Evaluation of a supported liquid membrane containing a macrocyclic ionophore for selective removal of strontium from nuclear waste solution

Transport behaviour of Sr(II) across a PTFE flat sheet supported liquid membrane (SLM) containing 4,4′(5′)di-t-butyl-cyclohexano-18-crown-6 (DtBuCH18C6) in 1-octanol as the carrier was investigated. The membrane based separation method was developed for the selective transport of Sr2+ from aqueous nitrate medium. Linear dependence of the permeability coefficient (P) on the crown ether concentration suggested that the ligand does not aggregate in the concentration range investigated. The P values increased with HNO3 concentration as well as with nitrate ion concentration. However, in the presence of 2 M Al(NO3)3 in the feed phase, any increase in the HNO3 concentration showed a decrease in the Sr(II) transport rate. Appreciable acid co-transport was observed in all the experiments which was attributed to the ligand assisted transport of the hydronium ion. A decrease in the transport rate was observed with increase in the membrane pore size. The transport rate was low as only ∼70% migration of Sr2+ was observed in 24 h. The mechanism of transport has been discussed. A synthetic nuclear waste solution spiked with 85,89Sr tracer containing 1 M nitric acid has also been tested. The selectivity of the crown ether containing membrane is demonstrated as none of the other metal ions present in the synthetic nuclear waste solution could permeate through the PTFE membrane filter.