JP2000264631A - Production of calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing calcium carbonate, capable of controlling an average major axis. SOLUTION: A slaking process for preparing a slurry of slaked lime by slaking quick lime with water is carried out by two-stage wet slaking. In a first stage for reacting water with quick lime in a changeable ratio of water/ quick lime, the weight ratio of water/quick lime is changed in a range of 1.5-10. A slurry of slaked lime whose weight ratio of water/quick lime is adjusted at the first stage and prepared through a second stage is carbonated by introducing carbon dioxide to produce particle calcium carbonate having 0.5-10 μm average major axis of primary particle and high uniformity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing calcium carbonate by digesting quick lime with water to prepare slaked lime slurry and reacting slaked lime slurry with carbon dioxide gas. The present invention relates to a method for producing calcium carbonate capable of controlling the particle diameter of the calcium carbonate.

[0002]

2. Description of the Related Art As a method for producing synthetic calcium carbonate, a "liquid-gas" method in which carbon dioxide gas is blown into slaked lime slurry to cause a reaction is typical, and the concentration of slaked lime slurry, reaction temperature, reaction method, and additives. It is known that calcium carbonate having various particle sizes and shapes can be obtained by controlling the reaction conditions such as the presence or absence and the type thereof.

[0003]

However, according to the "liquid-gas" method that is currently widely used in industry,
A simple production method for changing the average major axis of calcium carbonate between 0.5 and 2 μm has not been found. Synthetic calcium carbonate having an average major axis of about 0.5 to 2 μm is suitable for improving various properties as a coating pigment for papermaking, an internal additive, and the like, and an inexpensive production method has been desired. To solve this problem, a method of adding a seed crystal serving as a nucleus to slaked lime slurry or a partially carbonated slaked lime slurry serving as a growth medium is disclosed in Japanese Patent Publication No. 7-5303 and Japanese Patent Publication No.
Although described in each publication of US Pat. No. 19615, there is a problem in that the preparation of the seed crystal is a separate step and involves controlling the gas flow rate, which makes the whole process complicated.

[0004] Further, a method is known in which a part of carbonation is carried out under conditions that the pH value does not drop below 0.2 to produce plate-like basic calcium carbonate, and then carbonation is carried out until the reaction is completed. No., published in Japanese Unexamined Patent Publication No. However, it is necessary to switch the gas flow rate depending on the pH value while keeping the flow rate of the carbon dioxide gas low, so that the production takes time and the process becomes complicated.

Further, Japanese Patent Application Laid-Open No. 5-221634 discloses a method in which a partially carbonated slaked lime slurry is wet-milled and then a secondary slaked lime slurry is added to complete the carbonation. After that, the whole process becomes complicated due to wet grinding with a sand grinder.

On the other hand, in the "liquid-liquid" method, a solution containing mainly carbonate ions (aqueous sodium carbonate solution, ammonium carbonate solution, etc.) is reacted with a solution of a calcium compound (aqueous calcium chloride solution, calcium acetate solution, etc.) to form a carbonate. A calcium particle is obtained, and one of a carbonate solution and a calcium salt solution to which a reaction buffer has been added is dropped and mixed with the other, and the mixture is subjected to a carbonation reaction, and further reacted with calcium to form a water-insoluble salt or A method of obtaining a calcium carbonate having a particle size of 0.1 to 20 μm by dropping a water-soluble salt or a water-soluble acid which forms a hardly soluble salt is disclosed in JP-A-7-196316, but each raw material tank is required. In addition, the amount of dripping must be controlled, and the whole apparatus becomes complicated.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing calcium carbonate which can easily and inexpensively obtain calcium carbonate whose particle size is controlled to a desired size. .

[0008]

In order to achieve the above object, the present invention provides a digestion step of preparing slaked lime slurry by continuous or batch two-stage wet digestion in which quicklime is digested with water, and an aqueous solution prepared in the digestion step. A carbonation step of producing calcium carbonate by injecting carbon dioxide into the slaked lime slurry and carbonizing it in a batch or continuous manner, wherein the weight ratio of water / quick lime in the first stage of the digestion step (water The ratio was 1.5 to 10 and the method for producing calcium carbonate was configured.

This is because if we change the water ratio in the first stage of the digestion process within the range of 1.5 to 10,
Based on the finding that the particle diameter of calcium carbonate changes according to the water ratio. That is, when the water ratio is in the range of 1.5 to 10, it is found that particles having an average primary particle diameter of 0.5 to 2 μm measured by the method described later and having a particle size nearly uniform can be obtained. did.

In the present invention, the water ratio in the first digestion step is changed in the range of 1.5 to 10 depending on the target particle diameter of calcium carbonate. Water ratio 1.5-1
As the water ratio is increased within the range of 0, calcium carbonate having a large particle diameter can be obtained. If the water ratio is less than 1.5, steam digestion occurs at the time of digestion, the particle size of slaked lime becomes extremely large, and calcium carbonate synthesized in the subsequent step also forms aggregates. On the other hand, if the water ratio exceeds 10, the dispersibility of the calcium carbonate particles deteriorates, which is not preferable in terms of quality.

Preferably, in order to obtain calcium carbonate particles with high uniformity, in the first stage of the digestion step, from about the beginning of the digestion reaction to almost the entire region where the digestion reaction occurs, a range of 1.5 to 10 is preferred. A specified amount of quicklime and water are each contacted to perform digestion at a specific water ratio selected from within. That is, the reaction is carried out substantially at a specific water ratio at the same time as or immediately after the start of the reaction. Specifically, for example, a predetermined amount of quick lime is supplied to a predetermined amount of water within 1 minute from the start of the supply. If the charging time of quick lime exceeds 1 minute with respect to a predetermined amount of water, the initial digestion temperature rises slowly and the digestion reaction becomes slow, so that slaked lime particles tend to aggregate. This causes a problem that calcium carbonate particles generated from slaked lime easily aggregate, and may not be preferable in terms of quality depending on the use of calcium carbonate. In the case of industrial production, it is necessary to adjust the speed at which quick lime is introduced in accordance with conditions such as the lot amount, digestion method, temperature, etc., and the degree of uniformity of the particles required as a product and the degree of allowable aggregation. , An appropriate speed may be determined.

[0012] The two-stage wet digestion is a process capable of changing the water ratio, and comprises a first stage in which water and quick lime are reacted, and a second stage in which slaked lime slurry is adjusted to a predetermined concentration and aged. This is a digestion step, and both continuous two-stage wet digestion and batch two-stage wet digestion are applicable to the present invention.

As the digestion method in the first stage of the two-stage wet digestion, a digester batch system, a paddle continuous mixing system, a screw continuous mixing system, a kneader continuous mixing system, etc. can be applied. As long as you get the state to be done
The digestion method is not particularly limited. In order to supply a predetermined amount of quick lime substantially simultaneously, for example, a batch charging method using a hopper with a measuring device can be used.

The purpose of the second digestion method is not particularly limited, since the purpose is to adjust to a predetermined concentration and ripen it.

Before the carbonation reaction in the carbonation step, the slaked lime slurry preferably has a concentration of 3 to 15% by weight and a temperature of 30 to 30%.
Prepared at 90 ° C. By blowing carbon dioxide gas or a mixed gas containing carbon dioxide gas into the slaked lime slurry, the reaction is performed until the carbonation ratio becomes almost 100%. If the concentration of the slaked lime slurry is less than 3% by weight, the industrial productivity is inferior. If the concentration exceeds 15% by weight, the slurry viscosity becomes high and the handling property is deteriorated. is there. On the other hand, if the temperature of the slaked lime slurry before the start of the reaction is lower than 30 ° C., on the other hand, aggregate calcite is liable to be formed as an aggregate, whereas if it exceeds 90 ° C., the energy cost is high and disadvantageous.
The carbonation step may be a batch type or a continuous type.

[0016]

According to the method for producing calcium carbonate according to the present invention, it is possible to obtain calcium carbonate having an average primary particle diameter of 0.5 to 2 μm. Since the method for producing calcium carbonate according to the present invention can be used as it is with little modification or addition of existing equipment to existing equipment, it can be implemented simply and inexpensively without expensive capital investment.

The calcium carbonate produced by the method for producing calcium carbonate according to the present invention has excellent particle uniformity, and particularly when used as a coating pigment or an internal additive for papermaking, whiteness and glossiness are high. It can be expected to improve various performances such as smoothness and the like.

[0018]

Embodiments of the present invention will be described below. It is needless to say that the present invention is not limited to the following embodiments, and can be appropriately modified and implemented within the scope of the present invention.

(Example 1) In-house manufactured lime mass (lime for lime for industrial use, special grade of lime, particle size: 3 to 35 mm) was used as a raw material for lime, and water / quick lime was added to water at 70 ° C as a first digestion step. The mixture was added so that the ratio became 1.5, and the hydration reaction was carried out for 15 minutes. In the second digestion step, concentration adjustment, temperature adjustment, and aging were performed, and a slaked lime slurry having a temperature of 60 ° C. and 5% by weight was obtained. Obtained. To this slaked lime slurry, a carbon dioxide-containing gas (CO ₂ concentration: 20% by volume) was added at 34 L /
min.kg-Ca (OH) _{2 at} a flow rate of 100
% To complete the reaction to obtain calcium carbonate.

The obtained calcium carbonate was observed with an electron microscope. As a result, it was confirmed that the average particle diameter of primary particles was uniform and 0.5 μm.

Incidentally, the average primary particle diameter is defined as the longest chord of a particle measured by an electronic caliper with respect to two diagonal particles in an electron micrograph taken at a magnification of 30,000 at random. This was defined as the major axis of the particle, and the average value was determined and defined as the average major axis of the primary particle.

Example 2 Water / water was used as the first digestion step.
Calcium carbonate was obtained in the same manner as in Example 1 except that the ratio of quicklime was set to 3. Electron microscope observation confirmed that the obtained calcium carbonate was uniform particles having an average primary particle diameter of 1 μm.

Example 3 Water / water was used as the first digestion step.
Calcium carbonate was obtained in the same manner as in Example 1 except that the ratio of quicklime was set to 5. Electron microscope observation confirmed that the obtained calcium carbonate was uniform particles having a primary particle average major axis of 1.3 μm.

Example 4 Water / water was used as the first digestion step.
Calcium carbonate was obtained in the same manner as in Example 1 except that the ratio of quicklime was set to 7. Electron microscope observation confirmed that the obtained calcium carbonate was uniform particles having a primary particle average major axis of 1.7 μm.

Example 5 Water / water was used as the first digestion step.
Calcium carbonate was obtained by the same process as in Example 1 except that the ratio of quicklime was set to 10. Electron microscope observation confirmed that the obtained calcium carbonate was uniform particles having an average primary particle major axis of 2 μm.

Comparative Example 1 Water / water was used as the first digestion step.
Calcium carbonate was obtained in the same manner as in Example 1 except that the ratio of quicklime was 1. Electron microscope observation confirmed that the obtained calcium carbonate was non-uniform aggregated particles having an average primary particle diameter of 0.5 μm.

(Comparative Example 2) Calcium carbonate was obtained in the same manner as in Example 1 except that the digestion step was performed at a water ratio of 26, and a commonly used continuous single-stage digestion was carried out. According to electron microscope observation, the obtained calcium carbonate was found to have a primary particle average major axis of 2.
It was confirmed that the particles were non-uniform aggregated particles of 5 μm.

Table 1 is a table showing the relationship between the water ratio and the particle size of calcium carbonate in each of the above Examples and Comparative Examples.

[0029]

[Table 1] * Measuring equipment: HORIBA LA-500

[Brief description of the drawings]

FIG. 1 is an electron micrograph of the calcium carbonate of Example 2.

FIG. 2 is an electron micrograph of the calcium carbonate of Example 4.

FIG. 3 is an electron micrograph of calcium carbonate of Comparative Example 1.

FIG. 4 is an electron micrograph of calcium carbonate of Comparative Example 2.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsushi Iwashita 3-410-20, Aoto-machi, Ogaki-shi, Gifu (72) Inventor Hisao Dasukoshi 1 Oji-cho, Kasugai-shi, Aichi Oji Paper Co., Ltd. (72) Invention Person Toru Ando 1 Oji-cho, Kasugai-shi, Aichi Prefecture Inside Oji Paper Co., Ltd. (72) Inventor Satoshi Umeki 1 Oji-cho, Kasugai-shi, Aichi Prefecture Oji Paper Co., Ltd. F-term (reference) 4G076 AA15 AA16 AB06 AC02 BA30 BA34 BA45 BC08 BD02 CA02 CA05 CA26 DA02 DA15 4L055 AG12 AH01 AH02 EA16 EA32 FA23

Claims (5)

[Claims] 1. A digestion step of preparing a slaked lime slurry by two-stage wet digestion of quicklime with water, and a carbonation step of producing calcium carbonate by blowing carbon dioxide into the slaked lime slurry prepared in the digestion step to cause carbonation. Wherein the weight ratio of water / quick lime in the first stage of the digestion process is 1.5.
A method for producing calcium carbonate, which is 10 to 10. 2. The method for producing calcium carbonate according to claim 1, wherein the two-stage wet digestion is a continuous two-stage wet digestion. 3. The method for producing calcium carbonate according to claim 1, wherein the two-stage wet digestion is a batch two-stage wet digestion. 4. The method for producing calcium carbonate according to claim 1, wherein the average length of primary particles of the produced calcium carbonate is 0.5 to 2 μm. 5. In the first stage of the digestion process, a specific water / quick lime weight ratio selected from the range of 1.5 to 10 from substantially the beginning of the digestion reaction to substantially the entire region where the digestion reaction occurs. The method for producing calcium carbonate according to any one of claims 1 to 4, wherein the digestion is performed.