Environmental Soil Chemistry - Chapter 0 pdf

Environmental Soil Chemistry
Second Edition
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Environmental
Soil
Chemistry
Second Edition
Donald L. Sparks
University of Delaware
Amsterdam • Boston • London • New York • Oxford • Paris • San Diego •
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For Joy and my doctoral advisors, David C. Martens and Lucian W. Zelazny
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Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Environmental Soil Chemistry: An Overview . . . . . . . . . . . . . . . . . . . . . . . 1
Evolution of Soil Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
The Modern Environmental Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Contaminants in Water and Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Acid Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Trace Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Hazardous Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Case Study of Pollution of Soils and Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Soil Decontamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
In Situ Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Non-in-Situ Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Molecular Environmental Soil Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Electromagnetic Spectrum of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Synchrotron Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

X-Ray Absorption Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Other Molecular-Scale Spectroscopic and Microscopic Techniques . . . . . . . . . . 37
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Inorganic Soil Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Pauling’s Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Primary Soil Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Secondary Soil Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Phyllosilicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Oxides, Hydroxides, and Oxyhydroxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Carbonate and Sulfate Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Specific Surface of Soil Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
External Surface Area Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Total Surface Area Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Surface Charge of Soil Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Types of Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Cation Exchange Capacities of Secondary Soil Minerals . . . . . . . . . . . . . . . . . 64
CHAPTER 1
CHAPTER 2
Identification of Minerals by X-Ray Diffraction Analyses . . . . . . . . . . . . . . . . . . . . 68
Clay Separation and X-Ray Diffraction Analysis . . . . . . . . . . . . . . . . . . . . . . . 69
Use of Clay Minerals to Retain Organic Contaminants . . . . . . . . . . . . . . . . . . . . . 71
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Chemistry of Soil Organic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Effect of Soil Formation Factors on SOM Contents . . . . . . . . . . . . . . . . . . . . . . . . 77
Carbon Cycling and Sequestration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Composition of SOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Fractionation of SOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Molecular and Macromolecular Structure of SOM . . . . . . . . . . . . . . . . . . . . . . . . . 91

Functional Groups and Charge Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Humic Substance–Metal Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Factors Affecting Metal–Complexant (Ligand) Interactions . . . . . . . . . . . . . . 102
Determination of Stability Constants of Metal–HS Complexes . . . . . . . . . . . 106
Effect of HS–Metal Complexation on Metal Transport . . . . . . . . . . . . . . . . . 108
Effect of HS–Al
3+
Complexes on Plant Growth . . . . . . . . . . . . . . . . . . . . . . . 108
Effect of HS on Mineral Dissolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
SOM–Clay Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Mechanisms of Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Retention of Pesticides and Other Organic Substances by Humic Substances . . . 111
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Soil Solution–Solid Phase Equilibria . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Measurement of the Soil Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Speciation of the Soil Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Ion Activity and Activity Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Dissolution and Solubility Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Stability Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Sorption Phenomena on Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Introduction and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Surface Functional Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Surface Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Adsorption Isotherms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Equilibrium-based Adsorption Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Freundlich Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Langmuir Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Double-Layer Theory and Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

viii Contents
CHAPTER 3
CHAPTER 4
CHAPTER 5
Surface Complexation Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Deficiencies of Double-Layer and Surface Complexation Models . . . . . . . . . . 172
Sorption of Metal Cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Sorption of Anions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Surface Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Speciation of Metal-Contaminated Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
Points of Zero Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Definition of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Ion Exchange Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Characteristics of Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
Cation Exchange Equilibrium Constants and Selectivity Coefficients . . . . . . . . . . 190
Kerr Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Vanselow Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Other Empirical Exchange Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Thermodynamics of Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Experimental Interpretations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
Relationship Between Thermodynamics and Kinetics of Ion Exchange . . . . . . . . . 203
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
Kinetics of Soil Chemical Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Rate-Limiting Steps and Time Scales of Soil Chemical Reactions . . . . . . . . . . . . . 207
Rate Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
Determination of Reaction Order and Rate Constants . . . . . . . . . . . . . . . . . . . . . 211
Kinetic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

Elovich Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
Parabolic Diffusion Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Fractional Power or Power Function Equation . . . . . . . . . . . . . . . . . . . . . . . 216
Comparison of Kinetic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Multiple Site Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Chemical Nonequilibrium Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Physical Nonequilibrium Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Kinetic Methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Batch Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Flow Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Relaxation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Choice of Kinetic Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Effect of Temperature on Reaction Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Kinetics of Important Soil Chemical Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Sorption–Desorption Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Contents ix
CHAPTER 6
CHAPTER 7
Kinetics of Metal Hydroxide Surface Precipitation/Dissolution . . . . . . . . . . . 232
Ion Exchange Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Kinetics of Mineral Dissolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Redox Chemistry of Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Oxidation–Reduction Reactions and Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Eh vs pH and pe vs pH Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Measurement and Use of Redox Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Submerged Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Redox Reactions Involving Inorganic and Organic Pollutants . . . . . . . . . . . . . . . 255
Mechanisms for Reductive Dissolution of Metal Oxides/Hydroxides . . . . . . . 257
Oxidation of Inorganic Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

Reductive Dissolution of Mn Oxides by Organic Pollutants . . . . . . . . . . . . . 260
Reduction of Contaminants by Iron and Microbes . . . . . . . . . . . . . . . . . . . . 261
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
The Chemistry of Soil Acidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Environmental Aspects of Acidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
Historical Perspective of Soil Acidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Solution Chemistry of Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Monomeric Al Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Polymeric Al Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Exchangeable and Nonexchangeable Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . 274
Soil Acidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Forms of Soil Acidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Effect of Adsorbed Aluminum on Soil Chemical Properties . . . . . . . . . . . . . . 278
Titration Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Liming Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
The Chemistry of Saline and Sodic Soils . . . . . . . . . . . . . . . . . . . . . . . 285
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
Causes of Soil Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Soluble Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Evapotranspiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Irrigation Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Sources of Soluble Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
Important Salinity and Sodicity Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
Total Dissolved Solids (TDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
Electrical Conductivity (EC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
Parameters for Measuring the Sodic Hazard . . . . . . . . . . . . . . . . . . . . . . . . . 292
x Contents

CHAPTER 8
CHAPTER 9
CHAPTER 10
Classification and Reclamation of Saline and Sodic Soils . . . . . . . . . . . . . . . . . . . 294
Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
Sodic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
Saline–Sodic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Effects of Soil Salinity and Sodicity on Soil Structural Properties . . . . . . . . . . . . . . 295
Effects of Soil Salinity on Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
Effects of Sodicity and Salinity on Environmental Quality . . . . . . . . . . . . . . . . . . 298
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
Appendix A: Periodic Table of the Elements . . . . . . . . . . . . . . . . . . . . 301
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
Contents xi
This Page Intentionally Left Blank
Preface
Since the first edition of Environmental Soil Chemistry was published in
1995, a number of important developments have significantly advanced the
soil and environmental sciences. These advancements were the primary
motivation for publishing the second edition. The use of synchrotron-based
spectroscopic and microscopic techniques, which employ intense light, has
revolutionized the field of environmental soil chemistry and allied fields such
as environmental chemistry, materials science, and geochemistry. The intense
light enables one to study chemical reactions and processes at molecular and
smaller scales and in situ. A new multidisciplinary field has evolved, molec-
ular environmental science, in which soil chemists are actively involved. It
can be defined as the study of the chemical and physical forms and distri-
bution of contaminants in soils, sediments, waste materials, natural waters,
and the atmosphere at the molecular level. Chapter 1 contains a major

section on molecular environmental science with discussions on synchrotron
radiation and important spectroscopic and microscopic techniques. The
application of these techniques has greatly advanced our understanding of
soil organic matter macromolecular structure (Chapter 3), mechanisms of
metal and metalloid sorption on soil components and soils, and speciation of
inorganic contaminants (Chapter 5). This second edition also contains new
information on soil and water quality (Chapter 1), carbon sequestration
(Chapter 3), and surface nucleation/precipitation (Chapter 5) and disso-
lution (Chapter 7). Other material throughout the book has been updated.
As with the first edition, the book provides extensive discussions on the
chemistry of inorganic and organic soil components, soil solution–solid phase
equilibria, sorption phenomena, kinetics of soil chemical processes, redox
reactions, and soil acidity and salinity. Extensive supplementary readings are
contained at the end of each chapter, and numerous boxes in the chapters
contain sample problems and explanations of parameters and terms. These
should be very useful to students taking their first course in soil chemistry.
The second edition is a comprehensive and contemporary textbook for
advanced undergraduate and graduate students in soil science and for students
and professionals in environmental chemistry and engineering, marine
studies, and geochemistry.
Writing the second edition of Environmental Soil Chemistry has been
extremely enjoyable and was made easier with the support and encourage-
ment of a number of persons. I am most grateful to the administration at the
University of Delaware for providing me with a truly wonderful environment
xiii
in which to teach and conduct research. I particularly want to thank our
great president of the University of Delaware, David P. Roselle, for his
fabulous support of me and my soil chemistry program during the last
decade. I am also extremely fortunate to have had an extraordinarily bright
and dedicated group of graduate students and postdoctoral fellows. The

highlight of my career has been to advise and mentor these fine young
scientists. I am also deeply indebted to support personnel. I especially want
to acknowledge Fran Mullen who typed the entire manuscript, Jerry
Hendricks who compiled the figures and secured permissions, and Amy
Broadhurst who prepared references and permissions. Without their support,
this book would not have resulted. I also am grateful to Dr. Charles Crumly
at Academic Press for his support and encouragement. Lastly, I shall be
forever grateful to my wife, Joy, for her constant understanding, love, and
encouragement.
Donald L. Sparks
xiv Preface