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

The mining industry encounters substantial environmental challenges associated with cement consumption in cemented paste backfill (CPB) operations. Although the incorporation of supplemen-tary cementitious materials can mitigate carbon emissions, their application frequently results in com-promised mechanical strength of CPB. To overcome this limitation, the present study introduces a nov-el CO2-assisted activation (CAA) process technique that integrates mechanical activation with in situ carbonation to improve the performance of a ternary binder system composed of ordinary Portland ce-ment (OPC), blast furnace slag (BFS), and carbide slag (CS), herein referred to as OBC, for sustaina-ble CPB applications. Experimental investigations reveal that the OBC system achieved comparable early compressive strength (1.22 MPa vs. 1.52 MPa for OPC at 3 days) and superior long-term per-formance (3.31 MPa vs. 3.18 MPa at 28 days), while reducing the carbon footprint by 54.7% relative to conventional OPC-based systems, thereby confirming its potential as a high-performance, low-carbon alternative for mining operations. The observed enhancement in performance is attributed to synergistic physicochemical transformations induced by CAA. This process promoted particle size reduction, resulting in increased specific surface area and accelerated reaction kinetics, while concur-rently modifying the surface properties of BFS to favor the formation of key hydration products. Addi-tionally, the in situ generation of C-(A)-S-H gels and nano-scale calcium carbonate during CAA pro-vides supplementary nucleation sites, thereby enhancing binder hydration and refining the microstruc-ture. The findings position CAA as a transformative strategy for engineering sustainable backfill mate-rials that simultaneously achieve mechanical robustness and environmental sustainability.