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P. N. Pathak, Gregory R. Choppin

Kinetics and thermodynamics of uranium(VI) sorption on hydrous silica

Keywords: Kinetics, Thermodynamics, Uranium, Sorption, Silica

Sorption of uranyl ion, UO₂²⁺, on SiO₂· x H₂O (silica gel) has been investigated as a function of time, amount of silica gel (0.10–0.60 g), uranium concentration (5.00×10^-5–1.00×^-3 M), ionic strength (0.20–1.40 M NaClO₄), pH (∼2.0–6.0), and temperature (283–333 K). Based on kinetic data, the diffusion coefficient of UO₂²⁺ ion was calculated to be 6.83(±0.22)×10^-12 m² s^-1 under particle diffusion-controlled conditions. The rate of sorption of uranyl ion on silica gel was determined to be 8.56(±0.50)×10^-2 min^-1 at 298 K, pH 1.82±0.05 and 0.20 M NaClO₄. The uranyl sorption data on silica gel followed the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. Uranyl sorption (11.48±0.03 (0.20 M NaClO₄) to 34.81±0.20 (1.40 M NaClO₄) at pH 2.79±0.03 using 0.10 g silica gel. The sorption decreased in the presence of 1.00×10^-3 M fluoride and oxalate ions; while the presence of carbonate anion showed negligible change in uranyl sorption profile in the pH range of 2 to 6 at 0.20 M NaClO₄. Temperature variation experiments showed that the sorption of uranium on silica gel had an endothermic enthalpy, which became more spontaneous at elevated temperatures.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 95, 09/2007
Pages: 507 - 512

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