Method and apparatus for producing calcium carbonate particles

Abstract

To provide a method for producing calcium carbonate particles capable of producing calcium carbonate particles with a target particle size in a simple manner.SOLUTION: There is provided a method for producing calcium carbonate particles including the steps of: measuring a sulfur concentration of a material solution containing calcium; adjusting the sulfur concentration of the material solution to a predetermined sulfur concentration when the sulfur concentration is different from the predetermined sulfur concentration, which is determined according to the particle size of the calcium carbonate to be crystallized; and introducing carbon dioxide or carbonate ions into the material solution, whose sulfur concentration has been adjusted, to crystallize calcium carbonate.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In order to reduce the emission of carbon dioxide, a greenhouse gas, studies have been conducted on the reaction of carbon dioxide with calcium to immobilize it as calcium carbonate. As described in Patent Document 1 and Patent Document 2, calcium carbonate can be produced by reacting calcium extracted into water from calcium-containing waste such as concrete sludge and steel slag with carbon dioxide introduced into the water. These methods are expected to reduce the amount of calcium-containing waste that is disposed of, and therefore to suppress environmental deterioration caused by waste.

[0003] Calcium carbonate particles are used in a wide range of fields, including fillers for plastics, paper, and paints, soil conditioners such as pesticides and fertilizers, adhesives, sealants, erasers and dentifrices that utilize their abrasive properties, and food additives and cosmetic raw materials. Recently, sheet and film-like paper substitute products and plastic substitute products that use calcium carbonate particles as the main raw material have been developed and are widely used. Paper substitute products are used for clear files, business cards, booklets (pamphlets, photo books, etc.), promotional POP, menus, packages, posters, illuminated sheets, stickers and labels, maps, mask cases, and tags. Plastic substitute products are used for applications where plastics were previously used (various molded products, such as plastic shopping bags, shopping bags, food containers, drink cups, hangers, stationery, fans, cosmetic containers, bottles, building materials, etc.). Calcium carbonate particles with particle sizes appropriate for each of these applications are used. Therefore, a method for producing calcium carbonate particles with the desired particle size is required.

[0004] Several methods for controlling the particle size of calcium carbonate particles produced have been studied. For example, Patent Document 3 and Patent Document 4 describe that calcium carbonate particles having a small particle size of 0.03 μm or less can be produced by adding sulfates such as calcium sulfate, aluminum sulfite, and zinc sulfate to an aqueous calcium hydroxide solution and further controlling the conditions for introducing carbon dioxide gas. Patent Document 5 describes a method for precisely controlling carbonation conditions to produce easily disintegrating calcium carbonate particles having a particle size of 0.8 μm to 1.0 μm, and mechanically grinding or crushing these to obtain calcium carbonate particles having a particle size of 0.1 μm to 0.5 μm.

[0005] Furthermore, Patent Document 6 describes that the particle size of calcium carbonate particles can be reduced by adding barium sulfate to a neutral amino acid-containing aqueous solution that contains two types of amino acids, DL-alanine and glycine. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-279552 A [Patent Document 2] JP 2014-148432 A [Patent Document 3] Japanese Patent Application Laid-open No. 1973-103100 [Patent Document 4] Japanese Patent Application Publication No. 54-041299 [Patent Document 5] Japanese Patent Application Publication No. 62-202817 [Patent Document 6] JP 2019-052065 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described in Patent Documents 4 to 6, several methods for reducing the particle size of calcium carbonate particles are known. However, the methods described in Patent Documents 4 to 5 can produce ultrafine particles with a particle size of 0.03 μm or less, but cannot produce calcium carbonate particles with a larger particle size. Furthermore, the methods described in Patent Documents 4 to 5 require precise control of the conditions for crystallizing calcium carbonate particles, which is not practical.

[0008] In addition, the method described in Patent Document 6 can produce calcium carbonate particles having a size of about several μm, but the particle size of the resulting calcium carbonate particles is not stable, and calcium carbonate particles having a target particle size cannot be produced.

[0009] The present invention has been made in consideration of the problems of the conventional techniques described above, and has an object to provide a method for producing calcium carbonate particles, which can produce calcium carbonate particles having a target particle size in a simple manner, and an apparatus for producing calcium carbonate particles capable of carrying out the method. [Means for solving the problem]

[0010] One aspect of the present invention for solving the above problems relates to a method for producing calcium carbonate particles as set forth in the following items [1] to [6]. [1] A step of measuring a sulfur concentration of a material solution containing calcium; When the measured sulfur concentration is different from a predetermined sulfur concentration determined according to a particle size of calcium carbonate to be crystallized, the sulfur concentration of the material solution is adjusted to the predetermined sulfur concentration. and introducing carbon dioxide or carbonate ions into the material solution having the adjusted sulfur concentration to crystallize calcium carbonate. A method for producing calcium carbonate particles. [2] The step of measuring the sulfur concentration is carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS); A method for producing calcium carbonate particles according to [1]. [3] The predetermined sulfur concentration is 50 mg / L or more and 10,000 mg / L or less. A method for producing calcium carbonate particles according to [1] or [2]. [4] The predetermined sulfur concentration is equal to or greater than 0.01 mg / L and less than 50 mg / L. A method for producing calcium carbonate particles according to [1] or [2]. [5] A step of adjusting the barium concentration of the material solution to a predetermined barium concentration; In the step of crystallizing calcium carbonate, carbon dioxide is introduced into the material solution in which the sulfur concentration and the barium concentration have been adjusted. The method for producing calcium carbonate particles according to any one of [1] to [4]. [6] The crystallization step is carried out by adjusting the pH of the material solution to 7.0 or more and introducing carbon dioxide. The method for producing calcium carbonate particles according to any one of [1] to [5].

[0011] One aspect of the present invention for solving the above-mentioned problems relates to an apparatus for producing calcium carbonate particles as set forth in the following items [7] to [8]. [7] A measurement unit for measuring a sulfur concentration of a material solution containing calcium; a concentration adjusting unit that adjusts the measured sulfur concentration of the material solution to a predetermined sulfur concentration determined according to a particle size of calcium carbonate to be crystallized; and a crystallization section for introducing carbon dioxide into the material solution having the adjusted sulfur concentration to crystallize calcium carbonate. Manufacturing equipment for calcium carbonate particles. [8] The concentration adjusting unit adjusts the sulfur concentration of the material solution to a predetermined sulfur concentration when the measured sulfur concentration of the material solution is not the predetermined sulfur concentration. [7] An apparatus for producing calcium carbonate particles. Effect of the Invention

[0012] According to the present invention, there are provided a method for producing calcium carbonate particles, which can produce calcium carbonate particles having a target particle size in a simple manner, and an apparatus for producing calcium carbonate particles, which can carry out the method. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a flow chart of a method for producing calcium carbonate particles according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a calcium carbonate particle production apparatus capable of carrying out the calcium carbonate particle production method shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [First embodiment] FIG. 1 is a flowchart of a method for producing calcium carbonate particles according to one embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a production apparatus for calcium carbonate particles capable of carrying out the method for producing calcium carbonate particles shown in FIG.

[0015] As shown in FIG. 1, in this embodiment, a calcium-containing material (hereinafter, simply referred to as a “calcium raw material”) is " into water (step S110), and a calcium-containing solution (hereinafter simply referred to as "material solution") that contains calcium is separated by solid-liquid separation (step S120). The sulfur concentration in the material solution is then measured (step S130), and it is determined whether the measured sulfur concentration is a predetermined concentration (step S140). If the measured sulfur concentration is not the predetermined concentration, the sulfur concentration in the material solution is adjusted (step S150), and calcium carbonate particles are then crystallized from the material solution (step S160). The material solution is then filtered to recover the crystallized calcium carbonate particles (step S170).

[0016] As shown in FIG. 2, the calcium carbonate particle manufacturing apparatus 200 includes an extraction section 210 for extracting calcium, a separation section 220 for separating the material solution by solid-liquid separation, a concentration measurement section 230 for measuring the concentration of the solid-liquid separation, a concentration adjustment section 250 for adjusting the concentration of the solid-liquid separation, a crystallization section 260 for crystallizing calcium carbonate particles from the material solution, and a recovery section 270 for recovering the calcium carbonate particles by filtration.

[0017] Each component of the manufacturing apparatus 200 is configured to be able to transmit and receive data to and from the control unit 240. The control unit 240 has a computer such as a CPU, and a storage unit such as a ROM and a RAM. The control unit 240 controls the operation of these components, as well as the opening and closing of valves and the operation of a pump (not shown) provided in a flow path connecting these components. The control unit 240 does not need to be provided inside the manufacturing apparatus 200, and may be disposed outside the manufacturing apparatus 200 and control these operations and opening and closing through communication by a communication device.

[0018] Hereinafter, each step of the method for producing calcium carbonate particles using the production apparatus 200 will be described.

[0019] (Calcium extraction: step S110) First, the calcium raw material and water are placed in the extraction tank 212 of the extraction section 210, and are stirred to extract calcium from the calcium raw material.

[0020] The calcium raw material fed into the extraction tank 212 may be in a solid state, a liquid state (solution state), or a slurry state. The type of calcium raw material is not particularly limited, and may be a refined product such as limestone or marble, or may be a recovered product such as waste. Examples of the recovered products include waste concrete, ready-mixed concrete sludge, steel slag, waste gypsum, coal ash, biomass ash, incineration ash, alkaline wastewater, and shells. These calcium raw materials may be pretreated, such as neutralization, crushing, or grinding, or may not be pretreated. From the viewpoint of increasing the efficiency of calcium extraction, it is preferable that these calcium raw materials are subjected to crushing or grinding.

[0021] As the water, ion-exchanged water, tap water, industrial water, etc. can be used. Note that, as long as calcium is well dissolved, a solvent other than water may be used, or a mixture of water and another solvent may be used. Note that, when a liquid or slurry calcium raw material is introduced into the extraction tank 212, water does not need to be introduced if it is not necessary.

[0022] The extraction tank 212 has an agitator 216 driven by a motor 214. The extraction unit 210 rotates the agitator 216 under the control of the control unit 240 to agitate the calcium-containing material and water, and extract calcium into the water. This results in a suspension in which the calcium raw material is suspended in the calcium-containing material solution. The agitation conditions, such as the agitation speed and time, are not particularly limited. Since the amount of various elements extracted into the material solution varies depending on the agitation conditions, such as the agitation speed, agitation time, and pH during agitation, when the relationship between the type of calcium raw material, the agitation conditions, and the amount of sulfur extracted is known, the agitation conditions may be set so as to obtain a concentration close to a predetermined sulfur concentration that has been determined in advance.

[0023] The suspension thus obtained is sent to the separation section 220 under the control of the control section 240 .

[0024] (Solid-liquid separation: Step S120) The separation unit 220 separates the material solution by removing the solid calcium raw material and other impurities (such as fine particles) from the suspension by solid-liquid separation. The above-mentioned solid-liquid separation can improve the accuracy of the sulfur concentration in the concentration measurement unit 230. Furthermore, the above-mentioned solid-liquid separation can suppress the mixing of impurities into the calcium carbonate particles crystallized in the crystallization unit 260 to obtain calcium carbonate with high purity, suppress the aggregation of calcium carbonate particles through the surfaces of impurities, and suppress clogging of the flow path by the calcium raw material.

[0025] The type of separation section 220 is not particularly limited, and any known solid-liquid separation device such as a filter press, a vacuum belt filter, a vacuum rotary filter, a screw decanter, or a centrifugal dehydrator can be used.

[0026] The suspension that is subjected to solid-liquid separation in the separation section 220 may be added with a flocculant containing sodium, potassium, magnesium, etc. to flocculate fine particles such as colloidal particles. This allows these fine particles to be removed more efficiently in the separation section 220.

[0027] The material solution obtained by solid-liquid separation is sent to the crystallization section 260 under the control of the control section 240. A concentration measurement section 230 and a concentration adjustment section 250 are provided in a flow path connecting the separation section 220 and the crystallization section 260. The solid content removed by solid-liquid separation may be collected and discarded, or may be used for other purposes.

[0028] (Concentration measurement: Process S130) The concentration measuring unit 230 measures the sulfur concentration of the material solution flowing through the flow path.

[0029] The type of the concentration measuring unit 230 is not particularly limited, and it may be any measuring device that can measure the concentration of sulfur atoms (including compounds or ions containing sulfur atoms). 2- ) and sulfite ion (SO3 2-It is preferable that the concentration measuring unit 230 is also capable of measuring the concentration of sulfur-containing ions such as sulfur ions. For example, it is preferable that the concentration measuring unit 230 is a measuring device that measures the concentration by inductively coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS).

[0030] In addition to the sulfur concentration, the concentration measuring unit 230 may also measure the concentrations of other elements such as barium concentration, calcium concentration, etc. The above-mentioned measuring device can usually simultaneously measure the concentrations of multiple elements including sulfur, barium, and calcium.

[0031] The concentration measuring unit 230, under the control of the control unit 240, measures the sulfur concentration of the material solution flowing through a flow path connecting the separation unit 220 and the crystallization unit 260. Then, the concentration measuring unit 230 transmits the measured sulfur concentration to the control unit 240.

[0032] (Determination of concentration: step S140) When the control unit 240 receives the sulfur concentration from the concentration measurement unit 230, it determines whether or not the measured sulfur concentration is a predetermined sulfur concentration.

[0033] According to the new findings of the present inventors, the particle size of the calcium carbonate particles crystallized in the crystallization section 260 can be controlled by the sulfur concentration of the material solution. Specifically, the particle size of the calcium carbonate particles can be made smaller as the sulfur concentration of the material solution is increased, and the particle size of the calcium carbonate particles can be made larger as the sulfur concentration of the material solution is decreased.

[0034] Although the reason for this is unclear, the sulfur atoms in the material solution are converted into sulfate ions (SO4 2- ) and sulfite ion (SO3 2- ) and other ions, and these ions are calcium ions (Ca 2+) and increases the calcium concentration in the material solution. Therefore, the higher the sulfur concentration in the material solution, the more difficult it is for the calcium concentration in the material solution to decrease, and the more likely it is that calcium will become supersaturated. In a supersaturated state, calcium nucleation is promoted, and a large number of calcium carbonate particles with small particle sizes are likely to form. On the other hand, the lower the sulfur concentration in the material solution, the more difficult it is for calcium ions to become supersaturated, and the less likely nucleation is promoted. Therefore, it is believed that lowering the sulfur concentration promotes crystal growth in calcium carbonate particles, resulting in larger particle sizes.

[0035] According to the findings of the present inventors, when the sulfur concentration of the material solution is 50 mg / L or more and 10,000 mg / L or less, calcium carbonate particles having a relatively small particle size, in which D50 in the particle size distribution is 0.1 μm or more and less than 15 μm, and D90 is 5 μm or more and 25 μm or less, are easily produced. From the viewpoint of obtaining calcium carbonate particles having such a small particle size, the sulfur concentration of the material solution is preferably 100 mg / L or more and 5,000 mg / L or less, and more preferably 200 mg / L or more and 1,000 mg / L or less.

[0036] On the other hand, if the sulfur concentration of the material solution is 0.01 mg / L or more and less than 50 mg / L, calcium carbonate particles having a relatively large particle size, in which D50 in the particle size distribution is 15 μm or more and 30 μm or less and D90 in the particle size distribution is 25 μm or more and 50 μm or less, are likely to be produced. From the viewpoint of obtaining calcium carbonate particles having such a large particle size, the sulfur concentration of the material solution is preferably 0.05 mg / L or more and 10 mg / L or less, and more preferably 0.1 mg / L or more and 1 mg / L or less.

[0037] In this specification, the particle size (average particle size, D50, D90, etc.) of calcium carbonate particles is measured by a laser diffraction particle size distribution measuring device.

[0038] Based on such knowledge, the control unit 240 stores a predetermined sulfur concentration that is determined in advance according to the particle diameter of calcium carbonate particles to be generated. The predetermined sulfur concentration is preferably determined as a concentration range having a certain range. Then, the control unit 240 judges whether the sulfur concentration measured by the concentration measurement unit 230 is (within) the predetermined sulfur concentration or is a concentration different from (within) the predetermined sulfur concentration. Then, when the measured sulfur concentration is different from (within) the predetermined sulfur concentration (step S140: NO), the control unit 240 controls the operation of the concentration adjustment unit 250 so as to adjust the sulfur concentration of the material solution to (within) the predetermined sulfur concentration (next step).

[0039] In addition, Patent Document 6 describes that calcium carbonate particles can be made small by adding barium sulfate to the material solution. However, the particle size of the calcium carbonate particles obtained by the method described in Patent Document 6 was not stable. This is considered to be because the method described in Patent Document 6 does not take into account the concentration of sulfur atoms originally contained in the material solution, and the sulfur concentration after adding barium sulfate changes depending on the original sulfur concentration of the material solution. In contrast, in this embodiment, the sulfur concentration of the material solution is measured in the previous step, and then the sulfur concentration of the material solution is adjusted in the next step so that it becomes a predetermined concentration. Therefore, the sulfur concentration when crystallizing calcium carbonate particles can be set to a concentration according to the particle size of the particles to be crystallized, and calcium carbonate particles having a target particle size according to the sulfur concentration can be crystallized.

[0040] (Concentration adjustment: Step S150) When the sulfur concentration measured by the concentration measuring unit 230 is different from the predetermined sulfur concentration (step S140: NO), the concentration adjusting unit 250 adjusts the sulfur concentration of the material solution flowing through the flow path connecting the separation unit 220 and the crystallization unit 260 to the predetermined sulfur concentration under the control of the control unit 240. When the sulfur concentration measured by the concentration measuring unit 230 is the predetermined sulfur concentration (step S140: YES), the concentration adjusting unit 250 may or may not adjust the sulfur concentration.

[0041] Specifically, when the sulfur concentration of the material solution is lower than a predetermined sulfur concentration, the concentration adjusting unit 250 increases the sulfur concentration of the material solution to the predetermined sulfur concentration. Examples of methods for increasing the sulfur concentration include a method of adding a compound containing sulfur, such as sulfate or sulfite, to the material solution, and a method of introducing a gas containing sulfur oxide into the material solution. Either of these methods may be performed alone, or both may be performed simultaneously or separately.

[0042] Examples of the sulfates and sulfites include calcium sulfate, calcium sulfite, barium sulfate, sodium sulfate, sodium sulfite, potassium sulfate, potassium sulfite, etc. Among these, sodium sulfate and potassium sulfate are preferred from the viewpoint of suppressing the introduction of impurities that do not contribute to the production of calcium carbonate particles and increasing the calcium concentration of the material solution to increase the amount of calcium carbonate particles produced. Only one type of these sulfur-containing compounds may be added, or two or more types may be mixed and added separately.

[0043] Examples of the gas containing the sulfur oxides include sulfur monoxide (SO), sulfur dioxide (SO2), and sulfur trioxide (SO3). Among these, sulfur dioxide is preferred because it is likely to generate sulfate ions, which have a high effect of controlling the particle size of calcium carbonate particles, when introduced into the material solution. These sulfur oxides may be introduced together with a carrier such as nitrogen gas. Furthermore, only one type of these sulfur oxides may be introduced, or two or more types may be mixed and introduced separately.

[0044] Moreover, when the sulfur concentration of the material solution is higher than a predetermined sulfur concentration, the concentration adjusting unit 250 reduces the sulfur concentration of the material solution to the predetermined sulfur concentration. Examples of methods for reducing the sulfur concentration include a method of adsorbing and removing ions containing sulfur atoms or compounds containing sulfur atoms using an ion exchange resin or the like, and a method of precipitating sulfur as a poorly soluble salt such as ettringite and then removing the precipitated solids by filtration or the like. The above adsorption and removal can reduce the sulfur concentration in a short time. The above precipitation and removal can reduce the sulfur concentration in a simple manner. Either of these methods may be performed alone, or both may be performed simultaneously or separately.

[0045] The concentration adjustment unit 250 can have, for example, a concentration increase unit that performs the operation of increasing the sulfur concentration as described above, and a concentration decrease unit that performs the operation of decreasing the sulfur concentration as described above, which are independently controlled by the control unit 240. The concentration increase unit can have, for example, a compound storage tank that stores a compound containing sulfur and an addition unit that adds the compound to the material solution, or a gas storage tank that stores a gas containing sulfur oxide and an addition unit that adds the gas to the material solution. The concentration decrease unit can have, for example, a flow path having a remover such as an ion exchange resin, or an addition unit that adds an aluminum additive to generate ettringite.

[0046] The concentration adjustment unit 250 may have a stirring tank for homogenizing the concentration of the material solution after performing these concentration adjustment operations, and a filtration device for removing refined impurities, foreign matter, precipitated ettringite, etc.

[0047] The material solution having the sulfur concentration adjusted in this manner is sent to the crystallization section 260 under the control of the control section 240.

[0048] (Crystallization of calcium carbonate particles: step S160) The crystallization section 260 crystallizes calcium carbonate particles from a material solution having a predetermined sulfur concentration.

[0049] The method for crystallizing calcium carbonate particles is not particularly limited. However, the calcium ions (Ca ions) dissolved in the material solution can be crystallized by introducing carbon dioxide or adding carbonates such as potassium carbonate and sodium carbonate. 2+ ) and carbonate ions (CO3 2- Of these, the introduction of carbon dioxide is preferred because the process is simple, the effect of reducing the emission of carbon dioxide, a greenhouse gas, through carbon dioxide fixation is expected, and furthermore, the generation of unnecessary by-products is small.

[0050] In this embodiment, the crystallization unit 260 has a crystallization tank 262 for crystallizing calcium carbonate particles, and the crystallization tank 262 has an agitator 266 driven by a motor 264. The crystallization unit 260 also has a gas tank 268 for storing a gas containing carbon dioxide. The crystallization unit 260 rotates the agitator 266 under the control of the control unit 240 to agitate the material solution in the crystallization tank 262. At the same time, the crystallization unit 260 turns the gas containing carbon dioxide supplied from the gas tank 268 into bubbles under the control of the control unit 240 and introduces (bubbles) the gas into the crystallization tank 262 to crystallize calcium carbonate particles.

[0051] The concentration of carbon dioxide in the gas introduced is not particularly limited, and can be, for example, 10% by volume or more and 100% by volume or less of the gas introduced. By setting the carbon dioxide concentration to 10% by volume or more, calcium carbonate particles can be crystallized in a short period of time.

[0052] The gas containing carbon dioxide may be factory exhaust gas, combustion exhaust gas from petroleum and natural gas, waste incineration exhaust gas, etc. By using these exhaust gases, it is possible to reduce the amount of carbon dioxide emitted into the atmosphere, thereby contributing to reducing the environmental load.

[0053] The conditions for introducing carbon dioxide are not particularly limited. For example, the carbon dioxide introduction rate can be 0.01 L / min or more and 10 L / min or less. The carbon dioxide introduction time can be 60 minutes or more and 240 minutes or less. The carbon dioxide introduction temperature can be 10°C or more and 40°C or less.

[0054] The pH of the material solution when carbon dioxide is introduced is preferably 7.0 or more. By setting the pH at 7.0 or more, it is possible to prevent re-dissolution of calcium crystallized as calcium carbonate. The pH of the material solution is preferably 7.0 or more and 13.0 or less, and more preferably 8.0 or more and 13.0 or less.

[0055] In addition, seed crystals may be added to the material solution to promote the crystallization of calcium carbonate particles, but it is preferable not to add seed crystals from the viewpoint of suppressing the variation in particle size due to crystal growth occurring on the surface of the seed crystals and the seed crystals promoting the generation of new crystal nuclei.

[0056] The material solution containing the thus crystallized calcium carbonate particles is sent to the recovery section 270 under the control of the control section 240.

[0057] (Filtration: Step S170) The recovery section 270 filters the material solution containing the calcium carbonate particles to recover the calcium carbonate particles.

[0058] The filtration by the collection unit 270 may be performed by a known method such as suction filtration.

[0059] The recovered calcium carbonate particles may be dried or pulverized as necessary. In addition, surface treatment with fatty acid or the like may be performed depending on the application. The liquid component (treated liquid) separated by filtration may be disposed of as waste liquid, may be used for other applications, or may be reused as a material solution.

[0060] The calcium carbonate particles obtained in this way can be used in a wide range of applications, such as fillers for plastics, paper and paints, soil conditioners such as pesticides and fertilizers, adhesives, sealants, erasers and toothpastes that take advantage of their abrasive properties, sheet and film-like paper substitutes and plastic substitutes made primarily from calcium carbonate particles, as well as food additives and cosmetic ingredients.

[0061] [Other embodiments] It should be noted that the above-described embodiment is merely an example of the present invention, and the present invention is not limited to the above-described embodiment. Needless to say, various other embodiments are possible within the scope of the concept of the present invention.

[0062] For example, in the step of measuring the concentration of the material solution (step S130), the concentration measurement unit 230 may also measure the concentration of elements other than sulfur. Then, in the step of adjusting the concentration of the material solution (step S150) after the determination in the determination step (step S140), the concentration adjustment unit 250 may also adjust the concentration of elements other than sulfur. Note that, if the concentration measurement method described above is used, the concentration of elements other than sulfur can be measured simultaneously when the concentration measurement unit 230 measures the concentration. Note that the measurement, determination, and adjustment of the concentration of other elements may be performed simultaneously with the measurement, determination, and adjustment of the sulfur concentration, or may be performed separately.

[0063] According to the findings of the present inventors, the particle diameter of calcium carbonate particles can be further finely adjusted by adjusting the barium concentration and calcium concentration together with the sulfur concentration. Therefore, the concentration measuring unit 230 measures the barium concentration and calcium concentration in the material solution, and the control unit 240 determines whether or not the measured barium concentration and calcium concentration are predetermined. If the measured barium concentration and calcium concentration are different from the predetermined barium concentration and calcium concentration, the concentration adjusting unit 250 adjusts the barium concentration and calcium concentration in the material solution to the predetermined barium concentration and calcium concentration, thereby further finely adjusting the particle diameter of calcium carbonate particles.

[0064] In the above embodiment, the sulfur concentration of the material solution is measured, determined, and adjusted while the material solution flows from the separation section 220, which performs solid-liquid separation, to the crystallization section 260, which performs crystallization. However, these measurements, determinations, and adjustments may be performed in the crystallization section 260 before crystallization (for example, before carbon dioxide is introduced) or during crystallization (for example, while carbon dioxide is being introduced). The sulfur concentration may be measured and determined during the extraction of calcium by the extraction section 210, and the extraction conditions may be changed according to the determination results to change the amount of sulfur extracted from the calcium raw material. EXAMPLES

[0065] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0066] [Experiment 1] 1. Preparation of materials Commercially available Portland cement was prepared as the calcium raw material. 800 g of the calcium raw material was mixed with 3200 mL of ion-exchanged water and stirred to obtain a suspension in which the calcium raw material was suspended. The suspension was then filtered using a solid-liquid separator to obtain a calcium-containing solution (material solution).

[0067] At this time, the source of the Portland cement or the stirring conditions were changed to obtain four calcium-containing solutions 1 to 4 (hereinafter simply referred to as "Ca solution 1" to "Ca solution 4") with different compositions.

[0068] The compositions of these calcium-containing solutions were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) to examine the concentration of each element in 2000 mL of Ca solution. The element concentrations measured for Ca solution 1 to Ca solution 4 are shown in Table 1. The unit of concentration of each element shown in Table 1 is mg / L.

[0069] [Table 1]

[0070] The pH of each calcium-containing solution was adjusted to 7.0 or higher, and a mixed gas of carbon dioxide (CO2) and nitrogen (N2) was introduced (bubbled) to crystallize calcium carbonate. The mixed gas had a CO2 concentration of 10% by volume. The flow rate of the mixed gas during introduction was 50 mL / min. The introduction was carried out for 90 minutes.

[0071] After stopping the introduction of the mixed gas, each calcium-containing solution was subjected to suction filtration to obtain calcium carbonate particles (the calcium carbonate particles obtained from Ca solution 1 to Ca solution 4 are referred to as "CaCO3 particles 1" to "CaCO3 particles 4", respectively). The particle size distribution of each calcium carbonate particle was measured using a laser diffraction particle size distribution measuring device (MASTERSIZER3000 manufactured by Malvern Panalytical). From the measured particle size distribution, the D50 and D90 of each calcium carbonate particle were calculated.

[0072] In addition, the ratio of the amount of calcium (mol) in the calcium carbonate particles calculated from the mass of the obtained calcium carbonate particles to the amount of calcium (mol) in the calcium-containing solution was calculated to calculate the crystallization rate of each calcium carbonate particle.

[0073] The D50 and D90 of CaCO3 particles 1 to CaCO3 particles 4 are shown in Table 2.

[0074] [Table 2]

[0075] The results in Tables 1 and 2 show that the particle size of the calcium carbonate particles produced changes depending on the sulfur concentration of the calcium-containing solution (material solution).

[0076] [Experiment 2] Sodium sulfate was added to Ca solution 4 obtained in experiment 1 to obtain calcium solution 5 (Ca solution 5) in which the sulfur concentration was changed to 500 mg / L.

[0077] A mixed gas of carbon dioxide and nitrogen was introduced into Ca solution 5 under the same conditions as in Experiment 1 to obtain calcium carbonate particles (CaCO3 particles 5). The particle size of CaCO3 particles 5 was measured in the same manner as in Experiment 1, and D50 was 8.3 μm and D90 was 15.3 μm. The crystallization rate of the calcium carbonate particles was 69.6%.

[0078] The results of Experiment 2 show that by changing the sulfur concentration in the calcium-containing solution (material solution), the particle size of the calcium carbonate particles produced can be changed depending on the sulfur concentration.

[0079] [Experiment 3] Barium chloride was added to Ca solution 2 obtained in experiment 1 to obtain calcium solution 6 (Ca solution 6) in which the barium concentration was changed to 2.3 mg / L.

[0080] A mixed gas of carbon dioxide and nitrogen was introduced into Ca solution 6 under the same conditions as in Experiment 1 to obtain calcium carbonate particles (CaCO3 particles 6). The particle size of CaCO3 particles 6 was measured in the same manner as in Experiment 1, and the D50 was 11.4 μm and the D90 was 19.6 μm. The crystallization rate of the calcium carbonate particles was 42.0%.

[0081] The results of Experiment 3 show that by changing the barium concentration in the calcium-containing solution (material solution), the particle size of the calcium carbonate particles produced can be fine-tuned according to the barium concentration. [Industrial Applicability]

[0082] According to the present invention, calcium carbonate particles having a desired particle size can be obtained by a simple method. Therefore, the present invention is expected to increase the efficiency of carbon dioxide fixation by calcium carbonate particles, further reduce the environmental load, and further promote the spread of calcium carbonate particles to various applications. [Explanation of symbols]

[0083] 200 Manufacturing equipment 210 Extraction part 212 Extraction tank 214 Motor 216 Stirrer 220 Separation section 230 Concentration measurement section 240 Control Unit 250 Density adjustment section 260 Crystallization Section 262 Crystallization tank 264 Motor 266 Stirrer 268 Gas Tank 270 Recovery Department

Claims

1. Measuring a sulfur concentration of a material solution containing calcium; When the measured sulfur concentration is different from a predetermined sulfur concentration determined according to a particle size of calcium carbonate to be crystallized, the sulfur concentration of the material solution is adjusted to the predetermined sulfur concentration. and introducing carbon dioxide or carbonate ions into the material solution having the adjusted sulfur concentration to crystallize calcium carbonate. A method for producing calcium carbonate particles.

2. The step of measuring the sulfur concentration is carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS); The method for producing calcium carbonate particles according to claim 1 .

3. The predetermined sulfur concentration is 50 mg / L or more and 10,000 mg / L or less. The method for producing calcium carbonate particles according to claim 1 .

4. The predetermined sulfur concentration is a concentration of 0.01 mg / L or more and less than 50 mg / L. The method for producing calcium carbonate particles according to claim 1 .

5. A step of adjusting the barium concentration of the material solution to a predetermined barium concentration, In the step of crystallizing calcium carbonate, carbon dioxide is introduced into the material solution in which the sulfur concentration and the barium concentration have been adjusted. The method for producing calcium carbonate particles according to claim 1 .

6. The crystallization step is carried out by adjusting the pH of the material solution to 7.0 or more and introducing carbon dioxide. The method for producing calcium carbonate particles according to claim 1 .

7. A measurement unit for measuring a sulfur concentration of a material solution containing calcium; a concentration adjusting unit that adjusts the measured sulfur concentration of the material solution to a predetermined sulfur concentration determined according to a particle size of calcium carbonate to be crystallized; and a crystallization section for introducing carbon dioxide into the material solution having the adjusted sulfur concentration to crystallize calcium carbonate. Manufacturing equipment for calcium carbonate particles.

8. The concentration adjusting unit adjusts the sulfur concentration of the material solution to a predetermined sulfur concentration when the measured sulfur concentration of the material solution is not the predetermined sulfur concentration. The apparatus for producing calcium carbonate particles according to claim 7.

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