Effects of magnetic field on selenite removal by sulfidated zero valent iron under aerobic conditions

A novel strategy of sulfide modified zero valent iron (S-ZVI) coupled with the magnetic field (MF) is developed for selenite (Se(IV)) removal. The original ZVI particle size (30 μm), S/Fe ratio (1:80), solution pH (5), S-ZVI loading (0.75 g L^-1), and MF intensity (20 mT) can exhibit the optimal enhancement effects of MF on Se(IV) removal by S-ZVI. Common corrosion promoters (Cl^-, PO₄^3-, SO₄^2-, Mg²⁺, and Ca²⁺) and inhibitors (NO₃^-, SiO₃^2-, and CO₃^2-) show positive and negative effects on Se(IV) removal by S-ZVI, respectively. But MF can alleviate promoting or inhibiting effects of coexisting ions on Se(IV) removal by S-ZVI, and well preserve the reactivity of S-ZVI from background ions in water. Furthermore, MF can also enhance the reactivity of S-ZVI towards Se(IV) during consecutive experiments, the promotion factor (the ratio of k_obs with MF to k_obs without MF) increased from 2.57 to 5.83 with the increase of cycles. MF can not only improve the reactivity of ZVI covered with iron oxide or iron hydroxide but also effectively enhance the ability of ZVI covered with iron sulfide. S-ZVI exhibited good stability and recyclability in the presence of MF. XANES analysis of selenium species reveals that the reductive product of Se(IV) with or without MF is primarily Se(0), and Se(IV) removal by S-ZVI can be ascribed to adsorption and reduction. This work indicates that MF may widen the application of S-ZVI for pollutants removal in environmental remediation.