Preparation of chelating membranes to remove metal cations from aqueous solutions

The purpose of the present work is to prepare membranes with specific chelating properties for the removal of metal ions. The semi-interpenetrating polymer network technique was used to prepare tailor-made membranes from blends of poly(vinyl alcohol) with two polyelectrolytes, one with carboxylic groups (poly(acrylic acid)) and one with amine groups poly(ethyleneimine). The 60/40 poly(vinyl alcohol)/polyelectrolyte mass ratio was selected to obtain homogenous membranes with suitable mechanical properties. Gaseous 1,2-dibromoethane, glutaraldehyde and hydrochloric acid were tested as crosslinking agents. A crosslinked poly(vinyl alcohol) membrane was also tested as a reference. The membrane crosslinking was monitored by infrared spectroscopy and swelling measurements. The performances of the membranes were evaluated for the removal of copper (II), cadmium (II), lead (II) and chromium (III) in static experiments. The metal ion absorption efficiency f of the membrane (in %) was calculated from: 100 x [(amount of ions retained by the membrane (mole)]/[(amount of monomer repeat units in the membrane (mole)]. The complexation of Cr(III) was the most efficient at pH = 5 with the poly(vinyl alcohol)/poly(acrylic acid) membrane crosslinked by glutaraldehyde (f = 4.9%). The removal of Cu(II), Cd(II) and Pb(II) was more efficient at pH = 5 with the poly(vinyl alcohol) / poly(ethyleneimine) membrane crosslinked by gaseous 1,2-dibromoethane (f = 5.3, 4.5 and 3.7% respectively). Finally, dynamic experiments were performed in order to simulate the treatment of aqueous solutions. Dynamic experiments at pH = 5 were performed on the DBE-crosslinked PVA/PEI membrane either by flow through a membrane-packed column or by filtration. Using a membrane-packed column, the best result was observed for Cu(II) removal with 40.8% of metal ion uptake, but the system was limited by its high dead volume. With filtration, the best result was observed for Pb(II) removal: the metal ion uptake was 70.0% at the end of the sorption step.