JP2675465B2 - Hydrous calcium carbonate and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrous calcium carbonate and a method for producing the same. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Calcium carbonate is roughly classified into heavy calcium carbonate produced by mechanical crushing of natural limestone and synthetic (also called light or sedimentable) calcium carbonate produced by a chemical reaction. These calcium carbonates are available in various shapes and particle sizes, are inexpensive, are easy to color, and are harmless to the human body. Therefore, they are used in various fields such as fillers for papermaking and resins. Used in large quantities in.

As described above, calcium carbonate is widely and commonly used industrially, but it has been used only as an inexpensive inorganic powder until now, and most examples of calcium carbonate as a functional material. unknown.

Under such circumstances, CaCO ₃ .H ₂ O (monohydrate) and CaCO ₃ .can be added to calcium carbonate, which can be expected as a functional material and whose existence has been confirmed to date.
6H ₂ O (hexahydrate). Of these, the latter hexahydrate is well known as compared with the monohydrate, and has been used in J. Chem. Soc. , 123, 2409-2417
(1923), saccharose was added to synthesize,
The evaluated experiments have been reported, and Trans. Roy.
Soc. London, Vol. 243 A, 145-
167 (1950), when mixing the calcium chloride aqueous solution and the sodium carbonate aqueous solution, "Calgon (C
a kind of phosphate called "algon)" acts to synthesize hydrous calcium carbonate. Also, Date
r Res. , 14, 799-804 (1980), the characteristics of hexahydrate formed when softening river water are described.

According to various documents including these, hexahydrate is easily produced in a low temperature environment in the presence of saccharose, phosphate ions and the like, and is stable at 0 ° C. or lower. It has been clarified that there are many unclear points regarding the stability at higher temperatures, that it contains 52 wt% of water, and that the decomposition reaction has an endotherm of 50 kJ / mol and the release of water.

[0006]

As described above, the history of research on hydrous calcium carbonate is long, and despite the fact that it has interesting properties, there have been no examples of active synthesis so far. Good. It is considered that this is because hydrous calcium carbonate is inherently unstable, and even if it is formed, it is easily decomposed and cannot be stored.

In view of such circumstances, as a result of earnest studies, the present inventors have found a method capable of reliably producing hydrous calcium carbonate that is efficient and stable at a temperature higher than conventional ones, and arrived at the present invention. That is, an object of the present invention is to provide a stabilized hydrated calcium carbonate having a high practical value as a water supply agent, a moisturizing agent, a cooling agent, and a fire extinguishing agent, and a method for producing the same.

[0008]

Means and Actions for Solving the Problems The present invention addresses the above-mentioned problems by setting the water content in the range of 30 to 55 wt% at 5 ° C.
The problem was solved by obtaining stable hydrous calcium carbonate in an environment of 45 ° C. or lower.

The present invention also provides a method for producing calcium carbonate by subjecting an aqueous suspension of calcium hydroxide to a carbonation reaction, wherein phosphoric acid, carboxylic acid, hydrochloric acid,
The above problems have been solved by adding at least one of sulfuric acid, nitric acid, boric acid, amino acids or metal salts thereof.

Further, by adding at least one kind of phosphoric acid, carboxylic acid, hydrochloric acid, sulfuric acid, nitric acid, boric acid, amino acid or their metal salts to the produced water suspension of calcium carbonate to stabilize it. The above problems are solved.

The details of the present invention will be described below.

The hydrated calcium carbonate of the present invention can be added to calcium hydroxide slurry (hereinafter referred to as lime milk) with phosphoric acid or carbonate regardless of the conventionally known mixture of an aqueous solution containing calcium ion and an aqueous solution containing carbonate ion. It is produced by adding at least one kind of acid, hydrochloric acid, sulfuric acid, nitric acid, boric acid, amino acid or a metal salt thereof and conducting a carbonation reaction. As a raw material used when adjusting lime milk, calcium oxide and calcium hydroxide produced by burning limestone, which is abundant as a domestic resource, are practical, but even if metallic calcium is used, There will be no problem if the concentration and temperature are adjusted as described in. The concentration of lime milk is 40% by weight or less, and preferably 1 to 20% by weight based on the amount of calcium hydroxide. If the concentration is too low, the production efficiency will decrease, and if it is too high, sufficient stirring will not be possible and uniform reaction will not occur. The carbonation start temperature is 0 to 30 ° C, preferably 5 to 20 ° C. This is because the amount of the additive is smaller when the temperature is lower, and the hydrous calcium carbonate can be stably generated and exist in the lower temperature environment. Especially,
In the carbonation process, the heat of reaction raises the lime milk temperature, so caution is required. An additive such as phosphoric acid is added to lime milk adjusted to such conditions. The amount of the additive is 0.01 to 20 g, preferably 0.1 to 10 g, based on 100 g of calcium hydroxide. If the amount is too small, calcite may be mixed in in addition to hydrous calcium carbonate, or the target stability may not be obtained. On the contrary, even if a large amount of additive is added, the effect is limited and the additive is wasted. Carbonation gas may be used for the carbonation reaction, or a carbonate compound may be used. When carbon dioxide gas is used, it may be a pure gas obtained from a cylinder, but it is also possible to use a waste gas from a kiln which is generally industrially used during the production of quick lime. Examples of the carbonate compound include ammonium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate and the like. In this case, mechanical stirring is necessary because gas stirring is not performed.

The formation process can be grasped by continuously measuring the conductivity of the slurry during carbonation. For example, in the method of continuously introducing carbon dioxide gas into lime milk, which is the most common method of synthesizing calcium carbonate, the conductivity first drops, then recovers slightly, and then drops again. It is considered that amorphous calcium carbonate was mainly produced in the first drop, precipitation of hydrous calcium carbonate seed crystals was predominant in the recovery process, and crystal growth was mainly progressed in the second drop. The point where the electrical conductivity has dropped to the lowest level due to the second fall is the completion point of carbonation.

Phosphoric acid is added to an aqueous suspension of hydrous calcium carbonate,
Stabilized hydrous calcium carbonate can also be obtained by adding carboxylic acid, hydrochloric acid, sulfuric acid, nitric acid, boric acid, amino acids or metal salts thereof. In this case, the addition amount of the additive is 0.01 to 2 with respect to 100 g of calcium hydroxide.
It is 0 g, preferably 0.1 to 10 g.

The water-containing calcium carbonate thus obtained can be stored for a long period of time in a mother liquor at 45 ° C. or lower. If necessary, it can be taken out as a dry powder.

According to the present invention, limestone resources, which are abundant in Japan, are used to easily and efficiently produce hydrous calcium carbonate, which has previously been considered to be unstable and easily decomposed, in a stable state. Since it can be obtained and can be taken out as a dry powder, industrial use of hydrous calcium carbonate has become possible. Moreover, the calcium carbonate has completely different properties from so-called "tancal (calcium carbonate powder)" which is widely used industrially as a filler or a pigment.
The water content is in the range of 30-55 wt%. For example, when it consists only of hexahydrate, it contains 52 wt% of water, and in the decomposition reaction, there is an endotherm of 50 kJ / mol and release of water. After decomposition, it becomes calcite, which is completely harmless to the human body as well as the living world both before and after decomposition. In other words, this hydrated calcium carbonate can be safely used as a water supply agent, a moisturizing agent, a cooling agent, and a fire extinguishing agent, and it can be said that it is a new material with no concern for the global environment.

[0017]

EXAMPLES The present invention will be more specifically described below with reference to Examples and Comparative Examples.

Example 1 2 kg of tap water was placed in a cylindrical flask having a volume of 3 liters,
After adding 150 g of industrial slaked lime crushed to −325 mesh while stirring, 1 g of sodium pyrophosphate was added and cooled to 5 ° C. The conductivity at this time is 9.8 mS /
cm. This lime milk was maintained at 5 ° C. with stirring at 500 rpm, and introduction of carbon dioxide gas was started at a rate of 0.4 l / min. One minute after the start of introduction, the conductivity is 8.
It quickly decreased to 5 mS / cm, then gradually decreased, and decreased to 6.2 mS / cm 28 minutes after the start of carbonation and then started to increase. After 47 minutes, the conductivity was 8.4 mS.
/ Cm recovered. But after that, it started to fall again,
After 90 minutes, the conductivity had dropped to 0.5 mS / cm and carbonation was complete.

When the product was observed under an optical microscope, it was a granular to hexagonal thick plate-like transparent crystal having a size of 5 to 50 μm. When the product was filtered and subjected to powder X-ray diffraction,
JCPDS card 37- which is the data of the diffraction pattern
A diffraction pattern very close to 416 (CaCO ₃ .6H ₂ O) was obtained. Further, when a differential thermogravimetric analysis of the dry powder was performed, a weight loss of 50.59 wt% was observed by 120 ° C, and the starting temperature was 41.1 ° C.

Example 2 Hydrous calcium carbonate was synthesized under the same conditions as in Example 1.
Next, this slurry is heated at a rate of 0.7 ° C./min,
The slurry temperature at which changes in conductivity and pH appeared was taken as the decomposition temperature of hydrous calcium carbonate. The value obtained is 29
° C.

Example 3 Industrial quicklime is hydrated to give a solid calcium hydroxide content of 7 w.
The lime milk of t% was adjusted, and 2.15 kg was put into a cylindrical flask having a volume of 3 liters. 5 g of citric acid was added to this lime milk and cooled to 5 ° C. The conductivity at this time is 9.1 mS
/ Cm. This lime milk was maintained at 5 ° C. with stirring at 500 rpm, and introduction of carbon dioxide gas was started at a rate of 0.4 l / min. One minute after the start of introduction, the conductivity decreased promptly to 7.4 mS / cm, but then gradually decreased, and decreased to 6.5 mS / cm at 17 minutes after the start of carbonation, and then started to increase for 22 minutes. After that, the conductivity is 7.1.
Recovered to mS / cm. But after that, it started to drop again, and after 87 minutes, the conductivity dropped to 0.5 mS / cm,
Carbonation has ended.

When the product was observed under an optical microscope, it was a granular transparent crystal having a size of 5 to 50 μm. When the product was filtered and subjected to powder X-ray diffraction, a diffraction pattern very close to that of JCPDS card 37-416 was obtained. Further differential thermogravimetric analysis of the dry powder,
A weight loss of 50.93 wt% was observed by 120 ° C, and the starting temperature was 42.4 ° C.

Example 4 Hydrous calcium carbonate was synthesized under the same conditions as in Example 3.
Next, the decomposition temperature of hydrous calcium carbonate was measured in the same manner as in Example 2 to obtain a value of 28 ° C.

Example 5 2 kg of tap water was placed in a cylindrical flask having a volume of 3 liters,
After adding 150 g of industrial slaked lime crushed to −325 mesh while stirring, 2 g of sodium pyrophosphate and 3 g of sucrose were added, and the temperature was adjusted to 15 ° C. The electric conductivity at this time was 9.9 mS / cm. This lime milk is 500r
While maintaining at 15 ° C with stirring at pm, 1.0 liter /
The introduction of carbon dioxide gas was started at a rate of min. Introduction start 5
After a minute, when the conductivity was 6.0 mS / cm, the introduction of carbon dioxide gas was stopped. 96 minutes after the start of carbonation, the conductivity is 8.1 mS
When it was recovered to / cm, carbon dioxide gas was introduced again at a rate of 1.0 liter / min, and after 164 minutes, the conductivity was 0.7.
It decreased to mS / cm, and carbonation was completed.

When the product was observed under an optical microscope, it was a granular to hexagonal thick plate-like transparent crystal having a size of 5 to 120 μm. When the product was filtered and subjected to powder X-ray diffraction, a diffraction pattern very close to that of JCPDS card 37-416 was obtained.

Example 6 2 kg of pure water was placed in a cylindrical flask having a volume of 3 liters, 25 g of reagent metal calcium and 100 g of reagent calcium hydroxide were added while stirring, 3 g of sodium pyrophosphate was further added, and the temperature was adjusted to 5 ° C. did. The conductivity at this time is 9.
It was 2 mS / cm. This lime milk was maintained at 10 ° C. with stirring at 500 rpm, and introduction of carbon dioxide gas was started at a rate of 0.4 l / min. After 1 minute from the start of the introduction, the conductivity decreased promptly to 8.1 mS / cm, but after that, it gradually declined to 4.7 mS / cm 31 minutes after the start of carbonation.
After decreasing to cm, it started to increase, and after 48 minutes, the electric conductivity was recovered to 7.8 mS / cm. However, after that, it started to drop again, and after 103 minutes, the conductivity dropped to 0.9 mS / cm, and the carbonation was completed.

When the product was observed under an optical microscope, it was a granular to hexagonal plate-like transparent crystal having a size of 5 to 50 μm. When the product was filtered and subjected to powder X-ray diffraction,
A diffraction pattern very close to that of the JCPDS card 37-416 was obtained.

Example 7 1.5 kg of industrial slaked lime and 30 g of sucrose were put into a stainless container having a capacity of 30 liters containing 20 kg of tap water while stirring. The conductivity at this time is 9.6 mS
/ Cm, the temperature was 15 ℃. 16. While stirring a mixed gas of this lime milk and air having a carbon dioxide concentration of 30%, 16.
It was introduced at a rate of 7 liters / min. Fifteen minutes after the start of the introduction, when the conductivity dropped to 4.4 mS / cm, the introduction of carbon dioxide gas was stopped and only air was introduced. Conductivity is 7.1m
It quickly increased to S / cm and then gradually increased. 88 minutes after the start of introduction, when the conductivity recovered to 9.4 mS / cm, 10 g of sodium pyrophosphate was added, and the mixture was mixed with air having a carbon dioxide concentration of 30% again while stirring 1
It was introduced at a rate of 6.7 l / min. Introduction start 2
After 08 minutes, the conductivity dropped to 0.9 mS / cm and the carbonation was complete.

When the product was observed under an optical microscope, it was a granular to hexagonal thick plate-like transparent crystal having a size of 5 to 50 μm. When the product was filtered and subjected to powder X-ray diffraction,
A diffraction pattern very close to that of the JCPDS card 37-416 was obtained.

Example 8 1.5 kg of tap water was placed in a cylindrical flask having a capacity of 3 liters, 100 g of industrial slaked lime crushed to -325 mesh was added with stirring, 3 g of sodium pyrophosphate was added, and the temperature was adjusted to 5 ° C. did. Separately ammonium carbonate 154g
An aqueous solution of ammonium carbonate dissolved in 0.5 kg of tap water was prepared and gradually added to the lime milk prepared as described above while stirring and maintaining the temperature at 5 ° C. The addition was completed in 35 minutes, and stirring was continued for 15 minutes.

When the product was observed under an optical microscope, it was a granular to hexagonal thick plate-like transparent crystal having a size of 5 to 50 μm. When the product was filtered and subjected to powder X-ray diffraction,
A diffraction pattern very close to that of the JCPDS card 37-416 was obtained.

Example 9 The decomposition temperature of the hydrous calcium carbonate synthesized in Example 8 was
It measured by the method similar to Example 2, and obtained the value of 35 degreeC.

Comparative Example 1 2 kg of tap water was placed in a cylindrical flask having a volume of 3 liters,
While stirring, 150 g of industrial slaked lime crushed to −325 mesh was added and the temperature was adjusted to 5 ° C. The electrical conductivity at this time was 9.8 mS / cm. This lime milk is 500 rpm
Maintained at 5 ° C with stirring at 0.4 liter / min
The introduction of carbon dioxide gas was started at the speed of. One minute after the start of the introduction, the conductivity decreased promptly to 9.2 mS / cm.
After that, it gradually decreases, and 25 minutes after the start of carbonation, 5.9 m.
After decreasing to S / cm, it started increasing and after 43 minutes, the electric conductivity was recovered to 8.6 mS / cm. However, after that, it began to drop again, and after 74 minutes the conductivity was 0.3 mS / cm
And the carbonation has ended.

When the product was observed under an optical microscope, only a few crystals peculiar to hexahydrate were observed. The water-containing cake obtained by filtering the product was packed in a holder as it was, and immediately subjected to powder X-ray diffraction. Most of the peaks were calcite.

Comparative Example 2 2 kg of tap water was placed in a cylindrical flask having a volume of 3 liters,
After adding 150 g of industrial slaked lime crushed to −325 mesh while stirring, 1 g of sucrose was added and the temperature was adjusted to 5 ° C. The electrical conductivity at this time was 9.6 mS / cm. This lime milk was maintained at 5 ° C. with stirring at 500 rpm, and introduction of carbon dioxide gas was started at a rate of 0.4 l / min. Conductivity is 7.7 mS / c in 1 minute after starting the introduction.
It decreased rapidly until m, but then gradually decreased,
Seven minutes after the start of carbonation, it decreased to 6.6 mS / cm, then started to rise, and after 26 minutes, the electrical conductivity recovered to 8.6 mS / cm. However, after that, it started to drop again, and after 84 minutes, the conductivity dropped to 0.3 mS / cm, and the carbonation was completed.

When the product was immediately observed under an optical microscope, it was found to be transparent crystals peculiar to granular hexahydrate having a size of 5 to 50 μm, but the water-containing cake obtained by filtering the product was directly held in a holder. Then, powder X-ray diffraction was carried out promptly, but most of the peaks of calcite were observed, and it was revealed that the hexahydrate formed was an unstable one which decomposed in a short time.

Example 10 Sucrose was added under the same conditions as in Comparative Example 2, and 1 g of sodium pyrophosphate was added immediately after the carbonation of lime milk was completed. When a part of this water suspension was filtered and subjected to powder X-ray diffraction, a diffraction pattern very close to that of JCPDS card 37-416 was obtained. Further, when the decomposition temperature of this hydrous calcium carbonate was measured by the same method as in Example 2, it was 32 ° C.

In addition to the above, each additive was synthesized in the same manner as in Examples 1 and 2, and the decomposition temperature of hexahydrate was measured. The results are shown below.

[0039]

[Table 1]

The hydrated calcium carbonate synthesized by adding saccharose in the same manner as in Comparative Example 2 and stabilized by adding sodium pyrophosphate or citric acid as a stabilizer was measured in the same manner as in Example 2. The decomposition temperature is shown below.

[0041]

[Table 2]

[0042]

INDUSTRIAL APPLICABILITY According to the present invention, limestone resources which are abundant in Japan are used to easily and efficiently stabilize hydrated calcium carbonate, which has been conventionally considered to be unstable and easily decomposed. Can be manufactured well. Moreover, since it can be taken out as a dry powder, industrial use of hydrous calcium carbonate has become possible. Moreover, the hydrous calcium carbonate of the present invention has a water content of 30 to 55 wt%. For example, when it is composed only of hexahydrate, it contains 52 wt% of water, and in the decomposition reaction, there is an endotherm of 50 kJ / mol and release of water. Therefore, the hydrous calcium carbonate of the present invention has a high practical utility value as a water supply agent, a moisturizing agent, a cooling agent, a fire extinguishing agent, and a functional new material having no problem in the global environment.

[Brief description of the drawings]

FIG. 1 is a differential thermogravimetric analysis result of hydrous calcium carbonate obtained in Example 1.

FIG. 2 is a powder X-ray diffraction pattern of hydrous calcium carbonate obtained in Example 1.

FIG. 3 shows particles of hydrous calcium carbonate obtained in Example 1.
It is an optical microscope photograph (170 times) of the structure .

Claims (3)

(57) [Claims] 1. A hydrous calcium carbonate having a water content in the range of 30 to 55 wt% and stable under an environment of 5 ° C. or higher and 45 ° C. or lower. 2. In producing calcium carbonate by subjecting an aqueous suspension of calcium hydroxide to a carbonation reaction, phosphoric acid, carboxylic acid, hydrochloric acid, sulfuric acid, nitric acid, boric acid, and amino acid are added to the aqueous suspension. Or at least one of these metal salts
A method for producing hydrous calcium carbonate, which comprises adding seeds. 3. Stabilizing by adding at least one of phosphoric acid, carboxylic acid, hydrochloric acid, sulfuric acid, nitric acid, boric acid, amino acid or metal salts thereof to an aqueous suspension of hydrous calcium carbonate. The method for producing hydrous calcium carbonate according to claim 1.