ADSORPTION OF URANIUM(VI) ON AMORPHOUS FERRIC OXYHYDROXIDE AT HIGH-CONCENTRATIONS OF DISSOLVED CARBON(IV) AND SULFUR(VI)

Amorphous ferric oxyhydroxide is being used to treat groundwater contaminated with uranium(VI); the compound also has potential for use as a component in in situ chemical barriers. To quantitatively evaluate its effectiveness in such applications, adsorption of uranium(VI) onto amorphous ferric oxyhydroxide was experimentally investigated under a wide range of uranium(VI) (8.40.10(-7)-2.10.10(-3) mol L-1; 0.2-500 mg L-1), sulfur(VI) (0-0.07 mol L-1; 0-2240 mg L-1) and carbon(IV) (0-0.0195 mol L-1; 0-234 mg L-1) concentrations, and pH-values (4-9.6). The adsorption behavior of uranium(VI) (uranyl ion and its complexes) is similar to that of other cations; it exhibits a sharp rise in the extent of adsorption with increasing pH. Interactions among uranyl complexes and surface sites are interpreted using a site complexation model. Although the model does not incorporate electrostatics and includes only a single type of adsorption site, it provides a reasonable match to measured adsorption and proton exchange data. The simplicity of the model and the resulting reduction in computational demand allow its efficient incorporation into coupled reaction-transport models.