Geochemical conditions present during the formation and post-formation of uranium ores results in rare earth element signatures (REE) unique to each deposit. Nuclear forensics harnesses the information provided through these REE signatures to ascertain deposit types and location to identify the origin of unknown uranium materials. The REE signatures persist though uranium processing in the beginnings of the fuel cycle, however aging processes during storage can cause these materials to undergo morphological, structural, chemical, and redox changes. This study investigates the influence of REE on uranium oxide aging in an aqueous environment. Inductively coupled plasma mass spectrometry, powder X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy (SEM) are used to describe the behavior of REEs with uranium oxides (UO2, U3O8-pitchblende, and carnotite) and characterize changes in the solid phase. Results of batch sorption experiments carried out as a function of pH (3-9), ionic strength (&lt; 0.5 M NaNO3), and total REE concentration (1000 ppb – 200 ppm) indicate complete sorption of REEs between pH 6-7. Sorption decreases when the ionic strength is raised, which is indicative of the formation of outer-sphere sorption complexes. An overall trend of preferential sorption of light REEs was observed regardless of solution conditions, suggesting that uranium oxide aging in REE solutions alters the solid-phase REE signature. SEM imaging did not reveal any major morphological changes.

Rare-earth element interactions with uranium oxides

2019 Spring National Meeting

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