Multi-scale synergistic modification of CO2 carbonation coal-based solid waste backfill utilizing high-salinity mine water: Balancing carbon sequestration and engineering performance

Addressing the dual challenges of solid and liquid waste management and carbon emissions in the coal industry, this study developed a novel CO ₂ -carbonated backfill material (CCB) by synergistically utilizing high salinity mine water (HSW), coal-based solid wastes, and a multi-scale modifier system. The modifiers-rick husk biochar (RHB), natural clinoptilolite (NCP), sepiolite (SEP), and γ-nano Al ₂ O ₃ (NA)-were incorporated to enhance CO ₂ sequestration and engineering performance. Results demonstrate that the composite modifiers significantly improved the carbonation efficiency, achieving a CO ₂ uptake of 9.33 mg-CO ₂ /g-CCB in the optimal group (CCB-RNn), representing a 25.9% increase over the control. Rheological analysis confirmed the modified slurry retained suitable shear-thinning behavior for transport, while mechanical strength reached 7.48 MPa due to synergistic pore-filling and fiber-reinforcement effects. Microstructural characterization revealed that the modifiers promoted the formation of dense gel networks and finely dispersed carbonate crystals (calcite/magnesite), with NA effectively densifying the matrix and serving as nucleation sites. This work provides a feasible strategy for integrated management of mine water streams and carbon emission, contributing to the development of high-performance, carbon negative backfill technology.