JPS6335571B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing magnesium hydroxide used in the field of fine materials such as fillers for synthetic resins. This invention relates to a method for producing magnesium hydroxide with improved crystal shape, crystal size, and dispersibility by hydration in an aqueous solution. Magnesium clinker is a major use of magnesium hydroxide, and it is already used in large quantities in magnesia fertilizers and flue gas desulfurization agents. There is a field in which the excellent properties of magnesium hydroxide are utilized, although the amount is small compared to the above-mentioned uses. For example, magnesium oxide is used as a filler for synthetic resins, a flame retardant, a sizing agent, and a pharmaceutical antacid, and the calcined magnesium oxide is used in various applications as activated magnesia. A commonly known method for producing magnesium hydroxide is to precipitate magnesium hydroxide by reacting slaked lime or caustic alkali with an aqueous solution containing Mg ions, such as seawater or bittern. However, in the case of magnesium hydroxide produced by known methods, the smallest unit of crystal that makes up the particles is less than 0.1μ, and even if the reaction temperature is raised or the reaction rate is strictly controlled, the crystal size is only about 0.2μ. However, it is extremely difficult to increase the size of magnesium hydroxide crystals. In addition, conventional magnesium hydroxide forms relatively strongly entangled aggregates with irregular crystals, resulting in secondary particles ranging from several micrometers to several tens of micrometers, and this is the basic particle size of magnesium hydroxide. be observed. Furthermore, the magnesium hydroxide of the known method contains various ions (Na ⁺ , K ⁺ , Cl ^- , SO ^2- ₄ Ca ²⁺ , B ₂ O ₃ ^2- ₃ ) derived from the raw materials;
There are many impurities due to adsorption, etc., making it difficult to obtain highly pure magnesium hydroxide. For example, when such magnesium hydroxide is mixed with a synthetic resin, the resin does not penetrate into the details of the particles, making it difficult to obtain a homogeneous composition, which causes a mottled pattern on the surface of the resulting molded product. . For this reason, magnesium hydroxide used in the fine arts field not only has high chemical purity, but also requires special physical properties such as the size, shape, particle size distribution, and dispersibility of the crystal, which is the smallest unit. ing. However, it has been extremely difficult to change these physical properties (particularly the crystal shape) or to control them within desired values. Conventionally known methods for producing magnesium hydroxide used in the fines field include high-temperature, high-pressure treatment of magnesium hydroxide, alkali treatment, or reaction precipitation of magnesium hydroxide using slaked lime. A method has been proposed in which a portion of the magnesium hydroxide is reacted with magnesium chloride to control the production rate of magnesium hydroxide. However, although these methods are excellent for obtaining magnesium hydroxide suitable for each purpose, they require expensive equipment and complicated processes, and cannot cover a wide range of uses of magnesium hydroxide with one equipment and method. There is a drawback that it cannot be done. As a result of intensive research in order to solve the above-mentioned drawbacks of the conventional technology, the present inventors found that by hydrating inert magnesium oxide calcined at a temperature of 1400°C or higher in the presence of a certain amount of acid groups, The inventors have discovered that the above object can be achieved, and have completed the present invention. That is, the present invention provides magnesium oxide calcined at 1400° C. or higher in a water-suspended slurry state containing an amount of acid groups as an acid or a magnesium salt corresponding to an amount exceeding the number of equivalents of calcium oxide in the raw material of the raw magnesium oxide. This is a method for producing magnesium hydroxide, which is characterized by hydration in a medium. According to the present invention, as a method of changing the physical properties of magnesium hydroxide, magnesium oxide is subjected to a hydration reaction under conditions where the type of acid group and temperature are controlled. From this, it is possible to control the crystal shape, crystal size, dispersibility, etc., which are the basic physical properties of magnesium hydroxide, as shown in the electron micrographs in Examples below. The crystals obtained by the present invention are ``prismatic crystals'' that are extremely difficult to produce using conventional methods, or ``hexagonal plate-shaped crystals'' with significantly developed crystals, and the single crystals are larger than those of conventional magnesium hydroxide. It is extremely uniform and has excellent dispersibility and orientation. Therefore, when magnesium hydroxide obtained by the method of the present invention is mixed with, for example, a synthetic resin, the resin penetrates well and a homogeneous composition can be obtained. It has characteristics such as excellent film properties when applied. Activated magnesia, which is obtained by thermally decomposing a magnesium compound, reacts with water to easily produce magnesium hydroxide through the _formula MgO + H ₂ O → Mg (OH).
It is known that this magnesium oxide rapidly loses its chemical reactivity even with a slight increase in firing temperature, and the rate of hydration reaction with water becomes extremely slow.
Therefore, in conventional technology, the appropriate firing temperature for magnesia to produce magnesium hydroxide by hydrating magnesium oxide is around 1000℃.
A method of hydrating activated magnesia calcined to this degree with water, seawater, or an aqueous solution of MgCl ₂ or MgSO ₄ (Japanese Patent Publication No. 49-40602, French Patent No.
975099) has already been published. However, the purpose of these methods is to remove water-soluble impurities or recover highly active magnesium hydroxide, and these methods do not change the crystal shape of the magnesium hydroxide produced. Or,
It was thought that it would be extremely difficult to make crystals larger. The present inventors investigated magnesium oxide calcined at temperatures below 1400°C, which had previously been considered disadvantageous as conditions for producing magnesium hydroxide industrially due to its extremely slow hydration reaction rate. If acid groups are present during the process, depending on the type of acid group, for example, due to the presence of NO ^- ₃ , Cl ^- , SO ^2- ₄ , magnesium hydroxide crystals become prismatic, and organic compounds such as acetate ions form. Due to the presence of acid groups, the shape of the crystal changes significantly, such as becoming "hexagonal plate-like", producing magnesium hydroxide with various different physical properties, and by adjusting the concentration of acid groups, It was also discovered that by appropriately increasing the hydration reaction temperature, the size of the crystals can be controlled, and the hydration rate can be accelerated to an industrially practicable level, thereby achieving the objective. On this occasion,
In principle, the higher the hydration reaction temperature, the smaller the crystals will be, but by adjusting the concentration of acid groups and the hydration reaction temperature, it is possible to control the crystal size and at the same time form single crystals with good dispersibility. can be generated. The present invention revealed for the first time that magnesium hydroxide has different crystal shapes depending on the type of acid group. The magnesium oxide used in the present invention may be produced from any magnesium compound, but the calcination temperature is 1400°C or higher, preferably 1700°C or higher.
The temperature must be above ℃. Firing temperature is 1400
If the temperature is lower than ℃, there is little development of magnesia, which is usually called periclase, and the hydration reaction rate of such magnesium oxide is too fast, resulting in fine crystals and irregular aggregates, so it is not suitable for use in the method of the present invention. It's inappropriate. In addition, when magnesium oxide that has been oxidized by firing at a temperature lower than 1400°C is used as a raw material, the reaction is such that magnesium hydroxide with good dispersibility can be obtained even if the type and amount of acid groups added are changed. is difficult to control. If there are many impurities in magnesium oxide, these ions will elute during the hydration reaction and inhibit crystal growth, so it is preferable that the MgO purity in the raw material is 96% or more, and more preferably 97.5% or more. . High-purity magnesia clinker, which is currently used in large quantities as a refractory in steel manufacturing, not only meets the above requirements, but also allows the particle size of the raw material to be subjected to the reaction to be adjusted arbitrarily, and is therefore suitable as a raw material for the present invention. The hydration reaction needs to be carried out in a slurry state in which much excess water is coexisting than the amount of water required to convert magnesium oxide to magnesium hydroxide, and the concentration is not particularly limited, but it is carried out at a concentration of 200 to 300 g. is appropriate. The hydration reaction of this slurry is carried out in a reactor capable of stirring and heating, and the acid groups to be added include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid, or their magnesium salts, as well as complex acids, formic acid, citric acid, etc. organic acids or their magnesium salts are used. The amount of acid groups to be added varies depending on the amount of calcium oxide in the raw material, but preferably acid groups equivalent to 0.5% or more of the equivalent number of raw material magnesium oxide (preferably 0.5% to 5%) Hereinafter, it is more preferably the total amount of acid groups corresponding to the number of equivalents of 1% or more and 3% or less) and the acid groups corresponding to the number of equivalents of calcium oxide. If the amount of acid groups is less than 0.5% equivalent to the raw material magnesium oxide, the effect of controlling crystal growth of magnesium hydroxide will be reduced and the hydration reaction rate will be slow. In addition, if the amount of acid groups is too large, the hydration reaction rate of magnesium oxide will be faster than necessary, causing problems such as finer crystals and uneven particle sizes, as well as increased costs due to the increase in acid groups. It's not a good idea because it will increase. If cations other than Mg ions are present in the magnesium oxide slurry at a concentration equal to or higher than the Mg ion concentration, the effect of controlling the crystal shape will be significantly inhibited, so it is desirable that the amount of these ions present be as small as possible. In particular, it is necessary to minimize the coexistence of ions such as sodium and potassium, so the acid groups to be added are inorganic and
Magnesium salts that dissolve in organic acids or slurries to generate Mg ions and acid groups are preferred. The particle size of magnesium oxide has a significant effect on the rate of magnesium hydroxide formation. Naturally, if the particles are large, the completion of the hydration reaction will be delayed, so
It is necessary to carry out the hydration reaction for a long time, which increases the size of the hydration reaction equipment and requires a step to separate unhydrated coarse particles from the hydrated magnesium hydroxide slurry. In order to improve the productivity of such hydration equipment and simplify the manufacturing process, the thickness is preferably 250 μm or less,
More preferably, raw material magnesium oxide with a diameter of 100 μm or less is used. Furthermore, the production rate of magnesium hydroxide is significantly influenced by the hydration reaction temperature. Lower temperatures make it easier to control crystallization, but the hydration reaction rate is significantly slower, requiring larger hydration equipment and a process to separate unhydrated magnesium oxide from produced magnesium hydroxide. do. Since the hydration reaction rate is particularly slow at temperatures lower than 60°C, it is desirable to set the hydration reaction temperature to 60°C or higher. During the reaction, it is preferable to perform appropriate stirring in order to ensure the effects of the present invention and to make the reaction uniform. The magnesium hydroxide produced by the reaction is made into a product through processes such as water washing and purification as necessary.
It is also possible to adsorb and mix necessary components using this process from washing with water to drying, or to add appropriate physical properties to magnesium hydroxide using a spray drying method or the like. The effects of the present invention will be explained below with reference to Examples. Example 1 The commercially available magnesia clinker shown in Table 1 was ground with a fret mill to form a powder that passed through 105μ,
It was mixed with water and fed as a slurry of 200 g/l of MgO into a reactor equipped with a stirrer and a heating device. Magnesium nitrate equivalent to 40.8 g of calcium oxide contained in the MgO of this slurry and magnesium nitrate (255 g in anhydrous salt equivalent) equivalent to 1% of the mole of raw material MgO were added, and the mixture was stirred thoroughly. After heating to 100°C and reacting for 17 hours, the mixture was classified using a 44 μm screen. The rate of passage through the 44 μm screen was 96% based on the raw material MgO, and the hydration rate of the under-sieve product sieved through the screen was 99.6%. The composition and properties of magnesium hydroxide obtained by washing and drying this product are shown in Table 3, and the shape of the crystals taken with a scanning electron microscope (5000x magnification) is shown in Figure 1. As shown in FIG. 1, the magnesium hydroxide produced by this method had a center particle diameter of 1 μm to 0.5 μm, and the crystal grains were uniform prismatic crystals. Example 2 Twenty minutes of MgO slurry prepared in the same manner as in Example 1 was fed to a reactor. of this slurry
Add hydrochloric acid equivalent to 40.8 g of calcium oxide contained in MgO and equivalent number of hydrochloric acid equivalent to 2% of the number of moles of raw material MgO (198 g in pure terms),
The mixture was heated to 100° C. with sufficient stirring, reacted for 17 hours, and then classified using a 44 μm screen. 44μm
The screen passing rate is 94% based on raw material MgO,
The hydration rate of the undersieve product was 99.8%. The composition and properties of magnesium hydroxide treated in the same manner as in Example 1 are shown in Table 3, and the shape of the crystals taken with a scanning electron microscope (5000x magnification) is shown in FIG. As shown in FIG. 2, the magnesium hydroxide produced by this method had a center particle diameter of about 0.5 μm to 1 μm, and the crystal particles were uniform prismatic crystals. Note that the magnesium hydroxide obtained in Examples 1 and 2 was suitable as a synthetic resin filler. Example 3 Twenty minutes of MgO slurry prepared in the same manner as in Example 1 was fed to a reactor. of this slurry
Add magnesium acetate equivalent to 40.8 g of calcium oxide contained in MgO and magnesium acetate (245 g in terms of anhydrous salt) equivalent to 1% of the mole of raw material MgO, and stir well.
After heating to 100°C and reacting for 14 hours, the mixture was classified using a 44 μm screen. The rate of passage through the 44 μm screen was 96% based on raw material MgO, and the hydration rate of the product under the sieve was 99.8%. The composition and properties of magnesium hydroxide treated in the same manner as in Example 1 are shown in Table 3, and the shape of the crystals photographed with a transmission electron microscope (10,000x magnification) is shown in FIG. As shown in FIG. 3, the magnesium hydroxide produced by this method was a hexagonal tabular crystal with a diameter of about 1 μm, and was extremely highly oriented. Example 4 Twenty minutes of MgO slurry prepared in the same manner as in Example 1 was supplied to a reactor. of this slurry
Add an equivalent amount of formic acid to 40.8 g of calcium oxide contained in MgO and an equivalent number of formic acid equivalent to 2% of the number of moles of raw material MgO (250 g in terms of pure content),
The mixture was heated to 100° C. under sufficient stirring, reacted for 14 hours, and then classified using a 44 μm screen. 44μm
The screen passing rate is 90% based on raw material MgO,
The hydration rate of the undersieve product was 99.1%. The composition and properties of magnesium hydroxide treated in the same manner as in Example 1 are shown in Table 3, and the shape of the crystals photographed with a transmission electron microscope (10,000x magnification) is shown in FIG. As shown in FIG. 4, the magnesium hydroxide produced by this method was a hexagonal tabular crystal with a diameter of about 1 μm. Comparative Example 1 A MgO slurry prepared in the same manner as in Example 1 was supplied to a hydration reactor without adding any additives. This slurry was heated to 100 °C under good stirring for 40 min.
After reacting for a period of time, the mixture was classified using a 44 μm screen. 44μm screen passing rate is based on raw material MgO
The hydration rate of the product under the sieve was 90%. Table 2 shows the composition and properties of magnesium hydroxide that has been washed, filtered, and dried.
Figure 5 shows the shape of the crystal photographed at 100% magnification. Fifth
As shown in the figure, magnesium hydroxide hydrated without additives has irregular crystal shapes;
The dispersibility was also poor. As is clear from the above Examples and Comparative Examples, it was recognized that the acid group not only has a remarkable effect of controlling the crystal growth of magnesium hydroxide, but also has a catalytic effect of promoting the hydration reaction. Example 5 Twenty minutes of MgO slurry prepared in the same manner as in Example 1 was fed to a reactor. of this slurry
Add an equivalent amount of magnesium acetate to 40.8 g of calcium oxide contained in MgO and an equivalent number of magnesium acetate equivalent to 0.1, 0.5, 1, or 5% of the number of moles of raw material MgO, and heat to 100°C with sufficient stirring. Mg of MgO by heating and reaction time lapse
(OH) ₂ conversion rate was measured. The results are shown in FIG. In Figure 7, A represents 0.1% equivalent, B represents 0.5% equivalent, C represents 1% equivalent, and D represents 5% equivalent. As shown in Figure 7, the hydration rate changes greatly depending on the amount of acid groups added, with acid groups below 0.5% equivalent the hydration reaction slows down significantly, and amounts over 5 equivalents the hydration reaction speeds up. However, finer crystals are observed.

[Table] Comparative Example 2 The raw material was light calcined magnesia, which was obtained by refining the precipitate obtained by reacting seawater and slaked lime, washing with water, filtering, and firing at around 1100°C in a Herefschoff furnace. The composition of the raw materials is shown in Table 2.

[Table] In the same manner as in Example 1, raw material MgO was made into a slurry of 200 g/mt, and 20 g/m of slurry was supplied to the reactor. Magnesium chloride equivalent to 45.2g of calcium oxide contained in MgO of this slurry, and raw material MgO
Add equivalent number of magnesium chloride (237 g in terms of anhydrous magnesium chloride) corresponding to 2% of the number of moles of
The mixture was heated to 70° C. under sufficient stirring, reacted for 3 hours, and then classified using a 44 μm screen. The rate of passage through the 44 μm screen was 98.8% based on raw material MgO, and the hydration rate of the product under the sieve was approximately 100%. Table 3 shows the composition and properties of magnesium hydroxide treated in the same manner as in Example 1, and FIG. 6 shows the shape of the crystals photographed with a scanning electron microscope. 6th
As shown in the figure, the magnesium hydroxide produced by this method does not form monodispersed crystals as shown in the examples, but is an aggregate, and has extremely poor dispersibility.

【table】

【table】 [Brief explanation of drawings]

Fig. 1 is a scanning electron micrograph of the magnesium hydroxide produced in Example 1, Fig. 2 is a scanning electron micrograph of the magnesium hydroxide produced in Example 2, and Fig. 3 is a scanning electron micrograph of the magnesium hydroxide produced in Example 3. A transmission electron micrograph of magnesium hydroxide, FIG. 4 is a transmission electron micrograph of magnesium hydroxide produced in Example 4, and FIG. 5 is a scanning electron micrograph of magnesium hydroxide produced in Comparative Example 1. Figure 6 is a scanning electron micrograph of magnesium hydroxide produced in Comparative Example 2, and Figure 7 is a graph showing the relationship between the amount of acid groups added and the Mg(OH) ₂ conversion rate of MgO over reaction time. It is.

Claims (1)

[Claims] 1 Magnesium oxide calcined at 1400℃ or higher,
A method for producing magnesium hydroxide, which comprises hydration in a water-suspended slurry state containing acid or magnesium salt in an amount of acid groups corresponding to an amount exceeding the number of equivalents of calcium oxide in the raw material of magnesium oxide. .