Thermodynamics of Cm(III) in concentrated salt solutions: Carbonate complexation in NaCl solution at 25 degrees C

The carbonate complexation reactions of Cm(III) were studied by time-resolv ed laser fluorescence spectroscopy in 0-6 m NaCl at 25 degrees C. The ionic strength dependence of the stepwise formation constants for the carbonate complexes Cm(CO3)(n)(3-2n) with n = 1, 2, 3, and 4 is described by modeling the activity coefficients of the Cm(III) species with Fitter's ion-interac tion approach. Based on the present results and literature data for Cm(III) and Am (III), the mean carbonate complexation constants at I = 0 are calcu lated to be: log beta(101)(o) = 8.1 +/- 0.3, log beta(102)(o) = 13.0+/-0.6, log beta(103)(o) = 15.2+/-0.4, and log beta(104)(o) = 13.0+/-0.5. Combinin g these equilibrium constants at infinite dilution and the evaluated set of Pitzer parameters, a model is obtained, that reliably predicts the thermod ynamics of trivalent actinide An(III) carbonate complexation in dilute to c oncentrated NaCl solution.