Coal Materials Research Articles

Relationship between multiscale nanopore structure and coal connectivity during coalification process

The complex nanopore structures in coal provide the space for gas adsorption and migration, which is crucial for the development of coalbed methane. However, the mechanism of the evolution of multi-scale nanopore structures during coalification is still unclear. In this work, a combined method of CO2/N2 adsorption and synchrotron radiation Nano-CT experiments were used to reveal the multi-scale pore structure characterization during coalification. The synchrotron radiation Nano-CT experiment reconstructed the 3D pore network model for different rank coal and revealed the effective diameter is less than 0.5 μm, accounting for 97.4%–99.6% of the total number of macropores. The combination of these methods, including CO2/N2 adsorption and Nano-CT, accurately characterizes the multi-scale pore distribution in coal, ranging from <2 nm, 2–300 nm and 64 nm - 3.5 μm. The ultra-micropores occupy the primary advantage, accounting for approximately 60.3%–95.2% of the total pore volume and the micropores, mesopores and macropores are more poorly developed than ultra-micropores. During the coalification process, the proportion of porosity contributed by ultra-micropores to the total porosity gradually increases, with the contribution rising by 57.9%. The proportion of porosity contributed by micropores, mesopores and macropores to the total porosity gradually decreases, with the contribution decreasing by 81.0%, 82.8% and 93.6%, respectively. Besides, with growing coal maturity, the total permeability gradually decreases by 9.26 × 10−3 - 3.05 × 10−1 mD, which is negatively correlated with coal maturity during coalification. And the total permeability is mainly provided by macropores, which account for about 99% of the total permeability. This research provides an in-depth understanding of the storage and transport of coalbed methane in a multi-scale nanopore structure.

Effect of the Chemical Composition of Coals on Surface Wettability and Filtration Properties

The method of liquid filtration through a layer of coal powder was used for a comprehensive characterization of surface wettability in conjunction with the determination of the contact angle. The effect of the degree of chemical maturity (metamorphism) of coal on the filtration characteristics of a layer with fractured porous properties was evaluated. Different activity of coal surfaces to water wettability upon a change from the native state to the surface-oxidized one was established. It was shown that the wetting and filtration properties of the coal surfaces increased from native to surface-oxidized coals and decreased as the degree of metamorphism increased from low to medium metamorphosed coals.

Evolutionary Response Model of Low Maturity Coal Measure Reservoir Space to Temperature-Water Pressure Under Hydrous Pyrolysis

Evolutionary Response Model of Low Maturity Coal Measure Reservoir Space to Temperature-Water Pressure Under Hydrous Pyrolysis

Coal gangue-based magnetic porous material for simultaneous remediation of arsenic and cadmium in contaminated soils: Performance and mechanisms

Remediation of arsenic (As) and cadmium (Cd) co-contaminated soil is a challenge in environmental remediation. In this study, coal gangue-based magnetic porous material (MPCG) was designed for simultaneous immobilization of As and Cd in contaminated soil. After the incubation experiment, the effects of CG and MPCG on the availability and fractions of As and Cd and the related microbial functional genes were analyzed to explore the potential remediation mechanisms of MPCG for As and Cd in contaminated soil. The results showed that the stabilization effect of MPCG on As and Cd was significantly higher than that of coal gangue. It reduced the available As and Cd by 17.94–29.81% and 14.22–30.41%, respectively, and transformed unstable As/Cd to stable. The remediation mechanisms of MPCG on As included adsorption, oxidation, complexation and precipitation/co-precipitation. Meanwhile, the remediation mechanisms of MPCG for Cd included adsorption, ion exchange, complexation and precipitation. In addition, MPCG increases the abundance of sulfate-reducing bacteria (dsrA) by 43.39–381.28%, which can promote sulfate reduction. The sulfide can precipitate with As and Cd to reduce the availability of As and Cd in soil. Thus, MPCG is a promising amendment for achieving the remediation of As and Cd co-contaminated soil.

A Step-By-Step Classification Method Of Coal And Miscellaneous Materials By Laser-Induced Breakdown Spectroscopy

A Step-By-Step Classification Method Of Coal And Miscellaneous Materials By Laser-Induced Breakdown Spectroscopy

Preparation and structure analysis of aluminum oxide/water glass/polyurethane composite grouting material for mining

In order to achieve safer and more efficient coal mining, the utilization of water glass/polyurethane (WG/PU) composite grouting material has become widespread in treating fractured coal mining faces. The reaction temperature and mechanical properties of WG/PU are crucial considerations that significantly impact safety and reinforcement effectiveness. However, reducing the reaction temperature without compromising the material's mechanical properties poses a challenge with conventional modification methods. Therefore, this study presents the development of a novel hybrid grouting material, namely Al2O3-WG/PU, which incorporates thermally conductive aluminum oxide (Al2O3) into WG/PU. The response surface method was employed to investigate the effects of key factors such as modules, mass ratio, Al2O3 content, and plasticizer content on the reaction temperature and compressive strength. Additionally, the static and dynamic compression properties of Al2O3-WG/PU were measured and analyzed. The morphology, elemental distribution, chemical composition, and valence information of the composite materials were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the introduction of A2O3 and scientific formula design reduces the maximum reaction temperature of Al2O3-WG/PU by 14.9 °C (12.7%). Although the percentage reduction may not seem significant, it represents substantial progress in the field of coal mine grouting materials. Moreover, this modification method not only maintains the material's mechanical properties but also enhances its compressive strength by 13.84 MPa (27.3%). Based on the characterization results, this study proposes a mechanism for temperature reduction and strength enhancement. The hybrid composite materials produced from Al2O3 and WG/PU show lower reaction temperatures and improved mechanical properties, presenting a promising solution for improving the safety performance of coal grouting materials.

Solvent extraction of superfine pulverized Coal. Part 4. Carbon skeleton characteristics

To better understand the molecular structure of superfine pulverized coal and promote its practical utilization, the NMR (nuclear magnetic resonance) technology is adopted to study the structural information of all the products from the solvent extraction process, including raw coal, residue, and extract. The whole set of NMR spectra is resolved into different individual curves with specific linewidths, shapes, and intensities. According to the chemical shift, the carbon skeleton characteristics like the aromaticity, cluster size, and other structural lattice parameters are analyzed in detail. More importantly, the influences of coal maturity, coal size, and solvent on the carbon structural evolution during the extraction process are focused on. The results show that the aromatic ring stacking and aromatic ring exposure and fragmentation occur competitively during the superfine comminution, promoting the structural evolution of the coal. In addition, aliphatic carbon transfers more from raw coal into the extract than aromatic carbon in the whole extraction process, which is accompanied by the disappearance of carbonyl groups. Furthermore, the reduction of particle size can promote the extraction effect of the extractant on the coal powder, and reduce the proportion of aliphatic carbon in the residue. The work introduces the correlations among the raw coal, residue and extract from a carbon skeleton point of view, providing a reference for elucidating the solvent extraction mechanisms. The results shed light on better understanding the coal structure and its further molecular modeling.

Eulerian–Eulerian RSTM-PDF Modeling of Turbulent Particulate Flow

A novel 3D computational model was developed for the turbulent particulate two-phase flow simulation in the rectangular channel. The model is based on the Eulerian approach applied to 3D Reynolds-averaged Navier–Stokes modeling and statistical Probability Distribution Function method. The uniqueness of the method lies in the direct calculation of normal and transverse components of the Reynolds stresses for both gas and particles. Two cases were examined: a conventional channel flow and grid-generated turbulence flow. The obtained numerical results have been verified and validated by the experimental data, received from the turbulent particle dispersion test. The computed values of the particles’ turbulent dispersion and the maximum value of the particulate concentration distribution show good agreement with the experimental results. The examples are ranged from coal and other bulk material pneumatic transport, vertical fluidized beds, coal gasifiers, and chemical reactors.

Development and evaluation of coal mine waste materials for gainful utilization

Coal mine overburden and thick inseam parting materials found in the lower Gondwana basin are treated as mine wastes. Unused fly ash from coal-fired plants is another waste material. This investigation focused on using these wastes to develop better composite materials. Composite materials of varying compositions with coal mine wastes from 50 to 90% and fly ash from 10 to 50% with 2–6% cement additives were developed and evaluated. Their physical, chemical and geotechnical properties were determined. Ordinary Portland cement strongly influenced the geotechnical parameters. The fly ash content was optimized for unconfined compressive strength (UCS) and California bearing ratio for both mine wastes. Composite materials with 70% overburden, 30% fly ash and 6% cement showed a UCS of 4.01 MPa at 56 days. Composites with 80% inseam parting, 20% fly ash and 6% cement produced 4.90 MPa UCS at 56 days. Linear correlations were observed between fly ash percentage in the two composites and their UCS values. Pearson’s and Spearman’s coefficients produced a high correlation of −0.9 for the composite prepared with parting material. Microstructural analysis showed calcium silicate hydrate gel formation occurring at 28 days. The composites meet the strength criterion for the base and subbase of coal mine haul roads.

Effects of source materials on desorption kinetics of carcinogenic PAHs from contaminated soils

Research investigating the desorptive behaviour of PAHs from contaminated soils often overlooked the effects of source materials, especially coal tar and coal tar pitch and materials alike. In this study, a refined experimental approach was adopted to establish a simple-to-complex continuum of systems that allow the investigation of desorption kinetics of benzo(a)pyrene (BaP) and 3 other carcinogenic PAHs (cPAHs) over an incubation period of 48 d. By comparing the modelled desorption parameters, elucidation of the effects of PAH source materials on their desorptive behaviour was achieved. Desorption of cPAHs from coal tar and pitch was enhanced when they were added to soils, with rapidly desorbing fraction (Frap) of BaP increased from 0.68% for pitch to 1.10% and 2.66% for pitch treated soils, and from 2.57% for coal tar to 6.24% for coal tar treated soil G and 8.76% for coal tar treated sand (1 d). At 1 d, desorption of target cPAHs from solvent and source material spiked soils generally followed the order of solvent > coal tar > pitch. Increases in Frap of cPAHs were observed in coal tar-treated soils after 48 d soil incubation (0.33%–1.16% for soil M, p ≥ 0.05, 6.24%–9.21% for soil G, p < 0.05) and was attributed to the continuous migration of coal tar as a non-aqueous phase liquid (NAPL) into soil pore structures. Slow desorption was dominated by source materials, whereas the extents and rates of rapid desorption (Frap and krap) were more controlled by the quantity of soil organic matter (SOM), rather than quality of SOM (as in solvent-spiked soils). The results of this study challenged the role of PAH source materials as ‘sinks’ and led to the proposed roles of coal tar and pitch and source materials alike as ‘reservoirs’ with a risk-driven perspective.

Improved YOLOv7 Network Model for Gangue Selection Robot for Gangue and Foreign Matter Detection in Coal.

Coal production often involves a substantial presence of gangue and foreign matter, which not only impacts the thermal properties of coal and but also leads to damage to transportation equipment. Selection robots for gangue removal have garnered attention in research. However, existing methods suffer from limitations, including slow selection speed and low recognition accuracy. To address these issues, this study proposes an improved method for detecting gangue and foreign matter in coal, utilizing a gangue selection robot with an enhanced YOLOv7 network model. The proposed approach entails the collection of coal, gangue, and foreign matter images using an industrial camera, which are then utilized to create an image dataset. The method involves reducing the number of convolution layers of the backbone, adding a small size detection layer to the head to enhance the small target detection, introducing a contextual transformer networks (COTN) module, employing a distance intersection over union (DIoU) loss border regression loss function to calculate the overlap between predicted and real frames, and incorporating a dual path attention mechanism. These enhancements culminate in the development of a novel YOLOv71 + COTN network model. Subsequently, the YOLOv71 + COTN network model was trained and evaluated using the prepared dataset. Experimental results demonstrated the superior performance of the proposed method compared to the original YOLOv7 network model. Specifically, the method exhibits a 3.97% increase in precision, a 4.4% increase in recall, and a 4.5% increase in mAP0.5. Additionally, the method reduced GPU memory consumption during runtime, enabling fast and accurate detection of gangue and foreign matter.

Mass Spectrometric Evaluation of the Catalytic Deoxygenation of Soluble Organic Matter in Xiaolongtan Lignite

The organic matter in Xiaolongtan lignite was thermally dissolved by cyclohexane, methanol and isopropanol (2-propanol) in sequence to obtain thermal dissolution (TD) extracts. Co-Mo/γ-Al2O3 was used as the catalyst for the catalytic hydrogenation of TD extracts to remove oxygen. Both TD extracts and the corresponding catalytic products were analyzed by the combination of gas chromatography/mass spectrometry (GC/MS) and Orbitrap MS to reveal more molecular details. GC/MS analysis shows that cyclohexane can extract low polar organic matter in coal, while methanol and isopropanol as nucleophilic reagents can break C-O bonds in coal, thus removing oxygen. Catalyst can trigger the fracture of alkyl chains and the activation of H2, thus promoting the removal of oxygen atom and the generation of aromatics. Double bond equivalent (DBE) value and carbon number (CN) were obtained through Orbitrap MS data. The decrease of both DBE and CN after catalytic conversion indicates the breaking of bridged bonds. The introduction of various MS systems provides an effective analytical tool for studying the catalytic deoxidation of lignite, thereby guiding the conversion of lignite to clean liquid fuels and high value-added chemicals. Co-Mo/ γ- Al2O3 catalysts activates H2 to H⋯H, which further splits into H+ and H−. H⋯H deoxygenates by hydrogenating C=C bond, attacking C-O bond or directly attacking oxygen atom. H+ will preferentially attack oxygen atom with high electronegativity, and break Cal-O bridge bond to achieve deoxygenation, thus reducing the relative abundance of oxygen containing compounds.

Multiscale in-situ elemental characterization of critical elements in low rank coal, implications for modes of occurrence

This study investigated the distribution characteristics and modes of occurrence of rare elements (Li, V, Co, Mo, Ni, Sb, W, Nb), dispersed elements (Ga, Ge), and rare earth elements (REEs) in two selected coal samples: the Al-Li-Ga-rich coal from the Jungar Coalfield in the Ordos Basin, China, and the Ge-rich coal from the Shengli Coalfield in the Erlian Basin, China. Multiscale in-situ elemental characterization techniques, including BSE-EDS, EMPA mapping, and LA-ICP-MS mapping, were used for this purpose. The results showed that in the Al-Li-Ga-rich Jungar coal, Li was mainly associated with kaolinite with various origins, dominated by epigenetic kaolinite, followed by syngenetic kaolinite. Gallium was highly concentrated in organic matter, led by collodetrinite, followed by collotelinite. The majority of Nb was associated with organic matter, while a minority was distributed in Al-bearing minerals, including boehmite and epigenetic and syngenetic kaolinite. In the Ge-rich Shengli coal, Ge, W, and Sb were consistently distributed in coal and concentrated in organic matter, mainly semifusinite. V was widespread in organic matter, including textinite, fusinite, and semifusinite. Cobalt, Mo, and Ni occurred in a similar distribution and were associated with organic matter, led by collodetrinite in the Al-Ga-rich coal and cutinite in the Ge-rich coal. REEs, except for La and Ce, were associated with organic matter, led by vitrinite in Al-Ga-rich coal and huminite in Ge-rich coal. Lanthanum and Ce were highly concentrated in La, Ce-rich minerals, even if they were widespread in organic matter as well. The visualized results of this study confirm most of the previous findings obtained from indirect analyses but also reveal some differences. Gallium was rarely detected in Al-rich minerals such as boehmite and kaolinite, but highly concentrated in organic matter. Lithium was detected in both epigenetic and syngenetic kaolinite. Ge, W, and Sb were organically associated and concentrated in semifusinite in Shengli Ge-rich coal. Overall, this study provides a way to determine the modes of occurrence of trace elements in organic matter in coal, and these findings could be applied to coal from other geological backgrounds.

Experimental Study of Mechanical Properties and Failure Characteristics of Coal-Rock-like Composite Based on 3D Printing Technology.

Coal contains cracks and has strong heterogeneity, so the data dispersion is large in laboratory tests. In this study, 3D printing technology is used to simulate hard rock and coal, and the rock mechanics test method is used to carry out the coal-rock combination experiment. The deformation characteristics and failure modes of the combination are analyzed and compared with the relevant parameters of the single body. The results show that the uniaxial compressive strength of the composite sample is inversely proportional to the thickness of the weak body and directly proportional to the thickness of the strong body. The Protodyakonov model or ASTM model can be used as a verification method for the results of a uniaxial compressive strength test of coal-rock combination. The elastic modulus of the combination is the equivalent elastic modulus, and the elastic modulus of the combination is between the elastic modulus of the two constituent monomers, which can be analyzed using the Reuss model. The failure of the composite sample occurs in the low-strength material, while the high-strength section is rebounding as an extra load on the low-strength body, which may cause a sharp increase in the strain rate of the weak body. The main failure mode of the sample with a small height-diameter ratio is splitting, and the failure mode of the sample with a large height-diameter ratio is shear fracturing. When the height-diameter ratio is not greater than 1, it shows pure splitting, and when the height-diameter ratio is 1~2, it shows a mixed mode of splitting and shear fracture. The shape has a significant effect on the uniaxial compressive strength of the composite specimen. For the impact propensity, it can be determined that the uniaxial compressive strength of the combination is higher than that of the single body, and the dynamic failure time is lower than that of the single body. It can hardly determine the elastic energy and the impact energy of the composite with the relationship to the weak body. The proposed methodology provides new cutting-edge test technologies in the study of coal and coal-like materials, with an exploration of their mechanical properties under compression.

The Permian gas potential of the Taroom Trough, Queensland: new ideas to unlock a multi-TCF play

The Taroom Trough in Queensland is the main synclinal depression and southern extent of the Bowen Basin. Both the Bowen Basin and the overlying Surat Basin have been the focus of Australia’s coal seam gas (CSG) liquefied natural gas (LNG) export industry since 2014, but with CSG production now in decline and with a greater focus on domestic gas, it is timely to review the potential of new plays in this region. Although exploration and development in the Taroom Trough over the past decade have focussed on shallow Permian and Jurassic CSG resources, the early hydrocarbon potential of the trough was realised through conventional discoveries. Regardless of the reservoir, all conventional hydrocarbons in the trough have been typed to the same prolific Permian coals. These source rocks produce enormous volumes of oil and gas, yet only a small percentage of those volumes have been trapped in known conventional structures. This implies that a significant volume of oil and gas could remain trapped in tight reservoirs, including Fractured Thermally Mature Coals. Elixir Energy Limited plans to commence a drilling program in 2023 in ATP2044 (Grandis Gas Project) to unlock the gas potential of the Taroom Trough. The project will investigate the potential of Permian coals and sandstones at &gt;3700 m depth using new understandings developed from recent studies into the critical role of elastic rock properties and stress anisotropy on coal fracture growth. This paper describes the opportunity that Elixir has identified and details the legacy technical work in the area and new research and ideas which have since evolved.

Influence of Gas Pressure on the Failure Mechanism of Coal-like Burst-Prone Briquette and the Subsequent Geological Dynamic Disasters

Rock bursts and coal and gas outbursts are geodynamic disasters in underground coal mines. Laboratory testing of raw coal samples is the dominant research method for disaster prediction. However, the reliability of the experimental data is low due to the inconsistency of the mechanical properties of raw coal materials. The utilization of structural coal resources and the development of new coal-like materials are of significance for geodynamic disaster prediction and prevention. This paper studies the failure characteristics and dynamic disaster propensities of coal-like burst-prone briquettes under different gas pressures. A self-made multi-function rock–gas coupling experimental device was developed and burst-prone briquettes were synthesized, which greatly improved the efficiency and precision of the experimental data. The results showed that the burst proneness of the briquette was thoroughly reduced at a critical gas pressure of 0.4 MPa. When the gas pressure was close to 0.8 MPa, both the bearing capacity and the stored burst energy reduced significantly and the dynamic failure duration extended considerably, indicating the typical plastic-flow failure characteristics of coal and gas outbursts. The acoustic emission monitoring results showed that with the increase in gas pressure, the post-peak ringing and the AE energy ratio of coal samples increased, suggesting that the macroscopic damage pattern changed from bursting-ejecting of large pieces to stripping–shedding of small fragments adhered to mylonitic coal. In addition, the transformation and coexistence of coal failure modes were discussed from the perspectives of coal geology and gas migration. This study provides a new method for the scientific research of compound dynamic disaster prevention in burst coal mines with high gas contents.

Occurrence Modes of Critical Metals (Li+ and Ge4+) in the Organic Molecular Structures of Coal: A Density Functional Theory Study.

To explore the mechanism of critical metal (Li+ and Ge4+) occurrence in the organic molecular structures of different rank coals, simulations were investigated using quantum chemical density functional theory. In this paper, Wender lignite, bituminous, and anthracite molecular models were used as organic molecular structures in coal. The electrostatic potential (ESP), frontier molecular orbitals, and Mulliken charges were used to identify adsorption sites in organic molecular structures. Mulliken charge, bond length, Mayer bond order (MBO), and adsorption energy values were used to estimate the binding conformation and strength between organic molecular structures and critical metals (Li+ and Ge4+). The results showed that the negative ESP, the highest occupied molecular orbitals, and negative Mulliken charges in the organic molecular structures were located at the O atom of oxygen functional groups and the aromatic structures, respectively, which were the active sites for critical metal adsorption. Mulliken charge transfer, bond length, MBO, and adsorption energy data suggested that the binding of Li+ with organic molecular structures was controlled by the carbonyl group (C=O), while the aromatic structures had less effect on the occurrence of Li+ in the organic molecular structures. The maximum adsorption energy value for binding Li+ with organic molecular structures was -742.16 kJ/mol. The Ge4+ ions not only showed strong binding ability with oxygen functional groups, but also Ge4+ formed thermodynamically stable half-sandwich complexes with aromatic structures. Therefore, the coal rank had little effect on the binding of Ge4+ with organic molecular structures. Moreover, the binding of Ge4+ with organic molecule structures was enhanced by the synergistic interactions of oxygen functional groups and aromatic structures. The adsorption energy values were up to -8511.43 kJ/mol. The adsorption of organic matter in coal to critical metals (Li+ and Ge4+) generated changes in the spatial configuration of the organic molecular structure, including local twisting of the organic molecular structure in lignite and bending of the aromatic structure in anthracite.

Effect of demineralization on pyrolysis characteristics of LPS coal based on its chemical structure

The critical issue in developing mature Oxy-Coal Combustion Steam System technology could be the reactivity of demineralized coal which, is closely related to its chemical structure. The chemical structures of Liupanshui raw coal (LPS-R) and Liupanshui demineralized coal (LPS-D) were analyzed by FTIR and solid-state 13C-NMR. The pyrolysis experiments were carried out by TG, and the pyrolysis kinetics was analyzed by three iso-conversional methods. FTIR and 13C-NMR results suggested that the carbon structure of LPS coal was not altered greatly, while demineralization promoted the maturity of coal and the condensation degree of the aromatic ring, making the chemical structure of coal more stable. The oxygen-containing functional groups with low bond energy were reduced, and the ratio of aromatic carbon with high bond energy was increased, decreasing the pyrolysis reactivity. DTG curve-fitting results revealed that the thermal weight loss of LPS coal mainly came from the cleavage of aliphatic covalent bonds. By pyrolysis kinetics analysis of LPS-R and LPS-D, the apparent activation energies were 76 ± 4 to 463 ± 5 kJ/mol and 84 ± 2 to 758 ± 12 kJ/mol, respectively, under different conversion rates. The reactivity of the demineralized coal was inhibited to some extent, as the apparent activation energy of pyrolysis for LPS-D increased by acid treatment.

Effects of coals microscale structural features on their mechanical properties, propensity to crushing and fine dust formation

The work is dedicated to revealing the structural features of coals with different ranks, such as anthracites, metaanthracite and graphite, that determine their ability to crush and form fine dust. For this purpose, a combination of various nanoindentation techniques and Raman spectroscopy was used. The mechanical behavior of the selected coals was investigated by cyclic nanoindentation with increasing peak load and quasi-static loading. The alteration of the mechanical properties was studied by analysis of elastic moduli and damage indices Rw. Three groups of coals were identified based on their propensity to crushing during cyclic nanoindentation. Coals assigned to the first and second groups are characterized by local destruction in the contact zone with the indenter and the formation of a core of crushed material. Coals assigned to the third group are characterized by bulk destruction (outside the zone of contact with the indenter). In general, the ability of coals to fracture under mechanical loading decreases in the series of metamorphism due to microscale compaction of vitrinite matter. In the series of anthracite, metaanthracite and graphite, it is established that the coal matter compaction takes place for the anthracite and metaanthracite, whereas graphite reveals rather different behavior due to abrupt change of its structure. The ratios between the amorphous and crystalline phases of carbon (S) were determined by deconvolution of coals Raman spectra. The propensity of coals to crushing (a damage index Rw) increases with growth of the proportion of amorphous carbon in the coal matter. For the considered coals and metaanthracite, it is established that the proneness to destruction outside the contact zone with the indenter is determined by the ratio of amorphous and crystalline carbon of 1 and higher. When S parameter is lower than 1, the coals are being crushed only in the zone of contact with the indenter.

Experimental Study on Catalytic Action of Intrinsic Metals in Coal Spontaneous Combustion.

In order to study the effect of inherent metals in coal on spontaneous combustion, Hongmiao lignite and Hongqingliang long-flame coal were demineralized by hydrochloric acid, the raw coal and demineralized coal were characterized by Fourier transform infrared spectrometry, X-ray diffraction, and synchronous thermal analysis experiments, and the corresponding ash content was detected by inductively coupled plasma mass spectrometry. The results show that the effect of demineralization on the volatile matter of low-rank coal is small, and the change of crystallite structure is not significant. The removed parts are mainly water-soluble salts and soluble minerals, such as carbonates and metal ions, that are not tightly bound to the organic matter of coal structure. The removed metal elements are mainly alkali metals Na and K, alkaline earth metals Ca, Mg, Sr, and Ba, and transition metals Fe, Mn, Ti, and so forth. The temperatures corresponding to the end of weight loss, ignition, and maximum weight loss rates were elevated on the thermogravimetric curves of the demineralized coal samples. The heat absorbed by evaporation of water in coal and the heat released by oxidation and combustion of coal are decreased to different degrees, indicating that the spontaneous combustion tendency of coal after demineralization is reduced, and alkali metal, alkaline earth metals, and transition metals in coal have a catalytic effect on spontaneous combustion of coal. After adding the metal chelating agent ethylenediaminetetraacetic acid (EDTA), the apparent activation energy decreased by 33.08 and 2.42%, respectively. EDTA and the alkali metal, alkaline earth metal, or transition-metal ions formed a stable chelate in coal. The catalytic activity of metals is weakened or even lost, thereby inhibiting spontaneous combustion of coal, and verifying the catalytic effect of internal metals in coal on the spontaneous combustion of coal.