UC oxidation with HNO2 in aqueous solutions of HNO3 and HClO4

Abstract

The oxidation of UC powder was studied in 0.5-6.0 M HNO 3 and HClO 4 , containing 0.01-0.1 M NaNO 2 , at ambient temperature. The addition of nitrous acid caused the oxidation potential to exceed 400 mV/SCE and thus accelerated the dissolution and increased the dissolution yield to exceed 95%. One hundred percent dissolution at room temperature was achieved within 30 to 40 min when 3.0-6.0 M HNO 3 was used that contained more than 0.005 M HNO 2 .The dissolution rate increased with increasing HNO 3 concentration and initial solid-to-liquid ratio. The effective dissolution rate constants and reaction orders were estimated for the UC oxidation with H + , NO 3 − and HNO 2 in 0.5-6.0 M HClO 4 . The rate of UC oxidation with HNO 2 exceeded 50-80 times its oxidation rates with NO 3 − ions. During UC oxidation with HNO 2 in 0.5-6.0 M HClO 4 , 60-85% carbon was oxidized to CO 2 . The C/U(VI) ratio in the dissolver solution decreased from 0.5 to 0.1 mg eq/mol with increasing of HClO 4 and HNO 2 solution concentration. Two to five percent of the carbon remained in the insoluble residue of the HNO 3 dissolver solutions, even when a 100% U(VI) yield was observed. Scanning electron microscopy of the insoluble residue showed the carbon particle size between 1.0 and 5.0 µm.

On the Stability of Uranium Carbide in Aqueous Solution—Effects of HCO3– and H2O2

“…Similarly to the other metal carbides, uranium carbide undergoes hydrolysis. Hydrolysis of uranium carbide has been studied quite extensively under acidic conditions for the purpose of developing nuclear fuel reprocessing. − UC exposed to water at neutral pH between 25 and 99 °C has been shown to yield hydrous uranium oxide, hydrogen gas, and a complex mixture of gaseous hydrocarbons, mainly methane with small amount of ethane and saturated C3- to C6- hydrocarbons. The hydrolysis reaction is often generally described as …”