Studies of the formation of uranyl(VI) from uranium dioxide and chlorine in molten alkali chlorides

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.

Section: Resultsmentioning

confidence: 99%

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

Wei

2022

“…Similar phenomenon was also discovered in chloride melts, that is, the decreasing competition of molten salt cations for anionic ligands could increase the stability of uranyl. 12 The electrodeposition of UO 2 2+ in FLiBe melt.-Based on above experiments, UO 2 2+ can be reduced to UO 2 through a single-step process with two electrons in FLiBe, indicating it is feasible to separate UO 2 2+ from FLiBe by electrolysis. Potentiostatic electrolysis (550°C, 4 h) at 1.25 V (vs. Be 2+ /Be) was employed in the UO 2 F 2 -KF-FLiBe melt.…”

Section: Resultsmentioning

confidence: 84%

Communication—Electrochemical Behavior of UO₂²⁺ and Its Electrodeposition from UO₂F₂-FLiBe Melt

Han

Liu

et al. 2019

To support the proposal for separating uranium from used fuel salt of Molten Salt Reactor (MSR), the electrochemical behavior of UO 2 2+ in the carrier salt of MSR (LiF-BeF 2 , FLiBe) was investigated in this work. Cyclic voltammetry and square wave voltammetry measurements showed that the reduction of UO 2 2+ in UO 2 F 2 -FLiBe melt with addition of KF exhibited one step with two exchanged electrons: UO 2 2+ +2e − →UO 2 , with reduction peak of 1.93 V (vs. Be 2+ /Be). By potentiostatic electrolysis, the product of octahedral UO 2 single crystals with micron size was obtained.

“…[12][13][14][15][16][17][18] With these auxiliary chlorination reagents, uranium oxides can be converted to soluble U III , U IV , U V , or U VI , the latter two of which exist as uranyl ions UO 2 + and UO , 2 2+ respectively. [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.…”

Section: Supplementary Materials For This Article Is Available Onlinementioning

confidence: 99%

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

Wang,

Liu,

Zhong

et al. 2023

In this work, we explored the electrochemical behavior and reduction process of uranyl ions UO22+ in molten LiCl-KCl eutectic at 773 K. Cyclic voltammetry (CV) and square wave voltammetry (SWV) results showed that the reduction of UO22+ ions on the inert W electrode was a three-step process: (1) UO22+ + e- ↔ UO2+, (2) UO2+ + e- ↔ UO2 and (3) UO2 + 4e- ↔ U. Electrolysis experiments further confirmed this reduction mechanism that UO22+ ions were reduced to UO2 on the molybdenum electrode by applying a constant potential of -1.00 V vs. Ag/AgCl and subsequently to uranium metal at a more negative potential of -2.35 V vs. Ag/AgCl. In addition, UO22+ ions could be thoroughly reduced to uranium metal through a 4-h constant current electrolysis at -18 mA cm-2. Electronic absorption spectroscopy (EAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) respectively illustrated that the oxidation state of uranium was unchanged and uranium concentration gradually decreased during the electrolysis. Finally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the phase composition and microstructure of deposited products. Nano-sized UO2 and U metal particles were successfully obtained by constant potential and current electrolysis.