For safe disposal of nuclear wastes, it is necessary to improve our understanding on the long-term behavior of long-lived actinides in the environment. With respect to the problems of potential migration of radionuclides from a nuclear waste repository, the oxidation state of the actinide can make a difference of a factor of as much as 250 in the rate of migration of the species through the geologic media. The organic (humic) compounds via the phenolic hydroxyl and the carbonyl groups can be of potential importance in the reduction reactions. To study such behavior, the Np(VI) reduction reactions with kojic acid and with tropolone were investigated at tracer level concentration of Np(VI). / From results on the kinetic studies of these reactions, the NpO(,2)('++) is reduced to the NpO(,2)('+) in a one-electron transfer process with no structural change of the dioxo neptunium species. The rates for both reactions are directly proportional to the total concentrations of Np(VI) ion and of oxidizing organic compounds : i.e., kojic acid or tropolone. However, the hydrogen ion dependence on the rate is inverse first-order for kojic acid and inverse second-order for tropolone. The Np(VI) reduction proceeds from the precursor complex via an activated complex and results in oxidation products from radicals formed in the rate-limiting step. The rate for the formation of Np(V) by kojic acid ( k(,1) = 6.06 (+OR-) 0.30 sec('-1)) is faster than by tropolone ( k(,1) = 2.49 (+OR-) 0.10 sec('-1)). The rate of reduction increases with the pK(,a) values (basicity) of the hydroxyl group in oxidizing organic compounds. / The activation parameters for the Np(VI) reduction with kojic acid and tropolone have the same values within the uncertainties: i.e., (DELTA)H('(NOT=)) = 82.7 (+OR-) 3.4 KJ/mol, (DELTA)S('(NOT=)) = 34 (+OR-) 12 J/mol/deg for kojic acid and (DELTA)H('(NOT=)) = 67.2 (+OR-) 3.4 KJ/mol, (DELTA)S('(NOT=)) = 15 (+OR-) 12 J/mol/deg for tropolone. Therefore, the Np(VI) reduction reaction occurs through the same mechanism in both reactions. / Source: Dissertation Abstracts International, Volume: 48-03, Section: B, page: 0753. / Thesis (Ph.D.)--The Florida State University, 1987.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76091 |
| Contributors | KIM, WON-HO., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 121 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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