Chemical Species Transformation during the Dissolution Process of U3O8 and UO3 in the LiCl-KCl-AlCl3 Molten Salt.

In this work, we investigated the dissolution behavior of U3O8 and UO3 in the LiCl-KCl molten salt using 2.9 or 9.5 wt % AlCl3 as a chlorination agent under an argon atmosphere at 450 °C. Ultraviolet-visible/Ultraviolet-visible-near infrared absorption spectroscopy (UV-vis/UV-vis-NIR), fluorescence emission spectroscopy (FL), X-ray absorption fine structure (XAFS), and electrochemical techniques were used to systematically study the chemical species and the transformation of the dissolved products of U3O8 and UO3. It was found that with the aid of AlCl3, the initial products of U3O8 and UO3 dissolution were different. The initial products of U3O8 were UO2Cl42- and UCl62-, while the initial product of UO3 dissolution was UO2Cl42-. Interestingly, regardless of U3O8 or UO3, with the increase of AlCl3 content, the UO2Cl42- in their dissolved products showed a tendency to transform into UCl62-. In addition, UCl4 was produced by mixing 0.05 g of U3O8/UO3 powders with 10 times the amount of AlCl3 and heating them at 300 °C for 2 h. This work focuses on the pyrochemical reprocessing of spent oxide fuels, deepening the understanding of the dissolution of uranium oxides in higher oxidation states, and enriching the knowledge of uranium in the transformation of chemical species in molten salts.