Production method of calcium carbonate

Abstract

To provide a method which enables production of microgranular calcium carbonate to be performed in an objectively optimum condition.SOLUTION: A production method of calcium carbonate includes a step of introducing carbon dioxide into an aqueous calcium hydroxide suspension. The electric conductivity of the aqueous suspension is measured while the carbon dioxide is introduced into the aqueous suspension. Introduction of the carbon dioxide is continued until the electric conductivity of the aqueous suspension becomes 1.0 mS / cm or less. Preferably, the introduction of the carbon dioxide is continued until a value of MCO2 / MCa becomes more than 0.0 and 1.5 or less where, on the basis of a time point when the electric conductivity of the aqueous suspension becomes 1.0 mS / cm or less, a cumulative molar number of the carbon dioxide introduced from the time point into the aqueous suspension is MCO2 and a molar number of total calcium contained in the aqueous suspension is MCa.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing calcium carbonate. [Background technology]

[0002] Calcium carbonate is used in various fields, for example, as an additive for plastics and rubber, a building material, an additive for electronic materials, etc. In particular, when used in electronic materials, fine calcium carbonate is desired from the viewpoint of improving the performance of electronic devices.

[0003] The present applicant has previously proposed a method for producing fine calcium carbonate by introducing carbon dioxide gas into an aqueous suspension of calcium hydroxide and adding an additive when 95% by mass or more of the calcium hydroxide has been carbonated (Patent Document 1). This production method has the advantage that particle growth is less likely to occur even when the calcium carbonate is stored for a long period of time by treating the surface of the calcium carbonate with an additive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-231917 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the technology described in Patent Document 1, it is possible to produce fine calcium carbonate. However, it is not easy to determine the optimum conditions for reacting calcium hydroxide with carbon dioxide to obtain fine calcium carbonate, and conventionally, the optimum reaction conditions have been determined empirically by measuring the pH and temperature of the liquid. Therefore, a method for objectively determining the optimum reaction conditions has been desired. An object of the present invention is to provide a method for producing finely divided calcium carbonate under objectively optimal conditions. [Means for solving the problem]

[0006] The present invention provides a method for producing calcium carbonate, comprising the step of introducing carbon dioxide into an aqueous suspension of calcium hydroxide, measuring the conductivity of the aqueous suspension while introducing carbon dioxide into the aqueous suspension; The above-mentioned problems have been solved by providing a method for producing calcium carbonate, in which the introduction of carbon dioxide is continued until the electrical conductivity of the aqueous suspension becomes 1.0 mS / cm or less. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for producing fine calcium carbonate under objectively optimal conditions. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described below based on its preferred embodiments. The present invention relates to a method for producing calcium carbonate. The production method of the present invention is broadly divided into the following steps (1) to (4). Step (1), step (2), step (3), and step (4) are performed in this order. After completion of step (4), a step of adding a dispersant may be performed, if necessary. Furthermore, additional steps may be performed, if necessary, between steps (1) and (2), between steps (2) and (3), and / or between steps (3) and (4). Steps (1) to (4) will be described below, respectively. Step (1): Preparing an aqueous suspension of calcium hydroxide. Step (2): A step of introducing carbon dioxide into the aqueous suspension. Step (3): A step of measuring the conductivity of the aqueous suspension while introducing carbon dioxide into the aqueous suspension. Step (4): A step of continuing the introduction of carbon dioxide until a predetermined time point.

[0009] [Process (1)] In this step, a calcium hydroxide suspension (hereinafter simply referred to as "suspension") is prepared. The suspension contains a calcium hydroxide source and an aqueous liquid. The calcium hydroxide source can be any compound that contains at least calcium hydroxide or that can generate calcium hydroxide in an aqueous liquid, without particular limitation. An example of the latter compound is calcium oxide. The calcium hydroxide source can be a natural or synthetic product. Examples of calcium hydroxide sources that can be used include compositions and mixtures containing calcium hydroxide, compositions and mixtures containing calcium oxide, calcium hydroxide itself, and calcium oxide itself. Examples of calcium hydroxide-containing compositions and mixtures and calcium oxide-containing compositions and mixtures that can be used include quicklime powder, lump quicklime, salt-burned quicklime, and slaked lime. These can be used alone or in combination. In this specification, the term "aqueous liquid" refers to a liquid (such as a solution, dispersion, or emulsion) containing 5% by mass or more of water. The amount of water contained in the aqueous liquid is preferably 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, and may be 100% by mass. As the aqueous liquid used in step (1), for example, water, a mixture of water and a water-soluble organic solvent, or the like can be used. Among these, the use of water is preferred from the viewpoint of being able to produce fine calcium carbonate under objectively optimal conditions.

[0010] Once the above raw materials are obtained, the calcium hydroxide source and the aqueous liquid are mixed in a reaction vessel to prepare a suspension. The mixing conditions can be appropriately changed depending on the types of calcium hydroxide source and the aqueous liquid. In this step, it is preferable to prepare a suspension having a total calcium concentration within a predetermined range. Specifically, from the viewpoint of successfully producing fine calcium carbonate in the step described below, it is preferable that the molar concentration of the total calcium contained in the suspension is 0.25 kmol / m 3 Preferably, it is 0.50 kmol / m or more. 3 From the same viewpoint, it is more preferable that the molar concentration of the total calcium contained in the suspension is 4.25 kmol / m or more.3 Preferably, it is 2.00 kmol / m or less. 3 It is more preferable that:

[0011] [Process (2)] Once the suspension is prepared, carbon dioxide is introduced into the suspension, which causes the calcium hydroxide in the suspension to react with the carbon dioxide, initiating a reaction to produce calcium carbonate. In this step, it is preferable to introduce carbon dioxide into the suspension at a predetermined flow rate. When a suspension having a total calcium concentration in the above range is used, specifically, from the viewpoint of successfully producing fine calcium carbonate particles with a relatively small variation in physical properties, it is preferable to introduce carbon dioxide into the suspension at a predetermined flow rate. 3 per 1000 m3, carbon dioxide is 20 (Nm3) 3 / h) / m 3 It is preferable to introduce the gas at a flow rate of 50 (Nm 3 / h) / m 3 In order to successfully produce fine calcium carbonate particles with relatively small variations in physical properties, the amount of the suspension is 3 per 200 (Nm 3 / h) / m 3 It is preferable to introduce the gas at a flow rate of 120 (Nm 3 / h) / m 3 The following is the result.

[0012] Carbon dioxide may be blown into the suspension from one position in the reaction vessel or simultaneously from multiple positions depending on the volume of the reaction vessel. Carbon dioxide may be blown into the suspension continuously or intermittently. When carbon dioxide is blown intermittently, the period during which carbon dioxide is not blown can be set to be short enough to be regarded as continuous blowing of carbon dioxide. Carbon dioxide alone may be blown into the suspension, or carbon dioxide diluted with another gas may be blown in. Examples of the other gas include nitrogen gas and rare gases. When carbon dioxide diluted with another gas is blown into the suspension, the flow rate of carbon dioxide mentioned above refers to the flow rate of carbon dioxide alone, excluding the flow rate of the other gas. From the viewpoint of promoting the reaction between calcium hydroxide and carbon dioxide, it is preferable to stir the suspension while blowing carbon dioxide into the suspension.

[0013] In this step, it is preferable to cool the suspension to a predetermined temperature before introducing carbon dioxide into the suspension. Specifically, from the viewpoint of successfully producing fine calcium carbonate particles with relatively small variations in physical properties, the temperature of the suspension is preferably set to 25°C or less, more preferably 18°C ​​or less. From the same viewpoint, it is preferable to set the temperature of the suspension to 7°C or more, more preferably 10°C or more.

[0014] [Process (3)] In this step, the conductivity of the suspension is measured while carbon dioxide is being introduced into the suspension. In the past, when calcium hydroxide was reacted with carbon dioxide, changes in the pH and temperature of the liquid were used as indicators to determine whether the target fine calcium carbonate particles had been produced. However, because the optimal pH and temperature differ depending on, for example, the purity of the raw material, it was not easy to determine the optimal conditions for the raw material. Therefore, there was a demand for an objective method for producing fine calcium carbonate particles regardless of the type of raw material. As a result of extensive investigations into this issue, the present inventors have focused on the fact that the electrical conductivity of a suspension decreases during a reaction for producing calcium carbonate, and have found that by using the electrical conductivity as an index, the production method of the present invention can be applied to calcium hydroxide sources having various physical properties, and that a method for producing fine calcium carbonate can be found.

[0015] The conductivity can be measured, for example, by a conductivity meter attached to a reaction vessel containing the suspension and carbon dioxide. From the viewpoint of detecting a change in conductivity without delay, it is preferable to measure the conductivity by immersing the conductivity meter in the suspension in the reaction vessel. Measurement of the conductivity of the suspension may be started before or simultaneously with the injection of carbon dioxide.

[0016] [Process (4)] In this step, the introduction of carbon dioxide is continued until a predetermined time point while measuring the conductivity of the suspension, as in the previous step. The end point of the introduction can be changed depending on the desired physical properties of calcium carbonate. For example, the end point of the introduction may be (i) the time point when the conductivity of the suspension becomes equal to or lower than a predetermined value, or (ii) the time point when a predetermined time has elapsed from the above time point. In the case of (i), specifically, it is preferable to continue the introduction of carbon dioxide until the electrical conductivity of the suspension becomes 1.0 mS / cm or less. In other words, it is preferable to end the introduction when the electrical conductivity of the suspension becomes 1.0 mS / cm or less. By stopping the introduction of carbon dioxide at that point, it is possible to successfully obtain fine calcium carbonate particles with relatively small variations in physical properties. The end point of the introduction of carbon dioxide can be any time point when the electrical conductivity of the suspension becomes 1.0 mS / cm or less. However, from the viewpoint of more successfully obtaining fine calcium carbonate particles having relatively small variations in physical properties, it is preferable to terminate the introduction of carbon dioxide when the electrical conductivity becomes 1.0 mS / cm.

[0017] In the case of (ii), it is preferable to continue the introduction of carbon dioxide until a predetermined time has elapsed from the time when the electrical conductivity of the suspension reaches preferably 1.0 mS / cm or less, more preferably 0.0 mS / cm to 0.7 mS / cm, and even more preferably 0.01 mS / cm to 0.5 mS / cm. The end point of the introduction can be appropriately changed depending on the desired physical properties of calcium carbonate. For example, it is preferable to set the end point as the time when the ratio of the number of moles of carbon dioxide to the number of moles of total calcium in the suspension falls within a predetermined range, because this more successfully enables the production of fine calcium carbonate with relatively small variations in physical properties.

[0018] Specifically, in order to make the above-mentioned effect more pronounced, the cumulative number of moles of carbon dioxide introduced into the suspension from that point onward is set to M CO2 The total number of moles of calcium contained in the suspension is M Ca When M CO2 / M Ca It is preferable to continue introducing carbon dioxide until the value of is more than 0.0 and 1.5 or less, more preferably 0.1 or more and 1.4 or less, and particularly preferably 0.3 or more and 1.3 or less. The calcium carbonate obtained in this manner has relatively small variations in physical properties such as BET specific surface area, and is finely divided. CO2 / M Ca The value of increases over time, while M CO2 / M Ca The introduction of carbon dioxide is terminated when the value of exceeds the range of more than 0.0 and 1.5.

[0019] Total moles of carbon dioxide M CO2 can be calculated from the flow rate and time of carbon dioxide blown into the suspension. Total calcium moles M Ca can be calculated from the amount of calcium hydroxide charged into the reaction vessel.

[0020] After the step (4), after the completion of the reaction for producing calcium carbonate, i.e., after the completion of blowing carbon dioxide into the suspension, an additional step (5) of mixing calcium carbonate with a dispersant may be carried out for the purpose of further reducing the variation in physical properties and obtaining fine calcium carbonate particles.

[0021] [Process (5)] It is preferable to use a water-soluble substance as the dispersant. For example, polycarboxylic acids and their ammonium salts can be used. Polycarboxylic acids are compounds having two or more carboxy groups. The polycarboxylic acid may be an aliphatic polycarboxylic acid or an unsaturated aliphatic polycarboxylic acid. Examples of aliphatic polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, citric acid, malic acid, maleic acid, fumaric acid, itaconic acid, isophthalic acid, and terephthalic acid. Examples of unsaturated aliphatic polycarboxylic acids include acrylic acid, propiolic acid, methacrylic acid, crotonic acid, isocrotonic acid, oleic acid, elaidic acid, maleic acid, fumaric acid, and itaconic acid. These may be used alone or in combination.

[0022] The polycarboxylic acid preferably has a carbon number within a predetermined range. Specifically, from the viewpoint of further reducing the variation in physical properties and obtaining fine calcium carbonate, the polycarboxylic acid preferably has a carbon number of 1 or more, more preferably 2 or more, and even more preferably 3 or more. From the same viewpoint, the polycarboxylic acid preferably has a carbon number of 22 or less, more preferably 20 or less, and even more preferably 18 or less.

[0023] The polycarboxylic acid may be a copolymer. For example, it may be a block copolymer or a random copolymer. An example of such a copolymer is a copolymer of acrylic acid and maleic acid. These may be used alone or in combination of two or more. When the polycarboxylic acid is a copolymer, it is preferable that the mass average molecular weight thereof is within a predetermined range. Specifically, from the viewpoint of further reducing the variation in physical properties and obtaining fine calcium carbonate particles, the mass average molecular weight of the copolymer is preferably 10,000 or more, more preferably 15,000 or more. From the same viewpoint, the mass average molecular weight of the copolymer is preferably 30,000 or less, more preferably 25,000 or less.

[0024] The mass average molecular weight of the copolymer can be measured by the GPC method.

[0025] From the viewpoint of further reducing the variation in physical properties and obtaining fine calcium carbonate particles, it is preferable to use an ammonium salt of a copolymer of acrylic acid and maleic acid as the polycarboxylic acid or its ammonium salt. From the same viewpoint as above, the polycarboxylic acid or the ammonium salt thereof is preferably used in an amount of 0.1 part by mass to 10 parts by mass per 100 parts by mass of calcium carbonate.

[0026] The mixing of calcium carbonate and a dispersant can be carried out at any time after the completion of blowing carbon dioxide into the suspension. However, from the viewpoint of further reducing the variation in physical properties and obtaining fine calcium carbonate particles, it is preferable to carry out the mixing after a predetermined time has elapsed after the completion of blowing carbon dioxide into the suspension. Specifically, from the viewpoint of making the above-mentioned effect remarkable, it is preferable to mix calcium carbonate and a dispersant after a lapse of preferably 1 minute or more and 1 hour or less, more preferably 3 minutes or more and 40 minutes or less, and even more preferably 5 minutes or more and 20 minutes or less, after the blowing of carbon dioxide into the suspension is completed.

[0027] In this step, once calcium carbonate and a dispersant have been mixed, it is preferable to continue mixing them further. Specifically, from the viewpoint of spreading the dispersant throughout the calcium carbonate, stabilizing the physical properties, and facilitating the production of fine calcium carbonate particles, calcium carbonate and a dispersant are mixed preferably for 1 minute or more and 180 minutes or less, more preferably 30 minutes or more and 100 minutes or less, and even more preferably 50 minutes or more and 80 minutes or less. Thereafter, the produced calcium carbonate is subjected to solid-liquid separation to recover the solid content, and the solid content is dried to obtain calcium carbonate having the desired physical properties. Drying is preferably carried out at a temperature of 150°C or higher and 250°C or lower, for example.

[0028] The calcium carbonate obtained in this manner has relatively small variations in physical properties such as BET specific surface area, and is in the form of fine particles. Specifically, the BET specific surface area of ​​calcium carbonate is preferably 15.00 m 2 / g or more, more preferably 20.00m 2 / g or more, more preferably 25.00m 2 / g or more. The BET specific surface area of ​​calcium carbonate is 80.00 m 2 / g or less, and 2 / g or less, and 2 / g or less. In addition, calcium carbonate is measured by a laser diffraction scattering particle size distribution measurement method, and the volume cumulative particle size D 90 (Hereinafter, simply referred to as "particle size D 90 The particle diameter D of calcium carbonate is preferably 1.50 μm or less, more preferably 0.70 μm or less, and even more preferably 0.40 μm or less. 90 may be 0.05 μm or more, 0.10 μm or more, or 0.20 μm or more.

[0029] The calcium carbonate obtained by the method of the present invention has a relatively small variation in its physical properties. Specifically, the variance of the BET specific surface area of ​​the calcium carbonate is preferably 10.00 or less, more preferably 6.00 or less, and even more preferably 4.00 or less. The variance of the BET specific surface area may be 0.10 or more, 1.00 or more, or 2.00 or more. In addition, calcium carbonate has a particle size D 90 The variance of is preferably 0.10 or less, more preferably 0.50 or less, even more preferably 0.20 or less, and even more preferably 0.00.

[0030] The BET specific surface area can be measured by the BET single-point method using a TriStar II manufactured by Micromeritics Instrument Corporation after pre-treatment with degassing at 180°C for 10 minutes. The variance of the BET specific surface area can be calculated using general mathematical unbiased variance. Particle size D 90 is the median diameter measured using a particle size distribution analyzer MT3300EX manufactured by Microtrac Bell Corporation. 90 The variance of can be calculated using general mathematical unbiased variance.

[0031] The calcium carbonate obtained by the present invention is useful as an electronic material such as an IC substrate or a green sheet for a capacitor.

[0032] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments. [Example]

[0033] The present invention will be specifically described below based on examples. However, the scope of the present invention is not limited to these examples. In the following examples, "%" means "% by mass" unless otherwise specified.

[0034] Example 1 Calcium oxide powder and water were prepared. These were placed in a reaction vessel equipped with a cooling device and a conductivity meter to prepare 850 kg of calcium hydroxide suspension with a concentration of 8.8%. The molar concentration of the total calcium contained in the suspension was 1.14 kmol / m 3 It was. The suspension was cooled to 16°C, and carbon dioxide was introduced into the suspension while stirring to initiate the carbonation reaction. 3 per 90 (Nm 3 / h) / m 3 At this time, the conductivity of the suspension was 8.86 mS / cm. Continue introducing carbon dioxide, and set the point when the conductivity of the suspension reached 0.13 mS / cm as the reference point. CO2 / M Ca When the value reached 0.5, the introduction of carbon dioxide was stopped. Ten minutes after the end of the carbon dioxide introduction, 3.2 kg of polycarboxylic acid ammonium salt (mass average molecular weight: 20,000) was added while stirring the suspension. Stirring was continued for an additional 60 minutes, after which solid matter was recovered by solid-liquid separation. This solid matter was dried using a spray dryer at an inlet gas temperature of 200°C to obtain the desired calcium carbonate.

[0035] Comparative Example 1 In Example 1, electrical conductivity was not measured. Carbon dioxide was introduced into the suspension, and the introduction was completed 50 minutes after the introduction. Except for this, the target calcium carbonate was obtained in the same manner as in Example 1.

[0036] 〔evaluation〕 The calcium carbonate obtained in the examples and comparative examples was measured for BET specific surface area and particle size D 90 was measured.

[0037] [Table 1]

[0038] As is clear from the results shown in Table 1, the calcium carbonate of the Examples has a higher BET specific surface area and particle size D than the calcium carbonate of the Comparative Examples. 90 From the above, it can be seen that the production method of the present invention can produce fine calcium carbonate having a large BET specific surface area under objectively optimal conditions.

Claims

1. 1. A method for producing calcium carbonate, comprising the step of introducing carbon dioxide into an aqueous suspension of calcium hydroxide, measuring the conductivity of the aqueous suspension while introducing carbon dioxide into the aqueous suspension; The method for producing calcium carbonate, wherein the introduction of carbon dioxide is continued until the electrical conductivity of the aqueous suspension becomes 1.0 mS / cm or less.

2. The time when the electrical conductivity of the aqueous suspension becomes 1.0 mS / cm or less is used as a reference point, and the cumulative number of moles of carbon dioxide introduced into the aqueous suspension from that time point is expressed as M ＣＯ２ and the total number of moles of calcium contained in the aqueous suspension is M Ｃａ When M ＣＯ２ / M Ｃａ The method according to claim 1, wherein the introduction of carbon dioxide is continued until the value of is greater than 0.0 and not more than 1.

5.

3. 1 m of the aqueous suspension ３ per 1000 m3, carbon dioxide is 20 (Nm3 ３ / h) / m ３ More than 200 (Nm ３ / h) / m ３ 2. The method of claim 1, wherein the water is introduced at a flow rate of:

4. The molar concentration of the total calcium contained in the aqueous suspension is 0.25 kmol / m ３ More than 4.25 kmol / m ３ The method of claim 1, wherein:

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