Effect of CO2 Mineralization on the Composition of Alkali-Activated Backfill Material with Different Coal-Based Solid Wastes

Abstract

Research focusing on waste management and CO2 mineralization simultaneously has been a popular topic in the mining community, and a common approach is to mineralize CO2 with coal-based solid waste (CSW, e.g., gangue (CG), fly ash (FA), coal gasification slag (CGS)) produced by mining activities. Despite the understanding of CO2 mineralization by cementitious materials, the mineralization capacity of alkali-activated CSWs remains unknown. Therefore, the mineral composition evolution and mineralization capacity of different alkali-activated materials (prepared with CG, FA, CGS, and sodium hydroxide (which works as the alkali-activator), respectively) are investigated with the adoption of Gibbs Energy Minimization Software (GEMS). The results indicate that the abovementioned three alkali-activated CSWs are majorly composed of calcium silicate hydrate, magnesium silicate hydrate, kaolinite, sodium zeolite, and liquid. Due to the difference in the chemical composition of different CSWs, the amount of hydration products varies. Specifically, the alkali-activated CSWs made with CGS have the maximum calcium silicate hydrate (C-S-H), while those prepared with FA enjoy the lowest porosity. In addition, the CO2 mineralization process will result in the formulation of carbonate and, theoretically, the maximum quantity of mineralized CO2 is less than 20% of the binder used. Furthermore, compared with CG and CGS, FA is characterized with the highest mineralization capacity. The findings in this study contribute to the understanding of CO2 mineralization with alkali-activated CSWs.