Variations in Depleted Uranium Sorption and Solubility with Depth in Arid Soils

Abstract

This study examined the ability of alkaline desert soils to sorb depleted uranium (DU) as a function of soil horizon and assessed the solubility of corrosion and migration products from two DU kinetic energy penetrators exposed on the desert surface for a 22-y period. Both uranium corrosion products on the surface, and subsurface uranium originating from the dissolution of surface corrosion products followed by reprecipitation or sorption, were examined. A four-step sequential extraction method was used to classify uranium solubility at each site. Results show that distribution coefficient for uranium is highly variable, but can be correlated with the clay content (r = 0.55) and soil pH (r = 0.73) of the soil horizon considered. Surface corrosion products and near-surface uranium easily dissolve in a weak acid solution (25% acetic acid for two hours), suggesting a uranyl hydroxide form. As uranium migrates beyond several centimeters in depth, it forms insoluble aggregates with silicate minerals and requires strong acids to leach it. The formation of uranium-silicate mineral aggregates appears to be the limiting factor in vertical vadose zone transport of DU at the site investigated.

Removal of depleted uranium from contaminated soils

“…Johnson et al [15] reported 29-52% DU in the residuals fraction of their sequential extraction tests. Coatings of amorphous silica around schoepite particles and aggregates with clays and calcium carbonate were found to inhibit U solubility during extraction experiments and cause it to be recovered in the residual phase.…”

“…Sequential analysis of the upper 4 cm of the soil profile showed that at least half of the total DU may be attributed to the carbonate fraction (Stage 2 of the sequential extraction). The relative ease of DU dissolution implied that uranyl hydroxide minerals were present [15]. No DU was in the exchangeable fraction for the first 8 cm below the surface.…”

“…Like Soil A, the amount of U in the residual fraction was very small. In another study [15], an arid alkaline soil located directly below a DU penetrator for 22 years, in the open air, was tested. Sequential analysis of the upper 4 cm of the soil profile showed that at least half of the total DU may be attributed to the carbonate fraction (Stage 2 of the sequential extraction).…”

Solid state speciation and potential bioavailability of depleted uranium particles from Kosovo and Kuwait

“…However, U 4 O 9 , U 3 O 7 and UO 3 have also been reported from DU penetrator tests (Chazel et al, 2003). Fragments and particles are also formed as unspent DU penetrators deposited in the field will corrode over time due to oxidation of the metal Johnson et al, 2004;Mellini and Riccobono, 2005;Salbu et al, 2005). In the environment, U metal can also experience passivation where an oxide, hydroxide or salt coating can protect against further corrosion.…”

Models of Solute Aggregation Using Cellular Automata

“…Depleted uranium can undergo a variety of transitions from dissolution of surface corrosion products, followed by re-precipitation and sorption through the formation of insoluble aggregates with minerals [11].…”