Research on CO2 sequestration performance of lignin-modified coal-based solid waste cementitious sealing material

A CO 2 uptake of 65.7 mg/g was achieved in the lignin-modified cementitious sealing material under a 30% CO₂ atmosphere. • A competitive microstructural mechanism of C-A-S-H decalcification and carbonate precipitation was proposed. • The carbonated lignin-modified cementitious sealing material retains both low permeability and high compressive strength. To integrate in-situ CO 2 sequestration with coal mine sealing and fire prevention, this study investigated the carbonation behavior and comprehensive sealing performance of a lignin-modified coal-based solid waste cementitious material (LFGS). Synthesized via the alkali activation of fly ash, coal gangue, and ground granulated blast furnace slag, the LFGS specimen was evaluated under varying CO 2 concentrations and carbonation durations, utilizing ordinary Portland cement (P·O 42.5) as a reference. Results indicate that the carbonation depth of the LFGS specimen follows a square-root-of-time relationship indicative of diffusion-controlled kinetics, demonstrating superior long-term CO 2 accessibility compared to P·O 42.5. After 28 days of exposure to 30% CO 2 , the CO 2 uptake of the LFGS specimen reached 65.7 mg/g. Furthermore, quantitative analysis confirmed that the low lignin dosage (0.1 wt%) exerts a negligible effect on the reactive calcium reservoir. Microstructural characterization revealed a competitive mechanism of matrix deconstruction and pore filling during carbonation. While the decalcification of C-A-S-H gel induces degradation and pore coarsening within its network, the concurrent precipitation of calcite and vaterite effectively fills capillary pores and microcracks. Despite this microstructural reorganization, the LFGS specimen retained a compressive strength of 29.8 MPa even after achieving a CO 2 uptake of 65.7 mg/g. This mechanical performance substantially exceeds that of conventional mine sealing materials. Crucially, the carbonated material maintained a low permeability coefficient, ensuring effective gas barrier properties. These findings demonstrate that the LFGS system fulfills the mechanical and permeability requirements for underground sealing operations while acting as a CO 2 sink, providing a viable pathway for the synergistic management of solid waste utilization, mine safety, and greenhouse gas mitigation.