JPH10167725A - Continuous production of alumina - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for the continuous production of alumina powder having spherical form and sharp particle size distribution at a low cost. SOLUTION: Alumina is continuously produced by using a baking apparatus composed of a supplying line 1 for aluminum hydroxide, a baking oven 2 for baking the supplied aluminum hydroxide, a line 3 for delivering the baked alumina from the system, an exhaust gas line 4 to introduce the gas exhausted from the baking oven 2 into a dust-collector 5, a line 6 for discharging the exhaust gas from the dust-collector 5 and a line 7 to discharge the collected powder. In the above system, the powder collected by the dust-collector 5 is recycled to the baking oven 2 through a line 8. The aluminum hydroxide produced by Bayer's process is added together with fine alumina powder having an average particle diameter of 0.1-10μm and a fluorine compound to the baking oven 2 while recycling at least a part of the collected powder to the oven 2 and the mixture is baked to obtain the objective alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for continuously producing alumina. More specifically, the present invention relates to a method for continuously producing alumina having a spherical alumina particle and a sharp particle size distribution.

[0002]

2. Description of the Related Art Alumina is molded, sintered and used as various mechanical parts and electric parts because of its excellent chemical stability, excellent mechanical strength and physical properties. In these applications, a low-priced dimensional stability and a high sintering density are required, so that a spherical alumina powder having a sharp particle size distribution is required. As a method for producing alumina by firing aluminum hydroxide obtained by the Bayer method, various production methods have been proposed for the purpose of controlling characteristics such as particle diameter, particle size distribution, and BET specific surface area. For example, (1) a method of using at least one kind or a combination of two or more kinds selected from fluorine, chlorine, and boron as a mineralizer, (2) a method of using a silica-based compound such as silica sand or a chlorine-based compound as a soda remover, (3) A method of combining the above, and (4) a method of adding alumina fine particles to aluminum hydroxide at the time of firing and firing the combined alumina with the above method have also been proposed (Japanese Patent Publication No. 6-104570). Gazette, JP-A-7-41318). However, chlorine compounds and / or
Alternatively, when a fluorine-based compound is used, the amount of the halogen-based compound remaining in the α-alumina increases in proportion to the amount of the halogen-based compound added as a mineralizer to the raw material, and aggregates generated during firing are reduced. More. As a countermeasure, a method of removing a halogen compound has been proposed (Japanese Patent Application Laid-Open No. 7-206432). In addition, when a silica-based compound as a soda remover is added, silica contamination increases in proportion to the fluorine-based compound added to the raw material.

[0003]

In view of such circumstances,
The inventor of the present invention used inexpensive aluminum hydroxide obtained by the Bayer method and sintered it continuously to obtain an inexpensive, spherical, and sharp particle size distribution alumina powder. When aluminum oxide and fine particles of alumina and a fluorine compound as seeds are added to aluminum hydroxide, and the mixture is calcined, the above-mentioned purpose is used. Have been found to be able to be continuously produced, and the present invention has been completed.

[0004]

That is, the present invention provides an aluminum hydroxide supply line (1), a sintering furnace (2) for sintering the supplied aluminum hydroxide, and leading the baked alumina out of the system. Line (3), an exhaust gas line (4) for introducing gas discharged from the firing furnace (2) to the dust collector (5), a dust collector (5) for collecting powder contained in the exhaust gas, A method for continuously producing alumina using a baking apparatus comprising a line (6) for discharging exhaust gas after body collection from a dust collector (5) and a line (7) for discharging collected powder to the outside of the system. In the apparatus, a line (8) for circulating and supplying the powder collected by the dust collector (5) to the firing furnace (2) is provided, and at least the powder collected by the dust collector (5) is provided. A part is circulated into the firing furnace (2) while being obtained by the Bayer method in the firing furnace (2). The average particle diameter of 0 for the aluminum hydroxide and water aluminum oxide (Al ₂ O ₃ conversion) was.
1 μm to 10 μm fine alumina 0.5 to 20% by weight
(In terms of Al ₂ O ₃ ) and 20 to 200p of fluorine compound
pm (calculated as F), and calcined so that the fluorine compound content in alumina discharged from the line (3) after firing is 1 to 200 ppm (calculated as F). It is to provide a continuous manufacturing method.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a block diagram of a continuous firing apparatus for aluminum hydroxide used in the method of the present invention.
(1) is a supply line of aluminum hydroxide, (2) is a firing furnace, (3) is a line for leading the alumina after firing out of the system, and (4) is a gas collected from the firing furnace (2). An exhaust gas line (4) introduced into the dust device (5), a dust collector (5) for collecting powder contained in the exhaust gas, and (6) a dust collector (5) for collecting the exhaust gas after the powder is collected. ) More discharging line,
(7) is a line for discharging the collected powder out of the system, (8)
Denotes a line for circulating and supplying the powder collected by the dust collecting device (5) to the firing furnace (2).

In the practice of the present invention, the average particle size of the aluminum hydroxide obtained by the Bayer method and the aluminum hydroxide (in terms of Al ₂ O ₃ ) is about 0.2 in a firing furnace (2). 1 μm to about 10 μm fine alumina about 0.5
To about 20% by weight (in terms of Al ₂ O ₃ ) and a fluorine compound in an amount of about 20 to less than about 200 ppm (in terms of F),
Bake. Exhaust gas from the firing furnace (2) is introduced into a dust collector (5) through an exhaust gas line (4) to collect powder mainly composed of fine alumina in the exhaust gas, and to collect at least a part of the collected powder. By the line (8)
Circulated and supplied for firing.

In the method of the present invention, the product alumina after calcination is taken out of the system from the sintering furnace (2) via the line (3), but is taken out of the system from the line (3). It is essential that the compound content be less than about 1 to 200 ppm (F conversion). The product alumina containing the fluorine compound in this range can be prepared by the amount of the fluorine compound added to the firing furnace (2) and the amount of the powder circulated through the firing furnace (2) from the line (8). .

[0008] As the fine alumina added to the aluminum hydroxide at the time of firing, α alumina and / or transition alumina are usually used. The average particle diameter (average secondary particle diameter) of these fine alumina particles is about 0.1 μm to about 10 μm, preferably about 0.5 μm to about 8 μm.
The addition amount of about 0.5 to about 20 wt% in terms of Al ₂ O _3, preferably about 1% to about 5 wt%. If the amount of the fine alumina added is less than the above range, the particle size distribution of the obtained alumina is not sharp. On the other hand, even if it exceeds the above range, the effect corresponding to the added amount is not exhibited.

The content of the fluorine compound in the alumina taken out from the line (3) after the firing is less than about 1 to 200 ppm (in terms of F), preferably about 1 to 100 ppm. If the amount is small, it is difficult to obtain a desired spherical product, while if too large, it becomes a plate-like product.

Although the fluorine compound applied to the present invention is not particularly limited, it is usually aluminum fluoride, hydrogen fluoride,
At least one selected from ammonium fluoride, sodium fluoride, magnesium fluoride, and calcium fluoride may be used.

The dust collector applied to the present invention is not particularly limited, but includes, for example, a cyclone, an electric dust collector, a bag filter, a scrubber and the like. As the firing furnace, a rotary kiln, an SP rotary kiln,
NSP rotary kilns and fluidized bed furnaces can be used. In order to increase the thermal efficiency, it is recommended to use an internal combustion type firing furnace in which the combustion gas as the heat medium and the alumina powder are of a countercurrent type.

The conditions for sintering aluminum hydroxide are not unique depending on the kind of sintering furnace to be used, the amount of sintering, the required degree of sintering of aluminum hydroxide, etc., but usually the sintering temperature is about 1100 ° C. to 1500 ° C. The residence time of alumina in the reaction is in the range of about 1 hour to 10 hours.

[0013] In addition, as long as the effect of the method of the present invention is not impaired, when the silica-based compound as a soda removal agent is calcined, it is 1 to 1 with respect to aluminum hydroxide (in terms of Al ₂ O ₃ ).
It can be added and used in the range of 20% by weight. It is also possible to use other additives in combination.

[0014]

As described in detail above, in the method of the present invention, inexpensive aluminum hydroxide obtained by the Bayer method is used, and at least one part of the powder collected by the dust collecting device is mixed with a specific small amount. Adjust the amount of fluorine compound added to the firing furnace,
Inexpensive, spherical, and sharp particle size distribution (usually, D90 / D10 is less than 4.0, preferably, by the continuous production method of alumina in which the content of the fluorine compound contained in the calcined product is in a specific range. (Less than 3.5) alumina can be obtained, and its industrial utility value is extremely large from the aspect of raw material supply for various mechanical parts and electric parts.

[0015]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, the measurement shown in the Example adopted the following method.

(1) BET specific surface area: measured by a BET method using nitrogen adsorption. (2) Composition analysis Fluorine (F): Measured by steam distillation-ion electrode method. Sodium oxide (Na ₂ O): According to JIS H1901. Silicon dioxide (SiO ₂ ): According to JIS H1901. (4) Particle size distribution: Measured using Microtrac HRA X-100. (5) Pulverization Test Method 1: A 3 liter alumina pot was charged with 3 kg of alumina balls having a diameter of 15 mm and 400 g of α-alumina as a sample, and treated at 80 rpm for 12 hours. Method 2: In a 3.3 liter alumina pot, 3 kg of alumina balls having a diameter of 15 mm and 400 g of α-alumina as a sample, 8 g of silicon dioxide (manufactured by Wako Pure Chemical Industries), 7 g of magnesium hydroxide (manufactured by Wako Reagent), 2 g of calcium carbonate ( (Manufactured by Wako Reagent), and crushed at a rotation speed of 80 rpm. (6) Molding density: measured by a mercury Archimedes method. (7) Sintering density: Measured by the underwater Archimedes method.

Example 1 Aluminum hydroxide C-12 (center particle diameter 50 μm, Na ₂ O 0.2
%, F 20 ppm, 7650 g, Sumitomo Chemical Co., Ltd., 25 g of α-alumina AES-12 (Sumitomo Chemical Co., Ltd.) having an average particle size of 0.5 μm, aluminum fluoride (Wako Pure Chemical Industries, Ltd.)
After adding and mixing 1 g in order, the mixed slurry was filtered.
The filtered wet cake is placed in a small rotary ceramic baking furnace made of alumina ceramics (inner diameter 7 cm, length 140 cm, 130
0 ° C uniform temperature zone 60cm, tilt angle 2 °, rotation speed 2r
pm, a glass fiber filter was installed at the top of the firing furnace to recover alumina, and the recovered alumina was removed from the filter by a vibrator and then returned to the kiln) and continuously supplied to the kiln at a supply rate of 50 g / h. . The residence time of alumina in the firing furnace was 6 hours. The α-alumina obtained after the calcination had a BET specific surface area of 0.5 m ² / g and a fluorine content of 190 ppm. FIG. 2 shows a photograph of the obtained α-alumina. The center particle size of alumina pulverized by the method 1 was 2 μm, and D90 / D10 was 3.0. Alumina pulverized by Method 2 for 9 hours is pressed at a molding pressure of 300 kg.
/ Cm ² and then sintered at 1650 ° C. for 2 hours. The center particle size of the crushed alumina is 2.5 μm, D9
0 / D10 was 3.2, the molding density was 2.10, and the sintering density was 3.84 g / cm ³ .

Example 2 Example 1 was repeated, except that 1000 g of transition alumina KC-508 (manufactured by Sumitomo Chemical Co., Ltd.) having an average particle size of 8 μm was used instead of α-alumina having an average particle size of 0.5 μm.
The same operation was performed. The BET specific surface area of the obtained α-alumina was 1 m ² / g, and the fluorine content was 180 ppm. The center particle size of alumina pulverized by the method 1 is 1.5
μm, D90 / D10 was 3.5.

Example 3 The same operation as in Example 1 was performed, except that the amount of aluminum fluoride was changed to 0.1 g. Obtained firing α
The alumina had a BET specific surface area of 1.5 m ² / g and a fluorine content of 27 ppm. The center particle diameter of the alumina pulverized by the method 1 was 1.0 μm, and D90 / D10 was 3.5.

Example 4 In Example 1, 500 g of silica sand having an average particle diameter of about 1 mm was added.
g was newly mixed, and the same operation as in Example 1 was performed except that silica sand was sieved from alumina with a sieve having an opening of 149 μm after firing. The obtained calcined α-alumina has a BET specific surface area of 0.5 m ² / g, a fluorine content of 170 ppm, and a Na content of 170 ppm.
₂ O 0.05% and SiO ₂ 0.05%. The center particle size of the alumina pulverized by the method 1 is 1.9 μm,
D90 / D10 was 3.0.

Comparative Example 1 In Example 1, α-alumina A having an average particle size of 0.5 μm was used.
The same operation as in Example 1 was performed except that ES-12 (manufactured by Sumitomo Chemical Co., Ltd.) was not mixed. The obtained calcined α-alumina has a BET specific surface area of 0.5 m ² / g and a fluorine content of 190.
ppm. The center particle size of the alumina pulverized by the method 1 was 2.2 μm, and D90 / D10 was 4.5.

Comparative Example 2 The same operation as in Example 1 was performed, except that the amount of aluminum fluoride was changed to 2 g. The BET specific surface area of the obtained calcined α-alumina was 0.4 m ² / g, and the fluorine content was 270 ppm. FIG. 3 shows a photograph of the obtained α-alumina. The center particle diameter of the alumina pulverized by the method 1 was 3.0 μm, and D90 / D10 was 5.0. Method 2
Alumina ground for 18 hours with a molding pressure of 300 kg /
After CIP molding in cm ² , sintering was performed at 1650 ° C. for 2 hours. The center particle size of the crushed alumina is 2.5 μm, D90
/ D10 is 5.5, the molding density of 2.05 g / cm ^3, the sintered density was 3.78 g / cm ^3.

Comparative Example 3 In Example 1, 50 g of the filtered wet cake was used.
The same operation as in Example 1 was performed, except that the mixture was placed in a chamotte-like container instead of being supplied to the small rotary firing furnace, and was fired at 1300 ° C. for 6 hours in a stationary electric furnace. Obtained firing α
The alumina had a BET specific surface area of 4.5 m ² / g and a fluorine content of 1 ppm. The center particle size of alumina pulverized by the method 1 was 0.8 μm, and D90 / D10 was 7.0.

Comparative Example 4 In Example 1, the amount of aluminum fluoride was increased to 2 g.
500 g of silica sand having a particle diameter of about 1 mm is newly mixed,
The same operation as in Example 1 was performed except that silica sand was sieved from alumina with a sieve having an opening of 149 μm after firing. The BET specific surface area of the obtained sintered α-alumina 0.4, the fluorine content is _{220ppm, Na 2 O 0.04%,} SiO 2
0.15%. The center particle diameter of the alumina pulverized by the method 1 was 3.0 μm, and D90 / D10 was 5.0.

[Brief description of the drawings]

FIG. 1 shows a schematic view of a continuous firing apparatus used in the method of the present invention.

FIG. 2 is an electron micrograph showing the particle structure of alumina.

FIG. 3 is an electron micrograph showing the particle structure of alumina.

[Explanation of symbols]

(1) A supply line of aluminum hydroxide (2) A firing furnace (3) A line to lead the alumina after firing out of the system (4) An exhaust gas line (5) A dust collector (6) A powder A line (7) for discharging the collected exhaust gas from the dust collector is a line for discharging the collected powder to the outside of the system, and (8) is a line for circulating and supplying the collected powder to the firing furnace.

Claims (5)

[Claims] 1. An aluminum hydroxide supply line (1), a firing furnace (2) for firing the supplied aluminum hydroxide, a line (3) for leading alumina after firing out of the system, and a firing furnace (2). An exhaust gas line (4) for introducing the gas discharged from the exhaust gas into a dust collector (5), a dust collector (5) for collecting powder contained in the exhaust gas, and a dust collector for collecting the exhaust gas after collecting the powder. In a method for continuously producing alumina using a baking device comprising a line (6) for discharging from the (5) and a line (7) for discharging the collected powder to the outside of the system, a dust collecting device is provided for the device. A line (8) for circulating and supplying the powder collected in (5) to the firing furnace (2) is provided, and at least a portion of the powder collected by the dust collector (5) is introduced into the firing furnace (2). While circulating, the aluminum hydroxide obtained by the Bayer method and the aluminum hydroxide were introduced into the firing furnace (2). 0.5 to 20% by weight (calculated as Al ₂ O ₃ ) of fine alumina having an average particle diameter of 0.1 μm to 10 μm with respect to minium (calculated as Al ₂ O ₃ ) and 20 to 200 ppm (calculated as F) of a fluorine compound. A continuous process for producing alumina, characterized in that the process is carried out in such a manner that the content of the fluorine compound in the alumina discharged from the line (3) after firing is from 1 to 200 ppm (in terms of F). 2. The continuous alumina production method according to claim 1, wherein the fine alumina is α-alumina and / or transition alumina. 3. The method according to claim 1, wherein the fluorine compound is at least one selected from aluminum fluoride, hydrogen fluoride, ammonium fluoride, sodium fluoride, magnesium fluoride, and calcium fluoride. Continuous production method of alumina. 4. Use of a silica-based compound as a soda remover
The method for continuously producing alumina according to claim 1, wherein 20% by weight is added. 5. The continuous alumina production method according to claim 1, wherein the average residence time of the alumina in the firing furnace is 1 to 10 hours.