Investigation of the complexation properties of a natural water towards copper(II), manganese(II) and aluminium(III), based on sorption of metal ions on complexing resin.

A competion method is proposed to characterize natural metal complexes present in a high salinity spring water. The competitor is a strong complexing resin containing the iminodiacetic group, Chelex 100. Its sorbing properties towards the metal ions here considered, Cu(II), Mn(II) and Al(III), are well known and could be quantified through K*, the ratio of the concentration of the metal in the resin phase to that of the free metal in solution. It can be calculated for the considered metal ion for the particular experimental conditions. From the fraction of metal experimentally sorbed on the resin it is possible to obtain information about the distribution of the metal in the original water solution. Two different methods are proposed. In the resin titration (RT), different volumes of sample are treated with the same amount of resin. RT allows to determine the total metal concentration and the reaction coefficient of that metal in solution. In the ligand titration (LT), the free metal is added stepwise into the original sample, and the ligand concentration and the complexation constant are determined. This was done by the Ruzic linearization method, modified to take unto account the variation of the pH of the solution. Also the data from RT were elaborated by the modified Ruzic linearization. The study of metal ions distribution among different chemical species by the combined methods is discussed in detail. The three metal ions in the considered high salinity water were found to be mainly combined in complexes with high complexation constant. The concentration of the strong ligands involved was near to that of the metals. # 2002 Elsevier Science Ltd. All rights reserved.