Dual regulation of As release and soil environment by Fe(Ⅱ) assisted steel slag and coal fly ash: Effects and potential mechanisms

Multiple solid waste-based amendments are used for arsenic (As)-contaminated soil remediation, but their mechanisms in inhibiting As release and the effects on soil health in real sites remain poorly understood. Here, an amendment consisting of steel slag (SS), coal fly ash (CFA) and Fe(Ⅱ), namely, Fe(Ⅱ) assisted SS and CFA, was applied to an As-contaminated mining soil. 120 days field experimental results revealed that amendment addition in low-As soil (LA soil) and high-As soil (HA soil) significantly increased amorphous Fe(Ⅲ) (hydro)oxides content and decreased dissolved organic carbon (DOC), and thus inhibited As mobilization. More importantly, the soil microbial community activity was improved in HA soil, while it significantly decreased in LA soil. Correlation analyses demonstrated that the activation of fungal and bacterial communities was directly correlated with soil pH, amorphous Fe(Ⅲ) (hydro)oxides, soil organic matter (SOM), and DOC. The C-containing functional groups, newly generated Fe(Ⅲ) (hydro)oxides and Fe-As-SOM complexes inhibit As release, while the Fe(Ⅲ) reduction drove the As release. This work highlighted the importance of Fe(Ⅱ) assisted SS and CFA in inhibiting As release and regulating soil microbial communities, providing a new strategy for the remediation of heavy metals contaminated mining soil using solid waste-based amendment.