Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

George K. Schweitzer

Committee Members

Zi-Ling (Ben) Xue, Michael J. Sepaniak, Robert M. Counce

Abstract

The rare-earth elements Y and La-Lu share many similar physical and chemical properties. These similarities are reflected by the difficulty in the complete separation of the rare earths, often requiring hundreds to thousands of stages for the production of pure rare earths. Yttrium, traditionally known to be separated with Ho, has also been observed to be separated with other elements within the lanthanide series, and even outside the bounds of the lanthanide series itself. Previous publications by several authors have indicated that steric factors could influence the position of Y in solvent extractions of the rare earths using carboxylic acid extractants, and steric parameters such as Es′ could be used to rationalize the position of Y versus the overall steric bulk of these extractants.

The purpose of this research project was to build upon the primary findings of these previous investigations and to gain further insight into the structural characteristics that influence the position of Y in solvent extraction systems. Solvent extraction experiments were performed on nine-element rare-earth solutions using a total of 29 carboxylic acid extractants. Rare-earth concentrations were determined using inductively-coupled plasma-optical emission spectrometry (ICP-OES). The results of these experiments showed that -Es′ values less than 2 placed Y in the light rare-earth region (La-Eu), while -Es′ values greater than 2 placed Y in the heavy rare-earth region (Gd-Lu). Additionally, substitutions at the α-carbon atom relative to the carboxyl group in these extractants were found to have the greatest influences on the position of Y. It was found that extractants which posessed an α-carbon atom which was not a component of a phenyl or cyclohexyl ring placed Y in three distinct locations—Ce-Pr, Gd-Tb, and Ho-Er, depending on the number of hydrogen atoms located at the α-carbon. Extractants which had an α-carbon atom that was contained within a cyclohexyl or phenyl ring placed Y into two possible regions—Ce-Pr and Gd-Tb.

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