Characterization of the sorption of uranium(VI) on different complexing resins

The sorption of uranium(VI) on two cationic resins containing different complexing groups, the iminodiacetic resin Chelex 100 and the weak carboxylic resin Amberlite CG-50, was investigated. The Gibbs-Donnan model was used to describe and to predict the sorption through the determination of the intrinsic complexation constants. These quantities, even though non-thermodynamic, characterize the sorption as being independent of experimental conditions. The sorption mechanism of the metal on the complexing resins was also studied by adding a competitive soluble ligand that shifts the sorption curves to higher pH values. The ligand competes with the resin for the complexation with the metal ion. Uranium is also strongly sorbed on Chelex 100 at very acid pH, through formation of two complexes in the resin phase: ML with logbeta(110i)=-1.16, in more acidic solution, and ML2 with logbeta(120i)=-5.72. Only the presence of the competitive ligand in solution makes the determination of the second complex possible. Also on Amberlite CG-50 the sorption is strong and involves the formation of the complex ML2, in more acidic solution, with logbeta(120i)=-3.16. In the presence of the ligand EDTA, the complex ML2(OH)2 was characterized with logbeta(12-2i)=-5.15. In all the experiments the hydrolysis reaction in the aqueous phase was quantitatively considered.