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Liu J.,China University of Mining and Technology | Yang Z.,Yunnan Institute of Coal Geology Prospection | Yan X.,China University of Mining and Technology | Ji D.,China University of Mining and Technology | And 2 more authors.
Fuel | Year: 2015

Abstract The concentrations and modes of occurrence of highly-elevated trace elements including V, Cr, Se, Mo, Cd, Re, and U in some late Permian coals preserved within marine carbonate successions from Southwest China, were investigated using inductively coupled-plasma mass spectrometry (ICP-MS), sequential chemical extraction procedures (SCEP), field emission-scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer (FE SEM-EDS), and X-ray powder diffraction analysis (XRD). The coals present in this study are characterized by superhigh-organic-sulfur, ranging from 5.01% to 9.87%, and by highly-elevated concentrations of V (859 ppm on average), Cr (370 ppm), Se (29.3 ppm), Mo (364 ppm), Cd (3.87 ppm), Re (0.47 ppm), and U (214 ppm). The minerals in the coals are predominantly composed of illite or mixed-layer illite/smectite, which, together with quartz, were derived from sediment-source region. The SCEP results showed that elements V, Cr, Se, Re, U, and Mo are mainly associated with organic matter of the coal, and to a lesser extent, are associated with illite or mixed-layer illite/smectite. Traces of U-bearing minerals (coffinite and brannerite) were identified in the coal. Cadmium is mainly and Cr and Mo are partially distributed in sulfide minerals. A significant proportion of Re is also associated with the carbonate fraction. © 2015 Elsevier Ltd. All rights reserved. Source

Dai S.,China University of Mining and Technology | Wang X.,China University of Mining and Technology | Chen W.,China University of Mining and Technology | Li D.,Chongqing Institute of Geology and Mineral Resources | And 8 more authors.
International Journal of Coal Geology | Year: 2010

The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5μg/g), V (121μg/g), Cr (33.6μg/g), Co (27.2μg/g), Ni (83.5μg/g), Cu (48.5μg/g), Ga (17.3μg/g), Y (68.3μg/g), Zr (444μg/g), Nb (23.8μg/g), and REE (392μg/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that enriched trace elements above were largely derived from mafic tuffs, in addition to a minor amount from the Kandian Oldland. © 2010 Elsevier B.V. Source

Dai S.,China University of Mining and Technology | Seredin V.V.,RAS Institute of Geology and Mineralogy | Ward C.R.,University of New South Wales | Jiang J.,198 Coal Geology Exploration Group | And 9 more authors.
International Journal of Coal Geology | Year: 2014

The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04% Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles. © 2013 Elsevier B.V. Source

Dai S.,China University of Mining and Technology | Ren D.,China University of Mining and Technology | Chou C.-L.,Illinois State Geological Survey | Finkelman R.B.,University of Texas at Dallas | And 2 more authors.
International Journal of Coal Geology | Year: 2012

China will continue to be one of the largest coal producers and users in the world. The high volume of coal use in China has focused attention on the amounts of toxic trace elements released from coal combustions and also the valuable trace elements extracted or potentially utilized from coal ash.Compared to world coals, Chinese coals have normal background values for most trace elements, with the exception of higher Li (31.8. μg/g), Zr (89.5. μg/g), Nb (9.44. μg/g), Ta (0.62. μg/g), Hf (3.71. μg/g), Th (5.84. μg/g), and rare earth elements (∑. La-Lu. +. Y, 136. μg/g). This is not only due to the higher ash yields of Chinese coals but also to alkali volcanic ashes found in some southwestern coals. The background values of toxic elements of Hg (0.163. μg/g), As (3.79. μg/g), and F (130. μg/g) in Chinese coals are comparable to coals from most other countries.The genetic types for trace-element enrichment of Chinese coals include source-rock- controlled, marine-environment-controlled, hydrothermal-fluid-controlled (including magmatic-, low-temperature-hydrothermal-fluid-, and submarine-exhalation-controlled subtypes), groundwater-controlled, and volcanic-ash-controlled. The background values of trace elements were dominated by sediment source regions. Low-temperature hydrothermal fluid was one of the major factors for the local enrichment of trace elements in southwestern China.Serious human health problems caused by indoor combustion of coal in China include endemic fluorosis, arsenosis, selenosis, and lung cancer. Endemic fluorosis, mainly occurring in western Guizhou, was mostly attributed to the high fluorine in clay that was used as a briquette binder for fine coals, in addition to a small quantity of fluorine from coal. Fluorine in the coal from endemic-fluorosis areas of western Guizhou is within the usual range found in China and the world. Endemic arsenosis in southwestern Guizhou is attributed to indoor combustion of high-As coal. Endemic selenosis in Enshi of Hubei was due to high Se in carbonaceous siliceous rocks and carbonaceous shales. Fine particles of quartz, released into air during coal combustion, are hypothesized as a possible cause for the lung cancer epidemic in Xuanwei, Yunnan, China.Valuable elements, including Ge, Ga, U, REE (rare earth element), Nb, Zr, and Re are concentrated to levels comparable to conventional economic deposits in several coals or coal-bearing strata in China. The Ge deposits at Lincang, Yunnan province and Wulantuga, Inner Mongolia have been exploited and industrially utilized. The enrichment of Ge in the two deposits was caused by hydrothermal fluids associated with adjacent granitoids. The Ga (Al) ore deposit in the Jungar Coalfield, Inner Mongolia, was derived from the neighboring weathered and oxidized bauxite of the Benxi Formation (Pennsylvanian). The Nb(Ta)-Zr(Hf)-REE-Ga deposits in the Late Permian coal-bearing strata of eastern Yunnan and Chongqing of southwestern China were attributed to ashes of the alkali volcanic eruptions. © 2011 Elsevier B.V. Source

Dai S.,China University of Mining and Technology | Wang X.,China University of Mining and Technology | Zhou Y.,Yunnan Institute of Coal Geology Prospection | Hower J.C.,University of Kentucky | And 4 more authors.
Chemical Geology | Year: 2011

Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO2/Al2O3 values are 0.02-0.08 for alkali, <0.02 for silicic, and >0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt. © 2010 Elsevier B.V. Source

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