ADSORPTION OF HEAVY-METAL IONS ONTO DITHIZONE-ANCHORED POLY (EGDMA-HEMA) MICROBEADS

The dithizone-anchored poly (EGDMA-HEMA) microbeads were prepared for the removal of heavy metal ions (i.e. cadmium, mercury, chromium and l ead) from aqueous media containing different amounts of these ions (25 -500 ppm) and at different pH values (2.0-8.0). The maximum adsorption s of heavy metal ions onto the dithizone-anchored microbeads from thei r solutions was 18.3, Cd(II); 43.1, Hg(II); 62.2, Cr(III) and 155.2 mg g(-1) for Pb(II). Competition between heavy metal ions (in the case o f adsorption from mixture) yielded adsorption capacities of 9.7, Cd(II ); 28.7, Hg(II); 17.6, Cr(III) and 38.3 mg g(-1) for Pb(II). The same affinity order was observed under non-competitive and competitive adso rption, i.e. Cr(III)> Pb(II)> Hg(II) > Cd(II). The adsorption of heavy metal ions increased with increasing pH and reached a plateaue value at around pH 5.0. Heavy metal ion adsorption from artificial wastewate r was also studied. The adsorption capacities are 4.3, Cd(II); 13.2, H g(II); 7.2, Cr(III) and 16.4 mg g(-1) for Pb(II). Desorption of heavy metal ions was achieved using 0.1 M HNO3. The dithizone-anchored micro beads are suitable for repeated use (for more than five cycles) withou t noticeable loss of capacity. (C) 1998 Elsevier Science B.V. All righ ts reserved.