Late Permian Coals Research Articles

Geological controls on the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons in late Permian coals from the Qiandongbei Coalfield, Guizhou Province, SW China

The abnormal enrichment of the REY (rare earth elements and yttrium)-Zr (Hf)-Nb (Ta) assemblage in Late Permian coals occurring in some coalfields in SW China has been extensively investigated, but the geological controlling factors of this assemblage are still under debate. This study reports on the mineralogical and geochemical features of coals and noncoal rocks collected from the Yudai and Jinqi coal mines within the Qiandongbei Coalfield in Guizhou Province to elucidate the geological controls on the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The studied coals show rather consistent clay mineral assemblage of kaolinite, together with varying amounts of quartz, gypsum, pyrite, and calcite. Notably, the coals are anomalously enriched in REY, Nb, Ta, Zr, and Hf and enriched in other incompatible elements (e.g., Ga, Th, and U). Phosphates (e.g., florencite) and, to a lesser extent, zircon are the primary carriers of REY. Zirconium and Hf are mainly incorporated into zircon and then anatase, the latter of which is a predominant carrier of Nb and Ta. The detrital materials originate from a mixture of the erupted felsic volcanic ash resembling a peralkaline rhyolite composition and the eroded materials of Emeishan Large Igneous Province (ELIP) basalts. The studied coals owe their highly enhanced concentrations of the REY-Zr (Hf)-Nb (Ta) assemblage to the input of felsic volcanic ash, wherein the highly acidic aqueous solutions allowed these elements to become mobile and be redistributed. Both geological processes governed the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The highly acidic solutions were possibly derived from the oxidation of peat bogs and volcanism-related acidic rain. The concentrations of REY, Zr, and Nb in the coal ashes exceed their corresponding cut-off grades; thus, these coals can be considered highly promising raw material sources for the REY-Zr (Hf)-Nb (Ta) assemblage.

Assessment of the External Costs of Life Cycle of Coal: The Case Study of Southwestern China

Coal will continue to be the main energy source in China for the immediate future, although the environmental pollution and ecological impacts of each stage in the full life cycle of coal mining, transportation, and combustion generate large quantities of external costs. The Late Permian coals in southwestern (SW) China usually contain high amounts of fluorine (F), arsenic (As), and ash, which together with high-F clays cause abnormally high levels of endemic fluorosis, As poisoning, and lung cancer in areas where coal is mined and burned. In this paper, we estimate the external costs of the life cycle of coal. The results show that the externalities of coal in SW China are estimated at USD 73.5 billion or 284.3 USD/t, which would have accounted for 6.5 % of the provincial GDP in this area in 2018. The external cost of human health accounts for 87.2% of the total external costs, of which endemic skeletal fluorosis diseases and related lung cancers have the most important impact. Our study provides a more precise estimate of externalities compared with its counterparts in other provinces in China. Therefore, several policy recommendations would be proposed to internalize the external cost.

Revisiting the thermally metamorphosed coals of the Transantarctic Mountains, Antarctica

Petrographic and geochemical data for Late Permian coals and carbonaceous shales from the Transantarctic Mountains, Antarctica (source: Polar Rock Repository, PRR), were used to evaluate maturation levels and assess the effects of contact metamorphism. Coals were evaluated for locations in the Southern Transantarctic Mountains, the Central Transantarctic Mountains, and South Victoria Land, including samples from the Buckley, Mt. Glossopteris, and Queen Maud formations and the Weller Coal Measures. These formations have been intruded by sills and dikes of the Jurassic Ferrar Group (177–183 Ma) associated with the breakup of Gondwanaland. Proximate (129 samples), total sulfur (69) analyses, vitrinite reflectance analysis (92), and petrographic composition (34) were determined. One third of the samples have >50% ash yields (dry basis). A subset of samples (87) with <50% ash (dry basis) was treated with 6 N HCl to remove any carbonates formed during the intrusive events. Acid treatment did not significantly reduce ash, suggesting silicates are a major component; sulfur contents of 1–2% (dry basis) decreased to <0.8% reflecting gypsum dissolution (as confirmed by XRD). Volatile matter (VM) contents (dry, ash-free or daf basis) for samples with <50% ash range from 3 to 43%. Based on VM, samples range from high volatile bituminous to anthracite; however, reflectance analysis indicates anthracite to meta-anthracite, with some reflectances >7%. Thus, VM does not reveal true rank of the Antarctic coals. Vitrinite reflectance (Rr) typically surpasses that of inertinite. The VM–Rr relationship for these coals does not follow that of coals matured by normal burial maturation, but more closely follows that of intruded coals. Coke textures, including isotropic coke and anisotropic mosaics, vacuoles, pyrolytic carbon, and coked bitumen are observed, indicating alteration by contact metamorphism and providing insights to the rank of the coal at the time of intrusion. Coarse-grained circular and fine-grained lenticular mosaic textures suggest coal rank at the time of intrusion was medium volatile bituminous coal (maximum vitrinite reflectance ~1.2%). This would imply a burial depth by time of intrusion of ~5–5.5 km (assuming 25 °C/km) or ~ 4 km (assuming 34 °C/km). Modern-day background reflectance levels of ~2.5% Rr indicate continued post-intrusion maturation, possibly due to exposure to higher regional heat flow. Coals and carbonaceous shales from the Polar Rock Repository (PRR) can provide reliable petrographic and maturation data (using reflectance) to help decipher the burial history for various parts of the Transantarctic Mountains. However, geochemical data must be used with caution due to the high original inorganic content, and possible formation of gypsum and changes in VM during long-term storage. HCl-treatment removes some of the neoformed minerals, but samples should be treated extensively with HCl-HF to remove all silicate minerals prior to proximate and ultimate analysis to ensure more reliable data.

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

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.

Evidence for multiple sources for inorganic components in the Tucheng coal deposit, western Guizhou, China and the lack of critical-elements

Terrigenous materials from sediment-source regions are important controls on the types and concentrations of inorganic components in coal. The Kangdian Upland (dominated by the Emeishan basalts) is the dominant terrigenous supplier for most of the Late Permian coals, as well as for their associated host rocks (roof and floor strata) in southwestern China. The high volatile bituminous coals (Nos. 3 and 6 coals) are the two major minable coal seams in the Tucheng coal deposit in southwestern China. Unlike most Late Permian coals in this region that are characterized by elevated concentrations of the element assemblage Sc-V-Cr-Co-Ni-Cu-Zn-Se, these two coals are not enriched in this assemblage although Se is slightly concentrated.The mineralogical (e.g., relatively abundant quartz and mixed-layer illite/smectite) and elemental distribution patterns (e.g., spider diagrams of rare earth elements, discrimination diagrams of Al2O3-TiO2 and Zr/TiO2-Nb/Y, and elemental assemblages) indicate that the inorganic components in the two coal seams were mainly derived from unidentified volcanic arc and/or distal orogens, while the clastic components in the roof and floor strata of the two coal seams were mainly supplied by the high-Ti Emeishan basalts. The two partings in the two coal seams, identified as tonsteins, were probably derived from the final (rejuvenated) activity of the Emeishan plume. Critical elements in the two coals and associated non-coal horizons (partings, roof and floor strata) are economically unpromising, indicating that prospecting for Late Permian coal-hosted critical metal ore deposits in the vicinity of the Emeishan plume in southwestern China, should not be focused on coals with inorganic components derived mostly from distal volcanic arcs and orogens and high-Ti Emeishan basalts, and a minor contribution of volcanic ashes resulting from the final rejuvenated activity of the Emeishan plume.

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

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).

Mineralization zoning of coal-metal deposits in China

Substantive progress has been made in extracting germanium, gallium, rare earth elements (REEs), lithium, and other metals from coal. Coal deposits are becoming important sources of many strategic metal resources. However, ore deposit theory study for coal-metal resources has not been systematic. This paper summarizes the mineralization characteristics of germanium, gallium, lithium, and REEs in coal on the basis of previous research results and field investigations, including those on seven metallogenic zones of coal metal deposits in China. Coal-germanium deposits, products of magmatic hydrothermal activity, mainly occur in low rank coal in the areas of Erlian, the Hailaer Basin, Inner Mongolia, and the Sanjiang district in the Yunnan Province. Occasionally, rich-germanium-coal can be found in other areas. Coal-gallium deposits are mainly in the Permian coal of North China, Jurassic coal of Northwest China, and late-Permian coal of South China. The accumulation of gallium in coal is closely related to aluminum-containing minerals. Coal-lithium deposits mainly occur in the Zhungeer coal field, Inner Mongolia, the Pingshuo coal field, and the Jingcheng coal field in the Shanxi Province, and some coal fields in South China. Similarly to gallium, the accumulation of lithium in coal is also closely related to aluminum-containing minerals. Coal-REE deposits mainly occur in the Early Jurassic coal of the Erlian Basin and Inner Mongolia, and Late Permian coal in South China. REEs of Erlian basin coal likely entered in ionic forms in early stages of coal or peat bog formation. REEs of South China coal are likely associated with REE-rich trass volcanic ash which deposited synchronously with peat bog accumulation. Abundant abnormal metal elements in coal are important for classification of metallogenic zones. Regional tectonic background and evolution, characteristics of stratigraphic sedimentary environment, and coal quality are also important factors. (1) Delineation of germanium metallogenic zones in the coal follows the principles that: coal in the coal area should be low-metamorphic bituminous (long-flame) coal; the basement of the coal-bearing basin was broken and faults developed in the region; and there are obvious traces of hydrothermal intrusion in or around the coal measures in the zone. (2) Delineation of gallium metallogenic zones in coal is based on these traits: an obvious gallium source should exist in the region; the provenance area has favorable weathering and denudation conditions; and an aluminum-gallium formation under strong leaching is contained within. (3) Delineation of lithium metallogenic zones in coal requires: relatively clear sources of lithium in the zones; favorable weathering and denudation conditions in the provenance area; and aluminum-lithium containing rocks under strong leaching. (4) Delineation of rare earth mineralization zones in coal is based on: large scale volcanic eruptions in or near peat bogs during the accumulation period, with tuff in the coal-bearing strata; and hydrothermal intrusion into coal-measure strata during the peat bog period or early coal-forming period. According to the principles above, seven coal-metal metallogenic zones were identified, including: (1) the Erlian Basin-Hailaer Basin coal-germanium and REE deposit zone; (2) the Tianshan coal-gallium deposit zone; (3) the South-Yinshan coal-gallium-lithium deposit zone; (4) the East-Taihang Mountain coal-gallium deposit zone; (5) the Qilian-Qinling coal-gallium-lithium deposit zone; (6) the Sichuan-Yunnan-Guangxi coal-gallium-lithium and REE deposit zone; and (7) the Sanjiang (west Yunnan Province) germanium deposit zone.

Using geophysical logs to identify Milankovitch cycles and to calculate net primary productivity (NPP) of the Late Permian coals, western Guizhou, China

Milankovitch periodicities of 123 kyr (eccentricity), 35.6 kyr (obliquity), and 21.2 kyr (precession) were identified in geophysical logs of three Late Permian coals: 17#, 18#, and 17 + 18#, from the Songhe mining area in western Guizhou Province. Based on the astronomic temporal framework, the periods of deposition of the 17# (5.6 m), 18# (6.4 m), and 17 + 18# (5.4 m) coals were constrained to 140.8–119.8 kyr, 160–136.2 kyr, and 135–114.9 kyr, respectively. The overall depositional period of the 18# coal of 160–136.2 kyr was further subdivided using the wavelet analysis method, into short and precise periods corresponding to the Milankovitch periodicities. It includes one eccentricity periodicity (123 kyr), three obliquity periodicities (35.6 kyr), and five precession periodicities (21.2 kyr). Different thicknesses of the subdivided coal sections, equivalent to the same time span of deposition, indicate different rates of coal deposition, i.e., thicker sections imply higher rates while the thinner sections represent lower rates. The combination of the measured average carbon concentration with the density of the coals gave rise to long-term average values of carbon accumulation rates for the Late Permian coals, in the range of 42.4–50.6 g⋅C⋅m− 2⋅a− 1. This range corresponds to the long-term average carbon accumulation rates for the initial peat in the range of 60.6–72.3 g⋅C⋅m− 2⋅a− 1. Based on the known quantitative relation between net primary productivity (NPP) values and long-term average carbon accumulation rates for the Holocene tropical peatlands, the range of NPP values for the Late Permian tropical peatlands was estimated as 242.4–433.8 g⋅C⋅m− 2⋅a− 1.A comparison of existing information about peatland NPP levels of various ages and latitudes indicated that when conditions of high rain and high humidity prevail in the palaeo-peatland at given latitude, the NPP rates will vary with changes in atmospheric concentration of CO2 and O2. This relationship may lead to the use of coals as an indicator for the concentration of these gases (CO2 and O2) in the contemporaneous atmosphere encompassing the long records of coal deposition.

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

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.

Comments on Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China

The paper Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China by Qin et al. in Energy & Fuels provides potentially useful data on the proximate analysis, geochemical, and mineralogical properties of the Late Permian (No. K2) coal from the Moxinpo Mine, Chongqing, China. However, after a careful examination of the whole paper, we regrettably found that the paper by Qin et al. is affected by issues of coal rank determination, mineralogical identification, geochemical composition, and geological interpretation, some of which at least may need careful reconsideration.

Response to Comments by Dai et al. on Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China

Response to Comments by Dai et al. on Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China

Geochemistry of elements associated with Late Permian coal in the Zhongliangshan mine, Chongqing, Southwest China

The enrichment and geochemical significance of elements associated with Late Permian coals in Southwest China have always gained widespread interest in the field of coal geology. The present study focuses on the geochemical characterization of Late Permian coal in the Zhongliangshan mine. Twenty-three samples were collected from the K1a coal seam of the Zhongliangshan mine, and the major and trace elements in the coal were analyzed by using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry. The composition of minerals in the Zhongliangshan coal, and the modes of occurrence of coal-associated elements, especially those with elevated contents, were studied through a combination of microscopic analyses, X-ray powder diffraction, and scanning electron microscope – energy dispersive X-ray spectrometer. The minerals in coal mainly consist of kaolinite, pyrite, calcite, and quartz, as well as small amount of gypsum and anatase. Compared with the average elemental concentrations in world coal, the Zhongliangshan coal is enriched in Cr, and slightly enriched in Li, U, Sr, V and Ag. Combining the correlation analysis and sequential chemical extraction experiments, it can be inferred that many trace elements in the Zhongliangshan coal have both inorganic and organic affinities. The elements Cr, Li, and V mainly occur in clay minerals, and also are related to organic matter in the coal. Uranium presents firstly in the organic and then silicate states. Strontium shows multiple modes of occurrence including carbonate, silicate, and exchangeable ion states, and Ag primarily occurs in sulfides followed by silicates. The terrigenous debris input from the Emeishan basalt is the major reason for the enrichment of above elements in the Zhongliangshan coal.

Washability and Distribution Behaviors of Trace Elements of a High-Sulfur Coal, SW Guizhou, China

The float-sink test is a commonly used technology for the study of coal washability, which determines optimal separation density for coal washing based on the desired sulfur and ash yield of the cleaned coal. In this study, the float-sink test is adopted for a high-sulfur Late Permian coal from Hongfa coalmine (No.26), southwestern Guizhou, China, to investigate its washability, and to analyze the organic affinities and distribution behaviors of some toxic and valuable trace elements. Results show that the coal is difficult to separate in terms of desulfurization. A cleaned coal could theoretically be obtained with a yield of 75.50%, sulfur 2.50%, and ash yield 11.33% when the separation density is 1.57 g/cm3. Trace elements’ distribution behaviors during the gravity separation were evaluated by correlation analysis and calculation. It was found that Cs, Ga, Ta, Th, Rb, Sb, Nb, Hf, Ba, Pb, In, Cu, and Zr are of significant inorganic affinity; while Sn, Co, Re, U, Mo, V, Cr, Ni, and Be are of relatively strong organic affinity. LREE (Light rare earth elements), however, seem to have weaker organic affinity than HREE (Heavy rare earth elements), which can probably be attributed to lanthanide contraction. When the separation density is 1.60 g/cm3, a large proportion of Sn, Be, Cr, U, V, Mo, Ni, Cd, Pb, and Cu migrate to the cleaned coal, but most of Mn, Sb and Th stay in the gangue. Coal preparation provides alternativity for either toxic elements removal or valuable elements preconcentration in addition to desulfurization and deashing. The enrichment of trace elements in the cleaned coal depends on the predetermined separation density which will influence the yields and ash yields of the cleaned coal.

Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China

The rare-metal, rare-scattered (dispersed), and rare-earth elements (TREs) and minerals of the K2 coal from the Moxinpo mine, Chongqing, were analyzed using inductively coupled plasma mass spectrometry and scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry, respectively. In addition, three-fold geochemical classification of TREs (Li–Be–Rb(Cs)–Sr–Ge–Se–Tl, Zr(Hf)–Nb(Ta)–Ga(In)–Te–Re–Cd, and REY–Sc) was used to determine the vertical distribution. Compared to world bituminous coals, the K2 coal is enriched in Li, Be, Zr, Nb, Hf, Ta, Ga, Se, Cd, In, Te, Re, Sc, and REY elements (except Eu and Tm), especially in Zr, Nb, Ta, Se, Re, and Sc (>5 times). Compared with the upper continental crust, the K2 coal is enriched with REY, and the fractionation of individual light-REY is higher than that of heavy-REY except for few cases. The value of δEu showed a well-pronounced negative anomaly and that of δCe showed a slightly negative anomaly, which indicate that the K2 coal-seam was intermitt...

Partitioning of hazardous elements during preparation of high‑uranium coal from Rongyang, Guizhou, China

The Late Permian coal from Rongyang Mine in southwestern China is characterized by high content of sulfur (5.44%) and elevated concentrations of trace elements U (70.5μg/g), V (283μg/g), Cr (63.2μg/g), Co (12.8μg/g), Cu (59.5μg/g), Se (5.28μg/g), and Mo (87.5μg/g). Because of their potential adverse effects on human health and environments, it is important to understand the pathways of these elements during preparation. This study focuses on the distribution of hazardous elements in the size- and density-fractionated samples of this coal. The results indicated that: (1) The minerals in the Rongyang coals are mainly composed of quartz, pyrite, marcasite, calcite, anatase, illite, and kaolinite, along with traces of coquimbite, bassanite, roemerite, gypsum, dolomite, rutile, and siderite. Most of the minerals can be effectively liberated from cleaned coal by gravity separation. (2) Elements U, V, Cr, Co, Cu, Se, and Mo with a high content in the Rongyang coal are derived from exfiltrational hydrothermal fluids during syngenetic or early diagenetic stages, and are associated with inorganic components such as clay minerals, pyrite, anatase, and guadarramite as well as organic components. Selenium mainly occurs in pyrite (particularly epigenetic pyrite) in the coal. (3) Uranium is the easiest to remove through gravity separation (the removability is 68.33%) and has lowest concentration (10.5μg/g) in the 3–6mm size fractions compared to the others size fractions. It was also found that uranium cannot be removed through gravity separation completely, due to its association with the organic components and fine-grained minerals. The U concentration in the cleaned coal is still much higher than the average value for world hard coals. The ash from the cleaned coal with particle size of 6–13mm and <0.5mm could be potentially used for industrial extraction of uranium. (4) The minerals that are epigenetic in origin are easily liberated during coal cleaning. Therefore, hazardous elements Co, Ni, Cu, As, Se, Cd, Sb, Hg, Tl, and Pb that are associated with epigenetic pyrite are thus relatively easy to remove, whereas elements V, Cr, and Mo that are evenly distributed in inorganic and organic components, are more difficult to be removed.

Chromium and vanadium bearing nanominerals and ultra-fine particles in a super-high-organic-sulfur coal from Ganhe coalmine, Yanshan Coalfield, Yunnan, China

The Late Permian coal of the Ganhe coalmine (Ganhe coal) from Yanshan coalfield, Yunnan, southwestern China, is a super-high-organic-sulfur (SHOS) coal that has a total sulfur content of 9.3–12.4% (dry basis) and an organic sulfur content of 7.4–10.5% (dry basis). Compared with average trace elemental abundances of ordinary Chinese coals and worldwide hard coals, the Ganhe coal is remarkably rich in chromium (Cr, 389μg/g) and vanadium (V, 554μg/g) (on the whole coal basis), which show negative correlations with ash yield. The result from statistical analysis seems to imply predominately the organic association of Cr and V in the Ganhe coal. Furthermore, Cr and/or V were identified in association with Al-Si (muscovite, illite, and pyrophyllite), Fe (pyrite, jarosite, Fe-S-Cr particle, and Fe-Cr-Au particles), and Ti (Ti-oxides) nanominerals in maceral components through further nanoscale mineralogical examination using high resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectrometry (EDS). Furthermore, compared with Fe-bearing nanominerals in two medium-organic sulfur coals from northeast India (Ribeiro et al., 2010), more types of nanominerals (Al-Si, Fe, Ti nanominerals) are found in the Ganhe SHOS coal. Additionally, in these nanominerals, nano Ti-oxides are associated with the largest proportions of Cr and V. The origin and association mechanism of Cr and/or V bearing nanominerals still need further investigation.

Geochemical characteristics of the Late Permian coals from the Yueliangtian Coalfield, western Guizhou, southwestern China

This paper investigated geochemical characteristics of the Late Permian No. 6 upper (YLT6U) and No. 6 lower (YLT6L) coals from the Yueliangtian Coalfield, Guizhou, southwestern (SW) China, using x-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, field emission-scanning electron microscopy plus an energy-dispersive x-ray spectrometry, and optical microscopy. The YLT6U coal is slightly enriched in Se and W. The YLT6L coal is enriched in elements Hg, As, Tl, Co, Cu, Se, Mo, and Cd. Different with other Late Permian coals from SW China, the Yueliangtian coals are depleted in Sc, V, Cr, Ni, and Zn. The enrichment patterns of rare earth elements and yttrium (REY, or REE if Y is not included) in the benches of the Yueliangtian coal are characterized by heavy-REY enrichment and, to a lesser extent, light- and medium-enrichment types. Germanium in the YLT6U coal is mainly organic-associated and relatively enriched in the middle portion of the coal seam. It is due to Ge adsorption by organic matter during the input of Ge-rich solution into peat swamp of the YLT6U coal. Boron in the Yueliangtian coal mainly occurs in clay minerals and is derived from terrigenous materials rather than marine influence. Owing to the parting leaching by circulated hydrothermal solutions, the Nb/Ta, U/Th, Yb/La, and Zr/Hf ratios are higher in the coal benches relative to their corresponding overlying partings. The parent rocks of the sediment-source region for the Yueliangtian coal are not only the mafic basalts but also the felsic-intermediate rocks in the upper portion of the Kangdian Upland.

Enrichment and distribution of elements in the Late Permian coals from the Zhina Coalfield, Guizhou Province, Southwest China

This paper investigates the mineralogy and geochemistry of four coal beds (WJB-6, WJB-7, FHS-23 and FHS-27 Coals) of the Late Permian in the Zhina Coalfield, western Guizhou Province, China. The investigated coals reach the semianthracite -anthracite coal rank and have super-low to low ash yields. The sulfur contents vary considerably through coal sections and are mostly in the range of medium-high sulfur coal. The mineral assemblage present in the FHS-23 and FHS-27 Coals is mainly made up of pyrite and rectorite; the WJB-6 and WJB-7 Coals have different mineralogy, with kaolinite and rectorite dominant in the former as well as quartz and rectorite in the latter. These coals contain high concentrations of Nb and Ta, but Li is only enriched in the WJB-6 Coal. Rectorite and anatase in these coals are important hosting phases of Nb and Ta while kaolinite, and to a lesser extent chamosite in the WJB-6 Coal, are dominant carriers for the elevated Li concentration.The terrigenous material input, the marine influence and the effect of circulating hydrothermal solution are the pivotal geological factors causing geochemical anomalies in coals investigated. The high-sulfur coals were subjected to an enhanced marine influence in the depositional environment, as well as to a higher terrigenous influx, when compared with the medium-sulfur and low-sulfur coals, resulting in higher concentrations of S-Fe-As-Mo-U-Hg in the former coals than in the latter ones. The anomalous enrichment of Nb and Ta in these coals, as well as of Li in the WJB-6 Coal, is the result of the contributions from ascending hydrothermal solutions, although source rocks (e.g., high-Ti basalt) may provide relatively high background abundances of Nb, Ta and Li.

Structural Characterization of Coal Components of Late Permian Coals from Southern China by X-ray Diffraction and Raman Spectroscopy

Structural Characterization of Coal Components of Late Permian Coals from Southern China by X-ray Diffraction and Raman Spectroscopy

Organic geochemistry of the Late Permian coals from the Huoshaopu and Jinjia Mines, Liupanshui Coalfield, China

Four coal samples from the Huoshaopu Mine and six coal samples from the Jinjia Mine, Liupanshui Coalfield, China were collected and analyzed, focusing on their petrological and organic geochemical features. The microscopic results show that the vitrinite random reflectance ( Ro) of all samples is 0.97%, which is classified as high-volatile A bituminous coal. The maceral groups are dominated by vitrinite followed by inertinite. The low ratios (0.07–0.42) of saturated to aromatic hydrocarbons indicate a terrestrial plant input for the coals. Gas chromatography and gas chromatography/mass spectrometry were employed to analyze the composition of organic matter in the samples. The gas chromatography chromatograms of saturates display a monomodal outline of n-alkanes with a predominance of short chains. The odd-even preference values around 1 reflect the thermal maturity of the coals. Based on the different pristine/phytane ratios and dibenzofuran contents, we infer a relatively weak oxic coal-forming environment for Huoshaopu coals and a relatively anoxic environment for Jinjia coals. Among the aromatics, thermodynamically stable compounds, including 2-methylnaphthalene, 2,6 + 2,7-dimethylnaphthalenes, 3 and 4-methylbiphenyls, 4,4′-dimethylbiphenyl, methylphenanthrene, 2 and 3-methyldibenzofurans, were the dominant isomers in the respective homologs. The occurrence of dibenzothiophenes and benzonaphthothiophenes may confirm the paralic depositional environment of Late Permian coals from the Huoshaopu and Jinjia mines.