JPS61168522A - Magnesium hydroxide and production thereof - Google Patents

Abstract

PURPOSE:To produce dense magnesium hydroxide having large particle diameter and high sphericity, by reacting a water-soluble magnesium salt with ammonia under specific condition, agglomerating a part of the particles, and crystallizing the secondary particles having definite particle diameter and specific surface area. CONSTITUTION:Ammonia gas is introduced into an aqueous solution of a water- soluble magnesium salt such as magnesium chloride to crystallize the crystal of magnesium hydroxide. The crystallization load of the magnesium hydroxide in the above process is adjusted preferably to <=500kg/m<2>.h, and the concentra tion of the magnesium hydroxide slurry in the crystallizer is made to be 1-6wt%. The primary particles are agglomerated to form secondary particles of magnesium hydroxide in a nearly spherical form with an average particle diameter of 5-500mu and a specific surface area of 25-1m<2>/g. Since the particle is composed of a number of flaky primary particles collected along various directions orienting the flakes almost radially from the center toward the out side, the produced secondary particle takes a spherical form in appearance.

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 large porosity, poor sphericity, and low particle strength, so it could easily be 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 density, but the magnesium hydroxide particles are formed only from primary particles, and therefore In most cases, the average particle size was less than tp.

As mentioned above, conventionally known magnesium hydroxide is granular with large voids inside the particles (that is, not dense),
In other words, although the density was high to some extent, the particles were formed only from primary particles and were small in size.

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

[Means for Solving the Problems] The present invention has been made to solve the above problems, and is formed by aggregation of primary particles. Magnesium hydroxide and a water-soluble magnesium salt having approximately spherical secondary particles having an average particle diameter of 5 to 500p and a specific surface area of 25 to 1 m'/g are reacted with an aqueous solution and ammonia to produce magnesium hydroxide. Particle crystallization load is 500kg/
rn' h or less, and the concentration of the water-1-pimagnesium slurry in the crystallizer is 1 to 80 wt%, so that the average particle size of secondary particles formed by aggregation of primary particles is 5. ~500 liters, and its specific surface area is 25~1 go/
The present invention provides a method for producing magnesium hydroxide, which is characterized by crystallizing magnesium hydroxide of g.

FIG. 1 is a 5000x electron micrograph showing the particle structure of secondary particles having an average particle size of 17.3 g, which is an example of the magnesium hydroxide of the present invention.

Figure 2 shows the particle structure of secondary particles with an average particle size of 13.8 g, which is another example of magnesium hydroxide of the present invention.
This is a 0x electron micrograph.

Figure 3 shows the magnesium hydroxide of the present invention (average particle size 35J).
2000 showing the particle structure of secondary particles in the cross section of L)
This is a magnified electron micrograph.

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

-) DtinMJt6kl-wH4+j/r'yI,
I-) As shown in the 111iGmF mem2 section, it has a large particle size that is almost spherical and has an average particle size of 5 to 500.
It ranges from 10 to 350 tons. The magnesium hydroxide of the present invention is a secondary particle formed by aggregation of many scale-like primary particles that appear string-like on the surface of the secondary particle in FIGS. The primary particles are strongly adhered to each other and do not easily decompose into primary particles even when subjected to mechanical treatment.

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, the voids formed between the primary particles inside the secondary particles are very small (l/).

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 to 11 Tf/g.
Furthermore, it is 20 to 1 rrIl/g, which is very small compared to 30 to 1 (lQrn'/g) of a conventional normal seawater mug.

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 higher than the solidified apparent specific gravity of around 0.6 of conventionally known seawater mugs. It is becoming a big thing.

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

The primary particles constituting the magnesium hydroxide of the present invention are scale-like, and the thickness of the scales is in the range of 100 to 5,000 particles, depending on the size of the secondary particles. scaly 1
In the manufacturing method described below, the secondary particles grow in the plane direction of the scales, with their thickness increasing slightly as the secondary particles grow. The scale-like primary particles are made of single crystal or polycrystal, and crystallographically, the strain in the <101> direction is 4X 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. 1157913/1983.

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, with very small pores inside the particles, and
The pore volume is also small; specifically, the cumulative pore volume of pores with a pore diameter of 0.5 l or less inside the secondary particle is O,
Ice/g or less, furthermore 0.07cc/g or less, this value is 0.3 to 0.4cc/g in the case of a normal seawater mug.
It is very small compared to g.

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 amount is 7 according to JISK5101.
0/100g or less, even BO/100. It is as follows.

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 esters. It is suitable for producing so-called artificial marble by filling it into a system or resin.

Moreover, the magnesium hydroxide of the present invention becomes a suitable raw material for obtaining magnesium oxide having good water resistance (that is, low hydration) by calcining.

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.

There is no particular restriction on the type of device for the reaction crystallization of magnesium hydroxide by the reaction between an aqueous magnesium chloride solution and ammonia, but there is
~80wt%, preferably 3~40wt% of solid magnesium hydroxide is suspended, that is, the reaction solution is a slurry of an aqueous magnesium chloride solution containing solid magnesium hydroxide; The crystallization load of magnesium hydroxide in the analyzer is 5 to 500 kg.
/m3 -h or less, preferably 30 to 120 kg/m'
- Must be h. Here, the crystallization load is
It means the amount ('kg) of solid magnesium hydroxide crystallized in 1 hour per 1 m of magnesium chloride slurry containing solid magnesium hydroxide in the reaction crystallizer, and the amount of solid solid in the slurry is The reason for adopting the specific crystallization conditions as described above in the present invention, which corresponds to increasing the weight of the components, is as follows.

That is, the slurry concentration in the reaction crystallizer is 1 wt%.
If the magnesium hydroxide to be crystallized is smaller than the existing magnesium hydroxide in the slurry, the new finer particle size (e.g., average particle size lJ
L or less) is precipitated as magnesium hydroxide.

Furthermore, if the slurry concentration exceeds 80 wt%, the viscosity of the slurry increases too much, and the ammonia supplied to the reaction crystallizer is not uniformly dispersed, resulting in the resulting magnesium hydroxide having a wide range of particle sizes. Become.

On the other hand, regarding the crystallization load, if it exceeds 500 kg/rn'·h, many of the precipitated particles will be fine particles of 5 l or less, so an upper limit for the crystallization load is necessary. On the other hand, the lower limit of the crystallization load does not need to be limited, but it is 5 kg.
If it is less than /rn'·h, it is necessary to increase the size of the device, so it is preferable to set it to 5 kg/m″·h or more.

To maintain a slurry concentration of 1 to 60 wt% in the reaction crystallizer, control the ratio of the amount of clarified liquid containing no solids extracted from the reaction crystallizer to the amount of slurry containing solids. This is achieved by Specific means for this include, for example, directly extracting the clear liquid and slurry from the device at a fixed ratio, or after extracting the clear liquid and slurry in this manner or as a slurry, using a solid-liquid separator to separate the slurry from the slurry. Separate the solid or obtain a slurry with a high solid content concentration, and transfer this solid or slurry and/or the clarified liquid from the solid-liquid separator to a reaction crystallization tank while controlling the reflux rate. The method of feedback is the one that can be adopted industrially.

Further, the concentration of magnesium chloride supplied to the reaction crystallizer is preferably about 2 to 30 wt%, and 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. Ammonium chloride can be recovered as ammonia and recycled using the known ammonium chloride distillation method using quicklime, and calcium chloride, which is a by-product during ammonium chloride distillation, can be reacted with seawater and used to produce magnesium chloride, which is a raw material. can.

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

Example 1 After decarboxylating seawater by a conventional method, a magnesium hydroxide slurry was obtained by a known method using milk of lime.

This slurry is separated by a vacuum filter, and the obtained magnesium hydroxide has an MgO concentration of 34. Ovt% wet cake as an impurity Ca0 = 0.41 +! l;+
02 = 0.12 + A I203 Seal 0-12
+Fe203=0.03. B203-0.09.
It contained SO3-1,0 (unit: wt%).

Calcium chloride at a concentration of 2G and 0 wt% per kg of such magnesium hydroxide wet cake; and 2. After revalping by adding 8.55 kg of an aqueous solution containing Owt% magnesium chloride, 100% carbon dioxide gas was heated at a temperature of 60°C.
The 0 reaction product reacted and absorbed in the filter is filtered out using a filter,
An aqueous solution containing magnesium chloride at a concentration of 12.7 wt% was obtained. After decarboxylating the magnesium chloride aqueous solution by acidifying it with hydrochloric acid,
21 kg of this aqueous solution and 2 ml of ammonia gas were placed in a reaction tank with an internal volume of 35 J1 in which a sufficient stirring state was maintained using a stirring device and magnesium hydroxide crystals were present as seed crystals.
．． 2Nm'/b was continuously supplied to precipitate magnesium hydroxide crystals while maintaining the temperature at 40°C. The crystallization load of magnesium hydroxide at this time is 40 kg/rf
- h, slurry concentration was 6 wt%. The precipitate of magnesium hydroxide is separated by a filter and washed with water at 140°C.
It was dried. The obtained magnesium hydroxide was MgO 88.7. CaO-0,06,Si0? -0,04,
Al20311O,01,Fe2O2-0,001,B
203- 0.09,503- 0.01 (unit: wt
%)Met.

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 were distributed outward from the center. The #i pieces had a thickness of 200 to 1,000 particles and an average particle size of 30, forming an apparent spherical body.

In addition, the strain in the <101> direction of the scaly primary particles is 1.8X
It was 10-3. The specific surface area determined by the BET method using nitrogen gas was 3rrf/g, and the specific gravity of the particles determined by the JIS 28807 method was 2.27.

Further, the solidified apparent specific gravity of the secondary particles was 1.4, the angle of repose was 37 degrees, and the oil absorption amount according to JIS K5101 was 35 mb/100g.

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

Example 2 55 kg/b of an aqueous magnesium chloride solution with a concentration of 12.7 wt% obtained from bittern and the amount of ammonia supplied were 5.5 kg/b.
8Xm''/h, crystallization load 105kg/ln''-h
Magnesium hydroxide was obtained in the same manner as in Example 1 except that the slurry concentration of magnesium hydroxide was 30 wt%. The obtained magnesium hydroxide had a structure similar to that shown in Figures 1 and 2 and had an average particle size of 300 mm. The strain in the <101> direction was 1.8X 10-3.

Other properties measured in the same manner as in Example 1 were as follows.

Specific surface area 1.1 rrI'/g particle specific gravity
2.28 Solidified apparent specific gravity 1.37 Oil absorption 30 g/100 g Pore volume 0.02 cc/g Example 3 In Example 2, the crystallization load was set to 350 kg/rn'・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 wt%.

The properties of this magnesium hydroxide were as follows.

Average particle size 11 Final specific surface area 7 ml/g Thickness of scale-like primary particles 150-800 people Strain of hard primary particles in the <101> direction 1.68X 10-3 Triple layer of particles 2.28 Takumi Specific gravity: 0.85 Oil absorption: 46 min. 800 g Pore volume: 0.05 cc/g Comparative Example 1 A seawater mug with an average particle size of 1.5 pots obtained by a conventional method was prepared in the same manner as in Example 1. When various characteristics were measured, they were as follows.

Specific surface area 41rn'/g Strain in the <101> direction 3.7X Specific gravity of 10-3 particles 2.13 Apparent solidified specific gravity of powder 0.61 Oil absorption 75ral/100g Pore volume (1,32cc/g Comparative example) 2 Magnesium hydroxide was produced according to Example 1 of JP-A-52-115799.

The properties of the obtained magnesium hydroxide were as follows.

Average particle size 0.9 Final specific surface area 4.2 rn'/g Strain in <101> direction 1.2X Specific gravity of 10-3 particles 2.
31 Solidification of particles Apparent specific gravity 0.70 Comparative Example 3 In Example 2, magnesium hydroxide was used in the same manner as in Example 2 except that the crystallization load was 800 kg/m''·h and the slurry concentration was 0.5 wt%. The properties of the obtained magnesium hydroxide were as follows.

Average particle size 2. Iμ Specific surface area 33rn'/g Primary particle thickness 110-330 Strain in <101> direction 2. IX 10-3 particle strain 2.2
9 Hardened apparent specific gravity of particles 0.75 Oil absorption amount 80 cm/100 g Pore volume
0.20cc/g

[Brief explanation of the drawing]

Figure 1 shows the magnesium hydroxide of the present invention (average particle size 17
．． 3) is an electron micrograph at a magnification of 5000 times showing the particle structure of the sample. Figure 2 shows magnesium hydroxide of the present invention (average particle size 13).
．． This is an electron micrograph with a magnification of 5,000 times showing the grain structure of 6 ml. Figure 3 shows the magnesium hydroxide of the present invention (average particle size 35K).
) is an electron micrograph at 2000 times magnification showing the grain structure of a cross section. FIG. 4 shows the magnesium hydroxide of the present invention according to Example 1 (
5 (100 times magnified electron micrograph) showing the particle structure with an average particle size of 30.

Claims (1)

[Claims] (1) The average particle size of the approximately spherical secondary particles formed by aggregation of primary particles is 5 to 500 μ, and the specific surface area is 25 to 1 m^2/g. Some magnesium hydroxide. (2) The strain in the <101> direction of the primary particle is 4×10^-^
The glacial magnesium oxide according to claim 1, wherein the glacial magnesium oxide is 3 or less. (3) Magnesium hydroxide according to claim 1, wherein the solidified apparent specific gravity of the secondary particles is 0.8 or more. (4) The primary particles are scaly and the thickness of the scales is 100 to 500.
Magnesium hydroxide according to claim 1, which has a particle diameter of 0 Å. (5) The magnesium hydroxide according to claim 1, wherein the oil absorption amount of the secondary particles is 70 ml/100 g or less. (8) The magnesium hydroxide according to claim 4, wherein the scale-like primary particles are oriented substantially radially outward from the center of the secondary particles. (7) The magnesium hydroxide according to claim 1, wherein the cumulative pore volume of pores of 0.5 μ or less inside the secondary particles is 0.1 cc/g or less. (8) React an aqueous solution containing a water-soluble magnesium salt with ammonia so that the crystallization load of magnesium oxide is 500 kg/m^3・h or less and the concentration of magnesium hydroxide slurry in the crystallizer is 1 to 60 wt. %, and the average particle size of secondary particles formed by aggregation of primary particles is 5 to 5.
A method for producing magnesium hydroxide, which comprises crystallizing magnesium hydroxide with a specific surface area of 00μ and a specific surface area of 25 to 1 m^2/g. (9) 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.