Influence of photoirradation on reduction of hexavalent chromium by zero-valent iron in the presence of organic acids

Reduction of hexavalent chromium (Cr(VI)) by zero-valent iron (Fe⁰) was investigated systematically in the present study. No change in Cr(VI) concentration occurs using untreated Fe⁰ powders even after a long contact time. The Fe⁰ powders treated with acid washing shows a weak activity and a poor long-term performance to reduction of Cr(VI). The activity and long-term performance of treated Fe⁰ powders is not effectively improved in the presence of citric acid. In contrast, introduction of photoirradiation not only dramatically increases the reduction rate of Cr(VI) in the presence of citric acid but also effectively stabilizes the activity of Fe⁰ powders and films. Such enhancement should be attributed to photoreductive dissolution of the oxide layer on Fe⁰ surface. For this newly developed system, effective reduction of Cr(VI) is favored at low pH values and oxalic and tartaric acid are also effective as complex reagents.