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https://hdl.handle.net/2440/76190
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Type: | Journal article |
Title: | Speciation of nickel (II) chloride complexes in hydrothermal fluids: In situ XAS study |
Author: | Tian, Y. Etschmann, B. Liu, W. Borg, S. Mei, Y. Testemale, D. O'Neill, B. Rae, N. Sherman, D. Ngothai, Y. Johannessen, B. Glover, C. Brugger, J. |
Citation: | Chemical Geology, 2012; 334:345-363 |
Publisher: | Elsevier Science BV |
Issue Date: | 2012 |
ISSN: | 0009-2541 1872-6836 |
Statement of Responsibility: | Yuan Tian, Barbara Etschmann, Weihua Liu, Stacey Borg, Yuan Mei, Denis Testemale, Brian O'Neill, Nick Rae, David M. Sherman, Yung Ngothai, Bernt Johannessen, Chris Glover, Joël Brugger |
Abstract: | In situ XAS data of Ni(II) chloride solutions with various salinities (0-7.68m) were collected to investigate the stoichiometry and geometry of Ni(II) chloride complexes from room temperature up to 369°C at 400bar, and to 434°C at 600bar. Increasing temperature and/or salinity results in a change in the coordination of the Ni(II) chlorocomplexes from octahedral to (distorted) tetrahedral. Octahedral species predominate within the whole salinity range at room temperature and up to ~200°C, and tetrahedral species become significant beyond this temperature. At 369°C and 400bar, octahedral species remain in equilibrium with tetrahedral species, and the number of chloride ligands in the first coordination shell depends on the Cl:Ni molar ratio. EXAFS refinements and ab initio XANES calculations show that the highest order chlorocomplex present over the investigated pressure, temperature and composition ranges is the distorted tetrahedral complex [NiCl3(H2O)]-, which predominates in the highest Cl concentration (7.68m) solution at 434°C and 600bar. A quantitative thermodynamic analysis of the XANES and EXAFS data reveals that the XAS data are consistent with the speciation models derived from recent UV-Vis spectrophotometric measurements (25°C-250°C, 100bar; Liu et al., 2012b) and the high temperature, high pressure solubility experiments of Lin and Popp (1984) and Fahlquist and Popp (1989), if the NiCl2(aq) species exists in both octahedral ([NiCl2(H2O)4](aq)) and tetrahedral ([NiCl2(H2O)2](aq)) forms, with the ratio of octahedral to tetrahedral decreasing at high temperature (>200°C). The new XAS data show that the octahedral to tetrahedral transition in Ni(II) chloride complexes occurs at higher temperature and/or salinity than the corresponding Co(II) complexes (Liu et al., 2011). © 2012 Elsevier B.V. |
Keywords: | X-ray absorption spectroscopy Speciation Ni(II) chloride complexes Coordination change ab initio XANES Hydrothermal fluids |
Rights: | Copyright © 2012 Elsevier B.V. All rights reserved. |
DOI: | 10.1016/j.chemgeo.2012.10.010 |
Published version: | http://dx.doi.org/10.1016/j.chemgeo.2012.10.010 |
Appears in Collections: | Aurora harvest Chemical Engineering publications |
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