Control method of gypsum conversion reaction and manufacturing method of calcium carbonate

Abstract

To provide a control method of gypsum conversion reaction and a manufacturing method of calcium carbonate having high versatility to be applicable to a variety of materials and capable of corresponding by minor and easy work.SOLUTION: In a gypsum conversion reaction to obtain calcium carbonate by allowing a solution A containing at least one kind of an alkali metal salt A selected from an alkali metal carbonate salt and an alkali metal hydrogen carbonate salt to be contact with a gypsum-containing material, the control method of gypsum conversion reaction and a manufacturing method of calcium carbonate are characterized by that one condition selected from a pH of a reaction liquid of the solution A and the gypsum containing material and at least one concentration selected from a carbonate ion concentration, a hydrogen carbonate ion concentration, and a calcium ion concentration of the reaction liquid are monitored to determine an end point of the reaction.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for controlling a gypsum conversion reaction and a method for producing calcium carbonate. [Background technology]

[0002] Gypsum-containing materials, particularly waste containing gypsum such as waste gypsum boards and waste materials recovered from flue gas desulfurization processes, are generally treated and disposed of as industrial waste as is, and the disposed waste containing gypsum is landfilled in a final disposal site. However, the amount of waste containing gypsum has been steadily increasing in recent years, and it is expected that the final disposal sites will become strained. In consideration of the environmental burden, it has been considered to reuse waste containing gypsum instead of disposing of it as is (for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses an apparatus and method for crushing and separating waste gypsum boards, which continuously and efficiently separate and recover high-purity gypsum and base paper for gypsum boards from waste gypsum boards. Patent Document 2 discloses a method for treating industrial waste containing gypsum, which treats industrial waste containing calcium sulfate, such as gypsum boards, by using ammonia and carbon dioxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-011210 A [Patent Document 2] JP 2001-000947 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for controlling a gypsum conversion reaction and a method for producing calcium carbonate, which have high versatility applicable to a wide variety of materials and can be implemented with minor and easy operations. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following method for controlling a gypsum conversion reaction. 1. A gypsum conversion reaction for obtaining calcium carbonate by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from alkali metal carbonates and alkali metal hydrogencarbonates, The pH of the reaction solution between the solution A and the gypsum-containing material and one condition selected from at least one concentration selected from a carbonate ion concentration, a bicarbonate ion concentration, and a calcium ion concentration in the reaction solution are monitored to determine the end point of the reaction. A method for controlling the gypsum conversion reaction.

[0007] Furthermore, the present invention provides the following method for controlling a gypsum conversion reaction as a preferred embodiment. 2. The method for controlling a gypsum conversion reaction according to the above item 1, wherein the gypsum-containing material is continuously or intermittently supplied to solution A containing the alkali metal salt A. 3. The method for controlling a gypsum conversion reaction according to the above item 1, wherein solution A containing the alkali metal salt A is continuously or intermittently supplied to the gypsum-containing material. 4. The method for controlling a gypsum conversion reaction according to the above item 1, wherein the solution A containing the alkali metal salt A is a solution obtained by electrolyzing a salt solution by bipolar electrodialysis to prepare an alkaline solution, and contacting the alkaline solution with a gas containing carbon dioxide. 5. The method for controlling a gypsum conversion reaction according to the above item 4, wherein the salt solution is solution B containing alkali metal salt B. 6. The method for controlling a gypsum conversion reaction according to the above item 5, wherein the alkali metal salt B is at least one metal salt selected from the group consisting of alkali metal chlorides, alkali metal sulfates and alkali metal nitrates. 7. The method for controlling a gypsum conversion reaction according to the above item 5, wherein the alkali metal of the alkali metal salt B is the same as the alkali metal of the alkali metal salt A. 8. The method for controlling a gypsum conversion reaction according to the above item 1, wherein the alkali metal of the alkali metal salt A is at least one metal selected from sodium and potassium.

[0008] The present invention also provides the following method for producing calcium carbonate. 9. A gypsum conversion reaction is carried out by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from an alkali metal carbonate and an alkali metal hydrogencarbonate, The gypsum conversion reaction is terminated by monitoring one condition selected from the pH of the reaction liquid between the solution A and the gypsum-containing material and at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction liquid, and determining an end point of the reaction. A method for producing calcium carbonate. Effect of the Invention

[0009] According to the present invention, it is possible to provide a method for controlling a gypsum conversion reaction and a method for producing calcium carbonate, which have high versatility that can be applied to a wide variety of materials and can be implemented with minor and easy operations. [Brief description of the drawings]

[0010] [Figure 1] 1 is a graph showing the results of Example 1. [Diagram 2] 1 is a graph showing the results of Example 2. [Diagram 3] 13 is a graph showing a simulation result of Example 3. [Figure 4] 11 is a graph showing the pH of a reaction solution from the simulation results of Example 3. [Diagram 5] 13 is a graph showing the pH of a reaction solution from the simulation results of Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described below. The present invention is not limited to the following embodiment, and can be modified as desired within the scope that does not impair the effects of the invention. In this specification, the numbers associated with "greater than or equal to," "less than or equal to," and "to" in describing a numerical range are numbers that can be combined in any way. For example, when a certain numerical range is described as "CC-DD" and "EE-FF," the numerical ranges "CC-FF" and "EE-DD" are also included.

[0012] [Method of controlling gypsum conversion reaction] The method for controlling a gypsum conversion reaction of the present embodiment includes the steps of: In a gypsum conversion reaction for obtaining calcium carbonate by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from alkali metal carbonates and alkali metal hydrogencarbonates, The pH of the reaction liquid between the solution A and the gypsum-containing material and one condition selected from at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction liquid are monitored to determine the end point of the reaction.

[0013] The applicant has been conducting research into the reuse of gypsum-containing materials that are mainly discarded as industrial waste, and has noticed that calcium carbonate, a valuable material, can be obtained by reacting gypsum contained in the gypsum-containing materials with an alkali metal salt.The applicant then wondered whether it would be possible to use an alkali metal salt (e.g., an alkali metal carbonate) that is by-produced in a business establishment as the alkali metal salt.

[0014] However, the concentration of gypsum-containing materials and alkali metal salts that are usually by-produced in the form of a solution is almost always unknown. For example, in the case of gypsum-containing materials, especially in the case of gypsum-containing materials that are considered waste, the amount of gypsum contained therein is almost always unknown, and the alkali metal salts that are replicated in the business are usually by-produced as solutions, but their concentrations vary and are almost always unknown. In addition, examples of alkali metal salts that are by-produced in the business include alkali metal carbonates and alkali metal hydrogen carbonates, and these may be produced alone or as a mixture. Furthermore, alkali metal salts such as alkali metal carbonates and alkali metal hydrogen carbonates are not limited to those produced by-produced in the business, and those generated outside the business may be brought in, but even in such cases, the concentration is often unknown.

[0015] In this way, when it is necessary to use a raw material whose properties are unknown and to react a gypsum-containing material with a solution containing an alkali metal salt, it is necessary to measure the concentrations of gypsum and alkali metal salt contained in each and supply them in equal amounts. In addition, it may be necessary to identify the type of alkali metal salt. However, these operations are complicated and have low productivity.

[0016] As a method for treating gypsum-containing waste, for example, the above-mentioned Patent Document 1 focuses on separating and recovering high-purity gypsum and base paper for gypsum board from waste gypsum board material. However, it does not focus on converting gypsum-containing materials into other valuable materials through chemical reactions. Also, Patent Document 2 focuses on the chemical reaction between industrial waste such as gypsum board and ammonia and carbon dioxide. However, the chemical reaction focused on in Patent Document 2 is extremely slow, in which various raw materials are placed in a container in a predetermined ratio, stirred and mixed, sealed with a lid, and left for 1 to 3 months while stirring once every 2 to 3 days (Patent Document 2, paragraph

[0024] ). Therefore, it is not necessary to identify the type of raw material in advance and measure its concentration.

[0017] Under such circumstances, the present inventors have focused on the pH of a reaction liquid between a solution containing at least one alkali metal salt selected from alkali metal carbonates and alkali metal hydrogencarbonates and a gypsum-containing material, and the carbonate ion concentration, hydrogencarbonate ion concentration, and calcium ion concentration in the reaction liquid in a gypsum conversion reaction in which calcium carbonate is obtained by contacting a gypsum-containing material with a solution containing at least one alkali metal salt selected from alkali metal carbonates and alkali metal hydrogencarbonates.The inventors have then provided a method for controlling a gypsum conversion reaction and a method for producing calcium carbonate, which are highly versatile and applicable to a wide variety of materials and can be handled with minor and easy operations by monitoring one condition selected from the above pH and concentrations and determining the end point of the reaction.

[0018] The method for controlling the gypsum conversion reaction of this embodiment will be described starting from the gypsum conversion reaction.

[0019] [Gypsum Conversion Reaction] The gypsum conversion reaction is a reaction in which a gypsum-containing material is contacted with solution A containing at least one alkali metal salt A selected from alkali metal carbonates and alkali metal hydrogencarbonates. In this reaction, the alkali metal salt A contained in solution A reacts with the gypsum contained in the gypsum-containing material to produce calcium carbonate.

[0020] (Gypsum-containing material) The gypsum-containing material can be used without any particular limitation as long as it is a material containing gypsum, which is a material mainly composed of at least one of calcium sulfate and calcium sulfate hydrate. Calcium sulfate is an anhydride, and is called anhydrous gypsum. Examples of calcium sulfate hydrates include dihydrates called dihydrate gypsum and 1 / 2 hydrates called hemihydrate gypsum. As for anhydrides, for example, by calcining the hydrates, soluble anhydrous gypsum (also called "type II anhydrous gypsum"), insoluble anhydrous gypsum (also called "type II anhydrous gypsum"), and even calcined gypsum of α-type, β-type, etc., are available, and any of these anhydrides can be used. In the control method of this embodiment, either the anhydride or the hydrate can be used.

[0021] Further, examples of gypsum-containing materials include products using gypsum, such as gypsum board and waste gypsum board, or waste products thereof, as well as by-products produced in the production process of chemical products, such as recovered products from flue gas desulfurization treatment (also referred to as "flue gas desulfurization gypsum" and, for example, a product recovered during flue gas desulfurization treatment in copper refining, etc.), hydrofluoric gypsum (a by-product in the process of producing hydrogen fluoride), phosphate gypsum (a by-product in the process of producing wet phosphoric acid), titanic gypsum (a by-product in the process of producing titanium oxide), and active silicate gypsum (a by-product in the process of producing active silicic acid).

[0022] In addition, for example, incineration ash generated during the incineration process of municipal waste contains anhydrous gypsum. Therefore, waste such as incineration ash can also be used as a gypsum-containing material. As another waste, gypsum-containing sludge obtained in various wastewater treatment processes can also be used as a gypsum-containing material. As described above, in the method for fixing carbon dioxide which is one embodiment of the present invention, in addition to gypsum itself, a wide variety of waste materials and by-products can be used as the gypsum-containing material.

[0023] As described above, the gypsum-containing material is a material containing gypsum, which is composed mainly of at least one of calcium sulfate and calcium sulfate hydrate. By contacting the gypsum-containing material with the above-mentioned solution, a reaction occurs between calcium sulfate and the alkali metal salt contained in the above-mentioned solution. More specifically, in the gypsum conversion reaction, the reactions shown in the following reaction formulas (1) and (2) proceed. Ma2CO3+CaSO4→CaCO3+Ma2SO4(1) 2MaHCO3+CaSO4→CaCO3+Ma2SO4+CO2+H2O (2) (In the above reaction formulas (1) and (2), Ma represents an alkali metal.)

[0024] The gypsum contained in the gypsum-containing material is converted to calcium carbonate by the reactions shown in the above reaction formulas (1) and (2). The resulting calcium carbonate is a valuable material that can be used in cement compositions, materials for mortar and concrete, fillers, building materials, etc. Therefore, the gypsum conversion reaction can also be said to be a reaction for producing calcium carbonate.

[0025] As will be described in the examples below, when an alkali metal salt is added in an amount equal to the calcium sulfate contained in the gypsum-containing material, or when a gypsum-containing material containing calcium sulfate in an amount equal to the alkali metal salt is added, the gypsum conversion reaction proceeds all at once before and after the addition of the equal amount. Therefore, the alkali metal salt added after the gypsum conversion reaction proceeds remains as a surplus and is disposed of. On the other hand, the gypsum-containing material added after the gypsum conversion reaction proceeds remains as a surplus, and becomes an impurity when calcium carbonate is used. According to the control method of this embodiment, in the gypsum conversion reaction, which is a fast-acting reaction, the gypsum-containing material and the alkali metal salt can be brought into contact with each other without excess or deficiency by minor measures and easy work, regardless of the type of material used.

[0026] The amount of gypsum contained in a gypsum-containing material cannot be generalized because it can vary depending on whether the gypsum is present in the form of anhydrous gypsum or a hydrate (gypsum dihydrate or hemihydrate) and also depending on whether the gypsum, by-products, or waste material is used as the gypsum-containing material. Gypsum may be contained in a small amount in the gypsum-containing material, or may be contained in a large amount, and in either case, it can be subject to the control method of this embodiment, but the content as calcium sulfate (anhydride) is usually 1 mass% or more, 3 mass% or more, or 5 mass% or more. There is no particular upper limit, and the total amount (i.e., 100 mass%) may be gypsum, and it is usually 97 mass% or less, 95 mass% or less, or 90 mass% or less. The types of gypsum-containing materials and the content of gypsum in gypsum-containing materials are diverse and unknown, but the control method of this embodiment can be used to widely handle such gypsum-containing materials.

[0027] (Alkali metal salt A) In the gypsum conversion reaction, the alkali metal salt A to be reacted with the gypsum-containing material is at least one alkali metal salt selected from alkali metal carbonates and alkali metal hydrogencarbonates (hereinafter, the alkali metal carbonates and alkali metal hydrogencarbonates are also collectively referred to as "alkali metal carbonates, etc.").

[0028] The control method of this embodiment can be applied without any particular limitation to any alkali metal salt A such as carbonate containing the above alkali metal, and is preferably used for the alkali metal such as lithium (Li), potassium (K), or sodium (Na), more preferably potassium (K), sodium (Na), and even more preferably sodium (Na). The above alkali metal salt A (alkali metal carbonate, etc.) is produced in large quantities both inside and outside the business premises, and the gypsum conversion reaction using the above alkali metal salt A (alkali metal carbonate, etc.) proceeds quickly, so that the control method of this embodiment can be more effectively utilized.

[0029] The solution containing the above-mentioned alkali metal salt A (alkali metal carbonate, etc.) may be, for example, a solution produced inside or outside the business premises, or a surplus solution of a produced solution. Such a solution may be, for example, a solution containing an alkali metal carbonate, etc. obtained by reacting an alkali metal salt, such as an alkali metal hydroxide, with carbon dioxide, as the alkali metal salt A. Such a solution may be, for example, a solution obtained by reacting an alkali solution (i.e., a solution containing a salt, such as an alkali metal hydroxide) with a gas containing carbon dioxide.

[0030] The alkaline solution may be, for example, an aqueous solution of an alkali metal salt such as an alkali hydroxide produced in various devices such as an electrolysis device for an aqueous solution of an alkali metal salt such as an alkali metal chloride, or a hydration reaction device for a solid alkali metal hydroxide. A solution A containing an alkali metal salt A, which is at least one type of alkali metal carbonate selected from alkali metal carbonates and alkali metal hydrogen carbonates, is obtained by reacting an aqueous solution of an alkali metal salt such as an alkali hydroxide with carbon dioxide. In this case, the obtained solution A containing the alkali metal salt A is an aqueous solution, and in the control method of this embodiment, it is preferable that the solution A is an aqueous solution.

[0031] As the solution containing an alkali metal salt, a solution obtained by reacting an alkali solution obtained by an electrolysis device using an ion exchange membrane method with a gas containing carbon dioxide, and a solution obtained by bipolar membrane electrodialysis with a gas containing carbon dioxide are also preferred, because the alkali solution can be obtained with low energy. Here, the alkali solution is the above-mentioned alkali solution, that is, an aqueous solution of an alkali metal salt such as an alkali metal chloride. The content of the alkali metal salt A in the solution obtained by any of the above methods is often unknown. Therefore, it is preferable to use the solution obtained by the above method as solution A containing the alkali metal salt A, in that the control method of this embodiment can be effectively utilized.

[0032] Among the above, it is preferable to use solution A containing an alkali metal salt A obtained by bipolar membrane electrodialysis, since an alkaline solution can be obtained with low energy. The method using bipolar membrane electrodialysis is a method in which an alkaline solution is prepared by electrolyzing a salt solution by bipolar membrane electrodialysis, and the alkaline solution is brought into contact with a gas containing carbon dioxide, thereby obtaining solution A containing the alkali metal salt A. The bipolar electrodialysis produces, as a by-product, an acid solution corresponding to the alkali metal salt contained in the salt solution (hydrochloric acid when the alkali metal chloride is used) together with the alkaline solution.

[0033] The salt solution is preferably a solution (hereinafter also referred to as "solution B") containing a salt containing an alkali metal, such as an alkali metal chloride, an alkali metal sulfate, an alkali metal nitrate, etc. (hereinafter also referred to as "alkali metal salt B"). These alkali metal salts may be used alone or in combination. In a method using bipolar membrane electrodialysis, the alkali metal of the alkali metal salt B and the alkali metal of the alkali metal salt A are the same. When a solution containing these alkali metal salts B is used as a salt solution, an alkali solution containing a hydroxide of the alkali metal of the alkali metal salt B is obtained by electrolyzing the salt solution by bipolar membrane electrodialysis, and the alkali solution is brought into contact with a gas containing carbon dioxide to produce a carbonate or hydrogen carbonate of the alkali metal of the alkali metal salt B, thereby obtaining a solution A containing the alkali metal salt A.

[0034] As described above, the content of alkali metal salt A in solution A containing alkali metal salt A is unknown, but taking into consideration the above method and the conditions under which it is obtained inside and outside the business premises, it is usually 0.1 mol / L or more, 0.3 mol / L or more, or 0.5 mol / L or more, with the upper limit being 2 mol / L or less, 1.5 mol / L or less, 1.3 mol / L or less, or 1.0 mol / L or less. The content of alkali metal salt A in solution A containing alkali metal salt A varies widely and is unknown, but the control method of this embodiment can be used to deal with a wide variety of such solutions A.

[0035] (contact) In the control method of the present embodiment, the gypsum conversion reaction is carried out by contacting the gypsum-containing material with solution A containing an alkali metal salt A. By contacting the gypsum-containing material with solution A containing an alkali metal salt A, a reaction occurs between the alkali metal salt A and the gypsum contained in the gypsum-containing material, and calcium carbonate is obtained.

[0036] In the control method of the present embodiment, the contact method is not particularly limited as long as the gypsum-containing material can be contacted with the solution A containing the alkali metal salt A. For example, the contact can be performed while the gypsum-containing material is continuously or intermittently supplied to the solution A containing the alkali metal salt A, or while the solution A containing the alkali metal salt A is continuously or intermittently supplied to the gypsum-containing material.

[0037] When the contact is performed while continuously or intermittently supplying the gypsum-containing material to solution A containing an alkali metal salt A, a certain amount of solution A may be stored in a reaction tank, and the gypsum-containing material may be continuously or intermittently supplied to the reaction tank. The gypsum-containing material may be pulverized to a predetermined size and supplied in consideration of ease of supply, ease of reaction, etc. Examples of the gypsum-containing material include material passing through a 5 mm sieve, material passing through a 10 mm sieve, material passing through a 15 mm sieve, material passing through a 30 mm sieve, and material passing through a 50 mm sieve.

[0038] In consideration of ease of supply and control of the supply amount, the gypsum-containing material can be supplied using, for example, a powder / granular material constant-volume supply device, a hopper equipped with a damper, or the like.

[0039] In addition, the amount of solution A stored in the reaction tank cannot be generally stated because it depends on the treatment amount and size of the gypsum-containing material, the size of the reaction tank, etc., but it is preferable that the depth of solution A stored in the reaction tank is a depth that covers the entire surface of the gypsum-containing material, i.e., is equal to or greater than the size of the gypsum-containing material.

[0040] The size of the gypsum-containing material in the case where the contact is performed while continuously or intermittently supplying solution A containing an alkali metal salt A to the gypsum-containing material is similar to the case where the contact is performed while continuously or intermittently supplying the gypsum-containing material.

[0041] Considering ease of supply and control of the amount of solution A supplied, solution A can be supplied using a liquid constant-amount supplying device or the like.

[0042] [Determination of the reaction end point] The method for controlling a gypsum conversion reaction of the present embodiment is characterized in that, in the gypsum conversion reaction, one condition selected from the pH of a reaction liquid between the solution A and the gypsum-containing material and at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction liquid is monitored, and an end point of the reaction is determined. By monitoring one condition selected from the pH and the concentration and determining the end point of the reaction, the method has high versatility applicable to a wide variety of materials, and can be handled with minor measures and easy work.

[0043] When the above-mentioned solution A is brought into contact with a gypsum-containing material, the pH of the reaction solution and the concentrations of carbonate ion, bicarbonate ion, and calcium ion vary with an increase in the amount of solution A and the gypsum-containing material in contact with each other.

[0044] (Continuous or intermittent supply of gypsum-containing material) When the contact is performed while continuously or intermittently supplying a gypsum-containing material to solution A containing an alkali metal salt A, as the amount of the gypsum-containing material supplied increases, the pH of the reaction solution decreases, the carbonate ion concentration and the hydrogen carbonate ion concentration decrease, and the calcium ion concentration increases.

[0045] As shown in Example 1 described later, when the reaction starts, that is, when the supply of the gypsum-containing material starts, the pH of the reaction solution gradually decreases, and when the gypsum-containing material (more strictly speaking, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equal to the alkali metal salt A in solution A, the pH of the reaction solution suddenly decreases, and even if the gypsum-containing material is supplied thereafter, the pH of the reaction solution hardly changes. The gypsum-containing material supplied after the above-mentioned sudden decrease does not contribute to the reaction and remains as a surplus, and becomes an impurity when calcium carbonate is used. Therefore, in the control method of this embodiment, when the pH of the reaction solution is monitored while the gypsum-containing material is continuously or intermittently supplied, the end point of the reaction is determined to be the point at which the pH suddenly changes.

[0046] It is considered that the behavior of at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction solution also changes rapidly when gypsum (calcium sulfate) contained in the gypsum-containing material is supplied, based on the results of Example 3 described later. When a gypsum-containing material is supplied, the carbonate ions in the reaction solution gradually decrease when the reaction starts, and rapidly decrease when the gypsum-containing material (more strictly, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equivalent to the alkali metal salt A in solution A, and thereafter, even if the gypsum-containing material is supplied, there is little change. In addition, the bicarbonate ions and calcium ions in the reaction solution gradually increase when the reaction starts, and rapidly increase when the gypsum-containing material (more strictly, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equivalent to the alkali metal salt A in solution A, and thereafter, even if the gypsum-containing material is supplied, there is little change. Therefore, in the control method of the present embodiment, when at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction solution is monitored while the gypsum-containing material is continuously or intermittently supplied, the end point of the reaction is determined to be the time point at which these concentrations suddenly change (increase or decrease).

[0047] A sudden decrease in the pH of the reaction solution and a sudden change in the various concentrations described above can be judged by monitoring the amount of change per unit time or per unit supply amount. The unit time and unit supply amount cannot be generalized because they can vary depending on the supply amounts of solution A and the gypsum-containing material subjected to the gypsum conversion reaction, the contents of alkali metal A and gypsum, etc., but in consideration of the ease of judging a sudden decrease in the pH of the reaction solution and a sudden change in the various concentrations described above, it is advisable to select the following ranges as a guide.

[0048] The unit time may be selected from the range of 15 seconds or more, 30 seconds or more, 45 seconds or more, 1 minute or more, 2 minutes or more, 3 minutes or more, and 5 minutes or more as the lower limit, and 10 minutes or less, 9 minutes or less, 8 minutes or less, and 7 minutes or less as the upper limit. Also, taking into consideration the same as the above unit time, the unit supply amount may be selected from the range of 10 g or more, 25 g or more, 50 g or more, 75 g or more, and 90 g or more as the lower limit, and 300 g or less, 250 g or less, 200 g or less, 175 g or less, and 150 g or less as the upper limit.

[0049] The rapid change in the reaction solution is determined by the pH of the reaction solution, more specifically, by the nth pH change per unit time or per unit supply amount (pH n , n indicates the number of times and is an integer.) and the previous pH (pH n-1 ) and the ratio of change in pH n / pH n-1 ) should be used as a guideline for determining whether a sudden change has occurred when it is 96.0% or less, 95.0% or less, 94.0% or less, 93.0% or less, or 92.0% or less.

[0050] As shown in Example 1, a slope of the pH change (d(pH) / dW) obtained by dividing the amount of pH change (d(pH)) by the amount of gypsum-containing material supplied when the change was reached (dW) can be used as a guide to determine whether a rapid change has occurred. The slope of the pH change (d(pH) / dW) may be determined by calculating, for example, the amount of gypsum-containing material (dW) as the unit supply amount, from the corresponding amount of pH change (d(pH)).

[0051] Furthermore, as shown in FIG. 1 of Example 1, when there is a point at which the amount of change in pH clearly becomes large (the point at which the amount of the gypsum-containing material added is changed from 875 g to 1000 g in FIG. 1), the point can be determined as the end point of the reaction without taking into consideration the rate and slope of the amount of change in pH.

[0052] When determining based on the above various concentrations, the sudden change is, more specifically, when the concentration is carbonate ion, the nth concentration (C(X1)n , X1 is a carbonate ion, and n is the number of times and is an integer.) and the previous one (C(X1) n-1 ) and the rate of change of (C(X1) n / C(X1) n-1 ) should be used as a guideline for determining whether a sudden change has occurred when it is 93.0% or less, 90.0% or less, 85.0% or less, or 80.0% or less. As with the pH of the reaction liquid, the amount of change in carbonate ion concentration can be determined based on the slope of the amount of change in concentration obtained by dividing the amount of gypsum-containing material supplied when the amount of change was reached. Alternatively, when there is a point at which the amount of change clearly becomes large, the point can be determined as the end point of the reaction without considering the rate of the amount of change.

[0053] In the case of bicarbonate ion and calcium ion, the concentration (C(X2)) for the nth time per unit time or per unit supply amount is n , X2 is a hydrogen carbonate ion or a calcium ion, and n indicates the number of times and is an integer.) and the previous time (C(X2) n-1 ) and the rate of change of (C(X2) n / C(X2) n-1 ) can be used as a guideline for determining whether a change has occurred rapidly. Similarly to the pH of the reaction solution, the end point of the reaction can also be determined based on the slope of the change in concentration obtained by dividing the amount of change in concentration of bicarbonate ions and calcium ions by the amount of the gypsum-containing material supplied when the change in concentration was reached. Also, when there is a point at which the change in concentration clearly becomes large, the end point of the reaction can be determined as the point without considering the rate of the change.

[0054] As shown in Example 1, there are cases where the above-mentioned criteria for judging a rapid change are met at multiple points, and the reaction can be judged to be at its end point. In this case, it is preferable to terminate the reaction at the first point met, but the reaction may also be terminated at the last point met.

[0055] The supply amount of the gypsum-containing material is not particularly limited because it can vary depending on the amount of gypsum contained in the gypsum-containing material and the content of the alkali metal salt A in solution A. In consideration of the ease of judging a sudden decrease in pH of the reaction liquid and a sudden change in the above various concentrations, when the gypsum-containing material is continuously supplied, it is preferable to adopt, as a guideline for the supply amount of the gypsum-containing material, a range of 1 g / min or more, 3 g / min or more, 5 g / min or more, 10 g / min or more, and 15 g / min or more as lower limits and 50 g / min or less, 40 g / min or less, 30 g / min or less, and 25 g / min or less as upper limits relative to a volume of 10 L of solution A. In addition, when the supply is intermittent, the supply amount should correspond to the supply speed and unit time in the case of continuous supply, for example, 1 g or more (corresponding to the above-mentioned "1 g / min or more"), 3 g or more (corresponding to the above-mentioned "3 g / min or more") for a unit time of 1 minute, and 2 g or more (corresponding to the above-mentioned "1 g / min or more"), 6 g or more (corresponding to the above-mentioned "3 g / min or more") for a unit time of 2 minutes.

[0056] (Solution A is supplied continuously or intermittently) When the contact is performed while continuously or intermittently supplying solution A containing alkali metal salt A to the gypsum-containing material, as the amount of the gypsum-containing material supplied increases, the pH of the reaction solution increases, the carbonate ion concentration and bicarbonate ion concentration increase, and the calcium ion concentration decreases.

[0057] As shown in Example 2 described later, when the reaction starts, that is, when the supply of solution A starts, the pH of the reaction solution gradually increases, and when a gypsum-containing material (more strictly, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equal to the alkali metal salt A in solution A, the pH of the reaction solution increases rapidly, and when solution A is supplied thereafter, the pH of the reaction solution gradually increases again. The pH of the reaction solution after the above-mentioned rapid increase increases with the supply of solution A, but the increase in pH means that the pH increases to approach the pH of solution A. For this reason, solution A supplied after the rapid increase in pH does not contribute to the reaction and remains as a surplus, and is wasted. Therefore, in the control method of this embodiment, when the pH of the reaction solution is monitored while continuously or intermittently supplying solution A, the end point of the reaction is determined to be the point at which the pH changes rapidly.

[0058] It is considered that the behavior of at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction solution also changes rapidly when gypsum (calcium sulfate) contained in the gypsum-containing material is supplied, based on the results of Example 3 described later. When solution A is supplied, the carbonate ions in the reaction solution gradually increase when the reaction starts, and rapidly increase when the gypsum-containing material (more strictly, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equivalent to the alkali metal salt A in solution A, and thereafter, even if the gypsum-containing material is supplied, there is little change. In addition, the bicarbonate ions and calcium ions in the reaction solution gradually decrease when the reaction starts, and rapidly decrease when the gypsum-containing material (more strictly, gypsum (calcium sulfate) contained in the gypsum-containing material) is supplied in an amount equivalent to the alkali metal salt A in solution A, and thereafter, even if the gypsum-containing material is supplied, there is little change. Therefore, in the control method of this embodiment, when solution A is supplied continuously or intermittently and at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction solution is monitored, the end point of the reaction is determined to be the point at which these concentrations suddenly change (increase or decrease).

[0059] A sudden decrease in the pH of the reaction solution and a sudden change in the various concentrations described above when solution A is supplied continuously or intermittently can be determined in the same manner as in the case where the gypsum-containing material is supplied continuously or intermittently.

[0060] The unit time is the same as that in the case of continuously or intermittently supplying the gypsum-containing material. The unit supply amount may be selected from the ranges of 0.1 L or more, 0.2 L or more, 0.3 L or more, and 0.5 L or more as the lower limit, and 10.0 L or less, 8.0 L or less, 6.0 L or less, 5.0 L or less, and 3.5 L or less as the upper limit.

[0061] When solution A is supplied continuously or intermittently, a sudden decrease in the pH of the reaction solution and a sudden change in the various concentrations can be determined by monitoring the amount of change per unit time or per unit supply amount, as in the case of supplying the gypsum-containing material continuously or intermittently. The unit time and unit supply amount cannot be generalized because they can vary depending on the supply amounts of solution A and the gypsum-containing material supplied to the gypsum conversion reaction, the contents of alkali metal A and gypsum, etc., but in consideration of the ease of determining a sudden decrease in the pH of the reaction solution and a sudden change in the various concentrations, the following ranges can be selected as a guide.

[0062] The rapid change in the reaction solution is determined by the pH of the reaction solution, more specifically, by the nth pH change per unit time or per unit supply amount (pH n , n indicates the number of times and is an integer.) and the previous pH (pH n-1 ) and the ratio of change in pH n / pH n-1 ) can be used as a guideline for determining whether a sudden change has occurred when the index of change is 103.0% or more, 105.0% or more, 106.0% or more, 107.0% or more, 108.0% or more, or 108.2% or more.

[0063] As shown in Example 2, the slope of the pH change (d(pH) / dV) obtained by dividing the amount of pH change (d(pH)) by the amount of solution A supplied when the change was reached (dV) can be used as a guide to determine whether a change is rapid. The slope of the pH change (d(pH) / dV) may be determined by calculating, for example, the amount of solution A (dV) as the unit supply amount, from the corresponding amount of pH change (d(pH)).

[0064] As shown in FIG. 2 of Example 2, when there is a point at which the gradient of the pH change clearly becomes large (the point at which the amount of solution A added changes from 10 L to 11 L in FIG. 2), the point can be determined as the end point of the reaction without taking into consideration the rate and gradient of the pH change.

[0065] More specifically, when the concentration is hydrogen carbonate ion or calcium ion, the sudden change is determined by the nth concentration (C(Y1)) per unit time or per unit supply amount. n , Y1 is a hydrogen carbonate ion or a calcium ion, and n indicates the number of times and is an integer.) and the previous time (C(Y1) n-1 ) and the rate of change (C(Y1) n / C(Y1) n-1 ) should be considered as a guideline for determining whether a change has occurred rapidly. Similarly to the pH of the reaction solution, the change in concentration of bicarbonate ions and calcium ions can be determined from the slope of the change in concentration, calculated by dividing the change in concentration by the amount of Solution A supplied when the change in concentration was reached. If there is a point at which the change in concentration clearly becomes large, the point can be determined as the end point of the reaction without taking into account the rate of change in concentration.

[0066] In the case of carbonate ions, the concentration (C(Y2)) for the nth time per unit time or per unit supply amount is n , Y2 is a carbonate ion, and n indicates the number of times and is an integer.) and the previous one (C(Y2) n-1 ) and the rate of change (C(Y2) n / C(Y2) n-1 ) can be used as a guideline for determining whether a change has occurred rapidly. Similarly to the pH of the reaction solution, the change in carbonate ion concentration can be determined from the slope of the change in concentration obtained by dividing the change in concentration by the amount of solution A supplied when that change was reached. If there is a point at which the change is clearly large, that point can be determined as the end point of the reaction without taking into account the rate of change.

[0067] The supply amount of solution A is not particularly limited because it can vary depending on the amount of alkali metal salt A contained in solution A and the gypsum content in the gypsum-containing material. In consideration of the ease of judging a sudden decrease in pH of the reaction liquid and a sudden change in the above various concentrations, when solution A is continuously supplied, it is preferable to adopt, as a guideline for the supply amount of solution A, a range of 0.1 L / min or more, 0.2 L / min or more, 0.3 L / min or more, 0.5 L / min or more, and 1.0 L / min or more as lower limits and 10.0 L / min or less, 8.0 L / min or less, 6.0 L / min or less, and 5.0 L / min or less as upper limits per 1 kg of the mass of the gypsum-containing material. In addition, when the liquid is supplied intermittently, the supply amount should correspond to the supply rate and unit time of the continuous supply, for example, 0.1 L or more, 0.2 or more when the unit time is 1 minute, and 0.3 L or more, 0.5 L or more when the unit time is 2 minutes.

[0068] In the control method of this embodiment, the pH of the reaction solution may be continuously measured by an online pH meter, or may be sampled and measured each time. The concentrations of carbonate ions, hydrogen carbonate ions, and calcium ions in the reaction solution may be continuously measured by an online TOC meter or the like, or may be sampled and measured each time.

[0069] [Calcium carbonate manufacturing method] The method for producing calcium carbonate according to the present embodiment includes the steps of: The method includes carrying out a gypsum conversion reaction by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from an alkali metal carbonate and an alkali metal hydrogencarbonate, The gypsum conversion reaction is terminated by monitoring one condition selected from the pH of the reaction liquid between the solution A and the gypsum-containing material and at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction liquid, and determining an end point of the reaction.

[0070] According to the method for producing calcium carbonate of the present embodiment, the method has high versatility that can be applied to a wide variety of materials, can be applied with minor measures and easy operations, and can perform a gypsum conversion reaction without excess or deficiency, so that calcium carbonate can be produced efficiently.

[0071] As described above, the gypsum conversion reaction is a reaction in which a gypsum-containing material is brought into contact with solution A containing at least one alkali metal salt A selected from alkali metal carbonates and alkali metal hydrogencarbonates, and the alkali metal salt A contained in solution A reacts with the gypsum contained in the gypsum-containing material to produce calcium carbonate.

[0072] In the method for producing calcium carbonate of the present embodiment, the gypsum conversion reaction, the alkali metal salt A used in the reaction, the solution A containing the same, the gypsum-containing substance, and the contacting method are as described above in the control method of the present embodiment. In addition, the pH of the reaction solution, at least one concentration selected from the carbonate ion concentration, the bicarbonate ion concentration, and the calcium ion concentration in the reaction solution, or one condition selected from these is monitored to determine the end point of the reaction, as described in the control method of this embodiment above. EXAMPLES

[0073] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0074] Example 1 A 0.55 M aqueous sodium carbonate solution was prepared as a typical sample of solution A containing an alkali metal salt A, and gypsum dihydrate (calcium sulfate dihydrate, purity: 98%, size: 100 μm full-pass sieve product) was prepared as a gypsum-containing substance. 11.6 L of sodium carbonate aqueous solution was placed in the reaction tank, and while gypsum dihydrate was being fed at a feed rate of 20 g / min, the pH of the reaction solution was measured every time 125 g of the gypsum-containing material was fed. The measurement results are shown in Figure 1. Figure 1 also shows the amount of change in pH (d(pH) / dW).

[0075] According to Example 1, when the supply of the gypsum-containing material is started, the pH of the reaction solution immediately drops, which indicates that the gypsum conversion reaction starts immediately. Furthermore, when the supply of the gypsum-containing material is continued, the pH of the reaction solution gradually drops, and when the supply amount reaches 900 g or more and 1000 g, the pH drops sharply. The pH further drops to the same extent until the supply amount reaches 1200 g, and even if the gypsum-containing material is further supplied, there is almost no change in the pH of the reaction solution.

[0076] In Example 1, the end point of the gypsum conversion reaction can be determined as the end point of the reaction when the amount of gypsum-containing material supplied is 1000 g, because the pH at the time of supplying 1000 g (the 8th time when the unit supply amount is 125 g) is 9.5 (pH8 is 9.5), and the pH at the time of supplying the previous 875 g is 10.4 (pH7 is 10.4), and the rate of change (pH8 / pH7) is 91.3%. Also, when the times of 1125 g and 1250 g are considered in the same manner as the time of 1000 g, the rate of change (pH9 / pH8) at 1125 g is 95.8% (=9.1 / 9.5), and the rate of change (pH 10 1, a clear rapid drop in pH can be confirmed when the amount of gypsum-containing material supplied is from 875 g to 1000 to 1125 to 1250 g, and therefore, the end point of the reaction can be determined to be any of the points when the amount of gypsum-containing material supplied is 1000 g, 1125 g, or 1250 g. In this way, in Example 1, the end point of the reaction can be determined at multiple points, but when actually implementing the control method of this embodiment, the reaction can be terminated at the point where the end point of the reaction is first determined.

[0077] Example 2 The solution A and gypsum-containing material used in Example 1 were used. 1,700 g of the gypsum-containing material was placed in a reaction tank, and while solution A was being supplied at a supply rate of 1.0 L / min, the pH of the reaction solution was measured every time 1 L of solution A was supplied. The measurement results are shown in Figure 2. Figure 2 also shows the amount of change in pH (d(pH) / dV).

[0078] According to Example 2, when the supply of solution A is started, the pH of the reaction solution rises immediately, which indicates that the gypsum conversion reaction starts immediately. If the supply of solution A is continued, the pH of the reaction solution gradually rises, and when the supply amount reaches 10 L or more and reaches 11 L, it rises sharply. The pH further rises at a slower rate until the supply amount reaches 14 L. If solution A is further supplied, solution A does not contribute to the reaction, so it is considered that the pH of the reaction solution approaches the pH of solution A.

[0079] In Example 2, the end point of the gypsum conversion reaction is when the supply amount of solution A reaches 11 L, and the pH at the time of supplying 11 L (the 11th time when the unit supply amount is 1 L) is 10.5 (pH 11 The pH of the previous 10L supply was 9.7 (pH 10 is 9.7), and the rate of change (pH 11 / pH 10 ) is 108.2%, which can be determined as the end point of the reaction. In addition, as shown in Figure 2, when the supply amount of solution A is increased from 10 L to 11 L, a clear rapid increase in pH can be confirmed, which can be used to determine the end point of the reaction.

[0080] Example 3 A simulation of the gypsum conversion reaction was carried out under the same conditions as in Example 2 using simulation software ("PHREEQC Ver.3 (product name)" manufactured by the United States Geological Survey). A reaction tank was charged with 1,700 g of a gypsum-containing material, and solution A was supplied at a supply rate of 1.0 L / min. Simulation results for the concentrations of carbonate ions, hydrogen carbonate ions, and calcium ions in the reaction solution were plotted every time 0.3 L was supplied. The results are shown in Fig. 3. Fig. 4 is a diagram plotting the simulation results for the pH of the reaction solution.

[0081] According to Example 3, as shown in Fig. 4, the behavior of the pH of the reaction solution is similar to that of Example 2 in which Solution A is supplied to the gypsum-containing material, and the results of the simulation are considered to be valid, including the results of the concentrations of each ion shown in Fig. 3. Therefore, it is considered that the concentrations of each ion in Example 2 behave as shown in Fig. 3 of Example 3.

[0082] Example 4 A simulation of the gypsum conversion reaction was performed under the same conditions as in Example 1 using simulation software ("PHREEQC Ver.3 (product name)" manufactured by the United States Geological Survey). 11.6 L of an aqueous sodium carbonate solution was placed in a reaction tank, and while gypsum dihydrate was being supplied at a supply rate of 20 g / min, the simulation results for the pH of the reaction solution were plotted every time 125 g of the gypsum-containing material was supplied. The results are shown in FIG. 5.

[0083] According to Example 4, as shown in FIG. 5 , the behavior of the pH of the reaction solution is similar to that of Example 1 in which a gypsum-containing material is supplied to the solution A. Similarly to the above-described Example 3, the simulation results are considered to be valid.

Claims

1. In a gypsum conversion reaction for obtaining calcium carbonate by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from alkali metal carbonates and alkali metal hydrogencarbonates, The pH of the reaction solution between the solution A and the gypsum-containing material and one condition selected from at least one concentration selected from a carbonate ion concentration, a bicarbonate ion concentration, and a calcium ion concentration in the reaction solution are monitored to determine an end point of the reaction. A method for controlling the gypsum conversion reaction.

2. The method for controlling a gypsum conversion reaction according to claim 1, wherein the gypsum-containing material is continuously or intermittently supplied to the solution A containing the alkali metal salt A.

3. The method for controlling a gypsum conversion reaction according to claim 1, wherein the solution A containing the alkali metal salt A is continuously or intermittently supplied to the gypsum-containing material.

4. 2. The method for controlling a gypsum conversion reaction according to claim 1, wherein the solution A containing the alkali metal salt A is a solution obtained by electrolyzing a salt solution by bipolar electrodialysis to prepare an alkaline solution, and contacting the alkaline solution with a gas containing carbon dioxide.

5. The method for controlling a gypsum conversion reaction according to claim 4, wherein the salt solution is solution B containing an alkali metal salt B.

6. The method for controlling a gypsum conversion reaction according to claim 5, wherein the alkali metal salt B is at least one metal salt selected from the group consisting of alkali metal chlorides, alkali metal sulfates, and alkali metal nitrates.

7. The method for controlling a gypsum conversion reaction according to claim 5, wherein the alkali metal of the alkali metal salt B is the same as the alkali metal of the alkali metal salt A.

8. 2. The method for controlling a gypsum conversion reaction according to claim 1, wherein the alkali metal of the alkali metal salt A is at least one metal selected from sodium and potassium.

9. The method includes carrying out a gypsum conversion reaction by contacting a gypsum-containing material with a solution A containing at least one alkali metal salt A selected from an alkali metal carbonate and an alkali metal hydrogencarbonate, The gypsum conversion reaction is terminated by monitoring one condition selected from the pH of a reaction liquid between the solution A and the gypsum-containing material and at least one concentration selected from a carbonate ion concentration, a bicarbonate ion concentration, and a calcium ion concentration in the reaction liquid, and determining an end point of the reaction. A method for producing calcium carbonate.

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