Evans, R. D.

Soluble uranium (U) has been observed continuously in the porewaters of Bentley Lake,

a lake with semi-permanent anoxic sediments, despite the fact that reduced U(IV) is known to be

insoluble. To be able to predict the fate and mobility of U that has been deposited in lake

sediments, it is very important to understand the factors that determine soluble uranium in anoxic

environments. Understanding soluble U species is crucial for predicting its behavior in natural

systems as well as for the development of U remediation schemes.

To explore the factors affecting soluble U in natural environments, anoxic lake sediments

and porewaters were tested using two analytic methods, ICP-MS and ESI-HR-MS. Reduced

uranium (U(IV)) can be precipitated as U(IV)-NdF3. Using this method revealed that most of the

uranium in porewater is not able to be co-precipitated with NdF3. In addition, UO2+ was found

using ESI-HR-MS, showing uranyl ions exist in reduced porewater. However, the UO2+ might be

attached to some organic groups rather than present as free ions.

Seasonal variation and air exposure experiments on the mobility of U between sediments

and porewater were observed to test for changes of the redox state of U as a function of sample

collection and storage. The results of this study will contribute to better remediation strategies for

U tailings and will help U mining operations in the future.