In 1995 Zhu and coworkers found that the liquid-liquid extraction from a slightly acidic (pH about 3-4) aqueous solution using purified Cyanex 301 [bis(2,4,4-trimethyl-pentyl)dithiophosphinic acid; HL) in kerosene exhibits a high separation factor of more than 5000 between Am(III) and Eu(III) [1]. The explanations are usually the formation of different extraction complexes for lanthanides(III) and actinides(III) or stronger covalent bonding contributions in the extraction complexes of the actinides(III) compared to the lanthanides(III). Quantum chemical calculations using relativistic f-in-core pseudopotentials and density functional theory however yielded ML3 extraction complexes for both Eu(III) and Am(III), and no evidence for a significantly stronger covalent bonding in the latter [2,3]. It was shown in a comparison of ab initio results using relativistic f-in-core and f-in-valence pseudopotentials that the treatment of the open Eu(III) 4f6 shell within density functional theory tends to lead to a too high f occupancy when Eu(III) is complexed by soft ligands X, e.g., S atoms in Cyanex 301, and as a consequence to too long Eu-X bond distances [4]. The conclusion that Eu(III)-S bonds are significantly less covalent than Am(III)-S bonds (only) drawn from their longer bond lengths obtained in such calculations is thus invalid. The preference of Am(III) over Eu(III) can be rather attributed to the more stable lanthanide(III) hydration complexes [5-8]. The computational model used to explain the preference of Am(III) over Eu(III) by Cyanex 301 was recently shown also to predict correctly the preference of Eu(III) over Am(III) by Cyanex 272 [bis(2,4,4-trimethyl-pentyl)diphosphinic acid [9]. [1] Y. Zhu, C. Song, C., R. Jiao, Global 95 International Conference on Evaluation of Emerging Nuclear Fuel Cycle System, Versailles, France, Sept 11-14, 1995; pp. 571. [2] X. Cao, D. Heidelberg, J. Ciupka, M. Dolg, Inorg. Chem. 49 (2010) 10307. [3] D. Weissmann, doctoral thesis, University of Cologne (2015). [4] M. Dolg, X. Cao, J. Ciupka, J. Electr. Spectr. Rel. Phen. 194 (2014) 8. [5] J. Wiebke, A. Moritz, X. Cao, M. Dolg, Phys. Chem. Chem. Phys. 9 (2007) 459. [6] J. Ciupka, X. Cao-Dolg, J. Wiebke, M. Dolg, Phys. Chem. Chem. Phys. 12 (2010) 13215. [7] J. Zhang, N. Heinz, M. Dolg, Inorg. Chem. 53 (2014) 7700. [8] N. Heinz, J. Zhang, M. Dolg, J. Chem. Theor. Comput. 10 (2014) 5593. [9] X. Cao, J. Zhang, D. Weissmann, M. Dolg, X. Chen, Phys. Chem. Chem. Phys. 17 (2015) 20605.

Quantum chemical modelling of the separation of Am(III) from Eu(III) by liquid-liquid extraction with Cyanex 272 and 301

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.