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 CO 2, this study first prepares a composite activated coal gangue (CACG) with mechanical-thermal composite activation. Thereafter, the CO 2 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 CO 2 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 Al 2 O 3 and SiO 2, 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 CO 2 sequestration ability by CACG; (iii) temperature is inversely proportional to the CO 2 sequestration capacity of CACG, while pressure, liquid–solid ratio, and stirring speed are all directly proportional to the CO 2 sequestration capacity; (iv) the maximum CO 2 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.