Red mud-based Fe/C nanostructured materials for multi-interface remediation of Cr(vi)-contaminated soil and stabilization†

The stabilization remediation performance of Cr(VI)-contaminated soil hinges on the remediation behaviors at soil–Cr(VI)–stabilizer multiple interfaces. Fe/C nanostructured materials featuring high chemical affinity, quick electron transfer and tunable active sites might tackle the problems of substance transport and structure evolution across multiple interfaces. Herein, we report that the co-pyrolysis of red mud and straw, two abundant solid wastes, can realize the scaled-up synthesis of biochar-supported nanoscale zero-valent iron (nZVI/BC). At an initial Cr(VI) concentration of 1000.00 mg kg⁻¹ and stabilizer dosage of 10%, the optimal nZVI/BC converted the Cr(VI)-contaminated soil into non-hazardous waste, with toxicity characteristic leaching procedure (TCLP) leaching concentrations of 3.13 mg L⁻¹ Cr(VI) and 11.26 mg L⁻¹ Cr(T). Experimental and theoretical results revealed that nZVI/BC altered the species evolution at the multiple interfaces of nZVI/BC–Cr(VI)–soil, where the acid-soluble Cr in soil shifted into stable residual Cr owing to the microscopically increased bidentate-binuclear inner-sphere coordination modes and the reduction process over the nZVI/BC surface. Meanwhile, the released iron species from nZVI/BC was immobilized on the soil surface, thereby regulating organic matter adsorption to recover soil agglomeration. Therefore, this study presents the feasibility of obtaining Fe/C nanostructured materials by one-step upgrading agricultural and industrial waste into eco-friendly stabilizers for remediating Cr(VI)-contaminated soils.