Speaker
Description
The AmSel (Americium Selective) process has been developed for the selective separation of Am(III) from PUREX (Plutonium Uranium Reduction Extraction) raffinate. It is based on the combined use of two ligands: the lipophilic TODGA, which exhibits a slight selectivity towards Cm with respect to Am, and the hydrophilic SO3-Ph-BTBP, which instead shows the inverse selectivity. The two ligands work in a push-pull system, allowing a satisfactory separation of Am(III) from Cm(III) and all the Ln(III). At the conditions of 0.7-0.8 M HNO3, 0.2 M TODGA, and 0.02 M SO3-Ph-BTBP, the SF(Cm/Am) of the system is 2.5. Ethoxyethanol-bis-triazolyl-phenanthroline (EBTzPhen) is investigated as a more sustainable alternative to SO3-Ph-BTBP, since it is only made by C, H, O and N and hence completely incinerable.
The aim of the study is to assess the extraction performance of the EBTzPhen and its selectivity towards Am, in presence of Cm and all the lanthanides. Specifically, batch experiments have been performed by contacting an equal volume of 0.2 M TODGA in 5% v/v octanol/ISANE IP-175 with nitric acid solutions containing the EBTzPhen and all the lanthanides (all but Pm, plus Y, each 10-5 M) and spiked with Eu-152, Am-241, Cm-244. The behaviour of the system has been investigated as a function of different parameters: initial ligand concentration, initial nitric acid concentration, temperature and mixing time. Distribution ratios and separation factors are evaluated for all the ions by gamma and alpha spectrometry and ICP-MS measurements. Additionally, back-extraction tests are performed, to test the stripping capability of the ligand from a loaded organic phase.
In all tests heavy Ln are extracted almost completely into the organic phase, due to their high affinity with TODGA. On the other hand, light Ln tend to remain in the aqueous phase, with La being the most retained: EBTzPhen has to ensure not only a good selectivity towards Am with respect to Cm, but also to La. Experimental points at different HNO3 concentration have shown an important dependency of the distribution ratios on this parameter, more than in TODGA only systems, indicating that nitrate ions also participate in complexes with the hydrophilic ligand. The optimal HNO3 concentration was identified to be 0.3 M at room temperature (22°C): Cm and La are extracted in the organic phase, while Am is retained in the aqueous phase, with a SF(Cm/Am) of 2-2.5 and similar values for the SF(La/Am). Moreover, the variation of ligand concentration highlights a different stoichiometry for lanthanides and actinides complexes. Finally, the distribution ratios decrease more with temperature in the investigated system with respect to a TODGA only system, suggesting that, in addition to TODGA being an exothermic complexant, the EBTzPhen has an endothermic behaviour.
The results of the extraction experiments and complexation studies will be presented and discussed.
This work is funded by the European Union through the EURATOM research and training programme, project TRANSPARANT (Technological Research Action Necessary for Safe PARtitioning and Nuclear Transmutation), Grant Agreement: 101166386.