JPH033605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for producing cubic calcium carbonate with uniform particle size. More specifically, the present invention relates to a method for producing calcium carbonate whose crystals are mainly cubic in shape and whose particle size is uniform in the range of 0.1 to 1 μm.

[Background of the Invention] Calcium carbonate is widely used as a white filler in paints, a filler in composite plastics, and the like.

In particular, recently, neutral paper has been increasingly manufactured using calcium carbonate instead of talc, which was widely used as a filler for paper manufacturing. Conventionally, heavy calcium carbonate has been used as the filler for neutral paper, but due to the large amount of wear on paper-making wire, especially plastic wire, light calcium carbonate is increasingly being used. There is.

[Prior art and its problems] Light calcium carbonate is generally known to have a spindle shape, a columnar shape, a cubic shape, etc.
Various particle sizes have been obtained by changing the reaction conditions.

Conventionally, light calcium carbonate was produced using the soluble chlorination method.
Produced by carbonation method and lime milk soda method. In particular, lime produced in Japan has a high purity, so calcium carbonate is often manufactured by the carbonation method. However, it is often difficult to control the particle size of calcium carbonate produced using the carbonation method;
It has been considered difficult to produce calcium carbonate in the 0.1-1.0 μm range. In addition, it is difficult to make the particles of calcium carbonate obtained using this method into a specific shape, and if no precautions are taken, the calcium carbonate will have a needle-like, spindle-like, or columnar crystal form. Calcium carbonate is obtained.

Therefore, it can be said that the method for producing calcium carbonate using the carbonation method focuses on two points: control of particle size and selectivity of crystal form.

Methods for controlling the particle size and particle shape in the production method of calcium carbonate using the carbonation method in which carbon dioxide is introduced into milk of lime include Japanese Patent Publications No. 14704, No. 42-14706, and No. 54-28399.
No. 58-43331, JP-A No. 53-43097, No. 57-
It is described in various publications such as No. 123822.

Broadly speaking, these can be categorized as follows: As described in Japanese Patent Publication No. 42-14704, Japanese Patent Publication No. 57-123822, and Japanese Patent Publication No. 58-43331, calcium carbonate, which becomes the nucleus of crystals, is added to milk of lime to be carbonated. The main feature is that this calcium carbonate is used as a core to produce calcium carbonate with a uniform particle size. By using the above method, the particle size of the calcium carbonate obtained can be controlled to a certain extent by the particle size of the calcium carbonate crystals that become the core, but when adjusting the calcium carbonate that becomes the core, The particle size must be controlled, and the operation remains complicated.

On the other hand, Special Publication No. 42-14706, Japanese Patent Application Publication No. 43-43097
No. 54-28399 discloses a method for controlling the particle size of calcium carbonate obtained by limiting the particle size or particle shape of calcium hydroxide used in preparing milk of lime. ing. However, these methods also have problems in that it is difficult to prepare calcium hydroxide and the entire process for producing calcium carbonate is complicated.

Furthermore, most of the calcium carbonate obtained by the above method has a spindle-like or columnar crystal form.

On the other hand, calcium carbonate, which has a cubic crystal form, is
It is disclosed in various publications such as No. 54-28397 and No. 56-44016.

The method described in these publications is a method in which milk of lime is sprayed to a specific droplet size and brought into contact with carbon dioxide.

Calcium carbonate obtained by these methods has a cubic shape and a uniform particle size, but the reaction equipment is very complicated because the milk of lime and carbon dioxide are brought into contact while the milk of lime is sprayed. Furthermore, there is the problem that the reaction cannot be completed without using multiple complex devices.

[Object of the Invention] An object of the present invention is to provide a method for producing calcium carbonate having a mainly cubic shape and having a uniform particle size.

Furthermore, in the present invention, the average particle size is 0.1~
The object of the present invention is to provide a method for producing calcium carbonate having a uniform particle size in the range of 1.0 μm.

[Summary of the Invention] The present invention involves adding calcium hydroxide in milk of lime to milk of lime containing calcium hydroxide at a concentration of 3 to 25 g/100 ml, the liquid temperature of which is adjusted to 25°C or less at the start of the reaction. Until at least 9% by weight is carbonated, carbon dioxide is introduced under the condition that the PH value of the milk of lime does not fall substantially by 0.2 or more than the PH value before carbon dioxide is introduced to produce plate-shaped basic carbonic acid. A method for producing cubic calcium carbonate, characterized in that calcium is produced, and then carbon dioxide is continued to be introduced until substantially all of the remaining calcium hydroxide is carbonated.

[Effects of the Invention] According to the production method of the present invention, calcium carbonate having a particle size in the range of 0.1 to 1 μm, which has been relatively difficult to produce in the past, can be easily produced.

[Detailed Description of the Invention] In producing the calcium carbonate of the present invention, milk of lime (calcium hydroxide suspension) is first prepared.

Ordinary quicklime or slaked lime can be used as a source of calcium hydroxide for preparing milk of lime. Examples of quicklime and slaked lime include quicklime powder, lump quicklime, salt-baked quicklime and ordinary slaked lime.

Milk of lime is prepared by adding calcium hydroxide as described above into water. The concentration of calcium hydroxide in milk of lime usually ranges from 3 to 25 g/100 ml, preferably from 5 to 16 g/100 ml. When the concentration of calcium hydroxide in milk of lime is 3 to 25 g/ml, the pH of milk of lime is within the range of 12.0 to 13.5. If the concentration of milk of lime is less than 3 g/100 ml, the concentration is too low and it is not economical. On the other hand, if it exceeds 25 g/100 ml, the viscosity of milk of lime may become high and workability may deteriorate.

Next, it is necessary that the temperature of this milk of lime be adjusted to 25°C or less, preferably in the range of 7 to 18°C, at the time of starting the carbonation reaction. Furthermore, until at least 9% by weight of calcium hydroxide is carbonated, i.e. the carbonation rate is at least 9%.
It is preferable to maintain the temperature of the milk of lime at this temperature until reaching . If the temperature of the milk of lime exceeds 25℃ at the time of starting the carbonation reaction, even if other conditions are met, it will be difficult to effectively generate the nuclei for producing cubic calcium carbonate at this stage, and the main problem will occur. The cubic calcium carbonate of the invention cannot be obtained effectively. Furthermore, by controlling the temperature of the milk of lime at the above-mentioned temperature until the carbonation rate reaches at least 9%, it is advantageous that nuclei are formed well. Since the carbonation reaction is an exothermic reaction, the temperature of the milk of lime can be controlled, for example, by attaching a cooling device to the reaction vessel.

The present invention reduces the PH value of the milk of lime to substantially 0.2 below the PH value before the introduction of carbon dioxide until at least 9% by weight of the calcium hydroxide in the milk of lime is carbonated.
It is necessary to introduce carbon dioxide under conditions that will not cause a drop in the atmosphere.

By performing carbonation within this pH value range, the calcium hydroxide in the milk of lime reacts with carbon dioxide, producing amorphous calcium carbonate on the surface of suspended calcium hydroxide particles. do.
The formation of amorphous calcium carbonate controls the dissolution of calcium hydroxide and lowers the PH value, but in order to effectively generate cubic calcium carbonate, the drop in PH value must be It is necessary to introduce carbon dioxide under the condition that the value does not drop by more than 0.2 from the value before the introduction of carbon.

In particular, it is preferable to introduce carbon dioxide while controlling the drop in pH value within the range of 0.01 to 0.17.

If carbon dioxide is introduced under conditions such that the pH value falls below 0.2, cubic calcium carbonate with a particle size of 0.1 to 1 μm will not be produced.

By controlling the pH value within this range and carrying out the carbonation reaction, amorphous calcium carbonate is produced on the calcium hydroxide in the milk of lime, which is then converted into plate-like basic calcium carbonate through subsequent carbonation. By further carbonation, the form of the plate-like basic calcium carbonate that is produced changes to produce cubic calcium carbonate.

Carbonation rate is [carbonated Ca(OH) ₂ /Ca
(OH) _2- converted total amount of Ca] x 100.

Various methods are possible as specific methods for maintaining the above PH value, but for example, it is preferable to set the carbon dioxide introduction rate to 1 g of calcium hydroxide contained in milk of lime. 1~7ml
This is possible by setting an appropriate value within the range of .

When controlling the rate of introduction of carbon dioxide to keep the PH value within the above range, if the rate of introduction of carbon dioxide exceeds 7 ml/min per 1 g of calcium hydroxide, the PH value will essentially fall below the above range. It becomes difficult to maintain the

Although amorphous calcium carbonate is produced even at a flow rate of less than 1 ml/min, it takes a long time to reach the cube-shaped core of calcium carbonate.

However, even if the rate of introduction of carbon dioxide is within the above range, if the drop in PH value exceeds 0.2, cubic calcium carbonate having a particle size of 0.1 to 1 μm cannot be obtained.

When the carbonation rate exceeds 20%, the amorphous calcium carbonate produced in this way disappears with the formation of plate-shaped basic calcium carbonate, and calcium hydroxide dissolves again, raising the PH value. do.

The carbon dioxide introduced may be carbon dioxide alone or a mixed gas of calcium hydroxide and a substantially non-reactive gas (eg, air, nitrogen gas). Furthermore, carbon dioxide-containing gas discharged during calcining of limestone can be used. When using a mixed gas, the concentration of carbon dioxide in the mixed gas is usually 10% by volume or more, preferably 20% by volume or more.

Incidentally, the above carbonation reaction is carried out under stirring.

Carbon dioxide is further introduced into the milk of lime thus carbonated to carbonate almost the entire amount of calcium hydroxide remaining in the milk of lime.

Through this carbonation, plate-shaped basic calcium carbonate is produced up to a carbonation rate of 60-75%, and by continuing to introduce carbon dioxide, the form of the produced plate-shaped basic calcium carbonate changes and becomes cubic. It becomes calcium carbonate.

Carbonation is usually carried out until the carbonation rate reaches 100%, but if the carbonation rate is 95% or more, it can be used as calcium carbonate.

The temperature of the milk of lime during this carbonation reaction can be carried out without particular cooling or heating, but it is generally 45°C or lower, preferably 10°C or lower.
Perform at a temperature of 45℃. In particular, the milk of lime at the start of the reaction is preferably adjusted to a temperature of 45°C or lower.

Furthermore, it is not necessary to introduce carbon dioxide at a specific introduction rate; generally, it is 1 to 15 ml/min per 1 g of calcium hydroxide in milk of lime (calcium hydroxide added when preparing milk of lime). is within the range of Incidentally, it is also possible to continuously introduce carbon dioxide at the introduction rate when carbonating the initial calcium hydroxide.

The carbonation reaction of the present invention is carried out under stirring.

If stirring is not performed or stirring is insufficient, the carbonation reaction may not be carried out uniformly, and the introduced carbon dioxide may be released unreacted, increasing the cost of the product. It can also be a factor.

The calcium carbonate thus obtained contains at least 50% by weight, generally 90% by weight or more, of cubic (diced) particles with a particle size of 0.1 to 1 μm.

The cube-shaped calcium carbonate thus obtained can be used as a paint or coating material for paper manufacturing, as well as as a material for resin-mixed composite building materials or as a filler for various types of plaster.

Next, examples of the present invention will be shown.

Example 1 Milk of lime 5 having a calcium hydroxide concentration of 7.1 g/100 ml was prepared by putting industrial quicklime powder (average particle size 74 μm or less) and water into a reaction vessel with a capacity of 6 and equipped with a cooling device. The pH value before the start of the reaction was 12.9.

A PH meter electrode was inserted into this milk of lime to continuously measure the PH value of the milk of lime.

This milk of lime is cooled, and while stirring, carbon dioxide with a purity of 99.5% or more is introduced at a reaction starting temperature of 17°C.The rate of introduction of carbon dioxide is 1 g of calcium hydroxide in the milk of lime.
The carbonation reaction was carried out by introducing the carbonate at a rate of 4.6 ml/min.

The PH value of milk of lime is higher than the PH value before the carbonation reaction starts.
When the milk of lime was collected at the point when the temperature had dropped by 0.13, and the carbonation rate was measured, the carbonation rate was 15.5%. The liquid temperature during this period was 17-20°C.

Next, the above carbon dioxide was further introduced into this milk of lime at a reaction initiation temperature of 20°C so that the introduction rate of carbon dioxide was 9.3 ml/min per 1 g of calcium hydroxide in the milk of lime. The carbonation reaction was carried out until the carbonation rate reached 100%.

This carbonated milk of lime was filtered, dehydrated, washed with methyl alcohol, and then dried at 100°C to obtain 460 g of calcium carbonate.

The time required for the carbonation reaction was 45 minutes.

As a result of detailed examination of the electron micrograph of the obtained calcium carbonate, it was found that the calcium carbonate was cube-shaped and had a uniform particle size with an average particle size of 1 μm.

Further, as a result of X-ray diffraction, it was found that it was calcite crystal.

Example 2 Industrial quicklime powder (200 mesh passes) and water were put into the reaction vessel used in Example 1 to prepare milk of lime 5 having a calcium hydroxide concentration of 6.68 g/100 ml.

A PH meter electrode was inserted into this milk of lime to continuously measure the PH value of the milk of lime. The pH value before the start of the reaction was 12.9.

This milk of lime was cooled, and while stirring, the carbon dioxide used in Example 1 was added at a reaction initiation temperature of 20°C.The rate of introduction of carbon dioxide was 1
The carbonation reaction was carried out by introducing the carbonate at a rate of 6.7 ml/min per gram.

The PH value of milk of lime is higher than the PH value before the carbonation reaction starts.
The carbonation rate at the time of 0.08 drop was 10.4%.
The liquid temperature during this period was 20-24°C.

Next, the above-mentioned carbon dioxide was further introduced into this milk of lime at a reaction initiation temperature of 20°C so that the rate of introduction of carbon dioxide was 6.7 ml/min per 1 g of calcium hydroxide in the milk of lime to carbonate it. The carbonation reaction was carried out until the carbonation rate reached 100%.

This carbonated milk of lime was filtered, dehydrated, washed with methyl alcohol, and then dried at 100°C to obtain 445 g of calcium carbonate.

The time required for the carbonation reaction was 45 minutes.

As a result of detailed examination of the electron micrograph of the obtained calcium carbonate, it was found that the calcium carbonate was cube-shaped and had a uniform particle size with an average particle size of about 0.6 μm.

Further, as a result of X-ray diffraction, it was found that it was calcite crystal.

Example 3 Industrial lime powder (200 mesh) and water were put into the reaction vessel used in Example 1 to prepare milk of lime 5 having a calcium hydroxide concentration of 5.4 g/100 ml.

A PH meter electrode was inserted into this milk of lime to continuously measure the PH value of the milk of lime. The pH value before the start of the reaction was 12.7.

This milk of lime was cooled and, while stirring, a carbon dioxide-containing gas (carbon dioxide concentration 20
(volume %, nitrogen gas 80 volume %) and carbon dioxide introduction rate per 1 g of calcium hydroxide in milk of lime.
The carbonation reaction was carried out by introducing the gas at a rate of 6.5 ml/min.

The PH value of milk of lime is higher than the PH value before the carbonation reaction starts.
The carbonation rate at the time of 0.08 drop was 10.7%.
The liquid temperature during this time was 20-23°C.

Next, the above carbon dioxide was further introduced into this milk of lime at a reaction initiation temperature of 27°C so that the introduction rate of carbon dioxide was 3.2 ml/min per 1 g of calcium hydroxide in the milk of lime. The carbonation reaction was carried out until the carbonation rate reached 100%.

This carbonated milk of lime was filtered, dehydrated, washed with methyl alcohol, and then dried at 100°C to obtain 360 g of calcium carbonate.

The time required for the carbonation reaction was 85 minutes.

As a result of detailed examination of the electron micrograph of the obtained calcium carbonate, it was found that the calcium carbonate was cube-shaped and had a uniform particle size with an average particle size of about 0.6 μm.

Further, as a result of X-ray diffraction, it was found that it was calcite crystal.

Claims (1)

[Claims] 1. The liquid temperature at the start of the reaction is adjusted to 25°C or less,
Add milk of lime containing calcium hydroxide at a concentration of 3 to 25 g/100 ml, and while stirring the milk of lime, adjust the pH of the milk of lime until at least 9% by weight of the calcium hydroxide in the milk of lime is carbonated. Carbon dioxide is introduced to produce plate-like basic calcium carbonate under conditions where the pH value does not drop substantially by 0.2 or more than the PH value before carbon dioxide introduction, and then substantially all of the remaining calcium hydroxide is removed. A method for producing cubic calcium carbonate, characterized by continuing to introduce carbon dioxide until the entire amount is carbonated. 2 The temperature of the milk of lime during carbonation to at least 9% by weight of calcium hydroxide in the milk of lime is 10 to 25%.
2. The method for producing cubic calcium carbonate according to claim 1, wherein the temperature is maintained within a range of .degree. 3. Claim 1, characterized in that the temperature of the milk of lime at the start of the reaction is adjusted to a range of 5 to 20°C.
A method for producing cubic calcium carbonate as described in .