Search Results (12)

The co-firing of coal and refuse-derived fuel (RDF) from municipal solid waste recycling is gaining support in countries in which energy production is based on solid fuels. It is the result of the rising priority given to renewable energy sources, the circular economy, and effective waste management through sorting, recycling, and thermal conversion. Despite the increasing efficiency of recycling and the ever-lower quantities of waste delivered to waste dumps, the problem of the residual fraction remains unsolved. The portion of mixed municipal waste that cannot be recycled exhibits a high energy value. For this reason, it should be neither stored nor burnt in household boiler rooms, as doing so would constitute an environmental hazard. However, the waste can be used as an additive to fine coal in power boilers, provided that they are equipped with flue gas monitoring and purification systems. Tests involving proportionally prepared compositions of fine coal and refuse-derived fuel burnt in a laboratory boiler revealed a major variability in the flue gas parameters (physicochemical), depending on the applied proportions of the individual components. For instance, when burning a composition of 50% fine coal and 50% refuse-derived fuel, a reduction in CO₂ emissions by about 12% was noted compared with that when burning fine coal exclusively. Furthermore, when burning refuse-derived fuel, an addition of 20% fine coal is enough to produce a 2.8% reduction in CO emission. Meanwhile, a composition of 80% fine coal and 20% refuse-derived fuel would reduce the emissions by 393 ppm. During the measurements, it was also noted that most of the measured parameters indicated a decrease in individual gas contents relative to the emissions obtained when burning fine coal or refuse-derived fuel exclusively. These relationships can be applied to prepare fuel compositions based on refuse-derived fuel and fine coal, depending on the power and flue gas purification capabilities of individual cogeneration systems. Full article

The crystal structure, thermal behavior, and vibrational spectra of the anthropogenic analogue of boussingaultite, (NH₄)₂Mg(SO₄)₂·6H₂O, and its dehydrated counterpart efremovite, (NH₄)₂Mg₂(SO₄)₃, were studied in detail. The sample from the Chelyabinsk burning coal dumps has the composition of (NH₄)_1.92(Mg_1.02Mn_0.01Fe_0.01)_∑1.04(SO₄)₂·6H₂O and crystallizes in the space group P2₁/a, with a = 9.3183(4), b = 12.6070(4), c = 6.2054(3) Å, β = 107.115(5)°, V = 696.70(5) ų (at 20 °C), Z = 2. The thermal evolution steps are as follows: boussingaultite (NH₄)₂Mg(SO₄)₂·6H₂O (25–90 °C) → X-ray amorphous phase (100–150 °C) → efremovite (NH₄)₂Mg₂(SO₄)₃ (160–340 °C) → MgSO₄ Cmcm + Pbnm (340–580 °C) → MgSO₄ Pbnm (580–700 °C). Thermal expansion is anisotropic, with the coefficients (×10⁶ °C⁻¹) α₁₁ = 52(2), α₂₂ = 68(2), α₃₃ = –89(3), and α_v = 31(3) at T = –123 °C; and α₁₁ = 53(2), α₂₂ = 67(2), α₃₃ = 15(1), and α_v = 136(3) at T = 60 °C. The maximal thermal expansion is along the b-axis and is due to straightening of corrugated pseudolayers (within the ab plane) of Mg(H₂O)₆ octahedra and SO₄ tetrahedra with NH₄ groups in the interlayer space. Vibrational spectroscopy outlines the general trend of dehydration and deammonization as the difference in the temperature intervals of these transformation steps allows separation of O–H and N–H vibrations in the process of dehydration by infrared and Raman spectroscopy. The intermediate partially dehydrated modification of boussingaultite was detected by in situ Raman spectroscopy at 110 °C that may correspond to ammonium leonite. Full article

Overburden rock massifs resulting from open-pit coal mining are very common objects in the world’s mining regions. These locations pose a significant challenge as the global mining industry expands. These dumps are capable of self-burning for quite a long time. The displacement and sliding of these massifs can cause catastrophic consequences. In addition, these objects emit a significant amount of greenhouse gases into the atmosphere. Therefore, it is necessary to manage such objects and implement appropriate measures to limit their impact on the environment. In this work, we studied soil radon volume activity (VAR) and radon flux density (RFD) on the surface of the overburden rock massif of coal-bearing mining rocks and also made visual fixation of disturbances in the body of the massif, which appeared in the process of its movement. We found anomalies of VAR and RFD on the surface of the overburden extending from north to south. These anomalies were extended along the strike of the faults found in the body of the massif. Additionally, the radon anomalies coincided with the anomalies of methane gas emission previously measured for this object. Thus, we determined that the exit of gases from the body of the massif is carried out through fault (weakened) zones in the body of the massif. According to the results of the study, we propose to carry out radon monitoring in order to detect the spontaneous ignition process of the massif or the increase of its mobility. This will also allow us to take appropriate measures to stabilize the massif or to extinguish the dump before or simultaneously with the biological stage of reclamation. Full article

The mineral-like anthropogenic phase Zn(NH₃)₂Cl₂, with ammine (NH₃⁰) complexes from the burned dumps of the Chelyabinsk coal basin (South Urals, Russia), has been investigated using single-crystal and high-temperature powder X-ray diffraction, and Raman and infrared (IR) spectroscopy. The anthropogenic Zn(NH₃)₂Cl₂ is orthorhombic, Imma, a = 7.7399(6), b = 8.0551(5), c = 8.4767(8) Å, V = 528.49(7) ų, R₁ = 0.0388 at −73 °C. Its crystal structure is based upon isolated ZnN₂Cl₂ tetrahedra connected by hydrogen bonds (between NH₃ groups and Cl atoms) into a three-dimensional network. Upon heating, the Zn(NH₃)₂Cl₂ phase is stable up to about 150 °C, which is in good agreement with the data on the temperature of its formation. The crystal structure of Zn(NH₃)Cl₂ expands anisotropically with the strongest thermal expansion observed along the a axis. The thermal expansion of the structure is controlled by the changes in the hydrogen bonding system. The Raman and IR spectroscopic characteristics of this phase are close to those of the mineral ammineite, CuCl₂(NH₃)₂. The studied anthropogenic phase, formed in the unique conditions of burned coal dumps, is identical to the synthetic Zn(NH₃)₂Cl₂. Full article

The new mineral radvaniceite, GeS₂, was found on the burning coal mine dump of the abandoned Kateřina coal mine at Radvanice, near Trutnov, northern Bohemia, Czech Republic. It occurs as aggregates resembling cotton tufts up to 5 mm in size; they are composed of acicular crystals up to fibres about 1–5 μm thick and up to 3 mm in length. Individual fibres are distorted and partly resemble bent wires nucleated on rock fragments or on black, crumbly ash, in association with minerals of solid solutions of Bi-Sb and stangersite, herzenbergite, and greenockite. Radvaniceite was also observed as irregular grains in a range of 10–50 μm in size, forming part of earlier multicomponent aggregates upon which the above-described crystals grow. These aggregates are formed, in addition to radvaniceite, by minerals of Bi-Sb, Bi₂S₃-Sb₂S₃ and Bi₂S₃-Bi₂Se₃ solid solutions, Bi₃S₂, Bi-sulpho/seleno/tellurides, tellurium, unnamed PbGeS₃, Cd₄GeS₆, GeAsS, Sn₅Sb₃S₇, stangersite, greenockite, cadmoindite, herzenbergite, teallite, and Sn- and/or Se-bearing galena. Radvaniceite is formed under reducing conditions by direct crystallization from hot gasses (250–350 °C) containing Cl and F at a depth of 30–60 cm under the surface of a burning coal mine dump; the mine dump fire started spontaneously, and no anthropogenic material was deposited there. Acicular crystals up to fibres of radvaniceite are elastic to flexible; are white to yellowish grey in colour, with white streaks; are translucent in transmitted light; and have vitreous to adamantine lustre. Cleavage and fracture were not observed. The calculated density is 3.05 and 2.99 g·cm⁻³ for the empirical and ideal formulae, respectively. Radvaniceite is transparent under the microscope, with a very weak pleochroism (from colourless to pale greenish yellow), and has a refraction index > 1.8. Under reflected light, radvaniceite is light grey; bireflectance and pleochroism were not observed due to abundant, white to grey, internal reflections. Anisotropy in crossed polars is distinct with grey rotation tints. Reflectance values of radvaniceite in air (R_min–R_max, %) are: 15.4–18.8 at 470 nm, 16.1–20.4 at 546 nm, 16.4–20.8 at 589 nm, and 16.9–20.9 at 650 nm. The empirical formula, based on electron-microprobe analyses, is (Ge_0.99Bi_0.01)_Σ1.00(S_1.97Se_0.03)_Σ2.00. The ideal formula is GeS₂, which requires Ge 53.10, S 46.90, total 100 wt. %. Radvaniceite is monoclinic, Pc, a = 6.8831(12), b = 22.501(3), c = 6.8081(11) Å, β = 120.365(9)°, with V = 909.8(4) ų and Z = 12. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I) (hkl)] are: 5.7395 (100) (11-1, 110), 5.2067 (16) (021), 3.3650 (33) (111, 11-2), 2.8417 (33) (022), 2.8236 (16) (170, 17-1), 2.8134 (20) (080) and 2.6257 (19) (240, 24-2). According to X-ray powder diffraction data and Raman spectroscopy, radvaniceite is a natural analogue of synthetic monoclinic low-temperature β-GeS₂ with distorted GeS₄ tetrahedra forming four corner-sharing tetrahedral chains, which are connected by corner-sharing tetrahedra in a three-dimensional structure. We named the mineral after its type locality, Radvanice, one of the past centres of coal mining in the Czech limb of the Intra-Sudetic Basin. This mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (number 2021-052). Full article

The subject of this work is the assemblage of anhydrous sulfate minerals formed on burning coal-heaps. Three burning heaps located in the Upper Silesian coal basin in Czerwionka-Leszczyny, Radlin and Rydułtowy near Rybnik were selected for the research. The occurrence of godovikovite, millosevichite, steklite and an unnamed MgSO₄, sometimes accompanied by subordinate admixtures of mikasaite, sabieite, efremovite, langbeinite and aphthitalite has been recorded from these locations. Occasionally they form monomineral aggregates, but usually occur as mixtures practically impossible to separate. The minerals form microcrystalline masses with a characteristic vesicular structure resembling a solidified foam or pumice. The sulfates crystallize from hot fire gases, similar to high temperature volcanic exhalations. The gases transport volatile components from the center of the fire but their chemical compositions are not yet known. Their cooling in the near-surface part of the heap results in condensation from the vapors as viscous liquid mass, from which the investigated minerals then crystallize. Their crystallization temperatures can be estimated from direct measurements of the temperatures of sulfate accumulation in the burning dumps and studies of their thermal decomposition. Millosevichite and steklite crystallize in the temperature range of 510–650 °C, MgSO₄ forms at 510–600 °C and godovikovite in the slightly lower range of 280–450 (546) °C. These values are higher than those previously reported. Full article

Coal-waste dumps are an integral part of the environment and shape the landscape of coal basins. This study aimed to present an analysis of environmental changes in terms of land use and changes in vegetation on self-heating coal-waste dumps of different ages. Spatial and temporal analyses of land relief and land cover in the area of the investigated coal-waste dumps were performed. The investigated areas differed in size, shape, management, and land cover. Thermally active zones were identified. The results showed that the species composition of the flora is diverse, but representatives of the Asteraceae family dominate on both dumps. The diversity of flora in the investigated dumps depends on the presence of mosaic- and microhabitats (often of an extreme nature) and the nature of the vegetation in the surroundings, which is manifested by the participation of socioecological groups of flora. The pace and dynamics of succession on burning coal-waste dumps depends on the stage of the fire, the topography, and the nature of the substrate. The investigated changes in the elements of the environment are important from the point of view of application research and monitoring of postindustrial areas, which may allow for the optimal management of postmining dumps. Full article

Orange greenockite (CdS) aggregates were found in a small fumarole at a burned coal dump near Bytom, Upper Silesia, Poland and were studied using a variety of techniques in order to determine their chemistry, morphology, and most importantly, the mechanism of crystal growth. Greenockite rods, wires, and whiskers with bismuth drops on crystal tops are predominant in these aggregates. Greenockite rods oriented sub-perpendicular to the substrate surface. The rod thickness reaches 5–6 μm and about 10 μm in length. The catalyst bismuth drop has a diameter comparable to the rod thickness. Fiber forms (wires and whiskers) are sub-parallel to the substrate surface. The thickness of these forms is usually less than 2 μm, and the length can be close to 1 mm. The bismuth drop diameter can show a large excess over the fiber thickness. Catalyst drops on the tops of whiskers began to change their form dynamically and exploded, spraying bismuth under the electron beam effect. Rods grow along the [01–10] direction, and whiskers and wires (axial forms) along the [0001] direction. Greenockite rod crystals, carrying on top a relatively homogenous bismuth catalyst drop, were formed on the heated substrate according to the VLS (vapor–liquid–solid) mechanism at temperatures not lower than 270 °C. Greenockite whiskers and wires grew just above of the substrate surface according to the VQS (vapor–quasiliquid–solid) mechanism at temperatures lower than 200 °C. These mechanisms of growth have very rarely been recorded to occur in nature and even less so in burning coal dumps. The cooperative growth effects of the fiber greenockite crystals were also described. Full article

In the Czech part of the Upper Silesian Coal Basin (Moravian-Silesian region, Czech Republic), there are many deposits of endogenous combustion (e.g., localized burning soil bodies, landfills containing industrial waste, or slag rocks caused by mining processes). The Hedwig mining dump represents such an example of these sites where, besides the temperature and the concentrations of toxic gases, electric and non-electric quantities are also monitored within the frame of experimentally proposed and patented technology for heat collection (the so-called “Pershing” system). Based on these quantities, this paper deals with the determination and evaluation of negative heat sources and the optimization of the positive heat source dependent on measured temperatures within evaluation points or on a thermal profile. The optimization problem is defined based on a balance of the heat sources in the steady state while searching for a local minimum of the objective function for the heat source. From an implementation point of view, it is the interconnection of the numerical model of the heat collector in COMSOL with a user optimization algorithm in MATLAB using the LiveLink for MATLAB. The results are elaborated in five case studies based on the susceptibility testing of the numerical model by input data from the evaluation points. The tests were focused on the model behavior in terms of preprocessing for measurement data from each chamber of the heat collector and for the estimated value of temperature differences at 90% and 110% of the nominal value. It turned out that the numerical model is more sensitive to the estimates in comparison with the measured data of the chambers, and this finding does not depend on the type optimization algorithm. The validation of the model by the use of the mean-square error led to the finding of optimal value, also valid with respect to the other evaluation. Full article

The crystal structure of dmisteinbergite has been determined using crystals from the type locality in Kopeisk city, Chelyabinsk area, Southern Urals, Russia. The mineral is trigonal, with the following structure: P312, a = 5.1123(2), c = 14.7420(7) Å, V = 333.67(3) ų, R₁ = 0.045, for 762 unique observed reflections. The most intense bands of the Raman spectra at 327s, 439s, 892s, and 912s cm ⁻¹ correspond to different types of tetrahedral stretching vibrations: Si–O, Al–O, O–Si–O, and O–Al–O. The weak bands at 487w, 503w, and 801w cm⁻¹ can be attributed to the valence and deformation modes of Si–O and Al–O bond vibrations in tetrahedra. The weak bands in the range of 70–200 cm⁻¹ can be attributed to Ca–O bond vibrations or lattice modes. The crystal structure of dmisteinbergite is based upon double layers of six-membered rings of corner-sharing AlO₄ and SiO₄ tetrahedra. The obtained model shows an ordering of Al and Si over four distinct crystallographic sites with tetrahedral coordination, which is evident from the average <T–O> bond lengths (T = Al, Si), equal to 1.666, 1.713, 1.611, and 1.748 Å for T1, T2, T3, and T4, respectively. One of the oxygen sites (O4) is split, suggesting the existence of two possible conformations of the [Al₂Si₂O₈]²⁻ layers, with different systems of ditrigonal distortions in the adjacent single layers. The observed disorder has a direct influence upon the geometry of the interlayer space and the coordination of the Ca2 site. Whereas the coordination of the Ca1 site is not influenced by the disorder and is trigonal antiprismatic (distorted octahedral), the coordination environment of the Ca2 site includes disordered O atoms and is either trigonal prismatic or trigonal antiprismatic. The observed structural features suggest the possible existence of different varieties of dmisteinbergite that may differ in: (i) degree of disorder of the Al/Si tetrahedral sites, with completely disordered structure having the P6₃/mcm symmetry; (ii) degree of disorder of the O sites, which may have a direct influence on the coordination features of the Ca²⁺ cations; (iii) polytypic variations (different stacking sequences and layer shifts). The formation of dmisteinbergite is usually associated with metastable crystallization in both natural and synthetic systems, indicating the kinetic nature of this phase. Information-based complexity calculations indicate that the crystal structures of metastable CaAl₂Si₂O₈ polymorphs dmisteinbergite and svyatoslavite are structurally and topologically simpler than that of their stable counterpart, anorthite, which is in good agreement with Goldsmith’s simplexity principle and similar previous observations. Full article

The technogenic mineral phases NH₄MgCl₃·6H₂O and (NH₄)₂Fe³⁺Cl₅·H₂O from the burned dumps of the Chelyabinsk coal basin have been investigated by single-crystal X-ray diffraction, scanning electron microscopy and high-temperature powder X-ray diffraction. The NH₄MgCl₃·6H₂O phase is monoclinic, space group C2/c, unit cell parameters a = 9.3091(9), b = 9.5353(7), c = 13.2941(12) Å, β = 90.089(8)° and V = 1180.05(18) ų. The crystal structure of NH₄MgCl₃·6H₂O was refined to R₁ = 0.078 (wR₂ = 0.185) on the basis of 1678 unique reflections. The (NH₄)₂Fe³⁺Cl₅·H₂O phase is orthorhombic, space group Pnma, unit cell parameters a = 13.725(2), b = 9.9365(16), c = 7.0370(11) Å and V = 959.7(3) ų. The crystal structure of (NH₄)₂Fe³⁺Cl₅·H₂O was refined to R₁ = 0.023 (wR₂ = 0.066) on the basis of 2256 unique reflections. NH₄MgCl₃·6H₂O is stable up to 90 °C and then transforms to the less hydrated phase isotypic to β-Rb(MnCl₃)(H₂O)₂ (i.e., NH₄MgCl₃·2H₂O), the latter phase being stable up to 150 °C. (NH₄)₂Fe³⁺Cl₅·H₂O is stable up to 120 °C and then transforms to an X-ray amorphous phase. Hydrogen bonds provide an important linkage between the main structural units and play the key role in determining structural stability and physical properties of the studied phases. The mineral phases NH₄MgCl₃·6H₂O and (NH₄)₂Fe³⁺Cl₅·H₂O are isostructural with natural minerals novograblenovite and kremersite, respectively. Full article

Long-term deposition of coal spoil piles may lead to serious pollution of soil and water resources in the dumping sites and surrounding areas. Karst aquifers are highly sensitive to environmental pollution. In this study, the occurrence and release/mobilization of polycyclic aromatic hydrocarbons (PAHs) in coal waste and coal spoils fire gas mineral (CSFGM) were evaluated by field and indoor investigations at Yangquan city, one of the major coal mining districts in the karst areas of northern China. Field investigations showed that dumping of coal waste over decades has resulted in soil and water pollution via spontaneous combustion and leaching of coal spoil piles. Indoor analysis revealed that the 2-ring and 3-ring PAHs contribute to 65–80% of the total PAHs in coal spoils, with naphthalene (Nap), Chrysene (Chr), and Phenanthrene (Phe) as the dominant compounds. Based on a heating/burning simulation experiment, the production of PAHs is temperature-dependent and mainly consists of low-ring PAHs: 2-ring, 3-ring, and part of the 4-ring PAHs. The PAHs in the leachate are light-PAHs (Nap, 20.06 ng/L; Phe, 4.76 ng/L) with few heavy-PAHs. The distribution modes of PAHs in two soil profiles suggest that the precipitation caused downward movement of PAHs and higher mobility of light-PAHs. Full article