Leveraging Extreme Thermoacidophily for Sustainable Purification of Rare Earth Elements

Rare Earth Elements (REEs) are hard to obtain in highly purified forms. They are used in everything from cell phones to cars. REEs can be obtained through conventional mining operations or salvaged from waste streams of various industries. The challenge is to first recover REEs in bulk and then purify specific REEs from resulting mixtures. This is made difficult because of their chemical similarities. Current purification processes present environmental and safety issues. This project will leverage microorganisms that grow in nearly boiling water. They are found in acidic hot springs in Yellowstone National Park and ocean floor thermal vents. The organisms will be used to recover REEs and purify them through novel bioseparation processes that are safe, efficient and environmentally benign. The project will provide local high school students with opportunities to visit NC State University’s biotechnology facilities and undergraduate students with REE case studies relevant to their engineering curriculum. The biological properties of extremely thermoacidophilic microorganisms that naturally inhabit REE-rich geothermal environments will be exploited to develop strategies for sustainable recovery and purification of REEs. Specifically, the organisms will liberate REEs from coal and from by-products of a variety of industries. Furthermore, protein scaffolds and REE-binding proteins derived from these microorganisms will be engineered to develop scalable separation processes to purify REEs. Select extreme thermoacidophiles and metagenomic samples recently obtained from hot springs in Yellowstone National Park will be examined for evidence of REE utilization. If detected, metabolic roles and associated proteins will be determined. Extreme thermoacidophiles that oxidize reduced iron and sulfur compounds as energy sources will be used to liberate REEs from coal and coal fly ash through bioleaching. Subsequently, yeast surface display-based methods will be used to directly evolve and tune thermophilic binding proteins for affinity to specific REEs. These will be deployed in multi-stage, affinity chromatography purification schemes to recover individual REEs. Advanced analytical methods for physical, chemical, and biological characterization will support the work. Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (SEM-EDS) will be used to assay for REEs bound to magnetic nanoparticles. This will serve as a first step in yeast surface display methods for screening proteins to be used for purification of these elements from solutions and from each other. 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.