Method for oxidizing slag

Abstract

To provide a slag oxidation method capable of suppressing reduction in slag fluidity and enabling oxidation treatment of slag through a simple process.SOLUTION: The present invention provides a method for oxidizing slag, the method comprising a step of subjecting slag containing iron oxide to oxidation treatment, wherein the oxidation treatment is performed in the presence of CaO-Na2O-SiO2-based slag. The slag is preferably copper smelting slag. The method for oxidizing slag of the present invention is capable of suppressing a decrease in fluidity of slag during the oxidation treatment and enables oxidation treatment of slag by a simple method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for oxidizing 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] The slag mentioned above is primarily composed of fayalite, which has a composition similar to 2FeO·SiO2, with a small amount of Fe3O4. It also contains metal oxides formed by oxidizing metal sulfides contained in copper concentrate, molten matte particles (Cu2S + FeS), and precious metal particles. Of these, the molten matte particles (Cu2S + FeS) and precious metal particles are not reduced by Fe, so they tend to remain in the slag. For this reason, the technology disclosed in Patent Document 1 involves blowing oxygen onto the slag in step 1 as a pretreatment for the "soft reduction," thereby oxidizing the molten matte particles and precious metal particles.

[0005] In the oxidation treatment, 2FeO·SiO2 changes 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 2Fe2O3·SiO2-based slag generated in the oxidation treatment process, Na2O and a fluoride-based flux (particularly NaF) are added and the slag temperature is set to 1450°C, thereby adjusting the fluidity of the slag to an appropriate range. [Prior art documents] [Patent documents]

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

[0007] However, recent environmental standards have placed strict restrictions on the amount of fluoride ion leaching from slag, making it desirable to avoid the use of fluoride-based fluxes. Therefore, it is important to develop a technology that improves the fluidity of 2Fe2O3·SiO2-based slag without using fluoride-based fluxes. Furthermore, since the technology disclosed in Patent Document 1 increases fluidity by increasing the treatment temperature, it is also desirable to keep this temperature as low as possible. From this perspective, it is desirable to avoid the use of fluoride-based fluxes and to perform the treatment at low temperatures in slag oxidation treatment.

[0008] The present invention has been made in view of the above, and aims to provide a method for oxidizing slag that can suppress a decrease in the fluidity of slag and enable oxidation treatment of slag in a simple manner. [Means for solving the problem]

[0009] As a result of extensive research into achieving the above object, the present inventors have discovered that the above object can be achieved by covering a refractory layer with a stainless steel plate in a slag treatment vessel for treating slag containing iron oxide, and have thus completed the present invention.

[0010] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 1. A method for oxidizing slag, comprising: The method includes a step of oxidizing slag containing iron oxide, A method for oxidizing slag, wherein the oxidation treatment is carried out in the presence of CaO-Na2O-SiO2-based slag. Section 2 Item 1. The method for oxidizing slag according to Item 1, wherein the slag is copper smelting slag. Section 3 Item 3. The method for oxidizing slag according to item 1 or 2, wherein the oxidation treatment is carried out in the absence of fluoride. Section 4 The oxidation treatment is carried out in a slag treatment vessel, The slag treatment vessel 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, 4. The method for oxidizing slag according to any one of items 1 to 3, wherein the inner layer is formed of a stainless steel plate or a heat-resistant steel plate. Section 5 The outer shell is made of ordinary steel, 5. The method for oxidizing 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. [Effects of the Invention]

[0011] The method for oxidizing slag of the present invention can suppress the decrease in fluidity of slag during oxidation treatment, and can oxidize slag in a simple manner. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing an example of a slag treatment vessel used in the slag oxidation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013]

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

[0014] The method for oxidizing slag of the present invention includes a step of oxidizing slag containing iron oxide, in which the oxidation is carried out in the presence of CaO-Na2O-SiO2 slag. This oxidation method prevents the fluidity of the slag from decreasing during the oxidation, allowing the oxidation reaction of the slag to proceed smoothly, and the slag can be oxidized in a simpler manner.

[0015] In the slag oxidation method of the present invention, the step of oxidizing slag containing iron oxide will be referred to as "step A" hereinafter.

[0016] In step A, various types of slag can be used as the slag containing iron oxide, and among them, 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.

[0017] Specific examples of the copper refining slag include slag generated in copper smelting furnaces such as blast furnaces, electric furnaces, reverberatory furnaces, and flash furnaces. 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.

[0018] Hereinafter, slag containing iron oxide will be abbreviated simply as "slag."

[0019] The slag used in step A 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.

[0020] On the other hand, slag also 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 elements, so they 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 it difficult to recover them as valuable metals.

[0021] In this regard, in the present invention, the slag is oxidized in step A, so that the molten matte particles (CuS+FeS) and precious metal particles present in the slag become oxides, and as a result, valuable metals can be easily recovered by the reduction treatment described above. In other words, oxidizing the slag in step A is advantageous in that valuable metals derived from the molten matte particles (CuS+FeS) and precious metal particles can be easily recovered.

[0022] In step A, oxidation treatment is performed in the presence of CaO-Na2O-SiO2-based slag. By performing oxidation treatment in the presence of such CaO-Na2O-SiO2-based slag, the melting point of the slag can be lowered. That is, by performing oxidation treatment in the presence of CaO-Na2O-SiO2-based slag, the melting point of the slag during the oxidation reaction is lowered, so that the fluidity of the slag is less likely to increase even at relatively low oxidation treatment temperatures, making the oxidation treatment easier to perform. This means that oxidation treatment in the presence of CaO-Na2O-SiO2-based slag can be performed at lower temperatures.

[0023] 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.

[0024] The type of CaO-Na2O flux used in the oxidation treatment is not particularly limited.

[0025] 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.

[0026] 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.

[0027] 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:

[0028] 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)".

[0029] 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)".

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 a "slag treatment vessel" described below.

[0037] Fig. 1 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. 1 shows a state in which slag S is filled in the slag vessel.

[0038] As shown in Fig. 1, 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.

[0039] In the slag treatment vessel A shown in Fig. 1, a heat insulating layer 4 is provided between the refractory layer 2 and the outer shell 1. The provision of such a heat insulating layer 4 can 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.

[0040] The term "stainless steel sheet" as used herein 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] A lid 5 can be provided at the top opening of the slag treatment vessel A, as shown in FIG. 1, 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.

[0047] The embodiment shown in Fig. 1 is an example of a slag treatment vessel equipped with a lid. As shown in Fig. 1, 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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. 1, 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.

[0052] 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, through which gas introduced through the air supply pipe 6 can be released into the vessel space (or the slag S filled therein). 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.

[0053] 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 in the downstream region from the oxygen injection position, or copper scrap can be added as a coolant throughout the entire region.

[0054] As shown in FIG. 1, the slag treatment vessel A can be provided 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.

[0055] In addition, the slag treatment vessel A shown in Figure 1 can also 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, performing a known reduction treatment. Stainless steel pipes can be used for both the exhaust pipe 7 and the slag discharge pipe 11.

[0056] The slag treatment vessel A may be installed independently, or may be installed in parallel with a furnace (called a flash smelting furnace) in which copper smelting, the process for obtaining slag, is carried out. Furthermore, when reducing the slag oxidized in the slag treatment vessel A (for example, the soft reduction and subsequent hard reduction described in Patent Document 1), the slag treatment vessel A and a reduction furnace for the reduction treatment may be installed in parallel. For example, the flash smelting furnace, slag treatment vessel A, and reduction furnace 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 reduction furnace may be connected.

[0057] Therefore, the slag oxidized in step A can be supplied to the reduction step, thereby recovering valuable metals. The method for reducing the slag oxidized in step A is not particularly limited, and can be, for example, the same conditions as those for the soft reduction and subsequent hard reduction described in Patent Document 1.

[0058] 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. [Explanation of symbols]

[0059] A Slag treatment vessel 1 outer shell 2 Refractory layer 3 Inner layer 4. Insulation layer

Claims

1. 1. A method for oxidizing slag, comprising: The method includes a step of oxidizing slag containing iron oxide, The oxidation treatment is carried out using CaO—Na ２ O—SiO ２ A method of oxidizing slag carried out in the presence of a system slag.

2. 2. The method of claim 1, wherein the slag is copper smelting slag.

3. 3. The method for oxidizing slag according to claim 1, wherein the oxidation treatment is carried out in the absence of fluoride.

4. The oxidation treatment is carried out in a slag treatment vessel, The slag treatment vessel 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, 3. The method for oxidizing slag according to claim 1, wherein the inner layer is formed of a stainless steel plate or a heat-resistant steel plate.

5. The outer shell is made of ordinary steel, 5. The method of claim 4, wherein a layer of heat insulating material is provided between the shell and the refractory layer.

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