Thermodynamics of Rare Earth Minerals

稀土元素对于磁铁、电池和LED照明等技术中使用的材料至关重要。它们被认为是“关键”材料，因为这些技术离不开它们，同时，它们的供应是有限的，并且/或受到地缘政治操纵。和所有元素一样，稀土的来源是地球，人们开采各种各样的岩石来获取这些元素，然后必须对这些元素进行浓缩、分离和纯化。这些岩石（矿石）含有各种各样的宿主矿物，其中通常含有低浓度的稀土，以及其他元素，如铀、钍和铌。虽然这些多组分矿物固溶体的热力学性质决定了它们在地球上的形成和分布，并限制了稀土元素的开采、加工和纯化过程，但目前对这些性质的了解甚少。这个项目需要系统地研究一组合成稀土材料的形成热力学，以了解不同稀土和其他元素以及结构对稳定性的影响。研究结果将为更全面、高效、经济地从矿物资源中提取和分离稀土提供基础数据，从而实现可持续化学、工程和材料（SusChEM）的目标。同时，这些数据将有助于模拟地质环境中稀土的运移、稀土矿床的成因以及在岩石学过程中将稀土作为地球化学指标。高温氧化物熔体溶液量热法是一种专门用于测定难熔氧化物系统生成热的技术，将用于测量选定系统的生成热。在量热法之前，将对样品进行广泛的合成和表征。总体目标是量化矿物中稀土的电荷平衡离子取代的热化学。将研究RE2O3- H2O- CO2- HF体系中的相，包括主要的稀土矿氟碳铈矿。稀土固溶体在钙钛矿和焦绿石体系中的形成焓和混合焓将被表征。

Rare earth elements are critical to materials used in technologies ranging from magnets to batteries to LED lighting. They are considered 'critical' materials in the sense that such technologies cannot work without them and, at the same time, their supply is limited and/or subject to geopolitical manipulation. The source of rare earths, as of all elements, is the Earth, and a variety of rock types are mined for these elements, which must then be concentrated, separated, and purified. These rocks (ores) contain a variety of host minerals, which typically contain rare earths in low concentrations in complex minral structures together with other elements such as uranium, thorium and niobium. Though the thermodynamic properties of these multicomponent mineral solid solutions define their formation and occurrence in the Earth and constrain processes for the mining, processing, and purification of the rare earth elements, these properties are poorly known at present. This project entails a systematic study of the thermodynamics of formation of a selected set of synthetic rare earth materials in order to understand the effects of different rare earths and other elements, as well as of the structures, on stability. The results will provide fundamental data for more complete, efficient, and economical extraction and separation of rare earths from mineral sources, thus fulfilling the Sustainable Chemistry, Engineering, and Materials (SusChEM) objectives. At the same time the data will be useful in modeling the transport of rare earths in the geologic environment, the origin of rare earth deposits, and the use of rare earths as geochemical indicators in petrologic processes. High temperature oxide melt solution calorimetry, a specialized technique tailored to determing heats of formation of refractory oxide systems, will be used to measure heats of formation of selected systems. The samples will be synthesized and characterized extensively prior to calorimetry. The overall goal is to quantify the thermochemistry of charge-balanced ionic substitutions of rare earths in minerals. Phases in the RE2O3- H2O- CO2- HF system, including the major rare earth ore bastnasite, will be studied. The enthalpies of formation and mixing of RE solid solutions in perovskite and pyrochlore systems will be characterized.