Electrolysis device comprising a cathode with a removable part

Abstract

The electrolysis device (1) for reducing iron oxides into metallic iron comprises at least one anode (6) and at least one cathode (8) immersed into an electrolytic bath (4), the cathode (8) comprising a collecting surface (18) on which metallic iron is deposited after reduction of iron oxides. At least a removable part (16) of the cathode (8), comprising at least the collecting surface (18), is made in a melting material adapted to be melted with the deposited metallic iron on the collecting surface (18) to produce a steel material, said removable part (16) being removable from the electrolysis device together with the deposited metallic iron.

Description

[0001] Electrolysis device comprising a cathode with a removable part

[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 the cathode and can be collected.

[0006] However, to collect the metallic iron, the outer surface, or collecting surface, of the cathode has to be stripped or scratched to separate the metallic iron from the collecting surface of the cathode.

[0007] Moreover, the metallic iron deposited on the collecting surface may be fragile and can break during stripping, making its collection even more complex. The collection of the metallic iron is thus a time consuming step and cannot be easily automated, which makes the electrolysis method for producing metallic iron unprofitable.

[0008] One of the aims of the invention is to overcome the above-mentioned drawbacks by providing a profitable electrolysis device for producing metallic iron from iron oxides.

[0009] To this end, the invention relates to an electrolysis device for reducing iron oxides into metallic iron, comprising at least one anode and at least one cathode immersed into an electrolytic bath, the cathode comprising a collecting surface on which metallic iron is deposited after reduction of iron oxides, wherein at least a removable part of the cathode, comprising at least the collecting surface, is made in a melting material adapted to be melted with the deposited metallic iron on the collecting surface to produce a steel material, said removable part being removable from the electrolysis device together with the deposited metallic iron.

[0010] By providing a cathode having a removable part made of a material adapted to be melted with the collected metallic iron, it is possible to easily remove the metallic iron from the electrolysis device together with the removable part of the cathode. The need to strip the outer surface of the cathode is therefore removed and the method for electrolyzing iron oxides is less time consuming. Furthermore, by choosing a proper material to make the removable part of the cathode, it is possible to adapt the composition of the steel material produced by melting the produced metallic iron with the removable part of the cathode. The electrolysis device according to the invention makes therefore the electrolysis method to produce metallic iron very profitable.

[0011] 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:

[0012] - the cathode comprises a support extending outside of the electrolytic bath and a body attached to the support and immersed into the electrolytic bath, said support being connected to a power source of the electrolysis device and electrically connecting said body to said power source;

[0013] - at least an outer face of the body forms the collecting surface of metallic iron, said outer face facing the anode, the body forming the removable part of the cathode and being removably attached to the support, said body being made of the melting material;

[0014] - the body is made of two sheets extending substantially parallel to each other and electrically connected together by a connecting element;

[0015] - the electrolysis device comprises an insulating rod extending between the two sheets, said insulating rod extending between a first end extending outside of the electrolytic bath and a second end extending in the electrolytic bath, the connecting element being attached to the second end;

[0016] - the cathode further comprises at least one sheet made of the melting material, said sheet of melting material comprising an inner face extending around the body of the cathode and an outer face forming the collecting surface, said sheet of melting material forming the removable part of the cathode and being removably attached to the body;

[0017] - the body of the cathode is movable in rotation around a rotation axis, the anode presenting a cylindrical shape extending according to the rotation axis, the anode extending around the cathode and the cathode rotating inside the anode and relative to said anode;

[0018] - the electrolysis device further comprises a blade element arranged to remove an excess of metallic iron from the collecting surface when the body of the cathode rotates in order to maintain the thickness of metallic iron on the collecting surface inferior to the distance between the collecting surface and the anode;

[0019] - the electrolysis device comprises a magnetic field generation device arranged to generate a magnetic field on the collecting surface such that metallic iron is attracted towards said collecting surface;

[0020] - the removable part presents a thickness substantially comprised from 0.10 mm to 2 mm;

[0021] - the melting material comprises steel; - the melting material comprises carbon fibers;

[0022] - the electrolytic bath is an alkaline solution;

[0023] According to another aspect, the invention also relates to a method for producing a steel material from iron oxides, comprising the following steps:- reducing iron oxides using a electrolysis device as described above;

[0024] - removing the removable part of the cathode with the metallic iron obtained from the reduction of the iron oxides on the collecting surface;

[0025] - melting the metallic iron together with the removable part to produce a steel material comprising at least the metallic iron and the material of the removable part of the cathode.

[0026] According to an optional feature of the method, the metallic iron and the removable part of the cathode are melted in an electric arc furnace.

[0027] 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:

[0028] Fig. 1 is a diagrammatical representation of an electrolysis device according to a first embodiment of the invention;

[0029] Fig. 2 is a diagrammatical representation of an electrolysis device according to a second embodiment of the invention;

[0030] Fig. 3 is a diagrammatical representation of an electrolysis device according to variant of the first and second embodiments of the invention, seen from above; and

[0031] Fig. 4 is a diagrammatical representation of the electrolysis device of Fig. 3 in cross section.

[0032] In reference to the figures, an electrolysis device 1 according to the invention is described.

[0033] The electrolysis device 1 comprises an enclosure 2 containing an electrolytic bath 4. The electrolytic bath 4 is for example an alkaline solution. According to an embodiment, the electrolytic bath 4 comprises soda in a liquid form. More particularly, the electrolytic bath 4 for example comprises a solution of soda. In such a solution, caustic soda is for example at a concentration substantially comprised between 30% and 60%, for example substantially equal to 50%. The solution of soda is for example at a temperature substantially comprised in the range of 80°C to 115°C, for example substantially equal to 110°C. Alternatively, the electrolytic bath 4 is an acidic solution.

[0034] The electrolysis device 1 comprises at least one anode 6 and a cathode 8 immersed into the electrolytic bath 4. The anode 6 and the cathode 8 are connected to a power source 10, via an electrical circuit 11 , arranged to provide an electric current between the anode 6 and the cathode 8. According to an embodiment, the electrolytic device 1 comprises at least two anodes 6 extending on either sides of the cathode 8, as shown in Fig. 1 .

[0035] The anode(s) 6 and the cathode 8 extend parallel to each other, for example vertically or horizontally, in the electrolytic bath 4.

[0036] Iron oxides are placed in the electrolytic bath, for example in a powder form, and power is supplied by the power source 10 to the anode(s) 6 and cathode 8 to reduce iron oxide into metallic iron at the cathode 8 as it is well known for conventional electrolysis methods.

[0037] Apart from the cathode 8 which will now be described, the electrolysis device 1 according to the invention is conventional and will not be described in greater details herein.

[0038] Generally speaking, the cathode 8 comprises a support 12 and a body 14 attached to the support 12. The support 12 extends outside of the electrolytic bath 4 and is connected to the power source 10. The body 14 is immersed into the electrolytic bath 4 and is electrically connected to the power source 10 via the support 12. The cathode 8 comprises a removable part 16 either formed by the body 14 itself according to the first embodiment shown in Fig. 1 or by a separate part attached to the body 14 according to the second embodiment shown in Fig. 2, as will be described in greater details subsequently.

[0039] The removable part 16 defines a collecting surface 18 on which the metallic iron, obtained by electrolyzing iron oxides, is gathered or collected. In other words, thanks to the reduction occurring at the cathode 8 when an electrical current is supplied to the anode(s) 6 and the cathode 8, the resulting metallic iron attaches to the collecting surface 18 of the removable part 16 of the cathode 8. The collecting surface 18 is formed by the surface of the removable part 16 which is in contact with the electrolytic bath 4.

[0040] By removable part 16, it is meant a part of the cathode 8 that can be separated from the rest of the cathode 8 and can be removed from the electrolytic bath 4 together with the metallic iron attached to the collecting surface 18. According to the invention, the removable part 16 is made of a melting material. By melting material, it is meant either that the removable part 16 is made of a material adapted to be melted with the metallic iron collected on the collecting surface 18 to produce a steel material or that the melting material is transformed into fine particles that are diffused in the steel material when the metallic iron is melted. In other words, the removable part 16 is made of a melting material which becomes a component of the composition of the steel material obtained by melting the metallic iron with the removable part 16, possibly with other additives, the removable part 16 being also melted or being transformed in fine particles during this operation. To this end, the removable part 16 is for example made of a steel material, for example having a composition identical to the composition of the steel material to be produced by melting the metallic iron and the removable part 16 or a composition which is to be completed with other components to obtain the desired composition of the steel material to be produced.

[0041] According to another embodiment, the removable part 16 is made of a melting material comprising at least one component of the steel material to be produced by melting the metallic iron and the removable part 16 or consisting of one component of this steel material. For example, the removable part 16 is made of carbon, and notably of carbon fibers, such that carbon is added to the steel material obtained by melting the metallic iron and the removable part 16. When the melting material 16 is for example graphite, the melting material transforms into fine particles diffused in the steel material when the metallic iron is melted.

[0042] This may be particularly advantageous in steelmaking process wherein Direct Reduced Iron (DRI) is currently used to produce molten metal. The carbon content of DRI will progressively decrease with the new decarbonized processes. Replacing this DRI with low carbon by the metallic iron together with a removable part 16 made of carbon, will allow maintaining a required level of carbon in the molten bath.

[0043] According to an embodiment, the collecting surface 18 of the removable part 16 is arranged to collect all the metallic iron produced by the electrolytic reaction. According to this embodiment, all the produced metallic iron can therefore be removed from the electrolytic bath 4 together with the removable part 16 in a single operation and all the metallic iron is collected at once with the removable part 16.

[0044] According to an embodiment, the removable part 16 extends over the whole height of at least the part of the cathode 8 which is immersed in the electrolytic bath 4. In other words, the part of the cathode in contact with the electrolytic bath 4 is formed by the removable part 16, when the removable part 16 is attached to the rest of the cathode 8. The height of the cathode corresponds to the largest dimension of the cathode and is measured in the direction according to which the cathode is immersed in the electrolytic bath 4.

[0045] According to the first embodiment shown in Fig. 1 , the removable part 16 of the cathode 8 is formed by the whole body 14 of the cathode 8. This means that the body 14 can be separated from the support 12 and be melted with the metallic iron collected on an outer surface of the body 14 in contact with the electrolytic bath 4 and forming the collecting surface 18.

[0046] According to a variant of the first embodiment, the body 14 is formed by a sheet made of the melting material, for example a steel sheet. Such a steel sheet comprises at least a face extending parallel to and opposite the anode 6. Preferably, the steel sheet comprises two opposite faces, each facing one of the anodes 6 extending on either sides of the cathode 8. Each face the sheet forms a collecting surface 18 of the cathode 8.

[0047] According to another variant of this embodiment and as shown in Fig. 1 , the body 14 comprises two sheets 20 parallel to each other and to the anodes 6. Each sheet 20 is attached to a support 12 and comprises an inner face 22 facing the inner face 22 of the other sheet 20 and an outer face 24 facing one of the anodes 6. The outer face 24 of the two sheets form together the main collecting surface 18 of the cathode 8 but the inner face 22 of both sheets 20 is also susceptible of collecting metallic iron. By main collecting surface 18, it is meant that, during the electrolysis, the major part of the formed metallic iron is collected on the outer faces 24 of the sheets 20. The thickness of each sheet 20, corresponding to the distance between the inner face 22 and the outer face 24, is for example comprised from 0.10 mm to 0.2 mm, for example comprised from 0.10 mm to 0.25 mm and more particularly for example substantially equal to 0.18 mm. In the direction corresponding to the depth of the electrolytic bath 4, each sheet 20 extends between a first end 26 attached to the support 12 and extending outside of the electrolytic bath 4 and a second end 28 extending in the electrolytic bath 4. The distance between the outer faces 24 of the sheets 20 and the anodes 6 is arranged such that the metallic iron collected on these faces does not contact an anode 6 in order to prevent a short-circuit in the electrolysis device 1 .

[0048] The sheets 20 are electrically connected together by a connecting element 30, for example arranged between the second ends 28 of the sheets 20. The connecting element 30 closes the electrical circuit 11 , the current passing through the sheets 20 and through the connecting element 30. According to the embodiment shown in Fig. 1 , the connecting element 30 is for example made integral with the sheets 20 such that the body 14 is made of a single sheet defining two cathodes facing the anodes 6.

[0049] According to the embodiment shown in Fig. 1 , the electrolytic device 1 further comprises an insulating rod 32 extending between the sheets 20, more particularly between the inner faces 22 of the sheets 20. The insulating rod 32 is made of a nonconductive material and extends between a first end 34, extending outside of the electrolytic bath 4, and a second end 36 extending in the electrolytic bath 4. The second end 36 of the insulating rod 32 for example carries a cylindrical element 37, the connecting element 30 electrically connecting the two sheets 20 passing around the cylindrical element 37. According to the embodiment shown in Fig. 1 , wherein the body 14 is made of a single sheet, the part of the sheet forming the connecting element passes around the cylindrical element 37 such that the sheet defines two cathodes spaced from each other and parallel to each other to face the anodes 6. The insulation rod 32 and, if provided, the cylindrical element 37 act as a tensioner on the sheet(s) 20 allowing maintaining the flatness of the cathodes in the electrolytic bath 4 and the distance between the cathodes. In other words, the insulating rod 32 and the cylindrical element 37 act as a weight on the connecting element 30, for example formed by a part of the sheet defining the two cathodes as shown in Fig. 1 .

[0050] According to a variant (not shown), additional anodes 6 could be provided between the two sheets 20 to improve the electrolytic reaction.

[0051] It is understood that, according to the first embodiment, the body 14 could have a shape different from the sheet(s) described above as long as the body 14 is made of the melting material. For example, the body 14 could be formed by a steel or carbon fiber rod, a steel ingot or any other shape. However, providing the body 14 as one or two sheets allows having a cathode 8 at a relatively low cost.

[0052] According to the second embodiment shown in Fig. 2, the removable part 16 of the cathode 8 is formed by at least one sheet 38 removably attached to the body 14 of cathode 8 and forming the collecting surface 18 of the cathode 8. In other words, once the electrolysis is completed, the body 14 remains attached to the support 12 and only the sheet 38 is removed from the body 14 to be melted with the collected metallic iron to produce the steel material. In this case, the body 14 of the cathode 8 is for example formed by a conductive element 40 electrically connected to the circuit 11 and covered by the sheet 38 of melting material. The sheet 38 comprises an inner face 42 applied against an outer surface of the conductive element 40 and an outer face 44 in contact with the electrolytic bath 4 and forming the collecting surface 18 of the cathode 8. The conductive element 40, for example in the shape of a rod, transmits the electric current to the sheet 38 of melting material. According to this embodiment, only the outer surface 44 of the sheet 38 collects metallic iron but the body 14 allows an efficient maintaining of the sheet 38 in the electrolytic bath 4. The sheet 38 of melting material presents a thickness, corresponding to the distance between the inner face 42 and the outer face 44, for example comprised from 0.10 mm to 2 mm, for example comprised from 0.10 mm to 0.25 mm and more particularly for example substantially equal to 0.18 mm. The sheet 38 of melting material can for example be a steel sheet or a carbon fiber sheet as described previously. Depending on the dimensions of a sheet 38 of melting material and / or of the body 14, several sheets 38 of melting material can be provided to surround the whole body 14.

[0053] Such an embodiment is advantageous in that the body 14 also provides an improved current distribution with a sheet 38 of melting material having a low thickness. Using such a sheet of melting material alone could indeed result in a poor electrical conductivity. According to another embodiment shown in Figs. 3 and 4 and that can be combined with the first embodiment, i.e. wherein the body 14 forms the removable part 16 of the cathode 8, and with the second embodiment, i.e. wherein the removable part 16 is attached to the body 14 of the cathode 8, the cathode 8 is movable in rotation around a rotation axis R relative to the anode 6 such that a more uniform layer of metallic material is deposited on the collecting surface 18 of the cathode 8. According to the variant shown in Figs. 3 and 4, the embodiment is applied to the second embodiment described previously and the body 14 is covered by a sheet 38 of melting material. The body 14 is for example cylindrical and is movable in rotation, for example together with the support 12, around the axis of the cylinder as shown by the arrow A in Fig. 3. In this case, the anode 6 also has a cylindrical shape extending along an axis parallel to the rotation axis R of the cathode 8 and surrounds at least a part of the cathode 8. In other words, the anode 6 has the shape of a tube and the cathode 8 extends and rotates in the hollow space inside the anode 6, while the anode 6 remains immovable. As explained previously, according to this embodiment, the metallic iron is deposited in a more regular fashion on the whole collecting surface 18 of the cathode 8, such that the removable part 16 and the metallic iron deposited thereon are easier to process to produce a steel material.

[0054] It should be noted that a cylindrical hollow anode 6 can also be implemented around an immovable cathode 8 as described previously in reference to Figs. 1 and 2.

[0055] When the cathode 8 is movable in rotation relative to the anode, an excess of metallic iron deposited on the collecting surface 18 can be removed to prevent the deposited metallic iron from contacting the anode 6 and causing a short-circuit. To this end, as shown in Fig. 3, a blade element 46 is for example placed at a predetermined distance from the collecting surface 18 and is arranged to cut away the metallic iron when the thickness of metallic iron on the collecting surface 18 exceeds the predetermined distance as the cathode 8 rotates relative to the blade element 46 as shown in Fig. 3. In this manner, the thickness of metallic iron on the collecting surface 18 can be kept inferior to the distance between the collecting surface 18 and the anode 6. This blade element 46 efficiently prevents the formation of dendrites of metallic iron on the collecting surface 18.

[0056] To place the blade element 46 opposite the collecting surface 18, the anode 6 for example comprises a slit 47 extending through the anode 6 and receiving the blade element 46.

[0057] As also shown in Fig. 3, the electrolysis device 1 comprises according to an embodiment a magnetic field generation device 48 arranged to generate a magnetic field on the collecting surface 18 of the cathode 8 to attract metallic iron on the collecting surface 18. This embodiment further improves the collection of metallic iron on the collecting surface 18. According to the embodiment shown in Fig. 3, the magnetic field generation device 48 for example comprises a plurality of magnets arranged in the body 14 of the cathode 8 and arranged to generate a magnetic field towards the collecting surface 18 of the cathode 8. It should be noted that such a magnetic field generation device 48 can be implemented in the cathode 8 whether the cathode 8 is movable in rotation or not.

[0058] When the cathode 8 is movable in rotation, the rotation of the cathode 8 can be used to promote a circulation of the electrolytic bath 4 in the enclosure 2. To this end, as shown in Fig. 4, the body of the cathode 8, for example the second end 28 thereof can be arranged to move the electrolytic bath 4 in the enclosure 2 along the body of the cathode 8 during the rotation of the cathode 8 as shown by arrows B in Fig. 4. The second end 28 of the body 14 is for example shaped into a helix 50 to promote such a movement of the electrolytic bath 4. This embodiment allows doing without a pump arranged to move the electrolytic bath 4 in the enclosure.

[0059] According to the embodiment shown in Fig. 4, which is also compatible with the first and second embodiments, the electrolysis device 1 comprises two cathodes 8 and two anodes 6, surrounding each of the cathodes 8, placed in the same electrolytic bath 4.

[0060] The electrolytic device 1 described above allows recuperating metallic iron from oxidized iron in an efficient manner by using cathodes having a disposable part formed by the removable part 16 of the cathode 8. Furthermore, the removable part 16 can be used to improve the composition of the steel material obtained by melting the collected metallic iron, which can reduce the need to add additional components in the furnace wherein the metallic iron is melted.

[0061] After the electrolysis, the collected metallic iron and the removable part 16 are for example melted together in an electric arc furnace to produce the steel product. The removable part 16 can be removed from the electrolytic bath 4 by any appropriate manner, for example by making the cathode 8 movable relative to the enclosure 2 to remove the body of the cathode from the electrolytic bath or by emptying the enclosure 2 from the electrolytic bath 4 to make the removable part 16 of the cathode more accessible.

Claims

CLAIMS1.- Electrolysis device (1) for reducing iron oxides into metallic iron, the electrolysis device comprising at least one anode (6) and at least one cathode (8) immersed into an electrolytic bath (4), the cathode (8) comprising a collecting surface (18) on which metallic iron is deposited after reduction of iron oxides, wherein at least a removable part (16) of the cathode (8), comprising at least the collecting surface (18), is made in a melting material adapted to be melted with the deposited metallic iron on the collecting surface (18) to produce a steel material, said removable part (16) being removable from the electrolysis device together with the deposited metallic iron.2.- Electrolysis device according to claim 1 , wherein the cathode (8) comprises a support (12) extending outside of the electrolytic bath (4) and a body (14) attached to the support (12) and immersed into the electrolytic bath (4), said support (12) being connected to a power source (10) of the electrolysis device and electrically connecting said body (14) to said power source (10).3.- Electrolysis device according to claim 2, wherein at least an outer face (24) of the body (14) forms the collecting surface (18) of metallic iron, said outer face (24) facing the anode (6), the body (14) forming the removable part (16) of the cathode (8) and being removably attached to the support (12), said body (14) being made of the melting material.4.- Electrolysis device according to claim 3, wherein the body (14) is made of two sheets (20) extending substantially parallel to each other and electrically connected together by a connecting element (30).5.- Electrolysis device according to claim 4, comprising an insulating rod (32) extending between the two sheets (20), said insulating rod (32) extending between a first end (34) extending outside of the electrolytic bath (4) and a second end (36) extending in the electrolytic bath (4), the connecting element (30) being attached to the second end (36).6.- Electrolysis device according to claim 2, wherein the cathode (8) further comprises at least one sheet (38) made of the melting material, said sheet (38) of melting material comprising an inner face (42) extending around the body (14) of the cathode (8) andan outer face (44) forming the collecting surface (18), said sheet (38) of melting material forming the removable part (16) of the cathode (8) and being removably attached to the body (14).7.- Electrolysis device according to any one of claims 2 to 6, wherein the body (14) of the cathode (8) is movable in rotation around a rotation axis (R), the anode (6) presenting a cylindrical shape extending according to the rotation axis (R), the anode (6) extending around the cathode (8) and the cathode (8) rotating inside the anode (6) and relative to said anode (6).8.- Electrolysis device according to claim 7, further comprising a blade element (46) arranged to remove an excess of metallic iron from the collecting surface (18) when the body (14) of the cathode (8) rotates in order to maintain the thickness of metallic iron on the collecting surface (18) inferior to the distance between the collecting surface (18) and the anode (6).9.- Electrolysis device according to any one of claims 1 to 8, comprising a magnetic field generation device (48) arranged to generate a magnetic field on the collecting surface (18) such that metallic iron is attracted towards said collecting surface (18).10.- Electrolysis device according to any one of claims 1 to 9, wherein the removable part (16) presents a thickness substantially comprised from 0.10 mm to 2 mm.11.- Electrolysis device according to any one of claims 1 to 10, wherein the melting material comprises steel.12.- Electrolysis device according to any one of claims 1 to 11 , wherein the melting material comprises carbon fibers.13.- Electrolysis device according to any one of claims 1 to 12, wherein the electrolytic bath (4) is an alkaline solution.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- removing the removable part (16) of the cathode (8) with the metallic iron obtained from the reduction of the iron oxides on the collecting surface (18),- melting the metallic iron together with the removable part (16) to produce a steel material comprising at least the metallic iron and the material of the removable part (16) of the cathode (8).15.- Method according to claim 14, wherein the metallic iron and the removable part (16) of the cathode (8) are melted in an electric arc furnace.

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