Studies on Stability Constants of Europium(III) Carbonate Complexes and Application of SIT and Ion-Pairing Models

Abstract

A synergic solvent extraction method using 1 -nitroso-2-naphthol and trioctylphosphine oxide (TOPO) in chloroform has been applied to study the carbonate complexes of Eu(III). These studies have been performed at 1.0 Μ ionic strength and at varied total carbonate (SC0 2 = 1χ10~3 -0.5M) concentrations and pH (8.0-9.0). The following species have been identified: EuCOa, EU(C0 3 )J, EU(C0 3 )|~ and Eu(C0 3 )4~; and their formation constants (log/?) have been calculated as 5.88 + 0.05, 10.03 + 0.06,12.4 + 0.08 and 14.3+0.1, respectively. The specific ion interaction theory (SIT) and ion-pairing model have been used to extrapolate the stability constants of EuCOj and EU(C0 3 )2 to zero ionic strength. The corresponding log/? 0 values are 8.06 and 12.91 by SIT and 7.91 and 13.07 by the ionpairing model.

Rare earth element partitioning between Fe oxyhydroxide precipitates and aqueous NaCl solutions doped with NaHCO3: Determinations of rare earth element complexation constants with carbonate ions.

“…We compare our REE(III)-carbonate complexation constants with the previously reported data obtained by solvent-extraction methods. We cite Eu(III)-carbonate complexation constant data from Lundqvist (1982), Rao and Chatt (1991), Lee and Byrne (1992) and Liu and Byrne (1998) in Table 3. Our results and the literature values were re-calculated at infinite dilution by using the following equations: log log log log log , Activity coefficients for the literature data obtained by using NaClO 4 solutions were calculated according to Millero (1992).…”

“…Our results and the literature values were re-calculated at infinite dilution by using the following equations: log log log log log , Activity coefficients for the literature data obtained by using NaClO 4 solutions were calculated according to Millero (1992). Rao and Chatt (1991), Lee and Byrne (1992) and Liu and Byrne (1998) reported their REE(III)-carbonate complexation constants by using total CO 3 2-(aq) concentration ([CO 3 2-, aq ] + [NaCO 3 -, aq ]). According to Millero and Schreiber (1982), activity coefficients of total CO 3 2-(aq) are calculated from the following equation;…”

“…where γ T and γ F denote total and free activity co- Rao and Chatt (1991) and 0.457 according to Lee and Byrne (1992). We estimated γ Eu 3+ in our 0.5 M NaCl solution from Pitzer et al (1978) and Millero and Schreiber (1982), and γ CO 3 2− from Millero (1992).…”

Thermodynamics of Cm(III) in Concentrated Electrolyte Solutions. Carbonate Complexation at Constant Ionic Strength (1 m NaCl)

“…Although, to our knowledge, the tetracarbonato complexe has not yet been confirmed for trivalent actinides, its formation is reported for trivalent lanthanides [24][25][26], Phase equilibrium experiments at constant ionic strength in Na 2 C0 3 -NaHC0 3 -NaC10 4 solutions (pH range 8-10), e.g. solubility experiments with Ce(III) [24] and solvent extraction with Eu(III) [25,26], are interpreted assuming the formation of a tetracarbonato complex as the limiting Ln(III) carbonate complex (Ln = lanthanide). Since the experimental data do not depend on pH, but only on the C0 3~ concentration, the formation of mixed hydroxo-carbonato complexes is considered negligible.…”

Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: A capillary electrophoresis‐mass spectrometry study

“…However, the stoichiometry of the aqueous carbonate limiting complex (complex with maximum number of ligands) of lanthanides (Ln) and actinides (An) is still discussed, even after the well-accepted Nuclear Energy Agency review of Am published thermochemical data [1,2]. Indeed, two stoichiometries have been reported for their limiting complexes: MðCO 3 Þ 3À 3 [3][4][5][6][7][8][9] and MðCO 3 Þ 5À 4 [3,[9][10][11][12][13][14][15][16]. The latter stoichiometry has been reported for light lanthanides only, since the lanthanides heavier than Tb had never been evidenced as MðCO 3 Þ 5À 4 complexes.…”