[en] Structural analyses of uranyl complexes with isomers of N,N'-diethyl-N,N'-ditolyl-dipicolinamide were carried out using IR spectroscopy and single crystal x-ray diffraction. From these analyses it was determined that complexation takes place through coordination with the carbonyl and pyridine nitrogen moieties. The uranium-oxygen and uranium-nitrogen bond distances for Et(p)TDPA are U(1)-O(1): 2.394(3), U(1)-O(2): 2.460(3), U(1)-N(1): 2.661(3) and for Et(o)TDPA U(1)-O(1): 2.415(5), U(1)-O(2): 2.432(4), and U(1)-N(1): 2.647(5).

[en] The Universal Extraction (UNEX) process has been developed for simultaneous extraction of cesium, strontium, and actinides from acidic solutions. This process utilizes an extractant consisting of 0.08 M chlorinated cobalt dicarbollide (HCCD), 0.007-0.02 M polyethylene glycol (PEG-400), and 0.02 M diphenyl- N,N-di-n-butyl-carbamoyl-methyl-phosphine oxide (Ph₂CMPO) in the diluent tri-fluoro-methyl-phenyl sulfone (CF₃C₆H₅SO₂, designated FS-13) and provides simultaneous extraction of Cs, Sr, actinides, and lanthanides from HNO₃ solutions. The UNEX process is of limited utility for processing acidic solutions containing large quantities of lanthanides and/or actinides, such as dissolved spent nuclear fuel solutions. These constraints are primarily attributed to the limited concentrations of CMPO (a maximum of ∼ 0.02 M) in the organic phase and limited solubility of the CMPO-metal complexes. As a result, alternative actinide and lanthanide extractants are being investigated for use with HCCD as an improvement for waste processing and for applications where higher concentrations of the metals are present. Our preliminary results indicate that diamide derivatives of di-picolinic acid may function as efficient actinide and lanthanide extractants. The results to be presented indicate that, of the numerous diamides studied to date, the tetra-butyl-diamide of di-picolinic acid, TBDPA, shows the most promise as an alternative actinide/lanthanide extractant in the UNEX process. (authors)

[en] Three structural isomers of diamides of dipicolinic acid (N,N'-diethyl-N,N'-ditolyl-dipicolinamide, EtTDPA) with varying position of the methyl group on the tolyl ring have been synthesized and investigated on extractability toward U(VI). The polar diluent FS-13 was used, and distribution ratios of U(VI) were studied as a function of nitric acid, ligand, and lithium nitrate concentrations. Extractability of uranium was shown to increase with increased concentration of nitrate and ligands. Infrared spectra of organic extraction phases indicate that nitric acid is coextracted as part of the neutral metal-ligand complex with U(VI) and EtTDPA through hydrogen bonding with the carbonyl group in the amide moiety. (orig.)