Next-Generation Solvent for Caustic-Side Solvent Extraction of Cesium from Supernatant Tank Waste - 23473

This paper describes a robust formulation of solvent and corresponding test results for the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) process for removal of cesium from the legacy salt waste stored in underground tanks at the Savannah River Site (SRS). The focus of the study was to identify a more stable suppressor component for the solvent and to validate its performance in batch tests simulating the process conditions expected to be employed when NG-CSSX is implemented in the SRS Salt Waste Processing Facility (SWPF). A guanidine compound, the suppressor enables efficient stripping but is unstable to hydrolysis. Guided by theoretical computations, two new guanidine compounds predicted to have improved stability were subjected to a battery of tests in comparison with two previous suppressors. Density matching with the currently used Caustic-Side Solvent Extraction (CSSX) process necessitated choice of a new modifier concentration, and aggressive flow ratios were tested that would maximize waste throughput. Overall, a more stable guanidine suppressor called DCNDG was identified with otherwise no impacts to the NG-CSSX process, reducing overall technical risk. (authors)