Synthesis of porous-magnetic chitosan beads for removal of cadmium ions from waste water

Milled chitosan, average molecular weight 120,000 with 94 per cent deacetylation, was dissolved in 4 per cent acetic acid. Magnetite powder was added and gelled beads produced by precipitation in a bath of 2 M sodium hydroxide. These were cross-linked with 2.5 per cent glutaraldehyde solution over 24 h. Following freeze-drying, beads of diameters 1 and 3 mm were produced. The 1 mm beads, which were insoluble in acid media, had surface areas exceeding 150 m2 per g and mean pore sizes of 560 A. Both metal and hydrogen ions competed for available adsorption sites by a chelation mechanism. Adsorption isotherms at 25C and pH 6.5 in the concentration range of 1-1690 mg cadmium per litre were step-shaped; this was ascribed to pore blockage. Maximal adsorption capacities were 518 and 188 mg cadmium per g of bead for 1 and 3 mm diameter beads, respectively.