Role of pH in metal adsorption from aqueous solutions containing chelatingagents on chitosan

The role of pH in adsorption of Cu(II) from aqueous solutions containing ch elating agents on chitosan was emphasized. Four chelating agents including ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, and sod ium gluconate were used. It was shown that the adsorption ability of Cu(II) on chitosan from its chelated solutions varied significantly with pH varia tions. The competition between coordination of Cu(II) with unprotonated chi tosan and electrostatic interaction of the Cu(II) chelates with protonated chitosan took place because of the change in solution pH during adsorption. The maximum adsorption capacity was obtained within each optimal pH range determined from titration curves of the chelated solutions. Coordination of Cu(II) with the unprotonated chitosan was found to dominate at pH below su ch an optimal pH value.