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In this project, now completing its third year of its second renewal period, a collaborative project involving Oak Ridge National Laboratory, Pacific Northwest National Laboratory, and the University of North Texas has been addressing outstanding questions regarding the separation of the bulk sodium constituents of alkaline tank waste. The principal potential benefit of this research is a major reduction in the volume of radioactive tank waste, obviating the building of expensive new tanks and reducing the costs of vitrification. As a general approach, principles of ion recognition are being explored toward discovery and basic understanding of liquid-liquid extraction systems that selectively separate sodium hydroxide and sodium salts from waste-like matrices. Questions being addressed pertain to applicable extraction equilibria and how extraction properties relate to extractant structure. Progress has included the elucidation of the promising concept of pseudo hydroxide extraction (PHE), demonstration of crown-ether synergized PHE, demonstration of combined sodium hydroxide/sodium nitrate separation, and synthesis of novel ditopic receptors for ditopic PHE. In future efforts (pending renewal), a thermochemical study of PHE relating extractant acidity to extraction strength is proposed, and this study will be extended to systems containing crown ethers, including proton-ionizable ones. A series of crown ethers will be synthesized for this purpose and to investigate the extraction of bulk sodium salts (e.g., nitrate, nitrite, and sulfate), possibly in combination with sodium hydroxide. Simple proof-of-principle tests with real tank waste at PNNL will provide feedback toward solvent designs that have desirable properties. In view of the upcoming milestone of completion of the second renewal period, this report will, in addition to providing a summary of the past year's progress, summarize all of the work completed since the start of this project

Ion Recognition Approach to Volume Reduction of Alkaline Tank Waste by Separation of Sodium Salts