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

Chitosan is a glucosamine bipolymer capable of adsorbing transition-me tal ions from aqueous solution. Highly porous chitosan beads were prep ared 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- a nd 3-mm diameter were prepared. Beads of 1-mm diameter possessed surfa ce areas exceeding 150 m2/g and mean pore sizes of 560 angstrom and we re insoluble in acid media at pH 2. Well-mixed batch adsorption experi ments revealed that both metal and hydronium ions compete for availabl e adsorption sites by a chelation mechanism. Adsorption isotherms at 2 5-degrees-C and pH 6.5 over the concentration range 1-1690 mg Cd2+/L p ossessed 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 mechani sm.