Research on long-term migration behaviors of heavy metals after close-distance coal seam backfill mining.

The backfill mining of coal-based solid waste in goaf poses a potential risk of heavy metal pollution to the groundwater environment, and the migration behavior of heavy metals differs significantly under the disturbance of backfill mining in close-distance multi-layer coal seams and single-layer coal seams. In this study, a migration model of heavy metals after solid backfilling in the goaf of shallow-buried close-distance thick coal seams was established, and the impact of the overburden damage and the layered distribution of the filling body on the long-term migration behavior of heavy metals were analyzed. The results show that the migration of heavy metals after close-distance coal seam backfill mining exhibits a higher risk of heavy metal pollution. The peak permeability of overburden after close-distance coal seam backfill mining is about 600 × 10-19 m2 higher than that after single-layer coal seam backfill mining. The migration distance of heavy metals in the floor after backfill mining of close-distance coal seams is 7.41 m farther than that of single-layer coal seam backfill mining, and its migration time of heavy metals to the surface is 27 a earlier than that of single-layer coal seam. This research provides theoretical and empirical support for the ecological risk assessment and heavy metal pollution control in close-distance coal seam backfill mining. ENVIRONMENTAL IMPLICATION: The main filling material of close-distance coal seams backfill mining is coal gangue. Heavy metal elements such as Mn and Cr will be released in the underground environment for a long time, and the migration behavior of heavy metal elements will have an impact on the groundwater environment for more than 1000 years. This research provides theoretical and empirical support for the ecological risk assessment of close-distance coal seam backfill mining and the mitigation of heavy metal pollution.

Research on coal mine safety management based on digital twin.

Coal mine safety management is the foundation and decisive factor of coal mining. The manual detection model is the main way for traditional coal mine safety management, which has problems such as inefficient identification of safety risks in coal mines, poor control accuracy and slow response measures and so on. Therefore, to make up for the shortcomings in the traditional coal mine safety management model, this paper introduces digital twin technology into coal mine safety management to achieve intelligent and efficient management of coal mine safety accidents. Firstly, we introduce the digital twin technology, select the five-dimensional model as the modeling basis, based on the existing twin model architecture, analyze the types of coal mine accidents and disasters, select the most destructive gas accidents as the research object, construct a twin safety management model for coal mine gas accidents using the digital twin five-dimensional model. Secondly, analyses of the actual operation mechanism of the digital twin model, and the advantages of the twin model in achieving prior prevention, rapid response and accurate control of gas incidents are pointed out. Finally, the house of quality of the gas accident digital twin model is established through the quality functional deployment tool, and key technical requirements for the construction of the twin model are given to accelerate the application of the gas accident twin model in the field. This study innovatively introduces digital twin technology into the field of coal mine safety management, proposes the application scenarios of emerging technologies such as digital twins in the coal mine field, and provides the possibility of multi-scene application of smart mine construction and technologies such as digital twins.

Study on the distribution characteristics and ecological risk of heavy metal elements in coal gangue taken from 25 mining areas of China.

The long-term, high-yield production of coal has resulted in the large-scale accumulation of coal gangue on the ground surface, which causes serious environmental problems. Therefore, clean and environmental treatment of coal gangue is urgently needed. In this study, the inductively coupled plasma mass spectrometer and atomic fluorescence spectrometer were used to test the background values of ten heavy metals in coal gangue taken from 25 coal mines across China; the average content, distribution characteristics, and genesis of heavy metals in these coal gangue were investigated, and the ecological risk of heavy metals in coal gangue in different regions and different geological ages was analyzed and tested. The results show that the average contents of Hg, Pb, Cd, Cr, As, Cu, Zn, Mn, Se, and Be in the coal gangue are 0.081, 17.444, 0.234, 63.329, 2.658, 43.697, 59.290, 427.460, 1.205, and 1.819 mg/kg, respectively; the enrichment sequence of heavy metal elements of coal gangue in geographical areas and geological ages are ordered as follows: South China region > North China region > Northeast China region > Northwest China region, P2 > C2-P1 > K1 > J1-2 > E-N. The results also show that Hg has a strong pollution risk, Cd has a moderate pollution risk, and the remaining eight heavy metals have minor pollution risks, and the overall ecological risk indices (RI) of heavy metals in different geographical areas are ordered as [Formula: see text] (South China) > [Formula: see text] (North China) > [Formula: see text] (Northeast China) > [Formula: see text] (Northwest China). Moreover, the hydrothermal process occurring in unique sedimentary environments during the formation period is a key factor for the regional heavy metal enrichment in coal gangue.

Explanation of heavy metal pollution in coal mines of china from the perspective of coal gangue geochemical characteristics.

In the process of coal gangue surface accumulation and underground filling disposal, the heavy metals contained in coal gangue will inevitably precipitate out and migrate, which will cause serious environmental pollution. Seventy-five gangue samples of different geological ages are obtained from 25 coal mines in China. The contents of Hg, Pb, Cd, Cr, As, Cu, Zn, Mn, Se, and Be in gangue samples are determined. The enrichment coefficients of heavy metal elements in coal gangue are analyzed. The formation of heavy metal elements in gangue is studied by cluster analysis and principal component analysis. The results showed that the contents of Pb, Se, and As in gangue samples formed in Late Carboniferous and Early Permian are highest; the contents of Cr, Cd, Be, Cu, and Zn in gangue samples formed in Late Permian are highest. The later the formation age of coal gangue, the lower the overall enrichment of heavy metal elements. The contents of Cu, Be, Cd, Zn, and Cr in coal gangue are mainly controlled by sedimentation. The contents of Pb and Se are mainly affected by the affinity between heavy metal elements in coal gangue. The affinity between Mn and other heavy metal elements is weak, and sulfur had a certain influence on the content of Mn.

Triaxial compression behaviour of gangue solid wastes under effects of particle size and confining pressure.

Underground coal mining leads to environmental problems such as gangue pollution, surface subsidence and soil erosion, etc. Solid backfilling coal mining (SBCM) can control the strata movement, reducing gangue discharge and environmental pollution in mining areas. Gangue solid wastes (GSW) are backfilled into the goaf space as the supports for the overburden strata in solid backfilling coal mining. In this case, GSW are under triaxial compression. The deformation characteristics of the GSW under this loading condition are the key factors determining the control efficiency of strata movement and surface subsidence. The influence of the particle size grade and the confining pressure condition on the deformation and breakage characteristics of the GSW is studied based on large-scale triaxial compression tests in this paper. Also, the effect of particle breakage on the deformation of the GSW is revealed. The results indicate that in the triaxial compression process, the GSW exhibits strain hardening characteristics and volume decrease under compressive loading. The maximum load-bearing stress is more sensitive to the confining pressure condition but less sensitive to the particle size grade. The maximum load-bearing stress increases linearly with the confining pressure. Particle breakage of the GSW is notably influenced by the particle size grade but almost independent of the confining pressure condition. The S1 specimen with a reasonable proportion has the minimum relative breakage index, while the S3 specimen that mainly contains large particles has the maximum relative breakage index. The research outcomes are significant to the understanding of the mechanical characteristics of GSW, the selection and preparation of the backfilling materials in the field practices and the ensurence of the backfilling efficiency.