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This study investigated the differences and correlation between the occurrence characteristics of alkali and alkaline earth metals (AAEMs) among different maceral groups in high-alkali, high-inertinite coal, and provides scientific guidance for the co-separation of AAEMs and inertinite groups in Xinjiang coal. The total AAEMs of inertinite-enriched samples were significantly higher than those in raw coals and vitrinite-enriched samples. Five-step sequential extraction showed that Na mainly occurs as water-soluble sodium (Na-Water) in raw coal and inertinite-enriched samples, accounting for about 53% of the total content, while it exists as organic sodium (Na-NH4Cl and Na-EDTA) in vitrinite-enriched samples, accounting for about 52% of the total content. Ca and Mg are both mainly present in organic form (Ca/Mg-NH4Cl and Ca/Mg-EDTA) in all the samples, with slightly higher proportions present in vitrinite-enriched samples. The contents of K are low in all the samples, which exist in an insoluble state (K-I). Combined microscopy and SEM-EDS analyses have revealed that the localized enrichment of Na in raw coal and inertinite-enriched samples occurs in the inertinite cell cavity, which primarily exists as NaHCO3 combined with quartz crystals, with a maximum content of up to 5.85 wt%. In this study, although EDS spectra could not directly characterize organic Ca and Mg, dolomite and calcite minerals were repeatedly found in the inertinite cell cavity. Moreover, the contents of Ca and Mg in the vitrinite-enriched samples were significantly lower than those in the other samples, which suggests that Ca and Mg are enriched with the inertinite groups. The localized enrichment of AAEMs could not be detected in any of the vitrinite-enriched samples. In summary, though there are significant differences between the occurrence modes of AAEMs in different maceral groups of high-alkali coal, AAEMs have a strong affinity with inertinite, which may be due to the inertinite's abundant pore structures. [ABSTRACT FROM AUTHOR]

The coal found in the Zhundong Coalfield is highly suitable for power generation and gasification. However, the high sodium content within the coal leads to severe boiler slagging and contamination. Additionally, sodium disperses into the gaseous phase to form haze, adversely affecting the local atmospheric environment. This study delved into the distribution and occurrence characteristics and enrichment causes of sodium in the coal, employing sequential extraction experiments and testing methods such as XRF, ICP-OES and SEM-EDS. The findings of this research indicate the following: (1) With the increasing burial depth of coal seams, there is a noticeable decrease in the sodium content within the coal. Sodium is primarily distributed within the coal seam, with higher concentrations observed in the upper portions of the same coal seam. Furthermore, the distribution of sodium within the epipedon, overlying rocks and coal seam also exhibits a decreasing trend. (2) Sodium primarily exists in a water-soluble state within coal seams, with H2O-Na accounting for over 70% of its composition. The ion-exchangeable sodium is higher than that in the roof, floor and gangue. Sodium exists in coal seams in both ionic and hydrated ionic forms. It is worth noting that the minerals within coal are not the primary carriers of sodium. (3) These coal seams were formed in a warm and humid shallow lake peat swamp environment, which is not significantly influenced by terrestrial or marine sources. The enrichment of sodium is primarily influenced by later hydrodynamic conditions. [ABSTRACT FROM AUTHOR]

Mineral matter, including minerals and non-mineral elements, in coal is of great significance for geological evolution, high-value coal utilization, and environment protection. The minerals and elemental geochemistry of Late Permian coals from the M8 coal seam, Shihao mine, Songzao coalfield in Chongqing, were analyzed to evaluate the sediment source, sedimentary environment, hydrothermal fluids, and utilization prospects of critical metals. The average total sulfur (4.21%) was high in coals, which mainly exists in the forms of pyritic sulfur. Kaolinite, pyrite, calcite, quartz, illite and illite/smectite (I/S) mixed layers, and anatase predominated in coals, with trace amounts of chlorite, ankerite, and siderite. Epigenetic cell- and fracture-filling pyrite, veined calcite, and ankerite were related to hydrothermal fluids and/or pore water after the diagenesis stage. Compared to the world's hard coals, As and Cd are enriched in the Shihao M8 coals, and Li, Cr, Co, Zr, Mo, Pb, and Tb are slightly enriched. These high contents of sulfophile elements may be related to seawater intrusion. The terrigenous clastics of the Shihao M8 coals originated from the felsic–intermediate rocks atop the Emeishan Large Igneous Provinces (ELIP) (Kangdian Upland), while the roof and floor samples were derived from Emeishan high-Ti basalt. Through the combination of sulfur contents and indicator parameters of Fe2O3 + CaO + MgO/SiO2 + Al2O3, Sr/Ba and Y/Ho, the depositional environment of peat swamp was found to be influenced by seawater. Although the critical elements in coal or coal ash did not reach the cut-off grade for beneficial recovery, the concentration of Li and Zr were high enough in coal ash. [ABSTRACT FROM AUTHOR]

The occurrence and separation relationships of Na and maceral groups in Zhundong coals were investigated in this study. The sequential extraction results indicate that the total Na content of all samples decreased with increasing sampling depth, and the level in inertinite-enriched samples (inertinite content 81.0%–84.0%) was significantly higher than that in corresponding raw coals and vitrinite-enriched samples (vitrinite content 90%). Additionally, H2O-Na (soluble salt species) and insoluble Na (acid-insoluble residues) were found to be concentrated in the inertinite-enriched samples. In combined SEM–EDS and microscope observations, local Na enrichments were detected in all raw coal and inertinite-enriched samples except for the vitrinite-enriched samples, but only inertinite-enriched samples were found to generally have over 10 wt% of Na enrichments, all of which occurred as NaCl. Moreover, Na is mostly filled or associated with cell-filling minerals in cells of fusinite. The maceral separation and Na removal of Zhundong coal were simultaneously achieved using triboelectrostatic separation. The vitrinite content in concentrates increased up to 60%, along with a reduced Na level, while the inertinite and sodium levels were both evidently raised in tailings. The obvious positive occurrence and separation correlation between sodium and inertinite offers new insight into, and a technical reference for, the sodium removal and maceral processing of Zhundong coal. [ABSTRACT FROM AUTHOR]

During the Late Permian period, the coal from the Jiashun Mine in Xingren City, Guizhou Province, China, is characterized by a high sulfur (5.84%) and lithium (Li) (94.5 μg/g) content. Lithium is a critical metal in the context of global energy transition. Considering the importance of environmental protection and resource utilization, the mode of occurrence and distribution of trace elements in different coal preparation products were investigated. The obtained results indicated the following: (1) The minerals in Jiashun coal were mainly composed of veined and epigenetic pyrite, quartz, and kaolinite. Most of the minerals could be effectively removed from the cleaned coal through gravity separation. (2) The mode of occurrence of rare earth elements and yttrium (REY) in the coal was relatively complex, and they were mainly found in middlings from gravity separation and in flotation tailings. (3) The mode of occurrence of the trace elements in the coal significantly influenced their removal rate. The removal rate was significantly higher for trace elements removed through gravity separation compared to those removed using flotation. The trace elements mainly found in fine-grained minerals wrapped by organic matter or combined with organic portions had better removal results through flotation. The trace elements that occurred both in the minerals and organic matters had low removal rates (<25%) using two coal preparation methods. (4) Li was more enriched in the middlings from gravity separation (98 μg/g) and in flotation tailings (102 μg/g), reaching the marginal grade (80 μg/g) of Li in coal. (5) Li in Jiashun coal may be derived from intermediate-felsic rocks at the top of the Kangdian Upland and late hydrothermal solutions. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) are considered to be one of the most important metal raw materials, and coal seams are one of the potential sources of REEs. As a low-molecular-weight organic acid, oxalic acid has a strong ability to migrate and dissolve minerals. The coal seam is formed by herbaceous plants and contains more oxalic acid, which may affect the enrichment and transport of REEs during coal formation. Based on the provenance minerals and enrichment carriers of REEs in the coal seam, granite and its weathered minerals (plagioclase, kaolinite, montmorillonite, and quartz) were selected for oxalic acid leaching experiments, to clarify the activation ability of oxalic acid for REEs in coal seams. Experimental results have shown that oxalic acid dissolves minerals and leads to the dissolution and migration of REEs. The higher the concentration of oxalic acid, the stronger the dissolution ability. Each element has a similar dissolution ability in high-concentration oxalic acid solutions, while the ionic radius and electronegativity can cause abnormal distribution of individual elements. The REE dissolution ability in different minerals is controlled by the crystal structure, and the re-adsorption of minerals inhibits the dissolution of REEs in low-concentration oxalic acid solutions. In addition, comparative analysis of REE distribution characteristics in natural water shows that the dissolution and migration of REEs are complexly affected by many factors in addition to pH and fluid environment. Therefore, the activation effect of oxalic acid on REEs in coal seams needs to be further studied. [ABSTRACT FROM AUTHOR]

The occurrence characteristics of sodium and its potential relationship with macerals in Zhundong coal, as well as in Shenfu coal with average sodium levels, are investigated in this study. A new five-step sequential extraction method was first conducted for determination. The occurrence status of sodium and its related macerals in samples was determined by microscope and SEM–EDS (scanning electron microscope–energy dispersive X-ray spectroscopy). Soluble sodium salts (H2O-Na) make up the primary proportion of sodium in Zhundong coal, at approximately 50%, while various sodium species are distributed in Shenfu coal with nonobvious differences. Inertinite contains more sodium than vitrinite does in both coals, and the highest enrichment degree of sodium was discovered in inertinite from Zhundong coal, which presented primarily as NaCl crystals (H2O-Na) in fusinite cells, with a local weight percentage of over 15%. More specifically, H2O-Na and insoluble Na both tend to enrich in fusinite. Additionally, it is found that maceral-rich products can be gathered using triboelectrostatic separation, and a portion of sodium can thus be removed from the coal by removing inertinite. This study may provide new insights and references regarding sodium removal from Zhundong coal. [ABSTRACT FROM AUTHOR]

Processes controlling selenium concentrations ([Se]) in mine waters were studied at an operating coalmine district in Xuzhou city, China. The geochemistry and mobility of selenium was studied through leaching experiments, multivariate analysis, and numerical modeling. Results showed that selenium leaching was influenced by selenium occurrence in minerals, pH, electron activity (pe), and sulfur concentration in the water. Selenium occurrence in host rock was mainly sulfide minerals, and clay minerals in coal, respectively. Therefore, the oxidation and dissolution of sulfide minerals and transformation of clays may control the release of selenium. Experimental leaching experiments suggested selenium tends to leach more when the solution has more sulfur dissolved. A positive relationship is established between pH and the amount of Se released into solution with four times more Se released at pH 12 compared to pH 2 when leached with high-purity water. This release behavior is higher in O2-rich environments. The numerical modeling results showed that pH, pe, and sulfur presence in the solution play important roles in selenium adsorption. Selenium was desorbed from adsorbing surfaces under alkaline conditions, specifically when the solution pH was higher than 8. Higher pe values in the solution caused reduced selenium adsorption. In addition, dissolved sulfur competed with selenate for surfaces of adsorption, thus, selenium adsorption decreases as the sulfur concentration increased. [ABSTRACT FROM AUTHOR]

Abstract After flotation cleaning of high-U coal from the Ganhe Mine in China, it was found that levels of V (561 μg/g), Cr (215 μg/g), Mo (159 μg/g), and U (234 μg/g) were still significantly enriched in the clean fraction. However, it was not initially clear whether these elements were associated with organic matter or occurred in fine-grained minerals. In this study, coal samples were analyzed by acid leaching and transmission electron microscopy coupled with energy dispersive spectroscopy (TEM + EDS). Our results showed the following: (1) V and Mo were weakly bonded to organic matter, whereas Cr and U were predominantly associated with organic matter, thereby indicating that Cr and U had a strong organic affinity; (2) the results of high-resolution TEM showed that U occurred in poorly crystalline nanoscale U Ti minerals in flotation-cleaned coals where the mineral was associated with organic matter; and (3) organic-bonded V and Mo were negatively correlated with organic S, but organic-bonded Cr and U were positively related to organic S. Through acid leaching, the contents of V, Cr, Mo, and U in the residue were still much higher than those in world hard coal. Thus, the use of flotation-cleaned Ganhe coals is not recommended to avoid environmental pollution and adverse effects. Highlights • The flotation cleaned coal of Ganhe is significantly enriched with V, Cr, Mo, and U. • Vanadium and Mo are weakly banded to organic matter, but Cr and U are closely associated with organic matter. • Uranium occurs in nanoscale U-Ti minerals, where the mineral is encased in macerals. • The use of Ganhe flotation-cleaned coals are not recommend to avoid the adverse effects. [ABSTRACT FROM AUTHOR]

Rare earth elements and yttrium (REY) in coal, fly ash as well as coal preparation products have attracted much attention due to the increasing demand worldwide. In this paper, the distribution of REY in different size and density fractions, their mode of occurrence, and the insight they provide on the sediment source region of the Reshuihe coal in southern China are studied. The results show that the physical separation method caused light-REY (LREY) to be enriched in the low-density and large-sized coal particles, whereas medium-REY (MREY) and heavy-REY (HREY) are enriched in small-sized and high-density fractions. In addition, LREY are more closely associated with organic matter, while MREY and HREY occur more often in aluminosilicate minerals. Moreover, the sediment source of the Reshuihe coal was mainly derived from the felsic–intermediate rocks at the top of the Emeishan basalt sequence. Further, REY in the feed coal are generally not enriched, though REY are enriched in density fractions of 1.4 kg/L. The combustion products of coal with a density of 1.4 kg/L obtained by gravity separation have a potential economic value as promising raw materials for REY. • LREY (MREY and HREY) are enriched in the larger (smaller) size fractions with low (high) density grades. • LREY are more closely associated with organic matter, while MREY and HREY tend to occur in aluminosilicate minerals. • The combustion products of coals with a density of 1.4 kg/L have a potential economic value. [ABSTRACT FROM AUTHOR]

High-uranium (U) coal is the dominant form of coal in Southwestern China. However, directly utilizing this resource can also harm the environment because this element is radioactive; it is, therefore, necessary to clean this kind of coal before burning. This research studied the geochemistry of toxic elements and their partitioning during the preparation of high-U coal in China. The results show that high-U coals are mainly distributed in Southwestern China and are characterized by a high organic sulfur (S) content and vanadium (V)-chromium (Cr)-molybdenum (Mo)-U element assemblage. These elements are well-correlated with one another, but are all negatively related to ash yield, indicating that all four are syngenetic in origin and associated with organic materials. A mineralogical analysis shows that U in Ganhe and Rongyang coal occurs within fine-grained anatase, clay minerals, guadarramite, and pyrite, while V occurs in clay minerals, pyrite, and dolomite, and Cr occurs in dolomite. Other elements, such as fluorine (F), lead (Pb), selenium (Se), and mercury (Hg), mainly occur in pyrite. By applying a gravity separation method to separate minerals from coal, the content of the enrichment element assemblage of V-Cr-Mo-U in Rongyang coal is still shown to be higher than, or close to, that of the original feed because this element assemblage is derived from hydrothermal fluids during syngenetic or early diagenetic phases, but other elements (beryllium [Be], F, manganese [Mn], zinc [Zn], Pb, arsenic [As], Se, Hg) can be efficiently removed. Once cleaned, the coal obtained by gravity separation was subject to a flotation test to separate minerals; these results indicate that while a portion of V and Cr can be removed, Mo and U remain difficult to extract. It is evident that the two most commonly utilized industrialized coal preparation methods, gravity separation and flotation, cannot effectively remove U from coal where this element occurs in large proportions. Finally, dilute hydrochloric acid (HCl) leaching experiments show that the majority of Mo and a portion of V, Cr, and U are adsorbed in clay minerals and organic matter and, therefore, exist in an adsorbed state. In this state, these elements can be removed using the acid method. Thus, as U cannot be fully removed from coal, the use of high-U coals is not recommended. [ABSTRACT FROM AUTHOR]

The contents of Au, Ga, As, Sb and other elements in two hundred and thirty-four samples of coal, partings, roof and floor collected from Guizhou Province, China were analyzed by Instrumental Neutron-Activation Analysis (INAA). In order to discuss the relationship between Au, Ga in coal and in coal ash, the contents of Au and Ga in 815 °C coal ash were also determined by INAA and partial Ga by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The analysis results showed that: (1) the average contents of Au and Ga in upper Permian coal from Guizhou are 6.92 ng/g and 10.65 μg/g, respectively, far higher than that in Chinese coal and world coal; the average contents of Au (59.73 ng/g) and Ga (19.16 μg/g) in partings, roof and floor are higher than that in the coal and the Clarke value of sedimentary rock (especially for Au); (2) during the coal ashing process, Ga is enriched in the residues more easily than Au, which is mainly because of the difference in the mode of occurrence of the two elements. Gallium mainly occurs as the substitute of Al in the form of isomorph, which makes it hard to volatize; while Au shows a high association with organic matter, sulfide, and carbonates, and some may be nano-gold, which is easily volatile during coal combustion. Only Au occurred in the aluminosilicate is easily left in the residues; (3) we collected data on the Au and Ga contents in coal and coal ash from China and then conducted correlation analysis by combining data from coals and coal ashes worldwide; the cut-off grades of Au and Ga in coal are considered to be 200 ng/g and 60 μg/g, respectively. This method could also be used to determine the cut-off grade of other valuable elements in coal. [ABSTRACT FROM AUTHOR]

Nowadays the industrial coal beneficiation in China could only reduce the ash yield to about 10%, which could not meet the requirement or standard of environment protection. In this work, the possibility of reducing the ash yield was studied from the aspect of geochemistry. The channel samples were collected from two coal seams in Guizhou and Shanxi province, China and then conducted analysis by combining data from coals worldwide. The result reveals that the same coal seam or the coals deposited in the same peat swamp show a significantly positive correlation between ash yield and Al2O3+SiO2 content, and the intercept of regression equation on the ash axis is always less than 5% (generally 2-5%). Overall, the coal from China is featured with a higher intercept compared with that in the other countries. The intercept of 2-5% on the ash axis indicates an original inorganic component in coal-forming peat. The research result also presents a theoretical limitation of coal ash by coal cleaning, because 2-5% of inorganic components in medium-high quality ash coal could hardly be separated by traditional physical coal beneficiation. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the geochemical impact of gob piles on the environment of Tetraena mongolica , a Chinese nationally protected plant. Twenty-five major and trace elements in samples of soil, gangue, roof and floor of coal seams collected from Wuhai, Inner Mongolia, China, were analyzed by atomic fluorescence spectrometry (AFS), X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). The results show that the elements, such as Cu, Pb, Mo, and As, were highly enriched in soil, coal and coal gangue. Between 2003 and 2012, heavy metal concentrations had increased in soil due to mining activities. Leaching and volatilization are the two main pathways that gob piles affect the environment, with the leaching range of the gob piles extending about 0–10 m while the range for volatilization is 3–5 km. The concentration of Cu, Pb, Mo, and As in T. mongolica also shows a positive correlation with the elemental compositions of the roof and floor of the coal seam, and adult individuals have a higher correlation than juveniles. Therefore, the distribution of coal resources and the local geology contribute to the restricted range of T. mongolica in Wuhai. [ABSTRACT FROM AUTHOR]

Highlights: [•] We mainly discuss the partitioning of more than 30 elements during coal extraction. [•] Elements with a higher content in coal are relatively enriched in the organic solvent extracts. [•] The element contents in extracts are positively correlated with the polarity of solvent. [•] The difference in extraction rate could reflect the organic affinity of elements with coal. [Copyright &y& Elsevier]

Abstract: A preliminary method for determining acceptable trace element levels in coal was established. In addition to the conventional coal quality parameters ash and sulfur, potentially hazardous trace elements As, Be, Cd, Cl, Cr, F, Hg, Mn, Ni, Pb and Se were selected for the evaluation, and their environmentally acceptable concentrations in coal were quantified at 5 and 0.5 weight %, and 6.5, 1, 0.8, 400, 15, 120, 0.15, 80, 30, 15 and 2.5mg/kg, respectively. A pollution index (I) is proposed, by which coal is ranked into four classes: acceptable (I ≤0.252), marginal (0.252< I ≤0.514), unacceptable (0.514< I ≤0.751), and ultra-unacceptable coal (I >0.751). 36 coal samples collected from the north of Ordos basin and Shanxi Province, China were classified with the method. Most of the cleaned coals were rated as acceptable or marginal, while the run-in-mine coals, feed coals, middlings and coal slimes were generally ranked as unacceptable or ultra-unacceptable coal. The evaluation results reflect the degree of cleanliness of these coal samples. [Copyright &y& Elsevier]

Abstract: Twenty-six samples including roof, bottom and coal plies of a marine influenced coal bed were collected from the Antaibao mining district, Shanxi, China. The rare earth elements (REEs) were determined in solids and organic solvent extracts. The distribution pattern showed three distinct patterns: shale-like, LREE-rich and HREE-rich. This is attributed to the variable microenvironment of peat-forming swamp, the degree of marine influences and different REE sources. REEs in the coal are mainly controlled by detrital minerals but also affected by seawater. The chondrite-normalized REE patterns of the organic solvent extracts are distinctly different from those of corresponding original coal samples, which show a negative Eu anomaly, a depletion of middle REEs and an enrichment of HREEs. The LREEs in coal extracts are likely adsorbed by hydrogen-containing functional groups, and HREEs are likely bonded to carbon atoms. [Copyright &y& Elsevier]

Abstract: The roof, bottom and 24 coal ply samples were collected by finely partitioning No. 11 coal seam from Antaibao mining district, Shanxi, China in terms of lithotypes. Proximate and sulfur analyses, ICP-AES, ICP-MS, AFS, XRD, SEM–EDX techniques were used on these samples, in order to investigate the vertical variability and origin of sulfur and also the geochemistry of major and trace elements in the seam. The weighted mean content of total sulfur of the 24 coal plies is 2.4wt%, belonging to the medium-sulfur coal, but there are great differences in the contents of total sulfur and forms of sulfur between the 24 plies: total sulfur content >3.0wt% for 5 plies, organic sulfur content >1.0wt% for 13 plies and pyritic sulfur content >2.0wt% for 4 plies. It is found that the differences were mainly caused by the degree of marine influences and the contents of clay minerals as well as the organic matter. The ply 21 has an abnormal high content of inorganic sulfur (pyritic sulfur 9.45wt% and sulfate sulfur 5.97wt%). This was caused by the presence of bauxite minerals-bearing kaolinite in the underlying ply 22 blocking the further infiltration of sulfate from the overlying plies during the deposition. The seam is dominated in kaolinite and, to a lesser extent, in pyrite, and there also exist minor amounts of szomolnokite, diaspore, boehmite, calcite, siderite, dolomite, magnesite, feldspar, gypsum. Szomolnokite and gypsum possibly resulted from the oxidation of pyrite. The seam is greatly characterized by finely-grained pyrite concentrating in cutinite. Hazardous trace elements Hg, Pb and As are mainly concentrated in pyrite, so that they can be partially removed by physical coal cleaning with an aim of removal of sulfur, while thalassophile elements Br,Ca,Cl,Mg and Sr, are clearly associated with the organic sulfur, reflecting that their contents can be decreased by coal blending means due to a partial organic affinity. [Copyright &y& Elsevier]

Abstract: Analyses of the macerals, ash, sulfur and 43 major and trace elements were performed on samples of feed coal, cleaned coal, middlings and slime collected from the Antaibao coal preparation plant, China, and also on samples from coal preparation experiments. This study is focused on the partitioning of elements and macerals during coal preparation and potential environment aspects of the elements. The conclusions are as follows: (1) in comparison with the feed coal, the cleaned coal has a higher vitrinite content and relatively lower inertinite and exinite contents, whereas the middlings and slime have lower vitrinite and exinite contents, and relatively higher inertinite contents. The vitrinite contents in the size-segregated cleaned coals were observed to show a slightly increasing tendency with increasing particle size, while the inertinite contents decreased. (2) Physical coal cleaning is not only effective for removal of ash and sulfur, but also in reducing the concentration of most elements. As, Cd, Co, Cs, Hg, Fe, K, Mg, Nb and Ni are observed to show a high degree of removal, while Br, Be, Cu, U, Mn, Zn and organic sulfur are enriched in the cleaned coal and show a lower degree of removal. The large-sized cleaned coal is cleaner than the smaller sized fractions. (3) The middlings, especially the slime, are enriched in S, Hg, Cr, V, Zn, etc., so that these fractions should not be directly used as fuel. In addition, the concentration of Pb and V in the process water exceeds the limit of relevant environmental water quality standard. Consequently, it is necessary to develop new processes to remove ash, sulfur and hazardous trace elements to the maximum extent. Further studies on deep processing of the middlings and slime and cleaning of the process water should also be performed. [Copyright &y& Elsevier]

Abstract: Mineralogy, sulfur and 40 other element contents were determined on eight samples of the Taixi coal and its preparation products from the Rujigou mining district, China. INAA, ICP-AES, CV-AAS, GAAS, XRD, SEM/EDX, conventional chemical and maceral analysis were carried out on the samples. This study is focused on the partitioning behavior of the minerals and elements during the coal cleaning, and the main factors influencing the partitioning behavior of elements were also discussed. The clay minerals (kaolinite, illite, montmorillonite and chlorite), quartz and, to a lesser extent, carbonate minerals (calcite, dolomite and siderite) dominate the mineralogy of Taixi coal. There is also minor amounts of pyrite and trace amounts of gypsum and feldspar. The quartz is dominantly epigenetic in origin, and clay minerals were modified by the thermal metamorphism. They are easily liberated from the coal by cleaning. However, although the majority of carbonate minerals are also mainly epigenetic in origin, its degree of removal is relatively low, especially with respect to dolomite and siderite, which are often finely dispersed in coal macerals, so that they are mostly retained in cleaned coal. Most of the elements studied could be removed effectively during the cleaning processes, especially for the elements predominantly hosted in coarse, epigenetic minerals. Compared with other sized cleaned coals, the coarse-grained cleaned coal is cleanest and has a relatively low potential of environmental risk. The majority of the potentially hazardous elements are notably enriched in the coal waste so that the waste is not feasible to be used as fuel. The partitioning of elements during the coal cleaning processes is essentially controlled by some factors such as the modes of occurrence of elements, maceral type, grain size and textural relation of minerals, and types of cleaning technique used. [Copyright &y& Elsevier]

Contents of the rare-earth elements (REE) in two coal seams from North Shanxi Province, China, were determined using the instrumental neutron activation method. Based on the REE distribution patterns, and correlation analysis and cluster analysis, the main conclusions were drawn as follows. The REE contents are controlled mainly by the coal-forming environments, but might be affected by acidic solution leaching after peat sedimentation. The REE distribution patterns should be nearly the same in the sublayers of the same coal seam, and the occurrence of abnormal patterns might indicate the geological effect during post-sedimentation. The REE in coals are present mainly in the inorganic phase, and might be derived mainly from terrigenous detrital minerals. Some harmful elements, such as V, P, Mo, Cr, Cu, Mo, Th and Cd, might have cleaning potential during processing and dressing by washing because they are associated with REE. [ABSTRACT FROM AUTHOR]

The indicative significance of organic matter in fossil fuels, particularly polycyclic aromatic compounds (PACs), is a current research hotspot. Petrology, minerals, and organic matter in Late Permian coals from the Moxinpo (MXP) mine located in Chongqing, southwestern China, were analyzed to evaluate the coal rank, coal-forming material source and thermal maturity of organic matter, and sedimentary environment of the peat swamp. Vitrinite and inertinite were dominated by collotelinite, collodetrinite, inertodetrinite, fusinite, and semifusinite. Owing to the high maturity of the coals, liptinite was not observed under the microscope. Clay (kaolinite) and pyrite were the primary minerals in the MXP coals, followed by calcite, quartz, trace amounts of anatase, gypsum, xenotime, and bastnaesite. The minerals in the MXP coals were authigenic primarily in the epigenetic stage. The extract yield of organic matter in coals was low (0.30%), and the saturated and aromatic fractions accounted for approximately 60% of the extractable organic matter. Low ratios of saturated to aromatic compounds reflected the terrestrial higher plants input and high maturity level of the coals. The extracted yield in the host rock samples was much lower than in the coals, while the proportion of saturated hydrocarbons was relatively high. The marine-continental transitional sedimentary environment, distribution of n -alkanes, ∑ C 21 − /∑ C 22 + , and pristane (Pr)/ n -C 17 vs. phytane (Ph)/ n -C 18 indicated that the organic matter originated from the input of terrestrial higher plants and was accompanied by the contribution of marine lower phytoplankton and aquatic organisms. The coal-forming environment of the coal seam was reductive according to the Pr/Ph and sulfur-containing compounds of dibenzothiophenes and benzonaphthothiophenes. The thermodynamic stability controls the presence of polycyclic aromatic hydrocarbons in extractable organic matter. Isomeric compounds with high stability had higher concentrations, such as 2-methylnaphthalene, 2,6 + 2,7-DMN, 4- methylbiphenyl, and 2- methylphenanthrene. [Display omitted] • Macerals were primarily vitrinite and inertinite, while liptinite was absent. • Minerals were dominated by kaolinite, pyrite, calcite, and quartz in the MXP coal. • Organic matter in coals was dominated by the input of terrestrial higher plants. • Coal-forming environment was a reductive and marine-continental transitional environment. • Concentration of isomer compounds was controlled by thermodynamic stability. [ABSTRACT FROM AUTHOR]

• Triboelectrostatic separation efficiency order of three typical inorganic minerals could be expected as kaolinite > quartz > montmorillonite. • Stainless steel would be the best material for tribo-charger among four candidates and copper could also be preferred in a dry environment. • Basic separation could be achieved under low relative humidity but better effect needs high temperature condition. Clay minerals are the inorganic components in low-rank coal, which are particularly hard to remove as they commonly stick to the organic carbonaceous parts. Surface tribocharging characteristics including charge-to-mass ratio and specific resistivity of three typical minerals (kaolinite, montmorillonite and quartz) and clean coal under different relative humidity and temperature conditions were investigated in the present study for the prediction and evaluation of their effect on triboelectrostatic separation. X-ray diffraction (XRD) and X-ray fluorescence (XRF) were applied to minerals for phase and element identification, their microstructures features were also provided for supplementary analyses. Four candidate materials (stainless steel, copper, polyvinyl chloride and polyamide) for tribo-charger were arranged in charge-to-mass ratio measurements. Stainless steel would be the best choice for tribocharging three minerals and clean coal, which could be gathered in opposite plates with a considerable charge gap. Copper could also be a good choice in dry ambient atmosphere. In both comparison of charge-to-mass ratio and specific resistivity, separation efficiency order of three minerals were same in predictions as kaolinite ＞ quartz ＞ montmorillonite. Montmorillonite is weak in charging and holding charges, and the most likely factors should be its interlayer swelling with water molecules and greater isomorphous substitution, which makes it the hardest to separate from coal among three minerals. A basic separating could be achieved if the relative humidity is kept in low range but better results need to be reached under higher environmental temperature. [ABSTRACT FROM AUTHOR]

Transformation of pore and fracture structure of coals with supercritical CO 2 (scCO 2) –H 2 O is a key to CO 2 injection and CH 4 production efficiencies during the CO 2 enhanced coalbed methane process. To study the transformation of pores and fractures in the coals with CO 2 , two reservoir conditions, which simulate1000m (45 °C, 10 MPa) and 2000 m (80 °C, 20 MPa) depths, are applied to four types of high metamorphic coals from Qinshui Basin to study the influences of temperature and pressure on pore volume and pore sized distribution change. Nuclear magnetic resonance, high pressure mercury intrusion, X-ray CT scanning and permeability experiments are performed and the effects of scCO 2 on coal permeability and the influencing factors are discussed. The results show that scCO 2 -H 2 O has a positive effect on the improvement on the pore fracture system. It could add or expand pores and fractures, leading to the increase in pore number, porosity, pore volume, pore specific surface area, connected pore volume, and pore throat number. And then, increased the permeability which had a positive correlation with the experimental temperature and pressure. The growth of permeability could be as high as 114.10 times, and it was higher in horizontal to bedding direction than that of the vertical to bedding direction. Coal expansion could lead to the addition and enlargement of micro-fractures and enhance the connectivity between seepage pores and fractures. Mineral dissolution could lead to the formation of a large number of effectively connected and non-effectively connected pores, especially the latter, which was positively correlated with simulated temperature and pressure. In addition, the effectively connected pores tend to develop in vertical original micro-fractures. Moreover, the more complete the reaction is, the more favorable it is to increase the pore volume of fractures. [ABSTRACT FROM AUTHOR]

The highly effectively removing Na and enriching vitrinite for high-Na high-inertinite low-rank Zhundong coal is of great significance for its efficient and clean utilization. The effect of Na removal by low concentration HCl and AcOH on vitrinite enrichment before and during the flotation process of Zhundong coal are investigated. The vitrinite content in raw coal is only 48.67%, it can be increased to 61.85% and the yield of clean coal is only 26.44% by flotation for raw coal. However, if Na is nearly fully removed by HCl and AcOH before flotation, the vitrinite content can reach as high as 70.22% and the yield of clean coal can be significantly increased to 39.77% for AcOH-treated coal. The comprehensive efficiency is significantly improved to 57.38% from 33.60% for raw coal. When directly adding low concentration AcOH and HCl during flotation process of raw coal, the flotation effects are nearly the same to those of the above Na-removed coals in advance. The results clearly indicate that the effective removal of organic Na on surface and in macropores of coal plays a decisive role in synergistically enriching vitrinite by flotation. Further studies on vitrinite-rich coal (VC) and inertinite-rich coal (IC) and their Na-removed samples show the improvement of flotation effect can be attributed to the effective adjustment of the surface properties of Zhundong coal accompanying the Na removal, which not only improves the hydrophobicity of coal, but also promotes the hydrogen bonding interactions between collector and coal, especially vitrinite. [Display omitted] • The clean coal yield and vitrinite content are increased significantly using Na-removed coal for flotation. • The use of low concentration acids significantly increases the flotation effects of raw coal. • The removal of organic Na plays a decisive role in the synergistically enriching vitrinite by flotation. • The effect of Na removal on vitrinite enrichment in Zhundong coal is studied for the first time. [ABSTRACT FROM AUTHOR]

Magmatic intrusion is a key factor affecting the uranium concentration in coal. It has long been reasoned that magmatic intrusions generally enrich uranium in low-uranium coal. However, less attention has been paid to the redistribution of uranium in uranium-rich coal caused by magmatic intrusions. Thus, a total of 558 uranium data points obtained by spectrophotometric determination were collected from 57 boreholes in the northern Datong Coalfield, rich in lamprophyre intrusions, to determine their effect on the concentration and mode of occurrence of uranium in this Permo-Carboniferous coal. Coal in this area can be classified as either intrusion-affected or unaffected. The uranium concentration was relatively high in both unaffected coal and highly thermally affected coal, while relatively low in slightly thermally affected coal, indicating that lamprophyre intrusions redistributed the uranium in coal. The carbonate content within coal increased markedly with increasing degree of coalification caused by the intrusion. Uranium in unaffected coal was mainly associated with organic compounds, whereas that in intrusion-affected coal occurred mainly in secondary minerals (e.g., carbonates). The uranium concentrations in fresh lamprophyre and carbonatite veins, interspersed therein, were 0.23–0.86 μg/g and 0.97–2.34 μg/g, respectively, suggesting that higher concentrations of uranium in intrusion-affected coal may not have been directly derived from intrusions, but rather from hydrothermal processes at intrusion-coal contacts. The lamprophyre intrusions can reactivate, relocate, or enrich uranium initially complexed with organic matter. With an increase in the degree of coalification, active functional groups responsible for complexation are progressively broken down, resulting in decreased uranium concentrations. However, the uranium concentration was positively correlated with MgO and CaO contents in intrusion-affected coal, indicating that uranyl ions shedding from organic matter may be complexed and subsequently coprecipitated with secondary carbonate minerals. • Lamprophyre intrusion redistributes the uranium in the Permo-Carboniferous coal. • Uranium in unaffected coal is mainly associated with organic matter. • Intrusion reactivates and relocates uranium initially complexed with organic matter. • High-concentration uranium in intrusion-affected coal occurs mainly in dolomite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Particle size screening and desilication make Al in HACFA more enriched. • The contents of Al, Li, Ga, and REE in HACFA reach industrial cut-off grade. • The molecular structure of glass phase is silicon oxygen tetrahedron Q4(0Al). • REE minerals composed of Al, Si, Ca, REE, O, P, F, and Th were found. The abundance and distribution of minerals and elements in high-alumina coal fly ash (HACFA) is the basis for evaluating the resource utilization potential of HACFA and the key to developing a rare element extraction process. The geochemistry and mineralogy of HACFA were investigated by using alkali desilication and particle size screening, combined with multiple analytical techniques. As fly ash particles become finer, the content of mullite decreases, the content of quartz, corundum, and glass increases, and the content of hematite decreases first and then increases. The molecular structure of the glass phase is silicon-oxygen tetrahedron Q4(0Al). Minerals containing REE appear in the shape of fish eggs or oolitic particles, mainly composed of Ai, Si, REE, O. The maximum contents of Al, Li, Ga, and REE in HACFA are 67.65%, 240.57 μg/g, 77.97 μg/g, and 672.95 μg/g, showing a high utilization potential. However, the high contents of harmful elements Cd and Cr need special attention. Most of the trace elements in HACFA mainly reside in the glass phase. The iron-rich minerals are the main carriers of the ferrophilic elements Fe, Zn, Cr, Co, Mn, and Mg. The oxyphilic elements Al, Sc, Ta, Nb, and Ga mainly occur in corundum or mullite. [ABSTRACT FROM AUTHOR]

Pores in coal and their connectivity are important properties of coal, providing network or channels for gas storage and migration within coal, e.g. during the coalbed methane (CBM) recovery. To investigate the growth characteristics and genetic types of pores in coal in terms of macropore and mesopore, the pores of a high-rank coal were measured by various techniques such as the mercury intrusion method, nitrogen adsorption, focused ion beam scanning electron microscopy (FIB-SEM), and X-ray micro-CT (Computed Tomography). Two high-rank coals formed from regional metamorphism collected from the southern Qinshui basin were selected. The FIB-SEM and X-ray micro-CT provides detailed experimental information for development of a three dimensional (3D) pore network model, which was further used to characterize the pore connectivity. Volume percent of pores of these high-rank coals are dominated by mesopores of approximately 10–50 nm in width, and then followed by micropores, along with the smallest volume percent of macropores. The connectivity within this high-rank coal was mesopore-dominated pore network. Electron microscopy observations further revealed there are coalification-related pores and mineral-related pores in the high-rank coal. The coalification-related pores can be classified as secondary gas pores in organic matter and shrinkage-induced pores around quartz and clay minerals; and the mineral-related pores are developed within minerals, and can be classified as dissolution-created pores and intercrystalline pores. The secondary gas pores are macropores and have poor connectivity. The mineral-related pores can be both macropores and mesopores, and have little influence on pore connectivity due to small content of carbonate minerals in these samples. Under electron microscopy, the shrinkage-induced pores are mainly mesopores. The regional metamorphism, with a high abnormal old thermal field in the research area, is the precondition of the formation of the shrinkage-induced pores. The quartz and clay minerals in the coal provide different formation conditions and hence form different shapes of the shrinkage-induced pores. The coal samples include a large number of shrinkage-induced pores that act as the interconnected pores in the coal and exhibit good connectivity. The quartz and clay minerals play a significant role in developing the interconnected pores in the high-rank coal formed from regional metamorphism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mineral composition and element geochemistry of high-alumina coal were clarified. • Enrichment regularity of Al-Li-Ga-REEs in high-alumina coal were revealed. • The provenance of the enriched elements and their parent rocks are identified. • The sedimentary facies and environment with rich elements are established. The content, distribution, and origin of aluminum, lithium, gallium, and rare earth elements (REEs) in the Permo-Carboniferous coal of the Datong coalfield, China, were investigated using optical microscopy and field-emission scanning electron microscopy in conjunction with energy-dispersive X-ray spectrometry, X-ray powder diffraction, and inductively coupled plasma mass spectrometry. The Permo-Carboniferous coal of the Datong coalfield had a high volatile bituminous rank (R o,max = 0.72% on average), and low sulfur and medium ash contents (0.58% and 25.74% on average, respectively). The main minerals in the Datong coal included kaolinite, boehmite, muscovite, calcite, dolomite, siderite, aluminum phosphate, and quartz. Of these, kaolinite, boehmite, calcite, quartz, and phosphates mainly occurred as cell fillings, indicating an authigenic origin. Compared to hard coals worldwide, the Datong coal is enriched in SiO 2 (49.12%; up to 89.93%), Al 2 O 3 (38.88%; up to 71.37%), Li (67 μg/g; up to 354.1 μg/g), Ga (18.1 μg/g; up to 70.2 μg/g), Y (20.8 μg/g; up to 46.1 μg/g), La (34 μg/g; up to 158.5 μg/g), Ce (61.3 μg/g; up to 353.8 μg/g), Tb (0.7 μg/g; up to 3.0 μg/g), Er (2.3 μg/g; up to 5.7 μg/g), and Yb (2.2 μg/g; up to 5.4 μg/g). High-alumina coal (Al 2 O 3 content in ash > 40%) occurred in the northern and southern parts of the coalfield. In the No. 3–5 coal seam, the areas of Li enrichment were located in the north and middle of the coalfield. In the Tashan and Chaigou mines, the Ga content exceeded 30 μg/g. An area of REEs enrichment (REEs content > 300 μg/g) was identified in the Tashan and Xiaoyu mines. In the No. 3–5 coal seam, the REEs distribution pattern showed a wide and gentle "V" curve with a high left and a low right limb. These seams were characterized by a marked depletion in Eu (δ Eu = 0.51) and a weak negative Ce anomaly (δ Ce = 0.95). In the No. 3–5 coal seam, Al, Li, Ga, and REEs mainly occurred in kaolinite. Boehmite and phosphate minerals were the main carriers of Ga and REEs, respectively. The enrichment in Al-Li-Ga-REEs in the No. 3–5 coal seam was mainly influenced by the sedimentary provenance and the environment of coal accumulation. The sediment sources were oxidized bauxite in the weathering crust of the Benxi Formation and the Middle Proterozoic moyite of the Yinshan Oldland to the north and west of the coalfield. Al, Li, Ga, and REEs were transported from the source region as solutes and colloids, and they became enriched in the swamp facies of the delta plain. The Li, Ga, and REEs contents gradually increased from the bottom to the top of the Permo-Carboniferous coal seam. This increase is mainly attributed to the weak influence of seawater. The marked enrichment in heavy REEs at the bottom of the No. 5 coal seam may be related to marine transgression. [ABSTRACT FROM AUTHOR]

Abstract: The concentration, distribution and modes of occurrence of trace elements in thirty coals, four floors and two roofs from Northern China were studied. The samples were collected from the major coalfields of Shanxi Province, Shaanxi Province, Inner Mongolian Autonomous Region, and Ningxia Hui Autonomous Region. The concentrations of seventeen potential hazardous trace elements, including Hg, As, Se, Pb, Cd, Br, Ni, Cr, Co, Mo, Mn, Be, Sb, Th, V, U, Zn, and five major elements P, Na, Fe, Al, and Ca in coals were determined. Compared with average concentration of trace elements in Chinese coal, the coals from Northern China contain a higher concentration of Hg, Se, Cd, Mn, and Zn. They may be harmful to the environment in the process of combustion and utilization. Vertical variations of trace elements in three coal seams indicated the distributions of most elements in coal seam are heterogeneous. Based on statistical analyses, trace elements including Mo, Cr, Se, Th, Pb, Sb, V, Be and major elements including Al, P shows an affinity to ash content. In contrast, Br is generally associated with organic matter. Elements As, Ni, Be, Mo, and Fe appear to be associated with pyrite. The concentrations of trace elements weakly correlate either to coal rank or to maceral compositions. [Copyright &y& Elsevier]

The effects of supercritical CO 2 (scCO 2) on coal pores play a critical role in the geological storage of CO 2 and enhanced coalbed methane recovery (CO 2 -ECBM). To investigate the effects of scCO 2 - H 2 O on the mesopore - macropore structure of high-rank coals, a series of experimental simulations and analyses were performed. Coal samples from the Qinshui Basin, China were exposed to scCO 2 and deionized water for 240 h at 45 °C and 10 MPa and at 80 °C and 20 MPa. The influences on the pore structure were analyzed by performing a mercury intrusion capillary pressure (MICP) measurement. Using a field emission scanning electron microscope (FE-SEM) and an advanced mineral identification control system (AMICS), the geochemical effects of scCO 2 -H 2 O on the same minerals and the same pore or fracture (nanometer to micrometer scale) before and after the reaction were investigated. Based on the changes of the minerals, pores and fractures, the types, targets, expressions, and scopes of the geochemical effects were explored. The experimental results show that after the injection of scCO 2 into the coal samples, the pores and fractures were newly generated or expanded under the interactions of mineral dissolution-precipitation, clay hydration and swelling, coal swelling, and pyrite oxidation with gypsum precipitation. Moreover, the largest improvement of the pore volume was observed in pores larger than 30 μm or smaller than 100 nm, and higher temperatures and pressures were beneficial to the formation of large pores and fractures. The change in the specific surface area (SSA) was mainly caused by the change in pore volume. The corrosion of carbonate minerals showed the most significant contribution to the pore volume of full-scale macropores and mesopores, while most geochemical effects on other minerals had impacts on the mesopores and the macropores smaller than 1 μm. The coal swelling had the most significant effect on the connectivity of the pores in the coal reservoir. • Achieved quantitative characterization on the same mineral and pore-fracture (nanometer to micrometer scale) before and after the reaction. • Summarized the type, mode and scope of geochemical effects on pore-fracture system. • The corrosion of carbonate minerals showed the most significant contribution to the pore volume. • The coal expansion had the most significant effect on the connectivity of the pores in coal reservoir. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) wells with abnormally high H 2 S contents present higher CBM productivity in the low rank coal development areas of Xinjiang, China. The influence of abnormally high H 2 S contents on the coal reservoir properties is an important research topic. Therefore, acidization experiments using a H 2 S solution on low rank coal of the Kuqa-Bay coalfield were conducted. The pore structure characteristics and permeability at the horizontal and vertical stratifications were compared before and after the acidization experiments using various methods including X-ray diffraction (XRD), permeability test, high pressure mercury injection porosimetry (HPMIP), and field emission scanning electron microscope (FESEM). The results show that the H 2 S solution can significantly enhance the permeability of low rank coal. The higher the primary permeability, the greater the permeability amplification would be. The total pore volume (TPV) of the coal increased after the acidization experiment, and the pore distribution and connectivity among micropores, transition pores, and mesopores were also improved. Additionally, the pore volume ratio of the semi-closed pores increased, while that for the macropores showed an opposite trend. The permeability enhancement mechanisms after the H 2 S solution acidizing experiments indicated that the H 2 S solution can dissolve the carbonate minerals in the coal, thus, increasing the permeability, and this was considered as a positive permeability enhancement effect. Meanwhile, the clay minerals in the coal expanded with the H 2 S solution, and this decreased the permeability and was considered a negative permeability enhancement effect. The positive effect precedes the negative effect, leading to an increase in the coal permeability. Additionally, the acidization experiment indicated that the closed pores transform to semi-closed pores, improving the connectivity of the pores and indicating that the permeability of the coal can be further increased. Image 1 • Acidization experiments with H 2 S solution were conducted. • Permeabilities at different stratification directions were increased obviously after H 2 S solution acidizing. • The increment of permeability at horizontal stratification direction is higher. • The pore volumes were increased after the H 2 S solution acidizing. [ABSTRACT FROM AUTHOR]