Studies on the conversion of uranium-containing pyrochemical salt waste into metallic uranium by direct oxide electrochemical reduction

The study aims to establish a method for converting uranium-containing pyrochemical salt waste matrix into metallic uranium using a direct oxide electrochemical reduction method. Initially, the uranium-containing salt matrix was treated with aqueous ammonia to precipitate uranium as ammonium diuranate (ADU). The main impurities found in the ADU were cadmium and copper. However, their levels were below 2 wt%. Subsequently, ADU was converted into UO2 through calcination and reduction steps. The direct oxide electrochemical reduction of UO2 was performed in a LiCl-Li2O melt at 650 °C, with platinum serving as the anode. Two batches of impure ADU were processed for the conversion into metallic uranium. Despite the low impurity levels, their presence affected the process, resulting in brownish-black deposits during calcination steps and a black residue in the LiCl-Li2O melt after electrochemical reduction. To address this issue, ADU was purified using a solvent extraction method, which resulted in a cleaner process.