| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1997: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1996: ¥6,000,000 (Direct Cost: ¥6,000,000)
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| Research Abstract |
Naturally occurring heterogeneous complex-forming materials such as hydrous metal oxides from weathered rocks and organic degradation/condensation products (humic substances) are expected to have a strong influence on the migration behavior of radionuclides in the geosphere. However, the interaction of metal ions with these materials cannot be easily described since (i) the interaction occurs between solution species and functional groups fixed on the solid or polymeric matrices, and (ii) these materials are heterogeneous both in their composition and structure. To estimate the polyelectrolyte effect independently, polyacrylic acid has been selected as a representative of well-defined, homogeneous polymeric weak acid, and its acid dissociation and interaction with Np (V) have been investigated. The result of the acid-base titration indicated that the acid dissociation of the polyacrylic acid decreased with the increase in the degree of ionization, and increased with the increase in ionic strength. Based on this observation, the equation to describe the relationship between the degree of ionization, pH and ionic strength has been derived. The apparent formation constant of Np (V) -polyacrylate complex obtained by the solvent extraction method indicated that the apparent constant increased with the degree of ionization, decreased with ionic strength. These tendencies suggest the multidentate coordination of carboxylate groups to NpO^+ ion and the electrostatic attraction between cations and negatively charged polyacrylate ion.
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