JP2001199721A - Method for producing both of calcium carbonate and sodium hydroxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously obtain both of calcium carbonate of aragonite crystal useful as filler and pigment for various kind of materials and an aqueous solution of sodium hydroxide not jointly producing chlorine by utilizing caustification reaction. SOLUTION: Quiklime and/or slaked lime are/is mixed with an aqueous solution of sodium hydroxide having a specific concentration or below and containing carbonate ions in a specific concentration range based on 1 mol in terms of quicklime while being stirred to prepare milk of lime. An aqueous solution of sodium carbonate derived from soda ash in a specific amount necessary for producing sodium hydroxide is added to the milk of lime under a condition that addition rate and reaction temperature are controlled to obtain both of calcium carbonate of aragonite crystal and sodium hydroxide not jointly producing chlorine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing calcium carbonate of aragonite crystals useful as fillers and pigments for various materials by a causticization reaction and sodium hydroxide used in many industries. Specifically, a specific sodium hydroxide aqueous solution is used as a liquid used when stirring quick lime and / or slaked lime, and an aragonite crystal useful as a filler / pigment is obtained by adding a sodium carbonate aqueous solution derived from soda ash to the lime milk. The present invention relates to a method for producing calcium carbonate and a method for producing sodium hydroxide used in many industries.

[0002]

2. Description of the Related Art Calcium carbonate is used in a wide range of industrial fields such as papermaking, rubber, plastics and the like, and its use is rapidly increasing especially in the papermaking field. These reasons are
(1) Inexpensive, (2) High whiteness, (3) Controllable in various shapes, etc., and therefore, its utility value is high. Calcium carbonate contains calcite, aragonite, and vaterite.
There are three types of crystalline polymorphs, most of which are calcite in nature, and vaterite is not generally present, only aragonite is present in some shells. Among these crystalline polymorphs, aragonite has characteristic crystal habits such as needle-like, column-like, and digging-like, and is useful not only as fillers and pigments for paper but also as fillers for rubber and plastic. It is. For example, when aragonite crystal calcium carbonate is used as a filler for paper, the opacity, bulkiness, stiffness, whiteness, etc. of the paper are improved as compared with naturally occurring heavy calcium carbonate. However, since it is hardly produced in nature, there is no other method than artificial production. The methods for producing calcium carbonate include (1) a carbon dioxide gas method by the reaction of carbon dioxide gas and an aqueous suspension of calcium hydroxide, (2) a calcium chloride soda method by the reaction of sodium carbonate and calcium chloride, and (3) carbon dioxide. The reaction of the lime method by the reaction between sodium and milk of lime is exemplified. Among these methods for producing calcium carbonate, the method for producing aragonite crystalline calcium carbonate is a method using an additive such as a phosphoric acid compound using the carbon dioxide method of (1) (JP-A-63-256514).
Japanese Patent Application Laid-Open No. 4-250010, and a method for defining the viscosity of an aqueous suspension of calcium hydroxide (Japanese Patent Application Laid-Open No. 4-295010). However, these carbon dioxide methods are costly because calcium carbonate is the only product. In the method (2), it is difficult to effectively use the by-products, so that there is a problem in cost. As another method, there is a method using the lime method of (3) disclosed by the present inventors (JP-A-10-226974). This method is basically the same as the method of (3), but produces white liquor, a chemical used to make wood chips into pulp, in the chemical recovery process of the sulphate method and the soda method, which are pulp manufacturing processes. The purpose is to obtain pure sodium hydroxide which can be used in many industries. In addition, the green liquor contains Na ₂ S ₃ in addition to Na ₂ CO ₃ , so that it was necessary to reduce the addition rate of the green liquor in order to produce calcium carbonate having a high content of aragonite crystals. Furthermore, in the case of paper filler, the opacity of the paper is considered to be the best when the minor axis of the needle shape is about 0.2 to 0.4 μm, but when compared at the same sodium carbonate addition rate, sodium carbonate derived from soda ash is It is easier to control this minor diameter range when using green liquor than when using green liquor. In addition, since the pulping process is of a circulating type, impurities derived from wood chips enter calcium carbonate and sodium hydroxide. As a result, calcium carbonate causes a decrease in whiteness.

On the other hand, sodium hydroxide is widely used as a raw material for various chemical products such as bleaching of paper pulp and synthetic resins such as vinyl chloride resins and epoxy resins.
As a method for producing sodium hydroxide, there is an electrolytic method for obtaining sodium hydroxide and chlorine by electrolyzing a salt. The electrolysis method includes an asbestos diaphragm method, a mercury method, and an ion exchange membrane method, and the ion exchange membrane method is currently the mainstream. However, in this electrolysis method, chlorine is generated together with sodium hydroxide.In recent years, awareness of environmental issues has increased, and there is a growing tendency to be tired of chlorine, which is a cause of dioxin formation. A method for producing sodium is desired. Thus, examples of a method for producing sodium hydroxide without producing chlorine include the lime method of reacting sodium carbonate and lime milk, a bleaching method, and an iron oxide method using sodium carbonate and iron oxide. , Both of which have long been considered but not industrialized, were manufactured industrially until more than 30 years ago. However, as described above, this lime method is not currently employed as a method for producing sodium hydroxide, but is only used in the chemical recovery step of the sulfate method or soda method, which is a pulp production process. . This is partly due to the fact that this production method was considered only as a production method of sodium hydroxide, and as described above, calcium carbonate produced co-produced was not much studied. As described above, there has been no example of a method capable of producing sodium hydroxide without producing chlorine simultaneously with producing aragonite crystal calcium carbonate useful as a filler / pigment of various materials.

[0004]

In view of the above situation, in order to simultaneously provide an aqueous sodium hydroxide solution which does not produce calcium carbonate and chlorine in aragonite crystals useful as fillers and pigments for various materials, An object of the present invention is to obtain calcium carbonate and sodium hydroxide of aragonite crystals by utilizing a chlorination reaction.

[0005]

Means for Solving the Problems The present inventors utilize a causticizing step of a pulp production process by a sulfate method or a soda method so that quick lime or quick lime may be adjusted to a concentration of 1 to 60% by weight. Add an aqueous alkali solution of a specific concentration or less containing a specific amount of carbonate ion or less per mol of quicklime to slaked lime, and stir to prepare lime milk.Continuously add green liquor, and then add It has been found that aragonite crystals can be obtained by controlling the rate and the reaction temperature. However, in this method, sodium sulfate is contained in the sulfate method, and since the sulfate method and the soda method are circulating processes, impurities derived from wood chips are increased.As a result, the whiteness of calcium carbonate is reduced, and Neither can pure sodium hydroxide be produced. Therefore, the present inventors have further studied intensively, and as a result, 1 mol in terms of quick lime is converted into quick lime and / or slaked lime so that the concentration of quick lime becomes 1 to 60% by weight, preferably 20 to 40% by weight by a causticization reaction. 0 for
25 mol, preferably containing 0.10 mol or less of carbonate ions, 2 mol
/ l or less sodium hydroxide aqueous solution, and a predetermined amount of sodium carbonate aqueous solution derived from soda ash necessary for producing sodium hydroxide is added to the lime milk prepared while stirring, and the addition rate and the reaction temperature. It has been found that by controlling the concentration of sodium hydroxide, sodium hydroxide that does not co-produce calcium carbonate and chlorine in aragonite crystals can be produced, and the present invention has been accomplished based on this finding. Here, the pH of the aqueous sodium hydroxide solution containing carbonate ions preferably exceeds 13.5. Further, in the above-mentioned aqueous sodium hydroxide solution, the lower limit of the concentration of carbonate ions is not specified, because the numerical value fluctuates due to dissolution of carbon dioxide gas in air in the aqueous sodium hydroxide solution, so that control is impossible. . According to the method of the present invention, it is possible to produce calcium carbonate having a high aragonite crystal content and a high whiteness with a controlled shape, and having a minor axis of 0.1 to 1.5 μm and a major axis of 0.3 to 15 μm. It was found that calcium carbonate in the form of powder was prepared. For example, when used as a filler for papermaking, the whiteness, opacity,
Excellent in bulkiness and strain. On the other hand, sodium hydroxide produced simultaneously with calcium carbonate can be produced without co-producing chlorine, so that pure sodium hydroxide can be produced as compared with the sulfate method or the soda method. Therefore, calcium carbonate produced by this production method can be produced at a low cost because sodium hydroxide can be produced together with calcium carbonate produced by this production method as compared with calcium carbonate obtained by a conventional method of reacting milk of lime with carbon dioxide gas.

[0006]

DETAILED DESCRIPTION OF THE INVENTION Quicklime used in the preparation of lime milk of the present invention is limestone containing calcium carbonate as a main component and sodium carbonate is converted into sodium hydroxide in a causticizing step of pulp production by a sulfate method or a soda method. What is necessary is just to calcine calcium carbonate generated at the time of conversion. In addition, regarding the firing apparatus at that time, Beckenbach furnace, Meltz furnace, rotary kiln, Kunii type furnace, KH
D (Car Hardy) furnace, Coma furnace, Calmatic furnace,
The apparatus is not particularly limited as long as it is an apparatus for converting calcium carbonate into quick lime (calcium oxide), such as a fluidized sintering furnace and a mixed sintering furnace.

[0007] Regarding the content of impurities in calcium carbonate, for example, when used for paper, especially coloring components (Fe, Mn, etc.)
May be a problem, but quick lime obtained from raw limestone having a low coloring component content may be appropriately selected according to the use of the product.

The slaked lime used in the preparation of milk of lime may be one obtained by slaking the quick lime by a wet method and a dry method, but the slaked lime slaked by a dry method is more preferable for the form of calcium carbonate to be formed.

As a liquid to be added in the preparation of lime milk, a 2 mol / l or less aqueous sodium hydroxide solution containing 0.25 mol, preferably 0.1 mol or less, of carbonate ion per mol of quick lime is used. Preferably, an aqueous sodium hydroxide solution having a pH above 13.5 is used. In order to obtain higher quality aragonite crystals, it is more preferable to use an aqueous solution of sodium hydroxide containing less carbonate ions. When the carbonate ion is more than 0.25 mol per 1 mol of quicklime, the calcium carbonate formed becomes a spindle-shaped or amorphous calcite crystal. Further, when the concentration of the aqueous sodium hydroxide solution containing carbonate ions in the above concentration range exceeds 2 mol / l, the causticization reaction becomes difficult to proceed, and the conversion rate from sodium carbonate to sodium hydroxide decreases. If the amount of sodium carbonate increases after the reaction, the purification step after the causticizing step is hindered, which is not preferable from the viewpoint of the production of sodium hydroxide.

The concentration of quicklime at the time of the preparation of lime milk must be 10 to 60% by weight, preferably 20 to 40% by weight in terms of quicklime. Here, if the concentration of quicklime exceeds 60% by weight, the viscosity of lime milk is too high and stirring becomes difficult in practice,
If the concentration of quicklime is less than 10% by weight, the productivity is low and it is not practical. Furthermore, in the production of sodium hydroxide, the final sodium hydroxide concentration is 70 g / l to 130 g / l, preferably 110 to
Since the load in the next evaporation step can be reduced by setting the concentration to 130 g / l, it is necessary to determine the concentration of quick lime, the concentration of sodium hydroxide and the concentration of sodium carbonate added during the preparation of lime milk so that the final concentration falls within the above range. Good.

For the mixing of slaked lime and dissolution of slaked lime, general stirring blades, pumps, extruders,
It may be appropriately selected from kneading machines and kneading machines according to the viscosity of the liquid or slurry at the time of mixing (refer to Chemical Engineering Handbook, published by Maruzen Co., Ltd. on March 18, 1988).

As the aqueous sodium carbonate solution derived from soda ash in the causticization reaction of the present invention, an aqueous solution in which natural soda ash or synthetic soda ash is dissolved in water can be used.
Considering the whiteness of the obtained calcium carbonate, it is preferable to use a raw material having a small amount of elements such as Fe and Mn, which are substances causing coloring, and a high purity of sodium carbonate. The lime concentration is low, and the sodium hydroxide concentration after the causticization
Sodium carbonate solids can also be used to bring the range from 70 g / l to 130 g / l. When an aqueous sodium carbonate solution is used, it is necessary to carry out the reaction at a sodium carbonate concentration of 100 to 230 g / l, preferably at a sodium carbonate concentration of 150 to 200 g / l. If the concentration of sodium carbonate is lower than 100 g / l, the concentration of sodium hydroxide after the causticization reaction becomes low, and the load in the subsequent evaporation step becomes undesirably large. on the other hand,
Since a solution with a concentration of 230 g / l is close to the saturation concentration, a solution with a higher concentration cannot be produced.

The mixing method of the lime milk and the aqueous solution of sodium carbonate is characterized in that the addition rate of the sodium carbonate component is set to
0.002-0.12 g / min / g, preferably 0.002-0.04 g / min / g
Must be done in At this time, if the addition rate of sodium carbonate is less than 0.002 g / min / g, productivity is poor and not practical. When it is higher than 0.12 g / min / g, massive calcite crystals are formed.

Regarding the causticization reaction temperature, the reaction temperature is 30
It must be carried out at ~ 105 ° C, preferably 40-90 ° C. 105 ℃
If the pressure is higher than the above, the temperature exceeds the boiling point under the atmospheric pressure, so that a pressurized causticizer or the like is required, which is uneconomical. On the other hand, if the temperature is lower than 30 ° C., it is not preferable because aragonite crystals are hardly formed and the conversion rate to sodium hydroxide is lowered. The stirring at the time of the causticization reaction includes, among general stirring blades, pumps, extruders, kneaders and kneaders, lime milk prepared by slaking quicklime and dissolving slaked lime. What is necessary is just to appropriately select and use one that can uniformly mix the sodium carbonate solution (see Chemical Engineering Handbook, published by Maruzen Co., Ltd. on March 18, 1988). The mixed suspension of calcium carbonate and sodium hydroxide after the causticization reaction is separated into calcium carbonate and an aqueous sodium hydroxide solution using a thickener, a vacuum rotary cylindrical filter, a pressurized filter, a centrifugal separator, etc. Is further washed with water. The washing water generated at this time can be used for dissolving the soda ash to prepare an aqueous sodium carbonate solution.

Under the above-described conditions, it is possible to adjust the needle-like, columnar, or digging-like calcium carbonate of aragonite crystals having a minor axis of 0.1 to 1.5 μm and a major axis of 0.3 to 15 μm. Furthermore, a pure sodium hydroxide aqueous solution can be obtained without producing chlorine.

By using the calcium carbonate of aragonite crystals obtained by the present invention, for example, as a filler or pigment for paper, excellent characteristics such as whiteness, opacity, bulkiness, and strain are imparted. In addition to papermaking, it can be used for rubber, plastic, paint, sealant, adhesive, fertilizer, and the like.

Further, the aqueous solution of sodium hydroxide obtained in the present invention can be used for bleaching paper pulp, and the obtained aqueous solution of sodium hydroxide can be used as a chemical raw material for synthetic resins and the like through a purification process which is generally performed. it can. Further, the sodium hydroxide can be circulated and used as an aqueous sodium hydroxide solution used when stirring quicklime and / or slaked lime as described above.

[0018]

EXAMPLES The present invention will be described below in more detail with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited to only Examples. [Test Method] Light Cal Average Particle Size: The product was washed with water, filtered, diluted with water, and then subjected to laser diffraction type particle size distribution analyzer (Cirrus Model 71).
The average particle diameter was measured in 5). Morphological observation: The product was washed with water, filtered, dried, and observed with a scanning electron microscope (JSM-5300, manufactured by JEOL Ltd.). Based on this observation, the minor axis and major axis were measured for 30 particles. Crystal structure: Measured by X-ray diffraction RAD-2C manufactured by Rigaku. Measurement of whiteness: The dried light calm was pressed at 5 ton for 3 minutes to form a pellet, which was measured with a Hunter whiteness meter (manufactured by Toyo Seiki Seisaku-sho, Ltd.). [Example 1] In a four-neck flask container having an appropriate capacity (the same container is used for the following Examples and Comparative Examples), slaked lime and 1
Using a mol / l-NaOH aqueous solution, lime milk is made by mixing at a ratio of 10% by weight as quicklime, and a sodium carbonate aqueous solution (composition: Na ₂ CO ₃ = 1.6 mol /
l), the addition rate is 0.02 g (sodium carbonate) / min /
g (quicklime), temperature 50 ° C, stirring speed 400rpm (KYOEI POWER S
The causticization reaction was carried out under the conditions of TIRRER TYPE PS-2N and the same stirrer for the following Examples and Comparative Examples. As a result of observing the average particle diameter and morphology of the produced reaction product, the average particle diameter was 6.8 μm, and the constituent primary particles had an average major axis of 6.3 μm,
Needle-like calcium carbonate of aragonite crystals having an average minor diameter of 0.3 μm was observed. The whiteness of the acicular calcium carbonate was 96.5%. Table 1 shows the experimental conditions and results. [Example 2] Example 2 except that slaked lime and a 2 mol / l-NaOH aqueous solution were mixed at a ratio of a quicklime concentration of 30% by weight to produce lime milk and a causticization reaction was performed at a temperature of 75 ° C. This was performed under the conditions of 1. The product was found to have columnar calcium carbonate of aragonite crystals having an average particle diameter of 5.7 μm and constituent primary particles having an average major axis of 4.5 μm and an average minor axis of 0.3 μm. The whiteness of the columnar calcium carbonate was 96.0%. Table 1 shows the experimental conditions and results. [Comparative Example 1] 1 m containing 0.8 mol / l-Na ₂ CO ₃ for the preparation of lime milk
Using an aqueous solution of ol / l-NaOH, the same procedure as in Example 1 was performed.
The reaction product at this time has an average particle size of 3.6 μm,
The constituent primary particles were found to be spindle calcium carbonate of calcite crystals having an average major axis of 2.8 μm and an average minor axis of 0.5 μm. The whiteness of the spindle calcium carbonate was 95.8%. Table 1 shows the experimental conditions and results. [Comparative Example 2] The addition rate of sodium carbonate was 2 g / min / g.
The procedure was performed in the same manner as in Example 1, except that The reaction product at this time had an average particle diameter of 4.3 μm, and the constituent primary particles were found to be calcite crystal spindle calcium carbonate having an average major axis of 3.5 μm and an average minor axis of 0.6 μm. The whiteness of the spindle calcium carbonate was 95.7%. Table 1 shows the experimental conditions and results.

[Comparative Example 3] The same operation as in Example 1 was carried out except that the causticizing temperature was set at 20 ° C. The reaction product at this time had an average particle diameter of 8.2 μm, and it was confirmed that the constituent primary particles were a mixture of spindle-shaped and amorphous calcium carbonate of calcite crystals. The whiteness of the amorphous calcium carbonate was 96.0%. Table 1 shows the experimental conditions and results. [Comparative Example 4] Instead of an aqueous solution of sodium carbonate, a green liquor (composition (molar ratio) of a sulfate method), Na ₂ CO ₃ : Na ₂ S = 1.6: 0.
The procedure was performed in the same manner as in Example 1 except that 5) was used. As a result of observing the average particle diameter and morphology of the produced reaction product, it was found that the primary particles of the average particle diameter were 7.3 μm, and that the aragonite crystals of average diameter of 3.2 μm and average short diameter of 0.4 μm were ragged calcium carbonate. The lightness of this light Kal is 94.5%
Met. Table 1 shows the experimental conditions and results.

[0020]

[Table 1]

[0021]

As shown in Examples 1 and 2, the calcium carbonate according to the present invention was high in whiteness and was needle-shaped, columnar, and igaki-like calcium carbonate of aragonite crystals. Further, a pure sodium hydroxide aqueous solution could be obtained without co-producing chlorine. In this method, a pure sodium hydroxide aqueous solution can be produced by utilizing the causticization reaction without simultaneously producing calcium carbonate and chlorine.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the crystal particle structure of acicular calcium carbonate obtained in Example 1.

FIG. 2 is a view showing a result of X-ray diffraction of a product obtained in Example 1.

FIG. 3 is a scanning electron micrograph showing the crystal particle structure of columnar calcium carbonate obtained in Example 2.

FIG. 4 is a view showing a result of X-ray diffraction of a product obtained in Example 2.

FIG. 5 is a scanning electron micrograph showing the crystal particle structures of spindle-shaped and amorphous calcium carbonate obtained in Comparative Example 3.

FIG. 6 is a view showing a result of X-ray diffraction of a product obtained in Comparative Example 3.

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Claims (5)

[Claims] 1. A method for producing calcium carbonate and sodium hydroxide of aragonite crystals by a causticization reaction, wherein the concentration of quicklime is 1 to 60% by weight, preferably 20 to 40%.
Aqueous lime and / or slaked lime is added with 2 mol / l or less aqueous sodium hydroxide solution containing 0.25 mol or less, preferably 0.10 mol or less of carbonate ions, per mol of quick lime to quicklime and / or slaked lime, and prepared while stirring. A predetermined amount of sodium carbonate aqueous solution derived from soda ash required to produce sodium hydroxide in the milk of lime is 0.002 to 0.1 with respect to the milk of lime.
2 g (sodium carbonate) / min / g (quick lime), preferably 0.1 g
Add at an addition rate of 002 to 0.04 g / min / g,
A method for producing an aqueous solution of calcium carbonate and sodium hydroxide of aragonite crystals, which comprises performing a caustic reaction at 5 ° C, preferably 40 to 90 ° C. 2. The method for producing an aqueous solution of calcium carbonate and sodium hydroxide according to claim 1, wherein the aqueous solution of sodium hydroxide added to the slaked lime has a pH exceeding 13.5. 3. Manufactured by the method of claim 1;
Calcium carbonate useful as a filler for papermaking or a coating pigment for coated paper. 4. A coating composition using the calcium carbonate according to claim 3 as a coating pigment. 5. A paper characterized in that the calcium carbonate according to claim 3 is used as a filler for papermaking, or a coated paper characterized in that it is used as a coating pigment.