Noble metal-catalyzed homogeneous and heterogeneous processes in treating simulated nuclear waste media with formic acid
- Univ. of Georgia, Athens, GA (United States)
- Pacific Northwest Lab., Richland, WA (United States); and others
Simulants for the Hanford Waste Vitrification Plant feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO{sub 3}{sup 2}-, NO{sub 3}-, and NO{sub 2}- were used to study reactions of formic acid at 90{degrees}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 microammonia electrode to analyze the NH{sub 4}+/NH{sub 3} in the liquid phase as a function of time. The following reactions have been studied in these systems since they are undesirable side reactions in nuclear waste processing: (1) Decomposition of formic acid to CO{sub 2} + H{sub 2} is undesirable because of the potential fire and explosion hazard of H{sub 2}. Rhodium, which was introduced as soluble RhCl{sub 3}-3H{sub 2}O, was found to be the most active catalyst for H{sub 2} generation from formic acid above {approximately} 80{degrees}C in the presence of nitrite ion. The H{sub 2} production rate has an approximate pseudo first-order dependence on the Rh concentration, (2) Generation of NH{sub 3} from the formic acid reduction of nitrate and/or nitrite is undesirable because of a possible explosion hazard from NH{sub 4}NO{sub 3} accumulation in a waste processing plant off-gas system. The Rh-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was found to exhibit the following features: (a) Nitrate rather than nitrite is the principal source of NH{sub 3}. (b) Ammonia production occurs at the expense of hydrogen production. (c) Supported rhodium metal catalysts are more active than rhodium in any other form, suggesting that ammonia production involves heterogeneous rather than homogeneous catalysis.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 135035
- Report Number(s):
- PNL-SA-25954; CONF-9509175-1; ON: DE96002718; TRN: 96:000249
- Resource Relation:
- Conference: 8. international symposium on relations between homogeneous and heterogeneous catalysis, Balatonfuered (Hungary), 10-14 Sep 1995; Other Information: PBD: Sep 1995
- Country of Publication:
- United States
- Language:
- English
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