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Valorisation de résidus miniers riches en fer : Conception et développement d’un procédé de production de fer électrolytique à partir de matrices complexes

Abstract : The increase in world population (from 2.5 billion in 1950 to 10 billion in 2050 according to the United Nations) is leading to an increase in the need for metals. These metals come from mines, but their production from ores generates huge quantities of tailings. These tailings occupy large storage areas and very often contain metals that can be extracted. The recovery of these metals would not only make it possible to reduce their volume and ecological footprint, but also and above all to produce metals with high added value to meet the needs of new technologies. Two types of iron-rich residues were studied in this work in order to extract iron and zinc by electroplating: red mud and jarosite. In the first case, these are residues from the production of alumina from bauxite ore by the Bayer process (alkaline process). The second type of residues, jarosite, comes from the production of zinc by the "jarosite" process. Two experimental approaches have been set up for this purpose. Direct electrodeposition in the case of red mud: the samples are directly suspended in a 12.5 mol/L NaOH solution and the iron (in the form of hematite and/or goethite) is electrodeposited on a graphite cathode at a temperature of 110°C. In the case of jarosite, a different approach has been used: (i) a leaching of the jarosite in a sulphuric acid medium, (ii) a blende leaching to reduce the ferric iron to ferrous iron and to enrich the bath in zinc, (iii) a cementation of the copper by a zinc powder and finally (iv) an iron-zinc alloy electrodeposition step. In both cases of residues, several operating parameters were tested in order to optimize leaching yield, electrodeposition, deposit quality and faradaic yield. For the red mud, the best faradaic yield (72%) were obtained for a solid/liquid ratio of 1/3 (g/mL), a NaOH concentration of 12.5 mol/L, a current density of 41 A/m² and a temperature of 110°C. The electrolytic iron deposits, analyzed by ICP-AES, DRX, SEM/EDX, have a purity of more than 97% iron by mass. For jarosite, the best leaching yield (for zinc and iron were 73% and 70% respectively) were obtained for a sulphuric acid concentration of 1.5 M, a solid/liquid ratio of 1/10 (g/mL) and a temperature of 80°C for 7 hours. Electrodeposition tests produced zinc-iron alloys with different iron contents. The faradaic yield obtained under optimal conditions (current density of 800 A/m² and a temperature of 20°C) was of the order of 89%. The results obtained in this study confirm the technical feasibility of iron and iron-zinc alloy electroplating from complex matrices. This opens up a new alternative to the valorisation of mining residues by the metal electrodeposition technique.
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Abdoulaye Maihatchi-Ahamed. Valorisation de résidus miniers riches en fer : Conception et développement d’un procédé de production de fer électrolytique à partir de matrices complexes. Génie des procédés. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0028⟩. ⟨tel-02881266⟩

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