Method for reducing slag

Abstract

To provide a method for reducing slag capable of efficiently recovering valuable metals.SOLUTION: There is provided a method for reducing slag, which comprises a step 1 of subjecting a slag containing iron oxide to reduction reaction by a reducing agent A in a slag processing container A, wherein the reducing agent A is at least one selected from the group consisting of carbon monoxide gas and hydrogen gas, the slag processing container A comprises at least an outer shell 1, a refractory layer 2 and an inner layer 3, the inner layer 3 is a layer in contact with the slag and is formed to cover the refractory layer 2, the inner layer 3 is formed of a stainless steel plate or a heat-resistant steel plate, a metal-recovering board 20 is disposed in the slag processing container A, the metal-recovering board 20 is formed with nail-like protrusions 23 protruding from the surface, a copper plating layer 22 is formed on the metal-recovering board 20 and the nail-like protrusions 23 and metals generated by the reduction reaction are absorbed in the copper plating layer, followed by recovering.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for reducing slag. [Background technology]

[0002] Conventionally, copper smelting has been carried out by roasting copper concentrate in a flash furnace or the like. This copper smelting process allows for the recovery of necessary metals, such as copper, and the residue is a by-product known as "slag" or flash furnace slag. Methods for recovering additional metals from the slag produced by copper smelting have also been widely studied.

[0003] For example, Patent Document 1 discloses a method for recovering valuable metals from slag. In particular, the technology disclosed in Patent Document 1 includes: Step 1, in which slag (copper smelting slag) is oxidized using an oxygen-containing gas in the presence of a flux; Step 2, in which the oxidized reaction product obtained in Step 1 is contacted with a Cu-Fe alloy bath; and Step 3, in which the contacted Cu-Fe alloy bath obtained in Step 3 is subjected to a smelting process to recover valuable metals. More specifically, the technology disclosed in Patent Document 1 describes a two-stage technique for recovering valuable metals from slag, with the first stage of recovering valuable metals being termed "soft reduction" and the second stage of recovering valuable metals being termed "hard reduction." The "soft reduction" technique reduces only metal oxides that are more easily reduced than FeO and recovers them in molten Cu, leaving FeO in the slag. On the other hand, "hard reduction" involves reducing the FeO remaining in the slag using C in carbon-saturated molten iron as a reducing agent, and simultaneously absorbing the generated Fe as carbon-saturated molten iron.

[0004] In the technology disclosed in Patent Document 1, slag is subjected to an oxidation treatment prior to soft reduction. The oxidation treatment disclosed in Patent Document 1 involves blowing oxygen into remelted granulated slag to convert all sulfides in the slag to oxides. The reason for the need for oxidation in the technology disclosed in Patent Document 1 is that most of the Cu in the slag is actually sulfide matte particles, and Cu2S can account for the majority of copper loss. In other words, when starting from Cu2S, it is not possible to reduce and recover Cu by reduction treatment. Therefore, in the technology disclosed in Patent Document 1, oxygen is blown onto the slag to convert Cu2S to Cu2O, and then reduction is performed with Fe from a Cu-Fe alloy.

[0005] Specifically, the technology disclosed in Patent Document 1 is a method in which oxides of valuable metals (Cu, Sn, Pb, Sb, Mo, etc.) in slag are reduced on the surface of Cu-Fe alloy droplets using Fe in the liquid phase Cu-Fe alloy as a reducing agent, and at the same time, the valuable metals (e.g., Cu, Sn, Pb, Sb, Mo, etc.) generated by the reduction are absorbed into the Cu-Fe alloy droplets. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6516264 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a demand for the development of a technology for more efficiently recovering valuable metals from copper smelting slag. The present invention has been made in view of the above, and an object of the present invention is to provide a method for reducing slag that can efficiently recover valuable metals. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above object, the present inventors have discovered that the above object can be achieved by utilizing a specific reduction method, and have thus completed the present invention.

[0009] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 The method includes a step 1 of reducing slag containing iron oxide with a reducing agent A in a slag treatment vessel, the reducing agent A is at least one selected from the group consisting of carbon monoxide gas and hydrogen gas, The slag treatment vessel comprises: The furnace comprises at least an outer shell, a refractory layer, and an inner layer; the inner layer is a layer that comes into contact with the slag and is formed to cover the refractory layer, the inner layer is formed of a stainless steel plate or a heat-resistant steel plate, A metal recovery plate is disposed within the slag treatment vessel, The metal recovery disk has nail-shaped protrusions formed on its surface, a copper plating layer is formed on the metal recovery disk and the nail-shaped protrusions; The method for reducing slag comprises recovering the metal produced by the reduction reaction by allowing it to be absorbed into the copper plating layer. Section 2 a dam is provided opposite to a surface of the metal recovery board on the nail-shaped protrusion side; the weir is formed of a stainless steel plate or a heat-resistant steel plate, Item 1. The slag reduction method according to Item 1, wherein a plurality of gas outlets are provided on the surface of the weir facing the nail-shaped protrusions. Section 3 Item 3. The slag reduction method according to Item 2, wherein the reducing agent A is ejected from the gas ejection port of the weir and flows into the spaces between the nail-shaped projections, thereby causing the metal produced by the reduction reaction to be absorbed into the copper plating layer. Section 4 The method for reducing slag according to any one of items 1 to 3, further comprising step 1' of carrying out a reduction reaction of the slag using a hydrocarbon gas as a reducing agent prior to the reduction reaction with reducing agent A in step 1. Section 5 The outer shell is made of ordinary steel, 5. The method for reducing slag according to any one of items 1 to 4, wherein a heat insulating layer is provided between the outer shell and the refractory layer. Section 6 The slag treatment vessel is provided with a molten Cu supply pipe for supplying molten Cu from the outside, and the molten Cu supply pipe has a plurality of holes for allowing the molten Cu in the pipe to flow into the slag treatment vessel, and the molten Cu supply pipe is arranged in a position close to the metal recovery board so as to span the entire width of the metal recovery board. [Effects of the Invention]

[0010] The slag reduction method of the present invention makes it possible to reduce the risk of vessel corrosion and to efficiently recover valuable metals. [Brief explanation of the drawings]

[0011] [Figure 1] 1(a) is a schematic diagram showing an example of an embodiment of a slag treatment vessel B used in the reduction method of the present invention, and FIG. 1(b) is a schematic diagram showing a part of the structure thereof. [Figure 2] 1A and 1B are schematic diagrams showing an example of a metal recovery board used in the slag reduction method of the present invention, in which (a) is a side view and (b) is a plan view. [Figure 3] 1A and 1B are schematic diagrams showing an example of a weir 30 used in the slag reduction method of the present invention, in which (a) is a plan view and (b) is a side view. [Figure 4] 1 is a schematic diagram showing an example of a slag treatment vessel A used in the slag oxidation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0013] The drawbacks of the technology disclosed in the aforementioned Patent Document 1 include: (1) Fe is consumed, so a Cu-Fe alloy melting process is required to add the necessary Fe. (2) Since the reduction reaction occurs on the surface of the Cu-Fe alloy droplets, the droplet size must be optimized to allow them to settle and separate from the slag according to Stokes' law. (3) It is difficult to uniformly disperse the droplets in the slag. (4) The recovered Cu contains a large amount of Fe, which reduces the electrical efficiency when electrolyzing Cu-Fe alloys containing valuable metals. To solve this problem, a reduction treatment using a reducing gas is considered.

[0014] In reduction treatment using a reducing gas, carbon monoxide gas (CO) can be used as a reducing agent, which does not have the reducing power to reduce FeO to Fe in the copper smelting temperature range. However, even in reduction methods using a reducing gas, the following problems can be considered. (a) The reduction reaction occurs only on the surface of the CO gas bubbles; (b) Carbon dioxide generated by the reaction accumulates inside the CO bubbles, so the reducing power of the CO bubbles decreases as the reaction progresses. (c) The metal obtained by the reduction reaction floats up in the slag while adhering to the CO bubble surface in the form of a molten coating or solid fine particles. (d) Therefore, the reaction stops on the surface of the CO bubble where the reduction reaction has occurred. (e) When the CO bubbles burst at the slag-air interface, the metal adhering to the CO bubble surfaces breaks down into fine particles and scatters into the slag. (f) The metal particles scattered into the slag are so fine that it takes a long time for them to settle and separate in the slag according to Stokes' law, and most of the fine metal particles flow out of the reducing furnace together with the slag flow, making them impossible to recover.

[0015] The inventors have studied and found that, in order to overcome the above-mentioned problems, CO and / or hydrogen, which do not have the reducing power to reduce FeO to Fe, should be used as the reducing gas, and the following steps should be taken: (A) Stripping and recovering metal attached to the surface of reducing gas bubbles (e.g., CO bubbles) from the surface of the reducing gas bubbles under conditions that do not cause the reducing gas bubbles to burst, i.e., inside the slag; (B) By doing so, the reducing power of the reducing gas is restored; (C) The reducing gas bubbles necessarily burst at the slag-air interface, so the reducing power of the CO bubbles must be reduced to as close to zero as possible before the reducing gas bubbles reach the slag surface. was devised.

[0016] From this perspective, in order to efficiently recover valuable metals, a slag treatment vessel A is used for the reduction reaction, and in particular, a slag treatment vessel B, which is a modified version of the slag treatment vessel A, is used. This allows for efficient recovery of valuable metals, and since corrosion of the vessel by slag is less likely to occur, the inventors of the present application have discovered that valuable metals can be recovered more safely, leading to the completion of the present invention. The reduction method of the present invention will be described in detail below.

[0017] 1. Slag reduction method The method for reducing slag of the present invention includes step 1 in which slag containing iron oxide is reduced by a reducing agent A in a slag treatment vessel, and the reducing agent A is at least one selected from the group consisting of carbon monoxide gas and hydrogen gas. That is, in step 1 of the method for reducing slag of the present invention, the reducing agent A is used as a gas for the reduction reaction (reducing gas), and the reducing agent is carbon monoxide gas, hydrogen gas, or a mixed gas consisting of carbon monoxide gas and hydrogen gas. However, as described below, a reduction reaction with a hydrocarbon gas (step 1' described below) can also be performed prior to the reduction reaction with the reducing agent A.

[0018] In this specification, the reducing agent A and the hydrocarbon gas may be collectively referred to as "reducing gas."

[0019] (Slag treatment vessel used in reduction method) The slag treatment vessel used in the reduction method of the present invention comprises at least an outer shell, a refractory layer, and an inner layer. The inner layer is in contact with the slag and is formed to cover the refractory layer. The inner layer is formed of a stainless steel plate or a heat-resistant steel plate. A metal recovery disk having a copper-plated layer formed on its surface is placed inside the slag treatment vessel. The metal produced in the reduction reaction is absorbed into the copper-plated layer and recovered. First, the slag treatment vessel used in the reduction method of the present invention will be described.

[0020] 1(a) is a schematic diagram showing an example of a slag treatment vessel (hereinafter referred to as slag treatment vessel B). As shown in FIG. 1, the slag treatment vessel B is formed with a fireproof structure 100 that constitutes the vessel body.

[0021] 1(b) shows a cross section of the fireproof structure 100. As can be seen from FIG. 1(b), the fireproof structure 100 comprises at least an outer shell 1, a refractory layer 2, and an inner layer 3. The inner layer 3 is a layer that comes into contact with the slag S contained in the slag treatment vessel B and is formed so as to cover the refractory layer 2.

[0022] Here, the stainless steel sheet referred to in this specification includes various stainless steel sheets listed in JIS G0203 (2009), such as stainless steel, austenitic stainless steel, ferritic stainless steel, austenitic-ferritic stainless steel, precipitation hardened stainless steel, low-carbon stainless steel, stabilized stainless steel, free-cutting stainless steel, and painted stainless steel.

[0023] The heat-resistant steel plate referred to in this specification may include various heat-resistant steel plates listed in JIS G0203 (2009), such as heat-resistant steel, martensitic heat-resistant steel, ferritic heat-resistant steel, austenitic heat-resistant steel, and precipitation-hardened heat-resistant steel.

[0024] The inner layer 3 is formed of a stainless steel plate or a heat-resistant steel plate. For example, the inner layer 3 can be formed of SUS308.

[0025] Furthermore, the inside of the stainless steel plate or heat-resistant steel plate, i.e., the inside of the vessel, is preferably made of a highly corrosion-resistant material, which makes corrosion by slag less likely to occur.

[0026] The refractory layer 2 is a layer formed of a refractory material. The refractory layer 2 can be formed of, for example, a known refractory material. Specifically, a wide range of refractory materials that can be used in a container for treating slag can be used. Examples of such refractory materials include magnesium oxide-chromium oxide refractory materials, alumina-silica refractory materials, silicon carbide refractory materials, and alumina-chromium oxide refractory materials.

[0027] The outer shell 1 is the layer that forms the outermost part of the container and can be made of, for example, the same material as the outer shells of known slag treatment containers, such as ordinary steel. By making the outer shell 1 out of ordinary steel, it can have sufficient strength to support the weight of the contents of the slag treatment container.

[0028] The fireproof structure 100 constituting the slag treatment vessel B may be provided with a heat insulating material. For example, as shown in FIG. 1(b), a heat insulating material layer 4 may be provided between the refractory layer 2 and the outer shell 1. By providing such a heat insulating material layer 4, it is possible to prevent the outer shell 1 from becoming too hot. For example, a wide range of known heat insulating materials can be used as the heat insulating material.

[0029] The opening at the top of the slag treatment vessel of the present invention can be provided with a lid 5 as shown in Fig. 1, for example, to seal the vessel. Alternatively, the opening at the top of the slag treatment vessel of the present invention can be provided with a ceiling to seal the vessel. In this case, the inner surface of the lid or the inner surface of the ceiling may be made of the above-mentioned ordinary steel, and it is also preferable that they be made of stainless steel plate or heat-resistant steel plate.

[0030] A storage tank 10 for the raw material slag S is connected to the top of the slag treatment vessel B. The storage tank 10 is equipped with a heating electrode 10a, which allows the slag in the storage tank 10 to be heated to a predetermined temperature.

[0031] In addition, a recovery tank 11 for storing slag discharged from the slag treatment vessel B is installed so as to be connected to the slag treatment vessel B.

[0032] Both the storage tank 10 and the collection layer 11 can have a fireproof structure 100. That is, both the storage tank 10 and the collection layer 11 can have at least an outer shell, a refractory layer, and an inner layer. In addition, a heat insulating layer may be provided between the refractory layer and the outer shell.

[0033] Furthermore, even the piping for connecting the storage tank 10 and the slag treatment container B, and the piping for connecting the recovery tank 11 and the slag treatment container A can have the fireproof structure 100.

[0034] 1(b), molten Cu may be stored in advance at the bottom of the slag treatment vessel B, forming a molten Cu layer 50. An outlet 12 for allowing the molten Cu to flow out may be provided at the bottom of the slag treatment vessel B, and the molten Cu that flows out of the vessel through the outlet 12 may be temporarily stored in a molten Cu storage tank 13.

[0035] The molten Cu can also be overflowed from the molten Cu storage tank 13 into the ladle. The purpose of forming such a structure is to maintain a constant molten Cu surface in the slag treatment vessel B by using the siphon principle. By maintaining a constant top surface of the molten Cu layer 50 in the slag treatment vessel B, the molten slag S in the slag treatment vessel B can flow smoothly.

[0036] As shown in Fig. 1(b), at least one metal recovery disk 20 is disposed in the slag treatment vessel B. The configuration of the metal recovery disk 20 will be described in detail below.

[0037] FIG. 2 is a schematic diagram showing an example of the metal recovery board 20, where (a) is a side view and (b) is a plan view.

[0038] As can be seen from Figure 2, the metal recovery board 20 is a plate-like member formed in a generally rectangular shape in a plan view. The metal recovery board 20 has nail-shaped protrusions formed on its surface. More specifically, the metal recovery board 20 is composed of a base material 21 and nail-shaped protrusions 23 bonded to the base material 21. A copper plating layer 22 is formed on the metal recovery board 20 and the nail-shaped protrusions. That is, in the metal recovery board 20, the entire surfaces of the base material 21 and the nail-shaped protrusions 23 are covered with the copper plating layer 22.

[0039] As shown in FIG. 2, for example, a large number of nail-like projections 23 can be formed at predetermined intervals over the entire surface of the substrate 21.

[0040] In the metal recovery board 20, the base material 21 and the nail-like projections 23 are preferably both formed of stainless steel or heat-resistant steel plate. The nail-like projections 23 can be provided on the base material 21 by an appropriate fastening method.

[0041] It is preferable to apply nickel strike plating or chromium strike plating to the surface of the stainless steel or heat-resistant steel metal recovery board 20 before applying the copper plating layer 22. Considering that the melting point of chromium is 1907°C and the lowest melting point in the Cu-Cr binary phase diagram is approximately 1075°C at 1.48 wt% Cr, chromium strike plating is likely to dissolve into the molten Cu layer more slowly than nickel strike plating, making chromium strike plating more preferable. Chromium strike plating can suppress the amount of Fe eluted from the stainless steel or heat-resistant steel metal recovery board. Therefore, according to the reduction method of the present invention, the amount of Fe dissolved into the molten Cu layer is limited to a maximum of approximately 3%, significantly reducing the electrical efficiency problem during Cu electrolysis compared to the technique disclosed in Patent Document 1.

[0042] As shown in Fig. 1, a weir 30 is provided in the slag treatment vessel B so as to face the surface of the metal recovery board 20 on the copper plating layer 22 side. Specifically, the weir 30 is provided so as to face the surface of the metal recovery board 20 on the nail-shaped protrusions 23 side. The configuration of the weir 30 will be described in detail below with reference to Fig. 3.

[0043] 3A and 3B are schematic diagrams showing an example of a weir 30, where (a) is a plan view and (b) is a side view. As can be seen from Fig. 3, the weir 30 is a plate-shaped member, and is formed from, for example, a stainless steel plate or a heat-resistant steel plate.

[0044] A pipe 31 for introducing a reducing gas is formed inside the weir 30, and is formed so as to penetrate from one side surface to the other side surface of the weir 30. For example, the pipe 31 can be provided so as to extend along the width direction of the weir 30.

[0045] As shown in Fig. 3, a plurality of gas outlets 32 for ejecting the reducing gas introduced into the pipe 31 are formed on the surface of the weir 30. In Fig. 1, a plurality of gas outlets 32 are provided on the surface of the weir 30 facing the nail-shaped protrusions 23. Therefore, the surface of the metal recovery panel 20 facing the nail-shaped protrusions 23 and the gas outlets 32 of the weir 30 are arranged so as to face each other.

[0046] The gas outlet 32 ​​is formed in communication with the pipe 31, and is formed so that the gas (reducing gas) passing through the pipe 31 can be blown out from the gas outlet 32. A copper plating layer 35 may be formed on the surface of the weir 30 on the gas outlet 32 ​​side.

[0047] 3, the pipe 31 is provided along the width direction at the center of the weir 30 and also at one end thereof. The two pipes 32 are arranged substantially parallel to each other. Each pipe has a plurality of the gas outlets 32 formed at predetermined intervals along the entire length of the pipe 31.

[0048] In the embodiment shown in Fig. 3, two pipes 32 are provided for introducing the reducing gas, but the number of pipes 32 is not limited to two as shown in Fig. 3 and may be one, or three or more pipes 32. Generally, the smaller the diameter of the bubbles of the reducing gas described below, the more easily the reduction proceeds and the faster the reducing power is lost. In this case, the depth at which the reducing power of the bubbles will be lost can be predicted in advance, and the pipes 32 can be provided at desired positions so that the bubbles can be blown in from that depth.

[0049] As shown in FIG. 1, in the slag treatment vessel B, the metal recovery plate 20 is disposed so as to be inclined relative to the bottom surface of the vessel. The inclination angle can be, for example, 30°±15° in the longitudinal direction relative to the perpendicular to the vessel bottom, but is not limited to this and can be set as appropriate. The weir 30 can be disposed parallel to the metal recovery plate 20 at a predetermined distance. The distance between the weir 30 and the metal recovery plate 20 should be sufficient to allow the slag S in the vessel to flow.

[0050] The method for fixing the metal recovery plate 20 inside the container is not particularly limited, and the metal recovery plate 20 can be fixed by closely contacting one end of the metal recovery plate 20 to the ceiling via a stainless steel plate 40 and inserting the side of the metal recovery plate 20 into a groove made in the wall of the slag treatment container B. This makes it possible to prevent the reducing agent A, such as carbon monoxide gas, which is a reducing gas, from leaking upstream.

[0051] The method for fixing the weir 30 in the vessel is not particularly limited. For example, a stand 33 made of a magnesia-chromium refractory or the like can be placed on the molten Cu layer 50 arranged on the bottom of the vessel, and the weir 30 can be placed in close contact with the stand 33. This prevents the molten slag S from flowing out from the bottom of the weir 30. The surface of the stand 33 that comes into contact with the molten slag S can also be covered with a stainless steel plate, such as a SUS plate, to prevent corrosion by the molten slag S. The sides of the weir 30 can be fixed by inserting them into grooves made in the wall of the slag treatment vessel B. This prevents the molten slag S from flowing out from the sides of the weir 30.

[0052] Within the slag treatment vessel B, a metal recovery plate 20 and a weir 30 can be arranged as a pair; that is, as shown in Figure 1, two or more sets of metal recovery plate 20 and weir 30 can be installed within the slag treatment vessel B. Specifically, the necessary number of weirs can be installed so that 90% or more of the valuable metals (Cu, Sn, Zn, Mo, etc.) in the slag S can be recovered. In addition, the height of the weir 30 from the bottom surface decreases as the slag S moves downstream, allowing the slag to flow out naturally.

[0053] As described above, the slag treatment vessel B has a refractory layer 2 covered with an inner layer 3, i.e., a stainless steel plate or a heat-resistant steel plate. This prevents direct contact between the refractory layer 2 and the slag containing iron oxides such as FeO inside the slag treatment vessel, thereby reducing the risk of the refractory layer 2 being corroded by the slag. Therefore, even when slag (particularly copper smelting slag, as described below) is treated in the slag treatment vessel B, corrosion of the refractory layer 2 is unlikely to occur, reducing repair work compared to conventional vessels and extending the vessel's lifespan, thereby achieving energy savings and improved work efficiency. Furthermore, the fact that the refractory layer 2 is unlikely to corrode reduces the risk of slag leaking from the vessel to the outside, allowing for safer work.

[0054] (Process 1) The reduction treatment of slag using the slag treatment vessel B (step 1) can be carried out, for example, by the following procedure.

[0055] The slag S contained in the storage tank 10 is heated to a molten state, which is then poured into the slag treatment vessel B. In the reduction treatment of the slag S in the slag treatment vessel B, it is preferable to heat the slag S so that it can be maintained at a temperature of, for example, above 1200°C.

[0056] By controlling the flow and amount of slag S, it is possible to immerse the weir 30 from its lower end to its upper end in the molten slag. The molten slag S can overflow the upper end of the weir 30, pass through the back of the weir 30, and flow downstream. If a thick copper plating layer is formed on the entire surface of the weir 30, the molten slag S will flow more easily.

[0057] When molten slag at about 1100°C to about 1300°C flows into the metal recovery board 20, the copper plating layer 22 melts and becomes a molten Cu layer, forming a metal-absorbing Cu layer.

[0058] While the slag S maintained at a predetermined temperature as described above is flowed into the slag treatment vessel B, a reducing agent A such as carbon monoxide gas (CO) is introduced through the piping 31 of the weir 30 and sprayed from the gas outlet 32. The reducing agent A can be introduced as a reducing gas into the piping 31 of the weir 30 through a gas pipe or the like connected to the outside of the slag treatment vessel B.

[0059] The reducing gas is ejected from the gas ejection port 32 perpendicularly to the copper-plated layer 22 side of the metal recovery plate 20. If the reducing gas is, for example, carbon monoxide gas, the carbon monoxide gas bubbles (also referred to as CO bubbles) ejected from the gas ejection port 32 flow into the gaps between the nail-shaped protrusions 23 along with the molten slag S that flows through the lower end of the metal recovery plate 20. During this process, the ejected carbon monoxide gas bubbles (CO bubbles) come into contact with the slag, which causes a reduction reaction of the slag. As a result, reduced valuable metals (Cu, Sn, Zn, Mo, etc.) are generated on the surface of the CO bubbles.

[0060] The reducing gas bubbles (e.g., CO bubbles) from which valuable metals have been generated collide with the copper plating layer 22 on the surface of the metal recovery board 20. Here, the copper plating layer 22 melts at high temperature to form a metal-absorbing Cu layer, and the valuable metals generated by the reduction treatment are attached to or absorbed by the molten copper plating layer 22 (metal-absorbing Cu layer). This makes it possible (A) to strip and recover the metals attached to the surfaces of the CO bubbles from the CO bubble surfaces under conditions that do not cause the CO bubbles to burst, i.e., inside the slag, and simultaneously (B) to restore the reducing power of the CO bubbles.

[0061] Furthermore, reducing gas bubbles (e.g., CO bubbles) rise to the surface through the gaps between the nail-shaped protrusions 23 carrying molten Cu derived from the molten Cu layer. However, compared to the metal particles and matte particles in the slag that settle and separate to the bottom of the furnace in accordance with Stokes' law, the reduction method of the present invention forcibly presses the molten Cu layer against the metal particles and matte particles in the slag, thereby dramatically shortening the time that the reduced metal is in contact with the molten Cu (metal-absorbed Cu layer). The temperature of the metal-absorbed Cu layer is, for example, 1100°C to 1300°C.

[0062] Reducing gas bubbles can be forced into contact with molten Cu in the slag, and the molten metal film or solid-phase Mo particles adhering to the CO bubble surface can be absorbed into the molten Cu (metal-absorbed Cu layer). The molten Cu (metal-absorbed Cu layer) is initially formed by copper plating a stainless steel or heat-resistant steel structure. However, as Cu is recovered from the slag during the reduction reaction, the molten Cu is continuously replenished. If the CuO content in the molten slag is insufficient, copper oxide ore can be added.

[0063] If the Cu content in the slag is insufficient, molten Cu can be supplied separately from outside the slag treatment vessel B as needed. For example, a ceramic pipe (hereinafter referred to as a molten Cu supply pipe) whose surface is covered with a stainless steel plate or a heat-resistant steel plate can be attached to the slag treatment vessel B, and molten Cu can be supplied to the slag treatment vessel B through this molten Cu supply pipe. The molten Cu supply pipe has multiple holes formed therein for allowing the molten Cu inside the pipe to flow into the slag treatment vessel B. Such a molten Cu supply pipe can be disposed, for example, in a position close to the metal recovery plate 20, spanning the entire width of the metal recovery plate 20. Specifically, the molten Cu supply pipe is preferably disposed in a position where the molten Cu flows from the holes toward the metal recovery plate 20, and more preferably disposed near the top of the metal recovery plate 20. By supplying molten Cu into the vessel through the molten Cu supply pipe as described above, the recovery of metal films or Mo particles can be more efficiently performed.

[0064] If the reducing agent A is, for example, CO bubbles, they move left and right between the nail-shaped protrusions 23, rising along the slope of the metal recovery plate, eventually reaching the top of the molten slag and bursting, releasing a CO-CO2 mixed gas. If the CO bubbles lose their reducing power before bursting and no metal adheres to their surfaces, metal particles will not be scattered. After the CO bubbles burst, the molten slag overflows from the top of the weir and flows downstream. As slag containing CO bubbles rises continuously from the bottom, the slag flows smoothly downstream if the slag temperature is maintained at around 1200°C. The reduced slag S flows into the recovery tank 11.

[0065] The bubble diameter of the reducing agent A used in the reduction process (e.g., CO bubble diameter) is not particularly limited and can be appropriately set depending on the diameter of the gas outlet 32, the depth position, and the CO injection pressure. When the reducing agent A is, for example, CO bubbles, the CO bubble diameter determines the "CO-CO2 ratio" within the bubbles when they burst at the top. This "CO-CO2 ratio" determines the amount of metal film formed on the bubble surface, which in turn determines the amount of fine metal particles scattered when the CO bubbles burst. These fine metal particles become unrecoverable and are lost. Ideally, the CO bubbles lose their reducing power at the top of the metal recovery plate, and no metal is reduced to the CO surface. Achieving this would allow the reducing power of the CO bubbles to be reduced to as close to zero as possible before they reach the slag surface. Therefore, the optimal CO bubble diameter can be determined by conducting multiple experiments. Generally, the smaller the bubble diameter, the more easily reduction proceeds, and the faster the reducing power is lost.

[0066] The reduction process described above allows for efficient recovery of valuable metals. Valuable metals include various metals derived from the slag, such as Cu, Sn, Zn, and Mo. The reduction process described above eliminates the problem of electrical efficiency during Cu electrolysis, since almost no Fe dissolves into the molten copper plating layer 22.

[0067] The basic principle of the reduction treatment using the slag treatment vessel of the present invention (assuming carbon monoxide gas is used here) is as follows: (i) Reduction of oxides of valuable metals (Cu, Sn, Zn, Mo, etc.) in the slag by carbon monoxide gas (CO bubbles); (ii) absorbing valuable metals, specifically, molten metal films of Cu, Sn, and Zn or solid fine particles of Mo, adhering to the surface of the CO bubbles into the molten copper plating layer by contacting the molten copper plating layer with the molten copper plating layer inside the slag under conditions where the CO bubbles cannot burst; (iii) Because CO bubbles burst at the slag-air interface, the reducing power of the CO bubbles must be reduced to as close to zero as possible before they reach the slag surface.

[0068] If CO2 bubbles burst with metals adhering to their surfaces, the reduced metal will scatter as fine particles and become impossible to recover. In contrast, in the present invention, the CO2 bubbles are brought into contact with molten Cu for absorption in the molten slag to prevent them from bursting, allowing the valuable metals adhering to the surfaces of the CO2 bubbles to be efficiently recovered.

[0069] For reference, the characteristics of each metal are summarized below. The metal contents per ton of slag are Cu = 1.75%, Mo = 1.51%, Sn = 0.25%, Pb = 0.29%, and Zn = 3.01%, with Zn being the most abundant metal, followed by Cu. In the Cu-Zn binary phase diagram, the entire range becomes liquid above approximately 1100°C. Therefore, a molten Cu-Zn alloy layer is formed first, and Sn dissolves into it. Mo, being a solid, is absorbed and recovered in a suspended state. Pb may dissolve into the molten Cu-Zn alloy layer, settle as a heterogeneous molten Pb, or evaporate due to its boiling point of 907°C, but its recovery has not been confirmed experimentally. Although Zn has a boiling point of 907°C, it does not evaporate because it combines with Cu to form an alloy. ZnO, with a boiling point of 906°C, is also absorbed by the Fayalite slag and does not evaporate. Similarly, the boiling point of MoO3 is 1155°C, but this is also absorbed in the Fayalite slag and does not evaporate.

[0070] (Process 1´) In step 1, the slag is reduced using reducing agent A as a reducing gas. However, the reduction method of the present invention can further include step 1' in which a reduction reaction of the slag is carried out using a hydrocarbon gas as a reducing agent prior to the reduction reaction with reducing agent A in step 1.

[0071] Examples of hydrocarbon gases include hydrocarbon compounds having three or less carbon atoms, specifically methane gas, ethane gas, and propane gas, with methane gas being preferred.

[0072] If the slag were subjected to an oxidation treatment described below, the FeO in the slag would be converted to Fe2O3 by the oxidation treatment, but the amount of carbon monoxide required to reduce the slag would increase by 50% compared to when the slag was converted to Fe2O3. However, if the slag were pre-reduced with a hydrocarbon gas, this 50% increase could be reduced to about one-third when methane gas is used, and to about one-seventh when propane gas is used. However, because the hydrocarbon gas reduces FeO to Fe, it is preferable to use an amount less than the amount required to convert Fe2O3 to FeO.

[0073] The amount of hydrocarbon gas can be determined based on the Fe2O3 concentration in the molten slag. For example, the Fe2O3 concentration in the molten slag can be measured, and if Fe2O3 is present, an amount of hydrocarbon gas necessary to reduce the Fe2O3 to FeO can be injected through the pipe 31 for introducing the reducing gas. In this case, it is preferable to inject the hydrocarbon gas through the pipe 31 at the bottom (closest to the bottom), and in the subsequent step 1, it is preferable to inject a reducing agent A (e.g., carbon monoxide) through the pipe 31 above. As described above, in one preferred embodiment of the reduction method of the present invention, reduction with reducing agent A is performed after the reduction of Fe2O3 is completed.

[0074] (Slag used in reduction methods) In the reduction method of the present invention, slag containing iron oxide is reduced. Examples of slag containing iron oxide include various slags, and the slag containing iron oxide is preferably copper smelting slag. Copper smelting slag refers to the residue generated during copper smelting, and contains iron oxide such as FeO. Copper oxide can also be added to the slag.

[0075] Specific examples of the copper refining slag include slag generated in copper smelting furnaces such as blast furnaces, electric furnaces, reverberatory furnaces, flash furnaces, and PS converters. Copper refining slag includes, for example, Cu compounds, Si compounds, Ag compounds, Au compounds, Pt compounds, Fe compounds, Mo compounds, Zn compounds, As compounds, Sb compounds, Pb compounds, and Sn compounds.

[0076] Hereinafter, slag containing iron oxide will be abbreviated simply as "slag."

[0077] The slag used in step 1 contains iron oxides such as Fe2O3 and Fe3O4 in addition to FeO etc. When the slag is copper smelting slag, it may contain a large amount of FeO among the iron oxides.

[0078] Copper smelting slag, in particular, contains metal oxides formed by oxidizing metal sulfides, molten matte particles (CuS + FeS), and precious metal particles. These are difficult to reduce with Fe and other substances, and therefore tend to remain in the slag. For this reason, even if the slag is reduced to recover valuable metals from it, the molten matte particles (CuS + FeS) and precious metal particles tend to remain in the slag, making them difficult to recover as valuable metals. For example, in the technology disclosed in Patent Document 1, oxygen is blown onto the slag in step 1 as a pretreatment for "soft reduction," to oxidize the molten matte particles and precious metal particles.

[0079] From this perspective, it is preferable to oxidize the slag before carrying out the reduction treatment. This oxidation treatment converts the molten matte particles (CuS+FeS) and precious metal particles present in the slag into oxides, which allows the valuable metals to be easily recovered by the reduction treatment. In other words, oxidizing the slag in step A is advantageous in that it allows the valuable metals derived from the molten matte particles (CuS+FeS) and precious metal particles to be easily recovered.

[0080] Just to be clear, if the oxidation smelting process of copper concentrate is improved and the generation of magnetite is suppressed, the content of matte particles in the slag will decrease, which will reduce copper loss itself, and there is a possibility that there will be no benefit in oxidizing the slag to recover Cu. Therefore, oxidation treatment is not necessarily required as a pretreatment for reduction treatment. This is because the slag without oxidation treatment is mainly fayalite, so there is no need to add flux.

[0081] 2. Slag oxidation method The method for oxidizing the slag used in the reduction treatment is not particularly limited, and a wide variety of known oxidation treatment methods can be used, such as the oxidation treatment method disclosed in Patent Document 1. In particular, when the slag to be reduced is the copper smelting slag described above, it is preferable to employ "Step A" described below.

[0082] Step A is an oxidation treatment performed in the presence of CaO-Na2O-SiO2-based slag. During the oxidation treatment of copper smelting, 2FeO·SiO2 is converted to 2Fe2O3·SiO2, which increases the melting point and reduces the fluidity of the slag. Therefore, in the technology disclosed in Patent Document 1, in order to improve the fluidity of the 2FeO·SiO2-based flux generated during the oxidation treatment, Na2O and a fluoride-based flux (particularly NaF) are added, and the slag temperature is raised to 1450°C, thereby adjusting the fluidity of the slag to an appropriate range. However, in light of recent environmental standards, it is preferable to avoid the use of fluorine-based fluxes. Therefore, in Step A, oxidation treatment is performed in the presence of CaO-Na2O-SiO2-based slag.

[0083] Such oxidation treatment can lower the melting point of the slag. That is, by performing oxidation treatment in the presence of CaO-Na2O-SiO2 slag, the melting point of the slag during the oxidation reaction is lowered. As a result, even if the oxidation treatment temperature is relatively low, the fluidity of the slag is less likely to increase, and the oxidation treatment can be performed more easily. This means that oxidation treatment in the presence of CaO-Na2O-SiO2 slag can be performed at a lower temperature.

[0084] To perform oxidation treatment in the presence of CaO-Na2O-SiO2-based slag, for example, CaO-Na2O flux may be added to the copper smelting slag to be oxidized. Since SiO2 can be present in copper smelting slag, adding CaO-Na2O flux allows oxidation treatment to be performed in the presence of CaO-Na2O-SiO2-based slag.

[0085] The type of CaO-Na2O flux used in the oxidation treatment is not particularly limited.

[0086] In step A, the content ratios of CaO, Na2O, and SiO2 in the slag can be adjusted as desired within a range that does not increase the melting point of the slag undergoing oxidation treatment. In particular, if the content ratios of CaO, Na2O, and SiO2 in the slag are expressed as Mc (mass%), Mn (mass%), and Ms (mass%), respectively, and Mc:Mn:Ms = 5.2:21.3:73.5, the melting point of the slag undergoing oxidation treatment can be lowered to 1250°C or below. In addition, the Ms value is inevitably determined primarily by the composition of the copper concentrate (the amount of Fe and the amount and composition of gangue), and the amount of flux to be added can be determined based on the measured Ms value and the slag flow rate W (kg / min). CaO addition amount = Ms / 100×W×5.2×73.5 Na2O addition amount = Ms / 100×W×21.3×73.5 As a result, the optimum ratio of slag is Mc:Mn:Ms=5.2:21.3:73.5.

[0087] The method for adding the CaO-NaO flux to the oxidation reaction system is not particularly limited. For example, the entire amount of the CaO-NaO flux can be added all at once to slag heated to a predetermined temperature. Alternatively, the CaO-NaO flux can be added at a predetermined rate. In this case, the rate can be adjusted so that the slag reaches the desired melting point.

[0088] Here, when the ratio of Mc:Mn:Ms is 5.2:21.3:73.5, the addition rate (inflow rate) can be set, for example, as follows: Specifically, when the slag treatment rate is W (kg / min), Inflow rate of SiO2 in slag = W × Ms / 100 (kg / min) It is expressed as:

[0089] When CaO-NaO flux is added to slag to convert it into CaO-NaO-SiO-based slag, the rate of CaO addition to the slag is preferably within "W × Ms / 100 × (5.2 / 73.5) ± 20% (kg / min)", more preferably within "W × Ms / 100 × (5.2 / 73.5) ± 10% (kg / min)", and particularly preferably within "W × Ms / 100 × (5.2 / 73.5) ± 5% (kg / min)".

[0090] When CaO-NaO flux is added to slag to convert it into CaO-NaO-SiO-based slag, the rate of addition of NaO to the slag is preferably within "W × Ms / 100 × (21.3 / 73.5) ± 20% (kg / min)", more preferably within "W × Ms / 100 × (21.3 / 73.5) ± 10% (kg / min)", and particularly preferably within "W × Ms / 100 × (21.3 / 73.5) ± 5% (kg / min)".

[0091] In oxidation treatment using slag converted to a CaO-Na2O-SiO2 system, the melting point of the slag during the oxidation reaction can be lowered to 1250°C or below by setting the addition rate of the CaO-Na2O system flux as described above.

[0092] CaO-Na2O-SiO2 slag with an Mc:Mn:Ms ratio of 5.2:21.3:73.5 has a melting point of approximately 725°C. Therefore, by measuring the mass of SiO2 contained in the slag during oxidation treatment and adding CaO and Na2O to achieve a mass ratio of Mc:Mn:Ms = 5.2:21.3:73.5, it is possible to lower the melting point of SiO2, the main component of gangue, to approximately 725°C.

[0093] In step A, the temperature for the oxidation treatment of the slag can be, for example, 1500°C or lower. In particular, the oxidation method of the present invention can lower the melting point of the slag, and as a result, the temperature can be lower than conventional slag oxidation treatment temperatures. From this perspective, the temperature for the oxidation treatment of the slag is preferably 1400°C or lower, more preferably 1300°C or lower, even more preferably 1250°C or lower, and particularly preferably 1200°C or lower. The temperature for the oxidation treatment of the slag is, for example, 700°C or higher, preferably 800°C or higher, and more preferably 900°C or higher.

[0094] In step A, the time for the oxidation treatment of the slag is not particularly limited and can be set within an appropriate range depending on the temperature.

[0095] From the viewpoint of environmental standards, etc., it is preferable that the oxidation treatment in step A be performed in the absence of fluorides. In this regard, since the present invention uses the above-mentioned CaO-Na2O-based flux, the melting point of the slag can be lowered without using a flux containing fluorides as described in Patent Document 1, for example, and the desired oxide can be easily obtained even in the absence of fluorides.

[0096] In the oxidation treatment of step A, the slag is brought into contact with oxygen. This oxidizes the sulfides in the slag, particularly the copper (I) sulfide (CuS) in the molten matte grains, to copper (I) oxide (CuO). For example, the oxidation treatment of step A can be carried out by sharing oxygen in the container containing the slag.

[0097] The oxidation treatment in step A can be carried out in various reactors, and for example, a wide range of known reactors can be used in the present invention. Among these, the oxidation treatment in step A is preferably carried out in the "slag treatment vessel A" described below.

[0098] Fig. 4 is a schematic explanatory diagram of the oxidation method of the present invention, which is an example of an oxidation method using a slag treatment vessel A. Fig. 4 shows the state in which slag S is filled in the slag vessel.

[0099] As shown in Figure 4, the slag treatment vessel A comprises at least an outer shell 1, a refractory layer 2, and an inner layer 3. The inner layer 3 is in contact with the slag S and is formed to cover the refractory layer 2. The inner layer 3 is formed of a stainless steel plate or a heat-resistant steel plate. For example, the inner layer 3 can be formed of SUS308.

[0100] In the slag treatment vessel A shown in Fig. 4, a heat insulating layer 4 is provided between the refractory layer 2 and the outer shell 1. By providing such a heat insulating layer 4, it is possible to prevent the outer shell 1 from becoming too hot.

[0101] Materials for forming the outer shell 1, the refractory layer 2, the inner layer 3 and the heat insulating layer 4 can be the same as those for forming the slag treatment vessel B described above.

[0102] A lid 5 can be provided at the top opening of the slag treatment vessel A, as shown in FIG. 4, to seal the vessel. Alternatively, a ceiling can be provided at the top opening of the slag treatment vessel A to seal the vessel. In this case, the inner surface of the lid or ceiling may be made of the aforementioned ordinary steel, or it is also preferable that they be made of stainless steel plate or heat-resistant steel plate. In particular, when the atmospheric gas inside the vessel contains SO2, forming the innermost surface of the lid or ceiling of the vessel from stainless steel plate or heat-resistant steel plate instead of ordinary steel makes it easier to prevent the lid or ceiling from being corroded by SO2.

[0103] The embodiment shown in Fig. 4 is an example of a slag treatment vessel equipped with a lid. As shown in Fig. 4, the lid 5 is made of a heat insulating material 4 covered with a steel plate 8. The steel plate 8 may be ordinary steel, or may be a stainless steel plate or a heat-resistant steel plate.

[0104] Even if the top surface of the slag treatment vessel A is not a lid but a ceiling portion integrated with the vessel, the interior of such a ceiling portion may contain a heat insulating material.

[0105] It should be noted that the inner surface of the lid and the inner surface of the ceiling refer to the surfaces facing the inside of the container.

[0106] As described above, the slag treatment vessel A has a refractory layer 2 covered by an inner layer 3, i.e., a stainless steel plate or heat-resistant steel plate. This prevents direct contact between the refractory layer 2 and the slag containing iron oxides such as FeO inside the slag treatment vessel, thereby reducing the risk of slag corrosion. Therefore, even when copper smelting slag is oxidized in the slag treatment vessel A, corrosion of the refractory layer 2 is unlikely to occur. This reduces the frequency of repair work compared to conventional methods, extends the vessel's life, and improves energy savings and work efficiency. Furthermore, while slag containing 2Fe2O3·SiO2 easily corrodes refractory materials, the slag treatment vessel A suppresses this corrosion, thereby reducing the risk of slag leaking from the vessel. Using the slag treatment vessel A allows for safer work.

[0107] The slag treatment vessel A can be similar in configuration to known slag treatment vessels, as long as it has at least an outer shell 1, a refractory layer 2, and an inner layer 3. For example, as shown in Fig. 4, an introduction pipe 9a for introducing the raw material slag into the vessel and an introduction pipe 9b for introducing CaO-NaO-based flux into the vessel can be provided. Stainless steel pipes can be used for both the introduction pipe 9a for introducing the slag and the introduction pipe 9b for introducing the flux.

[0108] Furthermore, the slag treatment vessel A can be provided with an air supply pipe 6 for introducing gas (air or oxygen) into the vessel. One end of the air supply pipe 6 is formed with a gas storage tank 6a for storing gas, and the gas storage tank is located, for example, at the bottom of the vessel. A portion of the surface of the gas storage tank is formed with a number of through-holes, and the gas introduced through the air supply pipe 6 can be released from the multiple outlets 6b into the vessel space (or the filled slag S). Therefore, for example, oxygen-rich air can be supplied to the vessel interior through the air supply pipe 6, allowing the slag to be oxidized. A stainless steel pipe can be used for the air supply pipe 6.

[0109] During the oxidation process, an exothermic reaction occurs in which the FeO in the fayalite is oxidized to Fe2O3, causing the slag temperature to rise. Therefore, the refractory layer 2 of the slag treatment vessel A can be omitted downstream of the oxygen injection point, or copper scrap or copper oxide can be added as a coolant throughout the entire process.

[0110] As shown in Figure 4, the slag treatment vessel A can be equipped with a stirring means 10. The stirring means 10 is, for example, composed of a stirring rod with a stirring blade at its tip, and the rotation of the stirring blade applies shear to the slag S in the vessel. This makes it possible to promote the oxidation reaction of the slag and suppress a decrease in fluidity. Stainless steel pipes can be used for both the exhaust pipe 7 and the slag discharge pipe 11. The stirring means 10 can be made of a stainless steel material.

[0111] In addition, the slag treatment vessel A shown in Figure 4 can be equipped with an exhaust pipe 7, a slag discharge pipe 11, etc. The exhaust pipe 7 allows the gas introduced into the vessel to be discharged, and the slag discharge pipe 11 allows the oxidized slag to be recovered. Valuable metals can be recovered from the oxidized slag by, for example, a known reduction treatment. Stainless steel pipes can be used for both the exhaust pipe 7 and the slag discharge pipe 11.

[0112] The slag treatment vessel A may be installed alone or in parallel with a furnace (called a flash smelting furnace) in which copper smelting, the process for obtaining slag, is performed. The slag treatment vessel A may also be installed in parallel with a slag treatment vessel B for reduction treatment. For example, the flash smelting furnace, slag treatment vessel A, and slag treatment vessel B may be installed in parallel in this order. The flash smelting furnace and slag treatment vessel A may be connected, and similarly, the slag treatment vessel A and slag treatment vessel B may be connected.

[0113] Therefore, the slag oxidized in step A can be supplied to the reduction step, step 1 or (step 1'), and valuable metals can be recovered thereby.

[0114] The shape of the slag treatment vessel A is not particularly limited and can be formed into various container shapes, trough shapes, tubular shapes, etc. For example, the slag treatment vessel A may be a trough connecting the flash smelting furnace and the reduction furnace. In this case, when it becomes necessary to replace the trough (slag treatment vessel A), the replacement work becomes simple, and for example, it becomes possible to hot switch from the slag treatment vessel A to be replaced to a new slag treatment vessel A using a switching valve in the trough.

[0115] The present invention encompasses a method comprising step A (oxidation treatment), step 1' (reduction of slag with a hydrocarbon gas), and step 1 (reduction of the slag reduced with a hydrocarbon gas with a reducing agent A). Such a method comprises steps A, 1', and 1 in this order, and some or all of these steps may be performed continuously. [Explanation of symbols]

[0116] A Inside the slag treatment vessel 1 outer shell 2 Refractory layer 3 Inner layer 20 Metal Recovery Board 22 Copper plating layer 23 Nail process 30 Weir 32 Gas outlet

Claims

1. The method includes a step 1 of reducing slag containing iron oxide with a reducing agent A in a slag treatment vessel, the reducing agent A is at least one selected from the group consisting of carbon monoxide gas and hydrogen gas, The slag treatment vessel comprises: The furnace comprises at least an outer shell, a refractory layer, and an inner layer; the inner layer is a layer that comes into contact with the slag and is formed to cover the refractory layer, the inner layer is formed of a stainless steel plate or a heat-resistant steel plate, A metal recovery plate is disposed within the slag treatment vessel, The metal recovery disk has nail-shaped protrusions formed on its surface, a copper plating layer is formed on the metal recovery disk and the nail-shaped protrusions; The method for reducing slag comprises recovering the metal produced by the reduction reaction by allowing it to be absorbed into the copper plating layer.

2. a dam is provided opposite to a surface of the metal recovery board on the nail-shaped protrusion side; the weir is formed of a stainless steel plate or a heat-resistant steel plate, 2. The method for reducing slag according to claim 1, wherein a plurality of gas outlets are provided on the surface of the weir facing the nail-shaped protrusions.

3. 3. The slag reduction method according to claim 2, wherein the reducing agent A is ejected from the gas ejection port of the weir and flows into the spaces between the nail-shaped projections, thereby causing the metal produced by the reduction reaction to be absorbed into the copper plating layer.

4. 3. The method for reducing slag according to claim 1, further comprising a step 1' of carrying out a reduction reaction of the slag using a hydrocarbon gas as a reducing agent prior to the reduction reaction with the reducing agent A in the step 1.

5. The outer shell is made of ordinary steel, 3. The method for reducing slag according to claim 1, wherein a heat insulating layer is provided between the outer shell and the refractory layer.

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