Sorption Equilibria of U(VI) Ions with Oxide–Graphene Composite TiO2||C and with TiO2 in the Region of the Henry Law

The results of studying the sorption equilibria of U(VI) ions with TiO2||C oxide–graphene composite and with the oxide TiO2 prepared from it were analyzed within the framework of the surface complexation theory. According to the established equilibrium mechanism, the following species participate in the sorption in the region of the Henry law at pH 2–11: UO22+, UO2(OH)+, UO2(OH)20, UO2(OH)3–, and UO2(CO3)0; they react with the surface {≡Ti–OH} groups. Anionic carbonate complexes are not adsorbed onto titanium oxide. Oligomeric titanium complexes do not affect the resultant sorption because of a sharp decrease in the equilibrium analytical concentration of uranium due to the extremely high distribution coefficient Kd (mL/g) of the sorbent, exceeding 6 log units at рН 6.5. The linear correlation between the Henry constants of the sorption of uranium species onto titanium oxide and their stability constants in the electrolyte solution confirms the similarity of energy processes in the formation of U(VI) species in the contacting phases.