Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Konstantinos Kavallieratos

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Christopher Dares

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Raphael Raptis

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Joerg Reinhold

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Anthony DeCaprio

Fifth Advisor's Committee Title

Committee Member


Chemistry, Radiochemistry, Actinide, Lanthanides, Mercury, Dipicolinamides, Dithiopicolinamides

Date of Defense



Spent nuclear fuel (SNF) – or used nuclear fuel (UNF) – contains long-lived minor actinides such as 241Am, 245Cm, and 237Np, together with fission products that include lanthanides. Minor actinides are responsible for much of the radiotoxicity and heat generation that limits the capacity of geological repositories. Thus, removing minor actinides from UNF can reduce storage time required for decay to natural levels of activity by several orders of magnitude. Actinide(An)/Lanthanide(Ln) separation processes via solvent extraction by selective complexation with organic or aqueous ligands have to overcome difficulties due to similarities in their ionic radii for the +3 oxidation state. Actinide valence orbitals (5f) allow for a stronger covalent component in metal-ligand interactions with soft-donor ligands, as compared to the 4f orbitals in lanthanides. Therefore, we have synthesized ligands with soft-donor sites that can take advantage of slight differences in hardness between An(III) and Ln(III) for selective An3+ separations.

We have investigated the binding and extraction properties of An and Ln with ligands that contain the C=O vs. the C=S group, specifically dipicolinamides vs. dithiopicolinamides. The S-donor thioamide ligand did not show strong binding towards Ln(III) in the UV-visible and NMR spectra in CH3CN, yet it was shown to extract Am(III) over Ln(III) from highly acidic solutions. Gas-phase studies and theoretical DFT calculations both showed stronger binding of An(III) vs. Ln(III) for the thioamide vs. the amide ligand in agreement with extraction results. Moreover, a dipyridine-dipicolinamide ligand was also used on an aqueous environment as a holdback reagent that keeps Am(III) selectively in the aqueous phase while HDEHP complexes Ln(III) in the organic phase, taking advantage of the difference on hardness between An(III) and Ln(III).

Our dipicolinamide and dithiopicolinamide results open new possibilities for efficient waste transmutation processes and for minor actinide recycling that can increase uranium utilization. Aside from SNF, dithiopicolinamide ligands also showed promise for addressing the presence of mercury in cold war nuclear waste. As Hg is present in the nuclear waste tanks at the Savannah River Site in several forms, including organic Hg, the mercury problem has been of concern.





Rights Statement

Rights Statement

In Copyright. URI:
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).