Mikhail Alyapyshev

Pyridinedicarboxylic Acid Diamides as Selective Ligands for Extraction and Separation of Trivalent Lanthanides and Actinides: DFT Study

This article presents a general approach to solving the urgent practical problem of separation of 4f-(lanthanides, Ln3+) and 5f-elements (actinides, An3+) very similar in properties based on the DFT quantum-chemical supercomputer simulation of Ln3+ and An3+ complexes with polydentate nitrogen-containing heterocyclic ligands. The method allows to calculate the geometry parameters of ligands and complexes and the metal to ligand binding energies with accuracy, permitting a direct comparison of calculation results with the experimental data, and estimate selectivity factors for separation of Eu3+/Am3+ model pair cations (SFAm/Eu) in extraction experiments on a semi-quantitative level. The applicability of the method and the approach demonstrated by DFT-modeling (nonempirical PBE functional, extended relativistic full-electron basis set) of a large series of diamides of pyridine-2,6-dicarboxylic (dipicolinic) acid (L) with different substituents at the amide nitrogen atoms and in the pyridine cycle, as well as their complexes [LM]3+, (H2O)nM(NO3)3 (n = 3, 4), and LM(NO3)3 (M = Eu, Am). Based on the theoretical analysis a new model is proposed that describes the mechanism of Ln3+ and An3+ extraction in two-phase system highly acidic water solution-organic solvent, according to which the formation of An3+ and Ln3+ complexes occurs at the water/organic interface as a substitution reaction of hydroxonium ion in a cavity of a protonated ligand for the metal cation. Calculation results confirm the experimentally established higher extraction ability of dipicolinic acid diamides containing one aryl and one alkyl substituent at the amide nitrogen atoms compared to the N,N,N′,N′-tetraalkyl diamides (“effect of anomalous aryl strengthening”). Based on the simulation results the structure of the modified ligand L suggested that it should ensure maximum An3+/Ln3separation selectivity in the series of dipicolinic acid diamides.

Various flowsheets of actinides recovery with diamides of heterocyclic dicarboxylic acids

Solvents on the base of diamides of heterocyclic dicarboxylic acids are promising alternatives for studied Grouped ActiNide EXtraction (GANEX) solvents. Advantage of these ligands is the possibility of simultaneous extraction not only of residual uranium and plutonium, but also minor actinides—neptunium, americium and curium. Two flowsheets on the base of diamides of heterocyclic dicarboxylic acids for separation of actinides form acidic solutions were developed, tested in laboratory scale and compared. Both flowsheets allow separation of more than 99.95% of actinides from raffinates with high content of lanthanides.

New polar fluorinated diluents for diamide extractants

The extraction properties of TODGA solutions in novel polar fluorinated diluents were investigated. The extraction of nitric acid, Am and lanthanides was studied. It was found that aromatic fluorinated diluents provide the highest loading capacity of organic phase comparing with aliphatic diluents. A new solvent on the base of TODGA in meta-nitrobenzotrifluoride is the most promising for technological purposes.