Synergistic valorization of mine drainage, cement kiln flue gas, and low-quality demolition waste: Toward potential contaminant immobilization, carbon sequestration, and carbon-negative construction materials

The large-scale generation of mine drainage, cement kiln flue gas, and low-quality demolition waste poses significant environmental challenges while providing opportunities for resource recovery and carbon utilization. This study proposes a synergistic resource utilization strategy by employing mine drainage and cement kiln flue gas for the carbonation modification of recycled brick aggregate (RBA), aiming to simultaneously enhance aggregate quality, improve recycled brick aggregate concrete (RBC) performance, immobilize contaminants, and achieve carbon sequestration. The physical properties, phase composition, and pore structure of RBA after different treatments were characterized through water absorption and crushing value tests, thermogravimetric analysis, and mercury intrusion porosimetry. The mechanical performance and microstructural evolution of RBC were further evaluated through strength tests, low-field nuclear magnetic resonance, and nanoindentation. The results show that mine-drainage-assisted carbonation exhibits the most pronounced modification effect. Compared with untreated RBA, mine-drainage-assisted carbonation reduces water absorption and crushing value by 16.32% and 27.83%, respectively, while decreasing porosity by 22.73% and refining the dominant pore size from 880 nm to approximately 110 nm. The compressive and splitting tensile strengths of WC–RBC increase by 16.46% and 28.63%, respectively. Microstructural analyses reveal that CaCO₃ precipitation refines the pore structure, improves aggregate micromechanical properties, and densifies the interfacial transition zone. Furthermore, the proposed approach achieves a net carbon reduction of 20.13 kg CO₂/t RBA and exhibits the lowest carbon emission–strength and cost–strength indices. This strategy provides a promising pathway for the simultaneous valorization of construction waste, mine drainage, and cement kiln flue gas toward eco-friendly materials.