Method for preparing calcium carbonate using oyster shells

Abstract

The present invention relates to a method for producing calcium carbonate, and calcite-type calcium carbonate produced thereby, wherein the method comprises the steps of: reacting oyster shells with an acid solution to prepare a calcium chloride solution; filtering the prepared calcium chloride solution; adding sodium carbonate to the filtered calcium chloride solution and stirring same to prepare recrystallized calcium carbonate; subjecting the recrystallized calcium carbonate to solid-liquid separation; and washing and drying the separated calcium carbonate. According to the method of the present invention, high-purity calcium carbonate can be mass-produced and thus can be advantageously used for relevant purposes.

Description

Method for producing calcium carbonate using oyster shells

[0001] The present invention relates to a method for producing calcium carbonate using oyster shells.

[0002] Blue carbon is a carbon sink in marine ecosystems, including marine life, including salt-producing plants, tidal flats, and seagrass. While scientific research and policy on blue carbon are still in their infancy compared to terrestrial carbon sinks, the international community is focusing on its potential for carbon neutrality and climate crisis response.

[0003] Oyster shells, in particular, are attracting attention as a new candidate for blue carbon, and their carbon absorption mechanism is related to the carbonate system of seawater. Carbon dioxide in the atmosphere dissolves in seawater and changes into bicarbonate and carbonate, and when clams or oysters combine this with calcium ions to form shells (calcium carbonate (CaCO3)), carbon dioxide is absorbed and fixed. Although some carbon dioxide is released through respiration during this process, the carbon absorbed is greater than the carbon emitted, as approximately 70% (-) is removed through shells, biomass, and sediment deposition, while approximately 30% (+) is released through calcification, respiration, and decomposition. Therefore, it is expected that oyster shells can be recognized as a new blue carbon.

[0004] Currently, oyster shells are most commonly recycled by being crushed and used as fertilizer. However, even this amount is gradually increasing due to factors such as the high production cost of oyster shell fertilizer and sluggish consumption. A significant portion of these unrecycled shells are currently left abandoned on the coast, necessitating the urgent development of a solution for their disposal.

[0005] The inventors of this invention have diligently researched effective methods for recycling oyster shells. As a result, they have developed a method for mass-producing high-purity calcium carbonate from oyster shells, thereby completing the present invention.

[0006] Accordingly, an object of the present invention is to provide a method for producing calcium carbonate.

[0007] Another object of the present invention is to provide calcite-type calcium carbonate manufactured by the above method.

[0008] The inventors of this invention have diligently researched effective methods for recycling oyster shells. As a result, they have discovered a method for mass-producing high-purity calcium carbonate from oyster shells.

[0009] The present invention relates to a method for producing calcium carbonate from oyster shells and calcite-type calcium carbonate produced thereby.

[0010] Hereinafter, the present invention will be described in more detail.

[0011]

[0012] According to one aspect of the present invention, the present invention provides a method for producing calcium carbonate, comprising the following steps:

[0013] Step 1: Making a calcium chloride (CaCl2) solution by reacting oyster shells with an acid solution;

[0014] The second step is to filter the manufactured calcium chloride (CaCl2) solution;

[0015] The third step is to prepare recrystallized calcium carbonate by adding sodium carbonate (Na2CO3) to the filtered calcium chloride (CaCl2) solution and stirring;

[0016] The fourth step is to separate the recrystallized calcium carbonate into solid and liquid; and

[0017] Step 5: Washing and drying the separated calcium carbonate.

[0018] In one embodiment of the present invention, the oyster shell may be used without pretreatment (e.g., calcination).

[0019] According to one embodiment of the present invention, it was confirmed that the method for producing calcium carbonate of the present invention can increase the purity of calcium carbonate while reducing unnecessary manufacturing processes by using oyster shells without a separate pretreatment (calcination) process.

[0020] In another embodiment of the present invention, the first step is a step of preparing a calcium chloride (CaCl2) solution from oyster shells using an acid solution.

[0021] The above acid solution may be hydrochloric acid (HCl) or acetic acid (CH3COOH), but is not limited thereto.

[0022] According to one embodiment of the present invention, it was confirmed that the method for producing calcium carbonate of the present invention forms calcium carbonate particles in the form of spherical to hexahedral calcite by using hydrochloric acid or acetic acid as the acid solution.

[0023] The above acid solution can be used at a concentration of 3 to 6 M.

[0024] The above acid solution can be used in a volume ratio of 4:0.1 to 1 with oyster shells.

[0025] In another embodiment of the present invention, the second step is a step of filtering the prepared calcium chloride solution to remove solid impurities.

[0026] In another embodiment of the present invention, the third step is a step of producing recrystallized calcium carbonate by adding sodium carbonate (Na2CO3) to a filtered calcium chloride solution and then stirring.

[0027] The above calcium chloride solution and sodium carbonate can be mixed in a volume ratio of 1:1.

[0028] The above stirring can be performed at a speed of 200 to 300 rpm for 4 to 6 hours.

[0029] In another embodiment of the present invention, the fourth step is a step of solid-liquid separation of recrystallized calcium carbonate.

[0030] The above solid-liquid separation can be performed by centrifugation at a speed of 4,500 to 5,500 rpm for 3 to 7 minutes.

[0031] In another embodiment of the present invention, the fifth step is a step of washing and then drying the separated calcium carbonate.

[0032] Distilled water can be used for the above washing.

[0033] According to one embodiment of the present invention, it was confirmed that the method for producing calcium carbonate of the present invention greatly reduces the Na content by using distilled water as the washing solution compared to the method using ethanol.

[0034] The above drying can be performed by drying at 80 to 100°C for 12 hours or more.

[0035] Calcium carbonate (CaCO3), the manufactured product of the present invention, contains calcium ions (Ca 2+ ) and carbonate ions (CO3 2- ) is an ionic compound, and at the beginning of the reaction, it changes from amorphous calcium carbonate (ACC) to three crystalline forms: calcite, aragonite, and vaterite.

[0036] In another embodiment of the present invention, the calcium carbonate produced by the method of the present invention may be in the calcite form.

[0037] Therefore, according to another aspect of the present invention, the present invention provides calcite-type calcium carbonate manufactured by the above-described method for manufacturing calcium carbonate.

[0038] The overlapping contents of the above calcium carbonate manufacturing method and the calcite-type calcium carbonate manufactured thereby are omitted in consideration of the complexity of this specification.

[0039] The present invention relates to a method for producing calcium carbonate and calcite-type calcium carbonate produced thereby. According to the method for producing calcium carbonate of the present invention, mass production of high-purity calcium carbonate is possible, and thus, it can be usefully used for related purposes.

[0040] FIG. 1 is a photograph of calcium carbonate particles manufactured according to one embodiment of the present invention.

[0041] Figure 2 shows the XRD results of calcium carbonate manufactured according to one embodiment of the present invention and calcium carbonate manufactured as a comparative example [addition of a pretreatment step].

[0042] FIGS. 3A to 3C are scanning electron microscope (SEM) photographs of calcium carbonate manufactured according to one embodiment of the present invention and calcium carbonate manufactured using a comparative example [acid solution], wherein FIG. 3A shows the results using hydrochloric acid, FIG. 3B shows the results using acetic acid, and FIG. 3C shows the results using oxalic acid.

[0043] Hereinafter, the present invention will be described in more detail through examples. These examples are intended solely to illustrate the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

[0044]

[0045] Example. Preparation of calcium carbonate

[0046] [Basic] Bulk oyster shells were crushed into 1,000-1,500㎛ sizes (using a multi-mill), and 1g of the crushed powder was added to 5mL of 5M hydrochloric acid (HCl) and reacted at room temperature for 30 minutes. After filtering using a paper filter, 5mL of 1M sodium carbonate (Na2CO3) was added and stirred at 700rpm for 10 minutes. Afterwards, the mixture was washed with ethanol, filtered, and dried at 100℃ for 12 hours to produce calcium carbonate (see Fig. 1).

[0047] [Scale Up] Bulk oyster shells were crushed into 1,000-1,500㎛ sizes, and 235g of the crushed powdered oyster shells were added to 1,000mL of 4M hydrochloric acid (or acetic acid) and reacted at room temperature for 30 minutes. After vacuum filtration twice using a paper filter, 1,000mL of 2M sodium carbonate was added and stirred using an overhead stirrer at 250rpm for 5 hours. (Magnetic stir, stirring at 700rpm is not possible.) Afterwards, solid-liquid separation was performed using a centrifuge (5,000rpm for 5 minutes). Afterwards, the mixture was washed and filtered three times with distilled water and dried at 100℃ for 12 hours to obtain approximately 200g of calcium carbonate.

[0048]

[0049] Comparative Example. [Scale Up] Calcium Carbonate Manufacturing

[0050] [Additional pretreatment step] Calcium carbonate was manufactured in the same manner as in the example, except that the oyster shells were calcined (heated) at 550°C before treatment with the acid solution.

[0051] [Acid solution] Calcium carbonate was prepared in the same manner as in the example, except that oxalic acid was used instead of hydrochloric acid.

[0052] [Washing solution] Calcium carbonate was prepared in the same manner as in the example, except that ethanol was used instead of distilled water.

[0053]

[0054] Experimental Example 1. Component Analysis Using XRD

[0055] The XRD results of calcium carbonate manufactured as an example [Scale Up] and a comparative example [Addition of pretreatment step] are shown in Fig. 2.

[0056] As can be seen in Fig. 2, in the case of the example, calcite-type calcium carbonate was produced, whereas in the case of the comparative example, vaterite-type calcium carbonate was produced, and it was found that not only the shape but also the overall crystal shape and quantity were different.

[0057]

[0058] Experimental Example 2. Observation of particle shape and size

[0059] Calcium carbonate prepared as Example [Scale Up] and Comparative Example [Acid Solution] was observed using a scanning electron microscope (SEM), and the results are shown in Figures 3a to 3c.

[0060] As can be seen in Figures 3a to 3c, in the case of the examples (Figure 3a: hydrochloric acid and 3b: acetic acid), it was found that calcium carbonate particles were formed in the shape of spheres or hexahedrons. On the other hand, in the case of the comparative example (Figure 3c: oxalic acid), it was found that the shape and size of the calcium carbonate were not controlled at all.

[0061]

[0062] Experimental Example 3. Component Analysis Using XRF

[0063] The components of calcium carbonate manufactured by Example [Scale Up] and calcium carbonate of Comparative Example (oyster shell in powder state) were analyzed using an X-ray fluorescence spectrometer (XRF), and the results are shown in Table 1 below.

[0064] Item Implementation Preliminary Comparative Example (Powder) CaO 97.50 91.80 SiO 2 0.18 3.63 Al 2 O 3 0.19 1.05 MgO 0.59 0.69 P 2 O 5 0.50 0.57 SO 3 0.39 0.59 K 2 O 0.01 0.26 TiO 2 0.00 0.09 MnO 0.59 0.06 Fe 2 O 3 0.07 0.66

[0065] Referring to Table 1 above, when the method of the present invention was used, calcium oxide (CaO) was measured to be 97.50 wt%, and when this was converted to calcium carbonate (CaCO3) according to the equation below, it was found that a calcium carbonate recovery rate of approximately 90% was observed. That is, it was found that the purity of calcium carbonate increased by approximately 6% by weight, and it was confirmed that Si and Al were also removed.

[0066]

[0067]

[0068] Next, the components of the calcium carbonate manufactured by Example [Scale Up] and the calcium carbonate manufactured by Comparative Example [Addition of Pretreatment Step] were analyzed using an X-ray fluorescence spectrometer (XRF), and the results are shown in Table 2 below.

[0069] Item implementation comparative example (sintering) CaO 97.50 85.30 SiO 2 0.18 6.61 Al 2 O 3 0.19 2.68 MgO 0.59 0.00 P 2 O 5 0.50 1.52 SO 3 0.39 0.89 K 2 O 0.01 0.11 TiO 2 0.00 0.06 MnO 0.05 0.17 Fe 2 O 3 0.07 1.89

[0070] Referring to Table 2 above, it was found that when oyster shells were calcined (heated) and pretreated before treating with an acid solution, the purity of the final product (calcium carbonate) was greatly reduced.

[0071]

[0072] Finally, the components of the calcium carbonate prepared by Example [Scale Up] and the calcium carbonate of Comparative Example [Washing Solution] were analyzed using an X-ray fluorescence spectrometer (XRF), and the results are shown in Table 3 below.

[0073] Item implementation comparative example (ethanol) Al0.040.06Ca98.4896.20K0.040.10Li0.000.00Na1.193.34Mn0.020.02P0.150.13Si0.010.07Ti0.000.00Fe0.060.07

[0074] Referring to Table 3 above, it can be seen that the Na content is greatly reduced when washing with distilled water compared to washing with ethanol in the final stage.

Claims

1. A method for producing calcium carbonate, comprising the following steps: Oyster shells are reacted with acid solution to produce calcium chloride (CaCl 2 ) Step 1 of preparing a solution; Manufactured calcium chloride (CaCl 2 ) Second step of filtering the solution; Filtered calcium chloride (CaCl 2 ) solution of sodium carbonate (Na 2 CO 3 ) and stirring to produce recrystallized calcium carbonate; Step 4 of solid-liquid separation of recrystallized calcium carbonate; and Step 5: Washing and drying the separated calcium carbonate.

2. In paragraph 1, A method for producing calcium carbonate, wherein the acid solution in the first step is a hydrochloric acid or acetic acid solution.

3. In paragraph 1, A method for producing calcium carbonate, wherein in the third step, calcium chloride solution and sodium carbonate are mixed in a volume ratio of 1:

1.

4. In paragraph 1, A method for producing calcium carbonate, wherein in the third step, stirring is performed at a speed of 200 to 300 rpm for 4 to 6 hours.

5. In paragraph 1, A method for producing calcium carbonate, wherein in the fourth step, solid-liquid separation is performed by centrifugation at a speed of 4,500 to 5,500 rpm for 3 to 7 minutes.

6. In paragraph 1, A method for manufacturing calcium carbonate, wherein in the fifth step, washing is performed using distilled water.

7. In paragraph 1, A method for manufacturing calcium carbonate, wherein the calcium carbonate manufactured by the above manufacturing method is calcite-type calcium carbonate.

8. Calcite-type calcium carbonate manufactured by the method of clauses 1 to 7.

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