A SURFACE PRECIPITATION MODEL FOR THE SORPTION OF CATIONS ON METAL-OXIDES

A new model for the sorption of cations on metal oxides is formulated which allows for a continuum between surface reactions and precipitation. The model extends the surface complexation approach by considering precipitation on the solid to be described by the formation of a solid solution whose composition varied continuously between that of the original solid and a pure precipitate of the sorbing cation. The ability of the surface precipitation model to describe the equilibrium sorption of metal cations on amorphous iron hydroxide is demonstrated. The model can also be extended to describe cation competition and anion sorption.