JPH06206722A - Apparatus for producing active magnesium hydroxide and production process - Google Patents

Abstract

PURPOSE:To quickly and efficiently produce active magnesium hydroxide having low viscosity even at high concentration from light burnt magnesia with small number of steps. CONSTITUTION:Roughly crushed light burnt magnesia is pulverized in wet state with a wet pulverizer 5 and hydrated in the presence of an alkaline aqueous medium heated at >=70 deg.C. At the same time, fractions coarser than a prescribed particle size are separated by a classifier 10 and recycled to the pulverizer. Pulverization and hydration reaction can be carried out under quick heating by the hydration of light burnt magnesia under wet-pulverization to obtain a slurry having low viscosity even at a high concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to light burned magnesia,
The present invention relates to an apparatus and method for producing active magnesium hydroxide useful as a neutralizing agent and a desulfurizing agent.

[0002]

2. Description of the Related Art Magnesium hydroxide is used for flue gas desulfurization and neutralization of waste water. This magnesium hydroxide is conventionally manufactured using magnesium chloride in seawater as a raw material. However, the content of magnesium in seawater is very small, and the manufacturing process is complicated. Moreover, since the slurry containing magnesium hydroxide has a concentration of about 30% by weight, it has a high viscosity, resulting in high manufacturing and transportation costs.

On the other hand, a method of hydrating light-burned magnesia obtained by burning natural magnesite is also known. For example, Japanese Examined Patent Publication No. 3-60774 discloses an active magnesium hydroxide that hydrates naturally-burned magnesite and finely pulverizes lightly baked magnesia and water while heating at pH 11 or higher to 85 ° C. or higher. A manufacturing method is disclosed. By this method, active magnesium hydroxide having a high solubility in water and a high hydration rate and a high reaction rate with an acid can be obtained.

However, according to this method, not only it takes a long time to pulverize the lightly burned magnesia, but also large-scale equipment is required for mass production. Moreover, in order to increase the hydration rate, it is necessary to use a finely pulverized product of about 1 to 30 μm obtained by finely pulverizing and classifying lightly burned magnesia. Further, powder is scattered along with the pulverization and classification, and the working environment is contaminated, which is not preferable in terms of safety and hygiene. Furthermore, the obtained magnesium hydroxide has a wide range of particle diameters of about 1 to 40 μm, so that it is difficult to obtain magnesium hydroxide of uniform quality.

Further, the fine powder of light-burned magnesia tends to agglomerate due to humidity and water to form a lump. Once the lumps are formed, it is difficult to uniformly hydrate the lumps of light-burned magnesia within a short time.

Further, it requires a fine pulverization step, a classification step, and a hydration step, so that it is difficult to increase the productivity.

[0007]

Therefore, an object of the present invention is to easily and finely pulverize lightly burned magnesia in a short time without contaminating the working environment, and to hydrate it uniformly and efficiently in a short time. An object of the present invention is to provide a manufacturing apparatus and a manufacturing method capable of obtaining magnesium hydroxide having a uniform quality.

Another object of the present invention is to provide an apparatus and method capable of producing highly active magnesium hydroxide which can be rapidly and efficiently hydrated in a small number of steps.

Still another object of the present invention is to provide an apparatus and method capable of producing an active magnesium hydroxide slurry having a low viscosity even at a high concentration.

[0010]

The present inventor has made earnest studies as a result of paying attention to the fact that the hardness of a hydroxide such as magnesium hydroxide is lower than that of an oxide such as light-burned magnesia and that it is easily crushed. It was found that when the coarsely pulverized product of light-burned magnesia was wet-milled in the presence, it was possible to efficiently pulverize into a particle size having a sharp particle size distribution in a short time, and there was no scattering or aggregation of the powder. In particular, it has been found that when wet pulverization is performed in the presence of a heated alkaline aqueous medium, the pulverization and hydration reaction of light-burned magnesia proceed rapidly, and a slurry having a low viscosity is obtained even at a high concentration. The present invention is
It was completed based on these findings.

That is, the production apparatus of the present invention for producing active magnesium hydroxide comprises a wet pulverizing means for wet pulverizing lightly burned magnesia and a lightly pulverized pulverized product in the presence of a heated alkaline aqueous medium. And a reactor for hydrating magnesia.

Another manufacturing apparatus of the present invention is a wet crushing means for wet crushing light burned magnesia, a supplying means for supplying water and an alkali to the crushing means, and a reaction system in the wet crushing means. And heating means for heating. This apparatus may be provided with a classifying means and a recycling means for circulating a pulverized material having a predetermined particle size or more to the pulverizing means.

Further, in the method of the present invention for producing active magnesium hydroxide, lightly calcined magnesia is wet-ground and hydrated at a temperature of 70 ° C. or higher in the presence of an alkaline aqueous medium. In another method, lightly baked magnesia is hydrated in the presence of an alkaline aqueous medium at a temperature of 70 ° C. or higher while wet grinding. In this method, light burned magnesia may be added to an alkaline aqueous medium at 70 ° C. or higher and hydrated while wet pulverizing.

The present invention will be described in detail below with reference to the accompanying drawings as needed.

FIG. 1 is a schematic block diagram showing an example of the manufacturing apparatus of the present invention, and FIG. 2 is a partially cutaway schematic view showing a wet crusher of the apparatus of FIG.

This device comprises a wet crusher 5. As shown in FIG. 2, the wet crusher 5 includes a screw 2 rotatably arranged in a casing 1, and the screw 2
It has a motor 3 for rotationally driving and a grinding medium 4 loaded in the casing 1. A coarse crushed product of lightly burned magnesia is supplied to the wet crusher 5 from a hopper 6 at a predetermined ratio.

In order to hydrate the coarsely crushed light burned magnesia in the wet crusher 5 while wet crushing it, the wet crusher 5 has a supply line 7a for supplying water and a supply line for supplying alkali. 7b and a steam supply line 8 for heating the inside of the wet pulverizer 5 are connected. Also,
A discharge line 9 for discharging the slurry containing the generated magnesium hydroxide particles is provided above the wet crusher 5.
Are connected.

A classifier 10 is attached to the discharge line 9 for selecting particles of magnesium hydroxide pulverized and hydrated to a predetermined particle size. Moreover, since the coarse particles are recycled to the wet crusher 5, the classifier 1
0 and the wet crusher 5 are connected by a recycle line 11. Further, the slurry containing magnesium hydroxide classified into a predetermined particle size by the classifier 10 is sent to the aging tank 12. The magnesium hydroxide slurry aged in the aging tank 12 is transferred by the pump 13 and is commercialized.

In such a wet crusher 5, the screw 2
The grinding medium 4 rises along the blades of the screw 2 in accordance with the rotation of, and the coarsely pulverized product of lightly burned magnesia is finely pulverized in the process. At that time, the light-baked magnesia can be crushed while being heated by steam while supplying water and alkali from the supply lines 7a and 7b, so that the hydration reaction can be carried out in the crushing process, and the predetermined particles can be efficiently supplied in a short time. A slurry containing magnesium hydroxide having a diameter can be continuously produced.

More specifically, when light burned magnesia comes into contact with an aqueous alkali solution, hydration reaction produces magnesium hydroxide. This magnesium hydroxide has a lower hardness than light burned magnesia. This means that the hardness of naturally-produced magnesia (periclase) is about 5.5 to 6.5, whereas the hardness of naturally-produced magnesium hydroxide (brucite) is about 2.5. It is clear from this. Moreover, since the cohesive force of the particles becomes smaller in the aqueous medium, the particles can be pulverized smoothly. If a shear force is applied to the light-burning magnesia by wet crushing, the crushing of the light-burning magnesia, the desorption / crushing of the magnesium hydroxide formed on the surface, and the renewal of the light-burning magnesia surface may occur in parallel. Thus, a high-concentration slurry containing magnesium hydroxide having a predetermined particle size can be efficiently obtained.

The wet grindability and hydratability of magnesia are
It is very different from light lime (calcium oxide). That is, the Mohs hardness of calcium hydroxide is about 4, the reactivity of calcium oxide with water is higher than that of light burned magnesia, and calcium hydroxide is naturally generated along with an exothermic reaction in water. Therefore, even if the calcium oxide is not pulverized, the hydration of calcium oxide can be smoothly carried out in water with spontaneous disintegration and high heat generation, and fine particles of calcium hydroxide are produced. Therefore, dry hydration and wet pulverization are not always necessary for hydration of calcium oxide.

The number of revolutions of the screw and the peripheral speed of the stirring blade can be appropriately selected within a range that does not adversely affect the wet pulverizability. The rotation speed of the screw is, for example, about 30 to 50.
0 rpm, preferably about 50 to 300 rpm, more preferably about 50 to 300 rpm. The peripheral speed of the stirring blade is, for example, about 0.5 to 10 m / sec, preferably about 1
-8 m / sec, more preferably 2-4 m / sec.

For flue gas desulfurization and neutralization, magnesium hydroxide is usually marketed as a slurry of about 30% by weight. Therefore, simply adjusting the water supply
Magnesium hydroxide can be used as a slurry as it is. Since it is crushed in an aqueous medium, generation of dust can be prevented, and aggregation of crushed products can be prevented as in the conventional case.

Further, frictional heat is generated along with the pulverization, and reaction heat is also generated along with the hydration reaction of light burned magnesia. Therefore, the frictional heat and the reaction heat can be effectively used for the hydration reaction of lightly burned magnesia, and not only can the hydration reaction and fine pulverization be promoted, but also the amount of steam used and eventually the energy cost can be reduced. For example, the temperature in the wet pulverizer 5 can be raised to about 50 to 60 ° C. by the friction heat associated with the pulverization and the reaction heat associated with the hydration reaction. Further, since lightly burned magnesia may be roughly crushed, it is possible to reduce energy required for fine pulverization, which has been conventionally required.

Further, the fine particles are conveyed by the upward flow generated inside the wet pulverizer 5 and reach the discharge line 9. Therefore, a classification effect of fine particles occurs inside the wet pulverizer 5. Even if the slurry from the discharge line 9 contains coarse particles, the coarse particles are classified by the classifier 10.
It can be recycled to the wet crusher 5 through the recycling line 11. Therefore, the magnesium hydroxide slurry having a predetermined particle size can be stored in the aging tank 12. Further, even if the fine particles are not hydrated from the wet pulverizer 5 to the ripening tank 12, the fine particles can be hydrated in the aging tank 12, so that no problem occurs. In addition,
Lightly burned magnesia is usually finely pulverized during the process of circulating the wet pulverizer 5 a plurality of times.

The slurry thus obtained has the characteristic that the viscosity is extremely low even if the concentration is high. That is, the particle size of magnesium hydroxide obtained by using seawater magnesium as a raw material is about 4 to 10 μm, and its slurry viscosity is 1000 cp even if the concentration is about 30% by weight.
It has a high viscosity of about s. In addition, lightly baked magnesia and water finely pulverized to 1 to 30 μm (300 mesh or less),
Magnesium hydroxide obtained by hydrating while heating to pH 11 or higher and 85 ° C. or higher shows a broad particle size distribution of about 1 to 40 μm, and the average particle size is usually 10 to 15 μm.
The slurry viscosity is 40 at a concentration of 30% by weight.
It is about 0 cps.

On the other hand, according to the apparatus and method of the present invention, the slurry viscosity is 200 cps at the concentration of 30% by weight.
Hereafter, a magnesium hydroxide slurry of about 50 to 200 cps is preferably obtained.

It is considered that this is because the particle shape greatly affects the slurry viscosity. That is, when the generated magnesium hydroxide is observed with a microscope, fine particles having a particle size of 5 to 6 μm or less are aggregated, and a sharp particle size distribution of about 5 to 20 μm is shown. In addition, the average particle size of the agglomerates of magnesium hydroxide fine particles is usually 10
It is about 25 μm, preferably about 12 to 20 μm. In this way, the primary particles of magnesium hydroxide are minute,
And even at high concentration, it shows extremely low viscosity. Moreover, since the aggregated particles are easily redispersed by external force,
When neutralizing or desulfurizing, fine primary particles of active magnesium hydroxide are involved and do not impair the neutralization reaction.

Therefore, the magnesium hydroxide obtained by the apparatus and method of the present invention is excellent in the fluidity of the slurry and can improve the workability such as storage of the slurry and pipe transportation. Further, since the slurry viscosity is small, the concentration can be increased to about 50% by weight, and the transportation and storage costs can be greatly reduced.

As the light-burning magnesia, natural magnesite (periclase) is used at a temperature of 550 to 1500.
C., preferably 650 to 1300.degree. C., and more preferably 800 to 1200.degree. If the firing temperature is deviated, the activity of magnesium hydroxide will decrease.

In the present invention, it is not necessary to use the fine powder of light-burned magnesia which has been finely pulverized to a predetermined particle size. Therefore, the size of the light burned magnesia can be selected in a wide range in which wet pulverization is possible, and for example, a coarse pulverized product having a maximum grain size of 10 mm or less and an average grain size of 0.5 to 3 mm can be used. In addition,
Light burned magnesia often uses a coarsely pulverized product of 10 mesh or less in order to enhance the pulverization efficiency.

As the wet crushing means, various devices such as a sand mill and an attritor capable of continuously crushing light burned magnesia in an aqueous medium can be used. Furthermore, the wet crusher is not limited to a continuous crusher that continuously crushes light-burning magnesia,
It may be a batch type crusher such as a ball mill or a kneader. Specific examples of preferable wet crushing means capable of continuous wet crushing include Kubota Tower Mill (manufactured by Kubota Corporation). A continuous wet mill is described in US Pat. No. 426.
No. 9808 describes it as a vertical grinding mill.

Unlike the combination of dry pulverization and hydration, when wet pulverization and hydration are simultaneously performed by a wet pulverizer, the pulverization time, the peripheral speed of a stirring blade, etc. are controlled to obtain, for example, a particle diameter of 0. It is also possible to efficiently generate fine particles of magnesium hydroxide having a size of about 5 to 2 μm.

The type of the heating means is not particularly limited, but the temperature of the reaction system is 70 ° C. or higher, preferably 85 to 12
0 ° C, more preferably 90 to 110 ° C, especially 95 to 1
Various heating means capable of heating to about 05 ° C. are preferable. When wet grinding in an alkaline aqueous medium at such a temperature,
Lightly burned magnesia and alkali can be crushed while rapidly reacting, and as described above, a slurry having a low viscosity can be efficiently obtained even at a high concentration.

In the present invention, it is not necessary to simultaneously perform the crushing of the coarsely crushed light burned magnesia and the hydration reaction of the light burned magnesia in the wet crusher. That is, the apparatus of the present invention may be provided with a wet pulverizing means for wet pulverizing the light burned magnesia, and a reactor for hydrating the crushed light burned magnesia in the presence of the heated alkaline aqueous medium. Good. In this apparatus, heating means such as steam is usually connected to the reactor. In this apparatus, the temperatures of the wet pulverization system and the reaction system may be different as long as the reaction system is heated. The structure of the reactor is not particularly limited, and a normal reactor such as a stirring tank equipped with a rotatable stirring blade can be used.

Water and alkali may be supplied individually or as an aqueous alkali solution. The alkali may be supplied as a high-concentration aqueous solution. Alkali is often supplied as an aqueous solution of, for example, about 10 to 50% by weight. The heating means may heat at least one component of light burned magnesia, water and alkali, which are components of the reaction system, to raise the temperature of the reaction system, but usually, water or an alkaline aqueous solution which is used in a large amount is preheated. Is preferred. If steam is directly blown into the reaction system, it can be heated simply and quickly. Further, water or an alkaline aqueous solution may be heated and supplied to the reaction system.

The classifying means can be constituted by a conventional classifier equipped with a screen mesh or the like, and the degree of classification can be appropriately selected according to the desired particle size of magnesium hydroxide. The classification means is usually 20 μm
In many cases, it is set so as to restrict the passage of particles that pass over.

One method of the present invention comprises a step of wet-milling light-burned magnesia and a hydration step of hydrating the pulverized product in the presence of an alkaline aqueous medium.

The pH of the alkaline aqueous medium can be selected within a range capable of efficiently hydrating light burned magnesia, and is 11 or more,
It is preferably 11.5 or more, more preferably 12 or more. If the pH is less than 11, the hydration reaction rate is low and the yield of highly active magnesium hydroxide is reduced.

As the alkali, for example, hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide are frequently used. Further, water is often used as the aqueous medium.

The ratio of light burned magnesia and water can be selected according to the slurry concentration and the like. For example, light burned magnesia 1
Water is 100 to 400 parts by weight, preferably 150 to 300 parts by weight, relative to 00 parts by weight.

The amount of alkali used may be any amount that can adjust the pH of the reaction system. The amount of alkali used varies depending on the type of alkali, but when sodium hydroxide is used, it is, for example, 0.75 to 1.25 parts by weight, preferably 0.9 to 1.1, relative to 100 parts by weight of light burned magnesia.
It is about part by weight.

The reaction temperature in the hydration step is 70 ° C. or higher, preferably 85 to 120 ° C., more preferably 90 ° C.
To 110 ° C, particularly preferably 95 to 110 ° C. If the reaction temperature is lower than 70 ° C, the hydration reaction rate will decrease.

Further, in the hydration reaction, for example, 8
5 to 120 ° C., preferably 90 to 110 ° C., more preferably about 95 to 110 ° C. in water or an alkaline aqueous solution,
It is preferable that the wet pulverized product of light burned magnesia is continuously or intermittently added and mixed, and the wet pulverized product of light burned magnesia is rapidly heated to be hydrated.

In the above method, the hydration reaction time is usually 45 minutes to 2 hours, preferably 1 to 2 hours.

In another preferred method, the lightly ground magnesia coarsely ground product is wet-hydrated in the presence of an alkaline aqueous medium. That is, in such a method, the crushing of light-burned magnesia and the hydration reaction can be carried out at the same time, and an active magnesium hydroxide slurry having a low viscosity even at a high concentration can be efficiently produced within a short time. In addition, the hydration reaction can proceed smoothly even when the reaction temperature is lower than in the conventional method.

In particular, it is preferable that the wet pulverization and hydration reaction of light burned magnesia be rapidly advanced at a high temperature. In this case, 70 ° C. or higher, preferably 85 to 120 ° C., more preferably 90 to 110 ° C., and further preferably 95 to 11
Light burned magnesia may be wet-milled in the presence of water or an alkaline aqueous medium heated to a temperature of about 0 ° C.

In a preferred method, alkali and lightly burned magnesia are added to water at 70 ° C. or higher, and hydrated while wet pulverizing.

According to the method in which the wet pulverization and the hydration reaction proceed at the same time, a highly active magnesium hydroxide slurry can be obtained within an extremely short time as compared with the conventional method in which the hydration reaction requires 2-3 hours. can get. More specifically, when the wet pulverization and the hydration reaction are continuously carried out, after about 20 minutes have passed from the start of the pulverization, the activated magnesium hydroxide slurry is continuously produced and the batch process is carried out. But 4
Active magnesium hydroxide can be obtained in about 0 minutes. The wet pulverization and hydration reaction are usually sufficient for about 1 hour to obtain active magnesium hydroxide.

The slurry produced by the hydration reaction is
It may be supplied to the aging tank to complete the hydration reaction. After the hydration reaction, a magnesium hydroxide slurry can usually be obtained by cooling. The concentration of the magnesium hydroxide slurry may be controlled by adjusting the amount of water during the hydration reaction or adjusting the amount of water in the aging tank. Further, the concentration of the magnesium hydroxide slurry may be controlled by dilution or concentration.

[0051]

According to the apparatus and method of the present invention, since light burned magnesia is wet-milled, the light burned magnesia can be easily and finely milled within a short time without contaminating the working environment, and can be uniformly and shortly It can be hydrated efficiently in time and can obtain magnesium hydroxide of uniform quality.

When the wet pulverization and the hydration reaction are carried out at the same time, hydration can be carried out rapidly and efficiently with a small number of steps, and active magnesium hydroxide having high activity can be produced.

Further, when the wet pulverization and the hydration reaction are carried out simultaneously, activated magnesium hydroxide having a low viscosity can be efficiently produced even at a high concentration.

[0054]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 A small kneader (capacity 10 liters) having a jacket on three sides was charged with 700 g of water, and the jacket was 2.5 k.
Steam was blown at g / cm ² and the water was heated to 90 ° C. Then, 240 g of lightly burned magnesia coarse particles having a maximum particle size of 10 mm or less and 2.4 g of sodium hydroxide were charged, and the mixture was heated and kneaded for 1 hour and then cooled to obtain a magnesium hydroxide slurry.

The slurry thus obtained had a hydration ratio of lightly burned magnesia of 97% and was almost completely hydrolyzed to have an average particle size of 17
It contained magnesium hydroxide having a particle size distribution width of 5 to 20 μm. Further, when the particles in the slurry were observed with a microscope, fine particles of about 5 μm were aggregated. And
The viscosity of the 30 wt% slurry was 110 cps (20 ° C.) as measured by a B-type viscometer.

Example 2 Kubota Tower Mill (Kubota Co., Ltd.) as a wet small crusher equipped with a classifier for restricting passage of particles of 20 μm or more.
Manufactured by KM-5) was charged with 105 kg of water and heated with steam to heat the water to 90 ° C. Next, 35 kg of lightly burned magnesia coarse particles having a maximum particle size of 10 mm or less and 350 g of sodium hydroxide were added and reacted while wet pulverizing. The specifications of the wet mill are a tower diameter of 440 mm and a tower height of 830 mm. Particles having a size of more than 20 μm were circulated to the wet pulverizer by a classifier. Wet grinding uses a screw rotation speed of 85 rp
m, an iron ball (diameter 20 mmφ) as a grinding medium, and a charging amount of the grinding medium of 350 kg.

Then, the wet pulverizer was operated for 40 minutes.
The resulting slurry was aged at 85 ° C. for 1 hour and cooled to obtain a magnesium hydroxide slurry.

The obtained slurry had a hydration ratio of lightly burned magnesia of 98% and was almost completely hydrolyzed to have an average particle size of 14
It contained magnesium hydroxide having a particle size distribution width of 5 to 20 μm. Further, when the particles in the slurry were observed with a microscope, fine particles of about 5 μm were aggregated. And
When the viscosity of the slurry having a concentration of 30% by weight was measured with a B-type viscometer, it was 100 cps (20 ° C.).

Further, in order to examine the wet crushing efficiency of the wet crusher, except that the wet crusher is operated for 2 hours,
Wet grinding was performed in the same manner as above. The resulting slurry is
It contained magnesium hydroxide having an average particle size of 1.5 μm and a particle size distribution width of 0.7 to 3.3 μm.

Comparative Example 1 Using the small kneader of Example 1, wet milling was carried out in the same manner as in Example 1 without adding sodium hydroxide and without heating. The temperature finally increased to 60 ° C. by this wet pulverization. The obtained slurry has a hydration ratio of lightly magnesia of 40% and an average particle size of 30 μm.
m particles.

Comparative Example 2 Using the wet pulverizer of Example 2, wet pulverization was carried out in the same manner as in Example 2 without adding sodium hydroxide and without heating. The obtained slurry had a hydration ratio of light burned magnesia of 45% and contained particles having an average particle size of 25 μm.

Comparative Example 3 Light burned magnesia 2 finely pulverized to a particle size of 5 to 30 μm in an aqueous solution in which 2.4 g of sodium hydroxide was dissolved in 700 g of water.
40 g was added, heated to 90 ° C. with stirring and hydrated for 3 hours. After the reaction was completed, it was cooled to obtain a magnesium hydroxide slurry.

The obtained slurry had a hydration ratio of lightly burned magnesia of 97% and was almost completely hydrolyzed, and had an average particle size of about 1
It contained magnesium hydroxide having a particle size distribution width of 1 to 40 μm. Moreover, when the viscosity of the slurry having a concentration of 30% by weight was measured with a B-type viscometer, the viscosity was 380 cps (20
℃).

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a manufacturing apparatus of the present invention.

2 is a partially cutaway schematic view showing a wet crusher of the apparatus of FIG. 1. FIG.

[Explanation of symbols]

 5 ... Wet crusher 7a ... Water supply line 7b ... Alkali supply line 8 ... Steam supply line 10 ... Classifier 12 ... Aging tank

Claims (6)

[Claims] 1. Active water comprising wet crushing means for wet crushing light burned magnesia and a reactor for hydrating the crushed light burnt magnesia in the presence of a heated alkaline aqueous medium. Magnesium oxide manufacturing equipment. 2. A wet grinding means for wet grinding light burned magnesia, a supply means for supplying water and alkali to the grinding means, and a heating means for heating a reaction system in the wet grinding means. An apparatus for producing active magnesium hydroxide, which comprises: 3. The activated magnesium hydroxide according to claim 2, further comprising a classifying unit for classifying the pulverized product by the wet pulverizing unit and a recycling unit for circulating the pulverized product having a predetermined particle size or more to the wet pulverizing unit. Manufacturing equipment. 4. A method for producing active magnesium hydroxide, wherein light-burned magnesia is wet-ground and hydrated at a temperature of 70 ° C. or higher in the presence of an alkaline aqueous medium. 5. A method for producing active magnesium hydroxide, which comprises hydrating light-burned magnesia while wet pulverizing it at a temperature of 70 ° C. or higher in the presence of an alkaline aqueous medium. 6. The method for producing active magnesium hydroxide according to claim 5, wherein light burned magnesia is added to an alkaline aqueous medium at 70 ° C. or higher, and hydrated while wet pulverizing.