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The Reduction of Uranyl and Chromate to Insoluble Species by Green Rust and Other Ferrous Hydroxides Surfaces


EMSL Project ID
12701a

Abstract

Electron transfer reactions play an important role in the determination of the fate of many environmental contaminants. Of particular importance are the transitions from high-oxidation states (+5/+6), where the metal is stabilized in solution as an oxo-anion, to mid-oxidation states, where the metal is insoluble (+3/+4). Iron is a particularly effective reductant in alkaline conditions, where hydroxide ligands lower the Fe+2/Fe+3 redox couple.
We propose to examine the electron transfer kinetics in the uranium/green rust system using theoretical calculations. The work will entail utilization of the EMSL computing resources of the MSCF, including the use of the program NWChem. This study will focus on computational evaluation of secondary electron transfer steps, focusing on electronic structure changes between soluble and insoluble forms of the metal. Effects of solvation and hydrolysis will be considered, as well as proton transfers, as they are likely to play an important mechanistic role. In the case of chromium, one of the particular challenges will be to identify the structure of the Cr(IV) intermediate. Adsorption trajectories and configurations will be simulated using classical molecular dynamics methods and periodic boundary conditions.
Future directions of this work could include an examination of the effects of solid solutions of nickel or chromium, and iron, and the potential kinetic enhancements to the electron transfer that the nickel or chromium dopant may provide.

Project Details

Project type
Exploratory Research
Start Date
2006-04-01
End Date
2007-03-22
Status
Closed

Team

Principal Investigator

Martin Schoonen
Institution
State University of New York at Stony Brook

Team Members

Matthew Wander
Institution
Drexel University

Richard Reeder
Institution
State University of New York at Stony Brook