The influence of food waste compost on the formation of humic substances and microorganisms during soil formation from coal gangue of different particle sizes

This study systematically evaluated the effects of coal gangue with different particle sizes on humic acid formation and microbial community during the composting and soil formation process. Four treatment groups were established: <0.5 mm (M1), 0.5-1 mm (M2), 1-2 mm (M3), and 2-4 mm (M4). The results demonstrated that after 80 days of composting, the M1 treatment group was more prone to forming granular structures, with scanning electron microscopy revealing the highest amount of organic carbon bound to its surface. The M1 group exhibited a 7.28% increase in total organic carbon and a 7.36% increase in humic substances. Fourier transform infrared spectroscopy further indicated that the relative content of aromatic functional groups in humic acid was highest in the M1 group. Microbial community analysis showed that the M1 group had the highest richness and most effective performance of microbial taxa promoting humic acid formation and the soil formation process. These findings confirm that fine-grained coal gangue effectively facilitates organic carbon conversion and humus accumulation, thereby accelerating the composting-mediated soil formation process. This study provides a new technical pathway for the resource utilization of coal gangue and offers theoretical and practical references for the ecological disposal of industrial solid waste and the development of soil amendment materials.