Copper slag-aided mechanochemical detoxification soda ash chromite ore processing residue and long-term stabilization: Efficient reduction and reoccurrence inhibition of Cr(VI)

Abstract

The soda ash chromite ore processing residue (SA-COPR) is a hazardous solid waste generated inevitably in the production process of chromate, even if detoxified, it is prone to the reoccurrence of Cr(VI). Copper slag (CS) is mainly composed of Fe(II) rich mineral-fayalite and can be used as a potential reductant. In this study, the SA-COPR detoxification assisted by CS under ball milling was investigated and the optimal results indicated a TCLP total Cr concentration of 3.65 mg/L, which met the US EPA standards (<5 mg/L). The detoxified SA-COPR was then solidified by montmorillonite for long-term stabilization. Results showed that the Cr in solidified body is further fixed in three forms: physical encapsulation, physical adsorption, and chemical bonding. The 28d compressive strength of the solidified body with 50% SA-COPR content is 11.83 ± 0.83 MPa, meeting the GB/T 50081-2002 standard (>10 MPa). Moreover, the long-term stabilization of the solid body after 120 days was examined by TCLP and only yielded a total Cr concentration of 0.139 mg/L, which was significantly lower than the EPA standard. Overall, this complex reduction and immobilization of SA-COPR by copper slag-ball mill-montmorillonite provide a new reference for the efficient reduction and “re-yellowing” inhibition as well as subsequent resource utilization.