Sorption coefficients of Am(III) and Cm(III) on kaolinite were determined at pH from 3.5 to 10 and humic acid (HA) concentrations of 0 to 20 ppm at ionic strength of 0.1 M (NaClO 4 ) at 298 K with N 2 bubbling. The sorption ratio of HA on kaolinite was also measured under the same experimental conditions. The sorption coefficients of Am(III) and Cm(III) in the absence of HA increased with pH over the whole pH range. The presence of HA enhanced sorption coefficients at pH values up to around 5, above which the sorption coefficients were lowered by introducing HA. The effects of HA on sorption coefficients were interpreted by the use of a linear additive model, modified for metal-humate complex formation in the aqueous phase. The model was found to be in fairly good agreement with the experimental data.
Np(V) / Complex formation / Humic acids / Polyacrylic acid / Solvent extraction / Metal concentration effectSummary. By using 239 Np and/or 237 Np, the complexation of Np(V) with Aldrich humic acid and polyacrylic acid has been studied at the concentration of Np(V) from ∼ 10 −13 to ∼ 10 −4 M by the solvent extraction method using TTA and 1,10-phenanthroline in isoamyl alcohol. By defining the apparent formation constant as βthe total concentration of proton exchanging sites and α is the degree of dissociation, [M] and [ML] respectively denote the concentrations of free and bound NpO 2 + , log β α have been obtained at pH 6-7 in 0.1 and 1.0 M NaClO 4 . For both humate and polyacrylate, log β α slightly increased with the degree of dissociation, and slightly decreased with ionic strength. While the variation of Np(V) concentration had no appreciable influence on the log β α of polyacrylate (ranging from 1.8 to 3.0 depending on pH and ionic strength), log β α of humate decreased from 4.7-5.3 (depending on pH and ionic strength) at [M] < 10 −9 M to 2.8-3.1 at [M] = 10 −5 M, indicating the coexistence of weak and strong binding sites in the humic acid.
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