International Journal of Coal Geology最新文献

{"title":"Chemistry imaging and distribution analysis of rare earth elements in coal using LIBS and LA-ICP-MS instruments","authors":"Chet R. Bhatt ,&nbsp;Jinesh C. Jain ,&nbsp;Alexander A. Bol'shakov ,&nbsp;Dustin L. McIntyre","doi":"10.1016/j.coal.2025.104710","DOIUrl":"10.1016/j.coal.2025.104710","url":null,"abstract":"<div><div>Currently, demand for rare earth elements (REEs) increased significantly. Coal is actively evaluated as potential economic sources for extraction of REEs. In this work, laser-induced breakdown spectroscopy (LIBS) was evaluated for rapid estimation of REEs content and their distribution in the natural coal samples. The results were compared with similar laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) measurements. Thirteen coal samples (nine standard samples and five natural samples) were used in this study. Powder samples were pressed into pellets while coal chunks were directly ablated for data recording. Pellets of the powder standard samples were used to optimize the data acquisition system and then data recorded with this optimized system was used to identify the proper data acquisition and analysis models. After establishing the proper data acquisition system and analysis model using the standard samples, natural coal samples in powder form and their chunks were utilized to record LIBS and LA-ICP-MS spectra. Multivariate calibration models were developed using four of the natural samples, which were evaluated by predicting the REE content in the fifth sample. Principal component analysis was performed on the LIBS data obtained from the natural samples and it classified all the samples with high accuracy. Two-dimensional (2D) elemental mapping on coal chunk samples was also performed using both LIBS and LA-ICP-MS to study the distribution of REEs in the samples. The resulting elemental images and their correlations can be used to infer mineral distributions.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104710"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143427996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nanomechanical properties of anthracite and graphite: The role of heteroatom functional groups and structural evolution","authors":"Yuhui Wang ,&nbsp;Suping Yao ,&nbsp;Hanlin Zheng ,&nbsp;Zhaoxi Zuo ,&nbsp;Yang Liu","doi":"10.1016/j.coal.2025.104714","DOIUrl":"10.1016/j.coal.2025.104714","url":null,"abstract":"<div><div>This study investigates the anthracite and graphite samples from the Hanpoao mining area in Hunan Province, China, to understand their structural deformation characteristics in relation to tectonic stress and magmatic intrusion. Despite previous research highlighting the influence of tectonic stress on the microcrystalline structure of organic matter, there remains a gap in comprehensively understanding how these factors interact and affect the mechanical properties of coal and graphite. To address this, the research employed a combination of optical microscopy, reflectance measurements, Raman spectroscopy, and high-resolution atomic force microscopy, along with powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. Studies have shown that the Young's modulus of anthracite and graphite exhibits a certain correlation with both coal rank and the degree of graphitization. Notably, the presence of heteroatom functional groups, particularly sulfur-containing groups, plays a crucial role in modulating the Young's modulus. The study reveals an inverse correlation between thiophene sulfur content and Young's modulus, and a positive correlation with sulfone and sulfoxide sulfur content, suggesting that these groups significantly influence the mechanical properties of anthracite and graphite. We have done comprehensive investigation of the interplay between coal rank, microcrystalline structure, and heteroatom functional groups on the nanomechanical properties of anthracite and graphite. These studies provide a novel perspective for the assessment of the mechanical properties of coal and coal-based graphite, while also offering important theoretical foundations for the efficient utilization and advanced processing technologies of coal resources.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104714"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Intelligent identification of coal macerals using improved semi-supervised semantic segmentation methods","authors":"Na Xu ,&nbsp;Qingfeng Wang ,&nbsp;Pengfei Li ,&nbsp;Jiapei Kong ,&nbsp;Qing Li ,&nbsp;Mark A. Engle ,&nbsp;James C. Hower ,&nbsp;Wei Zhu","doi":"10.1016/j.coal.2025.104712","DOIUrl":"10.1016/j.coal.2025.104712","url":null,"abstract":"<div><div>Recently, the demand for automatic coal maceral identification has gradually received much attention, and hence deep learning has been applied to the identification of coal macerals. However, a large number of labels are necessary for supervised learning, which imposes challenges for automatic coal maceral identification. In this study, the methods for identifying coal macerals were fully reviewed. Considering the limited data and the complexity of annotation, a semi-supervised semantic segmentation model combined with conditional random fields (CRF) algorithm was suggested for pixel-level identification of coal macerals. Initially, a new dataset of coal macerals was established. The dataset contains many different coal maceral images collected from the USA and China, as well as the corresponding labeled images. Then the model was trained through adversarial loss, and the prediction results were evaluated through pixel accuracy (PA) and intersection over union (IoU). The results are compared with other three existing unsupervised image segmentation methods. The semi-supervised model achieved, on average, PA and IoU of 84 % and 74 %, respectively. The results show that semi-supervised semantic segmentation can achieve high-precision identification of coal macerals. The CRF algorithm is then employed on the predictions of the model, and the accuracies for the three coal maceral groups achieved 81 %, 84 %, and 88 %, respectively. Finally, the application results of the model on the testing dataset are discussed to compare the differences between artificial intelligence and manual identification. This study demonstrates that semi-supervised semantic segmentation combined with CRF algorithm can be successfully applied to automatic coal maceral identification.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104712"},"PeriodicalIF":5.6,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143238665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanisms of strain rate-dependent response of naturally fractured coal","authors":"Linan Su,&nbsp;Hamid Roshan","doi":"10.1016/j.coal.2025.104711","DOIUrl":"10.1016/j.coal.2025.104711","url":null,"abstract":"<div><div>The mechanical characteristics of naturally fractured coal under strain rate-dependent loadings can affect engineering activities such as coal seam gas production, gas drainage and CO₂ sequestration. While the macro-(core) scale strain-rate dependent response of fractured coal has been investigated previously, the micro-scale mechanisms driving this core-scale behaviour particularly under recoverable (elastic) bulk deformation remains unexplored. In this study, we conduct a series of systematic multi-scale experiments to shed light on the mechanisms controlling the strain rate dependency of coal.</div><div>Core-scale triaxial tests are initially performed on coal specimens under isotropic and deviatoric loading conditions at different strain rates to identify their strain rate dependency. The results indicate a clear strain rate dependency in dry specimens only under isotropic loading, where the bulk modulus increases with increasing strain rates. Notably, unloading of the specimens shows a considerable strain rate-dependent energy dissipation without any permanent deformation in these isotropic loading tests.</div><div>To explore the identified micro-scale processes causing the energy dissipation and strain rate-dependency, a series of micro-scale mechanical tests are conducted on a coal joint specimen, coupled with microscopy and digital image correlation (DIC) analysis. The results from triaxial and micro-scale tests indicate that the asperity damage within pre-existing fractures during their closure is the primary driver of strain rate dependency at core-scale, without inducing any permanent deformation in bulk specimens.</div><div>To gain further insights into the relationship between asperity damage and energy dissipation under varying strain rates, a series of normal stress loading tests are conducted on identical synthetic joint specimens. These tests confirm a strong correlation between asperity damage and energy dissipation in the identical specimens, demonstrating that slower strain rates lead to greater asperity damage, higher energy dissipation, and reduced stiffness. These findings substantially enhance our understanding of asperity damage-driven strain rate dependency of fractured rock through the evolution of energy dissipation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104711"},"PeriodicalIF":5.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143237897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of high pressure on hydrocarbon generation from Type-I kerogen source rocks: Implications for petroleum system evolution","authors":"Ahmed Khairy ,&nbsp;Clement N. Uguna ,&nbsp;Christopher H. Vane ,&nbsp;Waleed Sh. El Diasty ,&nbsp;Kenneth E. Peters ,&nbsp;Colin E. Snape ,&nbsp;Sherif Farouk ,&nbsp;Will Meredith","doi":"10.1016/j.coal.2025.104708","DOIUrl":"10.1016/j.coal.2025.104708","url":null,"abstract":"<div><div>This study examines the effect of high water pressure (up to 900 bar) on hydrocarbon generation from Type-I kerogen-rich source rocks and compares the results with previously observed effects on Type-II and Type-III kerogens. An immature Type-I oil shale sample from the Duwi Formation, Egypt, was pyrolysed under anhydrous, low-pressure hydrous, and high water-pressure conditions at 320 °C (end of bitumen generation) and 350 °C (oil window) for 6 and 24 h, respectively.</div><div>Pyrolysis at 320 °C showed that bitumen generation was promoted in the presence of water under low-pressure hydrous compared to anhydrous conditions but retarded at high water pressures. At 350 °C, oil generation was also retarded by increasing pressure, with maximum oil yield at 500 bar before dropping by 72% at 900 bar. Lower bitumen yields at 500 bar and higher yields at 900 bar confirm more retention of oil and bitumen in the rock at higher pressure. High water pressure systematically decreased hydrocarbon gas yields, with a more prominent effect at 320 °C because of temperature's dominant impact over pressure at 350 °C. Similarly, non-hydrocarbon gas yields decreased as water pressure increased, with maximum yields under anhydrous and low-pressure hydrous conditions. The retardation effect on bitumen generation was less significant than that on oil and gas generation.</div><div>This study highlights pressure's impact on petroleum generation, particularly in overpressured basins. Elevated pressures on Type-I kerogen source rocks retard oil expulsion, and the retained oil and bitumen within the rock can be directly cracked to gas, suggesting that under such conditions, oil yields may be lower, while unconventional gas resources are likely to be more abundant.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104708"},"PeriodicalIF":5.6,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143237898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Element geochemical characteristics for the roof and floor rocks of coal seams in the Shendong mining area: Emphasis on hazardous element fluorine","authors":"Zheng Zhang ,&nbsp;Guoqing Li ,&nbsp;Lei Wang","doi":"10.1016/j.coal.2025.104709","DOIUrl":"10.1016/j.coal.2025.104709","url":null,"abstract":"<div><div>The Shendong mining area produces over 200 million tonnes of coal annually, resulting in notable gangue output, including materials from coal roof, floor and gangue itself. The hazardous elements, particularly fluorine (F), present in the gangues pose challenges for energy utilization and safe use of mine water. Despite this, studies on the elemental geochemical characteristics of gangues in the Shendong mining area are limited. This study collected 19 samples of coal roof and floor and employed methods such as SEM-EDS, XRD, XRF and ICP-MS to analyse the mineral compositions and quantify major-element oxides, rare earth elements and yttrium (REY), and most trace elements. Additionally, fluorine concentration was determined using the alkali fusion–ion selective electrode method. Results indicate that fluorine has the highest average concentration (655 μg/g) among the trace elements, with an enrichment coefficient of 1.21. The major minerals identified in the samples include clay minerals, quartz, and feldspar. The REY distribution patterns in the investigated samples predominantly show L-type enrichment. Combined analysis of B/Ga, Sr/Ba, V/Cr, U/Th, Ni/Co and <em>δ</em>U suggest that the coal roof and floor formations occurred in a continental freshwater and oxic sedimentary environment. The material source analysis indicates that coal roof and floor rocks are primarily derived from felsic rocks in the upper continental crust, especially a mixed provenance of granite and calcareous mudstone. Principal component analysis (PCA) reveals that the fluorine primarily exists on the surface of illites in an adsorption state, with Cu, Cs, Se, Th and Rb exhibiting similar states of occurrence. Correlation analyses between fluorine concentrations in the coal roof and floor rocks and parameters of ∑LREY, La_N/Lu_N, and <em>δ</em>Ce suggest that fluorine tends to be enriched in weathering residues; additionally, a weakly oxidising environment appears to facilitate fluorine enrichment in these coal roof and floor rocks. The findings in this study can guide the development of effective strategies to reduce fluorine contamination in the mine water; additionally, they aid in developing approaches to address fluorine-related issues during combustion, thereby promoting the safe and efficient utilization of coal gangue as a supplemental fuel resource.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104709"},"PeriodicalIF":5.6,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143083307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A novel hybrid machine learning and explainable artificial intelligence approaches for improved source rock prediction and hydrocarbon potential in the Mandawa Basin, SE Tanzania","authors":"Christopher N. Mkono ,&nbsp;Chuanbo Shen ,&nbsp;Alvin K. Mulashani ,&nbsp;Grant C. Mwakipunda ,&nbsp;Edwin E. Nyakilla ,&nbsp;Erasto E. Kasala ,&nbsp;Fravian Mwizarubi","doi":"10.1016/j.coal.2025.104699","DOIUrl":"10.1016/j.coal.2025.104699","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The oil and gas industry are heavily dependent on hydrocarbon resources, and the identification of potential source rocks is a critical aspect of exploration. Accurate determination of the hydrocarbon generation potential (S1 and S2), thermal maturity (Tmax), and total organic carbon (TOC) of source rocks is essential for predicting both the quantity and quality of hydrocarbons. Traditional methods for evaluating these parameters involve laboratory analyses of drill to cuttings or core samples, which can be time-consuming, expensive, and sometimes biased. Moreover, these methods may not be feasible in cases where core material is unavailable. Therefore, this study evaluates the efficacy of machine learning (ML) models for source rock prediction and hydrocarbon potential in the Mandawa Basin, Tanzania, highlighting their application in sparse data scenarios and for complementing analytical techniques. The ML models evaluated include Group Method of Data Handling Differential Evolution (GMDH-DE), Group Method of Data Handling (GMDH), and Random Forest (RF). The results show that GMDH-DE outperforms both GMDH and RF in predicting S2, S1, Tmax, and TOC. Specifically, GMDH-DE achieved R&lt;sup&gt;2&lt;/sup&gt; values of 0.9932 (training) and 0.9794 (testing) for TOC prediction, highlighting its superior accuracy and generalization capability. For Tmax prediction, GMDH-DE exhibited R&lt;sup&gt;2&lt;/sup&gt; values of 0.9926 (training) and 0.9802 (testing), indicating a precise fit to the data and a strong correlation between input parameters and Tmax values. Furthermore, GMDH-DE demonstrated excellent performance in predicting S1 and S2 during training/testing, with R&lt;sup&gt;2&lt;/sup&gt; values of 0.9919/0.9822 for S1 and 0.9854/0.9708 for S2, showcasing its potential for assessing hydrocarbon generation capacity. The findings also suggest that the source rocks contain a combination of kerogen types II, mixed II/III and III, capable of generating both oil and gas, across a range from immature to mature thermal maturity stages.&lt;/div&gt;&lt;div&gt;Additionally, as GMDH-DE is a black-box model, an Explainable Artificial Intelligence (XAI) tool was integrated into this study to ensure transparency and interpretability of the model's predictions, thereby enhancing trust and reliability in its application. The XAI tool of Shapley Additive Explanation (SHAP) revealed that the model performed most accurately when wireline log measurement of bulk density (RHOB), deep resistivity (LLD), and sonic travel time (DT) were used as input variables, suggesting that these variables significantly impact the model's output.&lt;/div&gt;&lt;div&gt;The findings suggest that GMDH-DE is a reliable tool for source rock prediction, offering valuable insights into source rock quality, quantity, and kerogen type, especially in scenarios with sparse data or to complement traditional methods. By addressing the challenges of limited analytical data and providing robust corrections, this research contributes to advancing machi","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104699"},"PeriodicalIF":5.6,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143437644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic matter accumulation, paleoenvironment and kerogen structure of the Middle Jurassic Dameigou Formation, Qaidam Basin: Evidence from organic petrography and geochemistry","authors":"Zhongrui Wu ,&nbsp;Ralf Littke ,&nbsp;Tianxu Guo ,&nbsp;Sheng He ,&nbsp;Sebastian Grohmann","doi":"10.1016/j.coal.2025.104707","DOIUrl":"10.1016/j.coal.2025.104707","url":null,"abstract":"<div><div>The organic matter in terrestrial sediments provides not only a record of geological events but is also as a vital source of fossil fuels. Its enrichment is fundamentally governed by the interplay of complex depositional environments and diverse climatic conditions. This study presents an integrated investigation utilizing major element oxides, trace elements, rare-earth elements, organic petrography, pyrolytic analysis, and infrared spectroscopy to systematically evaluate the provenance, tectonic setting, paleoclimate, weathering conditions, and organic matter accumulation of the Middle Jurassic Dameigou Formation, as well as to elucidate the chemical composition of kerogen. Geochemical parameters, particularly the Th/Sc vs. Zr/Sc ratios, indicate the absence of recycled sediments throughout the studied succession. Geochemical discrimination diagrams, particularly the Th/Sc vs. Zr/Sc and La/Th vs. Hf plots, provide compelling evidence for felsic volcanic rocks serving as the predominant source material.The interpretation of the tectonic setting as an active continental margin is constrained by multiple discrimination diagrams, such as the La–Th–Sc and Th–Co–Zr/10 ternary systems. The depositional sequence exhibits distinct vertical variations in organic matter composition and paleoenvironmental conditions. Unit 1 is characterized by terrestrially derived macerals (vitrinite and inertinite), while units 2 and 3 show a progressive transition to liptinite-dominated assemblages, primarily composed of lamalginite. Multiple chemical weathering proxies, specifically the Chemical Index of Alteration, Weathering Index, and Sr/Cu ratios, demonstrate that paleoclimatic conditions evolved from warm/humid environments characterized by intense chemical weathering towards cooler conditions with diminished continental weathering intensity. Molecular-level characterization using μ-FTIR and CP-Py-GC/MS reveals distinctive organic matter compositions: unit 1 is dominated by aromatic structures (73.0–83.5 %), while unit 2 shows predominant aliphatic compounds (41.6–72.9 %). The decrease in aliphatic compounds to 39.2 % in unit 3 correlates with increased water salinity, suggesting environmental control on kerogen composition. The δ¹³C values exhibit stratigraphic variations, with comparatively higher values in Unit 1 (−33.01 ‰ to −25.70 ‰) compared to lower values in Units 2 and 3 (−41.56 ‰ to −28.79 ‰), reflecting the higher abundance of terrestrial maceral components in Unit 1 and proximal Unit 2 deposits. These findings provide crucial insights into the depositional evolution and organic matter accumulation mechanisms in the study area.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104707"},"PeriodicalIF":5.6,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143083369","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic modes of occurrence and evolution mechanism of germanium and lithium in coal: Insights from density functional theory","authors":"Ruifeng Mu ,&nbsp;Shaoqing Wang ,&nbsp;Xiaoling Wang ,&nbsp;Haofan Su ,&nbsp;Yan Shao","doi":"10.1016/j.coal.2024.104661","DOIUrl":"10.1016/j.coal.2024.104661","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Critical elements in coal, such as Ge and Li, recently have attracted attention due to their economic significance. Modes of occurrence of these critical elements are academically and practically important, because they can not only provide evidence for sources of elements and minerals in coal and regional geological background information, but also help with design of recovery methods. However, conventional analytical methods are unable to observe precisely the organic binding sites of Ge and Li in coal, and this limits the understanding of their enrichment mechanism and the improvements for recovery techniques. In this study, organic modes of occurrence and evolution mechanism of Ge&lt;sup&gt;4+&lt;/sup&gt; and Li&lt;sup&gt;+&lt;/sup&gt; were investigated at the atom level by constructing molecular models of Ge- and Li-rich coals combined with density functional theory (DFT) methods. The solid-state &lt;sup&gt;13&lt;/sup&gt;C nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and helium pycnometry analyses indicate that the molecular formulas of Ge- and Li-rich coals are C&lt;sub&gt;166&lt;/sub&gt;H&lt;sub&gt;162&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;32&lt;/sub&gt; and C&lt;sub&gt;153&lt;/sub&gt;H&lt;sub&gt;174&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;24&lt;/sub&gt;S, respectively. The DFT analysis reveals that the binding sites for Ge&lt;sup&gt;4+&lt;/sup&gt; in Ge-rich coal are located near the carboxyl group (-COOH) and the pyrrole ring, while those for Li&lt;sup&gt;+&lt;/sup&gt; in Li-rich coal are near the carbonyl group (-C=O) and the pyrrole ring. The Ge&lt;sup&gt;4+&lt;/sup&gt; is immobilized in the Ge-rich coal molecular model through coordination bonds with the O atom in the -COOH and the C atom in the pyrrole ring, while being away from the N atom in the pyrrole ring. Li&lt;sup&gt;+&lt;/sup&gt; forms a coordination bond with the O atom in the -C=O and additional coordination bond with the nearby hydroxyl group during binding to the pyrrole ring. The impact of coal rank on the organic modes of occurrence of Ge&lt;sup&gt;4+&lt;/sup&gt; and Li&lt;sup&gt;+&lt;/sup&gt; was investigated using Wender coals of different ranks, which were one of the earliest proposed coal models. At the lignite stage, oxygen-containing functional groups and aromatic rings show a strong binding ability to Ge&lt;sup&gt;4+&lt;/sup&gt; and Li&lt;sup&gt;+&lt;/sup&gt;, facilitating their enrichment in coals. Along with coal rank advance to bituminous coal, the reduction of oxygen-containing functional groups (e.g., -COOH and -C=O) and the relatively low condensation of aromatic rings decrease binding sites for Ge&lt;sup&gt;4+&lt;/sup&gt; and Li&lt;sup&gt;+&lt;/sup&gt;, and the binding ability also decline, resulting in a decrease in their concentration. In anthracite stage, highly condensed aromatic rings provide binding sites for Ge&lt;sup&gt;4+&lt;/sup&gt; and Li&lt;sup&gt;+&lt;/sup&gt;. The strong binding ability of aromatic rings to Ge&lt;sup&gt;4+&lt;/sup&gt; indicates that it is probably enriched in anthracite, whereas Li&lt;sup&gt;+&lt;/sup&gt; is difficult to enrich owing to its relatively weak binding ability to aromatic rings. The low conte","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"298 ","pages":"Article 104661"},"PeriodicalIF":5.6,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143127865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"","authors":"James C. Hower","doi":"10.1016/j.coal.2024.104672","DOIUrl":"10.1016/j.coal.2024.104672","url":null,"abstract":"","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"298 ","pages":"Article 104672"},"PeriodicalIF":5.6,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}