Adsorption Equilibria of Cu²⁺, Zn²⁺, and Cd²⁺ on EDTA-Functionalized Silica Spheres

Abstract

Ethylenediaminetetraacetic acid (EDTA) functionalized silica spheres were used to remove metal ions from aqueous solutions. The adsorption kinetics of Cu2+, Zn2+, and Cd2+ (60 mg·L–1, pH 5.5) were fitted to the pseudosecond order model. Adsorption equilibria were reached within 20 min, indicating that chemisorption may be the limiting step in the adsorption process. Adsorption isotherms were analyzed with nonlinear models by considering the ERRSQ error function and the determination coefficient R2. The data with monoion solutions (10 mg·L–1 to 300 mg·L–1) were tested with Langmuir, Freundlich, and Redlich–Peterson isotherm models. The best fit was found with the Langmuir model, and maximum adsorption capacities followed the order: Cu2+ > Zn2+ > Cd2+. Breakthrough curves were obtained using filled columns. The adsorbed ions were quantitatively recovered on elution with hydrogen chloride (0.10 M). After three adsorption–recovery cycles, the metal ions could still be recovered almost quantitatively, which demonstrates the good performance of the EDTA-functionalized silica spheres.