Synergetic Transformations of Multiple Pollutants Driven by Cr(VI)–Sulfite Reactions

Abstract

Reduction of Cr­(VI) is often deemed necessary to detoxify chromium contaminants; however, few investigations utilized this reaction for the purpose of treating other industrial wastewaters. Here a widely used Cr­(VI)–sulfite reaction system was upgraded to simultaneously transform multiple pollutants, namely, the reduction of Cr­(VI) and oxidation of sulfite and other organic/inorganic pollutants in an acidic solution. As­(III) was selected as a probe pollutant to examine the oxidation capacity of a Cr­(VI)–sulfite system. Both ^•OH and SO₄^•– were considered as the primary oxidants for As­(III) oxidation, based on the results of electron spin resonance, fluorescence spectroscopy, and specific radicals quenching. As­(III)-scavenging, oxidative radicals greatly accelerated Cr­(VI) reduction and simultaneously consumed less sulfite. In comparison with a Cr­(VI)–H₂O₂ system with 50 μM Cr­(VI), Cr­(VI), the sulfite system had excellent performance for both As­(III) oxidation and Cr­(VI) reduction at pH 3.5. Moreover, in this escalated process, less sulfite was required to reduce Cr­(VI) than the traditional Cr­(VI) reduction by sulfite process. This effectively improves the environmental compatibility of this Cr­(VI) detoxification process, alleviating the potential for SO₂ release and sulfate ion production in water. Generally, this study provides an excellent example of a “waste control by waste” strategy for the detoxification of multiple industrial pollutants