Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Sorption of U(VI) onto TiO2 as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO2 below pH4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO2 particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.