The reduction of pellets composed of individual CeO₂, Nd₂O₃ and a La₂O₃-Nd₂O₃-CeO₂ mixture by lithium extracted on a cathode during lithium chloride electrolysis at 650 °C was studied. The methods of cyclic voltammetry, electron microscopy, including determination of the elemental composition of the studied objects, and X-ray diffraction analysis were applied for the present study. The reduction degree of rare-earth metal (REM) oxides was determined using both the bromine method and reduction melting of the samples in the graphite crucible. The formation of the metallic phase composed of the rare-earth elements (REEs) was not observed even at the cathode potentials, corresponding to the formation of the liquid alkali metal phase, and lithium extraction, which, in the quantitative ratio, exceeds greatly the values needed for the reduction reaction. CeO₂ was found to reduce to Ce₂O₃.

The present paper is dedicated to the quantitative determination of oxygen-containing impurities in the LiF–NaF–KF eutectic using electrochemical (cyclic and square-wave voltammetry) and reduction melting methods. The LiF–NaF–KF melt was analyzed before and after purifying electrolysis. The amount of oxygen-containing impurities removed from the salt during purification was determined. It was found that after electrolysis, the concentration of oxygen-containing impurities decreased by 7 times. The results obtained via electrochemical techniques and reduction melting were well-correlated, which made it possible to evaluate the quality of the LiF–NaF–KF F melt. To verify the analysis conditions, mechanical mixtures of LiF–NaF–KF containing Li₂O were analyzed using the reduction melting method. The oxygen concentration in the mixtures varied from 0.672 to 2.554 wt. %. Based on the analysis results, the dependence approximated by the straight line was obtained. These data may be used to draw calibration curves and to further develop the procedure of oxygen analysis of fluoride melts.

The electrochemical reduction of pelleted heterophase powder Pd-Nd₂O₃-CeO₂ mixtures was studied in molten LiCl-Li₂O (1–1.5 wt%) at 650 °C. The influence of the composition of the mixture, as well as electrochemical factors—i.e., the amount of electricity passed and the cathode potential during electrolysis—were considered. It was found that in the presence of metallic palladium, neodymium and cerium oxides are reduced by lithium released at the cathode and form intermetallic compounds of different compositions. At potentials more positive than the formation of a phase based on liquid lithium at 0.5–0.8 V, CePd₃ and NdPd₃ intermetallic compounds are present in the reduced product. At potentials close to the formation of liquid lithium, a whole spectrum of intermetallic compounds is synthesized: CePd, NdPd, Ce₃Pd₄, and Nd₃Pd₄. The mechanisms of formation of palladium alloys with neodymium and cerium are proposed and considered. The degree of the reduction of lanthanide oxides was calculated from the data on the concentration of residual oxygen in the reduced product.

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 % LiF + 34 kmol % BeF₂ + 1 kmol % BeO + 10 kmol % C with the specified activity coefficient of beryllium (10^–2 → 10^–4 → 10^–6 → 10^–8) shows that the reduction of BeO occurs at 1640°C by 99.2% at the activity coefficient f(Be) = 10^–4 in the alloy and by 99.98% at f(Be) = 10^–6. The Cu–Be alloy with the activity coefficient of Be of 10^–6 to 10^–4 in the temperature range from 1000 to 1700°C can be used to decrease the reduction temperature. The determined reduction conditions (copper bath) and parameters (1640°C) are successfully tested on FLiBe–BeO samples with a known oxygen concentration on a Metavak-K gas analyzer.

—The main problems hindering the determination of oxygen in fluoride salts by carbothermic reduction have been identified. They include the volatility of salts when heated to high temperatures, hygroscopicity, and the absence of appropriate standard samples and determination techniques. Most of these problems can be eliminated by selecting the correct analysis conditions and modifying the equipment. A bench setup installed in a glove-box for carbothermic oxygen determination has been created at the Institute of High-Temperature Electrochemistry in cooperation with ZAO Spectroscopic Systems, a Russian manufacturer of glove-box systems, and NPO Eksan, a manufacturer of gas analyzers. Potassium, sodium, and lithium fluorides and the LiF–NaF–KF salt system synthesized by melting the initial components are analyzed using the modified and classical apparatus systems. According to the results of analysis, the oxygen concentration in hygroscopic FLiNaK and KF powders, the sample preparation and analysis of which were carried out in the box-containing setup, is significantly lower than that determined in air.