Bench-Scale Testing of the Continuous Sludge Leaching Process

Abstract

Boehmite has proved to be a difficult aluminum phase to dissolve out of high-level waste (HLW), requiring longer residence times and higher temperatures than the gibbsite phase for more complete dissolution. To provide a simple, compact, effective, and proven method to remove aluminum from HLW sludges, HLW feed can be blended with caustic in a reaction vessel while continuously removing permeate from the reactor. This approach allows for a concurrent addition of fresh caustic and HLW feed while simultaneously removing concentrated reacted slurry. Separation in this manner will keep solids in the reactor for longer periods of time, allowing for higher conversions than could be achieved in a normal batch reactor. The advantages for this continuous sludge leaching process are the reduction of the number of high level waste canisters by one-third to one-half at the Hanford Tank Waste Treatment and Immobilization Plant, resulting in billions of dollars in life-cycle cost savings. Bench-scale continuous reactor tests confirmed that the boehmite removal can be achieved to meet these canister reduction goals.

Keywords:

• boehmite
• filtration
• high level waste
• leaching