JPH11278829A - High purity aluminum hydroxide and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high purity aluminum hydroxide having Na2 O and Fe contents not higher than prescribed values, and an average particle diameter suitable for industrially easy production, and its production method. SOLUTION: A supersatd. sodium aluminate soln. having a prescribed concn. of dissolved Na2 O is used at a temp. of <=75 deg.C and satisfying the condition of T<=1.2×10<6> /C<2> . Seeds are added to the soln. while maintaining the amt. of Fe entering from the seeds at below the permissible max. value Y represented by the equation Y=2.0×10<-3> ×A×(3.0-M) [where A is the concn. (g/l) of dissolved Al2 O3 and M is the molar ratio of the dissolved Na2 O content to the dissolved Al2 O3 content]. The temp. T of the soln. is then lowered to <=55 deg.C under stirring and the sodium aluminate is decomposed until the molar ratio M attains to >=3.0 to produce the objective high purity aluminum hydroxide having 1-6 μm average particle diameter, <=0.1 wt.% total Na2 O content and <=4 ppm Fe content.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity aluminum hydroxide from a sodium aluminate solution obtained by the Bayer method, and more particularly to a method for producing iron (Fe) and soda (Na ₂ O). The present invention relates to a method for producing high-purity aluminum hydroxide, which has a low content and is useful as a raw material for producing high-performance optical lenses or the like or as an electric or electronic material.

[0002]

2. Description of the Related Art Hitherto, several methods have been proposed for producing high-purity aluminum hydroxide from a sodium aluminate solution obtained by the Bayer method. For example, Japanese Patent Application Laid-Open Nos. 62-246961 and 59-2
No. 04632 and Japanese Unexamined Patent Application Publication No. 2-74521 disclose that the Na ₂ O content is 0.1% by mass for the purpose of improving heat resistance and further for filling a resin for electronic and electrical insulating materials. The following high-purity aluminum hydroxide is described, and Japanese Patent Application Laid-Open No. Hei 8-508559 discloses a filler having a Na ₂ O content of 0 as a filler for a flameproof thermosetting plastic used in the field of the electronics industry. A high-purity aluminum hydroxide having a soluble Na ₂ O content of not more than 0.1% by mass and not more than 0.005% by mass is described.

[0003] However, these high-purity aluminum hydroxides have no specific description of Fe-based impurities. However, in order to reduce the Na ₂ O content to 0.1% by mass or less, aluminum hydroxide is used in a relatively small amount. Since it is necessary to gradually precipitate at a high temperature, it is considered that it contains Fe at least equal to or more than aluminum hydroxide obtained by a usual Bayer method.

In Japanese Patent Publication No. 3-51654,
A small amount of aluminum hydroxide seed having a predetermined property is added to the supersaturated sodium aluminate solution to precipitate a small amount of aluminum hydroxide, and when the small amount of aluminum hydroxide is precipitated, Fe in the supersaturated sodium aluminate solution is removed. First, impurities such as oxides, hydrates, and salts of metals such as Ca, Mg, and Ti are adsorbed and removed as much as possible together with this small amount of aluminum hydroxide. It has been described that by adding aluminum seeds to precipitate aluminum hydroxide, a high-purity aluminum hydroxide useful as a refractory filler for synthetic polymers and a low abrasive for cosmetics, and even ceramics. I have.

However, in this method, the supersaturated concentration of the decomposition step increases, will incorporate many Na ₂ O content in the aluminum hydroxide to reduce the content of Na ₂ O to less than 0.1 wt% In addition, it is necessary to use a pulverized aluminum hydroxide having a BET specific surface area of at least 8 m ² / g or more as aluminum hydroxide to be added as seeds. Requires a large amount of energy, and the obtained aluminum hydroxide crystals also have an extremely small average particle size, so that solid-liquid separation is difficult with a normal vacuum filtration device and a special filtration device is required. In addition to the large cost required for manufacturing equipment and its operation, there is a limit to mass production, and it is not industrially suitable.

Further, Japanese Patent Application Laid-Open No. Hei 2-188424 discloses a method for producing aluminum hydroxide having a low Fe content in a Bayer precipitation tank, a storage tank and a structure immersed in the tank. It is described that a voltage is applied, thereby preventing Fe from being eluted from these precipitation tanks, storage tanks and structures, and producing low-Fe aluminum hydroxide, but the Fe content was reduced to 5 ppm. Only aluminum hydroxide is mentioned.

[0007] In recent years, the use of aluminum hydroxide has expanded to a wide variety of applications, and it has been used as a raw material in the fields of optical equipment such as optical fibers and optical lenses, insulating materials, electric and electronic materials, and the like. Higher purity is required to reflect the higher performance, and Fe-based impurities have a higher light transmission rate in applications such as optical lenses, and in electrical and electronic materials, Na ₂
Since O sometimes has an adverse effect on electrical properties such as insulating properties, a higher-purity aluminum hydroxide in which these are simultaneously reduced is desired. In particular, for the Fe component, p
Reduction to the pm order is required.

[0008]

The inventors of the present invention have conducted intensive studies on high-purity aluminum hydroxide containing both low contents of Na ₂ O and Fe-based impurities and suitable for industrial production. In addition to controlling the concentration of dissolved Na ₂ O in the supersaturated sodium aluminate solution and the hydrolysis temperature of the supersaturated sodium aluminate solution in a predetermined relationship, mixed Fe-derived Fe mixed from aluminum hydroxide added as seeds It has been found that the desired amount of aluminum hydroxide can be produced by restricting the amount to not more than a predetermined value and performing hydrolysis, and thus the present invention has been completed.

[0009] Accordingly, the object of the present invention is to provide a composition comprising Na ₂ O and F
The present invention is to provide a high-purity aluminum hydroxide having an e content of not more than a predetermined value and having an average particle diameter of a size that is industrially easy to produce.

It is another object of the present invention to provide an
It is an object of the present invention to provide a method capable of industrially easily producing a high-purity aluminum hydroxide having an a ₂ O content and an Fe content each of which is equal to or less than a predetermined value and having an average particle size of a predetermined size. .

[0011]

That SUMMARY OF THE INVENTION The present invention has an average particle diameter of 1 to 6 m, the total Na ₂ O content 0.1 wt% or less,
And high-purity aluminum hydroxide having an Fe content of 4 ppm or less, or having an average particle size of 15 to 40 μm, a total Na ₂ O content of 0.1 mass% or less, and F
e is a high-purity aluminum hydroxide having a content of 4 ppm or less. Further, the present invention relates to an aluminum hydroxide having a total Na ₂ O content of 0.1% by mass or less and an Fe content of 4 ppm or less, or an average particle diameter of 15 to 40 μm and a total Na ₂ O content of 0%. 0.1 mass% or less, and an average particle diameter of 1 to 6 μm obtained by pulverizing high-purity aluminum hydroxide having an Fe content of 4 ppm or less, a total Na ₂ O content of 0.1 mass% or less, and an Fe content of 4 ppm or less. Pure aluminum hydroxide.

Further, the present invention relates to a method for dissolving Na ₂ O concentration (C)
100 g / L or more and Fe concentration in liquid of 0.4 mg /
Liters or less, and dissolved Na ₂ O content and dissolved Al ₂ O
Molar ratio to ₃ minutes (M, dissolved Na ₂ O content / dissolved Al ₂ O ₃
Min) of 1.6 to 2.0 is used as a raw material solution.
5 ° C. or less and the following formula (1)

At a solution temperature (T, ° C.) satisfying the condition of T ≦ 1.2 × 10 ⁶ / C ² (1), aluminum hydroxide having a BET specific surface area of 1 to 7 m ² / g is used as a seed.
At a rate of 15 m ² / liter. At this time, mixed Fe from the seed brought into the raw material solution from the added seed is added.
The amount is expressed by the following formula (2) Y = 2.0 × 10 ⁻³ × A × (3.0-M) (2) [where A is the dissolved Al ₂ O ₃ concentration (g / liter)]
Is maintained below the allowable maximum value Y (mg / liter) represented by the following formula (3).

[0014]

(Equation 2)

The supersaturated concentration X of the raw material solution represented by
g / l ≦ X ≦ 50 g / l, while stirring, the solution temperature (T) was lowered to 55 ° C. or less, and the solution was decomposed until the molar ratio (M) became 3.0 or more; Obtaining the precipitated aluminum hydroxide by solid-liquid separation,
This is a method for producing high-purity aluminum hydroxide.

In the method for producing high-purity aluminum hydroxide according to the present invention, the supersaturated sodium aluminate solution used as a raw material solution has a dissolved Na ₂ O concentration (C)
Is 100 g / L or more, and the Fe concentration in the liquid is 0.4 mg / L or less, preferably 0.3 mg / L.
Liter or less, and furthermore, dissolved Na ₂ O content and dissolved Al
It is necessary that the molar ratio (M) with respect to ₂ O ₃ minutes is 1.6 to 2.0.

If the concentration of dissolved Na ₂ O (C) is less than 100 g / l, the amount of aluminum hydroxide deposited will decrease, and the productivity will decrease. If it exceeds, the amount of Fe taken into the precipitated aluminum hydroxide cannot be ignored, and there is a problem that the Fe content in the aluminum hydroxide increases. In addition, dissolved Na ₂ O and dissolved Al ₂
If the molar ratio (M) with respect to the O ₃ content is lower than 1.6, the amount of nuclei generated is increased, the particle diameter is reduced, and the Na ₂ O content incorporated in the precipitated aluminum hydroxide is also increased. The problem arises. Conversely, if it is higher than 2.0,
There is a problem that not only the amount of precipitated aluminum hydroxide is reduced and the productivity is reduced, but also the Fe content in the aluminum hydroxide is increased.

The supersaturated sodium aluminate solution as such a raw material solution may be prepared by any method, but preferably, the dissolved Na ₂ O concentration (C) is 100 to 20.
0 g / liter, molar ratio (M) of dissolved Na ₂ O component to dissolved Al ₂ O ₃ component of 1.5 to 1.8, and Fe concentration in the liquid of 1 to 1
Aluminum hydroxide having a BET specific surface area of 3 to 7 m ² / g is added as a seed to a 15 mg / l supersaturated sodium aluminate solution at a rate of 15 to 50 m ² / l as a seed. It is preferable to obtain a purified supersaturated sodium aluminate solution by contacting for 3 hours and then performing solid-liquid separation.

When the raw material solution is hydrolyzed to produce the high-purity aluminum hydroxide of the present invention, the solution temperature (T) is 75 ° C. or less and the following formula (1) T ≦ 1. The temperature is controlled so as to satisfy 2 × 10 ⁶ / C ² (1), and the BET specific surface area is 1 to 7 m ² / g, preferably 2 to 5
^{2 to} 15 m using m ² / g aluminum hydroxide as seed
² / liter, preferably 3 to 10 m ² / liter. At this time, the amount of Fe introduced from the seed brought into the raw material solution from the added seed is determined by the following formula (2) Y = 2.0 × 10 ⁻³ × A × (3.0-M) (2) [where A is the dissolved Al ₂ O ₃ concentration (g / liter)
Is required to be maintained at or below the allowable maximum value Y (mg / liter).

If the solution temperature (T, ° C.) during the hydrolysis reaction deviates from the above conditions, the amount of Fe eluted from the wall surface of the precipitation tank made of Fe-based metal becomes remarkable when the precipitation tank is formed of Fe-based metal. Since the amount of Fe is adsorbed on the precipitated aluminum hydroxide and taken in, there is a problem that the Fe content in the product aluminum hydroxide is increased as a result. Further, the amount of mixed Fe is the maximum allowable value Y (m
g / liter), the Fe content derived from the added seeds becomes the Fe content of the product aluminum hydroxide as it is, making it difficult to obtain aluminum hydroxide having a Fe content less than or equal to a desired value. Furthermore, BE of the seed added to the raw material solution
If the T specific surface area is less than 1 m ² / g, it is not industrially necessary to add a large amount of seed, and the amount of Fe mixed in from the seed increases with an increase in the amount of added seed. If it exceeds 7 m ² / g, the degree of agglomeration increases, so that the specific surface area becomes extremely small, the amount of nuclei generated increases, the particle size of the obtained aluminum hydroxide decreases, and solid-liquid separation occurs. It has a broad particle size distribution that is difficult to perform. In addition, the amount of the seed added is 2 to 15 m.
^When the ratio is out of the range of ² / liter, there is a problem that the particle size distribution becomes hard to be separated into solid and liquid.

In the method of the present invention, the hydrolysis of the supersaturated sodium aluminate solution is carried out by a so-called White formula (Light Metals, (1984), pp. 237-253) in order to obtain a desired high-purity aluminum hydroxide. Equation (3) derived from

(Equation 3) While maintaining the supersaturated concentration X of the supersaturated sodium aluminate solution represented by the formula below in the range of 30 g / L ≦ X ≦ 50 g / L, the solution temperature (T) was lowered to 55 ° C. or less while stirring, and ₂ O content (C) and dissolved Al ₂
It is necessary to carry out until the molar ratio (M) with respect to the O ₃ minute (A) becomes 3.0 or more, preferably 3.2 or more.

When the supersaturated concentration X is less than 30 g / liter, the degree of aggregation is reduced, the particle diameter of the precipitated aluminum hydroxide is reduced, and the deposition rate is reduced, so that the molar ratio (M) is 3.0 or more. It takes a long time to reach, and as a result, productivity is undesirably reduced. When the supersaturated concentration X exceeds 50 g / liter,
The nucleation is remarkable, the particle size of the obtained aluminum hydroxide is reduced, and Na ₂
O content increases, and the desired product cannot be obtained. On the other hand, when the solution temperature (T) to be lowered is higher than 55 ° C., it takes a long time until the molar ratio (M) of the dissolved Na ₂ O component to the dissolved Al ₂ O _{3 component} becomes 3.0 or more. Productivity decreases. Further, the molar ratio (M) at the end of the reaction is 3.0.
If it is less than 1, the precipitation amount of aluminum hydroxide decreases, and not only does the productivity decrease, but also, as a result, the Fe content in aluminum hydroxide increases.

After the hydrolysis reaction of the raw material solution is completed, the reaction mixture is separated into solid and liquid by a usual method.
The desired product aluminum hydroxide is obtained. At the time of solid-liquid separation of the reaction mixture, the precipitated aluminum hydroxide has an average particle diameter of 15 to 40 μm, so that solid-liquid separation can be easily performed by a usual method, for example, using a vacuum filtration device.

The high-purity aluminum hydroxide of the present invention obtained by the method of the present invention has an average particle size of 15 to 4
0 μm, the total Na ₂ O content must be 0.1% by mass or less, and the Fe content must be 4 ppm or less. When the average particle diameter is smaller than 15 μm, solid-liquid separation by a filter cloth becomes difficult, and when the average particle diameter is larger than 40 μm, friction with a contact metal is liable to be caused in a precipitation step and a subsequent operation in a subsequent step.

The high-purity aluminum hydroxide of the present invention has an average particle size of 15 to 40 μm. If a smaller average particle size is desired, the high-purity aluminum hydroxide is pulverized. Thus, it is a pulverized high-purity aluminum hydroxide preferably pulverized to an average particle diameter of 1 to 6 μm. As a means for this pulverization, a means capable of suppressing contamination of Fe and other impurities as much as possible is preferable, and a dry vibration ball mill using alumina balls, a wet vibration using alumina beads, glass beads, zirconia beads, etc. A bead mill, an impingement plate type airflow pulverizer, a supersonic airflow type pulverizer, or the like can be suitably used, and a collision plate type airflow pulverizer or a supersonic airflow type pulverizer is more preferable.

The high-purity aluminum hydroxide having an average particle diameter of 15 to 40 μm or the pulverized high-purity aluminum hydroxide having an average particle diameter of 1 to 6 μm according to the present invention contains Fe-based impurities which have an adverse effect on the light transmission rate. The total Na ₂ O content, which may adversely affect the electrical characteristics such as
In particular, the content of Fe is reduced to the order of ppm, and can be suitably used for both applications such as optical lenses and electric / electronic materials. In particular, the average particle diameter of 15 to 40 μm of the present invention, obtained by pulverizing high-purity aluminum hydroxide having an average particle diameter of 1 to 6 μm,
₂ O content 0.1 wt% or less, and Fe content 4ppm following milling high purity grinding aluminum hydroxide, and the specific surface area is increased to improve the reactivity and miscibility with other materials, especially such electronic materials Suitable for use.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below based on test examples, examples and comparative examples.

Test Example: Examination of Fe-elution behavior from Fe-based metal precipitation tank to supersaturated sodium aluminate solution Concentration of 90-185 in a 3-liter stainless steel beaker
g / l of a supersaturated sodium aluminate solution, 2 liters, and kept at a temperature of 50 to 90 ° C. under stirring for 24 hours, and the amount of Fe eluted into the supersaturated sodium aluminate solution from a stainless steel beaker is calculated as follows: Calculate the Fe concentration in the initial liquid and the Fe concentration in the final liquid by 1,10-phenanthroline absorption spectrophotometry, and examine the elution behavior of Fe from the Fe-based metal deposition tank into the supersaturated sodium aluminate solution. did.

[0029] The supersaturated sodium aluminate solution used in this, the dissolution concentration of Na ₂ O and C (g / liter), also, C ² when the liquid temperature was set to T (° C.)
Using the value of × T as an index, it was determined whether the amount of Fe eluted from the stainless beaker into the supersaturated sodium aluminate solution was large or small, and the dissolved Na ₂ O concentration (C) of the supersaturated sodium aluminate solution and the liquid temperature ( T) was examined.

As a result, the value of C ² × T is approximately 1.2 × 1
0 ⁶ as a boundary, less the amount of elution of Fe in the case where this value or less, the amount of elution of Fe can increases were found exceeds this value. Therefore, the dissolved Na ₂ O concentration (C) and the solution temperature (T) in the supersaturated sodium aluminate solution
Is set in accordance with C ² × T ≦ 1.2 × 10 ⁶ , that is, T ≦ 1.2 × 10 ⁶ / C ² .

Next, dissolved Na ₂ molar ratio of the O content and the dissolved Al ₂ O ₃ minutes (dissolution Na ₂ O content / dissolved Al ₂ O ₃ minutes) M
The amount of precipitation per liter of supersaturated sodium aluminate solution when aluminum hydroxide was precipitated from this supersaturated sodium aluminate solution until the molar ratio reached 3.0 was defined as P (g / liter). The dissolved Al ₂ O ₃ concentration of the sodium acid solution was changed to A (g
/ Liter) from Al ₂ O ₃ to Al (OH) ₃
P is 1.53 × A × ｛(3.0-M) because the conversion coefficient to is 1.53.
/3.0}.

Further, the amount of Fe eluted in the precipitation stage is zero.
(0), hydroxylation added as seed in this precipitation stage
Product from aluminum hydroxide mixed from aluminum
When the amount of Fe reaches the maximum allowable value of 4 ppm,
Assuming that the amount of mixed Fe is Y (mg / liter), this Y
Is: Y (mg / liter) = P × 0.000004 × 100
It is represented as 0. Therefore, from these formulas, contamination from seeds
Maximum allowable value of Fe amount Y and dissolved Al _TwoO_ThreeConcentration (A)
And dissolved Na_TwoO content and dissolved Al_TwoO_ThreeMolar ratio to minutes
(M, dissolved Na_TwoO content / dissolved Al_TwoO_ThreeMinutes) between
Is: Y = 2.0 × 10^-3× A × (3.0-M) holds. In the present invention, water used as a seed
Fe content from seeds mixed from aluminum oxide
Control is performed according to this equation.

Example 1 A dissolved Na ₂ O concentration of 162.0 obtained by the Bayer method
g / liter, a molar ratio of dissolved Na ₂ O component to dissolved Al ₂ O ₃ component of 1.69, and a BET specific surface area of 3.1 m ^{2 in} a supersaturated sodium aluminate solution having an Fe concentration of 2.5 mg / liter in the liquid. / G of aluminum hydroxide 31 m ² / l was added as a seed, and the mixture was hydrolyzed with stirring at a solution temperature of 75 ° C. for 2 hours. Then, precipitated aluminum hydroxide was separated and removed to obtain a purified supersaturated sodium aluminate solution. .

The obtained purified supersaturated sodium aluminate solution was diluted so that the concentration of dissolved Na ₂ O became 124.6 g / l. The purified supersaturated sodium aluminate solution had a molar ratio of dissolved Na ₂ O to dissolved Al ₂ O ₃ of 1.96, and the Fe concentration in the solution was 0.30 mg / liter.

Next, the purified sodium supersaturated aluminate solution thus obtained was heated to 75 ° C., and 4.7 m ² of aluminum hydroxide having a BET specific surface area of 3.1 m ² / g was used as a seed in this solution. ² / liter was added. At this time, the amount of Fe introduced from the seeds brought into the purified supersaturated sodium aluminate solution was 0.01 mg /
Liters. Next, the solution temperature was increased from 75 ° C to 50 ° C.
While gradually lowering the temperature to 0 ° C., the mixture was hydrolyzed with stirring until the molar ratio of the dissolved Na ₂ O component to the dissolved Al ₂ O _{3 component} reached 3.71 to precipitate aluminum hydroxide. After the precipitation, solid-liquid separation was performed using a vacuum filtration device.
One liter gave aluminum hydroxide.

濾過: extremely good, ：: good, Δ: slightly poor, ×
The evaluation was made in four stages of failure. Further, regarding the obtained aluminum hydroxide, the average particle diameter (Dp50), the total Na ₂ O
, Fe, Ca, Si, Mg, and Ti contents were measured. Table 1 shows the results.

[0037] The average particle diameter (Dp50) is measured using a laser diffraction particle size distribution analyzer (manufactured by Nikkiso Co., Ltd. Microtrac X100), the total Na ₂ O is JIS H1
901 (1977) method, Ca and Mg are measured by atomic absorption method, and Fe is JIS H1901 (19
77, measured by the extraction 1,10-phenanthroline absorption spectrophotometry according to JIS H1901 (197).
Molybdenum blue-extracted absorption spectrophotometry according to 7), and Ti was measured by diantipyrylmethane absorption spectrophotometry according to JIS H1901 (1977).

Example 2 A purified supersaturated sodium aluminate solution was obtained in the same manner as in Example 1 above, using aluminum hydroxide having a BET specific surface area of 6.2 m ² / g as a seed under the conditions shown in Table 1.
The obtained purified supersaturated sodium aluminate solution was diluted to adjust its dissolved Na ₂ O concentration to 114.1 g / liter. This purified supersaturated sodium aluminate solution
The molar ratio between the dissolved Na ₂ O concentration and the dissolved Al ₂ O ₃ concentration was 1.88, and the Fe concentration in the liquid was 0.30 mg / liter.

The solution temperature of the purified sodium persulfate solution thus obtained was set at 75 ° C., and 7.8 m ² / liter of aluminum hydroxide having a BET specific surface area of 3.1 m ² / g was used as a seed in this solution. Was added so that At this time, the amount of Fe introduced from the seeds brought into the purified supersaturated sodium aluminate solution was 0.02 mg /
Liters. Next, the solution temperature was increased from 75 ° C to 50 ° C.
While gradually lowering the temperature to ° C., hydrolysis was carried out with stirring until the molar ratio between the dissolved Na ₂ O concentration and the dissolved Al ₂ O ₃ concentration became 4.27, thereby precipitating aluminum hydroxide. After the precipitation, solid-liquid separation was performed using a vacuum filtration device, and the amount of the precipitate was 85.3.
g / l of aluminum hydroxide was obtained.

With respect to the obtained aluminum hydroxide, the average particle diameter (Dp50), total Na ₂ O content, Fe content, Ca content, Si content, Mg content, and T content were obtained in the same manner as in Example 1.
The measurement for i minutes was performed. Table 1 shows the results.

Comparative Examples 1 to 7 Purified supersaturated sodium aluminate solutions were prepared in the same manner as in the above Examples under the conditions shown in Table 1, and the obtained purified supersaturated sodium aluminate solution was hydrolyzed under the conditions shown in Table 1. It was decomposed to precipitate aluminum hydroxide, and solid-liquid separation was performed to obtain aluminum hydroxide.

With respect to the obtained aluminum hydroxide, the average particle diameter (Dp50), total Na ₂ O content, Fe content, Ca content, Si content, Mg content, and T content were obtained in the same manner as in Example 1.
The measurement for i minutes was performed. The results are shown in Table 1 or Table 2.

[0043]

[Table 1]

[0044]

[Table 2]

Example 3 Concentration of dissolved Na ₂ O obtained by the Bayer method is 118.9.
g / liter, a molar ratio of dissolved Na ₂ O component to dissolved Al ₂ O ₃ component of 1.79, and a BET specific surface area of 3.0 m ^{2 in} a supersaturated sodium aluminate solution having a Fe concentration of 9.9 mg / liter in the liquid. / G of aluminum hydroxide 30.0 m ²
/ Liter as seeds, and hydrolyzed with stirring at a solution temperature of 70 ° C. for 2 hours, and then separated and removed aluminum hydroxide to obtain a purified supersaturated sodium aluminate solution.

The purified supersaturated sodium aluminate solution had a dissolved Na ₂ O concentration of 120.8 g / l. The purified supersaturated sodium aluminate solution had a molar ratio of dissolved Na ₂ O to dissolved Al ₂ O ₃ of 1.9.
8, and the Fe concentration in the liquid was 0.14 mg / liter.

The purified supersaturated sodium aluminate solution thus obtained was hydrolyzed in the same manner as in Examples 1 and 2 to precipitate aluminum hydroxide. As a result, solid-liquid separation was performed using a vacuum filtration device. As a result, similarly to Examples 1 and 2, a desired high-purity aluminum hydroxide could be obtained.

Example 4 Average particle diameter (Dp50) obtained in the same manner as in Example 1.
28.4 μm, chemical composition Na ₂ O: 0.06% by weight, F
e: 4 ppm, Ca: <10 ppm, Si: 4 ppm,
For high-purity aluminum hydroxide of Mg: 3 ppm and Ti: 2 ppm, an impingement plate type air current pulverizer [manufactured by Nippon Pneumatic Industries, Ltd .: pulverizing part IDS-5 type, classification part DS-
5 type] and pulverized under the conditions of air pressure of 7 kg / cm ² and feed amount of pulverized raw material of 30 kg / hr.

The pulverized high-purity aluminum hydroxide thus obtained has an average particle diameter (Dp50) of 4.1 μm and the same chemical composition as before the pulverization: Na ₂ O: 0.06% by weight;
e: 4 ppm, Ca: <10 ppm, Si: 4 ppm,
Mg: 3 ppm and Ti: 2 ppm.

Example 5 Average particle diameter (Dp50) obtained in the same manner as in Example 1
30.2 μm, chemical composition Na ₂ O: 0.05% by weight, F
e: 3 ppm, Ca: <10 ppm, Si: 2 ppm,
High-purity aluminum hydroxide of Mg: 2 ppm and Ti: 1 ppm was ground in the same manner as in Example 4.

The obtained pulverized high-purity aluminum hydroxide has an average particle size (Dp50) of 4.8 μm, and the same chemical composition as before the pulverization: Na ₂ O: 0.05% by weight;
e: 3 ppm, Ca: <10 ppm, Si: 2 ppm,
Mg: 2 ppm and Ti: 1 ppm.

[0052]

The high-purity aluminum hydroxide of the present invention
It has a low content of both Na ₂ O and Fe-based impurities and has a particle size range suitable for industrial production, and is particularly useful as a raw material for producing high-performance optical lenses and the like, or as an electric / electronic material. It is something. Further, according to the method of the present invention, high-purity aluminum hydroxide having an average particle diameter of a predetermined size, in which the Na ₂ O content and the Fe content are each equal to or less than a predetermined value, can be industrially easily produced. Can be manufactured.

Claims (6)

[Claims] An average particle diameter of 1 to 6 μm, and a total N
a ₂ O content is 0.1% by mass or less, and Fe content is 4% by mass.
High-purity aluminum hydroxide, which is not more than ppm. 2. The high purity according to claim 1, which is obtained by pulverizing aluminum hydroxide having a total Na ₂ O content of 0.1% by mass or less and an Fe content of 4 ppm or less. Aluminum hydroxide. 3. An average particle diameter of 15 to 40 μm,
A high-purity aluminum hydroxide having a total Na ₂ O content of 0.1% by mass or less and an Fe content of 4 ppm or less. 4. The high-purity aluminum hydroxide according to claim 1, which is obtained by pulverizing the aluminum hydroxide according to claim 3. 5. The dissolved Na ₂ O concentration (C) is 100 g / L or more and the Fe concentration in the liquid is 0.4 mg / L or less, and the molar ratio of dissolved Na ₂ O content to dissolved Al ₂ O ₃ content (M , Dissolved Na ₂ O content / dissolved Al ₂ O ₃ content)
A supersaturated sodium aluminate solution of 2.0 is used as a raw material solution, and the raw material solution has a temperature of 75 ° C. or less and a condition of the following formula (1) T ≦ 1.2 × 10 ⁶ / C ² (1) At a solution temperature (T, ° C) that satisfies the above condition, aluminum hydroxide having a BET specific surface area of 1 to 7 m ² / g
At a rate of 15 m ² / liter. At this time, mixed Fe from the seed brought into the raw material solution from the added seed is added.
The amount is expressed by the following formula (2) Y = 2.0 × 10 ⁻³ × A × (3.0-M) (2) [where A is the dissolved Al ₂ O ₃ concentration (g / liter)]
Is maintained at or below the allowable maximum value Y (mg / liter) represented by the following formula (3). The solution temperature (T) was lowered to 55 ° C. or less while stirring while maintaining the supersaturated concentration X of the raw material solution represented by A high purity aluminum hydroxide, which is obtained by decomposing the aluminum hydroxide until it becomes 3.0 or more, and obtaining the precipitated aluminum hydroxide by solid-liquid separation. 6. A raw material solution is prepared by a Bayer method, and has a dissolved Na ₂ O concentration (C) of 100 to 200 g / liter and a molar ratio (M) of dissolved Na ₂ O content to dissolved Al ₂ O ₃ content of 1. 5 to 1.8 and Fe concentration in liquid of 1 to 15 mg
/ L in supersaturated sodium aluminate solution
An aluminum hydroxide having an ET specific surface area of 3 to 7 m ² / g is added as a seed at a rate of 15 to 50 m ² / l, and the mixture is contacted with stirring at 70 to 80 ° C. for 1 to 3 hours. The method for producing a high-purity aluminum hydroxide according to claim 5, which is a purified supersaturated sodium aluminate solution obtained by the above method.