JP2001354415A - Method for manufacturing lightweight calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing lightweight calcium carbonate having almost equal functions, especially high Hunter whiteness, as those of high-quality crystalline limestone by using low-quality limestone which exists abundantly as a source material. SOLUTION: In the method for manufacturing lightweight calcium carbonate, carbonic acid gas is introduced into a suspension liquid consisting of quicklime or slaked lime obtained by calcining limestone, quicklime or slaked lime obtained by calcining shell, Mg2+ ion and water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing light calcium carbonate having a high whiteness.

[0002]

2. Description of the Related Art The distribution of crystalline limestone is very limited because it is produced only when geological conditions are met. In Japan, only about several percent of limestone is expected to exist. And generally only form small deposits. In contrast, low-grade limestone other than crystalline limestone is extremely abundant in Japan, accounting for more than 90% of all limestone.

[0003] Calcium carbonate, which is the main component of limestone, has three types of polymorphs, namely, calcite, aragonite, and vaterite, that is, three types of 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.
For this reason, in the above-mentioned use as an industrial raw material,
Among calcium carbonates having various crystal systems, aragonite-type calcium carbonate can impart high functions similarly to crystalline limestone.

The above crystalline limestone has an intensity ratio of a peak derived from calcite to a peak derived from aragonite in X-ray diffraction, specifically, C104 / A111 of 2 or less,
Therefore, it can be said that it is substantially aragonite-type calcium carbonate.

[0008] High-quality crystalline limestone having a high hunter whiteness is a part of the above-mentioned crystalline limestone and forms only a small-scale ore deposit, and is extremely limited in resources. It is a valuable resource to produce. All of the domestic crystalline limestone mines are small and located inland,
High transportation cost and not suitable for long distance supply.
In addition, there is a tendency for ore depletion as a whole. As described above, there are various problems in obtaining crystalline limestone, particularly in obtaining high-quality crystalline limestone having high Hunter whiteness.

In the above three crystal systems, aragonite-type calcium carbonate is used as an industrial raw material when:
As with crystalline limestone, higher functions can be provided. In addition, synthetic calcium carbonate, that is, light calcium carbonate, has a wider application range in which a function suitable for industrial raw materials can be imparted than natural calcium carbonate, that is, heavy calcium carbonate. For this reason, aragonite-type calcium carbonate has been attempted to be manufactured industrially as light calcium carbonate.

However, according to previous studies, there is a problem that high-purity aragonite-type calcium carbonate cannot be synthesized at 80 ° C. or lower, especially at room temperature.

[0011]

The research and development group to which the present inventors belong has made various studies to obtain aragonite-type calcium carbonate at room temperature. Then, the starting material is a calcined material containing calcium oxide as a main component, which is obtained by pulverizing and calcining the shell to remove organic substances, and
It was discovered that high-purity aragonite-type calcium carbonate can be obtained at room temperature according to the method of producing light calcium carbonate in an aqueous solution using ²⁺ ions as a calcite-type calcium carbonate growth inhibitor. (Keiko Sasaki: Metal, Vol. 68, No. 9, P8
07 (1998); Keiko Sasaki, Masami Tsunekawa: Materials of the 1998 Autumn Meeting of the Society of Natural Resources and Materials; Keiko Sasaki, Hongo Univ.
Masami Tsunekawa: Resources and Materials, Vol. 114, No. 1
0, P715 (1998)).

However, in the above-mentioned method for synthesizing aragonite-type calcium carbonate, only shells are used as a starting material, and aragonite-type calcium carbonate having a high hunter whiteness using a large amount of inexpensive low-grade limestone as a starting material is used. Did not get.

The present inventors have further studied and found that even when low-grade limestone is used as a starting material,
It has been found that under a predetermined condition, aragonite-type light calcium carbonate having a high Hunter whiteness can be obtained, and the present invention has been completed.

Therefore, an object of the present invention is to solve the above-mentioned problems and to use low-grade limestone which is abundant in resources and have the same functionality as high-quality crystalline limestone.
It is an object of the present invention to provide a method for producing light calcium carbonate having particularly high Hunter whiteness.

[0015]

In order to achieve the above object, the present invention relates to [1] quicklime or slaked lime obtained by firing limestone, quicklime or slaked lime obtained by firing shells, and Mg ^{2 A} method for producing light calcium carbonate, characterized by passing carbon dioxide gas through a suspension comprising ⁺ ions and water, and [2] quicklime or slaked lime obtained by calcining limestone, and Mg ²⁺ Carbon dioxide gas is passed through a suspension composed of ions and water, and when the pH of the suspension becomes 8.5 or less, quicklime or slaked lime obtained by calcining the shell is added and carbonated. The present invention proposes a method for producing light calcium carbonate, characterized by passing gas, [3] keeping carbon dioxide gas in the suspension while keeping the temperature of the suspension at 0 to 60 ° C. Including.

Hereinafter, the present invention will be described in detail.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As a starting material of light calcium carbonate produced in the present invention, limestone and shells can be used.

As the limestone as a starting material, any limestone can be used as long as it is limestone, but it is particularly preferable to use low-grade limestone which is abundant in resources.

Further, according to the method for producing light calcium carbonate of the present invention, the colored component Fe ₂ O ₃ is added to limestone at a time when the limestone is calcined to obtain quick lime (based on CaO).
Those containing at least 02% by mass, particularly at least 0.2% by mass can also be used.

As the shell of the starting material, any shell can be used as long as the whiteness of the light calcium carbonate obtained by using it together with quicklime or slaked lime obtained by calcining limestone can be increased. The shells include scallops, oysters, oysters, clams, idiots,
Shells such as red shellfish can be exemplified.

Of these shells, shells that are easily available are particularly preferred.

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.

Quick lime or slaked lime obtained by calcining limestone can also be obtained in the same manner as in the method of producing quick lime or slaked lime obtained by calcining a shell. These processes are known to those skilled in the art.

The limestone and shell-derived quicklime obtained as described above can be used as a raw material for light calcium carbonate, but slaked lime obtained by hydrating these quicklimes is used as a raw material for light calcium carbonate. You can also.

The carbon dioxide gas is passed through a suspension of lime milk and lime or slaked lime derived from the limestone and shell obtained as described above, Mg ²⁺ ions, and water to cause a reaction. Even when limestone is used as a starting material, the Hunter brightness is 91% or more, preferably 92% or more, more preferably 92.5% or more, and particularly preferably 9% or more.
Light calcium carbonate of 4% or more can be produced.

The obtained light calcium carbonate has an intensity ratio of C104 / A111 of a peak derived from calcite to a peak derived from aragonite in X-ray diffraction of 2 or less, preferably 1 or less, more preferably 0 or less. It is characterized by being a high-purity aragonite-type calcium carbonate having a purity of 0.8 or less, particularly preferably 0.6 or less.

The above-mentioned lime milk composed of quicklime or slaked lime derived from limestone and shells, Mg ²⁺ ions and water is obtained by mixing quicklime or slaked lime and a water-soluble magnesium salt such as magnesium chloride with water. be able to.

Here, when the quick lime or slaked lime and the water-soluble magnesium salt are added to water, the order of addition is such that the water-soluble magnesium salt is added to the quick lime or slaked lime in order to surely dissolve the water-soluble magnesium salt in the water. Is more preferably added first. That is, when adding quicklime or slaked lime to water, it is preferable to add and dissolve a water-soluble magnesium salt in water in advance.

In the method for producing light calcium carbonate of the present invention, Mg ²⁺ ions are allowed to coexist in the suspension reaction solution.
In this suspension reaction solution, by allowing quick lime or slaked lime derived from limestone and shells to coexist with Mg ²⁺ ions, high-purity aragonite-type calcium carbonate at 80 ° C. or lower can be produced.

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. However, when the amount of Mg ²⁺ ions in the suspension reaction solution exceeds 100 at the initial molar ratio Mg / Ca in the suspension reaction solution, the remaining amount of the magnesium hydroxide that has not been redissolved increases. It is not preferable.

In the method for producing light calcium carbonate of the present invention, in order to keep the crystallinity of the obtained light calcium carbonate uniform and not to lower the yield,
In the reaction tank, there is an upward flow, a downward flow and other flows,
It is preferable to create a violent mixing state in which water streams having different flow directions coexist and to mix strongly.

As described above, in the case of mixing by forming a mixed state in which water flows having different flow directions coexist in the reaction tank, the calcium compound concentration of the suspension reaction solution is 5 based on Ca (OH) _2.
0 g / dm ³ or more, and even 60 g / dm ³ or more, especially 8 g / dm ³ or more.
Even at 0 g / dm ³ or more, the obtained aragonite-type calcium carbonate has uniform crystallinity and high yield, which is preferable.

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.

In the reaction between calcium hydroxide (slaked lime) and carbon dioxide in the suspension, immediately after the start of the reaction (start of blowing of carbon dioxide), the calcium hydroxide rapidly dissolves and exhibits a high pH, for example, pH9.

The later after the initiation of the reaction, calcium hydroxide was gradually dissolved, Ca ²⁺ is gradually reacted with CO ₃ ^2-, Ca ²⁺ in the suspension reaction mixture is reduced gradually, calcium carbonate crystals PH gradually decreases with the growth of.

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 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. In addition, about reaction temperature, 0-80
° C, preferably from 0 to 60 ° C, more preferably from 0 to 40 ° C.
° C, particularly preferably 0 to 30 ° C. Reaction temperature is 0 ° C
When the reaction temperature is lower than 80 ° C., the whiteness of the light calcium carbonate decreases, which is not preferable because the amount of calcite-type calcium carbonate generated increases.

In another embodiment of the method for producing light calcium carbonate of the present invention, carbon dioxide gas is added to a suspension comprising calcined lime or slaked lime obtained by calcining limestone, Mg ²⁺ ions, and water. This is a method for producing light calcium carbonate in which quick lime or slaked lime obtained by baking shells is added when the suspension is brought into conduction and the pH of the suspension becomes 8.5 or less.

In this case, the quicker the addition of quicklime or slaked lime obtained by firing the shell, the higher the whiteness of the obtained light calcium carbonate tends to be.

The reason is presumed as follows.

Before the addition of quicklime or slaked lime obtained by calcining shells in the carbonation reaction, light calcium carbonate derived from quicklime or slaked lime obtained by calcining limestone is produced. Light calcium carbonate derived from calcined lime or slaked lime obtained by calcining this limestone contains a large amount of iron oxide Fe ₂ O ₃ and thus has low whiteness. On the other hand, light calcium carbonate derived from quicklime or slaked lime obtained by firing shells has high whiteness.

From the above, in the carbonation reaction, when the addition time of quicklime or slaked lime obtained by calcining a shell is late, the surface of the light calcium carbonate particles having low whiteness containing limestone-derived Fe ₂ O ₃ is removed. It is presumed that the whiteness was enhanced by coating with light calcium carbonate having high whiteness derived from the shell.

[0045]

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.

As a slaked lime sample for increasing the whiteness, Ca (OH) ₂ derived from scallop shell was used. The composition analysis result of this slaked lime sample was P 52.5 mg / 100 g, F
e 3.67 mg / 100 g, Ca 51.4 g / 100
g, Mg 87.2 mg / 100 g, Zn 1.2 pp
m, Mn 10.1 ppm, Ni 0.9 ppm, Al
40 ppm, S 0.42 mass%, Sr 1320 ppm
Met.

The Fe ₂ O ₃ content of the low-grade quicklime sample was as follows:
0.18% by mass.

High-purity carbon dioxide was used for the carbonation reaction of Ca (OH) ₂ derived from low-grade quicklime and / or scallop shells. In addition, magnesium chloride hexahydrate special grade reagent was used as a calcite inhibitor.

Study Example 1 0.4 dm ³ of pure water was put into a glass double cylinder with a lid made of styrene foam (0.4 dm ³ reaction tank), and then 130.102 g of magnesium chloride hexahydrate was added and dissolved. Was. To this magnesium chloride aqueous solution, low-grade quick lime 11.24 was added.
5 g was added, and 470 was added using a screw-type stirring blade.
The suspension was stirred and stirred at a speed of rpm. In this suspension,
High-purity carbon dioxide was blown at a rate of 0.1 dm ³ / min. LAUDA RM20 for adjusting the temperature of the reactor
And the temperature was set to 23.8 ° C. The pH of the suspension during the reaction was measured using the TOA HM-14P described above. After reacting for 310 minutes, the suspension was solid-liquid separated by filtration. The solid after separation is purified water 0.4d
Washed once with m ³ . The solid after washing was vacuum dried at 40 ° C. to obtain a product having physical properties shown in FIGS. 1 and 6.

Examination Example 2 An aqueous magnesium chloride solution was obtained in the same manner as in Examination Example 1, and the calcium chloride derived from scallop shell was added to this aqueous magnesium chloride solution.
14.817 g of (OH) ₂ was added, and the mixture was stirred and suspended at a speed of 470 rpm using a screw-type stirring blade. 0.1 dm ^{3 of} high-purity carbon dioxide is added to this suspension.
/ Min. To adjust the temperature of the reactor
Use a constant temperature bath of LAUDA RM20 and adjust the temperature to 22.
Set to 4 ° C. Thereafter, the same operation as in Study Example 1 was performed to obtain a product, and the physical properties shown in FIGS. 1 and 6 were obtained for the product.

Study Example 3 A magnesium chloride aqueous solution was obtained in the same manner as in Study Example 1, and low-grade quick lime 11.24 was added to this magnesium chloride aqueous solution.
5g and 14.817g of Ca (OH) ₂ derived from scallop shell were added at the same time.
The suspension was stirred at a speed of 0 rpm and suspended. High-purity carbon dioxide was blown into this suspension at a rate of 0.1 dm ³ / min. LAUDA RM2 for adjusting the temperature of the reactor
The temperature was set to 22.5 ° C. using a thermostat of 0.
The pH of the suspension during the reaction is determined by the TOA HM-14P described above.
Was used to obtain the results of pH change over time shown in FIG. After reacting for the time shown in FIG. 2, the suspension was subjected to solid-liquid separation by filtration. The solid matter after separation is purified with pure water 0.4 dm ³
Was washed once. The washed solid was dried under vacuum at 40 ° C. to obtain products having the physical properties shown in FIGS. 1, 3, and 4.

The yield of this product was 37.6515 g, and the yield was 94.06% by mass.

Study Example 4 An aqueous magnesium chloride solution was obtained in the same manner as in Study Example 1, and low-grade quick lime 11.24 was added to the aqueous magnesium chloride solution.
5 g was added, and 470 was added using a screw-type stirring blade.
The suspension was stirred and stirred at a speed of rpm. In this suspension,
High-purity carbon dioxide was blown at a rate of 0.1 dm ³ / min. LAUDA RM20 for adjusting the temperature of the reactor
And the temperature was set to 22.5 ° C. The pH of the suspension during the reaction was measured using the above-mentioned TOA HM-14P, and the result of the time-dependent change in pH shown in FIG. 2 was obtained. 190 minutes after the start of carbon dioxide blowing, 14.817 g of scallop shell-derived Ca (OH) ₂ was added to the above suspension, that is, scallop was added at the pH drop point during the carbonation reaction of low-grade quicklime. Shell-derived Ca (OH) ₂ was added and the carbonation reaction continued. In addition, Ca (OH) ₂ derived from scallop shell
PH at the time of addition was 8.0. Hereinafter, after reacting for the time shown in FIG. 2, the same operation as in Study Example 3 was performed to obtain products having the physical properties shown in FIGS. 1, 3, and 4.

The yield of this product was 37.9575 g, and the yield was 94.89% by mass.

Study Example 5 A magnesium chloride aqueous solution was obtained in the same manner as in Study Example 1, and low-grade quicklime was added to this magnesium chloride aqueous solution.
5 g was added, and 470 was added using a screw-type stirring blade.
The suspension was stirred and stirred at a speed of rpm. In this suspension,
High-purity carbon dioxide was blown at a rate of 0.1 dm ³ / min. LAUDA RM20 for adjusting the temperature of the reactor
And the temperature was set to 22.5 ° C. The pH of the suspension during the reaction was measured using the above-mentioned TOA HM-14P, and the result of the time-dependent change in pH shown in FIG. 2 was obtained. 310 minutes after the start of carbon dioxide blowing, 14.817 g of Ca (OH) ₂ derived from scallop shell was added to the above suspension, that is, Ca (OH) ₂ derived from scallop shell was terminated after the carbonation reaction of low-grade quicklime was completed. OH) ₂ was added and the carbonation reaction continued. The pH at the time when Ca (OH) ₂ derived from the scallop shell was added was 6.0. Hereinafter, after reacting for the time shown in FIG. 2, the same operation as in Study Example 3 was performed to obtain products having the physical properties shown in FIGS. 1, 3, and 4.

The yield of this product was 37.0337 g, and the yield was 92.51% by mass.

As shown in the results of the yields of Study Examples 3 to 5, light calcium carbonate obtained by adding Ca (OH) ₂ derived from scallop shell at any time in the carbonation reaction of low-grade quicklime. Also had a high yield of 90% by mass or more.

As shown in the X-ray diffraction chart of FIG. 3, in the carbonation reaction of low-grade quicklime, carbon derived from scallop shells
Regarding the light calcium carbonate obtained by adding a (OH) ₂ at any point, the intensity ratio of the peak derived from calcite to the peak derived from aragonite in X-ray diffraction was C104 /
A111 was less than 1 and high purity aragonite-type calcium carbonate, but not a single phase of aragonite.
It was a mixed phase of aragonite and calcite.

As described above, instead of a single phase of aragonite, a mixed phase of aragonite and calcite became a crystal system because the flow rate of CO ₂ was 0.1 dm ^{3 with} respect to 0.4 dm ³ of the suspension.
It is presumed to be as large as ³ / min. That is, Ca ²⁺ +
The reaction of CO ₃ ^2- → CaCO ₃ quickly proceeds to the right, and the carbonation reaction rate increases. Therefore, it is presumed that calcite that is likely to be generated is generated when the carbonation reaction rate is high.

In the case of adding the low-grade quicklime and Ca (OH) ₂ derived from the scallop shell in the examination example 3 simultaneously, and in the carbonation reaction of the low-grade quicklime in the examination examples 4 and 5, the scallop shell-derived lime was used. In comparison with the case where Ca (OH) ₂ was added at another time, the obtained light calcium carbonate
As shown in the scanning electron micrograph, the addition time tends to increase the grain size of the crystal.

As shown in the results of the whiteness measurement in FIG. 1, in the carbonation reaction of low-grade quicklime, C derived from scallop shells was used.
Regarding the whiteness of the light calcium carbonate obtained at each addition time of a (OH) ₂ , 92.8 in the case of simultaneous addition in Study Example 3
2%, 94.54% in the case of addition at the pH lowering point of the carbonation reaction of low-grade quick lime in Study Example 4, and 95.82 in the case of addition after completion of the carbonation reaction of low-grade quick lime in Study Example 5. %.

From the results of the whiteness measurement of FIG. 1, Ca (OH) derived from scallop shells in the carbonation reaction of low-grade quicklime.
_It was found that the later the addition time of _2, the higher the whiteness of the obtained light calcium carbonate.

This is presumed as follows.

When Ca (OH) ₂ derived from scallop shells is added late in the carbonation reaction of low-grade quicklime, light calcium carbonate is previously generated by the carbonation reaction of low-grade quicklime. Since light calcium carbonate from this low-grade quicklime contains a large amount of iron oxide Fe ₂ O ₃ , the whiteness is as low as 90.52% as shown in Study Example 1 of the whiteness measurement result in FIG. On the other hand, light calcium carbonate from Ca (OH) ₂ derived from scallop shells is the same as in Example 2 of the whiteness measurement results shown in FIG.
As shown in Table 2, the whiteness is as high as 96.29%.

From the above, when Ca (OH) ₂ derived from scallop shells is added late in the carbonation reaction of low-grade quick lime, the surface of light calcium carbonate particles having low whiteness derived from low-grade quick lime is reduced by scallop. Ca (OH) ₂ derived from shells
It is presumed that light calcium carbonate having a high degree of whiteness is coated. On the other hand, in the carbonation reaction of low-grade quick lime, when the addition time of Ca (OH) ₂ derived from scallop shells is early, the surface of light calcium carbonate particles with low whiteness from low-grade quick lime or slaked lime is not coated, The proportion of particles that are crystallized only by light calcium carbonate from Ca (OH) ₂ derived from shells increases. Therefore, it is presumed that the whiteness was not so high because the thickness of the light calcium carbonate from Ca (OH) ₂ derived from the scallop shell surrounding the scallop shell did not increase.

Study Example 6 The carbonation reaction temperature was 57.5 ° C., and 14.817 g of Ca (OH) ₂ derived from scallop shell was added to the suspension 220 minutes after the start of the carbonation reaction of low-grade quicklime. Then, the same operation as in Study Example 5 was performed to obtain a product, except that the results of the time-dependent change in pH shown in FIG. 5 were obtained.
The physical properties shown in FIGS. 7 and 8 were obtained. The yield of this product was 39.9049 g, and the yield was 99.68% by mass.

Examination Example 7 The temperature of the carbonation reaction was 35.5 ° C., 190 minutes after the start of the carbonation reaction of low-grade quicklime, 14.817 g of Ca (OH) ₂ derived from scallop shell was added to the suspension. Then, the same operation as in Study Example 5 was performed to obtain a product, except that the results of the time-dependent change in pH shown in FIG. 5 were obtained.
The physical properties shown in FIGS. 7 and 8 were obtained. The yield of this product was 37.4614 g, and the yield was 93.58% by mass.

Examination Example 8 The carbonation temperature was 22.5 ° C. and 310.817 g of scallop shell-derived Ca (OH) ₂ was added to the suspension 310 minutes after the start of the carbonation reaction of low-grade quicklime. Then, the same operation as in Study Example 5 was performed to obtain a product, except that the results of the time-dependent change in pH shown in FIG. 5 were obtained.
The physical properties shown in FIGS. 7 and 8 were obtained. The yield of this product was 37.0337 g, and the yield was 92.51% by mass.

The product of the study example 8 is the same as that of the study example 5 described above.

As shown in the yield results of Examples 6 to 8, when Ca (OH) ₂ derived from scallop shell is added at the time after the end of the reaction for carbonating low-grade quicklime, the carbonation reaction temperature However, at any of 57.5 ° C., 35.5 ° C., and 22.5 ° C., the obtained light calcium carbonate had a high yield of 90% by mass or more.

As shown in the X-ray diffraction chart of FIG. 7, the carbonation reaction temperatures were 57.5.degree. C., 35.5.degree.
At any of 5 ° C., the obtained light calcium carbonate had an intensity ratio between the peak derived from calcite and the peak derived from aragonite in X-ray diffraction of C104 / A111 of 0.5.
The aragonite-type calcium carbonate was as low as below and high purity, but was not a single phase of aragonite but a mixed phase of aragonite and calcite. However, especially 57.5 ° C
Was a single phase of aragonite.

As described above, instead of a single phase of aragonite, a mixed phase of aragonite and calcite became a crystal system because of a suspension of 0.4 dm ^{3 and} a CO ₂ flow rate of 0.1 dm ³ .
It is presumed to be as large as ³ / min. This presumption is the same as the presumption in the case of examining the addition time of Ca (OH) ₂ derived from scallop shells in the carbonation reaction of low-grade quicklime in the above-mentioned examination examples 3 to 5.

As shown in the scanning electron micrograph of FIG.
It can be seen that the higher the carbonation reaction temperature, the larger the crystal grains grow.

As shown in the results of the whiteness measurement in FIG. 6, the whiteness of the obtained light calcium carbonate was 92.3% at the carbonation reaction temperature of 57.5.degree. 92.92% at a carbonation reaction temperature of 35.5 ° C., Study Example 8
At a carbonation reaction temperature of 22.5 ° C. was 95.82%.

From the results of the whiteness measurement shown in FIG. 6, it was found that the lower the carbonation reaction temperature, the higher the whiteness of the obtained light calcium carbonate.

From the above, it is considered that the mechanism of crystal growth plays a role in increasing the whiteness of light calcium carbonate.

[0082]

According to the method of the present invention, light calcium carbonate having high whiteness can be produced by using quicklime or slaked lime produced using a shell such as a scallop shell in the production of calcium carbonate. Therefore, low-grade limestone which is abundant in resources can be used as a starting material. Moreover, light calcium carbonate having the same functionality as high-quality crystalline limestone, particularly having high Hunter whiteness, can be produced at low reaction temperature and high yield.

The light calcium carbonate obtained by the method of the present invention is a high-purity aragonite-type calcium carbonate in which the non-uniformity of crystallinity is eliminated, the crystallinity is good, and the crystal is not broken. Due to its high degree of solubility, insolubility in pure water, and moderate specific gravity, it can be used as an important industrial raw material such as rubber, plastics, coatings, fillers and papermaking coatings. it can.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing the results of whiteness measurement of each product in each of the addition periods of Ca (OH) ₂ derived from scallop shells in the carbonation reaction of low-grade quick lime in Study Examples 1 to 5.

FIG. 2 is a graph showing the change over time of the pH of each suspension in the addition of Ca (OH) ₂ derived from scallop shells in the carbonation reaction of low-grade quick lime in Study Examples 3 to 5.

FIG. 3 shows (a), (b), and (c) in an X-ray diffraction chart.
Is the scallop shell-derived Ca in the carbonation reaction of low-grade quicklime in Examination Examples 3, 4, and 5, respectively.
4 is an X-ray diffraction chart showing the crystal system of each product for each addition time of (OH) ₂ .

FIG. 4 is a scanning electron micrograph showing A and B, C and D,
And E and F are respectively in the carbonation reaction of low-grade quick lime in Examination Examples 3, 4, and 5,
5 is a scanning electron micrograph at × 2000 and × 5000 magnifications showing the crystal morphology of each product according to the time of addition of Ca (OH) ₂ derived from scallop shell.

FIG. 5 is a graph showing the change over time of the pH of each suspension at different reaction temperatures in Examination Examples 6 to 8.

FIG. 6 After the carbonation reaction of low-grade quicklime, the carbonation reaction of Ca (OH) ₂ derived from scallop shell, or the carbonation reaction of low-grade quicklime in Study Example 1, 2, or 6 to 8 FIG. 9 is a graph showing the results of whiteness measurement of each product of the carbonation reaction at different reaction temperatures when Ca (OH) ₂ derived from scallop shells was added at the time point of FIG.

7] In the X-ray diffraction charts, A, B, and C are X-ray diffraction charts showing the crystal systems of the respective products at different reaction temperatures in Examination Examples 6, 7, and 8, respectively.

FIG. 8 is a scanning electron micrograph showing A and B, C and D,
In addition, E and F are scanning electron micrographs at × 2,000 and × 5000 magnifications, respectively, showing the crystal morphology of each product according to the reaction temperature in Examined Examples 6, 7, and 8.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Yamashita 3-1-1-12 Shinnakano-cho, Tomakomai-shi, Hokkaido F-term in Hokkaido Joint Lime Co., Ltd. 4G076 AA16 AB02 AB06 AB28 AC01 BA34 BB03 BC10 BD01 BD02 CA29 CA33

Claims (3)

[Claims] (1) quicklime or slaked lime obtained by calcining limestone; and quicklime or slaked lime obtained by calcining a shell;
A method for producing light calcium carbonate, comprising passing carbon dioxide gas through a suspension comprising Mg ²⁺ ions and water. 2. A carbon dioxide gas is passed through a suspension composed of quick lime or slaked lime obtained by calcining limestone, Mg ²⁺ ions, and water, so that the pH of the suspension becomes 8.5 or less. A method for producing light calcium carbonate, comprising adding calcined lime or slaked lime obtained by calcining a shell at the time of the addition, and conducting carbon dioxide gas. 3. The method for producing light calcium carbonate according to claim 1, wherein the temperature of the suspension is maintained at 0 to 60 ° C., and carbon dioxide gas is passed through the suspension.