Stirring-assisted CO2 mineralization of a ternary solid-waste backfill material: Effects of temperature and CO2 pressure on carbon sequestration capacity and performance

The synergistic integration of coal mine backfill mining and CO 2 mineralization storage provides a new technical pathway for the resource utilization of bulk industrial solid wastes, stability control of mined-out voids, and long-term CO 2 fixation. In this study, a ternary solid-waste backfill material (TSBM) was developed using fly ash, steel slag, and carbide slag as the main raw materials. A self-developed high-temperature and high-pressure stirred CO 2 mineralization reaction system was employed to systematically investigate the effects of stirred mineralization temperature (30~60℃) and CO 2 pressure (1~7 MPa) on slurry flowability, uniaxial compressive strength at multiple ages, CO 2 mineralization efficiency, and microstructural product evolution, reveal the regulatory mechanisms of temperature and CO 2 pressure on the hydration–mineralization coupled reactions during TSBM stirring, and clarify the intrinsic relationship between strength evolution and carbon sequestration capacity of TSBM after mineralization treatment. The results showed that the flowability of TSBM generally decreased with increasing stirred mineralization temperature and CO 2 pressure, with temperature exerting a more pronounced effect, and increasing temperature more readily accelerating slurry structural build-up. Stirred CO 2 mineralization improved the early-age strength of the material, with the 3d strength increasing by up to 48.5% at 5 MPa. However, excessively high temperature or CO 2 pressure was unfavorable for later-age strength development, resulting in an age-dependent strength response characterized by enhanced early-age strength but reduced later-age strength development. Microstructural characterization further showed that stirred mineralization temperature and CO 2 pressure drove peak-type and cumulative-type characteristics of product evolution and carbon sequestration response in TSBM, respectively. However, the peaks of mechanical performance and mineralization efficiency did not coincide, and greater mineralization did not necessarily translate into improved later-age load-bearing performance. This study preliminarily established a conceptual framework for the coordinated regulation of “flowability–strength–carbon sequestration” of TSBM under stirred mineralization, providing a parameter basis and methodological reference for the low-carbon design of carbon-sequestering backfill materials in coal mines, optimization of mineralized slurry preparation, and engineering application of carbon storage in mined-out voids.