Green-synthesized nanosize Mont-supported Fe0 via tea extract for enhanced transport and in situ remediation of Pb(II) in soil

Abstract

Lead (Pb(II)) can be accumulated in soil and transferred to humans via the food chain. Therefore, it is essential to improve Pb(II) immobilization during soil remediation. Nanosized zero-valent iron (nZVI) from green tea extract (tea polyphenols, TPs) was successfully synthesized as an additive reductant. Further, the nZVI was supported on montmorillonite (Mont), resulting in a GT-nZVI@Mont composite characterized by multiple techniques, including Zeta potential, SEM, TEM, XRD, and XPS. Moreover, the transport experiments and the toxicity characteristic leaching procedure (TCLP) were conducted to identify the optimum conditions (i.e., GT-nZVI@Mont dosage, Pb(II) concentration, and pH) for the remediation. The experimental results showed that the enhanced transportability of GT-nZVI@Mont was about 40% more than that of GT-nZVI. Meanwhile, Pb(II) immobilization was increased at various pH values (especially under anoxic conditions). The Pb(II) immobilization capacity of GT-nZVI@Mont was 900.8 mg∙g-1 (per unit of Fe content), which was significantly higher than 530.1 mg∙g-1 per unit of Fe content in GT-nZVI. Such enhancement could be ascribed to the synergistic effects of the wrapped TP around the Fe0 core and the Mont interlayer support, capable of protecting the Fe0 surface from further oxidation. When GT-nZVI@Mont reacted with the Pb(II) in soil, TPs’ unwrapped coverage increased the reaction sites of Fe0 cores for Pb(II) reduction and adsorption. GT-nZVI@Mont with sufficient transportability provided efficient in situ remediation of Pb(II) in contaminated soil at a wide pH range.