SOIL COLLOIDS PROPERTIES AND ION RINDING Fernando V. Molina University of Bueno Aires Buenos Aires, Argentina CRC Press Taylor & Francis Croup Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Croup, an informa business
Contents Preface List of Common Greek Symbols List of Common Symbols List of Common Acronyms xxi xxiii xxv xxvii PART I Foundations Chapter 1 Introduction 3 1.1 Soil 3 1.2 Soil Chemistry, Soil Colloids, and Metal Ions 3 1.3 Book Contents 4 References 5 Chapter 2 Colloidal Particles and Colloidal Suspensions 7 2.1 Colloidal Particles 7 2.2 Soil Colloids 10 2.3 Colloidal Suspensions: General Properties and Classification 14-2.3.1 Importance of Surface in Colloidal Systems 17 2.3.2 Surface Energy 18 2.4 Fundamentals of Interfacia) Thermodynamics 19 2.4.1 Surface Excesses i9 2.4.2 Gibbs Equation 21 2.5 Summary 24 References 25 Chapter 3 Electrified Interface 27 3.1 Basic Principles 27 3.1.1 Electrochemical Equilibrium 27 3.1.2 Poisson and Poisson-Boltzmann Equations 29 3.1.2.1 Poisson Equation 29 3.1.2.2 Poisson-Boltzmann Equation 29 3.2 Application of the Poisson-Boltzmann Equation 31 3.2.1 Linearization of the PB Equation and the Debye-Huckel Theory 31 3.2.2 Gouy-Chapman Theory 3s xiii
(jv Contents 3.2.3 Analytical Solutions for Other Cases 37 3.2.3.1 Cylindrical Coordinates 37 3.2.3.2 Other Cases 39 3.2.4 Numerical Solutions to the Poisson-Boltzmann Equation 39 3.3 Interfacial Capacitance and the Stern and Grahame Models 42 3.3.1 Interfacial Capacitance 43 3.3.2 Stern Modification 44 3.3.3 Grahame Modification of the Gouy-Chapman- Stern Theory 47 3.4 Beyond the Poisson-Boltzmann Equation 49 3.5 Approximate Solutions of the PB Equation 55 3.6 Summary 56 References 56 Chapter 4 Sorption onto Colloidal Particles 63 4.1 General Concepts 63 4.2 Sorption Isotherms 63 4.2.1 Gas Phase Isotherm Types 64 4.2.2 Isotherm Classification for Sorption from Solution 69... 4.3 Physical Nature of Adsorption 75 4.3.1 Adsorption from Gas Phase 75 4.3.2 Adsorption from Solution 76 4.3.3 Interaction between a Molecule or Ion and a Surface 78 4.3.3.1 Intermolecular Interactions 78 4.3.3.2 Interactions with a Macroscopic Particle 83... 4.4 Theory of Adsorption Isotherms 86 4.4.1 Limiting (Henry) Isotherm 86 4.4.2 Ideal Monolayer: Langmuir Isotherm 86 4.4.3 Competitive and Multisite Langmuir Isotherms 89 4.4.4 Ideal Multilayer (BET) Isotherm 91 4.4.5 Beyond Ideal Isotherms 94 4.4.6 Adsorption with Interactions: The Fowler- Guggenheim Isotherm 95 4.4.7 Surface Heterogeneity 98 4.4.7.1 Sips Distribution Function 98 4.4.7.2 Langmuir-Freundlich and Freundlich Isotherms 99 4.5 Other Isotherm Equations 100 4.6 Isotherm Comparison and Assignment 103 4.7 Summary 106 References 106
Contents xv Chapter 5 Surface Charge of Colloidal Particles 111 5.1 Contributions to Surface Charge 111 5.1.1 Permanent Charge Ill 5.1.2 Protonic and Intrinsic Charge 112 5.1.3 Inner and Outer Sphere Complex Charges 113 5.1.4 Particle Charge Balance 114 5.1.5 Soil Charge 115 5.2 Ion Sorption and Surface Charge Development 116 5.3 Ion Exchange 118 5.3.1 Thermodynamics of Ion Exchange: Vanselow Convention 119 5.3.2 Other Conventions and Selectivity Coefficient Expressions 122 5.3.2.1 Kerr Convention 122 5.3.2.2 Gaines and Thomas Convention 122 5.3.2.3 Krishnamoorthy and Overstreet Convention 124 5.3.2.4 Gapon Selectivity Coefficient 125 5.3.2.5 Cerniketal. Convention 125 5.3.2.6 Other Aspects 126 5.3.3 Ion Exchange Analysis and Parameter Computation... 127 5.3.3.1 Argensinger Method 127 5.3.3.2 Rothmund-Kornfeld Method 130 5.3.4 Ion Exchange in Soils 131 5.3.4.1 Examples of Ion Exchange in Soils 133 5.3.4.2 Ion Preference 135 5.4 Determination of Surface Charge 138 5.4.1 Electrophoretic Methods 138 5.4.2 Titration Methods 144 5.5 Charge Contributions and Points of Zero Charge 147 5.5.1 Indifferent Electrolytes 148 5.5.2 Charge in the Presence of Specific Adsorption 151 5.6 Summary 153 References '54 Chapter 6 Interparticle Interactions and Colloid Stability 159 6.1 Thermodynamics of Particle-Particle Interaction 159 6.2 van der Waals Particle-Particle Interactions 161 6.3 Energies and Forces of Interaction 166 6.4 Eleciroslatic Interactions 16H 6.4.1 Constant Potential Conditions 170 6.4.1.1 Linear Approximation: The Hogg- Healy-Fuerstenau Theory 170
xvi Contents 6.4.1.2 Identical Particles: Verwey-Overbeek Results 171 6.4.1.3 Derjaguin Theory 172 6.4.2 Constant Charge Conditions and Comparison with Constant Potential 174 6.4.3 Charge Regulation 176 6.5 Total Long-Range Interactions 178 6.5.1 Similar Surfaces: Classic DLVO Theory 178 6.5.2 Dissimilar Particles 182 6.5.3 Colloidal Suspension Stability 183 6.6 Beyond DLVO 188 6.6.1 DLVO Theory Limitations 188 6.6.2 DLVO Extensions 190 6.6.3 Alternative Models 191 6.7 Summary 192 References 193 PART II Soil Components Chapter 7 Soil Composition and Characterization 201 7.1 General Characteristics 201 7.1.1 Soil Structure 201 7.1.2 Gas, Liquid, and Solid Soil Phases 203 7.1.3 Soil Particles 205 7.1.4 Soil Solution 205 7.2 Soil Composition 207 7.2.1 Soil Minerals 207 7.2.1.1 Primary Minerals 208 7.2.1.2 Secondary Minerals 210 7.2.1.3 Structural Elements of Soil Minerals 2! 1 7.2.2 Soil Organic Matter 212 7.2.2.1 Humic Substances 214 7.2.2.2 Nonhumic Substances 215 7.3 X-Ray-Based Characterization Methods 218 7.3.1 X-Ray Diffraction 218 7.3.2 X-Ray Absorption-Based Methods 219 7.3.3 X-Ray Fluorescence 224 7.3.4 X-Ray Photoelectron Spectroscopy 224 7.4 Other Spectroscopic Methods 227 7.4.1 UV-Visible Molecular Spectrometries 227 7.4.2 UV-Visible Atomic Spectrometry 228 7.4.3 Infrared Spectroscopy 229 7.4.4 Nuclear Magnetic Resonance 232
Contents xvii 7.5 Microscopies 237 7.5.1 Optical Microscopy 237 7.5.2 Electron Microscopy 237 7.5.3 Atomic Force Microscopy 238 7.6 Miscellaneous Methods 241 7.6.1 Neutron Activation Analysis 241 7.6.2 Electrophoretic Separations 242 7.6.3 Field-Flow Fractionation 243 7.6.4 Surface Area Measurement 243 7.6.4.1 Physical Methods 243 7.6.4.2 Positive Adsorption Methods 244 7.6.4.3 Negative Adsorption Methods 248 7.6.5 Thermal Analysis Methods 249 7.6.5.1 Differential Thermal Analysis 249 7.6.5.2 Differential Scanning Calorimetry 252 7.6.5.3 Thermogravimetry 253 7.7 Chemical Characterization 253 7.8 Soil Analysis 253 7.9 Summary 255 References 255 Chapter 8 Silicate-Based Minerals 265 8.1 Structure and Classification of Silicate-Based Minerals 265 8.2 Kaolin-Serpentine Group (1:1) Clays 277 8.3 Low Permanent Charge 2:1 Phyllosilicates: Pyrophyllite- Talc Group 278 8.4 Permanently Charged 2:1 Phyllosilicate Minerals 279 8.4.1 Micas 279 8.4.2 Vermiculites 281 8.4.3 Smectites 282 8.4.4 Chlorites 283 8.4.5 Interstratified Phyllosilicates 285 8.5 Other Aluminosilicate Minerals 286 8.5.1 Allophane and Imogolite 286 8.5.2 Palygorskite and Sepiolite 287 8.5.3 Zeolites 288 8.6 Characterization of Silicate Minerals 289 8.6.1 Identification and Crystalline Structure 289 8.6.2 Ion Exchange 290 8.6.3 Specific Surface Area 291 8.7 Ion Binding to Silicate-Based Minerals 293 8.8 Summary 293 References 295
xvjjj Contents Chapter 9 Oxide Minerals 299 9.1 Silica Minerals 299 9.2 Aluminum (Hydr)Oxides 300 9.3 Iron (Hydr)Oxides.' 307 9.4 Manganese Oxides 311 9.5 Titanium and Zirconium Oxide Minerals 314 9.5.1 Titanium Oxides 314 9.5.2 Zirconium Minerals 318 9.6 Characterization of Oxides 318 9.6.1 Identification and Crystalline Structure 318 9.6.2 Spectroscopic Studies 318 9.6.3 Specific Surface Area and Surface Charge 321 9.6.4 Miscellaneous Methods 323 9.7 Ion Binding to Oxide Minerals 323 9.7.1 Cation Binding 324 9.7.2 Anion Binding 328 9.8 Summary 332 References 332 Chapter 10 Humic Substances 337 10.1 Nature and Classification of Soil Humic Substances 337 10.2 Extraction of HS 338 10.2.1 Alkaline Extraction 339 10.2.2 Mild Extractants 341 10.2.2.1 Na4P207 and Other Neutral Salts 341 10.2.2.2 Formic Acid (HCOOH) 341 10.2.2.3 Organic Chelating Agents 341 10.2.3 Sequential Extractions 342 10.3 Characterization, Composition, and Structure of HS 342 10.3.1 Elemental Composition 342 10.3.2 Molecular Weight and Size Distributions 342 10.3.2.1 Colligative Properties 343 10.3.2.2 Light Scattering 344 10.3.2.3 Size-Exclusion Chromatography 345 10.3.2.4 Ultracentrifugation 345 10.3.2.5 Viscosimetry 347 10.3.2.6 Microscopic Observation 348 10.3.2.7 Other Techniques 349 10.3.3 Spectroscopic Methods 350 10.3.3.1 Infrared Spectroscopy 350 10.3.3.2 Nuclear Magnetic Resonance 350 10.3.3.3 UV-Visible and Fluorescence Spectroscopy 352
Contents xix 10.3.4 Functional Groups and Acid-Base Properties 359 10.3.4.1 Functional Group Analysis 359 10.3.4.2 Structural Studies by Chemical Degradative Methods 361 10.3.4.3 Structural Studies by Thermal Degradation 362 10.3.5 Molecular Structure of HS 364 10.4 Ion Binding to Hs 370 10.5 Summary 373 References 373 PART III Ion Binding to Soil Colloids Chapter 11 Modeling Ion Binding: General Concepts 383 11.1 General Problem 383 11.1.1 Chemical Modeling 385 11.1.2 Modeling Bases 387 11.2 Affinity Spectra 388 11.2.1 Discrete Affinity Spectra 389 11.2.1.1 Proton-Binding Equilibrium 389 11.2.1.2 Competitive Binding 390 11.2.2 Continuous Affinity Spectra 391 11.2.2.1 Proton Binding 392 11.2.2.2 Competitive Metal Binding 393 11.3 Extraction of Affinity Spectra 396 11.3.1 Intrinsic and Conditional Equilibrium Constants...397 11.3.2 Semianalytical Methods 397 11.3.3 Modified Least Squares Methods 399 11.3.4 Maximum Entropy Formalism 405 11.4 Kinetic Aspects 406 11.5 Summary 408 References 408 Chapter 12 Ion Binding to Minerals: Discrete Site Modeling 415 12.1 Ion Binding to Mineral Components 415 12.2 Generic Surface Description: Classical Electrostatic Models...416 12.2.1 Triple-Layer Model 416 12.2.1.1 Model Statement 416 12.2.1.2 Applications of the Triple-Layer Model...420 12.2.1.3 Further Advances: Extended Triple-Layer Model 422
XX Contents 12.2.2 Simplified Modeling: Basic Stern and Constant Capacitance Models 424 12.2.3 Stern Extended or Quad Layer Model 428 12.3 Detailed Surface Description: CD-MUSIC Model 430 12.3.1 Model Formulation 430 12.3.2 Application of the CD-MUSIC Model 433 12.4 Comparison between Models 434 12.5 Application to Charge Regulation between Particles 437 12.6 Summary 441 References 442 Chapter 13 Ion Binding to Humic Substances: Distributed Site Modeling 447 13.1 Ion Binding to Soil Organic Matter 447 13.2 Affinity Spectra of Humic Substances 447 13.2.1 Discrete Affinity Spectra 448 13.2.2 Continuous Affinity Spectra 452 13.2.3 Structure-Based Affinity Spectra 453 13.3 Electrostatic Modeling of Ion Binding to Humic Particles... 455 13.3.1 Particle Models 455 13.3.2 Donnan Phase Models 457 13.4 Models for Ion Binding to Humic Substances 460 13.4.1 Windermere Humic Models 460 13.4.2 Stockholm Humic Model 462 13.4.3 NICA-Donnan Model 466 13.4.4 NICA-EPN Model 468 13.4.5 Comparison of the Different Models 470 13.5 Summary 472 References 473 Chapter 14 Ion Binding to Soils 479 14.1 State of Soil Components in Natural Soils 479 14.2 Ion Binding to Several Soil Components 480 14.2.1 Additivity Rule 480 14.2.2 Sorption to Binary and Ternary Component Systems 481 14.2.3 Sorption in Complex Systems and Whole Soils 485 14.3 Models for Ion Sorption to Soils 490 14.3.1 Assemblage Models 490 14.3.2 Incorporation of HS-Mineral Interaction: LCD Model 493 14.4 Summary and Perspectives 495 References 496 Index 501