Multiscale investigation of clay mineral effects on coal slime dewatering: From molecular interactions to industrial filtration performance

The efficient dewatering of high-moisture coal slime, a byproduct of coal washing processes, remains a significant technological challenge in resource recovery operations. This investigation systematically examines how clay minerals (particularly montmorillonite and kaolinite) impede dewatering processes through three key mechanisms: surface hydrophilicity modification, filter cake porosity alteration, and bound water retention enhancement. By employing an innovative multiscale approach combining molecular dynamics simulation with laboratory-scale filtration experiments, the fundamental interactions between mineral components and water molecules under pressure filtration conditions were elucidated. Molecular simulation results revealed distinct adsorption energy hierarchies: montmorillonite exhibited the strongest water affinity (−8750 ± 150 kcal/mol), followed by kaolinite (−5500 ± 90 kcal/mol), with quartz showing minimal adsorption (−1400 ± 50 kcal/mol). These molecular-scale findings were corroborated by macroscopic wettability measurements, where contact angles followed the inverse sequence: montmorillonite (34°±2°) < kaolinite (52°±3°) < quartz (65°±2°), confirming the mineral-dependent hydrophilicity gradient. Filtration performance metrics demonstrated clear mineralogical dependence. Quartz-dominated systems achieved peak initial flow rates (2.05 ± 0.04 mL/s) but experienced rapid flux decay (τ = 8.2 min), ultimately yielding the driest filter cakes (28.1 ± 0.3% moisture). In contrast, montmorillonite-rich samples showed severely constrained dewatering, with initial flow rates limited to 0.87 ± 0.02 mL/s and final moisture contents reaching 40.5 ± 0.4%. The dewatering resistance coefficient (DRC) followed the sequence: montmorillonite (DRC = 1.00) > kaolinite (DRC = 0.68) > quartz (DRC = 0.42), exhibiting strong correlation (R2=0.96) with simulated adsorption energies. Industrial validation tests confirmed these laboratory findings, with quartz-bearing coal slimes demonstrating 35∼40% faster dewatering cycles compared to clay-rich counterparts. The mechanistic understanding developed in this study provides a scientific foundation for process optimization through: (1) feedstock mineral composition control, (2) targeted dewatering aid development, and (3) equipment parameter adjustment based on mineralogical characteristics. Future research directions should address the scaling effects in industrial filter presses and the economic feasibility of mineral-based process modifications.