The coal-fire gases are the main actors in terms of element and heat transfer within burning post-mining waste heaps (BPWHs). Although they mainly comprise CO₂ and water, they can locally be enriched in dimethyl (di)sulfide (as much as 15000 ppm, Bytom site), thiophene, SO₂, H₂S; 1,1- and 1,2-dichloroethane, dichloromethane and other halocarbons; chlorobenzene, ammonia, pyridine, HCN, numerous NO_x, (iso)cyanogen halides, and triazine-based and imine-type compounds, AsH₃, PH₃, SiF₄, and SF₆, to mention some. Metals are most likely transported as neutral hydroxides, and/or carbonyl, nitrosyl, and hydride complexes, while iodine - as I₂, iodosomethane, iodocyanoacetylene, and - alongside with Br and Cl - as halocarbons. Occurrence of exotic gases is possible considering their transient nature. The most recent proposal compounds include HNC, formaldoxime isocyanate, peroxyethyl nitrate; tetrafluoro-p-xylylene, perfluorinated p-benzyne, CHClF, HCFBr, 1,2,4-trixolane, thioacetaldehyde, thiocarbonyl fluoride, bromomethane, dithio-p-benzoquinone, monomethylsilane, and titanacyclopropene (e.g., Kruszewski, 2021). Still, the image of the coal-fire exhalative processes is not full. Here, crystal chemistry of some major minerals deposited within exhalative vents of the Upper Silesian Coal Basin heaps is presented. Chemistry of godovikovite - the major component of the Czerwionka-Leszczyny sulfate crust - is [(NH₄)_0.94K_0.04Ca_0.01Mg_0.01]_Σ1.00(Al_0.90Fe_0.09Ti_0.01)_Σ1.00[(SO₄)_1.99 (n=24); it thus bears 8 mol% sabieite and 3% steklite end-members. The local sabieite's formula is [(NH₄)_0.96K_0.03Mg_0.01]_Σ1.00(Fe_0.58Al_0.40Ti_0.02)_Σ1.00(SO₄)_2.00. Chemistry of millosevichite from sulfate crust of Radlin is expressed as  (Al_1.73Fe_0.19Ca_0.07K_0.02Na_0.01Mg_0.01Ti_0.01)_Σ2.04[(SO₄)_2.97(PO₄)_0.01]_Σ2.98 (n=16), while that for its minor Fe-analogue mikasaite is (Fe_1.38Al_0.51K_0.04Ca_0.03Ti_0.02Na_0.02)_Σ2.00[(SO₄)_2.90(PO₄)_0.02]_Σ2.92 (n=3). The local dolerophanite is likely stabilized by iron: (Cu_1.96Fe_0.03)_Σ1.99O_1.03(SO₄)_0.98 (n=15). Locally, a Fe-rich variety is observed, its chemistry being, possibly, (Cu_1.26Fe_0.65Na_0.04K_0.03Al_0.02)_Σ2.00[(SO₄)_0.95(SiO₄)_0.01]_Σ0.96(O_0.99Cl_0.01)_Σ1.00 (n=5). Dolerophanite is associated with honey-yellow crystals with the (Cu_3.85Fe_0.15)_Σ3.00O_1.33(SeO₃)_0.96(SO₄)_1.93 (n=6) formula, likely representing a new mineral species. So is true for a Cu-I-S species and a iodobismuthate (known both at Radlin and Rydułtowy), the forming abundant inclusions in extremely (Br,I)-enriched salammoniac. The wealth of the heap's exhalative zones is "completed" by (NH₄)₃XCl₅ (X = Zn, Fe, Mg, Mn, Cu), a sodium thiosulfate pentahydrate, a potassium sodium dithionate chloride, an ammonium sulfate nitrate, and a phosphimate (tetra-μ-imidocyclotetraphosphate). Both the above halogen-bearing gaseous species and minerals result from transformation of the pore-contained post-mining brines.

Kruszewski, Ł., 2021. Burning Coal-Mining Heaps as an Organochemical Laboratory: Interesting Trace Compounds and Their Potential Sources.  Chapter 3, in: Organic Compounds, Las Vegas, Nevada, USA, ISBN: 978-93-87500-41-9, 38 pp., openaccessebooks.com/organic-compounds.html

How to cite: Kruszewski, Ł.: Gas-phase element transfer, rare mineral deposition, and other exhalative phenomena associated with coal fires in heaps: the state of art based on the data from the Upper Silesian Coal Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6008, https://doi.org/10.5194/egusphere-egu23-6008, 2023.

Modelling oxygen-limited and self-sustained smoldering propagation is of significance for prevention of underground coal fire hazards. However, coupling oxidative reaction and oxygen transport in multi-scale porous media has been still a challenging issue and the conventional models have been questioned by inadequacy of TG-scale kinetic parameters applied to bed-scale propagation. In this work, an analytic expression of oxidative reaction rates limited by oxygen transport was derived from the conservation equations of oxygen species transport in gas and solid. Along with the Darcy air flow driven by thermal buoyancy, the oxygen-limited and self-sustained smoldering propagation of underground coal fires was modeled in this work. The model was compared with laboratory experiments and the conventional model. Results show that the proposed model well predicts the oxygen-limited and self-sustained smoldering propagations of underground bituminous and anthracite coal fires. The predictability of the proposed model is better than the conventional model in spite of great effort to modify kinetic parameters best fitting with experimental data. It is validated that the proposed model addresses the two puzzled issues in the conventional model with respect to buoyancy-driven, oxygen-limited, and self-sustained smoldering propagation of underground coal fires. This work may help to develop green countermeasures to mitigate underground coal smoldering fires.

How to cite: Song, Z.: Modelling oxygen-limited and self-sustained smoldering propagation of underground coal fires driven by thermal buoyancy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1959, https://doi.org/10.5194/egusphere-egu23-1959, 2023.

Abstract: Atmospheric pressure fluctuation is one of the most important factors affecting the climate environment and gas emission in the fire area. In order to obtain the influence rule of the surface atmospheric pressure change on the gas sampling and abnormal emission in the mine closed goaf, the No. 1 coal mine in Dananhu, Xinjiang was taken as the research object. Using Fourier transform and Fisher harmonic analysis and other methods, the influence of the periodic variation of atmospheric pressure on the gas leakage and outflow in the closed goaf was studied. The results showed that there were three atmospheric pressure periods of 15.2d, 1d and 182.2d, and the probability was greater than 95%. The time period with the highest number of atmospheric pressure peaks was 7:00-8:00, which accounted for 20.2% of total occurrence number in a day. And the time periods with the highest number of atmospheric pressure trough were 2:00, 15:00 and 16:00, accounting for 27.4%. The peak-to-trough transition time was mainly concentrated around 6h, and the diurnal variation curve of atmospheric pressure was mainly bimodal. The atmospheric pressure change rate was mostly concentrated in 10~50 Pa/h. It was determined that the distance that the gas sampling pipe was pre-laid into the inner side of the closed wall should be greater than 44.4m, and the CO concentration and atmospheric pressure in the closed goaf were both periodic and negative with atmospheric pressure. The research results have important guiding significance for the disaster warning and environmental protection of the goaf.

How to cite: Shao, Z. and Tan, B.: Research on the effect of periodic wide atmospheric pressure change on CO emission in closed goaf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4676, https://doi.org/10.5194/egusphere-egu23-4676, 2023.

In the coal fire control project, the multiple water injections used to extinguish coal fires and the coal fires that reignite can cause many forms of ground collapse to occur, threatening project safety. Therefore, studying the thermal damage and capturing disaster signals of sandstone, a main weight bearer in coal measure strata, exposed to heating-cooling, cycles is critical to ensure the engineering safety. In this work, the coal-measure sandstones from Urumqi, Xinjiang and Yulin, Shaanxi, China, were collected. For the sandstones from Urumqi, China (Type A sandstone), the samples were first heated to 800 °C, and cooled using water, heated to a setting temperature (100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C and 800 °C), and cooled using water again. The ultrasonic p-wave velocity, density and water absorption of the sandstones were tested. Uniaxial compression tests and shear tests were conducted on the sandstones. The thermal damage in sandstones were analysed using rock energy theory. For the sandstones from Yulin, China (Type B sandstone), the X-ray diffraction test, scanning electron microscope test and uniaxial compression experiment with AE monitoring were carried out for the raw sandstone and the sandstone exposed to 800 °C and water cooling twice (cooling shock sandstone), respectively. The results show that, for the type A sandstone, compared with the mechanical strength of the sandstone at room temperature, the mechanical strength of the sandstone exposed to 800 °C for the first time is decreased by less than 20%. When the sandstone is exposed to high temperature again, the critical threshold temperature is 400 °C. When the temperature exceeds 400 °C, the thermal damage aggravated again and the mechanical strength rapidly degraded. For the type B sandstone, the results showed that the crack density and volume of cooling shock sandstone increased by 8.79% and 2.69%, respectively, and p-wave velocity decreased by 51.83%, compared with those of the raw sandstone. The mechanical strength of cooling shock sandstone decreased, including a 50.68% reduction in elastic modulus. The AE attenuation coefficient α=(1-E_c/E₀) /k_c, related to the elastic modulus and the crack change rate, was derived, which providing an approach to count the attenuation of AE signal caused by thermal damage for cooling shock sandstone. Increasing the preamplifier amplification factor is feasible to improve the accuracy for monitoring the fracture of cooling shock sandstone in coal-fire control project.

How to cite: Ge, S., Shi, B., Zhang, S., Deng, J., and Wu, C.: Effect of thermal damage on capturing fracture signal of high temperature sandstone subjected to cooling shock from the coal fire control project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3848, https://doi.org/10.5194/egusphere-egu23-3848, 2023.

As a new green chemical inhibitor, ionic liquids can inhibit spontaneous combustion of coal by dissolving and destroying the active structure in coal. In order to investigate the influence of ionic liquids with different concentrations on the molecular structure and the characteristics of low temperature oxidation kinetics of coal at oxygen-poor environment, taking Wucaiwan coal sample in Zhundong mining area as the research object, the molecular structure model of Wucaiwan coal in Zhundong mining area is constructed, and 1-(2-hydroxyethyl)-3-methylimidazole tetrafluoroborate [HOEtMIm] [BF4] ionic liquid is selected. The effect of ionic liquid on coal is investigated from macroscopic and microscopic levels by means of NMR carbon spectroscopy, X-ray photoelectron energy, infrared spectroscopy, thermogravimetry and X-ray diffraction. The results show that different concentrations of [HOEtMIm] [BF4] ionic liquids increase the ignition temperature point and the maximum weight loss rate temperature point of coal samples. The percentage of weight loss in the rapid oxidation stage and the whole combustion process of spontaneous combustion decreases with the increase of ionic liquid concentration. Compared with coal samples treated with other concentrations, the coal samples treated with 15% ionic liquids show good stability, and the fluctuation range of combustion characteristics parameters is small, which shows that high concentration ionic liquids can effectively reduce the influence of temperature on coal samples. Different stages of coal spontaneous combustion oxidation follow different reaction mechanism. The activation energy of the coal samples treated with different concentrations of [HOEtMIm] [BF4] ionic liquids did not change obviously in the evaporation and desorption stages of water, and the flame retardant effect was mainly shown in the oxygen absorption and weight gain stages and thermal decomposition stages. Higher concentration of ionic liquids can make aliphatic, oxygen-containing functional groups and side chains in coal structure fall off , so that the macromolecules of coal are arranged more closely, and the arrangement of organic carbon atoms tends to be oriented and regular gradually. The concentration of ionic liquids changed the polymerization degree of coal macromolecules, and the concentration of ionic liquids was proportional to the polymerization degree of coal macromolecules.

How to cite: Hao, R. and Zeng, Q.: Effect of Ionic Liquids with Different Concentrations on Molecular Structure and Combustion Performance of Coal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10504, https://doi.org/10.5194/egusphere-egu23-10504, 2023.

Underground mining operations, in which large amounts of rock are extracted, can induce seismic events. Furthermore, draining the water to prevent it from flowing into the mining works is necessary for hard coal mines. Once mining stops, the pumping rates of groundwater decrease or is no longer necessary, allowing the water level to return to its state prior to the construction of such mines. During the post-mining phase in hard coal regions, induced micro-seismicity represents a risk for future land use. The EU-PostMinQuake project, funded by the Research Fund for Coal and Steel (RFCS), aims to study the dependency of such events and the rising water table in hard coal basins to detect and manage the risks of post-mining seismicity. This contribution shows the relation between water and seismicity in four former underground hard coal mines located in Czech Republic, France, Germany and Poland.

How to cite: Primo Doncel, P., Rudolph, T., and Möllerherm, S.: PostMinQuake: analysis of post-mining induced micro-seismicity in former European hard coal regions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7247, https://doi.org/10.5194/egusphere-egu23-7247, 2023.

Dust suppressant is an important way to improve the efficiency of wet dust removal，but the dust suppressant currently used in mine is generally chemical dust suppressant，which faces challenging problems of low interfacial activity, high cost， poor degradation，as well as environmental pollution and other issues. To synthesis biological dust suppressant (BDS), a new idea of microbial fermentation technology is proposed. Response surface optimization method was used to explore optimal fermentation conditions. These results show that BDS can be produced to the maximum capacity under the conditions of temperature =37.56℃, pH =7.99, rotating speed =220 r/min, inoculant =2.17%, and liquid loading =59.89 ml.XRD, FTIR and HPLC-MS/MS were adopted to explore the structural features of BDS. Its molecular structure shows a cyclic lipopeptide. The wettability was tested with interface rheometer and we found its good wetting ability under the concentration of 0.06wt‰ compared with chemical dust suppressant. At the same time, dust reduction performance was studied with self-developed test system and BDS showed good performance in dust reduction efficiency. Its application prospects are broad, which may open a new situation for green and efficient control of mine dust.

How to cite: Wang, H. and Zhang, Q.: Basic research on application of green dust suppression materials in mines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10676, https://doi.org/10.5194/egusphere-egu23-10676, 2023.

Grouting treatment in old goafs is an effective method to achieve sustainable development of mining areas after coal seam mining. Due to the concealment of the old goaf and the lack of historical information, it is difficult to directly obtain the distribution of the residual void in the old goaf. In this study, the residual void distribution law of the longwall old goaf area was studied through similar material simulation test, gangue compression test and stress arch theory. The results showed that the collapse zone can be divided into regular collapse zone and irregular collapse zone. Fissure zone and regular collapse zone have few grouting voids due to the closing effect. Due to the different forms of crushing, the irregular collapse zone has large voids and was difficult to completely close with the passage of time, which is the key area of grouting treatment. For the longwall old goaf area that has reached full mining, the stress relief zone was formed at both ends of the open-off cut and the stop-mining line, and the stress recovery zone and the stress stabilization zone were formed in turn close to the middle of the goaf area. The evolution process of stress arch and fracture arch in the stope can be divided into two stages and three periods. The first stage: the development stage of fracture arch and stress arch, that is, the stress relief and stress recovery period of broken gangue in the goaf. The second stage: the fracture arch and stress arch formation stage, that is, the stress stabilization period of broken gangue in the goaf area. On the basis of the above research, the concept of residual void equivalent height was proposed, and its calculation formula was given, and furthermore, the formula for the estimation of grouting volume was given. The height of the irregular collapse zone was 0.915~0.975 times of the coal seam mining thickness, the residual void equivalent height was about 0.3 times the mining thickness (take its upper limit value), and the residual void equivalent height in insufficiently collapsed area was 0.5 times the mining thickness.

How to cite: Guo, Z., Lu, W., Zhou, Y., Zhang, M., Liao, C., and wang, C.: residual space distribution law in long-wall old mining  area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4239, https://doi.org/10.5194/egusphere-egu23-4239, 2023.

Uncontrolled coal fires are a universal coal mining and post-mining concern. Efforts to extinguish these fires are often unsuccessful and these fires can result in major catastrophes such as the abandonment of the town of Centralia Pennsylvania in the U.S. and displacement of many thousands of villagers in India. The physical threat of these fires, often a result of coal mining, is a serious issue that has taken the lives of people in the U.S., Asia, and Africa. However, an equally though more insidious issue is the long-term health impacts of the emissions of these uncontrolled coal fires. Recent studies in the Jharia region of India has shown that villagers living about one mile from active coal fires reported twice as many health concerns as villagers living about five miles away. Yet, there are many villages in this region and elsewhere where people are living in immediate proximity to these fires. Studies of the gases emitted from these fires and condensates formed from the escaping gases document the mobilization of potentially toxic gases such as benzene, xylene, toluene, methane, carbon monoxide and elements such as As, Se, Hg, F, Pb, Sb. An SEM/EDX study of a small (30mm X 20mm) piece of condensate collected from an active underground coal fire just meters from a village revealed several generations of deposition with at least 30 phases containing ammonia, B, F, Al, Si, S, Cl, Fe, Cu, Zn, As, Se, Br, Mo, Cd, I, Ba, Pb, and Bi. Clearly, more attention should be paid to this post mining catastrophe to minimize the health problems and deaths resulting from these uncontrolled coal fires.

How to cite: Finkelman, R. and Dodds, H.: Underground coal fires – A global post-mining catastrophe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1643, https://doi.org/10.5194/egusphere-egu23-1643, 2023.