Ion Exchange in Environmental Processes

Arup K. SenGupta, PhD is the P.C. Rossin Professor in the Department of Civil and Environmental Engineering and Department of Chemical Engineering at Lehigh University. Over the last 35 years he has studied, learned, taught and conducted extensive research into nearly every facet of ion exchange. Dr. SenGupta is recognized as the inventor of hybrid ion exchange nanotechnology (HIX-Nano) that offers enhanced separation through the Donnan Membrane Principle. HIX-Nano materials are currently in use in six different countries including the USA to remove arsenic, fluoride and phosphate from contaminated water and waste water. In 2004, Dr. SenGupta received the International Ion Exchange Award at Cambridge University in England. He was the North American Editor of the Reactive and Functionalized Polymers Journal from 1996-2006.

Preface xiii

Acknowledgment xvii

1 Ion Exchange and Ion Exchangers: An Introduction 1

1.1 Historical Perspective 1

1.2 Water and Ion Exchange: An Eternal Kinship 6

1.3 Constituents of an Ion Exchanger 9

1.4 What is Ion Exchange and What it is Not? 10

1.5 Genesis of Ion Exchange Capacity 12

1.5.1 Inorganic 12

1.5.2 Organic/Polymeric Ion Exchanger 13

1.5.3 Strong-Base Type I and Type II Anion Exchanger 20

1.6 Biosorbent, Liquid Ion Exchanger, and Solvent Impregnated Resin 23

1.6.1 Biosorbent 23

1.6.2 Liquid Ion Exchange 25

1.6.3 Solvent-Impregnated Resins 27

1.7 Amphoteric Inorganic Ion Exchangers 28

1.8 Ion Exchanger versus Activated Carbon: Commonalities and Contrasts 33

1.9 Ion Exchanger Morphologies 34

1.10 Widely Used Ion Exchange Processes 34

1.10.1 Softening 35

1.10.2 Deionization or Demineralization 40

Summary 44

References 45

2 Ion Exchange Fundamentals 50

2.1 Physical Realities 50

2.2 Swelling/Shrinking: Ion Exchange Osmosis 51

2.3 Ion Exchange Equilibrium 55

2.3.1 Genesis of Non-Ideality 57

2.4 Other Equilibrium Constants and Equilibrium Parameters 59

2.4.1 Corrected Selectivity Coefficient 59

2.4.2 Selectivity Coefficient, K IXse 60

2.4.3 Separation Factor (α A B) 60

2.4.4 Separation Factor: Homovalent Ion Exchange 61

2.4.5 Separation Factor: Heterovalent Exchange 62

2.4.6 Physical Reality of Selectivity Reversal: Role of Le Châtelier’s Principle 65

2.4.7 Equilibrium Constant: Inconsistencies and Potential Pitfalls 66

2.5 Electrostatic Interaction: Genesis of Counterion Selectivity 69

2.5.1 Monovalent–Monovalent Coulombic Interaction 69

2.6 Ion Exchange Capacity: Isotherms 73

2.6.1 Batch Technique 75

2.6.2 Regenerable Mini-Column Method 79

2.6.3 Step-Feed Frontal Column Run 81

2.7 The Donnan Membrane Effect in Ion Exchanger 84

2.7.1 Coion Invasion or Electrolyte Penetration 84

2.7.2 Role of Cross-linking 90

2.7.3 Genesis of the Donnan Potential 90

2.8 Weak-Acid and Weak-Base Ion Exchange Resins 92

2.8.1 pKa Values of Weak Ion Exchange Resins 94

2.8.2 Weak-Acid and Weak-Base Functional Groups 96

2.9 Regeneration 98

2.9.1 Selectivity Reversal in Heterovalent Ion Exchange 100

2.9.2 pH Swings 101

2.9.3 Ligand Exchange with Metal Oxides 105

2.9.4 Use of Co-Solvent 106

2.9.5 Dual-Temperature Regeneration 108

2.9.6 Carbon Dioxide Regeneration 111

2.9.7 Regeneration with Water 112

2.10 Resin Degradation and Trace Toxin Formation 112

2.10.1 Formation of Trace Nitrosodimethylamine (NDMA) from Resin Degradation 114

2.11 Ion Exclusion and Ion Retardation 115

2.11.1 Ion Exclusion 115

2.11.2 Ion Retardation 116

2.12 Zwitterion and Amino Acid Sorption 118

2.12.1 Interaction with a Cation Exchanger: Role of pH 119

2.13 Solution Osmotic Pressure and Ion Exchange 121

2.14 Ion Exchanger as a Catalyst 124

Summary 126

References 127

3 Trace Ion Exchange 130

3.1 Genesis of Selectivity 130

3.2 Trace Isotherms 136

3.3 Multi-Component Equilibrium 138

3.4 Agreement with Henry’s Law 140

3.5 Multiple Trace Species: Genesis of Elution Chromatography 143

3.5.1 Determining Separation Factor from Elution Chromatogram 143

3.6 Uphill Transport of Trace Ions: Donnan Membrane Effect 149

3.7 Trace Leakage 151

3.8 Trace Fouling by Natural Organic Matter 153

3.9 Ion Exchange Accompanied by Chemical Reaction 156

3.9.1 Precipitation 156

3.9.2 Complexation 157

3.9.3 Redox Reaction 157

3.10 Monovalent–Divalent Selectivity 158

3.10.1 Effect of Charge Separation: Mechanistic Explanation 158

3.10.2 Nitrate/Sulfate and Chloride/Sulfate Selectivity in Anion Exchange 160

3.10.3 Genesis of Nitrate-Selective Resin 162

3.10.4 Chromate Ion Selectivity 164

3.11 Entropy-Driven Selective Ion Exchange: The Case of Hydrophobic Ionizable Organic Compound (HIOC) 166

3.11.1 Focus of the Study and Related Implications 167

3.11.2 Nature of Solute–Sorbent and Solute–Solvent Interactions 169

3.11.3 Experimental Observations: Stoichiometry, Affinity Sequence, and Cosolvent Effect 173

3.11.4 Energetics of the Sorption Process 177

3.11.5 Unifying Hydrophobic Interaction: From Gas–Liquid to Liquid–Solid System 179

3.11.6 Effect of Polymer Matrix and Solute Hydrophobicity 182

3.12 Linear Free Energy Relationship and Relative Selectivity 183

3.13 Simultaneous Removal of Target Metal Cations and Anions 186

3.14 Deviation from Henry’s Law 188

3.14.1 Ions Forming Polynuclear Species 188

3.15 Tunable Sorption Behaviors of Amphoteric Metal Oxides 192

3.16 Ion Sieving 195

3.17 Trace Ion Removal 201

3.17.1 Uranium(VI) 201

3.17.2 Radium 203

3.17.3 Boron 204

3.17.4 Perchlorate (ClO − 4) 205

3.17.5 Emerging Contaminants of Concern and Multi-Contaminant Systems 208

3.17.6 Arsenic and Phosphorus: As(V), P(V), and As(III) 210

3.17.7 Fluoride (F −) 214

Summary 215

References 216

4 Ion Exchange Kinetics: Intraparticle Diffusion 224

4.1 Role of Selectivity 224

4.2 State of Water Molecules inside Ion Exchange Materials 232

4.3 Activation Energy Level in Ion Exchangers: Chemical Kinetics 235

4.3.1 Activation Energy Determination from Experimental Results 236

4.4 Physical Anatomy of an Ion Exchanger: Gel, Macroporous and Fibrous Morphology 242

4.4.1 Gel-Type Ion Exchanger Beads 242

4.4.2 Macroporous Ion Exchanger Beads 243

4.4.3 Ion Exchange Fibers 246

4.5 Column Interruption Test: Determinant of Diffusion Mechanism 248

4.6 Observations Related to Ion Exchange Kinetics 250

4.6.1 Effect of Concentration on Half-time (t 1∕2) 251

4.6.2 Major Differences in Ion Exchange Rate 252

4.6.3 Chemically Similar Counterions with Significant Differences in Intraparticle Diffusivity 252

4.6.4 Effect of Competing Ion Concentrations: Gel versus Macroporous 254

4.6.5 Intraparticle Diffusion during Regeneration 255

4.6.6 Shell Progressive Kinetics versus Slow Diffusing Species 255

4.7 Interdiffusion Coefficients for Intraparticle Diffusion 257

4.8 Trace Ion Exchange Kinetics 264

4.8.1 Chlorophenols as the Target Trace Ions 264

4.8.2 Intraparticle Diffusion inside a Macroporous Ion Exchanger 266

4.8.3 Effect of Sorption Affinity on Intraparticle Diffusion 268

4.8.4 Solute Concentration Effect 271

4.9 Rectangular Isotherms and Shell Progressive Kinetics 272

4.9.1 Anomalies in Arrival Sequence of Solutes 274

4.9.2 Quantitative Interpretation 275

4.10 Responses to Observations in Section 4.6 276

4.10.1 Effect of Concentration on Half-time (t 1∕2) 276

4.10.2 Slow Kinetics of Weak-Acid Resin 277

4.10.3 Chemically Similar Counterions: Drastic Difference in Intraparticle Diffusivity 277

4.10.4 Gel versus Macroporous 278

4.10.5 Intraparticle Diffusion during Regeneration 278

4.10.6 Shrinking Core or Shell Progressive Kinetics 279

4.11 Rate-Limiting Step: Dimensionless Numbers 280

4.11.1 Implications of Biot Number: Trace Ion Exchange 281

4.12 Intraparticle Diffusion: From Theory to Practice 284

4.12.1 Reducing Diffusion Path Length: Short-Bed Process and Shell–Core Resins 285

4.12.2 Development of Bifunctional Diphonix ® Resin 288

4.12.3 Ion Exchanger as a Host for Enhanced Kinetics 289

Summary 292

References 293

5 Solid- and Gas-Phase Ion Exchange 297

5.1 Solid-Phase Ion Exchange 297

5.1.1 Poorly Soluble Solids 297

5.1.2 Desalting by Ion Exchange Induced Precipitation 303

5.1.3 Separation of Competing Solid Phases 305

5.1.4 Recovery from Ion Exchange Sites of Soil 306

5.1.5 Composite or Cloth-like Ion Exchanger (CIX) 307

5.1.6 Heavy Metals (Me 2+) with Solids Possessing High Buffer Capacity 309

5.1.7 Ligand-Induced Metal Recovery with a Chelating Exchanger 315

5.2 Coagulant Recovery from Water Treatment Sludge 317

5.2.1 Development of Donnan IX Membrane Process 318

5.2.2 Alum Recovery: Governing Donnan Equilibrium 318

5.2.3 Process Validation 322

5.3 Gas Phase Ion Exchange 323

5.3.1 Sorption of Acidic and Basic Gases 324

5.3.2 CO2and SO2 Capture with Weak-Base Anion (WBA) Exchanger 325

5.3.3 Effect of Ion Exchanger Morphology 327

5.3.4 Redox Active Gases: Hydrogen Sulfide and Oxygen 330

5.4 CO2 Gas as a Regenerant for IX Softening Processes: A Case Study 334

Summary 339

References 340

6 Hybrid Ion Exchange Nanotechnology (HIX-Nanotech) 345

6.1 Magnetically Active Polymer Particles (MAPPs) 347

6.1.1 Characterization of MAPPs 351

6.1.2 Factors Affecting Acquired Magnetic Activity 353

6.1.3 Retention of Magnetic Activity and Sorption Behavior 355

6.2 Hybrid Nanosorbents for Selective Sorption of Ligands (e.g., HIX-NanoFe) 357

6.2.1 Synthesis of Hybrid Ion Exchange Nanomaterials 359

6.2.2 Characterization of Hybrid Nanosorbents 361

6.2.3 Parent Anion Exchanger versus Hybrid Anion Exchanger (HAIX-NanoFe(III)): A Comparison 363

6.2.4 Support of Hybrid Ion Exchangers: Cation versus Anion 365

6.2.5 Efficiency of Regeneration and Field Application 369

6.2.6 Hybrid Ion Exchange Fibers: Simultaneous Perchlorate and Arsenic Removal 370

6.3 HAIX-NanoZr(IV): Simultaneous Defluoridation and Desalination 376

6.3.1 Field-Scale Validation 377

6.4 Promise of HIX-Nanotechnology 381

Summary 383

References 384

7 Heavy Metal Chelation and Polymeric Ligand Exchange 391

7.1 Heavy Metals and Chelating Ion Exchangers 391

7.1.1 Heavy Metals: What are They? 391

7.1.2 Properties of Heavy Metals and Separation Strategies 393

7.1.3 Emergence of Chelating Exchangers 395

7.1.4 Lewis Acid–Base Interactions in Chelating Ion Exchangers 398

7.1.5 Regeneration, Kinetics and Metals Affinity 402

7.2 Polymeric Ligand Exchange 405

7.2.1 Conceptualization and Characterization of the Polymeric Ligand Exchanger (ple) 406

7.2.2 Sorption of Polymeric Ligand Exchangers 407

7.2.3 Validation of Ligand Exchange Mechanism 410

Summary 413

References 413

8 Synergy and Sustainability 417

8.1 Waste Acid Neutralization: An Introduction 417

8.1.1 Underlying Scientific Concept 418

8.1.2 Mechanical Work through a Cyclic Engine 421

8.2 Improving Stability of Anaerobic Biological Reactors 423

8.2.1 Potential Use of Selective Ion Exchanger 424

8.2.2 Ion Exchange Fibers: Characterization and Performance 424

8.3 Sustainable Aluminum-Cycle Softening for Hardness Removal 429

8.3.1 Current Status and Challenges 429

8.3.2 Sodium-Free Approaches and Alternatives to Na-Cycle Softening 429

8.3.3 Underlying Scientific Approach of Al-cycle Cation Exchange 430

8.3.4 Comparison in Performance: Na-Cycle versus Al-Cycle 432

8.3.5 Regeneration Efficiency and Calcium Removal Capacity 436

8.3.6 Sustainability Issues and New Opportunities 438

8.4 Closure 438

Summary 439

References 440

A Commercial Ion Exchangers 445

B Different Units of Capacity, Concentration, Mass, and Volume 457

B.1 Capacity 457

B.2 Concentration (Expressed as CaCO 3) 457

B.3 Mass 458

B.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