Method for producing calcium carbonate, method for producing ready-mix mortar or ready-mix concrete, method for improving the ground, method for filling underground cavities, and method for fixing carbon dioxide

Abstract

To provide a novel method for producing calcium carbonate from carbide sludge, most of which has conventionally been discarded, which does not decrease fluidity of ready-mixed concrete when mixed with the ready-mixed concrete and does not decrease strength of a hardened product.SOLUTION: A method for producing calcium carbonate includes: a classification step of classifying carbide sludge containing calcium hydroxide and hydrophobic impurities and removing the hydrophobic impurities; an adjustment step of adjusting a solid content concentration of the carbide sludge from which the hydrophobic impurities have been removed in the classification step; and a carbon dioxide introduction step of introducing carbon dioxide into the carbide sludge from which the hydrophobic impurities have been removed in the classification step and whose solid content concentration has been adjusted in the adjustment step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for producing calcium carbonate. Furthermore, this invention relates to a method for producing ready-mix mortar or ready-mix concrete using calcium carbonate. This invention also relates to a method for improving ground and a method for filling underground cavities using calcium carbonate. Furthermore, this invention relates to a method for fixing carbon dioxide. [Background technology]

[0002] Calcium carbide (CaC2), used in the industrial production of acetylene, is obtained by heating a mixture of calcium oxide and coke to approximately 2000°C. Calcium carbide is known to contain impurities derived from the raw materials, such as calcium phosphide and sulfur. Acetylene can be produced by reacting calcium carbide with water. The by-product of this reaction, carbide slag (also called carbide lime, carbide sludge, or carbide slurry, whose main component is calcium hydroxide, Ca(OH)2), is an aqueous slurry containing various impurities. Carbide slag is defined as a type of industrial waste sludge (Article 2, Paragraph 4 of the Industrial Waste Law, Article 2 of the Cabinet Order) and must be disposed of after proper treatment. Although carbide slag is sometimes used as a neutralizing agent for acidic soil as a substitute for slaked lime (calcium hydroxide), the majority of it is not effectively utilized.

[0003] Patent Document 1 discloses a method for producing light calcium carbonate by granulating carbide slag, charging it into a rotary kiln, blowing carbon monoxide and oxygen into the rotary kiln, and carbonizing it at a temperature of 500-900°C. Patent Document 2 discloses a method for producing calcium carbonate from lime such as carbide lime, comprising the steps of: (i) providing an aqueous solution containing 10% to 35% by weight of a dissolved polyhydroxy compound and 1% to 5% by weight of dissolved calcium hydroxide, with a pH of at least 11.5; (ii) treating the solution prepared in step (i) to remove solids containing suspended matter; (iii) dispersing carbon dioxide in the solution to form calcium carbonate by the resulting decrease in pH of the reaction mixture; (iv) adding an alkaline reagent to terminate the dispersion of carbon dioxide and maintain the pH of the product mixture at at least 9.5 during a period that begins at the start of a short, sharp rise in pH and ends during the subsequent decrease in pH but before the pH reaches 9.5; and (v) recovering the precipitated calcium carbonate. Patent Document 2 discloses that the polyhydroxy compound in step (i) is glycerol, sugar alcohol, sugar, etc., and that step (ii) involves removing suspended matter using a flocculant such as a cationic polymer.

[0004] Incidentally, attempts have been made to increase the strength of concrete by adding calcium carbonate to ready-mix concrete and ready-mix mortar. Patent Document 3 discloses an admixture for high-strength concrete containing light calcium carbonate powder with an average particle size of 0.19 μm to 0.33 μm and a pH of 8.5 to less than 11. Patent Document 4 also discloses an admixture slurry for high-strength concrete containing water, a water-reducing agent (polycarboxylic acid type), and light calcium carbonate powder with an average particle size of 0.1 μm to 0.4 μm and a pH of 8.5 to less than 11, with the light calcium carbonate powder making up 60% to 75% by mass.

[0005] It is known that achieving both the fluidity of the concrete and the strength of the hardened material is difficult when dispersing admixtures in ready-mix concrete. However, Patent Documents 3 and 4 describe how admixtures containing calcium carbonate powder or their slurry can be dispersed in ready-mix concrete at relatively high concentrations, while also somewhat suppressing the decrease in the fluidity of the concrete. Nevertheless, there is a constant demand for the development of ready-mix concrete with even better workability (overall construction characteristics of concrete such as mixing, transportation, placement, compaction, and finishing). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 54-43897 [Patent Document 2] Special Publication No. 2013-506613 [Patent Document 3] Patent No. 6011926 [Patent Document 4] Patent No. 6011927 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, an object of the present invention is to provide a novel method for producing calcium carbonate that does not reduce the fluidity of fresh concrete and does not reduce the strength of the hardened product when mixed into fresh concrete, using carbide slag that has been mostly discarded conventionally. Furthermore, an object of the present invention is to provide a method for producing calcium carbonate-blended fresh mortar or calcium carbonate-blended fresh concrete using the produced calcium carbonate, a method for improving the ground by injecting a ground improvement material containing the produced calcium carbonate into the ground, and a method for filling an underground cavity with a filler containing the produced calcium carbonate. Furthermore, an object of the present invention is to provide a method for producing industrially usable calcium carbonate using carbide slag that has been conventionally discarded, while immobilizing carbon dioxide contained in exhaust gas and the like as calcium carbonate.

Means for Solving the Problems

[0008] One aspect of the present invention includes the following steps: A classification step of classifying carbide slag containing calcium hydroxide and hydrophobic impurities and removing the hydrophobic impurities; An adjustment step of adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed in the classification step; and A carbon dioxide introduction step of introducing carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed in the classification step and the solid content concentration of which has been adjusted in the adjustment step This is a method for producing calcium carbonate.

[0009] Here, it is preferable that the particle size of the hydrophobic impurities removed in the classification step is 45 μm or more.

[0010] In the adjustment step, it is preferable to adjust the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed to 1-30 mass%.

[0011] In the carbon dioxide introduction step, it is preferable to introduce carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration of which has been adjusted so that the carbonation rate of calcium ions is 1-40 cation% / hour.

[0012] It is preferable that calcite-type calcium carbonate having a spindle shape is produced.

[0013] Furthermore, a second aspect of the present invention is to classify carbide slag containing calcium hydroxide and hydrophobic impurities, and remove the hydrophobic impurities; adjust the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduce carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration has been adjusted to obtain calcium carbonate, and mix the obtained calcium carbonate with raw mortar or raw concrete to produce calcium carbonate-blended raw mortar or calcium carbonate-blended raw concrete.

[0014] Furthermore, a third aspect of the present invention is to classify carbide slag containing calcium hydroxide and hydrophobic impurities, and remove the hydrophobic impurities; adjust the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduce carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration has been adjusted to obtain calcium carbonate, and mix the obtained calcium carbonate with a ground improvement material, and mix or inject the obtained calcium carbonate-blended ground improvement material into the ground to improve the ground.

[0015] A fourth aspect of the present invention is to classify carbide slag containing calcium hydroxide and hydrophobic impurities, and remove the hydrophobic impurities; adjust the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduce carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration has been adjusted to obtain calcium carbonate, and mix the obtained calcium carbonate with a filler, and fill the obtained calcium carbonate-blended filler into an underground cavity.

[0016] Furthermore, a fifth aspect of the present invention is to classify carbide slag containing calcium hydroxide and hydrophobic impurities, and remove the hydrophobic impurities; The solid content concentration of the carbide slag from which hydrophobic impurities have been removed is adjusted; This method involves removing hydrophobic impurities and adjusting the solid content of carbide slag, then introducing exhaust gas containing carbon dioxide into the slag to fix the carbon dioxide contained in the exhaust gas. [Effects of the Invention]

[0017] Calcium carbonate can be produced from carbide slag, which was previously mostly discarded, without reducing the fluidity of the concrete or decreasing the strength of the hardened material when mixed with it. This produced calcium carbonate can be mixed with fresh mortar and fresh concrete for use in the construction of structures, and can also be mixed with ground improvement materials and underground cavity filling materials for ground improvement and backfilling of underground cavities. Furthermore, industrially usable calcium carbonate can be produced from waste carbide slag and exhaust gas, which is also waste, and carbon dioxide gas in the exhaust gas can be fixed. [Brief explanation of the drawing]

[0018] [Figure 1] This is a scanning electron microscope image (magnification: 10,000x) of the calcium carbonate obtained in Example 2. [Figure 2] This is a scanning electron microscope image (magnification: 20,000x) of the calcium carbonate obtained in Example 2. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in more detail below, but the present invention is not limited to the following embodiments.

[0020] One embodiment involves the following steps: A classification process in which carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and the hydrophobic impurities are removed; A preparation step to adjust the solid content concentration of the carbide slag from which hydrophobic impurities have been removed in the classification step; and Carbon dioxide introduction process: Carbon dioxide is introduced into carbide slag, which has had hydrophobic impurities removed in the classification process and its solid content adjusted in the adjustment process. This is a method for producing calcium carbonate, which includes [the specified ingredient].

[0021] In one embodiment, carbide slag is mainly the residue obtained after industrially obtaining acetylene from calcium carbide (calcium carbide, CaC2), and is an aqueous slurry. Carbide slag contains calcium hydroxide (Ca(OH)2) and hydrophobic impurities. The hydrophobic impurities contained in carbide slag are mainly coke residue, but may also contain sulfur or silicon carbide, etc. Hydrophobic impurities refer to all impurities other than calcium hydroxide that exist in the aqueous carbide slag without dissolving. One embodiment includes a step of classifying the carbide slag. This classification step is a step of removing hydrophobic impurities contained in the carbide slag by classification operation. The particle size of the calcium hydroxide particles, which are the main component of carbide slag, and the particle size of the hydrophobic impurities differ, and generally the particle size of the hydrophobic impurities is larger. Therefore, hydrophobic impurities can be removed from carbide slag by known classification operations (filtration using filter paper, filter cloth, filters, etc., classification using a classification device, etc.). Preferably, the particle size of the hydrophobic impurities removed in the classification process is 45 μm or larger. If the lower limit of the particle size of the hydrophobic impurities removed from carbide slag is increased (for example, setting the lower limit of the particle size to 200 μm, etc.), more hydrophobic impurities remain in the carbide slag, and therefore hydrophobic impurities are more likely to remain in the calcium carbonate finally produced in one embodiment. Also, if the lower limit of the particle size of the hydrophobic impurities removed from carbide slag is decreased (for example, setting the lower limit of the particle size to 10 μm, etc.), the hydrophobic impurities in the carbide slag can be removed almost completely, but calcium hydroxide particles are also removed, and the yield of the calcium carbonate finally produced in one embodiment decreases. The particle size values ​​of calcium hydroxide and hydrophobic impurities are obtained by either image analysis using an electron microscope or optical microscope, or by wet sieving residue measurement; the same value is obtained regardless of the method used. The separation process to remove hydrophobic impurities from carbide slag is a crucial step in producing calcium carbonate for mixing into fresh mortar and fresh concrete.If the carbon dioxide introduction process described below is carried out without removing hydrophobic impurities from the carbide slag, hydrophobic impurities will remain in the final calcium carbonate. In that case, the surface of the calcium carbonate particles will become water-repellent, making it difficult for the calcium carbonate to mix with fresh mortar or fresh concrete.

[0022] One embodiment includes an adjustment step for adjusting the solid content concentration of carbide slag from which hydrophobic impurities have been removed in a classification step. The adjustment step is a step for adjusting the solid content concentration of carbide slag. Here, solid content refers to all components other than water contained in the carbide slag after the removal of hydrophobic impurities. The carbide slag from which hydrophobic impurities have been removed in the classification step mainly contains calcium hydroxide particles with a particle size of less than 45 μm as solid content, and trace amounts (5% by mass or less) of hydrophobic impurities may remain. Solid content concentration refers to the mass ratio of all components other than water to the mass of the carbide slag from which hydrophobic impurities have been removed. In the adjustment step, the solid content concentration of the carbide slag from which hydrophobic impurities have been removed can be adjusted to 1-30% by mass, preferably 5-20% by mass, and more preferably 7-10% by mass. If the solid content concentration of the carbide slag from which hydrophobic impurities have been removed is higher than the desired range, water can be added to the carbide slag from which hydrophobic impurities have been removed. If the solid content concentration of the carbide slag from which hydrophobic impurities have been removed is lower than the desired range, calcium hydroxide can be added to the carbide slag from which hydrophobic impurities have been removed, or a portion of the supernatant can be removed after the solid content of the carbide slag from which hydrophobic impurities have been removed has settled over time. By adjusting the solid content concentration to an appropriate range in the adjustment process, the fluidity of the carbide slag (slurry) from which hydrophobic impurities have been removed can be maintained, thereby improving the efficiency of the reaction in the carbon dioxide introduction process described below. If the solid content concentration of the carbide slag from which hydrophobic impurities have been removed is too high or too low, the properties of the calcium carbonate produced in one embodiment may become unsuitable for mixing with fresh mortar or fresh concrete. The desired properties and characteristics of the calcium carbonate produced in one embodiment will be described in detail later.

[0023] One embodiment includes a carbon dioxide introduction step, in which carbon dioxide is introduced into carbide slag from which hydrophobic impurities have been removed in a classification step and whose solid content concentration has been adjusted in a conditioning step. This step involves reacting carbon dioxide with calcium hydroxide contained in the carbide slag to synthesize calcium carbonate. In the carbon dioxide introduction step, it is preferable to introduce carbon dioxide into the carbide slag from which hydrophobic impurities have been removed in a classification step and whose solid content concentration has been adjusted in a conditioning step, while adjusting the carbon dioxide introduction rate so that the carbonation rate of calcium ions is 1 to 40 cation% / hour. A carbonation rate of 1 to 40 cation atoms / hour means that all calcium ions (cations) of calcium hydroxide contained in the carbide slag from which hydrophobic impurities have been removed in a classification step and whose solid content concentration has been adjusted in a conditioning step react at a rate of 1 to 40% per hour to change into calcium carbonate. In other words, a carbonation rate of 1 cation% / hour means that it takes 100 hours for calcium hydroxide to react and be converted into calcium carbonate. Furthermore, a carbonation rate of 40 cation% / hour means that the conversion reaction from calcium hydroxide to calcium carbonate is completed in 2.5 hours. Carbon dioxide can be introduced into carbide slag, which has been prepared by removing hydrophobic impurities in a classification step and adjusting the solid content in a preparation step, so that the carbonation rate is preferably 5-30 cation% / hour, and more preferably 10-20 cation% / hour.

[0024] The temperature of the carbon dioxide introduction step, particularly the reaction start temperature before carbon dioxide introduction of the carbide slag after hydrophobic impurities have been removed in the classification step and the solid content concentration has been adjusted in the adjustment step, is important. The reaction start temperature can be 8-60°C, preferably around 15-50°C. If the reaction start temperature is too low or too high, it will lead to a decrease in the properties of the calcium carbonate produced in one embodiment. It is preferable that the carbon dioxide introduction step be carried out so as to constantly maintain the above temperature range.

[0025] The calcium carbonate produced in one embodiment is a calcium carbonate represented by the chemical formula CaCO3, and is the main component of seashells, eggshells, limestone, and chalk. Calcium carbonate is classified into heavy calcium carbonate (natural calcium carbonate) obtained by crushing and classifying limestone, and light calcium carbonate (synthetic calcium carbonate) obtained by chemical reactions, but the calcium carbonate produced in one embodiment is light calcium carbonate. Calcium carbonate exists in various crystalline polymorphs, such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), and vaterite crystals (hexagonal crystals). The calcium carbonate produced in one embodiment is preferably a calcite-type crystal with a spindle shape.

[0026] The calcium carbonate produced in one embodiment can be used in a wide range of applications, similar to conventional calcium carbonate. For example, calcium carbonate can be used for neutralizing wastewater and desulfurizing flue gas, as well as for filling in building materials, concrete, fertilizers, paints, etc. The calcium carbonate obtained in one embodiment is particularly effective as an additive to fresh mortar and fresh concrete, and is intended for use in ground improvement and filling underground cavities. Fresh concrete is a composite material made by mixing granular aggregates such as sand and gravel, hydraulic cement, binders containing slag powder and fly ash, water, and various admixtures. High-strength fresh concrete, which has been in demand in recent years, has a low water-to-binder ratio (weight ratio of water to binder), resulting in low fluidity and potentially poor workability during construction. Furthermore, high-strength fresh concrete may require long mixing times to obtain fresh concrete with good workability and fluidity, resulting in a significant amount of time required for concrete construction. Therefore, attempts have been made to improve the fluidity of ready-mix concrete and shorten the mixing time by adding calcium carbonate to it.

[0027] The properties required of ready-mixed concrete containing calcium carbonate are generally called workability. Workability refers to the ease of concrete construction, taking into account both the resistance to plastic deformation and flow (consistency) of the ready-mixed concrete and the resistance to the separation of components contained in the ready-mixed concrete. It is the most important indicator of the properties of ready-mixed concrete. Specifically, workability is a general indicator of the workability of concrete in relation to a series of operations from mixing, transportation, placement, and compaction of the ready-mixed concrete to the finishing of the constructed concrete. The criteria for judgment vary depending on the type of structure, construction location, and construction method. One embodiment allows for the production of calcium carbonate as an additive, which does not hinder the ease of mixing of the ready-mixed concrete, one of the elements for determining the workability of ready-mixed concrete, using carbide slag, a waste material, as a raw material.

[0028] A second embodiment of the present invention involves classifying carbide slag containing calcium hydroxide and hydrophobic impurities, and removing the hydrophobic impurities; The solid content concentration of the carbide slag from which hydrophobic impurities have been removed is adjusted; By removing hydrophobic impurities and adjusting the solid content of the carbide slag, carbon dioxide is introduced to obtain calcium carbonate. This method involves mixing the obtained calcium carbonate with fresh mortar or fresh concrete to produce calcium carbonate-containing fresh mortar or fresh concrete.

[0029] The second embodiment includes all the steps of the manufacturing method of the first embodiment. The calcium carbonate produced in the first embodiment can be mixed with fresh mortar or fresh concrete to produce calcium carbonate-containing fresh mortar or fresh concrete. Fresh mortar is a mixture of cement, water, and fine aggregate such as sand, while fresh concrete is a mixture of mortar and coarse aggregate such as gravel. In addition to these components, fresh mortar or fresh concrete may appropriately contain admixtures such as water-reducing agents to increase the fluidity of the fresh mortar or fresh concrete, and retarders to delay the setting of the fresh mortar or fresh concrete for a predetermined time. As water-reducing agents, so-called anionic surfactants such as carboxyl group-containing polyethers, lignin sulfonates, and oxycarboxylates can be used. As retarders, agents containing oxycarboxylates such as sodium gluconate as the main component can be used. Various admixtures such as water-reducing agents and retarders for fresh mortar or fresh concrete are commercially available to suit various conditions such as the shape of the structure, construction site, and construction period, and can be appropriately obtained from among these.

[0030] The calcium carbonate-containing fresh mortar or fresh concrete produced by the second embodiment is easy to mix and has high workability. Furthermore, the hardened product obtained by curing the calcium carbonate-containing fresh mortar or fresh concrete produced by the second embodiment has increased strength compared to the hardened product obtained by curing fresh mortar or fresh concrete without calcium carbonate, resulting in a high-strength mortar structure or high-strength concrete structure.

[0031] The third embodiment involves classifying carbide slag containing calcium hydroxide and hydrophobic impurities, and removing the hydrophobic impurities; The solid content concentration of the carbide slag from which hydrophobic impurities have been removed is adjusted; By removing hydrophobic impurities and adjusting the solid content of the carbide slag, carbon dioxide is introduced to obtain calcium carbonate. This method involves mixing the obtained calcium carbonate with a ground improvement material, and then mixing or injecting the resulting calcium carbonate-containing ground improvement material into the ground to improve the ground.

[0032] The third embodiment includes all the steps of the manufacturing method of the first embodiment. The calcium carbonate produced in the first embodiment can be mixed with a ground improvement material, and the ground can be improved by mixing or injecting the calcium carbonate-containing ground improvement material into the ground. A ground improvement material is a material used to improve the bearing capacity of land that cannot be used as a foundation for a building or structure in its original state when constructing a building or structure. Ground improvement materials are used to increase the strength of the ground from the viewpoint of suppressing deformation, settlement, liquefaction, etc., of soft ground. As ground improvement methods, direct foundations (surface improvement method in which ground improvement material is mixed or injected down to stable ground) and pile foundations (columnar improvement method in which ground improvement material is mixed or injected down to stable ground to build columnar columns, and steel pipe pile method in which steel pipe piles are injected down to stable ground) are known, and the method of the third embodiment can be applied in particular to the surface improvement method and the columnar improvement method. Cement, cement-based solidifying agents, lime, lime-based solidifying agents, cement / lime composite solidifying agents, and polymer-based solidifying agents are known as ground improvement materials. Various types of ground improvement materials are commercially available to suit the topography, environment, and other conditions of the construction site, and it is possible to obtain them as appropriate. The third embodiment can be applied to any type of ground improvement material. Ground improvement materials are materials made of almost the same materials as ready-mix mortar or ready-mix concrete. Although it depends on the characteristics of the ground to be improved, generally, the amount of water mixed into the ground improvement material is often higher than that of ready-mix mortar or ready-mix concrete.

[0033] By implementing the third embodiment, a strong ground suitable for buildings and structures can be obtained, enabling the creation of stable foundations for buildings and structures. The calcium carbonate-based ground improvement material used in the third embodiment is easy to mix and has high workability.

[0034] The fourth embodiment involves classifying carbide slag containing calcium hydroxide and hydrophobic impurities, and removing the hydrophobic impurities; The solid content concentration of the carbide slag from which hydrophobic impurities have been removed is adjusted; By removing hydrophobic impurities and adjusting the solid content of the carbide slag, carbon dioxide is introduced to obtain calcium carbonate. This method involves mixing the obtained calcium carbonate with a filler material and then filling the underground cavity with the resulting calcium carbonate-containing filler material.

[0035] The fourth embodiment includes all the steps of the manufacturing method of the first embodiment. The calcium carbonate produced in the first embodiment can be mixed with a filler material, and the calcium carbonate-containing filler material can be filled into underground cavities. When constructing buildings or structures on the surface, if underground cavities that are not visible from the surface are discovered through boring surveys, etc., it may be necessary to backfill such underground cavities. If underground cavities are left unattended, surface subsidence or ground settlement may occur, so it may be necessary to fill the underground cavities to prevent these from happening. Here, underground cavities refer to all underground cavities, including natural cavities such as limestone caves, dolines, lava tunnels, and weathered caves, mining sites such as metal mines, coal mining sites, stone mining sites, underground bunkers such as air raid shelters, and underground shopping areas, tunnels, and pipework sites. The filler material used to backfill underground cavities is required to have fluidity that can reach every corner of the cavity when filling it, and to become a solid with the necessary strength after solidification. Typical filling materials for such underground cavities include solidifying agents containing gypsum and lime, cement-based solidifying agents, and slag-based filling materials containing molten slag, blast furnace slag, and aggregate. Various types of filling materials for underground cavities are commercially available to suit the topography, environment, and other conditions of the construction site, and can be obtained as appropriate from among these. The fourth embodiment can be applied to any type of filling material.

[0036] By implementing the fourth embodiment, a highly strong solidified material can be formed in every corner of the underground cavity, making it possible to safely backfill the underground cavity. The calcium carbonate-based filler used in the fourth embodiment has high fluidity, is easy to mix, and has high workability.

[0037] The fifth embodiment involves classifying carbide slag containing calcium hydroxide and hydrophobic impurities, and removing the hydrophobic impurities; The solid content concentration of the carbide slag from which hydrophobic impurities have been removed is adjusted; This method involves removing hydrophobic impurities and adjusting the solid content of carbide slag, then introducing exhaust gas containing carbon dioxide into the slag to fix the carbon dioxide contained in the exhaust gas.

[0038] Embodiment 5 essentially includes all the steps of the manufacturing method of Embodiment 1. In producing calcium carbonate in Embodiment 1, exhaust gas is used as the source of carbon dioxide. Exhaust gas refers to all gases emitted from gasoline engines, diesel engines, internal combustion engines, and factories. Untreated exhaust gas usually contains water vapor, harmful gases such as carbon monoxide, and large amounts of carbon dioxide, a greenhouse gas. Discharging such exhaust gas into the atmosphere without treatment is undesirable as it leads to environmental pollution and global warming. Embodiment 5 is a method for obtaining calcium carbonate that can be used in the methods of Embodiments 2, 3, or 4 above by reacting carbon dioxide in exhaust gas with carbide slag, which was conventionally discarded as industrial waste, as a raw material. By implementing Embodiment 5, carbon dioxide in exhaust gas is fixed as calcium carbonate, and the obtained calcium carbonate can be used in addition to being mixed into fresh mortar and fresh concrete, as well as in ground improvement materials, underground cavity filling materials, etc. [Examples]

[0039] The embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments.

[0040] [Example 1] <Production of calcium carbonate> Carbide slag obtained from High Pressure Gas Industry Co., Ltd. was passed through a sieve with a mesh diameter of 100 μm (Japanese Industrial Standard JIS Z 8801, company name: Iida Seisakusho Co., Ltd.) to remove particles with a diameter of 100 μm or more. The solid content concentration of the obtained carbide slag was adjusted to 10%. Next, the temperature of the obtained carbide slag was set to 28°C, and the carbide slag was stirred while introducing carbon dioxide gas so that the carbonation rate of calcium ions was 12 cation% / hour (the reaction time to be completed was 8.1 hours). The obtained slurry was filtered and dried in an oven at 105°C for 1 hour to obtain spindle-shaped calcite-type calcium carbonate (BET specific surface area measured according to JIS Z 8830: 5.9 m²). 2 ( / g).

[0041] <Manufacturing of ready-mixed concrete> Ordinary Portland cement (Japanese Industrial Standard JIS R 5210, Density: 3.14~3.17 g / cm³) 3 ), blast furnace slag fine powder 4000 (Japanese Industrial Standard JIS A 6206, density: 2.8 g / cm³) 3 (The above) As fine aggregate, crushed sand with a particle size of 5 mm or less (Japanese Industrial Standard JIS A 5005, produced in Joyo City, Kyoto Prefecture, density: 2.5 g / cm³) 3 (The above) Crushed stone with a particle size of 5-15 mm as coarse aggregate (Japanese Industrial Standard JIS A 5005, produced in Kameoka City, Kyoto Prefecture, density: 2.5 g / cm³) 3 (The above) As admixture A, a high-performance water-reducing agent (Type I) containing a carboxyl group-containing polyether compound as the main component (Japanese Industrial Standard JIS A 6204, density: 1.04~1.08 g / cm³) 3 ), as admixture B, a water-reducing agent of the delayed type (Type I) mainly composed of oxycarboxylate salt (Japanese Industrial Standard JIS A 6206, density: 1.17~1.21 g / cm³) 3), and fresh cement containing water were prepared. The calcium carbonate obtained above was added to the fresh concrete and mixed using an inverter twin-shaft forced-mix concrete mixer (name: MIC-109-0-31, company name: Marui Co., Ltd.). The detailed mixing ratio of the calcium carbonate-added fresh concrete is shown in Table 1. Concrete specimens to be used in the compressive strength test described below were prepared from this fresh concrete.

[0042] <Compression strength test> The compressive strength test was conducted according to the Japanese Industrial Standard JIS A 1108:2018 "Test Method for Compressive Strength of Concrete," measuring the compressive strength of the concrete after 24 hours and after 14 days.

[0043] [Example 2] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 150 μm (Japanese Industrial Standard JIS Z 8801, Company name: Iida Seisakusho Co., Ltd.), and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 17 cation% / hour (so that the reaction would take 5.9 hours to complete). spindle Calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 8.4 m²). 2 ( / g). A compressive strength test was conducted by mixing the obtained calcium carbonate with fresh concrete containing the same components as in Example 1. The detailed mixing ratios of the fresh concrete and calcium carbonate are shown in Table 1. Scanning electron microscope images of the spindle-shaped calcite-type calcium carbonate obtained in Example 2 are shown in Figure 1 (magnification: 10,000x) and Figure 2 (magnification: 20,000x).

[0044] [Table 1]

[0045] [Comparative Example 1] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was not passed through any sieve and the reaction start temperature in the carbon dioxide introduction step was 30°C. Spindle-shaped calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 8.5 m 2 / g). The obtained calcium carbonate was blended at the same blending ratio as in Example 1 into fresh concrete having the same components and blending ratio as in Example 1, and a compressive strength test was conducted.

[0046] [Comparative Example 2] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, company name: Iida Manufacturing Co., Ltd.) and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 50 cation% / hour (so that the time until the reaction was completed was 2.0 hours). Cubical calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 27.0 m 2 / g). The obtained calcium carbonate was blended at the same blending ratio as in Example 1 into fresh concrete having the same components and blending ratio as in Example 1, and a compressive strength test was conducted.

[0047] [Comparative Example 3] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, company name: Iida Manufacturing Co., Ltd.) and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 0.5 cation% / hour (so that the time until the reaction was completed was 200 hours). Spindle-shaped calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 4.0 m 2 / g). The obtained calcium carbonate was blended at the same blending ratio as in Example 1 into fresh concrete having the same components and blending ratio as in Example 1, and a compressive strength test was conducted.

[0048] [Comparative Example 4] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was not passed through any sieve, the reaction initiation temperature for the carbon dioxide introduction step was set to 8°C, and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 8.9 cation% / hour (so that the reaction time to completion was 11.3 hours). Cubic calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 42.0 m²). 2 ( / g). The obtained calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 2, and a compressive strength test was performed.

[0049] [Comparative Example 5] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, Company name: Iida Seisakusho Co., Ltd.), the reaction start temperature for the carbon dioxide introduction step was set to 65°C, and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 16.7 cation% / hour (so that the reaction would take 6 hours to complete). spindle Calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 4.0 m²). 2 ( / g). The obtained calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 2, and a compressive strength test was performed.

[0050] [Comparative Example 6] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, Company name: Iida Seisakusho Co., Ltd.), the solid content concentration of the carbide slag was adjusted to 0.5% in the adjustment process, and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 200 cation% / hour (so that the reaction would be completed in 0.5 hours). Cubic calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 3.0 m²).2 ( / g). The obtained calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 2, and a compressive strength test was performed.

[0051] [Comparative Example 7] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, Company: Iida Seisakusho Co., Ltd.), the reaction start temperature in the carbon dioxide introduction step was set to 14°C, the solid content concentration of the carbide slag was adjusted to 32% in the adjustment step, and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 13 cation% / hour (so that the reaction would be completed in 7.6 hours). Calcite-type calcium carbonate aggregates were obtained (BET specific surface area measured according to JIS Z 8830: 16.9 m²). 2 ( / g). The obtained calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 2, and a compressive strength test was performed.

[0052] Table 2 shows the experimental conditions and concrete mix ratios for the comparative example.

[0053] [Table 2-1]

[0054] [Table 2-2]

[0055] [Reference example 1] Commercially available light calcium carbonate (Brilliant 1500, Shiraishi Kogyo Co., Ltd., BET specific surface area: 13m²) 2 A sample of ( / g) was prepared. Calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, except that it did not contain admixture B, in the proportions shown in Table 3, and a compressive strength test was conducted.

[0056] [Reference example 2] Commercially available light calcium carbonate (Silver W, Shiraishi Kogyo Co., Ltd., BET specific surface area: 6m²) 2 A sample (spindle-shaped, per gram) was prepared. Calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 3, and a compressive strength test was conducted.

[0057] [Reference example 3] Commercially available large-particle heavy calcium carbonate (Whiten H, Toyo Fine Chemical Co., Ltd., BET specific surface area: 1.5 m²) 2 A sample of calcium carbonate ( / g) was prepared. Calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 3, and a compressive strength test was conducted.

[0058] [Reference example 4] Calcium carbonate (BET specific surface area: 0.26 m²) produced by the method disclosed in Japanese Patent Publication No. 2014-148432 (method for producing calcium carbonate from concrete waste containing unsolidified cement fine particles (concrete sludge)). 2 A sample of calcium carbonate ( / g) was prepared. Calcium carbonate was added to ready-mixed concrete with the same components as in Example 1, according to the mixing ratio shown in Table 3, and a compressive strength test was conducted.

[0059] [Table 3]

[0060] [Example 3] <Production of calcium carbonate> Spindle-shaped calcite-type calcium carbonate was obtained under the same conditions as in the calcium carbonate production method of Example 1 (BET specific surface area measured according to JIS Z 8830: 5.9 m²). 2 ( / g).

[0061] <Manufacturing of ground improvement materials> Blast furnace slag fine powder 4000 (Japanese Industrial Standard JIS A 6206, Density: 2.8 g / cm³) 3 (The above) Crushed stone powder with a particle size of 2.5 mm or less as aggregate (Japanese Industrial Standard JIS A 5041, density: 2.5 g / cm³) 3(The above) Sodium silicate (SiO2 / Na2O molar ratio 2.0, mass percentage concentration of Na2O: 14.1-14.5 wt%, density 1.48-1.53 ​​g / cm³) 3 As described above, a ground improvement material containing water was prepared. The calcium carbonate obtained above was mixed into the ground improvement material and mixed using a mixer (name: Mortar Mixer MIC-362-1-01, company name: Marui Co., Ltd.). The detailed mixing ratio of the calcium carbonate-containing ground improvement material is shown in Table 4. From this ground improvement material, specimens for use in the uniaxial compression test described below were prepared.

[0062] <Uniaxial compression test> Uniaxial compression tests were conducted in accordance with the Japanese Industrial Standard JIS A 1216:2020 "Uniaxial Compression Test Method for Soil," measuring the uniaxial compressive strength of the ground improvement material specimens after 28 days and after 91 days, respectively.

[0063] [Example 4] Spindle-shaped calcite-type calcium carbonate was obtained under the same conditions as in the calcium carbonate production method of Example 2 (BET specific surface area measured according to JIS Z 8830: 8.4 m²). 2 ( / g). A uniaxial compression test was conducted using a ground improvement material containing the same components as in Example 3, blended with the obtained calcium carbonate. The detailed blending ratios of the ground improvement material and calcium carbonate are shown in Table 4.

[0064] [Table 4]

[0065] [Comparative Example 8] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was not passed through any sieve. Spindle-shaped calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 6.6 m²). 2 ( / g). A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with the obtained calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0066] [Comparative Example 9] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, Company name: Iida Seisakusho Co., Ltd.), and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 50 cation% / hour (so that the reaction would take 2.0 hours to complete). spindle Calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 27.0 m²). 2 ( / g). A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with the obtained calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0067] [Comparative Example 10] Calcium carbonate was produced under the same conditions as in Example 1, except that the carbide slag was passed through a sieve with a mesh diameter of 75 μm (Japanese Industrial Standard JIS Z 8801, Company name: Iida Seisakusho Co., Ltd.), and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 0.5 cation% / hour (so that the reaction would take 200 hours to complete). spindle Calcite-type calcium carbonate was obtained (BET specific surface area measured according to JIS Z 8830: 4.0 m²). 2 ( / g). A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with the obtained calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0068] [Table 5]

[0069] [Reference example 5] Commercially available light calcium carbonate (Shirataka CC, Shiraishi Kogyo Co., Ltd., BET specific surface area: 26m²) 2A sample of ( / g) was prepared. A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0070] [Reference example 6] Commercially available light calcium carbonate (PC, Shiraishi Kogyo Co., Ltd., BET specific surface area: 6m²) 2 A sample (spindle-shaped, per gram) was prepared. A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0071] [Reference example 7] Commercially available large-particle heavy calcium carbonate (Whiten P50, Toyo Fine Chemical Co., Ltd., BET specific surface area: 1.5m²) 2 A sample of ( / g) was prepared. A ground improvement material with the same components and mixing ratio as in Example 3 was mixed with calcium carbonate in the same mixing ratio as in Example 3, and a uniaxial compression test was performed.

[0072] [Reference example 8] Commercially available light calcium carbonate (Silver W, Shiraishi Kogyo Co., Ltd., BET specific surface area: 6m²) 2 A sample (spindle-shaped, per gram) was prepared. A ground improvement material with the same components and proportions as in Example 3 was mixed with calcium carbonate in the same proportions as in Example 3, and a uniaxial compression test was performed.

[0073] [Reference example 9] Commercially available light calcium carbonate (Brilliant 1500, Shiraishi Kogyo Co., Ltd., BET specific surface area: 13m²) 2 A sample ( / g) was prepared. A ground improvement material with the same components and proportions as in Example 3 was mixed with calcium carbonate in the same proportions as in Example 3, and a uniaxial compression test was performed.

[0074] [Table 6]

[0075] The meanings of the abbreviations in Tables 1-6 are as follows: P: Amount of powder, sum of B and F below B: Amount of binder, the sum of C and BFS below. C: Amount of cement BFS: Blast furnace slag fine powder amount F: Amount of calcium carbonate W / P: water powder ratio s / a: Fine aggregate ratio, s / a = Sv / Av × 100 [%], Sv is the volume of fine aggregate, Av is the total aggregate volume (volume of fine aggregate + volume of coarse aggregate) A: Admixture A, the addition rate is a percentage of the total weight of the ready-mixed concrete, "Addition amount P·wt%" is the weight of the powder contained in the ready-mixed concrete relative to the total volume. B: Admixture B, "Addition Rate" is the percentage relative to the total weight of the ready-mixed concrete, "Addition Amount P·wt%" is the weight relative to the total volume of powder contained in the ready-mixed concrete. S2: Aggregate (crushed stone powder) amount WG: Amount of sodium silicate

[0076] In Tables 1-6 above, the evaluation refers to the workability of the concrete or ground improvement material. Workability, as described above, is a comprehensive evaluation considering the workability and constructability of the concrete or ground improvement material. In the series of experiments described herein, the mixing characteristics of the ready-mixed concrete or ground improvement material and the compressive strength of each hardened product were comprehensively judged, and the workability was categorized as excellent, good, fair, or poor, from highest to lowest. The remarks are comments on notable characteristics of the ready-mixed concrete or ground improvement material during mixing and on the strength of the hardened product. "Thixotropic immediately after mixing" means that the ready-mixed concrete or ground improvement material exhibited thixotropy (the property of viscosity decreasing when shear force is continuously applied) immediately after mixing began. Thixotropy is not considered a good property for typical ready-mixed concrete.

[0077] The ready-mixed concrete containing calcium carbonate produced by the manufacturing method of the present invention exhibits excellent mixing performance without losing fluidity, and the concrete has high strength after hardening. Reference examples show experimental cases where commercially available calcium carbonate (limestone) was mixed into ready-mixed concrete or ground improvement materials. However, the calcium carbonate produced by the manufacturing method of the present invention exhibited performance equivalent to commercially available calcium carbonate (for example, Reference Examples 2 and 6), providing superior ready-mixed concrete or ground improvement materials. The manufacturing method of the present invention can produce industrially and commercially useful calcium carbonate using carbide slag, an industrial waste, as a raw material. In the manufacturing method of the present invention, applying exhaust gas as a carbon dioxide source can reduce carbon dioxide emissions into the atmosphere, thus contributing to curbing global warming and environmental pollution.

Claims

1. The following steps: A classification process in which carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and hydrophobic impurities with a particle size of 45 μm or larger are removed; A preparation step in which the solid content concentration of the carbide slag obtained by removing hydrophobic impurities with a particle size of 45 μm or larger in a classification step is adjusted to 1-30% by mass; and In the carbon dioxide introduction step, carbon dioxide is introduced into the carbide slag, which has been prepared by removing hydrophobic impurities with a particle size of 45 μm or larger in the classification step and adjusting the solid content concentration to 1-30% by mass in the adjustment step, so that the carbonation rate of calcium ions is 1-40 cation% / hour. A method for producing spindle-shaped calcite-type calcium carbonate, including the method described above.

2. Carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and hydrophobic impurities with a particle size of 45 μm or larger are removed; The solid content concentration of the carbide slag, from which hydrophobic impurities with a particle size of 45 μm or larger have been removed, is adjusted to 1-30% by mass; Hydrophobic impurities with a particle size of 45 μm or larger are removed, and the solid content concentration is adjusted to 1-30% by mass. Carbon dioxide is then introduced into the carbide slag so that the carbonation rate of calcium ions is 1-40 cation% / hour, thereby obtaining spindle-shaped calcite-type calcium carbonate. A method for producing calcium carbonate-containing fresh mortar or fresh concrete by mixing the obtained spindle-shaped calcite-type calcium carbonate with fresh mortar or fresh concrete.

3. Carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and hydrophobic impurities with a particle size of 45 μm or larger are removed; The solid content concentration of the carbide slag, from which hydrophobic impurities with a particle size of 45 μm or larger have been removed, is adjusted to 1-30% by mass; Hydrophobic impurities with a particle size of 45 μm or larger are removed, and the solid content concentration is adjusted to 1-30% by mass. Carbon dioxide is then introduced into the carbide slag so that the carbonation rate of calcium ions is 1-40 cation% / hour, thereby obtaining spindle-shaped calcite-type calcium carbonate. A method for improving the ground by mixing the obtained spindle-shaped calcite-type calcium carbonate with a ground improvement material, and then mixing or injecting the resulting calcium carbonate-containing ground improvement material into the ground.

4. Carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and hydrophobic impurities with a particle size of 45 μm or larger are removed; The solid content concentration of the carbide slag, from which hydrophobic impurities with a particle size of 45 μm or larger have been removed, is adjusted to 1-30% by mass; Hydrophobic impurities with a particle size of 45 μm or larger are removed, and the solid content concentration is adjusted to 1-30% by mass. Carbon dioxide is then introduced into the carbide slag so that the carbonation rate of calcium ions is 1-40 cation% / hour, thereby obtaining spindle-shaped calcite-type calcium carbonate. A method comprising mixing the obtained spindle-shaped calcite-type calcium carbonate with a filler material, and then filling an underground cavity with the resulting calcium carbonate-containing filler material.

5. Carbide slag containing calcium hydroxide and hydrophobic impurities is classified, and hydrophobic impurities with a particle size of 45 μm or larger are removed; The solid content concentration of the carbide slag, from which hydrophobic impurities with a particle size of 45 μm or larger have been removed, is adjusted to 1-30% by mass; A method for fixing carbon dioxide contained in exhaust gas by introducing exhaust gas into carbide slag, which has been prepared by removing hydrophobic impurities with a particle size of 45 μm or larger and adjusting the solid content concentration to 1-30% by mass, so that the carbonation rate of calcium ions is 1-40 cation% / hour.

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