Closing the nuclear fuel cycle remains a large-scale industrial challenge due to the long-lived radioactivity of the minor actinides found in nuclear waste. Lanthanides (Ln) metal ions are also found in nuclear waste and due to their applicability in medical imaging and the development of advanced luminescent materials, Ln recycling via metal-specific separation is a growing field. Recently, a multi-podal tris (2-aminoethyl) amine [TREN]-capped carbamoylmethylphosphine oxide (CMPO)-based chelator was shown to exhibit extraction affinity for terbium(III) from acidic solution. In order to understand this complexation and extraction selectivity, we report the structural, bonding, energetic, and thermodynamic properties of 7 trivalent lanthanides (Ce3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, and Lu3+) with the tripodal TREN-CMPO-EtO chelator in the gas and solvent phases. Density functional theory was employed with the hybrid PBE0 functional and using the def2-SVP and def2-TZVP basis sets. Each complex geometry, as well as its isolated ligand and Ln ion, was first optimized using the def2-SVP basis set and the Stuttgart RSC 1997 effective core potential. Single point energies were obtained at the triple zeta basis set level, from which the energetic and thermodynamic properties were calculated. Binding energy data shows no preference for terbium (III) metal over the other nearby Ln ions (i.e. Gd3+ and Dy3+). When the free energy of extraction is evaluated, the calculated preferential selectivity trend follows the experimental trend, with only a few exceptions.

Complexation energetics and thermodynamics of a CMPO-based chelator for selective lanthanide extraction from acidic solution

255th National Meeting (2018)

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