Degree

Doctor of Philosophy (PhD)

Department

School of Plant, Environmental, and Soil Science

Document Type

Dissertation

Abstract

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.

Date

11-1-2022

Committee Chair

Gaston, Lewis

Available for download on Tuesday, October 30, 2029

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