Removal of Cr(III) and Cr(VI) ions from aqueous solutions by means of polyelectrolyte-enhanced ultrafiltration

The possibility of applying polyelectrolyte-enhanced ultrafiltration to the removal of chromium ions from aqueous solutions has been discussed. Two water-soluble polyelectrolytes containing weak ion-exchange groups were chosen to bind metal ions and enable chromium retention on ultrafiltration membranes. These were sodium polyacrylate to bind Cr(III) ions and polyethylenimine for Cr(VI) ions. These two forms of chromium ions, Cr(III) and Cr(VI), were tested in separate solutions. The main parameters which determine the effectiveness of chromium retention (the polyelectrolyte quantity and solution pH) were examined. Ultrafiltration concentration of Cr(III) and Cr(VI) solutions (initial concentrations of 5 and 50 mg Cr/dm3) were carried out according to the previously determined polymer : metal concentration ratios, and at optimum pH. The volume reduction factor (VRF) of 50 was obtained. The retention coefficient for chromium observed during the process fell within the range of 0.82–1.