Crossflow Surfactant-Based Ultrafiltration of Heavy Metals from Waste Streams

Five heavy metals (cadmium, lead, copper, nickel, and zinc) in a simulated wastewater, alone and together, were substantially removed by surfactant-based ultrafiltration using natural surfactants such as a derivative of cholesterol (deoxycholic acid) and lecithins. Selective and total removal of metal ions has been achieved by applying an appropriate level of surfactant-to-metal ratio (S/M). The underlying principle is to increase the size of the target metal ions by fixing them to larger surfactant macromolecules so they can be retained by a compatible membrane. Deoxycholic acid exhibited more efficiency in metal removal than did lecithin and sodium dodecyl sulfate. This research showed that transmembrane pressure had a minimal effect on metal removal whereas S/M had a substantial influence. The optimal S/M for considerable metal removal (99.9 + rejection ratio) is around 2.5 and 5 for deoxycholic acid and sodium dodecyl sulfate, respectively. The binding of metals to surfactant in the absence of membrane interferences was also determined by a centrifuge method.