Thermodynamics and laser luminescence spectroscopy of binary and ternary complexation of Am3+, Cm3+ and Eu3+ with citric acid, and citric acid + EDTA at high ionic strength

he binary complexation of Am3+, Cm3+and Eu3+ with citrate has been studied at I = 6.60 m (NaClO4), pcH 3.60 and in the temperatures range of 0–60 °C employing a solvent extraction technique with di-(2-ethylhexyl)phosphoric acid/heptane. Two complexes, MCit and View the MathML sourceMCit23-, were formed at all temperatures. For the three metal ions, the log β101 was between 5.9 and 6.2 and log β102 between 10.2 and 10.6 at 25 °C. The thermodynamic parameters for the Am–Cit system have been calculated from the temperature dependence of the β101 and β102 values. Positive enthalpy and entropy values for the formation of both complexes are interpreted as due to the contributions from the dehydration of the metal ions exceeding the exothermic cation–anion pairing. The formation of the ternary complex M(EDTA)(Cit)4− (M = Cm and Eu) was measured to have large stability constants (log β111 between 20.9 and 24.4) at 25 and 60 °C. Time resolved laser luminescence spectroscopy and lifetime measurement data validated the nature of the complexes of Eu(III) formed in the presence of Cit and EDTA + Cit in 6.60 m (NaClO4) solution.