The synthesis and use of nitrogen derived titanates for the adsorption of uranium from aqueous waste streams

Abstract

The synthesis and use of layered hydrazinium and ammonium titanate as an adsorbent for uranium in a nitric acid solution was investigated. Several different titanate synthesis methods were identified from literature. Three of these methods, namely solid state, hydrothermal and sol-gel synthesis were further explored for the production of the titanate adsorbents. The chosen sol-gel method delivered the highest ordered crystalline, single phase titanates, and was subsequently used for the synthesis of all titanates investigated. The adsorption of uranium in the form of the uranyl specie was shown to be successful with both hydrazinium and ammonium titanate. These adsorptions were shown to be highly pH dependent, thereby allowing for possible selective extraction by manipulating the pH of the reactant solution. High resolution transmission electron microscopy showed the primary sites of adsorption to be the outer surface for hydrazinium and ammonium titanates. Using the Langmuir adsorption isotherm, the adsorption was confirmed to be a monolayer adsorption of equivalent energetic sites. Raman analysis showed no visible vibrations that could be associated with bonds between the uranyl species and the hydrazinium and ammonium titanates. Further Raman analysis revealed the conversion of hydrazine into ammonium during the adsorption reaction. The discovery of an alternate synthesis route for caesium titanate by making use of the Pechini sol-gel method led to the production of highly ordered titanates. Additionally, the adsorption of uranium in the form of uranyl species was characterized for both hydrazinium and ammonium titanates. The use of an ammonium titanate as an adsorbent for uranium species was pioneered by this study. Furthermore, the discovery of the role that hydrazine plays in the adsorption of uranium elucidated the mechanisms involved with the adsorption of cationic species by layered hydrazinium and ammonium titanate in nitric acid media.