Ligand exchange of oxyanions on synthetic hydrated oxides of iron and aluminum

Abstract

The adsorption of oxyanions, P(V), As(V), Se(IV), Mo(VI), and Cr(VI), on the synthetic hydrated oxides of iron and aluminum was studied. The adsorption sequence of the oxyanions was in the order of As(V), Se(IV)>Mo(VI)>P(V)>Cr(VI) on the goethites, hydrons ferric oxide and hydrous aluminum oxide, and P(V)>Mo(Vl)> As(V)>Se(IV), Cr(VI) on the gibbsites. The amount of adsorption of the oxyanions on the hydrated oxides of iron and aluminum was larger in the amorphous hydrous oxides than in the crystalline ones. Ligand exchange took place between oxyanions and OH or OH2 coordinated on the hydrated oxides of iron and aluminum during the adsorption. The OH2 ligand exchange mainly occurred at pH 5.5 for the adsorption of As(V), Se(IV), and P(V) on the amorphous hydrated oxides of iron and aluminum.