ENHANCEMENT OF METAL-ION SORPTION PERFORMANCES OF CHITOSAN - EFFECT OF THE STRUCTURE ON THE DIFFUSION PROPERTIES

Chitosan is a well-known sorbent of biological diluted effluents. Upta ke capacities and sorption rates are restricted by diffusion mechanism s. A grafting of specific functional groups onto a chitosan backbone a llows sorption performances to be improved due to the appearance of ne w sorbing functions and by an improvement in diffusion properties. Sca nning electron microscopy coupled with an X-ray energy dispersed analy sis demonstrates that an uranium concentration gradient exists in the chitosan. polymer but disappears in the glutamate glucan polymer. Chit osan displays a surface controlled sorption mechanism, unlike glutamat e glucan in which sorption occurs in the mass of the polymer. Microcry stalline chitosan produced for the sorption of uranyl ions shows diffu sion constants comparable to those obtained with glutamate glucan by a pplication of two single models of intraparticular diffusion. This sim ple technique of modification of the structure of the chitosan allows the uptake capacity and sorption kinetics to be increased. Recrystalli zation causes chitosan to behave in a way intermediate between raw and substituted forms of chitosan.