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)MII], while cadmium and calcium are adsorbed as [(-L)MII] and [(-LH)2MII]. Addition of salts may enhance the deprotonation of IDA groups, interfere with the adsorption as [(-LH)2MII], and yield remarkable changes in adsorption curves, depending on the metal ions.