Objective This study investigated three types typical alkaline industrial solid waste: steel slag, fly ash, and bottom ash, highlighting the differences in their CO₂ mineral trapping efficiency and the degradation patterns of their cementitious activity after carbon fixation. The purpose is to reveal the mechanisms underlying CO₂ mineral trapping in solid waste and evaluate their application potential in backfill engineering, thereby promoting the synergistic development of industrial solid waste recycling and carbon emission reduction.

Methods Through experiments on CO₂ mineral trapping using the direct wet method, the kinetics and product characteristics of solid waste-CO₂ interactions were systematically investigated. In combination with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), the phase composition and microstructures of the products formed during CO₂ mineral trapping were characterized. Finally, the cemented backfill specimens were prepared using carbonated solid waste, and their mechanical properties, along with the evolutionary patterns of their pore structures, were compared and analyzed.

Results and Conclusions The alkalinity reduction process during CO₂ mineral trapping was governed by the content and dissolution kinetics of Ca²⁺. The pH values of the solutions of steel slag, fly ash, and bottom ash exhibited rapid-stable decreases, slow-rapid-stable decreases, and a sudden decrease, respectively. Under the condition of 0.3 MPa and 25 ℃, steel slag demonstrated the highest carbon (CO₂) fixation capacity (136.1 g/kg), significantly outperforming both fly ash (81.86 g/kg) and bottom ash (16.2 g/kg). The primary products of the solid waste included calcite CaCO₃ (steel slag and bottom ash) and aragonite CaCO₃ (fly ash). Influenced by the consumption of active calcium and the interfacial effect, the compressive strength of the specimens decreased by 45.65%-73.48% after carbon fixation. Specifically, the steel slag-based specimens exhibited the highest decreased amplitude (from 10.22 MPa to 2.71 MPa), followed by fly ash-based specimens (from 9.8 MPa to 3.61 MPa). In contrast, the bottom ash-based specimens showed a minimal decline in the compressive strength (from 7.82 MPa to 4.25 MPa) due to incomplete reactions during CO₂ mineral trapping. The results of this study provide theoretical support and a technical reference for the synergy between the treatment of industrial solid waste and CO₂ mineral trapping.