Micellar–enhanced ultrafiltration of chromate [Cr(VI)] ion from aqueous streams by using cationic surfactant

Hexavalent chromium [Cr(VI)] in industrial effluent is one of the most serious environmental problems in India and also in other countries. Micellar-Enhanced Ultrafiltration (MEUF) of the chromate anions from aqueous solutions has been studied at room temperature (28±2°C) using cationic surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), micelles of which adsorb the chromate ions by electrostatic interactions. The solution is processed by ultrafiltration, using a membrane with a pore size small enough to block the passage of the micelles and the adsorbed ions. The process is highly efficient in removing the chromate ions. In the absence of other electrolytes, chromate ion rejection up to 99% was observed at optimal conditions of pH, pressure, temperature, feed chromate and surfactant concentrations. The presence of added NaCl reduces the chromate rejection, but it was still considerable (up to 82%), even in the presence of 100 mM NaCl. The rejection rate of chromate was found to be highly dependent on the pH of the feed solution. The solute rejection is also affected by anion charge density, and interaction of fixed membrane charge sites with ionic solutes.