(155d) Copper Catalyzed Peroxide Oxidation Testing for Tetraphenylborate Decomposition in Srs Tank 48h

A new processing option, copper catalyzed hydrogen peroxide oxidation of tetraphenylborate under alkaline conditions, was demonstrated in laboratory testing. High-level-waste Tank 48H at the Savannah River Site (SRS) contains about 50,000 pounds of tetraphenylborate, which must be destroyed to return the tank to active service. The TPB was added during an in-tank precipitation process to removed soluble cesium-137, but excessive benzene generation curtailed this treatment method. In-tank processing is desirable because of low capital cost and complete destruction of the organic, even on the tank surfaces and the residual waste left in the tank. Also, an in-tank process is likely to generate much less waste because transferring the waste to another facility and cleaning of the tank internals will generate additional waste. To return the tank to routine waste tank service, the tank must have less than 380 grams of tetraphenylborate left. The cost of a shielded out-of-tank process is too expensive to be feasible for this relatively small waste stream. An alternative in-tank process, catalytic hydrolysis of tetraphenylborate, was unsuccessful. Corrosion control considerations for the carbon steel waste tank limit the conditions of the in-tank process to a pH over 10.3 and a temperature less than 75 ºC. Laboratory-scale tests were conducted to evaluate the use of copper catalyzed hydrogen peroxide oxidation to treat simulants of the Tank 48H waste. Oxidation process involves the reaction of hydrogen peroxide with a copper catalyst to form hydroxyl free radicals. With an oxidation potential of 2.8 volts, the hydroxyl free radical is a very powerful oxidant, second only to fluorine, and will react with a wide range of organic molecules. The goal is to oxidize the tetraphenylborate completely to carbon dioxide, with minimal benzene generation. Testing was completed in a lab-scale instrumented demonstration apparatus at the Savannah River National Laboratory. Complete tetraphenylborate destruction was achieved in less than three weeks. Offgas benzene analysis by a gas chromatograph demonstrated low benzene generation. Analysis of the resulting slurry demonstrated complete destruction of tetraphenylborate and its decomposition products. The only detectable carbon compounds detected were formate, oxalate and carbonate. The results of this testing will be reported.