Method for producing calcium carbonate

Abstract

To provide a method for producing calcium carbonate that can suppress coloring components in calcium carbonate and obtaining calcium carbonate with high whiteness at a low cost.SOLUTION: A method for producing calcium carbonate according to one aspect of the present invention include the steps of: introducing carbon dioxide into a solution or slurry that contains calcium and one or more elements selected from iron, manganese, silicon, aluminum, and magnesium to control pH of the solution or slurry to 7 or lower; precipitating a precipitate in the solution or slurry with pH controlled in the control step; removing the precipitate precipitated in the precipitation step from the solution or slurry; and degassing from the solution or slurry after the removal step to obtain calcium carbonate.SELECTED DRAWING: Figure 2

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 measure against this global warming problem, a technique for fixing carbon dioxide in a solution or slurry containing calcium to produce calcium carbonate (CaCO3) has attracted attention. The calcium carbonate thus obtained can be used in a wide range of applications by improving its whiteness. For this reason, a method for improving the whiteness of calcium carbonate has been invented (Japanese Patent Laid-Open No. 51-47597).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Even with the method of Patent Document 1, if coloring components such as iron are present in calcium carbonate, the coloring components may develop color after the whitening treatment and reduce the whiteness. Further, in the method of Patent Document 1, chemicals such as hydrosulfite are used, making it difficult to reduce the cost for whitening calcium carbonate.

[0005] In view of such circumstances, an object of the present invention is to provide a method for producing calcium carbonate that can suppress coloring components in calcium carbonate and obtain calcium carbonate with high whiteness at low cost.

Means for Solving the Problems

[0006] A method for producing calcium carbonate according to one aspect of the present invention, which solves the aforementioned problems, comprises the steps 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; precipitating a precipitate in the solution or slurry whose pH has been controlled in the control step; removing the precipitate precipitated in the precipitation step from the solution or slurry; and obtaining calcium carbonate by degassing the solution or slurry after the removal step. [Effects of the Invention]

[0007] The present invention's method for producing calcium carbonate suppresses coloring components in calcium carbonate, enabling the production of high-whiteness calcium carbonate at low cost. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing a calcium carbonate production apparatus used in one embodiment of the present invention. [Figure 2] Figure 2 is a graph showing the whiteness of the calcium carbonate obtained in the examples. [Modes for carrying out the invention]

[0009] A method for producing calcium carbonate according to one aspect of the present invention comprises the steps 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; precipitating a precipitate in the solution or slurry whose pH has been controlled in the control step; removing the precipitate precipitated in the precipitation step from the solution or slurry; and degassing the solution or slurry after the removal step to obtain calcium carbonate.

[0010] The method for producing calcium carbonate (hereinafter also simply referred to as "the production method") involves introducing carbon dioxide into a solution or slurry containing a coloring component such as iron and calcium (Ca) and allowing it to react. This reaction causes calcium carbonate containing the coloring component to precipitate as a precipitate in the solution or slurry. Since calcium components remain in the solution or slurry in the form of calcium bicarbonate ions after the precipitate is removed, degassing the solution or slurry from which the precipitate has been removed allows for the production of highly white calcium carbonate with suppressed coloring. Furthermore, since this production method does not require any chemicals, it allows for the production of highly white calcium carbonate at low cost.

[0011] The aforementioned element may contain at least one of iron or manganese. Iron and manganese are elements that should be particularly removed from calcium carbonate because they readily produce color. Since this manufacturing method precipitates iron and manganese in the precipitate, it is possible to suppress the remaining presence of iron and manganese in the solution or slurry after the precipitate has been removed.

[0012] The aforementioned element is preferably derived from steel slag. That is, calcium carbonate is preferably obtained from a solution or slurry containing steel slag. In this way, calcium carbonate can be obtained at a lower cost.

[0013] The solution or slurry may contain water. Since calcium dissolves in water, the inclusion of water in the solution or slurry can improve the efficiency of obtaining calcium carbonate.

[0014] The solution or slurry may further contain a polyol compound. Since calcium is readily soluble in polyol compounds, the efficiency of obtaining calcium carbonate can be further improved by further including a polyol compound in the solution or slurry.

[0015] The polyol compound may be a diol compound or a triol compound. By doing so, the efficiency of obtaining calcium carbonate can be further improved.

[0016] The polyol compound may be one or more diol compounds selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol. By doing so, the efficiency of obtaining calcium carbonate can be further improved.

[0017] The polyol compound may be glycerin. By doing so, the efficiency of obtaining calcium carbonate can be further improved.

[0018] Here, the "polyol compound" refers to an organic compound having a plurality of alcoholic hydroxyl groups (groups in which the hydrogen atoms of aliphatic hydrocarbons are substituted with hydroxy groups (-OH)). Similarly, the "diol compound" refers to an organic compound having two of the alcoholic hydroxyl groups, and the "triol compound" refers to an organic compound having three of the alcoholic hydroxyl groups.

[0019] [Details of the Embodiment for Carrying Out the Invention] Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate. The drawings are for explanatory purposes, and each configuration (each member) is drawn schematically, and the shape, scale, etc. may be different from the actual ones. Some members such as pumps for transferring liquids (solvents etc. described later) or valves for transferring liquids at appropriate timings are omitted. Also, in this specification, there may be cases where a plurality of upper limit values and a plurality of lower limit values are described as the numerical range of the configuration of the present invention. These plurality of upper limit values and plurality of lower limit values are described such that any value of either one can be selected, or any upper limit value and lower limit value can be combined.

[0020] [Method for Producing Calcium Carbonate] The manufacturing method mainly includes 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 the slurry whose pH has been controlled in the control step, a step of removing the precipitate precipitated in the precipitation step from the solution or the slurry, and a step of degassing the solution or the slurry after the removal step to obtain calcium carbonate.

[0021] As one or more elements (hereinafter referred to as "coloring components") selected from iron, manganese, silicon, aluminum, and magnesium, those derived from steel slag are preferable. Steel slag is a by-product inevitably generated in the steel manufacturing process and contains coloring components and calcium. Steel slag includes steelmaking slag generated in the steelmaking process such as converter slag or electric furnace slag, blast furnace slag generated in the pig iron making process, and the like. In these steel slags, calcium exists, for example, in the form of calcium oxide (CaO).

[0022] It is preferable that the element contains at least one of iron and manganese. Since iron and manganese are likely to develop color, if they remain in calcium carbonate, the whiteness may decrease. For example, if trivalent iron ions (iron element) are contained in the solution or the slurry, this iron element may form a red precipitate as Fe2O3 or Fe(OH)3. Since the manufacturing method can precipitate iron and manganese in the precipitation step described later, it is possible to suppress the remaining of iron and manganese in the solution or the slurry, and it is possible to obtain calcium carbonate with high whiteness.

[0023] The solution or the slurry preferably contains water. Water serves as a source of protons (H + ) for ionizing (carbonic acid ionization) the carbon dioxide introduced into the solution or the slurry. Calcium dissolved in the solution or the slurry migrates (diffuses) into water as calcium ions, and the carbon dioxide introduced into this water becomes carbonate ions (CO3 2-It dissolves as ). As a result, calcium ions and carbonate ions react with this water as the reaction site to form calcium carbonate. Such water is not particularly limited as long as it functions catalytically as described above, for example, pure water.

[0024] Preferably, the solution or slurry further contains a polyol compound. Since calcium is readily soluble in polyol compounds, the efficiency of obtaining calcium carbonate can be further improved by further including a polyol compound in the solution or slurry.

[0025] The polyol compound is a medium for extracting calcium from the slag. The polyol compound is an organic compound having a plurality of alcoholic hydroxyl groups. The alcoholic hydroxyl groups are hydroxyl groups obtained by substituting hydrogen atoms of aliphatic hydrocarbons, and do not include hydroxyl groups obtained by substituting hydrogen atoms of hydrocarbons constituting an aromatic ring (for example, the hydroxyl group of phenol).

[0026] The polyol compound is not particularly limited as long as it is an organic compound having multiple alcoholic hydroxyl groups, but it is preferably a diol compound or a triol compound. Since diol compounds and triol compounds are usually liquid at room temperature and pressure, they can be mixed with water relatively easily.

[0027] The diol compound is not particularly limited as long as it is an organic compound having two alcoholic hydroxyl groups, and examples include ethylene glycol, propylene glycol, diethylene glycol, butanediol, or diethanolamine. Of these, the diol compound is preferably one or more selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol.

[0028] For example, it is generally known that the solubility of calcium in ethylene glycol is about 10 times that of calcium in water. In other words, the solubility of calcium in ethylene glycol is far greater than that in water. Therefore, by using diol compounds such as ethylene glycol, calcium can be extracted more efficiently from the aforementioned steel slag.

[0029] The aforementioned triol compound is not particularly limited as long as it is an organic compound having three alcoholic hydroxyl groups, but glycerin is preferred. By using glycerin, calcium can be extracted more efficiently from the steel slag.

[0030] When the solution or slurry contains water and a polyol compound, the ratio of the mass of the polyol compound (P) to the mass of the water (W) (P / W) 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 even more preferably 0.89. If the ratio (P / W) exceeds the upper limit, there will be insufficient water relative to the polyol compound, which may make it difficult for the reaction between calcium ions and carbonate ions in the control step described later to occur. If the ratio (P / W) is below the lower limit, there will be an excess of water relative to the polyol compound, which may reduce the extraction efficiency of calcium from the steel slag.

[0031] The manufacturing method is carried out, for example, using a calcium carbonate manufacturing apparatus as shown in Figure 1. This manufacturing apparatus mainly comprises a container 1 for filling with steel slag to form a slag layer S, a supply unit 2 for supplying a solution M to the container 1, a storage unit 3 for storing the calcium extract that flows through the slag layer S and is discharged from the container 1, an introduction unit 4 for introducing carbon dioxide C into the extract M1 stored in the storage unit 3, and a separation unit 5 for solid-liquid separation of precipitates D in the mixed liquid M2 obtained by the introduction of carbon dioxide by the introduction unit 4.

[0032] [Control process] The control process includes the steps of: circulating a solution M through a slag layer S formed by filling a container with steel slag containing a coloring component and calcium; and introducing carbon dioxide C into the solution (calcium extract M1) that has circulated through the slag layer S.

[0033] In the aforementioned distribution procedure, the solution M supplied by the supply unit 2 is distributed through the slag layer S formed in the container 1, thereby extracting the coloring components and calcium from the steel slag forming the slag layer S into the solution M. The calcium is calcium ions (Ca 2+ The coloring components and calcium are extracted from the solution. The supply unit 2 supplies solution M to container 1 via a solvent supply pipe P1 that connects container 1 and supply unit 2. The solution M from which the coloring components and calcium have been extracted is supplied to storage unit 3 as calcium extract M1 via an extract supply pipe P2. The steel slag from which the coloring components and calcium have been extracted can be removed from container 1 and dried, and used as a resource such as roadbed material (road material) or fertilizer.

[0034] In the introduction procedure described above, the introduction unit 4 introduces carbon dioxide C into the calcium extract M1 stored in the storage unit 3. The introduction unit 4 is not particularly limited, and examples include known gas blowing devices. It is preferable to introduce carbon dioxide C by the introduction unit 4 while stirring the calcium extract M1 in the storage unit 3.

[0035] The introduction unit 4 introduces carbon dioxide C so that the pH of the calcium extract M1 is 7 or less. The upper limit of the pH of the calcium extract M1 is preferably less than 7, and more preferably less than 6.9. The lower limit of the pH of the calcium extract M1 is not particularly limited, but can be, for example, 4.0 or higher. By keeping the pH of the calcium extract M1 from exceeding the upper limit, the whiteness of the resulting calcium carbonate is improved.

[0036] The gas introduced from the introduction unit 4 may be a gas consisting of carbon dioxide, or it may be air containing carbon dioxide, or it may be exhaust gas containing carbon dioxide emitted from industrial activities such as factories, power plants, and transportation.

[0037] [Precipitation process] 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 precipitates as precipitate D. This manufacturing method controls the pH of the calcium extract M1 into which carbon dioxide C is introduced to be 7 or lower, thus improving the incorporation of many coloring components in the calcium extract M1 into precipitate D.

[0038] The calcium extract M1, whose pH value is controlled by the introduction of carbon dioxide C, is supplied to the separation unit 5 as a mixture M2 via the mixture supply pipe P3, together with the precipitate D.

[0039] [Removal process] 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 the precipitate D from the mixed liquid M2 (separated liquid M3) from which the precipitate D has been removed. The separation unit 5 is not particularly limited and, for example, a known centrifuge can be used. The separated precipitate D can be used as a resource, for example, as a resin filler.

[0040] [Acquisition process] In the separation section 5, calcium ions remain in the separated liquid M3 from which precipitate D has been removed. Further calcium carbonate can be obtained by degassing this separated liquid M3. Since the coloring components in the steel slag precipitate in precipitate D, the amount remaining in the separated liquid M3 is reduced. Therefore, the calcium carbonate obtained by degassing the separated liquid M3 has high whiteness. Such high-whiteness calcium carbonate is suitably used as a raw material for products that require high whiteness, such as resins, paper, and concrete.

[0041] The degassing method is not particularly limited as long as it can remove carbon dioxide from the separated liquid M3, and known methods such as atmospheric curing degassing, heating and boiling degassing, ultrasonic degassing, vacuum degassing, centrifugal degassing, and gas blowing degassing can be employed. When degassing is performed by gas blowing, it is preferable that the blown gas be an insoluble gas such as nitrogen or argon.

[0042] 〔advantage〕 In this manufacturing method, a solution obtained by extracting coloring components and calcium from steel slag is mixed with carbon dioxide while controlling the pH to precipitate the coloring components. As a result, the coloring components precipitate within the precipitate, and the amount remaining in the solution after the precipitate is removed is reduced. Therefore, this manufacturing method can improve the whiteness of the calcium carbonate obtained by degassing the solution after the precipitate has been removed. Furthermore, since this manufacturing method uses steel slag as a by-product and does not use any chemicals to improve the whiteness of the calcium carbonate, it is possible to produce highly white calcium carbonate at a low cost.

[0043] [Other embodiments] The embodiments described above do not limit the configuration of the present invention. Accordingly, the embodiments may omit, substitute, or add components of each part of the embodiments based on the description herein and common technical knowledge, and all such additions should be interpreted as falling within the scope of the present invention.

[0044] The coloring components and calcium are extracted, and the resulting mixture does not necessarily have to be a solution; it may also be a slurry.

[0045] The materials containing coloring agents and calcium are not limited to steel slag, but may also include, for example, cement, concrete waste, glass waste, coal ash, sludge incineration ash, woody biomass ash, etc.

[0046] The solution or slurry may contain polyol compounds, solvents other than water, additives, etc., to the extent that they do not impede the calcium extraction efficiency. Examples of other solvents and additives include hydrophilic solutions. Examples of hydrophilic solutions include ethanol or methanol. In the distribution process, a mixture of the polyol compound and an aqueous solution obtained by dissolving additives other than solvents in water may also be used. [Examples]

[0047] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0048] As the first test, a comparative test of the whiteness of precipitates and calcium carbonate was conducted. Two steelmaking slags were prepared as substances containing coloring components and calcium. The coloring components contained in these two steelmaking slags are shown in Table 1. The two steelmaking slags were crushed in a jaw crusher to a size of less than 4.75 mm.

[0049] [Table 1]

[0050] As a solution for extracting calcium from steelmaking slag, we prepared glycerin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity exceeding 99.5%) and pure water.

[0051] 400g of the above glycerin and 600g of the above pure water were mixed in a prepared container to make a solution. Nitrogen gas was blown into this solution at a rate of 0.5 L / min for 10 minutes, and then 100g of steelmaking slag 1 was added. Subsequently, while circulating nitrogen gas at a rate of 0.5 L / min through the gas phase in the container, the mixture was stirred at 300 rpm for 90 minutes using a stirrer to extract calcium. After extraction, the mixture was centrifuged at 3000 rpm for 5 minutes, and the solution was filtered using filter paper (Type 5A) to obtain a calcium extract.

[0052] Table 2 shows the results of the analysis of the components contained in this calcium extract. It can be seen that, in addition to calcium, the calcium extract contains iron and manganese, which are coloring components. The above analysis was performed using an ICP emission spectrometer.

[0053] [Table 2]

[0054] Five other containers and five containers of the calcium extract obtained by the method described above were prepared. 900g of the calcium extract was poured into each container, and a pH meter (Hanna Instruments Japan Co., Ltd., benchtop pH / EC HI 5522) was inserted.

[0055] Carbon dioxide was introduced into the calcium extract in each container at a rate of 0.5 L / min while controlling the pH. Once the predetermined pH was reached, the calcium extract was filtered using filter paper (Type 5C) to separate it into precipitate and separated liquid. The precipitate was washed with 100 g of pure water and then vacuum-dried at 10 mmHg and 105°C for at least 3 hours. The separated liquids were each poured into other containers and degassed by curing in the atmosphere at room temperature for at least 48 hours. After degassing, calcium carbonate was obtained using filter paper (Type 5C). The calcium carbonate was washed with 100 g of pure water and then vacuum-dried at 10 mmHg and 105°C for at least 3 hours. Table 3 shows the pH of each calcium extract, the whiteness of the precipitate, and the whiteness of the calcium carbonate. Whiteness was evaluated using a spectrophotometer (Komica Minolta CM-600d) to measure Hunter whiteness.

[0056] [Table 3]

[0057] In Test Examples 1-3, where the pH was above 7, the Hunter whiteness of calcium carbonate was lower than that of the precipitate. On the other hand, in Test Examples 4-5, where the pH was 7 or lower, the Hunter whiteness of calcium carbonate was higher than that of the precipitate. Furthermore, the Hunter whiteness of calcium carbonate in Test Examples 4-5 was higher than that of Test Examples 1-3. From these results, it can be seen that by introducing carbon dioxide to lower the pH of the calcium extract to 7 or lower, calcium carbonate with high whiteness can be obtained.

[0058] As a second test, a comparative test of the whiteness of calcium carbonate was conducted based on the amount of coloring components contained in steelmaking slag. Two containers were prepared, and 120 g of glycerin and 280 g of pure water were mixed in each container to make a solution. Nitrogen gas was blown into this solution at a rate of 0.5 L / min for 10 minutes, and then 40 g of steelmaking slag 1 was added to one container and 40 g of steelmaking slag 2 was added to the other container. Subsequently, while circulating nitrogen gas at a rate of 0.5 L / min through the gas phase in the containers, the mixture was stirred at 300 rpm for 90 minutes using a stirrer to extract calcium. After extraction, centrifugation was performed at 3000 rpm for 5 minutes, and the solution was filtered using filter paper (Type 5A) to obtain the calcium extract.

[0059] 300 g of each calcium extract was poured into the other two containers, and a pH meter was inserted. Carbon dioxide was introduced into the calcium extract in each container at a rate of 0.5 L / min while controlling the pH. When the predetermined pH was reached, the calcium extract was filtered using filter paper (Type 5C) to separate it into precipitate and separated liquid. The precipitate was washed with 100 g of pure water, and then vacuum-dried at 10 mmHg and 105°C for at least 3 hours. The separated liquids were each poured into other containers and degassed by curing in the atmosphere at room temperature for at least 48 hours. After degassing, calcium carbonate was obtained using filter paper (Type 5C). The calcium carbonate was washed with 100 g of pure water, and then vacuum-dried at 10 mmHg and 105°C for at least 3 hours. Table 4 shows the pH of each calcium extract, the whiteness of the precipitate, and the whiteness of the calcium carbonate.

[0060] [Table 4]

[0061] Comparing Test Example 6 and Test Example 7, the difference in Hunter whiteness of the precipitates is relatively large, but the difference in Hunter whiteness of the calcium carbonate is small. Furthermore, the Hunter whiteness of all calcium carbonate samples is higher than that of the precipitates. From these findings, it can be seen that, regardless of the amount of coloring components contained in the steelmaking slag, highly white calcium carbonate can be stably obtained by introducing carbon dioxide so that the pH of the calcium extract is 7 or less. [Industrial applicability]

[0062] This invention allows for the production of high-whiteness calcium carbonate at low cost and by effectively utilizing carbon dioxide as a resource, thereby providing high-value-added calcium carbonate. [Explanation of Symbols]

[0063] 1 container 2 Supply section 3. Storage section 4. Introduction 5 Separation part C Carbon dioxide D Precipitate M solution M1 Calcium Extract M2 mixture M3 separation liquid P1 Solvent supply tube P2 Extract supply pipe P3 Mixed liquid supply pipe S slag layer

Claims

1. 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 containing calcium carbonate in the solution or slurry whose pH has been controlled in the control step, A step of removing the precipitate formed in the precipitation step from the solution or slurry, The process involves degassing the solution or slurry after the removal step without adding calcium carbonate seed crystals to obtain calcium carbonate. Equipped with, A method for producing calcium carbonate, wherein the calcium carbonate obtained in the step of obtaining the calcium carbonate has a higher Hunter whiteness than the precipitate removed in the removal step.

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

3. A method for producing calcium carbonate according to claim 1 or claim 2, wherein the element is derived from steel slag.

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

5. The method for producing calcium carbonate according to claim 4, wherein the solution or 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 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 glycerin.

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