Electrochemical behavior of uranium(III) in NaCl–KCl molten salt

The electro-redox behavior of uranium(III) on Mo electrode in NaCl–KCl molten salt in the temperature range 973–1073 K has been investigated using cyclic voltammetry electrochemical method and so on, such research will help to understand uranium behavior in pyro-reprocessing. The results showed that UCl₃ could be reduced into uranium metal in a quasi-reversible one-step process exchanging three electrons. The diffusion coefficients of U(III) ions were determined and the activation energy for diffusion was found to be 55.794 kJ mol⁻¹. The apparent standard potentials of U(III)/U(0) at several temperatures were calculated. The thermodynamic properties of UCl₃ have also been investigated.

     

Electrochemical properties and extraction of Dy on liquid Sn electrode in LiCl–KCl molten salt

Journal of Solid State Electrochemistry - To extract dysprosium (Dy) from LiCl–KCl molten salt, the electrochemical properties of Dy on liquid Sn electrode were explored by various...     

Electrochemical and spectroscopic investigations of Tb(III) in molten LiCl–KCl eutectic at high temperature

Electrochemical and spectroscopic properties of Tb(III) in molten LiCl–KCl eutectic at high temperature were investigated by cyclic voltammetry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The diffusion coefficient of Tb(III) and the formal standard potential of Tb(III)/Tb⁰ were determined to be 2.06 ± 0.4 × 10^? 5 cm² s^? 1 and ? 2.83 ± 0.03 V vs. Cl₂/Cl^? at 887 K, respectively. Additionally, visible fluorescence of Tb(III) due to the electronic transitions from ⁵D₃ and ⁵D₄ to ⁷F_J was observed and measured by TRLFS for the first time. These results provide the first fluorescence spectroscopic evidence for a direct in situ quantification of Tb(III) in the high temperature molten salt system.     

The distillation behavior of fluorides in LiCl–KCl molten salt

Journal of Radioanalytical and Nuclear Chemistry - The distillation behaviors of some fission product fluorides in LiCl–KCl system were investigated. For rare earth element, the corresponding...     

Electrochemical extraction of cerium and formation of Al–Ce alloy from CeO_2 assisted by AlCl_3 in LiCl–KCl melts

This work presents an electrochemical extraction of cerium and synthesization of Al–Ce alloy in LiCl–KCl melts on Mo and Al electrodes by chlorination of CeO2 using AlCl3 at 873 K. The cyclic voltammogram on Mo electrodes in LiCl–KCl–CeO2 melt showed no obvious reduction wave other than the reduction of Li(I). After the addition of AlCl3, the signals of the reaction of Ce(ⅡI)/Ce(0) and the synthesization of Al–Ce and Al–Li alloys were investigated by cyclic voltammetry, square-wave voltammetry, open-circuit chronopotentiometry and chronopotentiometry. These results indicated that AlCl3 can chloridize CeO2 and that it is possible to extract cerium and form Al–Ce and Al–Li–Ce alloys in LiCl–KCl–CeO2–AlCl3 melts. According to potentiostatic electrolysis, only the Al4 Ce layer coated the Al electrodes. According to galvanostatic electrolysis, Al–Ce(Al4Ce, Al3 Ce, and Al92Ce8), Al2Li3, and Al phases were formed on Mo electrodes, and the content of cerium in the Al–Li–Ce alloys was more than 17 wt%.     

Electrochemical preparation and spectroelectrochemical study of neptunium chloride complexes in LiCl–KCl eutectic melts

Lyoluminescence (LL) is a good technique for radiation dosimetry of high-energy radiations. Dosimetry of γ rays from ⁶⁰Co radioactive source has been done using MgB₄O₇:Mn²⁺ phosphor material. It was synthesized by simple solid state diffusion method. The material shows good linear LL response with the γ rays for the dose rage of 10 Gy–10 kGy. The studies have also been done for different particle sizes (250–45 µm) and particles having average size ~85 µm were found to be the most suitable for this dosimetry. Effect of solvent pH on LL and fading on storage has also been studied.     

Electrochemical behaviour of NpO2(VI) and Npo2(V) in molten LiClKCl

A chronopotentiometric study of the reactions NpO₂(VI) + 2 e⁻ → NpO₂ and NpO₂(V) + e⁻ → NpO₂ is reported. At 400°C, the diffusion coefficient of NpO₂(VI) is (2.0 ± 0.2)10⁻⁶ cm².sec⁻¹ and that of NpO₂(V) is (4.8 ± 0.45).10⁻⁶ cm².sec⁻¹.The standard potential E°_NpO2(V)/NpO2 - E°_Cl2/2Cl⁻ was found equal to (0.119 ± 0.002) volt at 400°C.     

Investigation of the evaporation of rare earth chlorides in a LiCl–KCl molten salt

Uranium dendrites which were deposited at a solid cathode of an electrorefiner contained a certain amount of salts. These salts should be removed for the recovery of pure metal using a cathode processor. In the uranium deposits from the electrorefining process, there are actinide chlorides and rare earth chlorides in addition to uranium chloride in the LiCl–KCl eutectic salt. The evaporation behaviors of the actinides and rare earth chlorides in the salts should be investigated for the removal of salts in the deposits. Experiments on the salt evaporation of rare earth chlorides in a LiCl–KCl eutectic salt were carried out. Though the vapor pressures of the rare earth chlorides were lower than those of the LiCl and KCl, the rare earth chlorides were co-evaporized with the LiCl–KCl eutectic salt. The Hertz–Langmuir relation was applied for this evaporation, and also the evaporation rates of the salt were obtained. The co-evaporation of the rare earth chlorides and LiCl–KCl eutectic were also discussed.     

Development of a simple spectrophotometric method to estimate uranium concentration in LiCl–KCl matrix

“Off-the-shelf” clinical linear electron accelerators (LINAC) have been suggested as alternative to research accelerators once they are no longer suitable for the medical applications. We investigated feasibility of utilising a modified LINAC for instrumental photon activation analysis (IPAA) as a tool in environmental geochemistry studies. The IPAA results were compared with those obtained using a MT-25 research accelerator at Joint Institute for Nuclear Research in Dubna, Russia. To investigate soil pollution in Antalya, Turkey, 90 surface soil samples were analysed and significant enrichments of Ni, Cr and As were found.

     

Electrochemical reduction of UO2 to U in a LiCl–KCl-Li2O molten salt

An electrochemical reduction of UO₂ to U in a LiCl–KCl-Li₂O molten salt has been investigated in this study. A diagram showing equilibrium potentials (relative to Cl₂/Cl^?) plotted versus the negative logarithms of oxide-ion activity (pO^2?) was constructed. The crushed UO₂ pellets in the cathode basket of an electrolytic reducer were successfully reduced to U. The reduction of UO₂ is proved to proceed mainly through chemical reaction with in situ generated Li and K at the cathode. The control of cathode potential is essential to prevent the deposition and subsequent vaporization of K metal at the cathode for the applications of a LiCl–KCl-Li₂O molten salt as an electrolyte for the metal production from its oxide sources.     

Electrochemical response of various metals to oxygen gas bubbling in molten LiCl–Li2O melt

The electrochemical response of several alloys (stainless steel 316, Hastelloy C276, Inconel 600, and tantalum) was investigated in molten LiCl–Li₂O (1 wt%) at 923 K while bubbling oxygen gas into the molten salt. Tafel and zero resistance ammeter (ZRA) electrochemical methods were used to measure electrochemical effects of oxidation processes at the surface of each alloy. The Tafel method required approximately 15 min and was, thus, applied only in intervals between periods of oxygen bubbling in the salt. ZRA measurements were made in real time, while the O₂ was actively being bubbled into the salt. This method recorded both open circuit potential of the alloy relative to a Ni/NiO reference electrode and current between the alloy and the galvanically coupled platinum plate that served as the counter electrode. Both open circuit potential and galvanic oxidation current started to increase at the initiation of oxygen flow. Based on the observed oxidation current trend, it was inferred that the metals in order of increasing resistance to oxidation in molten LiCl–Li₂O are as follows: tantalum < SS-316 < Inconel 600 < Haynes C276. Scanning electron microscopy images indicated formation of an oxide layer of thickness 560–3370 nm that correlates with the galvanic oxidation current measurements.

     

Exhaustive electrolysis for recovery of actinides from molten LiCl–KCl using solid aluminium cathodes

An electrorefining process in molten chloride salts using solid aluminium cathodes is being developed in Institute for Transuranium Elements in order to separate actinides (An) from spent nuclear fuel. In this process, the fuel including fission products (FP) is dissolved into an electrolyte. Without purification of the salt, the process would have to be stopped when the FP concentration would become too high to allow a selective deposition of An on the cathode. Exhaustive electrolysis is proposed as the first purification step, consisting of a group-selective recovery of An on solid aluminium cathodes. On the anodic side, chlorine gas is produced by electrochemical decomposition of the salt. In order to prove the feasibility of the method, two galvanostatic electrolyses were carried out and the potentials of both electrodes were constantly monitored. Uranium was recovered from LiCl–KCl melts containing UCl₃ and a mixture of UCl₃–NdCl₃, in which its concentration decreased from 1.7 to 0.1 wt% with no co-deposition of neodymium. Although the maximum applicable current densities were relatively low, the results are promising, demonstrating high current efficiency and selectivity of the proposed method. A design and application of a special chlorine gas producing inert anode is also discussed.     

Electrochemical study on various types of anode materials in LiCl–KCl eutectic salt used in the electro-winning process

The electrochemical behaviors of the molybdenum, graphite, and glassy carbon anode have been observed during the electrolysis of uranium chloride in an UCl₃–LiCl–KCl molten salt. The cyclic voltammogram data of the molybdenum anode showed that Mo anode could be corroded by the formation of Mo compounds or its dissolution. However, the experimental data of the graphite and the glassy carbon anode showed that the chlorine evolution started from 1.2 V and the anode potential remained stable during uranium electrolysis. Therefore, the graphite and glassy carbon may be used as an inert anode in the electro-winning process of pyroprocessing.     

The solid–liquid separation characteristics of pure LiCl–KCl eutectic salt using different types of crucibles

Uranium deposits were recovered at the solid cathode of an electrorefining system, and deposited uranium dendrite normally contains about 30–40 wt% LiCl–KCl eutectic salts. Therefore, a separation of the eutectic salts from deposited uranium is essential for reusing these salts and uranium. A process such as distillation was employed for cathode processing due to the advantages of a minimal generation of secondary waste, a compact unit process, and simple and low-cost equipment. However, the realization of a wide evaporation area or high distillation temperature is limited by various factors such as the material or structure of a distiller. Also, the electrical energy flow from outside has a lot of consumption to maintain the high temperature. Hence, in this study, solid–liquid separation experiments are proposed to increase the throughput of the salt removal process by the separation of the liquid salt prior to the distillation of the LiCl–KCl eutectic salt. The solid–liquid separation of salt was carried out in a vertical type distiller. The behavior of the solid–liquid separation of pure eutectic salt was investigated as a function of temperature, pressure, sieve size, and crucible shape. From the experimental results using pure eutectic salts, the amount of salt separation was achieved at more than 94 wt%. The rate of solid–liquid separation of salt using 600 °C is higher than that of 500 °C under the same condition. The influence of a vacuum for solid–liquid separation can be disregarded, and the separation rate of a 100 mesh was higher than that of a 150 mesh. In addition, the rate of separation for salts using a porous crucible is higher than that in a non-porous crucible.     

Electroreduction of Dy(III) assisted by Zn and its co-deposition with Zn(II) in LiCl–KCl molten salt

To recover dysprosium (Dy) from LiCl–KCl molten salt, the electrochemical mechanism of Dy(III) on liquid Zn electrode and co-deposition of Dy(III) and Zn(II) on W electrode were studied using electrochemical methods. Cyclic voltammetry results demonstrated that the redox process of Dy on liquid Zn electrode is reversible and controlled by diffusion. Reverse chronopotentiograms showed that the transition time ratio of reduction and oxidation is ~3:1, revealing the redox of Dy on liquid Zn electrode is a kind of soluble–soluble system: Dy(III) + 3e⁻ = (Dy–Zn)_solution. The half-wave potential of Dy(III) was almost constant with the increase in scanning rate. The electrochemical separation of metallic Dy from the molten salt was performed using constant potential electrolysis, and the product characterized using X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy was the thermodynamic unstable compound DyZn₅. Also, the co-deposition mechanism of Dy(III) and Zn(II) was explored, indicating that Dy(III) could deposit on pre-deposited Zn and form Dy–Zn compounds: Zn(II) + 2e⁻ = Zn and xDy(III) + yZn + 3xe⁻ = Dy_xZn_y. Moreover, the effect of Dy(III) concentration on the formation of Dy–Zn compounds was investigated. The redox peak currents corresponding to different Dy–Zn compounds changed with the increase in Dy(III) concentration. The co-deposition of Dy(III) and Zn(II) was performed using constant current electrolysis at diverse Dy(III) concentrations. The different Dy–Zn compounds were produced by controlling Dy(III) concentration.