Metallic ion extraction using polymer inclusion membranes (PIMs): Optimising physical strength and extraction rate

This study investigated both extraction performance and physical properties of a novel type of facilitated transport membrane known as polymer inclusion membrane (PIM). Five different types of poly(vinyl chloride) representing a wide range of viscosity and average molecular weights were used as the base polymer and Aliquat 336 was used as the carrier. Physical properties including membrane hydrophobicity and tensile strength were measured and systematically correlated against the fraction of PVC and Aliquat 336 in the PIMs. Selective extraction between Cd(II) and Cu(II) of the membranes from aqueous solution was then investigated. Results reported in this study indicate that tensile testing can be excellent tool to tune the membrane composition for an optimised mechanical strength. Membranes synthesized in this study showed excellent extraction selectivity between Cd(II) and Cu(II). This could be explained by examining the extraction mechanisms of metal cations involving Aliquat 336 and the speciation of Such metals in a chloride matrix which was used in the extraction experiments. Results reported here indicate that physical properties of PIMs are primarily governed by types and composition of the base polymer. In addition, the optimum composition for physical strength does not necessarily result in the best extraction capability. There is a significant scope to fine tune both the extraction rate and physical properties for an optimum PIM performance.