Date of Award

May 2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Mark L. Dietz

Committee Members

Joseph H. Aldstadt, Arsenio A. Pacheco, Nicholas R. Silvaggi, Alan W. Schwabacher

Keywords

Alkali, Alkaline Earth, Anion, Crown Ether, Imidazolium, Ionic Liquids

Abstract

As part of a broader program directed at the development of improved approaches to the removal of actinides and heat-producing fission products from spent nuclear fuel, the fundamental aspects of the partitioning of selected metal ions between aqueous solution and various room-temperature ionic liquids (ILs) containing a neutral extractant have been investigated.

Prior work has shown that in contrast to the partitioning of alkaline earth cations into conventional solvents in the presence of a crown ether, which is known to proceed via a single pathway (i.e., neutral complex extraction), their extraction into an IL is often a complex, multi-path process in which the ionic liquid itself plays an active role. Specifically, in addition to the extraction of a neutral complex, ion exchange involving a protonated extractant molecule or the cationic constituent of the ionic liquid can also comprise important modes of ion transfer. In an effort to clarify the factors governing the balance among these various pathways, the influence of the aqueous phase and IL anions has been examined. In addition, the effect of the presence of an extractable anion (here, TcO4-) has been explored. The results indicate that the predominant mode of extraction of an alkaline earth cation by crown ethers is strongly influenced by both the aqueous phase anion (with low hydration energy favoring neutral complex extraction) and the IL anion (with hydrophilic anions also favoring extraction of a neutral species). The nature of the extracted species has also been determined to influence the preferred mode(s) of partitioning. That is, for an extractable anion, additional pathways are observed, with ion exchange involving either a cation-crown ether-nitrato ion-pair or the anionic constituent of the IL representing important routes for extraction.

In related work, the radiolysis of two families of ILs has been examined and the structural features of the IL cation and anion leading to satisfactory radiolytic stability have been identified. Taken together with the extraction studies, these results represent an important step in the development of viable, IL-based separation systems for the removal of fission products from nuclear waste streams and for their analytical-scale separation for subsequent determination.

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