Study on the fluidity and mechanical properties of multi-source coal-based solid waste (MCSW) filling material

Abstract

The backfilling mining technology for multi-source coal-based solid waste (MCSW) aligns with the key challenges and emerging paradigms in the coal industry, aiming at intelligent and cleaner coal mining, high efficiency, and low carbon utilization. This research area has gained considerable attention and significance for promoting high-quality coal mining, low environmental impact, and sustainable development. In this study, a response surface experiment was designed with desulfurization gypsum (DG), gasification slag (GS), and furnace bottom slag (FBS) as factors to analyze the performance of backfill materials with varying compositions. Parameters such as bleeding rate, compactness, viscosity, setting time, and age strength were tested. An optimal composition of backfill materials was obtained, with a MCSW content exceeding 90 %, 28-day strength exceeding 2 MPa, initial setting time between 240 and 480 min, and final setting time ranging from 300 to 600 min. The investigation of the optimal materials involved characterizing the pore structure, microstructure, composition, and silica gel structure through techniques such as X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Additionally, the study explored micro-interface structures and enhancement mechanisms. After 28 days of curing, the backfill with a composition of DG 0.3, FBS 0.2, GS 0.1 exhibited a compressive strength of 5.18 MPa, with an initial setting time as short as 140 min. This can be attributed to the precipitation of silica gel on the grain surface, which mitigated the segregation effect. The silica gel promoted inter-particle bonding and rapid viscosity, preventing particle settling. This method not only ensures the safe disposal of coal-based solid waste but also contributes to the coordinated development of coal resource exploitation, environmental protection, and reduced carbon footprint.