SLUDGE CHARACTERIZATION AND SRAT SIMULATIONS USING A NITRITE-FREE SLUDGE SIMULANT

[摘要] Understanding catalytic hydrogen generation is fundamental to the safe operation of the Defense Waste Processing Facility (DWPF) Chemical Process Cell (CPC). Two Sludge Receipt and Adjustment Tank (SRAT) simulations were completed at the Aiken County Technology Laboratory (ACTL) of the Savannah River National Laboratory (SRNL) using a nitrite-free starting simulant. One simulation was trimmed with Rh and Hg and the other with Ru and Hg. The two noble metals were trimmed at the upper end of the recent Rh-Ru-Hg study. Mercury was trimmed at 1.5 wt% in the total solids. Excess acid comparable in quantity to that in the recent Rh-Ru-Hg matrix study was used. In spite of the favorable conditions for hydrogen generation, virtually no hydrogen production was observed during either SRAT simulation. The Rh test result confirmed the postulated significance of nitrite ion to the catalytic reactions producing hydrogen in CPC testing with normal DWPF sludge simulants. As for Ru, however, previous testing has shown that Ru activated for hydrogen generation only after nitrite destruction. Therefore, Ru could have potentially been catalytically active from the start of the nitrite-free SRAT test, but no such activity was seen. The nitrite-free Ru test result suggests that the intermediate form detected in the bead-frit melter feed preparation Ru solubility profiles was some form of nitro-Ru complex. The nitro-Ru complex is apparently not catalytically active for hydrogen generation but is a precursor to the catalytically active form (presumably a different complex not involving nitrite ligands). Removing nitrite ion from the system prevented the Ru catalyst precursor from forming and consequently blocked formation of the catalytically active form. These results, along with the results of a simulation in which sodium nitrite was metered into the SRAT to prevent ligand substitution reactions that occur during nitrite destruction from occurring in order to reduce hydrogen generation, have greatly clarified the role of the nitrite ion in SRAT hydrogen generation. The new findings add to the overall fundamental understanding of catalytic hydrogen generation during waste processing in the DWPF. These findings also address one of the issues raised in the Future Work section of the recent summary document concerning catalytic hydrogen generation in the CPC. The knowledge gained should facilitate planning future experiments.

[发布日期] 2009-12-17

[学科分类] 再生能源与代替技术

[关键词] CATALYSTS;HYDROGEN;HYDROGEN PRODUCTION;MERCURY;NITRITES;PLANNING;PRECURSOR;SAVANNAH RIVER PLANT;SIMULATION;SLUDGES;SODIUM;SOLUBILITY;TANKS;TESTING;WASTE PROCESSING