LiCl-KCl Melt Research Articles

Electrochemistry of Zn and co-reduction of Zn and Sm from LiCl–KCl melt

SEM image and element mapping analysis of Zn–Sm alloy obtained by galvanostatic electrolysis.

Electrochemical extraction of cerium and formation of Al-Ce alloy from CeO2 assisted by AlCl3 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 Al4Ce layer coated the Al electrodes. According to galvanostatic electrolysis, Al-Ce (Al4Ce, Al3Ce, 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%.

Molybdenum(V) Species in Alkali Chloride Melts: An Electronic Absorption Spectroscopy Study

Molybdenum in chloride melts can form chloro-species containing the metal in the oxidation states +3, +4 and +5. In the highest oxidation state, +6, molybdenum can form oxygen-containing ions. Amongst the molybdenum chloro-species those of the higher oxidation states (+5 and +4) are the least studied. In the present work the behavior of Mo(V) chloride was studied in a range of alkali chloride melts employing electronic absorption spectroscopy. The experiments were performed in LiCl-KCl, NaCl-CsCl, NaCl-KCl-CsCl eutectics and NaCl-KCl equimolar mixture between 450 and 750 oC, depending on the melt composition. Molybdenum(V) ions were introduced into the melt by feeding MoCl5vapor using the procedure described earlier (1). Analysis of the melt samples taken after the experiments showed that the mean oxidation state of molybdenum in the salt phase was +5.Electronic absorption spectra recorded upon dissolution of MoCl5 in an alkali chloride melt contained a broad band with a maximum around 13000 cm-1 (770 nm). Resolution of the spectra into individual bands, however, showed that this band represents a superposition of two bands with maxima around 15500 and 12500 cm-1, Fig. 1. The ratio between the intensities of these two component bands depends on temperature. At low temperatures the spectrum contains essentially one band (marked as 1 in Fig. 1) around 767 nm (13100 cm-1) corresponding to 2T2g→2Eg transition in the octahedral MoCl6 - ion. The energy of this transition agrees with that observed for WCl6 - ion, isoelectronic with MoCl6 - (2). On increasing temperature the second band (marked as 2 in Fig. 1) around 650 nm (15500 cm-1) becomes more prominent. The ratio of intensities of bands 1 and 2 changes with temperature, e.g. in LiCl-KCl melt it decreases from 1 : 0.2 at 450 oC to 1 : 2.6 at 850 oC.The band around 650 nm corresponds to the absorption of molecular MoCl5 (3). In the present study the absorption spectra of gaseous MoCl5 were measured at various temperatures and an example is shown in Fig. 2. Resolution of the spectrum of gaseous MoCl5 into individual bands, Fig. 3, shows that in the visible region there are two bands, a very intense one above 17000 cm-1 and a medium intensity band around 15000 cm-1. These bands can account for the changes in the spectra of Mo(V) solutions in the chloride melts occurring upon increasing temperature. Analysis of the spectroscopic data therefore shows that there are two species present in alkali chloride melts containing the products of MoCl5 dissolution, MoCl6 - and MoCl5. Most likely that these species are present in the equilibrium:MoCl6 - ↔ MoCl5 + ½ Cl2 and this equilibrium is shifted to the right with temperature.1. V. A. Volkovich, I. B. Polovov, R. V. Kamalov, B. D. Vasin and T. R. Griffiths, in Molten Salts Chemistry and Technology, M. Gaune-Escard and G. M. Haarberg, Editors, p. 489, John Wiley & Sons Inc., Hoboken (2014).2. V. A. Volkovich, D. A. Danilov, I. B. Polovov, B. D. Vasin, T. R. Griffiths, D. E. Aleksandrov, O. A. Tropin and D. V. Tsarevskii, ECS Transactions, 3(35), 555 (2007).3. R. F. W. Bader and A. D. Westland, Can. J. Chem., 39, 2306 (1961).

Anodic dissolution of irradiated metallic fuels in LiCl–KCl melt

Electrorefining is the main step in pyro-process of spent nuclear fuels, where actinides are recovered and separated from fission products. In the present study, electrorefining of irradiated metallic fuels called METAPHIX-1 (U–19wt%Pu–10wt%Zr alloy irradiated at PHENIX reactor, approximate maximum burn-up 2.5at%) was performed. A major focus was on minimization of Zr co-dissolution from spent metallic fuels to reduce the burden to the pyro-process. Based on the ICP-MS analysis results and the SEM–EDX observations, the anodic dissolution behavior of the irradiated metallic fuels and the mass balances of actinides and fission products during the electrorefining were evaluated.

Electrochemical formation of Al–Tm intermetallics in eutectic LiCl–KCl melt containing Tm and Al ions

This work focuses on investigating the electrochemical formation of Al–Tm and Al–Li–Tm alloys in LiCl–KCl–AlCl3–Tm2O3 melt on both W and Al electrodes. Thermodynamic calculation and electrochemical behavior of LiCl–KCl melt containing both AlCl3 and Tm2O3 showed that AlCl3 can chlorinate Tm2O3 to release Tm(III) ions. Three kinds of Al–Tm intermetallics at about −1.26, −1.32 and −1.43V were detected by means of various electrochemical measurement techniques, i.e. cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry. Potentiostatic and galvanostatic electrolysis were carried out on Al and W electrodes to prepare Al–Tm and Al–Li–Tm alloys, respectively. The composition of Al–Li–Tm alloys was analyzed by inductive coupled plasma atomic emission spectrometer (ICP-AES).

Electrochemical reduction of Tm on Mg electrodes and co-reduction of Mg, Li and Tm on W electrodes

The reduction process of Tm(III) ions was investigated in LiCl–KCl–MgCl2 melt on a W electrode and in LiCl–KCl melt on a Mg electrode at 753K, respectively. On the W electrode, in LiCl–KCl–MgCl2 melt the reduction of Tm(III) ions was a two-step process: Tm(III)+e−1 → Tm(II) and yTm(II)+2ye−1+xMg → MgxTmy. The reduction process of Tm(III)/Tm(II) was not observed on the Mg electrode, and only two signals, related to Mg–Tm intermetallic compounds were observed, in the cyclic voltammogram and chronopotentiogram. Galvanostatic electrolysis was employed to prepare Mg–Li–Tm alloys on both W and Mg electrodes. The deposits were characterized by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). Mg24Tm5 and Mg2Tm phases were detected in the deposits. The effect of Tm addition on Mg–Li alloy was investigated via potentiodynamic polarization and OM at room temperature. The grain size of Mg–Li alloy becomes much smaller after addition of Tm element. The corrosion potentials of Mg–Li–Tm alloys shift toward a more positive direction than that of Mg–Li alloy.

Real-time monitoring of metal ion concentration in LiCl–KCl melt using electrochemical techniques

Cyclic voltammetry (CV) and chronoamperometry (CA) were employed to develop a real-time monitoring system for the pyrochemical process. These electrochemical techniques showed a good linearity of the current and the passed charges with the concentration of a solute even up to 9wt.% in a LiCl–KCl melt, showing the potential for real application. To apply CA to the pyrochemical process, where the concentration of actinides and/or lanthanides is largely variable, the repeating chronoamperometry was designed and successfully tested at a wide range of Nd3+ ion concentration of up to 9wt.%.

ZnCl2 and Liquid Zinc Assisted Electrochemical Extraction of Thulium from LiCl–KCl Melt

This work presents a study of the electrochemical behavior of Tm at liquid Zn electrode in LiCl–KCl–TmCl3 melt and the co-reduction of Zn, Li and Tm on W electrodes in LiCl–KCl–ZnCl2–TmCl3 melt at 753 K. The deposition potential of Tm in liquid Zn material was found to be 0.9 V more positive than that at a solid W electrode. In LiCl–KCl–ZnCl2–TmCl3 melt, five Zn–Tm intermetallic compounds were detected in Zn-coated W electrode by cyclic voltammetry and chronopotentiometry. Extraction of Tm was carried out on a W electrode in LiCl–KCl–ZnCl2–TmCl3 melt and at liquid Zn electrode in LiCl–KCl–TmCl3 melt. The obtained deposits showed Tm2Zn17 phase. The morphology and micro-zone chemical analysis of the deposits was characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The composition of the deposits was analyzed by inductive coupled plasma atomic emission spectrometer (ICP-AES). The deposits obtained at W and liquid Zn electrodes were composed of 50.6 wt% and 22.3 wt% Tm, respectively.

Stability of Electrode Materials During Electrolysis in LiCl-KCl Melt

Stability of Electrode Materials During Electrolysis in LiCl-KCl Melt

Electrochemical extraction of samarium from LiCl-KCl melt by forming Sm-Zn alloys

The co-reduction of Sm(III) and Zn(II) ions on the Mo electrode and the under potential deposition of Sm(III) ions on the liquid Zn electrode were investigated in LiCl-KCl molten salt at 873K. Cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry techniques were employed to study the electrochemical behaviors of Sm(III), Zn(II) and Sm-Zn alloy formation. The results showed that on the inert Mo electrode the electro-reduction of Sm(III) took place in only one soluble-soluble electrochemical step Sm(III)/Sm(II), and the electrochemical step Sm(II)/Sm(0) was not observed within the electrochemical window. In contrast, the deposition potential of Sm(II)/Sm(0) shifted to the positive direction by forming SmxZny intermetallic compounds in both the co-reduction and under potential deposition process. In the co-reduction process, the signals of forming six kinds of SmxZny intermetallic compounds were observed in the high ZnCl2 containing melt, and the formation of SmxZny at about -1.56V is dominant. In the under potential deposition process, the dominant deposition process is also at about -1.6V. The formation of Sm-Zn alloys were carried out by potentiostatic electrolysis on both the Mo electrode and liquid Zn electrode. All the Sm-Zn alloys were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and inductively coupled plasma atomic emission spectrometer (ICP-AES). The XRD results showed that the SmxZny compound prepared on the Mo electrode in the high ZnCl2 containing melt was SmZn12, while the SmxZny compound prepared on the liquid Zn electrode was predominantly Sm2Zn17.

Selective extraction of gadolinium from Sm2O3 and Gd2O3 mixtures in a single step assisted by MgCl2 in LiCl–KCl melts

The chloration of MgCl2 was studied in the LiCl–KCl–MgCl2–Gd2O3–Sm2O3 melts. Gd(III) and Sm(III) ions were observed by cyclic voltammetry and square wave voltammetry assisted by MgCl2 in melts. X-ray diffraction (XRD) patterns of melts indicated Gd2O3 and Sm2O3 were chlorinated by MgCl2 and formed GdCl3 and SmCl3. XRD patterns of non-dissolved residues, which were left after the melts were washed with water to remove the soluble salt, showed that the new compounds (i.e., GdOCl, SmOCl, MgO, Gd(OH)3, and Sm(OH)3) were produced. Potentiostatic electrolysis experiments were performed to extract Gd from Gd2O3 and Sm2O3 mixtures assisted by MgCl2. Separation between Gd2O3 and Sm2O3 was also achieved in a single step with the formation of Mg–Li–Gd alloys. XRD patterns of alloys indicated that Mg3Gd phase was formed. Scanning electron microscope images with energy dispersive X-ray spectroscopy showed Gd elements were mainly distributed in the grain boundary.

Extraction of ytterbium via co-reduction of Al(III) and Yb(III) from LiCl–KCl melt on W electrode

Anhydrous ytterbium chloride was obtained via solid-phase reaction from Yb2O3 with AlCl3 as a chlorination agent. The electrochemical behavior of the chloridized Yb2O3 was investigated on W electrodes in LiCl–KCl and LiCl–KCl–AlCl3 melts by cyclic voltammetry and square wave voltammetry. The results showed that the reduction/reoxidation of Yb(III)/Yb(II) was reversible and controlled by diffusion. The signals related to the formation of two Al–Yb intermetallic compounds were detected in LiCl–KCl–AlCl3 melt. Potentiostatic electrolysis was carried out in LiCl–KCl–AlCl3–YbCl3 melt on W electrodes at 943 K at different potentials and Al3Yb, Al2Yb, AlLi and Al2Li3 phases were detected in deposits. Then, the extraction of ytterbium was performed. The currents evolution was recorded by square wave voltammetry and the extraction efficiency was evaluated via inductive coupled plasma atomic emission spectrometer analysis during electrolysis. The initial extraction rate is much higher than that at longer times. The extraction efficiency was about 98.0 % for Yb(III) after potentiostatic electrolysis for 60 h at −1.84 V in LiCl–KCl–AlCl3–YbCl3 melt.

The equilibrium between metallic titanium and titanium ions in LiCl–KCl melts

Abstract The equilibrium between metallic titanium and titanium ions (Ti2+, Ti3+) dissolved in LiCl–KCl melts and the influence of the electrolyte composition on the equilibrium were investigated. The accurate concentrations of titanium ions had been obtained based on a reliable approach for taking samples. Furthermore, accurate values of the equilibrium constants were calculated by the best-fitting method under the consideration of the TiOCl dissolution. The influence of the electrolyte composition on the equilibrium was evaluated by determining the equilibrium constant Kc between titanium metal and titanium ions in LiCl–KCl melts with different concentration of LiCl. It was shown that LiCl could affect the equilibrium and the Kc values decreased with the increase of concentration of LiCl.

Electrochemical behavior of cerium ion in molten LiCl-KCl

The electrode process of cerium(III) on the Mo electrode in eutectic LiCl-KCl melt was investigated by electrochemical transient techniques in the temperature range of 673–783 K, respectively. These results unanimously indicated that the reduction process of cerium(III) to cerium metal was a single step exchanging three electrons which was controlled by diffusion of cerium(III). Diffusion coefficients (DCe(III)) in eutectic LiCl-KCl melt were determined by cyclic voltammetry, chronopotentiometry and square wave voltammetry. An empirical diffusion coefficient function depending on temperature was proposed: lnDCe(III)=−2.129−5704/T. The formal potentials (Eθ′Ce(III)/Ce(0) versus Ag/AgCl reference electrode) at different temperatures were obtained from chronopotentiometry, which were –2.10 V (673 K) and –2.07 V (733 K), respectively.

Anodic Reactions on Some Materials in LiCl-KCl Melt

The anodic reactions on some materials in LiCl-KCl eutectic melt have been investigated. Palladium and Mo were dissolved seriously though Mo showed passivation behavior. In the melt including Li2O, O2 gas generation occurred at both metal anodes along with their anodic dissolution. At carbon anode, some anodic reactions besides the Cl2 gas generation reaction were observed in the melt with Li2O. The visual observation and the weight change of the anode indicated that the anodic reaction without gas generation and the electrode consumption preceded the CO2 gas generation. The potential of the CO2 gas generation reaction on carbon looked more positive than that of the O2 gas generation on Pd and Mo, which suggested the overpotential of the CO2 generation reaction on carbon was rather large in the melt.

The Solubility of Rare Earth with Variable Valent and Electrochemical Behavior in LiCl–KCl–AlCl3 Melts

The solubility of RE2O3 (RE=Sm, Yb, and Eu) with variable valent in LiCl–KCl melts is extremely low. It is impossible to directly extract variable valent metals from RE2O3 using electrolysis in molten salts. After adding AlCl3 to the melt system, the solubility measurements of RE2O3 in LiCl–KCl and LiCl–KCl– AlCl3 melts indicate that AlCl3 can effectively chloridize RE2O3. Take Yb2O3 as an example, the solubility of Yb2O3 in the LiCl–KCl–AlCl3 melts increases first and decreases afterwards due to the rapid volatility of AlCl3 with increase of temperature. The thermodynamic calculation of the reaction of Yb2O3 and AlCl3 also indicates that the reaction would proceed forward at 753K. Electrochemical behavior of RE2O3 on a molybdenum electrode in LiCl–KCl melts containing AlCl3 also indicates that RE2O3 is effectively chloridized by AlCl3, and then discharges in the form of RE(III) ions in the cathode. The underpotential deposition of RE on pre-deposited aluminum leads to the formation of Al-RE alloy. The extraction of RE with variable valent from RE oxide in LiCl–KCl melts is proven to be feasible.

Cathodic Behaviour of Samarium (III) in LiCl-KCl Melts on Molybdenum and Aluminium Electrodes

The electrochemical behavior of samarium ions was investigated in LiCl-KCl melt at molybdenum and aluminium electrodes using different electrochemical techniques such as cyclic voltammetry, square wave voltammetries, chronopotentiometry and open circuit chronopotentiometry. On Mo electrode the electroreduction process of Sm(III) to Sm(II) is reversible within the electroactive window. The reduction of Sm(II) is not observed in cyclic voltammogram, but it can be reduced on Al electrode by forming Al-Sm alloy. It is an effective approach to extract Sm from spent nuclear fuel.

Corrosion of samarium and lanthanum in molten eutectoid mixture of lithium and potassium chlorides

The effect of temperature and duration of the process on the corrosion rate of samarium and lanthanum is studied in the melt of LiCl (60 mol %)-KCl. It is found that the corrosion rate of samarium is by an order of magnitude higher than that of lanthanum at similar temperatures. Satisfactory coincidence of the corrosion current density of lanthanum calculated on the basis of the gravimetric data, experimental data on steady-state potentials, and information on anodic polarization points to the electrochemical mechanism of lanthanum corrosion in the LiCl-KCl melt.

Corrosion resistance of steel materials in LiCl-KCl melts

The corrosion behaviors of 304SS, 316LSS, and Q235A in LiCl-KCl melts were investigated at 450°C by Tafel curves and electrochemical impedance spectroscopy (EIS). 316LSS shows the best corrosion resistance behaviors among the three materials, including the most positive corrosion potential and the smallest corrosion current from the Tafel curves and the largest electron transfer resistance from the Nyquist plots. The results are in good agreement with the weight losses in the static corrosion experiments for 45 h. This may be attributed to the better corrosion resistance of Mo and Ni existing as alloy elements in 316LSS, which exhibit the lower corrosion current densities and more positive corrosion potentials than 316LSS in the same melts.

Formation of metallic Si and SiC nanoparticles from SiO2 particles by plasma-induced cathodic discharge electrolysis in chloride melt

Silicon nanoparticles are formed from SiO2 particles by conducting plasma-induced cathodic discharge electrolysis. In a LiCl–KCl melt in which SiO2 particles were suspended at 450°C, we obtained Si nanoparticles with diameters around 20nm. During the electrolysis period, SiO2 particles are directly reduced by discharge electrons on the surface of the melt just under the discharge, and the deposited Si atom clusters form Si nanoparticles, which leave the surface of the original SiO2 particle due to free spaces caused by a molar volume difference between SiO2 and Si. We also found that SiC nanoparticles can be obtained using carbon anode. Based on Faraday's law, the current efficiency for the formation of Si nanoparticles is 70%.