CO2 Mineralized Full Solid Waste Cementitious Material for Coal Mine Goaf Filling and Carbon Sequestration Potential Assessment

Coal is an essential component of global energy; however, the processes of coal mining and utilization produce significant amounts of coal mine goafs, accompanied by coal-based solid wastes and emitted CO₂, resulting in severe ecological and environmental challenges. In response to this issue, this study proposes a novel approach for filling coal mine goafs using cementitious materials prepared by coal-based solid wastes mineralized with CO₂ (15% in concentration). The CO₂ sequestration capacities of individual solid wastes are ranked as follows: carbide slag (CS) > red mud (RM) > fly ash (FA). The performance of filling material prepared from composite solid waste (FA–CS–RM) mineralized with CO₂ meets the filling requirements of goaf. The filling material (F60C20R20) obtained by CO₂ mineralization was 14.9 MPa in maximum compressive strength, increasing by 32.2% compared to the non-mineralized material. The prepared filling material exhibits excellent CO₂ sequestration capacity (i.e., 14.4 kg·t⁻¹ in maximum amount of CO₂ sequestration). According to the analysis of carbon sequestration potential, in China, the annual production of FA, CS, and RM is approximately 899, 30, and 107 Mt, respectively in the year of 2023. The utilization of FA, CS, and RM individually can achieve carbon emission reductions of 3.42, 10.78, and 0.61 Mt, respectively. The composite solid waste (FA–CS–RM) mineralized with CO₂ can achieve 1.23 Mt in carbon emissions reduction. Additionally, taking Yellow River Basin of China as a case study, the total volume of underground space in coal mine goafs from 2016 to 2030 is estimated at 8.16 Gm³, indicating that this technology can sequester 0.18 Gt of CO₂. This approach offers a promising solution for large-scale flue gas CO₂ sequestration, recycling coal-based solid wastes, and remediating coal mine goafs, contributing to green utilization of coal and the emission reduction of carbon.