The Nopal I site in the Pena Blanca uranium deposit has been considered to be a close analog to nuclear waste disposal sites, making it a useful to evaluate process models for radionuclide transport. Investigating the release of heavy elements from phases in Pena Blanca sediments could provide information regarding long-term retention of actinides. Electron microscopy investigations of selected particles from the deposit were examined with an aberration-corrected scanning transmission electron microscope. The specimen consisted of an iron oxide (hematite) matrix with deposits of (Zr,Y)(Si,P) oxide with Ca, Mg, U, and Pb present. Microscopic evidence indicated that the Pb had diffused from the Zr-bearing phase; whereas, the U was retained. Atomic resolution imaging of the iron oxide (hematite) revealed the presence of the Pb in the phase. The Cs-corrected STEM was operated for simultaneous bright field and high angle annular dark field imaging that enabled the different phases to be viewed and analyzed. Phases were determined with electron diffraction and electron energy-loss spectroscopy was used to determine the chemical state of some elements in the specimen, as well as the distribution of these elements.

Lead and uranium distribution in particles from the Pena Blanca site using Cs-corrected STEM

256th National Meeting (2018)

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