Cr(Vi) Secondary Pollution in Cr(Iii)-Containing Waste Residue Triggered by Sulfite Under Visible Light Irradiation: The Formation of •Oh and Fe(V)

Abstract

The reduced chromite ore processing residue (rCOPR) deposited in environments causes reoccurrence of Cr(VI), resulting in serious secondary pollution. In this work, we studied the release and oxidation behaviors of Cr(III)–Fe(III) hydroxide under visible light, in presence of sulfite, the common reductant in rCOPR. At acidic conditions, only Cr(III) released from CrxFe1−x(OH)3 under light, while a large amount of Cr(VI) was produced after adding sulfite. At basic pH of 9, there is still 1.71 μM Cr(VI) released into environment. Radicals fitting results reveal that sulfite triggers radical chain reactions and promotes hydroxyl radical (•OH) production, which is responsible for Cr(III) oxidation and dissolution at acidic conditions. XANES and HPLC-MS analysis demonstrate the formation of Fe(V) on solid surface, which leads to the oxidation of Cr(III) into Cr(VI) through non-radical mechanism. Moreover, coarsening grain size was proposed to enhance solid stability, and Cr(VI) release efficiency significantly decreased 93.57%.

Keywords: reduced chromite ore processing residue (rCOPR), Cr(III) oxidation, CrxFe1−x(OH)3, visible light, sulfite activation.