Decolorization of Orange II in Aqueous Solution by an Fe(II)/sulfite System: Replacement of Persulfate

A novel process for decolorizing dyes with sulfate radicals (SO4•–) using an Fe(II)/sulfite system is reported in this manuscript. The objective of this study was to investigate the conditions under which Fe(II) activates Na2SO3 to produce SO4•– and decolorize organic dyes. Orange II, Rhodamine B, Indigo Carmine, and Reactive Brilliant Blue X-BR could be efficiently decolorized using this novel system, which was compared with the Fe(II)/persulfate and Fenton (Fe(II)/H2O2) systems. The Fe(II)/sulfite system surpassed the other two in the decolorization of these dyes, and detailed mechanisms of the Fe(II)/sulfite system were researched. Primary radical identification through quenching experiments using tert-butyl alcohol and ethanol confirmed the existence of SO4•–, HO•, and SO5•–. A kinetic model was established for the halide ion effect, and kI–,SO4•– (3.2 × 1011 mol–1 L s–1) and RSO4•–f (10–4–10–3 mol L–1 s–1) were indirectly derived. In conclusion, the Fe(II)/sulfite system is a good candidate for use in detoxifying water contaminants.