REUSABILITY OF CHITOSAN AND SAWDUST-MODIFIED CHITOSAN FOR ADSORPTION/DESORPTION OF ANIONIC AND CATIONIC DYES

We explored the multiple uses of chitosan in the form of beads and beech sawdust immobilised in chitosan to remove anionic (Reactive Yellow 85 and Reactive Blue 5) and cationic (Basic Violet 10 and Basic Green 4) dyes. For both anionic dyes, with the next adsorption/desorption cycle, the amount of dye accumulated in the adsorbent increased, which resulted in a decrease in the desorption efficiency. The number of possible adsorption/desorption cycles was regulated by the occupation of all active sites. We observed the opposite trend for the cationic dyes: the charge accumulated in the adsorbent after both adsorption and desorption decreased with subsequent cycles. Despite the low accumulated charge compared with the total adsorption capacity of the adsorbents, it was impossible to further adsorb and desorb the dye. The results demonstrated that for both adsorbents tested, it was possible to carry out 6–7 adsorption/desorption cycles, but the desorption efficiency decreased with each cycle.