JPH0867515A - Production of highly active magnesium hydroxide - Google Patents

Abstract

PURPOSE: To obtain a highly active magnesium hydroxide suitable as a neutralizing agent and a desulfurizing agent without adding a strong alkali by baking natural magnesite and grinding to give light burnt magnesia containing specific amounts of MgO an CaO and having a specific grain size and heating a mixture of the light burnt magnesia and water having a specific pH at a specific temperature. CONSTITUTION: Natural magnesite is baked and ground to give light burnt magnesia containing >=90wt.% MgO and 0.5-2wt.% of CaO an having >=75μ particle size. The light burnt magnesia is mixed with water to give a mixture having neutral liquid property of neutrality to <pH11. The mixture is heated to &h85 deg.C. Consequently, highly active magnesium hydroxide suitable as a neutralizing agent and a desulfurizing agent is obtained without using a strong alkali such as caustic soda.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing highly active magnesium hydroxide, and more specifically, it has a high activity which can be used as a neutralizing agent or a desulfurizing agent and can be made into a slurry having a high concentration. The present invention relates to a method for producing highly active magnesium hydroxide, which allows magnesium hydroxide to be obtained without using a strong alkaline agent.

[0002]

2. Description of the Related Art Conventionally, magnesium hydroxide has been used for desulfurization of flue gas and neutralization of waste water. As the magnesium hydroxide for neutralization, magnesium hydroxide produced from magnesium in seawater as a raw material (hereinafter, abbreviated as seawater mug) was often used.

However, the synthetic method using magnesium in seawater as a raw material requires many steps such as decarboxylation, reaction with calcium hydroxide, precipitation, washing, and concentration, and the production steps are complicated and the production efficiency is high. There is a problem that is low.
Further, since the seawater mug produced through such a process contains calcium hydroxide as an impurity, if this is used as a desulfurizing agent, for example, calcium sulfite will be deposited in the desulfurization tower, and frequent operations such as desulfurization will occur. There is a problem that the inside of the desulfurization tower must be cleaned after stopping the operation.

When further concentrated to a slurry, the concentration becomes 3
Even at around 0%, there was a problem that the viscosity was extremely high and transportation and the like became difficult.

In recent years, as a technique for eliminating such inconvenience, light burned magnesite (hereinafter sometimes referred to as light burned mug) obtained by burning naturally produced magnesite (MgCO ₃ ). A technique has been developed for producing magnesium hydroxide suitable for desulfurization of flue gas and neutralization of wastewater by being hydrated under specific conditions.

That is, Japanese Patent Publication No. 3-60774 discloses a conventional drawback in that the light-burning mug has a slow rate of dissolution, and the magnesium hydroxide obtained by soaking the light-burning mug has a slow rate of reaction with acid. A method for producing active magnesium hydroxide using a light-burning mug as a raw material, which has solved the above problem, is disclosed.

However, in this manufacturing method,
Since the light-baked mug is reacted with water at a pH of 11 or higher and at a temperature of 85 ° C. or higher, it is necessary to use a strong alkaline compound, which is dangerous in operation.

Moreover, since the reaction is carried out at a high temperature, there is a possibility that the strongly alkaline reaction liquid will boil due to the heat generated by the self-reaction, and the strongly alkaline reaction liquid will blow up. There's a problem. Furthermore, in order to adjust the pH to 11 or more, it is necessary to add a strong alkali such as caustic soda and calcium hydroxide to the reaction liquid, caustic soda and calcium hydroxide are required, and before the light-burning mug is stored in the reaction tank. A step of dissolving caustic soda, calcium hydroxide, etc. in water is also required.

The present invention has been completed based on the above circumstances. That is, an object of the present invention is to solve the above-mentioned problems, and it is possible to produce a highly active magnesium hydroxide that can be preferably used as a neutralizing agent or a desulfurizing agent without using a strong alkaline compound. It is to provide a method for producing active magnesium hydroxide.

An object of the present invention is to provide a method for producing highly active magnesium hydroxide which does not pose a risk of boiling or blowing up a strongly alkaline reaction solution.

An object of the present invention is to provide a method for producing highly active magnesium hydroxide, the production process of which is further simplified.

Another object of the present invention is to provide a method for producing highly active magnesium hydroxide which can provide highly active magnesium hydroxide at a lower cost.

[0013]

The preferred embodiments of the present invention will be listed below.

The first aspect is obtained by calcining and crushing naturally occurring magnesite and contains at least 90% magnesium oxide and 0.5 to 2% by weight calcium oxide,
And the light-burning magnesia having a particle size of at most 75 μm is mixed with water, and the liquidity of the resulting mixture is neutral to pH.
A method for producing highly active magnesium hydroxide, characterized in that the temperature is within the range of less than 11.0 and is heated to at most 85 ° C., and the second aspect is obtained by firing and crushing natural magnesite, Containing at least 90% magnesium oxide and 0.5-2% by weight soluble calcium oxide,
And the light-burning magnesia having a particle size of at most 75 μm is mixed with water, and the liquidity of the resulting mixture is neutral to pH.
A method for producing highly active magnesium hydroxide, characterized in that the temperature is within the range of less than 11.0 and is heated to at most 85 ° C., and the third aspect is the light burning according to the first or second aspect. A fourth aspect of the present invention is a method for producing highly active magnesium hydroxide in which magnesia and water are mixed at room temperature. The fourth aspect is obtained by firing and crushing naturally occurring magnesite.
A method for producing highly active magnesium hydroxide, which comprises mixing light-burned magnesia, which is an ultrafine powder that passes through a 30-mesh screen, and water, and subjecting it to high-temperature treatment under pressure without adding an alkali agent, In the fifth aspect, in the fourth aspect, the pressure is 1.
5 to 3.5 atm, preferably 2 to 2.5 atm, and the temperature is 110 to 135 ° C., preferably 115 to 130 ° C.,
Particularly preferred is a method for producing highly active magnesium hydroxide, which has a temperature of 120 to 126 ° C. and a high temperature treatment under pressure of 0.3 to 0.5 hours, and the sixth aspect is any one of the first to fifth aspects. In one embodiment, the method for producing highly active magnesium hydroxide, wherein the naturally-occurring magnesite is magnesite produced in Liaoning, China.

The present invention will be described in detail below.

As the light-burning magnesia in the present invention, light-burning magnesia obtained by firing and crushing naturally produced magnesite is used. The natural magnesite is produced in China, North Korea, India, Australia and the like, and the magnesite used in the present invention may be any of the origins. However, among the magnesium produced in each of the above regions, it is preferable to use magnesite produced in China as a raw material. Among the magnesite produced in China, the magnesite produced in Liaoning Province is particularly preferable.

The firing of the magnesite is generally 550
C.-1,500.degree. C., but in this method, 650.degree. C.-1,300.degree. C., particularly 800.degree.
Baking at 200 ° C. is preferred. When the calcination temperature is within the above-mentioned preferable temperature range, lightly calcined magnesia that can be particularly preferably used in the practice of the present invention can be obtained, and particularly highly active magnesium hydroxide having excellent activity against acid is obtained. be able to.

The light-burning magnesia in the present invention contains at least 90% of magnesium oxide, preferably 93 to 99.5%, particularly preferably 97 to 99.5%, and calcium oxide of 0.5 to 2%. %, Preferably 1 to 2%, particularly preferably 1 to 1.5% is used.

In the present invention, among lightly burned magnesia obtained by firing and crushing naturally occurring magnesite,
It is important to select light burned magnesia containing the above proportions of magnesium oxide and calcium oxide.

By selecting the light-burning mag magnesia having such a composition, the light-burning mug can be satisfactorily desolved without adding an alkali agent, and it can be used as a desulfurizing agent. It is possible to produce highly active magnesium hydroxide that does not cause rocks such as gypsum in the desulfurization tower. When the content of calcium oxide exceeds 2%, when the obtained magnesium hydroxide is used as a desulfurizing agent, deposition of calcium sulfite or the like derived from a calcium component may occur in the desulfurization tower, which is preferable. Absent. Conventionally, when using seawater magnesia, since seawater magnesia contains a large amount of calcium hydroxide as an impurity, if magnesium hydroxide obtained from seawater magnesia is used as a desulfurizing agent, calcium sulfite etc. Taking into consideration that the above-mentioned lock occurs, the method of the present invention in which the conventional drawbacks are solved by limiting the content of calcium oxide to a specific range amount and a highly active magnesium hydroxide is obtained is unexpected. That is.

The calcium oxide used in the present invention is water-soluble calcium oxide. In general, calcium oxide may be a concept including a double salt of SiO ₂ and CaO, for example, but such a double salt is not soluble in water and cannot be used as calcium oxide in the present invention. Therefore, it may be appropriate to describe the calcium oxide that can be used in the present invention as soluble calcium oxide, in order to eliminate water-insoluble double salts containing CaO.

In the present invention, the particle size of light burned magnesia is at most 75 μm, preferably 1 to 50.
μm, and particularly preferably 1 to 45 μm. When the particle size of the light-burning magnesia is within the above range, the light-burning magnesia and water can be satisfactorily dissolved without adding an alkali agent, and highly active magnesium hydroxide can be obtained.

Such light-baked magnesia is mixed with water to be hydrated. The mixing ratio of light burned mug and water is
When expressed as a ratio of H ₂ O / MgO, it is usually 2.7 to 3.3.
And preferably 2.3 to 2.7. However, the mixing ratio can be appropriately set according to the concentration of the slurry to be finally obtained.

The water temperature at the start of the soaking reaction, that is, at the time of mixing is preferably room temperature. By setting the water temperature at the time of mixing to room temperature, it is possible to avoid the risk that the liquid boils due to the heat generated by the self-reaction. In particular, the water temperature during mixing is preferably within the range of 1 to 29 ° C.

In the present invention, the p of the reaction solution during the reaction is
H is neutral to less than 11.0 as measured at room temperature by calcium oxide contained in light burned magnesia, and preferably 9
Maintained below ~ 11. When the pH is within the above range,
Light burned magnesia is promoted to be absorbed, and there is no adverse effect such as equipment deterioration due to strong alkali.

The reaction temperature in the soaking reaction is usually 85 ° C.
Less, preferably 30 to less than 85 ° C, preferably 50 to less than 85 ° C, particularly preferably 80 to less than 85 ° C.
It is less than 85 ° C. By setting the reaction temperature within the above range, cleavage of the periclase-type structure of the light-burning mug can be achieved, and slakedness can be accelerated. Further, since the temperature is lower than 85 ° C., boiling of the liquid is prevented.

The slaking reaction is usually continued for 2 hours to 3.5 hours, with the time point when the treatment is started at the time point when the light burned mug and water are mixed. In particular, it is preferable to continue for 2.5 to 3.5 hours. Within this range, the relationship between the progress of the reaction and the time required for the reaction is particularly efficient. Also, although it depends on the mixing ratio of the light burned mug and water, it is also efficient in relation to the progress of the reaction and the energy required to maintain the temperature.

Another aspect of the present invention will be described below.

The composition of light burned magnesia in the present invention is not limited, but light burned magnesia having the same composition as the light burned magnesia described above can be preferably used.

In the present invention, light burned magnesia is crushed before use. The particle size of the lightly baked mug at this time is 1 to 7
It is 5 μm, preferably 1 to 50 μm, and particularly preferably 1 to 45 μm. Light-burning mugs with such grain sizes have meshes of 200, 300, and 3, respectively.
It can be obtained by sieving with a sieve that is 30.

By adopting such an ultrafine powder and further performing a high-temperature treatment under pressure described later, it is possible to satisfactorily dissolve the light-burned magnesia and water without adding an alkali agent.

The mixing ratio of lightly burned magnesia and water in the soaking reaction in the present invention is usually 2.7 to 3.3, preferably 2. 3, when expressed as a ratio of H ₂ O / MgO.
It is 3 to 2.7.

The pH of the mixed solution is not particularly required to be adjusted, but it is preferably maintained at neutral to less than 11.0 measured at room temperature. When the pH is within the above range, it is not necessary to use an alkali-resistant compound, the production cost can be reduced, and the working environment can be made safe. On the other hand, if the pH is set to 11 or more, the alkali-resistant compound must be used, and the working environment deteriorates.

In the present invention, lightly burned magnesia and water are made to dissolve by performing high-temperature treatment under pressure. That is, light-burned magnesia and water are contained and mixed in a pressure-resistant container, and the temperature of the mixed solution inside is 110 to 135.
C, preferably 115-130 C, particularly preferably 12
Increase until 0-126 ° C is reached. In order to raise the temperature, it may be heated by steam, or may be heated by a heater of a heating wire or the like. Further, it is desirable to maintain the pressure in the pressure resistant container at 1.5 to 3.5 atm, preferably 2 to 2.5 atm.

In such a pressurized high temperature treatment, the time point when the light burned magnesia and water are mixed is set as the start point of the treatment, and 0.3
Continue for ~ 0.5 hours.

By such pressurizing and high temperature treatment, pre-MgO in the raw material can be hydrated to highly active magnesia hydroxide in a short time.

In any of the embodiments of the present invention, when the obtained reaction solution is cooled after completion of the reaction, highly active magnesium hydroxide can be obtained as a high-concentration slurry.

[0038]

EXAMPLES The first and second inventions of the present invention will be described more specifically by way of examples. The present invention is not limited to the embodiments, and various modifications can be made as long as the effects of the respective inventions are exhibited.

(Example 1) Capacity 15 with an agitator made of iron
9 m ³ of water was poured into a reaction tank of m ³ , and naturally-produced light-burned magnesianesia (containing 90% or more of magnesium oxide and 1.5% of calcium oxide and having a particle size of 45 μm or less ( 3,600 kg of light-baked magnesianesia having an average particle size of 10 μm) was charged into the reaction tank. When the pH of this mixed solution was measured at room temperature, it was pH 10.8. Next, the mixed liquid was heated with steam to raise the liquid temperature to 75 ° C. While continuing stirring for 2.5 hours, heating by steam was stopped, the liquid temperature was adjusted to 84 ° C., and a soaking reaction was carried out.

After the reaction was completed, the inside of the reaction vessel was cooled to obtain a slurry of highly active magnesium hydroxide. This slurry was analyzed and the results are shown in Table 1. Commercially available magnesium hydroxide produced from seawater was also analyzed, and the results are shown in Table 1.

In Table 1, the viscosity is a value obtained by measuring the viscosity at a liquid temperature of about 20 ° C. using a B-type viscometer (using rotor No. 2), and the particle size distribution uses water as a solvent, It is a value measured with a sedigraph after adjusting the liquid temperature to 34 to 35 ° C.

Further, the slurry was weighed so that the highly active magnesium hydroxide contained was 0.208 mol, and 200 cc (0.2 mol) of 2N sulfuric acid was mixed, and the pH of the mixed solution was adjusted. The time (sec) until reaching 6 was measured. The liquid temperature during the neutralization reaction was 42 ° C. Table 2 shows changes in pH with time after mixing. In addition, commercially available magnesium hydroxide produced from seawater (hereinafter sometimes referred to as seawater mug) was also analyzed, and the results are also shown in Table 2.

(Example 2) Capacity 8 m ³ with iron stirrer
In a pressure-resistant reaction vessel, 5 m ³ of water was poured, and while stirring, natural magnesite was calcined and then crushed to obtain light-burned magnesianesia that passed through a 330-mesh sieve. 2,000 kg of fine powder was added. When the pH of this mixed solution was measured at room temperature, the pH was 10.8.
Met. Then, after sealing the reaction vessel, the temperature of the mixed solution was raised to 126 ° C. with steam to perform high temperature heating treatment. This temperature was maintained for 0.5 hour to allow the quenching reaction to take place. After the reaction was completed, the inside of the reaction tank was cooled to obtain a slurry of highly active magnesium hydroxide. This slurry was analyzed in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

(Comparative Example 1) Capacity 15 with an agitator made of iron
A reaction vessel is m ^3, water 10 m ³ imposition ,, stirred caustic soda 30kg was added with and sufficiently dissolving the. This solution was 12.5. Then, an average particle size of 5 to 30 mμ obtained by firing natural light-burning magnesia
4,000 kg of light-baked magnesianesia (containing 90% magnesium oxide and 1.5% calcium oxide) was further added and sufficiently stirred. After that, while continuing stirring,
The mixed liquid was heated with steam, and when the liquid temperature reached 100 ° C., the heating was stopped. After the addition of the calcined mug, the slag was added for 3 hours. After the reaction was completed, the inside of the reaction tank was cooled to obtain a magnesium hydroxide slurry. This slurry was analyzed in the same manner as in Example 1 above, and the results are shown in Tables 1 and 2.

(Comparative Example 2) Instead of the light burned magnesianesia in Example 1, 90% magnesium oxide and 0.3% calcium oxide were contained, and the average particle size was 10 μm.
Example 1 except that the light-burning magnesianesia which is
A magnesium hydroxide slurry was obtained in the same manner as in. This slurry was analyzed in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

(Comparative Example 3) Instead of the light burned magnesianesia in Example 1, 90% magnesium oxide and 2.5% calcium oxide were contained, and the average particle size was 10 μm.
Example 1 except that the light-burning magnesianesia which is
A magnesium hydroxide slurry was obtained in the same manner as in. This slurry was analyzed in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

(Comparative Example 4) Instead of the light burned magnesianesia in Example 1, 90% magnesium oxide and 1.5% calcium oxide were contained, and the average particle size was 70 μm.
Example 1 except that the light-burning magnesianesia which is
A magnesium hydroxide slurry was obtained in the same manner as in. This slurry was analyzed in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

COMPARATIVE EXAMPLE 5 Instead of the fine powder of light-baked magnesianesia obtained in Example 2 by calcining and crushing the naturally occurring magnesite and passing through a 330-mesh sieve, 120-300. A magnesium hydroxide slurry was obtained in the same manner as in Example 2 except that a mesh particle size product was used. This slurry was analyzed in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

Industrial Applicability According to the present invention, it is possible to provide a method for producing highly active magnesium hydroxide, which is capable of obtaining highly active magnesium hydroxide without adding a strong alkali such as caustic soda to the reaction system.

According to the present invention, it is possible to provide a method for producing highly active magnesium hydroxide, which is capable of obtaining highly active magnesium hydroxide without using a strong alkaline resistant reaction tank or the like.

According to the present invention, the reaction is carried out without adding a strong alkaline agent, and the blowing up of the reaction solution is prevented, so that the high activity magnesium hydroxide avoiding the danger at the time of working, especially at the time of reaction. Can be provided.

According to the present invention, a slurry having a higher concentration than that of magnesium hydroxide produced from seawater can be obtained, which can be easily transported and stored, and can be used as a neutralizing agent or a desulfurizing agent. It is possible to provide a suitable method for producing highly active magnesium hydroxide, which is capable of inexpensively producing highly active magnesium hydroxide.

[0055]

Claims (4)

[Claims] 1. Naturally produced magnesite is calcined and crushed to obtain at least 90% magnesium oxide and 0.5 to 0.5%.
Light burned magnesia containing 2% by weight of calcium oxide and having a particle size of at most 75 μm is mixed with water, and the liquidity of the resulting mixture is adjusted to a range of neutral to pH less than 11.0, A method for producing highly active magnesium hydroxide, characterized in that both are heated to 85 ° C. 2. The method for producing highly active magnesium hydroxide according to claim 1, wherein the lightly burned magnesia and water are mixed at room temperature. 3. A mixture of lightly burned magnesia, which is ultrafine powder obtained by firing and crushing naturally occurring magnesite and passing through a 330-mesh screen, and water, and is pressurized at a high temperature without adding an alkali agent. A method for producing highly active magnesium hydroxide, which comprises subjecting to treatment. 4. The conditions of the pressurized high temperature treatment are a pressure of 1.5 to 3.5 atm and a temperature of 120 to 126.
The method for producing highly active magnesium hydroxide according to claim 3, wherein the method is at a temperature of 0 ° C.