Potential Liberation Behavior and Mechanism of Mica in High-Mica Quartzite: Insights from MLA and DFT Calculations

To elucidate the liberation behavior and microscopic mechanism of mica during the comminution of high-mica quartzite, mineral liberation analysis (MLA) combined with density functional theory (DFT) calculations was employed to investigate the occurrence characteristics, liberation state, and fracture-energy characteristics of biotite. The results showed that the high-mica quartzite was mainly composed of quartz, biotite, and albite, with quartz and biotite contents of approximately 45.45% and 28.56%, respectively. Biotite was mainly distributed along quartz grain boundaries, intergranular contact zones, and microfractures, exhibiting complex intergrowth relationships. MLA results showed that only 17.62% of biotite was completely liberated in the manufactured sand, whereas the proportions of binary and ternary intergrowths between biotite and quartz reached 14.68% and 28.13%, respectively. DFT calculations revealed that the cleavage energies of quartz (101) and biotite (001) were 3.79 and 0.89 J·m−2, respectively, while the interfacial cleavage energy of the quartz (101)–biotite (001) heterointerface was 2.34 J·m−2. The relatively low interlayer cleavage energy of biotite promotes preferential crack propagation along the (001) plane and subsequent platy fragmentation, rather than complete separation along the quartz–biotite interface, thereby giving rise to the formation of numerous biotite-enriched intergrowth particles.