The partitioning of minor trivalent actinides (An) from lanthanides (Ln) is one of the challenges in the chemical treatment of nuclear waste. The optimal ligand to carry out the separation of An(III) and Ln(III) using solvent extraction has to meet several important criteria: high selectivity towards the solute, chemical and radiolytic stability, stripping possibilities and recycling of the organic phase, high separation factors and good distribution ratio, to name just a few of them. A chronological line can be drawn along the development of each extraction ligand family and some milestones are emphasized in this overview.Further developments in organic synthesis of extracting ligands are expected.
Solvents intended for the separation of trivalent actinides from trivalent lanthanides in spent nuclear fuel have been irradiated with gamma-radiation. The solvents initially contained 0.005 M C5-BTBP dissolved in either hexanol or cyclohexanone and they were exposed to doses up to 20 kGy. Identification of degradation products was done using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). Structures were suggested for a number of degradation products and the relative intensity of the peaks in the MS spectra was estimated. It was clear that the content of the original molecule, C5-BTBP, decreased with dose, while the content of the various degradation products increased. It was also shown that both the choice of diluent and the dose rate (Gy/h) affect the amount of degradation products formed. A degradation scheme was proposed for the radiolytic degradation of C5-BTBP.
The extraction of Am(III), Th(IV), Np(V), and U(VI) from nitric acid by 6,6 0 -bis(5,6-dialkyl-[1,2,4]-triazin-3-yl)-[2,2 0 ]-bipyridines (C2-, C4-, C5-, and CyMe 4 -BTBP) was studied. Since only americium and neptunium extraction was dependent on the BTBP concentration, computational chemistry was used to explain this behavior. It has been shown that the coordination of the metal played an important role in forming an extractable complex into the organic phase, thus making it possible to extract pentavalent and trivalent elements from tetravalent and hexavalent elements. This is very important, especially because it shows other possible utilizations of a group of molecules meant
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