Model of Earth and Planetary Chemistry: Prediction of Solid/Liquid/Gas Equilibria in Aluminosilicate, Evaporite and Carbonate Systems to High Concentration and Temperature 0- 250C

铝硅酸盐矿物遍布地球表面和地壳，通常在变质岩和火成岩中以长石的形式存在，在风化良好的土壤中以粘土的形式存在，作为蒸发岩的自生成分存在。这项为期一年的研究项目开发了基于水溶液自由能的Pitzer表示的建模技术，以准确预测在高溶液浓度和温度下与铝硅酸盐矿物接触的天然流体的化学行为。该小组开发的Pitzer模型(TEQUIL，getherm.ucsd.edu)可以预测蒸发岩、碳酸盐和硅酸盐体系中低于300℃的地层流体的溶质物种活度、矿物溶解度和溶液上方的蒸汽压等性质，预测精度接近数据。TEQUIL模型包括确定与铝硅酸盐矿物接触的天然流体的饱和状态所需的许多溶液物种，但不包括铝溶液物种。铝的水化学很复杂，而且由于含铝矿物的低溶解度，很难获得准确的数据。在这个项目中，计划利用最近通过溶解度研究和电位滴定(Wesolowski，Palmer，Benezeth，Bourcier，Castet)测定的单核Al形态反应的有效平衡常数，建立一个铝在氯化钠溶液中的水化学模型，温度为~250℃。这个溶液模型将是第一个总结这些数据的高精度状态方程，并为提供高浓度区域的混合性质而量身定做。然后，还计划开始开发铝硅酸盐矿物(包括碱性长石)的热力学数据库，该数据库与所获得的溶液模型一致。这项工作将开发必要的方法，将许多固体包括在这一极其重要的造岩矿物类别中，以高度浓度、依赖温度的模型进行。

Aluminosilicate minerals are found throughout the earth's surface and crust, commonly as feldspars in metamorphic and igneous rock, as clays in well-weathered soils and as authigenic constituents of evaporites. This one year research project develops modeling technology, based on the Pitzer representation of the aqueous solution free energy, to accurately predict the chemical behavior of natural fluids in contact with aluminosilicate minerals to high solution concentration and temperature. The Pitzer models developed by this group (TEQUIL, geotherm.ucsd.edu), can predict properties such as the activity of solute species, the solubility of minerals and the vapor pressure above solutions for formation fluids below 300C in evaporite, carbonate and silica systems with accuracies near that of data. The TEQUIL models include many of the solution species necessary to determine the saturation status of natural fluids in contact with aluminosilicate minerals but do not include Al solution species. The aqueous chemistry of aluminum is complex, and, because of the low solubility of Al containing minerals, precise data are difficult to obtain. In this project it is planned to generate a model of aluminum aqueous chemistry to ~250C in sodium chloride solutions using recently determined effective equilibrium constants for mononuclear Al speciation reactions via solubility studies and potentiometric titrations (Wesolowski, Palmer, Benezeth, Bourcier, Castet). This solution model will be the first high accuracy equation of state that summarizes these data and is tailored to provide mixing properties in the high concentration region. It is also planned to, then, initiate development of a thermodynamic data base for aluminosilicate minerals (including alkali feldspars) that is consistent with the solution models obtained. This work will develop the methods necessary to include many solids in this extremely important class of rock forming minerals in a high concentration, temperature-dependent model.