Method for producing aragonite-like calcium carbonate

Abstract

This invention provides a novel method for producing aragonite-like calcium carbonate from vaterite-like calcium carbonate, which allows for the efficient and simple production of aragonite-like calcium carbonate without the need for seed crystals of aragonite-like calcium carbonate. [Solution] The present invention provides a method for producing aragonite-like calcium carbonate, which involves preparing vaterite-like calcium carbonate by reacting a calcium ion-containing aqueous solution with a carbonate ion-containing aqueous solution at a pH of 7 to 9.7, and then immersing the prepared vaterite-like calcium carbonate in water at 65 to 95°C to produce aragonite-like calcium carbonate.

Description

[Technical Field]

[0001] The present invention relates to a method for producing aragonite-like calcium carbonate, and more particularly to a method for producing needle-shaped aragonite-like calcium carbonate from spherical vaterite-like calcium carbonate. [Background technology]

[0002] Calcium carbonate is used in a wide range of industrial fields as a filler in cement, pharmaceuticals, plastics, resins, rubber, paper, paints, and cosmetic ingredients, and is utilized to improve various physical properties. It is also used in agriculture and the food industry.

[0003] Calcium carbonate exists in three crystalline forms with different crystalline structures: calcite, aragonite, and vaterite. Calcite and aragonite are naturally occurring, and in water at room temperature, calcite is in a stable phase, aragonite in a metastable phase, and vaterite is highly unstable. Furthermore, vaterite calcium carbonate is usually spherical, while aragonite calcium carbonate has a needle-like shape.

[0004] When using calcium carbonate in building materials, a form with a larger aspect ratio, such as needle-shaped aragonite-like calcium carbonate, is expected to have increased strength because the particles intertwine more tightly than crystalline forms with a smaller aspect ratio, such as calcite or vaterite.

[0005] Vaterite calcium carbonate does not occur naturally, and its crystalline structure is less stable than that of aragonite and calcite. Therefore, in the presence of water, it undergoes a crystalline transformation to become calcite-like. Furthermore, argonite-like calcium carbonate is produced in various forms, such as coral limestone, but its production volume is insufficient. There is a growing demand for it, particularly as a plastic filler, coating pigment, and concrete additive. However, when attempting to artificially produce aragonite, there is a problem in that it is often mixed with a large amount of calcite.

[0006] A common method for producing aragonite-like calcium carbonate is the heterogeneous precipitation method, which involves directly blowing carbon dioxide gas into a calcium hydroxide solution to produce calcium carbonate. However, this method is complicated and has many constraints on reaction conditions, so to efficiently produce aragonite-like calcium carbonate, it is necessary to prepare seed crystals of aragonite-like calcium carbonate in advance and add them.

[0007] Japanese Patent Publication No. 2-302317 (Patent Document 1) describes a method for producing aragonite calcium carbonate by adding a divalent or trivalent metal salt to a vaterite-type calcium carbonate aqueous suspension (vaterite emulsion), and then heating the vaterite emulsion at 40°C or higher to cause a crystallization transition of vaterite-type calcium carbonate to aragonite-type calcium carbonate.

[0008] Furthermore, Japanese Patent Publication No. 2002-293537 (Patent Document 2) describes a method for producing calcium carbonate that includes a carbon dioxide absorption step of absorbing carbon dioxide in the exhaust gas of a combustion furnace or the like with a 6-12% aqueous caustic soda solution by gas-liquid contact to produce a sodium carbonate solution with a sodium carbonate concentration of 8-15%, a step of hydrating quicklime to produce lime milk, and a carbonation step of reacting the lime milk with the sodium carbonate solution produced in the carbon dioxide absorption step, thereby producing spindle-shaped or columnar calcium carbonate.

[0009] Furthermore, Japanese Patent Publication No. 7382091 (Patent Document 3) describes a method for producing aragonite crystalline calcium carbonate while efficiently utilizing carbon dioxide contained in exhaust gases that will be discharged into the atmosphere. This method includes: a carbon dioxide absorption step in which a gas containing carbon dioxide is introduced into an aqueous sodium hydroxide solution to obtain an aqueous sodium carbonate solution; a hydration step in which calcium oxide is reacted with an aqueous sodium hydroxide solution with a concentration of 0 to less than 6% by mass to obtain an aqueous calcium hydroxide dispersion; and a carbonation step in which the aqueous sodium carbonate solution is added to the aqueous calcium hydroxide dispersion so that the rate of addition of sodium carbonate per mole of calcium hydroxide in the aqueous calcium hydroxide dispersion is 0.25 moles / min or less to obtain calcium carbonate. The BET specific surface area is 2.0 to 15.0 m². 2 A method for producing calcium carbonate containing aragonite-based calcium carbonate as the main component is disclosed, with a concentration of / g.

[0010] However, conventional methods for producing aragonite-like calcium carbonate have several drawbacks: the reaction conditions are complex, the manufacturing process is cumbersome, the method is not economical, and the resulting calcium carbonate tends to be calcite-like. Therefore, it is not a simple method that can sufficiently transfer aragonite-like calcium carbonate from vaterite-like calcium carbonate to calcite-like calcium carbonate. Therefore, a simple method is desired that can transfer vaterite-like calcium carbonate to aragonite-like calcium carbonate. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2-302317 [Patent Document 2] Japanese Patent Publication No. 2002-293537 [Patent Document 3] Patent No. 7382091 [Overview of the project] [Problems that the invention aims to solve]

[0012] The problem that the present invention aims to solve is to provide a novel method for producing aragonite-like calcium carbonate that solves the above-mentioned problems and allows for the efficient and simple production of aragonite-like calcium carbonate from vaterite-like calcium carbonate without the need for seed crystals of aragonite-like calcium carbonate. [Means for solving the problem]

[0013] To solve the above problems, the method for producing aragonite-like calcium carbonate of the present invention has the following technical features. (1) The present invention provides a method for producing aragonite-like calcium carbonate, characterized in that a vaterite-like calcium carbonate prepared by reacting a calcium ion-containing aqueous solution with a carbonate ion-containing aqueous solution at a pH of 7 to 9.7 is immersed in water at 65 to 95°C to produce aragonite-like calcium carbonate.

[0014] (2) A preferred method for producing aragonite-like calcium carbonate of the present invention is the method for producing aragonite-like calcium carbonate of the present invention, characterized in that the vaterite-like calcium carbonate is immersed in water at 65 to 95°C so that the concentration is 1.5 to 3.5% by mass. (3) A more preferable method for producing aragonite-like calcium carbonate according to the present invention is the method for producing aragonite-like calcium carbonate according to (2) above, characterized in that when the vaterite-like calcium carbonate is immersed in water at a temperature of 65 to 95°C, the aspect ratio of the agoranite-like calcium carbonate obtained decreases as the temperature increases.

[0015] (4) A more preferred method for producing the aragonite calcium carbonate of the present invention is the method for producing aragonite calcium carbonate according to the above (1) or (2), wherein the aqueous calcium solution is a solution in which an inorganic compound selected from the group consisting of calcium chloride, calcium nitrate, calcium nitrite and calcium hydroxide is dissolved, and the aqueous solution containing carbonate ions is a solution in which an inorganic compound selected from the group consisting of sodium carbonate, potassium carbonate and ammonium carbonate is dissolved. This is a method for producing aragonite calcium carbonate.

Effects of the Invention

[0016] The method for producing aragonite calcium carbonate of the present invention can efficiently prepare aragonite calcium carbonate from vaterite calcium carbonate by a very simple method, so that aragonite calcium carbonate can be prepared at a low cost, and the obtained aragonite calcium carbonate can be economically provided to a wide range of industrial fields including the plastic industry and the like.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing the relationship between the pH when producing vaterite calcium carbonate and the production rate of the obtained vaterite calcium carbonate. [Figure 2] It is another chart diagram by X-ray diffraction method (XRD) showing the relationship between the pH when producing vaterite calcium carbonate and the crystal form of the obtained calcium carbonate. [Figure 3] It is a chart diagram by X-ray diffraction method (XRD) showing the relationship between the pH when producing vaterite calcium carbonate and the crystal form of the obtained calcium carbonate. [Figure 4] It is a chart diagram by X-ray diffraction method (XRD) showing the relationship between the temperature of pure water in which vaterite calcium carbonate is immersed and the crystal form of the obtained calcium carbonate. [Figure 5]This chart, obtained by X-ray diffraction (XRD), shows the relationship between the immersion time when vaterite calcium carbonate is immersed in pure water at 70°C and the resulting crystalline form of calcium carbonate. [Figure 6] This chart, obtained by X-ray diffraction (XRD), shows the relationship between the immersion time when vaterite calcium carbonate is immersed in pure water at 82°C and the resulting crystalline form of calcium carbonate. [Figure 7] This chart, obtained by X-ray diffraction (XRD), shows the relationship between the immersion time when vaterite calcium carbonate is immersed in pure water at 90°C and the resulting crystalline form of calcium carbonate. [Figure 8] Figure 5 is an electron microscope image of calcium carbonate obtained. [Figure 9] Figure 6 is an electron microscope image of calcium carbonate obtained. [Figure 10] Figure 7 is an electron microscope image of calcium carbonate obtained. [Figure 11] This figure shows the relationship between the temperature of the pure water in which the vaterite-like calcium carbonate is immersed, the reaction time, and the aspect ratio. [Figure 12] This chart, obtained by X-ray diffraction (XRD), shows the relationship between the immersion time and the crystalline form of calcium carbonate obtained when calcium carbonate prepared at pH 10 (outside the scope of the present invention, containing 20% ​​by mass of calcite-like calcium carbonate and 80% by mass of vaterite-like calcium carbonate) is immersed in pure water at 82°C. [Modes for carrying out the invention]

[0018] The method for producing aragonite-like calcium carbonate according to the present invention will be described in detail with reference to the following preferred embodiments, but the present invention is not limited to the following embodiments. The present invention provides a method for producing aragonite-like calcium carbonate, which involves reacting a calcium ion-containing aqueous solution with a carbonate ion-containing aqueous solution at a pH of 7 to 9.7 to prepare vaterite-like calcium carbonate, and then immersing the prepared vaterite-like calcium carbonate in water at 65 to 95°C to produce aragonite-like calcium carbonate.

[0019] Thus, the present invention provides a method for producing aragonite-like calcium carbonate, which involves reacting an aqueous solution containing calcium ions, obtained by dissolving calcium chloride or the like in water, with an aqueous solution containing carbonate ions, obtained by dissolving sodium carbonate or the like in water, under the above-mentioned specific pH conditions to produce vaterite-like calcium carbonate. The vaterite-like calcium carbonate thus produced is then immersed in water within the above-mentioned specific temperature range to transfer the vaterite-like calcium carbonate to aragonite-like calcium carbonate, thereby preparing aragonite-like calcium carbonate.

[0020] The aqueous solution containing calcium ions used to prepare the vaterite-like calcium carbonate used in the present invention is not particularly limited and can be used as long as it is an aqueous solution containing calcium ions. Furthermore, the calcium material used to prepare the aqueous solution containing calcium ions is not particularly limited as long as it is a calcium-containing material that can dissolve in water and generate calcium ions in the water. For example, inorganic compounds such as calcium chloride, calcium nitrate, calcium nitrite, and calcium hydroxide can be used. In addition, calcium (Ca)-containing waste can also be used, such as incinerated ash from general waste and industrial waste, fly ash discharged from thermal power plants, slag, waste concrete, ready-mix concrete sludge, and bio-ash. Calcium-containing waste materials are preferably processed to have a particle size of 1000 μm or less, more preferably 500 μm or less, and within a range of 100 μm or more. This makes it easier to extract calcium into water.

[0021] As the aqueous solution containing calcium ions, the calcium ion-containing aqueous solution obtained by dissolving the above-mentioned calcium material in water is applied to the present invention. Furthermore, as a specific example of a method for obtaining an aqueous solution containing calcium ions using calcium-containing waste as a calcium material, for example, hydrochloric acid water can be added to calcium-containing waste to dissolve the calcium and produce a crude aqueous solution containing calcium ions. The hydrogen ion concentration index of the aqueous solution containing calcium ions can then be adjusted, and impurities such as Si, Al, Mg, and heavy metal components can be separated from the crude calcium ion-containing aqueous solution to prepare an aqueous solution containing calcium ions for producing vaterite-like calcium carbonate used in the present invention.

[0022] To dissolve calcium in calcium-containing waste by adding hydrochloric acid solution, hydrochloric acid solution is added to the calcium-containing waste with adjusted particle size, preferably so that the pH of the hydrogen ion concentration index is in the range of less than 2.5. At this time, if necessary, washing water such as clean water may be added, and this washing is performed in order to replace the liquid contained in the solids with clean water during solid-liquid separation. The temperature of the aqueous solution containing hydrochloric acid used for calcium extraction is preferably above room temperature, and more preferably in the range of 20°C to 70°C. Calcium is dissolved and separated into a residue and a calcium ion-containing aqueous solution. The residue can then be used, for example, as a cement raw material in cement manufacturing equipment.

[0023] Furthermore, by adjusting the pH of the calcium ion-containing aqueous solution to, for example, pH 5-6 using sodium hydroxide or potassium hydroxide, it is possible to remove Si and Al ions contained in the calcium ion-containing aqueous solution as a gel. If necessary, washing water such as clean water can be added to wash away any solid components. These gels can be used as raw materials for cement.

[0024] Next, the pH of the Ca ion-containing aqueous solution, after removing Si and Al ions, can be adjusted to, for example, pH 7-10 using sodium hydroxide or potassium hydroxide to separate heavy metals such as Pb and Cr ions derived from calcium-containing waste. Furthermore, if necessary, washing water such as clean water can be added to wash away any solid components.

[0025] Furthermore, before removing the heavy metals mentioned above, it is possible to add a flocculant to the Ca ion-containing aqueous solution as needed. Examples of flocculants include polymer flocculants and inorganic flocculants. Examples of inorganic flocculants include iron salts such as ferric polysulfate, or aluminum salts such as aluminum sulfate and polyaluminum chloride. As for polymer flocculants, any flocculant suitable for the pH and particle properties of anionic, nonionic, or cationic flocculants can be used, and examples include polyacrylamide-based, sodium polyacrylate-based, and polyacrylic acid ester-based flocculants.

[0026] Furthermore, by adjusting the pH of the Ca ion-containing aqueous solution from which the heavy metal ions have been removed to 11.5-12.5 using sodium hydroxide or potassium hydroxide, it becomes possible to remove Mg ions contained in the aqueous solution derived from calcium-containing waste as a gel. In addition, if necessary, washing water such as clean water can be added, and this washing will remove any solid components.

[0027] A calcium ion-containing aqueous solution, such as a calcium ion-containing aqueous solution from which the above-mentioned unwanted impurities have been separated and removed, is to be combined with an aqueous solution containing carbonate ions to produce vaterite-like calcium carbonate used in the present invention under specific pH conditions of pH 7 to 9.7, preferably pH 7.0 to 9.0, and more preferably pH 7.0 to 8.0. If necessary, the pH of the calcium ion-containing aqueous solution can be adjusted to the acidic side by adding hydrochloric acid or the like, and then an aqueous solution containing carbonate ions can be added to this to react and precipitate vaterite-like calcium carbonate crystals. By setting the pH conditions during this reaction to be within the above range, vaterite-like calcium carbonate used in the present invention can also be produced. Aragonite-like calcium carbonate according to the present invention can be prepared by using vaterite-like calcium carbonate obtained by reacting a calcium ion-containing aqueous solution with a carbonate ion-containing aqueous solution under pH conditions within the above range. If the pH is below 7, the mixture becomes acidic, causing the calcium carbonate to dissolve and making it impossible to obtain it as a solid. If the pH exceeds 9, calcite-like calcium carbonate is formed, making it impossible to effectively apply the method of the present invention. The vaterite-like calcium carbonate prepared under these specific pH conditions can be recovered by separating it from the potassium chloride and / or sodium chloride aqueous solutions produced as by-products after the reaction.

[0028] The solution containing carbonate ions is not particularly limited, but a solution containing an inorganic compound that produces carbonate ions when dissolved in water, such as sodium carbonate, potassium carbonate, or ammonium carbonate, can be used.

[0029] Next, the vaterite-like calcium carbonate obtained in this way is immersed (reacted) in water to prepare aragonite-like calcium carbonate. The water temperature should be 65-95°C, preferably 70-95°C, and more preferably 80-95°C. This temperature allows for the efficient preparation of aragonite-like calcium carbonate from vaterite-like calcium carbonate. Immersing the vaterite-like calcium carbonate prepared as described above in water outside the above temperature range, especially in water below 60°C, is impractical because it is difficult for the vaterite-like calcium carbonate to be converted into argonite-like calcium carbonate.

[0030] Furthermore, when immersing (reacting) in water at 65-95°C, the aspect ratio of the resulting aragonite-like calcium carbonate tends to decrease as the temperature increases. In other words, the longer axis grows at low temperatures, and the shorter axis grows thicker at high temperatures, so it is possible to adjust the aspect ratio of the needle-shaped aragonite by adjusting the immersion temperature. Here, aspect ratio refers to the ratio of length (major axis) to width (minor axis) in an image of a needle-shaped crystal (for example, an electron microscope image).

[0031] Furthermore, any water such as tap water or purified water can be used to immerse vaterite-like calcium carbonate to produce aragonite-like calcium carbonate, but it is particularly desirable to use purified water. Here, "purified water" means highly pure water that contains almost no impurities, and examples include water prepared by ion exchange, distillation, filtration, reverse osmosis membrane treatment, etc. The electrical conductivity of such purified water is not particularly limited, but it is preferably 0.1 to 1.0 μS / cm. Moreover, purified water also includes ultrapure water, which is extremely pure among purified waters, and can be prepared by Milli-Q, etc. The electrical conductivity of ultrapure water is not particularly limited, but it is preferably less than 0.1 μS / cm.

[0032] The immersion time in water is not particularly limited and should be sufficient to allow the transformation from vaterite calcium carbonate to aragonite calcium carbonate. For example, aragonite calcium carbonate can be obtained by immersing for about 1 hour or more, preferably 2 hours or more.

[0033] Thus, the method of the present invention makes it possible to easily prepare needle-shaped aragonite-like calcium carbonate in a simple manner that does not require seed crystals. [Examples]

[0034] The present invention will be described with reference to examples and comparative examples, but is not limited thereto. (Examples and comparative examples) (material) • Calcium chloride (special grade reagent; manufactured by Kanto Chemical Co., Ltd.) • Sodium carbonate (special grade reagent; manufactured by Kanto Chemical Co., Ltd.) • Pure water (ion-exchanged water: electrical conductivity is 0.1~1.0 μS / cm)

[0035] Dissolve the above calcium chloride in pure water to obtain 0.2 to 0.5 moles / dm³.-3 A calcium chloride aqueous solution was prepared. Separately, the above sodium carbonate was dissolved in pure water to make 0.2 to 0.5 mol / dm³. -3 A sodium carbonate aqueous solution was prepared. 0.05 mol·dm -3 Aqueous solution of sodium hydroxide or 0.05 mol / dm -3 The calcium chloride aqueous solution was prepared by adding hydrochloric acid aqueous solution to adjust the pH to 500 cm³. 3 Then, 500 cm³ of the sodium carbonate aqueous solution 3 After adding the calcium carbonate and allowing it to react with carbonate ions while stirring, the pH during crystallization was adjusted to the values ​​shown in Figures 1 and 2-3. The resulting calcium carbonate was then filtered and dried using acetone to prepare calcium carbonate.

[0036] Figure 1 shows the variation in the amount of vaterite calcium carbonate produced depending on the pH of a mixture obtained by reacting an aqueous solution of calcium chloride (calcium ion-containing aqueous solution) obtained by dissolving calcium chloride in pure water with an aqueous solution of sodium carbonate (carbonate ion-containing aqueous solution) obtained by dissolving sodium carbonate in pure water. From Figure 1, it can be seen that when the reaction is carried out under conditions where the pH is between 7 and 9.7, the resulting calcium carbonate is 100% vaterite calcium carbonate. The rate of vaterite-like calcium carbonate formation was calculated using Rao's formula, based on the intensities of the vaterite and calcite diffraction peaks in the X-ray diffraction (XRD) patterns of calcium carbonate obtained at each pH. The particle size of the obtained vaterite was 3–5 μm.

[0037] Figures 2 and 3 are XRD charts showing the crystal forms obtained by X-ray diffraction of the resulting calcium carbonate when the pH of the mixed solution obtained by reacting the calcium chloride aqueous solution (calcium ion-containing aqueous solution) obtained by dissolving calcium chloride in pure water with the sodium carbonate aqueous solution (carbonate ion-containing aqueous solution) obtained by dissolving sodium carbonate in pure water is (a) 9.7, (b) 10.0, (c) 10.8, (d) 11.3, (f) 7.0, (g) 8.0, and (h) 9.0. From FIGS. 2 and 3, it can be seen that by carrying out the reaction under the conditions where the pH is 7 to 9.7, the calcium carbonate obtained is 100% vaterite calcium carbonate.

[0038] Next, as a representative example of the conditions within the scope of the present invention, 5.0 g (concentration 2.5% by mass) of 100% vaterite calcium carbonate obtained by reacting under the conditions of (h) above (pH is 9.0) was added to 200 cm of pure water at each temperature of 60°C, 70°C, 77°C, 82°C, and 95°C. 3 It was immersed therein, stirred for 2 hours, and the calcium carbonate obtained by filtration was dried. The situation of the crystal form of the calcium carbonate is shown in the graphical chart by X-ray diffraction (XRD) of the calcium carbonate (FIG. 4).

[0039] From FIG. 4, when the temperature is 60°C, aragonite calcium carbonate is not generated. When the temperature of the pure water is 70°C, 77°C, 82°C, and 95°C within the range of 65 to 95°C of the present invention, as shown in FIG. 4, by immersing vaterite calcium carbonate for a sufficient time, it can be seen that aragonite calcium carbonate is generated. Furthermore, the numerical values of the aragonite formation rate (%) in FIG. 4 show the values obtained by calculating the formation rate of aragonite calcium carbonate from Wada's formula using the diffraction peak intensities of calcite calcium carbonate and aragonite calcium carbonate. For example, at an immersion temperature of 77°C, the aragonite formation rate was 90.1%.

[0040] Also, in FIGS. 5 to 7, 5.0 g (concentration 2.5% by mass) of 100% vaterite calcium carbonate obtained by reacting under the conditions of (h) above (pH is 9.0) was added to 200 cm of pure water at each temperature of 70°C, 82°C, and 90°C. 3 It was immersed therein, and the situation of the crystal form of each calcium carbonate after stirring for 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours is respectively shown in the graphical chart of X-ray diffraction (XRD) of the calcium carbonate. Also, in FIGS. 8 to 10, scanning electron micrographs (SEM) of each calcium carbonate obtained at each immersion time of 1 hour, 2 hours, 3 hours or 1.5 hours, 2 hours, 3 hours in FIGS. 5 to 7 are shown. These figures show that aragonite-like calcium carbonate is produced by immersing vaterite-like calcium carbonate in pure water at a temperature of 65-95°C for a sufficient amount of time, for example, more than one hour.

[0041] Furthermore, 5.0 g (2.5% by mass concentration) of 100% vaterite-like calcium carbonate obtained by reacting under the conditions of (h) above (pH 9.0) was added to 200 cm³ of pure water at each temperature shown in Figure 11. 3 Figure 11 shows the relationship between the aspect ratio of aragonite-like calcium carbonate obtained after immersion and stirring for 1, 2, and 3 hours, the temperature of the pure water used for immersion, and the immersion time (reaction time). From Figure 11, it can be seen that the aspect ratio decreases with time and decreases almost linearly with increasing temperature. In other words, the lower the immersion temperature, the larger the aspect ratio of the produced aragonite-like calcium carbonate, indicating growth in the long axis direction and an increase in the aspect ratio, while the short axis grows as the immersion temperature increases. For example, the aspect ratio obtained by immersing the object in 70°C pure water for 3 hours was 33.4. The aspect ratio is the average of the aspect ratios obtained by measuring the major and minor axes of 100 arbitrary particles when the generated aragonite-like calcium carbonate is imaged using an electron microscope (SEM).

[0042] On the other hand, 5.0 g (concentration 2.5% by mass) of calcium carbonate obtained by reacting under conditions outside the scope of the present invention, for example, under the conditions of (b) above (pH 10), where 20% by mass is calcite-like calcium carbonate and 80% by mass is vaterite-like calcium carbonate, is mixed with 200 cm³ of water at 82°C. 3 The crystalline structure of each calcium carbonate sample after immersion and stirring for 0, 1, 2, and 3 hours is shown in the X-ray diffraction (XRD) chart of calcium carbonate (Figure 12). Figure 12 shows that while increasing the immersion time does produce some aragonite-like calcium carbonate, the amount of calcite-like calcium carbonate produced increases compared to the initial amount, indicating that sufficient aragonite-like calcium carbonate cannot be obtained.

[0043] Thus, according to the method of the present invention, aragonite-like calcium carbonate can be produced from vaterite-like calcium carbonate in a simple manner. [Industrial applicability]

[0044] The method of the present invention provides aragonite-like calcium carbonate in a simple manner, and can be effectively applied in various fields such as rubber, plastics, paper, paints, cosmetic raw materials, concrete additives, and pharmaceuticals, and can be provided economically.

Claims

1. A method for producing aragonite-like calcium carbonate, characterized by preparing vaterite-like calcium carbonate by reacting a calcium ion-containing aqueous solution with a carbonate ion-containing aqueous solution at a pH of 7 to 9.7, and then immersing the prepared vaterite-like calcium carbonate in water at 65 to 95°C.

2. A method for producing aragonite-like calcium carbonate according to claim 1, characterized in that the vaterite-like calcium carbonate is immersed in water at 65 to 95°C so that its concentration is 1.5 to 3.5% by mass.

3. A method for producing aragonite-like calcium carbonate according to claim 2, characterized in that when the vaterite-like calcium carbonate is immersed in water at a temperature of 65 to 95°C, the aspect ratio of the argoraite-like calcium carbonate obtained decreases as the temperature increases.

4. A method for producing aragonite-like calcium carbonate according to claim 1 or 2, characterized in that the calcium aqueous solution is a solution in which an inorganic compound selected from the group consisting of calcium chloride, calcium nitrate, calcium nitrite, and calcium hydroxide is dissolved, and the carbonate ion-containing aqueous solution is a solution in which an inorganic compound selected from the group consisting of sodium carbonate, potassium carbonate, and ammonium carbonate is dissolved.

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