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

摘要

New membranes with complexing abilities were obtained by grafting titanate coupling agents bearing ethylenediamine groups (EDA, strong chelating ligand towards Cu(2+)) or pyrophosphate groups (PP, weak chelating lignad towards Cu~(2+) and Zn~(2+)) on inorgnaic nanofiltration membranes. The retention of 10 mmol l~(-1) chloride solutions of Cu~(2+) and Zn~(2+) by the unmodified NF membrane (no complex formation0 and the PP grafted membrane (formation of weak complex) was about 50% which is roughly the retention of Ca~(2+) (no complex formation) with the EDA grafted membrane. Complex formation with the PP grafted membrane does not appear strong enough to enhance Zn~(2+) and Cu~(2+) retention. The retention of Cu~(2+) was enhanced up to 80-90% with the EDA grafted membrane, due to the occurrede of formation of a strong complex with EDA groups. Contrary to resin process where a breakthrough curve is expected, a steady-state of Cu~(2+) retention was observed, whereas Cu~(2+) in the feed solution was about 50 times the membrane capacity to bind the metal cation.