ADSORPTION OF ACID DYE ON CROSS-LINKED CHITOSAN FIBERS - EQUILIBRIA

Two different cross-linked chitosan fibers (ChF-A and ChF-B) were developed for use as adsorbents or ion exchangers for the recovery of dyestuffs. The concentration of amino group in the adsorbent phase was 3 to 5 times larger than that of the commercial weak-base ion exchangers and decreased with increasing degree of cross-linking. For pH = 6.9, the experimental equilibrium isotherms for adsorption of Acid Orange II (acid dye) were correlated by the BET equation for a finite number of layers. The maximum amounts of the dye adsorbed on ChF (original non-cross-linked chitosan fiber), ChF-A, and ChF-B were about 10, 6, and 3.2 mol/kg, respectively, for initial liquid-phase concentration of the dye C0 = 1 mol/m3 and 298 K. These values are much larger than the corresponding values for activated carbon fiber. The amount of the dye adsorbed increased with increase in C0 and decreased with increasing temperature. The presence of an inorganic salt also increased the amount of the dye adsorbed. For pH less-than-or-equal-to 4, the selectivity of adsorption of the dye was extremely high and the isotherm was almost rectangular. The saturation capacities of the dye on ChF-A and ChF-B in pH less-than-or-equal-to 4 were 4,8 and 3.5 mol/kg, respectively, almost the same as the concentrations of the amino group in the solid phase of ChF-A and ChF-B, respectively.