Phase Transition of Ca- and Mg-Bearing Minerals of Steel Slag in Acidic Solution for CO2 Sequestration

Large amounts of steel slag (SS) and CO2 are produced by the steel industry worldwide. Indirect aqueous carbonation of SS using Ca and Mg is a promising way for carbon capture, utilization, and storage (CCUS). However, some Ca and Mg enriched in refractory minerals affect the extraction efficiency. Therefore, understanding the phase transition of various Ca- and Mg-bearing minerals in strong or mild acidic solutions is of vital importance for SS-based CCUS. This work evaluated the leachability of common minerals of SS in an acidic solution based on thermodynamic analysis and leaching tests. The results showed that the order of leachability of the phases is as follows: CaO>(Ca3Al2O6, gamma-Ca2SiO4, Ca3MgSi2O8, and Ca2MgSi2O7)>(Ca12Al14O33, CaAl2O4, and Ca2Fe2O5). Under the experimental conditions employed in this study, an amorphous phase of silica gel and aluminum hydroxide formed in the dissolution process of Ca3MgSi2O8, Ca3Al2O6 and Ca12Al14O33 phases, which covered the surface of the particles hindering further decomposition. Moreover, a Ca-depleted layer was observed after leaching of Ca2MgSi2O7, Ca12Al14O33, CaAl2O4, and Ca2Fe2O5, and their phase transitions were studied and a mechanism was proposed in this work.

Automated summary

This study evaluated the leachability of common minerals of steel slag (SS) in an acidic solution through thermodynamic analysis and leaching tests. The results showed differences in the leachability of different minerals, and the importance and mechanism of SS-based CCUS were studied.