Coupled Hydrothermal Extraction and Ligand-Associated Swellable Glass Media Recovery of Rare Earth Elements from Coal Fly Ash

Technology Partner: Wayne State University (WSU)Award Number: FE0031565

Project Duration: 3/15/2018 – 9/14/2019
Total Project Value: $518,849

Key Technology Area: Separation Technologies

This project will investigate the use of hydrothermal leaching under alkaline conditions to rapidly dissolve rare earth elements (REEs) from coal ash solids to an aqueous solution; transfer REEs from the solution to an Osorb platform (commercially available swellable organically modified silica) functionalized with the appropriate ligand system; and extract the REEs to an acidic aqueous system that will have high concentrations of the targeted REEs (2–10 percent by weight). The project will examine the potential to couple hydrothermal leaching of coal fly ash with a custom-engineered, ligand-associated medium to provide an organic solvent-free method of extracting and recovering REEs. The fly ash feedstock will be collected from Detroit-area coal-fired power plants, characterized for composition, and subjected to a bench-top batch hydrothermal leaching/dissolution process inside custom-built pressure reactors. Ligands

known to be effective in lanthanide/actinide separation will be evaluated based on a series of criteria, such as selectivity and association to Osorb through hydrophobicity. Batch experiments will then be conducted to establish the best conditions (e.g., pH, eluent, etc.) and best ligand systems for effectively extracting REEs from the alkaline feed solution obtained from the hydrothermal leaching process. Once the Osorb-ligand extraction system is optimized for REE concentration, an aqueous solution adjusted to the appropriate pH will be used to back-extract and concentrate the REEs into a heavily REE-laden solution. This project will result in a solvent-free extraction process that is more environmentally benign than many liquid-liquid extractions that typically incorporate organic solvents. The successful completion of this project will allow for easy expansion to the bench scale and future pilot scale.

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