Direct Electrolytic Reduction Research Articles

(Invited) Consumable Fe Anode for Use in Direct Electrolytic Reduction of Spent Oxide Fuel

The direct electrolytic reduction (DER) process can be used to reduce UO2 to U metal in a molten LiCl-Li2O electrolyte. In the baseline process, UO2 is loaded in a steel basket that serves as the cathode, while O2 gas is generated at a Pt anode. The use of Pt for anodes is non-optimal because of its cost and tendency to corrode via lithium platinate formation during the DER process. Other inert metals and cermets for DER anodes have been extensively researched to reduce the cost. Alternatively, reactive anodes may be considered that form disposable metal oxides rather than O2 gas. Thus, we investigated the behavior of pure iron rods as anodes for this process. Experiments were performed using a LiCl-2wt%Li2O electrolyte at 650oC in an Ar atmosphere glove box with <10 ppm O2 and H2O. UO2 powder was loaded into a stainless-steel cathode basket. A 7.56-mm diameter iron rod was used as the anode. Anode and cathode potentials were measured relative to a Ni/NiO reference electrode encased in a MgO tube with a porous MgO plug. The cell was run via controlled anode potential with increments from 0.2–1.0 V versus Ni/NiO. The headspace gas was sampled during experiments and analyzed for O2. Throughout the experiment, the cathode potential was consistent with either direct reduction of UO2 or reduction of Li2O, which forms Li that will also reduce UO2 to U metal. LECO oxygen analysis indicated 32% reduction of UO2 with a cell efficiency of 37%. Li2O concentration remained constant in the salt; thus, net oxidation must have occurred at the anode. The Fe anode was pulled out of the salt and photographed after stages of holding the potential at 0.2–1.0 V versus Ni/NiO in 0.1 V increments for about 11-12 min at each stage. Yet unidentified metal oxides were observed on the anode surface after holding at potentials of 0.4 V and 0.6–1.0 V. O2 was detected in the headspace gas when the anode potential was increased to 1.0 V. Thus, iron oxides form at lower potentials, while O2 gas formation occurs at a threshold potential. O2 formation may be enabled by the oxide layer passivating the iron against further oxidation. Results of ICP-MS of salt samples taken throughout the experiment showed no increase in Fe concentration in the salt. A metallic deposit formed on the outside of the cathode basket, implying some electrotransport occurred from the anode to the cathode. The results of this study show that cheap, disposable iron anodes are promising for the DER process. After an initial stage of formation of an iron oxide phase on the surface of the anode, O2 gas forms at a sufficiently high potential (1.0 V versus Ni/NiO). Further work is needed to achieve a more detailed mechanistic understanding of the effect of anode potential on specific reactions at the anode. Optimization of the anode potential may serve to promote O2 formation and minimize the rate of consumption of iron anodes.DISCLAIMERThis work of authorship and those incorporated herein were prepared by Consolidated Nuclear Security, LLC (CNS) as accounts of work sponsored by an agency of the United States Government under Contract DE-NA-0001942. Neither the United States Government nor any agency thereof, nor CNS, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility to any non-governmental recipient hereof for the accuracy, completeness, use made, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency or contractor thereof, or by CNS. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency or contractor (other than the authors) thereof.COPYRIGHT NOTICEThis document has been authored by Consolidated Nuclear Security, LLC, under Contract DE-NA-0001942 with the U.S. Department of Energy/National Nuclear Security Administration, or a subcontractor thereof. The United States Government retains and the publisher, by accepting the document for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this document, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, or allow others to do so, for United States Government purposes.

Production of Iron Alloy by Direct Electrolytic Reduction Using Suspension Electrolysis in an Alkaline Electrolyte

Iron alloys were produced by suspension electrolysis in a 50 wt% NaOH–H2O electrolyte at 383 K, and Fe–Cr and Fe–Ni alloys were obtained using a suspension of Fe2O3+Cr2O3 and Fe2O3+Ni(OH)2 particles, respectively. Highly ordered columnar deposits comprising cubic Fe–Cr particles with approximately 5-micrometer-long sides were obtained on a disk cathode with a current efficiency higher than 90% at 100–300 mA･cm−2. In contrast, disordered columnar deposits of Fe–Ni particles with diameters of approximately 1.0 μm were obtained on a disk cathode with a current efficiency of approximately 50% at 200 mA･cm−2. The proposed method affords iron alloys with compositions in the stainless-steel region that depend on the electrolysis conditions, namely, the current density and Fe2O3/Cr2O3 or Fe2O3/Ni(OH)2 content ratio.

Corrosion of anode materials during direct electrolytic reduction of uranium oxide in molten LiCl-Li2O

Direct electrolytic reduction of UO2 in LiCl-Li2O was performed with a platinum anode surrounded by a mesh shroud. The anode shroud was comprised of three pieces; shaft, cage and screen. The shaft and cage were made of Haynes C2000 and the screen was made of Hastelloy C276. Five reduction tests were performed sequentially with the same anode/shroud set, while two other reduction tests did not use an anode shroud. Based on mass measurements, the average rate of platinum loss from corrosion was determined to be 1.69 µm/hr. It was confirmed with X-ray diffraction that a layer of lithium platinate forms on the surface of the anode. The anode shroud was found to increase the anodic potential by 0.25 V. After each test, a corrosion coupon was removed from the Haynes C2000 anode shroud and analyzed via scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Salt samples were taken after each test and analyzed using inductively coupled plasma mass spectrometry. The results indicated that nickel, chromium, and molybdenum were all depleted from the Hastelloy C276 shroud and accumulated in the molten salt. SEM-EDS line scans were used to estimate linear corrosion rates. Based on nickel, chromium, and molybdenum, the shroud corrosion rates were determined to be 0.36, 0.49, and 0.51 µm/hr, respectively.

Accelerating 1H NMR Detection of Aqueous Ammonia.

Direct electrolytic N2 reduction to ammonia (NH3) is a renewable alternative to the Haber–Bosch process. The activity and selectivity of electrocatalysts are evaluated by measuring the amount of NH3 in the electrolyte. Quantitative 1H nuclear magnetic resonance (qNMR) detection reduces the bench time to analyze samples of NH3 (present in the assay as NH4+) compared to conventional spectrophotometric methods. However, many groups do not have access to an NMR spectrometer with sufficiently high sensitivity. We report that by adding 1 mM paramagnetic Gd3+ ions to the NMR sample, the required analysis time can be reduced by an order of magnitude such that fast NH4+ detection becomes accessible with a standard NMR spectrometer. Accurate, internally calibrated quantification is possible over a wide pH range.

Dissolution Behavior of SiO2 and Electrochemical Reduction of Dissolved SiO2 in Molten Chlorides

1. Introduction The global production of photovoltaic (PV) cells has increased by a factor of approximately 360, i.e., 0.285 GW year−1 to 102.4 GW year−1, from the year 2000 to 2018 [1,2]. Among the many types of solar cells, crystalline Si solar cell accounted for 96.9% of the worldwide production in 2018 [3]. Therefore, crystalline Si would be most likely to remain as the main stream of the PV industry in the long term.Due to the high energy cost of the current production process of solar-grade silicon (SOG-Si), the next-generation production process for SOG-Si with low energy cost is required. For the past two decades, we have been studying the direct electrolytic reduction of solid SiO2 to Si in molten CaCl2 as a new production process of SOG-Si [4–6]. Recently, we have focused on electrochemical reduction of dissolved SiO2 in CaO-added molten salts [7].In this study, we selected eutectic molten NaCl–CaCl2 as the electrolyte, because its melting point is comparatively lower than that of single CaCl2 melt, which enables the investigation in a wide temperature range. The structure and electrochemical reduction of dissolved SiO2 were investigated in molten NaCl–CaCl2–CaO. 2. Experimental All experiments were conducted in a dry Ar atmosphere. The molten salts were prepared as follows: Firstly, NaCl and CaCl2 powders were mixed in a eutectic composition (NaCl:CaCl2 = 47.9:52.1 mol%), and then certain amounts of CaO (0–2.0 mol%) and SiO2 (0 or 1.0 mol%) powders were added to the molten eutectic mixture. For Raman spectroscopy, a platinum pan loaded with the mixed salt was placed in an air-tight high-temperature stage, and then heated to 1023 K.Then the structure of dissolved SiO2 was investigated by Raman spectroscopy. For electrochemical measurement, the mixed salts were loaded into a graphite crucible. A graphite plate was used as a working electrode. The counter and quasi-reference electrodes were a graphite rod and a Si rod, respectively. The potential was calibrated by the deposition potential of Na metal on a Mo wire. Samples obtained by the galvanostatic electrolysis were analyzed by XRD and SEM/EDX. 3. Result and discussion Fig. 1 shows Raman spectra of molten (a) eutectic NaCl–CaCl2, (b) NaCl–CaCl2–2.0 mol% CaO, and (c) NaCl–CaCl2–2.0 mol% CaO–1.0 mol% SiO2 at 1023 K. Within the wave number range of 700–1200 cm−1, a band at 845 cm−1 is observed only for molten salt (c), whereas no apparent bands for molten salts (a) and (b). The structure of dissolved SiO2 in molten salt (c) is considered as SiO4 4− ion, considering that the main Raman bands for the stretch vibration of SiO4 4−, SiO3 2−, and Si2O5 2− in silicate melts have been reported at around 850, 950, and 1100 cm−1, respectively [8]. Since the SiO4 4− ion is regarded as the dissolved species of Ca2SiO4, this ion is consistent well with the ratio of added CaO/SiO2 (2.0 mol% and 1.0 mol%).The galvanostatic electrolyses were also carried out at graphite plates at 50–200 mA cm−2 in molten NaCl–CaCl2–1.9 mol% CaO–0.97 mol% SiO2. From XRD and SEM/EDX analysis of the samples, deposition of Si was confirmed, which suggested the reduction of SiO4 4− ion as follows:SiO4 4− + 4 e− → Si(s) + 4 O2− (1)In the presentation, the effect of CaO concentration on the dissolution behavior of SiO2 and electrochemical reduction of dissolved SiO2 will be discussed. Acknowledgement The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University. R eferences [1] Photovoltaic Market 2017, RTS Corp., Tokyo, Japan (2017). [in Japanese][2] Industrial Rare Metal 2019, Arumu Publ. Co., Tokyo, Japan (2019). [in Japanese][3] Photovoltaic Market 2019, RTS Corp., Tokyo, Japan (2019). [in Japanese][4] T. Nohira, K. Yasuda, and Y. Ito, Nat. Mater., 2, 397 (2003).[5] K. Yasuda, T. Nohira, R. Hagiwara, and Y. H. Ogata, Electrochim. Acta, 53, 106 (2007).[6] T. Toba, K. Yasuda, T. Nohira, X. Yang, R. Hagiwara, K. Ichitsubo, K. Masuda, and T. Homma, Electrochemistry, 81, 559 (2013).[7] Y. Ma, K. Yasuda, and T. Nohira, s of The 51st Symposium on Molten Salt Chemistry, p. 24-25, Sapporo, Japan (2019).[8] B. O. Mysen, Structure and Properties of Silicate Melts, Elsevier, Amsterdam, Netherlands (1988). Figure 1

Study of entrainment of Li2O in product from direct electrolytic reduction of UO2 in molten LiCl–Li2O. Part 1: Post-processing and analysis techniques

This paper describes experimental and characterization methods for gram-scale uranium oxide electrolytic reduction tests in molten LiCl–Li2O. Post-test analysis of the cathodically reduced UO2 involves acid-base titration and thermogravimetric analysis under flowing air. The titration was used to measure Li2O entrained inside reduced UO2 particles. Centrifugal salt removal was demonstrated to eliminate Li2O from the basket, but the Li2O entrained in the reduced uranium particles remained and was reacted over a period of several days in an autotitrator. Measuring the mass increase by thermogravimetry while heating to 800 °C and flowing air was found to be an effective way to measure the reduction extent, which was verified with pure U metal. The error of this measurement was estimated to be 1.65%. In addition, a LECO oxygen compositional analyzer was used to independently verify the oxygen content in the product from the thermogravimetric analysis.

Corrosion Behavior of Fe-Cr-Al Alloy for Anode Current Collector in Oxygen Atmosphere

Solid Oxide membranes (SOMs) have been applied to metal production through oxide reduction in order to accomplish low-cost production of primary products through simple pre-processing, low capital costs, small manufacturing plants, and low energy costs. Especially, the SOM process is eco-friendly, which makes it even more attractive. The SOM process is a direct electrolytic reduction process using a solid-oxide oxygen ion conducting membrane with high-temperature molten salts as a reaction medium. The transported oxygen ions from the cathode during the direct electroreduction process create a chemically harsh environment that can be corrosive for the alloy. Therefore, there is a need for the high-temperature corrosion behavior of alloy in high-temperature oxygen atmosphere. In this study, the hot corrosion behavior of FeCrAl alloy was investigated at 1150 ℃ in oxygen atmosphere with alumina shielding and without alumina shielding. The surface and cross-sectional morphologies and the characteristics of alloy were analyzed by SEM, EDS. As a result, FeCrAl alloy with alumina shielding was less oxidation than that without alumina shielding.

Eco-Friendly Electroreduction of Indium Tin Oxide Using SOM Anode in Molten Salts

Indium Tin Oxide(ITO) has been widely used at transparent electrode of Light Emitting Diode(LED) or the material of Liquid Crystal Display(LCD). However, waste ITO is generated after process and wet recycling technology has been used. In the case of wet recycling technology, a large amount of acid required and process time is so long. Then, if waste ITO could be recycled by dry process, electroreduction process, it is expected to solve the economic and environmental problems. However, when graphite is used as anode, it generates greenhouse gases such as CO or CO2 gas and causes formation of dirty C dusts. In this study, electroreduction of Indium Tin Oxide using Solid Oxide Membrane anode was investigated in a molten salt of CaF2-NaF-CaO at 1150 °C under the inert atmosphere to replacing previous anode materials. The SOM process is a direct electrolytic reduction process using a solid-oxide oxygen ion conducting membrane, namely, yttria-stabilized zirconia (YSZ), with high-temperature molten salts as a reaction medium. To verify the possibility of replacing, waste ITO was used because of the large use in industry. Electrochemical behavior was investigated by CV(Cyclic Voltammetry) in molten salts using waste ITO and inert working electrodes. As a result, InSn metal was reduced by SOM process. After electroreduction process, the optimum ITO particle size is considered to be the range of 600 μm to 1000 μm due to considering the maximum reduction efficiency dependent on the sedimentation rate, specific melt droplet growth, and reduced InSn film formation. The reduced InSn alloy was analyzed by XRD and EDS and they were confirmed as InSn alloy, which is almost the same as the initial ITO composition.

Mechanism of Electrolytic Reduction of SiO2 at Liquid Zn Cathode in Molten CaCl2

The reaction mechanism of electrolytic reduction of SiO2 at a liquid Zn cathode in molten CaCl2 was investigated with the aim of establishing a new production process of solar-grade Si. Three types of Zn/SiO2 contacting electrodes were prepared depending on the objectives. Cyclic voltammetry suggested two reduction mechanisms of SiO2 at a Zn electrode. One is a direct electrolytic reduction that proceeds at potentials more negative than 1.55 V vs. Ca2+/Ca. The other is an indirect reduction by liquid Ca–Zn alloy at potentials more negative than 0.85 V. The both reduction mechanisms were confirmed to proceed at 0.60 V by electrolysis and immersion experiments. Impurity analysis by ICP-AES was conducted for the Si prepared by potentiostatic electrolysis at 0.60 V, and confirmed that the concentrations of the metal elements and P were lower than the target levels for primary Si before directional solidification process.

Identification, measurement, and mitigation of key impurities in LiCl-Li2O used for direct electrolytic reduction of UO2

Direct electrolytic reduction (DER) of UO2 utilizes a molten LiCl-Li2O electrolyte operating at 650 °C.Productive processes at the cathode are UO2 and Li2O reduction (followed by metallothermic reduction of UO2 by Li metal). Non-productive reduction current has been observed that could be attributed to impurities produced from interaction of the salt with water. Cyclic voltammetry (CV) scans of molten mixtures of LiCl containing Li2O, LiOH, and/or Li2O2 indicate that LiOH is the primary cause of reduction current preceding UO2 and Li2O reduction. LiOH reduction appears as a broad soluble-soluble transition and forms a pre-reduction plateau characteristic of micro-electrode reactions. Electrochemical response to LiOH in the salt is reduced with addition of Li0, providing a practical approach to eliminating LiOH from LiCl-Li2O salt before the DER process. Generation of H2 gas was detected while heating Li0 with LiCl-Li2O-LiOH, consistent with a reaction mechanism where LiOH reduction causes formation of Li2O and H2.

Purity and Minority Carrier Lifetime in Silicon Produced by Direct Electrolytic Reduction of SiO&lt;sub&gt;2&lt;/sub&gt; in Molten CaCl&lt;sub&gt;2&lt;/sub&gt;

Purity and Minority Carrier Lifetime in Silicon Produced by Direct Electrolytic Reduction of SiO&lt;sub&gt;2&lt;/sub&gt; in Molten CaCl&lt;sub&gt;2&lt;/sub&gt;

Historical Development of Pyrochemical Methods for Treating Used Nuclear Fuel

Pyrochemical processing (often referred to as “pyroprocessing”) of used nuclear fuel utilizes molten salts and molten metals at elevated temperatures as process fluids to separate actinides from fission products. In broad terms, separations are achieved by taking advantages of differences in reactivity of the U, Pu, Am, Np, lanthanide and fission product metals as a function of pO2 and pX2, where X is a halide such as chlorine or fluorine. The presentation will cover highlights in the development of pyroprocessing technology with an emphasis on how the technology has reached its current state of development1 and the remaining challenges that are driving the current R&D in this area.2 In the U.S., pyroprocess development for civilian applications began in earnest in the 1960s with the recycling of used metal fuel from the Experimental Breeder Reactor II (EBR-II). At that time, a technique of “melt refining” was employed in which the fuel was melted in a single-use zirconia crucible. The crucible reacted with the lanthanide and active metal fission products as well as a fraction of the transuranics (TRUs) to form an insoluble oxide skull leaving uranium, noble metals, and most of the TRUs in the molten metal phase. This approach was abandoned because of incomplete TRU recovery. Interest in recycling EBR-II fuel was revived in the 1980s during the Integral Fast Reactor (IFR) program. In the IFR program, there was shift away from the use of chemical redox agents and to drive redox the reactions electrochemically in an electrolytic cell. This approach allows for more precise control of the reaction driving force and potentially decreases the volume of waste generated. For example, electrorefining, was chosen as the main separation method.1 Used metallic fuel is placed in an anode basket and inserted in to a bath of molten LiCl-KCl-UCl3. Passing current between the anode and a cathode results in the anodic dissolution of uranium and all metals more active than uranium. At the cathode only metallic uranium or a U+TRU metal alloy is deposited because the uranium chloride and transuranic chlorides are the noblest species in the molten salt. Fission products less noble than the TRUs (e.g., lanthanides) remain in the salt as chlorides and fission products more noble than, uranium (e.g. Fe, Zr, Ru, Mo, Tc) remain as metals in the anode basket. Improvements in equipment design and additional refinement to the overall process flowsheet continued through the 1990s and into the 21st century. Direct electrolytic reduction of used oxide fuel technology was developed to expand the application of the technology to pyroprocessing of light water reactor (LWR) fuel. Process development has not been limited solely to recovery of uranium and transuranics. Back-end processes for recovery of fission products and placing them in durable wasteforms for geologic disposal were also developed. References J.L. Willit, W.E. Miller, J.E. Battles, J. Nuc. Mat., 195, 3, 229-249C.E. Till and Y.I. Chang, Plentiful Energy, 2011, ISBN: 978-1466384606 _______________ The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Kinetic Studies on Direct Electrolytic Reduction of SiO2 Granules in Molten CaCl2

1. Introduction The photovoltaic (PV) industry develops rapidly in recent years. As the main raw material of solar cells, solar-grade silicon (SOG-Si; 6N purity) is dominantly produced by the Siemens process which is based on hydrogen reduction and thermal decomposition of trichlorosilane (SiHCl3). The disadvantages of the Siemens process such as low productivity, low reaction efficiency and high energy consumption could seriously restrict the mass dissemination of solar cells in the future. Therefore, the development of a new production process of SOG-Si is urgently needed. Our group has been investigating a new process to produce SOG-Si via the combination of molten salt electrolysis and directional solidification in recent years.[1,2] Solid SiO2 granules can be directly reduced to Si by electrolysis in molten CaCl2. In this paper, the kinetics of direct electrolytic reduction of SiO2 granules in molten CaCl2 was investigated. The effects of the SiO2 granule size and cathodic potential on the reaction rate were clarified. The improvement of kinetics by using SiO2-Si mixtures as the raw material was confirmed. 2. Experimental The experiment was conducted in molten CaCl2 at 1123 K in an Al2O3 crucible. Before melting, the CaCl2 was dried well under vacuum to remove the residual moisture. The working electrode was an Al2O3 tube with SiO2 granules inside and with a graphite plate at the bottom. The counter electrode was a glassy carbon rod. The reference electrode was an Ag+/Ag electrode prepared by immersing a silver wire into molten CaCl2containing 0.5 mol% AgCl in a mullite tube. Approximately 0.1 g of SiO2 granules with four size ranges (<0.1 mm, 0.10-0.25 mm, 0.5-1.0 mm, and 1.0-2.0 mm) were electrolyzed at different cathodic potentials (0.6 to 1.2 V vs. Ca2+/Ca). In some cases, SiO2-Si mixtures with different composition ratios were used as the raw material. The reduction kinetics was evaluated on the basis of the growth of the reduced Si layer and the current behavior during electrolysis. The post-electrolysis samples were observed by SEM and analyzed by EDX. 3. Results and Discussion The observation of the cross-sections of the post-electrolysis samples indicates that the reduced Si layer grows from the bottom to the top. The reduction occurs via two routes: along the surface of SiO2 granules and from the surface to the core, to form a core (SiO2)-shell (Si) structure.[3] Smaller SiO2 granules are favorable for faster reduction because the contact resistance between the bottom graphite plate and the reduced Si particles is small and the diffusion of O2- ions in CaCl2inside the porous Si shells is easy.[4] A more negative cathodic potential is also favorable for faster reduction due to the fact that electron transfer is involved in the rate-determining step of the overall process. Figure 1 shows the photographs of the cross-sections of the working electrodes using SiO2-Si mixtures with different composition ratios as the raw material after electrolysis at 0.6 V for 20 min. The thickness of the reduced layer apparently increases with the increase of Si amount in the raw material. Since Si has a high electrical conductivity at 1123 K, new electron transfer paths are created and thus the reaction area is larger by using SiO2-Si mixtures compared with using only SiO2granules as the raw material. Therefore, the reduction kinetics is improved by the addition of Si. Acknowledgement This study was partly supported by JST-CREST and Grants-in-Aid for Scientific Research A from the Japan Society for the Promotion of Science (JSPS).

Direct Electrolytic Reduction of Solid Ta2O5 to Ta with SOM Process

A process that uses the solid-oxide–oxygen-ion conducting membrane has been investigated to produce tantalum directly from solid Ta2O5 in molten CaCl2 or a molten mixture of 55.5MgF2-44.5CaF2 (in wt pct). The sintered porous Ta2O5 pellet was employed as the cathode, while the liquid copper alloy, saturated with graphite powder and encased in a one-end-closed yttria-stabilized-zirconia (YSZ) tube, acted as the anode. The electrolysis potential in this method is higher than that of the Fray–Farthing–Chen Cambridge process because the YSZ membrane tube blocks the melts to electrolyze, and only Ta2O5 is will be electrolyzed. The microstructures of reduced pellets and a cyclic voltammogram of solid Ta2O5 in molten CaCl2 were analyzed. In addition, the influence of particle size and porosity of the cathode pellets on metal-oxide-electrolyte, three-phase interlines was also discussed. The results demonstrate that the sintering temperature of cathode pellets and electrolytic temperature play important roles in the electrochemical process. Furthermore, this process can be used to produce Ta metal efficiently without the expensive cost of pre-electrolysis and generation of harmful by-products.

Direct Electroreduction of Indium and Tin Oxides in Molten Salts

Indium is a rare metal. The largest end use for indium is in thin-film coatings as indium oxide combined with 10 percent tin oxide (ITO). However, indium has recycling rates less than 1%. Indium and tin are especially well suited for fused salt electrolysis because of their low melting points. The electrochemical behaviour of indium and tin oxides was studied by cyclic voltammetry (CV) in molten LiCl-KCl. The direct deoxidation of indium and tin oxides were investigated. A new design of direct electrolytic reduction was proposed considering the low melting points of indium and tin.

Direct Electrolytic Reduction of Hematite Pellets in Alkaline Electrolyte for Iron Production

not Available.

STEP carbon capture – The barium advantage

We have recently introduced the theory of the Solar Thermal Electrochemical Process for carbon capture and utilization (STEP carbon). We have also provided experimental validation of that theory using electrolysis of molten lithium and eutectic alkali carbonates at high (∼50%) solar efficiency and high rate, and delineated the materials required to use STEP carbon to decrease atmospheric CO2 to preindustrial levels in ten years. In this communication an effective, alternative STEP carbon electrolyte is introduced. It is demonstrated thermodynamically that barium carbonate can provide more than an order of magnitude greater affinity for direct carbon dioxide absorption from the air than our prior lithium carbonate electrolyte. It is demonstrated experimentally that molten barium carbonate mixtures provide an effective medium for the direct electrolytic reduction of absorbed carbon dioxide at high rate and lower energy. The products of the electrolysis are graphite, which is readily stored as a valued added commodity for future generations, and oxygen. The electrolyte is not consumed in this carbon dioxide splitting process.

Improving Purity and Process Volume During Direct Electrolytic Reduction of Solid SiO2 in Molten CaCl2 for the Production of Solar‐Grade Silicon

AbstractThe direct electrolytic reduction of solid SiO2 is investigated in molten CaCl2 at 1123 K to produce solar‐grade silicon. The target concentrations of impurities for the primary Si are calculated from the acceptable concentrations of impurities in solar‐grade silicon (SOG‐Si) and the segregation coefficients for the impurity elements. The concentrations of most metal impurities are significantly decreased below their target concentrations by using a quartz vessel and new types of SiO2‐contacting electrodes. The electrolytic reduction rate is increased by improving an electron pathway from the lead material to the SiO2, which demonstrates that the characteristics of the electric contact are important factors affecting the reduction rate. Pellet‐ and basket‐type electrodes are tested to improve the process volume for powdery and granular SiO2. Based on the purity of the Si product after melting, refining, and solidifying, the potential of the technology is discussed.

Fundamental Study on Reduction Rate for Electrolytic Reduction of SiO2 Powder in Molten CaCl2

Direct electrolytic reduction of powdery SiO2 has been investigated in molten CaCl2 at 1123 K aiming at a low cost and mass production of solar-grade Si. SiO2 powder was set on a Si plate which was installed at the bottom of the crucible and connected to a graphite rod used as a current lead. SiO2 powder was reduced to Si by cathodic polarization of the Si plate. The reduction rate was evaluated by the magnitude of the reduction current, in which three parameters were varied: electrode potential, SiO2 layer thickness, and SiO2 particle size. As a result, the rate-determining step of the reduction is suggested to be the diffusion of O2- ions inside the reduced porous Si particles filled with the electrolyte. During the reduction process, however, other factors such as contact resistance between Si particles and porosity of SiO2 particles possibly influence the reduction rate.

Electrolytic Reduction of Titania Slag in Molten Calcium Chloride Bath

Ferro-titanium is prepared by direct electrolytic reduction of titania-rich slag obtained from plasma smelting of ilmenite in molten CaCl2. The product after electro-reduction is characterized by x-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The electrolysis is carried out at a cell voltage of 3.0 V, taking graphite as the electrolysis cell as well as the anode, and a titania-rich slag piece wrapped by a nichrome wire is used as the cathode.