Calcium carbonate particles and method for producing the same
By removing conchiolin and chitin from seashells and using emulsion mixing, the method produces nanoparticle-sized calcium carbonate efficiently, addressing the limitations of conventional methods.
Patent Information
- Application Number
- JP2024068310
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-19
- Publication Date
- 2025-10-30
AI Technical Summary
Conventional methods for producing calcium carbonate result in large particle sizes and require time-consuming processes to remove salt from shells, such as desalination or high-temperature treatments.
A method involving the removal of conchiolin and chitin from seashells to obtain nanoparticle-shaped calcium carbonate particles, using a base treatment to form a suspension, followed by mixing water-in-oil emulsions of calcium and carbonate sources to produce nanoparticles.
Enables the production of calcium carbonate nanoparticles in a simple and efficient manner, eliminating the need for lengthy desalination or heat treatments and achieving desired particle sizes.
Smart Images
Figure 2025164373000001 
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Abstract
Description
[Technical Field]
[0001] The present invention relates to calcium carbonate particles and a method for producing the same. [Background technology]
[0002] Calcium carbonate is used in various fields, such as pharmaceuticals, cosmetics, foods, fertilizers, paints, and adhesives. A known method for producing calcium carbonate is, for example, to produce quicklime by calcining limestone, add water to the quicklime, and then blow carbon dioxide gas into the milk of lime. Furthermore, since calcium carbonate is the main component of seashells, crushed seashells are also used as calcium carbonate. Summary of the Invention [Problem to be solved by the invention]
[0003] Conventional methods for producing calcium carbonate have room for improvement. For example, the above-mentioned production method, which includes calcining limestone, has the problem that the particle size of the resulting calcium carbonate is large. Furthermore, when using crushed shells as calcium carbonate, it is necessary to take the time to remove salt contained in the shells beforehand. Therefore, an object of the present invention is to provide a simple method for producing nanoparticle-shaped calcium carbonate particles. [Means for solving the problem]
[0004] The present inventors have found that by removing conchiolin and chitin from seashells, calcium carbonate particles in the form of nanoparticles can be obtained. The present inventors have also found that nanoparticle-shaped calcium carbonate particles can be obtained by mixing a water-in-oil emulsion containing a water-soluble calcium salt with a water-in-oil emulsion containing a water-soluble carbonate.
[0005] The present invention includes the following embodiments. [1] removing conchiolin and chitin from shell powder in water to form a suspension containing first calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising: [2] treating shell powder with a base in water to form a suspension comprising first calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising: [3] The method according to [2], wherein the base comprises at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides. [4] The method according to [2] or [3], wherein the base comprises sodium hydroxide. [5] The method according to any one of [1] to [4], wherein the particle diameter of the first calcium carbonate particles is 30 to 800 nm. [6] The method according to any one of [1] to [5], wherein the size of the shell powder is 0.01 to 10 mm. [7] The method according to any one of [1] to [6], wherein the shells are shells that have not been subjected to a desalting treatment. [8] The method according to any one of [1] to [7], wherein the shells are not heat-treated. [9] The method according to any one of [1] to [8], wherein the shells are not chemically treated.
[10] The method according to any one of [1] to [9], wherein the shells are oyster shells.
[11] isolating the first calcium carbonate particles from the suspension; The method according to any one of [1] to
[10] , further comprising:
[12] purifying the first calcium carbonate particles; The method according to any one of [1] to
[11] , further comprising:
[13] drying the first calcium carbonate particles; The method according to any one of [1] to
[12] , further comprising:
[14] converting the first calcium carbonate particles into a water-soluble calcium salt; The method according to any one of [1] to
[13] , further comprising:
[15] mixing the aqueous solution containing the water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion; mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion; mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in nanoparticle form;
[14] The method for producing a semiconductor device according to
[14] , further comprising:
[16] the water-soluble calcium salt is calcium chloride;
[15] The method according to
[15] , wherein the water-soluble carbonate is sodium carbonate.
[17] The method according to
[15] or
[16] , wherein the second calcium carbonate particles have a particle diameter of 10 to 100 nm.
[18] mixing an aqueous solution containing a water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion; mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion; mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising:
[19] Calcium carbonate particles having a particle diameter of 10 to 100 nm.
[20]
[19] Calcium carbonate particles according to
[19] , which have a spherical shape. [twenty one] The calcium carbonate particles according to
[19] or
[20] , wherein the surfaces of the calcium carbonate particles are not coated with an organic compound. [Effects of the Invention]
[0006] The present invention can provide a simple method for producing calcium carbonate particles in the form of nanoparticles. [Brief explanation of the drawings]
[0007] [Figure 1] FIG. 1 shows an SEM image of the first calcium carbonate particles. [Figure 2] FIG. 2 shows an SEM image of the second calcium carbonate particles. DETAILED DESCRIPTION OF THE INVENTION
[0008] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these and various modifications are possible without departing from the gist of the present invention.
[0009] <First method for producing calcium carbonate particles> One embodiment of the present invention relates to a method for producing calcium carbonate, comprising the step of removing conchiolin and chitin from seashell powder in water to form a suspension comprising first calcium carbonate particles in nanoparticle form (the "suspension-forming step").
[0010] Generally, a shell has a layered structure in which a layer of calcium carbonate crystal particles, a layer of conchiolin, and a layer of chitin are stacked on top of each other, and the high strength of the shell is maintained by the composite of the conchiolin and chitin.
[0011] According to the manufacturing method of this embodiment, by removing conchiolin and chitin from the shells, the calcium carbonate crystalline particles contained in the shells can be released into water. In other words, this method does not require operations such as dissolving the calcium carbonate particles contained in the shells, but simply releases the calcium carbonate particles contained in the shells, so the calcium carbonate particles formed by the shells themselves can be used as they are, making the operation simple. Furthermore, currently, in order to extract calcium carbonate from shells, a desalination treatment in which the shells are dried in the sun for six months or more, or a long-term high-temperature treatment of the shells is required, which takes a long time. In contrast, the production method according to the present embodiment does not require such treatment, and therefore calcium carbonate can be extracted in a short time.
[0012] The conchiolin-chitin complex can be removed, for example, by hydrolysis. Hydrolysis of the complex can be carried out, for example, by treatment with a base. Therefore, one embodiment of the present invention can also be expressed as a method for producing calcium carbonate, which includes treating shell powder with a base in water to form a suspension containing first calcium carbonate particles in nanoparticle form ("suspension formation step").
[0013] [Suspension formation process] The suspension formation step is a step of removing conchiolin and chitin from shell powder in water (e.g., by treating the shell powder with a base) to form a suspension containing first calcium carbonate particles in nanoparticle form.
[0014] (base) The type of base is not particularly limited as long as it can hydrolyze the complex of conchiolin and chitin. Examples of the base include hydroxides of alkali metals and hydroxides of alkaline earth metals. Alkali metal hydroxides include, for example, sodium hydroxide and potassium hydroxide. Examples of the hydroxides of alkaline earth metals include magnesium hydroxide and calcium hydroxide.
[0015] The base may be one type only or a combination of two or more types.
[0016] The conditions for the base treatment (e.g., base concentration, treatment temperature, and treatment time) are not particularly limited and may be changed as appropriate depending on the amount, type, etc. of shells. The base treatment is preferably carried out until all of the conchiolin and chitin are removed (i.e., until all of the calcium carbonate particles contained in the shells are released).
[0017] (shell) The type of shell is not particularly limited, but examples include shells of oysters, scallops, pearl oysters, abalone, mussels, short-necked clams, and cockles. Although not particularly limited, it is preferable to use oyster shells, which are discharged in large quantities as waste.
[0018] It is preferable to use the shells in a crushed form, since the use of powdered shells can increase the rate of removal of conchiolin and chitin, thereby improving the productivity of calcium carbonate particles.
[0019] The size of the shell powder is not particularly limited, but taking into consideration the balance between the productivity of calcium carbonate particles and the labor required for the pulverization process, it is preferably 0.01 to 10 mm, more preferably 0.01 to 8 mm, and even more preferably 0.01 to 5 mm.
[0020] As used herein, the term "shell powder size" means that the amount of powder of that size is 60% by mass or more of the total powder. For example, when the shell powder size is 1 to 5 mm, it means that the amount of powder of 1 to 5 mm is 60% by mass or more of the total powder. Sieving can be used to determine the powder size.
[0021] Except for the crushing of shells, pretreatment of shells is not necessarily required, and examples of such pretreatment include desalination, heat treatment (e.g., heat treatment at 100°C or higher), and chemical treatment (e.g., acid treatment).
[0022] The desalination treatment of shells is a treatment for removing salt contained in the shells. For example, one method of desalination treatment is to leave the shells outdoors for a long period of time (for example, six months or more). Because the desalination treatment takes time, omitting this process can improve the productivity of calcium carbonate particles. In the production method according to this embodiment, the salt contained in the shells can be separated from the calcium carbonate particles together with conchiolin and chitin, so it is not necessarily necessary to remove the salt in advance.
[0023] (suspension) The suspension is formed by removing conchiolin and chitin from shell powder in water, in which first calcium carbonate particles in nanoparticle form are dispersed in water, and the removed conchiolin and chitin, as well as salts and other components contained in the shells, are dissolved in the water.
[0024] The particle diameter of the first calcium carbonate particles is preferably 30 to 800 nm, more preferably 30 to 500 nm, and even more preferably 30 to 200 nm.
[0025] In this specification, the "particle diameter of the first calcium carbonate particles" means the average particle diameter of 100 particles randomly selected from an SEM image of the first calcium carbonate particles dispersed in water ("total particle diameter of each particle / 100").
[0026] [Isolation process] The production method according to this embodiment may further include an isolation step, which is a step of isolating the first calcium carbonate particles from the suspension formed in the suspension formation step.
[0027] The isolation method is not particularly limited, and examples thereof include a method of centrifuging the suspension and a method of filtering the suspension. By performing the isolation step, the first calcium carbonate particles can be separated from the conchiolin, chitin, salt, and the like contained in the shells.
[0028] [Refining process] The production method according to this embodiment may further include a purification step. The purification step is a step of purifying the first calcium carbonate particles. The purification step is preferably carried out after the isolation step.
[0029] The purification method is not particularly limited, but may be, for example, a method in which the first calcium carbonate particles are dispersed in a liquid, followed by the above-mentioned isolation procedure. From the viewpoint of utilizing the calcium carbonate particles formed by the shellfish themselves as they are, it is preferable to use a liquid in which calcium carbonate is insoluble or poorly soluble. Examples of the liquid used in the purification step include water, alcohol (e.g., methanol and ethanol), and mixtures thereof.
[0030] [Drying process] The production method according to this embodiment may further include a drying step. The drying step is a step of drying the first calcium carbonate particles. The drying step is preferably carried out after the purification step.
[0031] The drying step is preferably carried out under conditions that do not convert the first calcium carbonate particles into calcium oxide. The drying method is not particularly limited, but examples thereof include drying under vacuum conditions and drying under low-temperature conditions (for example, 100°C or lower).
[0032] <Second method for producing calcium carbonate particles> One embodiment of the present invention relates to a method for producing a water-in-oil emulsion, comprising the steps of: mixing an aqueous solution containing a water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion (the "first emulsion-forming step"); a step of mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion ("second emulsion formation step"); and mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in nanoparticle form (the "particle formation step").
[0033] According to the production method of this embodiment, an emulsion containing a calcium source and an emulsion containing a carbonate source are mixed and reacted to form calcium carbonate particles that are finer than the first calcium carbonate particles.
[0034] The production method according to this embodiment may be carried out subsequently to the above-mentioned <Production method of first calcium carbonate particles> or may be carried out independently. When carried out subsequently, the first calcium carbonate particles are converted into a water-soluble calcium salt.
[0035] The method for converting the first calcium carbonate particles into a water-soluble calcium salt is not particularly limited, but may be, for example, a method of reacting the first calcium carbonate particles with an acid. For example, when the water-soluble calcium salt is calcium chloride, calcium chloride can be obtained by reacting the first calcium carbonate particles with hydrochloric acid.
[0036] [First emulsion formation step] The first emulsion-forming step is a step of mixing an aqueous solution containing a water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion.
[0037] (Water-soluble calcium salt) As used herein, the term "water-soluble calcium salt" refers to a calcium salt having a solubility of 1 g / 100 ml or more in water at 20°C. The water-soluble calcium salt is not particularly limited, but examples thereof include calcium chloride, calcium nitrate, and calcium acetate. When the water-soluble carbonate used in the second emulsion formation step described below is sodium carbonate, the water-soluble calcium salt is preferably calcium chloride, from the viewpoint of facilitating treatment of the by-product generated in the particle formation step described below (the by-product is sodium chloride).
[0038] (First surfactant) The first surfactant is not particularly limited as long as it can form a water-in-oil emulsion, and examples of the first surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.
[0039] Examples of nonionic surfactants include polyol fatty acid esters, glycerin monostearate, lipophilic glycerin monooleate, ethylene glycol monostearate, propylene glycol monostearate, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene sorbitol fatty acid esters, N-acylamino acid esters, sucrose fatty acid esters, fatty acid alkylolamides, polyoxyethylenated sterols, polyoxyethylenated lanolin, and polyoxyethylenated hydrogenated castor oil.
[0040] Examples of anionic surfactants include lauryl sulfate, polyoxyethylene alkyl ether sulfate, alkylbenzene sulfonate, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, N-acylamino acid salt, sodium stearate, potassium palmitate, sodium cetyl sulfate, sodium lauryl sulfate, triethanolamine palmitate, polyoxyethylene sodium lauryl phosphate, and sodium acyl glutamate.
[0041] Examples of cationic surfactants include benzalkonium chloride, benzethonium chloride, stearyltrimethylammonium chloride, distearyldimethylammonium chloride, and stearyldimethylbenzylammonium chloride.
[0042] Examples of amphoteric surfactants include alkyldiaminoethylglycine hydrochloride, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, lauryldimethylaminoacetic acid betaine, and lecithin.
[0043] The first surfactant may be a single type or a combination of two or more types.
[0044] (First organic solvent) The first organic solvent is not particularly limited as long as it is immiscible with water, and examples of the first organic solvent include aromatic solvents, hydrocarbon solvents, ether solvents, ester solvents, and ketone solvents.
[0045] Aromatic solvents include, for example, benzene, toluene, xylene, and ethylbenzene.
[0046] Examples of hydrocarbon solvents include cyclohexane and hexane.
[0047] Examples of ether solvents include tetrahydrofuran, cyclopentyl methyl ether, 4-methyltetrahydrofuran, and 2-methyltetrahydrofuran.
[0048] Ester solvents include ethyl acetate, butyl acetate, cellosolve acetate, and cellosolve acetate.
[0049] Examples of ketone solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone.
[0050] The first organic solvent may be a single type or a combination of two or more types.
[0051] (First water-in-oil emulsion) The method for forming the first water-in-oil emulsion is not particularly limited, and may be any method including mixing an aqueous solution containing a water-soluble calcium salt, a first surfactant, and a first organic solvent, followed by stirring until a water-in-oil emulsion is formed.
[0052] [Second emulsion formation step] The second emulsion-forming step is a step of mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion.
[0053] (Water-soluble carbonate) As used herein, the term "water-soluble carbonate" refers to a carbonate having a solubility of 1 g / 100 ml or more in water at 20°C. The water-soluble carbonate is not particularly limited, but examples thereof include sodium carbonate, potassium carbonate, and ammonium carbonate. When the water-soluble calcium salt used in the first emulsion formation step described above is calcium chloride, the water-soluble carbonate is preferably sodium carbonate, from the viewpoint of facilitating the treatment of by-products generated in the particle formation step described below (the by-product is sodium chloride).
[0054] (Second surfactant) The second surfactant is not particularly limited as long as it can form a water-in-oil emulsion. Examples of the second surfactant include those exemplified as the first surfactant above. The second surfactant may be the same as or different from the first surfactant. The second surfactant may be a single type or a combination of two or more types.
[0055] (Second organic solvent) The second organic solvent is not particularly limited as long as it is immiscible with water. Examples of the second organic solvent include those exemplified above as the second organic solvent. The second organic solvent may be the same as or different from the first organic solvent. The second organic solvent may be one type or a combination of two or more types.
[0056] (Second water-in-oil emulsion) The method for forming the second water-in-oil emulsion is not particularly limited, and may be any method including mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent, followed by stirring until a water-in-oil emulsion is formed.
[0057] [Particle formation process] The particle formation step is a step of mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in the form of nanoparticles.
[0058] The method for forming the second calcium carbonate particles is not particularly limited, and it is sufficient to stir the water-soluble calcium salt contained in the first water-in-oil emulsion and the water-soluble carbonate contained in the second water-in-oil emulsion so that they react sufficiently.
[0059] The particle size of the second calcium carbonate particles is preferably 10 to 100 nm, more preferably 10 to 60 nm, and even more preferably 10 to 30 nm.
[0060] In this specification, the "particle diameter of the second calcium carbonate particles" means the average particle diameter of 100 particles randomly selected from an SEM image of the second calcium carbonate particles dispersed in water ("total particle diameter of each particle / 100").
[0061] [Isolation process] The production method according to this embodiment may further include an isolation step, which is a step of isolating the second calcium carbonate particles from the reaction liquid obtained in the particle formation step.
[0062] The isolation method is not particularly limited, but examples thereof include a method of centrifuging the reaction solution and a method of filtering the reaction solution.
[0063] [Refining process] The production method according to this embodiment may further include a purification step. The purification step is a step of purifying the second calcium carbonate particles. The purification step is preferably carried out after the isolation step.
[0064] The purification method is not particularly limited, but may be, for example, a method in which the second calcium carbonate particles are dispersed in a liquid, followed by the above-mentioned isolation operation. In the purification step, it is preferable to use a liquid in which calcium carbonate is insoluble or poorly soluble. Examples of the liquid used in the purification step include water, alcohol (e.g., methanol and ethanol), and mixtures thereof.
[0065] [Drying process] The production method according to this embodiment may further include a drying step. The drying step is a step of drying the second calcium carbonate particles. The drying step is preferably carried out after the purification step.
[0066] The drying step is preferably carried out under conditions that do not convert the second calcium carbonate particles into calcium oxide. The drying method is not particularly limited, but examples thereof include drying under vacuum conditions and drying under low-temperature conditions (for example, 100°C or lower).
[0067] <Calcium carbonate particles> One embodiment of the present invention relates to first calcium carbonate particles obtained by the above-mentioned <method for producing first calcium carbonate particles>.
[0068] The particle diameter of the first calcium carbonate particles is preferably 30 to 800 nm, more preferably 50 to 500 nm, and even more preferably 70 to 200 nm.
[0069] The first calcium carbonate particles are preferably spherical in shape.
[0070] The surfaces of the first calcium carbonate particles are preferably not coated with an organic compound.
[0071] One embodiment of the present invention relates to second calcium carbonate particles obtained by the above-mentioned <method for producing second calcium carbonate particles>.
[0072] The particle size of the second calcium carbonate particles is preferably 10 to 100 nm, more preferably 10 to 60 nm, and even more preferably 10 to 30 nm.
[0073] The second calcium carbonate particles are preferably spherical in shape.
[0074] The second calcium carbonate particles preferably have surfaces that are not coated with an organic compound. [Example]
[0075] The present invention will be described in more detail below using examples, but the technical scope of the present invention is not limited to these examples.
[0076] <Production of first calcium carbonate particles> Unwashed oyster shells (5 g) were crushed to obtain powders with sizes of approximately 1–5 mm. Oyster shell powder (5 g) and sodium hydroxide (11.98 g) were placed in a conical tube, and purified water (50 g) was added little by little. The mixture was stirred at 1000 rpm using a magnetic stirrer for approximately 2 hours to form a milky white suspension containing calcium carbonate particles. The calcium carbonate particles were isolated by centrifuging the suspension and removing the supernatant. The isolated calcium carbonate particles were suspended in purified water, centrifuged (3000×g / 5 minutes), and the supernatant was removed to wash the calcium carbonate particles. This washing procedure was repeated three times. The washed calcium carbonate particles were suspended in pure water and filtered through filter paper (Whatman qualitative filter paper No. 1), and the collected calcium carbonate particles were dried at 90° C. The obtained calcium carbonate particles were white and weighed approximately 4 g. An SEM image of the first calcium carbonate particles thus obtained in water is shown in Figure 1. The particle diameter of the first calcium carbonate particles was approximately 100 nm.
[0077] <Production of second calcium carbonate particles> The first calcium carbonate particles were reacted with hydrochloric acid to prepare a 1 M aqueous calcium chloride solution. Span 80 (16.64 ml), Tween 80 (17.32 ml), and toluene (55.17 ml) were mixed and stirred at 1000 rpm, to which the prepared 1 M calcium chloride aqueous solution (16 ml) was added, followed by stirring at 2500 rpm for approximately 12 hours to form a first water-in-oil emulsion. Span 80 (16.64 ml), Tween 80 (17.32 ml), and toluene (55.17 ml) were mixed and stirred at 1000 rpm, to which 1 M aqueous sodium carbonate solution (16 ml) was added, followed by stirring at 2500 rpm for approximately 12 hours to form a second water-in-oil emulsion. The second water-in-oil emulsion was added little by little to the first water-in-oil emulsion while stirring at 27 to 33°C to form a suspension containing calcium carbonate particles. The calcium carbonate particles were isolated by centrifuging the suspension and removing the supernatant. The isolated calcium carbonate particles were washed by adding 50% aqueous methanol to form a suspension, centrifuging the suspension, and removing the supernatant. This washing procedure was repeated twice, and then the calcium carbonate particles were washed with pure methanol. The washed calcium carbonate particles were dried in a vacuum. An SEM image of the second calcium carbonate particles thus obtained in water is shown in Figure 2. The particle diameter of the second calcium carbonate particles was approximately 20 nm.
Claims
1. removing conchiolin and chitin from shell powder in water to form a suspension containing first calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising:
2. treating shell powder with a base in water to form a suspension comprising first calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising:
3. The base includes at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides. The method of claim 2.
4. the base comprises sodium hydroxide; The method of claim 2.
5. The particle diameter of the first calcium carbonate particles is 30 to 800 nm. The method according to claim 1 or 2.
6. The size of the shell powder is 0.01 to 10 mm. The method according to claim 1 or 2.
7. The shells are shells that have not been subjected to desalting treatment. The method according to claim 1 or 2.
8. The shells are not heat-treated. The method according to claim 1 or 2.
9. The shells are not chemically treated. The method according to claim 1 or 2.
10. The shell is an oyster shell. The method according to claim 1 or 2.
11. isolating the first calcium carbonate particles from the suspension; Further comprising: The method according to claim 1 or 2.
12. purifying the first calcium carbonate particles; Further comprising: The method according to claim 1 or 2.
13. drying the first calcium carbonate particles; Further comprising: The method according to claim 1 or 2.
14. converting the first calcium carbonate particles into a water-soluble calcium salt; Further comprising: The method according to claim 1 or 2.
15. mixing the aqueous solution containing the water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion; mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion; mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in nanoparticle form; Further comprising: The method of claim 14.
16. the water-soluble calcium salt is calcium chloride; The water-soluble carbonate is sodium carbonate. The method of claim 15.
17. The particle diameter of the second calcium carbonate particles is 10 to 100 nm. The method of claim 15.
18. mixing an aqueous solution containing a water-soluble calcium salt, a first surfactant, and a first organic solvent to form a first water-in-oil emulsion; mixing an aqueous solution containing a water-soluble carbonate, a second surfactant, and a second organic solvent to form a second water-in-oil emulsion; mixing the first water-in-oil emulsion with the second water-in-oil emulsion to form second calcium carbonate particles in nanoparticle form; A method for producing calcium carbonate, comprising:
19. Calcium carbonate particles having a particle diameter of 10 to 100 nm.
20. It is spherical in shape, Calcium carbonate particles according to claim 19.
21. the surfaces of the calcium carbonate particles are not coated with an organic compound; Calcium carbonate particles according to claim 19.