Neodymium and gadolinium extraction from molten fluorides by reduction on a reactive electrode

This work describes the electrochemical extraction on a reactive cathode (Cu, Ni) of two lanthanides Ln (Ln = Nd and Gd) from molten LiF-CaF2 medium at 840 and 920°C for Nd and 940°C for Gd. Extraction runs have been performed and the operating conditions (cathodic material and temperature) optimised. The titration of the Nd and Gd concentrations in the melt during extraction used square wave voltammetry. At the end of each run, the residual Ln content was checked by ICP-AES; the extraction efficiencies of the two lanthanides were found to be more than 99.8% on both reactive substrates

Anodic dissolution of metals in oxide-free cryolite melts

The anodic behavior of metals in molten cryolite-alumina melts has been investigated mostly for use as inert anodes for the Hall-Héroult process. In the present work, gold, platinum, palladium, copper, tungsten, nickel, cobalt and iron metal electrodes were anodically polarized in an oxide-free cryolite melt (11%wt. excess AlF3 ; 5%wt. CaF2) at 1273 K. The aim of the experiments was to characterize the oxidation reactions of the metals occurring without the effect of oxygen-containing dissolved species. The anodic dissolution of each metal was demonstrated, and electrochemical reactions were assigned using reversible potential calculation. The relative stability of metals as well as the possibility of generating pure fluorine is discussed

Electrodeposition of alloys or compounds in molten salts and applications

This article deals with the different modes of preparation of alloys or intermetallic compounds using the electrodeposition in molten salts, more particularly molten alkali fluorides. The interest in this process is to obtain new materials for high technology, particularly the compounds of reactive components such as actinides, rare earth and refractory metals. Two ways of preparation are considered: (i) electrocoating of the more reactive metal on a cathode made of the noble one and reaction between the two metals in contact, and (ii) electrocoating on an inert cathode of the intermetallic compound by coreduction of the ions of each elements. The kinetic is controlled by the reaction at the electrolyte interface. A wide bibliographic survey on the preparation of various compounds (intermetallic compounds, borides, carbides…) is given and a special attention is paid to the own experience of the authors in the preparation of these compounds and interpretation of their results

Electrochemical oxidation of binary copper-nickel alloys in cryolite melts

Anodic oxidation of copper, nickel and two copper-nickel alloys was studied in cryolite melts at 1000°C. In an oxide-free melt, anodic dissolution of each material was observed, and the dissolution potential increases with the content of copper. SEM characterization of a Cu55-Ni45 alloy showed that nickel is selectively dissolved according to a de-alloying process. In an alumina-containing melt, a partial passivation occurs at the copper-containing electrodes, at potentials below the oxygen evolution potential. A passive film forms on the copper electrode, while on the nickel electrode no dense oxide layer develops. Copper-nickel alloys were found to form a mixed oxide layer. At higher potentials, the formation of oxygen bubbles on the electrodes results in a degradation of the passive films and a strong corrosion

Cyclic Voltammetric Experiment - Simulation. Comparisons of the Complex Mechanism Associated with Electrochemical Reduction of Zr4+ in LiCl-KCl Eutectic Molten Salt

Nuclear energy increasingly represents an important option for generating largely clean CO2-free electricity and zirconium is a fission product that is expected to be present in irradiated fuels. The present investigation addresses the electrochemical reduction of Zr4+ to Zro in LiCl - KCl eutectic molten salt in the temperature range 425–550◦C using cyclic voltammetry (CV), square-wave voltammetry (SWV) and bulk electrolysis. Simulations of the CV data indicate that the initial reduction proceeds through surface confined steps: Zr4+* + 2e− ↔Zr2+* and Zr2+* + 2e− ↔Zr* processes (* adsorbed species) followed by a peak-shaped complex diffusion controlled step that consists of a combination of closely spaced processes associated with the reactions Zr4+ + 4e− →Zr and Zr4+ + 3e− →Zr+*. Zr+*, probably in the form of ZrCl* is then further reduced to Zro* at even more negative potentials. The simulations provide the first quantitative analysis of the thermodynamics and kinetics of the Zr4+ reduction in the LiCl-KCl eutectic

A multimaterial based on metallic copper and spinel oxide made by powder bed laser fusion: A new nanostructured material for inert anode dedicated to aluminum electrolysis

Coherent 3D parts of cermets, made of spinel ferrite and metallic copper, are prepared in a nitrogen atmosphere by powder bed additive manufacturing of a mixture of oxide and metallic powders. The cermets obtained are constituted by the association of blocks of about 500 μm, which create between them, a relatively large porosity (# 35%). Each block is subdivided into intimately nested zones that are either predominantly metallic or predominantly oxide type. In the metal parts, a dispersion of oxide crystals is observed, whose size varies from ten nanometers to a few micrometers. A similar distribution of metal particles in the oxide zones is also demonstrated. The chemical compositions of metallic and oxide phases are slightly different from those in the initial powders. Due to the high energy density of the laser, the melting temperature of the metal and oxides could be reached and therefore this could explain the chemical composition variations in the phases and the shape of oxide and metallic nanometric grains. The process used can therefore be described as powder bed fusion. These nanostructured cermets have been used as "inert" anodes for the electrolysis of aluminum in molten cryolite. Although penalized by a high porosity, 5 mm in diameter anodes allowed to carry out an electrolysis for 4 h. Since Spark Plasma Sintering can greatly reduce their porosity, while retaining their specific microstructure, the implementation of additive manufacturing for producing "inert" anodes is therefore of real interest

Experimental and simulation study of the electrode reaction mechanism of La3+ in LiCl-KCl eutectic molten salt

Nuclear energy increasingly represents an important option for generating largely clean CO2-free electricity. The present investigation addressed the electrochemical reduction of La3+, a rare earth element, in LiCl - KCl eutectic molten salt in the temperature range 450–550°C using transient techniques such as cyclic voltammetry (CV) and square-wave voltammetry (SWV). Simulation of the CV data suggested a reaction mechanism in which lanthanum reduction occurred in a single three-electron step (La3+ + 3e− → La°). The rate constant, k° was determined to be 5.7 x 10−3, 14.6 x 10−3 and 31.7 x 10−3 cm/s and the Matsuda et al.1 dimensionless parameter Ʌ was 0.82, 1.52 and 2.89 for temperatures of 450, 500 and 550°C, respectively and therefore it was concluded that the was process quasi reversible

Open Archive Toulouse Archive Ouverte (OATAO) Electrochemistry of uranium in molten LiF-CaF 2

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@inp-toulouse. a b s t r a c t This article is focused on the electrochemical behaviour of U ions in molten LiF-CaF 2 (79-21 wt.%) eutectic. On a W electrode, U(III) is reduced in one step to U metal and U(III) can be also oxidised to U(IV). Both systems were studied by cyclic and square wave voltammetry. Reversibility of both systems for both techniques was verified and number of exchanged electrons was determined, as well as diffusion coefficients for U(III) and U(IV). The results are in a good agreement with previous studies. On a Ni electrode, the depolarisation effect due to intermetallic compounds formation was observed. Electrorefining of U metal in a melt containing U and Gd ions was carried out using a reactive Ni electrode with promising results

Electrochemical behavior of neodymium in molten chloride salts

International audienceThe discovery of NdFeB permanent magnets helps to perform technologies with reduced weight and gives them access to miniaturization. The industrial process of production of the Nd-Fe alloy by electrolysis used to manufacture of NdFeB magnets consists in reducing Nd$^{3+}$ ions dissolved in a LiF-NdF$_3$-N$_2$O$_3$ salt on iron cathode at 1050 DC. This route was chosen since the electroplating of neodymium at low temperature molten chloride leads to low recovery yields. This is usually attributed to the comproportionation reaction between the electrodeposited metal and its chloride salt (NdCl$_3$) leading to the formation of NdCl$_2$.In this work, the neodymium electrochemical behavior is reviewed in order to understand its reduction mechanism. Meal addition to LiCl-KCl-NdCl$_3$ melt is usually used to simulated comproportionation reaction in solution. Neodymium deposition yields are studied. Stability of Nd$^{2+}$ in two different solvent (LiCl-KCl and LiCl) is also discussed through electrodeposition tests on the gram scale