Next Generation Extractants for Cesium Separation from High-Level Waste

This project unites expertise at Oak Ridge National Laboratory (ORNL) and Texas Tech University (TTU, Prof. Richard A. Bartsch) to answer fundamental questions addressing the problem of cesium removal from high-level tank waste. Efforts focus on novel solvent-extraction systems containing calixcrown extractants designed for enhanced cesium binding and release. Exciting results are being obtained in three areas: (1) a update lipophilic cesium extractant with a high solubility in the solvent, (2) update proton-ionizable calixcrowns that both strongly extract cesium and "switch off" when protonated, (3) an improved solvent system that may be stripped with more than 10-fold greater efficiency. Scientific questions primarily concern how to more effectively reverse extraction, focusing on the use of amino groups and proton-ionizable groups to enable pH-switching. Synthesis will be performed at ORNL (amino calixcrowns) and TTU (proton-ionizable calixcrowns). At ORNL, the extraction behavior is being surveyed to assess the effectiveness of candidate solvent systems, and systematic distribution measurements are under way to obtain a thermodynamic understanding of partitioning and complexation equilibria. Crystal structures obtained at ORNL are revealing the structural details of cesium binding. The overall objective is a significant advance in the predictability and efficiency of cesium extraction from high-level waste in support of potential implementation at U. S. Department of Energy (USDOE) sites.