Method for producing calcium carbonate

Abstract

The present invention provides a method for producing calcium carbonate that can produce calcium carbonate having desired properties regardless of changes in ambient temperature. [Solution] A method for producing calcium carbonate comprising mixing a calcium-containing aqueous solution with a pH of 12.0 ± 0.5 with an aqueous solution of an alkali metal carbonate, and adding an inorganic acid, wherein the addition of the inorganic acid is (1) carried out continuously or intermittently while mixing, or (2) carried out before mixing.

Description

[Technical Field]

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

[0002] Calcium carbonate is widely used in various industrial fields as a filler in building and paving materials such as cement compositions, mortar, concrete, and asphalt; raw materials for processed products such as plastics, resins, rubber, and paper; and materials for products such as paints and cosmetics.

[0003] As a method for producing calcium carbonate, for example, Patent Document 1 discloses a method for producing calcium carbonate that includes a first step of contacting a first solution containing an alkali metal hydroxide with a gas containing carbon dioxide to produce a second solution containing at least one alkali metal salt, such as an alkali metal carbonate or an alkali metal bicarbonate, and a second step of contacting the second solution with a gypsum-containing material to produce calcium carbonate. Also, for example, Patent Document 2 discloses a method for producing calcium carbonate with high opacity, characterized by mixing an aqueous solution containing calcium ions with an aqueous solution containing alkali carbonate, and adjusting the pH of the mixture to 11.5 to 13 to prepare cubic calcium carbonate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2023 / 054239 Brochure [Patent Document 2] Japanese Patent Publication No. 2024-031279 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the above circumstances, and aims to provide a method for producing calcium carbonate that can produce calcium carbonate having desired properties regardless of changes in ambient temperature. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides the following method for producing calcium carbonate. 1. Mixing a calcium-containing aqueous solution with a pH of 12.0 ± 0.5 with an aqueous solution of an alkali metal carbonate, and Adding inorganic acids, Includes, The addition of the inorganic acid is carried out by (1) or (2) below. A method for producing calcium carbonate. (1) The mixing is carried out continuously or intermittently. (2) This is done before the mixing.

[0007] Furthermore, the present invention provides the following method for producing calcium carbonate as a preferred embodiment. 2. The method for producing calcium carbonate according to claim 1, wherein the calcium-containing aqueous solution comprises at least one calcium compound selected from calcium hydroxide and calcium chloride. 3. The method for producing calcium carbonate according to claim 1 or 2 above, wherein the alkali metal carbonate is at least one carbonate selected from sodium carbonate and potassium carbonate. 4. A method for producing calcium carbonate according to any one of 1 to 3 above, wherein the inorganic acid is at least one acid selected from hydrochloric acid, nitric acid, and sulfuric acid. 5. A method for producing calcium carbonate according to any one of 1 to 4 above, wherein the pH of the substances to be mixed during the mixing process is lower than the pH of the calcium-containing aqueous solution. 6. The method for producing calcium carbonate according to item 5, wherein the pH of the substances to be mixed during the mixing process is less than 11.5. 7. The method for producing calcium carbonate according to any one of the above 1 to 6, wherein the mixing is performed at a temperature above 0°C and not higher than 50°C. 8. The method for producing calcium carbonate according to any one of the above 1 to 7, wherein the calcium carbonate has a calcite crystal structure.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a method for producing calcium carbonate that can produce calcium carbonate having desired properties regardless of changes in environmental temperature.

Brief Description of the Drawings

[0009] [Figure 1] These are the particle size distributions of the calcium carbonates of Examples 1, 2 and Comparative Example 1. [Figure 2] These are the particle size distributions of the calcium carbonates of Examples 3, 4 and Comparative Example 2. [Figure 3] These are the particle size distributions of the calcium carbonates of Examples 5 and 6. [Figure 4] These are the SEM photographs of the calcium carbonates of Examples 1, 3 and Comparative Example 1. [Figure 5] These are the SEM photographs of the calcium carbonates of Examples 2, 4 and Comparative Example 2. [Figure 6] These are the SEM photographs of the calcium carbonates of Examples 5 and 6.

Modes for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present invention (hereinafter may be referred to as "the present embodiment") will be described. The present invention is not limited to the following embodiments, and may be arbitrarily modified and implemented within a range that does not impair the effects of the invention. In addition, in the present specification, the numerical values related to "or more", "or less" and "to" in the description of numerical ranges are numerical values that can be arbitrarily combined. For example, when a certain numerical range is described as "CC to DD" and "EE to FF", numerical ranges such as "CC to FF" and "EE to DD" are also included.

[0011] [Method for producing calcium carbonate] The method for producing calcium carbonate in this embodiment is: Mixing a calcium-containing aqueous solution with a pH of 12.0 ± 0.5 with an aqueous solution of alkali metal carbonate, and Adding inorganic acids, Includes, The method involves adding the inorganic acid as described in (1) or (2) below. (1) The mixing is carried out continuously or intermittently. (2) This is done before the mixing.

[0012] As mentioned above, calcium carbonate is used in various industrial fields, but there is a growing demand for calcium carbonate with a particle size distribution suited to its application and with more homogeneous properties, and these required properties are becoming stricter year by year. Regarding particle size distribution, it can vary depending on the application, but calcium carbonate with small particle size, small variation in particle size, and a unimodal particle size distribution is highly versatile and desirable. Furthermore, regarding homogeneous properties, for example, a crystal structure that is closer to a single crystal structure is desirable, and even more so, a single crystal structure is highly versatile and desirable.

[0013] The manufacturing method disclosed in Patent Document 2 yields calcium carbonate that can be used in various applications and has high opacity, making it an extremely useful manufacturing method. Furthermore, since it is possible to prepare an aqueous solution containing calcium ions obtained from calcium-containing waste and use the calcium ions contained in the aqueous solution to produce calcium carbonate, it can be said that this manufacturing method can be adapted to various calcium sources. On the other hand, when the present inventors examined the manufacturing method disclosed in Patent Document 2, they found that in some cases, calcium carbonate with different properties, or more specifically, calcium carbonate with different particle size distributions, could be obtained depending on the manufacturing period. Furthermore, because the resulting calcium carbonate was in an aggregated state, it was sometimes necessary to adjust the particle size by crushing or other means when using it for the desired application. Therefore, the manufacturing method disclosed in Patent Document 2 has room for improvement in terms of producing calcium carbonate with the desired properties regardless of the manufacturing period.

[0014] Furthermore, the manufacturing method described in Patent Document 1 above uses gypsum-containing material as the calcium source. However, it cannot be applied when other calcium sources are used, and the development of a manufacturing method that can accommodate a wider variety of calcium sources is desired.

[0015] The inventors focused on the reaction between calcium-containing aqueous solutions, which include calcium compounds obtained from various calcium sources, and alkali metal carbonates, and conducted research. They confirmed that the reaction between the calcium compounds and alkali metal carbonates, rather than differences in the calcium source, is affected by the manufacturing time. Specifically, they confirmed that the ambient temperature during the reaction between the calcium compounds and alkali metal carbonates affects the properties of the resulting calcium carbonate, such as particle size distribution and crystal structure. Further investigation into this phenomenon revealed that adding an inorganic acid during the reaction between the calcium-containing aqueous solution and alkali metal carbonates can suppress differences in properties due to manufacturing time (which can also be described as differences in properties due to fluctuations in ambient temperature). Thus, the present inventors have provided a method for producing calcium carbonate that can produce calcium carbonate having desired properties regardless of changes in ambient temperature.

[0016] The method for producing calcium carbonate in this embodiment will be explained by mixing a calcium-containing aqueous solution with an aqueous solution containing an alkali metal carbonate.

[0017] [Mixing] The method for producing calcium carbonate in this embodiment involves mixing a calcium-containing aqueous solution with an aqueous solution containing an alkali metal carbonate. By mixing, a reaction occurs between the calcium compound and the alkali metal carbonate, yielding calcium carbonate.

[0018] (Calcium-containing aqueous solution) The calcium-containing aqueous solution used in the manufacturing method of this embodiment is an aqueous solution containing a calcium compound and having a pH of 12.0 ± 0.5. As for the calcium compound to be included in the calcium-containing aqueous solution, considering its reactivity with alkali metal carbonates, calcium hydroxide and calcium chloride are preferred, with calcium chloride being more preferred. In the production method of this embodiment, the calcium compound may be a single compound or a combination of several compounds.

[0019] The pH of the calcium-containing aqueous solution must be 12.0 ± 0.5, i.e., between 11.5 and 12.5. When the pH is within this range, calcium carbonate with the desired properties can be produced regardless of changes in ambient temperature. Furthermore, from the viewpoint of producing calcium carbonate with the desired properties more efficiently regardless of changes in ambient temperature, the pH is preferably 11.6 or higher, more preferably 11.8 or higher, with an upper limit of preferably 12.4 or lower, and more preferably 12.2 or lower.

[0020] The calcium compound content in the calcium-containing aqueous solution is preferably 0.05 mol / L or more, more preferably 0.10 mol / L or more, with an upper limit of preferably 2.0 mol / L or less, and more preferably 1.0 mol / L or less. When the calcium compound content is within the above range, mixing of the calcium-containing aqueous solution and the alkali metal carbonate aqueous solution can be performed more efficiently and smoothly, and it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature.

[0021] Calcium compounds and aqueous solutions containing them may be commercially available products, or, for example, calcium hydroxide may be produced by the hydration reaction of quicklime (calcium oxide) and water, or calcium chloride may be used as a by-product of the production of sodium carbonate by the Solvay process.

[0022] (Production of calcium-containing aqueous solution) Calcium-containing aqueous solutions can be produced by the hydration reaction described above, the Solvay process, etc., but it is preferable to prepare them by the following method. As the calcium-containing aqueous solution, an aqueous solution containing calcium compounds extracted from calcium-containing waste can also be used. From the viewpoint of promoting the effective utilization of waste and reducing the production cost of calcium carbonate, it is preferable to use a calcium-containing aqueous solution extracted from calcium-containing waste. That is, it is preferable that the calcium-containing aqueous solution used in the production method of this embodiment is obtained by a method that includes extracting calcium compounds from calcium-containing waste.

[0023] Extracting calcium compounds from calcium-containing waste can be done, for example, by contacting the calcium-containing waste with hydrochloric acid, or more specifically, by adding hydrochloric acid to the calcium-containing waste or adding the calcium-containing waste to hydrochloric acid. Here, any waste containing calcium can be used without particular restrictions as the calcium-containing waste, and examples of such waste include general waste, industrial waste, and their incinerated ash, as well as fly ash, slag, waste concrete, ready-mix concrete sludge, and bio-ash discharged from cement firing facilities, thermal power plants, etc. The particle size of calcium-containing waste is usually 5 cm or less, and it can be used as is or crushed as needed. From the viewpoint of improving reactivity with hydrochloric acid and facilitating the extraction of calcium compounds, it is preferably 10 μm to 10 mm, and more preferably 100 μm to 5 mm.

[0024] The hydrochloric acid used in contact with the calcium-containing waste can be any hydrochloric acid without particular restrictions. For example, hydrochloric acid obtained by treating an aqueous solution of alkali metal chlorides such as potassium chloride or sodium chloride with bipolar membrane electrodialysis can be used. From the viewpoint of more efficiently extracting calcium from calcium-containing waste, the concentration of hydrochloric acid is preferably 0.2 mol / L or higher, more preferably 0.5 mol / L or higher, with an upper limit of preferably 2.0 mol / L or lower, and more preferably 1.5 mol / L or lower.

[0025] In extracting calcium compounds, the pH is preferably 5 or less, more preferably 4 or less, even more preferably 2.5 or less, and even more preferably less than 2.5. There is no particular lower limit, but considering the ease of operation, it is preferable to set it to 0.5 or higher. When adding hydrochloric acid to calcium-containing waste, washing water may also be added. By adding washing water, the liquid contained in the solids can be replaced with washing water (i.e., clean water), making it easier to obtain a calcium-containing aqueous solution containing higher purity calcium compounds.

[0026] The temperature conditions for extracting calcium compounds are preferably at room temperature (usually around 20°C) or higher than room temperature after heating, more preferably 20°C or higher, with an upper limit of preferably 80°C or lower, and more preferably 70°C or lower, from the viewpoint of efficiently improving the reactivity between calcium-containing waste and hydrochloric acid.

[0027] The extraction of calcium compounds preferably involves contacting the calcium-containing waste with hydrochloric acid followed by purification. This makes it easier to obtain a calcium-containing aqueous solution of higher purity and to produce calcium carbonate with the desired properties regardless of changes in ambient temperature.

[0028] The fluid obtained by contacting calcium-containing waste with hydrochloric acid contains impurities derived from the calcium-containing waste, including calcium compounds, as well as Si and Al ions, heavy metals such as Pb and Cr, and Mg ions. It is preferable to purify the fluid to remove these impurities. Purifying the fluid preferably involves removing Si and Al ions, heavy metals, and Mg ions. By removing these impurities, the resulting calcium-containing aqueous solution is suitable for use as a calcium-containing aqueous solution in the production method of this embodiment. From the viewpoint of more efficient purification, it is more preferable to remove Si and Al ions, heavy metals, and Mg ions in that order.

[0029] The removal of Si and Al ions can be carried out, for example, by contacting the calcium-containing waste with hydrochloric acid to obtain a fluid, adjusting the pH of the fluid using an alkali metal hydroxide selected from sodium hydroxide, potassium hydroxide, etc., to form a gel containing Si and Al. The alkali metal hydroxide may be a single hydroxide or a combination of multiple hydroxides. The pH of the above fluid is preferably 5 to 8, more preferably 6 to 7. This promotes the formation of a gel containing Si and Al, and allows for more efficient removal of Si and Al ions. The Si and Al gel thus obtained can be reused as a cement raw material.

[0030] Heavy metals such as Pb and Cr can be removed by adjusting the pH of the fluid after the removal of Si and Al ions using an alkali metal hydroxide selected from sodium hydroxide, potassium hydroxide, etc. The alkali metal hydroxide may be used as a single type of hydroxide or as a combination of multiple types of hydroxides. The pH of the above fluid is preferably 7 to 11, more preferably 8 to 10. This allows for more efficient removal of heavy metals.

[0031] Furthermore, when removing heavy metals, a flocculant can be added. Adding a flocculant makes the removal of heavy metals more efficient. Preferred flocculants include inorganic flocculants such as iron salts like ferric polysulfate, aluminum salts such as aluminum sulfate and polyaluminum chloride, and polymer flocculants such as polyacrylamide, sodium polyacrylate, and polyacrylic acid ester.

[0032] Furthermore, the removal of Mg ions can be carried out by adjusting the pH of the fluid after the removal of the heavy metals described above using an alkali metal hydroxide selected from sodium hydroxide, potassium hydroxide, etc. The alkali metal hydroxide may be used as a single type of hydroxide or as a combination of multiple types of hydroxides. The pH of the above fluid is preferably 11.0 or higher, more preferably 11.5 or higher, with an upper limit of preferably 12.5 or lower, more preferably 12.0 or lower. This allows for more efficient removal of Mg ions.

[0033] The fluid obtained in this way is a calcium-containing aqueous solution with few impurities and high purity of calcium compounds. Furthermore, since the pH of the resulting aqueous solution containing calcium compounds is in the range of 11.0 to 12.5, it can be used as a calcium-containing aqueous solution with a pH of 12.0 ± 0.5 in the manufacturing method of this embodiment without adjusting the pH or with only slight pH adjustment.

[0034] (Aqueous solution of alkali metal carbonate) The aqueous solution of alkali metal carbonate used in the manufacturing method of this embodiment can be any aqueous solution containing alkali metal carbonate without any particular restrictions. Sodium carbonate and potassium carbonate are preferred examples of alkali metal carbonates. In the manufacturing method of this embodiment, one type of alkali metal carbonate may be used alone, or a combination of multiple types of carbonates may be used.

[0035] Alkali metal carbonates may be commercially available products, or they may be obtained using carbon dioxide contained in combustion exhaust gases emitted from various facilities such as cement firing equipment and thermal power plants. In the manufacturing method of this embodiment, it is preferable to use a carbonate obtained using the above-mentioned combustion exhaust gas as the alkali metal carbonate. This can reduce the amount of carbon dioxide emitted from various facilities such as cement firing facilities and thermal power plants, and contribute to reducing the environmental burden.

[0036] A method for producing alkali metal carbonates using combustion exhaust gases discharged from various facilities includes, for example, a method that involves contacting an alkali metal hydroxide selected from sodium hydroxide, potassium hydroxide, etc., with combustion exhaust gases discharged from various facilities. This causes a reaction between the alkali metal hydroxide and carbon dioxide contained in the combustion exhaust gas, yielding alkali metal carbonates. There are no particular restrictions on the method of contacting the alkali metal hydroxide with the combustion exhaust gases discharged from various facilities, and any known method may be used.

[0037] The alkali metal carbonate content of the aqueous solution of alkali metal carbonate is preferably 0.05 mol / L or more, more preferably 0.1 mol / L or more, with an upper limit of preferably 2.0 mol / L or less, and more preferably 1.0 mol / L or less. When the alkali metal carbonate content is within the above range, mixing of the calcium-containing aqueous solution and the alkali metal carbonate aqueous solution can be carried out more efficiently and smoothly, and it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature.

[0038] (mixture) There are no particular restrictions on the method for mixing a calcium-containing aqueous solution with an alkali metal carbonate aqueous solution, as long as the fluids containing these solutions (also referred to as "substances to be mixed") can be mixed. For example, the alkali metal carbonate aqueous solution may be added to the calcium-containing aqueous solution and mixed, or the calcium-containing aqueous solution may be added to the alkali metal carbonate aqueous solution and mixed. In this case, the addition of the alkali metal carbonate aqueous solution and the calcium-containing aqueous solution may be done continuously or intermittently (i.e., dropwise). Alternatively, the entire amounts of the calcium-containing aqueous solution and the alkali metal carbonate aqueous solution may be introduced into a mixing apparatus and mixed there.

[0039] From the viewpoint of more efficiently mixing a calcium-containing aqueous solution with an aqueous solution containing an alkali metal carbonate and more efficiently producing calcium carbonate, it is preferable to continuously add the aqueous solution containing the alkali metal carbonate or the calcium-containing aqueous solution, and more preferably to continuously add the aqueous solution containing the alkali metal carbonate.

[0040] In this case, the amount to add can vary depending on the concentration of the aqueous solution and the total amount of the aqueous solution used, so it is difficult to give a general answer. However, when adding an aqueous solution containing alkali metal carbonate, the amount to add is equal to the total number of moles (M) of calcium compounds contained in the calcium-containing aqueous solution. Ca The number of moles of alkali metal carbonate contained in an aqueous solution containing alkali metal carbonate (M) CO3 ) ratio (M CO3 / M Ca The ratio is preferably 1.0 or higher, more preferably 1.05 or higher, and even more preferably 1.1 or higher, with a preferred upper limit of 1.5 or lower. Furthermore, the amount added when a calcium-containing aqueous solution is added is the above ratio (M CO3 / M CaThe amount of additive is preferably 1.1 or less, more preferably 1.05 or less, and even more preferably 1.0 or less, with a lower limit of preferably 0.9 or more. By using such an amount, the reaction between the calcium compound and the alkali metal carbonate can proceed more reliably and efficiently, making it easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature. In addition, the properties of the resulting calcium carbonate will be more uniform.

[0041] The mixing of a calcium-containing aqueous solution and an aqueous solution containing an alkali metal carbonate is preferably carried out using equipment such as a mixer or agitator. Examples of agitators and mixers include mechanical agitators equipped with agitating blades in the mixing tank for stirring. Examples of mechanical agitators include high-speed agitators and dual-arm mixers. Examples of high-speed agitators include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used.

[0042] When mixing a calcium-containing aqueous solution with an aqueous solution containing an alkali metal carbonate, the temperature of the fluid (the substance to be mixed) containing these aqueous solutions is preferably greater than 0°C and 50°C or less, more preferably between 15°C and 35°C, and even more preferably between 20°C and 30°C. When the temperature of the substance to be mixed is within the above range, the reaction between the calcium compound and the alkali metal carbonate is promoted, and calcium carbonate can be produced more efficiently. Furthermore, it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and the properties of the resulting calcium carbonate become more uniform.

[0043] When mixing a calcium-containing aqueous solution and an alkali metal carbonate aqueous solution, it is preferable that the pH of the fluid containing these solutions (the mixture) be lower than the pH of the calcium-containing aqueous solution (less than the pH of the calcium-containing aqueous solution). The specific numerical value of the pH of the mixture is not general, as it should be lower than the pH of the calcium-containing aqueous solution and will vary depending on the method of adding the inorganic acid described later. However, it is preferably 12.0 or lower, more preferably 11.8 or lower, and even more preferably 11.5 or lower. There is no particular lower limit; for example, it should be 0.5 or higher, preferably 1.5 or higher, and more preferably 2.5 or higher. The pH of the mixture can be adjusted by adding the inorganic acid described later. By keeping the pH of the mixture within the above range, the reaction between the calcium compound and the alkali metal carbonate is promoted, allowing for more efficient production of calcium carbonate. Furthermore, it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and the properties of the resulting calcium carbonate become more uniform.

[0044] The mixing time (which can also be called the reaction time between the calcium compound and the alkali metal carbonate) for mixing a calcium-containing aqueous solution with an aqueous solution containing an alkali metal carbonate can vary depending on the amount being mixed and therefore cannot be generalized, but it is usually 3 minutes or more, preferably 5 minutes or more, and the upper limit is usually 3 hours or less, preferably 2 hours or less. If the mixing time is within the above range, The reaction between calcium compounds and alkali metal carbonates is accelerated, allowing for more efficient production of calcium carbonate. Furthermore, it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and the properties of the resulting calcium carbonate become more uniform. When mixing a calcium-containing aqueous solution with an alkali metal carbonate aqueous solution by continuously or intermittently adding either of these solutions, the entire amount should be added during the mixing time described above. Similarly, when adding an inorganic acid, as described later, while mixing the calcium-containing aqueous solution with the alkali metal carbonate aqueous solution, the entire amount should be added during the mixing time described above.

[0045] [Adding inorganic acid] The manufacturing method of this embodiment includes the addition of an inorganic acid. By adding an inorganic acid, the pH of the fluid (the substance to be mixed) containing the calcium-containing aqueous solution and the alkali metal carbonate aqueous solution can be adjusted when these aqueous solutions are mixed, as described above.

[0046] The addition of inorganic acids is carried out by (1) or (2) below. (1) The mixing is carried out continuously or intermittently. (2) This is done before the mixing. Thus, in the manufacturing method of this embodiment, it can be said that at least the calcium-containing aqueous solution and the aqueous solution containing an alkali metal carbonate must be mixed in the presence of an inorganic acid. By mixing in the presence of an inorganic acid, it becomes possible to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and the properties of the resulting calcium carbonate become more uniform.

[0047] As for the inorganic acid, any inorganic acid can be used without particular restrictions. From the viewpoint of making it easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and ensuring that the properties of the resulting calcium carbonate are more uniform, inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid are preferred, with hydrochloric acid being preferred among them.

[0048] The concentration of the inorganic acid is preferably 0.1 mol / L or higher, more preferably 0.2 mol / L or higher, with an upper limit of preferably 2.0 mol / L or lower, more preferably 1.5 mol / L or lower, and even more preferably 1.0 mol / L or lower. When the concentration of the inorganic acid is within the above range, it becomes easier to adjust the pH of the mixture, making it easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature, and the properties of the resulting calcium carbonate can be made more uniform.

[0049] The addition of the inorganic acid may be appropriately performed according to the pH behavior of the fluid (mixing target) including the calcium-containing aqueous solution and the aqueous solution containing the alkali metal carbonate, and may be performed in accordance with the above methods (1) and (2) so that the mixing target has a desired pH.

[0050] In the case of the method (1), for example, the inorganic acid may be added while adding and mixing the aqueous solution containing the alkali metal carbonate to the calcium-containing aqueous solution, the inorganic acid may be added while adding and mixing the calcium-containing aqueous solution to the aqueous solution containing the alkali metal carbonate, or the inorganic acid may be added while mixing after the entire amount of the calcium-containing aqueous solution and the aqueous solution containing the alkali metal carbonate is introduced into an apparatus. In this case, as described above, the inorganic acid may be added continuously or intermittently.

[0051] In the case of the method (2), for example, the aqueous solution containing the alkali metal carbonate may be added after the inorganic acid is added to the calcium-containing aqueous solution, the calcium-containing aqueous solution may be added after the inorganic acid is added to the aqueous solution containing the alkali metal carbonate, or the inorganic acid may be added and then mixed after the entire amount of the calcium-containing aqueous solution and the aqueous solution containing the alkali metal carbonate is introduced into an apparatus. In this case, it is preferable to add the aqueous solution containing the alkali metal carbonate after adding the inorganic acid to the calcium-containing aqueous solution, or to add the calcium-containing aqueous solution after adding the inorganic acid to the aqueous solution containing the alkali metal carbonate.

[0052] The addition rate of the inorganic acid may be appropriately adjusted according to the pH behavior, and cannot be unconditionally specified because it may vary depending on the total usage amount of the aqueous solution, but the addition amount of the inorganic acid is defined as the total number of moles of the inorganic acid (M A ), the ratio of the total number of moles of the calcium compound contained in the calcium-containing aqueous solution (M Ca ) (M Ca / M AThe pH is preferably 3.0 or higher, more preferably 5.0 or higher, with an upper limit of preferably 30.0 or lower, more preferably 25.0 or lower. By using such an amount, it becomes easier to adjust the pH of the mixture, and it becomes easier to produce calcium carbonate with the desired properties regardless of changes in ambient temperature. In addition, the properties of the resulting calcium carbonate become more uniform. The inorganic acid should be added in the above amount as appropriate within the above mixing time.

[0053] When adding an inorganic acid, the decrease in pH of the fluid (the substance to be mixed) containing the calcium-containing aqueous solution and the alkali metal carbonate aqueous solution is preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.5 or more, relative to the pH of the calcium-containing aqueous solution. Furthermore, as an upper limit, when the inorganic acid is added by the method described in (1) above, it is preferably 5.0 or less, more preferably 4.0 or less. When the inorganic acid is added by the method described in (2) above, the pH may decrease to a maximum of about 9.5 (i.e., the decrease may be 9.5 or more), and together with the addition of the calcium-containing aqueous solution or the alkali metal carbonate aqueous solution, it will be within the same range of decrease as when the method described in (1) above is used.

[0054] [Other operations] The manufacturing method of this embodiment may also include drying the fluid containing calcium carbonate obtained by the above mixing. By drying, powdered calcium carbonate can be obtained. In addition, depending on the application, calcium carbonate may be used in slurry form, in which case drying is not necessary.

[0055] The fluid containing calcium carbonate obtained by the above mixing includes not only calcium carbonate but also water from the calcium-containing aqueous solution and the aqueous solution containing alkali metal carbonate, which are the substances to be mixed. Therefore, when using the calcium carbonate obtained by the manufacturing method of this embodiment as a powder, it is preferable to dry it.

[0056] The drying method is not particularly limited as long as calcium carbonate powder can be obtained. For example, the calcium carbonate-containing fluid can be dried by filtration using a glass filter, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge. Alternatively, it may be dried by heating using a dryer, for example.

[0057] [Properties of calcium carbonate] As described above, the calcium carbonate obtained by the manufacturing method of this embodiment has the desired properties. Specifically, it has the following properties. Calcium carbonate may have at least one crystalline structure of calcite, vaterite, and aragonite, but the calcium carbonate obtained by the manufacturing method of this embodiment will have at least a calcite crystalline structure. The calcite crystalline structure content is usually 90% by volume or more, and may further have a single crystalline structure of 95% by volume or more, 98% by volume or more, 99% by volume or more, 99.5% by volume or more, 99.9% by volume or more, and 100% by volume. Thus, the calcium carbonate obtained by the manufacturing method of this embodiment has a calcite crystalline structure and may have a single crystalline structure of calcite. The crystalline structure of calcium carbonate can be confirmed by powder X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) images. Furthermore, the content ratio of the calcite crystalline structure can be determined by methods such as using the diffraction pattern obtained by powder X-ray diffraction (XRD) measurements and calculating it from the peak intensity using the formula of Rao et al. (Bull. Chem. Soc. Japan, Vol.45, No.5, 1414-1417, MSRao (1973)), or by quantitative analysis using Rietveld analysis.

[0058] Regarding the particle size of calcium carbonate, D10 is defined as 0.5 μm or more, more specifically 1.0 μm or more, with an upper limit of 15.0 μm or less, and more specifically 12.0 μm or less; D50 is defined as 1.0 μm or more, more specifically 2.0 μm or more, with an upper limit of 25.0 μm or less, and more specifically 20.0 μm or less; and D90 is defined as 3.0 μm or more, more specifically 5.0 μm or more, with an upper limit of 150.0 μm or less, and more specifically 80.0 μm or less, and 60.0 μm or less. Here, D10 is the particle size at 10% of the cumulative volume in the laser diffraction scattering particle size distribution method, D50 is the particle size at 50% of the cumulative volume in the laser diffraction scattering particle size distribution method, and D90 is the particle size at 90% of the cumulative volume in the laser diffraction scattering particle size distribution method. For more specific measurement methods, follow the methods in the examples.

[0059] Regarding the particle size of calcium carbonate, the D90-D10 ratio is 80.0 μm or less, further 50.0 μm or less, and 25.0 μm or less. There is no particular lower limit, but it is usually 3.0 μm or more, and further 5.0 μm or more. The smaller the D90-D10 ratio, the smaller D90 is relative to D10, so it can be used as an indicator that the particle size is more uniform and the powder is less prone to aggregation. As the D90-D10 ratio of the calcium carbonate obtained by the manufacturing method of this embodiment is small as described above, it can be said that the particle size is uniform and the powder is less prone to aggregation.

[0060] Furthermore, regarding the particle size of calcium carbonate, the D50 / D90 ratio is 0.30 or higher, more specifically 0.35 or higher, and 0.40 or higher. There is no particular upper limit, but it is usually 0.80 or lower, more specifically 0.75 or lower, and 0.70 or lower. The larger the D50 / D90 ratio, the smaller D90 is relative to D50, so it can be used as an indicator that the particle size is more uniform and the powder is less prone to aggregation. As the D50 / D90 ratio of the calcium carbonate obtained by the manufacturing method of this embodiment is large as described above, it can be said that the particle size is uniform and the powder is less prone to aggregation.

[0061] The presence or absence of aggregation of calcium carbonate obtained by the manufacturing method of this embodiment can be determined by the D90-D10 and D50 / D90 values ​​mentioned above. It can also be determined by the particle size distribution. For example, if the particle size distribution shows a single peak, it can be determined that there is no aggregation or that even if there is aggregation, the degree is low and does not cause any problems, and if it shows two or more peaks, it can be determined that aggregation has occurred. The presence or absence of aggregation of calcium carbonate can be determined using the D90-D10 and D50 / D90 values ​​mentioned above, as well as the particle size distribution, and can also be determined comprehensively based on these values ​​and the particle size distribution.

[0062] As described above, the calcium carbonate obtained by the manufacturing method of this embodiment is a powder that does not easily aggregate, which offers advantages such as making it easier to prepare paints without aggregation when used as a paint filler. Furthermore, when used for purposes other than paints, aggregated calcium carbonate cannot be used as is, requiring processing such as grinding. Since the calcium carbonate obtained by the manufacturing method of this embodiment does not easily aggregate, processing such as grinding is not necessary, reducing energy loss and enabling efficient utilization.

[0063] The calcium carbonate obtained by the manufacturing method of this embodiment has secondary particle diameters of 1.0 μm or more, and more specifically, 2.0 μm or more, with an upper limit of typically 30.0 μm or less. Here, for any 10 samples of calcium carbonate powder, the particle diameter of the secondary particles is defined as the longest major axis of the largest secondary particle in the SEM image obtained using a scanning electron microscope (SEM), and the average value of the 10 samples is used as the particle diameter. [Examples]

[0064] The present invention will now be specifically described with reference to examples, but the present invention is not limited in any way by these examples.

[0065] (Example 1) In a reaction vessel equipped with a stirring blade and placed in a constant temperature bath, 1000 mL of a calcium-containing aqueous solution (pH=12.0, calcium chloride content: 0.613 mol / L, temperature: 5°C) containing calcium chloride as the calcium compound was added. While rotating the stirring blade, 100 mL of hydrochloric acid (concentration: 1.0 M, temperature: 5°C) was added as an inorganic acid to adjust the pH to 3.0. Then, 1350 mL of an aqueous solution containing sodium carbonate (sodium carbonate content: 0.5 mol / L, temperature: 5°C) as the alkali metal carbonate was added at an addition rate of 120 mL / min (added over approximately 11 minutes). Stirring with the stirring blade was continued for 10 minutes to bring the calcium-containing aqueous solution with the sodium carbonate aqueous solution into contact and react the calcium chloride with sodium carbonate. During the contact between the calcium chloride aqueous solution and the sodium carbonate aqueous solution, the pH of the mixture fluctuated between 3.0 and 11.0. The constant temperature bath was set to 5°C, and the temperature of the mixture was maintained at 5°C. After stopping the stirring blade and terminating the reaction, the resulting fluid was separated into solid and liquid components using a solid-liquid separator, and the solid components were dried in a dryer at a temperature of 110°C to obtain calcium carbonate powder. The amount of alkali metal carbonate used was determined by the number of moles (M) of calcium atoms contained in the calcium-containing aqueous solution. Ca The number of moles of carbonate ions contained in an aqueous solution of alkali metal carbonate (M) CO3 ) ratio (M CO3 / M Ca The amount was 1.1 as the total number of moles of inorganic acid (M A The total number of moles of calcium compounds in the calcium-containing aqueous solution (M) Ca ) ratio (M Ca / M A ) was 6.1.

[0066] The obtained calcium carbonate powder was pre-treated by ultrasonic treatment (ultrasonic output: 40W, irradiation time: 30 seconds) using a laser diffraction scattering particle size distribution analyzer ("MT3000 (model number)", manufactured by Microtrac-Bell Co., Ltd.), and then the volume-based particle size distribution was measured. Table 1 shows the particle size corresponding to a cumulative frequency of 10 volume percent (D10), 50 volume percent (D50), and 90 volume percent (D90), starting from the smallest particle size. Figure 1 shows the particle size distribution.

[0067] Figure 4 shows a scanning electron microscope (SEM) image of the obtained calcium carbonate powder, taken with a "S-3400N" (model number), manufactured by Hitachi High-Tech Fielding Co., Ltd. As shown in the SEM image in Figure 4, the particle size of the secondary calcium carbonate particles was 2.2 μm.

[0068] Furthermore, when the obtained calcium carbonate powder was measured by X-ray diffraction (XRD) using an X-ray diffractometer ("X'Pert-PRO MPD (model number)", manufactured by PANanalytical), a diffraction peak appeared around 2θ = 29.4°, confirming that it was composed of a single crystal with a calcite crystal structure.

[0069] (Example 2) In a reaction vessel equipped with a stirring blade and placed in a constant temperature bath, 5000 mL of a calcium-containing aqueous solution (pH=12.0, calcium chloride content: 0.525 mol / L, temperature: 5°C) containing calcium chloride as the calcium compound was added. While rotating the stirring blade, 5780 mL of an aqueous solution containing sodium carbonate (sodium carbonate content: 0.5 mol / L, temperature: 5°C) as the alkali metal carbonate was added at an addition rate of 120 mL / min (added over approximately 47 minutes). Hydrochloric acid (concentration: 1.0 M, temperature: 5°C) was added as the inorganic acid to maintain the pH of the mixture at 11.5 (total added amount: 120 mL). Stirring with the stirring blade was continued for 10 minutes to bring the calcium-containing aqueous solution containing calcium chloride into contact with the aqueous solution containing sodium carbonate, and to react the calcium compound with the alkali metal carbonate. The constant temperature bath was set to 5°C, and the temperature of the mixture was maintained at 5°C. After stopping the stirring blade and terminating the reaction, the resulting fluid was separated into solid and liquid components using a solid-liquid separator, and the solid component was dried in a dryer at a temperature of 110°C to obtain calcium carbonate powder. The number of moles of calcium atoms contained in the calcium-containing aqueous solution (M Ca The number of moles of carbonate ions contained in an aqueous solution of alkali metal carbonate (M) CO3 ) ratio (M CO3 / M Ca ) was calculated to be 1.1. Also, the total number of moles of inorganic acid (M A The total number of moles of calcium compounds in the calcium-containing aqueous solution (M) Ca ) ratio (M Ca / M A The value was 21.9.

[0070] The particle size distribution of the obtained calcium carbonate was measured in the same manner as in Example 1. The results are shown in Table 1, the particle size distribution in Figure 1, and the SEM image in Figure 4. Furthermore, X-ray diffraction (XRD) measurements were performed in the same manner as in Example 1, confirming that it is composed of single crystals with a calcite crystal structure.

[0071] (Examples 3 and 5) In Example 1, calcium carbonate was prepared in the same manner as in Example 1, except that the temperature of the constant temperature bath was set to the temperature shown in Table 1. The particle size distribution and crystal structure of the obtained calcium carbonate were measured. These results are shown in Table 1, the particle size distribution is shown in Figures 2 and 3, and SEM images are shown in Figures 4 and 6. Furthermore, when X-ray diffraction (XRD) measurements were performed in the same manner as in Example 1, the calcium carbonate of Example 3 was composed of a single crystal with a calcite crystal structure, and the calcium carbonate of Example 5 showed diffraction peaks due to the calcite crystal structure as well as diffraction peaks due to the vaterite crystal structure (2θ=27.0°), confirming that it contained both calcite and vaterite crystal structures.

[0072] (Examples 4 and 6) In Example 2, calcium carbonate was prepared in the same manner as in Example 2, except that the temperature of the constant temperature bath was set to the temperature shown in Table 1. The particle size distribution and crystal structure of the obtained calcium carbonate were measured. These results are shown in Table 1, the particle size distribution is shown in Figures 2 and 3, and SEM images are shown in Figures 5 and 6. Furthermore, X-ray diffraction (XRD) measurements were performed in the same manner as in Example 1, and it was confirmed that the calcium carbonate was composed of a single crystal with a calcite crystal structure.

[0073] (Comparative Examples 1 and 2) In Examples 1 and 3, calcium carbonate for Comparative Examples 1 and 3 were obtained in the same manner as in Examples 1 and 3, except that hydrochloric acid was not added. The particle size distribution and crystal structure of the obtained calcium carbonate were measured. These results are shown in Table 1, the particle size distribution is shown in Figures 1 and 2, and SEM images are shown in Figures 4 and 5. Furthermore, X-ray diffraction (XRD) measurements were performed in the same manner as in Example 1, and it was confirmed that the calcium carbonate was composed of a single crystal with a calcite crystal structure.

[0074] [Table 1] *1, a: added before mixing, b: added while mixing *2, C: Calcite crystal structure, V: Vaterite crystal structure

[0075] From the results of the examples, it was confirmed that the properties of the calcium carbonate obtained by the manufacturing method of this embodiment are generally consistent regardless of temperature changes, i.e., changes in ambient temperature. More specifically, in terms of particle size distribution, it was confirmed that the obtained calcium carbonate has a small D90, small variation in particle size, a unimodal particle size distribution, and is of high quality with uniform particle size. Furthermore, the results shown in Figures 4-6 confirm that the calcium carbonate obtained in the examples exists as secondary particles in the form of aggregates of minute primary particles. It was also confirmed that it easily separates into primary particles when actually used. Therefore, it was confirmed that the calcium carbonate obtained by the manufacturing method of this embodiment does not undergo aggregation and is of excellent quality.

[0076] On the other hand, the results from Comparative Examples 1 and 2 showed that when inorganic acid was not added, the resulting calcium carbonate had significantly different particle sizes depending on the ambient temperature, and in all cases, the D50 and D90 values ​​were extremely high. From the results in Figures 4 and 5, it was confirmed that the calcium carbonate obtained in the comparative examples had aggregated primary particles to such an extent that the presence of primary particles could not be confirmed. Furthermore, it was necessary to crush it before actual use, and it could not be used as is. Therefore, the calcium carbonate in the comparative examples had aggregated particles and could not be considered high-quality calcium carbonate.

[0077] Regarding the crystal structure, all calcium carbonates obtained in the examples had a calcite crystal structure, and it was confirmed that the calcium carbonates of Examples 1-4 and 6 had a single calcium crystal structure. Furthermore, powder X-ray diffraction (XRD) measurements of the calcium carbonate of Example 5 showed diffraction peaks (2θ=27.0°) attributable to the vaterite crystal structure in addition to the calcite crystal structure (2θ=29.4°), confirming that it also possessed a vaterite crystal structure. Quantitative analysis using Rietveld analysis from the XRD pattern revealed that the calcite crystal structure content was 34.6% (vaterite crystal structure content was 65.4%), confirming that the majority was calcite.

Claims

1. Mixing a calcium-containing aqueous solution with a pH of 12.0 ± 0.5 with an aqueous solution of an alkali metal carbonate, and Adding inorganic acids, Includes, The addition of the inorganic acid is carried out by (1) or (2) below. A method for producing calcium carbonate. (1) The mixing is carried out continuously or intermittently while mixing is taking place. (2) This is done before the mixing.

2. The method for producing calcium carbonate according to claim 1, wherein the calcium-containing aqueous solution comprises at least one calcium compound selected from calcium hydroxide and calcium chloride.

3. The method for producing calcium carbonate according to claim 1 or 2, wherein the alkali metal carbonate is at least one carbonate selected from sodium carbonate and potassium carbonate.

4. The method for producing calcium carbonate according to claim 1 or 2, wherein the inorganic acid is at least one acid selected from hydrochloric acid, nitric acid, and sulfuric acid.

5. The method for producing calcium carbonate according to claim 1 or 2, wherein the pH of the substances to be mixed during the mixing process is lower than the pH of the calcium-containing aqueous solution.

6. The method for producing calcium carbonate according to claim 5, wherein the pH of the substances to be mixed during the mixing process is 12.0 or less.

7. The method for producing calcium carbonate according to claim 1 or 2, wherein the mixing is performed at a temperature greater than 0°C and less than or equal to 50°C.

8. A method for producing calcium carbonate according to claim 1 or 2, wherein the calcium carbonate has a calcite crystal structure.

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