Calcium carbonate manufacturing method and calcium carbonate

Abstract

To provide a method for producing calcium carbonate and calcium carbonate which can achieve small particle size, homogenization of primary particle size and high dispersibility for calcium carbonate obtained by immobilizing carbon dioxide.SOLUTION: A method for producing calcium carbonate comprises a step of contacting sea water, used water containing calcium after producing magnesium hydroxide from sea water, or a mixture thereof, an alkali agent and a gas containing carbon dioxide at a pH of 9 or more and less than 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Seawater is rich in minerals, for example, it contains about 1,300 ppm of magnesium and about 400 ppm of calcium. To effectively utilize these minerals, a known method is to produce magnesium hydroxide by reacting seawater with dolomite or other minerals, and then separate and recover the magnesium.

[0003] Since the seawater after magnesium separation using the above-mentioned method (hereinafter also referred to as "used water") still contains a large amount of calcium, the development of technology to effectively utilize this remaining calcium is underway. Specifically, a technology has been proposed that utilizes the calcium contained in the used water to capture carbon dioxide, thereby aiming for industrial applications of the calcium component and contributing to the reduction of carbon dioxide emissions, which is considered an effective measure against problems such as global warming in recent years (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7138256 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to expand the applications and improve the functionality of calcium carbonate obtained by capturing (fixing) carbon dioxide into calcium components, calcium carbonate with 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, which can achieve small particle size, uniform primary particle size, and high dispersibility of calcium carbonate obtained through fixation of carbon dioxide, and also to provide calcium carbonate. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following configuration, and have thus completed the present invention.

[0008] In one embodiment, the present invention relates to a method for producing calcium carbonate, the method comprising a step of contacting seawater, calcium-containing used water remaining after producing magnesium hydroxide from seawater, or a mixture thereof (hereinafter, seawater, used water, and a mixture thereof are also collectively referred to as "seawater, etc."), with an alkaline agent, and a gas containing carbon dioxide at a pH of 9 or higher and lower than 11.

[0009] According to this method for producing calcium carbonate, it is possible to produce calcium carbonate that has a small particle size, a uniform primary particle size, and good dispersibility while immobilizing carbon dioxide. Although the reason for this is not clear, it is presumed as follows: In the contacting step, carbonate ions are generated by contacting an alkaline agent with carbon dioxide, and calcium carbonate particles are generated by contacting these with calcium (calcium ions) in seawater or the like. It is presumed that the contacting under relatively mild alkaline conditions of pH 9 or higher but lower than 11 slows down the particle growth rate, resulting in calcium carbonate that has a small particle size and a regular particle shape.

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

[0011] By contacting the three components of seawater or the like, an alkaline agent, and a gas containing carbon dioxide in either of the specific sequences 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, which can more efficiently reduce the particle size of calcium carbonate.

[0013] In one embodiment, the temperature in the contact step is preferably 50° C. or less. This allows calcium carbonate to be produced as calcite, and provides a usage mode that suits the application and function of calcium carbonate.

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

[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 calcium carbonate preferably has an average particle size of 5 μm or less as measured by a laser diffraction method, which can improve the physical properties of products containing calcium carbonate and enable the expansion of applications and the enhancement of functionality.

[0019] In one embodiment, the present invention provides The present invention relates to calcium carbonate having a coefficient of variation of primary particle size, represented by the following formula, of 5% to 30%, an average particle size measured by a laser diffraction method of 5 μm or less, and primary particles having a spherical polyhedral or plate-like 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) from an electron microscope image.

[0020] In one embodiment, the present invention provides The present invention relates to 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 primary particles having a spherical polyhedral or plate-like shape. Monodispersity = (d pri / d ave ) x 100 (In the formula, d pri is the average primary particle size (μm) in an electron microscope image, and d ave is the average particle size (μm) measured by laser diffraction.)

[0021] The calcium carbonate has the above-mentioned properties, which can stabilize, activate, and enhance the functionality of the calcium carbonate itself, thereby expanding the range of applications of products that use the calcium carbonate. The calcium carbonate is suitable for use in inorganic molded bodies. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a method for producing calcium carbonate that can efficiently fix carbon dioxide and has a small particle size with little variation in primary particle size and good dispersibility, and calcium carbonate. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is an SEM photograph of calcium carbonate in Example 1 of the present invention. [Figure 2] 1 is an SEM photograph of calcium carbonate in Example 2 of the present invention. [Figure 3] 1 is an SEM photograph of calcium carbonate in Example 3 of the present invention. [Figure 4] 1 is an SEM photograph of calcium carbonate of Example 4 of the present invention. [Figure 5] 1 is an SEM photograph of calcium carbonate of Example 5 of the present invention. [Figure 6] 1 is an SEM photograph of calcium carbonate in Comparative Example 1 of the present invention. [Figure 7] 1 is an SEM photograph of calcium carbonate in Comparative Example 2 of the present invention. [Figure 8] FIG. 2 is a partial perspective view schematically showing a heating tester. DETAILED DESCRIPTION OF THE INVENTION

[0024] A method for producing calcium carbonate and calcium carbonate according to one embodiment of the present invention will be described below, but 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 contacting seawater, calcium-containing water obtained after producing magnesium hydroxide from seawater, or a mixture thereof with an alkaline agent and a gas containing carbon dioxide at a pH of 9 or higher and lower than 11. The production method may include other steps.

[0026] <Contact process> The order of contacting the three components in the contacting step is not particularly limited as long as calcium carbonate is obtained. However, it is preferable to contact the seawater, utilized water, or a mixture thereof with the alkaline agent and the gas in either the following order 1) or 2). 1) After the seawater, utilized water, or a mixture thereof is brought into contact with the alkaline agent, the gas is further brought into contact with the alkaline agent. 2) After the alkaline agent and the gas are brought into contact with each other, the seawater, utilized water, or a mixture thereof is further brought into contact with each other.

[0027] Hereinafter, the contacting method in step 1) will be referred to as a direct method, and the contacting method in step 2) will be referred to as an indirect method.

[0028] (direct method) In the direct method, calcium carbonate is produced directly by contacting seawater or the like with an alkaline agent and then contacting it with a gas. The reaction formula here is as shown in formula (1) below. Ca 2+ +2OH - +CO2→CaCO3+H2O (1)

[0029] Seawater may be directly drawn from the sea near a magnesium hydroxide manufacturing plant, for example, or may be used after being subjected to processing such as filtration. Drawing is not limited to nearby seas, and may be carried out at any location as long as seawater is available.

[0030] Used water is a component discharged after producing magnesium hydroxide (Mg(OH)2) from seawater. Used water is discharged, for example, from a magnesium hydroxide manufacturing plant. When producing magnesium hydroxide, seawater is reacted with hydrated dolomite or hydrated lime after calcination. The used water after the reaction contains a larger amount of calcium than seawater. In this respect, it is preferable to use used water in this production method. The produced magnesium hydroxide is used, for example, as a neutralizing agent for flue gas desulfurization.

[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 derived mainly from seawater, and the upper limit of the calcium concentration is derived mainly from the utilized water. As described above, the lower limit of the calcium concentration in seawater alone is preferably 300 ppm, more preferably 350 ppm, and even more preferably 380 ppm. 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 utilized water alone is preferably 1500 ppm, more preferably 1800 ppm, and even more preferably 2000 ppm. As mentioned above, the upper limit of the calcium concentration in the water to be used alone is preferably 3000 ppm, more preferably 2800 ppm, and even more preferably 2600 ppm, but is not limited thereto, and the calcium concentration may be adjusted by adding a calcium source (e.g., calcium chloride, calcium sulfate, etc.) to seawater or by concentrating or diluting the seawater.

[0032] The alkaline agent is not particularly limited as long as it can adjust the pH in the contact step to within a predetermined range. Examples include alkaline earth metal or alkali metal hydroxides such as magnesium hydroxide (Mg(OH)), calcium hydroxide (Ca(OH)), barium hydroxide (Ba(OH)), sodium hydroxide (NaOH), and potassium hydroxide (KOH); alkaline earth metal or alkali metal oxides such as magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), sodium oxide (NaO), and potassium hydroxide (KO); carbonates such as neutral magnesium carbonate (MgCO 3H O), sodium carbonate (NaCO ), and potassium carbonate (NaCO ); and industrial waste materials such as lime residue, cement sludge water, washing wastewater from raw cement plants, residual cement, and waste cement. Among these, magnesium hydroxide, magnesium oxide, and neutral magnesium carbonate are preferred as alkaline agents that can easily adjust the pH to within a predetermined range. Magnesium hydroxide and magnesium oxide are more preferred, and magnesium hydroxide is even more preferred.

[0033] The alkaline agent may be a commercially available synthetic product, a commercially available natural mineral product, or industrial waste. Commercially available natural mineral products and industrial waste are preferred because they emit very little carbon dioxide from the mining of raw materials to the completion of production. An example of a natural mineral product as an alkaline agent is finely ground brucite ore (Mg(OH)2) (10 μm or less). The industrial waste as an alkaline agent is preferably waste magnesium hydroxide or waste magnesium oxide, which is inevitably generated during the manufacturing process of magnesium hydroxide or magnesium oxide, the brand switching process, etc. Examples of waste magnesium hydroxide include filter cloth leaks during the filtration process, leaks from the gland packing of a slurry transport pump, and washed products during brand switching. Examples of waste magnesium oxide include rotary kiln firing dust (collected dust) and washed products during brand switching. While these industrial wastes have traditionally been discarded as waste, they are often used in applications with a BET specific surface area of 10 to 200 m. 2 / g, and the average particle size is 10 μm or less, and the reactivity is relatively high, so it can be effectively used as an alkaline agent in the production method. The alkaline agent may be subjected to treatment such as pulverization or crushing in terms of reactivity and handling. This treatment may be either wet or dry.

[0034] In the direct method, seawater or the like is first contacted with an alkaline agent. The contact may be carried out by directly adding the alkaline agent to the seawater or the like, or by dispersing the alkaline agent in a solvent such as water in advance to form a slurry, which is then added to the seawater or the like. The addition may be carried out all at once or in multiple stages. When the alkaline agent is an oxide, from the viewpoint of reactivity, it is preferable to dissolve or disperse it in water or the like to hydrate it and form a slurry before adding it. The concentration of the alkaline agent in the slurry is not particularly limited, and may be in the range of 10 g / L or more and 500 g / L or less.

[0035] The amount of alkaline agent to be added is not particularly limited as long as it is set so that the amount of hydroxide ions necessary 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 alkaline agent is magnesium hydroxide (Mg(OH)2), the amount of Mg in the alkaline agent is reduced by the amount of Ca in 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, i.e., equimolar amounts. By setting the molar ratio within the above range, coprecipitation of the reaction product of Mg in the alkaline agent can be suppressed, and calcium carbonate with high purity can be produced. Ca 2+ The amount of magnesium hydroxide to be added to 10 L of water with a concentration of 2500 ppm is preferably 32.7 g to 36.4 g, more preferably 34.5 g to 36.4 g. When the alkaline agent is magnesium oxide (MgO), the amount of Mg in the alkaline agent is reduced by 32.7 g to 36.4 g, and more preferably 34.5 g to 36.4 g. 2+ Molar ratio (Mg / Ca 2+ ) can be suitably used in the same range as in the case of magnesium hydroxide. 2+The amount of magnesium oxide to be added to 10 L of seawater with a concentration of 400 ppm is preferably 3.6 g to 4.0 g, and more preferably 3.8 g to 4.0 g. Even when the alkaline agent is other than magnesium hydroxide or magnesium oxide, the amount to be added can be set based on the same considerations.

[0036] In this production method, when seawater or the like is brought into contact with an 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, even more preferably 9.6, and particularly preferably 9.8. The upper limit of the pH is preferably 10.9, more preferably 10.8, even more preferably 10.6, even more preferably 10.4, and particularly preferably 10.2.

[0037] The temperature at which seawater or the like is brought into contact with the alkaline agent is not particularly limited, and may be the temperature of the seawater as drawn, may be left standing for a while at room temperature, or may be heated. The temperature is preferably 50°C or lower, and is preferably in the range of 0°C to 30°C. By keeping the temperature at 50°C or lower, calcium carbonate can be produced as calcite with small particle size and good dispersibility. From the standpoints of reactivity and efficiency, the temperature is preferably around room temperature, more preferably 10°C to 30°C, and even more preferably 15°C to 28°C.

[0038] The gas to be contacted in the direct method is not particularly limited as long as it contains carbon dioxide. Suitable examples of the gas include exhaust gas from combustion engines such as boilers, thermal power plants (power plants that use the heat from combustion of fossil fuels such as petroleum, coal, and liquefied natural gas (LNG) or biomass), and blast furnaces, and exhaust gas from dryers. Exhaust gas from combustion engines is preferred because it has a high carbon dioxide concentration and provides good calcium carbonate production efficiency in the contact step. The lower limit of the carbon dioxide concentration in the gas is preferably 1% by volume, more preferably 2% by volume, more preferably 5% by volume, and particularly preferably 8% by volume. While a higher upper limit of the concentration is preferable, it may be 30% by volume, 20% by volume, 15% by volume, or 12% by volume. This production method not only reduces emissions by immobilizing carbon dioxide, but also promotes industrial use in the production of calcium carbonate.

[0039] In the direct method, gas contact can be carried out by blowing (bubbling) into seawater or the like that has been in contact with an alkaline agent. The flow rate and blowing time of the gas can be appropriately set taking into consideration the carbon dioxide concentration, reaction efficiency, and the progress of the carbonation reaction of reaction formula (1). For example, for 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 even more preferably 3.0 L / min or more and 20.0 L / min or less. Ca in seawater 2+ It is sufficient to introduce CO2 in amounts greater than the theoretical number of moles required for complete precipitation of calcium carbonate. 2+ It is determined by the concentration, amount used, and CO2 concentration in the exhaust gas. For example, Ca 2+ When CO2 with a concentration of 10% by volume in the exhaust gas is injected at 5.0 L / min into 10 L of water with a concentration of 2500 ppm, an injection time of 0.5 hours or more is required, more preferably 1.0 to 8.0 hours, and even more preferably 2.0 to 6.0 hours.

[0040] By going through the above contacting step, it is possible to produce calcium carbonate having a small particle size, little variation in primary particle size, and good dispersibility. The obtained calcium carbonate may be subjected to filtration, washing, drying, pulverization, classification, etc.

[0041] (indirect method) In the indirect method, an alkaline agent is brought into contact with a gas to first generate carbonate salts (carbonate ions) of the alkaline agent, and then the resulting mixture is brought into contact with seawater or the like to indirectly generate calcium carbonate. The reaction formulas used here are 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 produce carbonate (carbonate ions), which is then brought into contact with calcium (calcium ions) from seawater or the like to carry out salt exchange to produce calcium carbonate. Below, we will explain the differences between the indirect method and the direct method.

[0043] The contact of the alkaline agent with 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 solution (hereinafter, collectively referred to as "slurry, etc."), and then blowing (bubbling) the gas into the slurry, etc. The concentration of the alkaline agent in the slurry, etc. is not particularly limited and can be set appropriately in the range of 10 g / L or more and 100 g / L or less.

[0044] The gas flow rate and injection time can be appropriately set taking into consideration the carbon dioxide concentration, reaction efficiency, and the progress of the carbonate (carbonate ion) production reaction of Reaction Formula (2-1). For example, for 10 L of slurry, the gas flow rate 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 injection 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)), a slurry of neutral magnesium carbonate (MgCO3 3H2O) is obtained as a carbonate via 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 is, but it is preferable to subject it to a particle size reduction treatment such as wet grinding in order to improve the reaction activity before subjecting it to the reaction of reaction formula (2-2). 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 via 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 adding a slurry of the carbonate to seawater or the like, or by adding seawater to the slurry. The amount of carbonate to be added 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 seawater or the like is obtained according to the above reaction formula (2-2) and the pH after addition is within a predetermined range. For example, when the carbonate is neutral magnesium carbonate, the amount of Mg in the carbonate is reduced to Ca in 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, i.e., equimolar amounts. By setting the molar ratio within the above range, coprecipitation of the reaction product of Mg in the carbonate can be suppressed, and calcium carbonate with high purity can be produced. Ca 2+The amount of neutral magnesium carbonate to be added to 10 L of water to be used, which has a concentration of 2500 ppm, is preferably 77.6 g or more and 86.2 g or less, and more preferably 81.9 g or more and 86.2 g or less.

[0047] The pH of the carbonate when it comes into contact with seawater or the like is preferably 9 or more and less than 11 immediately after the contact. 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, even more preferably 9.6, and particularly preferably 9.4.

[0048] The salt exchange reaction caused by contact of carbonate with seawater etc. proceeds relatively quickly. The reaction time may be set to a time sufficient for the salt exchange reaction to proceed sufficiently, and can be set to 0.1 hours or more, preferably 0.5 hours to 8.0 hours, and more preferably 1.0 hours to 6.0 hours.

[0049] Calcium carbonate Each aspect of calcium carbonate will be described below. Calcium carbonate having the following characteristics can be efficiently produced by the above-described method for producing calcium carbonate. The methods for measuring or evaluating the standard deviation of primary particle diameters in electron microscope images, the average value of primary particle diameters in electron microscope images, and the average particle diameter and shape of primary particles by laser diffraction method shown below are as described in the Examples.

[0050] (First aspect) The calcium carbonate has 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 of 5 μm or less as measured by a laser diffraction method, and the primary particles have a spherical polyhedral or plate-like 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) from an electron microscope image.

[0051] The lower limit of the coefficient of variation is preferably 6%, more preferably 7%, and even more preferably 8%, and 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 in 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 primary particle size measured by the electron microscope image is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 0.8 μm, and the upper limit of the average primary particle size 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 size measured by the laser diffraction method is preferably 0.5 μm, more preferably 1.0 μm, and even more preferably 1.5 μm, and the upper limit of the average particle size measured by the laser diffraction method is preferably 4.8 μm, more preferably 4.6 μm, and even more preferably 4.0 μm.

[0055] The primary particles have a spherical polyhedron or plate-like shape. A spherical polyhedron refers to a shape that is spherical overall, but has a surface that is not spherical but is formed by combining polygonal planes.

[0056] (Second aspect) The calcium carbonate has a monodispersity of 50% or more and 100% or less, as determined by the following formula, an average particle size of 5 μm or less as measured by a laser diffraction method, and primary particles having a spherical polyhedral or plate-like shape. Monodispersity = (d pri / d ave ) x 100 (In the formula, d pri is the average primary particle size (μm) in the electron microscope image, and d ave is the average particle size (μm) measured by laser diffraction.)

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

[0058] In the second embodiment, the average value of the primary particle diameter in an electron microscope image, the average particle diameter by laser diffraction method, and the shape of the primary particles can be suitably the same as those in the first embodiment.

[0059] (Common matters between the first and second aspects) Examples of the crystal structure of calcium carbonate include calcite and aragonite, with calcite being preferred.

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

[0061] The P funnel flow time of the calcium carbonate is preferably 7 to 10 seconds, more preferably 7.5 to 9.8 seconds, and even more preferably 8 to 9.5 seconds. The calcium carbonate has excellent dispersibility and therefore exhibits excellent fluidity, particularly in concrete applications.

[0062] The uses of calcium carbonate are not particularly limited, and examples include fillers for resins, compounding agents for inorganic molded bodies (aggregates for concrete structures (cement) and compounding agents for building materials), thickeners for sealants, etc. By adding calcium carbonate, it is possible to expand the applications and improve the functionality of these products.

[0063] Although not particularly limited, the resin is preferably a thermoplastic resin. Examples of the thermoplastic resin include, but are not limited to, acrylic resins such as homopolymers or copolymers of (meth)acrylic acid esters, such as polymethyl methacrylate (PMMA), ethylene / (meth)acrylic acid ester copolymers, and methyl acrylate / methyl methacrylate copolymers; high-density polyethylene, low-density polyethylene, linear low-density polyethylene, very-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), ultra-high molecular weight polyethylene, and the like. Examples of suitable resins include polyethylene resins (PE) such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and other polyester resins; and 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.

[0064] (Aggregate for concrete structures (cement)) The concrete structure is composed of a hardened hydraulic composition. The hydraulic composition is made of a powder containing calcium carbonate and at least one of blast furnace slag, expansive agent, slaked lime, quicklime, fly ash, and Portland cement. The calcium carbonate described above can be suitably used as the calcium carbonate.

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

[0066] The hardened hydraulic composition is obtained by hardening a paste obtained by kneading the hydraulic composition with water. The hardened hydraulic composition mixture is obtained by hardening a mixture (equivalent to fresh mortar or fresh concrete) obtained by kneading the hydraulic composition mixture with water, and corresponds to mortar or concrete.

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

[0068] It is desirable to use ground granulated blast furnace slag used in JIS (Japanese Industrial Standards) R5211 "Blast furnace cement" or ground granulated blast furnace slag conforming to JIS A6206 "Blast furnace slag for concrete." In addition, blast furnace slag should have a specific surface area of 2000 to 10000 cm. 2 / g, preferably 3500 to 7000 cm 2 It is desirable to use one with a saturation of 0.15 to 0.25 g.

[0069] The expansive material may be, for example, one specified in JIS A6202 “Expansive materials for concrete.” The expansive material is preferably added in an amount of 2 to 9 mass % based on the total amount of the hydraulic composition.

[0070] For example, slaked lime specified in JIS R9001 "Industrial Lime" can be used. Furthermore, because quicklime becomes slaked lime when it comes into contact with water, quicklime specified in JIS R9001 "Industrial Lime" can be used instead of slaked lime. In this case, it is advisable to adjust the amount of water required to convert quicklime into slaked lime. The fly ash used may be one that conforms to JIS A6201 "Fly ash for concrete," for example.

[0071] Ordinary Portland cement is used as Portland cement, but other types of Portland cement such as high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement, as specified in JIS R5210 "Portland cement," and JIS R5214 "Ecocement" can also be used.

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

[0073] Furthermore, when Portland cement and blast furnace slag or fly ash are used, the components may be pre-mixed, for example, JIS R5211 "blast furnace cement" or, for example, JIS R5213 "fly ash cement," and the pre-mixed components may be used alone or in combination.

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

[0075] The density of the concrete structure is 0.7 g / cm 3 More than 2.0g / cm 3 Preferably, it is 0.8 g / cm or less. 3 More than 1.8g / cm 3 More preferably, it is 0.9 g / cm or less. 3 More than 1.6g / cm 3 It is even more preferable that:

[0076] (Building material compounding agent) The building material is preferably a molded board for building materials. The molded 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, high-early-strength cement, moderate-heat cement, fly ash cement, blast furnace slag cement, and alumina cement. Examples of gypsum include anhydrous gypsum, 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.

[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 materials constituting the molded board. By setting the content of the hydraulic material within the above range, it is possible to improve the physical properties of the molded board, such as bending strength and peel strength, and to prevent the molded board from becoming too high in bulk density, thereby improving workability during construction.

[0079] (siliceous material) Examples of siliceous materials include materials containing a large amount of SiO, such as silica sand, silica powder, silica fume, fly ash, diatomaceous earth, layered silicates (e.g., mica, talc, kaolin, bentonite), perlite, wollastonite, and lightweight aggregates (e.g., fly ash balloons, perlite, shirasu balloons, glass foam, etc.). These siliceous materials can be used alone or in combination of two or more. Talc, mica, and wollastonite can also be used as reinforcing fiber materials, as described below.

[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 materials constituting the molded board. 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 molded board within the desired range. Incidentally, as the siliceous material, perlite, fly ash balloons, shirasu balloons, etc., having a unit volume mass of 0.5 g / cm are preferred. 3When mixing the following lightweight aggregates, it is preferable to use other siliceous materials in combination so that the content of lightweight aggregate is 20 mass% or less, based on the total amount of materials constituting the molded board, in order to prevent the bulk density from becoming too light and weakening strength such as bending strength and peel strength.

[0081] (reinforcing fiber material) Examples of reinforcing fiber materials that can be used include pulps such as softwood pulp, hardwood pulp, fibrillated pulps thereof, 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. These reinforcing fiber materials can be used alone or in combination of two or more.

[0082] To improve the strength and toughness of the molded board, the content of the reinforcing fiber material is preferably 2% by mass to 30% by mass, more preferably 3% by mass to 26% by mass, and even more preferably 4% by mass to 22% by mass, based on the total amount of materials constituting the molded board. By setting the content of the reinforcing fiber material within this range, it is possible to achieve a sufficient reinforcing effect while suppressing the protrusion of fibers from the surface of the molded board, thereby improving smoothness. When an inorganic reinforcing fiber material with an average length of 1 mm to 50 mm is blended as the reinforcing fiber material, it is preferable to use another reinforcing fiber material in combination so that the content is 10% by mass or less, based on the total amount of materials constituting the molded board, in order to improve the smoothness of the molded board.

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

[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 materials constituting the molded board. By blending calcium carbonate with low thermal conductivity in the above content range, the strength and fire resistance of the molded board can be improved.

[0085] (optional ingredient) In addition to the above materials, various materials can be blended into the molded board depending on the purpose to impart various functions, such as hollow resin bodies, wood chips, wood flour, resin powder, antifoaming agents, flocculants, water repellents, thickeners (methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, etc.), dispersants, etc. It is also possible to add recycled materials made by crushing scraps generated during the processing of the molded board as appropriate.

[0086] The bulk density of the molded plate is 0.7 g / cm 3 More than 2.0g / cm 3 Preferably, it is 0.8 g / cm or less. 3 More than 1.8g / cm 3 More preferably, it is 0.9 g / cm or less. 3 More than 1.6g / cm 3 It is even more preferable that:

[0087] (Method of manufacturing molded plate) The method for producing the molded plate according to this embodiment is not particularly limited, and commonly used methods such as papermaking, extrusion, flow-on molding, casting, and press (compression) molding can be used. The molded plate can be obtained by subjecting a green sheet molded by these methods to press dehydration or patterning by embossing, etc., followed by curing at room temperature, steam curing, autoclave curing, etc. The molded plate can then be dried and, if necessary, shaped or painted.

[0088] (Uses of molded boards) The uses of the molded board are not particularly limited, and it can be suitably used as a performance maintaining material for wall construction, flooring, roofing, various boards, exterior decorative members, interior and exterior finishing materials such as fittings, sealing materials, heat insulating materials, sound absorbing materials, waterproofing materials, etc. The molded board is preferably a cementitious molded board containing a cementitious material, and more preferably a calcium silicate molded body. [Example]

[0089] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Measurements and evaluations of physical properties, etc. were carried out as follows.

[0090] [Analysis of seawater and used water] The results of analyzing the components and pH of seawater collected from the Seto Inland Sea near Konoshima Chemical Co., Ltd. and the water used in the company's magnesium hydroxide manufacturing process are shown in Table 1. 2+ It is the supernatant liquid remaining after magnesium hydroxide "Mg(OH)2" is precipitated and collected by reacting it with an alkaline agent (calcium hydroxide, etc.). 2+ was measured using ICP-AES (Hitachi High-Tech Science Corporation, inductively coupled plasma atomic emission spectrometer, SPECTROBLUE FMS36). The pH of seawater and used water was measured using a pH meter (Toa DKK Corporation, main unit: multi-water quality meter MM-43X, pH electrode: GST5841C).

[0091] [Table 1]

[0092] [Evaluation of raw materials, calcium carbonate (filler), and resin composition] The calcium carbonate and other materials obtained in the examples and comparative examples were analyzed as follows. The analytical results are shown in Tables 2 to 3 and Figures 1 to 7.

[0093] (1) BET specific surface area The sample powder was pretreated in an 8-well preheat unit (MOUNTECH) at approximately 130°C for approximately 30 minutes under a nitrogen gas atmosphere. The BET specific surface area (m) was measured by nitrogen gas adsorption using a Macsorb HM Model-1208 (MOUNTECH) BET specific surface area measuring device. 2 / g) was measured.

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

[0095] (3)XRD measurement The sample powder was pressed and fixed onto a designated sample stage with a spatula, and then measured using an XRD device (MiniFlex600-C, manufactured by Rigaku Corporation) to perform an identification analysis as a crystalline substance.

[0096] (4) Scanning electron microscope Double-sided tape was attached to an aluminum sample stage, and the sample powder was applied to it by tracing it with a spatula. After platinum deposition, particle images of the sample powder were taken at 5,000 magnifications using a scanning electron microscope (FE-SEM: Hitachi S-4700). Figures 1 to 7 show the SEM images.

[0097] (5) Measurement of coefficient of variation For the SEM photograph obtained in (4) above, 20 particles were randomly selected from the photograph using image analysis software (Image J), and the average value of the primary particle diameter (the longest diameter of the primary particle) (d pri ) and standard deviation (σ pri ) was calculated. Here, the dimensions of the particles to be measured were measured from all directions, and the longest diameter of the primary particles was taken as the dimension of the particle in the direction in which the particle dimension was the largest (i.e., the longest diameter). Furthermore, the coefficient of variation of the primary particle diameter was calculated using the following formula. 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) from an electron microscope image.

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

[0099] (7) Bending test (bending stress, elastic modulus) PP (polypropylene) resin (product name: BC-6D, manufacturer: Japan Polypropylene Corporation) was used as the polyolefin resin. 20 parts by mass of calcium carbonate (filler) powder (described below) was melt-kneaded with 100 parts by mass of PP resin at 180°C for 5 minutes using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho). The resulting mixture was press-molded at 180°C to produce a sheet molded product with a thickness of 3 mm. Test pieces (length 120 mm, width 13 mm) were punched out of this sheet molded product into strips, and the maximum bending stress and elastic modulus were measured in accordance with the three-point bending test (JIS-K-7171). The target value was a bending stress of 33 N / mm. 2 The elastic modulus is 1400N / mm 2 That's all.

[0100] [Example 1] Six liters of water discharged from Konoshima Chemical Co., Ltd. was placed in an 8-liter SUS container with a baffle plate and stirred at a room temperature of 25°C using a stirrer equipped with one turbine blade at a rotation speed of 350 rpm. While stirring, powder of waste magnesium hydroxide "Mg(OH)2" (BET specific surface area: 38 m) generated within the company was added. 2 / g, average particle size: 3.5 μm) was added (Mg / Ca 2+The pH value was measured immediately after the reaction (molar ratio: 1.0) using a pH meter, which showed a pH of 10.1. A flue gas extraction pipe was connected to the exhaust outlet of an LNG-fueled steam production boiler, and the flue gas was drawn in using a laboratory blower. Measurements using a CO2 concentration meter (XP-3140, manufactured by New Cosmos Electric Co., Ltd.) showed a CO2 concentration of 10% by volume. The flue gas was introduced into the aforementioned 8-liter SUS vessel using a laboratory blower at a rate of 3.3 L / min, and the reaction was carried out for 4 hours. The mixture was then filtered, washed with water in an amount approximately five times the solid content, and dried at 110°C for 12 hours to obtain a powder sample of the product.

[0101] [Example 2] 38 L of seawater collected from the Seto Inland Sea near Konoshima Chemical Co., Ltd. was placed in a 50 L SUS container with a baffle, and then the waste magnesium oxide (MgO) powder (BET specific surface area: 75 m) generated within the company was collected and mixed. 2 A slurry of 15.0 g of Mg / Ca (average particle size: 3.3 μm) dispersed in 200 mL of pure water was added. 2+ The pH value immediately thereafter was 10.0. Except for this, the same procedure as in Example 1 was carried out to obtain a powder sample of the product.

[0102] [Example 3] A flue gas extraction pipe was connected to the exhaust outlet of an LPG-fueled hot air dryer, and the flue gas was drawn in using a laboratory blower. Measurements were made with a CO2 concentration detector tube (No. 2H, manufactured by Gastec Corporation), which showed a CO2 concentration of 2% by volume. A sample powder of the product was obtained by the same procedure as in Example 1, except that flue gas was introduced into the aforementioned 8-L SUS container at a rate of 15.3 L / min using a laboratory blower.

[0103] [Example 4] 165.3g of waste magnesium hydroxide "Mg(OH)2" powder generated within the company was dispersed in 6L of pure water to form a slurry, which was placed in an 8L SUS container with a baffle plate, and exhaust gas was introduced at a rate of 3.3L / min using a laboratory blower at a room temperature of 25°C, and the mixture was left to react for 120 minutes to obtain a slurry of neutral magnesium carbonate (MgCO3·3H2O). 1L of this slurry was placed in a 4L pot mill filled with 1kg of zirconia balls with a diameter of 8mm, and wet-milled for 24 hours at a rotation speed of 90 rpm. A portion of the slurry after wet-milling was filtered and dried, resulting in a neutral magnesium carbonate with a BET specific surface area of 21m 2 The pH was 1.0 / g and the average particle size was 7.8 μm. To the 8-L SUS container, 6 L of water was added, along with the neutral magnesium carbonate slurry after wet milling, so that the "MgCO3·3H2O" content was 51.7 g. The pH immediately after addition was 9.3. The same procedure as in Example 1 was then repeated, except that the reaction was completed by stirring for 1 hour. A sample powder of the product was obtained.

[0104] [Example 5] 250 g of coarsely crushed brucite ore (under 2 mm) was placed in a 4-liter pot mill filled with 1 kg of zirconia balls with a diameter of 8 mm, and 1 L of pure water was placed in the pot mill. The mixture was then wet-ground at 90 rpm for 24 hours. A portion of the slurry obtained after wet-grounding was filtered and dried, and the BET specific surface area of the brucite obtained was 15 m. 2 The solubility was 1 / g and the average particle size was 3.8 μm. To the 8 L SUS container, 6 L of water was added and the wet-milled brucite slurry was added so that the "Mg(OH)2" content was 22.0 g. The pH value immediately after addition was 10.6. Otherwise, the same procedure as in Example 1 was carried out to obtain a sample powder of the product.

[0105] [Comparative Example 1] 6L of water discharged from the company was placed in an 8L SUS container with a baffle plate, and then the quicklime hydrate slag "Ca(OH)2" (slag that passed the 45μm sieve after hydrating quicklime, BET specific surface area: 14m) generated in the company was poured into the container. 2 / g, average particle size: 50 μm) was added and mixed (Ca / Ca2+ (molar ratio: 1.0). The pH value immediately thereafter was 12.6. Except for this, the same procedure as in Example 1 was carried out to obtain a sample powder of the product.

[0106] Comparative Example 2 A mixed slurry of 6980 g of slaked lime powder (calculated as CaO), 630 g of aragonite seed crystal powder, and 500 g of disodium hydrogen phosphate dodecahydrate was prepared by stirring a 220 L stainless steel vessel equipped with a baffle and containing 180 L of water. The mixture was then heated to 70 °C and stirred at 150 rpm using a stirrer equipped with a single turbine blade. A flue gas extraction pipe was connected to the exhaust outlet of an LNG-fueled steam production boiler. A test blower was used to draw in the flue gas. Measurements using a CO2 meter (XP-3140, manufactured by New Cosmos Electric Co., Ltd.) revealed a CO2 concentration of 10% by volume. The test blower was used to introduce flue gas into the 220 L stainless steel vessel at a rate of 100 L / min, and the reaction was carried out for 7 hours. Thereafter, the solid was filtered, washed with about five times as much water as the solid content, dried at 110°C for 24 hours, and pulverized to obtain a powder sample of the product.

[0107] [Table 2]

[0108] [Table 3]

[0109] As shown in Tables 2 and 3, the calcium carbonate obtained in the Examples had smaller particle sizes, less variation in primary particle size, and better dispersibility than the Comparative Examples. It is also clear that the physical properties of the resin compositions containing calcium carbonate as a filler were improved compared to the Comparative Examples.

[0110] <Evaluation for concrete use> Using calcium carbonate of Example 1 (spherical polyhedron) and Comparative Example 2 (acicular), the measurement of the P funnel flow-down time, 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 it 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 type and amount 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 it 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] The P funnel flow time was measured in accordance with the "Test method for fluidity of injection mortar for prepacked concrete (method using P funnel)" (JSCE-F521-1999). The outlet of the P funnel was held with a finger, and each of the prepared cement milks was poured up to the mark on the P funnel (1750 ml). Measurement was started as soon as the finger was released using a time watch, and the time until the cement milk was discharged from the P funnel was measured.

[0115] <Production of cement molded body> [Example 6-1] 400 mL of the prepared cement milk 1 was poured into a cylindrical polyethylene bag (approximately 50 mm in diameter x approximately 550 mm in length x approximately 0.05 mm in thickness) up to the marked line. After injecting as much air as possible and sealing the bag, the bag was hung in an incubator set at 22°C. The bag was left hanging in the incubator for 28 days to harden the contents, producing a total of three cement molded bodies. The resulting cement molded bodies were cylindrical, approximately 5 cm in diameter and 20 cm in length.

[0116] [Examples 6-2 to 6-3 and Comparative Examples 6-1 to 6-4] A cement molded body was produced in the same manner as in Example 6-1, except that the cement milk shown in the following Table 5 was used. In Comparative Example 6-4, the cement milk was not discharged from the P funnel, so evaluation could not be performed.

[0117] (density) The density was measured in accordance with JIS A 5430:2008 (apparent density test).

[0118] (Compression strength test) The compressive strength of the resulting cement compact was measured in accordance with JIS A 1108:2018 (Method for compressive testing of concrete).

[0119] [Table 5]

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

[0121] <Evaluation for building materials> (Molded plate manufacturing) Molded plates were manufactured by extrusion molding according to the following procedure. The amounts of the components used are all expressed in "parts by mass" unless otherwise specified. In the table below, "-" indicates that the corresponding component was not used.

[0122] [Example 7-1] Manufacturing of molded plate by extrusion molding method The materials shown in Table 6 below were charged into an omnimixer, and the raw materials were dry-mixed for 3 minutes. The calcium carbonate used was the calcium carbonate of Example 1. Next, water was added and wet-mixed for 2 minutes. The wet-mixed raw materials were kneaded in an Ishikawa extruder, and then extrusion-molded using the Ishikawa extruder. This produced a molded body (long side 600 mm x short side 190 mm x thickness 13 mm). After obtaining the molded body, it was placed in a thermo-hygrostat set at 60°C / 98% for primary curing, and then autoclave-cured for 12 hours at a pressure of 9 kgf. Both sides of the molded body were sanded with a sander to reduce the thickness to 12 mm, producing a molded plate.

[0123] [Comparative Example 7-1] Production of molded plate by extrusion molding method A molded plate was obtained in the same manner as in Example 7-1, except that the materials and contents shown in Table 6 below were used and calcium carbonate was not added.

[0124] <Evaluation of molded plates> The molded plates produced by extrusion molding in the examples and comparative examples were evaluated as follows. The results are shown in Table 4.

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

[0126] (3-point bending test) The three-point bending test was carried out in accordance with JIS A 5430. The results were used to calculate the strength of the formed plate (N / mm 2 ) was decided.

[0127] (heating test) The heating test was carried out using the following equipment and procedure. Figure 8 is a partial perspective view that shows a schematic diagram of the heating tester. As shown in Figure 8, an electric heater was used as the heat source, and fireproof material was installed between the test specimen and the heat source to stabilize the temperature at around 900°C, and a thermocouple was used to measure the temperature on the backside of the test specimen. Specifically, an electric heater (1.2 kW heater) was used as the heat source, and a K-type thermocouple and a temperature controller were connected. Each thermocouple was also connected to a data logger. The distance between the heating surface of the test specimen and the heat source was fixed at approximately 70 mm.

[0128] The test procedure was as follows. (1) A scrap board was placed, preheated to 902°C, and then heated once. (2) The specimen was inserted after the heated surface had cooled to below 200°C. (3) A thermocouple was placed in the center of the back surface (top surface in the figure) of the test specimen, and a calcium silicate plate (approximately 30 mm x 70 mm) and a weight were placed on top and fixed in place. (4) Heating was started, and the sample was left for the specified time (45 minutes), after which the temperatures on the front and back sides were recorded with a data logger. During this time, the temperature setting of the electric heater was set to 902°C on the heating surface side, and the temperature was controlled with a temperature controller with a lower limit of 900°C. The data logger also measured the temperature every 10 seconds, and the data was recorded at this interval. (5) After the test was completed, the specimen was removed and the following items were measured (each item was also measured before the test): Dimensions: The length and width of the back surface and heating surface were measured with a vernier caliper. The area of the heating surface (mm 2 ) was calculated, and the heating surface shrinkage (%) was calculated based on the following formula. Heating surface shrinkage (%) = {|S1-S0| / S0} x 100 (where S0 is the area of the heated surface before the test, and S1 is the area of the heated surface after the test.) Warpage: The specimen was placed on an iron surface plate, and the height of the center of each side of the specimen from the iron surface plate was measured with a thickness gauge, and the average value (mm) was calculated. This average value was taken as the warpage (mm) after heating. - Photographs of the sample before and after the test (photos showing the extent of cracks before and after heating)

[0129] [Table 6]

[0130] The molded plates of the Examples were superior to the Comparative Examples in strength, heating surface shrinkage, and post-heating warpage. Furthermore, the molded plates of the Examples did not develop cracks after heating (not shown).

Claims

1. A method for producing calcium carbonate, comprising a step of contacting seawater, calcium-containing water remaining after producing magnesium hydroxide from seawater, or a mixture thereof with an alkaline agent and a gas containing carbon dioxide at a pH of 9 or higher and lower than 11, the alkaline agent is magnesium hydroxide, magnesium oxide, or neutral magnesium carbonate; The method for producing calcium carbonate, wherein the calcium carbonate has an average particle size of 5 μm or less as determined by a laser diffraction method.

2. 2. The method for producing calcium carbonate according to claim 1, wherein the seawater, utilized water, or a mixture thereof, the alkaline agent, and the gas are contacted in the following order 1) or 2): 1) After the seawater, utilized water or a mixture thereof is brought into contact with the alkaline agent, the gas is further brought into contact with the seawater, utilized water or a mixture thereof. 2) After the alkaline agent and the gas are brought into contact with each other, the seawater, utilized water, or a mixture thereof is further brought into contact with each other.

3. The method for producing calcium carbonate according to claim 1 or 2, wherein the alkaline agent is magnesium hydroxide or magnesium oxide.

4. The method for producing calcium carbonate according to claim 1 or 2, wherein the temperature in the contacting step is 50°C or lower.

5. 3. The method for producing calcium carbonate according to claim 1, wherein the concentration of calcium in the seawater, utilized water, or a mixture thereof is 300 ppm or more and 3000 ppm or less.

6. The method for producing calcium carbonate according to claim 1 or 2, wherein the gas is exhaust gas from a combustion engine.

7. 3. The method for producing calcium carbonate according to claim 1, wherein the concentration of carbon dioxide in the gas is 1% by volume or more and 20% by volume or less.

8. The method for producing calcium carbonate according to claim 1 or 2, wherein the calcium carbonate is calcite.

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