Performance study of modified magnesium-coal based solid waste negative carbon backfill material: Strength characteristics and carbon fixation efficiency

To address the challenges of large-scale solid waste treatment and achieve the "dual carbon" goal, mixing modified magnesium-coal based solid waste with industrial CO2 is an effective carbon-reduction technique. In this study, a novel modified magnesium-coal based solid waste CO2 backfill material (CO2-MCSB) was produced. The mechanical characteristics, microstructure, and carbon sequestration impact of CO2-MCSB after CO2 absorption were studied using uniaxial compressive strength, acoustic emission, X-ray diffraction, thermogravimetry, Scanning electron microscopy, and other tests. CO2-MCSB's mechanical properties improve greatly after absorbing CO2, with a 28-day strength increase of 0.514-3.103 MPa. Additionally, it has a high carbon sequestration effect (5.6-6.8 %). Under uniaxial compression, CO2-MCSB mainly exhibits tensile failure, and exhibits different acoustic emission characteristics under different stirring rates, ventilation rates, and stirring times, corresponding to the evolution process of its microstructure. The carbonation reaction of CO2-MCSB boosted its hydration reaction process, according to a thorough investigation of X-ray diffraction, thermogravimetry, scanning electron microscopy, and other techniques. Following aeration, the hydration of CO2-MCSB produced a significant number of needle-like AFt and C -S -H gel, as well as a large number of microscopic calcium carbonate crystals created following carbonization filled the pores, which was the main reason for the improvement of the strength of the backfill body. CO2-MCSB, a novel type of carbon sequestration backfill material, has huge applications in mining backfill.