Study of redox and complexation interactions of neptunium with humic acid and chemical analogs
The redox and complexation interactions of neptunium with humic acid and chemical analogs are studied in this research by solvent extraction and spectrophotometry. In the redox study, dicarboxylic acids and substituted phenolic compounds are selected as models for humic acids. Np(VI) is found to be reduced to Np(V) by both series of compounds, but phenolic compounds reduce Np(VI) more rapidly under the same experimental conditions. Reaction products and various effects on the reaction rate were studied, including the kinetic solvent isotope, salt, photoexcitation, concentration and micelle effects. Results suggest that the reduction of Np(VI) by dicarboxylic acids proceeds via the formation of 1:1 complex (NpO[sub 2]L) while the formation of 1:2 complex (NpO[sub 2]L[sub 2][sup 2[minus]]) inhibits the redox reaction. The magnitude of the rate constants depends on the stability of the 1:1 complex and the presence of a methylene proton in those dicarboxylic acids. Results also suggest that the reduction of Np(VI) by phenolic compounds occurs through the interaction of Np(VI) with the hydroxy group, which results in the formation of phenoxy radicals. The rate constant sequence is explained by the electronic effect of various substitution groups. A correlation between the rate constant and the basicity of the hydroxy group is discussed. Np(VI) is reduced rapidly by humic acid to Np(V), which exists as free Np(V) and Np(V)-humate complex. In the subsequent study of complexation between Np(V) and humic acid, Np(V) is found to form a single type of complex with humic acid in the pH range of 4.5-7.5, which is probably the 1:1 Np(V)-carboxylate species. There is a slight trend that humic acids with lower molecular weights form weaker complexes with Np(V). Different approaches for correction of the apparent binding constants are discussed. The binding strength of Np(V)-humate is compared with those of other metal-humate or Np(V)-dicarboxylate systems.
- Research Organization:
- Florida State Univ., Tallahassee, FL (United States)
- OSTI ID:
- 7101772
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
DICARBOXYLIC ACIDS
REDOX REACTIONS
HUMIC ACIDS
NEPTUNIUM
PHENOLS
CHEMICAL REACTION KINETICS
ENVIRONMENTAL TRANSPORT
ACTINIDES
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
ELEMENTS
HYDROXY COMPOUNDS
KINETICS
MASS TRANSFER
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
REACTION KINETICS
TRANSURANIUM ELEMENTS
400702* - Radiochemistry & Nuclear Chemistry- Properties of Radioactive Materials
540230 - Environment
Terrestrial- Radioactive Materials Monitoring & Transport- (1990-)