In order to reveal the macroscopic thermodynamic characteristics and microscopic reaction mechanism of low-temperature oxidation of lignite in eastern Inner Mongolia, this study systematically studied it by combining thermogravimetric analysis (TG), programmed temperature experiments, and ReaxFF MD molecular dynamics simulations. The experimental results indicate that the apparent activation energy (Ea) exhibits a dynamic pattern of decrease increase decrease. During the dehydration stage, Ea decreases with an average value of 46.29 kJ/mol; During the oxygen adsorption stage, the apparent Ea increased to 373 kJ/mol, reflecting the enhanced effective kinetic resistance caused by desorption adsorption competition and intermediate accumulation; Then during the combustion phase, with the intensification of structural activation and heat accumulation, Ea decreases to 60.25 kJ/mol. The ReaxFF MD simulation captured a phased mass evolution consistent with the TG results and further revealed the atomic level formation pathways of key gaseous products. CO is mainly related to the cleavage pathway of ketones/aldehydes, which is consistent with the energy barriers calculated by density functional theory (DFT) previously reported. CO2 mainly comes from carboxyl decomposition and secondary CO oxidation, while the formation of H2O is driven by hydrogen extraction involving hydroxyl radicals. C2H4 is mainly generated through the cleavage and recombination of long-chain aliphatic side chains. By combining the kinetic parameters obtained from TG, programmed temperature gas release, and ReaxFF MD reaction trajectory, this study established a connection between macroscopic thermal behavior and microscopic bond breaking mechanisms, providing a theoretical basis for early warning and prevention of low rank coal spontaneous combustion.
Liquid fuel fires pose growing risks to environmental sustainability and industrial safety. Conventional foam extinguishing agents are limited by poor thermal stability, increasing the risk of re-ignition, and often rely on fluorinated surfactants, which persist in the environment. This study proposes a novel thermo-responsive gel foam that integrates heat-induced gelation with high-temperature ceramization. The foam is made from environmentally benign materials, such as konjac glucomannan (KGM) and low-melting glass powders (LGP). By optimizing KGM concentration (0.5 wt%) and NaHCO3/Na2CO3 ratio (0.2–0.4), precise control over the gelation transition was achieved. At room temperature, the foam rapidly spreads over the liquid fuel surface. Upon flame exposure, it undergoes in-situ gelation, forming a stable foam layer that significantly reduces the likelihood of re-ignition. Experimental results show a 366.7–464.7% increase in drainage time on an n-heptane surface. At elevated temperatures, melted LGP infiltrates the carbonaceous residue from the carbonized gel network, forming an in-situ thermal barrier and protective char/silica layer. In small-scale flame suppression tests, the gel foam prolonged the burning delay by 297.0% compared to standard film-forming fluoroprotein (FFFP) foam. In large-scale suppression and anti-reignition tests, although the extinguishing time was similar to that of commercial FFFP foam, the gel foam completely prevented re-ignition, highlighting its potential as a high-performance fire-extinguishing agent for liquid fuel fires.
Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage applications, primarily owing to the abundance of sodium and the cost-effectiveness of their components. Among various anode materials, hard carbons (HCs) have attracted considerable attention due to their high capacity, low cost, and wide availability. With high carbon content and economic viability, coal represents a potential precursor for producing HCs. However, the heterogeneity of coal's maceral groups can significantly influence the electrochemical properties of the resulting hard carbon-a relationship that has been largely overlooked in previous studies. Herein, hard carbons were synthesized from distinct maceral groups of low-rank coal via a straightforward two-step carbonization process, aiming to clarify the impact of maceral variations on sodium storage performance. The findings reveal that the electrochemical behavior of the produced hard carbons is significantly influenced by the ratio between amorphous carbon and graphite-like microcrystalline content within the electrode material. Notably, semifusinite a type of inertinite enhances sodium storage capabilities by introducing structural defects and favorable pore architectures, thereby facilitating improved ion transport and charge storage. The I-1200 electrode demonstrated excellent rate performance, with the highest reversible capacity of 327mAh g- 1 and the lowest interfacial resistance observed at a current rate of 0.1C. These results underscore the potential of tailoring coal maceral groups to optimize the performance of hard carbon anodes in next-generation sodium-ion batteries.
The evolution of aromatic structures is a fundamental factor determining the degree of graphitization during the transformation of coal into graphite. However, the graphite-and carbon onion-like structures in coal are limited to the coalification or graphitization stage, and their formation mechanisms and relationships with the evolution of aromatic fringes remain ambiguous. In this study, the Raman spectroscopy was conducted to analyze the graphitization degree of coal. The HRTEM was introduced to observe the evolution process of aromatic fringes. The results show that before heating the coal sample, a large number of small sized aromatic rings (2 x 2) with a weak degree of orientation are randomly distributed as a single layer in the coal. After heating the coal sample (0 similar to 800 degrees C), significant reorganization of aromatic structures occurs. Small aromatic rings are connected and rearranged, leading to an increase in fringe length and a significant enhancement in orientation. Conversely, the proportion of single-layer aromatic fringes decreases, while the stacking degree of aromatic fringes increases for the two-, three-, and four-fringe stacks, respectively. Once the temperature reaches 1000 degrees C, the aromatic fringes form graphite-and onion-like structures in the coal. Graphite-like structures are characterized by long, well-aligned aromatic fringes with a high stacking degree, reflecting a well-ordered structure. Onion-like structures consist of layers of curved aromatic rings with poor orientation. Besides, large aromatic fringes with a higher degree of stacking indicate the development of a local highly ordered carbon structure. These findings provide direct microstructural evidence that supports the formation of graphite-and onion-like structures during coalification and graphitization. They also demonstrate that the progressive connection, rearrangement and stacking of aromatic fringes is key to forming a graphitic structure.
Coal fly ash (CFA) is an abundant industrial byproduct and an underexploited source of rare earth elements (REEs). This study uses multiple analytical techniques, including electron probe microanalysis (EPMA) and high-resolution transmission electron microscopy (HRTEM) to quantitatively characterize REE-bearing phases in a REE-rich CFA from southwestern China and to investigate the transformation pathways of REE-bearing minerals during coal combustion. In the feed coal, REEs occur mainly as REE phosphates (monazite and xenotime) and REE-bearing aluminophosphates (florencite and goyazite). During combustion, monazite remains largely unaltered, whereas the less refractory REE-bearing aluminophosphates decompose and react with aluminosilicates, producing a REE-enriched melt that partially devitrifies into REE silicate (cerite-like), REE oxide, and REE-bearing glass. EPMA Ce-mapping of 11 randomly selected regions identified 67 REE-bearing particles, showing that 80.9% and 19.1% of the total REE mass were associated with aluminosilicate glass and crystalline phases, respectively. Within the aluminosilicate glass, REE concentration is heterogeneous, being higher in Al-rich than Si-rich compositions. These results identify both REE-bearing crystalline phases and Al-rich aluminosilicate glass as priority targets for selective recovery from coal combustion residues. Micro-submicron REE phases indicate fine grinding and liberation of these phases could facilitate more selective and efficient recovery strategies.
