INVESTIGATION OF THE SPECIATION OF ALUMINUM IN DRINKING WATERS BY SORPTION ON A STRONG ANIONIC-EXCHANGE RESIN AG1X8

The sorption properties of the strong anion exchange resin AG1X8 towar ds aluminium(III) were investigated in view of the study of the specia tion of this metal ion in drinking waters. This was done by determinin g the side reaction coefficients of the metal ion in the sample soluti on in the presence of the resin. It was found that aluminium(III) is s orbed on AG1X8 by the formation of Al(OH)(3) and Al(OH)(4)(-). The exc hange coefficients were determined at different conditions and the int rinsic complexation constants were evaluated on the basis of the Gibbs -Donnan model. From the exchange coefficients the ratio of metal ion s orbed on the resin to the free metal ion in solution, K was evaluated . It is a measure of the sorbing properties of a resin towards a metal ion at a given pH. AG1X8 was used for the determination of total alum inium(III) concentration in drinking water samples by the resin titrat ion (RT) method at pH 7.5 and 6.2. In the first case the total concent ration obtained by RT was equal to that determined directly, showing t hat all aluminium is either quantitatively sorbed or in equilibrium wi th AG1X8. The side reaction coefficient alpha(M(I)), was evaluated to be around 10(12) in the considered drinking water samples at this pH. Not any aluminium(III) was sorbed on AG1X8 from the considered drinkin g water samples at pH = 6.2 suggesting that aluminium is present here as species with alpha(M(I)) > 10(7). These results were compared with those obtained using Chelex 100, which is able to sorb aluminium(III) also at pH 6.2. More information about the speciation of aluminium can be obtained by comparing the results from two different sorbing resin s. (C) 1998 Elsevier Science B.V. All rights reserved.