Surface complexation of methylated arsenates by hydrous oxides

Abstract

The adsorption of methyl arsenate and dimethyl arsenate on hydrous ferric oxide and activated alumina was measured as a function of pH, ionic strength and sorbate-sorbent ratio by the bottle-point method and the characteristics of the two oxide surfaces were determined by surface titration. Adsorption decreased with increasing pH while it was only weakly dependent on ionic strength. The results were interpreted in terms of the triple-layer surface complexation model by assuming that arsenicals formed inner-sphere complexes with the oxide surface. A satisfactory interpretation of results could be made by modifying the triple-layer model to include surface sites of two different adsorption energies. Attempts to model adsorption considering a homogeneous surface were unsatisfactory. © 1994.