Advances in research on technologies for large-scale coal gangue utilization for green mine construction

BackgroundThe coal gangue, a solid waste, features high production and a continuous increase in the amount piled in China. The long-term piling up of coal gangue will cause the waste of land resources and environmental pollution in mining areas. Various methods for utilizing coal gangue, such as preparing high-value-added chemical products and extracting useful elements, suffer a limited consumption capacity, failing to meet the requirements of large-scale disposal and utilization of solid wastes and green mine construction. AdvancesThe comprehensive utilization of coal gangue for mining area reclamation and underground backfilling represents a critical direction for its large-scale disposal and utilization. This study systematically summarizes the physicochemical properties and resource attributes of coal gangue and analyzes the impacts of its long-term piling up on the atmosphere, soils, and water in mining areas. From the perspective of green mine construction, this study highlights the principles, advances, and application effects of technologies for large-scale disposal and utilization of coal gangue. These technologies include the utilization of coal gangue as materials for the reclamation of collapse areas, geopolymer grouting materials, solid filling materials, paste filling materials, and paste-like filling materials. The results reveal that when used as materials for reclamation, coal gangue can improve soil properties and promote plant growth, yet it poses challenges of short-term heavy metal migration and environmental contamination. When used as geopolymer grouting materials, coal gangue can effectively immobilize heavy metals within it, suppressing their release and reducing their damage to the environment. The solid backfilling technology tailored to coal gangue enjoys advantages including simple coal gangue processing technique and minimal consumption of auxiliary materials. However, this technology faces challenges like uneven filling and groundwater contamination. Furthermore, this study summarizes the composition and flowability advantages of coal gangue when used as paste and paste-like filling materials and analyzes its microscopic hydration mechanisms and flow properties, providing key technical support for backfill mining of mines. Finally, this study points out some issues concerning the utilization of coal gangue, including challenges in the full stimulation and utilization of the activity of coal gangue, the absence of classification and pretreatment in the early stage, high cost of utilization as underground backfilling and grouting materials, and a lack of incentive policies for large-scale utilization. ProspectsTo promote the large-scale utilization of coal gangue in mining areas in a safe, efficient, and risk-controllable manner, future research will focus on the cost-effective composite activation methods, environmental friendliness assessment of utilization processes, CO2 mineralization and sequestration, and carbon-negative utilization of coal gangue. These efforts will provide insights for the comprehensive utilization of coal gangue following the "green-efficient-high value" roadmap, expand the large-scale utilization of coal gangue, and enhance the risk prevention abilities in this regard, thus promoting the synergetic development of solid waste utilization and green mine construction.