Adsorption of Metal Ions on Chitosan and Crosslinked Copper(II)-Complexed Chitosan

Abstract

A fundamental investigation on the adsorption behavior of metal ions on chitosan from aqueous ammonium nitrate and hydrochloric acid solutions was conducted by batch-wise examining the effects by various factors: the pH, concentrations of ammonium nitrate and hydrochloric acid, and initial metal concentration on the amount of metals adsorbed. In order to prevent the dissolution loss of chitosan into an acidic aqueous solution, crosslinked copper(II)-complexed chitosan was prepared and its adsorption behavior was compared with that of the original chitosan. The amount of adsorption, not only of metal ions, but also of the hydrogen ion, was decreased by crosslinking in the adsorption from an ammonium nitrate solution. The decrease, however, was least for copper(II), compared with the other divalent metal ions examined: oxovanadium(II), zinc(II), nickel(II), and cobalt(II). It was considered that this result may be attributable to the “template” effect by the copper(II) ion, which was employed during crosslinking in order to protect the active adsorption site of chitosan from an attack by a crosslinking reagent. It was found that chitosan has an excellent loading capacity and a selectivity much greater than the commercial iminodiacetic acid type of chelating resin. A qualitative discussion is given concerning the excellent adsorption behavior. Contrary to the case of adsorption from an aqueous ammonium nitrate solution, no significant decreases in the distribution ratios were observed between the crosslinked copper(II)-complexed chitosan and the original chitosan regarding the adsorption of palladium(II) and platinum(IV) from hydrochloric acid.