Method for producing calcium carbonate

Abstract

Using calcium sulfate (gypsum) as a raw material, the BET specific surface area is 30m². 2 This invention provides a method for producing calcium carbonate containing extremely fine and valuable calcite in a high yield, with a calcite content of 1 / g or more. [Solution] A method for producing calcium carbonate, comprising the following steps 1 and 2. Step 1: A step of preparing an aqueous calcium sulfate dispersion by mixing (a) calcium sulfate, (b) calcite, (d) one or more selected from alkali metal hydroxides and ammonia, and water. Step 2: A step of blowing carbon dioxide gas into the aqueous calcium sulfate dispersion prepared in Step 1 to produce an aqueous calcium carbonate dispersion.

Description

[Technical Field]

[0001] This invention relates to a method for producing calcium carbonate. [Background technology]

[0002] Limestone is an abundant resource found in countries around the world, including Japan, and various materials have been developed from it since ancient times. One such material is powdered calcium carbonate. Calcium carbonate can be divided into "heavy calcium carbonate," which is produced by crushing limestone, and "synthetic calcium carbonate (or light calcium carbonate)," which is synthesized in water using calcium, carbon dioxide, and alkali. Depending on their characteristics such as particle shape, particle size, purity, and whiteness, these calcium carbonates are widely used as fillers for asphalt paving, aggregates and additives for cement concrete, neutralizers for industrial wastewater, fertilizers, animal feed, papermaking coatings, fillers for plastics and rubber, paints, and pigments. On the other hand, due to the heavy consumption of fossil fuels since the Industrial Revolution, the concentration of carbon dioxide in the atmosphere is increasing year by year. For this reason, the development of technologies and materials that effectively utilize carbon dioxide has attracted attention in recent years. Synthetic calcium carbonate can be manufactured using carbon dioxide as a raw material, and by giving it characteristics such as particle shape, particle size, particle diameter, purity, and whiteness, it can be used as a high-value-added material for various applications. For this reason, synthetic calcium carbonate has recently attracted attention as a material that effectively utilizes carbon dioxide.

[0003] Patent Document 1 discloses a method for producing calcium carbonate, which can simultaneously produce alkali metal sulfates using various types of gypsum, including various by-product gypsums such as exfoliated gypsum, as raw materials. This method is characterized by introducing carbon dioxide into a slurry in which one or more hydroxides selected from alkali metals, gypsum, and water are mixed. Patent Document 2 discloses a method for producing high-purity calcite and ammonium sulfate, which has a purity of 95% or more, by adding a predetermined amount of carbon dioxide to a slurry of water, aqueous ammonia, and gypsum to cause a carbonation reaction. Patent Document 3 discloses a method for processing large quantities of waste gypsum board, which is conventionally mainly used as a cement additive after heat treatment, and is generated in large quantities. This method involves contacting the waste gypsum board with an alkaline hydroxide aqueous solution to recover the contained calcium as a calcium hydroxide precipitate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2003-292321 [Patent Document 2] Japanese Patent Publication No. 2014-520754 [Patent Document 3] Japanese Patent Publication No. 2005-161300 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention uses calcium sulfate (gypsum) as a raw material and has a BET specific surface area of ​​30 m². 2 This invention provides a method for producing calcium carbonate containing extremely fine and valuable calcite in a high yield, with a calcite content of 1 / g or more. [Means for solving the problem]

[0006] The present invention relates to a method for producing calcium carbonate (hereinafter also simply referred to as the "production method of the present invention") comprising the following steps 1 and 2. Step 1: A step to prepare an aqueous calcium sulfate dispersion by mixing (a) calcium sulfate (hereinafter referred to as component (a)), (b) calcite (hereinafter referred to as component (b)), (d) one or more selected from alkali metal hydroxides and ammonia (hereinafter referred to as component (d)), and water. Step 2: A step of blowing carbon dioxide gas into the aqueous calcium sulfate dispersion prepared in Step 1 to produce an aqueous calcium carbonate dispersion. [Effects of the Invention]

[0007] According to the present invention, there is provided a method for producing calcium carbonate which uses calcium sulfate (gypsum) as a raw material and contains calcite, which is extremely fine and valuable, in a high yield with a BET specific surface area of 30 m 2 / g or more.

[0008] When the calcium carbonate obtained by the production method of the present invention is added to a hydraulic composition such as concrete or mortar, the strength of the hydraulic composition can be improved, for example, 5 to 20 hours after the preparation of the hydraulic composition. In addition, when the calcium carbonate obtained by the production method of the present invention is added to a polymer composition such as a sealant, rubber, or plastic, the modulus and tensile strength of the polymer composition can be improved. [Embodiments for Carrying Out the Invention]

[0009] [Method for Producing Calcium Carbonate] By the production method of the present invention, using calcium sulfate (gypsum) as a raw material, although the reason for obtaining calcium carbonate with a BET specific surface area of 30 m 2 / g or more and containing extremely fine and valuable calcite in a high yield is not necessarily clear, it is presumed as follows. Generally, when synthesizing extremely fine calcium carbonate by bubbling carbon dioxide into a calcium hydroxide slurry, it is known that the slurry viscosity increases in the initial stages of the reaction, and an intermediate is formed in which calcium hydroxide and calcite aggregate into rod-shaped structures (Hiroshi Miki: Effect of the initial reaction of lime milk and carbon dioxide on calcium carbonate crystals, Gypsum and Lime, No. 91, pp. 260-268, 1967). On the other hand, when calcium carbonate is synthesized using gypsum, carbon dioxide, and an alkaline agent as raw materials, it is presumed that no intermediate is formed and extremely fine calcium carbonate cannot be stably produced because sufficient amounts of calcium carbonate and calcium hydroxide are not present in the initial stages of the reaction. Furthermore, it is presumed that the influence of coexisting sulfate ions, alkali metal ions, ammonium ions, etc., makes the formation of vaterite more stable and makes it difficult for calcite to form. On the other hand, in the calcium carbonate production method of the present invention, in step 1, in addition to calcium sulfate (gypsum) as component (a) and one or more alkaline agents selected from alkali metal hydroxides and ammonia as component (d), a calcite seed crystal as component (b) and optionally calcium hydroxide as component (c) are mixed, and in step 2, carbon dioxide is blown in, so that a sufficient amount of calcium carbonate and calcium hydroxide is present in the initial stages of the reaction, and an intermediate is formed between the calcium hydroxide produced by the reaction of the alkaline agent and gypsum and the calcite seed crystal, thereby stably producing extremely fine calcium carbonate. Furthermore, it is presumed that the formation of vaterite is suppressed because the formation of calcite becomes dominant with the seed crystal as a nucleus. The mechanism of action of the present invention is not limited to those described above.

[0010] Step 1 is the step of preparing an aqueous calcium sulfate dispersion by mixing component (a), component (b), component (d), and water.

[0011] In step 1, calcium sulfate is used as component (a). Calcium sulfate is commonly known as gypsum, and there are two main types: natural gypsum and chemical gypsum. Depending on the amount of water used in crystallization, gypsum can be one or more of the following: dihydrate gypsum (CaSO4·2H2O), hemihydrate gypsum (CaSO4·1 / 2H2O), and anhydrous gypsum (CaSO4). Furthermore, for dihydrate gypsum, one or more types of gypsum selected from natural gypsum, by-product gypsum, and gypsum product waste can be used.

[0012] Natural gypsum can be obtained from large-scale deposits in various countries, such as Canada, the United States, and France. As by-product gypsum, one or more types selected from excavated gypsum, titanium gypsum, phosphate gypsum, titanium gypsum, hydrofluoric acid gypsum, and mineral water / refined gypsum can be used. Hydrofluoric acid gypsum is produced as a by-product during the manufacture of phosphoric acid, titanium oxide, and hydrofluoric acid, while excavated gypsum is generated by capturing sulfur in flue gases emitted from thermal power plants, petrochemical industries, etc. Mineral water / refined gypsum is acid neutralization gypsum. Furthermore, as described in Japanese Patent Publication No. 63-182243, gypsum produced as a by-product during the manufacture of naphthalene sulfonic acid formalin condensate can be used. Furthermore, in addition to these types of gypsum dihydrate, it is also possible to use gypsum dihydrate that has been used as waste after being used for gypsum boards, etc.

[0013] (a) There are no particular limitations on the form of the components, but a powder form is preferred from the viewpoint of ease of handling. (a) When the component is in powder form, the average particle size is preferably 0.1 μm or more, more preferably 0.5 μm or more, and preferably 500 μm or less, and more preferably 100 μm or less, from the viewpoint of ease of reaction during the production of calcium carbonate. (a) Methods for measuring the average particle size of component include image analysis using an electron microscope, nitrogen adsorption devices, and laser diffraction particle size analyzers.

[0014] In step 1, calcite is used as component (b). The calcite of component (b) may be used as a seed crystal to suppress the formation of vaterite and promote the formation of calcite. Calcite is calcium carbonate that has the crystalline structure of calcite.

[0015] (b) The calcite of component (b) preferably has a crystallite size of 50 nm or less, more preferably 40 nm or less, even more preferably 35 nm or less, and preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, calculated by Scherrer's formula, from the viewpoint of the ease with which extremely fine calcium carbonate is formed at the end of the reaction. Furthermore, for component (b), it is preferable to use calcite containing calcite in which the crystallite size of the (10⁴) plane, calculated by Scherrer's formula, is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 35 nm or less, and preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, from the viewpoint of the ease with which extremely fine calcium carbonate can be formed at the end of the reaction.

[0016] The crystallite size of the (10⁴) plane of calcite can be calculated using an X-ray structural diffractometer (for example, a desktop X-ray diffractometer MiniFlex600, manufactured by Rigaku Corporation) using the following Scherrer formula. D = Kλ / (βcosθ) D: Crystallite size (nm) K: Scherrer constant λ: Wavelength of the X-ray being measured β: Full width at half maximum of the X-ray peak being measured θ: Bragg angle of the X-ray peak of the target X-ray. In this invention, the crystallite size is preferably measured using CuKα X-rays. When using CuKα, the wavelength is λ = 1.5406 Å. The Scherrer constant is set to 0.9, and the Bragg angle of the (10⁴) plane of calcite is set to 14.657 degrees for calculation.

[0017] (b) The BET specific surface area of calcite in the component is preferably 1 m 2 / g or more, more preferably 5 m 2 / g or more, still more preferably 10 m 2 / g or more, and preferably 100 m 2 / g or less, more preferably 80 m 2 / g or less, still more preferably 60 m 2 / g or less from the viewpoint of the ease of formation of extremely fine calcium carbonate at the end of the reaction. The BET specific surface area is a gas adsorption method in which gas particles such as nitrogen (N2) are adsorbed on solid particles and the surface area is measured from the adsorbed amount. Specifically, the specific surface area is obtained by measuring the monolayer adsorption amount VM by the BET equation (Brunauer, Emmet and Teller’s equation) from the relationship between the pressure P and the adsorption amount V. As the measuring device, it can be measured using a fully automatic specific surface area measuring device (for example, Macsorb, a fully automatic specific surface area measuring device, manufactured by Mount Tech Co., Ltd.).

[0018] (b) The average primary particle diameter of calcite in the component is preferably 5 nm or more, more preferably 10 nm or more, still more preferably 15 nm or more, even more preferably 20 nm or more, even more preferably 25 nm or more, and preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less from the viewpoint of the ease of formation of extremely fine calcium carbonate at the end of the reaction. (b) The average primary particle diameter of calcite in the component can be calculated using the following formula. d = 6 / (ρ×s)[[ID=​​​​​​​​

[0019] In step 1, component (b) calcite may be used as a primary aggregate. In the present invention, "primary aggregate" refers to a particle aggregate in which primary calcite particles have irreversibly aggregated and fused together, and which is the smallest unit of particle aggregate that cannot be dispersed further. In the present invention, "primary aggregate" is a particle aggregate that corresponds to what is called an aggregate in carbon black. (b) The primary aggregates of component calcite are preferably rod-shaped or spherical, and more preferably spherical, from the viewpoint of the ease with which extremely fine calcium carbonate is formed at the end of the reaction. Spherical does not mean only perfectly spherical, but may also be elliptical or nearly spherical, or have fine holes or irregularities on the surface, with a ratio of short axis to long axis of 1:1 or more and 1:2 or less. Rod-shaped means that the primary calcite particles are linked together in a chain, and the ratio of the short axis to long axis of the primary aggregate is greater than 1:2 and 1:20 or less, preferably 1:4 or more and 1:10 or less. The shape of the primary calcite aggregates can be observed with a transmission electron microscope or a scanning electron microscope.

[0020] In step 1, component (b) calcite may be used as aggregated secondary particles. In the present invention, "secondary particles" means particles that are isolated from other particles, formed when primary calcite particles or primary aggregates aggregate so as to share a portion of their outer circumference (grain boundary). (b) The average secondary particle size of the calcite component is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.4 μm or more, and preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of the ease with which extremely fine calcium carbonate is formed at the end of the reaction. (b) The average secondary particle size of the calcite component can be measured using a laser diffraction / scattering particle size distribution analyzer (for example, the LA-920 laser diffraction / scattering particle size distribution analyzer, manufactured by Horiba, Ltd.). In this invention, it is preferable to use water as the dispersion medium when measuring the average secondary particle diameter. Furthermore, it is preferable to perform ultrasonic treatment to ensure sufficient dispersion in the dispersion medium.

[0021] (b) The secondary calcite particles of component (b) are preferably spherical in shape, from the viewpoint of facilitating the formation of extremely fine calcium carbonate at the end of the reaction. Spherical does not mean only perfectly spherical, but may also be elliptical, nearly spherical, or have fine holes or irregularities on the surface. Among these, those with a ratio of short axis to long axis of 1:1 to 1:2 are preferable. Spherical does not include primary calcite particles linked together in a chain. The shape of the secondary calcite particles can be observed with a transmission electron microscope or scanning electron microscope.

[0022] (b) The following are examples of methods for producing the calcite component. (b) A water dispersion is prepared by mixing calcium hydroxide, any compound other than calcium hydroxide, and water, and calcium carbonate calcite is produced by introducing carbon dioxide into the water dispersion under constant water temperature conditions until the pH becomes 7 or less. Examples of compounds other than calcium hydroxide include alkaline earth metal hydroxides such as barium hydroxide (excluding magnesium salts), sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, calcium sulfate, aluminum sulfate, and alum (excluding magnesium and zinc salts), magnesium salts such as magnesium hydroxide, magnesium sulfate, magnesium chloride, magnesium nitrate, and magnesium acetate, zinc salts such as zinc sulfate, zinc chloride, and zinc nitrate, organic acids such as acetic acid, citric acid, and gluconic acid and their salts, and high molecular weight organic acids such as polyacrylic acid and their salts. One or more of these can be used. From the viewpoint of the crystallite size of the resulting calcite, one or more compounds other than calcium hydroxide are preferred, one or more are preferred from sodium sulfate and magnesium hydroxide, and magnesium hydroxide is even more preferred. Here, the mass ratio of the amount of calcium hydroxide mixed to the amount of compounds other than calcium hydroxide in the aqueous dispersion (calcium hydroxide / compounds other than calcium hydroxide) is preferably 10 or more, more preferably 30 or more, even more preferably 50 or more, and preferably 100 or less, and more preferably 80 or less, from the viewpoint of the crystallite size of the calcite produced.

[0023] (b) The calcite component can be produced by a method comprising the following steps A, B, and C. Step A: A step of preparing an aqueous dispersion of calcium hydroxide by mixing calcium hydroxide with water. Step B: A step in which the aqueous dispersion prepared in Step A is maintained at a temperature of 7°C to 30°C, and carbon dioxide is blown into the aqueous dispersion to produce a calcite aqueous dispersion. Step C: A step in which the calcite aqueous dispersion obtained in Step B is aged, stored, or dried at a temperature of 40°C or below.

[0024] In step A, it is preferable to mix in component (e) below. (e) Components: One or more compounds selected from alkaline earth metal hydroxides, sulfates, magnesium salts, zinc salts, organic acids and their salts, and polyacrylic acid and its salts. (e) Specifically, the components include alkaline earth metal hydroxides such as barium hydroxide (excluding magnesium salts), sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, calcium sulfate, aluminum sulfate, and alum (excluding magnesium salts and zinc salts), magnesium salts such as magnesium hydroxide, magnesium sulfate, magnesium chloride, magnesium nitrate, and magnesium acetate, zinc salts such as zinc sulfate, zinc chloride, and zinc nitrate, organic acids such as acetic acid, citric acid, and gluconic acid and their salts, and high molecular weight organic acids such as polyacrylic acid and their salts, and one or more of these can be used. (e) Component is preferably one or more selected from magnesium hydroxide, sodium sulfate, magnesium sulfate, and zinc sulfate, more preferably one or more selected from sodium sulfate and magnesium hydroxide, and even more preferably magnesium hydroxide, from the viewpoint of the crystallite size of the calcite produced.

[0025] In step A, when preparing the aqueous dispersion by mixing component (e), component (e) is mixed in the aqueous dispersion in an amount of 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 4% by mass or less, preferably 2.5% by mass or less, more preferably 2.3% by mass or less, and even more preferably 2.0% by mass or less, relative to the amount of calcium hydroxide mixed, from the viewpoint of the shape and stability of the calcite particles produced. Furthermore, when preparing the aqueous dispersion, water is mixed in the aqueous dispersion in an amount of 1500% by mass or more, more preferably 1800% by mass or more, and preferably 2500% by mass or less, and more preferably 2000% by mass or less, relative to the amount of calcium hydroxide mixed. Furthermore, when preparing the aqueous dispersion by mixing component (e), the mass ratio of the amount of calcium hydroxide mixed to the amount of component (e) (calcium hydroxide / (e)) is preferably 10 or more, more preferably 30 or more, even more preferably 50 or more, and preferably 100 or less, and more preferably 80 or less, from the viewpoint of the crystallite size of the calcite produced.

[0026] In step B, the aqueous dispersion prepared in step A is kept at a temperature of 10°C or higher, preferably 12°C or higher, more preferably 14°C or higher, and 30°C or lower, preferably 25°C or lower, more preferably 20°C or lower, from the viewpoint of the size and stability of the calcite particles produced, and carbon dioxide is blown in to produce a calcite aqueous dispersion. The carbon dioxide blown into the aqueous dispersion may be a mixed gas containing an inert gas such as nitrogen, and the proportion of carbon dioxide in the blown gas is preferably 10% by volume or higher, preferably 20% by volume or higher, more preferably 50% by volume or higher, and preferably 100% by volume or lower, from the viewpoint of the size and shape of the calcite particles produced. It is preferable to blow in carbon dioxide until the pH of the aqueous dispersion becomes 7 or lower.

[0027] There are no particular restrictions on the method of blowing carbon dioxide gas as described above. Examples of methods for blowing carbon dioxide gas include supplying it via a nozzle or a shower-like system with multiple pores. Furthermore, carbon dioxide gas can be supplied continuously, intermittently, or by using a combination of these methods as appropriate.

[0028] In step C, the calcite aqueous dispersion obtained in step B is aged, stored, or dried at an ambient temperature of 40°C or lower, preferably 35°C or lower, and more preferably 30°C or lower, from the viewpoint of the shape of the primary calcite aggregates. The aging, storage, or drying time is preferably 60 minutes or more, more preferably 120 minutes or more, and preferably 48 hours or less, and more preferably 24 hours or less, from the viewpoint of the shape of the primary calcite aggregates.

[0029] The calcite of component (b) produced by the above method may contain unreacted components from the carbonation reaction, such as calcium hydroxide, vaterite, aragonite, calcium carbonate hydrates such as squamite, basic calcium carbonate, and other amorphous calcium carbonates. However, these calcium carbonates other than calcite are not included in component (b) of the present invention. In the production method of the present invention, in step 1, a mixture containing these calcium carbonates other than the calcite of component (b) may be mixed with component (b) to prepare an aqueous calcium sulfate dispersion. Vaterite is calcium carbonate with the crystalline structure of vaterite (or vaterite). Aragonite is calcium carbonate that has the crystalline structure of aragonite (aragonite stone). Icaite is a calcium carbonate hexahydrate that has the crystalline structure of squid stone (icaite). Basic calcium carbonate is a crystalline mineral with the chemical composition Ca3(OH)2(CO3)2·1.5H2O.

[0030] In the method for producing calcium carbonate of the present invention, the calcite of component (b) may be, for example, the calcite remaining in the reaction vessel when the calcium carbonate of the previous batch is discharged from the reaction vessel during continuous production in a batch system. When using the calcite remaining in the reaction vessel when the calcium carbonate of the previous batch is discharged from the reaction vessel as component (b), it is preferable not to clean the inside of the reaction vessel after the previous batch is discharged. Even in the above case, in the production method of the present invention, in step 1, a mixture containing these calcium carbonates other than the calcite of component (b) may be mixed with component (b) to prepare an aqueous dispersion of calcium sulfate.

[0031] Furthermore, the calcite of component (b) of the present invention is preferably produced by a method comprising the following preliminary steps 1 and 2. Preliminary step 1: A step of preparing an aqueous dispersion of calcium salt by mixing calcium salt with one or more selected from alkali metal hydroxides and alkaline earth metal hydroxides (except calcium salt) and water. Preliminary step 2: A step of blowing carbon dioxide gas into the aqueous dispersion prepared in preliminary step 1 to produce an aqueous dispersion of component (b). By the method described above, calcite of component (b) can be obtained, and the method for producing calcium carbonate of the present invention can be carried out.

[0032] The calcium salts used in preliminary step 1 specifically include inorganic calcium salts such as calcium hydroxide, calcium chloride, calcium sulfate, calcium sulfite, calcium nitrate, calcium nitrite, calcium cyanate, calcium thiocyanate, calcium thiosulfate, calcium silicate, calcium phosphate, calcium phosphite, and calcium hypophosphite; organic calcium acid salts such as calcium acetate, calcium formate, calcium lactate, calcium citrate, calcium glycolate, calcium p-toluenesulfonate, and calcium naphthalenesulfonate; and hydrates of these calcium salts. One or more of these can be used.

[0033] In preliminary step 1, the calcium salt is mixed in the aqueous dispersion of the calcium salt in an amount that is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, even more preferably 2% by mass or more, even more preferably 3% by mass or more, and from the viewpoint of the ease with which extremely fine calcium carbonate is formed at the end of the reaction, preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 9% by mass or less, even more preferably 8% by mass or less, and even more preferably 7% by mass or less.

[0034] The alkali metal hydroxide used in preliminary step 1 specifically includes one or more selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide. The alkaline earth metal hydroxide used in preliminary step 1 specifically includes one or more selected from beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, and radium hydroxide.

[0035] In preliminary step 1, one or more alkali metal hydroxides and alkaline earth metal hydroxides are selected in the aqueous dispersion of the calcium salt, with a ratio of the number of moles of calcium ions to the number of moles of hydroxide ions ([Ca 2+ ] / [OH - However, from the viewpoint of how easily extremely fine calcium carbonate is formed at the end of the reaction, the mixture is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, even more preferably 0.6 or more, and for the same reason, preferably 1.5 or less, more preferably 1.3 or less, even more preferably 1.1 or less, and even more preferably 1.0 or less.

[0036] In preliminary step 1, from the viewpoint of the crystallite size of the calcite produced, it is preferable to further mix in one or more compounds selected from (f) sulfates, magnesium salts, zinc salts, organic acids and their salts, and polyacrylic acid and its salts (hereinafter referred to as component (f)). (f) Specifically, the components include sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, calcium sulfate, aluminum sulfate, and alum (excluding magnesium and zinc salts), magnesium salts such as magnesium sulfate, magnesium chloride, magnesium nitrate, and magnesium acetate, zinc salts such as zinc sulfate, zinc chloride, and zinc nitrate, organic acids and their salts such as acetic acid, citric acid, and gluconic acid, and high molecular weight organic acids and their salts such as polyacrylic acid, and one or more of these may be used. (f) Component is preferably one or more selected from sodium sulfate, magnesium sulfate, and zinc sulfate, more preferably one or more selected from sodium sulfate and zinc sulfate, and even more preferably zinc sulfate, from the viewpoint of the crystallite size of the calcite produced.

[0037] In the preliminary step 1, when component (f) is mixed into the aqueous dispersion of the calcium salt, component (f) is mixed in the aqueous dispersion in an amount of the calcium salt that is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, and similarly preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of the shape and stability of the calcite particles produced.

[0038] In the preliminary step 1, when preparing the aqueous dispersion of the calcium salt, water is mixed into the aqueous dispersion in an amount of preferably 100% by mass or more, more preferably 200% by mass or more, and preferably 10,000% by mass or less, and more preferably 5,000% by mass or less, relative to the amount of calcium salt mixed.

[0039] In the preliminary step 2, carbon dioxide can be blown into the aqueous dispersion of the calcium salt at a temperature of preferably 10°C or higher, more preferably 12°C or higher, even more preferably 13°C or higher, and for the same reason preferably 25°C or lower, more preferably 20°C or lower, and even more preferably 17°C or lower, from the viewpoint of facilitating the formation of extremely fine calcium carbonate at the end of the reaction. This makes it possible to produce an aqueous dispersion of component (b) calcite.

[0040] In preliminary step 2, there are no particular restrictions on the method of blowing in the carbon dioxide gas. Examples of methods for blowing in carbon dioxide gas include supplying it via a nozzle or in a shower-like manner with multiple pores. Furthermore, the carbon dioxide gas can be supplied continuously, intermittently, or by using these methods interchangeably as appropriate. Furthermore, the reaction vessel used for the reaction with carbon dioxide may be either an open system or a closed system.

[0041] In the preliminary step 2, the carbon dioxide blown into the aqueous dispersion of the calcium salt may be blown in as a mixed gas containing an inert gas such as nitrogen. The proportion of carbon dioxide in the mixed gas is preferably 10% by volume or more, preferably 20% by volume or more, more preferably 30% by volume or more, even more preferably 50% by volume or more, even more preferably 70% by volume or more, even more preferably 90% by volume or more, and preferably 100% by volume or less, and may exceed 100% by volume. It is preferable to blow in the carbon dioxide until the pH of the aqueous dispersion of the calcium salt becomes 7.5 or less. The flow rate of carbon dioxide injected into the aqueous dispersion of the calcium salt is preferably 0.05 L / min or more, more preferably 0.1 L / min or more, even more preferably 0.2 L / min or more, even more preferably 0.3 L / min or more, and preferably 10.0 L / min or less, more preferably 5.0 L / min or less, even more preferably 2.0 L / min or less, even more preferably 1.0 L / min or less, even more preferably 0.8 L / min or less, and even more preferably 0.6 L / min or less, per 100 g of alkali metal hydroxide and alkaline earth metal hydroxide, from the viewpoint of how easily extremely fine calcium carbonate is formed at the end of the reaction.

[0042] In the preliminary step 2, from the viewpoint of the ease with which extremely fine calcium carbonate is formed at the end of the reaction, it is preferable that the viscosity of the aqueous dispersion of calcium salt increases when carbon dioxide is blown into the aqueous dispersion of calcium salt, and it is preferable to adjust the maximum viscosity of the aqueous dispersion of calcium salt when carbon dioxide is blown in. The maximum viscosity of the aqueous dispersion of calcium salt when carbon dioxide is blown in (measured using a B-type viscometer with an M2 rotor, rotated at a rotation speed of 60 rpm for 180 seconds) is preferably 100 mPa·sec or more, more preferably 120 mPa·sec or more, more preferably 150 mPa·sec or more, and from the same viewpoint, preferably 2000 mPa·sec or less, more preferably 1000 mPa·sec or less, and even more preferably 500 mPa·sec or less. The maximum viscosity of the aqueous dispersion of the calcium salt can be measured, for example, by the following method. Pour approximately 200 ml of the aqueous dispersion of the calcium salt into a 300 ml glass beaker and leave it in an immersion-type constant-temperature water bath until the liquid temperature reaches 15°C. Measure the viscosity after installing the M2 rotor on a Type B viscometer (TVB10 viscometer manufactured by Toki Sangyo Co., Ltd.) and rotating it at a speed of 60 rpm for 180 seconds. If the measured value exceeds 500 mPa·sec, use the M1 rotor.

[0043] In the preliminary step 2, the ratio V / V0 of the maximum viscosity V of the aqueous dispersion of the calcium salt when carbon dioxide is blown into it to the aqueous dispersion of the calcium salt before carbon dioxide is blown into it is preferably 10 or more, more preferably 50 or more, even more preferably 100 or more, even more preferably 150 or more, and from the viewpoint of how easily extremely fine calcium carbonate is formed at the end of the reaction, preferably 2000 or less, more preferably 1000 or less, and even more preferably 500 or less.

[0044] The component (b) of the present invention obtained by preliminary steps 1 and 2 may be a mixture containing unreacted calcium salts and the like in addition to component (b), and in step 1, the mixture may be mixed to prepare an aqueous calcium sulfate dispersion. The unreacted calcium salt may contain component (a) of the present invention and component (c) described later in the raw materials used, but these components can be used as they are in step 1 as components (a) and (c).

[0045] In the manufacturing method of the present invention, it is preferable that in step 1, calcium hydroxide of component (c) is further mixed to prepare an aqueous calcium sulfate dispersion. In other words, it is preferable that step 1 is a step of mixing component (a), component (b), calcium hydroxide (c) (hereinafter referred to as component (c)), component (d), and water to prepare an aqueous calcium sulfate dispersion. Step 1 does not require the inclusion of component (c) if sufficient calcite of component (b) is present, but adding component (c) can further accelerate the production of calcite by reaction.

[0046] (c) The calcium hydroxide in component (c) can be obtained by adding slaked lime, which can be obtained by adding calcium oxide (quicklime) obtained by decarboxylating calcium carbonate to water; carbide slag, which is replicated when obtaining acetylene from calcium carbide; calcium hydroxide obtained by the chemical reaction between alkali metal hydroxide and soluble calcium salt; or calcium hydroxide produced as a by-product in other chemical processes. Soluble calcium salts include one or more selected from calcium chloride, calcium sulfate, calcium sulfite, calcium nitrate, calcium nitrite, calcium cyanate, calcium thiocyanate, calcium thiosulfate, calcium acetate, calcium formate, calcium lactate, calcium citrate, and hydrates of these calcium salts.

[0047] In step 1, one or more components selected from alkali metal hydroxides and ammonia are used as component (d). Examples of alkali metal hydroxides include one or more selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide. (d) The component is preferably one or more selected from sodium hydroxide and potassium hydroxide, with potassium hydroxide being more preferred, from the viewpoint of suppressing the formation of vaterite by-products.

[0048] In step 1, when preparing the aqueous calcium sulfate dispersion, component (b) is mixed in the aqueous calcium sulfate dispersion with respect to the amount of component (a) on an anhydrous basis, preferably in an amount of 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1% by mass or more, even more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 1000% by mass or less, more preferably 500% by mass or less, even more preferably 100% by mass or less, even more preferably 50% by mass or less, and even more preferably 10% by mass or less.

[0049] In step 1, when preparing the aqueous calcium sulfate dispersion, if component (c) is mixed, component (c) is mixed in the aqueous calcium sulfate dispersion in an amount of (a) converted to anhydrous, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1% by mass or more, even more preferably 2% by mass or more, even more preferably 4% by mass or more, and preferably 100% by mass or less, more preferably 50% by mass or less, even more preferably 10% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of suppressing the formation of vaterite by-products.

[0050] In step 1, when preparing the aqueous calcium sulfate dispersion, component (d) is mixed in the aqueous calcium sulfate dispersion with respect to the amount of component (a) on an anhydrous basis, preferably in an amount of 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction, and from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction and economic efficiency, preferably 150% by mass or less, more preferably 130% by mass or less, even more preferably 100% by mass or less, even more preferably 70% by mass or less, and even more preferably 50% by mass or less.

[0051] In step 1, when preparing the calcium sulfate aqueous dispersion, component (d) is mixed in the calcium sulfate aqueous dispersion with respect to the amount of component (a) in an amount preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 100 mol% or more, from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction, and from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction and economic efficiency, in an amount preferably 300 mol% or less, more preferably 200 mol% or less, even more preferably 150 mol% or less, and even more preferably 130 mol% or less.

[0052] In step 1, when preparing the aqueous calcium sulfate dispersion, water is mixed in the aqueous calcium sulfate dispersion with respect to the amount of component (a) in terms of anhydrous form, preferably at a rate of 200% by mass or more, more preferably 300% by mass or more, even more preferably 400% by mass or more, even more preferably 500% by mass or more, and preferably 10000% by mass or less, more preferably 5000% by mass or less, even more preferably 2000% by mass or less, even more preferably 1500% by mass or less, and even more preferably 1000% by mass or less, with respect to the amount of component (a) mixed in terms of anhydrous form, from the viewpoint of ease of formation of extremely fine calcium carbonate at the end of the reaction.

[0053] Step 2 is a step in which carbon dioxide gas is blown into the calcium sulfate aqueous dispersion prepared in Step 1 to produce a calcite aqueous dispersion. Step 2 may be carried out concurrently with Step 1. That is, in Step 2, carbon dioxide may be blown in while preparing the aqueous calcium sulfate dispersion (while carrying out Step 1). Furthermore, step 2 may be performed after step 1. That is, step 2 may be a step of blowing carbon dioxide into the calcium sulfate aqueous dispersion prepared in step 1 to produce a calcite aqueous dispersion.

[0054] In step 2, the aqueous calcium sulfate dispersion prepared in step 1 is kept at a liquid temperature of preferably 7°C or higher, more preferably 10°C or higher, even more preferably 12°C or higher, and preferably 30°C or lower, more preferably 25°C or lower, and even more preferably 20°C or lower, from the viewpoint of facilitating the formation of extremely fine calcium carbonate at the end of the reaction, and carbon dioxide is blown in to produce an aqueous calcite dispersion.

[0055] In step 2, there are no particular restrictions on the method of blowing in the carbon dioxide gas. For example, it can be supplied using a nozzle or a shower-like method with multiple pores. Furthermore, the carbon dioxide gas can be supplied continuously, intermittently, or by using both methods as appropriate. Furthermore, the reaction vessel used for the reaction with carbon dioxide may be either an open system or a closed system.

[0056] In step 2, the carbon dioxide gas blown into the aqueous calcium sulfate dispersion may be blown in as a mixed gas containing an inert gas such as nitrogen. The proportion of carbon dioxide gas in the mixed gas is preferably 10% by volume or more, preferably 20% by volume or more, more preferably 30% by volume or more, even more preferably 50% by volume or more, even more preferably 70% by volume or more, even more preferably 90% by volume or more, and preferably 100% by volume or less, and may exceed 100% by volume. It is preferable to blow in the carbon dioxide gas until the pH of the aqueous calcium sulfate dispersion becomes 7.5 or less. The flow rate of carbon dioxide injected into the aqueous calcium sulfate dispersion is preferably 0.05 L / min or more, more preferably 0.1 L / min or more, even more preferably 0.2 L / min or more, even more preferably 0.3 L / min or more, and preferably 10.0 L / min or less, more preferably 5.0 L / min or less, even more preferably 2.0 L / min or less, even more preferably 1.0 L / min or less, even more preferably 0.8 L / min or less, and even more preferably 0.6 L / min or less, based on anhydrous basis, per 100 g of component (a). If the injected carbon dioxide is the mixed gas described above, its flow rate shall be within the range described above when converted to carbon dioxide.

[0057] From the viewpoint of suppressing the generation of by-products, step 2 preferably includes the following steps 2-1 and 2-2. Step 2-1: A step of blowing carbon dioxide into the aqueous calcium sulfate dispersion prepared in Step 1 until the pH of the aqueous calcium sulfate dispersion reaches 9 or less. Step 2-2: After the pH of the calcium sulfate aqueous dispersion in Step 2-1 reaches 9 or less, one or more selected from alkali metal hydroxides and ammonia is mixed with the calcium sulfate aqueous dispersion until the pH of the calcium sulfate aqueous dispersion reaches 7.5 or less, and carbon dioxide is blown in to produce a calcite aqueous dispersion.

[0058] In step 2-1, the aqueous calcium sulfate dispersion prepared in step 1 can be kept at a liquid temperature of preferably 5°C or higher, more preferably 7°C or higher, even more preferably 10°C or higher, and preferably 40°C or lower, more preferably 30°C or lower, and even more preferably 20°C or lower, from the viewpoint of the ease with which extremely fine calcium carbonate can be formed, and carbon dioxide gas can be blown in until the pH of the aqueous calcium sulfate dispersion reaches 9 or lower.

[0059] In step 2-1, the carbon dioxide blown into the aqueous calcium sulfate dispersion may be blown in as a mixed gas containing an inert gas such as nitrogen, in the same manner as in step 2. The proportion of carbon dioxide in the mixed gas is preferably within the same range as described in step 2. With respect to the aqueous calcium sulfate dispersion, the flow rate of carbon dioxide gas blown in is preferably 0.05 L / min or more, more preferably 0.1 L / min or more, even more preferably 0.2 L / min or more, even more preferably 0.3 L / min or more, and preferably 10.0 L / min or less, more preferably 5.0 L / min or less, even more preferably 2.0 L / min or less, even more preferably 1.0 L / min or less, even more preferably 0.8 L / min or less, and even more preferably 0.6 L / min or less, per 100 g of component (a) on an anhydrous basis. If the carbon dioxide gas blown in is the mixed gas described above, it is preferable that the flow rate, when converted to carbon dioxide gas, is within the range described above.

[0060] In step 2-2, after the pH of the calcium sulfate aqueous dispersion has reached 9 or less in step 2-1, the liquid temperature is preferably maintained at 5°C or higher, more preferably 7°C or higher, even more preferably 10°C or higher, and preferably 60°C or lower, more preferably 45°C or lower, even more preferably 30°C or lower, and even more preferably 20°C or lower, from the viewpoint of suppressing the generation of by-products, and one or more selected from alkali metal hydroxides and ammonia is mixed into the calcium sulfate aqueous dispersion until the pH of the calcium sulfate aqueous dispersion reaches 7.5 or lower. In step 2-2, one or more selected from alkali metal hydroxides and ammonia are mixed in the aqueous calcium sulfate dispersion in an amount of (a) on an anhydrous basis in step 1, preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, preferably 100% by mass or less, more preferably 75% by mass or less, and even more preferably 50% by mass or less, from the viewpoint of suppressing the generation of by-products. One or more substances selected from alkali metal hydroxides and ammonia may be added to the calcium sulfate aqueous dispersion as one or more substances selected from aqueous alkali metal hydroxide solutions and aqueous ammonia solutions to which water has been added, preferably over a period of 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, even more preferably 20 minutes or more, and preferably 120 minutes or less, more preferably 90 minutes or less, even more preferably 60 minutes or less, and even more preferably 40 minutes or less, from the viewpoint of suppressing the generation of by-products. The addition can be done in installments or continuously.

[0061] After mixing one or more substances selected from alkali metal hydroxides and ammonia into the aqueous calcium sulfate dispersion until the pH of the aqueous calcium sulfate dispersion reaches 7.5 or less, carbon dioxide is blown in. The carbon dioxide blown into the aqueous calcium sulfate dispersion may be blown in as a mixed gas containing an inert gas such as nitrogen in the same manner as in step 2. The proportion of carbon dioxide in the mixed gas is preferably within the same range as described in step 2. With respect to the aqueous calcium sulfate dispersion, the flow rate of carbon dioxide gas blown in is preferably 0.05 L / min or more, more preferably 0.1 L / min or more, even more preferably 0.2 L / min or more, even more preferably 0.3 L / min or more, and preferably 10.0 L / min or less, more preferably 5.0 L / min or less, even more preferably 2.0 L / min or less, even more preferably 1.0 L / min or less, even more preferably 0.8 L / min or less, and even more preferably 0.6 L / min or less, per 100 g of component (a) on an anhydrous basis. If the carbon dioxide gas blown in is the mixed gas described above, it is preferable that the flow rate, when converted to carbon dioxide gas, is within the range described above. The time for blowing carbon dioxide into the aqueous calcium sulfate dispersion is preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, preferably 300 minutes or less, more preferably 240 minutes or less, even more preferably 180 minutes or less, even more preferably 120 minutes or less, even more preferably 80 minutes or less, and even more preferably 60 minutes or less, from the viewpoint of how easily extremely fine calcium carbonate is formed at the end of the reaction. When blowing carbon dioxide into the calcium sulfate aqueous dispersion, the liquid temperature of the calcium sulfate aqueous dispersion is preferably maintained at 7°C or higher, more preferably 10°C or higher, even more preferably 12°C or higher, and preferably 30°C or lower, more preferably 25°C or lower, and even more preferably 20°C or lower, from the viewpoint of facilitating the formation of extremely fine calcium carbonate at the end of the reaction, while blowing in carbon dioxide.

[0062] In steps 1, 2-1, and 2-2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed in the aqueous calcium sulfate dispersion to the amount of ammonia is preferably 20 / 80 or higher, more preferably 40 / 60 or higher, even more preferably 50 / 50 or higher, even more preferably 60 / 40 or higher, even more preferably 70 / 30 or higher, even more preferably 80 / 20 or higher, and preferably 100 / 0 or lower, from the viewpoint of easily forming extremely fine calcium carbonate at the end of the reaction and suppressing the formation of by-products.

[0063] In steps 1, 2-1, and 2-2, the molar ratio (component (a) / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia mixed is preferably 10 / 90 or more, more preferably 20 / 70 or more, and even more preferably 30 / 70 or more, from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction, and from the viewpoint of suppressing the remaining unreacted gypsum at the end of the reaction and economic efficiency is preferably 60 / 40 or less, more preferably 50 / 50 or less, and even more preferably 40 / 60 or less.

[0064] In the method for producing calcium carbonate of the present invention, it is preferable to further include the following step 3. Step 3: A step of aging, storing, or drying the calcite aqueous dispersion obtained in Step 2 (Steps 2-1 and 2-2) at a temperature of 40°C or lower. In step 3, the calcite aqueous dispersion obtained in step 2 (steps 2-1 and 2-2) is aged, stored, or dried at an ambient temperature of 40°C or lower, preferably 35°C or lower, and more preferably 30°C or lower, from the viewpoint of the shape of the primary calcite aggregates. The aging, storage, or drying time is preferably 60 minutes or more, more preferably 120 minutes or more, and preferably 48 hours or less, and more preferably 24 hours or less, from the viewpoint of the shape of the primary calcite aggregates.

[0065] In the method for producing calcium carbonate of the present invention, it is preferable to further include the following step 4. Step 4: A step of separating solids and water from the calcite aqueous dispersion obtained in Step 2 (Steps 2-1, Steps 2-2) or Step 3. In step 4, the solids and water are separated from the calcite aqueous dispersion obtained in step 2 (steps 2-1 and 2-2) or the calcite aqueous dispersion obtained in step 3. Methods for separating the solids and water include natural sedimentation, filtration using a filter press or Nutsche filter, and centrifugal separation using a decanter. The solids separated in step 4 may be recovered as a cake containing moisture. When recovered as a cake, dissolved sulfate ions, alkali metal ions, ammonium ions, and sparingly soluble salts such as singenite derived from these ions will be mixed into the calcite; therefore, it is preferable to wash the solids separated in step 3 with water. Washing with water can reduce the amount of contamination from sulfate ions, alkali metal ions, ammonium ions, and sparingly soluble salts such as singenite derived from these ions.

[0066] The BET specific surface area of ​​the calcium carbonate obtained by the manufacturing method of the present invention is 30 m², from the viewpoint of strength improvement effect for hydraulic compositions and reinforcement effect for polymer compositions. 2 / g or more, preferably 40m 2 / g or more, comfortably 50m 2 / g or more, more preferably 60m 2 / g or more, and preferably 200m 2 Less than / g, more preferably 150m2 / g or less, more preferably 100m 2 It is less than / g. The BET specific surface area of ​​calcite can be measured by the method described above.

[0067] The manufacturing method of the present invention yields calcium carbonate containing calcite. The crystallite size of the (10⁴) plane of the calcite obtained by the manufacturing method of the present invention, calculated using Scherrer's formula, is preferably 30 nm or less, more preferably 25 nm or less, even more preferably 20 nm or less, and preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, from the viewpoint of improving the strength of the hydraulic composition and reinforcing the polymer composition. The crystallite size of the (10⁴) plane of the calcite, calculated using Scherrer's formula, can be measured by the method described above.

[0068] The average primary particle diameter of the calcite obtained by the manufacturing method of the present invention is preferably 5 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, even more preferably 20 nm or more, even more preferably 25 nm or more, and preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less, from the viewpoint of strength improvement effect on hydraulic compositions and reinforcement effect on polymer compositions. The average primary particle diameter of the calcite can be measured by the method described above.

[0069] The calcite obtained by the manufacturing method of the present invention may be a primary aggregate in which calcite has aggregated. From the viewpoint of improving the strength of the hydraulic composition and reinforcing the polymer composition, the primary aggregates of calcite are preferably rod-shaped or spherical, and more preferably spherical. Spherical does not mean only perfectly spherical, but may also be elliptical, nearly spherical, or have fine holes or irregularities on the surface. Among these, those with a ratio of short axis to long axis of 1:1 or more and 1:2 or less are preferred. Rod-shaped may be a chain of primary calcite particles. The ratio of short axis to long axis of the primary aggregates should be greater than 1:20 or less, preferably 1:4 or more and 1:10 or less. The shape of the primary calcite aggregates can be observed with a transmission electron microscope or scanning electron microscope.

[0070] The calcite obtained by the manufacturing method of the present invention may be aggregated secondary particles. The average secondary particle size of calcite is preferably 1 μm or more, more preferably 1.5 μm or more, even more preferably 2.0 μm or more, and preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and even more preferably 5 μm or less, from the viewpoint of strength-enhancing effect on hydraulic compositions and reinforcing effect on polymer compositions. The average secondary particle size of calcite can be measured by the method described above. Secondary calcite particles are preferably spherical in shape, from the viewpoint of improving the strength of the hydraulic composition and reinforcing the polymer composition. Spherical does not mean only perfectly spherical, but may also be elliptical, nearly spherical, or have fine holes or irregularities on the surface, with a ratio of minor axis to major axis of 1:1 to 1:2. Spherical does not include primary calcite particles linked together in a chain. The shape of secondary calcite particles can be observed using a transmission electron microscope or scanning electron microscope.

[0071] In addition to calcite, the calcium carbonate obtained by the production method of the present invention may also contain unreacted components from the carbonation reaction, such as calcium hydroxide, calcium sulfate, calcium sulfate hemihydrate, calcium sulfate dihydrate, calcium carbonate such as singenite, vaterite, and aragonite, calcium carbonate hydrate such as ikaite, basic calcium carbonate, and other amorphous calcium carbonates. Singenite is a double salt of calcium sulfate and other sulfates, including CaSO4·(NH4)2SO4, 2CaSO4·(NH4)2SO4, 5CaSO4·(NH4)2SO4·2H2O, 2Na2SO4·CaSO4·2H2O, Na2SO4·CaSO4, Na2SO4·5CaSO4·3H2O, and CaSO4·K2SO4·H2O.

[0072] The calcium carbonate obtained by the manufacturing method of the present invention has a BET specific surface area of ​​30 m². 2 Because it contains extremely fine and valuable calcite in high yield at a concentration of 1 / g or more, when added to polymer compositions such as sealants, rubber, and plastics, it can improve the dispersibility, modulus, and tensile strength of the polymer composition. When calcium carbonate obtained by the manufacturing method of the present invention is added to a polymer composition, for example, it may be surface-treated to improve its dispersibility. For example, calcium carbonate obtained by the manufacturing method of the present invention may be surface-treated with at least one treatment agent selected from the group consisting of fatty acids, resin acids and their derivatives, silica, coupling agents, organosilicon compounds, and condensed phosphoric acid.

[0073] <Rapid-strengthening agent for hydraulic compositions> The calcium carbonate obtained by the manufacturing method of the present invention has a BET specific surface area of ​​30 m². 2 Because it contains extremely fine and valuable calcite in high yield at a concentration of 1 / g or more, when added to hydraulic compositions such as concrete or mortar, it can improve the early strength of the hydraulic composition, for example, 5 to 20 hours after the preparation of the hydraulic composition. In other words, the present invention provides a rapid strengthening agent for hydraulic compositions, comprising calcium carbonate obtained by the calcium carbonate production method of the present invention. Furthermore, the present invention provides for the use of calcium carbonate obtained by the calcium carbonate production method of the present invention as a rapid strengthening agent for hydraulic compositions.

[0074] <Hydraulic composition> The calcium carbonate obtained by the manufacturing method of the present invention can be used as a rapid strengthening agent for hydraulic compositions. In other words, the present invention provides a hydraulic composition containing calcium carbonate, hydraulic powder, and water obtained by the manufacturing method of the present invention. The hydraulic composition of the present invention can be appropriately adapted to the embodiments described in the method for producing calcium carbonate of the present invention. In the hydraulic composition of the present invention, the calcium carbonate obtained by the manufacturing method of the present invention is used as a rapid strengthening agent for the hydraulic composition.

[0075] The hydraulic powder used in the hydraulic composition of the present invention is a powder that hardens when mixed with water, and examples include ordinary Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, sulfate-resistant Portland cement, low-heat Portland cement, white Portland cement, and eco-cement (e.g., JIS R5214). Among these, from the viewpoint of shortening the time it takes for the hydraulic composition to reach the required strength, cement selected from rapid-hardening Portland cement, ordinary Portland cement, sulfate-resistant Portland cement, and white Portland cement is preferred, and cement selected from rapid-hardening Portland cement and ordinary Portland cement is more preferred.

[0076] Furthermore, the hydraulic powder may contain blast furnace slag, fly ash, silica fume, anhydrous gypsum, etc., and may also contain non-hydraulic limestone fine powder, etc. As the hydraulic powder, blast furnace cement, fly ash cement, or silica fume cement, which are mixtures of cement with blast furnace slag, fly ash, silica fume, etc., may be used. Furthermore, hydraulic powders include cement or a mixture of cement and bentonite powder.

[0077] The hydraulic composition of the present invention contains calcium carbonate obtained by the manufacturing method of the present invention in an amount of 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of hydraulic powder, from the viewpoint of rapid strengthening of the hydraulic composition, and from the viewpoint of rapid strengthening and economic efficiency of the hydraulic composition, preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 4.0 parts by mass or less.

[0078] In the hydraulic composition of the present invention, the mass percentage of water to hydraulic powder in the hydraulic composition (water / hydraulic powder ratio (W / C)) is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, even more preferably 30% by mass or more, and preferably 200% by mass or less, more preferably 100% by mass or less, even more preferably 70% by mass or less, and even more preferably 50% by mass or less, from the viewpoint of rapid strengthening, economy, workability, and durability of the hardened product of the hydraulic composition. Here, the water / hydraulic powder ratio (W / C) is the mass percentage (mass%) of water and hydraulic powder in the hydraulic composition, and is calculated as water / hydraulic powder × 100. Furthermore, if the hydraulic powder contains powders that harden through hydration reactions such as cement, as well as powders with pozzolanic properties and powders with latent hydraulic properties, the amounts of these are also included in the amount of hydraulic powder in this invention (however, the amount of calcium carbonate, which is component (a), is not included). Also, if the powder that hardens through hydration reactions contains a high-strength admixture, the amount of the high-strength admixture is also included in the amount of hydraulic powder. This also applies to other parts of mass related to the mass of hydraulic powder. In the hydraulic composition of the present invention, the water can be tap water, distilled water, supernatant water, sludge water, or deionized water.

[0079] From the viewpoint of workability, the hydraulic composition of the present invention may further contain cement admixtures. Examples of admixtures for cement include lignin-based water-reducing agents, naphthalene sulfonic acid-based water-reducing agents, aminosulfonic acid-based water-reducing agents, polycarboxylic acid-based water-reducing agents, polyether-based water-reducing agents, high-performance water-reducing agents, and high-performance AE water-reducing agents, of which one or more can be used. From the viewpoint of ensuring fluidity at low water-cement ratios, high-performance water-reducing agents containing carboxyl group-containing polyether compounds (especially those included as the main component) are preferred as cement admixtures.

[0080] The hydraulic composition of the present invention contains, with respect to 100 parts by mass of hydraulic powder, a cement admixture in an amount of preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, from the viewpoint of rapid strengthening of the hydraulic composition, and preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, even more preferably 2.0 parts by mass or less, and even more preferably 1.0 part by mass or less, from the viewpoint of rapid strengthening and economic efficiency of the hydraulic composition.

[0081] The hydraulic composition of the present invention may contain aggregate. Examples of aggregate include fine aggregate and coarse aggregate. Examples of fine aggregate include those specified in JIS A 0203-2014, number 2311. Examples of fine aggregate include river sand, land sand, mountain sand, sea sand, lime sand, silica sand and their crushed sand, blast furnace slag fine aggregate, ferronickel slag fine aggregate, lightweight fine aggregate (artificial and natural), and recycled fine aggregate. From the viewpoint of the fluidity of the mortar slurry, the fine aggregate preferably contains 70-98% by mass of particles with a particle size of 0.15 mm or less, and can also be prepared by mixing two or more types of fine aggregate with different particle sizes. Examples of coarse aggregate include those specified in JIS A 0203-2014, number 2312. Examples of coarse aggregates include river gravel, land gravel, mountain gravel, sea gravel, lime gravel, crushed stone of these materials, blast furnace slag coarse aggregate, ferronickel slag coarse aggregate, lightweight coarse aggregate (artificial and natural), and recycled coarse aggregate. Fine aggregate and coarse aggregate may be mixed from different types, or a single type may be used.

[0082] When the hydraulic composition is concrete, the amount of coarse aggregate used is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less, from the viewpoint of developing the strength of the hydraulic composition, reducing the amount of hydraulic powder such as cement used, and improving the ability to fill into formwork, etc. The bulk volume is 1 m³ of concrete. 3 This is the ratio of the volume of coarse aggregate (including voids) inside. Furthermore, when the hydraulic composition is concrete, the amount of fine aggregate used is preferably 500 kg / m³ from the viewpoint of improving the ability to fill into formwork, etc. 3 Above, a comfortable 600 kg / m 3 More preferably 700 kg / m 3 The above is true, and preferably 1000 kg / m 3 More preferably 900 kg / m 3 The following applies: When the hydraulic composition is mortar, the amount of fine aggregate used is preferably 800 kg / m³.3 In summary, a comfortable 900 kg / m 3 More preferably 1000 kg / m 3 The above is true, and preferably 2000 kg / m 3 More preferably, 1800 kg / m 3 More preferably, 1700 kg / m 3 The following applies:

[0083] The hydraulic composition of the present invention may be concrete or mortar. The hydraulic composition of the present invention is useful in any field, such as self-leveling, refractory materials, plaster, lightweight or mass concrete, AE, repair, pre-packed materials, tremies, ground improvement, grouting, and cold weather applications. From the viewpoint of developing strength in about 5 to 20 hours after the preparation of the hydraulic composition, and enabling early demolding from the formwork, it is preferable to use it in concrete products such as concrete vibrated products and centrifugal molded products, secondary tunnel linings, bridge piers, beams, box culverts, and concrete pavements of civil engineering structures.

[0084] The hydraulic composition of the present invention can be cured by air curing at room temperature (e.g., 10-35°C). The hydraulic composition of the present invention can be obtained in which the strength of the cured body is improved 5-20 hours after the preparation of the hydraulic composition, without curing under heating at 40°C or higher, i.e., without so-called heat curing.

[0085] <Method for producing a hydraulic composition> The present invention provides a method for producing a hydraulic composition by mixing calcium carbonate obtained by the production method of the present invention, hydraulic powder, and water. The method for producing the hydraulic composition of the present invention may further involve mixing in a cement admixture. The method for producing the hydraulic composition of the present invention may further involve mixing in aggregate. The method for producing the hydraulic composition of the present invention can appropriately apply the matters described in the method for producing calcium carbonate and the hydraulic composition of the present invention. For example, specific examples and preferred embodiments of each component are the same as those described in the method for producing calcium carbonate and the hydraulic composition of the present invention. Furthermore, the content and mass ratio of each component in the hydraulic composition of the present invention can be applied to the method for producing the hydraulic composition of the present invention by replacing the content of each component with the mixing amount.

[0086] From the viewpoint of rapid strengthening of the hydraulic composition, the method for producing the hydraulic composition of the present invention preferably involves mixing the calcium carbonate obtained in advance by the production method of the present invention in an aqueous dispersion in water. To disperse the calcium carbonate obtained by the production method of the present invention in water, it is preferable to use some or all of the cement admixture to be mixed with the hydraulic composition. That is, from the viewpoint of rapid strengthening of the hydraulic composition, the method for producing the hydraulic composition of the present invention preferably involves mixing the calcium carbonate obtained in advance by the production method of the present invention, some or all of the cement admixture, and some or all of the water, and then mixing them in an aqueous dispersion in which the calcium carbonate is dispersed.

[0087] <Method for producing cured hydraulic composition> The present invention provides a method for producing a hardened hydraulic composition, which involves mixing calcium carbonate, hydraulic powder, aggregate, and water obtained by the manufacturing method of the present invention to prepare a hydraulic composition, and then filling the hydraulic composition into a mold and allowing it to harden. In the method for producing a hardened hydraulic composition of the present invention, the preparation of the hydraulic composition is the same as in the method for producing a hydraulic composition of the present invention, and the methods described in the method for producing a hydraulic composition of the present invention can be applied as appropriate. The present invention provides a method for producing a hardened hydraulic composition, which involves using the prepared hydraulic composition as is, filling a mold with it, and allowing it to harden to obtain a hardened hydraulic composition. For example, a hardened body with high hardness can be obtained quickly by filling the mold with the hydraulic composition and then leaving it to stand. Furthermore, a hardened hydraulic composition with high hardness can be obtained even more quickly by performing heat curing or sealing curing after filling the mold with the hydraulic composition. [Examples]

[0088] [Example 1] A slurry was prepared by mixing 400 g of deionized water and 5 g of calcium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) in a glass reaction vessel (four-necked flask) equipped with a stirrer. Under constant conditions of a water temperature of 15°C, carbon dioxide (100 vol%) was blown into the prepared slurry at a flow rate of 0.4 L / min until the pH reached 7. A portion of the slurry was sampled, filtered by suction using a Buchner funnel, and then nitrogen-blown dried. The resulting powder was measured by XRD, and as a result, 6.8 g of calcite containing calcite with a crystallite size of 25 nm on the (10⁴) plane was obtained as component (b). Next, 5 g of calcium hydroxide as component (c), 42 g of potassium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as component (d), 116 g of calcium sulfate dihydrate (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as component (a), and 382 g of deionized water were mixed in the above four-necked flask to prepare a calcium sulfate aqueous dispersion (Step 1). The pH of the prepared calcium sulfate aqueous dispersion was 13. Under constant conditions of a water temperature of 15°C, carbon dioxide was blown in at a flow rate of 0.4 L / min (0.44 L / min per 100 g of component (a) on an anhydrous basis). When the pH reached 9.7, it rose to 13, and the calcium sulfate aqueous dispersion thickened. The thickened calcium sulfate aqueous dispersion was sampled, and its viscosity was measured. The maximum viscosity of the calcium sulfate aqueous dispersion was 260 mPa·sec. Furthermore, carbon dioxide was continuously blown in until the pH reached 9 (Step 2-1). Under constant conditions of a water temperature of 15°C, 50g of 25% aqueous ammonia (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) was added dropwise over 30 minutes. After the dropwise addition was completed, carbon dioxide was continuously blown in at a flow rate of 0.4 L / min (0.44 L / min per 100g of component (a) on an anhydrous basis) for 30 minutes starting when the pH reached 7.5. After that, the carbon dioxide was stopped to obtain an aqueous calcium carbonate dispersion (Step 2-2). Throughout Steps 1, 2-1, and 2-2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed in the aqueous calcium sulfate dispersion to the amount of ammonia was 50 / 50.Furthermore, across steps 1, 2-1, and 2-2, the molar ratio (component (a) / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia was 31 / 69. The obtained calcium carbonate aqueous dispersion was filtered by suction using a Buchner funnel, and then suction filtration was performed while adding a large amount of deionized water to the Buchner funnel to obtain a calcium carbonate cake. The obtained calcium carbonate cake was nitrogen-blown dry, crushed in a mortar, and the BET specific surface area was measured, resulting in a specific surface area of ​​62 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, revealing that it was 97.8 mass% calcite and 2.2 mass% vaterite. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 20 nm.

[0089] [Example 2] A slurry was prepared by mixing 400 g of deionized water and 5 g of calcium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) in a glass reaction vessel (four-necked flask) equipped with a stirrer. Under constant conditions of a water temperature of 15°C, carbon dioxide (100 vol%) was blown into the prepared slurry at a flow rate of 0.4 L / min until the pH reached 7. A portion of the slurry was sampled, filtered by suction using a Buchner funnel, and then nitrogen-blown dried. The resulting powder was measured by XRD, and as a result, 6.8 g of calcite containing calcite with a crystallite size of 25 nm on the (10⁴) plane was obtained as component (b). Next, 5 g of calcium hydroxide as component (c), 42 g of potassium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as component (d), 116 g of calcium sulfate dihydrate powder (a by-product of naphthalene sulfonic acid formalin condensate production) which was washed with running water and dried in a 60°C constant temperature bath as component (for example, Example 2 of Japanese Patent Application No. 62-13804, naphthalene sulfonic acid formalin condensate content: 0% by mass) as component (a), and 307 g of deionized water were mixed in the above four-necked flask to prepare an aqueous calcium sulfate dispersion (Step 1). The pH of the prepared aqueous calcium sulfate dispersion was 13. Under constant conditions of a water temperature of 15°C, carbon dioxide was continuously blown in at a flow rate of 0.4 L / min (0.34 L / min per 100 g of component (a) on an anhydrous basis). When the pH reached 9 (Step 2-1), 125 g of 10% aqueous ammonia (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) was added dropwise over 30 minutes under constant conditions of a water temperature of 15°C. After the dropwise addition was completed, carbon dioxide was continuously blown in at a flow rate of 0.4 L / min (0.34 L / min per 100 g of component (a) on an anhydrous basis) for 30 minutes from the point when the pH reached 7.5, and then the carbon dioxide was stopped to obtain an aqueous calcium carbonate dispersion (Step 2-2). Throughout Steps 1, 2-1, and 2-2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed with the aqueous calcium sulfate dispersion to the amount of ammonia was 50 / 50. Furthermore, across steps 1, 2-1, and 2-2, the molar ratio (component (a) / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia was 31 / 69. The obtained calcium carbonate aqueous dispersion was filtered by suction using a Buchner funnel, and then a large amount of deionized water was added to the Buchner funnel while suction filtration was performed to obtain a calcium carbonate cake. The obtained calcium carbonate cake was nitrogen-blown dry, crushed in a mortar, and the BET specific surface area was measured, resulting in a specific surface area of ​​62 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, revealing that it consisted of 93.6 mass% calcite, 4.5 mass% vaterite, 1.0 mass% calcium sulfate dihydrate, and 0.9 mass% singenite. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of calcite was found to be 20 nm.

[0090] [Example 3] (a) Except for using 116 g of waste gypsum board powder (calcium sulfate dihydrate content: 89% by weight) as a by-product gypsum, the procedure was the same as in Example 1 to obtain a calcium carbonate aqueous dispersion. The calcium carbonate aqueous dispersion obtained in the same manner as in Example 1 was subjected to suction filtration, washed with water, and nitrogen blow-dried, and the BET specific surface area was measured, resulting in a specific surface area of ​​43 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, and it was determined to be 100% calcite by mass. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 30 nm.

[0091] [Example 4] A slurry was prepared by mixing 400 g of deionized water and 5 g of calcium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) in a glass reaction vessel (four-necked flask) equipped with a stirrer. Under constant conditions of a water temperature of 15°C, carbon dioxide (100 vol%) was blown into the prepared slurry at a flow rate of 0.4 L / min until the pH reached 7. A portion of the slurry was sampled, filtered by suction using a Buchner funnel, and then nitrogen-blown dried. The resulting powder was measured by XRD, and as a result, 6.8 g of calcite containing calcite with a crystallite size of 25 nm on the (10⁴) plane was obtained as component (b). Next, 5 g of calcium hydroxide as component (c), 88 g of 48% potassium hydroxide aqueous solution (prepared by dissolving reagent grade potassium hydroxide in deionized water) as component (d), 116 g of calcium sulfate dihydrate powder (containing 4% by mass of naphthalene sulfonic acid formalin condensate) which was a by-product of the production of naphthalene sulfonic acid formalin condensate and dried at room temperature without washing as component (a), and 299 g of deionized water were mixed in the above four-necked flask to prepare a calcium sulfate aqueous dispersion (Step 1). The pH of the prepared calcium sulfate aqueous dispersion was 13. Under constant conditions of a water temperature of 15°C, carbon dioxide was continuously blown in at a flow rate of 0.4 L / min (0.36 L / min per 100 g of component (a) on an anhydrous basis), and when the pH reached 9 (Step 2-1), 87 g of 48% potassium hydroxide aqueous solution was added dropwise over 30 minutes under constant conditions of a water temperature of 15°C. After the dropwise addition was complete, carbon dioxide was continuously blown in at a flow rate of 0.4 L / min (0.36 L / min per 100 g of component (a) on an anhydrous basis) for 30 minutes starting when the pH reached 7.5, and then the carbon dioxide was stopped to obtain an aqueous calcium carbonate dispersion (Step 2-2). Throughout Steps 1, 2-1, and 2-2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed with the aqueous calcium sulfate dispersion to the amount of ammonia mixed was 100 / 0. Also, throughout Steps 1, 2-1, and 2-2, the molar ratio ((a) component / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed with the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia mixed was 31 / 69. The aqueous calcium carbonate dispersion obtained in the same manner as in Example 1 was washed with water while suction filtration, then nitrogen-blown dried, and the BET specific surface area was measured. The specific surface area was found to be 81 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, revealing that it was 92.2 mass% calcite and 7.8 mass% vaterite. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 16 nm.

[0092] [Example 5] A calcium sulfate aqueous dispersion was prepared by mixing 786 g of deionized water, 6.8 g of calcium carbonate (calcite 97.8% by mass) obtained in Example 1 as component (b), 5 g of calcium hydroxide as component (c), 84 g of potassium hydroxide (reagent grade) as component (d), and 120 g of calcium sulfate dihydrate powder (naphthalene sulfonic acid formalin condensate content: 4% by mass), which was dried at room temperature without washing as a by-product during the production of naphthalene sulfonic acid formalin condensate, as component (a) (Step 1). Under constant conditions of a water temperature of 15°C, carbon dioxide was continuously injected at a flow rate of 0.4 L / min (0.36 L / min per 100 g of component (a) on an anhydrous basis). From the point when the pH reached 7.5, carbon dioxide was continuously injected at a flow rate of 0.4 L / min (0.36 L / min per 100 g of component (a) on an anhydrous basis) for 30 minutes, after which the carbon dioxide injection was stopped to obtain an aqueous calcium carbonate dispersion (Step 2). Throughout Steps 1 and 2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed with the aqueous calcium sulfate dispersion to the amount of ammonia mixed was 100 / 0. Also, throughout Steps 1 and 2, the molar ratio ((a) component / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed with the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia mixed was 31 / 69. The aqueous calcium carbonate dispersion obtained in the same manner as in Example 1 was washed with water while suction filtration, then nitrogen-blown dried, and the BET specific surface area was measured. The result was a specific surface area of ​​30 m². 2The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, and it was determined to be 100% calcite by mass. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 28 nm.

[0093] [Example 6] In a glass reaction vessel (four-necked flask) equipped with a stirrer, 400 g of tap water, 23 g of calcium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as a calcium salt, 0.5 g of magnesium hydroxide (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as an alkaline earth metal hydroxide, and 1 g of zinc sulfate heptahydrate (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as component (f) were mixed to prepare an aqueous dispersion of calcium salt (preliminary step 1-1). Under constant conditions of a water temperature of 14°C, carbon dioxide (100 vol%) was blown into the prepared aqueous dispersion of calcium salt at a flow rate of 1.0 L / min (4.26 L / min per 100 g of alkali metal hydroxide and alkaline earth metal hydroxide) until the pH reached 7 (preliminary step 1-2). During the process, the thickened aqueous dispersion was sampled and its viscosity was measured, and the maximum viscosity of the aqueous dispersion was 230 mPa·sec. After reaching pH 7, a portion of the aqueous dispersion was sampled, filtered by suction using a Buchner funnel, washed with ethanol, filtered again by suction, and then nitrogen-blown dried. XRD analysis of the obtained powder revealed that component (b) was calcite with a crystallite size of 17 nm. The BET specific surface area of ​​the obtained powder was measured to be 10⁸ m². 2The result was / g. Next, 350g of tap water, 81g of powder (containing naphthalene sulfonic acid formalin condensate: 4% by mass) of calcium sulfate dihydrate, a by-product of the production of naphthalene sulfonic acid formalin condensate, dried at room temperature without washing as component (a), and 0.03g of defoaming agent No. 21 (manufactured by Kao Corporation) were mixed into the above four-necked flask to prepare an aqueous dispersion of calcium sulfate. 170g of 10% aqueous ammonia solution (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) as component (d) was added dropwise to the aqueous dispersion of calcium sulfate over 30 minutes (Step 1), while carbon dioxide was blown in at a flow rate of 0.4 L / min (0.57 L / min per 100g of component (b) on an anhydrous basis). After the dropwise addition was completed, carbon dioxide was continued to be blown in at a flow rate of 0.4 L / min for 10 minutes from the point when the pH reached 7.5, and then the carbon dioxide was stopped to obtain an aqueous dispersion of calcium carbonate (Step 2). Throughout steps 1 and 2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed in the calcium sulfate aqueous dispersion to the amount of ammonia mixed was 0 / 100. Also, throughout steps 1 and 2, the molar ratio ((a) component / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the calcium sulfate aqueous dispersion to the total amount of alkali metal hydroxide and ammonia mixed was 49 / 51. The obtained calcium carbonate aqueous dispersion was filtered by suction using a Buchner funnel, then nitrogen-blown dry, and the BET specific surface area was measured. The specific surface area was found to be 65 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, and it was determined to be 100% calcite by mass. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 19 nm.

[0094] [Example 7] In a glass reaction vessel (four-necked flask) equipped with a stirrer, 750 g of tap water, 23 g of calcium hydroxide as the calcium salt, and 81 g of unwashed calcium sulfate dihydrate powder (containing naphthalene sulfonic acid formalin condensate: 4% by weight), which was a by-product of the production of naphthalene sulfonic acid formalin condensate, were mixed to prepare an aqueous dispersion of calcium salt (preliminary step 1-1). The prepared aqueous dispersion was then subjected to carbon dioxide (100 vol%) at a flow rate of 1.0 L / min (4.26 L / min per 100 g of alkali metal hydroxide and alkaline earth metal hydroxide) until the pH reached 7 under conditions of a water temperature of 14°C (preliminary step 1-2). The liquid temperature when the pH reached 7 was 17°C. During the process, a sample of the thickened aqueous dispersion was taken and its viscosity was measured. The maximum viscosity of the aqueous dispersion was found to be 150 mPa·sec. After reaching pH 7, a portion of the aqueous dispersion was sampled, filtered by suction using a Buchner funnel, washed with ethanol, filtered again by suction, and then nitrogen-blown dried. The resulting powder was measured by XRD, and component (b), calcite with a crystallite size of 19 nm, was confirmed. Next, the aqueous dispersion in the four-necked flask was a calcium sulfate aqueous dispersion containing the generated (b) component calcite, unreacted calcium sulfate dihydrate ((a) component), and calcium hydroxide (referred to as (c) component). To the aqueous dispersion, 170 g of 10% aqueous ammonia solution was added dropwise as (d) component over 30 minutes (Step 1), while carbon dioxide was blown into the aqueous dispersion at a flow rate of 0.4 L / min (0.57 L / min per 100 g of (b) component on an anhydrous basis). The liquid temperature at the start of the dropwise addition was 17°C. After the dropwise addition was completed, carbon dioxide was blown in at a flow rate of 0.4 L / min for 10 minutes from the point when the pH reached 7.5, and then the carbon dioxide was stopped to obtain a calcium carbonate aqueous dispersion (Step 2). The liquid temperature when the pH reached 7.5 was 20°C. Throughout steps 1 and 2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed in the calcium sulfate aqueous dispersion to the amount of ammonia mixed was 0 / 100. Also, throughout steps 1 and 2, the molar ratio ((a) component / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the calcium sulfate aqueous dispersion to the total amount of alkali metal hydroxide and ammonia mixed was 49 / 51. The obtained calcium carbonate aqueous dispersion was filtered by suction using a Buchner funnel, then nitrogen-blown dry, and the BET specific surface area was measured. The specific surface area was found to be 55 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, and it was determined to be 100% calcite by mass. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 22 nm.

[0095] [Comparative Example 1] A calcium sulfate aqueous dispersion was prepared by mixing 684 g of deionized water, 116 g of calcium sulfate dihydrate as component (a), and 100 g of 25% aqueous ammonia as component (d) in a glass reaction vessel (four-necked flask) equipped with a stirrer. Under constant conditions of a water temperature of 15°C, carbon dioxide (100 vol%) was blown into the prepared calcium sulfate aqueous dispersion at a flow rate of 0.4 L / min until the pH reached 7.5. Carbon dioxide was continued to be blown in at a flow rate of 0.4 L / min for 30 minutes after the pH reached 7.5, and then the carbon dioxide was stopped to obtain a calcium carbonate slurry. The aqueous calcium carbonate dispersion obtained in the same manner as in Example 1 was washed with water while suction filtration, then nitrogen-blown dried, and the BET specific surface area was measured. The specific surface area was 7 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, and it was determined to be 100% by mass of vaterite.

[0096] [Comparative Example 2] A calcium sulfate aqueous dispersion was prepared by mixing 792 g of deionized water, 42 g of potassium hydroxide as component (d), and 116 g of calcium sulfate dihydrate as component (a) in a glass reaction vessel (four-necked flask) equipped with a stirrer. Under constant conditions of a water temperature of 15°C, carbon dioxide was blown into the prepared calcium sulfate aqueous dispersion at a flow rate of 0.4 L / min. When the pH reached 9, 50 g of 25% aqueous ammonia (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries) was added dropwise over 30 minutes. After the dropwise addition was complete, carbon dioxide was continued to be blown in at a flow rate of 0.4 L / min for 30 minutes from the point when the pH reached 7.5, and then the carbon dioxide was stopped to obtain a calcium carbonate slurry. The aqueous calcium carbonate dispersion obtained in the same manner as in Example 1 was washed with water while suction filtration, then nitrogen-blown dry, and the BET specific surface area was measured. The result showed a specific surface area of ​​10 m². 2 The result was / g. Subsequently, the mineral composition was identified by the XRD / Rietveld method, revealing that it was 44 mass% calcite and 56 mass% vaterite. Furthermore, the crystallite size of the (10⁴) plane, calculated using Scherrer's formula, was measured using the method described below, and the crystallite size of the calcite was found to be 19 nm.

[0097] [Measurement of BET specific surface area] The BET specific surface area of ​​each calcium carbonate obtained in the examples and comparative examples was measured by the BET method using a fully automatic specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.) with nitrogen gas as the adsorption gas.

[0098] [Measurement of crystallite size] The crystallite size of the (10⁴) plane of each calcium carbonate obtained in the examples and comparative examples was measured using an X-ray structure diffractometer (benchtop X-ray diffractometer MiniFlex600, manufactured by Rigaku Corporation) and calculated using the following Scherrer formula. D = Kλ / (βcosθ) D: Crystallite size (nm) K: Scherrer constant λ: Wavelength of the X-ray being measured β: Full width at half maximum of the X-ray peak being measured θ: Bragg angle of the X-ray peak of the target X-ray. Measurements were performed using CuKα X-rays, with a CuKα wavelength of λ = 1.5406 Å. The Scherrer constant was set to 0.9, and the Bragg angle of the (10⁴) plane of calcite was calculated to be 14.657 degrees. The X-ray structural diffraction apparatus was used with a high-speed one-dimensional detector, tube voltage of 40 kV, tube current of 15 mV, step width of 0.02 degrees, and step speed of 10 min / deg.

[0099] [Analysis using XRD / Rietveld method] Each calcium carbonate obtained in the examples and comparative examples was measured using an X-ray structural diffractometer (MiniFlex600 desktop X-ray diffractometer, manufactured by Rigaku Corporation), and Rietveld analysis was performed using the integrated powder X-ray analysis software PDXL (manufactured by Rigaku Corporation). The X-ray structural diffraction (X-ray diffractometer) was used under the following measurement conditions: a high-speed one-dimensional detector, tube voltage of 40kV, tube current of 15mV, step width of 0.02deg, and step speed of 10min / deg. The measurement target was 2θ = 5 to 70°. The minerals targeted for quantification in the Rietveld analysis were calcium sulfate dihydrate (Gypsum), calcite, vaterite, and syngenite (K2Ca(SO4)2·H2O). For each mineral, the scale factor (s: parameter related to peak height), lattice constant (a, b, c, α, β, γ: parameters related to peak location), profile function (U, V, W, a0, a1, η0L,H, η1L,H: parameters related to peak shape), orientation function (h, k, l, rn: parameters related to peak orientation), peak shift function (t0, t1, t2: parameters related to peak shift), and background function (B0, B1…Bn: parameters related to background shape) were optimized.

[0100] [Viscosity measurement] For the viscosity measurements of the examples and comparative examples, approximately 200 ml of each aqueous dispersion was placed in a 300 ml glass beaker, and the mixture was left to stand in an immersion-type constant-temperature water bath until the liquid temperature reached 15°C. An M2 rotor was then attached to a Type B viscometer (TVB10 viscometer manufactured by Toki Sangyo Co., Ltd.), and the viscosity was measured after rotating at a rotation speed of 60 rpm for 180 seconds.

[0101] [Evaluation as a quick-strengthening agent for hydraulic compositions] The strength of the hardened hydraulic compositions was evaluated when each of the calcium carbonates obtained in Examples 1-7 and Comparative Examples 1 and 2 was used as a rapid strengthening agent for hydraulic compositions. The materials used are listed below. • Cement: Ordinary Portland cement (a mixture of Pacific Cement Corporation and Sumitomo Osaka Cement Corporation in a 50 / 50 mass ratio, specific gravity 3.16) • Water: Tap water (Wakayama City tap water, specific gravity 1.00) • Fine aggregate: Mountain sand (from Joyo, Kyoto City, surface-dry specific gravity 2.50) • Admixture 1: Mighty 21HP (manufactured by Kao Corporation)

[0102] (1) Preparation of mortar In a test chamber adjusted to 20℃±2℃, 400g of cement (C) and 700g of fine aggregate (S) were added to a mortar mixer (Dalton Co., Ltd., universal mixing and stirring machine, model: 5DM-03-γ) and dry-mixed for 10 seconds at low speed (63rpm) of the mortar mixer. Admixture 1 was added as a cement admixture, and the calcium carbonate synthesized in Examples 1-7 and Comparative Examples 1 and 2 were added to the mixing water (W) to obtain 160g of mixing water, so that the contents were as shown in Table 1. This mixing water was then added to the mortar mixer and mixed for 120 seconds at low speed (63rpm) to prepare the mortars listed in Table 1. For Comparative Examples 1-3, mortars were prepared without the addition of calcium carbonate. In Table 1, the content of cement admixtures and calcium carbonate is expressed per 100 parts by mass of cement, with admixtures being in their natural state and calcium carbonate being the effective content.

[0103] (2) Formwork filling and curing Based on JIS A1132, each mortar, immediately after preparation, was filled into a cylindrical plastic mold (base diameter: 5 cm, height: 10 cm) using a two-layer filling method. The mold was then sealed and cured in a constant temperature bath (ESPEC Corporation PR-3J) adjusted to 20°C to allow it to harden. Starting from the point when the mixing water first came into contact with the cement, specimens were demolded after reaching the predetermined ages listed in Table 1 to obtain specimens for strength testing. Three specimens were prepared for each type of mortar.

[0104] (3) Evaluation of curing strength The compressive strength of each prepared specimen was measured according to JIS A1108, and the average value of three specimens was calculated. The results are shown in Table 1. In Table 1, for the compressive strengths of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-2, the relative hardening strength is also shown, with Comparative Example 1-3 set to 100.

[0105] [Table 1]

Claims

1. A method for producing calcium carbonate, comprising the following steps 1 and 2. Step 1: A step to prepare an aqueous calcium sulfate dispersion by mixing (a) calcium sulfate (hereinafter referred to as component (a)), (b) calcite (hereinafter referred to as component (b)), (d) one or more selected from alkali metal hydroxides and ammonia (hereinafter referred to as component (d)), and water. Step 2: A step of blowing carbon dioxide gas into the aqueous calcium sulfate dispersion prepared in Step 1 to produce an aqueous calcium carbonate dispersion.

2. The method for producing calcium carbonate according to claim 1, wherein step 1 is a step of mixing component (a), component (b), (c) calcium hydroxide (hereinafter referred to as component (c)), component (d), and water to prepare an aqueous dispersion of calcium sulfate.

3. A method for producing calcium carbonate according to claim 1 or 2, wherein component (b) in step 1 is obtained by the following preliminary steps 1 and 2. Preliminary step 1: A step of preparing an aqueous dispersion of calcium salt by mixing calcium salt with one or more selected from alkali metal hydroxides and alkaline earth metal hydroxides (except calcium salt) and water. Preliminary step 2: A step of blowing carbon dioxide gas into the aqueous dispersion prepared in preliminary step 1 to produce an aqueous dispersion of component (b).

4. (b) A method for producing calcium carbonate according to claim 1 or 2, wherein the component comprises calcite having a crystallite size of 30 nm or less for the (10⁴) plane calculated by Scherrer's formula.

5. (d) The method for producing calcium carbonate according to claim 1 or 2, wherein the component is an alkali metal hydroxide.

6. A method for producing calcium carbonate according to claim 1 or 2, further comprising the following step 3. Step 3: A step of aging, storing, or drying the calcite aqueous dispersion obtained in Step 2 at a temperature of 40°C or lower.

7. A method for producing calcium carbonate according to claim 1 or 2, wherein step 2 comprises the following steps 2-1 and 2-2. Step 2-1: A step of blowing carbon dioxide into the aqueous calcium sulfate dispersion prepared in Step 1 until the pH of the aqueous calcium sulfate dispersion reaches 9 or less. Step 2-2: After the pH of the calcium sulfate aqueous dispersion in Step 2-1 reaches 9 or less, one or more selected from alkali metal hydroxides and ammonia are mixed into the calcium sulfate aqueous dispersion until the pH of the calcium sulfate aqueous dispersion reaches 7.5 or less, and carbon dioxide is blown in to produce a calcium carbonate aqueous dispersion.

8. A method for producing calcium carbonate according to claim 7, wherein in step 2-1, carbon dioxide gas is blown into the aqueous calcium sulfate dispersion at a flow rate of 0.05 L / min or more and 5.0 L / min or less per 100 g of component (a).

9. The method for producing calcium carbonate according to claim 7, wherein in step 2-2, carbon dioxide gas is blown into the aqueous calcium sulfate dispersion at a flow rate of 0.05 L / min or more and 5.0 L / min or less per 100 g of component (a) for 5 minutes or more and 300 minutes or less.

10. A method for producing calcium carbonate according to claim 7, wherein, across steps 1, 2-1, and 2-2, the molar ratio (alkali metal hydroxide / ammonia) of the amount of alkali metal hydroxide mixed in the aqueous calcium sulfate dispersion to the amount of ammonia mixed is 20 / 80 or more and 100 / 0 or less.

11. A method for producing calcium carbonate according to claim 7, wherein, across steps 1, 2-1, and 2-2, the molar ratio (component (a) / (alkali metal hydroxide + ammonia)) of the amount of component (a) mixed in the aqueous calcium sulfate dispersion to the total amount of alkali metal hydroxide and ammonia mixed is 60 / 40 or more and 10 / 90 or less.

12. The BET specific surface area of ​​the resulting calcium carbonate is 30 m². ２ A method for producing calcium carbonate according to claim 1 or 2, wherein the amount is 1 / g or more.

13. A quick-setting agent for a hydraulic composition comprising calcium carbonate obtained by the method for producing calcium carbonate according to claim 1 or 2.

14. A hydraulic composition containing calcium carbonate obtained by the method for producing calcium carbonate according to claim 1 or 2, hydraulic powder, and water.

15. The hydraulic composition according to claim 14, further containing a cement admixture.

16. A method for producing a hydraulic composition, comprising mixing calcium carbonate obtained by the method for producing calcium carbonate according to claim 1 or 2, hydraulic powder, and water.

17. A method for producing a hardened hydraulic composition, comprising: mixing calcium carbonate obtained by the method for producing calcium carbonate according to claim 1 or 2, hydraulic powder, aggregate, and water to prepare a hydraulic composition; and filling the hydraulic composition into a mold and hardening it.

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