Electrochemical deposition of uranium oxide in highly concentrated calcium chloride

Abstract

The coordination circumstances and redox reactions of UO2[2+] in the aqueous solution concentrated by calcium chloride, such as CaCl2·6H2O (6.9 M CaCl2), were studied by Raman spectroscopy and electrochemical methods. The frequency of the O=U=O symmetrical stretching vibration suggested that the complex formation of UO2[2+] with Cl[−] leads to the weakening of U=O bond. In the electrochemical measurements, two-step cathodic currents were observed at −0.090 and −0.4 V (vs. Ag|AgCl) corresponding to the reduction of UO2[2+] to UO2[+] and that of UO2[+] to UO2, respectively. It was found that UO2[+] formed at first cathodic current was disproportionated to form UO2[2+] and UO2. The UO2 was identified by X-ray diffraction analysis. Electrolytic deposition of UO2 was observed in 6.9–4.7 M CaCl2 and in 14 M LiCl. When small amount of proton, i.e., 0.005 M was coexisted in 6.9 M CaCl2, UO2[2+] was reduced to form U[4+] instead of UO2.