Evaluation of a calix[4]-bis-crown-6 ionophore-based supported liquid membrane system for selective 137Cs transport from acidic solutions

Facilitated transport of Cs(I) from aqueous nitrate feed solutions to a receiver solution containing distilled water through a supported liquid membrane (SLM) containing calix[4]-bis-2,3-naphtho-crown-6 (CNC) in 0.45 μm PTFE (polytetrafluoroethylene) membranes was investigated. The carrier solution usually consisted of CNC dissolved in a mixture of 80% 2-nitrophenyl octyl ether and 20% n-dodecane. The transport rates were found to be influenced by the mobile carrier concentration, cesium concentration as well as the feed acidity. The extracted species conformed to a stoichiometry of 1:1 metal to ligand ratio suggesting the extraction of an organophilic mono-Cs-crown complex. Fission products obtained from an irradiated natural uranium target were found to be poorly transported while Cs-137 got significantly transported suggesting the possible application of the separation method for the removal of bulk Cs-137 from radioactive waste solutions. Durability/chemical stability of the membrane was remarkably good when tested over 20 days of continuous operation.