JPH0329004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to magnesium hydroxide, particularly to dense magnesium hydroxide particles having a large particle size and good sphericity.

[Prior Art] Conventionally, magnesium hydroxide is produced by decarboxylating seawater and reacting with calcium hydroxide, caustic soda, ammonia, etc. to obtain a precipitate of magnesium hydroxide, which is then separated to produce a product (so-called seawater mug). ). This seawater mug had a large porosity, poor sphericity, and low particle strength, so it could be easily loosened by hand and become fine particles.

On the other hand, a method of hydrothermally treating basic magnesium chloride has also been proposed as a method of providing highly pure magnesium hydroxide. (Refer to Japanese Unexamined Patent Publication No. 115799/1983) Magnesium hydroxide produced by this method does indeed have a certain degree of compactness, but the magnesium hydroxide particles are formed only from primary particles, and therefore, In most cases, the average particle size was 1μ or less.

As mentioned above, conventionally known magnesium hydroxide has large pores inside the particles (i.e., it is not dense).
Although they were granular or had a certain degree of density, they were only small-sized particles that were formed from primary particles only.

[Problems to be Solved by the Invention] The present invention provides magnesium hydroxide with high density, good sphericity, and large particle size, which was hitherto unknown, and a method for producing the same.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. An aqueous solution containing magnesium hydroxide and a water-soluble magnesium salt having an average particle size of 5 to 500 μm and a specific surface area of 25 to 1 m ² /g and ammonia are reacted to form magnesium hydroxide particles. The crystallization load is 500Kg/ ^m3・h or less, and the concentration of magnesium hydroxide thriller in the crystallizer is 1 to 1.
60 wt%, and the average particle size of the almost spherical secondary particles formed by aggregation of primary particles of scale-like primary particles with a thickness of 100 to 5000 Å is 5 to 5000 Å.
The present invention provides a method for producing magnesium hydroxide, which is characterized by crystallizing magnesium hydroxide having a size of 500μ and a specific surface area of 25 to 1 m ² /g.

Figure 1 shows the particle structure of secondary particles with an average particle size of 17.3μ, which is an example of magnesium hydroxide of the present invention.
This is an electron micrograph at 5000x magnification.

Figure 2 shows another example of magnesium hydroxide according to the present invention.
This is an electron micrograph with a magnification of 5000 times showing the particle structure of secondary particles having an average particle size of 13.6 μm as an example.

FIG. 3 is a 2000x electron micrograph showing the particle structure of secondary particles in a cross section of magnesium hydroxide (average particle size 35 μm) of the present invention.

FIG. 4 is a 5000x electron micrograph showing the particle structure of secondary particles of magnesium hydroxide (average particle size: 30 μm) according to the present invention according to Example 1.

The magnesium hydroxide of the present invention is shown in Figures 1 and 2.
As shown in the figure, it is almost spherical and has a large particle size, with an average particle size of 5 to 500μ, and even 10 to 500μ.
It spans a range of 350μ. The magnesium hydroxide of the present invention has scale-like particles that appear like strings on the surface of the secondary particles in FIGS. 1 and 2.
Secondary particles are formed by aggregation of many primary particles, and these scaly primary particles are strongly attached to each other and do not easily decompose into primary particles even when subjected to mechanical treatment. It is. Furthermore, as shown in FIG. 3, the primary particles are oriented outward from the center of the secondary particles, almost radially, and the primary particles are densely arranged, as described above. Tightly intertwined or attached. Therefore 2
The voids created between the primary particles inside the primary particles are very small.

From the particle structure of the magnesium hydroxide of the present invention as described above, its specific surface area (according to the BET method) is 25~
1 m ² /g, and even 20 to 1 m ² /g, which is extremely small compared to the 30 to 100 m ² /g of conventional ordinary seawater mugs.

As a result of the above, the solidified apparent specific gravity of the magnesium hydroxide particles of the present invention is 0.8 or more, and even 0.9 or more, which is much larger than the solidified apparent specific gravity of the conventionally known seawater mug, which is around 0.6. .

Here, the hardened apparent specific gravity means the apparent specific gravity in a state in which particles are densely packed, and is specifically measured using a powder tester manufactured by Hosokawa Micron Co., Ltd.

Now, 1 constituting the magnesium hydroxide of the present invention
The secondary particles are scaly, and the thickness of the scaly is 2
Although it depends on the size of the secondary particle, it is in the range of 100 to 5000 Å. The scale-like primary particles are produced in the manufacturing method described below.
As the secondary particles grow, their thickness increases little by little, and the particles grow in the plane direction of the scales. These scale-like primary particles are composed of single crystals or polycrystals, and crystallographically, the strain in the <101> direction is 4×
10 ^-3 or less. Note that the strain in the <101> direction is measured by the method described in Japanese Patent Application Laid-open No. 115799/1983.

Furthermore, since the magnesium hydroxide of the present invention has good fluidity, it has a small angle of repose.

Moreover, since the scale-like primary particles of the magnesium hydroxide of the present invention are arranged substantially radially, it has high light transmittance.

As mentioned above, the magnesium hydroxide secondary particles of the present invention are very dense, have very small pores inside the particles, and have a small pore volume. The cumulative pore volume of pores with a pore diameter of 0.5μ or less is 0.1cc/g or less, and even 0.07
cc/g or less, and this value is very small compared to 0.3-0.4 cc/g for normal seawater mugs.

Furthermore, the magnesium hydroxide of the present invention has a small oil absorption and is suitable as a filler for resins and the like. The specific oil absorption is JISK5101
70ml/100g or less, or even 60ml
ml/100g or less.

Thus, the magnesium hydroxide of the present invention has good sphericity, dense, large particle size, high strength, and good fluidity, so it is suitable as a filler for various resins, and is particularly suitable for ester-based, It is suitable when filling resin to produce so-called artificial marble.

Moreover, the magnesium hydroxide of the present invention is calcined,
It is also a suitable raw material for obtaining magnesium oxide with good water resistance (that is, low hydration).

Next, a preferred method for producing the above-mentioned magnesium hydroxide of the present invention will be explained.

The magnesium hydroxide of the present invention can be obtained by reacting a water-soluble magnesium salt such as magnesium chloride, magnesium nitrate, and magnesium sulfate with ammonia under specific conditions. Among the water-soluble magnesium salts mentioned above, magnesium chloride is most preferred.

Hereinafter, the case where the water-soluble magnesium salt is magnesium chloride will be explained in more detail.

The type of reaction crystallizer for producing magnesium hydroxide by reacting a magnesium chloride aqueous solution with ammonia is not particularly limited, but the magnesium chloride aqueous solution at the time of reaction crystallization contains 1 to 60 wt%, preferably 3 to 60 wt%.
It is necessary that 40wt% of solid magnesium hydroxide is suspended, that is, the reaction solution is a slurry of an aqueous magnesium chloride solution containing solid magnesium hydroxide, and that the crystallization of magnesium hydroxide in the reaction crystallizer is Analysis load is 5-500Kg/
It is necessary that it is less than m ³ ·h, preferably 30 to 120 Kg/m ³ ·h. Here, the crystallization load means the amount (Kg) of solid magnesium hydroxide that crystallizes in 1 hour per 1 m ³ of magnesium chloride slurry containing solid magnesium hydroxide in the reaction crystallizer. The amount corresponds to the weight increase of solids in the slurry. In the present invention, the reason for employing the above-mentioned specific crystallization conditions is as follows.

That is, the slurry concentration in the reaction crystallizer is
If less than 1 wt%, the magnesium hydroxide that is crystallized will form a new fine particle size (e.g., average particle size of 1μ or less) hydroxide, rather than precipitating on the existing magnesium hydroxide solids in the slurry. Much of it precipitates as magnesium.

Furthermore, if the slurry concentration exceeds 60wt%, the viscosity of the slurry increases too much, and the ammonia supplied to the reaction crystallizer is not uniformly dispersed.
The resulting magnesium hydroxide has a wide range of particle sizes.

On the other hand, as for the crystallization load, if it exceeds 500 Kg/m ³ ·h, many fine particles of 5 μm or less will precipitate, so it is necessary to set an upper limit on the crystallization load. On the other hand, the lower limit of the crystallization load does not need to be limited, but if it is less than 5 Kg/m ³ ·h, it is necessary to increase the size of the apparatus, so it is preferably set to 5 Kg/m ³ ·h or more.

To maintain the slurry concentration in the reaction crystallizer from 1 to 60 wt%, control the ratio between the amount of clarified liquid containing no solids extracted from the reaction crystallizer and the amount of slurry containing solids. This is achieved by As a specific means for this, for example, the clarified liquid and slurry may be extracted directly from the device at a fixed ratio, or after such a process or after extraction as a slurry, a solid-liquid separator is used to remove solids from the slurry. This solid or slurry and/or the clarified liquid from the solid-liquid separator are transferred to a reaction crystallization tank while controlling the reflux rate. Methods such as feeding back data can be adopted industrially.

Further, the concentration of magnesium chloride supplied to the reaction crystallizer is preferably about 2 to 30 wt%. Also,
The reaction temperature is preferably 20 to 80°C.

In the present invention, in the step of producing magnesium hydroxide, ammonium chloride is produced as a by-product and is recovered together with some unreacted magnesium chloride. Alternatively, it can be recovered as ammonium chloride by a known ammonium chloride distillation method using quicklime and used for circulation. Calcium chloride, which is a by-product during ammonium chloride distillation, can be reacted with seawater and used to produce magnesium chloride as a raw material. .

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 After decarboxylating seawater using a conventional method, a magnesium hydroxide slurry was obtained using coal milk using a known method. This slurry is separated by a vacuum filtration machine, and the obtained magnesium hydroxide is
As an impurity in a wet cake with an MgO concentration of 34.0wt%
CaO=0.41, _SiO2 =0.12, _Al2O3 = _0.12 , _{Fe2O3 =}
0.03, B ₂ O ₃ = 0.09, and SO ₃ = 1.0 (unit: wt%).

To 1 kg of the magnesium hydroxide wet cake, 6.55 kg of an aqueous solution containing calcium chloride with a concentration of 20.0 wt% and magnesium chloride with a concentration of 2.0 wt% is added at a ratio of 6.55 kg, and after revalping, carbon dioxide gas with a concentration of 100% is heated to temperature.
The reaction was absorbed at 60°C. The reaction product was filtered using a filter to obtain an aqueous solution containing magnesium chloride at a concentration of 12.7 wt%. The magnesium chloride aqueous solution was made acidic with hydrochloric acid and decarboxylated by air ration. After that, sufficient stirring was maintained using a stirring device, and an internal volume of 35 cm was prepared with magnesium hydroxide crystals as seed crystals. In the reaction tank, 21Kg/h of this aqueous solution and 2.2Nm ³ /h of ammonia gas
was continuously supplied, and crystals of magnesium hydroxide were precipitated while maintaining the temperature at 40°C. The crystallization load of magnesium hydroxide at this time is 40Kg/ ^m3 .
h. The slurry concentration was 6 wt%. The precipitate of magnesium hydroxide is separated by a filter and washed with water.
Dry at 140°C. The obtained magnesium hydroxide has MgO = 68.7, CaO = 0.06, SiO ₂ = 0.04,
Al ₂ O ₃ = 0.01, Fe ₂ O ₃ = 0.001, B ₂ O ₃ = 0.09, SO ₃
= 0.01 (unit: wt%).

When the obtained magnesium hydroxide was observed with an electron microscope at a magnification of 5,000 times, as shown in the photograph in Figure 4, a large number of scale-shaped primary particles aggregated in multiple directions, and the scales spread outward from the center. The scales were oriented almost radially toward the surface, and the scales had an apparent spherical shape with a thickness of 200 to 1000 Å and an average particle size of 30 μm.

In addition, the strain in the <101> direction of the scale-like primary particles is 1.8
It was ×10 ^-3 . The specific surface area determined by the BET method using nitrogen gas was 3 m ² /g, and the specific gravity of the particles determined by the JIS Z8807 method was 2.27.

In addition, the solidified apparent specific gravity of these secondary particles is 1.4, the angle of repose is 37 degrees, and the oil absorption amount according to JIS K5101 is 35ml/
It was 100g.

The cumulative pore volume occupied by pores of 0.5 μm or less inside the secondary particles was 0.03 cc/g.

Example 2 Magnesium chloride aqueous solution with a concentration of 12.7 wt% obtained from bittern was fed at 55 kg/h, and the amount of ammonia supplied was
Magnesium hydroxide was obtained in the same manner as in Example 1 except that the crystallization load was 5.8Nm ³ /h, the crystallization load was 105Kg/m ³ ·h, and the slurry concentration of magnesium hydroxide was 30wt%. The obtained magnesium hydroxide is the first
Average grain size with structure similar to Figure and Figure 2
It was 300μ.

In addition, the thickness of the scale-like primary particles is approximately 300 to 1500 Å.
The strain in the <101> direction was 1.6×10 ^-3 . Other properties measured in the same manner as in Example 1 were as follows.

Specific surface area 1.1 m ² /g Particle specific gravity 2.28 Solidified apparent specific gravity 1.37 Oil absorption 30 ml/100 g Pore volume 0.02 cc/g Example 3 In Example 2, the crystallization load was set to 350 Kg/m ³ h,
Magnesium hydroxide of the present invention was obtained in the same manner as in Example 2 except that the slurry concentration was changed to 45%.

The properties of this magnesium hydroxide were as follows.

Average particle size 11μ Specific surface area 7m ² /g Thickness of scale-like primary particles 150-800Å Strain of scale-like primary particles in <101> direction 1.66×10 ^-3 Specific gravity of particles 2.28 Hardened apparent specific gravity 0.95 Oil absorption 46ml /100g Pore volume 0.5cc/g Comparative example 1 Various properties were measured in the same manner as in Example 1 for seawater mugs with an average particle size of 1.5μ obtained during regular visits, and the following results were obtained. .

Specific surface area 41m ² /g Distortion in <101> direction 3.7×10 ^-3 Specific gravity of particles 2.13 Apparent solidified specific gravity of powder 0.61 Oil absorption 75ml/100g Pore volume 0.32cc/g Comparative example 2 JP-A-115799-1987 Magnesium hydroxide was produced according to Example 1 of the publication.

The properties of the obtained magnesium hydroxide were as follows.

Average particle size 0.9μ Specific surface area 4.2m ² /g Strain in the <101> direction 1.2×10 ^-3 Specific gravity of particles 2.31 Apparent solidified specific gravity of particles 0.70 Comparative example 3 In Example 2, the crystallization load was increased to 600Kg/m ³・h
Magnesium hydroxide was crystallized in the same manner as in Example 2 except that the slurry concentration was 0.5 wt%.
The properties of the obtained magnesium hydroxide were as follows.

Average particle size 2.1μ Specific surface area 3.3m ² /g Primary particle thickness 110-330Å Strain in <101> direction 2.1×10 ^-3 Particle strain 2.29 Apparent solidified specific gravity of particles 0.75 Oil absorption 80ml/100g Pore Volume 0.20cc/g

[Brief explanation of the drawing]

FIG. 1 is a 5000x electron micrograph showing the particle structure of magnesium hydroxide (average particle size 17.3μ) of the present invention. Figure 2 shows the particle structure of magnesium hydroxide (average particle size 13.6μ) according to the present invention.
This is a magnified electron micrograph. FIG. 3 is a 2000x electron micrograph showing the cross-sectional particle structure of magnesium hydroxide (average particle size 35 μm) of the present invention. Fourth
The figure is a 5000x electron micrograph showing the particle structure of magnesium hydroxide (average particle size 30μ) of the present invention according to Example 1.

Claims (1)

[Scope of Claims] 1. Almost spherical secondary particles formed by an aggregation of scale-like primary particles with a thickness of 100 to 5000 Å, the average particle size of the secondary particles being 5 to 500 μm. can be,
Magnesium hydroxide whose specific surface area is 25-1 m ² /g. 2. The magnesium hydroxide according to claim 1, wherein the strain in the <101> direction of the primary particles is 4×10 ^-3 or less. 3. Magnesium hydroxide according to claim 1 or 2, wherein the solidified apparent specific gravity of the secondary particles is 0.8 or more. 4. Magnesium hydroxide according to any one of claims 1 to 3, wherein the secondary particles have an oil absorption of 70 ml/100 g. 5. Magnesium hydroxide according to any one of claims 1 to 4, wherein the scale-like primary particles are oriented substantially radially outward from the center of the secondary particles. 6. Magnesium hydroxide according to any one of claims 1 to 5, wherein the cumulative pore volume of pores with a diameter of 0.5 μ or less inside the secondary particles is 0.1 cc/g or less. 7. React an aqueous solution containing a water-soluble magnesium salt with ammonia so that the crystallization load of magnesium hydroxide is 500 Kg/m ² ·h or less, and the magnesium hydroxide slurry concentration in the crystallizer is 1 to 1.
Almost spherical secondary particles formed by aggregation of scale-like primary particles with a thickness of 100 to 5000 Å, with an average particle size of 5 to 500 μm. A method for producing magnesium hydroxide, which is characterized by crystallizing magnesium hydroxide having a specific surface area of 25 to 1 m ² /g. 8. The method for producing magnesium hydroxide according to claim 7, wherein the water-soluble magnesium salt is selected from magnesium chloride, magnesium nitrate, and magnesium sulfate.