[001] The invention is related to an apparatus to produce iron metal from iron oxides by an electrolysis process.

[002] Steel can be currently produced at an industrial scale through two main manufacturing routes. Nowadays, most commonly used production route consists in producing pig iron in a blast furnace, by use of a reducing agent, mainly coke, to reduce iron oxides. In this method, approx. 450 to 600 kg of coke, is consumed per metric ton of pig iron; this method, both in the production of coke from coal in a coking plant and in the production of the pig iron, releases significant quantities of CO2.

[003] The second main route involves so-called “direct reduction methods”. Among them are methods according to the brands MIDREX, FINMET, ENERGIRON/HYL, COREX, FINEX etc., in which sponge iron is produced in the form of HDRI (Hot Direct Reduced Iron), CDRI (cold direct reduced iron), or HBI (hot briquetted iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, and HBI usually undergo further processing in electric arc furnaces. Even if this second route emits less CO2 than the previous one it still releases some and rely moreover on carbon fossil fuels.

[004] Current developments thus focus on methods allowing to produce iron which release less or even no CO2 and which is carbon-neutral.

[005] A known alternative method to produce steel from iron ores made of iron oxides is based on electrochemical techniques. In such techniques, iron is produced from iron oxide using an electrolyser unit comprising two electrodes - an anode and a cathode - connected to a source of electric current, an electrolyte circuit and an iron oxide entry into the electrolyser unit. The anode and cathode are constantly immersed in the circulating electrolyte in order to ensure good electrical conduction between said electrodes. The electrolytic reaction produces pure iron plates, gaseous dioxygen at the anode and some hydrogen at the cathode. Iron plates thus obtained may then be melted with other elements such as a carbon source and scrap in electric furnaces to produce steel.

[006] One of the problems of existing electrolysis cells is the gas accumulation. Indeed, gaseous dioxygen and hydrogen formed by the electrolysis reactions tend to remain trapped between the anode and the cathode where they accumulate. Gaseous dioxygen being an electrical insulator, it has a detrimental effect on the electrical conduction between the electrodes and thus on the productivity of the cell. One solution would be to have a continuous extraction of the electrolyte containing said gases, but this would mean a constant supply at high rate of fresh electrolyte which would also be detrimental to the productivity and to the environmental footprint of the process.

[007] An aim of the present invention is therefore to remedy the drawbacks of the prior art by providing a system for electrochemical iron production with an improved productivity. The apparatus according to the invention allows notably to provide an enhanced gas discharge while reducing electrolyte losses and associated energy needs.

[008] Another aim of the present invention is to provide a method for recirculating the electrolyte inside the apparatus enhancing gas discharge while reducing electrolyte losses.

[009] For this purpose, the invention is related to an apparatus for the production of iron metal through reduction of iron ore by an electrolysis reaction, said electrolysis reaction generating a gas, the apparatus comprising a casing including a gas permeable anode plate, a cathode plate, both facing each other and being separated by an electrolyte chamber, said casing being provided with means for circulating an electrolyte within the chamber and with means to supply iron ore to said chamber, the casing further including a degassing unit comprising:

• a gas recovery part extending along the opposite side of the anode plate to the chamber and being able to recover gas from the electrolysis reaction escaping through the anode plate, an electrolyte recirculation part extending in continuity with the gas recovery part up to a gas outlet and being in fluidic connection with the chamber, said recirculation part comprising a gas-liquid partition means in contact with the anode plate and extending along the recirculation part and comprising a perforated portion which is at least partially immersed in the electrolyte when the apparatus is operating.

[0010] The apparatus may also include the following optional characteristics considered individually or according to all possible combination of techniques:

- The gas-liquid partition means comprises a solid portion located between the anode plate and the perforated portion.

- The casing extends along a longitudinal axis, wherein the perforations of the perforated portion have an oblong shape and are transversely disposed following a plurality of parallel lines extending along a transverse axis.

- All the perforations of the perforated portion are in a staggered configuration.

- All the perforations of the perforated portion have the same size and are regularly spaced.

- The void fraction of the perforated portion is defined following the formula 2 L R

— , L and R being respectively the length and the width of each oblong perforation, Zi.Z ₂

Zi being the double of the distance between two parallel lines and Z2 being the periodical distance between two successive perforations located in the same line, and wherein the void fraction of the perforated portion is comprised between 0,12 % and 50%.

- The width of each perforation of the perforated portion is at least 1 mm.

[0011] Another subject of the invention is a method for recirculating an electrolyte inside an apparatus producing iron through reduction of iron ore by an electrolysis reaction, said electrolysis reaction generating a gas, the apparatus comprising a casing including a gas permeable anode plate, a cathode plate, both facing each other and being separated by an electrolyte chamber, said casing being provided with means for circulating an electrolyte within the chamber, with means to supply iron ore to said chamber and with a gas outlet, the method comprising the following steps:

• Recovering the electrolyte flowing through the anode plate and gases generated during the electrolysis reaction and escaping through the anode plate;

• Recirculating the electrolyte emerging from the anode plate to the electrolyte chamber;

• Continuously degassing the recirculating electrolyte before entering inside the electrolyte chamber, and

• Evacuating gases resulting from the step of continuous degassing through the gas outlet.

[0012] Other characteristics and advantages of the invention will be apparent in the below description, by way of indication and in no way limiting, and referring to the appended figures among which:

- Figure 1 , which represents a longitudinal section view of an apparatus according to the invention,

- Figure 2, which represents a three-dimensional view of a part of the casing of the invention,

- Figure 3, which represents a front view of the perforated portion of the gas-liquid partition means of the invention.

[0013] First, it is noted that on the figures, the same references designate the same elements regardless of the figure on which they feature and regardless of the shape of these elements. Similarly, should elements not be specifically referenced in one of the figures, their references may be easily found by referring to another figure.

[0014] It is also noted that the figures represent mainly one embodiment of the object of the invention but other embodiments which correspond to the definition of the invention may exist. Elements in the figures are illustration and may not have been drawn to scale. [0015] The invention refers to an apparatus 1 provided for the production of iron metal (Fe) through the reduction of iron ore, containing notably hematite (Fe2Os) and other iron oxides or hydroxides, by an electrolysis reaction. Said chemical reaction is well known and described in the case of hematite at 110°C and 1 atmosphere by the following equation (1 ):

(1 ) Fe ₂ O ₃ 2Fe + -O ₂

[0016] It thus appears that the electrolysis reaction generates gases - mainly dioxygen - that has to be extracted from the apparatus 1 .

[0017] With reference to figures 1 and 2, the apparatus 1 comprises a casing 4 extending along a longitudinal axis X in which the electrolysis reaction occurs. Said casing 4 is delimited by a base plate 16, a cover plate 17 and two lateral plates 24. In addition, the casing includes a gas permeable anode plate 2 intended to be totally immersed in an electrolyte 5 and a cathode plate 3, both plates facing each other, and being kept at the required distance with fastening means (not depicted). The casing 4 also includes an electrolyte chambers extending longitudinally between the anode plate 2 and the cathode plate 3 up to an evacuation chamber 27. The apparatus 1 finally comprises an electrical power source (not depicted) connected to the anode plate 2 and the cathode plate 3.

[0018] In order to produce iron metal through the electrolysis reaction, the electrolyte 5 - preferably a sodium hydroxide solution - flows through the casing 4 inside the electrolyte chamber 6 while the apparatus 1 is operating. The apparatus 1 thus comprises means for circulating the electrolyte which comprises an electrolyte circuit (not depicted) connected to an inlet 18 and an outlet 22 managed in the casing 4 and both flu idical ly connected to the electrolyte chamber 6. Iron ore is preferentially supplied into the apparatus 1 as a powder suspension within the electrolyte 5 through the inlet 18.

[0019] During the electrolysis reaction, oxidised iron is reduced to iron metal according to reaction (1 ) and reduced iron is deposited on the cathode plate 3 while gaseous oxygen is generated. The electrolysis reaction further generates dihydrogen at the cathode plate 3. As depicted above, gases are generated inside the casing 4. Since these gases are electrical insulator, they prevent the good working of the electrolysis reaction and must be continuously evacuated outside of the casing 4.

[0020] For this purpose, the casing 4 includes a degassing unit 7 comprising a gas recovery part 8 extending longitudinally along the opposite side 23 of the anode plate 2 to the electrolyte chamber 6. This gas recovery part 8 is a compartment provided to be filled with the electrolyte 5 and disposed between the anode plate 2 and the cover plate 17. Said gas recovery part 8 is thus provided to recover gases (dioxygen and dihydrogen) escaping through the anode plate 2.

[0021] As depicted in figures 1 and 3, the degassing unit 7 also comprises an electrolyte recirculation part 9 extending in continuity with the gas recovery part 8 up to a gas outlet 10 managed in the casing 4. The electrolyte recirculation part 9 is provided to be at least partly filled with the electrolyte 5. In addition, said recirculation part 9 is in fluidic connection with the electrolyte chamber 6. When the apparatus 1 is operating, the recirculation part 9 allows the electrolyte 5 flowing from the gas recovery part 8 to be redirected towards the electrolyte chamber 6 via an elbow duct 25 of the electrolyte recirculation part 9 which is adjacent to the anode plate 2 and fluidically connected to the electrolyte chamber 6. This will be explained in more details when describing the apparatus 1 in operation.

[0022] According to the invention, the recirculation part 9 comprises a gas-liquid partition means 11 in contact with the anode plate 2 and extending longitudinally from the opposite side 23 of the anode plate 2 along the recirculation part 9. This gas-liquid partition means 11 extends in a plane parallel to the longitudinal axis X and comprises a perforated portion 12 provided to be at least partially immersed in the electrolyte 5 when the apparatus 1 is operating, and a solid portion 13 located between the anode plate 2 and the perforated portion 12 and totally immersed in the electrolyte 5. When the apparatus 1 is operating, the recirculated electrolyte 5 flows through the perforated portion 12 before being redirected towards the electrolyte chamber 6 via the elbow duct 25. The perforated portion 12 prevents the passage of gases and thus allows degassing of the electrolyte 5 before its entry into the elbow duct 25. [0023] The solid portion 13 is disposed between the anode plate 2 and the perforated portion 12 to keep said perforated portion 12 away from the anode plate 2 where the electrolysis reaction occurs and thus avoid any gas bubble formation due to the electrolysis reaction at the level of said perforated portion 12.

[0024] With reference to figure 3, the perforated portion 12 preferentially comprises several oblong perforations 14 which are transversely disposed following a plurality of parallel lines 15 extending along a transverse axis Y. This specific disposition of the perforations 14 enhances degassing of the electrolyte 5. The specific orientation of the perforations 14 following the transverse axis Y, which is thus perpendicular to the electrolyte flow, enhances gas-liquid separation.

[0025] The void fraction is the sum of the surfaces of each perforation 14 versus the total area of the perforated portion 12. The bigger the void fraction is, the bigger the flow of electrolyte 5 through the perforated portion 12 is, and the smaller the void fraction is, the better the degassing of the recirculating electrolyte 5 is. The value of the void fraction is thus a compromise between degasification and electrolyte 5 flow. Typically, the void fraction is comprised between 0,12 % and 50 %, and preferentially between 0,12 % and 5,6 %.

[0026] In a preferred embodiment, all the perforations 14 have the same size and are regularly spaced, the void fraction can then be determined following the equation 2 L R

- , where L and R are respectively the length and width of each perforation 14, Zi Z1.Z ₂ is the double of the distance between two parallel lines 15 and Z2 is the periodical distance between two successive perforations 14 located in the same line. This allows to have a better control of the void fraction so as to get an optimum between the degassing and the flow of electrolyte.

[0027] Advantageously, the width of each perforation 14 is at least 1 mm, in order to avoid occlusion of said perforations 14. More advantageously, the perforations 14 are in a staggered configuration in order to keep enough stiffness to the perforated portion 12.

[0028] The working of the apparatus 1 during the electrolysis reaction will now be described. [0029] The electrolyte 5 is continuously circulating inside a circuit, through the electrolyte chamber 6 from the inlet 18 to the outlet 22, thanks to an operating pump (not represented). The electrical power source connected both to the anode plate 2 and to the cathode plate 3 is turned on and the electrolyte chamber 6 is regularly fed with iron ore coming from the means 21 to supply iron ore to the apparatus 1. The casing 4 is almost filled with electrolyte 5, as depicted in figure 1 , and only the gas outlet 10 and a part of the perforated portion 12 are free of electrolyte. In these conditions the electrolysis reaction may occur.

[0030] Iron ore is reduced, and pure iron is deposited on the cathode surface 3, while generated oxygen and hydrogen flow, together with the electrolyte, through the anode plate 2 towards the gas recovery part 8 of the degassing unit 7.

[0031] To allow gases circulation from the gas recovery part 8 towards the electrolyte recirculation part 9 and finally to the gas outlet 10, the longitudinal axis X is preferentially inclined relative to a horizontal direction following an angle comprised between 40° and 60°, preferentially 50°. The gas outlet 10 is thus in the highest position of the casing 4 to allow gases evacuation.

[0032] While circulating through the gas recovery part 8, the moving gases drive electrolyte 5 from said recovery part 8 to the recirculation part 9. The electrolyte 5 is then driven in the recirculation part 9 by the gases along the solid portion 13 of the gas-liquid partition means 11 in direction of the perforated portion 12. Once the electrolyte 5 has flown beyond the solid portion 13, said electrolyte 5 flows thanks to gravity through the perforations 14 of the perforated portion 12 while the gases are retained above the gas-liquid partition means 11 by said perforated portion 12.

[0033] The gases are continuously flowing along the gas-liquid partition means 11 toward the gas outlet 10, while the electrolyte 5 which has circulated through the perforated portion 12 is driven by gravity to the electrolyte chamber 6 and recirculates in the circuit 20. The electrolyte 5 is thus continuously degassed. It is then possible to recirculate the electrolyte 5 within the electrolyte chamber 6 without inducing gas accumulation at the cathode level. This prevents the need to regularly inject a fresh electrolyte flow within the apparatus 1 .