| Abstract
| - Simulants for the Hanford Waste Vitrification Plant feedcontaining the major nonradioactive components Al, Cd, Fe,Mn, Nd, Ni, Si, Zr, Na, CO32-, NO3-, and NO2- wereused to study redox potential changes in reactions offormic acid at 90 °C catalyzed by the noble metals Ru, Rh,and/or Pd found in significant quantities in uraniumfission products. Such reactions were monitored usinggas chromatography to analyze the CO2, H2, NO, and N2Oin the gas phase and a redox electrode to follow redoxpotential changes as a function of time. In the initial phaseof formic acid addition to nitrite-containing feed simulants,the redox potential of the reaction mixture rises typicallyto +400 mV relative to the Ag/AgCl electrode because ofthe generation of the moderately strongly oxidizingnitrous acid. No H2 production occurs at this stage ofthe reaction as long as free nitrous acid is present. Afterall of the nitrous acid has been destroyed by reductionto N2O and NO and disproportionation to NO/NO3-, the redoxpotential decreases upon further formic acid addition.Hydrogen production typically begins to occur when theredox potential of the reaction mixture becomes more negativethan the Ag/AgCl electrode. The experiments outlined inthis paper suggest the feasibility of controlling the productionof H2 by limiting the amount of formic acid used andmonitoring the redox potential during formic acid treatment.
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