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首页> 外文期刊>Journal of Virological Methods >Yttrium complexation and hydration in chloride-rich hydrothermal fluids: A combined ab initio molecular dynamics and in situ X-ray absorption spectroscopy study
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Yttrium complexation and hydration in chloride-rich hydrothermal fluids: A combined ab initio molecular dynamics and in situ X-ray absorption spectroscopy study

机译：富含氯化物水热流体的钇络合和水合：AB初始分子动力学和原位X射线吸收光谱研究

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Accurate knowledge of rare earth elements (REE) speciation in high pressure - high temperature fluids is required to model REE transport and precipitation in subduction zones and magmatic-hydrothermal environments, and the formation of rare metal deposits. Recent experiments (lanthanum, ytterbium, erbium) have demonstrated that REE chloride complexes are the main REE form in many hydrothermal fluids (Migdisov et al., 2016). However, the speciation of yttrium (Y(III)), a cation with an ionic radius similar to that of Ho(III), remains poorly constrained in chloride-rich hydrothermal solutions. We used ab initio molecular dynamics (MD) simulations to calculate the nature of Y(III)-Cl complexes and the thermodynamic properties of these species at temperatures up to 500 degrees C and pressures of 800 bar and 1000 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results indicate that at temperatures below 200 degrees C, chloro-complexes do not form readily, even in highly concentrated brines. At ambient condition, the Y(III) aqua ion binds to eight water molecules in a square antiprism geometry, which is consistent with previous ab initio studies (Ikeda et al., 2005a). The thermodynamic integration method was employed to calculate the formation constants (logK(Theta)) of Y(III)-Cl- complexes in two simulation boxes containing different Y:Cl ratios; we obtained very consistent results of the standard logK(Theta) of the individual complexes from the two independent calculations, which confirms that the thermodynamic integration method is reliable and not significantly affected by technical limitations in box size, box composition, or simulation time. Based on the derived formation constants, we fit modified Ryzhenko-Bryzgalin (MRB) equation of state parameters, which enable extrapolation of the formation constants at elevated temperature and pressure. The results are consistent with the XAS data, and show that the stability of Y(III)-Cl complexes increases with increasing temperature, Y(III) forming high order Cl- complexes (up to YCl4-) in high salinity solutions at high temperature and pH = 3. We also compare the extrapolated logK(Theta) with the available data for other REE at 150 degrees C, 200 degrees C and 250 degrees C. At 200 degrees C, yttrium behaves more like a heavy REE, but from 200 degrees C to 250 degrees C, the formation constants of Y(III)-Cl complexes increase dramatically and behave more like the light REE. The difference of Cl- dominant species between Ho(III) (HoCl2+) and Y(III) (YCl2+) may account for the formation of anomalous Y/Ho ratios in some hydrothermal environments. (C) 2020 Elsevier Ltd. All rights reserved.
机译：准确了解高压 - 高温流体中的稀土元素（REE）形态，需要在俯冲区和岩浆 - 水热环境中模拟REE运输和沉淀，以及稀有金属沉积物的形成。最近的实验（镧，Ytterbium，erbium）已经证明了Ree氯化物配合物是许多水热流体中的主要REE形式（MIGDISOV等，2016）。然而，钇（Y（III））的形状，具有与HO（III）类似的离子半径的阳离子，富含氯化物的水热溶液仍然受到严重限制。我们使用AB Initio分子动力学（MD）模拟来计算y（iii）-cl复合物的性质和这些物种在高达500℃的温度和800 bar和1000巴的压力下的热力学性质。 MD结果通过原位X射线吸收光谱（XAS）测量互补。我们的结果表明，在低于200℃的温度下，即使在高度浓缩的盐水中，氯复合物也不会容易地形成。在环境条件下，Y（III）AQUA离子在方形抗逆转几何中结合八个水分子，这与先前的AB初始研究一致（Ikeda等，2005a）。采用热力学积分法计算含有不同Y：Cl比的两种模拟盒中Y（III）-Cl-复合物的形成常数（Logk（θ））;我们获得了来自两个独立计算的个体复合物的标准逻辑（Theta）的非常一致的结果，这证实了热力学集成方法可靠，并且不会受到框大小，盒子组成或模拟时间的技术限制的显着影响。基于衍生的形成常数，我们适用于状态参数的改性Ryzhenko-Bryzgalin（MRB）方程，其能够在升高的温度和压力下推断形成常数。结果与XAS数据一致，表明Y（III）-Cl复合物的稳定性随着在高温下的高盐度溶液中形成高阶CL-复合物（最多）的温度，Y（III）的稳定性增加和pH = 3.我们还将外推的伐木（THETA）与其他REE的可用数据进行比较，在150摄氏度，200摄氏度和250摄氏度，钇的行为更像是重型ree，但是从200度C至250℃，Y（III）-CL复合物的形成常数显着增加，更像轻质雷。 HO（III）（HOCL2 +）和Y（III）（III）（YCL2 +）之间的CL-优势物种的差异可以考虑在一些水热环境中形成异常Y / HO比。 （c）2020 elestvier有限公司保留所有权利。

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