Removal of arsenate and antimonate by acid-treated Fe-rich clays

Iron impurities in clays degrade the quality in many aspects, but available Fe oxides can significantly improve adsorption affinity of clays to anionic particles. Two natural Fe-rich clays (kaolin and bentonite) were treated in 0.5 M HCl (pH = 1.1) and 0.15 M (COOH)(2) (pH = 1.2), and then used to adsorb As-V/Sb-V oxyanions from model solutions. After acid leaching, the equilibrium sorption capacities (q(max)) increased from 2.3 x 10(-3) to 39.2 x 10(-3) mmol g(-1) for As-V and from 2.4 x 10(-3) to 40.1 x 10(-3) mmol g(-1) for Sb-V, more than doubling the adsorption yields approximate to 95%) of both oxyanions. Leaching in 0.5 M HCl enhanced both As-V and Sb-V adsorption, whereas leaching in 0.15 M (COOH)(2) mainly improved the adsorption of Sb-V. Bentonite, which contained fewer crystalline forms of Fe, exhibited better sorption properties for both oxyanions. The leaching of Fe followed first-order kinetics, whereas the adsorption of As-V/Sb-V followed second-order kinetics. Acid leaching of Fe-rich clays can be used for the preparation of highly selective anionactive sorbents.