Reduction Rates for Higher Americium Oxidation States in Nitric Acid

Technical Report · Wed Sep 30 04:00:00 EDT 2015

DOI:https://doi.org/10.2172/1244636· OSTI ID:1244636

Grimes, Travis Shane ^[1]; Mincher, Bruce Jay ^[1]; Schmitt, Nicholas C ^[1]

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1. Idaho National Lab. (INL), Idaho Falls, ID (United States)

The stability of hexavalent americium was measured using multiple americium concentrations and nitric acid concentrations after contact with the strong oxidant sodium bismuthate. Contrary to our hypotheses Am(VI) was not reduced faster at higher americium concentrations, and the reduction was only zero-order at short time scales. Attempts to model the reduction kinetics using zero order kinetic models showed Am(VI) reduction in nitric acid is more complex than the autoreduction processes reported by others in perchloric acid. The classical zero-order reduction of Am(VI) was found here only for short times on the order of a few hours. We did show that the rate of Am(V) production was less than the rate of Am(VI) reduction, indicating that some Am(VI) undergoes two electron-reduction to Am(IV). We also monitored the Am(VI) reduction in contact with the organic diluent dodecane. A direct comparison of these results with those in the absence of the organic diluent showed the reduction rates for Am(VI) were not statistically different for both systems. Additional americium oxidations conducted in the presence of Ce(IV)/Ce(III) ions showed that Am(VI) is reduced without the typical growth of Am(V) observed in the systems sans Ce ion. This was an interesting result which suggests a potential new reduction/oxidation pathway for Am in the presence of Ce; however, these results were very preliminary, and will require additional experiments to understand the mechanism by which this occurs. Overall, these studies have shown that hexavalent americium is fundamentally stable enough in nitric acid to run a separations process. However, the complicated nature of the reduction pathways based on the system components is far from being rigorously understood.

• Research Organization: Idaho National Laboratory (INL), Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• DOE Contract Number: AC07-05ID14517
• OSTI ID: 1244636
• Report Number(s): INL/EXT--15-36767
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
ABUNDANCE
AMERICIUM
Americium VI oxidation
Americium reduction kinetics
BISMUTH COMPOUNDS
CERIUM IONS
CHEMICAL REACTION KINETICS
COMPARATIVE EVALUATIONS
CONCENTRATION RATIO
DODECANE
NITRIC ACID
OXIDATION
OXYGEN COMPOUNDS
PERCHLORIC ACID
REDUCTION
SEPARATION PROCESSES
SODIUM COMPOUNDS
STABILITY
VALENCE
americium reduction nitric acid