Doctor of Philosophy (PhD)
Chemistry and Biochemistry
First Committee Member
Second Committee Member
Third Committee Member
Fourth Committee Member
Number of Pages
Lithium and uranium are critical materials in both the energy industry and for national security. Lithium is necessary for the next generation of batteries and 6Li is valuable for the production of tritium necessary for both fusion energy and to maintain our nuclear stockpiles. Uranium is a fuel source or precursor fuel source for commercially operating nuclear fission power. The monitoring of uranium hexafluoride (UF6) enrichment at foreign facilities is important for the monitoring of nuclear safeguards and enforcement of non-proliferation treaties. Recovery methods for lithium at the end of life of batteries are necessary to ensure abundance of the element for commercial use. The ionic liquid (IL), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide ([MPPi][TFSI]) has an electrochemical window which encompasses the very negative (-3.04 V vs SHE) reduction potential of lithium. Pathways for direct and indirect dissolution of Li2CO3 into [MPPi][TFSI] were developed. The dissolved LiTFSI species was evaluated electrochemically. Two methods for recovery were explored. The first method consisted of holding the working electrode at one potential, and the second method pulsed the potential of the working electrode. Deposition was exhibited on both gold and several carbon electrodes. The recovered lithium was characterized using PXRD and SEM imaging. The f-elements also typically have negative reduction potentials that are difficult to achieve in aqueous systems and the metals are often produced in traditional molten salts. ILs have the potential to achieve recovery of f-elements without the need for molten salt systems which require high quantities of thermal energy and are corrosive. The direct dissolution of UF6 into [MPPi][TFSI] was completed. The characterization and stability of the dissolved species was evaluated. The UF6 was found to be stable in inert atmosphere in the [MPPi][TFSI]. Characterization was done using XAFS, UV-Vis, FT-IR, and Raman. Three routes for recovery of the uranium were completed. Two routes of recovery involved the precipitation of air and water stable uranium fluoride compounds. It was shown that uranium oxides could be obtained by heating the precipitates with available oxygen. The third route of recovery was electrochemically driven. This method achieved deposits of lithium hydride but was a low throughput method. Precipitates and deposits were evaluated through TGA, SEM-EDS, PXRD, UV-Vis, FT-IR, and Raman. Ultimately it was shown ILs could be used to stabilize the volatile UF6 for conversion to stable waste forms. It was also shown that UF6 in an IL could be shipped to another facility for recovery of the uranium for isotopic evaluation.
Characterization; Dissolution; Ionic Liquid; Lithium; Recovery; Uranium Hexafluoride
University of Nevada, Las Vegas
Higgins, Cassara, "The Dissolution and Recovery of Critical Materials (Li2CO3 and UF6) from Ionic Liquid" (2022). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4409.
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