Using calcined sulfate-modified titanium-bearing blast furnace slag (STBBFS) as photocatalyst, the photocatalytic activity of STBBFS photocatalyst toward a Cr(VI)-citric acid [Cr(VI)-CA] system and a Cr(VI)-citric acid-ferric nitrate [Cr(VI)-CA-FN] system was studied. The results indicate that the photocatalytic activity of STBBFS photocatalyst is more efficiently enhanced in the Cr(VI)-CA-FN compound system than in the single Cr(VI) or Cr(VI)-CA system, indicating that the photocatalytic activity of STBBFS photocatalyst can be improved in the presence of citric acid and ferric nitrate. The acidic solutions are favorable for the photocatalytic reduction of Cr(VI), and the optimum pH for the photocatalytic reduction of Cr(VI) is 2.5 in both compound systems. For the Cr(VI)-CA system, Cr(VI) is completely reduced after 50 min reaction when the photocatalytic activity of STBBFS photocatalyst is 0.426 mg•min－1•g－1. As for the Cr(VI)-CA-FN system, Cr(VI) is completely reduced after 16 min reaction when the photocatalytic activity of STBBFS photocatalyst is 1.2425 mg•min－1•g－1. Both the photocatalytic reductions of Cr(VI) in the Cr(VI)-CA system and Cr(VI)-CA-FN system follow a Langmuir-Hinshelwood kinetic model. Though the effect of adsorption on the photocatalytic reduction of Cr(VI) was decreased, the adsorption of Cr(VI) on the catalyst surface still affected the photocatalytic activity of STBBFS photocatalyst remarkably.

Key words: sulfate-modified titanium-bearing blast furnace slag, Cr(VI)-citric acid compound system, Cr(VI)-citric acid-ferric nitrate compound system, photocatalytic activity, Cr(VI)