JP2003292321A - Method for manufacturing calcium carbonate and method for flue gas desulfurization or method for neutralization of sulfuric acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing calcium carbonate capable of simultaneously manufacturing an alkali metal sulfate using various kinds of gypsum containing various kinds of byproduct gypsum of flue gas desulfurization gypsum, and the like, and to provide a method for flue gas desulfurization or a method for neutralization of sulfuric acid. <P>SOLUTION: The calcium carbonate is manufactured by introducing carbon dioxide into slurry mixed with ≥1 kinds of hydroxides of metals selected from alkali metals such as sodium hydroxide, gypsum and water, and at this time, the alkali metal sulfate such as sodium sulfate can be simultaneously manufactured secondarily. Further, the flue gas desulfurization or the neutralization of the sulfuric acid is performed utilizing the obtained calcium carbonate. When introducing the carbon dioxide, the calcium carbonate having various kinds of particle shapes desired can be manufactured by controlling the introducing speed and the slurry temperature. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing calcium carbonate using gypsum as a raw material, and a flue gas desulfurization method or an acid neutralization method using the calcium carbonate. A method for producing calcium carbonate by using various by-product gypsums such as smoke desulfurization gypsum and simultaneously obtaining a sulfate of an alkali metal, and a flue gas desulfurization method utilizing the calcium carbonate Or, it relates to a sulfuric acid neutralization method.

[0002]

2. Description of the Related Art The product of the production method of the present invention is calcium carbonate, which contains limestone, which can be said to be the only resource that can be self-sufficient in Japan, and has long been an auxiliary raw material for steelmaking, a raw material for cement, and an aggregate. It is used in large quantities as etc. Physically crushed products of this limestone include ordinary calcium carbonate and ground calcium carbonate, and on the other hand, there are also calcium carbonate products produced by chemical methods, such as those produced by the carbonation and precipitation reaction of calcium salts. There is a synthetic calcium carbonate which is a fine particle.

The ordinary calcium carbonate is a relatively large average particle size of 10 μm or more produced by crushing limestone. It is a filler for asphalt pavement, a neutralizer for flue gas desulfurization and industrial waste water, a glass raw material, and a fertilizer. Used as feed, etc. Further, heavy calcium carbonate produced by physically crushing limestone having a particularly high whiteness generally has an average particle size of 10 μm or less, and by taking advantage of its high whiteness, papermaking, plastics, rubber, paint It is widely used as a filler and a pigment.

Synthetic calcium carbonate produced by a chemical precipitation reaction is also called light calcium carbonate or precipitated (produced) calcium carbonate in contrast to the above-mentioned heavy calcium carbonate. Specific manufacturing methods thereof include a carbon dioxide gas compounding method in which calcium carbonate is precipitated by blowing carbon dioxide gas into a calcium hydroxide slurry, a calcium chloride soda method by reacting calcium chloride and sodium carbonate, calcium hydrogen carbonate and water. A water treatment method by reaction with calcium oxide is industrially adopted.

Particularly in Japan, synthetic calcium carbonate is
It is general and economically most advantageous to use a carbon dioxide gas compounding method using quicklime obtained as a raw material obtained by firing abundantly produced high-quality limestone at a high temperature of 1000 ° C or higher. The characteristic of this synthetic calcium carbonate is that it is produced by a chemical precipitation reaction, so that the carbon dioxide produced by adjusting the production conditions such as the carbonation temperature, the rate of the carbonation reaction, and the calcium concentration in the calcium hydroxide slurry. It is possible to control the particle shape and particle diameter of calcium.

The particle shape is well known such as spindle shape, cubic shape, and columnar shape, and the particle size distribution width is relatively narrow and the particle diameter is uniform. For example, spindle-shaped calcium carbonate has a long diameter of 1.5 to 6 μm and a short diameter of 0.3 to 2 μm.
It has a spindle shape (average particle size by electron microscope observation, the same as the particle size shown below), has a high whiteness and is excellent in economic efficiency, and is mainly used as a large amount as a filler for papermaking.

Cubic calcium carbonate has a cubic shape with an average particle diameter of 0.02 to 0.3 μm, and a relatively large particle diameter of 0.08 μm or more is used as a pigment for papermaking coating or As an extender pigment for paints, one having a smaller particle size and called colloidal calcium carbonate is surface-treated and used as a filler for plastics and rubber.
Furthermore, columnar calcium carbonate has a short diameter of 0.1 to 0.5 μ.
m, major axis 0.5 to 2.0 μm, and excellent in dispersibility, it is used as a coating pigment for papermaking.

As described above, synthetic calcium carbonate has many particle shapes, and the particle shape and particle diameter of calcium carbonate produced can be controlled by adjusting the production conditions. By synthesizing calcium and taking advantage of the unique functions and characteristics derived from the difference in particle shape and particle diameter, various fields such as papermaking, plastics, rubber, paints, and other polymeric materials as well as heavy calcium carbonate Used in large quantities in.

In the present invention, since it is possible to concurrently produce calcium carbonate and a sulfate of an alkali metal as a sub-product, conventional production of sodium sulfate or potassium sulfate, which is the most common sulfate among them, can be performed. The method etc. are described. Sodium sulfate is called Glauber's salt and is naturally produced in the United States. In the United States and Canada, a double salt (Na ₂ SO ₄ C
A method of treating aSO ₄ ) with sodium chloride is also practiced.

[0010] Industrially, the method called the Leblanc method to ignite sodium chloride and sulfuric acid to make an anhydrous product was popular in the olden days, but it is hardly practiced at present.
A large amount of human silk glauber is produced, which is a by-product of manufacturing viscose human silk. Other by-product Glauber's salt is a product by-produced of sodium dichromate, ammonium perchlorate, boric acid, formic acid, sodium glutamate and the like. It is also known that sodium hydroxide is reacted during the treatment of waste sulfuric acid or flue gas desulfurization.

A large amount of potassium sulfate is naturally present in Germany and the like as a double sulfate of potassium sulfate. To obtain potassium sulfate industrially, using this double sulfate as a raw material,
It is made by crystallization by double decomposition from an aqueous solution containing potassium chloride, magnesium sulfate, sodium chloride, etc. It is also produced as a byproduct of metathesis of potassium chloride and ammonium sulfate, a by-product when chlorine is added to potassium chloride to generate chlorine, a dimethyl terephthalate production from toluene or a vinyl chloride production byproduct from acetylene.

Sodium sulphate, which is well known under the name of Glauber's salt, is an additive for enhancing the detergency of synthetic detergents, including builder, pulp production, sodium sulfide, glass production, synthetic detergents, dyes and dyes. It is used as a raw material for various chemical industries such as intermediates, metal refining, and the manufacture of pharmaceuticals as laxatives. In addition, potassium sulfate is important as a potassium fertilizer, and is also used in glass manufacturing, potassium alum, potassium carbonate, a quenching agent for metals, a pharmaceutical as a laxative, and the like.

In the present invention, calcium sulfate is used as a raw material.
I use sium, which is commonly called plaster,
There are two main types, natural gypsum and chemical gypsum. That
Gypsum can be used according to the amount of water of crystallization._Four・ 2
H₂O), hemihydrate gypsum (CaSO _Four・ 1 / 2H₂O), anhydrous
Gypsum (CaSO_Four) Is roughly divided into
Gypsum absorbs water and easily changes to dihydrate gypsum,
Gypsum naturally produced is limited to gypsum dihydrate and anhydrous gypsum
Most of which is gypsum dihydrate.

The above-mentioned chemical gypsum is called by the names of phosphoric acid gypsum, titanium gypsum, hydrofluoric acid gypsum, flue gas desulfurization gypsum (exhaust gypsum), mineral water, refined gypsum, etc., depending on the production process. Phosphate gypsum, titanium gypsum, and hydrofluoric acid gypsum are produced during the production of phosphoric acid, titanium oxide, and hydrofluoric acid, and exhaust gypsum captures the sulfur content in the flue gas emitted from thermal power plants, petrochemical industries, etc. It is caused by doing. Mineral water and refined gypsum are acid-neutralized gypsum, and since they are all produced as by-products, they are also called by-product gypsum.

These natural or chemical gypsums are used in large amounts as raw materials for cement, gypsum board, gypsum plaster, fertilizer, etc., but in recent years, the import amount of natural gypsum has increased or the demand for cement and gypsum board has decreased. Due to
By-product gypsum, such as discharged gypsum, tends to be in excess. From this, new applications such as ground improvement material, soil improvement material, road roadbed material, solidifying material for harmful substances, etc. have been studied, and many technologies have been proposed. To use.

Under such circumstances, a proposal has recently been made to use gypsum as a different substance by chemically changing it instead of using it as it is.
There is a method of using it as a fertilizer described in JP 1-947 A. It is a technology to obtain ammonium sulfate and calcium carbonate by reacting ammonia and carbon dioxide generated at the time of compost production with gypsum board to be discarded. In this way, proposals to use chemically modified gypsum instead of just using it have emerged recently, but chemical gypsum still has a surplus tendency, and more effective gypsum is available. The reality is that it is expected to be utilized.

[0017]

Under such circumstances, the present inventors have been engaged in the above-mentioned calcium carbonate synthesis research for a long time, and the above-mentioned waste gypsum or byproduct gypsum can also be hydrated. As with calcium, there is calcium, which is the main source of calcium carbonate for the production of calcium carbonate, and as described above, the waste source or by-product cannot be fully utilized as a calcium source for the production of calcium carbonate. , Repeated intensive studies on effective use of gypsum.

As a result, it was possible to utilize various plasters such as this waste or by-product as a calcium source to produce calcium carbonate, and succeeded in developing a technique capable of secondarily producing a sulfate of an alkali metal. did. That is,
An object of the present invention is to provide a new effective utilization method of various gypsums such as waste gypsum or byproduct gypsum, and also to provide a method of utilizing the produced calcium carbonate. It is what More specifically, it provides a method for producing calcium carbonate, which is used in a large amount in various fields, and a sulfate of an alkali metal having a wide range of applications, using various gypsums such as drainage gypsum as a raw material, as well as manufactured. It is an object of the present invention to provide a method of utilizing calcium carbonate for flue gas desulfurization or sulfuric acid neutralization.

[0019]

The present invention provides a method for producing calcium carbonate for solving the above-mentioned problems, which production method is selected from alkali metals.
One or more hydroxides, gypsum, and is characterized by introducing carbon dioxide into a slurry mixed with water, by this method, such as sodium sulfate and the like secondary to calcium carbonate at the same time Alkali metal sulfates can also be prepared. Further, in the flue gas desulfurization method or sulfuric acid neutralization method of the present invention, the produced calcium carbonate is used for the flue gas desulfurization or sulfuric acid neutralization to produce gypsum, and the gypsum is used as gypsum in the production method. Is what you use.

In the present invention, 1 selected from alkali metals
The present invention was completed by finding that the carbonation reaction with calcium proceeds by introducing carbon dioxide into a slurry in which at least one kind of hydroxide, gypsum, and water are mixed. Therefore, this carbonation reaction requires the presence of an alkali metal hydroxide, gypsum and carbon dioxide, and the pH of the slurry should be about 12.0 or higher at the start of the reaction, and the slurry should be at the end of the reaction. It is preferably almost neutral, and the pH is preferably about 7.

Further, in this reaction, calcium carbonate having various particle shapes can be obtained by changing at least one of the reaction conditions at the time of introducing carbon dioxide, that is, the slurry concentration, the slurry temperature and the carbon dioxide introducing rate. The particles can be in the shape of a spindle, a pillar, a cube, a rhombohedron, a sphere, or the like. The particle size of calcium carbonate produced by this reaction may be influenced by the particle size of gypsum used as a raw material, and it is desirable to adjust the particle size of gypsum in advance according to the desired particle size of calcium carbonate. .

In the present invention, gypsum as a raw material can be by-product gypsum such as discharged gypsum or titanium gypsum, or waste gypsum such as waste gypsum board, which is preferable from the viewpoint of environmental protection and economy. Further, if sodium hydroxide or potassium hydroxide is selected as the alkali metal hydroxide, it is easily available, has excellent economical efficiency, and is highly useful as a later sulfate salt. Furthermore, as carbon dioxide used for carbonation, carbon dioxide-containing gas discharged as exhaust gas or the like can be used, and this point is also preferable in terms of environmental protection and economy. It is also preferable in that the produced calcium carbonate is used for flue gas desulfurization or sulfuric acid neutralization to produce gypsum as a by-product, and this by-product gypsum can be utilized as the gypsum in the production method.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and details of the method for producing calcium carbonate of the present invention will be described below. However, the present invention is not limited to these, and the description of the scope of the claims. It goes without saying that it is specified. The method for producing calcium carbonate of the present invention is characterized by introducing carbon dioxide into a slurry in which one or more hydroxides selected from alkali metals, gypsum, and water are mixed as described above. Is.

The gypsum, which is the raw material of the present invention, may be an anhydrous salt of calcium sulfate, a hemihydrate (1/2 hydrate), or a dihydrate. Examples of the anhydrous salt include natural anhydrite and hydrofluoric acid gypsum. Hemihydrate gypsum is also called calcined gypsum and can be easily obtained by heating gypsum dihydrate at a low temperature. Further, with respect to gypsum dihydrate, various types of gypsum such as natural gypsum, by-product gypsum or gypsum product waste can be used.

This natural gypsum is obtained from large-scale deposits in foreign countries such as Canada, the United States and France. In addition, as the by-product gypsum, there are various kinds such as drainage gypsum, titanium gypsum, phosphate gypsum, titanium gypsum, hydrofluoric acid gypsum, mineral water and refined gypsum. Further, in addition to these gypsum dihydrate, gypsum dihydrate, which has been used as a gypsum board or the like and then becomes a waste, can also be used.

The form and particle size of the gypsum that can be used in the present invention are not particularly limited, but depending on the conditions during carbonation, most of the gypsum particles used as the raw material are fine calcium carbonate particles that retain their crystalline form. It becomes an aggregate of crystals. Therefore, the particle size of the produced calcium carbonate may be affected by the particle size of the gypsum used as the raw material. In such a case, the particle size distribution measured by the laser diffraction / scattering method is the same as that of the raw material gypsum, or the particle size of the produced calcium carbonate is slightly smaller.

Regarding the production of the slurry, if gypsum is added to an aqueous solution of an alkali metal hydroxide and mixed, or a slurry in which the gypsum is suspended is first produced, and then an alkali metal hydroxide is added and mixed. Good. The amount of gypsum to be suspended is preferably 1 to 40% by weight, more preferably 5 to 2
It is 0% by weight. If it is too small, the production efficiency will be poor, and if it is too large, stirring will be difficult and uniform reaction will be hindered.

Examples of the alkali metal hydroxides include hydroxides of lithium, sodium, potassium and the like. Particularly, sodium hydroxide and potassium hydroxide are preferable because they are easily available and economical. It can be used, and even if two or more kinds of hydroxides are contained, there is no problem in obtaining calcium carbonate. As for the amount of alkali metal hydroxide used, in order to consume the entire amount of gypsum and obtain particles consisting of only calcium carbonate, it is necessary to be at least twice the molar amount of gypsum. It may remain.

Carbon dioxide is introduced into the slurry thus prepared to carry out a carbonation reaction. As the carbon dioxide at that time, it is needless to say that a pure gas obtained from a commercially available cylinder can be used, but a carbon dioxide-containing gas containing other components may be used, for example, the pure gas is diluted with air or the like. Anything is okay. Further, in consideration of the global environment and economic efficiency, it is considered that the most preferable carbonation method is to use the carbon dioxide-containing gas discharged into the atmosphere at the time of fuel combustion.

Regarding this carbonation reaction, in order to make the reaction proceed smoothly, the pH at the start of the reaction should be 12.0 or higher, and in order to prevent the alkali metal hydroxide from becoming excessive. Should not exceed 13.5. Further, in this reaction, the pH decreases as the reaction proceeds, and the pH approaches 7 at the time when the carbonation reaction is complete, so the reaction is preferably completed near pH 7. Also,
Although the reaction temperature is not particularly limited, it is preferably in the range of 5 to 80 ° C., which is a simple condition. This reaction temperature has almost no effect on the reaction rate, but the type and particle shape of calcium carbonate produced vary depending on the reaction temperature.

When the produced calcium carbonate is observed with a scanning electron microscope, for example, when the slurry amount is 2 liters, the slurry concentration is 50 g / liter, and the carbon dioxide introduction rate is 1 liter / minute, the carbonation start temperature is Is 10
If it is ~ 30 ° C, the particles of cubic to rhombohedral are aggregated 2
Calcium carbonate particles having a spherical to elliptical shape of -5 μm are produced, and at 40 ° C., spindle-shaped calcium carbonate having a major axis of 1.5 to 2.0 μm and a minor axis of 0.3 to 0.5 μm is produced.

When the reaction temperature is further raised to carry out the carbonation reaction, the major axis is 1 to 5 μm and the minor axis is 0.5 to 5 at 60 ° C.
Spindle-shaped particles of 1 μm, length of 1-2 μm and diameter of 0.
Aragonite having a columnar shape of 3 to 0.5 μm is produced, and columnar aragonite is produced at 70 ° C. Further, as in Example 5 where the carbon dioxide introduction rate was 0.35 liter / min, spindle-shaped calcium carbonate was produced, and in Example 10 where the same rate was 5 liter / min, cubic calcium carbonate was produced. The shape can also be controlled by adjusting the carbon dioxide introduction rate.

As described above, there is a carbonation condition that replaces the aggregate of calcium carbonate crystals while leaving the form of the raw gypsum, and many particles show such agglomeration under the scanning electron microscope observation. Since aggregates are formed, in the present invention, the produced calcium carbonate has a 10% particle size of 1 μm or more in the integrated particle size from the small particle size side by the laser diffraction / scattering method, and 90% of the particle size was used as the raw material. The gypsum can have a particle size of 90% or less.

Furthermore, in the present invention, as described above, the 10% particle diameter of calcium carbonate is 1 μm or more and the 90% particle diameter (according to the embodiment) in the integrated particle diameter from the small particle diameter side by the laser diffraction / scattering method. The 10% particle diameter and the 90% particle diameter in Examples and the like are the same as the above-mentioned particle diameters, but in Examples and Comparative Examples, the description "in the cumulative particle diameter from the small particle diameter side" was omitted. The particle size of gypsum can be adjusted to 90% or less of that of the gypsum used as the raw material. Therefore, the particle size of gypsum can be adjusted in advance by a ball mill, sieving, wet cyclone, etc. to obtain calcium carbonate having a desired particle size. Can be obtained.

The calcium carbonate produced in the present invention can be used not only as a conventional heavy calcium carbonate or a synthetic calcium carbonate as a pigment or a filler for paper making, resins, rubbers or paints, but also ordinary calcium carbonate is used. Scavengers and neutralizers for existing acidic substances such as SO _x and chlorine, glass raw materials, soda industry, civil engineering materials such as road paving fillers and fine aggregate of concrete, fertilizer and feed fields of agriculture and animal husbandry Can also be used in.

The alkali metal sulphate formed as a by-product may be various ones such as sodium sulphate depending on the hydroxide used, which can be widely used as industrial raw materials and materials. For example, sodium sulphate is a builder that is an additive to enhance the detergency of synthetic detergents, pulp manufacturing, sodium sulfide, glass manufacturing, synthetic detergents, dyeing and dyeing intermediates, metal refining, and manufacturing of pharmaceuticals as laxatives. Recently, it can be used as a raw material for various chemical industries, such as being used as a raw material for bath salts. Further, potassium sulfate is important as a potassium fertilizer, and can be used as glass manufacturing, potassium alum, potassium carbonate, a quenching agent for metals, a laxative, and the like for manufacturing pharmaceuticals.

According to the present invention, as described above, calcium carbonate is produced by carbonating a slurry in which one or more hydroxides selected from alkali metals, gypsum, and water are carbonized. Alkali metal sulfates can also be produced secondarily, and these can be used as various chemical industrial raw materials and materials. It is also preferable in that the produced calcium carbonate is used for flue gas desulfurization or sulfuric acid neutralization to produce gypsum as a by-product, and this by-product gypsum can be utilized as the gypsum in the production method. Therefore, the present invention has a feature that its industrial utility value is extremely high as a novel method of utilizing natural gypsum and chemical gypsum.

[0038]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples and is specified by the scope of claims. Needless to say. As the carbon dioxide in the following examples and comparative examples, pure gas, that is, carbon dioxide gas supplied from a cylinder was used.

[Measurement of Particle Size Distribution / Observation of Particle Shape] Regarding the particle diameters of gypsum and calcium carbonate in the examples,
Laser diffraction / scattering method (Nikkiso, Microtrack X
-100). The particle shape and its size were observed by a scanning electron microscope.

[Example 1] 90% particle diameter measured by laser diffraction / scattering method was 234.7 μm (average particle diameter: 76.
4 g, particle size range: 7.13 to 645.6 μm) 100 g of decalcified gypsum was put into 2 liters of sodium hydroxide solution having a concentration of 1 mol / liter heated to 60 ° C. and maintained at 60 ° C. While stirring for 10 minutes. The pH at that time was 12.6. After that, set the slurry temperature to 60.
The temperature was maintained at 0 ° C., and carbon dioxide was introduced at a rate of 1.0 liter / min while stirring to carry out a carbonation reaction. PH of slurry
When the value reached 7.8, the carbon dioxide gas was stopped and the reaction was terminated.

The product obtained was filtered to separate the solid from the solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope. As a result, spindle-shaped particles having a major axis of 1 to 5 μm and a minor axis of 0.5 to 1 μm and a length were obtained. Is 1-2 μm and diameter is 0.3-0.5
It was confirmed that the columnar particles of μm formed aggregates having a diameter of 10 to 20 μm.

When the particle size distribution was measured by the laser diffraction / scattering method, the 10% particle size was 10.16 μm and 90%.
% Particle size is 166.4 μm (average particle size: 60.03 μ
m, particle diameter range: 3.57 to 456.5 μm). Further, when powder X-ray diffraction was performed, only calcite and aragonite were confirmed, so it can be judged that the discharged gypsum used as the raw material disappeared and calcium carbonate was produced. The solution separated from the solid was analyzed to find that sodium was 22.8 g / liter and sulfate ion was 26.6 g / liter.

[Example 2] 100 g of the same discharged gypsum as used in Example 1 was put into 2 liters of potassium hydroxide solution having a concentration of 1 mol / liter, which was heated to 60 ° C, and maintained at 60 ° C. While stirring, the mixture was stirred for 1 hour. P at that time
H was 12.6. After that, the slurry temperature is 60 ° C.
While stirring, carbon dioxide gas (mixed gas with air having a concentration of 25%) was introduced at a rate of 5.0 l / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 8.0, the carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that spindle-shaped particles having a major axis of 2 to 10 μm and a minor axis of 0.5 to 1.5 μm. , Diameter 10
It was confirmed that aggregates of 20 μm were formed.

The particle size distribution of the dried solid was measured by a laser diffraction / scattering method. The 10% particle size was 8.20 μm and the 90% particle size was 137.9 μm (average particle size: 31.64 μm). , Particle size range: 3.00-38
3.9 μm). Furthermore, when powder X-ray diffraction was performed, only calcite was confirmed, so it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. The solution separated from the solid was analyzed to find that potassium was 49.4 g / liter and sulfate ion was 26.1 g / liter.

[Example 3] 100 g of the same discharged gypsum as used in Example 1 was put into 2 liters of sodium hydroxide solution having a concentration of 1 mol / liter and adjusted to 20 ° C, and maintained at 20 ° C. While stirring, the mixture was stirred for 1 hour. The pH at that time was 13.5. Then, carbon dioxide was introduced at a rate of 1.0 liter / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 7.5, carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. After the solid matter was washed with ion-exchanged water and methanol and dried at 105 ° C., it was observed with a scanning electron microscope to find that spherical to elliptical particles of 2 to 5 μm in which cubic to rhombohedral particles were aggregated were formed. It was confirmed that

When the particle size distribution was measured by the laser diffraction / scattering method, the 10% particle size was 5.03 μm and 90%.
Particle size is 110.3 μm (average particle size: 20.43μ
m, particle size range: 1.78 to 383.9 μm). Furthermore, when powder X-ray diffraction was performed and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was found to be 2
The amount was 1.3 g / liter and the amount of sulfate ion was 25.2 g / liter.

[Example 4] 90% measured by the laser diffraction / scattering method obtained by firing the same discharged gypsum as used in Example 1 for 8 hours in an electric furnace heated to 350 ° C. Anhydrous gypsum 8 having a particle size of 174.9 μm (average particle size: 77.8 μm, particle size range: 7.78 to 456.5 μm)
0 g was put into 2 liters of a sodium hydroxide solution having a concentration of 1 mol / liter, the temperature of which was adjusted to 60 ° C., and the mixture was stirred for 1 hour. The pH at that time was 12.5.

The slurry temperature was adjusted to 60 ° C., and carbon dioxide was introduced at a rate of 1.0 l / min while stirring to carry out a carbonation reaction. When the pH of the slurry reached 8.0, carbon dioxide was stopped and the reaction was terminated. The resulting product was filtered to separate solid and solution. The solid matter is washed with deionized water and methanol to obtain 105
After drying at 0 ° C., it was observed with a scanning electron microscope. As a result, spindle-shaped particles having a long diameter of 2 to 4 μm and a short diameter of 0.5 to 1 μm and a length of 1 to 2 μm and a diameter of 0.2 to 0. It was confirmed that the 4 μm columnar particles formed aggregates having a diameter of 5 to 10 μm.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 9.21 μm and 90%.
Particle size is 190.7 μm (average particle size: 83.79 μ
m, particle diameter range: 3.00 to 383.9 μm). Further, powder X-ray diffraction analysis confirmed that calcite and aragonite were present, so it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was 22.8 g / liter and sulfate ion was 29.
It was 8 g / liter.

[Example 5] 325 g of the same discharged gypsum as used in Example 1 was put into 2 liters of a sodium hydroxide solution having a concentration of 2 mol / liter, which was heated to 60 ° C, and stirred for 60 minutes. The pH at that time was 12.7. Thereafter, the slurry temperature was adjusted to 28 ° C., and carbon dioxide was introduced at a rate of 0.35 liter / min while stirring to carry out a carbonation reaction. When the pH of the slurry reached 6.9, carbon dioxide was stopped to terminate the reaction.

The obtained product was filtered to separate a solid matter and a solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that the major axis was 1-2 μm and the minor axis was 0.2-.
It was confirmed that the 0.5 μm spindle-shaped particles formed aggregates having a diameter of 10 to 50 μm.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 9.78 μm and 90%.
Particle size is 76.83 μm (average particle size: 24.57μ
m, particle diameter range: 5.04 to 271.4 μm). Furthermore, when powder X-ray diffraction was performed, and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was found to be 1
The amount was 6.0 g / liter and the amount of sulfate ion was 30.6 g / liter.

[Example 6] The same 325 g of the waste gypsum as used in Example 1 was put into 2 liters of a potassium hydroxide solution having a concentration of 2 mol / liter, which was heated to 60 ° C, and stirred for 60 minutes. The pH at that time was 13.6.
While maintaining the slurry temperature at 60 ° C. as it was, carbon dioxide was introduced at a rate of 1 liter / min while stirring to carry out a carbonation reaction. When the pH of the slurry reached 7.3, the carbon dioxide gas was stopped to terminate the reaction.

The product obtained was filtered to separate the solid from the solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that the major axis was 0.5 to 1 μm and the minor axis was 0.1.
It was confirmed that the spindle-shaped particles having a diameter of ˜0.2 μm formed aggregates having a diameter of 5 to 20 μm.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 3.28 μm and 90%.
The particle size is 19.59 μm (average particle size: 7.01 μm,
The particle size range was 1.50 to 67.86 μm).
Further, when powder X-ray diffraction was performed, only calcite was confirmed, so it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, potassium was 4
The amount was 3.3 g / liter and the amount of sulfate ion was 22.8 g / liter.

Example 7 90% particle diameter measured by laser diffraction / scattering method was 140.3 μm (average particle diameter: 52.
23 μm, particle diameter range: 4.24 to 383.9 μm)
100 g of gypsum dihydrate gypsum (Kanto Chemical Reagent first grade) at 60 ° C
The mixture was poured into 2 liters of a sodium hydroxide solution having a concentration of 1 mol / liter, which had been heated, and stirred for 60 minutes. The pH at that time was 13.0. While maintaining the slurry temperature at 60 ° C as it is, add 1 liter / liter of carbon dioxide gas while stirring.
It was introduced at a rate of minutes to carry out a carbonation reaction. Slurry p
When H reached 8.2, the carbon dioxide gas was stopped to terminate the reaction.

The obtained product was filtered to separate a solid matter and a solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that the major axis was 1.5 to 2 μm and the minor axis was 0.3.
It was confirmed that spindle-shaped particles having a size of 0.5 μm and columnar particles having a length of 3 to 5 μm and a diameter of 0.2 to 0.3 μm form a slag-like aggregate having a diameter of 5 to 10 μm. .

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 5.67 μm and 90%.
Particle size is 31.72 μm (average particle size: 11.19μ
m, particle size range: 1.06 to 191.9 μm). Further, when powder X-ray diffraction was performed, aragonite and calcite were confirmed. Therefore, it can be determined that the discharged gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was 24.5 g / liter and sulfate ion was 29.
It was 4 g / liter.

[Example 8] 100 g of the same discharged gypsum as used in Example 1 was added to a sodium hydroxide solution having a concentration of 1 mol / liter heated to 40 ° C, and stirred for 60 minutes to prepare a slurry 2. 0 liter was prepared. P at that time
H was 13.6. As it is, the slurry temperature is 40 ℃.
The temperature was maintained at 1, and carbon dioxide was introduced at a rate of 1 liter / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 8.4, carbon dioxide gas was stopped and the reaction was terminated. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope.
It was confirmed that the spindle-shaped particles having a diameter of ˜2 μm and a short diameter of 0.3 to 0.5 μm formed spherical aggregates having a diameter of 3 to 5 μm.

The particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 6.71 μm and 90%.
Particle size is 112.3 μm (average particle size: 21.09μ
m, particle diameter range: 2.12 to 383.9 μm). Furthermore, when powder X-ray diffraction was performed, and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was found to be 2
The amount was 3.7 g / liter and the amount of sulfate ion was 28.4 g / liter.

[Example 9] 100 g of the same discharged gypsum as used in Example 1 was suspended in 2 liters of water heated to 60 ° C, and then the reagent was hydroxylated to a concentration of 1 mol / liter. Sodium was added and stirred for 60 minutes to prepare a slurry. The pH at that time was 12.7. While maintaining the slurry temperature at 60 ° C., carbon dioxide was introduced at a rate of 1.0 liter / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 7.0,
The carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope.
Spindle-shaped particles with a short diameter of 0.5 to 1 μm and a diameter of 1
It was confirmed that aggregates of about 0 μm were formed.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 7.42 μm and 90%.
Particle size is 170.7 μm (average particle size: 61.33 μ
m, particle diameter range: 3.00 to 439.3 μm). Furthermore, when powder X-ray diffraction was performed, and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was found to be 2
It was 2.9 g / liter and sulfate ion was 27.9 g / liter.

[Example 10] 325 g of the same waste desorption gypsum as that used in Example 1 was added to a sodium hydroxide solution having a concentration of 2 mol / liter heated to 60 ° C, and stirred for 60 minutes to obtain a slurry 2. 0 liter was prepared. After that, the slurry temperature was adjusted to 28 ° C., and carbon dioxide gas was adjusted to 5 while stirring.
It was introduced at a rate of liter / minute to carry out a carbonation reaction.

When the pH of the slurry reached 6.8,
The carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that it was 0.2 μm.
It was confirmed that the front and rear cubic particles formed aggregates having a diameter of 2 to 3 μm.

When the particle size distribution was measured by the laser diffraction / scattering method, the 10% particle size was 6.1 μm, the 90% particle size was 61.5 μm (average particle size: 13.7 μm, particle size range: 2). .1 to 271 μm). Furthermore, when powder X-ray diffraction was performed, and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid substance was analyzed, sodium was 81.6 g / liter and sulfate ion was 43.6 g / liter.

Example 11 325 g of the same waste gypsum as used in Example 1 was added to a sodium hydroxide solution having a concentration of 2 mol / liter heated to 60 ° C. and stirred for 60 minutes to obtain a slurry 2. 0 liter was prepared. P at that time
H was 12.5. Then, the slurry temperature was adjusted to 13 ° C., and carbon dioxide was introduced at a rate of 1 liter / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 7.3, carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope.
A spindle-shaped particle having a short diameter of about 0.1 μm and a cubic diameter of 0.04 to 0.06 μm has a diameter of 3 to 0.5 μm.
It was confirmed that aggregates of ˜5 μm were formed.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 10.4 μm and 90%.
The particle size was 130 μm (average particle size: 22.5 μm, particle size range: 4.2 to 457 μm). Furthermore, when powder X-ray diffraction was performed, and calcite was confirmed, it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was 41.2 g / liter and sulfate ion was 79.5 g / liter.

[Example 12] 325 g of the same discharged gypsum as used in Example 1 was added to a sodium hydroxide solution having a concentration of 2 mol / liter heated to 60 ° C, and stirred for 60 minutes to obtain a slurry 2. 0 liter was prepared. P at that time
H was 12.3. The slurry temperature is kept at 60 ℃
The temperature was kept at 1, and carbon dioxide was introduced at a rate of 0.1 l / min while stirring to carry out a carbonation reaction.

When the pH of the slurry reached 7.3, carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope.
It was confirmed that the spindle-shaped particles having a diameter of ˜0.3 μm and a short diameter of 50 to 60 nm formed aggregates having a diameter of about 5 to 10 μm.

When the particle size distribution was measured by the laser diffraction / scattering method, the 10% particle size was 3.4 μm and the 90% particle size was 11.5 μm (average particle size: 6.1 μm, particle size range: 1). 0.1 to 33.9 μm). Further, powder X-ray diffraction confirmed calcite, so that it can be determined that the discharged gypsum used as the raw material disappeared and calcium carbonate was produced. The solution separated from the solid was analyzed to find that sodium was 47.8 g / liter and sulfate ion was 94.8 g / liter.

Example 13 90% particle size measured by laser diffraction / scattering method was 96.2 μm (average particle size: 55.0).
100 g of phosphate gypsum having a particle size range of 8.5 μm and a particle size range of 8.5 to 228 μm) was added to a sodium hydroxide solution having a concentration of 1 mol / liter heated to 60 ° C. and stirred for 60 minutes to prepare 2.0 liters of a slurry. did. PH at that time is 1
It was 2.6. Thereafter, the slurry temperature was raised to 70 ° C., and carbon dioxide gas was introduced at a rate of 1.0 liter / min while stirring at the temperature to carry out a carbonation reaction.

When the pH of the slurry reached 8.1, carbon dioxide gas was stopped to terminate the reaction. The resulting product was filtered to separate solid and solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find columnar particles having a major axis of 1 to 1.5 μm and a minor axis of 0.2 to 0.3 μm. But diameter 5-15
It was confirmed that a μm aggregate was formed.

When the particle size distribution was measured by the laser diffraction / scattering method, the 10% particle size was 7.1 μm, the 90% particle size was 37.5 μm (average particle size: 11.7 μm, particle size range: 3). .0 to 136 μm). Further, when powder X-ray diffraction was performed, only aragonite was confirmed, so it can be determined that the waste gypsum used as the raw material disappeared and calcium carbonate was produced. When the solution separated from the solid was analyzed, sodium was 22.8 g /
Liter and sulfate ion were 26.9 g / liter.

Comparative Example 1 100 g of the same discharged gypsum as used in Example 1 was added to tap water heated to 60 ° C.,
The mixture was stirred for 60 minutes to prepare 2.0 liters of gypsum slurry. The pH at that time was 7.4. While maintaining the slurry temperature at 60 ° C. as it was, carbon dioxide gas was introduced at a rate of 1.0 liter / min while stirring. PH of slurry after 70 minutes
When the temperature became constant at 4.6, the introduction of carbon dioxide gas was terminated.

After the introduction was completed, the slurry was filtered to separate a solid matter and a solution. The solid matter was washed with ion-exchanged water and methanol, dried at 50 ° C., and then observed with a scanning electron microscope. As a result, it was confirmed that the shape of gypsum remained as it was. Further, when powder X-ray diffraction was performed, only gypsum was confirmed, so it can be judged that the discharged gypsum used as a raw material remained and calcium carbonate could not be produced.

Comparative Example 2 100 g of the same discharged gypsum as used in Example 1 was put into 2 liters of calcium hydroxide slurry having a concentration of 1 mol / liter adjusted to 20 ° C. and maintained at 20 ° C. While stirring, the mixture was stirred for 1 hour. The pH at that time was 12.7. After that, the slurry temperature was kept at 20 ° C., and carbon dioxide was introduced at a rate of 1.0 liter / min while stirring. When the pH of the slurry reached 6.2, the introduction of carbon dioxide gas was stopped.

After completion of the introduction, the slurry was filtered to separate a solid matter and a solution. The solid matter was washed with ion-exchanged water and methanol, dried at 105 ° C., and then observed with a scanning electron microscope to find that the major axis was 0.5 to 1 μm and the minor axis was 0.05 to
Chain-like particles of 0.1 μm adhere to the surface of particles in the form of short columns peculiar to gypsum, or individually have a diameter of 1-10.
It was confirmed that a μm aggregate was formed.

Further, the particle size distribution was measured by the laser diffraction / scattering method, and the 10% particle size was 3.98 μm and 90%.
Particle size is 203.4 μm (average particle size: 70.66μ
m, particle size range: 0.89 to 622.8 μm). Further, when powder X-ray diffraction was performed, gypsum dihydrate and calcite were confirmed. From these, it can be judged that the calcium hydroxide was carbonated to produce calcium carbonate, but the discharged gypsum used as a raw material remained.

Regarding the above Examples and Comparative Examples, the type and amount of gypsum used for the carbonation reaction, the type and concentration of the alkali hydroxide used, the carbonation reaction conditions, and the particle shape of the produced calcium carbonate. The particle size and the like are shown in one table. From this table, it can be simply understood that the present invention can produce calcium carbonate having a desired shape and particle size.

[0085]

[Table 1]

[0086]

According to the method for producing calcium carbonate of the present invention, one or more hydroxides selected from alkali metals,
Gypsum and carbon dioxide are introduced into a slurry in which water is mixed, and by controlling the slurry temperature and / or the carbon dioxide introduction speed at the time of introduction, a spindle shape,
It is possible to produce calcium carbonate with a desired shape and particle size such as columnar, cubic, rhombohedral or spherical shapes, as well as secondary salts of alkali metal sulfates, which are used as various chemical industrial raw materials and materials. it can.

Further, in the present invention, not only natural gypsum but also by-product gypsum such as exhausted gypsum and titanium gypsum can be used for gypsum which is one of the main raw materials. In addition to these, waste gypsum such as waste gypsum board can be used. Since it can be used effectively, it is preferable in terms of environmental protection and economy. Moreover, gypsum is still cheap and surplus even at present, and further effective utilization is expected, and this point is also preferable. Further, as carbon dioxide used for carbonation, carbon dioxide-containing gas discharged as exhaust gas or the like can be used, which is also preferable from the viewpoint of environmental protection and economical efficiency.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kohei Mikami             8-1, Hirai, Hinode-cho, Nishitama-gun, Tokyo             Mining Co., Ltd. F-term (reference) 4D002 AA02 AB01 BA02 DA05 DA16                       FA03                 4G076 AA16 AB06 AB08 AB26 BA34                       BB01 BC02 BD02 BD06 CA26                       DA29

Claims (7)

[Claims] 1. A method for producing calcium carbonate, which comprises introducing carbon dioxide into a slurry in which one or more hydroxides selected from alkali metals, gypsum and water are mixed. 2. The calcium carbonate having a desired particle shape is obtained by adjusting at least one of a slurry concentration, a slurry temperature and a carbon dioxide introduction rate at the time of introducing carbon dioxide. Method for producing calcium carbonate. 3. The method for producing calcium carbonate according to claim 1, wherein the particle shape of calcium carbonate is spindle-shaped, columnar, cubic, rhombohedral or spherical. 4. In the integrated particle size from the small particle size side measured by the laser diffraction / scattering method, the 10% particle size of calcium carbonate is 1 μm or more, and the 90% particle size is 90% of the gypsum used as the raw material. The method for producing calcium carbonate according to any one of claims 1 to 3, wherein: 5. The method for producing calcium carbonate according to claim 1, wherein the particle size of gypsum is adjusted in advance to obtain calcium carbonate having a desired particle size. 6. The alkali metal according to claim 1, wherein the alkali metal is sodium or potassium.
The method for producing calcium carbonate according to the item. 7. The calcium carbonate produced by the production method according to any one of claims 1 to 6 is used for flue gas desulfurization or neutralization of sulfuric acid to produce gypsum as a byproduct, and the gypsum is produced by the production method. A flue gas desulfurization method or a sulfuric acid neutralization method, which is used as gypsum.