Macromolecular structural changes in contact metamorphosed inertinite-rich coals from the No. 2 Seam, Witbank Coalfield (South Africa): Insights from petrography, NMR and XRD
“…The microcrystalline structural parameters of the coal sample can be calculated based on the Bragges and Scherrer formulas from the XRD pattern. The structural parameters of coal, including intercrystalline spacing , microcrystalline stacking height ., coal aromaticity and average layer number of crystal stacking, can be obtained by the following formula 39 where, λ is the wavelength of X-rays, λ = 0.154 mm; θ 002 is the central position of the (002) peak; is the full width at half maximum of the 002 peak; and A λ are the peak areas of the (002) peak and γ peak, respectively. Figure 9 XRD curve fitting results for 002 peak of coal samples (1–4).…”
This study explores the detonation characteristics and compositional changes of pulverized coal, focusing on its use in Rotary Detonation Wave (RDW) technologies. While pulverized coal has shown high fuel efficiency in RDW settings, transitioning from theory to practical detonation engineering presents substantial scientific and technical hurdles. A key issue is the reprocessing of detonation byproducts for in-situ coal mine gob filling, a topic that has received little attention. Utilizing advanced methods like X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), this paper investigates the micro-morphology, composition, and aromatic structures of gas–solid products pre and post-detonation at the Tashan Coal Mine's 2305 working face. Results indicate that coal dust from the underground mining face has enhanced detonation characteristics, with the addition of coal powder fuel extending the gas detonation limits. This benefits economic aspects by reducing reliance on gas fuel and lowering detonation fuel costs. The highest recorded detonation wave velocity was 2450 m/s, 14.8% greater than that of coal dust from external sources, suggesting more effective energy release and pressure gain. Furthermore, the study links detonation combustion intensity to coal's aromatic properties, noting a post-detonation aromaticity index (I) of 0.4941. This indicates an improvement in the aromatic structure under high-temperature conditions, vital for coal's reactivity and energy efficiency in RDW applications. This research not only deepens the understanding of coal dust combustion mechanisms but also advances clean coal utilization and deep coal fluidization mining, addressing significant RDW technological challenges.
“…The microcrystalline structural parameters of the coal sample can be calculated based on the Bragges and Scherrer formulas from the XRD pattern. The structural parameters of coal, including intercrystalline spacing , microcrystalline stacking height ., coal aromaticity and average layer number of crystal stacking, can be obtained by the following formula 39 where, λ is the wavelength of X-rays, λ = 0.154 mm; θ 002 is the central position of the (002) peak; is the full width at half maximum of the 002 peak; and A λ are the peak areas of the (002) peak and γ peak, respectively. Figure 9 XRD curve fitting results for 002 peak of coal samples (1–4).…”
This study explores the detonation characteristics and compositional changes of pulverized coal, focusing on its use in Rotary Detonation Wave (RDW) technologies. While pulverized coal has shown high fuel efficiency in RDW settings, transitioning from theory to practical detonation engineering presents substantial scientific and technical hurdles. A key issue is the reprocessing of detonation byproducts for in-situ coal mine gob filling, a topic that has received little attention. Utilizing advanced methods like X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), this paper investigates the micro-morphology, composition, and aromatic structures of gas–solid products pre and post-detonation at the Tashan Coal Mine's 2305 working face. Results indicate that coal dust from the underground mining face has enhanced detonation characteristics, with the addition of coal powder fuel extending the gas detonation limits. This benefits economic aspects by reducing reliance on gas fuel and lowering detonation fuel costs. The highest recorded detonation wave velocity was 2450 m/s, 14.8% greater than that of coal dust from external sources, suggesting more effective energy release and pressure gain. Furthermore, the study links detonation combustion intensity to coal's aromatic properties, noting a post-detonation aromaticity index (I) of 0.4941. This indicates an improvement in the aromatic structure under high-temperature conditions, vital for coal's reactivity and energy efficiency in RDW applications. This research not only deepens the understanding of coal dust combustion mechanisms but also advances clean coal utilization and deep coal fluidization mining, addressing significant RDW technological challenges.
“…In each of the laboratories (e.g., chemical analysis, XRD, and electron microscopies), all twenty-six obtained BFCT samples were dried in ovens with ventilation at a maximum of 40 • C for 48 h to avoid volatilization of volatile elements (e.g., halogens and Hg) [27,36,46,52,53]. Subsequently, the samples from Lauro Muller and Siderópolis were homogenized to evaluate the two areas of interest so that they are truly representative, thus ensuring greater reliability of the results obtained [53][54][55][56].…”
The objective of this study is to obtain a more detailed assessment of particles that contain rare-earth elements (REEs) in abandoned deposits of Brazilian fine coal tailings (BFCTs), so as to aid current coal mining industries in the identification of methodologies for extracting such elements (Santa Catarina State, Brazil). The BFCT areas were sampled for traditional mineralogical analysis by X-ray Diffraction, Raman Spectroscopy and nanomineralogy by a dual beam focused ion beam (FIB) coupled with field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) coupled with an energy dispersive X-ray microanalysis system (EDS). The results show that the smaller the sampled coal fines were, the higher the proportion of rare-earth elements they contained. Although the concentration of REEs is below what would normally be considered an economic grade, the fact that these deposits are already ground and close to the surface negate the need for mining (only uncovering). This makes it significantly easier for REEs to be extracted. In addition, owing to their proximity to road and rail transport in the regions under study, the opportunity exists for such resources (BFCTs) to be utilized as a secondary market as opposed to simply being discarded as has been done in the past.
“…Since the 1960s, various studies have proposed different models for the macromolecular structure of coal, such as Fuchs [ 5 ], Given [ 6 ], Wiser [ 7 ], Shinn [ 8 ], and other models. With the emergence of various modern analytical techniques and the improvement of molecular model construction methods, some scholars have used a combination of physical methods [ 9 , 10 , 11 , 12 , 13 ] and chemical methods [ 14 , 15 ] to establish molecular models of coal of different regions, to gain a deeper understanding of the reactions and structural properties of coals. Chai et al [ 16 ] constructed a molecular model of Zhundong Wucaiwan coal by extracting information characterizing coal microstructural parameters using computer software and experimental data, and heating it to obtain the changes in its macroscopic and microscopic characteristics.…”
In order to comprehend the molecular composition of coal and better understand the process of coal combustion, this study involved the development of a molecular structure model for Heiyanquan coal in Xinjiang, as well as the optimization and annealing dynamics simulation of the model. Thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), and high-resolution transmission electron microscopy (HRTEM) were utilized to investigate the spontaneous combustion characteristics of coal at different temperatures (room temperature, 50–500 °C with 50 °C interval). The findings revealed that the coal primarily consists of aromatic carbon, with the aromatic structure mainly comprising naphthalene, anthracene, and phenanthrene, and the aliphatic carbon mainly consisting of CH2 and CH, along with a small quantity of minerals. The empirical molecular formula of Heiyanquan coal was determined to be C175H125O21N3. After the optimization, the total energy of the model was significantly reduced, and the aromatic layers tended to align in a regular parallel manner, with van der Waals energy playing a crucial role in maintaining structural stability. As the temperature increased, the activation energy of the three stages also increased, with the combustion stage exhibiting the highest activation energy. The presence of hydroxyl groups and oxygen-containing functional groups was found to mainly participate in the reaction, while the content of aromatic hydrocarbons remained relatively stable, C=C exhibited a decreasing trend, and C-O displayed an increasing trend. Moreover, it was observed that 1 × 1 and 2 × 2 were the predominant aromatic stripes in the coal samples, accounting for more than 90% of the total stripes.
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