WO2022264668A1 - Method for carbonating cao-containing substance and method for producing carbonated substance - Google Patents

Abstract

Provided is a method for carbonating a CaO-containing substance, wherein the method does not carry out moisture adjustment on the CaO-containing substance and can realize a high carbon dioxide fixation ratio. The present invention is a method for carbonating a CaO-containing substance, in which method a carbon dioxide-containing gas is blown for at least 10 minutes into the CaO-containing substance in a state in which the temperature of the CaO-containing substance is 400-1200°C.

Description

Method for carbonating CaO-containing substance and method for producing carbonated substance

The present invention relates to a method for carbonating a CaO-containing substance and a method for producing a carbonated substance, including a step of blowing a gas containing carbon dioxide against a solidified CaO-containing substance to carbonate the CaO-containing substance.

With the blast furnace method, it is said that 2 tons of carbon dioxide are generated for the production of 1 ton of pig iron, and efforts to reduce carbon dioxide emissions are urgently needed. Therefore, as one method for reducing the amount of carbon dioxide emissions, a carbonation treatment has been devised in which the CaO component contained in the slag generated in steelworks is reacted with carbon dioxide to fix carbon dioxide as a carbonate. It's here.

For example, Patent Document 1 describes a method for efficiently carbonating steelmaking slag while suppressing granulation of slag particles by supplying a gas containing carbon dioxide to dry-treated steelmaking slag.

JP 2014-234332 A

However, in the method of Patent Document 1, since the carbonation treatment is performed at a low temperature of 0 to 80° C., it is assumed that the reaction rate is slow and the amount of carbon dioxide fixed is reduced, that is, the carbonic acid fixation rate is reduced. be. Moreover, it is necessary to adjust the water content of the slag, and the treatment is complicated.

Therefore, in view of the above problems, the present invention provides a method for carbonating a CaO-containing substance that can realize a high carbonic acid fixation rate without adjusting the water content of the CaO-containing substance, and a carbonation method using the carbonation method. It is an object of the present invention to provide a method for producing carbonated substances.

As a result of studies by the present inventors, a high carbonic acid fixation rate can be achieved by blowing a gas containing carbon dioxide to the CaO-containing material for 10 minutes or more while the temperature of the CaO-containing material is set to 400 ° C. or higher and 1200 ° C. or lower. It was found that it can be realized.

The gist and configuration of the present invention completed based on the above findings are as follows.
[1] A method for carbonating a CaO-containing substance, wherein a gas containing carbon dioxide is blown to the CaO-containing substance for 10 minutes or more while the temperature of the CaO-containing substance is 400 ° C or higher and 1200 ° C or lower. A method of carbonating a substance.

[2] The method for carbonating a CaO-containing substance according to [1] above, wherein the gas contains water vapor.

[3] The method for carbonating a CaO-containing substance according to [1] or [2] above, wherein the flow rate ratio of H ₂ O/(H ₂ O+CO ₂ ) in the gas is 0.03 or more and 0.30 or less. .

[4] The CaO according to any one of [1] to [3] above, wherein the gas is blown to the CaO-containing material so that the amount of carbon dioxide supplied is 5 kg or more per 1 ton of the CaO-containing material. A method of carbonating the contained material.

[5] Any one of the above [1] to [4], wherein the CaO-containing substance contains 30% by mass or more of CaO and has a CaO/SiO ₂ mass ratio of 1.5 or more. A method for carbonation of CaO-containing materials.

[6] The method for carbonating a CaO-containing material according to any one of [1] to [5] above, wherein the CaO-containing material is steel slag.

[7] The method for carbonating a CaO-containing substance according to [6] above, wherein the iron and steel slag is steelmaking slag.

[8] The method for carbonating a CaO-containing substance according to any one of [1] to [5] above, wherein the CaO-containing substance is waste concrete.

[9] Production of a carbonated substance, wherein the CaO-containing substance is subjected to a carbonation treatment in the method for carbonating a CaO-containing substance according to any one of [1] to [8] above to produce a carbonated substance. Method.

According to the method for carbonating a CaO-containing substance and the method for producing a carbonated substance of the present invention, a high carbonic acid fixation rate can be achieved without adjusting the water content of the CaO-containing substance. Since fixing carbon dioxide in the atmosphere to a CaO-containing substance at a high carbonic acid fixation rate in this way greatly contributes to the reduction of carbon dioxide emissions, the present invention is an industrially extremely effective process.

4 is a graph showing the relationship between slag temperature and carbonic acid fixation rate in Experimental Example 1. FIG.

(Method for carbonating CaO-containing substance)
A method for carbonating a CaO-containing material according to one embodiment of the present invention is a step of blowing a gas containing carbon dioxide onto the CaO-containing material for 10 minutes or more while the temperature of the CaO-containing material is 400° C. or higher and 1200° C. or lower. including. Details of the method for carbonating a CaO-containing substance according to the present embodiment will be described below.

[CaO-containing substance]
The material to be treated in this embodiment is a solidified CaO-containing material. A gas containing carbon dioxide is supplied to the solidified CaO-containing substance, and the carbon dioxide is fixed to the CaO-containing substance while carbonating the CaO-containing substance by the following reaction.
CaO + _CO2 → _CaCO3

In the present embodiment, the CaO-containing substance, which is the substance to be treated, preferably has a CaO/SiO ₂ mass ratio of 1.5 or more and a component composition containing 30 mass% or more of CaO. A CaO-containing material having such a composition contains free-CaO and β-2CaOSiO ₂ (hereinafter referred to as “β-C ₂ S”) as mineral phases. Free-CaO is preferably carbonated with a gas containing carbon dioxide. Although the details will be described later, β-C ₂ S exhibits a high carbonic acid fixation rate with a gas containing water vapor and carbon dioxide.

Steel slag generated as a by-product in the steel manufacturing process is exemplified as the above CaO-containing substance. Iron and steel slag is roughly classified into blast furnace slag and steelmaking slag. Iron and steel slag contains 30 to 50% by mass of CaO, depending on the type, so it can be expected to fix carbon dioxide by blowing carbon dioxide against the mineral phase containing this CaO. Moreover, not only CaO but also MgO, which is an oxide of an alkali metal, can be expected to have the same effect.

The steel slag used as the CaO-containing substance is preferably steelmaking slag. Steelmaking slag contains a large amount of free-CaO among iron and steel slags, so a higher carbonic acid fixation rate can be achieved. Steelmaking slag is also preferable in that it also contains β-C ₂ S.

Another example of the above CaO-containing substance is waste concrete. Waste concrete is construction waste material, such as concrete, which is a specific construction material that is obligated to be sorted, dismantled and recycled according to the Construction Recycling Law. For these waste concrete, the used concrete is crushed and recycled material for concrete conforming to Annex A of JIS A 5023: 2018 recycled aggregate concrete L, JIS A 5023: 2018 recycled aggregate concrete M attached Recycled aggregate M for concrete conforming to Book A, and recycled crusher run and recycled sand described in pavement recycling handbook (Japan Road Association, 2010) are included. These waste concretes contain cement such as Portland cement, and contain about 60% by mass of CaO, so that a higher carbonic acid fixation rate can be achieved.

Although the particle size of the CaO-containing material is not particularly limited, it can be, for example, a particle size suitable for steel slag for roads. The particle size distribution of steel slag for roads is specified in JIS A 5015-2018, and CS-40 is used in particular. CS-40 has a particle size range of 40 to 0 mm, a nominal opening of a metal mesh sieve specified in JIS Z 8801-1, a 53 mm sieve passing rate of 100% by mass, and a 37.5 mm sieve passing rate of 95 to 100% by mass, a 19 mm sieve passage rate of 50 to 80% by mass, a 4.75 mm sieve passage rate of 15 to 40% by mass, and a 2.36 mm sieve passage rate of 5 to 25% by mass. .

[Carbonation treatment]
In the present embodiment, it is important to keep the temperature of the CaO-containing material within the range of 400° C. or higher and 1200° C. or lower during the carbonation treatment. If the temperature is less than 400° C., the reaction rate is slow and a high carbonic acid fixation rate cannot be achieved. Therefore, the temperature is set to 400° C. or higher. From the viewpoint of realizing a higher carbonic acid fixation rate, the temperature is preferably 600° C. or higher, more preferably 800° C. or higher. On the other hand, when the temperature exceeds 1200 ° C., the Fe and CO ₂ contained in the slag react with each other to change into FeO and CO gas, and the supplied carbon dioxide is used to generate calcium carbonate. I don't like it because it becomes difficult. Therefore, the temperature is set to 1200° C. or lower. Moreover, from the viewpoint of realizing a higher carbonic acid fixation rate, the temperature is preferably 1100° C. or lower, more preferably 1000° C. or lower.

The method for setting the temperature of the CaO-containing material within the above range is not particularly limited, but for example, when the temperature of the CaO-containing material after hot crushing is within the above range, the carbonation treatment of the present embodiment is performed as it is. be able to.

The carbonation treatment time (gas blowing time) when the temperature of the CaO-containing substance is within the above range shall be 10 minutes or longer. Thereby, a high carbonic acid fixation rate can be realized. If the treatment time is less than 10 minutes, the treatment time is too short to achieve a high carbonic acid fixation rate. From the viewpoint of achieving a higher carbonic acid fixation rate, the treatment time is preferably 30 minutes or longer. On the other hand, if the treatment time is too long, the temperature of the CaO-containing substance is lowered, which is not preferable. Therefore, the treatment time is preferably 180 minutes or less, more preferably 60 minutes or less.

The carbonation treatment may be performed by arranging the CaO-containing substance in the atmosphere, or by storing the CaO-containing substance in a closed container and performing it in the closed container. The initial atmosphere in the sealed container is not particularly limited, and may be air or an inert gas such as nitrogen (N ₂ ). When the carbonation treatment is performed in a closed container, the carbonation treatment may be performed while stirring the CaO-containing substance by, for example, rotating the closed container. The temperature of the atmosphere in which the CaO-containing substance is placed during the carbonation treatment is preferably the same as the temperature of the CaO-containing substance.

The gas (supply gas) that is blown onto the CaO-containing material is not particularly limited as long as it contains carbon dioxide. From the viewpoint of achieving a high rate of carbon dioxide fixation, an example of a preferred feed gas is a gas containing water vapor and carbon dioxide, preferably a gas consisting of water vapor and carbon dioxide. According to studies by the present inventors, it was found that when the CaO-containing substance contains β-C ₂ S, this β-C ₂ S exhibits a high carbonic acid fixation rate with a gas containing water vapor and carbon dioxide. In this case, the flow ratio (volume ratio) of H ₂ O/(H ₂ O+CO ₂ ) in the supplied gas is preferably 0.03 or more and 0.30 or less. By setting the flow ratio to 0.03 or more, the carbonic acid fixation rate in β-C ₂ S is significantly improved. On the other hand, from the viewpoint of achieving stable flow rate control and suppressing corrosion of the gas supply device, the flow rate ratio is preferably 0.30 or less.

From the viewpoint of achieving a high carbonic acid fixation rate, the amount of carbon dioxide supplied is preferably 5 kg or more, more preferably 50 kg or more, per 1 ton of the CaO-containing substance, regardless of whether the supplied gas contains water vapor. . The upper limit of the amount of carbon dioxide supplied is not particularly limited, but if the amount of gas supplied is too large relative to the mass of the CaO-containing material, the temperature of the CaO-containing material will decrease due to the supplied gas. It is preferably 200 kg or less per 1 ton of the CaO-containing substance. The temperature of the supply gas is preferably 20° C. or higher and 1300° C. or lower, and more preferably the same temperature as the CaO-containing substance.

(Method for producing carbonated substance)
A method for producing a carbonated substance according to an embodiment of the present invention includes a step of carbonating a CaO-containing substance by the method for carbonating a CaO-containing substance according to the above embodiment to produce a carbonated substance. This makes it possible to produce a carbonated substance in which a large amount of carbon dioxide is fixed.

(Experimental example 1)
A carbonation treatment test was conducted in the following procedure. First, unaged decarburized slag, which is a kind of steelmaking slag, was prepared as a CaO-containing substance. The decarburized slag was classified to obtain CS-40 particle size distribution. Table 1 shows the composition of the decarburized slag. Place decarburized slag in an electric furnace, set the inside of the electric furnace to a N ₂ atmosphere, heat the decarburized slag to the slag temperature shown in Table 2, and in the state of that temperature, gas having the composition shown in Table 2 (gas Temperature: 100° C.) was blown in for 10 minutes to perform carbonation treatment. In each example, the amount of carbon dioxide supplied was 200 kg per 1 ton of decarburized slag. After furnace cooling, the carbonic acid fixation rate was measured from the amount of change in slag weight. Table 2 and FIG. 1 show the test results.

As is clear from Table 2 and FIG. 1, when the slag temperature was within the range of 400 to 1200° C., a high carbonic acid fixation rate of 5 kg-CO ₂ /t-slag or higher was achieved. It is believed that the free-CaO in the decarburized slag will be carbonated even if the feed gas does not contain water vapor. When the slag temperature exceeded 1200°C, the slag itself began to melt and carbon dioxide was decomposed, resulting in a low carbonic acid fixation rate.

(Experimental example 2)
Of the main mineral phases contained in steelmaking slag, single phases of five types of mineral phases shown in Table 3 were produced, and the particle diameter was made 0.075 mm or less. Using a thermogravimetric differential thermal analysis device (TG-DTA device) capable of controlling the atmosphere, _N2 gas is blown until the temperature of the mineral phase reaches 500 ° C., the temperature of the mineral phase is raised in the _N2 atmosphere, and the mineral phase is When the temperature reached 500° C., the N ₂ gas was switched to gas having the composition shown in Table 3 (gas temperature: 100° C.) and blown into each mineral phase to carry out the carbonation treatment. Carbonation was carried out for 60 minutes, after which the _N2 gas was switched to cool each mineral phase. The amount of carbon dioxide supplied was 100 kg per 1 ton of the mineral phase. Carbonic acid fixation rate in each mineral phase was measured from the amount of change in weight of each mineral phase. Table 3 shows the results.

As can be seen from Table 3, the rate of carbonic acid fixation with β-C ₂ S was significantly increased when the feed gas contained water vapor. Other mineral phases fixed little carbon dioxide. Since this reaction was completed in a short time of 10 minutes or less, it is possible to sufficiently fix carbon dioxide to β-C ₂ S by blowing a gas containing steam and carbon dioxide to the high-temperature steelmaking slag for 10 minutes or more. Understand. If the flow rate ratio of H ₂ O/(H ₂ O+CO ₂ ) exceeds 0.30, the supply of water vapor increases, condensation of water occurs, and the flow rate becomes unstable, making it impossible to create conditions. rice field.

(Experimental example 3)
A single phase of β-C ₂ S was produced using the reagent, and the particle size was 0.075 mm or less. Using a thermogravimetric differential thermal analysis apparatus (TG-DTA apparatus) capable of controlling the atmosphere, N ₂ gas is blown until the temperature of β-C ₂ S reaches the value shown in Table 4, and β-C is measured in the N ₂ atmosphere. 2S was heated, and when the temperature of β-C ₂ S reached the value shown in Table 4, the N ₂ gas was changed to a gas having the composition shown in Table _{4 for β-C 2 S} (gas temperature: 100 ℃) and blown in to carry out the carbonation treatment. Carbonation was carried out for 60 minutes, after which the β-C ₂ S was cooled by switching to N ₂ gas. The amount of carbon dioxide supplied was 100 kg per 1t of β-C ₂ S. From the change in the weight of β-C ₂ S, the carbonic acid fixation rate in β-C ₂ S was measured. Table 4 shows the results. The same test as in Experimental Example 2 was performed when the temperature of β-C ₂ S was 500°C. That is, in Experimental Example 3, the same test as in Experimental Example 2 was conducted by changing the temperature of β-C ₂ S among the five types of mineral phases in Experimental Example ₂ . is.

As is clear from Table 4, the rate of carbonic acid fixation in β-C ₂ S is remarkably increased when the feed gas contains water vapor, and this effect can be seen when the temperature of β-C ₂ S is between 400 and 1200°C. It works when it's within range.

According to the method for carbonating a CaO-containing substance and the method for producing a carbonated substance of the present invention, a high carbonic acid fixation rate can be achieved without adjusting the water content of the CaO-containing substance. Since fixing carbon dioxide in the atmosphere to a CaO-containing substance at a high carbonic acid fixation rate in this way greatly contributes to the reduction of carbon dioxide emissions, the present invention is an industrially extremely effective process.

Claims (9)

A method for carbonating a CaO-containing material, comprising:
A method for carbonating a CaO-containing material, comprising blowing a gas containing carbon dioxide onto the CaO-containing material for 10 minutes or longer while the temperature of the CaO-containing material is 400° C. or higher and 1200° C. or lower. The method for carbonating a CaO-containing substance according to claim 1, wherein the gas contains water vapor. The method for carbonating a CaO-containing substance according to claim 1 or 2, wherein the flow rate ratio of _H2O /( _H2O + _CO2 ) in the gas is 0.03 or more and 0.30 or less. The method for carbonating a CaO-containing material according to any one of claims 1 to 3, wherein the gas is blown to the CaO-containing material so that the amount of carbon dioxide supplied is 5 kg or more per 1 ton of the CaO-containing material. . Carbonation of a CaO-containing substance according to any one of claims 1 to 4, wherein the CaO-containing substance contains 30% by mass or more of CaO and has a CaO/SiO ₂ mass ratio of 1.5 or more. Method. The method for carbonating a CaO-containing material according to any one of claims 1 to 5, wherein the CaO-containing material is steel slag. The method for carbonating a CaO-containing substance according to claim 6, wherein the iron and steel slag is steelmaking slag. The method for carbonating a CaO-containing material according to any one of claims 1 to 5, wherein the CaO-containing material is waste concrete. A method for producing a carbonated substance, wherein the method for carbonating a CaO-containing substance according to any one of claims 1 to 8, wherein the CaO-containing substance is subjected to a carbonation treatment to produce a carbonated substance.

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