Method for treating aluminum dross particles and method for producing alumina particles

Abstract

To provide an Al dross treatment technique that substantially inhibits the generation of ammonia gas from the treated Al dross and enables recycling of it.SOLUTION: Al dross particles (100) are brought into contact with water in an aqueous medium at 75-95°C, to decompose aluminum nitride in the particles. Scale (110) on the Al dross particles (100) is removed from the surfaces by the introduction of microbubbles (120) into the particle slurry.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for treating aluminum dross particles and a method for producing alumina particles. [Background technology]

[0002] Aluminum dross is generated during melting in aluminum refining and alloy casting. Aluminum dross contains aluminum nitride and generates ammonia gas in a humid environment, so methods for rendering the aluminum dross harmless have been investigated.

[0003] Known techniques for detoxifying aluminum dross include, for example, decomposing the aluminum dross in heated water while recovering ammonia, and then recovering the aluminum dross discharged together with bubbles using a bubble catcher (see, for example, Patent Document 1). Also known as a detoxifying technique for aluminum dross is agitating aluminum dross with water at 90 to 200°C in the presence of beads to detoxify the aluminum dross (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-177556 [Patent Document 2] Japanese Patent Application Publication No. 10-008154 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-described conventional techniques, the decomposition treatment of aluminum nitride in the aluminum dross does not proceed sufficiently, and therefore, in a wet environment, ammonia gas may still be generated from the aluminum dross after the treatment. Thus, the conventional techniques leave room for further study from the perspective of substantially suppressing the generation of ammonia gas from aluminum dross after wet treatment.

[0006] An object of one aspect of the present invention is to provide a technology for treating aluminum dross that substantially suppresses the generation of ammonia gas from treated aluminum dross and enables the aluminum dross to be reused. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a method for treating aluminum dross particles according to one embodiment of the present invention includes a first step of contacting aluminum dross particles containing aluminum nitride with water in an aqueous medium at 75 to 95°C to decompose the aluminum nitride, and a second step of removing scale adhered to the surfaces of the aluminum dross particles by the first step from the surfaces, wherein the second step includes a microbubble introducing step of introducing microbubbles into the aqueous medium containing the aluminum dross particles.

[0008] In order to solve the above-mentioned problems, a method for producing alumina particles according to one embodiment of the present invention includes a step of firing aluminum dross particles treated by the above-mentioned method to produce alumina particles. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a technology for treating aluminum dross that substantially suppresses the generation of ammonia gas from treated aluminum dross and enables reuse of the treated aluminum dross. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration of a processing apparatus used in one embodiment of the present invention. [Figure 2] 1 is a diagram for explaining the state of aluminum dross particles subjected to a method for treating aluminum dross particles according to one embodiment of the present invention. FIG. [Figure 3] FIG. 2 is a diagram illustrating the decomposition of aluminum dross particles in heated water in a method for treating aluminum dross particles according to one embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a first state of aluminum dross particles in heated water in the presence of microbubbles in a method for treating aluminum dross particles according to one embodiment of the present invention. [Figure 5] FIG. 10 is a diagram illustrating a second state of aluminum dross particles in heated water in the presence of microbubbles in a method for treating aluminum dross particles according to one embodiment of the present invention. [Figure 6] FIG. 2 is a diagram for explaining the state of aluminum dross particles being processed in a wet grinding device in a method for processing aluminum dross particles according to one embodiment of the present invention. [Figure 7] FIG. 2 is a diagram for explaining the final state of aluminum dross particles in heated water in the presence of microbubbles in a method for treating aluminum dross particles according to one embodiment of the present invention. [Figure 8] 1A and 1B are diagrams for explaining the generation of alumina particles in a method for producing alumina particles according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described. In this specification, the symbol "to" indicates a numerical range that is inclusive of both the numerical values ​​at both ends.

[0012] [Method for treating aluminum dross particles] A method for treating aluminum dross particles according to an embodiment of the present invention includes a first step of contacting aluminum dross particles (hereinafter also referred to as "Al dross particles") with water in an aqueous medium at 75 to 95°C to decompose aluminum nitride, and a second step of removing scale adhered to the surfaces of the Al dross particles in the first step from the surfaces. The first and second steps may be performed simultaneously, separately, or sequentially until the generation of ammonia gas from the Al dross particles substantially stops.

[0013] Al dross particles are particles of a composition mainly containing aluminum oxides and nitrides, which are produced during aluminum refining. The Al dross particles contain nitrogen-based compounds, including at least aluminum nitride, and may also contain trace amounts of metallic aluminum and halogens. Aluminum nitride is a product formed by the reaction of aluminum and nitrogen, and generates ammonia upon contact with water. The Al dross particles may contain aluminum oxynitrides, such as AlON, as other nitrogen-based compounds. Examples of halogens include fluorine and chlorine. The Al dross particles may have a number-average particle size of 20 to 500 μm.

[0014] [First step] The aqueous medium is a liquid medium containing water as a main component. The aqueous medium may be water, an aqueous solution of a water-soluble organic solvent, or an aqueous solution of an acid or alkali. From the viewpoint of easy availability, the aqueous medium is preferably water.

[0015] The aqueous medium can be heated appropriately using a known heater. If the temperature of the aqueous medium is too low, the removal of nitrides from the Al dross particles may be insufficient. From the viewpoint of sufficiently removing nitrides from the Al dross particles, the temperature of the aqueous medium is preferably 75°C or higher, more preferably 80°C or higher, and even more preferably 85°C or higher. From the viewpoint of accelerating the removal of nitrides from the Al dross particles, the higher the temperature of the aqueous medium, the better. On the other hand, if the Al dross particles contain a high content of metallic aluminum and nitride (aluminum nitride), the temperature of the aqueous medium may rise suddenly due to the oxidation heat generated in the first step. Therefore, it is preferable to carry out the first step at a high temperature that can sufficiently handle such a sudden temperature rise. From the viewpoint of suppressing a sudden temperature rise of the aqueous medium, the temperature of the aqueous medium is preferably 97°C or lower, more preferably 95°C or lower, and even more preferably 93°C or lower.

[0016] The temperature of the aqueous medium in the first step may be constant or may vary. For example, as the time for the first step increases, the amount of water and other solvents evaporated from the aqueous medium increases, and the mass ratio of the Al dross particles to the aqueous medium in the mixture of the aqueous medium and the Al dross particles (hereinafter also referred to as the "aqueous slurry") (hereinafter also referred to as the "solubility ratio") may decrease. If the solution ratio decreases, the content of metal aluminum particles and Al dross particles in the aqueous medium increases, as described above, and a sudden temperature rise occurs, such as bumping of the aqueous slurry, making it difficult to maintain the temperature of the aqueous medium or the solution ratio.

[0017] From the viewpoint of stably and efficiently carrying out the first step, it is preferable that the amount of the aqueous medium in the first step is about 7 to 10, when the amount of the Al dross particles is 1. Furthermore, when the content of metallic aluminum in the Al dross particles is more than 20 mass%, it is preferable from the viewpoint mentioned above to control the solid solution ratio in the water slurry in the first step to be within the above range.

[0018] The first step can be carried out by stirring an aqueous slurry of Al dross particles (hereinafter simply referred to as "slurry") obtained by adding Al dross particles to an aqueous medium, heating the slurry to a temperature within the above-mentioned range, and maintaining the temperature.

[0019] [Second step] The second step includes a microbubble introduction step of introducing microbubbles into an aqueous medium containing aluminum dross particles.

[0020] Here, microbubbles are bubbles having a diameter of 1.0 to 100 μm. The diameter of the microbubbles is a diameter based on the number of bubbles. From the viewpoint of sufficiently removing scale from the surfaces of Al dross particles in the slurry, the diameter of the microbubbles is preferably 50 μm or more, more preferably 80 μm or more, and more preferably 100 μm or more, in terms of the mode. Furthermore, from the above viewpoint, the mode diameter of the microbubbles is preferably 150 μm or less, more preferably 120 μm or less, and more preferably 100 μm or less.

[0021] Furthermore, from the viewpoint of removing the scale, the number concentration of microbubbles at the mode of diameter is preferably 500 bubbles / mL or more, more preferably 1,000 bubbles / mL or more, and even more preferably 1,500 bubbles / mL or more. On the other hand, a high number concentration of microbubbles may damage the treatment tank, and shock waves caused by the collapse of microbubbles in the aqueous medium may be absorbed by other microbubbles. Therefore, from the viewpoint of reducing damage to treatment equipment such as the treatment tank 10 and achieving efficient scale removal using microbubbles, the number concentration of microbubbles at the mode of diameter is preferably 3,000 bubbles / mL or less, more preferably 2,500 bubbles / mL or less, and even more preferably 2,000 bubbles / mL or less.

[0022] The method for generating microbubbles may be determined appropriately depending on the desired size and amount of microbubbles. The method for generating microbubbles may involve liquid flow or may not involve liquid flow. Examples of methods involving liquid flow include swirling liquid flow, ejector, Venturi, static mixer, and pressurized dissolution methods. Examples of methods not involving liquid flow include pore, rotation, ultrasonic, vapor condensation, and electrolysis methods.

[0023] In particular, the second step may include an ultrasonic wave generating step of generating ultrasonic waves in the aqueous medium to generate microbubbles. Microbubbles may be generated by the ultrasonic wave generating step alone, or the ultrasonic wave generating step may be performed in parallel with another method for generating microbubbles. Generating ultrasonic waves in the aqueous medium is preferable from the viewpoint of further promoting the decomposition and oxidation of components in the Al dross particles in the aqueous medium.

[0024] When ultrasonic waves are generated in an aqueous medium, fluctuations in acoustic pressure occur as microbubbles are generated. This fluctuation in acoustic pressure rapidly compresses the microbubbles. For example, cavitation bubbles generated under negative pressure are rapidly reduced by the subsequent high-pressure wave. Because the pressure inside the bubbles increases inversely proportional to their diameter, the rapid reduction (collapse) of the microbubbles results in a rapid increase in their internal pressure and a rapid increase in their temperature due to an adiabatic compression effect. Thus, by generating microbubbles in an aqueous medium (water slurry) using ultrasonic waves, a region of several thousand atmospheres and several thousand degrees Celsius is formed when the generated microbubbles disappear, generating free radicals such as hydroxyl radicals. These ultra-high temperatures and free radicals can promote the oxidative decomposition of various components. Therefore, including an ultrasonic wave generation step in the second step is expected to reduce the content of various components contained in Al dross particles, such as metallic aluminum and halogens such as fluorine and chlorine.

[0025] The diameter of microbubbles can be measured by known methods such as quantitative laser diffraction / scattering. For example, the diameter of microbubbles can be calculated from the difference between a measured value A obtained by the above-mentioned method for a slurry before microbubbles are generated and a measured value B obtained by the above-mentioned method for the slurry after microbubbles are generated.

[0026] The introduction of microbubbles into the slurry in the second step promotes the decomposition of aluminum nitride in the Al dross particles (the generation of ammonia gas from the Al dross particles). This is thought to be because the shock waves generated when the microbubbles collapse in the slurry destroy the scale on the surface of the aluminum dross particles, and the ammonia gas generated inside the Al dross particles is released into the slurry directly from the surface of the Al dross particles or through the scale that has been made thinner by the destruction caused by the shock waves.

[0027] The second step may include a further step of removing the scale from the Al dross particles. For example, the second step may include a polishing step of polishing the Al dross particles treated in the first step with beads to remove the scale from the surface.

[0028] A bead mill can be preferably used for the polishing step. By appropriately setting the particle size of the beads, it is possible to polish the Al dross particles to an appropriate size with adequate scale removal. The scale is considered to be solid aluminum hydroxide, as will be described later, and the material of the beads can be appropriately selected from known materials capable of pulverizing or polishing the scale depending on the components of the scale. It is preferable to perform the polishing step at a time separate from the aforementioned microbubble introduction step, from the viewpoint of further promoting the decomposition of aluminum nitride in the Al dross particles in the aqueous medium.

[0029] [Other processes] In an embodiment of the present invention, the method for treating Al dross particles may further include a step other than the first step and the second step, as long as the effect of the method is obtained. For example, the method may further include a third step of collecting ammonia generated in the first step.

[0030] As described above, ammonia gas is generated from the heated slurry due to the decomposition reaction of aluminum nitride in the Al dross particles with water. Ammonia is useful as a raw material for fertilizers or as a fuel. From the viewpoint of effective utilization of resources, it is preferable to recover the ammonia generated by the above-mentioned treatment method.

[0031] An example of the third step includes a step of capturing ammonia in water. Such ammonia capturing step can be carried out using a known capture device for capturing gas into liquid. An example of such a capture device is an absorption tower having a shower nozzle and a packed bed disposed below the shower nozzle, and circulating an absorbing liquid such as water in the tower to the shower nozzle.

[0032] Water can be used as the ammonia absorption liquid in the collection step. If the amount of absorption liquid in the collection step is insufficient, the ammonia will be saturated in the absorption liquid and will no longer be absorbed by the absorption liquid. Therefore, from the viewpoint of more reliably collecting ammonia, it is preferable to use two or more collection devices connected in series in the collection step. Furthermore, from the viewpoint of continuously collecting ammonia, two or more collection devices connected in parallel may be used.

[0033] When collection devices are connected in series, if the absorption solution of the upstream collection device becomes saturated with ammonia, ammonia will flow into the downstream collection device. Therefore, from the viewpoint of accurately determining the amount of ammonia generated by the treatment of Al dross particles, it is preferable to measure the pH of each of the absorption solutions (water) of two or more collection devices.

[0034] Furthermore, if the amount of absorption liquid in the collector is too small, the ammonia generated during the treatment of Al dross particles may not be sufficiently collected. From the viewpoint of sufficiently collecting the ammonia generated during the treatment of Al dross particles, it is preferable that the amount of absorption liquid in the collector be large, for example, a volume of 50% or more, and more preferably 80% or more, of the volume of the aqueous medium in the first step. On the other hand, from the viewpoint of suppressing an increase in the size of the apparatus and an increase in operating costs, and from the viewpoint of circulating and reusing the absorption liquid in the treatment method of the present invention, it is preferable that the amount of absorption liquid in the collector be approximately the same as the volume of the aqueous medium in the first step. From these viewpoints, the amount of absorption liquid in the collector may be 100% of the volume of the aqueous medium in the first step.

[0035] Furthermore, in the present invention, the third step may be used to determine the start time of the second step. For example, in the present invention, the polishing step may be performed depending on the amount of ammonia recovered in the third step. The amount of ammonia recovered can be detected by the pH of the water that absorbs the ammonia gas generated from the slurry. For example, when the increase in pH falls below a specific rate, it can be determined that the generation of ammonia gas has substantially stopped, and therefore the polishing step can be started. For example, when measuring the pH of the absorption liquid in the series-connected collectors, the start time of the polishing step may be when the pH of the absorption liquid on the upstream side stabilizes or when the rate of increase in pH of the absorption liquid on the downstream side slows down.

[0036] The above-described treatment method can produce Al dross particles from which aluminum nitride has been decomposed and removed. The treated Al dross particles essentially contain aluminum oxide and aluminum hydroxide as aluminum components. The treated Al dross particles have a composition of, for example, 0.1 to 0.3 mass% or less of aluminum, 0.1 to 0.4 mass% or less of nitrogen, 1.5 mass% or less of fluorine, and 1.0 mass% or less of chlorine. Therefore, the treated Al dross particles do not generate hydrogen gas or ammonia even in a humid environment, making them reusable as aluminum-based inorganic materials for a variety of applications.

[0037] The content of water-soluble components in the Al dross particles can be reduced by increasing the amount of the aqueous medium. For example, since chlorine tends to become a water-soluble component, the content of chlorine in the Al dross particles can be reduced sufficiently by increasing the amount of the aqueous medium.

[0038] [Method for producing aluminum oxide (alumina) particles] A method for producing alumina particles according to an embodiment of the present invention includes a step of producing alumina particles by calcining Al dross particles treated by the above-described treatment method. Ignition of the Al dross particles obtained by the above-described treatment method causes the aluminum hydroxide in the Al dross particles 100 to release water and become aluminum oxide. This results in particles whose aluminum component is essentially alumina. The composition of the produced alumina particles is, for example, 0.1% by mass or less of aluminum, 0.1% by mass or less of nitrogen, 0.1% by mass or less of fluorine, and 0.2% by mass or less of chlorine.

[0039] The content of volatile components in Al dross particles can be reduced by ignition. For example, the fluorine content in the resulting alumina particles can be sufficiently reduced by igniting at 1400°C in the alumina particle production process. Furthermore, if the Al dross particles are washed with water during the ignition process, the content of the aforementioned water-soluble components, such as chlorine, can be further reduced.

[0040] Alumina particles have high hardness and a high melting point, and are heat-resistant, electrically insulating, and wear-resistant. Therefore, by adjusting the particle size according to the application, they can be used in various ceramic materials. Examples of applications of alumina particles include materials for light-emitting diodes, lithium batteries, and industrial machine parts such as automotive products, refractory materials such as bricks, glass materials, heat-dissipating materials, abrasives, catalysts, and catalyst supports.

[0041] The method for producing alumina particles according to an embodiment of the present invention may further include a step other than the calcination step. For example, the method may further include a step of pulverizing the calcined alumina particles to adjust the particle size of the alumina particles. This step is preferable from the viewpoint of obtaining alumina particles suitable for the intended use. From the same viewpoint, the method may further include a step of classifying the calcined or pulverized alumina particles.

[0042] [Specific Embodiments of Treatment of Al Dross Particles and Production of Alumina Particles] Next, a method for treating Al dross particles and a method for producing alumina particles according to an embodiment of the present invention will be described in more detail. First, a processing apparatus capable of carrying out the method for treating Al dross particles will be described. First, a processing apparatus used in one embodiment of the present invention will be described.

[0043] [Processing device configuration] Fig. 1 is a diagram showing a schematic configuration of a treatment apparatus used in one embodiment of the present invention. As shown in Fig. 1, the treatment apparatus includes a treatment tank 10, a microbubble generator 20, a circulation pump 30, a heater 40, an ammonia recovery apparatus 50, a wet-grinding apparatus 60, and a solid-liquid separator 70.

[0044] The treatment tank 10 is a container capable of accommodating a slurry of an aqueous medium and Al dross particles. The treatment tank 10 is configured to be airtight. The treatment tank 10 has, at the top, a supply pipe for supplying Al dross particles into the treatment tank 10 and an exhaust pipe for exhausting the gas phase inside the treatment tank 10. The treatment tank 10 also has, at the bottom, an outlet for discharging the slurry stored therein. Furthermore, the treatment tank 10 has an agitator 11 for agitating the slurry stored therein.

[0045] The microbubble generator 20 is a device for generating microbubbles in the slurry contained in the treatment tank 10. The microbubble generator 20 has a nozzle 21 for generating microbubbles in the slurry.

[0046] The circulation pump 30 is a pump for returning the slurry discharged from the discharge outlet of the treatment tank 10 to the treatment tank 10. It is disposed in a first pipeline connecting the discharge outlet of the treatment tank 10 to the supply pipe. The circulation pump 30 may be any pump capable of pumping the slurry, and may be appropriately selected from known pumps having such a pumping function.

[0047] The heating device 40 is a device for heating the slurry returned to the treatment tank 10 by the circulation pump 30. The heating device 40 is disposed in the first pipeline between the circulation pump 30 and the supply pipe of the treatment tank 10. The heating device 40 may be any device capable of heating the slurry in the treatment tank 10 so as to adjust the temperature of the slurry to 75 to 95°C, and may be appropriately selected from known heating devices having such a heating function.

[0048] The ammonia recovery system 50 is a system for absorbing ammonia gas generated from the slurry in the treatment tank 10. The ammonia recovery system 50 includes a first absorption tower 51 and a second absorption tower 52. The first absorption tower 51 and the second absorption tower 52 are both gas-liquid contactors for bringing water as an absorption liquid into contact with ammonia in the gas phase, and are systems for spraying and circulating water from above into the interior of the tower against ammonia gas supplied from below. In addition, both the first absorption tower 51 and the second absorption tower 52 are equipped with a pH meter (not shown) for measuring the pH of the absorption liquid that flows down. The first absorption tower 51 is connected to the exhaust pipe of the treatment tank 10, and the second absorption tower 52 is connected to an exhaust pipe at the top of the first absorption tower 51. The exhaust pipe at the top of the second absorption tower 52 is connected to an exhaust treatment device (not shown).

[0049] The wet-milling device 60 is a device for polishing particles in the slurry discharged from the discharge port of the treatment tank 10 in a wet environment. The wet-milling device 60 is disposed in a second pipeline that serves as a bypass pipeline for the first pipeline connecting the treatment tank 10 and the circulation pump 30. An example of the wet-milling device 60 is a bead mill. The wet-milling device 60 may be any device capable of heating the slurry in the treatment tank 10 so as to adjust the temperature of the slurry to 75 to 95°C, and may be appropriately selected from known heating devices having such a heating function.

[0050] The solid-liquid separator 70 is a device for separating the slurry discharged from the outlet of the treatment tank 10 into solid and liquid particles and extracting particles. The solid-liquid separator 70 is disposed in a third pipeline separate from the first pipeline and the second pipeline described above. The solid-liquid separator 70 is, for example, a cyclone-type centrifugal separator.

[0051] 1 includes a valve V1 that opens and closes a first pipeline between the processing tank 10 and the circulation pump 30, a valve V2 that opens and closes a second pipeline between the processing tank 10 and the wet-grinding device 60, and a valve V3 that opens and closes a third pipeline between the processing tank 10 and the solid-liquid separator 70. Valves V1 to V3 are, for example, diaphragm valves.

[0052] The processing apparatus of FIG. 1 further includes a calcining apparatus 80 and a dry-grinding apparatus 90 .

[0053] The calciner 80 is a device for calcining the particles separated by the solid-liquid separator 70. The calciner 80 is a device for dehydrating the aluminum hydroxide in the particles to form aluminum oxide. Since aluminum oxide can have various crystal structures depending on the degree of thermal decomposition of aluminum hydroxide, the calciner 80 can be appropriately selected from known devices capable of heating the particles to a temperature at which aluminum oxide of the desired crystal structure can be produced. For example, to produce α-alumina, the calciner 80 is preferably a device capable of heating the core particles to 1100 to 1450°C.

[0054] The dry grinding device 90 is a device for crushing the particles calcined in the calcining device 80 and adjusting the particle size of the particles. The dry grinding device 90 will be described in detail later, but it is sufficient if it can adjust the particle size of the calcined particles to a particle size appropriate for the intended use of the resulting alumina particles, and can be appropriately selected from known devices that can be used for dry grain size distribution of alumina particles.

[0055] [More specific aspects of the method for treating Al dross particles] Next, an example of a method for treating Al dross particles using the treatment apparatus of Fig. 1 will be described. First, Al dross particles are introduced into the treatment tank 10 through the supply pipe of the treatment tank 10. Next, water is introduced into the treatment tank 10, and stirring is started with the stirring device 11 to produce a slurry of Al dross particles. The concentration of the Al dross particles in the slurry is 10 to 15 mass % in terms of solid solution ratio.

[0056] Next, the valve V1 is opened, the circulation pump 30 is operated, and the slurry is heated by the heating device 40 to circulate the slurry in the treatment tank 10 through the first flow path. Then, the temperature of the slurry is heated to and maintained at 75 to 95°C.

[0057] Next, the microbubble generator 20 is operated to generate microbubbles into the slurry from the nozzle 21. In the slurry in the treatment tank 10, the Al dross particles come into contact with the microbubbles generated from the nozzle 21. In the treatment tank 10, the pH of the slurry increases, and ammonia gas is generated from the slurry.

[0058] The generated ammonia gas is supplied to the first absorption tower 51 through the exhaust pipe of the treatment tank 10, and is absorbed into the absorbing liquid upon contact with water serving as the absorbing liquid in the first absorption tower 51. This increases the pH of the absorbing liquid in the first absorption tower 51. The ammonia gas that is not absorbed in the first absorption tower 51 is supplied to the second absorption tower 52, and is absorbed into the absorbing liquid upon contact with water serving as the absorbing liquid in the first absorption tower 51. As a result, the ammonia in the gas phase is substantially absorbed into the water serving as the absorbing liquid.

[0059] In this way, if the slurry is circulated through the first pipeline, stirred in the treatment tank 10 while maintaining the temperature, and kept in contact with the microbubbles, the generation of ammonia gas from the slurry may substantially stop. The cessation of ammonia gas generation can be confirmed by the fact that the increase in pH of the absorption liquid in the first absorption tower 51 or the second absorption tower 52 substantially stops.

[0060] At this time, the slurry in the treatment tank 10 is introduced into the wet-milling apparatus 60. More specifically, the valve V2 is opened and the valve V1 is closed, and the slurry is introduced into the wet-milling apparatus 60. In the wet-milling apparatus 60, the Al dross particles in the slurry are polished by the beads in the wet-milling apparatus 60. In this way, the Al dross particles with polished surfaces are supplied to the treatment tank 10. As a result, ammonia gas is generated again in the treatment tank 10. The regeneration of ammonia gas is confirmed by measuring the pH of the first absorption tower 51 or the second absorption tower 52.

[0061] As described above, while ammonia gas is being generated, the Al dross particles in the heated slurry are kept in contact with the microbubbles in the treatment tank 10. When the generation of ammonia gas stops or the amount of generated ammonia gas decreases, the slurry is supplied to the wet grinding device 60 to grind the Al dross particles.

[0062] When the generation of ammonia gas from the slurry in the treatment tank 10 has substantially stopped, for example, when the generation of ammonia gas in the treatment tank 10 from the slurry treated in the wet-grinding device 60 is no longer confirmed, the valves V1 and V2 are closed, and the valve V3 is opened to supply the slurry in the treatment tank 10 to the solid-liquid separator 70. Then, the Al dross particles are separated from the slurry.

[0063] The final pH of the aqueous medium of the slurry fed to the solid-liquid separator 70 is, for example, greater than 10. The liquid separated in the solid-liquid separator 70 is returned to the treatment tank 10 and reused as the aqueous medium in the next treatment of Al dross particles.

[0064] The final pH of the absorption solution in the first absorption tower 51 is, for example, slightly less than 11. Thus, the absorption solution in the first absorption tower 51 tends to become concentrated aqueous ammonia such as a saturated aqueous ammonia solution. Therefore, the absorption solution in the first absorption tower 51 can be suitably used as a material for products containing ammonia as a raw material, such as fertilizer, or as fuel.

[0065] The final pH of the absorption liquid in the second absorption tower 52 is, for example, around 9. Thus, the absorption liquid in the second absorption tower 52 tends to become a dilute aqueous ammonia solution. The absorption liquid in the second absorption tower 52 can be used as the next absorption liquid after the first absorption tower 51. The absorption liquid in the second absorption tower 52 can also be used as the dispersion medium for the next slurry in the treatment tank 10.

[0066] The Al dross particles separated by the solid-liquid separator 70 are used as a material for alumina particles.

[0067] [More specific aspects of the method for producing alumina particles] The Al dross particles separated in the solid-liquid separator 70 are calcined in the calciner 80. This converts the aluminum hydroxide in the Al dross particles to aluminum oxide through dehydration. The calcination temperature can be appropriately determined depending on the use of the powder after calcination. For example, a temperature of 1180 to 1280°C is sufficient for converting aluminum hydroxide to aluminum oxide (α-alumina), and a temperature of 1350 to 1450°C is sufficient for removing fluorine from the Al dross particles when higher fire resistance is required.

[0068] Next, the Al dross particles fired in the firing device 80 are pulverized in a dry pulverizer 90 and extracted as alumina particles with a volume-based median diameter of 10 to 100 μm. The alumina particles can be used as a material powder for ceramic products.

[0069] [Description of the State of Al Dross Particles in an Embodiment of the Present Invention] The state of the Al dross particles in the above-described processing method and manufacturing method is considered to be as follows: The state of the Al dross particles will be explained below with reference to Figs.

[0070] Fig. 2 is a diagram illustrating the state of Al dross particles used in a method for treating Al dross particles according to one embodiment of the present invention. As shown in Fig. 2, Al dross particles 100 contain metallic aluminum, aluminum oxide (alumina), and aluminum nitride. When supplied to a treatment tank 10, the Al dross particles 100 are in contact with water.

[0071] 3 is a diagram illustrating the decomposition of Al dross particles in heated water in a method for treating Al dross particles according to one embodiment of the present invention. As shown in FIG. 3, the aluminum component of the Al dross particles 100 reacts in heated water heated to 75 to 95°C as follows: Metallic aluminum reacts with water to produce aluminum hydroxide and hydrogen; aluminum nitride reacts with water to produce aluminum hydroxide and ammonia; and alumina oxide is stable in the heated water and does not react.

[0072] 4A to 4C are diagrams illustrating a first state of Al dross particles in heated water in the presence of microbubbles in a method for treating Al dross particles according to one embodiment of the present invention. In Fig. 4 to Fig. 8, the gas-permeable surface state is indicated by a dashed line.

[0073] As shown in Figure 4, in the heated water, hydrogen and ammonia generated in the Al dross particles 100 are released as gas from the Al dross particles 100. The hydrogen is released as it is from the slurry, the ammonia is absorbed into the slurry water, and the excess is released from the slurry. As a result, the ammonia concentration in the heated slurry water becomes saturated, and the pH of the slurry rises due to the dissolved ammonia.

[0074] In addition, in heated water, aluminum hydroxide generated in the Al dross particles 100 covers the surface of the Al dross particles 100, forming scale 110. The scale 110 becomes thicker as aluminum hydroxide is generated. Meanwhile, the microbubbles 120 in the slurry act to reduce the thickness of the scale 110. That is, the microbubbles 120 come into contact with the Al dross particles 100 in the slurry or condense and collapse, generating shock waves. These shock waves remove part of the scale 110 from the surface of the Al dross particles 100. If the thickness of the scale 110 is sufficiently thin, the hydrogen and ammonia generated in the Al dross particles 100 pass through the scale 110 and are released from the Al dross particles 100 as gas.

[0075] FIG. 5 is a diagram illustrating a second state of Al dross particles in heated water in the presence of microbubbles in a method for treating Al dross particles according to one embodiment of the present invention. As shown in FIG. 5, the growth of the scale 110 exceeds the reduction in the thickness of the scale 110 due to the microbubbles 120. When the scale 110 becomes sufficiently thick, the ammonia gas and hydrogen gas generated inside the Al dross particles 100 cannot pass through the scale 110 due to the microbubbles 120. Therefore, the ammonia gas and hydrogen gas are released into the slurry. As a result, the increase in the pH of the slurry substantially stops, or the increase in the pH of the absorption liquid in the first absorption tower 51 or the second absorption tower 52 substantially stops.

[0076] 6 is a diagram illustrating the state of Al dross particles being processed in a wet mill in a method for processing Al dross particles according to one embodiment of the present invention. In the wet mill 60, the Al dross particles 100 initially have a sufficiently thick scale 110 formed thereon, as shown in FIG. 5. In the wet mill 60, the Al dross particles 100 in the slurry are milled to a target particle size set by milling beads 610. This milling process polishes the scale 110 on the surface of the Al dross particles 100, resulting in a sufficiently thin surface, allowing ammonia gas and hydrogen gas generated in the Al dross particles 100 to be released into the slurry through the scale 110.

[0077] The thickness of the scale 110 in the Al dross particles 100 returned from the wet-milling apparatus 60 to the treatment tank 10 increases again. Therefore, the Al dross particles 100 assume the state shown in Fig. 5. By supplying the slurry in this state to the wet-milling apparatus 60, the Al dross particles 100 assume the state shown in Fig. 6 (or Fig. 4).

[0078] 7 is a diagram illustrating the final state of Al dross particles in heated water in the presence of microbubbles in a method for treating Al dross particles according to one embodiment of the present invention. When substantially all of the aluminum components in the Al dross particles 100 that react with water have reacted, as shown in FIG. 7, the aluminum components in the Al dross particles 100 essentially consist of only aluminum oxide and aluminum hydroxide. At this state, gas release from the Al dross particles 100 stops, and no ammonia gas release is observed. Because the slurry is basic due to ammonia, aluminum hydroxide remains stable in the Al dross particles 100.

[0079] Fig. 8 is a diagram illustrating the generation of alumina particles in a method for producing alumina particles according to one embodiment of the present invention. When Al dross particles 100 as shown in Fig. 7 are ignited, aluminum hydroxide in the Al dross particles 100 releases water, producing aluminum oxide, as shown in Fig. 8. Thus, alumina (aluminum oxide) particles 800 are produced by the aforementioned firing step.

[0080] [Experimental Example 1] 1000 g of Al dross particles and 10 L of water were placed in a reaction vessel, stirred, and the resulting slurry was heated to 85°C. Microbubbles were generated in the slurry at this temperature at a rate of approximately 3000 bubbles / mL. The gas in the reaction vessel was introduced into a water trap, and the ammonia gas generated in the trap was collected. Treatment under the above conditions was carried out for 3 hours. The slurry was then filtered, and the Al dross particles after the microvalve treatment were recovered.

[0081] The composition of the Al dross particles before and after the microvalve treatment is shown in Table 1. In Table 1, the values ​​are in mass%. In Table 1, Al and Si are analytical values ​​obtained by the hydrogen gas collection method, N is analytical values ​​obtained by steam distillation and titration, F and Cl are analytical values ​​obtained by X-ray fluorescence spectroscopy (briquette method), and C is analytical value obtained by carbon analysis.

[0082] [Table 1]

[0083] [Experimental Example 2] 100 g of microbubble-treated Al dross particles were mixed with 1 L of water and stirred to produce a slurry. The resulting slurry was stirred and polished in a bead mill for 1 hour. Alumina beads with a particle size of 2 mm were used. The slurry was then separated from the beads, and the Al dross particles after bead polishing were recovered from the slurry.

[0084] The compositions of the Al dross particles before and after the bead polishing treatment are shown in Table 2. The analytical values ​​in Table 2 were obtained by the same method as the values ​​in Table 1. The units of the values ​​are mass %.

[0085] [Table 2]

[0086] [Experimental Example 3] The same microvalve treatment as in Experimental Example 1 was carried out, and the Al dross particles obtained thereby were subjected to the same bead polishing treatment as in Experimental Example 2. The obtained Al dross particles were then subjected to the above microvalve treatment. In this way, the microvalve treatment and the bead polishing treatment were repeated once (each was carried out twice in total). The Al dross particles obtained from the final bead polishing treatment were then collected.

[0087] The compositions of the Al dross particles before and after the above repeated treatment are shown in Table 3. The analytical values ​​in Table 3 were obtained by the same method as the values ​​in Table 1. The units of the values ​​are mass %.

[0088] [Table 3]

[0089] [Experimental Example 4] The Al dross particles obtained by the same process as in Experimental Example 3 were fired at 1400°C for 5 hours. Fired particles were thus obtained. The compositions of the Al dross particles before and after firing are shown in Table 4. The analytical values ​​in Table 4 were obtained by the same method as the values ​​in Table 1. The units of the values ​​are mass%.

[0090] [Table 4]

[0091] [Consideration] In ceramic materials, recycled materials are usually mixed with new materials. According to Experimental Example 4, both fired particles can be reused as ceramic materials by mixing them with new materials to meet the compositional constraints depending on the application.

[0092] [Modification] 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 invention.

[0093] For example, in the treatment apparatus according to the embodiment of the present invention, the microbubble generator 20 may be an ultrasonic generator that generates ultrasonic waves in the slurry in the treatment tank 10 to generate microbubbles in the slurry. The ultrasonic generator may be used in combination with other types of microbubble generators. Examples of ultrasonic generators include ultrasonic microbubble generators such as ultrasonic vibrators and hollow ultrasonic horns. The ultrasonic generator is preferably arranged to generate ultrasonic waves in the slurry in the treatment tank 10, from the viewpoint of promoting the oxidation and decomposition of various components in the Al dross particles by the free radicals described above.

[0094] Moreover, the treatment apparatus may have a heating device that directly heats the slurry in the treatment tank 10 instead of the heating device 40 or in addition to the heating device 40 .

[0095] In the treatment device, the ammonia recovery device 50 may be a device that recovers ammonia gas generated in the treatment tank 10 in a gaseous state.

[0096] In the processing apparatus, the wet grinding device 60 may be a grinding device other than a bead mill, such as a roller mill, as long as it is a grinding device that can wet set the particle size of the particles to be ground.

[0097] In addition, in the treatment device, the solid-liquid separator 70 may be a centrifugal separator other than a cyclone type, or may be a filtering device.

[0098] In addition, in the processing apparatus, the valves V1 to V3 may be other valves such as ball valves.

[0099] In addition to the dry-type grinding device 90, the processing device may further include a classifying device for classifying the alumina particles ground by the dry-type grinding device 90 according to particle size.

[0100] Furthermore, the treatment device may use automatic valves for the valves V1 to V3, and may further include a control unit that controls the opening and closing of the valves V1 to V3 in accordance with information from a pH meter in the ammonia recovery device 50. This configuration is advantageous from the viewpoint of labor saving in the treatment of Al dross particles.

[0101] In addition, in the method for treating Al dross particles according to the embodiment of the present invention, the supply of the slurry to the solid-liquid separator 70 may be controlled according to sampling of the gas phase in the treatment tank 10 and the ammonia gas content in the sample.

[0102] Alternatively, in the method for treating Al dross particles, the start time of the second step (polishing step) may be determined according to a predetermined timetable, such as by carrying out scale removal using a wet grinding device at specific treatment times in a treatment tank.

[0103] In this treatment method, the gas phase portions of the wet-pulverizing device 60 and the solid-liquid separator 70 may also be supplied to the first absorption tower 51 in order to increase the recovery rate of ammonia.

[0104] 〔summary〕 As is clear from the above description, the method for treating Al dross particles according to an embodiment of the present invention includes a first step of contacting aluminum nitride-containing aluminum dross particles with water in an aqueous medium at 75 to 95°C to decompose the aluminum nitride, and a second step of removing scale adhered to the surfaces of the aluminum dross particles in the first step from the surfaces. The second step includes a microbubble introduction step of introducing microbubbles into the aqueous medium containing the aluminum dross particles. The above-described embodiment of the present invention can be used with general-purpose equipment to treat Al dross under relatively mild conditions, such as the boiling point of water, without generating substantial ammonia, regardless of the scale of the treatment. Thus, the above-described embodiment of the present invention provides a treatment technology for Al dross that substantially suppresses the generation of ammonia gas from treated Al dross and enables its reuse.

[0105] Furthermore, a method for producing alumina particles according to an embodiment of the present invention includes a step of firing the Al dross particles treated by the above-described treatment method to produce alumina particles, thereby making it possible to reuse the Al dross particles as alumina particles as a ceramic material.

[0106] In an embodiment of the present invention, the second step may include an ultrasonic wave generating step of generating ultrasonic waves in the aqueous medium to generate microbubbles, which is more effective in promoting the decomposition and oxidation of components in the Al dross particles in the aqueous medium.

[0107] In the treatment method, the second step may include a polishing step in which the aluminum dross particles treated in the first step are polished with beads to remove scale from the surface. This configuration is more effective from the viewpoint of further reducing the aluminum nitride content in the Al dross particles.

[0108] The treatment method may further include a third step of collecting ammonia generated in the first step. This configuration is more effective from the viewpoint of recovering ammonium resulting from the decomposition of aluminum nitride and from the viewpoint of promoting the oxidation of trace amounts of metallic aluminum remaining in the Al dross particles.

[0109] In the treatment method, the third step may be a step of collecting ammonia in water, which is more effective from the viewpoint of effectively utilizing the ammonia generated in the detoxification treatment of the Al dross particles.

[0110] In this treatment method, a polishing step may be performed depending on the amount of ammonia recovered in the third step, which is more effective in terms of increasing the efficiency of the decomposition treatment of aluminum nitride in the Al dross particles.

[0111] In the above-described embodiment of the present invention, ammonia generation from Al dross particles is substantially prevented. This reduces the environmental burden associated with aluminum production and enables effective use of waste materials. Therefore, the present invention is expected to contribute to the achievement of the Sustainable Development Goals (SDGs) regarding the conservation of land and sea resources and the ensuring of sustainable patterns of production activities. [Explanation of symbols]

[0112] 10 Treatment tank 11 Stirring device 20 Microbubble generator 21 nozzles 30 Circulation Pump 40 Heating device 50 Ammonia recovery unit 51 First Absorption Tower 52 Second Absorption Tower 60 Wet grinding equipment 70 Solid-liquid separator 80 Baking equipment 90 Dry grinding equipment 100 Al dross particles 110 scale 120 Microbubbles 610 beads 800 alumina particles V1, V2, V3 valves

Claims

1. a first step of contacting aluminum dross particles containing aluminum nitride with water in an aqueous medium at 75 to 95°C to decompose the aluminum nitride; a second step of removing scale adhered to the surfaces of the aluminum dross particles in the first step from the surfaces; Including, The second step includes a microbubble introduction step of introducing microbubbles into the aqueous medium containing the aluminum dross particles; an ultrasonic wave generating step of generating ultrasonic waves in the aqueous medium to generate microbubbles; Including, a solid solution ratio of the mixture of the aqueous medium and the aluminum dross particles in the first step is such that the amount of the aqueous medium is 7 to 10 when the amount of the aluminum dross particles is 1; A method for treating aluminum dross particles.

2. 2. The method for treating aluminum dross particles according to claim 1, wherein the number concentration of the microbubbles at the mode of diameter is 500 particles / mL or more and 3,000 particles / mL or less.

3. 3. The method for treating aluminum dross particles according to claim 1, wherein the second step includes a polishing step of polishing the aluminum dross particles treated in the first step with beads to remove the scale from the surface.

4. The method for treating aluminum dross particles according to any one of claims 1 to 3, further comprising a third step of collecting ammonia generated in the first step.

5. a third step of collecting the ammonia generated in the first step; The method for treating aluminum dross particles according to claim 3, wherein the polishing step is carried out depending on the amount of ammonia recovered in the third step.

6. 6. The method for treating aluminum dross particles according to claim 4, wherein the third step is a step of collecting ammonia in water.

7. A method for producing alumina particles, comprising a step of calcining aluminum dross particles treated by the method according to any one of claims 1 to 6 to produce alumina particles.

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