Method for producing calcium carbonate, method for producing raw mortar or ready-mixed concrete, method for improving ground, method for filling underground cavity, 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] The present invention relates to a method for producing calcium carbonate. Further, the present invention relates to a method for producing green mortar or green concrete using calcium carbonate. The present invention relates to a method for improving ground and filling underground cavities using calcium carbonate. Further, the present invention relates to a method for immobilizing carbon dioxide.

Background Art

[0002] Calcium carbide (calcium carbide, CaC2) used in the industrial production of acetylene is obtained by heating a mixture of calcium oxide and coke to about 2000°C. It is known that calcium carbide contains calcium phosphide, sulfur, and other impurities derived from raw materials. Acetylene can be produced by reacting calcium carbide with water. Carbide sludge (also referred to as carbide lime, carbide sludge, carbide slurry, etc., the main component of which is calcium hydroxide, Ca(OH)2) is an aqueous slurry containing various impurities. Carbide sludge is defined as a type of industrial waste sludge (Article 2, Paragraph 4 of the Industrial Waste Law, Cabinet Order Article 2) and must be properly treated before being discarded. Carbide sludge may be used as a neutralizing agent for acidic soil as a substitute for slaked lime (calcium hydroxide), but most of it has not been 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 carbonating it at a temperature of 500-900°C. Patent Document 2 discloses a method for producing calcium carbonate from lime such as carbide lime, which includes step (i) of providing an aqueous solution containing 10 wt% to 35 wt% of a dissolved polyhydroxy compound and 1 wt% to 5 wt% of a dissolved calcium hydroxide and having a pH of at least 11.5; step (ii) of treating the solution prepared in step (i) to remove solid substances containing suspended substances; step (iii) of dispersing carbon dioxide in the solution to form calcium carbonate due to a decrease in the pH of the resulting reaction mixture; step (iv) of terminating the dispersion of carbon dioxide and adding an alkaline reagent to maintain the pH of the product mixture at at least 9.5 during a period that starts at the beginning of a short rapid increase in pH and ends during the subsequent decrease in pH but before the pH reaches 9.5; and step (v) of recovering the precipitated calcium carbonate. In Patent Document 2, it is disclosed that the polyhydroxy compound in step (i) is glycerol, sugar alcohol, sugar, etc., and step (ii) is to remove suspended substances using a flocculant such as a cationic polymer.

[0004] By the way, attempts have been made to increase the strength of concrete by adding calcium carbonate to fresh concrete, fresh mortar, etc. Patent Document 3 discloses an admixture for high-strength concrete containing light calcium carbonate powder having an average particle diameter of 0.19 μm or more and 0.33 μm or less and a pH of 8.5 or more and less than 11. Patent Document 4 discloses an admixture slurry for high-strength concrete containing water, a water reducing agent (polycarboxylic acid type), and light calcium carbonate powder having an average particle diameter of 0.1 μm or more and 0.4 μm or less and a pH of 8.5 or more and less than 11, with the light calcium carbonate powder contained in an amount of 60 mass% or more and 75 mass% or less.

[0005] When dispersing admixtures in fresh concrete, it is known that it is difficult to achieve both the fluidity of fresh concrete and the strength of the hardened product. However, Patent Documents 3 and 4 disclose that admixtures containing calcium carbonate powder or their slurries can be dispersed at a relatively high concentration in fresh concrete, and the decrease in the fluidity of fresh concrete can be somewhat suppressed. However, the development of fresh concrete with further improved workability (overall construction characteristics of concrete such as mixing, transportation, placing, compaction, and finishing) has always been desired.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] Accordingly, an object of the present invention is to provide a novel method for producing calcium carbonate which, when mixed with fresh concrete, does not reduce the fluidity of the fresh concrete and does not reduce the strength of the hardened product, and which is produced from carbide slag that has hitherto been mostly discarded. 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 hitherto been discarded, while immobilizing carbon dioxide contained in exhaust gas or the like as calcium carbonate.

Means for Solving the Problems

[0008] One aspect of the present invention is 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, which includes these steps.

[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 classifies carbide slag containing calcium hydroxide and hydrophobic impurities, and removes the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduces 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 mixes the obtained calcium carbonate with fresh mortar or fresh concrete to produce calcium carbonate-blended fresh mortar or calcium carbonate-blended fresh concrete.

[0014] Furthermore, a third aspect of the present invention classifies carbide slag containing calcium hydroxide and hydrophobic impurities, and removes the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduces 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 mixes the obtained calcium carbonate with a ground improvement material, and mixes or injects the obtained calcium carbonate-blended ground improvement material into the ground to improve the ground.

[0015] A fourth aspect of the present invention classifies carbide slag containing calcium hydroxide and hydrophobic impurities, and removes the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduces 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 mixes the obtained calcium carbonate with a filler, and fills the obtained calcium carbonate-blended filler into an underground cavity.

[0016] Furthermore, a fifth aspect of the present invention classifies carbide slag containing calcium hydroxide and hydrophobic impurities, and removes the hydrophobic impurities; Adjust the solid content concentration of carbide slag from which hydrophobic impurities have been removed; A method in which exhaust gas containing carbon dioxide is introduced into carbide slag from which hydrophobic impurities have been removed and the solid content concentration has been adjusted, to immobilize the carbon dioxide contained in the exhaust gas.

Advantages of the Invention

[0017] 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 can be produced from carbide slag, most of which has been conventionally discarded. The calcium carbonate produced in this way can be mixed into fresh mortar or fresh concrete and used for constructing structures, or mixed into ground improvement materials or fillers for underground cavities and used for ground improvement or backfilling underground cavities. Furthermore, industrially usable calcium carbonate can be produced from carbide slag, which is a waste product, and exhaust gas, which is also a waste product, and the carbon dioxide gas in the exhaust gas can be immobilized.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Modes for Carrying Out the Invention

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

[0020] One embodiment includes the following steps: A classification step of classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove 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 carbide slag from which hydrophobic impurities have been removed in a classification step and the solid content concentration has been adjusted in an adjustment step A method for producing calcium carbonate, which comprises the above steps.

[0021] In one embodiment, carbide slag mainly refers to the residue obtained after industrially producing 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 residues, and may also contain sulfur or silicon carbide, etc. Hydrophobic impurities are components other than calcium hydroxide, and refer to all impurities that exist without dissolving in aqueous carbide slag. One embodiment includes a step of classifying carbide slag. This classification step is a step of removing the hydrophobic impurities contained in carbide slag by a classification operation. The particle size of the calcium hydroxide particles, which are the main component of carbide slag, is different from that of the hydrophobic impurity particles, and generally the particle size of the hydrophobic impurity particles is larger. Therefore, the hydrophobic impurities can be removed from carbide slag by known classification operations (filtration using filter paper, filter cloth, filters, etc., classification by a classification device, etc.). The particle size of the hydrophobic impurities removed in the classification step is preferably 45 μm or more. Increasing the lower limit value of the particle size of the hydrophobic impurities removed from carbide slag (for example, setting the lower limit value of the particle size to 200 μm, etc.) will increase the amount of hydrophobic impurities remaining in the carbide slag, so hydrophobic impurities are likely to remain in the calcium carbonate finally produced in one embodiment. Also, decreasing the lower limit value of the particle size of the hydrophobic impurities removed from carbide slag (for example, setting the lower limit value of the particle size to 10 μm, etc.) can almost completely remove the hydrophobic impurities in the carbide slag, but the calcium hydroxide particles will also be removed together, resulting in a decrease in the yield of the calcium carbonate finally produced in one embodiment. Here, the particle size values of the calcium hydroxide and hydrophobic impurity particles are values obtained by either measurement by image analysis using an electron microscope or an optical microscope or measurement by wet sieve residue, and the values are the same regardless of the measurement method. The separation step of removing hydrophobic impurities from carbide slag is a very important step in producing calcium carbonate for mixing into green mortar or green concrete.If the carbon dioxide introduction step described below is carried out without removing the hydrophobic impurities from the carbide slag as it is, the hydrophobic impurities will remain in the finally obtained calcium carbonate. In that case, since the surface of the calcium carbonate particles becomes water-repellent, it becomes difficult for the calcium carbonate to mix into fresh mortar or fresh concrete.

[0022] One embodiment includes an adjustment step of adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed in a classification step. The adjustment step is a step of adjusting the solid content concentration of the carbide slag. Here, the solid content refers to all components other than water contained in the carbide slag after removing the hydrophobic impurities. The carbide slag from which the hydrophobic impurities have been removed in the classification step mainly contains calcium hydroxide particles having a particle size of less than 45 μm as the solid content, and a small amount (5% by mass or less) of hydrophobic impurities may remain. The solid content concentration refers to the mass ratio of all components other than water to the mass of the carbide slag after removing the hydrophobic impurities. In the adjustment step, the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed can be adjusted to 1 to 30% by mass, preferably 5 to 20% by mass, and more preferably 7 to 10% by mass. When the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed is greater than the desired range, water is added to the carbide slag from which the hydrophobic impurities have been removed. When the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed is less than the desired range, calcium hydroxide is added to the carbide slag from which the hydrophobic impurities have been removed, or after allowing the solid content of the carbide slag from which the hydrophobic impurities have been removed to settle over time, a part of the supernatant may be removed. By adjusting the solid content concentration to an appropriate range in the adjustment step, the fluidity of the carbide slag (slurry) after removing the hydrophobic impurities can be maintained, and thereby the efficiency of the reaction in the carbon dioxide introduction step described below can be improved. If the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed is too large or too small, the properties of the calcium carbonate produced in one embodiment may not be suitable for mixing into 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 of introducing carbon dioxide into carbide slag from which hydrophobic impurities have been removed in a classification step and the solid content concentration has been adjusted in an adjustment step. This step is a step of reacting carbon dioxide with calcium hydroxide contained in the carbide slag to synthesize calcium carbonate. In the carbon dioxide introduction step, when introducing carbon dioxide into the carbide slag from which hydrophobic impurities have been removed in the classification step and the solid content concentration has been adjusted in the adjustment step, it is preferable to introduce carbon dioxide while adjusting so that the carbonation rate of calcium ions is 1 to 40 cation % / hour. The carbonation rate of calcium ions being 1 to 40 cation atomic % / hour means that all calcium ions (cations) of calcium hydroxide contained in the carbide slag from which hydrophobic impurities have been removed in the classification step and the solid content concentration has been adjusted in the adjustment step react by 1 to 40% per hour and change to calcium carbonate. That is, a carbonation rate of 1 cation % / hour means that it takes 100 hours for calcium hydroxide to react and convert to calcium carbonate. Also, 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 the carbide slag from which hydrophobic impurities have been removed in the classification step and the solid content concentration has been adjusted in the adjustment step so that the carbonation rate is preferably 5 to 30 cation % / hour, more preferably 10 to 20 cation % / hour.

[0024] The temperature of the carbon dioxide introduction step, particularly the reaction start temperature before the introduction of carbon dioxide of the carbide slag from which 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 about 15 - 50°C. If the reaction start temperature is too low or too high, it will cause a deterioration in the properties of the calcium carbonate produced in one embodiment. The carbon dioxide introduction step is preferably carried out so as to constantly maintain the above temperature range.

[0025] Calcium carbonate produced in one embodiment is a carbonate of calcium represented by the compositional formula CaCO3, and is the main component of shells, chicken eggshells, limestone, chalk, etc. Calcium carbonate is classified into heavy calcium carbonate (natural calcium carbonate) obtained by pulverizing and classifying limestone and light calcium carbonate (synthetic calcium carbonate) obtained by chemical reaction. However, the calcium carbonate produced in one embodiment is light calcium carbonate. Calcium carbonate has crystal polymorphs such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), vaterite crystals (hexagonal crystals), etc. The calcium carbonate produced in one embodiment is a calcite-type crystal and preferably has a spindle shape.

[0026] Calcium carbonate produced in one embodiment can be used for a wide range of applications in the same manner as conventional calcium carbonate. Calcium carbonate can be used, for example, for neutralizing wastewater and desulfurizing flue gas, and can also be used as a filler for building materials, concrete, fertilizers, paints, etc. The calcium carbonate obtained in one embodiment can be effectively used as an additive for fresh mortar and fresh concrete, and is further intended to be used for ground improvement and filling underground cavities. Fresh concrete is a composite material obtained by mixing granular aggregates such as sand and gravel, hydraulic cement, a binder containing slag fine powder, fly ash, etc., water, and various admixtures. Fresh concrete for high-strength concrete, which has been demanded in recent years, has a reduced water-binder ratio (weight ratio of water to binder), has low fluidity, and may have poor workability during construction. In addition, fresh concrete for high-strength concrete may need to be kneaded for a long time until fresh concrete with good workability and fluidity is obtained, which requires a great deal of time for concrete construction. Therefore, attempts have been made conventionally to add calcium carbonate to fresh concrete to improve the fluidity of fresh concrete and shorten the kneading time.

[0027] The properties required of fresh concrete containing calcium carbonate are generally referred to as workability. Workability is the workability in concrete construction that takes into account both the resistance (consistency) to plastic deformation and flow of fresh concrete and the resistance to separation of the components contained in the fresh concrete, and is the most important index as a property of fresh concrete. Specifically, workability is a general index of the constructability of concrete regarding a series of operations from the kneading, transportation, placement, and compaction of fresh concrete to the finishing of the placed concrete, and the criteria for judgment vary depending on the type of structure, construction location, and construction method. One embodiment can manufacture calcium carbonate as an additive from carbide slag, which is waste, so as not to inhibit the ease of mixing of fresh concrete, which is one of the elements for judging the workability of fresh concrete.

[0028] A second embodiment of the present invention classifies carbide slag containing calcium hydroxide and hydrophobic impurities and removes the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduces 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 a method of mixing the obtained calcium carbonate into fresh mortar or fresh concrete to produce calcium carbonate-containing fresh mortar or calcium carbonate-containing fresh concrete.

[0029] The second embodiment includes all the steps of the manufacturing method of the first embodiment. Calcium carbonate produced in the first embodiment can be mixed into fresh mortar or fresh concrete to produce calcium carbonate-containing fresh mortar or calcium carbonate-containing fresh concrete. Fresh mortar refers to a mixture obtained by kneading cement, water, and fine aggregates such as sand, and fresh concrete refers to a mixture obtained by further adding coarse aggregates such as gravel to the mortar and kneading. In addition to these components, fresh mortar or fresh concrete can appropriately contain admixtures such as water-reducing agents for enhancing the fluidity of fresh mortar or fresh concrete and retarders for delaying the setting of fresh mortar or fresh concrete for a predetermined time. As the water-reducing agent, so-called anionic surfactants such as carboxyl group-containing polyethers, lignin sulfonates, and oxycarboxylates can be used. Also, as the retarder, a chemical containing an oxycarboxylate such as sodium gluconate as the main component can be used. Admixtures such as water-reducing agents and retarders for fresh mortar or fresh concrete are commercially available in various types according to conditions such as the shape of the structure, the construction site, and the construction period, and it is possible to appropriately obtain them from among these.

[0030] The calcium carbonate-containing fresh mortar or calcium carbonate-containing fresh concrete produced according to the second embodiment is easy to knead and has high workability. Furthermore, the cured product obtained by curing the calcium carbonate-containing fresh mortar or calcium carbonate-containing fresh concrete produced according to the second embodiment has increased strength compared to the cured product obtained by curing fresh mortar or fresh concrete without calcium carbonate added, and can result in high-strength mortar structures or high-strength concrete structures.

[0031] The third embodiment classifies carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; introduces carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and whose solid content concentration has been adjusted to obtain calcium carbonate, A method for improving the ground, which comprises mixing the obtained calcium carbonate with a ground improvement material and mixing or injecting the obtained ground improvement material containing calcium carbonate into the ground.

[0032] The third embodiment includes all steps of the manufacturing method of one embodiment. Calcium carbonate produced in one embodiment can be mixed with a ground improvement material, and the ground improvement material containing calcium carbonate can be mixed or injected into the ground to improve 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 as it is when constructing a building or structure. The ground improvement material is used to increase the strength of the ground from the viewpoint of suppressing deformation, settlement, liquefaction, etc. of soft ground. As ground improvement methods, a direct foundation (a surface improvement method of mixing or injecting a ground improvement material to stable ground) and a pile foundation (a columnar improvement method of mixing or injecting a ground improvement material to stable ground to build a columnar column, a steel pipe pile method of pressing a steel pipe pile to stable ground) are known, and the method of the third embodiment can be particularly applied to the surface improvement method and the columnar improvement method. As ground improvement materials, cement, cement-based solidifying materials, lime, lime-based solidifying materials, cement / lime composite solidifying materials, and polymer-based solidifying materials are known. Ground improvement materials are commercially available in various types according to various conditions such as the terrain and environment of the construction site, and can be appropriately obtained from these. The third embodiment can be applied to any type of ground improvement material. A ground improvement material is a material composed of almost the same materials as raw mortar or raw 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 larger than that of raw mortar or raw concrete.

[0033] By implementing the third embodiment, a high-strength ground suitable for a building or structure can be obtained, so that a stable foundation for a building or structure can be constructed. The ground improvement material containing calcium carbonate used in the third embodiment is easy to knead and has high workability.

[0034] The fourth embodiment classifies carbide slag containing calcium hydroxide and hydrophobic impurities and removes the hydrophobic impurities; Adjust the solid content concentration of carbide slag from which hydrophobic impurities have been removed; Introduce carbon dioxide into carbide slag from which hydrophobic impurities have been removed and the solid content concentration has been adjusted to obtain calcium carbonate, A method of mixing the obtained calcium carbonate with a filler and filling the obtained calcium carbonate-containing filler into an underground cavity.

[0035] The fourth embodiment includes all the steps of the manufacturing method of one embodiment. The calcium carbonate produced in one embodiment can be mixed with a filler, and the calcium carbonate-containing filler can be filled into an underground cavity. When constructing a building or structure on the ground surface, when an underground cavity that cannot be visually recognized from the ground surface is discovered by a boring survey or the like, such an underground cavity may need to be filled in. If the underground cavity is left unattended, subsidence of the ground surface and ground settlement may occur. Therefore, it may be necessary to fill the underground cavity to prevent these in advance. Here, the underground cavity refers to all natural cavities such as limestone caves, dorners, lava tunnels, weathered caves, mining traces of metal mines, etc., mining traces of coal, etc., mining traces of stone materials, etc., artificial cavities such as underground trenches such as air raid shelters, and all underground cavity parts existing underground including underground shopping malls, tunnels, and piping construction traces. The filler for filling the underground cavity is required to have fluidity that spreads to every corner of the cavity during filling and become a solidified product with the required strength after solidification. As such a filler for an underground cavity, typically, solidifying materials containing gypsum and lime, cement-based solidifying materials, and slag-based fillers containing molten slag and blast furnace slag and aggregates are used. Fillers for underground cavities are commercially available in various types according to various conditions such as the topography and environment of the construction site, and it is possible to appropriately obtain them from these. The fourth embodiment can be applied to any type of filler.

[0036] By implementing the fourth embodiment, a highly strong solidified product can be formed up to every corner of the underground cavity, and it becomes possible to safely fill in the underground cavity. The calcium carbonate-containing filler used in the fourth embodiment has high fluidity, is easy to knead, and has high workability.

[0037] The fifth embodiment classifies carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; adjusts the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; A method in which exhaust gas containing carbon dioxide is introduced into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration has been adjusted, and the carbon dioxide contained in the exhaust gas is immobilized.

[0038] The fifth embodiment generally includes all steps of the manufacturing method of one embodiment. When producing calcium carbonate in one embodiment, exhaust gas is used as the source of carbon dioxide. Exhaust gas refers to all gases discharged from gasoline engines, diesel engines, internal combustion engines, and factories. Untreated exhaust gas usually contains a large amount of carbon dioxide, which is a greenhouse gas, in addition to water vapor and harmful gases such as carbon monoxide. Discharging such exhaust gas into the atmosphere without treatment leads to environmental pollution and global warming, which is not desirable. The fifth embodiment uses carbide slag, which was conventionally discarded as industrial waste, as a raw material, and reacts the carbon dioxide in the exhaust gas to obtain calcium carbonate that can be used in the methods of the second, third, or fourth embodiments above. By implementing the fifth embodiment, the carbon dioxide in the exhaust gas is immobilized as calcium carbonate, and the obtained calcium carbonate can be used not only for blending into fresh mortar and fresh concrete but also as a ground improvement material, a filling material for underground cavities, etc.

Example

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

[0040] [Example 1] [Production of Calcium Carbonate] The carbide slag obtained from The Kobelco Eco-Solutions 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 from the carbide slag. 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 while introducing carbon dioxide gas so that the carbonation rate of calcium ions would be 12 cation % / hour (so that the time until the reaction was completed would be 8.1 hours), the carbide slag was stirred. The obtained slurry was filtered and dried in an oven at 105 °C for 1 hour, and spindle-shaped calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 5.9 m 2 / g).

[0041] <Manufacture of fresh concrete> Ordinary Portland cement (Japanese Industrial Standard JIS R 5210, density: 3.14 - 3.17 g / cm 3 ), blast furnace slag fine powder 4000 (Japanese Industrial Standard JIS A 6206, density: 2.8 g / cm 3 or more), crushed sand with a particle size of 5 mm or less as fine aggregate (Japanese Industrial Standard JIS A 5005, produced in Johto City, Kyoto Prefecture, density: 2.5 g / cm 3 or more), 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 / cm 3 or more), high-performance water-reducing agent (Type I) containing a carboxyl group-containing polyether-based compound as the main component as admixture A (Japanese Industrial Standard JIS A 6204, density: 1.04 - 1.08 g / cm 3 ), water-reducing agent retarder type (Type I) containing oxycarboxylate as the main component as admixture B (Japanese Industrial Standard JIS A 6206, density: 1.17 - 1.21 g / cm 3) Prepared raw cement containing [cement components], [additives], and water. Added the calcium carbonate obtained above to the fresh concrete and kneaded it using an inverter two-shaft forced mixing type concrete mixer (Model: MIC-109-0-31, Company Name: Marui Co., Ltd.). The detailed mixing ratio of the calcium carbonate-containing fresh concrete was as shown in Table 1. From this fresh concrete, concrete specimens for the compressive strength test described below were prepared.

[0042] <Compressive Strength Test> In the compressive strength test, in accordance with Japanese Industrial Standard JIS A 1108:2018 "Test Method for Compressive Strength of Concrete", the compressive strength of the concrete after 24 hours and the compressive strength after 14 days were measured respectively.

[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 Manufacturing Co., Ltd.), and carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 17 cation % / hour (so that the time until the reaction was completed was 5.9 hours). Spindle Calcite-type calcium carbonate of [shape] was obtained (BET specific surface area measured by the method according to JIS Z 8830: 8.4 m 2 / g). The obtained calcium carbonate was added to the fresh concrete containing the same components as in Example 1, and a compressive strength test was conducted. The detailed mixing ratio of the fresh concrete and the mixing ratio of calcium carbonate are shown in Table 1. Also, scanning electron micrographs of the spindle-shaped calcite-type calcium carbonate obtained in Example 2 are shown in Fig. 1 (Magnification: 10,000 times) and Fig. 2 (Magnification: 20,000 times).

[0044]

Table 1

[0045] [Comparative Example 1] Please note that some parts in the original text such as "[cement components]" and "[additives]" are placeholders that need to be filled with specific content in the actual situation. The translation above just keeps the form for the purpose of translation.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 Seisakusho 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 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 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] The carbide slag was not passed through any sieve, the reaction start temperature in the carbon dioxide introduction step was set to 8°C, and calcium carbonate was produced under the same conditions as in Example 1 except that carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 8.9 cation % / hour (the time until the reaction was completed was 11.3 hours). Cubic calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 42.0 m 2 / g). The obtained calcium carbonate was blended into green concrete having the same components as in Example 1 at the blending ratios shown in Table 2, and a compressive strength test was conducted.

[0049] [Comparative Example 5] 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.), the reaction start temperature in the carbon dioxide introduction step was set to 65°C, and calcium carbonate was produced under the same conditions as in Example 1 except that carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 16.7 cation % / hour (the time until the reaction was completed was 6 hours). Spindle Calcite-type calcium carbonate of a certain shape 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 into green concrete having the same components as in Example 1 at the blending ratios shown in Table 2, and a compressive strength test was conducted.

[0050] [Comparative Example 6] 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.), in the adjustment step, the solid content concentration of the carbide slag was adjusted to 0.5%, and calcium carbonate was produced under the same conditions as in Example 1 except that carbon dioxide gas was introduced so that the carbonation rate of calcium ions was 200 cation % / hour (the time until the reaction was completed was 0.5 hours). Cubic calcite-type calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 3.0 m2 / g). Calcium carbonate obtained was blended into fresh concrete having the same components as in Example 1 at the blending ratios shown in Table 2, and a compressive strength test was conducted.

[0051] [Comparative Example 7] Calcium carbonate was produced under the same conditions as in Example 1, except that 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 in the carbon dioxide introduction step was 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 time until the reaction was completed was 7.6 hours). Aggregates of calcite-type calcium carbonate were obtained (BET specific surface area measured by the method according to JIS Z 8830: 16.9 m 2 / g). Calcium carbonate obtained was blended into fresh concrete having the same components as in Example 1 at the blending ratios shown in Table 2, and a compressive strength test was conducted.

[0052] The experimental conditions and fresh concrete mixing ratios of the comparative examples are shown in Table 2.

[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: 13 m 2 / g) was prepared. Calcium carbonate was blended into fresh concrete having the same components as in Example 1 at the blending ratios shown in Table 3, except that admixture B was not included, 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: 6 m 2 / g, spindle shape) was prepared. Calcium carbonate was added to green concrete having the same components as in Example 1 at the mixing ratios shown in Table 3, and a compressive strength test was conducted.

[0057] [Reference Example 3] Commercially available large-particle heavy calcium carbonate (Whiton H, Toyo Fine Chemical Co., Ltd., BET specific surface area: 1.5 m 2 / g) was prepared. Calcium carbonate was added to green concrete having the same components as in Example 1 at the mixing ratios shown in Table 3, and a compressive strength test was conducted.

[0058] [Reference Example 4] Calcium carbonate (BET specific surface area: 0.26 m 2 / g) produced by the method disclosed in JP-A-2014-148432 (a method for producing calcium carbonate from concrete waste (concrete sludge) containing uncured cement fine particles) was prepared. Calcium carbonate was added to green concrete having the same components as in Example 1 at the mixing ratios shown in Table 3, and a compressive strength test was conducted.

[0059]

Table 3

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

[0061] <Production of Ground Improvement Material> 4000 of blast furnace slag fine powder (Japanese Industrial Standard JIS A 6206, density: 2.8 g / cm 3 or more), crushed stone powder with a particle size of 2.5 mm or less as an aggregate (Japanese Industrial Standard JIS A 5041, density: 2.5 g / cm 3Silica soda (SiO2 / Na2O molar ratio of 2.0, mass percentage concentration of Na2O: 14.1 to 14.5 wt%, density 1.48 to 1.53 g / cm 3 or more), and a ground improvement material containing water was prepared. Calcium carbonate obtained above was blended into the ground improvement material and kneaded using a kneader (name: Mortar Mixer MIC-362-1-01, company name: Marui Co., Ltd.). The detailed mixing ratio of the calcium carbonate-blended ground improvement material was as shown in Table 4. Specimens for the uniaxial compression test described below were prepared from this ground improvement material.

[0062] <Uniaxial Compression Test> In accordance with the Japanese Industrial Standard JIS A 1216:2020 "Test Method for Uniaxial Compression of Soils", the uniaxial compression strength of the ground improvement material specimen after 28 days and the uniaxial compression strength after 91 days were measured respectively.

[0063] [Example 4] Under the same conditions as the production method of calcium carbonate in Example 2, spindle-shaped calcite calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 8.4 m 2 / g). The obtained calcium carbonate was blended into the ground improvement material containing the same components as in Example 3, and a uniaxial compression test was conducted. The detailed mixing ratio of the ground improvement material and the mixing ratio of 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 carbide slag was not passed through any sieve. Spindle-shaped calcite calcium carbonate was obtained (BET specific surface area measured by the method according to JIS Z 8830: 6.6 m 2 / g). The obtained calcium carbonate was blended into the ground improvement material with the same components and mixing ratio as in Example 3 at the same mixing ratio as in Example 3, and a uniaxial compression test was conducted.

[0066] [Comparative Example 9] Calcium 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 calcium carbonate was produced under the same conditions as in Example 1 except that 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). Spindle Calcite-type calcium carbonate of a certain shape 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 3 with a ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0067] [Comparative Example 10] Calcium 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 calcium carbonate was produced under the same conditions as in Example 1 except that 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 Calcite-type calcium carbonate of a certain shape 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 3 with a ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0068]

Table 5

[0069] [Reference Example 5] Commercially available light calcium carbonate (Shirayukika CC, Shiraishi Kogyo Co., Ltd., BET specific surface area: 26 m 2(g) was prepared. Calcium carbonate was blended at the same blending ratio as in Example 3 into the ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0070] [Reference Example 6] Commercially available light calcium carbonate (PC, Shiraishi Kogyo Co., Ltd., BET specific surface area: 6 m 2 / g, spindle shape) was prepared. Calcium carbonate was blended at the same blending ratio as in Example 3 into the ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0071] [Reference Example 7] Commercially available large-particle heavy calcium carbonate (Whitron P50, Toyo Fine Chemical Co., Ltd., BET specific surface area: 1.5 m 2 / g) was prepared. Calcium carbonate was blended at the same blending ratio as in Example 3 into the ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0072] [Reference Example 8] Commercially available light calcium carbonate (Silver W, Shiraishi Kogyo Co., Ltd., BET specific surface area: 6 m 2 / g, spindle shape) was prepared. Calcium carbonate was blended at the same blending ratio as in Example 3 into the ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0073] [Reference Example 9] Commercially available light calcium carbonate (Brilliant 1500, Shiraishi Kogyo Co., Ltd., BET specific surface area: 13 m 2 / g) was prepared. Calcium carbonate was blended at the same blending ratio as in Example 3 into the ground improvement material having the same components and blending ratio as in Example 3, and a uniaxial compression test was conducted.

[0074]

Table 6

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

[0076] In the tables of Table 1 - Table 6 above, the evaluation is the workability of the concrete or ground improvement material. Workability is a comprehensive evaluation in view of the workability and constructability of the concrete or ground improvement material as described above. In a series of experiments in this specification, in particular, the mixing characteristics of fresh concrete or ground improvement material and the compressive strength of each hardened product were comprehensively judged, and from the ones with higher workability, they were rated as excellent, good, acceptable, and unacceptable. Also, the remarks are comments on the remarkable characteristics during the mixing of fresh concrete or ground improvement material and the strength of the hardened product. "Thixotropy immediately after mixing" means that thixotropy (the property that the viscosity decreases when a shear force is continuously applied) was exhibited immediately after starting the mixing of fresh concrete or ground improvement material. Thixotropy is not a property that can be said to be good as a characteristic of general fresh concrete.

[0077] The fresh concrete blended with calcium carbonate produced by the production method of the present invention has excellent kneading performance without losing fluidity, and the strength of the concrete after hardening is high. In the reference examples, experimental examples of blending commercially available calcium carbonate (limestone) into fresh concrete and ground improvement materials were shown. However, the calcium carbonate produced by the production method of the present invention exhibits the same performance as commercially available calcium carbonate (for example, Reference Example 2, Reference Example 6, etc.), and can provide excellent fresh concrete or ground improvement materials. The production method of the present invention can produce industrially and commercially useful calcium carbonate using carbide slag, which is an industrial waste, as a raw material. In the production method of the present invention, if exhaust gas is applied as a source of carbon dioxide, the carbon dioxide emitted into the atmosphere can be reduced, thus contributing to stopping the progress of global warming and environmental pollution.

Claims

1. The following steps: A classification step of classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove 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 A method for producing calcium carbonate, comprising the steps.

2. The method for producing calcium carbonate according to claim 1, wherein the particle size of the hydrophobic impurities removed in the classification step is 45 μm or more.

3. The method for producing calcium carbonate according to claim 1 or 2, wherein in the adjustment step, the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed is adjusted to 1-30% by mass.

4. The method for producing calcium carbonate according to claim 1 or 2, wherein in the carbon dioxide introduction step, carbon dioxide is introduced 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.

5. The method for producing calcium carbonate according to claim 3, wherein in the carbon dioxide introduction step, carbon dioxide is introduced 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.

6. The method for producing calcium carbonate according to claim 4, wherein calcite-type calcium carbonate having a spindle shape is produced.

7. The method for producing calcium carbonate according to claim 5, wherein calcite-type calcium carbonate having a spindle shape is produced.

8. Classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; Adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; Introducing carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration of which has been adjusted to obtain calcium carbonate, and A method of mixing the obtained calcium carbonate into raw mortar or fresh concrete to produce calcium carbonate-blended raw mortar or calcium carbonate-blended fresh concrete.

9. Classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; Adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; Introducing carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and the solid content concentration of which has been adjusted to obtain calcium carbonate, and A method for improving the ground by mixing the obtained calcium carbonate into a ground improvement material and then mixing or injecting the obtained calcium carbonate-containing ground improvement material into the ground.

10. Classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; Adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; Introducing carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and whose solid content concentration has been adjusted to obtain calcium carbonate, A method of mixing the obtained calcium carbonate into a filler and filling the obtained calcium carbonate-containing filler into an underground cavity.

11. Classifying carbide slag containing calcium hydroxide and hydrophobic impurities to remove the hydrophobic impurities; Adjusting the solid content concentration of the carbide slag from which the hydrophobic impurities have been removed; A method of introducing exhaust gas containing carbon dioxide into the carbide slag from which the hydrophobic impurities have been removed and whose solid content concentration has been adjusted to immobilize the carbon dioxide contained in the exhaust gas.

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