Thermal Degradation of the Solvent Employed in the Next-Generation Caustic-Side Solvent Extraction Process and its Effect on the Extraction, Scrubbing, and Stripping of Cesium

As part of the ongoing development of the Next-Generation Caustic-Side Solvent Extraction (NG-CSSX) process, the thermal stability of its process solvent, the Next-Generation Caustic-Side Solvent (NGS) was investigated and shown to be adequate for industrial application. The solvent was thermally treated at 35°C over a period of 13 months whilst in dynamic contact with each of the aqueous phases of the current NG-CSSX process, namely SRS−15 (a highly caustic waste simulant), sodium hydroxide scrub solution (0.025 M), and boric acid strip solution (0.01 M). The effect of thermal treatment was evaluated by assessing batch extract/scrub/strip performance as a function of time, by monitoring the sodium extraction capacity of the solvent, and by analysis of the solvent using electrospray mass spectrometry. Current studies indicate that the NGS should be thermally robust without replenishment for a period of 7 months in the Modular Caustic-Side Solvent Extraction Unit (MCU), which has been treating waste using ...