Speciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440 °C and 600 bar: An in-situ XAS study

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dc.contributor.authorLiu, W.
dc.contributor.authorBorg, S.
dc.contributor.authorTestemale, D.
dc.contributor.authorEtschmann, B.
dc.contributor.authorHazemann, J.
dc.contributor.authorBrugger, J.
dc.date.issued2011
dc.description.abstractAqueous Co(II) chloride complexes play a crucial role in cobalt transport and deposition in ore-forming hydrothermal systems, ore processing plants, and in the corrosion of special Co-bearing alloys. Reactive transport modelling of cobalt in hydrothermal fluids relies on the availability of thermodynamic properties for Co complexes over a wide range of temperature, pressure and salinity. Synchrotron X-ray absorption spectroscopy was used to determine the speciation of cobalt(II) in 0-6m chloride solutions at temperatures between 35 and 440°C at a constant pressure of 600bar. Qualitative analysis of XANES spectra shows that octahedral species predominate in solution at 35°C, while tetrahedral species become increasingly important with increasing temperature. Ab initio XANES calculations and EXAFS analyses suggest that in high temperature solutions the main species at high salinity (Cl:Co>>2) is CoCl<inf>4</inf> <sup>2-</sup>, while a lower order tetrahedral complex, most likely CoCl<inf>2</inf>(H<inf>2</inf>O)<inf>2(aq)</inf>, predominates at low salinity (Cl:Co ratios ~2). EXAFS analyses further revealed the bonding distances for the octahedral Co(H<inf>2</inf>O)<inf>6</inf> <sup>2+</sup> (<sup>oct</sup>Co-O=2.075(19)Å), tetrahedral CoCl<inf>4</inf> <sup>2-</sup> (<sup>tet</sup>Co-Cl=2.252(19)Å) and tetrahedral CoCl<inf>2</inf>(H<inf>2</inf>O)<inf>2(aq)</inf> (<sup>tet</sup>Co-O=2.038(54)Å and <sup>tet</sup>Co-Cl=2.210(56)Å). An analysis of the Co(II) speciation in sodium bromide solutions shows a similar trend, with tetrahedral bromide complexes becoming predominant at higher temperature/salinity than in the chloride system. EXAFS analysis confirms that the limiting complex at high bromide concentration at high temperature is CoBr<inf>4</inf> <sup>2-</sup>. Finally, XANES spectra were used to derive the thermodynamic properties for the CoCl<inf>4</inf> <sup>2-</sup> and CoCl<inf>2</inf>(H<inf>2</inf>O)<inf>2(aq)</inf> complexes, enabling thermodynamic modelling of cobalt transport in hydrothermal fluids. Solubility calculations show that tetrahedral CoCl<inf>4</inf> <sup>2-</sup> is responsible for transport of cobalt in hydrothermal solutions with moderate chloride concentration (~2m NaCl) at temperatures of 250°C and higher, and both cooling and dilution processes can cause deposition of cobalt from hydrothermal fluids. © 2010 Elsevier Ltd.
dc.description.statementofresponsibilityWeihua Liu, Stacey J. Borg, Denis Testemale, Barbara Etschmann, Jean-Louis Hazemann, Joël Brugger
dc.identifier.citationGeochimica et Cosmochimica Acta, 2011; 75(5):1227-1248
dc.identifier.doi10.1016/j.gca.2010.12.002
dc.identifier.issn0016-7037
dc.identifier.issn1872-9533
dc.identifier.urihttp://hdl.handle.net/2440/70227
dc.language.isoen
dc.publisherPergamon-Elsevier Science Ltd
dc.rightsCopyright © 2010 Elsevier Ltd. All rights reserved.
dc.source.urihttps://doi.org/10.1016/j.gca.2010.12.002
dc.titleSpeciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440 °C and 600 bar: An in-situ XAS study
dc.title.alternativeSpeciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35-440 degrees C and 600 bar: An in-situ XAS study
dc.typeJournal article
pubs.publication-statusPublished

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