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Removal of waste-limiting components of sludge (Al, Cr, S, P) in underground tanks at Hanford by treatment with concentrated alkali has proven less efficacious for Al and Cr removal than had been hoped. More aggressive treatments of sludges, for example, contact with oxidants targeting Cr(III), have been tested in a limited number of samples and found to improve leaching efficiency for Cr. Oxidative alkaline leaching can be expected to have at best a secondary influence on the mobilization of Al. Our earlier explorations of Al leaching from sludge simulants indicated acidic and complexometric leaching can improve Al dissolution. Unfortunately, treatments of sludge samples with oxidative alkaline, acidic or complexing leachates produce conditions under which normally insoluble actinide ions (e.g., Am3+, Pu4+, Np4+) can be mobilized to the solution phase. Few experimental or meaningful theoretical studies of actinide chemistry in strongly alkaline, strongly oxidizing solutions have been completed. Unfortunately, extrapolation of the more abundant acid phase thermodynamic data to these radically different conditions provides limited reliable guidance for predicting actinide speciation in highly salted alkaline solutions. In this project, we are investigating the fundamental chemistry of actinides and important sludge components in sludge simulants and supernatants under representative oxidative leaching conditions. We are examining the potential impact of acidic or complexometric leaching with concurrent secondary separations on Al removal from sludges. Finally, a portion of our research is directed at the control of polyvalent anions (SO4=, CrO4=, PO43-) in waste streams destined for vitrification. Our primary objective is to provide adequate insight into actinide behavior under these conditions to enable prudent decision making as tank waste treatment protocols develop. We expect to identify those components of sludges that are likely to be problematic in the application of oxidative, acidic, and complexometric leaching protocols

Characterization of Actinides in Simulated Alkaline Tank Waste Sludges and Leachates