Surface catalyzing action of hematite (α-Fe2O3) on reduction of Cr(VI) to Cr(III) by citrate

The surface catalyzing action of hematite (α-Fe2O3) in reduction of hexavalent chromium (Cr(VI)) by citric acid was studied. The results revealed that Cr(VI) could be reduced to Cr(III) by citrate in the presence of 1% (m/v) hematite in the darkness at pH range of 2.0–6.3. The reaction completed within a week to totally reduce 10mgL−1 of Cr(VI) by 20 mM citrate in the presence of 1% hematite at pH 4.2, well fitted with zero-order kinetic model (R2>0.99). Though ferric ions (Fe(III)) dissolved from hematite surface could also stimulate the Cr(VI) reduction by citrate, hematite surface played a much more important role in this process. The Fe atoms of hematite surface could transport electrons from citrate to Cr(VI) through Fe(III)-Fe(II) cycling, which was proposed as the underlying mechanism of reduction of Cr(VI) by citrate in the presence of iron oxides under certain environmental conditions. Our results suggest that Fe redox cycling may be driven Cr(VI) reduction in the soil/water with the coexist of low molecular organic matters, which could be a sustainable remediation strategy for chromate contamination.