Mining Science and Technology (China)最新文献

A fully mechanized coal mining with backfilling (FMCMB) provides advantages of safety and efficiency for coal mining under buildings, railways, and water bodies. According to the field geological conditions, we analyzed the controlling effect of strata movement by the waste and fly ash backfilling in FMCMB face. Based on the key strata theory, we established the equivalent mining thickness model, and analyzed the action of the bulk factor of backfilling body to the equivalent mining thickness. In addition, we numerically simulated the controlling function of the strata movement by backfilling bodies with different strength. And the numerical simulation result show that the deformation of stratum and the subsidence of surface can be controlled by FMCMB. The result provides references to the effective execution of fully mechanized coal mining with solid waste backfilling in goaf.

Chemical analysis, methane isothermal adsorption studies, and mercury porosimetry were performed on ten samples taken from the magma intrusion boundary in the Wolonghu coalfield. The physico-chemical properties of coals from the magma intrusion region are compared to those from the normal regions. The results show that the volatile content (V_ad), the limiting adsorption constant (a), and the initial methane diffusion rate of samples from the magma intrusion region are generally smaller than those values from samples from the normal region. The number three coal sample from the magma intrusion region has a large vitrinite reflectance, well developed macropores, a small surface area, and weak methane adsorption capacity. The number ten coal sample from the normal region has a small vitrinite reflectance, well developed micropores, a large surface area, and a strong methane adsorption capacity. The maceral of the coal samples from the magma intrusion region and the normal region are similar. The coal in the area near the magma intrusion boundary is rich in methane and is an area where coal and gas outbursts often occur.

High temperature affects rocks in a way that changes the physical and mechanical properties of them. The temperature field in rock overlying a high temperature zone has been estimated using experimental research on thermal conductivity of the overlying strata. Numerical analysis software was used to estimate rock thermal conductivity at different temperatures. These estimates were then used with COMSOL Multiphysics to perform a numerical analysis with the heat conduction model. The results show that rock thermal conductivity decreases as the temperature increases and that various lithologies show similar behavior. The thermal conductivity of each rock type differs from the others at a given temperature. Exact values for the temperature distribution in the overlying strata during the process of underground coal gasification are obtained from the numerical simulation. The temperature in the rock changes with the height and direction from the gasifier. Temperature gradients vary for different types of rock. This result provides an important reference for further study of the strength of overlying strata subject to the process of underground coal gasification.

Ground stress is the fundamental cause of deformation and failure during underground structural engineering. Field stress measurements in the main coal bed in the Lüliang mining area were made by the bore hole, stress relief method. From these data the ground stress distribution of the mining area was obtained. The relationship between the horizontal principal stress and the deformation and failure of a roadway is discussed with an engineering example. The results indicate that horizontal stress dominates in the shallow crust in the Lüliang mining area. Roadways at different angles to the maximum principal stress have different levels of stress concentration. This leads to a significant difference in stability of the corresponding roadways. These research results provide an important criterion for determining roadway position and direction, stope layout, and roadway support design.

Pilot scale column flotation studies were conducted on a low grade siliceous limestone ore. Silica content was reduced to less than 1% in the concentrate so that it became satisfactory for use in the paper or rubber industries. The limestone sample was crystalline and constituted primarily of calcite that contained quartz, feldspar, pyroxene, and biotite as gangue minerals. Quartz is the major silicate gangue whereas feldspar, pyroxene, and biotite exist in minor to trace quantities. Traces of pyrite were also observed within the sample. A reverse flotation process was adopted where the silicate gangue minerals were floated using two different commercial cationic collectors: Chem-750 F or Floatamine-D. The studies clearly suggest it is possible to produce a limestone concentrate assaying around 96–97% CaCO₃ containing less than 1% SiO₂. The effect of feed flow rate, percent solids, froth depth, and wash water on the grade and recovery of the CaCO₃ concentrate is discussed.