Effects of competing cations on cadmium biosorption by chitin

In natural aqueous systems several metallic ions will be present, and a selective uptake of these ions by chitin surface groups can be expected. In order to investigate this phenomenon, the effect of co-ions Cu2+ and Zn2+ on the cadmium biosorption kinetic and equilibrium on chitin was examined, at free solution pH and 25 °C, in static conditions. All experimental cadmium biosorption rate curves exhibited common characteristics. The apparent equilibrium biosorption was reached within the 6 h of contact. All determined biosorption isotherms exhibited a similar shape resembling that of Langmuir type isotherm of gas adsorption. The biosorption of individual metals followed the sequence Cu>Cd>Zn. While, Zn2+ ions had any appreciate effect on the cadmium uptake capacity of chitin under the conditions examined, the presence of Cu2+ ions alter the affinity of chitin for cadmium: the uptake of Cd decreased.