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The interaction of acidic (pH in 3 and 4) aqueous uranium solutions with an Italian chabazite-rich tuff (Vesuvio area) and pure Ca-chabazite crystals from Isle of Skye (Scotland) in raw and Na form were investigated in the presence of background electrolyte (0.1 M NaNO 3) under ambient conditions using a batch equilibrium technique. The maximum uranium uptake by the chabazitic-tuff, its Na form and the pure chabazite crystals from Isle of Skye was found to be ca. 23 mg/g whereas the Na form of the pure chabazite crystals showed higher uptake ability (ca. 34 mg/g). The experimental data have been analyzed using the Langmuir, Freundlich, Redlich-Peterson, Sips, Toth and Dubinin-Radushkevich models. The surface heterogeneity, as well as the chemical nature and behavior of uranium species produced deviations far too complicated to be mathematically described by simple empirical model. Additionally, difficulties in attaining global convergence were encountered when using the three-parameter models due to the substantial sensitivity to initial parameter guesses. According to microscopic measurements and literature data related to the structure of CHA-type zeolites, the uranium uptake took place mainly through surface sorption processes (adsorption and surface precipitation). © 2011 Elsevier Inc. All rights reserved. |
