Effects of temperature on the modification and carbon sequestration of lignite via synergistic supercritical CO2 and microbial treatment

• Optimal temperature for synergistic modification was identified as 40 °C. The synergistic treatment was most effective at 40 °C, optimally developing the lignite's pore structure and increasing oxygen-containing functional groups. • Synergistic treatment effectively disrupted the coal's macromolecular structure. This process disrupted the coal's macromolecular structure, reducing the order of aromatic crystallites and enhancing surface polarity to create more active sites for CO 2 . • Microbial activity and CO 2 conversion were most efficient at 40 °C. Microbial activity peaked at 40 °C, efficiently neutralizing acidity and converting dissolved CO 2 into bicarbonate and carbonate ions to facilitate mineralization. Against the backdrop of global climate change, coal seam CO 2 geological sequestration technology has garnered extensive attention due to its significant potential. To enhance the CO 2 adsorption capacity of coal, the synergistic modification of lignite using supercritical CO 2 (ScCO 2 ) and microorganisms has emerged as a promising technical approach, in which temperature regulation plays a pivotal role. Through experimental studies conducted under different temperature conditions, the evolution of coal structure and variations in the liquid-phase environment were systematically analyzed. The experimental results indicate that 40 °C is the optimal temperature for the synergistic effects, at which the pore structure of coal is most notably developed, with the specific surface area and total pore volume increasing to 11.253 m 2 /g and 0.14589 cm 3 /g, respectively. Concurrently, the oxygen-containing functional groups on the coal surface increased notably, the degree of ordering of the microcrystalline structure was reduced, and the reactivity of the coal matrix was enhanced. Under this temperature condition, microbial metabolism was most active, which efficaciously neutralized the system’s acidity and promoted the formation of HCO 3 – and CO 3 2– , thereby creating favorable conditions for the conversion of CO 2 into stable carbonate minerals. In contrast, when the temperature was raised to 45 °C, microbial activity was inhibited, leading to a significant reduction in the modification effect. These findings confirm that temperature is a key parameter controlling the efficiency of synergistic carbon sequestration. Future research should further explore the coupling effects of temperature and pressure, as well as microbial metabolic mechanisms, to facilitate the practical application of this technology.