The electrolytic extraction of liquid copper at 1105 • C from a molten sulfide electrolyte composed of 57 wt% BaS and 43 wt% Cu 2 S was investigated. DC cyclic voltammetry, Fourier transformed AC voltammetry, and galvanostatic electrolysis revealed that the electrodeposition of copper is possible in the selected molten sulfide electrolyte. The half wave potential for the reaction on graphite was determined, and liquid copper of high purity was obtained by galvanostatic electrolysis. These preliminary results confirm that molten sulfides free of alkaline elements could be used as an electrolyte for faradaic applications, despite the semi-conducting nature of the melt. In addition to demonstrating the need for enhanced understanding of the transport properties of such electrolyte, the results show the critical impact of the cell design to improve the process faradaic efficiency. Sulfide-containing ores are the main raw material for copper extraction. The conventional chemical principle underlying metal extraction from such ore (smelting) is the selective oxidation of sulfide ions (S 2− ) by oxygen. The reaction 1 forms copper metal and sulfur dioxide (SO 2 ) as products, as written here for chalcocite (Cu 2 S):Such principle leads to a process characterized by large capital investments and significant environmental challenges. 1 This route requires handling SO 2 as a by-product, typically converted to sulfuric acid. To circumvent this issue, additional pyrometallurgical steps to convert SO x into elemental sulfur have been devised, using for example reduction or chlorination. Hydrometallurgy is an alternative to traditional smelting that does not involve SO 2 .3-5 It involves a succession of leaching, solvent extraction and finally electrowinning of Cu in an aqueous electrolyte. This route is also characterized by a relatively large footprint and capital cost. One of the limitations is inherited from the electrowinning/ refining steps, where the current density for copper electrodeposition is typically limited to 0.05 A.cm −2 . 6An alternative approach to avoid SO 2 formation is the direct decomposition of copper sulfide into copper and elemental sulfur, following reaction 2:At 1106• C, more than 20• C above copper melting point, reaction 2 is not spontaneous ( r G • = 90.5 kJ.mol −1 ) and would require a minimum amount of energy of 267 kJ.mol −1 (equivalent to 583 kWh.t Cu −1 ) a . 7 This reaction could therefore be driven by electricity, as practiced industrially for most metals, including copper and aluminum. In principle, electrolysis can also offer the selective recovery of multiple metals contained in the sulfides ores, for example elements more noble than copper, e.g. silver or molybdenum.The direct electrolysis of sulfides was proposed in concept by Townsend in a patent in 1906.2 Since then, the challenge remains in selecting a supporting electrolyte with an acceptable solubility for copper sulfide concentrates to guarantee large cathode current density, a requirement for tonnage production. Previous studi...

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The liquid metal battery (LMB) is attractive due to its simple construction, its circumvention of solid-state failure mechanisms and resultantly long lifetimes, and its particularly low levelized cost of energy. Here, we provide a study of a unique binary electrolyte, NaOH-NaI, in order to pursue a low-cost and low-temperature sodium-based liquid metal battery (LMB) for grid-scale electricity storage. Thermodynamic studies have confirmed a low eutectic melting temperature (220 • C) as well as provided data to complete the phase diagram of this system. X-ray diffraction has further supported the existence of a recently discovered compound, Na 7 (OH) 5 I 2 , as well as offered initial evidence toward a NaI-rich compound displaying Pm-3m symmetry. These phase equilibrium data have then been used to optimize parameters from a two-sublattice thermodynamic solution model to provide a starting point for study of higher order systems. Further, a detailed electrochemical study has identified the voltage window and related oxidation/reduction reactions and found greatly improved stability of the pure sodium electrode against the electrolyte. Finally, an Na|NaOH-NaI|Pb-Bi proof-of-concept cell was assembled. This cell achieved over 100 cycles and displayed leakage currents below 0.40 mA/cm 2 . These results highlight an exciting class of low-melting molten salt electrolytes that may enable low cost grid-scale storage. The pressing need for highly scalable and economically viable battery systems for grid-storage has prompted many researchers to pursue entirely new electrochemical approaches. One such technology that has recently grown from the university lab bench to the commercial production floor is the liquid metal battery (LMB) 1,2 -a system that takes advantage of a three liquid-layer design to store and deliver large quantities of energy at particularly low levelized costs.The LMB is designed with an electropositive liquid metal anode, A, separated from an electronegative liquid metal cathode, B, by a molten salt electrolyte. Upon discharge, the anode, A, oxidizes, transports across the A-itinerant electrolyte, and reduces at the cathode interface to form an A-B alloy. The reaction is driven by the partial free energy difference of A in the high activity negative electrode environment versus that of the alloyed metal A (in B) in the positive electrode.Because all three active battery components are liquid phase, the system is able to operate at high current densities with minimal overpotential losses. In addition, because the cell is restored to its virgin liquid state upon each recharge, the device is immune to solid-state failure mechanisms common in lithium-ion batteries 3 and, as a result, is expected to provide exceptionally long amortizable service lifetimes.In spite of the benefits of the LMB system, the high temperatures required to achieve a fully molten state present challenges when scaling the battery to production. Higher temperatures drive costs due to issues associated with device sealing, expensive wiri...

All available thermodynamic and phase diagram data for the ternary reciprocal system Al2O3–SiO2–AlF3–SiF4 have been critically reviewed. The oxyfluoride liquid solution was modeled using the Modified Quasichemical Model in the Quadruplet Approximation and the most reliable data have been used to optimize the model parameters. The mullite solid solution was previously modeled using the Compound Energy Formalism. Data for fluor‐topaz have been critically reviewed and a new thermodynamic description has been obtained. Phase equilibrium with the gas phase in the reciprocal system at 1 bar is reproduced.

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Current industrial methods used for rare earth element (REE) extraction involve: 1) ore enrichment, 2) separation of rare earth oxides (REOs), 3) chlorination or hydrofluorination, and 4) individual electrowining of REEs from a molten halide electrolyte. The complexity of REE extraction is inherited from their electronic configuration. Recently, molten oxide electrolysis (MOE) has been used to produce reactive metals directly from their oxides, e.g. titanium. As a single-step alternative to processes 3) and 4), or laboratory has investigated rare earth extraction by MOE. A key challenge is to find a molten electrolyte more stable than REOs. One possibility is to use binaries of REOs directly as a solvent. We have, therefore, developed two experimental approaches for studying molten REOs at temperatures exceeding 2200 o C. The present work reports the most recent experimental results obtained with La 2 O 3-Y 2 O 3. Those promising results demonstrate potential for operating with molten REOs and refine the underlying materials challenge for electrodes to enable metal recovery.

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