INITIAL CHARACTERIZATIONS AND SRAT SIMULATIONS OF FOUR SLUDGE MATRIX STUDY SIMULANTS
The Savannah River National Laboratory (SRNL) initiated a sludge matrix study to evaluate the impact of changing insoluble solid composition on the processing characteristics of slurries in the Defense Waste Processing Facility (DWPF). Three compositional ranges were developed for three groups of elements in the waste. The first was high iron/low aluminum versus low iron/high aluminum. The second was high calcium-manganese/low nickel, chromium, and magnesium versus low calcium-manganese/high nickel, chromium, and magnesium. The third was high noble metals (Ag, Pd, Rh, Ru) versus low noble metals. These three options can be combined to form eight distinct sludge compositions. The sludge matrix study called for testing each of these eight simulants near the minimum acid required for nitrite destruction and at a second acid level that produced significant hydrogen by noble metal catalyzed decomposition of formic acid. Four simulants were prepared based on the four possible combinations of the Al/Fe and Mn-Ca/Mg-Ni-Cr options. Preliminary simulant preparation work has already been documented. The four simulants can be used for both high and low noble metal concentration testing and high and low acid testing. This report summarizes preliminary testing of each of the four simulants at low noble metals and low acid stoichiometry. The remaining matrix study tests are on hold. Chemically processed simulant was needed for U. S. Department of Energy-Office of Environmental Management and DWPF funded melt rate studies. Therefore, a preliminary assessment of the processing characteristics of the four sludge matrix simulants was completed using the low noble metal concentration option to meet this need. Sludge Receipt and Adjustment Tank (SRAT) testing was at low total acid stoichiometry (near the minimum acid end of the stoichiometric acid window). Composition and physical property measurements were made on the SRAT products. Updated values for formate loss and nitrite-to-nitrate conversion were found that can be used in the acid calculations for future sludge matrix process simulations. A reasonable determination of the minimum acid requirement for nitrite destruction was found to be slightly less than 105% of the Koopman minimum stoichiometric acid equation prediction for all four simulants at the low noble metal concentrations. The Koopman minimum stoichiometric acid equation is based on supernate carbonate, plus total Mg and Ca, in addition to the usual DWPF inputs such as base equivalents and Mn. This group of four tests extends the range of bulk insoluble solids concentrations over which the new Koopman minimum stoichiometric acid equation has been validated. The low iron-low manganese case appeared to have somewhat more excess acid than the other three combinations. Preliminary results of the initial testing indicate: (1) Hydrogen generation rate was not an issue in these tests. (2) Mercury stripping was less efficient than expected at about 1000 g steam/g mercury stripped. Only about 25% of the initial concentration of 1.5 wt% Hg in the total solids was removed in 13-14 hours of boiling, when 70% needed to be removed to meet the DWPF SRAT product specification of 0.45 wt% in the total solids. (3) Foaminess was not an issue using the nominal antifoam addition strategy in these tests. (4) Ammonia generation was not an issue based on off-gas condensate analyses. (5) One of the SRAT products (an HM-type simulant) was much more viscous than the other three SRAT products even though it had the lowest wt% insoluble solids. More comprehensive results concerning the impact of insoluble solids composition on processing, melt rate, etc. must await completion of the full sludge matrix study experimental scope.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 969296
- Report Number(s):
- SRNL-STI-2009-00606; TRN: US201001%%623
- Country of Publication:
- United States
- Language:
- English
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