JPH0350116A - Production of spherical calcium carbonate - Google Patents

Abstract

PURPOSE:To obtain spherical particles of calcium carbonate having a narrow distribution of particle size with using a simple device by dissolving a reaction buffer in a carbonate ion solution, mixing the solution with a Ca ion solution and then adding an inhibitor against growth of crystals in the reaction process of the mixture solution. CONSTITUTION:The Ca-ion solution is mixed with the carbonate-ion solution containing the reaction buffer which controls the shape of particles. When particles of calcium carbonate produced in this reaction process of the mixture solution grow to a desired particle size, an inhibitor against growth of crystals is added thereto to control the particle size. By this method, calcium carbonate having desired spherical form can be obtained at room temp. and atmospheric pressure. The reaction buffer to be used is an electrolyte such as nitrate, sulfate, chloride, etc., of alkali metal or ammonium. If the buffer is not dissolved, cubic crystalline calcite is produced. The inhibitor against growth of crystals is an alkali agent such as sodium hydroxide, ammonium hydroxide, ammonia, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing calcium carbonate having a spherical crystal particle shape, and more specifically, to producing homogeneous spherical vaterite carbonate having a true spherical shape and a sharp particle size distribution. This invention relates to a method for producing calcium.

BACKGROUND OF THE INVENTION Calcium carbonate powder is widely used as a filler in industrial materials such as plastics, rubber, paints, and paper, as well as in pharmaceuticals, cosmetics, and abrasives for toothpastes.

Calcium carbonate has three crystal forms: cubic calcite, columnar arabite, and spherical vaterite. Generally, by spheroidizing particles, filling properties and
The spheroidization of various powders has been attempted, and the spheroidization of various powders has been attempted, as it has many industrial advantages, such as improved dispersibility, smoothness, and fluidity, and increased uniformity of mixing. This is also the reason why spherical vaterite calcium carbonate is attracting attention.

Conventionally, the following methods for producing vaterite-type spherical calcium carbonate are known.

First, there is a method in which calcium hydroxide suspension and carbon dioxide gas are reacted in a sealed container at elevated temperatures to generate the product (Japanese Patent Publications No. 43-25148 and 48-35159). However, this method requires a complicated device, is complicated to operate, and has many problems in terms of workability.

In addition, calcium ion solution was prepared in W/Q form (
There is a method of producing spherical calcium carbonate by emulsifying it into a water-in-oil solution, mixing it with a carbonate ion solution, and reacting it (Kuchikashi, 5.732 (1976)). The spherical calcium carbonate obtained by this method has a true spherical shape and a sharp particle size distribution, but it requires extra labor after the reaction, such as separation from an organic solvent and washing with alcohol, making it economically unsatisfactory. There is a drawback of high cost.

Next, there is a method of producing spherical calcium carbonate by adding divalent cations other than calcium when producing calcium carbonate through an aqueous reaction between a water-soluble calcium salt and a carbonate (Japanese Patent Laid-Open No. 57-92520). Public bulletin). In this case, depending on the amount of divalent cation added, the formation of cubic calcite is observed when the amount is small, and as the amount added increases, coalescence of generated particles increases, and the particle size distribution becomes broader. There's a problem.

Furthermore, there is a method in which spherical calcium carbonate is produced by mixing a calcium ion solution and a carbonate ion solution and applying physical impact to the mixture from the initial stage of the reaction (Japanese Patent Laid-Open No. 108117/1993).

Calcium carbonate obtained by this method has relatively small spheres and a sharp particle size distribution, but has the disadvantage of poor crystal morphology and a shape that is considerably more deviated than a true sphere.

Problems to be Solved by the Invention As mentioned above, the conventional method has problems such as requiring special manufacturing equipment, difficulty in workability, complexity due to increased number of steps, and rising manufacturing costs. Furthermore, it is difficult to say that the granule properties of the product, such as purity, particle size distribution, and particle shape, are perfect, and therefore, measures to improve these properties have been strongly desired.

That is, an object of the present invention is to produce high-quality spherical carbonic acid that can be easily operated using simple production equipment, has a true spherical shape, a sharp particle size distribution, and is highly homogeneous. The object of the present invention is to provide a new production method for obtaining calcium. This invention was made to solve the problems of the conventional method and to meet the above-mentioned demands for improvement.

Means for Solving the Problems The structure of the present invention to achieve the object is to mix a carbonate ion solution and a calcium ion solution in which a reaction buffer for controlling particle shape is dissolved, and then to mix this mixed solution. When the calcium carbonate produced in the reaction process has grown to a desired particle size, a crystal growth inhibitor is added to control the particle size.

Effect When the calcium ion solution and carbonate ion solution are mixed, the following reaction proceeds. That is, immediately after mixing, CaA-t-BCO=CaCO3+BA holds true.

Here, the calcium ion solution used in this invention is
An aqueous solution of a calcium salt such as sodium chloride or calcium nitrate, and A in the above formula means CI-NO3'' or the like. In addition, the carbonate ion solution is an aqueous solution of carbonates such as sodium carbonate, sodium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, etc., as long as it dissociates into carbonate ions, and B in the above formula is an alkali metal ion or means ammonium ion.

The produced calcium carbonate is fine particles, and when the reaction buffer of the present invention is not dissolved, calcite, which is a cubic crystal, is produced. The reaction buffer used in the present invention may be any electrolyte such as alkali metal or ammonium nitrate, sulfate, or chloride, such as sodium chloride, ammonium chloride, sodium nitrate, ammonium nitrate, sodium sulfate, ammonium sulfate, etc.

Subsequently, in the process of crystal growth, CaCO3+H2CO3 , ::Ca 2++ 2 I-I C0 is established, and due to the relationship of surface energy, fine particles dissolve while large particles grow.

Therefore, when the particles have grown to the desired particle size, the reaction is stopped by adding a crystal growth inhibitor. The crystal growth inhibitor used in the present invention is a lukewarm agent such as sodium hydroxide, ammonium hydroxide, or ammonia gas.

Ca(HCO2)2 + 2 Na OH−”Ca C
o 10 Na Co +2) I203 2
3 In this way, the desired spherical calcium carbonate can be obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 0.1 mol/1 sodium carbonate and 0.1 mol/1 sodium carbonate. 2mol
/g sodium chloride buffer) was stirred in the reaction tank, and the same volume of Q, 1 mol/g was added to it.
After adding a calcium monochloride solution and reacting by stirring for 8 minutes, sodium hydroxide was added as a crystal growth inhibitor, and the produced particles were collected by filtration. The liquid temperatures before and after the reaction were 17.5°C and 117°C, respectively. The yield of calcium carbonate in this case was 96.2% of the theoretical value. The obtained calcium carbonate is 100% perfectly spherical with an average particle diameter of about 7 μm, but there are scattered particles in which two or three of these particles have grown together. Note that the reaction tank used can be any very common container, whether round or square.
Further, the mixing agitator may be a propeller-type general-purpose stirrer with a variable speed device, a homomixer with a variable speed device, or a homojetter, and can be easily implemented using a simple general-purpose mechanical device that is usually commercially available.

Example 2 0.4 mol/ρ 0.1 mol containing sodium chloride
/1 sodium carbonate solution and 0. Calcium carbonate was produced in exactly the same manner as in Example 1 by mixing the same volume with a 1 mol/n calcium chloride solution. The liquid temperatures before and after the reaction were 7.6°C, 17.4°C, respectively. The yield in this case was 95% of the theoretical value, and the crystals were 100% true spherical calcium carbonate with an average particle size of about 6 to 7 μm, with almost no coalescing particles observed.

Example 3 0.2m containing 0.4mol/fl ammonium chloride
ol/fl ammonium carbonate solution and 0.2 mol
/g calcium chloride solution in the same volume and stirred for 1 hour.
After 8 minutes, a crystal growth inhibitor was added and the produced particles were collected. The liquid temperature before and after the reaction was 11.5°C111,8, respectively.
°C1 The yield at this time was 93.5% of the theoretical value, and the obtained calcium carbonate was perfectly spherical with an average particle size of about 2 to 4 μm.

Examples 1 to 3 will be described below in comparison with Comparative Examples 1 to 4. Table 1 summarizes the contents of these chemical component compositions.

(Left below) These examples are cases where a carbonate ion solution and a calcium ion solution are mixed in an equimolar ratio, and in contrast to Example 1,
Example 2 is an example in which the concentration of the reaction buffer was increased, and Example 3 is an example in which the concentration of the mixed reaction solution of a carbonate ion solution and a calcium ion solution was increased and the components of the reaction buffer were changed. . Furthermore, in Example 1 and Example 2, the liquid temperature before and after the reaction was almost the same, whereas in Example 3,
This is an example of production at a low temperature. Regarding the influence of liquid temperature, many experimental results have confirmed that the crystal growth rate is slow at low temperatures and very fast at high temperatures, but there is almost no change in crystal morphology due to temperature changes.

An example of the results of a study on the crystal structure of calcium carbonate of the present invention is shown in FIG. Figure 1 is an X-ray diffraction diagram of calcium carbonate obtained in Example 1, in which cubic calcite, which is generally considered to be a stable phase at room temperature and pressure, is extremely rare (and is mostly occupied by spherical vaterite). I understand that.

Moreover, FIG. 2 is an optical micrograph (800X) of the calcium carbonate obtained in Example 2, and the particle form is almost perfectly spherical. FIG. 3 is a scanning electron micrograph of the calcium carbonate obtained in Example 3, which was taken to observe the details of the perfect sphere.

Comparative Example 1 shown in Table 1 is a case in which no reaction buffer and no crystal growth inhibitor were added. For comparison, an optical micrograph (800X) of the obtained product is shown in Figure 4. show. Furthermore, an optical micrograph (800X) of Comparative Example 2 without the addition of a crystal growth inhibitor is shown in FIG. As can be easily understood from these photographs, in Comparative Example 1, the product did not have a spherical shape, and had a shape significantly different from the object of the present invention. Furthermore, the product according to Comparative Example 2 has a spherical shape due to the addition of a reaction buffer that controls the particle shape, but the particle size is large and irregular, which does not meet the purpose of the present invention. It has not become something that can be done.

Comparative Example 3 is a method in which physical impact is applied from the initial stage of the reaction, and the product is stirred at a high speed of 3500 rpm using a homomixer.
00X) is shown in FIG.

Calcium carbonate obtained by this method is relatively microspherical, and has a shape that is considerably deviated from a true spherical shape.

Comparative Example 4 is an example of production by adding divalent cations (Mg''), and the optical micrograph (800X) of the product is
As shown in the figure. However, (A), (B), and (C) in the same figure are each 0.002 mol/f as a divalent cation.
l, 0.004 mol/1.0, 006 mol/
The case where magnesium chloride of I is used is shown. When very small amounts of divalent cations are added, cubic calcium carbonate is not formed, but the coalescence of particles is so severe that it is not the object of this invention. In other words, the same figure (A
) and (B), in addition to true spherical calcium carbonate with a particle diameter of approximately 3 to 7 μm, there are approximately 30 to 40% deformed particles that have grown by coalescence. , except for about 10% of true spherical calcium carbonate with a particle diameter of several μm, the particles are gourd-shaped with a size of about 8×15 μm.

Example 4 This example describes comparative test results of reaction buffers. As a mixed solution of reaction buffer and carbonate ions, A: ammonium sulfate 0. 0 containing 1 mol/1,
2mol/fl Sodium carbonate solution B: Sodium nitrate 0. 0.2 mol/1 sodium carbonate solution C containing 2 mol/l: Sodium sulfate O, 1 mol/ρ
0.2mol/ρ Sodium carbonate solution containing 0.2mol/fl Sodium chloride 0.2mol/fl
l/fl sodium carbonate solution and these A,
The same volume of each mixed solution of B, C, and D, 0.2 mol/
Calcium carbonate was produced in the same manner as in Example 1.The liquid temperature before and after the reaction was as follows:
The temperatures were 16.0°C and 15.5°C, respectively.

The crystal morphology of the product in each case is A: 100% spherical calcium carbonate, but compared to C1D (deviated from a true sphere), B: 10% cubic calcium carbonate in addition to spherical calcium carbonate. C: 100% spherical calcium carbonate; D=almost 100% spherical calcium carbonate with scattered coalescent particles.

Example 5 This example describes the influence of the amount of reaction buffer added on crystal morphology.

A: 0 containing 0.05 mol/fl of sodium sulfate;
2 mol/II sodium carbonate solution B: sodium sulfate 0. 0, 2 mol including 10 mol/ρ
/1 sodium carbonate solution C: sodium sulfate 0. 1
0.2 mol/fl sodium carbonate solution D containing 5 mol/1: sodium sulfate 0.188 mol/fl
Mixed solutions of 0 and 2 mol/fl sodium carbonate solutions A, B, C, and D containing 0. 18mol/g
Calcium carbonate was produced in the same manner as in Example 1 by mixing the same volume with the calcium chloride solution. The liquid temperature before and after the reaction is
The temperatures were 17.2°C and 17.0°C, respectively.

The crystal forms of the calcium carbonate produced in each case are: A: In addition to true spherical calcium carbonate with a particle size of 2 to 7 μm, 5.
~6 coalescing particles scattered (spherical), B: particle size 2-7μ
In addition to true spherical calcium carbonate of m, several coalesced particles are scattered (spherical); C: Slightly formed coalesced spheres consisting of two particles in addition to true spherical calcium carbonate with a particle diameter of 2 to 6 μm; D = Only true spherical calcium carbonate with a particle size of 2 to 6 μm,
There were no coalesced deformed particles.

FIG. 8 shows an optical micrograph (800X) of the particles produced when the mixed solution was used.

In Examples, the relationship between the concentration of the reaction solution and the crystal form will be described.

After mixing and reacting a sodium carbonate solution and a calcium chloride solution at the following concentrations, a crystal growth inhibitor was added and the produced particles were collected. The concentration of sodium sulfate as a reaction buffer is 0.2 mol/E regardless of the concentration of the reaction solution.
And so. The reaction time was 8 minutes, and the liquid temperatures before and after the reaction were 17.5°C and 117°C, respectively.

A: 0.3 mol/fl calcium chloride solution and 0
, 0,3 containing 2 mol/fl sodium sulfate
5 mol/f) Same volume mixture B with sodium carbonate solution: 0. 0.5 containing 5 mol/fl calcium chloride solution and 0.2 mol/j7 sodium sulfate
Same volume mixture C with 5 mol/1 sodium carbonate solution: 0.7 mol/ρ calcium chloride solution and 0,
0.80m containing 2+mol/fl sodium sulfate
The crystal morphology of the calcium carbonate produced in each case of mixing the same volume with ol/1 sodium carbonate solution is as follows: A: true spherical calcium carbonate with a particle size of ~6 μm; B: spherical calcium carbonate with a particle size of 1~4 μm; Approximately 20% of the particles were mixed with particles that were slightly skewed from being spherical. C: Calcium carbonate had a uniform particle size of around 2 μm and was skewed from being perfectly spherical as a whole.

Table 2 summarizes the properties of the calcium carbonate produced in each case of D in Example 5, A in Example 6, and B in Example 6.

(Margin below) Incidentally, the particle size distribution of the products shown in Table 2 is shown in FIG.

However, in the figure, the particle size distribution of the product according to Comparative Example 4 is also illustrated. As is clear from FIG. 9, the spherical calcium carbonate according to the present invention exhibits an extremely sharp particle size distribution, and is of high quality with uniform particle size and high homogeneity.

To summarize the main points of the method of this invention, including the examples described above, (1) The mixing ratio of carbonate ions and the corresponding calcium ions is an equimolar ratio, or when there is a somewhat large amount of carbonate ions, crystal growth occurs. promoted. On the contrary, calcium carbonate obtained under conditions with few carbonate ions is a brittle crystal and easily disintegrates.

(2) As the concentration of the mixed reaction solution increases, the particle size shifts to the fine particle side and the particle size becomes uniform, but the particle shape tends to deviate from a true spherical shape, preferably O, 1 mol.
/1~0. 5 mol/fl is good.

If the concentration is higher than this, it is difficult to obtain perfectly spherical calcium carbonate.
1.0 mol/ρ, 0.1 to 0.0 with divalent electrolyte. 5m
oi/n, more preferably 0.2 to 0.4 mol
/p is appropriate. Under additive-free conditions, a large amount of cubic calcite is produced.

(4) The amount of the crystal growth inhibitor to be added may be determined based on the fact that particle growth of the produced calcium carbonate stops at a pH of about 12. If no additive is added, crystals will grow even during the solid-liquid separation process, making it difficult to obtain particles with the desired particle size.

(5) Regarding liquid temperature, although temperature changes have little effect on crystal morphology, there is a close relationship with crystal growth rate.

Effects of the Invention As explained above with specific examples, according to the present invention, by mixing a calcium ion solution, a carbonate ion solution, and a reaction buffer at room temperature and normal pressure, the coalescence phenomenon of spherical particles is effective. By adding a crystal growth inhibitor, it is possible to easily and economically produce true spherical calcium carbonate with a target particle size and a narrow particle size range, with a recovery rate close to the theoretical value. . In addition, by appropriately selecting the temperature of the reaction solution and the reaction time, the particle size of the produced calcium carbonate can be varied from about 1 μm to more than 10 μm.
It is possible to arbitrarily change up to

[Brief explanation of drawings]

Figure 1 shows the calcium carbonate product obtained in Example 1.
Linear diffraction diagram, Figure 2 is an optical micrograph of the product obtained in Example 2, and Figures 3 (A) to C) are scanning electron micrographs of the product obtained in Example 3. . Figures 4 to 6 are optical micrographs of the products obtained in Comparative Examples 1 to 3, respectively, and Figures 7 (A) to C) show the amount of divalent cation added in Comparative Example 4, respectively. Separately obtained optical micrograph of the product, FIG. 8 is an optical micrograph of the product according to D of Example 5. FIGS. 9(A) to 9(C) show D and D of Example 5, respectively.
Particle size distribution diagram of the product according to 6 A1 and 6 B, the same figure (
D) or F) are respectively shown in Figure 7 (A) or C.
) is a particle size distribution map of the product of Comparative Example 4 corresponding to

Claims (1)

[Claims] 1) A spherical particle shape characterized by mixing a carbonate ion solution and a calcium ion solution in which a reaction buffer that controls the particle shape is dissolved, and adding a crystal growth inhibitor during the reaction process of the mixed solution to control the particle size. Method for producing calcium carbonate.