Aging of zerovalent iron in various coexisting solutes: Characteristics, reactivity toward selenite and rejuvenation by weak magnetic field

Aging can influence the performance and subsequent application of zerovalent iron (ZVI) in water treatment. In this study, eight aged ZVI (AZVI) samples were fabricated in different coexisting solutes and their reactivity toward selenite removal were investigated. It showed that the characteristics and reactivity of ZVI varied widely with the aging matrices. The rate constants for selenite removal by ZVI aged in different backgrounds for 24 h were ranked in the order (from most to least reactive): HCO₃⁻ (10.00 mM) > NO₃⁻ (5.00 mM) > SO₄²⁻ (2.00 mM) > Cl⁻ > none (i.e., pristine ZVI without pretreatment, Pri-ZVI) > PO₄³⁻ (0.50 mM) > H₂O > SiO₃²⁻ (2.50 mM) > synthetic groundwater (SGW, 1.50 mM SO₄²⁻, 4.50 mM Cl⁻, 2.00 mM HCO₃⁻, 1.00 mM NO₃⁻, 0.89 mM SiO₃²⁻, 0.05 mM PO₄³⁻, 5.00 mg/L DOC, 2.00 mM Ca²⁺, and 12.43 mM Na⁺). Additionally, the selenite sequestration rates by AZVI were enhanced by 4.3–39.6 folds due to the application of a weak magnetic field (WMF). Moreover, the enhancing effect of WMF on AZVI samples was more outstanding than that on Pri-ZVI based on a wide-spectrum analysis, which may be ascribed to the promoted mass transfer and enrichment of reactants by coupled effects of WMF and aging. In sum, WMF was proved to be a promising method to rejuvenate AZVI samples for wastewater treatment.