Removal of zinc ions from aqueous solution using micellar-enhanced ultrafiltration at low surfactant concentrations

Abstract

Micellar-enhanced ultrafiltration (MEUF) of zinc ions (Zn 2+) from aqueous solutions using single anionic surfactant sodium dodecyl sulphate (SDS) at low critical micelle concentrations (cmc) (0.2×cmc – 3×cmc) was investigated. When the initial SDS concentration was below the cmc, unexpectedly high rejection (97.5%) was obtained due to concentration polarisation occurring near the membrane-solution interface. Based on this mechanism, the true rejection of the solute is no longer a function of the initial SDS concentration in the bulk solution but a function of the SDS concentration at the concentration polarisa tion layer. The removal of Zn 2+ at low Zn2+ feed concentrations was very efficient. The characteristics of Zn 2+ ion adsorption to surfactant micelle were also studied. The Langmuir model could be used to elucidate the Zn 2+ adsorption isotherm to the SDS micelle. The study demonstrates the potential practicality of the MEUF technique for the removal of heavy metal ion pollutants such as Zn 2+ at low surfactant concentrations.

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