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 (eaq–), along with oxidative SO3•– radicals generated by the photolysis of sulfite, in which H• and eaq– 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 eaq–, 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.