Electrolysis device comprising an anode placed in a housing

Abstract

The electrolysis device (1) for reducing iron oxides into metallic iron comprises : - at least one anode (6), extending between an inner surface (10) and an outer surface (12), opposite the inner surface (10), - at least one cathode (4) comprising a collecting surface (8) on which metallic iron is deposited after reduction of iron oxides, the collecting surface (8) facing the inner surface (10) of the anode (6), - an electrolytic bath comprising an anolyte (16), in which the anode (6) is immersed, and a catholyte (18), in which the cathode (4) is immersed, wherein the anode (6) extends in a housing (14) separating in a fluid tight manner the anolyte (16) from the catholyte (18), the chemical composition of the anolyte (16) being different from the chemical composition of the catholyte (18).

Description

[0001] Electrolysis device comprising an anode placed in a housing

[0002] The present invention relates to an electrolysis device for reducing iron oxides into metallic iron.

[0003] The invention also relates to a method for producing a steel material from iron oxides using such an electrolysis device.

[0004] In order to produce a steel material having satisfactory properties, iron oxides, which are naturally found in nature, have to be converted into metallic iron, which is then melted with other materials to produce a steel material with the required composition.

[0005] To this end, it is for example known to treat iron oxides by electrolysis to produce metallic iron suitable to be melted to produce a steel material. The iron oxides, for example in form of a powder, scrap or in a solution, are placed in an electrolytic bath of an electrolysis device and power is supplied to the anode(s) and cathode of the electrolysis device. Metallic iron is then deposited on a collecting surface of the cathode and can be collected.

[0006] However, such a method for producing the metallic iron does not present a satisfactory yield for several reasons.

[0007] The electrolysis reaction generates gas: dioxygen around the anode and dihydrogen around the cathode. The dioxygen is more particularly produced in large quantities and the gas bubbles flowing along the collecting surface of the cathode are an obstacle to the deposition of metallic iron on this surface. Indeed, gas has a much lower electrical conductivity than the electrolytic bath and the gas bubbles therefore act as an insulating barrier between the metallic iron and the collecting surface of the cathode. When the bubbles adhere to the collecting surface, they also reduce the available surface for the deposition of metallic iron. Furthermore, the generated dioxygen and dihydrogen mix with each other in the electrolytic bath, meaning that particular measures have to be implemented to mitigate the risks of explosion of the resulting reaction. In particular, air can be injected on top of the electrolytic bath to dilute the generated mix at the exit of the electrolysis cell and reduce its explosive nature. This however implies high flow rate of air to be injected in order to sufficiently dilute hydrogen and this fresh air will cool down the bath and increase thermal losses by evaporation.

[0008] The electrolytic bath containing iron ore particles in suspension presents an important viscosity, thereby reducing the electrolyte velocity in the gap between the anode and the cathode, which impairs gas evacuation in this gap, thereby reducing the efficiency of metallic iron deposition on the collecting surface. To reduce the viscosity of the electrolytic bath and ensure proper gas evacuation, the concentration of iron ore particles in the electrolytic bath can be reduced, which also results in a reduction of the quantity of metallic iron produced by the electrolysis reaction.

[0009] One of the aims of the invention is to overcome the above-mentioned drawbacks by providing an electrolysis device for producing metallic iron from iron oxides with an increased productivity.

[0010] To this end, the invention relates to an electrolysis device for reducing iron oxides into metallic iron, the electrolysis device comprising:

[0011] - at least one anode, extending between an inner surface and an outer surface, opposite the inner surface,

[0012] - at least one cathode comprising a collecting surface on which metallic iron is deposited after reduction of iron oxides, the collecting surface facing the inner surface of the anode,

[0013] - an electrolytic bath comprising an anolyte, in which the anode is immersed, and a catholyte, in which the cathode is immersed, wherein the anode extends in a housing separating in a fluid tight manner the anolyte from the catholyte, the chemical composition of the anolyte being different from the chemical composition of the catholyte.

[0014] Placing the anode in a housing and separating the catholyte from the anolyte improves the yield of the electrolysis reaction. More particularly, since the gas generated around the anode is generated in the housing, this gas does not impair the deposition of metallic iron on the collecting surface of the cathode. Furthermore, since this gas is isolated from the gas generated around the cathode, the risks of creating an exploding mixture are eliminated; without needing to inject air to dilute the mixture. Such a removal of the need of air injection also reduces the need to have a powerful aspiration device to remove the mixture from the catholyte. An additional benefit of such a gas separation is that the gas can be recovered for other purposes, for example for heating purposes in a plant in which the electrolysis device is installed. This allows a better valorization of the exhaust gas which increase the overall performance of the system by decreasing the operational costs. Separating the catholyte from the anolyte also makes it possible to adjust the composition of both the catholyte and the anolyte. More particularly, only the catholyte has to comprise iron ore particles such that the viscosity of the anolyte can be reduced. Such a reduction allows improving the gas evacuation at the anode side and, since this gas is not present in the catholyte, the concentration of iron ore particles in the catholyte can be increased without impairing gas evacuation at the cathode side. The quantity of produced metallic iron can therefore be increased. Furthermore, since the injection of anolyte in the housing is only used to renew the anolyte in the housing, while the injection of catholyte is also used to inject the iron ore particles, the flow of anolyte can be reduced compared to the flow of catholyte, thereby reducing the energy consumption to inject the anolyte. The anolyte can also be easily recovered to be reused since it does not contain iron ore particles. The flow of the injected catholyte can also be reduced because this flow is not used to promote the evacuation of dioxygen, which is only produced in the housing and not around the cathode.

[0015] The electrolysis device according to the invention can comprise one or more of the following features, considered alone or according to any technically feasible combination:

[0016] - the housing is delimited at least in part by at least one fluid tight membrane delimiting at least a part of an inner volume receiving the anode and the anolyte, said inner volume being isolated from the catholyte in a fluid tight manner,

[0017] - the membrane is applied against the inner surface of the anode, the outer surface of the anode being turned towards a central portion of the inner volume of the housing,

[0018] - the membrane is an ion exchange membrane having a gas permeability inferior to inferior to 20L / min / cm2 H2 at 5 Bar,

[0019] - the anode comprises openings extending through the anode from the inner surface to the outer surface, the openings being arranged such that gas generated by the electrolysis reaction on the inner surface side of the anode is transferred to the outer surface side of the anode inside the housing,

[0020] - the electrolysis device comprises a catholyte injection device arranged to inject the catholyte in an enclosure receiving the cathode and the housing, the catholyte being injected around the cathode and around the housing,

[0021] - the electrolysis device comprises a anolyte injection device arranged to inject the anolyte in the housing, the anolyte being injected around the anode,

[0022] - the electrolysis device comprises a dihydrogen extraction device arranged to extract dihydrogen from an enclosure receiving the cathode and the housing, said dihydrogen being generated around the collecting surface of the cathode by the electrolysis reaction,

[0023] - the electrolysis device comprises a dioxygen extraction device arranged to extract dioxygen from the housing receiving the anode, said dioxygen being generated around the anode by the electrolysis reaction,

[0024] - the catholyte comprises a sodium hydroxide solution with a suspension of iron ore particles,

[0025] - the anolyte comprises a sodium hydroxide solution without iron ore particles,

[0026] - the concentration of sodium hydroxide in the anolyte is inferior to said concentration in the catholyte,

[0027] -the pressure in the catholyte is superior to the pressure of the anolyte. According to another aspect, the invention also relates to a method for producing a steel material from iron oxides, comprising the following steps:

[0028] - reducing iron oxides using a electrolysis device as described above,

[0029] - collecting metallic iron from the collecting surface of the cathode,

[0030] - producing a steel from the collected metallic iron.

[0031] According to an optional feature of the method, the method comprises a step of extracting the gas generated by the electrolysis reaction in the catholyte independently from the gas generated in the anolyte by the electrolysis reaction.

[0032] Other aspects and advantages of the invention will appear upon reading the following detailed description, given by way of example and made in reference to the appended drawings, wherein:

[0033] Fig. 1 is a diagrammatical representation of an electrolysis device according to an embodiment of the invention, and

[0034] Fig. 2 is a diagrammatical representation of an enlarged view of an electrolysis device according to another embodiment of the invention.

[0035] In reference to Figs. 1 and 2, an electrolysis device 1 for reducing iron oxides into metallic iron according to the invention is described.

[0036] The electrolysis device 1 comprises an enclosure 2 arranged to receive at least one cathode 4 and one anode 6 immersed in an electrolytic bath contained in the enclosure 2. As known per se, the cathode 4 and the anode 6 are connected to a power source (not shown) arranged to provide an electric current between the cathode 4 and the anode 6. It is preferably operated using CO2 neutral electricity which includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, and geothermal heat. In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced.

[0037] The cathode 4 defines at least one collecting surface 8 on which metallic iron, produced by the reduction of iron oxides is deposited when the electrolysis reaction takes place as will be described subsequently. The cathode 4 may be made of copper, or graphite, one face of which forming the collecting surface 8. The cathode 4 may optionally be covered with a removable part such as steel sheet or a removable part made of carbon, and notably of carbon fibers, said removable part then forming the collecting surface 8. According to an embodiment that will be described in greater details subsequently, each face of the cathode 4 forms a collecting surface 8. The collecting surface 8 for example has a substantially rectangular shape and extends according to an elevation direction Z, corresponding to the height of the cathode 4, and to a transversal direction, substantially perpendicular to the elevation direction Z and corresponding to the width of the cathode 4. The two collecting surfaces 8 of the cathode 4 are spaced from each other according to a longitudinal direction L, substantially perpendicular to the elevation and transversal directions and corresponding to the thickness of the cathode 4.

[0038] The anode 6 extends between an inner surface 10 and an outer surface 12, opposite the inner surface 10. The inner face 10 and the outer face 12 are substantially parallel and are spaced from each other according to the longitudinal direction L. The inner face 10 faces the collecting surface 8 of the cathode 4 and is substantially parallel to the collecting surface 8. The inner surface 10 and the collecting surface 8 are spaced therefrom along the longitudinal direction L, the space between the collecting surface 8 and the inner surface 10 being designated as the inter-electrode gap. The inter-electrode gap has for example a width measured in the longitudinal direction L substantially comprised from 10 mm to 25 mm.

[0039] The anode 6 extends in a housing 14 arranged to fluidically isolate the anode 6 and an anolyte 16, forming part of the electrolytic bath, from the cathode 4 and a catholyte 18 forming the other part of the electrolytic bath, while allowing the electrolytic reaction to take place.

[0040] To this end, according to an embodiment, the housing 14 is delimited at least in part by a fluid tight membrane 20 arranged to prevent gas and liquid exchanges between the anolyte 16 extending in an inner volume 22 of the housing 14 and the catholyte 18 extending in the enclosure 2 around the housing 14. In other words, the inner volume 22 of the housing 14, containing the anolyte 16 and the anode 6, is fluidically isolated from the catholyte 18 by the fluid tight membrane 20. In order to do so while allowing the electrolytic reaction, the fluid tight membrane 20 is for example an ion exchange membrane having a low gas permeability arranged to prevent gas exchanges between the inner volume 22 and the catholyte 18. By low gas permeability, it is meant a gas permeability inferior to 20L / min / cm2 H2 at 5 Bar, measured according to procedure of the ASTM standard G148. The membrane 20 for example has a thickness, measured in the longitudinal direction L, comprised from 0.40 mm to 0.80 mm. The fluid tight membrane 20 is for example made of thermoplastics, such as polysulfone or polyphenylene sulfide, optionally coated with a material comprising zirconium The membrane 20 preferably has a ionic resistance lower than 0.30 ohm / cm.

[0041] The fluid tight membrane 20 extends at least between the inner surface 10 of the anode 6 and the collecting surface 8 of the cathode 4. In other words, the fluid tight membrane 20 extends in the transversal direction and in the elevation direction Z in the inter-electrode gap. According to an embodiment, the fluid tight membrane 20 is applied against the inner surface 10 of the anode 6. More particularly, the membrane 20 is for example pressed against the inner surface 10 of the anode 6, as more particularly described subsequently.

[0042] According to an embodiment, the membrane 20 completely surrounds the inner volume 22 of the housing 20 except at both ends of the housing 20 in the elevation direction Z. In other words, the membrane 20 for example has a cylindrical shape with an axis extending in the elevation direction Z. According to an embodiment, the housing 20 comprises several membranes, for example two membranes 20 parallel to each other and extending on either sides of the anode 6 around the inner volume 22. The housing 20 for example comprises a frame 24 closing the housing 20 at both ends of the housing 20 in the elevation direction Z and arranged to hold the membrane 20 around at least a part of the inner volume 22. In this case, the membrane 20 is attached in a fluid tight manner to the frame 24 in order to isolate the inner volume 22 of the housing 14 in a fluid tight manner, as described previously. The frame 24 is for example made of plastic materials.

[0043] Advantageously and as shown in Fig. 1 , the cathode 4 extends in the longitudinal direction L between two anodes 6, each extending in separate housing 14. In this case, each face of the cathode 4 forms a collecting surface 8 and the inner surfaces 10 of the anodes 6 each face one the collecting surfaces 8. More advantageously, the electrolysis device 1 comprises a plurality of cathodes 4, each immersed in the catholyte 18 and extending in the longitudinal direction between two anodes 6. In this case, each housing 14 for example receives two anodes 6 parallel to each other. In this case, as shown in the central housing 14 of Fig. 1 , the outer surfaces 12 of the anodes 6 face each other and are spaced from each other according to the longitudinal direction L to extend on either sides of a central portion of the inner volume 22 of the housing 14. The distance between the outer surfaces 12 of the anodes 6 extending in the same housing 14, corresponding to the width of the central portion of the inner volume 22 measured in the longitudinal direction L, is for example comprised from 5 mm to 50 mm. As will be disclosed subsequently, the membrane(s) 20 is (are) applied against the inner surfaces 10 of the anodes 6 in the interelectrode gaps extending between the anodes 6 and the corresponding cathodes 4 thanks to the overpressure in the catholyte 18 compared to the anolyte 16. According to this embodiment, the electrolytic bath therefore comprises a single catholyte 18 in which all the cathodes 4 are immersed and several anolytes 16, in each of which two anodes 6 are immersed. Such an embodiment allows increasing the quantity of metallic iron that can be collected by increasing the number of electrolysis reactions between the various cathodes 4 and anodes 6. In this case, it is understood that the power source is connected to the cathodes 4 and to the anodes 6 to power all these electrolysis reactions. Thanks to the invention fluidically isolating the catholyte 18 from the anolyte(s) 16, it is possible for the anolyte(s) 16 to have a different chemical composition than the catholyte 18.

[0044] More particularly, the invention makes it possible to add the iron ore particles as a source of iron oxides in the catholyte 18 only and not in the anolyte(s) 16. Indeed, since the reduction of the iron oxides to form metallic iron occurs around the cathode(s) 4 such that the metallic iron is deposited on the collecting surface(s) 8, iron ore particles can be absent from the anolyte(s) 16. This allows reducing the viscosity of the anolyte(s) 16, compared to the catholyte 18, which in turn improves gas evacuation from the inner volume 22 of the housing(s) 14, as will be described in greater details subsequently.

[0045] According to an embodiment, the catholyte 18 comprises a sodium hydroxide (NaOH) solution with a suspension of iron ore particles. The concentration of NaOH in the catholyte is for example comprised from 40% to 60% in weight, for example substantially equal to 50% in weight. The suspension of iron ore particles is for example comprised from 20% to 35% in weight, for example close to 30% in weight. For comparison purposes, when the electrolytic bath is not separated in a catholyte and an anolyte, the concentration of the suspension of iron ore particles preferably remains inferior to 20% in weight, for example around 10% in weight, in order to maintain the viscosity of the electrolytic bath compatible with the required gas evacuation. For example, the viscosity of the catholyte is inferior to 30 mPa.s. Consequently, the invention enables increasing the quantity of iron ore particles in the electrolytic bath thereby increasing the quantity of metallic iron that can be deposited on the collecting surface(s) 8.

[0046] According to an embodiment, the or each anolyte 16 comprises a NaOH solution without any iron ore particles. The concentration of the NaOH solution in the anolyte 16 is preferably inferior to the concentration of the NaOH solution in the catholyte 18 to further reduce the viscosity of the anolyte. For example, the concentration of the NaOH solution in the anolyte 16 is substantially comprised from 30% to 50% in weight, for example less than 50% in weight when the concentration of the NaOH solution in the catholyte is substantially equal to 50% in weight.

[0047] The catholyte 18 is for example injected in the enclosure 2 around the cathode(s) 4 via a catholyte injection device 26. The catholyte injection device 26 is in fluidic communication with a catholyte source on the one hand and opens in the enclosure 2 on the other hand. The catholyte injection device 26 is for example arranged to inject the catholyte 18 such that it flows along the collecting surface(s) 8 of the cathode(s) 4. To this end, the catholyte injection device 26 for example comprises at least one outlet opening in the bottom of the enclosure 2 according to the elevation direction Z in the vicinity of at least one of the collecting surface 8 of one of the cathode 4, the outlet being arranged such that the catholyte 18 flows along the collecting surface 8 in the elevation direction Z as shown by arrows Fc in Fig. 1. According to an embodiment, the catholyte injection device 26 comprises several outlets opening opposite each cathode 4 of the electrolysis device 1 .

[0048] The anolyte 16 is for example injected in the housing(s) 14 around the anode(s) 6 via an anolyte injection device 28. The anolyte injection device 28 is in fluidic communication with an anolyte source on the one hand and opens in the inner volume 22 of the housing(s) 14 on the other hand. The anolyte injection device 28 is for example arranged to inject the anolyte 16 such that it flows along the anode(s) 6 in each housing 14. To this end, the anolyte injection device 28 for example comprises at least one outlet opening in the bottom of the housing 14 according to the elevation direction Z, the outlet being arranged such that the anolyte 16 flows along the anode(s) 6 in the elevation direction Z as shown by arrows Fa in Fig. 1 . According to an embodiment, the anolyte injection device 28 comprises several outlets, each one opening in one of the housings 14 of the electrolysis device 1. According to the embodiment shown in Fig. 2, one electrolysis device 1 , or cell, comprises several housings containing the anodes, each connected in series by a set of tubes, the electrolysis device 1 further comprising one anolyte injection device 28 which injects the anolyte in a first housing 14, the anolyte being then circulated from one housing to the next one by a pump. The anolyte may then be recovered from the last housing 14, which is the opposite one of the first housing in the electrolysis device in the longitudinal direction, and optionally recycling back to the first housing 14 or as part of the catholyte. A treatment step, including a degassing step, in an intermediary tank, may be performed before the recycling.

[0049] When the electrolysis reaction between an anode 6 and a corresponding cathode 4 is powered by the power source, this reaction causes the iron oxides to reduce into metallic iron which is deposited on the collecting surface 8 of the cathode 4. The main reaction occurring at the cathode 4 is:

[0050] Fe2O3+ 3 H2O + 6e~ 2Fe + 6 OH~

[0051] While the main reaction occurring at the anode 6 is:

[0052] 4 OH“ O2+ 2 H2O + 4e~

[0053] A side reaction also occurs at the cathode, which is electrolysis of water, according to the following formula:

[0054] 2 H2O + 2 e~ H2+ 2 OH~

[0055] As shown by these formulas, the electrolysis reaction further generates gases around the anode 6 and around the cathode 4. More particularly, dioxygen O2 is generated around the anode 6 and dihydrogen H2 is generated around the cathode 4. Thanks to the invention, which allows only OH- ions to circulate through the membrane 20, O2 is generated in the inner volume 22 of the housing(s) 14 as shown by bubbles O2 in Fig. 1 , while H2 is generated in the enclosure 2, as shown by bubbles H2 in Fig. 1 . In other words, O2 is isolated from H2 and do not mix with each other, thereby preventing any formation of an explosive mixture.

[0056] Furthermore, since 02 is generated inside the housing 14, this gas does not flow along the collecting surface 8 of the cathode 4 and therefore does not impair the deposition of metallic iron on the collecting surface 8. This is particularly advantageous since, O2 is generated in greater quantities than H2and that O2 bubbles have generally a larger volume than H2 bubbles. In other words, H2 is less detrimental to metallic iron deposition on the collecting surface 8 than O2 such that the invention enables larger quantities of metallic iron to be collected on the collecting surface(s).

[0057] Another advantage of this gas separation is that the gas generated in the anolyte 16 and the gas generated in the catholyte can be recovered independently. To this end, the electrolysis device 1 for example comprises a dioxygen extraction device 30 in fluidic communication with the inner volume 22 of the housing(s) 14 and a dihydrogen extraction device 32 in fluidic communication with the enclosure 2. More particularly, the dioxygen extraction device 30 for example comprises inlet(s) opening into an upper end of the inner volume of the housing(s) 14 according to the elevation direction Z to extract O2 flowing in the inner volume in the elevation direction from the bottom to the upper end of the inner volume 22. Likewise, the dihydrogen extraction device 32 for example comprises one or more inlets opening into an end of the enclosure 2 in the vicinity of the cathode(s) 4 to extract H2 flowing in the catholyte 18 in the elevation direction Z from the bottom to the upper end of the enclosure 2. The dioxygen extraction device 30 and the dihydrogen extraction device 32 are for example arranged to feed the extracted gases to other installations of a plant in which the electrolysis device 1 is installed to use the extracted gases to be used in the plant. Extracted H2 can in particular be used for heating purposes. It may be sold externally or used within the steelmaking plant, for example as a reducing gas in a blast furnace or in a direct reduction process. According to a particular embodiment, extracted H2 can be used to heat the anolyte and / or the catholyte to a temperature suitable for the electrolysis reactions, for example around 110°C. This further reduce the operational costs of the process.

[0058] It should be noted that, since the viscosity of the anolyte 16 can be reduced thanks to its isolation from the catholyte, the evacuation of O2 can be improved thanks to the increased velocity of the flow of 02 in the elevation direction Z.

[0059] This evacuation can be further increased by arranging the anode(s) 6 such that the gas generated on the inner surface side of the anode(s) 6 is transferred to the outer surface side of the anode(s) 6 such that this gas flows in the central portion of the inner volume 22 of the housing(s) 14. To this end, the or each anode 6 for example comprises openings 34 extending through the anode 6 from the inner surface 10 to the outer surface 12 such that the gas generated on the inner surface side flows to the outer surface side as shown by arrows F02 in Fig. 1. The openings 34 are for example distributed in the anode 6 according to the elevation direction Z such that the gas generated at any height of the anode 6 is transferred from the inner surface 10 to the outer surface 12. The openings 34 can further be distributed in the anode in the transversal direction such that the whole inner surface 10 of the anode 6 is provided with openings towards the outer surface 12. In other words, the anode 6 for example has the shape of a grill or of a meshed sheet with openings 34 distributed in the elevation and in the transversal directions regularly extending through the anode in the longitudinal direction L. The openings 34 can have any appropriate shape allowing O2 bubbles to transfer from the inner surface 10 to the outer surface 12. The openings 34 for example have a circular, rectangular or any other polygonal shaped crosssection in a plane according to the transversal and elevation directions. The pattern of openings can be regular or irregular and the openings do not necessarily all have the same shape, in particular depending on their position according to the elevation direction Z. According to the embodiment shown in Fig. 1 , the openings 34 are tilted relative to the elevation direction Z to present a slope oriented upwards from the inner surface 10 to the outer surface 12 of the anode 6. Such a slope facilitates the circulation of 02 generated on the inner surface side to the outer surface side, in particular thanks to the flow of anolyte 16 oriented upwards.

[0060] The rapid evacuation of O2 increases the quantity of metallic iron deposited in the collecting surface 8 of the cathode(s) 4 since the effect of O2 on the electric field in the interelectrode gap is reduced.

[0061] When the fluid-tight membrane 20 is applied against the inner surface 10 of one or more anodes, the effect of gas and liquid leaks between the catholyte 18 and the anolyte 16, for example in case of damage to the membrane 20 or of a default in the attachment between the membrane 20 and the frame 24, can be reduced. Indeed, as indicated previously, during the electrolysis reaction(s), the pressure in the catholyte 18 is superior to the pressure of the anolyte 16, thereby pressing the fluid-tight membrane 20 against the inner surface 10 of the anode 6, which limits the penetration of H2 and of catholyte 18 into the inner volume 22 of the housing 14.

[0062] As disclosed previously, the electrolysis device 1 according to the invention allows increasing the quantity of metallic iron collected on the collecting surface 8 of the cathode(s) 4, in particular thanks to the fast evacuation of the gases generated by the electrolysis reaction(s). This gas separation also allows increasing the height of the cathode(s) 4 and of the anode(s) measured in the elevation direction Z. Indeed, this separation and rapid evacuation of the gases significantly reduces the gas volume fraction in the electrolytic bath, in particular in the upper end of the enclosure 2. The dimensions of the collecting surface(s) 8 can therefore be increased, thereby further improving the quantity of metallic iron that can be collected.

[0063] Furthermore, thanks to the gas evacuation and low viscosity in anolyte which can be achieved with the electrolysis device 1 according to the invention, the need to add a pumping device for promoting the circulation of the electrolytic bath is reduced, even suppressed. The energy consumption of the electrolytic device can therefore be reduced and the structure of the electrolytic device can be simplified.

[0064] All the above advantages make the electrolytic device suitable to produce metallic iron for producing a steel material from iron oxides. The metallic iron can be melted with other materials to produce a steel once it has been collected from the collecting surface 8 of the cathode(s).

Claims

CLAIMS1.- Electrolysis device (1) for reducing iron oxides into metallic iron, the electrolysis device comprising :- at least one anode (6), extending between an inner surface (10) and an outer surface (12), opposite the inner surface (10),- at least one cathode (4) comprising a collecting surface (8) on which metallic iron is deposited after reduction of iron oxides, the collecting surface (8) facing the inner surface (10) of the anode (6),- an electrolytic bath comprising an anolyte (16), in which the anode (6) is immersed, and a catholyte (18), in which the cathode (4) is immersed, wherein the anode (6) extends in a housing (14) separating in a fluid tight manner the anolyte (16) from the catholyte (18), the chemical composition of the anolyte (16) being different from the chemical composition of the catholyte (18).2.- Electrolysis device according to claim 1 , wherein the housing (14) is delimited at least in part by at least one fluid tight membrane (20) delimiting at least a part of an inner volume (22) receiving the anode (6) and the anolyte (16), said inner volume (22) being isolated from the catholyte (18) in a fluid tight manner.3.- Electrolysis device according to claim 2, wherein the membrane (20) is applied against the inner surface (10) of the anode (6), the outer surface (12) of the anode (6) being turned towards a central portion of the inner volume (22) of the housing (14).4.- Electrolysis device according to claim 2 or 3, wherein the membrane (20) is an ion exchange membrane having a gas permeability inferior to inferior to 20L / min / cm2 H2 at 5 Bar.5.- Electrolysis device according to any one of claims 1 to 4, wherein the anode (6) comprises openings (34) extending through the anode (6) from the inner surface (10) to the outer surface (12), the openings (34) being arranged such that gas generated by the electrolysis reaction on the inner surface side of the anode (6) is transferred to the outer surface side of the anode (6) inside the housing (14).6.- Electrolysis device according to any one of claims 1 to 5, comprising a catholyte injection device (26) arranged to inject the catholyte (16) in an enclosure (2) receivingthe cathode (4) and the housing (14), the catholyte (16) being injected around the cathode (4) and around the housing (14).7.- Electrolysis device according to any one of claims 1 to 6, comprising a anolyte injection device (28) arranged to inject the anolyte (16) in the housing (14), the anolyte (16) being injected around the anode (6).8.- Electrolysis device according to any one of claims 1 to 7, comprising a dihydrogen extraction device (30) arranged to extract dihydrogen from an enclosure (2) receiving the cathode (4) and the housing (14), said dihydrogen being generated around the collecting surface (8) of the cathode (4) by the electrolysis reaction.9.- Electrolysis device according device according to any one of claims 1 to 8, comprising a dioxygen extraction device (32) arranged to extract dioxygen from the housing (14) receiving the anode (6), said dioxygen being generated around the anode (6) by the electrolysis reaction.10.- Electrolysis device according to any one of claims 1 to 9, wherein the catholyte (18) comprises a sodium hydroxide solution with a suspension of iron ore particles.11.- Electrolysis device according to any one of claims 1 to 10, wherein the anolyte (16) comprises a sodium hydroxide solution without iron ore particles12. Electrolysis device according to claims 10 and 11 , wherein the concentration of sodium hydroxide in the anolyte (16) is inferior to said concentration in the catholyte (18).13.- Electrolysis device according to any one of claims 1 to 12, wherein the pressure in the catholyte (18) is superior to the pressure of the anolyte (16).14.- Method for producing a steel material from iron oxides, comprising the following steps:- reducing iron oxides using a electrolysis device (1) according to any one of claims 1 to 13,- collecting metallic iron from the collecting surface (8) of the cathode (4),- producing a steel from the collected metallic iron.15.- Method according to claim 14, comprising a step of extracting the gas generated by the electrolysis reaction in the catholyte (18) independently from the gas generated in the anolyte (16) by the electrolysis reaction.

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