Experimental Study on the Environmental Effects and Mechanical Characteristics of Solidified Cr(VI)-Contaminated Soil Based on Slag and Desulfurization Gypsum

This study proposed a new curing agent consisting of slag and desulfurization gypsum industrial waste to solidify Cr(VI)-contaminated soils and prevent its migration and bioaccumulation in the ecosphere. The curing agent dosage of 10–30% resulted in a Cr(VI) toxic leaching concentration, compressive strength, and hydraulic conductivity range of 0.118–5.824 mg/L, 2.70–10.22 MPa, and 1.70 × 10−9–1.37 × 10−6 cm/s, respectively. Following four dry and wet cycles, the dosage of the curing agent was found to be 20–30% to achieve minimum environmental safety requirements. Cr(VI) in the cured specimens mainly existed as CrO42−, or acid salt, in which a portion was changed to Cr(III) during precipitation or directly was encased in the silica-alumina mesh structure. The adsorption capacity of hexavalent chrome on the outer of the hydration product groups was insignificant owing to the electronegativity. Hence, the Cr(VI) was solidified by hydrides such as C-S(A)-H and calcium alumina inclusions. Calcite, quartz, and several zeolite-like substances were also found to be colloidal in the pores to block Cr(VI).