The Impact of Iron Oxide Concentration on the Performance of Molten Oxide Electrolytes for the Production of Liquid Iron
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MOLTEN oxide electrolysis (MOE) is a promising route for metal extraction from its oxide ore.[1] Products obtained are O2 gas at the anode and metal at the cathode 2Mx Oðs or lÞ ! 2xMðlÞ þ O2 ðgÞ
½1
The possibility to produce metal samples using this technique has been addressed by several authors.[2–8] As known for aluminum production, the advantage of metal production at liquid state is given by facile recovery of the produced metal and continuous operation.[9] The use of electricity for metal extraction also implies the possibility for the usage of renewable
JAN WIENCKE is with the Department of Ironmaking, Global Research and Development ArcelorMittal, 57283 Maizie`res-le`s-Metz, France and also with the De´partement CP2S, Universite´ de Lorraine, IJL-UMR 7198, 54000 Nancy, France. Contact e-mail: [email protected] HERVE´ LAVELAINE is with the Department of Ironmaking, Global Research and Development ArcelorMittal. PIERRE-JEAN PANTEIX, CARINE PETITJEAN, and CHRISTOPHE RAPIN are with the De´partement CP2S, Universite´ de Lorraine, IJL-UMR 7198. Manuscript submitted February 20, 2019. Article published online December 12, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
energies and thus the decoupling of metal production from CO2 emissions. Therefore, this technology marks a major interest for steel industry, if applicable to industrial scales of production.[10,11] Presence of multivalent elements, such as iron, at high concentration allows electronic and ionic conduction to occur simultaneously in the molten oxide electrolyte.[12] For an operation at a high faradaic yield, current flow has to occur entirely via ionic conduction. The participation of electronic conduction in the overall conduction is mainly dependent on the ratio of the multivalent species. For iron this value, the ferric ratio, is given via: Ferric ratio ¼
FeðIIIÞ FeðIIÞ þ FeðIIIÞ
½2
with Fe(II) and Fe(III) being the respective molar quantities. It was shown that current flow by electronic conduction in molten oxides is dominant if the ferric ratio is in the range of 0.25 to 0.75.[13,14] The ferric ratio itself is coupled to the temperature, to the partial pressure of oxygen,[15] to the basicity of the molten oxide[16] and to the concentration of iron oxide.[17] An experimental approach, ‘‘Molten Iron by Direct Electrolysis of Iron Ore’’—MIDEIO, in which the ferric ratio was decreased to a minimum, has confirmed recently the feasibility of the liquid iron metal by electrolysis of iron oxide in molten silicates.[18] VOLUME 51B, FEBRUARY 2020—365
The identification of side reactions and of resistances to current flow phenomena during electrolysis is an imperative step for further large-scale process development. Favorable operating conditions for the MIDEIO process are defined by a low electronic current contribution, a maximum current density and an anodic yield for O2 production close to unity. To describe the dependence of these parameters on the iron oxide concentration, stepped linear scan voltammetry technique has been
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