Chromium(VI) removal from aqueous solutions by polyelectrolyte-enhanced ultrafiltration with polyquaternium

Polyelectrolyte-enhanced ultrafiltration was investigated for the removal of chromium(VI) anion from aqueous solutions with the help of cationic polyquaternium-6 (PQ6). The ultrafiltration behavior of Cr(VI) aqueous solutions was studied at pH 6. Owing to an effect of electrostatic repulsion, the membrane with a molecular weight cutoff (MWCO) of 10 000 Da rejected about 30% of Cr(VI). Then, ultrafiltration of aqueous solutions of a Cr(VI)–PQ6 complex was further studied. Factors affecting Cr(VI) rejection coefficient ( R Cr ) and permeate flux ( J ) such as pH, polymer metal ratio (PMR), the added salts, temperature, operating pressure and MWCO were investigated. The best operating parameters, such as pH 9 and PMR 10, were obtained in order to achieve high R Cr (>0.97). By increasing the concentrations of the added salts (KCl, KNO 3 and K 2 SO 4 ), R Cr was found to decrease significantly. J decreases slightly in the pH range of 2–5. Cl − or SO 4 2− does not affect J , whereas NO 3 − results in the decrease of J . The binding mechanisms of dichromate, chromate and nitrate with PQ6 were proposed. Finally, the concentration experiment was carried out under the optimal conditions. R Cr was close to 1, and J decreases slightly. Chromium was effectively concentrated by the membrane. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.