Date of Award

12-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering

Advisor

Lindsay Shuller-Nickles

Committee Member

Tim DeVol

Committee Member

Brian Powell

Abstract

Incorporation of uranium into iron oxide minerals is a promising mechanism for the environmental immobilization of U(VI). In this study, synthesized hematite was doped with uranium and analyzed with SEM-EDS, TEM, XRD, and ICP-MS. The results of this analysis strongly indicate uranium incorporation into the mineral, as well as the possible presence of a co-precipitated uranium mineral clarkeite. Preliminary results also shows an increase in the amount of uranium associated with the hematite particles as a function of mineral aging. Cyclic Voltammetry (CV) was used to induce and characterize electrochemical changes of uranium in the doped hematite system; these changes may possibly affect the stability of the bulk hematite, as well as the solubility of incorporated uranium should the hematite dissolve. The latter scenario is of particular interest, given the possibility of corrosive pH and temperature conditions in a geological waste repository. For this reason, uranium redox reactions were investigated at varying physical conditions. CV experiments demonstrated that a rapid and reversible U(V)-U(VI) redox couple will form in the presence of an applied cyclical voltage. The redox reactions between U(IV) and U(VI) are also possible, but are kinetically slower. All uranium redox reactions were most strongly observed in a narrow pH range centered around pH 3.5. The rate of each redox reaction increased with increasing temperature, while the electrochemical potential decreased with increasing temperature. These results are the groundwork upon which to conduct additional testing to further assess the viability of uranium incorporation as a strategy for uranium waste sequestration.

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