Minerals

2021

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13 pages, 4648 KiB

Open AccessFeature PaperArticle

Distribution of As within Magnetic and Non-Magnetic Fractions of Fluidized-Bed Coal Combustion Ash

by Filip Kovár and Lucie Bartoňová

Minerals 2021, 11(12), 1411; https://doi.org/10.3390/min11121411 - 13 Dec 2021

Cited by 2 | Viewed by 2827

Abstract

Separation of coal ash into magnetic and non-magnetic fractions facilitates their utilization when processed separately. Due to desulphurization additives added to coal during the fluidised-bed combustion, non-magnetic fractions often contain elevated CaO levels (while magnetic concentrates are typically rich in Fe₂O [...] Read more.

Separation of coal ash into magnetic and non-magnetic fractions facilitates their utilization when processed separately. Due to desulphurization additives added to coal during the fluidised-bed combustion, non-magnetic fractions often contain elevated CaO levels (while magnetic concentrates are typically rich in Fe₂O₃). Both CaO and Fe₂O₃ are known for their ability to bind As during the combustion, whose distribution is a crucial parameter in terms of proper utilization of these fractions. Therefore, the study deals with the As partitioning within magnetic and non-magnetic fractions of fluidized-bed coal combustion ashes. Two different (successive) procedures of dry magnetic separation were used to separate each ash into strongly magnetic, less magnetic, and a non-magnetic fraction. Due to their optimal utilization, the concentrations of As and other target elements in these fractions were evaluated and compared. Magnetic concentrates from the first separation step (in vibrofluidized state) contained 60–70% Fe₂O₃, magnetic concentrates separated manually out of the residues after the first separation contained 26–41% Fe₂O₃, and the non-magnetic residues contained 2.4–3.5% Fe₂O₃. Arsenic levels were the highest in the non-magnetic residues and gradually decreased with the increasing Fe₂O₃ content in the magnetic fractions. The dominant As association in the studied samples was to CaO (r = +0.909) and with SO₃ (r = +0.906) whereas its joint occurrence with Fe₂O₃ was improbable (r = −0.834). Full article

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16 pages, 6381 KiB

Open AccessArticle

Petrological Composition of the Last Coal Seam in the Longmendong Section before the End-Permian Mass Extinction

by Chunguang Zhang, Jun Wang, Mingshi Feng, Zhiqiang Shi, Fang Xiang, Mingcai Hou, Shuai Yang, Ben Kneller and Hongde Chen

Minerals 2021, 11(11), 1230; https://doi.org/10.3390/min11111230 - 5 Nov 2021

Cited by 1 | Viewed by 2337

Abstract

Late Permian coal deposits are widely distributed throughout southwestern China. This paper describes the petrological composition of the last coal seam in the Longmendong section of the Emeishan area during the latest Changhsingian (Permian) and records important information regarding the evolution of the [...] Read more.

Late Permian coal deposits are widely distributed throughout southwestern China. This paper describes the petrological composition of the last coal seam in the Longmendong section of the Emeishan area during the latest Changhsingian (Permian) and records important information regarding the evolution of the mass extinction event that occurred at the end of the Permian. The results show that the dominant coal maceral group is vitrinite, followed by liptinite and inertinite macerals, and the coal minerals include quartz, chamosite and pyrite. The pyrofusinite and carbon microparticles occurrence modes could have been formed during wildfires in the adjacent areas. The β-tridymite occurrence modes and the high proportions and occurrence modes of magmatic quartz indicate that synchronous felsic volcanic activity occurred during the peat mire accumulation period. The chamosite and quartz occurrence modes suggest that they primarily precipitated from Fe-Mg-rich siliceous solutions that was derived from the weathering of nearby Emeishan basalt. The pyritic coal balls occurrence modes in the C1 coal seam are likely the result of coal-forming plants and Fe-Mg-rich siliceous solutions in neutral to weak alkaline conditions during late syngenetic stages or early epigenetic stages within paleomires. Full article

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2020

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39 pages, 18793 KiB

Open AccessArticle

Mineral Matter in the Late Permian C1 Coal from Yunnan Province, China, with Emphasis on Its Origins and Modes of Occurrence

by Xiao Li, Shifeng Dai, Victor P. Nechaev, Ian T. Graham, David French, Xibo Wang, Lei Zhao and Jingtao Zhao

Minerals 2021, 11(1), 19; https://doi.org/10.3390/min11010019 - 25 Dec 2020

Cited by 18 | Viewed by 4602

Abstract

This paper reports the mineralogy and geochemistry of the Late Permian C1 Coal from Bole and Laibin mines in eastern Yunnan, Southwestern China (C1 Coal in Laibin mine is composed of three layers termed B1, B2, and B3). The coals are characterized by [...] Read more.

This paper reports the mineralogy and geochemistry of the Late Permian C1 Coal from Bole and Laibin mines in eastern Yunnan, Southwestern China (C1 Coal in Laibin mine is composed of three layers termed B1, B2, and B3). The coals are characterized by medium-high ash yields and very low sulfur contents. Compared with average values of trace element concentrations in hard coals worldwide, the Bole and Laibin coals are enriched in V, Co, Cu, Zn, and Se, which were mainly derived from the sediment-source region of the Kangdian Upland. Major minerals in the coal samples and roof and floor strata include quartz, interstratified berthierine/chamosite (B/C), as well as kaolinite, mixed layer illite/smectite, calcite, pyrite, and anatase. Unlike a pure chamosite, the 7 Å peak of interstratified B/C is sharp and narrow, while the 14 Å peak is broad and weak, or absent in some coal samples. Interstratified B/C was largely precipitated from low-temperature Fe-rich and Mg-rich hydrothermal fluids or, in some cases, is an alteration product of kaolinite. Secondary phases of quartz, calcite, pyrite, kaolinite, chalcopyrite, gypsum, and REE-phosphates in the coal samples are the dominant authigenic minerals formed at syngenetic and early diagenetic stages. Four intra-seam partings in C1 Coal, B1, and B3 layers are identified as tonsteins derived from felsic volcanic ashes. These tonsteins consist mainly of cryptocrystalline kaolinite with graupen and vermicular textures, and minor amounts of high-temperature quartz, zircon, apatite, monazite, and anatase. The floor of the C1 Coal in the Bole mine is a tuffaceous claystone and consists of altered high-Ti basalt volcaniclastics, characterized by high concentrations of Zr, Nb, V, Co, Cu, and Zn, low Al₂O₃/TiO₂ ratio (~4.62), high Ti/Y ratio (~900), enrichment of middle rare earth elements, and positive Eu anomalies. Full article

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24 pages, 6236 KiB

Open AccessArticle

Geochemistry of Carboniferous–Permian Coal from the Wujiawan Mine, Datong Coalfield, Northern China: Modes of Occurrence, Origin of Valuable Trace Elements, and Potential Industrial Utilization

by Jialiang Ma, Lin Xiao, Ke Zhang, Yukun Jiao, Zhenzhen Wang, Jinxiao Li, Wenmu Guo, Pengpeng Gao, Shenjun Qin and Cunliang Zhao

Minerals 2020, 10(9), 776; https://doi.org/10.3390/min10090776 - 31 Aug 2020

Cited by 12 | Viewed by 3538

Abstract

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and [...] Read more.

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 μg/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al₂O₃/TiO₂ and the figure of Zr/TiO₂ vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 μg/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield. Full article

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16 pages, 4447 KiB

Open AccessArticle

Mineralogical Characteristics of Early Permian Paragonite-Bearing Coal (No. 3) in the Jinyuan Mine, Tengxian Coalfield, Shandong Province, Eastern China

by Wenmu Guo, Jinxiao Li, Zhenzhen Wang, Ke Zhang, Zheng Gao, Jialiang Ma and Cunliang Zhao

Minerals 2020, 10(8), 714; https://doi.org/10.3390/min10080714 - 12 Aug 2020

Cited by 3 | Viewed by 3352

Abstract

The Early Permian coal is of great value in the Tengxian Coalfield, Shandon Province, Eastern China. This work deals with the new data focusing on mineralogical characteristics in the Early Permian Shanxi Formation No. 3 coal from the Jinyuan Mine. The Jinyuan coal [...] Read more.

The Early Permian coal is of great value in the Tengxian Coalfield, Shandon Province, Eastern China. This work deals with the new data focusing on mineralogical characteristics in the Early Permian Shanxi Formation No. 3 coal from the Jinyuan Mine. The Jinyuan coal is a low ash and highly volatile A bituminous coal. Minerals in the No. 3 coal mainly comprise of kaolinite, ankerite, illite, calcite, siderite, and quartz, with varying compositions of trace amounts of pyrite, jarosite, bassanite, anatase, and rutile. According to mineral assemblage in the coal plies, three Types (A to C) can be identified in the No. 3 coal. The dominant minerals in Type A are poorly-ordered kaolinite, illite, quartz, pyrite, and jarosite. Type B is mainly composed of well-ordered kaolinite, illite, siderite, ankerite, and calcite. Type C, with just one sample (JY-3-7c), which contains high proportions of calcite (54%) and ankerite (34%). Terrigenous minerals are elevated in coal plies that typically have relatively high contents of ash yield. The formation of syngenetic pyrite was generally due to seawater, while the sulphate minerals (jarosite and coquimbite) were derived from the oxidation of pyrite. Epigenetic vein-like or fracture-fillings carbonate minerals (ankerite, calcite, and siderite), kaolinite, and pyrite, as well as authigenic quartz were derived from the influx of hydrothermal fluids during different periods, from the authigenic to epigenetic. The paragonite in the coal may have been formed by the precipitated from Na-rich hydrothermal fluids. No effects of magmatic intrusion on mineralogy were investigated in this research. Full article

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15 pages, 3827 KiB

Open AccessArticle

Gold in Irish Coal: Palaeo-Concentration from Metalliferous Groundwaters

by Liam A. Bullock, John Parnell, Joseph G.T. Armstrong, Magali Perez and Sam Spinks

Minerals 2020, 10(7), 635; https://doi.org/10.3390/min10070635 - 17 Jul 2020

Cited by 5 | Viewed by 7891

Abstract

Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with [...] Read more.

Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (–platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals. Full article

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17 pages, 7343 KiB

Open AccessArticle

Mineralogical and Geochemical Characteristics of Lithium and Rare Earth Elements in High-Sulfur Coal from the Donggou Mine, Chongqing, Southwestern China

by Jianhua Zou, Longfei Cheng, Yuanchen Guo, Zhengcheng Wang, Heming Tian and Tian Li

Minerals 2020, 10(7), 627; https://doi.org/10.3390/min10070627 - 15 Jul 2020

Cited by 24 | Viewed by 4716

Abstract

Coal and coal by-products are considered as the potential raw materials for critical elements (e.g., rare earth elements, Li, Ga, Ge, etc.), which have attracted much attention in recent years. The purpose of this study is to investigate the mineralogical and geochemical characteristics, [...] Read more.

Coal and coal by-products are considered as the potential raw materials for critical elements (e.g., rare earth elements, Li, Ga, Ge, etc.), which have attracted much attention in recent years. The purpose of this study is to investigate the mineralogical and geochemical characteristics, and controlling geological factors of lithium and rare earth elements in the Lopingian (Wujiaping Formation) coal from the Donggou Mine, southeastern Chongqing Coalfield, China. Results indicate that lithium and rare earth elements are significantly enriched in the Donggou coals, which could be new potential alternative sources for critical elements. Concentrations of lithium and rare earth elements in the Donggou coals gradually increase from top to bottom. Lithium is mainly associated with kaolinite, while rhabdophane, florencite, goyazite, and xenotime are the main hosts of rare earth elements. The controlling geological factor is the groundwater leaching of underlying tuff, and to a lesser extent, the terrigenous clastic materials input from the top layer of the Kangdian Upland. This study provides mineralization information for lithium and rare earth elements exploration in coal measures. Full article

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16 pages, 5010 KiB

Open AccessArticle

Origin of a Petrographic Coal Structure and Its Implication for Coalbed Methane Evaluation

by Wei Cheng, Ruidong Yang and Qin Zhang

Minerals 2020, 10(6), 543; https://doi.org/10.3390/min10060543 - 16 Jun 2020

Cited by 1 | Viewed by 3993

Abstract

A petrographic coal structure of Late Permian coals from the Liupanshui coalfield, Western Guizhou, SW China, has been distinguished for its novel macro-lithological characteristics. Petrographic, mineralogical and geochemical studies have been conducted for a typical coal sample (No.3 coal, Songhe coalmine, Panzhou County, [...] Read more.

A petrographic coal structure of Late Permian coals from the Liupanshui coalfield, Western Guizhou, SW China, has been distinguished for its novel macro-lithological characteristics. Petrographic, mineralogical and geochemical studies have been conducted for a typical coal sample (No.3 coal, Songhe coalmine, Panzhou County, China) and its geological genesis and significance for coalbed methane (CBM) evaluation is accordingly discussed. It was found that coal is characterized by a banded structure with intensively fractured vitrain sublayers, where a great number of fractures were developed and filled with massive inorganic matter. The study of coal quality, coal petrography, mineralogy and lanthanides and yttrium (REY) geochemistry of the infilling mineral matter (IMM) indicates that this fractured coal structure resulted from the tissues of coal-forming plants or coal matrix shrinkage, as well as the precipitation of calcium rich groundwater and the addition of terrigenous materials. The coal depositional environment and coal-forming plant are considered to have played a role in inducing the special fractures. This provides a scientific reference for the study of CBM for coal with this fractured structure, such as the Late Permian coal from the western border of Guizhou Province, SW China. Full article

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30 pages, 9918 KiB

Open AccessArticle

Lithium Enrichment in the No. 2₁ Coal of the Hebi No. 6 Mine, Anhe Coalfield, Henan Province, China

by Yingchun Wei, Wenbo He, Guohong Qin, Maohong Fan and Daiyong Cao

Minerals 2020, 10(6), 521; https://doi.org/10.3390/min10060521 - 5 Jun 2020

Cited by 19 | Viewed by 4066

Abstract

Lithium (Li) is an important strategic resource, and with the increasing demand for Li, there are some limitations in the exploitation and utilization of conventional deposits such as the pegmatite-type and brine-type Li deposits. Therefore, it has become imperative to search for Li [...] Read more.

Lithium (Li) is an important strategic resource, and with the increasing demand for Li, there are some limitations in the exploitation and utilization of conventional deposits such as the pegmatite-type and brine-type Li deposits. Therefore, it has become imperative to search for Li from other sources. Li in coal is thought to be one of the candidates. In this study, the petrology, mineralogy, and geochemistry of No. 2₁ coal from the Hebi No. 6 mine, Anhe Coalfield, China, was reported, with an emphasis on the distribution, modes of occurrence, and origin of Li. The results show that Li is enriched in the No. 2₁ coal, and its concentration coefficient (CC) value is 6.6 on average in comparison with common world coals. Lithium in the studied coal is mainly present in aluminosilicates, mainly clay minerals, some of which contain a significant amount of Ti. The Li enrichment in the No. 2₁ coal is mainly controlled by the terrigenous materials and sourced from the moyite of the Yinshan Upland. Furthermore, Li in the No. 2₁ coal is more enriched in coals formed in acidic and humid conditions and coals influenced by fresh water during peat accumulation. Full article

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28 pages, 8376 KiB

Open AccessArticle

Comparison of Geochemical and Mineralogical Characteristics of Palaeogene Oil Shales and Coals from the Huangxian Basin, Shandong Province, East China

by Xue Zheng, Baruch Spiro and Zuozhen Han

Minerals 2020, 10(6), 496; https://doi.org/10.3390/min10060496 - 29 May 2020

Cited by 1 | Viewed by 3683

Abstract

Coal and oil shale are both organic matter-rich sedimentary rocks. However, their sources of organic matter and their depositional environments are different. The present study focuses on the Palaeogene Lijiaya Formation sequence in the Huangxian Basin, Shandong Province, East China, which has oil [...] Read more.

Coal and oil shale are both organic matter-rich sedimentary rocks. However, their sources of organic matter and their depositional environments are different. The present study focuses on the Palaeogene Lijiaya Formation sequence in the Huangxian Basin, Shandong Province, East China, which has oil shales showing marine geochemical indicators overlain by coals indicating marine regression. We investigated the C1 coal seam and underlying OS2 oil shale layers, compared their geochemical and mineralogical characteristics, clarified the details of their constituents, in order to elucidate the features of their sources, their depositional environments, and the post depositional processes in the context of the geological evolution of the basin. The Al₂O₃/TiO₂ (18.1–64.9) and TiO₂/Zr ratios (28.2–66.5) in the C1 coals and OS2 oil shales, respectively, suggest a felsic to intermediate source, and the Mesozoic granite on the South of Huangxian Fault may be one of the provenances of these sediments. The low sulphur content (0.53–0.59%) and low Sr/Ba ratios (0.32–0.67) suggest a freshwater depositional environment for the C1 coals. In contrast, the higher total sulphur contents (0.60–1.44%), the higher Sr/Ba ratios (0.31–1.11%), and the occurrence of calcareous shells, indicate seawater intrusions during deposition of the oil shales. The V/Ni, V/(V + Ni), and V/Cr ratios of the OS2 oil shale suggest oxic to suboxic conditions with a distinct change in palaeo-redox between the lower and upper parts of OS2 seam. The high boron contents in C1 coals (average, 504 ppm) is related to the high content of analcime (with the correlation coefficient of 0.96), and the high concentration of boron was attributed to a secondary enrichment by epigenetic hydrothermal solutions. The occurrence of idiomorphic-authigenic albite in association with analcime and quartz in veins in the coals suggests that albite is a product of a reaction between analcime and silica, both of volcanic origin. The reaction takes place at about 190 °C, indicating that the area was affected by hydrothermal fluids. Full article

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24 pages, 18881 KiB

Open AccessArticle

Greenockite Whiskers from the Bytom Burned Coal Dump, Upper Silesia, Poland

by Katarzyna Nowak, Irina Galuskina and Evgeny Galuskin

Minerals 2020, 10(5), 470; https://doi.org/10.3390/min10050470 - 22 May 2020

Cited by 2 | Viewed by 3694

Abstract

Orange greenockite (CdS) aggregates were found in a small fumarole at a burned coal dump near Bytom, Upper Silesia, Poland and were studied using a variety of techniques in order to determine their chemistry, morphology, and most importantly, the mechanism of crystal growth. [...] Read more.

Orange greenockite (CdS) aggregates were found in a small fumarole at a burned coal dump near Bytom, Upper Silesia, Poland and were studied using a variety of techniques in order to determine their chemistry, morphology, and most importantly, the mechanism of crystal growth. Greenockite rods, wires, and whiskers with bismuth drops on crystal tops are predominant in these aggregates. Greenockite rods oriented sub-perpendicular to the substrate surface. The rod thickness reaches 5–6 μm and about 10 μm in length. The catalyst bismuth drop has a diameter comparable to the rod thickness. Fiber forms (wires and whiskers) are sub-parallel to the substrate surface. The thickness of these forms is usually less than 2 μm, and the length can be close to 1 mm. The bismuth drop diameter can show a large excess over the fiber thickness. Catalyst drops on the tops of whiskers began to change their form dynamically and exploded, spraying bismuth under the electron beam effect. Rods grow along the [01–10] direction, and whiskers and wires (axial forms) along the [0001] direction. Greenockite rod crystals, carrying on top a relatively homogenous bismuth catalyst drop, were formed on the heated substrate according to the VLS (vapor–liquid–solid) mechanism at temperatures not lower than 270 °C. Greenockite whiskers and wires grew just above of the substrate surface according to the VQS (vapor–quasiliquid–solid) mechanism at temperatures lower than 200 °C. These mechanisms of growth have very rarely been recorded to occur in nature and even less so in burning coal dumps. The cooperative growth effects of the fiber greenockite crystals were also described. Full article

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25 pages, 5701 KiB

Open AccessArticle

Spatial Macroscale Variability of the Role of Mineral Matter in Concentrating Some Trace Elements in Bituminous Coal in a Coal Basin—A Case Study from the Upper Silesian Coal Basin in Poland

by Henryk R. Parzentny

Minerals 2020, 10(5), 422; https://doi.org/10.3390/min10050422 - 9 May 2020

Cited by 8 | Viewed by 3328

Abstract

As there are numerous claims that the mode of occurrence of trace elements in coal influences the quality of the substrates as well as the course and results of the coal preparation processes, it is necessary to analyse the differences in the mode [...] Read more.

As there are numerous claims that the mode of occurrence of trace elements in coal influences the quality of the substrates as well as the course and results of the coal preparation processes, it is necessary to analyse the differences in the mode of occurrence of the elements in coal within a coal basin or a coal deposit. With the use of concentration distribution functions and the Pearson correlation coefficient, it was concluded that (1) mineral matter plays a significant and nearly constant or constant role in concentrating V, Cr, Co, As, Rb, Sr, Ba, and Pb in coal; (2) organic matter plays a stable role in concentrating Sn; and (3) there are significant differences in the role of organic and mineral matter in concentrating Mn, Ni, Cu, Zn, Mo, Cd, and Sb in coal throughout the USCB (Upper Silesian Coal Basin). Moreover, there was observed a difference in the mode of occurrence of Cr, Mn, Co, Ni, Cu, Zn, Mo, Cd, Sn, and Sb in coal in the vertical profile of the USCB. At the same time, there were observed no differences and a stable significant role of mineral matter in concentrating V, As, Rb, Sr, Ba, and Pb in coal, while the role of the petrographic groups of the coal components in concentrating the elements in raw coal was differentiated. It is believed that the difference in the mode of occurrence of the trace elements in coal within coal seams and coal deposits is a geochemical regularity. Full article

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19 pages, 4429 KiB

Open AccessArticle

Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China

by Yuan Li, Wenhui Huang, Bo Jiu, Qilong Sun and Qingsong Che

Minerals 2020, 10(5), 399; https://doi.org/10.3390/min10050399 - 29 Apr 2020

Cited by 8 | Viewed by 3563

Abstract

Minerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion) coal [...] Read more.

Minerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion) coal samples collected from the Huainan coalfield, providing new insight into the origins and modes of occurrence of the minerals in coal and their geological evolution. The results showed that the studied coal samples were low rank bituminous coal, with low ash yield (11.92–38.31%, average 24.80%) and high volatile content (25.13–43.43%, average 37.29%). Minerals in the coal mainly included kaolinite and quartz; varying proportions of calcite, siderite, ankerite, and pyrite; and traces of chlorite, zircon, strontianite, apatite, and gorceixite. Typical modes of mineral occurrence could be used to determine the formation stage of minerals. The detrital mineral, occurring as sub-angular to rounded discrete fragments or thin layers intimately admixed with organic matter at particular horizons, was of terrigenous origin, deposited during peat accumulation. Cell infillings, as well as nodule siderites and polycrystalline aggregates of pyrite, precipitated during the syngenetic to early diagenetic stages. Cleat infillings, compressed cell infillings, and fracture infillings precipitated in the epigenetic stage. However, the stage of mineral formation of the pore infilling was difficult to determine. Combined with coal quality, mineralogy, and geochemical analysis, the sedimentary environment of Shanxi Formation was affected by seawater, and Fe-rich hydrothermal fluids filled into the No. 3 coal seam in the epigenetic stage. The sedimentary environment of the No. 8 coal seam had widespread reduction and acid conditions due to basin subsidence, and sulfate-rich hydrothermal fluids may have been formed during the peat deposition stage. In contrast, the peat accumulation environment of the Upper Shihezi Formation was oxidized with a low pH condition. Alkaline fluid then flowed into the No. 13-1 coal seam in the epigenetic stage. Full article

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19 pages, 1600 KiB

Open AccessArticle

Towards Consistent Interpretations of Coal Geochemistry Data on Whole-Coal versus Ash Bases through Machine Learning

by Na Xu, Mengmeng Peng, Qing Li and Chuanpeng Xu

Minerals 2020, 10(4), 328; https://doi.org/10.3390/min10040328 - 7 Apr 2020

Cited by 16 | Viewed by 3444

Abstract

Coal geochemistry compositional data on whole-coal basis can be converted back to ash basis based on samples’ loss on ignition. However, the correlation between the concentrations of elements reported on whole-coal versus ash bases in many cases is inconsistent. Traditional statistical methods (e.g., [...] Read more.

Coal geochemistry compositional data on whole-coal basis can be converted back to ash basis based on samples’ loss on ignition. However, the correlation between the concentrations of elements reported on whole-coal versus ash bases in many cases is inconsistent. Traditional statistical methods (e.g., correlation analysis) for compositional data on both bases may sometimes result in misleading results. To address this issue, we hereby propose an improved additive log-ratio data transformation method for analyzing the correlation between element concentrations reported on whole-coal versus ash bases. To verify the validity of the method proposed in this study, a data set which contains comprehensive analyses of 106 Late Paleozoic coal samples from the Datanhao mine and Adaohai Mine, Inner Mongolia, China, is used for the validity testing. A prediction model was built for performance evaluation of two methods based on the hierarchical clustering algorithm. The results show that the improved additive log-ratio is more effective in prediction for occurrence modes of elements in coal than the previously reported stability method, and therefore can be adopted for consistent interpretations of coal geochemistry compositional data on whole-coal vs. ash bases. Full article

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23 pages, 4650 KiB

Open AccessArticle

Mineralogical and Chemical Characteristics of Coal Ashes from Two High-Sulfur Coal-Fired Power Plants in Wuhai, Inner Mongolia, China

by Qiang Wei and Weijiao Song

Minerals 2020, 10(4), 323; https://doi.org/10.3390/min10040323 - 4 Apr 2020

Cited by 13 | Viewed by 4776

Abstract

The mineralogical and chemical characteristics of the feed coals and coal combustion products (CCPs) from two power plants (Xilaifeng and Damo) that consume coals from the Wuda Coalfield, Inner Mongolia, were investigated, using XRD, SEM–EDS, XRF, and ICP-MS. The feed coals from Xilaifeng [...] Read more.

The mineralogical and chemical characteristics of the feed coals and coal combustion products (CCPs) from two power plants (Xilaifeng and Damo) that consume coals from the Wuda Coalfield, Inner Mongolia, were investigated, using XRD, SEM–EDS, XRF, and ICP-MS. The feed coals from Xilaifeng and Damo are both of high ash yield (52.93% and 48.36%, respectively), and medium and high total sulfur content (2.22% and 3.32%, respectively). The minerals in the feed coals are primarily composed of kaolinite, quartz, illite, pyrite, and, to a lesser extent, gypsum and anatase. In addition to the elevated incompatible elements (Nb, Ta, Zr, Hf and Th), Li and Hg are enriched in the feed coals from the Xilaifeng and Damo power plants, respectively. Rare earth elements and yttrium (REY) are more enriched in the feed coals from Xilaifeng (194 μg/g) than those of Damo (93.9 μg/g). The inorganic phases of CCPs from both power plants are mainly composed of amorphous phase, quartz, hematite, illite, and anhydrite. Compared with the feed coals, concentrations of most trace elements in the CCPs are elevated, and they are preferentially enriched in the fly ashes relative to the bottom ashes (*f/b > 1), especially F, As, Sr, Mo, Se, and Hg (*f/b > 2.5). Furthermore, most trace elements (Xilaifeng: excluding Li, Cr, Co, Ni, Rb, Nb and Cs; Damo: excluding Li, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Cs and Ba) are more enriched in the (fine) fly ashes relative to the laboratory high-temperature coal ashes (HTAs). The REY barely differentiate in either the fly ash or bottom ash from Xilaifeng. In contrast, the REY in the fine and coarse fly ashes from Damo have very similar H-type distribution patterns with negative Ce and slightly positive Y anomalies. Attention should be paid to the enriched toxic elements (including F, As and Hg) in the fly ashes from both power plants due to possible adverse environmental effect. Full article

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34 pages, 11483 KiB

Open AccessArticle

Geological Controls on Mineralogy and Geochemistry of the Permian and Jurassic Coals in the Shanbei Coalfield, Shaanxi Province, North China

by Yunfei Shangguan, Xinguo Zhuang, Jing Li, Baoqing Li, Xavier Querol, Bo Liu, Natalia Moreno, Wei Yuan, Guanghua Yang and Lei Pan

Minerals 2020, 10(2), 138; https://doi.org/10.3390/min10020138 - 6 Feb 2020

Cited by 6 | Viewed by 3399

Abstract

Coal as the source of critical elements has attracted much attention and the enrichment mechanisms are of significant importance. This paper has an opportunity to investigate the mineralogical and geochemical characteristics of the Permian and Jurassic bituminous coals and associated non-coals from two [...] Read more.

Coal as the source of critical elements has attracted much attention and the enrichment mechanisms are of significant importance. This paper has an opportunity to investigate the mineralogical and geochemical characteristics of the Permian and Jurassic bituminous coals and associated non-coals from two underground coal mines in the Shanbei Coalfield (Northeast Ordos basin), Shaanxi Province, North China, based on the analysis of X-ray diffraction (XRD), inductively coupled plasma atomic-emission spectrometry (ICP-AES/MS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). The Jurassic and Permian coals have similar chemical features excluding ash yield, which is significantly higher in the Permian coals. Major mineral matters in the Jurassic coals are quartz, kaolinite, and calcite. By contrast, mineral assemblages of the Permian coals are dominated by kaolinite; and apatite occurring in the middle section’s partings. The Jurassic coals are only enriched in B, whereas the Permian coals are enriched in some trace elements (e.g., Nb, Ta, Th, and REY). Boron has a mixed inorganic and organic association which may be absorbed by organic matter from fluid (or groundwater) or inherited from coal-forming plants. Additionally, climatic variation also plays an important role. As for the Permian coals, kaolinite and apatite as the major carriers of elevated elements; the former were derived from the sedimentary source region (the Yinshan Oldland and the Benxi formation) and later precipitated from Ca-, and P-rich solutions. We deduced that those elevated elements may be controlled by the source rock and diagenetic fluid input. The findings of this work offered new data to figure out the mechanism of trace element enrichment of coal in the Ordos basin. Full article

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2019

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27 pages, 7074 KiB

Open AccessArticle

Mineralogy and Geochemistry of Late Permian Coals within the Tongzi Coalfield in Guizhou Province, Southwest China

by Baoqing Li, Xinguo Zhuang, Xavier Querol, Natalia Moreno, Linjian Yang, Yunfei Shangguan and Jing Li

Minerals 2020, 10(1), 44; https://doi.org/10.3390/min10010044 - 31 Dec 2019

Cited by 8 | Viewed by 3858

Abstract

The lowermost Late Permian coal seam (C4 Coal) in the Tongzi Coalfield offers an opportunity to investigate the influence of terrigenous detrital materials from the Qianbei Upland on the mineralogical and geochemical patterns of the C4 Coal. The minerals are mainly dominated by [...] Read more.

The lowermost Late Permian coal seam (C4 Coal) in the Tongzi Coalfield offers an opportunity to investigate the influence of terrigenous detrital materials from the Qianbei Upland on the mineralogical and geochemical patterns of the C4 Coal. The minerals are mainly dominated by pyrite and, to a lesser extent, tobelite, kaolinite, and calcite, along with traces of Al-oxyhydroxide minerals. The various degrees of marine influence may have resulted in the variation in the amount of Fe-sulfides (e.g., pyrite) and elements having Fe-sulfides affinity. Furthermore, the abundant Fe ions involved in the formation of Fe-sulfides were most likely derived from the claystone on the Qianbei Upland. The tobelite identified in the C4 Coal probably originated from the interaction between pre-existing kaolinite and NH₄⁺ from NH₃ released from the thermally affected organic matter at least shortly after the highly volatile bituminous stage under NH₄⁺-rich and K⁺-poor conditions. The terrigenous detrital materials were derived from two possible sediment-region sources—the Qianbei Upland and Kangdian Upland—which is different from Late Permian coals in Western Guizhou Province. The claystone on the Qianbei Upland may have served as parent rock, as indicated by the presence of the Al-oxyhydroxide minerals as well as low SiO₂/Al₂O₃ ratio (0.66 on average) and low quartz content. Meanwhile, the detrital materials from the Kangdian Upland most likely originated from the erosion of the felsic rocks at the uppermost part of the Kangdian Upland, as evidenced by the high Al₂O₃/TiO₂ ratio (36.0 on average) and the strongly negative Eu anomaly (0.61 on average). Full article

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19 pages, 3759 KiB

Open AccessArticle

Calcium-Bearing Minerals Transformation during Underground Coal Gasification

by Shuqin Liu and Weiping Ma

Minerals 2019, 9(11), 708; https://doi.org/10.3390/min9110708 - 15 Nov 2019

Cited by 10 | Viewed by 5196

Abstract

Calcium-bearing minerals are one of the main typical minerals in coal and coal ash. In the process of coal thermal conversion, calcium-bearing minerals undergo different morphological transformation in which the reaction temperature, pressure, and atmosphere are important factors affecting their transformation. The reaction [...] Read more.

Calcium-bearing minerals are one of the main typical minerals in coal and coal ash. In the process of coal thermal conversion, calcium-bearing minerals undergo different morphological transformation in which the reaction temperature, pressure, and atmosphere are important factors affecting their transformation. The reaction process of underground coal gasification (UCG) could be clearly divided into pyrolysis, reduction, and oxidation and the typical calcium-bearing minerals are expected to indicate the actual reaction conditions of UCG. A high-calcium coal, Zhundong coal, was used in this research. The products of UCG were prepared and the minerals were identified by X-ray diffraction (XRD) and a scanning electron microscope coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic calculation was used to assist in understanding the transformation behaviors of calcium-bearing minerals. The experimental results show that the calcium-bearing mineral is gradually converted from gypsum (CaSO₄·2H₂O) in the raw coal into anhydrite (CaSO₄) during the pyrolysis process. In the reduction stage, anhydrite reacts with the reducing gas (CO) to produce oldhamite (CaS), and the oldhamite is stably present in the reduction ash. During the oxidation process, oldhamite is first transformed into CaSO₄, and then CaSO₄ is converted into CaO. Finally, CaO reacts with Al₂O₃ and SiO₂ to produce gehlenite (Ca₂Al₂SiO₇) at 1100 °C. As the oxidation temperature rises to 1400 °C, gehlenite is transformed into the thermodynamically stable anorthite (CaAl₂Si₂O₈). With the further progress of the reaction, anorthite will co-melt with iron-bearing minerals above 1500 °C. The ternary phase diagram of SiO₂–Al₂O₃–CaO system proves that anorthite and gehlenite are the typical high-temperature calcium-bearing minerals when the mole fraction of SiO₂ is higher than 0.6. Moreover, the gehlenite is converted to anorthite with the temperature rise, which is consistent with experimental results. This study provides a scientific basis for understanding the UCG reaction conditions. Full article

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19 pages, 4009 KiB

Open AccessArticle

Mineralogical and Environmental Geochemistry of Coal Combustion Products from Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, Northwest China

by Peng Wu, Jing Li, Xinguo Zhuang, Xavier Querol, Natalia Moreno, Baoqing Li, Dongfeng Ge, Shihua Zhao, Xiaoping Ma, Patricia Cordoba and Yunfei Shangguan

Minerals 2019, 9(8), 496; https://doi.org/10.3390/min9080496 - 19 Aug 2019

Cited by 7 | Viewed by 4777

Abstract

The mineralogical and geochemical characteristics of feed coals and coal combustion products (CCPs) from the Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, were studied by means of proximate analysis, Power X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray analyzer [...] Read more.

The mineralogical and geochemical characteristics of feed coals and coal combustion products (CCPs) from the Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, were studied by means of proximate analysis, Power X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray analyzer (SEM-EDX), inductively coupled plasma atomic emission spectrometry (ICP-MS) and inductively coupled plasma mass spectrometry (ICP-AES). The environmental geochemistry of CCPs was evaluated by Al-normalized enrichment factor as well as European Standard EN-12457 leaching test. Two feed coals have the characteristics of low sulfur content, medium to high volatiles matter yields, medium moisture content, super low to medium ash yield, medium to high calorific value and low mineral content. The main crystalline facies in fly ash and slag are quartz and mullite, with a small amount of calcite, and some unburned carbon. Hematite, SrSO₄ and barite also can be observed in fly ashes by SEM. Typical plerophere occurs in fine fly ash rather than the coarse fly ash. The concentration of most trace elements in CCPs falls within the lower concentration range of European fly ashes. With respect to the partitioning behavior of trace elements during coal combustion, S is highly volatile, and Mg, Na, Zn, B, Co, As, Nb, Zr, Cu and K also show certain volatility, which may to some extent emit to the atmosphere. Furthermore, leaching experiments show that leachable concentrations of most of the potentially toxic elements in CCPs are low, and the CCPs fall in the range between inert and nonhazardous landfill material regulated by the 2003/33/EC Decision. Full article

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36 pages, 12935 KiB

Open AccessArticle

Mineralogy and Geochemistry of the No. 5⁻² High-Sulfur Coal from the Dongpo Mine, Weibei Coalfield, Shaanxi, North China, with Emphasis on Anomalies of Gallium and Lithium

by Guohong Qin, Daiyong Cao, Yingchun Wei, Anmin Wang and Jincheng Liu

Minerals 2019, 9(7), 402; https://doi.org/10.3390/min9070402 - 30 Jun 2019

Cited by 20 | Viewed by 4573

Abstract

This paper reports the mineral compositions and geochemical characteristics of the No. 5⁻² high-sulfur coal (Taiyuan Formation) from Dongpo Mine, Weibei Coalfield, Shaanxi, Northern China via transmitted and reflected light microscopy, scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), X-ray [...] Read more.

This paper reports the mineral compositions and geochemical characteristics of the No. 5⁻² high-sulfur coal (Taiyuan Formation) from Dongpo Mine, Weibei Coalfield, Shaanxi, Northern China via transmitted and reflected light microscopy, scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray fluorescence spectrometry (XRF). We also confirmed the input of intermediate-felsic volcanic ashes into the Taiyuan Formation coals in Dongpo Mine, Weibei Coalfield. The results show that Dongpo coals are enriched in Ga and Li compared to the average values for world hard coals, and they are depleted in Al₂O₃ compared to Chinese coals. The coal low temperature ash contains kaolinite, illite, quartz, calcite, pyrite, and to a lesser extent, chlorite, plagioclase, dolomite, ankerite, and apatite. The concentration anomalies of Ga and Li in No. 5⁻² high-sulfur coal were not caused by the Benxi Formation Bauxite, but by the influence of multiple geological factors. The Middle Proterozoic moyite from the Yinshan Oldland led to the slightly higher Ga and Li contents of the No. 5⁻² coal than those in world hard coals. Input of synchronization volcanic ash, injection of hydrothermal fluids during the syngenetic or early diagenetic stages and influence of seawater further contributed to the Ga and Li enrichment of the No. 5⁻² coal. Full article

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16 pages, 2873 KiB

Open AccessArticle

Structural Characterizations of Aluminosilicates in Two Types of Fly Ash Samples from Shanxi Province, North China

by Yunxia Liu, Fangui Zeng, Beilei Sun, Peng Jia and Ian T. Graham

Minerals 2019, 9(6), 358; https://doi.org/10.3390/min9060358 - 12 Jun 2019

Cited by 66 | Viewed by 5659

Abstract

In order to determine the structural characterization of aluminosilicates in two types of fly ashes, two samples from Shanxi Province, China were selected for study. One was from a pulverized coal boiler (FA-1), and the other from a circulating fluidized bed boiler (FA-2). [...] Read more.

In order to determine the structural characterization of aluminosilicates in two types of fly ashes, two samples from Shanxi Province, China were selected for study. One was from a pulverized coal boiler (FA-1), and the other from a circulating fluidized bed boiler (FA-2). FA-1 had a much higher content of silicon dioxide (SiO₂) (70.30%) than FA-2(42.19%), but aluminum oxide (Al₂O₃) was higher in FA-2 (25.41%) than in FA-1 (17.04%). The characterizations were investigated using various methods including X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, and X-ray photoelectron spectroscopy (XPS). The XRD analysis showed that FA-1 contained aluminosilicate glass, quartz and mullite, while FA-2 contained significant amounts of amorphous aluminosilicate, quartz and gypsum. The FTIR results showed an increased substitution of Al³⁺ for Si⁴⁺ as the band of asymmetric stretching vibrations Si–O(Si) (1100 cm⁻¹) moved to 1090 cm⁻¹ for FA-2, much lower than for FA-1(1097 cm⁻¹). Moreover, the sharpness of the bands in the 1250–1000 cm⁻¹ region for FA-2 indicates that the silicate structure of FA-2 was more ordered than for FA-1. It can be understood from the ²⁹Si MAS–NMR results that Q⁴(mAl) (Q⁴ are connected via 4 bridging O atoms to mAl) is the main structural type in FA-1 and FA-2, and that FA-2 contains more Al, which substitutes for Si in the Q⁴ structure. ²⁷Al MAS–NMR demonstrated that a combination of tetrahedral, pentahedral, and octahedral Al existed in FA-1 and FA-2. The Si 2p XPS spectra suggested that there were three forms of Si, including bridging Si (Si–O₂), non–bridging Si (Si–O), and SiO₂ gel. The content of Si–O₂ for FA-1 was 37.48% higher than Si–O (28.57%), while the content of Si–O₂ was 30.21% lower than Si–O (40.15%) for FA-2. The Al 2p XPS spectra showed that octahedral Al was the dominant form for FA-1 with a content of 40.25%, while the main phase was tetrahedral Al for FA-2 with a proportion of 37.36%, which corresponds well with the ²⁷Al MAS–NMR results. Full article

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18 pages, 3079 KiB

Open AccessArticle

The Role of Mineral Matter in Concentrating Uranium and Thorium in Coal and Combustion Residues from Power Plants in Poland

by Henryk R. Parzentny and Leokadia Róg

Minerals 2019, 9(5), 312; https://doi.org/10.3390/min9050312 - 20 May 2019

Cited by 16 | Viewed by 5057

Abstract

Based on the results of tests on feed coal from the Lublin Coal and Upper Silesian Coal Basin and its fly ash and slag carried out using X-ray diffraction and X-ray fluorescence analysis, atomic emission spectroscopy, and scanning electron microscopy, it was found [...] Read more.

Based on the results of tests on feed coal from the Lublin Coal and Upper Silesian Coal Basin and its fly ash and slag carried out using X-ray diffraction and X-ray fluorescence analysis, atomic emission spectroscopy, and scanning electron microscopy, it was found that in feeds, coal Th is associated with phosphates and U with mineral matter. The highest Th content was found in anhedral grains of monazite and in Al-Si porous particles of fly ash of <0.05 mm size; whereas in the slag, Th is concentrated in the massive Al-Si grains and in ferrospheres. U is mainly concentrated in the Al-Si surface of porous grains, which form a part of fly ash of <0.05 mm size. In the slag, U is to be found in the Al-Si massive grains or in a dispersed form in non-magnetic and magnetic grains. Groups of mineral phase particles have been identified that have the greatest impact on the content of Th and U in whole fly ash and slag. The research results contained in this article may be important for predicting the efficiency of Th and U leaching from furnace waste storage sites and from falling dusts to soils and waters. Full article

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17 pages, 1077 KiB

Open AccessFeature PaperArticle

Threshold Value Determination Using Machine Learning Algorithms for Ba Interference with Eu in Coal and Coal Combustion Products by ICP-MS

by Na Xu and Qing Li

Minerals 2019, 9(5), 259; https://doi.org/10.3390/min9050259 - 29 Apr 2019

Cited by 7 | Viewed by 4265

Abstract

Ba-based ion interference with Eu in coal and coal combustion products during quadrupole-based inductively coupled plasma mass spectrometry procedures is problematic. Thus, this paper proposes machine-learning-based prediction models for determination of the threshold value of Ba interference with Eu, which can be used [...] Read more.

Ba-based ion interference with Eu in coal and coal combustion products during quadrupole-based inductively coupled plasma mass spectrometry procedures is problematic. Thus, this paper proposes machine-learning-based prediction models for determination of the threshold value of Ba interference with Eu, which can be used to predict such interference in coal. The models are trained for Eu, Ba, Ba/Eu, and Ba interference with Eu. Under different user-defined parameters, different prediction models based on the corresponding model tree can be applied to Ba interference with Eu. We experimentally show the effectiveness of these different prediction models and find that, when the Ba/Eu value is less than 2950, the Ba-Eu interference prediction model is

y = - 0.18419411 + 0.00050737 \times x, 0 < x < 2950 .

Further, when the Ba/Eu value is between 2950 and 189,523, the Ba-Eu interference prediction model of

y = 0.293982186 + 0.00000181729975 \times x, 2950 < x < 189, 523

yields the best result. Based on the optimal model, a threshold value of 363 is proposed; i.e., when the Ba/Eu value is less than 363, Ba interference with Eu can be neglected during Eu data interpretation. Comparison of this threshold value with a value proposed in earlier works reveals that the proposed prediction model better determines the threshold value for Ba interference with Eu. Full article

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10 pages, 2699 KiB

Open AccessCommunication

Nano-Scale Rare Earth Distribution in Fly Ash Derived from the Combustion of the Fire Clay Coal, Kentucky

by James C. Hower, Dali Qian, Nicolas J. Briot, Eduardo Santillan-Jimenez, Madison M. Hood, Ross K. Taggart and Heileen Hsu-Kim

Minerals 2019, 9(4), 206; https://doi.org/10.3390/min9040206 - 30 Mar 2019

Cited by 27 | Viewed by 5342

Abstract

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy [...] Read more.

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy dispersive X-ray spectroscopy (EDS) showed that rare earth elements (REE; specifically, La, Ce, Nd, Pr, and Sm) were distributed within glassy particles. In certain cases, the REE were accompanied by phosphorous, suggesting a monazite or similar mineral form. However, the electron diffraction patterns of apparent phosphate minerals were not definitive, and P-lean regions of the glass consisted of amorphous phases. Therefore, the distribution of the REE in the fly ash seemed to be in the form of TEM-visible nano-scale crystalline minerals, with additional distributions corresponding to overlapping ultra-fine minerals and even true atomic dispersion within the fly ash glass. Full article

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23 pages, 4563 KiB

Open AccessArticle

Geochemical and Mineralogical Characteristics of the Middle Jurassic Coals from the Tongjialiang Mine in the Northern Datong Coalfield, Shanxi Province, China

by Yue Yuan, Shuheng Tang and Songhang Zhang

Minerals 2019, 9(3), 184; https://doi.org/10.3390/min9030184 - 16 Mar 2019

Cited by 18 | Viewed by 4299

Abstract

There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry [...] Read more.

There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDS). No.12 coal is a low-medium volatile bituminous coal and is characterized by low ash yield content, low moisture content, and ultra-low sulfur content. Compared with Chinese coals, the Tongjialiang coals have slightly higher average percentages of MgO and P₂O₅, and lower average percentages of the other major oxides, including SiO₂, TiO₂, Al₂O₃, Fe₂O₃, CaO, MnO, Na₂O, and K₂O. Compared with the World hard coals, Be, Cr, Co, Ni, Ge, Sn, Ta, and W are slightly enriched in the Tongjialiang coals. The concentrations of Li, F, Sc, V, Cu, Ga, Se, Sr, Zr, Nb, Hf, Pb, Th, and U are close to the average values of the world’s hard coals. The minerals in No.12 coal mainly include quartz, kaolinite, siderite, and ankerite, along with smaller amounts of pyrite, illite, calcite, and rutile. The formation of syngenetic siderite in No.12 coal is related to the weathering of biotite in the gneiss of the Yinshan Upland. The modes of occurrence of ankerite indicate that the coals may be affected by the injection of low temperature hydrothermal fluids. It is noteworthy that a portion of epigenetic ankerite may be a product of metasomatism between syngenetic siderite and the epigenetic Fe-Mg-Ca rich hydrothermal fluids. The ratios of Al₂O₃/TiO₂, REY (rare earth elements and yittrium) enrichment patterns, the modes of occurrence of siderite and ankerite, as well as the enriched lithophile and siderophile elements indicate that the No.12 coal may have originated from the Yinshan Upland and may also have been influenced by low temperature hydrothermal fluids that might have circulated in the coal basin. Full article

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2018

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27 pages, 7690 KiB

Open AccessArticle

Minerals and Enrichment of W, Rb, and Cs in Late Permian Coal from Meitian Mine, Meitian Coalfield, Southern China by Magmatic Hydrothermal Fluids

by Zhenghui Xiao, Yunjiang Cao, Wei Jiang, Ping Zhou, Yanran Huang and Jisong Liu

Minerals 2018, 8(11), 504; https://doi.org/10.3390/min8110504 - 5 Nov 2018

Cited by 11 | Viewed by 3862

Abstract

We report on the effects of magmatic hydrothermal fluids on the mineralogical and geochemical compositions of 12U and 12L Coals from the Meitian Mine in the Meitian Coalfield, southern China. The minerals in 12U Coal are predominantly chlorite, quartz, and calcite, while the [...] Read more.

We report on the effects of magmatic hydrothermal fluids on the mineralogical and geochemical compositions of 12U and 12L Coals from the Meitian Mine in the Meitian Coalfield, southern China. The minerals in 12U Coal are predominantly chlorite, quartz, and calcite, while the minerals in 12L Coal consist mainly of illite, quartz, chlorite, kaolinite, and mixed-layer illite/smectite (I/S). The vesicle- and fracture-filling illite, chlorite, I/S, pyrite, and fluorite, cleat- and fracture-filling carbonate minerals (i.e., calcite, and dolomite), and cleat-filling tremolite, diopside, and talc have epigenetic hydrothermal origins. Tremolite, diopside, and talc were probably formed from the reaction between dolomite and Si-rich magmatic hydrothermal fluids. Elevated Pb–Zn–Sn–Cd assemblages are characteristic for the 12U Coal, while 12L Coal is enriched in W, Rb, Cs, Th, V, Zn, and Zr, most notably W, Rb, and Cs. REY (Rare Earth Elements and Yttrium) plots for almost all coals, partings and host rocks are similar, showing an M-type REY distribution, Gd-maximum, positive Y anomalies, and negative Ce anomalies, suggesting acid hydrothermal circulation in the coal-bearing strata. Rubidium and cesium in the coal is clearly associated with K-rich clay minerals (illite + I/S), and to a lesser extent with silicate minerals that were precipitated from hydrothermal solutions. W in the coals mainly occurs in the inorganic constituents of illite and pyrite, especially illite. Enrichment of W, Rb, and Cs in the coal and host rocks is genetically associated with magmatic hydrothermal fluids. Specifically, magmatic hydrothermal fluids of relatively high temperatures that are rich in volatile matter can extract abundant W, Rb, and Cs from granitic melts. The enrichment of these rare metals in the coal is mainly related to illitization. Our study results suggest that, for coal intruded by magmatic rocks, the type of hydrothermal alteration may greatly influence the enrichment of elements. Full article

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