TRLFS Studies on the Complexation of Cm(III) and Eu(III) With BTBP Ligands in Organic Solution

Full text of publication follows: Bis-triazinyl-bi-pyridyl (BTBP) ligands are the current reference class of molecules for the separation of An(III) from Ln(III) in a SANEX process. To achieve better understanding of their effectiveness, we perform a comparative TRLFS study on the complexation of Cm(III) and Eu(III) with BTBPs in organic solution. Emission spectra from Cm(III) or Eu(III) complexed with various BTBPs dissolved in 1-octanol are recorded at varied ligand concentrations, varied temperatures, and varied equilibration times. Both the 1:1 complex, [M(III)BTBP]3+ and the 1:2 complex, [M(III)BTBP2]3+ are identified. Thermodynamic and kinetic data for the reaction [M(III)BTBP]3+ + BTBP = [M(III)BTBP2]3+ are derived. The thermodynamic (speciation) study shows a better affinity for Cm(III) than for Eu(III); the Cm(III) 1:2 complex forms at lower [BTBP] than the Eu(III) 1:2 complex. The kinetic study does not reveal a common trend as to whether the complexation is faster with Cm(III) or with Eu(III). However, bulky alkyl moieties slow down kinetics (C2H5 > C5H11 > CyMe4), which is in agreement with experience from liquid-liquid extraction. (authors)