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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. * 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. † 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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