 for each sorption front. The ( L c ' s g ) k , k + l

value

correspondsto the ratio of liquid and solid phases flows m which the k,k+ lth sorption fiont stays stationary about the column walls. The equations system (10)-(12) was solved by a

49 1

Ion Exchange in Inorganic Materials and its Theory

1 b

0

0.05

0.00

0.10

0.00

Figure 2. ~ i o i ofqx s (a) ami ( L /S

5

K E

Xsr,o=

= 7.9 and

0.10

Ca,O

%3,O

solution:

0.05

)

h, me

@) values versus composition of the initial

0.001 ( w e I); 0.004 ( k v e 2); 0.01 ( w e 3); and 0.1 ( w e 4) at

K E

= 4.8

numerical method applied to the problem of strontium recovery fiom natural brines. Input parameterswere the species concentrationm the initialphases and the selectivdy coefficieuts. The Mhres of the degree of enrichment for Strontium m the solution (qx), flow ratio

(Ls

/s5)12,and accumulationflow, PA,were calculated. In these calculationsthe species

concentrations m the zones 1,2 and 3 corresponded to those m the zones 0, P and H m the above d d e r a t i o n (see, Figure 1). 3. RESULTS AND DISCUSSION

3.1. Composition of the Initial Solution

Composition of natural brines widely varies with source. Natural underground waters as well as technological wastes can be used for strontium recovery. The qx and

(L5 / S5) 1,2 values versus equivalent fractions of calcium and strontium ions m the initial

solution for separation on Na-form of the resin are plotted m Figure 2. Figure 2a shows that the value of the degree of enrichment decrenses with rise m strontium concentration and mcreaseswith calcium concentration.The flow ratio falls with increases m the umcentration of both two-charged ions (Figure 2b). The PAvalue depends slightly on the calcium concentration and riseswith strontium concentration.

Progress in Ion Exchange: Advances and Applications

492

24 -

,

8O

W

0

40

(Kg)’

Figure 3. plots of qx (a) and ( L / s

5

xc4o=O.027 and xsr,o = 0.004;::a

0

8o

5 1,2

(b) values versus selectivity coeficients at 2 = 1.5 (curve 1); 2 (curve 2); 2.5

=(K$/Kz)

(curve 3); and 5 (curve 4).

8

0.0

0.1

Figure 4. plots

0.2

Mqx (curve

0.3 YCB,H

I

0.0

1

0.1

0.2

0.3 YCa,H

I ) and x c 4 p ( m e 2)- (a) m well m ( L / S

5

)

5 1,2

Sr values versus composition of the initial resin at xcqo= 0.027; xsr,o= 0.004; KNa K E = 4.8

- p)

= 7.9 ;

Ion Exchange in Inorganic Materials and its Theory

493

3.2. Selectivity Coeffieienta

We have found that equiliirium properties of carboxylic cation-exchange resins m contact with solutions, such as natural brines, strongly depend on the composition and total concentration of the solution as wen as on temperature6. ~ ~ e n of c ethe selectivity coe5cients on the separation process characteristics (when the Na-form of the resin is treated by the initial solution with fixed composition) is shorn m Figure 3. Figure 3a show that degree of enrichment rises with mcreasing K E value and falls with rising K E selectivity coefficient. The flow ratio mcreases with the increase of both seledvity coefficients (Figure 3b). The accumulation flow depends slightly on K E and increases with

K E values. 3.3. Composition of the Initial Resin

As it is shown m Figure 4 the degree of enrichment (Figure 4a, m e l), the flow ratio (Figure 4b), and the accumulation flow decrease with increasing calcium umceutration m the initial resia Cdcium impurity increases m the zone of enriched strontium under the same conditions (Figure 4a, m e 2). These resuits can be used to estimate r values by using equation (9). It can be shown that the degree of strontium recovery decreasesm this case. Jncrease of calcium concentration in the initial resin results in tnnsformation of the steady-state sorption fionts to the dispersive ones It is dilEuIt to avoid losses of strontium when carrying out the fiontal separation stage at the conditions of the dispersive iiont formation. Akhough the criterion for the type of transitionzone formation is the shape of the isotherm’o, the limit ofthe value of calcium umceutration m the initial resin (when steadystate sorption iiont is transformed to the dispersive type) can be estimated by using the results of calculation above. This occurs when qx = 1 (xc40 = xc4p) and correspond to YC~H = 0.4 value. 4. CONCLUSIONS

The equilibrium model with plug flow does not describe the length and shape of the sorption fionts appearing m the real chromatograpfic separation systems. Nevdeless, it is easy to estimate the influence of different factors on the finctionation process. It allows, m certain cases, the avoidance of numerous lq-time separation experiments. These estimations often have good agreement with experimental results. In any case they correctly show the direction of the change m process characteristics with variation of the experimental conditions. References 1. D. DeVauh, J.Am.Chem.Soc., 1943,65,532. 2. G. IUein and F. Helfferch, ‘Multicomponent chromatography’, Marcel Dekker, New York, 1970,415p. 3. B.J. Bennet and F.G. HeHerich, m ‘Ion Exchange Technology’, by eds. D.Naden and M. Streat, Ellis Horwood, Chichestery1984,322.

494

Progress in Ion Exchange: Advances and Applications

4. V.I. Gorshkov, M.S. Safonov, and N.M. Voskresensky, ‘Ion Exchange m CounterCurrent Columns’, Nauka, Moscow, 1981, 224 p.(Rus.); V.I. Gorshkov, m ‘Ion Exchange and Solvent Extraction’, by eds. J.A. Marinsky and Y. Marcus, Marcel Dekker, New York, 1995, VoL 12,29. 5. N.P. Nikolaev, V.A Ivanov, V.I. Gorshkov, V.A Nikashina, and N.B. Ferapontov, Reactive Polymers, 1992,18,25. 6. V.A Ivanov, V.D. Timofeewkaya, and V.I. Gorshkov, Reactive Polymers, 1992, 17, 101. 7. N.P. Nikolaev, V.A. Ivanov, V.I. Gorshkov, D.N. Muraviev, A.D. Saurin, and N.B. Ferapontov, Pat. USSR, No 1590441,1988. 8. J.N. Whn,J.Am.Chem.Soc., 1940,62,1583. 9. N.K. HeiSter and T. Vermeulen, Chem.Eng.Progr.,1952,48,505. 1O.M.S.Safonov, Separ.Sci.,1971,6,35.

Subject Index acetoxystyrene resins, 9 acrylic polymer matrix, 369 actinide removal, 275-278 activity coefficient, 268-270 adsorption isotherms, 334 adsorption, of phenolics, 332-340 affinitychromatogmphy, 222 air flotation,239 dgi~te beads, 3 14-322 alkali metal ions, 431 alkalimetalseparation, 140,141, 153-159,298-306 alkaline earth metal separation, 140,141,153-159 alkyl sulphonic acids, 178 alkylcontaininganions, 410 aurylation reactions,87-95 aluminium, 355 americum, 277 amidoxime resins, 378-381 ammonium phosphomolybdate, 289-297 ammonium, 167 amphoteaic polyelectrolytes, 78-85 anion analysis, 172 anion capidties, 261 anion exchange resins, 365-371 anion exchange, 403411 anionic ion exchangers, 87-95 mle liganh 9 basic anion exchangers, 70-77 BET equation, 333 biomaterials, 256 bhpolymers, 314 Muproduct purification,219-226 biosorbents, 235-24 1 BiPbqNQ ,3947 cadmium,biosorption of,236-241 Caesium fixatian,279-288 d u m isolation, 289-297 caesium radioiso ,260-266 cae$ium removal, 67-274 calcium alginate, 314-322 calcium, 167 dxarenes, 153 capillaryelecbophoresl‘s, 115-123,124-132,160-196 capillary zone eledraphoresiq 120 Carboxybetainic group^, 78-85 canier ions, 176,177 catalysts, phase transfer, 87-95 cation exchange columns, 137-143 celluloseion exchange, 357-364 caium phosphate, 260-266 chelating resins, 34 1-348,378-381 chemical potential 448-456

T

chloride salts, 153-159 chloride, 166-168 chloride, in inkjet dyes, 128,129 chlommethylation, of resins, 6,7 chromium accumulation, 323-331 chromium separation,372-377 clinqtilolite,260 cobalt, 341-348 mmplexing eluents, 144 conductivity &tection, 130 copper adsorption, 386-388 copper hexacyanofelTates, 279-288 copper hydroxy double salts, 4034 11 copper mention, 3 16 copper, 167,341-348,355 counter current columns, 99 counter current ion exchanhge, 486-494 counter current systems,246,247 counterion binding, 6248 curium, 275-278 detergency 393 diamines, 142 distribution coefficient,268,376 distribution ratio, 293,321 dodecylamine, 239 dyes, ink jet, 124-132 dynamics, of ion exchange, 457-469 of sorption, 457469 EDTA-metal complexes, 145-152 effluents, metal bearing, 349-356 electmctivepolymers., 22 electrode, membme, 104-111 electrolyte separation, 96-103 electropherograms, 131,164,170 EMF measuements, 105 EnhancedActini&Removal plant, 133-136 environmental clean-up, 245-258 environmental technology, 245-258 epoxide nesins, 7 equilibrium constant,308 equilibrium studies, 3 14-322 EXAFS spedra, 27 exchange capacity, 385 exchange capacity,&urn, 290,291 extraction chromabography, 275-278 retention, ) 74,75,277 Fe (III fibrous ion exchanger, 372-377 fission products, 289-297 flotation, biosorptive 235-241 fluoride, 166-168 fluoride,in forage vegetation, 119 fly ash, 48 Freundlich equation, 333

496

Progress in Ion Exchange: Advances and Applications

gels, interlayer, 21 glycidyl resins, 7 granular inorganic exchanger, 289-297 halogenated resin, 227-234 heavy metals, 323,341-348 hexamine cobalt, 4 12-420 hydrophobic interacton chromatograph ,222 hydrostatic loading, 164,!66 hyperfiltration, 254 ideal behaviour, 448 iminodiacetic ion exchanger, 349 ink jet dyes, 124-132 inorganic ion exchangers, 289-297 inorganic ions, 176-186 intercalation compounds, 42 1-429 intercalation nanmmposites, 20-24 interferring cations, 376 interlayer distance, 407 intersbtial water, 291 iodide removal, 3947 iodide, in seawater, 115-117 iodinated resin, 227-234 ion exchange isotherms, 43 1 ion Chromatography, 115-123 on-line,117-119 ion chromatography, 124, 133-136, 144-152, 153-159 ion exchange, 245-258,444 cellulose 357-364 chromatography, 22 1 counter cumnt, 486-494 dual temperature, 349-356 dynamics of, 457-469 equilibria, 145-152,323-331, 441-446 in zeolites 393-411 isotherm, 50,271 p r o c e ~ ~307-313,341-348 e~, resins, 96103,2998-306, 470-479 selectivities, 430438 separation, 383-390 ion exchanger, fibrous 372-377 ion exchangers, 17 ion pairing HPLC, 124 ionisation control, 144-152 ionophoric 153 IR spectra, of titanium phosphate, 34 IR studies, 292,293 iron (In), see Fe (Zrl) isocratic separation, 141 itacomic acid, 53-61 kanemite, 412-420 Kielland plots, 270,271,432-434 kinetics of adsorption, 361 kinetics, 347 kinetics, of akylation, 88-95

Langmuir equation, 333 Langmuir isotherm,360 lanthanum carrier, 275 latex-coated exchangers, 138 lead-sodium exchange, 50 liquid-liquid extraction, 253 lithium manganate, 18, 19 lithium, 167 lutetium hydroxide, 276 macroporous resin, 3-5,298 magnesium, 167 maleic acid, 53-61 manganesedetermination, 139 membrane electrode, 104-111 membranes, 254 metal adsorption, 252 metal capacities, 257 metal cation solubilities, 252 metal chelate separation, 144-152 metals, removal of 235-241 methane sulphuric acid, 247 migration times, 166,168 mine waters, 349-356 molecular baskets, 153-159 Monte Car10 simulations, 401 morpholine, 141, 165 N,N-dimethyl- 1,3-diaminopropane, 62 N,N-dimethyl-2 -hydroxypropylammonium chloride, 53-61 nanmmposite materials, 16-28 nanofiltration, 254 neptunium, 277 nitrate, 166-168 nitrogen adsorption, 408 NMR, 430-438 nomenclature, harmonisation of, 4 3 9 4 7 non - electrolyte solution, 449 Nuclear Power Indus nuclear waste, 267-27 oxidative regenemtion, 323-331 oxirane function, 7 pellicular cation exchangers, 138 phase transfer catalysts, 87-95 phenol function, 7 phenol-formaldehyde resins, 298-306 phenolic compounds, 332-340 phenyl acetonitrile, 90 phillipsite, 50 pillared layered structure, 24,25 31 P nmr, 33,34 polyacrylic acid, 53-61 polyacrylic resin, 349 polyanion, 53 poIycarboxybetaine, 8@86 polycation, 53 polyelectrolyte complexes, 53-61 polyelectrolytes, 62-68,78-85 polymer resins, 3-15,314-322 polymerisation, 22

7

Subject Index

polystyrene membrane, 106-110 polystyrene resins, 3- 15 polysulphobetaines, 78 polyvinyl pyridine, 79 porous solids, 24 potassium isotherm,272 purification, bioproduct 219-226 purification, mle of temperature, 307-322 PVC membrane, 106111 quatemuy ammonium ions, 142 radioactive caesium, 279-288 radioactive iodide, 39 radioactive Wastes, 287 regeneration,oxidative 323-331 resins, acetoxystyrene, 9 amidoxime 378-381 anion exchange, 365-371 azole ligands in, 9 chelathg, 341-348,378-381 chloromethylation, 6,7 epoxide containing, 7 glycidyl m-late, 7 iodinated, 227 2 4 ion exchange, 96-103,470-479 library, 225 macroporous, 3-5,298 oxirane function in, 7 polymer, 3-15 phenol formaldehyde, 298-306 phenol function in, 7 polyacrylic, 349 polymer, 314-322,332-340 selectivity, 352 styrene divin 1benzene, 3-15 sulfionic, 3J3-331 technology, 246 thermal degradation, 369 thermo-oxidativdy stable, 1 1 thiirane function in, 7 reverse osmosis, 254 reverse phase chromatography, 222 reversibility of anion exchange, 408 rhodium uptake, 421-429 rubidium separation, 298-306 rubidium, 271,272 salicyladoximeformaldehyde resin, 104-111 scanning electron mimgraphs, 45-47 seawater, 115-117 seawater, uranium h m 378-38 1 selectivities, 430438 selectivity coefficient, 108,394 selectivity constants, 150 selectivity, of anions, 120 selectivity, resin 352

497

separation, of caesium, 295,298-306 of chromium, 372-377 of rubidium. 298-306 separation, role of temperatm, 307-322 silica. 25 silica; in waste waters, 357-364 silica-bonded molecular baskets, 153-159 s i l i ~ ~ A t a267-274 ~~k~, silver adsorption, 360 silver stripping, 357-364 SIXEP process, 260 size exclusion chromatography, 222 smectite clays, 25 sodium sulphate, 335 sodium, 167 sodium-lead exchange, 50 solvent extxaction, 253 smptomyces, 235-24 1 strontium radioisotope, 260-266 styrene divin 1benzene resins, 3-15 sulphate, 1631168 sulphate, in inkjet dyes, 128,129 sulphonic acid ion exchangers, 137 sulphonic resins, 323-331 surhctant mixtures, 121 tetraphenylphosphonium, 133-136 tetrathiafulvalene,23 thermal behaviour, 426 theamal degradation, of resins 369 thermo-oxidatively stable resins, 11 themolysis curves, 291 thermosorption, 353-356 thermostripping, 351-356 thiime function, 7 titanium phosphate, 30-37,289-297 titanium phosphonates, 30-37 transfer ratios, 122,123 ultrafiltration, 254 uranium recovery, 378-381 4-vinyl pyridine-divinyl benzene, 70-77 volume capacity, 441 waste effluents,chromium removal h m , 377 waste waters, 357-364 waste, nuclear, 267-278 wastes, radioactive, 287 water disinfection, 227-234 water, interstitial, 291 waters, mine 349-356 weak acid cation exchangers, 138 X-ray absorption spectroscopy, 19 X-ray diffractionpatterns, oftitanium phosphte, 33 Of B W N O , , 40,41 X-ray diffr;iction,291,292 X-ray microanalysis, 345 X-ray photoelectron ~pe~trosc~py, 19

498

X-ray powder diffraction studies, 406,407,416,417 zeolites, 48-52,393-411 zinc adsorption, 386-388

Progress in Ion Exchange: Advances and Applications

zinc, 355 zirconium hydrogen phosphate, 17-24 zirconium phosphate, 260,421-429