Retention of heavy metal ions with nanofiltration inorganic membranes by grafting chelating groups

New membranes with complexing abilities were obtained by grafting titanate coupling agents bearing ethylenediamine groups (EDA, strong chelating ligand towards Cu2+) or pyrophosphate groups (PP, weak chelating ligand towards Cu2+ and Zn2+) on inorganic nanofiltration membranes. The retention of 10 mmol l(-1) chloride solutions of Cu2+ and Zn2+ by the unmodified NF membrane (no complex formation) and the PP grafted membrane (formation of weak complex) was about 50% which is roughly the retention of Ca2+ (no complex formation) with the EDA grafted membrane. Complex formation with the PP grafted membrane does not appear strong enough to enhance Zn2+ and Cu2+ retention. The retention of Cu2+ was enhanced up to 80-90% with the EDA grafted membrane, due to the occurrence of formation of a strong complex with EDA groups. Contrary to resin process where a breakthrough curve is expected, a steady-state of Cu2+ retention was observed, whereas Cu2+ in the feed solution was about 50 times the membrane capacity to bind the metal cation. (C) 2001 Elsevier Science B.V. All rights reserved.