Redox potential monitoring as a method to control unwanted noble metal-catalyzed hydrogen generation from formic acid treatment of simulated nuclear waste media
- Univ. of Georgia, Athens, GA (United States). Dept. of Chemistry
- Pacific Northwest National Lab., Richland, WA (United States)
Simulants for the Hanford Waste Vitrification Plant feed containing the major nonradioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO{sub 3}{sup 2{minus}}, NO{sub 3}{sup {minus}}, and NO{sub 2}{sup {minus}} were used to study redox potential changes in reactions of formic acid at 90 C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the CO{sub 2}, H{sub 2}, NO, and N{sub 2}O in the gas phase and a redox electrode to follow redox potential changes as a function of time. In the initial phase of formic acid addition to nitrite-containing feed simulants, the redox potential of the reaction mixture rises typically to +400 mV relative to the Al/AgCl electrode because of the generation of the moderately strongly oxidizing nitrous acid. No H{sub 2} production occurs at this stage of the reaction as long as free nitrous acid is present. After all of the nitrous acid has been destroyed by reduction to N{sub 2}O and NO and disproportionation to NO/NO{sub 3}{sup {minus}}, the redox potential of the reaction mixture becomes more negative than the Ag/AgCl electrode. The experiments outlined in this paper suggest the feasibility of controlling the production of H{sub 2} by limiting the amount of formic acid used and monitoring the redox potential during formic acid treatment.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 290180
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 20 Vol. 32; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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