Thermodynamics of Cm(III) in concentrated electrolyte solutions. Fluoride complexation in 0-5 m NaCl at 25 degrees C

The fluoride complexation of Cm(III) is investigated by means of time-resol ved laser fluorescence spectroscopy (TRLFS) at 25 degrees C. In the first s et of experiments, the speciation of Cm(III) is investigated in 1 m NaCl as function of the fluoride concentration (m(F) < 8 . 10(-3) m). The monofluo ride complex CmF2+ is identified and its formation constant is determined t o be log beta(CmF2+) = 2.46 +/- 0.05. At the highest fluoride concentration there is evidence for the formation of a Cm(III) difluoride complex to a s mall extent. However, as the fluoride concentration interval is limited by the precipitation of CmF3(s), the stability constant of CmF2+ can not be qu antified. In the second set of experiments the formation of CmF2+ is studie d in 0-5 m NaCl. The ionic strength dependence of the formation constant is described by modeling the activity coefficients with the ion interaction a pproach (Pitzer equations). The formation constant at I = 0 is calculated t o be log beta degrees(CmF2+) = 3.44 +/- 0.05.