WO2025053194A1 - Aluminum recovery method and aluminum recovery device - Google Patents

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

Aluminum recovery method and aluminum recovery device

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

When melting aluminum, slag (hereafter referred to as "aluminum dross" or simply "dross"), which is primarily composed of aluminum oxides produced during melting, forms on the surface of the molten metal in the melting furnace and is suspended in the molten metal, and also forms on the surface of the molten metal, where it floats and grows. It is necessary to remove this slag to prevent it from mixing with or contaminating the molten aluminum, maintain the quality of the molten metal, and also to make the heat transfer from the burner to the molten aluminum more efficient. Also, if it is left adhering to the furnace walls, it can cause damage to the furnace walls.

For this reason, flux is added to the molten metal in the furnace to separate and float suspended foreign matter such as oxides from the molten aluminum, thereby purifying the molten metal. On the surface of the molten metal, there are oxides and nitrides that are generated when the aluminum comes into contact with the burner combustion gas, and these, together with the floating aluminum oxides, some of the unreacted flux, and unseparated aluminum, form floating aluminum dross.

Floating aluminum dross needs to be discharged outside the furnace at appropriate times, but since the aluminum dross contains large amounts of unseparated molten aluminum and other useful metals, operations are carried out to separate and recover these. The weight of the aluminum dross generated is equivalent to 1-5 wt% of the molten aluminum, and the aluminum content in the aluminum dross accounts for 70-80 wt% of the weight of the aluminum dross generated.

A large proportion of the metals, such as aluminum, in the aluminum dross exists as fine molten droplets, but when discharged outside the furnace, the droplets, which consist of metals such as aluminum, solidify as the temperature drops, making it difficult to separate them from oxides, etc., and difficult to aggregate or combine, making it difficult to recover metals such as aluminum. For this reason, in conventional technology, a flux composed mainly of fluorine compounds, chlorine compounds, and nitrates, which act as combustion aids, is added in an amount equivalent to 5% to 15% of the weight of the discharged aluminum dross, making it easier to recover useful metals such as aluminum from the aluminum dross.

Fluxes used in the manufacturing process of aluminum products are primarily composed of chlorine and fluorine compounds, and are essential substances for the dissolving process and for the treatment of aluminum dross. However, they also cause a certain amount of environmental pollution, as they cause air pollution due to decomposition gases during use and remain in the aluminum dross residue after use.

The effect of adding flux is that, for example, fluorine compounds (NaF- _AlF3 type compounds) have a melting effect on the oxide film ( _Al2O3 ) that covers the aluminum droplets, dissolving the film and increasing the surface tension of the molten aluminum, etc., thereby promoting the separation of aluminum from the oxide _, etc. On the other hand, when reacting with aluminum dross, they decompose, releasing fluorine gas, which causes environmental pollution.

Chlorine compounds, unlike fluorine, have the effect of reducing the surface tension of aluminum droplets, which promotes the aggregation and coalescence of the droplets. In addition, when they coexist with fluorine compounds, they also have the effect of lowering the melting point of the fluorine compounds, making their reactions more efficient.

The nitrates decompose at high temperatures, accelerating the combustion of the aluminum and raising the temperature, further accelerating the separation.

For example, the Soil Contamination Countermeasures Act stipulates that the standard value for fluorine and its compounds in soil is 400 mg or less per kg of soil, and the standard value for the amount of fluorine leaching from soil is 0.8 mg or less per liter of test solution. On the other hand, as a result of using the above-mentioned flux, a considerable amount of fluorine compounds and chlorine compounds remain in the aluminum dross residue after metals such as aluminum are recovered from the aluminum dross, and the fluorine content can exceed 10%.

This is the main reason why aluminum dross residue is being restricted from being used as a secondary material for steel, which is the main recycling destination. For the same reason, it is also difficult to reuse it as roadbed material. Furthermore, aluminum dross contains several percent or more of aluminum nitride, which easily undergoes a chemical reaction when it comes into contact with water, generating large amounts of ammonia gas. For this reason, it is not easy to dispose of aluminum dross, and the number of managed waste disposal sites that can accept it is also running out.

To solve these problems, the following methods have been proposed to reduce the amount of flux used. For example, Patent Document 1 (JP Patent No. 3001080) discloses a technique in which aluminum dross scraped into a container is pressurized and vibrated from above and below, causing molten metal to drip from an opening in the bottom of the container and be collected in a metal receiver. Patent Document 2 (JP Patent Publication 2002-69541) discloses a technique in which vibration is applied to aluminum dross scraped into a container, causing molten metal to drip from an opening in the bottom of the container and be collected in a metal receiver.

Japanese Patent No. 3001080 Japanese Patent Application Publication No. 2002-69541

However, these technologies have only been adopted in limited areas because the aluminum recovery rate is relatively low compared to the mixing method that uses the conventional amount of flux.

One aspect of the present invention aims to provide a technology that can recover aluminum from aluminum dross discharged outside the furnace to at least the same extent as conventional technology, without using flux or by using a reduced amount of flux in the operation of recovering useful metals such as aluminum from aluminum dross discharged outside the furnace. This technology can reduce the amount of flux used in the entire aluminum melting process, including the process of recovering aluminum from aluminum dross.

In order to solve the above problems, one embodiment of the aluminum recovery method of the present invention is a method for recovering aluminum from aluminum dross, and includes the steps of: storing the aluminum dross heated to a temperature equal to or higher than the melting point of aluminum in a container; inserting a vibrating plate into the aluminum dross and vibrating the vibrating plate to impart vibration to the aluminum dross and promote the oxidation reaction of the aluminum dross, thereby agglomerating aluminum droplets while maintaining the temperature of the aluminum dross at 700 to 900°C; and pressurizing and stirring in parallel to perform pressurization and stirring.

In order to solve the above problems, an aluminum recovery device according to one embodiment of the present invention is an aluminum recovery device that recovers aluminum from aluminum dross, and includes a container that stores the aluminum dross heated to or above the melting point of aluminum, a vibration device that applies vibrations to the aluminum dross by inserting a vibration plate into the aluminum dross in the container and vibrating it, and a pressurized agitator that agitates and applies pressure to the aluminum dross by inserting it into the aluminum dross in the container and rotating it.

According to one aspect of the present invention, it is possible to recover aluminum from aluminum dross discharged outside the furnace at least to the same extent as with conventional technology, without using flux or by using a reduced amount of flux.

FIG. 1 is a block diagram showing a configuration of an aluminum recovery device 1 according to a first embodiment of the present invention. 2 is a schematic diagram showing a specific configuration example of a container and a vibration device according to the first embodiment. FIG. FIG. 2 is a schematic diagram showing an example of the arrangement of a vibration plate inserted into aluminum dross. FIG. 11 is a schematic diagram showing another example of the arrangement of the vibration plate inserted into the aluminum dross. FIG. 13 is a schematic diagram showing yet another example of the arrangement of the vibration plate inserted into the aluminum dross. FIG. 4 is a schematic diagram showing an example of the shape of a diaphragm. FIG. 2 is a schematic diagram showing an example of the shape of an agitation blade of a stirring device. 1 is a flowchart showing the flow of an aluminum recovery method S1. FIG. 6 is a schematic diagram showing a propeller-type pressurized stirring device according to a second embodiment. FIG. 6 is a schematic diagram showing a helical screw type pressurized stirring device according to a second embodiment. 1 is a flowchart showing the flow of an aluminum recovery method S2 according to a second embodiment. This is an example of a photograph of a cut surface when aluminum dross is vibrated by a vibrating plate, causing the dispersed molten aluminum droplets to aggregate and form a lump, which is then cooled in that state. This is an example of a photograph of a cut surface when aluminum dross under different conditions was subjected to vibration by a vibrating plate to cause molten aluminum droplets to aggregate into lumps, which were then cooled in that state.

Before explaining the embodiments of the present invention, we will first explain aluminum dross. Aluminum dross discharged into a container from a melting furnace in an aluminum product manufacturing plant is composed of nonmetallic substances such as aluminum oxide and aluminum nitride, and fine molten metal droplets mainly composed of aluminum. Because aluminum is a very chemically active metal in a molten state, an oxide film instantly forms on its surface, and this oxide film continues to grow as it undergoes repeated phase transformations. Since this phase transformation process involves volumetric contraction, the oxide film develops tears, exposing the active droplet surfaces inside and causing new oxidation. Therefore, the oxide film covering the molten aluminum-based metal droplets (aluminum droplets) continues to grow and become thicker as long as oxygen is supplied.

By vibrating the aluminum dross in the container, the aluminum-based metal droplets that are finely dispersed in the powder of oxides and nitrides of metals such as aluminum are made to collide with each other due to the shock waves (energy) generated by the vibration. During this process, the metal droplets undergo elastic deformation but are not destroyed, while the outer shells that cover the droplets and are made of non-metallic substances such as oxides are destroyed as they are brittle materials, and the droplets inside come into direct contact with each other, coagulating and merging, and becoming larger.

When the outer shell, which is made of a non-metallic material, is destroyed, in the presence of oxygen, a part of the aluminum droplet is instantaneously oxidized, releasing heat of oxidation and raising the temperature of the entire surrounding aluminum dross, raising the temperature to a temperature range suitable for recovering metal droplets such as aluminum. Oxygen is present in the air contained in the aluminum dross, which contains solids. Oxygen is also supplied by mixing air into the aluminum dross due to vibration. The temperature rise of the aluminum dross due to the heat of oxidation caused by the bond between oxygen and aluminum can reach 1000°C or more if vibration is continued for a long period of time. In this case, the aluminum will be worn down excessively, so it is preferable to limit the rise to about 100°C to 200°C and manage the temperature of the aluminum dross to about 700°C to 900°C. This promotes the oxidation reaction of the aluminum dross, and while maintaining the temperature of the aluminum dross at 700-900°C, the aluminum droplets can be coagulated.

Although this heat generation phenomenon is similar in effect to the chemical reaction effect obtained by adding flux, it is due to a mechanism based on a fundamentally different physical phenomenon. By utilizing this physical phenomenon, there is no need to add flux, preventing air pollution that occurs when flux is used and significantly reducing residual flux components in the aluminum dross residue after metals such as aluminum are recovered. Therefore, even when the aluminum dross residue is further recycled or treated as waste, environmental pollution caused by residual flux components such as fluorine is significantly reduced.

The inventors conducted an experiment to aggregate aluminum-based metal droplets by vibration. In this experiment, aluminum dross generated in a factory was discharged and then rapidly cooled, then heated again in a crucible, a vibrator (vibration plate) was inserted and vibration was added, and then the crucible was rapidly cooled together to preserve its state. The aluminum dross removed was impregnated with resin to fix it, then cut in a direction perpendicular to the vibration plate, and the cross section was photographed and observed. This experiment was repeated with different samples and vibration conditions. It was believed that the differences in the aggregation and coalescence state of the aluminum in the dross were influenced by differences in the vibration conditions, the amount of aluminum present in the aluminum dross used in the test, the remaining amount of flux used in the furnace before being discharged, and other sample properties.

[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 an aluminum melting process. The aluminum recovery apparatus 1 includes a vibration device 20 that imparts vibrations to aluminum dross heated to or above the melting point of aluminum. The aluminum recovery apparatus 1 may further include a stirring device 30.

(Aluminum recovery device 1)
The configuration of the aluminum recovery apparatus 1 will be described. Fig. 1 is a block diagram showing the configuration of the aluminum recovery apparatus 1 according to the first embodiment of the present invention. The aluminum recovery apparatus 1 includes a container 10 and a vibration device 20. Furthermore, the aluminum recovery apparatus 1 may include a stirring device 30 as shown in the figure.

2 is a schematic diagram showing a specific example of the configuration of the container 10 and the vibration device 20. In FIG. 2, 201 shows a front view (viewed from the A direction of 203), 202 shows a side view (viewed from the B direction of 203), and 203 shows a plan view and a cross-sectional view of the container 10. The container 10 and the vibration device 20 are supported by a stand 50. The container 10 has a spherical bottom. The vibration device 20 includes a vibration plate 21 and a vibration unit 22. The vibration unit 22 is a device that vibrates the vibration plate 21. The vibration 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 a jack. Then, the vibration plate 21 is vibrated using the vibration unit 22 to impart vibration to the aluminum dross.

The container 10 stores aluminum dross heated to above the melting point of aluminum. The container 10 is made of steel or other material that can withstand high temperatures in order to store aluminum dross at approximately 700°C to 900°C. In the example shown in Figure 2, the container 10 has a hemispherical bottom, but the shape of the container 10 can be box-shaped or any other shape. An outlet port for removing the accumulated molten aluminum may be provided at the bottom of the container 10.

The vibration device 20 applies vibration to the aluminum dross contained in the container 10 by inserting a vibration plate into the aluminum dross and vibrating it. As shown in FIG. 2, the vibration device 20 includes a plurality of vibration plates 21 and a vibration unit 22 that vibrates the vibration plates 21. The shape of the vibration plate 21 depends on the size of the container 10, but for example, in 601 in FIG. 6, it is flat with a width of about 5 to 10 cm and a thickness of about 0.5 to 1.5 cm, and in 602 in FIG. 6, it has a shape with an increased width and thickness at the tip. Also, 603 in FIG. 6 shows the case of a vibrator that rotates and vibrates in the axial direction. The length of the vibration plate 21 is longer than the length inserted into the aluminum dross, and it is sufficient that it has a length that can be connected to the vibration unit 22. The material of the vibration plate 21 needs to withstand high temperatures like the container 10, so it is preferable to form it from, for example, steel, cast iron, or titanium, which has better heat resistance and strength.

The upper end of the diaphragm 21 is connected to the vibration unit 22. The vibration unit 22 can vibrate the diaphragm 21 with an amplitude of, for example, about 0.8 to 50 mm and a vibration frequency of about 5 to 300 Hz.

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

When performing the stirring process, the container 10 after vibration may be moved from the vibration device 20 to the stirrer 30 and the stirring process may be performed. The vibration device 20 may be replaced with the stirrer 30 and the stirring process may be performed. After the vibration device 20 is moved, the stirrer 30 may be inserted into the aluminum dross stored in the container 10 to stir the aluminum dross. In other words, the vibration device 20 and the stirrer 30 may be configured as replacement type devices that can be separately attached to the container 10. The structure of the stirrer 30 will be described later.

Alternatively, the container 10 may be configured to be portable, and when vibration treatment is performed, the aluminum dross stored in the container 10 may be subjected to vibration treatment using the vibration device 20, and when stirring treatment is 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 may be provided for stirring treatment, and when stirring treatment is performed, the aluminum dross in the container 10 may be transferred to another container for stirring treatment and stirred. The side view shown at 201 in Figure 2 shows a spout 11 for transferring the aluminum dross from the container 10 to another container.

Next, the shapes of the vibration plate 21 and the stirring blades 31 of the stirring device 30 will be described. Note that the figures described below are examples, and the shapes of the vibration plate 21 and the stirring blades 31 are not limited. Figure 3 is a schematic diagram showing an example of the arrangement of the vibration plate 21 inserted into the aluminum dross in the container 10. In Figure 3, 301 shows a top view, 302 shows a front view, and 303 shows a side view. Note that the container 10 is square, and a cross-sectional view is shown. The vibration plate 21 shown in Figure 3 is formed in a substantially rectangular flat plate shape. The length of the vibration plate 21 is made different according to the depth of the container 10. The vibration plates 21 are arranged in the same direction and substantially parallel to each other. Each vibration plate 21 may be vibrated collectively, or may be vibrated in groups of several. The vibration direction is perpendicular to the flat plate surface.

Figure 4 is a schematic diagram showing another example of the arrangement of the vibration plate 21 inserted into the aluminum dross. In Figure 4, 401 shows a top view, 402 shows a front view, and 403 shows a side view. The container 10 is square, and a cross-sectional view is shown. The vibration plate 21 shown in Figure 4 is formed in a substantially rectangular flat plate shape. The length of the vibration plate 21 is made different according to the depth of the container 10. There are two groups of vibration plates 21 arranged in the same direction, and the two groups are arranged in directions perpendicular to each other. The groups of vibration plates 21 arranged in the same direction may be vibrated together, or each group may be vibrated separately. The vibration direction is perpendicular to the flat plate surface.

FIG. 5 is a schematic diagram showing yet another example of the arrangement of the vibration plates 21 inserted into the aluminum dross. In FIG. 5, 501 shows a top view, and 502 shows a front view. The container 10 is round and hemispherical. The vibration plate 21 shown in FIG. 5 is formed in a substantially rectangular flat plate shape. The length of the vibration plate 21 is made to differ according to the depth of the container 10. The arrangement of the vibration plates 21 is such that three groups are arranged in directions that differ from each other by 120°. Each vibration plate 21 is vibrated in groups of three. The vibration direction is perpendicular to the flat plate surface.

FIG. 6 is a schematic diagram showing an example of the shape of the vibration plate 21. 601 in FIG. 6 shows a side view and a front view of a rectangular vibration plate 21. 602 shows a side view and a front view of a drumstick-shaped vibration plate 21 with a wider bottom. 603 shows a side view and a top view of a vibration plate with four trapezoidal fins attached to the bottom of a cylindrical support rod. In the case of the vibration plate 21 shown in 603, the aluminum dross is vibrated by rotating and vibrating the cylindrical support rod alternately clockwise and counterclockwise when viewed from above.

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

(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. FIG. 8 is a flow chart 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 include step S13. Furthermore, the aluminum recovery method S1 may include step S14. The aluminum dross is generated, for example, in an aluminum melting process. Alternatively, it may be aluminum dross remaining after primary recovery of aluminum from aluminum dross generated in the aluminum melting process.

Step S11 is a process of storing aluminum dross heated to above the melting point of aluminum in a container. The aluminum dross generated in the aluminum melting process is itself heated to above the melting point of aluminum, and can be used as is. The aluminum dross after the primary aluminum recovery is at room temperature, and is heated to above the melting point of aluminum in an electric furnace or the like. The heated aluminum dross is then stored in the container 10. Alternatively, the container 10 may be equipped with an electric heating device for heating, and the aluminum dross stored in the container 10 may be heated to above the melting point of aluminum.

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

Step S13 is a stirring process in which an agitator is inserted into the aluminum dross after it has been vibrated in the vibration process of step S12 and operated to stir the aluminum dross. By keeping the temperature at 700-900°C and stirring the aluminum dross, which has become agglomerated clumps of aluminum droplets, the remaining molten aluminum is combined and can be efficiently recovered.

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

The aluminum recovery device 1 and aluminum recovery method S1 for recovering aluminum from aluminum dross described above make it possible to recover aluminum from aluminum dross discharged outside the furnace at least to the same extent as with conventional technology, without using flux or by using a reduced amount of flux.

In addition, because it is possible to recover aluminum to the same extent as with conventional technology without using flux, or to recover aluminum to the same extent as with conventional technology by using a reduced amount of flux, it is possible to dramatically reduce the content of fluorine, an environmental pollutant, in the recycling of aluminum dross residue after recovering metals such as aluminum from aluminum dross, thereby promoting the recycling of this into auxiliary materials for steel, roadbed materials, etc.

[Embodiment 2]
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

The aluminum recovery device (not shown) of the second embodiment includes a pressurized agitator 40 instead of the agitator 30. The pressurized agitator 40 is a device that applies pressure to the aluminum dross while agitating it. The pressure is applied in the direction of gravity (downward), for example.

FIG. 9 is a schematic diagram showing a propeller-type pressurized agitator 40. In FIG. 9, 901 shows a perspective view of the pressurized agitator 40 arranged inside the container 10, 902 shows a top view thereof, and 903 shows a side view thereof. In 903, the container 10 is shown in cross section. The propeller-type pressurized agitator 40 is equipped with a rotating shaft 41 and a pressurized agitator blade (propeller) 42. The propeller-type pressurized agitator 40 has three to four propellers 42 arranged around the rotating shaft 41. By rotating the pressurized agitator 40 around the rotating shaft 41, pressure is generated that presses the aluminum dross toward the bottom of the container 10. At the same time, a stirring force is also generated that rotates and stirs the aluminum dross. In this way, the pressurized agitator 40 can simultaneously stir and pressurize the aluminum dross. This applies a shear force to the aluminum dross, promoting the destruction and coalescence of tiny molten aluminum particles. This allows for a reduction in the amount of flux used and allows for the recovery of aluminum from aluminum dross to be achieved to the same extent as with conventional technology.

FIG. 10 is a schematic diagram showing a pressurized agitator 40 using a helical screw. In FIG. 10, 1001 shows a top view of the pressurized agitator 40 placed inside the vessel 10, and 1002 shows a side view of the pressurized agitator 40. The helical screw type pressurized agitator 40 has a pressurized agitator blade (helical screw) 42, such as 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 toward the bottom of the vessel 10. The effect of the pressurized agitator 40 using this helical screw 42 is similar to that of the pressurized agitator 40 using a propeller 42. The pressurized agitator 40 is equipped with a known rotation drive unit (motor), but this is not shown in FIGS. 9 and 10.

The aluminum recovery method S2 according to this embodiment will be described with reference to the drawings. FIG. 11 is a flow chart showing the flow of the aluminum recovery method S2 according to this embodiment for recovering aluminum from aluminum dross. 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.

Steps S21 and S22 are the same as steps S11 and S12 of the aluminum recovery method S1 described in embodiment 1, and therefore will not be described here. Step S23 is a pressure stirring step in which the aluminum dross after vibration in the vibration step of step S22 is stirred while applying pressure (pressurization and stirring are performed in parallel).

More specifically, the pressurized stirring process applies a rotational force to the aluminum dross that rotates it in a circular shape when viewed from above, and a pressure that presses it downward. This process pushes the block-shaped molten aluminum lumps that have aggregated and coalesced due to the vibration effect of the previous process downward. It also applies a shear force that destroys the coating of the aluminum droplets present in the aluminum dross. This breaks down and coalesces the tiny molten aluminum droplets.

Step S24 is a process for 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 at the bottom of the container 10 and allowing it to fall under its own weight and the applied pressure.

The estimated aluminum recovery rate when using conventional technology, in which aluminum dross is agitated to recover aluminum, and the estimated aluminum recovery rate when using the present invention, in which aluminum dross is vibrated and then further pressurized and agitated to recover aluminum, are shown in Table 1 below.

As shown in Table 1 above, according to the aluminum recovery device and aluminum recovery method S2 of embodiment 2, similar to the effect of embodiment 1, it is possible to recover aluminum from aluminum dross at least to the same extent as with the conventional technology without using flux or by using a reduced amount of flux.

In addition, since it is possible to recover aluminum to the same extent as with conventional technologies without using flux, or to recover aluminum to the same extent as with conventional technologies using a reduced amount of flux, it is possible to dramatically reduce the content of fluorine, an environmental pollutant, in the recycling of aluminum dross residue after recovering metals such as aluminum from aluminum dross, thereby promoting the recycling of this into auxiliary materials for steel, roadbed materials, etc.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of this disclosure also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments.

[Vibration experiment - reference example]
An example of an experiment conducted by the inventors to apply vibration to aluminum dross will be described. This experiment was conducted to confirm the effect of agglomerating aluminum in aluminum dross by applying vibration to the aluminum dross. Specifically, aluminum dross generated in a melting process in an aluminum factory was discharged and then rapidly cooled, and then heated again to 800°C in a crucible to melt it. After a vibration plate was inserted and vibration was applied, the crucible was immersed in a container filled with dry ice to preserve the state, and rapidly cooled to 300°C or less in about 15 minutes.

The aluminum dross was then impregnated with resin and solidified, after which it was cut and the cross section photographed for observation. This experiment was repeated with different samples and vibration conditions. Figures 12 and 13 are photographs of the cut surface of aluminum dross treated under different vibration conditions after cooling. Figure 12 is an example of a photograph of a cut surface of aluminum dross that was cooled in a state in which it was vibrated by a vibrating plate to aggregate the dispersed molten aluminum droplets and form a mass. Specifically, the vibration experiment was performed for a total of 5 minutes, with a vibration frequency of 20 Hz and a vibration time of 2 minutes, followed by 25 Hz for 3 minutes, with an amplitude of 25 mm, and the aluminum dross set temperature of 800°C. Figure 13 is the vibration experiment result for a vibration frequency of 10 Hz, an amplitude of 25 mm, a vibration time of 5 minutes, and the aluminum dross set temperature of 800°C. These temperatures were measured using a thermocouple temperature measurement method.

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

The photographs on the right side of Figure 12 and Figure 13 are photographs of the left and right cut sections of the aluminum dross after it has been impregnated with resin. The white parts in the cross-sectional photographs are aluminum, and a white lump-like object can be seen near the diaphragm; this is a block-like growth formed when tiny aluminum droplets gather and coalesce due to vibration. The fine white particles present away from the diaphragm are solidified aluminum droplets that did not coalesce.

The cross-sectional observations revealed that the range of vibration influence may differ from experiment to experiment, and that the proportion of aluminum that aggregates may differ from experiment to experiment. These differences were interpreted as being influenced by differences in the vibration conditions, the amount of aluminum present in the aluminum dross used in the tests, the amount of residual flux used in the furnace before discharge, and other sample properties.

As a result of repeating such experiments, it was found that the vibration amplitude should be approximately 0.8 to 50 mm, preferably 0.8 to 30 mm, and more preferably 1 to 20 mm. It was also found that the vibration frequency should be approximately 2 to 100 Hz, preferably 5 to 50 Hz, and more preferably 5 to 25 Hz. The vibration direction of the diaphragm is roughly perpendicular to the plate surface of the diaphragm, in other words, the thickness direction of the diaphragm. This is to maximize the transmission of the pressing force of the diaphragm caused by vibration to the aluminum dross.

As shown by the above data, by adding a pressurized stirring process to the vibration process, the aluminum droplets can be broken down and agglomerated by applying additional impact and shear forces, so it is expected that even if a smaller amount of flux is used, it will be possible to recover at least the same amount of aluminum from aluminum dross as with conventional technology.

Reference Signs List 1: Aluminum recovery device 10: Container 20: Vibration device 21: Vibration plate 30: Stirring device 31: Rotating shaft 32: Stirring blade 40: Pressurized stirring device 41: Rotating shaft 42: Pressurized stirring blade (propeller or helical screw)
50: stand 60: support rod 70: lifting device

Claims (8)

An aluminum recovery method for recovering aluminum from aluminum dross, comprising the steps of:
A step of placing the aluminum dross heated to a melting point of aluminum or higher in a container;
The aluminum recovery method includes a vibration step of inserting a vibrating plate into the aluminum dross, vibrating the vibrating plate to impart vibration to the aluminum dross and promote an oxidation reaction of the aluminum dross, thereby agglomerating aluminum droplets while maintaining the temperature of the aluminum dross at 700 to 900°C, and a pressurizing and stirring step of performing pressurization and stirring in parallel. The aluminum recovery method according to claim 1, wherein the pressurized stirring process is a process of applying a rotational force to the aluminum dross that rotates the aluminum dross in a circular shape when viewed from above, and a pressure that presses the aluminum dross downward. The aluminum recovery method according to claim 1, wherein the pressurized stirring process is a process of applying a shear force to the aluminum dross that breaks the coating of aluminum droplets present in the aluminum dross. The aluminum recovery method according to any one of claims 1 to 3, wherein the pressurized stirring step is a step of pressurizing and stirring the aluminum dross using a helical screw. The aluminum recovery method according to any one of claims 1 to 3, wherein the vibration step is a step of maintaining the temperature of the aluminum dross at 700 to 900°C by introducing air into the aluminum dross by vibration, or by destroying the oxide film covering the surface of the aluminum droplets by vibration to expose the chemically active aluminum surface, thereby promoting oxidation of the surface of the aluminum droplets. Aluminum dross residue remaining after aluminum is recovered using the aluminum recovery method according to any one of claims 1 to 3. An aluminum recovery apparatus for recovering aluminum from aluminum dross, comprising:
A container for storing the aluminum dross heated to a temperature equal to or higher than the melting point of aluminum;
a vibration device that applies vibration to the aluminum dross by inserting a vibration plate into the aluminum dross in the container and vibrating the aluminum dross;
a pressurizing stirring device that is inserted into the aluminum dross in the container and rotated to stir and pressurize the aluminum dross;
An aluminum recovery device comprising: The aluminum recovery device according to claim 7, wherein the pressurized agitator is equipped with a helical screw.

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