Catalytic reduction of U(VI) with hydrazine using Pt/SiO₂ catalyst in nitric acid medium-kinetics and equilibrium

Kinetics of catalytic reduction of uranyl species, U(VI) to U(IV) with hydrazine nitrate was studied over Pt/SiO₂ catalyst in nitric acid medium. Experiments were carried out in a stainless-steel autoclave as a function of mixing intensity, temperature, catalyst loading and concentration of nitric acid, hydrazine and uranium. Langmuir-Hinshelwood approach was considered to derive various model equations and each of them was evaluated. Results of the present study indicated that catalytic reduction of U(VI) can be described by surface reaction between adsorbed molecules. The activation energy of the reaction was calculated to be 74.5 kJ/mol, suggesting a chemical reaction controlled process. (author)