The effects of impurities in carbide slag on the morphological evolution of CaCO₃ during carbonation

Carbide slag (CS) is a kind of solid waste generated by the hydrolysis of calcium carbide for acetylene production. Its major component is Ca(OH)₂, which shows great potential in CO₂ mineralization to produce CaCO₃. However, the types of impurities in CS and their mechanisms for inducing the morphological evolution of CaCO₃ are still unclear. In this work, the influence of impurities in CS on the morphology evolution of CaCO₃ was investigated. The following impurities were identified in the CS: Al₂O₃, MgO, Fe₂O₃, SiO₂ and CaCO₃. Ca(OH)₂ was used to study the influence of impurities (Al₂O₃ and Fe₂O₃) on the evolution of CaCO₃ morphology during CS carbonation. Calcite (CaCO₃) was the carbonation product produced during CS carbonation under varying conditions. The morphology of calcite was changed from cubic to rod-shaped, with increasing solid-liquid ratios. Moreover, rod-shaped calcite was converted into irregular particles with increasing CO₂ flow rate and stirring speed. Rod-shaped calcite (CaCO₃) was formed by CS carbonation at a solid-liquid ratio of 10:100 under a stirring speed of 600 rpm and a CO₂ flow rate of 200 ml/min; and spherical calcite was generated during Ca(OH)₂ carbonation under the same conditions. Al₂O₃ impurities had negligible effects on spherical CaCO₃ during Ca(OH)₂ carbonation. In contrast, rod-shaped CaCO₃ was generated by adding 0.13 wt% Fe₂O₃ particles, similar to the content of Fe₂O₃ in CS. Rod-shaped calcite was converted into particulate calcite with increasing Fe₂O₃ content. The surface wettability and surface negative charge of Fe₂O₃ appeared to be responsible for the formation of rod-shaped CaCO₃. This study enhances our understanding and utilization of CS and CO₂ reduction and the fabrication of high-value rod-shaped CaCO₃.