A remarkable enhancement in Am³⁺/Eu³⁺selectivity by an ionic liquid based solvent containing bis-1,2,4-triazinyl pyridine derivatives: DFT validation of experimental results

Abstract

Mutual separation of trivalent actinide (An(3+)) and lanthanide (Ln(3+)) using several soft (N) donor ligands (bis(5,6-dialkyl-1,2,4-triazinyl)pyridine (R-BTP)) is attempted for the first time in room temperature ionic liquid (RTIL) medium. The results indicate a spectacular enhancement in the selectivity as compared to that in molecular diluents with a separation factor (S.F.) of >3000 for Am(3+) over Eu(3+) using the methyl derivative (Me-BTP) in RTIL medium using [C(n)mim]·[NTf2] as the diluents (where n = 2, 3, 4, 6 or 8). Such a high S.F. value has never been reported before with any of the R-BTP derivatives in molecular diluents. An opposite trend in the distribution ratio values of both Am(3+) and Eu(3+) with the increasing size of the alkyl (R) group is observed in RTIL medium when compared with that in molecular diluents. The differences in the extraction behaviour of R-BTPs in RTILs vis-à-vis molecular diluents are explained on the basis of the difference in the nature of complexes extracted in these two distinctly different media as supported by the time resolved fluorescence (TRFS) study. An unusually high extractability and selectivity for Am(3+) over Eu(3+) with Me-BTP was attributed to the formation of a 1 : 4 complex for Am(3+), which was never reported earlier with any of the R-BTP derivatives in molecular diluents. DFT studies indicated higher metal 'd' and 'f' orbital participation (covalence) in the bonding with R-BTP in the case of Am(3+) complexes as compared to that in the case of Eu(3+) complexes, which resulted in the selectivity of these classes of ligands. The observed results may have a great significance in the radioactive waste management involving the partitioning and transmutation strategy.

Selective extraction of trivalent actinides using CyMe4BTPhen in the ionic liquid Aliquat-336 nitrate

“…Such diluent mixtures of 1-octanol/toluene or 1-octanol/hydrogenated tetrapropylene (TPH) were tested by Lewis et al 17 Ionic liquids (ILs) are a relatively new class of compounds that can provide several advantages over molecular diluents in solvent extraction processes at the back-end of the nuclear fuel cycle. [27][28][29][30] ILs can be used as extractants, diluents or both, depending on the chosen conditions and metal ions to be separated. A main reason and driving force to consider ILs instead of classical organic diluents is their radiation stability.…”

Are fancy acidic or neutral ligands really needed for synergism in ionic liquids? A comparative study of lanthanoid extraction in CHCl3 and an ionic liquid

“…Under this frame, modern extraction chemistry focuses on supramolecules and the chemical engineering aspect pertaining to the design and synthesis of new extractants, to be used in molecular solvents. [10][11][12][13][14] Tremendous efforts have been put on improving the capabilities of both the acidic and the neutral components of synergistic systems. For example, trivalent lanthanoid ions are hard acids and therefore interact preferentially with hard bases, typical examples of which are oxygencontaining molecules or anions such as b-diketones.…”

“…24 Last but not least, it is well recognized that ILs offer unique liquid media for liquid/liquid extraction. 14,[25][26][27] Although a wide variety of ionic compounds are liquids at room temperature, those involving 1-alkyl-3-methylimidazolium cations and bis(trifluoromethylsulfonyl)imide anions have been the most investigated. 25,28 ILs based on the (CF 3 SO 2 ) 2 N À anion are non-coordinating, and, in the absence of an extractant, most of the time do not significantly extract metal ions from aqueous phases, although some counter-examples providing huge distribution ratios could be found.…”

Worthy Extraction and Uncommon Selectivity of 4f-Ions in Ionic Liquid Medium: 4-Acylpyrazolones and CMPO

“…In terms of contemporary priorities the extraction systems must be adjusted to accommodate the chemistry of both efficient extraction and selectivity as a target and to minimize the possible contaminants. For the first time, a sensational high separation factor has been announced by Bhattacharyya et al higher than 3 × 10 3 for Am 3+ over Eu 3+ using methyl derivative of N-donor ligand (bis­(5,6-dialkyl-1,2,4-triazinyl)­pyridine) in ionic liquid medium ([C 1 C n im + ]­[Tf 2 N – ], n = 2, 3, 4, 6 or 8). Recently, it has been demonstrated as well that ILs can and should be used in more imaginative ways in order to exhibit their remarkable properties to enable robust nuclear separations that have not been realized previously: D (Ln 3+ )/ D (An 3+ ) > 10 …”