AQUATIC CHEMISTRY

Chemical Equilibria and Rates in Natural Waters

Third Edition

WERNER STUMMEAWAG, Swiss Federal Institute of Technology (ETH), Zurich

JAMES J. MORGANEnvironmental Engineering Science, California Institute of Technology

A WILEY-MTERSCIENCE PUBLICATION

JOHN WILEY & SONS, INC.New York • Chichester • Brisbane • Toronto • Singapore

CONTENTS

1. Introduction 1

1.1 Scope of Aquatic Chemistry 11.2 The Solvent Water 61.3 Solute Species 9

Suggested Readings 11Appendix 1.1: Some Useful Quantities, Units, Conversion

Factors, Constants, and Relationships 11

2. Chemical Thermodynamics and Kinetics 16

2.1 Introduction 162.2 Chemical Thermodynamic Principles 202.3 Systems of Variable Composition: Chemical

Thermodynamics 292.4 Gibbs Energy and Systems of Variable Chemical

Composition 322.5 Chemical Potentials of Pure Phases and Solutions 352.6 Chemical Potentials of Aqueous Electrolytes 382.7 The Equilibrium Constant 412.8 The Gibbs Energy of a System 442.9 Driving Force for Chemical Reactions 492.10 Temperature and Pressure Effects on Equilibrium 522.11 Equilibrium Tools 572.12 Kinetics and Thermodynamics: Time and Reaction

Advancement, £ 582.13 Rate and Mechanism 612.14 Concentration Versus Time 642.15 Theory of Elementary Processes 692.16 Elementary Reactions and ACT 762.17 Equilibrium Versus Steady State in Flow Systems 79

Suggested Readings 81Problems 82Answers to Problems 85

XI

xii Contents

3. Acids and Bases 88

3.1 Introduction 883.2 The Nature of Acids and Bases 903.3 The Strength of an Acid or Base 923.4 Activity and pH Scales 973.5 Equilibrium Calculations 1053.6 pH as a Master Variable; Equilibrium Calculations Using

a Graphical Approach 1183.7 Ionization Fractions of Acids, Bases, and Ampholytes 1273.8 Titration of Acids and Bases 1303.9 Buffer Intensity and Neutralizing Capacity 1343.10 Organic Acids 140

Suggested Readings 144Problems 144Answers to Problems 147

4. Dissolved Carbon Dioxide 148

4.1 Introduction 1484.2 Dissolved Carbonate Equilibria (Closed System) 1504.3 Aqueous Carbonate System Open to the Atmosphere 1574.4 Alkalinity and Acidity, Neutralizing Capacities 1634.5 Alkalinity Changes 1724.6 Analytical Considerations: Gran Plots 1794.7 Equilibrium with Solid Carbonates 1864.8 Kinetic Considerations 1924.9 Carbon Isotopes and Isotope Fractionation 195

Suggested Readings 202Problems 202Answers to Problems 204

5. Atmosphere-Water Interactions 206

5.1 Introduction 2065.2 Anthropogenic Generation of Acidity in the Atmosphere 2075.3 Gas-Water Partitioning: Henry's Law 2125.4 Gas-Water Equilibria in Closed and Open Systems 2165.5 Washout of Pollutants from the Atmosphere 2275.6 Fog 2295.7 Aerosols 2335.8 Acid Rain-Acid Lakes 2355.9 The Volatility of Organic Substances 2385.10 Gas Transfer Across Water-Gas Interface 241

Suggested Readings 248Problems 249Answers to Problems 251

Contents xiii

6. Metal Ions in Aqueous Solution: Aspects of CoordinationChemistry 252

6.1 Introduction 2526.2 Protons and Metal Ions 2586.3 Hydrolysis of Metal Ions 2636.4 Solubility and Hydrolysis: Solid Hydroxides and Metal

Oxides 2726.5 Chelates 2756.6 Metal Ions and Ligands: Classification of Metals 2816.7 Speciation in Fresh Waters 2896.8 Seawater Speciation 3056.9 Kinetics of Complex Formation 311

Suggested Readings 319Problems 320Answers to Problems 322Appendix 6.1: Stability Constants 325Appendix 6.2: The Various Scales for Equilibrium

Constants, Activity Coefficients, and pH 335

7. Precipitation and Dissolution 349

7.17.27.37.47.5

7.67.7

7.87.9

IntroductionThe Solubility of Oxides and HydroxidesComplex Formation and Solubility of (Hydr)oxidesCarbonatesThe Stability of Hydroxides, Carbonates, and HydroxideCarbonatesSulfides and PhosphatesThe Phase Rule: Components, Phases, and Degrees ofFreedom >Solubility of Fine ParticlesSolid SolutionsSuggested ReadingsProblemsAnswers to Problems

349359368370

389398

409413416420420424

8. Oxidation and Reduction; Equilibria and MicrobialMediation 425

8.1 Introduction 4258.2 Redox Equilibria and the Electron Activity 4268.3 The Electrode Potential: The Nernst Equation and the

Electrochemical Cell '. 4418.4 pe-pH, Potential-pH Diagrams 4558.5 Redox Conditions in Natural Waters 4648.6 Effect of Complex Formers on the Redox Potential 489

xiv Contents

8.7 Measuring the Redox Potential in Natural Waters 491§.8 The Potentiometric Determination of Individual Solutes 498

Suggested Readings 506Problems 507Answers to Problems 512Appendix 8.1: Activity Ratio Diagrams for Redox Systems 513

9. The Solid-Solution Interface 516

9.1 Introduction 5169.2 Adsorption 5199.3 Adsorption Isotherms 5219.4 Hydrous Oxide Surfaces; Reactions with H+ , OH~, Metal

Ions, and Ligands 5339.5 Surface Charge and the Electric Double Layer 5499.6 Correcting Surface Complex Formation Constants for

Surface Charge 5689.7 Sorption of Hydrophobic Substances on Organic Carbon-

Bearing Particles 5759.8 Ion Exchange 5869.9 Transport of (Ad)sorbable Constituents in Groundwater

and Soil Systems 594Suggested Readings 599Problems 601Appendix 9.1: The Gouy-Chapman Theory 604Appendix 9.2: Contact Angle, Adhesion and Cohesion, the

Oil-Water Interface 608

10. Trace Metals: Cycling, Regulation, and Biological Role 614

10.1 Introduction: Global Cycling of Metals 61410.2 Analytical Approaches to Chemical Speciation 61510.3 Classification of Metal Ions and the Inorganic Chemistry

of Life 62510.4 Organometallic and Organometalloidal Compounds 62810.5 Bioavailability and Toxicity 63210.6 Metal Ions as Micronutrients 63710.7 The Interaction of Trace Metals with Phytoplankton at

the Molecular Level 64110.8 Regulation of Trace Elements by the Solid-Water

Interface in Surface Waters *64810.9 Regulation of Dissolved Heavy Metals in Rivers, Lakes,

and Oceans 65410.10 Quality Criteria in Fresh Waters: Some Aspects 666

Suggested Readings ^ 670

Contents xv

11. Kinetics of Redox Processes 672

11 1 Introduction 67211.'2 How Good an Oxidant Is O2? 67211.3 Can pe Be Defined for a Nonequilibrium System? 67711.4 Kinetics of Redox Processes: Case Studies 67911.5 Oxidants Used in Water and Waste Technology: A Few

Case Studies 69111.6 Linear Free Energy Relations (LFERs) 70211.7 The Marcus Theory of Outer-Sphere Electron Transfer:

An Introduction 70311.8 Nucleophile-Electrophile Interactions and Redox

Reactions Involving Organic Substances 71011.9 Corrosion of Metals as an Electrochemical Process 720

Suggested Readings 725

12. Photochemical Processes 726

12.1 Introduction 72612.2 Absorption of Light 72912.3 Photoreactants 73512.4 Photoredox Reactions: Photolysis of Transition Metal

Complexes 74312.5 Photochemical Reactions in Atmospheric Waters: Role of

Dissolved Iron Species 74412.6 Heterogeneous Photochemistry 74812.7 Semiconducting Minerals 753

Suggested Readings 759

13. Kinetics at the Solid-Water Interface: Adsorption,Dissolution of Minerals, Nucleation, and Crystal Growth 760

13.113.213.3

13.413.5

13.613.7

IntroductionKinetics of AdsorptionSurface-Controlled Dissolution of Oxide Minerals: AnIntroduction to WeatheringSimple Rate Laws in DissolutionRates of CaCO3 Dissolution (and of CaCO3 CrystalGrowth)Inhibition of DissolutionNucleation and Crystal GrowthSuggested Readings

760760

771776

788795800816

14. Particle-Particle Interaction: Colloids, Coagulation, andFiltration < 818

14.1 Colloids 81814.2 Particle Size Distribution 826

xvi Contents

14.3 Surface Charge of Colloids 834J4.4 Colloid Stability: Qualitative Considerations 83714.5 Effects of Surface Speciation on Colloid Stability 84214.6 Some Water-Technological Considerations in

Coagulation, Filtration, and Flotation 85214.7 Filtration Compared with Coagulation 85714.8 Transport in Aggregation and Deposition 858

Suggested Readings 866Appendix 14.1: A Physical Model (DLVO) for Colloid

Stability 867

15. Regulation of the Chemical Composition of Natural Waters 872

15.1 Introduction 87215.2 Weathering and the Proton Balance 87515.3 Isothermal Evaporation 88015.4 Buffering 88415.5 Interactions Between Organisms and Abiotic

Environment: Redfield Stoichiometry 88615.6 The Oceans: Relative Constancy of the Composition and

Chemical Equilibria 89515.7 Constancy of Composition: Steady State 89715.8 Hydrothermal Vents 90115.9 The Sediment-Water Interface 90315.10 Biological Regulation of the Composition 90815.11 Global Cycling: The Interdependence of Biogeochemical

Cycles 91415.12 The Carbon Cycle 91615.13 Nitrogen Cycles: Pollution by Nitrogen Compounds 92715.14 The Sulfur Cycle 932

Suggested Readings 933

References 935

Appendixes: Thermodynamic Data 976

1 Revised Chemical Equilibrium Data for Major Water-Mineral Reactions 977

2 Thermodynamic Data for Trace Metal Speciation in Seawater 9843 Thermodynamic Properties 990

Index 1005