Passivation efficiency and mechanism of arsenic-contaminated mining soil with iron-based solid wastes in collaboration with ferrous sulfate

Abstract

Iron-based solid wastes could realize the remediation of arsenic (As) contaminated mining soil, but their proper selection and passivation mechanisms need further assessment. Herein, we proposed a novel and efficient remediation strategy for contaminated mining soil utilizing iron-based solid wastes in collaboration with FeSO4. In comparison with the control soil, the application of high Fe0-steel slag (SS)/FeSO4, Fenton sludge (FS)/FeSO4 and red mud (RM)/FeSO4 removed the water-soluble As completely, and reduced available As content by 95.3 %, 88.6 % and 83.8 %, respectively, under the optimal passivation conditions (amendments dosage=5 wt%, solid wastes: FeSO4 =3: 2, passivation time=30 days). Meanwhile, the As leaching concentrations were lower than the drinking water standard (GB 5749–2022, China). The enhanced stability of As in amended soils was ascribed to the remarkable transformation from labile As fractions (F1 and F2) to the most stable As fraction (F5), which was significant for the long-term passivation of As, particularly in SS/FeSO4 amended soil. The synergistic passivation mechanisms involved the release of H+ and SO42- ions from FeSO4 hydrolysis, promoting the dissolution of unstable As species. The released As was adsorbed/complexed/coprecipitated by amorphous Fe(Ⅲ) oxides and FeO(OH), and then the amorphous Fe-As-O complexes and crystalline Fe-As-O coprecipitates were generated with increasing As loading. This work gives a novel strategy for the utilization of iron-based solid wastes to passivate As-contaminated mining soil.