JP7089311B1 - Calcium carbonate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb carbon dioxide gas in exhaust gas of a combustion furnace or the like installed in a place other than a calcium carbonate manufacturing place into a high-concentration sodium hydroxide aqueous solution and transport it to a manufacturing place as a high-concentration sodium carbonate for use. Provided is a method for producing calcium carbonate, which makes it possible, suppresses the amount of carbon dioxide released into the environment as a whole, and contributes to the improvement of global warming. SOLUTION: A carbon dioxide absorption step of absorbing carbon dioxide gas into a 13-21% aqueous solution of sodium hydroxide to obtain an aqueous solution of sodium carbonate having a concentration of 15-24% or less, calcium oxide, and a concentration of 0-6. A hydration step of reacting with an aqueous solution of sodium hydroxide of less than% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m2 / g, and the carbon dioxide gas absorption in the lime milk. It is a method for producing calcium carbonate including a carbon dioxide step of adding and reacting the sodium carbonate aqueous solution obtained in the step. [Selection diagram] Fig. 1

Description

The present invention relates to a method for synthesizing calcium carbonate using flue exhaust gas from a combustion furnace or the like. In particular, the present invention relates to a method for producing spindle-shaped or needle-shaped calcium carbonate.

As an industrial method for synthesizing calcium carbonate, a carbon dioxide gasification method is known in which carbon dioxide gas is blown into lime milk to carbonate it. As the carbon dioxide gas used in the carbon dioxide gasification method, the flue exhaust gas of the lime firing furnace installed in the vicinity of the calcium carbonate production plant is often used. In addition, exhaust gas from boilers, waste incinerators, etc. can also be used as a source of carbon dioxide gas. However, in this case, it may not be possible to install the calcium carbonate production plant near the firing furnace, and it becomes necessary to lay a flue exhaust gas pipe leading from the facility that is the source of carbon dioxide gas to the calcium carbonate production plant. Even when the flue exhaust gas is used, there is a problem that the carbon dioxide gas supply amount is not constant and the carbon dioxide gas concentration of the flue exhaust gas is not always uniform, and carbon dioxide cannot be efficiently performed. Further, since the temperature of the flue exhaust gas cannot be controlled, the properties of the calcium carbonate produced are easily affected by the temperature of the flue exhaust gas, and there is also a problem that calcium carbonate having a desired shape cannot be produced. On the other hand, in the calcium carbonate synthesis reaction by the carbon dioxide gasification method, since the carbon dioxide gas needs to be once dissolved in water, the reaction time is long and the reaction efficiency is not high. It is often reacted at a low temperature in order to increase the absorption efficiency of carbon dioxide gas, and is not suitable for a reaction at a high temperature. There was also the problem that not all of the carbon dioxide was used in the reaction, and the unused carbon dioxide was released into the atmosphere.

In Patent Document 1, a caustic soda (sodium hydroxide) aqueous solution absorbs carbon dioxide gas to form sodium carbonate (sodium carbonate), and the sodium carbonate and lime milk (calcium hydroxide aqueous suspension) are reacted to produce calcium carbonate. The method of manufacture is disclosed. In the method of Patent Document 1, even if the carbon dioxide gas concentration is non-uniform, it can be absorbed into the caustic soda aqueous solution, and the carbon dioxide gas can be stored. Therefore, it is possible to install a calcium carbonate production plant in a place away from the place where carbon dioxide gas is generated. Sodium carbonate has a much higher solubility in water than that of carbon dioxide, and its solubility does not decrease even at high temperatures, so that calcium carbonate can be produced under high temperature and high concentration conditions. If the carbon dioxide gas that was not used in the reaction by the carbon dioxide gasification method described above can be recovered with the caustic soda aqueous solution, the amount of carbon dioxide gas released into the atmosphere can be expected to be reduced.

Japanese Unexamined Patent Publication No. 2002-293537

In the production method of Patent Document 1, when carbon dioxide gas is absorbed by low-concentration caustic soda, the absorption efficiency of carbon dioxide gas is lowered, so that carbon dioxide gas cannot be fully utilized. In this case, the concentration of the obtained sodium carbonate is also low, so that the productivity and production efficiency of the obtained calcium carbonate are also lowered. Further, the size, crystal shape, and shape of the calcium carbonate particles obtained by the production method of Patent Document 1 are unclear. Therefore, the first object of the present invention is to efficiently and continuously produce calcium carbonate controlled in the form of calcite and aragonite by using exhaust gas or the like in some cases.
Further, the present invention recycles carbon dioxide gas that was not used in the carbon dioxide gas absorption process in the carbon dioxide carbonization process, and hydroxides contained in the filtrate and used cleaning liquid obtained in the calcium carbonate production process. The second purpose is to recirculate sodium in the carbon dioxide absorption process and the liquefaction process and reuse it.
That is, in the present invention, carbon dioxide gas in the exhaust gas of a combustion furnace or the like installed in a place other than the place where calcium carbonate is manufactured is absorbed by a high-concentration sodium hydroxide aqueous solution, and is transported to the place of manufacture as high-concentration sodium carbonate for use. By further implementing the present invention, it is an object of the present invention to suppress the amount of carbon dioxide released into the environment as a whole and to contribute to the improvement of global warming.

The present invention comprises the following steps: a carbon dioxide gas absorption step of absorbing carbon dioxide gas in a sodium hydroxide aqueous solution having a concentration of 13-21% to obtain a sodium carbonate aqueous solution having a concentration of 15-24% or less.
A hydration step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. ,
A carbonation step in which the sodium carbonate aqueous solution obtained in the carbon dioxide absorption step is added to the lime milk and reacted.
The present invention relates to a method for producing calcium carbonate, including.
In the method for producing calcium carbonate, in the carbonation step, the initial concentration of the lime milk is 11-19%, the concentration of the aqueous sodium carbonate solution is 15-24%, and the reaction is carried out in the range of 20-40 ° C. It is characterized by obtaining a spindle-shaped calcium carbonate crystalline calcium carbonate having a BET specific surface area of 4-20 m ² / g.

Here, the carbon dioxide gas that was not used in the carbon dioxide gas absorption step can be used again in the carbonation step.

After the carbonation step, a solid-liquid separation step of separating the filtrate containing sodium hydroxide and calcium carbonate,
A washing step of washing the calcium carbonate obtained in the solid-liquid separation step with a washing liquid, and
Can be further included.

Further, a high-concentration sodium hydroxide aqueous solution is added to the filtrate obtained in the solid-liquid separation step and the used cleaning solution obtained in the cleaning step, or the filtrate and the used cleaning solution are heated. This can be concentrated to obtain an aqueous solution containing sodium hydroxide at a concentration of 13-21%, and the aqueous solution can be used in the carbonation step.

An aqueous solution obtained by adjusting the filtrate obtained in the solid-liquid separation step and the used washing solution obtained in the washing step so that the concentration of sodium hydroxide is less than 6% is obtained, and the aqueous solution is hydrated. It is also preferable to use it in the process.

Further, the present invention has the following steps:
A carbon dioxide absorption step of absorbing carbon dioxide gas in a sodium hydroxide aqueous solution having a concentration of 13-21% to obtain a sodium carbonate aqueous solution having a concentration of 15-24% or less.
A hydration step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. ,
A carbonation step in which the sodium carbonate aqueous solution obtained in the carbon dioxide absorption step is added to the lime milk and reacted.
The present invention relates to a method for producing calcium carbonate, including.
In the method for producing calcium carbonate, in the carbonation step, the initial concentration of the lime milk is 11-24%, the concentration of the aqueous sodium carbonate solution is 15-24%, and the reaction is carried out in the range of 40-80 ° C. It is characterized by obtaining acicular aragonite crystalline calcium carbonate having a BET specific surface area of 3-10 m ² / g.

Here, the carbon dioxide gas that was not used in the carbon dioxide gas absorption step can be used again in the carbon dioxide gas absorption step.

After the carbonation step, a solid-liquid separation step of separating the filtrate containing sodium hydroxide and calcium carbonate,
A washing step of washing the calcium carbonate obtained in the solid-liquid separation step with a washing liquid, and
Can be further included.

Further, a high-concentration sodium hydroxide aqueous solution is added to the filtrate obtained in the solid-liquid separation step and the used cleaning solution obtained in the cleaning step, or the filtrate and the used cleaning solution are heated. Thereby, it is concentrated to obtain an aqueous solution containing sodium hydroxide at a concentration of 13-21%, and the aqueous solution can be used in the carbon dioxide gas absorption step.

An aqueous solution obtained by adjusting the filtrate obtained in the solid-liquid separation step and the used washing solution obtained in the washing step so that the concentration of sodium hydroxide is less than 6% is obtained, and the aqueous solution is hydrated. It is also preferable to use it in the process.

According to the present invention, by preparing a sodium carbonate aqueous solution and sodium hydroxide in a high concentration in the process as compared with the conventional method, and by using a calcium hydroxide slurry having a high concentration as compared with the conventional method, it is efficient. Calcium carbonate having a desired particle shape can be continuously obtained. In addition, by returning the flue gas and unreacted carbon dioxide gas during the process to the process and using it, and by increasing the concentration of the above reaction solution, the amount of carbon dioxide gas generated during manufacturing and the amount of alkaline waste liquid containing sodium hydroxide released during the process can be reduced. It can be suppressed and the burden on the environment can be reduced. In addition, since it is possible to use carbon dioxide gas in the exhaust gas of a combustion furnace or the like installed in a place other than the manufacturing site, it is also useful as a method for fixing carbon dioxide gas conventionally released into the environment.
In the production method of the present invention, calcium carbonate having a desired particle size can be obtained. It is possible to continuously control and produce calcium carbonate suitable for each application such as papermaking, coating pigments, plastics, sealants, rubbers, and foods.

FIG. 1 is a flow chart illustrating the manufacturing method of the present invention. FIG. 2 is an electron micrograph (magnification: 20000 times) of spindle-shaped calcium carbonate obtained in Example 1. FIG. 3 is an electron micrograph (magnification: 10000 times) of needle-shaped calcium carbonate obtained in Example 2. FIG. 4 is an electron micrograph (magnification: 10000 times) of needle-shaped calcium carbonate obtained in Example 3. FIG. 5 is an electron micrograph (magnification: 10000 times) of needle-shaped calcium carbonate obtained in Example 4.

The embodiments of the present invention will be described in more detail, but the present invention is not limited to the following embodiments.

One embodiment of the present invention comprises the following steps: a carbon dioxide gas absorption step of absorbing carbon dioxide gas in a sodium hydroxide aqueous solution having a concentration of 13-21% to obtain a sodium carbonate aqueous solution having a concentration of 15-24% or less; A hydration step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. In the carbonation step, the sodium carbonate aqueous solution obtained in the carbon dioxide gas absorption step is added to the lime milk and reacted.
Is a method for producing calcium carbonate, including
In the carbonation step, the initial concentration of the lime milk was 11-19%, the concentration of the aqueous sodium carbonate solution was 15-24%, and the reaction was carried out in the range of 20-40 ° C., and the BET specific surface area was 4-20 m ² . The production method is characterized by obtaining / g of spindle-shaped calcite crystalline calcium carbonate. The present embodiment is a method for producing calcium carbonate, which comprises at least a carbon dioxide gas absorption step, a liquefaction step, and a carbonation step. The carbon dioxide absorption step is a step of absorbing carbon dioxide (carbon dioxide) with a sodium hydroxide aqueous solution to obtain a sodium carbonate aqueous solution. Sodium hydroxide is also generally called caustic soda, and commercially available products can be appropriately used. The sodium hydroxide aqueous solution can be obtained by dissolving sodium hydroxide in water, or can use a liquid containing sodium hydroxide (so-called "white liquid") obtained in the papermaking process. The concentration of sodium hydroxide in the aqueous sodium hydroxide solution used in this step can be 13-21%, preferably 15-20%. By setting the concentration of the sodium hydroxide aqueous solution to 21% at the maximum in this step, the absorption efficiency of carbon dioxide gas can be improved. In the present embodiment, the carbon dioxide gas absorbed in the sodium hydroxide aqueous solution may be a gas containing carbon dioxide alone or a mixed gas containing carbon dioxide gas and another gas. As the carbon dioxide gas used in this embodiment, exhaust gas containing carbon dioxide gas can be used. Such exhaust gas includes, for example, a lime firing furnace, a boiler, a waste incinerator, a cement firing furnace, a refractory heating furnace, a steelmaking converter, a steelmaking smelting furnace, a cupola, a coke gas generator, a coal gas generator, and petroleum decomposition. Exhaust gas from a furnace, a glass manufacturing reflex furnace, an oil gas generating furnace and an acetylene generating furnace can be mentioned. Sodium carbonate is produced when carbon dioxide gas is absorbed by an aqueous solution of sodium hydroxide. Carbon dioxide can be absorbed until the concentration of sodium carbonate reaches 15-24%. In the present specification,% means% by weight unless otherwise specified.
From the viewpoint of environmental conservation, it is very important to reuse the carbon dioxide gas that was not used in the carbon dioxide gas absorption process so that it can be absorbed by the sodium hydroxide aqueous solution in the carbonation process, instead of releasing it into the atmosphere as it is. preferable.

In the embodiment, the hydration step is a step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk. Here, lime milk is an aqueous suspension of calcium hydroxide (calcium hydroxide aqueous slurry). Calcium oxide used in the liquefaction process is an oxide of calcium, which is also generally called quicklime. Commercially available calcium oxide can be appropriately used. The concentration of the aqueous sodium hydroxide solution to react with calcium oxide in this step is less than 0-6%. The calcium hydroxide obtained in this step is a hydroxide of calcium, which is also generally called slaked lime. In the liquefaction step, it is preferable to obtain a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. The BET specific surface area can be measured according to Japanese Industrial Standards JIS Z 8830 "Method for measuring the specific surface area of powder (solid) by gas adsorption". By adjusting the amount and concentration of the calcium oxide to be reacted and the aqueous sodium hydroxide solution, calcium hydroxide having a BET specific surface area of 5-40 m ² / g can be obtained. By increasing the amount of the sodium hydroxide aqueous solution with respect to the amount of calcium oxide, calcium hydroxide having a large BET specific surface area can be obtained. On the contrary, if the amount of the sodium hydroxide aqueous solution is smaller than the amount of calcium oxide, calcium hydroxide having a small BET specific surface area can be obtained. Further, if an aqueous solution of sodium hydroxide having an excessively high concentration is used in the hydration step, the BET specific surface area of the obtained calcium hydroxide tends to be high, and calcium hydroxide having a desired BET specific surface area cannot be obtained. In addition, the viscosity of lime milk becomes high and it becomes difficult to handle. In particular, setting the BET specific surface area of calcium hydroxide contained in the lime milk obtained in this step to 15-40 m ² / g is the most crystalline form of calcium carbonate obtained in the carbonation step described below. Is preferable for forming a spindle shape. The liquefaction step and the above-mentioned carbon dioxide gas absorption step can be performed simultaneously in parallel, such as a carbon dioxide gas absorption step followed by a liquefaction step, or a liquefaction step followed by a carbon dioxide gas absorption step. , It is also possible to continue. Obtaining calcium hydroxide having a BET specific surface area in an appropriate range in the liquefaction step is important for finally obtaining the desired form of calcium carbonate in the present embodiment.

In the embodiment, the carbonization step is a step of reacting the lime milk obtained in the liquefaction step with the sodium carbonate aqueous solution obtained in the carbon dioxide gas absorption step to obtain calcium carbonate. This process is also commonly referred to as the caustic process. In this step, it is very preferable to adjust the solid content concentration of lime milk to 11-23% before use. In particular, it is preferable to set the initial concentration of lime milk to 11-19% and the concentration of the aqueous sodium carbonate solution to 15-24% for the reaction. The sodium carbonate aqueous solution is used by appropriately adjusting the concentration of the sodium carbonate aqueous solution having a concentration of 15-24% or less obtained in the carbon dioxide gas absorption step. At this time, although it depends on the reaction scale in which the carbonation step is performed, the sodium carbonate aqueous solution is gradually added to the lime milk, for example, it is added over a certain period of time such as 60-180 minutes or 100-150 minutes. Is very preferable. Further, the reaction in the carbonation step is preferably carried out by stirring the reaction solution. Preferably, the stirrer is adjusted so that the time until the sodium carbonate aqueous solution is gradually added to the lime milk and these are completely mixed (complete mixing time) is 3-25 seconds or 5-22 seconds. Can be done. Conventionally used propeller stirrer, paddle blade stirrer, ribbon stirrer, turbine blade stirrer, horseshoe blade stirrer, thread winding blade stirrer, mixer stirrer, magnetic stirrer, etc. as means for stirring the reaction vessel. Can be used.
A BET specific surface area of 4- 20 m ² / g of spindle-shaped calcite crystalline calcium carbonate can be obtained. If the reaction temperature of the carbonation step is too high or too low, the cost required for energy required for heating and cooling increases, and calcium carbonate having a desired BET specific surface area and shape can be obtained. It disappears. In the reaction of this step, calcium carbonate and sodium hydroxide are generated, water-soluble sodium hydroxide is dissolved in the reaction solution, and calcium carbonate having low water solubility is precipitated as a solid.

A solid-liquid separation step of separating calcium carbonate generated by the reaction of the carbonation step from the reaction solution and taking it out in a solid state may be further included. Further, a washing step of washing the solid calcium carbonate obtained in the solid-liquid separation step with a washing liquid may be further included. The calcium carbonate obtained in the solid-liquid separation step is preferably washed with water. The liquid (filtrate) remaining after separating solid calcium carbonate in the solid-liquid separation step and the used cleaning liquid obtained in the washing step are sodium hydroxide aqueous solutions. This sodium hydroxide aqueous solution can be reused in the carbon dioxide gas absorption step described above. When the filtrate and used cleaning liquid are reused in the carbon dioxide gas absorption step, it is preferable to adjust the concentration of sodium hydroxide to 13-21%. The concentration of sodium hydroxide can be adjusted, for example, by adding a high-concentration sodium hydroxide aqueous solution (a sodium hydroxide aqueous solution having a concentration of 13% or more), adding solid sodium hydroxide, or the filtrate and the filtrate. This is done by concentrating the used cleaning solution by heating it.
Further, the filtrate obtained in the solid-liquid separation step and the used washing liquid obtained in the washing step can be reused in the above-mentioned liquefaction step. When the filtrate and used washing liquid are reused in the hydration step, it is preferable to adjust the concentration of sodium hydroxide to less than 6%. The concentration of sodium hydroxide is adjusted, for example, by diluting with water.

Subsequently, in the second embodiment of the present invention, carbon dioxide gas (carbon dioxide) is absorbed by a sodium hydroxide aqueous solution having a concentration of 13-21% in the following step, and a sodium carbonate aqueous solution having a concentration of 15-24% or less is applied. The carbon dioxide absorption step obtained; lime which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g by reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6%. A method for producing calcium carbonate, comprising a slaked step of obtaining milk; a carbon dioxide step of adding and reacting the sodium carbonate aqueous solution obtained in the carbon dioxide gas absorption step with the lime milk;
In the carbonation step, the initial concentration of the lime milk was 11-24%, the concentration of the aqueous sodium carbonate solution was 15-24%, and the reaction was carried out in the range of 40-80 ° C., and the BET specific surface area was 3-10 m ² . The production method is characterized by obtaining / g needle-shaped aragonite crystalline calcium carbonate. Similar to one embodiment, the present embodiment is also a method for producing calcium carbonate, which comprises at least a carbon dioxide gas absorption step, a hydration step, and a carbonation step. The carbon dioxide gas absorption step of the second embodiment is a step of absorbing carbon dioxide gas with a sodium hydroxide aqueous solution to obtain a sodium carbonate aqueous solution. The carbon dioxide gas absorption step of the second embodiment can be performed in exactly the same manner as the carbon dioxide gas absorption step of the first embodiment.
It is very preferable from the viewpoint of environmental conservation to reuse the carbon dioxide gas that was not used in the carbon dioxide gas absorption step so that it can be absorbed by the sodium hydroxide aqueous solution in the carbonation step, instead of releasing it into the atmosphere as it is. Is the same as the above-mentioned embodiment.

The hydration step of the second embodiment is a step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk. The liquefaction step of the second embodiment can be performed in exactly the same manner as the carbon dioxide gas absorption step of the first embodiment. Also in the second embodiment, the liquefaction step and the above-mentioned carbon dioxide gas absorption step can be performed at the same time in parallel, and the carbon dioxide gas absorption step is followed by the liquefaction step or the liquefaction step is followed by carbon dioxide. It is also possible to carry out the process continuously, such as the gas absorption step. In particular, setting the BET specific surface area of calcium hydroxide contained in the lime milk obtained in this step to 5-20 m ² / g is the most crystalline form of calcium carbonate obtained in the carbonation step described below. Is preferable for forming needle-shaped aragonite. Obtaining calcium hydroxide having a BET specific surface area in an appropriate range in the liquefaction step is important for finally obtaining the desired form of calcium carbonate in the present embodiment.

In the second embodiment, the carbonization step is a step of reacting the lime milk obtained in the liquefaction step with the sodium carbonate aqueous solution obtained in the carbon dioxide gas absorption step to obtain calcium carbonate. This process is also commonly referred to as the caustic process. In this step, it is very preferable to adjust the solid content concentration of lime milk to 11-24% before use. In particular, it is preferable to set the initial concentration of lime milk to 11-24% and the concentration of the aqueous sodium carbonate solution to 15-24% for the reaction. The sodium carbonate aqueous solution is used by appropriately adjusting the concentration of the sodium carbonate aqueous solution having a concentration of 15-24% or less obtained in the carbon dioxide gas absorption step. At this time, although it depends on the reaction scale in which the carbonation step is performed, the sodium carbonate aqueous solution is gradually added to the lime milk, for example, it is added over a certain period of time such as 60-180 minutes or 100-150 minutes. Is very preferable. Further, the reaction in the carbonation step is preferably carried out by stirring the reaction solution. Preferably, the stirrer is adjusted so that the time until the sodium carbonate aqueous solution is gradually added to the lime milk and these are completely mixed (complete mixing time) is 3-25 seconds or 5-22 seconds. Can be done. Conventionally used propeller stirrer, paddle blade stirrer, ribbon stirrer, turbine blade stirrer, horseshoe blade stirrer, thread winding blade stirrer, mixer stirrer, magnetic stirrer, etc. as means for stirring the reaction vessel. Can be used.
A BET specific surface area of 3- It is possible to obtain 10 m ² / g of acicular aragonite crystalline calcium carbonate.
If the reaction temperature of the carbonation step is too high or too low, the cost required for energy required for heating and cooling increases, and calcium carbonate having a desired BET specific surface area and shape can be obtained. It disappears. Further, when the BET specific surface area of calcium hydroxide is adjusted as described above in order to produce calcium carbonate containing a large amount of needle-shaped aragonite crystals, when the reaction temperature of the carbonation step is raised, the shape of the aragonite crystals (needle-shaped) is increased. Tends to get thicker. In the reaction of this step, calcium carbonate and sodium hydroxide are generated, water-soluble sodium hydroxide is dissolved in the reaction solution, and calcium carbonate having low water solubility is precipitated as a solid.

In the second embodiment, a solid-liquid separation step of separating calcium carbonate generated by the reaction of the carbonation step from the reaction solution and taking it out in a solid state may be further included. Further, a washing step of washing the solid calcium carbonate obtained in the solid-liquid separation step with a washing liquid may be further included. The calcium carbonate obtained in the solid-liquid separation step is preferably washed with water. The liquid (filtrate) remaining after separating solid calcium carbonate in the solid-liquid separation step and the used cleaning liquid obtained in the washing step are sodium hydroxide aqueous solutions. This sodium hydroxide aqueous solution can be reused in the carbon dioxide gas absorption step described above. When the filtrate and used cleaning liquid are reused in the carbon dioxide gas absorption step, it is preferable to adjust the concentration of sodium hydroxide to 13-21%. The concentration of sodium hydroxide can be adjusted, for example, by adding a high-concentration sodium hydroxide aqueous solution (a sodium hydroxide aqueous solution having a concentration of 13% or more), adding solid sodium hydroxide, or the filtrate and the filtrate. This is done by concentrating the used cleaning solution by heating it.
Further, the filtrate obtained in the solid-liquid separation step and the used washing liquid obtained in the washing step can be reused in the above-mentioned liquefaction step. When the filtrate and used washing liquid are reused in the hydration step, it is preferable to adjust the concentration of sodium hydroxide to less than 6%. The concentration of sodium hydroxide is adjusted, for example, by diluting with water.

Subsequently, the flow of the first and second embodiments of the present invention will be described with reference to FIG. FIG. 1 shows a flow in which the method for producing calcium carbonate according to the first and second embodiments of the present invention is carried out using carbon dioxide gas in the exhaust gas discharged from a combustion furnace or the like. In the figure, 1: carbon dioxide gas absorption step, 2: liquefaction step, 3: carbonation step, 4: solid-liquid separation step, 5: cleaning step. Exhaust gas discharged from a combustion furnace or the like is appropriately dust-removed to obtain a refined gas containing carbon dioxide gas. On the other hand, a sodium hydroxide aqueous solution adjusted to a concentration of 13-21% by a method such as appropriately mixing production water and a high-concentration sodium hydroxide aqueous solution is prepared, and purified gas is absorbed therein (carbon dioxide gas absorption step 1). ). In this way, an aqueous sodium carbonate solution having a concentration of 15-24% or less is obtained. The unreacted gas that could not be completely absorbed in the carbon dioxide gas absorption step 1 is returned as shown by the arrow 10 and used again in the carbon dioxide gas absorption step 1.
On the other hand, calcium oxide and water for hydration (aqueous solution of sodium hydroxide having a concentration of less than 0-6%) are prepared and reacted with each other (hydration step 2), and if necessary, a classification operation is performed to BET. Purified lime milk, which is a suspension of calcium hydroxide having a specific surface area of 5-40 m ² / g, is obtained.
When the purified lime milk thus obtained is reacted with an aqueous sodium carbonate solution (carbonation step 3), calcium carbonate is produced. The generated calcium carbonate is filtered (solid-liquid separation step 4), and the obtained solid calcium carbonate is washed with a washing liquid (washing step 5). The filtrate obtained in the solid-liquid separation step 4 and the used washing liquid obtained in the washing step 5 are recovered and reused as the aqueous sodium hydroxide solution in the carbon dioxide gas absorption step 1 or the water for hydration in the liquefaction step 2. (Arrows 20 and 30).

In one embodiment, in the carbonation step 3 of FIG. 1, the initial concentration of lime milk is 11-19%, the concentration of the aqueous sodium carbonate solution is 15-24%, and the reaction is carried out in the range of 20-40 ° C. This makes it possible to obtain spindle-shaped calcite crystalline calcium carbonate having a BET specific surface area of 4-20 m ² / g. On the other hand, in the second embodiment, in the carbonation step 3 of FIG. 1, the initial concentration of lime milk is 11-24%, the concentration of the aqueous sodium carbonate solution is 15-24%, and the reaction is carried out in the range of 40-80 ° C. .. As a result, acicular aragonite crystalline calcium carbonate having a BET specific surface area of 3-10 m ² / g can be obtained.

According to the method for producing calcium carbonate according to the embodiment of the present invention, carbon dioxide gas can be efficiently absorbed in a relatively high concentration sodium hydroxide aqueous solution. At this time, a sodium carbonate aqueous solution having a desired concentration can be obtained regardless of the concentration of carbon dioxide gas. Further, in the carbonation step, calcium carbonate having a desired shape can be produced by reacting a sodium carbonate aqueous solution having a predetermined initial concentration and lime milk having a predetermined initial solid content concentration in a predetermined temperature range for a predetermined time. It will be possible.

In the method for producing calcium carbonate according to the embodiment of the present invention, carbon dioxide gas and an aqueous solution of sodium hydroxide can be repeatedly reused, so that carbon dioxide and waste liquid discharged to the environment are small, and the burden on the environment can be reduced. can.

Hereinafter, examples of the present invention will be described.
[Example 1]

[Example 1] Synthesis of spindle-shaped calcite crystalline calcium carbonate (1)
(1) Carbon Dioxide Absorption Step A carbon dioxide-air mixed gas containing 30% by volume of carbon dioxide was introduced into an aqueous solution of sodium hydroxide having a concentration of 12.9% until the pH of the aqueous solution reached 11.5. 630 kg of an aqueous sodium carbonate solution having a concentration of 16.0% was obtained.
(2) Watering step Calcium oxide was mixed with water and hydrated to obtain lime milk as a suspension of calcium hydroxide. The BET specific surface area of the obtained calcium hydroxide was measured according to Japanese Industrial Standards JIS Z 8830 and found to be 15.9 m ² / g. The concentration of lime milk was adjusted to obtain 389 kg of lime milk having a solid content concentration of 15.0%.
(3) Carbonation step 389 kg of lime milk obtained in the liquefaction step was introduced into a reaction tank equipped with a propeller agitator. 630 kg of the sodium carbonate aqueous solution obtained in the carbonation step was added over 120 minutes, and the reaction solution was stirred. At this time, the propeller agitator was operated so that the complete mixing time in the reaction tank was 21 seconds, and the temperature in the reaction tank was adjusted to 25 ° C. The obtained calcium carbonate suspension was filtered, the filtered cake was washed with water, and then dried in a constant temperature dryer at 105 ° C. for 1 hour. 79 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed with an electron microscope, it had a spindle-shaped shape. FIG. 2 is an electron micrograph (magnification of 20000 times) of calcium carbonate obtained in Example 1. The BET specific surface area (measured according to JIS Z 8830) of this spindle-shaped calcite crystalline calcium carbonate was 5.9 m ² / g. (Table 1, row of carbonation step reaction temperature 25 ° C, column of sodium carbonate aqueous solution concentration 16%)

[Example 2] Synthesis of acicular aragonite crystalline calcium carbonate (1)
(1) Carbon Dioxide Absorption Step A carbon dioxide-air mixed gas containing 30% by volume of carbon dioxide was introduced into an aqueous solution of sodium hydroxide having a concentration of 12.9% until the pH of the aqueous solution reached 11.5. 630 kg of an aqueous sodium carbonate solution having a concentration of 16.0% was obtained.
(2) Watering step Calcium oxide was mixed with water and hydrated to obtain lime milk as a suspension of calcium hydroxide. The BET specific surface area of the obtained calcium hydroxide was measured according to Japanese Industrial Standards JIS Z 8830 and found to be 15.9 m ² / g. The concentration of lime milk was adjusted to obtain 389 kg of lime milk having a solid content concentration of 15.0%.
(3) Carbonation step 389 kg of lime milk obtained in the liquefaction step was introduced into a reaction tank equipped with a propeller agitator. 630 kg of the sodium carbonate aqueous solution obtained in the carbonation step was added over 120 minutes, and the reaction solution was stirred. At this time, the propeller agitator was operated so that the complete mixing time in the reaction tank was 21 seconds, and the temperature in the reaction tank was adjusted to 50 ° C. The obtained calcium carbonate suspension was filtered, the filtered cake was washed with water, and then dried in a constant temperature dryer at 105 ° C. for 1 hour. 79 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed with an electron microscope, it was aragonite having a needle-like shape. FIG. 3 is an electron micrograph (magnification of 10000 times) of calcium carbonate obtained in Example 2. The BET specific surface area (measured according to JIS Z 8830) of this needle-shaped aragonite crystalline calcium carbonate was 6.3 m ² / g. (Table 1, row of carbonation step reaction temperature 50 ° C, column of sodium carbonate aqueous solution concentration 16%)

[Example 3] Synthesis of acicular aragonite crystalline calcium carbonate (2)
(1) Carbon Dioxide Absorption Step A carbon dioxide-air mixed gas containing 30% by volume of carbon dioxide was introduced into an aqueous solution of sodium hydroxide having a concentration of 15.6% until the pH of the aqueous solution reached 11.5. 666 kg of an aqueous sodium carbonate solution having a concentration of 19.0% was obtained.
(2) Watering step Calcium oxide was mixed with water and hydrated to obtain lime milk as a suspension of calcium hydroxide. The BET specific surface area of the obtained calcium hydroxide was measured according to Japanese Industrial Standards JIS Z 8830 and found to be 15.9 m ² / g. The concentration of lime milk was adjusted to obtain 366 kg of lime milk having a solid content concentration of 20.0%.
(3) Carbonation Step 366 kg of lime milk obtained in the liquefaction step was introduced into a reaction tank equipped with a propeller agitator. 666 kg of the sodium carbonate aqueous solution obtained in the carbonation step was added over 120 minutes, and the reaction solution was stirred. At this time, the propeller agitator was operated so that the complete mixing time in the reaction tank was 21 seconds, and the temperature in the reaction tank was adjusted to 50 ° C. The obtained calcium carbonate suspension was filtered, the filtered cake was washed with water, and then dried in a constant temperature dryer at 105 ° C. for 1 hour. 99 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed with an electron microscope, it was aragonite having a needle-like shape. FIG. 4 is an electron micrograph (magnification of 10000 times) of calcium carbonate obtained in Example 3. The BET specific surface area (measured according to JIS Z 8830) of this needle-shaped aragonite crystalline calcium carbonate was 8.5 m ² / g. (Table 2, row of carbonation step reaction temperature 50 ° C, column of sodium carbonate aqueous solution concentration 19%)

[Example 4] Synthesis of acicular aragonite crystalline calcium carbonate (3)
(1) Carbon Dioxide Absorption Step A carbon dioxide-air mixed gas containing 30% by volume of carbon dioxide was introduced into an aqueous solution of sodium hydroxide having a concentration of 12.9% until the pH of the aqueous solution reached 11.5. 630 kg of an aqueous sodium carbonate solution having a concentration of 16.0% was obtained.
(2) Watering step Calcium oxide was mixed with water and hydrated to obtain lime milk as a suspension of calcium hydroxide. The BET specific surface area of the obtained calcium hydroxide was measured according to Japanese Industrial Standards JIS Z 8830 and found to be 15.9 m ² / g. The concentration of lime milk was adjusted to obtain 389 kg of lime milk having a solid content concentration of 15.0%.
(3) Carbonation step 389 kg of lime milk obtained in the liquefaction step was introduced into a reaction tank equipped with a propeller agitator. 630 kg of the sodium carbonate aqueous solution obtained in the carbonation step was added over 120 minutes, and the reaction solution was stirred. At this time, the propeller agitator was operated so that the complete mixing time in the reaction tank was 21 seconds, and the temperature in the reaction tank was adjusted to 80 ° C. The obtained calcium carbonate suspension was filtered, the filtered cake was washed with water, and then dried in a constant temperature dryer at 105 ° C. for 1 hour. 79 kg of calcium carbonate powder was obtained. When the obtained calcium carbonate was observed with an electron microscope, it was aragonite having a needle-like shape. FIG. 5 is an electron micrograph (magnification of 10000 times) of calcium carbonate obtained in Example 4. The BET specific surface area (measured according to JIS Z 8830) of this needle-shaped aragonite crystalline calcium carbonate was 3.4 m ² / g. (Table 1, row of carbonation step reaction temperature 80 ° C, column of sodium carbonate aqueous solution concentration 16%)

[Other synthetic examples of spindle-shaped calcite crystalline calcium carbonate]
In Example 1, various aqueous sodium carbonate solutions having different concentrations were prepared. To the lime milk having a solid content concentration of 15.0% obtained in the liquefaction step of Example 1, aqueous sodium carbonate solutions having different concentrations were gradually added and stirred using a propeller stirrer, and the temperature inside the reaction tank was increased. The carbonation step was carried out at 20 ° C./25 ° C./40 ° C. The results of each synthesis example are shown in Table 1 below.

[Other synthetic examples of acicular aragonite crystalline calcium carbonate]
In Example 2, various aqueous sodium carbonate solutions having different concentrations were prepared. To the lime milk having a solid content concentration of 15.0% obtained in the liquefaction step of Example 2, aqueous sodium carbonate solutions having different concentrations were gradually added and stirred using a propeller stirrer, and the temperature inside the reaction tank was increased. Was 50 ° C./65 ° C./70 ° C./80 ° C., and the carbonation step was performed. The results of each synthesis example are shown in Table 1 below.
Further, in Example 3, various aqueous sodium carbonate solutions having different concentrations were prepared. To the lime milk having a solid content concentration of 20.0% obtained in the liquefaction step of Example 3, sodium carbonate aqueous solutions having different concentrations are gradually added and stirred using a propeller stirrer, and the temperature in the reaction tank is increased. Was 40 ° C./50 ° C./60 ° C./70 ° C./80 ° C., and the carbonation step was performed. The results of each synthesis example are shown in Table 2 below.

Tables 1 and 2 show the crystal shape and BET specific surface area of calcium carbonate produced in each synthetic example. For example, Example 1 is described in "Spindle 6" in the row of the carbonation step reaction temperature of 25 ° C. in Table 1 and the column of the sodium carbonate aqueous solution concentration of 19%. It means that a spindle-shaped calcite crystalline calcium carbonate having a BET specific surface area of 6 m ² / g (the value of the BET specific surface area in the table is a value rounded off from the measured value) was obtained by the method of Example 1. Further, in Tables 1 and 2, "-" means that the reaction under the specified conditions was difficult because sodium carbonate was precipitated from the aqueous sodium carbonate solution under the relevant conditions.
As shown in Tables 1 and 2, the desired crystal shape and BET were obtained by adjusting the solid content concentration, sodium carbonate aqueous solution concentration, and reaction temperature of the initial lime milk in the carbonation step by the method of the present invention. Calcium carbonate having a specific surface area can be made separately.

In the method of the present invention, carbon dioxide gas is absorbed by a relatively high-concentration sodium hydroxide aqueous solution, so that carbon dioxide gas can be used efficiently. By the method of the present invention, acicular crystals and spindle-shaped crystals of calcium carbonate could be produced. By changing the concentration, reaction temperature, reaction time, mixing time, etc. of lime milk and sodium carbonate aqueous solution in the carbonation step, calcium carbonate having a desired crystal form can be produced separately. Since the method of the present invention reuses carbon dioxide gas, a filtrate and the like, the load on the environment can be reduced as a whole.

The calcium carbonate produced by the method of the present invention is particularly used as a filler for sealing materials, adhesives, rubber compositions, plastic compositions and papers, as well as pigments for paper coating and pigments for paints and inks. Can be widely used as.

Claims (10)

The following steps:
A carbon dioxide absorption step of absorbing carbon dioxide gas in a sodium hydroxide aqueous solution having a concentration of 13-21% to obtain a sodium carbonate aqueous solution having a concentration of 15-24% or less.
A hydration step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. ,
A carbonation step in which the sodium carbonate aqueous solution obtained in the carbon dioxide absorption step is added to the lime milk and reacted.
Is a method for producing calcium carbonate, including
In the carbonation step, the initial concentration of the lime milk was 11-19%, the concentration of the aqueous sodium carbonate solution was 15-24%, and the reaction was carried out in the range of 20-40 ° C., and the BET specific surface area was 4-20 m ² . The production method, which comprises obtaining / g of spindle-shaped calcite crystalline calcium carbonate. The production method according to claim 1, wherein the carbon dioxide gas not used in the carbon dioxide gas absorption step is used again in the carbon dioxide gas absorption step. After the carbonation step, a solid-liquid separation step of separating the filtrate containing sodium hydroxide and calcium carbonate,
A washing step of washing the calcium carbonate obtained in the solid-liquid separation step with a washing liquid, and
The production method according to any one of claims 1 or 2, further comprising. By adding a high-concentration aqueous sodium hydroxide solution to the filtrate obtained in the solid-liquid separation step and the used cleaning solution obtained in the cleaning step, or by heating the filtrate and the used cleaning solution. The production method according to claim 3, wherein the concentration is obtained to obtain an aqueous solution containing sodium hydroxide at a concentration of 13-21%, and the aqueous solution is used in the carbon dioxide gas absorption step. An aqueous solution obtained by adjusting the filtrate obtained in the solid-liquid separation step and the used washing solution obtained in the washing step so that the concentration of sodium hydroxide is less than 6% is obtained, and the aqueous solution is hydrated. The manufacturing method according to claim 3 or 4, which is used in the process. The following steps:
A carbon dioxide absorption step of absorbing carbon dioxide gas in a sodium hydroxide aqueous solution having a concentration of 13-21% to obtain a sodium carbonate aqueous solution having a concentration of 15-24% or less.
A hydration step of reacting calcium oxide with an aqueous solution of sodium hydroxide having a concentration of less than 0-6% to obtain lime milk which is a suspension of calcium hydroxide having a BET specific surface area of 5-40 m ² / g. ,
A carbonation step in which the sodium carbonate aqueous solution obtained in the carbon dioxide absorption step is added to the lime milk and reacted.
Is a method for producing calcium carbonate, including
In the carbonation step, the initial concentration of the lime milk was 11-24%, the concentration of the aqueous sodium carbonate solution was 15-24%, and the reaction was carried out in the range of 40-80 ° C., and the BET specific surface area was 3-10 m ² . The production method, which comprises obtaining / g needle-shaped aragonite crystalline calcium carbonate. The production method according to claim 6, wherein the carbon dioxide gas not used in the carbon dioxide gas absorption step is used again in the carbon dioxide gas absorption step. After the carbonation step, a solid-liquid separation step of separating the filtrate containing sodium hydroxide and calcium carbonate,
A washing step of washing the calcium carbonate obtained in the solid-liquid separation step with a washing liquid, and
The production method according to claim 6 or 7, further comprising. By adding a high-concentration aqueous sodium hydroxide solution to the filtrate obtained in the solid-liquid separation step and the used cleaning solution obtained in the cleaning step, or by heating the filtrate and the used cleaning solution. The production method according to claim 8, wherein the concentration is obtained to obtain an aqueous solution containing sodium hydroxide at a concentration of 13-21%, and the aqueous solution is used in the carbon dioxide gas absorption step. An aqueous solution obtained by adjusting the filtrate obtained in the solid-liquid separation step and the used washing solution obtained in the washing step so that the concentration of sodium hydroxide is less than 6% is obtained, and the aqueous solution is hydrated. The manufacturing method according to claim 8 or 9, which is used in the process.

Images