Geochemical Characteristics of Critical Metal Elements in the No. 9 Coal Seam from the Xinyuan Mine, Northern Qinshui Coalfield, Shanxi Province, China
1
Shanxi Institute of Geology and Mineral Resources Company Limited, Taiyuan 030001, China
2
Shanxi Key Laboratory of Coal and Coal-Measure Gas Geology, Taiyuan 030024, China
3
Provincial Center of Technology Innovation for Coal Measure Gas Co-Production, Taiyuan 030001, China
*
Author to whom correspondence should be addressed.
Minerals 2023, 13(2), 278; https://doi.org/10.3390/min13020278
Submission received: 29 December 2022
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Revised: 5 February 2023
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Accepted: 10 February 2023
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Published: 16 February 2023
(This article belongs to the Special Issue Coal: Chemical, Geochemical and Petrographical Aspects)
Abstract
:As one of the main fossil fuels globally, coal can be enriched with a variety of critical metal elements in specific geological conditions. This paper investigates the mineral compositions and concentrations of major and minor element oxides and trace elements in the No. 9 coal from the Xinyuan mine of the northern Qinshui coalfield, China, and discusses the modes of occurrence and enrichment mechanisms of critical metal elements such as Li, Ga, Th and REY. The mineral compositions of the No. 9 coal are primarily represented by clay minerals and quartz, with a small amount of calcite, siderite, anatase, etc. The major element oxides in the No. 9 coal are dominated by SiO2 and Al2O3. Compared with world hard coal, the No. 9 coal of the Xinyuan mine is rich in Li (CC = 8.00) and Th, slightly enriched with Pb, Sc, Ga, Y, La, Ce, Tb, Dy, Er, Yb and Hg, and depleted in Mn, Co, Ni, Rb, Cs and Tl. The critical metal elements such as Li, Ga, Th and REY that enriched No. 9 coal mainly occur in aluminum silicates. The genetic type of the critical metal elements in the No. 9 coal from the Xinyuan mine is source rock-controlled type. The critical metal minerals and solutions from the source area were transported to the study area by the action of water. Due to the change of swamp water conditions, the critical metal elements were combined with clay minerals and enriched the coal.
1. Introduction
Critical metals and mineral resources play an irreplaceable and important role in new materials, new energy, information technology, and the aerospace industry [1]. As one of the main fossil fuels globally, coal can be enriched with a variety of beneficial elements, including critical metal elements (e.g., Li, Sc, V, Ga, Ge, Se, Y and rare earth elements, Zr, Nb, Au, Ag, and platinum group elements, Re, and U [2]), in specific geological conditions [2,3,4], and can form ‘coal-hosted rare metal deposits’ or ‘metalliferous coal’ [5,6].
Coal-hosted critical metal elements are an important direction in the study of coal geology and mineral deposits. In recent years, researchers from the United States [7,8], Europe [9,10,11], Russia [12,13], South Africa [14] and China [15,16,17,18] have all conducted research in this field and achieved a set of high-level research results. The Qinshui coalfield is an important lean coal and anthracite base in Shanxi Province, and it is also one of the most important areas for coalbed methane exploration and exploitation. In terms of the research on critical metal elements, Zhao et al. [19,20] systematically studied the distribution and enrichment origin of critical metals such as Li, and rare earth elements in the coal from Jincheng mining area in the southeastern Qinshui coalfield. Wang et al. [21] studied the distribution characteristics of rare earth elements in coal from the Qinshui coalfield. Hou et al. reported the latest data on the petrology, mineralogy, and coal geochemistry of the No. 15 coal seam in the southeastern Qinshui basin [22]. However, there is little research on critical metals from the northern Qinshui coalfield. In this study, we investigate the mineralogical and geochemical characteristics of critical metal elements in the No. 9 coal from the Xinyuan mine of the northern Qinshui coalfield, Shanxi Province, and evaluate the factors influencing its enrichment with critical metal elements.
2. Geological Setting
The Qinshui coalfield is located between the Taiyue Mountain and the middle southern section of the Taihang Mountain in the southeast of Shanxi Province. The coal-bearing area of the Qinshui coalfield is 32,084 km2. The main coal-bearing strata are the Carboniferous Taiyuan formation and the Permian Shanxi formation. The Taiyuan formation is mainly composed of limestone and clastic rocks, and has several layers of coal seams. It results from the interactive deposition of the lagoon–tidal flat and the carbonate platform against the background of the epicontinental sea. The Shanxi formation is dominated by clastic rocks, with several layers of coal seams, which are a set of shallow water delta deposits. The Shanxi formation shows characteristics of coastal transgression and regression, and gradually transitions to fluvial facies deposition. The coal rank distribution within the Qinshui Basin was intimately associated with magmatic activity due to a tectono-thermal event during the Yanshanian Orogeny of the Late Jurassic/Early Cretaceous age [20].
The Xinyuan mine is located in Yangquan mining area of the northern Qinshui coalfield and covers an area of 135.66 km2, with an intended production capacity of 5 million tons per year. The Xinyuan mine is currently mining the No. 3 and the No. 9 coals. The No. 9 coal is located in the middle of the Taiyuan formation. The thickness of the coal seam ranges from 0 m to 5.79 m, with an average thickness of 2.03 m. It is a thin-thick coal seam with a mining index of 0.69 and a thickness variation coefficient of 76%. The floor is mainly composed of mudstone, sandy mudstone, fine sandstone, and siltstone.
3. Sampling and Analytical Techniques
A total of 13 samples were collected from a vertical profile of the No. 9 coal in the working face at the Xinyuan mine, including 10 coal samples and 3 roof samples. From top to bottom, the samples were labeled XY-D1, XY-D2, XY-D3, XY-M1, XY-M2, XY-M3, XY-M4, XY-M5, XY-M6, XY-M7, XY-M8, XY-M9, and XY-M10. The roof sample XY-D1, XY-D2 and XY-D3 was made up of a pyrite layer, carbonaceous mudstone and mudstone, respectively. After sampling, all samples were immediately packed in plastic bags to minimize oxidation and contamination.
Proximate analyses were conducted to determine the moisture content, ash yield and volatile matter yield of the collected samples based on ASTM Standard D7582-2015 [23]. The contents of C, H, and N were determined using an elemental analyzer (Leco CHN628SO, St. Joseph, MI, USA). The total sulfur (St,d) was determined based on the Chinese Standard Method GB/T 214-2007 [24]; the forms of sulfur (Sp,d, pyritic sulfur; Ss,d, sulfate sulfur; So,d, organic sulfur) were determined based on the Chinese Standard Method GB/T 215-2003 [25].
The mineral contents and compositions were determined using an X-ray powder diffractometer (XRD, Rigaku, SmartLab, Osaka, Japan). The morphology and modes of occurrence were observed using a field emission scanning electron microscope (FE-SEM, Tescan, Mira3-LMU, Brno, Czech) equipped with an energy-dispersive X-ray spectrometer (EDS, Oxford, MAX-20, High Wycombe, UK).
The concentrations of the major element oxides were measured using an X-ray fluorescence spectrometer (XRF, Regaku, ZSXPrimusIV, Osaka, Japan). The concentrations of trace elements were determined using an inductively coupled plasma mass spectrometer (ICP-MS, ThermoFisher, iCAP Q, Bremen, Germany).
The main steps of the sample digestion were as follows: (30 ± 0.4) mg samples were weighed and ground to less than 200 mesh and placed into the digestion tank, and 2 mL HNO3, 0.5 mL HF and 0.25 mL HClO4 were added in turn. The digestion tank was numbered and placed on the electric heating plate for cold digestion. After the gas was completely released, the samples were kept in the oven at 180 °C for 12 h. After cooling, the digestion tank was taken out and placed on the electric heating plate for treatment. When the solution was gelatinized, 2mL diluted nitric acid was added to mix it. Then, the digestion tank was placed in the oven at 165 °C for 5 h, taken out and cooled, and then filled to (30 ± 0.1) g with pure water.
4. Results and Discussion
4.1. Coal Chemistry
Table 1 shows the result of proximate analysis, ultimate analysis, total sulfur, and forms of sulfur from the No. 9 coal and roof samples of the Xinyuan mine. The moisture content in the No. 9 coal ranges from 0.61% to 1.02%, with an average value of 0.82%. The ash yield ranges from 14.81% to 41.00%, with an average of 28.90%. The volatile matter yield ranges from 13.01% to 20.65%, with an average of 16.53%. The total sulfur content ranges from 0.33% to 0.59%, with an average of 0.43%. According to the Chinese Standard GB/T 15224.1-2018 [26] and GB/T 15224.2-2010 [27], coal samples XY-M1~XY-M4 in the No. 9 coal are ultra-low sulfur and medium-high ash coal, coal samples XY-M5~XY-M8 are low-sulfur and low-ash coal, and coal samples XY-M9~XY-M10 are ultra-low sulfur and medium-high ash coal.
4.2. Mineral Compositions
The mineral compositions of the No. 9 coal and related roof samples from the Xinyuan mine are shown in Table 2. The major minerals (>3%) in the roof samples are primarily represented by clay minerals and quartz, and to a lesser extent, by pyrite and ankerite. Scanning electron microscope (SEM) images of the roof sample XY-D1 (pyrite layer) show that most of the pyrites are broken (Figure 1A) and scattered in clay minerals and organic matter (Figure 1B).
The major minerals (>3%) in the upper part of the No. 9 coal (samples XY-M1~XY-M4) are clay minerals and quartz, followed by the minor minerals (>1%) such as anatase, magnesite, gypsum, barite, etc. SEM images of the sample XY-M1 show that the clay minerals mainly occur in the infillings of cell cavities, or are mixed with the organic matter (Figure 1C); the anatases are embedded in organic matter as blocks or layers (Figure 1D). The major minerals in the middle part of the No. 9 coal (samples XY-M5~XY-M8) are clay minerals, quartz, calcite, dolomite, ankerite, analcime, barite and anatase, and the mineral compositions are mainly characterized by a higher content of carbonate minerals. SEM images of the sample XY-M7 show that carbonate minerals coexist closely with clay minerals (Figure 1E) and organic matter (Figure 1F). The mineral compositions of the lower part of the No. 9 coal (sample XY-M9~XY-M10) are similar to the upper part; the major minerals are clay minerals, quartz and anatase with occasional siderite, gypsum, etc.
4.3. Concentrations of Major and Minor Element Oxides
The studied elements can be grouped as major elements (>1%), minor elements (1–0.1%) and trace elements (<0.1%). The concentrations of major and minor elements are shown as oxides and listed in Table 3. The major element oxides in the No. 9 coal are dominated by SiO2 and Al2O3. The concentration of SiO2 ranges from 14.81% to 41.00%, with an average of 13.89%; the concentration of Al2O3 content ranges from 5.73% to 18.36%, with an average of 12.48%. Compared with the average value of major and minor element oxides in common Chinese coal [28], the No. 9 coal from the Xinyuan mine has relatively higher concentrations of SiO2, Al2O3 and TiO2, and lower concentrations of Fe2O3, CaO, MgO, P2O5, Na2O, K2O. Vertically, the upper and lower part of the No. 9 coal from the Xinyuan mine (sample XY-M1~XY-M4, XY-M9~XY-M10) are mainly characterized by higher SiO2, Al2O3, TiO2 and lower CaO, while the middle part of the No. 9 coal (sample XY-M5~XY-M8) is mainly characterized by higher CaO and lower SiO2, Al2O3, and TiO2. The vertical distribution of the major and minor element oxides (Table 3) is coherent with the mineral compositions (Table 2).
The average ratio of SiO2/Al2O3 is 1.12, which is higher than the average of Chinese coal (1.42), indicating a higher level of Al2O3. Coal with Al2O3 ≥ 40% in ash is called high-aluminum coal; the concentration of Al2O3 in ashes from the No. 9 coal of the Xinyuan mine ranges from 38.72% to 44.94%, with an average of 42.16%, reaching the standard of high-aluminum coal. The fly ash produced by the combustion of high-aluminum coal can be used as a substitute for bauxite to prepare alumina, which has high exploitation and utilization potential.
4.4. Concentrations of Trace Elements
The concentrations of trace elements in the No. 9 coal and roof samples from the Xinyuan mine are shown in Table 4. Figure 2 shows the concentration coefficients (CC [29], the ratio of elemental concentrations between the studied sample and world hard coal). Compared with world hard coals [30], the No. 9 coal from the Xinyuan mine is enriched (CC > 5) with Li (CC = 8.00) and Th (CC = 5.41), slightly enriched (2 < CC < 5) with Pb (CC = 4.84), Sc (CC = 2.24), Ga (CC = 3.48), Y (CC = 2.74), La (CC = 2.09), Ce (CC = 2.42), Tb (CC = 2.29), Dy (CC = 2.02), Er (CC = 2.50), Yb (CC = 2.31) and Hg (CC = 2.71), and depleted(CC < 0.5) in Mn, Co, Ni, Rb, Cs and Tl; the rest of the trace elements have similar concentration levels to the average of world hard coal.
4.5. Geochemical Characteristics of Selected Critical Metal Elements
4.5.1. Li
The distribution area of lithium-rich coal in China is mainly located in the Junger coalfield of Inner Mongolia [32], the Ningwu coalfield [33,34,35] and the Jincheng mining area of Shanxi [20]. The concentrations of Li in the No. 9 coal from the Xinyuan mine range from 45.8 to 191 μg/g, with an average value of 111.9 μg/g, which is much higher than the average value of world coal [30] and Chinese coal [28]. According to the concentration coefficient (CC) classification levels proposed by Dai et al. [29], the CC value of Li in the No. 9 coal from the Xinyuan mine is 8.00, which is classified as an enrichment level of (5 < CC < 10), close to a high enrichment level (CC > 10). The vertical distribution of Li in the No. 9 coal is shown in Figure 3. The concentrations of Li in the roofs range from 48.2 to 120 μg/g, with an average value of 86.0 μg/g. The concentrations of Li in the upper part of the No. 9 coal (sample XY-M1~XY-M4) are higher, with an average value of 142.5 μg/g; the concentrations of Li in the middle part of the No. 9 coal (sample XY-M5~XY-M8) are lower, with an average value of 48.35 μg/g; the concentrations of Li in the lower part of the No. 9 coal (sample XY-M9~XY-M10) are the highest, with an average value of 178 μg/g.
4.5.2. Ga
The distribution area of gallium-rich coal in China is mainly located in Junger coalfield [36,37] and the Daqingshan coalfield [38,39] in Inner Mongolia. The concentrations of Ga in the No. 9 coal from the Xinyuan mine range from 18 to 27 μg/g, with an average value of 20.9 μg/g, which is higher than the average value of world coal and Chinese coal. According to the concentration coefficient (CC) classification levels proposed by Dai et al. [29], the CC value of Ga in the No. 9 coal from the Xinyuan mine is 3.48, which is classified as slightly enriched. The vertical distribution of Ga in the No. 9 coal is shown in Figure 3. The concentrations of Ga in the roofs range from 31 μg/g to 39 μg/g, with an average value of 34 μg/g. The average concentration of Ga in the upper part of the No. 9 coal (sample XY-M1~XY-M4) is 22.5 μg/g, and the average concentration of Ga in the middle part of the No. 9 coal (sample XY-M5~XY-M8) is 19 μg/g; the average concentration of Ga in the lower part of the No. 9 coal (sample XY-M9~XY-M10) is 21.5 μg/g. Vertically, there is little difference in the concentrations of Ga in the No. 9 coal.
4.5.3. Th
The concentrations of Th in the No. 9 coal from the Xinyuan mine range from 7 μg/g to 35 μg/g, with an average value of 17.3 μg/g, which is higher than that in world coal and Chinese coal. According to the concentration coefficient (CC) classification levels proposed by Dai et al. [29], the CC value of Th in the No. 9 coal from the Xinyuan mine is 5.41, which is classified as slightly enriched. The vertical distribution of Th is shown in Figure 3. The vertical distribution of Th is similar to Li. The concentrations of Th in the roofs range from 15 μg/g to 34 μg/g, with an average value of 23 μg/g. The concentrations of Th in the upper part of the No. 9 coal (sample XY-M1~XY-M4) are higher, with an average value of 23.5 μg/g; the concentrations of Th in the middle part of the No. 9 coal (sample XY-M5~XY-M8) are lower, with an average value of 7.5 μg/g; and the concentrations of Th in the lower part of the No. 9 coal (sample XY-M9~XY-M10) are the highest, with an average value of 24.5 μg/g.
4.5.4. Modes of Occurrence of Li, Ga and Th
Previous studies have shown that Li in coal mainly occurs in silicate minerals [40], especially in clay minerals and muscovite [41]; Ga in coal mainly occurs in clay minerals [40], partly in boehmite or diaspore [36,37,42], and Th in coal mainly occurs in aluminosilicate minerals [40]. The Pearson correlation coefficients between Li, Ga, Th, REY, ash yield, total sulfur and some major oxides in the No. 9 coal from the Xinyuan mine are shown in Table 5. Li, Ga and Th have substantial positive correlations with ash yield, with correlation coefficients of 0.924, 0.640 and 0.810, respectively, indicating that Li, Ga and Th mainly exist in inorganic components. Li, Ga and Th are negatively correlated with total sulfur, indicating that they do not occur in sulfur minerals. The correlation coefficients of Li, Ga and Th with SiO2 are 0.912, 0.633 and 0.799, respectively, and the correlation coefficients of Li, Ga and Th with Al2O3 are 0.922, 0.632 and 0.804, respectively, indicating that Li, Ga and Th mainly occur in aluminum silicates. Clay minerals may be the main carrier.
4.6. Geochemical Characteristics of Rare Earth Elements
The concentrations of REY in the No. 9 coal from the Xinyuan mine range from 80.18 μg/g to 232.85 μg/g, with an average value of 147.74 μg/g (Table 6), which is higher than that in world coal and Chinese coal. The concentrations of REY in the roofs range from 191.63 μg/g to 335.05 μg/g (Figure 3), with an average value of 258.09 μg/g, which is higher than the average concentration of REY in coal. The upper part of the No. 9 coal (samples XY-M1~XY-M4) has higher concentrations of REY, with an average value of 170.10 μg/g, while the middle part of the No. 9 coal (samples XY-M5~XY-M8) has lower concentrations of REY, with an average value of 90.26 μg/g; the lower part of the No. 9 coal (samples XY-M9~XY-M10) has the highest concentration level of REY, with an average of 218.01 μg/g. The vertical distribution of REY is consistent with the ash yield, SiO2, Al2O3, Li and Th. The correlation coefficients of REY with ash yield, Al2O3 and SiO2 are 0.822, 0.801 and 0.813, respectively, suggesting that REY mainly occurs in aluminosilicate minerals.
REY is classified into three categories, following Seredin and Dai [43]: LREY (Light REY), including La, Ce, Pr, Nd and Sm; MREY (Medium REY), including Eu, Gd, Tb, Dy and Y; and HREY (heavy REY), including Ho, Er, Tm, Yb and Lu. The corresponding enrichment types of REY are also classified into L-type (LaN/LuN > 1), M-type (LaN/SmN < 1 and GdN/LuN > 1) and H-type (LaN/LuN < 1) (Table 6). The concentrations of rare earth elements in the No. 9 coal are normalized to the average concentrations of the upper continental crust (UCC) [44]. The distribution patterns of REY in the No. 9 coal and related roof samples from the Xinyuan mine are shown in Figure 4.
The REY enrichment type in the upper part of the No. 9 coal from the Xinyuan mine is M-type, while in the middle and lower part of the No. 9 coal, the REY enrichment types are L-type and H-type. The REY enrichment types in the roof samples are L-type and H-type. The EuN/EuN* values of the No. 9 coal range from 0.79 to 0.97, with an average of 0.91, showing slight negative Eu anomalies. Most of the negative Eu anomalies are inherited from the source rocks [45], indicating that the main source of REY is terrigenous debris. The average EuN/EuN* value of the roof samples is 0.82, suggesting a greater influence of terrigenous debris. The CeN/CeN* values of the No. 9 coal range from 0.99 to 1.29, with an average value of 1.11. Generally, there are no significant Ce anomalies in the No. 9 coal, while the CeN/CeN* values in the middle and lower part of the No. 9 coal are lower than that in the upper part. The negative Ce anomalies indicate that the lower part of the No. 9 coal is more affected by the seawater [46].
4.7. Enrichment Mechanism of Critical Metal Elements in Coal
The genetic types of trace element enrichment in Chinese coals mainly include source rock-controlled, marine environment-controlled, hydrothermal fluid-controlled, groundwater-controlled, and volcanic ash-controlled types. [28]. The concentrations of critical metal elements such as Li, Ga, Th and REY in the No. 9 coal from the Xinyuan mine are distributed in a pattern of high in the upper part, low in the middle part and high in the lower part, which is consistent with the distribution of ash yield, SiO2 and Al2O3; thus, the Li, Ga, Th and REY mainly occur in aluminosilicate minerals, i.e., clay minerals. SEM images show that the clay minerals, calcite, siderite and organic matter in the No. 9 coal and roof samples are mixed with each other, and some of the mineral crystals had been broken into fragments, which may suggest a transporting process. The genetic type of critical metal elements such as Li, Ga, Th and REY in the No. 9 coal from the Xinyuan mine is source rock-controlled type.
The critical metal minerals and solutions from the source area were transported to the study area by the action of water. Due to a change in swamp water conditions, the critical metal elements were combined with clay minerals and enriched the coal. The No. 9 coal from the Xinyuan mine can be divided into upper, middle and lower parts according to the vertical distribution of the critical metal elements. The upper and lower parts of the No. 9 coal have a higher concentration of critical metal elements due to a higher content of clay minerals. The clay minerals are negatively charged in nature and have a high surface-to-volume ratio, which enables the critical metal elements, usually positively charged, to be adsorbed [47]. However, the higher content of carbonate minerals in the middle part of the No. 9 coal leads to the weakening of its adsorption capacity for critical metal elements.
5. Conclusions
The mineral compositions of the No. 9 coal from the Xinyuan mine are primarily represented by clay minerals and quartz, and to a lesser extent, contain a small amount of calcite, siderite, magnesite, anatase, and gypsum. SEM images show that the clay minerals, calcite, siderite and organic matter in the No. 9 coal and roof samples are mixed with each other, and most of the mineral crystals had been broken into fragments, suggesting a transporting process.
The major element oxides in the No. 9 coal are dominated by SiO2 and Al2O3. Compared with the average value of major element oxides in common Chinese coal, the No. 9 coal has relatively higher concentrations of SiO2, Al2O3 and TiO2, and lower concentrations of Fe2O3, CaO, MgO, P2O5, Na2O, and K2O. The No. 9 coal of the Xinyuan mine is enriched with Li and Th, slightly enriched with Pb, Sc, Ga, Y, La, Ce, Tb, Dy, Er, Yb and Hg, and depleted in Mn, Co, Ni, Rb, Cs and Tl compared with world hard coals. The rest of the trace elements have similar concentration levels to the averages of world hard coal.
The critical metal elements such as Li, Ga, Th and REY that enriched the No. 9 coal mainly occur in aluminum silicates; clay minerals may be the main carrier. The genetic type of the critical metal elements such as Li, Ga, Th and REY in the No. 9 coal from the Xinyuan mine is source rock-controlled type. The critical metal minerals and solutions from the source area were transported to the study area by the action of water. Due to a change in swamp water conditions, the critical metal elements were combined with clay minerals and enriched the coal.
Author Contributions
Conceptualization, J.L.; methodology, J.L.; software, J.L.; validation, S.Z., H.W. and X.X.; formal analysis, J.L.; investigation, J.L.; resources, S.Z., H.W. and X.X.; data curation, J.L.; writing—original draft preparation, J.L.; writing—review and editing, J.L.; visualization, J.L.; supervision, S.Z. and H.W.; project administration, S.Z., H.W. and X.X.; funding acquisition, S.Z., H.W. and X.X. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the National Key Research & Development Program of China (grant number: 2021YFC2902004), the Central Guidance on Local Science and Technology Development Fund Project of Shanxi Province (grant number: YDZX20201400001051) and the National Natural Science Foundation of China (grant number: 41802193, 41902180).
Data Availability Statement
Not applicable.
Acknowledgments
The authors would like to thank the anonymous reviewers for their helpful suggestions and comments.
Conflicts of Interest
The authors declare no conflict of interest.
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Figure 1.
SEM images of minerals in the No. 9 coal and related roof samples from the Xinyuan mine: (a) Pyrite in sample XY-D1; (b) Pyrite and clay minerals in sample XY-D1; (c) Clay minerals in sample XY-M1; (d) Anatase in sample XY-M1; (e) Siderite and clay minerals in sample XY-M7; (f) Siderite and calcite in sample XY-M7.
Figure 1.
SEM images of minerals in the No. 9 coal and related roof samples from the Xinyuan mine: (a) Pyrite in sample XY-D1; (b) Pyrite and clay minerals in sample XY-D1; (c) Clay minerals in sample XY-M1; (d) Anatase in sample XY-M1; (e) Siderite and clay minerals in sample XY-M7; (f) Siderite and calcite in sample XY-M7.
Figure 2.
Concentration coefficients of trace elements in the No. 9 coal and related roof samples from the Xinyuan mine.
Figure 2.
Concentration coefficients of trace elements in the No. 9 coal and related roof samples from the Xinyuan mine.
Figure 3.
Vertical distribution of Li, Ga, Th and REY in the No. 9 coal and related roof samples from the Xinyuan mine.
Figure 3.
Vertical distribution of Li, Ga, Th and REY in the No. 9 coal and related roof samples from the Xinyuan mine.
Figure 4.
Distribution patterns of REY in the No. 9 coal and related roof samples from the Xinyuan mine; values are normalized by the average concentration of REY in upper continental crust [44].
Figure 4.
Distribution patterns of REY in the No. 9 coal and related roof samples from the Xinyuan mine; values are normalized by the average concentration of REY in upper continental crust [44].
Table 1.
Proximate and ultimate analysis and sulfur contents of the No. 9 coal and related roof samples from the Xinyuan mine (%).
Table 1.
Proximate and ultimate analysis and sulfur contents of the No. 9 coal and related roof samples from the Xinyuan mine (%).
| Sample | Mad 1 | Ad 2 | Vdaf 3 | Cdaf 4 | Hdaf 5 | Odaf 6 | Ndaf 7 | St,d 8 | Sp,d 9 | Ss,d 10 | So,d 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| XY-D1 | 0.88 | 69.41 | 12.00 | nd 12 | nd | nd | nd | 7.87 | 6.65 | 0.18 | 1.04 |
| XY-D2 | 1.06 | 53.89 | 11.45 | 79.40 | 4.79 | 7.50 | 1.58 | 3.10 | 2.46 | 0.20 | 0.44 |
| XY-D3 | 0.99 | 74.23 | 13.40 | nd | nd | nd | nd | 0.16 | nd | nd | nd |
| XY-M1 | 0.70 | 41.00 | 13.31 | 83.91 | 4.49 | 9.76 | 1.28 | 0.33 | 0.10 | 0.02 | 0.21 |
| XY-M2 | 0.84 | 40.86 | 13.01 | 83.24 | 4.61 | 10.29 | 1.30 | 0.33 | 0.10 | 0.04 | 0.19 |
| XY-M3 | 0.74 | 36.21 | 20.06 | 85.36 | 4.33 | 8.48 | 1.30 | 0.34 | 0.13 | 0.03 | 0.18 |
| XY-M4 | 0.61 | 36.95 | 20.65 | 85.21 | 4.34 | 8.64 | 1.28 | 0.34 | 0.08 | 0.01 | 0.25 |
| XY-M5 | 0.98 | 15.35 | 14.58 | 90.34 | 3.89 | 2.83 | 1.31 | 0.54 | 0.07 | 0.00 | 0.47 |
| XY-M6 | 0.90 | 14.81 | 14.37 | 90.17 | 3.92 | 3.79 | 1.47 | 0.55 | 0.06 | 0.00 | 0.49 |
| XY-M7 | 1.02 | 15.84 | 14.79 | 90.28 | 3.91 | 3.64 | 1.51 | 0.56 | 0.08 | 0.00 | 0.48 |
| XY-M8 | 1.02 | 17.15 | 14.95 | 89.79 | 4.00 | 3.97 | 1.54 | 0.59 | 0.09 | 0.00 | 0.50 |
| XY-M9 | 0.68 | 34.86 | 19.60 | 86.12 | 4.22 | 7.74 | 1.36 | 0.36 | 0.07 | 0.00 | 0.29 |
| XY-M10 | 0.68 | 35.94 | 19.99 | 84.78 | 4.21 | 9.11 | 1.35 | 0.35 | 0.07 | 0.00 | 0.28 |
1 M, moisture; ad, air-dry basis; 2 A, ash yield; d, dry basis; 3 V, volatile matter yield; daf, dry and ash-free basis; 4 C, carbon; 5 H, hydrogen; 6 O, oxygen; 7 N, nitrogen; 8 St, total sulfur; 9 Sp, pyritic sulfur; 10 Ss, sulfate sulfur; 11 So, organic sulfur; 12 no data; 12 nd, no data.
Table 2.
Mineral compositions of the No. 9 coal and related roof samples from the Xinyuan mine, determined by XRD (%).
Table 2.
Mineral compositions of the No. 9 coal and related roof samples from the Xinyuan mine, determined by XRD (%).
| Sample | Qz 1 | CM 2 | Cal 3 | Dlm 4 | Ank 5 | Py 6 | Sd 7 | Mag 8 | Gp 9 | Fsp 10 | Anc 11 | Bar 12 | Ant 13 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| XY-D1 | 37.8 * | 47.7 * | -14 | - | - | 10.1 * | - | - | - | 0.5 | 1.0 | 1.1 | 1.8 |
| XY-D2 | 23.5 * | 65.7 * | - | - | 3.9 * | 2.8 | - | - | - | 0.4 | - | 1.7 | 2.0 |
| XY-D3 | 25.2 * | 72.4 * | - | - | - | - | - | - | 0.3 | - | - | - | 2.1 |
| XY-M1 | 12.7 * | 82.6 * | - | - | - | - | - | 2.1 | - | - | - | - | 2.6 |
| XY-M2 | 11.7 * | 79.7 * | - | - | - | - | - | 1.7 | 2.0 | - | 2.3 | 2.6 | - |
| XY-M3 | 12.0 * | 80.0 * | - | - | - | - | 1.0 | 2.0 | 2.0 | - | 3.0 | - | - |
| XY-M4 | 12.5 * | 82.6 * | - | - | - | - | - | 2.0 | 2.9 | - | - | - | - |
| XY-M5 | 6.9 * | 59.1 * | 5.9 * | 5.5 * | 5.5 * | - | 1.4 | 0.9 | - | 0.9 | 6.5 * | 7.4 * | - |
| XY-M6 | 7.7 * | 62.6 * | 4.0 * | - | 0.9 | - | 2.3 | 0.6 | - | 1.5 | 6.9 * | 7.7 * | 5.8 * |
| XY-M7 | 7.0 * | 71.6 * | 4.2 * | 4.8 * | - | - | 2.0 | 2.5 | - | 1.7 | - | - | 6.2 * |
| XY-M8 | 14.5 * | 77.3 * | 0.6 | - | - | - | 1.9 | - | - | - | - | 5.7 * | |
| XY-M9 | 12.0 * | 80.2 * | - | - | - | - | 1.6 | 2.1 | - | 0.6 | - | - | 3.5 * |
| XY-M10 | 12.9 * | 80.0 * | - | - | - | - | - | 2.8 | 1.7 | - | - | - | 2.6 |
1 Qz, quartz; 2 CM, clay minerals; 3 Cal, calcite; 4 Dlm, dolomite; 5 Ank, ankerite; 6 Py, pyrite; 7 Sd, siderite; 8 Mag, magnesite; 9 Gp, gypsum; 10 Fsp, feldspar; 11 Anc, analcime; 12 Bar, Barite; 13 Ant, anatase; -, not identified or below detection of XRD; *, major mineral (>3%).
Table 3.
Concentrations of major and minor element oxides (%) in the No. 9 coal and related roof samples (on whole coal/rock basis) from the Xinyuan mine.
Table 3.
Concentrations of major and minor element oxides (%) in the No. 9 coal and related roof samples (on whole coal/rock basis) from the Xinyuan mine.
| Sample | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | TiO2 | P2O5 | K2O | Na2O |
|---|---|---|---|---|---|---|---|---|---|
| XY-D1 | 36.68 | 19.16 | 11.10 | 0.11 | 0.17 | 1.24 | 0.03 | 0.57 | 0.36 |
| XY-D2 | 29.84 | 16.39 | 4.21 | 0.26 | 0.23 | 0.73 | 0.05 | 0.77 | 0.26 |
| XY-D3 | 37.87 | 32.01 | 1.20 | 0.12 | 0.15 | 0.86 | 0.05 | 0.51 | 0.21 |
| XY-M1 | 20.27 | 18.25 | 0.76 | 0.30 | 0.10 | 0.53 | 0.04 | 0.07 | 0.11 |
| XY-M2 | 20.36 | 18.36 | 0.68 | 0.20 | 0.07 | 0.55 | 0.04 | 0.07 | 0.13 |
| XY-M3 | 17.89 | 16.13 | 0.68 | 0.18 | 0.07 | 0.49 | 0.04 | 0.06 | 0.10 |
| XY-M4 | 18.31 | 16.47 | 0.56 | 0.19 | 0.06 | 0.77 | 0.06 | 0.06 | 0.10 |
| XY-M5 | 6.86 | 6.02 | 0.77 | 0.62 | 0.09 | 0.14 | 0.02 | 0.02 | 0.14 |
| XY-M6 | 6.62 | 5.73 | 1.10 | 0.33 | 0.11 | 0.16 | 0.01 | 0.02 | 0.15 |
| XY-M7 | 7.08 | 6.15 | 0.93 | 0.45 | 0.10 | 0.22 | 0.03 | 0.03 | 0.14 |
| XY-M8 | 7.75 | 6.65 | 0.89 | 0.53 | 0.10 | 0.23 | 0.10 | 0.04 | 0.12 |
| XY-M9 | 16.29 | 14.99 | 1.40 | 0.22 | 0.16 | 0.68 | 0.16 | 0.06 | 0.13 |
| XY-M10 | 17.44 | 15.99 | 0.71 | 0.13 | 0.09 | 0.52 | 0.10 | 0.05 | 0.12 |
| AV-C 1 | 13.89 | 12.48 | 0.85 | 0.31 | 0.10 | 0.43 | 0.06 | 0.05 | 0.12 |
| AV-R 2 | 34.80 | 22.52 | 5.50 | 0.16 | 0.18 | 0.94 | 0.05 | 0.62 | 0.28 |
| Chinese coal 3 | 8.47 | 5.98 | 4.85 | 1.23 | 0.22 | 0.33 | 0.092 | 0.19 | 0.16 |
1 AV-C, average concentration in coal samples; 2 AV-R, average concentration in roof samples; 3 Chinese coal; average values in Chinese coal from Dai et al. [28].
Table 4.
Concentrations of trace elements (μg/g) in the No. 9 coal and related roof samples from the Xinyuan mine.
Table 4.
Concentrations of trace elements (μg/g) in the No. 9 coal and related roof samples from the Xinyuan mine.
| Sample | XY- D1 | XY- D2 | XY- D3 | XY- M1 | XY- M2 | XY- M3 | XY- M4 | XY- M5 | XY- M6 | XY- M7 | XY- M8 | XY- M9 | XY- M10 | AV-C 1 | AV-R 2 | Chinese Coal 3 | World Coal 4 | World Clay 5 | CC 6 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Li | 120 | 48.2 | 89.8 | 144 | 142 | 144 | 140 | 53.6 | 46.4 | 45.8 | 47.6 | 165 | 191 | 111.9 | 86.0 | 31.8 | 14 | 54 | 8.00 |
| Sc | 12.1 | 10.9 | 7.7 | 12.2 | 10.2 | 10.8 | 16.2 | 3.55 | 3.88 | 3.37 | 3.70 | 9.36 | 9.58 | 8.28 | 10.2 | 4.38 | 3.7 | 15 | 2.24 |
| V | 63 | 63 | 69 | 18 | 19 | 20 | 27 | 17 | 17 | 20 | 19 | 26 | 22 | 20.50 | 65.0 | 35.1 | 28 | 120 | 0.73 |
| Cr | 50.0 | 38.2 | 22.0 | 15.2 | 14.5 | 14.5 | 24.0 | 8.92 | 9.31 | 9.48 | 11.3 | 16.8 | 18.0 | 14.20 | 36.7 | 15.4 | 17 | 110 | 0.84 |
| Mn | 44.9 | 82.2 | 27.4 | 32.2 | 18.9 | 20.1 | 17.1 | 32.6 | 25.3 | 30.7 | 33.3 | 22.6 | 13.3 | 24.61 | 51.5 | 94.8 | 71 | 0.35 | |
| Co | 12.8 | 8.99 | 6.62 | 1.12 | 2.09 | 0.95 | 0.89 | 1.64 | 1.88 | 1.92 | 2.10 | 0.850 | 0.496 | 1.39 | 9.47 | 7.08 | 6.0 | 19 | 0.23 |
| Ni | 86.2 | 16.9 | 12.9 | 5.82 | 6.06 | 5.00 | 6.22 | 2.79 | 2.94 | 2.98 | 3.74 | 2.72 | 4.15 | 4.24 | 38.7 | 13.7 | 17 | 49 | 0.25 |
| Cu | 33.1 | 32.6 | 18.0 | 26.4 | 25.8 | 23.9 | 39.0 | 15.5 | 28.8 | 22.0 | 22.4 | 31.6 | 34.4 | 26.98 | 27.9 | 17.5 | 16 | 36 | 1.69 |
| Zn | 31.4 | 45.8 | 71.9 | 24.3 | 25.4 | 24.6 | 38.4 | 8.67 | 7.26 | 6.16 | 7.20 | 13.4 | 8.57 | 16.40 | 49.7 | 41.4 | 28 | 89 | 0.59 |
| Ga | 32 | 39 | 31 | 22 | 27 | 21 | 20 | 18 | 20 | 18 | 20 | 24 | 19 | 20.9 | 34.0 | 6.55 | 6.0 | 16 | 3.48 |
| Ge | 8 | 8 | 5 | 3 | 3 | 3 | 3 | 2 | 2 | 2 | 3 | 3 | 3 | 2.7 | 7.0 | 2.78 | 2.4 | 2 | 1.13 |
| Rb | 40.0 | 69.9 | 33.2 | 4.55 | 4.16 | 3.01 | 3.53 | 1.20 | 0.950 | 1.07 | 2.16 | 2.12 | 1.94 | 2.47 | 47.7 | 9.25 | 18 | 133 | 0.14 |
| Sr | 108 | 144 | 137 | 124 | 152 | 129 | 160 | 136 | 73 | 92 | 129 | 642 | 335 | 197 | 130 | 140 | 100 | 240 | 1.97 |
| Y | 18.7 | 35.5 | 21.5 | 33.0 | 27.1 | 31.3 | 42.0 | 13.2 | 10.6 | 10.4 | 12.8 | 19.3 | 24.8 | 22.45 | 25.2 | 18.2 | 8.2 | 31 | 2.74 |
| Mo | 16.6 | 8.14 | 2.72 | 1.68 | 2.82 | 1.92 | 3.44 | 2.66 | 2.82 | 2.96 | 3.35 | 3.05 | 2.11 | 2.68 | 9.15 | 3.08 | 2.1 | 1.6 | 1.28 |
| Cs | 4.41 | 9.05 | 3.16 | 0.422 | 0.437 | 0.318 | 0.358 | 0.135 | 0.122 | 0.163 | 0.311 | 0.232 | 0.222 | 0.27 | 5.54 | 1.13 | 1.1 | 13 | 0.25 |
| Ba | 232 | 252 | 248 | 102 | 125 | 124 | 119 | 73 | 60 | 68 | 78 | 184 | 140 | 107 | 244 | 159 | 150 | 460 | 0.72 |
| La | 36.8 | 63.4 | 49.3 | 17.0 | 16.2 | 15.6 | 20.8 | 14.2 | 14.6 | 16.2 | 22.4 | 58.5 | 34.6 | 23.01 | 49.83 | 22.5 | 11 | 48 | 2.09 |
| Ce | 84.0 | 138 | 104 | 55.9 | 52.7 | 57.8 | 67.3 | 30.1 | 30.4 | 32.7 | 43.2 | 104 | 83.6 | 55.77 | 108.67 | 46.7 | 23 | 75 | 2.42 |
| Pr | 7.08 | 13.0 | 10.4 | 6.40 | 5.55 | 6.26 | 8.18 | 3.29 | 3.18 | 3.41 | 4.40 | 8.08 | 7.88 | 5.66 | 10.16 | 6.42 | 3.4 | 10 | 1.67 |
| Nd | 24.4 | 48.3 | 36.2 | 25.2 | 21.5 | 24.5 | 31.6 | 12.0 | 11.2 | 12.0 | 15.6 | 23.8 | 27.7 | 20.51 | 36.30 | 22.3 | 12 | 36 | 1.71 |
| Sm | 4.35 | 8.04 | 5.65 | 5.66 | 4.66 | 5.26 | 7.12 | 2.38 | 2.05 | 2.14 | 2.76 | 3.61 | 5.08 | 4.07 | 6.01 | 4.07 | 2.2 | 8 | 1.85 |
| Eu | 0.754 | 1.47 | 1.02 | 1.14 | 0.988 | 1.02 | 1.46 | 0.510 | 0.403 | 0.408 | 0.524 | 0.750 | 0.866 | 0.81 | 1.08 | 0.84 | 0.43 | 1.2 | 1.88 |
| Gd | 4.52 | 8.00 | 5.96 | 5.59 | 4.90 | 5.19 | 6.95 | 2.53 | 2.12 | 2.19 | 2.88 | 4.36 | 5.23 | 4.19 | 6.16 | 4.65 | 2.7 | 5.8 | 1.55 |
| Tb | 0.719 | 1.12 | 0.914 | 0.980 | 0.859 | 0.924 | 1.24 | 0.447 | 0.348 | 0.344 | 0.435 | 0.646 | 0.864 | 0.71 | 0.92 | 0.62 | 0.31 | 0.83 | 2.29 |
| Dy | 4.22 | 6.48 | 5.23 | 5.98 | 5.10 | 5.68 | 7.66 | 2.50 | 2.04 | 1.98 | 2.48 | 3.82 | 5.14 | 4.24 | 5.31 | 3.74 | 2.1 | 4.4 | 2.02 |
| Ho | 0.797 | 1.36 | 0.994 | 1.19 | 0.986 | 1.13 | 1.51 | 0.504 | 0.414 | 0.392 | 0.488 | 0.757 | 0.988 | 0.84 | 1.05 | 0.96 | 0.57 | 0.9 | 1.47 |
| Er | 2.37 | 4.41 | 2.94 | 3.58 | 2.90 | 3.38 | 4.52 | 1.43 | 1.26 | 1.19 | 1.46 | 2.32 | 2.94 | 2.50 | 3.24 | 1.79 | 1.00 | 1.9 | 2.50 |
| Tm | 0.332 | 0.645 | 0.398 | 0.494 | 0.398 | 0.468 | 0.621 | 0.220 | 0.184 | 0.169 | 0.204 | 0.330 | 0.404 | 0.35 | 0.46 | 0.64 | 0.30 | 0.5 | 1.16 |
| Yb | 2.26 | 4.62 | 2.69 | 3.28 | 2.65 | 3.10 | 4.10 | 1.30 | 1.20 | 1.14 | 1.38 | 2.26 | 2.70 | 2.31 | 3.19 | 2.08 | 1.0 | 2.5 | 2.31 |
| Lu | 0.331 | 0.708 | 0.384 | 0.458 | 0.371 | 0.433 | 0.573 | 0.203 | 0.178 | 0.164 | 0.201 | 0.320 | 0.374 | 0.33 | 0.47 | 0.38 | 0.20 | 0.39 | 1.64 |
| Hg | 0.365 | 0.250 | 0.296 | 0.305 | 0.342 | 0.274 | 0.196 | 0.230 | 0.305 | 0.263 | 0.247 | 0.27 | 0.163 | 0.10 | 0.068 | 2.71 | |||
| Tl | 1.80 | 1.64 | 0.538 | 0.089 | 0.084 | 0.098 | 0.072 | 0.069 | 0.052 | 0.061 | 0.082 | 0.066 | 0.060 | 0.07 | 1.33 | 0.47 | 0.58 | 1.3 | 0.13 |
| Pb | 284 | 34.8 | 56.3 | 64.3 | 45.2 | 49.6 | 111 | 14.3 | 24.6 | 20.8 | 24.6 | 40.4 | 41.2 | 43.6 | 125.0 | 15.1 | 9.0 | 14 | 4.84 |
| Th | 34 | 15 | 20 | 20 | 22 | 17 | 35 | 7 | 7 | 8 | 8 | 30 | 19 | 17.3 | 23.0 | 5.84 | 3.2 | 14 | 5.41 |
| U | 9 | 5 | 5 | 4 | 7 | 5 | 7 | 2 | 2 | 2 | 2 | 5 | 5 | 4.1 | 6.3 | 2.43 | 1.9 | 4.3 | 2.16 |
| ∑REY 7 | 191.6 | 335.1 | 247.6 | 165.9 | 146.9 | 162.0 | 205.6 | 84.8 | 80.2 | 84.8 | 111.2 | 232.9 | 203.2 | 147.74 | 258.09 | 135.89 | 68.41 | 226.4 | 2.16 |
1 AV-C, average concentration of coal samples; 2 AV-R, average concentration of roof samples; 3 Chinese coal, average values in Chinese coal from Dai et al. [28]; 4 World coal, average values in hard coal from around the world from Ketris and Yudovich [30]; 5 World clay, average values in clay from around the world from Grigoriev [31]; 6 CC, concentration coefficient = AV-C/World coal; 7 ∑REY, total rare earth elements and yttrium.
Table 5.
Correlations between Li, Ga, Th, REY, ash yield, total sulfur and some major oxides in the No. 9 coal and related roof samples from the Xinyuan mine.
Table 5.
Correlations between Li, Ga, Th, REY, ash yield, total sulfur and some major oxides in the No. 9 coal and related roof samples from the Xinyuan mine.
| Ad | St,d | SiO2 | Al2O3 | Li | Ga | Th | REY | |
|---|---|---|---|---|---|---|---|---|
| Li | 0.924 ** | −0.943 ** | 0.912 ** | 0.922 ** | - | - | - | - |
| Ga | 0.640 * | −0.578 | 0.633 * | 0.632 | 0.480 | - | - | - |
| Th | 0.810 ** | −0.834 ** | 0.799 ** | 0.804 ** | 0.789 ** | 0.502 | - | - |
| REY | 0.822 ** | −0.824 ** | 0.801 ** | 0.813 ** | 0.917 ** | 0.413 | 0.902 ** | - |
**, The correlation is significant at the 0.01 level (double tailed); *, The correlation is significant at the 0.05 level (double tailed).
Table 6.
Geochemical parameters of REY in the No. 9 coal and related roof samples from the Xinyuan mine.
Table 6.
Geochemical parameters of REY in the No. 9 coal and related roof samples from the Xinyuan mine.
| Sample | ΣLREY 1 | ΣMREY 2 | ΣHREY 3 | ΣREY 4 | LaN/LuN 5 | LaN/SmN | GdN/LuN | CeN/CeN* 6 | EuN/EuN* 7 | Type |
|---|---|---|---|---|---|---|---|---|---|---|
| XY-D1 | 156.63 | 28.91 | 6.09 | 191.63 | 1.19 | 1.27 | 1.15 | 1.18 | 0.79 | L 8 |
| XY-D2 | 270.74 | 52.57 | 11.74 | 335.05 | 0.96 | 1.18 | 0.95 | 1.09 | 0.86 | H 9 |
| XY-D3 | 205.55 | 34.62 | 7.41 | 247.58 | 1.37 | 1.31 | 1.31 | 1.05 | 0.82 | L |
| XY-M1 | 110.16 | 46.69 | 9.00 | 165.85 | 0.40 | 0.45 | 1.03 | 1.19 | 0.95 | M 10 |
| XY-M2 | 100.61 | 38.95 | 7.31 | 146.86 | 0.47 | 0.52 | 1.11 | 1.25 | 0.97 | M |
| XY-M3 | 109.42 | 44.11 | 8.51 | 162.05 | 0.38 | 0.44 | 1.01 | 1.29 | 0.91 | M |
| XY-M4 | 135.00 | 59.31 | 11.32 | 205.63 | 0.39 | 0.44 | 1.02 | 1.14 | 0.97 | M |
| XY-M5 | 61.97 | 19.19 | 3.66 | 84.81 | 0.75 | 0.89 | 1.05 | 1.00 | 0.97 | M |
| XY-M6 | 61.43 | 15.51 | 3.24 | 80.18 | 0.87 | 1.07 | 1.00 | 1.02 | 0.90 | H |
| XY-M7 | 66.45 | 15.32 | 3.06 | 84.83 | 1.05 | 1.14 | 1.12 | 1.00 | 0.88 | L |
| XY-M8 | 88.36 | 19.12 | 3.73 | 111.21 | 1.19 | 1.22 | 1.21 | 0.99 | 0.87 | L |
| XY-M9 | 197.99 | 28.88 | 5.99 | 232.85 | 1.95 | 2.43 | 1.15 | 1.05 | 0.87 | L |
| XY-M10 | 158.86 | 36.90 | 7.41 | 203.17 | 0.99 | 1.02 | 1.18 | 1.15 | 0.79 | H |
1 ΣLREY, total concentration of light REY elements (La, Ce, Pr, Nd and Sm); 2 ΣMREY, total concentration of medium REY elements (Eu, Gd, Tb, Dy and Y); 3 ΣHREY, total concentration of heavy REY elements (Ho, Er, Tm, Yb and Lu); 4 ΣREY, total concentration of rare earth elements and yttrium; 5 N, values normalized by the average concentration of REY in the upper continental crust [44]; 6 CeN/CeN* = 2 × CeN/(LaN + PrN); 7 EuN/EuN* = 2 × EuN/(SmN + GdN); 8 L, L-type, LaN/LuN > 1; 9 H, H-type, LaN/LuN < 1; 10 M, M-type, LaN/SmN < 1 and GdN/LuN > 1.
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Li, J.; Zhang, S.; Wang, H.; Xie, X. Geochemical Characteristics of Critical Metal Elements in the No. 9 Coal Seam from the Xinyuan Mine, Northern Qinshui Coalfield, Shanxi Province, China. Minerals 2023, 13, 278. https://doi.org/10.3390/min13020278
AMA Style
Li J, Zhang S, Wang H, Xie X. Geochemical Characteristics of Critical Metal Elements in the No. 9 Coal Seam from the Xinyuan Mine, Northern Qinshui Coalfield, Shanxi Province, China. Minerals. 2023; 13(2):278. https://doi.org/10.3390/min13020278
Chicago/Turabian StyleLi, Jian, Shaowei Zhang, Hongdong Wang, and Xichao Xie. 2023. "Geochemical Characteristics of Critical Metal Elements in the No. 9 Coal Seam from the Xinyuan Mine, Northern Qinshui Coalfield, Shanxi Province, China" Minerals 13, no. 2: 278. https://doi.org/10.3390/min13020278
APA StyleLi, J., Zhang, S., Wang, H., & Xie, X. (2023). Geochemical Characteristics of Critical Metal Elements in the No. 9 Coal Seam from the Xinyuan Mine, Northern Qinshui Coalfield, Shanxi Province, China. Minerals, 13(2), 278. https://doi.org/10.3390/min13020278
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