Calcium carbonate

Abstract

Provided is calcium carbonate capable of achieving a reduction in the particle size of calcium carbonate obtained by carbon dioxide fixation, homogenization of the primary particle size, and high dispersibility. 【Solution means】 Calcium carbonate having a coefficient of variation of the primary particle size represented by the following formula of 5% or more and 30% or less, an average particle size by the laser diffraction method of 5 μm or less, and the shape of the primary particles having a spherical polyhedron. Coefficient of variation = (σ pri / d pri ) × 100 (In the formula, σ pri is the standard deviation (μm) of the primary particle size by an electron microscope image, and d pri is the average value (μm) of the primary particle size by an electron microscope image.)

Description

Technical Field

[0001] The present invention relates to a method for producing calcium carbonate and calcium carbonate.

Background Art

[0002] Seawater contains abundant mineral components. For example, magnesium is contained at about 1300 ppm and calcium is contained at about 400 ppm. In order to effectively utilize these, a method is known in which dolomite or the like is reacted with seawater to produce magnesium hydroxide and magnesium is separated and recovered.

[0003] After separating magnesium by the method as described above, the seawater (hereinafter also referred to as "utilized water") contains a rich calcium component. Therefore, the development of a technology for effectively utilizing this remaining calcium component has been promoted. Specifically, by taking in carbon dioxide using the calcium component contained in the utilized water, an industrial application of the calcium component is attempted, and a technology that contributes to reducing the emission amount of carbon dioxide, which is considered an effective measure against problems such as recent global warming, has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to develop the uses and enhance the functionality of calcium carbonate obtained by incorporating (immobilizing) carbon dioxide into the calcium component, calcium carbonate with a small particle size, little variation in primary particle size, and good dispersibility is required.

[0006] An object of the present invention is to provide a method for producing calcium carbonate and calcium carbonate that can achieve a reduction in the particle size of calcium carbonate obtained by carbon dioxide fixation, homogenization of the primary particle size, and high dispersibility.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventor has found that the above problems can be solved by the following configuration, and has completed the present invention.

[0008] In one embodiment, the present invention relates to a method for producing calcium carbonate, which includes a step of bringing seawater, service water containing calcium after producing magnesium hydroxide from seawater, or a mixture thereof (hereinafter, seawater, service water, and a mixture thereof are also collectively referred to as "seawater etc."), an alkaline agent, and a gas containing carbon dioxide into contact at a pH of 9 or more and less than 11.

[0009] According to the method for producing calcium carbonate, calcium carbonate having a small particle size, no variation in the primary particle size, and good dispersibility can be produced while fixing carbon dioxide. Although the reason for this is not clear, it is presumed as follows. In the contact step, carbonate ions are generated by the contact between the alkaline agent and carbon dioxide, and calcium carbonate particles are generated by the contact between these and calcium (calcium ions) in seawater etc. At that time, by contacting under relatively mild alkaline conditions of pH 9 or more and less than 11, the growth rate of the particles also becomes slow, and as a result, it is presumed that calcium carbonate having a small particle size and a regular particle shape can be obtained.

[0010] In one embodiment, it is preferable to bring the seawater, service water, or a mixture thereof, the alkaline agent, and the gas into contact in any one of the following orders 1) or 2). 1) After bringing the seawater, service water, or a mixture thereof into contact with the alkaline agent, further bring the gas into contact. 2) After bringing the alkaline agent into contact with the gas, further bring the seawater, service water, or a mixture thereof into contact.

[0011] By bringing the three components of seawater or the like, an alkaline agent, and a gas containing carbon dioxide into contact with each other in either the specific order 1) or 2), the generation of carbonate ions and the growth of calcium carbonate particles can be promoted.

[0012] In one embodiment, the alkaline agent is preferably magnesium hydroxide or magnesium oxide. Thereby, the reduction of the particle size of calcium carbonate can be achieved more efficiently.

[0013] In one embodiment, the temperature of the contacting step is preferably 50°C or lower. Thereby, calcium carbonate can be produced as calcite, and a utilization mode corresponding to the use and function of calcium carbonate can be provided.

[0014] In one embodiment, the concentration of calcium in the seawater, service water, or a mixture thereof is preferably 300 ppm or more and 3000 ppm or less from the viewpoint of the production efficiency of calcium carbonate.

[0015] In one embodiment, the gas may be exhaust gas from a combustion engine.

[0016] In one embodiment, the concentration of carbon dioxide in the gas is preferably 1% by volume or more and 20% by volume or less from the viewpoint of the production efficiency of calcium carbonate.

[0017] In one embodiment, the calcium carbonate may be calcite.

[0018] In one embodiment, the average particle size of the calcium carbonate by the laser diffraction method is preferably 5 μm or less. Thereby, the physical properties of products containing calcium carbonate can be improved, and the application development and high functionality can be achieved.

[0019] In one embodiment, the present invention It relates to calcium carbonate having a coefficient of variation of the primary particle diameter represented by the following formula of 5% or more and 30% or less, an average particle diameter of 5 μm or less by the laser diffraction method, and the shape of the primary particles being spherical polyhedra or plate-like. Coefficient of variation = (σ pri / d pri ) × 100 (In the formula, σ pri is the standard deviation (μm) of the primary particle diameter from an electron microscope image, and d pri is the average value (μm) of the primary particle diameter from an electron microscope image.)

[0020] In one embodiment, the present invention relates to calcium carbonate having a monodispersity represented by the following formula of 50% or more and 100% or less, an average particle diameter of 5 μm or less by the laser diffraction method, and the shape of the primary particles being spherical polyhedra or plate-like. Monodispersity = (d pri / d ave ) × 100 (In the formula, d pri is the average value (μm) of the primary particle diameter from an electron microscope image, and d ave is the average particle diameter (μm) by the laser diffraction method.)

[0021] Due to having the above characteristics, the calcium carbonate can achieve its own stabilization, activation, and high functionality, and can expand the application development of products using the calcium carbonate. The calcium carbonate is suitable for use in inorganic molded bodies.

Advantages of the Invention

[0022] According to the present invention, it is possible to efficiently immobilize carbon dioxide, and to provide a method for producing calcium carbonate and calcium carbonate having a small particle size, little variation in primary particle diameter, and good dispersibility.

Brief Description of the Drawings

[0023]

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Mode for Carrying Out the Invention

[0024] A method for producing calcium carbonate and calcium carbonate according to an embodiment of the present invention will be described below. The present invention is not limited to these embodiments.

[0025] 《Method for Producing Calcium Carbonate》 The method for producing calcium carbonate according to this embodiment includes a step of bringing seawater, service water containing calcium after producing magnesium hydroxide from seawater, or a mixture thereof, an alkaline agent, and a gas containing carbon dioxide into contact at a pH of 9 or more and less than 11. The production method may include other steps.

[0026] <Contact Step> Although the contact order of the three components in the contact step is not particularly limited as long as calcium carbonate can be obtained, it is preferable to bring the seawater, service water or a mixture thereof, the alkaline agent, and the gas into contact in any one of the following orders 1) or 2). 1) After bringing the seawater, service water or a mixture thereof into contact with the alkaline agent, the gas is further brought into contact. 2) After bringing the alkaline agent into contact with the gas, the seawater, service water or a mixture thereof is further brought into contact.

[0027] Hereinafter, the mode of contacting in order 1) will be described as the direct method, and the mode of contacting in order 2) will be described as the indirect method.

[0028] (Direct method) In the direct method, after bringing seawater or the like into contact with an alkaline agent, a gas is further brought into contact therewith to directly produce calcium carbonate. The reaction formula here is as shown in the following formula (1). Ca 2+ +2OH - +CO2→CaCO3+H2O (1)

[0029] Seawater may be directly pumped and used from the sea near, for example, a magnesium hydroxide production factory, or may be used after being subjected to treatment such as filtration. The pumping is not limited to coastal waters and may be performed at any location as long as seawater can be obtained.

[0030] The utility water is a component discharged after producing magnesium hydroxide (Mg(OH)2) from seawater. The utility water is discharged from, for example, a magnesium hydroxide production factory. When producing magnesium hydroxide, a hydrate after dolomite calcination or slaked lime is reacted with seawater. The utility water after the reaction contains a rich calcium component as compared with seawater. In this regard, it is preferable to use the utility water in this production method. The produced magnesium hydroxide is used, for example, as a neutralizing agent for flue gas desulfurization or the like.

[0031] The lower limit of the calcium concentration in seawater or the like is preferably 300 ppm, more preferably 350 ppm, and even more preferably 380 ppm. The upper limit of the calcium concentration is preferably 3000 ppm, more preferably 2800 ppm, and even more preferably 2600 ppm. The lower limit of the calcium concentration is mainly derived from seawater, and the upper limit of the calcium concentration is mainly derived from the water for use. The lower limit of the calcium concentration in seawater alone is preferably 300 ppm, more preferably 350 ppm, and even more preferably 380 ppm as described above. The upper limit of the calcium concentration in seawater alone is preferably 500 ppm, more preferably 480 ppm, and even more preferably 450 ppm. The lower limit of the calcium concentration in the water for use alone is preferably 1500 ppm, more preferably 1800 ppm, and even more preferably 2000 ppm. The upper limit of the calcium concentration in the water for use alone is preferably 3000 ppm, more preferably 2800 ppm, and even more preferably 2600 ppm as described above. However, it is not limited thereto, and the calcium concentration may be adjusted by adding a calcium source (for example, calcium chloride, calcium sulfate, etc.) to seawater or the like, or by concentrating or diluting seawater or the like.

[0032] The alkali agent is not particularly limited as long as it can adjust the pH within a predetermined range in the contact step. For example, hydroxides of alkaline earth metals or alkali metals such as magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), barium hydroxide (Ba(OH)2), sodium hydroxide (NaOH), potassium hydroxide (KOH); oxides of alkaline earth metals or alkali metals such as magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), sodium oxide (Na2O), potassium oxide (K2O); carbonates such as neutral magnesium carbonate (MgCO3·3H2O), sodium carbonate (NaCO3), potassium carbonate (NaCO3); industrial waste materials such as lime residue, cement sludge water, washing wastewater from a raw cement plant, residual cement, waste cement, etc. Among them, as the types of alkali agents that are easy to adjust the pH within a predetermined range, magnesium hydroxide, magnesium oxide, and neutral magnesium carbonate are preferred, magnesium hydroxide and magnesium oxide are more preferred, and magnesium hydroxide is even more preferred.

[0033] As the alkali agent, commercially available synthetic products, commercially available natural mineral products, or industrial waste can be used. Among them, commercially available natural mineral products and industrial waste are preferred in that the carbon dioxide emissions from raw material extraction to the completion of production are extremely small. Examples of natural mineral products as the alkali agent include finely pulverized products (10 μm or less) such as brucite ore (Mg(OH)2). Industrial waste as the alkali agent is preferably waste magnesium hydroxide and waste magnesium oxide that are inevitably generated in the production process of magnesium hydroxide or magnesium oxide and the brand switching process. Waste magnesium hydroxide includes products leaking through the filter cloth in the filtration process, products leaking from the gland packing of the slurry transport pump, and products washed during brand switching. Waste magnesium oxide includes products of calcined dust (dust collection) from a rotary kiln and products washed during brand switching. These industrial waste materials, although conventionally discarded as waste, have a BET specific surface area of 10 to 200 m 2 / g, and the average particle diameter is also 10 μm or less. Since the reaction activity is relatively high, it can be effectively used as an alkali agent in the production method. From the viewpoints of reactivity and handleability, the alkali agent may be subjected to treatments such as grinding or crushing. This treatment may be either wet or dry.

[0034] In the direct method, first, seawater or the like is brought into contact with the alkali agent. The contact may be carried out by directly adding the alkali agent to seawater or the like, or the alkali agent may be previously dispersed in a solvent such as water to form a slurry and then added to seawater or the like. The addition may be carried out at once or in multiple stages. When the alkali agent is an oxide, from the viewpoint of reactivity, it is preferably dissolved or dispersed in water or the like for hydration and then added after being made into a slurry. The concentration of the alkali agent in the slurry is not particularly limited, and a range of 10 g / L or more and 500 g / L or less can be mentioned.

[0035] The input amount of the alkali agent is not particularly limited as long as the amount of hydroxide ions required for the reaction with the amount of calcium ions in seawater or the like is obtained according to the above reaction formula (1), and the pH of the contact step is within a predetermined range. For example, when the alkali agent is magnesium hydroxide (Mg(OH)2), the molar ratio (Mg / Ca 2+ in the alkali agent to Ca in seawater or the like 2+ ) is preferably 1.0 or less, more preferably 0.9 or more and 1.0 or less, and even more preferably 0.95 or more and 1.0 or less. It is particularly preferable that the molar ratio is 1.0, that is, an equimolar amount. By setting the molar ratio within the above range, the coprecipitation of Mg in the alkali agent with the reactant can be suppressed, and calcium carbonate with high purity can be produced. For 10 L of service water with a Ca 2+ concentration of 2500 ppm, the input amount of magnesium hydroxide is preferably 32.7 g or more and 36.4 g or less, and more preferably 34.5 g or more and 36.4 g or less. Also, when the alkali agent is magnesium oxide (MgO), the molar ratio (Mg / Ca 2+ in the alkali agent to Ca in seawater or the like 2+ ) can preferably adopt the same range as in the case of magnesium hydroxide. Ca 2+As the amount of magnesium oxide added to 10 L of seawater with a concentration of 400 ppm, 3.6 g or more and 4.0 g or less is preferable, and 3.8 g or more and 4.0 g or less is more preferable. Even when the alkaline agent is other than magnesium hydroxide and magnesium oxide, the amount added may be set based on the same concept.

[0036] In the said production method, when seawater or the like is brought into contact with the alkaline agent, the pH becomes 9 or more and less than 11. The lower limit of the pH is preferably 9.2, more preferably 9.4, still more preferably 9.6, and particularly preferably 9.8. The upper limit of the pH is preferably 10.9, more preferably 10.8, still more preferably 10.6, even more preferably 10.4, and particularly preferably 10.2.

[0037] The temperature when seawater or the like is brought into contact with the alkaline agent is not particularly limited, and it may be the temperature of the pumped seawater, it may be at normal temperature after standing for a while, or it may be heated. The said temperature is preferably 50°C or lower, and preferably in the range of 0°C or higher and 30°C or lower. By setting the said temperature to 50°C or lower, calcium carbonate can be produced as calcite with a small particle size and good dispersibility. From the viewpoints of reactivity and efficiency, around normal temperature is preferable, 10°C or higher and 30°C or lower is more preferable, and 15°C or higher and 28°C or lower is still more preferable.

[0038] The gas to be brought into contact by the direct method is not particularly limited as long as it contains carbon dioxide. As the gas, for example, exhaust gas from combustion engines such as boilers, thermal power plants (power plants that utilize the combustion heat of fossil fuels such as oil, coal, liquefied natural gas (LNG), or biomass), blast furnaces, exhaust gas from dryers, etc. can be preferably used. From the viewpoint of high carbon dioxide concentration and good production efficiency of calcium carbonate in the contact step, exhaust gas from combustion engines is preferred as the gas. The lower limit of the carbon dioxide concentration in the gas is preferably 1% by volume, more preferably 2% by volume, still more preferably 5% by volume, and particularly preferably 8% by volume. Although the higher the upper limit of the said concentration is, the more preferable it is, it may be 30% by volume, may be 20% by volume, may be 15% by volume, or may be 12% by volume. According to this production method, not only can the reduction of emissions by carbon dioxide fixation be achieved, but also the industrial utilization of calcium carbonate production can be promoted.

[0039] The contact of the gas in the direct method can be carried out by blowing (bubbling) it into seawater or the like that has been brought into contact with an alkaline agent. The gas flow rate and blowing time can be appropriately set in consideration of the carbon dioxide concentration, reaction efficiency, and the progress of the carbonation reaction in reaction formula (1). For example, with respect to 10 L of seawater or the like, the gas flow rate is preferably 0.5 L / min or more and 30.0 L / min or less, more preferably 2.0 L / min or more and 25.0 L / min or less, and still more preferably 3.0 L / min or more and 20.0 L / min or less. Ca 2+ It is only necessary to introduce CO2 in an amount equal to or more than the theoretical number of moles required until Ca is completely precipitated as calcium carbonate. The minimum blowing time of the gas is determined by the Ca 2+ concentration and usage amount of seawater or the like and the CO2 concentration in the exhaust gas. For example, when blowing CO2 with a concentration of 10% by volume in the exhaust gas at 5.0 L / min into 10 L of service water with a Ca 2+ concentration of 2500 ppm, a blowing time of 0.5 hours or more is required. Furthermore, 1.0 hour or more and 8.0 hours or less is more preferable, and 2.0 hours or more and 6.0 hours or less is still more preferable.

[0040] By undergoing the above contact process, calcium carbonate with a small particle size, little variation in primary particle size, and good dispersibility can be produced. Filtration, washing, drying, pulverization, classification, etc. may be performed on the obtained calcium carbonate.

[0041] (Indirect method) In the indirect method, by bringing an alkaline agent into contact with a gas, carbonate (carbonate ions) of the alkaline agent is once generated, and then by further bringing seawater or the like into contact, calcium carbonate is indirectly generated. The reaction formulas here are as shown in the following formulas (2-1) and (2-2). 2OH - +CO2→CO3 2- +H2O (2-1) Ca 2+ +CO3 2- →CaCO3(2-2)

[0042] In the indirect method, an alkaline agent is brought into contact with a gas (carbon dioxide) to generate carbonate (carbonate ions), and then salt exchange is performed by bringing it into contact with calcium (calcium ions) such as seawater to produce calcium carbonate. Hereinafter, the parts different from the direct method in the indirect method will be described.

[0043] The contact between the alkaline agent and the gas (reaction formula (2-1)) can be carried out by dissolving or dispersing the alkaline agent in a solvent such as water to form a slurry or a solution (hereinafter, collectively referred to as "slurry, etc."), and blowing the gas into this slurry, etc. (bubbling). The concentration of the alkaline agent in the slurry, etc. is not particularly limited and can be appropriately set from the range of 10 g / L or more and 100 g / L or less.

[0044] The flow rate and blowing time of the gas can be appropriately set in consideration of the concentration of carbon dioxide, reaction efficiency, and the progress of the carbonate (carbonate ion) generating reaction of reaction formula (2-1). For example, for 10 L of slurry, the flow rate of the gas is preferably 1.0 L / min to 30.0 L / min, more preferably 2.0 L / min to 25.0 L / min, and even more preferably 3.0 L / min to 20.0 L / min. The blowing time is preferably 0.5 hours to 8.0 hours, more preferably 1.0 hours to 6.0 hours, and even more preferably 2.0 hours to 4.0 hours.

[0045] For example, when the alkaline agent is magnesium hydroxide (Mg(OH)2), a slurry of neutral magnesium carbonate (MgCO3·3H2O) is obtained as a carbonate through the reaction of reaction formula (2-1). The obtained slurry of neutral magnesium carbonate may be subjected to the reaction of reaction formula (2-2) as it is, but it is preferable to subject it to the reaction of reaction formula (2-2) after carrying out a particle size reduction treatment such as wet grinding in order to improve the reaction activity. The wet grinding treatment can be carried out by a conventionally known method such as a ball mill. The particle size reduction treatment can be carried out appropriately depending on the shape and size of the carbonate obtained through reaction formula (2-1).

[0046] Next, the carbonate is brought into contact with seawater or the like (reaction formula (2-2)). The contact may be carried out by introducing a slurry of the carbonate into seawater or the like, or by introducing seawater or the like into the slurry. The amount of carbonate introduced is not particularly limited as long as it is set so that the amount of carbonate ions required for the reaction with the amount of calcium ions in the seawater or the like is obtained according to the above reaction formula (2-2) and the pH after introduction is within a predetermined range. For example, when the carbonate is neutral magnesium carbonate, the amount of Mg in the carbonate is reduced by 1 / 2 the amount of Ca in the seawater or the like. 2+ Molar ratio (Mg / Ca 2+ ) is preferably 1.0 or less, more preferably 0.9 or more and 1.0 or less, and even more preferably 0.95 or more and 1.0 or less. The molar ratio is particularly preferably 1.0, that is, equimolar amounts. By setting the molar ratio within the above range, it is possible to suppress coprecipitation of the reaction product of Mg in the carbonate, and to produce calcium carbonate with high purity. Ca 2+As the amount of magnesium carbonate added to 10 L of service water with a concentration of 2500 ppm, 77.6 g or more and 86.2 g or less is preferable, and 81.9 g or more and 86.2 g or less is more preferable.

[0047] When the carbonate comes into contact with seawater or the like, the pH immediately after contact is preferably 9 or more and less than 11. The lower limit of the pH is preferably 9.1, more preferably 9.2. The upper limit of the pH is preferably 10.0, more preferably 9.8, still more preferably 9.6, and particularly preferably 9.4.

[0048] The salt exchange reaction due to the contact between the carbonate and seawater or the like proceeds relatively rapidly. The reaction time may be set to such an extent that the salt exchange reaction proceeds sufficiently, and can be set to 0.1 hour or more, preferably 0.5 hour or more and 8.0 hours or less, and more preferably 1.0 hour or more and 6.0 hours or less.

[0049] 《Calcium Carbonate》 Hereinafter, each aspect of calcium carbonate will be described. Calcium carbonate having the following characteristics can be efficiently produced by the method for producing calcium carbonate. The standard deviation of the primary particle size by the electron microscope image, the average value of the primary particle size by the electron microscope image, the average particle size by the laser diffraction method, and the measurement or evaluation method of the shape of the primary particles shown below are based on the description of the examples.

[0050] (First Aspect) For the calcium carbonate, the coefficient of variation of the primary particle size represented by the following formula is 5% or more and 30% or less, the average particle size by the laser diffraction method is 5 μm or less, and the shape of the primary particles is a spherical polyhedron or a plate shape. Coefficient of variation = (σ pri / d pri ) × 100 (In the formula, σ pri is the standard deviation (μm) of the primary particle size by the electron microscope image, and d pri is the average value (μm) of the primary particle size by the electron microscope image.)

[0051] The lower limit of the coefficient of variation is preferably 6%, more preferably 7%, and even more preferably 8%. The upper limit of the coefficient of variation is preferably 28%, more preferably 26%, and even more preferably 25%.

[0052] The lower limit of the standard deviation of the primary particle diameter by the electron microscope image is preferably 0.10 μm, more preferably 0.12 μm, and even more preferably 0.14 μm. The upper limit of the standard deviation of the primary particle diameter is preferably 0.95 μm, more preferably 0.90 μm, and even more preferably 0.85 μm.

[0053] The lower limit of the average value of the primary particle diameter by the electron microscope image is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 0.8 μm. The upper limit of the average value of the primary particle diameter is preferably 5.0 μm, more preferably 4.5 μm, and even more preferably 4.0 μm.

[0054] The lower limit of the average particle diameter by the laser diffraction method is preferably 0.5 μm, more preferably 1.0 μm, and even more preferably 1.5 μm. The upper limit of the average particle diameter by the laser diffraction method is preferably 4.8 μm, more preferably 4.6 μm, and even more preferably 4.0 μm.

[0055] The shape of the primary particles is spherical polyhedron or plate-like. A spherical polyhedron refers to a shape that is spherical as a whole, but the surface is not a spherical surface, but is formed by a combination of polygonal planes.

[0056] (Second aspect) For the calcium carbonate, the monodispersity represented by the following formula is 50% or more and 100% or less, the average particle diameter by the laser diffraction method is 5 μm or less, and the shape of the primary particles is spherical polyhedron or plate-like. Monodispersity=(d pri / d ave )×100 (In the formula, d pri is the average value (μm) of the primary particle diameter by the electron microscope image, and d ave is the average particle diameter (μm) by the laser diffraction method.)

[0057] The lower limit of the monodispersity is preferably 55%, more preferably 60%. The upper limit of the monodispersity is preferably 100%, more preferably 98%.

[0058] Regarding the second aspect, the average value of the primary particle diameter by electron microscope image, the average particle diameter by laser diffraction method, and the shape of the primary particles can preferably adopt the values and shapes for the first aspect.

[0059] (Common matters of the first aspect and the second aspect) Examples of the crystal structure of the calcium carbonate include calcite and aragonite, but calcite is preferred.

[0060] The BET specific surface area of calcium carbonate is 2 m 2 / g or more and 20 m 2 / g or less is preferred, 3 m 2 / g or more and 18 m 2 / g or less is more preferred, 4 m 2 / g or more and 15 m 2 / g or less is even more preferred.

[0061] The P funnel flow-down time of the calcium carbonate is preferably 7 seconds or more and 10 seconds or less, more preferably 7.5 seconds or more and 9.8 seconds or less, and even more preferably 8 seconds or more and 9.5 seconds or less. Since the calcium carbonate has excellent dispersibility, it can exhibit excellent fluidity particularly in concrete applications.

[0062] The use of calcium carbonate is not particularly limited, and examples include fillers for resins, compounding agents for inorganic molded bodies (aggregates for concrete buildings (for cement), compounding agents for building materials), thickeners for sealing materials, etc. By incorporating calcium carbonate, the application development and high functionality of these products can be achieved.

[0063] Although there are no particular restrictions on the resin, it is preferable to use a thermoplastic resin. Although there are no particular restrictions on the thermoplastic resin, acrylic resins such as polymethyl methacrylate (PMMA), ethylene / (meth)acrylate copolymer, and homopolymers or copolymers of (meth)acrylic esters such as methyl acrylate·methyl methacrylate copolymer; polyethylene resins (PE) such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, EVA (ethylene vinyl acetate resin), EEA (ethylene ethyl acrylate resin), EMA (ethylene methyl acrylate copolymer resin), EAA (ethylene acrylic acid copolymer resin), and ultra-high molecular weight polyethylene; polypropylene resins (PP) such as polypropylene homopolymer and ethylene propylene copolymer; ABS resin (acrylonitrile·butadiene·styrene copolymer); polystyrene resin; polycarbonate resin; polyphenylene resin; polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyamide resins including various nylons such as nylon 6, nylon 66, nylon 610, nylon 612, nylon 11, nylon 12, and nylon 46. These resins may be used alone or in combination of two or more.

[0064] (Aggregates for concrete structures (for cement)) The concrete structure is composed of a hardened body of a hydraulic composition. The hydraulic composition is composed of a powder containing at least one of blast furnace slag, an expanding agent, slaked lime, quicklime, fly ash, and Portland cement in addition to calcium carbonate. As the calcium carbonate, the aforementioned calcium carbonate can be preferably adopted.

[0065] In addition to the above hydraulic composition, aggregates such as sand and gravel, chemicals such as chemical admixtures for concrete, and fiber materials made of metals or polymer materials may be blended to form a hydraulic composition mixture material.

[0066] The hardened body of the hydraulic composition is obtained by hardening the paste obtained by kneading water into the above hydraulic composition. Further, the hardened body of the hydraulic composition mixture material is obtained by hardening the kneaded material (corresponding to fresh mortar or fresh concrete) obtained by kneading water into the above hydraulic composition mixture material, and corresponds to mortar or concrete.

[0067] The proportion of calcium carbonate in the above powder (the proportion of calcium carbonate to cement) is in the range of 1% to 60% by mass, preferably 3% to 50% by mass, and more preferably 5% to 40% by mass.

[0068] For blast furnace slag, it is desirable to use blast furnace slag fine powder used in JIS (Japanese Industrial Standards) R5211 "Blast Furnace Cement" or blast furnace slag fine powder conforming to JIS A6206 "Blast Furnace Slag for Concrete". Further, the blast furnace slag has a specific surface area of 2000 to 10000 cm 2 / g, preferably 3500 to 7000 cm 2 / g is preferably used.

[0069] As the expansion agent, for example, an expansion agent defined in JIS A6202 "Expansion Agent for Concrete" may be used. The expansion agent is preferably added at a ratio of 2 to 9% by mass based on the entire hydraulic composition.

[0070] For slaked lime, for example, those defined in JIS R9001 "Lime for Industrial Use" may be used. Further, since quicklime becomes slaked lime when it comes into contact with water, for example, quicklime defined in JIS R9001 "Lime for Industrial Use" can be used instead of slaked lime. In this case, it is advisable to correct the amount of water required when quicklime changes to slaked lime. For fly ash, for example, those conforming to JIS A6201 "Fly Ash for Concrete" may be used.

[0071] For Portland cement, ordinary Portland cement is used. In addition to this, other types of Portland cement such as early-strength Portland cement, ultra-early-strength Portland cement, medium-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, etc., as defined in JIS R5210 "Portland Cement", and JIS R5214 "Eco-Cement" can also be used.

[0072] When Portland cement is included in the hydraulic composition, the proportion of Portland cement in the powder other than calcium carbonate is preferably 70% by mass or less, and more preferably 30% by mass or less.

[0073] When using Portland cement and blast furnace slag or fly ash, those in which the components are pre-mixed, such as JIS R5211 "Blast Furnace Cement", or, for example, JIS R5213 "Fly Ash Cement", can be used alone or in combination.

[0074] Since calcium carbonate having the above characteristics is used, the hydraulic composition and the hydraulic composition admixture exhibit good fluidity, and the concrete hardened body can exhibit excellent compressive strength.

[0075] The density of the concrete structure is preferably 0.7 g / cm 3 or more and 2.0 g / cm 3 or less, more preferably 0.8 g / cm 3 or more and 1.8 g / cm 3 or less, and even more preferably 0.9 g / cm 3 or more and 1.6 g / cm 3 or less.

[0076] (Blending agent for building materials) As the building material, a formed board for building materials is preferred. The formed board preferably contains a hydraulic material, a siliceous material, a reinforcing fiber material, and calcium carbonate.

[0077] (Hydraulic material) Examples of hydraulic materials include cementitious materials, gypsum, lime, slag, etc. Examples of cementitious materials include commonly used cements such as ordinary Portland cement, early-strength cement, medium-heat cement, fly ash cement, blast furnace slag cement, and alumina cement. Examples of gypsum include anhydrite, hemihydrate gypsum, and dihydrate gypsum. Examples of slag include blast furnace slag and converter slag. These hydraulic materials can be used alone or in combination of two or more kinds.

[0078] The content of the hydraulic material is preferably 5% by mass or more and 45% by mass or less, more preferably 8% by mass or more and 42% by mass or less, and even more preferably 10% by mass or more and 40% by mass or less based on the total amount of the materials constituting the forming plate. By setting the content of the hydraulic material within the above range, physical properties such as the bending strength and peel strength of the forming plate can be improved, and the increase in the bulk specific gravity of the forming plate can be suppressed, thereby enhancing the workability during construction.

[0079] (Siliceous material) Examples of siliceous materials include materials rich in SiO2 such as silica sand, silica powder, silica fume, fly ash, diatomaceous earth, layered silicates (e.g., mica, talc, kaolin, bentonite), perlite, wollastonite, lightweight aggregates (e.g., fly ash balloons, perlite, shirasu balloons, glass foams), etc. These siliceous materials can be used alone or in combination of two or more kinds. Talc, mica, and wollastonite can also be used as the reinforcing fiber materials described later.

[0080] The content of the siliceous material is preferably 10% by mass or more and 55% by mass or less, more preferably 12% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 45% by mass or less based on the total amount of the materials constituting the forming plate. If the content of the siliceous material is within the above range, it becomes possible to set the bending strength, bulk specific gravity, water absorption rate, dimensional stability, etc. of the forming plate within the target range. Note that as the siliceous material, the unit volume mass of perlite, fly ash balloons, shirasu balloons, etc. is 0.5 g / cm 3When blending the following lightweight aggregates, in order to prevent the bulk specific gravity from becoming too low and the strength such as flexural strength and peel strength from becoming weak, it is preferable to use other siliceous materials in combination so that the content of the lightweight aggregate is 20% by mass or less based on the total amount of the materials constituting the forming plate.

[0081] (Reinforcing fiber material) As the reinforcing fiber material, for example, pulp such as softwood pulp, hardwood pulp, fibrillated pulp of these, and pulp obtained by defibrating waste paper, organic reinforcing fiber materials such as vinylon fiber, acrylonitrile fiber, and polypropylene fiber, and inorganic reinforcing fiber materials such as rock wool and glass fiber can be used. These reinforcing fiber materials can be used alone or in combination of two or more.

[0082] In order to improve the strength and impart toughness of the forming plate, the content of the reinforcing fiber material is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 26% by mass or less, and even more preferably 4% by mass or more and 22% by mass or less based on the total amount of the materials constituting the forming plate. By setting the content of the reinforcing fiber material within the above range, it is possible to suppress the fibers from protruding from the surface of the forming plate and improve the smoothness while exhibiting a sufficient reinforcing effect. When blending an inorganic reinforcing fiber material with an average length of 1 mm to 50 mm as the reinforcing fiber material, in order to improve the smoothness of the forming plate, it is preferable to use other reinforcing fiber materials in combination so that the content thereof is 10% by mass or less based on the total amount of the materials constituting the forming plate.

[0083] (Calcium carbonate) As the calcium carbonate, the above-mentioned calcium carbonate can be preferably adopted.

[0084] The content of calcium carbonate is preferably 5% by mass or more and 60% by mass or less, more preferably 8% by mass or more and 55% by mass or less, and even more preferably 12% by mass or more and 50% by mass or less based on the total amount of the materials constituting the forming plate. By blending calcium carbonate with low thermal conductivity in the content within the above range, the strength and fire resistance of the forming plate can be improved.

[0085] (Optional component) In addition to the above materials, in order to impart various functions to the formed plate, materials such as resin hollow bodies, wood chips, wood powder, resin powder, defoaming agents, flocculants, water repellents, thickeners (such as methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, etc.), and dispersants can be variously blended according to the purpose. It is also possible to appropriately add and use recycled materials obtained by pulverizing end materials and the like generated during the processing of the formed plate.

[0086] The bulk density of the formed plate is preferably 0.7 g / cm 3 or more and 2.0 g / cm 3 or less, more preferably 0.8 g / cm 3 or more and 1.8 g / cm 3 or less, and even more preferably 0.9 g / cm 3 or more and 1.6 g / cm 3 or less.

[0087] (Manufacturing method of formed plate) The manufacturing method of the formed plate according to this embodiment is not particularly limited, and generally used papermaking methods, extrusion molding methods, flow-on molding methods, pouring molding methods, press (compression) molding, etc. can be used. The formed plate can be obtained by subjecting the green sheet formed by these methods to press dehydration or pattern processing such as embossing, and then curing at normal temperature, steam curing, autoclave curing, etc. Furthermore, drying may be performed, and shape processing or painting may be performed as necessary.

[0088] (Uses of formed plate) The uses of the formed plate are not particularly limited, and it can be suitably used as interior and exterior finishing materials such as wall materials, floor materials, roof materials, various boards, exterior decoration members, and furniture, and as performance maintenance materials such as sealing materials, heat insulation materials, sound absorption materials, and waterproof materials. The formed plate is preferably a cement-based formed plate containing a cementitious material, and more preferably a calcium silicate formed body.

Examples

[0089] Hereinafter, the present invention will be described in detail using examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The measurement and evaluation of physical properties and the like were performed as follows.

[0090] [Analysis of Seawater and Service Water] Table 1 shows the results of analyzing the respective components and pH of seawater collected in the Seto Inland Sea near Kojima Chemical Industry Co., Ltd. and service water discharged from the magnesium hydroxide manufacturing process of the same company. Here, service water refers to the remaining supernatant liquid obtained by reacting Mg 2+ contained at about 1300 ppm in seawater with an alkaline agent (such as calcium hydroxide) to precipitate and recover magnesium hydroxide "Mg(OH)2". The component analysis of seawater and service water was performed for Ca 2+ by the ICP-AES method (manufactured by Hitachi High-Technologies Corporation, inductively coupled plasma optical emission spectrometer SPECTROBLUE FMS36 type). Also, the pH of seawater and service water was measured using a pH meter (manufactured by Toa DKK Corporation, main body: multi-water quality meter MM-43X, pH electrode: GST5841C type).

[0091]

Table 1

[0092] [Evaluation of Raw Materials, Calcium Carbonate (Filler), and Resin Composition] For the calcium carbonate and the like obtained in the examples and comparative examples, the following analyses were performed. The results of each analysis are shown in Tables 2 to 3 and Figures 1 to 5.

[0093] (1) BET Specific Surface Area The sample powder pretreated at about 130°C for about 30 minutes in a nitrogen gas atmosphere using an 8-series preheating unit (manufactured by MOUNTECH) was measured for BET specific surface area (m 2 / g) by the nitrogen gas adsorption method using a Macsorb HM Model-1208 (manufactured by MOUNTECH) as a BET specific surface area measuring device.

[0094] (2) Average particle size by laser diffraction method 50 mL of ethanol was placed in a 100 mL beaker, and about 0.2 g of sample powder was added. Ultrasonic treatment (UD - 201 manufactured by Tomy Seiko Co., Ltd.) was performed for 3 minutes to prepare a dispersion. Using this prepared solution and a laser diffraction method - particle size distribution analyzer (Microtrac HRA Model 9320 - X100 manufactured by Nikkiso Co., Ltd.), the D 50 value was measured with the average particle size (μm).

[0095] (3) XRD measurement After fixing the sample powder on a predetermined sample stage with a spatula blade by pressing, measurement was performed using an XRD apparatus (MiniFlex600 - C manufactured by Rigaku Corporation), and identification analysis as a crystalline substance was carried out.

[0096] (4) Scanning electron microscope Double - sided tape was attached to an aluminum sample stage, and the sample powder was applied thereon by tracing with a spatula blade. After platinum evaporation, a 5000 - fold magnification photograph of the particle image of the sample powder was taken using a scanning electron microscope (FE - SEM: S - 4700 manufactured by Hitachi, Ltd.). SEM photographs are shown in Figs. 1 - 5.

[0097] (5) Measurement of coefficient of variation Regarding the SEM photograph obtained in (4) above, using image analysis software (Image J), 20 particles in the photograph were randomly selected, and the average value (d pri ) and standard deviation (σ pri ) of the primary particle diameter (the longest diameter of the primary particle) were obtained. Here, the longest diameter of the primary particle was defined as the dimension of the particle in the direction where the dimension of the measured particle was the largest when measuring the dimensions of the particle from each corner (i.e., the longest diameter). Furthermore, the coefficient of variation of the primary particle diameter was obtained by the following formula. Coefficient of variation = (σ pri / d pri ) × 100 (In the formula, σ pri is the standard deviation (μm) of the primary particle diameter from the electron microscope image, and d pri is the average value (μm) of the primary particle diameter from the electron microscope image.)

[0098] (6) Measurement of monodispersity Regarding the SEM photograph obtained in (4) above, 20 particles in the photograph were randomly selected using image analysis software (Image J), and the average value of the primary particle diameter (the longest diameter of the primary particle) was determined. Furthermore, the monodispersity was determined by the following formula together with the average particle diameter by the (2) laser diffraction method. Monodispersity = (d pri / d ave ) × 100 (In the formula, d pri is the average value (μm) of the primary particle diameter by the electron microscope image, and d ave is the average particle diameter (μm) by the laser diffraction method.)

[0099] (7) Bending test (bending stress, elastic modulus) PP (polypropylene) resin (product name: BC-6D, manufacturer: Nippon Polypropylene Co., Ltd.) was used as the polyolefin resin. 20 parts by mass of the powder of calcium carbonate (filler) described later was melt-kneaded with 100 parts by mass of the PP resin at 180 ° C for 5 minutes using a lab plastomill (manufactured by Toyo Seiki), and the kneaded product was press-molded at 180 ° C to prepare a sheet molded body with a thickness of 3 mm. Using a test piece (length 120 mm, width 13 mm) punched out in a strip shape from this sheet molded body, the maximum bending stress and elastic modulus were measured in accordance with the three-point bending test (JIS-K-7171). The target values were 33 N / mm 2 or more for the bending stress and 1400 N / mm 2 or more for the elastic modulus.

[0100] [Example 1] 6 L of service water discharged within Kojima Chemical Industry Co., Ltd. was placed in an 8 L capacity SUS container with a baffle plate, and stirred at a rotational speed of 350 rpm using a stirrer equipped with a single-stage turbine blade at room temperature of 25 ° C. Under stirring, 21.8 g of the powder of waste magnesium hydroxide "Mg(OH)2" (BET specific surface area: 38 m 2 / g, average particle diameter: 3.5 μm) generated within the company was added (Mg / Ca 2+Molar ratio: 1.0), and when measured immediately thereafter with a pH meter, the pH value was 10.1. An exhaust gas extraction pipe was connected to the exhaust outlet of a boiler for steam production using LNG as fuel, and while drawing in the exhaust gas using a laboratory blower, when measured with a CO2 concentration measuring instrument (XP-3140 manufactured by Shin Cosmos Electric Co., Ltd.), the CO2 concentration showed 10% by volume. Exhaust gas was introduced into the above-mentioned 8 L capacity SUS container at a rate of 3.3 L / min using a laboratory blower and reacted for 4 hours. Thereafter, it was filtered, washed with about 5 times the amount of water of the solid content, and dried at 110 °C for 12 hours to obtain a sample powder of the product.

[0101] [Example 2] After putting 38 L of seawater collected in the Seto Inland Sea near Shinshima Chemical Industry Co., Ltd. into a 50 L capacity SUS container with a baffle plate, a slurry in which 15.0 g of the dust collection powder of waste magnesium oxide "MgO" (BET specific surface area: 75 m 2 / g, average particle size: 3.3 μm) generated within the company was dispersed in 200 mL of pure water was added (Mg / Ca 2+ Molar ratio: 1.0), and the pH value immediately thereafter showed 10.0. Otherwise, the same operations as in Example 1 were performed to obtain a sample powder of the product.

[0102] [Example 3] An exhaust gas extraction pipe was connected to the exhaust outlet of a hot air dryer using LPG as fuel, and while drawing in the exhaust gas using a laboratory blower, when measured with a CO2 concentration detector tube (No. 2H manufactured by Gastec Co., Ltd.), the CO2 concentration showed 2% by volume. Otherwise, the same operations as in Example 1 were performed except that the exhaust gas was introduced into the above-mentioned 8 L capacity SUS container at a rate of 15.3 L / min using a laboratory blower to obtain a sample powder of the product.

[0103] [Example 4] 165.3 g of the waste magnesium hydroxide powder "Mg(OH)₂" generated within the company was dispersed in 6 L of pure water to form a slurry, which was placed in an 8 L capacity SUS container with a baffle plate. At room temperature of 25 °C, exhaust gas was introduced at a rate of 3.3 L / min using a laboratory blower, and the reaction was carried out for 120 minutes to obtain a slurry of magnesium carbonate (MgCO₃·3H₂O). 1 L of this slurry was put into a 4 L capacity pot mill filled with 1 kg of zirconia balls with a diameter of 8 mmφ, and wet grinding was carried out at a rotation speed of 90 rpm for 24 hours. The BET specific surface area of the magnesium carbonate obtained by filtering and drying a part of the slurry after wet grinding was 21 m 2 / g, and the average particle size was 7.8 μm. 6 L of service water and the slurry of magnesium carbonate after the above-mentioned wet grinding were added to the above-mentioned 8 L capacity SUS container so that the content of "MgCO₃·3H₂O" was 51.7 g. The pH value immediately after that was 9.3. Thereafter, the same operations as in Example 1 were carried out except that stirring was carried out for 1 hour to complete the reaction, and a sample powder of the product was obtained.

[0104] [Example 5] 250 g of the crushed product (undersize of 2 mm) of the natural mineral brucite ore and 1 L of pure water were put into a 4 L capacity pot mill filled with 1 kg of zirconia balls with a diameter of 8 mmφ, and wet grinding was carried out at a rotation speed of 90 rpm for 24 hours. The BET specific surface area of the brucite obtained by filtering and drying a part of the slurry after wet grinding was 15 m 2 / g, and the average particle size was 3.8 μm. 6 L of service water and the slurry of brucite after the above-mentioned wet grinding were added to the above-mentioned 8 L capacity SUS container so that the content of "Mg(OH)₂" was 22.0 g. The pH value immediately after that was 10.6. Otherwise, the same operations as in Example 1 were carried out to obtain a sample powder of the product.

[0105] [Comparative Example 1] 6 L of service water discharged within the company was put into an 8 L capacity SUS container with a baffle plate, and further 27.7 g of hydrated lime sludge "Ca(OH)₂" (sludge oversize after sieving with a 45 μm sieve after hydrating quicklime, BET specific surface area: 14 m 2 / g, average particle size: 50 μm) was added and mixed (Ca / Ca2+ Molar ratio: 1.0). The pH value immediately after that was 12.6. Otherwise, the same operations as in Example 1 were carried out to obtain a sample powder of the product.

[0106] [Comparative Example 2] 6980 g of slaked lime powder in terms of CaO, 630 g of aragonite seed crystal powder, and 500 g of disodium hydrogen phosphate dodecahydrate were prepared, and each was charged into a 220 L capacity SUS container with a baffle plate pre-filled with 180 L of water under stirring to prepare a mixed slurry of raw materials. Then, the temperature was raised to 70°C, and under that temperature, a stirrer equipped with a single-stage turbine blade was used to stir at a rotational speed of 150 rpm. An exhaust gas extraction pipe was connected to the exhaust outlet of a boiler for producing steam using LNG as fuel, and while drawing in the exhaust gas using a test blower, when measured with a CO2 concentration measuring instrument (XP-3140 manufactured by Shin Cosmos Electric Co., Ltd.), the CO2 concentration showed 10% by volume. The exhaust gas was introduced into the above-mentioned 220 L capacity SUS container using a test blower at a speed of 100 L / min and reacted for 7 hours. Then, it was filtered, washed with about 5 times the amount of water with respect to the solid content, dried at 110°C for 24 hours, and pulverized to obtain a sample powder of the product.

[0107]

Table 2

[0108]

Table 3

[0109] As shown in Table 2 and Table 3, it can be seen that the calcium carbonate obtained in the examples had a smaller particle size than the comparative examples, less variation in the primary particle size, and good dispersibility. Also, it can be seen that the physical properties of the resin composition containing calcium carbonate as a filler were improved compared to the comparative examples.

[0110] ≪Evaluation for Concrete Applications≫ Using calcium carbonate of Example 1 (spherical polyhedron) and Comparative Example 2 (needle-shaped), the measurement of the P funnel flow-down time, as well as the production of the cement molded body and the compressive strength test were carried out. The results are shown in Table 5. In Table 5, "-" indicates that the evaluation could not be performed. In the following tables, except for Table 5, "-" indicates that the corresponding component was not used.

[0111] (Preparation Example 1) Preparation of Cement Milk 1 2 kg of cement (manufactured by Tokuyama Corporation, "Ordinary Portland Cement (N)") was put into 1600 mL of water in about 20 seconds, and mixed with a stirrer (manufactured by Yamato Scientific Co., Ltd., "Lab Stirrer (LR500B)") for 3 minutes from the start of input. After stopping the stirring and allowing to stand for 3 minutes, it was stirred 10 times by hand with a stirring rod (manufactured by AS ONE Corporation, "Stirring rod (POM-made) φ10×300 mm") to prepare Cement Milk 1.

[0112] (Preparation Examples 2 to 7) Preparation of Cement Milks 2 to 7 Calcium carbonate of the types and amounts shown in Table 4 below was put into 1600 mL of water, stirred by hand with the above stirring rod for about 30 seconds, and then stirred at 400 rpm using the above stirrer to obtain a mixture. 2 kg of cement (manufactured by Tokuyama Corporation, "Ordinary Portland Cement (N)") was put into this mixture in about 20 seconds, and mixed with the above stirrer for 3 minutes from the start of input. After stopping the stirring and allowing to stand for 3 minutes, it was stirred 10 times by hand with the above stirring rod to prepare Cement Milks 2 to 7.

[0113]

Table 4

[0114] In accordance with the "Test Method for Fluidity of Injection Mortar of Prepacked Concrete (Method Using P-Funnel)" (JSCE-F521-1999), the P-funnel flow-down time was measured. With the outlet of the P-funnel held down with a finger, each of the prepared cement milks was poured up to the marked line of the P-funnel (1750 ml), and measurement was started simultaneously with releasing the finger with a stopwatch. The time until the cement milk was discharged from the P-funnel was measured.

[0115] <Manufacture of Cement Moldings> [Example 6-1] 400 mL of the prepared cement milk 1 was poured into a cylindrical polyethylene bag (diameter: approximately 50 mm × length: approximately 550 mm × thickness: approximately 0.05 mm) up to the marked line. After injecting air as much as possible and sealing it, it was suspended in a thermostat set at 22°C. It was left for 28 days while suspended in the thermostat, and the contents were cured to manufacture a total of 3 cement moldings. The obtained cement moldings were cylindrical, with a diameter of approximately 5 cm and a length of approximately 20 cm.

[0116] [Examples 6-2 to 6-3 and Comparative Examples 6-1 to 6-4] Cement moldings were manufactured in the same manner as in Example 6-1, except that the cement milks shown in Table 5 below were used. In Comparative Example 6-4, since the cement milk was not discharged from the P-funnel, evaluation could not be performed.

[0117] (Density) The density was measured in accordance with JIS A 5430:2008 (Apparent Density Test).

[0118] (Compressive Strength Test) The compressive strength of the obtained cement moldings was measured in accordance with JIS A 1108:2018 (Test Method for Compression of Concrete).

[0119]

Table 5

[0120] In the cement molded body of the example, even when the calcium carbonate content was increased, there was no significant increase in the P funnel flow-down time compared to Comparative Example 6-1 which did not contain calcium carbonate, and it had good fluidity. On the other hand, in Comparative Examples 6-2 to 6-4, the fluidity decreased significantly.

[0121] ≪Evaluation for building material use≫ (Manufacture of molding plate) A molding plate was manufactured by an extrusion molding method according to the following procedure. The blending amounts of the components used are all shown in "parts by mass" unless otherwise specified. In the following table, "-" indicates that the corresponding component was not used.

[0122] [Example 7-1] Manufacture of molding plate by extrusion molding method The materials shown in Table 6 below were put into an omnimixer and the raw materials were dry-stirred for 3 minutes. The calcium carbonate of Example 1 was used as the calcium carbonate. Next, water was added and wet-stirred for 2 minutes. The raw materials after wet-stirring were kneaded with an Ishikawa-type extruder and then extrusion-molded with an Ishikawa-type extruder. Thereby, a molded body with long side 600 mm × short side 190 mm × thickness 13 mm) was produced. After obtaining the molded body, it was put into a thermo-hygrostat set at 60 °C / 98% for primary curing, and further pressurized to 9 kgf for 12 hours of autoclave curing. A molding plate was produced by polishing both sides of the molded body with a sander to a thickness of 12 mm.

[0123] [Comparative Example 7-1] Manufacture of molding plate by extrusion molding method Using the materials and contents shown in Table 6 below, a molding plate was obtained in the same manner as in Example 7-1 except that calcium carbonate was not blended.

[0124] (Evaluation of molding plate) The following evaluations were performed on the molding plates produced by the extrusion molding method in the examples and comparative examples. The results are shown in Table 4.

[0125] (Bulk density) The bulk density was measured in accordance with JIS A 5430.

[0126] (Three-point bending test) The three-point bending test was measured in accordance with JIS A 5430. The results were taken as the strength of the formed plate (N / mm 2 ).

[0127] (Heating test) The heating test was conducted using the following apparatus and procedure. Fig. 6 is a partial perspective view schematically showing the heating tester. As shown in Fig. 6, between the test piece and the heat source was assembled with refractory material so that it could be stabilized at around 900 °C using an electric heater as the heat source, and the temperature of the back surface of the test piece could be measured with a thermocouple. Specifically, an electric heater (1.2 kW heater) was used as the heat source equipment, and a K thermocouple and a temperature controller were connected. Also, each thermocouple was connected to a data logger. The distance between the heating surface side of the test piece and the heat source was fixed to be about 70 mm.

[0128] The test procedure was as follows. (1) A discard plate was installed, and after preheating to 902 °C, the heating was once stopped. (2) After the heating surface side reached 200 °C or lower, it was replaced with the test piece. (3) A thermocouple was placed on the center of the back surface (upper surface in the figure) of the test piece, and a calcium silicate plate (about 30 mm × 70 mm) and a weight were placed and fixed. (4) Heating was started and left for a predetermined time (45 minutes), and the temperatures on the front surface side and the back surface side were recorded with a data logger. During this period, the temperature setting of the electric heater was 902 °C on the heating surface side, and it was controlled with a temperature controller with 900 °C as the lower limit. Also, the temperature measurement interval of the data logger was set to every 10 seconds, and data was recorded at this interval. (5) After the test was completed, the test piece was taken out and the following items were measured (each item was also measured before the test). · Dimensions: The longitudinal and transverse lengths of the back surface and the heating surface were measured with calipers. The area of the heating surface (mm 2 ) before and after the test was calculated, and the heating surface shrinkage (%) was obtained based on the following formula. Heating surface shrinkage (%) = {|S1 - S0| / S0} × 100 (In the formula, S0 is the area of the heating surface before the test, and S1 is the area of the heating surface after the test.) · Warpage: The test piece was placed on an iron surface plate, and the height from the iron surface plate at the center of each side of the test piece was measured with a thickness gauge, and the average value (mm) was obtained. This average value was taken as the warpage after heating (mm). · Photographing of the sample before and after the test (a photograph that shows the degree of cracking before and after heating)

[0129]

Table 6

[0130] In the formed plates of the examples, all of the strength, shrinkage of the heating surface, warpage after heating, and warpage after heating were superior to those of the comparative examples. Also, in the formed plates of the examples, no cracks occurred after heating (not shown).

Claims

1. Calcium carbonate having a coefficient of variation of primary particle size, represented by the following formula, of 5% or more and 30% or less, an average particle size measured by a laser diffraction method of 5 μm or less, and primary particles having a spherical polyhedral shape. Coefficient of variation = (σ ｐｒｉ / d ｐｒｉ ) x 100 (In the formula, σ ｐｒｉ is the standard deviation of the primary particle size (μm) in the electron microscope image, and d ｐｒｉ is the average primary particle size (μm) based on an electron microscope image.

2. Calcium carbonate having a monodispersity of 50% or more and 100% or less, an average particle size of 5 μm or less as measured by a laser diffraction method, and a primary particle shape of which is a spherical polyhedron. Monodispersity = (d ｐｒｉ / d ａｖｅ ) x 100 (In the formula, d ｐｒｉ is the average primary particle diameter (μm) in an electron microscope image, and d ａｖｅ is the average particle size (μm) measured by laser diffraction method.)

3. 3. The calcium carbonate according to claim 1 or 2, which is for use in an inorganic molded product.

Images