The equilibrium potentials of platinum in a KCl–PbCl2—PtCl2 melt at various temperatures and platinum dichloride contents are measured by the emf method. The empirical equations of the isotherms and polytherms of the equilibrium potentials of platinum are derived. The conditional standard potentials of platinum in a molten mixture of potassium and lead are calculated. The changes in the Gibbs energy upon platinum dichloride formation from elements in the melt under study are determined. The separation factors of the metals from the alloys are estimated. The obtained results indicate prospects of the separation processes of lead and noble metals in chloride melts.

Anode dissolution of lead, silver, antimony and liquid lead-bismuth-antimony alloys has been studied by the polarization method depending on the alloy composition in the molten KCl-PbCl2 eutectic. Lead was found to dissolve and to form Pb2+ ions within the whole range of anode current densities in the Pb-Ag-Sb (49.0-28.0-23.0) and Pb-Ag-Sb (11.0-55.0-34.0) melts. The limiting diffusion current of lead dissolution was observed at the anode current density of 0.34 & Acy; cm(-2) in the Pb-Ag-Sb (5.0-65.0-30.0) alloy. At the anode current densities exceeding these values the antimony dissolution was observed. To define a mechanism of metals electro dissolution, the number of electrons participating in the electrode reactions was calculated. Based on the polarization curves analysis the regime of electrochemical separation of lead alloys was selected. Metallic lead and the remaining Ag-Sb-Pb alloy with the valuable components concentration exceeding 90 wt% were obtained in the laboratory-scale electrolytic cell.

Abstract—The equilibrium potentials of silver are measured by the emf method in a KCl–PbCl2–AgCl melt at different temperatures and silver chloride concentrations. Empirical equations are derived for the equilibrium potential isotherms and polytherms of silver. The conditional standard potentials of silver in a molten mixture of potassium and lead chlorides are calculated. The changes in the Gibbs energy during the formation of silver chloride from the elements are calculated. The separation coefficients of the metals from the alloys are estimated. The obtained results indicate that the processes of lead and silver separation in chloride melts are promising.

Equilibrium potentials of uranium (U3+/U0) have been measured in the LiF-BeF2-UF3 melt as a function of temperature and uranium fluoride concentration. The empirical equation of uranium potential isotherms and polytherms have been obtained. Cathode polarization of uranium in the molten mixture of beryllium and lithium fluorides has been measured using the current switch off method form the stationary state. Uranium ions were found to have primarily the-valence of three in the LiF-BeF2 electrolyte in the studied temperature and uranium fluoride concentration ranges. A conditional standard potential of uranium (U3+/U0) in the molten mixture of lithium and beryllium fluorides was calculated relative to the reference fluorine electrode according to the experimentally obtained data on the equilibrium potentials of the uranium electrode in the LiF-BeF2-UF3 melt. Standard conditional changes in the Gibbs energy, enthalpy and entropy at the formation of uranium trifluoride from the elements in the form of dilute solutions were determined. The enthalpy of mixing of liquid uranium fluoride and the 0.73LiF–0.27BeF2 melt was calculated.

A thermodynamic analysis of the equilibrium in the LiF–BeF2–BeO–C system at temperatures below 3000°C is carried out. The conditions and parameters of the carbothermic reduction of beryllium oxide dissolved in FLiBe are chosen on the basis of the analysis results. The occurrence of the reaction BeO(s) + C(s) = Be(s/l) + CO(g) is thermodynamically possible at temperatures above 2500°C. Such a high temperature undesirable for an analysis of a molten salt with a significantly lower liquidus temperature can be decreased by adding a metal that forms alloys with beryllium with a low activity coefficient via the reaction BeO(s) + C(s) = M(Be)(l) + CO(g). A thermodynamic analysis of the system 66 kmol

Electrodeposition of molybdenum in the NaCl-KCl-MoCl3 (10 wt% of \Mo) melt was studied by the pulsed electrolysis at 780 degrees C. The compact Mo deposits were obtained. The electrolyte deposits were studied using scanning electron microscopy and X-ray diffraction analysis. It was found that the solid Mo cathode deposits of the primarily (110) orientation may be obtained by the pulse electrolysis at the cathode current (ic) ranging from 2 up to 6 A/cm2, average cathode current density (im) ranging from 0.286 up to 0.875 A/cm2 and ratio of the relaxation time to the pulse time (Tr/Tc) ranging from 6 up to 18. The influence of the electrodeposition con-ditions on the current efficiency at the pulse electrolysis was studied. The pulse electrolysis parameters allowing the electroreduction with 100% current efficiency are determined. An increase in the cathode pulse time (Tc) was found to result in a decrease in the current efficiency of the im and Tr/Tc constants. An increase of the cathode current density (ic) as well as a decrease of the cathode pulse time (Tc) lead to a decrease of the crystal di-mensions. The optimization of the im and Tr/Tc parameters increases the electrodeposition rate by factor 5 comparing to the galvanostatic electrolysis.

The interaction between CrF 2 and a molten binary LiF-BeF 2 mixture has been studied using the electrochemical methods. The polarization of the chromium electrode relative to the dynamic beryllium electrode was measured. The obtained voltammetry data elucidates that under the experimental conditions, chromium is observed exclusively in one valence form. According to the cathode polarization dependences, it is established that the reduction of chromium ions in the metal occurs by a two-electron electrode reaction. The equilibrium concentrations of chromium were experimentally measured at the temperatures of 923, 973, and 1023 K at different chromium fluoride concentrations in the melt. The oxidation degree of chromium, dissolved in the melt, was calculated according to the concentration dependences of the equilibrium potentials. A thermodynamic analysis of the chromium difluoride dissolution in a molten mixture of lithium and beryllium fluorides was performed. The formation of dilute solutions of chromium difluoride is accompanied by slight deviations of the salt system from Raoult’s laws.

The equilibrium potentials of iron in a LiF-BeF2-FeF2 melt were measured using the EMF method and were dependent upon the temperature and iron fluoride concentrations. The empirical equations for the isotherms and equilibrium polytherms of the iron fluoride concentration were obtained. The cathode polarization of iron fluoride in the molten mixture of lithium and beryllium fluoride was measured using the current switch off method from the stationary state. It was found that in the studied temperature and concentration ranges of iron fluoride in the LiF-BeF2 electrolyte, the valence state of iron in the melt is mainly +2. According to the experimental values of the equilibrium potentials of the iron electrode in the LiF-BeF2-FeF2 melt, the conditional standard potentials of iron were calculated relative to the fluoride reference electrode in the molten mixture of lithium and beryllium fluoride. The conditional standard values of the Gibbs energy change were calculated at the formation of iron difluoride from the element in the form of dilute solutions, as were the thermodynamic values (enthalpy and entropy) when iron difluoride was mixed with LiF-BeF2.

The anode dissolution of ternary Pb-Ag-Bi metallic alloys with different components concentration has been studied in the molten KCl-PbCl2 eutectics. A lead dissolution was found to be the main process in the Pb-Ag-Bi (60.0-15.0-25.0), Pb-Ag-Bi (42.9-21.4-35.7), Pb-Ag-Bi (7.0-34.9-58.1) alloys within the whole interval of studied anode current densities. The Pb-Ag-Bi ((4.8-35.7-59.5) and Pb-Ag-Bi ((2.4-36.6-61.0) alloys at the anode current densities of 2.3 A/cm(2) and 0.14 A/cm(2) have the limiting diffusion current of lead dissolution. At the anode current densities exceeding the aforesaid values a bismuth dissolution takes place. The number of electrons participating in each electrode reaction is determined for each mechanism of metal electrodissolution. A regime of electrochemical separation of lead alloys is chosen based on the analysis of polarization curves. Metallic lead and Ag-Bi-Pb (5.1 wt%) alloy were obtained in the laboratory electrolytic cell. (C) 2022 Elsevier B.V. All rights reserved.

The electrochemical behavior of rhenium ions in the molten KF-KBF4-B2O3 salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF4-B2O3 were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10−5 cm2/s and 4.61 × 10−5 cm2/s for R1 and R2, respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF4-B2O3 at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO4 and K3ReO5). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component.

A new way to reduce the energy consumption during the operation of powerful aluminum reduction cells is suggested via reducing the resistance of the electrolyte, i.e., increasing its electrical conductivity. The electrical conductivity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 with cryolite ratio (CR) of 2.1–3.0 and content of CaF2 and Al2O3, up to 8 wt%, was measured at the temperatures from liquidus to 1300 K. Based on the experimental results, a multifunctional equation for the electrical conductivity of oxide-fluoride cryolite melts was evaluated. The experimental and calculated values of the electrical conductivity agree within 1.5%. The activation energy of the electrical conductivity of the NaF-AlF3-CaF2-Al2O3 melts was estimated. The activation energy of electrical conductivity for molten NaF-AlF3 mixtures with CR 3.0 and 2.1, determined by the most mobile cations Na+, increased from 15.8 kJ/mol up to 18.5 kJ/mol. It was found that CR had a greater impact on the activation energy than the changes in the Al2O3 or CaF2 concentrations. Based on the ratio of the activation energies of the electrical conductivity and the viscous flow, the correlation between the electrical conductivity and viscosity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 was illustrated.

This paper presents experimental data on the dependence on alumina and calcium fluoride concentrations of the viscosity of the industrial electrolytes NaF-AlF3-CaF2-Al2O3 with cryolite ratios (CR) of 2.1, 2.3, 2.5 in the temperature range 1243–1293 K. The temperature dependence of the formation of a solid phase on the graphite crucible wall in cryolite-alumina electrolyte during aluminium electrolysis was studied in a laboratory-scale electrolytic cell. The viscosity of the industrial electrolytes was found to depend more on the temperature and cryolite ratio than on the alumina concentration in the melt. A long period of electrolysis with controlled solid phase formation on the cell wall was carried out, with a constant electrolyte composition (CR = 2.4), a calcium fluoride concentration of 5 wt% and an alumina content of 4.0 wt%. The formation of a stable solid phase layer on the graphite crucible wall was found to depend on the electrolysis temperature. A correlation was observed between the formation of a solid under the influence of temperature and the viscosity of the melt.

The paper illustrates the results of experimental study on the formation of the solid phase on the graphite crucible wall in the cryolite-alumina electrolyte depending on the temperature, rates of the liquid phase motion and heat flow in the laboratory electrolytic cell. The side ledge stability is shown to depend on the rate of the heat flow, which is caused by changes in the temperatures of the electrolyte, electrolytic cell walls and liquidus. When the temperature of the inside wall is higher than the electrolyte liquidus temperature the side ledge does not form, but in the case when it is lower than the liquidus temperature the side ledge formation proceeds until the temperatures equalize. As the electrolyte motion rate increases the thickness of the bottom ledge exceeds the thickness of the side ledge. The changes in the heat resistance of the electrolytic cell walls have a significant influence on the crust growth over the electrolyte and have less influence on the thickness of the bottom and side ledges.

Equilibrium potentials of antimony in the KCl–PbCl2–SbCl3 melt are measured by the EMF method as a function of the temperature and the content of antinomy chloride. Empirical equations of isotherms and polytherms of equilibrium potentials of antimony are obtained. The arbitrary standard potentials of antimony in the molten mixture of potassium and lead chlorides are calculated. The changes in the Gibbs energy at the formation of antimony trichloride from elements in the melt under study are calculated. The separation factors of metals from alloys are assessed. These results suggest that the processes of separation of lead and antimony in chloride melts hold much promise.

The present paper is devoted to the study of the electrolyte temperature influence on the cathode process of rhenium reduction on the glassy carbon anode by the cyclic voltammetry method. Experimental dependencies, which characterize the influence of the KReO4 addition on the KF-KBF4-B2O3 system liquidus temperature, were built according to the obtained data on the thermal analysis. It was found that rhenium reduction at lower electrolyte temperatures requires higher values of cathode overpotential.

The paper is aimed at the study of the influence of bismuth, antimony, and lead concentrations on the Pb-Bi, Sb-Pb alloys anode dissolution in the equimolar KCl-PbCl2 melt. The process of lead dissolution, which occurs at the potentials close to equilibrium ones, was found to be a basic process up to the definite values of current densities. According to changes in the theoretical and experimental polarization curves, the element concentrations at the liquid anodes surface were evaluated depending on the current load. The electrolytic cell with a bipolar metallic electrode, the electrolytic cell with two anodes and one cathode, and the electrolytic cell with a porous diaphragm were studied. The tests demonstrated that lead is effectively separated from the metal impurities in all constructions under study.

A KCl-PbCl2 (50.0-50.0 mol %) molten system was used as an electrolyte for secondary lead refining. As a result, pure lead and an anode product containing 52.81 mol % Sb, 33.66 mol % Bi, 7.54 mol % Pb, 3.74 mol % Ag, and 2.24 mol % As were obtained. Long-term electrochemical refining was found to be possible in the KCl-PbCl2 electrolyte. Thermal analysis was applied to determine liquidus temperatures of the KCl-PbCl2 (50.0-50.0 mol %) mixture with the PbO concentration ranging from 0 to 20 mol %. The temperature dependence of the PbO solubility in the KCl-PbCl2 (50.0-50.0 mol %) melt was studied, and the thermodynamic parameters of the PbO solubility were calculated. Electrical conductivities and densities of oxy-chloride melts were measured.

In order to develop a strategy of alumina supplying the electrolysis cell, a change of the alumina content dissolved in cryolite electrolyte during long-term aluminum electrolysis was studied under different modes of alumina feeding. The experiment was carried out using a lab setup providing the electrolyte convection due to the anode gas evolution. The electrolyte composition was close to the conventional one: NaF-AlF3 with CR=2.7, CaF2 5 wt%. The initial content of Al2O3 in the electrolyte was 4 wt%. The electrolyte samples were withdrawn during electrolysis in order to determine the Al2O3 content by means of an Oxygen Analyzer. The alumina dissolution rate in the electrolyte was found by comparing the values of the dissolved alumina content, determined in the electrolyte sample, and the loss of alumina consumed in the electrochemical reaction of the aluminum production. Measurements of the side ledge thickness formed due to solidification of the electrolyte during electrolysis were conducted. Under the conditions of electrolysis, at a rate of the alumina addition of 10 g/h, 36% of the added alumina was spent on increasing the alumina content in the melt; 44.6% was depleted on the electrochemical reaction; 19.4% did not dissolve in the electrolyte, but was involved in the formation of the side ledge. Thus, the content of dissolved alumina in the electrolyte increased and the side ledge was observed, which indicated an incorrect mode of the alumina supply. A decrease in the alumina feeding rate to an average value of 5.88 g/h contributed to the stabilization of electrolysis. In this case the side ledge was not formed and the content of dissolved alumina in the melt was constituted during electrolysis. That is, the conditions for optimal alumina feeding have been found for the electrolysis process under studied conditions.

An experimental setup is created to study the dynamic behavior of the side ledge under the electrolysis in a cryolite-alumina electrolyte. The installation has a built-in window on the side panel, which allows the lining material and, hence, the heat flow to be varied. The dynamic formation of a side ledge is experimentally studied as a function of temperature, the electrolyte velocity, and the heat flow during the electrolysis of aluminum. The rate of the ledge formation and the ledge thickness are determined by the heat flow caused by the electrolyte temperature, the cell side temperature, and the liquidus temperature. As in an industrial electrolysis cell, the side ledge profile formed in the experimental cell can be conventionally divided into the following three zones: the ledge at the bottom in contact with liquid aluminum, the ledge at metal/electrolyte interface, and the ledge at the electrolyte level. If the temperature of the inner wall is higher than the liquidus temperature, the side ledge does not form; if it is lower, the side ledge forms until these temperatures become the same. Therefore, the stability of the side ledge depends on the heat flow from the center to the walls; however, the dynamic behavior (solidification/melting) of the ledge in the metal zone occurs slowly and differs from the behavior of the side ledge.