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) (pH = 1.2), and then used to adsorb As/Sb oxyanions from model solutions. After acid leaching, the equilibrium sorption capacities (q) increased from 2.3 × 10 to 39.2 × 10mmol g for As and from 2.4 × 10 to 40.1 × 10 mmol g for Sb, more than doubling the adsorption yields (≈95%) of both oxyanions. Leaching in 0.5 M HCl enhanced both As and Sb adsorption, whereas leaching in 0.15 M (COOH) mainly improved the adsorption of Sb. 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/Sb followed second-order kinetics. Acid leaching of Fe-rich clays can be used for the preparation of highly selective anionactive sorbents.