Sorption of protons and metal ions from aqueous solutions by a strong-base anion-exchange resin loaded with sulphonated azo-dyes

Two sulphonated azo-dyes, which bear a nitrogen donor atom in the diazo group and are known to complex many heavy metal ions in aqueous solution, have been found to be sorbed by a strong-base anion-exchange resin (Dowex 1-X8) simply by ion-exchange. The resin containing the dyes behaves like a chelating resin, able to sorb copper(II) and nickel(II) from aqueous solution, if the proper conditions are chosen. The acidity, ionic composition and volume of the aqueous solution, and the amount and nature of the sorbed ligand are the factors which determine the fraction of metal ion sorbed when the batch technique is used. The experimental results are interpreted by using a model of the resin based on the Donnan equilibrium concept, which allows prediction of the sorption conditions on the basis of some independently determined quantities, such as the protonation and complex formation constants in aqueous solution, and the activity of the counter-ion in the resin phase. The exchange of protons between the resin and the aqueous solution can also be explained with this model.