Extraction of U(VI), Th(IV), and REE(III) from nitrate solutions with diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO 3 and NH 4 NO 3 solutions with solutions of diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge was studied. The stoichiometry of the complexes extracted from nitric acid solutions with N,N,N',N '-tetrabutyl-2-(di- p -anisylphosphinyl)butanedioic diamide I was determined. The influence of the extractant structure and aqueous phase composition on the efficiency and selectivity of the extraction of U(VI), Th(IV), and REE(III) into the organic phase was examined. Introduction of the–CH 2 C(O)NAlk 2 fragment into the methylene bridge of the diaryl(dialkylcarbamoylmethyl)phosphine oxide molecule considerably enhances the extraction of REE(III) from neutral nitrate solutions. Such modification of the extractant molecule only slightly influences the extraction of REE(III) from nitric acid solutions, but leads to a considerable increase in the U(VI) extraction and to a decrease in the Th(IV) extraction. The selectivity of the extraction of U(VI) and REE(III) is thus considerably increased.