Removal of cadmium, zinc, copper and lead by red mud, an iron oxides containing hydrometallurgical waste

Abstract

Abstract Red mud, a residue of the alumina production industry which is actually a solid waste, has been studied as a potential sorbent for the removal of toxic bivalent cations (i.e. Cd, Zn, Cu and Pb) from aqueous solutions in the presence of 0.01 M NaNO3. The experimental data were modeled with Langmuir and Freundlich isotherms and fitted quite well. The relatively high uptake indicated that red mud can adsorb considerable amounts of cadmium and zinc from near-neutral aqueous solutions (maximum uptake capacity for cadmium: 68 mg-g1 at pH 6 and ca. 133 mg-g1 for zinc at pH 7). A significant uptake was also observed for copper and lead at pH 6 and 7 respectively which was attributed to precipitation of the respective insoluble hydroxides. TCLP leaching tests before and after the metal removal have shown that read mud is an environmentally compatible material that could be used for the wastewater treatment. Regeneration possibilities have also been observed.