Iron and calcium interaction for soil As remediation in As waste mine site: Risk assessment and In-situ stabilization

The migration of arsenic (As) in soils poses a serious threat to human health. Iron and calcium-based solid waste may facilitate strategies for As-contaminated soil remediation, but its efficacy and potential mechanisms in real site need to be revealed. This study focused on As waste mine sites and employed established indices to assess both ecological risk and human health risk associated with As. Furthermore, the combination of carbide sludge, plant ash and FeSO₄ was utilized as Fe-Ca based passivator (CFP) for the contaminated soil remediation. Risk assessment results indicated significant As contamination in the study area, with both carcinogenic and non-carcinogenic risks exceeding acceptable thresholds for the exposed population. In-situ stabilization results demonstrated that 7% dosage of CFP effectively decreased soil bioavailable and leaching concentration of As. Meanwhile, the soil pH was elevated from 4.23 to 7.51 after remediation. Notably, the CFP effectively inhibited the migration of As under the long-term rainfall. The amorphous Fe(Ⅲ) hydroxides associated with As formed Fe-As precipitates (FeAsO₄). Importantly, CaSO₄⋅2H₂O could favor the generation of amorphous Fe-As precipitates and inhibit the As release. This work identified target heavy metal(loid)s through systematic risk assessment and demonstrates cost-effective As stabilization under field conditions.