THE INFLUENCE OF EXTRACTANT STRUCTURE ON THE SOLVENT-EXTRACTION OF URANIUM(VI) AND THORIUM(IV) FROM NITRATE MEDIA BY DIALKYL SULFOXIDES

The solvent extraction of uranium(VI) and thorium(IV) from sodium nitr ate solutions (0.20-6.00 M) by a series of dialkyl sulphoxides with di fferent structures was studied. For sulphoxides with n-alkyl groups (R 2SO, where R = n-hexyl, n-octyl and n-decyl) using 0.20 M solutions in xylene, the extractions of both uranium and thorium are relatively hi gh, and the values of the separation factor beta(Th)(U) are correspond ingly low (approximate to 20). Replacement of an n-hexyl group by a cy clohexyl group has little effect on metal extraction, whilst the intro duction of a second cyclohexyl group causes a slight decrease in extra ction. Similarly, there is little variation in the extraction of urani um and thorium through the series of asymmetrical compounds RR'SO, whe re R=n-octyl and R'=cyclopentyl, cyclohexyl or cyclooctyl. When two ar omatic (phenyl) rings are introduced into the sulphoxide, however, the extraction of both metals falls to zero. For the series of isomeric c ompounds R2SO with C-8 alkyl groups, the separation factors increase i n the order: R = n-octyl, 2-ethylhexyl, 2-octyl, 3-octyl, which is als o the order of increasing steric bulk of the alkyl group. For these co mpounds, slope analysis studies are consistent with the formulation of the extracted metal complexes as UO2(NO3)(2)(R2SO)(2) and Th(NO3)(4)( R2SO)(3).