Extraction of Np4+ and Pu4+ from nitric acid feeds using three types of tripodal diglycolamide ligands.

• Three tripodal diglycolamide extractants were evaluated for the extraction of Np(IV and Pu(IV). • The tripodal ligand with a benzene center was considered as the most efficient. • Pu(IV) was extracted to a much higher extent than Np(IV) with all the three ligands. • The order of extraction for other metal ions was: Am3+ > UO 2 2+ ~ NpO 2 2+ > Sr2+ > Cs+. Studies on the liquid – liquid extraction of Np4+ and Pu4+ were carried out using three tripodal diglycolamide ligands with different centers viz. a carbon atom (termed as C-pivot tripodal DGA or T-DGA), a nitrogen atom (termed as N-pivot tripodal DGA or TREN-DGA) and a benzene centered tripodal diglycolamide (termed as TAETEB) in an aliphatic diluent mixture of n -dodecane (95%) and isodecanol (5%). The extraction efficiency of the ligands followed the trend: TAETEB > T-DGA > TREN-DGA, while Pu4+ was far more efficiently extracted than Np4+. A solvation type extraction mechanism was proposed based on the extraction profiles obtained as a function of the feed nitric acid concentration where the extracted species was found out to be M(NO 3) 4 · n L (where M = Np or Pu and n was in between 1 and 2). The extraction of other relevant metal ions was also investigated which followed the trend: Am3+ > UO 2 2+ ~ NpO 2 2+ > Sr2+ > Cs+. While Am3+ extraction was lower with TREN-DGA as compared to that of Np4+ and Pu4+, the trend being Am3+ < Np4+ < Pu4+, the relative extraction trend changed with the extractants to Np4+ < Am3+ < Pu4+ for T-DGA and to Np4+ < Pu4+ < Am3+ for TAETEB. The radiolytic stability of the extractants showed contrasting behavior with respect to the metal ion extraction. While the solvent containing 1 × 10−3 M solutions of the ligands showed decreased metal ion extraction for T-DGA and TAETEB when exposed to 200 kGy gamma radiation, an opposite trend was seen for TREN-DGA where the metal ion extraction was found to increase by over 2 times. The metal ions were efficiently stripped using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. Temperature variation studies were carried out to determine the thermodynamic parameters. [ABSTRACT FROM AUTHOR]