Bismuth speciation in hydrothermal fluids: an X-ray absorption spectroscopy and solubility study
Date
2013
Authors
Tooth, B.
Etschmann, B.
Pokrovski, G.
Testemale, D.
Hazemann, J.
Grundler, P.
Brugger, J.
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Journal article
Citation
Geochimica et Cosmochimica Acta, 2013; 101:156-172
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Blake Tooth, Barbara Etschmann, Gleb S. Pokrovski, Denis Testemale, Jean-Louis Hazemann, Pascal V. Grundler, Joël Brugger
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Abstract
The solubility of bismuth oxide (α-Bi<inf>2</inf>O<inf>3(s)</inf>; bismite) in near-neutral sodium perchlorate solutions at 65 and 80°C, and pure water from 150 to 600°C, P<inf>Sat</inf> to 800bar was studied using various batch-reactor techniques and in situ XAS spectroscopy. The solubility of Bi<inf>2</inf>O<inf>3(s)</inf> follows a similar trend to Sb<inf>2</inf>O<inf>3(s)</inf> (senarmontite), which has been interpreted in terms of a neutral Sb(OH)<inf>3(aq)</inf> complex. Thus a similar neutral complex, Bi(OH)<inf>3(aq)</inf>, is inferred for Bi. XANES spectroscopy confirms that the Bi(OH)<inf>3(aq)</inf> complex carries a stereochemically active lone electron pair, and EXAFS data suggest that the geometry of the complex changes little over the temperature range 380-610°C at 800bar, with three oxygen neighbors at ∼2.08å. The solubility data obtained in this study are used in conjunction with thermodynamic properties for α-Bi<inf>2</inf>O<inf>3(s)</inf> to obtain thermodynamic parameters for Bi(OH)<inf>3(aq)</inf> within the framework of the revised Helgeson-Kirkham-Flowers (HKF) equation of state. Speciation calculations using these new properties indicate that, similarly to arsenic and antimony, bismuth is transported predominantly as a neutral hydroxide complex in a wide range of temperature, pressure, and fluid compositions. In contrast to arsenic and antimony, bismuth is much less soluble in typical hydrothermal fluids in the form of hydroxide complexes, and high temperatures (≥400°C) are required for significant Bi transport by aqueous fluids. These results are consistent with the common association between Bi mineralization and magmatism. © 2012 Elsevier Ltd.
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Copyright © 2012 Elsevier Ltd. All rights reserved.