Abstract
Two kinds of crosslinked chitosan derivatives were synthesized by introducing the N-methylene phosphonic acid(=NMPC) and N-2-pyridylmethyl(=PMC) groups to chitosan in order to remove heavy metals from wastewaters. The adsorption of metal ions on NMPC and PMC was dependent on an equilibrium pH of 1 mol dm-3(=M) aqueous ammonium nitrate solution and was shifted to lower pH region compared with crosslinked original chitosan(=CLC). NMPC began to adsorb all metal ions used in this study at pH around 2. Especially, the adsorption of copper(II) showed the maximum value at pH 5-6 and then it decreased in the higher pH region. The adsorption of copper(II) was independent of the ammonium nitrate concentration at pH < 5, however, beyond which it decreased with increasing concentration of ammonium nitrate. While, PMC adsorbed copper(II) and nickel(II) at pH below 2. Cobalt(II), zinc(II) and cadmium(II) that form octahedral-type complexes were adsorbed at pH around 3. This result suggests that PMC has a high selectivity for copper(II) and nickel(II) which form planar-type complexes. It was found that copper(II) was adsorbed on PMC as a chelate complex accompanied by two nitrate anions as the counter-ion.
