Sorption of divalent metal ions on an iminodiacetic resin from artificial seawater

The sorption of some bivalent metal ions on the iminodiacetic resin Chelex 100 was examined in artificial seawater as an example of a complex matrix, and in the presence of an organic chelating substance in the aqueous phase. The curves reporting the fraction of sorbed metal ions in function of the solution pH were determined experimentally under different conditions and the exchange coefficients were calculated. The intrinsic complexation constants, which are independent of the conditions, were evaluated on the basis of the Gibbs-Donnan model for the resin and agree with those previously obtained in the case of the sorption of the same metals on Chelex 100 from solutions of simpler composition. In some instances the intrinsic complexation constants were similar to the corresponding complexation constants in aqueous solution, while in other cases they were different, depending on the activity coefficient ratio of the species inside the resin. It has been demonstrated that the method derived from the Gibbs-Donnan model can be used for describing and predicting the sorption equilibria also from complex solutions, if all the equilibria set up in the considered system are known.