Method for producing calcium carbonate

Abstract

A method for producing calcium carbonate according to one embodiment of the present invention comprises: a step in which carbon dioxide is introduced into a solution or slurry containing calcium and one or more elements selected from among iron, manganese, silicon, aluminum, and magnesium, and the pH is controlled to 7 or less; a step for precipitating a precipitate in the solution or the slurry, the pH of which has been controlled in the control step; a step for removing the precipitate precipitated in the precipitation step from the solution or the slurry; and a step for obtaining calcium carbonate by degassing the solution or the slurry after the removal step.

Description

Technical Field

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

[0002] In recent years, carbon dioxide is considered to have a great impact on global warming. As an effective countermeasure to the global warming problem, the technology of fixing carbon dioxide in a calcium-containing solution or slurry to generate calcium carbonate (CaCO3) has attracted much attention. The calcium carbonate obtained in this way can be used for a wide range of purposes by improving the whiteness. Therefore, a method for improving the whiteness of calcium carbonate has been proposed (Japanese Patent Publication No. 51-47597).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 51-47597 Summary of the invention

[0006] Problems to be solved by the invention

[0007] According to the method of patent document 1, if there is a coloring component such as iron in calcium carbonate, the coloring component may still develop color after bleaching and reduce whiteness. In addition, in the method of patent document 1, the agent such as hyposulfite is used, which is difficult to reduce the cost for bleaching calcium carbonate.

[0008] In view of such situation, the present invention aims to provide a method for producing calcium carbonate, which can suppress the coloring components in the calcium carbonate and obtain calcium carbonate with high whiteness at low cost.

[0009] Means of solving the problem

[0010] A method for producing calcium carbonate according to one embodiment of the present invention for solving the above-mentioned problems comprises the following steps: a step of controlling the pH to below 7 by introducing carbon dioxide into a solution or slurry containing calcium and one or more elements selected from iron, manganese, silicon, aluminum and magnesium; a step of precipitating a precipitate in the solution or slurry whose pH is controlled in the control step; a step of removing the precipitate precipitated in the precipitation step from the solution or slurry; and a step of degassing the solution or slurry after the removal step to obtain calcium carbonate.

[0011] Effects of the Invention

[0012] The method for producing calcium carbonate of the present invention can suppress the coloring components in calcium carbonate and can obtain calcium carbonate with high whiteness at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1This is a schematic diagram showing a calcium carbonate production apparatus used in one embodiment of the present invention.

[0014] Figure 2 This is a graph showing the whiteness of calcium carbonate obtained in Examples. DETAILED DESCRIPTION

[0015] A method for producing calcium carbonate according to one embodiment of the present invention comprises the following steps: a step of controlling the pH to below 7 by introducing carbon dioxide into a solution or slurry containing calcium and one or more elements selected from iron, manganese, silicon, aluminum and magnesium; a step of precipitating a precipitate in the solution or slurry whose pH is controlled in the control step; a step of removing the precipitate precipitated in the precipitation step from the solution or slurry; and a step of degassing the solution or slurry after the removal step to obtain calcium carbonate.

[0016] The method for producing calcium carbonate (hereinafter, also referred to as "the method for producing calcium carbonate") introduces carbon dioxide into a solution or slurry containing a coloring component such as iron and calcium (Ca) to react. Through the reaction, the calcium carbonate containing the coloring component is precipitated as a precipitate in the solution or slurry. Since the calcium component remains in the form of calcium bicarbonate ions in the solution or slurry from which the precipitate has been removed, the solution or slurry from which the precipitate has been removed is degassed to obtain a high-whiteness calcium carbonate with suppressed coloring components. In addition, the method for producing calcium carbonate does not require a medicament, etc., and thus a high-whiteness calcium carbonate can be obtained at a low cost.

[0017] The element may contain at least one of iron or manganese. Since iron and manganese are easy to develop color, they are elements that should be removed from calcium carbonate in particular. The manufacturing method allows iron or manganese to precipitate in the precipitate, thereby being able to suppress the iron and manganese from remaining in the solution or slurry from which the precipitate has been removed.

[0018] The element may be derived from steel slag. That is, calcium carbonate may be obtained from a solution or slurry containing steel slag. In this way, calcium carbonate can be obtained at a lower cost.

[0019] The solution or the slurry may contain water. Since calcium is soluble in water, the solution or the slurry contains water, which can improve the efficiency of obtaining calcium carbonate.

[0020] The solution or the slurry may further contain a polyol compound. Since calcium is easily soluble in a polyol compound, the solution or the slurry further contains a polyol compound to further improve the efficiency of obtaining calcium carbonate.

[0021] The polyol compound may be a diol compound or a triol compound. In this way, the efficiency of obtaining calcium carbonate can be further improved.

[0022] The polyol compound can be one or more diol compounds selected from the group consisting of ethylene glycol, propylene glycol and diethylene glycol. In this way, the efficiency of obtaining calcium carbonate can be further improved.

[0023] The polyol compound may be glycerol. This can further improve the efficiency of obtaining calcium carbonate.

[0024] Here, the term "polyol compound" refers to an organic compound having a plurality of alcoholic hydroxyl groups (a group in which hydrogen atoms of aliphatic hydrocarbons are substituted with hydroxyl groups (-OH)). Similarly, the term "diol compound" refers to an organic compound having two of the above alcoholic hydroxyl groups, and the term "triol compound" refers to an organic compound having three of the above alcoholic hydroxyl groups.

[0025] [Details of Modes for Carrying Out the Invention]

[0026] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In addition, the accompanying drawings are explanatory drawings, which schematically describe each structure (each component), and their shapes, scales, etc. are different from the actual ones, and components such as pumps for transferring liquids (solvents described later) or valves for transferring liquids at appropriate times are sometimes omitted. In addition, in this specification, multiple upper limits and multiple lower limits are described as the numerical range of the composition of the present invention. These multiple upper limits and multiple lower limits are described as arbitrary values ​​of either side, or arbitrary upper limits and lower limits can be selected and combined.

[0027] [Method for producing calcium carbonate]

[0028] The manufacturing method mainly comprises the following steps: a step of controlling the pH to below 7 by introducing carbon dioxide into a solution or slurry containing one or more elements selected from iron, manganese, silicon, aluminum and magnesium and calcium; a step of precipitating a precipitate in the solution or slurry whose pH is controlled in the control step; a step of removing the precipitate precipitated in the precipitation step from the solution or slurry; and a step of degassing the solution or slurry after the removal step to obtain calcium carbonate.

[0029] One or more elements selected from iron, manganese, silicon, aluminum and magnesium (hereinafter referred to as "coloring components") are preferably derived from steel slag. Steel slag is a byproduct inevitably produced in the process of manufacturing steel, and contains coloring components and calcium. Steel slag includes steelmaking slag produced in the steelmaking process such as converter slag or electric furnace slag, and blast furnace slag produced in the ironmaking process. In these steel slags, calcium exists in the form of calcium oxide (CaO), for example.

[0030] The element preferably contains at least one of iron and manganese. Since iron and manganese are easy to develop color, if they remain in the calcium carbonate, the whiteness will be reduced. For example, if trivalent iron ions (iron element) are contained in the solution or the slurry, the iron element may generate a red precipitate as Fe2O3 or Fe(OH)3. The manufacturing method can precipitate iron and manganese in the precipitation step described later, so that the residual iron and manganese in the solution or the slurry can be suppressed, and calcium carbonate with high whiteness can be obtained.

[0031] The solution or the slurry preferably contains water. Water is a proton (H 2 O) for ionizing the carbon dioxide introduced into the solution or the slurry (carbonic acid ionization). ＋ ) supply source. The calcium dissolved in the solution or the slurry migrates (diffuses) in the water as calcium ions, and the carbon dioxide introduced into the water dissolves as carbonate ions (CO3 2－ As a result, calcium ions and carbonate ions react with the water as a reaction site to form calcium carbonate. Such water is not particularly limited as long as it functions in a catalytic manner as described above, and for example, pure water can be cited.

[0032] The solution or the slurry preferably further contains a polyol compound. Since calcium is easily soluble in a polyol compound, the solution or the slurry further contains a polyol compound to further improve the efficiency of obtaining calcium carbonate.

[0033] The polyol compound is a medium for extracting calcium from the slag. The polyol compound is an organic compound having a plurality of alcohol hydroxyl groups. Alcohol hydroxyl groups are hydroxyl groups that replace hydrogen atoms in aliphatic hydrocarbons, and hydroxyl groups that replace hydrogen atoms in hydrocarbons constituting aromatic rings (e.g., hydroxyl groups in phenols) are not included.

[0034] The polyol compound is not particularly limited as long as it is an organic compound having a plurality of alcoholic hydroxyl groups, but is preferably a diol compound or a triol compound. Diol compounds and triol compounds are usually liquid at normal temperature and pressure, and thus can be mixed with the water relatively easily.

[0035] The diol compound is not particularly limited as long as it is an organic compound having two alcoholic hydroxyl groups, and examples thereof include ethylene glycol, propylene glycol, diethylene glycol, butanediol, or diethanolamine. Among them, the diol compound is preferably one or more selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol.

[0036] For example, it is generally known that the solubility of calcium in ethylene glycol is about 10 times that in water. In other words, the solubility of calcium in ethylene glycol is much higher than that in water. Therefore, calcium can be extracted more efficiently from the steel slag by using a diol compound such as ethylene glycol.

[0037] The triol compound is not particularly limited as long as it is an organic compound having three alcoholic hydroxyl groups, but glycerol is preferred. By using glycerol, calcium can be extracted more efficiently from the steel slag.

[0038] When the solution or the slurry contains water and a polyol compound, the ratio (P / W) of the mass (P) of the polyol compound to the mass (W) of the water is preferably 0.2 or more and 0.93 or less. The upper limit of the ratio (P / W) is more preferably 0.90, and further preferably 0.89. If the ratio (P / W) is higher than the upper limit, water is insufficient relative to the polyol compound, and calcium ions and carbonate ions may be difficult to react in the control process described later. If the ratio (P / W) is lower than the lower limit, the amount of water becomes excessive relative to the polyol compound, and the efficiency of extracting calcium from the steel slag may be reduced.

[0039] The manufacturing method, for example, uses Figure 1 The manufacturing device of calcium carbonate as shown in the figure is mainly equipped with the following: a container 1, which is used to fill steel slag to form a slag layer S; a supply part 2, which supplies a solution M to the container 1; a storage part 3, which stores the calcium extraction solution that flows through the slag layer S and is discharged from the container 1; an introduction part 4, which introduces carbon dioxide C into the extraction solution M1 stored in the storage part 3; and a separation part 5, which performs solid-liquid separation on the precipitate D in the mixed solution M2 obtained by introducing carbon dioxide through the introduction part 4.

[0040] 〔Control process〕

[0041] The control process includes the following steps: a step of causing the solution M to flow through a slag layer S formed by filling a container with steel slag containing coloring components and calcium; and a step of introducing carbon dioxide C into the solution (calcium extract M1) flowing through the slag layer S.

[0042] In the circulation step, the solution M supplied by the supply unit 2 is circulated in the slag layer S formed in the container 1, so that the coloring components and calcium in the steel slag forming the slag layer S are extracted into the solution M. The calcium is in the form of calcium ions (Ca 2 ＋ ) is extracted. The supply unit 2 supplies the solution M to the container 1 via the solvent supply pipe P1 connecting the container 1 and the supply unit 2. The solution M from which the coloring component and calcium are extracted is supplied to the storage unit 3 as a calcium extract M1 via the extract supply pipe P2. The steel slag from which the coloring component and calcium have been extracted is taken out from the container 1 and dried, so that it can be used as a resource such as a roadbed material (road material), a fertilizer, etc.

[0043] In the introduction step, the introduction part 4 introduces carbon dioxide C into the calcium extract M1 stored in the storage part 3. The introduction part 4 is not particularly limited, and for example, a known air blowing device can be cited. The introduction of carbon dioxide C by the introduction part 4 is preferably performed while stirring the calcium extract M1 in the storage part 3.

[0044] The introduction part 4 introduces carbon dioxide C in a manner that the pH of the calcium extract M1 is below 7. The upper limit of the pH of the calcium extract M1 is preferably below 7, more preferably below 6.9. The lower limit of the pH of the calcium extract M1 is not particularly limited, and for example, may be above 4.0. By making the pH of the calcium extract M1 not exceed the upper limit, the whiteness of the obtained calcium carbonate is improved.

[0045] The gas introduced from the introduction section 4 may be a gas composed of carbon dioxide, atmosphere (air) containing carbon dioxide, or exhaust gas containing carbon dioxide discharged from industrial activities such as factories, power plants, and transportation.

[0046] 〔Precipitation process〕

[0047] By introducing carbon dioxide into the calcium extract M1, carbon dioxide C dissolves in the calcium extract M1 as carbonate ions. When the calcium ions react with the carbonate ions, calcium carbonate is precipitated as a precipitate D. In this manufacturing method, since the pH of the calcium extract M1 into which carbon dioxide C is introduced is controlled to be below 7, it is possible to increase the absorption of a large amount of coloring components in the calcium extract M1 into the precipitate D.

[0048] The calcium extract M1 whose pH is controlled by the introduction of the carbon dioxide C is supplied to the separation unit 5 together with the precipitate D as a mixed solution M2 through the mixed solution supply pipe P3.

[0049] 〔Removal process〕

[0050] The mixed liquid M2 supplied from the storage unit 3 to the separation unit 5 is subjected to solid-liquid separation. That is, the separation unit 5 separates it into a precipitate D and a mixed liquid M2 (separated liquid M3) from which the precipitate D is removed. The separation unit 5 is not particularly limited, and for example, a well-known centrifugal separator can be cited. The separated precipitate D can be used as a resource such as a filler for a resin.

[0051] 〔Acquisition process〕

[0052] Calcium ions remain in the separated liquid M3 from which the precipitate D is removed by the separation unit 5. By degassing the separated liquid M3, calcium carbonate can be further obtained. The coloring components in the slag are precipitated in the precipitate D, so the residual amount in the separated liquid M3 is reduced. Therefore, the calcium carbonate obtained by degassing the separated liquid M3 has a high whiteness. Such high-whiteness calcium carbonate is suitable for use as a part of the raw materials of products with high whiteness, such as resin, paper, concrete, etc.

[0053] The degassing method is not particularly limited as long as the carbon dioxide in the separated liquid M3 can be removed, and known methods such as atmospheric curing degassing, heating boiling degassing, ultrasonic degassing, vacuum decompression degassing, centrifugal degassing, and air blowing degassing can be used. The gas blown in during degassing by air blowing is preferably an insoluble gas such as nitrogen and argon.

[0054] 〔advantage〕

[0055] In this manufacturing method, the pH of the solution from which the coloring component and calcium are extracted from the steel slag is controlled, and carbon dioxide is introduced to precipitate the precipitate, so that the coloring component is precipitated in the precipitate, and the residual amount of the coloring component in the solution from which the precipitate is removed is reduced. Therefore, in this manufacturing method, the whiteness of the calcium carbonate obtained by degassing the solution from which the precipitate is removed can be improved. In addition, this manufacturing method uses steel slag as a residual product, and does not use a reagent or the like to improve the whiteness of the calcium carbonate, so that calcium carbonate with high whiteness can be manufactured at low cost.

[0056] [Other embodiments]

[0057] The embodiments do not limit the configuration of the present invention. Therefore, the embodiments may omit, replace or add constituent elements of each part of the embodiments based on the description of this specification and technical common sense, and all of these should be interpreted as belonging to the scope of the present invention.

[0058] The material from which the coloring components and calcium are extracted is not necessarily a solution but may be a slurry.

[0059] The material containing coloring components and calcium is not limited to steel slag, and may be, for example, cement, concrete waste, glass waste, coal ash, sludge incineration ash, wood bioash, etc.

[0060] In the range that does not hinder the extraction efficiency of calcium, the solution or slurry may also contain other solvents, additives, etc. other than polyol compounds and water. As other solvents, additives, etc., for example, hydrophilic solutions, etc. are provided. As hydrophilic solutions, ethanol or methanol, etc. may be cited. In addition, in the circulation process, a mixed solution formed by mixing an aqueous solution in which a polyol compound and an additive other than a solvent are dissolved in water may also be used.

[0061] Example

[0062] The present invention will be further described below by way of examples, but the present invention is not limited to these examples.

[0063] As the first test, a whiteness comparison test of the precipitate and calcium carbonate was conducted. As a material containing a coloring component and calcium, two types of steelmaking slag were prepared. The coloring components contained in the two types of steelmaking slag are shown in Table 1. The two types of steelmaking slag were crushed by a jaw crusher to less than 4.75 mm.

[0064]

Table 1

[0065]

[0066] As a solution for extracting calcium from steelmaking slag, glycerin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity exceeding 99.5%) and pure water were prepared.

[0067] 400 g of the above glycerol and 600 g of the above pure water were mixed in a prepared container to prepare a solution. After nitrogen was blown into the solution at 0.5 L / min for 10 minutes, 100 g of steelmaking slag 1 was added. Thereafter, while nitrogen was circulated in the gas phase in the container at 0.5 L / min, calcium was extracted while stirring at 300 rpm for 90 minutes with a stirrer. After extraction, centrifugal separation was performed at 3000 rpm for 5 minutes, and the solution was filtered with filter paper (5 types A) to obtain a calcium extract.

[0068] The analysis results of the components contained in the calcium extract are shown in Table 2. It is known that the calcium extract contains iron and manganese as coloring components in addition to calcium. The above analysis was performed using an ICP emission spectrometer.

[0069]

Table 2

[0070]

[0071] Five other containers and the calcium extract obtained by the above method were prepared, respectively. 900 g of the calcium extract was poured into each container, and a pH meter (tabletop pH / EC HI 5522 manufactured by Hanna Instruments Japan Co., Ltd.) was inserted.

[0072] For the calcium extract in each container, carbon dioxide was introduced at 0.5 L / min while controlling the pH. When the specified pH was reached, the calcium extract was filtered with filter paper (5 types C) to separate it into a precipitate and a separated liquid. The precipitate was washed with 100 g of pure water and then vacuum dried at 10 mmHg and 105°C for more than 3 hours. The separated liquid was then injected into other containers and degassed by atmospheric curing at room temperature for more than 48 hours. After degassing, calcium carbonate was obtained using filter paper (5 types C). After the calcium carbonate was washed with 100 g of pure water, it was vacuum dried at 10 mmHg and 105°C for more than 3 hours. The pH of each calcium extract, the whiteness of the precipitate, and the whiteness of calcium carbonate are shown in Table 3. The whiteness was evaluated by Hunter brightness using a spectrophotometer (CM-600d manufactured by Konica Minolta, Inc.).

[0073]

Table 3

[0074]

[0075] In Test Examples 1 to 3 where the pH is higher than 7, the Hunter brightness of calcium carbonate is lower than the Hunter brightness of the precipitate. On the other hand, in Test Examples 4 to 5 where the pH is lower than 7, the Hunter brightness of calcium carbonate is higher than the Hunter brightness of the precipitate. In addition, the Hunter brightness of calcium carbonate in Test Examples 4 to 5 is higher than that in Test Examples 1 to 3. It can be seen from this that by introducing carbon dioxide in a manner such that the pH of the calcium extract is lower than 7, calcium carbonate with high whiteness can be obtained.

[0076] As a second test, a comparative test of the whiteness of calcium carbonate was conducted based on the amount of coloring components contained in the steelmaking slag. Two containers were prepared, and 120 g of glycerol and 280 g of pure water were mixed in each container as a solution. After blowing nitrogen into the solution at 0.5 L / min for 10 minutes, 40 g of steelmaking slag 1 was added to one container, and 40 g of steelmaking slag 2 was added to the other container. After that, while nitrogen was circulated in the gas phase in the container at 0.5 L / min, calcium was extracted by stirring at 300 rpm for 90 minutes using a stirrer. After extraction, centrifugal separation was performed at 3000 rpm for 5 minutes, and the solution was filtered with filter paper (5 types A) to obtain a calcium extract.

[0077] Into the other two containers, 300g of each calcium extract was injected, and a pH meter was inserted. For the calcium extract in each container, carbon dioxide was introduced at 0.5L / min while controlling the pH. At the moment of reaching the specified pH, the calcium extract was filtered using filter paper (5 types of C) to separate it into a precipitate and a separated liquid. After the precipitate was washed with 100g of pure water, it was vacuum dried for more than 3 hours under the conditions of 10mmHg and 105°C. The separated liquid was injected into other containers respectively, and degassed by atmospheric curing for more than 48 hours at room temperature. After degassing, calcium carbonate was obtained using filter paper (5 types of C). After the calcium carbonate was washed with 100g of pure water, it was vacuum dried for more than 3 hours under the conditions of 10mmHg and 105°C. The pH of each calcium extract, the whiteness of the precipitate, and the whiteness of calcium carbonate are shown in Table 4.

[0078]

Table 4

[0079]

[0080] If we compare Test Example 6 and Test Example 7, the difference in Hunter brightness of the precipitates is relatively large, but the difference in Hunter brightness of calcium carbonate is very small. In addition, the Hunter brightness of calcium carbonate is higher than the Hunter brightness of the precipitates. It can be seen that regardless of the amount of coloring components contained in the steelmaking slag, by introducing carbon dioxide in a manner such that the pH of the calcium extract is below 7, calcium carbonate with high whiteness can be stably obtained.

[0081] Industrial Applicability

[0082] The present invention can obtain high-whiteness calcium carbonate at low cost and effectively utilize carbon dioxide as a resource, thereby providing calcium carbonate with high added value.

[0083] Description of Reference Numerals

[0084] 1 Container

[0085] 2 Supply Department

[0086] 3 Storage

[0087] 4. Import section

[0088] 5 Separation

[0089] C Carbon dioxide

[0090] D Precipitate

[0091] M solution

[0092] M1 Calcium Extract

[0093] M2 Mixture

[0094] M3 separation solution

[0095] P1 Solvent supply pipe

[0096] P2 Extraction liquid supply tube

[0097] P3 Mixed liquid supply pipe

[0098] S Slag layer

Claims

1. A method for producing calcium carbonate, wherein: The following processes are available: A step of controlling the pH to 7 or less by introducing carbon dioxide into a solution or slurry containing one or more elements selected from iron, manganese, silicon, aluminum and magnesium and calcium; a step of precipitating a precipitate in the solution or slurry whose pH is controlled in the control step; A step of removing the precipitate precipitated in the precipitation step from the solution or the slurry; A step of degassing the solution or the slurry after the removal step to obtain calcium carbonate.

2. The method for producing calcium carbonate according to claim 1, wherein The element contains at least one of iron and manganese.

3. The method for producing calcium carbonate according to claim 1 or claim 2, wherein The elements are derived from steel slag.

4. The method for producing calcium carbonate according to claim 1 or claim 2, wherein The solution or the slurry comprises water.

5. The method for producing calcium carbonate according to claim 4, wherein The solution or the slurry further comprises a polyol compound.

6. The method for producing calcium carbonate according to claim 5, wherein The polyol compound is a diol compound or a triol compound.

7. The method for producing calcium carbonate according to claim 5, wherein The polyol compound is one or two or more diol compounds selected from the group consisting of ethylene glycol, propylene glycol and diethylene glycol.

8. The method for producing calcium carbonate according to claim 5, wherein The polyol compound is glycerol.

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