Studies on the Electrodeposition of UO₂ Production in UO₂Cl₂-LiCl-KCl Melt

Abstract

UO2 is an important nuclear fuel, and also has potentials in the field of functional materials. In this work, the electrochemical behavior of UO2 2+ in LiCl-KCl molten salt was studied, and its electrochemical reduction process and reduction potential were confirmed. The electrolytic product of UO2 2+ was UO2 crystal. The reduction potential was found playing a decisive role in the morphology of cathodic products, and when the potential was ≤-0.4 V (vs. Pt(II)/Pt), dendritic and cracked characteristic of the UO2 crystal appeared. The average current density had a positive correlation with the grain size of cathodic products, and it increased first and then decreased with the increase of reduction potential, having a maximum at -0.6 V (vs. Pt(II)/Pt). On the other hand, the uranyl concentration also had a positive correlation with the grain size of the cathodic product without changing the integrity of grain morphology. For the preparation of large and granular UO2 crystal, the reduction potential of -0.2~-0.3 V (vs. Pt(II)/Pt), as well as the uranyl concentration of greater than 2.0 wt% were recommended, and UO2 crystal with average grain size greater than 500 μm and high uniformity could be finally obtained.

Electrochemical Behavior and Reduction of UO22+ in LiCl-KCl Molten Salt

“…It has been reported in the literature that the particle size of UO 2 obtained on nano-WO 3 /W electrodes is about 4.5 μm. 27 On the contrary, it is hundreds of microns on the Pt plate electrode, 29 which indicates that the UO 2 particle size is highly dependent on the surface area and is consistent with the results of this paper.…”

“…[16][17][18][19][20][21] Therefore, there is great interest in the electrochemical reduction of these soluble uranium ions in molten chloride salts. [22][23][24][25][26][27][28][29][30][31][32][33][34] It was reported that the reduction of U III was one-step process involving the transfer of three electrons in molten chloride salts: U III →U, while the reduction of U IV was a successive two-step process involving the transfer of one and three electrons respectively in molten chloride salts: U IV →U III →U. All steps were reversible and controlled by ions diffusion.…”

“…[22][23][24][25][26] For uranyl ions, it was revealed that UO 2 2+ ions could be reduced to UO 2 in molten chloride salts. Thus, the electrowinning of UO 2 was studied on various electrodes such as WO 3 /W, 27 Pt, 28,29 glassy carbon, 30 and tin oxide, 31 the products on which present different sizes and morphologies. In addition, the diffusion coefficient of UO 2 2+32 and the equilibrium potential 33 of…”

“…2+ 27,30,34 Nevertheless, there are few systematic studies of the electrochemical behavior of uranyl ions in the literature, [27][28][29][30]34 and some questions still exist that needs to be solved. For instance, it is not clear whether the electrowinning product UO 2 can be further reduced to U metal.…”

Study on the electrodeposition of uranium in chloride molten salt

“…Different cathode has different reduction processes for UO 2 2+ . 19 When W 20–22 and glassy carbon 23 were used, the reaction took two steps, and the formation of intermediate product UO 2 + was found in the molten salt, which was unstable and easily disproportionated into UO 2 and UO 2 2+ , while SnO 2 , 24 Pt, 25 graphite 26 could reduce UO 2 2+ to UO 2 directly.…”