JPH0816012B2 - Preparation method of activated magnesium hydroxide - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for preparing activated magnesium hydroxide. More specifically, the present invention relates to a method for preparing activated magnesium hydroxide suitable for uses such as neutralization of acidic effluent and desulfurization of sulfur oxides in flue gas.

[0002]

2. Description of the Related Art Magnesium hydroxide (seawater mug) obtained from seawater has been used for flue gas desulfurization and neutralization of wastewater. The main reaction for the production of magnesium hydroxide is represented by the following formula. MgCl ₂ + Ca (OH) ₂ → Mg (OH) ₂ + CaC
l ₂ As an alternative to seawater mag, there is light-burning magnesia (calcining mug) obtained by firing natural magnesite (MgCO ₃ ) and sizing or pulverizing. The main reaction for producing the baked mug is represented by the following formula. Magnesium hydroxide obtained by hydrating MgCO ₃ → MgO + CO ₂ MgO + H ₂ O → Mg (OH) ₂ light burned mug is generally called hydromag, and its main composition is represented by a molecular formula:
It is represented by MgO.nH ₂ 0.

[0003]

By the way, the former seawater mug has various processes for producing magnesium hydroxide produced by reacting magnesium chloride contained in seawater with calcium hydroxide using seawater as a raw material. Since it has been concentrated through the process, the process of concentrating and separating magnesium hydroxide (Mg (OH) ₂ ) is complicated, and the viscosity of the slurry obtained by concentration is extremely high, which makes transportation difficult. Have a point. Therefore, the seawater mug has a relatively high manufacturing cost. Further, since the seawater mug contains calcium hydroxide (Ca (OH) ₂ ) as an impurity, if the seawater mug is used as a desulfurizing agent, for example, Ca (OH) ₂ + SO ₂ → CaSO ₃ + H ₂ 0
The reaction, was deposited calcium sulfite solubility is less in the apparatus (CaSO _3), or prone to trouble to the operation of the apparatus, chlorine ions (Cl ^-) for the content of and sulfate ions is high, corrosion Need to address the problem.

On the other hand, in the latter light-burning mug, the viscosity of magnesium hydroxide obtained by the reaction with water is lower than that in the case of seawater mug, so that it is easy to handle and has no relation to seawater as a source. Since it does not contain chlorine ions, etc., it is less corrosive and is advantageous for transportation and storage. Also, in the production, it has an advantage that it can be produced at a lower cost with a simple apparatus as compared with seawater mug, but on the other hand, its solubility and reactivity in water are relatively slow, and the obtained magnesium hydroxide does not react with the acid component. There are drawbacks such as a slow reaction rate.

Therefore, as a method for solving the above-mentioned drawbacks of the light-burning mug, crushed light-burning magnesia obtained by firing natural magnesite and water, and the liquid property thereof are PH1.
There has been proposed a method for synthesizing activated magnesium hydroxide, which is characterized in that it is made 1 or more and is made to dissolve while being heated to 85 ° C or more. However, according to such a synthesis method, caustic soda (NaOH) and potassium hydroxide (KO
H) corresponds to dangerous goods and deleterious substances that are legally handled and controlled, so special storage is required. A storage facility is required, and when handling it, it is obligatory to be managed by the person in charge of handling dangerous materials.

Storage of flakes and pellets of caustic soda and potassium hydroxide is strictly prohibited. In addition, it is necessary to stop contact with air, deliquesce and solidify due to moisture absorption, and It has the property of reacting with carbon gas (CO ₂ ). Further, caustic soda and potassium hydroxide are handled and used in the state of an aqueous solution having a concentration of about 50%, but they are easily frozen in the winter season, and for winter use, it is necessary to keep them warm by forced heating. Since potassium (KOH) is more expensive than caustic soda (NaOH), it is rarely used widely.

[0007] The soaking reaction of the light-burning mug itself is a reaction under basicity, and the addition of caustic soda (NaOH), which is a strong base, theoretically means that common ions (OH ...
・ The tendency to interfere with hydration due to the effect of hydroxide ion (group) cannot be ruled out, but it is stronger against the decomposition of magnesite (main component MgCO ₃ ) which is considered to remain in the light-burning mug. It is considered that an attack by a base produces magnesium hydroxide (Mg (OH) ₂ ) by the reaction of the following formula. MgCO ₃ +2 NaOH → Mg (OH) ₂ + Na ₂ CO
_{3 In} addition, when a strong base is added to the base, the heat of reaction due to the exothermic reaction cannot be utilized in principle, and it is necessary to heat it to a considerably high temperature. There are drawbacks such as need.

The object of the present invention is to obtain the above-mentioned caustic soda (Na).
OH) or potassium hydroxide (KOH) is added to the reaction system, and the method for synthesizing activated magnesium hydroxide, in which it is dissolved while heating at 85 ° C. or higher, is modified, and the viscosity of the slurry is It is intended to provide a method for preparing activated magnesium hydroxide which has a low viscosity, is excellent in fluidity, is excellent in non-sedimentation property and non-aggregation property, and can maintain a stable dispersed state.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention comprises firing a naturally occurring magnesite in a warm aqueous solution in which an anionic surfactant containing an alkali metal salt of a fatty acid as a main component is dissolved. It is a method for preparing activated magnesium hydroxide, characterized in that the obtained crushed or sized light-burned magnesia is added and allowed to dissolve while heating.

The fatty acid used in the method of the present invention preferably has 6 to 18 carbon atoms. In addition, the addition rate of the additive (alkali metal salt of fatty acid) to light-burned magnesia is
0.05-0.5% by weight, preferably 0.1-0.4
It is better to use the weight percent. Further, other known components having a low foaming property or a defoaming effect may be added to the additive.

Next, embodiments and operations for implementing the method of the present invention will be described in detail.

[0012]

EXAMPLES Example 1. 14.5 liters of warm water (clean water) at 40 ° C. was stored in a reaction tank with a stirrer made of stainless steel and having an internal volume of 50 liters, and an anionic surfactant containing fatty acid sodium as a main component in warm water while stirring Two
4 g was added and this was fully dissolved. Next, add 6 kg of crushed or sized light-baked magnesia obtained by firing natural magnesite to the above warm aqueous solution, and heat the mixture by heating with an electric heater while mixing and stirring to 75 ° C. When the heating was stopped when the temperature reached, a slight bubbling phenomenon due to fine bubbles covering the surface was observed, but the temperature of the reaction solution slurry rose even though the heating was stopped, After 20 minutes from the stop, the temperature reached 95 ° C, and a temperature increase of 20 ° C was observed.

When the temperature of the reaction liquid slurry has dropped to 90 ° C., heating is restarted, and while the temperature of the slurry is maintained at 85 ° C. to 90 ° C. while adjusting the voltage of the electric heater, stirring is continued for another hour. After continuing, the reaction was terminated. Next, 31.4 g of the obtained slurry was sampled, mixed with 200 ml of 2N sulfuric acid, stirred for 5 minutes, filtered and dried, and the weight of the reaction residue was measured to be 2 It was 0.4 g. In the above process, the time required for the pH of the mixed solution to reach 10.0 is 10.0 seconds,
The time required for the pH of the mixed solution to reach 6 was 14.7 seconds. Therefore, although the activated magnesium hydroxide-containing slurry obtained in Example 1 of the present invention had a little viscosity, it had excellent fluidity and no sedimentation or cohesiveness was observed, which was good. A stable dispersed state was obtained.

Example 2. 4.83 liters of warm water (clean water) at 45 ° C. was stored in a container made of stainless steel and having an internal volume of about 15 liters, and 4 g of anionic surfactant containing fatty acid potassium as a main component was added to the warm water while stirring. , Which was fully dissolved. Next, add 2 kg of crushed or sized light-burned magnesia obtained by firing natural magnesite to the above warm aqueous solution, and heat the mixture with heat generated by an electric heater while mixing and stirring to 75 ° C. When the heating was stopped when the temperature reached, generation of a slightly large and easily defoaming bubble was observed only in the inner peripheral wall of the container, but no bubble generation was observed within 2 to 3 minutes. Although the heating was stopped, the temperature of the reaction solution slurry increased, reaching 85 ° C. 5 minutes after the heating was stopped, and could be kept at 80 ° C. or higher for about 30 minutes.

When the temperature of the reaction solution slurry has dropped to 79 ° C., heating is restarted and the temperature of the slurry is maintained at 85 ° C. to 90 ° C. while adjusting the voltage of the electric heater.
After continuing stirring for 5 hours, the reaction was terminated. Next, 31.4 g of the obtained slurry was sampled, 200 ml of 2N sulfuric acid was mixed therein, and the mixture was stirred for 5 minutes, filtered and dried, and the weight of the reaction residue was measured. It was 1.8 g. In the above process, the time required for the pH of the mixed solution to reach 5 is 5.
1 second, the time required until the pH of the mixture reaches 6
It was 7.3 seconds. Therefore, the activated magnesium hydroxide-containing slurry obtained in Example 2 of the present invention is
Although it was slightly viscous, it had excellent fluidity, neither sedimentation nor aggregation was observed, and a good and stable dispersion state was obtained.

Comparative Example 1. Under the same conditions as those shown in Example 1, light burned magnesia was added to warm water, and a reaction product slurry was prepared without adding an anionic surfactant containing potassium fatty acid as a main component. When the activator was not added, the foaming phenomenon was not observed, and the temperature rise was not observed at the same time. Therefore, the heating was not stopped and the temperature was maintained at 85 ° C to 90 ° C for the same time as in Example 1. Then, the reaction was terminated. Similarly, the weight of the reaction residue was measured and found to be 3.7 g.
Also, the time required for the pH of the mixed solution to reach 5 is 1
8.8 seconds, the time required for the pH of the mixed solution to reach 6 was 33.5 seconds. The resulting slurry had a high sedimentation rate, and a tendency to easily agglomerate was clearly recognized, the boundary between the transparent supernatant and the agglomerated sedimentation cake part was clear, and the fluidity of the slurry was lowered, resulting in remarkable A tendency for sedimentation was recognized. Comparative example 2. Under the same conditions as in Example 2, 20 g of caustic soda was added as an additive to hot water and dissolved, and 2 Kg of lightly baked magnesia was added to this aqueous solution, and heating was started while mixing and stirring. Since neither phenomenon nor temperature rise was observed, the reaction was terminated by keeping the temperature at 85 ° C to 90 ° C for the same time as in Example 2 without stopping the heating. Similarly, when the weight of the reaction residue is measured,
It was 3.4 g. The time required for the pH of the mixed solution to reach 5 was 13.4 seconds, and the time required for the PH of the mixed solution to reach 6 was 18.9 seconds. The obtained slurry has a relatively low viscosity and is relatively excellent in fluidity under stirring conditions, but in the stationary state after stirring is stopped, cohesiveness and sedimentation are observed, and a uniform slurry state is obtained. Was difficult to hold.

[0017]

The above-mentioned conventional method of adding a strong alkali such as caustic soda (NaOH) or potassium hydroxide (KOH) to the reaction system and heating the mixture to 85 ° C. or above to neutralize it is a light burning mug. The soaking time for reacting the water with water is usually 2 to 3 hours. On the other hand, according to the method of the present invention, as is clear from the results of Example 1.2, the continuous heating at the time of soaking can be eliminated, and the soaking time of the lightly baked mug can be shortened. In addition, although the viscosity slightly increases, it has excellent fluidity, non-sedimentation property and non-aggregation property in a uniform slurry state, and can maintain a stable slurry dispersion state. Furthermore, the addition rate of the additive can be reduced, and at the same time, the reaction rate of the slurry is improved by self-heating, and the unreacted residue is reduced, etc., and compared with the conventional method using caustic soda. The running cost can be reduced. Furthermore, since the present invention does not require addition of caustic soda to the reaction system during soaking, not only maintenance management of caustic soda is unnecessary, but also a slurry containing activated magnesium hydroxide at a lower cost than caustic soda and conventional seawater mugs. A liquid is obtained.

Front Page Continuation (72) Inventor Susumu Kokubu 3-11-10 Taihei, Sumida-ku, Tokyo Inside Environmental Engineering Co., Ltd. (56) Reference JP-A-5-208810 (JP, A)

Claims (1)

[Claims] 1. An anionic surfactant containing an alkali metal salt of a fatty acid as a main component , the addition rate of which is 0.05 to 0.5 w.
t%, preferably 0.1-0.4 wt% (relative to MgO) is dissolved in a warm aqueous solution, and crushed or sized light-burned magnesia obtained by firing natural magnesite is added and heated. A method for preparing activated magnesium hydroxide, which is characterized in that it is dissolved.