Synergistic mechanism between mineralization and capillary trapping in MSWIFA-based carbon sequestration material

Municipal solid waste incineration fly ash (MSWIFA), a waste product of urban operations, is threatening the sustainable development of cities, yet its significant self-foaming potential for CO₂ sequestration remains largely unexplored. MSWIFA contributes to enhancing the porosity and Ca²⁺ content of backfill material, thereby improving the storage capacity. To elucidate the coupled mechanisms of CO₂ mineralization and capillary trapping within backfill systems, this study investigates the effects of in-situ goaf environmental conditions on the mineralization process, alongside the hydrodynamic behavior governed by mineral composition, pore structure, and surface properties. Our results reveal a strong synergistic effect between mineral carbonation and capillary trapping, significantly enhancing CO₂ storage capacity in MSWIFA-based backfill materials. Elevated temperature and pressure in the goaf environment were found to accelerate the decomposition of calcium silicate hydrate (C-S-H), promoting the formation of abundant carbonate minerals. These mineral transformations increase the prevalence of hydrophilic functional groups and surface roughness, while carbonate accumulation in the throats induces the formation of fine pores (<6 μm) and segment large pore structures. The optimization of surface characteristics and pore architecture thus plays a critical role in improving overall CO₂ sequestration efficiency. This work provides a novel strategy for the high-value utilization of hazardous solid waste and contributes meaningfully to greenhouse gas mitigation efforts.