Date of Award
Doctor of Philosophy
George K. Schweitzer
Craig E. Barnes, Michael J. Sepaniak, Charles L. Melcher
The rare earths include elements Sc, Y, and La through Lu are important in many modern technologies. With the exception of Sc and Ce the rare earths are all have similar chemical behaviors with the preferred oxidation state in aqueous solution being +3. Currently, industrial purification of the rare earths is completed by counter current solvent extraction (CCSX). In most CCSX separations, Y extracts with Ho making their separation difficult. However, in a few systems Y exhibits an itinerant behavior. Carboxylic acids of varying sizes and substitutions were investigated in a study of Y itinerant behavior. It was found when carboxylic acids have only one branch that was an alkyl group Y extracted with the early rare earths. As branches are added to the carboxylic acid Y extracted with the heavier rare earths.
This series of studies also investigated the rare earths with mechanochemical reactions. Lutetium oxyorthosilicate (LSO) was synthesized by mechanochemical methods using a planetary ball mill which is usually completed at high temperatures. It may be possible to reduce the rare earths using mechanochemical methods at room temperature with no solvents. Mechanochemistry may offer a new method of synthesizing rare earth compounds.
The final study involved lowering the operational costs of the production of LSO. Iridium is used as the crucible for melting LSO. It is a platinum group metal with a high value. However, during the synthesis of LSO iridium is lost to the insulating material by a vapor deposition process. A method to recover this lost iridium was developed using a gravity concentration method.
Stewart, Jake Anson, "Rare Earth Production and Characterization Studies. " PhD diss., University of Tennessee, 2015.