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Ion Exchange in Environmental Processes
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Ion Exchange in Environmental Processes
Fundamentals, Applications and Sustainable Technology
Arup K. SenGupta
ProfessorLehigh UniversityBethlehem, USA
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This edition first published 2017© 2017 John Wiley & Sons, Inc.
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Library of Congress Cataloging-in-Publication Data
Names: SenGupta, Arup K. author.Title: Ion exchange in environmental processes: fundamentals, applications and sustainable technology /
by Arup K. SenGupta, Professor, Lehigh University, Bethlehem, USA.Description: First edition. | Hoboken, NJ, USA : Wiley, [2017] | Includes
bibliographical references and index. |Identifiers: LCCN 2017016090 (print) | LCCN 2017016885 (ebook) | ISBN
9781119421283 (pdf) | ISBN 9781119421290 (epub) | ISBN 9781119157397(cloth)
Subjects: LCSH: Ion exchange–Industrial applications.Classification: LCC TP156.I6 (ebook) | LCC TP156.I6 S45 2017 (print) | DDC
660/.29723–dc23LC record available at https://lccn.loc.gov/2017016090
Cover image: Courtesy of Arup SenGupta and Michael German; Background: © MirageC/GettyImagesCover design by Wiley
Set in 11/13pt WarnockPro by SPi Global, Chennai, India
10 9 8 7 6 5 4 3 2 1
Printed in the United States of America
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ToSusmita, Neal and Soham for their love and supportandMother Nature for Her infinite tolerance
“Thy right is to the work only, but never to the fruits thereof”
Bhagvad Gita: Verse II:47
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Contents
Preface xiiiAcknowledgment xvii
1 Ion Exchange and Ion Exchangers: An Introduction 11.1 Historical Perspective 11.2 Water and Ion Exchange: An Eternal Kinship 61.3 Constituents of an Ion Exchanger 91.4 What is Ion Exchange and What it is Not? 101.5 Genesis of Ion Exchange Capacity 121.5.1 Inorganic 121.5.2 Organic/Polymeric Ion Exchanger 131.5.3 Strong-Base Type I and Type II Anion Exchanger 201.6 Biosorbent, Liquid Ion Exchanger, and Solvent Impregnated Resin 231.6.1 Biosorbent 231.6.2 Liquid Ion Exchange 251.6.3 Solvent-Impregnated Resins 271.7 Amphoteric Inorganic Ion Exchangers 281.8 Ion Exchanger versus Activated Carbon: Commonalities and Contrasts 331.9 Ion Exchanger Morphologies 341.10 Widely Used Ion Exchange Processes 341.10.1 Softening 351.10.2 Deionization or Demineralization 40
Summary 44References 45
2 Ion Exchange Fundamentals 502.1 Physical Realities 502.2 Swelling/Shrinking: Ion Exchange Osmosis 512.3 Ion Exchange Equilibrium 552.3.1 Genesis of Non-Ideality 572.4 Other Equilibrium Constants and Equilibrium Parameters 592.4.1 Corrected Selectivity Coefficient 592.4.2 Selectivity Coefficient, K se
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2.4.3 Separation Factor (𝛼AB ) 60
2.4.4 Separation Factor: Homovalent Ion Exchange 612.4.5 Separation Factor: Heterovalent Exchange 622.4.6 Physical Reality of Selectivity Reversal: Role of Le Châtelier’s Principle 652.4.7 Equilibrium Constant: Inconsistencies and Potential Pitfalls 662.5 Electrostatic Interaction: Genesis of Counterion Selectivity 692.5.1 Monovalent–Monovalent Coulombic Interaction 692.6 Ion Exchange Capacity: Isotherms 732.6.1 Batch Technique 752.6.2 Regenerable Mini-Column Method 792.6.3 Step-Feed Frontal Column Run 812.7 The Donnan Membrane Effect in Ion Exchanger 842.7.1 Coion Invasion or Electrolyte Penetration 842.7.2 Role of Cross-linking 902.7.3 Genesis of the Donnan Potential 902.8 Weak-Acid and Weak-Base Ion Exchange Resins 922.8.1 pKa Values of Weak Ion Exchange Resins 942.8.2 Weak-Acid and Weak-Base Functional Groups 962.9 Regeneration 982.9.1 Selectivity Reversal in Heterovalent Ion Exchange 1002.9.2 pH Swings 1012.9.3 Ligand Exchange with Metal Oxides 1052.9.4 Use of Co-Solvent 1062.9.5 Dual-Temperature Regeneration 1082.9.6 Carbon Dioxide Regeneration 1112.9.7 Regeneration with Water 1122.10 Resin Degradation and Trace Toxin Formation 1122.10.1 Formation of Trace Nitrosodimethylamine (NDMA) from Resin
Degradation 1142.11 Ion Exclusion and Ion Retardation 1152.11.1 Ion Exclusion 1152.11.2 Ion Retardation 1162.12 Zwitterion and Amino Acid Sorption 1182.12.1 Interaction with a Cation Exchanger: Role of pH 1192.13 Solution Osmotic Pressure and Ion Exchange 1212.14 Ion Exchanger as a Catalyst 124
Summary 126References 127
3 Trace Ion Exchange 1303.1 Genesis of Selectivity 1303.2 Trace Isotherms 1363.3 Multi-Component Equilibrium 1383.4 Agreement with Henry’s Law 1403.5 Multiple Trace Species: Genesis of Elution Chromatography 143
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3.5.1 Determining Separation Factor from Elution Chromatogram 1433.6 Uphill Transport of Trace Ions: Donnan Membrane Effect 1493.7 Trace Leakage 1513.8 Trace Fouling by Natural Organic Matter 1533.9 Ion Exchange Accompanied by Chemical Reaction 1563.9.1 Precipitation 1563.9.2 Complexation 1573.9.3 Redox Reaction 1573.10 Monovalent–Divalent Selectivity 1583.10.1 Effect of Charge Separation: Mechanistic Explanation 1583.10.2 Nitrate/Sulfate and Chloride/Sulfate Selectivity in Anion Exchange 1603.10.3 Genesis of Nitrate-Selective Resin 1623.10.4 Chromate Ion Selectivity 1643.11 Entropy-Driven Selective Ion Exchange: The Case of Hydrophobic Ionizable
Organic Compound (HIOC) 1663.11.1 Focus of the Study and Related Implications 1673.11.2 Nature of Solute–Sorbent and Solute–Solvent Interactions 1693.11.3 Experimental Observations: Stoichiometry, Affinity Sequence, and Cosolvent
Effect 1733.11.4 Energetics of the Sorption Process 1773.11.5 Unifying Hydrophobic Interaction: From Gas–Liquid to Liquid–Solid
System 1793.11.6 Effect of Polymer Matrix and Solute Hydrophobicity 1823.12 Linear Free Energy Relationship and Relative Selectivity 1833.13 Simultaneous Removal of Target Metal Cations and Anions 1863.14 Deviation from Henry’s Law 1883.14.1 Ions Forming Polynuclear Species 1883.15 Tunable Sorption Behaviors of Amphoteric Metal Oxides 1923.16 Ion Sieving 1953.17 Trace Ion Removal 2013.17.1 Uranium(VI) 2013.17.2 Radium 2033.17.3 Boron 2043.17.4 Perchlorate (ClO−
4 ) 2053.17.5 Emerging Contaminants of Concern and Multi-Contaminant Systems 2083.17.6 Arsenic and Phosphorus: As(V), P(V), and As(III) 2103.17.7 Fluoride (F−) 214
Summary 215References 216
4 Ion Exchange Kinetics: Intraparticle Diffusion 2244.1 Role of Selectivity 2244.2 State of Water Molecules inside Ion Exchange Materials 2324.3 Activation Energy Level in Ion Exchangers: Chemical Kinetics 2354.3.1 Activation Energy Determination from Experimental Results 236
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4.4 Physical Anatomy of an Ion Exchanger: Gel, Macroporous and FibrousMorphology 242
4.4.1 Gel-Type Ion Exchanger Beads 2424.4.2 Macroporous Ion Exchanger Beads 2434.4.3 Ion Exchange Fibers 2464.5 Column Interruption Test: Determinant of Diffusion Mechanism 2484.6 Observations Related to Ion Exchange Kinetics 2504.6.1 Effect of Concentration on Half-time (t1∕2) 2514.6.2 Major Differences in Ion Exchange Rate 2524.6.3 Chemically Similar Counterions with Significant Differences in Intraparticle
Diffusivity 2524.6.4 Effect of Competing Ion Concentrations: Gel versus Macroporous 2544.6.5 Intraparticle Diffusion during Regeneration 2554.6.6 Shell Progressive Kinetics versus Slow Diffusing Species 2554.7 Interdiffusion Coefficients for Intraparticle Diffusion 2574.8 Trace Ion Exchange Kinetics 2644.8.1 Chlorophenols as the Target Trace Ions 2644.8.2 Intraparticle Diffusion inside a Macroporous Ion Exchanger 2664.8.3 Effect of Sorption Affinity on Intraparticle Diffusion 2684.8.4 Solute Concentration Effect 2714.9 Rectangular Isotherms and Shell Progressive Kinetics 2724.9.1 Anomalies in Arrival Sequence of Solutes 2744.9.2 Quantitative Interpretation 2754.10 Responses to Observations in Section 4.6 2764.10.1 Effect of Concentration on Half-time (t1∕2) 2764.10.2 Slow Kinetics of Weak-Acid Resin 2774.10.3 Chemically Similar Counterions: Drastic Difference in Intraparticle
Diffusivity 2774.10.4 Gel versus Macroporous 2784.10.5 Intraparticle Diffusion during Regeneration 2784.10.6 Shrinking Core or Shell Progressive Kinetics 2794.11 Rate-Limiting Step: Dimensionless Numbers 2804.11.1 Implications of Biot Number: Trace Ion Exchange 2814.12 Intraparticle Diffusion: FromTheory to Practice 2844.12.1 Reducing Diffusion Path Length: Short-Bed Process and Shell–Core
Resins 2854.12.2 Development of Bifunctional Diphonix® Resin 2884.12.3 Ion Exchanger as a Host for Enhanced Kinetics 289
Summary 292References 293
5 Solid- and Gas-Phase Ion Exchange 2975.1 Solid-Phase Ion Exchange 2975.1.1 Poorly Soluble Solids 2975.1.2 Desalting by Ion Exchange Induced Precipitation 303
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5.1.3 Separation of Competing Solid Phases 3055.1.4 Recovery from Ion Exchange Sites of Soil 3065.1.5 Composite or Cloth-like Ion Exchanger (CIX) 3075.1.6 Heavy Metals (Me2+) with Solids Possessing High Buffer Capacity 3095.1.7 Ligand-Induced Metal Recovery with a Chelating Exchanger 3155.2 Coagulant Recovery fromWater Treatment Sludge 3175.2.1 Development of Donnan IX Membrane Process 3185.2.2 Alum Recovery: Governing Donnan Equilibrium 3185.2.3 Process Validation 3225.3 Gas Phase Ion Exchange 3235.3.1 Sorption of Acidic and Basic Gases 3245.3.2 CO2 and SO2 Capture with Weak-Base Anion (WBA) Exchanger 3255.3.3 Effect of Ion Exchanger Morphology 3275.3.4 Redox Active Gases: Hydrogen Sulfide and Oxygen 3305.4 CO2 Gas as a Regenerant for IX Softening Processes: A Case Study 334
Summary 339References 340
6 Hybrid Ion Exchange Nanotechnology (HIX-Nanotech) 3456.1 Magnetically Active Polymer Particles (MAPPs) 3476.1.1 Characterization of MAPPs 3516.1.2 Factors Affecting Acquired Magnetic Activity 3536.1.3 Retention of Magnetic Activity and Sorption Behavior 3556.2 Hybrid Nanosorbents for Selective Sorption of Ligands (e.g.,
HIX-NanoFe) 3576.2.1 Synthesis of Hybrid Ion Exchange Nanomaterials 3596.2.2 Characterization of Hybrid Nanosorbents 3616.2.3 Parent Anion Exchanger versus Hybrid Anion Exchanger
(HAIX-NanoFe(III)): A Comparison 3636.2.4 Support of Hybrid Ion Exchangers: Cation versus Anion 3656.2.5 Efficiency of Regeneration and Field Application 3696.2.6 Hybrid Ion Exchange Fibers: Simultaneous Perchlorate and Arsenic
Removal 3706.3 HAIX-NanoZr(IV): Simultaneous Defluoridation and Desalination 3766.3.1 Field-Scale Validation 3776.4 Promise of HIX-Nanotechnology 381
Summary 383References 384
7 Heavy Metal Chelation and Polymeric Ligand Exchange 3917.1 Heavy Metals and Chelating Ion Exchangers 3917.1.1 Heavy Metals: What are They? 3917.1.2 Properties of Heavy Metals and Separation Strategies 3937.1.3 Emergence of Chelating Exchangers 3957.1.4 Lewis Acid–Base Interactions in Chelating Ion Exchangers 398
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7.1.5 Regeneration, Kinetics and Metals Affinity 4027.2 Polymeric Ligand Exchange 4057.2.1 Conceptualization and Characterization of the Polymeric Ligand Exchanger
(PLE) 4067.2.2 Sorption of Polymeric Ligand Exchangers 4077.2.3 Validation of Ligand Exchange Mechanism 410
Summary 413References 413
8 Synergy and Sustainability 4178.1 Waste Acid Neutralization: An Introduction 4178.1.1 Underlying Scientific Concept 4188.1.2 Mechanical Work through a Cyclic Engine 4218.2 Improving Stability of Anaerobic Biological Reactors 4238.2.1 Potential Use of Selective Ion Exchanger 4248.2.2 Ion Exchange Fibers: Characterization and Performance 4248.3 Sustainable Aluminum-Cycle Softening for Hardness Removal 4298.3.1 Current Status and Challenges 4298.3.2 Sodium-Free Approaches and Alternatives to Na-Cycle Softening 4298.3.3 Underlying Scientific Approach of Al-cycle Cation Exchange 4308.3.4 Comparison in Performance: Na-Cycle versus Al-Cycle 4328.3.5 Regeneration Efficiency and Calcium Removal Capacity 4368.3.6 Sustainability Issues and New Opportunities 4388.4 Closure 438
Summary 439References 440
A Commercial Ion Exchangers 445
B Different Units of Capacity, Concentration, Mass, and Volume 457B.1 Capacity 457B.2 Concentration (Expressed as CaCO3) 457B.3 Mass 458B.4 Volume 458
C Table of Solubility Product Constants at 25 ∘C 459
D Acid and Base Dissociation Constants at 25 ∘C 461
Periodic Table and Atomic Weights of Elements 463
Index 467
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Preface
Ion exchange is a fascinating scientific field, as central to natural and biological systems,as to the engineered processes. Historically, application of ion exchange always stayedfar ahead of theory and the design approaches for ion exchange systems were mostlyempirical. The intrinsic complexity of the field was poorly understood and the scienceof ion exchange was accepted as mere exchange of ions. After the Second World War,ion exchange theory took root, progressed gradually on a scientific foundation and newapplications were conceived and implemented. The intrinsic complexity of the field ofion exchange and itsmany seemingly eccentric behaviors were unraveled. Understand-ably, learning the subject requires revealing its scientific core in appropriate sequence,interjected with key scientific inquiries of “why” and “how.”It was during the fall of 1996 when I was in England on a sabbatical leave at the
invitation of long-time friend and colleague, Prof. Michael Streat, that the thought ofwriting a book on Ion Exchange dawned onme and I initiated the process.While there,I was informally giving a series of lectures to a group of senior graduate students andyoung faculty members on topics related to fundamentals and recent developments inion exchange. Some difficulties arose. I struggled to communicate some experimen-tal observations of others that are seemingly counter-intuitive. So I started prepar-ing notes of my own and that was the modest beginning. Needless to say, the effortwent back and forth, the book project proceeded at a snail’s pace and turned dormant.Finally, 3 years ago, I undertook the assignment as amission that needs to be brought toa closure. However, the key questions or motivating factors – Is such a book necessaryand whom is this book for – remained unchanged throughout.No specialty grows in isolation. Ion exchange is not a recent invention, but over the
last five decades, the science of ion exchange has permeated into a myriad of othergrowing fields – from decontamination to deionization, from mining to microelec-tronics, from gas separation to green processes, from novel synthesis to nanotechnol-ogy, from drug delivery to desalination, to name a few. The following figure from theGoogle patent search includes the number of ion exchange-related US patents issuedduring the last three decades, illustrating continued inventions of new products andprocesses.
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Very highUSpatent numbers only reinforce the dynamics of the field and its blendingwithmany other seemingly disjointed scientific areas. It is only appropriate tomentionthat the worldwide push for sustainability and stringent environmental regulations hasseen ion exchange technology as a major player in the development of the next gener-ation of environmental processes and efficient materials. Such a move has demandeda need to revisit the fundamentals of ion exchange with a renewed perspective. Asexpected, this book presents the “why” and the “how” of multiple ion exchange phe-nomena with varying degrees of complexity. However, a conscious attempt has beenmade to present physical realities of every ion exchange phenomenon of interest rightup front. Only then, underlying theories and quantitative approaches have been dis-cussed to validate observed physical realities.Presentation of theoretical tools that might help the reader in solving or address-
ing specific problems were given due importance. At the same time, overemphasison mathematical models and abstract theories has been avoided. Even when mathe-matical deductions and related equations have been adequately presented, qualitativeexplanations and interpretations have not been ignored. Thus, a mathematically or athermodynamically disinclined reader, with deep understanding of the subject throughexperience or othermeans,may comfortably navigate through the entire book and gainnew knowledge or identify areas warranting further innovation.Writing or introducing a new book on Ion Exchange will always remain incomplete
unless an honest discussion is made about how it complements or adds to the existingtitle on Ion Exchange written by Fred Helfferich over 50 years ago. Helfferich’s bookis a seminal contribution in the field and will continue to remain so. I take pride instating that I knew Fred Helfferich. He was an esteemed professional colleague andwe interacted in several ways. I personally keep a copy of his book both at home andin the office, consulting it whenever necessary. Nevertheless, it is also my finding thatpeople always refer to Helfferich’s book when confronted with a question or uncer-tainty, but rarely do they read it for learning the subject of ion exchange. Classicalstep-by-step learning through Helfferich’s book and applying the knowledge appro-priately pose some genuine challenges. The book was not really written to serve thatpurpose. Also, during the last few decades, new ion exchangers, namely, macroporous,fibrous, hybrid and biomaterials have emerged with distinctive attributes; novel use of
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the Donnan membrane principle has opened up new opportunities to produce sus-tainable materials and processes. Further, gas- and solid-phase ion exchange may soonprovide new platforms for novel, environmentally benign processes. More and more,ion exchange is being used synergistically with other known processes resulting in keybreakthroughs in processes with enhanced sustainability. This new book will substan-tially complement the existing body of knowledge in the public domain and serve as amajor learning tool for young scientists and engineers.Readers with a moderate knowledge of physical chemistry, chemical/environmental
engineering principles and mathematics, should be able to progress through indi-vidual chapters on their own. For academic teaching, the book is suitable as a textor a reference for an undergraduate senior or first- year graduate level chemicalor environmental engineering course in separation, environmental processes orion exchange. Attempts have been made so that a potential reader, while graduallyassimilating the content, will be prepared to apply the acquired knowledge for real-lifescenarios, improve existing processes and develop an instinct for innovation throughuse of fundamentals. From that perspective, the content of the book will be usefulalso for polymer chemists, consulting engineers and technology companies seekinglong-term holistic solutions. To facilitate the use of this book as a text or a handout ina short course, several numerical exercises have been included.The book has altogether eight chapters that unfold connecting ion exchange
processes and materials with fundamentals:Chapter 1. Ion Exchange and Ion Exchangers: An IntroductionChapter 2. Ion Exchange FundamentalsChapter 3. Trace Ion ExchangeChapter 4. Ion Exchange Kinetics: Intraparticle DiffusionChapter 5. Solid- and Gas-Phase Ion ExchangeChapter 6. Hybrid Ion Exchange Nanotechnology (HIX-Nanotech)Chapter 7. Heavy Metal Chelation and Polymeric Ligand ExchangeChapter 8. Synergy and SustainabilityA reader with prior exposure to the field of ion exchange, does not need to be deterredfrom jumping into any chapter of choice out of sequence and still comprehending thematerials. Over the decades, widely used softening and deionization processes havebeen tailored to be more sustainable from chemical usage point of view and the sub-ject has been discussed in bothChapters 1 and 2. Along the same vein, the ion exchangefundamentals have been appropriately harnessed to produce selective sorbents fornitrate, arsenic, fluoride, phosphate, boron and others. A relatively new field of hybridion exchange nanotechnology or HIX-Nanotech has emerged and the Donnan mem-brane principle plays a crucial role in expanding its application potential. Solid andgas-phase separations show promise for recovery of valuable materials with minimumchemical usage. In every such discussion presented in Chapters 5–8, the role of scien-tific fundamentals has been adequately articulated. Chapter 8 includes a new route toa simple-to-apply softening process without using an excessive amount of brine, oftencausing major disposal problems in arid regions.It is generally agreed that the solutions to challenging problems of our timewill not so
much occur through evolution of new fundamental knowledge, but through synergistic
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integration of knowledge from seemingly disconnected fields. As the author of thisbook, I am quite optimistic that the science, technology and materials related to ionexchange, as presented here, will help fill some void and create new synergy for thenext generation of innovators and inventors in the field.
Arup K. SenGuptaNovember, 2016Lehigh UniversityBethlehem, USA
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Acknowledgment
During my first job as a process chemical engineer, my then supervisor in earlyseventies, N. K. Chowdhury, introducedme to the complexity and excitement of waterscience and technology.The excitement is yet to cease and my professional world dur-ing the last four decades has truly revolved around water in so many ways. In the sameperiod, I was also exposed to the field of producing ultra-pure water for electric powergenerating utilities using ion exchange processes. Subsequently, I worked with Profes-sor Dennis Clifford for my PhD; my graduate student life in the University of Houstonwas truly eventful and intellectually stimulating.The concept of gradual breakthroughduring fixed-bed column runs was solidly confirmed through my doctoral workon chromate ion exchange. Dennis and I have remained friends and professionalcolleagues for nearly four decades and I am thankful to him in so many ways.During the eighties and nineties, I had the opportunity and privilege to meet, chat,
befriend and discuss matters of mutual professional interest related to different sep-aration processes including ion exchange with many personalities around the worldduring Gordon Conferences on Reactive Polymers, IEX conferences at Cambridge(UK), and various ACS and AIChE conferences. I have very fond and rewarding mem-ories of meeting and interacting with George Boyd, Robert Kunin, Fred Helfferich,Jacob Marinsky, Mike Streat, Charlie O’Melia, Wolfgang Hoell, David Sherrington,Spiro Alexandratos, Robert Albright, Steve Cramer, Menachem Elimelech, RuslanKhamizov, Zdenek Matezka, Mimo Petruzzelli, Nalan Kabay, Kesava Rao, GaryFoutch and others. I am thankful to Jacob Brodie and Francis Boodoo for theircontinued cooperation with material support pertaining to our research efforts inenvironmental separation. The electron microscopy work of Debra Phillips for HybridIon Exchanger-Nanotechnology is gratefully acknowledged. I sincerely acknowledgethe US Department of State, US Fulbright Program, the Department of Science andTechnology of the Government of India, WIST, Inc., Rite Water Solutions (I) Ltd.and Technology with a Human Face (NGO) for their support and assistance towardfield-level implementation of ion exchange technologies invented in LehighUniversity.However, more than anything, I am most grateful to my graduate students and
post-docs with whom I have worked closely for over three decades. Since I may nothave many more opportunities, I would like to recognize them by name who havemade meaningful contributions to push the frontiers of ion exchange science andtechnology inch by inch through their research: Yuewei Zhu, Sukalyan Sengupta, AnuRamana, Yi-min Gao, Ping Li, Indra Mitra, Dongye Zhao, Esmeralda Millan, Matthew
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DeMarco, David Leun, Luis Cumbal, Arthur Kney, John Greenleaf, Parna Mukherje,Sudipta Sarkar, Prakhar Prakash, Lee Blaney, Prasun Chatterjee, Surapol Padungthon,Ryan Smith, Mike German, Yu Tian, Jinze Li, Chelsey Shepsko, Robert Creighton andHang Dong. Most of them started as students, but down the stretch, most of thembecame mature, thoughtful and innovative in their own rights. I sincerely believe thatthe knowledge acquisition has truly been a two way process and the students haveenriched my professional life. It is likely that some names may have been omitted butthat is unintentional and I offer my sincere apology in advance.During the last four years, Beth Yen, the department secretary, unfailingly responded
to my every request – be it copying, typing, scanning, editing or even running anerrand, and often with time constraints due to poor planning on my part. I amimmensely thankful for her cooperation and continued service.For my education, from the second grade in the elementary school in India to my
PhD in the US, I never paid any tuition. It was gratis all the way for my entire studentcareer. Now I know that ordinary people, who pay taxes or are undercompensated,truly funded my education. I consider myself immensely fortunate and blessed.I acknowledge continued cooperation from Wiley, the publisher of the book, and I
am thankful to SaleemHameed, Beryl Mesiadhas andMichael Leventhal for attendingto necessary details and bringing the book project to a successful closure.Last but by no means the least, without the incessant help and involvement of
Michael German, this book could not be brought to a successful completion. Inaddition to carrying out his regular duties as a senior PhD student, Mike relentlesslyresponded to various details about the book project – from completing figuresto collecting copyright permissions and many other associated pieces of work inbetween. Mike helped me overcome the activation energy barrier with his unselfisheffort and I am indeed indebted to him.
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Ion Exchange and Ion Exchangers: An Introduction
1.1 Historical Perspective
Evolution is traditionally viewed to occur in a slow but continuous manner for livingorganisms and creatures gradually acquiring new traits. To the contrary, many areasof “science” undergo periods of rapid bursts of fast development separated by virtualstandstill with no significant activity.The first historically recorded use of ion exchangephenomenon is from theOld Testament of the Holy Bible in Exodus 15:22–25 describ-ing how Moses rendered the bitter water potable by apparently using the process ofion exchange and/or sorption. Another often quoted ancient reference is to Aristotle’sobservation that the salt content of water is diminished or altered upon percolationthrough certain sand granules. From a scientific viewpoint, however, the credit forrecognition of the phenomenon of ion exchange is attributed to the English agricul-ture and soil chemists, J.T. Way and H.S. Thompson. In 1850, these two soil scientistsformulated a remarkably accurate description of ion exchange processes in regard toremoval of ammonium ions from manure by cation exchanging soil [1,2]. They essen-tially simulated the following naturally occurring cation exchange reactions as follows:
NH+4 (aq) +Na+(soil) ↔ NH+
4 (soil) +Na+(aq) (1.1)2NH+
4 (aq) + Ca2+(soil) ↔ (NH+4 )2(soil) + Ca2+(aq) (1.2)
Some of the fundamental tenets of ion exchange resulted from this work: first, theexchange of ions differed from true physical adsorption; second, the exchange of ionsinvolved the exchange in equivalent amounts; third, the process is reversible andfourth, some ions were exchanged more favorably than others.
As often with many groundbreaking inventions, the findings of Way and Thompsoncast doubts, disbeliefs and discouragement from their peers. In the following years, thesetwo soil scientists discontinued persistent research in this field.As a result, the evolutionof ion exchange process progressed rather slowly due to the difficulties inmodifying ormanipulating naturally occurring inorganic clayey materials with low cation exchangecapacities.Inorganic zeolites (synthetic or naturally occurring aluminosilicates) later found
wide applications in softening hard waters, that is, removal of dissolved calciumand magnesium through cation exchange. However, the anion-exchange processesremained unexplored and practically unobserved. Even at that time, it was not difficultto conceptualize that the availability of both cation exchangers and anion exchangersIon Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology,First Edition. Arup K. SenGupta.© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
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2 Ion Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology
in the ionic forms of hydrogen and hydroxyl ions, respectively, would create a newnon-thermal way to produce water free of dissolved solids as indicated below:
H+(solid) +OH−(solid) +Na+(aq) + Cl−(aq)↔ H2O(aq) +Na+(solid) + Cl−(solid) (1.3)
The biggest obstacle to realize this concept was to identify and/or synthesize ionexchangers which will be chemically stable and durable under the chemically harshenvironments at very high and low pH. The immense potential of ion exchangetechnology scaled a new height when the first organic-based (polymeric) cationexchanger was synthesized by Adams and Holmes [3]. In less than ten years, D’Alelioprepared the first polymeric, strong/weak cation and anion exchangers [4–6]. Sincethen, synthesis of new ion exchangers never seemed to slow down and applicationof ion exchange technology in industries as diverse as power utilities, biotechnology,agriculture, pharmaceuticals, pure chemicals, microelectronics, etc. are continuallygrowing. No specialty grows in isolation; ion exchange fundamentals, ion exchangeresins and ion exchange membranes continue to find new and innovative applicationsglobally. Figure 1.1 includes the number of ion exchange related US patents issuedduring the last three decades, illustrating continued inventions in new products andprocesses.Ironically, the Second World War and, more specifically, the race for nuclear tech-
nology helped catalyze the growth and maturity of the field of ion exchange at anaccelerated pace. Ion exchange was found to be a viable process for separating someof the transuranium elements and, for understandable reasons, its application arouseda great deal of interest. In fact, some of the most fundamental works on ion exchangeequilibria and kinetics were carried out during the SecondWorldWar period by Boydet al. and reported afterwards in the open literature [9–11]. All along, the scientificunderstanding of ion exchange fundamentals consistently lagged well behind its appli-cations. Table 1.1 attempts to summarize milestones in regard to the development andapplication of ion exchange technology over time.
0
2000
4000
6000
8000
10,000
12,000
14,000
16,000
18,000
20,000
1985 1990 1995 2000 2005 2010
Num
ber
of pate
nts
Figure 1.1 Number of patents per year for “anion exchange” and “cation exchange” per a GooglePatents search. Source: Data taken with permission from Google [7,8].
�
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Table1.1
His
toric
alm
ilest
ones
inio
nex
chan
ge.
Year
Description
Patent#
Authors
1850
Disc
overyof
ionexchan
geprop
ertie
sofsoil
N/A
Thom
pson
andWay
[1,2]
1876
Zeolite
sora
luminosilicatesrecog
nizedforb
aseexchan
gean
dequivalenceof
exchan
geisproved
N/A
Lemberg
[12,13
]
1906
–191
5Indu
stria
lmanufacture
ofsodium
perm
utitforh
ardn
essrem
oval
914,40
5;94
3,53
5;1,13
1,50
3
Gan
s[14
]
1934
Inventionof
sulfo
natedcond
ensatio
npo
lymersa
scationexchan
gers
2198
378A
Ellis
1935
Firstsyn
theticorganicionexchan
gers
2104
501A
,21
5188
3AAdamsa
ndHolmes
[15]
1938
Mixed
-bed
ionexchan
geprocesso
rdup
lexionexchan
ger
2275
210A
Stem
en,U
rbain,
andLe
wis
1939
Inventionof
sulfo
natedpo
lystyren
epo
lymerizationas
catio
nexchan
gers
Inventionof
aminated
polystyren
epo
lymerizationas
anionexchan
gers
2283
236A
2304
637A
Soday
Vernal
1942
Cationexchan
geresin
beadsm
adefrom
polymerized
acrylic
acids
Cationexchan
geresin
swith
sulfo
nated,po
lymerized
poly-vinylarylparent
resin
Anion
exchan
geresin
swith
aminated
,polym
erized
poly-vinylarylparent
resin
2340
110A
,23
4011
1A23
6600
7A23
6600
8A
D’Alelio
1947
Elem
ent6
1(Promethium
)was
discovered
byionexchan
geof
theby-produ
cts
offissio
nN/A
Marinsky,Glend
enin,and
Coryell[16]
1953
Use
ofzeolite
sasm
olecular
sieves
Magne
ticionexchan
geresin
forN
OM
removal(M
IEXprocess)
Inventionof
weakacid
catio
nexchan
gers
Firstc
ountercurrention
exchan
geusingsuspen
ded/agita
tedbe
dsof
resin
2882
243A
2642
514A
2838
440A
N/A
Milton
Herkenh
offTh
urmon
Swintonan
dWeiss
[17]
1954
Higgins
coun
tercurrent
ionexchan
gecontactorinv
ented
2815
322A
Higgins
[18]
1955
Ligand
exchan
ge28
3924
1AAlbise
tti19
56Pellicularion
exchan
geresin
2933
460A
Richtera
ndMcB
urne
y19
58Agitatedbe
dcontactorfor
semicon
tinuo
usionexchan
geIonexchan
gein
drug
delivery
N/A
2990
332A
Arden
,Davis,and
Herwig[19]
Keating
(Con
tinue
d)
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Table1.1
(Con
tinue
d)
Year
Description
Patent#
Authors
1958
(pub
licly
released
)
Uranium
separatio
n,intrapartic
lediffu
sion(M
anhatta
nProject)
2956
858A
Powell
1959
–196
0Th
ebo
okon
“Ion
Exchan
ge”b
yFriedrichHelffe
richwas
printedan
dlaid
the
theoretic
alfoun
datio
nsforthe
field
ofionexchan
geN/A
Helffe
rich[20]
1962
–197
1Cloete–
Streat
coun
tercurrent
contactorinv
ented
3551
118A
(196
2)37
3881
4A(196
9)39
5763
5A(197
1)
Cloetean
dStreat
[21]
1964
Cellulosic
ionexchan
gefib
erss
ynthesized
3379
719A
Rulison
1965
Sirotherm
process–
thermallyregene
rableionexchan
geresin
s274-029;
59,441
/65
(Australia)
Bolto
,Weiss,and
Willis
Partially
func
tiona
lized
catio
nexchan
ge(sha
llow-shelltechno
logy)
3252921A
Han
senan
dMcM
ahon
1966
Macropo
rous
ionexchan
geresin
3418
262A
Grammon
tand
Werotte
1968
Boronselectiveresin
2011
0108
488A
1Che
mtob
1969
Develop
mento
fpoly(methylm
etha
crylate)
anionexchan
geresin
sor
macroretic
ular
polymersthatred
uced
foulingby
naturalo
rgan
icman
ner
N/A
Kressm
anan
dKu
nin[22,23
]
1971
Con
tinuo
usmovingbe
dionexchan
ge37
5136
2AProb
stein,
Schw
artz,and
Sonin
1972
Phen
olicionexchan
gefib
ers
3835
072A
Econ
omyan
dWoh
rer
1973
Iminod
iacetic
acid
chelatingresin
Metal-selectiv
ebiosorbents
3936
399A
CA10
3671
9A1
Hira
i,Fu
jimara,an
dKa
zigase
Stam
berg,P
rochazka,and
Jilek
1973
Iminod
iacetic
acid
chelatingresin
3936
399A
Hira
i,Fu
jimara,an
dKa
zigase
Metal-selectiv
ebiosorbents
CA1036719A
1Stam
berg,P
rochazka,and
Jilek
1975
“Him
sleycontactor”multistage
fluidized
bedcontinuo
uscoun
ter-currention
exchan
gecontactor
CA980467A1
Him
sley
1976
Solventimpregnatedresin
s4220726A
Warshaw
sky
etal
.[24
,25]
�
� �
�
1980
Mon
osph
ereionexchan
geresin
(Dow
Che
micalCo.)
4444961A
Timm
1979
Ionexchan
geindu
cedsupe
rsaturation(IX
ISS)
N/A
Muraviev[26,27
]1981
Radium
selectiveresin
sEP
0071810A1
Hatch
1983
Nitrateselectiveresin
CARIX(carbo
ndioxideregene
ratedionexchan
ge)p
rocess
forb
rackish
water
desalin
ation
4479
877A
EP00
5685
0B1
Guter
Kiehlin
gan
dWolfgan
g
1985
Shortb
edionexchan
ger
EP02
0164
0B2
Brow
n19
90Selectivean
ionexchan
geforg
oldfrom
cyan
idesolutio
nwith
asim
plean
dstraightforw
ardchem
icalregene
ratio
nN/A
Schw
ellnus
andGreen
[28]
1991
Bifunc
tiona
lion
exchan
geresin
s(Dipho
nix)
EP06
1884
3A1
Alexand
ratos,Chiarizia,and
Gatrone
1997
Polymericlig
andexchan
ge61
3619
9ASenG
upta
andZh
ao20
03Fluo
rideselectiveresin
s:strong
acid
catio
nexchan
geresin
inalum
inum
form
WO20
0506
5265
A2
Jang
barw
alaan
dKr
ulik
2004
Don
nanprinciple-basedhybrid
ionexchan
ger
7291
578B2
SenG
upta
andCu
mbal
(IonEx
chan
ge)M
embran
ecapacitiv
edeionizatio
n(M
CDI)
6709560B2
And
elman
andWalker
2007
Macropo
rous
copo
lymersw
ithlargepo
res(0.5–
200μ
m)
2008
0237
133A
1Dale,So
chilin,
andFrom
ent
2008
Rapidsensingof
toxicmetalsw
ithhybrid
inorganicmaterials
WO20
0815
1208
A1
Chatte
rjeean
dSenG
upta
2009
Removalof
alkyliod
ides
bystrong
acid
catio
nexchan
geresin
loaded
inAg+
-form
7588
690B
1Tsao
2010
Separatio
nof
ionicaque
ousm
ixturesw
ithionexchan
gematerialsin
anim
misc
ibleorganicph
ase
8940175B
2Kh
amizov
2013
Hybrid
ionexchan
ge-reverse
osmosisprocesses
Fluo
ride-selectiveresin
s:hybrid
anionexchan
geresin
with
zircon
ium
oxide
nano
particles
WO20
1419
3955
A1
2013
0274
357A
1SenG
upta
andSm
ithSenG
upta
andPa
dung
thon
Not
e:Pa
tentsa
reiss
uedfrom
theUSA
,unlessm
entio
nedothe
rwise
.
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6 Ion Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology
1.2 Water and Ion Exchange: An Eternal Kinship
Ion exchange is a heterogeneous process where water, themost abundant polar solventin our planet, is inevitably present. Even the ion exchange processes involving gases orsolids require the presence of water. It is imperative that we understand the fundamen-tal properties of water in order to follow the science of ion exchange. Oxygen is presentin Group VIA of the periodic table and water (H2O) is essentially a dihydride of oxy-gen. Note that sulfur (S) and selenium (Se) are also in the same group with oxygen buttheir dihydride, namely H2S and H2Se are volatile at room temperature. In contrast,water is liquid and an excellent solvent for salts with ionic bonds. In the electroneg-ativity scale, hydrogen and oxygen are far apart. While hydrogen is electropositive,oxygen is strongly electronegative. Thus, covalent O—H bonds in water molecules arepolar due to unequal sharing of bonding electrons with residual negative and posi-tive charges on oxygen and hydrogen atoms, respectively. Hence, water molecules areessentially dipoles (dipole moment= 1.85D), as shown in Figure 1.2a. The electronicstructure of the water molecule corresponds to the tetrahedral arrangement with theoxygen atom having two lone pairs of electrons as presented in Figure 1.2b.The dipolarwater molecules experience a torque when placed in an electric field and this torque iscalled a dipole moment. When molecules have dipole moments, their intermolecularforces are significantly greater, especially when dipole–dipole interactions or hydrogenbonding is possible. Water molecules are particularly well suited to interact with oneanother because each molecule has two polar O—H bonds and two lone pairs on theoxygen atom. This can lead to the association of four hydrogen atoms with one oxy-gen through a combination of covalent and hydrogen bonding as shown in Figure 1.3.Watermolecules thus exist as trimers (H6O3) and boiling requires a high heat of vapor-ization to break the intermolecular hydrogen bonds among water molecules. Thus,water has the highest boiling point among the entire Group VIA hydrides as shown inFigure 1.4.
2.202.20
The bent structure of a water molecule
(a) (b)
Tetrahedron
Lone
electron
pairs
3.44
Figure 1.2 Shape of water molecules (a) Dipolar O—H bonds with electronegativity values;(b) Electronic structure with tetrahedral arrangement.
�
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Ion Exchange and Ion Exchangers: An Introduction 7
Figure 1.3 Interaction of water moleculesthrough association of four hydrogen atoms witheach oxygen atom.
8+
8+
8+
8+
8–
8–
8–
8–
–100
–50
0
50
100
0 1 2 3 4
Boili
ng p
oin
t (˚
C)
Period on atomic table
H2S
H2O
H2Se
H2Te
Figure 1.4 Anomalous boiling point behavior of H2O in Group VIA hydrides.
Like dissolves like. Ionic compounds such as sodium chloride (NaCl) are highly sol-uble in water, which is an excellent polar solvent. When sodium chloride is addedto water, the dipolar water molecules separate sodium from chloride ions forming acluster of solvent molecules around them due to the ion–dipole interaction as pre-sented in Figure 1.5. This interaction is known as hydration and the hydrated ionicradius of an ion is always greater than its ionic radius.The degree of hydration dependsprimarily on the charges and the atomic mass of the ions. Ions with higher charges,and similar masses, always are more hydrated, that is, divalent calcium ion (Ca2+) ismore hydrated than monovalent sodium ion (Na+). For monatomic ions with identi-cal charges, hydrated ionic radius increases with a decrease in atomic mass or crystal
�
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8 Ion Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology
O
H
+ –
H
H H
HH
H
O
O
O
Na CIO O
Oδ+
δ+
δ–
δ–
O
H
H
HH H
HH
H
H
δ+δ
+
Figure 1.5 Illustration of ion–dipole interaction: Sodium chloride (ionic compound) solution inwater (polar solvent).
Table 1.2 Hydrated ionic radius and atomic mass of typicalmonatomic ions of interest.
Ions Atomic massCrystal ionicradii (pm)
Hydrated ionicradii (pm)
Li+ 6.94 59 382Na+ 22.99 102 358K+ 39.09 151 331Rb+ 85.46 161 329F− 18.99 133 352Cl− 35.45 181 332Br− 79.9 196 330Be2+ 9.01 27 459Mg2+ 24.3 72 428Ca2+ 40.07 100 412Sr2+ 87.62 126 412Ba2+ 137.33 142 404
Source: Conway 1981 [29]. Reproduced with permission of Elsevier.
ionic radius as illustrated in Table 1.2. Since the process of heterogeneous ion exchangeinevitably involves hydrated ions, the following observations are universally true:
(i) Binding of an ion onto a rigid ion exchanger requires partial shedding of water ofhydration and hence, all other conditions remaining identical, an ion with lowerhydrated ionic radius shows higher affinity. For example, both K+ and Na+ aremonovalent cations, but K+ is preferred over Na+ by cation exchange resins dueto its lower hydrated ionic radius.
(ii) An ion with a larger hydrated ionic radius is less mobile, that is, it has a lowerdiffusion coefficient. The kinetics of ion exchange are often a diffusion-controlledprocess. Thus, binding of an ion with a higher hydrated ionic radius is always akinetically slower process.
�
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�
Ion Exchange and Ion Exchangers: An Introduction 9
1.3 Constituents of an Ion Exchanger
An ion exchanger is ideally defined as a framework of fixed coions, which can be per-meated and electrically neutralized by mobile counterions from the aqueous (liquid)phase. The underlined terms in the foregoing definition require further elaboration.FRAMEWORK is much like a skeleton that constitutes a continuous phase, which
is held together by covalent bonds or lattice energy. For polymeric ion exchangers,covalent bonds predominate and the framework is often referred to as the matrix. Ininorganic ion exchangers, the lattice energy helps retain the ion exchange sites in thesolid phase and the framework is constituted by amorphous or crystalline structures.FIXED COIONS are electric surplus charges (positive or negative) on the framework,or the matrix, unable to leave their phase.This surplus charge is due to covalent bond-ing for polymeric ion exchangers and isomorphous substitution for zeolites and clays.MOBILE COUNTERIONS are solutes with charges opposite to the fixed coions.Theycompensate the charges of fixed coions in the exchanger phase and can also be replacedby other ions of the same sign on an equivalent basis. Unlike fixed coions, the counte-rions can permeate in and out of the exchanger phase and by doing so, they maintainelectroneutrality in both the liquid and the solid phase.For synthetic ion exchangers, fixed coions are known as functional groups or
ionogenic groups, while the exchanging ions are known as counterions. To readilygrasp the underlying concept without loss of generality, let us consider a polymeric ionexchanger where the three-dimensional cross-linked polymer constitutes a separateinsoluble phase or matrix. The covalently attached functional group is essentially thefixed coion that is permeated and electrically balanced by an exchangeable counterion.Figure 1.6 shows a simple schematic of a cation exchanger with sulfonic acid functionalgroups loaded with sodium counterions.Thermodynamically, the activity or concentration of an ion exchanger is not a
unique number, but it varies with the type and concentration of the counterion in the
Legend
Counterion
Functional group
Crosslinking:
Divinyl-benzene (DVB)
Polystyrene matrix
Commonly represented as: R-SO3–Na+
Figure 1.6 Schematic illustration of a strong acid cation exchange resin bead wherematrix/framework is represented by R, fixed coions or functional groups by —SO3
− andcounterions/exchanging ions by Na+.
�
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10 Ion Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology
exchanger phase. However, the fixed coions in an ion exchanger are always balancedby permeating counterions, that is, the ion exchanger is always electrically neutral.Ideally, the ion exchange capacity is equal to the concentration of the fixed coions.We will later see that the capacity is not a constant and it depends, to some extent, onthe external liquid phase concentration.To be familiar with the basic premise and terminologies of ion exchange processes,
let us consider the following cation exchange reaction between potassium and sodiumions:
(R − SO−3 )Na+ + K+(aq) + Cl−(aq) ↔ (R − SO−
3 )K+ +Na+(aq) + Cl−(aq) (1.4)
where the overbar denotes the exchanger phase; sulfonic acid functional group(—SO3
−) is the fixed, non-diffusible coion and Na+ and K+ are the permeable orexchanging counterions. The chloride ion does not participate in the cation exchangereaction and is referred to as a mobile coion. Both the exchanger and aqueous-phaseelectroneutrality remain undisturbed at every stage of the cation exchange reaction.Likewise, the anion exchange process is fundamentally the same, but the exchangerphase has positively charged fixed coions (e.g., quaternary ammonium functionalgroups, R4N+) as shown for the nitrate-chloride exchange reaction below:
(R4N+)Cl− +NO−3 (aq) +Na+(aq) ↔ (R4N+)NO−
3 + Cl−(aq) +Na+(aq) (1.5)
While NO−3 and Cl− are the permeating counterions, R4N+ and Na+ are the fixed and
mobile coions, respectively.
1.4 What is Ion Exchange andWhat is it Not?
Prior to getting into the details of the various materials presented in this book, it isimperative that we present a scientifically coherent definition of what we call “ionexchange.” A list of reactions, as shown below, are often mistakenly presented in theopen literature as ion exchange simply because the process appears to involve anexchange of equivalent amounts of cations or anions:
Pseudo-cation exchange:
FeS(s) + Cu2+(aq) ↔ CuS(s) + Fe2+(aq) (1.6)Fe2+(aq) + Zn0(s) ↔ Fe0(s) + Zn2+(aq) (1.7)
Pseudo-anion exchange:
BaCO3(s) + SO2−4 (aq) ↔ BaSO4(s) + CO2−
3 (aq) (1.8)
These are essentially precipitation–dissolution and redox reactions involving a puresolid phase denoted by “(s).” Since the activity of a pure independent solid phase(e.g., crystalline) is unity, the equilibrium constant of Reaction 1.6, consideringideality, is given by
K = [Fe2+][Cu2+]
(1.9)