High Temperature Electrochemistry V: Session I
Sponsored by: TMS Extraction and Processing Division, TMS: Hydrometallurgy and Electrometallurgy Committee
Program Organizers: Prabhat Tripathy, Batelle Energy Alliance (Idaho National Laboratory); Guy Fredrickson, Idaho National Laboratory
Monday 8:30 AM
March 20, 2023
Room: 28B
Location: SDCC
Session Chair: Guy Fredrickson, Idaho National Laboratory
8:30 AM Introductory Comments
8:35 AM Invited
Optimisation of the Anodic and Cathodic Current Densities during Nd Electrowinning Process: Mathieu Gibilaro1; Christophe Remazeilles1; Laurent Massot1; Pierre Chamelot1; 1University of Toulouse
Nd metal is industrially produced in LiF-NdF3-Nd2O3 by electrolysis at around 1000 °C using a carbon anode, according to the reaction: Nd2O3 + 3/2 C→2 Nd + 3/2 CO2 On the anodic part, in case of Nd2O3 depletion, the production of carbon oxide CO and perfluorocarbons CFx was observed. The point is that CO production leads to the anode over-consumption meanwhile CFx are powerful greenhouse effect gases. The influences of Nd2O3 content in LiF-NdF3-Nd2O3 on the anode oxidation was investigated by coupling IR-spectroscopy and electrochemical techniques, to prevent CFX formation during Nd electrolysis. It was observed that carbon anode was only oxidized into CO2(g) until the limiting current density was reached. Beyond this value, CFx were also produced.On the cathodic part, the influence of the current density was investigated as a function of the production yield. A minimum current density is required to obtain a good metallic Nd coalescence.
9:15 AM
Thermodynamic Properties of Nd-Fe Alloys via EMF Measurements in Molten Salts: Sanghyeok Im1; Hojong Kim1; 1Pennsylvania State University
Thermodynamic properties of the Nd-Fe alloys were investigated via electromotive force (emf) measurements in molten LiCl-KCl-NdCl3 and LiF-CaF2-NdF3 electrolytes at 500–900 ºC at mole fractions of xNd = 0.05–0.50, relative to pure Nd(s). The temperature-dependent emf values of the Nd-Fe alloys were used to determine the partial molar Gibbs energy (chemical potential), entropy, and enthalpy. In addition, the first-order phase transitions detected during emf measurements were corroborated with thermal analysis via differential scanning calorimetry (DSC). To understand the phase behavior of the Nd-Fe alloys near equilibrium, selected alloy compositions were annealed for microstructural analysis by a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and structural analysis by powder X-ray diffraction (XRD).
9:35 AM
On the Separation of Niobium and Tantalum Metals via Molten Sulfide Electrolysis: Charles Boury1; Antoine Allanore1; 1Massachusetts Institute of Technology
Niobium and tantalum exhibit a wide range of physicochemical similarities, hindering their separation. Coltan is often found over the African continent and consists of a mix of niobium and tantalum oxides. Their actual recovery technologies possess economical bottlenecks while hindering the sustainability of the overall separation process. Herein is proposed a new route for the separation and production of niobium and tantalum metals from their oxides (Nb2O5 and Ta2O5 respectively) via sulfidation and molten sulfide electrolysis. First Nb2O5 and Ta2O5 are sulfidized to NbS2 and TaS2 under specific conditions. These sulfides are then mixed in a barium sulfide (BaS) and lanthanum sulfide (La2S3) supporting electrolyte to selectively recover tantalum metal. Niobium metal recovery is demonstrated in a tantalum free molten sulfide electrolyte. The decomposition behavior of TaS2 and NbS2 is further informed by standard electrochemical techniques and High Amplitude Fourier Transform Alternative Current Voltammetry.
9:55 AM
Formation of Carbon Layer on Ni and Mo Through Electrochemical Reduction of Carbonate Ions in Molten LiCl: Chongrui Zhuang1; Xin Lu1; Osamu Takeda1; Hongmin Zhu1; 1Tohoku University
Carbon film, one kind of carbon material, is a promising candidate for the protective films or coatings on the metal surfaces due to its unique chemical and physical properties. The electrochemical reduction of carbonate in molten salt is considered as a promising method for carbon materials preparation. In this study, Ni and Mo were selected as electrodes to investigate the reduction process of carbonate on their respective electrode surfaces, and to explore how to prepare uniform and dense carbon film in molten LiCl. The influences of electrolysis conditions such as substrate material, current density and electrolysis method were investigated. The formation of a dense and uniform carbon layer on Ni was difficult as nickel carbide was hard to form. On the contrary, electrochemical reduction of carbon on molybdenum substrate is easy account for the molybdenum carbide formation.
10:15 AM Break
10:35 AM
Chloro-aluminate Species Distribution Correlation with Electrical Conductivity of 1-ethyl-3-methyl Imidazolium Chloride (EMIC)-Aluminum Chloride (AlCl3) System: Aninda Nafis Ahmed1; Md Khalid Nahian1; Ramana Reddy1; 1University of Alabama Tuscaloosa
The chloroaluminate species distribution of EMIC-AlCl3 system was modeled using thermodynamic data in the temperatures range from 90 to 110oC and 0 to 1.0 mole fraction of AlCl3. Thermodynamic model was developed considering activity (ai) of species and equilibrium constant (k) for the polymeric reactions. The model species distribution results were compared with the available literature data. The main anion species exist from 0 to 0.5 mole fraction of AlCl3 are Cl- and AlCl4- , and Al2Cl7-, Al3Cl10- and Al4Cl13- species exist at higher concentrations of AlCl3. At all temperatures, the distribution peak maxima of AlCl4-, Al2Cl7-, Al3Cl10- and Al4Cl13- occurs at 0.5, 0.67, 0.75 and 0.8 mole fraction of AlCl3 respectively. With increase in temperature, the mole fraction of Al2Cl7-, Al3Cl10-, and Al4Cl13- peak maxima decreases. These species distribution data were used in analyzing the change in physical properties of ionic melts such as electrical conductivity.
10:55 AM
A Revised High Temperature Synthesis of UCl3 via Reaction of U with FeCl2: Jacob Yankey1; Jarom Chamberlain1; Marisa Monreal2; Matt Jackson2; Michael Simpson1; 1University of Utah; 2Los Alamos National Laboratory
To synthesize NaCl-MgCl2-UCl3 mixtures with a specific concentration of UCl3 for accurate electrochemical and vapor pressure measurements, a new method of U chlorination was devised and tested. Reaction of U metal directly immersed in molten salt with FeCl2 has previously been reported to form UCl3 (1.5FeCl2(liq.) + U(s) = UCl3(liq.) + 1.5Fe(s)) with iron particles separable using a magnet. This process is complicated by the need for nested crucibles, a high temperature magnet, and pouring molten salt. A process improvement is reported here in which U metal is contained in a stainless steel basket while immersed in the salt. Iron dendrites form on the basket via galvanically coupled reactions. Reaction progress was monitored via open circuit potential difference between the basket and a reference electrode. Salt samples were analyzed with inductively coupled plasma mass spectrometry indicating 89.5% yield with final concentrations of 6.19 wt.% U and 0.12 wt.% Fe.
11:15 AM
Blind Identification and Quantification of Analytes in Molten LiCl-KCl Eutectic: Tyler Williams1; Greg Chipman1; Ranon Fuller1; Mark Schvaneveldt1; Jason Torrie1; Devin Rappleye1; 1Brigham Young University
Electroanalytical techniques are promising tools for process monitoring and material accountancy in molten salt processes. However, most published studies demonstrating their potential begin with some process knowledge of the compounds present and the range of concentrations expected. This study tests the ability of electroanalytical measurements to identify unknown species and quantify their concentrations in molten LiCl-KCl eutectic by performing blind measurements and analysis on mixtures prepared by someone other than the operator performing the measurement. The operator will use the published literature and their knowledge of electrochemical methods to identify and quantify the analyte(s) present. The results of each blind measurement and analysis will be presented.
11:35 AM
Study of Potentiometry for Monitoring Activity of GdCl3 in Molten LiCl-KCl Salt: Guoping Cao1; Steven Herrmann1; Guy Fredrickson1; Robert Hoover1; 1Idaho National Laboratory
In pyroprocessing spent nuclear fuels by electrorefining in molten LiCl-KCl salt, it is desired to monitor in real time the UCl3 concentration in the salt for safeguards purposes. Current chemical analysis of the highly radioactive salt for electrorefining by an inductively coupled plasma technique is inconvenient and usually time-consuming in generating the salt composition results. In this paper, we evaluated whether a simple potentiometry approach can be used for real-time monitoring the concentration of GdCl3, which was used as a surrogate for UCl3, in LiCl-KCl-GdCl3 salt by measuring the open circuit potential of a Gd metal electrode with respect to a Ag/AgCl reference electrode (RE) when GdCl3 salt was incrementally added to the LiCl-KCl salt. Additions of LaCl3, CeCl3 and NdCl3 salts were used for evaluating the effects of other chloride salts on the selectivity of the Gd metal electrode versus Ag/AgCl RE.