Reduction recovery of Sb(III) and Sb(V) from wastewater by UV/thiourea dioxide system: Efficiency, radical generation and mechanism.

For antimony-containing wastewater, conventional methods, such as chemical precipitation, adsorption and membrane separation inevitably generate substantial quantities of hazardous waste. This paper introduces a UV/thiourea dioxide(TDO) reduction method, which efficiently recovers Sb(III)/Sb(V) from wastewater as the metalloid Sb(0) within 30 min, achieving a purity greater than 99.8 wt%. This work innovatively found that TDO could generate SO and e under UV light. The e primarily originates from the photodecomposition of TDO and SO, an oxidation product of SO. Mechanistic investigations revealed that SO and e jointly played the pivotal role in antimony reduction. The estimated contribution ratios of SO and e were approximately 2.5 % and 97.5 % for Sb(III) removal and 1.5 % and 98.5 % for Sb(V) removal. The enhancement of antimony removal as the increased pH was attributed to the accelerated cleavage of C-S bond in TDO and the enhanced photolysis of TDO. The presence of dissolved oxygen and humic acid(HA) suppressed the antimony removal due to the scavenging effect of e and light absorbance. This method could hierarchically recover antimony and arsenic, with antimony being removed first followed by arsenic, which has a practical prospect for antimony and arsenic-containing wastewater treatment.