Improving the Reactivity of Zerovalent Iron by Taking Advantage of Its Magnetic Memory: Implications for Arsenite Removal

Premagnetization was employed to enhance the reactivity of zerovalent iron (ZVI) toward As­(III) sequestration for the first time. Compared to the pristine ZVI (Pri-ZVI), the rate of As­(III) elimination by the premagnetized ZVI (Mag-ZVI) was greater over the pH_ini range of 4.0–9.0 and increased progressively with increasing intensity of the magnetic field for premagnetization. Mag-ZVI could keep its reactivity for a long time and showed better performance than Pri-ZVI for As­(III) removal from synthetic groundwater in column tests. The Fe K-edge XAFS analysis for As­(III)-treated ZVI samples unraveled that premagnetization promoted the transformation of ZVI to iron (hydr)­oxides and shifted the corrosion products from maghemite and magnetite to lepidocrocite, which favored the arsenic sequestration. The arsenic species analysis revealed that premagnetization facilitated the oxidation of As­(III) to As­(V). ZVI pretreated with grinding was very different from Mag-ZVI with regard to As­(III) removal, indicating that the improved reactivity of Mag-ZVI should not be associated with the physical squeezing effect of the ZVI grains during magnetization. The positive correlation between the remanence of Mag-ZVI and the rate constants of total arsenic removal indicated that the enhanced reactivity of Mag-ZVI was mainly ascribed to its magnetic memory, i.e., the remanence kept by Mag-ZVI.