Doctor of Philosophy (PhD)
School of Plant, Environmental, and Soil Science
Depleted uranium (DU) projectiles have been used at several military bases across the United States encompassing a broad range of soil types and properties. Dissolution of the corrosion products, schoepite, (UO2)8O2(OH)12 12H2O, and metaschoepite, UO3(H2O)2 release U can be transported in the soil environment. The environmental fate of the products released from DU projectiles and/or their fragments is principally of interest regarding human health. This work examined corrosion of metallic U, transformation of schoepite, sorption and transport of dissolved U in soil, and remediation of U-contaminated soil with soil from five of these bases for the broad objective of a more comprehensive understanding of these processes. Salinity accelerated DU corrosion and rates of corrosion varied among soils in the absence of salinity, rate positively related to concentration of oxalate-extractable Fe (Feox). Schoepite may weather to metaschopite or another U mineral depending on soil properties but weathering had no significant effect on the extraction of U averaged over aged / unaged soils and by acetic or citric acid. However, weathering decreased U recovery with HNO3, indicating that the organic acids are more effective. The Freundlich model adequately described the nonlinear shape of U sorption isotherms for Jefferson, Knox, Polk and Yuma soils, and could be used for sorption in the Aberdeen soil which was nearly linear. Stirred-flow methodology was used to study sorption kinetics but results were not consistent with the batch isotherm data, particularly for Yuma. Transport of U through columns of soil diluted with minimally reactive sand showed similar behavior to stirred-flow, however, U transport could not be accurately modeled using kinetic rate constants from stirred-flow. In part, this reflected the effect of slight but non-negligible sorption by sand. Although this confounding effect may be removed by modeling sorption as a system of two sorbents, the experimental data alone demonstrated that U mobility in the soils is likely many times slower than in sand, and, depending on soil, U is likely immobile. Limited mobility makes remediation more practicable, whether by standard extraction or biomineralization. The latter was shown to remove up to 90% of U in contaminated Yuma soil.
Wynter, Michelle, "Evaluation of Depleted Uranium in Multiple Soils" (2022). LSU Doctoral Dissertations. 5997.
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