Residual Waste from Hanford Tanks 241-C-203 and 241-C-204. I. Solids Characterization
Bulk X-ray diffraction (XRD), synchrotron X-ray microdiffraction (microXRD), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) were used to identify the individual phases, phase associations, morphologies, particle sizes, and compositions of solids in residual sludge from single-shell underground waste tanks C-203 and C-204 at the U.S. Department of Energy's Hanford Site in southeastern Washington state. Cejkaite [Na4(UO2)(CO3)3] was determined to be the dominant crystalline phase in the C-203 and C-204 sludges. This is only the second documented occurrence of cejkaite reported in the literature, and the first documented occurrence of this phase in radioactive wastes from DOE sites. XRD and SEM/EDS analyses of cejkaite found in the sludge solids are consistent with analyses of a natural mineral specimen of cejkaite. Characterization of residual solids from water leach and selective extraction tests indicates that cejkaite has a high solubility and a rapid rate of dissolution in water at ambient temperature, and that these sludges may also contain poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H2O)0-1], as well as nitratine (soda niter, NaNO3), goethite [FeO(OH)], and maghemite (Fe2O3). SEM/EDS analysis also shows that the C-204 sludge contains a solid composed of Na, Al, P, O, and possibly C that is likely amorphous. Other identified solids include Fe oxides that often also contain Cr and Ni and occur as individual particles, coatings on particles and botryoidal aggregates; a porous-looking material (or an aggregate of sub-micrometer particles) that typically contained Al, Cr, Fe, Na, Ni, Si, U, P, O, and C; Si oxide (probably quartz); and Na-Al silicate(s). The latter two solids probably represent minerals from Hanford sediment that were introduced into the tank during prior sampling campaigns or other tank-related activities. Preferential dissolution cavities were found on the surfaces of some of the Fe oxide particles present in residual solids from the water leach and selective extraction tests. If these solids contain contaminants, then their release into infiltrating water would be limited by dissolution of the low solubility Fe oxides. This process may account for at least some of the slow release of recalcitrant Tc-99 found in these sludges as discussed in the companion Part II paper by Cantrell et al.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 884816
- Report Number(s):
- PNNL-SA-45610; ESTHAG; 830403000; TRN: US0603691
- Journal Information:
- Environmental Science and Technology, Vol. 40, Issue 12; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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Characterization of Solids in Residual Wastes from Underground Storage Tanks at the Hanford Site, Washington, U.S.A.
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Related Subjects
43 PARTICLE ACCELERATORS
AMBIENT TEMPERATURE
CLARKEITE
GOETHITE
OXIDES
PARTICLE SIZE
RADIOACTIVE WASTES
SAMPLING
SOLUBILITY
SYNCHROTRONS
TANKS
WASTES
X-RAY DIFFRACTION
cejkaite
clarkeite
sodium uranate
goethite
maghemite
SEM
XRD
X-ray microdiffraction