Manufacturing method and manufacturing system of calcium carbonate having high hiding property

Abstract

To provide a manufacturing method and a manufacturing system of calcium carbonate capable of synthesizing calcium carbonate having high whiteness and high hiding property.SOLUTION: A manufacturing method of calcium carbonate having high hiding property includes a step of preparing cubic calcium carbonate by mixing an aqueous solution containing calcium ion and an aqueous solution containing an alkali carbonate to control pH of the mixed solution to 11.5-13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and a system for producing calcium carbonate having high hiding properties, and in particular to a method and a system for producing calcium carbonate having high hiding properties that can be used as a filler for plastics, paints, etc. [Background technology]

[0002] Calcium carbonate and titanium oxide are used in a wide range of industrial fields as fillers for plastics, resins, rubber, paper, paints, cosmetic ingredients, etc., and are used to improve various physical properties. In particular, calcium carbonate, which has a small refractive index, is mainly used as an "extender pigment," while titanium oxide, which has a large refractive index, is mainly used as a "white pigment." Calcium carbonate includes ground calcium carbonate, which is prepared by crushing high-purity natural limestone and classifying it to adjust the particle size. In addition, calcium carbonate is calcined to form lime, which is then reacted with water to form slaked lime, which is then reacted with carbon dioxide to form calcium carbonate again, which is then recovered, dried, crushed, and classified to produce light calcium carbonate.

[0003] However, limestone (heavy calcium carbonate), which is crushed calcium carbonate, has the problem that it does not have a high hiding power and is insufficient in hiding power. In addition, titanium oxide is expensive as a filler compared to calcium carbonate, and when it is filled into resin or the like, there is a problem that the applied surface deteriorates when exposed to sunlight.

[0004] As a method for producing calcium carbonate, for example, Japanese Patent Application Laid-Open No. 2008-156204 (Patent Document 1) discloses a method for producing fine-particle-aggregated precipitated calcium carbonate, which comprises a step (1) of obtaining milk of lime by wet slaking quicklime, a step (2) of blowing carbon dioxide gas into a calcium hydroxide suspension obtained by suspending calcium hydroxide in water to obtain a colloidal particulate calcium hydroxide suspension by carbonation to a carbonation rate of 20% or less, and a step (3) of adding the colloidal particulate calcium hydroxide suspension obtained in step (2) to the milk of lime obtained in step (1), blowing in carbon dioxide gas, and reacting until the carbonation rate reaches 100%, and thereby producing a fine-particle-aggregated precipitated calcium carbonate having a BET specific surface area of ​​10 to 25 m. 2 / g or less, and the pore volume of 0 to 1000 Å by nitrogen adsorption method is 0.05 cm 3 It is described that the resulting fine particle aggregated light calcium carbonate has a pore volume ratio of 250 Å or less to the total pore volume of 25% or more and an oil absorption by liquid paraffin of 100 cc / 100 g or more. It is further described that when the resulting calcium carbonate is used as a filler for printing paper, the printing paper can be given excellent ink absorbency and opacity (especially opacity after printing).

[0005] Furthermore, JP2012-207346A (Patent Document 2) discloses a calcium carbonate slurry having an average particle size of 0.5 to 1.5 μm and a gradient coefficient (D30 / D70) (wherein DX represents a finer equivalent spherical diameter when X weight % of the particles corresponds to this diameter) of 40 or more, and a coated paper having a coating layer containing the calcium carbonate, for the purposes of providing a calcium carbonate slurry that can provide a coating layer having concealing properties and providing a coated paper having a coating layer containing calcium carbonate and having concealing properties.

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 2002-233851 (Patent Document 3) discloses that, for the purpose of using calcined ash to provide light calcium carbonate-coated particles having high whiteness and low abrasion properties and paper using the same, the calcined ash is pulverized to an average particle size of 3 μm or less, the calcined ash particles after pulverization are mixed into an aqueous suspension containing calcium hydroxide, carbon dioxide or a gas containing carbon dioxide is passed through the aqueous suspension to coat the periphery of the calcined ash particles with light calcium carbonate, and the light calcium carbonate-coated particles thus produced are used as a filler for filler-containing paper or as a pigment for coated paper.

[0007] However, the above-mentioned conventional calcium carbonate does not have sufficient hiding power, and calcium carbonate with higher hiding power is desired. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2012-96975 A [Patent Document 2] Patent Publication No. 2021-79377 [Patent Document 3] JP 2002-233851 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method and system for producing calcium carbonate having high concealment properties, which can solve the problems described above and prepare calcium carbonate that is almost free of impurities, has high purity, high whiteness, and excellent concealment properties. [Means for solving the problem]

[0010] In order to solve the above problems, the method and system for producing calcium carbonate of the present invention mainly have the following technical features. (1) The method for producing calcium carbonate having high hiding property of the present invention is a method for producing calcium carbonate having high hiding property by mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, adjusting the pH of the mixture to 11.5 to 13, and preparing cubic calcium carbonate.

[0011] (2) In the method for producing calcium carbonate described in (1) above, hydrochloric acid water is added to the calcium-containing waste to dissolve the calcium and produce an aqueous solution containing calcium ions.

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

[0013] (4) In the method for producing calcium carbonate according to the above (3), as the carbon dioxide, a combustion exhaust gas containing carbon dioxide discharged from a cement production facility is used.

[0014] (5) The system for producing calcium carbonate having high concealment property of the present invention is a system for producing calcium carbonate having high concealment property, which includes a calcium carbonate production means for mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, adjusting the pH of the mixed solution to 11.5 to 13, and producing cubic calcium carbonate.

[0015] (6) The calcium carbonate production system according to (5) above, further comprising a calcium dissolving means for adding hydrochloric acid water to the calcium-containing waste to dissolve calcium and generate an aqueous solution containing calcium ions.

[0016] (7) In the system for producing calcium carbonate according to the above (5) or (6), the alkali carbonate further includes an alkali carbonate generating means for generating an aqueous solution containing potassium carbonate and / or sodium carbonate by bringing carbon dioxide into contact with an aqueous solution containing potassium hydroxide and / or sodium hydroxide. Effect of the Invention

[0017] The production method of the present invention can produce calcium carbonate which has a uniform cubic morphology, a sharp and narrow particle size distribution, high purity, and high whiteness, and which has excellent hiding power when used as a filler. In addition, in producing calcium carbonate, calcium-containing waste can be used as a calcium source, and combustion exhaust gas can be used as carbon dioxide, so that effective utilization of waste can be promoted. Furthermore, even if heavy metals, magnesium, etc. are contained in calcium-containing waste, the heavy metals and magnesium can be removed by applying the production method of the present invention, and as a result, it becomes possible to produce cubic calcium carbonate with high purity and high whiteness. The production system of the present invention also makes it possible to effectively carry out the above-mentioned production method of the present invention. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a flow diagram of an example of a method for producing calcium carbonate of the present invention. [Diagram 2] FIG. 2 is a diagram of an example that summarizes FIG. 1 and incorporates a process for fixing carbon dioxide and producing alkali carbonate. [Diagram 3] FIG. 1 is a photographic diagram of an example for measuring the hiding ratio of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 4] FIG. 2 is a photograph of another example for measuring the hiding ratio of calcium carbonate obtained by the present invention and other calcium carbonates. [Diagram 5]FIG. 2 is an electron microscope photograph showing the state of each calcium carbonate contained in a paint containing calcium carbonate obtained by the present invention and other calcium carbonates when the paint is applied. [Figure 6] FIG. 2 shows the color of particles of calcium carbonate obtained according to the invention and other calcium carbonates. [Figure 7] FIG. 1 is an electron microscope photograph showing the shapes of calcium carbonate obtained by the present invention and other calcium carbonates. [Figure 8] FIG. 2 is an electron microscope photograph showing the shape of calcium carbonate obtained by the present invention and the shape of other calcium carbonate obtained by adjusting the pH in the calcium carbonate production step in the method of the present invention outside the range of the present invention. [Figure 9] FIG. 2 shows particle size distributions of calcium carbonate obtained according to the present invention and other calcium carbonates. [Figure 10] FIG. 2 is a diagram obtained by X-ray analysis of calcium carbonate obtained according to the present invention and other calcium carbonates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a method and system for producing calcium carbonate according to the present invention will be described. The method for producing calcium carbonate having high hiding property of the present invention comprises mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, adjusting the pH of the mixture to 11.5 to 13, and preparing cubic calcium carbonate. A preferred production method includes adding hydrochloric acid water to calcium-containing waste to dissolve calcium and generate an aqueous solution containing calcium ions.

[0020] In addition, the production system for calcium carbonate having high concealment property of the present invention is a production system for calcium carbonate having high concealment property, which is provided with a calcium carbonate production means for mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, adjusting the pH of the mixed solution to 11.5 to 13, and preparing cubic calcium carbonate. Preferably, the production system further comprises calcium dissolving means for adding hydrochloric acid water to calcium-containing waste to dissolve calcium and generate an aqueous solution containing the calcium ions.

[0021] The aqueous solution containing calcium ions 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 using calcium-containing waste and adding hydrochloric acid water to the calcium-containing waste to dissolve calcium can be exemplified.

[0022] Preferred embodiments of the present invention will now be described with reference to the drawings, but the present invention is not limited to these. FIGS. 1 and 2 show an example of a method (system) for producing calcium carbonate of the present invention, and are schematic diagrams illustrating a method (production system) for producing calcium carbonate having a step (calcium carbonate production means) of mixing an aqueous solution containing calcium ions with a solution containing an alkali carbonate, such as an aqueous solution containing potassium carbonate and / or sodium carbonate, and adjusting the pH to 11.5 to 13, desirably 12 to 12.5, to prepare calcium carbonate.

[0023] In particular, Fig. 1 shows, as an example, a method (system) for producing calcium carbonate from calcium (Ca)-containing waste, and the method includes a calcium dissolving step (calcium dissolving means) of adding hydrochloric acid water to calcium-containing waste to dissolve calcium and produce an aqueous solution containing calcium ions. Preferably, the method then includes a separation step (separation means) of adjusting the hydrogen ion concentration index of the aqueous solution containing calcium ions, separating a component containing at least one selected from the group consisting of Si, Al, Mg, and heavy metals from the aqueous solution, and particularly for the Mg component, adjusting the pH to 11.5 to 12.5 to separate impurities, and then mixing the aqueous solution containing calcium ions 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 producing means). In addition, in Figures 1 and 2, double-lined arrows indicate the flow of solids, single-lined arrows indicate the flow of liquids, and dotted lines indicate the flow of gas.

[0024] The calcium material for preparing the aqueous solution containing calcium ions used in the present invention is not particularly limited as long as it is a material containing calcium, and for example, calcium (Ca)-containing waste can be used. Examples of such waste include incineration ash from general waste and industrial waste, fly ash discharged from thermal power plants, slag, waste concrete, ready-mixed concrete sludge, and bioash. The particle size of the Ca-containing waste is adjusted to 1000 μm or less, more preferably 500 μm or less and 100 μm or more, which makes it easier to extract Ca.

[0025] In the Ca dissolving step (Ca dissolving means), hydrochloric acid water is added to the Ca-containing waste whose particle size has been adjusted, and the pH of the hydrogen ion concentration exponent is preferably adjusted to a range of less than 2.5. In this case, washing water may be added as necessary. Washing is carried out in order to replace the liquid contained in the solids with clean water during solid-liquid separation. The reaction time required for extracting Ca from Ca-containing waste is 120 minutes or less, more preferably 30 minutes or more and 60 minutes or less. It is also possible to carry out dissolution extraction in multiple stages, particularly in a multi-stage countercurrent flow.

[0026] The temperature of the aqueous solution containing hydrochloric acid when extracting Ca is preferably room temperature or higher, and more preferably in the range of 20°C or higher and 70°C or lower.

[0027] In the Ca dissolution step, the solution is separated into a residue and an aqueous solution containing Ca ions, and the residue can be used as a cement raw material, for example, in a cement manufacturing facility.

[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 exponent. By adjusting the pH of the aqueous solution containing Ca ions obtained from the Ca dissolving step (dissolving means) to, for example, pH 5 to 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. In addition, if necessary, it is also possible to add washing water such as fresh water to wash the solid content. These gels can be used as cement raw materials.

[0029] Next, the pH of the Ca ion-containing aqueous solution after removing the Si and Al ions is adjusted to, for example, pH 7 to 10 using sodium hydroxide or potassium hydroxide, thereby separating heavy metals such as Pb and Cr ions derived from the calcium-containing waste. If necessary, cleaning water such as fresh water can be added, and the solid content is washed by such cleaning.

[0030] In addition, before removing heavy metals, it is possible to add a flocculant to the Ca ion-containing aqueous solution as necessary. For example, polymer flocculants or inorganic flocculants can be used. Inorganic flocculants include iron salts such as polyferric sulfate, and aluminum salts such as aluminum sulfate and polyaluminum chloride. Polymer flocculants can be anionic, nonionic, cationic, or other suitable ones depending on the pH and particle properties, and examples of such polymer flocculants include polyacrylamide, sodium polyacrylate, and polyacrylic ester.

[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 to 12.5 using sodium hydroxide or potassium hydroxide, it becomes possible to remove the Mg ions contained in the aqueous solution derived from the calcium-containing waste as a gel. If necessary, it is also possible to add washing water such as fresh water, and the solid content is washed by such washing.

[0032] An aqueous solution containing potassium carbonate and / or sodium carbonate is added to the aqueous solution obtained by separating and removing the unnecessary impurities from the Ca ion-containing aqueous solution, and the pH of the mixed solution is adjusted to 11.5 to 13, preferably 12 to 12.5. This produces high-purity cubic calcium carbonate (calcium carbonate production means), and the produced calcium carbonate is separated from the aqueous potassium chloride and / or sodium chloride solution to recover calcium carbonate. 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] By the method (system) of the present invention, it is possible to obtain high-purity, cubic, uniform calcium carbonate with a narrow particle size distribution that is free of impurities such as magnesium carbonate. The calcium carbonate thus obtained can be used as a filler for plastics, paper, paints, etc., or as a cosmetic raw material, and can be applied in various fields where high hiding power is desired.

[0034] FIG. 2 is a diagram that summarizes FIG. 1 and incorporates a process (system) for fixing carbon dioxide and producing alkali carbonate. The hydrochloric acid used in the Ca dissolution step as an example for preparing an aqueous solution containing calcium ions is not particularly limited as long as it is hydrochloric acid, but for example, hydrochloric acid produced by a bipolar membrane electrodialysis (BMED) treatment (BMED treatment means) containing potassium chloride and / or sodium chloride can be used (not shown). As the potassium chloride and / or sodium chloride, an aqueous solution containing potassium chloride and / or sodium chloride produced in the calcium carbonate production step in FIG. 1 can also be used.

[0035] As shown in FIG. 2, carbon dioxide is brought into contact with an aqueous solution containing potassium hydroxide and / or sodium hydroxide to absorb the carbon dioxide and generate an aqueous solution containing potassium carbonate and / or sodium carbonate (alkali carbonate generating means). This aqueous solution containing potassium carbonate and / or sodium carbonate is applied to the calcium carbonate recovery step of FIG. 1 and used for producing calcium carbonate. The carbon dioxide used may be, for example, carbon dioxide contained in combustion exhaust gas from thermal power generation facilities or exhaust gas from cement manufacturing facilities. It is also possible to directly absorb carbon dioxide in the atmosphere and use it.

[0036] 3 shows a diagram of a coating film formed on a hiding ratio test paper (a white part and a black part are printed adjacent to each other, and a varnish is applied, which is easily wetted with a paint diluted with a solvent or water but does not penetrate) with the same thickness (same thickness in the range of 50 to 100 μm) by mixing calcium carbonate obtained by the method (system) of the present invention (shown as SOC-CR-001 in FIG. 3) with an aqueous acrylic emulsion (Lionbond A, manufactured by Sumitomo Osaka Cement Co., Ltd.) in a mass ratio of 5:6, kneading until uniform, and forming a coating film with the same thickness (same thickness in the range of 50 to 100 μm) on a hiding ratio test paper (a white part and a black part are printed adjacent to each other, and a varnish is applied, which is easily wetted with a paint diluted with a solvent or water but does not penetrate) in accordance with JIS 5600-4-1. The tristimulus values ​​on the white part and the black part of the hiding ratio test paper were measured with a colorimeter (CR-400 / 410, manufactured by Konica Minolta) to obtain the hiding ratio. The results are shown in Table 1. For comparison, a commercially available heavy calcium carbonate (special grade heavy carbon in FIG. 3) having 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 experiment was carried out. The results are shown in Table 1 below.

[0037] [Table 1]

[0038] Fig. 4 shows a diagram of a coating film formed on a hiding rate test paper with the same thickness (same thickness in the range of 50 to 100 μm) by mixing calcium carbonate obtained by the method (system) of the present invention (SOC-CR-002 in Fig. 4) with an aqueous acrylic emulsion (Lionbond A, manufactured by Sumitomo Osaka Cement Co., Ltd.) in a mass ratio of 7:6, kneading until uniform, and conforming to JIS5600-4-1. The tristimulus values ​​on the white and black parts of the hiding rate test paper were measured with a colorimeter (CR-400 / 410, manufactured by Konica Minolta) to obtain the hiding rate. The results are shown in Table 2. For comparison, a similar experiment was carried out using a commercially available light calcium carbonate (light carbon (1) in FIG. 4) having similar physical properties such as average particle size and whiteness instead of the calcium carbonate obtained by the method (system) of the present invention. The results are shown in Table 2 below.

[0039] [Table 2]

[0040] In addition, when the state of the applied coating film in Fig. 4 is observed by an electron microscope photograph, it is in the state shown in Fig. 5, and in the coating film containing calcium carbonate obtained by the method of the present invention, the calcium carbonate particles are uniformly arranged in the coating film, and maintain high hiding power. On the other hand, in the coating film coated with a paint containing light calcium carbonate, the particle size of the calcium carbonate contained varies and is irregularly arranged. In addition, in the coating film in which another commercially available light calcium carbonate (light carbon (2): spherical calcium carbonate) was used instead of the light calcium carbonate (light carbon (1)), the gaps between the spherical particles (acrylic resin parts) were increased, as shown in Figure 5. Therefore, the calcium carbonate obtained by the method of the present invention has excellent hiding power.

[0041] In addition, the whiteness of the calcium carbonate (SOC-CR-001), heavy calcium carbonate, and light calcium carbonate obtained by the method (system) of the present invention was measured using a Konica Minolta colorimeter (CR-400 / 410). The conditions and results are shown in FIG.

[0042] [Table 3]

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

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

[0045] In addition, the particle size distribution of the calcium carbonate of the present invention, heavy calcium carbonate, and light calcium carbonate shown in FIG. 6 was measured using a particle size distribution measuring device (MT-3000, manufactured by Microtrack Bell Co., Ltd.), and the results are shown in FIG. 9.

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

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

[0048] [Table 4]

[0049] Referring to the results in FIG. 6 and Table 4, the whiteness of calcium carbonate produced by the method (system) of the present invention is superior to that of the compared heavy calcium carbonate and light calcium carbonate. In addition, from FIGS. 3 and 4, it can be seen that the calcium carbonate obtained by the method (system) of the present invention has a higher purity than heavy calcium carbonate and light calcium carbonate, and therefore has a higher whiteness and excellent hiding power.

[0050] 7, it can be seen that the calcium carbonate obtained by the method (system) of the present invention has a cubic morphology with almost no variation in particle size, while the calcium bicarbonate contains a mixture of large and small particles, and the precipitated calcium carbonate has small primary particles but secondary agglomerates. Furthermore, from FIG. 8, it can be seen that the calcium carbonate obtained by the method (system) of the present invention has a uniform cubic shape, but when the pH in the calcium carbonate production step in the method (system) of the present invention is set outside the pH range of the present invention, the calcium carbonate prepared has not only cubic calcite but also spherical vaterite.

[0051] It is clear from Fig. 9 that the particle size distribution of calcium carbonate obtained by the method (system) of the present invention is sharp and narrow. On the other hand, it is seen that the particle size distribution of heavy calcium carbonate and light calcium carbonate is wide and varies. Moreover, it is seen from Fig. 10 that calcium bicarbonate and calcium carbonate produced by the present invention are calcite, and light calcium carbonate contains calcium hydroxide.

[0052] In this way, according to the method (system) of the present invention, it is possible to produce calcium carbonate which has a uniform cubic morphology, a sharp and narrow particle size distribution, high whiteness, and excellent hiding power 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 with little variation in particle size and a uniform cubic shape, and therefore has high hiding power and can be effectively applied as a filler in various fields such as plastics, paper, paints, and cosmetic raw materials, particularly as a filler in materials where hiding power is desired.

Claims

[Claim 1] A method for producing calcium carbonate having high hiding power, comprising mixing an aqueous solution containing calcium ions with an aqueous solution containing an alkali carbonate, and adjusting the pH of the resulting mixture to 11.5 to 13 to prepare cubic calcium carbonate.

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