CO2-Modified Bentonite-Based Multifunctional Sealing Material for Carbon-Negative Mine Fire Prevention and Gas Sequestration

The prevention of coal mine fires and the sequestration of CO2 represent two grand challenges that have traditionally been addressed separately. Here we report a CO2-modified bentonite-based sealing material that concurrently achieves fire resistance, gas sealing and mineral-carbonation CO2 uptake through rational materials engineering. In this work, “carbon-negative” is used as a comparative property: the material’s cradle-to-gate embodied emissions combined with its measured 28-day mineral uptake are lower than the cradle-to-gate footprint of a conventional cement-based benchmark under the stated system boundary. High-pressure CO2 intercalation expanded the montmorillonite d-spacing from 12.48 to 14.79 Å and introduced carbonate functional groups (1435 cm−1), as confirmed by FTIR and XRD. Systematic optimization of a bicomponent formulation incorporating municipal solid waste incineration slag and CO2-saturated zeolite yielded a material with 28-day compressive strength of 37.9 MPa, a fire resistance limit of 186 s and O2 reduction from 13.7% to 4.9%. Notably, carbon sequestration reached 24–40 kg CO2 per ton through mineral carbonation, validated by carbonate peaks in FTIR and calcite detection in XRD. Carbon accounting based on a cradle-to-gate inventory (342–408 kg CO2-eq/t) combined with the measured 28-day mineral uptake (24–40 kg CO2/t) yields a comparative net balance of −46 to −188 kg CO2-eq/t relative to a conventional cement-based benchmark under the stated system boundary. The synergistic mechanism involves CO2-modified bentonite-regulating layer spacing, alkali-activated slag releasing Ca2+/Mg2+ for carbonate precipitation, and zeolite providing endogenous carbon slow-release. This work establishes a materials-chemistry paradigm for transforming industrial waste streams into functional carbon sinks while addressing critical mining safety needs.