KR20200141798A - A method for producing high purity aragonite calcium carbonate using seawater - Google Patents

Abstract

The present invention relates to a method for producing high-purity aragonite-type calcium carbonate using indirect carbonation of seawater. Particularly, the present invention relates to a method for producing high-purity aragonite-type calcium carbonate with excellent economic efficiency by using a small amount of magnesium chloride hexahydrate (MgCl_2·6H_2O), which is a magnesium additive, by using seawater as an indirect carbonation solvent.

Description

Method for producing high purity aragonite calcium carbonate using seawater}

The present invention relates to a method of producing high-purity aragonite-type calcium carbonate using seawater.

Calcium carbonate largely has more than three homogeneities: calcite, aragonite, and vaterite. Calcite is the most common because it has a hexahedral structure and is the most stable form of calcium carbonate. Aragonite is a needle-shaped or orthorhombic particle, and batterite is a spherical particle, both of which are metastable compared to calcite.

Aragonite, which has a large aspect ratio, can improve strength, improve whiteness, and control opacity when added industrially to rubber, plastic, paint fillers or paper pigments, so it is a new functional inorganic powder that can impart mechanical and optical properties. Is in the limelight.

Aragonite is produced under high temperature conditions of 60-80°C or higher or in the presence of magnesium ions. When the precipitation reaction of calcium carbonate occurs under these conditions, the initial calcium carbonate is produced in the form of Magnesian Calcite, not calcite. The magnesian calcite has a higher solubility than the existing calcite-type calcium carbonate, thereby generating aragonite. As such, aragonite is more expensive than other forms of calcium carbonate, so it is more expensive and is the most expensive form.

Aragonite is mostly prepared in a state in which the Mg/Ca molar ratio is adjusted to about 3 to 5. This means that about 3 to 5M of magnesium is required to precipitate 1M of calcium into aragonite-type calcium carbonate. As the magnesium additive, magnesium chloride hexahydrate (MgCl _{2 ·} 6H ₂ O) is mainly used, and the amount used at this time is about 610 to 1000 g, which requires a considerably large amount. The cost of magnesium chloride hexahydrate on the market is about $250 per ton, so the cost of magnesium chloride hexahydrate added to produce one ton of aragonite-type calcium carbonate is $1525 to 2500. Due to the amount of such additives, the overall production cost of aragonite is increased, and thus economic feasibility is poor.

Therefore, development of a method for producing high-purity aragonite calcium carbonate by improving production economy is required.

Korean Patent Registration No. 1090432

An object of the present invention in a method for producing high purity aragonite type calcium carbonate,

It is intended to provide a method for producing high-purity aragonite-type calcium carbonate in an economical way by reducing the amount of magnesium chloride hexahydrate (MgCl _{2 ·} 6H ₂ O) used as a magnesium additive.

On the one hand, the present invention

(i) preparing a suspension in which calcium raw materials are added to seawater;

(ii) adding a magnesium raw material to the solution to adjust the Mg/Ca molar ratio to be 0.5 to 5.0; And

(iii) performing an indirect carbonation reaction by stirring while injecting carbon dioxide into the solution whose molar ratio of Mg/Ca is adjusted to obtain aragonite-type calcium carbonate (CaCO ₃ ); including, using seawater It provides a method for producing high-purity aragonite-type calcium carbonate.

According to the present invention, by using low-cost or free seawater as a solvent, high-purity aragonite-type calcium carbonate is economical even when a small amount of magnesium chloride hexahydrate (MgCl ₂ 6H ₂ O) is used. It can be manufactured with

1 shows an overall process diagram of a method for producing aragonite-type calcium carbonate according to an embodiment of the present invention.
Figure 2 shows the XRD analysis results of calcium carbonate generated according to the Mg/Ca molar ratio change when artificial seawater and distilled water according to an embodiment of the present invention are used as a solvent (c: calcite (CaCO ₃ ), m: magnesian calcite, a: aragonite (CaCO ₃ )).
3 shows the results of SEM analysis of aragonite-type calcium carbonate generated when artificial seawater according to an embodiment of the present invention is used as a solvent.
Figure 4 shows the XRD analysis results of calcium carbonate generated according to the Mg/Ca molar ratio change when artificial seawater according to an embodiment of the present invention is used as a solvent ((a): Mg/Ca 0.5, (b) : Mg/Ca 0.6, (c): Mg/Ca 0.7, (d): Mg/Ca 0.8 (c: calcite (CaCO ₃ ), a: aragonite (CaCO ₃ ))).
Figure 5 shows the XRD analysis results of calcium carbonate generated under various carbon dioxide flow conditions when artificial seawater according to an embodiment of the present invention is used as a solvent (c: calcite (CaCO ₃ ), a: aragonite (CaCO ₃ ), b: brucite (Mg(OH) ₂ ).

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

The present invention relates to a method of producing high-purity, high-content aragonite crystalline calcium carbonate by using seawater as a solvent and adding a calcium raw material and a magnesium raw material to the seawater to react indirect carbonation (see FIG. 1 ). ).

A method for producing high-purity aragonite-type calcium carbonate using seawater according to an embodiment of the present invention,

(i) preparing a suspension in which calcium raw materials are added to seawater;

(ii) adding a magnesium raw material to the solution to adjust the Mg/Ca molar ratio to be 0.5 to 5.0; And

(iii) performing an indirect carbonation reaction by stirring while injecting carbon dioxide into the solution in which the molar ratio of Mg/Ca is adjusted to obtain aragonite-type calcium carbonate (CaCO ₃ ); characterized by comprising: .

In one embodiment of the present invention, first, a calcium raw material is added to the seawater.

The calcium raw material is for an indirect carbonation reaction, and a calcium compound such as calcium oxide (CaO) and calcium hydroxide (Ca(OH) ₂ ) may be used, but is not limited thereto.

The seawater includes, but is not limited to, general seawater, seawater desalination concentrated water, brine, bittern, and artificial seawater. In addition, seawater filtered using a membrane filter or the like may be used to filter out impurities present in seawater. Table 1 below shows the average concentration of main ions dissolved in general seawater.

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

In one embodiment of the present invention, magnesium chloride hexahydrate (MgCl ₂ 6H ₂ O) aqueous solution is added to the mixture of seawater and calcium raw material to adjust the molar ratio of Mg/Ca to 0.5 to 5.0. The Mg/Ca molar ratio is preferably 0.5 to 1.0, more preferably 0.5 to 0.8.

When the molar ratio of Mg/Ca is 0.5 to 0.8, aragonite-type calcium carbonate in an amount of about 80.0% or more may be prepared.

In the manufacturing method according to the present invention, even when the molar ratio of Mg/Ca is 0.5 to 0.8, the molar ratio of Mg/Ca is 0.5 to 0.8 in order to show excellent economic efficiency as it exhibits high purity compared to the case of 1.0 to 5.0. More preferable.

Conventionally, when distilled water or other solvents are used as the solvent for indirect carbonation, the content of aragonite is about 50 to 87%, and the purity is low even when the molar ratio of Mg/Ca is as high as 3.0 to 5.0.

Accordingly, according to the present invention, by using seawater as a reaction solvent, the molar ratio of Mg/Ca can be reduced to 0.5 to 0.8, thereby reducing the amount of magnesium additive used, thereby effectively reducing the production cost of aragonite-type calcium carbonate.

Next, carbon dioxide is injected into a solution in which the molar ratio of Mg/Ca is adjusted 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 in the eluate to form calcium carbonate (CaCO ₃ ). The dissolution of carbon dioxide and the formation of calcium carbonate can be represented by Equation 1 below.

[Equation 1]

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 Equation 1 above, it can be seen that hydrogen ions (H ⁺ ) are generated in the process of forming carbonate ions (CO ₃ ^2- ) by dissolving carbon dioxide (CO ₂ ) in the eluate, and thus calcium carbonate formation As the harmful carbon dioxide is injected, the pH of the eluate is gradually lowered.

According to an 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 solution, and when the pH of the eluate reaches 7.5 or less, the injection and stirring of carbon dioxide are stopped to cause carbonation. It is preferable to terminate the reaction.

At this time, it is preferable to inject the carbon dioxide at a flow rate of 0.15 L/min or more (based on 1 L of solution). When carbon dioxide is injected at less than 0.15 L/min, the carbonation reaction does not proceed completely, so that a sufficient amount of aragonite calcium carbonate may not be produced.

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

In the present invention, calcium hydroxide (Ca(OH) ₂ , >96.0%) and magnesium chloride hexahydrate (MgCl _2· 6H ₂ O, >98.0%) were used as raw materials for calcium and magnesium, respectively. As the solvent, artificial seawater and distilled water were used, and the artificial seawater was prepared by the method of Kester et.al. (1967).

Examples 1 to 5: Preparation of aragonite-type calcium carbonate using artificial seawater

When calcium hydroxide and magnesium chloride hexahydrate were added to 1 L of artificial seawater, the Mg/Ca molar ratio was adjusted to be 0, 1, 2, 3, and 5, respectively. The temperature of seawater (suspension) to which calcium and magnesium were added was adjusted to 80° C., and 99.9% carbon dioxide was injected at a flow rate of 2.0 L/min. The resulting solid was filtered through a 0.45 μm membrane filter and dried at 60° C. for 24 hours to prepare calcium carbonate.

Comparative Examples 1 to 5: Preparation of aragonite-type calcium carbonate using distilled water

Calcium carbonate was prepared in the same manner as in Examples 1 to 5, except that distilled water was used instead of artificial seawater.

Changes in the form of calcium carbonate prepared in Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Table 2 below. In addition, X-ray diffraction analysis (XRD, Smart lab, Rigaku) and scanning electron microscope analysis (SEM, MIRA-3, Tescan) results of the calcium carbonate prepared in Examples 1 to 5 and Comparative Examples 1 to 5 are shown in FIG. 2 And shown in 3.

division Mg/Ca mole ratio artificial seawater division Mg/Ca mole ratio DI water CaCO ₃ morphology particle size
(μm) CaCO ₃ morphology aragonite
(%) calcite
(%) aragonite
(%) calcite ^* or magnesian calcite ^**
(%) Example 1 0 39.1 60.9 3.85 Comparative Example 1 0 0 100 ^* Example 2 One 95.8 4.2 4.27 Comparative Example 2 One 0 100 ^** Example 3 2 96.4 3.6 4.61 Comparative Example 3 2 58.4 41.6 ^** Example 4 3 95.0 5.0 3.27 Comparative Example 4 3 65.4 34.6 ^** Example 5 5 96.0 4.0 5.46 Comparative Example 5 5 87.4 12.6 ^**

Referring to Table 2, when artificial seawater was used as a solvent, the aragonite content of calcium carbonate produced when the Mg/Ca ratio was 1 or more was very high, about 95%. On the other hand, when distilled water was used as a solvent, it was found that when the Mg/Ca ratio was 1, the aragonite content was 0%, and even when the ratio was 3, the aragonite content was 65%.

In addition, calcium carbonate produced by using artificial seawater as a solvent appeared as a mixture of aragonite and calcite, but in the case of distilled water, it was not in the form of calcite, but in the form of magnesian calcite (Ca _0.871 Mg _0.129 CO ₃ ). This is because the solubility of magnesian calcite is higher in seawater than in distilled water, and it is a result indicating that aragonite synthesis is easier in seawater.

The average particle diameter of calcium carbonate produced when artificial seawater was used was in the range of about 3-5 μm, regardless of the Mg/Ca ratio.

Examples 6 to 9: Measurement of the minimum Mg/Ca molar ratio for preparing a high content of aragonite-type calcium carbonate using artificial seawater

When generating aragonite using artificial seawater as a solvent, the experiment was conducted by adjusting the Mg/Ca molar ratio in artificial seawater to 1 or less in order to derive the minimum Mg/Ca ratio capable of generating aragonite with a high content.

When calcium hydroxide and magnesium chloride hexahydrate were added to 1 L of artificial seawater, the Mg/Ca molar ratios were adjusted to be 0.5, 0.6, 0.7, and 0.8, respectively. The temperature of seawater (suspension) to which calcium and magnesium were added was adjusted to 80°C, and then 99.9% carbon dioxide was injected at a flow rate of 0.15 L/min. The resulting solid was filtered through a 0.45 μm membrane filter and dried at 60° C. for 24 hours to prepare calcium carbonate.

The change in the form of calcium carbonate according to the change in the Mg/Ca molar ratio prepared in Examples 6 to 9 is shown in Table 3 below. In addition, the results of X-ray diffraction analysis (XRD, Smart lab, Rigaku) of calcium carbonate prepared in Examples 6 to 9 are shown in FIG. 4.

division Mg/Ca
mole ratio artificial seawater CaCO ₃ morphology particle size
(μm) aragonite
(%) calcite
(%) Example 6 0.5 81.3 18.7 3.30 Example 7 0.6 88.0 12.0 2.91 Example 8 0.7 93.4 6.6 3.04 Example 9 0.8 95.6 4.4 2.95

Referring to Table 3, when the Mg/Ca molar ratio was 0.5, the content of aragonite was about 81.3%, and as the Mg/Ca molar ratio increased, the content of aragonite increased. When the Mg/Ca molar ratio was 0.8, the same as when the Mg/Ca molar ratio was 1 to 5, calcium carbonate having an aragonite content of about 96% was produced.

Therefore, in the case of distilled water, when the Mg/Ca molar ratio is about 2 to 5, 58-87% aragonite was produced, whereas in seawater, even if the Mg/Ca molar ratio was as low as 0.8, aragonite having a content of about 96% could be produced.

Experimental Example 1: Effect of carbon dioxide flow rate when preparing aragonite-type calcium carbonate using artificial seawater

When calcium hydroxide and magnesium chloride hexahydrate were added to 1 L of artificial seawater, the Mg/Ca molar ratio was adjusted to be 0.5 and 0.7, respectively. The temperature of seawater (suspension) to which calcium and magnesium were added was adjusted to 80° C., and then 99.9% carbon dioxide was adjusted at a flow rate of 0.02, 0.10, and 0.15 L/min. The resulting solid was filtered through a 0.45 μm membrane filter and dried at 60° C. for 24 hours. The results are shown in Table 4 below.

Mg/Ca mole ratio CO ₂ flow rate
(L/min) artificial seawater CaCO ₃ morphology final
pH aragonite
(%) calcite
(%) 0.5 0.02 - 8.91 0.5 0.15 81.3 18.7 6.40 0.7 0.02 - 8.61 0.7 0.1 - 8.45 0.7 0.15 93.4 6.6 7.16

Referring to Table 4, for all the tested Mg/Ca molar ratios (0.5, 0.7), when the carbon dioxide flow rate was 0.02, 0.1 L/min, the carbonation reaction did not proceed completely. That is, according to the XRD analysis result of FIG. 5, Mg(OH) ₂ was included in the generated solid. However, when the flow rate was 0.15 L/min, 100% carbonation reaction was completed, and the content of aragonite was about 81-93%. As shown in the XRD results of FIG. 5, Mg(OH) ₂ was not included in the resulting solid, and only calcium carbonate (aragonite, calcite) peaks appeared.

When calcium hydroxide and magnesium chloride hexahydrate are added to seawater, magnesium is precipitated as Mg(OH) ₂ and calcium is dissolved at the same time. The precipitation and calcium dissolution reaction of Mg(OH) ₂ can be expressed as Equation 2 below, which corresponds to a reaction in which equilibrium is dominant (K ≒ 10 ¹¹ ) as a positive reaction.

[Equation 2]

Mg ²⁺ + Ca(OH) ₂ (s) → Mg(OH) ₂ (s) + Ca ²⁺

Mg(OH) ₂ generated in Equation 2 is dissolved as Mg ²⁺ as the carbonation reaction proceeds, and the dissolved Mg ²⁺ contributes to the aragonite formation reaction. In addition, Mg(OH) ₂ acts as an alkali to facilitate carbonation reaction.

Therefore, the fact that Mg(OH) ₂ is included in the generated solid means that the carbonation reaction has not been completed, and the aragonite content may be low because the aragonite generation reaction does not proceed sufficiently.

When the resulting solid contained Mg(OH) ₂ , the final pH value of the solution was high as 8.60 to 8.90, but if not, the pH was relatively low as 6.40 to 7.20.

Under the conditions according to the present invention, when the carbon dioxide flow rate was 0.15 L/min or more and the final pH value of the solution was 7.50 or less, all Mg(OH) ₂ was dissolved to complete the carbonation reaction, and a high content of aragonite was produced. That is, it was found that in order to generate aragonite with a high content, not only the Mg/Ca molar ratio but also the carbon dioxide flow rate should be considered.

As described above, specific parts of the present invention have been described in detail, and it is obvious that these specific techniques are only preferred embodiments and are not intended to limit the scope of the present invention for those of ordinary skill in the art to which the present invention belongs. Do. Those of ordinary skill in the art to which the present invention belongs will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Therefore, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (6)

(i) preparing a suspension in which calcium raw materials are added to seawater;
(ii) adding a magnesium raw material to the solution to adjust the Mg/Ca molar ratio to be 0.5 to 5.0; And
(iii) performing an indirect carbonation reaction by stirring while injecting carbon dioxide into the solution whose molar ratio of Mg/Ca is adjusted to obtain aragonite-type calcium carbonate (CaCO ₃ ); including, using seawater Method for producing high-purity aragonite-type calcium carbonate. The method of claim 1, wherein in step (ii), the molar ratio of Mg/Ca is adjusted to be 0.5 to 1.0. The method of claim 1, wherein the stirring in step (iii) is performed simultaneously with injecting carbon dioxide into the solution at 0.15 L/min or more. The method of claim 1, wherein the seawater is any one selected from the group consisting of general seawater, seawater desalination concentrated water, brine, bittern, artificial seawater, and mixtures thereof. Method for producing calcium carbonate. The method of claim 1, wherein the calcium raw material is calcium oxide (CaO) or calcium hydroxide (Ca(OH) ₂ ), and high purity aragonite-type calcium carbonate using seawater. The method of claim 1, wherein the magnesium raw material is magnesium chloride hexahydrate (MgCl _{2 ·} 6H ₂ O), and high purity aragonite type calcium carbonate using seawater.

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