JPH09221318A - Production of acicular crystal basic magnesium chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acicular crystal basic magnesium chloride expressed by a formula, Mg2 (OH)3 Cl.4H2 O by dispersing Mg(OH)2 in an aq. solution of a MgCl2 or a mixture of MgCl2 with CaCl2 and allowing react with each other. SOLUTION: The concentration of the MgCl2 aq. solution or the aq solution of mixture of MgCl2 with CaCl2 is 2.5-4.0mol/kg in total of Mg and Ca and 0.5-4.0mol/kg in Mg. The reaction of the aq. solution with Mg(OH)2 is carried out at 10-80 deg.C and the washing at 0-20 deg.C is completed within 1hr. As Mg(OH)2 used as a raw material, a coarse aggregate having relatively low purity such as a sea water method Mg(OH)2 can be used. The mixture of the Mg salt aq. solution with Mg(OH)2 can be left standing without stirring or slowly stirred. By the time elapsed for about one day at the temp. condition of 10-80 deg.C, a plate like or granular crystal of Mg(OH)2 is vanished and a viscous slurry of the acicular crystal basic magnesium chloride is obtained.

Description

Detailed Description of the Invention

[0001]

This invention relates to the formula Mg ₂ (OH) ₃ C
The present invention relates to a method for producing basic magnesium chloride having needle-like crystals represented by l · 4H ₂ O. More specifically, it can be used as a raw material for obtaining needle-shaped magnesium oxide by firing the basic magnesium chloride in the range of about 500 to 1200 ° C., and it is contacted with an alkali under specific conditions. Accordingly, the present invention relates to a method for producing needle-shaped crystalline basic magnesium chloride suitable for use as a raw material for obtaining needle-shaped magnesium hydroxide.

[0002]

2. Description of the Related Art Conventionally, in order to obtain these acicular magnesium hydroxide and magnesium oxide, various kinds of acicular crystalline basic magnesium compounds as precursors thereof and a method for producing the same have been proposed. For example, in JP-A-60-11223, 11 kinds of needle-shaped crystalline basic magnesium compounds are exemplified, and as a method for producing the same, a method of reacting an aqueous solution of a magnesium salt with an alkali such as lime in a specific range, or the like,
A method of reacting an aqueous solution of magnesium salt with a specific range of amount of magnesium oxide is exemplified. Further, for example, in JP-A-60-21813, magnesium oxide having a specific surface area in a specific range is dispersed in an aqueous solution of magnesium chloride in a specific concentration range, and a heat treatment, a production reaction, and an aging operation are performed to form a needle crystal basic Methods have been proposed for obtaining magnesium chloride.

[0003]

As in the conventional method, an aqueous solution of a magnesium compound is used as a magnesium source,
When ammonia, ammonia water, slaked lime, sodium hydroxide, potassium hydroxide, etc. are used as the alkali, the mother liquor after the reaction will contain cations derived from the alkali and will be diluted because water is brought in with the alkali. It Therefore, it is difficult to repeatedly use the mother liquor after the reaction for the reaction of forming the basic magnesium compound in the form of needles. Further, when magnesium oxide is used as the alkali, such disadvantages can be avoided, but it is relatively expensive because a step of firing magnesium hydroxide or magnesium carbonate to form magnesium oxide is required. Furthermore, in JP-A-60-21813,
It has also been pointed out that plate-like or colloidal particles, which are considered to be produced by hydrolysis of the compound, are mixed in the obtained needle-shaped basic magnesium compound.

[0004]

[Means for Solving the Problems] A needle-like crystalline base is prepared from a relatively inexpensive substance by a simple process and by a method in which the composition of the mother liquor does not substantially change due to the reaction and the concentration is not lowered. As a result of intensive studies on a method of synthesizing water-soluble magnesium chloride, magnesium hydroxide is brought into contact with an aqueous solution of magnesium chloride or a mixture of magnesium chloride and calcium chloride in a specific concentration range and kept at a specific temperature range Thus, it is possible to obtain basic magnesium chloride in the form of needles while suppressing changes in the concentration of the mother liquor to a minimum, and by washing under specific temperature conditions, the plate-like crystals of hydrolysis can be obtained. The present invention has been completed in which generation can be suppressed.

That is, the needle-like shape represented by the formula Mg ₂ (OH) ₃ Cl.4H ₂ O is obtained by dispersing magnesium hydroxide in an aqueous solution of magnesium chloride or an aqueous solution of a mixture of magnesium chloride and calcium chloride and reacting it. This is a method for producing crystalline basic magnesium chloride.

More specifically, as the magnesium salt solution, an aqueous solution of magnesium chloride or an aqueous solution of a mixture of magnesium chloride and calcium chloride is used, the concentration of which is M.
The total of g and Ca is 2.5 to 4.0 mol / Kg, preferably 2.75 to
4.0 mol / Kg, of which Mg is more preferably 0.5-4.0 mol / Kg
It is necessary to be 0.75 to 4.0 mol / Kg. If the concentration is lower than this, the reaction with magnesium hydroxide does not occur at all, or even if it reacts, it remains a partial reaction and only a mixture of raw material magnesium hydroxide and needle-like basic magnesium chloride can be obtained. . Further, within this specific concentration range, the higher the concentration, the quicker the reaction occurs, which is advantageous in operation, but the actual maximum is the value shown by the upper limit.

Any magnesium hydroxide can be used as a raw material. For example, the so-called seawater magnesium hydroxide which is widely used for neutralization of exhaust acid or flue gas desulfurization, that is, While circulating part of the product slurry as seed crystals, seawater and lime milk were brought into contact with each other to form magnesium hydroxide, and a polymer flocculant was added to cause coagulation and precipitation. Magnesium hydroxide containing aggregates can also be used. It goes without saying that the finer the particles of magnesium hydroxide, the more rapidly the reaction of forming basic magnesium chloride proceeds, but in that case, precipitation separation and filtration of magnesium hydroxide is difficult, and it is not always advantageous overall. I can't say that there is. When lime milk is used as an alkaline raw material when producing magnesium hydroxide, foreign matter derived from lime is generally mixed in magnesium hydroxide, but after the basic magnesium chloride needle-like crystals are produced, the foreign matter is Since it is difficult to separate the foreign matter, it is preferable to remove foreign matter in advance by classification or the like.

In mixing the magnesium salt aqueous solution and magnesium hydroxide, either a filtered / dehydrated cake can be mixed, or the filtered cake can be mixed as a dried / crushed powder, but it is costly. It is advantageous to mix in a cake state. The mixing amount of magnesium hydroxide is preferably about 4% or less of the weight of the aqueous magnesium salt solution in terms of solid matter. When the content is more than 4%, the whole is hard solid due to the entanglement of basic magnesium chloride of needle-like crystals, which is difficult to disintegrate. If the magnesium hydroxide particles are coarse, they tend to settle, and they may settle at the bottom of the reaction vessel to form a hard solid, but by mixing a small amount of the needle-shaped basic magnesium chloride prepared in advance, It is possible to prevent the precipitation of magnesium oxide, and it is possible to obtain basic magnesium chloride in the form of needle crystals with good dispersibility. Furthermore, the addition of a small amount of needle-shaped basic magnesium chloride has the effect of significantly promoting the reaction.

The mixture of the aqueous magnesium salt solution and magnesium hydroxide may be allowed to stand without stirring, or may be gently stirred so as not to destroy the needle crystals. It is necessary to keep the temperature within the range of 10 to 80 ° C. When the temperature is higher than 80 ° C., the hydrolysis of magnesium chloride lowers the pH of the reaction system and suppresses the formation of basic magnesium chloride. When the temperature of the reaction system is lower than 10 ° C, the reaction rate becomes slow and the reaction takes a long time. Considering both the equilibrium and rate of the reaction, it is necessary to keep the temperature within the range of 10 to 80 ° C.

After about 1 day under these conditions, the plate-like or granular crystals of magnesium hydroxide disappear and a viscous slurry of needle-like crystals of basic magnesium chloride is obtained. This crystal was confirmed to be Mg ₂ (OH) ₃ Cl.4H ₂ O by X-ray diffraction and chemical analysis. The reaction is 3Mg (OH) ₂ + MgCl ₂ + 8H ₂ O →
2Mg ₂ (OH) ₃ is considered to have progressed by Cl · 4H ₂ O, although Mg concentration in the solution by the reaction decreases, otherwise the not change basically composition, to replenish the depleted magnesium chloride This allows the magnesium-containing solution to be used repeatedly as many times as desired.

If a slurry containing acicular crystalline basic magnesium chloride is gently stirred and filtered, a crystalline cake of acicular crystalline basic magnesium chloride can be obtained, but a highly concentrated reaction mother liquor adheres to the crystal surface. Therefore, it is necessary to wash and remove with water. At this time, the needle crystals are stable for at least 1 hour by operating while keeping the temperature of the system below 20 ° C. When the temperature of the system is higher than 20 ° C, basic magnesium chloride is hydrolyzed within a shorter period of time to form fine plate crystals of magnesium hydroxide, and the characteristic morphology of needle crystals is lost.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail based on the following examples.

Example 1 Ionic bitter soup containing Mg ions at a concentration of 1.2 mol / Kg was heated to about 60 ° C., and calcium hydroxide equivalent to 0.95 times equivalent to the amount of Mg ions was used as lime milk for a short time. Then, the mixture was vigorously stirred for about 10 minutes and then gently stirred for about 20 minutes. Next, impurities derived from lime milk were removed using a 38 μm sieve, washed with water, filtered, dried and ground.
According to chemical analysis, the obtained powder was Mg = 41.09%, Ca
= 0.258% magnesium hydroxide, which was a flaky shape with a diameter of 0.1 μm or less and almost no agglomerates were observed by a scanning electron microscope.

200 g of a solution of Mg = 2.0 mol / Kg and Ca = 1.5 mol / Kg was prepared by dissolving crystalline magnesium chloride and crystalline calcium chloride.
After adding g, the mixture was ultrasonically dispersed, heated to 60 ° C., and then allowed to stand at room temperature for 5 days. After that, solid content was filtered, washed with ethanol, and air-dried sample was chemically analyzed to find Mg = 23.44.
%, OH = 24.29%, Cl = 18.87%, and it was Mg ₂ (OH) ₃ Cl.4H ₂ O by X-ray diffraction. When the crystal morphology was observed with an optical microscope at 400 times, no plate-like crystals were observed and all were needle-like crystals.

Example 2 As a solution containing magnesium, Mg = 3.5 mol / K
The same operation as in Example 1 was performed except that a solution having a composition of g and Ca = 0.0 mol / Kg was used. When the obtained solid substance was observed with an optical microscope at 400 times, all of them were needle crystals. Its composition is Mg = 23.56%, OH = 24.39%, Cl = 16.70%
Met.

Example 3 As a solution containing magnesium, Mg = 1.25 mol / K
The same operation as in Example 1 was performed except that a solution having a composition of g and Ca = 2.25 mol / Kg was used. When the obtained solid substance was observed with an optical microscope at 400 times, all of them were needle crystals. Its composition is Mg = 23.44%, OH = 24.26%, Cl = 16.64%
Met.

Example 4 As a solution containing magnesium, Mg = 2.5 mol / K
The same operation as in Example 1 was performed except that a solution having a composition of g and Ca = 0.25 mol / Kg was used. When the obtained solid substance was observed with an optical microscope at 400 times, all of them were needle crystals. The relationship between the solution composition and crystal morphology of Examples 1 to 4 is shown in the upper column of Table 1, and it was confirmed that all were needle crystals.

[0018]

[Table 1]

Example 5 Magnesium hydroxide as a seed crystal in decarbonated seawater 30 g / l
Disperse it, react it with lime milk, add polyacrylic acid amide type polymer flocculant and precipitate and separate,
Magnesium hydroxide was obtained. This was passed through a 38 μm sieve to remove coarse particles, filtered, washed, dried and pulverized to obtain magnesium hydroxide powder having a composition of Mg = 40.17% and Ca =
It was 0.55%.

By dissolving crystalline magnesium chloride and crystalline calcium chloride, Mg = 3.242 mol / Kg, Ca = 0.300mo
200 g of a 1 / Kg solution was prepared, a small amount of the acicular crystal basic magnesium chloride obtained in Example 1 was dispersed therein, and 4 g of the above magnesium hydroxide was further dispersed and kept at 50 ° C. Table 2 shows the composition of the solids from time to time that some of the samples were taken and washed with ethanol.

[0021]

[Table 2]

In pure Mg ₂ (OH) ₃ Cl.4H ₂ O, the Mg content is 23.467%, and the reaction is almost complete in about 2 days.

Example 6 The needle-shaped crystals of basic magnesium chloride obtained in Example 5 were filtered under reduced pressure to obtain a filter cake in which the reaction mother liquor was attached to the surface of the crystals. The product itself was stable when left at room temperature and did not change its shape over a long period of time. 100g of pure water was adjusted to 20 ° C and 2g of the above filter cake
Was charged, dispersed and maintained at this temperature. A part of this dispersion was sampled from time to time and observed under an optical microscope at 400 times. As a result, no change was observed in the morphology of needle crystals even after 60 minutes had elapsed.

Comparative Example 1 Mg = 0.5 mol / Kg as a solution containing magnesium,
The exact same operation as in Example 1 was performed except that a solution having a composition of Ca = 3.0 mol / Kg was used. When the obtained solid is observed with an optical microscope at 400 times, it is a mixture of needle crystals and unreacted magnesium hydroxide, the composition of which is Mg = 36.50%,
OH = 48.60% and Cl = 4.19%.

Comparative Example 2 Mg = 2.25 mol / Kg as a solution containing magnesium,
The exact same procedure as in Example 1 was performed except that a solution having a composition of Ca = 0.25 mol / Kg was used. When the obtained solid substance was observed with an optical microscope at 400 times, most of it was unreacted magnesium hydroxide, and only a few needle-like crystals were observed.

Comparative Example 3 Mg = 1.5 mol / Kg as a solution containing magnesium,
The exact same operation as in Example 1 was performed except that a solution having a composition of Ca = 0.0 mol / Kg was used. When the obtained solid matter was observed with an optical microscope at a magnification of 400 times, all of it was unreacted magnesium hydroxide and no needle crystals were observed. Comparative Example 1
The relationship between the solution composition and the crystal morphology of Nos. 3 to 3 is shown in the lower column of Table 1, but unlike Examples 1 to 4 in the upper column, needle crystals are partially formed or not observed at all. Met.

Comparative Example 4 The same operation as in Example 5 was carried out except that the acicular crystalline basic magnesium chloride was not dispersed in the magnesium salt solution. Table 2 shows the change over time in the composition of the solid content.

Comparative Example 5 The same operation as in Example 6 was carried out except that the temperature was kept at 30 ° C. Only after 30 minutes, fine plate-like crystals that were considered to be produced by hydrolysis were observed, and thereafter, the ratio of plate-like crystals to the total solids increased. The composition of the solid content after 2 hours was Mg = 40.05%, OH = 54.76%, Cl =
It was 0.78%, and it is considered that almost all needle crystals were changed to magnesium hydroxide.

[0029]

According to the present invention, needle-shaped crystalline basic magnesium chloride useful as a raw material for acicular magnesium hydroxide or acicular magnesium oxide can be produced by a simple process using an inexpensive raw material. . According to the present invention, it is possible to produce needle-like crystalline basic magnesium chloride containing almost no plate-shaped crystals. Further, according to the present invention, the reaction mother liquor can be repeatedly used any number of times to produce basic magnesium chloride in the form of needle crystals without generating by-products to be discarded, which is economical.

Claims (2)

[Claims] 1. A needle-shaped compound represented by the formula Mg ₂ (OH) ₃ Cl.4H ₂ O, which is obtained by dispersing magnesium hydroxide in an aqueous solution of magnesium chloride or an aqueous solution of a mixture of magnesium chloride and calcium chloride and reacting it. Method for producing crystalline basic magnesium chloride. 2. The concentration of the aqueous solution of magnesium chloride or the aqueous solution of a mixture of magnesium chloride and calcium chloride is 2.5 to 4.0 mol / Kg in total of Mg and Ca, of which Mg is
0.5 to 4.0 mol / Kg, and the reaction between the aqueous solution and magnesium hydroxide is performed at 10 to 80 ° C., and water-soluble impurities derived from the reaction mother liquor are removed from the obtained basic magnesium chloride of needle crystals. 1 at the temperature of 0 ~ 20 ℃ to
2. The washing with water is completed within the time.
A process for producing the basic needle-shaped crystalline basic magnesium chloride.