Geochemical Analysis of Depleted Uranium in Firing Range Soils.

The historical testing of depleted uranium (DU) munitions at a number of military installations within the US has led to environmental build-up (up to 50 metric tons of metallic DU), and release of DU to the environment.  After environmental exposure, DU may readily oxidize creating species that have different toxicity and geochemical properties.  A series of both fired and unfired DU penetrator rods were buried at different depths at the Yuma Proving Grounds (YPG) in AZ over 10 years ago in order to monitor DU oxidation and migration under natural soil conditions.  Several rods and the soils surrounding them were harvested, in addition to “legacy soils” experiencing historical DU firings were collected and analysed using liquid and solid- state analytical techniques. U in the samples was characterized with respect to solubility in batch studies, and synchrotron based-techniques XRF mapping, X-ray Absorption Spectroscopy and XRD were used to identify elemental associations and DU minerals present at the rod surface and in surrounding soils.  Synchrotron data were collected at beamline X27A at the NSLS.  The highest concentrations of DU were found in the soil within 10 cm of the rods, with minimal evidence of U migration past 15 cm of the rod.  Also, noticeable DU mineral “blooms” coated all rod surfaces, and in some cases DU metallic rods were completely oxidized and transformed into new U phases.  The metallic DU oxidized to form a number of U minerals including: Schoepite (UO₂)₈O₂(OH)12^.H₂O), Metaschoepite ((UO₂)₄O(OH)₆·5H₂O), Becquerelite (Ca(UO₂)₆O₄(OH)₆^.8(H₂O)), Billietite (Ba(UO₂)₆O₄(OH)₆•8(H₂O)) and Fourmariertite (Pb(UO₂)₄O₃(OH)₄^.4(H₂O)).  These findings confirm that soil constituents (Ba, Pb) influence U mineral formation in these systems, and, in the timeframe of this study (10 years), U from DU penetrator rods has limited mobility in the subsoil.