Adsorption And Intercalation of Rare Earth Elements In Micas: What Can We Learn About Separation of Rare Earth Elements

Rare earth elements (REEs) are essential to the economic growth and national security of the United States. Increasingly, the supply chain of these critical minerals becomes vulnerable to disruptions. To exploit secondary sources of REEs effectively, there is an urgent need to learn about the localized environment of REEs in these sources, thereby enabling enhanced recovery and separation approaches optimized across a broad variety of REE and sources, with greater efficiency and selectivity. Regolith-hosted ionic-adsorption clay minerals preferentially adsorb heavy REEs (HREEs) released through the weathering and dissolution of granites and igneous rocks by rainwater. This REE-containing water then flows through the clays, resulting in a natural separation process. The most soluble and lightest elements (LREEs) pass through clays, while the least soluble and heaviest remain adsorbed, resulting in the formation of heavy REE-enriched minerals with minable concentrations from 50 to 1500 ppm.<br/><br/>In contrast, in micas, the REE observed retention trend is reversed, with the light REEs adsorbed at larger amounts and intercalating deeper into the mineral structure, compared to HREEs. By determining the speciation, spatio-chemical environment and quantum mechanical interactions and polarity of rare earths in micas, we are working to obtain the information on key issues affecting REE adsorption, including structural, electrostatic and hydration effects, coordination and oxidation state of the RE ions in these natural layered minerals.