Laboratory stabilization/solidification of tank sludges: maximizing sludge loading

Highly radioactive, mixed-waste sludges that have been collected in tanks at Oak Ridge over several decades are being combined for treatment and disposal. Stabilization of the sludges in the different tank sets was tested prior to the proposed combination and treatment. This paper is the third one in a series on the laboratory stabilization/solidification of these tank sludges. It discusses efforts to maximize the sludge loading with no strength criterion for the grout formulation. Grout formulations were tested in the laboratory both with surrogates and with actual samples of tank sludge. Hydrogels eliminated free water generation, even at sludge loadings of >90 wt%, albeit strong monoliths did not form at such high loadings. Correlations established the dependence of the chromium and mercury performance in the Toxicity Characteristic Leach Procedure for the surrogates on the slag content of the grout while the lead performance depended on the extract pH. The surrogate sludge loading was limited by the chromate content to about 90 wt%, meeting Universal Treatment Standard limits. However, tests with actual sludges at such high loadings revealed problems with lead and silver stabilization that were not experienced with the surrogate testing.