Efficient selenate removal by zero-valent iron in the presence of weak magnetic field

•Efficient Se(VI) removal was achieved by ZVI at very low dosage coupling with WMF.•The rate of Se(VI) removal by ZVI with WMF increased with increasing ZVI dosage.•Se(VI) adsorption to the ZVI surface was the first step of Se(VI) removal by ZVI.•The adsorbed Se(VI) was rapidly reduced to Se(IV) and then slowly to Se(0).•Employing WMF to enhance Se(VI) removal by ZVI under oxic conditions is promising.

Se(VI) was very refractory to be removed by zero-valent iron (ZVI), therefore weak magnetic field (WMF) was employed to achieve efficient Se(VI) removal by ZVI. Batch experiments showed that negligible Se(VI) (<4%) was removed by ZVI without the application of WMF within 72 h. The presence of WMF dramatically enhanced Se(VI) sequestration by ZVI and complete removal of 10.0 mg L−1 Se(VI) was achieved by ZVI in 90 min. The main portion of kinetics of Se(VI) removal by ZVI in the presence of WMF followed zero-order rate law and the rate constants of Se(VI) sequestration by ZVI increased progressively with increasing the ZVI dosage. Fe K-edge XAFS spectra and synchrotron radiation-XRD analysis revealed that ZVI was transformed to X-ray amorphous Fe3O4 before finally transformed to lepidocrocite (γ-FeOOH). The LCF analysis of Se K-edge XANES spectra indicated that adsorptive removal of Se(VI) was minor but adsorption of Se(VI) to the corroded ZVI surface was the first step of Se(VI) removal. Se(VI) was rapidly reduced to Se(IV), which could be further transformed to Se(0). Comparison of the performance of Se(VI) removal in the literature suggested that employing WMF to enhance Se(VI) removal by ZVI under oxic conditions be a promising method.

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