EFFECT OF LANDFILL LEACHATE ORGANIC-ACIDS ON TRACE-METAL ADSORPTION BY KAOLINITE

Hexanoic (hex) and fulvic acid (FA), representing early and later stag es of landfill leachate evolution, were examined for influence on trac e metal adsorption by a poorly crystallized kaolinite (KGa-2). Our exp eriments represented a model approach to examine possible reaction mec hanisms in an environmentally important ternary metal-ligand-mineral s urface system. Batch experiments were conducted in 0.01 mol kg(-1) NaC lO4 at pH 3-8. Concentrations of metals (Cu, Cd, and Pb) and ligands w ere representative of those found typically in groundwater immediately downgradient of a landfill. The presence of FA resulted in enhancemen t of metal adsorption below pH 5, whereas the presence of hex produced no significant net change in metal uptake. Measured surface charge pr operties of KGa-2 were combined with binary and ternary system data in constructing a quantitative model of the system. The simple combinati on of binary system results was not effective in predicting the observ ed ternary system behavior. In both ternary systems, the addition of t ernary surface complexes (TSCs) to the models resulted in a satisfacto ry fit to the data. Our work suggests the strong possibility that TSC involvement in surface reactions of natural adsorbents may be a useful concept.