Uranium Adsorption by Chelating Resins Containing Amino Groups

A series of porous polymers containing primary amino groups has been tested for their ability to complex the uranyl ion in aqueous solutions. The maximum capacity is obtained around pH 6, but that value is much lower than the theoretical value calculated on the basis of the loading in amino groups and the assumed stoichiometry of the metal ligand complex. Electron probe x-ray microanalysis demonstrated that the uranyl ion is chelated in a narrow surface layer, the thickness of which never exceed 250 μm, i.e., about 15% of the total diameter. On the other hand, copper can access all the chelating sites which are uniformly distributed inside the resins. This was explained by the formation of a precipitate of polyuranates in the first layer of the beads, preventing further penetration of the uranyl ion. This process is reversible, as shown by successive cycles of fixation and elution of the metal ion. The capacity of the resins toward uranium is not affected by the presence of an excess of calcium or magnesium or both.