Selective Cd-Ni separation from aqueous solution by polymer in membrane systems

Polymer enhanced ultrafiltration (PEUF) is a comprising method for selective separation of ions using the membrane technology. A laboratory scale ultrafiltration set was used to study the separation of heavy metal ions i.e. cadmium from nickel in aqueous solutions. Polyethylenimine was used as the water soluble complexation agent. Experimental data collected from the retentate stream was analyzed to assess the ability of polymer to bind with the metal ion. While the retentate consists of polymer bound to the metal ions and those rejected from the membrane surface, the permeate stream gives the free metal ions passing through the ultrafiltration membrane which had a molecular weight cut off of 3000 Da. The mechanism of polymer and that of metal ion binding and the ultrafiltration setting, dictates the success of the removal process. The effect of pH, temperature, polymer dosage on the retention of cadmium ions was determined. Three different metal ions to polymer ratios (L) were used to determine the optimum conditions on a 3D graphics in order to represent a wide range of pH and temperature that gives the highest cadmium retention in the permeate. Preliminary experiments on nickel ion revealed that every metal ion has a unique pH range over which it binds to polyethylenimine. A mixture of Cd and Ni prepared for membrane test runs indicates that a pH value of 4.2 at a temperature range of 20-22°C resulted in an enrichment coefficient of up to 10.