Method for treating aluminum dross, method for producing low-halogen aluminum dross, method for producing halide, method for refining molten aluminum, method for producing aluminum material, method for producing mud material for blast furnace tap hole, and method for producing refractory molded article

Abstract

To provide a method for treating aluminum dross, the method enabling treatment regardless of the concentration of metallic aluminum and enabling low-cost and easy reduction of halide.SOLUTION: A method for treating aluminum dross according to one embodiment of the present disclosure includes a step in which aluminum dross is held under an atmosphere where pressure P is 10000 Pa or less and temperature T is 700°C or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for treating aluminum dross, a method for producing low-halogenated aluminum dross, a method for producing a halide, a method for refining molten aluminum, an aluminum material, a method for producing a mud material for a blast furnace tapping hole, and a method for producing a refractory molded body.

Background Art

[0002] Currently, from the perspective of resource depletion, recycling of various things has been progressing, and recycling of metals that are consumed in large quantities has also been carried out for a long time. When refining molten aluminum, the aluminum dross generated is sometimes recycled by recovering the contained metallic aluminum and reusing this aluminum. The aluminum dross from which metallic aluminum has been recovered is sometimes discarded as aluminum ash or further metallic aluminum is recovered. Aluminum ash from which as much metallic aluminum as possible has been recovered and aluminum ash that does not contain recoverable metallic aluminum are sometimes discarded as residual ash. The discarded aluminum ash and residual ash may contain harmful substances that have an adverse impact on the environment, and as methods for reducing such harmful substances, Patent Documents 1, 2, and 3 below are known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the processing method of Patent Document 1, aluminum dross is calcined at 1000°C or higher. However, at this temperature, there is a risk that halogen elements (halides) containing fluorides may remain in the processed aluminum dross. In the processing method of Patent Document 2, it is conditioned that the aluminum dross contains 10% by mass or more of metallic aluminum, and there is a risk that it may not be applicable to aluminum dross with a low content of metallic aluminum. In the processing method of Patent Document 3, since arc plasma is used to melt aluminum dross, there is a risk that the energy cost cannot be reduced.

[0005] In view of such circumstances, an object of the present disclosure is to provide a method for treating aluminum dross that can be processed regardless of the content concentration of metallic aluminum and can easily reduce halides at low cost.

Means for Solving the Problems

[0006] The method for treating aluminum dross according to one aspect of the present disclosure for solving the above problems includes a step of holding aluminum dross in an atmosphere where the pressure P is 10000 Pa or less and the temperature T is 700°C or higher.

Effects of the Invention

[0007] The method for treating aluminum dross of the present disclosure can be processed regardless of the content concentration of metallic aluminum and can easily reduce halides at low cost.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) The method for treating aluminum dross according to one aspect of the present disclosure includes a step of holding the aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher.

[0011] Since the method for treating the aluminum dross (hereinafter also referred to as the treatment method) heats the aluminum dross under reduced pressure, the halides in the aluminum dross can be efficiently reduced. In addition, since the heating temperature can be made relatively low by reducing the pressure, the energy cost can be suppressed. Since the treatment method is performed while maintaining a predetermined pressure and temperature, it can be treated regardless of the content of metallic aluminum.

[0012] (2) In the above (1), the atmosphere of the holding step may be formed by a procedure of reducing the pressure to 10,000 Pa or less and a procedure of heating to 700 °C or higher after reducing the pressure. By heating after reducing the pressure, the halides in the aluminum dross can be reduced more efficiently.

[0013] (3) In the above (1) or (2), the treatment method may further include a step of heating the aluminum dross under normal pressure before the holding step. By doing so, moisture and organic substances in the aluminum dross are removed, and scattering of the aluminum dross during heating under reduced pressure can be suppressed.

[0014] (4) In any one of the above (1) to (3), the treatment method may further include an air holding step of holding the aluminum dross in an air atmosphere before or after the holding step. By doing so, metallic aluminum and aluminum nitride in the aluminum dross can be efficiently removed.

[0015] (5) In any one of the above (1) to (4), the holding step may have a procedure of removing components volatilized into the atmosphere. By doing so, volatile components in the aluminum dross can be efficiently removed.

[0016] (6) In the above (5), the removing procedure may include a procedure for maintaining the pressure of the atmosphere constant and a procedure for reducing the partial pressure of the volatilized component below the equilibrium state. By doing so, the removal effect of the volatile component can be improved.

[0017] (7) In any one of the above (1) to (6), the reduction rate of the fluorine concentration in the aluminum dross after treatment with respect to the aluminum dross before treatment may be 10% or more. That is, the treatment method can reduce the fluorine concentration in the aluminum dross by 10% or more.

[0018] (8) In any one of the above (1) to (7), the fluorine concentration in the aluminum dross after treatment may be 0.5% by mass or less and the chlorine concentration may be 0.1% by mass or less. That is, the treatment method can make the fluorine concentration in the aluminum dross after treatment 0.5% by mass or less and the chlorine concentration 0.1% by mass or less.

[0019] (9) In any one of the above (1) to (8), the pressure P and the temperature T in the holding step may satisfy the following formula 1. By controlling the pressure P and the temperature T so as to satisfy the following formula 1, the volatilization effect of the volatile component can be improved. P < 10 {(T+273.15) / 50-22.5} ····(1)

[0020] (10) In any one of the above (1) to (9), the aluminum dross may contain at least one of aluminum ash and residual ash. That is, the treatment method can be applied to any of aluminum dross, aluminum ash obtained by recovering at least a part of metallic aluminum from the aluminum dross, residual ash obtained by further recovering metallic aluminum from the aluminum ash, or residual ash which is aluminum ash not containing recoverable metallic aluminum.

[0021] (11) The method for producing a low-halogenated aluminum dross according to one aspect of the present disclosure includes a step of removing the halide volatilized into the atmosphere by holding the aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher.

[0022] Since the method for producing the low-halogenated aluminum dross heats the aluminum dross under reduced pressure, the halide in the aluminum dross can be efficiently volatilized. Since the volatilized halide is removed, a less harmful aluminum dross can be easily obtained.

[0023] (12) The method for producing a low-halogenated aluminum dross according to one aspect of the present disclosure is a method for producing a less harmful aluminum dross used as a refractory raw material or a deoxidizer or desulfurizer for steelmaking, and includes the removing step of (11) above.

[0024] Since the method for producing the low-halogenated aluminum dross heats the aluminum dross under reduced pressure, the halide in the aluminum dross can be efficiently volatilized. Since the volatilized halide is removed, a less harmful aluminum dross can be easily produced. By using this low-halogenated aluminum dross as a refractory raw material or a deoxidizer or desulfurizer for steelmaking, the aluminum dross can be effectively recycled.

[0025] (13) The method for producing a halide according to one aspect of the present disclosure includes a step of recovering the halide volatilized into the atmosphere by holding the aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher.

[0026] Since the method for producing the halide heats the aluminum dross under reduced pressure, the halide in the aluminum dross can be efficiently volatilized. By recovering this volatilized halide, the halide can be efficiently produced from the by-product aluminum dross.

[0027] (14) The method for producing a halide according to one aspect of the present disclosure is a method for producing a halide used as a flux, and includes the step of recovering the above (13).

[0028] Since the method for producing the halide heats the aluminum dross under reduced pressure, the halide in the aluminum dross can be efficiently volatilized, and the halide can be efficiently produced by recovering the volatilized halide. By using this halide as a flux, the halide recovered from the aluminum dross can be effectively recycled, and the amount of refined flux containing halide can be reduced.

[0029] (15) The method for refining molten aluminum according to one aspect of the present disclosure includes a first refining step of refining molten aluminum, a step of holding the aluminum dross generated in the above refining step in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher, a step of recovering the halide volatilized into the atmosphere in the above holding step, and a second refining step of refining molten aluminum using the halide recovered in the above recovering step as a flux.

[0030] The method for refining molten aluminum (hereinafter also referred to as the refining method) treats the aluminum dross generated from the refining of molten aluminum (first refining) by the treatment method, and uses the halide volatilized from this aluminum dross as a flux in the next refining of molten aluminum (second refining). Therefore, the amount of refining flux used in the second refining can be reduced. In addition, since the halide, which is a harmful substance generated in the factory, is recycled in the factory without being discharged, the environmental pollution risk can be reduced, and closed-loop recycling is also possible. The above halide can also be used as a flux in the refining of molten aluminum in other factories (refining facilities).

[0031] (16) The method for producing an aluminum material according to one aspect of the present disclosure includes a step of solidifying the molten aluminum refined by the method for refining molten aluminum in the above (15).

[0032] Since the manufacturing method of the aluminum material (hereinafter also referred to as the manufacturing method) solidifies the molten aluminum refined by the refining method, the aluminum material can be manufactured while reducing the cost and environmental load.

[0033] (17) In the above (16), the manufacturing method may further include a step of solidifying the molten aluminum to obtain an aluminum ingot or an aluminum casting. By solidifying the molten aluminum, an aluminum ingot or an aluminum casting can be easily obtained.

[0034] (18) In the above (17), the manufacturing method may further include a step of plastically working the aluminum ingot. By plastically working the aluminum ingot, an extended material can be easily obtained.

[0035] (19) The manufacturing method of the mud material for the blast furnace tapping hole according to one aspect of the present disclosure includes a step of mixing the low-halogenated aluminate dross produced by the manufacturing method of the low-halogenated aluminate dross described in the above (11) and a refractory aggregate.

[0036] Since the manufacturing method of the mud material for the blast furnace tapping hole manufactures the mud material for the blast furnace tapping hole using the above low-halogenated aluminate dross, the mixing of halides into the blast furnace slag can be suppressed.

[0037] (20) The manufacturing method of the refractory molded body according to one aspect of the present disclosure includes a step of molding a material containing the low-halogenated aluminate dross produced by the manufacturing method of the low-halogenated aluminate dross described in the above (11), and a step of firing the molded material.

[0038] Since the manufacturing method of the refractory molded body manufactures the refractory molded body using the material containing the above low-halogenated aluminate dross, the obtained refractory molded body can suppress deterioration due to contact with halides and can be suitably used for refractory equipment and the like.

[0039] Note that the "halide" means a substance containing a halogen element, and also means a substance containing at least one of the halogen simple substances (F2, Cl2).

[0040] [Details of the Embodiment for Carrying Out the Present Disclosure] Hereinafter, an example of an embodiment of the present disclosure will be described in detail.

[0041] [Method for Treating Alumidros] The treatment method includes a step of holding alumidros in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher. The treatment method may be carried out using, for example, a known heating furnace.

[0042] The alumidros treated by the treatment method may contain at least one of aluminum ash and residual ash. That is, the material treated by the treatment method may be alumidros generated in the refining of molten aluminum before the contained metallic aluminum is recovered, may be aluminum ash obtained by recovering at least a part of metallic aluminum from alumidros by ash squeezing, may be residual ash obtained by further recovering metallic aluminum from aluminum ash, or may be residual ash containing no recoverable metallic aluminum, or a combination thereof. Note that the "alumidros" in the following description is used to mean not only alumidros before recovering metallic aluminum, but also aluminum ash, residual ash, and a combination thereof.

[0043] For example, when carrying out the treatment method using a heating furnace, the timing of charging alumidros into the heating furnace (the timing of exposing alumidros to the reduced pressure and the heating environment) is not particularly limited. It may be possible to first charge alumidros into the heating furnace and then start reducing the pressure and heating, charge alumidros during the reduction of pressure and heating, or charge alumidros after forming a desired atmosphere by reducing the pressure and heating.

[0044] The order of the depressurization and heating in the holding step is not particularly limited, but the atmosphere in the holding step is preferably formed by a procedure of depressurizing the atmosphere to 10,000 Pa or less and then heating to 700°C or more after depressurizing. That is, heating after depressurizing is preferable. By doing so, halides in the aluminum dross can be efficiently reduced and energy costs can be reduced. Furthermore, when aluminum dross is charged into a heating furnace and the depressurization and heating of the heating furnace are carried out, heating after depressurizing suppresses chemical changes in halides that occur during heating at normal pressure, thereby improving the halide removal rate.

[0045] The upper limit of the pressure P in the holding step is 10,000 Pa. The upper limit of the pressure P may be 5,000 Pa, 2,000 Pa, 1,000 Pa, 500 Pa, 200 Pa, 100 Pa, or 1 Pa. The lower limit of the pressure P is not particularly limited and may be, for example, 0.1 Pa, which is feasible in general pressure-reducing equipment such as a heating furnace. By setting the pressure P within the above range, it is possible to promote the volatilization of volatile components such as halides in the aluminum dross.

[0046] The lower limit of the temperature T in the holding step is 700°C. The lower limit of the temperature T may be 800°C, 1000°C, or 1200°C. The upper limit of the temperature T is not particularly limited and may be, for example, 1400°C, 1200°C, or 950°C, taking into consideration the refractories constituting the heating furnace. By setting the temperature T within the above range, the volatilization of the volatile components in the aluminum dross can be further promoted.

[0047] In the maintaining step, it is preferable that the pressure P and the temperature T satisfy the following formula 1. By controlling the pressure P and the temperature T so as to satisfy the following formula 1, it is possible to improve the volatilization effect of the volatile components and the effect of reducing the energy cost for heating. P<10 {(T+273.15) / 50-22.5} ····(1)

[0048] The lower limit of the time for holding the aluminum dross in the above atmosphere may be 20 minutes, 30 minutes, 40 minutes, or 60 minutes. The upper limit of the holding time may be 360 minutes, 300 minutes, 240 minutes, or 200 minutes. By setting the holding time within the above range, it is possible to sufficiently volatilize the volatile components while effectively suppressing the energy cost for heating.

[0049] In the above holding step, it is preferable to hold the aluminum dross while stirring it. By holding the aluminum dross while stirring, the aluminum dross can be reacted uniformly. The means for stirring the aluminum dross is not particularly limited. For example, a rotating blade may be arranged in the heating furnace, or the aluminum dross may be held while being stirred using a rotary furnace (kiln).

[0050] The treatment method may further include a step of heating the aluminum dross under normal pressure (preheating step) before the above holding step. The aluminum dross contains moisture and organic substances (hereinafter referred to as moisture, etc.), and in the above holding step, the moisture, etc. may generate gas and cause the aluminum dross to scatter. By preheating the aluminum dross under normal pressure before the above holding step, the moisture, etc. in the aluminum dross can be removed, and the working efficiency of the treatment method can be improved.

[0051] The heating temperature of the aluminum dross in the above preheating step is not particularly limited as long as it can remove the moisture, etc. For example, the lower limit of the heating temperature may be 200°C, 250°C, or 300°C. The upper limit of the heating temperature may be 600°C, 550°C, or 500°C.

[0052] The heating time of the aluminum dross in the preheating process may be appropriately set according to the heating temperature. For example, the lower limit value of the heating time may be 10 minutes, 20 minutes, or 30 minutes. The upper limit value of the heating time may be 120 minutes, 90 minutes, or 60 minutes.

[0053] The treatment method may further include an air retention step of retaining the aluminum dross in an air atmosphere before or after the retaining step. The aluminum dross contains metallic aluminum, aluminum nitride, etc. Since metallic aluminum may generate heat upon contact with water, and aluminum nitride may emit a bad smell upon contact with water, it is preferable to remove both. By providing the air retention step in the treatment method, the oxidation of metallic aluminum and aluminum nitride is promoted, and the content can be reduced.

[0054] The lower limit value of the retention time of the aluminum dross in the air retention step may be 20 minutes, 30 minutes, or 40 minutes. The upper limit value of the retention time is not particularly limited, and for example, it may be 600 minutes.

[0055] The aluminum dross is derived from the flux used in the refining of aluminum and the removal of metallic aluminum, and contains halides (fluorides and chlorides) that generate harmful gases by reacting with water, as well as other impurities. The retaining step of the treatment method volatilizes the halides as volatile components.

[0056] The fluorides are chemically more stable than the chlorides and are therefore difficult to remove. Fluorides are inevitably mixed in from fluxes used in refining molten aluminum and removing ash from aluminum dross, and react with the molten aluminum to form compounds such as KF, AlF3, and MgF2 in the aluminum dross. Among these, MgF2 is highly stable as a compound and is therefore difficult to remove. The heating process, performed under reduced pressure, promotes the volatilization of fluorides and prevents MgF2 from reacting with other fluorides in the aluminum dross during processing.

[0057] Like the fluorides, the chlorides are inevitably mixed in from the fluxes used in refining molten aluminum and in removing ash from aluminum dross, and exist in the aluminum dross as compounds such as KCl, AlCl3, and MgCl2 after reacting with the molten aluminum. In this treatment method, heating is performed under reduced pressure, which also promotes the volatilization of chlorides.

[0058] The other impurities include metallic aluminum and aluminum nitride. When metallic aluminum in aluminum dross comes into contact with water, it generates heat and causes hydrogen to be generated. This treatment method can remove at least a portion of the metallic aluminum, and the atmospheric holding step can more effectively remove metallic aluminum and also effectively remove aluminum nitride.

[0059] The holding step may include a procedure for removing volatilized components in the atmosphere, which can promote volatilization of volatile components remaining in the aluminum dross.

[0060] The removing step preferably includes a step of maintaining the pressure of the atmosphere constant and a step of reducing the partial pressure of the volatilized components below the equilibrium state. By maintaining the pressure of the atmosphere constant, it is possible to prevent the volatile components from filling the atmosphere, thereby promoting the volatilization effect. Furthermore, by reducing the partial pressure of the volatile components in the atmosphere below the equilibrium state, it is possible to further promote the volatilization effect. Note that the equilibrium state refers to the equilibrium state when the pressure of the atmosphere is maintained constant.

[0061] The method for maintaining the pressure of the atmosphere constant is not particularly limited, but for example, it can be a method of continuously evacuating the inside of the furnace with a pump, etc. The means for reducing the partial pressure of the volatile components in the atmosphere below the equilibrium state is not particularly limited, but for example, it can be a method of blowing air or an inert gas such as nitrogen into the heating furnace to replace the gas inside the heating furnace and then restoring the pressure to a reduced pressure.

[0062] [Method for producing halides] Among the volatile components, it is preferable to recover the halide derived from the flux and reuse it as a flux. That is, it is preferable to use the halide volatilized by the treatment method as a flux. In other words, a halide can be obtained by a halide production method including a step of recovering the volatilized halide by holding aluminum dross at a pressure P of 10,000 Pa or less and a temperature T of 700°C or more, and this halide can be used as a flux for aluminum refining, aluminum dross ash extraction, etc. The recovered halide can be cooled and agglomerated by a known method to form a powder, etc.

[0063] [Method of manufacturing low-halogenated aluminum dross] The aluminum dross from which harmful halides have been removed by this treatment method has low halogen content. That is, the method for producing low-halogen aluminum dross includes a step of removing volatilized halides by maintaining the aluminum dross at a pressure P of 10,000 Pa or less and a temperature T of 700°C or more.

[0064] The low-halogenated aluminum dross can be easily disposed of. Specifically, since the risk of contamination is reduced by removing the halides, it can be disposed of, for example, by landfilling. In addition, the low-halogenated aluminum dross can be reused as a deoxidizing agent or desulfurizing agent in steelmaking. Furthermore, since the low-halogenated aluminum dross contains oxides such as alumina as its main component, it can be reused, for example, as a refractory raw material or a secondary material for steelmaking.

[0065] The reduction rate of fluorine concentration in aluminum dross after treatment compared to aluminum dross before treatment is: Preferably, the fluorine concentration is 10% or more. That is, this treatment method can reduce the fluorine concentration in the aluminum dross (low-halogenated aluminum dross) after treatment by 10% or more compared to the aluminum dross (aluminum dross generated during the refining of molten aluminum) before the treatment method. This makes it possible to easily produce low-halogenated aluminum dross that can be disposed of and reused. The lower limit of the reduction rate is more preferably 30%, even more preferably 50%, and even more preferably 80%. The upper limit of the reduction rate is not particularly limited and may be, for example, 99%. The reduction rate refers to a value calculated using the following formula 2. {(Fluorine concentration in aluminum dross before treatment [mass%]) - (Fluorine concentration in aluminum dross after treatment [mass%])} / (Fluorine concentration in aluminum dross before treatment [mass%]) ····(2)

[0066] The upper limit of the fluorine concentration in the treated aluminum dross may be 3.0 mass%, 2.0 mass%, or 1.0 mass%. A preferred upper limit of the fluorine concentration is 0.5 mass%. The upper limit of the chlorine concentration in the treated aluminum dross may be 3.0 mass%, 2.0 mass%, or 1.0 mass%. A preferred upper limit of the chlorine concentration is 0.1 mass%. That is, it is preferable that the treated aluminum dross have a fluorine concentration of 0.5 mass% or less and a chlorine concentration of 0.1 mass% or less. In other words, this treatment method can convert the aluminum dross into low-halogenated aluminum dross having a fluorine concentration of 0.5 mass% or less and a chlorine concentration of 0.1 mass% or less. This improves the reliability of disposal of low-halogenated aluminum dross and the ease of reuse. The lower limits of the fluorine concentration and chlorine concentration are not particularly limited and may each be, for example, 0.01 mass%.

[0067] [Manufacturing method for blast furnace taphole mud] The method for producing a blast furnace taphole mud material includes mixing the low-halogenated aluminum dross obtained by the method for producing the low-halogenated aluminum dross with a refractory aggregate. The low-halogenated aluminum dross contains a relatively large amount of residual aluminum nitride compared to aluminum dross obtained by general dry processing. It is primarily composed of alumina and aluminum nitride, which are commonly used as refractory raw materials, making it suitable as a refractory raw material. It is known that a higher aluminum nitride concentration in a refractory material reduces wettability to molten metal and reduces pore size, thereby improving corrosion resistance. For this reason, the low-halogenated aluminum dross is particularly suitable as a blast furnace taphole mud material (hereinafter simply referred to as "mud material"). The term "major component" refers to the component with the highest content, e.g., a component with a content of 50% by mass or more.

[0068] If the mud material contains halides, there is a risk that the halides will be mixed into the blast furnace slag as the blast furnace taps the slag. The inclusion of halides, which are harmful impurities to the blast furnace slag, can significantly limit the uses of the blast furnace slag. The low-halogen mud material allows the blast furnace slag to be easily reduced in halogen content. The method for producing blast furnace taphole mud material uses the low-halogen aluminum dross, allowing the mud material to be easily reduced in halogen content.

[0069] The method for producing a blast furnace taphole mud material preferably includes a step of crushing the low-halogenated aluminum dross to 500 μm or less. The low-halogenated aluminum dross crushed to 500 μm or less may be mixed with the refractory aggregate. The crushing step may include, for example, a step of crushing the low-halogenated aluminum dross using a known crusher such as a roller crusher or a ball mill, and a step of sieving the crushed low-halogenated aluminum dross through a sieve with a mesh size of 500 μm. The mesh size is a value in accordance with JIS Z 8801-1:2019.

[0070] The upper limit of the particle size of the pulverized low-halogenated aluminum dross may be 300 μm, 150 μm, or 75 μm. By setting the particle size of the low-halogenated aluminum dross to the upper limit, an increase in the porosity and a decrease in the bulk density of the resulting mud material can be suppressed.

[0071] In the mixing step, it is preferable to further mix an organic binder. The amount of organic binder can be reduced by pulverizing the low-halogenated aluminum dross. The organic binder is not particularly limited, and known organic binders for mud materials, such as coal tar and phenol resin, may be used. The amount of organic binder mixed in the mixing step is not particularly limited, and may be adjusted depending on the amount of low-halogenated aluminum dross mixed.

[0072] The refractory aggregate is not particularly limited, and for example, known refractory aggregates such as alumina, bauxite, fireclay shale, chamotte, grog, chromite ore, spinel, magnesia, zirconia, zircon, silicon nitride, aluminum nitride, silicon carbide, boron carbide, and carbon such as graphite may be used.

[0073] The refractory aggregate is preferably granular. The particle size range of the refractory aggregate is not particularly limited, and it may be such that particles of 1.0 mm or more are 10% by mass or more, particles of 75 μm or less are 20% by mass or more, and the balance is particles of less than 1.0 mm and more than 75 μm.

[0074] The upper limit of the blending amount of the low-halogenated aluminum dross in the mixing step may be 50% by mass, or may be 40% by mass or 30% by mass. The lower limit of the blending amount may be 1% by mass, or may be 2.5% by mass or 5% by mass. By setting the blending amount within the above range, an increase in the porosity and a decrease in the bulk density of the mud material can be suppressed, and the amount of the organic binder can be reduced. The means for mixing the low-halogenated aluminum dross and the refractory aggregate is not particularly limited, and a known mixer or the like may be used.

[0075] [Method for manufacturing refractory molded body] The method for manufacturing the refractory molded body includes a step of molding a material containing the low-halogenated aluminum dross produced by the method for producing the low-halogenated aluminum dross, and a step of firing the molded material. The molded body of the refractory may deteriorate due to containing a halide. By using the low-halogenated aluminum dross as a refractory raw material, the deterioration of the molded body can be suppressed, and thus the deterioration of the equipment using the molded body can be suppressed.

[0076] The method for manufacturing the refractory formed body further includes a step of mixing the above-mentioned low-halogenated aluminum dross, alumina powder, and aluminum nitride powder. The above-mentioned materials are obtained by this mixing step. In the above-mentioned mixing step, it is preferable to further mix a known binder for refractories such as a cellulose-based, polyvinyl alcohol-based, or starch-based binder. The alumina powder includes alumina powder and alumina-silica powder containing 20% by mass or less of silica.

[0077] The blending amount of the aluminum nitride powder in the above-mentioned mixing step is not particularly limited, and is, for example, 5% by mass or more and 65% by mass or less. That is, the blending amounts of the low-halogenated aluminum dross and the alumina powder in the above-mentioned mixing step are 35% by mass or more and 95% by mass or less. The blending ratio of the low-halogenated aluminum dross and the alumina powder in the above-mentioned mixing step is not particularly limited and may be arbitrarily adjusted.

[0078] The particle size of the above-mentioned alumina powder is not particularly limited, and may be 1 mm or more, 5 μm or less, may have a uniform particle size, or may have a non-uniform particle size. The particle sizes of the above-mentioned low-halogenated aluminum dross and the above-mentioned alumina powder are not particularly limited, but from the viewpoint of promoting a decrease in the wettability of the refractory and refinement of the pore diameter, etc., they may be, for example, 20 μm or less.

[0079] In the above-mentioned forming step, the above-mentioned materials are formed into a predetermined shape by a known press molding machine or the like. The molding pressure in the above-mentioned press molding is not particularly limited, and is, for example, 200 kg / cm 2 or more and 1000 kg / cm 2It is as follows. The formed material may be dried. The drying is not particularly limited, and for example, it may be dried at 90°C or higher and 120°C or lower for 10 hours or longer and 24 hours or shorter. When the material contains the refractory binder, it is advisable to remove the refractory binder after drying. The removal of the refractory binder is not particularly limited, and for example, it may be removed by heating to 450°C or higher and 600°C or lower at a heating rate of 0.05°C / min or higher and 1°C / min or lower.

[0080] In the firing step, the material after the forming step is fired. The firing is not particularly limited, and for example, it may be fired by heating to 1600°C or higher and 1750°C or lower at a heating rate of 0.5°C / min or higher and 3°C / min or lower and maintaining this temperature for 2 hours or longer and 3 hours or shorter. In order to suppress the oxidation of aluminum nitride, the firing step is preferably carried out in a nitrogen atmosphere or by packing and firing in a powder such as aluminum nitride or silicon nitride.

[0081] In the method for manufacturing the refractory molded body, in the mixing step, the low-halogenated aluminum dross, the alumina powder, and the aluminum powder may be mixed. The obtained material (second material) may be formed, and the formed second material may be put into a reaction furnace and fired. The firing may be carried out, for example, by heating at a temperature of 560°C or higher and 660°C or lower under the flow of nitrogen gas, utilizing the reaction heat accompanying the nitridation of aluminum.

[0082] The refractory obtained by this method for producing a molded refractory body may contain, in addition to alumina and aluminum nitride, 2% or less each of substances such as MgO, Fe2O3, Na2O, K2O, TiO2, and ZrO2, which may be present as impurities in the raw materials. The total content of these substances is preferably 5% or less. The refractory may also contain 3% or less each of components such as Y2O3, HfO2, and CaO, which may be added or mixed in the manufacturing method of the molded refractory body as sintering aids or in other forms. The refractory may also contain 5% or less of phosphoric acid, phosphates, or both, which are known to have the effect of suppressing pore formation. However, to avoid impairing the properties of the refractory, the total amount of the above substances other than alumina and aluminum nitride, the above components, the above phosphoric acid, the above phosphate, etc., should not exceed 10%.

[0083] The refractories mentioned above are made of Al, which may be formed during firing. 10 N8O3, Al9N7O3, Al3O3N, AlN5O 14 It may contain 30% or less of an oxynitride such as the above.

[0084] [Method for refining molten aluminum] The refining method mainly includes a first refining step of refining molten aluminum, a step of holding the aluminum dross generated in the refining step in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700°C or more, a step of recovering the halide that has volatilized into the atmosphere in the holding step, and a second refining step of refining the molten aluminum using the halide recovered in the recovering step as a flux.

[0085] That is, the refining method includes refining of molten aluminum (primary refining) and a method for treating aluminum dross generated by refining the molten aluminum, recovering halides volatilized during the treatment of the aluminum dross, and using the recovered halides as a flux for refining molten aluminum (secondary refining) that is carried out after the primary refining using the same refining equipment as the primary refining. The refining method can achieve reduction of harm caused by aluminum dross inevitably generated by refining molten aluminum, utilization of the recovered halides (partial reuse of the generated aluminum dross), and cost reduction of the secondary refining by using the halides.

[0086] [Method for manufacturing aluminum material] The manufacturing method includes a step of solidifying the molten aluminum refined by the refining method. Since the aluminum material obtained by the manufacturing method uses the molten aluminum refined by the refining method, it can be manufactured at low cost. The manufacturing method may further include a step of solidifying the molten aluminum to obtain an aluminum ingot or an aluminum casting. When manufacturing an extruded material, the manufacturing method may further include a step of plastically processing the aluminum ingot. The plastic processing is not particularly limited and examples thereof include rolling, forging, extrusion, pressing, and the like.

[0087] [Other embodiments] The above embodiments do not limit the configuration of the present invention. Therefore, based on the description in this specification and common technical knowledge, components of each part of the above embodiments can be omitted, replaced, or added, and all of them should be construed as belonging to the scope of the present invention.

Examples

[0088] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0089] A graphite crucible containing 500 g of raw aluminum dross (residual ash) with a metallic aluminum concentration of 1.15% by mass was placed in a vacuum induction heating furnace. The furnace was first evacuated, then purged with argon gas. The vacuum pump was operated to reduce the pressure and control it to a predetermined level. The graphite crucible was heated by induction heating and held for a predetermined period of time. In Test Example 6 in Table 1 below, the pressure was reduced after heating. In the holding step, argon gas was supplied into the heating furnace to restore atmospheric pressure, and a gas (atmosphere) exchange operation was immediately performed to reduce the pressure. The gas exchange operation was performed 10 minutes after the start of the holding step and at 30-minute intervals thereafter. The aluminum dross after the holding step (treated aluminum dross) was chemically analyzed for fluorine, chlorine, and metallic aluminum concentrations. The chlorine concentration was measured by titration after distillation and extraction of the treated aluminum dross. The fluorine concentration was measured by Alfusson absorptiometry after distillation and extraction of the treated aluminum dross. The metallic aluminum concentration was calculated by ICP atomic emission spectrometry. The test conditions and results are shown in Table 1, along with the chlorine concentration, fluorine concentration, and metallic aluminum concentration of the raw aluminum dross (aluminum dross before treatment).

[0090] [Table 1]

[0091] In Test Example 1, it was confirmed that the fluorine concentration and chlorine concentration could be significantly reduced by the holding step in the treatment method. In Test Example 2, it was confirmed that the fluorine concentration and chlorine concentration could be further reduced by performing the gas exchange operation. In Test Example 3, it was confirmed that by extending the treatment time, the fluorine concentration could be reduced to 0.5% by mass or less and the chlorine concentration could be reduced to 0.1% by mass or less. In particular, the fluorine concentration and chlorine concentration in Test Example 3 are considered to be concentrations that can be used as cement raw materials or steel by-products. In Test Example 4, even when the holding temperature was set to 800°C, which was lower than that in Test Examples 1 to 3, it was confirmed that the fluorine concentration and chlorine concentration were significantly reduced. In Test Example 5, even when the holding pressure was set to 1000 Pa, which was higher than that in Test Examples 1 to 3, it was confirmed that the fluorine concentration and chlorine concentration were significantly reduced. In both Test Examples 4 and 5, the reduction amounts of the fluorine concentration and chlorine concentration were small, and it is considered that high-temperature and low-pressure holding conditions are desirable to further reduce the fluorine concentration and chlorine concentration. Test Example 6 was carried out under the same conditions as Test Example 2 except that the procedure of reducing the pressure after heating was performed. In Test Example 6, although the reduction rates of the fluorine concentration and chlorine concentration were lower than those in Test Example 2, they are considered to be within a sufficiently practical range. Test Example 7 was a treatment at normal pressure, and as a result, the fluorine concentration and chlorine concentration hardly changed even when compared with the raw materials before the holding step.

[0092] Furthermore, equilibrium calculations simulating the above test were conducted for comparison with the test results. The equilibrium calculations were performed using the commercially available thermodynamic calculation software Factsage 8.1 (Thermfact Ltd. / CRCT & GTT-Technologies). The weight of the aluminum dross and the volume of the heating furnace were the same as those used in the test. The equilibrium state was calculated when the aluminum dross was held at a specified temperature and pressure for a specified time under an argon atmosphere. Because it is difficult to accurately evaluate the effects of gas exchange in equilibrium calculations, gas exchange was not taken into account in the calculations. The composition of the aluminum dross at the start of the holding process was estimated from chemical analysis results. The equilibrium calculation results were organized with a focus on the fluorine concentration reduction rate among the fluorine and chlorine components. Figure 1 shows a graph of the temperature and pressure conditions under which a fluorine concentration reduction rate of 30% or more was calculated.

[0093] 1 represents the following formula 3, which satisfies the temperature and pressure conditions at which the fluorine concentration reduction rate is calculated to be 30% or more from the above equilibrium calculation. In order to improve the fluorine concentration reduction rate, it is preferable to carry out a step of maintaining the temperature T at such a temperature that the pressure P in the following formula 3 does not exceed the value on the right side (satisfies the above formula 1). P=10 {(T+273.15) / 50-22.5} ····(3)

[0094] As a result of the above equilibrium calculation, the temperature and pressure conditions under which the fluorine concentration reduction rate is calculated to be 50% or more are graphed and shown in Figure 2. The dashed line in Figure 2 shows, as an example, the following formula 4, which satisfies the temperature and pressure conditions under which the fluorine concentration reduction rate is calculated to be 50% or more from the above equilibrium calculation. In order to further improve the fluorine concentration reduction rate, it is more preferable to carry out a step of maintaining the temperature T at such a temperature that the pressure P in the following formula 4 does not exceed the value of the right-hand side of the formula (satisfying the following formula 5). P=10 {(T+273.15)×3 / 175-20} ····(4) P<10 {(T+273.15)×3 / 175-20} ····(5) [Industrial Applicability]

[0095] The aluminum dross processing method of the present disclosure can effectively reduce the halogen content of aluminum dross, thereby promoting cost reduction in the production of aluminum materials and improving the efficiency of aluminum dross disposal and reuse.

Claims

1. A method for treating aluminum dross, comprising: a step of holding the aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700°C or higher; A method for treating aluminum dross comprising the above step.

2. The atmosphere in the above holding step is a procedure for reducing the pressure to 10,000 Pa or less, and a procedure for heating to 700°C or higher after reducing the pressure. The method for treating aluminum dross according to Claim 1, formed by the above.

3. The method for treating aluminum dross according to Claim 1, further comprising a step of heating the aluminum dross under normal pressure before the above holding step.

4. The method for treating aluminum dross according to Claim 1, further comprising an air holding step of holding the aluminum dross in an air atmosphere before or after the above holding step.

5. The method for treating aluminum dross according to Claim 1, wherein the above holding step has a procedure for removing components volatilized in the above atmosphere.

6. The method for treating aluminum dross according to Claim 5, wherein the above removing procedure includes a procedure for maintaining the pressure of the above atmosphere constant and a procedure for reducing the partial pressure of the volatilized components below the equilibrium state.

7. The method for treating aluminum dross according to Claim 1, wherein the reduction rate of the fluorine concentration in the aluminum dross after treatment with respect to the aluminum dross before treatment is 10% or more.

8. The method for treating aluminum dross according to Claim 1, wherein the fluorine concentration in the aluminum dross after treatment is 0.5% by mass or less and the chlorine concentration is 0.1% by mass or less.

9. The method for treating aluminum dross according to Claim 1, wherein the pressure P and the temperature T in the above holding step satisfy the following formula 1. P < 10 ｛（Ｔ＋２７３．１５）／５０－２２．５｝ ・・・・(1)

10. The method for treating aluminum dross according to any one of Claims 1 to 9, wherein the above aluminum dross contains at least one of aluminum ash and residual ash.

11. A method for producing low-halogenated aluminum dross, comprising a step of removing halides volatilized in the above atmosphere by holding the aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700°C or higher.

12. A method for producing aluminum dross with reduced halides so as to be used as a refractory raw material or a deoxidizer or desulfurizer for steelmaking, comprising: The method for producing low-halogenated aluminum dross according to Claim 11, including the above removing step.

13. A method for producing a halide, comprising a step of recovering a halide volatilized into the atmosphere by holding aluminum dross in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher.

14. A method for producing a halide used as a flux, comprising: The method for producing a halide according to claim 13, comprising the step of recovering.

15. A first refining step of refining molten aluminum, A step of holding aluminum dross generated in the refining step in an atmosphere where the pressure P is 10,000 Pa or less and the temperature T is 700 °C or higher, A step of recovering a halide volatilized into the atmosphere in the holding step, A second refining step of refining molten aluminum using the halide recovered in the recovering step as a flux A method for refining molten aluminum, comprising:

16. A method for producing an aluminum material, comprising a step of solidifying the molten aluminum refined by the method for refining molten aluminum according to claim 15.

17. The method for producing an aluminum material according to claim 16, further comprising a step of solidifying the molten aluminum to obtain an aluminum ingot or an aluminum casting.

18. The method for producing an aluminum material according to claim 17, further comprising a step of plastically working the aluminum ingot.

19. A method for producing a mud material for a blast furnace tapping hole, comprising a step of mixing a low-halogenated aluminum dross produced by the method for producing a low-halogenated aluminum dross according to claim 11 with a refractory aggregate.

20. A step of forming a material containing a low-halogenated aluminum dross produced by the method for producing a low-halogenated aluminum dross according to claim 11, A step of firing the formed material A method for producing a refractory molded body, comprising:

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