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Traitement de minerais de fer par lixiviation alcaline suivi de leur électrolyse en milieu alcalin

Abstract : An innovative ironmaking process by alkaline electrolysis of suspended iron oxides is being developed at ArcelorMittal Global R&D Maizières-lès-Metz. Were it to achieve industrial maturity, this process would permit a significant reduction of steelmaking CO2 emissions. Indeed, the use of carbon as a reducing agent in blast furnace would be replaced by electricity. Although this process enables iron production from commercial hematite (Fe2O3) at current density of 1000 A.m-2 with faradaic efficiency higher than 80%, these performances are systematically lower when using iron ore instead. The main impurities in these ores are aluminium and silicon oxides and hydroxides, these compounds are soluble in concentrated sodium hydroxide solutions. These compounds could be the source of the decrease in reactivity observed when feeding the process with iron ores. To raise the electrolysis performance with iron ores, alkaline leaching treatments were conducted on a defined iron ore. Reactivity of iron ores before and after treatment was compared by chronoamperometry. Although the elimination of aluminous compounds resulted in the ore gaining a faradaic yield increase to a value of 80%, compared with 65% before treatment, its current density remained twice as low as the one of hematite for a same applied voltage. Furthermore, complementary experiments of aluminate and silicate ions addition during pure hematite electrolysis did not have any deleterious effect on its electrolysis. Based on all the experiments undertaken in this PhD, it seems unlikely that siliceous and aluminous impurities hold an important effect on iron ore reactivity in alkaline electrolysis. The process is nonetheless very sensitive to iron ores granulometry. On this subject, strong agglomeration phenomena were witnessed when measuring iron ores granulometry but did not occur with pure iron oxides. Therefore, it would seem that other phenomena may be the main cause of reactivity loss, these phenomena may well be linked to secondary granulometry of iron ores in concentrated alkaline media. In parallel, an advanced thermodynamic analysis was carried out to describe the best theoretical conditions for pressure, temperature and NaOH concentration to realize hematite electrolysis. Gangue compounds solubility was represented with Pitzer equations, and new parameters were calculated for Na-SiO3-Al(OH)4 interactions. This thermodynamic study enabled the design and pre-sizing of a treatment step for iron ores by alkaline leaching
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Submitted on : Saturday, December 8, 2018 - 10:23:04 AM
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Vincent Feynerol. Traitement de minerais de fer par lixiviation alcaline suivi de leur électrolyse en milieu alcalin. Génie des procédés. Université de Lorraine, 2018. Français. ⟨NNT : 2018LORR0163⟩. ⟨tel-01948704⟩



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