The Reduction of Uranyl and Chromate to Insoluble species by Green Rust and other ferrous hydroxide surfaces.
EMSL Project ID
33094
Abstract
Electron transfer reactions play an important role in determining the fate of many environmental contaminants. Reduction from high-oxidation state (+5/+6), where the metal is stabilized in solution as an oxo-ion, to mid-oxidation states, where the metal is insoluble (+3/+4) are of particular importance for uranium and chromate. Iron is particularly effective reductant for these metals in alkaline conditions, where hydroxide ligands lower the Fe2+/Fe3+ redox couple and ferrous hydroxides and green rust can be found. Molecular-scale factors controlling the magnitude of the thermodynamic driving force and the kinetics of step-wise reduction of uranium and chromium through the 'unstable' oxidations states are poorly understood. We propose to examine the electron transfer kinetics in the reduction for uranium and chromium by green rust materials and analogues using computational molecular modeling methods. While our prior work has focused on primarily DFT methods, at this stage we intend to examine correlated methods including MP2 and coupled cluster approaches to evaluate the feasibility of their application to these types of systems, starting with homogenous electron transfers between iron and uranium. Our work will entail use of the EMSL computing resources and NWChem. This study will focus on computational evaluation of rates of intermediate electron transfer steps, concentrating on the atomic and electronic structure changes between soluble and insoluble forms of the metal (e.g., U5+ and U4+). Effects of solvation and hydrolysis, as well as proton transfer coupling to electron transfer, will be explicitly considered using state-of-the-art molecular modeling tools.
Project Details
Project type
Exploratory Research
Start Date
2009-03-05
End Date
2010-03-14
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Matthew C. F. Wander, Kevin M. Rosso, and Martin A. A. Schoonen Structure and Charge Hopping Dynamics in Green Rust J. Phys. Chem. C, Vol. 111, No. 30, 2007 11414-11423
Wander MC, and MA Schoonen. 2010. "Green Rust Reduction of Chromium Part 2: Comparison of Heterogeneous and Homogeneous Chromate Reduction." Journal of Physical Chemistry C 114(39):16408-16415. doi:10.1021/jp1021328