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

Two kinds of chemically modified chitosan immobilizing the ligands of ethylenediamine- N, N, N′, N′-tetraacetic acid (EDTA) or diethylenetriamine- N, N, N′, N″, Ni″- pentaacetic acid (DTPA) onto polymer matrices of chitosan (EDTA– and DTPA–chitosan) were prepared by interacting the anhydrides of these complexing agents with chitosan. By incorporating these ligands, the adsorption of metal ions are much enhanced compared with original chitosan. For example, 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 observed 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(III)=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 chelates with these complexing agents, suggesting that the chelating ability of these ligands is still maintained after immobilizing these on polymer matrices of chitosan. Based on these basic data obtained in batchwise experiments, breakthrough and elution tests were carried out using a column packed 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 Al(III). These tests demonstrated that very clear-cut mutual separations between these pairs of metal ions can be successfully achieved by these complexing agent types of chemically modified chitosan.