TW202208284A - Crystallization reaction method and crystallization reaction device - Google Patents

Abstract

An object of the invention is to provide a crystallization reaction method and a crystallization reaction device that are capable of improving the recovery rate in a method for recovering a crystallization target substance from a water to be treated that contains the crystallization target substance such as fluorine. The crystallization reaction method includes a crystallization reaction step of adding a calcium preparation to the water to be treated containing the crystallization target substance in a crystallization reaction vessel (10) to produce crystals of an insoluble calcium salt, wherein during the crystallization reaction step, the SiO2 concentration inside the crystallization reaction vessel (10) is 100 mg/L or less.

Description

Crystallization reaction method and crystallization reaction device

The present invention relates to a crystallization reaction method and a crystallization reaction device.

The present invention proposes a method for recovering the crystallization target material from the water to be treated containing the crystallization target material such as fluorine. The water containing the crystallization target material and a calcium agent are injected into a reaction tank filled with seed crystals to make the insoluble A method for obtaining a crystalline product by precipitation of salt on the surface of the seed crystal. As the calcium agent used in this method, there are calcium chloride, slaked lime (calcium hydroxide), and the like. Although slaked lime is very cheap compared to calcium chloride, if commercially available slaked lime is used directly as a calcium agent, the crystallization reaction will be unstable, and there is a problem that the recovery rate of insoluble calcium salts varies.

In order to solve this problem, for example, Patent Document 1 describes that a stable recovery rate can be ensured by using slaked lime that has been washed so that the sulfur content in the slaked lime is 0.1% or less in terms of SO ₃ . technology, but sometimes the recovery rate is not sufficient.

On the other hand, as a method for reducing the fluorine concentration of the fluorine-containing water to be treated, for example, Patent Document 2 describes a method in which a silicon compound is added to the fluorine-containing water, and the fluorine is converted into hexafluorosilicate ion. In this form, the salt type and/or hydroxyl type anion exchange resin is captured, and the anion exchange resin is contacted with an acid to desorb the captured fluorine, and at the same time, the anion exchange resin is regenerated into a salt type. However, this method is a method of adding silicon in order to increase the adsorption amount of fluorine, not for the purpose of removing silicon. Moreover, since the waste water of fluorine concentrated by this method contains silicon, it is not suitable to be recovered as an economically valuable thing. (Prior Art Literature) ﹝Patent Documents﹞

(Patent Document 1) Japanese Patent No. 5139376 (Patent Document 2) Japanese Patent Application Laid-Open No. 6-015266

﹝The problem that the invention intends to solve﹞

An object of the present invention is to provide a crystallization reaction method and a crystallization reaction apparatus capable of improving the recovery rate in the method for recovering the crystallization target substance from the treated water containing the crystallization target substance such as fluorine. ﹝Technical means to solve problems﹞

The present invention relates to a crystallization reaction method, comprising: a crystallization reaction step, in which a calcium agent is added to the water to be treated containing a crystallization object substance in a crystallization reaction tank, so as to generate crystals of a poorly soluble calcium salt; and in the crystallization reaction tank In the crystallization reaction step, the SiO ₂ concentration in the crystallization reaction tank is below 100 mg/L.

In the crystallization reaction method, the concentration of SiO ₂ contained in the calcium agent is preferably 0.2 mass % or less.

In the crystallization reaction method, it is preferable to further include an adjustment step, which is adjusted so that the SiO ₂ concentration in the crystallization reaction tank becomes 100 mg/L or less before the crystallization reaction step.

In the crystallization reaction method, the adjustment step preferably includes at least one of the following steps: a dilution step, diluting the treated water; an ion exchange treatment step, treating the treated water with an ion exchange resin; a washing step, Wash the calcium.

In the crystallization reaction method, the adjustment step preferably includes the ion exchange treatment step, and includes a reverse osmosis membrane treatment step of concentrating the treated water using a reverse osmosis membrane in the latter stage of the ion exchange treatment step.

In the crystallization reaction method, the content of sulfur contained in the calcium agent is preferably 0.1% or less in terms of SO ₃ .

The present invention relates to a crystallization reaction apparatus, wherein a calcium agent is added to the water to be treated containing a crystallization target substance in a crystallization reaction tank to generate crystals of a poorly soluble calcium salt, and includes an adjustment mechanism in the The first stage of the crystallization reaction apparatus is adjusted so that the SiO ₂ concentration in the crystallization reaction tank is 100 mg/L or less.

In the crystallization reaction device, the adjustment mechanism preferably includes at least one of the following mechanisms: a dilution mechanism, which dilutes the water to be treated; an ion exchange treatment mechanism, which uses an ion exchange resin to treat the water to be treated; cleaning mechanism, and the calcium agent is cleaned.

In the crystallization reaction apparatus, the adjustment mechanism preferably includes the ion exchange treatment mechanism, and includes a reverse osmosis membrane treatment mechanism for concentrating the water to be treated using a reverse osmosis membrane in the latter stage of the ion exchange treatment mechanism.

In the crystallization reaction device, the content of sulfur contained in the calcium agent is preferably 0.1% or less in terms of SO ₃ .

The present invention relates to a calcium agent, which is used in a crystallization reaction method for adding the calcium agent to the water to be treated containing a crystallization target substance in a crystallization reaction tank to generate crystals of insoluble calcium salts; and SiO2 in the calcium agent ₂ The concentration is 0.2 mass % or less. ﹝The effect of invention﹞

The present invention can provide a crystallization reaction method and a crystallization reaction apparatus capable of improving the recovery rate in the method for recovering the crystallization target substance from the treated water containing the crystallization target substance such as fluorine.

The following describes the implementation of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited by this embodiment.

The outline of an example of the crystallization reaction apparatus according to the embodiment of the present invention is shown in FIG. 1 below, and the structure is demonstrated.

The crystallization reaction apparatus 1 includes a crystallization reaction tank 10 for performing a crystallization reaction.

In the crystallization reaction apparatus 1 of FIG. 1, the to-be-processed water supply piping 22 is connected to the to-be-processed water inlet of the crystallization reaction tank 10. The inner peripheral wall of the crystallization reaction tank 10 is arranged so as to face the peripheral wall of the crystallization reaction tank 10 , and the treated water discharge path 18 is formed between the inner and outer peripheral walls. A treated water discharge pipe 24 is connected to the treated water outlet in the upper part of the treated water discharge path 18 . The sparingly soluble salt discharge pipe 26 is connected to the sparingly soluble salt outlet in the lower part of the crystallization reaction tank 10 . Calcium addition piping 28 is connected as calcium addition means to the calcium inlet of the crystallization reaction tank 10, and acid addition piping 30 is connected to the acid inlet as pH adjustment means. The seed crystal inlet of the crystallization reaction tank 10 and the outlet of the seed crystal tank 14 are connected by a seed crystal addition pipe 32 . The motor 12 is provided in the seed crystal addition piping 32 . The crystallization reaction tank 10 is provided with a stirring device 16 and a drainage pipe 20 as "a stirring mechanism including a motor and a stirring blade for stirring the fluid in the crystallization reaction tank 10". The stirring blades of the stirring device 16 are arranged in the drainage pipe 20, and are rotated by the "rotational force generated by the motor" transmitted through the stirring shaft.

Hereinafter, the crystallization reaction method and the operation of the crystallization reaction apparatus 1 according to the present embodiment will be described.

The water system to be treated containing a substance to be crystallized such as fluorine is supplied to the crystallization reaction tank 10 through the water to be treated supply piping 22 . On the other hand, the seed crystal system in the seed crystal tank 14 is added to the crystallization reaction tank 10 by the motor 12 through the seed crystal addition pipe 32 , and the calcium agent system is added to the crystallization reaction tank through the calcium agent addition pipe 28 . 10. The calcium agent is preferably added to the vicinity of the stirring blade of the crystallization reaction tank 10 . The pH value in the crystallization reaction tank 10 can also be adjusted by adding the acid which is a pH value adjuster to the crystallization reaction tank 10 through the acid addition piping 30. The inside of the crystallization reaction tank 10 is stirred by the stirring device 16 .

Furthermore, in the crystallization reaction tank 10, the crystallization target substance such as fluorine contained in the water to be treated reacts with the calcium agent to generate insoluble calcium salts such as calcium fluoride, and precipitate on the surface of the seed crystal to generate insoluble calcium Crystallization of the salt (crystallization reaction step). Substances to be crystallization such as fluorine are reduced through the crystallization reaction in the crystallization reaction tank 10 , and the treated water is discharged from the treated water discharge path 18 through the treated water discharge pipe 24 . The sparingly soluble calcium salts such as calcium fluoride generated in the crystallization reaction tank 10 are extracted and discharged from the sparingly soluble salt discharge piping 26 .

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, the concentration of silicon dioxide (SiO ₂ ) in the crystallization reaction tank 10 is set to 100 mg/L or less in the crystallization reaction step. As a result of investigations by the present inventors, it was found that when the SiO ₂ concentration in the crystallization reaction tank 10 exceeds 100 mg/L, silicon dioxide is precipitated on the surface of the seed crystals and hinders the crystallization reaction. Silica is sometimes not only contained in the treated water, but also in calcium agents such as slaked lime.

Generally, the solubility of silica with respect to water is about 120 mg/L at room temperature, and if its concentration is below the solubility, it should not be precipitated but flow out into the treated water. In addition, it is assumed that the pH value in the crystallization reaction tank is generally about 1.0 to 2.0, and if the pH value is in this low pH value range, the crystallization rate of silica becomes significantly slow and does not precipitate. However, considering the presence of seed crystals in the crystallization reaction tank as in the crystallization reaction apparatus according to the present embodiment, the seed crystals become cores to promote the precipitation of silicon dioxide, and it is presumed that even localized If the concentration of silicon oxide exceeds the solubility of silicon dioxide, the place will be used as a core to promote the crystallization of silicon dioxide. In particular, it is presumed that, for example, when the seed crystal is present at a high concentration of 30 w/v % in the crystallization reaction tank, and the residence time is long, for example, 1 hour or more, the crystallization of silicon dioxide is further promoted.

In addition, although we think that even if silicon dioxide is precipitated, the precipitation part alone does not particularly hinder the crystallization reaction of poorly soluble calcium salts such as calcium fluoride, but we think that once there is a The precipitation of silica will hinder the reaction of insoluble calcium salts.

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, in the crystallization reaction step, the concentration of silicon dioxide (SiO ₂ ) in the crystallization reaction tank 10 can be set to 100 mg/L or less. The crystallization of silicon dioxide is suppressed, and the recovery rate is improved in the method of recovering the crystallization target substance from the water to be treated containing the crystallization target substance such as fluorine by a crystallization reaction.

The SiO ₂ concentration in the crystallization reaction tank 10 may be 100 mg/L or less, preferably 50 mg/L or less, and more preferably 30 mg/L or less. When the SiO ₂ concentration in the crystallization reaction tank 10 exceeds 100 mg/L, silicon dioxide is precipitated on the surface of the seed crystal, and the crystallization reaction is likely to be inhibited.

As mentioned above, sometimes silica is included not only in the water to be treated, but also in calcium agents such as slaked lime. Therefore, the SiO ₂ concentration contained in the calcium agent is preferably 0.2 mass % or less, more preferably 0.15 mass % or less, and even more preferably 0.10 mass % or less. When the SiO ₂ concentration contained in the calcium agent exceeds 0.2 mass %, silicon dioxide is precipitated on the surface of the seed crystal, and the crystallization reaction is likely to be inhibited. For example, what is necessary is just to use the calcium agent whose _SiO2 density|concentration is 0.2 mass % or less.

Moreover, an adjustment process may be provided, and it may adjust so that the _SiO2 concentration in the crystallization reaction tank 10 may become 100 mg/L or less before a crystallization reaction process.

For example, in order to reduce the amount of the silica contained in the calcium agent used, it is also possible to adjust the silica by cleaning it with a cleaning solution such as water (cleaning step). For example, in the washing step, the calcium agent may be washed with water or the like so that the SiO ₂ concentration contained in the calcium agent may be 0.2 mass % or less.

Moreover, it is also possible to adjust so that the SiO ₂ concentration in the crystallization reaction tank 10 becomes 100 mg/L or less by diluting the water to be treated with a diluent such as water (dilution step); The silicon dioxide is removed to reduce the silicon dioxide content of the water to be treated so that the SiO ₂ concentration in the crystallization reaction tank 10 becomes 100 mg/L or less (silicon dioxide removal step). As the silica removal step, water to be treated may be treated with an ion exchange resin such as a weakly basic ion exchange resin (an ion exchange treatment step), and a coagulation precipitation treatment may be used (a coagulation precipitation treatment step).

There is also a method of removing silica by pre-treatment of ion exchange resin. Generally, when wastewater containing fluoride ions and silica is injected into anion exchange resin at an acidic pH value, silica will act as a Fluorosilicate ions are removed. The above-mentioned Patent Document 2 describes a method of increasing the amount of adsorption of fluorine by adding silica to wastewater containing fluorine to form hexafluorosilicic acid, but this method is a technique for increasing the amount of adsorption of fluorine .

As a result of research by the inventors of the present case, it was found that if the treated water containing fluorine and silica was injected into the anion exchange resin, the silica continued to be adsorbed even after the cleavage of the fluoride ions. Although this mechanism is not yet clear, it is thought that it is due to the adsorption of other silicas due to the adsorption of silica once adsorbed.

Examples of the ion exchange resin include weakly basic anion exchange resins containing amine groups as anion exchange groups, and strongly basic anion exchange resins containing quaternary ammonium groups as anion exchange groups. In terms of weakly basic anion exchange resin, it is better.

A reverse osmosis membrane treatment step for concentrating the water to be treated by using a reverse osmosis membrane may be provided in the latter stage of the ion exchange treatment step in the adjustment step. Thereby, the effect of improving the fluorine recovery rate of the crystallization apparatus in the latter stage may be obtained by concentrating fluorine ions.

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, the sulfur content contained in the calcium agent used is preferably 0.1% or less in terms of SO ₃ , and more preferably 0.01% or less. Since the generation of insoluble calcium salts such as fine calcium fluoride can be suppressed by reacting a calcium agent having a sulfur content of 0.1% or less in terms of SO ₃ with a substance to be crystallized such as fluorine, it can be suppressed from being accompanied by the treatment of water. It is discharged to the outside of the crystallization reaction tank 10 at the same time, and the recovery rate of the poorly soluble calcium salt can be improved. In addition, by setting the sulfur content of the calcium agent to 0.1% or less in terms of SO ₃ , the generation of by-products such as calcium sulfate can be suppressed, so that the recovery rate of poorly soluble calcium salts such as calcium fluoride can be improved.

FIG. 2 shows that, in the configuration of the crystallization reaction apparatus 1 of FIG. 1 , as an “adjustment mechanism for adjusting the SiO ₂ concentration in the crystallization reaction tank to be 100 mg/L or less”, “by water or the like” is provided. A schematic configuration of an example of a crystallization reaction apparatus that dilutes the water to be treated and adjusts the dilution mechanism.

The crystallization reaction apparatus 2 shown in FIG. 2 includes a dilution tank 34 and a dilution water addition pipe 36 as dilution means.

In the crystallization reaction device 2, the treated water piping 37 is connected to the treated water inlet of the dilution tank 34, and the treated water outlet of the dilution tank 34 and the treated water inlet of the crystallization reaction tank 10 are connected by the treated water The water supply piping 22 is connected. A dilution water addition pipe 36 is connected to the dilution water inlet of the dilution tank 34 .

The water system to be treated containing a substance to be crystallized such as fluorine is sent to the dilution tank 34 through the water to be treated piping 37 . In the dilution tank 34, the dilution water is added to the water to be treated through the dilution water addition pipe 36, and the water to be treated is diluted (dilution step). The diluted to-be-treated water system is supplied to the crystallization reaction tank 10 through the to-be-treated water supply pipe 22 . 1, in the crystallization reaction tank 10, the crystallization target substance such as fluorine contained in the water to be treated reacts with the calcium agent to generate insoluble calcium salts such as calcium fluoride, And it precipitates on the surface of the seed crystal to produce the crystallization of insoluble calcium salt (crystallization reaction step).

In the dilution step, dilution water may be added to the water to be treated so that the SiO ₂ concentration in the crystallization reaction tank 10 becomes 100 mg/L or less, and the water to be treated may be diluted.

FIG. 3 shows that, in the configuration of the crystallization reaction apparatus 1 of FIG. 1 , as an “adjustment mechanism for adjusting the SiO ₂ concentration in the crystallization reaction tank to be 100 mg/L or less”, “by pretreatment” is provided. Schematic configuration of an example of a crystallization reaction device that removes silicon dioxide to reduce and adjust the silicon dioxide content of the water to be treated.

The crystallization reaction device 3 shown in FIG. 3 includes a silicon dioxide removing device 38 as a silicon dioxide removing mechanism.

In the crystallization reaction device 3, the treated water piping 39 is connected to the treated water inlet of the silica removal device 38, and the treated water outlet of the silica removal device 38 is connected to the treated water of the crystallization reaction tank 10. The inlet is connected by the water supply pipe 22 to be treated.

The water system to be treated containing a substance to be crystallized such as fluorine is sent to the silica removal device 38 through the water to be treated piping 39 . In the silicon dioxide removal device 38, the silicon dioxide in the water to be treated is removed, so that the silicon dioxide content is reduced (silicon dioxide removal step). The water to be treated after the silica content is reduced is supplied to the crystallization reaction tank 10 through the water to be treated supply piping 22 . 1, in the crystallization reaction tank 10, the crystallization target substance such as fluorine contained in the water to be treated reacts with the calcium agent to generate insoluble calcium salts such as calcium fluoride, And it precipitates on the surface of the seed crystal to produce the crystallization of insoluble calcium salt (crystallization reaction step).

In the silicon dioxide removal step, the silicon dioxide in the water to be treated may be removed so that the SiO ₂ concentration in the crystallization reaction tank 10 is 100 mg/L or less, and the silicon dioxide content may be reduced.

Examples of the silica removal device include an ion exchange treatment device that treats water to be treated with an ion exchange resin such as a weakly basic ion exchange resin, and a coagulation sedimentation treatment device that uses a coagulation sedimentation treatment.

FIG. 4 shows that, in the configuration of the crystallization reaction apparatus 1 of FIG. 1 , as an “adjustment mechanism for adjusting the SiO ₂ concentration in the crystallization reaction tank to be 100 mg/L or less”, “as silicon dioxide” is provided. An example of the removal mechanism is "Ion-exchange treatment mechanism that removes silica by ion-exchange treatment to reduce and adjust the silica content of water to be treated"" and "Concentration using reverse osmosis membrane in the latter stage of the ion-exchange treatment mechanism" A schematic configuration of an example of a crystallization reaction device of a reverse osmosis membrane treatment mechanism for water to be treated.

The crystallization reaction device 4 shown in FIG. 4 includes: an ion exchange treatment device 40 as an ion exchange treatment mechanism; and a reverse osmosis membrane treatment device 42 as a reverse osmosis membrane treatment mechanism.

In the crystallization reaction device 4 , the treated water piping 41 is connected to the treated water inlet of the ion exchange treatment device 40 , and the treated water outlet of the ion exchange treatment device 40 and the treated water inlet of the reverse osmosis membrane treatment device 42 It is connected by the to-be-processed water piping 43. The concentrated water outlet of the reverse osmosis membrane treatment device 42 and the to-be-treated water inlet of the crystallization reaction tank 10 are connected by the to-be-treated water supply piping 22 . A permeated water pipe 45 is connected to the permeated water outlet of the reverse osmosis membrane treatment device 42 .

The water system to be treated containing a substance to be crystallized such as fluorine is sent to the ion exchange treatment device 40 through the water to be treated piping 41 . In the ion-exchange treatment device 40, silica in the water to be treated is removed by ion-exchange treatment using an ion-exchange resin, thereby reducing the silica content (an ion-exchange treatment step). The water to be treated after the silica content has been reduced is sent to the reverse osmosis membrane treatment device 42 through the water to be treated piping 43 . In the reverse osmosis membrane treatment device 42, permeated water and concentrated water are obtained by reverse osmosis membrane treatment using a reverse osmosis membrane (a reverse osmosis membrane treatment step). The concentrated water system is supplied to the crystallization reaction tank 10 through the water supply pipe 22 to be treated. 1, in the crystallization reaction tank 10, the crystallization target substance such as fluorine contained in the water to be treated reacts with the calcium agent to generate insoluble calcium salts such as calcium fluoride, And it precipitates on the surface of the seed crystal to produce the crystallization of insoluble calcium salt (crystallization reaction step). The permeated water treated by the reverse osmosis membrane may be discharged through the permeated water pipe 45 and used for other purposes such as water recovery.

In the ion exchange treatment step, the silica content in the water to be treated may be reduced so that the SiO ₂ concentration in the crystallization reaction tank 10 is 100 mg/L or less by removing silica.

FIG. 5 shows that, in the configuration of the crystallization reaction apparatus 1 of FIG. 1 , as an “adjustment mechanism for adjusting the SiO ₂ concentration in the crystallization reaction tank to be 100 mg/L or less”, “in order to reduce the use of The amount of silicon dioxide contained in the calcium agent, and the schematic configuration of an example of a crystallization reaction device of a cleaning mechanism for cleaning silicon dioxide with water, etc.

The crystallization reaction device 5 shown in FIG. 5 includes a cleaning tank 48 as a cleaning mechanism. The crystallization reaction device 5 may also include a dissolution tank 50 .

The outlet of the calcium agent tank 44 and the calcium agent inlet of the cleaning tank 48 are connected by the calcium agent piping 62, the outlet of the cleaning tank 48 and the calcium agent inlet of the dissolving tank 50 are connected by the calcium agent piping 68 via the pump 52, The outlet of the dissolution tank 50 and the inlet of the calcium agent of the crystallization reaction tank 10 are connected by the calcium agent addition piping 28 via the pump 56 and the valve body 58 which are calcium agent addition means. The motor 46 is provided in the calcium agent piping 62 . The washing water addition piping 64 is connected to the washing tank 48 . A cleaning waste water discharge pipe 66 is connected to the cleaning waste water outlet of the cleaning tank 48 . A pump may be inserted into the cleaning waste water discharge pipe 66 . "Between the pump 56 and the valve body 58 on the calcium addition pipe 28" and the "return calcium inlet of the dissolution tank 50" may be connected by the return pipe 70. The dissolving tank 50 is provided with a stirring device 54 as "a stirring mechanism including a motor and a stirring blade for stirring the fluid in the dissolving tank 50".

The calcium agent in the calcium agent tank 44 is added to the cleaning tank 48 by the motor 46 through the calcium agent piping 62 . On the other hand, cleaning water systems such as pure water and ultrapure water are added to the cleaning tank 48 through the cleaning water addition piping 64 . In addition, the calcium agent is washed in the washing tank 48 (washing step).

Next, the washed calcium agent is added to the dissolution tank 50 through the calcium agent piping 68 by the pump 52 . The calcium agent is stirred by the stirring device 54 of the dissolution tank 50, and is made into a calcium agent slurry (calcium agent slurry preparation step). The calcium agent (slurry) is supplied to the crystallization reaction apparatus 1 through the calcium agent addition pipe 28 by the pump 56 with the valve body 58 in the open state. 1, in the crystallization reaction tank 10, the crystallization target substance such as fluorine contained in the water to be treated reacts with the calcium agent to generate insoluble calcium salts such as calcium fluoride, And it precipitates on the surface of the seed crystal to produce the crystallization of insoluble calcium salt (crystallization reaction step).

In order to obtain a more uniform calcium agent slurry, a part of the calcium agent slurry that has passed through the calcium agent addition pipe 28 may be returned to the dissolution tank 50 through the return pipe 70 (return step). In addition, in this embodiment, the dissolving tank 50 (calcium slurry preparation step) is not necessarily required.

In the cleaning step, the silicon dioxide in the calcium agent may be removed so that the SiO ₂ concentration in the crystallization reaction tank 10 is 100 mg/L or less, and the silicon dioxide content may be reduced. For example, in the washing step, the calcium agent may be washed with water or the like so that the SiO ₂ concentration contained in the calcium agent may be 0.2 mass % or less.

In the cleaning step, the concentration of SiO ₂ contained in the calcium agent in the cleaning tank 48 may be measured, and the calcium agent may be cleaned according to the measured value. However, if the SiO ₂ concentration in the calcium agent is pre-specified, the relationship between the SiO ₂ concentration in the calcium agent and the cleaning time can be measured in advance, and the cleaning time of the calcium agent can be determined according to the measurement data.

The cleaning mechanism is not limited to the tank type such as the cleaning tank 48 as long as the cleaning mechanism is capable of cleaning so as to reduce the SiO ₂ concentration in the calcium agent. For example, a pipe having a predetermined length is used as the cleaning mechanism, and the pipe It is also possible to mix water, etc. with the calcium agent and wash it.

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, the addition (injection point) of the calcium agent to the crystallization reaction tank 10 is preferably performed in the vicinity of the stirring blade. By adding the calcium agent in the vicinity of the stirring blade, once the calcium agent is injected into the crystallization reaction tank 10, it will diffuse immediately, and its concentration will decrease rapidly. Therefore, the formed salt is less likely to be directly precipitated in the liquid, and the crystallization target substance (fluorine, etc.) in the liquid can be taken as a crystal of a poorly soluble salt on the granular seed crystals in the crystallization reaction tank 10 over time. enter. In addition, the calcium agent becomes easy to dissolve, and the rapid reaction between the undissolved calcium agent and fluorine can also be suppressed. These results make it possible to generate a poorly soluble calcium salt with high particle uniformity and low water content.

The addition (injection point) of the water to be treated to the crystallization reaction tank 10 is also preferably performed in the vicinity of the stirring blade. By adding the water to be treated in the vicinity of the stirring blade, the water to be treated is diffused as soon as it is injected into the crystallization reaction tank 10, and the concentration of the crystallization target substance such as fluorine is rapidly reduced. Therefore, the crystallization target substance (fluorine etc.) in the liquid can be taken in as crystals of the poorly soluble salt on the granular seed crystals in the crystallization reaction tank 10 over time. As a result, it becomes possible to generate a poorly soluble calcium salt with higher particle uniformity and lower water content.

The acid is added to the crystallization reaction tank 10, and the pH value of the crystallization reaction liquid in the crystallization reaction tank 10 is preferably set, for example, in the range of 0.8 to 3, and more preferably in the range of 1 to 1.5. By adding an acid and operating the crystallization reaction tank 10 in the range of pH 0.8 to 3, the concentration of crystallization target substances such as fluorine in the treated water can be reduced. As a reason for this, it is thought that by operating at a low pH value such as pH 0.8 to 3, the calcium agent becomes easy to dissolve, and it has the effect of suppressing the rapid reaction between the undissolved calcium agent and the crystallization target substance. .

As shown in the crystallization reaction apparatuses of FIGS. 1 to 5 , under the water surface of the crystallization reaction tank 10 , the drainage pipe 20 is preferably arranged so that the stirring blades of the stirring device 16 are located in the pipe. At this time, the stirring blade is preferably one that can form a downflow. If the drainage pipe 20 is arranged in this way, a downward flow will be generated toward the lower part of the pipe, and a region with a relatively large diffusion flow velocity will be formed. Therefore, the water to be treated or the calcium agent can be diffused more rapidly, and the direct generation of poorly soluble calcium salt particles due to contact between regions where the concentration of the treated water or the calcium agent is locally concentrated can be suppressed as much as possible.

When the draft tube 20 and the stirring blade are provided as described above, an upward flow region with slow flow is formed on the outer peripheral portion of the draft tube 20 . In this area, the particles are classified, and the particles with small particle size rise along the outer side of the tube, and then enter the inside of the tube from the upper end of the tube, and then descend to the point where the water to be treated or calcium is injected or the lower part of the agitation Regional recycling. The crystals with these small particle diameters serve as cores to promote the crystallization reaction. Therefore, a crystal of a poorly soluble calcium salt having a large particle size can be stably formed, and the recovery rate can be improved.

In addition, since the crystals with larger particle sizes as the crystallization reaction progresses do not rise through the upward flow of the outer peripheral portion of the tube, but sink down and are difficult to re-enter the drainage tube 20, so the crystals after growth can be suppressed from causing and stirring. Damaged by the collision of the blades. Such advantages also help to stably obtain the crystals of insoluble calcium salts with large particle size, and can help to improve the recovery rate.

In order to form a region with relatively large stirring flow velocity in the lower part of the drainage pipe 20 and to stably form an upward flow on the outer periphery of the pipe, the stirring blade is preferably located somewhere in the lower half of the pipe. More preferably, it is a position slightly above the lower end of the tube. With such an arrangement, a region with a high stirring flow velocity is formed in the vicinity of the lower end of the tube like a vortex, and an upward flow is stably formed along the outer circumference of the tube from there. Therefore, it is possible to efficiently perform diffusion of water to be treated, calcium agent, or the like, or classification of particles.

When the drainage pipe 20 is provided, the injection point of the treated water or the calcium agent is arranged in the pipe of the drainage pipe 20 so that the water to be treated or the calcium agent can catch on the downflow in the drainage pipe 20 and diffuse quickly and efficiently. Inside is better. A better location is in the tube of the drainage tube 20 and above the stirring blade.

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, if the water to be treated containing the crystallization target substance contains the crystallization target substance such as fluorine removed by the crystallization treatment, the water from any source shall be Any water to be treated may be used, for example, wastewater discharged from the electronics industry, power plants, and aluminum industries represented by semiconductor-related industries, etc., are listed, but are not limited to these.

Examples of the crystallization target substance include phosphorus and the like in addition to fluorine. As long as fluorine etc. which become a crystallization target substance are crystallized by a crystallization reaction, it can exist in to-be-processed water in an arbitrary state. From the viewpoint of being dissolved in water to be treated, the crystallization target substance is, for example, an ionized state.

Wastewater containing fluorine is also discharged from, for example, an aluminum electrolytic refining process, a steel-making process, and the like, but is discharged in large quantities especially in semiconductor factories. Concentrated hydrofluoric acid is used for cleaning of semiconductor silicon wafers, etc., and is discharged as a concentrated hydrofluoric acid waste liquid with a fluorine content of a percentage level. At this time, since ammonia, hydrogen peroxide, phosphoric acid, etc. are also used as cleaning agents, it may become waste water containing these components. In addition, a large amount of water is used to clean the hydrofluoric acid remaining on the semiconductor silicon wafer, and to clean the HF contained in the gas after the decomposition of the perfluorinated compounds (PFCs). wastewater is discharged. The crystallization reaction method and the crystallization reaction apparatus according to this embodiment can be particularly suitably used for the purpose of removing fluorine from waste water containing hydrofluoric acid (hydrogen fluoride).

The amount of fluorine contained in the water to be treated is not particularly limited, but is, for example, 1000 mg/L or more, particularly in the range of 5000 to 10000 mg/L. There are cases where silica is contained in the water to be treated. In the case where silica is contained, the amount of silica is not particularly limited. range of L.

When the amount of fluorine contained in the water to be treated is, for example, 10,000 mg/L or more, it is preferable to perform a dilution step as an adjustment step; for example, when it is less than 10,000 mg/L, or preferably less than 10,000 mg/L In the case of 5000 mg/L, it is preferable to perform an ion exchange treatment step as an adjustment step.

Calcium chloride, slaked lime (calcium hydroxide), and the like are used as calcium agents, and slaked lime is particularly suitable for use from the viewpoint of chemical cost and the like. As a form of adding a calcium agent, a powder state may be sufficient, and a slurry state may be sufficient. A preferable aspect of adding the calcium agent is the aspect of adding the calcium agent slurry.

As long as the concentration of silicon dioxide (SiO ₂ ) in the crystallization reaction tank 10 is 100 mg/L or less, a calcium agent of any grade may be used.

When adding as a calcium agent slurry, the density|concentration of a calcium agent slurry is not specifically limited, For example, it can be in the range of 1 mass % - 20 mass % which are generally used.

As the injection amount of the calcium agent, for example, the chemical equivalent of calcium can be in the range of 0.8 to 2 times, more preferably in the range of 1 to 2 times, and still more preferably in the range of 1 to 1.2 times the chemical equivalent of calcium. times the range. If the chemical equivalent of calcium is more than twice the chemical equivalent of the crystallization target substance such as fluorine in the water to be treated, calcium fluoride and the like are not easily precipitated on the seed crystal and are generated as fine particles, and calcium fluoride and the like are mixed in the treatment process. In the case of water, if it is less than 0.8 times, the proportion of the crystallization target substances such as fluorine in the water to be treated that are not converted into calcium fluoride or the like increases, and fluorine and the like may be mixed into the treated water.

In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, the seed crystals may be pre-existed in the crystallization reaction tank 10 before the water to be treated and the calcium agent are added to the crystallization reaction tank 10, and the seed crystals may be present in the crystallization reaction tank 10 in advance. The water to be treated and the calcium agent may be added to the crystallization reaction tank 10 and then stored in the crystallization reaction tank 10 . For stable treatment, it is preferable that the seed crystals are present in the crystallization reaction tank 10 before the water to be treated and the calcium agent are added to the crystallization reaction tank 10 .

The seed crystal may be any material as long as it can precipitate the crystals of the generated insoluble calcium salt on the surface thereof, and examples thereof include filter sand, activated carbon, zircon sand, garnet sand, and Sakurandam (commercial products). Name, "particles composed of oxides of metal elements" such as "particles composed of oxides of metal elements" and particles composed of "insoluble salts as precipitates precipitated by crystallization reaction", etc. , but not limited to these. From the viewpoint that a purer poorly soluble salt can be obtained as pellets or the like, particles composed of a poorly soluble salt that is a precipitate through a crystallization reaction (for example, in the case of calcium fluoride) Fluorite) is preferred.

The crystallization reaction tank 10 only needs to be a reaction tank that "reacts the fluorine in the water to be treated with the calcium agent to precipitate the crystals of the insoluble calcium salt, and can generate "the treated water in which the fluorine and the like are reduced". , the inner diameter, the shape, etc. can be in any form, and are not particularly limited.

Examples of the crystallization reaction tank 10 include a stirring-type crystallization reaction tank in which a stirring device including a stirring blade and the like is provided, and the inside of the crystallization reaction tank 10 is stirred by the stirring device to flow pellets. The stirring blade should just be able to stir the content in the crystallization reaction tank 10, and the installation aspect of a stirring blade, the size of a stirring blade, etc. are not specifically limited.

As the stirring-type crystallization reaction tank 10, the inner peripheral wall of the crystallization reaction tank 10 may be arranged so as to face the peripheral wall of the crystallization reaction tank 10, and the treated water discharge path may be formed between the inner and outer peripheral walls, and It has a separation area that improves the separation ability of the poorly soluble calcium salt particles and the treated water and suppresses the poorly soluble calcium salt particles from flowing out into the treated water. In this aspect, it is preferable that the treated water discharge pipe 24 is connected to the upper part of the treated water discharge path 18 . In addition, in this treated water discharge path 18, in order to improve the separation ability of the pellets, the baffle plate composed of a plurality of baffle plates or the baffle plate composed of a plurality of baffle plates may be located in the The inlet portion of the treated water discharge path 18 . The details of this aspect are described in JP 2005-230735 A and JP 2005-296888 A, and the crystallization reaction tank described in these patent documents can also be used in this embodiment.

Since the treated water in which the crystallization target substances such as fluorine are reduced by the crystallization reaction in the crystallization reaction tank 10 is acidic (for example, pH 1.5 to 3), neutralization treatment (pH adjustment) can also be performed (neutralization step) . For example, the treated water can also be sent to the neutralization tank and neutralized in the neutralization tank. When neutralizing the treated water, an alkaline agent such as sodium hydroxide may be added to the neutralization tank to neutralize the treated water, but in the case of the configuration of the crystallization reaction apparatus 5 shown in FIG. The discharged cleaning wastewater may be added to the neutralization tank to neutralize the treated water. Thereby, the processing cost can be reduced.

The amount of fluorine contained in the treated water reduced by the crystallization target substances such as fluorine through the crystallization reaction in the crystallization reaction tank 10 is not particularly limited, but is, for example, 3000 mg/L or less, especially 200 to 2000 mg/L. scope.

The poorly soluble calcium salt such as calcium fluoride generated through the crystallization reaction in the crystallization reaction tank 10 is extracted from the poorly soluble salt discharge pipe 26 and discharged to the outside of the system. The extraction method of the insoluble calcium salt is not particularly limited, and a method of extracting the insoluble calcium salt from the crystallization reaction tank 10 using a slurry pump such as a tube pump can also be used, as shown in the crystallization reaction device 5 in FIG. 5 . Generally, the valve body 60 is attached to the sparingly soluble salt discharge piping 26, and a method of extracting the sparingly soluble calcium salt from the crystallization reaction tank 10 by gravity alone may be used.

In the configuration of the crystallization reaction apparatus 5 in FIG. 5 , a classification device as a classification mechanism may be provided in the front stage of the cleaning tank 48 or in the rear stage of the cleaning tank 48 to classify the calcium agent (classification step).

The classification device is not particularly limited as long as it can classify the calcium agent. For example, a tubular container that allows the calcium agent to flow upward may be used, and a device for classifying by a mechanical mechanism such as a cyclone may be used. .

Through the classification step, for example, the particle size distribution of the calcium agent is classified into a particle size distribution of 53 μm or less, accounting for more than 90%. Thereby, the calcium agent with a fine particle diameter is added to the crystallization reaction tank 10 . By adding the calcium agent with a fine particle size to the crystallization reaction tank 10, since the calcium agent becomes easy to dissolve, fine particles caused by a rapid reaction between the undissolved calcium agent and the crystallization target substance such as fluorine are suppressed. The production of insoluble calcium salts. As a result, the insoluble calcium salt can be suppressed from being discharged out of the crystallization reaction tank 10 with the treated water, and the recovery rate of the insoluble calcium salt can be improved.

Calcium agents (that is, calcium agents with large particle diameters) classified by the classification step and whose particle size distribution is outside the above-mentioned range, for example, can also be supplied to the neutralization tank and used for the treatment of discharge from the crystallization reaction tank 10. Neutralization of water (pH adjustment). Thereby, the processing cost can be reduced.

In the crystallization reaction apparatus of FIGS. 1-5, although the to-be-processed water supply piping 22 and the calcium agent addition piping 28 are each one, it is not limited to this, You may provide a plurality of these. ﹝Example﹞

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely and in detail, this invention is not limited by the following Example.

<Examples and Comparative Examples>

Using the crystallization reaction apparatus shown in FIG. 1 and using the following conditions, using slaked lime as a calcium agent, and changing the kind of slaked lime, the crystallization reaction was performed, and the fluorine concentration of the treated water was compared. In Examples 1-2 and 1-3, batch cleaning using pure water was performed as a cleaning method for the calcium agent (1 L of pure water for 100 g of the calcium agent × 3 times). The experimental results thereof are shown in Table 1. 6 shows the fluorine concentration (mg/L) of the treated water with respect to the SiO ₂ concentration (mg/L) in the crystallization reaction tank, and FIG. 7 shows the fluorine concentration (mg/L) with respect to the slaked lime in the crystallization reaction tank The fluorine concentration (mg/L) of the treated water containing the SiO ₂ concentration (mass %).

The fluorine concentration of the water to be treated and the treated water was measured using an ion chromatograph (761 Compact IC, manufactured by Metrohm). The SiO ₂ concentration in the crystallization reaction tank was measured in accordance with JIS K 0101 molybdenum blue absorptiometry using an absorptometer (manufactured by Hitachi, Ltd., U-2900). The SiO ₂ concentration contained in the slaked lime was dissolved in hydrochloric acid, and was measured in accordance with JIS K 0101 molybdenum blue absorptiometry in the same manner as described above.

(experimental conditions) Crystallization reaction tank capacity: 100L (440mmψ×1000mmH) Fluorine concentration of treated water containing fluorine: 10000mg/L or 5000mg/L Flow rate of treated water containing fluorine: 25L/h or 50L/h Slaked lime slurry concentration: 5% by mass Acid: Hydrochloric acid (5 mass %) Stirring blade diameter: 160mm

【Table 1】 treated water SiO ₂ in treated water [mg/L] Types of slaked lime Slaked lime SiO ₂ [mass %] SiO ₂ in the reaction tank (measured) [mg/L] Treatment water F concentration [mg/L] Comparative Example 1-1 HF simulated water F=10000mg/L 0 Industrial Special A 0.39 420 3500 Comparative Example 1-2 Industrial special number B 0.25 330 3200 Comparative Example 1-3 Reagent grade 1 slaked lime + added SiO ₂ 0.22 200 3100 Example 1-1 Reagent grade 1 slaked lime 0.02 twenty two 350 Example 1-2 Industrial special A with cleaning 0.08 98 1000 Examples 1-3 Special B for industrial use with cleaning 0.01 15 440 Comparative Example 2-1 Semiconductor factory wastewater A 180 Special grade C for industrial use (SiO ₂ concentration 0.01%) 0.01 140 2600 Example 2-1 Semiconductor factory wastewater A (2-fold dilution) 90 89 680 Example 2-2 Semiconductor factory wastewater B 30 36 550

In Comparative Example 1-1, when slaked lime having a SiO ₂ concentration of 0.39 mass % was used, the recovery rate of fluorine was low. In Comparative Example 1-2, when slaked lime having a SiO ₂ concentration of 0.25 mass % was used, the recovery rate of fluorine was almost the same as in Comparative Example 1-1. In Comparative Examples 1-3, when SiO ₂ was added to the slaked lime of the low SiO ₂ concentration reagent, the recovery rate was low.

In Example 1-1, when slaked lime with a low _SiO2 concentration reagent was used, the recovery rate was higher. In Example 1-2, when the slaked lime whose SiO ₂ concentration was 0.1 mass % after washing was used, the recovery rate of fluorine was considerably improved compared with the comparative example. In Example 1-3, when the slaked lime whose SiO ₂ concentration was 0.01 mass % after washing was used, the recovery rate of fluorine was further improved as compared with Example 1-2.

In Comparative Example 2-1, when wastewater from a semiconductor factory containing SiO ₂ (fluorine concentration=10000 mg/L, SiO ₂ concentration=180 mg/L) was treated as the water to be treated, the recovery rate of fluorine was low. In Example 2-1, when the above-mentioned semiconductor factory wastewater was diluted twice with water (fluorine concentration = 5000 mg/L, SiO ₂ concentration = 90 mg/L) and treated by injecting water at a double flow rate of 50 L/h, although the inflow into The loading of fluorine is the same, but the recovery of fluorine is improved. In Example 2-2, the recovery rate of fluorine was high when treating wastewater from a semiconductor factory with low SiO ₂ concentration (fluorine concentration=10000 mg/L, SiO ₂ concentration=30 mg/L).

As described above, according to the method of the Examples, the recovery rate has been successfully improved in the method of recovering the crystallization target substance from the water to be treated containing the crystallization target substance such as fluorine.

1, 2, 3, 4, 5: Crystallization reaction device 10: Crystallization reaction tank 12,46: Motor 14: Seed tank 16,54: Stirring device 18: Treatment water discharge path 20: Drainage tube 22: Treated water supply piping 24: Treated water discharge piping 26: Insoluble salt discharge piping 28: Calcium Addition Piping 30: Acid addition piping 32: Seed crystal addition piping 34: Dilution tank 36: Dilution water addition piping 37, 39, 41, 43: Treated water piping 38: Silicon dioxide removal device 40: Ion exchange treatment device 42: Reverse osmosis membrane treatment device 44: Calcium tank 45: Permeable water piping 48: Cleaning tank 50: Dissolving tank 52,56: Pump 58,60: Valve body 62,68: Calcium piping 64: Rinse water addition piping 66: Cleaning waste water discharge piping 70: Return piping

FIG. 1 is a schematic configuration diagram showing an example of a crystallization reaction apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of the crystallization reaction apparatus according to the embodiment of the present invention. FIG. 3 is a schematic configuration diagram showing another example of the crystallization reaction apparatus according to the embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of the crystallization reaction apparatus according to the embodiment of the present invention. FIG. 5 is a schematic configuration diagram showing another example of the crystallization reaction apparatus according to the embodiment of the present invention. Fig. 6 is a graph showing "fluorine concentration in treated water (mg/L)" with respect to "SiO ₂ concentration in crystallization reaction tank (mg/L)" in Examples and Comparative Examples. Fig. 7 shows the ratio of "fluorine concentration (mg/L) of treated water" to "SiO ₂ concentration (mass %) contained in slaked lime in the crystallization reaction tank" in Examples and Comparative Examples chart.

2: Crystallization reaction device

10: Crystallization reaction tank

12: Motor

14: Seed tank

16: Stirring device

18: Treatment water discharge path

20: Drainage tube

22: Treated water supply piping

24: Treated water discharge piping

26: Insoluble salt discharge piping

28: Calcium Addition Piping

30: Acid addition piping

32: Seed crystal addition piping

34: Dilution tank

36: Dilution water addition piping

37: Treated water piping

Claims (11)

A crystallization reaction method, which is characterized in that: it comprises a crystallization reaction step, in which a calcium agent is added to the treated water containing a crystallization object substance in a crystallization reaction tank, so that the crystallization of a poorly soluble calcium salt is generated; In the crystallization reaction step, the SiO ₂ concentration in the crystallization reaction tank is below 100 mg/L. The crystallization reaction method according to claim 1, wherein the SiO ₂ concentration contained in the calcium agent is 0.2 mass % or less. The crystallization reaction method according to claim 1 or 2, further comprising: an adjustment step of adjusting the SiO ₂ concentration in the crystallization reaction tank to be 100 mg/L or less before the crystallization reaction step. The crystallization reaction method as claimed in claim 3, wherein, The adjustment step includes at least one of the following steps: A dilution step, diluting the treated water; an ion exchange treatment step of treating the treated water with an ion exchange resin; and In the cleaning step, the calcium agent is cleaned. The crystallization reaction method as claimed in claim 4, wherein, The adjustment step includes the ion exchange treatment step, and in the latter stage of the ion exchange treatment step, includes a reverse osmosis membrane treatment step of concentrating the water to be treated using a reverse osmosis membrane. The crystallization reaction method according to claim 1 or 2, wherein the content of sulfur contained in the calcium agent is 0.1% or less in terms of SO ₃ . A crystallization reaction device, wherein a calcium agent is added to water to be treated containing a crystallization target substance in a crystallization reaction tank to generate crystals of a poorly soluble calcium salt, characterized by comprising an adjustment mechanism, wherein the crystallization reaction device In the preceding stage, the SiO ₂ concentration in the crystallization reaction tank was adjusted to be 100 mg/L or less. The crystallization reaction device according to claim 7, wherein, The adjustment mechanism includes at least one of the following institutions: A dilution mechanism to dilute the treated water; an ion exchange treatment mechanism for treating the water to be treated with an ion exchange resin; and Clean the mechanism to clean the calcium. The crystallization reaction device according to claim 8, wherein, The adjustment mechanism includes the ion exchange treatment mechanism, and further includes a reverse osmosis membrane treatment mechanism for concentrating the water to be treated by using a reverse osmosis membrane in a subsequent stage of the ion exchange treatment mechanism. The crystallization reaction apparatus according to any one of claims 7 to 9, wherein the sulfur content contained in the calcium agent is 0.1% or less in terms of SO ₃ . A calcium agent used in a crystallization reaction method for adding a calcium agent to water to be treated containing a crystallization target substance in a crystallization reaction tank to generate crystals of a poorly soluble calcium salt, characterized in that: the calcium agent contains SiO ₂ The concentration is 0.2 mass % or less.

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