Reductive removal of As(V) and As(III) from aqueous solution by the UV/ sulfite process: Recovery of elemental arsenic

The removal of arsenic (As(V) and As(III)) from contaminated water has attracted great attention. However, the generation of arsenic-containing hazardous waste by traditional methods has become an inevitable environ-mental problem. Herein, a UV/sulfite advanced reduction method was proposed to remove As(V) and As(III) from aqueous solution in the form of valuable elemental arsenic (As(0)), thus avoiding the generation of arsenic -containing hazardous waste. The results showed that greater than 99.9% of As(V) and As(III) were reduced to the high purity As(0) (> 99.5 wt%) with the residual arsenic concentration below 10 mu g L-1. The hydrated electrons (eaq?), H. and SO3.? radicals are generated by the UV/sulfite process, of which eaq? and H. serve as reductants of As (V) and As(III) while the SO3.? radicals inhibit arsenic reduction by oxidizing arsenic. The effective quantum efficiency (phi) for the formation of As(0) in the As(V) and As(III) removal process is approximately 0.0078 and 0.0055 mol/Einstein, respectively. The reduction of arsenic is favorable under alkaline conditions (pH > 9.0) due to the higher photolysis efficiency of SO32? than HSO3? (pKa = 7.2) and higher stability of eaq?/H. under alkaline conditions. The presence of dissolved oxygen (O2), NO2?, NO3?, CO32?, PO43? and humic acid (HA) inhibited arsenic reduction through light blocking or eaq?/H. scavenging effects while Cl-, SO42?, Ca2+ and Mg2+ had negligible effects on arsenic reduction. The proposed method can effectively remove and recover arsenic from contaminated water at a low cost, demonstrating feasibility for practical application. This study provides a novel technology for the reductive removal and recovery of arsenic from contaminated water.

Automated summary

This study proposes a UV/sulfite advanced reduction method for removing arsenic (As(V) and As(III)) from water. The results show that this method can effectively remove over 99.9% of arsenic and avoid the generation of hazardous waste. The reduction of arsenic is favorable under alkaline conditions, while the presence of dissolved oxygen and some other substances inhibits the reduction process.