Expansion Properties of Cemented Foam Backfill Utilizing Coal Gangue and Fly Ash

Research status of comprehensive utilization of coal-based solid waste (CSW) and key technologies of filling mining in China: A review

Coal-based solid waste (CSW) is the solid waste generated in the process of coal mining, washing and pyrolysis, which is an important industrial solid waste. The comprehensive utilization of CSW is a key link in the process of clean and efficient utilization of coal, and the use of CSW for coal mine filling mining is an important means of "harmless, resourceful and large-scale" utilization. In order to study the research status of comprehensive utilization of CSW and key technologies of filling mining in China, this paper combs and analyzes the current situation of comprehensive utilization of CSW from three parts, namely, physical and chemical properties of CSW, Industry-related policies, and ways and means of comprehensive utilization. It is found that coal mine filling mining is a green disposal method with relatively reliable technical means, low supervision cost and large-scale disposal of CSW in the comprehensive utilization of CSW in China. Furthermore, an analysis was conducted on the current research status of key technologies in the CSW filling and mining process, including the integration of "mining, selection and filling", adsorption and complexation passivation of heavy metals in CSW, the preparation of CSW collaborative filling materials, and monitoring and control of the whole filling process, etc. Based on the above analysis and research, it was pointed out that there were some problems, namely: (1) large output of CSW and low level of comprehensive utilization; (2) high investment and high cost of CSW filling and mining; and (3) imperfect CSW waste filling mining theory and technology. In response to these issues, prospects have been made from the aspects of policy incentive mechanisms, collaborative utilization of CSW with multi-industry links, and the theory and technology of CSW filling mining. This study provided reference and inspiration for the comprehensive utilization of CSW in the world, and provides guidance for the large-scale promotion and application of CSW filling mining methods.

Study on the macro-micro evolution of compaction characteristics of coal gangue with different grain sizes under side-limit compression conditions

Currently the main method of mine solid waste disposal and utilization is to apply gangue to underground filling. For the grading characteristics of coal gangue in the hollow zone in underground filling, the state of pressure and the mechanical properties of coal gangue filling materials under different particle sizes. In this paper, through laboratory tests and numerical simulations, the bearing characteristics and deformation damage of gangue are deeply investigated and analyzed from both macroscopic and microscopic perspectives. The results of the study show that when the axial pressure reaches a certain threshold, the strain increases accordingly with the increase in grain size. Under the axial pressure condition of 15MPa, the bearing capacity of gangue with different grain sizes under the lateral pressure of steel cylinder showed obvious positive correlation. In the software PFC3D simulation, as the particle size of gangue particles increases, it has a significant effect on the natural stacking porosity of the specimen, and gangue particles are more prone to force chain instability and failure. Mixed particle size gangue can significantly reduce the natural accumulation porosity of the specimen, thus improving its overall stability. Significant displacement triangles existed in the top and lateral directions of the B1 (0-5 mm), B2 (5-10 mm), and B5 (0-20 mm) specimens under the same circumferential pressure conditions. The results of the study are of great significance for further selection of reasonable gangue gradation and determination of its mechanical properties.

Green Mining Takes Place at the Power Plant

The number of large coal power plants, characterized by pithead plants, is increasing rapidly in major coal mining countries around the world. Overburden movement caused by coal mining and greenhouse gas emissions caused by coal thermal power generation are intertwined, and have become important challenges for mine ecological environment protection at present and in the future. In order to provide more options for green mining in large coal power plants, a large coal power base in northwest China was taken as the researching background in this paper, and a green mining model considering the above two aspects of ecological environment damages was proposed; that is, the carbon dioxide greenhouse gas produced by coal-fired power plants can be geologically trapped in goaf, whose overburden stability is controlled by backfill strips made of solid mine waste. In order to explore the feasibility of this model, the bearing strength of the filled gray brick consisting mainly of aeolian sand and fly ash under different curing methods was firstly studied, and it was discovered that the strength of the gray brick significantly improved after carbonization curing. After that, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to compare the mineral composition and its spatial morphology in gray brick before and after carbonization, and it is believed that the formation of dense acicular calcium carbonate after carbonization curing was the fundamental reason for the improvement of its bearing strength. Finally, a series of stope numerical models were established with UDEC software to analyze the surface settlement, crack propagation height and air tightness of the overlying strata, respectively, when goaf was supported by the backfilling strips with carbonized gray brick. The research results of this paper showed that the stability of overlying strata in goaf can be effectively controlled by adjusting the curing methods, width and spacing of the filled gray brick, so as to facilitate the following geological sequestration of carbon dioxide greenhouse gas in goaf. Consequently, the ecological environment damages caused by coal mining and utilization in a large coal power base can be resolved as a whole, and the purpose of green mining can be achieved as desired.