Reduction and sorption of chromium by Fe(II)-bearing phyllosilicates: Chemical treatments and X-ray absorption spectroscopy (XAS) studies

The reduction of hexavalent chromium species in aqueous solutions by intera ction with Fe(II)-bearing solid surfaces was studied using a 0.96 x 10(-3)M Cr(VI) solution and iron-rich clays with different Fe(II)/Fe(III) ratios, layer charge, and exchange properties, i.e., chlorite, corrensite, and mont morillonite. Experimental studies demonstrated that Fe(II)-bearing phyllosi licates reduce aqueous Cr(VI) ions at acidic pH. Chlorite and corrensite, o wing to the high Fe(II)/Fe(III) ratio, are electrochemically reactive, as r apid Cr(VI) reduction indicated. In contrast, montmorillonite showed minimu m to nil reactivity towards Cr(VI). Furthermore, corrensite, which is high in both Fe(II)/Fe(III) ratio and exchange capacity, adsorbs the greatest am ount of chromium. X-ray absorption spectroscopy at Al, Mg, Fe, and Cr K-edg es was used to investigate the adsorbed chromium species. The montmorilloni te sample, unaffected by treatment with Cr(VI) solution, displays no change at any investigated edge. Edge shape and energy also do not change for the Mg and Al spectra in corrensite, and changes are minor in chlorite. By con trast, the Fe K-edge changes both in chlorite and corrensite, and indicates an increase of Fe(III) in treated samples at the expense of pre-existing F e(II). Cr K-edge spectra show that chlorite and corrensite sorb Cr(III), wh ich implies its reduction from Cr(VI) in the interacting solution.