Carbon dioxide fixation method and carbon dioxide fixation apparatus

Abstract

To provide a carbon dioxide fixation method and a carbon dioxide fixation apparatus capable of efficiently fixing carbon dioxide and obtaining calcium carbonate.SOLUTION: Provided is a carbon dioxide fixation method comprising the following step of: mixing a calcium-containing waste with an extractant-containing fluid to obtain a fluid containing a reactant comprising the calcium-containing waste and the extractant; and obtaining calcium carbonate by having the fluid containing the reactant brought into contact with a gas containing carbon dioxide. When obtaining the fluid containing the reactant, the fluid containing the reactant has 11 pH or higher, and when obtaining the calcium carbonate, the temperature of the fluid containing the reactant is 50°C or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for immobilizing carbon dioxide and an apparatus for immobilizing carbon dioxide. [Background technology]

[0002] In recent years, interest in global warming has grown, and there is a demand for reducing the amount of carbon dioxide released into the atmosphere. At various facilities, such as power plants, incinerators, cement plants, steelworks, and industrial facilities, efforts are being made to reduce and capture the amount of carbon dioxide-containing exhaust gases emitted into the atmosphere during their operations. One known method for capturing carbon dioxide is to react it with Group 2 elements, such as calcium and magnesium, to produce carbonates.

[0003] For example, Patent Document 1 proposes a carbon dioxide fixation apparatus that can directly fix carbon dioxide at low cost by circulating an acid and an alkali and securing an alkali source from rocks or waste materials containing Group 2 elements such as calcium or magnesium. Patent Document 2 also proposes a method for fixating carbon dioxide, which is characterized by bringing a gas containing carbon dioxide into contact with an aqueous solution obtained from water, an alkaline earth metal-containing substance, and a salt of a weak base and a strong acid to produce an alkaline earth metal carbonate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-96975 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-97072 Summary of the Invention [Problem to be solved by the invention]

[0005] Rocks and waste materials are waste materials that primarily contain calcium, and it would be useful if the calcium contained therein could be utilized. However, these waste materials have already absorbed carbon dioxide from the atmosphere and been fixed as calcium carbonate. Therefore, the technology described in Patent Document 1 has the problem that when rocks or waste materials containing Group 2 elements are added to a strong acid, calcium carbonate is eluted from them, and when this calcium carbonate reacts with water, carbon dioxide is released back into the atmosphere. Furthermore, the technology described in Patent Document 2 adds an alkaline earth metal-containing substance to an aqueous solution containing a salt of a weak base and a strong acid, and the reaction is carried out at a temperature range of 60 to 91°C. However, at such high temperatures, the amount of volatilization of the salt of the weak base and the strong acid increases, resulting in a problem of reduced extraction ability of the alkaline earth metal.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for immobilizing carbon dioxide and an apparatus for immobilizing carbon dioxide, which are capable of efficiently immobilizing carbon dioxide and obtaining calcium carbonate. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following invention.

[0008] That is, the present invention relates to the following: [1] Mixing calcium-containing waste with a fluid containing an extractant to obtain a fluid containing a reaction product of the calcium-containing waste and the extractant; and contacting a fluid containing the reactants with a gas containing carbon dioxide to obtain calcium carbonate; In obtaining the fluid containing the reactants, the pH of the fluid containing the reactants is 11 or more; The method for fixation of carbon dioxide, wherein, in obtaining the calcium carbonate, the temperature of the fluid containing the reactants is 50°C or lower. [2] The method for fixation of carbon dioxide according to [1], wherein, in obtaining the calcium carbonate, the pH of the fluid when the fluid containing the reactants is brought into contact with the gas containing carbon dioxide is 9 or less. [3] The method for fixation of carbon dioxide according to [1] or [2] above, wherein the extractant is an ammonium salt. [4] The method for fixating carbon dioxide according to any one of [1] to [3] above, further comprising drying the calcium carbonate at a temperature of 70°C or higher and 200°C or lower. [5] The method for fixation of carbon dioxide according to [4] above, wherein the gas containing carbon dioxide comprises an exhaust gas containing at least one gas selected from water vapor and ammonia discharged in drying the calcium carbonate. [6] The method for fixation of carbon dioxide according to any one of [1] to [5], further comprising, after obtaining the fluid containing the reactants, subjecting the fluid containing the reactants to solid-liquid separation and recovering a solid content containing a calcium-containing substance. [7] The method for fixation of carbon dioxide according to [6], further comprising drying the solid content at 70°C or higher and 200°C or lower after recovering the solid content. [8] The method for fixation of carbon dioxide according to [7], wherein the gas containing carbon dioxide includes exhaust gas containing at least one gas selected from water vapor and ammonia discharged during drying of the solid content. [9] The method for fixation of carbon dioxide according to any one of [1] to [8] above, wherein obtaining the fluid containing the reactants is carried out at a temperature of 50°C or lower.

[10] A reaction device for contacting a fluid containing a calcium-containing waste and a reactant with a gas containing carbon dioxide to obtain calcium carbonate; a drying device for drying the calcium carbonate; a supply line (1) for supplying exhaust gas containing at least one gas selected from water vapor and ammonia from the drying device to the reaction device, The fluid containing the reactant has a pH of 11 or more before being contacted with a gas containing carbon dioxide, The carbon dioxide fixation device, wherein the temperature of the fluid is 50°C or less when the fluid containing the reactant is brought into contact with a gas containing carbon dioxide.

[11] The reaction device includes a first reaction device for obtaining a fluid containing a reaction product of the calcium-containing waste and the extractant; a second reaction device that brings the gas containing carbon dioxide into contact with the fluid containing the reactant to obtain calcium carbonate.

[12] The carbon dioxide fixation device according to

[11] , comprising: a supply line (2) for supplying a fluid containing the reactants from the first reactor to the second reactor; and a supply line (3) for supplying a fluid remaining after calcium carbonate obtained in the second reactor is recovered by solid-liquid separation from the second reactor to the first reactor. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method and an apparatus for immobilizing carbon dioxide, which are capable of efficiently immobilizing carbon dioxide and obtaining calcium carbonate. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a preferred embodiment of the carbon dioxide fixation device of the present embodiment. [Figure 2] 1 is an X-ray diffraction spectrum of calcium carbonate obtained in Example 5-3. [Figure 3] FIG. 1 is a diagram showing a scanning electron microscope (SEM) image (magnification: 200 times) of calcium carbonate obtained in Example 5-3. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. The present invention is not limited to the following embodiment, and can be implemented with any modifications within the scope that does not impair the effects of the invention. In this specification, the notation of a numerical range as "AA to BB" means "at least AA and at most BB." In addition, in this specification, the numbers associated with "at least," "at most," and "to" in describing a numerical range are numbers that can be arbitrarily combined. For example, when a certain numerical range is described as "CC to DD" and "EE to FF," the numerical ranges "CC to FF" and "EE to DD" are also included.

[0012] [Method for fixing carbon dioxide] The carbon dioxide fixation method of the present embodiment includes: mixing a calcium-containing waste with a fluid containing an extractant to obtain a fluid containing a reaction product of the calcium-containing waste with the extractant; and contacting a fluid containing the reactants with a gas containing carbon dioxide to obtain calcium carbonate; In obtaining the fluid containing the reactants, the pH of the fluid containing the reactants is 11 or more; In obtaining the calcium carbonate, the temperature of the fluid containing the reactants is 50°C or less.

[0013] In the method for immobilizing carbon dioxide of this embodiment, calcium-containing waste is mixed with a fluid containing an extractant to obtain a fluid containing a reaction product of the calcium-containing waste and the extractant, and the reactant can be efficiently produced by setting the pH of the fluid containing the reactant to 11 or higher. When the fluid containing the reactant obtained in this manner is brought into contact with a gas containing carbon dioxide, the temperature of the fluid containing the reactant is set to 50°C or lower, so that carbon dioxide can be efficiently immobilized and calcium carbonate can be obtained.

[0014] (Obtaining a fluid containing a reaction product of calcium-containing waste and an extractant) The method for immobilizing carbon dioxide of this embodiment includes mixing calcium-containing waste with a fluid containing an extractant to obtain a fluid containing a reaction product of the calcium-containing waste and the extractant, wherein the pH of the fluid containing the reaction product is 11 or higher.

[0015] Examples of calcium-containing waste include ready-mixed concrete sludge and waste concrete. Ready-mixed concrete sludge is obtained by sieving sludge generated during concrete production in ready-mixed concrete plants and concrete product plants using a sieve with an appropriate mesh size, and then collecting the sludge as a powder containing cement hydrate and unhydrated cement. Any waste material containing concrete, such as waste material generated during the demolition of a building that uses concrete, such as a reinforced concrete building, can be used as the waste concrete, without any particular restrictions. The waste concrete is preferably generated during the demolition work and treated to remove foreign matter other than concrete, such as reinforcing bars.

[0016] The extractant is a compound that extracts calcium from calcium-containing waste and produces calcium compounds other than calcium carbonate as a reaction product. Examples of the extractant include salts formed from weak bases and strong acids. Examples of weak bases include ammonia, methylamine, aniline, pyridine, aluminum hydroxide, magnesium hydroxide, iron hydroxide, copper hydroxide, and zinc hydroxide. Examples of strong acids include hydrochloric acid, sulfuric acid, nitric acid, chromic acid, permanganic acid, and perchloric acid. Examples of salts formed from a weak base and a strong acid include ammonium salts such as ammonium chloride, ammonium sulfate, and ammonium nitrate; aluminum salts such as aluminum chloride, aluminum sulfate, and aluminum nitrate; and magnesium salts such as magnesium chloride, magnesium sulfate, and magnesium nitrate. Among these, from the viewpoint of more efficiently immobilizing carbon dioxide and obtaining calcium carbonate, ammonium salts are preferred, and ammonium chloride is more preferred.

[0017] There is no particular limitation on the method for mixing the calcium-containing waste with the fluid containing the extractant, and the calcium-containing waste and the fluid containing the extractant may be mixed by being introduced into a reactor capable of mixing the calcium-containing waste with the fluid containing the extractant. Alternatively, the calcium-containing waste may be mixed with a solvent such as water to form a fluid containing the calcium-containing waste, and then introduced into the reactor. The order in which these compounds are added to the reaction device is not particularly limited.

[0018] The calcium-containing waste and the extractant may be mixed using a stirring device. The stirring device is not particularly limited, but examples thereof include a dual mixer, a Henschel mixer, a mixing shaker, a tumbler mixer, a V-type mixer, a double-cone type mixer, a ribbon type mixer, a Nauta mixer, a super mixer, etc. Among these, a dual mixer is preferred from the viewpoint of more efficiently carrying out the reaction between the calcium-containing waste and the extractant.

[0019] In obtaining the fluid containing the reactant, the pH of the fluid containing the reactant is 11 or higher. When the pH of the fluid containing the reactant is 11 or higher, the reaction between the calcium-containing waste and the extractant is promoted, and the reactant can be efficiently produced. From this viewpoint, the pH of the fluid containing the reactant is preferably 11.5 or higher, more preferably 12 or higher. Furthermore, the upper limit is not particularly limited, but is preferably 13 or lower. In this specification, pH is a value measured by a pH meter capable of measuring the hydrogen ion exponent of a fluid. Specifically, it can be measured by the method described in the examples.

[0020] From the viewpoint of more efficiently carrying out the reaction with the calcium-containing waste, the solids concentration of the fluid containing the extractant is preferably 0.3 to 30 mass %, more preferably 0.5 to 20 mass %, and even more preferably 0.8 to 10 mass %, based on the total amount of the fluid containing the extractant (100 mass %). In this specification, the term "solid content concentration" refers to the content (concentration) of components other than the solvent.

[0021] From the viewpoint of more efficiently carrying out the reaction with the extractant, the solids concentration of the fluid containing the calcium-containing waste is preferably 1 to 30 mass %, more preferably 3 to 20 mass %, and even more preferably 5 to 15 mass %, based on the total amount (100 mass %) of the fluid containing the calcium-containing waste.

[0022] The mixing ratio of the calcium-containing waste to the extractant is preferably 1:10 to 10:1 by mass, more preferably 2:8 to 8:2, and even more preferably 3:5 to 5:3. When the mixing ratio is within the above range, it becomes easier to adjust the pH of the fluid containing the reactants to 11 or higher, and the reactants can be produced more efficiently.

[0023] From the viewpoint of more efficiently producing the reactants, obtaining the fluid containing the reactants is preferably carried out at a temperature of 50°C or less, more preferably 45°C or less. The lower limit is not particularly limited, but is usually room temperature (23°C) or higher, preferably 25°C or higher. Furthermore, when an ammonium salt is used as the extractant, if the temperature is 50°C or less, the ammonium salt is less likely to deteriorate, and the reactants can be produced more efficiently. Moreover, from the viewpoint of more efficiently producing the reaction product, the mixing time is preferably 20 minutes to 25 hours, more preferably 30 minutes to 15 hours, and even more preferably 30 minutes to 5 hours.

[0024] The more calcium extracted from the calcium-containing waste by the extractant, the better. The calcium concentration in the fluid containing the reactants is preferably 1200 mass ppm or more, more preferably 2000 mass ppm or more, and even more preferably 3000 mass ppm or more. The upper limit of the calcium concentration is not particularly limited, but is preferably 100,000 mass ppm or less.

[0025] In the carbon dioxide fixation method of this embodiment, calcium compounds other than calcium carbonate are produced as reaction products between the calcium-containing waste and the extractant. Examples of calcium compounds other than calcium carbonate include calcium chloride, calcium sulfate, and calcium nitrate.

[0026] (Producing calcium carbonate by contacting a fluid containing a reactant with a gas containing carbon dioxide) The method for immobilizing carbon dioxide of this embodiment includes bringing a fluid containing a reactant into contact with a gas containing carbon dioxide to obtain calcium carbonate, and the temperature of the fluid containing the reactant is 50°C or lower. The fluid containing the reactants may include a filtrate containing the reactants, which will be described later (subjecting a fluid containing the reactants to solid-liquid separation and recovering a solid content containing a calcium-containing substance). The carbon dioxide-containing gas can be any gas containing carbon dioxide without any particular limitation. Representative examples include exhaust gases (also referred to as "combustion exhaust gases") emitted from various factory facilities. From the viewpoint of more efficiently immobilizing carbon dioxide to obtain calcium carbonate, the carbon dioxide-containing gas preferably contains exhaust gas containing at least one gas selected from water vapor and ammonia emitted in drying calcium carbonate, as described below, or preferably contains exhaust gas containing at least one gas selected from water vapor and ammonia emitted in drying a solid content, as described below.

[0027] There are no particular limitations on the method for contacting the fluid containing the reactant with the gas containing carbon dioxide, and for example, the gas containing carbon dioxide may be supplied by blowing it into a reaction device into which the fluid containing the reactant has been introduced. The reaction equipment is not particularly limited, but a fine bubble generator is preferred from the viewpoint of more efficiently immobilizing carbon dioxide and obtaining calcium carbonate. Fine bubble generation methods include swirling flow liquid type, ejector type, Venturi type, micropore type, static mixer type, pressure dissolution deposition type, heat deposition type, and vapor direct contact condensation type, and among these, the static mixer type is preferred.

[0028] Furthermore, as the reaction equipment used when contacting the fluid containing the reactant with the gas containing carbon dioxide, the stirring equipment that can be used when mixing the calcium-containing waste with the extractant may be used as is, or a different stirring equipment may be used.

[0029] In obtaining calcium carbonate by contacting a fluid containing a reactant with a gas containing carbon dioxide, the temperature of the fluid containing the reactant is 50°C or lower. When the temperature of the fluid containing the reactant is 50°C or lower, the reaction between the calcium compound reactant, such as calcium chloride, calcium sulfate, or calcium nitrate, and the gas containing carbon dioxide proceeds, and carbon dioxide is efficiently immobilized to obtain calcium carbonate. From this perspective, the temperature of the fluid containing the reactant is preferably 45°C or lower. The lower limit is not particularly limited, but is usually room temperature (23°C) or higher, and preferably 25°C or higher.

[0030] In obtaining the calcium carbonate, the pH of the fluid when the fluid containing the reactants is brought into contact with the gas containing carbon dioxide is, from the viewpoint of more efficiently immobilizing carbon dioxide and obtaining calcium carbonate, preferably 9 or less, more preferably 8 or less, and even more preferably 7 or less. The lower limit is not particularly limited, but is preferably 6 or more.

[0031] Calcium carbonate is produced by contacting the fluid containing the reactant with the gas containing carbon dioxide. The produced calcium carbonate can be recovered as a solid content by subjecting the fluid containing calcium carbonate to solid-liquid separation. Since the fluid from which calcium carbonate has been recovered contains the extractant produced as a by-product, it is preferable to reuse it for the reaction with the calcium-containing waste.

[0032] The method for solid-liquid separation of a fluid containing calcium carbonate is not particularly limited, and examples thereof include a method using a pressure separation device that separates a solid component from a liquid component by applying pressure or squeezing using a filter, a method using a centrifugal separator that separates a solid component from a liquid component by the action of centrifugal force, and a method using a sedimentation separation device that allows the solid component to settle by leaving the mixture to stand. Among these, the method using a pressure separation device is preferred from the viewpoints of reducing separation costs and shortening separation time.

[0033] (Drying calcium carbonate) The method for immobilizing carbon dioxide of this embodiment preferably further includes drying the calcium carbonate at a temperature of 70°C or higher and 200°C or lower. Water may adhere to the produced calcium carbonate. Furthermore, when an ammonium salt is used as the extractant, ammonia may adhere to the calcium carbonate, causing an ammonia odor. Therefore, by drying the calcium carbonate at a temperature of 70°C or higher and 200°C or lower, water and ammonia are removed from the calcium carbonate, and the ammonia odor is reduced, thereby enabling the production of higher quality calcium carbonate.

[0034] Drying the calcium carbonate within a desired temperature range is preferably carried out using a drying apparatus. The drying apparatus is not particularly limited and may be a batch type or a continuous type. Examples of drying apparatus include a flash dryer, a band dryer, a spray dryer, and a rotary dryer. Among these, a flash dryer is preferred from the viewpoint of more efficiently removing water and ammonia. Examples of flash dryers include an apparatus in which heated gas is supplied to a drying tube (which may be a cylindrical tank) and calcium carbonate (the object to be dried) is supplied to the drying tube.

[0035] The heating temperature when drying the calcium carbonate is preferably 70° C. or higher and 200° C. or lower, more preferably 90° C. or higher and 200° C. or lower, and even more preferably 110° C. or higher and 200° C. or lower. When the heating temperature is 70° C. or higher, water and ammonia that may adhere to calcium carbonate can be efficiently removed, and when the heating temperature is 200° C. or lower, water and ammonia can be removed without affecting the physical properties of calcium carbonate.

[0036] As the gas supplied to the flash dryer, a gas containing carbon dioxide (combustion exhaust gas) is preferably used. The temperature of the combustion exhaust gas cannot be generalized because it varies depending on the source of the exhaust gas used, but is usually 30°C or higher and 250°C or lower, preferably 50°C or higher and 200°C or lower, more preferably 70°C or higher and 180°C or lower, and even more preferably 80°C or higher and 150°C or lower. When the temperature of the combustion exhaust gas is within the above range, it is easy to adjust the heating temperature during drying of calcium carbonate to a desired temperature range.

[0037] By drying the calcium carbonate within a desired temperature range, at least one gas selected from water vapor and ammonia is discharged. The gas containing carbon dioxide (combustion exhaust gas) used in drying the calcium carbonate is preferably reused as an exhaust gas containing these gases in obtaining the calcium carbonate. Since the exhaust gas used in drying has a high temperature of 70°C or higher and 200°C or lower, reusing the exhaust gas in obtaining the calcium carbonate makes it easier to adjust the temperature of the fluid containing the reactants to 50°C or lower.

[0038] (Solid-liquid separation of the fluid containing the reactants and recovery of the solids containing calcium-containing substances) The method for fixation of carbon dioxide of the present embodiment preferably further comprises, after obtaining a fluid containing the reactants, subjecting the fluid containing the reactants to solid-liquid separation and recovering a solid content containing a calcium-containing material. The solid content may contain calcium carbonate that may be contained in the calcium-containing waste and unreacted calcium-containing waste as calcium-containing substances, and by recovering these, they can be reused as raw materials for roadbed materials, etc. The solid-liquid separation of the fluid containing the reaction products and the recovery of the solid content containing the calcium-containing substance are preferably carried out before obtaining the calcium carbonate.

[0039] As a method for performing solid-liquid separation of the fluid containing the reactants, the solid-liquid separation methods described in the above section (obtaining calcium carbonate by contacting a fluid containing the reactants with a gas containing carbon dioxide) can be employed, and among them, a method using a pressurized separation device is preferred from the viewpoints of reducing separation costs and shortening separation time.

[0040] The fluid containing the reactants is subjected to solid-liquid separation using the separation equipment into a solid fraction containing a calcium-containing substance and a filtrate containing the reactants, and the solid fraction containing the calcium-containing substance is recovered. The filtrate is basically supplied as a fluid containing the reactants in obtaining the calcium carbonate described above, but a part of the filtrate may be discarded, if necessary.

[0041] (Drying the solid content) The method for fixation of carbon dioxide of the present embodiment preferably further comprises drying the solid content at 70° C. or higher and 200° C. or lower after recovering the solid content. Water may adhere to the solid content containing calcium-containing substances. Furthermore, when an ammonium salt is used as an extractant, ammonia may adhere to the solid content containing calcium-containing substances, causing an ammonia odor. Therefore, by drying the solid content containing calcium-containing substances at a temperature of 70°C or higher and 200°C or lower, water and ammonia are removed from the solid content containing calcium-containing substances, and the ammonia odor is reduced, allowing the solid content containing calcium-containing substances to be reused as a raw material for roadbed materials, etc.

[0042] The solid content containing the calcium-containing material is preferably dried within a desired temperature range using a drying apparatus, such as any of the drying apparatuses exemplified as drying apparatuses that can be used to dry calcium carbonate, and preferably an airflow drying apparatus. The drying equipment used to dry the solid content containing the calcium-containing material may be a drying equipment integrated with the drying equipment used to dry the calcium carbonate, or may be a separate drying equipment.

[0043] The heating temperature when drying the solid content containing a calcium-containing substance is preferably 70° C. or higher and 200° C. or lower, more preferably 90° C. or higher and 200° C. or lower, and even more preferably 110° C. or higher and 200° C. or lower. When the heating temperature is 70° C. or higher, water and ammonia that may adhere to the solid content containing a calcium-containing substance can be efficiently removed, and when the heating temperature is 200° C. or lower, water and ammonia can be removed without affecting the physical properties of the solid content containing a calcium-containing substance.

[0044] The gas supplied to the flash dryer is preferably a gas containing carbon dioxide (combustion exhaust gas). The temperature of the combustion exhaust gas cannot be generalized because it varies depending on the source of the exhaust gas used, but it is usually 30°C or higher and 250°C or lower, preferably 50°C or higher and 200°C or lower, more preferably 70°C or higher and 180°C or lower, and even more preferably 80°C or higher and 150°C or lower. When the temperature of the combustion exhaust gas is within the above range, it is easy to adjust the heating temperature when drying the solid content containing a calcium-containing material to a desired temperature range.

[0045] By drying the solid content containing a calcium-containing material within a desired temperature range, at least one gas selected from water vapor and ammonia is discharged. The carbon dioxide-containing gas (combustion exhaust gas) used to dry the solid content containing a calcium-containing material is preferably reused as an exhaust gas containing these gases in obtaining the calcium carbonate. Since the exhaust gas used in drying has a high temperature of 70°C or higher and 200°C or lower, reusing the exhaust gas in obtaining the calcium carbonate makes it easier to adjust the temperature of the fluid containing the reactants to 50°C or lower.

[0046] (Calcium carbonate) Calcium carbonate is known to have the following crystalline structures: calcite (trigonal crystal), vaterite (hexagonal crystal), and aragonite (orthorhombic crystal). According to the carbon dioxide fixation method of the present embodiment, calcium carbonate having the vaterite crystalline structure can be obtained. The crystalline structure of calcium carbonate can be confirmed by powder X-ray diffraction (XRD) measurement and scanning electron microscope (SEM) images, and specifically by the methods described in the examples.

[0047] Calcium carbonate having a vaterite crystal structure is suitable for use in papermaking, ink, abrasives, cosmetics, and the like.

[0048] [Carbon dioxide fixation device] The carbon dioxide fixation device of this embodiment includes: a reaction device for bringing a gas containing carbon dioxide into contact with a fluid containing a reaction product of the calcium-containing waste and the extractant to obtain calcium carbonate; a drying device for drying the calcium carbonate; a supply line (1) for supplying exhaust gas containing at least one gas selected from water vapor and ammonia from the drying device to the reaction device, The fluid containing the reactant has a pH of 11 or more before being contacted with a gas containing carbon dioxide, When the fluid containing the reactant is brought into contact with the gas containing carbon dioxide, the temperature of the fluid is 50°C or less.

[0049] FIG. 1 is a schematic diagram showing a preferred embodiment of the carbon dioxide fixation device of this embodiment. As shown in FIG. 1, the carbon dioxide fixation apparatus 100 of this embodiment includes a reaction device 10 that brings a gas containing carbon dioxide into contact with a fluid containing a reaction product of calcium-containing waste and an extractant to obtain calcium carbonate, a drying device 13 that dries the calcium carbonate, and a supply line (1) that connects the reaction device 10 and the drying device 13. The reaction equipment 10 may include a first reaction equipment 11 for obtaining a fluid containing a reactant of the calcium-containing waste with the extractant, and a second reaction equipment 12 for obtaining calcium carbonate by bringing the gas containing carbon dioxide into contact with the fluid containing the reactant. The first reaction equipment 11 and the second reaction equipment 12 are preferably equipped with a pH meter and a temperature meter, respectively, which are not shown. The reaction equipment 10 may also include supply lines (2) and (3) connecting the first reaction equipment 11 and the second reaction equipment 12. The fluid containing the reactant obtained in the first reaction equipment 11 is supplied to the second reaction equipment 12 through the supply line (2). The fluid obtained in the second reaction equipment 12 after recovering calcium carbonate by solid-liquid separation is supplied to the first reaction equipment 11 through the supply line (3).

[0050] The calcium carbonate (CaCO3) recovered by the solid-liquid separation is supplied to a dryer 13 and dried by being heated to a desired temperature using exhaust gas (combustion exhaust gas) discharged from a boiler 15 and various factory facilities. In FIG. 1, the exhaust gas is supplied from the boiler 15 to the dryer 13 through a supply line (5) connecting the dryer 13 and the boiler 15. The dried calcium carbonate is recovered as higher quality calcium carbonate, with adhering water and ammonia removed and the ammonia odor reduced. The exhaust gas used for drying is supplied to the second reactor 12 through a supply line (1) together with at least one gas selected from water vapor and ammonia discharged by drying the calcium carbonate, and is used as a gas containing carbon dioxide.

[0051] It is preferable to separate the fluid containing the reaction product obtained in the first reaction device 11 into a solid and a liquid, and recover a solid content containing a calcium-containing substance (Ca-containing solid content). The recovered solid content containing a calcium-containing substance is supplied to a dryer 14, where it is dried by being heated to a desired temperature with exhaust gas (combustion exhaust gas) discharged from a boiler 15 or various factory facilities. In FIG. 1, the exhaust gas is supplied from the boiler 15 to the dryer 14 through a supply line (6) connecting the dryer 14 and the boiler 15. The dried solid content containing a calcium-containing substance has water and ammonia that may adhere thereto removed, reducing the ammonia odor, and therefore the solid content containing a calcium-containing substance can be reused as a raw material for roadbed materials, etc. The exhaust gas used for drying, together with at least one gas selected from water vapor and ammonia discharged by drying the solid content containing the calcium-containing material, is supplied to the second reaction device 12 through a supply line (4) connecting the drying device 14 and the second reaction device 12, and is utilized as a gas containing carbon dioxide. In FIG. 1, the supply line (1) and the supply line (4) are shown as separate supply lines, but the supply line (4) may merge with the supply line (1) between the drying device 13 and the second reaction device 12.

[0052] In FIG. 1, the drying device 14 is provided as a device separate from the drying device 13, but the drying device 14 may be a drying device integrated with the drying device 13.

[0053] As the reaction device 10, the first reaction device 11, and the second reaction device 12, the devices exemplified above as the reaction device and the stirring device can be used. As the drying device 13 and the drying device 14, the devices exemplified above as the drying devices can be used. [Example]

[0054] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0055] The extractants used are shown below. Ammonium chloride: "Ammonium chloride Shika Grade 1" (product name), manufactured by Kanto Chemical Co., Ltd. Ammonium nitrate: "Ammonium nitrate grade 1" (product name), manufactured by Kanto Chemical Co., Ltd. Aluminum nitrate: "Aluminum nitrate nonahydrate, Grade 1" (product name), manufactured by Kanto Chemical Co., Ltd. Aluminum chloride: "Aluminum chloride (III) Grade 1" (product name), manufactured by Kanto Chemical Co., Ltd.

[0056] (Examples 1-1 to 4-3 and Comparative Examples 1-1 to 3-2) 100 mL of fresh concrete sludge water (calcium concentration: 900 mg / L, solids concentration: 10% by mass) was charged into a mixing device, and 1 mL of a fluid containing the extractant listed in Table 1 (solids concentration: 1% by mass) was added. The mixture was stirred and mixed at 25°C. For each stirring time listed in Table 1, the calcium concentration (Ca concentration) in the resulting mixed fluid was measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy: ICP-AES, ICP-OES) using an ICP-AES analyzer (Hitachi High-Tech Science Corporation, Model: SPECTROARCOS MVICP). The calcium extraction rate (%) was calculated from the measured and theoretical Ca concentrations. The pH of the mixed fluid was also measured using a pH meter (HORIBA, Ltd., Model: D-52S). The results are shown in Table 1.

[0057] [Table 1]

[0058] Table 1 shows that in Examples 1-1 to 4-3, in which the pH of the fluid (mixed fluid) containing the reaction product of the fresh concrete sludge water and the extractant was 11 or higher, the calcium extraction rate was high at 84% or higher, and the reaction product (calcium compound) was efficiently produced.

[0059] (Examples 5-1 to 8-1 and Comparative Examples 4-1 to 7-1) 100 mL of simulated sludge water (cement: 2.4% by mass) was placed in a stirring device, and 1 mL of a fluid (solids concentration: 1% by mass) containing the extractant shown in Table 2 was added. The mixture was stirred at a liquid temperature of 25°C for 1 hour, and the pH of the resulting mixed fluid was confirmed to be 11 or higher. Next, while adjusting the temperature of the mixed fluid to the temperature shown in Table 2, carbon dioxide was supplied to the mixed fluid at a flow rate of 1 L / min until the pH reached one of the values ​​shown in Table 2. The amount of precipitate (calcium carbonate) at each pH value was measured, and the calcium carbonate recovery rate (%) was calculated from the precipitated amount of calcium carbonate (measured value) and the theoretical precipitated amount of calcium carbonate. The results are shown in Table 2. The calcium carbonate obtained in Example 5-3 was subjected to powder X-ray diffraction (XRD) measurement using an X-ray diffraction (XRD) device ("X'Pert-PRO MPD", manufactured by PANalytical). The obtained X-ray diffraction spectrum is shown in FIG. 2. In addition, scanning electron microscope (SEM) observation (magnification: 200x) was performed using a scanning electron microscope (SEM) device ("S-3400N", manufactured by Hitachi High-Tech Fielding Corporation). The obtained SEM image is shown in FIG. 3.

[0060] [Table 2]

[0061] Table 2 shows that in Examples 5-1 to 8-1 using the carbon dioxide fixation method of the present embodiment, when the mixed fluid (fluid containing reactants) had a pH of 9 or less, the calcium carbonate recovery rate was 50 to 97%, which is a higher yield than the comparative examples. In the calcium carbonate obtained in Example 5-3, a peak attributed to the vaterite crystal structure was detected as shown in the X-ray diffraction spectrum of Fig. 2. In addition, the SEM image shown in Fig. 3 reveals that the calcium carbonate has a vaterite crystal structure.

[0062] (Reference Examples 1 and 2: Recycling of extractants) 100 g of water, 10 g of the extractant shown in Table 3, and 10 g of sludge were added to a beaker and stirred at 25°C for 1 hour. After confirming that the pH of the resulting mixed fluid was 11 or higher, the mixed fluid was filtered, and the calcium content (ppm by mass) of the filtrate (supernatant) was measured by ICP atomic emission spectroscopy using an ICP atomic emission spectrometer (manufactured by Hitachi High-Tech Science Corporation, model number: SPECTROARCOS MVICP). Carbon dioxide was supplied to the mixed fluid at a flow rate of 1 L / min until the temperature of the supernatant reached 50°C or lower and the pH reached 7, and then the mixed fluid containing the precipitate was filtered. The amount of the filtered precipitate (calcium carbonate) was measured, and the calcium carbonate recovery rate (%) was calculated from the precipitated amount of calcium carbonate (measured value) and the theoretical precipitated amount of calcium carbonate. Next, 10 g of fresh sludge was added to the obtained filtrate (supernatant), and the same procedure as above was repeated. The results are shown in Table 3.

[0063] [Table 3]

[0064] Table 3 shows that even when fresh sludge is added to the filtrate obtained after calcium carbonate has been obtained by the carbon dioxide fixation method of the present embodiment and the same operation is repeated, almost no decrease in the calcium carbonate recovery rate is observed, and the extractant can be recycled.

[0065] (Reference Examples 3 and 4: Ammonia desorption rate and dehydration rate) 100 g of water, 10 g of ammonium chloride as an extractant, and 10 g of sludge were added to a beaker and stirred at a liquid temperature of 25°C for 1 hour. After confirming that the pH of the resulting mixed fluid was 11 or higher, the mixed fluid was filtered to separate into solids (solids including calcium-containing substances) and a filtrate (supernatant). Carbon dioxide was supplied to the resulting filtrate at a flow rate of 1 L / min until the temperature of the filtrate reached 50°C or lower and the pH reached 7, and then the mixed fluid containing the precipitate was filtered. 10 g of the filtered precipitate (calcium carbonate) and 10 g of the solids containing the calcium-containing material were collected and used as samples. For each sample, nitrogen (N), oxygen (O), and hydrogen (H) were quantified using an elemental analyzer (ELEMENTAR, model number: vario EL cube), and the amounts of ammonia and water contained in each sample were calculated. Each of the above samples was placed in a dryer, and after each hour of drying at the heating temperature shown in Table 4, the nitrogen (N), oxygen (O), and hydrogen (H) contents of each sample were quantified using the elemental analyzer, and the amounts of ammonia and water contained in the sample were calculated. The ammonia desorption rate (%) was calculated from the amount of ammonia contained in the sample before drying and the amount of ammonia contained in the sample after drying. The dehydration rate (%) was also calculated from the amount of water contained in the sample before drying and the amount of water contained in the sample after drying. The results are shown in Table 4.

[0066] [Table 4]

[0067] As can be seen from Table 4, the calcium-containing solid fraction obtained by solid-liquid separation of a fluid containing a reaction product of an extractant and sludge, and the calcium carbonate obtained by the method for fixation of carbon dioxide of the present embodiment can both be dried at a predetermined temperature to remove adhering water and ammonia, thereby further improving the quality. [Explanation of symbols]

[0068] 100: Carbon dioxide fixation device 10: Reaction equipment 11: First reaction device 12: Second reactor 13: Drying equipment 14: Drying equipment 15: Boiler 1: Supply line (1) 2: Supply line (2) 3: Supply line (3) 4: Supply line (4) 5: Supply Line (5) 6: Supply line (6)

Claims

1. mixing a calcium-containing waste with a fluid containing an extractant to obtain a fluid containing a reaction product of the calcium-containing waste with the extractant; and contacting a fluid containing the reactants with a gas containing carbon dioxide to obtain calcium carbonate; In obtaining the fluid containing the reactant, the pH of the fluid containing the reactant is 11 or more, The method for fixation of carbon dioxide, wherein, in obtaining the calcium carbonate, the temperature of the fluid containing the reactants is 50°C or lower.

2. 2. The method for fixation of carbon dioxide according to claim 1, wherein, in obtaining the calcium carbonate, the fluid has a pH of 9 or less when the fluid containing the reactants is brought into contact with the gas containing carbon dioxide.

3. 3. The method for fixation of carbon dioxide according to claim 1, wherein the extractant is an ammonium salt.

4. The method for fixation of carbon dioxide according to claim 1, further comprising drying the calcium carbonate at a temperature of 70°C or higher and 200°C or lower.

5. 5. The method for fixation of carbon dioxide according to claim 4, wherein the gas containing carbon dioxide comprises an exhaust gas containing at least one gas selected from water vapor and ammonia discharged in drying the calcium carbonate.

6. 2. The method for fixation of carbon dioxide according to claim 1, further comprising, after obtaining the fluid containing the reactants, subjecting the fluid containing the reactants to solid-liquid separation and recovering a solid content containing a calcium-containing substance.

7. 7. The method for fixation of carbon dioxide according to claim 6, further comprising drying the solid content at 70°C or higher and 200°C or lower after recovering the solid content.

8. 8. The method for fixation of carbon dioxide according to claim 7, wherein the gas containing carbon dioxide comprises exhaust gas containing at least one gas selected from water vapor and ammonia discharged in drying the solid content.

9. 3. The method for fixation of carbon dioxide according to claim 1, wherein the fluid containing the reactants is obtained at a temperature of 50°C or lower.

10. a reaction device for bringing a gas containing carbon dioxide into contact with a fluid containing a reaction product of the calcium-containing waste and the extractant to obtain calcium carbonate; a drying device for drying the calcium carbonate; a supply line (1) for supplying exhaust gas containing at least one gas selected from water vapor and ammonia from the drying device to the reaction device; the pH of the fluid containing the reactant is 11 or more before being contacted with the gas containing carbon dioxide; The carbon dioxide fixation device, wherein the temperature of the fluid is 50°C or less when the fluid containing the reactant is brought into contact with a gas containing carbon dioxide.

11. a first reactor for obtaining a fluid containing a reaction product of the calcium-containing waste and the extractant; a second reaction device that brings the gas containing carbon dioxide into contact with the fluid containing the reactant to obtain calcium carbonate.

12. 12. The carbon dioxide fixation device according to claim 11, comprising: a supply line (2) for supplying a fluid containing the reactants from the first reactor to the second reactor; and a supply line (3) for supplying a fluid remaining after calcium carbonate obtained in the second reactor is recovered by solid-liquid separation from the second reactor to the first reactor.

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