JPS5843329B2 - Method for manufacturing magnesium hydroxide cake - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a magnesium hydroxide cake.

One method for producing magnesium hydroxide is to sinter naturally occurring magnesite and hydrate the resulting magnesia, but in Japan, there is not enough natural magnesite available for industrial use. The manufacturing method of magnesium hydroxide in Japan is a so-called seawater magnesia manufacturing method in which an alkali is added to seawater and fine particles of magnesium hydroxide that are formed and precipitated are collected.

Conventionally, most of the magnesium hydroxide obtained in the seawater magnesia production process is dehydrated and dead-burned to become magnesia clinker, and this magnesia clinker is consumed as a raw material for refractories.

In the past, magnesium hydroxide obtained in the seawater magnesia production process has been dried and used as magnesium hydroxide fertilizer, but the use of magnesium hydroxide as an industrial chemical is not necessarily large. It wasn't.

However, recently it has been discovered that magnesium hydroxide has excellent properties in industrial fields such as flue gas desulfurization and exhaust acid neutralization, and the amount of magnesium hydroxide used in these fields will gradually increase. There is a tendency.

When using magnesium hydroxide industrially, it is important that it is not only a chemically superior substance, but also that it is easy to handle and that there are no problems such as dust generation when using magnesium hydroxide. Excellent physical properties and low cost when using magnesium hydroxide are required.

As a method of satisfying the physical properties required of magnesium hydroxide, a method of transporting, selling, and using magnesium hydroxide in the form of a slurry has been adopted.

Magnesium hydroxide in a slurry state can be transported by pump, so there is no need for manpower when using magnesium hydroxide, and automatic control to maintain appropriate reaction conditions can be performed accurately. It has many advantages such as not generating dust.

However, the content of magnesium hydroxide in the magnesium hydroxide slurry obtained in the seawater magnesia clinker production process cannot be arbitrarily selected, but is naturally determined by the sedimentation characteristics of magnesium hydroxide.

At present, the concentration of magnesium hydroxide in the magnesium hydroxide slurry most commonly obtained in the seawater magnesia manufacturing process is around 30%.

This means that when transporting this slurry, 2.3 ml of unnecessary water is used for 1 ml of magnesium hydroxide, which is the target substance.
transportation costs will be added, and this will cause a significant increase in transportation costs.

In order to reduce the cost of transporting magnesium hydroxide slurry, it is also possible to form a slurry from dried magnesium hydroxide at the destination.

However, it is difficult to make a slurry from dried magnesium hydroxide by just adding it to water and stirring it, and in order to make it into a slurry completely, a fairly large-scale slurry facility with a grinder etc. is required. do.

For this reason, the method of transporting dry magnesium hydroxide and turning it into a slurry at the site of use is not necessarily economically advantageous compared to transporting the magnesium hydroxide slurry itself, except in very large-scale cases. It is said that there is no.

Furthermore, it is possible to transport a magnesium hydroxide cake with a water content of about 50% obtained in the normal seawater magnesia clinker production process, and mix this cake with water at the destination to form a slurry. % magnesium hydroxide cake has a high thixotropy, and it easily fluidizes and unites due to vibration during transportation, so it is impossible to package it in large units, and in reality, it is impossible to package it in large units. Limited to methods of transportation in packaging.

Magnesium hydroxide cakes packaged in this way are consolidated at the destination, and the packaged product becomes a single solid magnesium hydroxide cake, which makes it difficult to unpack and create a slurry. The method of producing magnesium hydroxide slurry by transportation is considered to be a method that is not economically viable.

The method of the present invention was developed as a result of various studies aimed at eliminating the above-mentioned problems.

That is, the method of the present invention involves subjecting a slurry of magnesium hydroxide to calopressure dehydration to form a magnesium hydroxide cake with a moisture content of 40% to 15%, crushing this cake into cakes of 20 or less sizes, mixing with water, and stirring. This is a method for producing a magnesium hydroxide cake characterized by:

The moisture content of the magnesium hydroxide cake in the method of the present invention is:
It is prepared by dehydrating magnesium hydroxide slurry or magnesium hydroxide cake under pressure.

Adopting such a dehydration method is particularly important in the method of the present invention.

With other methods of adjusting the moisture content, such as drying a magnesium hydroxide cake with a moisture content of 50%, even if the moisture content is apparently the same, the moisture content will partially vary, solidifying during transportation, and forming a slurry. The water content of the magnesium hydroxide cake should be 40% or more to avoid problems such as uneven speed.
It is necessary to adjust the moisture content to 15%, especially when the moisture content is 30 to 2.
The case of 0% produces favorable results.

If the water content exceeds 40%, the amount of water to be transported per unit of magnesium hydroxide increases, which is not only not an economical method, but also causes thixotropy in the cake, making it unsuitable for the method of the present invention. When the moisture content of the cake becomes 15% or less, equipment such as a crusher, which is almost the same as that used for slurrying ordinary dry magnesium hydroxide, becomes necessary.

Further, the magnesium hydroxide cake needs to be crushed to a particle size of 205 m or less, and it is particularly desirable to crush it to a particle size of 10 IEil or less.

Since the magnesium hydroxide cake is soft and brittle, this crushing is carried out using extremely simple equipment such as passing it between grooved rolls.

If the particle size of the cake exceeds 20 mm, the rate of slurry formation becomes extremely slow, which is not preferred.

Furthermore, if this cake is kept in contact with the atmosphere for a long period of time during storage or transportation, it may be partially dried or react with carbon dioxide gas in the atmosphere, significantly slowing down the rate of slurrying the cake.

Therefore, it is necessary to store and transport this cake by packaging it in a non-breathable bag or the like.

The method of the present invention will be explained in detail below using Examples and Comparative Examples.

A slurry of magnesium hydroxide can be obtained simply by mixing the crushed magnesium hydroxide cake of the present invention with a necessary amount of water and stirring with a simple device such as a propeller.

The concentration of magnesium hydroxide in the slurry obtained by this method is limited to about 30% or less in the slurry obtained in the seawater magnesia clinker manufacturing process, whereas the concentration of magnesium hydroxide in the slurry obtained by the method of the present invention can be adjusted to any concentration. be able to.

Example 1 Magneium hydroxide slurry (magnesium hydroxide concentration 26.1%) obtained by reacting seawater and slaked lime milk was dehydrated using a tube-type pressure dehydrator to obtain a slurry with a water content of 26.5% and a thickness of 26.5%. A 17 mm plate-shaped magnesium hydroxide cake was obtained.

This cake is crushed into particles of 10 ml or less with a grooved roll, and this crushed material is filled into a normal flexible container so that the circulation of outside air is minimized so that the height is Im and the weight is about 11 cm. Distance 2
After transporting 00h by truck, it was stored in a warehouse for one month.

Thereafter, when this container was opened, the condition of the crushed cake was completely unchanged from before filling, and it was found to be granular and easy to handle during transportation.

When 100 kg of this crushed cake and 110 kg of industrial water were mixed and stirred for 15 minutes at a rotation speed of 15 Orpm using a stirrer with three propeller blades, 82% of the crushed cake passed through a sieve with a mesh size of 44 μm. After stirring for an additional 15 minutes, 98% of the crushed cake passed through a 44 μm mesh sieve, completing the slurry formation of the crushed cake.

It was confirmed that the reactivity of this slurry with respect to acids was almost the same as that of the magnesium hydroxide slurry before pressure dehydration.

Example 2 The plate-shaped magnesium hydroxide cake obtained in Example-1 was crushed into cakes of 20*tn or less using a grooved roll.

When this crushed cake was made into a slurry in the same manner as in Example 1, it took 2 hours and 10 minutes for 98% of the cake to pass through a 44 μm sieve, and then the slurry was completed.

Comparative Example 1 Magnesium hydroxide slurry obtained by reacting seawater and slaked lime milk was filtered with an Oliver filter, and the water content was 5.
After forming a cake with a moisture content of 0%, it was dried in a rotary drum dryer to obtain a dried product with a moisture content of 25.5%.

This dried material is crushed into 10 pieces or less using a grooved roll,
This crushed cake was made into a slurry by the same method as in Example-1.

As a result, after 15 minutes of stirring, 22% of the particles were
Although 31% of the solution passed through the 44 μm sieve after several minutes, the subsequent dissolution rate was extremely slow, and it was substantially difficult to form a slurry.

Comparative Example 2 The crushed magnesium hydroxide cake obtained in Example-1 was
This was stored in a constant temperature and humidity chamber containing 10% carbon dioxide gas to obtain a crushed magnesium hydroxide cake containing 23.8% cake moisture and 2.1% carbon dioxide gas.

When the crushed cake was made into a slurry using the method of Example 1, only 24% of the crushed cake turned into a slurry after 2 hours.
It only passed through a sieve with an opening of 4 μm, making it substantially difficult to form a slurry.

Comparative Example 3 Magnesium hydroxide slurry (magnesium hydroxide concentration 26.1%) obtained by reacting seawater and slaked lime milk was dehydrated using a pressure dehydrator, resulting in a water content of 27.2% and a thickness of approximately 50 mm.
A cylindrical magnesium hydroxide cake was obtained.

This cake was roughly crushed using a grooved roll, and 30 to 25 pieces were sieved to form a slurry cake.

When 100 kg of this crushed cake and 11 kg of industrial water were mixed and stirred using the same equipment as in Example 1, the amount passing through a 44 μm sieve after 15 minutes, 30 minutes, and 2 hours was They were 42%, 54%, and 71%, respectively.

Claims (1)

[Claims] 1. A slurry of magnesium hydroxide is dehydrated under pressure to form a magnesium hydroxide cake with a water content of 40% to 15%, and then this cake is crushed into cakes with a particle size of 20 m or less,
A method for producing a magnesium hydroxide cake characterized by hermetically sealed packaging. 2 Claim 1, characterized in that a cake of magnesium hydroxide is crushed into a cake with a particle size of 1o11 or less.
The method for producing magnesium hydroxide cake described in Section 1.