EFFECTS OF ACYLATION AND CROSS-LINKING ON THE MATERIAL PROPERTIES ANDCADMIUM ION ADSORPTION CAPACITY OF POROUS CHITOSAN BEADS

Chitosan is a novel glucosamine biopolymer derived from the shells of marine organisms. This biopolymer is very attractive for heavy metal i on separations from wastewater because it is selective for toxic trans ition metal ions over less toxic alkali or alkane earth metal ions. Hi ghly porous, 3-mm chitosan beads were prepared by an aqueous phase-inv ersion technique for casting gel beads followed by freeze drying. In t he attempt to simultaneously improve material properties and adsorptio n capacity, chitosan was chemically modified by 1) homogeneous acylati on of amine groups with nonanoyl chloride before bead casting, and 2) heterogeneous crosslinking of linear chitosan chains with the bifuncti onal reagent glutaric dialdehyde (GA) after bead casting but before fr eeze drying. The random addition of Ca hydrocarbon side chains to abou t 7% of the amine groups on uncrosslinked chitosan beads via N-acylati on improved the saturation adsorption capacity from 169 to 216 mg Cd2/g-bead at saturation (pH 6.5, 25 degrees C) but only slightly reduced solubility in acid solution. Crosslinking of the N-acylated chitosan beads with 0.125 to 2.5 wt% GA in the crosslinking bath increased the internal surface area from 40 to 224 m(2)/g and rendered the beads ins oluble in 1 M acetic acid (pH 2.36). However, crosslinking of the N-ac ylated chitosan beads reduced the saturation adsorption capacity to 13 6 mg Cd2+/g-bead at 0.75 wt% GA and 86 mg Cd2+/g-bead at 2.5 wt% GA. C rosslinking also significantly reduced the compression strength. There was no clear relationship between internal surface area and adsorptio n capacity, suggesting that the adsorbed cadmium was not uniformly loa ded into the bead.