Mechanistic Study on the Filtration Behavior Simulation of Suspended Solids in Mine Water by Coal Mine Goaf

Abstract Coal and water resources are inversely distributed in western China, and the resource utilization of mine water is recognized as one of the key pathways for the green development of coal. In underground coal mine reservoirs, gangue from mined-out areas is utilized as the core purification medium; however, the removal characteristics and synergistic mechanisms for suspended solids are not yet fully clarified.Gangue and suspended solids from the Daliuta mining area are selected as research subjects. Dynamic circulation simulation tests, XRD, SEM, and laser particle size analysis are employed to systematically investigate the purification effects of gangue on suspended solids in mine water under varying concentrations, settling times, settling heights, and settling distances, and the underlying mechanisms are elucidated.The turbidity of mine water is reduced from 77.43 NTU to 11.41 NTU by gangue, with a total removal rate of 85.26%, which is nearly 20 percentage points higher than that of natural sedimentation. A higher initial concentration of suspended solids results in a faster initial removal rate, and 750 mg/L is identified as the optimal purification concentration. The main removal process is completed within 15 minutes, and an increase in settling height significantly enhances the purification effect. Suspended solids are removed through the synergistic actions of physical interception, gravitational sedimentation, and surface adsorption by gangue. Coarse particles of 150–180 µm are effectively intercepted, while most residual particles are smaller than 60 µm.The regulatory patterns of gangue particle size gradation, hydraulic retention time, and settling conditions on suspended solids sedimentation efficiency are clarified. A theoretical basis and technical support are thereby provided for the structural optimization of mined-out areas in underground coal mine reservoirs and the in-situ, low-cost purification of mine water.