| Abstract: |
The constant capacitance model was used to describe arsenate adsorption on goethite, gibbsite, and amorphous Al hydroxide. Because the model assumes a ligand exchange mechanism it is appropriate for describing the specific adsorption of arsenate anions. Arsenate surface complexation constants were fitted to the experimental data using a nonlinear least squares optimization technique. The constant capacitance model was able to represent arsenate adsorption over the pH range 4.5 to 9 on each oxide using the same set of surface complexation constants. However, the values of the surface complexation constants varied with the mineral considered. The model was able to describe arsenate-phosphate competition on gibbsite quantitatively over the pH range 4.5 to 9 using the same set of anion surface complexation constants. A set of surface complexation constants obtained for one ternary system could be used to predict competitive phosphate and arsenate adsorption on the same material for other ternary systems containing different amounts of total anions in solution. |
