Adsorptive separation of some metal ions by complexing agent types of chemically modified chitosan

Two kinds of chemically modified chitosan immobilizing the ligands of ethyl enediamine-N,N, N',N'-tetraacetic acid (EDTA) or diethylenetriamine-N,N,N', N',Ni "- pentaacetic acid (DTPA) onto polymer matrices of chitosan (EDTA- a nd DTPA-chitosan) were prepared by interacting the anhydrides of these comp lexing agents with chitosan. By incorporating these ligands, the adsorption of metal ions are much enhanced compared with original chitosan. For examp le, adsorption of Cu(II) takes place at pH=0-1 on these chemically modified chitosan, while it takes place at pH= 4-6 on original chitosan. The observ ed order of selectivity for some metal ions are nearly the same for both of EDTA- and DTPA-chitosan in the adsorption from sulfuric acid solution: Ga( In)=In(III)=Fe(III)>Cu(II)=Mo(VI)>Ni(II)>V(IV)>>Zn(II)=Co(II)>>Al(III)>>Mn( II). This is nearly the same as the order of the stability of these metal c helates with these complexing agents, suggesting that the chelating ability of these ligands is still maintained after immobilizing these on polymer m atrices of chitosan. Based on these basic data obtained in batchwise experi ments, breakthrough and elution tests were carried out using a column packe d with the EDTA- or DTPA-chitosan together with glass beads for some pairs of metal ions: e.g. same dilute concentrations of Co(II) and Ni(II) as well as small amounts of Co(II) together with a large excess of AI(III). These tests demonstrated that very clear-cut mutual separations between these pai rs of metal ions can be successfully achieved by these complexing agent typ es of chemically modified chitosan. (C) 1999 Elsevier Science B.V. All righ ts reserved.