Environmental Characteristics, Mechanical and Hydraulic Behavior of Solidified Cr(VI) Contaminated Soil with Industrial Waste Residue

Hexavalent chromium Cr (VI) pollution is prevalent at decommissioned industrial sites and poses a serious risk to the surrounding ecosystem and human health. In this study, we presented a novel heavy metal-contaminated soil curing agent derived from industrial slag (slag and desulfurization gypsum) for the treatment and remediation of Cr (VI)-contaminated soil. This curing agent was used to treat Cr (VI)-contaminated soil at pollution control (78 mg/kg), light contamination (380 mg/kg), and heavy contamination (1000 mg/kg) levels. The migratory properties of Cr (VI) in the cured contaminated soil were evaluated using toxic leaching and soil column tests. The mechanical strength and hydraulic conductivity of the cured contaminated soil were obtained using unconfined compressive, direct shear, and penetration tests. The mineralogical composition, chemical characteristics, and micromorphological features of the cured soils were analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The unconfined compressive strength and shear strength parameters (c and phi, respectively) increased significantly as the curing agent dosage was increased, whereas the Cr (VI) leaching concentration and hydraulic conductivity decreased. However, with an increase in Cr (VI) contamination, the cured soil metrics demonstrated the opposite trend. Most of the chromate (CrO42-) ions were encapsulated in hydration gelation products, such as C-S(A)-H and C-A-H. A small portion of Cr (VI) was reduced to Cr (III) or sequestered in the curing agent via charge adsorption. These test results demonstrated the multiple advantageous properties, including environmental safety, high strength, and low permeability, of this novel heavy metal curing agent derived from industrial waste.