X-Ray Spectroscopic Studies of the Structure of Rare Earth Element Aqueous Ion Complexes under Hydrothermal Conditions

稀土元素（REE）离子与地壳流体（H2O，Cl-，F-，OH-等）中常见的配体的相互作用，涵盖了一系列的压力和温度的热液条件的代表，目前缺乏详细的了解。这样的知识是至关重要的充分评估的程度的配体与REE阳离子的缔合和所得到的水溶液离子络合物的稳定性，它发挥了直接的作用，在运输，分馏和矿化的REE矿床的热液成因。我们缺乏对这种地质过程的了解，在很大程度上是由于缺乏足够的实验数据的结构和水热溶液中的稀土配合物的键合性能，涵盖了广泛的温度和压力。本项目采用同步辐射X射线吸收精细结构（XAFS）技术和水热金刚石压砧装置，对水热条件下含稀土水溶液的结构性质进行了实验研究。稀土水离子和氯配合物的结构和相关性质将确定从温度高达500摄氏度和压力高达1 GPa的稀土轴承热液溶液的XAFS光谱的详细分析。均匀的三价电荷，离子半径随着原子序数的增加而减小，以及可能的4f电子壳层填充跨越一系列的显着部分对稀土水和氯配合物的结构的影响的系统研究将被完成。结果将用于测试建立的REE水离子络合物的稳定性的热力学计算，并作为未来的REE在热液中的建模的基础。由于化学性质相似，预计该项目的结果将用于解决放射性废物处置库中锕系元素的归宿和迁移问题。该项目包括在同步加速器设施内对学生进行科学培训。

A detailed understanding of the interaction of rare earth element (REE) ions with ligands common in crustal fluids (H2O, Cl-, F-, OH- and others), covering a range of pressures and temperatures representative of hydrothermal conditions, is presently lacking. Such knowledge is critical for a full assessment of the degree of association of ligands with REE cations and of the stability of the resultant aqueous ion complexes, which play a direct role in the transport, fractionation, and mineralization of REE in deposits of hydrothermal origin. Our lack of understanding of such geologic processes is in large measure due to insufficient experimental data on the structure and bonding properties of aqueous REE complexes in hydrothermal solutions, covering a broad range of temperatures and pressures. This project involves experimental investigations of the structure properties of REE bearing aqueous solutions under hydrothermal conditions using the synchrotron x-ray absorption fine structure (XAFS) technique and the hydrothermal diamond anvil cell. The structure and related properties of REE aquo ion and chloro complexes will be determined from a detailed analysis of the XAFS spectra measured from REE bearing hydrothermal solutions at temperatures up to 500 degrees C and pressures up to 1 GPa. A systematic study of the effects of uniform trivalent charge, decreasing ionic radius with increasing atomic number, and possibly of 4f electron shell filling across a significant portion of the series on the structure of REE aquo and chloro complexes will be accomplished. The results will serve to test established thermodynamic calculations of the stability of REE aqueous ion complexes and as a basis for future modeling of REE in hydrothermal solutions. Because of similar chemistry, it is anticipated that the results from this project will be used to address issues of fate and transport of actinides in radioactive waste repositories. This project includes the scientific training of students within synchrotron facilities.