Chemical Species Transformation during the Dissolution Process of U 3 O 8 and UO 3 in the LiCl-KCl-AlCl 3 Molten Salt.

In this work, we investigated the dissolution behavior of U 3 O 8 and UO 3 in the LiCl-KCl molten salt using 2.9 or 9.5 wt % AlCl 3 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 U 3 O 8 and UO 3 . It was found that with the aid of AlCl 3 , the initial products of U 3 O 8 and UO 3 dissolution were different. The initial products of U 3 O 8 were UO 2 Cl 4 2- and UCl 6 2- , while the initial product of UO 3 dissolution was UO 2 Cl 4 2- . Interestingly, regardless of U 3 O 8 or UO 3 , with the increase of AlCl 3 content, the UO 2 Cl 4 2- in their dissolved products showed a tendency to transform into UCl 6 2- . In addition, UCl 4 was produced by mixing 0.05 g of U 3 O 8 /UO 3 powders with 10 times the amount of AlCl 3 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.