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Etschmann, B.; Liu, W.; Li, K.; Dai, S.; Reith, F.; Falconer, D.; Kerr, G.; Paterson, D.; Howard, D.; Kappen, P.; Wykes, J.; Brugger, J. |
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Title |
Enrichment of germanium and associated arsenic and tungsten in coal and roll-front uranium deposits |
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2017 |
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Chemical Geology |
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463 |
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29-49 |
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Arsenic, Coal, EXAFS and XANES, germanium, Hydrothermal fluids, Metallogenesis, Speciation, Tungsten |
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Most of the World’s germanium (Ge) is mined from Ge-rich lignite, where it is commonly associated with elevated arsenic (As), tungsten (W) and beryllium (Be) contents. Over the past decade, new evidence showing that World-class Ge deposits result from the interaction of hydrothermal fluids with organic matter in coal seams has emerged. Yet, the chemical state of Ge and associated metals in lignite remains poorly understood. We used Mega-pixel Synchrotron X-ray Fluorescence (MSXRF), X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) to characterize the oxidation states and chemical bonding environment of Ge, As, and W in two world-class Mesozoic Ge-in-lignite deposits (Lincang, Yunnan, southwestern China; Wulantuga, Inner Mongolia, northeastern China); in lignite-bearing uranium (U) ores from the Beverley deposit (South Australia) hosted in Eocene sandstones; and in lignite and preserved wood in late Oligocene-Miocene fluviatile sediments (Gore, Southland, New Zealand). The aim was to improve our understanding of the enrichment mechanism of Ge in lignite and better evaluate the environmental mobility of Ge and some of the associated metals (specifically As and W) in lignite ores. In all samples, chemical maps show that Ge is distributed homogeneously (down to 2μm) within the organic matter. XANES and EXAFS data show that Ge exists in the tetravalent oxidation state and in a distorted octahedral coordination with O, consistent with complexing of Ge by organic ligands. In some pyrite-bearing samples, a minor fraction of Ge is also present as Ge(IV) in association with pyrite. In contrast, As displays a more complex speciation pattern, sometimes even in a single sample, including As(III), As(V), and As(−I/+II) in solid solution in sulfides. Arsenic in sulfides occurs in anionic and cationic forms, i.e., it shows both the common substitution for S22− and the substitution for Fe recently discovered in some hydrothermal pyrites. Tungsten was present as W(VI) in distorted octahedral (3+3) coordination. The EXAFS data confirm the absence or minor contribution of individual W-rich minerals such as scheelite or ferberite to W mass balance in the studied samples. These data show that Ge, W, and probably some As are scavenged via formation of insoluble, oxygen-bridged metal organic complexes in lignite. Destruction of the organic ligands responsible for fixing Ge and W (As) in these lignites is required for liberating the metals, e.g. from waste materials. Geochemical modelling suggests that Ge, W, Be and As all can be extracted from granitic rocks by dilute, low temperature hydrothermal fluids. Germanium is transported mainly as the tetrahedral Ge(OH)4(aq) complex, but fixed as an octahedral oxy-bridged organic complex. The same situation is valid for W, which is transported at the tetrahedral tungstate ion, but most likely scavenged via formation of a 6-coordinated metal-organic species. The Ge-Be-W±As association in Ge-rich coals reflects the source of the metals as well as related scavenging mechanisms. |
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0009-2541 |
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THL @ christoph.kuells @ etschmann_enrichment_2017 |
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183 |
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Bullock, L.A.; Parnell, J. |
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Title |
Selenium and molybdenum enrichment in uranium roll-front deposits of Wyoming and Colorado, USA |
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Journal Article |
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Year |
2017 |
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Journal of Geochemical Exploration |
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180 |
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101-112 |
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Molybdenum, Roll-fronts, Selenium, Tellurium, Uranium, Wyoming |
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Sandstone uranium (U) roll-front deposits of Wyoming and Colorado (USA) are important U resources, and may provide a terrestrial source for critical accessory elements, such as selenium (Se), molybdenum (Mo), and tellurium (Te). Due to their associated toxicity, MoSeTe occurrences in roll-fronts should also be carefully monitored during U leaching and ore processing. While elevated MoSe concentrations in roll-fronts are well established, very little is known about Te occurrence in such deposits. This study aims to establish MoSeTe concentrations in Wyoming and Colorado roll-fronts, and assess the significance of these deposits in an environmental and mineral exploration context. Sampled roll-front deposits, produced by oxidized groundwater transportation through a sandstone, show high MoSe content in specific redox zones, and low Te, relative to crustal means. High Se concentrations (up to 168ppm) are restricted to a narrow band of alteration at the redox front. High Mo content (up to 115ppm) is typically associated with the reduced mineralized nose and seepage zones of the roll-front, ahead of the U orebody. Elevated trace element concentrations are likely sourced from proximal granitic intrusions, tuffaceous deposits, and local pyritic mudstones. Elevated MoSe content in the sampled roll fronts may be regarded as a contaminant in U in-situ recovery and leaching processing, and may pose an environmental threat in groundwaters and soils, so extraction should be carefully monitored. The identification of peak concentrations of MoSe can also act as a pathfinder for the redox front of a roll-front, and help to isolate the U orebody, particularly in the absence of gamma signatures. |
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0375-6742 |
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THL @ christoph.kuells @ bullock_selenium_2017 |
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189 |
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Androvitsanea, A.; Fawzy, M.; Fuchs, J.; Külls, C.; Fahlbusch, H.; Heiden, J. |
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Hydrologische Bedingungen im Heraion von Samos vom 12. bis 8. Jh. v. Chr. und ihre Bedeutung für die wasserbauliche Infrastruktur |
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2018 |
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Environmental Water Engineering |
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1 |
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1 |
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1-21 |
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THL @ christoph.kuells @ Androvitsanea2018hydrologische |
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17 |
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Ardelt, G.; Külls, C.; Hellbrück, H. |
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Towards intrinsic molecular communication using isotopic isomerism |
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2018 |
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Open Journal of Internet Of Things (OJIOT) |
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4 |
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1 |
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135-143 |
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RonPub |
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THL @ christoph.kuells @ Ardelt2018towards |
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18 |
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Röttcher, K. |
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Book Chapter |
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2018 |
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Risikomanagement und Nachhaltigkeit in der Wasserwirtschaft: Erfolgreiche Navigation durch die Komplexität und Dynamik des Risikos |
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165-174 |
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Im vorliegenden Beitrag werden beispielhaft unterschiedliche Ansätze des Risikomanagements und das Verständnis von Nachhaltigkeit in der Wasserwirtschaft dargelegt. Die Darstellung richtet sich insbesondere an Leser aus anderen Fachdisziplinen, wie das Rechts- und Finanzwesen, den Fahrzeug- und Maschinenbau oder auch die sozialen Berufe. Die Zusammenhänge werden überblicksartig mit einzelnen konkreten Beispielen dargestellt mit dem Fokus auf die grundsätzlichen Denk- und Vorgehensweisen. |
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Springer Fachmedien Wiesbaden |
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Wiesbaden |
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Michalke, A.; Rambke, M.; Zeranski, S. |
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978-3-658-19684-4 |
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THL @ christoph.kuells @ Röttcher2018 |
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90 |
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