The morphologies and compositions of depleted uranium particles from an environmental case-study

Abstract

Uraniferous particles from contaminated environmental samples were analysed by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDXA) and microfocus extended X-ray absorption fine structure (mEXAFS) spectroscopy. The particles of interest are uranium oxides, which were released into the environment by the combustion of scrap depleted uranium (DU) metal at a factory in Colonie, New York, USA. Most of the identified particles appear to have primary, 'as emitted' morphologies; some have evidence of minor dissolution, including corrosion pitting. Polycrystalline and often hollow microscopic spheres were identified, which are similar to particles produced by DU munitions impacting armoured targets. They are attributed to the autothermic oxidation of melt droplets. The compositions of the analysed spheres are dominated by UO 2+x with variable amounts of U 3 O 8 , two of the least soluble and least bioaccessible phases of U. These particles, collected from dusts and soils, have survived more than 25 y in the terrestrial environment. This study further supports the case for using Colonie as an analogue for battlefield DU contamination.

The distribution of depleted uranium contamination in Colonie, NY, USA

“…Examination of contaminated soils and dusts reveals primary uranium oxide particles in the size range 0.5 -150 µm, including mixed UO 2+x and U 3 O 8 spheres with diameters 20 -64 µm, and rarely secondary uranium precipitates (Chapter 3 / Lloyd et al 2009b). These spheres and other specific particle morphologies are directly comparable to those from munitions.…”

“…However, the Colonie soils are generally well-drained, and at least for oxidation in air, kinetics and surface passivation may limit bulk oxidation beyond UO 2+x (s) (McEachern & Taylor 1998), as appears to be the case for a few primary particles recovered from Colonie soils (Chapter 3 / Lloyd et al 2009b). Schoepite has a solubility three orders of magnitude greater than UO 2+x (Ragnarsdottir & Charlet 2000), therefore speciation is significant for contaminant transport and bioaccessibility.…”

“…UO 3 and uranyl species are thermodynamically favoured, but bulk oxidation to these more soluble oxides is limited by slow kinetics and surface passivation (McEachern & Taylor 1998). This appears to be the case for the persistence of low solubility UO 2+x (hyperstoichiometric UO 2 ) and U 3 O 8 particles in soils (Chapter 3 / Lloyd et al 2009b). Radiogenic lead reduces the mobility of uranium from natural uraninite (e.g.…”

Pathways of Radioactive Substances in the Environment

“…26 The transport of DU particles will depend on particle properties (i.e., size and density) and on prevailing meteorological conditions. 51 54,55 investigated the dispersion of aerosols formed during the combustion of waste metal at a uranium and DU processing factory in Colonie (NY, USA). The distribution of the DU aerosol was controlled by prevailing winds, with DU contamination found up to 600 m from the factory.…”

Morphology of U3O8 materials following storage under controlled conditions of temperature and relative humidity

“…In particular, comparison of the morphology of precipitates with those of subsequent calcination products suggests that microstructures of the precursor precipitates are retained through heat treatment [6][7][8][13][14][15][16]. A number of studies have shown that U 3 O 8 , a common intermediate in the production of nuclear material, generates schoepite phases (UO 3 ÁxH 2 O) during storage under higher relative humidities presumably following oxidation and/or hydration [2,[17][18][19]. It would be valuable to understand the variables contributing to temporally-induced morphology changes, and if any changes occur, the prospect for using the temporal changes in morphology that arise during storage under different conditions for forensic analyses.…”