Kinetics of Triscarbonato Uranyl Reduction by Aqueous Ferrous Iron: A Theoretical Study

Journal Article · Tue Aug 01 04:00:00 EDT 2006 · Journal of Physical Chemistry A, 110(31):9691-9701

DOI:https://doi.org/10.1021/jp062325t· OSTI ID:891123

Wander, Matthew C; Kerisit, Sebastien N; Rosso, Kevin M; Schoonen, Martin A

Uranium is a pollutant whose mobility is tied to its oxidation state. While U(VI) in the form of the uranyl cation is capable of being reduced by a range of natural reductants, complexation by carbonate greatly reduces its reduction potential as well as imposing increased electron transfer (ET) distances. Very little is known about the elementary processes involved in uranium reduction from U(VI) to U(V) to U(IV) in general. In this study, we examine the theoretical kinetics of ET from ferrous iron to triscarbonato uranyl in aqueous solution. A combination of molecular dynamics (MD) simulations and density functional theory (DFT) electronic structure calculations are employed to compute the ET parameters that enter into Marcus’ model, including the thermodynamic driving force, reorganization energies, and electronic coupling matrix elements. MD simulations predict that two ferrous iron atoms will bind in an inner-sphere fashion to the three-membered carbonate ring of tricarbonato uranium, forming the charge-neutral Fe2UO2(CO3)3(H2O)8 complex. Through a sequential proton-coupled electron transfer mechanism, the first ET step converting U(VI) to U(V) is predicted by DFT to occur at a rate on the order of 1 s^-1. The second ET step converting U(V) to U(IV) is predicted to be significantly endergonic. Therefore, U(V) is a stabilized end-product in this ET system.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 891123
• Report Number(s): PNNL-SA-47151; 14102; KP1504010
• Journal Information: Journal of Physical Chemistry A, 110(31):9691-9701, Journal Name: Journal of Physical Chemistry A, 110(31):9691-9701
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
DENSITY FUNCTIONAL METHOD
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
IRON
MOLECULAR DYNAMICS METHOD
REDUCTION
URANYL COMPOUNDS