JP7531273B2 - How to treat by-products - Google Patents

Description

The present invention relates to a method for treating by-products generated during metal manufacturing processes.

In the refining of steel and non-ferrous metals such as copper, chromium, nickel, and zinc, large amounts of slag and dust are generated because impurities in the raw materials are separated from the metals at high temperatures. These refining processes require containers to hold the hot metal and slag, and the refractories used in these containers deteriorate over time and are discarded, becoming used refractories. In addition, when the steel slabs and ingots of various metals produced in the refining process are processed into products, they are rolled, processed, surface treated, etc. as appropriate, but the water and oil used in this process contain metal oxides, which separate out and produce sludge. In addition, at coal-fired power plants, etc., the ash in the fuel remains after combustion and is collected as fly ash.

Slag, dust, used refractories, sludge _{, etc. generated in metal manufacturing processes are all mainly composed of metal oxides such as SiO2, Al2O3 , CaO} , MgO, etc., and are expected to be used as crushed stone or concrete raw materials. However, depending on the composition of these by-products, for example, those with a high content of CaO or MgO may expand or powder over time, or may leach minute amounts of metal components, and many of them have not been effectively used.

To address these problems, Patent Document 1 discloses a technology for melting and reforming molten steelmaking slag by adding a _SiO2- containing substance and a reducing agent to the molten steelmaking slag and using waste plastics that meet special conditions as part or all of the reducing agent. Patent Document 1 discloses, as a specific method, blowing a reducing substance into molten converter slag held in a slag ladle together with blowing a _SiO2- containing substance and oxygen from an immersion lance.

JP 2009-114023 A

The technology disclosed in Patent Document 1 is applied to molten steelmaking slag, but most slag generated in metal refining processes is molten immediately after production, but cools over time and becomes solid. For this reason, there are few opportunities to effectively implement the technology disclosed in Patent Document 1. Furthermore, dust generated in metal refining processes is generated in a solid state, so it cannot be treated using the technology disclosed in Patent Document 1.

The present invention was made in consideration of the problems of the conventional technology, and its purpose is to provide a method for treating by-products that can separate metal and oxide components as useful materials from room temperature slag, dust, sludge, and used refractories.

The means for solving the above problems are as follows.
(1) A method for treating by-products generated in a metal production process, comprising heating the by-products to separate them into metal and oxide, the by-products being one or more selected from slag, dust, sludge and used refractories, the by-products being heated to 1,300°C or higher using an electric furnace, and the oxides having a chemical composition of CaO: 17% by mass or more and 59% by mass or less, _SiO2 : 17% by mass or more and 53% by mass or less, _Al2O3 : 5 _% by mass or more and 45% by mass or less _, MgO: 2% by mass or more and 20% by mass or less, and basicity (CaO/ _SiO2 ): 0.7 to 2.0.
(2) The method for treating by-products according to (1), wherein the by-products contain at least one type selected from metals and free carbon in a total amount of at least 1 mass%, and the electric furnace is a resistance heating electric furnace.
(3) The method for treating by-products according to (1) or (2), wherein the basicity (CaO/SiO ₂ ) is 0.7 or more and 1.6 or less.
(4) The method for treating by-products described in any one of (1) to (3), wherein the slag contains a reducing agent.
(5) The method for treating by-products according to any one of (1) to (4), wherein the used refractory contains a reducing material.
(6) The method for treating a by-product according to any one of (1) to (5), further comprising adding a raw material containing a reducing agent to the by-product for treatment.
(7) The method for treating by-products according to (6), wherein the raw material containing the reducing agent is one or more selected from the group consisting of coal, coke, paper sludge, waste tires, and waste plastics.
(8) The method for treating a by-product according to any one of (1) to (7), further comprising adding a raw material for adjusting a chemical composition of an oxide to the by-product for treatment.
(9) The method for treating by-products according to (8), wherein the raw material for adjusting the chemical composition of the oxide is one or more selected from fly ash, sand, and gravel.

By implementing the by-product processing method of the present invention, by-products such as slag and dust at room temperature can be separated into useful oxides that can be used as aggregates for roadbed materials and concrete, etc., and useful metals that can be used as raw materials for steelmaking.

The inventors have noticed that some of the by-products generated in the metal manufacturing process, such as slag, dust, sludge, or used refractories, contain either metal or free carbon, or both. If the by-products contain metal or free carbon, they can be generated by passing electricity through the by-products using, for example, a resistance heating electric furnace, partially melting the by-products even at room temperature, and then melting them further by passing electricity through them, thereby separating the by-products, such as slag and dust, into metal and oxide. Alternatively, they came up with the idea that if an arc furnace is used, the by-products can be separated into metal and oxide by melting them with arc heat. The present invention will be described below through the embodiments of the invention.

In the by-product processing method according to this embodiment, the by-product is heated to 1300°C or higher using an electric furnace. By heating the by-product to 1300°C or higher, the by-product can be melted and separated into metal and oxide. On the other hand, if the heating temperature is less than 1300°C, the by-product cannot be melted and cannot be separated into oxide and metal, or even if it can be melted, the viscosity is high and the by-product cannot be sufficiently separated into oxide and metal, resulting in a large amount of metal remaining in the oxide.

The higher the temperature of the molten oxide, the lower the viscosity and the easier it is to separate the oxide from the metal, so there is no need to set an upper limit for the heating temperature of the by-products, but there is no problem even if it is raised to about 2000°C. It is preferable to use an electric furnace for heating the by-products, which has a large amount of energy that can be input and is easy to control the temperature. As the electric furnace, various types such as a resistance heating electric furnace, an arc furnace, and an induction heating electric furnace can be used. When using an arc furnace or an induction heating electric furnace, molten metal such as hot metal or metal scrap can be added to the by-products for processing.

Among these electric furnaces, it is preferable to use a resistance heating electric furnace. For example, when an arc furnace is used, it is necessary to conduct an arc discharge between electrodes and transfer the heat generated by the arc discharge to the by-products to melt them. On the other hand, if the by-products, such as slag and dust, contain a total of 1 mass% or more of metal or free carbon, by using a resistance heating electric furnace, electricity flows through the metal or free carbon to generate resistance heat, and this heat is transferred directly to the by-products, so that heat transfer to the by-products is efficient. Therefore, the by-products can be heated to a predetermined temperature in about one-fifth the time required when heated in an arc furnace. The by-products in the embodiment are one or more selected from slag, dust, sludge, and used refractories generated in the metal manufacturing process. In the following explanation, a resistance heating electric furnace is used as the electric furnace, and slag and dust are used as the by-products.

The by-products, slag and dust, are loaded into a resistance-heated electric furnace. Electrodes are inserted into the furnace where the slag and dust have accumulated, and a voltage is applied. At this time, since the slag and dust contain a total of 1% by mass or more of metal and free carbon, current flows partially through the slag and dust, which generates resistance heat and raises the temperature of the slag and dust.

The main components of slag and dust are metal oxides, so they are electrically conductive when molten. For this reason, when the slag or dust itself begins to melt due to an increase in temperature, the amount of current flowing also increases. This causes the amount of heat generated to increase, and by raising the temperature to 1,300°C or higher, the slag and dust charged into the furnace can be completely melted. If the slag and dust can be completely melted, the metals contained in the slag and dust, such as iron, copper, and nickel, will melt and coagulate, making it possible to separate the metals from the oxides.

In the by-product processing method according to the present embodiment, the chemical composition of the oxide is CaO: 17% by mass to 59% by mass, SiO ₂ : 17% by mass to 53% by mass, Al ₂ O ₃ : 5% by mass to 45% by mass _, MgO: 2% by mass to 20% by mass, and basicity (CaO/SiO ₂ ): 0.7 to 2.0. By setting the chemical composition of the oxide in the above range, the viscosity of the molten oxide is in a range that is favorable for separation from the molten metal, and separation of the metal and oxide contained in the by-product is facilitated. Furthermore, by setting the chemical composition of the oxide in the above range, the hydration expansion of the oxide is also suppressed, making it a useful material that can also be used as an aggregate for roadbed materials and concrete. On the other hand, if the basicity (CaO/SiO ₂ ) of the oxide is higher than 2.0, the viscosity of the molten oxide increases, making it difficult to separate the metal and the oxide, and more metal is mixed into the oxide after separation. Furthermore, if the basicity (CaO/SiO ₂ ) of the oxide exceeds 2.0 or if the MgO content exceeds 20 mass %, f-CaO and f-MgO tend to precipitate from the oxide, causing hydration expansion.

The oxide basicity (CaO/SiO ₂ ) is preferably 0.7 or more and 1.6 or less. By making the oxide basicity (CaO/SiO ₂ ) 0.7 or more and 1.6 or less, the viscosity of the gold and molten oxide is lowered, and the metal and the oxide are more easily separated. Furthermore, the volume change of the oxide during the cooling process and the precipitation of f-CaO and f-MgO from the oxide are suppressed, thereby suppressing the powdering of the oxide and further suppressing hydration expansion.

On the other hand, if the basicity (CaO/SiO ₂ ) of the oxide becomes higher than 1.6, the volume starts to change due to the crystal transition of 2CaO.SiO ₂ (transition from α' type or β type to γ type) during the cooling process of the oxide, which causes the oxide to be powdered, which is not preferable.

Furthermore, the chemical composition of the oxide is preferably such that the total of CaO, _SiO2 , _{Al2O3 ,} and MgO is 80 mass% or more. The total of CaO, _SiO2 , _Al2O3 , and MgO being 80 mass% or more means that the oxide contains small amounts _of FeO, _Fe2O3 , and _{Cr2O3 .} It can be seen that by satisfying the above chemical composition, most of the metals contained in the by-products can be _separated and recovered as metals.

The chemical composition of the oxides can be controlled by checking in advance the chemical compositions of the slag, dust, sludge, and used refractories to be charged into the resistance-heated electric furnace, and adjusting the ratio of the slag, dust, sludge, and used refractories to be charged. In addition, one or more types selected from fly ash, sand, and gravel may be further added as raw materials to adjust the chemical composition of the oxides, and the chemical composition of the oxides may be controlled to be within a target range by adding these.

Here, some dust has the effect of increasing the oxide basicity while increasing the particle size to be collected, making it easier to collect. Some sludge has the effect of reducing the oxide while increasing its basicity. Some used refractories have the effect of reducing the oxide while decreasing its basicity. Some fly ash, sand, and gravel have the effect of lowering the oxide basicity. By taking these effects into consideration and adjusting the blending ratio of each raw material to control the chemical composition of the oxide within the above range, it is possible to eliminate sources of vitrification and expansion, and turn the oxide into a useful material that can be used as an aggregate for roadbed materials, concrete, etc.

Furthermore, a raw material containing a reducing agent may be added to the slag and dust. If the reducing agent is present when the slag and dust are entirely molten, some of the oxides are reduced, and the amount of metal that can be separated and recovered from the by-products increases. For example, one or more raw materials containing a reducing agent may be used that are selected from coal, coke, paper sludge, waste tires, and waste plastics. In addition, when slag or used refractories are used as by-products, it is preferable to use slag or used refractories that contain a reducing agent. By using slag or used refractories that contain a reducing agent, the amount of reducing agent added from outside to reduce the oxides can be reduced.

It is preferable to first charge the raw materials containing FeO, MnO, and _Al2O3 , which generate a melt at a _low temperature, into the resistance heating electric furnace, apply a voltage to melt them, and then charge the other raw materials in sequence. This allows the by-products to be melted as a whole with high efficiency. Furthermore, in addition to the raw material that generates a melt at the lowest temperature, a raw material that lowers the melting point of the entire raw materials may be charged first.

In addition, to protect the refractory material in the walls of a resistance-heated electric furnace, the furnace may be operated so that the by-products near the furnace walls do not melt, rather than melting all of the by-products charged. For example, the electrodes of the resistance-heated electric furnace may be moved closer to the center so that the by-products do not melt in their entirety. This reduces the melting damage of the refractory material that forms the self-lining layer, and as a result, extends the furnace's life. When operating so that the by-products do not melt in their entirety, it is necessary to ensure that the unmelted portions are not mixed in when the molten slag is discharged out of the furnace.

As described above, in the by-product processing method according to this embodiment, a resistance heating electric furnace is used to heat room temperature by-products such as slag and dust to 1300°C or higher to separate them into oxides and metals of specified chemical composition. This allows the room temperature by-products such as slag and dust to be separated into useful oxides that can be used as aggregates for roadbed materials and concrete, and useful metals that can be used as raw materials for steelmaking.

Next, an embodiment of the by-product processing method according to the present invention will be described. First, 20 kg of room temperature by-products were charged into a 100 kVA resistance heating electric furnace, electrodes were inserted into the by-products, and electricity was started. After melting of the by-products between the electrodes was confirmed, raw materials were added, and after 200 kg of the by-products were charged, the temperature was held at a predetermined temperature for 1 hour, and then cooled at 10 ° C/min to separate the by-products into metals and oxides. The chemical composition of each raw material, which is a by-product, is shown in Table 1. In Table 1, steelmaking slag B is a raw material that generates a molten liquid at a low temperature. Refractory scrap A and refractory scrap B, which are used refractories, and fly ash are raw materials that lower the melting point of the entire raw material. In addition, Cr ore melting reduction furnace slag, SUS dust, cold rolling sludge, used refractories, and fly ash are raw materials containing reducing materials. The reducing material contained in the used refractories is silicon carbide (SiC). In Table 1, "<0.1" indicates that the content is less than 0.1% by mass, and "<1" indicates that the content is less than 1% by mass. In addition, in Table 1, there are materials whose sum of chemical compositions is less than 100. This is because the raw materials shown in Table 1 contain other components in addition to the chemical components in question.

The blending ratios of each raw material in Invention Examples 1 to 38 are shown in Tables 2 to 5. Similarly, the blending ratios of each raw material in Comparative Examples 1 to 19 are shown in Tables 6 and 7. Coke, paper sludge, and waste tires in Tables 2 to 7 are all raw materials that contain reducing agents.

Tables 8 and 9 show the chemical composition of the oxide and metal after separation and the state of separation between the oxide and metal in Examples 1 to 38. Similarly, Table 10 shows the chemical composition of the oxide and metal after separation and the state of separation between the oxide and metal in Comparative Examples 1 to 19. In this example, separation was considered to be good when the amount of metal mixed into the oxide was 10% by mass or less, and is marked with "O" in the "Separation" column in Tables 8 to 10. On the other hand, separation was considered to be poor when the amount of metal mixed into the oxide was more than 10% by mass, and is marked with "X" in the "Separation" column in Tables 8 to 10. In addition, "<1" in Tables 8 to 10 means that the content is less than 1% by mass.

Examples 1 to 11, 37, and 38 are examples of the invention in which dust, sludge, used refractories (refractory scrap A or refractory scrap B), basicity adjuster (fly ash), and reducing agent are added to steelmaking slag A, B, C, and D. The heat treatment temperature is 1550°C. In Examples 1 to 11, oxides of a specified chemical composition can be separated and recovered with a metal contamination amount of 10 mass% or less, and dense oxides that can be used as aggregates for roadbed materials and concrete, etc. are obtained. In Examples 1 to 11, a reducing agent is added, so that FeO+Fe ₂ O ₃ is 2 mass% or less and Cr ₂ O ₃ is less than 1 mass%, and the metals in the oxides can be sufficiently recovered. In this embodiment, fly ash is used as a basicity adjuster, but the same effect can be obtained by using sand or gravel instead of fly ash.

Inventive Examples 12 to 22, dust, sludge, used refractories (scrap refractories A or scrap refractories B), and basicity adjuster (fly ash) were added to the Cr ore smelting reduction furnace slag. The heat treatment temperature was 1550°C. In Inventive Examples 12 to 22, oxides of a specified chemical composition could be separated and recovered with a metal contamination amount of 10 mass% or less, and dense oxides that can be used as aggregates for roadbeds and concrete were obtained. Since the Cr ore smelting reduction furnace slag contains free carbon, the FeO+Fe ₂ O ₃ in the oxide was 2 mass% or less and the Cr ₂ O ₃ was less than 1 mass%, and the metals in the oxide could be sufficiently recovered without adding a reducing agent.

Inventive Examples 23 to 33, dust, sludge, used refractories (scrap refractories A or scrap refractories B), basicity adjuster (fly ash), and reducing agent were added to copper slag. The heat treatment temperature was 1550°C. In Inventive Examples 23 to 33, oxides of a specified chemical composition could be separated and recovered with a metal contamination amount of 10 mass% or less, and dense oxides that can be used as aggregates for roadbeds and concrete were obtained. In Inventive Examples 23 to 33, a reducing agent was added, so FeO + Fe ₂ O ₃ was 2 mass% or less and Cr ₂ O ₃ was less than 1 mass%, and the metals in the oxides could be sufficiently recovered.

Examples 34 to 36 were the same as Examples 2, 16, and 28 in terms of raw material composition, but the heat treatment temperature was 1300°C. In Examples 34 to 36, oxides of the specified chemical components could be separated and recovered with a metal contamination level of 10% by mass or less, and dense oxides were obtained that could be used as aggregates for roadbeds and concrete, etc. However, the FeO+ _Fe2O3 concentration in the oxides was slightly higher than in Examples 2, 16, and ₂₈ , and the reducibility was slightly inferior to Examples 2, 16, and 28.

Comparative Examples 1 to 5 are comparative examples in which sludge, used refractories (scrap refractories A or scrap refractories B), and basicity adjuster (fly ash) were added to steelmaking slag A and B. The heat treatment temperature was 1550°C. Comparative Example 1 had a high basicity of 2.1, which resulted in high viscosity of the molten oxide, which prevented the metal and oxide from being completely separated, resulting in a large amount of metal being mixed into the oxide. Comparative Example 5 had a high basicity of 6.1, which prevented the raw materials from being completely melted, and the metal and oxide from being separated. Comparative Examples 2 to 4 had low basicity and low viscosity of the molten oxide, so the oxide was vitrified even at a cooling rate of 10°C/min, and dense oxides that could be used as aggregates for roadbeds and concrete could not be obtained.

Comparative Examples 6 to 11 are comparative examples in which dust, sludge, used refractories (refractory scrap A or refractory scrap B) and basicity adjuster (fly ash) were added to the Cr ore melting reduction furnace slag. The heat treatment temperature was 1550°C. Comparative Example 6 had a high basicity of 2.1, which resulted in high viscosity of the molten oxide, which prevented the metal and oxide from being completely separated, and a large amount of metal was mixed into the oxide. Comparative Example 9 had a high MgO content of 22 mass%, which resulted in high viscosity of the oxide, which prevented the metal and oxide from being completely separated, and a large amount of metal was mixed into the oxide. Comparative Example 11 had a high basicity of 6.2, which prevented the raw materials from being completely melted, and the metal and oxide from being separated. Comparative Examples 7, 8, and 10 had low basicities of 0.1 to 0.6, which resulted in low viscosity of the molten oxide, which prevented the oxide from being vitrified even at a cooling rate of 10°C/min, and therefore did not produce dense oxides that could be used as aggregates for roadbeds and concrete.

Comparative Examples 12 to 16 are comparative examples in which dust, sludge, used refractories (refractory scrap A, refractory scrap B), and basicity adjuster (fly ash) were added to copper slag. The heat treatment temperature was 1550°C. Comparative Example 12 had a high basicity of 2.1, which resulted in high viscosity of the molten oxide, which prevented the metal and oxide from being completely separated, resulting in a large amount of metal being mixed into the oxide. Comparative Example 16 had a high basicity of 6.2, which prevented the raw materials from being completely melted, and the metal and oxide from being separated. Comparative Examples 13 to 15 had a low basicity of 0.1 to 0.6, which resulted in low viscosity of the molten oxide, which resulted in vitrification even at a cooling rate of 10°C/min, and therefore did not produce a dense oxide that could be used as an aggregate for roadbeds, concrete, etc.

Comparative Example 17 is a comparative example in which the raw material composition is the same as that of Invention Example 1, but the heat treatment temperature is 1250°C. Comparative Example 18 is a comparative example in which the raw material composition is the same as that of Invention Example 13, but the heat treatment temperature is 1100°C. Comparative Example 19 is a comparative example in which the raw material composition is the same as that of Invention Example 25, but the heat treatment temperature is 1000°C. In all of these comparative examples, the heat treatment temperature is lower than 1300°C, and the raw materials could not be completely melted, and the metal and oxide could not be separated.

Claims (8)

A method for treating a by-product generated in a metal manufacturing process, comprising heating the by-product to separate the by-product into a metal and an oxide, the method comprising the steps of:
The by-product is at least one selected from slag, dust, sludge, and used refractories,
The by-product is heated to 1300° C. or higher using an electric furnace;
The chemical composition of the oxides is as follows: CaO: 17% by mass or more _{and 59% by mass or less; SiO2: 17% by mass or more and 53% by mass or less; Al2O3 : 5} % by mass or more and 45% by mass or less; MgO: 2% by mass or more and 20% by mass or less; and basicity (CaO/ _SiO2 ): 0.7 or more and 2.0 or less .
The method for treating a by-product , wherein the by-product contains at least one type selected from metals and free carbon in a total amount of at least 1 mass %, and the electric furnace is a resistance heating electric furnace . The method for treating by-products according to claim 1 , wherein the basicity (CaO/SiO ₂ ) is 0.7 or more and 1.6 or less. The method for treating by-products according to claim 1 or 2 , wherein the slag contains a reducing agent. The method for treating by-products according to claim 1 , wherein the used refractory contains a reducing material. The method for treating a by-product according to claim 1 , further comprising the step of adding a raw material containing a reducing agent to the by-product for treatment. 6. The method for treating by-products according to claim 5 , wherein the raw material containing the reducing agent is at least one selected from the group consisting of coal, coke, paper sludge, waste tires and waste plastics. The method for treating a by-product according to claim 1 , further comprising the step of adding a raw material for adjusting a chemical composition of an oxide to the by-product for treatment. 8. The method for treating by-products according to claim 7 , wherein the raw material for adjusting the chemical composition of the oxide is at least one selected from the group consisting of fly ash, sand and gravel.