Selective transport of radio-cesium by supported liquid membranes containing calix[4]crown-6 ligands as the mobile carrier

Facilitated transport of Cs-137 across supported liquid membranes (SLM) containing a calix-crown ligand viz. calix[4]arene-bis(crown-6) (CC), calix[4]arene-bis(o-benzocrown-6) (CBC) or calix[4]arene-bis(napthocrown-6) (CNC) was investigated. The feed consisted of dilute nitric acid solutions while the carrier solutions contained mainly CNC in several organic diluents inside the pores of polypropylene (PP) as well as PTFE flat sheet membranes. PTFE membranes containing CNC in a diluent mixture of 2-nitrophenyloctyl ether (NPOE) and n-dodecane were found to have high stability. Selectivity studies were carried out using simulated high level waste (SHLW) as well as fission products obtained from an irradiated natural uranium target.

The transport experiments have indicated that the Cs(I) transport rates decrease in the order of diluents: MIBK > DCE > NB > octanol which is not exactly the order of their extraction efficiencies. Addition of Alamine 336 to modify the carrier solvent can help effective stripping of the metal ion and hence reasonably high transport rates even with NB as the diluent. NPOE, by far gives the best transport behaviour as the carrier diluent with a possibility to quantitatively transfer Cs from the feed phase to the receiver phase. PTFE membranes show good mechanical stability and comparable transport behaviour with the PP flat sheets. Cs can be transported selectively from a SHLW solution though the flux is much lower as compared to those expected from pure HNO3.