Patent Application
20240052511
Priority is claimed to European Patent Application No. EP 22190058.2, filed on Aug. 11, 2022, the entire disclosure of which is hereby incorporated by reference herein.
The present invention relates to a device for producing iron or other pure metals or alloys via electrolytic route, and in particular to the means used for extracting plates of metal deposited at the cathode of an electrolytic cell. The invention also relates to specific uses of the device.
Traditionally, the production of cast iron, which is an alloy of iron and carbon in a content higher than 2%, is obtained by smelting iron ore in a blast furnace using a solid fuel with high carbon content, often coke or coal, as reducing agent. Another method is Direct Reduction of Iron (DRI) based on the use of natural gas (methane) as replacement of coal. As a second step, steel is obtained by refining, i.e. by decarbonizing cast iron in a converter.
These processes therefore lead to the release into the atmosphere of major amounts of fossil carbon in CO2 form.
Currently, tackling greenhouse gas emissions requires methods which involve a drastic reduction and even the elimination of CO2 release.
Further to the realization in the early 2000s of the growing needs for steel derived from primary materials, namely ore, a partnership was formed between the major European steelmaking groups to prepare a common R&D programme named ULCOS (for Ultra Low CO2 Steelmaking), to improve the sustainable production of steel from ore, targeting the reduction of CO2 emissions per tonne of produced steel by at least 50%.
One of the promising channels set up is the replacement of carbon monoxide by dihydrogen as ore-reducing gas. The gas currently used in direct reduction methods and chiefly composed of H2 and CO is replaced by pure dihydrogen when producing «pre-reduced» iron, which can then be charged into electric arc furnaces. Performance levels in terms of CO2 emissions are promising, namely less than 300 kg CO2 per tonne of steel (instead of 1850 kg via the conventional route), if the hydrogen is produced by water electrolysis using «green» electricity.
Electro-refining is also known, whereby an anode in impure metal is electrolytically dissolved in an acid or alkaline bath, the ions of pure metal then being deposited on the cathode in the metal state under the action of an electrical current. With this method, it is possible to purify metals such as copper, nickel, zinc, manganese, etc. but numerous purification steps are often required.
The electrodes are generally arranged vertically and the deposits are produced at very low current density. The voltage applied can be high, which means yield is unfavourable due to sensitivity to the anode/cathode distance. The cathodes are generally coated on both sides with an adhering deposit and are replaced when the amount of metal produced is sufficient. According to a first technique, the inert cathodes can be re-used and extraction, most often in clusters, is carried out by an overhead crane or robotized machines, extraction being followed by stripping whereby the plated metal deposit is detached from the cathode support via mechanical means. According to a second technique, the cathode is sacrificial. A thin deposit of a given metal can be generated at a first stage on a parallel line on an inert cathode, and then detached to be used as cathode in the production process. In this case, the cathode is solely composed of the desired metal.
The electrolytic process is especially advantageous for materials having only one oxidation state (e.g. Zn2+), but this is not the case with iron (Fe2+ and Fer3+). To avoid losing a high share of yield through Fe2+→Fe3+ changes and conversely, separating and ion-exchanging membranes could be used.
The electrolytic reaction generates plates of pure iron at the cathode and gaseous oxygen at the anode. These iron plates can then be melted with other elements or with scrap iron in an electric furnace to produce steel.
Boston Metal (U.S. Pat. No. 8,764,962 B2) has used this method by replacing a carbon anode, which produces CO2 during the reaction, by a chromium-based inert anode which does not corrode further to oxygen release. This electrolysis process via molten oxides (molten oxide electrolysis—MOE) essentially discharges oxygen and possibly fugitive hydrogen if the electrolytic yield is not 100%. If the electricity used is derived from a renewable source, the method is decarbonized.
This technique therefore entails robust, simple processes. It is well known that the electrolytic deposit of iron requires particular conditions to be energy-efficient. Constraints include a high concentration of sodium hydroxide and a relatively high temperature. Hence, the imperative need for a closed cell.
In addition, to obtain the lowest possible energy consumption, the cell must have a limited distance between the electrodes. The difficulty with closed cells lies in the extraction of the metal deposited on the cathode, especially if in large sizes (>1 m2), since the cathode must permanently remain in the cell. This in situ extraction also requires that deposits should be non-adhering or easily detachable from the cathodes to best facilitate mechanical extraction through a restricted opening in the cell.
To conclude, the need for a reduced distance between the electrodes in the electrolysis of iron ore practically prevents the mechanical extraction from cathodes and stripping outside the cell, as is the case in the current state of the art. This is heightened by the difficulty of operating in a closed cell. Means must first be found for easy opening of the cell to extract the cathodic deposits therefrom.
Document U.S. Pat. No. 6,632,333 B1 discloses a device for separating metal deposit from a mother plate used as a cathode in an electrolytic process, as metal electrorefining or metal electrowinning, in which device there is a supporting member for supporting the cathode to be treated, a member for releasing at least partly a metal deposit grown during the electrolytic process on a surface of the mother plate, and a member for supporting the released metal deposit. According to the invention the mother plate of a cathode is provided with a growth affecting means for creating an irregularity in the growth of the metal deposit to be used as a hinged member when the metal deposit is tilted to the mother plate of the cathode in order to break the metal deposit in two separate pieces along the irregularity in the growth.
Document U.S. Pat. No. 3,523,873 A discloses a parting agent applied on to an electrically conductive substrate, the parting agent serving as an aid for the stripping and removal of metal subsequently electrodeposited on said substrate, the improvement which comprises employing as said parting agent a composition comprising an aqueous emulsion containing 2-20% by weight of a polar, saturated, substantially water-insoluble, aliphatic, organic compound selected from the group consisting of fatty acids, fatty alcohols and ester and glyceride derivatives thereof and about 0.05-1% by weight of a sulfur-containing material.
Document FR 2 556 359 A1 discloses a peelable and electrically conductive coating intended for covering a metal cathode used in electrolytic metal production processes to allow electrolytic deposition of a metal, using an electrolyte, on the external surface of the coating, and then parting of said deposited metal at room temperature. This coating is made up of an electrically conductive dispersion of pigment particles in a peelable, non-electrically conductive binder. The coating is particularly intended for the production of high-purity copper cathodes.
In an embodiment, the present invention provides a device for producing a pure metal or an alloy of the pure metal via electrolytic reduction of an ore of the pure metal or of a substance containing an oxidized form of the pure metal, the device comprising: a cell equipped with an anode, a cathode, an electrolytic area comprising an electrolyte, and a removable cell closing system, the cathode having a coating non-adherent for an electrolytically deposited metal; and an electrically conductive metal sheet for extraction of a plate of the electrolytically deposited metal on the cathode, the metal sheet being arranged in the cell in a continuation of the cathode or partially overlapping the cathode, with mechanical and electrical contact at one end with the cathode and extending at least partly beyond the electrolytic area of the cell so as to allow simultaneous depositing of the pure metal on the cathode and on a portion of the metal sheet in contact with the electrolytic area, wherein an adherence between the cathode and the electrolytically deposited metal being less than an adherence between the metal sheet and the electrolytically deposited metal such that the electrolytically deposited metal is separated from the cathode and is drawn out by the metal sheet during a subsequent extraction of the metal sheet via a mechanical means applied on a portion of the metal sheet, which extends beyond the electrolytic area by a translational movement.
Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:
In an embodiment, the present invention provides a practical, easy means for separating the plates of metal deposited on the cathodes in electrolytic production processes, this extraction necessarily being in situ since it must take into consideration the physical constraints imposed by the electrolytic cell such as those relating to a closed cell, non-dismantling of the cell, a short anode-cathode distance to maintain good energy efficiency, etc.
A first aspect of the present invention relates to a device for the production of a pure metal or an alloy of this metal via electrolytic reduction of an ore of this metal or of a substance containing an oxidized form of this metal, said device comprising a cell equipped with an anode, a cathode, an electrolytic area comprising an electrolyte and a removable cell closing system, the cathode being provided with a non-adherent coating for the electrolytically deposited metal, wherein the device additionally comprises a metal sheet having advantageously a consumable function, which is electrically conductive and intended to facilitate the extraction of a plate of said metal electrolytically deposited on the cathode, said metal sheet being arranged in the cell in the continuation of the cathode or partially overlapping the latter, with mechanical and hence electrical contact at one end with the cathode, and extending partly beyond the electrolytic area of the cell so as to allow, when in operation, the simultaneous depositing of said metal on the cathode and on a portion of the metal sheet in contact with the electrolytic area, the adherence between the cathode and the deposit being less than the adherence between the metal sheet and the deposit, so that the metal deposit is separated from the cathode and drawn out by the metal sheet during a subsequent extraction of the metal sheet via a mechanical means applied on the portion of the latter extending beyond the electrolytic area by a translational movement.
According to preferred embodiments, the device is also limited by one of the following features or by any suitable combination thereof:
Another aspect of the invention relates to the use of the above-described device wherein, after extraction, the metal sheet is either separated from said deposited pure metal or metal alloy to prevent any pollution, or it is subsequently melted with the deposited metal.
Advantageously, the use relates to the electrolytic deposition of iron in a basic medium, wherein the metal sheet is a low-carbon steel sheet.
Also advantageously, the use relates to the electrorefining of zinc, nickel or copper in an acid medium, the metal sheet being a zinc, nickel, or copper plate respectively.
The present invention not only consists in obtaining an electrolytic metal deposit on a cathode, but also in co-depositing the metal adherently onto at least one portion of an electrically conductive consumable, more precisely a metal sheet, prepared for example in the form of a steel plate which can be compatible with subsequent melting steps of the metal. The consumable element is placed in the electrolytic cell before starting the depositing operation, and is positioned so that electrical contact with the cathode is ensured. This allows extraction of the deposit, deposition being performed simultaneously on the cathode and on the consumable, through the use of a grasping system such as grippers or similar elements preferably positioned on a portion of the consumable which has not received any deposit or only a scarce deposit. The cell is preferably positioned so that it is tilted, allowing the consumable to be positioned in a lower part and the cathode to be positioned in an upper part of the cell, with at least one portion of the consumable not covered by the deposit to permit mechanical gripping of the consumable when opening the cell in the lower part thereof, after draining and rinsing the cell.
In the description that follows, the terms consumable and metal sheet/plate are considered as equivalent terms.
Extraction of the deposited metal is therefore achieved by withdrawing the consumable concomitantly with the entire deposit which does not adhere to the cathode, preferably by means of a special coating of the cathode having for example a carbon or graphite base with low surface roughness. Metal extraction is performed by a guided translational movement.
The deposited metal plate/consumable is then transferred onto a supporting table to prevent material breakage during the extraction process.
According to the invention, the cell can be tilted at an angle between the horizontal and vertical, but preferably at an angle of between 20° and 60° from the horizontal to take advantage of the effect of gravity and also for compactness. The height of the cell is preferably between 50 mm and 700 mm, and further preferably between 100 mm and 300 mm. It has a length of 1 m to 4 m and preferably between 1 m and 3.5 m. The width of the cell is from 1 m to 2 m and preferably from 1 m to 1.5 m.
According to invention, the length of the consumable portion is less than 50% of the length of the cathode, and preferably less than 20% of the length of the cathode, and more preferably 10% less. The width of the consumable portion must be at least approximately equal to the width of the cathode with which it is in contact.
The expected thickness of the deposit is between 2 mm and 50 mm, preferably between 3 mm and 5 mm, depending on the surface area of the cathode, to obtain a plate that has sufficient mechanical strength to allow extraction thereof, whilst maintaining a minimum anode-cathode distance throughout the entire depositing phase.
In this cell 1, one end of the anode 2 is positioned facing part of the cathode 3 and also facing part of the consumable 5 which adjoins or overlaps the lower edge of the cathode 3, with which it is in physical contact, thereby ensuring perfect electrical continuity between the cathode 3 and the consumable 5. These two factors allow the obtention of a metal deposit 4 covering not only the cathode 3 but also a section 5′ of the consumable 5. The consumable 5 is therefore sized to project downwardly beyond the area of the cell containing the electrolyte 8. One portion of the consumable 5 will therefore not be covered by the electrolytically deposited metal and the protruding portion 5″ of the consumable 5 will allow easier grasping thereof.
According to the invention, the electrolytic cell 1 is constantly closed when in operation, and a removable closing system 6 is used to close the cell 1. The connection between the cell 1 and the closing system 6 is sealed to prevent any leakage of electrolyte 8.
The system according to the invention is advantageously designed to automate extraction of the deposited iron plate. In one embodiment, a table on runners 7 is able to be brought close to the cell 1 and to rotatably tilt at an angle to lie parallel with the cell (
According to the invention, there must be significant differential adherence between the cathode and the iron deposit, and between the consumable and the iron deposit, the first being weaker than the second. Therefore, the cathode is to be formed of a material that scarcely adheres to iron, such as a material in carbon, graphite with low surface roughness, graphite impregnated or coated with pore fillers, or pure metals such as silver or copper and some of the optionally coated alloys thereof.
Given the required short inter-electrode distance, at the time of extraction the deposited sheet 4 cannot be lifted to be directly detached from the cathode 3 as in prior art stripping methods. When the cell 1 is open, one portion of the consumable 5 must be able to protrude therefrom as indicated above, to allow recovery of the plate via a mobile grasping and recovery system 7 such as a table. The removable system 6 is then used to place a new consumable 5 in contact with the cathode 3. The plate 4 together with the consumable 5 is grasped by grippers, clamps, or similar elements 10 and is withdrawn along a guided translational movement parallel to the cell. The metal deposit «glued» to the consumable 5 but not to the cathode 3, which is non-adhering, detaches itself from the cathode 3 and is drawn out of the cell by the translational movement of the consumable 5 (see
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22190058.2 | Aug 2022 | EP | regional |
