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

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 NO3− at pH 1. The photolysis of NO3−, producing NO2− or H2O2, may contribute to Cr(VI) reduction. The addition of 0.001-0.1 M chlorite to NO3− enhanced Cr(VI) photo-reduction when 35.8 μM Fe(III) was present. This enhancement was the combinative result of photolysis of NO3− and Fe-Cl complexes, leading to the formation of NO2− 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 PO43− and SO42−. 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−, NO3−, and Fe(III) is a feasible strategy for eliminating Cr(VI).