Active Transport of Heavy Metal Ions through Polymeric Blended Membranes

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[1] Two kinds of polymeric membranes were prepared by blending poly(isobutylene-alt.comaleic anhydride)(ISBN) and polystylene sulfonic acid(PSA) with polyvinylalchol(PVA). Studies were made on the ion-exchange equilibria, permeation and enrichiment separation of sodium, magnesium and nickel ions. Having a trend to swelling in weak acid solution as well as in water, the ISBN/PVA membranes allowed to acetallize; however, the permeation fluxes decreased remarkably as a result of lowering of the ion-exchange capacity. The flux data are inversely proportional to the membrane thickness; then, effective diffusivities of the metal ions in the membrane were evaluated from the permeation rate and ion exchange equilibrium. For the binary ionic solutions, separation factor of heavier metal to sodium ion was also determined from the maximum concentrations under conditions of uphill transport. It was found that the separation factor corresponds to the ratio of each initial flux.[2] Permeation rates … More of metal ions across a cation-exchange membrane, Neosepta CM-1, have been explained from two Models. model-1 includes the three parameters of the equilibrium constant,Kex, self-diffusion coefficients of metal ion and proton, while model-2 does the reaction rate constant at the membrane surface and a modified rate constant within the membrane as well as Kex. The former could be applied only for the permeation of monovalent ions. Thus, it appears that during the ion permeation the interface between the aqueous and membrane phases is not in equilibrium: non-equilibrium process.[3] To develop the membrane preferential to ethanol permeation, plasma polymerization of siloxanes was taken place on a porous polypropylene substrate membrane (Duragard 2500)in a reactor as well as the plasma surface-treatment of silicone casting membranes. The membrane perm-selectivity was examined in terms of the separation factor of ethanol to water and the permeation flux in pervaporation experiments under reduced pressure. The maximum separation factor is found to be about 10 for a casting membrane similar to silicone rubbers; however, the plasma polymerization of hexamethyldisiloxane brought about lower selectivity but higher flux of ethanol. Presently more preferential membranes are being developed to apply for pervaporation processes. Less