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Osamu Tochiyama, Hirofumi Yoshino, Takumi Kubota, M. Sato, K. Tanaka, Yuichi Niibori, T. Mitsugashira
Complex formation of Np(V) with humic acid and polyacrylic acid
By using 239Np and/or 237Np, 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 βα=[ML]/([M]CRα), where CR is the total concentration of proton exchanging sites and α is the degree of dissociation, [M] and [ML] respectively denote the concentrations of free and bound NpO2+, log βα have been obtained at pH 6-7 in 0.1 and 1.0 M NaClO4. For both humate and polyacrylate, log βα 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 βα of polyacrylate (ranging from 1.8 to 3.0 depending on pH and ionic strength), log βα 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.
Radiochimica Acta, Oldenbourg Wissenschaftsverlag
Print ISSN: 0033-8230
Volume: 88, 09/2000
Pages: 547