JPS63307108A - Production of calcium carbonate - Google Patents

Abstract

PURPOSE:To enable production of calcium carbonate having an uniform shape and excellent water dispersibility in a short time, by feeding fine bubbles of gaseous carbon dioxide from a rotary gas diffuser pipe into an aqueous suspension of calcium hydroxide in a specific concentration in a reaction vessel. CONSTITUTION:An aqueous suspension of calcium hydroxide in 5-15wt.% concentration is filed in a reaction vessel equipped with a rotary gas diffuser pipe and fine bubbles of gaseous carbon dioxide are blown from the rotary gas diffuser pipe to carry out carbonation reaction. According to this method, variation in crystal form or particle size is small even if concentration and temperature of the aqueous suspension of calcium hydroxide, blowing rate of the gaseous carbon dioxide, concentration, etc., slightly fluctuate. Thereby calcium carbonate having excellent water dispersibility can be produced in a short time. Furthermore, if waste gas from lime kilns of pulp manufacturing plants is blown by the above-mentioned method, the aimed calcium carbonate useful as a paper filler coating pigment is obtained without using drying and disintegrating steps.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a new method for producing calcium carbonate, and in particular, the concentration of a slaked lime suspension, the temperature at the start of the reaction, the amount of carbon dioxide gas supplied, and the carbon dioxide gas concentration. The present invention relates to a method for producing calcium carbonate, which allows calcium carbonate with excellent water dispersibility to be produced in a short period of time, with less variation in polycrystalline shape than in conventional methods even if the concentration etc. varies to some extent.

[Conventional technology]

A typical industrial production method for calcium carbonate involves blowing carbon dioxide gas into an aqueous suspension with a calcium hydroxide concentration of about 5 to 20% by weight through a fixed spout such as a nozzle or straight pipe to carry out a carbonation reaction. This is a method to Continuing to blow carbon dioxide gas into the calcium hydroxide aqueous suspension causes the carbonation reaction to increase the viscosity of the suspension, and further carbonation causes the viscosity to decrease, eventually becoming more than the original suspension. This results in a suspension of low viscosity. Furthermore, carbonation is progressed until the pm of the suspension is 7.0 to an
The end point of carbonation is defined as the point at which carbonation is reached, after which the resulting suspension is filtered, and the lumps are dried and crushed.

In the above method, by appropriately adjusting the concentration, temperature, amount of carbon dioxide gas, etc. of the calcium hydroxide suspension, spindle-shaped particles with an average diameter (length of the long side) of about 1 to 5 μm are obtained by electron microscopy. Light calcium carbonate consisting of particles and/or columnar particles of calcite crystals and/or aragonite crystals, or average particle diameter (length of one side of cube) 103 ~ [L
A colloidal calcium carbonate consisting of calcite crystals with cubic particles of about 1 μm in size is produced.

Although the reaction time varies depending on the size and type of equipment, conventional methods require a long reaction time of 5 to 24 hours, resulting in low production efficiency, and batch production methods require a large number of reaction vessels.

[Problem that the invention seeks to solve]

In the conventional method of blowing carbon dioxide gas through one or more fixed jet ports, the concentration of calcium hydroxide suspension,
When the temperature, the amount of carbon dioxide gas blown, and the concentration of carbon dioxide gas are changed, the crystal form and particle size of the produced calcium carbonate vary greatly.

The reaction time is determined by the amount of carbon dioxide gas blown or the specifications of the equipment, but in conventional methods it usually takes 5 to 24 hours.
Production efficiency is low due to the long reaction time, and batch production methods have the disadvantage of requiring a large number of reaction vessels. Even if carbon dioxide gas is increased in order to shorten the reaction time, the bubbles are coarsely dispersed, the particle size increases, the effective contact area with the calcium hydroxide suspension decreases, and the number of bubbles increases. They fuse on the way, the particle size becomes even larger, and they quickly reach the liquid surface, which shortens the residence time in the calcium hydroxide suspension. As the ratio of carbon dioxide gas involved (hereinafter referred to as carbon dioxide utilization rate) decreases, it becomes necessary to increase the equipment capacity of the carbon dioxide gas blowing prower more than necessary, and its power consumption also increases, leading to an increase in manufacturing costs.

Furthermore, when calcium carbonate is produced by reacting carbon dioxide in the exhaust gas of a lime kiln in a pulp and paper mill, such as an alkali pulp or kraft pulp manufacturing plant, with a calcium hydroxide suspension, the exhaust gas is usually circulated. Heat is recovered during the lime mud dehydration process, but the carbon dioxide concentration may drop to 10 to 20 volumes in the subsequent process due to air leaking at that time. Traditionally, in calcium carbonate production,
The carbonation reaction is carried out at a carbon dioxide concentration of 25 to 55 volumes, but this is lower than that, so when carbon dioxide is injected from one or more conventional fixed jet ports, the gas volume remains the same. This increases reaction time and reduces production capacity. In addition, if a large amount of carbon dioxide gas is blown in to shorten the reaction time, the reaction efficiency decreases, so it is necessary to increase the installed capacity of the blowing blower more than necessary, which has the disadvantage of increasing manufacturing costs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing calcium carbonate, which improves the above-mentioned conventional drawbacks, and in particular effectively utilizes the exhaust gas of a lime kiln.

[Failure to solve the problem]

To summarize the present invention, the present invention relates to a method for producing calcium carbonate, in which a reaction tank equipped with a rotating aeration tube is charged with an aqueous suspension of calcium hydroxide having a concentration of 5 to 15% by weight, and the It is characterized by supplying microbubbles of carbon dioxide gas from an aeration tube to cause a carbonation reaction.

According to the method of the present invention, calcium carbonate with uniform crystal shape and excellent water dispersibility can be obtained in a shorter time than with conventional methods.

In addition, if lime kiln exhaust gas from a pulp manufacturing plant, such as an alkali pulp or kraft pulp manufacturing plant, is blown in by the method of the present invention, carbonic acid, which is useful as paper filler and coating pigment, can be produced without using drying and crushing steps. You can get calcium.

When using the carbon dioxide gas blowing method using the rotating aeration tube of the present invention, the calcium carbonate produced has a particle size and shape suitable for paper filler or pigment for matte coated paper with good smoothness. Even if you change the concentration, temperature, carbon dioxide gas injection amount, and carbon dioxide concentration of the gaseous calcium hydroxide suspension,
The variation in particle size and particle shape of calcium carbonate produced in a reaction tank equipped with a conventional stirrer with one or more fixed jets and a reaction tank without a stirrer is Calcium carbonate of stable quality can be produced with less fluctuation.

Further, even if the amount of carbon dioxide gas blown is increased, the bubbles are sufficiently broken down, so the reduction in the utilization rate of carbon dioxide gas is small, and the reaction time can be shortened to less than one hour.

The rotating air diffuser pipe has a large number of small holes drilled in the outer peripheral surface of the drum, rotates the drum around its axis, and simultaneously supplies carbon dioxide gas to the inside of the drum. The fine air is supplied into the calcium hydroxide suspension through the small pores, and its rotation violently stirs the calcium hydroxide and calcium carbonate suspension. Fine air bubbles are supplied into the suspension through the small pores. In addition, in order to increase the contact efficiency between the fine bubbles and the suspension, the rotating air diffuser has a small cylindrical body attached to a large number of small holes drilled in the outer circumferential surface of the drum. The dispersion is better and the reaction efficiency is improved. Calcium carbonate scale tends to adhere to the carbon dioxide gas blowing nozzle, but in the case of a rotating diffuser, even if the diameter of the small hole is reduced to 8 -, strong shearing force is generated between the tube and the suspension during rotation. As a result, the produced calcium carbonate is less likely to adhere and form scales that would clog the pores, allowing stable operation for long periods of time.

According to the present invention, compared to conventional fixed blowing pipes, the secondary particles of calcium carbonate produced are weakly agglomerated, uniform, and relatively fine, so they can be suspended without drying or crushing. When used in its liquid state as a papermaking compound, paper with high whiteness and opacity can be obtained. Further, depending on the case, the suspension may be wet-pulverized and used. Furthermore, if the calcium carbonate suspension is dehydrated and concentrated to a concentration of about 60% by weight and blended with a pigment for coated paper, FM coated paper with good smoothness can be obtained.

Carbon dioxide gas is usually generated from lime kilns at a concentration of 25-35
Although a capacity of 1 is often used, if a rotary aeration tube is used, it is also possible to use one with a concentration of 10 to 25 capacity after one step of a flash dryer, and the reaction efficiency will not decrease so much. Although calcium carbonate of stable quality can be obtained even at a carbon dioxide concentration of 10 g or less, the reaction time is prolonged and the power consumption of the blowing blower is increased, resulting in an increase in production cost.

The concentration of calcium hydroxide suspension used in the reaction is 5 to 15.
% by weight is preferred. If it exceeds 15% by weight, the viscosity of the suspension increases, and the fine bubbles blown in from the rotating aeration tube are not sufficiently dispersed, forming large bubbles that rise to the surface, reducing reaction efficiency. The utilization rate of carbon dioxide gas decreases. At the same time, the calcium carbonate crystals formed are fine and form a strongly aggregated ball.

In addition, when the weight is less than 5, the dispersion of carbon dioxide gas is good;
Although the reaction efficiency increases and the utilization rate of carbon dioxide gas increases,
The production capacity per reactor volume decreases. Most of the calcium carbonate crystals produced are coarse, but fine crystals are also mixed in, resulting in a heterogeneous mixture.

Since the calcium carbonate obtained by the present invention has a uniform crystal form, it can also be used in the production of paper filler and pigment #1, paints, inks, plastics, rubber, etc.

The concentration of carbon dioxide in the lime kiln exhaust gas from the causticizing process of an alkali pulp or kraft pulp manufacturing plant in a paper valve manufacturing plant is determined after heat recovery (at the outlet of the flash cyclone circulation section) or after dust removal with a scrubber or electrostatic precipitator. However, if a rotating air diffuser is used, calcium carbonate can be efficiently produced.

Calcium carbonate produced in this manner can be used as it is in the papermaking process without undergoing drying or crushing steps. Calcium carbonate has a good dispersion state, yielding relatively fine secondary particles with weak agglomeration, and when used as filler for papermaking, there is no retention problem in the wire bar of the paper machine.
It has excellent scattering ability in the added paper web and contributes to increasing the whiteness and opacity of the paper.

In addition, in a reaction tank equipped with a conventional fixed blowing pipe, the amount and concentration of carbon dioxide gas, the concentration of calcium hydroxide suspension,
If the reaction starting temperature is the same, the reaction time will not be long;
Furthermore, the particle size of the produced calcium carbonate tends to be somewhat coarse, and when added internally to paper, the effect of increasing whiteness and opacity becomes small.

Regarding the use of rotating air diffuser pipes, Japanese Patent Publication No. 56-24051
The publication introduces a method of increasing the specific contact area of gas and liquid by using a gas jet tube with many holes in the surface of a rotating drum, and shows an example of oxidation of a (NHa)tE'o4 solution. It can be used at a lower gas feed pressure than a sintered glass filter, and the oxidation efficiency is said to be on the same level as a diffuser tube set with a glass filter.

In addition, Japanese Patent Publication No. 52-2295'1 introduces a technology using a jet pipe that protrudes an appropriate length from the outer wall of a rotating drum, and improves gas-liquid contact efficiency by generating fine bubbles. It mentions the effect of reducing pressure loss during blowing.

However, the above-mentioned publications do not contain any suggestion regarding the method of the present invention.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Note that the measurement methods employed in the following examples and comparative examples will be explained.

(Average particle size) Measured using a Shimadzu centrifugal sedimentation type particle size distribution analyzer Model 8AOP 2. The sample is Aro 7T-40 [Toagosei ■]
39 (solid content) was dissolved in an aqueous solution containing Q, 015f (solid content) and dispersed for 5 minutes using an ultrasonic disperser. The average particle diameter was expressed as a median cumulative value (median diameter).

(Crystal Grain Size (Longer Axis)) The representative diameter of spindle-shaped or needle-shaped crystals was measured using a scanning electron micrograph.

(Powder whiteness) Based on the US TAPP engineering standard method T-6460EI-75.

The whiteness of the calcium carbonate suspension was determined by dehydrating it in a Buchner funnel using AIF paper (Toyo Roshi ■) and then drying it at 40° C. for 24 hours. A household mixer was used to crush and homogenize the sample.

(Dry Bic) Repeat printing about 5 times until the paper peels using R knee type 1 printing tester (Mei Seisakusho)) After transferring the pattern on the rubber roll to white paper, measure the ink density (ink density meter D)
M-275 type, Dainippon Screen Manufacturing Co., Ltd.).

(Wet Pick) After applying water to the sample with a sleeve-wound roll (wetted with water), printing is repeated to transfer the pattern on the rubber roll onto white paper, and then the ink density is measured.

(Water loss) Water 2- is placed between the metal roll and the rubber roll with a pipette, the rolls are slightly separated, and the patterns on the paper and the rubber roll are transferred to white paper, and then the ink density is measured.

(Ink set) After printing, a blank sheet of paper is placed on the printed surface, and the ink is transferred to the white sheet of paper using a presser roll after 30 seconds and 60 seconds, and the ink density is measured.

(Printed Surface Glossiness) Printing is performed by changing the amount of ink, and the glossiness when the ink density of the printed surface is t4O is measured.

(Smoothness, air permeability) Measured with Oken style air permeability and smoothness tester (Asahi Seiko).

(Specific scattering coefficient, specific absorption coefficient of filler) Basis weight with internal addition of filler 60 f/ln”% ash 10φ
Specific scattering coefficient (8 values) and specific absorption coefficient (k value) of the sheet
seek. Separately, the specific scattering coefficient (sp value) and specific absorption coefficient (kp value) of a sheet with a basis weight of 60 f/- without internally added filler are determined using the same valve. The 8 value and 2 value of the inner paper are the 8p value and kp value of the pulp, and Δ is also the specific scattering coefficient (B value)
Assuming that additivity holds between the and specific absorption △ coefficient (km value),
The following relational expression holds true: The 8m and nim of Tenka are calculated from this relational expression [Paper Technology Association Journal Vol. 55, No. 14, pp. 54-45 (1978)
(April)).

Example 1 A reaction tank equipped with a rotating air diffuser was charged with 6001 ml of calcium hydroxide aqueous suspension with a concentration of 10% by weight, and while diluting the carbon dioxide gas with air from a carbon dioxide gas cylinder, the diluted gas was supplied at a flow rate of 1500 ml. (15°C). The drum diameter of the diffuser pipe is 80 snow and the surface has a diameter of 11.5 fi.
It was equipped with 200 nozzles and rotated 1,500 times per minute. The shape of the nozzle was a straight tube (cylindrical) and protruded 51 fl. from the drum surface.

Table 1 shows these reaction conditions and the results of measuring the paper quality of the inner paper.

When the carbon dioxide concentration was 20 volumes, the reaction time was 100 minutes (Experiment 4105), which was significantly longer than 170 minutes (Experiment 4104) when the rotation of the aeration tube was stopped and carbon dioxide was blown directly from the aeration nozzle. was shortened to Similarly, when the carbon dioxide concentration is 10 volumes, the reaction time is 195 minutes (experimental volume 10
1), the reaction time when the air diffuser was stopped was 520 minutes (Experiment A
102). These results show that the reaction time was shortened by about 40 cm by rotating the aeration pipe.

The particle size of the produced calcium carbonate (the long axis of the spindle-shaped crystals) is 2 to 5 μm after rinsing, and the filler ratio is the same as when the calcium carbonate is internally added to paper as a suspension without going through the drying and crushing steps. The scattering coefficient is 2200 to 2600 dl''/9, and the whiteness of paper with a basis weight of 60 f/ln'' containing 15% by weight of ash is lower than that of paper with a basis weight of 6097 m'' that does not contain calcium carbonate. 3 to 4 points, and opacity increased significantly to 9 to 10 points.

Generally speaking, the tensile strength, bursting strength, and folding strength of paper with internal filler tend to decrease as the grain size of the filler becomes finer, as the interfiber bonding of the pulp is inhibited.
Even if the average particle size is the same, rotating the diffuser tube makes the shape and particle size of the generated calcium carbonate uniform and reduces the number of fine particles. Comparing 4105 and Grave 104), the paper strength of the inner paper tended to be slightly stronger when the diffuser was rotated.

In addition, light coal obtained by rotating the aeration tube (Experiment 4105
) and commercially available light coal (Shiraishi PC!-850), the average particle size was almost the same, but the paper strength of the former, which had the same shape and particle size, was slightly higher.

Example 2 A reaction tank equipped with a rotating air diffuser was charged with 750 g of calcium hydroxide aqueous suspension with a concentration of 6 to 10% by weight, and lime kill/exhaust gas (60°C) from the kraft pulp manufacturing process was heated to 100 g.
It was injected at a constant flow rate between 0 and 25001/@. The exhaust gas was a moist gas of about 60° C. that had been removed by a scrubber, and the carbon dioxide concentration was about 15 volumes. The specifications and rotation speed of the rotating air diffuser were the same as in Example 1. These reaction conditions and the quality of the paper internally added with the produced calcium carbonate were
Shown in the table.

The reaction time varied between 65 and 205 minutes by changing the flow rate of carbon dioxide gas or the concentration of the calcium hydroxide aqueous suspension, but the specific scattering coefficient of the produced calcium carbonate was 2.
000 tyi? / The increase in whiteness and opacity of the inner paper was 3 points and 10 points or more, respectively, and the improvement effect was satisfactory.

In addition, the concentration of the calcium hydroxide aqueous suspension was adjusted to 58 weight 1 (
10.2% by weight (Experiment A 20')
S ), the temperature at the start of the reaction was still 50℃.
When the temperature was lowered from (Experiment Ii205) to 30°C (Experiment A204), the particle size of the generated calcium carbonate became smaller, but the gas injection rate was reduced to 1000/min (Experiment Ii206).
) to 2500/min (Experiment A 207 ), the particle size of calcium carbonate hardly changed. Therefore, by further increasing the amount of gas blown, it is possible to shorten the reaction time to less than one hour without significantly changing the quality of the calcium carbonate produced, and the particle size and shape can be controlled by water. This can be dealt with by changing the concentration of the calcium oxide aqueous suspension or by changing the reaction initiation temperature.

Although the exhaust gas from the lime kiln used in the kraft valve manufacturing process contains trace amounts of sulfur compounds and unburned carbon, the produced calcium carbonate did not deteriorate in quality, such as coloring or odor.

Example 5 The calcium carbonate aqueous suspension (concentration a 5% by weight) obtained in Experimental Situation 204 of Example 2 was dehydrated, and oxidized starch (egg ace B
1 Oji Cornstarch) Styrene-butadiene latex (, rsRO691, 12.0 parts by weight Japanese synthetic rubber) Stearin i? Calcium (Fcobuisper, 'D
Heavy 'M1 Part Adeka Fine Chemical) Polyamide Polyurea Resin (Sumirez 6'56, 0
．． 5 parts by weight of sodium acrylate (Aron T-40, Toagosei) (Sumitomo Chemical) and 02 parts by weight were added and dispersed with a Colorless disperser to prepare a coating color with a concentration of 61 parts by weight. Next, apply this color to base paper for coating (basis weight 6 x 49/w2, thickness 90μ)
Coated with a test blade coater at a coating speed of 50 k/min to a solid content of 152/-, dried at 140°C, and passed through a super calender twice (linear pressure 19 DKg).
/am) Coated paper was obtained. Separately, as a reference example, commercially available coating grade calcium carbonate and kaolin Niscalon 2000 (dry-ground calcium carbonate, Sankyo Seifun), Kachtal 90 (wet-ground calcium carbonate,
Fuji Kaolin) Brilliant 15 (light calcium carbonate, Shiraishi Kogyo) Ultra Coat (imported kaolin)
, Engelhard), a coating color having a concentration of 64% by weight was prepared in the same manner as above, and a similar coated paper was obtained.

Table 3 shows the paper quality of these various coated papers and the reaction conditions for calcium carbonate.

Calcium carbonate used in coating pigments can be divided into heavy calcium carbonate, which is obtained by dry or wet grinding of limestone, and light calcium carbonate, which is produced by combining calcium hydroxide and carbon dioxide gas.

Calcium carbonate produced in an aeration tube type reaction tank belongs to light calcium carbonate, but it is similar to light calcium carbonate such as Brilliant 15 (Shiraishi Kogyo), which has fine cubic crystals (side length 0.15).
μm), coarse spindle-like to needle-like crystals (major axis 1.5
μfn), of the coated paper quality items, white paper gloss and printed surface gloss are low, but because of its high smoothness, it is considered to be a pigment suitable for matte coated paper. I can say that. On the other hand, heavy calcium carbonate Niscalon 200
Comparing Carbital 90 (average particle size: 2.2 μm) and Carbital 90 (average particle size: 1.3 μm), as the grinding progresses and the particle size becomes finer, the white paper gloss, printed surface gloss, and smoothness of the coated paper decrease. tends to be higher.

Calcium carbonate produced in a diffuser tube type reaction tank has low white paper gloss and printed surface gloss like Niscalon 2000, but gaps are created between pigment particles during coating, which are compressed and leveled in a supercalender. As the particle shape and particle size are uniform, the smoothness is extremely high.
The smoothness is close to that of Ultra Coat (kaolin). Higher smoothness is advantageous because it improves printability. Although Wet Vic and Dry Vic were inferior to Niscalon 2000, they are at a level that can be prevented by increasing the amount of binder (latex and starch) in the coating color or by using a mixture with other pigments.

As mentioned above, in order to compare the coating suitability of pigments, 100 parts of each pigment was mixed and coated, and the paper quality of the coated paper was examined.
It has been found that calcium carbonate produced in a diffuser tube type reaction tank exhibits excellent properties when used as a pigment for matte coated paper, either in its entirety or mixed with other pigments.

Comparative Example 1 A reaction tank in which carbon dioxide gas is blown downward from a cylindrical blowing pipe (
A concentration of 77.
~11IL1 weight of calcium hydroxide aqueous suspension
00/loading, and lime kiln exhaust gas (60° C.) from the kraft pulp manufacturing process was blown in at a rate of 2500/load (1500/load per 1-unit of calcium hydroxide aqueous suspension).

The carbon dioxide concentration was about 15 volumes (measured at 15°C).

The operating conditions of the rotary diffuser are the same as in Example 1. The results are shown in Table 4.

Calcium carbonate produced in a simple reaction tank had a coarser particle size and a non-uniform shape under the same reaction conditions than calcium carbonate produced in a rotating aeration tube reaction tank. Calcium carbonate produced in a stirred reactor had a more uniform shape than in a simple reactor, but the particle shape was not as uniform.

Calcium carbonate produced in the rotating aeration tube reactor contained spindle-shaped calcite-type crystals and some needle-shaped aragonite-type crystals, but the particle size was smaller than in the other two methods, and the filler content was smaller than that of the other two methods. The specific scattering coefficient was also the same or slightly higher. When used as filler for paper, there is no problem even if aragonite crystals are mixed in.

The reaction time is as follows: When the amount of carbon dioxide gas blown per slurry is the same, the calcium hydroxide suspension concentration is 6% by weight.
, the simple type takes 170 minutes compared to 105 minutes for the rotating diffuser type.
The stirring method took 180 minutes, 1.6 to 1.7 times as long. When the concentration of calcium hydroxide suspension is 10% by weight, the viscosity of the suspension increases compared to when the concentration is 6% by weight, so the dispersion of bubbles of the blown gas becomes worse and the reaction efficiency decreases. The simple method took 560 minutes and the stirring method took 550 minutes, which was 1.4 times longer than t2, but the difference was smaller.

When the slurry viscosity increases in a rotating aeration tube reactor, the difference between it and a simple reactor or a stirring reactor tends to decrease, but the suspension concentration 6 used in normal reactions tends to decrease.
It was found that a concentration of up to 10% by weight also had the effect of shortening the reaction time.

〔Effect of the invention〕

As explained above, according to the present invention, calcium carbonate with excellent dispersibility and uniform shape can be obtained in a shorter reaction time than with the conventional method of blowing carbon dioxide gas through a fixed jet nozzle. When used as a filler for paper, the scattering ability of the filler is large, so the whiteness and opacity of the internally added paper increase greatly, and the filler aggregates to an appropriate size, which reduces the bond between the fibers of the pulp. Because it does not inhibit paper strength (tensile, bursting, and folding strength), the amount of decrease in paper strength (tensile strength, bursting strength, and folding strength) can be reduced by internally adding calcium carbonate obtained by conventional methods or calcium carbonate obtained by crushing limestone to the same average particle size. It was very small.

In addition, when the calcium carbonate obtained according to the present invention is blended into a pigment for coating, it produces a matte coating with excellent smoothness and good printability compared to when calcium carbonate for pigments made by dry-pulverizing limestone is blended. paper is obtained.

By using carbon dioxide gas in the exhaust gas of a lime kiln in a pulp and paper mill, for example, an alkali pulp or kraft pulp manufacturing plant, calcium carbonate can be efficiently reacted with the method of the present invention. The carbon dioxide concentration in the exhaust gas after the shin process is 10-2
Even when the volume is as low as 0, the reaction can be completed in a shorter time than conventional methods, and the remarkable effect is that it can be internally added to or coated on paper without drying or crushing. is played.

Furthermore, according to the method of the present invention, the concentration of the reaction solution (which affects the stirring effect due to viscosity fluctuation) or the temperature of the reaction solution (
Even if the solubility of carbon dioxide changes (which affects the reaction), the change in the particle shape of calcium carbonate is smaller than in a method using a conventional fixed blowing tube, which is an excellent effect.

Claims (1)

[Claims] 1. A reaction tank equipped with a rotating aeration tube is charged with an aqueous suspension of calcium hydroxide having a concentration of 5 to 15% by weight, and fine bubbles of carbon dioxide gas are supplied from the rotary aeration tube to produce carbon dioxide. A method for producing calcium carbonate, characterized by carrying out a chemical reaction. 2. Claims for obtaining calcium carbonate, which is useful as paper filler and coating pigment, by using lime kiln exhaust gas from a pulp manufacturing plant as the carbon dioxide source, without going through the drying and crushing steps. The method for producing calcium carbonate according to item 1.