Direct evidence for two interaction modes in adsorption of divalent metal ions to iminodiacetate-type chelating resins.

The adsorption curves of divalent metal ions (M2+) to an iminodiacetate(IDA)-type chelating resin (-L2-) under the condition of metal ions in excess against IDA groups clearly indicated the difference in contribution between two species. Copper and nickel are adsorbed only as [(-L)M(II)], while cadmium and calcium are adsorbed as [(-L)M(II)] and [(-LH)2M(II)]. Addition of salts may enhance the deprotonation of IDA groups, interfere with the adsorption as [(-LH)2M(II)], and yield remarkable changes in adsorption curves, depending on the metal ions.