Date of Award

8-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

George K. Schweitzer

Committee Members

Laurence Miller, Clifton Woods

Abstract

This research project focused on the scale-up of an industrial facility for the continuous counter-current solvent extraction (CCCSX) separation of lutetium. CCCSX involves a multistage apparatus for the mixing in each stage of two immiscible liquid phases to transfer an analyte from one phase to the other. The two phases continuously flow in opposite directions in a CCCSX system. In this research, aqueous lutetium solutions, obtained from the acid leaching of lutetium oxyorthosilicate, were mixed with kerosene solutions of phosphorus based metal extractants (e.g. mono-2-ethylhexyl-(2- ethylhexyl) phosphonic acid, MEHEHP). This system extracted the lutetium from the aqueous phase, transferring the lutetium to the organic phase. The lutetium was stripped from the organic phase by mixing this phase with an aqueous solution of highly concentrated acid. The subsequent aqueous lutetium solution was processed to produce lutetium oxide.

Scale-up is a process which begins with bench-scale experiments and proceeds through pilot-scale experiments to the design of an industrial facility. Bench-scale experiments were performed to investigate the extraction characteristics of lutetium in a variety of systems. The information obtained from the bench-scale experiments was utilized in pilot-scale experiments. The pilot plant used for this research consisted of 15 interconnected mixer-settler units. This pilot plant was operated as a CCCSX system. The results of the pilot-scale experiments were used in the design of an industrial CCCSX facility with the capacity to produce 106 kg of 99.999% pure Lu203 from 127 kg of lutetium oxyorthosilicate per day.

Research was also conducted on the industrialization of a technique known as precipitation stripping. Precipitation stripping involves the removal of a metal from a metal-loaded organic phase as a solid metal compound by mixing the organic phase with an aqueous solution of an appropriate precipitating agent. Precipitation stripping was applied to the lutetium CCCSX system to determine the effect of this technique of an industrial facility. It was determined that precipitation stripping can potentially reduce the volume of aqueous effluent generated by an industrial CCCSX facility by a considerable amount.

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