Evaluation of the sorption of metal ions on a complexing resin from different solutions based on the Gibbs-Donnan model

The intrinsic protonation and complexation constants of an ion-exchange com plexing resin, previously determined in condition of trace metal ions on th e basis of the Gibbs-Donnan model of ion-exchange resins, were here used to evaluate the concentration of metal ions sorbed on the resin when the meta l ion is in excess. The resin considered was a commercial one, containing c arboxylic groups at a concentration of 10 mmol g(-1) of dry resin. Metal io ns complexable by' the active groups present in the resin phase, i.e. alkal ine earth metals and cadmium(II), were investigated, together with a not co mplexable metal ion, sodium, which enters in the resin phase only by diffus ion and ion-exchange. The calculation method is an iterative one, taking in to account the diffusion and ion-exchange in the case of the not complexabl e metals, and the complexation in the case of the complexable metal ions. T he concentration of metals in the resin phase calculated by the proposed pr ocedure was compared with that obtained experimentally in some representati ve solutions at different composition and acidity. The agreement was accept able, showing that the intrinsic complexation constants are of help not onl y in conditions of trace metal, but also for evaluations at completely diff erent conditions. In the case of complexable metal ions it was shown that t he complexation in the resin phase is the most important sorption mechanism , even if ion-exchange tithes place at high acidity, when the complexation is negligible. (C) 2001 Elsevier Science B.V. All rights reserved.