Morphology of colloids formed in soils reacted with simulated Hanford Waste Tank solutions and the distribution of incorporated and adsorbed cesium in the colloids
EMSL Project ID
2569
Abstract
High-level radioactive waste solutions stored in the underground tanks at Hanford sites have leaked into the vadose zone. The waste tank supernatants are known to consist of solutions with high pH (9-14), high ionic strength (sodium nitrate, sodium nitrite and other electrolytes), and high aluminate concentration. In simulated experiment, allophane, Linde Type A, cancrinite and sodalite formed when Hanford sediment contacted with the waste tank supernatants. These zeolite-like materials have high negative charge sites in their structures and therefore they are capable of incorporating and adsorbing cationic nuclides such as Cs in their framework and external surfaces. In addition to the high charge properties, the zeolite-like minerals have unique cages and channels within their structures, the radionuclides might be trapped in the cages or channels. Stacking faults in the zeolitic minerals may also block the channels or cages and therefore block the diffusion of the nuclides in the channels and increase their stability in the minerals. It is critical to know the quantity of the radionuclides that can be incorporated and adsorbed in the newly formed colloids and their stability in the minerals. It is also important to know the distribution of the nuclides within the particles of the minerals. To the best of our knowledge, the radionuclide distribution in the minerals has not been reported yet and the morphology, chemistry, electronic properties of the colloids are still not well characterized. In this proposed experiment, we will use the field emission scanning electron microscope to characterize the morphologies of the colloids and to map the distribution of the stable isotope 133Cs, as a surrogate of radioactive 137Cs when it is incorporated into or adsorbed on the minerals. Amorphous aluminum silicate (allophane) and crystalline materials Linde Type A, cancrinite, sodalite will be synthesized with relative high purity based on our previous trials. The colloids mostly have particle sizes of less than 2 micron. These minerals will be characterized with XRD, FTIR, conventional SEM and TEM in our lab at Washington State University (WSU). The images of the samples will be observed with the field emission scanning electron microscope. The chemical composition of the minerals will be determined by energy disperseve X-ray spectroscopy analysis (EDS). The minerals also will be synthesized in the presence of cesium. The quantity of incorporated cesium will be determined at WSU. The element distributions of Cs, Na, Si, and Al will be analyzed with elemental mapping. The samples will be embedded in epoxy resin and thin sectioned to about 100 nm thick before element mapping. The Cs- incorporated materials will be leached by Ca(NO3)2 and KNO3 solutions and the desorbed Cs will be quantified with atomic absorption spectroscopy at WSU. The distribution of Cs in the leached allophane and zeolitic minerals will be mapped again. The internal Cs within the minerals may not be leached out by the Ca(NO3)2 or KNO3 because the small size of the channels and also because of stacking faults in the mineral may block the channels. Similarly, a Cs adsorption experiment will be conducted on synthesized allophane and three zeolitic materials and quantified by atomic absorption spectroscopy. The distribution of Cs on the Cs-adsorbed particles will be mapped as described above. The experiments proposed will provide the mineralogy, surface chemistry, and electrochemical properties of the colloids formed in reactions similar to those between Hanford sediments and the leaked tank supernatants. These results will offer evidence whether the radionuclides are associated with the newly formed colloids and their stability on the colloids. This experiment ultimately improves our understanding of the fate and transport of radioactive Cs in the Hanford environment
Project Details
Project type
Exploratory Research
Start Date
2002-08-05
End Date
2005-08-07
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members