Carbon dioxide fixation method, carbon dioxide fixation carrier, aggregate for road, concrete aggregate, and soil improvement agent

Abstract

To provide a novel carbon dioxide fixation method enabling fixation processing of carbon dioxide and effective utilization of stainless slag, a carbon dioxide fixation carrier in which carbon dioxide is fixed to the carrier, an aggregate for roads comprising the carbon dioxide fixation carrier, a concrete aggregate, and a soil improvement agent.SOLUTION: In a carbon dioxide fixation method for fixing carbon dioxide to a carrier comprising a calcium component, the following steps are executed: a water adding step for adding water of 10-20 wt.% to the carrier by using stainless slag as the carrier; and a gas contacting step for bringing a gas containing carbon dioxide into contact with the carrier.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide fixation method in which carbon dioxide is brought into contact with a carrier containing a calcium component to produce calcium carbonate, thereby fixing carbon dioxide to the carrier; a carbon dioxide fixation carrier in which carbon dioxide is fixed to the carrier; and road aggregate, concrete aggregate, and soil improvement agent each containing the carbon dioxide fixation carrier. [Background technology]

[0002] Global warming is a phenomenon caused by a combination of various factors, but the prevailing theory is that one of the causes is greenhouse gases such as carbon dioxide (CO2) emitted into the atmosphere as a result of human industrial activity. Therefore, reducing carbon dioxide emissions has become an international challenge. Research is also underway into methods for capturing emitted carbon dioxide.

[0003] As a means for recovering carbon dioxide, for example, a method has been developed in which carbon dioxide is brought into contact with a carrier containing a calcium component to produce calcium carbonate, thereby fixing carbon dioxide to the carrier (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-214262 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method described in Patent Document 1 (method for immobilizing carbon dioxide), blast furnace slag is used as a carrier containing calcium components, and this is dispersed in alkaline water and brought into contact with carbon dioxide. In the alkaline water, the calcium components contained in the blast furnace slag become calcium hydroxide, and carbon dioxide that comes into contact with this calcium hydroxide becomes calcium carbonate and is immobilized in the blast furnace slag. Since the expansion and elution of the calcium components over time are suppressed in the blast furnace slag with immobilized carbon dioxide, it can be reused as road aggregate, concrete aggregate, etc.

[0006] On the other hand, stainless steel slag generated during stainless steel manufacturing is currently discarded without secondary use. This is because stainless steel slag is prone to powdering and requires a long period of time for curing (aging treatment) to prevent the expansion that occurs over time when the calcium component hydrates.

[0007] The present invention has been developed to solve the above-mentioned technical problems, and has an object to provide a novel carbon dioxide fixation method that enables carbon dioxide fixation treatment and effective utilization of stainless steel slag, a carbon dioxide fixation carrier in which carbon dioxide is fixed to the carrier, and road aggregate, concrete aggregate, and soil conditioner each containing the carbon dioxide fixation carrier. [Means for solving the problem]

[0008] The carbon dioxide fixation method of the present invention, which solves the above-mentioned technical problems, is a carbon dioxide fixation method in which carbon dioxide is brought into contact with a carrier containing a calcium component to produce calcium carbonate, thereby fixing carbon dioxide on the carrier, wherein the carrier comprises stainless steel slag, and the method comprises carrying out a hydration step of adding 10 to 20% by weight of water to the carrier, and a gas contacting step of bringing a carbon dioxide-containing gas into contact with the carrier (hereinafter referred to as the "fixation method of the present invention").

[0009] In the fixing method of the present invention, it is preferable that the carrier is stirred during the gas contact step.

[0010] The carbon dioxide fixation carrier of the present invention, which solves the above-mentioned technical problems, is a carbon dioxide fixation carrier formed by fixing carbon dioxide as calcium carbonate to a carrier containing stainless steel slag, and is characterized in that 6 mol or more of carbon dioxide is fixed per kg of stainless steel slag contained in the carrier (hereinafter referred to as the "fixation carrier of the present invention").

[0011] The road aggregate of the present invention, which solves the above technical problems, is characterized by containing the fixed carrier of the present invention (hereinafter referred to as "road aggregate of the present invention").

[0012] The concrete aggregate of the present invention, which solves the above technical problems, is characterized by containing the fixed carrier of the present invention (hereinafter referred to as "the concrete aggregate of the present invention").

[0013] The soil improver of the present invention, which solves the above technical problems, is characterized by comprising the above-mentioned immobilization carrier of the present invention (hereinafter referred to as "the soil improver of the present invention"). [Effects of the Invention]

[0014] According to the present invention, it is possible to fix carbon dioxide and effectively utilize stainless steel slag. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1(a) is a perspective view showing a reaction vessel for carrying out the fixing method of the present invention, and FIG. 1(b) is a perspective view showing the implementation of the fixing method of the present invention using the reaction vessel. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment.

[0017] <Fixation method of the present invention> In the immobilization method of the present invention, a "carrier" containing a calcium component is subjected to a "hydration step" and a "gas contact step," thereby immobilizing carbon dioxide in the form of calcium carbonate on the carrier.

[0018] -Carrier- The carrier contains stainless steel slag. In the present invention, stainless steel slag refers to slag generated during the refining process of stainless steel. Stainless steel slag is divided into two types: aluminum slag and silica slag, depending on the type of redox agent used during refining. Here, aluminum slag and silica slag both contain approximately 50% calcium components (mainly calcium oxide), and both can be used equally in the present invention. Note that, in the present invention, "containing stainless steel slag" means that the carrier may contain components other than stainless steel slag (e.g., other slags such as blast furnace slag). From the perspective of secondary reuse of stainless steel slag, the higher the content of stainless steel slag in the carrier, the better. In the present invention, the content of stainless steel slag in the carrier is preferably 50% by weight or more (more preferably 80% by weight or more).

[0019] -Hydrification process- In the hydration process, 10 to 20% by weight of water is added to the carrier. By performing the hydration process, a portion of the calcium component contained in the carrier is converted to calcium hydroxide (CaO + H2O → Ca(OH)2). The hydration method used in the hydration process is not particularly limited. For example, the hydration process can be performed by spraying or sprinkling water on the carrier, or by exposing the carrier to a humid environment for a certain period of time. The amount of water added during the hydration process refers to the percentage of the weight of water relative to the weight of the carrier in a substantially dry state (a state in which no water has been intentionally added to the stainless steel slag after cooling and removed from the furnace). Furthermore, during the hydration process, it is preferable to agitate the carrier so that the water is distributed throughout the carrier.

[0020] -Gas contact process- In the gas contacting step, the carrier is contacted with a gas containing carbon dioxide. Examples of the gas containing carbon dioxide include air and exhaust gas. By performing the gas contacting step, calcium hydroxide produced in the hydration step reacts with carbon dioxide and is fixed to the carrier as water-insoluble calcium carbonate (Ca(OH)2 + CO2 → CaCO3 + HO). The water produced in parallel with the production of calcium carbonate combines with the calcium component contained in the carrier to produce new calcium hydroxide. The method for contacting the carrier with the gas is not particularly limited, and examples include exposing the carrier to a gas atmosphere or introducing a gas toward the carrier filled in a container. During the gas contacting step, the carrier is preferably stirred to promote the reaction between calcium hydroxide and carbon dioxide and the production of new calcium hydroxide.

[0021] According to the fixation method of the present invention, which involves carrying out the above steps, it is possible to fix carbon dioxide and effectively utilize stainless steel slag.

[0022] That is, in the immobilization method of the present invention, the carbonation of the calcium component contained in the carrier can be promoted by adding 10 to 20% by weight of water to the carrier containing stainless steel slag in the hydration step.

[0023] Because the stainless steel slag contained in the carrier is in a fine powder state, it has been confirmed that when the amount of water added exceeds 20 wt%, the water acts as a barrier preventing contact between the stainless steel slag contained in the carrier and the carbon dioxide contained in the gas, ultimately reducing the amount of carbon dioxide that can be fixed on the carrier. Here, if the amount of water added is significantly in excess of the amount of water used, calcium hydroxide dissolved in the water will combine with carbon dioxide to produce calcium carbonate. However, the resulting calcium carbonate will further come into contact with carbon dioxide in the water to form calcium bicarbonate, which can be dissolved in water (CaCO3 + CO2 + H2O → Ca(HCO3)2), thereby reducing the amount of carbon dioxide fixed on the carrier. On the other hand, when the amount of water added is less than 10 wt%, the proportion of water that evaporates during the gas contact process relative to the amount of water added will be high, ultimately reducing the amount of carbon dioxide that can be fixed on the carrier.

[0024] In this embodiment, the gas contact step is carried out on the carrier after the hydration step has been carried out, but the gas contact step may be carried out while the hydration step is being carried out.

[0025] It has been confirmed that by carrying out the immobilization method of the present invention, 6 mol or more (maximum 7 mol) of carbon dioxide is fixed per kg of stainless steel slag contained in the carrier.

[0026] <The fixed carrier of the present invention, the road aggregate of the present invention, the concrete aggregate of the present invention, and the soil improvement agent of the present invention> The fixed carrier of the present invention has carbon dioxide fixed as calcium carbonate on the carrier, and 6 mol or more of carbon dioxide is fixed per kg of stainless steel slag contained in the carrier.

[0027] The calcium contained in the stainless steel slag is carbonated in the solidification carrier of the present invention, which makes it less susceptible to expansion over time and elution of alkaline components. Therefore, it can be used as road aggregate (road aggregate of the present invention) or concrete aggregate (concrete aggregate of the present invention). It can also be used as a soil improvement agent (soil improvement agent of the present invention) to increase soil strength.

[0028] [Examples 1 to 3, Comparative Examples 1 to 3] A hydration step was carried out by adding water to stainless steel slag as carrier (C) in varying amounts for each example and comparative example, allowing the water to soak into the entire surface, and then 5 kg of the slag was loaded into the vessel body 2 of the reaction vessel 1 shown in Figure 1. With the lid 3 of the vessel body 2 closed, a gas (exhaust gas) containing 30,000 ppm of carbon dioxide was introduced through the gas inlet pipe 4 at a flow rate of 20 liters / min for 1 hour to contact the carrier (C), thereby carrying out a gas contact step. The gas after contact with the carrier (C) was discharged through the gas outlet pipe 5. The reaction vessel 1 was also designed so that the carrier (c) could be stirred by operating a screw 6 disposed within the vessel body 2.

[0029] Table 1 shows the test conditions for each example and comparative example, and the amount of fixed carbon dioxide for each example and comparative example.

[0030] [Table 1]

[0031] The results shown in Table 1 confirm that the immobilization method of the present invention fixes 6 mol or more (maximum 7 mol) of carbon dioxide per kg of stainless steel slag contained in the carrier (C). This value is a calculated value derived from the change in weight of the carrier (C) before and after the method of the present invention.

[0032] On the other hand, in Comparative Examples 1 and 2, in which the amount of water added was less than 10% by weight, and in Comparative Example 3, in which the amount of water added was more than 20% by weight, it was confirmed that the amount of carbon dioxide fixed was smaller than that of each Example. It was also confirmed that as the amount of water added increased, the viscosity of the carrier (C) increased, and the efficiency of work such as stirring decreased.

[0033] The present invention can be embodied in various other forms without departing from its spirit or essential features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and variations within the equivalent range of the claims are within the scope of the present invention. [Industrial Applicability]

[0034] The present invention can be suitably used as a means for fixing carbon dioxide. [Explanation of symbols]

[0035] 1 reaction vessel 2 Container body 3 Lid 4 Gas inlet pipe 5 Gas exhaust pipe 6 screws C carrier

Claims

1. A method for fixing carbon dioxide, comprising bringing carbon dioxide into contact with a carrier containing a calcium component to produce calcium carbonate, and thereby fixing carbon dioxide to the carrier, comprising: the carrier comprises stainless steel slug; a hydration step of adding 10 to 20% by weight of water to the carrier; a gas contacting step of contacting the carrier with a gas containing carbon dioxide; A method for fixing carbon dioxide, characterized by carrying out the above steps.

2. The carbon dioxide fixation method according to claim 1, The method for fixing carbon dioxide, wherein the carrier is stirred during the gas contact step.

3. A carbon dioxide fixation carrier in which carbon dioxide is fixed as calcium carbonate in a carrier containing stainless steel slag, A carbon dioxide fixation carrier, characterized in that 6 mol or more of carbon dioxide is fixed per 1 kg of stainless steel slag contained in the carrier.

4. 4. Road aggregate, comprising the carbon dioxide fixation carrier according to claim 3.

5. A concrete aggregate comprising the carbon dioxide fixation carrier according to claim 3.

6. A soil improvement agent comprising the carbon dioxide fixation carrier according to claim 3.

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