Impact of Redox-driven Recrystallization on the Stability and Reactivity of Uranium and Lead Oxides

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This award is supported by the Chemistry Division's Environmental Chemical Sciences Program. Professors Daniel Giammar and Jeffrey Catalano and their groups at Washington University in St. Louis study uranium and lead, which are naturally-occurring, toxic elements and important environmental contaminants. Uranium and lead often exist in nature as oxides (bonded to oxygen). Uranium and iron oxide reactivity in the environment depend on their oxidation-reduction ("redox") chemistry. The recrystallization of these species can impact their toxicity. This study extends our understanding of the occurrence and environmental impacts of redox-driven recrystallization of uranium and lead oxides. The work builds on related studies of recrystallization of other metal oxides, notably iron oxides ("rust") and manganese oxides. The scientific knowledge gained by this project can be used to reduce exposure to uranium in contaminated groundwater and to lead in contaminated drinking water. The research is integrated with educational activities that involve curriculum enrichment, graduate student training, and outreach to K-12 students and other members of the public. The project explores redox-driven recrystallization as a general phenomenon of environmental significance common to many semiconducting metal oxides. Specific targets include measurements of the rates and the extent of isotope exchange between aqueous uranium (VI) and solid uranium (IV) oxides and between aqueous lead (II) and solid lead (IV) oxides. The impacts of recrystallization on the composition, structure and size of the resulting particles is being characterized. Isotope exchange and recrystallization under conditions relevant to remediation of uranium-contaminated groundwater and the control of lead in drinking water distribution systems are being used to quantify the impacts of recrystallization on contaminant mobility.