Postdoctoral Fellowship: EAR-PF: Untapped critical mineral resources and insights from rubidium isotopic variations in lithium-rich brines

Lithium-rich brines are among the world’s most important sources of lithium for rechargeable batteries used in electric vehicles and grid-scale energy storage. These brines also contain elevated concentrations of rubidium, a critical mineral used in fiber optics and advanced electronics, that is currently imported into the United States and remains poorly characterized as a resource. This postdoctoral fellowship will investigate how rubidium co-accumulates in lithium-rich brines across the western United States and the Lithium Triangle of South America. By improving understanding of critical mineral enrichment in saline environments, the project will support the national interest by advancing knowledge relevant to sustainable resource development, mineral exploration, and environmental monitoring. The project will also support geoscience workforce development by supporting undergraduate research training and fostering collaborations between academia and the private sector. This postdoc fellowship project will quantify rubidium (Rb) concentrations, resources, and isotopic variations in closed-basin lithium (Li) brine systems using field sampling, laboratory analyses, and isotope geochemistry. The study will test two primary hypotheses: (1) that Rb behaves conservatively within most Li brines until potassium salts form, allowing Rb resources to be estimated from Li-Rb systematics; and (2) that stable Rb isotope variations (δ87Rb) record low-temperature geochemical processes including adsorption, clay formation, and evaporite mineral precipitation. Results will establish the first quantitative framework for evaluating co-occurring Rb resources in Li brines and will determine whether Rb isotopes can serve as tracers of clay authigenesis, evaporative evolution, and potassium-salt precipitation in hypersaline systems. These outcomes will advance understanding of rubidium cycling in low-temperature environments and contribute to development of sustainable strategies for critical mineral resource characterization and recovery. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.