Aluminum recovery method and aluminum recovery apparatus

Abstract

The present invention efficiently recovers aluminum from aluminum dross without using a flux or while reducing an amount of a flux used. An aluminum recovery method according to the present invention comprises: a step (S11) for accommodating, in a container, aluminum dross which has been heated to a temperature equal to or higher than the melting point of aluminum; a vibrating step (S12) for applying vibration to the aluminum dross and causing aluminum droplets to aggregate while keeping the temperature at 700-900°C; and a pressurization-stirring step (S13) for performing pressurization and stirring in parallel.

Description

Technical Field

[0001] The present invention relates to an aluminum recovery method and an aluminum recovery apparatus for recovering aluminum from aluminum dross generated in the melting process during the manufacturing process of aluminum products.

Background Art

[0002] When melting aluminum, dross mainly composed of aluminum oxide generated during melting (hereinafter also referred to as "aluminum dross" or simply "dross") is generated on the surface of the molten metal in the melting furnace, suspended in the molten metal, and also generated, floating, and growing on the surface of the molten metal. It is necessary to remove this to prevent contamination and mixing into the molten aluminum, maintain the quality of the molten metal, and further improve the efficiency of heat transfer from the burner to the molten aluminum. Also, leaving it attached to the furnace wall will cause damage to the furnace wall.

[0003] For this reason, a flux is added to the molten metal in the furnace to separate and float foreign substances such as suspended oxides from the aluminum molten metal to clean the molten metal. On the surface of the molten metal, oxides and nitrides generated by the contact of aluminum with the combustion gas of the burner exist. The floating aluminum oxide, a part of the unreacted flux, and unseparated aluminum are added to this to form floating aluminum dross.

[0004] The floating aluminum dross needs to be discharged outside the furnace as appropriate. At this time, since the aluminum dross entrains a large amount of useful metal components such as unseparated molten aluminum, an operation to separate and recover these is being carried out. The weight of the generated aluminum dross corresponds to 1 to 5 wt% of the melting weight of the melted aluminum, and moreover, the aluminum content in the aluminum dross accounts for 70% to 80 wt% of the weight of the generated aluminum dross.

[0005] In aluminum dross, a large proportion of metals such as aluminum exist as molten fine droplets. However, once discharged outside the furnace, these droplets, consisting of metals such as aluminum, solidify as the temperature decreases, making separation from oxides and other substances difficult. This hinders aggregation and aggregation, thus making it difficult to recover the metals such as aluminum. For this reason, conventional technology involves adding a flux mainly composed of fluorine compounds, chlorine compounds, and nitrates (combustion aids) in an amount equivalent to 5% to 15% of the weight of the discharged aluminum dross to facilitate the recovery of useful metals such as aluminum from the aluminum dross.

[0006] Flux used in the manufacturing process of aluminum products consists mainly of chlorine and fluorine compounds and is an indispensable substance for the dissolution process and the treatment of aluminum dross. However, it also causes air pollution from decomposition gases during use and a certain degree of environmental pollution from residues remaining in the aluminum dross after use.

[0007] One effect of adding flux is that, for example, fluorine compounds (NaF-AlF3 compounds) dissolve the oxide film (Al2O3) covering aluminum droplets through a melting effect, increasing the surface tension of molten aluminum and promoting the separation of aluminum from oxides. On the other hand, they decompose when reacting with aluminum dross, releasing fluorine gas and causing environmental pollution.

[0008] Chlorine compounds, unlike fluorine, reduce the surface tension of aluminum droplets, thus promoting the aggregation and fusion of droplets. Furthermore, when present with fluorine compounds, they lower the melting point of the fluorine compounds, thereby improving the efficiency of their reactions.

[0009] Nitrates decompose at high temperatures, promoting the combustion of aluminum and raising the temperature, which further accelerates the separation process.

[0010] For example, the Soil Contamination Countermeasures Act stipulates that the soil content standard for fluorine and its compounds is 400 mg or less per kg of soil, and the elution standard for fluorine from soil is 0.8 mg or less per liter of test solution. On the other hand, as a result of using the flux described above, a considerable amount of fluorine compounds and chlorine compounds remain in the aluminum dross residue after recovering metals such as aluminum from the aluminum dross, and the content rate of fluorine may exceed 10%.

[0011] This is the main reason why the use of aluminum dross residue in steelmaking auxiliary materials, which is its primary recycling destination, is becoming restricted. For the same reason, its reuse as roadbed material is also becoming difficult. Furthermore, aluminum dross contains several percent or more of aluminum nitride, which readily undergoes a chemical reaction with water, generating large amounts of ammonia gas. For this reason, disposing of aluminum dross is not easy, and the number of controlled waste disposal sites that can accept it is becoming depleted.

[0012] To address these problems, the following methods have been proposed to reduce the amount of flux used. For example, Patent Document 1 (Japanese Patent No. 3001080) discloses a technique in which molten metal is dripped from an opening at the bottom of a container by applying pressure and vibration from both above and below to the aluminum dross scraped into the container, and then collected in a metal receiver. Patent Document 2 (Japanese Unexamined Patent Publication No. 2002-69541) also discloses a technique in which molten metal is dripped from an opening at the bottom of a container by applying vibration to the aluminum dross scraped into the container, and then collected in a metal receiver. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent No. 3001080 [Patent Document 2] Japanese Patent Publication No. 2002-69541 [Overview of the project] [Problems that the invention aims to solve]

[0014] However, these technologies have only gained limited traction because they yield relatively lower aluminum recovery rates compared to conventional agitation methods using the same amount of flux.

[0015] One aspect of the present invention aims to provide a technology that allows for the recovery of aluminum and other useful metals from aluminum dross discharged outside a furnace without using flux, or with reduced flux usage, to recover at least the same amount of aluminum as in the conventional technology. This technology makes it possible to reduce the amount of flux used throughout the entire aluminum melting process, including the aluminum recovery process from aluminum dross. [Means for solving the problem]

[0016] To solve the above problems, an aluminum recovery method according to one aspect of the present invention is an aluminum recovery method for recovering aluminum from aluminum dross, comprising: a step of placing the aluminum dross, which has been heated above the melting point of aluminum, into a container; a vibration step of inserting a vibrating plate into the aluminum dross, vibrating the vibrating plate to vibrate the aluminum dross, thereby promoting the oxidation reaction of the aluminum dross, maintaining the temperature of the aluminum dross at 700 to 900°C, and causing aluminum droplets to condense; and a pressurizing and stirring step of performing pressurization and stirring in parallel.

[0017] Also, in order to solve the above problems, an aluminum recovery device according to an aspect of the present invention is an aluminum recovery device that recovers aluminum from aluminum dross, and includes a container for storing the aluminum dross heated to a temperature equal to or higher than the melting point of aluminum, a vibration device for applying vibration to the aluminum dross by inserting and vibrating a diaphragm into the aluminum dross in the container, and a pressurized stirring device for stirring the aluminum dross and applying pressure by inserting and rotating it into the aluminum dross in the container.

Effect of the Invention

[0018] According to an aspect of the present invention, aluminum can be recovered from aluminum dross discharged outside the furnace at least to the same extent as in the prior art without using a flux or by reducing the amount of flux used.

Brief Description of the Drawings

[0019] [Figure 1] It is a block diagram showing the configuration of an aluminum recovery device 1 according to Embodiment 1 of the present invention. [Figure 2] It is a schematic diagram showing a specific configuration example of the container and the vibration device according to Embodiment 1. [Figure 3] It is a schematic diagram showing an example of the arrangement of the diaphragm inserted into the aluminum dross. [Figure 4] It is a schematic diagram showing another example of the arrangement of the diaphragm inserted into the aluminum dross. [Figure 5] It is a schematic diagram showing still another example of the arrangement of the diaphragm inserted into the aluminum dross. [Figure 6] It is a schematic diagram showing an example of the shape of the diaphragm. [Figure 7] It is a schematic diagram showing an example of the shape of the stirring blade of the stirring device. [Figure 8] It is a flowchart showing the flow of the aluminum recovery method S1. [Figure 9] It is a schematic diagram showing a propeller-type pressurized stirring device according to Embodiment 2. [Figure 10] It is a schematic diagram showing a spiral screw type pressurized stirring device according to Embodiment 2. [Figure 11] It is a flowchart showing the flow of the aluminum recovery method S2 according to Embodiment 2. [Figure 12] It is an example of a photograph of a cross section when vibration is applied to aluminum dross by a diaphragm, the molten aluminum droplets that were dispersed are aggregated into a lump, and the state is cooled as it is. [Figure 13] It is an example of a photograph of a cross section when vibration is applied to aluminum dross under other conditions by a diaphragm to aggregate molten aluminum droplets into a lump and the state is cooled as it is.

Mode for Carrying Out the Invention

[0020] Before explaining the embodiments of the present invention, first, aluminum dross will be explained. Aluminum dross discharged from a melting furnace in an aluminum product manufacturing factory into a container is composed of non-metallic substances such as aluminum oxide and aluminum nitride and fine metal droplets in a molten state mainly composed of aluminum. Since aluminum is a chemically very active metal in a molten state, an oxide film is instantaneously formed on its surface, and the oxide film continuously grows while repeating phase transformation. Since volume contraction occurs during this phase transformation process, the oxide film develops cracks, and the active droplet surface inside is exposed, resulting in new oxidation. Therefore, as long as oxygen is supplied, the oxide film covering the metal droplets mainly composed of aluminum in this molten state continues to grow and increase in thickness.

[0021] By applying vibration to the aluminum dross in the container, the metal droplets mainly composed of aluminum finely dispersed in the powder of oxides and nitrides of metals such as aluminum are collided with each other by shock waves (energy) generated by the vibration. At this time, the metal droplets are elastically deformed but not broken, and the outer shell part made of non-metallic substances such as oxides covering the droplets is a brittle substance, so it is broken, and the internal droplets come into direct contact with each other, aggregate, and grow larger.

[0022] Furthermore, when the outer shell, which is made of non-metallic material, is destroyed, under conditions where oxygen is present, a portion of the aluminum droplets are instantaneously oxidized, releasing heat of oxidation and raising the temperature of the entire surrounding aluminum dross to a temperature range suitable for recovering metallic droplets such as aluminum. Oxygen is present in the air contained within the aluminum dross, which is mixed with solid material. Oxygen is also supplied when air is mixed into the aluminum dross by vibration. The temperature rise of the aluminum dross due to the heat of oxidation from the combination of oxygen and aluminum can reach over 1000°C if vibration is continued for a long time, but in this case, the wear of aluminum becomes excessive, so it is preferable to limit the rise to about 100°C to 200°C and control the temperature reached by the aluminum dross to about 700°C to 900°C. This promotes the oxidation reaction of the aluminum dross, allowing the aluminum droplets to condense while maintaining the temperature of the aluminum dross at 700-900°C.

[0023] This exothermic phenomenon, while similar in result to the chemical reaction effect obtained by adding flux, is due to a fundamentally different physical mechanism. By utilizing this physical phenomenon, the addition of flux is unnecessary, thus preventing air pollution that occurs when flux is used and significantly reducing the residue of flux components in aluminum dross after the recovery of metals such as aluminum. Therefore, even when further recycling the aluminum dross residue or treating it as waste, environmental pollution caused by residual flux components such as fluorine is significantly reduced.

[0024] The inventors conducted an experiment to agglomerate aluminum-based metal droplets using vibration. In this experiment, aluminum dross generated in a factory was discharged, rapidly cooled, then reheated in a crucible, a vibrator (diaphragm) was inserted to apply vibration, and the crucible was rapidly cooled to preserve the state. The removed aluminum dross was impregnated with resin to fix it, then cut perpendicular to the diaphragm, and the cross-section was photographed and observed. This experiment was repeated with different samples and vibration conditions. The differences in the agglomeration and coalescence of aluminum in the dross were thought to be influenced by differences in vibration conditions, the amount of aluminum present in the aluminum dross used in the test, and the residual amount of flux used in the furnace before discharge, among other differences in the properties of the samples.

[0025] [Embodiment 1] Based on the above findings, an aluminum recovery apparatus 1 according to one embodiment of the present invention will be described in detail with reference to the drawings. The aluminum recovery apparatus 1 is an apparatus for recovering aluminum from aluminum dross generated in the aluminum melting process. The aluminum recovery apparatus 1 includes a vibrator 20 that vibrates the aluminum dross heated above the melting point of aluminum. The aluminum recovery apparatus 1 may further include a stirring device 30.

[0026] (Aluminum recovery device 1) The configuration of the aluminum recovery device 1 will now be described. Figure 1 is a block diagram showing the configuration of the aluminum recovery device 1 according to Embodiment 1 of the present invention. The aluminum recovery device 1 comprises a container 10 and a vibrator 20. Furthermore, the aluminum recovery device 1 may also be equipped with a stirring device 30 as shown in the figure.

[0027] Figure 2 is a schematic diagram showing a specific configuration example of the container 10 and the vibrating device 20. In Figure 2, 201 is a front view (viewed from direction A of 203), 202 is a side view (viewed from direction B of 203), and 203 is a plan view and a cross-sectional view of the container 10. The container 10 and the vibrating device 20 are supported by a frame 50. The container 10 has a spherical bottom. The vibrating device 20 comprises a vibrating plate 21 and an excitation unit 22. The excitation unit 22 is a device that vibrates the vibrating plate 21. The vibrating plate 21 is inserted into the aluminum dross stored in the container 10 from the top of the container 10 by a support rod 60 and a lifting device 70 such as a hydraulic or pneumatic cylinder or jack. Then, vibration is applied to the aluminum dross by vibrating the vibrating plate 21 using the excitation unit 22.

[0028] Container 10 stores aluminum dross heated above the melting point of aluminum. Since container 10 stores aluminum dross at temperatures between 700°C and 900°C, it is made of steel or other material that can withstand high temperatures. In the example shown in Figure 2, container 10 has a hemispherical bottom, but the shape of container 10 can be box-shaped or any other shape. An outlet for removing the accumulated molten aluminum may be provided at the bottom of container 10.

[0029] The vibration device 20 vibrates the aluminum dross contained within the container 10 by inserting a vibrating plate into the dross and vibrating it. As shown in Figure 2, the vibration device 20 comprises a plurality of vibrating plates 21 and an excitation unit 22 that vibrates the vibrating plates 21. The shape of the vibrating plate 21 depends on the size of the container 10, but for example, in Figure 6, 601, which has a width of about 5 to 10 cm and a thickness of about 0.5 to 1.5 cm, it is flat, and in Figure 6, 602, the tip has a shape in which the width and thickness increase. Figure 6, 603 shows the case of an oscillator that rotates and vibrates in the axial direction. The length of the vibrating plate 21 should be longer than the length to be inserted into the aluminum dross and long enough to be connected to the excitation unit 22. The material of the vibrating plate 21 needs to withstand high temperatures, just like the container 10, so it is preferable to form it from materials such as steel, cast iron, or titanium, which has better heat resistance and strength.

[0030] The upper end of the diaphragm 21 is connected to the excitation unit 22. The excitation unit 22 can vibrate the diaphragm 21 with an amplitude of approximately 0.8 to 50 mm and a frequency of approximately 5 to 300 Hz.

[0031] The diaphragms 21 can be arranged to efficiently vibrate in accordance with the shape of the container holding the aluminum dross. The cross-sectional view of 203 in Figure 2 shows an example in which the diaphragms 21 are arranged in an X shape. By arranging the diaphragms 21 in an X shape, vibration can be applied to the entire aluminum dross with a relatively small number of plates. However, the arrangement of the diaphragms 21 is not limited to an X shape. For example, the diaphragms 21 may be arranged evenly in parallel inside the container 10.

[0032] When performing a stirring process, the container 10, after vibration has been applied, may be moved from the vibrating device 20 to the stirring device 30 for stirring. Alternatively, the vibrating device 20 may be replaced with the stirring device 30 for stirring. The stirring device 30 may be inserted into the aluminum dross stored in the container 10 after the vibrating device 20 has been moved, and the aluminum dross may be stirred. In other words, the vibrating device 20 and the stirring device 30 may be configured as interchangeable devices that can be individually attached to the container 10. The structure of the stirring device 30 will be described later.

[0033] Alternatively, if the container 10 is configured to be portable and vibration treatment is to be performed, the aluminum dross stored in the container 10 may be vibrated using the vibration device 20, and if stirring treatment is to be performed, the container 10 may be moved to the bottom of the stirring device 30 and the aluminum dross may be stirred. Alternatively, a separate container for stirring treatment may be provided, and if stirring treatment is to be performed, the aluminum dross in the container 10 may be transferred to the separate container for stirring treatment. The side view shown in 201 of Figure 2 shows a spout 11 for transferring the aluminum dross from the container 10 to another container.

[0034] Next, the shapes of the vibrating plate 21 and the stirring blade 31 of the stirring device 30 will be described. Note that the figures described below are examples, and the shapes of the vibrating plate 21 and the stirring blade 31 are not limited. Figure 3 is a schematic diagram showing an example of the arrangement of the vibrating plate 21 inserted into the aluminum dross of the container 10. In Figure 3, 301 is a top view, 302 is a front view, and 303 is a side view. Note that the container 10 is rectangular, and a cross-sectional view is shown. The vibrating plate 21 shown in Figure 3 is formed in the shape of a roughly rectangular flat plate. The length of the vibrating plate 21 is varied according to the depth of the container 10. The vibrating plates 21 are arranged roughly parallel to each other in the same direction. Each vibrating plate 21 may be excited together, or they may be excited in several groups. The direction of excitement is perpendicular to the flat plate surface.

[0035] Figure 4 is a schematic diagram showing another example of the arrangement of the diaphragm 21 inserted into the aluminum dross. In Figure 4, 401 is a top view, 402 is a front view, and 403 is a side view. Note that the container 10 is rectangular, and a cross-sectional view is shown. The diaphragm 21 shown in Figure 4 is formed in the shape of a roughly rectangular flat plate. The length of the diaphragm 21 is varied to match the depth of the container 10. There are two groups of diaphragms 21 arranged in the same direction, and these two groups are arranged in orthogonal directions. Each group of diaphragms 21 arranged in the same direction may be excited together, or each group may be excited individually. The excitation direction is perpendicular to the flat plate surface.

[0036] Figure 5 is a schematic diagram showing yet another example of the arrangement of the diaphragms 21 inserted into the aluminum dross. 501 in Figure 5 shows a top view, and 502 shows a front view. The container 10 is round and hemispherical. The diaphragms 21 shown in Figure 5 are formed in a roughly rectangular flat plate shape. The length of the diaphragms 21 varies according to the depth of the container 10. The arrangement of the diaphragms 21 consists of three groups arranged in directions that are 120° apart from each other. Each diaphragm 21 is excited along with the other three groups. The excitation direction is perpendicular to the flat plate surface.

[0037] Figure 6 is a schematic diagram showing an example of the shape of the diaphragm 21. Figure 601 shows a side view and a front view of a rectangular diaphragm 21. Figure 602 shows a side view and a front view of a fan-shaped diaphragm 21 with a flared bottom. Figure 603 shows a side view and a top view of a diaphragm with four trapezoidal fins attached to the bottom of a cylindrical support rod. In the case of the diaphragm 21 shown in Figure 603, vibration is applied to the aluminum dross by rotating the cylindrical support rod alternately clockwise and counterclockwise when viewed from above.

[0038] Figure 7 is a schematic diagram showing an example of the shape of the stirring blade 31 of the stirring device 30. In Figure 7, 701 is a perspective view of the stirring blade 31, 702 is a top view, and 703 is a side view.

[0039] (Aluminum recovery method S1) Next, an aluminum recovery method S1 for recovering aluminum from aluminum dross using the aluminum recovery apparatus 1 having the above configuration will be described. Figure 8 is a flowchart showing the flow of the aluminum recovery method S1. The aluminum recovery method S1 includes steps S11 and S12. The aluminum recovery method S1 may also include step S13. Furthermore, the aluminum recovery method S1 may also include step S14. Aluminum dross is generated, for example, in the aluminum melting process. Alternatively, it may be aluminum dross remaining after primary aluminum recovery from the aluminum dross generated in the aluminum melting process.

[0040] Step S11 is the process of storing the aluminum dross, which has been heated above the melting point of aluminum, in a container. The aluminum dross generated in the aluminum melting process is itself heated above the melting point of aluminum, so it can be used as is. Since the aluminum dross after the primary recovery of aluminum is at room temperature, it is heated above the melting point of aluminum in an electric furnace or the like. Then, the heated aluminum dross is stored in container 10. Alternatively, the container 10 may be equipped with an electric heating device to heat the aluminum dross stored in container 10 above the melting point of aluminum.

[0041] Step S12 is a vibration process in which a vibrating plate is inserted into the molten aluminum dross, and the vibrating plate is vibrated to vibrate the aluminum dross, thereby promoting the oxidation reaction of the aluminum dross and maintaining the temperature of the aluminum dross at 700-900°C. This vibration process maintains the temperature of the aluminum dross at 700-900°C by introducing air into the interior of the aluminum dross through vibration, or by destroying the oxide film covering the surface of the aluminum droplets through vibration, thereby exposing the chemically active aluminum surface and promoting the oxidation of the aluminum droplet surface. In other words, the temperature can be maintained at 700-900°C by promoting the oxidation reaction of the substances in the aluminum dross. This vibration process also has the effect of agglomerating and coalescing the molten aluminum droplets dispersed in the aluminum dross into a solid mass. The temperature of the aluminum during vibration can be measured indirectly using an infrared thermometer or by a thermocouple temperature measurement method.

[0042] Step S13 is a stirring step in which a stirring blade is inserted into the aluminum dross after it has been vibrated in the vibration step of step S12 and activated to stir the aluminum dross. By stirring the aluminum dross, in which the aluminum droplets have aggregated into clumps while maintaining a temperature of 700-900°C, the molten remaining aluminum can be combined and recovered efficiently.

[0043] Step S14 is the process of removing the molten aluminum that has been combined by vibration and stirring. The molten aluminum can be removed, for example, by opening an outlet provided at the bottom of the container 10 and letting it fall by its own weight.

[0044] According to the aluminum recovery apparatus 1 and aluminum recovery method S1 described above, it is possible to recover aluminum from aluminum dross discharged outside the furnace to at least the same extent as the conventional technology, without using flux or with reduced flux usage.

[0045] Furthermore, since it is possible to recover aluminum to the same extent as conventional technology without using flux, or to recover aluminum to the same extent as conventional technology with reduced flux usage, the content of fluorine, an environmental pollutant, can be dramatically reduced in the recycling of aluminum dross residue after the recovery of metal components such as aluminum from aluminum dross, thereby promoting its recycling into auxiliary materials for steelmaking, roadbed materials, etc.

[0046] [Embodiment 2] Other embodiments of the present invention will be described below. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0047] The aluminum recovery apparatus (not shown) according to Embodiment 2 is equipped with a pressurized agitator 40 instead of the agitator 30. The pressurized agitator 40 is a device that agitates the aluminum dross while applying pressure. The direction in which the pressure is applied is, for example, in the direction of gravity (downward).

[0048] Figure 9 is a schematic diagram showing a propeller-type pressurized agitator 40. Figure 9 shows a perspective view of the pressurized agitator 40 located inside the container 10 (901), a top view (902), and a side view (903). 903 shows a cross-sectional view of the container 10. The propeller-type pressurized agitator 40 comprises a rotating shaft (41) and pressurized agitator blades (propellers) (42). Three to four propellers (42) are arranged around the rotating shaft (41). Rotating the pressurized agitator 40 around the rotating shaft (41) generates pressure that presses the aluminum dross toward the bottom of the container 10. Simultaneously, an agitation force is generated that rotates and agitates the aluminum dross. In this way, the pressurized agitator 40 can simultaneously agitate and pressurize the aluminum dross. This applies shear force to the aluminum dross, promoting the fracture and coalescence of minute molten aluminum particles. This allows for reduced flux usage while achieving the same level of aluminum recovery from aluminum dross as with conventional techniques.

[0049] Figure 10 is a schematic diagram showing a pressurized agitator 40 using a helical screw. Figure 10 shows a top view of the pressurized agitator 40 located inside the container 10, and 1002 shows a side view thereof. The helical screw type pressurized agitator 40 is equipped with pressurized agitation blades (helical screws) 42, similar to those of an Archimedes pump, around a rotating shaft 41. By rotating the pressurized agitator 40 around the rotating shaft 41, the aluminum dross can be agitated while applying pressure towards the bottom of the container 10. The effect of this pressurized agitator 40 using a helical screw 42 is the same as that of a pressurized agitator 40 using a propeller 42. The pressurized agitator 40 is equipped with a known rotary drive unit (motor), but it is not shown in Figures 9 and 10.

[0050] The aluminum recovery method S2 according to this embodiment will be described with reference to the drawings. Figure 11 is a flowchart showing the flow of the aluminum recovery method S2 for recovering aluminum from aluminum dross according to this embodiment. The aluminum recovery method S2 includes steps S21 and S22. The aluminum recovery method S2 may also include step S23. Furthermore, the aluminum recovery method S2 may also include step S24.

[0051] Steps S21 and S22 are the same as steps S11 and S12 of the aluminum recovery method S1 described in Embodiment 1, so their explanation will be omitted. Step S23 is a pressurized stirring step in which the aluminum dross that has been vibrated in the vibration step of step S22 is stirred while pressure is applied (pressurization and stirring are performed in parallel).

[0052] More specifically, the pressurized stirring process applies a rotational force to the aluminum dross, causing it to rotate in a circular motion when viewed from above, and a downward pressure. This process pushes the block-shaped molten aluminum mass, which has aggregated and coalesced due to the vibration effect of the previous process, downward. It also applies a shearing force that breaks the coating of aluminum droplets present in the aluminum dross. This allows the minute molten aluminum droplets to be broken and coalesced.

[0053] Step S24 is the process of removing the molten aluminum that has been combined by vibration and pressurized stirring. The molten aluminum can be removed, for example, by opening an outlet provided at the bottom of the container 10 and letting it fall due to its own weight and applied pressure.

[0054] Table 1 below shows the aluminum recovery rate when using the conventional technique of recovering aluminum by stirring aluminum dross, and the estimated aluminum recovery rate when using the present invention, which recovers aluminum by vibrating the aluminum dross and then further pressurizing and stirring it.

[0055] [Table 1]

[0056] As shown in Table 1 above, according to the aluminum recovery apparatus and aluminum recovery method S2 of Embodiment 2, similar to the effects of Embodiment 1, aluminum can be recovered from aluminum dross to at least the same extent as in the prior art, without using flux or with reduced flux usage.

[0057] Furthermore, since it is possible to recover aluminum to the same extent as conventional technology without using flux, or to recover aluminum to the same extent as conventional technology with reduced flux usage, the content of fluorine, an environmental pollutant, can be dramatically reduced in the recycling of aluminum dross residue after the recovery of aluminum and other metal components from aluminum dross, thereby promoting its recycling into auxiliary materials for steelmaking, roadbed materials, etc.

[0058] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Examples]

[0059] [Vibration experiment - example] This section describes an example of an experiment conducted by the inventors involving the application of vibration to aluminum dross. This experiment was conducted to confirm the cohesive effect of aluminum in aluminum dross caused by vibration. Specifically, aluminum dross generated in the melting process of an aluminum factory was discharged, rapidly cooled, then heated again in a crucible to 800°C and melted. A vibrating plate was inserted to apply vibration, and then the crucible was immersed in a container filled with dry ice to rapidly cool it to below 300°C in about 15 minutes in order to preserve the state.

[0060] The extracted aluminum dross was impregnated with resin to fix it in place, then cut, and the cross-section was photographed and observed. This experiment was repeated with different samples and vibration conditions. Figures 12 and 13 are photographs of the cooled cross-sections of aluminum dross treated under different vibration conditions. Figure 12 is an example of a photograph of a cross-section obtained by applying vibration with a diaphragm to aluminum dross, causing the dispersed molten aluminum droplets to condense into a mass, which was then cooled in that state. Specifically, the vibration was applied at a frequency of 20 Hz for 2 minutes, and then at 25 Hz for 3 minutes, for a total of 5 minutes, with an amplitude of 25 mm, and the set temperature of the aluminum dross was 800°C. Figure 13 is the result of a vibration experiment under the conditions of a frequency of 10 Hz, amplitude of 25 mm, vibration time of 5 minutes, and a set temperature of 800°C for the aluminum dross. These temperatures were measured using a thermocouple method.

[0061] The left side of the photographs in Figures 12 and 13 shows the top surface of the solid aluminum dross removed from the crucible. The black holes extending to the left and right are traces (holes) where the diaphragm was inserted. The vertical dotted lines indicate the cutting direction of the solid aluminum dross. The cutting direction is perpendicular to the diaphragm.

[0062] The right side of the photographs in Figures 12 and 13 shows the left and right cross-sections of the aluminum dross after resin impregnation. In the cross-sectional photographs, the white areas are aluminum, and near the diaphragm, white, lumpy objects can be observed. These are formed when fine droplets of aluminum aggregate and combine due to vibration, growing into block-like structures. The fine white particles located away from the diaphragm are solidified aluminum droplets that did not aggregate.

[0063] Cross-sectional observations revealed that the range of vibration influence varied from experiment to experiment, as did the proportion of aluminum aggregates. These differences were interpreted as being influenced by differences in vibration conditions, the amount of aluminum present in the aluminum dross used in the test, and the residual amount of flux used in the furnace before discharge, among other differences in the properties of the sample.

[0064] Through repeated experiments, it was found that the amplitude of the vibration should be approximately 0.8 to 50 mm, preferably 0.8 to 30 mm, and even more preferably 1 to 20 mm. Furthermore, the frequency should be approximately 2 to 100 Hz, preferably 5 to 50 Hz, and even more preferably 5 to 25 Hz. The direction of vibration of the diaphragm is roughly perpendicular to the surface of the diaphragm, that is, in the direction of the diaphragm's thickness. This is to maximize the transmission of the pressing force of the diaphragm due to vibration to the aluminum dross.

[0065] As shown in the data above, by adding a pressurized stirring process to the vibration process, impact and shear forces can be applied to the aluminum droplets, causing them to break down and aggregate. Therefore, even with a reduced amount of flux used, it is expected that aluminum can be recovered from the aluminum dross to at least the same level as with conventional technology. [Explanation of Symbols]

[0066] 1…Aluminum recovery device 10...Container 20...Vibration device 21...Diaphragm 30...Stirring device 31…Rotation axis 32...Agitation blade 40... Pressurized stirring device 41…Rotation axis 42…Pressurized agitator blades (propeller or helical screw) 50… Stand 60...Support rod 70... Lifting device

Claims

1. An aluminum recovery method for recovering aluminum from aluminum dross, A step of placing the aluminum dross, which has been heated above the melting point of aluminum, into a container, A vibration step is performed in which a diaphragm is inserted into the aluminum dross, and the diaphragm is vibrated to vibrate the aluminum dross, thereby introducing air into the interior of the aluminum dross to promote the oxidation reaction of the aluminum dross, and thereby maintaining the temperature of the aluminum dross at 700 to 900°C while causing aluminum droplets to condense. This includes a pressurized stirring step in which pressurization and stirring are performed in parallel, The aluminum recovery method is a process in which the pressurized stirring step applies a rotational force to the aluminum dross that causes it to rotate in a circular motion when viewed from above, and a downward pressure to press it down.

2. The aluminum recovery method according to claim 1, wherein the pressurized stirring step is a step of applying a shear force to the aluminum dross that breaks the film of aluminum droplets present in the aluminum dross.

3. The aluminum recovery method according to claim 1 or 2, wherein the pressurized stirring step is a step of pressurizing and stirring the aluminum dross using a helical screw.

4. An aluminum recovery device for recovering aluminum from aluminum dross, A container for storing the aluminum dross heated above the melting point of aluminum, A vibrating device that vibrates the aluminum dross by inserting a diaphragm into the aluminum dross in the container and vibrating it, A pressurized stirring device is inserted into the aluminum dross in the container and rotated to agitate the aluminum dross and apply pressure, Equipped with, The aforementioned vibrating device introduces air into the aluminum dross by vibrating the diaphragm, The pressurized stirring device is equipped with a helical screw that applies a rotational force to the aluminum dross, causing it to rotate in a circular motion when viewed from above, and a downward pressure to the aluminum dross. Aluminum recovery device.

5. The aluminum recovery apparatus according to claim 4, wherein the pressurized stirring device is equipped with a propeller instead of the helical screw.

6. An aluminum recovery method for recovering aluminum from aluminum dross without using flux, A step of placing the aluminum dross, which has been heated above the melting point of aluminum and does not contain the flux, into a container, A vibration step is performed in which a diaphragm is inserted into the aluminum dross, and the diaphragm is vibrated to vibrate the aluminum dross, thereby introducing air into the interior of the aluminum dross to promote the oxidation reaction of the aluminum dross, and thereby maintaining the temperature of the aluminum dross at 700 to 900°C while causing aluminum droplets to condense. This includes a pressurized stirring step in which pressurization and stirring are performed in parallel, The aluminum recovery method is a process in which the pressurized stirring step applies a rotational force to the aluminum dross that causes it to rotate in a circular motion when viewed from above, and a downward pressure to press it down.

7. Aluminum dross residue after recovering aluminum using the aluminum recovery method described in Claim 1 or 6.

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