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

Liquid-liquid extraction of the actinide ions UO22+, Pu4+, Am3+ 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 HNO3, HONTA being a superior extractant than HDDNTA. Slope analysis indicated ML2 type species for both Pu(IV) and Am(III) at 3 M HNO3 and pH 2.0, respectively, whereas, only in case of HONTA, a ML type species was obtained with U(VI) at 3 M HNO3. Back extraction data suggested that a mixture of 0.5 M HNO3 + 0.5 M oxalic acid was efficient for quantitative stripping (∼90%) of Pu(IV), whereas 1 M Na2CO3 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.