Preparation and characterization of a series of ion-exchange membranes for the purpose of separation and extraction of some heavy and toxic metal ions from their wastes were studied. Such ion-exchange membranes were prepared by ␥-radiation grafting of acrylonitrile (AN) and vinyl acetate (VAc) in a binary monomer mixture onto low-density polyethylene (LDPE) using the direct technique of grafting. The reaction conditions at which the grafting process proceeds successfully were determined. Many modification treatments were attempted for the prepared membranes to improve their ion-exchange properties. The possibility of their practical use in waste-water treatment to remove some heavy and toxic metal ions such as Pb 2ϩ , Cd 2ϩ , Cu 2ϩ , Fe 3ϩ , Sr 2ϩ , and Li ϩ were investigated. These grafted membranes showed great promise for possible use in the field of extraction and removal of some heavy and toxic metals from their wastes.
SynopsisCationic membranes were prepared by direct radiation grafting of methacrylic acid (MAA) onto poly(tetrafluoroethy1ene) (PTFE) f i l m s followed by alkaline treatment to confer ionic character in the graft copolymer. The complete inhibition of homopolymerization of MAA by using ammonium feqeous sulfate (Mohr's salt) failed. However, the addition of 0.5 w t ' % FeC1, to the monomer solution effectively inhibited the homopolymerization process and higher grafting yield was obtained. I t was found that the graft polymerization proceeded successfully in presence of methanol/water mixture (30/70 w t %), and much higher degrees of grafting were obtained as compared with those in the presence of other diluents used here. The influence of irradiation atmosphere (air, N, gas, and vacuum) on the grafting process was investigated. The dependence of the grafting rate on MAA concentration was found to be of orders 2.9 and 0.72 in the presence of 0.5 wt % Mohr's salt or 0.5 wt 5 % FeCl,, respectively. This grafting system proceeds by the front mechanism. Investigation of mechanical properties, electrical conductivity, and swelling behavior of the grafted films revealed that such a copolymer could be acceptable in practical use as a cation-exchange membrane.
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