System for producing calcium carbonate, method for producing calcium carbonate, method for producing sodium carbonate, method for producing gel containing silicon oxide, method for treating concrete material, and method for fixing carbon dioxide

Abstract

A system for producing calcium carbonate according to an embodiment includes: a base treatment device in which a concrete material is treated with a base to precipitate calcium hydroxide; and a calcium-hydroxide carbonation device in which the calcium hydroxide is carbonated to yield calcium carbonate.

Description

Calcium carbonate production system, calcium carbonate production method, sodium carbonate production method, silicon oxide-containing gel production method, concrete material treatment method, and carbon dioxide fixation method

[0001] Embodiments of the present invention relate to a calcium carbonate production system, a calcium carbonate production method, a sodium carbonate production method, a silicon oxide-containing gel production method, a concrete material treatment method, and a carbon dioxide fixation method. This application claims priority based on Japanese Patent Application No. 2023-222732, filed in Japan on December 28, 2023, the contents of which are incorporated herein by reference.

[0002] More than 3 billion tons of construction and demolition waste is generated every year, and approximately 40% of that is concrete. For this reason, technologies for recycling concrete waste have been developed (see, for example, Patent Document 1).

[0003] Furthermore, carbon dioxide, which is thought to be one of the causes of global warming and climate change, is not only emitted as exhaust gas from automobiles and factories, but also in large quantities during the production of cement, the raw material for concrete. Technologies have also been developed to fix this carbon dioxide gas as a solid such as calcium carbonate (see, for example, Patent Document 2).

[0004] Japanese Patent Publication No. 2021-070868 Japanese Patent Publication No. 2023-137509

[0005] However, current methods have various drawbacks, such as complicated processes, the need for expensive treatments, and insufficient purity of the recovered materials. For this reason, new methods are continually being sought.

[0006] The problem to be solved by the present invention is to provide a novel method for recovering calcium carbonate from concrete materials.

[0007] The problem to be solved by the present invention is to provide a novel method for recovering silicon oxide-containing gel and / or sodium carbonate from concrete materials.

[0008] Another problem that the present invention aims to solve is to facilitate the extraction of calcium components from concrete materials.

[0009] Another problem to be solved by the present invention is to provide a novel method for immobilizing carbon dioxide.

[0010] The present invention aims to solve one or more of the above problems, for example, but the problems of the present invention are not limited to those mentioned above, and the present invention may solve other problems.

[0011] The present invention may include the following aspects. [1] A calcium carbonate manufacturing system comprising: a base treatment device that treats concrete material with a base to precipitate calcium hydroxide; and a calcium hydroxide carbonation device that produces calcium carbonate by carbonating the calcium hydroxide. [2] The system described in [1], further comprising a water washing device that washes the precipitated calcium hydroxide. [3] The system described in [2], wherein the water washing device separates the precipitated calcium hydroxide in the form of a calcium hydroxide aqueous solution from other precipitates. [4] The system described in [3], wherein the carbonation device carbonates the calcium hydroxide aqueous solution. [5] The system described in any one of [1] to [4], further comprising a concrete carbonation device that carbonates the concrete material, wherein the base treatment device performs a base treatment of the carbonated concrete material. [6] The system described in any one of [1] to [5], further comprising a separation device that separates a filtrate from the precipitated calcium hydroxide. [7] The system described in [6], further comprising a circulation device that supplies the separated filtrate to the base treatment device. [8] The system according to [6], further comprising a filtrate carbonation device for carbonating the separated filtrate. [9] The system according to [8], further comprising a filtrate separation device for separating sodium carbonate from the carbonated filtrate, wherein the base is sodium hydroxide.

[10] The system according to [9], wherein the separation device comprises a centrifuge.

[11] A method for producing sodium carbonate, using the system according to [9] or

[10] to produce sodium carbonate.

[12] The system according to [9], further comprising a filtrate separation device for precipitating a silicon oxide-containing gel from the carbonated filtrate.

[13] A method for producing a silicon oxide-containing gel, using the system according to

[12] to produce a silicon oxide-containing gel.

[14] A method for producing calcium carbonate, comprising the steps of precipitating calcium hydroxide by treating a concrete material with a base, and carbonating the precipitated calcium hydroxide to produce calcium carbonate.

[15] The method according to

[14] , wherein the step of producing calcium carbonate comprises: separating the precipitated calcium hydroxide from a water-insoluble precipitate by dissolving the precipitated calcium hydroxide in water; and carbonating the separated calcium hydroxide to produce calcium carbonate.

[16] The method according to

[15] , wherein the step of producing calcium carbonate comprises washing the calcium hydroxide-containing precipitate with a base before dissolving the precipitated calcium hydroxide in water.

[17] The method according to any one of

[14] to

[16] , further comprising carbonating the concrete material before treating the concrete material with a base.

[18] The method according to any one of

[14] to

[17] , further comprising, after the step of precipitating calcium hydroxide, supplying a filtrate separated from the precipitated calcium hydroxide to a reaction vessel for treating the base.

[19] The method according to any one of

[14] to

[17] , further comprising, after the step of precipitating calcium hydroxide, carbonating a filtrate separated from the precipitated calcium hydroxide.

[20] The method according to

[19] , further comprising, after the step of carbonating the filtrate, separating sodium carbonate from the carbonated filtrate.

[21] The method according to

[19] , further comprising, after the step of carbonating the filtrate, separating a silicon oxide-containing gel from the carbonated filtrate.

[22] The method according to any of

[14] to

[21] , wherein the base is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[23] The method according to any of

[14] to

[22] , wherein the concentration of the base is 1 mol / L or more and 20 mol / L or less.

[24] The method according to any of

[14] to

[23] , wherein the base treatment is carried out at a temperature of 10°C or more and less than 100°C.

[25] The method according to any of

[14] to

[24] , wherein the concrete material is concrete powder.

[26] The method according to any of

[14] to

[25] , wherein the concrete material is carbonated concrete.

[27] A method for treating concrete material, comprising the step of converting calcium carbonate contained in the concrete material into calcium hydroxide by treating the concrete material with a base.

[28] A method for immobilizing carbon dioxide, comprising the steps of carbonate the concrete material with carbon dioxide, precipitating calcium hydroxide by treating the carbonated concrete material with a base, and carbonate the precipitated calcium hydroxide with carbon dioxide.

[0012] According to the present invention, a novel method for recovering calcium carbonate from concrete materials can be provided.

[0013] Fig. 1 is a schematic diagram showing a calcium carbonate production system according to one embodiment. Fig. 2 is a configuration diagram showing a calcium carbonate production system according to a first embodiment. Fig. 3 is a configuration diagram showing a calcium carbonate production system according to a second embodiment. Fig. 4 is an SEM image of calcium carbonate powder obtained in an example.

[0014] Below, embodiments of a calcium carbonate production system, a calcium carbonate production method, a sodium carbonate production method, a silicon oxide-containing gel production method, a concrete material treatment method, and a carbon dioxide fixation method are described. Note that the following embodiments illustrate one aspect of the present invention, do not limit the present invention, and can be modified as desired within the scope of the technical concept of the present invention. Furthermore, each configuration and each feature of the embodiments can be combined as desired. Unless otherwise specified, a numerical range expressed as "lower limit value to upper limit value" includes both end values ​​and means "at least the lower limit value and at most the upper limit value."

[0015] <1. Calcium Carbonate Production System and Production Method> A calcium carbonate production system according to one embodiment includes a base treatment device that treats concrete materials with a base to precipitate calcium hydroxide, and a calcium hydroxide carbonation device that produces calcium carbonate by carbonating calcium hydroxide.

[0016] In one embodiment, a method for producing calcium carbonate includes precipitating calcium hydroxide by treating a concrete material with a base, and producing calcium carbonate by carbonating the precipitated calcium hydroxide.

[0017] 1 is a schematic diagram of a calcium carbonate production system 1 according to an embodiment. A raw concrete material M is supplied to a base treatment device 10 and subjected to base treatment, and then carbonation treatment is performed in a calcium hydroxide carbonation device 20, and the raw concrete material M is finally converted into calcium carbonate.

[0018] Typical concrete is a mixture of cement, gravel, sand, and water, and contains a large amount of calcium hydroxide. The calcium hydroxide in concrete reacts with carbon dioxide in the atmosphere and gradually changes to calcium carbonate (a process known as carbonation). Therefore, concrete generally contains the following components: Calcium hydroxide (Ca(OH)) ２ 　・ Calcium carbonate CaCO ３ Calcium silicate hydrate C—S—H (3CaO.2SiO ２ ・3H ２ O, etc.) Calcium aluminate hydrate Calcium sulfoaluminate hydrate Other various cement hydrates

[0019] (Base Treatment) By treating the concrete material M with a base using the base treatment device 10, calcium carbonate contained in the concrete material M reacts with a base. For example, when a high concentration of sodium hydroxide is used, calcium hydroxide Ca(OH) reacts with the concrete material M as shown in the following reaction formula (1). ２ CaCO ３ +2NaOH → Ca(OH) ２ +Na ２ CO ３ …(1)

[0020] (Calcium hydroxide carbonation) After calcium carbonate is converted into calcium hydroxide in this way, the calcium hydroxide is separated from other components as needed and supplied to the calcium hydroxide carbonation device 20. The calcium hydroxide carbonation device 20 carbonates the calcium hydroxide. As a result, calcium carbonate Ca(OH) is produced as shown in the following reaction formula (2). ２ Ca(OH) precipitates. ２ +CO ２ → CaCO ３ +H ２ O...(2)

[0021] In this way, according to the calcium carbonate manufacturing apparatus 1, calcium carbonate can be recovered from the concrete material M using a strong base and carbon dioxide.

[0022] (Concrete Carbonation) The concrete material M may be carbonated in the concrete carbonation device 30 before being supplied to the base treatment device 10. Alternatively, the concrete material M may be supplied in the form of a concrete material M that is already sufficiently carbonated. The carbonation treatment in the concrete carbonation device 30 converts calcium hydroxide and calcium silicate hydrate C-S-H contained in the concrete material M into calcium carbonate. The former chemical reaction is the same as the above reaction formula (2). The latter chemical reaction is expressed, for example, by the following reaction formula (3): 3CaO.2SiO ２ ・3H ２ O + 3CO ２ → 3CaCO ３ +2SiO ２ (Gel) + 3H ２ O...(3)

[0023] Thereafter, the calcium component derived from C—S—H can also be finally recovered as calcium carbonate through the above reactions (1) and (2) in the base treatment device 10 and the calcium hydroxide carbonation device 20. Therefore, when the concrete material M is carbonated before the base treatment, the recovery rate of calcium carbonate from the concrete material M can be significantly improved.

[0024] (Water washing) After the base treatment device 10 converts calcium carbonate into calcium hydroxide, the concrete material M may be washed with water by the water washing device 40. Because calcium hydroxide dissolves in water to a certain extent, washing the concrete material M with water allows the calcium hydroxide in the concrete material M to be efficiently separated from other solid components in the form of an aqueous calcium hydroxide solution. If the separated aqueous calcium hydroxide solution is subjected to a carbonation treatment in the calcium hydroxide carbonation device 20, highly pure calcium carbonate can be obtained.

[0025] A more specific configuration of the manufacturing system and a processing method will be described below. Representative embodiments will be described, including a first embodiment shown in FIG. 2 and a second embodiment shown in FIG. 3, but the present invention is not limited to these embodiments. For example, the following description will be given assuming that the components are connected by piping and that the product of one component is mechanically transferred to the next component. However, the components do not necessarily need to be connected to each other. For example, even if the product of one component (e.g., a reaction vessel) is manually transferred to the next component (e.g., a reaction vessel), the components as a whole can be said to constitute a manufacturing system.

[0026] <1-1. First embodiment> Hereinafter, a calcium carbonate production system 100 according to a first embodiment will be described. Fig. 2 is a configuration diagram of the calcium carbonate production system 100 according to the first embodiment.

[0027] 2, the calcium carbonate production system 100 according to the first embodiment includes a concrete supply source 50, a concrete carbonation device 30, a base treatment device 10, a first separation device 60, a circulation device 70, a water-washing device 40, and a calcium hydroxide carbonation device 20. Each component will be described below.

[0028] (Concrete Supply Source 50) The concrete supply source 50 supplies raw concrete material M to the concrete carbonation device 30 through a concrete supply pipe 51. The concrete supply source 50 can supply the concrete material M that has been made into a form suitable for processing in the calcium carbonate production system 100 by pretreatment devices such as a crusher, a particle size adjuster, and a separator, which are not shown.

[0029] (Concrete carbonation device 30) The concrete carbonation device 30 performs a carbonation process on the concrete material M supplied from the concrete supply source 50. The concrete carbonation device 30 includes a reaction vessel 31, a carbon dioxide supply source 33, and a water supply source 36. The reaction vessel 31 is a vessel that functions as a reaction field for carbonating the concrete material M. The carbon dioxide supply source 33 supplies carbon dioxide to the reaction vessel 31. The water supply source 36 supplies water to the reaction vessel 31. The concrete supply pipe 51 supplies the concrete material M to the reaction vessel 31.

[0030] The carbon dioxide supply source 33 includes a carbon dioxide storage tank 34 and a carbon dioxide supply pipe 35. The carbon dioxide storage tank 34 stores carbon dioxide. The carbon dioxide is stored in any form, such as gas, liquid, or solid. The carbon dioxide supply pipe 35 connects the carbon dioxide storage tank 34 to the reaction vessel 31. The carbon dioxide supply source 33 can adjust the amount and speed of carbon dioxide supplied to the reaction vessel 31 using a flow regulator and a valve (not shown).

[0031] The water supply source 36 includes a water storage tank 37 and a water supply pipe 38. The water storage tank 37 stores water. The stored water may be pure water or an aqueous solution of a specific substance. The water supply pipe 38 connects the water storage tank 37 to the reaction vessel 31. The water supply source 36 sends water from the water storage tank 37 to the reaction vessel 31 through the water supply pipe 38 using a water supply pump (not shown). The configurations of the carbon dioxide supply source 33 and the water supply source 36 are not limited to the above example. For example, the carbon dioxide supply source 33 and the water supply source 36 may be provided as a single component. For example, the integrated carbon dioxide supply source 33 and water supply source 36 may supply water with dissolved carbon dioxide to the reaction vessel 31. Alternatively, the carbon dioxide supply source 33 and the water supply source 36 may be mixed upstream of the reaction vessel 31 and then supplied to the reaction vessel 31. The same applies to the concrete material M; the timing of mixing these three components is not particularly limited.

[0032] The reaction vessel 31 reacts the concrete material M with carbon dioxide in water. The reaction vessel 31 is equipped with a stirring mechanism 32 that stirs the reaction solution. The stirring mechanism 32 may have any known configuration, such as a magnetic stirring bar or a stirring blade connected to a motor. The concrete material M is carbonated in the reaction vessel 31, and calcium hydroxide and C-S-H contained in the concrete material M are converted into calcium carbonate.

[0033] The reaction vessel 31 is connected to the reaction vessel 11 of the base treatment device 10 via a pipe 39. The reaction product in the reaction vessel 31 is supplied from the reaction vessel 31 to the reaction vessel 11 through the pipe 39.

[0034] (Base Treatment Apparatus 10) The base treatment apparatus 10 performs base treatment on the carbonated concrete material M supplied from the concrete carbonation apparatus 30. The base treatment apparatus 10 includes a reaction vessel 11 and a base supply source 13. The reaction vessel 11 is a vessel that functions as a reaction field between the concrete material M and a base. The base supply source 13 supplies a base to the reaction vessel 11.

[0035] The base supply source 13 includes a base storage tank 14 and a base supply pipe 15. The base storage tank 14 stores a base. For example, the base storage tank 14 stores an aqueous base solution. The base is not particularly limited as long as it reacts with calcium carbonate to produce calcium hydroxide. The base may be an inorganic base or an organic base. For example, the base may be one or more bases selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide. The base supply pipe 15 connects the base storage tank 14 to the reaction vessel 11. The base supply source 13 delivers the base from the base storage tank 14 to the reaction vessel 11 through the base supply pipe 15 using a pump (not shown). The base supply source 13 may dilute the base being delivered by mixing it with a separate solvent. The base supply source 13 may also include a base generator (not shown) that generates a base. The base generator is, for example, a device that generates a base from a salt by electrolysis. One example is a device that generates a base by bipolar membrane electrodialysis.

[0036] The reaction vessel 11 reacts the concrete material M with a base. The reaction vessel 11, like the reaction vessel 31, is equipped with an optional stirring mechanism 12. In the reaction vessel 11, calcium carbonate in the concrete material M reacts with hydroxide ions and is converted into calcium hydroxide.

[0037] The reaction vessel 11 is connected to the first separation device 60 via a pipe 16. The reaction product in the reaction vessel 11 is supplied from the reaction vessel 11 to the first separation device 60 through the pipe 16.

[0038] (First Separation Device 60) The first separation device 60 separates the reaction product obtained in the reaction vessel 11. For example, the first separation device 60 is a filtration device that filters the reaction product to separate a solid component from a filtrate. Specifically, the first separation device 60 separates the filtrate from a precipitate containing calcium hydroxide. The first separation device 60 may be provided integrally with the reaction vessel 11.

[0039] The first separation device 60 includes a filter 61. The first separation device 60 is connected to the base supply source 13 or another base supply source (not shown) via a base supply pipe 62, and the filtered solid components can be washed with a base. This makes it possible to remove components that dissolve in the base. Specifically, when sodium hydroxide is used as the base, sodium carbonate Na ２ CO ３ , sodium silicate Na ２ SiO ３ , calcium silicate CaSiO ３ etc. can be separated from the solid component as a filtrate in a state dissolved in an aqueous sodium hydroxide solution.

[0040] The filtered solid components are supplied from the first separation device 60 through a pipe 63 to the second separation device 41 of the water washing device 40. On the other hand, the filtrate is supplied from the first separation device 60 to a filtrate reservoir 71 through a first circulation supply pipe 72 of the circulation device 70.

[0041] (Circulation Device 70) The circulation device 70 circulates the filtrate filtered in the first separation device 60 within the system and supplies it again to the base treatment device 10. This allows unreacted calcium components in the filtrate to be treated with a base, thereby improving the recovery rate of the calcium components. In addition, the base components in the filtrate can also be reused for base treatment in the base treatment device 10.

[0042] The circulation device 70 includes a filtrate reservoir 71, a first circulation supply pipe 72, and a second circulation supply pipe 73. The filtrate reservoir 71 is connected to the first separation device 60 via the filtrate reservoir 71 and is connected to the reaction vessel 11 via the second circulation supply pipe 73. The filtrate reservoir 71 temporarily stores the filtrate to be circulated. The circulation device 70 can supply the filtrate stored in the filtrate reservoir 71 to the reaction vessel 11 through the second circulation supply pipe 73 using a pump (not shown). The filtrate reservoir 71 may be omitted, and the filtrate from the first separation device 60 may be immediately sent to the reaction vessel 11.

[0043] (Water Washing Device 40) The water washing device 40 washes the solid components filtered out in the first separation device 60 with water. Specifically, the water washing device 40 can wash the precipitated calcium hydroxide with water. This allows the calcium hydroxide in the solid components to be eluted into water and efficiently separated from other solid components. That is, the water washing device 40 can separate the precipitated calcium hydroxide in the form of an aqueous calcium hydroxide solution from other precipitates. The water washing device 40 includes a second separation device 41 and a water supply source 43.

[0044] The second separation device 41 separates calcium hydroxide dissolved in water from other solid components. For example, the second separation device 41 is a filtration device that filters the reaction product to separate the solid components from the filtrate, similar to the first separation device 60. The second separation device 41 includes a filter 42.

[0045] The water supply source 43 , like the water supply source 36 of the concrete carbonation device 30 , includes a water storage tank 44 and a water supply pipe 45 , and supplies water to the second separation device 41 .

[0046] For example, the water washing unit 40 washes the solid components filtered out in the first separation unit 60 with water while they are positioned on the filter 42. Calcium hydroxide dissolved in water passes through the filter 42, but other solid components that are insoluble in water cannot. As a result, the water washing unit 40 can efficiently separate calcium hydroxide from other solid components. The remaining solid components may be a mixture of various silicates that are poorly soluble in base. The calcium hydroxide aqueous solution that has passed through the filter 42 is supplied to the calcium hydroxide carbonation unit 20 through a pipe 46. Note that a base washing unit (not shown) that washes the calcium hydroxide aqueous solution with a base may be provided between the filter 42 and the calcium hydroxide carbonation unit 20. The base washing unit can precipitate calcium hydroxide again by adding a base to the calcium hydroxide aqueous solution.

[0047] (Calcium hydroxide carbonation device 20) The calcium hydroxide carbonation device 20 carbonates calcium hydroxide. Specifically, the calcium hydroxide carbonation device 20 carbonates the calcium hydroxide aqueous solution supplied from the water washing device 40. The calcium hydroxide carbonation device 20 includes a reaction vessel 21 and a carbon dioxide supply source 23. The reaction vessel 21 is a vessel that functions as a reaction field for carbonating calcium hydroxide. The carbon dioxide supply source 23 supplies carbon dioxide to the reaction vessel 21. The calcium hydroxide carbonation device 20 may further include a water supply source, as with the concrete carbonation device 30, if necessary.

[0048] The carbon dioxide supply source 23 includes a carbon dioxide storage tank 24 and a carbon dioxide supply pipe 25. The configuration of the carbon dioxide supply source 23 is similar to that of the carbon dioxide supply source 33, and therefore a description thereof will be omitted.

[0049] The reaction vessel 21 reacts the calcium hydroxide aqueous solution with carbon dioxide. Like the reaction vessel 31, the reaction vessel 21 is equipped with an optional stirring mechanism 22. In the reaction vessel 21, the calcium hydroxide is carbonated and converted into calcium carbonate. The calcium carbonate is dried in a drying device (not shown) to obtain calcium carbonate powder.

[0050] <1-1-2. Method of Using the Calcium Carbonate Production System 100> Next, a method of producing calcium carbonate using the calcium carbonate production system 100 will be described. Note that the points already explained regarding the configuration of the system 100 will be omitted as appropriate.

[0051] The method for producing calcium carbonate using the calcium carbonate production system 100 may include the following steps: (S10) concrete material supply step, (S11) concrete carbonation step, (S12) base treatment step, (S13) separation step, (S14) water washing step, and (S15) calcium hydroxide carbonation step.

[0052] (Concrete Material Supply Step) In the concrete material supply step, the concrete supply source 50 supplies the concrete material M to the manufacturing system 100. The concrete material M is preferably concrete powder, since it is highly reactive and can be easily processed uniformly throughout. The concrete material supply step may include a step of crushing the concrete material, a step of adjusting the particle size of the crushed concrete material, a step of separating the concrete powder, and the like.

[0053] (Concrete Carbonation Step) In the concrete carbonation step, the concrete carbonation device 30 carbonates the concrete material M. The concrete carbonation step may include a process of supplying carbon dioxide gas to the concrete material M to carbonate the concrete material M. The mixing ratio of the concrete material M to water is, for example, 1:2 to 1:50, preferably 1:5 to 1:20, on a mass basis. Within the above range, the concrete material M disperses well in water, and a reaction liquid with a viscosity suitable for carbonation can be obtained. The flow rate of the carbon dioxide gas is not particularly limited, but is, for example, 0.1 L / min to 10 L / min, preferably 1 L / min to 5 L / min. Within the above range, carbonation can be carried out efficiently.

[0054] (Base Treatment Step) In the base treatment step, the base treatment device 10 treats the concrete material M with a base to precipitate calcium hydroxide. The type of base is as described above. The concentration of the base is, for example, 1 mol / L to 20 mol / L, preferably 2 mol / L to 15 mol / L, more preferably 5 mol / L to 12 mol / L, and even more preferably 8 mol / L to 10 mol / L. If the concentration is within the above range, the reaction of converting calcium carbonate to calcium hydroxide can be sufficiently progressed, and calcium hydroxide can be precipitated.

[0055] The mixing ratio of the concrete material M to the base is, for example, 1:1 to 1:20, preferably 1:2 to 1:10, on a mass basis. Within this range, the reaction of converting calcium carbonate to calcium hydroxide can proceed sufficiently, and calcium hydroxide can be precipitated.

[0056] The base treatment can be carried out at a temperature of, for example, 10° C. or higher but lower than 100° C., 20° C. or higher but lower than 90° C., or 40° C. or higher but lower than 80° C. Within the above ranges, the reaction of converting calcium carbonate to calcium hydroxide can proceed sufficiently.

[0057] (Separation Step) In the separation step, the first separator 60 separates the solid component containing calcium hydroxide from the liquid component. The separation step can include filtering the precipitate containing calcium hydroxide from the liquid component and washing the precipitate containing calcium hydroxide with a base. The concentration of the base is, for example, 1 mol / L to 20 mol / L, preferably 2 mol / L to 15 mol / L, more preferably 5 mol / L to 12 mol / L, and even more preferably 8 mol / L to 10 mol / L. The mixing ratio of the precipitate to be washed to the base is, for example, 1:1 to 1:20, preferably 1:2 to 1:10, on a mass basis. Within the above range, the precipitate can be washed efficiently and sufficiently.

[0058] The filtrate separated from the precipitate containing calcium hydroxide can be supplied to the reaction vessel 11 of the base treatment device 10 by the circulation device 70.

[0059] (Water Washing Step) In the water washing step, the water washing device 40 dissolves the precipitated calcium hydroxide in water. Specifically, the water washing device 40 washes the precipitate with water to elute calcium hydroxide from the precipitate into water, allowing it to be separated from the water-insoluble precipitate. The mixing ratio of the precipitate to be washed to water is, for example, 1:100 to 1:5000, preferably 1:200 to 1:2000, and more preferably 1:300 to 1:1000, on a mass basis. Within the above range, calcium hydroxide can be efficiently separated from the precipitate.

[0060] (Calcium hydroxide carbonation step) In the calcium hydroxide carbonation step, the calcium hydroxide carbonation device 20 produces calcium carbonate by carbonating the calcium hydroxide separated in the water-washing step. The calcium hydroxide carbonation step can include a step of supplying carbon dioxide gas to the calcium hydroxide obtained in the water-washing step to carbonate the calcium hydroxide, a step of filtering out the precipitated calcium carbonate, and a step of drying the filtered out calcium carbonate. The flow rate of the carbon dioxide gas is not particularly limited and may be the same as that in the concrete carbonation step.

[0061] The calcium hydroxide carbonation step may further include a step of precipitating calcium hydroxide by adding a base to the aqueous calcium hydroxide solution obtained in the water-washing step before the step of carbonating calcium hydroxide. This can reduce the amount of calcium ions dissolved in the aqueous solution even after carbonation, thereby improving the recovery rate of calcium carbonate.

[0062] The calcium carbonate production system 100 described above realizes a novel method for producing calcium carbonate from concrete material M through base treatment and carbonation treatment. This method is inexpensive and simple because inexpensive sodium hydroxide and carbon dioxide can be used as treatment agents (although not limited to these). Furthermore, when calcium hydroxide is converted to calcium carbonate with carbon dioxide, the carbon dioxide is immobilized in the form of calcium carbonate, which is also advantageous from the perspective of global warming. The resulting calcium carbonate can be used for a variety of purposes, such as a cement raw material, filler, paper, rubber additive, and pigment.

[0063] When the concrete material M is carbonated, not only the calcium hydroxide component but also the C-S-H component contained in the concrete material M can be converted into calcium carbonate. Therefore, most of the calcium component of the concrete material M can be recovered as calcium carbonate. Furthermore, when carbon dioxide is used for carbonation, the carbon dioxide can be fixed in the form of calcium carbonate.

[0064] When calcium hydroxide is separated from other residues by washing the precipitate after base treatment with water, it is possible to simply and efficiently separate only calcium hydroxide, which is the raw material for calcium carbonate, from a mixture of calcium hydroxide and various silicates, and therefore calcium carbonate of much higher purity can be recovered compared to conventional methods.

[0065] <1-2. Second Embodiment> A calcium carbonate production system 200 according to a second embodiment will be described below. Differences from the first embodiment will be mainly described below, and the description of features common to the first embodiment will not be repeated. Fig. 3 is a configuration diagram of the calcium carbonate production system 200 according to the second embodiment.

[0066] 3 , the calcium carbonate production system 200 according to the second embodiment includes a concrete supply source 50, a concrete carbonation device 30, a base treatment device 10, a first separation device 60, a water-washing device 40, a calcium hydroxide carbonation device 20, a filtrate carbonation device 80, and a filtrate separation device 90. The filtrate carbonation device 80 and the filtrate separation device 90 are added instead of the circulation device 70 of the first embodiment, and the functions and configurations of the other components are basically the same as those of the first embodiment. Therefore, the following description will mainly focus on the filtrate carbonation device 80 and the filtrate separation device 90.

[0067] (Filtrate carbonation device 80) The filtrate carbonation device 80 carbonates the filtrate separated from the solid components in the first separation device 60. Specifically, the filtrate carbonation device 80 causes a reaction between the silicon-based components contained in the filtrate and carbon dioxide, thereby precipitating a gel containing silicon oxide.

[0068] For example, when sodium hydroxide is used as the base, the filtrate may be diluted with sodium carbonate Na ２ CO ３ , sodium silicate Na ２ SiO ３ , calcium silicate CaSiO ３The filtrate is subjected to a carbonation treatment in water, whereby silicates such as sodium silicate and calcium silicate are converted into silicon oxide (e.g., SiO ２ The resulting gel is thought to be rich in amorphous silicon oxide (amorphous silicon oxide of the same composition) (hereafter referred to as "silicon oxide-containing gel"). Meanwhile, the supernatant liquid contains dissolved sodium carbonate.

[0069] The filtrate carbonation device 80 includes a reaction vessel 81 and a carbon dioxide supply source 83. The reaction vessel 81 is a vessel that functions as a reaction field for carbonating the filtrate. The carbon dioxide supply source 83 supplies carbon dioxide to the reaction vessel 81. As with the concrete carbonation device 30, the filtrate carbonation device 80 may further include a water supply source, if necessary.

[0070] The carbon dioxide supply source 83 includes a carbon dioxide storage tank 84 and a carbon dioxide supply pipe 85. The configuration of the carbon dioxide supply source 83 is similar to that of the carbon dioxide supply source 33, and therefore will not be described here. The reaction vessel 81 reacts the filtrate with carbon dioxide. Like the reaction vessel 31, the reaction vessel 81 includes an optional stirring mechanism 82. The reaction vessel 81 is connected to a filtrate separator 90 via a pipe 86. The reaction product in the reaction vessel 81 is supplied from the reaction vessel 81 to the filtrate separator 90 through the pipe 86.

[0071] (Filtrate Separation Device 90) The filtrate separation device 90 separates the components of the reaction liquid (i.e., the carbonated filtrate) supplied from the filtrate carbonation device 80. For example, the filtrate separation device 90 separates the reaction liquid into a liquid component containing sodium carbonate and a solid component containing a silicon oxide-containing gel. The filtrate separation device 90 includes a centrifuge 91 and a drying device 93. The centrifuge 91 is connected to the drying device 93 via a pipe 92. The centrifuge 91 separates the carbonated filtrate into a liquid component containing sodium carbonate and a solid component containing a silicon oxide-containing gel by centrifuging the filtrate. The liquid component is supplied to the drying device 93 and dried, and recovered as sodium carbonate powder. Meanwhile, the centrifuged solid component is dried and recovered as a silicon oxide-containing gel. In this way, sodium carbonate and a silicon oxide-containing gel are obtained. Note that the separation method used in the filtrate separation device 90 is not limited to centrifugation, and any method capable of separating a liquid component from a solid component can be used.

[0072] <1-2-2. Method of Using the Calcium Carbonate Production System 200> Next, a method of producing calcium carbonate using the calcium carbonate production system 200 will be described. Note that the points already explained regarding the configuration of the system 200 will be omitted as appropriate.

[0073] The method for producing calcium carbonate using the calcium carbonate production system 100 may include the following steps. Of these, (S20) to (S25) are the same as (S10) to (S15) in the first embodiment, so the filtrate carbonation step and the filtrate separation step will be described below. (S20) Concrete material supply step (S21) Concrete carbonation step (S22) Base treatment step (S23) Separation step (S24) Water washing step (S25) Calcium hydroxide carbonation step (S26) Filtrate carbonation step (S27) Filtrate separation step

[0074] (Filtrate Carbonation Step) The filtrate carbonation step can be carried out after the separation step, independently of the water washing step and the calcium hydroxide carbonation step. In the filtrate carbonation step, the filtrate carbonation device 80 carbonates the filtrate supplied from the first separation device 60. The filtrate carbonation step can include a process of producing a silicon oxide-containing gel by supplying carbon dioxide gas to the filtrate obtained in the separation step.

[0075] The supply of carbon dioxide can be stopped when the pH of the reaction solution in the reaction vessel 81 decreases to a predetermined value. The predetermined value is, for example, pH 8 to pH 10, preferably pH 8.2 to pH 9, and more preferably pH 8.3 to pH 8.7. The flow rate of the carbon dioxide gas is not particularly limited and may be the same as that in the concrete carbonation step or the calcium hydroxide carbonation step.

[0076] (Filtrate Separation Step) In the filtrate separation step, the filtrate separator 90 separates the carbonated filtrate into a liquid component and a solid component. For example, when sodium hydroxide is used as the base, the filtrate separator 90 separates the carbonated filtrate into a liquid component containing sodium carbonate and a solid component containing a silicon oxide-containing gel. This allows the filtrate separator 90 to separate the sodium carbonate from the carbonated filtrate. The filtrate separator 90 can also separate the silicon oxide-containing gel from the carbonated filtrate. For example, the filtrate separation step can include a step of centrifuging the carbonated filtrate.

[0077] For example, the filtrate separation step can further include a step of drying each of the separated components. Sodium carbonate powder is obtained by drying the liquid component in the drying device 93. A silicon oxide-containing gel is obtained by drying the solid component. Alternatively, the liquid component may be re-supplied to the concrete carbonation device 30 or the base treatment device 10 and circulated without recovering the sodium carbonate as a powder.

[0078] According to the calcium carbonate production system 200 described above, not only calcium carbonate but also sodium carbonate and a silicon oxide-containing gel can be recovered. However, depending on the base used, sodium carbonate may be another carbonate. This allows carbon dioxide to be immobilized as a carbonate.

[0079] <2. Method for Producing Sodium Carbonate> In the second embodiment, sodium carbonate can be recovered from the filtrate. Therefore, sodium carbonate can be produced by the production system 200. That is, the method for producing sodium carbonate according to one embodiment is a method for producing sodium carbonate using the production system.

[0080] Specifically, the method can include the steps of: carbonating a filtrate obtained after treating concrete material M with sodium hydroxide; separating a liquid component containing sodium carbonate from the carbonated filtrate; and drying the liquid component to obtain sodium carbonate powder.

[0081] According to the method for producing sodium carbonate as described above, carbon dioxide can be solidified into the form of sodium carbonate.

[0082] 3. Method for Producing Silicon Oxide-Containing Gel In the second embodiment, a silicon oxide-containing gel can be recovered from the filtrate. Therefore, a silicon oxide-containing gel can be produced by the production system 200. That is, a method for producing a silicon oxide-containing gel according to one embodiment is a method for producing a silicon oxide-containing gel using the production system.

[0083] Specifically, the method can include a step of carbonating a filtrate obtained after treating the concrete material M with a base, and a step of obtaining a silicon oxide-containing gel by separating a solid component containing the silicon oxide-containing gel from the carbonated filtrate.

[0084] According to the above-described method for producing a silicon oxide-containing gel, a silicon oxide-containing gel can be obtained from concrete material M. The silicon oxide-containing gel thus obtained can be a nano-sized amorphous gel. This silicon oxide-containing gel can be used for a variety of purposes, such as accelerating the hydration of cement, increasing the early compressive strength of concrete, repairing cementitious materials, and removing heavy metal ions from wastewater.

[0085] 4. Method for Treating Concrete Material A method for treating a concrete material according to one embodiment includes a step of treating calcium carbonate contained in a concrete material with a base to produce calcium hydroxide.

[0086] The above-described treatment method corresponds to the base treatment step in the above-described calcium carbonate production method. The advantage of this treatment method is that it can convert poorly water-soluble calcium carbonate into calcium hydroxide, which has some water solubility, facilitating subsequent extraction of the calcium component. For example, when the above-described treatment method is applied to a mixture of calcium carbonate and other solid components that are poorly water-soluble (e.g., concrete), the calcium carbonate in the mixture is converted into calcium hydroxide, which makes it easy to separate the calcium hydroxide from the other solid components by rinsing with water. In this way, the calcium component can be easily extracted from a solid mixture containing calcium carbonate.

[0087] <5. Method for Immobilizing Carbon Dioxide> A method for immobilizing carbon dioxide according to one embodiment includes the steps of carbonate a concrete material with carbon dioxide, precipitating calcium hydroxide by treating the carbonated concrete material with a base, and carbonate the precipitated calcium hydroxide with carbon dioxide.

[0088] The above-mentioned immobilization method is an invention that views the above-mentioned calcium carbonate production method as an invention from the viewpoint of immobilizing carbon dioxide. That is, in the above-mentioned calcium carbonate production method, carbon dioxide is consumed in the carbonation step of the concrete material M by the concrete carbonation apparatus 30 and the carbonation step of calcium hydroxide by the calcium hydroxide carbonation apparatus 20, and can ultimately be immobilized in the form of calcium carbonate.

[0089] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and do not limit the scope of the invention. These embodiments may be implemented in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention.

[0090] The present invention will be described below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0091] <Preparation of concrete powder> The raw material concrete was ordinary Portland cement (density 434.5 kg / m ３ ), gravel (density 748.8 kg / m ３ ), and sand (density 1082.6 kg / m ３ The concrete was prepared from a mixture of 100% ammonium hydroxide (MAA) and 100% ammonium hydroxide (MAA). The mass ratio of water to cement was 0.4. The concrete was crushed, ball-milled, sieved through a 300 μm sieve, and dispersed in distilled water. The fine concrete powder was then separated from the cement paste by centrifugation at 4000 rpm for 10 minutes to improve reactivity in the carbonation process.

[0092] <Carbonation of concrete powder> 100 g of the concrete powder obtained by the above centrifugation was dispersed in 1 L of distilled water and stirred to obtain a uniform dispersion. Carbon dioxide gas (purity 99.9%) was poured into this dispersion at a flow rate of 2 L / min for 3 hours to carbonate the concrete powder. The slurry after the carbonation treatment was recovered and dried at 105°C for 24 hours.

[0093] <Base treatment of carbonated concrete powder> Carbonated concrete powder was dispersed in a high concentration aqueous solution of sodium hydroxide (NaOH) (9 mol / L). At this time, the mass ratio of the NaOH aqueous solution to the carbonated concrete powder was 5:1. The mixture was stirred at a reaction temperature of 50°C for 2 hours to perform the base treatment of the carbonated concrete powder. The precipitate after the reaction was collected by vacuum filtration. In order to prevent the obtained precipitate from being carbonated during drying, it was freeze-dried in a vacuum atmosphere at -80°C for 48 hours using a freeze dryer (EYELA / FDU-2100, manufactured by Tokyo Rikakikai Co., Ltd.). Residual Na ２ SiO ３ The precipitate was washed with a 5 mol / L aqueous NaOH solution to remove the filtrate. Filtrate A, which was separated from the precipitate by vacuum filtration, and filtrate B, which was obtained by washing the precipitate with an aqueous NaOH solution, were mixed together to obtain filtrate C.

[0094] <Preparation of calcium hydroxide aqueous solution> Next, 0.155 g of the obtained precipitate was washed with 100 mL of distilled water to obtain calcium hydroxide Ca(OH) in the precipitate. ２ is dissolved to give Ca(OH) ２ The aqueous solution and other precipitates were separated.

[0095] <Carbonation of calcium hydroxide> The obtained Ca(OH) ２ Sodium hydroxide was added to the aqueous solution until the pH reached 12.5, and calcium hydroxide was precipitated again. Carbon dioxide gas was introduced into the slurry containing calcium hydroxide at a flow rate of 0.5 L / min to carbonate the calcium hydroxide. This resulted in the precipitation of calcium carbonate. To prevent dissolution of calcium carbonate, the carbonation treatment was stopped when the pH decreased to 8.3. The resulting calcium carbonate precipitate was then dried at 105°C for 24 hours to obtain a high-purity calcium carbonate powder.

[0096] <Carbonation of Filtrate C> Carbonation treatment was carried out by flowing carbon dioxide gas into filtrate C after the vacuum filtration and NaOH washing. The carbonation treatment was stopped when the pH decreased to 9.8. ２ A rich gel is precipitated, and SiO ２ A slurry containing a rich gel was obtained.

[0097] <SiO ２ Centrifugation of Rich Gel> The obtained slurry was centrifuged at 4000 rpm for 5 minutes to separate the SiO ２ The rich gel precipitate and the aqueous sodium carbonate solution were separated. ２ The rich gel precipitate was washed with distilled water and dried at 105°C for 24 hours to obtain amorphous SiO ２ A rich gel was obtained. On the other hand, the aqueous sodium carbonate solution was dried to obtain sodium carbonate powder.

[0098] <Evaluation of Calcium Carbonate> The amount of calcium carbonate in the resulting calcium carbonate powder was evaluated using a thermogravimetry-differential thermal analysis (TG-DTA) device (STA 2500 Regulus, NETZSCH). The purity of the resulting calcium carbonate powder was 98.54%. The calcium carbonate recovery rate, calculated by dividing the mass of the resulting calcium carbonate by the mass of calcium carbonate in the raw concrete powder, was 81.5%. In this experiment, 0.24 g of carbon dioxide was captured and immobilized per 1 g of raw concrete powder. It should be noted that the calcium hydroxide aqueous solution could be carbonated without adding sodium hydroxide to re-precipitate calcium hydroxide as described above. However, the calcium carbonate recovery rate in this case was approximately 60%, lower than the recovery rate in the above example in which calcium hydroxide was re-precipitated.

[0099] The obtained calcium carbonate powder was observed with a scanning electron microscope (SEM, TM4000PlusII, Hitachi High-Technologies Corporation). Figure 4 shows an SEM image of the obtained calcium carbonate powder. The calcium carbonate particles had a rhombohedral shape and a narrow particle size distribution. The average particle size of the calcium carbonate particles was approximately 208 μm.

[0100] <Study on sodium hydroxide concentration and reaction temperature> Experiments were conducted under various conditions, with sodium hydroxide concentrations of 3 mol / L, 5 mol / L, 7 mol / L, and 9 mol / L and reaction temperatures of 30°C, 50°C, 70°C, and 90°C. Under all conditions, X-ray diffraction (XRD) patterns confirmed that at least a portion of the calcium carbonate was converted to calcium hydroxide and precipitated. In particular, when treated with 9 mol / L of sodium hydroxide, it was confirmed that almost all of the calcium carbonate was converted to calcium hydroxide. The amount of calcium hydroxide in the precipitate after base treatment is summarized in Table 1 below.

[0101]

[0102] 1, 100, 200... calcium carbonate production system, 10... base treatment device, 20... calcium hydroxide carbonation device, 30... concrete carbonation device, 40... water washing device, 50... concrete supply source, 60... first separation device, 70... circulation device, 80... filtrate carbonation device, 90... filtrate separation device, M... concrete material

Claims

1. A calcium carbonate production system, comprising: a base treatment device that precipitates calcium hydroxide by treating concrete materials with a base; and a calcium hydroxide carbonation device that produces calcium carbonate by carbonating calcium hydroxide.

2. The system according to claim 1, further comprising a water washing device that washes the precipitated calcium hydroxide.

3. The system according to claim 2, wherein the water washing device separates the precipitated calcium hydroxide from other precipitates in the form of an aqueous calcium hydroxide solution.

4. The system according to any one of claims 1 to 3, further comprising a concrete carbonation device that carbonates the concrete materials, wherein the base treatment device performs base treatment on the carbonated concrete materials.

5. The system according to any one of claims 1 to 3, further comprising a filtrate carbonation device that carbonates the filtrate separated from the precipitated calcium hydroxide.

6. The system according to claim 5, wherein the base is sodium hydroxide, and further comprising a filtrate separation device that separates sodium carbonate from the carbonated filtrate.

7. A method for producing sodium carbonate using the system according to claim 6.

8. The system according to claim 5, further comprising a filtrate separation device that precipitates a silicon oxide-containing gel from the carbonated filtrate.

9. A method for producing a silicon oxide-containing gel using the system according to claim 8.

10. A method for producing calcium carbonate, comprising: a step of precipitating calcium hydroxide by treating concrete materials with a base; and a step of producing calcium carbonate by carbonating the precipitated calcium hydroxide.

11. The method according to claim 10, wherein the step of producing calcium carbonate includes: a step of separating the precipitated calcium hydroxide from water-insoluble precipitates by dissolving the precipitated calcium hydroxide in water; and a step of producing calcium carbonate by carbonating the separated calcium hydroxide.

12. The method according to any one of claims 10 or 11, further comprising a step of carbonating the concrete materials before treating the concrete materials with a base.

13. The method according to claim 10 or 11, wherein the concentration of the base is 1 mol / L or more and 20 mol / L or less.

14. A method for treating a concrete material, the method comprising a step of converting calcium carbonate contained in the concrete material into calcium hydroxide by treating the concrete material with a base.

15. A method for immobilizing carbon dioxide, the method comprising: a step of carbonating a concrete material with carbon dioxide; a step of precipitating calcium hydroxide by treating the carbonated concrete material with a base; and a step of carbonating the precipitated calcium hydroxide with carbon dioxide.

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