Thermodynamics of Cm(III) in Concentrated Electrolyte Solutions. Fluoride Complexation in 0-5 m NaCl at 25°C

Abstract

Trivalent actinides / Curium / Fluoride complexation / Pitzer model SummaryThe fluoride complexation of Cm(III) is investigated by means of time-resolved laser fluorescence spectroscopy (TRLFS) at 25°C. In the first set of experiments, the speciation of Cm(III) is investigated in 1 m NaCl as function of the fluoride concentration (m F < 8 · 10 1 m). The monofluoride complex CmF 2+ is identified and its formation constant is determined to be log^(CmF 2+ ) = 2.46 ± 0.05. At the highest fluoride concentration there is evidence for the formation of a Cm(III) difluoride complex to a small extent. However, as the fluoride concentration interval is limited by the precipitation of CmF,(s), the stability constant of CmP + can not be quantified. In the second set of experiments the formation of CmF 2+ is studied in 0-5 m NaCl. The ionic strength dependence of the formation constant is described by modeling the activity coefficients with the ion interaction approach (Pitzer equations). The formation constant at / = 0 is calculated to be log^°(CmP + ) = 3.44 ± 0.05.

Structural incorporation of Cm(III) in trioctahedral smectite hectorite: A time-resolved laser fluorescence spectroscopy (TRLFS) study

“…It is well known that Cm(III) forms fluoride complexes, as indicated by a Cm(III) emission peak at 601.3 nm with a lifetime of 65 ls (Aas et al, 1999). The formation of sparingly soluble solid CmF 3 upon addition of LiF can be excluded, since CmF 3 exhibits an emission band at 597.0 nm (Stump et al, 1993).…”

Curium(III) species and the coordination states in concentrated LiCl-aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy

“…Mole fractions of Cm(III) species have been determined from the emission spectrum in various inorganic salt aqueous solution [9][10][11]. The method for determination of the mole fractions of Cm(III) species is based on the fact that the emission peaks of inner-sphere complexes of Cm(III) with inorganic ligands are shifted several nanometers to the red side relative to that of hydrated Cm 3+ ion.…”

“…On the other hand, it is well known that the luminescence properties of Am(III) and Cm(III), as well as several Ln(III), are sensitive to the species and the coordination states of An(III) at the inner-sphere. Therefore, luminescence techniques have become important tools for studying the species and the coordination states of An(III) not only dissolved in an aqueous solution [6][7][8][9][10][11] but also sorbed on such solid-liquid interface as ion exchange resin [12][13][14].…”

Equilibrium constants in aqueous lanthanide and actinide chemistry from time-resolved fluorescence spectroscopy: The role of ground and excited state reactions

“…This facilitates considerably the handling of highly radioactive materials and allows to study speciation under environmental conditions. When applied to radiochemical problems, TRLFS is more or less restricted to solutions of U(VI) [15][16][17][18][19][20][21][22], Cm(III) [23][24][25][26][27][28][29] and various lanthanide(III) elements [30][31][32][33][34][35][36][37][38]. Among these, Eu(III) is the most commonly used one, as it is considered a good homologue of *Author for correspondence (E-mail: isabelle.billard@ires.in2p3.fr).…”