Determination of the total concentration and speciation of Uranium in naturalwaters by the Resin Titration method

Different natural waters were investigated to determine the total concentration and the distribution of uranium in species of different stability. The method applied, named Resin Titration (RT), was described in detail in our previous investigations, but it was here proposed again to highlight its potentiality in the evaluation of strong metal species. The resin competes with natural ligands present in the sample to combine with the metal ions so, using a strong complexing resin, Chelex 100, very stable metal complexes can be investigated. This kind of complexes, while present at low concentration, most often lower than that of the total metal ion, is important for a realistic description of the metal speciation, because they may constitute a large fraction of the total metal content. In the present paper, high and low salinity waters were taken in different sites in the North part of Italy. The total uranium content in the samples here examined was in accordance with data obtained in previous studies. In most of the samples, strong complexes of uranium were detected, and the reaction coefficients found (ranging from 10^10 to 10^12 at pH around 8) were higher than those ascribable to the hydrolysis or to the reactions with macroconstituents of the samples.