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Kefa Cen - One of the best experts on this subject based on the ideXlab platform.
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characteristics of alkali species release from a Burning Coal biomass blend
2018Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Kaidi Wan, Ronald Whiddon, Kefa CenAbstract:Abstract Solvent fractionation, Laser induced breakdown spectroscopy (LIBS), X-ray Diffraction (XRD) and chemical analysis were applied to binary fuel mixtures of Zhundong Coal and cornstalk agricultural class to investigate the release characteristics of alkali species during co-firing of Coal and biomass. As the biomass proportion increases, the water-soluble, NH4Ac-soluble and HCl-soluble alkali species interconvert; the extent of the conversion depends on the composition of the blend. From LIBS measurements, it was found that adding the biomass accelerates combustion and outgassing processes. The higher the proportion of the biomass in the blend, the earlier the peak concentrations of alkali appear, and the magnitude of peak concentrations of sodium and potassium decrease and increase, respectively. Furthermore, the interaction between Coal and biomass can generate crystals causing the eutectic melting phenomenon (similar to feldspar in XRD results), which results in a sharp decline of the ash fusion temperatures (AFTs). The results not only provide the information of fundamental transformation but also guide industrial co-firing applications of lignite and agricultural class biomass to reduce the risk of ash deposition.
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3d imaging of individual Burning char and volatile plume in a pulverized Coal flame with digital inline holography
2017Co-Authors: Longchao Yao, Jia Chen, Gerard Grehan, Kefa CenAbstract:Abstract The Burning behaviors of an individual Coal particle in the combustion of a cloud of Coal particles is of great importance because it represents the realistic situation of pulverized Coal particle utilization. Digital inline holography is proposed as a tool for 3D quantitative imaging of the Burning Coal particle and its associated volatile flame, and demonstrated by its application to a laboratory scale pulverized Coal flame. The holographic fringes of Burning Coal particles with volatile plumes are characterized by concentric rings as well as parallel lines. Besides the conventional 3D positions and morphologies of irregular Coal particles, the volatile flames are clearly reconstructed. The instantaneous behaviors of the early stage combustion of individual Coal particle in a pulverized Coal flame have been observed. Typical modes of the volatile flame with respect to the Coal particle, including envelope volatile flame, attached wake flame, detached wake flame, side volatile flame, are observed in the experiments. The Burning behaviors of one Coal particle influenced by another particle in the combustion of a cloud of particles has also been evidenced. This work demonstrates that digital inline holography has the powerful capacity of simultaneously measuring reacting multiphase objects in hostile environments.
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simultaneous particle size and 3d position measurements of pulverized Coal flame with digital inline holography
2017Co-Authors: Longchao Yao, Zhiliang Xue, Hao Zhou, Kefa CenAbstract:Abstract 3D measurements of Burning Coal particles in the flame are challenging and of great interest. Digital inline holography is applied to perform 3D measurement of Coal particle size and 3D position in a laboratory-scale pulverized Coal flame. Pulsed laser beam illumination is used to record the Coal particle hologram with clear holographic fringes in the presence of high refractive index gradient and strong turbulence. Over 30,000 Coal particles have been reconstructed and analyzed. Results show that the particle size, 3D positions and particle number density distribution can be determined simultaneously. Digital inline holography presents to be a powerful tool in the 3D measurement of Burning particles in a turbulent and reacting medium.
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in situ measurement of sodium and potassium release during oxy fuel combustion of lignite using laser induced breakdown spectroscopy effects of o 2 and co2 concentration
2013Co-Authors: Jiajian Zhu, Marcus Alden, Zhihua Wang, Kefa CenAbstract:Laser-induced breakdown spectroscopy (LIBS) was used in this study to measure quantitatively the sodium (Na) and potassium (K) release from Burning Coal particles under oxy-fuel combustion environments. A specially designed laminar premixed burner was employed to provide a postflame environment with different O-2 and CO2 concentrations, in which the effects of O-2 and CO2 on the release of Na and K during Coal oxy-fuel combustion were studied systematically. For the devolatilization stage, neither O-2 nor CO2 had significant influence on the Na and K release. The release of Na and K during the char stage, however, changed significantly at different O-2 and CO2 concentrations. Under these experimental conditions, when the O-2 concentration increased from 3.9% to 10.6%, the peak concentration of Na at the char stage increased from 15.2 mg/m(3) to 33.7 mg/m(3), and the maximum concentration of K increased from 6.2 mg/m(3) to 11.7 mg/m(3). When the CO2 concentration increased from 35.8% to 69.4%, the release of Na and K was inhibited during the char stage, with the peak concentration decreasing from 8.9 mg/m(3) to 6.9 mg/m(3) for Na and from 3.7 mg/m(3) to 2.4 mg/m(3) for K. During the ash stage, the release of Na and K decreased with the O-2 concentration, whereas it increased with the CO2 concentration. (Less)
Joana Ribeiro - One of the best experts on this subject based on the ideXlab platform.
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distributed temperature measurement in a self Burning Coal waste pile through a gis open source desktop application
2017Co-Authors: Lia Duarte, Joana Ribeiro, Deolinda Flores, Ana Claudia Teodoro, J A Goncalves, Alexia Lopezgil, Alejandro Dominguezlopez, Xabier Angulovinuesa, Sonia Martinlopez, Miguel GonzalezherraezAbstract:Geographical Information Systems (GIS) are often used to assess and monitor the environmental impacts caused by mining activities. The aim of this work was to develop a new application to produce dynamic maps for monitoring the temperature variations in a self-Burning Coal waste pile, under a GIS open source environment—GIS-ECoal (freely available). The performance of the application was evaluated with distributed temperature measurements gathered in the S. Pedro da Cova (Portugal) Coal waste pile. In order to obtain the temperature data, an optical fiber cable was disposed over the affected area of the pile, with 42 location stakes acting as precisely-located control points for the temperature measurement. A monthly data set from July (15 min of interval) was fed into the application and a video composed by several layouts with temperature measurements was created allowing for recognizing two main areas with higher temperatures. The field observations also allow the identification of these zones; however, the identification of an area with higher temperatures in the top of the studied area was only possible through the visualization of the images created by this application. The generated videos make possible the dynamic and continuous visualization of the combustion process in the monitored area.
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Petrography and mineralogy of self-Burning Coal wastes from anthracite mining in the El Bierzo Coalfield (NW Spain)
2016Co-Authors: Joana Ribeiro, Isabel Suárez-ruiz, Colin R. Ward, David FloresAbstract:Coal fires Burning around the world over many years have been responsible for the loss of natural resources and also for negative environmental and human-health impacts. Study of self-Burning Coal wastes based on organic petrology, mineralogy and geochemistry allows the evaluation of factors responsible for the combustion process, and can also be used to assess the changes that are taking place in thermally affected materials. The main goal of this study is to characterize the materials from the Arroyo Galladas, Arroyo Mourin and Fabero Coal waste piles, which resulted from Coal mining in the El Bierzo Coalfield (NW Spain). Samples of Coal, and of unburned and burned or Burning Coal waste material, were studied by optical microscopy and X-ray powder diffraction (XRD). The results demonstrate that some of the organic matter has preserved its characteristics, but other organic material shows signs of thermal alteration such as cracks, devolatilization vacuoles, dark reaction rims, plasticized edges, and increased or decreased vitrinite reflectance. The resistance of the unaltered organic matter to thermal effects is attributed to the Coalification process previously undergone by these Coals. The mineralogical composition of the samples indicates that newly formed minerals are present in the burned or Burning material, including mullite, cristobalite, cordierite, hematite, jarosite, sanidine, anorthite, sulfur, pyrite, rozenite, coquimbite, tschermigite, boussingaultite and amorphous material. The formation of these minerals is attributed to combustion at maximum temperatures of at least 1100. °C in the Fabero Coal waste pile and lower temperatures in the Arroyo Galladas Coal waste pile, and to interaction of gases released by combustion with the solid particles, the waters and the atmosphere in and around the waste piles.
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polycyclic aromatic hydrocarbons pahs in Burning and non Burning Coal waste piles
2012Co-Authors: Joana Ribeiro, Tais Freitas Da Silva, Joao Graciano Mendonca Filho, Deolinda FloresAbstract:Abstract The Coal waste material that results from Douro Coalfield exploitation was analyzed by gas chromatography with mass spectrometry (GC–MS) for the identification and quantification of the 16 polycyclic aromatic hydrocarbons (PAHs), defined as priority pollutants. It is expected that the organic fraction of the Coal waste material contains PAHs from petrogenic origin, and also from pyrolytic origin in Burning Coal waste piles. The results demonstrate some similarity in the studied samples, being phenanthrene the most abundant PAH followed by fluoranthene and pyrene. A petrogenic contribution of PAHs in unburned samples and a mixture of PAHs from petrogenic and pyrolytic sources in the Burning/burnt samples were identified. The lowest values of the sum of the 16 priority PAHs found in Burning/burnt samples and the depletion LMW PAHs and greater abundance of HMW PAHs from the unburned Coal waste material relatively to the Burning/burnt material demonstrate the thermal transformation attributed to the Burning process. The potential environmental impact associated with the Coal waste piles are related with the release of petrogenic and pyrolytic PAHs in particulate and gaseous forms to soils, sediments, groundwater, surface water, and biodiversity.
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identification of nanominerals and nanoparticles in Burning Coal waste piles from portugal
2010Co-Authors: Joana Ribeiro, Colin R. Ward, Deolinda Flores, Luis F O SilvaAbstract:A range of carbon nanoparticles, agglomerates and mineral phases have been identified in Burning Coal waste pile materials from the Douro Coalfield of Portugal, as a basis for identifying their potential environmental and human health impacts. The fragile nature and fine particle size of these materials required novel characterization methods, including energy-dispersive X-ray spectrometry (EDS), field-emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) techniques. The chemical composition and possible correlations with morphology of the nanominerals and associated ultra-fine particles have been evaluated in the context of human health exposure, as well as in relation to management of such components in Coal-fire environments.
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Burning of Coal waste piles from douro Coalfield portugal petrological geochemical and mineralogical characterization
2010Co-Authors: Joana Ribeiro, Ferreira E Da Silva, Deolinda FloresAbstract:Abstract In the Douro Coalfield anthracites were exploited for decades (1795–1994). Besides many small mines Douro Coalfield had two principal mining areas (S. Pedro da Cova and Pejao). Coal mining activities cause several impacts on the environment, one of which is the amount of discard or waste which was disposed of all over Douro Coalfield resulting in one of the most significant and severe impacts on the environment. Over 20 waste piles exist in the old mining areas, geographically dispersed, and three of them are presently Burning. Their ignition was caused by forest fires during the summer of 2005. Samples from the Burning and unburned zones of the waste piles were studied as were the gas from vents and the minerals resulting after combustion. Geochemical processes and mineralogical transformations in the Burning Coal waste pile were investigated. Microscopic analyses of the samples identified some particular aspects related with combustion: oxidation of pyrite, the presence of iron oxides, organic particles with cracks and rims with lowered (suppressed) Rr, devolatilization vacuoles and some char structures. The occurrence of vitreous (glassy) material as well as Fe–Al spinels in the Burning Coal waste provide evidences that the combustion temperature could have reached values above 1000 °C. Due to combustion, and as expected, the samples studied reported high ash yields. Samples taken from the Burning zones reported an increase of As, Cr, Li, Nb, Ni, Pb, Rb, Sr and LREE concentrations and a decrease in Zr and HREE concentrations. Enrichment in Cs, Li and Rb was noted when comparing with the geochemical composition of black shales and world Coals composition that is related with the contribution of granitic rocks in the sediments that originated the main lithologies of the Douro Coalfield (carbonaceous shale and lithic arenites). Cluster analyses (R-type and Q-type) were performed to understand the trend between the unburned and Burning samples and it seems that some chemical variations are responsible for this separation. Elemental sulphur and salammoniac (ammonium salt) are the Coal fire gas minerals neoformed on the surface of piles, near the Burning zones. They were identified by different techniques, mainly SEM-EDX, XRD and FTIR. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied areas, as well as aliphatic hydrocarbons. The highest concentrations of aromatic hydrocarbons were measured in gas samples from S. Pedro da Cova waste pile. The exposure to hazardous compounds present in the gas is a serious risk to human health and the environment.
Deolinda Flores - One of the best experts on this subject based on the ideXlab platform.
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distributed temperature measurement in a self Burning Coal waste pile through a gis open source desktop application
2017Co-Authors: Lia Duarte, Joana Ribeiro, Deolinda Flores, Ana Claudia Teodoro, J A Goncalves, Alexia Lopezgil, Alejandro Dominguezlopez, Xabier Angulovinuesa, Sonia Martinlopez, Miguel GonzalezherraezAbstract:Geographical Information Systems (GIS) are often used to assess and monitor the environmental impacts caused by mining activities. The aim of this work was to develop a new application to produce dynamic maps for monitoring the temperature variations in a self-Burning Coal waste pile, under a GIS open source environment—GIS-ECoal (freely available). The performance of the application was evaluated with distributed temperature measurements gathered in the S. Pedro da Cova (Portugal) Coal waste pile. In order to obtain the temperature data, an optical fiber cable was disposed over the affected area of the pile, with 42 location stakes acting as precisely-located control points for the temperature measurement. A monthly data set from July (15 min of interval) was fed into the application and a video composed by several layouts with temperature measurements was created allowing for recognizing two main areas with higher temperatures. The field observations also allow the identification of these zones; however, the identification of an area with higher temperatures in the top of the studied area was only possible through the visualization of the images created by this application. The generated videos make possible the dynamic and continuous visualization of the combustion process in the monitored area.
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polycyclic aromatic hydrocarbons pahs in Burning and non Burning Coal waste piles
2012Co-Authors: Joana Ribeiro, Tais Freitas Da Silva, Joao Graciano Mendonca Filho, Deolinda FloresAbstract:Abstract The Coal waste material that results from Douro Coalfield exploitation was analyzed by gas chromatography with mass spectrometry (GC–MS) for the identification and quantification of the 16 polycyclic aromatic hydrocarbons (PAHs), defined as priority pollutants. It is expected that the organic fraction of the Coal waste material contains PAHs from petrogenic origin, and also from pyrolytic origin in Burning Coal waste piles. The results demonstrate some similarity in the studied samples, being phenanthrene the most abundant PAH followed by fluoranthene and pyrene. A petrogenic contribution of PAHs in unburned samples and a mixture of PAHs from petrogenic and pyrolytic sources in the Burning/burnt samples were identified. The lowest values of the sum of the 16 priority PAHs found in Burning/burnt samples and the depletion LMW PAHs and greater abundance of HMW PAHs from the unburned Coal waste material relatively to the Burning/burnt material demonstrate the thermal transformation attributed to the Burning process. The potential environmental impact associated with the Coal waste piles are related with the release of petrogenic and pyrolytic PAHs in particulate and gaseous forms to soils, sediments, groundwater, surface water, and biodiversity.
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identification of nanominerals and nanoparticles in Burning Coal waste piles from portugal
2010Co-Authors: Joana Ribeiro, Colin R. Ward, Deolinda Flores, Luis F O SilvaAbstract:A range of carbon nanoparticles, agglomerates and mineral phases have been identified in Burning Coal waste pile materials from the Douro Coalfield of Portugal, as a basis for identifying their potential environmental and human health impacts. The fragile nature and fine particle size of these materials required novel characterization methods, including energy-dispersive X-ray spectrometry (EDS), field-emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) techniques. The chemical composition and possible correlations with morphology of the nanominerals and associated ultra-fine particles have been evaluated in the context of human health exposure, as well as in relation to management of such components in Coal-fire environments.
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Burning of Coal waste piles from douro Coalfield portugal petrological geochemical and mineralogical characterization
2010Co-Authors: Joana Ribeiro, Ferreira E Da Silva, Deolinda FloresAbstract:Abstract In the Douro Coalfield anthracites were exploited for decades (1795–1994). Besides many small mines Douro Coalfield had two principal mining areas (S. Pedro da Cova and Pejao). Coal mining activities cause several impacts on the environment, one of which is the amount of discard or waste which was disposed of all over Douro Coalfield resulting in one of the most significant and severe impacts on the environment. Over 20 waste piles exist in the old mining areas, geographically dispersed, and three of them are presently Burning. Their ignition was caused by forest fires during the summer of 2005. Samples from the Burning and unburned zones of the waste piles were studied as were the gas from vents and the minerals resulting after combustion. Geochemical processes and mineralogical transformations in the Burning Coal waste pile were investigated. Microscopic analyses of the samples identified some particular aspects related with combustion: oxidation of pyrite, the presence of iron oxides, organic particles with cracks and rims with lowered (suppressed) Rr, devolatilization vacuoles and some char structures. The occurrence of vitreous (glassy) material as well as Fe–Al spinels in the Burning Coal waste provide evidences that the combustion temperature could have reached values above 1000 °C. Due to combustion, and as expected, the samples studied reported high ash yields. Samples taken from the Burning zones reported an increase of As, Cr, Li, Nb, Ni, Pb, Rb, Sr and LREE concentrations and a decrease in Zr and HREE concentrations. Enrichment in Cs, Li and Rb was noted when comparing with the geochemical composition of black shales and world Coals composition that is related with the contribution of granitic rocks in the sediments that originated the main lithologies of the Douro Coalfield (carbonaceous shale and lithic arenites). Cluster analyses (R-type and Q-type) were performed to understand the trend between the unburned and Burning samples and it seems that some chemical variations are responsible for this separation. Elemental sulphur and salammoniac (ammonium salt) are the Coal fire gas minerals neoformed on the surface of piles, near the Burning zones. They were identified by different techniques, mainly SEM-EDX, XRD and FTIR. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied areas, as well as aliphatic hydrocarbons. The highest concentrations of aromatic hydrocarbons were measured in gas samples from S. Pedro da Cova waste pile. The exposure to hazardous compounds present in the gas is a serious risk to human health and the environment.
Graham J Nathan - One of the best experts on this subject based on the ideXlab platform.
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sodium and potassium released from Burning particles of brown Coal and pine wood in a laminar premixed methane flame using quantitative laser induced breakdown spectroscopy
2011Co-Authors: Lijen Hsu, Zeyad T Alwahabi, Graham J Nathan, Marcus AldenAbstract:A quantitative point measurement of total sodium ([Na]total) and potassium ([K]total) in the plume of a Burning particle of Australian Loy Yang brown Coal (23 6 3 mg) and of pine wood pellets (63 6 3 mg) was performed using laser-induced breakdown spectroscopy (LIBS) in a laminar premixed methane flame at equivalence ratios ( U ) of 1.149 and 1.336. Calibration was performed using atomic sodium or potassium generated by evaporation of droplets of sodium sulfite (Na2SO3) or potassium sulfate (K2SO4) solutions seeded into the flame. The calibration compensated for the absorption by atomic alkalis in the seeded flame, which is significant at high concentrations of solution. This allowed quantitative measurements of sodium (Na) and potassium (K) released into the flame during the three phases of combustion, namely devolatilization, char, and ash cooking. The [Na]total in the plume released from the combustion of pine wood pellets during the devolatilization was found to reach up to 13 ppm. The maximum concentration of total sodium ([Na]maxMtotal) and potassium ([K]maxtotal) released during the char phase of Burning Coal particles for p = 1.149 was found to be 9.27 and 5.90 ppm, respectively. The [Na]maxtotal and [K]maxtotal released during the char phase of Burning wood particles for p = 1.149 was found to be 15.1 and 45.3 ppm, respectively. For the case of p = 1.336, the [Na]maxtotal and [K]maxtotal were found to be 13.9 and 6.67 ppm during the char phase from Burning Coal particles, respectively, and 21.1 and 39.7 ppm, respectively, from Burning wood particles. The concentration of alkali species was higher during the ash phase. The limit of detection (LOD) of sodium and potassium with LIBS in the present arrangement was estimated to be 29 and 72 ppb, respectively.
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simultaneous measurements of the release of atomic sodium particle diameter and particle temperature for a single Burning Coal particle
2009Co-Authors: P Van Eyk, Peter J Ashman, Zeyad T Alwahabi, Graham J NathanAbstract:Abstract The temporal history of the release of volatile alkali species during Coal combustion is a significant, but poorly understood factor in the fouling and corrosion of heat transfer surfaces within industrial Coal-fired boilers. We present new results of the simultaneous measurement of particle temperature, particle size and the atomic sodium concentration in the plume of a Burning Coal particle. During the char phase, the sodium concentration in the plume was found to be linearly dependent on the inverse of particle diameter, but during the ash phase the sodium concentration was found to decay exponentially with decreasing particle temperature. The centreline decay of Na within the plume above the Burning particle consists of one region controlled by a first order chemical reaction and a second region controlled by diffusion.
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quantitative measurement of atomic sodium in the plume of a single Burning Coal particle
2008Co-Authors: P Van Eyk, Peter J Ashman, Zeyad T Alwahabi, Graham J NathanAbstract:The release of volatile sodium during Coal combustion is a significant factor in the fouling and corrosion of heat transfer surfaces within industrial Coal-fired boilers. A method for measuring the temporal release of atomic sodium from a single Coal particle is described. Laser absorption was used to calibrate laser-induced fluorescence measurements of atomic sodium utilising the sodium D1 line (589.59 nm) in a purpose-designed flat flame environment. The calibration was then applied to planar laser-induced fluorescence measurements of sodium atoms in the plume from a single Victorian brown Coal particle (53 mg) suspended within the flat flame. The peak concentration of atomic sodium was approximately 64.1 ppb after 1080.5 s, which appears to correspond to the end of char combustion. To our knowledge this is the first in situ quantitative measurement of the concentration field of atomic sodium in the plume above a Burning particle. A simple kinetic model has been used to estimate the rate of sodium decay in the post-flame gases. Comparison of the estimated and measured decay rates showed reasonable agreement.
łukasz Kruszewski - One of the best experts on this subject based on the ideXlab platform.
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first multi tool exploration of a gas condensate pyrolysate system from the environment of Burning Coal mine heaps an in situ ftir and laboratory gc and pxrd study based on upper silesian materials
2018Co-Authors: łukasz Kruszewski, Monika J Fabianska, Justyna Ciesielczuk, Tomasz Segit, Ryszard Orlowski, Rafal Motylinski, Danuta Kusy, Izabela MoszumanskaAbstract:Abstract A methodological approach to the complex geochemical analysis of the Coal fire in Burning Coal mine heaps (BCMH) of Upper Silesian Coal Basin has been developed. The other approach used is gas chromatography and indicatory tubes. Powder X-Ray Diffraction is applied for phase analysis to determine the species composition of mineral condensates present within and around gas flues. The gas compositions are proved to be extremely variable, when comparing both different BCMH and flues or flue zones of the same heaps. One outstanding determination concerns GeCl4, found in most samples often in large quantities. No evident dependence between the gas and mineral condensate compositions is found: N-rich condensates may but do not have to be associated with NH3-, pyridine-, or NOx-rich gases. This is also true for S-rich and Cl-rich mineralization in connection with gases of SO2, H2S, OCS, CS2, thiophene, dimethyl sulfide, dimethyl disulfide, HCl, and various halogenated hydrocarbons. Fluorine is rarely present as HF, whereas SiF4 occurs more frequently and in much larger quantities. AsH3 is mainly a trace gas but may locally be enriched. Besides the common gases, a number of trace gases is also determined based on residual FTIR spectra. Those with the highest presence chance include cyanogen isocyanate, cyanogen N-oxide, (iso)cyanic acid, c-cyanomethanimine (ethylenediimine), isocyanatomethane, iodocyanoacetylene, acetonitrile, acetaldehyde, m-hydroxybenzonitrile (m-cyanophenol), isonitrosyl chloride, nitrosyl isocyanide, difluorosilane, pentacene, triphenylene, thiazolidine, cyclohexane, and a trinitrenetriazine. The occurrence of some metals and semimetals (e.g., Al, Mg, Ga) as neutral hydroxides, suggested by other authors to occur in natural gases, is possibly confirmed. The presence of trace metal carbonyls, nitrosyls and hydrides is also possible.
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supergene sulphate minerals from the Burning Coal mining dumps in the upper silesian Coal basin south poland
2013Co-Authors: łukasz KruszewskiAbstract:Abstract Sulphate minerals of various chemical compositions form subtle mixtures of small aggregated crystals on some Burning Coal-mining dumps in the Upper Silesian Coal Basin, Poland. They include Na and Mg sulphates — blodite and konyaite. Magnesium sulphates belong to the second group and hexahydrite is its most common representative. Aluminium sulphates include tamarugite, pickeringite, and alunogen. Iron sulphates are copiapite-group minerals, metavoltine, butlerite, and voltaite-group minerals. Calcium sulphates are almost exclusively represented by gypsum. EDS proved to be, in general, a better tool than WDS for the chemical analysis of the sulphates. Both the Rietveld and Pawley methods were found to be useful in the calculation of unit cell parameters. The analysed sulphates contain some rare and interesting elements, the most important being Tl, Ga, In, Cd, Se, and As. The sulphates formed as a result of the mutual action of various supergene processes, including the oxidation of S-rich Coal-fire gases, metal leaching from waste-rocks by H2SO4 solutions and evaporation. The complexity of the sulphate efflorescence composition is explained by the chaotic nature of settings involving a variety of waste rocks, hydration–dehydration reactions, and access of both ground and rain water- and atmospheric oxygen.
