Amides as Phase Modifiers for N,N′-Tetraalkylmalonamide Extraction of Actinides and Lanthanides from Nitric Acid Solutions

Abstract

The N,N'-tetraalLylinaloiiaiiiides are a class of compounds under development for transuranic (TRU) separations under high nitric acid conditions. There are several issues that challenge the further development of these ligands. One is the development of improved synthetic procedures that lend themselves to conuiiercial scale-up. Another major issue is the third-phase formation that occurs when the N,N-tetraalLy1malonamides are contacted with medium-to-high nitric acid concentrations in hydrocarbon solvents. To address the synthesis issue we have developed a new synthetic approach for preparing these materials. Third-phase formation can be eliminated by addition of diluent niodifiers such as tributylphosphate (TBP). TBP is inappropriate if a nonpliospliate-coiitainiiig process stream is required. h i d e s have been proposed as alternatives for TBP in a variety of applications because of their ease of synthesis and the variety of substitueiits that can be generated. We have been able to develop an aiiiide phase-modified system that extends the working process range of alLilmalonamides (0.5 M) in dodecane (unbranched hydrocarbon) from 3.5 M to 7.5 M nitric acid and in Isopar H (branched hydrocarbon) from 4.0 M to 10.0 M nitric acid using 1.0 &j di-2-etliylhexylacetamide/0.5 M alL~Imaloiiamide. The Kd values were comparable to extraction with alLylmalonamide in Isopar H or hydrogenated tetrapropylene (TPH) solvents. The overall extraction system was more robust than the phase-unmodified system allowing for greater temperature and acid concentration fluctuations without third-phase formation.

Extraction of UO 2 2 + with N , N -di(2-ethylhexyl)-2,2,3,3,4,4,4-heptafluorobutanamide from Nitric Acid Media

“…Some progresses have been made on amides extractants [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. For example, Siddall carried out investigations on N,N-dialkyl aliphatic amides as an alternative of TBP in the reprocessing of spent nuclear fuel in the early 1960's [3,4].…”