JPH08268713A - Refining method of magnesium oxide - Google Patents

Abstract

PURPOSE: To inexpensively and efficiently eliminate impurities contained in MgO by adding MgO to an inorganic acid solution in the ratio so as to make its pH in a special range and allowing to react under heating. CONSTITUTION: The MgO is added to the inorganic acid solution in the ratio so as to adjust its pH to >=7 and is allowed to react under heating. The reaction product is treated with a solid-liquid separation, and then, the cake of Mg(OH)2 is washed with water, dried and calcined, thus high purity MgO is obtained. As the inorganic acid, HCl, H2 SO4 , HNO3 H2 SO3 and H3 PO4 are cited. The pH of the reaction liquid is preferably in the range of 7-9. The reaction is preferably carried out preferably normally for more than one hour at a temp. in the range of 60-90 deg.C. The calcining is preferably carried out at a temp. in the range of 420-1200 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying magnesium oxide, and more particularly to a method for purifying magnesium oxide which can give highly pure magnesium oxide and magnesium hydroxide.

[0002]

2. Description of the Related Art Magnesium oxide and magnesium hydroxide are used as raw materials for electronic ceramics such as pyroelectric materials and dielectric materials, special glass or superconductor materials, or as an annealing separator for electromagnetic steel sheets or as an additive for plastics. However, in these applications, high purity is required. Usually, as a method for purifying magnesium oxide, a method of reacting magnesium oxide with water to produce a hydroxide, washing this with water, and calcining this, or when producing magnesium oxide by a solution reaction, the raw material liquid is ion-exchanged. A method of purifying by a method or the like and then reacting is adopted.

[0003]

However, the former method has a problem that impurities such as chlorine, potassium and sodium can be easily removed, but calcium and silicon can hardly be removed. In addition, the latter method has a problem that the cost becomes very high and that it can be applied when seawater or bitter juice is used as a raw material, but cannot be applied when magnesite is used as a raw material.

Therefore, an object of the present invention is to make it possible to remove impurities contained in magnesium oxide efficiently at low cost.

[0005]

[Means for Solving the Problems] As a means for solving the above problems, the present invention comprises adding magnesium oxide to a solution of an inorganic acid in a ratio such that its pH is 7 or more, and reacting under heating. It is the one.

The inorganic acid is usually hydrochloric acid, sulfuric acid,
Typical examples thereof include nitric acid, sulfurous acid, and phosphoric acid, which can be used alone or in a mixture. In a preferred embodiment, it is preferable to use an inorganic acid having a molar concentration of 1 M or less and to which magnesium oxide is added in such a ratio that the pH of the solution is 7 to 9. This is because if the pH is less than 7, magnesium hydroxide cannot be sufficiently recovered, and if the pH exceeds 9, the purification efficiency becomes poor.

Further, it is preferable that the reaction is usually carried out at a temperature in the range of 60 to 90 ° C. for 1 hour or more. This is because when the reaction temperature is lower than 60 ° C, the purification efficiency becomes poor.
This is because if the temperature exceeds 90 ° C., heat energy is consumed more than necessary, leading to an increase in cost.

When the magnesium oxide is reacted with an acid, magnesium hydroxide is produced, which is subjected to solid-liquid separation and then calcined to obtain high-purity magnesium oxide. In this case, it is preferable to perform the firing at a temperature within the range of 420 to 1200 ° C. This is because the firing temperature is 42
Below 0 ° C, magnesium hydroxide does not decompose thermally and
This is because if the temperature exceeds 00 ° C., grain growth occurs and fine powder cannot be obtained.

[0009]

[Function] Magnesium oxide is added to the solution of inorganic acid
When added at a ratio of 7 or more and heated at a predetermined temperature, magnesium oxide is hydrated in the presence of an acid to form magnesium hydroxide, and at the same time, impurities contained in magnesium oxide are dissolved in the acid to form a soluble salt. Form. For this reason,
When the reaction solution is filtered and solid-liquid separated, impurities are dissolved in the filtrate and removed outside the system, and magnesium hydroxide is obtained as a cake. This cake is washed with water, dried, and then baked to obtain high-purity magnesium oxide.

[0010]

Example 1 Magnesium oxide powder was added to 0.2 M hydrochloric acid at a rate of 2.5 mol / l, and the resulting solution having a pH of 7.5 was heated to 70 ° C. and kept at that temperature for 1 hour to react. After that, the reaction solution was filtered, and the cake was washed with water and dried to obtain magnesium hydroxide powder. Table 1 shows the results of analyzing the content of impurities in the raw material magnesium oxide and the purified magnesium hydroxide.

[0011]

[Table 1] Impurities (%) CaO ₂ SiO ₂ Fe ₂ O ₃ Raw material Magnesium oxide 1.63 0.39 0.37 Purified magnesium hydroxide 0.38 0.25 0.25

[0012]

Example 2 Magnesium oxide powder was added to 0.2 M sulfuric acid at a rate of 2.5 mol / l, and the resulting solution having a pH of 7.2 was heated to 85 ° C. and kept at that temperature for 2 hours for reaction. After that, the reaction solution was filtered, and the cake was washed with water and dried to obtain magnesium hydroxide powder. Table 2 shows the results of analysis of the content of impurities in the raw material magnesium oxide and the purified magnesium hydroxide.

[0013]

[Table 2] Impurities (%) CaO ₂ SiO ₂ Fe ₂ O ₃ Raw material Magnesium oxide 1.20 0.35 0.34 Purified magnesium hydroxide 0.34 0.22 0.20

From the results shown in Tables 1 and 2, according to the method of the present invention, Ca and Si which could not be obtained by the conventional method can be removed,
It can be seen that their contents can be significantly reduced. In particular, it can be seen that the content of calcium is reduced to about 1/4, and the content of silicon and iron is also reduced by about 30 to 40%.

[0015]

As is apparent from the above description, according to the present invention, by hydrating magnesium oxide in the presence of an acid, it is possible to remove Ca and Si which were impossible by the conventional method. Content can be significantly reduced, magnesium oxide can be easily purified with simple equipment, and the amount of impurities in calcium, silicon and iron can be adjusted by appropriately selecting the acid used according to the application. Can be adjusted to produce the desired magnesium oxide and magnesium hydroxide.

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[Procedure amendment]

[Submission date] April 6, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

From the results shown in Tables 1 and 2, according to the method of the present invention, Ca and Si which could not be obtained by the conventional method can be removed,
It can be seen that their contents can be significantly reduced. In particular, it can be seen that the content of calcium is reduced to about one third, and the content of silicon and iron is also reduced by about 10 to 20%.

Claims (5)

[Claims] 1. A method for purifying magnesium oxide, which comprises adding magnesium oxide to a solution of an inorganic acid in a ratio such that the pH is 7 or more, and reacting the solution under heating. 2. The method according to claim 1, wherein the inorganic acid is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, sulfurous acid and phosphoric acid. 3. The method according to claim 1, wherein the reaction product is solid-liquid separated and then calcined. 4. The method according to claim 1, wherein the reaction is carried out at 60 to 90 ° C. for 1 hour or longer. 5. The method according to claim 1, wherein magnesium oxide is added to the at least one acid in a ratio such that the pH of the obtained reaction liquid is 7 to 9.