Method and system for producing calcium carbonate with high opacity

Abstract

To provide a manufacturing method for calcium carbonate that is capable of synthesizing calcium carbonate having a high whiteness degree and a high hiding property, and a manufacturing system therefor.SOLUTION: A manufacturing method for calcium carbonate having a high hiding property includes a step of blending an aqueous solution containing calcium ions with an aqueous solution containing alkali carbonates, controlling the pH of the mixed liquor to 11.5-13, and preparing cubic calcium carbonate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing calcium carbonate having high hiding power and a production system thereof, and particularly to a method for producing calcium carbonate having high hiding power and a production system thereof that can be used as a filler for plastics, paints, and the like.

Background Art

[0002] Calcium carbonate and titanium oxide are used as fillers for plastics, resins, rubbers, papers, paints, cosmetic raw materials, etc. in a wide range of industrial fields and are used to improve various physical property values. In particular, calcium carbonate with a low refractive index is mainly used as a "extender pigment", and titanium oxide with a high refractive index is mainly used as a "white pigment". As calcium carbonate, there is heavy calcium carbonate prepared by pulverizing high-purity natural limestone and performing classification or the like for particle size adjustment. In addition, there is light calcium carbonate obtained by firing calcium carbonate once to form lime, then reacting with water to digest it into slaked lime, then reacting with carbon dioxide gas to form calcium carbonate again, and recovering, drying, crushing, and classifying it.

[0003] However, limestone (heavy calcium carbonate), which is pulverized calcium carbonate, has a problem that its hiding power is not high and its hiding property is not sufficient. In addition, titanium oxide as a filler is more expensive than calcium carbonate, and further, when filled in resins or the like, there are problems such as deterioration when the coated surface is exposed to sunlight.

[0004] As a method for producing calcium carbonate, for example, Japanese Patent Publication No. 2008-156204 (Patent Document 1) discloses a method for producing light calcium carbonate in the form of fine particles aggregated, characterized by comprising the steps of: (1) obtaining lime milk by wet scalding quicklime; (2) blowing carbon dioxide into a calcium hydroxide suspension obtained by suspending calcium hydroxide in water to carbonize it to a carbonation rate of 20% or less to obtain a colloidal particulate calcium hydroxide suspension; and (3) adding the colloidal particulate calcium hydroxide suspension obtained in step (2) to the lime milk obtained in step (1), blowing carbon dioxide into it, and reacting it until the carbonation rate reaches 100%. This method produces light calcium carbonate in the form of fine particles aggregated, characterized by comprising the steps of: (1) obtaining lime milk in step (1), and (2) blowing carbon dioxide into it to carbonize it to a carbonation rate of 100%. 2 For concentrations of less than / g, the pore volume of 0-1000 Å is 0.05 cm³ as determined by nitrogen adsorption. 3 It is described that a fine particle aggregate form of light calcium carbonate can be obtained with a concentration of 1 / g or more, a pore volume of 250 Å or less in the total pore volume accounting for 25% or more, and an oil absorption capacity of 100 cc / 100 g or more by liquid paraffin. Furthermore, it is described that when the obtained calcium carbonate is used as a filler for printing paper, it can impart excellent ink absorption and opacity (especially opacity after printing) to the printing paper.

[0005] Furthermore, Japanese Patent Publication No. 2012-207346 (Patent Document 2) discloses a calcium carbonate slurry capable of providing an opaque coating layer, and an opaque coated paper having a coating layer containing calcium carbonate, with an average particle size of 0.5 to 1.5 μm and a gradient coefficient (D30 / D70) (wherein DX represents the finer equivalent spherical diameter of the particles by weight) of 40 or more, and coated paper having the calcium carbonate in the coating layer.

[0006] Furthermore, Japanese Patent Publication No. 2002-233851 (Patent Document 3) discloses a method for providing light calcium carbonate coated particles with high whiteness and low abrasion properties, and paper using the same, using calcined ash. This method involves grinding calcined ash so that the average particle size is 3 μm or less, mixing the ground calcined ash particles in an aqueous suspension containing calcium hydroxide, passing carbon dioxide or a carbon dioxide-containing gas through the aqueous suspension to coat the calcined ash particles with light calcium carbonate, and using the light calcium carbonate coated particles produced in this way as a filler for filler-containing paper or as a pigment for coated paper.

[0007] However, the conventional calcium carbonate described above does not have sufficient opacity, and there is a need for calcium carbonate with higher opacity. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2012-96975 [Patent Document 2] Japanese Patent Publication No. 2021-79377 [Patent Document 3] Japanese Patent Publication No. 2002-233851 [Overview of the project] [Problems that the invention aims to solve]

[0009] The problem that the present invention aims to solve is to provide a method and system for producing calcium carbonate with high opacity, which can solve the above-mentioned problems and produce calcium carbonate that is almost free of impurities, has high purity and whiteness, and has excellent opacity. [Means for solving the problem]

[0010] To solve the above problems, the calcium carbonate production method and production system of the present invention have the following technical features. (1) The present invention provides a method for producing calcium carbonate with high opacity, which involves separating at least one element selected from the group consisting of Si, Al, Mg, and heavy metals from an aqueous solution containing calcium ions derived from calcium-containing waste, and mixing the separated calcium-containing aqueous solution with an aqueous solution containing alkali carbonate. and the This method for producing calcium carbonate with high opacity is characterized by adjusting the pH of the mixed solution to 11.5-13 to prepare cubic calcium carbonate (however, no water-soluble salts or water-soluble acids that react with calcium to produce water-insoluble or sparingly soluble salts are added to the calcium carbonate).

[0011] (2) In the calcium carbonate production method described in (1) above, hydrochloric acid water is added to the calcium-containing waste to dissolve the calcium, Derived from calcium-containing waste This method is characterized by producing an aqueous solution containing calcium ions.

[0012] (3) In the method for producing calcium carbonate described in (1) or (2) above, the alkali carbonate is produced by contacting carbon dioxide with an aqueous solution containing potassium hydroxide and / or sodium hydroxide to produce an aqueous solution containing potassium carbonate and / or sodium carbonate, and the aqueous solution containing potassium carbonate and / or sodium carbonate is used to prepare cubic calcium carbonate.

[0013] (4) The method for producing calcium carbonate described in (3) above is characterized in that the carbon dioxide is combustion exhaust gas containing carbon dioxide discharged from cement manufacturing equipment.

[0014] (5) Production of calcium carbonate with high opacity according to the present invention system This includes means for separating at least one selected from the group consisting of Si, Al, Mg, and heavy metals from an aqueous solution containing calcium ions derived from calcium-containing waste, and mixing the aqueous solution containing the separated calcium ions with an aqueous solution containing alkali carbonate. and,This is a calcium carbonate production system characterized by comprising a calcium carbonate production means that produces cubic calcium carbonate by adjusting the pH of the mixed solution to 11.5-13 (however, no water-soluble salts or water-soluble acids that react with calcium to produce water-insoluble or sparingly soluble salts are added to the calcium carbonate), and having high opacity.

[0015] (6) In the calcium carbonate production system described in (5) above, hydrochloric acid water is added to the calcium-containing waste to dissolve the calcium, Derived from calcium-containing waste This is a calcium carbonate production system with high opacity, further comprising a calcium dissolution means for generating an aqueous solution containing calcium ions.

[0016] (7) A calcium carbonate production system according to (5) or (6) above, wherein the alkali carbonate further comprises an alkali carbonate production means for producing an aqueous solution containing potassium carbonate and / or sodium carbonate by contacting an aqueous solution containing potassium hydroxide and / or sodium hydroxide with carbon dioxide, thereby providing a calcium carbonate production system with high opacity. [Effects of the Invention]

[0017] The manufacturing method of the present invention can produce calcium carbonate that has a uniform cubic shape, a sharp and narrow particle size distribution, high purity, high whiteness, and excellent opacity when used as a filler. Furthermore, in the production of calcium carbonate, calcium-containing waste can be used as a calcium source, and carbon dioxide can be obtained from combustion exhaust gas, thus promoting the effective utilization of waste. Furthermore, even if the calcium-containing waste contains heavy metals or magnesium, applying the manufacturing method of the present invention makes it possible to remove these heavy metals and magnesium, resulting in the production of highly pure, white, cubic calcium carbonate. In addition, the manufacturing system of the present invention enables the effective implementation of the manufacturing method of the present invention.

Brief Description of the Drawings

[0018] [Figure 1] It is a flow chart of an example of the method for producing calcium carbonate of the present invention. [Figure 2] Fig. 1 is schematized and is a diagram of an example incorporating a step of fixing carbon dioxide to produce an alkali carbonate. [Figure 3] It is a photographic diagram of an example for measuring the hiding power of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 4] It is another photographic diagram of an example for measuring the hiding power of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 5] It is an electron micrograph showing the state of each calcium carbonate when a paint containing calcium carbonate obtained by the present invention and other calcium carbonates is applied. [Figure 6] It is a diagram showing the colors of the particles of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 7] It is an electron micrograph showing the shapes of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 8] It is an electron micrograph showing the shape of calcium carbonate obtained by the present invention and the shape of other calcium carbonates obtained by adjusting the pH in the calcium carbonate production step in the method of the present invention outside the scope of the present invention. [Figure 9] It is a diagram showing the particle size distribution of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 10] It is a diagram obtained by X-ray analysis of calcium carbonate obtained by the present invention and other calcium carbonates.

Modes for Carrying Out the Invention

[0019] The method for producing calcium carbonate and the production system of the present invention will be described below. The present invention provides a method for producing calcium carbonate with high opacity, which involves mixing an aqueous solution containing calcium ions with an aqueous solution containing alkali carbonate, adjusting the pH of the mixture to 11.5 to 13, and preparing cubic calcium carbonate. Preferably, the manufacturing method involves adding hydrochloric acid water to calcium-containing waste to dissolve the calcium and produce an aqueous solution containing calcium ions.

[0020] Furthermore, the present invention provides a calcium carbonate production system that has high opacity, comprising a calcium carbonate production means for 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. Preferably, the manufacturing system further comprises a calcium dissolving means for adding hydrochloric acid water to calcium-containing waste to dissolve calcium and produce an aqueous solution containing calcium ions.

[0021] The aqueous solution containing calcium ions mentioned above is not particularly limited as long as it is an aqueous solution containing calcium ions. For example, an aqueous solution containing calcium ions obtained by dissolving calcium in calcium-containing waste by adding hydrochloric acid water to the calcium-containing waste can be used as an example.

[0022] Preferred examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples. Figures 1 and 2 illustrate an example of the method (system) for producing calcium carbonate according to the present invention. The diagram schematically illustrates a method (production system) for producing calcium carbonate, which includes a step (calcium carbonate production means) of mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, such as an aqueous solution containing potassium carbonate and / or sodium carbonate, to adjust the pH to 11.5 to 13, preferably 12 to 12.5, in order to prepare calcium carbonate.

[0023] Figure 1, in particular, illustrates an example of a method (system) for producing calcium carbonate from calcium (Ca)-containing waste. This method includes a calcium dissolution step (calcium dissolution means) in which hydrochloric acid water is added to the calcium-containing waste to dissolve the calcium and produce an aqueous solution containing calcium ions. Preferably, the method then includes a separation step (separation means) in which the hydrogen ion concentration index of the aqueous solution containing calcium ions is adjusted, and components including at least one selected from the group consisting of Si, Al, Mg, and heavy metals are separated from the aqueous solution, and in particular, the Mg component is separated by adjusting the pH to 11.5 to 12.5. Subsequently, the aqueous solution containing calcium ions is mixed with an aqueous solution containing potassium carbonate and / or sodium carbonate to adjust the pH to 11.5 to 13, preferably 12 to 12.5, to prepare calcium carbonate (calcium carbonate production means). This figure schematically illustrates an example of a method (production system) for producing calcium carbonate. In Figures 1 and 2, double arrows indicate solid flow, single arrows indicate liquid flow, and dotted lines indicate gas flow.

[0024] The calcium material used to prepare the aqueous solution containing calcium ions in the present invention is not particularly limited as long as it is a calcium-containing material, but for example, calcium (Ca)-containing waste can be used, and examples include 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. The calcium-containing waste is 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.

[0025] In the Ca dissolution process (Ca dissolution means), hydrochloric acid water is added to the Ca-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. Washing water may be added at this stage if necessary. Washing is performed to replace the liquid contained in the solid with clean water during solid-liquid separation. The reaction time required for extracting calcium from calcium-containing waste is 120 minutes or less, more preferably 30 minutes to 60 minutes or less. Furthermore, dissolution and extraction can be performed in multiple stages, particularly in a multi-stage countercurrent manner.

[0026] The temperature of the aqueous solution containing hydrochloric acid used for extracting Ca is preferably above room temperature, and more preferably in the range of 20°C to 70°C.

[0027] In the Ca dissolution process, the residue is separated from the Ca ion-containing aqueous solution, and the residue can be used, for example, as a cement raw material in cement manufacturing equipment.

[0028] The aqueous solution containing Ca ions obtained in the Ca dissolution process contains impurity ions other than Ca, and in the separation process (separation means), the following impurity ions can be separated by adjusting the hydrogen ion concentration index. By adjusting the pH of the aqueous solution containing Ca ions obtained from the Ca dissolution process (dissolution method) to, for example, pH 5-6 using sodium hydroxide or potassium hydroxide, it is possible to remove Si and Al ions contained in the aqueous solution containing Ca ions as a gel. Furthermore, if necessary, washing water such as clean water can be added to wash away any solid components. These gels can be used as cement raw materials.

[0029] 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.

[0030] Furthermore, before removing heavy metals, it is possible to add a flocculant to the Ca ion-containing aqueous solution as needed. Examples include polymer flocculants or inorganic flocculants. Inorganic flocculants include iron salts such as ferric polysulfate, or aluminum salts such as aluminum sulfate and polyaluminum chloride. Polymer flocculants should be selected based on pH and particle properties such as anionic, nonionic, or cationic properties, and examples include polyacrylamide-based, sodium polyacrylate-based, and polyacrylic acid ester-based flocculants.

[0031] 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.

[0032] An aqueous solution containing potassium carbonate and / or sodium carbonate is added to an aqueous solution obtained by separating and removing the unwanted impurities from a Ca ion-containing aqueous solution, and the pH of the mixture is adjusted to 11.5 to 13, preferably 12 to 12.5. This generates high-purity cubic calcium carbonate (calcium carbonate generation means), and the generated calcium carbonate is recovered by separating it from the potassium chloride and / or sodium chloride aqueous solution. In fact, when the purity of calcium carbonate was calculated from the weight loss at 550°C to 800°C using a thermal analyzer (TG), a value of 95.7% was obtained.

[0033] The method (system) of the present invention yields highly pure, cubic, uniform calcium carbonate with a narrow particle size distribution, free from impurities such as magnesium carbonate. This calcium carbonate can be used as a filler in plastics, paper, paints, etc., and as a raw material for cosmetics, making it applicable to various fields where high opacity is desired.

[0034] Figure 2 is a schematic representation of Figure 1, incorporating the process (system) of fixing carbon dioxide to produce alkali carbonate. The hydrochloric acid solution used in the Ca dissolution step, as an example for preparing an aqueous solution containing calcium ions, is not limited to any hydrochloric acid solution, but for example, hydrochloric acid solution produced by bipolar membrane electrodialysis (BMED) treatment (BMED treatment means) of an aqueous solution containing potassium chloride and / or sodium chloride can also be used (not shown). The aqueous solution containing potassium chloride and / or sodium chloride produced in the calcium carbonate production step shown in Figure 1 can also be used.

[0035] Furthermore, as shown in Figure 2, carbon dioxide is brought into contact with an aqueous solution containing potassium hydroxide and / or sodium hydroxide to absorb the carbon dioxide and produce an aqueous solution containing potassium carbonate and / or sodium carbonate (alkali carbonate production means). This aqueous solution containing potassium carbonate and / or sodium carbonate is applied to the calcium carbonate recovery process shown in Figure 1 and used for the production of calcium carbonate. The carbon dioxide in question can be, for example, carbon dioxide contained in combustion exhaust gases from thermal power plants or exhaust gases from cement manufacturing facilities, or it can be absorbed directly from the atmosphere and used.

[0036] Figure 3 shows the results of a coating film (identical film thickness in the range of 50-100 μm) formed on opacity test paper (which has adjacent white and black areas printed on it, is coated with varnish, and is easily wettable with paint diluted with solvent or water but not penetrated) in accordance with JIS 5600-4-1. The tristimulus values ​​on the white and black areas of the opacity test paper were measured using a colorimeter (CR-400 / 410, Konica Minolta) to determine the opacity, and the results are shown in Table 1. For comparison, a commercially available heavy calcium carbonate (heavy calcium carbonate special grade in Figure 3), which has similar physical properties such as average particle size and whiteness, was used instead of the calcium carbonate obtained by the method (system) of the present invention, and the same procedure was carried out. The results are shown in Table 1 below.

[0037] [Table 1]

[0038] Figure 4 shows the results of a coating film formed on opacity test paper with the same film thickness (same film thickness in the range of 50 to 100 μm) by mixing calcium carbonate (SOC-CR-002 in Figure 4) obtained by the method (system) of the present invention with aqueous acrylic emulsion (Lion Bond A, manufactured by Sumitomo Osaka Cement Co., Ltd.) in a mass ratio of 7:6, mixing until uniform, and in accordance with JIS 5600-4-1. The tristimulus values ​​on the white and black areas of the opacity test paper were measured with a colorimeter (CR-400 / 410, manufactured by Konica Minolta), and the results of determining the opacity are shown in Table 2. For comparison, commercially available light calcium carbonate (light carbon (1) in Figure 4), which has similar physical properties such as average particle size and whiteness, was used in the same manner as the calcium carbonate obtained by the method (system) of the present invention, and the results are shown in Table 2 below.

[0039] [Table 2]

[0040] Furthermore, when the state of the applied coating film in Figure 4 is observed using an electron microscope, it is as shown in Figure 5. In the coating film containing calcium carbonate obtained by the method of the present invention, uniform cubic calcium carbonate particles are arranged within the coating film, maintaining high opacity. On the other hand, in the coating film coated with paint containing light calcium carbonate, it can be seen that the particle size of the contained calcium carbonate varies and is arranged irregularly. Furthermore, in coatings in which other commercially available light calcium carbonates (light calcium carbonates (2): spherical calcium carbonates) are used instead of the above-mentioned light calcium carbonate (light calcium carbonate (1)), the gaps between the spherical particles (acrylic resin portion) are increased, as shown in Figure 5. Therefore, the calcium carbonate obtained by the method of the present invention has excellent opacity.

[0041] Furthermore, the whiteness of calcium carbonate (SOC-CR-001), heavy calcium carbonate, and light calcium carbonate obtained by the method (system) of the present invention described above was measured using a Konica Minolta colorimeter (CR-400 / 410). The state and results are shown in Figure 6 and Table 3.

[0042] [Table 3]

[0043] The shapes of the calcium carbonate and heavy calcium carbonate of the present invention shown in Table 1 (Figure 3) and the light calcium carbonate shown in Table 2 (Figure 4) were observed using an electron microscope. The results are shown in Figure 7.

[0044] Furthermore, in the manufacturing method (system) of the present invention, the calcium carbonate obtained when the pH of the calcium carbonate production step was set to pH 3, 6, and 9 instead of 11.5 to 13 was observed with an electron microscope, and the results are shown in Figure 8.

[0045] Furthermore, the particle size distribution of the calcium carbonate, heavy calcium carbonate, and light calcium carbonate of the present invention shown in Figure 6 above was measured using a particle size distribution analyzer (MT-3000, manufactured by Microtrac-Bel), and the results are shown in Figure 9.

[0046] Furthermore, the calcium carbonate, heavy calcium carbonate, and light calcium carbonate of the present invention shown in Figure 6 were measured using XRD (X'PertPro MPD, manufactured by Malvern Panalytical), and the results are shown in Figure 10.

[0047] The results above are summarized in Table 4 below.

[0048] [Table 4]

[0049] Referring to the results in Figure 6 and Table 4, the whiteness of the calcium carbonate produced by the method (system) of the present invention is superior to that of the heavy calcium carbonate and light calcium carbonate compared. Furthermore, as can be seen from Figures 3 and 4, the calcium carbonate obtained by the method (system) of the present invention has higher purity, resulting in higher whiteness and superior opacity compared to heavy calcium carbonate and light calcium carbonate.

[0050] Figure 7 shows that the calcium carbonate obtained by the method (system) of the present invention has a cubic shape with almost no variation in particle size. On the other hand, calcium bicarbonate has a mixture of large and small particles, and light calcium carbonate has small primary particles but undergoes secondary aggregation. Furthermore, as can be seen from Figure 8, the calcium carbonate obtained by the method (system) of the present invention has a uniform cubic shape, but when the pH of the calcium carbonate production step in the method (system) of the present invention is set outside the pH range of the present invention, the prepared calcium carbonate has not only cubic calcite but also spherical vaterite.

[0051] Figure 9 clearly shows that the calcium carbonate obtained by the method (system) of the present invention has a sharp and narrow particle size distribution. On the other hand, heavy calcium carbonate and light calcium carbonate have a broad and varied particle size distribution. Furthermore, Figure 10 shows that calcium bicarbonate and calcium carbonate produced by the present invention are calcite, while light calcium carbonate contains calcium hydroxide.

[0052] Thus, according to the method (system) of the present invention, it is possible to produce calcium carbonate that has a uniform cubic shape, a sharp and narrow particle size distribution, high whiteness, and excellent opacity when used as a filler. [Industrial applicability]

[0053] As described above, according to the method (system) of the present invention, the calcium carbonate obtained has a narrow particle size distribution, little variation in particle size, and a uniform cubic shape, resulting in high opacity. It can be effectively applied as a filler in various fields such as plastics, paper, paints, and cosmetic raw materials, especially as a filler in materials where opacity is desired.

Claims

1. A method for producing calcium carbonate with high opacity, characterized by separating at least one selected from the group consisting of Si, Al, Mg, and heavy metals from an aqueous solution containing calcium ions derived from calcium-containing waste, mixing the separated calcium-containing aqueous solution with an aqueous solution containing alkali carbonate, and adjusting the pH of the mixture to 11.5 to 13 to prepare cubic calcium carbonate (however, no water-soluble salts or water-soluble acids that react with calcium to produce water-insoluble or sparingly soluble salts are added to the calcium carbonate).

2. A method for producing calcium carbonate according to claim 1, characterized in that hydrochloric acid water is added to calcium-containing waste to dissolve the calcium and produce an aqueous solution containing calcium ions derived from the calcium-containing waste, thereby producing a calcium carbonate with high opacity.

3. A method for producing calcium carbonate according to claim 1 or 2, characterized in that the alkali carbonate is produced by contacting carbon dioxide with an aqueous solution containing potassium hydroxide and / or sodium hydroxide to produce an aqueous solution containing potassium carbonate and / or sodium carbonate, and the aqueous solution containing potassium carbonate and / or sodium carbonate is used to prepare cubic calcium carbonate, thereby providing a method for producing calcium carbonate with high opacity.

4. A method for producing calcium carbonate with high concealment properties, characterized in that the carbon dioxide used is combustion exhaust gas containing carbon dioxide discharged from a cement manufacturing facility, in the method for producing calcium carbonate according to claim 3.

5. A calcium carbonate production system with high opacity, comprising: means for separating at least one selected from the group consisting of Si, Al, Mg, and heavy metals from an aqueous solution containing calcium ions derived from calcium-containing waste; and means for producing calcium carbonate, which mixes the aqueous solution containing the separated calcium ions with an aqueous solution containing alkali carbonate to produce cubic calcium carbonate by adjusting the pH of the mixture to 11.5 to 13 (however, no water-soluble salt or water-soluble acid that reacts with calcium to produce a water-insoluble or sparingly soluble salt is added to the calcium carbonate).

6. A calcium carbonate production system according to claim 5, further comprising a calcium dissolving means for adding hydrochloric acid water to calcium-containing waste to dissolve calcium and generate an aqueous solution containing calcium ions derived from the calcium-containing waste, characterized in that it has high opacity.

7. A calcium carbonate production system according to claim 5 or 6, further comprising an alkali carbonate production means for producing an aqueous solution containing potassium carbonate and / or sodium carbonate by contacting an aqueous solution containing potassium hydroxide and / or sodium hydroxide with carbon dioxide, wherein the alkali carbonate is a calcium carbonate production system having high opacity.

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