Influence of Mechanical Properties on the Crushing and Liberation Behaviors of Middling Coking Coal: Insights from Experiments and Molecular Simulations.

To delve into the intrinsic mechanism of mineral liberation during the grinding process, this study systematically analyzed the coal petrographic composition and mineral occurrence forms in coking middling coal using electron probe microanalysis (EPMA) and X-ray diffraction (XRD) techniques. Results showed that quartz occurred primarily as coarse granules embedded in organic matter, kaolinite was mostly lumpy and disseminated, and calcite mainly filled fractures. The mechanical properties of minerals can significantly influence the grinding efficiency. The elastic constants of major minerals such as quartz, kaolinite, and calcite were calculated through density functional theory (DFT) and molecular dynamics (MD) simulations. On the basis of these calculations, their mechanical properties were deduced, and a connection was established between the mechanical properties of minerals and their liberation during the grinding process. Quartz exhibited remarkable resistance to compressive deformation and shear fracture owing to its ultrahigh stiffness (C11 = C22 = 245.47 and C33 = 221.66 GPa) and macroscopic moduli (K = 166.24, G = 69.61, and E = 183.25 GPa). Kaolinite exhibited high stiffness within its layers but weak interlayer shear properties (C11 = 161.38 and C44 = 23.14 GPa), which made it prone to interlayer dissociation. Calcite, due to its significant stiffness anisotropy (with C11 = C22 = 196.9 and C33 = 79.79 GPa), demonstrated strong anisotropy and cleavage-dominated fragmentation behavior during the process. Coal, characterized by weak bedding stiffness and extremely low moduli, is susceptible to brittle fracture. Broken resistance decreased in the order of quartz > kaolinite > calcite > coal. Excellent agreement existed between the elastic constant calculations and the mineral size distributions after grinding. This study innovatively correlates the mechanical properties of minerals with liberation behaviors during macroscopic grinding processes, providing significant insights into the selective liberation mechanisms of minerals in middling coking coal.