JPH03170325A - Production of magnesium hydroxide - Google Patents

Abstract

PURPOSE:To obtain Mg(OH)2 having small specific surface area and large crystal diameter in a low cost by filtering Mg(OH)2 having specific surface area larger than a fixed value obtained from reaction of Mg<2+>-containing solution with alkali, dehydrating, adding to aqueous solution of MgCl2 and subjecting to hydrothermal synthesis in a fixed condition. CONSTITUTION:A solution containing Mg<2+> such as bittern, sea water or aqueous solution of MgCl2 is reacted with alkali such as slaked lime or caustic alkali to obtain Mg(OH)2 having >=20m<2>/g specific surface area measured by BET method. Next, said Mg(OH)2 is filtered and dehydrated, then added to >=0.5wt.% aqueous solution of MgCl2. Thus, resultant MgCl2-containing Mg(OH)2 slurry is charged to a pressure-resistant vessel and subjected to hydrothermal synthesis in a condition of >=2.0kg/cm<2> pressure at >=120 deg.C with stirring. As the result, Mg(OH)2 having <=10m<2>/g specific surface area measured by BET method and hexagonal-frismatic crystal is obtained. said Mg(OH)2 has low reactivity and stable state is kept for a long period of time as the effect to other substance coexisting in a case of mixing with resin, etc., is small, therefore, said Mg(OH)2 is able to be effectively utilized as a non-halogen fire retardant filler, etc.

Description

[Detailed description of the invention] [Industrial application field] The present invention provides magnesium hydroxide (M g (OH) 2
), specifically, the specific surface area (hereinafter sometimes simply referred to as specific surface area) by the BET method is 10r.
The present invention relates to a method for producing magnesium hydroxide, which can produce magnesium hydroxide in the form of hexagonal columnar crystals at low cost and industrially advantageously.

[Prior Art] Magnesium hydroxide has a wide range of uses in various fields. As one of these, the use of thermoplastic resins as non-halogen flame retardants is attracting attention. When magnesium hydroxide is used as such a flame retardant filler, the surface of the magnesium hydroxide is coated with a surface treatment agent, so the specific surface area value is 10rn"/g.
It is preferable that the crystal grain size is large and that the filler can be uniformly dispersed during kneading in order to improve the strength of the product. For this reason, magnesium hydroxide with less secondary aggregation is desired. That is, the specific surface area is 1orr? /g, the crystal size is small and it is easy to form secondary agglomerated particles, and when mixed with resin,
The dispersibility in resin is extremely poor, and processing +1. , which has an adverse effect on various physical properties such as flame retardancy, mechanical strength, and water resistance and insulation properties.

Conventionally, methods for producing magnesium hydroxide with a small specific surface area, that is, a large crystal diameter, or magnesium hydroxide having hexagonal columnar crystals include: (1) adding 0.15 to 3% by weight of magnesium hydroxide to the amount of magnesia; of sodium hydroxide, 1,5 kg/cm'
A method for producing magnesium hydroxide having a small specific surface area value by heating to a temperature of 120° C. or higher under the above pressure (Japanese Patent Publication No. 50-23680).

■ A method for producing magnesium hydroxide with a small specific surface area value by heating a reaction product containing basic magnesium chloride or basic magnesium nitrate under pressurized conditions.
3-48809) have been proposed. In addition, ■ To obtain hexagonal Ayu crystals, pressurized heating conditions are required in an alkaline solution (edited by the Chemistry Encyclopedia Editorial Committee).
Chemistry Dictionary” Kyoritsu Shuppan (1964), No. 5. 37th
It is known that magnesium hydroxide with a specific surface area of 30 to 60 m2/g is added to a calcium chloride aqueous solution with a concentration of 10 to 40% by weight, and the specific surface area is reduced to 10 m' by autoclave feeding under high temperature and high pressure. /g or less (Japanese Patent Application Laid-open No. 100918/1983).

is recommended.

[Problems to be Solved by the Invention] The conventional method described above has a problem in that the autoclave is susceptible to corrosion because the treatment is performed using a highly concentrated calcium chloride aqueous solution. Furthermore, since wood thermal synthesis is carried out in an aqueous sodium hydroxide solution, there is also the problem of increased manufacturing costs.

The present invention solves the problems of conventional equipment corrosion, etc., and provides magnesium hydroxide that has hexagonal columnar crystals with a large particle size and improves the problem of secondary aggregation, and has a specific surface area of IOm.
It is an object of the present invention to provide a method for producing magnesium hydroxide having a small crystal size of 2/g or less and a large crystal size at low cost and industrially advantageously.

[Means for Solving the Problems] The method for producing magnesium hydroxide of the present invention includes obtaining magnesium hydroxide having a specific surface area of 20 d/g or more by the BET method by reacting a magnesium ion-containing liquid with an alkali,
After filtering and dehydrating the obtained magnesium hydroxide, 0.5
In addition to a magnesium chloride aqueous solution of % by weight or more, hydrothermal synthesis is performed under the conditions of a magnesium hydroxide concentration of 5% by weight or more, a temperature of 120°C or more, and a pressure of 2.0 kg/m' or more, so that the specific surface area by the BET method is 1 orr. ? /g or less,
The present invention, which is characterized in that magnesium hydroxide is obtained in the form of hexagonal columnar crystals, will be described in detail below.

In the method of the present invention, first, magnesium ions (
Magnesium hydroxide (Mg(OH)2) having a specific surface area of 20 m2/g or more by the BET method is produced by reacting a liquid containing Mg") with an alkali. Here, Mg
As the 2"-containing liquid, bittern, seawater, or an aqueous magnesium chloride (MgCJ22) solution can be used. As the alkali, slaked lime, caustic alkali, ammonia, etc. can be used.

These aqueous solutions containing Mg2+, such as seawater or bittern, can be reacted with an alkali by a known method, and the liquid is then filtered to obtain a Mg(OH)2 wet cake. When the obtained Mg(OH)2 was observed under an electron microscope, it was found that it had small irregular plate-shaped crystals of about 1 to 0.5 μm in size, and many Mg(OH)2 particles. They aggregate to form secondary particles of several micrometers to several tens of micrometers. The reaction solution is filtered, washed, dried, etc. to make it free of mother liquor, and if necessary, a part of it is pulverized to obtain M.
g(OH)2 powder usually has a specific surface area of 20 to 100rn
”/H irregular plate-like crystals.

In the present invention, the specific surface area 2 obtained in this way is
0 to 100 m"/g of Mg(OH)2 at 0.5% by weight or more, preferably 0.5 to 10.0% by weight, more preferably 1.0 to 5.0% by weight Mg C It 2 Add to the aqueous solution.Here, the MgCj2 of the MgCIt2 aqueous solution
2 concentration is less than 5% by weight of O, the specific surface area is 10rr? /
Mg (OH)2 having hexagonal columnar crystals cannot be obtained at less than 100 g. Further, even if the MgCA2 concentration exceeds 10.0% by weight, the specific surface area of Mg(OH)2 obtained will hardly become smaller any further, which is not preferable since there is a risk of equipment corrosion.

Note that the Mg(OH)2 concentration in the MgCu2 aqueous solution to which Mg(01{)2 is added is 5 to 30% by weight, q,
It is preferable to adjust the concentration of S to 10 to 20% by weight. If the Mg (OH)2 concentration is less than 5% by weight, /! (Due to the concentration, productivity is poor. If it exceeds 30% by weight, the fluidity of the reaction liquid slurry will decrease significantly, making it difficult to transport the slurry, stir, and operate the device.

Then, the thus obtained MgCA2-containing Mg
Put the (OH)2 slurry into a pressure container and weigh 2.0kg/c.
Pressurize and heat under stirring at a pressure of at least 3.0 kg/cm', preferably at least 3.0 kg/cm', and at a temperature of at least 120°C, preferably at least 130°C.The treatment time is Mg
Although it varies slightly depending on the concentration of CjZ2, pressure, temperature, etc., it usually takes 30 minutes to several hours. Note that if the pressure or temperature is too high, the processing cost will be high, so it is preferable to perform the processing at a pressure of 20 kg/cm 2 or less and a temperature of 200° C. or less.

As a means of implementing the present invention industrially, a specific concentration of M
Mg (OH)2 within the above range is added to an autoclave containing an aqueous solution of gCIta, and the temperature and pressure are raised and maintained for several hours.

Hydrothermal treatment under pressure and heating is more effective.
M having a specific surface area of zom"/g or less and hexagonal columnar crystals
g(OH)2 is obtained. The obtained Mg(OH)2 is
For example, it is made into a product through treatments such as filtration, dehydration, drying, and pulverization.

[Effect] Usually, Mg(OH)2 obtained from an aqueous solution containing Mg24-, such as seawater or bittern, has a peak at 2θ of 38.0 degrees in its X-ray diffraction rather than a peak at 18.6 degrees. Although higher, Mg(OH)2 obtained by the method of the invention
Hax#i! The peak at 2θ of 18.6 degrees in diffraction is higher than the peak at 38.0 degrees. That is, in X-ray diffraction, the peak intensity I186 at 2θ is 18.6 degrees and the peak intensity IBB.20 is 38.0 degrees. The ratio of O I+a.
It shows the characteristic that a/138.0 is larger than 1.

This indicates that M g (OH)2 obtained by the conventional method
This is thought to indicate that by treating the compound under high temperature and high pressure according to the method of the present invention, melting and precipitation are repeated, thereby forming crystals with a regular lattice arrangement.

For this reason, Mg(0
When 1{)2 is observed under an electron microscope, it shows hexagonal columnar crystals with uniform grain size and little secondary aggregation of crystals, which is different from Mg (OH)2 obtained by conventional methods. Furthermore, the specific surface area of Mg(OH)2 obtained by the conventional method by the BET method is 20 to 100 m''/g, whereas the Mg(OH)2 obtained by the present invention has a specific surface area of 10rrIf/g.
It shows a very small value below.

[Examples] The present invention will be described in more detail below with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Note that the measurement conditions for X-ray diffraction in each example are as follows.

Target: Cu-Ka Filter: Ni Voltage: 40kV Current: 25mA Scanning speed: 2”2θ/min Production Example 1 Bittern and milk of lime were mixed with CaCIt2 by a known method.
/MgCJ22=Q. 98 (molar ratio) to obtain a Mg(C)H)2 slurry, which was filtered to obtain a Mg(OH)2 wet cake. This Mg(OH)
2 was observed with an electron microscope, the obtained Mg(O
It can be seen that H)2 is a small, collapsed, irregular plate-like crystal with a grain size of about 0.1 to 0.5 μm. Also, as a result of X-ray diffraction, the intensity of 2θ, 18.6 degrees is 186, the intensity of 38.0 degrees is ISB. Intensity ratio I II s/I when O
38. 6 was 0.66, and the specific surface area value determined by the BET method was 25.3 rn''/g.

Production Example 2 N H 4 O H / M g C produced from bittern and aqueous ammonia at a reaction temperature of 50° C. by a known method.
React at a ratio of Jil 2 = 0.82 (molar ratio),
The resulting Mg(OH)2 slurry was filtered and Mg
A (OH)2 wet cake was obtained. The obtained Mg (01{
)2 was observed with an electron microscope, and the particle size was 0.05~
0.3 μm small broken irregular plate crystals.
Secondary agglomerated particles of about 5 to 1 μm were formed. Also,
X-ray diffraction result 2θ, peak intensity of 18.6 degrees I166
, the intensity ratio 1+a. when the peak intensity of 38.0 degrees is I31!1.0. a/131 (+ is 0.82, BET
The specific surface area value determined by the method was 45.2 m2/g.

Example 1 5 to the Mg(OH)2 wet cake produced in Production Example 1
Weight% Mg'Cj! 2 aqueous solution was added to produce a Mg(OH)2 slurry containing MgCu2. The Mg('OH)2 concentration in the slurry was adjusted to 20% by weight.

This Mg(OH)2 slurry in an autoclave at −10°C
and 2.8 kg/crrI″ at 130°C for 3 hours.
The mixture was hydrothermally treated with sufficient stirring and then slowly cooled to 8°C.

The slurry after the hydrothermal treatment was filtered, and the obtained Mg (OH
) 2 cakes were washed with 10 times the amount of water, dried and ground.

When the obtained Mg (OH) 2 powder was observed under an electron microscope, it was confirmed that hexagonal columnar crystals with uniform particle size and little secondary aggregation were obtained. In addition, as a result of X-ray diffraction, the intensity at 2θ, 18.6 degrees is I18.6, and the intensity at 38.0 degrees is rsa. Intensity ratio 1 when o + a. e/
I 3a. o was 1.11, and the specific surface area value according to the BET11 method was 8.2 d/g.

Example 2 Mg(OH)2 slurry containing MgCA2 produced in the same manner as in Example 1 - 10f! ．． Mg(OH) was prepared in the same manner as in Example 1 except that 6.3 kg/cm'' was placed in an autoclave and hydrothermally treated at 160°C for 2 hours.
Two powders were produced.

When the obtained Mg(OH)2 powder was observed under an electron microscope, it was confirmed that hexagonal columnar crystals with uniform particle size and little secondary agglomeration were obtained as in Example 1. Also,
As a result of X-ray diffraction, the peak intensity at 2θ, 18.6 degrees is ■1
86, the peak intensity of 38.0 degrees ■38. . Strength ratio when closed: 1+a. s/I38. is 1.92, and BE
The specific surface area value by T method is 5.8rr? /g.

Example 3 Using the Mg (OH) 2 produced in Production Example 2, Mg (OH) 2 powder was obtained in the same manner as in Example 1.

When the obtained Mg(OH)z powder was observed under an electron microscope, it was confirmed that, as in Examples 1 and 2, hexagonal columnar crystals with a uniform particle size and little secondary aggregation were obtained. Ta. In addition, as a result of X-ray diffraction, the peak intensity at 2θ, 18.6 degrees was 11.8, and the peak intensity at 38.0 degrees was 1
Intensity ratio I +a. when set to 38.0. a/Is
a. o was 1.88, and the specific surface area value determined by the BET method was 6.2 rn''/g.

Comparative Example 1 Mg (OH) 2 wet cake produced in Production Example 2 was added with 5
A wt% MgCJZ2 aqueous solution was added to produce a Mg(OH)2 slurry containing MgCu2. The Mg(OH)2 concentration in the slurry was adjusted to 20% by weight.

This Mg(OH)2 slurry in autoclave -10
Enter j2, 1, . The mixture was hydrothermally treated at 5 kg/cm2 and 110'e for 3 hours with sufficient stirring, and then slowly cooled to 8oC.

The slurry after the hydrothermal treatment was filtered, and the obtained Mg (OH
) 2 cakes were washed with 10 times the amount of water, dried and ground.

When the obtained Mg(OH)2 powder was observed using an electron microscope, it was found that the crystal particle size was smaller than that of the Mg(OH)2 obtained in Examples 1 to 3, and many secondary agglomerated particles were observed. . In addition, as a result of X-ray diffraction, the peak intensity at 2θ, 18.6 degrees is 1, and the peak intensity at 86, 38.0 degrees is rsa. Intensity ratio I when o is 18. a/I 36. 0 is 0.93, and the specific surface area value by BET method is 14.7
m'/g.

Comparative Example 2 A 5% by weight M g C 1 2 aqueous solution was added to the Mg (OH) 2 wet cake produced in Production Example 2, and the Mg C 1 2 aqueous solution was added.
A Mg(OH)2 slurry containing 12 was prepared. The concentration of magnesium hydroxide in the slurry was adjusted to 20% by weight.

This slurry 10A was heat-treated at 90°C under atmospheric pressure for 3 hours with sufficient stirring, and then the slurry was filtered, and the resulting Mg(OH)2 cake was washed with 10 times the amount of water, dried, and ground. .

When the obtained Mg(OH)2 powder was observed under an electron microscope, it was found that many secondary agglomerated particles were not formed into large crystals as obtained in Examples 1 to 3. In addition, as a result of X-ray analysis, the peak intensity at 2θ, 18.6 degrees was
The peak intensity at +38.0 degrees is 138. Intensity ratio I +a. a/I 3a. o was 0.90, and the specific surface area value by BET method was 22.8 m'/g.

[Effects of the Invention] As detailed above, according to the method for producing Mg(OH)2 of the present invention, the specific surface area can be reduced to 10rr1'/g or less without causing problems such as corrosion of equipment such as autoclaving. Mg(OH)2, which is small and has a hexagonal columnar crystal with little secondary aggregation under an electron microscope and a regular lattice arrangement, can be easily and efficiently produced at low cost.

Since the obtained Mg(OH)2 has low reactivity, it has little effect on other coexisting substances when blended with resin etc., and can maintain a stable state for a long period of time. It can be effectively used as a flame retardant filler, etc. Furthermore, when this is fired to produce magnesium oxide 15 (MgO), MgO with little change in activity and other physical properties over time is obtained, so it is suitable as magnesium hydroxide as a raw material for FRP and electrical steel sheets. be.

Claims (1)

[Claims] (1) Magnesium hydroxide with a specific surface area of 20 m^2/g or more is obtained by the BET method by the reaction of a magnesium ion-containing liquid and an alkali, and after filtering and dehydrating the obtained magnesium hydroxide, a concentration of 0.5% by weight or more is obtained. In addition to the magnesium chloride aqueous solution, a magnesium hydroxide concentration of 5% by weight or more,
By hydrothermal synthesis at a temperature of 120°C or higher and a pressure of 2.0 kg/m^2 or higher, magnesium hydroxide with a specific surface area of 10 m^2/g or less by the BET method and a hexagonal columnar crystal can be obtained. Characteristic manufacturing method of magnesium hydroxide.