Rare Earth Separations: Kinetics and Mechanistic Theories

Pure rare earth materials are critical to many technologies, and efficient industrial-scale solvent extraction processes are important to reducing costs and meeting the demands of this growing and essential industry. Unfortunately, the similar chemical properties of the rare earths make their separation difficult and time consuming. Understanding and optimizing the kinetics of rare earth separations represent an often overlooked approach to increasing the throughput of rare earth separations. However, the kinetics of solvent extraction can be incredibly complex. The presence of two bulk phases, stagnant diffusion layers, the interfacial regions as well as the interface itself, mandates careful experimentation across a wide range of conditions. To stimulate kinetic studies of rare earth separations, we provide an overview of liquid-liquid extraction chemistry relevant to rare earth separations, the equipment and methods for collecting kinetics data, and fundamental kinetic models for dealing with extractions controlled by diffusion or slow chemical reactions. Published kinetic studies available for rare earth extractions using the most viable and industrially applied systems are also reviewed and analyzed.