Novel Fission-Product Separation Based on Room-Temperature Ionic Liquids

U.S. DOE's underground storage tanks at SRS, Hanford, and INEEL contain liquid wastes with high concentrations of cesium-137 and strontium-90. The goal of the proposed research is to develop update non-flammable, and non-volatile ionic liquid solvents for use in improving extraction processes for separation of fission products from tank wastes. To date, this EMSP project has achieved key results indicating promise for selective extraction of cesium and strontium using crown ethers and ionic liquids, giving 4000 times larger distribution coefficients than for corresponding organic solvents, and high selectivity over competing cations. A concept of facilitated sacrificial ion-exchange and development of stripping approaches for solvent regeneration were demonstrated. With support of the DOE-EMSP program, needed studies to advance the separation of fission products from high-level tank wastes will be continued. Studies will be aimed at: (1)development of ionic liquid solvents that are stable in highly caustic solutions and which have enhanced extraction efficiency and selectivity for Sr2+ and Cs+, (2) synthesis of recyclable aza-substituted calixarene crown ethers for selective separation of Cs+ in ionic liquids and update task-specific regenerable ionic liquids tailored for the extractive separation of Sr2+, (3)investigation of sacrificial ion-exchange processes to enhance extraction efficiency and reduce the loss of ionic liquids, (4)development of electrochemical regeneration of ionic liquids loaded with fission products for exceptional volume reduction, (5)investigation of the stabilities of ionic liquids under aggressive chemical and high-level radiation conditions. This work will lead to the discovery and development of a update and very versatile class of solvent systems that will improve processes for separation of fission products by reducing hazards and process complexity.