Abstract: The transport behavior of Ag⁺, Cu⁺⁺ and Zn⁺⁺ across supported liquid membrane using dithio-18-crown-6 (DT18C6) and dicyclohexano-18-crown-6 (DC18C6) in chloroform, has been investigated. Phase distribution studies show that selectivity of the interface is much higher when the metal cation is inserted deeper in the polyether cavity. Ag⁺ specie are more adaptable to the cavities of DT18C6 and DC18C6 than are Cu⁺⁺ and Zn⁺⁺. Transport studies showed that fluxes obtained with DT18C6 were slightly lower than those of DC18C6 for all three ions studied. Use of different solid supports revealed that fluxes increase with increasing porosity of the support but decrease with increasing thickness. Differences in molar flow rates (F) at feed and strip membrane interfaces were observed, due to the reason that decomplexation rate at the strip side is slower than complexation rate at the feed side. The magnititude of separation factor (SF=2.51) showed that Ag⁺ could very well be separated from Cu⁺⁺ and Zn⁺⁺ using DC18C6/chloroform membrane. The feasibility of preconcentration of Ag⁺ was also studied by using the hollow fiber module system. Highest enrichment factor (EF) was obtained for 40 mg/L whereby all the metal ions were transported to the stripping phase and resulting Ag+ concentration was 490 mg/L (EF=12.3).

Keywords: SLM, crown ethers, enrichment factors, separation factors.