Manufacturing method of calcium carbonate and calcium carbonate

Abstract

To provide a method for efficiently manufacturing calcium carbonate having high content of aragonite and small particle size and calcium carbonate thereof.SOLUTION: A manufacturing method of calcium carbonate includes: preparing a calcium hydroxide water dispersion having a concentration of 10-23 mass%; adding 5.0 pts.mass or over of a strontium compound to a solid content mass of calcium hydroxide existing in the calcium hydroxide water dispersion to obtain a calcium hydroxide water dispersion containing a strontium compound; and adding a sodium carbonate aqueous solution having a concentration of 5-24 mass% to the calcium hydroxide water dispersion containing the strontium compound to obtain calcium carbonate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Calcium carbonate (CaCO3) is used as a base material and filler for various industrial products, and is also widely used in the agricultural and food industries. Various methods are known for synthesizing calcium carbonate, and a method can be selected depending on the desired calcium carbonate.

[0003] The main crystalline polymorphs of calcium carbonate are calcite, aragonite, and vaterite. Of these, aragonite is an acicular particle known to have a higher density and refractive index than other crystalline polymorphs. Therefore, the optical anisotropy and physical properties of aragonite are expected to lead to new applications. However, aragonite is a metastable phase, and can undergo a phase transition to calcite during long-term storage. The phase transition from aragonite to calcite is particularly accelerated when aragonite contains calcite.

[0004] Meanwhile, synthesized calcium carbonate is used as an inorganic filler in paper, rubber, sealing materials, plastics, and the like. For example, calcium carbonate can be used to fill paper to improve its whiteness and opacity, or added to rubber to improve its mechanical strength and abrasion resistance. Adding calcium carbonate to sealing materials can adjust the viscosity and thixotropy of the sealing material, while adding calcium carbonate to plastics can improve the mechanical strength and adjust the thermal properties of the plastic. Numerous attempts have been made to produce calcium carbonate with the desired particle size, BET specific surface area, and crystalline form for various applications, and methods for producing aragonite, in particular, have been proposed.

[0005] Patent Document 1 discloses a method for producing calcium carbonate characterized by producing aragonite calcium carbonate. The method disclosed in Patent Document 1 is a so-called carbon dioxide method for producing calcium carbonate, in which carbon dioxide gas is introduced into an aqueous suspension of calcium hydroxide having a concentration of 8-40% by weight and a temperature of 15-60°C to carry out a carbonation reaction, and proposes that the reaction be carried out in the presence of a crystal nucleating agent. The present inventors have also proposed a method for producing calcium carbonate with a very high aragonite content by utilizing a causticizing method (Patent Document 2). In this method, the BET specific surface area of ​​the primary particles is 15 m 2 It is possible to produce relatively large particles of less than 15 m / g. However, the BET specific surface area is 2 It has been difficult to produce particles smaller than 1 / g. It is generally known that the particle size of calcium carbonate correlates with the temperature during synthesis, and the particles tend to become smaller when synthesized at a lower temperature. However, synthesis at a lower temperature may also result in a lower aragonite content. Thus, there is a need to develop a method for producing calcium carbonate that has both a high aragonite content and a small particle size. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 59-223225 [Patent Document 2] Patent application 2022-162355 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel method for producing calcium carbonate having a high aragonite content and a small particle size. [Means for solving the problem]

[0008] The present invention provides an aqueous dispersion of calcium hydroxide having a concentration of 10 to 23% by mass, adding 5.0 parts by mass or more of a strontium compound relative to the mass of the solid content of calcium hydroxide present in the calcium hydroxide aqueous dispersion to obtain a calcium hydroxide aqueous dispersion containing the strontium compound; This is a method for producing calcium carbonate, in which an aqueous sodium carbonate solution having a concentration of 5 to 24 mass % is added to an aqueous dispersion of calcium hydroxide containing a strontium compound to obtain calcium carbonate.

[0009] Here, the strontium compound is preferably selected from the group consisting of strontium chloride, strontium bromide, strontium iodide, strontium hydroxide, strontium nitrate, strontium carbonate, and mixtures of two or more thereof. The calcium carbonate produced preferably contains aragonite calcium carbonate as a main component. The content of aragonite calcium carbonate is preferably 99 mass % or more. The BET specific surface area of ​​the produced calcium carbonate is 10.0-20.0m 2 / g is preferred.

[0010] The present invention is directed to a method for producing a polymer having a BET specific surface area of ​​10.0-20.0 m 2 / g, an aspect ratio of 10-20, and an aragonite calcium carbonate content of 99 mass % or more. [Effects of the Invention]

[0011] According to the present invention, calcium carbonate having a high aragonite content and a small particle size can be efficiently produced. The calcium carbonate obtained by the method of the present invention can be used as an additive to sealants, adhesives, inks, and various plastic materials, and is particularly suitable for use in papermaking. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is an electron microscope photograph (magnification: 10,000 times) of the aragonite crystalline calcium carbonate obtained in Example 1. [Figure 2] FIG. 2 is an electron microscope photograph (magnification: 10,000 times) of the aragonite crystalline calcium carbonate obtained in Example 2. [Figure 3] FIG. 3 is an electron microscope photograph (magnification: 10,000 times) of the aragonite crystalline calcium carbonate obtained in Comparative Example 1. [Figure 4] FIG. 4 is an electron microscope photograph (magnification: 10,000 times) of the aragonite crystalline calcium carbonate obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The embodiments of the present invention will be described in more detail below, but the present invention is not limited to the following embodiments.

[0014] In one embodiment of the present invention, a calcium hydroxide aqueous dispersion having a concentration of 10 to 23% by mass is prepared, adding 5.0 parts by mass or more of a strontium compound relative to the mass of the solid content of calcium hydroxide present in the calcium hydroxide aqueous dispersion to obtain a calcium hydroxide aqueous dispersion containing the strontium compound; This is a method for producing calcium carbonate, in which an aqueous sodium carbonate solution having a concentration of 5 to 24 mass % is added to an aqueous dispersion of calcium hydroxide containing a strontium compound to obtain calcium carbonate.

[0015] In one embodiment, calcium carbonate is a calcium carbonate represented by the composition formula CaCO3 and is a main component of seashells, eggshells, limestone, chalk, etc. Calcium carbonate is classified into heavy calcium carbonate (natural calcium carbonate) obtained by crushing and classifying limestone and light calcium carbonate (synthetic calcium carbonate) obtained by chemical reaction. The calcium carbonate used in this embodiment is light calcium carbonate. Therefore, when simply referring to calcium carbonate in this specification, it refers to light calcium carbonate (synthetic calcium carbonate) unless otherwise specified. Calcium carbonate exists in various crystal forms, such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), and vaterite crystals (hexagonal crystals). In one embodiment, calcium carbonate containing calcium carbonate having aragonite crystal form as its main component (referred to as "aragonite calcium carbonate" in this specification) can be produced. Here, "calcium carbonate containing aragonite calcium carbonate as a main component" means that, based on the total mass of calcium carbonate, approximately 98% or more, preferably 99% or more of the calcium carbonate is aragonite calcium carbonate.

[0016] One embodiment is based on a reaction in which an aqueous dispersion containing at least calcium hydroxide (sometimes referred to as "lime milk") is reacted with an aqueous sodium carbonate solution to obtain calcium carbonate (CaCO). This reaction is commonly referred to as a carbonation reaction or a causticization reaction, but is referred to herein as a carbonation reaction. Preferably, the calcium hydroxide concentration in the aqueous calcium hydroxide dispersion is 10-23% by mass, and the sodium carbonate concentration is 5-24% by mass at the beginning of the reaction. The sodium carbonate solution having an adjusted concentration can be added dropwise or gradually to the aqueous calcium hydroxide dispersion, and the reaction can proceed while stirring the reaction solution. Preferably, the sodium carbonate solution is gradually added to the aqueous calcium hydroxide dispersion, and the agitator is adjusted so that the time required for complete mixing (complete mixing time) is 3-25 seconds, or 5-22 seconds. As a means for stirring the reaction vessel, conventionally used propeller stirrers, paddle blade stirrers, ribbon stirrers, turbine blade stirrers, horseshoe blade stirrers, wound blade stirrers, mixer stirrers, magnetic stirrers, etc. can be used.

[0017] The aragonite content can be increased by adding an aqueous sodium carbonate solution so that the rate of addition of sodium carbonate per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion is 0.25 moles / minute or less. If the rate of addition of sodium carbonate per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion is too high, aragonite-type calcium carbonate cannot be obtained. Increasing the rate of addition of sodium carbonate per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion tends to decrease the aragonite-type calcium carbonate content of the resulting calcium carbonate and increase the BET specific surface area. In other words, increasing the rate of addition of sodium carbonate per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion can refine the resulting calcium carbonate. Furthermore, while a lower rate of addition of sodium carbonate per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion is preferable, it is industrially possible to reduce the rate to approximately 0.005 moles / minute.

[0018] The temperature at which the carbonation reaction is carried out is 40-80°C, preferably 45-65°C. If the carbonation reaction temperature is too high or too low, the cost of energy required for heating and cooling increases. Lowering the carbonation reaction temperature tends to produce smaller particle sizes of calcium carbonate, but synthesis at low temperatures also reduces the aragonite content. Furthermore, increasing the reaction temperature in the carbonation reaction tends to result in thicker aragonite (needle-like). It is important to properly balance the temperature during the carbonation reaction with the rate at which sodium carbonate is added per mole of calcium hydroxide in the calcium hydroxide-containing aqueous dispersion.

[0019] It is preferable that a strontium compound be further present in the aqueous dispersion containing calcium hydroxide used in the carbonation reaction. The strontium compound can be selected from the group consisting of strontium chloride, strontium bromide, strontium iodide, strontium hydroxide, strontium nitrate, strontium carbonate, and mixtures of two or more thereof. The strontium compound is preferably added in an amount of 5.0 parts by mass or more relative to the solid mass of calcium hydroxide present in the aqueous dispersion containing calcium hydroxide. Alternatively, the strontium compound can be present in an amount of 0.02-0.06 mol, preferably 0.03-0.05 mol, per mol of calcium hydroxide present in the aqueous dispersion containing calcium hydroxide. In one embodiment, when an aqueous dispersion of calcium hydroxide containing a strontium compound is used in the reaction, the particle size of the calcium carbonate obtained by the carbonation reaction tends to be smaller and the aspect ratio tends to be larger.

[0020] In the reaction according to one embodiment of the production method, calcium carbonate and sodium hydroxide are produced. The water-soluble sodium hydroxide dissolves in the reaction solution, while the less water-soluble calcium carbonate precipitates as a solid. The precipitated calcium carbonate is separated by filtration and dried to obtain calcium carbonate. The BET specific surface area of ​​calcium carbonate produced by the production method of one embodiment is 10-20 m 2 / g, preferably 12-18m 2 / g. Conventionally, calcium carbonate produced by carbonation reaction has a BET specific surface area of ​​10m 2 The calcium carbonate particles had a relatively large particle size of less than 1 / g. According to the present invention, calcium carbonate having a small particle size can be produced. The BET specific surface area can be measured in accordance with Japanese Industrial Standard JIS Z 8830 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption."

[0021] The aspect ratio of primary particles of calcium carbonate produced by the production method of one embodiment is preferably about 2 or more. In this specification, the aspect ratio refers to the aspect ratio (long-to-short ratio) of primary particles of calcium carbonate, i.e., the ratio of the major axis to the minor axis of a primary particle of calcium carbonate. The aspect ratio of calcium carbonate can be measured using an electron microscope. Specifically, it can be calculated by image analysis based on observation using an electron microscope. The aspect ratio of calcium carbonate produced in one embodiment is 10 to 20, preferably 12 to 18.

[0022] In this way, calcium carbonate whose main component is aragonite calcium carbonate, i.e., calcium carbonate having an aragonite calcium carbonate content of 98% by mass or more, preferably 99% by mass or more, can be produced. The aragonite calcium carbonate content can be calculated by measuring peak intensities by powder X-ray diffraction (XRD) for calcium carbonates whose aragonite calcium carbonate contents are known, and creating a calibration curve.

[0023] According to one embodiment, the BET specific surface area of ​​the primary particles is 10-20 m 2 / g, an aspect ratio of 10-20, and a content of aragonite calcium carbonate of 99 mass % or more can be produced.

[0024] The calcium carbonate of the second embodiment produced in the first embodiment has an average particle diameter [D 50 ] is 5-12 μm, preferably 6-10 μm. 50 ] can be calculated based on the number of particles measured using a laser diffraction particle size analyzer. 50 The term "size of higher-order particles formed by aggregation of primary particles of calcium carbonate" refers to the size of higher-order particles formed by aggregation of primary particles of calcium carbonate. In addition, the calcium carbonate of the second embodiment has an aragonite calcium carbonate content of 99 mass % or more, and it is also possible to obtain calcium carbonate consisting entirely of aragonite calcium carbonate.

[0025] When the calcium carbonate of the second embodiment is used as an additive for, for example, sealants, adhesives, inks, plastic compositions, etc., the surface of the calcium carbonate can be treated and used as surface-treated calcium carbonate. In this specification, surface-treated calcium carbonate refers to a state in which the surface of the calcium carbonate is covered with a surface treatment agent, or at least a state in which the surface treatment agent is attached to the surface of the calcium carbonate. In this case, the surface coverage rate of the surface treatment agent per unit BET specific surface area of ​​the calcium carbonate is 0.15-0.60 [% / (m 2 / g)]. The surface coverage rate of the surface-treated calcium carbonate by the surface treatment agent per unit BET specific surface area (i.e., the amount of surface treatment) can be measured from the weight loss after heating (heat loss), and can be measured, for example, by the following method: a specified amount of surface-treated calcium carbonate is weighed out, and the temperature is raised from room temperature using a thermogravimetric analyzer (TG) or the like, and the weight is measured when the temperature reaches 200°C and when the temperature reaches 500°C. The following formula: [Number 1] Heating weight loss ratio [%] = [{(weight of sample at 200°C [g]) - (weight of sample at 500°C [g])} / (weight of sample at 200°C [g])] × 100 The heat loss ratio of the surface-treated calcium carbonate is calculated by the above and divided by the BET specific surface area described above, whereby the surface coverage of the surface-treated calcium carbonate can be determined.

[0026] The surface treatment of calcium carbonate can be carried out using a surface treatment agent containing a substance selected from the group consisting of fatty acids and their derivatives, resin acids and their derivatives, silica, organosilicon compounds, condensed phosphoric acids, and condensed phosphate salts. In this embodiment, it is particularly preferred that the surface treatment be carried out using a surface treatment agent containing a metal salt of a fatty acid, particularly a fatty acid sodium salt or a fatty acid potassium salt. Examples of the fatty acid include saturated and unsaturated fatty acids having 6 to 24 carbon atoms, preferably 10 to 20 carbon atoms. Examples of such fatty acids include hexanoic acid (caproic acid), heptanoic acid (enanthic acid), octanoic acid (caprylic acid), nonanoic acid (pelargonic acid), decanoic acid (capric acid), dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), pentadecanoic acid (pentadecylic acid), hexadecanoic acid (palmitic acid), heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), eicosanoic acid (arachidic acid), docosanoic acid (behenic acid), tetracosanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, myristoleic acid, palmitoleic acid, sapienic acid, eicosenoic acid, and erucic acid. These fatty acids and their metal salts can be used alone or in combination. The surface treatment of calcium carbonate is carried out with a surface coverage rate of 0.15-0.60% / (m 2 / g)], preferably 0.20-0.45[% / (m 2 / g)], more preferably 0.25-0.40 [% / (m 2 / g)].

[0027] The surface treatment of calcium carbonate can be carried out by any known method, for example, by adding at least one of the above-mentioned fatty acids to a slurry containing calcium carbonate and water, followed by dehydration and drying (wet method). For example, the following method can be mentioned as a specific method for surface treating calcium carbonate with an alkali metal salt of a fatty acid.

[0028] A fatty acid is heated in an aqueous solution of an alkali metal such as an aqueous solution of sodium hydroxide or potassium hydroxide to obtain an aqueous solution of a fatty acid alkali metal salt. Next, the aqueous solution of the fatty acid alkali metal salt is added to a slurry of calcium carbonate and water, and the mixture is stirred. This allows the fatty acid alkali metal salt to adhere to the surface of the calcium carbonate.

[0029] The content of the solid content of calcium carbonate in the slurry of calcium carbonate and water may be adjusted appropriately taking into consideration the average particle size of calcium carbonate, the dispersibility of calcium carbonate in the slurry, the ease of dehydration of the slurry, etc. Generally, by adjusting the solid content of the slurry to about 2 to 30 mass %, preferably about 5 to 20 mass %, it is possible to obtain a slurry with an appropriate viscosity, which makes it possible to appropriately perform the surface treatment of calcium carbonate. When the surface coverage rate of the surface treatment agent per unit BET specific surface area of ​​calcium carbonate is 0.15 to 0.60 [% / (m 2 The solid content of the calcium carbonate water slurry, the concentration of the fatty acid alkali metal salt, the stirring time, the stirring speed, etc. can be adjusted so that the calcium carbonate water slurry satisfies the above condition.

[0030] The calcium carbonate water slurry whose surface has been treated with a fatty acid alkali metal salt can be dehydrated by a method such as a filter press. Drying can be performed using a box dryer, for example. In this way, the calcium carbonate of the second embodiment can be surface-treated as needed for use as the papermaking filler of the third embodiment.

[0031] The calcium carbonate of the second embodiment, with or without surface treatment, can be used as an additive to sealants, adhesives, inks, and various plastic materials, and can be particularly preferably used as a filler for papermaking. [Example]

[0032] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0033] [Example 1] Strontium chloride was added to 371 kg of a calcium hydroxide aqueous dispersion (lime milk, concentration 15%) in an amount of 5.4 parts by weight relative to the solid weight of calcium hydroxide to obtain an aqueous dispersion containing calcium hydroxide and strontium chloride. The aqueous dispersion containing calcium hydroxide and strontium chloride was introduced into a reaction tank equipped with a propeller agitator. 560 kg of aqueous sodium carbonate solution (concentration 14.8%) was added thereto over 120 minutes, and the reaction solution was stirred (the addition rate of sodium carbonate per mole of calcium hydroxide in the aqueous dispersion containing calcium hydroxide and strontium chloride was 0.01 mole / min). The propeller agitator was operated to achieve complete mixing in the reaction tank for 21 seconds, and the temperature inside the reaction tank was adjusted to 50°C. The resulting calcium carbonate aqueous slurry was filtered, and the filter cake was washed with water and then dried in a constant temperature dryer at 105°C for 1 hour. 75 kg of calcium carbonate powder was obtained. Observation of the obtained calcium carbonate under an electron microscope revealed that it was aragonite with a needle-like shape and an aspect ratio of 12. Fig. 1 is an electron microscope photograph (magnification 10,000 times) of the calcium carbonate obtained in Example 1. The BET specific surface area of ​​this calcium carbonate (measured according to JIS Z 8830) was 10.0 m 2 / g, and the aragonite content measured by the XRD method was 100%.

[0034] [Example 2] Example 1 was repeated, except that in the reaction of Example 1, the amount of strontium chloride relative to the weight of the solid content of calcium hydroxide in the aqueous dispersion containing calcium hydroxide and strontium chloride was 7.2 parts by weight. 75 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed under an electron microscope, it was found to be aragonite with a needle-like shape and an aspect ratio of 15. Figure 2 is an electron microscope photograph (magnification 10,000 times) of the calcium carbonate obtained in Example 2. The BET specific surface area of ​​this calcium carbonate (measured according to JIS Z 8830) was 12.0 m 2 / g, and the aragonite content measured by the XRD method was 100%.

[0035] [Example 3] Example 1 was repeated, except that in the reaction of Example 1, the amount of strontium chloride relative to the weight of the solid content of the aqueous dispersion containing calcium hydroxide and strontium chloride was 10.8 parts by weight. 75 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed under an electron microscope, it was found to be aragonite with a needle-like shape and an aspect ratio of 18. Figure 3 is an electron microscope photograph (magnification 10,000 times) of the calcium carbonate obtained in Example 3. The BET specific surface area of ​​this calcium carbonate (measured in accordance with JIS Z 8830) was 12.8 m 2 / g, and the aragonite content measured by the XRD method was 100%.

[0036] [Comparative Example 1] Example 1 was repeated, except that in the reaction of Example 1, the amount of strontium chloride relative to the weight of the solid content of the aqueous dispersion containing calcium hydroxide and strontium chloride was 3.6 parts by weight. 75 kg of calcium carbonate powder was obtained. Figure 4 is an electron microscope photograph (magnification 10,000 times) of the calcium carbonate obtained in Comparative Example 1. When observed under an electron microscope, the obtained calcium carbonate was found to be aragonite with a needle-like shape and an aspect ratio of 10. The BET specific surface area of ​​this calcium carbonate (measured in accordance with JIS Z 8830) was 6.5 m 2 / g, and the aragonite content measured by the XRD method was 100%.

[0037] Comparative Example 2 Example 1 was repeated, except that in the reaction of Example 1, the amount of strontium chloride relative to the weight of the solid content of the aqueous dispersion containing calcium hydroxide and strontium chloride was 0 parts by weight (strontium chloride was not added). 75 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed under an electron microscope, it was found to be aragonite with a needle-like shape and an aspect ratio of 5. The BET specific surface area of ​​this calcium carbonate (measured according to JIS Z 8830) was 3.6 m 2 / g, and the aragonite content measured by the XRD method was 100%.

[0038] In the method of the present invention, when an appropriate amount of a strontium compound is present in the reaction system of calcium hydroxide and sodium carbonate, relatively fine aragonite can be produced.

Claims

1. A calcium hydroxide aqueous dispersion having a concentration of 10-23% by mass is prepared. adding 5.0 parts by mass or more of a strontium compound relative to the mass of the solid content of calcium hydroxide present in the calcium hydroxide aqueous dispersion to obtain a calcium hydroxide aqueous dispersion containing the strontium compound; A method for producing calcium carbonate, comprising adding an aqueous sodium carbonate solution having a concentration of 5 to 24 mass % to an aqueous dispersion of calcium hydroxide containing a strontium compound to obtain calcium carbonate.

2. 2. The method of claim 1, wherein the strontium compound is selected from the group consisting of strontium chloride, strontium bromide, strontium iodide, strontium hydroxide, strontium nitrate, strontium carbonate, and mixtures of two or more thereof.

3. 3. The method according to claim 1, wherein the calcium carbonate produced contains aragonite calcium carbonate as a main component.

4. The method according to claim 3, wherein the content of aragonite calcium carbonate is 99% by mass or more.

5. The BET specific surface area of ​​the produced calcium carbonate is 10-20 m ２ The method according to claim 4, wherein the SiO2 content is 1 / g.

6. The BET specific surface area of ​​the primary particles is 10-20m ２ / g, an aspect ratio of 10-20, and a content of aragonite calcium carbonate of 99 mass% or more.

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