Thermal stability study of a new guanidine suppressor for the next-generation caustic-side solvent extraction process

Cesium stripping performance of thermally stressed solvent worsens slowly over time in batch tests of the Next-Generation Caustic-Side Solvent Extraction (NG-CSSX) process. NG-CSSX is currently used in full-scale equipment at the Savannah River Site for the selective removal of caesium from high-level salt waste. Recently, a new guanidine, N,N',N-tris(3,7-dimethyloctyl)guanidine (TiDG), was chosen for use as the suppressor, a lipophilic organic base needed for stripping, and the present study was undertaken to address the question of its stability. The NG-CSSX process solvent was evaluated for a period of three months under a variety of temperature and storage conditions. The performance of the solvent was tested at 30-day increments using an extraction, scrub, strip and extraction (ES2S3E) sequence. The results provide insights into the effects of storage and process conditions, the stripping behaviour of TiDG and the stability of the new solvent composition.