阅读说明：本技术 利用海水间接碳酸化的高纯度球霰石型及方解石型碳酸钙的制备方法 (Preparation method of high-purity vaterite-type and calcite-type calcium carbonate by utilizing seawater indirect carbonation ) 是由 金明珍 田俊赫 于 2019-03-26 设计创作，主要内容包括：本发明涉及利用海水间接碳酸化反应来制备高纯度的球霰石(vaterite)型及方解石(calcite)型碳酸钙的方法,将海水用作溶剂,溶出碱工业副产物(CKD,PSA)、CaO、Ca(OH)<Sub>2</Sub>的钙,从而可以利用海水含有的镁而使钙高效率溶出,利用碱工业副产物来使妨碍高纯度碳酸钙生成的海水内的镁沉淀,从而可以提高碳酸钙的纯度,替代高费用的溶剂而使用海水,从而可以经济地制备99.9％以上高纯度球霰石型及方解石型碳酸钙。(The invention relates to a method for preparing calcium carbonate of vaterite (vaterite) type and calcite (calcite) type with high purity by using seawater indirect carbonation reaction, wherein seawater is used as a solvent to dissolve alkali industrial byproducts (CKD, PSA), CaO, Ca (OH) 2 So that the magnesium contained in the seawater can be utilized to make calciumThe method can improve the purity of calcium carbonate by precipitating magnesium in seawater which inhibits the formation of high-purity calcium carbonate with the use of a by-product of the alkali industry, and can economically produce calcium carbonate of the vaterite type and the calcite type in high purity of 99.9% or more by using seawater instead of a solvent of high cost.)

1. A method for preparing high-purity calcium carbonate of the vaterite type and the calcite type by utilizing the indirect carbonation of seawater is characterized by comprising the following steps:

(i) mixing and stirring the indirect carbonation reaction raw materials according to the ratio of 1.0 to 10.0g of seawater per 50ml, and precipitating magnesium (Mg) existing in the seawater to prepare a calcium dissolution liquid dissolved out by calcium (Ca) existing in the indirect carbonation reaction raw materials;

(ii) step, removing magnesium precipitated in the calcium dissolving liquid;

(iii) injecting carbon dioxide into the calcium leachate without magnesium to obtain vaterite-type and calcite-type calcium carbonate (CaCO)₃) (ii) a And

(iv) step of mixing the vaterite-type and calcite-type calcium carbonates (CaCO)₃) Washing with water to raise the purity to over 99%.

2. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

in the step (iii), stirring is performed using an impeller, and as the stirring intensity increases, the content of the vaterite-type calcium carbonate increases.

3. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 2, wherein,

in the step (iii), the stirring is performed while injecting carbon dioxide into the calcium dissolution liquid.

4. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

when the seawater has an ionic strength of 0.15M or more, the stirring is performed by an impeller in the step (iii), and the content of the elliptic vaterite-type calcium carbonate increases as the stirring strength increases.

5. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

in the step (iii), stirring is performed using an impeller, and as the stirring intensity decreases, the content of calcite-type calcium carbonate increases.

6. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

in the step (iii), before injecting carbon dioxide, an alkali is added to the calcium dissolution liquid to adjust the pH of the calcium dissolution liquid to 12.70 or more.

7. The method for preparing calcium carbonate of the vaterite and calcite type in high purity according to claim 6, wherein the calcium carbonate is selected from the group consisting of calcium carbonate of the vaterite type and calcium carbonate of the calcite type,

the alkali is ammonia water (NH)₄OH), sodium hydroxide (NaOH), or potassium hydroxide (KOH).

8. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

in said step (iii), the injection of carbon dioxide is interrupted if the pH of the dissolution liquid reaches the range of 9 to 12.

9. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

the average particle diameter of the calcium carbonate is adjusted within the range of 1.0 to 5.0 μm.

10. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

the seawater is any one selected from the group consisting of general seawater, seawater desalination concentrate, brine and a mixture thereof.

11. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

the indirect carbonation reaction raw material is any one of alkali industry byproducts selected from paper making sludge incineration ash, cement kiln dust, fuel ash, bottom ash, fly ash, deinking ash, steel slag, waste concrete and a mixture of the two.

12. The method for preparing calcium carbonate of the vaterite and calcite type in high purity using indirect carbonation of seawater according to claim 1, wherein,

the indirect carbonation reaction raw material is CaO or Ca (OH)₂。

Technical Field

The present invention relates to a process for the preparation of calcium carbonate of the vaterite (vaterite) and calcite (calcite) type with high purity by means of indirect carbonation reaction of seawater.

Background

Excessive greenhouse gas emissions, beyond the range permissible in nature, resulting from industrial development are considered to be a major cause of global warming. The greenhouse gas is classified as carbon dioxide (CO)₂) Methane (CH)₄) Nitrogen dioxide (N)₂O), Freon (CFCs), ozone (O)₃) And the like, with about 80% carbon dioxide being a typical greenhouse gas.

With the official effect of the tokyo protocol in 2005, the carbon dioxide emission is being restricted, and the global warming problem is required to be actively coped with, and the industries and policies related to the greenhouse gas emission restriction are being developed. In order to meet such a demand, studies on carbon dioxide capture and storage (carbon capture & storage) are now actively being conducted.

Recently, it has been proposed to use CO₂Permanently sequester CO₂After the necessity of research on reuse of a potentially useful product, research on mineral carbonation has been carried out. Mineral carbonation is a technique of reacting carbon dioxide with a metal oxide containing calcium, magnesium, or the like to stably store the carbon dioxide as an insoluble carbonate mineral. As a raw material for mineral carbonation, natural minerals containing a large amount of calcium or industrial byproducts of alkali can be used. Recently, the use of a large amount of basic industrial by-products has been on the trend for environmental problems and economic advantages.

The indirect carbonation in the mineral carbonation technology is a technology of mixing and stirring the industrial by-product and the solvent to dissolve out calcium in the industrial by-product, injecting carbon dioxide into a dissolution liquid containing a large amount of calcium and generating carbonate while storing the carbon dioxide, and is different from direct carbonation and can generate high-purity carbonate. As a solvent used for indirect carbonation, distilled water, various acids (acids), ammonium salts, and various chelating agents have been used. However, the distilled water has insufficient calcium-releasing ability, and when an acid is used, the pH of the solution is too low to be suitable for the carbonation reaction, and other solvents have high calcium-releasing and carbonation efficiencies, but the cost of the solvent is high, and there is a problem that it is difficult to ensure economical efficiency.

On the other hand, calcium carbonate is classified into calcite (calcite), aragonite (aragonite) and vaterite (vaterite) according to morphology. Calcite is hexahedral in structure, being the most stable of the calcium carbonate morphologies and thus can be seen frequently. Aragonite is produced as needle-shaped or orthorhombic grains at a high temperature of 60-80 ℃ or above or in the presence of magnesium ions. Vaterite is a spherical particle, with a metastable morphology compared to calcite. In the process of calcium carbonate production, Amorphous Calcium Carbonate (ACC) is first produced, and metastable vaterite is produced through the process of dissolution and recrystallization of ACC. In addition, stable calcite is generated through the dissolution and recrystallization processes of vaterite.

Vaterite, as a calcium carbonate having a high specific surface area, a high solubility, a high dispersion force, and a small specific gravity, can be used in more various applications than other two forms of calcium carbonate, compared to calcite or aragonite. Especially, elliptic vaterite has a much higher specific surface area and solubility, dispersion force than those of a sphere, and has a smaller specific gravity, and thus is much more useful in industry. In order to promote the generation of vaterite, studies on the introduction of additives or the utilization of additional energy (ultrasonic waves, temperature, etc.) are being largely conducted, and studies on the regulation of the morphology of calcium carbonate generated by means of indirect carbonation reaction are being partially conducted.

The high solvent costs and the use of additives or additional energy present the problem of increasing the overall process costs and reducing the economics of the indirect carbonation technology.

Therefore, it is required to develop a method for preparing high-purity calcium carbonate by simultaneously improving the efficiency and economy of the indirect carbonation technology in the mineral carbonation technology.

Disclosure of Invention

The invention aims to provide a preparation method of high-purity vaterite-type and calcite-type calcium carbonate,

the method uses alkali industry by-products (cement kiln dust (CKD), paper sludge incineration ash (PSA)) with CaO, Ca (OH)₂Seawater (seawater) is used as a solvent as a raw material for the indirect carbonation reaction, thereby making it possible to utilize the alkali industrial by-products, which are waste resources, and to produce highly pure calcium carbonates of the vaterite type and the calcite type without using a costly solvent.

In another aspect, the present invention provides a method for preparing high-purity calcium carbonate of the vaterite type and the calcite type by indirect carbonation of seawater, comprising:

(i) mixing and stirring the indirect carbonation reaction raw materials according to the ratio of 1.0 to 10.0g of seawater per 50ml, and precipitating magnesium (Mg) existing in the seawater to prepare a calcium dissolution liquid dissolved out by calcium (Ca) existing in the indirect carbonation reaction raw materials;

(ii) step, removing magnesium precipitated in the calcium dissolving liquid;

(iii) injecting carbon dioxide into the calcium leachate with magnesium removed to obtain vaterite (vaterite) type and calcite (calcite) type calcium carbonate (CaCO)₃) (ii) a And

(iv) step of mixing the vaterite-type and calcite-type calcium carbonates (CaCO)₃) Washing with water to raise the purity to over 99%.

The method for preparing high-purity calcium carbonate of the vaterite type and the calcite type according to the present invention can use the alkali industry byproduct continuously generated in the industry as a raw material, and replace the solvent with high cost by using low-cost or uncompensated seawater, thereby preparing the high-purity calcium carbonate of the vaterite type and the calcite type by using the indirect carbonation reaction of the seawater and the alkali industry byproduct.

In the indirect carbonation reaction, the carbon dioxide is injected and the stirring is performed by the impeller, so that the stirring strength is increased, thereby producing a high-purity vaterite-type calcium carbonate.

In the indirect carbonation reaction, the stirring intensity is reduced when carbon dioxide is injected, and thus high-purity calcite-type calcium carbonate can be produced.

Drawings

FIG. 1 shows an overall process diagram of a process for preparing calcium carbonate according to one embodiment of the present invention.

Fig. 2 shows the results of calcium concentration measurements of the calcium leachate resulting from a change in the solid-to-liquid ratio of the by-product of the alkali industry to seawater in accordance with one embodiment of the present invention.

FIG. 3 shows XRD analysis results of calcium carbonate produced using multiple indirect carbonation reaction materials and seawater ((a) CKD with seawater, (b) CKD with seawater desalination concentrate, (c) PSA with seawater, (d) CaO with seawater, (e) Ca (OH)₂With seawater).

Fig. 4 shows SEM analysis results of calcium carbonate generated using various industrial byproducts and seawater according to one embodiment of the present invention ((a) CKD with seawater, (b) CKD with seawater desalination concentrate, and (c) PSA with seawater).

FIG. 5 shows the results of XRD analysis of calcium carbonate produced using 5 solvents comprising seawater according to one embodiment of the present invention ((a) seawater, (b) distilled water, (c)0.1M C₃H₂Na₂O₄，(d)0.3M HCl，(e)0.3M NH₄Cl)。

FIG. 6 shows SEM analysis results of calcium carbonate produced under various conditions of impeller diameter and stirring speed according to one embodiment of the present invention ((a)

300rpm，(b)

500rpm，(c)800rpm，(d)

300rpm)。

Best mode for carrying out the invention

The present invention is described in more detail below.

The reaction tank described in the present specification is used in the production process of calcium carbonate, and is not specifically described in the examples of the present invention, but is constituted by a constitution that can be easily understood by those skilled in the art to which the present invention pertains.

The invention relates to a method for using alkali industrial by-products or CaO, Ca (OH)₂A process for the production of high purity vaterite (vaterite) and calcite (calcite) crystalline calcium carbonate by indirect carbonation of a compound as a feedstock for the indirect carbonation reaction using seawater as the indirect carbonation reaction solvent. (refer to FIG. 1)

The method for preparing high-purity calcium carbonate of the vaterite type and the calcite type by utilizing the indirect carbonation of the alkali industrial byproduct and the seawater according to the embodiment of the invention is characterized by comprising the following steps:

(i) mixing and stirring the indirect carbonation reaction raw materials according to the ratio of 1.0 to 10.0g of seawater per 50ml, and precipitating magnesium (Mg) existing in the seawater to prepare a calcium dissolution liquid dissolved out by calcium Ca) existing in the indirect carbonation reaction raw materials;

(ii) step, removing magnesium precipitated in the calcium dissolving liquid;

(iii) injecting carbon dioxide into the calcium leachate from which the magnesium is removed to obtain vaterite (vaterite) type and calcite (calcite) type calcium carbonate (CaCO)₃) (ii) a And

(iv) step of calcium carbonate (CaCO) of the vaterite type and the calcite type₃) Washing with water to raise the purity to over 99%.

First, the indirect carbonation reaction raw material is added to the seawater to precipitate magnesium (Mg) present in the seawater and to dissolve calcium (Ca) present in the indirect carbonation reaction raw material.

The precipitation of magnesium and the elution reaction of calcium can be represented by the following reaction formula 1, which is considered to be a very strong equilibrium reaction of the forward reaction and serves as a motive force for the elution reaction of calcium.

[ reaction formula 1]

Mg²⁺+CaO+H₂O→Mg(OH)₂(s)+Ca²⁺

The indirect carbonation reaction raw material may use alkali industrial byproducts composed of paper sludge incineration ash (PSA), Cement Kiln Dust (CKD), fuel ash (fuel ash), bottom ash (bottom ash), fly ash (flash ash), deinking ash (de-inking ash), slag (slag), waste concrete and a mixture thereof, or calcium oxide (CaO), calcium hydroxide (ca (oh)₂) And the like, but is not limited thereto.

The calcium oxide (CaO), calcium hydroxide (Ca (OH)₂) Isocalcium compounds are also included in the alkali industry by-products and, even when used alone as a feedstock for an indirect carbonation reaction, can exhibit results similar to those obtained using alkali industry by-products.

Among them, Cement Kiln Dust (CKD) is preferably used, which has a CaO content of about 45% or more, a Ca content of about 20ml as a fine particle, and has an advantage that it can be used as a raw material for carbonation reaction without a pretreatment step such as pulverization and crushing.

The seawater includes general seawater, seawater desalination concentrate, brine (brine) or brine (bittern), and the following table 1 shows the average concentration of main ions dissolved in general seawater, and the seawater used in the present invention does not substantially exceed the average concentration range of ions shown in the following table 1.

[ Table 1]

Composition of seawater	Concentration (mg/L)
		Cl-	19,000
Na+	11,000
		SO4 2-	2,700
Mg2+	1,300
		Ca2+	400
HCO3 -	140
		Br-	65

This seawater is used as a solvent required for dissolving calcium from the raw material of the indirect carbonation reaction described below. As can be confirmed in Table 1 above, in seawater, calcium ions (Ca)²⁺) The magnesium entry mg/L is included, and the dissolution liquid can contain more calcium. In addition, in one embodiment of the present invention, in order to filter impurities present in the seawater, seawater filtered by a membrane filter or the like may be used.

The indirect carbonation reaction raw material may be characterized by being added at a rate of 1.0 to 10.0g per 50ml of seawater, and preferably, may be characterized by being added at a rate of 1.0 to 2.0g per 50ml of seawater. When the addition ratio of the indirect carbonation reaction raw material added to 50ml of seawater satisfies the above range, there is an advantage that the efficiency of calcium elution can be improved, and when it exceeds the above range, there are problems that the efficiency of calcium elution is lowered or a sufficient amount of calcium elution cannot be secured.

A preferred embodiment of the invention may be characterized in that magnesium ions (Mg) are also added to the seawater²⁺) Chlorine ionZi (Cl)^-) Bromine ion (Br)^-) Or a mixture thereof.

For example, chloride ion (Cl) in seawater^-) As shown in the following reaction formula 2, Ca (OH) contained in the industrial byproduct of alkali from the raw material of the indirect carbonation reaction₂React to form CaCl₂Thereby dissolving out calcium ions.

[ reaction formula 2]

Ca(OH)₂+2Cl^-→CaCl₂+2OH^-

On the other hand, magnesium present in seawater acts as a factor for improving the reaction efficiency in the calcium elution step as shown in the above reaction formula 1, but calcium carbonate (CaCO) is present thereafter₃) The formation step functions as a hindrance. I.e. magnesium ions (Mg) left undeposited²⁺) Reacts with carbon dioxide supplied to the sea water to form magnesium carbonate (MgCO)₃) Thereby competitively inhibiting calcium ion (Ca)²⁺) Calcium carbonate (CaCO) caused by reaction with carbon dioxide₃) Magnesium carbonate is formed as an impurity, and thus becomes an obstacle factor in the production of high-purity calcium carbonate.

However, for example, when calcium is dissolved out by reacting an alkaline industrial by-product in seawater, calcium oxide or calcium hydroxide of the alkaline industrial by-product dissolves in seawater, the pH of seawater increases, and at a high pH, magnesium and OH in seawater^-Reaction, precipitation as Mg (OH)₂The form of (1). This Mg (OH)₂The precipitation reaction of (a) can be represented by the following reaction formula 3, which is a positive reaction corresponding to a reaction in which the equilibrium is dominant (K ═ 10)¹¹) Most (99.99% or more) of the magnesium ions present in the seawater can be precipitated as Mg (OH)₂The form of (1).

[ reaction formula 3]

Mg²⁺+2OH^-→Mg(OH)₂(s)

Therefore, the method for producing calcium carbonate according to the present invention is characterized in that since magnesium existing in seawater can be precipitated and removed by adding the raw material for the indirect carbonation reaction to seawater, seawater can be used as a solvent in the reaction for producing high-purity calcium carbonate.

In order to produce calcium carbonate of high purity, the precipitated magnesium is separated and removed by using a membrane filter or the like. If referring to the reaction formulas 1 and 3, the precipitated magnesium has Mg (OH)₂Form, Mg (OH) thus isolated₂May be stored separately and used for other purposes.

Then, carbon dioxide was injected into the dissolution liquid from which the magnesium precipitate was removed, to obtain calcium carbonate. Injecting carbon dioxide of the dissolution liquid with carbonate ions (CO)₃ ^2-) Dissolving in the form of calcium carbonate, reacting with calcium ions in the dissolved liquid phase to form calcium carbonate (CaCO)₃). This dissolution of carbon dioxide and the formation reaction of calcium carbonate can be represented by the following reaction formula 4.

[ reaction formula 4]

Referring to the above reaction formula 4, it can be seen that carbon dioxide (CO) is present₂) Dissolved in the dissolution liquid to form carbonate ion (CO)₃ ^2-) Hydrogen ion (H) is generated in the process of (1)⁺) Therefore, carbon dioxide is injected to form calcium carbonate, and thus the pH of the dissolution liquid gradually decreases.

According to an embodiment of the present invention, before injecting carbon dioxide into the dissolution liquid from which the magnesium precipitate is removed to perform the indirect carbonation reaction, adding ammonia (NH) to the dissolution liquid may be further included₄OH), sodium hydroxide (NaOH), potassium hydroxide (KOH), etc., and adjusting the pH to 12.60 or more.

As explained above, the pH of the dissolution liquid is gradually lowered during the process of forming carbonate ions by dissolution of carbon dioxide, and thus the pH of the dissolution liquid is sufficiently raised before the reaction of forming calcium carbonate is performed, so that the efficiency of the overall carbonation reaction can be improved. It may be characterized in that the pH of the dissolution liquid is preferably adjusted to have a value of 12.60 or more, more preferably 12.70 or more. The method for adjusting the pH of the dissolution liquid is not particularly limited, and the pH may be preferably adjusted by adding a base.

According to an embodiment of the present invention, it may be characterized in that the stirring intensity by an impeller (impelleter) is adjusted while injecting carbon dioxide in order to produce high purity calcium carbonates of the vaterite type and the calcite type. The content of the vaterite-type calcium carbonate increases as the stirring strength of the impeller increases, and the content of the calcite-type calcium carbonate increases as the stirring strength decreases.

In addition, the carbonation reaction conditions such as impeller diameter and stirring speed affect the formation of vaterite-type and calcite-type calcium carbonates. For example, using polyurethane tubesWhen carbon dioxide was injected, the content ratio of vaterite to calcite of the calcium carbonate produced was different in all other conditions, 70mm and 50mm, respectively, based on 1L of the solution volume, and the content ratio of vaterite to calcite was different in all other conditions, as the stirring speed was increased to 300, 500 and 800rpm, respectively.

In addition, when the seawater used has a high ionic strength, for example, 0.15M or more, elliptic vaterite is generated instead of spherical vaterite.

According to an embodiment of the present invention, it is preferable that the stirring is performed while injecting carbon dioxide into the calcium dissolution liquid during the calcium carbonate formation reaction, and it is preferable that the injection of carbon dioxide and the stirring are terminated and the carbonation reaction is terminated when the pH of the dissolution liquid reaches 9 to 12.

When the pH of the dissolution liquid drops to less than 9 by the continuous supply of carbon dioxide, the formed calcium carbonate dissolves, and thus the carbonation efficiency drops, and when the pH of the dissolution liquid exceeds 12 at the time point when the supply of carbon dioxide is interrupted, the carbonation efficiency drops because sufficient carbon dioxide cannot be supplied.

According to one embodiment of the invention, the injection of carbon dioxide is terminated, the leachate which ends the carbonation reaction is filtered and the vaterite-type and calcite-type calcium carbonates (CaCO) are washed with water₃) And drying to prepare the high-purity calcium carbonate with the purity of more than 99 percent.

The drying is preferably performed at 40 to 60 ℃ for a period of 12 to 24 hours.

The present invention will be described more specifically with reference to examples. These examples are intended to illustrate the invention only, and the scope of the invention is not limited to these examples, which will be obvious to the practitioner.

In order to understand the components, forms, shapes, sizes, etc., of the raw materials (industrial by-products) of the indirect carbonation reaction and the calcium carbonate prepared, X-ray diffraction analysis (XRD, Smart lab, science corporation (Rigaku)), X-ray fluorescence analysis (XRF-1700, Shimadzu corporation), scanning electron microscope analysis (SEM, SUPRA-40VP, ZEISS corporation (ZEISS)), and laser diffraction particle size analysis (HELOS, newpatakco ltd, germany (Sympatec)) were performed. X-ray diffraction analysis Using CuK-a radiation at 40kV/30mA, at 2 θ; 5.0-80.0 degrees at 0.02 degree intervals.

The calcium concentration of the seawater, the desalinated concentrated seawater, and the solution produced in the reaction were measured by using an atomic absorption spectrophotometer (AAS, AA200, PerkinElmer), and the pH was measured by using a pH meter (Orionstar211, seemer).

Preparation example 1: raw materials ensuring an indirect carbonation reaction (Ca Source)

In this example, the by-product of alkali industry, calcium oxide (CaO) and calcium hydroxide (Ca (OH))₂) The reagent serves as a raw material for the indirect carbonation reaction. Cement Kiln Dust (CKD) and paper sludge incineration ash (pa) were usedper slurry ash, PSA) as a by-product of the alkali industry. Each industrial by-product was screened through a 425 μm sieve and used. The Pure Chemical company (Hayashi Pure Chemical Ind.) used as the reagent (assaymin.98%) and the Pure Chemical company (Junsei Chemical) used as the reagent (assaymin.96%) for calcium oxide.

The effective particle size of CKD used in this example was 23.6, and the results of chemical composition analysis using an XRF (X-ray fluorescence spectrometer) apparatus are shown in Table 2 below.

[ Table 2]

Preparation example 2: ensure the seawater and the seawater desalination concentrated water

The solvent of the indirect carbonation reaction uses seawater and seawater desalination concentrated water. Seawater is taken along the shore, and seawater desalination concentrated water is taken in a seawater desalination plant. Immediately after the seawater and the concentrated water were taken, they were filtered through a 5 μm filter paper (FilterPaper 2, advanced technologies, west river, inc. (ADVANTEC)) and then stored under refrigeration.

The seawater used in this example had a pH of 7.97, and the calcium and magnesium concentrations measured by atomic absorption spectrophotometer were 474 mg/L and 1,322 mg/L, respectively, similar to the normal seawater composition.

The pH of the desalinated seawater used in this example was 7.82, and the concentrations of calcium and magnesium were 900 mg/L and 3,900 mg/L, respectively.

Example 1: preparation of calcium-dissolving liquid from sea water

Using seawater or desalinated seawater as a solvent for an indirect carbonation reaction, using Cement Kiln Dust (CKD) or paper sludge incineration ash (PSA) as an industrial byproduct as a raw material for the indirect carbonation reaction, and further using calcium oxide (CaO) and calcium hydroxide (Ca (OH))₂) As a raw material for the indirect carbonation reaction, a calcium-dissolving liquid was prepared.