USE OF GENERAL-PURPOSE ADSORPTION-ISOTHERMS FOR HEAVY-METAL CLAY MINERAL INTERACTIONS

General purpose adsorption isotherm equations were fitted to the sorpt ion data of lead and cadmium on both unmodified and Ca-saturated kaoli nite and montmorillonite. Langmuir-Freundlich, Redlich-Petersen, Toth, Dubinin-Radushkevich, competitive Langmuir, and some modified forms o f these isotherms were fitted to experimental data, and their goodness es of fit are compared. The adjustable parameters of the Langmuir-and Freundlich-based isotherms were estimated by nonlinear least-squares a nalysis. The application of these two isotherms which allow for the ef fect of surface heterogeneity for both multiple and single desorbing i ons during the sorption process was also studied. It was concluded tha t Redlich-Petersen, Toth, and original and modified forms of Dubinin-R adushkevich isotherms perform superior to the others both in high and lour concentration regions for both unmodified and Ca-saturated clays. Competitive Langmuir adsorption isotherm for Ca-saturated clays fitte d web for Pb adsorption, while a change of slope was observed for Cd a dsorption. (C) 1998 Academic Press.