JPH0649574B2 - Method for producing fine cubic calcium carbonate - Google Patents

Description

The present invention relates to a method for producing fine cubic calcium carbonate,
Particularly, the present invention relates to a method for efficiently producing fine cubic calcium carbonate having a narrow particle size distribution and a small particle size at low cost by reacting lime milk and carbon dioxide gas.

[Prior Art] Toothpaste base, food, medicine, paint, synthetic resin,
Precipitable fine calcium carbonate is used as an inorganic filler and an additive for paper and ink.

The fine calcium carbonate is produced by reacting lime milk and carbon dioxide gas, and the production method shown in FIG. 2 is usually adopted. That is, first, limestone as a raw material is fired together with anthracite coke and an auxiliary agent in the lime firing furnace 1 while supplying air from the pump 2. The quicklime obtained by firing is hydrated in the elutriation tank 3 with a stirrer to obtain lime milk. The obtained lime milk is reacted in the compounder 5 with the carbon dioxide-containing gas obtained by treating the combustion gas distribution of the lime baking furnace 1 with the gas cleaner 4. The reaction conditions at this time are as follows: the reaction temperature is about 30 ° C., the lime milk has a Ca (OH) ₂ concentration of about 15% by weight, and the carbon dioxide gas-containing gas has a carbon dioxide concentration of 30% by volume.
Before and after. After completion of the reaction, the product is filtered in the elutriation tank 6, dehydrated by the press machine 7, dried and pulverized to be commercialized. The wastewater from the filtration and dehydration processes is discharged after being treated.

In such a method for producing finely divided calcium carbonate, the shape and crystal structure of the product differ depending on the reaction conditions, and in the case of calcite, cubic or spindle-like, and in the case of aragonite, rod-like calcium carbonate is obtained.

Among the calcium carbonate produced, a product with high added value is a calcite-type cubic calcium carbonate having a particle size of about 0.02 to 0.1 μm.

[Problems to be Solved by the Invention] The conventional production method shown in FIG. 2 has a problem that the yield during filtration and dehydration is low because the calcium carbonate produced is fine.

Further, the conventional manufacturing method described above has a drawback that the cost of wastewater treatment increases. That is, since the reaction product concentration of lime milk from the elutriation tank 3 is low, the amount of waste water during filtration and dehydration is large. Then, since the generated calcium carbonate is fine crystals, the wastewater becomes cloudy, which is not easy to treat. Therefore, a huge investment is required for the wastewater treatment facility, and the wastewater treatment cost is high.

[Means for Solving the Problems] The method for producing fine cubic calcium carbonate according to the present invention comprises Ca
(OH) ₂ concentration is 2 to 10% by weight and lime milk kept at 5 to 20 ° C. has a carbon dioxide concentration of 10 to 40% by volume.
In the method of blowing carbon dioxide-containing gas of 5 to react at 5 to 20 ° C., and then filtering and dehydrating, a calcium compound such as Ca (HCO ₃ ) ₂ or CaCO ₃ obtained by filtration and dehydration is converted into CaO. It is characterized in that filtered water containing 250 ppm or less is circulated and reused in the lime milk preparation and / or reaction system.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram illustrating a method according to an embodiment of the present invention.

In carrying out the method of the present invention, first, the raw material limestone crushed to an appropriate particle size, washed with water and carefully selected is sent to a general vertical kiln lime firing furnace 1 together with anthracite coke and various auxiliary agents, and pumped with air. And calcining to obtain quicklime. The calcination is performed at a gas temperature of about 12 at the center of the lime calcination furnace 1.
It is continuously performed under the condition of about 0 to 1300 ° C.

The quicklime extracted from the lime baking furnace is cooled and sorted. Then, lump quick lime having a particle size of about 20 to 50 mm is supplied to the elutriation tank 3 with a stirring device, and reacts with circulating drainage described later to prepare lime milk.

In this example, when preparing this lime milk, the mixing ratio of quicklime to the circulating drainage is adjusted so that the Ca (OH) ₂ concentration is 2 to 10% by weight.

On the other hand, carbon dioxide gas (CO ₂ ) discharged from the lime baking furnace 1
The contained gas is purified by the gas cleaner 4 and CO
₂ Concentration should be 10-40% by volume.

Lime milk 10 from elutriation tank 3 with stirring device in compounder 5
CO ₂ concentration of 10 to 40 passing through the gas cleaner 4
Blow in a gas containing CO _{2 by} volume. In the present invention, the temperature of the lime milk in the compounder 5 is maintained within the range of 5 to 20 ° C. By reacting lime milk and CO _{2 under} such conditions, it is possible to stably produce fine cubic calcium carbonate having a narrow particle size distribution and a small particle size.

In the present invention, in the reaction between lime milk and CO ₂ , when the Ca (OH) ₂ concentration of lime milk is less than 2% by weight, the amount of calcium carbonate obtained is small, and when it exceeds 10% by weight, stable fine cubic calcium carbonate is obtained. Less is.

If the reaction temperature is lower than 5 ° C, the cooling cost will be high, and if it exceeds 20 ° C, spindle-shaped calcium carbonate will be produced.

When the CO ₂ concentration of the CO ₂ containing gas is less than 10%, it is necessary to lengthen the reaction time for producing fine cubic calcium carbonate from lime milk, and when it exceeds 40%, it is an inexpensive carbon dioxide gas source. Can not use plant exhaust gas such as quick lime firing furnace.

The reaction product of the compounding device 5 is supplied to the elutriation tank 6 to be filtered, and then dehydrated and pressed by the pressing machine 7.

In the present invention, the dewatered filtered water obtained by the elutriation tank 6 and the press machine 7 is circulated to the elutriation tank 3 with a stirring device for use in the preparation of lime milk, or is circulated to the compounder 5. Used as dilution water for the reaction system. The dehydrated filtered water may be circulated in both the elutriation tank 3 with a stirring device and the compounding device 5.

By circulating and reusing the filtered water from the elutriation tank 6 or the press machine 7 in this manner, the treatment amount of the cloudy effluent is reduced (in addition, by circulating the whole amount of the filtered water, the effluent treatment is completely eliminated). It can be made unnecessary), and the yield of fine-grained cubic calcium carbonate can be improved.

The filtered water to be recycled and reused is a soluble salt which is an intermediate product of the reaction between lime milk and CO ₂ , such as Ca (HCO ₃ ) _{2 and the} like, which is fine calcium carbonate that has passed through the filter cloth of an elutriation tank or a press machine. It contains calcium carbonate and the like produced by the decomposition of a part of the soluble salt (Ca (HCO ₃ ) ₂ etc.). In the present invention, Ca (HCO in the filtered water is
₃ ) ₂ , the content of calcium compounds such as CaCO ₃ is
It is preferably 250 ppm or less in terms of CaO. C
Drainage containing a calcium compound in excess of 250 ppm in terms of aO is difficult to circulate because Ca (HCO ₃ ) _{2 and the} like are almost saturated.

By the way, when the reaction temperature of lime milk and CO ₂ is set to a temperature higher than 20 ° C. as in the conventional case in circulating and recycling the filtered water as described above, Ca (HCO ₃ ) ₂ contained in the filtered water is set.
Calcium compounds such as act as seed crystals, and the resulting calcium carbonate has a large particle size and a wide particle size distribution.

On the other hand, fine-grained cubic calcium carbonate obtained by dehydration with the press 7 is usually dried, crushed, sieved, and then bagged, and shipped as a product.

[Action] As a result of detailed examination of the relationship between slaked lime (Ca (OH) ₂ ) and CO ₂ such as temperature and solubility, the present inventors have found that the following conditions, that is, Ca (OH) _{2 of} lime milk: The concentration is 2 to 10% by weight, the reaction temperature between lime milk and CO ₂ is 5 to 20 ° C. The reason why the reason is not always clear by satisfying the CO ₂ concentration of the gas blown in is 10 to 40% by volume, but the particle size distribution It has been found that it is possible to efficiently produce fine cubic calcium carbonate having a narrow particle size and a small particle size.

Furthermore, when the filtered water of the reaction product of lime milk and CO ₂ is reused by circulation in the preparation and / or reaction system of lime milk, wastewater treatment can be omitted or reduced, and the drainage can be reduced. It is possible to obtain fine-grained cubic calcium carbonate having a uniform particle size, with almost no effect of the seed crystal due to the reuse of. By the circulation of this filtered water, the details of the reason why fine-grained cubic calcium carbonate with a uniform particle size is obtained are not clear, but the calcium component contained in the circulating filtered water has already produced a large number of nuclei, For this reason, in carbonation by introducing carbon dioxide gas into the filtered water, crystallization of calcium carbonate and grain growth due to the growth of the nuclei are the main constituents. On the other hand, it is presumed that fine-grained cubic calcium carbonate with good crystallinity and uniform grain size is generated by uniform growth.

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. For convenience of description, a comparative example will be described first.

Comparative Example 1 Soft burned lime was hydrated with tap water to prepare lime milk 7 having a Ca (OH) ₂ concentration of 4% by weight. While maintaining the reaction temperature at 25 ° C., CO ₂ -containing gas (CO ₂ content 3
0% by volume) was introduced as the amount of CO ₂ at 6 / min, the lime milk was reacted while continuously measuring the pH, and the introduction of the CO ₂ -containing gas was stopped at the time point when the pH was around 7 as the end point. .

The carbonation rate of lime milk at this end point was 100%.

The solution obtained by the reaction was filtered and dehydrated, and the solid content was dried, followed by X-ray diffraction and electron microscope observation. As a result, it was confirmed that cubic calcium carbonate having an average particle diameter of about 0.12 μm was obtained.

Example 1 In Comparative Example 1, filtered water obtained at the time of filtration was used as raw material water, lime milk was prepared in the same manner as in Comparative Example 1, and the temperature was 20 ° C.
The carbonation reaction was similarly performed at the reaction temperature of 1. The Ca content contained in the filtered water is 180 pp in terms of CaO.
It was m.

After that, the same operation as in Comparative Example 1 was performed, and X-ray diffraction and electron microscope observation were performed. As a result, the average particle diameter was 0.08 μm.
It was confirmed that about the degree of fine-grained cubic calcium carbonate was obtained.

An electron micrograph of the obtained fine-grained cubic calcium carbonate is shown in FIG.

Example 2 Soft-baked quicklime was hydrated with tap water to prepare lime milk 7 having a Ca (OH) ₂ concentration of 4% by weight. While maintaining the reaction temperature at 15 ° C, CO ₂ -containing gas (CO ₂ content 3
0% by volume) was introduced as the amount of CO ₂ at 6 / min and the reaction was performed while continuously measuring the pH of lime milk, and the introduction of the CO ₂ -containing gas was stopped at the time point when the pH reached around 7 as the end point. .

The carbonation rate of lime milk at this end point was 100%.

Using filtered water obtained by filtering and dehydrating the solution obtained by the reaction as raw material water, lime milk was prepared in the same manner as above,
The carbonation reaction was carried out in the same manner at a reaction temperature of 20 ° C.
The Ca content contained in this filtered water is 13 in terms of CaO.
It was 0 ppm.

Then, the solution obtained by the reaction was filtered and dehydrated, the solid content was dried, and then X-ray diffraction and electron microscope observation were performed.
It was confirmed that fine cubic calcium carbonate having an average particle diameter of about 0.08 μm was obtained.

An electron micrograph of the obtained fine-grained cubic calcium carbonate is shown in FIG.

Comparative Example 2 Lime milk was prepared in the same manner as in Example 2 by using filtered water containing 130 ppm of Ca as CaO, which was used as raw material water in Example 2, and was reacted at a reaction temperature of 30 ° C. as in Example 2. The carbonation reaction was carried out. After that, the same operation was performed and the product was subjected to X-ray diffraction and electron microscopic observation. As a result, it was confirmed that spindle-shaped calcium carbonate having a minor axis of 0.4 μm and a major axis of about 2 μm was obtained.

No. 5 electron micrograph of the obtained spindle-shaped calcium carbonate
Shown in the figure.

[Effects of the Invention] As described in detail above, according to the method for producing fine-grained cubic calcium carbonate of the present invention, a toothpaste base material, food, medicine, paint,
It is possible to extremely efficiently produce fine cubic calcium carbonate having a narrow particle size distribution and a small particle size, which is useful as an inorganic filler such as a synthetic resin, paper and ink, an additive and the like.

Moreover, since the filtered water obtained by filtration and dehydration is reused in the lime milk preparation and / or reaction system by circulation, it is not necessary to install a turbid wastewater purification facility, or the scale of the wastewater can be significantly reduced. In addition to being able to significantly reduce the manufacturing cost, it is possible to obtain fine-grained cubic calcium carbonate having a uniform grain size.

[Brief description of drawings]

FIG. 1 is a system diagram illustrating one embodiment of the present invention, and FIG. 2 is a system diagram showing a conventional method. 3, 4 and 5
The figures are electron micrographs showing the particle structures of the calcium carbonates obtained in Examples 1, 2 and Comparative Example 2, respectively. 1 ... Lime firing furnace, 3 ... Elutriation tank with stirring device, 5 ... Compounding device, 6 ... Elutriation tank.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keisuke Morita, 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Central Research Laboratory, Mitsubishi Mining Cement Co., Ltd. (72) Hiroshi Sasaki 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Mining & Cement Co., Ltd. Central Research Laboratory (56) Reference JP-A-59-217621 (JP, A)

Claims (1)

[Claims] 1. A carbon dioxide-containing gas having a carbon dioxide concentration of 10 to 40% by volume is blown into lime milk having a Ca (OH) ₂ concentration of 2 to 10% by weight and kept at 5 to 20 ° C. 5.
In the method for producing fine-grained cubic calcium carbonate, which comprises reacting at -20 ° C and then filtering and dehydrating, Ca (HCO ₃ ) ₂ obtained by the filtering and dehydrating.
Alternatively, a calcium compound such as CaCO ₃ is converted to CaO 2
A method for producing fine-grained cubic calcium carbonate, characterized in that filtered water containing 50 ppm or less is circulated and reused in the lime milk preparation and / or reaction system.