Influence of inorganic anion on Cr(VI) photo-reduction in the presence of ferric ion

Abstract Photo-reduction of Cr(VI) in a solution with single or multi-inorganic anions was evaluated. The results show that 38.5 μM Cr(VI) is photo-reduced in the presence of NO 3 − at pH 1. The photolysis of NO 3 − , producing NO 2 − or H 2 O 2 , may contribute to Cr(VI) reduction. The addition of 0.001–0.1 M chlorite to NO 3 − enhanced Cr(VI) photo-reduction when 35.8 μM Fe(III) was present. This enhancement was the combinative result of photolysis of NO 3 − and Fe–Cl complexes, leading to the formation of NO 2 − and Fe(II), respectively, for Cr(VI) reduction. On the contrary, a significant decrease in Cr(VI) photo-reduction was observed with the addition of PO 4 3− and SO 4 2− . This decrease was due to their strong competition with Fe(III) from Cl − , resulting in a marked decrease in the concentrations of Fe–Cl complexes. The results suggest that a direct irradiation of acidic wastewaters containing Cl − , NO 3 − , and Fe(III) is a feasible strategy for eliminating Cr(VI).