Uranium sorption in zeolite X: the valence effect

The capacity of zeolite X to sorb UO22+ and U4+ from aqueous solutions was investigated. The U4+ and UO22+ uptake was determined at various concentrat ions. The maximum uptake values in equilibrium using 0.05 N UO22+ or U4+ so lutions were 1.86 and 2.86 meg per gram of zeolite X, respectively. No deso rption of either UO22+ or U4+ was observed up to 200 h. The crystallinity o f the zeolite samples was lost when the concentration of the UCl4 or UO2(NO 3)(2) solutions was higher than 0.01 N. This effect was more evident for U4 +, showing that the uranium charge plays an important role in retention upt ake in zeolite X. The incorporation of radioactive material in zeolite X wa s confirmed by electron microscopy. The absorption and diffusion of radioac tive ions did not alter the surface of the zeolite grains. Radioactive ions were found to occupy preferentially cationic positions in the zeolite stru cture as a consequence of diffusion processes. (C) 1999 Elsevier Science B. V. All rights reserved.