An Experimental Study of Coal Gangue Pulverization for Slurry Making and a Field Test on Hulusu Coal Mine Overburden Grouting  
[PERSON]  
1 School of Mines, China University of Mining and Technology, Xuzhou 221116, China;  
1 [EMAIL_ADDRESS] (J.L. ); [EMAIL_ADDRESS] (J.X. )[EMAIL_ADDRESS] (J.X)[EMAIL_ADDRESS] (J.X)[EMAIL_ADDRESS] (J.X)15162183569@  
grow annually [5]. When exposed to rainfall or light, exposed piles of coal gangue can generate a substantial quantity of toxic and harmful substances, thereby polluting groundwater and the surrounding environment [6; 7]. This issue is particularly pronounced in the western mega-mines, where coal gangue output often exceeds a million tons. However, the market for resource utilization pathways, such as gangue power generation, cement and building material preparation, and chemical product extraction, is relatively limited [8; 9; 10; 11], making coal gangue disposal extremely challenging. Coal mining generates a significant number of fractures [12; 13; 14; 15], which are ideal for storing coal gangue. However, despite these unique conditions, current utilization remains inadequate. One effective method to mitigate the emission of coal gangue is through filling [16; 17]. Depending on the ratio of the filling volume to mining volume, the filling method can be categorized into full and partial filling. The full-filling method involves filling a hollow area, while partial filling can be applied to the hollow area, collapse zone, or mining-induced overburden fractures [18; 19]. A typical full-filling method involves filling the mining hollow area with coal gangue, which prevents the formation and upward propagation of mining fractures, thereby maintaining the stability of the overlying rock layers [20; 21; 22]. While this method has certain advantages in terms of coal gangue consumption, changes in coal mining equipment and technology have led to the mutual interference between mining and filling. Consequently, this method has not been widely adopted in coal mines at present. Overburden isolated grout filling technology does not need to change the arrangement of the mining face, and mining and filling have little mutual interference. The technical principle is to find the key strata to control the surface subsidence [23], construct several sets of surface boreholes above the longwall face to the bottom of the key strata, and implement high-pressure grouting and the filling of the fracture under the key strata through the boreholes before key strata breaks, compacting the fracture and bulking rock masses [24], and replacing the space for the future rock layers' subsidence with the filling body in advance, so as to maintain the stability of the key strata and control surface subsidence. This method has been successfully applied in more than ten pairs of coal mines under the damage reduction mining practice in China, and has shown remarkable results in terms of the filling volume and surface subsidence reduction rate. Therefore, how to utilize this technology to greatly dissipate coal gangue is a brand-new problem faced at present. The main zone of overburden isolated grout filling is mining-induced overburden fractures. It is required to match the grain size gradation of slurry with the opening degree of the fracture [25]. In the past, an overburden isolated grout filling project used in the filling zone included fly ash dry material generated by a coal-fired power plant. The fineness of this material is typically at the micrometer level, while raw gangue is significantly larger. This substantial difference in the fineness of the coal gangue and the fly ash renders them unsuitable for direct use in grout filling. Furthermore, overburden isolated grout filling involves grouting through surface boreholes, which imposes stringent requirements on the solid-material particle size.