Metal(loid)s removal by zeolite-supported iron particles from mine contaminated groundwater: Performance and mechanistic insights

Iron-based materials have been widely investigated because of their high surface reactivity, which has shown potential for the remediation of metal(loid)s in groundwater. However, the disadvantages of structural stability and economic feasibility always limit their application in permeable reactive barrier (PRB) technology. In this study, zeolite-supported iron particles (Zeo-Fe) were synthesized by an innovative low-cost physical preparation method that is suitable for mass production. The removal efficiency and mechanism of typical metal(loid)s (Pb2+, Cd2+, Cr6+ and As3+) were subsequently investigated using various kinetic and equilibrium models and characterization methods. The results of scanning electron microscopy and energy dispersive spectrometry (SEMEDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) confirmed that zero valent iron (Fe-0) and oxidation product (Fe3O4) were successfully loaded and efficiently dispersed on zeolite. The synthesized Zeo-Fe exhibited excellent adsorption and redox capacities for the cations Pb2+, Cd2+ and anions Cr6+, As3+. The increase in the pH resulting from Fe0 corrosion also enhanced the precipitation of Fe-metal(loid)s. The maximum removal capacity for Pb2+, Cd2+, Cr6+ and As3+ was up to 70.00, 9.12, 2.35 and 0.36 mg/g, respectively. The removal processes were well described by the pseudo-second-order kinetic model for Pb2+ and Cd2+, Lagergren pseudo first-order kinetics model for As3+ and double phase first order kinetics model l for Cr6+. Cr6+ was rapidly reduced to Cr3+ by the Fe-0 stabilized on Zeo-Fe, and the oxidation of As3+ to As5+ was attributed to the Fe-0/Fe2+ oxidation process at the interface over time, which was further demonstrated by the mineral phase and element valence analyses of reacted Zeo-Fe. The removal mechanism for metal(loid)s was a combination of physical and chemical processes, including adsorption, coprecipitation and reduction-oxidation. Conclusively, Zeo-Fe has been shown to have potential as an effective and economical material for removing various metal(loid)s used in PRB.

Automated summary

Iron-based materials have high surface reactivity and potential for remediating metal (loid)s in groundwater. However, their limited structural stability and economic feasibility hinder their application in permeable reactive barrier (PRB) technology. In this study, zeolite-supported iron particles (Zeo-Fe) were synthesized through a low-cost physical method, leading to efficient removal of metal (loid)s.