The Collection of Uranium from Sea Water with Hydrous Metal Oxide. II. The Mechanism of Uranium Adsorption on Hydrous Titanium(IV) Oxide

Abstract The mechanism of uranium adsorption from sea water by hydrous titanium(IV) oxide was investigated. The uranium adsorption experiments were conducted using a solution containing NaCl, NaHCO3, and uranium. Thermochemical calculation showed that the tris(carbonato)dioxouranate(VI) ion [UO2(CO3)3]4− found in sea water existed in the solution at pH 8 and 25 °C. The uranium uptake varied with the pH of the solution, exhibiting a minimum value at pH 8. The enthalpy change, ΔH, and the activation energy, E, of the uranium adsorption were found to be 23.6 kJ mol−1 and 52.7 kJ mol−1 respectively. The analysis of carbonate in the adsorbent showed that the carbonate ion in [UO2(CO3)3]4− was released into the solution during the uranium adsorption. On the basis of the present experimental results, the mechanism of uranium adsorption was discussed.