SOLVENT-EXTRACTION OF URANIUM(VI) AND THORIUM(IV) FROM NITRATE MEDIA BY CARBOXYLIC-ACID AMIDES

A series of nineteen N-alkyl carboxylic acid amides (R.CO.NHR') has be en prepared, in which the alkyl groups R and R' have been varied in or der to introduce different degrees of steric complexity into the compo unds. A smaller number of N,N-dialkyl amides (R.CO.NR(2)') and non-sub stituted amides (R.CO.NH2) has also been prepared for comparison purpo ses. These amides were characterized by measurement of their boiling p oints, melting points, refractive indices and densities. The solvent e xtraction of uranium(VI) and thorium(IV) from sodium nitrate media by solutions of the amides in toluene was studied. Increasing steric bulk of the alkyl groups R and R' was found to cause a marked decrease in the extraction of thorium, with a much smaller effect on the extractio n of uranium, thus considerably enhancing the separation between these metals. Vapour pressure osmometry studies indicate that the N-alkyl a mides are self-associated in toluene solution, with aggregation number s up to about 2.5 for 0.6 M solutions at 35 degrees C. In contrast, th e N,N-dialkyl amides behave as monomers under these conditions. The di stribution ratios for the extraction of uranium and thorium show secon d- and third-order dependences, respectively, on the extractant concen tration for both the N-alkyl and N,N-dialkyl amides.