Reaction of Nitrate Ion with Formic Acid in the Presence of Uranium

The reaction of nitric acid with formic acid, including that in uranium-containing solutions, was studied. Empirical equations for the dependence of the induction period (τ) on the reactant concentrations and temperature were determined. The dependence of τ on the formic acid concentration is exponential. The effect of uranium concentration on τ in denitrated solutions becomes noticeable only at temperatures lower than 60°C. The main factor affecting the denitration completeness is the [formic acid] : [NO₃]¯ molar ratio. Starting from the molar ratio of ≥3, uranium-containing solutions are denitrated at 90°C in an hour almost quantitatively. The resulting uranyl formate is partially precipitated. The initial stage of the reaction is accompanied by vigorous gas evolution. At 90°C, ~80% of the gas volume is released in this stage (about 10 s), whereas at 40°C, only ~10%.