Study on the performance of coal gangue and biomass ash cemented backfill under microbial induced calcium carbonate deposition

In this study, Microbially Induced Carbonate Precipitation (MICP) technology was applied to effectively consolidate closely spaced coal seams. The slurry and the entrained solid waste particles were stably cemented underground, thereby reducing pollutant migration and diffusion and preventing slurry inrush in the stope. A microbially cemented coal gangue filling material was developed. The mechanical properties and microstructural characteristics of microbially cemented coal gangue filling material with different biomass ash contents were investigated, and the effects of MICP modification on the mechanical properties of the materials were revealed. The results showed that MICP modification significantly improved the compressive strength and tensile strength of microbial-cemented coal gangue filling materials. The compressive strength and tensile strength of the coal gangue + 20% biomass ash + 10% cement + microorganism specimen reached 0.698 MPa and 0.0489 MPa respectively, which were 29.26% and 28.68% higher than those before microbial modification. The combined effects of MICP modification and the hydration reactions of cement and biomass ash generated substances containing flocculent structures, particle aggregation structures, and a small number of strip-like structures, which contributed to improving the pore structure of the specimens, enhancing interparticle cementation, increasing specimen compactness, and further improving the mechanical properties. The research results provide a new technical approach for grouting filling and coal gangue disposal in closely spaced coal seams and provide valuable insights for promoting green and efficient mining practices.