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

Abstract

Micellar-enhanced ultrafiltration (MEUF) of zinc ions (Zn2+) from aqueous solutions using single anionic surfactant sodium dodecyl sulphate (SDS) at low critical micelle concentrations (cmc) (0.2xcmc - 3xcmc) 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 polarisation layer. The removal of Zn2+ at low Zn 2+ feed concentrations was very efficient. The characteristics of Zn2+ ion adsorption to surfactant micelle were also studied. The Langmuir model could be used to elucidate the Zn2+ 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 Zn2+ at low surfactant concentrations.