Issue 23, 2014

Density functional theory investigations of the trivalent lanthanide and actinide extraction complexes with diglycolamides

Abstract

At present, designing novel ligands for efficient actinide extraction in spent nuclear fuel reprocessing is extremely challenging due to the complicated chemical behaviors of actinides, the similar chemical properties of minor actinides (MA) and lanthanides, and the vulnerability of organic ligands in acidic radioactive solutions. In this work, a quantum chemical study on Am(III), Cm(III) and Eu(III) complexes with N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and N,N′-dimethyl-N,N′-diheptyl-3-oxapentanediamide (DMDHOPDA) has been carried out to explore the extraction behaviors of trivalent actinides (An) and lanthanides (Ln) with diglycolamides from acidic media. It has been found that in the 1 : 1 (ligand : metal) and 2 : 1 stoichiometric complexes, the carbonyl oxygen atoms have stronger coordination ability than the ether oxygen atoms, and the interactions between metal cations and organic ligands are substantially ionic. The neutral ML(NO3)3 (M = Am, Cm, Eu) complexes seem to be the most favorable species in the extraction process, and the predicted relative selectivities are in agreement with experimental results, i.e., the diglycolamide ligands have slightly higher selectivity for Am(III) over Eu(III). Such a thermodynamical priority is probably caused by the higher stabilities of Eu(III) hydration species and Eu(III)–L complexes in aqueous solution compared to their analogues. In addition, our thermodynamic analysis from water to organic medium confirms that DMDHOPDA has higher extraction ability for the trivalent actinides and lanthanides than TODGA, which may be due to the steric hindrance of the bulky alkyl groups of TODGA ligands. This work might provide an insight into understanding the origin of the actinide selectivity and a theoretical basis for designing highly efficient extractants for actinide separation.

Graphical abstract: Density functional theory investigations of the trivalent lanthanide and actinide extraction complexes with diglycolamides

Supplementary files

Article information

Article type
Paper
Submitted
05 Jan 2014
Accepted
09 Apr 2014
First published
09 Apr 2014

Dalton Trans., 2014,43, 8713-8720

Density functional theory investigations of the trivalent lanthanide and actinide extraction complexes with diglycolamides

C. Wang, J. Lan, Q. Wu, Y. Zhao, X. Wang, Z. Chai and W. Shi, Dalton Trans., 2014, 43, 8713 DOI: 10.1039/C4DT00032C

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