Cover -- Half-title -- Series-title -- Title -- Copyright -- Contents -- Preface -- 1 Introduction -- 2 Humic substances - a brief review -- 2.1 Natural organic matter and humic substances -- 2.2 Isolation and classification of humic substances -- 2.2.1 Isolation and fractionation procedures -- 2.2.2 Buffle's classification scheme for natural organic matter -- 2.3 Formation and decomposition of humic substances -- 2.3.1 Formation -- 2.3.2 Decomposition -- 2.4 Chemical and physical properties of humic substances -- 2.4.1 Elemental composition -- 2.4.2 Molecular structure -- 2.4.3 Molecular weight -- 2.4.4 Size and shape -- 2.4.5 Specific surface area of HS -- 2.4.6 Optical properties -- 2.5 Environmental concentrations of humic substances -- 2.5.1 Soil contents of humic substances -- 2.5.2 Concentrations of humic substances in subsurface waters -- 2.5.3 Concentrations of humic substances in surface waters -- 2.5.4 Contents of humic substances in aquatic sediments -- 2.6 Humic substances - accident or design? -- 3 Environmental solution and surface chemistry -- 3.1 Solutions and solutes -- 3.1.1 Factors governing aqueous solubility -- 3.1.2 Amphiphiles -- 3.1.3 Solubilities of macromolecules -- 3.1.4 Solutes in natural waters -- 3.2 Natural particulate matter -- 3.2.1 Particle composition -- 3.2.2 Particle size -- 3.2.3 Colloids -- 3.3 Physico-chemical interactions in environmental aqueous systems -- 3.3.1 Complexation of metal ions and protons -- 3.3.2 Adsorption of ions by mineral particles -- 3.3.3 Mineral dissolution and precipitation -- 3.3.4 Reduction and oxidation -- 3.3.5 Sorption reactions of organic chemicals -- 3.3.6 Adsorption of humic substances by mineral surfaces -- 3.3.7 Aggregation -- 3.3.8 Photochemical reactions -- 3.4 Equilibrium and kinetics -- 3.5 Chemical speciation -- 3.6 Calculation of equilibrium concentrations.

3.6.1 Mass and charge balances -- 3.6.2 Concentrations and activities -- 3.6.3 Solving the equations -- 4 Proton dissociation from weak acids -- 4.1 Acids and bases -- 4.2 Buffering -- 4.3 Kinetics -- 4.4 Diprotic acids -- 4.5 Extension to higher polyprotic acids -- 4.6 Electrostatic interactions among sites -- 4.6.1 Derivation of w from the Debye-Hückel theory -- 4.6.2 Relationship between w and double layer capacitance -- 4.6.3 Relationship of w to activity coefficients -- 4.6.4 Magnitude of the electrostatic effect on proton dissociation -- 4.6.5 Beyond the Debye-Hückel theory -- 4.6.6 Binding due to counterion accumulation -- 4.6.7 Donnan model -- 4.7 Proton dissociation from well-defined polymers -- 4.8 Proton dissociation from humic substances -- 5 Metal-ligand interactions -- 5.1 Coordination -- 5.1.1 Complex formation -- 5.1.2 Stability constants -- 5.1.3 Trends in reactivity -- 5.1.4 Chelates -- 5.1.5 Mixed complexes -- 5.1.6 Kinetics of metal ion complexation -- 5.2 Chemical equilibria involving metal ions, protons and simple weak acid ligands -- 5.2.1 Monoprotic ligands -- 5.2.2 Interaction of a metal ion with more than one ligand atom or group -- 5.2.3 Effects of ionic strength -- 5.2.4 Experimental study of metal-ligand complexes -- 5.2.5 Metal binding in a mixture of ligands -- 5.3 Multisite ligands -- 5.4 Electrostatic interactions -- 5.5 Results with well-defined macromolecules -- 5.5.1 Synthetic polyelectrolytes -- 5.5.2 Results with proteins -- 6 Methods for measuring cation binding by humic substances -- 6.1 The humic sample -- 6.2 Determination of proton binding by potentiometry -- 6.2.1 Titration methodology -- 6.2.2 Computation of the titration curve -- 6.2.3 Interpretation of the titration curve -- 6.2.4 Estimation of metal binding by pH measurement -- 6.2.5 Adsorption of cobaltihexammine.

6.3 Analytical determination of acid group contents -- 6.3.1 Total acidity by barium exchange -- 6.3.2 Carboxylic acidity by calcium exchange -- 6.3.3 Other techniques -- 6.3.4 Metal-binding sites in relation to proton-binding sites -- 6.4 Direct measurement of equilibrium metal binding - principles -- 6.4.1 Data requirements -- 6.4.2 Ranges of measurement -- 6.4.3 Speciation of unbound metal -- 6.5 Separation methods to quantify equilibrium metal binding -- 6.5.1 Centrifugation-depletion -- 6.5.2 Equilibrium dialysis -- 6.5.3 Ultrafiltration -- 6.5.4 Chromatography -- 6.5.5 Diffusive gradients in thin films (DGT) -- 6.6 Competition methods -- 6.6.1 Schubert's method -- 6.6.2 Competing dissolved ligand -- 6.6.3 Kinetic discrimination -- 6.7 Electrochemical techniques -- 6.7.1 Ion-selective electrodes (ISEs) -- 6.7.2 Polarography -- 6.7.3 Anodic stripping voltammetry (ASV) -- 6.7.4 Ligand competition with cathodic stripping voltammetry (CSV) -- 6.8 Spectroscopic methods -- 6.9 Measurement of the kinetics of metal-humic interactions -- 7 Quantitative results with isolated humic substances -- 7.1 Proton dissociation -- 7.1.1 Titration curves for humic substances -- 7.1.2 Comparison of results for different samples of fulvic and humic acid -- 7.1.3 Hydrophilic acids -- 7.1.4 Effects of temperature and enthalpy changes -- 7.1.5 Conductimetric data -- 7.2 Equilibrium binding of metal ions -- 7.2.1 Binding as a function of free metal concentration at fixed pH -- 7.2.2 Metal binding to the abundant weak sites in humic matter -- 7.2.3 Effect of pH on metal binding by humic matter -- 7.2.4 Competition amongst metals -- 7.2.5 Effects of ionic strength -- 7.2.6 Ternary complexes -- 7.2.7 Binding as a function of temperature and enthalpies of interaction -- 7.2.8 Effects of humic concentration -- 7.2.9 Metal binding by different humic samples and humic fractions.

7.3 Kinetics of metal ion binding -- 7.3.1 Rates of forward reactions -- 7.3.2 Rates of dissociation -- 7.3.3 Change of dissociation rates with time after complex formation -- 7.3.4 Implications of kinetic results for metal-humic equilibria -- 8 Cation binding sites in humic substances -- 8.1 Proton-dissociating groups -- 8.2 Binding sites for metals - information from binding studies -- 8.3 Information from spectroscopy -- 8.3.1 Electron spin resonance (ESR) -- 8.3.2 Nuclear magnetic resonance (NMR) -- 8.3.3 Fluorescence -- 8.3.4 X-ray and Gamma-ray techniques -- 8.3.5 Infra-red (IR) spectroscopy -- 8.3.6 Combined spectroscopic methods -- 8.4 Viscometry -- 8.5 Summary -- 9 Parameterised models of cation-humic interactions -- 9.1 Overview and philosophy -- 9.1.1 Purposes of equilibrium modelling -- 9.1.2 Mixture and quasiparticle models -- 9.1.3 Opinions -- 9.2 Models that describe the binding of a single cation -- 9.2.1 Formation of a 1:1 complex -- 9.2.2 Multiple discrete sites -- 9.2.3 Empirical isotherms -- 9.2.4 Continuous distribution models -- 9.2.5 Electrostatic models for proton dissociation -- 9.3 Simpler models that include competition -- 9.3.1 Mixture models -- 9.3.2 Formation of 1:1 and 1:2 complexes -- 9.3.3 N-site model -- 9.3.4 The 'multiple equilibria' model -- 9.3.5 Triprotic acid model -- 9.3.6 Discrete log K spectrum model -- 9.3.7 The Charge Neutralisation Model -- 9.3.8 The Competitive Gaussian Model -- 9.4 The site heterogeneity/polyelectrolyte models of Marinsky and colleagues -- 9.5 Modelling electrostatic effects in humic substances -- 9.5.1 Modelling based on the Poisson-Boltzmann (PB) equation -- 9.5.2 Empirical model of Tipping et al. -- 9.5.3 The Donnan model -- 9.5.4 Remarks on electrostatic modelling -- 9.6 Humic Ion-Binding Models V and VI -- 9.6.1 Model V -- 9.6.2 Model VI -- 9.7 The NICA and NICCA models.

9.8 Summary -- 10 Applications of comprehensive parameterised models -- 10.1 Interactions with protons -- 10.1.1 Parameter values in Model V/VI -- 10.1.2 Parameter values in the NIC(C)A model -- 10.1.3 Proton-binding parameters and the modelling of metal binding -- 10.2 Binding of single metal cations interpreted with Model V -- 10.2.1 Interpretation of parameters -- 10.2.2 The failure of Model V -- 10.3 Binding of single metal cations interpreted with Model VI -- 10.3.1 Reducing the number of adjustable parameters in Model VI -- 10.3.2 Linear free energy relationships (LFERs) -- 10.3.3 Model VI parameter values and their influence -- 10.3.4 Contributions of different binding sites -- 10.3.5 Uncertainty in default values of log KMA -- 10.4 Application of the NICCA model -- 10.5 Metal binding as a function of ionic strength -- 10.5.1 Ionic strength effects predicted with Model VI -- 10.5.2 Ionic strength effects predicted with the NICCA-Donnan model -- 10.6 Non-specific binding -- 10.7 Competition between metals -- 10.7.1 Features of competitive reactions -- 10.7.2 Results with humic substances -- 10.7.3 Model predictions -- 10.8 Proton-metal exchange -- 10.8.1 Release of protons due to metal binding -- 10.8.2 The effect of metal ions on titration curves -- 10.9 Comparison of the NICCA-Donnan model and Model VI -- 10.10 Application of the models to field situations -- 11 Predictive modelling -- 11.1 Electrostatic interactions -- 11.2 Binding sites -- 11.2.1 The RANDOM model -- 11.2.2 Molecular modelling -- 11.3 Prospects for predictive modelling -- 12 Cation-humic binding and other physico-chemical processes -- 12.1 The conformation of humic matter -- 12.2 Aggregation of humic substances -- 12.2.1 Aggregation of humic substances in natural waters -- 12.2.2 Water treatment -- 12.3 Adsorption of humic substances by mineral surfaces.

12.3.1 Humic adsorption by oxides.