Enhancing Ferrate Oxidation of Micropollutants via Inducing Fe(V)/Fe(IV) Formation Needs Caution: Increased Conversion of Bromide to Bromate

Promoting thegeneration of Fe(V)/Fe(IV) to enhance Fe(VI)oxidation will also boost the conversion of Br- toBrO(3) (-). This study explores the formationof bromate (BrO3 (-)) in the copresenceof Fe(VI) and bromide(Br-). It challenges previous beliefs about therole of Fe(VI) as a greenoxidant and highlights the crucial role of intermediates Fe(V) andFe(IV) in the conversion of Br- to BrO3 (-). The results show that the maximum concentrationof BrO3 (-) of 48.3 mu g/L was obtainedat 16 mg/L Br- and that the contribution of Fe(V)/Fe(IV)to the conversion was positively related to pH. The study suggeststhat a single-electron transfer from Br- to Fe(V)/Fe(IV)along with the generation of reactive bromine radicals is the firststep of Br- conversion, followed by the formationof OBr- which was then oxidized to BrO3 (-) by Fe(VI) and Fe(V)/Fe(IV). Some common backgroundwater constituents (e.g., DOM, HCO3 (-),and Cl-) significantly inhibited BrO3 (-) formation by consuming Fe(V)/Fe(IV) and/or scavengingthe reactive bromine species. While investigations proposing to promoteFe(V)/Fe(IV) formation in Fe(VI)-based oxidation to enhance its oxidationcapacity have been rapidly accumulated recently, this work calledattention to the considerable formation of BrO3 (-) in this process.