Sorption of metal ions on a weak cation exchange resin containing carboxylic groups.

The sorption properties of a commercial resin containing a carboxylic active group, Amberlite CG-50, for magnesium, calcium, copper and zinc were investigated on the basis of the Donnan model. It is assumed that the main driving for the sorption of divalent metal ions is the complexation by the carboxylic groups inside the resin. Under typical batch conditions (large excess of ligand) only the 1:2 complexes are formed, for all metal ions considered, whereas in aqueous solutions only 1:1 complexes are reported for calcium and magnesium with the monomeric analogues of the active group of Amberlite CG-50. The intrinsic complexation constants obtained from the batch experiments well agree with those in aqueous solution. The same holds for the intrinsic complexation constants obtained from the chromatographic experiments. This confirms some previous results obtained with a chelating resin containing an iminodiacetic group, Chelex 100. the values of the complexation constants for the carboxylic groups found with the Chelex 100 are in agreement with those found with the Amberlite CG-50.