-The surface charge components of 2 Georgia kaolinites of differing degrees of crystallinity (KGa-1 and KGa-2) were determined using procedures based on charge balance concepts. Permanent structural charge density (tr0) was determined by measuring the surface excess of Cs, which is highly selective to permanent charge sites. The values of cr0 determined were -6.3 -~ 0.1 and -13.6 ---0.5 mmol kg -~ for kaolinites KGa-1 and KGa-2, respectively. The net proton surface charge density (trn) was determined as a function of pH by potentiometric titration in 0.01 mol dm -3 LiC1. Correction from apparent to absolute values of cr n was made by accounting for A1 release during dissolution, background ion adsorption and charge balance. Lithium and C1 adsorption accounted for the remainder of the surface charge components. Changes in surface charge properties with time were measured after mixing times of 1, 3 and 15 h. the latter representing "'equilibrium". Time-dependenl behavior is believed to be caused by mineral dissolution followed by readsorption or precipitation of A1 on the mineral surface. Both the point of zero net charge (p.z.n.c.) and the point of zero net proton charge (p.z.n.p.c.) changed with mixing time, generally increasing. The "'equilibrium" p.z.n.c, values were approximately 3.6 for KGa-1 and 3.5 for KGa-2, whereas the corresponding p.z.n.p.c, values were about 5.0 and 5.4. The p.z.n.c, results were in good agreement with previous studies, but the values of p.z.n.p.c, were higher than most other values reported for specimen kaolinite.

Hexanoic (hex) and fulvic acid (FA), representing early and later stages of landfill leachate evolution, were examined for influence on trace metal adsorption by a poorly crystal lized kaolinite (KGa-2). Our experiments represented a model approach to examine possible reaction mechanisms in an environmentally important ternary metal−ligand−mineral surface system. Batch experiments were conducted in 0.01 mol kg-1 NaClO4 at pH 3−8. Concentrations of metals (Cu, Cd, and Pb) and ligands were representative of those found typically in groundwater immediately downgradient of a landfill. The presence of FA resulted in enhancement of metal adsorption below pH 5, whereas the presence of hex produced no significant net change in metal uptake. Measured surface charge properties of KGa-2 were combined with binary and ternary system data in constructing a quantitative model of the system. The simple combination of binary system results was not effective in predicting the observed ternary system behavior. In both ternary systems, the addition of ternary surface complexes (TSCs) to the models resulted in a satisfactory fit to the data. Our work suggests the strong possibility that TSC involvement in surface reactions of natural adsorbents may be a useful concept.

-The surface charge components of 2 Georgia kaolinites of differing degrees of crystallinity (KGa-1 and KGa-2) were determined using procedures based on charge balance concepts. Permanent structural charge density (tr0) was determined by measuring the surface excess of Cs, which is highly selective to permanent charge sites. The values of cr0 determined were -6.3 -~ 0.1 and -13.6 ---0.5 mmol kg -~ for kaolinites KGa-1 and KGa-2, respectively. The net proton surface charge density (trn) was determined as a function of pH by potentiometric titration in 0.01 mol dm -3 LiC1. Correction from apparent to absolute values of cr n was made by accounting for A1 release during dissolution, background ion adsorption and charge balance. Lithium and C1 adsorption accounted for the remainder of the surface charge components. Changes in surface charge properties with time were measured after mixing times of 1, 3 and 15 h. the latter representing "'equilibrium". Time-dependenl behavior is believed to be caused by mineral dissolution followed by readsorption or precipitation of A1 on the mineral surface. Both the point of zero net charge (p.z.n.c.) and the point of zero net proton charge (p.z.n.p.c.) changed with mixing time, generally increasing. The "'equilibrium" p.z.n.c, values were approximately 3.6 for KGa-1 and 3.5 for KGa-2, whereas the corresponding p.z.n.p.c, values were about 5.0 and 5.4. The p.z.n.c, results were in good agreement with previous studies, but the values of p.z.n.p.c, were higher than most other values reported for specimen kaolinite.

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