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

Abstract

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 SO₂^•- and e_aq^- under UV light. The e_aq^- primarily originates from the photodecomposition of TDO and SO₃^2-, an oxidation product of SO₂^•-. Mechanistic investigations revealed that SO₂^•- and e_aq^- jointly played the pivotal role in antimony reduction. The estimated contribution ratios of SO₂^•- and e_aq^- 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_aq^- 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.