Yongliang Xiong

Thermodynamic modeling of trivalent Am, Cm and Eu-citrate complexation in concentrated NaClO4 media

Abstract The dissociation constants of citric acid (Cit), and the stability constants of Am3+, Cm3+and Eu3+ with Cit were determined as a function of ionic strength (NaClO4) using potentiometric titration and an extraction technique, respectively. The results have shown the presence of both 1:1 and 1:2 complexes under the experimental conditions. A thermodynamic model was constructed to predict the apparent stability constants at different ionic strengths by applying the Pitzer ionic interaction parameters β(0), β(1), and Cφ which were obtained to fit the experimental data. Thermodynamic stability constants of M(Cit) and M(Cit)23- (where M = Am3+, Cm3+ or Eu3+) were calculated to be log β0101 = 9.91 ± 0.10, log β0102 = 14.47 ± 0.14 for Am3+, log β0101 = 9.53 ± 0.16, log β0102 = 14.46 ± 0.16 for Cm3+ and log β0101 = 9.82 ± 0.14, log β0102 = 13.31 ± 0.12 for Eu3+ as obtained by extrapolation to zero ionic strength.