473～673K, 0～3mol/kg范围内几种典型地质流体二元及三元体系水溶液的饱和蒸汽压测定

Aqueous solution is one of the most common types of geological fluids, most of which can be represented by the components H2O, NaCl, KCl, CaCl2, MgCl2, and MgSO4. These fluids have great effects on the transport of material and energy in many geological processes, including magmatic activities, hydrothermal and metamorphic reactions, and formation of minerals, ores, oil, and natural gases. Vapor pressure, one of the most fundamental thermodynamic properties of aqueous solutions, can be used to describe the PVTX (pressure-volume-temperature-composition) behaviors of fluids, establish phase boundaries, and calculate other essential thermodynamic parameters, including osmotic coefficients and activities. However, vapor pressure data of some natural aqueous fluids are either not available, especially for the ternary systems, or have large uncertainties, caused by contaminants produced by reactions between metal pressure vessels and brines. To obtain reliable vapor pressure data of aqueous solutions for geological applications, the frontier technology in experimental geochemistry, an in-situ monitoring system using fused silica capillary - high pressure optical cell, will be applied. The “Hg-sealed” technique will be used to load the sample solution of known composition in the optical cell and then directly measure the vapor pressures of the binary and ternary aqueous solutions containing NaCl, KCl, CaCl2, MgCl2, and MgSO4 salts with concentrations up to 3 mol/kg at temperatures between 473 and 673 K. This study will be able to provide new and essential thermodynamic data for the experimental and numerical simulation studies of geological fluids and related geological processes.

水溶液是地质流体中最常见的类型之一，多数含有H2O、NaCl、KCl、CaCl2、MgCl2和MgSO4组分。这些流体对许多地质过程中的物质和能量的迁移有重大的影响。蒸汽压是地质流体最基本的热力学性质之一，对描述流体的PVTX行为、确定相边界及计算其他热力学参数等方面起着重要作用。然而，一些流体的蒸汽压数据还不够系统，三元体系的蒸汽压数据还很缺乏，且由金属材质的高压容器与咸水反应产生的污染物（如H2等）使实验数据存在较大的不确定性。为获得可靠的流体蒸汽压数据，本项目引入熔融毛细硅管-高压可视反应腔这一先进的实验地球化学手段，通过“汞封”技术制备已知组分的溶液样品，开展H2O、NaCl、KCl、CaCl2、MgCl2和 MgSO4二元及三元体系在473～673 K、0～3 mol/kg温度盐度范围内蒸汽压测量工作。本项目研究将为地质领域的实验及模拟研究提供新的热力学数据，具有重要的科学价值。

蒸气压是地质流体最基本的热力学性质之一，它对描述流体的PVTX（压力-体积-温度-组分）行为、计算热力学函数和推算气-液平衡关系、确定相边界等方面起着重要作用，也是推算诸如溶液的渗透系数、活度系数等热力学性质的必要基础。然而，由于实验技术和方法的限制，高温范围内几种常见地质流体饱和蒸气压数据还存在系统性的缺失，严重制约了相关前沿科学问题的解决。本项目利用熔融毛细硅管-高压可视反应腔（Fused Silica Capillary- High Pressure Optical Cell，FSC-HPOC）装置发展一种新的测量地质流体蒸气压的方法。利用新方法获得了高精度的纯水、NaCl-H2O、KCl-H2O、MgCl2-H2O、CaCl2-H2O、NaCl-KCl-H2O、NaCl-MgCl2-H2O和NaCl-CaCl2-H2O体系在473~693 K下的蒸气压数据。本项目建立的新方法也可应用于多组分复杂地质流体蒸气压的测定，为地质领域的实验及模拟研究提供新的热力学数据。