Removal characteristics of metal cations and their mixtures using micellar-enhanced ultrafiltration

Divalent ions were removed by ultrafiltration of anionic surfactant solution and the removal characteristics in single and mixed systems were investigated. The removal efficiency was >95% when the ratio of sodium dodecyl sulfate (SDS) to metal ions (S/M ratio) was >10. In single metal systems, the removal efficiency of each metal ion was almost the same. In the mixture, however, there was slight difference (ca. 1-2%) of removal efficiency and the order was Cd²⁺>Cu²⁺>Co²⁺≈ Zn²⁺. As S/M ratio increased, the difference in removal efficiency diminished. To explain the difference of removal efficiency in a mixture, complexation of divalent metal ion with counterion was considered. The distribution of complexed form of each metal ion was calculated, but it did not coincide with the experimental results. Further research will be necessary for a clear explanation.