A recent study published in Engineering presents a novel method for addressing the environmental challenges posed by coal mining, specifically focusing on the treatment of coal mine goafs, utilization of coal-based solid waste, and the sequestration of CO₂ through mineralization. The research, conducted by a team from Shanxi University in China and The University of Western Australia, offers a comprehensive solution that integrates these aspects into a single, sustainable process.

Coal mining, while a significant contributor to global energy supplies, generates substantial amounts of coal mine goafs—voids left by the extraction of coal. These goafs, along with the accompanying solid wastes such as fly ash (FA), carbide slag (CS), and red mud (RM), pose serious ecological and environmental challenges. The study proposes a method to utilize these solid wastes to create cementitious materials for filling coal mine goafs, while simultaneously sequestering CO₂ through a mineralization process.

The research investigates the feasibility of mineralizing low-concentration CO₂ (15% volume) using single coal-based solid wastes. The carbon sequestration capacities of FA, CS, and RM were found to be 3.8, 359.3, and 5.7 kg/t, respectively. The study then explores the creation of filling materials from a composite of these solid wastes, which not only meets the mechanical requirements for goaf filling but also significantly enhances CO₂ sequestration.

The mechanical properties of the filling material, particularly its compressive strength, were significantly improved through CO₂ mineralization. The maximum compressive strength of the mineralized filling material (F60C20R20) reached 14.9 MPa, a 32.2% increase compared to the non-mineralized material. Additionally, the material exhibited enhanced fluidity, with a 10.8% increase compared to the non-mineralized filling material. The CO₂-mineralized material also demonstrated a more uniform internal structure, with a reduction in the number of large pores, as evidenced by ultrasonic detection and CT scanning.

The study further evaluates the carbon sequestration potential of this technology on a larger scale. In China, the annual production of FA, CS, and RM is approximately 899, 30, and 107 Mt, respectively. Utilizing these wastes to create composite solid waste (FA–CS–RM) mineralized with CO₂ could reduce carbon emissions by 1.23 Mt. Moreover, considering the historical stockpiles of these solid wastes, the potential carbon emission reduction could reach 16.46 Mt. The Yellow River Basin in China, a major coal-producing region, was used as a case study. The total underground space volume of coal mine goafs from 2016 to 2030 in this region is estimated at 8.16 Gm³, which could sequester 0.18 Gt of CO₂.

This technology not only provides an effective solution for the remediation of coal mine goafs and the utilization of coal-based solid waste but also contributes to the reduction of CO₂ emissions. The findings of this study highlight the potential for integrating waste management and carbon sequestration in the coal industry, offering a sustainable approach towards achieving carbon neutrality goals.

The paper “CO₂ Mineralized Full Solid Waste Cementitious Material for Coal Mine Goaf Filling and Carbon Sequestration Potential Assessment,” is authored by Bo Wang, Huaigang Cheng, Xiong Liu, Zichen Di, Huiping Song, Dongke Zhang, Fangqin Cheng. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.02.017. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.