Carbon dioxide recovery / storage method

Abstract

The present invention provides a new carbon dioxide recovery / storage method in which a dewatered cake or slurry containing a water-insoluble artificial carbonate, said water-insoluble artificial carbonate having been prepared using waste and the carbon dioxide in exhaust gas, is dispersed on or injected into a ground surface, abandoned mine, or the like, and is stored in the form of a carbonate mineral that has long-term stability.　The carbon dioxide recovery / storage method is a method in which: the carbon dioxide in exhaust gas is brought into contact and reacted with an aqueous solution containing metal ions derived from waste, and the carbon dioxide is fixed by preparing a dewatered cake or a slurry containing sparingly water-soluble carbonate, or the carbon dioxide in exhaust gas is caused to react with an alkaline aqueous solution to prepare a water-soluble carbonate solution which is caused to react with metal ions derived from waste, and the carbon dioxide is fixed by preparing a dewatered cake or a slurry containing sparingly water-soluble carbonate; and the obtained dewatered cake or slurry containing carbonate is injected and stored in a shallow layer of the ground surface such that the carbon dioxide is stored in a carbonate mineral form.

Description

Method for carbon dioxide capture and storage

[0001] The present invention relates to a method for carbon dioxide capture and storage, and in particular to a method for carbon dioxide capture and storage that enables long-term stable storage of carbon dioxide in the form of artificial carbonate immediately after the start of storage by spraying artificial carbonate, which is obtained by immobilizing carbon dioxide in exhaust gas, onto the ground surface or injecting the same into abandoned mine shafts.

[0002] Carbon dioxide, one of the greenhouse gases, is emitted in large quantities industrially, for example, it is contained in exhaust gas from factories and the like. However, to address environmental issues, carbon neutrality initiatives to reduce carbon dioxide emissions into the atmosphere are being promoted in various countries around the world including Japan.

[0003] In particular, the steel industry, cement manufacturing industry and other industries have processes that generate large amounts of carbon dioxide apart from the use of fuels such as coal in the production process, and are classified as "hard-to-abate industries". For example, in the cement manufacturing industry, when clinker is produced by calcining limestone (the main component of which is calcium carbonate), which is a raw material, in a kiln while mixing it with other raw materials, carbon dioxide is emitted due to thermal decomposition of limestone, so it is extremely difficult to reduce carbon dioxide emissions only through fuel conversion and other such measures.

[0004] On the other hand, initiatives called CCU (CARBON DIOXIDE CAPTURE AND UTILIZATION), in which carbon dioxide in exhaust gas is separated and recovered before being utilized, or CCS (CARBON DIOXIDE CAPTURE AND STORAGE), in which carbon dioxide is stored underground, are being promoted worldwide, and the combination of the two is referred to as CCUS.

[0005] In CCU, methods such as methanation, in which separated and recovered carbon dioxide is reacted with hydrogen to convert it into methane, conversion into plastics such as polycarbonate, and conversion into minerals such as calcium carbonate to be immobilized in concrete are being developed.

[0006] Furthermore, regarding CCS, methods are being developed such as liquefying separated and recovered carbon dioxide under low temperature and low pressure or medium temperature and medium pressure conditions and injecting it into geological formations called reservoirs, such as sandy and gravelly layers, deep underground beneath shielding layers on the seabed or land, both domestically and internationally, to convert it into carbonate minerals over the long term, or enhanced oil recovery (EOR), which involves injecting it into crude oil reservoirs in depleted crude oil and gas fields to push out and recover the crude oil.

[0007] However, conventional processes for separating and recovering carbon dioxide from exhaust gases have problems in terms of technology, cost, and location. Technical problems in conventional processes include, for example, the following: In cement plants, separating and recovering carbon dioxide at a concentration of approximately 10-20% by volume in exhaust gases requires desulfurization of the exhaust gas and pretreatment of soot. In addition, chemical absorption methods such as the common amine method require a large amount of energy, such as heat sources (steam) and electricity, thus necessitating the use of ancillary equipment. Furthermore, since carbon dioxide is newly generated during energy consumption, it becomes necessary to recover this newly generated carbon dioxide, but recovering this carbon dioxide is difficult to achieve in terms of technological maturity and recovery efficiency.

[0008] Furthermore, CCS (Carbon Capture and Storage), which involves storing liquefied carbon dioxide underground, requires the injection of liquid into an underground reservoir, posing a risk of carbon dioxide leakage to the surface. Therefore, monitoring must continue for several decades even after the storage project is completed. Additionally, the amount injected into the reservoir may be less than expected, creating a high degree of uncertainty regarding storage capacity. Consequently, underground storage requires time-consuming and technically challenging procedures, such as drilling exploratory wells deep underground to conduct geological surveys. As a result, only oil and natural gas operators and similar companies are actually capable of implementing CCS projects.

[0009] Furthermore, cost-related issues include, for example, the following problems: Chemical absorption methods used to separate and recover carbon dioxide from exhaust gases require expensive amine absorbents. Moreover, the amine absorbent must be heated and cooled in a thermal cycle between 45°C and 120°C to absorb and desorb carbon dioxide, which requires a heat source such as steam, electricity, and cooling water, resulting in energy costs. In addition, it is necessary to construct new carbon dioxide separation and recovery facilities and liquefaction and storage facilities, and it is difficult to fully pass on the enormous construction and operating costs to the product price.

[0010] Furthermore, in the case of CCS, the emitter is required to pay storage costs to the transport and storage company, therefore CO ２ Increasing storage capacity would increase costs, making it extremely difficult in practice to achieve carbon neutrality through CCS (Carbon Capture and Storage).

[0011] In the case of CCUs, methanation involves not only the cost of separation and recovery to increase the purity of carbon dioxide, but also the use of large amounts of hydrogen, which necessitates the construction of new hydrogen production and hydrogen and methane storage facilities, resulting in high costs.

[0012] Furthermore, a technology is being considered in which carbon dioxide is directly injected into the calcium hydroxide contained in concrete and ready-mix concrete sludge to absorb it and fix it as calcium carbonate. However, this technology has problems such as the reaction rate, the neutralization of the concrete, and limitations on the amount of mineralization fixed due to the calcium hydroxide content that fixes the carbon dioxide.

[0013] While technological development is underway to recover carbon dioxide in the form of artificial calcium carbonate powder, its purity and particle size are inferior to natural limestone powder extracted and crushed from limestone mines, limiting its applications and range of use. Furthermore, artificial calcium carbonate is more expensive than natural limestone powder, resulting in a surplus of prepared artificial calcium carbonate and making it difficult to utilize the entire amount effectively.

[0014] Furthermore, regarding location-related issues, the following problems can be cited as examples. Factories and other facilities of large-scale carbon dioxide emitters are mainly located in industrial zones along the coast of major metropolitan areas, and it is possible to transport large quantities of separated and recovered liquefied carbon dioxide to storage sites both domestically and internationally via pipelines or ships. However, cement plants, for example, are often located inland near limestone mines, making it difficult to transport large quantities of separated and recovered liquefied carbon dioxide over long distances via pipelines. As a result, land transport by trucks and other means becomes the main method, making it difficult to implement large-scale CCS at inland plants. In addition, there are few inland waste gas fields suitable for CCS in Japan, and storage locations are extremely limited.

[0015] Conventional carbon dioxide storage methods are disclosed in Japanese Patent Publication No. 2024-137353 (Patent Document 1), which describes a method for storing carbon dioxide in the form of carbonate in a relatively shallow reservoir in a short time, in which two liquids, microbubble water in which carbon dioxide is dissolved and a capsule-shaped resin composition that reacts with carbon dioxide to form carbonate minerals, are simultaneously injected into a shallow underground aquifer. However, with this method, it is difficult to search for an underground aquifer with optimal storage performance even at shallow depths, and because the chemical reaction occurs within the aquifer, it can be difficult to continuously inject the material stably due to clogging and expansion caused by precipitated carbonates, and furthermore, the carbonate mineralization reaction takes a long time.

[0016] Furthermore, Japanese Patent Publication No. 3954009 (Patent Document 2) discloses a method for producing alkaline earth metal carbonates by contacting a gas containing carbon dioxide with water, an alkaline earth metal-containing material such as concrete construction waste, and an aqueous solution obtained from a salt of a weak base such as ammonium chloride and a strong acid. However, this method has a weak ability to elute alkaline earth metal ions from the alkaline earth metal-containing material, resulting in low carbon dioxide fixation efficiency.

[0017] Furthermore, Japanese Patent Publication No. 2024-106904 (Patent Document 3) proposes a method for producing calcium carbonate by eluting calcium ions from a calcium-containing substance and fixing carbon dioxide. This method involves reacting a calcium-containing substance such as waste concrete or slag with microorganisms capable of eluting calcium in an aqueous environment to elute calcium, and then blowing in carbon dioxide to fix it. However, because this method involves microorganisms, the reaction time is long, and it has limitations in terms of processing capacity for more efficiently fixing carbon dioxide, which is generated in large quantities industrially.

[0018] Japanese Patent Publication No. 2024-137353, Japanese Patent Publication No. 3954009, Japanese Patent Publication No. 2024-106904

[0019] The problem that the present invention aims to solve is to provide a novel carbon dioxide capture and storage method that solves the above-mentioned problems and allows for the direct or indirect reaction of carbon dioxide in exhaust gas with metal ions recovered from waste to precipitate sparingly water-soluble artificial carbonates, and then allows for the long-term storage of a stable carbonate mineral form by scattering a slurry or dewatered cake containing the sparingly water-soluble artificial carbonates on the ground surface or injecting it into abandoned mines, etc. Furthermore, in a preferred version of the present invention, in addition to solving the above problems, the invention also aims to provide a novel carbon dioxide capture and storage method that can increase the strength of the stored carbonate minerals.

[0020] To solve the above problems, the carbon dioxide capture and storage method of the present invention, which is a method for long-term stable storage of artificial carbonates in which carbon dioxide from exhaust gas has been fixed, has the following technical features.

[0021] (1) The carbon dioxide capture and storage method of the present invention is characterized by the following: contacting carbon dioxide in exhaust gas with an aqueous solution in which metal ions recovered from waste are dissolved, reacting the carbon dioxide with the metal ions to prepare a slurry or dehydrated cake containing a sparingly water-soluble artificial carbonate to fix the carbon dioxide; or contacting carbon dioxide in exhaust gas with an alkaline aqueous solution to absorb the carbon dioxide, adding waste to a water-soluble carbonate solution in which carbonate ions are dissolved to form a slurry, reacting the carbonate ions with metal ions contained in the waste to prepare a slurry or dehydrated cake containing a sparingly water-soluble artificial carbonate to fix the carbon dioxide; and then scattering the obtained slurry or dehydrated cake containing the artificial carbonate onto the ground surface or injecting it into an abandoned mine for storage, thereby storing the carbon dioxide in the form of carbonate minerals.

[0022] (2) A preferred carbon dioxide capture and storage method of the present invention is the carbon dioxide capture and storage method of (1) described above, characterized in that the metal ion is a calcium ion and / or a magnesium ion, and the water-insoluble artificial carbonate is artificial calcium carbonate and / or artificial magnesium carbonate.

[0023] (3) Another preferred carbon dioxide capture and storage method of the present invention is a carbon dioxide capture and storage method of the carbon dioxide capture and storage method of (1) or (2) above, characterized in that a solidifying agent is further added to the slurry or dewatered cake.

[0024] (4) A more preferable carbon dioxide capture and storage method of the present invention is the carbon dioxide capture and storage method of (3) above, characterized in that the solidifying agent is at least one selected from the group consisting of cement, cement-based solidifying agent, magnesium oxide, magnesium chloride, magnesium sulfate, and sodium chloride.

[0025] (5) Another preferred carbon dioxide capture and storage method of the present invention is the carbon dioxide capture and storage method of (3) above, characterized in that the solidifying agent is blended with the artificial carbonate in the slurry or dehydrated cake at an external ratio of 5 to 50% by mass.

[0026] (6) Another preferred carbon dioxide capture and storage method of the present invention is the carbon dioxide capture and storage method of (3) above, characterized in that the slurry containing the artificial carbonate has a solid-liquid ratio (mass ratio) of 1:0.75 to 1:25.

[0027] (7) A preferred carbon dioxide capture and storage method of the present invention is the carbon dioxide capture and storage method of (1) above, characterized in that the ground surface or abandoned mine is a mine site or final disposal site whose geological composition is mainly carbonate minerals.

[0028] (8) A more preferable carbon dioxide capture and storage method of the present invention is a carbon dioxide capture and storage method of the carbon dioxide capture and storage method of the present invention described in (1) or (7) above, characterized in that the obtained slurry or dewatered cake containing artificial carbonate is scattered on the ground surface or injected into an abandoned mine for storage in shallow layers of the ground surface at a depth of less than 800 m underground.

[0029] In this invention, "waste" means not only the solid waste itself, but also the waste slurry.

[0030] The carbon dioxide capture and storage method of the present invention eliminates the need for separation, capture, liquefaction, and storage processes using equipment used in chemical absorption methods that require large amounts of heat sources (steam) or energy such as electricity to capture carbon dioxide from industrially generated exhaust gases such as those from factories. Instead, it allows for the precipitation of sparingly water-soluble artificial carbonates by directly or indirectly reacting them with metal ions derived from waste at room temperature. Since it does not require the use of special carbon dioxide separation and capture equipment or energy sources such as boilers, it is cost-effective and also suppresses the emission of new carbon dioxide from energy sources during the reaction process for preparing the sparingly water-soluble artificial carbonates. Furthermore, by using waste as a raw material for the sparingly water-soluble carbonates, it offers excellent recyclability.

[0031] Preferably, carbon dioxide is stored in the form of a sparingly water-soluble artificial carbonate by scattering or injecting it into very shallow layers (shallow surface layers) such as the Earth's surface or abandoned mines. This eliminates the need to inject liquefied carbon dioxide into deep underground reservoirs inland or on the seabed, as is common in conventional CCS. Furthermore, because it can be scattered, injected, and stored in the form of a sparingly water-soluble carbonate, there is no risk of long-term leakage of the injected material, and long-term monitoring is unnecessary. In other words, generally, CCS uses liquid or supercritical fluid CO2. ２ This involves injecting and storing CO2 deep underground. ２ While conventional methods involve either keeping the substance in liquid form or gradually converting it to carbonate over time, in this invention, the substance can be stored in an artificial carbonate state from the moment of application and storage. Therefore, no chemical or physical changes are required, and it becomes possible to store the substance in a long-term stable artificial carbonate form immediately after the start of the process.

[0032] Furthermore, as mentioned above, since no chemical reactions occur after storage, the risk of volume expansion is eliminated, eliminating the need to install injection wells, etc., and no special construction work is required. Since it can be transported in the form of slurry or dewatered cake, dedicated tank trucks or transport ships for liquefied carbon dioxide are not needed, eliminating the risk of leakage. It can be transported using general-purpose dump trucks or tank trucks for transporting liquids at ambient temperature and pressure, thus reducing costs. Consequently, while CCS implementation previously required liquefaction treatment after carbon dioxide separation and recovery, and many carbon dioxide emitters implementing CCS were located in coastal areas due to the difficulty of transporting large quantities of liquefied carbon dioxide, this invention makes it possible to implement CCS even in inland factories.

[0033] Furthermore, the prepared sparingly water-soluble artificial carbonate can be stored stably for a long period until it is ready for application, such as spraying. In addition, since the slurry from which the prepared sparingly water-soluble artificial carbonate has precipitated can be used as is, solid-liquid separation processes such as filter presses can be omitted, reducing energy consumption and carbon dioxide emissions into the atmosphere. Moreover, since the slurry from which the sparingly water-soluble artificial carbonate has precipitated does not undergo chemical changes within the abandoned mine after injection, or does not require chemical reactions, ground expansion and cracking are less likely to occur, allowing for stable storage over a long period.

[0034] Furthermore, preferably, by incorporating a solidifying agent into the slurry or dewatered cake, the slurry or dewatered cake containing water-insoluble artificial carbonate with fixed carbon dioxide can maintain its strength even when scattered on the ground surface or injected into an abandoned mine. This prevents scattering by wind, enhances adhesion to the original ground, and increases the strength of the artificial carbonate mineral-containing material, enabling stable storage in abandoned mines and other locations.

[0035] This is a flowchart illustrating an overview of one example of the carbon dioxide capture and storage method of the present invention. This is a flowchart illustrating an overview of another example of the carbon dioxide capture and storage method of the present invention.

[0036] The present invention provides a carbon dioxide recovery and storage method which involves contacting carbon dioxide in exhaust gas with an aqueous solution containing metal ions recovered from waste, reacting the carbon dioxide with the metal ions to prepare a slurry or dehydrated cake containing a sparingly water-soluble artificial carbonate, thereby immobilizing the carbon dioxide; or contacting carbon dioxide in exhaust gas with an alkaline aqueous solution to absorb the carbon dioxide, adding waste to a water-soluble carbonate solution containing dissolved carbonate ions to form a slurry, reacting the carbonate ions with metal ions contained in the waste to prepare a slurry or dehydrated cake containing a sparingly water-soluble artificial carbonate, thereby immobilizing the carbon dioxide; and then scattering the obtained slurry or dehydrated cake containing the artificial carbonate onto the ground surface or injecting it into an abandoned mine for storage, thereby storing the carbon dioxide in the form of carbonate minerals.

[0037] The exhaust gas to which the present invention is applied is not particularly limited as long as it is an exhaust gas containing carbon dioxide emitted from industrial activities such as cement plants and petroleum refineries, and any exhaust gas can be targeted. For example, kiln exhaust gas containing carbon dioxide generated from a cement plant can be given as an example.

[0038] The carbon dioxide concentration in the exhaust gas is not particularly limited, but a higher carbon dioxide concentration in the exhaust gas facilitates the efficient precipitation of sparingly water-soluble carbonate minerals. Therefore, it is desirable that the exhaust gas contains carbon dioxide at a concentration of preferably 1% by volume or more, more preferably 5% by volume or more, and even more preferably 10% by volume or more. Furthermore, it is preferable to apply the present invention to the exhaust gas after performing a desulfurization and soot removal process and then cooling it to, for example, 50°C or below.

[0039] Furthermore, the waste to which this invention applies includes waste containing a metal element that can precipitate sparingly water-soluble carbonate particles by reacting directly with carbon dioxide or with carbonate ions in the form of a water-soluble carbonate solution. Any waste containing an element that can prepare sparingly water-soluble carbonates by reacting directly with carbon dioxide or with carbonate ions in the form of a water-soluble carbonate solution can be used.

[0040] The metal elements contained in the above-mentioned waste can be any substance (element) that reacts with carbon dioxide or carbonate ions to precipitate water-insoluble carbonate particles. There are no particular restrictions on the substances contained in the waste, however, waste containing Group 2 elements (alkaline earth metals) is preferred, and waste containing calcium and / or magnesium is even more preferred.

[0041] For example, suitable waste materials include waste concrete, waste ready-mix concrete sludge, and waste gypsum board. Preferably, the waste material is crushed before use, as this increases reactivity and allows for a shorter reaction time. More preferably, the waste material itself does not contain carbonates, so as not to release additional carbon dioxide during the reaction to prepare the sparingly water-soluble carbonate.

[0042] Furthermore, it is desirable that the waste does not contain harmful substances. If there is a risk that harmful substances will elute into water or the like, it is desirable to blend any known insolubilizing material, adsorbent or other such materials into the resulting slurry or dehydrated cake containing the poorly water-soluble artificial carbonate, and use them in combination, as long as this does not interfere with the precipitation and composition of the poorly water-soluble artificial carbonate particles that are ultimately precipitated, thereby suppressing the outflow of harmful substances into the surrounding environment.

[0043] As a method for immobilizing carbon dioxide in the above exhaust gas, the direct method or indirect method described below can be used. The direct method is a method for immobilizing carbon dioxide, comprising bringing the carbon dioxide in the exhaust gas into contact with an aqueous solution in which metal ions recovered from waste are dissolved, reacting the carbon dioxide with the metal ions, and preparing a slurry or dehydrated cake containing the poorly water-soluble artificial carbonate.

[0044] In the above direct method, the aqueous solution in which metal ions recovered from waste (waste-derived metal ions) are dissolved is an aqueous solution prepared by adding water or an acid to a solid waste alone, and converting the metal contained in the waste into the form of metal ions that react with carbon dioxide. In particular, by efficiently dissolving the waste using a strong acid or the like, a solution in which the metal ions contained in the waste are efficiently extracted and dissolved can be obtained, and such a solution can be suitably used.

[0045] Next, the exhaust gas is brought into contact with the aqueous solution by a method such as blowing the exhaust gas into the aqueous solution, so that the carbon dioxide in the exhaust gas is brought into contact with the aqueous solution in which metal ions recovered from the waste are dissolved, the carbon dioxide in the exhaust gas is reacted with the metal ions, and a slurry or dehydrated cake in which the poorly water-soluble artificial carbonate is precipitated is prepared to immobilize the carbon dioxide. Preferably, the metal ions are calcium ions and / or magnesium ions, whereby the suitably obtained poorly water-soluble artificial carbonate is artificial calcium carbonate and / or artificial magnesium carbonate.

[0046] In an indirect method, exhaust gas containing carbon dioxide is brought into contact with an alkaline aqueous solution to absorb the carbon dioxide, forming a solution of water-soluble carbonate in which carbonate ions are dissolved. To this solution in which carbonate ions are dissolved, pulverized waste, preferably such as waste gypsum board, is added and stirred to form a slurry. The metal ions contained in the waste react with the carbonate ions to precipitate water-insoluble artificial carbonate, thereby preparing a slurry or dehydrated cake to fix the carbon dioxide.

[0047] In this indirect method, first, carbon dioxide in the exhaust gas is brought into contact with an alkaline aqueous solution to absorb the carbon dioxide and prepare a water-soluble carbonate solution in which carbonate ions are dissolved. The alkaline solution is not particularly limited, but it is preferable to use a highly soluble monovalent strong alkaline solution such as a sodium hydroxide solution or a potassium hydroxide solution. Next, carbon dioxide in the exhaust gas is brought into contact with the alkaline aqueous solution by methods such as blowing the exhaust gas into it, and the carbon dioxide is absorbed by the alkaline aqueous solution to prepare a water-soluble carbonate solution in which carbonate ions are dissolved, preferably a water-soluble sodium carbonate solution or a potassium carbonate solution.

[0048] Next, the waste material, such as crushed waste gypsum powder obtained by crushing waste gypsum board, is added to the water-soluble carbonate solution in which the carbonate ions are dissolved, and the mixture is stirred to form a slurry. The metal contained in the waste is then dissolved and made to exist in the form of metal ions, and these metal ions are reacted with the carbonate ions to prepare a slurry in which a water-poorly soluble artificial carbonate is precipitated. From the viewpoint of reaction efficiency, it is desirable to use crushed waste material or waste powder as the waste material to be blended into the water-soluble carbonate solution. Preferably, the metal ions are calcium ions and / or magnesium ions, and the water-poorly soluble artificial carbonate preferably obtained is artificial calcium carbonate and / or artificial magnesium carbonate.

[0049] The slurry containing the sparingly water-soluble carbonate obtained in this way can be dehydrated as needed to prepare a dehydrated cake, taking into consideration the ease of spraying or injection.

[0050] When using a slurry containing sparingly water-soluble artificial carbonate for spraying on the ground surface or injecting into abandoned mines, the solid-liquid ratio of the slurry is not particularly limited, but preferably, to facilitate handling, the solid-liquid ratio (mass ratio) is 1:0.75 to 1:25, more preferably 1:1 to 1:20. In this invention, the solid-liquid ratio refers to the solid-liquid ratio of sparingly water-soluble artificial carbonate to water in the slurry, and even if a solidifying agent described later is included, the solid-liquid ratio refers to the solid-liquid ratio of sparingly water-soluble artificial carbonate to water in the slurry, excluding the solidifying agent. If the solid-liquid ratio is greater than 1:25, there may be an excess of water, and the efficiency of artificial carbonate storage may decrease. In this case, it is desirable to prepare the sparingly water-soluble artificial carbonate slurry and then, for example, by removing the clear supernatant after standing or by performing solid-liquid separation treatment using a filter press, etc., to adjust it to the above-mentioned suitable solid-liquid ratio, which facilitates handling during spraying or injection.

[0051] If the solid-liquid ratio is less than 1:0.75, the viscosity may be high and the reaction efficiency with carbon dioxide may decrease, which can be undesirable. For example, if the solid-liquid ratio is less than 1:0.75, it is desirable to adjust the solid-liquid ratio to a suitable one that facilitates handling during spraying or injection by adding water after preparing a water-insoluble artificial carbonate slurry.

[0052] When water-insoluble artificial carbonates are reduced to powder form through drying, energy is required for drying. Furthermore, the powder form is undesirable because it can be scattered into the surrounding environment by wind or during application, and can lead to insufficient strength due to poor filling properties in abandoned mines. For application to the ground surface or injection into abandoned mines, the form of slurry or dewatered cake is preferable.

[0053] By spreading the above-mentioned sparingly water-soluble carbonate slurry or dewatered cake on the ground surface or injecting and storing it in abandoned mines, carbon dioxide from exhaust gases can be spread and stored in the form of sparingly water-soluble carbonate, making it possible to achieve a state where long-term fixed storage is possible immediately after spreading or storage begins. Furthermore, by spreading it on the ground surface, strength can be obtained quickly due to the evaporation of moisture by wind and sunlight. Moreover, by injecting it into abandoned mines, only moisture penetrates into the ground, and strength can be obtained quickly as the water content of the artificial carbonate decreases.

[0054] In the present invention, it is particularly preferable to scatter or inject and store the material in a very shallow layer (shallow surface layer) including the ground surface. Any well-known method can be applied for the scattering or injection method. While general CCS storage is in a storage layer underground deeper than 800m, in the present invention, scattering and storage can be performed in a shallow surface layer including the ground surface, eliminating the need for shielding layers and storage layers. Preferably, storage is performed in a shallow surface layer such as the surface or abandoned mine, at a depth of less than 800m, preferably less than 500m, and more preferably less than 200m. In particular, in the case of abandoned mines, rather than injecting into independent voids underground or by digging a new hole underground, it is preferable to inject into an abandoned mine that is connected to the ground surface in a continuous surface. In this case, it becomes unnecessary to excavate new injection wells, and in some cases, injection can be performed by direct gravity fall from the ground surface. Furthermore, the use of general civil engineering heavy machinery becomes possible, making it more economically advantageous and the injection method simpler.

[0055] Furthermore, in this invention, by injecting carbon dioxide in the form of a water-insoluble artificial carbonate, no chemical changes occur in the abandoned mine, or there is no need to cause a chemical reaction. As a result, ground expansion and cracking are less likely to occur, and carbon dioxide can be stored in a mineralized form that is stable over the long term.

[0056] In particular, to more effectively prevent the scattering of poorly water-soluble artificial carbonate minerals by wind after scattering or injection onto the ground surface, to further enhance adhesion to the original ground and the early strength of the poorly water-soluble artificial carbonate minerals, and to enable the poorly water-soluble artificial carbonate minerals injected into abandoned mines to develop strength early and be stored in a stable carbonate mineral form, a solidifying agent can be added to the above-mentioned poorly water-soluble carbonate slurry or dewatered cake. In the case of dewatered cake, the solidifying agent can be added to either the slurry before dewatering or the cake after dewatering, and the timing of addition is not particularly limited.

[0057] Examples of the solidifying agent include at least one selected from the group consisting of various cements, cement-based solidifying agents, magnesium oxide, magnesium chloride, magnesium sulfate, sodium chloride, and magnesia cement-forming substances. The amount of solidifying agent to be added is not particularly limited, but preferably it is added at an external ratio of 5 to 50% by mass, and more preferably 10 to 30% by mass, relative to the water-insoluble artificial carbonate. For example, an example is to add 10% by mass of blast furnace cement as a solidifying agent to the water-insoluble artificial carbonate, such as calcium carbonate, which is precipitated in the slurry.

[0058] As described above, if the waste contains hazardous substances, an immobilizer or adsorbent for the hazardous substances can be added to the water-insoluble carbonate slurry or dewatered cake together with the solidifying agent, or if no solidifying agent is added, the immobilizer or adsorbent can be added separately. In the case of dewatered cake, the immobilizer or adsorbent can be added to either the slurry before dewatering or the cake after dewatering, and the timing of addition is not particularly limited. Any well-known immobilizer or adsorbent can be used as the immobilizer or adsorbent, as long as it does not hinder the effects of the present invention.

[0059] Examples of application of sparingly water-soluble carbonate slurry to the ground surface include application to depressions in open-cut mines for mineral resources such as limestone and ore. Furthermore, sparingly water-soluble carbonate can be injected into abandoned mines by any known method, such as natural fall from the ground surface or pumping. Suitable abandoned mines include those created by limestone extraction. Here, "sporadic water-soluble carbonate slurry" refers to a sparingly water-soluble carbonate slurry, a dewatered cake obtained by dewatering the slurry, and a slurry or dewatered cake containing solidifying agents and insoluble additives as needed.

[0060] The geological conditions of the area to be sprayed or injected are not particularly limited, but preferably, considering ease of handling and workability, the soil should be highly permeable and allow moisture to easily penetrate the ground. Furthermore, since the water-insoluble artificial carbonate is to be sprayed or injected, the soil should be composed mainly of carbonate minerals, and even more preferably, the soil should be composed mainly of limestone or dolomite, and even more preferably, the ground surface of limestone or dolomite mining mines, mine sites, mining shafts, and final disposal sites. This is because by spraying or injecting the water-insoluble carbonate slurry according to the present invention into depressions on the ground surface or abandoned mines of the original ground which was composed mainly of carbonate minerals, it is possible to achieve stability equivalent to that of the surrounding ground which is composed mainly of carbonate minerals for a long period of time, and thus have little impact on the surrounding environment.

[0061] Thus, the carbon dioxide capture and storage method according to the present invention can be a carbon dioxide capture and storage method that enables the capture and long-term storage of carbon dioxide in the form of stable, sparingly water-soluble carbonate by directly or indirectly contacting carbon dioxide in exhaust gas emitted from factories, etc., with an aqueous solution in which metal ions recovered from waste are dissolved, to prepare a slurry or dehydrated cake containing water-poorly soluble artificial carbonate particles, and then scattering the slurry or dehydrated cake containing the artificial carbonate on the ground surface or injecting it into an abandoned mine for storage.

[0062] The following is an example of testing a carbonate cured product using a water-insoluble artificial carbonate slurry in the carbon dioxide capture and storage method of the present invention. However, the following example is just one example included in the method of the present invention and does not limit the present invention.

[0063] (Preparation of Artificial Carbonate Slurry) Exhaust gas containing 12% by volume of carbon dioxide discharged from a cement plant was desulfurized and treated to remove soot, and then blown into a 1 mol / L sodium hydroxide solution to prepare an aqueous sodium carbonate solution. Next, waste gypsum powder, obtained by crushing and classifying waste gypsum board, was added to the aqueous sodium carbonate solution and stirred to react the carbonate ions in the aqueous sodium carbonate solution with the waste gypsum powder to prepare a slurry containing artificially synthesized sparingly water-soluble calcium carbonate. The average particle size of sparingly water-soluble artificial calcium carbonate in the obtained slurry was approximately 10 μm.

[0064] (Concentration adjustment of sparingly water-soluble artificial carbonate slurry) The obtained slurry of sparingly water-soluble artificial calcium carbonate was allowed to stand, and the clear supernatant solvent was removed to prepare two types of artificial carbonate slurries with solid-liquid ratios (mass ratios) of 1:0.8 and 1:20. Specifically, the amount of sparingly water-soluble artificial calcium carbonate in the slurry was set to 150 g, and the amount of water used as the solvent was adjusted to 120 g and 3000 g, respectively.

[0065] (Addition of solidifying agent to water-insoluble artificial carbonate slurry) The two types of slurries described above were each stirred using a stirrer or the like to ensure homogeneity and the absence of sediment. Then, a mixture of blast furnace cement type B, magnesium oxide, magnesium oxide, and magnesium chloride, which are solidifying agents, was added to the slurry in the proportions shown in Tables 1 and 2 below, relative to the mass of artificial calcium carbonate (artificial carbonate). The mixture was stirred for 5 minutes to prepare each sample of a uniform artificial carbonate slurry containing each solidifying agent. Samples A-1 and B-1 were samples of artificial carbonate slurry without the addition of the solidifying agents. Table 1 shows each sample (A-1 to A-4) with a solid-liquid ratio (mass ratio) of 1:0.8 in each slurry, and Table 2 shows each sample (B-1 to B-10) with a solid-liquid ratio (mass ratio) of 1:20 in the slurry.

[0066] The materials used for the solidification agent described above are as follows: Blast furnace cement type B (BB): Sumitomo Osaka Cement Co., Ltd. Magnesium oxide powder: Kanto Chemical Co., Ltd. Special grade magnesium chloride powder: Kanto Chemical Co., Ltd. Special grade hexahydrate The mixture of magnesium oxide and magnesium chloride used as the solidification agent described above is a solidification agent for the formation of magnesia cement, although magnesium oxide itself is a solidification agent.

[0067]

[0068]

[0069] (Solidification of Artificial Carbonate Slurry) To simulate the process of scattering artificial carbonate slurry onto the ground, a solidification test of each artificial carbonate slurry sample was conducted as follows, using a bottle-top filter container, which is a filtration device, to allow the water in the slurry to gradually penetrate into the ground. A bottle-top filter container (filter pore size 0.45 μm, membrane diameter 50 mm) was placed on a 250 mL bottle, and each artificial carbonate slurry (samples A-2 to A-4, B-2 to B-10) containing the solidifying agents shown in Tables 1 and 2, and an artificial carbonate slurry sample without solidifying agents (A-1, B-1) were poured into the bottle-top filter container.

[0070] Furthermore, in order to simulate the natural water infiltration process when artificial carbonate slurry is scattered on the ground surface, water absorption was not promoted by suction filtration. Each artificial carbonate slurry of the above samples was poured into a bottle-top filter container and allowed to stand. When water permeated from each artificial carbonate slurry in the bottle-top filter container and the volume decreased, the slurry was added again by pouring it into the same bottle-top filter container, and this process was repeated until the entire volume of each slurry was poured into the bottle-top filter container and allowed to stand.

[0071] During the standing period, the entire volume of each slurry was added to the bottle-top filter container. To suppress moisture evaporation due to drying from the top of the container and to avoid hindering the water permeability of the filter, the loosely sealed lids provided with the containers were placed over the top of each bottle-top filter and left to stand.

[0072] After allowing sufficient time for standing, and confirming that no more liquid was dripping from the bottle-top filter container into the bottle placed below it, the liquid that had passed through the bottle-top filter container and accumulated in the bottle was discarded as appropriate.

[0073] (Strength measurement of hardened artificial carbonate slurry) The strength of the hardened material from each artificial carbonate slurry sample remaining in the bottle-top filter container as described above was evaluated in accordance with JIS A 1147:2019 "Test method for setting time of concrete". Specifically, the hardened material from each artificial carbonate slurry sample was subjected to a cross-sectional area of ​​25 mm². ２ The penetration needle was inserted to a depth of 2 cm, and the penetration resistance value (N / mm) was measured. ２ The following measurements were taken: 7 days and 28 days of age. The results of these tests are shown in Tables 3 and 4, respectively. In particular, the penetration resistance value at 28 days of age was 0.8 N / m ２ The above characteristics indicate that the hardened material has sufficient strength and is a particularly desirable form. Furthermore, for reference, the volume of the hardened material was also measured, and the results are shown in Tables 3 and 4.

[0074]

[0075]

[0076] From the above test results, it can be seen that in all samples prepared using the method of the present invention, the penetration resistance value tended to increase between 7 and 28 days of age. As a solidifying agent, blast furnace cement type B resulted in a higher penetration resistance value with a smaller amount added compared to magnesium oxide alone or a mixture of magnesium oxide and magnesium chloride. Furthermore, the volume of the hardened material increased as the amount of solidifying agent added increased, which is thought to be because the solidifying agent solidifies while forming hydrates.

[0077] Furthermore, it was found that a smaller initial solid-liquid ratio (mass ratio) in the artificial calcium carbonate slurry resulted in superior strength development. This is presumed to be because a higher water content in the initial stages of hydration of the solidifying agent weakens the binding force with the artificial calcium carbonate, making it easier for highly soluble magnesium chloride to be drained away, thus reducing the amount of magnesia cement precipitated.

[0078] In particular, the reason why sample B-8 has a low penetration resistance value is thought to be that the added magnesium oxide finely clogged the membrane filter, hindering water discharge and resulting in a low density of the solidified material. Additionally, the absolute amount of solidifying agent was small, which prevented the development of high strength. However, by scattering it in areas with high ground permeability, the solid-liquid ratio (mass ratio) can be reduced, making it possible to increase the strength development, similar to the case where the solid-liquid ratio (mass ratio) is 1:0.8.

[0079] Samples A-1 and B-1, which did not contain a hardening agent, had the smallest volume of hardened material, suggesting that the increased penetration resistance was due to the ease with which moisture from the filter could be discharged and the material becoming tighter. Therefore, it can be seen that sufficient strength can be obtained without adding a hardening agent, but by incorporating a hardening agent, it is possible to harden the material more quickly and improve workability.

[0080] As described above, the method of the present invention is a simple method that can fix carbon dioxide in exhaust gases emitted from factories and the like, and then scatter or inject it onto the ground surface or abandoned mines, preferably shallow layers of the ground, for long-term stable storage. Therefore, it can be suitably applied to applications such as reducing the amount of carbon dioxide emitted into the atmosphere from exhaust gases generated by factories located not only in coastal areas but also inland areas.

Claims

1. A method for recovering and storing carbon dioxide, characterized by: contacting carbon dioxide in exhaust gas with an aqueous solution containing metal ions recovered from waste, reacting the carbon dioxide with the metal ions to prepare a slurry or dehydrated cake containing sparingly water-soluble artificial carbonate to fix the carbon dioxide; or contacting carbon dioxide in exhaust gas with an alkaline aqueous solution to absorb the carbon dioxide, adding waste to a water-soluble carbonate solution containing dissolved carbonate ions to form a slurry, reacting the carbonate ions with metal ions contained in the waste to prepare a slurry or dehydrated cake containing sparingly water-soluble artificial carbonate to fix the carbon dioxide; and storing the obtained slurry or dehydrated cake containing artificial carbonate on the ground surface or by injecting it into an abandoned mine for storage, thereby storing the carbon dioxide in the form of carbonate minerals.

2. A carbon dioxide capture and storage method according to claim 1, characterized in that the metal ion is a calcium ion and / or a magnesium ion, and the water-insoluble artificial carbonate is artificial calcium carbonate and / or artificial magnesium carbonate.

3. A carbon dioxide recovery and storage method according to claim 1 or 2, characterized in that a solidifying agent is further added to the slurry or dewatered cake.

4. A carbon dioxide capture and storage method according to claim 3, characterized in that the solidifying agent is at least one selected from the group consisting of cement, cement-based solidifying agent, magnesium oxide, magnesium chloride, magnesium sulfate, and sodium chloride.

5. A carbon dioxide recovery and storage method according to claim 3, characterized in that the solidifying agent is blended with the artificial carbonate in the slurry or dehydrated cake at an external ratio of 5 to 50% by mass.

6. A carbon dioxide capture and storage method according to claim 3, characterized in that the slurry containing artificial calcium carbonate has a solid-liquid ratio (mass ratio) of 1:0.75 to 1:

25.

7. A carbon dioxide capture and storage method according to claim 1, characterized in that the ground surface or abandoned mine is a mine site or final disposal site whose geological composition is mainly carbonate minerals.

8. A carbon dioxide capture and storage method according to claim 1 or 7, characterized in that the obtained slurry or dewatered cake containing artificial carbonate is scattered on the ground surface or injected into an abandoned mine for storage in a shallow layer of the ground surface less than 800 m underground.

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