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

ABSTRACT 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 × 10 -3 to 39.2 × 10 -3  mmol g -1 for As V and from 2.4 × 10 -3 to 40.1 × 10 -3  mmol g -1 for Sb V , more than doubling the adsorption yields (≈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.