JPS6126511A - High-purity acicular magnesium oxide and its preparation - Google Patents

Abstract

PURPOSE:To produce the titled MgO usable in the field of specialty ceramics, by treating an MgO-containing raw material with a mineral acid, adjusting the pH of the obtained solution to precipitate and remove the impurities, raising the pH above a specific level, heating under pressure in the presence of O2, washing the product with water, and heating at a high temperature. CONSTITUTION:An MgO-containing raw mateial is dissolved in a mineral acid (e.g. sulfuric acid) to obtain a crude solution of an Mg mineral acid salt. The pH of the solution is adhusted to 7-9 with an alkali (e.g. NH4OH) to effect the precipitation of impurities such as Fe, Ca, Al, etc. in the form of hydroxides. The precipitated impurities are removed by filtration, and the pH of the obtained refined solution of the Mg mineral acid salt is adjusted to >=10 with an alkali, and the solution is charged into an autoclave, pressurized with O2, and heated at >=80 deg.C. The resultant product is washed with water, dehydrated, and heated at >=1,000 deg.C to obtain high-purity MgO consisting of acicular crystal having a diameter of 0.1-0.5mu and a length of 5-20mu.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnesium oxide and its production method.

Conventionally, magnesium oxide has been produced by directly calcining magnesium salts (magnesium carbonate, magnesium hydroxide, etc.) in which various impurities remain. However, recent magnesium oxide used in the field of ceramics and the like is required to have even higher purity, but conventional magnesium oxide obtained by mere firing does not necessarily meet such requirements. For this reason, for example, there have been several proposals to produce highly pure magnesium hydroxide using a special method and then sintering such magnesium hydroxide, but all of these methods require complex and rigorous processes. There is a drawback.

An object of the present invention is to provide magnesium oxide with extremely high purity and a method for producing the magnesium oxide through a combination of relatively simple steps.

That is, according to the present invention, a crude raw material containing magnesium oxide is melted with a mineral acid to obtain a crude solution of a magnesium mineral salt; an alkali is added to the crude solution to precipitate impurities in the crude raw material. Removal to obtain a purified solution of magnesium mineral salt; Add an alkali to the purified solution until the pH becomes 10 or higher; Heat the alkali-added solution at a temperature of 80° C. or higher under pressure in the presence of oxygen gas. treatment; the product obtained by the heat treatment is washed with water and dehydrated; the dehydrated product is
A method for producing magnesium oxide is provided, the method comprising heating to a temperature of 00° C. or higher. However,
Magnesium oxide produced by the method of the present invention has an acicular or fibrous crystal structure, unlike magnesium oxide produced by conventional methods, which has a granular crystal structure. The diameter of the needle-shaped crystal is in the range of 0.1 to 0.5 μ and the length is in the range of 5 to 2
It has the characteristic that it is in the range of 0μ.

In the method for producing magnesium oxide of the present invention, first, various crude raw materials containing magnesium oxide are dissolved in mineral acid to prepare a crude solution of magnesium mineral salt. In addition to i80 clinker, various MgO product dusts can be used as crude raw materials, but from the viewpoint of facilitating the subsequent process, ng
Those containing 80% by weight or more of o are preferred. Sulfuric acid, hydrochloric acid, and nitric acid are used as mineral acids for dissolving magnesium oxide. The amount of mineral acid used is an amount sufficient to dissolve the magnesium oxide contained in the crude raw material 3. For example, in the case of sulfuric acid, it is used at a molar ratio of 1.2.

In the present invention, next, potassium is added to the magnesium mineral salt solution (crude liquid) obtained as described above to precipitate impurities in the crude raw material. That is, while stirring a solution containing a mineral acid salt of magnesium, the pH of the solution (by adding this alkali) is adjusted to 7.
By adjusting to ~9, Fe, Ca, A in the crude raw material
Impurities such as # are precipitated as hydroxide. In this way, the precipitated impurities are filtered out to obtain a purified solution of magnesium mineral salt. The alkalis used in this step include ammonium hydroxide, caustic soda, and caustic potash.

According to the method of the present invention, an alkali is added to the solution (purified liquid) of the mineral acid salt of magnesium obtained as described above while stirring the solution to react with the mineral acid salt of magnesium. This alkali addition reaction is caused by the pn of the solution.
Repeat until 10 or more. The alkalis used in this step include ammonium hydroxide, caustic soda, and caustic potash. Note that a pH buffer solution is added as necessary.

The buffer solution may be added after the alkali addition reaction is completed, but it can also be added simultaneously with the alkali addition. Examples of buffer solutions include NH4Cβ solution when ammonium hydroxide is used as the alkali.

The reaction solution (alkali-added solution) obtained in this way is
Next, it is subjected to heat treatment at a temperature of 80° C. or higher under pressure in the presence of oxygen gas. That is, the reaction solution is placed in an autoclave, oxygen is introduced to increase the pressure, and the autoclave is sealed.
Heat the reaction solution while stirring. The heating temperature is 80°C or higher, preferably 100 to 2-00°C. Also, by introducing oxygen, the pressure inside the odocrape increases to 5 kg/
cm” or more, especially 10 to 15k
g/cm". The time required for the heat treatment is between 2 and 5 hours, depending on the temperature and pressure. This heat treatment constitutes the most important feature of the method of the invention. That is, the reaction solution obtained by adding an alkali to the purified solution of magnesium mineral salt is subjected to pressure heat treatment in an oxygen gas atmosphere and dried.
As can be seen from the X-ray chart in the figure and the micrograph in FIG. 2, an oxide-based product consisting of needle-shaped crystals is produced in a relatively short time. Therefore, the method of the present invention
Instead of firing a hydroxide compound to produce magnesium oxide as in the conventional method, the oxide compound, in which needle-shaped crystals have developed through heat treatment in an oxygen gas atmosphere, is washed and then fired. This method produces high-purity magnesium oxide that has a crystal shape (acicular crystals) that is different from that of magnesium oxide.

The product thus obtained by the heat treatment in the oxygen atmosphere is subjected to calcination after washing and dehydration. Calcination is performed using a mineral acid plate (5O if sulfuric acid is used to dissolve the crude raw material)
4) should be carried out at a temperature sufficient to decompose the
The temperature is 0 to 1.200°C. The firing time is preferably 0.5 to 3 hours.

The magnesium oxide finally obtained by the method of the present invention comprising the above steps has a purity of 99.9% or more, and when observed under a microscope, it is found to have needle-like crystals. FIG. 3 shows a scanning electron micrograph of an example of magnesium oxide of the present invention (magnification: 1 o, ooo
times) are shown. As can be understood from the photograph, the magnesium oxide of the present invention has a diameter of each needle crystal of 0.1
~0.5μ and its length is in the range of 5 to 20μ.

The high purity acicular magnesium oxide of the present invention has several excellent properties. For example, the magnesium oxide of the present invention is a high-purity acicular crystal, and is therefore suitable for use in decomposing high-grade ceramics and the like.

Examples of the present invention will be shown below in order to further clarify the present invention.

Dissolve 20 g of MgO clinker in 60 ml of 98% sulfuric acid, and add 17°5% NI to the solution while stirring.
1. O11 solution was added to p118 to precipitate impurities. The precipitate was removed by filtration to obtain a purified solution of magnesium sulfate (Mg concentration 12 g/n).

While stirring this purified liquid 11, add 17.5% NH4OH.
The solution was added until p■ was 10.4.

NlI40H? After adding 8 solutions, add 10% No. 8 as a buffer solution.
20ml of 4c# aqueous solution was added.

Next, the reaction solution IE obtained as described above was placed in an autoclave (capacity 2β), and oxygen gas was introduced until the pressure inside the autoclave reached 10 kg/cIl. Seal the autoclave and stir the solution inside for 15 minutes.
The temperature was raised to 0°C and maintained at this temperature for 5 hours. After cooling the autoclave to room temperature, the product was taken out from the kneading autoclave, washed with water, and dehydrated. When the product after dehydration and drying was subjected to X-ray diffraction, the result was as shown in Figure 1, and when examined using a scanning electron photomicrograph (magnification: 10.000
Figure 2 shows that acicular magnesium oxide was produced by the reaction inside the autoclave. Next, the dehydrated product was heated in the atmosphere at 1100°C for 1 hour. The magnesium oxide finally obtained in this way exhibited an X-ray diffraction chart as shown in Figure 4 and a standard electron micrograph as shown in Figure 3, and was confirmed to have a needle-like crystal shape. Ta.

Further, when this magnesium oxide was analyzed by chemical analysis, it was found that it had a composition as shown in Table 1 below, and had extremely high purity.

Table 1 Table 2 Analysis values (wt%) MgONa Ca Fe So,
Cm! 99.98 0.001 <0.001 0.
01 <-0,010,001 Example 2 17.5% NH4,OH in purified magnesium sulfate solution
Instead of adding the solution, add a 20% NaOH solution to the purified magnesium sulfate solution 1z with pi of 10.
When the same method as in Example 1 was repeated except that the addition amount was increased to 1, high purity acicular magnesium oxide having the following composition was obtained.

Table 2: Analysis values (wt%) MgONa Ca Fe SO4 (I99
．． 97 0. , O050,0010,009<0.01
1-lace

[Brief explanation of drawings]

FIG. 1 is an X&'jl Yard diagram of the product obtained after autoclaving and drying according to the present invention, and FIG. 2 is a scanning electron micrograph showing the crystal structure of the product. be. FIG. 3 is a scanning electron micrograph showing the crystal structure of magnesium oxide obtained by heating the product of FIGS. 1 and 2, and FIG. 4 is an X-ray chart of the magnesium oxide. It is an X-ray chart diagram.

Claims (2)

[Claims] (1) Magnesium oxide characterized by comprising needle-like crystals having a diameter in the range of 0.1 to 0.5μ and a length in the range of 5 to 20μ. (2) A crude raw material containing magnesium oxide is dissolved with a mineral acid to obtain a crude solution of mineral acid salts of magnesium; an alkali is added to the crude solution to precipitate and remove impurities in the crude raw material to obtain magnesium. Obtain a crude solution of a mineral salt; add an alkali to the crude solution until the pH becomes 10 or higher; heat-treat the alkali-added solution at a temperature of 80° C. or higher under pressure in the presence of oxygen gas; A method for producing magnesium oxide, which comprises washing and dehydrating the product obtained by the treatment; and heating the dehydrated product to a temperature of 1000° C. or higher.