Use of polyelectrolyte-enhanced ultrafiltration to remove chromate from water

Polyelectrolyte-enhanced ultrafiltration (PEUF) is a process which can be used to remove multivalent ions from water. In PEUF a polyelectrolyte of opposite charge to the target ion is added to the water to bind the ion to be removed. The solution is then treated using ultrafiltration with membrane pore sizes small enough to reject the polymer and bound ion. In this study, chromate (CrO42-) is removed from water using poly(diallyldimethyl ammonium chloride) with an average molecular weight of 240K as the polyelectrolyte. In the absence of other added electrolytes, chromate rejections of up to 99.8% were observed. The presence of added NaCl reduces the chromate rejection substantially. A study of the flux of the system yielded a gel concentration of 0.55 M cationic polyelectrolyte. This high gel concentration and high rejection mean that the ultrafiltration can produce a concentrated, low-volume waste stream, and a purified stream containing chromate at low concentration.