Fluorescence Spectroscopy of U(VI)-Silicates and U(VI)-Contaminated Hanford Sediment
Time-resolved U(VI) laser fluorescence spectra (TRLFS) were recorded for a series of natural uranium-silicate minerals including boltwoodite, uranophane, soddyite, kasolite, sklodowskite, cuprosklodowskite, haiweeite, and weeksite, a synthetic boltwoodite, and four U(VI)-contaminated Hanford vadose zone sediments. Lowering the sample temperature from RT to {approx} 5.5 K significantly enhanced the fluorescence intensity and spectral resolution of both the minerals and sediments, offering improved possibilities for identifying uranyl species in environmental samples. At 5.5 K, all of the uranyl silicates showed unique, well-resolved fluorescence spectra. The symmetric O=U=O stretching frequency, as determined from the peak spacing of the vibronic bands in the emission spectra, were between 705 to 823 cm-1 for the uranyl silicates. These were lower than those reported for uranyl phosphate, carbonate, or oxy-hydroxides. The fluorescence emission spectra of all four sediment samples were similar to each other. Their spectra shifted minimally at different time delays or upon contact with basic Na/Ca-carbonate electrolyte solutions that dissolved up to 60 % of the precipitated U(VI) pool. The well-resolved vibronic peaks in the fluorescence spectra of the sediments indicated that the major fluorescence species was a crystalline uranyl mineral phase, while the peak spacing of the vibronic bands pointed to the likely presence of uranyl silicate. Although, an exact match was not found between the U(VI) fluorescence spectra of the sediments with that of any individual uranyl silicates, the major spectral characteristics indicated that the sediment U(VI) was a uranophane-type solid (uranophane, boltwoodite) or soddyite, as was concluded from microprobe, EXAFS, and solubility analyses.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15016050
- Report Number(s):
- PNNL-SA-42812; GCACAK; 4597; KP1301020; TRN: US0501807
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 69, Issue 6; Other Information: PBD: 24 Mar 2005; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
Similar Records
Cryogenic Laser Induced U(VI) Fluorescence Studies of a U(VI) Substituted Natural Calcite: Implications to U(VI) Speciation in Contaminated Hanford Sediments
RADIATION-INDUCED DECOMPOSITION OF U(VI) ALTERATION PHASES OF UO2
Related Subjects
ELECTROLYTES
EMISSION SPECTRA
FLUORESCENCE
FLUORESCENCE SPECTROSCOPY
LASERS
RESOLUTION
SEDIMENTS
SILICATE MINERALS
SKLODOWSKITE
SODDYITE
SOLUBILITY
SPECTRA
TIME DELAY
URANIUM MINERALS
URANOPHANE
URANYL PHOSPHATES
URANYL SILICATES
ENVIRONMENTAL MOLECULAR SCIENCES LABORATORY