CORROSION OF DEPLETED URANIUM IN AN ARID ENVIRONMENT: CHARACTERIZATION WITH XRD, SEM/EDS AND MICROPROBE ANALYSES

Understanding the effects of an arid environment on depleted uranium (DU) in soil is of increasing importance with events such as the use of DU penetrators in two Gulf Wars and the likely prospect of storage of radioactive materials at Yucca Mountain, Nevada. The soil beneath two DU penetrators at a 1km2 study site in the Mojave Desert was examined to characterize the uranium migration, mineralogy and the effects of soil chemistry and geomorphology on its movement. One DU penetrator was on the surface of Holocene sands that overlie Pleistocene beach deposits and playa sediments. The second penetrator was located on eolian deflation depressions that exposed the underlying playa deposits. This study analyzed two soil profiles with standard field and laboratory techniques such as texture, electrical conductivity, pH and CEC. We also applied the use of X-ray diffraction, scanning electron microscopy with an electron dispersive system and electron probe microanalyses with a wavelength dispersive system to evaluate the mineralogy and occurrence of the uranium leached in the soil beneath two depleted uranium penetrators. Our research shows that uranium precipitates as aggregates of tabular, hexagonal schoepite-metaschoepite crystals with silicate clay/silt particles, coated with amorphous silica. Crystals occur as rosettes and as book-like structures with high uranium composition ranging from 60-95%. SEM images of metaschoepite show dehydration cracks from the loss of water either in the natural environment or when samples were moved to the laboratory. Because the schoepite/metaschoepite is coated with amorphous silica/clays, dissolution is inhibited. We suggest testing an additional step for use in traditional sequential extraction analyses that include treating samples with hot KOH to dissolve the silicate materials. This study concludes that uranium in the study area does not move quickly and is probably inhibited by the silicate coatings. However, future changes in irrigation or significant regional climate changes causing a shift in soil pH may contribute to a more significant movement of uranium in these soils.