Highly efficient and selective extraction of Pu(IV) using two alkyl-substituted amides of nitrilo triacetic acid from nitric acid solutions

Abstract

• The extraction of U(VI), Pu(IV) and Am(III) was studied with two tripodal NTA amide ligands. • The extraction trend was Pu(IV) > >U(VI) > Am(III) with both the ligands and HONTA > HDDNTA. • The metal ion extraction was not significantly affected with U loading or absorbed gamma dose. • Stripping was facile and the encouraging reusability data promises for possible application. • Modifier content has a positive impact on water and nitric acid extraction and negative impact on metal ion extraction. Liquid-liquid extraction of the actinide ions UO 2 2+ , Pu 4+ , Am 3+ was carried out from nitric acid feed solutions using two tripodal amide extractants, viz., N,N,N’,N’,N”,N” - hexa - n -octylnitrilotriacetamide (HONTA) and N,N,N’,N’,N”,N” - hexa - n -dodecylnitrilotriacetamide (HDDNTA) in 10% isodecanol + 90% n -dodecane diluent. The metal ion extraction trend was: Pu(IV) ≫ U(VI) > Am(III) at 3 M HNO 3 , HONTA being a superior extractant than HDDNTA. Slope analysis indicated ML 2 type species for both Pu(IV) and Am(III) at 3 M HNO 3 and pH 2.0, respectively, whereas, only in case of HONTA, a ML type species was obtained with U(VI) at 3 M HNO 3 . Back extraction data suggested that a mixture of 0.5 M HNO 3 + 0.5 M oxalic acid was efficient for quantitative stripping (∼90%) of Pu(IV), whereas 1 M Na 2 CO 3 and 1 M α-HIBA gave satisfactory back extraction for U(VI) and Am(III), respectively. The ligand solutions showed reasonably good radiation stability up to an absorbed total gamma ray dose of 274 kGy. Distribution data were also obtained under U(VI) loading conditions for possible nuclear fuel cycle applications.