The environmental chemistry of actinide elements is of considerable interest since the release of actinides into the environment is considered the primary long-term hazard of nuclear waste disposal in geological repositories. While numerous studies have examined a great variety of organic and inorganic actinide complexes, the possible significance of complexes with orthosilicic acid, found in all natural waters, has been largely ignored. The aqueous complexes formed between trivalent europium or hexavalent uranyl cations and orthosilicic acid were studied in 0.1 M ionic strength solutions to improve the models used to predict actinide migration in the environment. / Ligand competition experiments were employed to measure the stability constants of these f-element-orthosilicate complexes. Europium-orthosilicate complexation was studied by solvent extraction and laser-induced fluorescence spectroscopy. Measurable amounts of the 1:1 complex begin to form at pcH 4 in solutions containing millimolar orthosilicate concentrations. At pcH values greater than 8, europium bisorthosilicate complexes form. The stability constant of the 1:1 uranyl:orthosilicate complex also was measured between pcH 4 and 5 using absorption spectroscopy. / Speciation calculations show that europium orthosilicate complexes are important inorganic species for waters between pcH 6 and 7.5 that are in equilibrium with atmospheric carbon dioxide and contain at least 0.03 mM orthosilicate. Orthosilicate complexes are less important for uranyl cations than for europium cations owing to increased hydrolysis and carbonato complex formation for the former. The presence of 0.1 ppm humic acid completely inhibits formation of aqueous europium and uranyl orthosilicate complexes. / Source: Dissertation Abstracts International, Volume: 55-07, Section: B, page: 2722. / Major Professor: Gregory R. Choppin. / Thesis (Ph.D.)--The Florida State University, 1994.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77198 |
| Contributors | Jensen, Mark P., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 216 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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