Reductive Removal of Antimony from Wastewater by a UV/Sulfite Process: Targeted Recovery of Strategic Metalloid Antimony

The removal of antimony from wastewater using traditional methods such as adsorption and membrane filtration generates large amounts of antimony-containing hazardous wastes, posing significant environmental threats. This study proposed a new treatment strategy to reductively remove and recover antimony from wastewater using an advanced UV/sulfite reduction process in the form of valuable strategic metalloid antimony (Sb(0)), thus preventing hazardous waste generation. The results indicated that more than 99.9% of Sb(V) and Sb(III) were removed from wastewater, reducing residual antimony concentration as low as 5 μg L^-1 and obtaining Sb(0) product with a high purity of over 99.9 wt %. Mechanistic investigations revealed the reductive H^• radicals and hydrated electrons (e_aq^-), along with oxidative SO₃^•- radicals generated by the photolysis of sulfite, in which H^• and e_aq^- are responsible for the reduction of Sb(V) and Sb(III) to Sb(0). Additionally, although Sb(0) can be further reduced to stibine (SbH₃) by H^• and e_aq^-, the formed SbH₃ rapidly decays and transforms back to Sb(0) through photolysis and oxidation by SO₃^•-. Thus, the proposed method can achieve the targeted reduction of Sb(III) and Sb(V) to Sb(0) but not to SbH₃. This study provides a theoretical foundation for the recovery of antimony from wastewater.