Premagnetization enhancing the reactivity of Fe0/(passivated Fe0) system for high concentration p-nitrophenol removal in aqueous solution

In order to strengthen the treatment efficiency of Fe⁰ based system for high concentration wastewater treatment, Fe⁰ particles were passivated by concentrated nitric acid, and a premagnetization Fe⁰/(passivated Fe⁰) system was setup for high concentration p-nitrophenol (PNP) removal in this study. The significant parameters of this system were optimized. Under the optimal conditions, the premagnetization Fe⁰/(passivated Fe⁰) system could obtain high k_obs value for PNP removal (0.100 min^-1) and COD removal (15.0% after 60 min) for high concentration PNP (500 mg/L) treatment. In addition, five control experiments were set up to confirm the advantage of the premagnetization Fe⁰/(passivated Fe⁰) system. The results suggest that passivated Fe⁰ particles could be stimulated better than Fe⁰ particles by premagnetization process, and the premagnetization Fe⁰/(passivated Fe⁰) systems is much superior to the other five control systems. Furthermore, the pathway for PNP destruction treated by 6 different systems was also proposed according to intermediates determination by High Performance Liquid Chromatography (HPLC) and UV-vis spectrum, and the carbon mass balance was demonstrated according to the COD and HPLC analyses. Finally, the characteristics of (premagnetization) Fe⁰ and passivated Fe⁰ was detected by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and vibrating sample magnetometer (VSM), and the mechanism of premagnetization effectively enhancing the reactivity of Fe⁰/(passivated Fe⁰) system (better than that of Fe⁰ system) was proposed. Consequently, the premagnetization for reactivity improvement of Fe⁰/(passivated Fe⁰) system is a promising technology to enhance the efficiency of this system for high concentration wastewater treatment.

Effects of oxygen and weak magnetic field on Fe(0)/bisulfite system: performance and mechanisms

The performance and mechanisms of 4-nitrophenol (4-NP) degradation by the Fe(0)/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 Fe(0)/bisulfite-driven 4-NP degradation. In the Fe(0)/bisulfite/O2 system, Fe(0) acted as a supplier of Fe(2+) 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 Fe(3+) to nascent Fe(2+) 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 Fe(0)/bisulfite/O2 and Fe(0)/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-Fe(0)/bisulfite/O2 system showed less pHini dependence. To facilitate the application of WMF-Fe(0)/bisulfite/O2 technology in real practice, premagnetization of Fe(0) was employed to combine with bisulfite/O2 and proved to be an effective and applicable method for 4-NP removal.