SYNTHESIS OF POROUS-MAGNETIC CHITOSAN BEADS FOR REMOVAL OF CADMIUM IONS FROM WASTE-WATER

Chitosan is a glucosamine bipolymer capable of adsorbing transition-metal ions from aqueous solution. Highly porous chitosan beads were prepared by dropwise addition of an acidic chitosan solution into a sodium hydroxide solution precipitation bath. The gelled chitosan beads were cross-linked with glutaraldehyde and then freeze dried. Beads of 1- and 3-mm diameter were prepared. Beads of 1-mm diameter possessed surface areas exceeding 150 m2/g and mean pore sizes of 560 angstrom and were insoluble in acid media at pH 2. Well-mixed batch adsorption experiments revealed that both metal and hydronium ions compete for available adsorption sites by a chelation mechanism. Adsorption isotherms at 25-degrees-C and pH 6.5 over the concentration range 1-1690 mg Cd2+/L possessed a stepped shape and maximum adsorption capacities for the 1- and 3-mm beads were 518 and 188 mg of Cd/g of bead, respectively. The stepped shape of the isotherm was explained by a pore-blockage mechanism.