1 20 the fermentation time and improve the fermentation effect, reduce the cost of preparing organic microbial fertilizer, and is essential for accelerating the disposal of mining waste. Microbial decomposition and humification are inherently slow processes. Therefore, continuous screening and optimization of microbial strains are required to ensure their effective integration, survival, and reproduction within the two types of solid waste. The objective is to convert the mineral elements in waste from a solid state into a free state absorbable by plants and enable the effective release of such beneficial trace elements, thereby realizing thorough activation and rapid decomposition of beneficial mineral elements in mining waste, while passivating heavy metals and balancing pH levels. Wang Hanxia[6] found in her research that mixed microbial strains exhibited superior decomposition performance compared to single-strain systems. Liu Ziwei[7] compared the effects of single-, dual-, and triple-microbial inoculants on the improvement of coal gangue-based substrates, and concluded that dual-microbial inoculants yielded better results for mining area soil than a single-microbial inoculant. Traditional aerobic fermentation takes 7-15 days. In the study, phosphate-solubilizing bacteria, thermophilic bacteria, and nitrogen-fixing bacteria suitable for decomposing coal gangue and capable of proliferating vigorously in forestry and agricultural residues were selected to form a composite microbial inoculant, and efficient microbial strains were cultivated and screened through optimal selection and cultivation. Pruned tree branches from the site of CCTEG Tangshan Research Institute, used as experimental materials, were crushed using specialized equipment and fermented efficiently into microbial fertilizer in the fermentation equipment. By measuring changes in nutrient elements and organic matter in the microbial fertilizer, the optimal inoculant amount ratio, optimal fermentation temperature, and optimal fermentation time were determined for complete fermentation of the microbial inoculant. The experimental results indicate that the complete fermentation of forestry, agricultural, and livestock residues is achieved within 24 hours at a composite inoculant amount ratio of 1:10 and a fermentation temperature of 60 °C-80 °C, and all indicators of the produced organic microbial fertilizer meet the national standards for organic fertilizers in China. The product is rich in organic microbial content and exhibits high activity. When subsequently co-processed with coal gangue, it enables the rapid activation and release of nutrient elements from the coal gangue. 2. COAL GANGUE GRADATION AND RAW MATERIAL BLENDING The coal gangue and tailing coal slime used in the experiment were sourced from Tangshan Mine of Kailuan Group. Through testing, the heavy metal content is below the screening limit for soil contamination risk specified by the Soil Environmental Quality – Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). There are significant differences in the physicochemical properties of coal gangue with different particle sizes. Previous studies[8-9] have shown that an appropriate gradation of coal gangue can improve the substrate's bulk density and porosity, thereby ensuring aeration and promoting crop growth. This study has shown that coal gangue with different particle sizes plays distinct roles in soil utilization. Tailing coal slime (-0.5 mm) has a large specific surface area and
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