Collaborative Research: Experimental Determination of REE-Chloride Complex Stability Constants and Monazite Solubilities in Hydrothermal Solutions

稀土元素（REE）在高温水溶液中的行为在以下领域是必需的：1)地质年代学（即岩石定年）；2)稀土矿床地质；3)核废料的修复和安全贮存。不幸的是，缺乏更好地了解稀土元素地球化学所需的相关数据。预计稀土在许多天然溶液中会与氯离子形成溶解配合物，并且已知稀土磷酸盐相（独居石、xenotime、rhabdophane）是常见的稀土矿物。因此，本提案的目标是：1)确定独居石/xenotime在高达350（C)的水热溶液中的溶解度；2)确定高达350(C)的REE氯化物配合物的化学计量学和稳定性；3）将我们的实验数据应用于与水岩相互作用过程中REE迁移率相关的问题。本研究获得的数据将解决文献中存在的理论估计差异，为稀土配合物在高温下的热力学数据提供首批实验推导的数据之一，允许对稀土氯化物配合物在稀土迁移率中的作用进行定量建模，并作为改进其他稀土配合物稳定性常数的理论预测的基础，直到获得更多的实验数据。本项目将对一名研究生和一名本科生进行热液实验技术、一些现代分析方法以及与经济地质学和环境地球化学研究相关的水地球化学各方面的培训。此外，将在蒙大拿理工学院建立一个新的实验地球化学实验室。

9705661 Wood Knowledge of the behavior of the rare earth elements (REE) in high temperature water solutions is required in the following areas: 1) geochronology (i.e., rock dating); 2) REE ore deposit geology; and 3) remediation and safe storage of nuclear waste . Unfortunately, there is a lack of the relevant data required for a better understanding od REE geochemistry. It is expected that the REE will form a dissolved complex with the chloride ion in many natural solutions, and it is known that REE phosphate phases (monazite, xenotime, rhabdophane) are common REE minerals. Thus, the objectives of this proposal are to: 1) determine the solubility of monazite/xenotime in hydrothermal solutions up to 350(C; 2) determine the stoichiometries and stabilities of REE chloride complexes up to 350(C; and 3) apply our experimental data to problems related to the mobility of REE during water-rock interaction. The data obtained in this study will resolve discrepant theoretical estimates in the literature, provide one of the first experimentally derived sets of thermodynamic data for REE complexes at elevated temperatures, permit quantitative modeling of the role of REE chloride complexes in REE mobility, and serve as a basis for improved theoretical predictions of stability constants for other REE complexes for use until additional experimental data become available. During the course of this project, one graduate and one undergraduate student will be trained in hydrothermal experimental techniques, a number of modern analytical methods, and various aspects of aqueous geochemistry relevant to studies in economic geology and environmental geochemistry. In addition, a new experimental geochemistry laboratory will be set up at Montana Tech.