Sustainable Valorization of Carbide Slag Through CO2 Mineralization: Process Sequence-Regulated Impurity Partitioning for High-Purity Calcium Carbonate Production

Direct CO2 mineralization of carbide slag offers considerable potential for sustainable waste valorization, CO2 utilization, and high-value CaCO3 production, although associated Si-, Fe-, and Al-bearing impurities limit product quality. This study comparatively evaluated six process routes to determine how process sequence and separation-stream selection affect impurity partitioning and final product performance. The results suggest that calcination-induced phase reconstruction may improve the separability of impurity-bearing material, while hydrocyclone classification preferentially partitions impurity-rich particles toward the underflow. Relative to the calcined feed, the Si and Fe concentrations in the overflow decreased by 58.4% and 86.9%, respectively, and subsequent magnetic separation further reduced residual Fe. The preferred calcination–hydrocyclone overflow–magnetic separation–mineralization route omitted flotation and produced CaCO3 with a purity of 98.3%, a whiteness approaching 100%, and a total impurity content of 0.57%. These findings provide a process-sequence framework for balancing impurity removal, product quality, resource recovery, and environmental performance during the sustainable conversion of carbide slag into high-value CaCO3.