Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms

In this study, the effects of major anions (e.g., ClO4–, NO3–, Cl–, and SO42–) in water on the reactivity of zerovalent iron (ZVI) toward As(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO4– and NO3– had negligible influence on As(III) removal by ZVI, but Cl– and SO42– could improve As(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO42– > Cl– > NO3– ≈ ClO4– (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO3–, HCO3–, and H2PO4– on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO42–. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe2+ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect.