Method for producing calcium carbonate particles

Abstract

To provide a method for producing calcium carbonate particles with a sharp particle size distribution and a small particle diameter.SOLUTION: A method for producing calcium carbonate particles includes the step for introducing bubble-form carbon dioxide into a calcium-containing solution, flowing in one direction inside a tubular member, to crystallize calcium carbonate particles. The Reynolds number of the calcium-containing solution within the tubular member is controlled in the range of 2000 or more and 30000 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing calcium carbonate particles. [Background technology]

[0002] Calcium carbonate particles are used in a wide range of fields, including fillers for plastics, paper, and paints, soil conditioners for pesticides and fertilizers, adhesives, and sealants, as erasers and toothpastes due to their abrasive properties, and as food additives and raw materials for cosmetics. Recently, sheet and film-like paper substitute products and plastic substitute products made mainly from calcium carbonate particles have been developed and are widely used. Paper substitute products are used in clear files, business cards, booklets (pamphlets, photo books, etc.), promotional POP, menus, packages, posters, illuminated sheets, stickers and labels, maps, mask cases, and tags. Plastic substitute products are used in applications where plastics were previously used (various molded products, such as plastic shopping bags, food containers, drink cups, hangers, stationery, fans, cosmetic containers, bottles, building materials, etc.).

[0003] In recent years, in order to reduce the emission of carbon dioxide, a greenhouse gas, it has been considered to react carbon dioxide with calcium and fix it as calcium carbonate. Patent Document 1 and Patent Document 2 describe a method of reacting calcium extracted into water from waste such as concrete sludge and steel slag with carbon dioxide. This method is expected to reduce the amount of waste containing calcium and suppress environmental deterioration caused by waste. Patent Document 3 describes a method of synthesizing calcium carbonate more efficiently by introducing carbon dioxide as fine bubbles into a calcium-containing solution containing calcium.

[0004] On the other hand, Patent Document 4 describes adjusting the Reynolds number when reacting carbon dioxide (carbonate ion) with calcium ions in order to synthesize calcium carbonate with excellent dispersibility in various components. Patent Document 5 describes adjusting the Reynolds number when reacting carbon dioxide (carbonate ion) with calcium ions in order to produce calcium carbonate having a vaterite crystal phase. Furthermore, Patent Document 6 describes adjusting the Reynolds number when reacting carbon dioxide (carbonate ion) with calcium ions in order to produce calcium carbonate particles with a uniform particle size. However, in all of the methods in Patent Documents 4 to 6, the reaction between carbonate ions and calcium ions is carried out in a stirring tank, i.e., in a batch system, and the above-mentioned Reynolds number is a Reynolds number determined based on the diameter of the stirring blade, etc. (hereinafter, also referred to as "stirring Reynolds number"). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-148432 A [Patent Document 2] JP 2023-035105 A [Patent Document 3] JP 2023-028788 A [Patent Document 4] Japanese Patent Application Publication No. 56-160322 [Patent Document 5] Special Publication No. 5-509282 [Patent Document 6] Japanese Patent Application Publication No. 9-165217 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, in order to use calcium carbonate for various applications, it is required to make the particle size distribution sharp and to make the particle size small. However, in any of the above-mentioned methods, it is difficult to make the obtained calcium carbonate particles small in particle size, and further difficult to make the particle size distribution sharp. For example, although the above-mentioned Patent Document 6 describes that the particle size can be made uniform, according to the verification by the present inventors, the particle size of the calcium carbonate particles is relatively large, and further improvement is required.

[0007] The present invention has been made in consideration of the above-mentioned problems of the conventional techniques. Specifically, an object of the present invention is to provide a method for producing calcium carbonate particles having a narrow particle size distribution and a small particle diameter. [Means for solving the problem]

[0008] Means for Solving the Problems The present inventors have conducted intensive studies and have found that in a method for producing calcium carbonate particles, which includes a step of introducing carbon dioxide bubbles into a calcium-containing solution containing a calcium compound within a tubular member, the Reynolds number of the calcium-containing solution flowing through the tubular member can be controlled within a specific range, thereby solving the above problems and completing the present invention.

[0009] One aspect of the present invention provides the following methods for producing calcium carbonate particles [1] to [4]. [1] A method for producing calcium carbonate particles, comprising the step of introducing carbon dioxide bubbles into a calcium-containing solution that contains calcium and flows unidirectionally inside a tubular member to crystallize calcium carbonate particles, and controlling the Reynolds number of the calcium-containing solution inside the tubular member to be between 2,000 and 30,000. [2] The method for producing calcium carbonate particles according to [1], wherein the tubular member is made of ceramics, and the bubble-like carbon dioxide is generated inside the tubular member by pressurizing carbon dioxide from the outside of the tubular member. [3] The method for producing calcium carbonate particles according to [1] or [2], wherein the average particle size of the bubble-like carbon dioxide is 100 μm or less. [4] The method for producing calcium carbonate particles according to any one of [1] to [3], wherein the calcium-containing solution has a pH of 7.0 or higher in the step of crystallizing the calcium carbonate particles. Effect of the Invention

[0010] According to the present invention, it is possible to produce calcium carbonate particles having a narrow particle size distribution and a small particle diameter. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a flow chart of a method for producing calcium carbonate particles according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a production apparatus capable of carrying out the method for producing calcium carbonate particles shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, one embodiment of the present invention will be described in detail. However, the present invention is not limited to this embodiment. In addition, in this specification, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits.

[0013] Fig. 1 is a flow chart of a method for producing calcium carbonate particles according to one embodiment of the present invention. As shown in Fig. 1, in this embodiment, a calcium-containing solution containing calcium is prepared (preparation step S110). Then, bubble-like carbon dioxide is introduced into the calcium-containing solution to crystallize calcium carbonate particles (crystallization step S120). After that, the calcium-containing solution after the calcium carbonate particles have crystallized is filtered to recover the calcium carbonate particles (recovery step S130).

[0014] In this embodiment, in the crystallization step S120, bubble-like carbon dioxide is introduced while the calcium-containing solution is flowed in one direction inside the tubular member. The Reynolds number of the calcium-containing solution in the tubular member is controlled to 2000 to 30000. The Reynolds number is preferably 2500 to 29000, more preferably 3000 to 28000. When the Reynolds number is 2000 or more, as described later, carbon dioxide can be uniformly dispersed in the calcium-containing solution to generate a large number of calcium carbonate nuclei. Therefore, calcium carbonate particles having a sharp particle size distribution and a small particle size can be produced. On the other hand, when the Reynolds number is excessively large, a special device or the like is required, but further effects cannot be expected. On the other hand, when the Reynolds number is 30000 or less, no special device is required and sufficient effects can be obtained.

[0015] As described above, the agitation Reynolds number described in the prior art documents (e.g., Patent Documents 4 to 6) is a value calculated based on the diameter of the agitation impeller, the peripheral speed of the agitation impeller tip, and the kinetic viscosity of the liquid being agitated, and is a value that represents the flow state of the fluid in a batch process. However, the agitation Reynolds number ignores factors that affect the circulating flow throughout the vessel, such as the width of the agitation impeller and the number of stages. In other words, even if the Reynolds number is the same, it is difficult to say that the fluid will necessarily be in the same state depending on the shape of the agitation impeller, the shape of the vessel, etc. Therefore, it was difficult with the techniques of Patent Documents 4 to 6 and the like to sharpen the particle size distribution of the obtained calcium carbonate particles or to reduce their particle size.

[0016] In contrast, the Reynolds number specified in this specification is the Reynolds number of a fluid moving in one direction inside a tubular member. In this embodiment, a tubular member is used whose interior (flow passage) has a circular cross section and a constant inner diameter. The Reynolds number Re of a fluid flowing through such a tubular member is calculated by the average flow velocity u (m / s) of the fluid (calcium-containing solution in this embodiment) flowing through the tubular member, the inner diameter d (m) of the tubular member, and the kinetic viscosity v (m) of the fluid (calcium-containing solution). 2The kinetic viscosity of a fluid is determined by the following formula based on the kinematic viscosity (kinematic viscosity per unit volume / s). The kinetic viscosity of a fluid is a value measured using a vibration viscometer (manufactured by A&D Co., Ltd.) conforming to JIS Z8803:2011. Re=u*d / v

[0017] According to the Reynolds number specified in this embodiment, the flow state of the fluid moving through the tubular member can be more accurately represented. In this embodiment, the Reynolds number is set to 2000 or more and 30000 or less, so that the calcium-containing solution flowing through the tubular member becomes turbulent. When carbon dioxide bubbles are introduced into such a calcium-containing solution, the carbon dioxide bubbles are broken down into smaller pieces, the surface area increases, and the carbon dioxide bubbles come into contact with the calcium-containing solution more easily. As a result, the reaction between carbonate ions and calcium ions is more likely to occur in the calcium-containing solution, and many calcium carbonate nuclei are generated. Therefore, it is considered that the particle size of the calcium carbonate particles finally obtained becomes smaller. On the other hand, it is considered that the turbulent flow of the calcium-containing solution makes it easier for the carbon dioxide bubbles to be uniformly dispersed in the calcium-containing solution, resulting in a sharp particle size distribution.

[0018] An example of a manufacturing apparatus 200 capable of carrying out the method for manufacturing calcium carbonate particles of the present embodiment is shown in Fig. 2. However, the method for manufacturing calcium carbonate particles of the present embodiment is not limited to the method using the manufacturing apparatus 200.

[0019] The production apparatus 200 has a circulation section 230 for carrying out the crystallization step S120, a separation section 250 for carrying out the recovery step S130, and a control section 260 for controlling these sections.

[0020] The circulation unit 230 has a crystallization tank 210 for crystallizing calcium carbonate particles, and a bubble introduction unit 220 for introducing carbon dioxide bubbles into the calcium-containing solution 310. The bubble introduction unit 220 includes the above-mentioned tubular member 224. The circulation unit 230 further has a flow path connecting the crystallization tank 210 and the bubble introduction unit 220, a valve for controlling opening and closing of the flow path, and a pump (not shown) for controlling the flow rate and flow of the calcium-containing solution 310 in the flow path. The circulation unit 230 also has a gas tank 222 for supplying carbon dioxide, which is connected to the bubble introduction unit 220. The circulation unit 230 may further have a measurement unit 242 for measuring the temperature and flow rate of the calcium-containing solution 310 circulating inside the circulation unit 230, an adjustment unit 244 for adjusting the temperature and flow rate of the calcium-containing solution 310, and the like.

[0021] On the other hand, the separation section 250 has a filtration section 252 for separating out the calcium carbonate particles crystallized in the circulation section 230, a flow path connecting the filtration section 252 and the circulation section 230, and the like.

[0022] The control unit 260 may be configured to be able to transmit and receive data to and from the circulation unit 230 and the separation unit 250. The control unit 260 usually has a computer such as a CPU, and a storage unit such as a ROM and a RAM. The control unit 260 controls the operation of each component of the circulation unit 230 and the separation unit 250, the opening and closing of valves, and the operation of a pump, thereby adjusting the Reynolds number in the tubular member 224 and operating the manufacturing apparatus 200. The control unit does not necessarily need to be provided inside the manufacturing apparatus 200, and may be disposed outside the manufacturing apparatus 200.

[0023] Here, the manufacturing apparatus 200 shown in FIG. 2 does not include a configuration for performing the above-mentioned preparation step S110, but may include a configuration for preparing a calcium-containing solution as necessary. Hereinafter, a method for producing calcium carbonate particles using the production apparatus 200 will be described in detail.

[0024] (Preparation step S110) In the preparation step S110, a calcium-containing solution 310 containing a calcium compound is prepared. The calcium-containing solution 310 also contains a solvent for dissolving the calcium compound. Note that the calcium-containing solution 310 may contain components (e.g., impurities, etc.) other than the calcium compound and the solvent as long as the purpose of this embodiment is not impaired.

[0025] The calcium compound contained in the calcium-containing solution 310 is not particularly limited as long as it is a compound that can dissolve in a solvent and generate calcium ions, and examples thereof include calcium hydroxide, calcium oxide, calcium sulfate, calcium chloride, and the like.

[0026] On the other hand, the solvent contained in the calcium-containing solution 310 is not particularly limited as long as it can dissolve calcium compounds, and an example thereof is water. The water may be any of ion-exchanged water, tap water, industrial water, etc. Note that, as long as the calcium compounds are well dissolved in the solvent, a solvent other than water may be used, or a mixture of water and another solvent may be used.

[0027] The calcium ion concentration in the calcium-containing solution 310 is preferably 800 mg / L or more and 1900 mg / L or less, and more preferably 1000 mg / L or more and 1700 mg / L or less. When the calcium ion concentration in the calcium-containing solution 310 is in this range, calcium carbonate particles are crystallized more efficiently by the crystallization step described below. The method for measuring the calcium ion concentration is not particularly limited, and known methods can be applied. For example, the concentration can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS).

[0028] The kinetic viscosity of the calcium-containing solution 310 can be appropriately adjusted by, for example, the concentration of the calcium compound.

[0029] Here, the method for preparing the calcium-containing solution 310 is not particularly limited, and the calcium-containing solution 310 may be prepared by mixing a raw material containing a calcium compound (hereinafter also referred to as a "calcium raw material") with a solvent. In addition, when the calcium raw material contains a solvent together with the calcium compound, this may be used as it is as the calcium-containing solution.

[0030] The calcium raw material may be in a solid state, a liquid state (solution state), or a slurry state. The type of calcium raw material is not particularly limited, and may be a refined product such as limestone or marble, or a recovered product such as waste. Examples of the recovered products include concrete sludge, steel slag, waste concrete, coal ash, biomass ash, incineration ash, waste gypsum, alkaline wastewater, and the like. These calcium raw materials may or may not have been subjected to pretreatment such as neutralization treatment, crushing treatment, or grinding treatment.

[0031] In addition, when preparing the calcium-containing solution 310, a solid-liquid separation operation may be performed. By performing the solid-liquid separation operation, it is possible to obtain a calcium-containing solution with fewer impurities (fine particles, etc.), which makes it easier to crystallize calcium carbonate particles of a desired shape in the crystallization step described below. The solid-liquid separation method is not particularly limited, and separation can be performed using a known solid-liquid separation device such as a filter press, a vacuum belt filter, a vacuum rotary filter, a screw decanter, or a centrifugal dehydrator. After the solid-liquid separation, a flocculant containing sodium, potassium, magnesium, etc. may be added to flocculate fine particles such as colloidal particles and then remove them.

[0032] (Crystallization process S120) In the crystallization step S120, carbon dioxide bubbles are introduced into the calcium-containing solution 310 prepared in the preparation step S110 in the tubular member 224 of the bubble introduction part 220, and calcium carbonate particles are crystallized in the crystallization tank 210. In the production apparatus 200 of this embodiment, the calcium-containing solution 310 is circulated between the crystallization tank 210 and the bubble introduction part 220, thereby efficiently producing calcium carbonate particles.

[0033] Here, the size and the like of the crystallization tank 210 are appropriately selected as long as it can accommodate a desired amount of the calcium-containing solution 310. In the present embodiment, the crystallization tank 210 is provided with an agitator 214 driven by a motor 212, but the present invention is not limited to this configuration.

[0034] On the other hand, the bubble introduction part 220 has a tubular member 224 for flowing the calcium-containing solution 310 and a configuration for supplying carbon dioxide bubbles into the tubular member 224. The configuration is connected to a gas tank 222 for storing a gas containing carbon dioxide. The bubble introduction part 220 is not particularly limited in configuration as long as it can introduce carbon dioxide bubbles into the calcium-containing solution 310 and can control the Reynolds number of the calcium-containing solution 310 inside the tubular member 224 within the above-mentioned range. The bubble introduction part 220 of this embodiment has a tubular porous ceramic (tubular member 224) and a gas injection part (not shown) arranged on the outside of the tubular porous ceramic. In the bubble introduction part 220, the inside of the tubular porous ceramic becomes a flow path for flowing the calcium-containing solution 310. On the other hand, the gas injection part is connected to the gas tank 222 and has a gas reservoir for temporarily storing the gas containing carbon dioxide supplied from the gas tank 222. When gas is injected into the gas reservoir of the gas injection section, the pressure causes the gas to penetrate into the porous ceramics and pass through it. As a result, the gas becomes bubbles and is introduced into the calcium-containing solution 310 flowing through the porous ceramics. The bubble introduction section 220 makes it easy to reduce the average particle size of the carbon dioxide bubbles and to control the Reynolds number of the calcium-containing solution 310. Furthermore, the bubble introduction section 220 has the advantage of being less likely to cause contamination with foreign matter and being able to introduce carbon dioxide bubbles into a material solution with high viscosity.

[0035] Here, the inner diameter of the porous ceramic (tubular member 224) is appropriately selected so that the Reynolds number falls within the above range.

[0036] The length of the tubular porous ceramics in the bubble introduction section 220, i.e., the length of the region for introducing carbon dioxide bubbles, is appropriately selected according to the desired amount of gas to be introduced. The gas introduction conditions are not particularly limited. For example, the bubble (gas) introduction speed can be 0.01 L / min or more and 10 L / min or less.

[0037] The concentration of carbon dioxide in the gas introduced into the calcium-containing solution 310 is not particularly limited, and can be, for example, 10% by volume or more and 100% by volume or less of the gas introduced. By setting the carbon dioxide concentration to 10% by volume or more, calcium carbonate particles can be crystallized in a shorter time. The gas may be factory exhaust gas, combustion exhaust gas of petroleum and natural gas, waste incineration exhaust gas, etc. By using these exhaust gases, it is possible to reduce the amount of carbon dioxide emitted into the atmosphere and contribute to reducing the environmental load.

[0038] The average particle diameter of the carbon dioxide bubbles (or gas containing carbon dioxide) introduced into the calcium-containing solution 310 is not particularly limited, and is determined by the pore diameter when a tubular porous ceramic is used as the tubular member 224. In this embodiment, the average particle diameter of the carbon dioxide bubbles (or gas containing carbon dioxide) may be several mm to several hundred mm. However, from the viewpoint of further increasing the surface area of ​​the bubbles and facilitating dissolution of carbon dioxide in the calcium-containing solution, it is preferable that the average particle diameter is small. Specifically, it is preferably 100 μm or less, more preferably 1 μm to 100 μm, and even more preferably 5 μm to 50 μm. In this specification, bubbles with an average particle diameter of 100 μm or less are also referred to as fine bubbles.

[0039] In this embodiment, the flow rate of the calcium-containing solution 310 in the tubular porous ceramic is adjusted to adjust the Reynolds number of the calcium-containing solution 310. The flow rate is appropriately selected depending on the kinetic viscosity of the calcium-containing solution 310 and the inner diameter of the tubular member 224.

[0040] On the other hand, the pH of the material solution when the bubble-like carbon dioxide is introduced is preferably 7.0 or more. By setting the pH at 7.0 or more, it is possible to prevent re-dissolution of the calcium crystallized as the crystallized calcium carbonate. The pH of the material solution is preferably 7.0 or more and 13.0 or less, and more preferably 8.0 or more and 13.0 or less.

[0041] The time for which the bubbles are introduced (the time for which the calcium-containing solution 310 is circulated in the circulation section 230) is not particularly limited, but may be, for example, from 60 minutes to 240 minutes.

[0042] In this step, seed crystals may be added to the calcium-containing solution 310 to promote crystallization of calcium carbonate particles. However, it is preferable not to add seed crystals from the viewpoint of suppressing variation in shape due to crystal growth on the surface of the seed crystals and promotion of the generation of new crystal nuclei.

[0043] Furthermore, the tubular member 224 of the above-mentioned bubble introduction part 220 and the configuration for supplying carbon dioxide bubbles into the inside of the tubular member 224 are not limited to those described above. For example, the bubble introduction part 220 may have a configuration for generating bubbles using a gas-liquid mixed shear type, a static mixer type, a Venturi type, a cavitation type, a steam condensation type, an ultrasonic type, a swirling jet type, a pressurized dissolution type, or the like.

[0044] (Recovery process S130) In the recovery step S130, the calcium-containing solution 310 after the above-mentioned crystallization step S120 is recovered, and calcium carbonate particles are separated from other components. In this embodiment, the calcium-containing solution 310 in which the calcium carbonate particles have been crystallized is filtered by the filtration section 252 of the separation section 250, and the calcium carbonate particles are recovered. In the filtration section 252, filtration is performed by a known method such as suction filtration. The recovered calcium carbonate particles may be dried or pulverized as necessary. In addition, the calcium carbonate particles may be subjected to a surface treatment with fatty acid or the like depending on the application.

[0045] On the other hand, the liquid component (treated liquid) separated by filtration may be disposed of after waste liquid treatment, or may be used for other purposes or may be reused as a calcium-containing solution.

[0046] (others) The method for producing calcium carbonate particles of the present embodiment may include steps other than the above-mentioned preparation step S110, crystallization step S120, and recovery step S130. For example, the method may further include a step of measuring the temperature, flow rate, and the like of the calcium-containing solution circulating through the circulation part 230 by the measurement part 242, a step of determining by the control part 260 whether the measured value is within a predetermined range, and a step of adjusting the temperature, flow rate, and the like by the adjustment part 244 based on the determined result.

[0047] [Calcium carbonate particles and their uses] The calcium carbonate particles obtained by the above-mentioned method preferably have an average particle size (D50) of 0.5 μm or more and 5 μm or less, and more preferably 1.0 μm or more and 4.8 μm or less. When the average particle size of the calcium carbonate particles is 5 μm or less, the calcium carbonate particles can be easily dispersed in various materials such as various plastics, paper, rubber, etc., and can be easily used for a wide variety of applications. On the other hand, when the average particle size (D50) is 0.5 μm or more, the handling property tends to be good.

[0048] On the other hand, the average particle size (D90) / average particle size (D50), which represents the particle size distribution of calcium carbonate particles, is preferably less than 2.5, and more preferably 2.4 or less. When the particle size distribution is less than 2.5, the physical properties of the calcium carbonate particles tend to be stable, and the particles are easier to use for various applications. In this specification, the particle sizes (average particle size, D50, D90, etc.) of calcium carbonate particles are values ​​measured by a laser diffraction particle size distribution measuring device.

[0049] The crystalline phase of the calcium carbonate particles is not particularly limited, but is preferably mainly calcite. However, a part of the calcium carbonate particles may contain a different crystalline phase. Calcite is known as a stable phase of calcium carbonate, and has a more stable crystalline form than other crystalline phases (aragonite, vaterite, etc.). Therefore, if the calcium carbonate particles are mainly calcite, the calcium carbonate particles can be easily used for various purposes. The crystalline phase of the calcium carbonate particles is identified by X-ray diffraction (XRD).

[0050] The calcium carbonate particles described above are not particularly limited, and may be used as is or mixed with other components. Examples of applications include fillers for plastics, paper, paints, etc., soil conditioners such as pesticides and fertilizers, adhesives, sealants, erasers and toothpastes that utilize the abrasive effect, sheet and film-like paper substitute products and plastic substitute products that use calcium carbonate as the main raw material, as well as food additives and cosmetic raw materials. EXAMPLES

[0051] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0052] [Example 1] Commercially available Portland cement was prepared as the calcium raw material. 800 g of the calcium raw material was mixed with 3200 mL of ion-exchanged water and stirred to obtain a suspension in which the calcium raw material was suspended. The suspension was then filtered using a solid-liquid separator to obtain a calcium-containing solution. The amount of calcium in the calcium-containing solution was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The kinetic viscosity of the calcium-containing solution was 0.939 mm 2 The kinematic viscosity was measured using a vibration viscometer (FEM-1000V-ST manufactured by A&D Co., Ltd.) conforming to JIS Z8803:2011.

[0053] The pH of the calcium-containing solution was adjusted to 7.0 or more. The calcium-containing solution was then introduced into the crystallization tank 210 of the circulation section 230 shown in FIG. 2 and circulated within the circulation section 230. Carbon dioxide (CO 2 ) and nitrogen (N 2 ) gas mixture was introduced to generate fine bubbles. 2 The concentration was set to 10% by volume. Furthermore, the speed (flow rate) of the calcium-containing solution flowing through the bubble introduction section 220 was set to 2.2 m / s. As the bubble introduction section 220, an in-line FB test device (inner diameter of the tubular member 224: 100 mm) manufactured by Noritake Co., Ltd., which has a tubular porous ceramic (tubular member 224) and a gas injection section disposed on the outside, was used. The average particle diameter of the fine bubbles to be introduced was adjusted to 50 μm. The flow rate of the mixed gas during introduction was set to 50 mL / min.

[0054] After 60 minutes had elapsed, the introduction of fine bubbles was stopped and the calcium-containing solution was subjected to suction filtration to obtain calcium carbonate particles. The average particle sizes (D50) and (D90) were determined using a laser diffraction particle size distribution analyzer.

[0055] [Examples 2 to 4] The stirring conditions for obtaining the calcium-containing solution were changed to prepare calcium-containing solutions with different calcium contents and kinetic viscosities. The flow rate of the calcium-containing solution in the bubble introduction section 220 was also changed as shown in Table 1. Furthermore, in Example 4, the carbon dioxide bubble size was changed. Other than these changes, calcium carbonate particles were obtained in the same manner as in Example 1.

[0056] [Comparative Examples 1 and 2] The stirring conditions for obtaining the calcium-containing solutions were changed to prepare calcium-containing solutions having different calcium contents and kinetic viscosities. The flow rate of the calcium-containing solution in the bubble introduction section 220 was set as shown in Table 1. Furthermore, in Comparative Example 2, the method was changed to a batch method, and the carbon dioxide bubble size was changed. Other than these changes, calcium carbonate particles were obtained in the same manner as in Example 1.

[0057] [Table 1]

[0058] [Consideration] As shown in Table 1 above, when the Reynolds number of the calcium-containing solution in the tubular member 224 of the bubble introduction part was 2000 or more and 30000 or less, the average particle size (D50) was 4.5 μm or less, and further, the particle size distribution ((D90) / (D50)) was 2.4 or less (Examples 1 to 3). In other words, calcium carbonate particles with a small particle size and a sharp particle size distribution were obtained.

[0059] On the other hand, when the Reynolds number was less than 2000, the average particle size (D50) was 5.0 μm, but the particle size distribution was very large at 16.4 (Comparative Example 1). This is thought to be due to the occurrence of variations in the distribution of carbon dioxide within the tubular member. On the other hand, when calcium carbonate particles were produced by the batch method, the average particle size (D50) could not be made sufficiently small (Comparative Example 2). [Industrial Applicability]

[0060] According to the production method of the present invention, it is possible to obtain calcium carbonate particles having a narrow particle size distribution and a small particle diameter, which is expected to further promote the spread of calcium carbonate to various applications. [Explanation of symbols]

[0061] 200 Manufacturing equipment 210 Crystallization tank 212 Motor 214 Mixer 220 Bubble Introduction 222 Gas Tank 224 Tubular members 230 Circulation Department 242 Measuring section 244 Adjustment section 250 Separation section 260 Control Unit 252 Filtration section 310 Calcium-containing solution

Claims

1. The present invention includes a step of introducing bubble-like carbon dioxide into a calcium-containing solution that flows in one direction inside a tubular member to crystallize calcium carbonate particles, The Reynolds number of the calcium-containing solution in the tubular member is controlled to be 2,000 or more and 30,000 or less. A method for producing calcium carbonate particles.

2. The tubular member is made of ceramics, Carbon dioxide is injected from the outside of the tubular member to generate the carbon dioxide bubbles inside the tubular member. The method for producing calcium carbonate particles according to claim 1 .

3. The average particle size of the bubble-like carbon dioxide is 100 μm or less. The method for producing calcium carbonate particles according to claim 1 .

4. In the step of crystallizing the calcium carbonate particles, the pH of the calcium-containing solution is 7.0 or more. The method for producing calcium carbonate particles according to claim 1 .

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