JP2001354416A - Method for manufacturing aragonite type calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing aragonite type calcium carbonate in a single phase with high purity which can be manufactured at low reaction temperature in a suspension reaction liquid of high concentration in a large volume. SOLUTION: In the method for manufacturing aragonite type calcium carbonate, while a suspension liquid consisting of slaked lime, Mg2+ ion and water is stirred by making flows with different flowing directions in a tank, carbonic acid gas is introduced into the suspension liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing high-purity aragonite-type calcium carbonate.

[0002]

2. Description of the Related Art In Hokkaido, about 200,000 tons of scallop shells are generated as waste every year. Landfill is the main disposal method for scallop shells, but in recent years it has become difficult to secure landfill sites, and there has been a strong demand for technological development to utilize scallop shells as resources and to effectively use them. The main component of the scallop shell is calcium carbonate.

[0003] Calcium carbonate has three polymorphs, calcite, aragonite, and vaterite, that is, three crystal systems.

At room temperature and 1 atm, calcite is more stable than aragonite, and aragonite, which is a metastable phase, gradually becomes calcite. Vaterite does not occur naturally. Aragonite has a different crystal system and coordination number from calcite and vaterite, which are the other two types of calcium carbonate, and has a large specific gravity and Mohs hardness. Because of these structural differences, aragonite is a chemical component of calcium carbonate, but its properties are more similar to strontium carbonate and barium carbonate, which have a larger cation radius.

[0005] In any of the three crystal systems, calcium carbonate is white, hardly soluble in pure water, and has an appropriate specific gravity.
It is used as an important industrial raw material such as fillers and papermaking coatings.

Aragonite has a different structure and properties from calcite and vaterite as described above,
In the above-mentioned use as an industrial raw material, higher performance can be imparted by applying aragonite among the above three types of calcium carbonate crystal systems.

According to previous studies, a single phase of aragonite was obtained at 80 ° C. via amorphous calcium carbonate.
(Yoshiyuki Kojima, Akio Kawanobe, Tsutomu Yasue, Yasuo Arai: J. Ceram. Soc. Jpn.,
Vol. 102, P1128 (1994)), using Mg ²⁺ ion as an inhibitor of calcite growth in an aqueous solution system (Yoshio Ota, Insaburo, Tetsushi Iwashita, Toshihiro Kasuga, Yoshihiro Abe: J. Ceram. Soc. Jpn.,
Vol. 104, P196 (1996)). However, in any case, a single phase of aragonite could not be synthesized at 80 ° C. or lower.

Further, a method of promoting the calcite → aragonite phase transition by adjusting the water content by pulverization utilizing the mechanochemical effect (AH Shinoha).
ra, K .; Sugiyama, E .; Kasai,
F. Saito & Y. Waseda: Adv. Po
wder Technology. , 4 (4), P311
(1993)), a single-phase aragonite is obtained by an X-ray diffraction pattern. However, in this method, 25
It takes a long time of about 0 hours to grind. Moreover, the influence of temperature during the long grinding cannot be ignored.
Due to slight fluctuations in temperature control, single-phase aragonite cannot be obtained, and there is a problem that temperature control is extremely difficult.

[0009]

As a result of various studies made by the research and development group to which the present inventors belong in order to solve the above problems, Mg ²⁺ ions were converted to a calcite-type calcium carbonate growth inhibitor in the above aqueous solution system. In the method used as, the shell was crushed and calcined to remove organic matter, and by using a calcined material containing calcium oxide as a main material as a starting material, it was found that aragonite-type calcium carbonate having high purity at room temperature was obtained. Reported earlier (Keiko Sasaki: Metals, Vol. 68, No. 9, P807 (1
998); Keiko Sasaki, Masami Tsunekawa: Materials for the 1998 Autumn Meeting of the Society of Natural Resources and Materials; Keiko Sasaki, Hongo University, Masami Tsunekawa:
Resources and Materials, Vol. 114, No. 10, P71
5 (1998)).

However, particularly when the concentration of solutes and solids in the reaction solution is high, and when the reaction tank is large, the resulting aragonite-type calcium carbonate becomes non-uniform in crystallinity and the yield decreases. there were. The present inventors have further studied to solve this new problem, and as a result of using a stirring blade having a predetermined shape to generate a water flow having a different flow direction in the tank, solutes and solids in the reaction solution are reduced. Even when the concentration is high or the reaction tank is large, the non-uniformity of the crystallinity is eliminated, the crystallinity is good, the crystal is not broken, and the aragonite-type calcium carbonate can be produced with a high yield. Knowing this, the present invention has been completed.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a high-concentration aragonite-type calcium carbonate which can be produced at a low reaction temperature in a large-volume suspension reaction solution. It is to provide a manufacturing method.

[0012]

Means for Solving the Problems To achieve the above object, the present invention provides [1] a suspension comprising quick lime or slaked lime, Mg ²⁺ ions and water in a water stream having different flow directions in a tank. And a method for producing aragonite-type calcium carbonate, wherein carbon dioxide gas is passed through the suspension, and [2] adding quicklime or slaked lime to water containing Mg ²⁺ ions. The suspension obtained by
Create and mix water streams with different flow directions in the tank,
The present invention proposes a method for producing aragonite-type calcium carbonate, characterized in that carbon dioxide gas is passed through the suspension, and [3] quicklime or slaked lime is quicklime or slaked lime obtained by firing a shell. including.

[0013] The present invention also relates to [4] mixing a suspension composed of quick lime or slaked lime, Mg ²⁺ ions and water at a temperature of less than 80 ° C to form a water flow having a different flow direction in a tank. And a method for producing aragonite-type calcium carbonate, characterized in that carbon dioxide gas is passed through the suspension, and [5] a suspension comprising quicklime or slaked lime, Mg2 ⁺ ions and water, A method for producing aragonite-type calcium carbonate, characterized in that the temperature is set to 0 to 35 ° C., and water flows having different flow directions are made and mixed in a tank, and carbon dioxide gas is passed through the suspension. Things.

Hereinafter, the present invention will be described in detail.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As a raw material of calcium carbonate,
Shells are preferred because they are readily available. Further, as the shell of this raw material, any shell can be used, and examples thereof include scallop, oyster, Akoya, clam, idiot, and red shell.

Due to the availability of shells, the collection or cultivation is carried out on a large scale, and the processing of the shells after collection or cultivation is carried out in factories and the like. It is preferable because it can be obtained collectively because there are many. Among them, scallop is one of the highest producing shells in Japan along with oysters, but the emissions of these two shells are in contrast. Oyster shell emissions have changed little over the last decade, while scallop shell emissions have increased 2.5- to 3-fold over the last 10 years. From such a viewpoint, among the shells, scallop shells are particularly preferable.

The above shell is calcined to obtain quick lime. Next, slaked lime derived from the shell is obtained by hydrating the shell quick lime.

Although the quicklime obtained as described above can be used as a raw material of the aragonite calcium carbonate of the present invention, slaked lime obtained by hydrating the quicklime is used as a raw material of the aragonite calcium carbonate of the present invention. Can also be used. Hereinafter, the case where slaked lime is used as a raw material of the aragonite-type calcium carbonate of the present invention will be described.

The slaked lime obtained as described above and Mg ²⁺
A suspension of lime milk composed of ions and water is mixed with a water flow having a different flow direction in a reaction tank, and carbon dioxide gas is passed through the suspension to cause a reaction. In large volume suspension reactions, at low reaction temperatures,
A high-purity aragonite-type calcium carbonate can be produced.

The above-mentioned lime milk comprising slaked lime, Mg ²⁺ ions and water can be obtained by adding slaked lime and a water-soluble magnesium salt such as magnesium chloride to water and mixing.

The order of addition of slaked lime to water and water-soluble magnesium salt to water is as follows.
In order to surely dissolve the water-soluble magnesium salt in water, it is more preferable to add the water-soluble magnesium salt to water first. That is, the water to which slaked lime is added is preferably prepared by adding and dissolving a water-soluble magnesium salt in advance to form an aqueous solution.

In the method for producing aragonite-type calcium carbonate of the present invention, the reaction vessel has an upward flow, a downward flow, and a flow in another direction, and a strong mixing state in which water flows having different flow directions coexist to form a strong flow. Mixing is preferred. More preferably, in the flow in the reaction tank in which the water flows having different flow directions have occurred, the flow is downward at the center of the reaction tank and upward at the wall of the reaction tank.

As an example of a stirring blade for making the above-mentioned water flows having different flow directions in the reaction tank and mixing strongly, for example, FIG. 1 shows an example of a mixing system capable of uniform mixing without particles settling down in the reaction tank. A screw-type stirring blade shown in the schematic diagram is exemplified.

The reaction tank is preferably a rounded tank so that the lower wall does not become a dead space.

The stirring intensity is set in advance so that the upward flow on the wall of the reaction vessel is higher than the sedimentation velocity of the maximum synthetic particles.

FIG. 2 is a schematic view of a stirring blade (flat blade) used in a conventional method for producing calcium carbonate. When the stirring blade of FIG. 2 is used, the flow direction is the same circumferential direction, the stirring is insufficient, and the flow is close to a laminar flow, which is not suitable. Therefore, when a large volume suspension reaction solution is stirred at the above-mentioned high concentration using the stirring blade of FIG. 2, particularly when the concentration of slaked lime of lime milk becomes 50 g / dm ³ or more, the obtained aragonite-type calcium carbonate It is not preferable because the crystallinity becomes non-uniform and the yield decreases.

[0027] In contrast, when the flow direction in the reaction vessel are mixed to create a different water flow, the concentration of slaked lime milk of lime 50 g / dm ³ or more, even more 60 g / dm ³ or more, particularly 80 g / dm ³ As described above, the obtained aragonite-type calcium carbonate has a uniform crystallinity and a high yield, which is preferable. Moreover, in the case the concentration of the slaked lime milk of lime of a high concentration of the, of course suspending reaction solution volume of 0.4dm ^3, 1dm ³ or more suspending reaction solution volume, further 5 dm ³ or more volume Can also produce high-purity aragonite-type calcium carbonate at a low reaction temperature.

In the case where water flows having different flow directions are formed in a reaction vessel using stirring blades and mixed vigorously, a preferable stirring speed can be appropriately adjusted and selected particularly according to the volume of the suspended reaction solution. For example, in the case of a suspension reaction solution having a volume of 0.4 dm ³ , the rotation speed is preferably 100 to 1000 rpm, more preferably 200 to 800 rpm, and particularly preferably 300 to 600 rpm. In the case of a suspension reaction solution having a volume of 10 dm ³ , the rotation speed is preferably 200 to 20,000 rpm, more preferably 400 to 10,000 rpm, and particularly preferably 1,000 to 4,000 rpm.

The amount of Mg ²⁺ ions in the suspension reaction solution is 0.01 to 0.01 based on the initial molar ratio Mg / Ca in the suspension reaction solution.
100 is preferable, 0.1 to 10 is more preferable, and 0.5 to 5 is particularly preferable. If the amount of Mg ²⁺ ions in the suspension reaction solution is less than 0.01 in terms of the initial molar ratio Mg / Ca in the suspension reaction solution, the amount of calcite-type calcium carbonate generated is undesirably increased. In the suspension reaction solution, magnesium hydroxide precipitates together with calcium carbonate in the initial stage of the reaction, and as the reaction proceeds, magnesium hydroxide is redissolved in the suspension reaction solution, and the amount of magnesium hydroxide deposited decreases.

Carbon dioxide is blown into the suspension. The blowing speed of carbon dioxide can be appropriately adjusted and selected particularly according to the volume of the suspension reaction solution. For example, 0.4 dm ³
0.004 to 0.4 dm in the case of a suspension reaction solution having a volume of
³ / min is preferred, more preferably 0.008 to
0.2 dm ³ / min, particularly preferably 0.02
０．０0.08 dm ³ / min. In the case of suspension reaction solution volume of 10dm ^3, 0.1~10dm ³ / min
And more preferably 0.2 to ⁵ dm ³ / min.
And particularly preferably 0.5 to ² dm ³ / min. This tendency holds over a wide volume range of the suspension reaction solution.

The reaction between calcium hydroxide (slaked lime) and carbon dioxide in the suspension follows the following chemical reaction formula.

[0032]

Embedded image Ca (OH) ₂ (aq) → Ca ²⁺ (aq) + 2OH ⁻ (aq) (1) CO ₂ (g) → CO ₂ (aq) (2) CO ₂ (aq) + OH ^{− _{(aq) → HCO 3 - (}} aq) (3) HCO 3 - (aq) + OH - (aq) → CO 3 2- (aq) + H 2 O (aq) (4) Ca 2+ (aq) + CO ₃ ²⁻ (aq) → CaCO ₃ (s) (5) According to the film theory, the mass transfer resistance in these elementary reactions is a) resistance through a gas film, b) liquid boundary on the gas-liquid interface side. Resistance through the membrane; and c) resistance through the liquid-liquid membrane on the solid-liquid interface side.

In the above film theory, it is considered that the resistance of a) is small. The chemical reactions (3), (4) and (5) are fast. Therefore, it is considered that the rate-determining step of the whole reaction is (1) the dissolution reaction of calcium hydroxide through the liquid film or (2) the absorption reaction of carbon dioxide.

The solubility of calcium hydroxide and carbon dioxide decreases with increasing temperature. Therefore, the pH at the start of the reaction tends to be lower as the reaction temperature is higher.

For example, in the case of a suspension reaction solution which takes 2,000 minutes to complete the reaction, calcium hydroxide rapidly dissolves for 10 minutes immediately after the start of the reaction, for example, pH 8.5.
Shows a high pH. Then, 10 minutes after the start of the reaction, the calcium hydroxide became supersaturated, and the pH became 8.
It falls instantly from 5 to 8.2. 1 after the start of this reaction
From 0 minutes onward, it is presumed that magnesium hydroxide and amorphous calcium carbonate cover the surface of undissolved calcium hydroxide and suppress the dissolution of calcium hydroxide. Therefore, it is considered that calcium ions in the suspension reaction solution rapidly decrease, and a sharp drop in pH occurs.

After a sharp drop in the pH at the beginning of the reaction, calcium hydroxide gradually dissolves and Ca ²⁺ becomes
O ₃ ^2-and continue to react, i.e., (4) because of a little faster reaction than the reaction (5), reduced Ca ²⁺ in the suspension reaction solution gradually, pH is with the growth of calcium carbonate crystals It descends gradually.

Next, when the amount of Ca ²⁺ in the suspension reaction solution becomes extremely small, it is considered that the pH drops sharply, and the magnesium hydroxide precipitated as a result dissolves.

It is considered that the reaction is completed when the Ca ²⁺ in the suspension reaction solution is completely consumed.

The time until the reaction is completed (reaction time), that is, the blowing time of carbon dioxide, depends on the amount of the suspended reaction solution,
The concentration can be adjusted as appropriate by adjusting conditions that affect the temporal change of pH, such as the concentration of slaked lime, the concentration of Mg ²⁺ ions, the blowing speed of carbon dioxide, the reaction temperature, and the stirring state. The reaction time is preferably from 200 to 20,000 minutes, more preferably from 400 to 10,000 minutes, particularly preferably from 1,000 to 4,000 minutes.

The pH of the suspension reaction solution at the beginning of the reaction is preferably from 7 to 11, and the pH of the suspension reaction solution at the completion of the reaction is from 5 to 6.5.
Is preferred.

When the reaction temperature is high, since the solubility of CO ₂ is low, the supply rate of CO _{2 into} the suspension reaction solution is low, and it takes a long time until the carbonation of calcium ions is completed. It is thought that this suppresses the growth of calcite in the product and leads to the production of high-purity aragonite. For this reason, in order to obtain conventional high-purity aragonite-type calcium carbonate, it was necessary to increase the reaction temperature to 80 ° C. or higher.

On the other hand, according to the method of the present invention, quick lime or slaked lime is used as a starting material, Mg ²⁺ ions are used as an inhibitor of calcite-type calcium carbonate, and a suspension reaction liquid is used in the reaction process. Is produced at a low reaction temperature of less than 80 ° C., preferably 75 ° C. or less, more preferably 0 to 60 ° C., and particularly preferably 0 to 35 ° C. by making and mixing water streams having different flow directions in a tank. be able to. Moreover, even when the concentration of solutes and solids in the suspension reaction solution is high, or when a large amount of the suspension reaction solution is used in a large reaction tank, the non-uniformity of the crystallinity is eliminated, and the crystallinity is improved. A single-phase aragonite-type calcium carbonate can be produced with good yield without crystal breakage and high yield.

[0043]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the examples. The main properties of the obtained product or intermediate product were determined by the following methods.

Crystal system of calcium carbonate: X-ray diffractometer JEOL JDC-3500 was used, and the cathode was Cu
The scanning axis is 2θ · θ, and the product is 15 ° to 65 °.
The measurement was performed at an angle of ゜, a tube voltage of 30 kV, and a tube current of 20 mA.

Crystal shape and crystal size: Analyzed from data of photographs obtained using a scanning electron microscope (SEM) JEOL JXA-8900M.

Specific surface area: AUTOSORB1 manufactured by Yuasa Ionics Co., Ltd. was used. The pretreatment was performed at 120 ° C., and high-purity nitrogen was used as the adsorption gas, and measurement was performed by a 5-point BET method.

Hunter whiteness: Measured using Model Z-1001DP manufactured by Nippon Denshoku Industries Co., Ltd. The numerical value of Hunter whiteness was shown as a relative value when the whiteness of dolomite was 75.4% and the blackboard that did not reflect light was 0%.

PH: TOA H manufactured by Toa Denpa Kogyo KK
Using M-14P, the time-dependent change in pH was measured.

The slaked lime samples include scallop shell-derived C
a (OH) ₂ was used. The composition analysis result of this slaked lime sample was P 52.5 mg / 100 g, Fe 3.67 mg /
100 g, Ca 51.4 g / 100 g, Mg 87.2
mg / 100g, Zn 1.2ppm, Mn 10.1p
pm, Ni 0.9 ppm, Al 40 ppm, S 0.
The content was 42% by mass and 1320 ppm of Sr.

High purity carbon dioxide was used in the carbonation reaction of the slaked lime sample. In addition, magnesium chloride hexahydrate special grade reagent was used as a calcite inhibitor.

Examples 1 to 3 (0.4 dm^ThreeIn the reaction tank
Preparation of Aragonite-type Calcium Carbonate) Styrofoam Double Glass Cylinder with Lid (0.4dm^Threereaction
Tank), pure water 0.4dm^ThreeAnd then magnesium chloride
And 144.532 g of dimethylhexahydrate was added and dissolved. This
Slaked lime sample 32.922
g, and using a screw-type stirring blade, 470 r
Stir at a speed of pm and suspend. In this suspension,
0.036 dm purity carbon dioxide^Three/ Min blowing
I got into it. LAUDA RM20 for adjusting the temperature of the reactor
 The temperature was set as shown in Table 1 using a constant temperature bath. reaction
The pH of the suspension in TOA HM-14P
And the results of the time-dependent change in pH shown in FIG. 3 were obtained.
Was. After reacting for the time shown in FIG. 3, the suspension was filtered.
More solid-liquid separation was performed. The solid matter after separation is purified water 0.4 dm ^Three
Was washed once. The solid after washing is vacuum dried at 40 ° C.
Then, products having physical properties shown in Table 1, FIG. 4 and FIG. 5 were obtained.

[0052]

[Table 1]

As shown in Table 1, all of the reaction temperatures in Examples 1 to 3 showed a high yield of 90% by mass or more.

As shown in the column of crystal system in Table 1 and the X-ray diffraction chart in FIG. 4, the reaction temperature was 55.5 ° C. and 36.5 ° C.
The calcium carbonate produced at ° C. was highly pure aragonite. The calcium carbonate produced at a reaction temperature of 15.1 ° C. contained a small amount of calcite, but had a high purity of aragonite.

As shown in the column of crystal shape and crystal size in Table 1 and the scanning electron micrograph of FIG. 5, when the reaction temperature is high, the crystal grows larger and the crystal shape tends to become acicular. Was in

As shown in the column of specific surface area in Table 1, the reaction temperatures in all of Examples 1 to 3 were as high as 4 m ² / g or more. Further, the specific surface area of the crystal particles generated at a reaction temperature of 36.5 ° C. is lower than the specific surface area of the crystal particles generated at a reaction temperature of 15.1 ° C. This tendency can be explained by the fact that the higher the reaction temperature is, the larger the crystal size is, as described above. Contrary to this tendency, the specific surface area of the crystal particles produced at a reaction temperature of 55.5 ° C. was high. This high specific surface area is presumed to be due to the remaining magnesium hydroxide.
That is, during the pretreatment of the specific surface area measurement, in the portion of magnesium hydroxide finely dispersed in the aragonite crystals,
It is presumed that the surface area structure of the aragonite crystal changes significantly. In fact, the above presumption is supported by the fact that 77 hours were required for the pretreatment for measuring the specific surface area of the crystal particles produced at a reaction temperature of 55.5 ° C.

As shown in Table 1, the Hunter whiteness was higher than 96% at any of the reaction temperatures in Examples 1 to 3.

As shown in FIG. 3, the higher the reaction temperature, the lower the initial pH of the reaction. This is presumed to be because the solubility of calcium hydroxide decreases linearly with increasing temperature.

[0059] Example 4 to 6 (10 dm ³ reactor aragonite-type preparation of calcium carbonate) styrofoam lid with glass double cylinder (10 dm ³ reactor), placed pure water 10 dm ^3, then the magnesium chloride six 3613 g of hydrate was added and dissolved. To this aqueous magnesium chloride solution, 823.04 g of slaked lime sample was added, and the mixture was stirred and suspended at a speed of 2000 rpm using a screw-type stirring blade. High-purity carbon dioxide was blown into this suspension at a rate of 0.9 dm ³ / min.
The following reaction procedures were in accordance with the procedures of Examples 1 to 3. The temperature of the reaction tank was set to the temperature shown in Table 2. As a result of the temporal change of the pH of the suspension during the reaction, the result of the temporal change of the pH shown in FIG. 6 was obtained. After reacting for the time shown in FIG. 6,
The suspension was subjected to solid-liquid separation by filtration. The solid after the separation was washed with 10 dm ³ of pure water, and the solid after the washing was dried to obtain a product having physical properties shown in Table 2, FIG. 7, and FIG.

[0060]

[Table 2]

As shown in Table 2, the reaction temperature in any of Examples 4 to 6 was 90% by mass or more, which was a high yield.

As shown in the column of the crystal system in Table 1 and the X-ray diffraction chart in FIG. 7, the reaction temperature was 56.7 ° C. and 35.7 ° C.
The calcium carbonate produced at ° C. was single-phase aragonite. Calcium carbonate produced at a reaction temperature of 15.7 ° C. contained a small amount of calcite, but had a high purity of aragonite.

As shown in the column of crystal shape and crystal size in Table 2 and the scanning electron micrograph of FIG. 8, when the reaction temperature is high, the crystal grows larger and the crystal shape tends to be acicular. Was in

As shown in the column of specific surface area in Table 2, all of the reaction temperatures in Examples 4 to 6 were as high as 4 m ² / g or more.

As shown in Table 2, the Hunter whiteness was higher than 96% at any of the reaction temperatures in Examples 4 to 6.

As shown in FIG. 6, the higher the reaction temperature, the lower the initial pH of the reaction. This is presumably because, as described in Examples 1 to 3, the solubility of calcium hydroxide decreases linearly with an increase in temperature.

Study Examples 1 to 6 (Characterization of Intermediate Product) Using a 10 dm ³ reaction tank, the reaction temperature was set to 57.0 ° C., the operation was carried out according to the procedures of Examples 4 to 6, and Sampling was performed at the reaction times of Nos. 1 to 6 in FIG. 9 showing the change over time of the pH of the suspension, and the respective intermediate products were used as the samples of Study Examples 1 to 6.

The physical properties of these samples were measured using an X-ray diffraction measuring device and a scanning electron microscope.
The measurement results are shown in FIG. 10, FIG. 11, and FIG.

As shown in the X-ray diffraction chart of FIG.
In Study Examples 1 to 4, that is, in the early stage of the reaction, the pH was high, so that it was found that magnesium hydroxide was generated.

Investigation Example 2, ie, 110 minutes after the start of the reaction, very small amounts of aragonite-type calcium carbonate and calcite-type calcium carbonate were formed. Study Example 4, ie, reaction start 87
After 0 minute, a large amount of the same aragonite-type calcium carbonate and the same calcite-type calcium carbonate came to be formed. Then, in Study Example 5, ie, 1660 minutes after the start of the reaction,
Magnesium hydroxide rapidly disappeared, and pure aragonite-type calcium carbonate was produced.

As shown in the scanning electron micrograph of FIG. 11, fine particles presumed to be magnesium hydroxide can be confirmed in Examination Examples 1 and 2, ie, up to 110 minutes after the start of the reaction.
In Study Example 3, ie, 290 minutes after the start of the reaction, needle-like crystals of aragonite-type calcium carbonate can be confirmed.

As shown in the scanning electron micrograph of FIG. 12, in Examination Example 4, ie, 870 minutes after the start of the reaction, the needle-like crystals of the aragonite-type calcium carbonate grew to 5 to 10 μm. 1660 minutes after the start of the reaction,
Needle-like crystals of the same aragonite-type calcium carbonate
It grew to 15 μm. Then, in Study Example 6, ie, 1860 minutes after the start of the reaction (after the end of the reaction), the needle-like crystals of the aragonite-type calcium carbonate became 10 to 20 μm.

[0073]

According to the method of the present invention, quick lime or slaked lime is used as a starting material, Mg ²⁺ ions are used as an inhibitor of calcite-type calcium carbonate, and a suspension reaction solution is used in the course of the reaction. Since the water flows with different flow directions are created and mixed in the tank, when the concentration of solutes and solids in the suspension reaction liquid is high, or when a large reaction tank is used with a large amount of suspension reaction liquid However, the non-uniformity of the crystallinity is eliminated, the crystallinity is good, the crystal is not broken, and the single-phase aragonite-type calcium carbonate can be produced at a low reaction temperature with a high yield.

The Hunter whiteness of the calcium carbonate produced by the method of the present invention is extremely high.

[Brief description of the drawings]

FIG. 1 is a schematic view of a stirring blade used in the method for producing aragonite-type calcium carbonate of the present invention.

FIG. 2 is a schematic view of a stirring blade used in a conventional method for producing calcium carbonate.

FIG. 3 is a graph showing the change over time of the pH of each suspension at different reaction temperatures in a 0.4 dm ³ reaction tank in Examples 1 to ³ .

4] In the X-ray diffraction chart, A, B, and C represent the crystal systems of the respective products at different reaction temperatures in the 0.4 dm ³ reactor in Examples 1, 2, and 3, respectively. It is a line diffraction chart.

FIG. 5 is a scanning electron micrograph showing A and B, C and D,
And E and F indicate the crystal morphology of each product by reaction temperature in the 0.4 dm ³ reactor in Examples 1, 2 and 3, respectively, magnifications x2000 and x500
0 is a scanning electron micrograph.

FIG. 6 is a graph showing time-dependent changes in the pH of each suspension at different reaction temperatures in a 10 dm ³ reactor in Examples 4 to 6.

7] In the X-ray diffraction charts, A, B and C are X-ray diffractions showing the crystal systems of the respective products according to the reaction temperature in the 10 dm ³ reactor in Examples 4, 5 and 6, respectively. It is a chart.

FIG. 8 is a scanning electron micrograph showing A and B, C and D,
And E and F represent the crystal morphology of each product at different reaction temperatures in the 10 dm ³ reactor in Examples 4, 5 and 6, respectively, magnifications x2000 and x5000
3 is a scanning electron micrograph of the sample.

FIG. 9 is a graph showing the change over time in the pH of a suspension and the time of sampling of an intermediate product in a reaction for studying the characterization of an intermediate product in a 10 dm ³ reaction tank in Study Examples 1 to 6. is there.

FIG. 10 is an X-ray diffraction chart showing (1), (2), (3),
(4), (5), and (6) are Examples 1, 2,
9 is an X-ray diffraction chart showing a crystal system of an intermediate product at each sampling in a reaction for examining characterization of an intermediate product in a 10 dm ³ reaction tank in 3, 4, 5, and 6.

FIG. 11 In the scanning electron micrographs, A and B, C and D, and E and F indicate the characterization of the intermediate product in the 10 dm ³ reactor in Examples 1, 2, and 3, respectively. In the reaction to consider,
4 is a scanning electron micrograph at × 2,000 and × 5000 magnifications showing the crystalline form of the intermediate product at each sampling.

FIG. 12 In the scanning electron micrographs, A and B, C and D, and E and F show the characterization of the intermediate product in the 10 dm ³ reactor in Examples 4, 5, and 6, respectively. In the reaction to consider,
4 is a scanning electron micrograph at × 2,000 and × 5000 magnifications showing the crystalline form of the intermediate product at each sampling.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G076 AA16 AB02 AB06 AB28 AC10 BA34 BB03 BD10 CA29

Claims (5)

[Claims] 1. A method of mixing a suspension composed of quick lime or slaked lime, Mg ²⁺ ions and water by forming water flows having different flow directions in a tank and passing carbon dioxide gas through the suspension. A method for producing aragonite-type calcium carbonate, comprising: 2. A suspension obtained by adding quick lime or slaked lime to water containing Mg ²⁺ ions and mixing them by creating water flows having different flow directions in a tank, and adding carbonic acid to the suspension. A method for producing aragonite-type calcium carbonate, characterized by passing gas. 3. The method for producing aragonite-type calcium carbonate according to claim 1, wherein the quicklime or slaked lime is quicklime or slaked lime obtained by firing a shell. 4. A suspension comprising quick lime or slaked lime, Mg ²⁺ ions and water is brought to a temperature of less than 80 ° C., and mixed by forming water flows having different flow directions in a tank. A method for producing aragonite-type calcium carbonate, characterized in that carbon dioxide gas is conducted therein. 5. A suspension comprising quicklime or slaked lime, Mg ²⁺ ions and water is brought to a temperature of 0 to 35 ° C., and mixed with a water flow having different flow directions in a tank. A method for producing aragonite-type calcium carbonate, characterized in that carbon dioxide is passed through the liquid.