JP2656443B2 - Method for producing magnesium hydroxide - Google Patents

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 magnesium hydroxide used as an alkaline agent for flue gas desulfurization or for neutralizing waste water.

[0002]

2. Description of the Related Art Magnesium hydroxide used for flue gas desulfurization or as an alkali agent for neutralizing wastewater is conventionally produced by reacting bittern (MgCl ₂ ) in seawater with slaked lime (Ca (OH) ₂ ). Was common. However, this method is to remove a small amount of bittern contained in seawater, it must treat a large amount of seawater, poor production efficiency,
Manufacturing equipment also required large equipment. Instead of this method, recently, a method has been developed in which natural magnesite is calcined to produce lightly burned magnesite (MgO) and then reacted with water (slaking reaction) to produce magnesium hydroxide. . In this method, the raw natural magnesite is converted to 80
It is calcined at 0 to 1000 ° C. for 4 to 5 hours to produce lightly burned magnesite, which has a particle size of 45 μm or less and an average particle size of 5 to 10 μm.
m, and is reacted with water (slaking reaction) at a temperature of 40 ° C. or higher to obtain magnesium hydroxide.

The step of reacting lightly burned magnesite with water is performed by mixing ground lightly burned magnesite with water and heating the mixture to a predetermined temperature while stirring. The average particle size is 8 μm, and the average particle size of magnesium hydroxide produced from conventional seawater is 3 μm
Since it is coarser, sedimentation and agglomeration are liable to occur, and the higher the concentration, the higher the viscosity. Therefore, an alkali treatment method (Japanese Patent Publication No. 3-60774) in which sodium hydroxide is added to adjust the pH to 11 or more and then a slaking reaction is performed.

[0004] However, magnesite as a raw material is a natural product, and it cannot be completely solved by this. The magnesite is commonly known in Haicheng District, Liaoning Province, China and Xiuyan District, but there is a great difference in the components in the magnesite and the crystal form depending on these producing places.
The crystals of magnesite from Haicheng district are fine and earthy amorphous, while the crystals of magnesite from Xiuyan district are:
It is coarse crystalline. There is also a difference in the crystal form when calcined and lightly fired magnesite, and the viscosity of the sodium hydroxide slurry obtained by slaking reaction using lightly fired magnesite from the Kaishiro district by the method of Japanese Patent Publication No. 3-60774 is as follows. , 3-8 times higher viscosity than when using lightly fired magnesite produced in the Xiuyan area.

[0005] As a measure for solving this drawback, an acid treatment method in which sulfuric acid is added to form an acidic solution and the reaction is carried out (Japanese Patent Laid-Open No. 3-25211) has been proposed. However, this method has enabled the production of a high-concentration magnesium hydroxide slurry, but has a disadvantage that aggregation and sedimentation are likely to occur because the surface charge of the particles in the slurry is neutralized. Also, a method of adding a carboxylic acid-based surfactant instead of sodium hydroxide or sulfuric acid after the start of the slaking reaction (Japanese Patent Laid-Open No. 5-2 / 1993)
No. 08810) has been proposed, but the viscosity of the resulting magnesium hydroxide slurry is not significantly reduced, and a large amount of a surfactant must be added to reduce the viscosity sufficiently, which is not economically preferable.

[0006]

SUMMARY OF THE INVENTION The present invention is applied to any conventional magnesite in the process of producing magnesium hydroxide from lightly burned magnesite, which is less affected by the origin and properties of the raw material magnesite. Provided is a method capable of preventing the aggregation of particles by reducing the viscosity of the produced magnesium hydroxide slurry without using dangerous hazardous substances.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on the process for producing magnesium hydroxide from lightly burned magnesite, and as a result, have found that the reaction (slaking reaction) between lightly burned magnesite and water has occurred. It has been found that the purpose can be achieved by adding a specific polymer having a dispersing function, and the present invention has been accomplished based on this finding. That is, the present invention relates to a process of adding water to lightly burned magnesite and subjecting it to a slaking reaction with stirring to produce magnesium hydroxide, wherein an acrylic acid homopolymer or a salt thereof is used.
Acrylate containing acrylic acid at least 50 mole% - consisting copolymer or a salt thereof, maleic acid copolymer, or a salt thereof, acrylic acid containing substantially 80 mol% or more of A acrylic acid with other copolymerizable monomers At least one of the acrylic acid polymers selected from the group is dissolved in part or all of the water in advance, and then the light-burned magnesite is added to the acrylic acid polymer in an amount of 0.1% by weight.
Ratio of 0.1 to 0.15% by weight, preferably 0.02%
A method for producing magnesium hydroxide, comprising adding and mixing at a ratio of up to 0.09% by weight to cause a slaking reaction.

The production of magnesium hydroxide is achieved by mixing lightly burned magnesite finely pulverized to about 45 μm or less and water and stirring the mixture at a predetermined temperature for a predetermined time. The present invention adds a predetermined amount of the acrylic acid-based polymer to water in advance,
Dissolve, add lightly-baked magnesite to this, mix,
This is what causes a slaking reaction. The acrylic acid polymer used in the present invention preferably has a molecular weight of 800 to 2,000.
0, more preferably 1,000 to 10,000. If the molecular weight is less than 800 or more than 20,000, the effect is not sufficiently large. In the acrylic acid-maleic acid copolymer, the composition ratio is such that the molar ratio of acrylic acid in the copolymer is 50% or more, and the molar ratio of acrylic acid in the copolymer of acrylic acid and another copolymerizable monomer is ratio is 80% or more are superior in their effect.

The salt of the acrylic acid polymer is an alkali metal salt such as sodium or potassium, an ammonium salt, or a salt with an amine. Examples of monomers copolymerizable with acrylic acid include itaconic acid, acrylamides, 2-acrylamido-2-methylpropanesulfonic acid, and styrenesulfonic acid. The addition amount of the acrylic acid-based polymer is preferably 0.01 to 0.15% by weight, more preferably 0.02 to 0.09% by weight, based on the lightly burned magnesite. If it is less than 0.01% by weight, the overall effect is not sufficient, and if it exceeds 0.15% by weight, the effect of decreasing the slurry viscosity corresponding to the increase in the added amount is not sufficient, which is economically undesirable.

In carrying out the method of the present invention, the acrylic acid-based polymer of the present invention is dissolved in water, light-burned magnesite is added thereto and mixed, and then the mixture is heated to 40 to 60 ° C. When the reaction starts, the temperature rises due to reaction heat as the reaction proceeds, and the slaking reaction proceeds more smoothly. Usually, the slaking reaction is completed at 95 ° C. or higher for 2 to 3 hours. The slack rate does not increase so much even if it takes more time.

[0011]

[Analysis method]

1) Concentration of solid content: Put the slurry in an evaporating dish, about 120 ° C
For 3 hours to obtain a solid component. 2) Viscosity: The liquid temperature was kept at 20 ° C, and the rotor No. was measured with a B-type viscometer. 3. Measured under the condition of a rotation speed of 60 rpm. 3) pH: Measured with a pH meter. 4) Measurement of adhesion: 200 g of magnesium hydroxide slurry was placed in a 200 ml measuring cylinder, stoppered, and
After vigorous shaking, the graduated cylinder was tilted and the content was poured out, and the content was determined from the weight of the residual slurry at the time when the continuous outflow of the slurry stopped.

5) Particle size distribution: Measured with a particle size distribution analyzer (Sedigraph, Shimadzu Corporation). 6) Composition analysis: The filtered and dried solid component * was measured at 2θ = 5 to 70 using an X-ray diffractometer. 7) Slaking rate: A thermogravimetric change at 250 to 500 ° C. of the filtered and dried solid component * was measured by a differential thermal analyzer. As a comparison, using a general reagent, magnesium hydroxide, a comparison was made with the thermogravimetric change at the same temperature. Filtration and drying of the solid component *: The slurry was suction-filtered, and the obtained cake was dried at about 120 ° C./2 hours. After cooling in a desiccator, it was crushed to 200 mesh with a mortar to obtain a sample for measurement.

[Test 1] (Example of production of magnesium hydroxide slurry in actual apparatus) 23 tons of industrial water was put into a 30 m ³ dissolution tank equipped with a stirrer, and 4.5 kg of sodium polyacrylate (molecular weight 5000) was added. (In terms of solid content) was added and dissolved. After that, 11 tons of pulverized lightly burned magnesite was charged to obtain a uniform slurry. Transfer to the reaction tank and stir at about 50 ° C
, And then the heating was stopped and stirring was continued.
Due to the self-reaction, the temperature rises to about 95 ° C.
It was kept under stirring for hours. Table 1 shows the properties of the produced magnesium hydroxide slurry.

[0014]

[Test 2] (Comparison of effects of various additives and timing of addition) Lightly burned magnesite (MgO) at room temperature in a 1-liter autoclave equipped with a stirrer
300 g were dispersed in 700 g of tap water. At this time, the additives (acrylic acid-based polymer, sodium hydroxide) were dissolved in tap water in advance to disperse the light-burned magnesite (addition time: "before" addition), or the light-burned magnesite was dispersed. Two cases of post-addition (addition time: "post" addition) were performed. Heating was started while stirring the dispersion at 600 rpm, the temperature was allowed to reach 100 ° C. in about 30 minutes, and then stirring was continued at 100 ° C. for 3 hours. Allow to cool for 1 hour while stirring, take out magnesium hydroxide slurry, viscosity,
The adhesion was measured. The light magnesite used was from the Xiuyan area of Liaoning Province, China.

[0016] From the results in Tables 2 and 3, it can be seen that the effect of the additive of the present invention is further improved by the prior addition. Even if the same additive is used, the effect of the post-addition is not sufficient, and a larger amount of addition is required to obtain the same effect as the pre-addition.
Further, an effect higher than that of sodium hydroxide can be obtained. In addition,
FIG. 1 shows that the additive of the present invention has a remarkable effect of lowering the viscosity of lightly burned magnesite slurry by pre-addition as compared to post-addition.

[Test 3] (Effects due to differences in the production area of raw magnesite) Example 2
In the same manner as described above, magnesium hydroxide slurries were produced using lightly burned magnesites produced from the Haicheng district and Liaoning province of Liaoning Province, China, respectively. Table 4 shows the viscosity, pH and slaking rate of the obtained slurry. From this result, in the conventional method using sodium hydroxide, the viscosity of the magnesium hydroxide slurry obtained by the difference in the production place of the lightly burned magnesite of the raw material greatly differs,
Lightly fired magnesite from the Kaishiro district had too high a viscosity and could not be practically adopted because of its handling.
By using the method of the present invention, it is understood that there is substantially no influence of the lightly-burned magnesite of the raw material, and the same method is used to produce a magnesium hydroxide slurry of the same quality from any of the lightly-burned magnesite, and there is no limitation on the production area. .

[0018]

The advantages of magnesium hydroxide production by the method of the present invention are as follows: the magnesium hydroxide slurry has a low viscosity at a low addition amount, and is easy to handle, and is affected by differences in the origin and properties of the raw material magnesite. Is small, so that a uniform magnesium hydroxide slurry can be produced by the same processing method for all the raw materials, and no harmful substances such as sodium hydroxide and sulfuric acid are used, which is preferable in terms of work safety.

[Brief description of the drawings]

FIG. 1 shows the effect of light-burned magnesite slurry viscosity on the amount of polyacrylic acid (molecular weight 5,000) (ppm relative to the weight of light-burned magnesite).

Claims (3)

(57) [Claims] In the step of adding magnesium to lightly burned magnesite and subjecting it to slaking reaction with stirring to produce magnesium hydroxide, an acrylic acid homopolymer or a salt thereof is used.
Acrylate containing acrylic acid at least 50 mole% - consisting copolymer or a salt thereof, maleic acid copolymer, or a salt thereof, acrylic acid containing substantially 80 mol% or more of A acrylic acid with other copolymerizable monomers At least one of the acrylic acid polymers selected from the group is dissolved in part or all of the water in advance, and then the light-burned magnesite is added to the acrylic acid-based polymer in an amount of 0.1% by weight.
A method for producing magnesium hydroxide, comprising adding and mixing at a ratio of 01 to 0.15% by weight to cause a slaking reaction. 2. The acrylic acid-based polymer according to claim 1, which is present in an amount of 0.02 to 0.09% by weight based on the weight of the light-burned magnesite.
A method for producing magnesium hydroxide, characterized by adding and mixing at a ratio of: 3. The molecular weight of the acrylic acid polymer is 800.
3. The method for producing magnesium hydroxide according to claim 1 or 2, wherein