Continuous flow solvent extraction system for the determination of trace amounts of uranium in nuclear waste reprocessing solutions

Abstract

A system is described for the continuous flow solvent extraction of uranium using isobutyl methyl ketone (IBMK) in the presence of a salting-out solution. This is used as a pre-step to spectrophotometric determination with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP) in methanol. The method utilises an on-line solvent extraction unit, interfaced to a spectrophotometric flow injection analysis (FIA) detection system. The extraction unit can be operated in two ways. In the first, 0.6 ml of a sample was loaded (injected) and then the separated organic phase was mixed directly with the reagent. This permits the handling of 20 samples per hour and a limit of determination of 0.2 p.p.m. of uranium. In the second method, a continuously pumped sample was brought into contact with a fixed volume of the organic phase, which was recirculated in a closed loop. Recirculation results in the extraction of more analyte with the same volume of the organic phase present in the loop. For a sample loading volume of 3 ml, and enrichment factor of 4 was obtained. The determination of uranium at the 50 p.p.b. level can be achieved using this automated liquid-liquid extraction system. Lower concentrations of uranium can also be measured by further increasing the sample volume. This method was tested on a synthetic nuclear waste solution.