Optimization of preparation conditions for phosphorus-modified gangue-based biochar and characterization of its adsorption properties

The high-value utilization of bulk coal gangue solid waste generated from coal mining is an important approach for the disposal and resource utilization of bulk solid waste in mining areas. Microbial agents are widely used for soil improvement in mining areas, and efficient microbial agent loading technology can significantly enhance their improvement effects. To develop coal gangue-based materials for microbial agent loading, this study prepared gangue-based biochar using microwave-activated decarbonization and phosphorus-modified pyrolysis. The preparation conditions were optimized by characterization methods including carbon fixation rate, BET specific surface area, XPS, and Zeta potential, and the adsorption performance of the gangue-based biochar was evaluated based on the microbial agent loading capacity. The results showed that at a pyrolysis temperature of 500 ℃ and a pyrolysis time of 4 h, the biochar achieved the maximum specific surface area and total pore volume, as well as the minimum average pore diameter, indicating optimal performance. Adding zeolite reduced the carbon loss rate of straw in the gangue-based biochar by 15.40%, and modification with Ca(H₂PO₄)₂ also significantly decreased the carbon loss rate. The gangue-based biochar prepared under the optimal pyrolysis conditions exhibited a macroscopic adsorption rate of 78.74% for microorganisms and a PLFA biomarker content of 388.622 nmol/g. Therefore, the gangue-based biochar prepared by the microwave-activated decarbonization and phosphorus-modified pyrolysis method possesses good adsorption performance and holds relatively great application potential in the development of microbial loading materials and soil remediation in mining areas.