Crystal manufacturing method

Abstract

To provide a crystal manufacturing method by which crystals of high purity can be obtained according to a simple operation.SOLUTION: A crystal manufacturing method includes the steps of: preparing a liquid in which crystals of a target component and crystals of another component excluding the target component are deposited according to crystallization, and adding at least one out of seed crystals of the target component and seed crystals of the other component to the liquid; depositing crystals of the target component and crystals of the other component, from the liquid; and recovering the crystals of the target component.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In salt production using the ion exchange membrane method, raw seawater is concentrated using an ion exchange membrane electrodialysis device to obtain brine. Sodium chloride is precipitated and recovered from the resulting brine by heating, evaporation and crystallization. The liquid remaining after sodium chloride recovery is discharged as bittern. In addition, potassium chloride can be precipitated from bittern, and potassium chloride is used in soft drinks, processed foods, salt substitutes (reduced-salt foods), horticultural products, feed, etc.

[0003] As a method for obtaining potassium chloride from bittern used in salt production, for example, Patent Document 1 discloses a method for producing potassium chloride, which comprises cooling bittern at a high temperature using an ion exchange membrane, separating a mixed precipitate formed that is mainly composed of potassium chloride and sodium chloride, and recovering potassium chloride by dissolving and separating the precipitate from water required for dissolving the sodium chloride contained therein. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 55-56014 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the production method described in Patent Document 1 has problems in that, in order to recover potassium chloride from a mixed precipitate mainly composed of potassium chloride and sodium chloride, a step of dissolving sodium chloride contained in the precipitate in water and separating the sodium chloride is necessary, making the operation complicated and requiring equipment for dissolving sodium chloride in water and a large amount of water.

[0006] One object of the present invention, which has been made in view of the above-mentioned conventional circumstances, is to provide a method for producing crystals, which enables high-purity crystals to be obtained by a simple operation. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors to achieve the above object, they have found that a method including a simple operation of adding either or both of sodium chloride seed crystals and potassium chloride seed crystals to bittern for salt production can provide high purity potassium chloride crystals. Furthermore, the present inventors have found that such a method is useful not only in cases where potassium chloride is to be obtained from bittern for salt production, but also in any cases where a desired component is to be precipitated and recovered by crystallization from a liquid, and components other than the desired component are precipitated together with the desired component, making separation difficult, and have completed the present invention.

[0008] That is, the present invention provides the following <1> This is regarding. <1> A step of adding at least one of seed crystals of the target component and seed crystals of the other component to a liquid in which crystals of the target component and crystals of the other component other than the target component are precipitated by crystallization; A step of precipitating crystals of the target component and crystals of the other components from the liquid; and recovering the crystals of the target component. Method for producing crystals. Effect of the Invention

[0009] According to the production method of the present invention, high-purity crystals can be obtained by a simple operation. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a graph showing the particle size and component distribution measured by sieving the crystals after solid-liquid separation in Example 1. [Diagram 2]FIG. 2 is a graph showing the particle size and component distribution measured by sieving the crystals after solid-liquid separation in Example 2. [Diagram 3] FIG. 3 is a graph showing the particle size and component distribution measured by sieving the crystals after solid-liquid separation in Comparative Example 1. [Figure 4] FIG. 4 is a graph showing the relationship between the amount (g) of sodium chloride seed crystals added and the purity (%) of the resulting potassium chloride in Examples 1 to 4 and Comparative Example 1. [Diagram 5] FIG. 5 is a graph showing the relationship between the amount (g) of sodium chloride seed crystals added and the median diameter D50 (μm) of the resulting potassium chloride crystals in Examples 1 to 4 and Comparative Example 1. [Figure 6] FIG. 6 is a graph showing the particle size and component distribution measured by sieving the crystals after solid-liquid separation in Example 5. [Figure 7] FIG. 7 is a graph showing the particle size and component distribution measured by sieving the crystals after solid-liquid separation in Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to the contents thereof.

[0012] <Crystal manufacturing method> A method for producing crystals according to an embodiment of the present invention includes a step (step A) of adding at least one of a seed crystal of a target component and a seed crystal of another component to a liquid in which crystals of the target component and crystals of other components other than the target component are precipitated by crystallization, a step (step B) of precipitating crystals of the target component and crystals of the other components from the liquid, and a step (step C) of recovering the crystals of the target component.

[0013] (Process A) In the method for producing crystals of this embodiment, first, at least one of seed crystals of the target component and seed crystals of the other component is added to a liquid in which crystals of the target component and crystals of components other than the target component are precipitated by crystallization. In the following, the "liquid from which crystals of the target component and crystals of components other than the target component are precipitated by crystallization" may be simply referred to as "liquid." Also, "at least one of the seed crystals of the target component and the seed crystals of the other components" may be collectively referred to as "seed crystals."

[0014] Here, the liquid from which crystals of the target component and crystals of components other than the target component precipitate by crystallization refers to, for example, a liquid containing various ions that constitute the target component and other components in a solvent, a liquid in which the target component and other components are dissolved in a solvent, etc. Examples of such liquids include bittern in salt-making, which will be described in detail later, and solutions to be purified in the purification process of organic compounds such as amino acids and pharmaceuticals, but are not limited to these. The target component refers to a component that is ultimately desired to be recovered as crystals. Furthermore, the component other than the target component may be of only one type, or of two or more types. The solvent may be water or various organic solvents.

[0015] Examples of crystallization include crystallization by cooling, crystallization by addition of a poor solvent, crystallization by evaporation, and crystallization by reaction or precipitation.

[0016] The seed crystals added to the liquid may be either or both of crystals of a target component that precipitates from the liquid by crystallization, and crystals of a component other than the target component that precipitates from the liquid by crystallization. The components of the seed crystals and the amounts of them added are appropriately selected depending on the composition of the liquid and the type of the target component, etc.

[0017] The particle size of the seed crystals to be added is not particularly limited and may be appropriately selected, but is usually 50 to 1000 μm.

[0018] (Process B) Next, crystals of the target component and crystals of other components are precipitated from the liquid to which the seed crystals have been added. In step B, the method (crystallization method) for precipitating crystals of the target component and crystals of other components from the liquid is not particularly limited as long as the liquid is in a supersaturated state, but examples include a method for cooling the liquid (cooling method), a method for adding a poor solvent to the liquid (poor solvent method), a method for evaporating the solvent in the liquid (evaporation method), and a method using a chemical reaction (reaction method). Among these, the method for cooling the liquid (cooling method) is preferable because the degree of supersaturation is likely to be uniform within the apparatus. Two or more of these methods may be combined.

[0019] (Process C) Next, the crystals of the target component are recovered from the mixture containing the crystals of the target component precipitated in the liquid and the crystals of other components. The method for recovering the crystals of the target component is not particularly limited, but may be, for example, the following method. That is, first, a mixture containing the crystals of the target component and the crystals of the other components is separated by solid-liquid separation from the liquid after the crystals of the target component and the crystals of the other components are precipitated. Next, the crystals of the target component are separated from the mixture containing the crystals of the target component and the crystals of the other components.

[0020] Examples of methods for performing solid-liquid separation of a mixture containing crystals of the target component and crystals of other components from a liquid after precipitation of the crystals of the target component and the crystals of other components include centrifugation, filtration, and the like.

[0021] In addition, as a method for separating the crystals of the target component from a mixture containing the crystals of the target component and the crystals of other components, a known classification method may be applied regardless of whether it is dry classification or wet classification, and examples thereof include dry classification such as sieving and air classification, and wet classification such as flow classification, sedimentation classification, and centrifugal classification. In addition, when performing dry classification, the mixture obtained by solid-liquid separation from the liquid may be dried before performing dry classification. In addition, when separating the crystals of the target component by wet classification, the crystals of the target component may be dried after wet classification.

[0022] According to the method for producing crystals according to the present embodiment described above, high-purity crystals of the target component can be obtained by a simple method of adding seed crystals to a liquid, precipitating crystals of the target component or the like from the liquid, and recovering the crystals of the target component.

[0023] This is presumably due to the following reasons, but the present embodiment is not limited to these reasons.

[0024] In other words, when crystals of a target component and crystals of other components are precipitated from a liquid in which crystals of the target component and crystals of components other than the target component are precipitated by crystallization without adding seed crystals, the precipitated crystals of the target component and crystals of the other components tend to have small particle sizes and tend to aggregate to form aggregates, making it difficult to separate the crystals of the target component from the aggregates that are formed, and therefore difficult to recover high-purity crystals of the target component.

[0025] On the other hand, when seed crystals are added to a liquid in which crystals of the target component and crystals of components other than the target component are precipitated by crystallization, and then the crystals of the target component and crystals of the other components are precipitated from the liquid, the generation of new crystal nuclei of the component to which the seed crystals were added is suppressed, and the number of tiny crystals that are prone to agglomeration is reduced. For example, when seed crystals of a component other than the target component are added, the precipitation of minute crystals of the other component is suppressed, and the aggregation of the target component crystals and the other component crystals is suppressed, which is considered to enable accurate separation of the target component crystals from the other component crystals. Furthermore, when seed crystals of the target component are added, the precipitation of minute crystals of the target component is suppressed and the crystal growth of the target component using the seed crystals as nuclei is promoted, which is believed to enable accurate separation of the target component crystals from the crystals of other components. In addition, when seed crystals of the target component and seed crystals of components other than the target component are added, the precipitation of minute crystals of the target component and crystals of the other components is suppressed, and aggregation is suppressed. Therefore, it is considered that it becomes possible to separate the crystals of the target component and the crystals of the other components with high accuracy. Therefore, it is believed that it is possible to ultimately recover crystals of the target component with high purity.

[0026] In addition, the method for producing crystals according to the present embodiment is preferable in that, even when the crystals of the target component and the crystals of other components are precipitated simultaneously in at least a part of the process for precipitating the crystals of the target component and the crystals of other components from the liquid, the crystals of the target component can be obtained with high purity. This is because the effect of suppressing the generation of new crystal nuclei and reducing the number of small crystals that tend to aggregate, as described above, continues from immediately after the addition of the seed crystals until the completion of the process.

[0027] <Method of producing potassium chloride> In the following, a method for producing potassium chloride, which is one application example of the production method of this embodiment, will be described in detail. In the method for producing potassium chloride according to the present embodiment, the liquid is bittern for salt production, the target component is potassium chloride, and the other components include sodium chloride, but this does not exclude the presence of other components besides sodium chloride.

[0028] (Salt bittern) First, the salt bittern used in the method for producing potassium chloride according to the present embodiment will be described. Salt bittern is produced using brine obtained by treating seawater. For example, seawater may be treated with an ion exchange membrane electrodialysis device.

[0029] The temperature of the seawater to be treated in the ion exchange membrane electrodialysis device is usually 10 to 50°C, and preferably 15 to 35°C, from the viewpoint of improving the efficiency of electrodialysis.

[0030] From the viewpoint of efficient electrodialysis, in the ion exchange membrane electrodialysis device, the linear velocity of seawater is usually 1 to 10 cm / s, preferably 4 to 6 cm / s, and the current density is usually 1 to 5 A / dm 2 and preferably 2 to 4 A / dm 2 It is. Thus, brine is obtained from seawater.

[0031] Next, the obtained brine is heated typically at 50 to 150°C to gradually evaporate water and precipitate sodium chloride (NaCl). The precipitated NaCl is recovered by solid-liquid separation to obtain salt bittern. The temperature of the salt bittern immediately after it is obtained is typically 50 to 150°C, and preferably 70 to 120°C. From the viewpoint of more efficiently obtaining high-purity potassium chloride (KCl), the heating is preferably carried out until the KCl concentration in the brine reaches a saturated concentration.

[0032] (Method of Producing Potassium Chloride) Next, an embodiment of the method for producing potassium chloride according to the present embodiment will be described. The method for producing potassium chloride of the present embodiment includes the following aspects 1 to 3. <Embodiment 1> A method for producing potassium chloride comprising the steps of adding sodium chloride seed crystals to salt-making bittern, precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern, and recovering the potassium chloride crystals. <Aspect 2> A method for producing potassium chloride comprising the steps of adding potassium chloride seed crystals to salt-making bittern, precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern, and recovering the potassium chloride crystals. <Embodiment 3> A method for producing potassium chloride, comprising the steps of adding potassium chloride seed crystals and sodium chloride seed crystals to salt-making bittern, precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern, and recovering the potassium chloride crystals.

[0033] Hereinafter, the method for producing potassium chloride according to embodiment 1 may be referred to as the "production method of embodiment 1," the method for producing potassium chloride according to embodiment 2 may be referred to as the "production method of embodiment 2," and the method for producing potassium chloride according to embodiment 3 may be referred to as the "production method of embodiment 3."

[0034] (Production method of embodiment 1) The manufacturing method of embodiment 1 includes a step of adding sodium chloride seed crystals to salt-making bittern (step 1-1), a step of precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern (step 1-2), and a step of recovering the potassium chloride crystals (step 1-3).

[0035] According to the production method of embodiment 1, it is possible to obtain high-purity potassium chloride (potassium chloride crystals). In addition, the particle size of the obtained potassium chloride crystals is relatively small. This is presumably due to the following reasons, but the present embodiment is not limited to these reasons. In other words, when crystals are precipitated from bittern without adding seed crystals, tiny potassium chloride crystals and sodium chloride crystals precipitate and aggregate to form aggregates, making it difficult to separate the potassium chloride crystals and sodium chloride crystals after crystallization. On the other hand, according to the manufacturing method of the first embodiment, sodium chloride seed crystals are added to bittern before crystallization. This is believed to suppress the generation of new sodium chloride crystal nuclei. In addition, the reduction in the number of small sodium chloride crystals that tend to aggregate suppresses the aggregation of potassium chloride crystals and sodium chloride crystals, making it possible to separate the potassium chloride crystals and sodium chloride crystals, and thus recovering high-purity potassium chloride. It is also believed that the addition of sodium chloride seed crystals to bittern reduces the size of the primary particles that form the potassium chloride aggregates, resulting in a relatively small particle size for the resulting potassium chloride crystals.

[0036] (Process 1-1) In step 1-1 of the manufacturing method of embodiment 1, sodium chloride seed crystals are added to salt-making bittern. Here, since salts dissolved in salt bittern are usually in a nearly saturated state, it is believed that crystals begin to precipitate early when the temperature of the salt bittern drops. Therefore, the timing for adding sodium chloride seed crystals is preferably before the temperature of the obtained salt bittern drops (before cooling the salt bittern in the case of applying a cooling method in step 1-2 described later), for example, immediately after the salt bittern is obtained. The temperature of salt bittern immediately after it is obtained is usually 50 to 150°C, and preferably 70 to 120°C, so it is preferable to add sodium chloride seed crystals to salt bittern in this temperature range, for example.

[0037] When sodium chloride seed crystals are added to bittern for salt production, the purity of the potassium chloride obtained tends to be higher as the amount of sodium chloride seed crystals added increases. This is presumably because the more sodium chloride seed crystals present, the more the generation of secondary particles of sodium chloride is suppressed. Also, the greater the addition ratio, the smaller the particle size of the potassium chloride obtained tends to be. This is presumably because the more sodium chloride seed crystals present, the more the generation of secondary particles of potassium chloride is promoted. Here, the amount of sodium chloride seed crystals added that is suitable for achieving such an effect is not particularly limited, as the suitable range is thought to differ depending on the particle size of the sodium chloride seed crystals, but for example, the ratio of sodium chloride seed crystals added per 1 L of bittern for salt production is 1 g / L or more. Although there is no particular upper limit to the amount of sodium chloride seed crystals added per 1 L of bittern, it is believed that the desired effect will be saturated even if a large amount is added. A practical upper limit to the amount of sodium chloride seed crystals added per 1 L of bittern is, for example, 200 g / L or less.

[0038] From the viewpoint of separability from potassium chloride crystals after recovery, the particle size of the sodium chloride seed crystals to be added is preferably 400 μm or more, more preferably 600 to 1000 μm, and even more preferably 850 to 1000 μm. The particle size of the sodium chloride seed crystals can be measured by a sieving method.

[0039] Furthermore, when adding sodium chloride seed crystals to bittern for salt production, it is preferable to add the sodium chloride seed crystals while stirring the bittern for salt production from the viewpoint of uniformity of the solution concentration and prevention of crystal aggregation. When stirring the bittern for salt production, an appropriate stirrer or stirring blade can be used. In addition, when stirring the bittern for salt production using a stirrer or stirring blade, a draft tube (a cylindrical body having a cylindrical shape such as a cylindrical shape or a conical shape), a wet classification layer, etc. may be used in combination. By using a draft tube, a wet classification layer, etc. in combination, the fluidity of the crystal group in steps 1-1 and 1-2 can be maintained. The stirring of the salt-making bittern may be continued during step 1-2 described below.

[0040] (Step 1-2) In step 1-2 in the manufacturing method of aspect 1, potassium chloride crystals and sodium chloride crystals are precipitated from the bittern to which the sodium chloride seed crystals have been added in step 1-1. At this time, crystals of components other than potassium chloride and sodium chloride may also be precipitated. In step 1-2, the method for precipitating potassium chloride crystals and sodium chloride crystals from bittern for salt production includes the cooling method, poor solvent method, evaporation method, reaction method, etc., which are listed in step B of the above-mentioned method for producing crystals. Two or more of these methods may be combined. Among these, the method of cooling the salt bittern (cooling method) is preferred because the degree of supersaturation is likely to be uniform within the apparatus. For example, when potassium chloride crystals and sodium chloride crystals are precipitated from salt bittern immediately after production, sodium chloride seed crystals are added to the salt bittern immediately after production in step 1-1, and the salt bittern is cooled in the subsequent step 1-2. In this case, the salt bittern is usually cooled to 0 to 50°C, preferably 0 to 35°C, and more preferably 0 to 25°C. The time required for cooling (cooling time) is usually 5 to 10 hours.

[0041] (Step 1-3) In step 1-3 of the production method of embodiment 1, potassium chloride crystals are collected. As a method for recovering potassium chloride crystals in step 1-3, the method explained for step C in the above-mentioned method for producing the crystals can be appropriately adopted. For example, first, after step 1-2, a mixture containing potassium chloride crystals and sodium chloride crystals is obtained by solid-liquid separation. Note that the mixture may contain crystals of other components and impurities in addition to the potassium chloride crystals and sodium chloride crystals. The liquid component obtained by solid-liquid separation is sometimes called potassium-free bittern. Potassium-free bittern contains bromine, magnesium, etc. Next, the potassium chloride crystals are separated and recovered from the mixture by sieving or the like.

[0042] The purity of the potassium chloride obtained by the production method of embodiment 1 is preferably 90% or more, and more preferably 95% or more. The purity of potassium chloride can be calculated by dissolving potassium chloride in a predetermined amount of water, analyzing the potassium ion concentration and sodium ion concentration of the solution by ion chromatography, and analyzing the chloride ion concentration by silver nitrate titration.

[0043] In addition, the median diameter D of the potassium chloride crystals obtained by the production method of embodiment 1 50 is, for example, 150 μm or more, and preferably 300 to 600 μm. 50 indicates the 50% particle size on a volume basis in the cumulative particle size distribution, specifically, the particle size when the integrated amount in the cumulative particle size curve of the particle size distribution measured by sieving accounts for 50% on a volume basis.

[0044] (Production method of embodiment 2) The manufacturing method of the second aspect includes a step of adding potassium chloride seed crystals to salt-making bittern (step 2-1), a step of precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern (step 2-2), and a step of recovering the potassium chloride crystals (step 2-3). According to the manufacturing method of the first aspect, high-purity potassium chloride can be obtained. Moreover, the obtained potassium chloride crystals have a sharp particle size distribution, a high proportion of single crystals, and a relatively large particle size. Note that single crystals refer to crystals that do not appear to be aggregated.

[0045] This is presumably due to the following reasons, but the present embodiment is not limited to these reasons. That is, according to the manufacturing method of embodiment 2, it is believed that by adding potassium chloride seed crystals to bittern, potassium chloride having a large particle size and high purity can be obtained. This is believed to be because the addition of potassium chloride seed crystals suppresses nucleation of potassium chloride and promotes crystal growth, resulting in a sharp particle size distribution and a tendency for potassium chloride to become large without agglomeration.

[0046] (Step 2-1) In step 2-1 of the production method of embodiment 2, potassium chloride seed crystals are added to bittern. Unless otherwise specified, the preferred embodiment for adding potassium chloride seed crystals to salt-making bittern is basically the same as the preferred embodiment for adding sodium chloride seed crystals to salt-making bittern in step 2-1 of the manufacturing method of embodiment 1.

[0047] When potassium chloride seed crystals are added to bittern for salt production, the purity of the potassium chloride obtained tends to be higher as the amount added increases. In addition, the proportion of single crystals in the potassium chloride obtained tends to be higher, and the particle size tends to be larger. Here, the amount of potassium chloride seed crystals added suitable for achieving such an effect is not particularly limited because the suitable range is thought to differ depending on the particle size of the potassium chloride seed crystals, but for example, the proportion of potassium chloride seed crystals added per 1 L of bittern for salt production is 1 g / L or more. Although there is no particular upper limit to the concentration of potassium chloride seed crystals added per 1 L of salt bittern, it is believed that the desired effect will be saturated even if a large amount is added. A practical upper limit to the amount of potassium chloride added per 1 L of salt bittern is, for example, 200 g / L or less.

[0048] From the viewpoint of separability from sodium chloride crystals, the particle size of the potassium chloride seed crystals to be added is preferably 300 μm or more, more preferably 400 to 1000 μm, and even more preferably 425 to 500 μm. The particle size of the potassium chloride seed crystals can be measured by sieving.

[0049] From the same viewpoint as in the production method of embodiment 1, it is preferable to add the potassium chloride seed crystals while stirring the salt bittern in the production method of embodiment 2. The stirring of the salt bittern may be continued during step 2-2 described below.

[0050] (Step 2-2) In step 2-2 in the production method of embodiment 2, potassium chloride crystals and sodium chloride crystals are precipitated from the salt-making bittern to which the potassium chloride seed crystals have been added in step 2-1. In addition, the specific aspects of the method for precipitating crystals from salt-making bittern in the manufacturing method of embodiment 2 are the same as those in the manufacturing method of embodiment 1, so the explanation will be omitted here.

[0051] (Step 2-3) In step 2-3 in the production method of embodiment 2, potassium chloride crystals are recovered. In addition, the specific embodiment of the method for recovering potassium chloride crystals in the production method of embodiment 2 is similar to that in the production method of embodiment 1, so the explanation will be omitted here.

[0052] The purity of the potassium chloride obtained by the production method of embodiment 2 is preferably 90% or more, and more preferably 95% or more. The method for calculating the purity of potassium chloride is the same as that explained in the production method of embodiment 1.

[0053] In addition, the median diameter D of the potassium chloride crystals obtained by the production method of the second embodiment 50 is, for example, 400 to 1000 μm, and preferably 500 to 1200 μm.

[0054] (Production method of embodiment 3) The manufacturing method of the third aspect includes a step of adding potassium chloride seed crystals and sodium chloride seed crystals to salt-making bittern (step 3-1), a step of precipitating potassium chloride crystals and sodium chloride crystals from the salt-making bittern (step 3-2), and a step of recovering the potassium chloride crystals (step 3-3). According to the manufacturing method of the third aspect, high-purity potassium chloride can be obtained. This is believed to be due to the fact that the addition of potassium chloride seed crystals and sodium chloride seed crystals suppresses the generation of secondary crystal nuclei of potassium chloride and sodium chloride, and there is almost no small potassium chloride or sodium chloride that is prone to aggregation. In addition, the resulting potassium chloride crystals have a relatively large particle size. This is believed to be due to the fact that, for the same reason, the particle size of the resulting potassium chloride crystals and sodium chloride crystals does not become smaller than the particle size of the added seed crystals.

[0055] (Step 3-1) In step 3-1 of the manufacturing method of embodiment 3, sodium chloride seed crystals and potassium chloride seed crystals are added to bittern. Unless otherwise specified, the preferred embodiment for adding sodium chloride seed crystals and potassium chloride seed crystals to salt-making bittern is basically the same as the preferred embodiment for adding sodium chloride seed crystals to salt-making bittern in step 3-1 of the manufacturing method of embodiment 1.

[0056] In the manufacturing method of the third embodiment, the suitable range of the amount of sodium chloride seed crystals to be added to the salt-making bittern is the same as that in the manufacturing method of the first embodiment. In the manufacturing method of the third embodiment, the suitable range of the amount of potassium chloride seed crystals to be added to the salt-making bittern is the same as that in the manufacturing method of the second embodiment.

[0057] From the viewpoint of separability from potassium chloride, the particle size of the sodium chloride seed crystals to be added is preferably 400 μm or more, more preferably 600 to 1000 μm, and even more preferably 850 to 1000 μm. The particle size of the sodium chloride seed crystals can be measured by sieving.

[0058] From the viewpoint of separability from sodium chloride, the particle size of the potassium chloride seed crystals to be added is preferably 300 μm or more, more preferably 400 to 1000 μm, and even more preferably 425 to 500 μm. The particle size of the potassium chloride seed crystals can be measured by sieving.

[0059] From the same viewpoint as in the manufacturing method of embodiment 1, it is preferable to add the sodium chloride seed crystals and the potassium chloride seed crystals while stirring the salt bittern in the manufacturing method of embodiment 3. The stirring of the salt bittern may be continued during step 3-2 described below.

[0060] (Step 3-2) In step 3-2 in the production method of embodiment 3, potassium chloride crystals and sodium chloride crystals are precipitated from the salt-making bittern to which the sodium chloride seed crystals and potassium chloride seed crystals have been added in step 3-1. In addition, the specific aspects of the method for precipitating crystals from salt-making bittern in the manufacturing method of embodiment 3 are the same as those in the manufacturing method of embodiment 1, so the explanation will be omitted here.

[0061] (Step 3-3) In step 3-3 in the production method of embodiment 3, potassium chloride crystals are recovered. In addition, the specific embodiment of the method for recovering potassium chloride crystals in the production method of embodiment 3 is similar to that in the production method of embodiment 1, so the explanation will be omitted here.

[0062] The purity of the potassium chloride obtained by the production method of embodiment 3 is preferably 90% or more, more preferably 95% or more. The method for calculating the purity of potassium chloride is the same as that explained in the production method of embodiment 1.

[0063] The median size of the potassium chloride crystals obtained by the production method of embodiment 3 is, for example, 200 to 600 μm, and preferably 300 to 500 μm.

[0064] According to the method for producing potassium chloride of the present embodiment described above, high-purity potassium chloride can be obtained. In the method of Patent Document 1 described in the Background Art, low-purity potassium chloride (a mixed precipitate mainly composed of potassium chloride and sodium chloride) is obtained by first cooling bittern in a cooling tank and then performing solid-liquid separation. However, since the mixed precipitate is an agglomerate, it is difficult to separate potassium chloride from it by classification. Therefore, in order to obtain potassium chloride of higher purity, it is necessary to send the mixed precipitate and water to a purification tank and purify it in the purification tank. In addition, after purification, a saturated solution of sodium chloride and potassium chloride is discharged, which is considered to become waste. In addition, the method of Patent Document 1 mentions circulating the saturated solution after purification to the salt production process, but since it is necessary to evaporate water in the salt production process in the amount added for purification, it is considered that the effect is low in principle. In addition, the method of Patent Document 1 mentions circulating the saturated solution after purification to the salt production process, but since the amount of salt bittern increases, the amount of potassium chloride and sodium chloride discharged also increases, and as a result, it is considered that the recovery rate of potassium chloride is low. On the other hand, the method for producing potassium chloride of the present embodiment is considered to have the following advantages. First, a purification step as described in Patent Document 1 is not necessary. Second, water and equipment for purification are not necessary. Third, waste material discharged after purification (saturated solution of sodium chloride and potassium chloride) can be reduced. Fourth, high-purity potassium chloride can be produced by the simple operation of adding seed crystals. These advantages also apply to the method for producing crystals of the present embodiment, which includes the method for producing potassium chloride of the present embodiment.

[0065] As described above, this specification describes the following: (1) adding at least one of seed crystals of the target component and seed crystals of the other component to a liquid in which crystals of the target component and crystals of the other component are precipitated by crystallization; A step of precipitating crystals of the target component and crystals of the other components from the liquid; and recovering the crystals of the target component. Method for producing crystals. (2) The method for producing crystals described in (1), further comprising subjecting a mixture containing crystals of the target component and crystals of the other components to solid-liquid separation from the liquid after the precipitation, and then separating the crystals of the target component from the mixture to recover the crystals of the target component. (3) A method for producing crystals described in (1) or (2), wherein in at least a part of the process of precipitating crystals of the target component and crystals of the other component from the liquid, the crystals of the target component and the crystals of the other component are precipitated simultaneously. (4) The method for producing crystals according to any one of (1) to (3), wherein the liquid is cooled to cause crystals of the target component and crystals of the other components to precipitate from the liquid. (5) The method for producing crystals according to any one of (1) to (4), wherein the liquid is salt-making bittern and the target component is potassium chloride. (6) A method for producing crystals according to (5), comprising adding potassium chloride seed crystals as seed crystals of the target component to the salt-making bittern. (7) A method for producing crystals as described in (5), in which seed crystals of sodium chloride are added to the salt-making bittern as crystals of the other component. (8) A method for producing crystals described in (5), in which potassium chloride seed crystals and sodium chloride seed crystals are added to the salt-making bittern as seed crystals of the target component and seed crystals of the other components. EXAMPLES

[0066] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0067] Example 1 A conical draft tube was installed on the top of the stirring blade of a stirring tank type crystallizer equipped with a stirring blade. 0.5 L of bittern saturated at 80 ° C was placed in the stirring tank type crystallizer, and 10 g of sodium chloride seed crystals with a particle size of 850 to 1000 μm were added while stirring at 300 rpm. That is, the ratio of sodium chloride seed crystals per 1 L of bittern was 20 g / L. After that, the liquid temperature was gradually cooled from 80 ° C to 25 ° C over 6 hours to precipitate crystals, and then solid-liquid separation was performed. The particle size distribution measured by sieving the crystals is shown in Figure 1. The color coding in the figure indicates the distribution of potassium chloride crystals and sodium chloride crystals calculated from the results of component analysis of the crystals classified by the sieve. From Figure 1, the particle size of the precipitated crystals is distributed in the range of 250 to 1180 μm, of which potassium chloride is concentrated in the range of 250 to 600 μm. In other words, if the recovered crystals are separated using a 600 μm sieve, potassium chloride with high purity can be recovered. The recovery rate of potassium chloride recovered as the 600 μm sieve, i.e., the ratio of potassium chloride separated and recovered using the sieve to the total potassium chloride contained in the precipitated crystals, was 92%, and the purity of potassium chloride was 85%. In addition, the median diameter D 50 The diameter of the grains was 446 μm, and the uniform number when approximated by the rosin Rammla distribution was 5.4. Here, the uniform number when approximated by the rosin Rammla distribution is larger, indicating that the distribution is sharper. As the above-mentioned sodium chloride seed crystals having a particle size of 850 to 1000 μm, sodium chloride seed crystals classified using a sieve with a mesh size of 1000 μm and a sieve with a mesh size of 850 μm were used. The ion concentrations in the salt-making bittern used are as follows: Ca 2+ : 23g / kg, Mg 2+ : 34g / kg, K + : 55g / kg, Na + : 26g / kg, Cl - : 225g / kg

[0068] Example 2 In Example 2, crystals were precipitated from salt bittern in the same manner as in Example 1, except that 20 g of sodium chloride seed crystals (40 g / L per 1 L of salt bittern) were added to 0.5 L of salt bittern, and solid-liquid separation was performed. The particle size and component distribution measured by sieving the crystals are shown in Figure 2. As shown in Figure 2, the particle size of the precipitated crystals is distributed in the range of 150 to 1180 μm, of which potassium chloride is concentrated in the range of 150 to 600 μm. The recovery rate of potassium chloride recovered as the 600 μm sieve was 99%, and the purity of potassium chloride was 95%. The median diameter D of the recovered potassium chloride crystals was 1.0 μm. 50 The particle size was 283 μm, and the uniformity number when approximated by the rosin Ramla distribution was 3.0.

[0069] Example 3 In Example 3, crystals were precipitated from salt bittern and subjected to solid-liquid separation in the same manner as in Example 1, except that 30 g of sodium chloride seed crystals (60 g / L per 1 L of salt bittern) were added to 0.5 L of salt bittern. As in Example 2, the recovery rate of potassium chloride recovered as the 600 μm sieve was 98%, and the purity was 96%. The median diameter D 50 The particle size was 295 μm, and the uniformity factor when approximated by the rosin Ramla distribution was 3.3.

[0070] Example 4 In Example 4, crystals were precipitated from salt bittern in the same manner as in Example 1, except that 40 g of sodium chloride seed crystals (80 g / L per 1 L of salt bittern) were added to 0.5 L of salt bittern, and solid-liquid separation was performed. As in Example 2, the recovery rate of potassium chloride recovered as a 600 μm sieve was 98%, and the purity was 95%. The median diameter D 50 The particle size was 267 μm, and the uniformity number when approximated by the rosin Ramla distribution was 5.1.

[0071] Comparative Example 1 In Comparative Example 1, crystals were precipitated from salt bittern and subjected to solid-liquid separation in the same manner as in Example 1, except that sodium chloride seed crystals were not added to the salt bittern and the salt bittern was cooled. The particle size and component distribution measured by sieving the crystals are shown in FIG. 3. As shown in FIG. 3, the particle size of the precipitated crystals is distributed in the range of 150 to 850 μm. Of these, potassium chloride is distributed in the range of 250 to 850 μm. The purity of the recovered potassium chloride was 80%. The median diameter D of the recovered potassium chloride crystals was 150 to 850 μm. 50 The particle size was 527 μm, and the uniform number when approximated by the rosin Ramla distribution was 3.8.

[0072] Moreover, the relationship between the amount (g) of sodium chloride seed crystals added and the purity (%) of the resulting potassium chloride in Examples 1 to 4 and Comparative Example 1 is shown in FIG. Furthermore, the amount (g) of sodium chloride seed crystals added and the median diameter D of the resulting potassium chloride crystals in Examples 1 to 4 and Comparative Example 1 are shown in Table 1. 50 The relationship between the thickness and the thickness (μm) is shown in FIG.

[0073] Example 5 In Example 5, crystals were precipitated from salt bittern in the same manner as in Example 1, except that 50 g of potassium chloride seed crystals (100 g / L per 1 L of salt bittern) were added to 0.5 L of salt bittern instead of 10 g of sodium chloride seed crystals (20 g / L per 1 L of salt bittern), and then the salt bittern was cooled. The particle size and component distribution measured by sieving the crystals are shown in FIG. 6. As shown in FIG. 6, the particle size of the precipitated crystals is distributed in the range of 0 to 850 μm, of which potassium chloride is concentrated in the range of 355 to 850 μm. The recovery rate of potassium chloride recovered as the 355 μm sieve was 99%, and the purity was 96%. The median diameter D of the recovered potassium chloride crystals was 1.0 μm. 50 The particle size of the potassium chloride seed crystals added to the bittern used in salt production was 0.425 to 0.500 mm, and the potassium chloride seed crystals used were classified using a sieve with a 500 μm mesh and a sieve with a 425 μm mesh.

[0074] Example 6 In Example 6, instead of 10 g of sodium chloride seed crystals (20 g / L per 1 L of salt bittern), 20 g of sodium chloride seed crystals (40 g / L per 1 L of salt bittern) and 50 g of potassium chloride seed crystals (100 g / L per 1 L of salt bittern) were added to 0.5 L of salt bittern, and then the salt bittern was cooled. The crystals were precipitated from the salt bittern and separated into solid and liquid in the same manner as in Example 1. The particle size and component distribution measured by sieving the crystals are shown in FIG. 7. As shown in FIG. 7, the particle size of the precipitated crystals is distributed in the range of 355 to 1180 μm, of which potassium chloride is concentrated in the range of 355 to 710 μm. The recovery rate of potassium chloride recovered as the 710 μm sieve was 95%, and the purity was 98%. The median diameter D of the recovered potassium chloride crystals was 1.0 μm. 50 The particle size of the sodium chloride seed crystals added to the bittern was 850-1000 μm, and the particle size of the potassium chloride seed crystals was 425-500 μm.

[0075] In Examples 1 to 4, in which sodium chloride seed crystals were added to bittern for making salt and then cooled, potassium chloride with a high purity of 85 to 95% was obtained. In Example 5, in which potassium chloride seed crystals were added to bittern for making salt and then cooled, potassium chloride with a high purity of 96% was obtained. Furthermore, in Example 6, in which sodium chloride seed crystals and potassium chloride seed crystals were added to bittern for making salt and then cooled, potassium chloride with a high purity of 98% was obtained. On the other hand, in Comparative Example 1 in which cooling was carried out without adding sodium chloride seed crystals or potassium chloride seed crystals to bittern produced by salt production, the purity of the obtained potassium chloride was as low as 80%.

Claims

1. A step of adding at least one of seed crystals of the target component and seed crystals of the other component to a liquid in which crystals of the target component and crystals of the other component other than the target component are precipitated by crystallization; A step of precipitating crystals of the target component and crystals of the other components from the liquid; and recovering the crystals of the target component. Method for producing crystals.

2. The method for producing crystals according to claim 1, further comprising the steps of: subjecting a mixture containing crystals of the target component and crystals of the other components to solid-liquid separation from the liquid after precipitation; and then separating the crystals of the target component from the mixture to recover the crystals of the target component.

3. The method for producing crystals according to claim 1 , wherein in at least a portion of the process of precipitating crystals of the target component and crystals of the other component from the liquid, the crystals of the target component and the crystals of the other component are precipitated simultaneously.

4. The method for producing crystals according to claim 1 , wherein the liquid is cooled to cause crystals of the target component and crystals of the other components to precipitate from the liquid.

5. The method for producing crystals according to any one of claims 1 to 4, wherein the liquid is bittern and the target component is potassium chloride.

6. A method for producing crystals as described in claim 5, wherein potassium chloride seed crystals are added to the salt-making bittern as seed crystals of the target component.

7. A method for producing crystals as described in claim 5, wherein seed crystals of sodium chloride are added to the salt-making bittern as crystals of the other component.

8. A method for producing crystals as described in claim 5, wherein potassium chloride seed crystals and sodium chloride seed crystals are added to the salt-making bittern as seed crystals of the target component and seed crystals of the other components.

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