Study of the retention mechanism of uranium on titanium oxide

We have studied the phenomenon of retention of uranium, as a carbonato complex UO2(CO3)34− on titanium oxide. We first proposed a method for preparing titanium oxide whose ion-exchange capacities (2.9 meq Na+/g, 0.11 meq UO22+/g) and physical properties (mechanical resistance and granulometry) make it quite suitable for liquid chromatography and particularly for the extraction process of uranium from sea-water. We prepared the sodium tricarbonatouranate, the major form of uranium in sea-water. We studied the retention of this compound on titanium oxide. From a thermodynamic study of the retention equilibrium we proposed a retention mechanism of the ligang-exchange type: uranyl is retained on titanium oxide, surrounded with two CO32− ligands and two ≥TiO− ligands. We shown that 2/3 of the exchanged hydroxyl groups have pKH1=4.9 and 1/3 of them have pKH2=9.3.