JPH0137330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-purity magnesia powder of 99.99% by weight or more, and more specifically, the present invention relates to a method for producing high-purity magnesia powder having a content of 99.99% by weight or more, and more specifically, a method for producing a magnesia powder having a high purity of 99.99% by weight or more. This invention relates to a method for producing high purity magnesia powder by easily removing ₂ .

Magnesia has excellent base resistance and electrical insulation at high temperatures, and has a large coefficient of thermal expansion and thermal conductivity.
Moreover, it has the characteristics of good transmittance to infrared rays and visible light at high temperatures, and is inexpensive. Therefore, it is widely used as a heat-resistant material, high-temperature insulating material, mixed-temperature lighting material, etc., and has recently attracted attention as a fine ceramic material.

Magnesia for high-temperature materials is required to have properties such as easy sinterability, corrosion resistance, and digestion resistance. However, magnesia as a high-temperature material currently used does not exhibit the high-temperature characteristics inherent to magnesia because of the low-melting-point oxides contained therein as impurities.

Its main impurities are SiO ₂ , CaO, Al ₂ O ₃ , Fe ₂ O ₃ ,
B ₂ O ₃ , and its content controls its properties in hot conditions. Among these, when CaO/SiO ₂ is about 1, CaO·SiO ₂ with a low melting point (1544° C.) is generated at the grain boundaries, which significantly reduces the hot bending strength. Also
When CaO/SiO ₂ is about 3 or more, unbound CaO is generated, which deteriorates the digestion resistance. When Al ₂ O ₃ and Fe ₂ O ₃ are included in addition to SiO ₂ and CaO, the melting point of the grain boundary product decreases in proportion to the content thereof, and the hot bending strength deteriorates. Moreover, B ₂ O ₃ acts as a silicate flux and deteriorates the hot bending strength, especially when CaO/SiO ₂ is about 2. Therefore, in order to create a magnesia high-temperature material with inherently excellent properties, it is necessary to reduce impurity oxides, particularly SiO ₂ and CaO, as much as possible.

Recently, through process control in the precipitation reaction of magnesium hydroxide, the content of Fe ₂ O ₃ , Al ₂ O ₃ and B ₂ O ₃ has been reduced to about 0.05% by weight or less, respectively. However, in the conventional method, _SiO2 is 0.1-0.2% by weight and CaO is 0.2-0.4% by weight.
Only up to % by weight can be removed. Therefore, regarding CaO, magnesium hydroxide is
It is known to remove CaO to 0.01 to 0.02% by weight by calcination at 900°C, then pouring into water and stirring, and utilizing the difference in solubility. However, this method requires repeated over-drying and calcining operations, resulting in poor productivity and high costs. Currently, there is no other way to remove SiO ₂ other than using raw stone and water with low SiO ₂ impurities. On the other hand, even with process control based on the precipitation reaction of basic magnesium carbonate, CaO and
There are no very effective methods for removing SiO ₂ .
In addition, spark discharge methods, ion exchange methods, solvent extraction methods, etc. are also known, but they all have the disadvantage of significantly increasing costs.

An object of the present invention is to provide a method for producing high-purity magnesia powder at low cost.

The gist of the present invention is to separate magnesium orthocarbonate trihydrate obtained by the carbon ammonium method, soda ash or water mug method from the mother liquor, add fresh water, and adjust the pH of this mother liquor to 9.0 to 9.8. After that, ripening temperature 30~40℃
The precipitate obtained is washed until the pH of the liquid becomes 10.3 to 10.6, dried, and then exposed to air. This method is characterized by firing in the atmosphere or in an oxygen atmosphere.

The orthomagnesium carbonate trihydrate used in the present invention includes (1) magnesium chloride, magnesium sulfate,
Aqueous reaction between magnesium compounds such as magnesium nitrate and basic precipitants such as sodium carbonate (soda ash method), ammonium carbonate (ammonium carbonate method), sodium bicarbonate, and ammonium bicarbonate. (2) It can be synthesized by reacting magnesium hydroxide suspension with carbon dioxide gas (water mug method) or carbonate. However, those containing amorphous magnesium carbonate or magnesium hydroxide are not preferred.

Regarding the method for the aqueous solution reaction of the magnesium compound and the base precipitating material in (1) above, the concentrations of both solutions may be the same, but it is preferable that the concentration of the magnesium compound be slightly higher in terms of reducing alkaline impurities. The initial concentration of these solutions is preferably 0.3 to 0.6 mol/. If it is diluted more than this, amorphous magnesium carbonate will be mixed in, and if it is more concentrated than 0.6 mol/ml, the crystallinity of the magnesium orthocarbonate trihydrate will become non-uniform and the aging time will be long.

The mixing ratio of both solutions is preferably the same volume in the case of carbonate and 1:2 volume of magnesium compound:bicarbonate in the case of bicarbonate. It is more preferable for the magnesium compound to be contained in a slightly larger amount in terms of reducing peroxidity and alkaline impurities.

For mixing both solutions, it is preferable to add the magnesium compound to the basic precipitant at a rate of 100 ml or less per minute at a temperature of 15 to 47°C. If it is added earlier than the above, the crystalline state of the magnesium orthocarbonate trihydrate becomes non-uniform and the amount of alkaline impurities adsorbed increases. Furthermore, if the reaction temperature is lower than 15℃, normal magnesium carbonate pentahydrate will be produced, which will deteriorate the peroxidation and aging effect, while if it exceeds 47℃, basic magnesium carbonate will be produced immediately after the reaction, and impurities (especially
The removal effect of SiO ₂ ) becomes worse.

In the present invention, it is necessary to filter and wash the obtained magnesium orthocarbonate trihydrate and suspend it in a fresh aqueous solution. Impurities (especially CaO) will not be removed unless the water is replaced with fresh water. Adjust the pH of this new mother liquor to 9.0-9.8, preferably 9.5-9.8. When the pH of this mother liquor is higher than about 9.8, basic magnesium carbonate octahydrate is produced, the purity of the aged precipitate deteriorates (particularly Na ₂ O), and the sinterability of the calcined product deteriorates. On the other hand, if the pH is lower than 9.0, the ripening speed will be extremely slow and the production cost will be high. To adjust the pH, use acids (hydrochloric acid, nitric acid, sulfuric acid,
Carbonic acid, acetic acid, etc.) may be used, but it is preferable to blow carbon dioxide gas in terms of buffering effect and yield.

The solution whose pH has been adjusted in this way is aged at 30 to 47°C, preferably 33 to 40°C, to perform an anion exchange reaction.
If this temperature is lower than 30℃, the rate of anion exchange reaction will be extremely slow, and if it exceeds 47℃, the rate of anion exchange reaction will be significantly faster, and the removal of SiO ₂ due to crystal structure recombination will be incomplete. .

After filtering out the resulting basic magnesium carbonate precipitate, the solution is washed until the pH value of the solution reaches a constant value of 10.3 to 10.6. This not only completely removes the remaining magnesium carbonate trihydrate, but also makes the chemical composition and crystalline state of the basic magnesium carbonate pentahydrate uniform.

After drying this (tetrahydrate), it is fired in air or in an oxygen atmosphere. This firing is done at 300~400℃
After completely removing the water of crystallization, it is preferable to perform decarbonation at a higher temperature and further heat to 800 to 1000°C. This results in uniform powder properties,
Moreover, it has a high purity of 99.99% by weight or more, which is low in SiO ₂ and CaO, and can be sintered to about 98% of the theoretical degree at a low temperature of 1400° C. without any additives.

Example 1 0.4 mol of magnesium chloride/1000 ml of solution was added to 0.4 mol of sodium carbonate/1000 ml of solution at a rate of 100 per minute.
ml at a rate and reacted at 25°C for 30 minutes to obtain magnesium orthocarbonate (MgCO ₃ .3H ₂ O). This was thoroughly washed, the same amount of ion-exchanged water was added, and the pH was adjusted to 9.7 by blowing carbon dioxide gas into it. This suspension was aged at 35°C for 24 hours to form basic magnesium carbonate (4MgCO ₃・Mg(OH) ₂・
5H ₂ O) was obtained. Pour this slurry into 1200ml
Washed and filtered six times with ion-exchanged water. This cake was dried at 110°C for a day and night, then dehydrated in a dry oxygen atmosphere at 400°C until the dew point became constant, and then thermally decomposed at a constant temperature increase of 10°C per minute, and then heated at 900°C for 20 hours. High purity magnesium powder was obtained by calcining. The impurities contained in this powder were as follows.

Impurity-containing Si Ca Al Fe Na content (ppm) 24 26 3 2 3 In the above method, in the magnesia powder produced without exchanging the mother liquor and changing the aging temperature and keeping other conditions the same, Figure 1 shows the Ca content contained in the sample.

In the figure, ● indicates the case where the water is replaced with new water, and ○ indicates the case where the water is not replaced with new water.

As this figure shows, (1) Ca cannot be excluded unless the mother liquor is replaced with fresh water, and the aging temperature is preferably 30-40℃, and even if the temperature is lower or higher, the Ca content is increases. (2) The content of SiO ₂ in magnesia powder is shown in Figure 2. ○ indicates the case where the water was replaced with fresh water, but the content of SiO ₂ was almost the same even without replacing the mother liquor with fresh water.

As the figure shows, when the aging temperature is higher than 40 °C, the SiO ₂ content increases.

(3) Magnesia was produced under the same conditions as in Example 1, except that the initial concentrations of magnesium chloride and sodium carbonate were both varied. The SiO ₂ contained in the obtained magnesia powder was as shown in FIG.

As the figure shows, the SiO ₂ content increases regardless of whether the initial concentration becomes higher or lower, and is 0.3 to 0.6 mol/
This indicates that it is preferable that

Example 2 Magnesia powder was produced in the same manner as in Example 1 except that magnesium sulfate and ammonium carbonate were used in place of magnesium chloride and sodium carbonate, respectively. The impurities contained in this powder were as follows.

Impurity element Si Ca Al Fe Na Content (ppm) 30 29 5 5 12 Example 3 Magnesium chloride 0.4 mol/in 500 ml of solution,
Magnesium hydroxide was precipitated by adding 28% ammonia water, and after filtering and washing the precipitate, 1500 ml of ion-exchanged water was added to prepare a magnesium hydroxide suspension. Carbon dioxide gas was blown into this suspension at a rate of 100 c.c. per minute to obtain orthomagnesium carbonate trihydrate.
This magnesium carbonate trihydrate was treated in the same manner as in Example 1 to obtain magnesium powder. The impurities contained in this powder were as follows.

Impurity element Si Ca Al Fe Na Content (ppm) 37 27 7 8 2

[Brief explanation of drawings]

Figure 1 is a comparison graph of the Ca content in magnesia powder produced in Example 1 without exchanging the mother liquor and at different aging temperatures under the same conditions. The content of SiO ₂ in magnesia powder when exchanged with
FIG. 3 is a graph of the SiO ₂ content in magnesia powder when both the initial concentrations of magnesium chloride and sodium carbonate are changed. ● indicates when the water is replaced with new water, and ○ indicates when the water is not replaced with new water.

Claims (1)

[Claims] 1. Separate magnesium orthocarbonate trihydrate obtained by the ammonium charcoal method, soda ash method, or water mug method from the mother liquor, add fresh water, and adjust the pH of this mother liquor to 9.0~
After adjusting the temperature to 9.8, it is aged at 30 to 40°C and anion exchange reaction is performed until the normal magnesium carbonate trihydrate becomes basic magnesium carbonate pentahydrate, and the resulting precipitate is heated to a pH of 10.3. A method for producing high-purity magnesia powder, which is characterized by washing the powder until the powder has a particle size of ~10.6, drying it, and then firing it in air or in an oxygen atmosphere.