JP2001026419A - Manufacture of calcium carbonate and whitening of precipitated calcium carbonate from limestone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain calcium carbonate product small in particle size and high in whiteness by preparing cream of lime by reacting water with slaked lime obtained by firing shells, if necessary, together with slaked lime obtained by firing limestone and introducing gaseous carbon dioxide to the cream of lime to precipitate the product. SOLUTION: Shells of scallop, oyster, pearl oyster, etc., are pulverized into about 1 mm or smaller, preferably around 1-150 μm and fired at about 850-1,200 deg.C to obtain slaked lime, preferably having 90 wt.% or more CaO content. If necessary, the unslaked lime obtained by firing limestone is mixed to the slaked lime so that CaO from the shell unsalked lime is 5% or more, to which water is added to prepare slurry of around 5-15% and hydration reaction is carried out at about 40-80 deg.C. Gaseous carbon dioxide is introduced into the obtained cream of lime at 40 l/min.kg-Ca(OH)2 or less at 0-80 deg.C, preferably 20-60 deg.C to react the lime with the carbon dioxide. As a result, minute precipitated calcium carbonate having 96 or higher Hunter whiteness is obtained as precipitates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing precipitated calcium carbonate having high whiteness from shells and limestone.

[0002]

2. Description of the Related Art In Japan, limestone is produced abundantly in Japan. Calcium carbonate products manufactured using this limestone are inexpensive, have high whiteness, are harmless, and can be obtained in various particle sizes. It has been used in various fields as an extender, a filler for paper making, a pigment for paper coating, an additive for pharmaceuticals, cosmetics, food, agricultural supplies and the like.

[0003] This calcium carbonate product is generally classified into two types: heavy calcium carbonate and precipitated calcium carbonate (synthetic calcium carbonate).

[0004] Heavy calcium carbonate is produced by mechanically pulverizing limestone and classifying the pulverized product to produce heavy calcium carbonate having various particle diameters.

However, the above-mentioned heavy calcium carbonate has a broad particle size distribution for reasons of its production method. Therefore, no heavy calcium carbonate of any grade can be produced having a fine particle size and a narrow particle size distribution. For this reason, at present, the above-mentioned heavy calcium carbonate cannot be used for advanced applications that require a fine particle size and a narrow particle size distribution.

On the other hand, precipitated calcium carbonate is produced by a chemical method such as a carbon dioxide compounding process, a lime soda process, or a soda process. Carbon dioxide compounding process is to synthesize calcium carbonate by reacting calcined lime obtained by baking limestone at high temperature and water to prepare lime milk and then passing carbon dioxide gas generated during limestone baking into the lime milk to synthesize calcium carbonate. Is the way. The lime soda process is a method of synthesizing calcium carbonate by reacting soda with lime milk. The soda process is a method of synthesizing calcium carbonate by reacting sodium carbonate with calcium chloride.

[0007] The precipitated calcium carbonate produced by the above-mentioned chemical method has a fine particle size and a narrow particle size distribution, and therefore can be used in applications where these are required.

[0008] Of the above-mentioned methods for producing precipitated calcium carbonate, a carbon dioxide compounding process is generally used from a practical and economical viewpoint.

However, in recent years, in the use of the above calcium carbonate, the required quality level of calcium carbonate has been more and more increased. In particular, the required level of whiteness is extremely high for calcium carbonate for papermaking such as filler for papermaking and pigment for paper coating. Therefore, the precipitated calcium carbonate produced by the conventional carbon dioxide compounding process has a problem in that the quality of the raw material limestone varies, so that the above-mentioned required level of high whiteness may not be met. Therefore, a method for producing calcium carbonate that can stably supply high-quality calcium carbonate has been desired.

[0010]

As a result of various studies to solve the above problems, the present inventor has found that the use of shells as a raw material in a carbon dioxide compounding process can stably cope with a required level of high whiteness. It has been found that calcium carbonate can be obtained.

Further, when a predetermined amount of the above-mentioned shell is added to limestone as a raw material in the carbon dioxide compounding process, the obtained calcium carbonate can significantly improve whiteness as compared with calcium carbonate obtained using limestone as a raw material. To complete the present invention.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method for producing calcium carbonate capable of stably obtaining a product having a fine particle size and high whiteness.

[0013]

Means for Solving the Problems In order to achieve the above object, the present invention is characterized in that [1] carbon dioxide gas is passed through milk of lime consisting of quicklime and water obtained by firing a shell. Production method of calcium carbonate, [2] production of calcium carbonate, characterized in that carbon dioxide gas is passed through milk of lime consisting of quick lime obtained by baking shells and quick lime obtained by baking limestone and water The method, and
[3] quicklime obtained by firing shells and limestone;
The present invention proposes a method for producing calcium carbonate, characterized in that carbon dioxide gas is passed through lime milk composed of water. [4] In any one of the above [1] to [3], the shell is calcined. CaO component of quicklime obtained by
[5] In the above [2] or [3], the addition ratio of the CaO content of the shell is 5 wt% or more based on the total CaO content of the shell and limestone. Including.

[0014] The present invention also relates to [6] a limestone characterized in that carbon dioxide gas is passed through milk of lime consisting of quicklime obtained by firing shells and quicklime obtained by firing limestone and water. Whitening method of calcium carbonate produced by precipitation
And [7] a method for whitening precipitated calcium carbonate from limestone, characterized in that carbon dioxide gas is passed through milk of lime, which is obtained by calcining shells and limestone, and water. It is.

Hereinafter, the present invention will be described in detail.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As shells which are a raw material of calcium carbonate, any shells can be used, and examples thereof include scallops, oysters, oysters, clams, idiots, and red shells.

[0017] From the standpoint of the availability of shells, it is preferable that the shells are collected or cultured on a large scale, and the shells of the shells, which are collected or cultured after being processed in factories or the like, can be obtained collectively. From this viewpoint, scallops, oysters, oysters and the like are preferred.

The shell whose particle size has been adjusted is 850 to 1200 ° C.
The calcined shell lime is obtained by baking. Firing temperature 850
If the temperature is lower than ℃, calcination is insufficient and a large amount of unreacted calcium carbonate remains, which is not preferable. Further, even if the temperature exceeds 1200 ° C., overheating occurs, which is uneconomical in terms of thermal energy and is not very meaningful.

The method of uniform mixing differs depending on the furnace type.
In other words, when the shell or limestone, which is a raw material described later, is used with a size of 5 mm or more, the furnace is a Beckenbach furnace, a Melz furnace, a rotary kiln, or the like. do it,
Mix evenly.

However, the size of the shell and limestone is 5 mm.
In the following cases, the shell and limestone are quantitatively mixed in a fluidized firing furnace,
If necessary, uniform mixing is possible by pulverizing, quantitatively mixing, and firing.

The quick lime of the above shell has an average particle diameter of 1 mm.
Hereinafter, it is preferably pulverized to 1 to 150 μm. In particular, it is important for uniform mixing with limestone described later. When the average particle size of the shell quicklime exceeds 1 mm, the reaction (hereinafter, referred to as digestion) of the quicklime in the next step to become slaked lime by hydration, the dissolution rate of slaked lime, and the carbon dioxide absorption reaction (hereinafter, carbon dioxide gas) This is not preferred because the speed is reduced and the productivity of calcium carbonate is reduced.

The crushed shell lime is added with water and added
It is preferable to make a quicklime slurry having a concentration of 15 wt%. This quicklime slurry is preferably stirred and digested in an emulsification tank at 40 to 80 ° C., and then the foreign matter is sieved. Next, it is preferable to perform stirring aging in an aging tank. Thereafter, a carbon dioxide gasification reaction is performed. After that, remove foreign matter appropriately according to the usual method,
Dehydrate, dry and classify to obtain calcium carbonate product.

In the carbon dioxide gasification reaction, the temperature is from 0 to 80.
C., preferably 20-60 ° C., and the CO ₂ concentration is 20 ° C.
% Is preferable. The CO ₂ flow rate is 40 L / min · kg Ca (OH) ₂ when the CO ₂ concentration is 100%.
The following is preferred, and more preferably 0.1 to 4 L / mi.
n · kg Ca (OH) ₂ . The carbon dioxide gasification rate increases as the flow rate of CO ₂ increases, but it is 40 L / min · kgCa
(OH) carbon dioxide rate if greater than ₂ will not change very much undesirable because the reaction efficiency per CO ₂ flow rate is reduced.

Under the above conditions, the whiteness of calcium carbonate produced from shells is extremely high.

Further, as the CaO component of the shell material increases, the whiteness of the obtained calcium carbonate tends to increase. The CaO component of quicklime obtained by baking shells is 9
When a shell of 5 wt% or more, for example, 96 wt% is used as a raw material, the whiteness of the obtained calcium carbonate is 99 or more in terms of Hunter whiteness. The required whiteness of calcium carbonate varies from high to low depending on the use of calcium carbonate. Some applications with high whiteness requirements include
Some have a hunter whiteness of 93 or more. Therefore, in view of safety, the target hunter whiteness is set to 95 or more (hereinafter, this hunter whiteness is referred to as target whiteness).

On the other hand, under the same conditions as those for producing calcium carbonate using shells, the whiteness of calcium carbonate produced using limestone as a raw material, when ordinary limestone is used as the raw material, contains CaO component. Even when the amount is 96 wt%, which is the same as in the case of the shell, the hunter whiteness is 93
It is about.

The conditions for producing calcium carbonate using limestone as a raw material are the same as those in the case of using shells as a raw material.

As described above, there is a remarkable difference in the whiteness between calcium carbonate produced from shells and calcium carbonate produced from limestone. The cause may be a difference in components between the shell and the limestone. As in the above example, the CaO content of both is 96
Same as wt%. However, among the trace components, particularly, the iron content of limestone is 10 times or more that of the shell. Seashell F
While e ₂ O ₃ is usually 0.005 to 0.008 wt%, limestone Fe ₂ O ₃ is usually 0.02 to 0.2 wt%. It is considered that the difference in the iron content is one of the causes for lowering the whiteness of calcium carbonate produced from limestone. It has been confirmed that as the iron content of limestone increases, the whiteness of calcium carbonate produced from the limestone tends to decrease. Therefore, in the case where a higher demand in the future, for example, a demand of 95 or more such as the above-mentioned target whiteness, arises, it is difficult to handle the raw material only with limestone.

On the other hand, calcium carbonate produced by passing carbon dioxide gas through lime milk consisting of quicklime obtained by calcining shells and calcined limestone and water, and shells and limestone are produced. The whiteness of calcium carbonate produced by passing carbon dioxide gas through calcined lime obtained from calcining and lime milk consisting of water is the whiteness of calcium carbonate produced using shells and the limestone The present inventor has found that the whiteness of calcium carbonate produced as is much higher than that of whiteness calculated simply by proportional distribution (hereinafter referred to as calculated whiteness).

The whiteness of the resulting calcium carbonate is extremely high even if the addition ratio of the raw material shell is only a small amount relative to the other raw material limestone. For example, when the CaO content of the shell is 10 wt% with respect to the total CaO content in the raw material, the whiteness of the obtained calcium carbonate is about 96 in Hunter whiteness. As described above, the target whiteness is 95 or more. Therefore, the target whiteness can be satisfied if the CaO content of the shell is 5 wt% or more based on the total CaO content in the raw material. The addition ratio of CaO in the shell is preferably 6 to 50 wt.
%, More preferably 8 to 40 wt%, and even more preferably 9 to 35 wt%.

The timing of adding and mixing the raw material shell and limestone may be before or after firing the respective raw materials. When the time of addition and mixing of the raw material shell and limestone is after the firing of each raw material, in order to uniformly mix the quicklime obtained by firing the shell and the quicklime obtained by firing limestone, the particle diameter of each quicklime is required. The average particle size is desirably 1 mm or less, preferably 1 to 150 μm.

The reason why the whiteness of the obtained calcium carbonate can be improved to an extremely high level even when the amount of the shell material as a raw material is smaller than that of the other raw material limestone is presumed as follows. ing.

Shell quicklime has a slower digestion rate, a rate of dissolving slaked lime, and a lower carbon dioxide gasification rate than quicklime obtained by calcining limestone (hereinafter referred to as mineral quicklime).
Among these carbonation reactions, particularly, the dissolution reaction of slaked lime and the carbonation gasification reaction are rate-determining reactions, and in terms of the overall reaction rate of the carbonation reaction, shellfish lime is about 1/2 of mineral lime (this The reaction rate can be determined from the results of hydrochloric acid titration, which is a test method of the Japan Lime Association.)

Therefore, in the carbonation reaction, precipitated calcium carbonate (hereinafter, referred to as PCC) nuclei are generated first from the mineral quicklime. The PCC nucleus has low whiteness because it is derived from limestone as a raw material. And the PCC derived from the raw material limestone is added to this PCC core.
(Hereinafter referred to as mineral quicklime PCC) precipitates and grows, and primary particles of mineral quicklime PCC are generated.

On the other hand, P from shell quicklime generated later
CC (hereinafter referred to as shell quicklime PCC) has a very high whiteness because it is derived from the shell of the raw material. Then, shell quicklime PCC precipitates and grows on the surface of the primary particles of mineral quicklime PCC generated earlier, and secondary particles of mineral quicklime PCC coated with the shell quicklime PCC are generated.

That is, the surface of the primary particles of the mineral quicklime PCC having a low whiteness is changed to the shell quicklime PC having an extremely high whiteness.
It is considered that by coating with C, the whiteness of the obtained calcium carbonate can be improved to an extremely high level even if the addition ratio of the shell material as the raw material is only a small amount relative to the limestone as the other raw material.

The reason why shellfish lime has a lower carbonation reaction rate than mineral quicklime is estimated as follows.

Mineral quicklime has a large specific surface area with many relatively small pores developed. In contrast, shellfish lime has a small specific surface area due to a larger pore diameter. Specifically, quicklime obtained by calcining limestone has an average pore diameter of 10 to 100 nm, whereas calcined quicklime has an average pore diameter of about 1000 nm. The specific surface area of calcined limestone is 10 times or more larger than that of calcined lime obtained by calcining scallop shells and calcined limestone. The difference in the carbonation rate is
It is considered that the difference in specific surface area is affected, and thus, the quick lime of the shell has a lower carbonation reaction rate than the quick lime of the mineral matter.

The PCC generated from the mineral quick lime alone, that is, the particles of the mineral quick lime PCC, and the PCC generated from the mixture of the mineral quick lime and the shell quick lime (hereinafter, mixed quick lime P)
Called CC. The shape and size of the particles in ()) greatly differ in the particle growth.

That is, although the total amount of the raw quicklime used was the same, the particle size of the mixed quicklime PCC was
It was larger than the particle size of the mineral quicklime PCC. This is thought to occur because, in the mixed quicklime PCC, shell quicklime PCC that precipitates later is more likely to precipitate on the surface of the primary particles of mineral quicklime PCC generated earlier than precipitate as a new PCC nucleus. Can be

The particle shapes of the two PCCs are also greatly different, and the particles of the mineral quicklime PCC grow in the shape of a spindle, whereas the particles of the mixed quicklime PCC and the particles of the shell quicklime PCC are aragonite, aragonite (columnar). ) Or flat. From the difference in the particle shape of the PCC, it is considered that in the mixed quicklime PCC, the shell quicklime PCC that precipitates later precipitates and grows on the surface of the primary particles of the mineral quicklime PCC generated earlier.

In addition, when used as calcium carbonate for papermaking, the concealing rate of aragonite PCC or aragonite-like (columnar) PCC is higher than that of a cubic concealing rate which is a typical representative of a shape having a high concealing rate. high.

Further, aragonite PCC and aragonite-like (columnar) PCC have excellent dispersibility. The high dispersibility is an important property particularly required for calcium carbonate for papermaking, in addition to the high whiteness and the high hiding factor.

The flat PCC also has properties similar to aragonite PCC and aragonite-like (columnar) PCC.

[0045]

EXAMPLES Hereinafter, the present invention will be described specifically and in detail with reference to examples, but the present invention is not limited to the examples. The main physical properties of PCC were determined by the following methods.

Hunter whiteness: Calculated from the following equation using the measurement results with model Z-100DP manufactured by Nippon Denshoku Industries Co., Ltd. W (B) = Z × 100 / 1.18 where W (B): Hunter white Degree, Z: reflectance at 457 nm Particle shape and particle size: JEOL Ltd. electron microscope JS
Analysis from photograph obtained using M-5800LV and data of MO preservation Synthesis Example: E1 to E4 (Preparation of quick lime shell) Scallop shell was crushed to a particle size of 2 to 60 mm, average 40 m
m were used as shell raw lime production raw materials. This raw material was charged into an electric furnace and calcined at the temperature and time shown in Table 1 to obtain shell lime having a residual CO ₂ component (hereinafter referred to as RCO ₂ ) and a CaO component shown in Table 1.

Synthesis Example: Stone 1 (Preparation of Mineral Quick Lime) Limestone was crushed to have a particle size of 10 to 90 mm and an average of 50 mm, which was used as a raw material for producing mineral quick lime. This raw material was charged into an electric furnace and calcined at the temperature and time shown in Table 1 to obtain mineral quicklime of the remaining CO ₂ component and CaO component shown in Table 1.

[0048]

[Table 1] Examples 1 to 7 and Comparative Example 1 Synthesis Example: Table 2 shows quicklime obtained in E1 to E4 and Stone 1.
25g of raw lime prepared under the simple or blended conditions shown in
Was added with water to prepare 500 mL of lime milk having a concentration of 5 wt%. The obtained lime milk is blown with 100% pure CO ₂ gas at a gas flow rate of 1.0 L / min while stirring at a stirring rotation speed of 280 rpm using a stirring blade having four replaceable square blades. The reaction was carried out. The reaction temperature was controlled in the range of about 20 to 35 ° C., although there was some variation in each reaction. When the pH of the reaction solution reaches 7, CO ₂
The gas injection was stopped, and the carbonation reaction was terminated. Water was removed from the reaction product to obtain PCC having the physical properties shown in Table 2.

[0049]

[Table 2] * 1 The raw quicklime uses the synthesis example code shown in Table 1. * 2 The numerical value in parentheses is the calculated whiteness. Synthesis example: Carbonation reaction of the shell quicklime obtained in E1 to E4 is simply performed. Was. Regarding the obtained PCC, as shown in Examples 1, 2, 6 and 7 in Table 2, the hunter whiteness of the PCC from the raw shell lime alone showed a high value of 95 or more. Table 1 Synthesis Example: The CaO component in E1 was a calcined product at 1000 ° C. and had a CaO content of 9
6.0 wt%. As shown in Example 1, the Hunter whiteness also showed a high value of 95.7, even with PCC synthesized using this quick shell of lime.

Synthesis Example: Mineral quicklime obtained in stone 1 was subjected to carbonation reaction simply. About the obtained PCC,
As shown in Comparative Example 1 of Table 2, the Hunter-whiteness of the PCC synthesized using the mineral quicklime alone was as low as 93.2.

In addition to the mineral quicklime which can only be obtained from the mineral quicklime PCC having a low whiteness, the shell quicklime PCC having a high whiteness is added to the mineral quicklime.
As shown in Examples 3 to 5 in Table 2, the hunter whiteness of PCCs obtained by causing a carbonation reaction of mixed quicklime to which a small amount of shell quicklime obtained by the above method was performed showed a high value of 95 or more. . The value of the hunter whiteness of the PCC from these mixed quicklimes is calculated using the value of the hunter whiteness of the PCC from the shell quicklime alone and the value of the hunter whiteness of the PCC from the mineral quicklime alone. Hunter whiteness value calculated by simply proportional distribution (ie, the calculated whiteness value shown in parentheses in Table 2 of Examples 3 to 5) shows a much higher value. .

PCC of Tables 2 of Examples 3 to 5 and Comparative Example 1
As can be seen from the particle size results, the CaO concentrations of all the lime milks of Synthesis Examples: E1 to E4 and Stone 1 were the same. Nevertheless, the particle size of the mixed quicklime PCC of Examples 3 to 5 was larger than the particle size of the mineral quicklime PCC of Comparative Example 1. This means that there is a difference between the carbonation reaction rate of mineral quick lime and the carbonation reaction rate of shell quick lime, so that in the mixed quick lime PCC, the shell quick lime PCC that precipitates later does not precipitate as a new PCC nucleus. It is considered that the mineral matter was deposited on the surface of the primary particles of the generated quicklime PCC, resulting in an increase in the particle diameter.

The mixed quicklime PCC and the quicklime shell P
The particle size of CC is slightly larger than the particle size of mineral quick lime PCC, but can be sufficiently applied to advanced applications requiring a fine particle size and a narrow particle size distribution.

Electron micrographs of the calcium carbonate produced in Examples 3 to 5 and Comparative Example 1 are shown in FIGS. The particle shape of the mineral quicklime PCC of Comparative Example 1 in FIG. 7 is a spindle shape. On the other hand, the particle shape of the mixed quicklime PCC of FIGS. 2 to 4 is columnar or flat like the particle shape of the shell quicklime PCC of FIGS.
The particle shape of these PCCs could also be confirmed from the results of X-ray diffraction measurement.

From the measurement results of the particle shape of the PCC, it was confirmed that the particle surface of the mixed quicklime PCC was made of the shell quicklime PCC, similarly to the PCC from the shell quicklime alone. It is considered that the whiteness of the mixed quicklime PCC is extremely high, partly because the particle surface of the mixed quicklime PCC is made of shell quicklime PCC.

[0056]

According to the present invention, in a method for producing precipitated calcium carbonate produced by a carbon dioxide compounding process, since shell is used as a raw material, the precipitated calcium carbonate having a small particle size and high whiteness can be stably produced. Can be manufactured.

As described above, the precipitated calcium carbonate produced by the carbon dioxide compounding process using shells as a raw material has extremely high applications such as filler for paper sintering and calcium carbonate for paper making such as pigments for paper coating. We can respond to requests.

The present invention also relates to a method for producing a precipitated calcium carbonate produced by a carbon dioxide compounding process, wherein the above-described shell is used as a raw material for limestone, which is a conventional raw material which can only obtain precipitated calcium carbonate having low whiteness. By adding a small amount, precipitated calcium carbonate with significantly improved whiteness can be produced.

Further, the present invention provides a method for producing a precipitated calcium carbonate produced by a carbon dioxide compounding process, wherein a mixture of calcined limestone and calcined shell is used as a raw material. In addition, it is possible to produce precipitated calcium carbonate having significantly improved whiteness.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of PCC particles obtained in Example 2.

FIG. 2 is an electron micrograph of PCC particles obtained in Example 3.

FIG. 3 is an electron micrograph of PCC particles obtained in Example 4.

FIG. 4 is an electron micrograph of PCC particles obtained in Example 5.

FIG. 5 is an electron micrograph of PCC particles obtained in Example 6.

FIG. 6 is an electron micrograph of PCC particles obtained in Example 7.

FIG. 7 is an electron micrograph of PCC particles obtained in Comparative Example 1.

Claims (7)

[Claims] 1. A method for producing calcium carbonate, wherein carbon dioxide gas is passed through milk of lime composed of quicklime and water obtained by firing shells. 2. A method for producing calcium carbonate, comprising passing carbon dioxide gas into milk of lime comprising quicklime obtained by firing shells and quicklime obtained by firing limestone and water. 3. A method for producing calcium carbonate, characterized in that carbon dioxide gas is passed through milk of lime composed of calcined lime obtained by firing shells and limestone, and water. 4. CaO of quicklime obtained by firing shells
The method for producing calcium carbonate according to any one of claims 1 to 3, wherein the component is 90 wt% or more. 5. The CaO content of the shell is at least 5 wt% based on the total CaO content of the shell and limestone.
Or the method for producing calcium carbonate according to 3. 6. A method for whitening precipitated calcium carbonate from limestone, wherein carbon dioxide gas is passed through lime milk composed of quicklime obtained by calcining shells and quicklime obtained by calcining limestone, and water. Method. 7. A method for whitening precipitated calcium carbonate from limestone, wherein carbon dioxide gas is passed through milk of lime comprising calcined lime obtained by calcining a shell and limestone, and water.