CO2 mineralization grouting into fractured gangue voids in post-mining goaf

The treatment of post-mining goafs presents a significant challenge for the coal industry, grappling with environmental safety and carbon neutrality goals. To address issues such as abandoned goafs, high carbon emissions, and conflicts in backfill operations during coal mining, this study proposes a CO 2 mineralization grouting method that targets voids in post-mining goafs. A two-stage mineralization process was designed with a focus on in-situ goaf grouting using open-pore materials. Grouting materials were prepared from carbide slag and fly ash, with cetyltrimethylammonium bromide (CTAB) as a surfactant and oleic acid acts as a foam stabilizer to regulate the pore structure alongside hydrogen peroxide (H 2 O 2 ) used to regulate the pore structure. Scanning electron microscopy, nuclear magnetic resonance, unconfined compressive strength tests, and random forest regression identified the optimal mix: CTAB = 1.2 g, oleic acid = 5.0 g, H 2 O 2 = 1.0 g, water-to-solid ratio = 0.7, Si/Al and Na/Al molar ratios are controlled at 3.0 and 2.7, respectively. Results from custom-built testing devices showed that open-pore materials doubled the mineralization depth compared with closed-pore materials. The method demonstrates technical feasibility and economic viability, while emphasizing the importance of rigorous risk management to ensure environmental and operational sustainability. Compatible with existing green mining systems, it offers economic and environmental benefits, providing a novel approach for low-carbon coal mining.