Method for producing alkaline earth metal carbonate

Abstract

This method for producing an alkaline earth metal carbonate includes: a step (I) for preparing a slurry containing an alkaline earth metal-containing substance, a salt of a first organic amine and an acid forming a water-soluble salt with an alkaline earth metal, a second organic amine, and water; a step (II) for subjecting the slurry prepared in the step (I) to solid-liquid separation to obtain a liquid component; a step (III) for bringing the liquid component obtained in the step (II) into contact with carbon dioxide to precipitate an alkaline earth metal carbonate; and a step (IV) for separating the alkaline earth metal carbonate precipitated in the step (III) from the liquid component, the method being characterized in that at least one of the first organic amine and the second organic amine is a tertiary amine.

Description

Method for producing alkaline earth metal carbonate

[0001] The present invention relates to a method for producing alkaline earth metal carbonates.

[0002] With the growing concern about global warming in recent years, there is a need to reduce carbon dioxide emissions into the atmosphere. Studies are being conducted to reduce the amount of carbon dioxide emitted into the atmosphere by capturing and fixing the carbon dioxide generated at various facilities such as power plants, incinerators, and cement plants.

[0003] For example, Patent Document 1 discloses a concrete sludge treatment device, which discloses that calcium carbonate can be produced by eluting calcium from concrete sludge into water as calcium hydroxide and supplying carbon dioxide to the water into which the calcium has eluted. However, in the production of calcium carbonate using the device disclosed in Patent Document 1, concrete sludge is dispersed in water, but the calcium oxide contained in the concrete sludge and the calcium hydroxide produced by its hydration only dissolve in an amount of about 0.17 g per 100 mL of water at 25°C. Therefore, the method disclosed in Patent Document 1 is inefficient, and there are limitations on the amount of calcium carbonate that can be produced, such as requiring larger facilities to increase the production amount.

[0004] Patent Document 2 also discloses a method for immobilizing carbon dioxide using a salt of a weak base and a strong acid. In this method, an alkaline earth metal-containing material, such as converter slag, is contacted with an aqueous solution obtained from a salt of a weak base and a strong acid. The alkaline earth metal, such as calcium, is first converted into a salt with the strong acid, thereby increasing its solubility in water. This increases the amount of alkaline earth metal carbonate produced when the water containing the dissolved alkaline earth metal is contacted with a gas containing carbon dioxide. However, Patent Document 2 only discloses an example in which ammonium chloride is used as the salt of a weak base and a strong acid, requiring the use of an excess amount of ammonium chloride relative to the converter slag. Furthermore, the ammonium chloride produced after the carbon dioxide fixation reaction is reused in the alkaline earth metal dissolution reaction to immobilize carbon dioxide. However, the amount of calcium carbonate obtained in the second reaction is significantly lower than that in the first reaction, suggesting that ammonium chloride or the produced ammonia is lost somewhere in the reaction system.

[0005] Patent Document 3 discloses a method for producing alkaline earth metal carbonates by contacting an extractable material containing alkaline earth metals with a substoichiometric amount of an amine-containing leaching agent to produce solvated alkaline earth metals, and then contacting the resulting alkaline earth metals with carbon dioxide. This method uses a salt of a basic compound, such as ammonia or an organic amine, and an acidic compound as the amine-based leaching agent. The method also discloses a method for recovering calcium from low-grade lime using monoethanolamine hydrochloride as the organic amine leaching agent and carbon dioxide, but does not provide any examples using calcium-rich waste such as concrete sludge. The inventors' investigations revealed that when alkaline earth metal carbonates were produced using concrete sludge as calcium-rich waste, the reaction did not proceed sufficiently.

[0006] JP 2009-136770 A JP 2005-097072 A JP 2017-513806 A

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for producing alkaline earth metal carbonates that allows for mass synthesis and improves the efficiency of producing high-purity alkaline earth metal carbonates.

[0008]

[0006] As a result of extensive research to solve the above-mentioned problems, the inventors have found that a high-purity alkaline earth metal carbonate can be produced in a high yield by first extracting the alkaline earth metal as a water-soluble salt from a slurry containing an alkaline earth metal-containing substance and water, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine, filtering the filtrate, and then contacting the filtrate with carbon dioxide in the presence of a second organic amine to precipitate the alkaline earth metal carbonate.

[0007] As a result of further extensive research, the inventors have found that by using a tertiary amine as at least one of the first organic amine and the second organic amine, the alkaline earth metal can be efficiently eluted from the alkaline earth metal-containing substance with a smaller amount, thereby increasing the yield, and have completed the present invention.

[0009] That is, the present invention is as follows: [1] A method for producing an alkaline earth metal carbonate, comprising: a step (I) of preparing a slurry containing an alkaline earth metal-containing substance, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine, a second organic amine, and water, a step (II) of performing solid-liquid separation of the slurry prepared in the step (I) to obtain a liquid component, a step (III) of contacting the liquid component obtained in the step (II) with carbon dioxide to precipitate an alkaline earth metal carbonate, and a step (IV) of separating the alkaline earth metal carbonate precipitated in the step (III) from the liquid component, wherein at least one of the first organic amine and the second organic amine is a tertiary amine.

[0010] [2] The method for producing alkaline earth metal carbonate according to [1] above, wherein in step (I), 50 mol % or more of the second organic amine is added relative to 100 mol % of the salt of the first organic amine and an acid that forms a water-soluble salt with the alkaline earth metal. [3] The method for producing alkaline earth metal carbonate according to [1] or [2] above, wherein in step (I), 90 mol % or more of the second organic amine is added relative to 100 mol % of the salt of the first organic amine and an acid that forms a water-soluble salt with the alkaline earth metal. [4] Use of the alkaline earth metal carbonate containing a tertiary amine produced by the method according to any one of [1] to [3] above as a grinding aid for clinker. [5] A method for producing cement, comprising: a step (I) of preparing a slurry containing an alkaline earth metal-containing substance, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine, a second organic amine, and water; a step (II) of obtaining a liquid component by solid-liquid separation of the slurry prepared in the step (I); a step (III) of contacting the liquid component obtained in the step (II) with carbon dioxide to precipitate an alkaline earth metal carbonate; a step (IV) of separating the alkaline earth metal carbonate precipitated in the step (III) from the liquid component; and a step (V) of adding the alkaline earth metal carbonate obtained in the step (IV) to lump cement clinker and grinding the lump cement clinker, wherein at least one of the first organic amine and the second organic amine is a tertiary amine, and the alkaline earth metal carbonate obtained in the step (IV) contains the tertiary amine.

[0011] According to the method of the present invention, high-purity alkaline earth metal carbonates can be produced efficiently.

[0012] Furthermore, the method of the present invention makes it possible to produce high-purity alkaline earth metal carbonates while reducing energy costs and carbon dioxide emissions.

[0013] The method for producing an alkaline earth metal carbonate of the present invention includes: a step (I) of preparing a slurry containing an alkaline earth metal-containing substance, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine (hereinafter, sometimes abbreviated as a first amine salt), a second organic amine, and water; a step (II) of performing solid-liquid separation of the slurry prepared in the step (I) to obtain a liquid component; a step (III) of contacting the liquid component obtained in the step (II) with carbon dioxide to precipitate an alkaline earth metal carbonate; and a step (IV) of separating the alkaline earth metal carbonate precipitated in the step (III) from the liquid component, wherein at least one of the first organic amine and the second organic amine is a tertiary amine.

[0014] Conventionally, CO ２ In the field of CO recovery, tertiary amines ２ While the release performance of CO ２ However, in the present invention, a tertiary amine is used.

[0015] According to the method of the present invention, a high-purity alkaline earth metal carbonate can be obtained in high yield and / or high yield. That is, by using a tertiary amine as at least one of the first organic amine and the second organic amine in step (I), basicity is reduced due to steric hindrance of the tertiary amine, making it easier to release acid, thereby efficiently eluting the alkaline earth metal from the alkaline earth metal-containing substance and increasing the yield. In addition, in step (III), the liquid component containing the second organic amine, obtained in step (II) subsequent to step (I), is contacted with carbon dioxide, making it possible to produce a high-purity alkaline earth metal carbonate in high yield.

[0016] In addition, even when exhaust gas is used as carbon dioxide in step (III), the tertiary amine is oxidized by the heat and oxidation of the exhaust gas and NO. Ｘ Since it is not easily degraded by heat, the amine can be effectively recycled.

[0017] The alkaline earth metal in the alkaline earth metal-containing substance is generally present as a hydroxide or oxide and does not have high solubility in water. Therefore, production of calcium carbonate using eluted calcium hydroxide as in Patent Document 1 is inefficient, and the production amount is limited relative to the size of the production equipment.

[0018] Furthermore, in Patent Documents 2 and 3, in order to dissolve the alkaline earth metal in water, the solubility of the alkaline earth metal is increased by using a salt of a weak base such as ammonium chloride and a strong acid, or an organic amine leaching agent such as monoethanolamine hydrochloride, thereby increasing the productivity of the alkaline earth metal carbonate, but this is not necessarily sufficient.

[0019] The present invention can further increase the productivity of alkaline earth metal carbonates. The mechanism by which such effects of the present invention are achieved is believed to be as follows.

[0020] As mentioned above, alkaline earth metals in alkaline earth metal-containing materials exist as hydroxides or oxides. These are converted into alkaline earth metal hydroxides (AE(OH)) in water. ２ In step (I), a slurry containing an acid (HX) that forms a water-soluble salt with an alkaline earth metal and a first organic amine (R ３ -N; R is a hydrogen atom or any organic residue, at least one of which is an organic residue) ３ The first amine salt contains a water-soluble alkaline earth metal salt (AEX). This first amine salt is acidic in water. Therefore, in step (I), a neutralization reaction occurs between the alkaline earth metal hydroxide and the first amine salt, resulting in the formation of a water-soluble alkaline earth metal salt (AEX). ２ ) and a first organic amine is produced (Equation 1).

[0021] AE (OH) ２ +2R ３ -N・HX → AEX ２ +2R ３ -N+2H ２ O (Formula 1)

[0022] In this case, by using a tertiary amine as at least one of the first organic amine and the second organic amine, the basicity is suppressed due to steric hindrance of the tertiary amine, making it easier to release the acid, and therefore the alkaline earth metal can be efficiently eluted from the alkaline earth metal-containing substance, thereby increasing the yield.

[0023] Subsequently, in step (II), solid-liquid separation is performed to separate the reaction solution from the unreacted residue of the alkaline earth metal-containing substance (hereinafter also referred to as the unreacted residue). The reaction solution contains the water-soluble alkaline earth metal salt and the first organic amine.

[0024] Furthermore, in step (III), the first organic amine is contacted with carbon dioxide to form a carbonate salt of the first organic amine ((R ３ -NH ＋ ) ２ CO ３ ２－ ) is generated (Equation 2).

[0025] 2nd Round ３ -N+CO ２ +H ２ O → (R ３ -NH ＋ ) ２ CO ３ ２－ (Formula 2)

[0026] In addition, the water-soluble alkaline earth metal salt present in the system is acidic, while the carbonate of the first organic amine produced is basic. Therefore, a neutralization reaction occurs, and the alkaline earth metal carbonate (AECO ３ ) is produced and the first amine salt is simultaneously regenerated (Equation 3).

[0027] AEX ２ + (R ３ -NH ＋ ) ２ CO ３ ２－ →AECO ３ +2R ３-N.HX (Equation 3) In step (III), two reactions occur: carbonation of the organic amine and neutralization of the resulting carbonate of the organic amine. Therefore, by blowing carbon dioxide into the reaction solution under the conditions of step (III) in an environment in which the first organic amine and a predetermined amount of the second organic amine prepared in step (I) are present as organic amines, the equilibrium of the reaction in equation 2 can be shifted to the right, and the reaction can be completed quickly.

[0028] Finally, the alkaline earth metal carbonate produced in step (IV) is separated from the reaction liquid by solid-liquid separation to recover the alkaline earth metal carbonate. In addition, the liquid component obtained by solid-liquid separation contains the first amine salt regenerated in step (III), and therefore, the liquid component can be reused in step (I).

[0029] Furthermore, when the alkaline earth metal carbonate (particularly calcium carbonate) produced in step (IV) contains a tertiary amine, it can be used as a grinding aid for cement clinker. For example, when the alkaline earth metal salt is separated into solid form, tertiary amines remain in the alkaline earth metal carbonate by not washing or by lightly washing the alkaline earth metal carbonate. Therefore, such alkaline earth metal carbonate containing a tertiary amine can be used as a grinding aid for cement clinker.

[0030] The components of the present invention will be described in detail below.

[0031] (Salt of a first organic amine and an acid that forms a water-soluble salt with an alkaline earth metal (first amine salt)) The salt of a first organic amine and an acid that forms a water-soluble salt with an alkaline earth metal used in the present invention is a salt formed between a first organic amine and an acid that forms a water-soluble salt with an alkaline earth metal, and as described above, has the function of neutralizing with an alkaline earth metal oxide or hydroxide in the alkaline earth metal-containing substance to produce a water-soluble salt of the alkaline earth metal.

[0032] Examples of acids that form water-soluble salts with alkaline earth metals include inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chloric acid, perchloric acid, hypobromous acid, bromic acid, perbromic acid, hypoiodous acid, iodic acid, periodic acid, nitrous acid, nitric acid, and formic acid, and organic acids such as citric acid, malic acid, acetic acid, thioacetic acid, propionic acid, and lactic acid. These acids may be used alone or in combination of two or more.

[0033] The acid that forms a water-soluble salt with an alkaline earth metal is preferably an acid that forms a salt having a solubility in water at 20°C of 10 g or more / 100 g, and more preferably hydrochloric acid, hydrobromic acid, hydroiodic acid, nitrous acid, nitric acid, formic acid, acetic acid, or propionic acid.

[0034] As the first organic amine, any commonly known organic amine can be used without limitation, but from the viewpoint of water solubility, it is preferable to use an alkylamine. Here, alkylamine refers to an amine in which the amino group is substituted with an alkyl group, and does not include aromatic amines or aromatic heterocyclic amines. Furthermore, the alkyl group of the alkylamine may be linear, branched, or cyclic. Alternatively, a polyamine having two or more amino groups per molecule may be used. Furthermore, a functional group such as a hydroxyl group may be present on the alkyl group to impart water solubility. Furthermore, primary amines, secondary amines, and tertiary amines exist depending on the number of substituents, with tertiary amines being preferred.

[0035] As the first organic amine, it is preferable to use an alkylamine, and among these alkylamines, it is preferable to use a cyclic amine or a polyamine from the viewpoint of reactivity.

[0036] Examples of alkylamines include methylamine, ethylamine, propylamine, dipropylamine, butylamine, diaminopropane, triethylamine, dimethylamine, trimethylamine, monoethanolamine, diethanolamine, triethanolamine, triisopropanolamine, N-methyldiethanolamine, diethanolisopropanolamine, morpholine, pyrrolidine, piperidine, piperazine, hexamethyleneimine, ethylenediamine, diethylenetriamine, triethylenetetramine, N,N'-bis(3-aminopropyl)ethylenediamine, spermine, spermidine, putrescine, cadaverine, hexamethylenediamine, tetraethylmethylenediamine, polyethyleneamine, and triethylenediamine (DABCO). Among these, tertiary amines such as triethylamine, trimethylamine, triethanolamine, triisopropanolamine, N-methyldiethanolamine, diethanolisopropanolamine, and triethylenediamine are preferred.

[0037] The salt of the first organic amine and an acid that forms a water-soluble salt with an alkaline earth metal is not particularly limited as long as it is a salt of the first amine and an acid that forms a water-soluble salt with an alkaline earth metal as described above. However, preferred salts are triethylamine, trimethylamine, triethanolamine, triisopropanolamine, N-methyldiethanolamine, diethanolisopropanolamine, and triethylenediamine with hydrochloric acid, hydrobromic acid, hydroiodic acid, nitrous acid, nitric acid, formic acid, acetic acid, and propionic acid.

[0038] (Alkaline earth metal-containing material) The alkaline earth metal-containing material used in the present invention is not particularly limited as long as it contains an alkaline earth metal, and examples thereof include alkaline earth metal oxides, hydroxides, natural minerals, and by-products and waste materials discharged during manufacturing processes. The alkaline earth metal may be contained in the form of an oxide, hydroxide, complex with silica, aluminum, or the like. Furthermore, as the alkaline earth metal, calcium, which is present in large quantities in terms of the amount of carbon dioxide fixed, is preferred, and among these, calcium oxide, calcium hydroxide, calcium (alumino) silicate, and the like are preferred. As the alkaline earth metal-containing material, it is more preferred to use waste materials that are currently landfilled due to their low usefulness.

[0039] Examples of waste materials containing calcium as an alkaline earth metal include coal ash, biomass ash, incineration ash, paper sludge ash, concrete sludge, crushed concrete, crushed cement, steel slag, soda-lime glass, and potassium-lime glass.

[0040] (Second organic amine) As the second organic amine used in the present invention, the first organic amine exemplified in the first amine salt can be suitably used. Furthermore, the second organic amine may be the same as or different from the first organic amine. In particular, a tertiary amine is preferred. From the viewpoint of the yield of the alkaline earth metal salt, it is particularly preferred that both the first organic amine and the second organic amine are tertiary amines.

[0041] Here, tertiary alkanolamines are generally suitable for use as clinker grinding aids, and among these, triethanolamine, triisopropanolamine, N-methyldiethanolamine, and diethanolisopropanolamine are particularly suitable. Therefore, when the produced alkaline earth metal salt is used as a cement clinker grinding aid, it is preferable to use triethanolamine, triisopropanolamine, N-methyldiethanolamine, or diethanolisopropanolamine as the first and / or second organic amine.

[0042] (Carbon dioxide) The carbon dioxide used in the present invention is preferably a gas. It may be 100% pure carbon dioxide gas, or may be carbon dioxide contained in air, the exhaled breath of living organisms, food waste, wood chips, waste plastic, organic sludge, or other waste materials produced when burning such waste, or in exhaust gases from thermal power plants, steel plants, cement plants, etc. The carbon dioxide content cannot be generalized, and the carbon dioxide-containing gas to which the present invention is applied is not particularly limited as long as it contains carbon dioxide. From the viewpoint of reaction efficiency, the carbon dioxide content is preferably 1% or more, more preferably 5% or more, and most preferably 10% or more. Carbon dioxide-containing exhaust gases emitted from various manufacturing facilities are also included. As described above, in the present invention, a tertiary amine is used as at least one of the first organic amine and the second organic amine, and therefore, even when exhaust gas is used as carbon dioxide, the heat, oxidation, and NOx generated by the exhaust gas are prevented. Ｘ Since it is not easily degraded by heat, the amine can be effectively recycled.

[0043] The steps (I) to (IV) of the present invention will be described in detail below.

[0044] [Step (I)] Step (I) is a step of preparing a slurry containing an alkaline earth metal-containing substance, a first amine salt, a second organic amine, and water. In this step, an alkaline earth metal oxide or hydroxide in the alkaline earth metal-containing substance is neutralized with the first amine salt to produce a water-soluble alkaline earth metal salt and the first organic amine. Here, the water-soluble alkaline earth metal salt produced is a salt of the alkaline earth metal contained in the alkaline earth metal-containing substance and an acid that forms a water-soluble salt with the alkaline earth metal that constitutes the first amine salt.

[0045] In the present invention, a tertiary amine is used as at least one of the first organic amine and the second organic amine, which allows the alkaline earth metal in the alkaline earth metal-containing substance to be efficiently eluted into the reaction solution, thereby increasing the yield of alkaline earth metal carbonate.

[0046] In the present invention, the pH of the aqueous solution of the first amine salt and the second organic amine is preferably 4.5 or higher. That is, it is preferable to adjust the blending ratio of the first amine salt and the second organic amine so that the pH of the aqueous solution of the first amine salt and the second organic amine is 4.5 or higher. The pH is more preferably 5.5 to 10.0.

[0047] The slurry containing an alkaline earth metal-containing substance, a first amine salt, a second organic amine, and water may be prepared by adding and mixing the alkaline earth metal-containing substance, the first amine salt, the second organic amine, and water in any order. The first amine salt may be formed by adding and mixing the first organic amine and an acid (a salt-forming component). In the present invention, it is preferable to adjust the blending ratio of the first amine salt and the second organic amine so that the pH of the aqueous solution is 4.5 or higher. Therefore, it is preferable to prepare an aqueous solution of the first amine salt and the second organic amine (after adjusting the pH) and then add and mix the alkaline earth metal-containing substance. Alternatively, the amounts of the first amine salt and the second organic amine to be added may be calculated in advance, and the alkaline earth metal-containing substance, the first amine salt, the second organic amine, and water may be added and mixed in an appropriate order. The prepared slurry contains the water-soluble alkaline earth metal salt, the first organic amine, the second organic amine, unreacted first amine salt, and unreacted residue.

[0048] Although the slurry concentration is not particularly limited, the mixing ratio of the alkaline earth metal-containing material to water (alkaline earth metal-containing material:water) is preferably in the range of 1:1.0 to 50.0, more preferably 1:2.0 to 30.0, and even more preferably 1:3.0 to 20.0. This range allows the alkaline earth metal-containing material and the first amine salt to react sufficiently.

[0049] The addition ratio of the alkaline earth metal-containing material to the first amine salt may be appropriately determined depending on the amount of alkaline earth metal contained in the alkaline earth metal-containing material. For example, when using a calcium-rich calcium-containing material such as concrete sludge, the first amine salt is preferably in the range of 5 to 500 mol%, more preferably 10 to 400 mol%, and even more preferably 20 to 300 mol%, relative to 100 mol% of calcium contained in the calcium-containing material. By setting the ratio in such a range, the alkaline earth metal-containing material and the first amine salt can be reacted well.

[0050] The temperature during the preparation of the slurry is not particularly limited, and the slurry may be prepared at room temperature or by heating.

[0051] The time for preparing the slurry is not particularly limited, but from the viewpoint of reaction efficiency, it is preferably from 1 minute to 24 hours, more preferably from 2 minutes to 6 hours, and most preferably from 5 minutes to 1 hour.

[0052] The preparation of the slurry is preferably carried out with stirring, and any stirring method can be used as long as it can uniformly mix the slurry to be treated, and a general stirrer can be used.

[0053] The amount of the second organic amine added varies depending on the type of the second organic amine, but is preferably 50 mol % or more, more preferably 90 mol % or more, relative to 100 mol % of the first amine salt. The upper limit is not particularly limited, but is preferably about 150 mol %.

[0054] [Step (II)] In step (II), the slurry prepared in step (I) is subjected to solid-liquid separation to obtain a liquid component. The liquid component contains a water-soluble alkaline earth metal salt, a first organic amine, and a second organic amine dissolved in water.

[0055] The method for solid-liquid separation of the slurry prepared in step (I) can be any known method such as filtration, centrifugation, sedimentation, etc., without limitation. From the viewpoint of obtaining a liquid component with few impurities, solid-liquid separation by filtration is preferred.

[0056] Any filtration method can be used, including, for example, methods using a filter press, a belt filter, a drum filter, etc. The filtration temperature can also be set to any temperature, since the dissolution amount of the water-soluble alkaline earth metal salt is sufficiently high even at room temperature. The liquid used for washing can be industrial water, tap water, distilled water, ion-exchanged water, etc., and is preferably used in an amount equal to or greater than the amount of alkaline earth metal-containing waste, and more preferably equal to or greater than two times the amount. For the reasons mentioned above, the temperature of the washing water can also be set to any temperature.

[0057] [Step (III)] Step (III) is a step in which the liquid component obtained in step (II) is contacted with carbon dioxide to precipitate an alkaline earth metal carbonate. In this step, the liquid component obtained in step (II) is contacted with carbon dioxide in the presence of a second organic amine. The presence of the second organic amine when the liquid component obtained in step (II) is contacted with carbon dioxide promotes the carbonation of the organic amine of formula 2 as described above, and as a result, the production of an alkaline earth metal carbonate can also be promoted.

[0058] The liquid component obtained in step (II) contains a water-soluble alkaline earth metal salt and organic amines (first organic amine and second organic amine). At this time, the liquid component contains the first organic amine so that there are two amino groups derived from the first organic amine per molecule of the alkaline earth metal, as shown in the reaction (Equation 1) in step (I), and also contains the second organic amine. Therefore, the amount of organic amine, which is the total of the first organic amine and the second organic amine, exceeds the stoichiometric amount relative to the water-soluble alkaline earth metal in the carbonation reaction of the organic amine in step (III) (Equation 2).

[0059] That is, the total number of amino groups in the organic amines derived from the first organic amine and the second organic amine before contact with carbon dioxide is more than two per molecule of the water-soluble alkaline earth metal.

[0060] In this step, the contact with carbon dioxide can be carried out by bringing the carbon dioxide into contact at the liquid surface or by blowing the carbon dioxide directly into the liquid. From the viewpoint of reaction efficiency, however, it is preferable to blow the carbon dioxide directly into the obtained liquid component.

[0061] The temperature at which carbon dioxide is contacted is not particularly limited, and the contact may be carried out at room temperature or by heating using an apparatus.

[0062] The time for contacting with carbon dioxide varies depending on the carbon dioxide concentration in the carbon dioxide-containing gas and is not particularly limited, but from the viewpoint of carbonation reaction efficiency, it is preferably from 1 minute to 24 hours, more preferably from 2 minutes to 6 hours, and most preferably from 5 minutes to 2 hours.

[0063] In this step, it is preferable to carry out the step with stirring from the viewpoint of uniformly dispersing carbon dioxide in the liquid component. Since the liquid component becomes a slurry due to the precipitation of alkaline earth metal carbonate, any stirring method can be used as long as it can uniformly mix the slurry, and a general stirrer can be used.

[0064] [Step (IV)] Step (IV) is a step of separating the alkaline earth metal carbonate precipitated in step (III) from the liquid component.

[0065] The alkaline earth metal carbonate can be separated from the liquid component by any known method, such as filtration, centrifugation, sedimentation, etc., without limitation. From the viewpoint of obtaining a liquid component with few impurities, solid-liquid separation by filtration is preferred.

[0066] The filtration method can be the same as that described in step (II). The filtration temperature can be any temperature because alkaline earth metal carbonates have low solubility in water regardless of the temperature. The liquid used for washing can be industrial water, tap water, distilled water, ion-exchanged water, or the like, and is preferably used in an amount equal to or greater than the amount of alkaline earth metal-containing waste, and more preferably equal to or greater than two times the amount. For the reasons mentioned above, the temperature of the washing water can also be any temperature.

[0067] In addition, since the regenerated first amine salt is present in a dissolved state in the liquid component separated from the alkaline earth metal carbonate in step (IV), the liquid component separated in this step can be returned to step (I) and reused as part of the first amine salt and water used in step (I).Furthermore, since the second organic amine is also contained, the liquid component can be returned to step (I) and reused as part of the second organic amine present in step (I).

[0068] Furthermore, when the alkaline earth metal carbonate obtained in step (IV) is, for example, calcium carbonate, it can be used as a grinding aid for cement clinker by leaving the tertiary amine as described above. Therefore, in this case, the alkaline earth metal carbonate is preferably washed with water in an amount of not more than three times, more preferably not more than two times, the amount of the alkaline earth metal carbonate obtained, and most preferably not at all. Leaving a larger amount of tertiary amine in the grinding aid for cement clinker allows the amount added to cement clinker to be reduced, so it is preferable not to wash.

[0069] Furthermore, the clinker grinding aid is generally added to cement clinker cooled to 100 to 200°C and cooled to room temperature together with the cement clinker grinding. Therefore, the alkaline earth metal carbonate can be used without drying.

[0070] Next, a method for producing cement of the present invention will be described. The method for producing cement of the present invention comprises the above steps (I) to (IV), and a step (V) of adding the alkaline earth metal carbonate obtained in step (IV) to a lump of cement clinker and grinding the lump of cement clinker, wherein at least one of the first organic amine and the second organic amine is a tertiary amine, and the alkaline earth metal carbonate obtained in step (IV) contains a tertiary amine.

[0071] [Step (V)] Step (V) is a step of adding the alkaline earth metal carbonate containing a tertiary amine obtained in step (IV) as a grinding aid to lumpy cement clinker to grind the cement clinker. Specifically, this is a step of adding the alkaline earth metal carbonate containing a tertiary amine to lumpy cement clinker that has been burned in a burning device such as a rotary kiln and then cooled to a predetermined temperature by a cooling device such as a clinker cooler, and grinding the resulting lumpy cement clinker.

[0072] The amount of alkaline earth metal salt to be added to cement clinker can be determined appropriately depending on the amount of tertiary amine contained in the alkaline earth metal salt. The alkaline earth metal salt may also be used together with a commonly used grinding aid.

[0073] At least gypsum is mixed with the crushed cement clinker and crushed to produce cement in a conventional manner.

[0074] Examples and comparative examples are shown below, but the technical scope of the present invention is not limited to these.

[0075] [Examples 1-10] Predetermined amounts of triethylenediamine (DABCO) as the first organic amine and second organic amine, which are components of the first amine salt, were weighed into a beaker and completely dissolved in 50 mL of water. A predetermined amount of 35% hydrochloric acid was added to prepare an aqueous solution of the first amine salt and the second organic amine. The pH of this aqueous solution was measured. 5 g of powdered concrete sludge (containing 48 mmol of calcium) dried at 105°C for 24 hours was added to the solution as an alkaline earth metal-containing substance. After stirring at room temperature for 10 minutes, the solution was filtered, and the solid unreacted residue was washed with 20 mL of water. The unreacted residue was dried at 105°C for 3 hours and used to calculate the amount of calcium hydroxide eluted from the alkaline earth metal-containing substance.

[0076] The resulting filtrate was reacted by blowing 100% carbon dioxide gas into it at 0.1 L / min while stirring for 30 minutes. The reaction was then continued for another 30 minutes with stirring. After 30 minutes of stirring, the reaction solution was subjected to solid-liquid separation by filtration, and the solid was washed with 20 mL of water. After washing, the solid was dried at 105°C for 3 hours, and the amount of calcium carbonate produced was calculated. The results are shown in Table 1.

[0077] Examples 11 and 12 The same procedure as in Example 1 was carried out, except that predetermined amounts of triethanolamine were used as the first organic amine and the second organic amine, which are components of the first amine salt.

[0078] [Example 13] The same operation as in Example 1 was carried out, except that a predetermined amount of piperazine (secondary amine) was used as the first organic amine, which was a component of the first amine salt, and a predetermined amount of DABCO was used as the second organic amine.

[0079] Comparative Example 1 The same procedure as in Example 1 was carried out except that 50 mmol of DABCO was used as the first organic amine, which is a component of the first amine salt, and no second organic amine was used.

[0080] Comparative Example 2 The same procedure as in Example 1 was carried out, except that 100 mmol of 2-ethanolamine (primary amine) was used as the first organic amine, which is a component of the first amine salt, and no second organic amine was used.

[0081] Reference Example 1 The same operation as in Example 1 was carried out, except that predetermined amounts of 2-ethanolamine (primary amine) were used as the first organic amine and the second organic amine, which are components of the first amine salt.

[0082] Reference Examples 2 to 4 The same operations as in Example 1 were carried out, except that predetermined amounts of piperazine (secondary amine) were used as the first organic amine and the second organic amine, which are components of the first amine salt.

[0083] Examples 1 to 13 are examples in which step (I) was carried out using a tertiary amine, and calcium carbonate was able to be produced in good yield and high yield. Furthermore, comparing Example 1 with Reference Example 2, Example 1, which used the tertiary amine DABCO, showed an increased yield of calcium carbonate despite the use of small amounts of the first amine salt and the second organic amine. Similarly, comparing Example 6 with Reference Example 2, the yield of calcium carbonate increased despite the use of the same amounts of the first amine salt and the second organic amine. Furthermore, comparing Example 7 with Reference Example 3, in order to obtain a calcium carbonate yield equivalent to that of Example 7 using the secondary amine piperazine, it was necessary to use 1.6-fold molar equivalents or more of the first amine salt and the second organic amine, and it was found that the use of a tertiary amine allowed for a reduction in the amount of amine used.

[0084] Example 14 2.0 g of calcium carbonate containing triethanolamine was obtained in the same manner as in Example 11, except that after precipitating calcium carbonate, solid-liquid separation by filtration was performed without washing. The obtained calcium carbonate containing triethanolamine was washed with 100 mL of water, and the amount of triethanolamine contained in the wash water was determined by ion chromatography. It was found that the unwashed calcium carbonate contained 0.18 g (9.0%) of triethanolamine. This calcium carbonate containing triethanolamine can be used as a good grinding aid by appropriately selecting the amount to be added to cement clinker.

[0085]

Claims

1. A method for producing alkaline earth metal carbonate, comprising: step (I) of preparing a slurry containing an alkaline earth metal-containing substance, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine, a second organic amine, and water; step (II) of performing solid-liquid separation of the slurry prepared in step (I) to obtain a liquid component; step (III) of contacting the liquid component obtained in step (II) with carbon dioxide to precipitate an alkaline earth metal carbonate; and step (IV) of separating the alkaline earth metal carbonate precipitated in step (III) from the liquid component, wherein at least one of the first organic amine and the second organic amine is a tertiary amine.

2. The method for producing alkaline earth metal carbonate according to claim 1, characterized in that in step (I), 50 mol % or more of the second organic amine is added relative to 100 mol % of the salt of the first organic amine and an acid that forms a water-soluble salt with the alkaline earth metal.

3. The method for producing alkaline earth metal carbonate according to claim 1, characterized in that in step (I), 90 mol % or more of the second organic amine is added relative to 100 mol % of the salt of the first organic amine and an acid that forms a water-soluble salt with the alkaline earth metal.

4. Use of an alkaline earth metal carbonate containing a tertiary amine produced by the method according to any one of claims 1 to 3 as a grinding aid for clinker.

5. A method for producing cement, comprising: step (I) of preparing a slurry containing an alkaline earth metal-containing substance, a salt of an acid that forms a water-soluble salt with the alkaline earth metal and a first organic amine, a second organic amine, and water; step (II) of performing solid-liquid separation of the slurry prepared in step (I) to obtain a liquid component; step (III) of contacting the liquid component obtained in step (II) with carbon dioxide to precipitate an alkaline earth metal carbonate; step (IV) of separating the alkaline earth metal carbonate precipitated in step (III) from the liquid component; and step (V) of adding the alkaline earth metal carbonate obtained in step (IV) to lump cement clinker and grinding the lump cement clinker, wherein at least one of the first organic amine and the second organic amine is a tertiary amine, and the alkaline earth metal carbonate obtained in step (IV) contains a tertiary amine.

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