Implications for practical application of commercial reduced iron powders to activate aqueous sulfite for decontamination of organics

Sulfate radicals (SO₄^•−) based advanced oxidation processes (AOPs), with high efficiency and selectivity toward degradation of refractory organic contaminants, have captured increasing worldwide attention. Here, an efficient advanced oxidation process based on SO₄^•− (i.e., a CRI/S(IV) process), induced by commercial reduced iron (CRI) powder-induced aqueous sulfite [S(IV)] activation for favorable degradation of refractory organics, is reported. The CRI/S(IV) coupled system efficiently decomposes rhodamine B (RhB) and 4-chlorophenol (4-CP) at weakly acidic and even neutral pHs. The distributions of active sulfur and iron species distribution in the CRI/S(IV) system were investigated and implied that HSO₃⁻, FeHSO₃⁺ and FeSO₃⁺ were the main active species for S(IV), Fe(II), and Fe(III), respectively. In addition, radical quenching experiments show that both SO₄^•− and hydroxyl radicals (^•OH) are present in this CRI/S(IV) system with SO₄^•− as the dominant reactive radical for contamination removal. Furthermore, this novel process surpassed both CRI/Oxone and CRI/persulfate systems towards the organic degradation. This work might provide an implication for an efficient practical route for SO₄^•− activation for wastewater decontamination, particularly for sulfite contaminated wastewaters with recalcitrant organic contaminants.