Method and system for electrochemical separation of tramp elements in iron scrap

Abstract

To provide an electrochemical separation method of tramp elements in iron scrap capable of highly efficiently removing the tramp elements from the iron scrap even if sulfide ions or the like are not incorporated into an electrolytic solution, and to provide an electrochemical separation system suitable for performing the electrochemical separation method.SOLUTION: An electrochemical separation system of tramp elements in iron scraps, comprising: electrochemically separating tramp elements in an iron scrap melt from iron by using the iron scrap melt as a cathode electrode and molten iron oxide containing 10 mass% or more of iron oxide as an electrolyte; and an electrochemical separation system of tramp elements in an iron scrap melt comprising the iron scrap melt acting as a cathode electrode, an iron scrap melt acting as an anode electrode, and an electrolyte comprising molten iron oxide containing 10 mass% or more of iron oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and system for electrochemical separation of tramp elements in iron scrap. [Background technology]

[0002] As the economy matures, the amount of steel scrap accumulated in the city is increasing. For example, in Japan, approximately 2% of accumulated steel resources become steel scrap annually, and the cumulative amount of steel scrap accumulated is said to exceed 1 billion tons. Steel scrap is reused as a source of iron for electric furnaces and converter steelmaking, contributing to energy savings in steel production and the recycling of steel resources. Approximately 80% of the scrap market comes from heavy scrap, such as construction. If high-quality steel could be produced from obsolete scrap, which makes up the majority of heavy scrap, a high level of steel resource recycling could be achieved.

[0003] When scrap iron is recycled as steel, it is necessary to remove concentrated tramp elements. Tramp elements are elements that are mixed into scrap iron as alloy elements or from various products and parts, and are difficult to remove by oxidation or evaporation. Typical tramp elements include copper (Cu) and tin (Sn). Tramp elements concentrate each time scrap iron is recycled, degrading the properties and workability of the steel material derived from the scrap iron. Therefore, there is concern that the concentration of tramp elements will limit the future recycling rate of steel resources. In order to minimize the contamination of steel with tramp elements, in recent years, thorough quality control has been implemented, such as by separating and recovering scrap steel, prior to processing in electric furnaces. However, with the future spread of electric vehicles, it is inevitable that copper wires, which are used in motors, will be mixed into steel scrap. Attempts to remove tramp elements in a solid state, such as by separating and recovering them, are limited to removing tramp elements present on or near the surface of the steel scrap, and it is difficult to deal with the tramp elements that become concentrated in steel as it is recycled.

[0004] In electric furnaces, scrap iron is melted at temperatures around 1500°C, impurities are oxidized by oxidation refining, and the molten oxide (molten slag) is discharged by gravity separation to improve the purity of molten iron (Fe). Oxidation refining and gravity separation are effective methods for removing non-ferrous elements. However, thermodynamically, it is known that more noble metals, such as Cu and Sn, remain in the molten iron without being oxidized during oxidation refining. To remove Cu from molten Fe by methods other than oxidation refining, methods such as evaporation removal using high vacuum or plasma and copper removal by reactive gas spraying have been proposed. However, these methods are difficult to put into practical use due to the complexity and cost of the equipment. Another copper removal method using sulfide-based fluxes has also been proposed, taking advantage of the preferential sulfidation of Cu in Fe. The copper removal method using sulfide-based flux is relatively easy to design even for large-scale processing, and is therefore promising for industrial use. However, the solubility of Cu in the flux is not very high, and this requires batch processing, which consumes large amounts of sulfide.

[0005] Several technologies have been proposed to address the problems inherent in existing copper removal methods. For example, Patent Document 1 describes an electrochemical separation method for tramp elements in iron scrap, which involves using molten iron scrap as an anode and separating the tramp elements from the molten iron through an electrochemical reaction. Patent Document 1 describes the use of molten slag as an electrolyte and the use of a highly heat-resistant carbon material as an anode electrode, which is combined with the molten iron scrap. This allows the molten iron scrap itself to function as an anode even at ultra-high temperatures when the slag and iron are in a molten state. Furthermore, it describes the preferential migration of tramp elements from the interior to the surface of the molten iron scrap through an electrochemical reaction, thereby enabling the separation and removal of the tramp elements from the iron scrap. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2022-129591 Summary of the Invention [Problem to be solved by the invention]

[0007] The technology described in Patent Document 1 is a groundbreaking technology that attempts to separate iron from tramp elements in iron scrap from a perspective different from that of conventional technologies. On the other hand, in a specific embodiment described in Patent Document 1, the electrolyte used is a melt of blast furnace slag for steelmaking (molten slag) composed of 27.5 wt% CaO-27.5 wt% SiO2-45 wt% Al2O3, to which CaS is added at a concentration of 1 mol%. This CaS is prone to oxidizing sulfide ions during an anodic reaction to produce elemental sulfur. This elemental sulfur preferentially reacts with tramp elements such as copper to produce sulfides (e.g., CuS, Cu2S), which then dissolve into the molten slag. In other words, the relatively high concentration of sulfide ions in the electrolyte promotes the migration of tramp elements contained in the iron scrap into the molten slag.

[0008] However, if sulfide ions derived from CaS or other substances are added to the electrolyte, it is inevitable that a certain amount of sulfur will be mixed into the molten iron scrap that functions as the anode. In other words, the impurity sulfur is being actively mixed into the iron scrap, which places limitations on the purity of the steel obtained from the iron scrap.

[0009] An object of the present invention is to provide an electrochemical separation method for tramp elements in iron scrap, which enables highly efficient removal of tramp elements from iron scrap without the need to add sulfide ions or the like to the electrolyte, and an electrochemical separation system suitable for carrying out this electrochemical separation method. [Means for solving the problem]

[0010] In view of the above problems, the inventors have conducted extensive research and have found that when a molten oxidized slag containing a predetermined high concentration of iron oxide (FeO) is used as an electrolyte, and molten iron scrap is used as a cathode electrode rather than an anode electrode to cause cathodic polarization, the tramp elements in the molten iron scrap, which serves as the cathode electrode, migrate efficiently from the interior to the surface of the molten iron scrap, enabling efficient separation of the iron and the tramp elements. Based on this finding, the inventors have conducted further research and have completed the present invention.

[0011] That is, the object of the present invention has been achieved by the following means. [1] A method for electrochemically separating tramp elements in iron scrap, comprising electrochemically separating the tramp elements in the molten iron scrap from the molten iron using molten iron scrap as a cathode and molten oxidized slag containing 10% by mass or more of iron oxide as an electrolyte. [2] The electrochemical separation method according to [1], wherein the potential of the cathode electrode is set to −2 V or less to separate the tramp elements in the molten iron scrap from the molten iron. [3] The electrochemical separation method according to [1] or [2], wherein the separation of the tramp elements in the molten iron scrap from the molten iron is carried out in an atmosphere containing oxygen. [4] An electrochemical separation system for tramp elements in iron scrap, comprising: molten iron scrap acting as a cathode electrode; an anode electrode; and an electrolyte made of molten oxidized slag containing 10% by mass or more of iron oxide, which electrochemically separates the tramp elements in the molten iron scrap from the molten iron. [5] A method for producing a steel product, comprising separating tramp elements in molten iron scrap from molten iron by the electrochemical separation method according to any one of [1] to [3], and removing the tramp elements. [6] A method for extracting tramp elements, comprising separating tramp elements in molten iron scrap from molten iron by the electrochemical separation method according to any one of [1] to [3], and extracting the tramp elements. [Effects of the Invention]

[0012] According to the electrochemical separation method and electrochemical separation system of the present invention, the tramp elements in the molten iron scrap and the molten iron can be electrochemically separated with high efficiency without the need to add elements that cause impurities to be mixed into the iron to the electrolyte, i.e., while suppressing the contamination of the iron with impurities.As a result, it becomes possible to prepare steel products with higher purity from the iron scrap and to extract tramp elements with higher efficiency. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an explanatory view (partial cross-sectional view) schematically illustrating one embodiment of an electrochemical separation system of the present invention. [Figure 2] 1 is a photograph showing that copper in Cu-containing molten iron is concentrated on or near the surface by the electrochemical separation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Electrochemical separation method] The electrochemical separation method for tramp elements in iron scrap according to the present invention (hereinafter also simply referred to as the "electrochemical separation method of the present invention") uses molten iron scrap (referred to as "molten iron scrap") as a cathode electrode (working electrode) and molten oxide slag containing 10% by mass or more of iron oxide as an electrolyte. A voltage is applied between an anode electrode (counter electrode, positive electrode) and a cathode electrode (negative electrode) (cathode polarization is generated) to separate the molten iron, which is the main component of the molten iron scrap, from the tramp elements mixed in the molten iron scrap. Because the iron scrap is used in a molten state, this electrochemical reaction takes place at an ultra-high temperature of approximately 1500°C. In the present invention, "separating the tramp elements in the molten iron scrap from the molten iron" means electrochemically (through an electrochemical action) migrating at least a portion of the tramp elements in the molten iron scrap that constitute the cathode electrode toward the surface of the molten iron scrap. This migration results in the formation of an inner portion with a higher concentration of molten iron and a surface portion with a higher concentration of tramp elements in the molten iron scrap after cathodic polarization (after voltage application) compared to before cathodic polarization (before voltage application). Note that if the molten iron scrap contains components other than the tramp elements, these components may migrate to the surface portion of the molten iron scrap like the tramp elements, or may remain inside the molten iron, or may exhibit behavior intermediate between that of the tramp elements and the molten iron.

[0015] <Scrap iron> The iron scrap used in the electrochemical separation method of the present invention can be any of commercially available scrap and self-generated scrap, and the grade of the scrap is also not particularly limited. Iron scrap may be used in the electrochemical separation method of the present invention as is, or scrap from which components other than iron have been separated and removed as much as possible may be used in the electrochemical separation method of the present invention. Iron scrap that has been subjected to oxidation refining or reduction refining may also be used in the electrochemical separation method of the present invention.

[0016] -Trump Element- In the present invention, tramp elements refer to elements that are difficult to remove by oxidation or evaporation from iron scrap. Copper (Cu) is known as a typical tramp element, and other known tramp elements include tin (Sn), antimony (Sb), arsenic (As), and zinc (Zn). In the present invention, the iron scrap to be subjected to the electrochemical separation method preferably contains at least copper as a tramp element.

[0017] A preferred embodiment of the electrochemical separation method of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below except as defined in the present invention.

[0018] <Electrochemical separation system> FIG. 1 shows a schematic partial cross-sectional view of an example of an electrochemical separation system for tramp elements in iron scrap (hereinafter also referred to as the "electrochemical separation system of the present invention") suitable for implementing the electrochemical separation method of the present invention. FIG. 1 is an explanatory diagram showing an electrochemical separation system 10 using a two-electrode method. In this embodiment, the electrochemical separation system 10 of the present invention includes molten iron scrap 1, which functions as a cathode electrode 1, and an anode electrode 2 (counter electrode). The electrolytic solution used is molten oxidized slag 5 containing 10% by mass or more of iron oxide (FeO) (hatching of the molten oxidized slag is omitted). The molten iron scrap 1 is electrically connected to an electrochemical device 6 via a conductive material 3, such as a carbon rod. The conductive material 3 is protected from high heat by being covered with a sheath 4, such as made of magnesia. A heat-resistant container 7 such as an alumina crucible or magnesia container is fixed on a support (not shown), filled with molten oxidized slag 5, and the cathode electrode 1 and the anode electrode 2 are immersed in the molten oxidized slag 5. A heater (e.g., a SiC heater, not shown) is installed around the heat-resistant container 7.

[0019] In this state, when a voltage is applied by the electrochemical device 6 to cause cathodic polarization, the tramp elements in the molten iron scrap 1 migrate from the inside of the molten iron scrap 1 to the surface side at the cathode electrode 1, increasing the iron purity inside the molten iron scrap 1 and increasing the tramp element concentration toward the surface side. In this way, the tramp elements in the molten iron scrap 1 can be separated from the molten iron while the molten iron scrap 1 functions as the cathode electrode 1. The reason for this is unclear, but it is hypothesized as follows. First, when cathodic polarization occurs, electrons flow into the cathode electrode 1 and accumulate near the interface between the molten scrap iron 1 (the cathode electrode 1) and the molten oxidized slag 5. As a result, iron ions constituting the iron oxide in the molten oxidized slag 5 are reduced at the interface with the molten scrap iron 1, becoming elemental iron and being incorporated into the molten scrap iron 1. Because the electron affinity of tramp elements such as copper is known to be significantly greater than that of iron, the tramp elements are attracted to the electrons present in large quantities at the interface. As a result, iron present near the interface of the molten scrap iron 1 is replaced by copper present further inside. Thus, at the cathode electrode 1, the tramp elements in the molten scrap iron 1 migrate from the interior to the surface. The iron purity increases within the molten scrap iron 1, and the tramp element concentration increases toward the surface. Note that the above mechanism is merely hypothetical and has not necessarily been scientifically verified. The present invention is not limited to the above mechanism except as defined in the present invention.

[0020] As described above, if a state is created in which the tramp elements in the molten iron scrap 1 are separated from the molten iron, and the surface layer of the molten iron scrap 1 or its solidified product is removed by scraping it off or the like, a steel product with a reduced amount of tramp elements can be obtained. Furthermore, since the tramp elements themselves are elements with industrially useful value, the tramp elements obtained by scraping off the surface layer of the molten iron scrap 1 or the like can also be reused industrially. In other words, by using the electrochemical separation method or system of the present invention, it is possible to obtain steel products in which the tramp elements have been reduced to a desired level. It is also possible to obtain products with high concentrations of tramp elements (extraction of tramp elements).

[0021] At least a portion of the tramp elements that have migrated from the interior to the surface of the molten iron scrap 1 due to cathodic polarization can be dissolved from the surface of the molten iron scrap 1 into the molten oxidized slag 5. If the copper concentration near the interface of the molten iron scrap 1 increases, the copper activity near this interface will increase, and a reaction, for example, 2Cu + FeO → Cu2O + Fe, will likely occur between the copper and the iron oxide in the molten oxidized slag 5, which is expected to facilitate the dissolution of copper from the molten iron scrap 1 into the molten oxidized slag 5. In this case, it is possible to obtain a steel product with a reduced amount of tramp elements without undergoing an operation such as scraping off the surface of the molten iron scrap 1 or its solidified product, as described above.

[0022] Next, preferred embodiments of each of the components constituting the electrochemical separation system of the present invention will be described.

[0023] -Cathode electrode 1- The cathode electrode 1 is composed of molten iron scrap 1. The molten iron scrap 1 is electrically connected to the electrochemical device 6 via a conductive material 3. Because the molten iron scrap 1 and the molten oxidized slag 5, which serves as the electrolyte, are extremely hot, at approximately 1500°C, the conductive material 3 must be heat-resistant enough to withstand this temperature. It must also be a material that is not chemically dissolved in the high-temperature molten oxidized slag 5 or the molten iron scrap 1. Examples of such conductive materials 3 include carbon materials (elementary carbon materials), solid iron wire / rods, and platinum wire. To protect the conductive material 3 from heat, the carbon material can be covered with a protective tube made of alumina, mullite, magnesia, or the like.

[0024] -Anode electrode 2- The anode electrode 2 must also be made of a material that can withstand ultra-high temperatures of around 1500°C and is required to be chemically insoluble in the high-temperature electrolyte. For example, carbon material or platinum wire is used. To protect the anode electrode 2 from heat, it can be covered with a protective tube made of alumina, mullite, magnesia, or other materials.

[0025] -Electrochemical Equipment 6- The electrochemical device 6 is not particularly limited in its form as long as it can apply a voltage between the cathode electrode 1 and the anode electrode 2 to induce cathode polarization. A wide variety of devices used in electrochemical measurements can be applied. Examples include a potentiostat, a galvanostat, and a function generator. The electrochemical device 6 may also include a computer (information processing device) that processes and displays data obtained from these devices. Furthermore, the output of the electrochemical device 6 can be designed appropriately to match the scale of the electrochemical separation system 10.

[0026] -Molten oxidized slag 5- The molten oxidizing slag 5 functions as an electrolyte. The molten oxidizing slag 5 is a melt of oxidizing slag containing 10% by mass or more of iron oxide. The molten oxidizing slag 5 preferably contains steelmaking slag, and is also preferably steelmaking slag. Components other than iron oxide that may be contained in the molten oxidizing slag 5 include SiO2, MnO, PO5, S, Cr2O3, Al2O3, MgO, CaF2, CaO, and TiO2. If the molten oxidizing slag 5 contains sulfur or sulfides, their total content in the molten oxidizing slag 5 is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, more preferably 0.20% by mass or less, and even more preferably 0.10% by mass or less. The iron oxide content in the molten oxidizing slag 5 is preferably 12% by mass or more, more preferably 14% by mass or more, even more preferably 16% by mass or more, still more preferably 18% by mass or more, still more preferably 20% by mass or more, and even more preferably 22% by mass or more. The iron oxide content in the molten oxidizing slag 5 is usually 50% by mass or less, but may be 40% by mass or less, 35% by mass or less, or even 30% by mass or less. The preferred range of the iron oxide content in the molten oxidizing slag 5 is preferably 10 to 50% by mass, more preferably 12 to 50% by mass, even more preferably 14 to 40% by mass, even more preferably 16 to 40% by mass, even more preferably 18 to 35% by mass, even more preferably 20 to 30% by mass, and even more preferably 22 to 30% by mass. The content of iron oxide in the molten oxidized slag 5 can be measured by elemental quantitative analysis using an energy dispersive X-ray fluorescence analyzer, elemental quantitative analysis using an inductively coupled plasma atomic emission spectrometry (ICP-AES) apparatus, or the like. If the heat-resistant container 7 contains alumina, the molten oxidized slag 5 is preferably saturated with Al2O3 to prevent the alumina from dissolving in the electrolyte. Similarly, if the heat-resistant container 7 contains magnesia, the molten oxidized slag 5 is preferably saturated with MgO to prevent the magnesia from dissolving in the electrolyte.

[0027] -Heat-resistant container 7- The heat-resistant container 7 is a container made of a material that can withstand an ultra-high temperature of about 1500°C and is not chemically dissolved in the high-temperature electrolyte or molten iron, and can be made of any material without particular limitations. For example, an alumina crucible, a carbon crucible, a magnesia crucible, a mullite crucible, etc. can be used.

[0028] -Support- The support is provided as a base as necessary for stable installation of the heat-resistant container 7. The support may be made of a material such as alumina, magnesia, or mullite.

[0029] Next, an example of the operating conditions of the electrochemical separation system of the present invention will be described. When separating the tramp elements from the molten iron scrap using the electrochemical separation system of the present invention, the iron scrap is kept in a molten state and cathodic polarization occurs, so the temperature is preferably 1500 to 1600°C. The atmosphere in which cathodic polarization occurs is not particularly limited. Because high-temperature melts are highly reactive and may be affected by the surrounding gas phase, it is also preferable to perform electrochemical separation in a reactive inert atmosphere. Examples of reactive inert gases that can be used include rare gases (such as argon gas) and nitrogen gas. It is also preferable to perform cathodic polarization in the presence of oxygen. In this case, the oxygen concentration in the atmosphere is preferably 10% by volume or less, more preferably 8% by volume or less, and even more preferably 6% by volume or less. The oxygen concentration in the atmosphere is preferably 1% by volume or more, and more preferably 2% by volume or more. The presence of oxygen in the atmosphere can more efficiently dissolve tramp elements in the molten iron scrap into the molten oxidized slag. When the atmosphere contains oxygen, the remainder, excluding oxygen, is preferably the reactive inert gas described above. Electrochemical separation can also be performed in the air atmosphere. Considering the copper removal efficiency, the potential difference between the anode and cathode electrodes caused by cathode polarization is preferably −2 V or less (a potential difference between the anode and cathode electrodes of 2 V or more), more preferably −5 V or less, even more preferably −7 V or less, even more preferably −9 V or less, and even more preferably −10 V or less. The potential of the cathode electrode caused by cathode polarization can be, for example, −50 V or more, or −40 V or more, or −30 V or more, or −20 V or more, or −15 V or more. The range of the potential of the cathode electrode caused by cathode polarization can be, for example, −2 V to −50 V, or −5 V to −40 V, or −7 V to −30 V, or −9 V to −20 V, or −9 V to −15 V. The time for which cathodic polarization is caused is not particularly limited, and can be set appropriately depending on the degree and scale of the desired separation. The scale of the electrochemical separation system of the present invention can be appropriately designed depending on the purpose, from a small-scale system to an industrially large-scale system. In the case of an industrially large-scale system, for example, the amount of molten iron scrap constituting the cathode electrode can be 10 to 1000 kg. In the electrochemical separation system of the present invention, the ratio of the amount of molten iron scrap constituting the cathode electrode to the amount of molten oxidized slag constituting the electrolyte is not particularly limited as long as an electrochemical reaction occurs, and can be appropriately set depending on the configuration of the system. For example, the ratio of molten iron scrap to molten oxidized slag can be set to 5 / 1 to 1 / 20 (mass ratio). [Example]

[0030] The present invention will be described in more detail based on examples, but the present invention should not be construed as being limited to the forms of the examples except as defined in the present invention.

[0031] [Equipment / Materials] An electrochemical separation system 10 having the configuration shown in FIG. 1 was used.

[0032] <Electrochemical Device 6> A potentiostat (product name: Electrochemical Measurement System HZ-7000, manufactured by Hokuto Denko Corporation) was used as the electrochemical device 6, and a two-electrode method was applied.

[0033] <Cathode electrode 1> As a simulated iron scrap containing tramp elements, Cu-containing molten iron (Fe-0.5 wt% Cu-0.1 wt% C) was used as the cathode electrode 1. This Cu-containing molten iron was prepared by weighing out pure iron (purity 99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.), pure copper (purity 99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and carbon-saturated iron (Fe-5.29 wt% C) to achieve the composition of the Cu-containing molten iron (30 g in total), filling the container 7 with oxidized slag (described below), and melting the mixture by heating with a heating element.

[0034] <Conductive material 3> A Pt wire (0.2 mm in diameter) bound to a porous graphite electrode (3 mm in diameter, 30 mm in length) was used as the conductive material 3. The conductive material 3 was protected by a magnesia tube (4, outer diameter 6 mm, inner diameter 4 mm, length 500 mm).

[0035] <Anode electrode 2> A graphite rod (diameter 3 mm, length 700 mm) was used as the anode electrode 2. The anode electrode 2 was partially protected by a quartz tube (outer diameter 6 mm, inner diameter 4 mm).

[0036] <Molten oxidized slag 5> Molten oxidizing slag 5, whose composition is shown in the table below, was used as the electrolyte. The values ​​in the table are in mass %. Molten oxidizing slag 5, whose composition is shown in the table below, contains a large amount of iron oxide (FeO), and also contains a small amount of fine iron particles with a diameter of 1 mm or less (collectively referred to as "T-Fe"), with an FeO content of approximately 25 mass %.

[0037] [Table 1]

[0038] <Heat-resistant container 7> A magnesia crucible (volume: 75 mL) was used as the heat-resistant container 7 .

[0039] <Support> A heat-resistant container 7 was placed on a support made of magnesia.

[0040] [Operation of electrochemical separation system] [Example 1] As shown in Figure 1, a cathode electrode 1, an anode electrode 2, and an electrolyte (molten oxidized slag 5) were placed in a heat-resistant container 7, which was a magnesia crucible, and an argon gas atmosphere was created to construct an electrochemical separation system 10. In this electrochemical separation system 10, 30 g of Cu-containing molten iron (cathode electrode 1) and 60 g of molten oxidized slag 5 were used, and the temperatures of the Cu-containing molten iron 1 and the molten oxidized slag 5 were controlled to 1550°C. In this electrochemical separation system 10, a voltage was applied from the potentiostat 6, and the potential of the Cu-containing molten iron (cathode electrode 1) was set to −10 V relative to the counter electrode (anode electrode 2), and cathodic polarization was performed for 1 hour. During this cathodic polarization, electrons flow into the Cu-containing molten iron (cathode electrode 1) through the conductive material 3.

[0041] [Comparative Example] Electrolysis was carried out in the same manner as in Example 1, except that cathodic polarization was replaced with anodic polarization. That is, in the electrochemical separation system of the comparative example, a voltage was applied from a potentiostat, and the Cu-containing molten iron was positioned as the anode electrode, with its potential set to +10 V relative to the counter electrode (cathode electrode, graphite rod), and anodically polarized for 1 hour. During this anodic polarization, electrons flow out from the Cu-containing molten iron (anode electrode) through the conductive material.

[0042] [Example 2] Cathodic polarization (-10 V) was performed in the same manner as in Example 1, except that the atmosphere was changed to a mixed gas of 95% argon gas by volume and 5% oxygen by volume. The Cu-containing molten iron was positioned as a cathode electrode.

[0043] After cathodic polarization in the examples and after anodic polarization in the comparative examples, the system was cooled, and the solidified Cu-containing molten iron was taken out, and the Cu concentration in the solidified product was measured as follows. The solidified Cu-containing molten iron was obtained in an approximately disk-shaped form (see Figure 2 in JP 2022-129591 A). The center of this disk-shaped solidified material was cut out in the thickness direction using a cutting machine (Heiwa Technica Corporation, product name: Fine Cutter). The oxide film on the surface of the cut sample was then scraped off using a cylindrical carbide cutter (Minitor Corporation, product name: BC2041). The sample was then divided into three sections: upper, middle, and lower. Each section weighed approximately 0.1 g. Each section was immersed in petroleum benzine and then its surface was cleaned using an ultrasonic cleaner. Each cleaned section was placed in a quartz beaker, and 3 mL of distilled water and 4 mL of aqua regia (a 3:1 mixture of hydrochloric acid and nitric acid by volume) were added. The beaker was then covered with a watch glass and heated on a hot plate at 200 °C for melting. After confirming that each section had dissolved, the lid was shifted to create a gap, and the liquid was allowed to completely evaporate and dry. After drying, 10 mL of a 1:1 mixture of nitric acid and distilled water was added to the sample and heated on a hot plate at 200°C to dissolve it. This solution was filtered, and the filtrate was placed in a 100 mL measuring flask, and distilled water was added to the measuring line. This liquid was diluted 10 times with a 1% by volume aqueous solution of nitric acid and analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The arithmetic mean of the Cu concentrations obtained from the analytical values ​​of each part was taken as the Cu concentration (mass%) of the solidified Cu-containing molten iron. Note that the Cu concentration of the Cu-containing molten iron before electrolysis was standardized to 0.5% by mass, as mentioned above. The results are shown in the table below.

[0044] [Table 2]

[0045] As shown in the above table, it is clear that by performing cathodic polarization using Cu-containing molten iron as a cathode, Cu can be removed more efficiently than when performing anodic polarization using Cu-containing molten iron as an anode (comparison between Example 1 and Comparative Example). It is also clear that by mixing oxygen into the electrolysis atmosphere, the Cu removal efficiency can be further improved (Example 2).

[0046] Furthermore, when the surface of the solidified product of Cu-containing molten iron in Example 1 was observed, copper aggregates glowing yellow were confirmed (Fig. 2). The interior of this solidified product was a uniform silver-white color, and it was clearly visually confirmed that copper migrated from the interior to the surface and was concentrated on the surface by performing cathodic polarization using Cu-containing molten iron as a cathode electrode.

[0047] JP 2022-129591 A discloses a method for efficiently removing tramp elements by anodic polarization. However, it has been found that by using molten oxidized slag containing a large amount of iron oxide as the electrolyte, tramp elements can be removed more efficiently by cathodic polarization rather than anodic polarization, while suppressing the addition of elements such as sulfur, which cause contamination of iron, to the electrolyte. [Explanation of symbols]

[0048] 1. Melted iron scrap (cathode electrode) 2 anode electrode 3 Conductive material (lead) 4. Sheath covering the conductive material 5. Molten oxidized slag (electrolyte, containing 10% or more FeO by mass) 6. Electrochemical equipment (potentiostat) 7 Heat-resistant container

Claims

1. A method for electrochemically separating tramp elements in iron scrap, comprising electrochemically separating the tramp elements in the molten iron scrap from the molten iron using molten iron scrap as a cathode and molten oxidized slag containing 10% by mass or more of iron oxide as an electrolyte.

2. 2. The electrochemical separation method according to claim 1, wherein the potential of the cathode electrode is set to −2 V or less to separate the tramp elements in the molten iron scrap from the molten iron.

3. 2. The electrochemical separation method according to claim 1, wherein the separation of the tramp elements in the iron scrap melt from the iron melt is carried out in an atmosphere containing oxygen.

4. An electrochemical separation system for tramp elements in iron scrap, comprising: molten iron scrap acting as a cathode electrode; an anode electrode; and an electrolyte comprising molten oxidized slag containing 10% by mass or more of iron oxide, the system electrochemically separating the tramp elements in the molten iron scrap from the molten iron.

5. A method for producing a steel product, comprising separating tramp elements in molten iron scrap from molten iron by the electrochemical separation method according to any one of claims 1 to 3, and removing the tramp elements.

6. A method for extracting tramp elements, comprising separating the tramp elements in molten iron scrap from the molten iron by the electrochemical separation method according to any one of claims 1 to 3, and extracting the tramp elements.

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