JPS61209911A - Production of high purity magnesium oxide - Google Patents

Abstract

PURPOSE:To obtain high purity magnesium oxide by effectively separating impurities from the crude soln. of an Mg salt by precipitation with alkali and hydrothermal treatment. CONSTITUTION:Raw material contg. Mg is dissolved in a mineral acid to obtain the crude soln. of the mineral acid salt of Mg such as MgSO4. The crude soln. is adjusted to 7.5-9.0pH by adding alkali to precipitate and remove a part of impurities such as Fe, Al, Si and Ca in the raw material. The resulting purified soln. of MgSO4 is adjusted to >=10pH by adding alkali, and the alkali added soln. is subjected to hydrothermal treatment at >= 120 deg.C (wet hot water synthesis treatment in an autoclave). By the treatment, Mg forms a complex salt consisting of hydroxide and oxysulfate, and impurities such as Ca, not removed sufficiently in the preceding stage remain in the soln. The formed Mg compound is washed, dehydrated and heated at >=1,000 deg.C to obtain MgO of >=99.99% purity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnesium oxide, particularly magnesium oxide with extremely high purity.

In recent years, magnesium oxide has been attracting attention as a so-called fine ceramic, and as a result, there has been a demand for increasing its purity.

Conventionally, magnesium oxide has been mainly produced by drying and thermally decomposing (calcining) precipitates of magnesium compounds, but in response to the above-mentioned demand for high purity, magnesium oxide has been produced in order to reduce impurities as much as possible. Several methods have been proposed. For example, in JP-A-58-120514, Fe5Al is removed as a hydroxide by keeping the pH value low (pH 2 to 7) when adding ammonia to an aqueous magnesium chloride solution, and then acetic acid is added to an aqueous magnesium chloride solution. However, it is described that by cooling this, calcium can be separated and magnesium chloride can be precipitated, and that highly pure magnesium oxide can be obtained by precipitating the magnesium chloride again with ammonia and calcining it.

This method is one of the useful methods for providing high-purity magnesium oxide, but the operation is relatively complicated, and the purity of magnesium oxide is three nines (99.9%).
), and it is desired to further increase the purity.

In addition to the wet method of firing the precipitate as described above, recently,
It seems that it has been devised to produce high-purity magnesium oxide by a gas phase method in which magnesium metal is directly oxidized, but such a method is understood to require sophisticated reaction operations, and furthermore, It is unlikely that a purity of about 99.9% or higher can be obtained.

The present invention is achieved by a combination of relatively simple steps.
The object of the present invention is to provide a method for producing magnesium oxide with a purity of 9% (four nines) or more.

The present invention is based on the fact that impurities contained in magnesium salts can be separated very effectively by carrying out a hydrothermal treatment in addition to the precipitation operation by adding alkali. That is, in the present invention, a crude raw material containing magnesium is dissolved with a mineral acid to obtain a crude solution of a magnesium mineral salt; an alkali is added to the crude solution to adjust the pH to 7.
, 5 to 9.0, and remove impurities in the crude raw material by precipitation to obtain a purified liquid of magnesium mineral salt;
Adding an alkali until H becomes 10 or more, and hydrothermally treating the alkali-added liquid at a temperature of 120° C. or more to produce a magnesium compound consisting of a double salt of magnesium hydroxide and sulfide; Provided is a method for producing magnesium oxide, which comprises washing a compound with water, dehydrating it, and heating the dehydrated product at a temperature of 1000° C. or higher.

In the method of the present invention, first, a crude raw material containing magnesium (for example, magnesia clinker 6-
A crude liquid of magnesium mineral salt is obtained by dissolving 1 part of monoxide and 1 part of water-measured steel with mineral acid. The mineral acids used are sulfuric acid, hydrochloric acid or nitric acid. Mineral acid salts of magnesium obtained by dissolution treatment with this mineral acid (for example,
The crude liquid of magnesium sulfate contains F due to the crude raw material.
It contains impurities such as es A 1 and Sis Ca.

Next, an alkali is added to the crude solution of magnesium mineral salt to neutralize it. Preferred alkalis for use are ammonium hydroxide, magnesium hydroxide, sodium hydroxide. This treatment removes some of the impurities mentioned above, and for this purpose, the pn of the aqueous solution of the mineral salt of magnesium must be 7.5-L9. Alkali must be added so that o. FIG. 1 shows an example of the relationship between pn and the concentration of impurities in the solution (ratio of each element to Mg) when an alkali is added to an aqueous magnesium sulfate solution. As understood from the figure,
Impurities such as St, AI, and re are precipitated by the addition of alkali, and are present in extremely small amounts in the magnesium mineral salt solution. By separating the precipitate containing these impurities, for example, by a filtration operation, a purified liquid of a mineral acid salt of magnesium such as magnesium sulfate can be obtained. At this time, as can be understood from FIG. 1, Ca (calcium) is hardly removed by this alkali addition. However, according to the method of the present invention, Ca content is also effectively removed by performing hydrothermal treatment (wet hydrothermal synthesis).

That is, in the method for producing magnesium oxide of the present invention, an alkali is added to the purified liquid of magnesium mineral salt obtained as described above until the pH becomes 10 or more, and the alkali-added liquid is heated at 120°C or more. Hydrothermal treatment (wet hydrothermal synthesis treatment using an autoclave) at a temperature of Preferred alkalis to be added in this hydrothermal treatment are ammonium hydroxide and sodium hydroxide. The temperature of the hydrothermal treatment is 120° C. or higher, but if the concentration of Mg is low, it is necessary to increase the temperature of the hydrothermal treatment. Generally speaking, it is preferable to carry out the hydrothermal treatment at a temperature of 18G...180C for 3 to S hours. Furthermore, it is observed that the higher the pH, the higher the yield of finally obtained magnesium oxide. According to the present invention, by this hydrothermal treatment,
Magnesium is a magnesium compound consisting of a double salt of hydroxide and mineral oxide (for example, when sulfuric acid is used as the mineral acid for dissolution treatment, 5 Mg(OR) z MgSO
On the other hand, impurities such as Ca that were not sufficiently removed in the first step (step of adding alkali to the crude liquid) as described above remain in the liquid.

Figure 2 shows the concentration of impurities and p
An example of the relationship with H is shown, and in Figure 3,
An example of the relationship between the concentration of impurities in the liquid and pi in the hydrothermal treatment is shown. Thus, according to the present invention, if the compound produced by the alkali-added hydrothermal treatment is separated by means such as filtration, 5iSFeSAIl can of course be obtained.
A highly pure magnesium compound containing almost no Ca can be obtained.

In the method of the present invention, next, a high purity magnesium compound consisting of a double salt of magnesium hydroxide and a mineral oxide is washed with water and dehydrated, and then the dehydrated product is heated at a high temperature. This high-temperature heat treatment removes OH groups, H2O (crystal water), and mineral residues (for example, SOX groups) in the magnesium compound.
is decomposed and removed to obtain magnesium oxide. FIG. 4 shows an example of analysis of the weight change when a magnesium compound is heated according to the present invention using a differential thermal method. As shown in the figure, a large weight loss was observed at 300-500°C, and then about 100°C.
The weight gradually decreases up to 0°C, and almost no weight loss is observed when the temperature exceeds 1000°C. (Thus, the magnesium compound should be heated (calcined) to a temperature of 1000°C or higher, but the higher the heating temperature, the shorter the firing time to obtain the desired high-purity magnesium oxide. Preferably, FIG. 5 shows the relationship between the firing time and 5O47JI degrees when a magnesium compound consisting of a double salt of magnesium hydroxide and sulfide is heated (calcined) at high temperature. As shown, when the magnesium compound is calcined at 1300° C., SOa is rapidly decomposed and becomes less than about o,oot% in 3 hours.

As is clear from the above description, the present invention can produce highly pure magnesium oxide through a combination of relatively simple steps. The magnesium oxide produced is
99. It is very stable and cannot be obtained with conventional wet methods.
It has a purity of more than 99%.

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

Crushed MgO clinker (MgO concentration, 98%) is crushed to 80μ or less, and 51g of it is 21! I put it in a beaker. Plus 700mj of pure water! and then sulfuric acid (97%)
The mixture was stirred while gradually adding 55 mjt. Further, pure water was added to make the solution 11, and the mixture was stirred to obtain a crude Mg5O aqueous solution (Mg concentration, 30 g/At).

To this crude MgSO4 aqueous solution was added N1 (4
00 (NH3, 28%) was added to adjust the pH to 8.6 to 9.0, and 12 g of NH and C were further added and stirred, followed by leaving the mesothelium. (The addition of NH2OI2 is particularly effective in removing the Si content.) Next, No. Suction filtration was carried out using two pieces of No. 131 filter paper, and mainly Fe, A1. The precipitate containing Si was removed.

Next, the filtrate Mg5O, the purified liquid (Mg concentration, about 3
Add NH40H (NH3, 28%) to
flo, 0 to 1016, and then 3 at 150℃
The magnesium compound was hydrothermally synthesized by hydrothermal treatment in an autoclave for an hour. Pure water 21 was added to this hydrothermally synthesized compound, stirred, filtered with suction, and dried at 100°C (dehydration).
did. When the composite (magnesium compound) after dehydration was analyzed, as shown in Table 1, 1a, Si, CaO
, A I2 gos , Fe! It was confirmed that almost no impurities such as Os and B2O3 were contained.

□Finally, the dehydrated magnesium compound was heated at 1300°C for 3 hours. The obtained magnesium oxide is
As shown in the second column of Table 1, it was confirmed that the purity was extremely high.

[Brief explanation of drawings]

FIG. 1 is a graph showing an example of the relationship between pn and the concentration of impurities in a magnesium sulfate aqueous solution when an alkali is added to the solution according to the method of the present invention. Figure 2 shows the concentration and pH of impurities contained in the magnesium compound in the alkali-added hydrothermal treatment according to the present invention.
It is a graph which shows an example of the relationship between. FIG. 3 is a graph showing an example of the relationship between the concentration of impurities in the liquid and pH in the hydrothermal treatment according to the present invention. FIG. 4 is a graph showing an example of analysis of the weight change when a magnesium compound is heated according to the present invention using a differential thermal method. FIG. 5 is a graph showing the relationship between firing time and soatM degree when magnesium compounds are fired at high temperatures according to the present invention. Fig. 1 pH Fig. 2 Fig. 3 Firing special release (8!)

Claims (1)

[Claims] A crude raw material containing magnesium is dissolved in a mineral acid to obtain a crude liquid of a mineral salt of magnesium, and an alkali is added to the crude liquid to adjust the pH to 7.5 to 9.0, and the crude raw material is dissolved in a mineral acid. Impurities in the raw materials are removed by precipitation to obtain a purified liquid of magnesium mineral salt, an alkali is added to the purified liquid until the pH becomes 10 or higher, and the alkali-added liquid is hydrothermally treated at a temperature of 120°C or higher. A magnesium compound consisting of a double salt of magnesium hydroxide and sulfate is produced, the magnesium compound is washed with water and dehydrated, and the dehydrated product is
1. A method for producing magnesium oxide, comprising heating at a temperature of 00° C. or higher.