Enhancing Ferrate Oxidation of Micropollutants via Inducing Fe(V)/Fe(IV) Formation Needs Caution: Increased Conversion of Bromide to Bromate
Guang Li, Jinchan Jiang, Maoxia He, Dandan Rao, Jian Zhang, Bo Sun
Abstract
This study explores the formation of bromate (BrO 3 – ) in the copresence of Fe(VI) and bromide (Br – ). It challenges previous beliefs about the role of Fe(VI) as a green oxidant and highlights the crucial role of intermediates Fe(V) and Fe(IV) in the conversion of Br – to BrO 3 – . The results show that the maximum concentration of BrO 3 – of 48.3 μg/L was obtained at 16 mg/L Br – and that the contribution of Fe(V)/Fe(IV) to the conversion was positively related to pH. The study suggests that a single-electron transfer from Br – to Fe(V)/Fe(IV) along with the generation of reactive bromine radicals is the first step of Br – conversion, followed by the formation of OBr – which was then oxidized to BrO 3 – by Fe(VI) and Fe(V)/Fe(IV). Some common background water constituents (e.g., DOM, HCO 3 –, and Cl – ) significantly inhibited BrO 3 – formation by consuming Fe(V)/Fe(IV) and/or scavenging the reactive bromine species. While investigations proposing to promote Fe(V)/Fe(IV) formation in Fe(VI)-based oxidation to enhance its oxidation capacity have been rapidly accumulated recently, this work called attention to the considerable formation of BrO 3 – in this process.