JP2005170733A - Production method for scallop-shell-derived light precipitated calcium carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing calcium carbonate with stable qualities, exhibiting small dispersion of, e.g., the shape expressed by an aspect ratio of primary particles or the crystal state of calcite, aragonite, or the like, by blowing a mixed gas of carbon dioxide and air (mixed carbon dioxide) into lime milk. <P>SOLUTION: A carbonization reaction is conducted by blowing a mixed carbon dioxide gas having a CO<SB>2</SB>concentration of 35 vol.% or higher into a suspension consisting of water and quicklime yielded by firing scallop shells or slaked lime yielded by slaking the quicklime, from a carbon dioxide jet port 16 of a carbon dioxide supply pipe 12 equipped with a carbon dioxide jet port opening and closing means 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing calcium carbonate (light calcium carbonate) produced by blowing a mixed gas of carbon dioxide and air (mixed carbon dioxide) into lime milk.

  In Japan, limestone is abundantly produced in the country. Calcium carbonate products produced using this limestone are inexpensive, have high whiteness, are harmless, and can be obtained in various particle sizes. For rubber, plastic fillers, paints, and inks. It is used in various fields as an extender pigment, a filler for paper filling, a pigment for paper coat, an additive for pharmaceuticals, cosmetics, foods, agricultural products and the like.

  This calcium carbonate product is generally roughly classified into two types: heavy calcium carbonate and light calcium carbonate (synthetic calcium carbonate).

  Heavy calcium carbonate mechanically pulverizes limestone and classifies the pulverized product to produce heavy calcium carbonate in various particle diameter ranges.

  However, the heavy calcium carbonate has a broad particle size distribution due to its manufacturing method. Therefore, any grade of heavy calcium carbonate cannot be produced having a fine particle size and a narrow particle size distribution. For this reason, the above-mentioned heavy calcium carbonate cannot be used in advanced applications requiring a fine particle size and a narrow particle size distribution.

  On the other hand, light calcium carbonate is produced by a chemical method such as a carbon dioxide compounding process, a lime soda process, or a soda process. In the carbon dioxide compounding process, calcium carbonate is synthesized by reacting quick lime obtained by baking limestone at high temperature and water to prepare lime milk, and then conducting carbon dioxide gas generated during limestone baking in lime milk. Is the method. The lime soda process is a method of synthesizing calcium carbonate by reacting lime milk with sodium carbonate. The soda process is a method of synthesizing calcium carbonate by reacting sodium chloride with calcium chloride.

  The light calcium carbonate produced by the chemical method as described above has a fine particle size and a narrow particle size distribution, and therefore can be used for applications where these are required.

  Among the light calcium carbonate production methods described above, a carbon dioxide gas compound process is generally used from a practical and economical viewpoint (see, for example, Patent Document 1).

  As disclosed in Patent Document 1, a typical industrial production method of a carbon dioxide compounding process is that a calcium hydroxide aqueous suspension (lime milk) having a concentration of about 5 to 20% by mass is replaced with a nozzle or a straight pipe. This is a method in which carbonation gas is blown from a fixed jet outlet or the like to perform a carbonation reaction.

  That is, by appropriately adjusting the concentration, temperature, carbon dioxide blowing amount, etc., of the calcium hydroxide suspension, spindle-shaped particles and columnar shapes having an average particle diameter (major axis length) of about 1 to 5 μm by electron microscope observation From light calcium carbonate (high aspect ratio calcium carbonate) composed of calcite crystals or aragonite crystals of particles, or from calcite crystals of cubic particles having an average particle diameter (length of one side of a cube) of about 0.03 to 0.3 μm A colloidal calcium carbonate (low aspect ratio calcium carbonate) is produced.

However, in the above-described carbon dioxide compounding process, when the concentration, temperature, carbon dioxide blowing amount, and carbon dioxide concentration of the calcium hydroxide suspension are changed, the crystal form of the generated calcium carbonate and the variation in the particle size are significant.
JP-A-5-163018 (paragraph numbers [0002] to [0006], [0042] to [0044])

The present inventors have in the discussion for solving the above problems, first, using the carbon dioxide gas supply pipe shown in FIG. 2 (nozzle), from carbon dioxide gas ejection port 4 formed in the lower surface of the nozzle 2, a predetermined CO ₂ concentration Carbonation reaction was performed by blowing mixed carbon dioxide into lime milk.

  However, during the carbonation reaction, clogging and clogging due to the adhesion / dropping off of calcium carbonate generated in the vicinity of the carbon dioxide gas outlet 4 occurred repeatedly, and the reaction situation such as carbon dioxide gas injection greatly fluctuated. Calcium carbonate obtained in such a carbonation reaction situation has variations in the shape and crystal form of primary particles.

  Then, carbonation reaction was performed using the carbon dioxide supply pipe (nozzle) shown in FIG. In this carbonation reaction, the present inventors have found that the condition of blowing carbon dioxide is improved, and calcium carbonate having a stable quality with little variation in the shape and crystal form of primary particles can be obtained. In addition, it is possible to obtain calcium carbonate with more stable quality by making lime milk into a suspension composed of quick lime obtained by baking scallop shells or slaked lime obtained by digesting the quick lime and water. The present inventors have learned and have come to complete the present invention.

  Accordingly, an object of the present invention is to provide a method for producing stable quality calcium carbonate which solves the above-mentioned problems.

  The present invention for achieving the above object is described below.

[1] A mixed gas of carbon dioxide gas and air having a CO ₂ concentration of 35% by volume or more in a suspension composed of quick lime obtained by baking scallop shells or slaked lime obtained by digesting the quick lime, and water, A method for producing light calcium carbonate derived from scallop shells, wherein the carbon dioxide gas supply pipe is provided with a carbon dioxide gas outlet opening / closing means between the carbon dioxide gas outlet and the carbon dioxide gas supply pipe.

  [2] The method for producing light calcium carbonate derived from scallop shells according to [1], wherein an average reaction temperature from the start of blowing to the end of blowing is 40 ° C. or higher.

  [3] The method for producing light calcium carbonate derived from scallop shells according to [1], wherein the average reaction temperature from the start of blowing to the end of blowing is less than 40 ° C.

According to the method for producing calcium carbonate of the present invention, in the method for producing light calcium carbonate produced by a carbon dioxide compounding process, quick lime obtained by baking scallop shells or slaked lime obtained by digesting the quick lime and water The carbon dioxide reaction state is improved since the mixed carbon dioxide gas having a CO ₂ concentration of a predetermined value or more is blown into the suspension consisting of the carbon dioxide gas outlet of the carbon dioxide gas supply pipe provided with the carbon dioxide gas outlet opening / closing means. In addition, it is possible to obtain calcium carbonate having a stable quality with little variation in the shape and crystal form of the primary particles.

  In addition to the above production conditions, the average reaction temperature from the start of blowing to the end of blowing is set to a predetermined high temperature region or low temperature region, thereby reducing variations in the high aspect ratio calcium carbonate or low aspect ratio calcium carbonate described above. Stable quality products can be created.

  Since the calcium carbonate produced by the production method of the present invention has the above-mentioned stable quality, it can be effectively used for various applications such as fortifying calcium by adding it to foods such as milk drinks and juices. In addition, it can be used as an additive for industrial materials such as rubber, plastic fillers, paints, extenders for inks, pharmaceuticals, cosmetics, and the like that require high dispersibility.

  Hereinafter, the present invention will be described in detail.

  An example of the production apparatus used in the method for producing calcium carbonate of the present invention is shown in FIG. 3 in which the flow of the apparatus is shown, and in FIG. 4, a partial outline of the vicinity of the nozzle in the reaction equipment (reaction tank) in this flow is shown. It is.

  Examples of the flow of the light calcium carbonate production apparatus include a carbon dioxide reaction circulation adjustment method shown in FIG. 1 and a carbon dioxide premix adjustment method shown in FIG. 3 from the carbon dioxide mixing adjustment method.

  One carbon dioxide reaction circulation system is a system in which unreacted carbon dioxide gas is reused. In this carbon dioxide reaction circulation system, as shown in FIG. 1, raw slaked lime and / or quick lime is supplied to the reaction equipment through the raw material loading equipment. This slaked lime and / or quick lime is stirred and mixed with water supplied from a recovered water line and / or a make-up water line in a reaction facility to form lime milk.

Carbon dioxide gas is supplied from the CO ₂ gas supply facility to the reaction facility through the CO ₂ gas supply line, and blown into the lime milk to perform a carbonation reaction. Exhaust gas from the reaction equipment is returned to the CO ₂ gas supply line via the unreacted CO ₂ recovery and recycling facilities as unreacted CO _2, it is recycled to the carbonation reaction.

  By the carbonation reaction in the reaction facility, the lime milk becomes a calcium carbonate slurry. This calcium carbonate slurry is sent from the reaction facility to the dehydration facility and separated into dehydrated cake and water. The separated water is returned to the reaction facility through the recovered water line.

  The dehydrated cake is sent from the dehydration facility to the drying facility, and after drying, becomes a calcium carbonate product.

On the other hand, in the carbon dioxide premixing adjustment method, carbon dioxide gas supplied from the CO ₂ gas supply facility to the reaction facility is mixed with air supplied from the air supply facility in the mixer in advance and then supplied to the reaction facility. Is done. Further, the exhaust gas from the reaction facility is discharged out of the system without being collected and circulated. Except for the above flow, it is the same as the carbon dioxide reaction circulation system.

When the carbon dioxide reaction circulation system shown in Fig. 1 is used as the flow of the light calcium carbonate production system, the CO ₂ concentration of the return gas from the unreacted CO ₂ recovery / circulation facility is likely to fluctuate, so that the reaction tank nozzles The CO ₂ concentration of the mixed carbon dioxide supplied is likely to fluctuate. In particular, in the case of carbonization, when clogging and releasing clogging occur repeatedly at the carbon dioxide gas outlet 4 shown in FIG. 2, the CO ₂ concentration in the carbon dioxide gas supply pipe (nozzle) 2 of the reaction tank and the carbon dioxide gas jet near the carbon dioxide gas outlet 4 The flow rate becomes unstable and the dispersion of gas into the reaction tank becomes unstable, so that the reaction situation greatly fluctuates, and as a result, the quality also fluctuates.

On the other hand, when the carbon dioxide premixing method is used, a mixed carbon dioxide gas with a stable CO ₂ concentration is supplied, the gas supply to the nozzle of the reaction tank is stabilized, and as a result, the reaction time becomes constant and the quality Also stable without fluctuations.

When the nozzle shown in FIG. 4 is used as the nozzle of the reaction tank, the generated calcium carbonate adheres to the carbon dioxide gas outlet 16 and the carbon dioxide gas outlet 16 is not clogged. The CO ₂ concentration fluctuation and the carbon dioxide jet flow rate fluctuation at the carbon dioxide jet outlet 16 are small, and the stability of the reaction and the stability of the obtained calcium carbonate are further improved.

  Further, when the nozzle shown in FIG. 4 is used, even when the carbon dioxide reaction circulation system shown in FIG. 1 is used, the stability of the reaction and the stability of the obtained calcium carbonate are good. When the carbon dioxide premixing method shown in 3 is used, the stability of the reaction and the stability of the resulting calcium carbonate are further improved.

  In the calcium carbonate production apparatus of this example, a carbon dioxide jet opening / closing means 14 is provided on the lower surface of the nozzle 12 shown in FIG. 4, and a carbon dioxide jet 16 is provided at the lower end of the carbon dioxide jet opening / closing means 14. ing. The carbon dioxide gas outlet opening / closing means is not particularly limited as long as it can prevent the adhesion of calcium carbonate by its operation. For example, when the mixed carbon dioxide gas is blown into lime milk, the carbon dioxide gas outlet 16 is provided. An opening / closing means or the like for making the carbon dioxide gas outlet 16 “closed” when the blowing is stopped can be used. Examples of the opening / closing system include a manual system or an automatic system that opens and closes by sensing the gas pressure in the nozzle 12.

  Moreover, what is provided with the non-return mechanism in addition to the opening / closing means is preferable. Furthermore, what can adjust an opening degree is preferable.

Furthermore, the carbon dioxide jet flow rate at the carbon dioxide jet port 16 greatly affects the stabilization, and the linear flow rate is preferably 26.6 to 133 L / min · cm ² . When deviating from this range, the dispersibility of carbon dioxide bubbles is poor, the foam particle size is increased, and the residence time required for the reaction with calcium hydroxide is shortened, so the efficiency of the carbonation reaction is lowered.

  Furthermore, in the nozzle 12 shown in FIG. 4, since the infiltration of the lime milk into the nozzle 12 can be prevented by the carbon dioxide gas outlet opening / closing means 14, the diameter of the carbon dioxide gas outlet 16 can be made larger. By using the large-diameter carbon dioxide gas outlet, the mixed carbon dioxide gas can be blown into the lime milk more stably.

The method for producing calcium carbonate according to the present invention comprises a mixed carbon dioxide gas having a CO ₂ concentration of 35% by volume or more in a suspension comprising quick lime obtained by firing scallop shells or slaked lime obtained by digesting the quick lime and water. In the carbonation reaction, the mixed carbon dioxide gas is blown from a carbon dioxide gas outlet of a carbon dioxide gas supply pipe provided with a carbon dioxide gas outlet opening / closing means.

  Hereinafter, the manufacturing method of the calcium carbonate of this invention is demonstrated in detail as an example of the manufacturing apparatus using the flowchart of FIG. 3, and the partial schematic diagram of the nozzle vicinity of FIG.

(Scallop shell)
The scallop shell used in the method for producing calcium carbonate of this example is calcium carbonate as a raw material having the composition exemplified in Table 1. In addition to scallop shells produced from the sea, limestone produced from land is the main source of calcium carbonate. Compared to this limestone, scallop shells have less variation between production areas as shown in Table 1.

石灰石に含有されたナトリウム分が１００ｐｐｍ以下に対し、ホタテ貝殻に含有されたナトリウム分は０．１〜０．５質量％と高い。なお、ホタテ貝殻のナトリウム分は同一ロット内ではバラツキが少ないのが特徴である。このホタテ貝殻に０．１〜０．５質量％、好ましくは０．２〜０．４質量％と適量が含有され且つバラツキが少ないナトリウム分は、貝殻焼成時に融点を低くし、焼成貝殻(生石灰)として、その後の反応に良好な影響を及ぼす。また、上記ナトリウム分は炭酸化反応においてマグネシウム分と共に、反応を遅くし、均一なアスペクト比のカルサイト結晶等の一次粒子を生成しやすくする。

The sodium content in scallop shells is as high as 0.1 to 0.5% by mass, whereas the sodium content in limestone is 100 ppm or less. In addition, the sodium content of scallop shells is characterized by little variation within the same lot. This scallop shell contains an appropriate amount of 0.1 to 0.5% by weight, preferably 0.2 to 0.4% by weight, and the sodium content with little variation lowers the melting point during shell firing, ) As a good influence on the subsequent reaction. In addition, the sodium content together with the magnesium content in the carbonation reaction slows the reaction and facilitates the formation of primary particles such as calcite crystals having a uniform aspect ratio.

(Fired shells)
The scallop shell is adjusted in particle size and then baked to obtain a shell baked product (shell lime) as an intermediate raw material. The firing temperature is preferably 800 ° C. or higher, more preferably 1000 to 1200 ° C. If the calcination temperature is less than 800 ° C., the calcination is insufficient and a large amount of unreacted calcium carbonate remains, which is not preferable.

(Reactivity of fired shells)
Quick lime (shell lime) burned from scallop shells has a lower digestion rate, dissolution rate of slaked lime, and carbon dioxide gasification rate than mineral lime such as quick lime (limestone quicklime) obtained by firing limestone. Among these carbonation reactions, the slaked lime dissolution reaction and carbon dioxide gasification reaction are rate-limiting reactions, and the shell quicklime is about 1/2 of the mineral quicklime in the reaction rate of the overall carbonation reaction.

  Mineral quicklime has a large number of relatively small pores and a large specific surface area. On the other hand, shellfish quicklime has a smaller specific surface area due to a larger pore diameter. Specifically, limestone quicklime has an average pore diameter of 10 to 100 nm, whereas shellfish quicklime has an average pore diameter of about 1000 nm.

  And between shellfish quicklime and limestone quicklime, the specific surface area of limestone quicklime is 10 times or more larger. The difference in carbonation reaction rate is affected by this difference in specific surface area, and therefore, shellfish quicklime is considered to have a slower carbonation reaction rate than mineral quicklime.

  In the examination using X-ray diffraction about the crystal size of limestone quicklime and shellfish quicklime, the crystal size of scallop shell-derived quicklime is more than 4 times the crystal size of limestone-derived quicklime. Therefore, it is estimated that the pore diameter is four times or more.

  Japanese Patent Application Laid-Open No. 2001-26419 discloses that when reacted under the same conditions, calcium carbonate from limestone quicklime has a spindle shape and calcium carbonate from shell quicklime has a rod shape (columnar shape).

  Furthermore, in the method for producing light calcium carbonate derived from scallop shells of this example, by setting the average temperature in the carbonation reaction to a predetermined high temperature region or low temperature region, calcium carbonate having a high aspect ratio [rod (columnar)] Alternatively, low-aspect-ratio [aggregate] calcium carbonates with little variation and stable quality can be produced.

  The primary particle (crystal) shape and crystal morphology of this light scallop shell-derived light calcium carbonate (mainly calcite crystals in the production method of light calcium carbonate from this scallop shell) are characteristic properties of the shell. It is affected.

(Conditions for carbonation reaction)
In the method for producing light calcium carbonate derived from scallop shell of this example, the above-mentioned shell lime or a suspension (lime milk) composed of slaked lime obtained by digesting this lime and water has a CO ₂ concentration of 35% by volume or more. Carbonation reaction is performed by blowing mixed carbon dioxide gas. When the CO ₂ concentration of the mixed carbon dioxide gas is less than 35% by volume, the amount of the mixed carbon dioxide gas blown is increased, which increases the operating power and equipment for blowing the gas, which is not preferable.

Regarding the shape and crystal form of primary particles of calcium carbonate obtained by the carbonation reaction, the physical properties of the raw calcium carbonate, the reactivity of the intermediate shell fired product, the shell fired product concentration in lime milk, the carbonation reaction temperature, the mixing The conditions of carbonation reaction such as the amount of carbon dioxide and the CO ₂ concentration in the mixed carbon dioxide influence.

In particular, to produce calcium carbonate with a uniform primary particle size and aspect ratio, control of carbon dioxide partial pressure, control of CO ₂ concentration drop, control of carbon dioxide jet flow velocity, control of carbon dioxide jet direction, and Control of carbonation reaction conditions such as control of carbon dioxide jet position is important.

However, as described above, when the nozzle 2 shown in FIG. 2 is used in the nozzle of the carbonation reaction tank, clogging and releasing of clogging are likely to occur repeatedly at the carbon dioxide gas outlet 4. In that case, the CO ₂ concentration in the nozzle 2 of the reaction tank and the carbon dioxide jet flow velocity in the vicinity of the carbon dioxide jet outlet 4 become unstable and the gas dispersion into the reaction tank becomes unstable, so that the reaction situation varies greatly. As a result, the primary particle size and aspect ratio become non-uniform.

In contrast, in the method for producing light calcium carbonate derived from scallop shells of this example, the nozzle shown in FIG. 4 is used in the nozzle of the carbonation reaction tank, so that the generated calcium carbonate adheres to the carbon dioxide gas outlet 16. Will be less. As a result, the carbon dioxide gas outlet 16 is not clogged, and the CO ₂ concentration in the nozzle 12 and the carbon dioxide gas jet velocity at the carbon dioxide gas outlet 16 are less changed, and the carbonation reaction is stable. Become a thing.

  Regarding the calcium carbonate obtained by this carbonation reaction, the aspect ratio of the primary particles is uniform with 65% by volume or more, preferably 85% by volume or more of the primary particles having an average aspect ratio within the range of ± 20%.

  Furthermore, in the method for producing light calcium carbonate derived from scallop shells of this example, when the average temperature in the carbonation reaction is 40 ° C. or higher, preferably 40 to 90 ° C., a high aspect ratio with an aspect ratio of 3 to 10 is used. It is possible to obtain calcium carbonate having a primary particle ratio of 85% by volume or more, preferably 90% by volume or more. When the average temperature in the carbonation reaction is lower than 40 ° C., preferably 5 to 35 ° C., the primary particles having a low aspect ratio with an aspect ratio of 1.0 to 1.5 are 43% by volume or more, preferably 95% or more by volume of calcium carbonate can be obtained.

  By the carbonation reaction described above, lime milk becomes a slurry of calcium carbonate having a uniform primary particle size and aspect ratio. This calcium carbonate slurry is sent from the reaction facility to the dehydration facility and separated into dehydrated cake and water. The separated water is returned to the reaction facility through the recovered water line. The dehydrated cake is sent from the dehydration facility to the drying facility, and after drying, becomes a calcium carbonate product.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely and in detail, this invention is not limited by an Example.

  The physical properties (aspect ratio and particle size of primary particles) of the obtained calcium carbonate were determined by the following method.

  Aspect ratio and particle size: Analyzed from photographs obtained by using an electron microscope JSM-5800LV manufactured by JEOL Ltd. and data of MO storage.

Examples 1-7 and Comparative Examples 1-3
Light calcium carbonate was produced under the conditions shown in Table 2 and below. The physical properties of the obtained calcium carbonate are also shown in Table 2.

  The light calcium carbonate production flow process used the flow process shown in FIG. 1 or FIG. 3, and the nozzle shown in FIG.

A reaction tank filled with a predetermined amount of liquid is controlled at a constant temperature, scallop shell-derived slaked lime is put into this, and high purity CO ₂ and recovered unreacted carbon dioxide gas are blown from the nozzle at the bottom of the reaction tank. Carbonation was carried out by stirring with two blades installed directly above and monitoring with a CO ₂ concentration sensor installed inside the nozzle, and a pH sensor and pressure sensor installed at the top of the reaction tank.

The basic condition items and range of the carbonation reaction are the amount of lime milk in the reaction tank of 6 m ³ or 3 m ³ , and the concentration of slaked lime at the start of the reaction of 8 to 18% by mass (the amount of slaked lime charged to the reaction tank is 500 to 530 kg). That is, the calcium carbonate concentration at the end of the reaction was 10 to 22% by mass, the introduced carbon dioxide concentration was 50% by volume, the stirring speed was 60 to 100 rpm, and the reaction start temperature was 10 to 40 ° C.

表２及び図５〜１４に示す結果から以下のことが明らかになった。なお、図５〜１１におけるスケール長さは２μｍを示し、図１２〜１４におけるスケール長さは１μｍを示す。

From the results shown in Table 2 and FIGS. In addition, the scale length in FIGS. 5-11 shows 2 micrometers, and the scale length in FIGS. 12-14 shows 1 micrometer.

  In Examples 1 to 7, the nozzle 12 shown in FIG. 4 and the calcium carbonate production apparatus having the flow shown in FIG. 1 or 3 were used. Regarding the calcium carbonate obtained in Examples 1 to 7, the aspect ratio of the primary particles is such that the primary particles within the range of the aspect ratio ± 20% are 65% by volume or more in Example 1, and 85 volumes in Examples 2 to 7. % Or more, both were uniform.

  In Comparative Examples 1 to 3, the nozzle 2 shown in FIG. 2 was used. Regarding the calcium carbonate obtained in Comparative Examples 1 to 3, the primary particles had an aspect ratio that was non-uniform, with primary particles having an aspect ratio in the range of ± 20% of less than 65% by volume.

  The average temperature in the carbonation reaction in Examples 5 to 7 was 40 ° C. or higher. About the calcium carbonate obtained in these Examples 5-7, the primary particle of the high aspect ratio of 3-10 of aspect ratio was 85 volume% or more.

  The average temperature in the carbonation reaction in Examples 1 to 4 was less than 40 ° C. Regarding the calcium carbonate obtained in Examples 1 to 4, the primary particles having a low aspect ratio with an aspect ratio of 1.0 to 1.5 are 43% by volume or more in Example 1, and 95% by volume or more in Examples 2 to 4. Met.

It is a flowchart which shows the basic process of the calcium carbonate manufacturing apparatus used in Comparative Examples 1-3 and Example 1. FIG. It is the partial schematic which shows the nozzle vicinity of the reaction tank in the calcium carbonate manufacturing apparatus used by Comparative Examples 1-3. It is a flowchart which shows the basic process of the calcium carbonate manufacturing apparatus used in Examples 2-7. It is the partial schematic which shows the nozzle vicinity of the reaction tank in the calcium carbonate manufacturing apparatus used in Examples 1-7. 3 is an electron micrograph of the calcium carbonate obtained in Comparative Example 1 in place of a drawing. 4 is an electron micrograph of the drawing of the calcium carbonate obtained in Comparative Example 2. 4 is an electron micrograph of the calcium carbonate obtained in Comparative Example 3 in place of a drawing. 2 is an electron micrograph of the calcium carbonate obtained in Example 1 for a drawing substitute. 4 is an electron micrograph of the calcium carbonate obtained in Example 2 in place of a drawing. 4 is an electron micrograph of the calcium carbonate obtained in Example 3 in place of a drawing. 4 is an electron micrograph of the calcium carbonate obtained in Example 4 instead of a drawing. 6 is an electron micrograph of the calcium carbonate obtained in Example 5 for a drawing substitute. 6 is an electron micrograph of the calcium carbonate obtained in Example 6 instead of a drawing. 4 is an electron micrograph of the calcium carbonate obtained in Example 7 for a drawing.

Explanation of symbols

2 Nozzle 4 Carbon dioxide gas outlet 12 Nozzle 14 Carbon dioxide gas outlet opening / closing means 16 Carbon dioxide gas outlet

Claims (3)

A mixed gas of carbon dioxide gas and air having a CO ₂ concentration of 35% by volume or more is injected into a suspension of quick lime obtained by firing scallop shells or slaked lime obtained by digesting the quick lime and water, A method for producing light calcium carbonate derived from scallop shells, wherein the carbon dioxide gas supply pipe is provided with a carbon dioxide gas outlet opening / closing means between the outlet and the carbon dioxide gas supply pipe. The method for producing light calcium carbonate derived from scallop shells according to claim 1, wherein the average reaction temperature from the start of blowing to the end of blowing is 40 ° C or higher. The method for producing light calcium carbonate derived from scallop shells according to claim 1, wherein the average reaction temperature from the start of blowing to the end of blowing is less than 40 ° C.

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