Removal of UO22+ onto synthetic NaA zeolite. Characterization, equilibrium and kinetic studies

The removal of UO22+ ions from aqueous solutions on zeolite NaA was investigated. The effects of initial uranium (VI) concentration, solution pH, solid/liquid ratio and temperature were studied in batch experiments. Zeolite NaA was synthesized according to a hydrothermal crystallization process. The Dubinin-Radushkevich, the Freundlich and the Langmuir models have been applied and the adsorption equilibrium has been found to follow the Langmuir model. Kinetic studies showed that the pseudo first-order sorption model was the most prevalent for the adsorption of UO22+ ions. The rate constant of the exchanged ions appears to be controlled by chemical sorption process. Rate limiting investigations suggested that the UO22+ ions diffusion was the determining step. The thermodynamic parameters were also determined and the negative values of adsorption entropies indicated that no significant change occurred in the framework of the NaA zeolite during the sorption of UO22+. The obtained optimal parameters were applied to real effluents containing UO22+ ions. (C) 2011 Elsevier B.V. All rights reserved.