Washing Demonstration using Nonradioactive Simulated Tank 7 Sludge-Slurry Page: 3 of 13
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WASHING DEMONSTRATION USING NONRADIOACTIVE
SIMULATED TANK 7 SLUDGE-SLURRY
Tank 7 will be processed as part of the next sludge batch (Sludge Batch 3*) in the Defense Waste
Processing Facility (DWPF). Prior to processing in DWPF, a sludge-slurry must be washed to
adjust the sodium content and weight percent total solids. In typical sludge slurries, sodium is
primarily soluble and easily adjusted by diluting and decanting the supernate (i.e., washing). For
Tank 7, sodium adjustment is complicated by the presence of sodium oxalate which is partially
soluble in aqueous solutions. To better understand how sodium oxalate would affect sludge
washing, nonradioactive simulated Tank 7 sludge-slurry was prepared and washed. Soluble
species (e.g., nitrate) were easily removed as expected. Sodium oxalate behaved like a partially
soluble compound. As sodium concentration in wash water decreased, oxalate concentration
increased until the equilibrium concentrations for sodium and oxalate were reached. Thus,
sludge-slurry washing, even in the presence of sodium oxalate, is predictable.
Tank 7 will be processed as part of Sludge Batch 3*) in the DWPF. Prior to processing in
DWPF, a sludge-slurry must be washed to adjust the sodium content and weight percent total
solids. In typical sludge-slurries, sodium is primarily soluble and easily adjusted by diluting
and decanting the supernate (i.e., washing). For Tank 7, sodium adjustment is complicated by
the presence of sodium oxalate which is partially soluble in aqueous solutions. The presence of
oxalate may also complicate glass processing (melter offgas, glass redox, etc.).
At the time of this work, the sodium and oxalate content in Sludge Batch 3 for DWPF processing
were not defined. Therefore, the purpose of this work was to better understand how sodium, in
the presence of oxalate, is washed from sludge slurry, and to provide input for washing the waste
qualification sample in the Savannah River Technology Center (SRTC) Shielded Cells. To
accomplish this purpose, two tests were conducted. The first was a small scale centrifuge tube
test. Sludge slurry was washed, allowed to sit overnight, and then centrifuged to facilitate
decanting. The second test was on a slightly larger scale. Also, instead of centrifuging, sludge
was allowed to gravity settle prior to each decant. The purpose of this larger scale test was to
identify any settling issues, especially as sodium supernate concentrations dropped below 0.5 M.
* Sludge Batch 3 for the Defense Waste Processing Facility will consist of the Sludge Batch 1B heel in Tank 51,
Am/Cm and Pu/Gd slurries transferred from F and H-Areas into Tank 51, and the sludge slurry in Tank 7. However,
the focus of this work is Tank 7 only; the other components of Sludge Batch 3 were not evaluated or considered.
t Although weight percent total solids adjustment is an important aspect of washing, the scope of this work was
sodium and oxalate adjustment/removal.
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Pareizs, J.M. Washing Demonstration using Nonradioactive Simulated Tank 7 Sludge-Slurry, report, February 10, 2003; South Carolina. (digital.library.unt.edu/ark:/67531/metadc737374/m1/3/: accessed July 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.