Effect of landfill leachate organic acids on trace metal adsorption by 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 crystallized 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.