The promotional role of peroxydisulfate in Arsenic(III) oxidation by Fe(III)/Sulfite: Boosting and regulating the generation of radical and non-radical species

Abstract

The Fe(III)-activated sulfite (S(IV)) process to yield powerful SO4•−/HO• radicals is increasingly recognized as an appealing advanced oxidation process (AOP). However, its application is constrained by its heavy reliance on dissolved oxygen and the low selectivity of these short-lived radicals. In this work, peroxydisulfate (PDS) was found to indeed amplify the capacity of the Fe(III)/S(IV) system for arsenite (As(III)) oxidation, with increasing the oxidation efficiency and rate constant from 47 % to 95 % and 0.165 min−1 to 0.455 min−1, respectively. The mechanistic study revealed that the predominant reactive species were identified as both radicals (SO4•−/HO•) and non-radical (Fe(IV)O2+ instead of 1O2), with HO• primarily originating from Fe(IV)O2+. Herein, PDS not only acted as an electron acceptor to react with the in-situ formed Fe(II), thus accelerating the Fe(II) ↔ Fe(III) cycle and producing Fe(IV)O2+, but also functioned as a substitute for dissolved oxygen to facilitate SO4•− generation even under anaerobic conditions. Moreover, the generation efficiency and distribution of these oxidizing reactive species were significantly influenced by adjusting experimental parameters (i.e., reagents dosage and solution pH). Overall, this work unveiled an enticing strategy to fine-tune the oxidative prowess and precision of the Fe(III)/S(IV)/PDS system for oxidizing specific contaminants by orchestrating the relative distribution of radicals (SO4•−/HO•) and non-radical (Fe(IV)O2+).