U(VI) sorption on kaolinite was studied as functions of contact time, pH, U(VI) concentration, solid-to-liquid ratio (m/V) by using a batch experimental method. The effects of sulfate and phosphate on U(VI) sorption were also investigated. It
was found that the sorption kinetics of U(VI) can be described by a pseudo-second-order model. Potentiometric titrations at
variable ionic strengths indicated that the titration curves of kaolinite were not sensitive to ionic strength, and that the
pH of the zero net proton charge (pHPZNPC) was at 6.9. The sorption of U(VI) on kaolinite increased with pH up to 6.5 and reached a plateau at pH >6.5. The presence
of phosphate strongly increased U(VI) sorption especially at pH <5.5, which may be due to formation of ternary surface complexes
involving phosphate. In contrast, the presence of sulfate did not cause any apparent effect on U(VI) sorption. A double layer
model was used to interpret both results of potentiometric titrations and U(VI) sorption on kaolinite.