EP4321652A1 - Device for extracting a metal deposited electrolytically on a cathode - Google Patents

Abstract

The present invention relates to a device for the production of a pure metal or an alloy of this metal by electrolytic reduction of an ore of this metal or of a substance containing an oxidized form of this metal, said device comprising a cell (1) provided with an anode (2), a cathode (3), an electrolyte (8) and a removable system for closing the cell (6), characterized in that the cathode (3) is provided with a non-adherent coating for the electrolytically deposited metal and in that the device further comprises an electrically conductive consumable element (5) intended to facilitate the extraction of a plate of said electrolytically deposited metal (4). on the cathode (3), said consumable (5) being placed in the cell (1) in the extension of the cathode (1) or in partial overlap with it, with mechanical and therefore electrical contact at one end with the cathode (1) and protruding from the electrolytic zone of the cell (1), so as to allow, in operation, a simultaneous deposition of said metal on the cathode (3) and on part of the consumable (5') and to allow the subsequent extraction from the cell (1) of the assembly consisting of the consumable (5) and the deposited metal (4), by mechanical means (7).

Description

Object of the invention

The present invention relates to a device for producing iron or other pure metals or even alloys by electrolytic means, and in particular to the means used for the extraction of metal plates deposited at the cathode of an electrolytic cell. The invention also relates to specific uses of the device.

Technological background and state of the art

Traditionally, the manufacture of cast iron, which is an alloy of iron and carbon with a content greater than 2%, is obtained by smelting iron ore in a blast furnace, using a solid fuel rich in carbon, often the coke and coal, as a reducing agent. Another method is direct iron reduction (DRI) based on the use of natural gas (methane) as a replacement for coal. In a second stage, the steel is obtained by refining, that is to say by decarburizing the cast iron, in a converter.

These processes thus lead to the release of significant quantities of fossil carbon in the form of CO ₂ into the atmosphere.

The fight against greenhouse emissions currently requires considering processes involving a drastic reduction, or even elimination, of CO ₂ emissions.

Based on the observation at the beginning of the 2000s that the need for steel from the primary sector, namely ore, would increase, the main European steel groups joined forces to prepare a common R&D program, called ULCOS (for Ultra Low CO2). Steelmaking ), to improve the sustainability of steel production from ore by reducing CO ₂ emissions per tonne of steel produced by at least 50%.

One of the promising sectors implemented consists of replacing carbon monoxide with dihydrogen as a reducing gas for the ore. The gas composed mainly of H ₂ and CO currently used in direct reduction processes is replaced by pure dihydrogen during the manufacture of "pre-reduced" iron, which can then be charged into electric arc furnaces. The performance in terms of CO ₂ emissions is promising, namely less than 300kg CO ₂ per tonne of steel (instead of 1850kg with the traditional sector), in the case where hydrogen is produced by electrolysis of water with “green” electricity.

We also know electro-refining which consists of electrolytically dissolving an impure metal anode in an acid or alkaline bath, the pure metal ions then being deposited on the cathode in the metallic state under the action of an electric current. . This method can purify metals like copper, nickel, zinc, manganese, etc. but many purification steps are often necessary.

The electrodes are generally arranged vertically and the deposits are made at very low current density. The applied voltage can be high, which implies unfavorable efficiency, due to sensitivity to the anode/cathode distance. The cathodes are generally coated on both sides with an adherent deposit and are replaced when the quantity of metal produced is sufficient. According to a first technique, the cathodes, inert, are reusable and the extraction, most often in clusters, is carried out on an overhead crane or by means of robotic machines, the extraction being followed by stripping, which is the stage of separation of the deposited metal plate from the cathode support using mechanical means. According to one second technique, the cathode is sacrificial. A fine deposit of a given metal can be generated initially in a parallel die on an inert cathode and then detached to itself serve as a cathode in the production process. In this case, the cathode consists exclusively of the desired metal.

The electrolytic process is especially interesting for materials presenting only one valence state (e.g. Zn ²⁺ ), but this is not the case for iron (Fe ²⁺ and Iron ³⁺ ). To avoid losing a significant part of the yield by looping Fe ²⁺ → Fe ³⁺ then vice versa, we could use separator and ion exchange membranes.

The electrolytic reaction generates pure iron plates at the cathode and oxygen gas at the anode. These iron plates can then be melted with other elements or scrap metal in an electric furnace to produce steel.

Boston Metal US 8,764,962 B2 ) used this process by replacing a carbon anode which produces CO ₂ during the reaction with an inert chromium-based anode which does not corrode following the release of oxygen. This process of electrolysis of molten oxides (MOE, for molten oxide electrolysis ) essentially rejects oxygen, and possibly parasitic hydrogen in the event that the electrolytic yield is not 100%. If the electricity used comes from a renewable source, the process is carbon-free.

This technique therefore involves robust and simple processes. It is well known that electroplating of iron requires special conditions to be energetically effective. Among the constraints, a high concentration of soda and a relatively high temperature are used. Hence the imperative need to have a closed cell.

In addition, to have the lowest possible energy consumption, the cell must have a limited distance between the electrodes. The difficulty with closed cells is then the extraction of the metal deposited on the cathode, especially for large sizes (>1 m ² ), because the cathode must remain permanently in the cell. This in situ extraction also implies that the deposits are non-adherent or easily detachable from the cathodes to best facilitate mechanical extraction through a limited opening in the cell.

In conclusion, the need for reduced distance between electrodes in iron ore electrolysis will practically prevent mechanical cathode extraction and stripping outside the cell, as is the case in the state of the art. Added to this is the difficulty of working in a closed cell. You must first find an easy way to open the cell in order to extract the cathodic deposits.

Aims of the invention

The present invention aims to provide a solution making it possible to overcome the disadvantages of the state of the art.

In particular, the invention aims to provide a means for separating in a practical and easy manner the metal plates deposited on the cathodes in electrolytic production processes, this extraction necessarily being in situ because it must take into account the physical constraints imposed on the electrolytic cell, such as having a closed cell, without dismantling the cell, a short anode-cathode distance to maintain good energy efficiency, etc.

Main characteristic elements of the invention

A first aspect of the present invention relates to a device for the production of a pure metal or an alloy of this metal by electrolytic reduction of an ore of this metal or of a substance containing an oxidized form of this metal , said device comprising a cell provided with an anode, a cathode, an electrolyte and a removable system for closing the cell, characterized in that the cathode is provided with a non-adherent coating for the metal electrolytically deposited and in that the device further comprises an electrically conductive consumable element intended to facilitate the extraction of a plate of said metal electrolytically deposited on the cathode, said consumable being placed in the cell in the extension of the cathode or in partial overlap with it, with mechanical and therefore electrical contact at one end with the cathode and protruding from the electrolytic zone of the cell, so as to allow, in operation, a simultaneous deposition of said metal on the cathode and on part of the consumable and to allow the subsequent extraction from the cell of the assembly consisting of the consumable and the deposited metal, by mechanical means.

• le consommable a une longueur inférieure à 50%, préférentiellement inférieur à 10%, de la longueur de la cathode ;
• la cathode est à base de carbone, de graphite à faible rugosité, de graphite imprégné ou revêtu de bouche-pores ou de métaux purs et/ou certains de leurs alliages, éventuellement revêtus ;
• le consommable est une tôle métallique ;
• une partie du consommable en prolongement de la cathode et dépassant de la zone électrolytique est accueillie dans le système amovible de fermeture, qui est fermé en opération pour maintenir l'électrolyte dans la cellule ;
• le dispositif comporte des moyens de préhension collaborant avec le consommable ou des éléments de celui-ci pour permettre l'extraction de l'ensemble consommable/métal déposé ;
• les moyens de préhension sont des moyens de serrage tels que des pinces ou vérins, des goujons ou crochets de traction collaborant avec des trous pratiqués dans le consommable, ou encore des éléments géométriques rapportés collaborant entre eux pour assurer une traction ;
• le dispositif comprend des moyens de blocage pour maintenir le consommable et la plaque déposée en position le temps d'ouvrir la cellule et d'extraire ensuite l'ensemble plaque et consommable par les moyens de préhension, les moyens de blocage pouvant coïncider avec les moyens de préhension ;
• la cellule électrolytique est inclinée d'un angle de 20° à 60° par rapport à l'horizontale, les électrodes sont planes avec une distance inter-électrodes comprise entre 1 et 50 mm, et préférentiellement entre 6 et 20 mm, la cathode est maintenue à demeure dans le dispositif et le moyen mécanique d'extraction est configuré pour effectuer l'extraction de l'ensemble consommable/métal selon un mouvement de translation parallèle aux électrodes.

According to preferred embodiments, the arrangement is further limited by one of the following characteristics or by an appropriate combination of several of them:

• the consumable has a length of less than 50%, preferably less than 10%, of the length of the cathode;
• the cathode is based on carbon, graphite with low roughness, graphite impregnated or coated with filler or pure metals and/or certain of their alloys, optionally coated;
• the consumable is a metal sheet;
• a part of the consumable extending from the cathode and protruding from the electrolytic zone is accommodated in the removable closure system, which is closed in operation to maintain the electrolyte in the cell;
• the device comprises gripping means collaborating with the consumable or elements thereof to allow the extraction of the consumable/deposited metal assembly;
• the gripping means are clamping means such as clamps or jacks, traction studs or hooks working with holes made in the consumable, or even added geometric elements working together to ensure traction;
• the device comprises locking means for holding the consumable and the plate deposited in position while the cell is opened and the plate and consumable assembly is then extracted by the means gripping means, the blocking means being able to coincide with the gripping means;
• the electrolytic cell is inclined at an angle of 20° to 60° relative to the horizontal, the electrodes are flat with an inter-electrode distance of between 1 and 50 mm, and preferably between 6 and 20 mm, the cathode is maintained permanently in the device and the mechanical extraction means is configured to extract the consumable/metal assembly in a translational movement parallel to the electrodes.

Another aspect of the invention relates to a use of the device described above, in which, after extraction, the consumable is either separated from said pure metal or alloy of the deposited metal in order to avoid any pollution, or subsequently melted with the deposited metal.

Advantageously, the use concerns the electrolytic deposition of iron in a basic medium, where the consumable is a low-carbon steel sheet.

Still advantageously the use relates to the electrorefining of zinc, nickel or copper, in an acidic medium, the consumable being respectively a zinc, nickel or copper plate.

Brief description of the figures

There figure 1 schematically represents a closed iron electrowinning cell according to one embodiment of the present invention, during the production phase of the metal deposit.

There figure 2 schematically represents an open iron electroextraction cell according to one embodiment of the present invention, during the iron plate extraction phase.

There Figure 3 represents an example of a realistic mode of execution of the present invention comprising an electrolytic cell with a removable closure system and a system for recovering the iron plate deposited at the cathode.

There Figure 4 shows an example of moving the removable cell closing system.

There figure 5 shows a detailed view in an example of the system allowing the extraction of the iron plate.

Description of preferred embodiments of the invention

The present invention consists not only of carrying out an electrolytic metallic deposition on a cathode, but also of co-depositing the metal in an adherent manner on at least part of an electrically conductive consumable, produced for example in the form of a steel plate. which may be compatible for the subsequent stages of metal melting. The consumable element is introduced into the electrolytic cell before starting the deposition and is positioned such that electrical contact with the cathode is ensured. This allows extraction of the deposit, this being carried out simultaneously on the cathode and on the consumable, thanks to the use of a gripping system such as pliers or similar elements preferably positioned on a part of the consumable which will not have received no deposit or a very low deposit. The cell will preferably be positioned in an inclined manner so that the consumable will be located in a lower part and the cathode in a higher part of the cell, with at least one part of the consumable not covered by the deposit, which will allow seizure mechanics of the consumable, when opening the cell at the lower part, after emptying and rinsing the cell.

The extraction of the deposited metal is therefore carried out by removing the consumable part concomitantly with the complete deposit which does not adhere to the cathode, preferably thanks to a particular coating of the latter, such as a carbon or graphite base. low roughness. The extraction of the metal is then done by a guided translation movement.

The deposited metal/consumable plate is then transferred to a table which supports it in order to avoid material breakage during the extraction process.

According to the invention, the cell can be oriented at an angle going from horizontal to vertical, but preferably at an angle between 20° and 60° relative to the horizontal to take advantage of the effect of gravity and also in order to limit the bulk. The cell preferably has a height of between 50 mm and 700 mm, and more preferably between 100 mm and 300 mm. Its length will be 1 m to 4 m, and preferably between 1 m and 3.5 m. The width of the cell will be 1 m to 2 m, and preferably 1 m to 1.5 m.

According to the invention, the length of the consumable part is less than 50% of the length of the cathode, preferably less than 20% thereof and still preferably less than 10% thereof. The width of the consumable part must be at least approximately equal to that of the cathode with which it is in contact.

The expected thickness for the deposit will be between 2 mm and 50 mm, preferably between 3 mm and 5 mm, depending on the surface of the cathode in order to present a plate of sufficient resistance for extraction while maintaining a minimum anode-cathode distance during the entire deposition phase.

There figure 1 schematically represents a configuration of electrolytic cell 1, adapted for the electroextraction of iron, during the production phase using the device according to the invention.

In this cell 1, one end of the anode 2 is positioned on the one hand opposite a part of the cathode 3 and on the other hand opposite a part of the consumable 5 which adjoins or covers the lower edge of the cathode 3, with which it is physically in contact, which ensures perfect electrical continuity between the cathode 3 and the consumable 5. These two factors make it possible to obtain a metallic deposit 4 covering not only the cathode 3 but also a section 5 ' of the consumable 5. The consumable 5 is therefore dimensioned to protrude downwards from the area of the cell which contains the electrolyte 8. A part of the consumable 5 will therefore not be covered by the electrolytically deposited metal and the protruding part 5 " consumable 5 will make it easier to grip.

According to the invention, the electrolytic cell 1 is constantly closed during its operation and a removable closing system 6 serves to close the cell 1. The connection between the cell 1 and the closing system 6 is waterproof to prevent any escape of electrolyte 8.

The system according to the invention will be advantageously designed to automate the extraction of the iron plate. According to one embodiment, a table on slides 7 is able to approach the cell 1 and to tilt rotatably at an angle making it parallel to the cell ( figure 2 ). For example three pneumatic grippers 10 equipping the table 7 ( figure 5 ) grab the consumable 5 and pull it out of the cell. Once the iron/consumable plate has been recovered, the table 7 can rotate back to a horizontal position and the plate can then be transferred to a cart to be used in the next step of the treatment process. According to another form of execution, the table could already be inclined and position itself in this way before leaving again. The deposit plate would then remain tilted until removed.

There figure 2 schematically shows an embodiment for extracting the iron plate 4 at the end of the production process. Cell 1 was previously emptied of its electrolyte 8 to prevent it from flowing out when the plate was extracted. The removable closure and collection system 6 is for example moved in a horizontal translation, to allow access to the consumable 5 and its recovery (see figure 4 ).

According to the invention, there must be a significant differential adhesion between the cathode and the iron deposit on the one hand, and between the consumable and the iron deposit on the other hand, the first being less than the second. Also, the cathode will be made of a material with poor adhesion to iron, such as a material based on carbon, graphite with low roughness, graphite impregnated or coated with filler or pure metals such as silver or copper and some of their alloys, possibly coated.

Given the small intra-electrode distance required, during extraction, plate 4 cannot be lifted to be detached directly from cathode 3 as in state stripping methods. art. When cell 1 is open, part of the consumable 5 must be able to exit by overflowing, as indicated above, in order to allow its recovery by a mobile system 7 for gripping and recovering the plate, such as a table. The removable system 6 will then be used to bring a new consumable 5 into contact with the cathode 3. The plate 4 with the consumable 5 is grasped by pliers, clamps or similar elements 10 and is then pulled by a guided translation movement, parallel to the cell. The metallic deposit, “glued” to the consumable 5 but not to the cathode 3, which is non-adherent, detaches from the cathode 3 and is driven by the consumable 5 out of the cell in its translation movement (see figure 5 ). The iron plate 4 is then transferred to a table during its extraction, as described above.

List of reference symbols

• 1: electroextraction cell
• 2: anode
• 3: cathode based on carbon or graphite with low roughness
• 4: iron deposit / plate
• 5: consumable
• 5': iron deposit zone on the consumable
• 5": protruding part of the consumable not covered with metallic deposit
• 6: removable cell closing system
• 7: iron plate extraction system
• 8: electrolyte
• 9: extraction movement
• 10: gripping means

Claims (12)

A device for the production of a pure metal or an alloy of this metal by electrolytic reduction of an ore of this metal or of a substance containing an oxidized form of this metal, said device comprising a cell (1) provided an anode (2), a cathode (3), an electrolyte (8) and a removable system for closing the cell (6), characterized in that the cathode (3) is provided with 'a non-adherent coating for the electrolytically deposited metal and in that the device further comprises an electrically conductive consumable element (5) intended to facilitate the extraction of a plate of said metal (4) electrolytically deposited on the cathode (3) , said consumable (5) being arranged in the cell (1) in the extension of the cathode (1) or in partial overlap with it, with mechanical and therefore electrical contact at one end with the cathode (1) and protruding from the electrolytic zone of the cell (1), so as to allow, in operation, a simultaneous deposition of said metal on the cathode (3) and on part of the consumable (5') and to allow subsequent extraction from the cell (1) of the assembly consisting of the consumable (5) and the deposited metal (4), by mechanical means (7). The device according to claim 1, characterized in that the consumable (5) has a length less than 50%, preferably less than 10%, of the length of the cathode (3). The device according to claim 1, characterized in that the cathode (3) is based on carbon, graphite with low roughness, graphite impregnated or coated with filler or pure metals and/or certain of their alloys, optionally coated. The device according to claim 1, characterized in that the consumable (5) is a metal sheet. The device according to claim 1, characterized in that a part of the consumable (5") in extension of the cathode and protruding from the electrolytic zone is received in the removable closure system (6), which is closed in operation to maintain the electrolyte (8) in the cell. The device according to claim 1, characterized in that it comprises gripping means (10) collaborating with the consumable (5) or elements thereof to allow the extraction of the consumable/deposited metal assembly. The device according to claim 6, characterized in that the gripping means (10) are clamping means such as clamps or jacks, traction studs or hooks collaborating with holes made in the consumable (5), or even added geometric elements working together to ensure traction. The device according to claim 1, characterized in that it comprises locking means to hold the consumable (5) and the deposited plate (4) in position while the cell is opened and then the plate assembly is extracted. (4) and consumable (5) by the gripping means (10), the blocking means being able to coincide with the gripping means (10). The device according to claim 1, characterized in that the electrolytic cell (1) is inclined at an angle of 20° to 60° relative to the horizontal, in that the electrodes are flat with an inter-electrode distance included between 1 mm and 50 mm, and preferably between 6 and 20 mm, in that the cathode (3) is held permanently in the device and in that the mechanical extraction means (7) is configured to carry out the extraction of the consumable/metal assembly in a translational movement parallel to the electrodes. Use of the device according to any one of the preceding claims, in which, after extraction, the consumable (5) is either separated from said pure metal or alloy of the deposited metal (4) in order to avoid any pollution, or subsequently melted with the metal deposit. Use of the device according to any one of claims 1 to 9, for the electrolytic deposition of iron in a basic medium, where the consumable (5) is a low carbon steel sheet. Use of the device according to any one of claims 1 to 9 for the electrorefining of zinc, nickel or copper, in an acidic medium, the consumable (5) being respectively a zinc, nickel or copper plate.

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