ORCID
https://orcid.org/0000-0002-5181-5168
Keywords
Nuclear Waste, Studtite, Uranyl Peroxide, Uranium Dioxide, EDTA
Abstract
The chemically diverse nature of nuclear waste creates a complex system that requires study from multiple fronts to effectively address storage strategies, contamination risks, and remediation efforts. The U.S. has a historical legacy of nuclear waste that necessitates ongoing remediation efforts. Uranium is a primary component of this waste, and its environmental mobility is largely controlled by its chemical speciation and oxidation state. Uranyl peroxides, including studtite (UO2O2·4H2O), are present both at the front-end of the nuclear fuel cycle during uranium purification and at the back-end during waste storage. Uranium dioxide (UO2) is a relatively stable uranium(IV) mineral that can be oxidized into more mobile uranium(VI) species. This work explores multiple pathways relevant to the environmental behavior of uranium, including the ligand assisted dissolution of studtite with EDTA, HEDTA, and NTA; the formation of studtite in the presence of aqueous species and their potential incorporation into studtite; and the oxidative dissolution of uranium dioxide by soluble Mn(III)-citrate and Mn(III)-tartrate. Results demonstrate that organic ligands significantly enhance studtite dissolution at neutral to mildly alkaline pH, increasing the concentration of aqueous uranium. The total aqueous uranium resulting from studtite dissolution is only impacted by select ligands at highly acidic and alkaline conditions despite changes in uranium speciation. During studtite formation, trace elements are incorporated into the solid at low concentrations. Notably, thorium addition appears to induce coprecipitation of an amorphous thorium phase on the studtite surface. Additionally, Mn(III)-citrate and Mn(III)-tartrate show a limited ability to oxidize uranium dioxide microparticles, despite their capacity to oxidize technetium (IV) both in competitive and single component systems. These findings collectively advance the understanding of uranium behavior under conditions relevant to nuclear waste storage and remediation, highlighting key factors influencing its mobility and stability in the environment.
Completion Date
2025
Semester
Fall
Committee Chair
Vasileios Anagnostopoulos
Degree
Doctor of Philosophy (Ph.D.)
College
College of Sciences
Department
Department of Chemistry
Format
Release Date
12-15-2026
Document Type
Dissertation
Campus Location
Orlando (Main) Campus
Subjects
Uranium--Research; Radioactive waste disposal--Research; Uranium compounds--Environmental aspects; Uranium--Environmental aspects; Uranium mines and mining--Waste disposal--Environmental aspects
STARS Citation
Murphy, Zachary J., "Investigating the Dissolution, Redox Chemistry, and Incorporation Capacity of Uranium Dioxide and Uranyl Peroxide in the Context of Nuclear Waste Management" (2025). Graduate Thesis and Dissertation post-2024. 539.
https://stars.library.ucf.edu/etd2024/539
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