Co-reduction of aluminium and lanthanide ions in molten fluorides : application to cerium and samarium extraction from nuclear waste

This work concerns the method of co-reduction process with aluminium ions in LiF–CaF2 medium (79–21 mol.%) on tungsten electrode for cerium and samarium extraction. Electrochemical techniques such as cyclic and square wave voltammetries, and potentiostatic electrolyses were used to study the co-reduction of CeF3 and SmF3 with AlF3. For each of these elements, specific peaks of Al–Ce and Al–Sm alloys formationwere observed by voltammetry aswell as peaks of pure cerium and aluminium, and pure samarium and aluminium respectively. The difference of potential measured between the solvent reduction and the alloy formation suggests expecting an extraction efficiency of 99.99% of each lanthanide by the process. Different intermetallic compounds were obtained for different potentiostatic electrolysis and were characterised by Scanning Electron Microscopy with EDS probe. The validity of the process was verified by carrying out cerium and samarium extractions in the form of Al–Ln alloy; the extraction efficiency was 99.5% for Ce(III) and 99.4% for Sm(III)

Nitrogen evolution as anodic reaction in molten LiF–CaF2

The electrochemical behaviour of nitride ions has been studied in fluoride melts (eutectic LiF-CaF2) by cyclic voltammetry and square wave voltammetry. The purpose of this work is to propose an alternative way for anodic reaction in molten fluorides processes. Thermodynamical analysis can be used for the evaluation of the anodic material regarding to its oxidation potential and reactivity with nitrogen. Then electrochemical investigations confirm the oxidation of nitride ions into nitrogen in a one-step process exchanging 3 electrons, and let propose several materials usable for nitrogen evolving

Investigations of Zr(IV) in LiF-CaF2: stability with oxide ions and electroreduction pathway on inert and reactive electrodes

In this work, a detailed electrochemical study of the molten LiF-CaF2-ZrF4 system is provided in the 810-920°C temperature range, allowing the determination of the reduction potential, the diffusion coefficient and the reduction mechanism of dissolved Zr(IV) on an inert Ta electrode. Addition of CaO in the molten salt is shown to cause Zr(IV) precipitation into a mixture of solid compounds, most likely ZrO2 and ZrO1.3F1.4. Underpotential deposition of Zr on Cu and Ni electrodes is also evidenced

Electrochemical extraction of europium from molten fluoride media

This work concerns the extraction of europium from molten fluoride media. Two electrochemical ways have been examined: (i) the use of a reactive cathode made of copper and (ii) the co-deposition with aluminium on inert electrode, leading to the formation of europium-copper and europium-aluminium alloys respectively, as identified by SEM-EDS analysis. Cyclic voltammetry and square wave voltammetry were used to identify the reduction pathway and to characterise the step of Cu-Eu and Al-Eu alloys formation. Then, electrochemical extractions using the two methodologies have been performed with extraction efficiency around 92 % for copper electrode and 99.7 % for co-reduction with aluminium ions

Supply chain dynamics after the Covid-19 pandemic and stock market performance: Evidence from the US

Supply chain risk is a strategic issue for managing multinational companies, and Covid-19 has shown the relevance of this type of risk for the firm's survival probability. The market may perceive the choice of replacing some of the main customers or suppliers as an increase or a decrease of the risk based on the features of the new supply chain members, and markets tend to penalize companies that increase their exposure to unaffordable events. During the pandemic, many supply chains suffered from glitches and companies were obliged to redefine their network by selecting their new strategic customers and/or suppliers. The paper evaluates the supply chain composition strategies of a set of multinational companies based in the US during the last decade. It highlights the differences in supply chain management behavior before and during the pandemic. Data collected allow testing the impact on the stock market performance of modifying the supply chain network by adding new members that may have a different level of risk. Results show that the market reaction to supply chain updates changed after the Covid-19, and nowadays there is greater attention on the credit risk of the new companies entering the supply chain

Lanthanides extraction processes in molten fluoride media. Application to nuclear spent fuel reprocessing

This paper describes four techniques of extraction of lanthanides elements (Ln) from molten salts in the general frame of reprocessing nuclear wastes; One of them is chemical: the precipitation of Ln ions in insoluble compounds (oxides or oxifluorides); the others use electrochemical methodology in molten fluorides for extraction and measurement of the progress of the processes: first electrodeposition of pure Ln metals on an inert cathode material was proved to be incomplete and cause problems for recovering the metal; electrodeposition of Ln in the form of alloys seems to be far more promising because on one hand the low activity of Ln shifts the electrodeposition potential in a more anodic range avoiding any overlapping with the solvent reduction and furthermore exhibit rapid process kinetics; two ways were examined: (i) obtention of alloys by reaction of the electroreducing Ln and the cathode in Ni or preferably in Cu, because in this case we obtain easily liquid compounds, that enhances sensibly the process kinetics; (ii) codeposition of Ln ions with aluminium ions on an inert cathode giving a well defined composition of the alloy. Each way was proved to give extraction efficiency close to unity in a moderate time

Direct electroreduction of oxides in molten fluoride salts

A new kind of electrolyte composed of molten fluorides has been evaluated in order to perform a feasibility study of the direct electroreduction reaction. The direct reduction of SnO2 and Fe3O4 was realised in LiF-NaF at 750°C and in LiF-CaF2 at 850°C for TiO2 and TiO. The electrochemical behaviour of these oxides was studied by linear sweep voltammetry: a current corresponding to the oxide reduction was evidenced for TiO2, SnO2 and Fe3O4. After intensiostatic electrolyses, a complete conversion was obtained for all oxides, except TiO, and the structure of reduced Ti and Fe samples had a typical coral-like structure while dense drops of Sn were recovered (Sn is liquid at operating temperature). After TiO electrolysis, a thin external metallic titanium layer was detected, acting as a barrier for the oxide ions diffusion and no complete reduction can be achieved. This could be explained by a Pilling-Bedworth ratio around 1 for Ti/TiO

Cross-border banking and foreign branch regulation in Europe

Purpose This paper aims to examine the relevance of cross-border activity in the European banking sector, evaluating the role of differences in regulation to explain the level of interest in entering foreign markets. Design/methodology/approach The sample considers all banks in the European Union (EU 28) existing at year-end 2017, and information about the ultimate owners’ nationality to classify local and foreign banks is collected. The analysis provides a mapping of regulatory restrictions for foreign banks and evaluates how they impact the role of foreign players in the deposit and lending markets. Findings Results show that the lower are the capital adequacy requirements, the higher are the amounts of loans and deposits offered by non-European Economic Area banks and, additionally, the higher the probability of having a foreign bank operating in the country. Originality/value This paper provides new evidence on regulatory arbitrage opportunities in the EU and outlines differences among EU countries not previously studied

Electrochemical behaviour of dysprosium (III) in LiF–CaF2 on Mo, Ni and Cu electrodes

The electrochemical behaviour of dysprosium(III) was investigated in the LiF–CaF2 eutectic mixture on molybdenum, nickel and copper electrodes in the 840–930 °C temperature range using cyclic voltammetry, square wave voltammetry and chronopotentiometry. On Mo electrode, the study showed that Dy(III) ions were reduced into Dy metal in a one-step diffusion-controlled process exchanging three electrons: View the MathML source The diffusion coefficients verify the Arrhenius law, allowing the activation energy to be calculated. The study of the electrochemical reduction of Dy(III) ions on reactive electrodes (Ni, Cu) first by cyclic voltammetry showed that the reduction potential of Dy(III)/Dy on reactive electrodes was observed at more positive values than those on inert electrode and then open-circuit chronopotentiometry put into evidence the formation of intermetallic compounds at more anodic potentials than pure dysprosium. Preparation of alloys layers was finally carried out by intentiostatic electrolyses at underpotential compared to the pure metal deposition; SEM observations of the layer allowed the most stable compounds prepared by this way to be identified

Fluoroacidity evaluation in molten salts

The fluoroacidity of several alkaline fluoride media was studied by monitoring the concentration of electroactive species which is decreasing versus time due to a gas species release, such as silicon fluorides, as indicated by the reaction: SiF(4+x)x- = SiF4(g) + x F- This article relates the Si(IV) reaction study to define a relative fluoroacidity scale by studying the silicon ions stability in different melts. Electrochemical techniques allow the measurement of SiF4+xx- concentration evolution and thus the reaction rate constant to be calculated at different temperatures and for several fluoride media. The article shows that the free F- content depends on the fluoride mixture and that the rate values are correlated with the fluoroacidity allowing a qualitative estimation. Then a fluoride solvents fluoroacidity scale was proposed, scaling the different eutectic melts from basic melt to acidic one: NaF-KF < LiF-KF < NaF-MgF2 < NaF-CaF2 < LiF-NaF < LiF < LiF-CaF2