Bismuth speciation in hydrothermal fluids: An X-ray absorption spectroscopy and solubility study

作者：Tooth Blake; Etschmann Barbara; Pokrovski Gleb S; Testemale Denis; Hazemann Jean Louis; Grundler Pascal V; Brugger Joel^*

来源：Geochimica et Cosmochimica Acta, 2013, 101: 156-172.

DOI：10.1016/j.gca.2012.10.020

The solubility of bismuth oxide (alpha-Bi2O3(s); bismite) in near-neutral sodium perchlorate solutions at 65 and 80 degrees C, and pure water from 150 to 600 degrees C, P-Sat to 800 bar was studied using various batch-reactor techniques and in situ XAS spectroscopy. The solubility of Bi2O3(s) follows a similar trend to Sb2O3(s) (senarmontite), which has been interpreted in terms of a neutral Sb(OH)(3(aq)) complex. Thus a similar neutral complex, Bi(OH)(3(aq)), is inferred for Bi. XANES spectroscopy confirms that the Bi(OH)(3(aq)) 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 degrees C at 800 bar, with three oxygen neighbors at similar to 2.08 angstrom. The solubility data obtained in this study are used in conjunction with thermodynamic properties for alpha-Bi2O3(s) to obtain thermodynamic parameters for Bi(OH)(3(aq)) 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 (%26gt;= 400 degrees C) are required for significant Bi transport by aqueous fluids. These results are consistent with the common association between Bi mineralization and magmatism.

• 出版日期2013-1-15