Carbon sequestration amount evolution characteristics and reaction mechanisms in coal-based solid waste backfill: A new whole-process carbon sequestration technique

Underground carbon sequestration (CS) by solid waste backfill (SWB) offers an effective pathway for collaborative disposal of coal-based solid waste and CO 2 , where the amount of carbon sequestration is an important evaluation parameter. In this study, the concept of whole-process carbon sequestration using coal-based solid waste and CO 2 , including sequential stirring and curing stages, was proposed to evaluate the performance evolution of CS. The results showed that CO 2 pressure and ambient temperature positively correlated with the CS amount from coal-based SWB. In particular, CO 2 pressure prevailed in the stirring stage, while the ambient temperature effect was more significant in the curing stage. The CS amounts obtained during the stirring stage alone, the curing stage alone, and two sequential stages ranged from 0.66 %–3.10 %, 3.53 %–5.09 %, and 5.12 %–6.02 %, respectively. The functional group and micromorphology analyses revealed that the prevailing mechanism at the CS stirring stage was the stirring-driven gas dissolution-leaching-mineralization reaction, while that at the curing stage was the hydration-driven gas permeation-dissociation-CS reaction. Both were essentially solid-liquid-gas multiphase chemical reactions. The results are instrumental in substantiating the coal-based SWB carbon sequestration evolution patterns and mechanisms and providing data support for waste disposal and carbon emission reduction in the coal industry.