Experimental Study on Solidification/Stabilization of Arsenic-Contaminated Soil Using Synergistic Cementitious Materials Based on Ferrous Sulfate and Solid Waste

Unlike soils contaminated with divalent toxic cations, trivalent arsenic (As)-contaminated soils are difficult to treat. In this context, the present study aims to propose a ferrous sulfate (FeSO₄) combined solid waste-based gelling material (MRS) method to solidify/stabilize As-contaminated soils. The interactions between FeSO₄ and gelling material components were further explored in this study using the response surface method (RSM). The results showed a decrease in the compressive strength of the solidified/stabilized soil with increasing FeSO₄ proportion. The leached As concentration decreased with increasing FeSO₄ proportion. The RSM-based quadratic polynomial model accurately predicted the leached As concentrations and compressive strength of the solidified soils. The X-ray diffraction analysis results demonstrated the promotion effect of FeSO₄ on the generation of ettringite and Fe–As in the gelling system, resulting in enhanced further pore filling and As stabilization in the soil. The X-ray photoelectron spectroscopy analysis showed that about 52% of the As(III) content was oxidized to As(V) in the FeSO₄-MRS system, enhancing the stabilization of As. The presence of As during the S/S process decreased the contents of Ca(OH)₂ and Fe oxides/hydroxides by precipitation as Ca–As–O and Fe–As–O, respectively, decreasing the As leaching rate by 96.4%. The strength of solidified/stabilized soil using MRS and FeSO₄ was close to that of cement-based solidified/stabilized soil. This paper provides a novel research idea and technical approach for the remediation of As-contaminated sites. Furthermore, the research results provide a scientific basis and theoretical support for the effective utilization of hazardous solid waste.