Complexation of Trivalent Actinide Ions (Am³⁺, Cm³⁺) with Humic Acid: A Comparison of Different Experimental Methods

Abstract

The complexation of trivalent metal ions with humic acid has been studied at pH 4 and 5 in 0.1 Μ NaC10 4 by three different experimental methods, i.e. UV spectroscopy, time resolved laser fluorescence spectroscopy (TRLFS) and ultrafiltration. The direct speciation of the metal ion and its humate complex in the reaction process has been made by UV spectroscopy for Am(III) in the micromolar concentration range and by TRLFS for Cm(III) in the nanomolar concentration range. The ultrafiltration is used with the lowest pore size of filter (ca. 1 nm) to separate the uncomplexed metal ion from its complexed species. The concentrations of both metal ion and humic acid are varied in such a manner that the effective functional groups of the humic acid becomes loaded with metal ions from 1 % to nearly 100%. The loading capacity of the humic acid for the trivalent metal ion, determined separately at each pH, is introduced into the evaluation of complexation constants. The variation of the metal ion concentration from 6 χ 10" 8 mol/1 to 4 χ 10" 5 mol/1 does not show any effect on the complexation reaction. The three different methods give rise to constants being comparable with one another. The average value of the constants thus determined is log β = 6.24 + 0.28 for the trivalent actinide ions.

Complexation of Radionuclides with Humic Substance: The Metal Concentration Effect

“…4). (Note, that the Cm data from [13] were re-evaluated starting with the raw experimental data given in Fig. 3 in [13] and using the same evaluation method as outlined in [11] and used in [14].…”

“…(Note, that the Cm data from [13] were re-evaluated starting with the raw experimental data given in Fig. 3 in [13] and using the same evaluation method as outlined in [11] and used in [14]. The values of [Cm 3+ ] and [CmHA(II)] given in Table 5 of [13], corresponding to [M] and [MHS] in our nomenclature, are the result of fitting the raw data to the humic complexation model of [13].)…”

“…3 in [13] and using the same evaluation method as outlined in [11] and used in [14]. The values of [Cm 3+ ] and [CmHA(II)] given in Table 5 of [13], corresponding to [M] and [MHS] in our nomenclature, are the result of fitting the raw data to the humic complexation model of [13].) The scatter in experimental data from different sources does not exceed one order of magnitude in C K (Fig.…”

Europium-binding abilities of dissolved humic substances isolated from deep groundwater in Horonobe area, Hokkaido, Japan

“…Based on these, the Dlog K values in this study were compared with those given in the literature at the same conditions of pH and C M /C L . For this condition, the data for the binding of Am 3þ to the groundwater HSs in Gorleben, Germany, were only available in the literature [3,35,36]. The Dlog K values for the Horonobe and Gorleben groundwater HSs are summarized in Table 4.…”

Actinides in Solution: Complexation and Kinetics

“…Different modeling approaches have been proposed to calculate the stability constants for metal ions bound by these ligands (Choppin and Labonne-Wall, 1997). Stability constants of certain humic and fulvic acid complexes have been reported for the most common actinides (Choppin and Allard, 1985;Kim and Sekine, 1991;Moulin et al, 1992;Kim et al, 1993;Marquardt and Kim, 1998). In addition to complexation of actinide cations, humic and fulvic acids can also be redox active, reducing the hexavalent NpO 2þ 2 and PuO 2þ 2 (Dahlman et al, 1976;Choppin, 1988;Jainxin et al, 1993;Yaozhong et al, 1993), and pentavalent PuO þ 2 (André and Choppin, 2000) and NpO þ 2 (Marquardt et al, 1996).…”