Sustainable mine backfill development through in situ CO₂ mineralization: Toward net-zero mining

The mining industry is responsible for significant carbon emissions owing to cement consumption in cemented paste backfill (CPB). Although the incorporation of supplementary cementitious materials can lower emissions, their use often compromises the mechanical strength of CPB. To address this limitation, this study introduces a CO₂-assisted activation (CAA) process that uniquely integrates mechanochemical activation with in situ carbonation to produce a sustainable mine backfill. Using a ternary binder system of ordinary Portland cement (OPC), blast furnace slag, and carbide slag (ordinary Portland cement–blast furnace slag–carbide slag, OBC), the CAA process simultaneously enhanced the mechanical performance and enabled stable CO₂ sequestration. The experimental results showed that OBC achieved comparable early compressive strength (1.22 vs. 1.52 MPa for OPC at 3 d) and slightly higher long-term strength (3.31 vs. 3.18 MPa at 28 d), while reducing carbon emissions by 54.7% compared with OPC when utilized in CPB. The improved performance arises from particle size refinement, increased surface area, and surface chemistry modifications that promote hydration, along with the in situ formation of C–(A)–S–H gels and nano-scale CaCO₃ that provide nucleation sites and refine the microstructure. Overall, this study demonstrates that CAA is a scalable strategy for developing high-performance, low-carbon backfill materials that contribute to net-zero mining.