The effect of air on oxidation decomposition of uranium-containing cationic exchange resins in Li2CO3–Na2CO3–K2CO3 molten-salt system

Abstract

With the development of nuclear energy, spent cationic exchange resins after purification of radioactive wastewater must be treated. Molten-salt oxidation (MSO) can minimize the disposal content of resins and capture SO₂. In this work, the decomposition of uranium-containing resins in carbonate molten salt in N₂ and air atmospheres was investigated. Compared to N₂ atmosphere, the content of SO₂ released from the decomposition of resins was relatively low at 386–454 °C in an air atmosphere. The SEM morphology indicated that the presence of air facilitated the decomposition of the resin cross-linked structure. The decomposition efficiency of resins in an air atmosphere was 82.6% at 800 °C. The XRD analysis revealed that uranium compounds had the reaction paths of UO₃ → UO_2.92 → U₃O₈ and UO₃ → K₂U₂O₇ → K₂UO₄ in the carbonate melt, and sulfur elements in resins were fixed in the form of K₃Na(SO₄)₂. The XPS result illustrated that peroxide and superoxide ions accelerated the conversion of sulfone sulfur to thiophene sulfur and further oxidized to CO₂ and SO₂. Besides, the ion bond formed by uranyl ions on the sulfonic acid group was decomposed at high temperature. Finally, the decomposition of uranium-containing resins in the carbonate melt in an air atmosphere was explained. This study provided more theoretical guidance and technical support for the industrial treatment of uranium-containing resins.