Amorphous aluminum hydroxide granules and method for producing the same

Abstract

The present invention provides amorphous aluminum hydroxide granulated particles with extremely low impurity content, high acid reactivity retention, controlled particle size, and a small angle of repose, thereby improving the flowability in the hopper and having good productivity. 【Solution means】 The present invention relates to (1) The particle size of the primary particles is 0.01 to 0.8 μm, (2) The particle size of the secondary particles has a D50 of 35 to 60 μm and a D90 of 50 to 120 μm, (3) It contains almost no impurities (i.e., sodium, magnesium, calcium, sulfur, chlorine, and iron), (4) The volatile content measured at 105 °C for 30 minutes with a heat drying type moisture meter is 4 to 12% by mass, (5) It has an angle of repose of 15 to 30°, (6) In the acid reactivity test, the time until the pH reaches 3 and 3.5 is 0 to 300 seconds, and the pH after 10 minutes from the start of measurement is 3.1 to 4.3 and provides amorphous aluminum hydroxide granulated particles characterized by the above.

Description

[Technical Field]

[0001] This invention relates to amorphous aluminum hydroxide granules and a method for producing the same. [Background technology]

[0002] Aluminum hydroxide gel has long been widely used as a pharmaceutical antacid. However, conventional aluminum hydroxide gels prioritize acid solubility and storage stability, so it is acceptable for them to contain certain amounts of impurities such as calcium, magnesium, sodium, potassium, or sulfur. However, for use in semiconductors and electronic materials, or for forming high-purity alumina particles through calcination, it is necessary to control impurities to an extremely low level. A drawback of using conventional aluminum hydroxide gel is that it cannot be used without significantly removing impurities.

[0003] Amorphous aluminum hydroxide granules are produced by various methods. For example, Japanese Patent No. 5328285 (Patent Document 1) describes aluminum hydroxide gel particles obtained by reacting a soluble aluminum salt aqueous solution with a carbonate ion supplying compound aqueous solution under conditions of pH 5.8 to 6.8 and temperature 10 to 40°C, separating the reaction product into solid and liquid phases, washing, and then spray drying or vacuum freeze-drying. The method uses aluminum sulfate and sodium carbonate as raw materials, and describes separating the reaction product into solid and liquid phases and washing. While this is acceptable as an antacid, it cannot be used as a synthetic or coating raw material for semiconductors and electronic materials unless the levels of alkali metals such as sodium and sulfur are controlled to be extremely low. Furthermore, although the spray drying outlet temperature is described as 120 to 160°C during manufacturing, if the temperature of the powder collection container is not designed to be controlled to 80°C or lower, prolonged exposure to heat may degrade the acid reactivity of the amorphous aluminum hydroxide granules.

[0004] In Japanese Patent Application Laid-Open No. 8-231557 (Patent Document 2) and Japanese Patent Publication No. 1-24731 (Patent Document 3), an aluminum hydroxide gel with a high reaction rate with an acid and low change over time is proposed, where the average secondary particle diameter of the gel before drying is 4 μm or less, and (M2O) x1 Al2O3(CO2) y R z ·mH2O, (M2O) x1 (CaO) x 2Al2O3(CO2) y R z ·mH2O, (M2O) x1 (MgO) x3 Al2O3(CO2) y R z ·mH2O, (M2O) x1 (CaO) x2 (MgO) x3 Al2O3(CO2) y R z ·mH2O (where M is a monovalent alkali metal and R is a divalent or higher organic acid). However, this aluminum hydroxide gel contains a large amount of alkali metals and alkaline earth metals.

[0005] Japanese Patent Publication No. 7835952 (Patent Document 4) provides amorphous aluminum hydroxide having an average circularity of 0.6 or higher, and in scanning electron microscope (SEM) images for circularity calculation, there are no isolated particles with a maximum length exceeding 50 μm. Furthermore, a method for producing amorphous aluminum hydroxide is described, comprising: (1) a first step of adding an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound, so as to maintain the pH of the mixture of the two aqueous solutions within the range of 6-7.5, and reacting them to produce gel-like aluminum hydroxide and obtain a rough slurry; (2) a second step of washing the rough slurry obtained in the first step to obtain an aluminum hydroxide-containing slurry; and (3) a third step of drying the aluminum hydroxide-containing slurry obtained in the second step. Temperature control in this process is important in the synthesis of amorphous aluminum hydroxide, but because there is no cooling step and the acid and base react directly, the system temperature tends to rise due to the heat of reaction, making it difficult to stabilize the pH, which may lead to the formation of byerlites, making it difficult to stably produce amorphous aluminum hydroxide. In the manufacturing method of Patent Document 4, upper limits for alkali metals, chlorine, and sulfur are specified in the specification, but in order to produce high-purity alumina by calcining amorphous aluminum hydroxide, which is a synthesis raw material for semiconductors and electronic materials, control of magnesium and calcium is necessary, but magnesium and calcium are not controlled. Temperature control during drying is important in order to maintain the acid-soluble physical properties of amorphous aluminum hydroxide, but temperature control is not specifically specified, and long-term drying at 100°C is performed, which is thought to cause degradation of amorphous aluminum hydroxide and make it impossible to produce amorphous aluminum hydroxide with stable reactivity. Furthermore, in production processes such as powder press molding, extrusion molding, and kneader mixing, it is necessary for the blending raw materials to be supplied in a fixed quantity from the hopper. In this process, an angle of repose of 15-30° is required, but because there are no independent particles larger than 50 μm and the average circularity is 0.6 or higher, the angle of repose exceeds 30°. This results in poor flowability, causing the material to stagnate in the hopper, leading to bridging and other issues, which poses challenges in product production during powder press molding, extrusion molding, kneader mixing, etc. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5328285 [Patent Document 2] Japanese Patent Publication No. 8-231557 [Patent Document 3] Special Publication No. 1-24731 [Patent Document 4] Patent No. 7835952 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention provides amorphous aluminum hydroxide granules with excellent productivity that can be adapted to various molding processes by controlling the particle size and reducing the angle of repose while maintaining high acid reactivity and containing very few impurities, thereby improving flowability within the hopper. [Means for solving the problem]

[0008] In other words, the present invention encompasses the following aspects: [1] Amorphous aluminum hydroxide granules, (1) The particle size of the primary particles is 0.01 to 0.8 μm. (2) The particle size of the secondary particles, as measured by a laser diffraction particle size analyzer, was 35-60 μm for D50 and 50-120 μm for D90. (3) Contains sodium in the range of 0-0.05% by mass, magnesium in the range of 0-0.05% by mass, calcium in the range of 0-0.05% by mass, sulfur in the range of 0-0.01% by mass, chlorine in the range of 0-0.05% by mass, and iron in the range of 0-0.01% by mass. (4) When measured with a heated drying type moisture meter at a temperature of 105°C for 30 minutes, the volatile content was 4 to 12% by mass. (5) Having an angle of repose of 15-30°, (6) In the acid reactivity test, the time to reach pH 3 and pH 3.5 is 0 to 300 seconds, and the pH 10 minutes after the start of measurement is 3.1 to 4.3. Amorphous aluminum hydroxide granulated particles characterized by the above. A method for producing amorphous aluminum hydroxide granules as described in [2][1], (Step 1) A step in which water is first added, and then an aqueous solution of aluminum chloride, an aqueous solution of sodium carbonate, and an aqueous solution of sodium aluminate are mixed and reacted while controlling the pH to 6 to 7.5 and the liquid temperature to 1 to 35°C to obtain a rough slurry containing gel-like amorphous aluminum hydroxide, wherein the concentration of Al2O3 in the rough slurry is 3% by mass or more. (Second step) The crude slurry obtained in the first step is washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing is 100-350 μS / cm, and then dewatered to obtain a cake containing amorphous aluminum hydroxide with few impurities. The obtained amorphous aluminum hydroxide-containing cake is measured using a heat-drying type moisture meter at 105°C for 45 minutes and the volatile content is 72-85% by mass. (Third step) A step of adding water to the amorphous aluminum hydroxide-containing cake obtained in the second step and redispersing it to prepare an amorphous aluminum hydroxide-containing slurry, and (Step 4) A step in which the amorphous aluminum hydroxide-containing slurry obtained in Step 3 is spray-dried to obtain amorphous aluminum hydroxide granules. A method for producing amorphous aluminum hydroxide granules, characterized by containing the following: [3] The method for producing amorphous aluminum hydroxide granules according to claim 2, characterized in that when the liquid temperature in the first step is controlled to 1 to 35°C, the jacket is cooled by circulating water using a chiller or ice water. [4] A method for producing amorphous aluminum hydroxide granules according to [2] or [3], characterized in that the second step of washing and dewatering is performed using a centrifuge, a filter press, or a rotary filter. [5] The method for producing amorphous aluminum hydroxide granules according to [2] or [3], characterized in that the fourth step of spray drying is performed using spray drying, with an inlet temperature of 200 to 330°C and an outlet temperature of 80 to 150°C, and the amorphous aluminum hydroxide particles in the collection container for collecting the spray-dried amorphous aluminum hydroxide are collected at a temperature of 5 to 80°C. [Effects of the Invention]

[0009] The amorphous aluminum hydroxide granules according to the present invention have an extremely low content of impurity elements, with a particle size of 0.01 to 0.8 μm for the primary amorphous aluminum hydroxide particles, and the amorphous aluminum hydroxide granules are formed as secondary particles. Because they are synthesized in an environment where the temperature during reaction and drying is appropriately controlled, they exhibit extremely high reactivity with acids and have the characteristics of being usable for the synthesis of aluminum oxide and aluminum composite oxides for semiconductors and electronic materials, as well as for the synthesis of catalyst supports. Furthermore, because the particle size D50 is 35 to 60 μm and D90 is 61 to 120 μm, the angle of repose of the amorphous aluminum hydroxide granules is 15 to 30°, resulting in extremely high fluidity in the hopper when using amorphous aluminum hydroxide granules for press molding, extrusion molding, or kneading, making weighing and loading during press molding, extrusion molding, and kneading easier. This makes it possible to provide highly productive amorphous aluminum hydroxide granules. The amorphous aluminum hydroxide particle granules of the present invention can be used as high-purity aluminum-based raw materials for semiconductors and electronic materials, as well as as high-performance compounding materials for resins, rubber, and the like.

[0010] Furthermore, in a method for producing amorphous aluminum hydroxide granules, the present invention facilitates pH control by controlling the material mixing and temperature control during the synthesis of a gel-like amorphous aluminum hydroxide crude slurry. Moreover, the crude slurry is washed multiple times with water to reduce impurities to below a certain level, and stable production is possible through a dehydration process to obtain a cake containing a certain amount of moisture, followed by a temperature-controlled drying process. In this invention, a method has been found for producing amorphous aluminum hydroxide granules that can be used as a crude raw material for high-purity alumina. [Brief explanation of the drawing]

[0011] [Figure 1] It is a graph of the particle size distribution measured by dry method using a laser diffraction particle size distribution analyzer (Mastersizer 3000 manufactured by Malvern Panalytical Ltd.) for the amorphous aluminum hydroxide granulated particles obtained in Example 1. [Figure 2] It is a diagram showing the results measured by the θ / 2θ method using a Cu target with an X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) for the amorphous aluminum hydroxide granulated particles obtained in Example 1. [Figure 3] It is a scanning electron microscope (SEM) image at 10,000 times magnification of the amorphous aluminum hydroxide granulated particles of Example 1 measured using a desktop scanning electron microscope (JCM-7000, manufactured by JEOL Ltd.). [Figure 4] It is a 200-fold SEM image of the amorphous aluminum hydroxide granulated particles of Example 1 measured using a desktop scanning electron microscope (JCM-7000, manufactured by JEOL Ltd.). [Figure 5] It is a 10,000-fold SEM image of the amorphous aluminum hydroxide granulated particles of Comparative Example 1 measured using a desktop scanning electron microscope (JCM-7000, manufactured by JEOL Ltd.). [Figure 6] It is a 200-fold SEM image of the amorphous aluminum hydroxide granulated particles of Comparative Example 1 measured using a desktop scanning electron microscope (JCM-7000, manufactured by JEOL Ltd.). [Figure 7] It is a diagram showing the results measured by the θ / 2θ method using a Cu target with an X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) for the powder obtained by firing the amorphous aluminum hydroxide granulated particles obtained in Example 1 at 1200 °C for 4 hours. [Figure 8] It is a diagram showing the results measured by the θ / 2θ method using a Cu target with an X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) for the powder obtained by firing the amorphous aluminum hydroxide granulated particles obtained in Comparative Example 4 at 1200 °C for 4 hours.

Mode for Carrying Out the Invention

[0012] The present invention provides amorphous aluminum hydroxide granules having the following characteristics: (1) The particle size of the primary particles is 0.01 to 0.8 μm. (2) The particle size of the secondary particles, as measured by a laser diffraction particle size analyzer, was 35-60 μm for D50 and 50-120 μm for D90. (3) Contains sodium in the range of 0-0.05% by mass, magnesium in the range of 0-0.05% by mass, calcium in the range of 0-0.05% by mass, sulfur in the range of 0-0.01% by mass, chlorine in the range of 0-0.05% by mass, and iron in the range of 0-0.01% by mass. (4) When measured with a heated drying type moisture meter at a temperature of 105°C for 30 minutes, the volatile content was 4 to 12% by mass. (5) Having an angle of repose of 15-30°, (6) In the acid reactivity test, the time to reach pH 3 and pH 3.5 is 0 to 300 seconds, and the pH 10 minutes after the start of measurement is 3.1 to 4.3. The amorphous aluminum hydroxide granules of the present invention can be manufactured in at least the following four steps: (Step 1) A step in which water is first added, and then an aqueous solution of aluminum chloride, an aqueous solution of sodium carbonate, and an aqueous solution of sodium aluminate are mixed and reacted while controlling the pH to 6 to 7.5 and the liquid temperature to 1 to 35°C to obtain a rough slurry containing gel-like amorphous aluminum hydroxide, wherein the concentration of Al2O3 in the rough slurry is 3% by mass or more. (Second step) The crude slurry obtained in the first step is washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing is 100-350 μS / cm, and then dewatered to obtain a cake containing amorphous aluminum hydroxide with few impurities. The obtained amorphous aluminum hydroxide-containing cake is measured using a heat-drying type moisture meter at 105°C for 45 minutes and the volatile content is 72-85% by mass. (Third step) A step of adding water to the amorphous aluminum hydroxide-containing cake obtained in the second step and redispersing it to prepare an amorphous aluminum hydroxide-containing slurry, and (Step 4) A step in which the amorphous aluminum hydroxide-containing slurry obtained in Step 3 is spray-dried to obtain amorphous aluminum hydroxide granules.

[0013] <Method for measuring special values> The method for measuring the particle size and angle of repose characteristics of amorphous aluminum hydroxide granules according to the present invention is summarized below.

[0014] (Particle size of primary particles) The particle size of the primary particles of amorphous aluminum hydroxide granules in this invention is visually confirmed by scanning electron microscope (SEM) images obtained using a table-type electron microscope (JCM-7000; manufactured by JEOL Ltd.).

[0015] (Secondary particle sizes D50 and D90) In the present invention, the particle sizes D50 and D90 of the secondary particles of amorphous aluminum hydroxide granules are determined by dry measurement of the cumulative particle size distribution using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical). D50 refers to the particle size when 50% of the total particle amount in the cumulative particle size distribution is of this particle size or smaller, and D90 refers to the particle size when 90% of the total particle amount in the cumulative particle size distribution is of this particle size or smaller.

[0016] (Concentration of impurities) The content of sodium, magnesium, calcium, sulfur, chlorine, and iron, which are impurities in the amorphous aluminum hydroxide granules of the present invention, is measured using an energy-dispersive X-ray fluorescence spectrometer (EDX) mounted on a benchtop scanning electron microscope.

[0017] (Measurement of volatile components) The volatile content of amorphous aluminum hydroxide granules in this invention is measured using a heat-drying type moisture meter (MX-50, manufactured by A&D) at 105°C for 30 minutes.

[0018] (Method for measuring the angle of repose) The angle of repose of amorphous aluminum hydroxide granules of the present invention is measured by the angle of repose measurement method described below: [1] Set a powder funnel with an inner diameter of 10 mm so that the bottom of the funnel is 40 mm above the glass substrate. Drop the powder from a 500 ml beaker from a position of 40 mm or more above the top of the funnel, and pour the powder from the beaker into the funnel. [2] Stop adding powder when the top surface of the powder reaches the bottom of the funnel. [3] A protractor is placed on the glass substrate surface, and the angle of repose is measured by reading the markings on the protractor from the side. The angle of repose refers to the angle of the slope (measured from the horizontal plane) at which a pile of granular material such as sand, soil, or powder can remain naturally stable without collapsing. In the measurement method described above, the angle of the slope at which the powder can naturally remain stable is measured from the base material surface.

[0019] (Acid reactivity test) The acid reactivity test for amorphous aluminum hydroxide granules is performed as follows. Accurately place 50 ml of 0.1 mol / l hydrochloric acid into a 100 ml beaker and immerse it in a 37°C constant temperature bath to maintain the liquid temperature at 37°C. Next, immerse the electrode of the pH meter in the liquid and add 1.0 g of the sample powder (amorphous aluminum hydroxide granules in this invention) while stirring with a magnetic stirrer. Simultaneously, start a stopwatch and measure the time it takes to reach pH 3 and pH 3.5, as well as the pH 10 minutes after the start of the stopwatch (start of measurement).

[0020] <Characteristics of amorphous aluminum hydroxide granules> In the present invention, amorphous aluminum hydroxide granules must have a primary particle diameter of 0.01 to 0.8 μm. Preferably, the primary particle diameter is 0.02 to 0.6 μm, and more preferably 0.05 to 0.6 μm. If the primary particle diameter is less than 0.01 μm, the reactivity is too high, causing thermal degradation even in the instantaneous thermal history of spray drying, and resulting in poor acid reactivity. On the other hand, if it exceeds 0.8 μm, there is a problem of poor acid reactivity.

[0021] In the present invention, the particle size of the secondary particles of amorphous aluminum hydroxide granules must be such that the D50 particle size is 35-60 μm and the D90 particle size is 50-120 μm in the particle size distribution measured by a laser diffraction particle size analyzer. If the D50 is less than 35 μm, the number of fine particles increases, causing the angle of repose of the amorphous aluminum hydroxide granules to exceed 30°, resulting in poor fluidity. On the other hand, if the D50 is 60 μm or more, there are too many coarse particles in the amorphous aluminum hydroxide granules, making dispersion during extrusion molding and kneading difficult. If the D90 is less than 50 μm, the particle size is too fine, resulting in a small angle of repose and poor fluidity, which makes it easy to form bridges when filling into hoppers, etc., resulting in poor productivity. If the D90 exceeds 120 μm, there are particles that are too large, resulting in poor dispersion of the amorphous aluminum hydroxide granules in resins, etc.

[0022] In the present invention, amorphous aluminum hydroxide granules must contain impurities ranging from 0 to 0.05 mass% sodium, 0 to 0.05 mass% magnesium, 0 to 0.05 mass% calcium, 0 to 0.01 mass% sulfur, 0 to 0.05 mass% chlorine, and 0 to 0.01 mass% iron. If the sodium content exceeds 0.05 mass%, the amount of sodium in the amorphous aluminum hydroxide is too high, causing a melting point depression and generating defects when synthesizing aluminum oxide, etc., making it unusable. Furthermore, in semiconductor and electronic materials, it generates ionic conductivity, making it unusable. Next, if magnesium is contained in the amorphous aluminum hydroxide granules in amounts exceeding 0.05 mass%, it forms an unintended crystalline phase when synthesizing aluminum oxide or aluminum composite oxides, resulting in defects, making it unusable. Furthermore, if the amorphous aluminum hydroxide granules contain more than 0.05% by mass of calcium, it can create an unintended crystalline phase when synthesizing aluminum oxide or aluminum composite oxides, resulting in defects and rendering the material unusable.

[0023] If the amorphous aluminum hydroxide granules of this invention contain more than 0.01% by mass of sulfur, the amount of sulfur in the amorphous aluminum hydroxide is too high, causing defects or corrosion when synthesizing aluminum oxide, aluminum composite oxides, etc., and therefore they cannot be used. If the amorphous aluminum hydroxide granules contain more than 0.05% by mass of chlorine, the amount of chlorine in the amorphous aluminum hydroxide granules is too high, causing defects or corrosion when synthesizing aluminum oxide, aluminum composite oxides, etc., and therefore they cannot be used. Furthermore, if the amorphous aluminum hydroxide granules contain more than 0.01% by mass of iron, discoloration due to iron oxide or defects due to different crystalline phases will occur when synthesizing aluminum oxide, aluminum composite oxides, etc.

[0024] In the present invention, the moisture content of amorphous aluminum hydroxide granules must be 4 to 12% by mass when measured using a heat-drying type moisture meter at 105°C for 30 minutes. If the volatile content of the amorphous aluminum hydroxide granules is less than 4% by mass, the moisture content is too low, which reduces the activity of amorphous aluminum hydroxide and worsens its acid solubility. On the other hand, if the volatile content of the amorphous aluminum hydroxide granules exceeds 12% by mass, the surface becomes sticky, which worsens handling. The volatile content is preferably 4.2 to 10% by mass, more preferably 4.5 to 9% by mass.

[0025] The angle of repose of amorphous aluminum hydroxide granules in this invention must be 15 to 30°. The angle of repose is measured by the method already described. If the angle of repose of amorphous aluminum hydroxide granules is less than 15°, the particles have too much fluidity and may be blown out of conveyors or discharge ports, potentially causing machine failure or scattering and contaminating the surroundings. On the other hand, if the angle of repose of amorphous aluminum hydroxide granules exceeds 30°, the amorphous aluminum hydroxide granules do not flow well, leading to problems such as bridging in filling or molding hoppers and inability to supply the particles. The angle of repose of amorphous aluminum hydroxide granules in this invention is preferably 16 to 28°, and more preferably 17 to 27°.

[0026] The amorphous aluminum hydroxide granules in this invention are subjected to an acid reactivity test using the method described above. The time it takes for the pH to reach 3 and 3.5 from the start of the acid reactivity test, using a stopwatch, must be between 0 and 300 seconds. Preferably, it is between 0 and 240 seconds, and more preferably between 0 and 200 seconds. If it exceeds 240 seconds, it is considered that the surface activity of the amorphous aluminum hydroxide granules has deteriorated, indicating a problem of poor acid reactivity.

[0027] In the acid reactivity test of amorphous aluminum hydroxide granules in this invention, the pH 10 minutes after the start of measurement (start of stopwatch operation) must be between 3.1 and 4.3. If the pH is less than 3.1, it is thought that there are undissolved or unreacted amorphous aluminum hydroxide granules remaining, which presents a problem of poor reactivity with acid. On the other hand, if the pH exceeds 4.3, it is predicted that the amorphous aluminum hydroxide granules contain basic substances, which presents a problem of not having high purity. Preferably, the pH 10 minutes after the start of measurement in the acid reactivity test is between 3.2 and 4.2, and more preferably between 3.3 and 4.1.

[0028] <Method for producing amorphous aluminum hydroxide granules> The amorphous aluminum hydroxide granules of the present invention are produced by the following method: (Step 1) A step in which water is first added, and then an aqueous solution of aluminum chloride, an aqueous solution of sodium carbonate, and an aqueous solution of sodium aluminate are mixed and reacted while controlling the pH to 6 to 7.5 and the liquid temperature to 1 to 35°C to obtain a rough slurry containing gel-like amorphous aluminum hydroxide, wherein the concentration of Al2O3 in the rough slurry is 3% by mass or more. (Second step) The crude slurry obtained in the first step is washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing is 100-350 μS / cm, and then dewatered to obtain a cake containing amorphous aluminum hydroxide with few impurities. The obtained amorphous aluminum hydroxide-containing cake is measured using a heat-drying type moisture meter at 105°C for 45 minutes and the volatile content is 72-85% by mass. (Third step) A step of adding water to the amorphous aluminum hydroxide-containing cake obtained in the second step and redispersing it to prepare an amorphous aluminum hydroxide-containing slurry, and (Step 4) A step in which the amorphous aluminum hydroxide-containing slurry obtained in Step 3 is spray-dried to obtain amorphous aluminum hydroxide granules.

[0029] (raw materials) The following raw materials must be selected for use in the production of amorphous aluminum hydroxide granules according to the present invention: (I) Aqueous solution of aluminum chloride with a basicity of 1-11% (II) Aqueous solution of sodium carbonate (III) Sodium aluminate aqueous solution

[0030] In this invention, in the first step, a rough slurry of amorphous aluminum hydroxide is prepared in an environment where the temperature and pH are controlled, using the raw materials (I), (II), and (III) above, with water added first. In the second step, the rough slurry is washed with water, and during washing, the electrical conductivity of the wastewater after washing is reduced to 100-350 μS / cm, and then dewatered to a predetermined amount of volatile matter to obtain a cake. Next, in the third step, water is added to the cake and redispersed to obtain an amorphous aluminum hydroxide-containing slurry. In the fourth step, the amorphous aluminum hydroxide-containing slurry is spray-dried at predetermined inlet temperature, outlet temperature, and collection container temperature, making it possible to obtain amorphous aluminum hydroxide particle granules that have predetermined particle size, volatile matter, predetermined impurity amount, predetermined angle of repose, and predetermined acid solubility test results.

[0031] (Explanation of manufacturing method) (Step 1) Water is added first, and then three aqueous solutions of aluminum chloride, sodium carbonate, and sodium aluminate are mixed. The pH of the mixture is maintained within the range of 6 to 7.5, and the temperature is controlled within the range of 1 to 35°C. The mixture is added and reacted to produce a gel-like amorphous aluminum hydroxide, and a crude slurry containing gel-like amorphous aluminum hydroxide is obtained. The Al2O3 concentration in the crude slurry is 3% by mass or more. (Second step) The crude slurry obtained in the first step is washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing is 100-350 μS / cm. After further reducing the content of sodium, magnesium, calcium, sulfur, iron, and chlorine, it is dehydrated to obtain a cake. A heat-drying type moisture meter is used to measure the volatile content of the cake, which contains amorphous aluminum hydroxide with a volatile content of 72-85% by mass, at 105°C for 45 minutes. (Step 3) Water is added to the amorphous aluminum hydroxide-containing cake obtained in Step 2, and the mixture is stirred to prepare a redispersed amorphous aluminum hydroxide-containing slurry. (Step 4) The amorphous aluminum hydroxide-containing slurry from Step 3 is spray-dried. Spray drying is performed using a spray dryer, with an inlet temperature of 200-330°C and an outlet temperature of 80-150°C. The amorphous aluminum hydroxide particles in the collection container that collects the spray-dried amorphous aluminum hydroxide are collected at a temperature of 5-80°C to obtain amorphous aluminum hydroxide granules.

[0032] (I) (Basic aluminum chloride aqueous solution) The basic aluminum chloride aqueous solution used in this invention has a basicity of 1 to 11%. Preferably, the basicity is 1.2 to 10%, and more preferably 1.5 to 9%. If the basicity is less than 1%, the pH is too low, making it difficult for the pH to move towards the basic side when sodium aluminate and sodium carbonate aqueous solutions are added, and it becomes difficult to stabilize the target pH at 6 to 7.5 by adding sodium aluminate and sodium carbonate aqueous solutions. On the other hand, if the basicity exceeds 11%, the pH moves rapidly towards the basic side when sodium aluminate and sodium carbonate aqueous solutions are added, the viscosity of the solution increases rapidly, and the reaction stops. "Basicity" is a value that indicates what percentage of the valencies that can be substituted by a base are filled. Since aluminum is trivalent, if 2 / 3 (2 out of 3 valencies) is used, it means that it will be 66.66% (i.e., about 67%). This basic aluminum chloride aqueous solution is preferably 8.5 to 12.5% ​​by mass of Al in terms of Al2O3 equivalent Al amount. The amount of Al in terms of Al2O3 is preferably 9.0 to 10.8% by mass, more preferably 9.5 to 10.5% by mass. If the amount of Al in terms of Al2O3 is less than 8.5%, the concentration of basic aluminum chloride is too low, and when sodium aluminate and sodium carbonate aqueous solutions are added, the pH rises rapidly, making it difficult to stabilize and stop at the target pH of 6 to 7.5. On the other hand, if the amount of Al in terms of Al2O3 exceeds 12.5% ​​by mass, Al precipitation is more likely during the reaction, and the desired amorphous aluminum hydroxide cannot be obtained. The amount of Al in terms of Al2O3 of the basic aluminum chloride aqueous solution is measured in accordance with the method for measuring the basicity of liquid polyaluminum chloride for water supply, as specified in JIS K1475.

[0033] (II) (Sodium carbonate solution) The sodium carbonate aqueous solution used in this invention is preferably 6 to 15% by mass. Preferably, the concentration of the sodium carbonate aqueous solution is 7 to 14% by mass, more preferably 8 to 13% by mass. If the concentration of the sodium carbonate aqueous solution is less than 6% by mass, the solution concentration is too dilute, requiring a large amount to be added during formulation, making it difficult to maintain a stable pH of 6 to 7.5. If the concentration of the sodium carbonate aqueous solution exceeds 15% by mass, the concentration is too high, causing precipitation during the reaction.

[0034] (III) (Sodium aluminate) The sodium aluminate used in this invention must contain 18 to 24% by mass of Al in terms of Al2O3 equivalent. The amount of Al in terms of Al2O3 is preferably 18.5 to 23% by mass, and more preferably 19 to 21% by mass. If the amount of Al in terms of Al2O3 is less than 18.5%, the Al concentration is too low, and when basic aluminum chloride is added, a large amount of sodium aluminate must be added to neutralize it, resulting in a shift in pH towards the basic side, making it impossible to stably stop the reaction at pH 6 to 7.5. On the other hand, if the amount of Al in terms of Al2O3 exceeds 24% by mass, the stability of the sodium aluminate deteriorates, precipitation of Al occurs during the reaction, and the desired amorphous aluminum hydroxide cannot be obtained. It becomes difficult to stably stop the reaction at pH 6 to 7.5. The amount of Al in terms of Al2O3 of the sodium aluminate used in this invention is measured in accordance with JWWA K112 (1967).

[0035] The sodium aluminate used in this invention must contain 16 to 21% by mass of Na in terms of Na2O equivalent. The amount of Na in terms of Na2O equivalent is preferably 17 to 20.5% by mass, and more preferably 18 to 20% by mass. If the amount of Na in terms of Na2O equivalent is less than 16% by mass, the Na concentration is too low, making the sodium aluminate unstable and causing Al precipitation during the reaction, thus preventing the acquisition of the desired amorphous aluminum hydroxide. On the other hand, if the amount of Na in terms of Na2O equivalent exceeds 21% by mass, the amount of Na in the reaction system becomes excessive, and Na cannot be sufficiently washed away during the washing process after the synthesis of amorphous aluminum hydroxide, resulting in the problem of not being able to obtain amorphous aluminum hydroxide with a low Na content. The amount of Na in terms of Na2O equivalent of the sodium aluminate used in this invention is measured in accordance with JWWA K112 (1967).

[0036] In the first step, water is added first, and then three solutions—aqueous aluminum chloride solution with a basicity of 1-11%, aqueous sodium carbonate solution, and aqueous sodium aluminate solution—are mixed. The amount of these solutions added must be adjusted so that the pH of the mixture remains within the range of 6-7.5. A pH of 6.1-6.9 is preferred, and a pH of 6.3-6.7 is more preferred. If the pH is below 6, precipitation as amorphous aluminum hydroxide becomes difficult, and the concentration of the crude slurry does not increase. On the other hand, if the pH exceeds 7.5, aluminum hydroxide such as byerlite is more likely to form, and there is a problem of an increase in impurities other than the desired amorphous aluminum hydroxide.

[0037] In the first step, it is necessary to add the three solutions—aqueous aluminum chloride solution, sodium carbonate solution, and sodium aluminate solution—to a mixture of water with a basicity of 1-11%, maintaining the pH of the mixture within the range of 6-7.5 and controlling the temperature within the range of 1-35°C. The temperature is preferably 3-30°C, and more preferably 5-25°C. If the temperature is below 1°C, the viscosity of the four solutions becomes extremely high, posing a problem as the reaction does not proceed. On the other hand, if the temperature exceeds 35°C, the activity of amorphous aluminum hydroxide deteriorates, and the acid dissolution test results worsen. The reason for adding aqueous solutions of aluminum chloride, sodium carbonate, and sodium aluminate to water first in this step is that the reaction of these chemicals is exothermic, and the use (addition) of water is necessary to control the temperature.

[0038] In the second step, the crude slurry obtained in the first step needs to be washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing reaches 100-350 μS / cm. If the water temperature used to wash the crude slurry is below 10°C, the solubility of impurities such as sodium in amorphous aluminum hydroxide decreases, making it impossible to reduce the impurity concentration in the crude slurry to the target value. On the other hand, if the water temperature used to wash the crude slurry exceeds 35°C, the activity of the amorphous aluminum hydroxide remaining after washing deteriorates, worsening the acid solubility test results.

[0039] In the second step, the crude slurry obtained in the first step needs to be washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing reaches 100-350 μS / cm. Achieving an electrical conductivity of less than 100 μS / cm in the wastewater after washing the crude slurry requires a very long washing time, resulting in reduced productivity. On the other hand, if the electrical conductivity of the wastewater exceeds 350 μS / cm, it indicates that a large amount of ions such as sodium and calcium are present in the wastewater, meaning that a large amount of these ions remain in the slurry, preventing the production of the desired high-purity amorphous aluminum hydroxide cake. The electrical conductivity of the wastewater is measured using a portable electrical conductivity meter (D-210C, manufactured by Horiba, Ltd.).

[0040] In the second step, the crude slurry obtained in the first step is washed with water controlled at 10-35°C until the electrical conductivity of the wastewater after washing reaches 100-350 μS / cm, thereby reducing the content of sodium, magnesium, calcium, sulfur, iron, and chlorine. After dehydration, a cake is obtained, and a cake containing amorphous aluminum hydroxide with a volatile content of 72-85% by mass is obtained when measured with a heated drying type moisture meter at 105°C for 45 minutes. Preferably, the volatile content is 73-84% by mass, more preferably 74-82% by mass. If the volatile content is less than 72% by mass, dehydration progresses too much, the cake becomes too hard, and redispersion in the third step becomes difficult. On the other hand, if the volatile content exceeds 84% ​​by mass, the cake becomes sticky, making handling difficult when moving to the next step.

[0041] In the second step, the volatile content of the dehydrated cake was measured using a heated drying type moisture meter (MX-50, manufactured by A&D) at 105°C for 45 minutes.

[0042] In the third step, water is added to the amorphous aluminum hydroxide-containing cake obtained in the second step, and the mixture is stirred to redisperse it and produce an amorphous aluminum hydroxide-containing slurry. This step of redispersing the amorphous aluminum hydroxide-containing cake with water is essential for spray drying in the next step (the fourth step). Without this step, the obtained amorphous aluminum hydroxide-containing cake will not return to a slurry state suitable for spray drying, making spray drying impossible. If the slurry is not redispersed, clumps will remain, and clogging is likely to occur during spray drying.

[0043] In the third step, water is added to the amorphous aluminum hydroxide-containing cake obtained in the second step, and when stirring, any of the following can be used: a propeller stirrer, a disperser, a universal stirrer, or a homogenizer. There are no particular restrictions as long as dispersion is achieved.

[0044] In the fourth step, when spray-drying the amorphous aluminum hydroxide-containing slurry, a spray dryer is used, and drying is performed at an inlet temperature of 200-330°C and an outlet temperature of 80-150°C. It is necessary to collect the amorphous aluminum hydroxide granules in the collection container at a temperature of 5-80°C after spray drying. The inlet temperature is preferably 210-320°C, more preferably 220-300°C. If the inlet temperature is below 200°C, the amorphous aluminum hydroxide-containing slurry will not dry sufficiently, and solidification inside the spray dryer will be severe. On the other hand, if it exceeds 330°C, the amorphous aluminum hydroxide in the amorphous aluminum hydroxide-containing slurry will degrade significantly due to heat, resulting in poor acid dissolution test results.

[0045] In the fourth step, when spray-drying the amorphous aluminum hydroxide-containing slurry, a spray dryer is used, and drying is performed at an inlet temperature of 200-330°C and an outlet temperature of 80-150°C. It is necessary to collect the amorphous aluminum hydroxide granules in the collection container that collects the spray-dried amorphous aluminum hydroxide at a temperature of 5-80°C. The outlet temperature is preferably 80-150°C, more preferably 90-130°C. If the outlet temperature is below 80°C, the amorphous aluminum hydroxide-containing slurry will not dry sufficiently, and solidification inside the spray dryer will become severe. On the other hand, if it exceeds 150°C, the amorphous aluminum hydroxide in the amorphous aluminum hydroxide-containing slurry will degrade significantly due to heat, and the acid dissolution test results will be poor.

[0046] In the fourth step, when spray-drying the amorphous aluminum hydroxide-containing slurry, spray drying is performed with an inlet temperature of 200-350°C and an outlet temperature of 80-150°C. It is necessary to collect the amorphous aluminum hydroxide granules in the collection container at a temperature of 5-80°C. The temperature inside the collection container is preferably 15-70°C, more preferably 20-60°C. If the temperature inside the collection container is below 5°C, condensation is likely to occur, and the volatile content of the dried amorphous aluminum hydroxide granules will increase. On the other hand, if the temperature inside the collection container exceeds 80°C, the thermal degradation of the amorphous aluminum hydroxide granules over time will be severe, and the acid dissolution test will deteriorate.

[0047] The spray dryer used for drying has an extremely short residence time for amorphous aluminum hydroxide in the drying area, resulting in very little thermal degradation. Furthermore, the temperature of the collection container can be controlled between 5 and 80°C, so thermal degradation over time is also kept to a minimum.

[0048] (Examples) The present invention will be described in more detail by reference to examples. The present invention should not be construed as being limited to these examples. In the examples, unless otherwise specified, percentages and parts are based on mass.

[0049] (Example 1) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0050] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a collection container temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6%. The volatile content was measured using a heated drying type moisture meter (MX-50, manufactured by A&D) at 105°C for 30 minutes. The volatile content was measured using the same method in the following examples and comparative examples.

[0051] Figure 1 shows the particle size distribution of amorphous aluminum hydroxide granules obtained by a laser diffraction particle size distribution analyzer in Example 1. The particle size distributions D50 = 52.4 μm and D90 = 80.1 μm are shown in Figure 1, confirming that amorphous aluminum hydroxide granules, the objective of the present invention, have been formed.

[0052] Figure 2 shows the results of X-ray diffraction measurements of amorphous aluminum hydroxide granules from Example 1 using a MiniFlex600 X-ray diffractometer (manufactured by Rigaku Corporation) with a Cu target using the θ / 2θ method. From this figure, no peaks indicating crystallization were observed, confirming that the particles are amorphous.

[0053] Figure 3 shows a micrograph of the surface of amorphous aluminum hydroxide granules from Example 1, measured at 10,000x magnification using a scanning electron microscope (JCM-7000; JEOL Ltd.). One of the primary particles is indicated by an arrow in Figure 3. The white band-shaped bar in the black area at the bottom of Figure 3 represents 1 μm, so it can be seen from Figure 3 that the particle size of the primary particles is fine, between 0.1 and 0.5 μm. The white band-shaped bar represents the size indicated above it in the same way in Figures 4 to 6. Next, Figure 4 shows a micrograph of the surface of amorphous aluminum hydroxide granules, measured at 200x magnification using a scanning electron microscope (JCM-7000; JEOL Ltd.). It can be confirmed that large particles have been formed.

[0054] Figure 7 shows the X-ray diffraction results of a calcined product of amorphous aluminum hydroxide granules from Example 1, calcined at 1200°C, measured using the θ / 2θ method with a Cu target on an X-ray diffractometer (MiniFlex600, Rigaku Corporation). The results show the crystal pattern of the α phase of alumina, confirming that high-purity α-alumina was produced.

[0055] (Example 2) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 93.6 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 10.0%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 569.2 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.2 mass%.

[0056] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 270 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.5%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 7%.

[0057] (Example 3) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 211.2 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 220.7 kg of 6% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0058] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 250 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 79.4%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 6.7%.

[0059] (Example 4) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 46.0 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 23.0 wt%, Na content equivalent to Na2O: 18.0%), and 147.1 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 562.2 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.4 mass%.

[0060] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing five times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 220 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 81.1%. Next, the amorphous aluminum hydroxide cake was stirred in a dispensing machine to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 6.6%.

[0061] (Example 5) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 30°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0062] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.4%. Next, the amorphous aluminum hydroxide cake was stirred in a dispensing machine to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 7.1%.

[0063] (Example 6) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0064] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 200 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 74.2%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6.9%.

[0065] (Example 7) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0066] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered and washed five times using a rotary filter, and then dewatered to obtain amorphous aluminum hydroxide cake. The electrical conductivity of the washing water was 182 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 75.9%. Next, the amorphous aluminum hydroxide cake was stirred in a disper to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6.6%.

[0067] (Example 8) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0068] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 290°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 5.1%.

[0069] (Example 9) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0070] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 11000 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 70°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 4.9%.

[0071] (Example 10) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0072] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 40°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 8.4%.

[0073] (Comparative Example 1) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 40.0%), 30.3 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 73.6 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 473 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0074] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.2%. Next, the amorphous aluminum hydroxide cake was stirred in a dispensing machine to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 6%.

[0075] (Comparative Example 2) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 371.7 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 10.0%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 60.2 kg of 22% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0076] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 77.5%. Next, the amorphous aluminum hydroxide cake was stirred in a disper to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 6.5%.

[0077] (Comparative Example 3) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 39°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0078] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.6%. Next, the amorphous aluminum hydroxide cake was stirred in a disper to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide particle aggregates. The volatile content of the amorphous aluminum hydroxide particle aggregates was 5.7%.

[0079] (Comparative Example 4) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0080] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator to obtain amorphous aluminum hydroxide cake. The electrical conductivity of the washing water was 1400 μS / cm, and the obtained cake weighed 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 77.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6.4%.

[0081] Figure 8 shows the X-ray diffraction results of the calcined product obtained by calcining amorphous aluminum hydroxide granules of Comparative Example 4 at 1200°C. In addition to the α phase of alumina, a β phase crystal pattern is also observed, confirming that the product is low-purity α-alumina due to the influence of residual sodium.

[0082] (Comparative Example 5) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0083] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was subjected to vacuum filtration to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 282 μS / cm, and the amount of cake obtained was 139.5 kg. The volatile content of the amorphous aluminum hydroxide cake was 90%.

[0084] (Comparative Example 6) Using a 500L jacketed stainless steel stirring kettle, first, cooling water at 5°C was circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0085] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disper to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 150°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 15%.

[0086] (Comparative Example 7) Using a 500L jacketed stainless steel stirring kettle, first, cooling water at 5°C was circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0087] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by Priss Co., Ltd.) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 120°C, and a repair machine temperature of 100°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 2.1%.

[0088] (Comparative Example 8) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 55.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution were added. The mixture was stirred for 40 minutes at a pH of 8.7 and a liquid temperature of 11°C to obtain 572 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.4 mass%.

[0089] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 520 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 77.6%. Next, the amorphous aluminum hydroxide cake was stirred in a disperser to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6.4%.

[0090] (Comparative Example 9) Using a 500L jacketed stainless steel stirring kettle, cooling water at 5°C was first circulated through the jacket. Next, 198.0 kg of tap water was added to the kettle and stirred. Simultaneously, 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 233.9 kg of 9% magnesium carbonate dispersion were added. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry. The Al2O3 concentration in the crude slurry was 3.1 mass%.

[0091] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing eight times, it was dewatered to obtain amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 270 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 79.2%. Next, the amorphous aluminum hydroxide cake was stirred in a dispensing machine to form a slurry, and then dried in a spray dryer (TR-160, manufactured by PRISCO Corporation) at an atomizer speed of 9500 rpm under the conditions of an inlet temperature of 250°C, an outlet temperature of 100°C, and a repair machine temperature of 50°C to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6.3%.

[0092] (Comparative Example 10) Using a 500L jacketed stainless steel stirring kettle, first, cooling water at 5°C was circulated through the jacket. Next, 284.8 kg of tap water was added to the kettle and stirred while simultaneously adding 84.3 kg of aluminum chloride aqueous solution (Al content equivalent to Al2O3: 10.0 wt%, basicity: 2.4%), 43.7 kg of sodium aluminate aqueous solution (Al content equivalent to Al2O3: 20.0 wt%, Na content equivalent to Na2O: 19.0%), and 147.1 kg of 9% sodium carbonate aqueous solution. The mixture was stirred for 40 minutes at a pH of 6.5 and a liquid temperature of 11°C to obtain 560 kg of amorphous aluminum hydroxide crude slurry.

[0093] Next, 560 kg of the obtained amorphous aluminum hydroxide crude slurry was dewatered using a centrifugal dehydrator, and after repeating the process of adding water and stirring and washing four times, it was dewatered to obtain an amorphous aluminum hydroxide cake. At that time, the electrical conductivity of the washing water was 280 μS / cm, and the amount of cake obtained was 64.3 kg. The volatile content of the amorphous aluminum hydroxide cake was 78.1%. Next, the amorphous aluminum hydroxide cake was stirred in a dispensing machine to form a slurry, and then divided into several trays and dried at 100°C for 6 hours to obtain amorphous aluminum hydroxide granules. The volatile content of the amorphous aluminum hydroxide granules was 6%.

[0094] Figure 5 shows a micrograph of the surface of amorphous aluminum hydroxide granules of Comparative Example 10 at 10,000x magnification using a scanning electron microscope (JCM-7000; JEOL Ltd.). It can be confirmed that the primary particles consist of fine particles of 0.1 to 0.5 μm. Figure 6 shows the results of measuring the surface of amorphous aluminum hydroxide granules of Comparative Example 10 at 200x magnification using a scanning electron microscope (JCM-7000; JEOL Ltd.). This confirms that the particle size is extremely fine, the shape is irregular, and the angle of repose is large.

[0095] For the amorphous aluminum hydroxide granules obtained in Examples 1-10 and Comparative Examples 1-10, the particle size of the primary particles, the particle size of the secondary particles, and the impurity content (i.e., sodium, magnesium, calcium, sulfur, chlorine, and iron) were measured and recorded in Tables 1-4. In addition, the angle of repose and the time (seconds) to reach pH 3 and pH 3.5 in the acid reactivity test of the obtained amorphous aluminum hydroxide granules, the pH after 10 minutes of the acid reactivity test, the crystalline phase, and the crystalline phase after calcination at 1200°C are recorded in Tables 5-8.

[0096] The characteristic values ​​of the amorphous aluminum hydroxide granules described above were measured as follows: Primary particle size: Confirmed using a tabletop electron microscope (JCM-7000; manufactured by JEOL Ltd.). The D50 and D90 values ​​for the particle size of secondary particles were determined by dry measurement using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern Panalytical). From this particle size distribution, the particle size at which 50% of the total particle amount in the cumulative particle size distribution is equal to or less was defined as D50, and the particle size at which 90% of the total particle amount in the cumulative particle size distribution is equal to or less was defined as D90. The content of impurities (i.e., sodium, magnesium, calcium, sulfur, chlorine, and iron) was measured using an energy-dispersive X-ray fluorescence spectrometer (EDX) mounted on a benchtop scanning electron microscope. Measurement of the angle of repose: [1] A powder funnel with an inner diameter of 10 mm was set so that the bottom of the funnel was 40 mm above the glass substrate. Powder from a 500 ml beaker was dropped from a position of 40 mm or more above the top of the funnel, and the powder was poured from the beaker into the funnel. [2] When the top surface of the powder reached the bottom of the funnel, the powder was stopped being added. [3] A protractor was set on the glass substrate surface, and the angle of repose was measured by reading the protractor's markings from the side. Acid Reactivity Test: Accurately place 50 ml of 0.1 mol / l hydrochloric acid into a 100 ml beaker and immerse it in a 37°C constant temperature bath to maintain the liquid temperature at 37°C. Subsequently, immerse the electrode of a pH meter in the liquid and add 1.0 g of the sample powder (amorphous aluminum hydroxide granules in this invention) while stirring with a magnetic stirrer. Simultaneously, start a stopwatch and measure the time it takes to reach pH 3 and pH 3.5, as well as the pH 10 minutes after the start of the stopwatch. Crystalline phase of aluminum granulated particles: Amorphous aluminum hydroxide granulated particles prepared in each example and comparative example were measured using an X-ray diffractometer (MiniFlex600, Rigaku Corporation) with a Cu target using the θ / 2θ method. Crystalline phase: Amorphous aluminum hydroxide granules prepared in each example and comparative example were placed in an alumina crucible and fired in a firing furnace at 1200°C for 4 hours. The crystalline phase of the resulting powder was measured using an X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) with a Cu target using the θ / 2θ method.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] [Table 4]

[0101] [Table 5]

[0102] [Table 6]

[0103] [Table 7]

[0104] [Table 8]

[0105] As shown in Tables 1, 2, 5, and 6, the amorphous aluminum hydroxide granules shown in Examples 1 to 10 had primary particle sizes of 0.01 to 0.8 μm, and particle size measurements using a laser particle size analyzer showed D50 to 35 to 60 μm and D90 to 50 to 120 μm. Furthermore, impurities were controlled within the ranges of 0 to 0.05 mass% for sodium, 0 to 0.05 mass% for magnesium, 0 to 0.05 mass% for calcium, 0 to 0.01 mass% for sulfur, 0 to 0.05 mass% for chlorine, and 0 to 0.01 mass% for iron, and volatile content was also controlled to 4 to 12 mass%. X-ray diffraction of the amorphous aluminum hydroxide granules was also measured, and similar to the X-ray diffraction pattern of Example 1 in Figure 2, no crystallization peaks were observed in the other examples, confirming their amorphous nature. Furthermore, the angle of repose, a physical property, was confirmed to be within the range of 15-30°C, and no problems were observed in acid reactivity tests.

[0106] Tables 3, 4, 7, and 8 show the data for comparative examples. In Comparative Example 1, a rough slurry of amorphous aluminum hydroxide granules was synthesized using a highly basic aluminum chloride solution and washed eight times, but it was confirmed that the chlorine inside was not completely washed away, and the chlorine concentration of the amorphous aluminum hydroxide granules after drying was high. In Comparative Example 2, a rough slurry of amorphous aluminum hydroxide granules was synthesized using a highly concentrated sodium carbonate aqueous solution and washed eight times, but it was confirmed that the sodium inside was not completely washed away, and the sodium concentration of the amorphous aluminum hydroxide granules after drying was high.

[0107] In Comparative Example 3, the temperature during the synthesis of the amorphous aluminum hydroxide crude slurry was too high, resulting in a deterioration of the surface activity of the amorphous aluminum hydroxide. As a result, the amorphous aluminum hydroxide granules after drying did not exhibit the required physical properties in the acid reactivity test. In Comparative Example 4, only dehydration was performed after the synthesis of the amorphous aluminum hydroxide crude slurry without washing to obtain a cake. Consequently, the internal sodium was not completely washed away, and it was confirmed that the sodium concentration in the amorphous aluminum hydroxide granules after drying was high. Furthermore, when the amorphous aluminum hydroxide granules of Comparative Example 4 were calcined at 1200°C, X-ray diffraction measurements revealed the presence of a β phase in addition to the α phase, confirming that it was undesirable as alumina.

[0108] In Comparative Example 5, although the amorphous aluminum hydroxide crude slurry was washed, only vacuum filtration was performed to obtain a cake. As a result, it was not completely dewatered, and the volatile content was extremely high, making it unhandling and preventing it from proceeding to the spray drying process. In Comparative Example 6, the inlet temperature of the spray dryer was too low, resulting in insufficient drying of the amorphous aluminum hydroxide slurry. This caused the amorphous aluminum hydroxide granules to adhere to each other in the collection container, creating coarse particles and increasing the angle of repose.

[0109] In Comparative Example 7, the collection container temperature during spray drying of the amorphous aluminum hydroxide crude slurry was high, and the particles were exposed to high temperatures for a long time, which degraded the surface activity of the amorphous aluminum hydroxide granules, resulting in poor acid solubility test results. In Comparative Example 8, the pH was high when preparing the amorphous aluminum hydroxide crude slurry, and sodium was not completely washed away during the washing of the amorphous aluminum hydroxide crude slurry. As a result of spray drying with sodium remaining inside, the amorphous aluminum hydroxide granules had a high sodium content. Furthermore, when the amorphous aluminum hydroxide granules of Comparative Example 8 were calcined at 1200°C, X-ray diffraction measurements of the particles showed the formation of a β phase in addition to the α phase, confirming that it was undesirable as alumina.

[0110] Comparative Example 9 uses magnesium carbonate instead of sodium carbonate when synthesizing the amorphous aluminum hydroxide crude slurry. However, when washing the amorphous aluminum hydroxide crude slurry, the internal magnesium content could not be sufficiently removed, resulting in a high magnesium content in the amorphous aluminum hydroxide granules after spray drying. Furthermore, X-ray diffraction measurements of the amorphous aluminum hydroxide granules from Comparative Example 9, calcined at 1200°C, revealed the presence of a spinel phase, a composite oxide of magnesium and aluminum, in addition to the α phase, indicating a problem with alumina formation during calcination. Comparative Example 10, due to prolonged vat drying at 100°C, showed deterioration of the surface activity of the amorphous aluminum hydroxide granules, leading to poor acid solubility tests. Additionally, because drying was done by spray drying without granulation, the particle size became finer and the angle of repose increased. [Industrial applicability]

[0111] The amorphous aluminum hydroxide granules according to the present invention have few impurities, a small primary particle size, and high reactivity with acids, making them suitable for use as raw materials for the synthesis of aluminum oxide and aluminum composite oxides for semiconductors and electronic materials, as well as for the synthesis of catalyst supports. Furthermore, their applications can be expanded to include raw materials for refractories and surface treatment of metals. By granulating primary particles and controlling the particle size of secondary particles, the angle of repose of the amorphous aluminum hydroxide granules can be set to 15-30°, improving handling during manufacturing processes such as press molding, extrusion molding, and kneading, thereby contributing to increased productivity.

Claims

1. Amorphous aluminum hydroxide granules, (1) The particle size of the primary particles is 0.01 to 0.8 μm, (2) The particle size of the secondary particles, as measured by a laser diffraction particle size analyzer, was 35 to 60 μm for D50 and 50 to 120 μm for D90. (3) Contains sodium in the range of 0 to 0.05% by mass, magnesium in the range of 0 to 0.05% by mass, calcium in the range of 0 to 0.05% by mass, sulfur in the range of 0 to 0.01% by mass, chlorine in the range of 0 to 0.05% by mass, and iron in the range of 0 to 0.01% by mass. (4) The volatile content measured at a temperature of 105°C for 30 minutes using a heat drying type moisture meter is 4 to 12% by mass. (5) Having an angle of repose of 15 to 30°, (6) In the acid reactivity test, the time to reach pH 3 and pH 3.5 is 0 to 300 seconds, and the pH 10 minutes after the start of measurement is 3.1 to 4.

3. Amorphous aluminum hydroxide granulated particles characterized by the above.

2. A method for producing amorphous aluminum hydroxide granules according to claim 1, (First step) A step in which water is first added, and then aqueous solutions of aluminum chloride, sodium carbonate, and sodium aluminate, each with a basicity of 1 to 11%, are mixed and reacted while controlling the pH to 6 to 7.5 and the liquid temperature to 1 to 35°C to obtain a rough slurry containing gel-like amorphous aluminum hydroxide, wherein the Al in the rough slurry ２ O ３ The process is such that the concentration is 3% by mass or more. (Second step) The crude slurry obtained in the first step is washed with water controlled at 10 to 35°C until the electrical conductivity of the wastewater after washing is 100 to 350 μS / cm, and then dewatered to obtain a cake containing amorphous aluminum hydroxide with few impurities, and the obtained amorphous aluminum hydroxide-containing cake is measured using a heat-drying type moisture meter at 105°C for 45 minutes and has a volatile content of 72 to 85% by mass, in order to obtain an amorphous aluminum hydroxide-containing cake. (Third step) A step of adding water to the amorphous aluminum hydroxide-containing cake obtained in the second step and redispersing it to prepare an amorphous aluminum hydroxide-containing slurry, and (Fourth step) A step to obtain amorphous aluminum hydroxide granules by spray drying the amorphous aluminum hydroxide-containing slurry obtained in the third step. A method for producing amorphous aluminum hydroxide granules, characterized by containing the following:

3. The method for producing amorphous aluminum hydroxide granules according to claim 2, characterized in that when the liquid temperature in the first step is controlled to 1 to 35°C, the jacket is cooled by circulating water using a chiller or ice water.

4. The method for producing amorphous aluminum hydroxide granules according to claim 2 or 3, characterized in that the second step of washing and dewatering is performed using a centrifuge, a filter press, or a rotary filter.

5. The method for producing amorphous aluminum hydroxide granules according to claim 2 or 3, characterized in that the fourth step, spray drying, is performed using spray drying, with an inlet temperature of 200 to 330°C and an outlet temperature of 80 to 150°C, and the amorphous aluminum hydroxide particles in the collection container for collecting the spray-dried amorphous aluminum hydroxide are collected at a temperature of 5 to 80°C.

Images