Transformation of tetrabromobisphenol a in the iron ions-catalyzed auto-oxidation of HSO₃²⁻/SO₃²⁻ process

In this study, Fe³⁺-catalyzed auto-oxidation of HSO₃⁻/SO₃²⁻ [Fe(III)/S(IV)] process was applied to treat tetrabromobisphenol A (TBBPA) in aqueous solution under different operational conditions. Both SO₄^•− and HO^• accounted for TBBPA degradation in the process, and HO^• was the dominant oxidant. In a Fe³⁺ range of 20–80 μM, the maximum TBBPA removal was observed when the initial Fe³⁺ dose was 40 μM. A first increasing then decreasing trend of TBBPA removal efficiency was also achieved as the initial HSO₃⁻/SO₃²⁻ dose gradually increased from 200 to 3000 μM, and the highest removal rate of TBBPA occurred when the initial HSO₃⁻/SO₃²⁻ dose was 2000 μM. Higher initial TBBPA concentration lowered the removal rate of TBBPA in the process. Weak acidic conditions benefited the removal of TBBPA in the process because HSO₃⁻ is easier to complex Fe³⁺ than SO₃²⁻. Oxygen is required when treating TBBPA by Fe(III)/S(IV) process as it can quickly oxidize SO₃^•− to SO₅^•− which can be subsequently transformed to SO₄^•− and HO^•. Both HCO₃⁻ and HA significantly inhibited the removal of TBBPA in the Fe(III)/S(IV) process through the competition for the reactive radicals. Based on the 21 detected intermediates by LC/MS and the DFT calculation, pathways of TBBPA degradation that was primarily initialed by the attack of bromine atom and the carbon on the aromatic rings were proposed. Debromination of TBBPA in the Fe(III)/S(IV) process could form Br⁻, but the formed Br⁻ couldn't be further transformed to BrO₃⁻. Although the treatment of TBBPA by the Fe(III)/S(IV) process increased the acute toxicity in the initial stage, the acute toxicity of the solution gradually reduced with prolonging the reaction time.