Direct electrochemical dissolution of metallic uranium into deep eutectic solvent

Deep eutectic solvents (DESs) could make uranium recycling processes greener than using conventional solvents, owing to their inherent advantages such as being biodegradable and non-toxic. However, the chemistry of uranium ions in DES systems, particularly the mechanism of direct anodic dissolution of uranium metal, remains unclear. The anodic dissolution of uranium metal in choline chloride (ChCl)–ethylene glycol (EG) DES was conducted by applying a constant current. The oxidation state of uranium in ChCl-EG DES was uranium(IV) when compared to concentration and applied charge. Absorption spectra showed 8 coordinated U(IV) centered complexes formed in the ChCl-EG DES, regardless of the uranium source (i.e. uranium chloride or metallic uranium anodic dissolution). The in situ spectroelectrochemistry during potentiostatic electrolysis, cyclic voltammograms, and absorption spectra of different times of potentiostatic electrolysis showed U(IV) oxidized to U(V), and then the U(V) disproportionated into U(IV) and U(VI) species. Understanding fundamental uranium speciation in DES systems and electrochemical properties could facilitate the development of an eco-friendly nuclear fuel cycle and nuclear uranium recycling process using green DESs.