Alternatives to Nitric Acid Stripping in the Caustic‐Side Solvent Extraction (CSSX) Process for Cesium Removal from Alkaline High‐Level Waste

Extraction equilibrium and thermodynamics of cesium with a new derivative of calix[4]biscrown

“…Processes like fission product extraction [18,19] and caustic-side solvent extraction [20,21] using calix [4]biscrowns to selectively separate cesium from the highly active liquid waste (HLW) have been reported. The Cs(I)/Na(I) selectivity of calix [4]-bis-crown-6 could reach a level of 1,500.…”

Robustness of the CSSX Process to Feed Variation: Efficient Cesium Removal from the High Potassium Wastes at Hanford

“…Used at a concentration of 0.75 M, the latter solubilizes BOBCalixC6 and its complexes primarily by hydrogen bonding [27,28] which also provides a critical enhancement to the cesium extraction strength, otherwise uselessly small in the isoparaffinic diluent IsoparH L. Tri-n-octylamine used at 0.003 M suppresses the effects of impurity anions [29] and feeble ion-pair dissociation of the cesium complexes, [30] thereby promoting efficient stripping. [1,12] Chemically, the effect of potassium on cesium amounts to the loading of the calixarene extractant BOBCalixC6, lowering the free extractant concentration even to the degree that the effective extractant may be viewed as the potassium complex functioning by cation exchange. Whereas the cesium/sodium separation factor (D Cs /D Na ) obtainable with calixarenecrown-6 compounds is excellent and can reach 5 orders of magnitude, [24][25][26] the selectivity for cesium over potassium is much lower (though still high), on the order of 100-200.…”

“…The third objective was to improve the overall performance by testing a previously suggested modification to the solvent system and flowsheet. [12] The data upon which the present work is based have been tabulated fully in the report literature. [7] The present emphasis builds upon that report in developing a better quantitative understanding of the potassium loading effect on the cesium extraction behavior and gaining a greater level of predictability useful in future extensions of the CSSX process to different feed types not yet assessed experimentally.…”

Recommended Guanidine Suppressor for the Next-Generation Caustic-Side Solvent Extraction Process

“…The NG-CSSX process [1,2] was designed to provide a step-jump improvement in waste decontamination factor (DF) and waste throughput vs. the CSSX process [3,4,5] in the removal of cesium from legacy high-level salt waste stored in underground storage tanks in the U.S. Department of Energy (DOE) complex. Following initial results pointing to its feasibility [6,7,8] , the NG-CSSX process has been under development since 2010 under funding from the DOE Office of Environmental Management, Office of Technology Innovation and Development. To reach the target cesium decontamination and concentration factors (DF = 40,000…”

“…In the CSSX process, tri-n-octylamine (TOA) is used as the suppressor, but it was found to be ineffective for stripping with the aqueous boric acid solution used in NG-CSSX [2] , requiring the use of a more basic suppressor. Stripping using the lipophilic guanidine DCiTG (Table 1), the active extractant in LIX® 79, as the suppressor in the NGS was found to be two orders of magnitude more effective than stripping in CSSX [2,7] . How DCiTG functions remains incompletely understood, but it is thought that the guanidine ties up all extractable anions and thereby allows the cesium to be driven out of the solvent [12] .…”