JPH02164713A - Production of magnesium hydroxide - Google Patents

Abstract

PURPOSE:To easily obtain hexagonal platy crystals having a small specific surface area and hardly causing secondary aggregation by adding Mg hydroxide having ordinary irregular crystal form to an aq. soln. of the Mg salt of an org. acid having a prescribed concn. and carrying out hydrothermal treatment at elevated temp. and pressure. CONSTITUTION:Mg hydroxide having 20-50m<2>/g specified surface area measured by the BET method is added to an aq. soln. of the Mg salt of an org. acid having 0.5-10wt.% concn. to prepare a slurry. This slurry is hydrothermally treated under the conditions of >=130 deg.C and >=3kg/cm<2> pressure to obtain Mg hydroxide having <=10m<2>/g specific surface area measured by the BET method and hexagonal platy crystal form.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnesium hydroxide (Mg (OH) 2 )
Specifically, the specific surface area (hereinafter simply referred to as specific surface area) by the BET method is 10rr.
? The present invention relates to a method for producing magnesium hydroxide that can produce magnesium hydroxide in the form of hexagonal plate-like 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 using magnesium hydroxide as such a flame retardant filler, the specific surface area of magnesium hydroxide is 10d1.
There is a demand for a material with a large crystal grain size of less than 100 g and no secondary agglomeration. That is, if the specific surface area exceeds 10 d/g, secondary aggregates are likely to be formed due to the small crystal size, and when kneaded with resin, the dispersibility in the resin is extremely poor, resulting in poor processability, flame retardancy, It has an adverse effect on physical properties such as mechanical strength and water resistance and insulation.

Conventionally, as a method for producing magnesium hydroxide having a small specific surface area, that is, a large crystal size, the following methods (1) and (2) have been proposed.

■ Magnesium hydroxide with a specific surface area of ・30 to 60 d1g is added to a calcium chloride aqueous solution with a concentration of 10 to 40% by weight, and by autoclave curing under high temperature and high pressure, magnesium hydroxide with a specific surface area of 10 m'/g or less is produced. (Japanese Unexamined Patent Publication No. 100918/1983).

■ Magnesium oxide calcined at 1400°C or higher is 0.0% of the equivalent number of raw material magnesium oxide. A method of hydration in an aqueous suspension slurry containing a total amount of acid groups corresponding to an equivalent number of 5% or more and an acid group corresponding to an equivalent number of raw material calcium oxide as an acid or magnesium salt (JP-A-56- 109
No. 820).

[Problems to be Solved by the Invention] Among the above-mentioned conventional methods, the method (2) uses a highly concentrated aqueous calcium chloride solution, so there is a problem in that the autoclave is likely to corrode.

In addition, in method (2), magnesium oxide (magnesia clinker) calcined at high temperature is finely pulverized and subjected to a hydration reaction, which requires a calcination process, a pulverization process, etc., which makes the processing operation complicated and increases the manufacturing cost. The problem is that it is expensive.

The present invention provides magnesium hydroxide which eliminates the firing and pulverizing steps of the conventional method, alleviates corrosion of the equipment, and improves the problem of secondary aggregation with hexagonal plate-shaped crystals having a large particle size. Moreover, the specific surface area is xorr? An object of the present invention is to provide a method for producing magnesium hydroxide having a small crystal size of less than /g 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 is to mix 7 g of magnesium hydroxide with a specific surface area of 20 to 50 m by the BET method to an organic acid magnesium salt at a concentration of 0.5 to 10% by weight. BET by adding to an aqueous solution and heating to a temperature of 130 °C or higher under a pressure of 3.0 kg/c rn” or higher.
The method is characterized in that magnesium hydroxide having a specific surface area of 10rn''7g or less and in the form of hexagonal plate crystals is obtained.

The present invention will be explained in detail below.

Mg (Of()) used as a raw material in the present invention
2 can be obtained, for example, by reacting an aqueous solution containing Mg 24-, such as seawater or bittern, with slaked lime or caustic alkali by a known method. When Mg (OH) 2 obtained by such a reaction is observed with an electron microscope, it has irregular plate-like crystals with a size of about 0.1 to 0.5 μm, and many Mg (
OH)2 particles aggregate to form secondary particles of several μm to several tens of μm.

Mg obtained by filtering, washing, drying, etc. the reaction solution to make it free of mother liquor, and partially pulverizing if necessary
(OH)2 powder usually has a specific surface area of 20 to 80 m”/
It is an irregular plate-like crystal of H.

In the present invention, Mg (O
H) 0.5 to 10.0% by weight, preferably 1.0 to 1.0% by weight of 2
Add to a 5.0% by weight aqueous organic acid magnesium salt solution. Even if the concentration of the organic acid magnesium salt aqueous solution is less than 0.5% by weight or more than 10.0% by weight, the specific surface area t
Mg (OH
)2 cannot be obtained. The organic acid magnesium salt used is preferably magnesium acetate, but magnesium formate, magnesium butyrate, etc. can also be used.

In addition, the Mg(OH)2 concentration in the organic acid magnesium salt aqueous solution to which Mg(OH)2 has been added is 5 as MgO.
It is preferable to adjust the concentration to 20% by weight.

If the Mg(OH)2 concentration is less than 5% by weight as MgO, the concentration is low, resulting in poor productivity. If it exceeds 20%, the magnesium hydroxide concentration is high relative to the organic acid concentration, so
After hydrothermal treatment, magnesium hydroxide having a small specific surface area of hexagonal plate crystals cannot be obtained.

Next, the organic acid magnesium-containing Mg(OH)2 slurry thus obtained was placed in a pressure-resistant container.3.
0kg/crn” or more, preferably 5.0kg/crr
? At the above pressure, the mixture is heated under pressure to a temperature of 130° C. or higher, preferably 150° C. or higher, with stirring. The treatment time varies depending on conditions such as the concentration of the organic acid magnesium salt aqueous solution, pressure, temperature, etc., but 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 the pressure should be set at 20 kg/c rn.
``Hereafter, it is preferable to process at a temperature of 200°C or less.

By performing such hydrothermal treatment under pressure and heating,
M with a specific surface area of 10 m'/g or less and hexagonal plate-like crystals
g (OH)2 is obtained. Obtained Mg(OH)2
is made into a product through treatments such as filtration, dehydration, drying, and pulverization.

[Effect] Normally, Mg (OH)2 obtained from an aqueous solution containing Mg 2+ such as seawater or bittern has a peak at 38.0 degrees in 2θ than a peak at 18.6 degrees in its X-ray diffraction. Although high, Mg (OH) obtained by the method of the present invention
2, the peak at 2θ of 18.6 degrees in X-ray diffraction is higher than the peak at 38.0 degrees. In other words, the peak intensity with 2θ of 18.6 degrees that can be induced in X-ray diffraction! ! e1.6
and 20° is 38.0° peak intensity■38. . The ratio of I+
It shows the characteristic that a, a/13+5° is larger than 1.

This indicates that Mg(O)l) obtained by the conventional method
This is thought to indicate that by treating No. 2 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 these reasons, Mg (
When OH)2 is observed under an electron microscope, unlike Mg(OH)2 obtained by conventional methods, it shows hexagonal plate-shaped crystals with uniform particle size and little secondary aggregation of crystals. Furthermore, the BE of Mg(OH)2 obtained by the conventional method
The specific surface area by T method is 20~aorr? /g, whereas Mg(OH)2 obtained in the present invention is 10m'/g.
It shows a very small value of less than g.

[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 on each side are as follows.

Target: Cu-Ka Filter: Ni Voltage: 40kV Current: 25mA Scanning speed: 2° 2θ/min Production Example 1 Magnesium hydroxide cake produced from bittern and milk of lime by a known method was filtered, washed, and dried. A powder of magnesium hydroxide was obtained by partially pulverizing the mixture. An electron micrograph of this magnesium hydroxide powder is shown in FIG. From FIG. 2, it can be seen that the obtained magnesium hydroxide is a small, collapsed, irregular plate-like crystal with a particle size of about 0.1 to 0.5 μm. In addition, as a result of X-ray diffraction, the intensity of 2θ, 18.6 degrees t+a, a,
Strength ■3♂ of 38.0 degrees. Strength ratio I l when closed
a, a/I 3a, O is 0.68, and BE
The specific surface area determined by the T method was 22.1 m2/g.

Example 1 A 1% by weight aqueous magnesium acetate solution was added to the magnesium hydroxide produced in Production Example 1 to produce a magnesium hydroxide slurry containing magnesium acetate. The concentration of magnesium hydroxide in the slurry was adjusted to a concentration of 101i mass % as magnesium oxide.

This magnesium hydroxide slurry in an autoclave
OIL was added and hydrothermally treated at 6.5 kg/cm2 at 160°C for 4 hours with sufficient stirring, followed by slow cooling to 80°C.

The slurry after the hydrothermal treatment was filtered, and the obtained magnesium hydroxide cake was washed with 10 times the amount of water, dried, and pulverized.

An electron micrograph of the obtained magnesium hydroxide powder is shown in FIG. As is clear from FIG. 1, hexagonal plate-shaped crystals with uniform particle size and little secondary aggregation were obtained. Also, X
As a result of line diffraction, the intensity at 2θ, 18.6 degrees is ■, 66.3
Strength of 8.0 degrees! , intensity ratio I la when closed at 8°
, a/I sa. was 1.54, and the specific surface area value by BET method was 7.2rn''/g.

Example 2 5% by weight mag acetate and a nesium aqueous solution were added to the magnesium hydroxide produced in Production Example 1 to produce a magnesium hydroxide slurry containing magnesium acetate. The concentration of magnesium hydroxide in the slurry was adjusted to 10% by weight as magnesium oxide.

This magnesium hydroxide slurry 1 in an autoclave
0j2 was added, and the mixture was subjected to hydrothermal treatment at 10.0 kg/am' at 180°C for 2 hours with sufficient stirring, and then slowly cooled to 80°C.

The slurry after the hydrothermal treatment was filtered, and the obtained magnesium hydroxide cake was washed with 10 times the amount of water, dried, and pulverized.

When the obtained magnesium hydroxide powder was observed under an electron microscope, hexagonal plate-shaped crystals with a uniform particle size and little secondary aggregation were obtained as in Example 1.

In addition, as a result of X-ray diffraction, the intensity at 2θ, 18.6 degrees was determined to be II
8.6.The intensity of 38.0 degrees is XSa. The strength ratio when closed is 1 ha, a/I 3a, o is 2.52, and the specific surface area value by BET method is 5.9rr? /g.

Comparative Example 1 A 0.3% by weight aqueous magnesium acetate solution was added to the magnesium hydroxide produced in Production Example 1 to produce a magnesium hydroxide slurry containing magnesium acetate. The concentration of magnesium hydroxide in the slurry was adjusted to 10% by weight as magnesium oxide.

This magnesium hydroxide slurry 1 in an autoclave
0JZ was added and hydrothermally treated at 2.0 kg/cm2 at 120°C for 4 hours with sufficient stirring, and then slowly cooled to 80°C.

The slurry after the hydrothermal treatment was filtered, and the obtained magnesium hydroxide cake was washed with 10 times the amount of water, dried, and pulverized.

An electron micrograph of the obtained magnesium hydroxide powder is shown in FIG. As is clear from Figure 3, this thing is
There are no large hexagonal plate crystals as obtained in Example 1.2, and many secondary grains are observed.

In addition, as a result of X-ray diffraction, the intensity at 2θ, 18.6 degrees was
l5.6.38.0 degree intensity. The intensity ratio I ra, a/I 310 when closed is 0.71,
The specific surface area value determined by the BET method was 18.3 m''/g.

[Effects of the Invention] As detailed above, according to the method for producing Mg (OH)2 of the present invention, it is possible to produce Mg (OH)2 without going through a calcination step or a pulverization step, and without causing the problem of corrosion of equipment such as an autoclave. , has a small specific surface area of less than 10 inches and 7 g, and is
a! Mg(OH)2 having hexagonal plate-like crystals with little secondary agglomeration and a regular lattice arrangement can be easily and efficiently produced at low cost under a mirror.

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. In addition, when this is fired to produce magnesium oxide, MgO with little change in activity and other physical properties over time can be obtained, so it can be used for FRP and electric appliances.
It is also suitable as raw material magnesium hydroxide for 111m plates.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are micrographs (10,000 times magnified) showing the particle structure of Mg (OH) 2 obtained in Example 1, Production Example 1, and Comparative Example 1, respectively. Agent Patent Attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) Specific surface area by BET method is 20 to 50 m^2/g
of magnesium hydroxide was added to an organic acid magnesium salt aqueous solution with a concentration of 0.5 to 10% by weight, and the mixture was mixed at 3.0 kg/cm^
By heating to a temperature of 130 ° C. or higher under a pressure of 2 or more, the specific surface area by the BET method is 10 m^2 / g or less,
A method for producing magnesium hydroxide, which is characterized in that magnesium hydroxide is obtained in the form of hexagonal plate-like crystals.