Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron

• WMF significantly enhances Se(IV) removal kinetics by ZVI over a wide pH range.
• WMF extends the working pH range of ZVI for Se(IV) removal from 4.0–6.0 to 4.0–7.2.
• WMF enhances Se(IV) removal more markedly at lower initial Se(IV) concentration.
• Employing WMF to enhance Se(IV) removal by ZVI is a promising method.

The effect of weak magnetic field (WMF) on Se(IV) removal by zero valent iron (ZVI) was investigated as functions of pH and initial Se(IV) concentrations. The presence of WMF significantly accelerated Se(IV) removal and extended the working pH range of ZVI from 4.0–6.0 to 4.0–7.2. The WMF induced greater enhancement in Se(IV) removal by ZVI at lower initial Se(IV) concentrations. The influence of WMF on Se(IV) removal by ZVI was associated with a more dramatic drop in ORP and a more rapid release of Fe2+ compared to the case without WMF. SEM and XRD analysis revealed that WMF accelerated the corrosion of ZVI and the transformation of amorphous iron (hdyr)oxides to lepidocrocite. XANES analyses showed that WMF expedited the reduction of Se(IV) to Se(0) by ZVI at pH 6.0 when its initial concentration was ≤20.0 mg L−1. Se(IV) dosed at 40.0 mg L−1 was removed by ZVI via adsorption followed by reduction to Se(0) at pH 7.0 but via adsorption at 7.2 in the presence of WMF. Regardless of WMF, Se(IV) applied at 40.0 mg L−1 was removed by reduction at pH 4.0–6.0. The WMF-induced improvement in Se(IV) removal by ZVI may be mainly attributable to the Lorentz force and magnetic field gradient force. Employing WMF to enhance Se(IV) removal by ZVI is a promising and environmental-friendly method since it does not need extra energy and costly reagents.

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