Electrochemical study of the properties of Nd(III) and Nd(II) ions in molten LiCl-KCl-CsCl eutectic and individual CsCl

The electrochemical behavior of NdCl₃ 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.     

Redox reaction Yb(III) + <Emphasis Type="Italic">e</Emphasis> = Yb(II) in a molten eutectic mixture NaCl-2CsCl

Potentiometric method was used to measure the redox potentials of Yb³⁺/Yb²⁺ 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 YbCl₂(s.) + 1/2Cl₂(g.) ai YbCl₃(s.) were calculated from the conditional standard potentials E*(Yb³⁺/Yb²⁺).     

Electrochemical study of the redox reaction Yb(III) + e ⇄ Yb(II) in a molten LiCl-KCl eutectic

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.     

NaCl-CsCl熔盐中Ce(Ⅲ)离子的阴极过程研究

以钨微盘为研究电极采用循环伏安法和方波伏安法研究了温度为873K的NaCl-CsCl熔盐中Ce3 离子的阴极行为.结果表明,摩尔比为1:2的NaCl-CsCl熔盐体系中Ce3 离子分两步还原,其电化学反应历程为:Ce3 e=Ce2 ,Ce2 2e-=Ce.进一步计算得到熔盐体系中Ce3 离子的扩散系数(D).     

Electrode processes and their kinetic parameters in the reduction and oxidation of Cr(III) and Cr(II) in molten CsCl

The reduction of chromium ions in the CsCl-CrCl₃ melt in wide concentration and temperature ranges is reported. It is assumed that the melt contains polynuclear chromium complexes. The reduction of Cr(III) to Cr(II) is a reversible one-electron process. The electroreduction of divalent chromium to chromium metal is an irreversible process involving dinuclear and mononuclear chromium complex ions. The electron transfer rate constant has been calculated for various temperatures and chromium chloride concentrations in the salt melt. The activation energy of electron transfer and its dependence on the CrCl₃ concentration in the electrolyte have been determined for the Cr(III) ↔ Cr(II) process.     

Thermogravimetric study of cobalt(II)-halide complexes in a molten nitrate eutectic

The temperatures and stoichiometries of reaction of cobalt(II) nitrate, chloride and bromide have been established by analysis, infrared, X-ray diffractometry and thermogravimetric analysis. Tricobalt tetraoxide and nitrogen dioxide were produced together with oxygen and nitrite from the first two reactants, but with nitric oxide and bromine from the third reactant. Reaction pathways are suggested. Addition of potassium chloride caused a large (150–200°) increase in temperature of maximum reaction rate, which was ascribed to the formation of chloro “complexes”. No stabilisation was observed on addition of potassium bromide, though broadening of the weight loss maxima when chloride and bromide were present suggested the formation of mixed complexes.     

Electrochemical reduction of the lanthanide ions: Part II. Second reduction step of europium(III), ytterbium(III) and samarium(III) in acidic tetramethylammonium perchlorate solution

The second reduction step of Eu(III), Yb(III) and Sm(III) in 0.04 M tetramethylammonium perchlorate in the pH range 1.8–7 was investigated by cyclic voltammetry and d.c. polarography. The proposed reaction scheme at large hydrogen ion/lanthanide ion concentration ratios involves the reduction of the lanthanide(II) ion to the metallic state accompanied by a surface catalytic reaction in which the reactant is regenerated and also hydroxyl ions are formed which induces the precipitation of lanthanide(II) hydrous oxide on the electrode surface. This lanthanide(II) hydroxide is reduced at more negative potentials than the hydrated lanthanide(II) species. At lower hydrogen ion/lanthanide ion concentration ratios a preceding chemical reaction, probably involving hydrolyzed lanthanide(II) species, becomes rate determining.     

Electrochemical and thermodynamic properties of thulium trichloride in a molten NaCl-KCl-CsCl eutectic

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 TmCl_2(solution) + 1/2Cl_2(g) ⇆ TmCl_3(solution) were calculate from the conditional standard potentials $ E_{{{Tm^{3 + } } mathord{left/ {vphantom {{Tm^{3 + } } {Tm^{2 + } }}} right. kern-nulldelimiterspace} {Tm^{2 + } }}}^* $ E_{{{Tm^{3 + } } mathord{left/ {vphantom {{Tm^{3 + } } {Tm^{2 + } }}} right. kern-nulldelimiterspace} {Tm^{2 + } }}}^* .     

Electrochemical reduction of the lanthanide ions: Part I. First reduction step of ytterbium(III) in acidic 1 M NaClO4 solution

The reduction of Yb(III) to Yb(II) in 1 M NaClO₄ in the pH range 1.9–6.6 was studied by d c. polarography, cyclic voltammetry and electrode impedance measurements as a function of frequency and electrode potential. It results that the d.c. reversible reduction is followed by a homogeneous chemical reaction and is accompanied, by an irreversible process which is attributed to a lowering of the overpotential of the reduction of the hydrogen ions. Values of the rate constant and transfer coefficient pertaining to the charge transfer step were deter mined.     

Electrochemical behaviour of tetravalent thorium in molten /Li-K/Cl eutectic

The electrochemical reduction of Th/IV/ in the /Li–K/Cl eutectic between 400 and 500 °C proceeds according to a four electron process without any intermediate step. The reduction is quasi-reversible and the diffusion coefficient deduced from the peak current of the voltammetric reduction equals 2.7×10^–6 cm² sec^–1 at 400°C.     

Electrochemical reduction of Fe(III), Cr(III), and Mn(III) porphyrin complexes in DMSO

The half-wave potentials are given for the electrochemical reduction of Fe(III), Cr(III), and Mn(III) porphyrin complexes. Cyclic voltamperometry was used to study the reversibility of these reactions. An effect was demonstrated for the structure of the porphyrin ligand on the half-wave potentials for the reduction of the Mn(III) complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1665–1668, July, 1991.     

Preparation of uranium(III) in a molten chloride salt: a redox mechanistic study

Journal of Radioanalytical and Nuclear Chemistry - The most advanced methodology for the pyroprocessing of spent nuclear fuel is the electrorefining of uranium metal in LiCl–KCl eutectic, in...     

Uptake of Tm(III) ions onto polyurethane foam from H2O - ethanol mixture containing 1-(2-pyridylazo)-2-naphthol (PAN)

Summary The sorption of microquantities of Tm(III) ions on washed polyurethane foam (PUF) from a mixture of aqueous solution and ethanol containing PAN was examined. The maximum sorption of 3.18^. 10^-6M solution of Tm(III) ions was observed at pH 8 with 30-minute equilibration time. The optimum ratio of aqueous-ethanol phase for the sorption of Tm(III) ions was found to be 3:1 v/v, respectively. The sorption rate of metal ions on PUF is followed a first order kinetics and obeyed the equation for an intra particle diffusion process. The equilibrium concentration data of Tm(III) ions could be described satisfactorily by several adsorption isotherms. The Freundlich adsorption isotherm constants 1/nand K_Fare 0.66±0.02 and (5.7±0.3)^. 10^-3mol^. g^-1, respectively. The Langmuir isotherm constants for monolayer coverage (Q) and binding strength of sorption (b) are (2.5±0.7)^. 10^-5mol^. g^-1and (1.6±0.1)^. 10⁴l^. mol^-1, respectively. The sorption capacity derived from Dubinin-Radushkevich (D-R) isotherm is (1.7±0.2)^. 10^-4mol^. g^-1and the sorption free energy (E) is 9.8±0.2 kJ^. mol^-1indicating chemisorption phenomena. The thermodynamic parameters indicate that the sorption of Tm(III) ions onto PUF is endothermic, entropy driven and spontaneous in nature.     

Diffusion characteristics of U(IV) and Pu(III) ions in eutectic melts LiF-NaF and LiF-CaF2 according to molecular dynamics calculations

The diffusion characteristics of U(IV) and Pu(III) ions in model melts 66LiF-44NaF at 1000–1600 K and 80LiF-20CaF₂ at 1050–1600 K have been calculated by the molecular dynamics method. The diffusion activation energies of U(IV) and Pu(III) ions in the these melts have been calculated.     

Electrochemical reduction of actinide ions in aqueous solution

Electrochemical reduction of heavy elements from aqueous solution to amalgams was studied by radiopolarography and radiocoulometry. Mechanism of actinide reduction on a mercury pool is discussed through simulation techniques. Special emphasis is placed on redox reactions and potentials, kinetics of the process and effect of acetate and citrate ions as complexing agents. Three groups of actinides have been found. The first group represents actinium and from uranium to berkelium. Reduction occurs in the experimental conditions via an irreversible 3–0 process. The second group consists of the elements from fermium to nobelium, which are reduced in non-complexing solutions, or with acetate ions, similarly as barium and radium, via a reversible 2–0 reaction. Finally, californium and einsteinium behave as intermediate elements. It is noticeable that such groups are also observed in the actinide series by studying the structure of the trivalent aqua ions. On the basis of the above mentioned investigations of actinides and lanthanides several examples of electrochemical application are presented. Californium has been separated from preceding transuranium and lanthanide elements (except europium) by electrochemical reduction to amalgams in acetic solution. Separation factors from 25–90 are achieved with appropriate cathodic potentials. Similarly, this element could be separated from several heavier actinides with citric media. The electrochemical preparation of mixed uranium-nickel and uranium-tin amalgams from aqueous acetate solutions is investigated. The dependence of redox potentials of mixed amalgams on different atomic ratio UNi and USn in amalgams is measured. The large shift of redox potentials of mixed amalgams to the positive direction is detected when the atomic ratio UNi or USn in amalgams reaches 15. The thermal distillation of mercury from mixed amalgams with different UNi and USn atomic ratios was carried out and the products were identified by chemical analysis and X-ray diffraction. The intermetallics UNi₅ and USn₃ were prepared from mixed amalgams with the atomic ratios UNi=15 and USn=13. The uranium and neptunium amalgams are prepared by electrolysis of aqueous acetate solutions and are processes into metals or nitrides U₂N₃, NpN by thermal distillation of mercury in vacuum or in nitrogen atmosphere.     

Electrochemical study of a soluble niobium anode in molten salts

Electrochemical studies of niobium were performed in various molten salts, including NaClKClKF, LiClNaFKF and LiFNaFKF. The cathodic current efficiency increased with increasing number of fluoride components, as did the quality of the metal deposited at the cathode. Thus, the order of cathodic current efficiency was NaClKCl < LiClNaClKCl < NaClKClKF < LiClNaFKF < LiFNaFKF, using equimolar mixtures of the salts. The possible electrode processes were determined to be

and the overall reaction was

in terms of m₁and m₂ mol.     

Electrochemical reduction of gallium(III) in non-aqueous solvents, assisted by 2,2'-bipyridine

The electrochemistry of gallium(III) perchlorate in dimethylsulfoxide (DMSO) and acetonitrile (MeCN) at a mercury drop electrode is described and compared to that in water. The reduction of 2,2'-bipyridine (DIPY) and its interaction with free protons in the solvents mentioned is also surveyed. The electrochemistry of tris-(2,2'-bipyridine) gallium(III) perchlorate was studied in DMSO and MeCN. A gallium metal deposit is obtained by reduction of the complex compound in the first solvent, whereas lower valence gallium-DIPY species are obtained in the second. The existence of different catalytic prepeaks in DMSO is described. The first catalytic peak, which renders a metal deposit, is studied in detail, together with the possible interference of oxygen and free protons. These studies serve the basis of future development of an analytical procedure for the determination of trace concentrations of gallium.