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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Chromium is one of the essential commodities for today's life, with applications in stainless and high-alloy steels, providing enhanced corrosion resistance and improved mechanical properties. Chromium is usually added to the steel in the form of ferrochrome (FeCr) alloy. The 'Ring of Fire' chromite deposit in northern Ontario presents an opportunity for Canada to enter the globally strategic market. It contains the only commercial quantities of chromite in North America and is the fourth largest deposit in the world. The resources, including Measured, Indicated, and Inferred, are 300 Mt grading approximately 33% Cr 2 O 3. However, the remote location of the deposits makes development challenging. The preference for processing the chromite ore to marketable ferrochromium alloy within Ontario constitutes an additional challenge due to high electricity costs. Currently, 80% of the world's FeCr is produced in submerged arc furnaces. There are four technologies currently used for the production of ferrochrome alloys. These are chromite, ferrochrome, prereduction, direct reduction, catalysts, Ring of Fire.

Electrodeposition of Si from cryolite based melts is a possible solution for mass production of solar grade silicon. The deposition potential of Si on the candidate cathode, such as graphite, is fundamental information that needs to be measured and applied to restrict the co-deposition of impurities. In this study this potential was measured using cyclic voltammetry. As the activity of SiO 2 in the electrolyte affects the deposition potential, the measurements were carried out in a range of SiO 2 concentrations, allowing the prediction of potential change during the actual deposition process, where the SiO 2 content undergoes fluctuations. The kinetics of the oxidation and reduction reactions were also studied using the recorded voltammograms, showing that reduction of Si is a two steps process controlled by diffusion.