ADSORPTION BEHAVIORS OF SOME METAL-IONS O N CHITOSAN MODIFIED WITH EDTA-TYPE LIGAND

Ethylenediaminetetraacetic acid-type chitosan (EDTA-type chitosan) was synthesized to examine its adsorption behavior for several base metal ions as well as a series of rare earth metals from dilute sulfuric ac id solution. The EDTA type functional group was incorporated onto chit osan nearly quantitatively. Unlike adsorption with original chitosan, that with EDTA-type chitosan takes place at a lower pH than that with diethylenetriamine-pentaacetic acid-type chitosan (DTPA-type chitosan) ; for example, copper(II)was adsorped at pH=0 on EDTA-type chitosan bu t at pH=4 on original chitosan. The selectivity series for the adsorpt ion of base metals was as follows: Cu2+ similar or equal to MoO22+ > N i2+ > VO2+ > Zn2+ greater than or equal to Co2+ > Al3+ The plots of th e distribution ratio of trivalent rare earths against pH lie on straig ht lines with a slope of 3, suggesting that adsorption takes place by a cation-exchange mechanism. The apparent equilibrium constants for ad sorption on EDTA-type chitosan were evaluated as well as those on DTPA -type chitosan. The sequence of the apparent equilibrium constants wit h a series of rare earths was roughly consistent with that of the stab ility constants in the case of EDTA-type chitosan as well as with DTPA -type chitosan. Consequently, EDTA and DTPA are still functional after immobilization on chitosan. The EDTA-type chitosan seems to exhibit p romise for the mutual separation of adjacent rare earths except for mi ddle rare earths.