Separation and removal of metal ions from dilute solutions using micellar-enhanced ultrafiltration

The removal of single metal ions including Cs⁺, Sr²⁺, Mn²⁺, Co²⁺, Cu²⁺, Zn²⁺, and Cr³⁺ from aqueous solutions (up to 200mg/l) by ultrafiltration (UF) with the help of an anionic surfactant sodium dodecyl sulfate (SDS) was investigated. Experiments were performed as a function of the membrane MWCO (1000-8000) and material (polyamide, polyethersulfone), solution pH (2-12), and molar concentration ratio of the surfactant to metals (the S/M ratio, 0.5-27). It was shown that complete removal of metal ions, except for monovalent Cs⁺, could be achieved as long as the SDS micelles were formed. The effects of added electrolyte NaCl and the transmembrane pressure (TMP) on metal rejection were also examined. The potential of this UF process for the separation of binary metals involving Sr²⁺ or Cr³⁺ was particularly demonstrated using a low-MWCO membrane (1000) and at a relatively low S/M ratio (<5-10). The recovery and reuse of surfactant from the retentate was finally studied.