The electrochemical behavior of Nd and U compounds in a 3LiCl–2KCl eutectic melt on Ga–Al eutectic alloy electrodes in the temperature interval 723–823 K was studied by zero-current potentiometry vs. chlorine reference electrode. The temperature dependences of the Nd and U activity coefficients in Ga–Al alloys were calculated: logγ Nd(Ga–Al) = 5.37–13467/ T ± 0.23, logγ U(Ga–Al) = 1.16–4962/ T ± 0.07. The U/Nd separation factors in the molten salt–liquid metal system were determined: logθ = 1.76 + 2605/ T ± 0.02. The separation factors obtained (θ = 2.29 × 10 5 at 723 K) show that the Ga–Al alloy is promising for future innovative technologies for spent nuclear fuel reprocessing.

Electrochemical and thermodynamic properties of Nd, Sm, Eu, Tm, and Yb chlorides in melts of individual LiCl, NaCl, KCl, and CsCl, of 3LiCl-2KCl, LiCl-KCl-CsCl, NaCl-KCl-CsCl, and NaCl-2CsCl eutectics, and of the equimolar NaCl-KCl mixture in the temperature interval 573–1173 K were studied by stationary and nonstationary methods. The mechanism of reduction of lanthanide(III) ions to metal was elucidated, and the main kinetic and thermodynamic characteristics of the process in alkali metal chloride melts were calculated. The influence of the ionic potential and polarizing power on the behavior of lanthanides in molten salts of various cationic compositions was determined.

The electrochemical behavior of NdCl 3 solutions in eutectic LiCl-KCl-CsCl and individual CsCl melts was studied on an inert molybdenum electrode at temperatures in the range 573–943 K. Cyclic and differential pulse voltammetry and potentiometry at zero current and the electromotive forces method were used. The cathode reduction of Nd(III) ions to the metal was found to occur as a sequence of two stages. The formed Nd(II) ions were unstable above 798 K and underwent disproportionation 3Nd(II) ⇔ 2Nd(III) + Nd (m) in the salt melts. The conventional standard redox potential of the Nd(III)/Nd(II) pair in a eutectic LiCl-KCl-CsCl melt was measured over a wide temperature range. The main thermodynamic characteristics of the reaction NdCl 2(m) + 1/2Cl 2(g) ⇔ NdCl 3(m) were determined.

Electrochemical behavior of TmCl 3 solutions in a NaCl-2CsCl eutectic melt at temperatures of 823–973 K on an inert Mo electrode was studied by cyclic and square-wave voltammetry and the method of electromotive forces. The mechanism of the cathodic process was determined, kinetic parameters of the Tm(III) + e ⇆ Tm(II) reaction were found, and the temperature dependence of the diffusion coefficients of Tm(III) ions was calculated. The conditional standard redox potential for the Tm(III)/Tm(II) pair was measured in the temperature range under study. The basic thermodynamic characteristics of the Tm(III) + e ⇆ Tm(II) redox reaction in a molten NaCl-2CsCl eutectic mixture were determined.

Potentiometric method was used to measure the redox potentials of Tm3+/Tm2+ in a eutectic melt of sodium, potassium, and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–973 K. The main thermodynamic characteristics of the redox reaction TmCl2(solution) + 1/2Cl2(g) ⇆ TmCl3(solution) were calculate from the conditional standard potentials \(E_{{{Tm^{3 + } } \mathord{\left/ {\vphantom {{Tm^{3 + } } {Tm^{2 + } }}} \right. \kern-\nulldelimiterspace} {Tm^{2 + } }}}^* \).

Potentiometric method was used to measure the redox potentials of Yb 3+ /Yb 2+ in a eutectic melt of sodium and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–973 K. The basic thermodynamic characteristics of the redox reaction YbCl 2 (s.) + 1/2Cl 2 (g.) ai YbCl 3 (s.) were calculated from the conditional standard potentials E *(Yb 3+ /Yb 2+ ).

Electrochemical process of reduction of Yb(III) ions and oxidation of Yb(II) ions in a molten LiCl-KCl eutectic in the range 723–973 K was studied by linear, cyclic, and square-wave voltammetry and zero-current potentiometry.

Electrochemical reduction of Yb(III) ions to Yb(II) was studied in an equimolar NaCl-KCl melt in the temperature range 973–1075 K. Linear, cyclic, and square-wave voltammetry, chronopotentiometry, and potentiostatic electrolysis with tungsten as the working electrode were used in the study.

Electronic absorption spectra of GaCl3 and Ga2O3 solutions in molten alkali metal chlorides and in NaCl-KCl-NaF and LiF-NaF melts were measured by reflection-absorption spectroscopy. The spectral data showed that the main structural units in the solutions are complexes GaHlg(4)(-) (Hlg = Cl, F) with T-d symmetry and GaOHlg(3)(2-) with C-3v symmetry, respectively. Molecular oxygen occurring in molten systems as an admixture causes exchange decomposition with formation in all the melts of molecular complexes of chlorine, Cl2Cl-, with C-infinity v symmetry.

Interaction of gallium cations with oxygen anions in the NaCl-KCl molten equimolar mixture and NaCl-KCl-CsCl eutectic salt mixture as influenced by the activity of the oxygen ions in the melt was studied at 823–1023 K by potentiometric titration in an electrochemical cell with two platinum-oxygen electrodes and a solid electrolyte membrane. The form of occurrence of gallium in the molten salts and the proceeding chemical reactions were discussed. The solubility of gallium oxychloride was determined, and the thermodynamic characteristics of its formation were calculated.

Electronic absorption spectra of GaCl 3 and Ga 2 O 3 solutions in molten alkali metal chlorides and in NaCl-KCl-NaF and LiF-NaF melts were measured by reflection-absorption spectroscopy. The spectral data showed that the main structural units in the solutions are complexes GaHlg 4 − (Hlg = Cl, F) with T d symmetry and GaOHlg 3 2− with C 3 v symmetry, respectively. Molecular oxygen occurring in molten systems as an admixture causes exchange decomposition with formation in all the melts of molecular complexes of chlorine, Cl 2 Cl − , with C ∝ v symmetry.

Fugacities of GaCl3 and alkali metal chlorides over molten dilute (up to 3 mol %) solutions of GaCl3 in LiCl, NaCl, KCl, RbCl, and CsCl were measured at 1100 K by dynamic and indirect static methods. The chemical composition of the saturated vapor over the mixed melts was determined. The partial pressures of the components were calculated. Their values substantially depend on particular alkali metal cation and on the concentration of GaCl3; their variation allows the parameters of GaCl3 distillation from the salt melt to be altered in a wide range.