Coupled Effects of Aging and Weak Magnetic Fields on Sequestration of Selenite by Zero-Valent Iron

Abstract

The sequestration of Se(IV) by zero-valent iron (ZVI) is strongly influenced by the coupled effects of aging ZVI and the presence of a weak magnetic field (WMF). ZVI aged at pH 6.0 with MES as buffer between 6 and 60 h gave nearly constant rates of Se(IV) removal with WMF but with rate constants that are 10- to 100-fold greater than without. XANES analysis showed that applying WMF changes the mechanism of Se(IV) removal by ZVI aged for 6-60 h from adsorption followed by reduction to direct reduction. The strong correlation between Se(IV) removal and Fe2+ release suggests direct reduction of Se(IV) to Se(0) by Fe0, in agreement with the XANES analysis. The numerical simulation of ZVI magnetization revealed that the WMF influence on Se(IV) sequestration is associated mainly with the ferromagnetism of ZVI and the paramagnetism of Fe2+. In the presence of the WMF, the Lorentz force gives rise to convection in the solution, which narrows the diffusion layer, and the field gradient force, which tends to move paramagnetic ions (esp. Fe2+) along the higher field gradient at the ZVI particle surface, thereby inducing nonuniform depassivation and eventually localized corrosion of the ZVI surface.

Enhanced paramagnetic Cu2+ ions removal by coupling a weak magnetic field with zero valent iron

“…Our previous studies showed that the application of a weak magnetic field (WMF) could promote ZVI corrosion and significantly enhance Se(IV) removal by both pristine ZVI and aged ZVI [16,17], and greatly improve As(V) and As(III) removal by ZVI at pH ini 3.0-9.0 [18]. Liang et al [17] conducted numerical simulation to evaluate the flux density distribution near the ZVI sphere surface and revealed that the observed WMF effects arose from the ferromagnetism of ZVI and the paramagnetism of Fe 2+ . In the presence of a WMF, the magnetic field gradient force (F GMF ) tends to induce localized corrosion of the ZVI surface, which consequently accelerated ZVI corrosion and contaminants removal [17].…”

“…Liang et al [17] conducted numerical simulation to evaluate the flux density distribution near the ZVI sphere surface and revealed that the observed WMF effects arose from the ferromagnetism of ZVI and the paramagnetism of Fe 2+ . In the presence of a WMF, the magnetic field gradient force (F GMF ) tends to induce localized corrosion of the ZVI surface, which consequently accelerated ZVI corrosion and contaminants removal [17]. However, no effort has been made to show that the positive effect of WMF on contaminants removal by ZVI corrosion was attributed to the enhanced mass transfer.…”

Factors affecting p-nitrophenol removal by microscale zero-valent iron coupling with weak magnetic field (WMF)

“…Hence, Guan et al 19,22 developed ZVI premagnetization before the reaction to enhance the reactivity of ZVI toward various contaminants. However, the reactivity of premagnetized ZVI was not stable and decreased with time before the reaction.…”

“…Recently, Guan et al 19,20 have done many comprehensive studies on weak magnetic eld (WMF) enhancing the removal of several heavy metals by microscale ZVI. The application of an inhomogeneous weak magnetic eld (WMF) (B max < 20 mT) could signicantly enhance Se(IV) removal by both pristine ZVI and aged ZVI 19,20 and greatly improve As(V) and As(III) removal by Fe 0 at pH ini 3.0-9.0.…”

“…The application of an inhomogeneous weak magnetic eld (WMF) (B max < 20 mT) could signicantly enhance Se(IV) removal by both pristine ZVI and aged ZVI 19,20 and greatly improve As(V) and As(III) removal by Fe 0 at pH ini 3.0-9.0. 21 The accelerated Se(IV), As(III) and As(V …”