Speciation of nickel (II) chloride complexes in hydrothermal fluids: In situ XAS study
Speciation of nickel (II) chloride complexes in hydrothermal fluids: In situ XAS study
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DOI：
10.1016/j.chemgeo.2012.10.010
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发表时间：
2012-12
期刊：
影响因子：
3.9
通讯作者：
Yuan Tian;B. Etschmann;Weihua Liu;S. Borg;Y. Mei;D. Testemale;B. O'Neill;Nick Rae;David M. Sherman;Y. Ngothai;B. Johannessen;Chris Glover;J. Brugger
中科院分区：
文献类型：
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作者：
Yuan Tian;B. Etschmann;Weihua Liu;S. Borg;Y. Mei;D. Testemale;B. O'Neill;Nick Rae;David M. Sherman;Y. Ngothai;B. Johannessen;Chris Glover;J. Brugger
收集了不同盐度（0-7.68m）的氯化镍（II）溶液的原位XAS数据，以研究氯化镍（II）络合物从室温至369°C（400 bar）和至434°C（600 bar）的化学计量和几何构型。增加温度和/或盐度的结果在从八面体（扭曲）四面体的镍（II）氯配合物的配位的变化。在室温和高达~200°C的整个盐度范围内，八面体物种占主导地位，超过该温度，四面体物种变得显著。在369°C和400 bar下，八面体物种与四面体物种保持平衡，第一配位壳层中的氯配体的数量取决于Cl：Ni摩尔比。EXAFS精细化和从头算XANES计算表明，在所研究的压力、温度和组成范围内存在的最高阶氯络合物是扭曲的四面体络合物[NiCl 3（H2O）]−，它在434°C和600 bar的最高Cl浓度（7.68m）溶液中占主导地位。XANES和EXAFS数据的定量热力学分析表明，XAS数据与从最近的UV-Vis分光光度测量（25°C-250°C，100巴; Liu等人，2012 b）以及Lin和Popp（1984）以及Fahlquist和Popp（1989）的高温高压溶解度实验，如果NiCl 2（aq）物质以八面体（[NiCl 2（H2O）4]（aq））和四面体（[NiCl 2（H2O）2]（aq）形式存在，且八面体与四面体的比例在高温（>200°C）下降低。新的XAS数据表明，氯化镍（II）络合物中的八面体到四面体的转变发生在比相应的钴（II）络合物更高的温度和/或盐度下（Liu等人，2011年）。
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).