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.

Removal of Cr(VI) by 3D TiO 2 -graphene hydrogel via adsorption enriched with photocatalytic reduction

“…The concentration of total Cr was determined by an inductively coupled plasma (ICP) direct reading spectrometer. The concentration of Cr(VI) was determined by the diphenyl hydrazine method [21] , and the concentration of Cr(III) was calculated by subtracting the Cr(VI) concentration from the total Cr concentration.…”

“…It is carcinogenic and thus is a threat to human healthy [1] . An rich array of physical and chemical approaches including ion exchange [2], chemical precipitation [3], electro-reduction [4] , and membrane separation [5] have been developed for removing chromium from industrial waste.…”

The Hazardous Origin of Photocatalytic Activity of ZnCr2O4

“…We present evidences that the more active species for photo degradation of y‐Eosin is Cr VI due to the Cr VI ‐Cr III /Cr IV /Cr V redox cycle, which produces two to six hydroxyl radicals per cycle from oxidation of H 2 O, i.e. reduction of Cr VI and reduction of H 2 O 2 or O 2 • – by stepwise oxidation of Cr III /Cr IV /Cr V back to Cr VI , , . All the generated radicals can react with surrounding organic molecules and initiate an advanced oxidation process (AOP) finally leading to nontoxic molecules like CO 2 and H 2 O …”

Pyrite-Based Cr(VI) Reduction Driven by Chemoautotrophic Acidophilic Bacteria

“…Two forms of Cr with different oxidation states, Cr(VI) and Cr(III), usually exist in the natural environment. Cr(VI) is also considered a priority pollutant, and its remediation has attracted increasing attention in the environmental area (Jiang et al, 2015). The toxicity of Cr(III) is far lower than that of Cr(VI), and it can be easily precipitated as Cr(OH) 3 , while Cr(VI) is soluble over a wide pH range.…”