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 microM 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 microM 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).