Enabling simultaneous redox transformation of toxic chromium(VI) and arsenic(III) in aqueous media-A review

Simultaneous conversion of most harmful As(III) and Cr(VI) to their less toxic counterparts is environmentally desirable and cost-effective. It has been confirmed that simultaneous oxidation of As(III) to As(V) and reduction of Cr(VI) to Cr(III) can occur via free radical or mediated electron transfer processes. While Cr(VI) is reduced by reacting with H-center dot, e(aq)(-), photoelectron directly or undergoing ligand exchange with H2O2 and SO32-, As(III) is oxidized by HO center dot, SO4 center dot-,O-2(center dot-), (I)+, and holes (h(+)) in free radical process. The ability to concentrate Cr and As species on heterogeneous interface and conductivity determining the co-conversion efficiency in mediated electron transfer process. Acidity has positive effect on these co-conversion, while mediated electron transfer process is not much affected by dissolved oxygen (O-2). Organic compounds (e.g., oxalate, citrate and phenol) commonly favor Cr(VI) reduction and inhibit As(III) oxidation. To better understand the trends in the existing data and to identify the knowledge gaps, this review elaborates the complicated mechanisms for co-conversion of As(III) and Cr(VI) by various methods. Some challenges and prospects in this active field are also briefly discussed.

Automated summary

The simultaneous conversion of As(III) and Cr(VI) to their less toxic forms is beneficial for the environment and cost-effective. The mechanisms for the oxidation of As(III) and reduction of Cr(VI) through different processes have been explored. Acidity has a positive effect on co-conversion, while the mediated electron transfer process is not significantly affected by dissolved oxygen. Organic compounds may influence the conversion process.