Effective Sb(V) immobilization from water by zero-valent iron with weak magnetic field

Abstract Weak magnetic field (WMF) was employed to enhance Sb(V) immobilization by zero-valent iron (ZVI) at pH_ini 4.0 in this study. The kinetics of Sb(V) removal by ZVI followed pseudo-first-order reaction law. Without WMF, the rate constants dropped substantially with increasing the initial Sb(V) concentration ([Sb(V)]_ini) from 5.0 to 40.0 mg/L. The application of a WMF increased the rate constants of Sb(V) sequestration by 5.56-7.71 times at [Sb(V)]_ini of 5.0-40.0 mg/L and enhanced the removal capacity of Sb(V) from 18.1 to 39.2 mg Sb(V)/g Fe. The co-existence of SO₄^2-, NO₃^-, Cl^-, CO₃^2-, SiO₃^2- and humic acid had minor influence on the removal efficiency of Sb(V) by ZVI when WMF was applied. The Fe K-edge XAFS, XRD and SEM results suggested that elevated [Sb(V)]_ini could inhibit the corrosion of ZVI without WMF while the application of WMF could alleviate the passivation of ZVI by Sb(V) and thus promote the removal of Sb(V) by corroded ZVI. The Sb K-edge XAFS spectra implied the incorporation of Sb(V) into the structure of iron (hydr)oxides. Consequently, no release of Sb(V) at pH 3.0, 6.0 or 9.0 from the Sb(V)-treated ZVI was observed in 30 days. Considering the large removal capacity of Sb(V) with low residual Sb(V) concentration, no release of Sb(V) after its incorporation into the structure of iron (hydr)oxides and slight influence of co-existing solutes, it was concluded that coupling ZVI with WMF was an effective Sb(V) immobilization technology.