Liquid–Liquid Extraction of Actinides from Nitric Acid Feeds Using Two Hexa-n-alkylnitrilotriacetamides

Abstract

Solutions of two nitrilotriacetamide (NTA) ligands, viz., N,N,N',N',N", N"-hexa-n-butylnitrilotriacetamide (HBNTA) and N,N,N',N',N",N"hexa-n-hexylnitrilotriacetamide (HHNTA) in 20% isodecanol-80% n-dodecane were employed for the extraction of U(VI), Np(IV), Pu(IV), and Am(III) from nitric acid feed solutions. Limitations of ligand solubility and third-phase formation when contacted with nitric acid solutions led to the choice of the diluent composition of 20% isodecanol and 80% n-dodecane. The results of the solvent extraction studies indicated poor extraction of the metal ions with HBNTA as compared to that with HHNTA as the extractant and hence, major part of this work involved HHNTA. Slope analysis suggested extraction of 1:1 (ML) species with Np(IV) and Pu(IV) at 3 M HNO 3 and mixed 1:2 (ML 2 ) and 1:3 (ML 3 ) species with U(VI) at pH 2. At 0.5 M HNO 3 , the observed trend for extraction was Pu(IV) > Np(IV) >> Am(III) > U(VI).

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

“…HONTA also showed ML 2 type complex formation with Am(III) in 10% isodecanol + 90% n-dodecane at pH 2, whereas ML type species were observed with HDDNTA under similar conditions. It was reported in another study that U(VI) formed a mixture of ML 2 and ML 3 type complexes with HHNTA in 20% isodecanol + 80% n-dodecane at pH 2 [28]. However, in the present study there was quite a contrasting behavior with ML type complex formation with HONTA in 10% isodecanol + 90% n-dodecane at pH 2.…”

“…In the present investigation, we have carried out a systematic study on the extraction of the relevant actinides Pu(IV), Am(III) and U(VI) using HONTA and HDDNTA as the extractant in a diluent mixture containing isodecanol and n-dodecane. The studies include the effect of isodecanol variation, loading of metal ions, irradiation, etc., on the extractability of Pu(IV), Am(III) and U(VI) and a comparison was made with the results reported with HBNTA [28].…”

“…The extraction kinetics of U(VI), Pu(IV) and Am(III) was studied by contacting the respective aqueous phases (at 3 M HNO 3 ) containing the respective radiotracers ( 233 U, 239 Pu and 241 Am, respectively) with the organic phase containing either 0.08 M HONTA or 0.08 M HDDNTA in 10% isodecanol + 90% n-dodecane. The concentration (0.08 M) used in this study was based on the fact that the same concentration and diluent composition were used in our previous study using HBNTA and HHNTA [28].…”

“…nine times better than HDDNTA, while the extraction of Pu 4+ is nearly comparable. This is attributed to the relatively higher steric crowding of the alkyl chains in HDDNTA visà-vis those in HONTA [28].…”

“…1). We have recently reported the extraction behavior of Pu(IV), U(VI) and Am(III) with a lower homolog of HONTA, i.e., HBNTA with n-butyl substituents, where the solubility was achieved with a diluent mixture containing n-dodecane and isodecanol [28]. Though previous reports used n-dodecane as the diluent, it was thought of interest to use a mixture of n-dodecane + isodecanol for studies involving higher homolog NTAmides viz., HONTA and HDDNTA.…”