Abstract
Dramatic potential improvements to the chemistry of the Caustic-Side Solvent Extraction (CSSX) process are presented as related to enhancement of cesium stripping. The current process for removing cesium from the alkaline high-level waste (HLW) at the USDOE Savannah River Site employs acidic scrub and strip stages and shows remarkable extraction and selectivity properties for cesium. It was determined that cesium stripping can be greatly improved with caustic or near-neutral stages using sodium hydroxide and boric acid as scrub and strip solutions, respectively. Improvements can also be achieved by appending pH-sensitive functional groups to the calix[4]arene-crown-6 extractant. Addition of a proton-ionizable group to the calixarene frame leads to a dramatic "pH swing" of up to 6 orders of magnitude change in cesium distribution ratio.
