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This paper describes the evaluation of petrographic textures in char and activated carbon derived from coal, coal by-products and biomass, formed during carbonization and activation processes. This work represents the results of interlaboratory exercises from 2016 to 2022 of the Microscopy of Carbon Materials Working Group in Commission III of the International Committee for Coal and Organic Petrology. The interlaboratory exercises were run on photomicrograph samples. For textural characterization of carbon materials, the existing American Society for Testing and Materials (ASTM) classification system for metallurgical coke was applied. Morphological differences were evaluated in 29 carbon material types, including 22 char samples, and 7 activated carbon (AC) samples obtained experimentally using conventional direct/indirect and microwave heating technologies. This approach gives an extended view on the identification of microporous carbons, and how a certain heat treatment develops a certain optical texture and structure in a raw material. The requested evaluation of carbon materials was related to their porosity, origin, extent, and characteristics, which are particular to each carbon material type. Because carbon matrices can form a wide range of optical textures during heat treatment it is important to demonstrate which carbon occurrences will have a crucial role in industrial applications dominated by adsorption phenomena. The interlaboratory exercises included 17 participants from 14 laboratories. Four sets of digital black and white and colour photomicrographs were distributed, which in total comprised 184 fields of different types of carbon material. The results were evaluated based on four levels: (i) optical texture (isotropic/anisotropic), (ii) optical type and size (punctiform, mosaic, fiber, ribbon, domain), iii) morphology (porous, non-porous/massive), and (iv) particle origin (precursor type). The statistical method applied to evaluate the results was based on "raw agreement indices". Comparative analyses of the average values of the level of overall agreement showed homogeneity in the results, the mean value was 89%, with a minimum value of 87% and a maximum value of 91% for those who participated in at least three out of four exercises. • Char and activated carbon derived from coal and biomass are evaluated. • Classification of metallurgical coke optical texture is used for carbon materials. • Interlaboratory exercise results prove the homogeneity of participants' answers. • Results show a level of overall agreement mean value of 89%. • Optical microscopy can be used as a quality control method for carbon materials. [ABSTRACT FROM AUTHOR]

Namurian and Langsettian coals representing a vertical span of about 650 m were sampled from cores in southern West Virginia and western Virginia. The coal rank ranges from medium through low volatile bituminous. Historically, a significant portion of the production from the region has been for smokeless steam coals and for metallurgical coal. Despite the presence of thrust faults and the potential for fault-induced movement of mineralizing fluids, a depth-of-burial/geothermal-gradient model, as proposed earlier, appears to be sufficient to describe the increase of rank with depth. The coals generally have >70% total vitrinite (mineral-free basis) and a telovitrinite/(telovitrinite + detrovitrinite) ratio exceeding 0.75. Fusinite dominates the inertinite group macerals. An unnamed Langsettian coal had a high liptinite content but, otherwise, in part owing to the difficulty of detecting liptinites in medium and low volatile bituminous coals, liptinite appears to be sparse. Among the coals in the study, not all of them have been extensively mined. The Pocahontas coals represent the most significant economic resource. • Namurian and Langsettian coals were studied southern West Virginia and western Virginia. • The coals are noted as high quality smokeless and coking resources. • Coal rank ranges from medium through low volatile bituminous. • The coals generally have >70% total vitrinite (mineral-free basis), dominated by telovitrinite. [ABSTRACT FROM AUTHOR]

Underground coal gasification (UCG) can be adopted to convert unminable coal resources into synthesis gas for use in the production of electricity, fuels, and chemicals. UCG is a promising technology with many health, safety, and environmental advantages over conventional mining techniques. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of the gasification processes and improve the utilization efficiency of coal seams. The presence of coal partings has an important impact on mineral transformation. In this paper, the UCG process has been subdivided into pyrolysis, reduction, and oxidation stages, and the progressive coal conversion products were prepared. Ulanqab lignite was used as the test coal. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic equilibrium simulation software, FactSage 7.2, was used to calculate the relevant phase diagram to assist in understanding the mineral transformations. The experimental results indicate that the different iron-bearing minerals occur in raw coal and non-coal partings which are nontronite (Na 0.3 Fe 2 Si 4 O 10 (OH) 2.4H 2 O) and glauconite (K (Fe, Al) 2 (Si, Al) 4 O 10 (OH) 2) respectively. Pyrrhotite is the main iron-bearing mineral in the pyrolysis products. In the reduction stage, the relative content of Al 2 O 3 is increased due to the presence of non-coal partings, which reacts with FeO to produce hercynite (FeAl 2 O 4) at a temperature above 1100 °C. When the temperature increases to 1300 °C, hercynite is converted to the thermodynamically-stable cordierite (Fe 2 Al 4 Si 5 O 18). In the oxidation stage, mullite (Al 6 Si 2 O 13) is produced when the oxidation temperature reaching 1300 °C, which could be used to reflect the underground reaction conditions in the coal seam. The phase diagram of (SiO 2) 6.2 Al 2 O 3 -CaO-Fe 2 O 3 proves that mullite and anorthite (CaAl 2 Si 2 O 8) are the dominant minerals when the mole fraction of (SiO 2) 6.2 Al 2 O 3 is above 0.7. In addition, the ash melting point rises with an increase of Si and Al content in the presence of non-coal partings. Unlabelled Image • The different iron-bearing minerals occur in raw coal and non-coal partings which are nontronite (Na 0.3 Fe 2 Si 4 O 10 (OH) 2.4H 2 O) and glauconite (K (Fe, Al) 2 (Si, Al) 4 O 10 (OH) 2) respectively. • In the reduction stage, the relative content of Al 2 O 3 is increased due to the presence of non-coal partings, which reacts with FeO to produce hercynite (FeAl 2 O 4) at a temperature above 1100 °C. • In the oxidation stage, mullite (Al 6 Si 2 O 13) is produced when the oxidation temperature reaching 1300 °C, which could be used to reflect the underground reaction conditions in the coal seam. • The phase diagram of (SiO 2) 6.2 Al 2 O 3 -CaO-Fe 2 O 3 proves that mullite and anorthite (CaAl 2 Si 2 O 8) are the dominant minerals when the mole fraction of (SiO 2) 6.2 Al 2 O 3 is above 0.7. [ABSTRACT FROM AUTHOR]

Graphical abstract Unlabelled Image Abstract The aim of the present study is to uncover hydrocarbon generation potential of an area intruded by lamprophyre dyke. Lamprophyre dyke induced a short-distance asymmetric thermal aureole in coal beds with more intense impact along the dip direction. Large ash yield, carbon content, lower volatile matter content, hydrogen indices, presence of natural coke, disordered kaolinite peaks, less pronounced aliphatic peaks, higher aromaticity under Fourier Transform Infra-Red spectroscopy (FTIR); highly rugged surface and large pores with the aid of Atomic force microscopy (AFM); abundant calcium carbonate mineral phases (calcite, dolomite, ankerite) and high-temperature silica phases (tridymite, sanidine) under X-ray diffraction (XRD) are the consequences of pronounced thermal effect and expulsion of hydrocarbons. Furthermore, the estimated vitrinite reflectance (EVRo) calculated through maximum pyrolysis temperature (T max) and measured mean random vitrinite reflectance (VRo) show the maximum difference in the heat-affected coal samples. In addition, parameters for source rock reconstruction and indices for quantification of FTIR spectra i.e. index of aliphaticity (IAL), index of aromaticity (IAR) and index for hydrocarbon generation (IHG) are introduced for coals. The distant (i.e. least-heat-affected) coals collected opposite to the dip direction of the coal bed have a higher potential for hydrocarbon generation. The igneous intrusion thus played a significant role in enhancing the maturity of the organic material, in turn, augmenting the hydrocarbon generation potential for targeting hydrocarbon plays of the area although at the expense of proximal samples. Highlights • Thermal aureole asymmetry induced by lamprophyre dyke. • Hydrocarbon generation and gas play analogs for exploration • Negative conversion factor in coals with larger TOC • I AL , I AR , I HG for FTIR quantification • Pore and surface features under AFM [ABSTRACT FROM AUTHOR]

Both unburning and burning coal mine dumps present serious hazards to the natural environment and human health. Bituminous coal has been produced in the Czech part of the Upper Silesian Basin since 18th century, with total production over 100 million metric tons of waste material (barren rock) deposited in dumps. Today, each dump has undergone remediation and reclamation works, and many of them were totaly removed. Only three dumps with signs of thermal activity (burning) remain, with the Heřmanice dump as the most important. The powder X-ray diffraction (XRD) in combination with electron dispersive spectroscopy (EDS) and backscattered electron (BSE) imaging were applied to identify and describe the products of both unburning and burning dumps. The ones without thermal activity released mostly sulfates such as jarosite group minerals, hexahydrite, ferrohexahydrite, gypsum, thenardite, konyanite, and baryte due to pyrite weathering processes, accompanied by ferrihydrite, schwertmannite, goethite, and aragonite. As expected, the mineral associations of thermally active dumps were more variable. Apart from hot gas vent products such as sulfur, salammoniac, and cryptohalite, we identified a zoned sulfate cap (crust) with an accumulation of newly formed phases (e.g., aluminopyracmonite, pyracmonite, godovikovite, mascagnite, koktaite, boussingaultite, and clairite). Both the gas vents and sulfate crust contained a number of rare and exotic phases, such as Bi, bismuthinite, demicheleite-(Br), demicheleite-(I), fluorite, selenium, NH 4 Br, NH 4 I, BiOCl, BiBr 3 , BiI 3 , native iodine, CdS, CdIn 2 S 4 , (NH 4 ,K)AlF 4 , (NH 4, K) 3 AlF 6 , Ce-dominant REE-sulfate, and others. Since coal ash and barren rock are not geochemicaly anomalous, the presence of such various phases could be atributed to the very effective leaching and transport of chemical elements by halide elements, which originated in brines in the roof of the Carboniferous rocks circulating in the strata prior to extraction and emplacement in the dump. This mineralization is to a great extent similar to that of natural volcanic vents, and must be studied by specific methods (low-vacuum electron microscopy with energy-dispersive detectors, use of natural unpolished samples). The composition of altered rock clasts within the dumps was monitored only occasionally, but newly formed feldspars (probably sanidine, albite, andesine), hematite, diopside to hedenbergite, cordierite, magnetite-magnesioferrite minerals, anhydrite, TiO 2 microcrystals, Mg-rich fayalite, and in case of more intensively burnt rocks also wollastonite, barium feldspar (celsian-hyalophane series), and a phase of Ca-SiO 4 -PO 4 system were also observed. It is clear that the burning of coal dumps presents a specific problem, and future steps towards understanding their potential environmental risks would require complex studies including the determination of their mass and chemical element balance, the estimation of the dump volume affected by the thermal mobilization of chemical elements, and the migration pathways of the potentially-hazardous elements. However, it is clear that the most problematic part incudes just the few uppermost meters with vents of hot gases and the sulfate cap, which are readily soluble in water after the end or lateral shift of burning. • Extreme phase heterogeneity in case of burning coal dumps. • 44 securely and 40 imperfectly identified minerals, including 12 potentially new ones. • Sulfate cap presents the major concentration of environmentaly harmful elements. • Halides (Cl, F, Br, I) play crucial role in transport of some elements. • Halides originate in salt-water (brine) accompanying coal-bearing rock massif. [ABSTRACT FROM AUTHOR]

The presence of vitrinite in sedimentary rocks of post-Silurian age allows its reflectance to be used to estimate the thermal maturation of organic matter in petroleum systems. Increasing reflectance of vitrinite, which is primarily driven by aromaticity, depends primarily on the time and temperature attributes of its evolutionary pathway. This study evaluated carbonaceous shales proximal to coal measures and coal samples via isothermal hydrous pyrolysis (HP) to compare differences in the maturation pathways of vitrinite. Sample residues were analysed via vitrinite reflectance (VR o), geochemical screening tests (organic carbon and programmed temperature pyrolysis), and infrared spectroscopy. The study included samples from Indian and North American basins, to observe differences in vitrinite evolution with respect to enclosing mineral matrix, starting degree of aromaticity, organic matter types, stratigraphic age, and depositional environment. The organic content of HP residues shows an intuitive response to the thermal stress of HP, e.g., a general depletion of total organic carbon (TOC) content, pyrolyzate (S2), and hydrogen index with increasing HP temperature. Infrared proxies including C-factor and CH 2 /CH 3 generally decrease with increasing thermal maturity indicating loss of O via CO 2 generation and the thermal cracking of aliphatic organic matter. T max , production index (PI), and VR o show intuitive increasing values with respect to HP temperature. The least mature sample (0.48 ± 0.05% VR o) generally experienced the maximum change in these parameters during maturation, whereas the most mature sample (0.99 ± 0.06% VR o) generally showed the least change. This observation is consistent with higher kinetic barriers to reaction in more aromatic vitrinite which contains higher bond dissociation energies. Devolatilization of vitrinite during HP causes formation of gas evacuation vacuoles and contraction cracks in the vitrinite grains of both coal and carbonaceous shale. Similarities in vitrinite response to HP between coal and carbonaceous shale suggest that thermal evolution of the vitrinite maceral is principally controlled by inherent rate-limiting kinetic parameters related to its molecular structure. Whereas, the stratigraphic age, sedimentary environment, surrounding organic matter, lithology, and catalysis by mineral composition have less effect. To further improve our understanding of vitrinite aromatization and kinetic parameters, future studies of vitrinite reflectance thermal evolution with temperature should include coal and carbonaceous shale from the same stratigraphic section and extant woody tissue from modern vascular plants. • Coal and carbonaceous shale were subjected to isothermal hydrous pyrolysis • Solid residues were evaluated by organic petrography, programmed temperature pyrolysis, and micro-FTIR • Vitrinite thermal evolution was similar in coal and carbonaceous shale • Thermal evolution of vitrinite is controlled by rate-limiting kinetic parameters related to its molecular structure • Enclosing mineral matrix or organic matter types, stratigraphic age, and depositional environment have little effect [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) sequestration in underground formations is one of the effective processes of decreasing carbon emissions. CO 2 injection in coalbeds improves methane recovery from coal formations (ECBM) with storing CO 2 for environmental purposes. The performance ECBM process and CO 2 injection depend on the wettability behavior in the coal formation. The wettability can be measured using different experiments; however, these measurements are time-consuming, expensive, and highly inconsistent. Therefore, this paper aims to apply function networks (FN), support vector machine (SVM), and random forests (RF) to predict the contact angle in the coal formation. A dataset of 250 points was collected for different coal samples at different conditions. The different machine learning (ML) tools were used to predict contact angle (CA) as a function of coal properties, system pressure, and temperature. The training to testing data set ratio was used to be 70:30. A set of data hidden from the model was used for the validation purpose of the predictive models. The ML models showed a high capability to accurately predict the CA as a function of coal properties and the system conditions. The R-value (correlation coefficient) and the AAPE (average absolute percentage error) were used to evaluate the models' performance. R-values between actual and estimated CA from the FN model were calculated to be 0.97 and 0.97 comparing to 0.99, and 0.97 from the RF model in the case of training and testing datasets, while it was 0.95 and 0.96 for the SVM model. AAPE was less than 9% in the different ML models. This study delivers ML tools to accurately estimate the contact angle in the coal formation based on the coal properties, pressure and temperature, and water salinity without the need for experimental measurements of complicated calculations. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) is an important energy source globally, thus understanding its origin and evolution is essential to the assessment of reserves and developing exploration strategies. This study aims to identify the origin of CBM in Liupanshui Coalfield (LPC) in southern China and evaluate the influence of basin exhumation on gas storage in different rank coals. Ten CBM samples were collected from four blocks that have different thermal histories and coal rank ranges. Based on the C 1 /(C 2 + C 3) ratio (16–971), δ13C CH4 (−41.6 to −34.9‰) and δD CH4 (−185 to −140‰), the methane is mainly thermogenic in origin. Systematic compositional differences between the four blocks are consistent with coal maturity. Noble gases in LPC CBM are a mixture of air-derived gas dissolved in local groundwaters and radiogenic gases that were generated in the coals and diffused in from deeper crust. The radiogenic 4He/40Ar⁎ and 21Ne⁎/40Ar⁎ are lowest in CBM from Qingshan block, strong evidence of diffusive loss of light noble gases. 20Ne/36Ar (0.23–0.70) in all gases are higher than local air-saturated water (0.16) and are most easily explained by re-dissolution of noble gases that exsolved from groundwater during basin inversion. 84Kr/36Ar and 132Xe/36Ar ratios are higher than predicted from this process and likely reflect desorption of Xe and Kr that has been trapped on the coal matrix at the time of coal formation. The noble gases are consistent with gas exsolution and loss from the reservoir during Mesozoic-Cenozoic basin inversion. Modelling the loss of both free and adsorbed gas during basin inversion we find that the Qingshan block has lost the highest proportion of free gas (77%), yet the total gas loss (free and adsorbed) is the lowest (25%) due to the strong adsorption capacity of the mature coals. The volume of groundwater that has interacted with the gas phase during the basin inversion is estimated according to the re-dissolution process model to evaluate the role of groundwater in gas preservation and gas extraction. Combining gas production data for the four blocks, high gas content and efficient gas extraction in LPC are expected for the high maturity coals that have seen low groundwater during basin inversion but more at shallow depth. • Methane in LPC is mainly thermogenic in origin. • Systematic compositional differences between blocks are consistent with coal maturity. • Noble gases in CBM are consistent with gas exsolution and loss during basin inversion. • The estimated water-gas volumetric ratio from the re-dissolution model is used to evaluate gas loss and gas production. [ABSTRACT FROM AUTHOR]

Abstract: A suite of thirteen Indian thermal coals have been subjected to FTIR examination to determine their quartz content. The coal samples were ashed at 815±10°C using standard procedures and the high temperature ash (HTA) of each coal was used to make a tablet with KBr under pressure. Each tablet was then subjected to FTIR scanning to obtain a spectrum at a resolution of 2cm−1. The 800cm−1 quartz doublet observed in each spectrum was used to obtain quantitative information on the percentage of quartz present. The data were compared with interpretations from ash analysis. The result showed a good correlation between the two sets of data (R 2 =0.84), suggesting the potential of the method for routine testing of quartz content of coal in laboratory, especially as it takes less time than other methods. [Copyright &y& Elsevier]

The first thorough study of PAHs in feed coals and FAs from combustion in six Bulgarian TPPs was done. Since coal-derived FAs are applied to many targets, it is imperative to enhance the knowledge for their geochemical composition and environmental impact. The gap of information on PAHs in feed coals and coal-derived FAs has outlined the aim of the study: (i) to compare by geochemical proxy PAHs in feed coals and FAs generated in six Bulgarian TPPs; (ii) to track the changes in PAHs compositions with feed coal ranks and in different ESP rows; and (iii) to estimate the potential toxicity of FAs (if any). Extractable organic matter (EOM) was prepared. PAHs were isolated in aromatic fractions and quantified in μg/kg. The total PAHs for lignite feed coal are in the range 400–530 μg/kg and for FAs 0.30–12.60 μg/kg: for subbituminous feed coal, they are 4000 μg/kg, and for FAs, 1.10–32.50 μg/kg. For bituminous feed coals, they are - 860 μg/kg and 9305 μg/kg, and for FAs from both TPPs, they are several times lower, from 69.4 μg/kg to 103.3 μg/kg, for the five ESP rows of Varna TPP and from 100.4 to 182.20 μg/kg, for the three rows of ESPs of Russe TPP. The EOM for low rank feed coals is strongly dominated by coal biomarkers, i.e., perylene and phenyl substituted PAHs. Therefore, calculations and ratios based on PAHs compositions are done only for bituminous feed coals and their FAs. Combustion has resulted in a regular shift to lighter PAHs compared to the signature PAHs of feed coals. PAHs distributions in FAs are dominated by phenanthrene. Distribution profiles according to the number of aromatic cycles (R) in PAHs are dominated by three-ring (3R) PAHs > four-ring (4R) PAHs. Only in the last row of ESP from the Varna TPP is there evidence for the presence of heavier PAH, five-ring (5R) benzo[ g , h , i ]fluoranthene, trapped by the finest particulate matter. Relatively low PAHs concentrations determined for FAs are compared with the values for PAHs in soils according to the Bulgarian regulation. [Display omitted] • Comparative study of PAHs in different rank feed coals and fly ashes from six TPPs. • PAHs in fly ashes range from 0.3 μg/kg to 182.2 μg/kg, depend on the feed coal rank. • Apparent shift to low molecular weight PAHs (3R, 4R) in FAs compared to feed coals. • Low rank feed coals distribution pattern dominated by native, non-carcinogenic PAHs. • Proof of higher molecular PAH in the finest particles of electrostatic precipitator. [ABSTRACT FROM AUTHOR]

Significant knowledge has been assembled on the marine Longmaxi Shale in the Sichuan Basin over the past ten years. However, the distribution of shale gas resources on the periphery of the Sichuan Basin and in other source rock formations are still not sufficiently understood. To improve our understanding on the depositional environment and thermal maturity, and their relevance to the source rock quality and shale gas potential of the thick, coal-bearing Longtan Shale, 36 organic-rich shale samples were selected from a single borehole located in the southwestern Guizhou Province for geochemical and petrographic analysis. Total organic carbon (TOC) contents are high with 7.7 wt% on average, reaching partly up to 28.21 wt%, while carbonate contents are low. Vitrinite reflectance (VR r) values and Rock-Eval T max temperatures range from 1.48 to 1.84% and 482 to 583 °C, respectively, indicating a high thermal maturity which is in accordance with aromatic molecular parameters. The remaining, present day hydrocarbon generation potential (Rock-Eval S2) is rather low due to the high maturity. Microscopic investigations further show that the organic matter in the rocks is mainly composed of higher land plant particles, present as large and poorly rounded vitrinite and inertinite particles indicating a rather short transport distance. TOC vs. total sulfur (TS) relationships as well as specific hydrocarbon ratios (e.g. pristane/phytane) and framboidal pyrite size distributions indicate a variable either marine or freshwater environment for the shales in the coal-bearing sequence and suggest that original kerogen was either type III or type II-III. Bottom water during deposition was probably oxygen depleted but not anoxic. High sedimentation rates can be assumed for the now 700 m thick, compacted sequence, favorable for the preservation of organic matter. Overall, the present results are in accordance with previous studies of the Longtan Shale which initially had a high hydrocarbon (mainly gas) generation potential; furthermore the thickness of the formation is much larger in the here studied southwestern part of the Guizhou Province than in the previously studied northern parts. • Depositional environment of Permian Longtan shales varied from freshwater to marine. • Shales in the coal-bearing Longtan Formation are very rich in organic matter. • Longtan shales originally had a high petroleum generation potential in southwestern Guizhou. • Thermal maturity of Longtan Formation is high, but still in the wet gas generation stage. [ABSTRACT FROM AUTHOR]

Canister desorption of freshly drilled coal cores is routinely employed for exploratory assessments of coalbed gas. Coals are molecular sieves containing both open and closed pores. However, little attention has been paid to the differences between the carbon isotopic compositions of CH 4 and C 2 H 6 from open and closed pores in coal and their influence on isotopic fractionation during desorption. In this study, canister desorption and pulverization–degassing experiments were conducted to study the carbon isotopic shifts of CH 4 and C 2 H 6 during desorption. The δ 13C values of CH 4 and C 2 H 6 desorbed from three coal samples from the Zhina Coalfield in southwest China displayed a two-stage shift over time during canister desorption (that is, an isotopic decrease followed by an increase), ranging from −38.4 to −30.6‰ and − 32.1 to −28.5‰, respectively. The δ 13C values of CH 4 and C 2 H 6 desorbed from the coal samples during pulverization ranged from −29.3 to −24.1‰ and − 31.5 to −27.2‰, respectively, approaching the isotopic ranges of coal-derived gas. Low-pressure N 2 adsorption measurements showed that many closed pores in coal were opened during progressive pulverization. Gases trapped in closed pores may be considered to be of their original nature, unaffected by subsequent geological processes (i.e., mixing of secondary biogenic gas). Thus, CH 4 and C 2 H 6 were more depleted in 13C in open pores than in closed pores. Some open pores on the surface of the coal core were previously closed when in situ but were opened during drilling. Therefore, the initial gas released from the cores was a mixture of gases desorbed from the open and closed pores. The 13C-enriched CH 4 and C 2 H 6 desorbed from the pores on the coal core surfaces may migrate into canister headspaces preferentially, thereby providing insight into the two-stage δ 13C shift observed during canister desorption. • Many of the closed pores in anthracite are opened during progressive pulverization. • CH 4 and C 2 H 6 are more depleted in 13C in open pores than in closed pores. • CH 4 and C 2 H 6 show two-stage δ 13C shifts over time during canister desorption. • Two-stage δ 13C shifts are due to the δ 13C differences between open and closed pores. [ABSTRACT FROM AUTHOR]

Calcium phosphate apatite, Ca 5 (PO 4) 3 (OH,F,Cl), is a common accessory mineral in coal seams. Although minor, its role in hosting phosphorus (P) and fluorine (F) can reduce the economic viability of coking and thermal coal deposits. Apatite in coal is commonly <50 μm and may have several modes of occurrence. The modes of occurrence investigated as part of this study include apatite infilling small (i.e. less than 30 μm) cell lumens of fusinite and semifusinite macerals (pore-apatite); apatite infilling fractures (fracture-apatite); apatite occurring as discrete crystals in organic layers or in lithic lenses or bands (detrital-apatite); and apatite nodules or encrustations on silicate minerals (encrusting-apatite). However, the small size of the apatite and its intermixed relationship with the coal and other mineral matter precludes separating the apatite from the coal for analysis and has implications for commercial beneficiation. Therefore, this study documents the trialling of different in situ techniques for evaluating the halogens, specifically F, within these different apatite micro-crystals in polished mounts. In general, standards-based, fully quantitative analysis of major and minor elements (including F, Cl) was accomplished using electron probe microanalysis (EPMA). This in conjunction with electron backscatter diffraction was used to evaluate the measured halogen contents for the different apatites and confirmed that all of the apatites are technically fluorapatite with F contents >1 wt%. However, the small crystallite size of the encrusting-apatites and the pits on the polished surface of the detrital-apatites intermixed with the coal layers hindered determining the halogens by this method. Although, all of the apatites in the coals were able to be analysed by infrared spectroscopy, both the combined kaolinite and apatite spectra, and the noise in the spectra at the lower wavelengths hindered evaluating the F in the apatites using this method. Despite these limitations, the findings of this study show that EPMA is probably the most suitable analytical technique for determining the halogen contents of the different modes of apatites in situ in coal pellets. Future work should focus on determining whether the modes of occurrence reflect paragenesis. • The fluorine (F) content of apatites varies with crystallographic orientation relative to the incident electron beam. • In situ analysis of halogens in small (<30 µm) apatite crystals can be achieved using electron probe microanalysis (EPMA). • F contents vary for the different modes of apatite (i.e. pores, fractures or adventitious minerals). • Apatite is a primary host of phosphorus and fluorine in the coal samples tested. • Almost all apatites tested, regardless of mode of occurrence are classified as fluorapatite. [ABSTRACT FROM AUTHOR]

Thermal maturity of source rocks indicated by vitrinite reflectance (R o) is an important and reliable parameter to determine the petroleum potential of sedimentary basins. Originally, R o was used to characterize the degree of coalification of coals and thus works well for coal seams, but it has limitations when used to determine the thermal maturity of black shale successions. A suite of six coal-shale pairs from the Upper Devonian black shale formations in the eastern United States (New Albany Shale, Ohio Shale, Dunkirk Shale, and Rhinestreet Shale) was selected to study the applicability of R o in assessing the thermal maturity of black shale successions. The results show that vitrinite in the studied coal samples is dominated by collotelinite, whereas vitrinite in black shales occurs as small dispersed particles (~5 μm) in the mineral matrix. When comparing the size and morphology of dispersed vitrinite particles in shales and collotelinite fragments in coals, vitrinite in shales and adjacent coals should have the same origin. The measured mean random R o of vitrinite in coals ranges from 0.51–0.68%, and is 0.04–0.11% (average 0.07%) lower than that of dispersed vitrinite particles in enclosing shales. This observation contrasts with previously reported R o suppression in liptinite-rich black shales. A high standard deviation of R o measurements indicates a highly heterogeneous nature of vitrinite in black shales. Three mechanisms can be envisioned to contribute to the higher R o of dispersed vitrinite particles in black shales relative to enclosed coals. First, small vitrinite particles may become more oxidized because small particles are more frequently suspended during transport to the site of deposition and reworking of bottom sediments after deposition than large pieces of driftwood that will turn into enclosed coal lenses during burial diagenesis. Second, misidentification of zooclast (e.g., chitinozoan) fragments as vitrinite due to loss of diagnostic morphology. Third, various macerals in the vitrinite group (e.g., corpogelinite and collotelinite) may have had different original reflectance values. Based on the petrographic characteristics of vitrinite and vitrinite-like particles, caution should be applied when using the R o values of dispersed vitrinite and vitrinite-like particles in black shales as indicators of thermal maturity. • R o values of Devonian black shales and enclosed coals were compared. • Vitrinite in black shales is more heterogeneous than that in enclosed coals. • R o of black shales is on average 0.07% higher than that of enclosed coals. • Oxidation of vitrinite, misidentification of zooclast fragments, and variation of vitrinite macerals could cause higher R o. [ABSTRACT FROM AUTHOR]

Raman spectroscopy was used to evaluate rank for a series of coals collected adjacent to an igneous intrusion. For these intruded coals, Raman parameters for collotelinite and its coked equivalent show complex changes during the transformation from low to very high levels of maturity (with vitrinite reflectance increasing from 0.55% to 5.0%). With increasing coal rank up to anthracite-level reflectance, the Raman spectra show a decrease in both G band full width at half maximum (FWHM) and D band intensity. The D band shape becomes increasingly asymmetric during the bituminization and de-bituminization stages, whereas in the anthracitization stage, the width of the D and G bands continues to decrease while D band intensity increases. In meta-anthracites (as seen in the ancillary Hunan samples), the G band has a low intensity and undergoes an apparent broadening due to the presence of the D2 band that occurs as a shoulder on the G band. Differences in Raman spectral parameters for vitrinite and inertinite macerals suggest differences in molecular structure between the macerals; as such, the heterogeneous nature of coal may affect Raman spectral results significantly if different maceral types are not considered. Within individual samples, Raman spectra indicate a high level of structural homogeneity between and within vitrinite particles, allowing assessment of differences between samples of different ranks. For vitrinite, the Raman spectral parameters G FWHM and DAs/GA (Area (1100-s) /Area (s-1650) , s is the saddle point between 1100 cm−1 and 1650 cm−1) are highly correlated (R2 > 0.9) with vitrinite reflectance (R r) and maximum alteration temperature (T peak), and allow establishment of geothermometers over the temperature range of ~70–300 °C that can be used to evaluate temperatures attained in intruded coals. • R r increases from 0.55%–5.0% for a coal transect adjacent to an intrusion. • With increased R r , Raman spectra parameters G FWHM and D band intensity decrease. • G FWHM and DAs/GA are correlated (R2 > 0.9) with R r and T peak. • Two equations were developed to estimate maximum temperature from Raman data. [ABSTRACT FROM AUTHOR]

This study reveals the hydrocarbon generation potential and thermal maturity of coal and coaly mudstones from the Eocene Urahoro Group in the Kushiro coal basin (Kushiro Basin) of eastern Hokkaido (Japan). The coal is classified as subbituminous or high volatile C bituminous, and characterized by high hydrogen content (6.1 ± 0.4 wt%, 1σ, dry ash free basis). The hydrogen index (HI = 180–409 mg hydrocarbon/g total organic carbon) and random mean vitrinite reflectance (VR r = 0.42–0.56%) indicate that the coal and coaly mudstones in the Urahoro Group are gas- and oil-prone or oil-prone. Based on the HI and VR r values, the effective oil window starts at vitrinite reflectance ranges of 0.55 to 0.80%. The vitrinite reflectance of coal samples from the Kushiro Coal Mine is inversely proportional to the HI value, although each coal seam has the identical thermal history. This result suggests that the vitrinite reflectance of the samples in the Kushiro Coal Mine is suppressed. Based on the corrected vitrinite reflectance (non-suppressed vitrinite reflectance), the maturity of the coal in the Kushiro Basin increases towards the north. The non-suppressed vitrinite reflectance of the samples from the northernmost part of the basin (Hokuyo Area) was approximately 0.8%, which is within the start of the oil window. The maturity of the coal-bearing strata in the northern area of the basin could be affected by volcanic activity along the volcanic front. In the Hokuyo Area, the Urahoro Group overlies a sequence of Cretaceous–Eocene marine clastic rocks (Nemuro Group), which are about 3000–4000 m in total thickness, suggesting that the organic matter in the marine clastic rocks should reach higher maturity (VR r > 0.8%). • The Urahoro coal is classified as subbituminous and high volatile C bituminous coal. • The VR r (%) and HI values indicate that the Urahoro coal has the potential to generate oil. • The relationship between VR r (%) and HI values suggests vitrinite suppression. • The maturity of the coal in the Kushiro Basin increases towards the north. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion continues to pose a significant hazard to mining operations. It is a complex process that ranges from low-temperature oxidation in the normal mine environment to thermal runaway once temperatures exceed 120 °C. At the thermal runaway stage, the coal becomes dry locally after moisture liberation and evaporation and a well-defined hot spot forms. This process takes place over a period of time, which can be referred to as the incubation period. Assessing the spontaneous combustion hazard likelihood has normally relied on the use of laboratory testing to produce index parameters that give a propensity rating. These are often a single value on a relative rating scale, which gives no indication of the nature of the coal self-heating with respect to time as it would occur under various mine site conditions. To overcome this deficiency it is necessary to consider the incubation behaviour of the spontaneous combustion process, particularly as it relates to coal self-heating at initial mine ambient temperatures. This has recently been achieved using adiabatic oven testing, which shows the modifying influences of moisture content, initial start temperature, seam gas content and reactive pyrite content on the low temperature coal self-heating rate. The incubation testing procedure is able to determine whether self-heating can reach thermal runaway and if so in what timeframe this can take place for the environmental conditions present at the mine site. • Coal spontaneous combustion is an incubation process where various factors can accelerate or decelerate the self-heating rate. • Variations in coal self-heating from low ambient temperatures using an improved adiabatic oven testing procedure are presented. • The new incubation test characterises the effects of moisture, seam gas and reactive pyrite on coal self-heating rates. • The examples shown in the paper illustrate a valid evaluation of the spontaneous combustion hazard likelihood for mine conditions. [ABSTRACT FROM AUTHOR]