The Determination of the First Hydrolysis Constant of Eu(lll) and Am(lll)

Abstract

AbstiactThe stability of the initial step of the hydrolysis reaction between Eu(III) and Am (III) and water has been calculated from measurements of the apparent stability constant of the complexes with Oxalate ligand in the pH ränge 6 to 8 by a solvent extraction technique. For the reaction M3+ + H,0 M0H2+ + H+ we obtained p = 7.31 ± 0.20 for Eu(III) and p = 7.54 ± 0.20 for Am (III) in 0.7 M NaCl solutions at 21°C.

Proceedings of the workshop on geochemical modeling

“…EQ3NR calculations of the distribution experiments were done by defining fictitious species to simulate Am(III) in an organic phase and by estimating a logK for these species from the experimental distribution coefficients. Calculations of Am(III) distribution and average ligand number (for the potentiometric titrations) showed good agreement with the data of Lundqvist (1982) and Caceci and Choppin (1983), but underpredicted the average ligand number of Nair et al (1982) over the pH range of 4 to 8.…”

“…The formation constant for AmOH 2+ was taken as the average of values reported by Lundqvist (1982), Caceci and Choppin (1983), Nair et al (1982), and Edelstein et al . (1983), corrected to \x = 0.…”

“…Lundqvist (1982) measured distribution coefficients in a perchlorate medium (p = 1 H) at pH 4 to 9 (p is ionic strength and M is concentration in molar units). Caceci and Choppin (1983) measured distribution coefficients in a chloride medium (p = 0.7 M) at pH 5.9 and 8.1 as a function of oxalate content and determined the first hydrolysis constant from data for oxalate complexes using competing reactions. Another measurement of Am(III) distribution between organic and aqueous phases (Desire et al .…”

Physicochemical study of the hydrolysis of Rare-Earth elements (III) and thorium (IV)

“…In aqueous solutions, the hydrolysis of trivalent lanthanides begins at a pH as low as 6. For example, for europium, log b 10-1 varies between -7.8 at I = 0.1 mol dm -3 and -8.1 at I = 1 mol dm -3 ) [3] . Schwinte et al [4], under identical experimental conditions as in this work, obtained the methanolysis constants of some lanthanide ions.…”

Thermodynamic Properties of Actinide Aqueous Species Relevant to Geochemical Problems

“…For the formation of Am(OH) 2 + , if one takes also in consideration the results in Table 1 suits [10] in 0.1 mol · Γ 1 and 0.6 mol · 1" 1 NaCl, the value of -(7.54 + 0.20) from distribution measurements [13] in 0.7 M NaCl, as well as the analogy with Cm(OH) 2+ , a value of log*ß 1A = -(7.5 ±0.3) can be accepted for μ=0.1 and, at μ = 01οξ*βι Λ = -(7.1 +0.5). It should be noted, however, that these values are not in good agreement with the upper value ^-8.2 given [14] from solubility measurements in 0.0015 mol · Γ 1 CaCl 2 .…”