The lack of a domestic source of rare earth elements (REEs), which have many critical uses in advanced technology components (e.g., electric vehicles, miniaturized magnets), has been identified by the US Department of Energy as a vulnerability to US economic security. Our work focuses on the development of a process to extract REEs from coal fly ash, the waste product left over after coal is burned for electricity generation. We examine the potential to couple hydrothermal leaching of coal fly ash with the engineering of a custom ligand-associated media to provide an organic solvent-free and environmentally friendly method of extracting and recovering REEs. We will first discuss the process of collecting and characterizing fly ash feedstock from coal-fired power plants near Detroit, MI by scanning electron microscopy (SEM), x-ray diffraction (XRD), and x-ray florescence (XRF). Ash samples are then subjected to hydrothermal conditions from 100-350 °C for 1-24 h and leachate concentrations are measured and compared to hydrofluoric acid digestion results. We will then present preliminary results for the selection and attachment of several commercially available and modified ligands to a swellable organically modified silica (SOMS) media to sorb/concentrate the REEs dissolved in the leachate after the hydrothermal extraction process. A 94% extraction efficiency was achieved from a 4 M nitric acid solution with a 1000 ppm uranium solution (analog for REEs) using a tri-butyl phosphate ligand-associated SOMS. The U was stripped, and the sorption process was repeated successfully with a minimal loss of efficiency. Tests with REEs are ongoing and expected to perform similar to uranium results and will be discussed.

Recovering rare earth elements (REEs) from coal fly ash using hydrothermal extraction and ligand-associated media sorption

256th National Meeting (2018)

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