Mineralization Mechanisms and Sequestration Capacity of CO ₂ Using Composite-Activated Coal Gangue

To expand the application of carbon dioxide capture, utilization, and storage (CCUS) and realize the synergy management of coal gangue and CO2, this study first prepares a composite activated coal gangue (CACG) with mechanical-thermal composite activation. Thereafter, the CO2 mineralization mechanisms of the obtained CACG under different conditions were revealed, and the effects of temperature, pressure, liquid–solid ratio, and stirring speed on the CO2 sequestration capacity were quantitatively analyzed. The results show that (i) mechanical-thermal composite activation significantly refines the particle size of coal gangue, generates a large amount of amorphous Al2O3 and SiO2, and thereby remarkably improves the leaching rate of alkaline ions; (ii) new carbonates are generated in CACG after mineralization, which proves the effectiveness of the CO2 sequestration ability by CACG; (iii) temperature is inversely proportional to the CO2 sequestration capacity of CACG, while pressure, liquid–solid ratio, and stirring speed are all directly proportional to the CO2 sequestration capacity; (iv) the maximum CO2 sequestration capacity of CACG reaches 15.67 g/kg, while the minimum is 0.34 g/kg. The findings in this study provide theoretical and technical support for the industrial application of coal gangue in CCUS technology.