Studies on the Electron Transfer Behavior of f-elements: Applications to Actinide Oxidation State Control

Authors

Xiangyang Hou, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Christopher J. Dares

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Prem Chapagain

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Watson J. Lees

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Stanislaw Wnuk

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Konstantinos Kavallieratos

Fifth Advisor's Committee Title

Committee member

Keywords

f-elements, electrochemistry, high valent, separation, nuclear waste, actinides, americium, uranium

Date of Defense

6-19-2023

Abstract

Nuclear reactors for energy production generate radioactive elements including fission products and neutron capture products. These neutron capture products include the minor actinides neptunium, americium, and curium. Reprocessing these radiotoxic elements is important to improve the long-term safety of nuclear energy. Partitioning and transmutation are used to manage these minor actinides, which need to be separated from fission products, including lanthanides whose species are usually in the trivalent oxidation state and have similar chemical characteristics to the actinides. These similarities result in challenges in selectively separating the minor actinides from the lanthanide fission products. One approach is to utilize the high valent actinides (hexavalent) that show distinct coordination properties and ligand selectivity compared to trivalent cations. Electrochemical access to high valent actinides is a viable option to adjust actinide oxidation states and can bring a profound impact on reprocessing of spent nuclear fuel. We have investigated the electrochemical redox behaviors of cerium, europium, uranium at our vii tripolyphosphate modified ITO electrode and have calculated their electron transfer kinetic parameters, which provide the basis for what is expected for trivalent americium electron transfer properties. UO22+ reduction mechanisms in 0.1 M HClO4 at the prepared electrode were revealed by using Foot of The Wave (FOTW) analysis and Kinetic Isotope Effects (KIE). The influence of presented lanthanide and temperature on the uranium reactions were elucidated and highlighted the stabilizing effect that lanthanides have on pentavalent uranium. Uranium redox behaviors in carbonate solution were conducted to study their migration characters in the environment. The key role that phosphate ligands play in the redox of uranium, including the stabilization of high valent f-elements and catalyzing their oxidation state transformations was carried out using a variety of electrochemical techniques and titration experiments with both electrochemical and spectroscopic monitoring. Cerium(III) oxidation in concentrated carbonate solutions were studied, with results suggesting promising implications for the analogous electrochemical generation of Am(IV) from Am(III). I hope these results inspire others to continue to work to develop systems to prepare a variety of transuranic elements in unusual oxidation states to further our understanding of these heavy elements.

Identifier

FIDC011123

Previously Published In

Hou, X.; McLachlan, J. R.; Dares, C. J. "Electrochemical Behaviour of Uranium at a Tripolyphosphate Modified ITO Electrode" Chem. Comm., 2021, 57, 10891-10894.

Recommended Citation

Hou, Xiangyang, "Studies on the Electron Transfer Behavior of f-elements: Applications to Actinide Oxidation State Control" (2023). FIU Electronic Theses and Dissertations. 5452.
https://digitalcommons.fiu.edu/etd/5452