Reduction mechanism of hexavalent chromium in aqueous solution by sulfidated granular activated carbon

Wide-spread use of chromium in many industrial and manufacturing processes contributes to its presence as a global water pollution issue. In this work, batch experiments were conducted to test the remediation performance of granular activated carbon modified with amorphous FeS (FeS-GAC) for hexavalent chromium (Cr(VI)) polluted water. 76% of Cr(VI) was removed in the first 15 min under neutral condition, compared to a 95% under acidic conditions. Lower initial concentration and reaction temperature favored the removal of Cr(VI). Some electron microscopy and spectral analyses were employed to investigate the reaction mechanism. A multi-step process was hypothesized for the Cr(VI) removal mechanism, including the (i) heterogeneous reaction: adsorption of Cr(VI) onto the solid surface, reaction with FeS, precipitation of Cr(III)/Fe(III) hydroxides, complexation of Cr(VI) with Fe2O3, and the (ii) homogeneously reaction of Cr(VI) and Fe(II)/S(-II). The results of this study demonstrate that the sulfidated GAC exhibites an effective and promising ability for treatment of Cr(VI) polluted water.