KR102385412B1 - Method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater - Google Patents

Abstract

The present invention relates to a method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation reaction of seawater, and alkali industrial by-products (CKD, PSA) using seawater as a solvent , CaO, Ca(OH) ₂ By eluting calcium, it is possible to elute calcium with high efficiency using magnesium contained in seawater, and precipitate magnesium in seawater that prevents the production of high-purity calcium carbonate using alkali industrial by-products. By doing so, the purity of calcium carbonate can be increased, and by using seawater instead of expensive solvents, it is possible to economically manufacture vaterite-type and calcite-type calcium carbonate with a purity of 99.9% or more.

Description

Method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater

The present invention relates to a method for producing high-purity vaterite-type and calcite-type calcium carbonate by using indirect carbonation reaction of seawater.

Excessive emission of greenhouse gases due to industrial development exceeds the allowable range of the natural world and is pointed out as the main culprit of global warming. Types of greenhouse gases include carbon dioxide (CO ₂ ), methane (CH ₄ ), nitrous oxide (N ₂ O), freon (CFCs), and ozone (O ₃ ). it is gas

With the Kyoto Protocol officially entering into force in 2005, regulations on carbon dioxide emissions have been strengthened, and it is required to actively deal with global warming and to develop industries and policies related to greenhouse gas emission control. To prepare for this, research on carbon capture & storage is being actively conducted.

Recently, since the need for recycling research that permanently sequesters CO ₂ and utilizes CO ₂ as a potentially useful product has been suggested, research on mineral carbonation has been in full swing. Mineral carbonation is a technology for stably storing carbon dioxide as insoluble carbonate minerals by reacting carbon dioxide with metal oxides containing calcium or magnesium. As a raw material for mineral carbonation, natural minerals or alkali industrial by-products containing a large amount of calcium can be used. Recently, for reasons such as environmental problems and economic advantages, alkaline industrial by-products have been widely used.

Among mineral carbonation technologies, indirect carbonation is a technology that mixes and stirs industrial by-products and solvents to elute calcium in industrial by-products, and injects carbon dioxide into an eluate containing a large amount of calcium to store carbon dioxide and generate carbonate at the same time. Alternatively, high-purity carbonate can be produced. Distilled water, various acids, ammonium salts, and various chelating agents have been used as solvents for indirect carbonation. However, distilled water lacks the ability to elute calcium, and when acid is used, the pH of the eluate is too low to be suitable for carbonation reaction. There is a problem.

On the other hand, calcium carbonate is divided into calcite (calcite), aragonite (aragonite) and vaterite (vaterite) according to the form. Calcite is the most common form of calcium carbonate because it has a hexahedral structure and is the most stable form of calcium carbonate. Aragonite is needle-shaped or orthorhombic particles, and is produced under high temperature conditions of 60-80 °C or higher or in the presence of magnesium ions. Vaterite is a spherical particle that is metastable compared to calcite. In the process of calcium carbonate formation, amorphous calcium carbonate (ACC) is first generated, and metastable vaterite is generated through dissolution and recrystallization of ACC. In addition, stable calcite is generated through the dissolution and recrystallization of vaterite.

Vaterite is calcium carbonate with high specific surface area, high solubility, high dispersing power and small specific gravity compared to calcite or aragonite. In particular, elliptical vaterite has a much higher specific surface area and solubility and dispersing power than spherical ones, as well as a smaller specific gravity, so it has much higher industrial application. In order to promote the formation of vaterite, many studies are being conducted by administering additives or using additional energy (ultrasound, temperature, etc.) .

The high solvent cost and the use of additives or additional energy increase the cost of the entire process, thereby lowering the economic feasibility of the indirect carbonation technology.

Therefore, the development of a method for producing high-purity calcium carbonate by simultaneously improving the efficiency and economic feasibility of the indirect carbonation technology among mineral carbonation technologies is required.

An object of the present invention is to provide a method for producing high-purity vaterite-type and calcite-type calcium carbonate,

Alkali industrial by-products (cement kiln dust (CKD), paper sludge incineration ash (PSA)) and CaO, Ca(OH) ₂ are used as raw materials for indirect carbonation reaction, and seawater is used as a solvent. An object of the present invention is to provide a method for manufacturing high-purity vaterite-type and calcite-type calcium carbonate that can utilize alkali industrial by-products and does not use expensive solvents.

On the one hand, the present invention

(i) The raw material for indirect carbonation reaction is mixed at a ratio of 1.0 to 10.0 g per 50 ml of seawater and stirred, so that magnesium (Mg) present in seawater is precipitated, and calcium (Ca) present in the raw material for indirect carbonation reaction is eluted preparing a calcium eluate;

(ii) removing the precipitated magnesium in the calcium eluate;

(iii) injecting carbon dioxide into the calcium eluate from which magnesium has been removed to obtain vaterite-type and calcite-type calcium carbonate (CaCO ₃ ); and

(iv) washing the vaterite-type and calcite-type calcium carbonate (CaCO ₃ ) with water to increase the purity to 99% or more; Provided is a method for producing type calcium carbonate.

The method for producing high-purity vaterite-type and calcite-type calcium carbonate according to the present invention uses alkali industrial by-products continuously generated in industry as a raw material, and uses low-cost or free seawater instead of expensive solvents, so that the seawater and It is possible to manufacture high-purity vaterite-type and calcite-type calcium carbonate through an indirect carbonation reaction using an alkali industrial by-product.

In addition, when carbon dioxide is injected during the indirect carbonation reaction, it is stirred using an impeller, and the stirring strength is increased to produce high-purity vaterite-type calcium carbonate.

In addition, when carbon dioxide is injected during the indirect carbonation reaction, the stirring strength is reduced, thereby producing high-purity calcite-type calcium carbonate.

1 shows an overall process diagram of a method for producing calcium carbonate according to an embodiment of the present invention.
Figure 2 shows the measurement result of the calcium concentration of the calcium eluate according to the change in the solid-liquid ratio of the alkali industrial by-product and seawater according to an embodiment of the present invention.
3 shows the XRD analysis results of calcium carbonate produced using various indirect carbonation reaction raw materials and seawater according to an embodiment of the present invention ((a) CKD and seawater, (b) CKD and seawater desalination concentrated water, (c) PSA and seawater, (d) CaO and seawater, (e) Ca(OH) ₂ and seawater).
4 shows the SEM analysis results of calcium carbonate produced using various industrial by-products and seawater according to an embodiment of the present invention ((a) CKD and seawater, (b) CKD and seawater desalination concentrated water, (c) ) PSA and seawater).
5 shows the XRD analysis results of calcium carbonate produced using five solvents including seawater according to an embodiment of the present invention ((a) seawater, (b) distilled water, (c) 0.1 MC ₃ H ₂ Na ₂ O ₄ , (d) 0.3 M HCl, (e) 0.3 M NH ₄ Cl).
6 shows the SEM analysis results of calcium carbonate produced under various impeller diameters and stirring speed conditions according to an embodiment of the present invention ((a) Ø _blade : 50 mm, 300 rpm, (b) Ø _blade : 50 mm, 500 rpm, (c) Ø _blade :50mm, 800 rpm, (d) Ø _blade :70mm, 300 rpm).

Hereinafter, the present invention will be described in more detail.

The reactor described in this specification is used during the manufacturing process of calcium carbonate and is not described in detail in the embodiments of the present invention, but has a configuration that can be easily understood by those skilled in the art to which the present invention belongs.

The present invention uses an alkali industrial by-product or CaO, Ca(OH) ₂ compound as a raw material for the indirect carbonation reaction, and uses seawater as a solvent for the indirect carbonation reaction. ) and a method for preparing calcium carbonate having a calcite crystal structure (see FIG. 1).

A method for producing high-purity vaterite-type and calcite-type calcium carbonate using an alkali industrial by-product and indirect carbonation of seawater according to an embodiment of the present invention,

(i) The raw material for indirect carbonation reaction is mixed at a ratio of 1.0 to 10.0 g per 50 ml of seawater and stirred, so that magnesium (Mg) present in seawater is precipitated, and calcium (Ca) present in the raw material for indirect carbonation reaction is eluted preparing a calcium eluate;

(ii) removing the precipitated magnesium in the calcium eluate;

(iii) injecting carbon dioxide into the calcium eluate from which magnesium has been removed to obtain vaterite-type and calcite-type calcium carbonate (CaCO ₃ ); and

(iv) washing the vaterite-type and calcite-type calcium carbonate (CaCO ₃ ) with water to increase the purity to 99% or more; characterized in that it comprises a.

First, a raw material for indirect carbonation reaction is added to seawater so that magnesium (Mg) present in the seawater is precipitated, and calcium (Ca) present in the raw material for indirect carbonation reaction is eluted.

The precipitation of magnesium and the elution of calcium can be expressed as in Scheme 1 below, which is a reaction with a very strong equilibrium to the forward reaction, and is considered to be the driving force of the calcium elution reaction.

[Scheme 1]

Mg ²⁺ + CaO + H ₂ O → Mg(OH) ₂ (s) + Ca ²⁺

The indirect carbonation reaction raw material is paper sludge ash (PSA), cement kiln dust (CKD), fuel ash (fuel ash), bottom ash (bottom ash), fly ash (fly ash), deinked ash (de-inking ash), steelmaking slag, waste concrete and alkali industrial by-products composed of mixtures thereof, or calcium compounds such as calcium oxide (CaO), calcium hydroxide (Ca(OH) ₂ ) However, the present invention is not limited thereto.

Calcium compounds such as calcium oxide (CaO) and calcium hydroxide (Ca(OH) ₂ ) are also included in alkali industrial by-products, and even when used alone as an indirect carbonation reaction raw material, results similar to those of using alkali industrial by-products. can

Of these, it is preferable to use cement kiln dust (CKD), which is fine particles having a CaO content of about 45% or more, a high Ca content, and a particle size of about 20 μm, and pretreatment such as grinding and crushing It has the advantage that it can be used as a carbonation reaction raw material without a step.

The seawater includes general seawater, seawater desalination concentrated water, brine or bittern water, and Table 1 below shows the average concentration of major ions dissolved in general seawater, and the seawater used in the present invention is also It does not deviate significantly from the average concentration range of ions shown in 1.

Component of seawater Concentration (mg/L) Cl ^- 19,000 Na ⁺ 11,000 SO ₄ ^2- 2,700 Mg ²⁺ 1,300 Ca ²⁺ 400 HCO ₃ ^- 140 Br ^- 65

Such seawater is used as a solvent for eluting calcium from the raw material for the indirect carbonation reaction to be described below. As can be seen in Table 1, seawater contains calcium ions (Ca ²⁺ ) at a concentration of about 400 mg/L, so that more calcium may be included in the eluate. Also, in one embodiment of the present invention, seawater filtered using a membrane filter or the like may be used to filter out impurities present in seawater.

The indirect carbonation reaction raw material may be characterized in that it is added in a ratio of 1.0 to 10.0 g per 50 ml of seawater, preferably in a ratio of 1.0 to 2.0 g per 50 ml of seawater. When the addition ratio of the indirect carbonation reaction raw material added to 50 ml of seawater satisfies the above range, there is an advantage in that the efficiency of calcium elution can be increased. There are problems such as not being able to.

A preferred embodiment of the present invention may be characterized in that magnesium ions (Mg ²⁺ ), chlorine ions (Cl ⁻ ), bromine ions (Br ⁻ ) or mixtures thereof are further added to seawater.

For example, chlorine ions (Cl ⁻ ) in seawater react with Ca(OH) ₂ contained in alkali industrial by-products of indirect carbonation reaction raw materials as shown in Reaction Equation 2 below to form CaCl ₂ , thereby eluting calcium ions.

[Scheme 2]

Ca(OH) ₂ + 2Cl ^- → CaCl ₂ + 2OH ^-

On the other hand, magnesium present in seawater acts as a factor to increase the efficiency of the reaction in the calcium elution step as shown in Scheme 1, but acts as an interfering factor in the subsequent calcium carbonate (CaCO ₃ ) formation step. That is, magnesium ions (Mg ²⁺ ) that remain ^{unprecipitated} react with carbon dioxide supplied to seawater to form magnesium carbonate (MgCO ₃ ), and calcium carbonate ( It competitively inhibits the formation of CaCO ₃ ) and forms an impurity, magnesium carbonate, which is an obstacle in the production of high-purity calcium carbonate.

However, for example, when calcium is eluted by reacting alkali industrial by-products with seawater, the pH of seawater increases as calcium oxide or calcium hydroxide of alkali industrial by-products is dissolved in seawater, and magnesium in seawater at high pH is OH- ^and The reaction is precipitated in the form of Mg(OH) ₂ . This precipitation reaction of Mg(OH) ₂ can be expressed as in Scheme 3 below, which is a forward reaction and corresponds to a reaction in which equilibrium prevails (K = 10 ¹¹ ), and most of the magnesium ions present in seawater (99.99% or more) are It can be precipitated in the form of Mg(OH) ₂ .

[Scheme 3]

Mg ²⁺ + 2OH ^- → Mg(OH) ₂ (s)

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

In order to prepare high-purity calcium carbonate, the precipitated magnesium is separated and removed using a membrane filter or the like. Referring to Schemes 1 and 3, the precipitated magnesium has the form of Mg(OH) ₂ , and the separated Mg(OH) ₂ may be separately stored and used for other purposes.

Next, carbon dioxide is injected into the eluate from which the magnesium precipitate is removed to obtain calcium carbonate. Carbon dioxide injected into the eluate is dissolved in the form of carbonate ions (CO ₃ ^2- ), and reacts with calcium ions on the eluate to form calcium carbonate (CaCO ₃ ). The dissolution of carbon dioxide and the formation of calcium carbonate can be expressed as in Reaction Formula 4 below.

[Scheme 4]

CO ₂ (aq) + H ₂ O ↔ H ₂ CO ₃ (aq) (1)

H ₂ CO ₃ (aq) ↔ H ⁺ + HCO ₃ ^- (2)

HCO ₃ ^- ↔ H ⁺ + CO ₃ ^2- (3)

Ca ²⁺ + CO ₃ ^2- ↔ CaCO ₃ (s) (4)

Referring to Scheme 4, it can be seen that hydrogen ions (H ⁺ ) are generated in the process where carbon dioxide (CO ₂ ) is dissolved in the eluate to form carbonate ions (CO ₃ ^2- ), and thus, calcium carbonate is formed. The pH of the eluate is gradually lowered as carbon dioxide is injected.

According to one embodiment of the present invention, before performing the indirect carbonation reaction by injecting carbon dioxide into the eluate from which the magnesium precipitate is removed, aqueous ammonia (NH ₄ OH), sodium hydroxide (NaOH), potassium hydroxide (KOH), etc. It may further include the step of adjusting the pH to 12.60 or more by adding an alkali of.

As described above, since the pH of the eluate gradually decreases during the process of dissolving carbon dioxide to form carbonate ions, the efficiency of the overall carbonation reaction can be increased by sufficiently raising the pH of the eluate before proceeding with the reaction to form calcium carbonate. there is. The pH of the eluate may be preferably adjusted to have a value of 12.60 or more, more preferably 12.70 or more. A method for adjusting the pH of the eluate is not particularly limited, and the pH may be adjusted by adding an alkali.

According to one embodiment of the present invention, it may be characterized in that the stirring intensity using an impeller is adjusted while injecting carbon dioxide to produce high-purity vaterite-type and calcite-type calcium carbonate. As the stirring strength of the impeller increases, the content of vaterite-type calcium carbonate may increase, and as the stirring strength decreases, the content of calcite-type calcium carbonate may increase.

In addition, carbonation reaction conditions such as the diameter of the impeller and the stirring speed may affect the formation of vaterite-type and calcite-type calcium carbonate. For example, when carbon dioxide is injected using a urethane tube (Ø: 6 mm), calcium carbonate is generated when all other conditions are the same and the impeller diameters are 70 mm and 50 mm based on 1 L of solution volume. The content ratio of vaterite and calcite may be different, and as all other conditions are the same and the stirring speed is increased to 300, 500, or 800 rpm, the content ratio of vatterite and calcite may be different.

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

According to one embodiment of the present invention, in the calcium carbonate formation reaction, the stirring is preferably performed simultaneously with the injection of carbon dioxide into the calcium eluate, and when the pH of the eluate reaches 9 to 12, the injection and stirring of carbon dioxide are stopped Thus, it is preferable to end the carbonation reaction.

When the pH of the eluate falls to less than 9 due to the continuous supply of carbon dioxide, there is a problem in that the carbonation efficiency decreases as the already formed calcium carbonate is dissolved. There is a problem in that carbonation efficiency is lowered as carbonation is not supplied.

According to an embodiment of the present invention, the carbonation reaction is terminated by stopping the injection of carbon dioxide, filtering the eluate, and washing and drying the vaterite-type and calcite-type calcium carbonate (CaCO ₃ ) with water to obtain a purity of 99 % or higher, calcium carbonate can be produced.

The drying is preferably performed at 40 to 60 °C for 12 to 24 hours.

Hereinafter, the present invention will be described in more detail by way of Examples. These examples are only for illustrating the present invention, and it is apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

X-ray diffraction analysis (XRD, Smart lab, Rigaku), X-ray fluorescence analysis (XRF-1700, Shimadzu) to examine the ingredients, shape, shape, size, etc. of the raw material for indirect carbonation reaction (industrial by-product) and the manufactured calcium carbonate , scanning electron microscopy (SEM, SUPRA-40VP, ZEISS) and laser diffraction particle size analysis (HELOS, Sympatec) were performed. X-ray diffraction analysis was performed using CuK-a radiation at 40 kV/30 mA; 5.0 ˚- 80.0 ˚ range was set at 0.02 ˚ intervals.

The concentration of calcium in seawater, seawater desalination concentrated water, and the solution produced during the reaction was measured using an atomic absorption spectrophotometer (AAS, AA200, Perkin Elmer), and the pH was measured using a pH meter (Orion star 211, Thermo). measured.

Preparation Example 1: Securing of Ca Source for Indirect Carbonation Reaction

In this example, alkali industrial by-products and calcium oxide (CaO) and calcium hydroxide (Ca(OH) ₂ ) reagents were used as raw materials for the indirect carbonation reaction. As the alkali industrial by-products, cement kiln dust (CKD) and paper sludge ash (PSA) were used. Each industrial by-product was sieved through a 425 μm sieve and then used. Calcium oxide is manufactured by Hayashi Pure Chemical Ind. A reagent (assay min. 98%) was used, and for calcium hydroxide, Junsei Chemical reagent (assay min. 96%) was used.

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

ingredient CaO K ₂ O Cl SiO ₂ Al ₂ O ₃ MgO Fe ₂ O ₃ SO ₃ Br TiO ₂ content (wt%) 46.41 21.02 15.74 6.42 2.32 1.27 1.39 3.65 0.54 0.2

Preparation Example 2: Securing seawater and seawater desalination concentrated water

As a solvent for the indirect carbonation reaction, seawater and seawater desalination concentrated water were used. Seawater was taken from the coast, and seawater desalination concentrated water was taken from the seawater desalination plant and used. The seawater and concentrated water were immediately filtered using a 5 ㎛ paper filter (Filter Paper 2, ADVANTEC), and then stored refrigerated.

The pH of the seawater used in this example was 7.97, and as a result of measuring the calcium and magnesium concentrations using an atomic absorption spectrophotometer, it was found to be 474 mg/L and 1,322 mg/L, respectively, which was similar to the components of general seawater.

In addition, the pH of the seawater desalination concentrated water used in this Example was 7.82, and the calcium and magnesium concentrations were 900 mg/L and 3,900 mg/L, respectively.

Example 1: Preparation of calcium eluate using seawater

Seawater or seawater desalination concentrated water is used as a solvent for the indirect carbonation reaction, and industrial by-products such as cement kiln dust (CKD) or paper sludge incineration ash (PSA) are used as raw materials for the indirect carbonation reaction, and also as a raw material for the indirect carbonation reaction. A calcium eluate was prepared using calcium oxide (CaO) and calcium hydroxide (Ca(OH) ₂ ).

Example 1-1:

1 g of cement kiln dust was added to 50 ml of seawater, and the mixture was stirred at 25° C. and 250 rpm for 1 hour. The suspension thus obtained was filtered through a 0.45 μm membrane filter to prepare an eluate.

Examples 1-2:

An eluate was prepared in the same manner as in Example 1-1, except that 2 g of cement kiln dust was added.

Examples 1-3:

An eluate was prepared in the same manner as in Example 1-1, except that 5 g of cement kiln dust was added.

Examples 1-4:

An eluate was prepared in the same manner as in Example 1-1, except that 10 g of cement kiln dust was added.

Examples 1-5:

An eluate was prepared in the same manner as in Example 1-1, except that seawater desalination concentrated water was used instead of seawater.

Examples 1-6:

An eluate was prepared in the same manner as in Example 1-1, except that paper sludge incineration ash was used instead of cement kiln dust.

Examples 1-7:

An eluate was prepared in the same manner as in Example 1-1, except that 2 g of paper sludge incineration ash was added instead of cement kiln dust.

Examples 1-8:

An eluate was prepared in the same manner as in Example 1-1, except that 5 g of paper sludge incineration ash was added instead of cement kiln dust.

Examples 1-9:

An eluate was prepared in the same manner as in Example 1-1, except that 10 g of paper sludge incineration ash was added instead of cement kiln dust.

Examples 1-10:

An eluate was prepared in the same manner as in Example 1-1, except that 5 g of CaO was added instead of the cement kiln dust.

Examples 1-11:

An eluate was prepared in the same manner as in Example 1-1, except that 5 g of Ca(OH) ₂ was added instead of the cement kiln dust.

Comparative Example 1: Preparation of a calcium eluate using a solvent other than seawater

Comparative Example 1-1:

1 g of cement kiln dust was added to 50 ml of distilled water (DI water), and the mixture was stirred at 25° C. and 250 rpm for 1 hour. The suspension thus obtained was filtered through a 0.45 μm membrane filter to prepare an eluate.

Comparative Example 1-2:

1 g of cement kiln dust was added to 0.1 M disodium malonate (disodium malonate, C ₃ H ₂ Na ₂ O ₄ ) in 50 ml, and the mixture was stirred at 25° C. and 250 rpm for 1 hour. The suspension thus obtained was filtered through a 0.45 μm membrane filter to prepare an eluate.

Comparative Examples 1-3:

1 g of cement kiln dust was added to 50 ml of 0.3 M hydrochloric acid (HCl), and the mixture was stirred at 25° C. and 250 rpm for 1 hour. The suspension thus obtained was filtered through a 0.45 μm membrane filter to prepare an eluate.

Comparative Examples 1-4:

1 g of cement kiln dust was added to 50 ml of 0.3 M ammonium chloride (NH ₄ Cl), and the mixture was stirred at 25° C. and 250 rpm for 1 hour. The suspension thus obtained was filtered through a 0.45 μm membrane filter to prepare an eluate.

Example 2: Production of calcium carbonate through indirect carbonation reaction

In this example, all carbonation reactions were carried out under atmospheric pressure and room temperature conditions, and 99.9% carbon dioxide was continuously injected into a 1 L pyrex reactor. The four holes at the top of the reactor were used for carbon dioxide inflow, sampling, stirring, and pH measurement. It was stirred at a constant speed using an impeller (HS-30D, WISD), and pH was measured in real time using a pH meter (Orion star 211, Thermo). The carbon dioxide flow rate was measured and controlled using a gas flow meter and flow controller (TSM-D220, MKP).

Examples 2-1 to 2-11:

1 L of the calcium eluate obtained according to Examples 1-1 to 1-11 was added to the reaction tank, respectively, and alkali was injected before carbon dioxide was injected to adjust the pH to 12.70 or more. Then, while stirring the calcium eluate at 300 rpm, 99.9% carbon dioxide was injected at a flow rate of 3 L/min for carbonation. At this time, it was stirred using an impeller (Ø: 6 mm, l _rod : 530 mm, Ø _blade : 70 mm), and carbon dioxide was injected using a urethane tube (Ø: 6 mm). When the pH of the eluate reached 9-12, the carbonation reaction was terminated, and filtered through a 0.45 μm membrane filter to recover a white solid and a filtrate. In order to increase the purity of calcium carbonate, the solid was washed thoroughly with water and dried at 60° C. for 24 hours to prepare calcium carbonate.

Examples 2-12:

Calcium carbonate was prepared in the same manner as in Example 2-1, except that an impeller having a diameter of 50 mm was used instead of an impeller having a diameter of 70 mm.

Examples 2-13:

Calcium carbonate was prepared in the same manner as in Example 2-12, except that the calcium eluate was stirred at 500 rpm.

Examples 2-14:

Calcium carbonate was prepared in the same manner as in Example 2-12, except that the calcium eluate was stirred at 800 rpm.

Comparative Example 2: Generation of calcium carbonate through an indirect carbonation reaction using a solvent other than seawater

Comparative Example 2-1:

Calcium carbonate was prepared in the same manner as in Example 2-1, except that the calcium eluate of Comparative Example 1-1 prepared by using distilled water (DI water) as a solvent instead of seawater was used.

Comparative Example 2-2:

Except for using the calcium eluate of Comparative Example 1-2 prepared by using 0.1 M disodium malonate (disodium malonate, C ₃ H ₂ Na ₂ O ₄ ) as a solvent instead of seawater, Example 2-1 and Calcium carbonate was prepared by the same method.

Comparative Example 2-3:

Calcium carbonate was prepared in the same manner as in Example 2-1, except that the calcium eluate of Comparative Example 1-3 prepared by using 0.3 M hydrochloric acid (HCl) as a solvent instead of seawater was used.

Comparative Example 2-4:

Calcium carbonate was prepared in the same manner as in Example 2-1 except for using the calcium eluate of Comparative Example 1-4 prepared by using 0.3 M ammonium chloride (NH ₄ Cl) as a solvent instead of seawater. prepared.

Experimental Example 1: Calcium concentration and pH change according to the change in the solid-liquid ratio of various raw materials and seawater

The calcium concentration and pH change of the eluate according to the change in the solid-liquid ratio of the raw material and the solvent for the indirect carbonation reaction in Examples 1-1 to 1-11 are shown in Table 3 and FIG. 2 below.

Raw material solvent division Solid-liquid ratio (g/mL) Calcium concentration (mg/L) pH CKD sea water Example 1-1 1:50 (1/50) 3507 12.53 Example 1-2 1:25 (1/25) 3647.5 12.57 Examples 1-3 1:10 (1/10) 3321.5 12.61 Examples 1-4 1:5 (1/5) 2572.5 12.67 Seawater desalination concentrated water Examples 1-5 1:50 (1/50) 3903 11.44 PSA sea water Examples 1-6 1:50 (1/50) 2532 11.92 Examples 1-7 1:25 (1/25) 2465.5 12.5 Examples 1-8 1:10 (1/10) 2324 12.57 Examples 1-9 1:5 (1/5) 1819.5 12.6 CaO sea water Examples 1-10 1:10 (1/10) 3692 12.52 Ca(OH) ₂ sea water Examples 1-11 1:10 (1/10) 2876 12.41

Referring to Table 3, as the solid-liquid ratio (g/mL) of industrial by-products and seawater increased, the calcium concentration decreased and the pH increased. When the solid-liquid ratio was 1:25-1:50, the calcium concentration of the eluate was the highest, and the maximum calcium concentration was 3648 mg/L and 2532 mg/L when CKD and PSA were used, respectively. All of the eluates had a pH of 11.9 or higher. When seawater desalination concentrated water was used as a solvent, the results were similar to those when seawater was used. Calcium concentration and pH were 3903 mg/L and 11.4, respectively. In addition, when calcium oxide and calcium hydroxide were used as calcium sources, calcium concentrations were 3692 and 2876 mg/L, respectively, and pHs were 12.52 and 12.41, respectively, which were similar to those when industrial by-products were used.

Among Examples 1-1 and 1-2, Example 1-1, which had a slightly lower calcium concentration, was determined as the optimal condition for the following reasons.

The solid-liquid ratios of Examples 1-1 and 1-2 are 1:50 and 1:25, respectively, which means that in Example 1-2 based on the same volume of seawater, industrial by-products are used twice as much as 1-1 do. Therefore, in both cases, if the calcium concentration of the eluate is similar, the amount of calcium eluted per unit weight of the industrial by-product in Example 1-1, in which the amount of industrial by-products used is half, is twice as large.

In the indirect carbonation reaction, the calcium concentration and pH of the eluate are important factors that determine the efficiency of the carbonation reaction. The more calcium is eluted from the industrial by-products and the higher the pH of the eluate is, the more favorable the carbonation reaction is. Therefore, it was found that the calcium eluate of Example 1-1 having a high calcium concentration and pH is advantageous for the indirect carbonation reaction.

Experimental Example 2: Comparison of calcium concentration and pH change of calcium eluate using 5 solvents including seawater

The calcium concentration and pH change of Examples 1-1 and 1-5 and Comparative Examples 1-1 to 1-4 using seawater and seawater desalination concentrated water were compared and shown in Table 4 below.

Raw material solvent division Calcium concentration (mg/L) pH CKD sea water Example 1-1 3507 12.53 Seawater desalination concentrated water Examples 1-5 3903 11.44 DI water Comparative Example 1-1 1322 12.99 0.1 MC ₃ H ₂ Na ₂ O ₄ Comparative Example 1-2 1672 12.82 0.3 M HCl Comparative Example 1-3 5340 6.71 0.3 M NH ₄ Cl Comparative Example 1-4 5524 9.92

Referring to Table 4, in the case of Examples 1-1 and 1-5 using seawater and seawater desalination concentrated water, the pH was 12.53 and 11.44, respectively, and the calcium concentration was 3507 and 3903 mg/L, respectively.

On the other hand, in Comparative Example 1-1 using distilled water, it was confirmed that more calcium was eluted when seawater and seawater desalination concentrated water were used than when distilled water was used.

In addition, it can be seen that the calcium concentration in Comparative Examples 1-3 and 1-4 using 0.3 M HCl or 0.3 M NH ₄ Cl, which were used as solvents for conventional indirect carbonation, was higher than that of seawater, but chemical It has great significance to elute more than 3,500 mg/L of calcium using only pure seawater without the use of chemicals.

Experimental Example 3: Comparison of shape, size and purity of calcium carbonate produced using various raw materials and seawater

The crystal form, particle size, and purity of the calcium carbonate prepared in Examples 2-1, 2-5, 2-6, 2-10 and 2-11 were analyzed and shown in Table 5 and FIGS. 3 and 4 below.

Raw material solvent division Calcium carbonate crystalline form (%) Particle size (㎛) Purity (%) vaterite calcite CKD sea water Example 2-1 100 0 2.29 96.50 Seawater desalination concentrated water Example 2-5 100 0 4.22 97.41 PSA sea water Example 2-6 97.0 3.0 5.27 95.73 CaO sea water Example 2-10 100 0 - - Ca(OH) ₂ sea water Example 2-11 100 0 - -

Referring to Table 5, when seawater is used as a solvent, the calcium carbonate produced under the carbonation conditions of Examples was almost 100% vaterite regardless of the type of industrial by-products (CKD, PSA). In addition, when seawater was used as a solvent, the resulting calcium carbonate was almost 100% vaterite regardless of the calcium source (CKD, PSA, CaO, Ca(OH) ₂ ). The particle size of the produced calcium carbonate was 2.29-5.27 ㎛, and the purity was as high as 97.4% at most.

3 and 4 are XRD analysis results and SEM analysis results of calcium carbonate produced using various indirect carbonation reaction raw materials and seawater and seawater desalination concentrated water, respectively. Through this, it is demonstrated that almost 100% vaterite is produced in all cases using seawater and seawater desalination concentrated water under the carbonation conditions of the example. In particular, as shown in FIG. 4, when seawater desalination concentrated water was used instead of general seawater as a solvent, elliptical vaterite was produced instead of spherical.

Experimental Example 4: Comparison of shape, size, and production volume of calcium carbonate produced using five solvents including seawater

The particle size, shape, and amount of calcium carbonate produced through the indirect carbonation reaction using CKD and 5 solvents (seawater, distilled water, 0.1 MC ₃ H ₂ Na ₂ O ₄ , 0.3 M HCl, 0.3 M NH ₄ Cl) are listed below. It is shown in Table 6 and FIG. 5 .

solvent division Calcium carbonate crystal form (%) Particle size (㎛) Calcium carbonate production (kg/ton-CKD) vaterite calcite sea water Example 2-1 100 0 2.29 341 DI water Comparative Example 2-1 14.2 85.8 7.24 139 0.1 MC ₃ H ₂ Na ₂ O ₄ Comparative Example 2-2 74.0 26.0 11.49 190 0.3 M HCl Comparative Example 2-3 44.8 55.2 10.38 607 0.3 M NH ₄ Cl Comparative Example 2-4 42.8 57.2 15.39 514

Referring to Table 6, the calcium carbonate produced using five solvents including seawater was vaterite and calcite. When seawater was used as a solvent for the indirect carbonation reaction, the vaterite content of the produced calcium carbonate was 100%, and the vaterite content was significantly higher than when other solvents were used.

In addition, referring to FIG. 5 , as a result of XRD analysis of the calcium carbonate produced by each solvent, only the vaterite peak was confirmed when seawater was used as the solvent, and both vaterite and calcite peaks were confirmed when a solvent other than seawater was used. These results show that seawater is a very advantageous solvent for vaterite production by indirect carbonation reaction.

The calcite and vaterite contents of the produced calcium carbonate were calculated by RaO's equation, and the fractions were calculated using the intensity values of each characteristic peak of calcite and vaterite. Calculation formulas are as in Equations 1 and 2 below.

[Equation 1]

= vaterite (wt.%)

= vaterite (wt.%)

[Equation 2]

f(c)= calcite (wt.%)= 100-f(v)

In Equation 1, I ₁₀₀ , I ₁₀₁ , I ₁₀₂ are the intensity values of the vaterite characteristic peak, and I ₁₀₄ is the intensity value of the calcite characteristic peak. I ₁₀₀ , I ₁₀₁ , and I ₁₀₂ exist in the vicinity of 2θ values of 24.81˚, 27.09˚, and 32.75˚, respectively, and in the case of I ₁₀₄ they exist in the vicinity of 2θ values of 29.32˚.

In addition, the particle size of calcium carbonate produced using seawater was 2.29 μm, which was significantly smaller than when other solvents were used. Also, when seawater was used as a solvent, the amount of generated calcium carbonate (vaterite) was 341 kg/ton-CKD, which was higher than when other solvents were used.

Experimental Example 5: Analysis of the effect of carbonation reaction conditions on the formation of vaterite-type and calcite-type calcium carbonate

The form, particle size, and purity of calcium carbonate produced under various impeller diameters and stirring speed conditions were compared and shown in Table 7 and FIG. 6 .

division Ø _blade (mm) RPM CO ₂ flow rate (L/min) CaCO ₃ morphology (%) Particle size (㎛) Purity (%) vaterite calcite Example 2-1 70 300 3.0 100 0 2.29 96.50 Example 2-12 50 300 3.0 36.1 63.9 2.23 98.78 Examples 2-13 50 500 3.0 72.0 28.0 1.96 96.56 Examples 2-14 50 800 3.0 97.0 3.0 2.40 98.19

Referring to Table 7, the larger the impeller diameter, the greater the vaterite content of the produced calcium carbonate. For example, when the other conditions were the same and the impeller diameters were different as 70 mm and 50 mm, the vaterite content of the produced calcium carbonate was 100.0% and 36.1%, respectively (Example 2-1, Example 2) -12). The same conditions except for the impeller diameter were a stirring speed of 300 rpm and a CO ₂ flow rate of 3.0 L/min.

And when the impeller diameter was small (Ø _blade : 50 mm), the vaterite content was greatly increased as the stirring speed increased (Examples 2-12 to 2-14). For example, as the stirring speed increased to 300, 500, and 800 rpm, the vaterite content increased to 36.1%, 72.0%, and 97.0%, respectively. Conversely, as the stirring speed decreased to 800, 500, and 300 rpm, the calcite content increased to 3.0%, 28.0%, and 63.9%.

The SEM analysis result of FIG. 6 demonstrates that almost 100% vaterite is produced when an impeller with a large diameter (70 mm) or a high stirring speed (800 rpm) is used. This result shows that although seawater is beneficial for vaterite formation, certain conditions (impeller diameter, stirring speed) must be satisfied to produce calcium carbonate with high vaterite content.

On the other hand, even when the impeller diameter and stirring speed conditions were changed, the particle size and purity of calcium carbonate hardly changed. The particle size of calcium carbonate produced in all experiments was very small, 1.96-2.40 ㎛, and the purity was very high, 96.50-98.78%.

As the specific part of the present invention has been described in detail above, for those of ordinary skill in the art to which the present invention pertains, it is clear that these specific techniques are only preferred embodiments, and the scope of the present invention is not limited thereto. Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Since the high-purity vaterite-type and calcite-type calcium carbonate according to the present invention is manufactured through an indirect carbonation reaction using an alkali industrial by-product, a waste resource, and low-cost or free seawater, A manufacturing method may be provided.

Claims (12)

(i) The raw material for indirect carbonation reaction is mixed at a ratio of 1.0 to 10.0 g per 50 ml of seawater and stirred, so that magnesium (Mg) present in seawater is precipitated, and calcium (Ca) present in the raw material for indirect carbonation reaction is eluted preparing a calcium eluate;
(ii) removing the precipitated magnesium in the calcium eluate;
(iii) injecting carbon dioxide into the calcium eluate from which magnesium has been removed to obtain vaterite-type and calcite-type calcium carbonate (CaCO ₃ ); and
(iv) washing the vaterite type and calcite type calcium carbonate (CaCO ₃ ) with water to increase the purity to 99wt% or more; Method for producing type calcium carbonate. According to claim 1,
High-purity vaterite type and calcite type using indirect carbonation of seawater, characterized in that stirring is performed using an impeller in step (iii), and the content of vaterite type calcium carbonate increases as the stirring intensity increases Method for producing calcium carbonate. 3. The method of claim 2,
In the step (iii), the stirring is a method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater, characterized in that the carbon dioxide is injected into the calcium eluate at the same time. According to claim 1,
When the ionic strength of the seawater is 0.15M or more, it is stirred using an impeller in step (iii), and as the stirring strength increases, the content of elliptical vaterite-type calcium carbonate increases. A method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater. The method of claim 1,
High-purity vaterite type and calcite type using indirect carbonation of seawater, characterized in that stirring is performed using an impeller in step (iii), and the content of calcite type calcium carbonate increases as the stirring strength decreases Method for producing calcium carbonate. According to claim 1,
A high-purity vaterite type using indirect carbonation of seawater, characterized in that the pH of the calcium eluate is adjusted to 12.70 or higher by adding an alkali to the calcium eluate before carbon dioxide is injected to increase the carbonation efficiency in step (iii); Method for producing calcite-type calcium carbonate. 7. The method of claim 6,
The alkali is aqueous ammonia (NH ₄ OH), sodium hydroxide (NaOH) or potassium hydroxide (KOH), characterized in that the method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater. According to claim 1,
When the pH of the eluate reaches the range of 9 to 12 in step (iii), the method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater, characterized in that the injection of carbon dioxide is stopped . The method of claim 1,
The method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater, characterized in that the average particle diameter of the calcium carbonate is controlled in the range of 1.0 to 5.0 μm. The method of claim 1,
The seawater is high-purity vaterite type and calcite using indirect carbonation of seawater, characterized in that any one selected from the group consisting of general seawater, seawater desalination concentrated water, brine, bittern and mixtures thereof Method for producing type calcium carbonate. The method of claim 1,
The indirect carbonation reaction raw material is paper sludge ash (PSA), cement kiln dust (CKD), fuel ash (fuel ash), bottom ash (bottom ash), fly ash (fly ash), deinked ash (de-inking ash), steelmaking slag, waste concrete, and high-purity vaterite-type and calcite-type carbonic acid using indirect carbonation of seawater, characterized in that any one selected from alkali industrial by-products consisting of waste concrete and mixtures thereof Method for producing calcium. The method of claim 1,
The indirect carbonation reaction raw material is CaO or Ca(OH) ₂ Method for producing high-purity vaterite-type and calcite-type calcium carbonate using indirect carbonation of seawater, characterized in that.

Images