Reduction furnace, and reduction method

Abstract

To a reduction furnace and a reduction method which can suppress energy cost, suppresses a fluorine ion elution amount to an environmental regulation value or less, and can suppress occurrence of waste slag in copper refining.SOLUTION: A reduction furnace of a molten slag has a strong insulation structure in which outer shell is formed of a steel plate, and an insulation refractory is constructed in its inside, where a highly corrosion-resistant refractory which is difficult to be corroded by molten iron and iron oxide-containing slag is constructed inside the strong insulation structure, wherein a stainless-based steel plate or a heat-resistant steel plate is stuck to the surface of the highly corrosion-resistant refractory brought into contact with the molten slag, the molten iron is held in the reduction furnace, molten slag is made to flow on the molten iron and thereby reduces iron oxide in the molten slag by C in the molten iron, and the obtained Fe is absorbed in the molten iron, and is recovered as the molten iron.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a reduction furnace and a reduction method. [Background technology]

[0002] In recent years, the copper grade in raw ore has been declining in copper smelting, making it increasingly important to reduce copper loss (slag loss) caused by metallic copper dissolving and contaminating the slag. The concentration of harmful elements such as As, Pb, Zn, and Sb in slag is also a problem. Against this background, various inventions related to slag purification technologies and the reduction of metallic copper slag loss have been disclosed by copper smelting companies.

[0003] Patent Document 1 discloses a method for recovering valuable metals from granulated slag generated during copper smelting by subjecting the granulated slag to (1) remelting, (2) an oxidation treatment in which a flux is added to the slag to oxidize the sulfides in the slag, (3) a soft reduction treatment in which oxides in the slag other than FeO are reduced with molten Cu-Fe and recovered as metals, and (4) a hard reduction treatment in which the FeO remaining in the slag after the soft reduction is reduced and recovered as carbon-saturated molten iron (hereinafter also referred to as "molten iron"). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6516264 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the method described in Patent Document 1 is an excellent method, no consideration has been given to the effective use of the slag after valuable metals have been recovered.

[0006] Furthermore, Patent Document 1 defines "soft reduction" as a method for reducing and recovering metal oxides in slag that are more easily reduced than FeO, and "hard reduction" as a reduction method in which FeO remaining in the slag after "soft reduction" is reduced by C in the molten iron to form Fe, which is then absorbed into the molten iron and recovered. However, the "hard reduction" method can generally be used as a method for recovering Fe from slag containing iron oxide.

[0007] Furthermore, the method described in Patent Document 1 has not been put into practice because the energy cost of remelting the 3 million tons of granulated slag produced annually would be enormous, exceeding 20 billion yen.

[0008] Furthermore, a detailed study of each technology revealed that there were problems with the implementation of each of the above-mentioned oxidation, soft reduction, and hard reduction processes. Therefore, technological development was carried out for the practical application of each process.

[0009] As a result of extensive research, the present inventors have found that further technological development is necessary to put the above-mentioned soft reduction treatment and hard reduction treatment into practical use, and have made improvements to each of them. As a result, in the present invention, they have discovered a reduction furnace and reduction method that can reduce energy costs in the hard reduction treatment and convert them into profits, resolve the issue of complying with environmental regulations on the amount of fluoride ion elution, and further reduce the generation of waste slag in copper smelting, and have completed the present invention.

[0010] In view of the above circumstances, an object of the present invention is to provide a reducing furnace and a reduction method that can reduce energy costs, suppress the amount of fluorine ion elution to be equal to or less than the environmental regulation value, and suppress the generation of waste slag in copper smelting. [Means for solving the problem]

[0011] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by a reducing furnace for molten slag having a highly insulating structure in which an outer shell is formed of steel plate and an insulating refractory is applied to the inside of the highly insulating structure, and a highly corrosion-resistant refractory that is resistant to erosion by molten pig iron and slag containing iron oxide is applied to the inside of the highly insulating structure, in which a stainless steel plate or a heat-resistant steel plate is attached to the surface of the highly corrosion-resistant refractory that comes into contact with the molten slag, and molten pig iron is held in the reducing furnace. By flowing molten slag over the molten pig iron, the iron oxide in the molten slag is reduced by the C in the molten pig iron, and the resulting Fe is absorbed into the molten pig iron and recovered as the molten pig iron, and have thus completed the present invention.

[0012] That is, the present invention relates to the following reduction furnace and reduction method. 1. The outer shell is made of steel plates, and the inside is lined with insulating refractories, providing a highly insulating structure. A molten slag reducing furnace in which a highly corrosion-resistant refractory material that is resistant to corrosion by molten iron and iron oxide-containing slag is installed inside the highly insulating structure, A stainless steel plate or a heat-resistant steel plate is attached to the surface of the highly corrosion-resistant refractory material that comes into contact with the molten slag, A molten slag reduction furnace characterized by holding molten pig iron in the reduction furnace and pouring molten slag onto the molten pig iron, whereby iron oxide in the molten slag is reduced by the C in the molten pig iron, and the resulting Fe is absorbed into the molten pig iron and recovered as the molten pig iron. 2. A reducing furnace according to Item 1, wherein the reducing furnace has a molten pig iron outlet in a layer of the molten pig iron held in the reducing furnace, the molten pig iron flowing out from the reducing furnace is stored in a molten pig iron storage tank installed outside the reducing furnace, and the molten pig iron overflows from the height of the molten pig iron surface level in the reducing furnace, and the molten pig iron surface level in the reducing furnace is maintained at a desired height by the siphon principle. 3. The surface area of ​​the molten iron in the reduction furnace is defined as s (cm 2 ), and the density of the molten slag to be charged is ρ (g / cm 3), the weight of the molten slag to be charged is m (g), and the calculated slag depth in the reduction furnace is h (cm), the following formula (1) is used: Formula h=m / (ρs)(cm) (1) and the surface area s (cm 2 Item 3. The reducing furnace according to Item 1 or 2, wherein 60% to 80% of the total cross-sectional area is in the front section and 20% to 40% is in the rear section, the ceiling height of the front section is (3h + α) (cm) from the surface level of the molten pig iron, the ceiling height of the rear section is (0.7h + α) (cm) from the surface level of the molten pig iron, and α is a margin. 4. The reduction furnace according to Item 3, wherein a three-phase AC electric heating device is provided in a region of the rear stage adjacent to the front stage. 5. The reduction furnace according to Item 4, wherein the rear region has a three-phase AC electric heating device and a KR agitator in the vicinity of the three-phase AC electric heating device. 6. The reducing furnace according to Item 4, wherein a hot exchange device for graphite electrodes and agitating blades of the KR agitator is installed outside the furnace in the latter stage region of the reducing furnace, and hot exchange is performed under conditions that do not allow CO leakage. 7. A method for reducing molten slag using a reducing furnace according to any one of items 1 to 6, The molten slag is poured onto the hot metal, whereby iron oxide in the molten slag is reduced by the C in the hot metal, the C in the hot metal that is consumed is continuously added, and the resulting Fe is absorbed into the hot metal and recovered as the hot metal. This is a reduction method characterized by the following. 8. A reduction method according to Item 7, wherein the iron oxide in the molten slag is recovered as molten pig iron, and then Si and Mn satisfying the specifications for foundry pig iron are dissolved to produce foundry pig iron having a Cu content of 0.6 mass% or less. 9. The reduction method according to item 7 or 8, wherein the slag after the reduction treatment, in which the FeO content is 4% by mass or less, is returned to the oxidation smelting furnace for copper concentrate and used as an absorbent for FeO. 10. The reduction method according to any one of items 7 to 9, wherein the slag after reduction treatment, in which the FeO content is 4 mass% or less, is used as a slag foaming agent in submerged arc operation of an electric furnace for steel making. 11. The reduction method according to any one of items 7 to 10, wherein NaO and CaO are dissolved in the slag remaining after reduction treatment in which the FeO content is 4 mass% or less, and the resulting slag is used as a hot metal desulfurization agent in steelmaking refining. 12. The reduction method according to any one of Items 7 to 11, wherein the content of the FeO remaining in the slag after reduction treatment is 4% by mass or less, and the FeO is completely removed by adding aluminum or Si to the slag, and the slag is used as a cover slag for molten steel in steelmaking refining. [Effects of the Invention]

[0013] The reduction furnace of the present invention can reduce energy costs, suppress the amount of fluorine ion elution to below the environmental regulation value, and suppress the generation of waste slag in copper smelting. Furthermore, by reducing copper smelting slag using the reduction method of the present invention, it is possible to reduce energy costs, suppress the amount of fluorine ion elution to below the environmental regulation value, and suppress the generation of waste slag in copper smelting. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of an entire reducing furnace according to the present invention. [Figure 2] FIG. 1 is a schematic plan view of the entire reducing furnace of the present invention. [Figure 3] FIG. 1 shows a layout diagram of graphite electrodes and hot exchange equipment for KR stirring blades in a reduction furnace of the present invention. [Figure 4] FIG. 4 is a cross-sectional schematic view (viewed from the direction AA in FIG. 3) of a swing tower for replacing a graphite electrode in a reduction furnace of the present invention. [Figure 5] FIG. 4 is a cross-sectional schematic view (viewed from the direction BB in FIG. 3) of a swing tower for replacing stirring blades in a reducing furnace of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] The following description of the components may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0017] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. Furthermore, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the upper and lower limits.

[0018] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "include," "consist essentially of," and "consist only of."

[0019] In this specification, "A and / or B" and "at least one of A and B" mean either one of A and B, or both A and B.

[0020] 1. Reduction furnace The reducing furnace of the present invention is a furnace for reducing molten slag, characterized in that it has a highly insulated outer shell made of steel plates and an insulating refractory lined inside the shell, and a highly corrosion-resistant refractory lined inside the highly insulating structure that is resistant to corrosion by molten pig iron and iron oxide-containing slag, and a stainless steel plate or a heat-resistant steel plate is attached to the surface of the highly corrosion-resistant refractory that comes into contact with the molten slag. The furnace holds molten pig iron, and the molten slag is poured over the molten pig iron to reduce the iron oxide in the molten slag with the carbon in the molten pig iron, and the resulting iron is absorbed into the molten pig iron and recovered as the molten pig iron. Because the reducing furnace of the present invention has the above features, it is possible to reduce energy costs, suppress the amount of fluorine ion elution to below the environmental regulation value, and suppress the generation of waste slag in copper smelting.

[0021] The present invention provides a new technology related to the hard reduction process in the invention described in Japanese Patent No. 6516264.

[0022] In the present invention, the slag to be treated is not granulated slag, but molten slag that is mainly generated in oxidation smelting furnaces for copper concentrate (hereinafter, flash slag may be referred to as "flash furnace slag" to refer to flash furnace slag as a representative example), which makes it possible to reduce the melting costs by more than 20 billion yen, or even to zero.

[0023] Furthermore, the present invention differs from the invention described in Japanese Patent No. 6,516,264 in that a flux containing fluorine ions is not used as a flux added to maintain the fluidity of the slag in all steps of treating the above-mentioned "flash furnace slag."

[0024] Furthermore, in the present invention, when a flux is added, it is preferable to add a flux that does not contain fluorine ions in a step prior to hard reduction, but it may also be added in the reduction furnace (hard reduction furnace) of the present invention.

[0025] The reducing furnace of the present invention will be described below with reference to the drawings.

[0026] FIG. 1 shows a schematic cross-sectional view of the entire reducing furnace of the present invention, and FIG. 2 shows a schematic plan view of the entire reducing furnace of the present invention.

[0027] In Fig. 1, the reducing furnace of the present invention has a highly insulated structure in which an outer shell is formed of steel plates and an insulating refractory is installed inside the shell. Furthermore, in the reducing furnace of the present invention, a highly corrosion-resistant refractory that is resistant to corrosion by molten pig iron and iron oxide-containing slag is installed inside the highly insulated structure. Furthermore, in Fig. 1, the reducing furnace of the present invention has a stainless steel plate or a heat-resistant steel plate attached to the surface of the highly corrosion-resistant refractory that comes into contact with the molten slag. Furthermore, in Fig. 1, the reducing furnace of the present invention holds molten pig iron in the reducing furnace, and by flowing molten slag over the molten pig iron, the iron oxide in the molten slag is reduced by the C in the molten pig iron, and the resulting Fe is absorbed into the molten pig iron and can be recovered as molten pig iron.

[0028] 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.

[0029] 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.

[0030] FIG. 1 describes the use of a stainless steel plate or a heat-resistant steel plate, and more specifically, for example, SUS308 can be used.

[0031] The temperature of the molten iron held in the reduction furnace is not particularly limited, and is preferably 1150°C to 1400°C, more preferably 1200°C to 1300°C, and even more preferably 1240°C to 1270°C. When the molten iron temperature is within the above range, iron oxide in the molten slag can be more easily reduced by the C in the molten iron, and the resulting Fe can be absorbed into the molten iron and easily recovered as molten iron.

[0032] The "reduction" in the present invention refers to the reduction of iron oxide in the molten slag with C in the molten pig iron in order to more efficiently recover the Fe component contained in the copper refining slag. The reduction in the present invention can be carried out, for example, by bringing molten slag such as copper refining slag into contact with liquid metal and / or alloy, such as an Fe-C alloy.

[0033] In the present invention, the treatment of molten slag is basically carried out based on the method described in Japanese Patent No. 6516264. That is, oxygen is blown onto the molten slag to convert all sulfides and metal particles in the slag into oxides. Next, metal oxides that are more easily reduced than FeO are reduced from the molten slag. In this specification, this reduction is sometimes referred to as "soft reduction." In soft reduction, a reducing agent that cannot reduce FeO is used, and FeO is left in the molten slag.

[0034] The molten slag after the soft reduction is an FeO-SiO2-based molten slag. In the present invention, Fe can be recovered from the molten slag by reduction. In this specification, the reduction is sometimes referred to as "hard reduction." In hard reduction, the reducing agent is C contained in carbon-saturated Fe-C molten iron. The recovered Fe is also recovered as carbon-saturated Fe-C molten iron.

[0035] For the above reasons, in this specification, "soft reduction" means weak reduction, and "hard reduction" means strong reduction. The difference between soft reduction and hard reduction is whether FeO remains in the molten slag after reduction. In soft reduction, FeO remains in the molten slag, while in hard reduction, only 4 wt% or less of FeO remains. The reducing furnace and reduction method of the present invention are related to the above hard reduction.

[0036] In the present invention, the molten slag is preferably copper refining slag, and is not particularly limited as long as it is slag generated in a copper smelting furnace such as a blast furnace, electric furnace, reverberatory furnace, or flash furnace. Copper refining slag contains, for example, Cu compounds, Si compounds, Al compounds, Mg compounds, Ag compounds, Au compounds, Pt compounds, Fe compounds, Mo compounds, Zn compounds, As compounds, Sb compounds, Pb compounds, or Sn compounds. It is preferable that two or more of these compounds are contained in the copper refining slag.

[0037] In the present invention, the molten slag preferably contains FeO. Normally, molten slag may contain FeO, Fe2O3, and Fe3O4 as iron oxides, but molten slag that has undergone soft reduction contains FeO. Therefore, in the present invention, the molten slag preferably contains FeO.

[0038] From the viewpoint of further improving the safety of furnace repairs, the reducing furnace of the present invention preferably has an outlet through which CO and nitrogen are blown in from one direction inside the reducing furnace and discharged from the opposite direction during furnace repairs, as shown in FIG.

[0039] The reducing furnace of the present invention preferably has a sealed structure that prevents CO from leaking outside the furnace and has a CO outlet in the space within the reducing furnace for recovering CO using a CO recovery device. The reducing furnace of the present invention is preferably designed with measures against CO. Because a large amount of CO is generated in the reducing furnace when FeO is reduced with C, the furnace has a sealed structure to prevent CO from leaking outside the furnace. A CO outlet is provided in the space within the reducing furnace so that the large amount of CO generated can be recovered and reused using a recovery device. Furthermore, for safety reasons, when repairing a reducing furnace, it is necessary to completely remove CO from the furnace. To this end, CO2 or nitrogen is blown into the furnace and discharged, and the CO is completely combusted at the tip of the CO discharge port and released into the atmosphere. To this end, an atmosphere replacement device is preferably provided that blows CO2 or nitrogen into the reducing furnace from one side and discharges it from the other side.

[0040] The reducing furnace of the present invention preferably has a structure in which the layer of molten pig iron held therein has a molten pig iron outlet, the molten pig iron flowing out of the reducing furnace is stored in a molten pig iron storage tank installed outside the reducing furnace, and the molten pig iron overflows from the height of the molten pig iron surface in the reducing furnace. By having such a structure in the reducing furnace of the present invention, the molten pig iron surface level in the reducing furnace can be maintained at a desired height by the siphon principle.

[0041] In the reducing furnace of the present invention, the surface of the highly corrosion-resistant refractory that comes into contact with the molten slag inside is covered with a stainless steel plate or a heat-resistant steel plate to prevent the highly corrosion-resistant refractory from being corroded by the slag with a high FeO content. However, the stainless steel plate or the heat-resistant steel plate melts when it comes into contact with the molten pig iron. Therefore, it is preferable that the level of the molten pig iron in the reducing furnace be constant. To this end, a molten pig iron outlet is provided in the molten pig iron layer in the reducing furnace of the present invention, a molten pig iron storage tank is installed outside the reducing furnace for temporarily storing the molten pig iron, and the molten pig iron that flows out of the reducing furnace overflows from the molten pig iron storage tank into the ladle. This structure allows the molten pig iron level in the reducing furnace to be kept constant by the siphon principle.

[0042] In the reducing furnace of the present invention, the location where the consumable carbon powder is added is preferably located in the upstream region of the reducing furnace where the reaction of FeO + C = Fe + CO has progressed to a certain extent, and the carbon powder is supplied by being pushed into the molten iron. As a result of this supply, the carbon powder dissolves in the molten iron, but the remaining carbon powder floats to the slag-molten iron interface and can contribute to the reaction of FeO + C = Fe + CO.

[0043] The reduction furnace of the present invention preferably has a surface area of ​​s (cm 2 ), and the density of the charged molten slag is ρ (g / cm 3 ), the weight of the molten slag to be charged is m (g), and the calculated slag depth in the reduction furnace is h (cm), the following formula (1) is used Formula h=m / (ρs)(cm) (1) Meet the following.

[0044] The reducing furnace of the present invention is more preferably configured such that the surface area s (cm 2 When 60 to 80%, preferably 80%, of the total length is the front section and 20% to 40%, preferably 20%, is the rear section, the ceiling height of the front section is (3h + α) (cm) from the surface level of the molten iron, the ceiling height of the rear section is (0.7h + α) (cm) from the surface level of the molten iron, and the cross-sectional shape is determined by the dimensions determined as α being a margin.

[0045] That is, in the cross-sectional shape of the reducing furnace of the present invention, the ceiling height of the region in the front stage where the reaction rate of FeO + C = Fe + CO is fast is made high, and the ceiling height of the region in which the reaction rate of FeO + C = Fe + CO is slow is made low. Specifically, the surface area of ​​the molten iron in the reducing furnace is set to s (cm 2 ), and the density of the charged molten slag is ρ (g / cm 3 ), the weight of the molten slag charged is m (g), and the calculated slag depth in the hard reduction furnace is h (cm), the following relationship holds: h=m / (ρs)(cm)

[0046] For this reason, the ceiling height of the front-stage region where the reaction rate is fast is set to (3h + α) (cm) from the surface level of the molten iron, and the ceiling height of the rear-stage region where the reaction rate is slower is set to (0.7h + α) (cm) from the surface level of the molten iron. Note that α is a margin and is not particularly limited and may be set appropriately.

[0047] In the upstream region of the reducing furnace of the present invention, the reaction FeO + C = Fe + CO occurs only at the slag-hot metal interface. Because of the large density difference, the molten slag does not penetrate into the hot metal. Therefore, for this reaction to proceed, FeO in the slag must be supplied to the hot metal surface; in other words, the slag layer must be vigorously stirred. The reaction rate rapidly decreases once the FeO concentration in the slag reaches approximately 10%. This is because the amount of CO generated decreases, weakening the stirring of the slag layer. As a result, the amount of FeO supplied to the hot metal surface decreases, further reducing the amount of CO generated.

[0048] In the upstream region of the reducing furnace of the present invention, a large amount of CO is generated and retained in the slag, causing the apparent volume of the slag to expand by approximately three times. As the reaction progresses and the FeO content in the slag decreases to approximately 10%, approximately 45% of the FeO, which was approximately 55%, is released from the slag as molten iron, resulting in a reduction in volume of approximately 45%. Since CO bubbles are retained there, the slag volume decreases to approximately 0.7 of its original volume. Therefore, it is preferable that the reducing furnace of the present invention have a cross-sectional shape with a variable ceiling height as described above.

[0049] The reducing furnace of the present invention preferably has a structure in which a three-phase AC electric heating device is provided in a region of the rear stage region that is close to the front stage.

[0050] In the reduction furnace of the present invention, the internal reaction is endothermic, so the molten iron must be heated. The molten iron temperature is preferably controlled to the minimum required temperature, taking into account the temperature drop that occurs after recovery, when Si and Mn are added to satisfy the specifications for cast iron. For this reason, three-phase AC electric heating is preferred, and in order to shorten the graphite electrodes, they are preferably installed in the latter region where the FeO concentration decreases to less than 10%. Because the graphite electrodes are in a CO atmosphere, they are hardly consumed, but it is preferable to provide hot exchange equipment to prepare for unexpected accidents such as electrode breakage.

[0051] The reduction furnace of the present invention may have a three-phase AC electric heating device in the latter stage region, and may have a KR agitator in the vicinity of the three-phase AC electric heating device.

[0052] In the reduction furnace of the present invention, the reduction reaction is preferably promoted by entraining slag in the molten iron in the latter region where the FeO concentration is less than 10%. In the reduction furnace of the present invention, the FeO content in the slag is preferably low, but 4% by mass or less is within the acceptable range. Therefore, it is preferable to install a mechanical stirrer in this region. A KR (Kannbara Reactor) stirrer is preferred as the mechanical stirrer. The stirring blades at the tip of the KR stirrer are made of graphite-based refractories and wear out due to contact with the molten slag. Therefore, a stirring blade is attached to the tip of the spindle that transmits the rotational force, and equipment is required to periodically replace the blades while hot, while suppressing CO leakage.

[0053] In the reducing furnace of the present invention, it is preferable to first determine the space of the rear-stage region where the KR agitator and three-phase AC electric heating device are installed. Next, the area of ​​the front-stage region is determined, and the rear-stage region and the front-stage region are connected. The area of ​​the front-stage region is an important factor that accounts for a major part of the reduction reaction rate of the entire reducing furnace of the present invention, and it is preferable to set it to about 3 to 5 times the area of ​​the rear stage. The area ratio can be determined in detail by confirming the reaction rate through a medium-scale experiment.

[0054] In the reduction furnace of the present invention, it is preferable to install a hot exchange device consisting of graphite electrodes and stirring blades of a KR stirrer outside the furnace in the latter stage region, and perform hot exchange under conditions that do not allow CO to leak.

[0055] Fig. 3 shows a layout diagram of a hot exchange equipment for graphite electrodes and KR stirring blades in a reduction furnace of the present invention. Fig. 3 shows a swing tower system as an example of the hot exchange equipment.

[0056] FIG. 4 is a cross-sectional schematic diagram of a swing tower for replacing graphite electrodes in a reducing furnace of the present invention (as viewed from the direction AA in FIG. 3), and FIG. 5 is a cross-sectional schematic diagram of a swing tower for replacing stirring blades (as viewed from the direction BB in FIG. 3).

[0057] Although not shown, the reduction furnace of the present invention may be equipped with a hot on-off valve below the upper chambers 1 and 2, which are the hot exchange equipment shown in FIG. 2. The hot on-off valve is a stainless steel plate that moves horizontally. During operation, the opening of the stainless steel plate is located below the upper chamber, and a graphite electrode and a spindle of a KR agitator are inserted into the hole. During hot exchange, the graphite electrode and the spindle of the KR agitator are withdrawn upward, and then the stainless steel plate moves horizontally, and the part without the hole is located below the upper chamber, blocking the opening. The stainless steel plate is fixed by pushing in an electric cotter (wedge). In this way, hot exchange is performed while maintaining conditions that prevent CO leakage. CO in the upper chamber can be burned at the outlet by introducing an atmosphere replacement gas and dissipating it into the atmosphere.

[0058] The reducing furnace of the present invention described above can reduce copper refining slag and reduce energy costs. Furthermore, it is not necessary to use a flux containing fluorine ions, and the amount of fluorine ion elution can be kept below the environmental regulation value, and the generation of waste slag in copper smelting can be reduced. The reducing furnace of the present invention can generate profits that far exceed the processing costs of "flash furnace slag," resolve the problem of the environmental regulation value for the amount of fluorine ion elution, and further reduce the amount of waste "flash furnace slag" to zero.

[0059] 2. Redemption method The reduction method of the present invention is a method for reducing molten slag using the reducing furnace of the present invention, characterized in that the molten slag is poured onto hot metal, iron oxide in the molten slag is reduced by the C in the hot metal, the C in the hot metal that is consumed is continuously added, and the resulting Fe is absorbed into the hot metal and recovered as the hot metal. The reduction method of the present invention can reduce energy costs, suppress the amount of fluorine ion elution to below the environmental regulation value, and suppress the generation of waste slag in copper smelting.

[0060] In the reduction method of the present invention, molten slag is poured onto molten pig iron in a reduction furnace, as shown in Figure 2. This allows iron oxide in the molten slag to be reduced by the C in the molten pig iron, and the resulting Fe is absorbed into the molten pig iron and recovered as molten pig iron.

[0061] The reduction method of the present invention may further include a step of producing foundry pig iron having a Cu content of 0.6 mass% or less by recovering iron oxide from the molten slag as molten pig iron and then dissolving Si and Mn that satisfy the specifications for foundry pig iron. By including this step, industrially useful foundry pig iron can be produced.

[0062] By dissolving Si and Mn in the molten iron recovered by the reduction method of the present invention in amounts that satisfy the specifications for foundry pig iron, it is possible to commercialize the product as foundry pig iron in which the Cu content is allowed to be 0.6 mass% or less, thereby achieving a significant improvement in profitability.

[0063] In the reduction method of the present invention, it is preferable to return the slag after the reduction treatment, in which the FeO content is 4 mass% or less, to the oxidation smelting furnace for the copper concentrate and use it as an absorbent for FeO. By having the above-mentioned configuration of the reduction method of the present invention, the slag after the reduction treatment can be reused without waste.

[0064] By using the reduction method of the present invention, a portion of the slag after reduction treatment is returned to the oxidation smelting furnace for copper concentrate without treating the 4 mass% or less of FeO remaining in the slag, and is recycled and used as an absorbent for the FeO generated there, thereby reducing the amount of slag equivalent to the amount of silica sand currently added.

[0065] While 4% by mass or less of FeO remains in the slag after the reduction treatment, the slag before the reduction treatment can dissolve more than 50% by mass of FeO. Therefore, if the slag after the reduction treatment is used instead of the silica sand added as an absorbent for the FeO generated in the oxidation smelting of copper concentrate, the slag simply circulates within the copper smelting system, thereby suppressing the generation of excess slag.

[0066] In the reduction method of the present invention, it is preferable to use the slag after reduction treatment, in which the FeO content is 4 mass% or less, as a slag foaming agent in submerged arc operation of an electric furnace for steel making. By having the above-mentioned configuration of the reduction method of the present invention, the slag after reduction treatment can be reused without waste.

[0067] When 4% by mass or less of FeO remaining in the slag after reduction treatment by the reduction method of the present invention is not treated and is used as a slag foaming agent in electric furnace smelting in the steel industry, the atmosphere inside the electric furnace is reducing, so even if 4% by mass or less of FeO remains, it is immediately reduced to Fe and no problem occurs.

[0068] In the reduction method of the present invention, it is preferable to dissolve NaO and CaO in the slag after reduction treatment, which contains 4 mass% or less of FeO, and use the slag as a desulfurization agent in steelmaking. By having the above-mentioned configuration of the reduction method of the present invention, the slag after reduction treatment can be reused without waste.

[0069] If the 4% or less by mass of FeO remaining in the slag after reduction by the reduction method of the present invention is not treated, and NaO and CaO are dissolved and used as a hot metal desulfurization agent in steelmaking, the 4% or less by mass of FeO remaining in the hot metal desulfurization agent will be reduced and eliminated by C and Si in the hot metal. Reduction by Si generates SiO, which may result in a loss of basic components in the hot metal desulfurization agent. However, considering the cost and additional processing steps of removing FeO by adding aluminum ash, it is preferable to leave the FeO as it is. It goes without saying that FeO may also be removed by adding aluminum ash or aluminum dross.

[0070] In the reduction method of the present invention, the content of FeO remaining in the slag after reduction is 4 mass% or less, and it is preferable that the FeO is completely removed by adding aluminum or Si and the slag is used as cover slag for molten steel in steelmaking. By having the above-mentioned configuration of the reduction method of the present invention, the slag after reduction can be reused without waste.

[0071] In the reduction method of the present invention, slag that has 4 mass% or less of FeO remaining in the slag after reduction treatment can be completely removed by adding aluminum ash, aluminum dross, or Si, and the resulting slag can be used as cover slag for molten steel in steelmaking refining.

[0072] In the steel industry, molten steel is received in a ladle after refining. While the molten steel is held in the ladle, some of it passes through a secondary smelting process before finally solidifying through continuous casting. During this process, an insulating material is required on the surface of the molten steel in the ladle to prevent heat dissipation. Typically, slag from the smelting process flows into the ladle and is used as an insulating material. However, refining slag often contains iron oxide, which contaminates the molten steel. Furthermore, when the surface of the molten steel in a continuous casting tundish comes into contact with air, it is contaminated by atmospheric oxygen. Cover slag is used to suppress this contamination, preventing heat dissipation and preventing oxygen contamination of the molten steel. Therefore, when the slag after reduction by the reduction method of the present invention is used as a cover slag for molten steel, it is preferable to completely remove FeO.

[0073] According to the reduction method of the present invention described above, copper refining slag can be reduced, energy costs can be reduced, and the amount of fluorine ions eluted can be kept below the environmental regulation value without using a flux containing fluorine ions, and the generation of waste slag in copper smelting can be reduced. [Industrial Applicability]

[0074] The reduction furnace and the reduction method of the present invention can be suitably used in the refining of non-ferrous metals, such as copper smelting.

Claims

1. The outer shell is made of steel plates, and the inside is lined with insulating refractory material, providing a highly insulating structure. A molten slag reducing furnace in which a highly corrosion-resistant refractory material that is resistant to corrosion by molten iron and iron oxide-containing slag is installed inside the highly insulating structure, A stainless steel plate or a heat-resistant steel plate is attached to the surface of the highly corrosion-resistant refractory material that comes into contact with the molten slag, A molten slag reduction furnace characterized by holding molten pig iron in the reduction furnace and pouring molten slag onto the molten pig iron, whereby iron oxide in the molten slag is reduced by the C in the molten pig iron, and the resulting Fe is absorbed into the molten pig iron and recovered as the molten pig iron.

2. 2. The reducing furnace according to claim 1, wherein a molten pig iron outflow outlet is provided in a molten pig iron layer held in the reducing furnace, the molten pig iron flowing out from the reducing furnace is stored in a molten pig iron storage tank installed outside the reducing furnace, and the molten pig iron overflows from a level of a surface of the molten pig iron in the reducing furnace, and the level of the surface of the molten pig iron in the reducing furnace is maintained at a desired height by the siphon principle.

3. The surface area of ​​the molten iron in the reduction furnace is defined as s (cm 2 ), and the density of the molten slag to be charged is ρ (g / cm 3 ), the weight of the molten slag to be charged is m (g), and the calculated slag depth in the reduction furnace is h (cm), the following formula (1) is used: Formula h=m / (ρs)(cm) (1) and the surface area s (cm 2 2. The reducing furnace according to claim 1, wherein, when 60% to 80% of the total cross section of the reducing furnace is defined as a front section and 20% to 40% as a rear section, the ceiling height of the front section is (3h + α) (cm) from the surface level of the molten pig iron, the ceiling height of the rear section is (0.7h + α) (cm) from the surface level of the molten pig iron, and the cross section of the reducing furnace is determined by dimensions determined using α as a margin.

4. 4. The reduction furnace according to claim 3, further comprising a three-phase AC electric heating device in a region of the rear stage adjacent to the front stage.

5. 5. The reduction furnace according to claim 4, further comprising a three-phase AC electric heating device in the rear region, and a KR agitator located adjacent to the three-phase AC electric heating device.

6. 5. The reducing furnace according to claim 4, wherein a hot exchange device for graphite electrodes and stirring blades of the KR stirrer is installed outside the furnace in the latter-stage region of the reducing furnace, and hot exchange is performed under conditions that do not allow CO leakage.

7. A method for reducing molten slag using the reducing furnace according to claim 1, The molten slag is poured onto the hot metal, whereby iron oxide in the molten slag is reduced by the C in the hot metal, the C in the hot metal that is consumed is continuously added, and the resulting Fe is absorbed into the hot metal and recovered as the hot metal. This is a reduction method characterized by the following.

8. 8. The reduction method according to claim 7, wherein after the iron oxide in the molten slag is recovered as molten pig iron, Si and Mn satisfying specifications for foundry pig iron are dissolved to produce foundry pig iron having a Cu content of 0.6 mass% or less.

9. 8. The reduction method according to claim 7, wherein the slag after the reduction treatment, in which the FeO content is 4% by mass or less, is returned to the oxidation smelting furnace for copper concentrate and used as an absorbent for FeO.

10. 8. The reduction method according to claim 7, wherein the slag after the reduction treatment, in which the FeO content remains at 4 mass% or less, is utilized as a slag foaming agent in submerged arc operation of an electric furnace for steel making.

11. The FeO is added to the slag remaining after the reduction treatment in a content of 4 mass% or less. 2 8. The reduction method according to claim 7, wherein O and CaO are dissolved and used as a desulfurization agent for hot metal in steelmaking and refining.

12. 8. The reduction method according to claim 7, wherein the content of the FeO remaining in the slag after the reduction treatment is 4% by mass or less, and the slag from which the FeO has been completely removed by adding aluminum or Si is used as a cover slag for molten steel in steelmaking refining.

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