Simultaneous stabilization of arsenic and antimony co-contaminated mining soil by Fe(Ⅱ) activated-Fenton sludge: Behavior and mechanisms

Fenton sludge (FS) with high iron contents that discharged from the Fenton process was rarely studied for soil remediation. Herein, a novel Fe(Ⅱ) activated-Fenton sludge (FS-FeSO₄) was proposed to stabilize arsenic (As) and antimony (Sb) co-contaminated soil meanwhile disposing FS. Multiple characteristic analyses revealed that the porous structures and rich functional groups of FS-FeSO₄ involved in As and Sb adsorption. Meanwhile, Fe (hydro)oxides played a key role in As and Sb stabilization. Under the optimal application parameters (stabilizers dosage: 5%, incubation time: 60 days), the available As and Sb content decreased by 88.6% and 83.3%, respectively, and the leachability of As and Sb was reduced by 100% and 72.6% for FS-FeSO₄ stabilized soil. Moreover, the mobile As and Sb fractions (F1 and F2) were transformed into the most stable fraction (F5). The adsorption of As and Sb on FS-FeSO₄ was well fitted by pseudo-second-order kinetic and Langmuir models, while FS-FeSO₄ exhibited a better affinity for As than Sb under competition conditions. Poorly crystalline α-FeOOH and amorphous Fe (hydro)oxides provided sufficient active sites for As and Sb, and the generation of Fe-As/Sb and Ca-Sb chemical bonds promoted the stability of As and Sb. This study demonstrated that FS-FeSO₄ was a potentially effective stabilizer for As and Sb co-contaminated soil remediation.