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Great attention has been focused on uncovering the physics of seismic wave attenuation in rocks in the past few decades. However, the contribution of different attenuation mechanisms on attenuation is not completely clear in coal. We use the fractal viscoelastic model to describe the P-wave attenuation in coal, and the model has a good approximation to the constant-Q model when choosing lower fractional order α . We experimentally measured attenuation in dry and water-saturated coal samples in the frequency range of 10–250 Hz, at room temperature, and approximately room pressure. Attenuation in the dry sample is frequency independent and the fractal viscoelastic model curves fit well with the data when α = 0.056 . For the partial water saturation cases, attenuation is frequency dependent, and the simple viscoelastic attenuation theory cannot describe the strong attenuation in seismic band; when water saturation is high ( ≥ 80 % ), we need wave-induced fluid flow mechanism to explain the high Q - 1 values. The final contribution of viscoelasticity to attenuation is about 63%, while the final contribution of wave-induced fluid flow mechanism to attenuation is about 37% in the test. [ABSTRACT FROM AUTHOR]

To investigate the effect of moisture content on coal in cryogenic treatment, based on a gas-containing coal cryogenic treatment simulation testing system and an automated mercury intrusion porosimeter, temperature changes, strains, and characteristic parameters of the pore structure of coal after cryogenic treatment were determined. In addition, a thermal–water–mechanical coupling theoretical model was established using COMSOL software to simulate the changes in temperature and volume of coal. It was observed that moisture content was correlated negatively with the rate of temperature drop of coal and correlated positively with the frost heave strain. After cryogenic treatment, the final volume of coal decreased and the pores increased. The experiment revealed that frost heave heat extended the temperature stabilization time by an average of 27%, while methane adsorption heat had almost no effect. It is recommended to control the moisture content of coal at around 5% when using cryogenic treatment for anti-outburst, while for frozen coring, the moisture content should be controlled below 3%. The research results provide significant understanding of changes caused by cryogenic treatment on coal and supply practical information for optimizing the industrial production application of cryogenic treatment on coal. [ABSTRACT FROM AUTHOR]

Coal-and-gas outbursts represent a significant hazard in coal mining, with gas expansion energy (GEE) in coal seams being a primary energy source. Accurate GEE assessment is vital for outburst prediction and mitigation, thereby enhancing mining safety. Traditional calculation models have struggled with limited understanding of outburst mechanisms and experimental constraints, leading to broad GEE estimates with considerable discrepancies. Addressing this gap, this study introduces an experiment-driven, highly practical calculation model, along with innovative experimental methods to measure accurately key determinants of GEE: fracture porosity, CH4 desorption amount, and gas pressure in coal seams. For the first time, this study employed remade and raw coal columns as media to simulate accurately the real conditions of tectonic and raw coal seams for exploring the coupling effects of stress and gas pressure on GEE. This study calculated the GEE as stress increases from 5 to 50 MPa and gas pressure decreases from 2 to 0.5 MPa. The results indicate that, for two remade coal columns, the GEE decreased from 1870 to 62 kJ/t and from 2039 to 356 kJ/t while for the raw coal column, the GEE dropped from 130 to 6 kJ/t. [ABSTRACT FROM AUTHOR]

This study investigates the production of biomethane, and variation in microbial community and coal molecular structures using gas chromatography, 16S rRNA high-throughput sequencing and Fourier transform infrared spectroscopy. Additionally, the factors influencing microbial community structure at a molecular level are discussed. The results demonstrate that bituminous coal exhibits a higher biomethane yield than anthracite coal. In bituminous coal samples, Escherichia and Proteiniphilum are the predominant bacteria at day 0, while Macellibacteroides dominates from days 5 to 35. Methanofollis is the dominated archaea during days 0 to 15, followed by Methanosarcina on day 35. In anthracite coal samples, Soehngenia is the dominant bacterial genus at day 0; however, it transitions to mainly Soehngenia and Aminobacterium within days 5–15 before evolving into Acetomicrobium on day 35. Methanocorpusculum is predominantly found in archaeal communities during days 0–15 but shifts to Methanosarcina on day 35. Alpha diversity analysis reveals that bacterial communities have higher species abundance and diversity compared to archaeal communities. Redundancy analysis indicates a significant correlation between coal molecular structure and bacterial community composition (P value < 0.05), whereas no correlation exists with archaeal community composition (P value > 0.05). The research findings provide theoretical support for revealing the biological gasification mechanisms of coal. [ABSTRACT FROM AUTHOR]

Deep close distance coal seam mining is affected by the goaf of upper coal and remaining coal pillar, and the roadway of lower coal is difficult to maintain stability. By means of theoretical analysis, physical simulation test and numerical simulation, this paper analyzes the failure characteristics of roadway in deep close distance coal seam and the evolution law of stress field, and optimizes the reasonable layout of lower coal roadway. The results show that: (1) The analytical formula of the evolution of the floor principal stress difference with depth is derived theoretically, and the distribution law of the shear stress of the rock mass in the floor of the coal seam is obtained. (2) The airway below the goaf can maintain good stability. High stress accumulation phenomenon occurs in the transport roadway below the coal pillar, which can not keep stable. (3) Due to the stress difference under the goaf and the coal pillar, the shear stress increases and the rock mass is damaged, and the left gang of the transport roadway is prone to instability destruction. (4) By comparing the distribution characteristics of plastic zones of transport roadway at different locations, it is determined that the transport roadway is more appropriate to be arranged 45 m below the coal pillar from the goaf. [ABSTRACT FROM AUTHOR]

Exploration of secondary resources for isolation of valuable constituents, such as rare earth elements (REEs) and trace elements (TEs), is of importance owing to the need to identify new domestic sources and reduce reliance on imports. The present study systematically discusses the distribution of REEs and TEs in core samples from the coal block of Bhalukasba Surni {(B1(125 m)-B9 (409 m)} located in Rajmahal coalfield, Jharkhand, India, which has not been investigated previously for its geochemistry. The studied coal samples were found to be enriched in TEs whose abundances were in the order of Mn > Mo > Zr > Ni > Cr > V > Cu > Zn > Pb, and REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Tm, Yb, Lu) along with Sc and Y. The average concentration of REEs with yttrium (ΣREY) on an ash basis was 528 ppm, which is significantly higher than the world average for coal ash (435 ppm). Of the samples investigated, B3 (182–184 m) and B8 (396–399 m) demonstrated relatively higher concentrations of potentially economic elements, with B3 containing a higher proportion of middle to heavy REEs Gd, Dy, Ho and Er, and B8 showing relative enrichment in Nd and Y. On dry whole coal basis, B6 (275–278 m) showed a considerably higher concentration of Ge (55 ppm) than other samples, whereas the concentration of Zr varied in the range of 90–160 ppm in the whole coal block. X-ray diffraction studies revealed the presence of quartz, keatite, hematite, zircon, anatase and orthoclase in the coal ash samples prepared at 815 °C. REEs exhibited prominent positive correlation with Al2O3 (0.4 < r > 0.9) which is supportive of their residence in primary clay minerals such as kaolinite and illite-smectite. Additionally, a positive correlation of REEs with P2O5 (0.4 < r > 0.9) suggests their association with phosphate minerals (such as monazite, xenotime, apatite). Positive correlation with TiO2 (r > 0.7) corroborates the possible association of REEs with anatase. The morphology of the coal ash samples viewed in SEM showed the presence of Al2O3 and SiO2 enriched irregular-sponge particles likely derived from partly-fused clay minerals, which accounted for the lower extent of REE encapsulation. The Bhalukasba Surni coal block is potentially of economic importance due to its enrichment in Ge, Zr, and the REEs. Highlights: A systematic study on the distribution of REEs and TEs in the coal block of Bhalukasba Surni in Rajmahal coalfield, Jharkhand, India was performed. The average concentration of ΣREY on an ash basis was 528 ppm as compared to the world average of 435 ppm. Enrichment of trace elements followed the order of Mn > Mo > Zr > Ni > Cr > V > Cu > Zn > Pb. X-ray diffraction studies revealed the presence of quartz, keatite, hematite, zircon, anatase and orthoclase in the coal ash samples prepared at 815 °C. [ABSTRACT FROM AUTHOR]

Solving the problem of gas extraction from low-permeability coal seams is an urgent issue in the global coal industry, and exploring green and efficient mining methods has potential applications in this field. In this study, the No. 9 coal seam of the Guizhou Longfeng Coal Mine was selected as the research object. The method of using a hydraulic horizontal slit to create a compensation space and then synergizing it with the coal body’s own stress to decompress and increase the permeability of the coal body was studied through similarity simulation and numerical simulation experiments. This study showed that the slit can cause the overall development, expansion, and penetration of coal seam fissures. Thereby, a large number of fissures are produced in the coal seam and its upper rock layer, which form, as a whole, a “positive trapezoid” shape. The three stages of the slit produced 165, 487, and 1572 fissures, which unpressurized and increased the penetration of the coal and rock body. The slit causes the upper coal body to lose its support, and the original stress balance of the coal and rock is broken, forming a decompression zone. At the same time, the coal body below starts to expand and deform after losing the vertical stress. The decompression zone gradually expands up and down, and the stress on both ends of the compensation space becomes larger, forming a stress concentration area. After the overall displacement of the coal seam caused by the slit, a “positive triangle” area is formed. In the upper part of the area, six displacement dividing lines are created, which form five areas. The displacement shows the distribution characteristics of a large displacement in the middle and a small displacement at both ends. The results of the similarity simulation and numerical simulation experiments were verified. The study provides a new way of thinking for effectively preventing coal and gas protrusion and improving mining efficiency. [ABSTRACT FROM AUTHOR]

As a typical sedimentary rock, coal seams are usually rich in bedding planes, which significantly affect the propagation process of hydraulic fracture (HF) network and reservoir permeability. In this study, the profile characteristics and the bedding roughness of the coal seam at depth of 2800 m from Daniudi Gas Field in China is investigated. The failure mechanism of shear-expansion effect under low pressure and dynamic shear under high pressure of coal beddings induced by the dissolution-corrosion effect of fracturing liquid is analyzed. The development process of HF network under different bedding angles, joint roughness coefficients (JRCs), stress differences, and confining pressures is numerically simulated by cohesive element method. Results show that the JRC of coal beddings has significant effects on the morphology of HF networks. When the JRC exceeds 15, a HF network structure with tensile main fractures and shear secondary cracks is developed. The shear fractures account for a considerable proportion (33–66%) multi-layer layered coal seams and should be taken seriously during reservoir reconstruction. As confining pressure increases, the total length of tensile HFs sharply decreases, while the change in the total length of shear HFs is not significant. When the confining pressure increases from 5 to 15 MPa, the length ratio of shear HFs to tensile hydraulic fractures increases from 0.36 to about 1, confirming that increasing confining pressure can promote the transformation of HF failure types from tension to shear. The ratio of secondary crack to main crack length is between 6.31 and 9.78, indicating the secondary fractures occupy an absolute proportion in the hydraulic fracture network. This study is of significance for understanding the hydraulic fracture network development in coal reservoirs. [ABSTRACT FROM AUTHOR]

To study the influence of cyclic disturbance stress on the mechanical behavior of coal during mining, a gas containing coal fluid-solid coupling servo seepage experimental system was used to conduct experimental research on the acoustic emission (AE) characteristics of gas containing coal under two stress paths of graded cyclic loading and unloading. The AE characteristics of coal damage and failure processes under different cyclic stress paths were analyzed. The research results indicate that: (1) The overall characteristics of AE signals for both graded cyclic loading and unloading paths are basically the same. With increasing of the amount of graded cyclic loading or unloading, the AE count reaches its maximum value when reaching failure, and the cumulative ringing calculation of AE increases exponentially. (2) The AE signals under the graded cyclic loading or unloading path exhibit obvious zoning characteristics. In the low and medium stress regions, the AE signal basically satisfies the Kaiser effect, while reaching the high stress region before failure, the AE signal exhibits a significant Felicity effect. (3) The concentration coefficient of AE and the intensity coefficient of the Kaiser effect have been newly defined. They are used to quantitatively characterize the extent of the Kaiser effect of AEs under graded cyclic stress. It was found that as the variation of graded cyclic stress increases, the concentration coefficient and Kaiser effect intensity coefficient both show a decreasing trend. (4) Combining the AF and RA values of AE, it was found that the coal failure signals of the two stress paths were basically similar, that is, the overall failure was mainly tensile failure, and the signals of cyclic unloading tensile failure were significantly more than those of cyclic loading. The AE signal characteristics studied in this article are of great significance for predicting coal power disasters. [ABSTRACT FROM AUTHOR]

The stability of coal pillars in fault areas is crucial for ensuring the safe passage of working faces. Based on field observations, frequent coal pillar spalling and substantial tectonic coal crumbs leakage, as well as tilting of hydraulic supports, are observed when working faces transition from primary coal to tectonic coal. To analyze the instability mechanisms behind these phenomena, this paper establishes a mechanical model of coal pillars in fault areas and analyzes the distribution of tectonic stresses and factors affecting the stability of coal pillars. The results indicate that horizontal tectonic stress adheres to an exponential function dependent on the angle factor, where (k0) is a parameter associated with the friction angle of the coal body, the dip angle of the fault, and the friction angle of the fault plane. The stability of coal pillars is influenced by factors such as roof and floor pressures, coal pillar integrity, mining height, and shield support force, with coal pillar integrity being the most critical. To ensure the smooth passage of working faces through faults, this study proposes a combined control technique of "inclined mining" and "grouting," including reducing mining heights, adjusting the slope of working face advancement, and pre-grouting of coal pillars. Industrial experiments conducted on-site have shown improved integrity of tectonic coal, enabling the working face to pass through faults smoothly and significantly increasing production efficiency. [ABSTRACT FROM AUTHOR]

This study assessed the impacts of wheat straw as a cosubstrate on coal biocoverion into methane and the associated mechanism within methane metabolic pathways. Co-digestion of coal with varying wheat straw concentrations resulted in a remarkable (1246.05%) increase in methane yield compared to that of the control (CK). Moreover, microbial analysis revealed a uniform distribution of Methanosarcinaceae (51.14%) and Methanobacteriaceae (39.90%) in the co-digestion of coal and wheat straw (CWS1) at a ratio of 3:1 (w/w) compared to other treatments such as coal and wheat straw (CWS2) at a ratio of 3:0.5. In addition, Hungatieclostridiaceae and Rhodobacteriaceae were abundant in both co-digesters, whereas the bacterial communities in the CK group were significantly different and more abundant than those in the Peptostreptococcaceae and Enterobacteriaceae groups. The key enzymes related to methanogenic metabolic pathways, including EC: 1.2.99.5 and EC: 2.1.1.86 (facilitating the conversion of CO2 into methane), and EC:1.12.98.1 exhibited significant abundance within CWS1. Aromatic compounds such as 4-(2-chloroanilino)-4-oxobutanoic acid and phthalic acid were substantially more abundant in CWS1 and CWS2 than in CK, indicating the increased bioavailability of coal to microbial activities. This novel approach demonstrates that wheat straw co-digestion with coal during anaerobic digestion modulates microbial communities and their metabolic pathways to enhance methane production from complex substrates such as coal. [ABSTRACT FROM AUTHOR]

This article presents an overview of the technology employed in the production of special types of coke obtained from non-sintering coals sourced from Kazakhstan. The microstructure of special types of coke is elucidated, and the effect of the heating rate on their microstructure and properties essential for use as a reducing agent in electrothermal processes for the production of technical silicon metal is studied. [ABSTRACT FROM AUTHOR]

The subsidence caused by coal mining could cause the destruction of roads and houses, and even the failure of infrastructures. Understanding of the mechanism of coal mining subsidence may provide early protecting to infrastructures on coming failure, but dynamic analysis of subsidence due to coal mining is currently needed. In this study we apply particle image velocimetry (PIV) method to reveal strata movement and subsidence according to the prototype and indoor physical model similarity experiment of Henan. Our result shows magnitude of the subsidence of overlying strata during the coal mining at different excavation thickness, that more coal mining thickness may produce more subsidence, and that shallower coal may cause more significant subsidence. Our result suggests that further PIV test combined with field monitoring data may be an effective measure to study subsidence mechanism and pattern helping to predict disaster caused by subsidence. [ABSTRACT FROM AUTHOR]

Borehole destressing is one of the most widely used techniques for mitigating coal bursts. Understanding the working principle of destressing boreholes, exploring the main efficiency factors, and proposing a quantitative method for determining the drilling parameters for coal burst control are essential for maximizing coal burst control. This study establishes a unified damage mechanics model of borehole bursts (that is, dynamic collapse in boreholes) and roadway coal bursts, deduces the critical indices of borehole bursts, and identifies the main factors. The theoretical relationship between the critical stresses of borehole burst and roadway coal burst is quantitatively explored, and a theoretical criterion for borehole effectiveness in coal burst control is proposed using the critical indices of borehole bursts. Finally, a design principle, determination method, and calculation formulae for the drilling parameters, which are directly related to the roadway burst risk state, coal seam thickness, coal properties, and drilling size, are proposed. The optimized drilling parameters of typical coal burst mines in Hebei and Inner Mongolia verify the engineering applicability and effectiveness of the proposed design method. This study proposes a quantitative determination method for destressing drilling parameters that supports coal burst occurrence theory. Highlights: Critical conditions for borehole bursts, directly related to the mechanical properties of coal and borehole size, are theoretically provided. Theoretical relationship between boreholes and roadway coal bursts is explored. Quantitative description of the borehole destressing principle to mitigate coal burst is provided. Theoretical criterion for boreholes to mitigate coal bursts, which is directly related to the critical conditions of borehole bursts, is provided. Quantitative method for determining the drilling parameters to mitigate coal bursts is proposed. [ABSTRACT FROM AUTHOR]

Original coal reservoir contains massive free and adsorbed methane, that directly affects the mechanical properties and permeability of coal with its unique dual effects, which may, thus, promote the gestation and occurrence of mine gas disasters. Mining disturbance and borehole drainage can facilitate the plastic rupture of surrounding rock mass, which would result in the gas migration law becoming more complex that, in turn, would be difficult to explain based on classical elastic deformation theory. Therefore, understanding elastoplastic deformation behavior and gas migration law relating to coal under engineering disturbance is crucial for preventing gas disasters. First, when mechanical and adsorption induced effects of gas on coal are considered, a concept of effective total pore pressure has been proposed. From which, calculation of plastic deformation in accordance with non-associated flow rule, a constitutive model that considered elastoplastic deformation (EPC Model) was established to simulate deformation and failure characteristics. Following that, a permeability jump coefficient was introduced to describe the sudden increase in permeability following damage and failure in coal, and an elastoplastic damage-permeability model (EPDP Model) was further deduced on basis of cubic law. Finally, through triaxial compression-seepage experimental data to verify the established EPC Model and EPDP Model. The results revealed that gas would weaken coal's mechanical properties (peak strength and elastic modulus) by changing its microstructure, whose deterioration would become more obvious with an increase of gas pressure. The changes to the permeability curve were of an "S" type, which showed a good corresponding relationship with the change trends relating to whole stress–strain curve. Both the EPC Model and the EPDP Model exhibited satisfactory matching effects with experimental data. Furthermore, EPDP Model was popularized and applied, with its universality being verified by the experimental data relating to a reduction in pore pressure seepage. This research will provide a new thinking for ensuring safe and efficient production in coal mines. Highlights: When the double effect of gas on coal were examined, Terzaghi's effective stress principle was modified appropriately, and a concept of effective total pore pressure has been proposed. The plastic strain on coal during triaxial compression was calculated, and an elastoplastic constitutive model that investigated gas action was further deduced. A permeability jump coefficient was introduced to describe permeability change following damage and failure to coal, thereby, making it possible to establish a damage-permeability model during elastoplastic deformation. The damage-permeability model was simplified appropriately, in order for it to be suitable to be employed as a classical elastic permeability model appropriate during CBM extraction stage, with its application scope of the permeability model being extended. [ABSTRACT FROM AUTHOR]

Hard carbon stands out as one of the most prospective anode materials for the storage of sodium due to its abundant resources, low cost, high conductivity, and suitable potential. In this study, S-doped hard carbon (SFC/S-3) was synthesized from a mixture of Shenfu bituminous coal (SFC) and S powder via the one-step pyrolysis method. S doping effectively enlarged the carbon layer spacing, formed -C-SOx-C- bonds, and increased the specific surface area of the hard carbon, which significantly enhanced the sodium storage capacity of hard carbons. Furthermore, coal-based graphene oxide (CGO) was used as a multi-functional binder to further boost the sodium storage performance of SFC/S-3 by reducing the surface defects and forming a conductive network. Consequently, the SFC/S-3@CGO exhibited an excellent sodium storage performance, delivering a high reversible capacity of 449.4 mAh g−1, a high-rate capacity of 224.7 mAh g−1 at 1 A g−1, and approximately 74% capacity retention after 500 cycles at 1 A g−1. This study offers a versatile approach for heteroatom doping and promotes the clean utilization of coal. [ABSTRACT FROM AUTHOR]

The presented paper is focused on the analysis of combustion behaviour and solid-state kinetic data of oxidation reactions of Soma-Manisa and Gediz-Kütahya lignite. Oxidation process was carried out with NI-TGA and tube furnace. The samples are heated up at temperature range from 25 to 1100 °C under multiple constant heating rates 10 °C/min, 15 °C/min, 20 °C/min and 30 °C/min in nitrogen atmosphere. Combustion characterizations of coal samples are studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Kinetic data analysis is based on model-free approaches by Kissinger-Akashiro-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) with the helping of data during experimental study. The estimated kinetic constants are compared with experimental results. Oxidation parameters such as weight loss rate, burn-out temperature and reactivity of coal samples are calculated. Maximum weight loss rates are estimated at 0.54%/min Soma-Manisa lignite and 0.51%/min and Gediz-Kütahya lignite at 30 °C/min heating rate. Activation energies of coal samples are exhibited in the range 37.6—63.7 kJ/mol and 41.5–74.5 kJ/mol using OFW and KAS methods, respectively. [ABSTRACT FROM AUTHOR]

Co-combustion of coal and biomass can achieve efficient and clean utilization of energy. This study investigated the combustion behaviors, gaseous pollutants (HCl, NO, SO2) emissions and coordinated control, and ash slagging characteristics of coal and CS using thermogravimetric analyzer, flue gas analyzer, and ash melting point test experiments. The results showed that the addition of CS decreased the ignition and final temperatures of coal, and the comprehensive combustibility index (CCI) increased linearly with increasing CS content. As the blending ratio of CS increased from 10 to 70%, the conversion rates of NO and SO2 decreased by 36.4% and 42.8%, respectively, but the conversion rate of HCl increased by 66.2%. When the combustion temperature increased from 750 to 950 °C, the conversion rate of HCl and SO2 increased from 63.1 to 70.1% and 28.7 to 41.3%, respectively. On the contrary, the NO conversion rate showed a slight downward trend with increasing temperature. The additives of Ca(OH)2, CaO, Mg(OH)2, MgO, and CaSiO3 all inhibited the emissions of gaseous pollutants, among which Ca(OH)2 and CaO had the best effect. The slagging characteristics of the coal would be worse after mixing with CS. However, when the proportion of CS was less than 20%, the slagging characteristics of the mixtures were close to that of coal. Moreover, co-combustion of coal and CS had a synergistic effect on combustion performances and pollutant emissions. [ABSTRACT FROM AUTHOR]

This research work presents an examination of the concentrations and modes of occurrence of environmentally sensitive elements within lignite deposits, located in Neyveli, within the Cauvery Basin of India. Coal is one of the most complex geologically formed materials, consisting of organic and inorganic matter. The inorganic mineral matter including the crystalline minerals, non-crystalline mineraloids, and elements with non-mineral associations. These lignite samples underwent complete analysis encompassing macroscopic, microscopic and geochemical assessments. The analysis reveals that the total mineral matter (MM) content, comprising significant proportions of sulphides, carbonate and argillaceous components. Geochemical characterization further elucidates the lignite's properties, with proximate analysis yielding values such as ash, volatile matter and fixed carbon and the Ultimate components analysis reveals the carbon, hydrogen, nitrogen, sulphur and oxygen. Inorganic mineral matters play a significant role in coal utilization, and also such modes of occurrence of elements provide useful geochemical information on coal formation and coal-bearing basin evolution. In this paper, we assess the associations of elements and minerals, as well as the associations of selected elements including environmentally-sensitive (e.g., S, As, U, and Hg), and some major elements (e.g., Ca, Mg, Fe, Al, and Ti) that have largely occurred in non-mineral forms in these low-rank coals. And also, comparative analysis is conducted between the concentrations of elements within the lignite samples and the values reported for World Clarke Brown Coals (WCBC). Particularly, some of these elements exhibit significantly high environmental sensitivity, demanding careful consideration in lignite extraction and utilization practices. [ABSTRACT FROM AUTHOR]

The instability and failure processes of coal-rock combinations are accompanied by the release of acoustic emission (AE) and infrared radiation (IR) signals. To investigate the characteristics of AE and IR signals during the failure process in coal-rock combinations with different ratios, and to analyze the effectiveness and applicability of the monitoring methods for these two signals in various specimen ratios. In this paper, the uniaxial compression tests were conducted on seven coal-rock combinations with different ratios by using the rock mechanics loading system and the cooperative monitoring platform of infrared and acoustic emission. The results show that (1) the AE counts for failure precursors in coal-rock combinations are positively correlated with the coal-rock ratio, whereas the AE peak counts are negatively correlated. Moreover, as the coal-rock ratio decreases, the slope of the cumulative AE count curve during the peak failure stage approaches 1. (2) During the elastic and yield stages, the maximum infrared radiation temperature (MIRT) curve fluctuates, and just before peak failure, the curve displays a distinctive "V" shape. This "V" shape becomes more pronounced as the coal-rock ratio decreases. (3) In the monitoring of damage precursors of coal-rock combinations, when the ratio of coal to rock is 1:3 or less, IR monitoring is better than AE monitoring. Conversely, when the ratio of coal to rock is greater than 1:3, AE monitoring is more suitable. Consequently, the combined monitoring of AE and IR signals can increase the reliability and precision of early warning signals for coal-rock assemblage damage precursors. [ABSTRACT FROM AUTHOR]

To study the dynamic mechanical characteristics of coal in the area affected by mining in front of the mining face under different mining methods, an improved split Hopkinson pressure bar (SHPB) was used to apply different static loads to different positions. Then, dynamic mechanical tests were conducted on coal at different positions on the mining face, analyzing the dynamic response under strong dynamic load disturbances, under three different mining layouts. Within the range of static water pressure to the peak support pressure, the dynamic strength of coal gradually increases with increasing distance from the mining face. The dynamic strength is the smallest at the peak support pressure stress, and under strong external disturbances, instability and failure are increasingly likely to occur at the peak stress. Under the same loading rate conditions, the dynamic strength of the peak stress in coal is as follows: Protective coal-seam mining (PCM) > Top-coal caving mining (TCM) > Nonpillar mining (NM). [ABSTRACT FROM AUTHOR]

Water inrush from underlying aquifers under the synergistic action of complex faults and mining activities seriously threatens the mining of coal seams in North China. The failure characteristics of the coal seam floor under complex fault conditions are the keys to understanding the water inrush mechanism during mining. To investigate floor failure characteristics and water inrush mechanisms influenced by complex fault structures, theoretical analysis and numerical simulation were carried out. An improved theoretical model is first proposed, including complex fault structures such as horst, graben, and step fault structures. The calculation formula for waterproof coal pillars under complex fault conditions is established based on the improved theoretical model. The failure and displacement characteristics of the coal floor under complex faults are analyzed via numerical simulation. Compared with those under normal mining conditions, the theoretical and numerical simulation results reveal the following: (1) Under the horst structure, the floor failure characteristics show an increase in the compression failure area on both sides, and shear failure occurs on the large-dip fault side. The simulation results reveal that the failure width on the large-dip fault side increases by 25%, indicating a failure trend toward the large-dip fault side. The width of waterproof coal pillars needs to be increased by 20% to ensure mining safety. (2) Under the graben structure, the floor failure characteristics show an increase in the compression failure area on both sides, and shear failure occurs on the small-dip fault side. The simulation results reveal that the failure width on the small-dip fault side increases by 25%, indicating a failure trend toward the small-dip fault side. The width of waterproof coal pillars needs to be increased by 40% to ensure mining safety. (3) Under the step fault structure, the floor failure characteristics show compression failure on both sides, increasing the floor compression failure area on the large-dip fault side. The simulation results show that the failure width on the small-dip fault side increases by 15%, the large-dip fault side increases by 50%, and the floor failure depth increases by 20%. The width of waterproof coal pillars needs to be increased by 50% to ensure mining safety. [ABSTRACT FROM AUTHOR]

Accurate and efficient identification of water inrush sources, as one of the three critical elements of mine water hazards, is crucial for mine water management. To identify the sources of mine water inrush effectively, a model named HBA-CatBoost is introduced. This model is established on the hybrid bat algorithm (HBA)-optimized category feature gradient boosting tree (CatBoost), and the shapley additive explanation (SHAP) method is employed to elucidate the model's decision-making process. Given the prevalent occurrence of water hazards in coal seam roofs and floors in the northern Guizhou coalfield, coupled with the challenges in pinpointing water inrush sources in mines, the HBA-CatBoost model is tested at the Longfeng Coal Mine in northern Guizhou to validate its practicality. Comparative analysis with the HBA-RF, HBA-XGBoost, CatBoost, RF, and XGBoost models demonstrates that the hybrid bat algorithm significantly enhances the classification performance of the CatBoost model, resulting in improved convergence speed and classification accuracy. The HBA-CatBoost model outperforms the aforementioned models in terms of classification effectiveness, achieving accuracy, recall, precision, and F1 scores of 96.43%, 97.22%, 96.43%, and 96.61%, respectively. The SHAP method elucidates the decision mechanism of the optimal HBA-CatBoost model, highlighting the significance of sample features and bolstering the model's credibility. These outcomes underscore the superior performance of the HBA-CatBoost model and its potential for effectively identifying water inrush sources in mines. [ABSTRACT FROM AUTHOR]

To explore the influence of surfactant concentration on the pore structure and permeability of coal samples during the chemical enhancement of coalbed methane production, different kinds and different concentrations of surfactants were added to the chemical solution, and the coal samples were soaked. Methods such as low-field nuclear magnetic resonance testing (NMR), fractal theory, permeability testing, surface tension testing, and contact angle testing were employed to analyze the variation patterns of coal sample pore structure, fractal characteristics, and permeability, and to explore the correlation between surface tension, contact angle, and the degree of pore structure development. The results show that the increase in total porosity of coal samples, the increase in the seepage pore porosity, the decrease in Dt, and the growth rate of permeability increase with the increase in surfactant concentration, and are negatively correlated with the surface tension of the solution and the contact angle of the coal-solution interface, while the decrease in Ds is not significantly correlated with surfactant concentration, surface tension, or contact angle. In terms of the erosion effect of a chemical solution on coal samples, the influence of contact angle is greater than that of surface tension, while surface tension has the greatest impact on the development of adsorption pores. By adding different surfactants, the surface tension of the chemical solution and the contact angle of the coal-solution interface can be controlled, further promoting the erosion of coal samples, which is of positive significance for the chemical enhancement of coalbed methane production. [ABSTRACT FROM AUTHOR]

In this study, the effects of coal seam slope, caving height and top coal drawing interval parameters on longwall top coal caving (LTCC) efficiency in LTCC applied in horizontal and near-horizontal thick coal seams were investigated. In addition to these researches, in the study, the relationship between top coal loss and rock mixture ratio, which are important disadvantages of LTCC, was evaluated and the importance of these parameters for LTCC was emphasized by determining the critical top coal loss and critical rock mixture ratio. As a research method, physical models that are effectively used in researching caving mechanism problems were used and a 2-dimensional physical model was developed for the study. The development processes of the physical model, test material selection processes and the suitability of the physical model are explained in detail in the study. A total of 47 physical model tests were carried out in the research. Test results showed that the caving height and top coal drawing interval are effective on the rock mixture ratio, the top coal drawing interval is effective on the top coal loss, and the caving height and coal seam slope are effective on the amount of top coal drawing. In addition, the study results showed that the relationship between top coal loss and rock mixture ratio is an important relationship for LTCC efficiency under all conditions, and the importance of critical top coal loss and critical rock mixture ratio for LTCC was revealed. Highlights: Applicability of 2D physical models in solving mining problems. Physical model development processes and critical points. Effect of coal seam slope, caving height, drawing interval parameters on LTCC efficiency. Effect of the relationship between top coal loss and rock mixing ratio on LTCC efficiency. [ABSTRACT FROM AUTHOR]

CO2 sequestered in deep coal seams (> 800 m) exists as supercritical state (ScCO2) due to high temperature and pressure, and the injection induced non-uniform in-situ stress changes would cause shear slip, affecting fracture permeability and increasing CO2-leakage risk. Thus, understanding the shear-induced permeability evolution of coal fracture subjected to ScCO2 soaking is crucial. A series of shear-flow tests under different confining pressure were conducted to study the permeability evolution of un-soaked and ScCO2-soaked fractured coal samples. The surface characteristics before and after the test was measured with 3D scanning methods to examine the shear-induced alteration of fracture geometries. The results show that, as the shear displacement increases, the permeability of coal fracture decreases at the early shearing stage, then increases due to shear dilation, but was offset by the gouge formation at the residual shear stages, leading to permeability reduction ranging from 9 to 70% under different confining pressure. After ScCO2 soaking, the mechanical strength of surface asperities is greatly reduced, resulting in an increase of 26% in asperity damage volume and a decrease of 56–90% in permeability after shear. The shear behavior after peak stress of fractured coal samples shows shear hardening, and based on which a shear constitutive model of coal fracture was built to calculate the gouge production related to shear plastic work. A theoretical permeability model was built, showing a good application to describe the ScCO2 effect on permeability of coal fracture subjected to shear stress. Highlights: Triaxial shear test was conducted to investigate the supercritical CO2 soaking effect on the permeability of coal fracture under shear slip. Long-time supercritical CO2 soaking-induced surface asperities degradation significantly affects the permeability evolution of coal fracture during shear. A theoretical model was built to characterize the supercritical CO2 soaking effect on the permeability evolution during shear. [ABSTRACT FROM AUTHOR]

Coal seams can enrich a variety of harmful trace elements under specific geological conditions. The spatial distribution of harmful trace elements in coal is extremely uneven, and the distribution characteristics of each element content are different. The harmful elements released in the process of coal mining and utilization will cause serious harm to the environment and the human body. It is of great resource significance to study the geochemistry of coal that affects the enrichment and distribution characteristics of harmful trace elements. Based on the domestic and foreign literature on coal geochemistry in Guizhou published by previous investigators, this study counted 1097 sample data from 23 major coal-producing counties in Guizhou Province, systematically summarized the relevant research results of harmful trace elements in the coal of Guizhou, and revealed the overall distribution and enrichment characteristics of harmful trace elements in the coal of Guizhou. The results show that the average contents of Cd, Pb, Se, Cu, Mo, U, V, As, Hg, and Cr in coal of Guizhou are higher than those in Chinese coal and world coal. A variety of harmful trace elements in the coal of Guizhou have high background values, especially in Liupanshui, Xingyi and Qianbei coalfield. The enrichment of various harmful trace elements in the Late Permian coal in Guizhou is mainly related to the combined action of various geological and geochemical factors. The supply of terrigenous debris and sedimentary environment may be the basic background of the enrichment of harmful elements in western Guizhou, while low-temperature hydrothermal activity and volcanic ash deposition may be the main reasons for the enrichment of harmful elements in southwestern Guizhou. [ABSTRACT FROM AUTHOR]

This research presents the results of a comprehensive study of mineralogical and geochemical features of REE distribution in coals of Central Kazakhstan deposits—Karaganda coal basin and Shubarkol deposit, which have large hard coal reserves and are industrially important for the coal industry of Kazakhstan; the research is based on 205 samples of clayey interlayers and coal seams. It shows basic patterns of distribution and features of concentration for impurity elements, gives an estimate of the impurity elements concentration, including REE, defines conditions and factors of their accumulation, and studies features of their forms in coal and coal-bearing rocks, which allows estimating the mechanisms of their migration and conditions of accumulation. According to the results of geochemical indicators, the article establishes the factors of REE dislocation, reveals the composition of margin rocks that have influenced REE concentration in coal seams, and the presented latest data on mineralogy allowed to establish the ways of their transportation to the paleobasin during the syn- and epigenetic periods of formation of the coal deposits of Central Kazakhstan being researched. It was found that the coals are insignificantly enriched with heavy lanthanides from Ho to Lu. The distribution curves of UCC normalized REE values in the coals are similar and coincide, but they are less than the average value for world coal, and amount to only one-third of the UCC. It was found that the highest concentrations of all REE are characteristic of clayey interlayers and oxidized coals. The La/Yb ratio in this case increases upwards along the section, indicating mainly clastogenic mechanism of REE delivery to the coals. In coal and clay samples, the predominant mineral form of REE is light lanthanide phosphates. Identified particles of REE from minerals and their composition peculiarities suppose autigene nature of their formation. The formation of the bulk of autigene minerals occurred during the maturation of brown coals and their transformation into hard ones. [ABSTRACT FROM AUTHOR]

Mercury intrusion porosimetry (MIP) is widely used for coal pore structure characterization, however, the matrix compressibility (MC) can lead to overestimated measurement results. Determination of MC is crucial for revealing the influence of pore structure on coalbed methane (CBM) flow behavior. In this study, MIP and low temperature N2 adsorption (LT-N2A) were conducted on 15 coal samples from major coal-producing regions in Northern China. The MIP data were corrected using MC theory, and the effects of coal rank and pore structure on coal MC were analyzed. The influence of MC on fractal dimension was elucidated, and the sensitivity of three fractal models to MC was effectively evaluated. Finally, the impact of MC on the coalbed methane (CBM) exploitation was discussed. The results show that low-rank coals have higher MC than medium/high-rank coals, and the MC coefficient follows a cubic polynomial relationship with coal rank, with two inflection points located at 1.4–2.5%, respectively. Micropores and transition pores are the main contributors to MC, for corrected data, the pore volume of both types of pores decreases significantly. The corrected pore size distribution exhibits better agreement with the LT-N2A measurement results, particularly in peak position and size for pores between 5 and 50 nm. This suggests the potential of corrected MIP data to supersede the combined use of MIP and LT-N2A data. MC can lead to overestimation of the fractal dimension, with the thermodynamic model showing the lowest sensitivity to MC. After the microfractures in medium/high-rank coal are greatly compressed, the compressional deformation of micropores and transition pores begins to have a significant impact on the CBM transport. The research results are of great significance for deeply understanding the mechanism of CBM transport. [ABSTRACT FROM AUTHOR]

The results of derivatographic studies of the decomposition of oil shale and thermolysis processes in the presence of oil shale are presented. It was found that the addition of oil shale to brown or hard coal intensified the process of thermal dissolution of coal, and the solubility of the organic matter of coal increased with the amount of added oil shale; gas formation decreased and the yield of liquid products increased. The activating role of oil shale was also revealed in the processes of thermolysis of oil residues, gasification (high-temperature thermolysis) of fuel oil and tar emulsions, and preparation of bitumen compositions for road construction. [ABSTRACT FROM AUTHOR]

Under the dual pressures of environmental protection and energy security, the development and application of coal-based nanocarbon materials, supported by the technical concepts of molecular chemical engineering and nanomaterial science, is of significant importance for achieving the high-value clean utilization of coal. Furthermore, it serves as an effective means to assist in the realization of dual carbon goals. Coal, with its abundant reserves, high carbon content, and aromatic and hydrogenated aromatic groups, exhibits great advantages and potential in the synthesis of nanocarbon materials. In addition to its applications in traditional power and chemical industries, coal-based nanocarbon materials also demonstrate significant value in the field of environmental pollution control. This article succinctly summarizes the preparation methods and properties of coal-based carbon nanotubes, coal-based carbon quantum dots, and coal-based graphene, elucidates their current applications in water pollution control and governance, and anticipates their development trends in water pollution control, aiming to provide support for the clean and efficient utilization of coal and water pollution control. [ABSTRACT FROM AUTHOR]

The presence of water in coal and its interaction plays pivotal roles in the storage and migration of coalbed methane (CBM), making it imperative to understand the water-occurrence across different coal ranks to guide CBM exploitation effectively. Here, a novel method for categorizing water into condensed and adsorbed forms based on their dehydration dynamics is proposed using differential thermogravimetric curve and the Arrhenius equation, offering a straightforward process and enabling the assessment of the interaction strength between water and coal. The result indicates that the total water capacity decreases initially before subsequently increasing as coal rank increases from 0.28 to 2.33% Ro,max, with the ratio of condensed water exhibiting an S-shaped curve. Remarkably, the condensed water capacity is correlated linearly with the total pore volume. The adsorbed water in low-rank coal is controlled primarily by the level of oxygen functional groups, whereas in medium-high rank coal it is controlled primarily by the specific surface area. Based on this, the controlling equations of water capacity and coal–water structure models were established. Additionally, coal–water interaction strength decreases significantly after the first coalification jump, with the strength of low-rank coal being approximately 2.54 times higher than that of medium-high rank coal. This discrepancy arises from the combined influence of multiple oxygen functional groups in low-rank coal on adsorbed water. This paper enhances the understanding of drainage process in coal reservoirs of varying ranks, which can facilitate the efficient extraction of CBM. [ABSTRACT FROM AUTHOR]

Combining multiple monitoring methods can improve the accuracy of coal damage and fracture behavior detection. In this study, nine coal samples, each with similar P-wave velocities and masses, were subjected to joint monitoring experiments involving multiple physical parameters. The acoustic emission (AE) and resistance information of coal samples were assessed from the initiation of loading to eventual failure under diverse uniaxial loading rates. The characteristic electrical and acoustic parameters were analyzed in combination with coal damage conditions. The results show that, throughout the loading process, resistivity declined gradually with escalation of coal strain, followed by an abrupt nonlinear increase. Deformation before failure reduced coal resistivity by up to 11.39%. As the coal crack area expanded, the resistivity post-failure reached threefold the initial value. The AE ring count peak value corresponded to crack growth, and the AE energy had a power law distribution feature. The frequency band effect of the AE peak frequency was significant, and shear cracks accounted for more than 80%. Resistance and AE ring count exhibited simultaneous responses to coal failure, and the characteristic parameters of acoustic-electrical behavior demonstrated consistent patterns for cracks induced by various loading rates. The time sequence characteristics of the RSD index, which quantified the degree of resistivity fluctuation, corresponded almost exactly to the development process of coal damage described by AE, and the peak value of this index corresponded to the AE event in the time scale. The overall fluctuation degrees in resistivity of coal samples with varying damage levels showed positive correlation with the AE ring count. An acoustic-electric method for characterizing coal damage is summarized, and corresponding resistivity characteristic parameters are proposed. These parameters have a significant response law to coal damage, which is helpful in supplementing a new index for early warning of geological disasters. [ABSTRACT FROM AUTHOR]

With the increase of mining scope, rockburst occurs frequently, but its generation mechanism has not been understood comprehensively. Based on a rockburst in the coal pillar area of high tectonic stress zones (HTSZs), this study analyzed the distribution characteristics of large-energy microseismic (MS) events by using data statistics. The mechanical cause of the MS event that induced the rockburst was revealed by means of seismic moment tensor inversion. On this basis, by using numerical simulation, this study explored the distribution characteristics of static load in rockburst area and the effect of dynamic load in the floor, and then proposed the rockburst mechanism. The results show that under the squeezing action, the floor strata in HTSZs implode and transmit energy outward in the form of stress waves. This causes the cumulative damage and stress of the coal body in the fast track of coal pillar area increase in a short time. Since the coal in this area has already been in the critical stress state, small stress changes may lead to coal failure and rockburst. In this case of rockburst, the high static load of coal is the main force source, and the dynamic load plays a role in increasing coal body damage and inducing rockburst. Combined with seismic moment tensor inversion and numerical simulation, this paper proposes a rockburst research scheme, which makes the simulation of dynamic load more reasonable. The results provide the theoretical basis for rockburst control under similar conditions. [ABSTRACT FROM AUTHOR]

The primary objective of this study was to evaluate the bound fractions of mercury (Hg), physicochemical parameters, and mineral composition of coal. Coal samples were collected from various depths within Block-VII of the Thar coalfield in Pakistan. The Hg associated with different chemical fractions of coal was extracted using a sequential extraction scheme as per the community bureau of reference (BCR) protocol. This study utilized both the BCR-sequential extraction method (BCR-SEM) and a single-step sequential extraction based on an ultrasonic-assisted method (SSE-UAM) for the fractionation analysis of Hg in coal. The extraction methodologies, BCR-SEM and SSE-UAM, were specifically designed for analyzing Hg fractionation in coal samples. The SSE-UAM offers an operational advantage, requiring only 2 h compared to the 51 h needed for BCR-SEM. The analyses were validated using standard reference material (SRM-1635a) and the spiking addition method, achieving a recovery percentage of 97.1% for total Hg concentrations using the pseudo-extraction method in SRM-1635A. Total Hg content in the coal samples ranged from 0.60 to 2.34 µg g−1 across four different coal seams from Block-VII of the Thar coalfield. Additionally, Hg concentration was observed to decrease with increasing depth, attributed to changes in mineralogical composition. The highest concentration of Hg was detected at a depth of 200–203 m, while the lowest concentration was at a depth of 152–154 m. The concentration of Hg in various fractions was 32–60% in the acid-soluble fraction, 1.72–4.92% in the reducible fraction, and 9.58–50.8% in the oxidizable fractions. The coal sample characteristics were analyzed using an elemental analyzer and scanning electron microscopy with energy-dispersive spectroscopy. Cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the extracted fractional concentration of Hg in coal. [ABSTRACT FROM AUTHOR]

Coalbed methane thermodynamic extraction, as an emerging ECBM recovery method, can effectively improve gas recovery rates. And clarifying methane diffusion and migration law in coal under thermal stimulation is crucial for the selection of its process parameters. Based on laboratory methane adsorption-release experiments, the evolution law of methane diffusion characteristics with temperature and pressure was studied, and the control mechanism of heat-dependent methane diffusion behavior was explored. The results show that both thermal stimulation and high adsorption pressure accelerated the methane diffusion rate in coal. Adsorption pressure had little effect on methane diffusion percentage, but thermal stimulation promoted a significant increase in diffusion percentage and improved the net methane yield. The influence mechanisms of adsorption pressure and thermal stimulation on methane diffusion characteristics are elucidated in relation to the amount and proportion of methane-activated molecules in the diffusion process. The constant diffusion coefficient of methane is heat-dependent, based on which a diffusion model is derived to accurately predict the methane release process in coal. Additionally, temperature has a more important effect on transient diffusion coefficient than pressure. Thermal stimulation leads to a net increase rather than a decrease in diffusion coefficient in the early diffusion stages and can also accelerate the attenuation of diffusion coefficient, with this intensifying effect becoming more pronounced at higher temperatures. The research results can provide some reference for the determination of coal seam gas content and the selection of heat injection process parameters. [ABSTRACT FROM AUTHOR]

This paper studied the minimum ignition temperature of the dust layer (MITL) of oil-immersed coal and the heat effect and apparent activation energy (Ea) of raw coal and oil-immersed coal. Based upon the results, the addition of crude oil to coal could reduce the MITL, ameliorate the ignition sensitivity, and increase the heat effect of coal dust. The average Ea of oil-immersed coal was lower than that of raw coal. When there was a 10.8 mass% oil-immersed concentration of oil-immersed coal with the most acceptable particle size (≤ 75 μm), the MITL was 24.24% lower than that of raw coal. Furthermore, the exothermic value of oil-immersed coal was 26.67% higher than that of raw coal. Besides, the average Ea of oil-immersed coal was 26.8% lower than that of raw coal. The research herein is expected to improve people's understanding of the thermal hazard characteristics of oil-immersed coal dust, reduce the risk of coal dust fires and explosions, and ensure production safety. [ABSTRACT FROM AUTHOR]

Since accidents such as roof caving, rock fragmentation, and severe deformation are particularly likely to occur during roadway excavation in soft and thick coal seams, grasping the range and distribution of deformation and fracturing of surrounding rock is of crucial for evaluating roadway stability and optimizing support design in such coal seams. In this study, based on the stress paths encountered during roadway excavation, true triaxial loading and unloading tests were carried out on soft coal, and the deformation and strength evolutions of soft coal under different intermediate principal stress conditions were analyzed. The test results show that the stress–strain relationship in the pre-peak plasticity-strengthening and post-peak plasticity-weakening stages follows a quadratic function, and the strengeth evolution conforms to the Mogi–Coulomb criterion. Moreover, analytical solutions for the displacement of surrounding rock, the radius of the broken zone, and the radius of the plastic zone of soft-coal roadways under excavation stress paths were derived after taking the nonlinear hardening and softening characteristics of the strain of soft coal, the Mogi–Coulomb criterion, the intermediate principal stress, and the dilatancy characteristics of surrounding rock into comprehensive consideration. Finally, in accordance with a practical engineering case, the influences of the intermediate principal stress coefficient, the lateral pressure coefficient, and the support force on the deformation and failure characteristics of the soft-coal roadway were analyzed. The analysis reveals that an increase in intermediate principal stress aggravates the deformation of surrounding rock and enlarges the plastic and broken zones; variations in the lateral pressure coefficient alter the shape of the broken zone and the distribution of surface displacement; and an increase in the support force effectively reduces the plastic zone, broken zone, and surface displacement of the roadway. The research results can provide valuable theoretical basis for the stability evaluation and support design of soft-coal roadways. [ABSTRACT FROM AUTHOR]

Three types of synthetic coal-derived adsorbents were characterized as potential enhanced structurers during the removal of chlorpyrifos pesticide. The raw coal (CA) was activated into porous graphitic carbon (AC), and both CA and AC were blended with polyaniline polymers (PANI/CA and PANI/AC) forming two advanced composites. The adsorption performances of the modified structures in comparison with CA were evaluated based on both the steric and energetic parameters of the applied advanced isotherm model (the monolayer model of one energy). The uptake performances reflected higher capacities for the PANI hybridized form (235.8 mg/g (PANI/CA) and 309.75 mg/g (PANI/AC) as compared to AC (156.9 mg/g) and raw coal (135.8 mg/g). This signifies the impact of activation step and PANI blending on the surface and textural properties of coal. The steric investigation determined the saturation of the coal surface with extra active sites after the activation step (Nm(AC) = 62.05 mg/g) and the PANI integration (Nm(PANI/CA) = 113.5 mg/g and Nm(PANI/AC) = 169.7 mg/g) as compared to raw coal (Nm(CA) = 39.6 mg/g). This illustrated the reported uptake efficiencies of the modified samples, which can be attributed to the enhancement in the surface area and the incorporation of additional chemical groups. The results also reflect that each site can be loaded with 3–4 molecules of chlorpyrifos, which are arranged vertically and adsorbed by multi-molecular mechanisms. The energetic studies (< 40 kJ/mol) suggested the physical uptake of pesticide molecules by dipole bonding and hydrogen bonding processes. The thermodynamic functions donate the exothermic properties of 47reactions that occur spontaneously. [ABSTRACT FROM AUTHOR]

This work assessed some properties and effects of biocoal briquettes on environmental pollution compared with utilising coal alone. A mixture of coal fines and rice husks was prepared, with cassava starch gel as a binder, before compaction in a briquetting machine and drying with a solar dryer. Samples of the coal fines, rice husk, cassava flour and briquettes were analysed for their elemental and oxide concentrations via an energy-dispersive X-ray fluorescence analyser. The heat fuels were analysed for their thermal behaviour via thermogravimetric analyser (TGA), whereas the specific surface area, pore size and pore volume were determined using a Brunner–Emmett–Teller (BET) analyser. The conversion of the tested coals to biocoal briquettes resulted in a reduction in the level of arsenic in the briquettes. Additionally, the sulphur level decreased from 1.96 to 1.11% in the Okobo-Enjema briquettes and from 1.78 to 0.90% in the Onyeama briquettes. However, the levels of manganese increased from 0.04 to 0.22% in the Okobo-Enjema briquettes and from 0.04 to 0.21% in the Onyeama briquettes. Thermogravimetric analysis at different heating rates revealed that derivative weight loss increased with increasing heating rate, from 4.4% at 10 °C/min to 5.5% at 20 °C/min. BET analysis revealed that the briquettes had larger pore diameters, volumes and specific surface areas than did the coal samples. The coal samples have greater propensity to pollute the environment as the amount of potentially hazardous elements in the samples is greater than in their biocoal briquettes. [ABSTRACT FROM AUTHOR]

The quest for scientifically advanced and sustainable solutions is driven by growing environmental and economic issues associated with coal mining, processing, and utilization. Consequently, within the coal industry, there is a growing recognition of the potential of microbial applications in fostering innovative technologies. Microbial-based coal solubilization, coal beneficiation, and coal dust suppression are green alternatives to traditional thermochemical and leaching technologies and better meet the need for ecologically sound and economically viable choices. Surfactant-mediated approaches have emerged as powerful tools for modeling, simulation, and optimization of coal-microbial systems and continue to gain prominence in clean coal fuel production, particularly in microbiological co-processing, conversion, and beneficiation. Surfactants (surface-active agents) are amphiphilic compounds that can reduce surface tension and enhance the solubility of hydrophobic molecules. A wide range of surfactant properties can be achieved by either directly influencing microbial growth factors, stimulants, and substrates or indirectly serving as frothers, collectors, and modifiers in the processing and utilization of coal. This review highlights the significant biotechnological potential of surfactants by providing a thorough overview of their involvement in coal biodegradation, bioprocessing, and biobeneficiation, acknowledging their importance as crucial steps in coal consumption. [ABSTRACT FROM AUTHOR]

Nowadays, some fracking fluids can enable resourceful extraction of coalbed methane and reduce greenhouse gas emissions. However, their toxicity or corrosiveness will cause harm to downhole workers and pollute groundwater resources. Thus, five kinds of clean composite fracturing fluids were developed in this paper by using starch solution as the matrix and adding various preparations. The change rule of methane adsorption capacity by microstructure changes of coal samples was investigated systematically, and the optimal composite fracturing fluid was determined. The results showed that the new fracturing fluid increased the degree of aromatic ring condensation by 43.3% and the average pore size by 52.1%. Also, the adsorption constants of a value decreased by 11.6% and b value decreased by 23.9%, which can remarkably reduce the methane adsorption. The experimental results provide theoretical support for the clean production of coalbed methane. [ABSTRACT FROM AUTHOR]

The preliminary results of experimental modeling of the impact process on a coal substance by short-pulse laser radiation are presented. During the experiments, extremely high temperatures and pressures were reached. Based on the analysis of the modified products of the target substance, coal melting was identified, followed by its cooling with subsequent solidification with the formation of glass-like carbon. The synthesis products may be of interest as novel carbon materials formed at ultrahigh pressures and temperatures, such as high-pressure carbon polymers and hollow fullerene-like structures. The results of experimental modeling can be used for comparison with naturally occurring materials in order to elucidate the mechanisms of the formation of natural high-pressure carbon substances from a non-graphite precursor. [ABSTRACT FROM AUTHOR]

The instability of the increasingly important photovoltaic (PV) electricity generation in Korea due to a dependence on meteorological conditions is an emerging problem. In this study, we examined the influence of various meteorological conditions on the prediction accuracy of PV generation and module temperature. The predictions were based on weather data acquired from the Korea Meteorological Administration and compared with actual PV generation data from the Dangjin coal yard PV power facility. The results were analyzed on the basis of meteorological conditions, insolation, ambient temperature, and wind velocity. [ABSTRACT FROM AUTHOR]

Underground coal mining operations are vital to global energy supply that often take place in challenging environments where structural stability and safety are paramount. Shotcrete is a widely adopted technique for reinforcing underground rock surfaces which has been proven effective in safeguarding against roof collapse and structural instability. However, the underground environment remains susceptible to low velocity impacts from falling debris, blasting and equipment interactions which can pose significant risks to miners and infrastructure. This research article presents an experimental investigation into the effectiveness of tuned mass dampers (TMDs) in enhancing the structural resilience of shotcrete reinforced coal mines when subjected to low velocity impact loads. Further, this study employs a systematic experimental approach using variable head-free falling impact testing equipment to explore the potential benefits of integrating tuned mass dampers into the support systems of shotcrete reinforced coal mines. The study employs drop weight falling head impact tests with varying drop height of 1.0 m, 1.5 m and 2.0 m to study the influence of the impact energy. It was observed that the peak force characteristics increased for all damped cases with an increase of 15 kN, 18.41 kN and 12.64 kN and corresponding increment of 17.64%, 14.13% and 9.15% respectively as compared to undamped cases in addition to the reduced strain values in coal mine for damped cases under drop weight impact. The findings of this study conclude that after installation of tuned mass dampers the structural damage caused by low velocity impact was reduced and provides valuable insights into the applicability of TMDs and their potential to enhance safety and structural integrity in underground coal mines. [ABSTRACT FROM AUTHOR]

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Looking at the development status of Nigeria and other developing nations, most low-income and rural households often use coal as a source of energy which necessitates its trade very close to the communities. Moreover, the effects of exposure to coal mining activities are rarely explored or yet to be studied, not to mention the numerous street coal vendors in Nigeria. This study investigated the oxidative stress levels in serum and urine through the biomarker 8-OHdG and DNA damage via single cell gel electrophoresis (alkaline comet assay). Blood and urine levels of 8-OHdG from 130 coal vendors and 130 population-based controls were determined by ELISA. Alkaline comet assay was also performed on white blood cells for DNA damage. The average values of 8-OHdG in serum and urine of coal vendors were 22.82 and 16.03 ng/ml respectively, which were significantly greater than those detected in controls (p < 0.001; 15.46 and 10.40 ng/ml of 8-OHdG in serum and urine respectively). The average tail length, % DNA in tail and olive tail moment were 25.06 μm, 18.71% and 4.42 respectively for coal vendors. However, for controls, the average values were 4.72 μm, 3.63% and 1.50 for tail length, % DNA in tail and olive tail moment respectively which were much lower than coal vendors (p < 0.001). Therefore, prolonged exposure to coal dusts could lead to higher serum and urinary 8-OHdG and significant DNA damage in coal vendors observed in tail length, % DNA in tail, and olive tail moment by single cell gel electrophoresis. It is therefore established that coal vendors exhibit a huge risk from oxidative stress and assessment of 8-OHdG with single cell gel electrophoresis has proven to be a feasible tool as biomarkers of DNA damage. [ABSTRACT FROM AUTHOR]

With the rapid economic growth, the energy demand is increasing in China. Coal accounts for the largest proportion of China's energy consumption, and low coal use efficiency will generate more undesirable output like CO2 and soot, which inevitably lead to environmental problems and human diseases. This paper aims to measure the impact of coal-fired, soot on industrial production efficiency and total factor energy production efficiency of China through directional Slacks-based Measure model (directional-SBM) and Total Factor Energy Efficiency model (TFEE), and pay more attention to the relationship between soot emissions and industrial production efficiency. The results show that China's industrial production efficiency and factor efficiency are underperforming, and there exist huge room for improvement in soot emissions and coal usage. Only a few developed provinces and provinces with small industrial scale are at the efficient frontier, and less than half of the regions exceeds 0.9. Moreover, from 2012 to 2016, while China's coal use has been increasing, the efficiency has been declining. The adjustment value of coal consumption has increased from 16 to 20%, resulting in serious pollution and waste of resources. In general, there is a big gap in industrial production and total factor energy production efficiency between China and developed economies. Therefore, it is necessary for China to accelerate technological reform and optimize the energy consumption structure to improve energy efficiency and reduce pollution, and provide a reference for the coal industry in other developing countries. [ABSTRACT FROM AUTHOR]

Considering the challenge posed by formidable mining pressure in the exploitation of island working faces, this study focuses on the control difficulties encountered in mining roadways. With the island working face 15,102 serving as the engineering context, the research delves into the lateral roof structure of the island working face. It scrutinizes the formation of the lateral roof structure after the breaking of overlying strata in the island working face, investigates the stress transfer and action mechanisms inherent in this lateral roof structure, and elucidates the patterns of stress evolution on the mining roadway. A judicious mining roadway control technology is then suggested to create a safe working environment for island working face mining. The results indicate that there are two distinct zones on the lateral roof of the island working face: the elastic deformation zone and the moving deformation zone. It is the latter that primarily contributes to the deformation and instability of the mining roadway. The elastic deformation zone acts as an intermediary stress propagation carrier, transmitting both the stress of the moving deformation zone and the mining influence to the mining roadway. Regardless of the stress component type, Key Stratum I (KS I) significantly impacts the lower coal, as evidenced by the analysis of various stress evolution programs for KS I and II. To address this, a mining roadway stability control technology is proposed for the island working face. This includes the determination of roof-cutting parameters and the definition of a stability scheme for the roof-cutting protection roadway. These measures serve as a valuable reference for enhancing mining roadway stability control in similar island working faces. [ABSTRACT FROM AUTHOR]

Thick-coal-seam with complex structures and thick-hard roof in the initial mining phase pose various challenges, including a long weighting interval, strong rock pressure, poor top coal caving performance (TCCP), and significant coal loss. These problems directly affect the safety and efficiency of the mining operations. This study employs the principles of elastic thin plates and ellipsoidal bodies to unravel the formation mechanism of strong rock pressure in thick-hard roof and the influence of parting on the TCCP. In addition, a hydraulic fracturing technique is proposed for safe-efficient recovery during the initial mining phase. The reliability of this technique is verified through numerical simulations and field experiments. The research findings reveal the following. (1) The primary causes of strong rock pressure in the mining face are attributed to a long weighting interval and wide collapse range of the main roof, and the weighting interval is primarily influenced by the thickness and tensile strength of the main roof. (2)The key factor affecting the TCCP is the cantilever beam structure formed by the fracture of the thick-hard parting, as it intersects the ellipsoidal body during coal caving. The simultaneous fracturing of both the top coal and roof can reduce the weighting interval on the working face. This process effectively decreased the strength of the thick-hard parting within the top coal, while simultaneously enhancing its load strength and eliminating the cantilever structure resulting from the parting fracture. It not only reduces the first weighting intensity but also promotes the early and proper coal release, thereby enhancing the TCCP and ensuring safe-efficient mining during the initial mining phase. (3) Aiming at the difference in the strengths of the top coal and roof, a graded hydraulic fracturing technique and system were proposed. Fracturing boreholes with a diameter of 60 mm, spacing of 10 m, and height of 20.85 m, which can economically and effectively ensure the fracturing results. Field applications have demonstrated that fractured coal and rocks in fracturing areas exhibit well-developed fractures. During the initial mining phase, the weighting interval in the working face was reduced by 20 m, resulting in a decrease in the overburden pressure and 26.9% reduction in the lumpiness of the top coal. Additionally, the recovery rate increased by 31.19%. [ABSTRACT FROM AUTHOR]