Selective removal of cesium from model nuclear waste solutions using a solid membrane composed of an unsymmetrical calix[4]arenebiscrown-6 bonded to an immobilized polysiloxane backbone

The extraction of the two long lived isotopes of cesium (135Cs and 137Cs) is an important issue because of the specific mobility of 135cesium from nuclear disposals. The selective removal of the latter from high active waste allows its destruction by transmutation or disposal in specific matrixes. Calix[4]biscrown-6 blocked in a 1,3-alternate cone conformation, extracts more cesium than sodium, with a high efficiency and selectivity from simulated acidic and high sodium content liquid wastes. In order to reduce the possible loss of the calixarene into the aqueous phases in supported liquid membranes (SLM) and answer, in a further stage, to a practical clean fixed-site carrier membrane separation process, an unsymmetrical calix[4]arenebiscrown-6 containing two different crown loops were synthesized for this specific purpose and grafted by a sol–gel process onto a polysiloxane backbone. Solid–liquid extraction was carried out with crushed powders and the results were compared to liquid–liquid extraction using a soluble analogous of the complexing site. The decrease of performances, efficiency and selectivity, can be explained in terms of steric hindrance, cavity deformation and micro-environment polarity due to the grafting of the carrier. Removal of cesium from acidic and high sodium content liquid waste by facilitated diffusion process was performed with membranes containing bonded. Again, the selectivity was strongly reduced compared to solid–liquid extraction. A mechanism of transport for cesium was proposed in which the step of stripping in the receiving phase is the limiting factor.