JP2604202B2 - Method for producing spindle-shaped calcium carbonate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing spindle-shaped calcium carbonate.

[Background of the Invention] Conventionally, clay has been used as a filler for papermaking, but the quartz contained therein often causes troubles in the papermaking process and the printing stage. The mainstream of the agent.

In recent years, demand for talc has been increasing due to demand for advanced specialization such as high whiteness (for example, 85 degrees or more) and low abrasion due to the trend toward higher-grade papermaking. However, since it tends to be difficult to secure high-purity raw talc, natural and synthetic calcium carbonate has been attracting attention as an alternative material.

Such calcium carbonate includes heavy calcium carbonate produced by pulverizing natural white limestone and light calcium carbonate chemically synthesized. As a method for producing light calcium carbonate, a carbon dioxide compounding method in which carbon dioxide is introduced into lime milk and reacted is widely used.
By this method, spindle-shaped calcium carbonate as well as calcium carbonate having a cubic shape, a needle shape, or the like is manufactured.

A method for producing spindle-shaped calcium carbonate by a carbon dioxide compounding method is already known, and for example, there is a method disclosed in JP-A-59-26927. This is because, by introducing a mixed gas having a low carbon dioxide concentration into lime milk having a low calcium hydroxide concentration and terminating the reaction in a short time, the growth of crystals is suppressed, and a particle diameter suitable for a papermaking filler is suppressed. It produces small spindle-shaped calcium carbonate.

However, the above-mentioned method is economically disadvantageous as an industrial production method of spindle-shaped calcium carbonate because both calcium hydroxide and carbon dioxide are used at a low concentration.

We have found that during carbonation, the conductivity or
We found that there was a correlation between the change in pH value and the carbonation rate of milk of lime, and based on this finding, by appropriately controlling the carbonation reaction in accordance with the change in conductivity or pH of lime milk, various shapes were obtained. Have completed the invention of a method for producing calcium carbonate, and applications for these inventions have already been filed (Japanese Patent Application Nos. 60-61289, 61-174400, and 61-174401).
issue). Among these inventions, Japanese Patent Application No. 60-61289 discloses that lime milk has carbon dioxide under a condition that the pH value does not drop by more than 0.2 from the value before the introduction of carbon dioxide until the carbonation rate becomes at least 5%. And then the carbonation rate is 60-75%
The basic plate-like calcium carbonate is obtained by performing carbonation until the temperature becomes as follows. Japanese Patent Application No. 61-174400 discloses that carbon dioxide is introduced into lime milk under the condition that the pH value does not drop by more than 0.2 from the value before introducing carbon dioxide until the carbonation rate becomes at least 5%. Then the carbonation rate is 10
A method of obtaining a cubic calcium carbonate by adding a seed crystal between about 75% and 75% is disclosed in Japanese Patent Application No. 61-174401 until the carbonation rate becomes at least 5%, and the pH value is determined before introducing carbon dioxide. Carbon dioxide is introduced into the lime milk under a condition that the carbonation rate does not fall by more than 0.2, then forced heating of the lime milk is started before the carbonation rate reaches 50%, and the carbonation rate is substantially reduced to 10%.
The aragonite-based acicular calcium carbonate is obtained by performing a carbonation reaction up to 0%.

The present inventors have further studied the above inventions and found that the pH value does not drop by more than 0.2 from the value before the introduction of carbon dioxide until at least the carbonation rate becomes 5%. By introducing carbon dioxide into the lime milk and then adding an additive consisting of at least one of the group consisting of water-soluble polysaccharides, sulfuric acid and sulfate when the carbonation rate reaches the range of 60-75%, It has been found that calcium carbonate having a spindle-like shape can be produced economically and advantageously,
The present invention has been completed.

[Object of the Invention] An object of the present invention is to provide an improved method for producing spindle-shaped calcium carbonate which is particularly useful as a filler for papermaking.

[Summary of the Invention] The present invention relates to a method for preparing a pH
Carbon dioxide is introduced into the lime milk under the condition that the value does not drop by more than 0.2 from the value before the introduction of carbon dioxide, and then the water-soluble polysaccharide is added to the lime milk at a carbonation rate of 60 to 75%. ,
After adding at least one additive selected from the group consisting of sulfuric acid and sulfate, the carbonation rate is substantially 100
% Carbonic acid is produced.

Preferred embodiments of the method for producing spindle-shaped calcium carbonate of the present invention are described below.

(1) A process for producing spindle-shaped calcium carbonate, characterized in that the amount of the additive is 1 × 10 ⁻⁴ mol or more per mol of calcium hydroxide contained in milk of lime.

(2) A method for producing spindle-shaped calcium carbonate, wherein the temperature of lime milk at the start of the reaction is adjusted to 25 ° C. or less.

(3) A process for producing spindle-shaped calcium carbonate, wherein a reaction temperature after a carbonation rate of 60 to 75% is 30 ° C or higher.

(4) The rate of introduction of carbon dioxide at a carbonation rate of 60-75% or less is based on 1 g of calcium hydroxide contained in milk of lime.
A process for producing spindle-shaped calcium carbonate, wherein the concentration is 4 ml / min or less.

(5) A method for producing spindle-shaped calcium carbonate, characterized in that the lime milk contains 3 to 25 g of calcium hydroxide per 100 ml of water.

(6) A method for producing spindle-shaped calcium carbonate, wherein the water-soluble polysaccharide is sucrose.

DETAILED DESCRIPTION OF THE INVENTION The present inventors have determined the conductivity or
We found that there was a correlation between the change in pH value and the carbonation rate of milk of lime, and based on this finding, by appropriately controlling the carbonation reaction in accordance with the change in conductivity or pH of lime milk, various shapes were obtained. Has completed the invention of a method for producing calcium carbonate.

In the present invention, the carbonation rate is (%).

The process for producing spindle-shaped calcium carbonate according to the present invention is characterized in that carbon dioxide is added to lime milk under the condition that the pH value does not drop by 0.2 or more from the value before the introduction of carbon dioxide until at least the carbonation rate becomes 5%. Introduced, then carbonation rate 60-75%
And adding at least one additive selected from the group consisting of water-soluble polysaccharides, sulfuric acid and sulfates to the lime milk.

In producing the calcium carbonate of the present invention, lime milk (aqueous calcium hydroxide suspension) is first prepared. Normal quick lime or slaked lime can be used as a calcium hydroxide source used for preparing lime milk. Examples of quicklime and slaked lime include quicklime powder, massive quicklime, salt burnt quicklime and ordinary slaked lime.

The quicklime and slaked lime as described above are put into water to prepare lime milk. The concentration of calcium hydroxide contained in lime milk is usually 3 to 25 g / 100 ml, preferably 7 to 16 g / 100 ml.
in the ml range. If the concentration of calcium hydroxide contained in the lime milk is less than 3 g / 100 ml, the concentration is too low to be economical, while if it exceeds 25 g / 100 ml, the viscosity of the lime milk becomes high and the workability decreases.

Next, the temperature of the lime milk at the start of the carbonation reaction is 25
C. or lower, preferably in the range of 10 to 17C.

After the start of the carbonation reaction, the pH value of the lime milk should not drop by more than 0.2 from the pH value before the introduction of carbon dioxide until at least 5% by weight of the calcium hydroxide in the lime milk is carbonated. Adjust the rate of carbon dioxide introduction. In this operation, while introducing carbon dioxide into the lime milk at 1 to 10 ml / min per 1 g of calcium hydroxide contained in the lime milk, the electrode of the pH meter is inserted into the lime milk to continuously measure the pH value. By doing so, it can be easily performed.

During the carbonation reaction, the temperature is kept below 45 ° C, preferably below 35 ° C. Since the carbonation reaction is an exothermic reaction, the temperature of the lime milk can be controlled, for example, by attaching a cooling device to the reaction vessel.

After the carbonation reaction is allowed to proceed under the above conditions, the carbonation reaction is further continued, and when 60 to 75% by weight of the calcium hydroxide contained in the lime milk is carbonated, the lime is removed. Add additive to milk. The carbonation rate of calcium hydroxide is measured by continuously inserting the electrode of a pH meter into lime milk and measuring the pH value to detect a sharp drop in the pH value (about 0.8 from the pH value at the start of the carbonation reaction). Can be determined.

The additive is at least one selected from the group consisting of water-soluble polysaccharides, sulfuric acid, and sulfates, preferably sucrose as the water-soluble polysaccharide, and ammonium sulfate, calcium sulfate, magnesium sulfate as the sulfate.
Potassium sulfate, sodium sulfate and the like can be mentioned. The amount of the additive is not less than 1.times.10.sup.- ⁴ mol per mol of calcium hydroxide contained in milk of lime.

The reaction temperature after the carbonation rate of 60 to 75% is preferably 30 ° C. or higher. The carbonation reaction at a carbonation rate of 60 to 75% or less is carried out by introducing carbon dioxide at a rate of 4 ml / min or less based on 1 g of calcium hydroxide contained in the lime milk.

The carbon dioxide to be introduced may be carbon dioxide alone or a mixed gas of calcium hydroxide and a gas (eg, air, nitrogen gas) having substantially no reactivity. Further, a carbon dioxide-containing gas discharged during the firing of limestone can also be used. When using a mixed gas, the concentration of carbon dioxide in the mixed gas is usually
Use at least 10% by volume, preferably at least 20% by volume.

Note that the above carbonation reaction is desirably performed with stirring.

[Effects of the Invention] The present invention is industrially advantageous in that a spindle-shaped calcium carbonate having excellent dispersibility and having a small particle diameter suitable as a filler for papermaking is used as a raw material and lime milk having a high concentration as a raw material using an additive. Can be manufactured.

 Next, examples of the present invention will be described.

Example 1 An industrial quicklime powder and water were charged into a reaction vessel having a capacity of 3 equipped with a cooling device, and a calcium hydroxide concentration of 9.5 g / 100 was added.
Two ml of lime milk were prepared.

Cool the lime milk to adjust the reaction start temperature to 17 ° C,
99.5% or more of carbon dioxide was introduced into the lime milk while stirring so as to give a rate of 4.6 ml / min with respect to 1 g of calcium hydroxide contained in the lime milk, thereby performing a carbonation reaction. The pH value of the lime milk is continuously measured by inserting an electrode of a pH meter into the lime milk, and the pH value is set at 0.
13 When the lime milk was collected at the time of descent and the carbonation rate was measured according to a conventional method, the carbonation rate of calcium hydroxide was 15.5.
%Met.

Next, the above-mentioned carbon dioxide was further introduced into the lime milk at a reaction start temperature of 20 ° C. at the same rate as above, and the carbonation rate was 65%.
Carbonation reaction was carried out until.

To this partially carbonated lime milk, sucrose was added in an amount of 2 × 10 ⁻³ mol per mol of calcium hydroxide contained in the lime milk, and the above-mentioned carbon dioxide was added to water in the lime milk at a reaction initiation temperature of 40 ° C. It is introduced into the milk of lime while stirring at a rate of 1.5 ml / min per 1 g of calcium oxide, and the carbonation rate is 100%.
Carbonation reaction was carried out until.

The time required from the introduction of carbon dioxide to the lime milk until the carbonation was completed, that is, the time required for the carbonation reaction was 115 minutes. By separating and drying the solids from the aqueous suspension
250 g of calcium carbonate were obtained.

Observation of the obtained calcium carbonate with an electron microscope revealed that the calcium carbonate had a spindle shape, and crystals having a shape other than the spindle shape were hardly observed.

The average major axis of the obtained spindle-shaped calcium carbonate was 1.
The average minor axis was 6 μm, and the average minor axis was 0.4 μm.

[Example 2] An industrial quicklime powder and water were charged into the same reaction vessel as used in Example 1, and the calcium hydroxide concentration was 8 g.
Two / 100 ml of lime milk were prepared.

Cool the lime milk to adjust the reaction start temperature to 17 ° C,
Carbonation reaction was carried out by introducing 99.5% or more of carbon dioxide into the lime milk with stirring at a rate of 4 ml / min per 1 g of calcium hydroxide contained in the lime milk.
The pH value of the lime milk is continuously measured by inserting an electrode of a pH meter into the lime milk, and a part of the lime milk is collected when the pH value is reduced by 0.15 from the pH value before the start of the carbonation reaction, The carbonation rate of calcium hydroxide was measured according to the standard method.
10%.

Next, the above-mentioned carbon dioxide was further introduced into the lime milk at a reaction start temperature of 19 ° C. at the same rate as above, and the carbonation rate was 65%.
Carbonation reaction was carried out until.

Calcium sulfate is added to the partially carbonated lime milk in an amount of 5 × 10 ⁻³ per mole of calcium hydroxide contained in the lime milk.
Molar addition, at a reaction initiation temperature of 50 ° C., the above-mentioned carbon dioxide was added at 1.5 ml / g to 1 g of calcium hydroxide contained in lime milk.
The mixture was introduced into the milk of lime with stirring at a rate of minutes, and a carbonation reaction was carried out until the carbonation rate reached 100%.

The time required for the carbonation reaction was 120 minutes. The solid was separated from the aqueous suspension and dried to obtain 210 g of calcium carbonate.

Observation of the obtained calcium carbonate with an electron microscope revealed that the calcium carbonate had a spindle shape, and crystals having a shape other than the spindle shape were hardly observed.

The average major axis of the obtained spindle-shaped calcium carbonate was 1.
The average minor axis was 5 μm, and the average minor axis was 0.4 μm.

Example 3 Lumpy lime (5-35 mm) and water were charged into the same reaction vessel used in Example 1 to prepare lime milk 2 having a calcium hydroxide concentration of 7.9 g / 100 ml.

Cool the lime milk to adjust the reaction initiation temperature to 15 ° C, and mix a mixed gas of nitrogen and carbon dioxide (30% by volume of carbon dioxide) with 2.2 g / min of 1 g of calcium hydroxide contained in the lime milk. The carbonation reaction was carried out by introducing the milk into the lime milk while stirring so as to achieve the desired speed. The pH value of the lime milk was continuously measured by inserting an electrode of a pH meter into the lime milk, and a part of the lime milk was collected when the pH value dropped 0.09 from the pH value before the start of the carbonation reaction. The carbonation rate of calcium hydroxide was 11.6% as measured by a conventional method.

Next, the above-mentioned mixed gas was further introduced into lime milk at a reaction start temperature of 16 ° C. while stirring at a rate of 5.0 ml / min as carbon dioxide with respect to 1 g of calcium hydroxide contained in the lime milk. Then, a carbonation reaction was performed until the carbonation rate reached 65%.

Magnesium sulfate was added to the partially carbonated lime milk in an amount of 5 × 10 5 per mole of calcium hydroxide contained in the lime milk.
^-3 mol was added, and the above-mentioned mixed gas was stirred in the lime milk at a reaction start temperature of 40 ° C. so as to have a rate of 1.5 ml / min as carbon dioxide with respect to 1 g of calcium hydroxide contained in the lime milk. The carbonation reaction was carried out until the carbonation rate reached 100%.

The time required for the carbonation reaction was 120 minutes. The solid was separated from the aqueous suspension and dried to obtain 210 g of calcium carbonate.

Observation of the obtained calcium carbonate with an electron microscope revealed that the calcium carbonate had a spindle shape, and crystals having a shape other than the spindle shape were hardly observed.

The average major axis of the obtained spindle-shaped calcium carbonate was 1.
The average minor axis was 6 μm, and the average minor axis was 0.4 μm.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naohiko Sasaki 8-1 Goi-minamikaigan, Ichihara-shi, Chiba Japan Lime Industry Co., Ltd. (72) Inventor Takashi Kutsuno 8-1-1 Goi-minamikaigan, Ichihara-shi, Chiba Japan Lime Industry Co., Ltd.Examiner Kazutaka Itabashi

Claims (1)

(57) [Claims] (1) The pH is adjusted until the carbonation ratio becomes at least 5%.
Carbon dioxide is introduced into the lime milk under the condition that the value does not drop by more than 0.2 from the value before the introduction of carbon dioxide, and then the water-soluble polysaccharide is added to the lime milk at a carbonation rate of 60 to 75%. ,
A method for producing spindle-shaped calcium carbonate, comprising adding at least one of sulfuric acid and a sulfate, and thereafter performing carbonation until the carbonation ratio substantially reaches 100%.