Weak magnetic field and coexisting ions accelerate phenol removal by ZVI/H₂O₂ system: Their efficiency and mechanism

Human activity and industrial production have led to phenol becoming a significant risk factor. The proper treatment of phenol in wastewater is essential. In this study, the utilization of weak magnetic field (WMF) and zero-valent iron (ZVI) was proposed to activate H₂O₂ to degrade phenol contaminant. The results show that the weak magnetic field has greatly enhanced the reaction rate of ZVI/H₂O₂ removal of phenol. The removal rates of phenol by ZVI/H₂O₂/WMF generally decreased with increasing initial pH and phenol concentrations, and firstly increase and then decrease with increasing Fe⁰ or H₂O₂ dosage. When the initial pH is 5.0, ZVI concentration of 0.2 g L^-1, H₂O₂ concentration of 6 mM, and phenol concentration of 100 mg L^-1 were used, complete removal of phenol can be achieved within 180 min at 25 °C. The degradation process was consistent with the pseudo-first-order kinetic model when the experimental data was fitted. The ZVI/H₂O₂/WMF process exhibited a 1.05-2.66-fold enhancement in the removal rate of phenol under various conditions, surpassing its counterpart lacking WMF. It was noticed that the presence of 1-5 mM of Ca²⁺, Mg²⁺, Cl^-, SO₄^2- ions can significantly enhance the kinetics of phenol removal by ZVI/H₂O₂ system with or without WMF to 2.22-10.40-fold, but NO₃^-, CO₃^2-, PO₄^3- inhibited the reaction significantly in the following order: PO₄^3- > CO₃^2- > NO₃^-. Moreover, pre-magnetization for 3 min could enhance the ZVI/H₂O₂ process which was valuable in treatment of real wastewater. The hydroxyl radical has been identified as the primary radical species responsible for phenol degradation. The presence of WMF accelerates the corrosion rate of ZVI, thereby promoting the release of Fe²⁺ ions, which in turn induces an increased production of hydroxyl radicals and facilitates phenol degradation. The compounds hydroquinone, benzoquinone, catechol, maleic acid, and CO₂ were identified using GC-MS, and degradation pathways were proposed. Employing WMF in combination with various ions like Ca²⁺, Mg²⁺, Cl^-, SO₄^2- is a novel method, which can enhance oxidation capacity of ZVI/H₂O₂ and may lead to economic benefit.