ABSTRACTThe study aims to characterize the structural features of Jordanian tar sand using analytical techniques including (FTIR, ultimate and proximate analysis, TGA, XRD, and XRF). The tar sand shows a low content of volatile matter (bitumen) with significant nitrogen content. The bitumen contains a high proportion of aliphatic hydrocarbons of which high content of it attached to oxygen atom. The minerals were mainly quartz and low concentration of carbonate with noticeable content of sulfite and potassium oxide from XRF. The recovery of bitumen was evaluated using three different extraction techniques: solvent extraction methods (ultrasound-assisted extraction, non-aqueous extraction) and thermal pyrolysis using the Fischer assay apparatus. The non-aqueous solvent extraction method gave the highest bitumen recovery using toluene as a solvent; however, the high-temperature Fischer assay method provided a low recovery. The extracted bitumen under the optimum condition was characterized using NMR, elemental analysis, and GC-MS analysis. The oil products from tar sand showed a high concentration of oxygen and noticeable concentration of sulfur atoms. The 1H-NMR revealed a high content of aliphatic hydrocarbons in good agreement with raw tar sand characteristics. The identified compounds in the GC-MS where mainly substituted with oxygen atom in the form of alcohols and ethers.

ABSTRACTCoal is a primary and conventional energy source, but it also adversely impacts the environment. To mitigate the adverse effects of fossil fuels, the world is compelled to switch to more environmentally friendly resources like shale gas and coal bed methane (CBM). In India, coal has been mined and utilized for more than a century, but now it is high time to use the coal resource more cleanly. In this regard, CBM can be a good alternative. It is essential to mark out the coal seams which pose a high CBM generation potential. The study aims to determine the relationship between methane content and adsorbed gas content with coal characteristics and its depth of occurrence. In the present study, an investigation was carried out on the coal samples from the Sohagpur coalfield to detect the relation mentioned above. Vitrinite reflectance was calculated, which ranges from 0.85% to 1.08%. Adsorbed gas content and methane content were calculated using proximate analysis results and the coal seam depth. The study revealed that these coals are High Volatile Bituminous in rank. Also, Methane content increases with vitrinite reflectance and fixed carbon. As the depth increases, the value of gas content also increases.

ABSTRACTTo extensively explore the advantage of using nanobubbles in the El-Maghara coal flotation process, the effect of nanobubbles on both column and mechanical flotation was investigated under different operating parameters such as diesel oil collector dosage, MIBC frother concentration, superficial feed velocity, superficial air velocity, and superficial wash water velocity in column flotation; besides the slurry flow rate through nanobubbles generator into a 25-liter mechanical flotation cell. The representative coal flotation feed acquired from the El-Maghara deposit located in Sinai, Egypt with chemical characterization using proximate analysis containing 25.27% mineral matter forming ash during coal combustion and with particle size distribution measurement using laser particle size analyzer is 57 µm d90. Also, the flotation kinetic experiments were done to show the influence of nanobubbles on the flotation time required to obtain high-quality coal products with high combustible recovery. Nanobubbles enhanced the flotation performance and kinetics by up to 24% combustible recovery based on the operation parameters reducing flotation time from 4 to 2.25 min for 80% combustible recovery.

ABSTRACTThere are abundant low-rank coal resources in China. However, its higher AAEMs (alkali and alkaline earth metals) content and the release of AAEMs during combustion cause serious fouling and slagging problems. In this paper, a method of removing AAEMs and ash from low-rank coal to produce clean coal by organic acid leaching was proposed. The leaching effects of four organic acids were compared, the leaching mechanism of citric acid was analyzed, and the removal behavior of AAEMs and ash was investigated. The results show the effect of citric acid is better than others. During the leaching process, the citric acid ionizes H+, which reacts with inorganic minerals of AAEMs, completes ion exchange with AAEMs Organics. Under the relative optimized experimental conditions, the content of Na2O in coal ash is 0.9%, which is in line with the standard of power coal in China. The removal efficiency of alkaline earth metals Ca and Mg are significantly lower than those of alkali metals Na and K. The trend in the removal efficiency of Ca and ash are consistent. Citric acid leaching is an effective and promising method to produce clean coal from low-rank coal.

ABSTRACTDry coal separation is the key technology for coal separation in arid and water-scarce areas. The content of −6 + 1 mm coal gradually increases, and the weak gravity affect of this part of coal restricts the separation effect, causing serious resource waste and environmental pollution. In this paper, a process intensification method for compound dry separation based on high-frequency vibration was proposed to improve the separation effect of fine coal. The kinematic characteristics of the bed surface with high-frequency vibration was captured by the three-channels acceleration sensor, and the motion trajectories of different regions on bed surface were reconstructed. The separation area was located at the front end of the vibrating bed, and the elliptical trajectory promoted the material to roll. However, the tail of the bed showed a linear trajectory, the main team to the transport of the material. And then the force characteristics of various density particles were studied by using spherical inertial sensors. Compared with low-density particle swarm, the collision between high-density particles was more obvious, causing serious loss of kinetic energy, which increased the motion difference of particles with different densities. Furthermore, the significance of the effects of vibration frequency, bed inclination and air velocity on the separation effect of −6 + 1 mm coal and the interaction between the factors were investigated. Furthermore, the influence of vibration frequency, inclination, and air velocity on the separation effect and the interaction among various factors were explored. The influence of frequency and inclination was more obvious than that of gas velocity. And then a mathematical model was established to predict the calorific value of clean coal. The results illustrated that at a vibration frequency of 37.52 Hz, a bed inclination angle of 13.69°, and an air velocity of 2.26 m/s, the calorific of product was increased from 4306 kcal/kg to 5868 kcal/kg, and the heat efficiency reached 90.18%. The results provide a referable way to realize the large-scale and high-efficiency dry separation of fine coal.

ABSTRACTCoal slurry is a semi-solid material formed by the water content of pulverized coal, which is a product of the coal production and transportation process and has viscous and wet characteristics, and is easy to cause blockage in the process of mechanized mining and transportation. To study the resistance law of the probe rod pressed into the quasi-static viscous particle medium at a uniform speed, coal dust and deionized water were mixed into different water content of coal slurry, and the resistance of the probe rod under pressure in different water content of coal slurry was measured. It is found that when the cohesion of coal slurry is small, the press-in process tends to be stable, and the intrusion resistance shows a linear-slowly increasing-suddenly increasing trend as the depth of pressure increases.

ABSTRACTREEs play a pivotal role in the manufacturing of numerous industrial, defense, consumer, and aviation-related gadgets. As many primary sources of REEs are either exhausted or depleted, coal can be a good secondary source of REEs in the near future. The traditional thermochemical processes to extract REEs are expensive and detrimental to the environment, and thus exploration of more environment friendly and sustainable recovery methods are of the utmost necessity at the present time. In this study, we present in-depth investigation of REEs extraction from the coal samples from the Sohagpur coalfield, Madhya Pradesh. We conducted multiple experiments mainly focusing on rotational movement with the help of a laboratory shaker, magnetic stirrer with hot plate, and a flocculator jar test apparatus in the presence of acidic solutions. Our study highlights that the flocculator jar test apparatus exhibits the maximum recovery of REEs (Ce- 95%, Nd- 83%, La- 82%, Eu- 82%, Pr- 76%, Sm- 74%, Gd- 69%, and Tb- 69%) from coal in the presence of 2 M HNO3. This technique of REEs recovery from coal is easy to use, effective, has little environmental impact, and can be applied on an industrial scale with only minor adjustments to the machinery.

ABSTRACTThe calculation of the dissipated thermal energy of mineral crushing is of great significance for the reduction of the heat loss in the crushing process. The traditional calculation method is relatively simple, which does not consider practical problems, such as cooling during the crushing process and uneven temperature distribution. This paper used infrared video to record the impact and crushing process of anthracite for more accurate calculation results. Considering the cooling of high-temperature particles and the temperature distribution of particles at different depths, a calculation model for heat dissipation energy was established. Based on this model, the average heat generation efficiency of impact crushing of cubic and disc anthracite specimens reached 9.70% and 4.55%, respectively.

ABSTRACTEqual-thickness screens are widely used in coal processing due to their advantages in overcoming the problems of material accumulation, low utilization of the screen surface, and poor screening accuracy. In this paper, the variable amplitude equal-thickness method was introduced into the combined screen, a novel variable trajectory combined equal-thickness screen was proposed and the combined excitation coefficient was introduced. The motion of the variable trajectory combined equal-thickness screen under different combined excitation coefficients was investigated using vibration test analysis system and the particle motion characteristics and the spatial distributions of materials in the screening process were analyzed using a high-speed camera system. The distribution law of the material was studied by screening experiment. The results show that when the combined excitation coefficient D is increased, the first section screen amplitude increases, the material transport speed of the first section increases, the material accumulation situation of the first section is resolved. When the unbalanced excitation coefficient k is increased, the material layer at the feeding end of each screen becomes thinner, the material transport speed of the first section screen is accelerated, the screen body does variable amplitude elliptical motion, the material is equal-thickness. When D = 1.2, k = 1.2, an optimum screening efficiency of 96.12% was obtained, with a total misplaced material content of only 1.82%.

ABSTRACTWith the rapid development of the lithium (Li)-ion battery industry in electric vehicles (EVs) and electronic devices, coal-based Li ore is expected to be a new-type Li resource to meet the rapidly growing demand for Li. However, the traditional Li extraction process involves high temperature to activate minerals. Herein, a low-temperature sulfuric acid baking followed by water leaching was investigated in this study. The influences of baking and leaching conditions on Li leaching rate were explored in detail. Under the optimal conditions of 70 wt% H2SO4, baking temperature 180°C, baking time 1 h, leaching temperature 25°C, and leaching time 1 h, the Li leaching rate reached 84.42%. In addition, the sequential chemical extraction, XRD, and SEM-EDS results indicated that Al-Li-containing minerals were converted to soluble minerals during the baking process with sulfuric acid and then were extracted through water leaching into the solution.

ABSTRACTA set of eight coals from the premium Argonne coal sample program were studied using thermogravimetric and evolved gas analysis. Gaseous combustion products were analyzed using an FTIR spectrometer and a chemiluminescence analyzer. Additionally, modulated thermogravimetric experiments were carried out to determine activation energies associated with the combustion of each sample. The exhaust from the thermogravimetric analyzer was directed to the gas analyzers for detecting and quantifying CO, CO2, and NO. Evolved gas analysis was conducted at a ramp rate of 5°C for CO, CO2 evolution, and 20°C per minute for nitric oxide evolution, with the furnace temperature varying between 20°C–750°C. Modulated thermogravimetric analysis experiments were carried out in the same temperature range. The temperature was increased at a rate of 2°C per minute for the modulated experiments. Each test had a superposed temperature modulation with amplitude ±5°C and a period of 200 seconds. The experiments provide valuable information on the combustion kinetics and emission characteristics of selected American coals.

ABSTRACTCoal-derived carbon material is considered as a high-quality raw material for artificial graphite. Herein, the demineralized coke was prepared by acid washing, and coke-based graphite samples were prepared by high-temperature graphitization (2000°C–2800°C). The electrochemical performance of coke-based graphite samples was investigated. It is found that the high-temperature graphitization of the coke is inhibited by demineralization treatment. The graphitization degree of graphitized samples decreased after demineralization treatment. The graphitization degree of the graphitized samples at 2800°C from the raw coke and the demineralized coke can reach 74.48% and 68.78%, respectively. Chemical predemineralization treatment can reduce the mesoporous structure and specific surface area of the product. Moreover, onion-like graphite microspheres are found in graphitized samples from the coke before and after demineralization treatment. The order degree of the raw coke graphitization sample is significantly reduced by extending the graphitization preservation time. The electrochemical test results show that the graphitized sample, e.g., CG-2400, from raw coke (without demineralized) has better comprehensive electrochemical performance. The reversible specific capacity is 301.1 mAh/g at 0.1 C (1 C = 372 mAh/g). After 150 cycles at 1 C, the reversible specific capacity reaches 160.1 mAh/g.

ABSTRACTEstablishing an alternative resource of rare earth elements (REEs) in coal by-products has been a topic of high interest for the past decade. Despite this, research that characterizes REEs in such materials produced in Australia is lacking. This paper focuses on the concentration and occurrence of REEs in power station coal ashes that represent a suite of major economic coal basins in Australia. The concentration of REEs in coal ash samples was determined by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). Fly ash and bottom ash generated at power stations that utilize coals from the Collie Basin in Western Australia contained elevated REE concentrations. A REE-rich fly ash containing 0.21% total rare earth oxides (REO) was subject to further analysis by Scanning Electron Microscopy with Energy Dispersive X-rays (SEM-EDX) and TESCAN Integrated Mineral Analysis (TIMA). Fine (avg. <5 μm) monazite grains were observed in the fly ash which were typically bound to Al/Si-rich phases. A substantial increase in the aqua regia-extractable fraction of REEs occurred when fly ash samples were milled to an ultrafine particle size. The current investigation has demonstrated that Australian coal ash may represent a promising resource of REEs as the demand for these metals increases.

ABSTRACTIn response to the deficiencies in visible-near infrared spectral identification of coal gangue under different working conditions, this paper employs multiple algorithms to construct local and global recognition models and conducts analysis. Simulating five different working conditions in the laboratory, including different detection angles, illumination angles, detection distances, coal powder content, and moisture content. Each working condition is further divided into four levels. Collecting spectral data of coal and gangue samples. Constructing global and local datasets, which are respectively derived from all levels and single levels under certain working conditions. Training local and global models to identify samples based on machine learning algorithms such as Lightgbm and 1DCNN. The results of the experiment indicate that there are variations in the sample spectra and recognition accuracy based on different working conditions. Furthermore, the local model exhibits lower recognition accuracy and inadequate robustness for other level samples under the same working condition. The global model is more robust and practical, as it achieves higher or equal recognition accuracy for local data compared to the local model. Among the global models, Lightgbm has the best overall performance, with an average F1-score of 99.34% and 97.9% for local and global datasets, respectively. It also has fast training time of 0.75s and recognition time of 1 ms. The Lightgbm global model can accurately identify coal and gangue in various working conditions, making it a reliable solution.

ABSTRACTIn present paper, structures and properties of degradation products of polystyrene (PS) waste were characterized by gel permeation chromatography (GPC), thermogravimetric (TG) analysis, Fourier transform infrared (FT-IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), and thus the degradation conditions including temperature, time, and assistant type and dosage were investigated and optimized. It is suitable to use 1.0 wt% K2S2O8 as an assistant to degrade PS waste at 300°C for 24 h. Subsequently by sulfonation and neutralization reactions, the degraded PS was prepared into sodium polystyrene sulfonate (PSS), a common dispersant for coal‒water slurry (CWS). The performance of PSS with different molecular weights and sulfonation degrees was studied. Experimental results showed that the PSS with the sulfonation degree of more than 75%, prepared from the degraded PS having number average molecular weight (Mn) of about 9000, was appropriate for dispersion and stabilization of CWS suspensions. Additionally, compared with commercial dispersant NSF, the obtained PSS had a better performance for CWS. CWSs prepared with dispersant PSS exhibited pseudo-plastic or shear-thinning rheological behaviors. Combined with coal‒water slurry technology, a new approach is provided for resource utilization of PS waste.

ABSTRACTWith the progress of control and communication technology, coal mining is gradually transformed and upgraded from traditional mechanism to automation, the concept of intelligent mining in fully mechanized caving is also put forward in the mining technology research of thick and extra-thick coal seams. As a key technology and necessary condition of intelligent mining in fully mechanized caving, intelligent recognition of coal and gangue is a technical bottleneck to be broken through, which has seriously affected the coal mining efficiency and recovery rate. Based on this, this paper carries out a systematic study on coal gangue recognition in fully mechanized caving from the perspective of tail beam vibration. Firstly, the impact-contact dynamic theoretical model between coal gangue and the hydraulic support tail beam and its rigid-flexible coupling dynamic simulation model was constructed respectively. The theoretical and numerical simulation was combined to study the vibration characteristics induced by the contact between coal gangue and the tail beam, and the vibration characteristics caused by the difference of coal and gangue properties were compared and analyzed. Meanwhile, coal gangue recognition capability is summarized, which provides theoretical support for the vibration characteristics-based coal gangue recognition. Secondly, through analysis of fully mechanized caving environment, a single coal drawing experimental platform and vibration information acquisition system are designed and built in the laboratory environment. Then, a research on signal eigenvalue recognition sensitivity based on “coal gangue binary classification” recognition was carried out through the combination of signal acquisition and features extraction as well as machine learning, the optimal recognition eigenvector based on recognition effect analysis was obtained. On that premise, recognition research of “coal gangue multi-category recognition” based on the single point and multi-point vibration signals were proposed and conducted, which successfully realized coal gangue mixture ratio recognition under the condition of multi-category. The research provided the theoretical basis and technical support for accurate and real-time coal gangue mixture ratio recognition in top coal caving.

ABSTRACTThe conversion of lignite into biomethane is of great significance in the field of energy research. However, the yield of biomethane is low. To improve the biomethane yield from lignite, the effects of ultrafine grinding lignite on the biomethanation fermentation system were analyzed. The daily biomethane yield, total biomethane yield, pH, glucose concentration, and volatile fatty acid concentration of lignite were used to determine the optimum particle size of lignite. The results demonstrated that the total biomethane yield of the fermentation group with ultrafine grinding lignite was 14.69 mL·g−1 at a reaction temperature of 50°C and a biomethane fermentation time of 39 d. This was 36.91, 33.42, and 26.75% higher than that of the 40, 150, and 250 mesh lignite biomethane fermentation groups, respectively. The daily biomethane yield reached the peak of the ultrafine grinding lignite fermentation group 1.30 mL·g−1 on the second day, which was 1.96, 1.63, and 1.04 times higher than that of the 40, 150, and 250 mesh lignite fermentation systems, respectively. The research demonstrated that ultrafine grinding of lignite can effectively increase the biomethane yield. This provides an effective method for improving the yield of biomethane from lignite.

ABSTRACTIndian coal fly ash generally comprises 50–60% SiO2SiO2SiO2, and 25–35% Al2O3Al2O3Al2O3 can potentially replace bauxite as an aluminum resource. Aluminum recovery from coal fly ash is highly dependent on removing amorphous silica, activating the inactive mullite phase, and increasing the Al/SiAl/SiAl/Si ratio. This work thoroughly investigated and compared the alkali-desilication operation by two widely used alkalis, KOHKOHKOH and NaOHNaOHNaOH, based on four operational parameters: liquid-to-solid ratio, KOHKOHKOH or NaOHNaOHNaOH concentration, leaching time and temperature. Using SEM, EDX, and XRD, the morphology and phase of fly ash and solid byproducts were analyzed. NaOHNaOHNaOH was more effective than KOHKOHKOH in SiO2SiO2SiO2 dissolution at all operational parameters. A 20 wt% concentration, 5:1 liquid-to-solid ratio, 2hrs leaching time, and 100°C temperature were the optimum removal conditions for silica from fly ash using NaOHNaOHNaOH. With KOHKOHKOH, the ideal desilication conditions were obtained at 28 wt% concentration, 3hrs leaching time, and 150°C temperature. The highest Al/SiAl/SiAl/Si ratios were obtained under the same optimal desilication conditions. Using KOHKOHKOH and NaOHNaOHNaOH, the Al/SiAl/SiAl/Si ratio was enhanced from 0.58 to 1.26 and 1.45, respectively. The main zeolitic products obtained were Hydroxysodalite in NaOHNaOHNaOH-treated fly ash and Linde F zeolite and Kalsilite in KOHKOHKOH-treated fly ash.

ABSTRACTThe demand of Rare Earth Elements (REEs) has increased for the development of clean and green technologies. Conventional geological sources of REE are insufficient to overcome the high demand of REE; hence, the secondary resources are being actively explored. Coal ashes (CAs), a potentially hazardous material, is one of the best secondary sources containing high concentration of REE. The present study aims to explore the abundance of REE in coal and coal ash from different Thermal Power Stations (TPS). The mineralogy and surface morphology of all samples have been determined. The coals mostly consist of quartz and kaolinite, whereas CAs predominantly contain quartz and mullite. Both coal and CAs are dominated by LREE elements, followed by MREE and HREE. The outlook coefficient (Cout) is close to “1” and the critical percentage (Cp) is more than 30%. Coal ash from some of the TPS is identified as secondary source for REE. Fractionation study of REE from coal to CA is carried out to understand the feasibility of CA. A Pearson correlation has been plotted for individual REE elements with other parameters to understand the affinity of REE to different phases of CA.

ABSTRACTIn order to grasp the laws of dust production from coal cutting and reduce dust production at source by optimizing cutting parameters, the cutting experiments of different brittle coals under different cutting parameters were carried out. Based on the self-developed dust generation simulation platform of road header, the effects of coal brittleness, conical pick top angle, rotational speed, and drilling speed on dust generation were studied, and the main control factors affecting dust generation were analyzed, so as to propose the suitable parameter matching scheme for different brittle coal. The research results can provide an important scientific basis for the premining evaluation of dust production characteristics of mines and the formulation of coal dust control engineering.