Aluminum recovery method and aluminum recovery device

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

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

[0002] When melting aluminum, slag (hereinafter referred to as "aluminum dross" or simply "dross"), primarily composed of aluminum oxides produced during melting, forms on the surface of the molten metal in a melting furnace and is suspended in the molten metal. It 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 ensure efficient heat transfer from the burner to the molten aluminum. Furthermore, if the slag is left adhering to the furnace walls, it can cause damage to the furnace walls.

[0003] For this reason, flux is added to the molten aluminum in the furnace to separate and float suspended foreign matter such as oxides from the molten aluminum, thereby cleaning the molten aluminum. On the surface of the molten aluminum, there are oxides and nitrides that are formed when the aluminum comes into contact with the combustion gas from the burner, and these, along with the floated aluminum oxides, some of the unreacted flux, and unseparated aluminum, make up floating aluminum dross.

[0004] The floating aluminum dross must be discharged outside the furnace at appropriate times, but since the aluminum dross entrains a large amount of useful metals such as unseparated molten aluminum, these are separated and recovered. The weight of the aluminum dross generated corresponds to 1 to 5 wt% of the weight of the molten aluminum, and the aluminum content in the aluminum dross accounts for 70 to 80 wt% of the weight of the aluminum dross generated.

[0005] A large proportion of metals such as aluminum in the aluminum dross exist as fine molten droplets, but when discharged outside the furnace, these droplets of metals such as aluminum solidify as the temperature drops, making it difficult to separate them from oxides, etc., and to aggregate and combine them, making it difficult to recover metals such as aluminum. For this reason, in conventional technology, a flux containing fluorine compounds, chlorine compounds, and nitrates, which act as combustion aids, as its main components 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.

[0006] Fluxes used in the manufacturing process of aluminum products are primarily composed of chlorine and fluorine compounds, and are essential substances for the dissolution process and for treating aluminum dross. However, they also cause a certain amount of environmental pollution, as they produce decomposition gases during use and remain in the aluminum dross residue after use.

[0007] The effect of adding flux is, for example, the effect of adding fluorine compounds (NaF-AlF ３ The oxide film (Al-based compounds) covering the aluminum droplets ２ O ３ ) and increases the surface tension of molten aluminum, promoting the separation of aluminum from oxides, etc. On the other hand, when it reacts with aluminum dross, it decomposes, releasing fluorine gas, which causes environmental pollution.

[0008] Contrary to fluorine, chlorine compounds have the effect of reducing the surface tension of aluminum droplets, which promotes the aggregation and coalescence of droplets. In addition, when coexisting with fluorine compounds, they also have the effect of lowering the melting point of the fluorine compounds, making their reaction more efficient.

[0009] The nitrates decompose at high temperatures and promote the combustion of the aluminum, increasing the temperature and thereby further promoting the separation.

[0010] For example, the Soil Contamination Countermeasures Act stipulates that the standard value for the content of fluorine and its compounds in soil is 400 mg or less per kg of soil, and that the standard value for the amount of fluorine eluted from soil is 0.8 mg or less per L of test solution. On the other hand, as a result of using the above-mentioned flux, considerable amounts 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 may exceed 10%.

[0011] This is the main reason why aluminum dross residue is being limited in its use as a secondary material for steelmaking, which is the main recycling destination for the residue. For the same reason, its reuse as roadbed material is also difficult. Furthermore, aluminum dross contains several percent or more of aluminum nitride, which readily undergoes a chemical reaction with water to generate 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 capable of accepting it is running out.

[0012] To solve these problems, the following methods have been proposed for the purpose of reducing the amount of flux used. For example, Patent Document 1 (Japanese Patent No. 3001080) discloses a technique in which aluminum dross scraped into a container is vibrated from above and below while being pressurized, causing molten metal to drip from an opening in the bottom of the container and be collected in a metal receiver. Also, Patent Document 2 (Japanese Patent Laid-Open No. 2002-69541) discloses a technique in which aluminum dross scraped into a container is vibrated, causing molten metal to drip from an opening in the bottom of the container and be collected in a metal receiver.

[0013] Japanese Patent No. 3001080 Japanese Patent Application Laid-Open No. 2002-69541

[0014] However, these technologies have only been widely adopted because the aluminum recovery rate is relatively low compared to the agitation method that uses the conventional amount of flux.

[0015] An object of one aspect of the present invention is to provide a technology that can recover aluminum from aluminum dross discharged outside a 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 treatment of recovering aluminum from aluminum dross.

[0016] In order to solve the above-described problems, an aluminum recovery method according to one embodiment of the present invention is a method for recovering aluminum from aluminum dross, and includes the steps of: placing 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 vibrations 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 pressurizing and stirring in parallel.

[0017] In order to solve the above-mentioned problems, an aluminum recovery apparatus according to one embodiment of the present invention is an aluminum recovery apparatus that recovers aluminum from aluminum dross, and includes: a container that stores the aluminum dross heated to a temperature equal to or higher than the melting point of aluminum; a vibration device that applies vibrations to the aluminum dross by inserting a vibrating plate into the aluminum dross in the container and vibrating it; and a pressurized agitator that is inserted into the aluminum dross in the container and rotates it to agitate and apply pressure to the aluminum dross.

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

[0019] 1 is a block diagram showing the configuration of an aluminum recovery apparatus 1 according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a specific configuration example of a container and a vibration device according to the first embodiment. FIG. 3 is a schematic diagram showing an example of the arrangement of a vibration plate inserted into aluminum dross. FIG. 4 is a schematic diagram showing another example of the arrangement of a vibration plate inserted into aluminum dross. FIG. 5 is a schematic diagram showing yet another example of the arrangement of a vibration plate inserted into aluminum dross. FIG. 6 is a schematic diagram showing an example of the shape of a vibration plate. FIG. 7 is a schematic diagram showing an example of the shape of an agitation blade of an agitation device. FIG. 8 is a flowchart showing the flow of an aluminum recovery method S1. FIG. 9 is a schematic diagram showing a propeller-type pressure agitation device according to a second embodiment. FIG. 10 is a schematic diagram showing a helical screw-type pressure agitation device according to the second embodiment. FIG. 11 is a flowchart showing the flow of an aluminum recovery method S2 according to the second embodiment. FIG. 12 is an example of a photograph of a cross section when aluminum dross is subjected to vibration by a vibration plate to agglomerate dispersed molten aluminum droplets, and the resulting agglomerated state is cooled as is. FIG. 13 is an example of a photograph of a cross section when aluminum dross under other conditions is subjected to vibration by a vibration plate to agglomerate molten aluminum droplets, and the resulting agglomerated state is cooled as is.

[0020] Before describing 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 non-metallic substances such as aluminum oxide and aluminum nitride, and fine molten metal droplets primarily composed of aluminum. Because aluminum is a highly chemically active metal in a molten state, an oxide film instantly forms on its surface. This oxide film continues to grow as it undergoes repeated phase transformations. This phase transformation process involves volumetric contraction, which causes tears in the oxide film, exposing the active droplet surfaces inside and leading to new oxidation. Therefore, the oxide film covering these molten aluminum-based metal droplets (aluminum droplets) continues to grow and thicken as long as oxygen is supplied.

[0021] By vibrating the aluminum dross in the container, the metal droplets, mainly aluminum, which are finely dispersed among the powder of oxides and nitrides of metals such as aluminum, are caused to collide with each other by the shock waves (energy) generated by the vibration. At this time, the metal droplets undergo elastic deformation but are not destroyed, while the outer shells made of non-metallic substances such as oxides that cover the droplets are destroyed because they are brittle, and the internal droplets come into direct contact with each other, coagulating and coalescing, and becoming larger.

[0022] Furthermore, when the nonmetallic outer shell is destroyed, in the presence of oxygen, a portion of the aluminum droplets is instantaneously oxidized, releasing heat of oxidation and raising the temperature of the surrounding aluminum dross 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. Vibration also supplies oxygen by mixing air into the aluminum dross. The temperature rise of the aluminum dross due to oxidation heat caused by the bonding of oxygen and aluminum can reach 1,000°C or more if vibration is continued for a long period of time. However, in this case, excessive aluminum wear occurs. Therefore, it is preferable to limit the temperature rise to approximately 100°C to 200°C and control the temperature of the aluminum dross to approximately 700°C to 900°C. This promotes the oxidation reaction of the aluminum dross, allowing the aluminum droplets to aggregate while maintaining the temperature of the aluminum dross at 700-900°C.

[0023] Although this heat generation phenomenon is similar in effect to the chemical reaction effect obtained by adding flux, it is actually due to a fundamentally different physical phenomenon. By utilizing this physical phenomenon, the addition of flux is not required, preventing air pollution that occurs when flux is used and significantly reducing the amount of flux components remaining 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.

[0024] The inventors conducted an experiment to induce the aggregation of aluminum-based metal droplets by vibration. In this experiment, aluminum dross generated in a factory was discharged and rapidly cooled, then reheated in a crucible. A vibrator (vibration plate) was inserted and vibration was applied, 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 vibration plate, and the cross section was photographed and observed. This experiment was repeated with different samples and vibration conditions. The differences in the aggregation and coalescence state of aluminum in the dross were thought to be influenced by differences in the vibration conditions, the amount of aluminum present in the aluminum dross used in the test, and the remaining amount of flux used in the furnace before discharge.

[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 an aluminum melting process. The aluminum recovery apparatus 1 includes a vibration device 20 that applies 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.

[0026] (Aluminum recovery apparatus 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 a 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 an agitator 30 as shown in the figure.

[0027] FIG. 2 is a schematic diagram showing a specific configuration example of the container 10 and the vibration device 20. In FIG. 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 cross-sectional view of the container 10. The container 10 and the vibration device 20 are supported on 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 vibrates the vibration plate 21. The vibration plate 21 is inserted into the aluminum dross stored in the container 10 from the top by a support rod 60 and an elevating device 70 such as a hydraulic or pneumatic cylinder or a jack. The vibration plate 21 is vibrated using the vibration unit 22, thereby applying vibration to the aluminum dross.

[0028] The container 10 stores aluminum dross heated to a temperature equal to or higher than the melting point of aluminum. The container 10 is made of a steel material or the like that can withstand high temperatures in order to store aluminum dross at a temperature of approximately 700°C to 900°C. In the example shown in Fig. 2, the container 10 has a hemispherical bottom, but the shape of the container 10 may be box-shaped or any other shape. A withdrawal port for withdrawing the accumulated molten aluminum may be provided at the bottom of the container 10.

[0029] 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 multiple vibration plates 21 and a vibration unit 22 that vibrates the vibration plates 21. The shape of the vibration plate 21 varies depending on the size of the container 10. For example, the vibration plate 21 shown in FIG. 6 is flat, approximately 5 to 10 cm wide and 0.5 to 1.5 cm thick, with a width of approximately 5 to 10 cm and a thickness of approximately 0.5 to 1.5 cm. Also, the vibration plate 21 shown in FIG. 6 has a shape with increased width and thickness at its tip. Also, the vibration plate 21 shown in FIG. 6 is a vibrator that rotates and vibrates in the axial direction. The length of the vibration plate 21 is sufficient as long as it is longer than the length inserted into the aluminum dross and can be connected to the vibration unit 22. The material of the vibration plate 21 must be able to withstand high temperatures, similar to the container 10, and is therefore preferably made of, for example, steel, cast iron, or titanium, which has superior heat resistance and strength.

[0030] 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.

[0031] The vibrating plates 21 can be arranged to efficiently vibrate the aluminum dross according to the shape of the container in which the aluminum dross is stored. The cross-sectional view of 203 in Fig. 2 shows an example in which the vibrating plates 21 are arranged in an X-shape. By arranging the vibrating 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 vibrating plates 21 is not limited to an X-shape. For example, the vibrating plates 21 may be arranged evenly in parallel inside the container 10.

[0032] When performing the stirring treatment, the container 10 after vibration may be moved from the vibration device 20 to the stirrer 30 and the stirring treatment may be performed. The vibration device 20 may be replaced with the stirrer 30 and the stirring treatment 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 and the aluminum dross may be stirred. In other words, the vibration device 20 and the stirrer 30 may be configured as replaceable devices that can be separately attached to the container 10. The structure of the stirrer 30 will be described later.

[0033] 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 below the stirring device 30 and the aluminum dross may be stirred. Alternatively, a separate container for stirring treatment may be provided, and when stirring treatment is performed, the aluminum dross in the container 10 may be transferred to another container for stirring treatment. The side view indicated at 201 in Figure 2 shows a spout 11 for transferring the aluminum dross from the container 10 to another container.

[0034] Next, the shapes of the vibration plate 21 and the agitator blades 31 of the agitator 30 will be described. Note that the figures described below are merely examples, and the shapes of the vibration plate 21 and the agitator blades 31 are not limited. FIG. 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 FIG. 3, 301 indicates a top view, 302 indicates a front view, and 303 indicates a side view. Note that the container 10 is rectangular, and a cross-sectional view is shown. The vibration plate 21 shown in FIG. 3 is formed in the shape of a substantially rectangular flat plate. The lengths of the vibration plates 21 are varied according to the depth of the container 10. The vibration plates 21 are arranged substantially parallel to each other in the same direction. Each vibration plate 21 may be vibrated collectively, or in groups. The vibration direction is perpendicular to the flat plate surface.

[0035] FIG. 4 is a schematic diagram showing another example of the arrangement of the vibrating plates 21 inserted into the aluminum dross. In FIG. 4, 401 indicates a top view, 402 indicates a front view, and 403 indicates a side view. The container 10 is rectangular, and a cross-sectional view is shown. The vibrating plates 21 shown in FIG. 4 are formed in the shape of a substantially rectangular flat plate. The lengths of the vibrating plates 21 are varied to match the depth of the container 10. The vibrating plates 21 are divided into two groups arranged in the same direction, and the two groups are arranged in directions perpendicular to each other. The groups of vibrating plates 21 arranged in the same direction may be vibrated together, or individually. The vibration direction is perpendicular to the flat plate surface.

[0036] FIG. 5 is a schematic diagram showing yet another example of the arrangement of the vibrating plates 21 inserted into the aluminum dross. In FIG. 5, 501 indicates a top view, and 502 indicates a front view. The container 10 is round and hemispherical. The vibrating plates 21 shown in FIG. 5 are formed in the shape of a substantially rectangular flat plate. The lengths of the vibrating plates 21 are varied according to the depth of the container 10. The vibrating plates 21 are arranged in three groups, arranged in directions that differ from each other by 120°. Each of the vibrating plates 21 is vibrated in groups of three. The vibration direction is perpendicular to the flat plate surface.

[0037] Fig. 6 is a schematic diagram showing an example of the shape of the diaphragm 21. Reference numeral 601 in Fig. 6 shows a side view and a front view of a rectangular diaphragm 21. Reference numeral 602 shows a side view and a front view of a drumstick-shaped diaphragm 21 with a wider bottom. Reference numeral 603 shows a side view and a plan view of a diaphragm having four trapezoidal fins attached to the bottom of a cylindrical support rod. In the case of the diaphragm 21 shown in Fig. 603, the aluminum dross is vibrated by alternately rotating and vibrating the cylindrical support rod clockwise and counterclockwise when viewed from above.

[0038] 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.

[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. FIG. 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. 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.

[0040] Step S11 is a process of storing aluminum dross heated to or above the melting point of aluminum in a container. The aluminum dross generated in the aluminum melting process is itself heated to or above the melting point of aluminum, and can be used as is. The aluminum dross after primary aluminum recovery is at room temperature, so it is heated to or 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 or 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 vibrates the aluminum dross to promote oxidation 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 or by destroying the oxide coating covering the surface of the aluminum droplets and exposing the chemically active aluminum surface. In other words, the temperature can be maintained at 700 to 900°C by promoting the oxidation of 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. The temperature of the aluminum during vibration can be measured indirectly using an infrared thermometer or by thermocouple temperature measurement.

[0042] Step S13 is a stirring step in which stirring blades are inserted into and operated on the aluminum dross after vibration has been applied in the vibration step of step S12. By keeping the temperature at 700 to 900°C and stirring the aluminum dross in which the aluminum droplets have become agglomerated, the remaining molten aluminum is coalesced and can be efficiently recovered.

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

[0044] According to the aluminum recovery apparatus 1 and aluminum recovery method S1 for recovering aluminum from aluminum dross described above, it is possible to recover aluminum from aluminum dross discharged outside the furnace to at least the same extent as in the prior art, without using flux or by using a reduced amount of flux.

[0045] Furthermore, since it is possible to recover aluminum to the same extent as with conventional techniques without using flux, or to recover aluminum to the same extent as with conventional techniques by using a reduced amount of flux, the content of fluorine, an environmental pollutant, can be dramatically reduced in the recycling of aluminum dross residue after recovering metal components such as aluminum from aluminum dross, thereby promoting the recycling of this residue into secondary materials for steel making, roadbed materials, etc.

[0046] [Embodiment 2] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0047] An aluminum recovery apparatus (not shown) according to a second embodiment includes a pressure stirring apparatus 40 instead of the stirring apparatus 30. The pressure stirring apparatus 40 is an apparatus that stirs the aluminum dross while applying pressure to it. The pressure is applied in the direction of gravity (downward), for example.

[0048] FIG. 9 is a schematic diagram showing a propeller-type pressure mixer 40. In FIG. 9, 901 shows a perspective view of the pressure mixer 40 disposed inside the vessel 10, 902 shows a top view thereof, and 903 shows a side view thereof. 903 shows a cross-sectional view of the vessel 10. The propeller-type pressure mixer 40 includes a rotating shaft 41 and pressure mixer blades (propellers) 42. The propeller-type pressure mixer 40 has three to four propellers 42 arranged around the rotating shaft 41. By rotating the pressure mixer 40 around the rotating shaft 41, pressure is generated that presses the aluminum dross toward the bottom of the vessel 10. At the same time, a stirring force is generated that rotates and stirs the aluminum dross. In this way, the pressure mixer 40 can simultaneously stir and pressurize the aluminum dross. This applies shear force to the aluminum dross, promoting the destruction and coalescence of tiny molten aluminum particles. This allows the amount of flux used to be reduced, and allows aluminum to be recovered from aluminum dross to the same extent as in the prior art.

[0049] FIG. 10 is a schematic diagram showing a pressure mixer 40 using a helical screw. In FIG. 10, 1001 indicates a top view of the pressure mixer 40 placed inside the vessel 10, and 1002 indicates a side view thereof. The helical screw type pressure mixer 40 has a pressure mixer impeller (helical screw) 42, such as an Archimedes pump, disposed around a rotation shaft 41. By rotating the pressure mixer 40 around the rotation shaft 41, the aluminum dross can be stirred while applying pressure toward the bottom of the vessel 10. The effect of the pressure mixer 40 using this helical screw 42 is similar to that of the pressure mixer 40 using a propeller 42. The pressure mixer 40 is equipped with a known rotation drive unit (motor), but this is not shown in FIGS. 9 and 10 .

[0050] The aluminum recovery method S2 according to this embodiment will be described with reference to the drawings. Fig. 11 is a flowchart showing the flow of the aluminum recovery method S2 according to this embodiment, in which aluminum is recovered 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.

[0051] Steps S21 and S22 are not described here because they are the same as steps S11 and S12 of the aluminum recovery method S1 described in embodiment 1. Step S23 is a pressure stirring step in which the aluminum dross that has been vibrated in the vibration step of step S22 is stirred while applying pressure (pressurization and stirring are performed in parallel).

[0052] More specifically, the pressurized stirring process applies a rotational force to the aluminum dross, rotating it in a circular shape when viewed from above, and a downward pressure. This process pushes downward the block-shaped molten aluminum mass that has aggregated and coalesced due to the vibration effect of the previous process. It also applies a shear force that destroys the coating of aluminum droplets present in the aluminum dross. This breaks down and coalesces tiny molten aluminum droplets.

[0053] Step S24 is a process of removing the molten aluminum that has been combined by the 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 allowing it to fall under its own weight and pressure.

[0054] The estimated aluminum recovery rates when using the conventional technology of agitating aluminum dross to recover aluminum, and when using the present invention, in which aluminum dross is vibrated and then further agitated under pressure to recover aluminum, are shown in Table 1 below.

[0055]

[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, it is possible to recover aluminum from aluminum dross to at least the same extent as in the prior art, without using flux or by using a reduced amount of flux.

[0057] Furthermore, since it is possible to recover aluminum to the same extent as with conventional techniques without using flux, or to recover aluminum to the same extent as with conventional techniques by using a reduced amount of flux, the content of fluorine, an environmental pollutant, can be dramatically reduced in the recycling of aluminum dross residue after recovering metal components such as aluminum from aluminum dross, thereby promoting the recycling of this residue into secondary materials for steel making, roadbed materials, etc.

[0058] The present invention is not limited to the above-described embodiments, 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 the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0059] [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 applying vibration to aluminum dross on agglomeration of aluminum in the aluminum dross. Specifically, aluminum dross generated in the melting process at an aluminum factory was discharged and then rapidly cooled. It was then reheated to 800°C in a crucible to melt it, and a vibration plate was inserted to apply vibration. After that, the crucible was immersed in a container filled with dry ice to preserve the state, and the crucible was rapidly cooled to 300°C or below in about 15 minutes.

[0060] The extracted aluminum dross was impregnated with resin and solidified, then cut, and the cross section was photographed and observed. This experiment was repeated using different samples and vibration conditions. Figures 12 and 13 are photographs of the cut surfaces of cooled aluminum dross treated under different vibration conditions. Figure 12 is an example of a photograph of the cut surface of aluminum dross in which dispersed molten aluminum droplets were agglomerated by vibrating the aluminum dross with a vibrating plate, and the resulting agglomerated state was cooled as is. Specifically, the results of the vibration experiment were obtained under the following conditions: a vibration frequency of 20 Hz, a vibration time of 2 minutes, and then a vibration time of 25 Hz for 3 minutes, for a total of 5 minutes, with an amplitude of 25 mm, and the aluminum dross temperature set to 800°C. Figure 13 is the results of the vibration experiment under the following conditions: a vibration frequency of 10 Hz, an amplitude of 25 mm, a vibration time of 5 minutes, and the aluminum dross temperature set to 800°C. These temperatures were measured using a thermocouple temperature measurement 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) 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.

[0062] The photographs on the right side of Figure 12 and Figure 13 are photographs of the left and right cross sections of the aluminum dross after it had been impregnated with resin. The white areas in the cross-sectional photographs are aluminum, and a white mass can be seen near the diaphragm. This is a block-like mass of fine aluminum droplets that have aggregated and coalesced due to vibration. The fine white particles present away from the diaphragm are solidified aluminum droplets that did not coalesce.

[0063] The cross-sectional observations revealed that the range of vibration influence and the rate of aluminum aggregation varied 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.

[0064] As a result of repeating such experiments, it was found that the vibration amplitude should be approximately 0.8 to 50 mm, preferably approximately 0.8 to 30 mm, and more preferably approximately 1 to 20 mm. It was also found that the vibration frequency should be approximately 2 to 100 Hz, preferably approximately 5 to 50 Hz, and more preferably approximately 5 to 25 Hz. The vibration direction of the vibrating plate is approximately perpendicular to the plate surface of the vibrating plate, that is, the plate thickness direction of the vibrating plate. This is to maximize the transmission of the pressing force of the vibrating plate due to vibration to the aluminum dross.

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

[0066] DESCRIPTION OF SYMBOLS 1...Aluminum recovery device 10...Container 20...Vibration device 21...Vibration plate 30...Agitator 31...Rotating shaft 32...Agitator blade 40...Pressurized agitator 41...Rotating shaft 42...Pressurized agitator blade (propeller or helical screw) 50...Frame 60...Support rod 70...Elevating device

Claims

1. An aluminum recovery method for recovering aluminum from aluminum dross, comprising: a step of placing the aluminum dross heated to above the melting point of aluminum in a container; a vibration step of inserting a vibrating plate into the aluminum dross and 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.

2. 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 in a plane, and a pressure that presses the aluminum dross downward.

3. The method for recovering aluminum according to claim 1, wherein the pressurized stirring step is a step of applying a shear force to the aluminum dross that breaks the coating of aluminum droplets present in the aluminum dross.

4. An aluminum recovery method according to any one of claims 1 to 3, wherein the pressurized stirring process is a process of pressurizing and stirring the aluminum dross using a helical screw.

5. The method for recovering aluminum 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 an oxide film covering the surface of the aluminum droplets by vibration to expose a chemically active aluminum surface, thereby promoting oxidation of the surface of the aluminum droplets.

6. An aluminum dross residue obtained after aluminum is recovered by the aluminum recovery method according to any one of claims 1 to 3.

7. An aluminum recovery apparatus for recovering aluminum from aluminum dross, comprising: a container for storing the aluminum dross heated to or above the melting point of aluminum; a vibration device for imparting vibrations to the aluminum dross by inserting a vibrating plate into the aluminum dross in the container and vibrating it; and a pressurized agitator for inserting into the aluminum dross in the container and rotating it to agitate and apply pressure to the aluminum dross.

8. The aluminum recovery apparatus of claim 7, wherein the pressurized agitator comprises a helical screw.

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