Hidden in plain sight: characterization of untapped U.S. rare earth and critical mineral resources

Rare earth elements (REEs) and other critical minerals (e.g., lithium, cobalt, nickel, manganese) are essential to technologies critical for domestic energy infrastructure and independence, decarbonization efforts, and defense applications. Increasing foreign supply dependency and consolidation of mineral supply and/or production resources since 2010 increases U.S. vulnerability to geopolitical weaponization of supply chains (e.g., trade disputes, resource nationalism) and black swan events (e.g., Covid-19). The purpose of this research was to characterize low-grade domestic source materials to develop a novel, modular biohydrometallurgy process for REE and critical mineral recovery. REE-containing allanite occurrences were discovered in Wyoming’s Laramie Mountains during the 1950s uranium prospecting rush but were never seriously explored. Initial drilling at the Halleck Creek project yielded an exploration target exceeding one-billion tonnes of REE-containing ores. The objective was to pulverize and analytically characterize REE-containing allanite ores from primary deposits in Halleck Creek to define major mineralogical and elemental compositions. Subsurface (132-kg) and near-surface (33-kg) ores were crushed to a top size of 4-mm via laboratory jaw and roll crushers. Mineralogical and total metal analyses were performed for representative samples and particle size-by-size fractions via XRD, XRF, and ICP-OES. Mineral liberation analysis was performed via SEM-EDAX to identify the minerology of REE-containing particles and quantify the extent to which they have been liberated from undesirable minerals. Grindability was investigated via laboratory rod mill to quantify the impact of slurry percentage, time, and critical speed on particle size and elemental distribution. The research identified what and where mineral value is in this untapped domestic reserve. Findings inform development of a REE biomining and purification workflow. Ultimately, this research could enable economical, eco-friendly critical mineral production to lessen U.S. foreign dependence. This research was funded by the Defense Advanced Research Projects Agency (DARPA) project “Synthetic Biology for Biomining of Rare Earth Elements (SynBREE)”