Effects of oxygen and weak magnetic field on Fe0/bisulfite system: performance and mechanisms
2016
Xiong, Xinmei | Gan, Jinhong | Zhan, Wei | Sun, Bo
The performance and mechanisms of 4-nitrophenol (4-NP) degradation by the Fe⁰/bisulfite system were systematically investigated for the first time. The evidences presented in this study verified that O₂ was a crucial factor that affected the mechanism of Fe⁰/bisulfite-driven 4-NP degradation. In the Fe⁰/bisulfite/O₂ system, Fe⁰ acted as a supplier of Fe²⁺ to catalyze bisulfite oxidation that induced a chain reaction to produce reactive radicals for 4-NP degradation. While under N₂ purging condition, bisulfite worked as a specified reductant that facilitated the transformation of Fe³⁺ to nascent Fe²⁺ ions, which principally accounted for the reductive removal of 4-NP. The application of a weak magnetic field (WMF) efficiently improved the removal rate of 4-NP and did not alter the mechanisms in both Fe⁰/bisulfite/O₂ and Fe⁰/bisulfite/N₂ processes. The secondary radicals, HO·, SO₄ ·⁻, and SO₅ ·⁻, were considered as the most possible active oxidants contributing to the oxidative removal of 4-NP and even partial mineralization under an oxic condition. Compared with anoxic conditions, the performance removal of 4-NP by the WMF-Fe⁰/bisulfite/O₂ system showed less pHᵢₙᵢ dependence. To facilitate the application of WMF-Fe⁰/bisulfite/O₂ technology in real practice, premagnetization of Fe⁰ was employed to combine with bisulfite/O₂ and proved to be an effective and applicable method for 4-NP removal.
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