Removal of Arsenic Anions from Water Using Polyelectrolyte‐Enhanced Ultrafiltration

Abstract

Polyelectrolyte‐enhanced ultrafiltration (PEUF), using cationic poly(diallyldimethyl ammonium chloride) polyelectrolyte, was used to investigate the removal of arsenic(V) from dilute aqueous solutions. In PEUF a water‐soluble polyelectrolyte of opposite charge to that of the target ion binds the charged arsenate complex. The solution is then treated by ultrafiltration with membrane pore sizes small enough to block the polymer. Only the residual unbound arsenate at the concentration in the retentate (solution not passing through membrane) is present in the permeate solution passing through the membrane. Arsenic rejections as high as 99.95% are obtained and increase with increasing polymer concentration and decrease with increasing ionic strength (added salt concentration). Arsenic rejection increases with increasing pH (pH of 6.5–8.5) as the HAsO4 2−/H2AsO4 − ratio in solution increases, improving arsenate binding to the polymer. Gel point concentration (polymer concentration at which flux becomes zero) was found to be 655–665 mM (approximately 5.98–6.07 wt%), consistent with previous PEUF studies. These high gel points mean that high water recoveries (>99%) are achievable in this separation process.