Mechanisms of Selective Fragmentation and Mineral Liberation During the Grinding of Fine-Grained Coal Gangue

Complex mineral associations in coal gangue inhibit mineral liberation and downstream utilization. This study employed automated mineralogy to measure the mineral composition, particle size distribution, intergrowth, and liberation for four size fractions obtained after a single grinding step (−80 + 150, −150 + 200, −200 + 400, and −400 mesh). Carnauba wax embedding was used to enhance the backscattered electron contrast between carbonaceous matter and the embedding medium. Kaolinite was preferred in the highest fraction, with Al2O3 and ash contents reaching 19.99% and 72.05%, respectively, and carbonaceous matter remaining relatively coarse. Carbonaceous matter exhibited the highest liberation degree (84.91%), followed by kaolinite (69.64%) and quartz (67.08%), and pyrite had a lower liberation degree of 51.40%. Unliberated pyrite consisted of 26.02% carbonaceous matter and 11.72% kaolinite. Fine inclusions and complex mineral intergrowths restricted further liberation by grinding alone. These results reveal mineral-specific size redistribution and liberation behavior, and provide a quantitative basis for size-selective separation and for avoiding unnecessary overgrinding in coal gangue processing.