Towards a Predictive Thermodynamic Model for Oxidation States of Uranium Incorporated in Fe (hydr)oxides
EMSL Project ID
47897
Abstract
Bacterially facilitated and abiotic heterogeneous reduction of UVI to UIV has been intensively studied due to the vastly different solubility of hexavalent and tetravalent uranium, with ramifications for the fate and transport, and remediation of U in the environment. Further, it has long been thought that the only two uranium oxidation states of environmental importance are U(IV) and U(VI). However, our laboratory has provided evidence for the existence and non-transient nature of sorbed U(V). Recently, we have demonstrated that reduction of U(VI) incorporated in the structure of hematite yields U(V) not U(IV). Here, we propose a combined experimental and computational study to develop a predictive thermodynamic model for oxidation states of uranium incorporated in Fe (hydr)oxides that will cover a broad range of Eh and pH. Our specific objective is to rigorously test our guiding hypothesis, based on preliminary experiments and theory, that the thermodynamic stability of U(V) is widened relative to both U(VI) and U(IV) by uranate coordination environments (i.e., lack short dioxo bonds) where the coordination number is less than 8. In particular, we conjecture that incorporation of U into octahedral sites of Fe (hydr)oxides accomplishes both requirements.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2013-10-01
End Date
2015-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members