Hydrogen peroxide supply concentration after restart with hydrogen peroxide addition closer to the top of the column.

Additional components such as nitrite and carbonate will be added to the test matrix. The results will be used to develop safe operating windows for safe waste transf=s at Hadord. In addition to the waste transfer, unwanted solids formation can occur during waste processing activities such as the Enhanced Sludge Washing (ESW). Previous work has shown that phosphate gels and particles are formed as the hot leach solutions from the ESW process are permitted to cool. In another study, insoluble aluminosilicates apparently formed during the hot caustic leaching, which significantly reduced the pefiormance of &e ESW process. The aluminosilicates, as well as the phosphate gels from the ESW process, could also forma pipeline plug. This study confirmed the formation of alurninosilicates during the ESWprocess and demonstrated the importance of a thorough water wash prior to the caustic leaches. The water wash improves the performance and the reproducibility of the ESW process. A key difference in the leach tests with washed sludge and unwashed sludge was the higher ionic strength in the unwashed tests due to the presence of water-soluble salts. In response to the alurninosilicate plug at Savannah River, an equilibrium model on the solubilities of silicate vii species at 25 'C was developed. After the solubilities of silicon and aluminum species at higher temperatures are incorporated into the model, safe operating windows for the evaporator system will -be provided to the tank farm operators. Finally, a simulated chemical plug based on the sodium phosphate plug was developed and provided to the Retrieval Program of the Tanks Focus Area to test recovery methods. Additional simulated plugs have been requested.

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