Reduction and immobilization of chromium(VI) by iron(II)-treated faujasite

Removal of hexavalent chromium (Cr(VI)) from wastewater typically involves reduction of Cr(VI) to insoluble Cr(III) using zerovalent iron (Fe-0) or ferrous iron (Fe(II)). This study investigates the effectiveness of Fe(II)-treated faujasite (zeolite Fe(II)-Y) for reduction of Cr(VI) and immobilization (adsorption/co-precipitation) of the Cr(III) reaction product. The Fe(II)-faujasite material effectively removed high concentrations of dissolved Cr(VI) from aqueous solution resulting in Cr solid loadings as high as 0.30 mmol Cr per grain Fe(II)-faujasite or similar to 1.5% Cr (w:w). Results of Cr K-edge X-ray absorption near edge spectroscopy (XANES) confirmed that the oxidation state of Cr in Cr(VI)-treated Fe(II)-faujasite was Cr(III). The local atomic structure of Cr was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and the structure of Cr in the product was described by a Cr-O first shell of six O atoms at 1.98(+/- 0.02) angstrom plus a second atomic shell of metal (Cr, Fe) at 3.13(+/- 0.02) angstrom. The EXAFS results, combined with SEM imaging and X-ray diffraction analyses, suggested that the product of the reaction of Cr(VI) with Fe(II)-faujasite is primarily a poorly order CrxFe1-x(OH)(3) mixed phase similar to previous investigations of the reaction of Cr(VI) with Fe-0 and not solely Cr(III) bound directly to zeolite cation exchange sites. (C) 2009 Elsevier B.V. All rights reserved.