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SUMMARYLiquid Waste Organization (LWO) identified aluminum dissolution as a method to mitigate the effect of having about 50% more solids in High Level Waste (HLW) sludge than previously planned. Previous aluminum dissolution performed in a HLW tank in 1982 was performed at approximately 85°C for 5 days, which became the baseline aluminum dissolution process. LWO initiated a project to modify a waste tank to meet these requirements.Subsequent to an alternative evaluation, LWO management identified an opportunity to perform aluminum dissolution on sludge destined for Sludge Batch 5, but within a limited window that would not allow time for any modifications for tank heating. A variation of the baseline process, dubbed Low Temperature Aluminum Dissolution (LTAD), was developed based on the constraint of available energy input in Tank 51 and the window of opportunity, but was not constrained to a minimum extent of dissolution, i.e. dissolve as much aluminum as possible within the time available. This process was intended to operate between 55 and 70°C, but for a significantly longer time than the baseline process. LTAD proceeded in parallel with the baseline project.The preliminary evaluation at the completion of LTAD focused on the material balance and extent of the aluminum dissolved. The range of values of extent of dissolution, 56% to 64%, resulted from the variation in liquid phase sample data available at the time. Additional solid phase data is available from a sample taken after LTAD to refine this range. This report provides additional detailed evaluation of the LTAD process based on analytical and field data and includes:• a summary of the process chronology,• a determination of an acceptable blending strategy for the aluminum-laden supernate stored in Tank 11, • an update to the determination of aluminum dissolved using more complete sample results, • a determination of the effect of LTAD on uranium, plutonium, and other metals, • a determination of the rate of heat loss from a quiescent tank, and • an evaluation of the aluminum dissolution rate model and actual dissolution rate.LTAD was successfully completed in Tank 51 with minimal waste tank changes. The following general conclusions may be drawn about the LTAD process:• Dissolution at about 60°C for 46 days dissolved 64% of the aluminum from the sludge slurry.• The aluminum-laden leach solution decan...