Magnetic biochar-supported nanoscale zero-valent iron for remediation of arsenic and cadmium-contaminated soils: The role of free radicals

Abstract

Remediating arsenic (As) and cadmium (Cd) in soils through immobilization faces challenges, primarily in isolating amendments from soil. While previous studies have focused on altering heavy metal speciation, they have not reduced total metal content, risking reactivation and secondary contamination. This study synthesized and characterized magnetic biochar loaded with nanoscale zero-valent iron (nZVI-MBC), which uses magnetic separation to decrease As and Cd levels in soil, offering a potential permanent solution for contaminant removal. The ability of nZVI-MBC to stabilize As and Cd in soil was evaluated. The results demonstrate that nZVI-MBC reduced total As and Cd content by 13.7 % and 12.3 %, respectively, and decreased their bioavailability by 34.1 % and 93.2 %, converting these metals into more stable forms. Post-treatment, increases in soil pH, cation exchange capacity, and organic matter were observed, along with enhanced soil enzyme activity. The stabilization mechanisms included electrostatic attraction, surface adsorption, complexation, and co-precipitation. Moreover, nZVI-MBC promoted the generation of hydroxyl radicals (•OH) and environmentally persistent free radicals (EPFRs), which facilitated the oxidation of As(III) to As(V), thereby reducing As migration. This study confirms that nZVI-MBC is a promising soil amendment for effective heavy metal remediation.