JPH02243514A - Production of spherical fine particle of vaterite-type calcium carbonate - Google Patents

Abstract

PURPOSE:To obtain spherical fine particles of vaterite-type calcium carbonate having high purity by adding a chelating agent and hydrogen peroxide to an aqueous suspension of calcium hydroxide and reacting the mixture with a CO2- containing gas. CONSTITUTION:The objective spherical particle of vaterite-type calcium carbonate can be produced by reacting an aqueous suspension of calcium hydroxide with a CO2-containing gas in the presence of a chelating agent and hydrogen peroxide and in the presence or absence of a metal salt. Spherical particle of vaterite-type calcium carbonate having a diameter of 0.8-1mum is obtained at a reaction temperature of <40 deg.C in the presence of the chelating agent and hydrogen peroxide as mentioned above. Addition of a metal salt in addition to the above two kinds of additives (i.e. the chelating agent and hydrogen peroxide) enables the formation of spherical vaterite-type calcium carbonate irrespective of the reaction initiation temperature. The particle diameter of the vaterite- type calcium carbonate can be decreased to a level in the range of 0.05-0.8mum by properly selecting the reaction initiation temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing vaterite-based calcium carbonate having spherical particles.

[Conventional technology]

-a As is well known, calcium carbonate is widely used in rubber, plastics, paper, food, agricultural chemicals, etc., and is known to have three crystal structures: calcite, arabite, and vaterite. Site exists naturally as an industrial material such as limestone, and artificially, colloidal or chain-like particles, cubic or spindle-shaped particles are manufactured and sold, and numerous patents and documents have been reported. ing.

Arabite is represented by natural resources such as coral stone, and artificially synthesized aragonite is attracting attention as a coating pigment for paper manufacturing, and columnar or needle-shaped ones are now being manufactured and sold.

Vaterite has an unstable crystal form compared to the above-mentioned calcite and arabite, but its characteristics include spherical particles with a highly active surface. There are also reports that this surface activity is effective as a low-molecular adsorbent such as a surfactant and as a reinforcing agent for synthetic rubber, and is expected to be used in applications other than those for calcite and arabite. . However, vaterite is
When water is present, the shape changes due to transition to other crystal systems.
The biggest drawback is that it cannot maintain its spherical shape. For this reason, vaterite is currently not manufactured and sold.
It can be seen that special synthesis conditions are required to produce vaterite. The main manufacturing methods that have been reported so far are as follows.

(2) A method in which a divalent metal salt is added when a water-soluble calcium salt such as calcium chloride is reacted with a water-soluble carbonate such as sodium carbonate (JP-A-57-92520).

(2) A method of making calcium chloride alkaline in a closed reaction vessel (autoclave) and adding carbon dioxide-containing gas (hereinafter referred to as carbon dioxide gas) or water-soluble carbonate in the coexistence of water glass (Japanese Patent Publication No. 42-22543).

■A method of introducing carbon dioxide gas into an aqueous suspension of calcium hydroxide (hereinafter referred to as milk of lime) containing 75% by volume or more of alcohol (Journal of Japan Adhesive Association, 21 (1985)).

However, since the above method Φ is a solution reaction, vaterite is generated very quickly, but it is easy for calcite to be mixed in and the particle size to be uneven, and it also requires the use of calcium salts and carbonates. This increases raw material costs. ■
In this method, special production conditions must be set such as pressurization in an autoclave, and a mixture of hydrous silicic acid and vaterite is produced. In method ■, alcohol 75
There are drawbacks such as vaterite not being produced unless the amount is at least % by volume. Furthermore, in both methods, the spherical particle diameter was 0.8%.
It is between 3% and above, and spherical particles of 0.8μ or less have not yet been obtained.

[Problems to be solved by the invention] Conventional vaterite production methods use water-soluble salts for both the calcium source and the carbonate source, or use a large amount of alcohol, resulting in uneven particle sizes. There are problems such as not being spherical and the cost of raw materials being high. Furthermore, the method using calcium hydroxide contains hydrated silicic acid as an impurity, making it difficult to easily produce a pure product. Furthermore, control of particle size has not been achieved with conventional methods.

[Means for Solving the Problems] Therefore, as a result of intensive research in order to solve the above problems, the present inventors found that when milk of lime and carbon dioxide are subjected to a contact reaction,
It has been found that spherical vaterite-based calcium carbonate can be produced by adding a chelating agent, hydrogen peroxide, or even a metal salt.

In this reaction system, the absolute condition is that the chelating agent and hydrogen peroxide coexist.
*A moderate amount of colloidal or chain-like particles of calcite-based calcium carbonate is produced. In addition, if only hydrogen peroxide is used, depending on the amount of hydrogen peroxide added, spherical particles of IP or higher or 0
．． More than 1% of cubic calcium carbonate is produced. However, in the coexistence of a chelating agent and hydrogen peroxide, spherical particles of vaterite calcium carbonate with an IP of 0.8 to IP are produced at a reaction temperature of less than 40°C. Furthermore, if a metal salt is added in addition to the two additives, chelating agent and hydrogen peroxide, spherical vaterite-based calcium carbonate can be produced regardless of the reaction initiation temperature; The spherical diameter of vaterite-based calcium carbonate can be made finer between 0.05 and O.Bs.

The timing of adding the chelating agent, hydrogen peroxide, and metal salts may be up to 30% carbonation before and during the reaction, but if they are added more than this, it will not be possible to obtain a spherical shape. The three types of additives may be added at the same time, or may be added individually. However, if they are added during the reaction, the later the addition time is, the more pond-shaped calcite-based calcium carbonate will be mixed in. Therefore, it is desirable to add the three types of additives before the start of the reaction if possible.

Chelating agents used in the present invention include various organic compounds that coordinate with metal ions to form polydentate metal compounds, such as aliphatic carboxylic acids such as oxalic acid and maleic acid, citric acid, etc. , oxy or ketocarboxylic acids such as pyruvic acid, thiocarboxylic M groups such as thiomalic acid and thioglycolic acid, aromatic carboxylic acids or aromatic aldehydes such as trimellitic acid and pyromellitic acid, aromatic compounds such as chromotrolic acid and tyron. Sulfonic acids, aminopolycarboxylic acids such as iminodiacetic acid, nitrotriacetic acid, and ethylenediaminetetraacetic acid, amino acids or proteins such as glutamic acid, aspartic acid, and gelatin, purine, purine bases or nucleoside molecules such as flavin mononucleoside, penicillin, etc. antibiotics, metal colorimetric indicators such as Eriofrom Black, dimethylglyoxime,
Examples of chelating agents include oximes such as methyloxine and acetylacetone, amines such as diketones, triethanolamine, and hydroxyethylamine, and their salts, and two or more of these may be used in combination. Among these, aminopolycarboxylic acids are effective, and ethylenediaminetetraacetic acid disodium salt (hereinafter referred to as EDTA) is particularly excellent.

The amount of chelating agent added is preferably 2 mol% or more based on calcium hydroxide, and if it is less than 2 mol%,
．． Calcite-based calcium carbonate, which is a cubic aggregate of 1 u or more, is produced.

On the other hand, it is desirable that the amount of hydrogen peroxide added is 2 mol% or more based on calcium hydroxide, and if it is less than that, it will be zero.
．． About 3 seconds of columnar calcite-based calcium carbonate is generated.

Here, the amount of additive added (mol%) is determined by the following formula: % Additive amount (mol%) = ((Number of moles of additive to be added)/(Number of moles of calcium hydroxide used) ) l X
100 In addition, the metal salt may be any divalent or trivalent water-soluble metal salt such as magnesium, zinc, barium, lead, nickel, cobalt, aluminum, etc., and the amount added is determined based on the amount of calcium hydroxide. It is sufficient if it is 0.5 mol% or more, but if it is less than that, spherical particles of about 15F at a reaction initiation temperature of less than 40°C, spindle shape of 2 to 3) 4 at a reaction initiation temperature of 40°C or more. This is not preferable because it produces calcite-based calcium carbonate.

There are no restrictions on the degree of carbon dioxide gas introduced, the amount introduced, and the reaction start temperature, but if possible, the 1 degree reaction start temperature is 80 degrees from the Ministry of Economic Affairs.
It is preferable to carry out the process at a temperature below ℃.

[Effects of the Invention] Compared to conventional methods, the present invention does not require a special reaction device, and by adding additives, reaction conditions such as reaction initiation temperature and milk of lime concentration can be varied over a wide range.
Further, there is an advantage that pure vaterite-based calcium carbonate of spherical particles with a single particle size can be freely produced with a spherical diameter between 0.705 and 0.8 seconds.

Furthermore, the spherical particles obtained in the present invention can be used as fillers for rubber, plastics, etc.

It is expected that workability will be improved by improving the roundness of the spherical shape, and reinforcing properties will be provided by the surface activity of vaterite.

Example C] Example 1 7.5 g of EDT A to 15 g of calcium hydroxide
(equivalent to 10 mol% relative to calcium hydroxide),
After the total amount was 200% dissolved in water, 23g of 30% by weight hydrogen peroxide solution (equivalent to 100% by mole relative to calcium hydroxide) was added to bring the concentration of milk of lime to 6g/100%. To make J, reduce the total amount to 250. It was set as λ. The temperature of the emulsion is 1
At 0°C, 25% by volume of carbon dioxide gas was continuously introduced at a flow rate of 600% 1/min to complete the carbonation reaction, followed by filtration, washing with water, and washing with methyl alcohol.
It was dried for 0 hours or more to obtain 19 g of calcium carbonate. When the obtained calcium carbonate was examined using an xm diffraction device, it was found that
No peaks other than vaterite calcium carbonate were observed. Furthermore, shape with a scanning electron microscope! I guessed that it was about 0.8. It was a spherical particle. FIG. 1 shows an X-ray diffraction diagram of this product, and FIG. 2 shows scanning electron micrographs of this product.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the reaction initiation temperature was adjusted to 45° CI. They were spindle-shaped particles with a long axis. The X-ray diffraction diagram of this product is shown in Figure 3, and the scanning electron microscope iM photograph is shown in Figure 4.
Shown in the figure.

Example 2.3 The same operation as in Example 1 was carried out while changing the amounts of EDTA and hydrogen peroxide added as shown in Table 1.

The reaction conditions and results are shown in Table 1.

Comparative Example 2.3 Example 1 without adding hydrogen peroxide or EDTA
Table 1 shows the zero reaction conditions and results conducted in the same manner as above.

Examples 4 to 6 In addition to the EDTA and hydrogen peroxide additives in Example 1, magnesium chloride hexahydrate was added before the reaction, and the reaction initiation temperature was set to 20°C, 40°C, and 60°C, respectively. The same reaction conditions and results as in Example 1 were used for the first reaction except for the following adjustments.
Shown in the table.

Example 7 The reaction conditions and results are shown in Table 1 in the same manner as in Example 5 except that the milk of lime concentration was 12% and the flow rate of 25% by volume carbon dioxide gas was 1200 tJ/min.

Examples 8-10 Instead of magnesium chloride hexahydrate, zinc chloride, barium chloride dihydrate, aluminum sulfate 14-1B
The same procedure as in Example 5 was carried out except that 10 mol% of the hydrate was added to the calcium hydroxide.

The reaction conditions and results are shown in Table 1.

Actual) IJ111-14 The same procedure as in Example 5 was carried out by changing the amounts of EDTA, hydrogen peroxide and magnesium chloride as shown in Table 1.

Example 11 pH 5-19 The same procedure as Example 5 was carried out except that disodium aminodiacetate hydrate, sodium glutamic acid hydrate, triethanolamine, ascorbic acid, and sorbitol were used instead of EDTA.

The reaction conditions and results are shown in Table 2.

4. (Brief explanation of iij1 side) FIG. 1 is an X-ray diffraction pattern diagram of the vaterite-based rj! acid calcium obtained in Example 1.

FIG. 2 is a scanning electron micrograph used as a drawing showing the particle structure of calcium carbonate obtained in Example fR1.

FIG. 3 is an X-ray diffraction pattern diagram of calcite-based calcium carbonate obtained in Comparative Example 1.

FIG. 4 is a scanning electron micrograph used as a drawing showing the particle structure of calcium carbonate obtained in Comparative Example 1.

2θ/deg.

No. figure No. figure 2θ/deg.

No. figure No. figure

Claims (1)

[Claims] A method for producing spherical vaterite-based calcium carbonate by reacting an aqueous calcium hydroxide suspension with a carbon dioxide-containing gas, with or without adding a metal salt, and further adding a chelating agent and hydrogen peroxide.