Remediation of As, Sb, and Pb co-contaminated mining soils by using Fe/C based solid wastes: Synergistic effects and field applications

Existing passivators for mining soil remediation suffer from high-costs and detriment to soil health. Here we reported the iron-carbon (Fe/C) based passivators (high-Fe/C, mid-Fe/C, and low-Fe/C) prepared by composing of high-Fe steel slag, high-C coal fly ash and FeSO4 for the remediation of As, Sb, and Pb co-contaminated mining soil. High-Fe/C, and mid-Fe/C addition (5 % dosage) for 30 days decreased soil available As, Sb, and Pb content by 85.5–87.3 %, 58.3–71.2 %, and 55.3–65.7 %, respectively, with only slight degradation of stabilization efficiency with 210 days. Moreover, the labile fractions of As, Sb and Pb were transformed to residual state. After high-Fe/C and mid-Fe/C amendment, the relative abundance of microbial community (bacteria and fungi) and soil fertility were enhanced. Facilitated by the Fe/C micro-electrolysis effect, As, Sb and Pb species were well passivated via adsorption with C-containing functional groups, and precipitation (Fe-As/Sb and Ca-Sb) mechanisms. Noteworthy, the increased soil organic matter (OM), cation exchange capacity (CEC) and microbial activity also enhanced the stabilization of As, Sb, and Pb. Field application results demonstrated that the stabilization efficiency of available As and TCLP-As/Sb/Pb was over 80 % after mid-Fe/C amendment. Fe/C based solid wastes hold the potential for being cost-effective in the remediation of mining soil while achieving large-scale utilization of solid wastes.