348 mineralization reaction (Han et al., 2022). Microbial carbon-negative cemented backfill materials can be prepared using MICP, the principle is illustrated in Fig. 8. Figure 17 - Technical principle of microbial carbon-negative backfill material preparation The mechanical and carbonation properties of microbial carbon-negative cemented backfill materials are significantly influenced by particle size distribution. As the particle size increases, the strength of the specimens tends to decrease, while the carbonation rate increases. The uniaxial compressive strength (UCS) of these microbial backfill materials can reach up to 3.28 MPa, with a carbonation rate of 2.45%. Analysis of the consolidation mechanism reveals that the CA bacteria convert environmental CO2 into HCO- 3 via the carbonic anhydrase enzyme. In an alkaline environment, HCO- 3 is converted to CO2- 3 , which then reacts with Ca2+ to form calcite-type CaCO3 crystals. One portion of these CaCO3 precipitates agglomerates to cement the gangue particles, providing overall structural strength. Another portion fills the interstices between the gangue particles, enhancing the specimen's density. These processes work together to provide the structural foundation for both effective carbonation and high mechanical performance (Hefni et al., 2020). However, existing research on microbial carbon-negative cemented backfill materials is still limited by unclear mechanisms regarding the synergy between carbon sequestration and mechanical properties. Furthermore, the specific influence of carbonation products on mechanical evolution remains poorly understood. In particular, more rigorous studies are required to elucidate the carbonation mechanisms specifically mediated by CA bacteria in backfill materials. 5. CONCLUSIONS A three-tier pathway for decarbonation of cemented backfill mining in coal mines is proposed, including carbon-reduced tier, low-carbon tier, and carbon-negative tier. Anhydrase CO2 Enzymatic CO2 ionization Gas phase Liquid phase CO3 2Ca2+ Polysaccharide Deposition Precipitated polymer CO2 HCO3⁻ OH⁻ CO3 2CaCO3 Ca2+ CA bacteria Legend High-strength consolidation CA bacteria Cemented backfill 0-1.2 0-2 0-5 0 1 2 3 4 5 UCS/MPa Particle size /mm Average UCS Measured UCS 0~1.2 0~2 0~5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Carbonation rate /% Particle size/mm Average carbonation rate Measured carbonation rate Carbonation Performance CA bacteria
RkJQdWJsaXNoZXIy MTM0Mzk2