JP2023106902A - Crystallization reaction method and crystallization reaction apparatus - Google Patents

Abstract

To provide a crystallization reaction method and a crystallization reaction apparatus capable of recovering fluorine at a high recovery rate even under a neutral condition in a crystallization reaction using a stirring type crystallization reaction tank.SOLUTION: There is provided a crystallization reaction method of adding a calcium agent to water to be treated containing fluorine to generate calcium fluoride crystals, followed by recovering the calcium fluoride crystals, wherein a dispersant is added to the water to be treated to perform a crystallization reaction under the condition of a pH of 4 or more and 9 or less using a crystallization reaction tank 10 equipped with a stirring device 20 having stirring blades.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a crystallization reaction apparatus and a crystallization reaction method for performing crystallization treatment of fluorine-containing water.

As a method for recovering fluorine from fluorine-containing water containing fluorine, for example, fluorine-containing water and a calcium agent are injected into a crystallization reaction tank filled with seed crystals, and sparingly soluble calcium salts are precipitated on the surfaces of the seed crystals. It is known how to let and recover. In such a method, attempts are being made to increase the recovery rate of fluorine.

For example, Patent Document 1 discloses recovery of fluorine by using calcium chloride as a calcium agent in a fluidized bed type crystallization reactor, further adding a dispersant to fluorine-containing water, and operating under conditions of pH 4 to 5. mentioned to increase the rate.

On the other hand, Patent Literature 2 describes that an agitated crystallization reaction tank is operated under conditions of pH 2 to 3 of fluorine-containing water using calcium chloride as a calcium agent.

Further, Patent Document 3 describes that a stirring type crystallization reaction tank is operated under conditions of pH 0.8 to 3 using slaked lime as a calcium agent.

By using the stirring type crystallization reaction tank as described in Patent Documents 2 and 3, fluorine can be recovered from fluorine-containing water having a higher concentration (for example, 5000 mg/L or more) than the fluidized bed type crystallization reaction tank. be able to. However, as described in Patent Documents 2 and 3, when using a stirred crystallization reactor, it is necessary to operate under strongly acidic conditions of pH 3 or less. This is because under weakly acidic pH conditions closer to neutrality, microcrystals of calcium salts are formed, making it difficult to separate them by precipitation and lowering the recovery rate. However, hydrofluoric acid is highly reactive under strongly acidic conditions of pH 3 or less, requiring sufficient care in handling and causing problems such as susceptibility to corrosion of peripheral equipment. Therefore, in a crystallization reaction using a stirring type crystallization reaction tank, it is required to increase the recovery rate of fluorine even under near-neutral conditions.

Japanese Patent No. 4785353 Japanese Patent No. 4590383 Japanese Patent No. 5650164

An object of the present invention is to provide a crystallization reaction method and a crystallization reaction apparatus capable of recovering fluorine at a high recovery rate even under near-neutral conditions in a crystallization reaction using a stirring-type crystallization reaction tank. It is in.

The present invention relates to a crystallization reaction method for adding a calcium agent to fluorine-containing water to be treated to generate calcium fluoride crystals and recovering the calcium fluoride crystals, which comprises a stirring means having a stirring blade. a dispersant is added to the water to be treated, and the crystallization reaction is carried out under the condition of pH 4 or more and 9 or less using a crystallization reaction tank.

In the crystallization reaction method, the fluorine concentration in the water to be treated is preferably in the range of 5000 to 50000 mg/L.

In the crystallization reaction method, the concentration of the dispersant in the water to be treated is preferably at least 300 times the weight milligram of the square of the molar concentration of fluorine as a solid concentration.

In the crystallization reaction method, the dispersant preferably contains an acrylic acid-based chelating agent.

The present invention is a crystallization reaction apparatus for adding a calcium agent to fluorine-containing water to be treated to generate crystals of calcium fluoride and recovering the crystals of calcium fluoride, the apparatus comprising stirring means having stirring blades. and dispersant addition means for adding a dispersant to the water to be treated, wherein the crystallization reaction is carried out in the crystallization reaction tank under conditions of pH 4 or more and 9 or less. It is a device.

In the crystallization reactor, the fluorine concentration in the water to be treated is preferably in the range of 5000 to 50000 mg/L.

In the crystallization reactor, the concentration of the dispersant in the water to be treated is preferably 300 times the molar concentration of fluorine in weight milligrams or more as a solid concentration.

In the crystallization reactor, the dispersant preferably contains an acrylic acid-based chelating agent.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a crystallization reaction method and a crystallization reaction apparatus capable of recovering fluorine at a high recovery rate in a crystallization reaction using a stirred crystallization reaction tank.

1 is a schematic configuration diagram showing an example of a crystallization reactor according to an embodiment of the present invention; FIG. 2 is a graph showing fluorine recovery rates (%) in Examples and Comparative Examples.

An embodiment of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

An outline of an example of a crystallization reactor according to an embodiment of the present invention is shown in FIG. 1, and the configuration thereof will be described.

The crystallization reaction apparatus 1 according to the embodiment of the present invention is a crystallization reaction apparatus for adding a calcium agent to fluorine-containing water to be treated to generate calcium fluoride crystals and recovering the calcium fluoride crystals. A crystallization reaction tank 10 for carrying out a crystallization reaction, which is equipped with a stirring device 20 as stirring means having stirring blades, and a dispersant supply pipe 30 as dispersant addition means for adding a dispersant to the water to be treated. And prepare. The crystallization reaction apparatus 1 may include a water tank 12 to be treated that stores water to be treated and a calcium agent tank 14 that stores a calcium agent.

In the crystallization reaction apparatus 1 of FIG. 1 , the outlet of the water tank 12 to be treated and the inlet of the water to be treated of the crystallization reaction tank 10 are connected by a water supply pipe 22 to be treated via a pump 16 . A dispersant supply pipe 30 is connected to the dispersant inlet of the water tank 12 to be treated. The outlet of the calcium agent tank 14 and the calcium agent inlet of the crystallization reaction tank 10 are connected by a calcium agent supply pipe 24 via a pump 18 . A treated water discharge pipe 26 is connected to the treated water outlet on the upper side surface of the crystallization reaction tank 10 . A crystal discharge pipe 28 is connected to the crystal outlet at the bottom of the crystallization reaction tank 10 . The crystallization reaction tank 10 is provided with a stirring device 20 as a stirring means having driving means such as a motor and stirring blades for stirring the fluid in the crystallization reaction tank 10 . The stirring blades of the stirring device 20 are rotated by a rotational force generated by a motor transmitted via a stirring shaft. A pH adjusting agent supply pipe 32 may be connected to the pH adjusting agent inlet of the crystallization reaction tank 10 as pH adjusting means for adjusting the pH in the crystallization reaction tank 10 .

The operation of the crystallization reaction method and the crystallization reaction apparatus 1 according to this embodiment will be described.

The water to be treated containing fluorine is stored in the water tank 12 to be treated as needed. Here, a dispersant is added to the water to be treated through the dispersant supply pipe 30 in the water tank 12 to be treated (dispersant addition step). The water to be treated to which the dispersant has been added is supplied to the crystallization reaction tank 10 through the water to be treated supply pipe 22 by the pump 16 . A dispersant may be added to the water to be treated in the water to be treated supply pipe 22 . On the other hand, the calcium agent is stored in the calcium agent tank 14 as needed and supplied to the crystallization reaction tank 10 through the calcium agent supply pipe 24 by the pump 18 (calcium agent addition step). The calcium agent is preferably added near the stirring blades of the crystallization reaction tank 10 . If necessary, seed crystals may be supplied to the crystallization reaction vessel 10 (seeding step). A pH adjuster is added to the crystallization reaction tank 10 through the pH adjuster supply pipe 32, and the pH in the crystallization reaction tank 10 is adjusted to pH 4 or more and 9 or less (pH adjustment step). The inside of the crystallization reaction tank 10 is stirred by the stirring device 20 .

Then, in the crystallization reaction tank 10, fluorine contained in the water to be treated reacts with the calcium agent under the condition of pH 4 or more and 9 or less, and crystals of the sparingly soluble calcium salt of calcium fluoride are generated (crystallization reaction step). When seed crystals are present, sparingly soluble calcium salts of calcium fluoride are precipitated on the surfaces of the seed crystals to form crystals of the sparingly soluble calcium salts. The treated water in which fluorine has been reduced by the crystallization reaction in the crystallization reaction tank 10 is discharged through the treated water discharge pipe 26 . The sparingly soluble calcium salt of calcium fluoride produced in the crystallization reaction tank 10 is drawn out from the crystal discharge pipe 28, discharged, and recovered.

The present inventors have found that, in a crystallization reaction using a stirring type crystallization reaction tank, when a dispersant is added to fluorine-containing water to be treated, the amount of the dispersant in particular is 300 times the molar concentration of fluorine in milligrams or more. When added to fluorine-containing water to be treated, fluorine is recovered at a high recovery rate even under near-neutral conditions by performing a crystallization reaction between fluorine and a calcium agent under conditions of pH 4 or more and 9 or less. I found out what I can do. In the crystallization reaction using a stirring-type crystallization reaction tank, even under weakly acidic to weakly alkaline neutral conditions of pH 4 or more and 9 or less, when the dispersant is added to the water to be treated, the concentration of the dispersant, in particular, in the molar concentration of fluorine When added to the water to be treated in an amount of 300 times the square of the weight in milligrams or more, the chelate effect works, fine crystals are less likely to precipitate, and fluorine can be recovered at a high recovery rate. In addition, if the recovery rate is the same as when the dispersant is not added to the water to be treated, the crystallization reaction tank can be made smaller, the amount of seed crystals to be used can be reduced, and the fluorine concentration of the water to be treated can be reduced. has the advantage of being able to increase the

As described in Patent Documents 2 and 3, when using a stirred crystallization reactor, it is necessary to operate under strongly acidic conditions of pH 3 or less. The stirring type crystallization reaction tank is not practical because the recovery rate is low unless the pH is 3 or less and the condition is not strongly acidic. This is because the crystallization of calcium fluoride has a high reaction rate under neutral pH conditions, so that fine crystals of calcium salt are formed, making separation by precipitation difficult and reducing the recovery rate. On the other hand, in Patent Document 1, in which a crystallization reaction is performed using a dispersant, a fluidized bed type crystallization reaction tank for treating low-concentration fluorine-containing water is used, and the reaction is originally near neutral (pH 4 to 5 in the examples). ), and the premise is different.

Acidic hydrofluoric acid (HF) used in a stirring-type crystallization reaction tank is highly reactive under strongly acidic conditions of pH 3 or less, and requires careful handling. rice field. Since the pKa of HF is 3.15, HF becomes a fluoride ion under near-neutral conditions, and its reactivity is lower than that of hydrofluoric acid when it is acidic. It is possible to suppress the corrosion of

The fluorine-containing water to be treated may be water of any origin as long as it contains fluorine. Fluorine-containing water such as Fluorine contained in the water to be treated can exist in any state in the water to be treated as long as it is crystallized by a crystallization reaction. From the viewpoint of being dissolved in the water to be treated, fluorine is preferably in an ionized state. Here, the ionized state of fluorine includes, but is not limited to, fluorine ions (F ⁻ ) and ionized compounds containing elemental fluorine. Fluorine contained in the water to be treated preferably exists in the form of fluoride ions. Moreover, since hydrofluoric acid is a weak acid, it may exist in the form of molecular hydrogen fluoride (HF) depending on the pH.

Fluorine-containing wastewater is discharged, for example, from the electrolytic refining process of aluminum, the steelmaking process, and the like, but in particular, a large amount is discharged from the electronics industry such as semiconductor factories. Concentrated hydrofluoric acid is used for cleaning semiconductor silicon wafers, etc., and is discharged as concentrated hydrofluoric acid waste liquid with a fluorine content on the order of %. At this time, since ammonia, hydrogen peroxide, phosphoric acid, etc. are also used as cleaning agents, the wastewater may contain them. In addition, a large amount of water is used to clean hydrofluoric acid remaining on semiconductor silicon wafers and HF contained in gases after decomposition of perfluoro compounds (PFCs), and is also discharged as dilute fluorine-containing wastewater. . The water treatment method and water treatment apparatus according to this embodiment are particularly suitable for 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, in the range of 5000 to 50000 mg/L, preferably in the range of 5000 to 20000 mg/L, and 5000 to 10000 mg/L. is more preferably in the range of If the amount of fluorine contained in the water to be treated is less than 5000 mg/L, the efficiency of crystallization may deteriorate. However, crystallization may become difficult and the recovery rate may deteriorate. According to the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, fluorine can be recovered at a high recovery rate even under near-neutral conditions from high-concentration water to be treated, for example, 5000 mg/L or more.

Dispersants suppress scale on the surface of membranes, pipes, etc. or block the action of metal ions in various water treatment fields such as cooling water treatment systems, wastewater treatment systems, industrial water treatment systems, and pure water treatment systems. It refers to a compound used to reduce the cohesion of substances by The weight average molecular weight of the dispersant is, for example, 100,000 or less, and may be 20,000 or less. The dispersant does not include a flocculant having an action of flocculating fine particles, particularly a compound corresponding to an organic polymer flocculant. Such flocculants and organic polymer flocculants are described in Japanese Patent Application No. 2003-114697.

The dispersant is, for example, a scale inhibitor that suppresses scale formation, or a chelating agent that sequesters the action of metal ions. The scale inhibitor is not particularly limited, but examples thereof include polymers containing acid groups such as carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, and phosphinic acid groups. Examples of scale inhibitors include acrylic acid-based polymers, maleic acid-based polymers, methacrylic acid-based polymers, sulfonic acid-based polymers, phosphoric acid-based polymers, isobutylene-based polymers, and polymers thereof. It may be in the form of a water-soluble salt of the combination. Further, these polymers may be homopolymers obtained by polymerizing one type of monomer, or may be copolymers obtained from a plurality of types of monomers. In the case of a copolymer, for example, it may be a copolymer of one or more monomers having an acid group as described above and one or more other monomers.

A chelating agent forms a chelate compound with a metal and sequesters the metal ion to suppress its function, thereby obtaining a dispersing effect. Here, the chelating agent is not particularly limited, but for example, an organic carboxylic acid-based chelating agent, an aminocarboxylic acid-based chelating agent, a phosphonic acid-based chelating agent, an aminophosphonic acid-based chelating agent, or a polyphosphoric acid-based chelating agent agents and the like. Organic carboxylic acid-based chelating agents include gluconic acid, citric acid, oxalic acid, formic acid, tartaric acid, phytic acid, succinic acid, lactic acid, and acrylic acid. Aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraaminehexaacetic acid (TTHA), hydroxyethyl iminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG) and the like. Phosphonic acid-based chelating agents include hydroxyethylidene diphosphonic acid (HEDP) and the like. Examples of aminophosphonic acid-based chelating agents include ethylenediaminetetramethylenephosphonic acid (EDTMP) and the like. Polyphosphoric acid-based chelating agents include pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, and hexametaphosphoric acid.

As the dispersant, among these, chelating agents that are effective in suppressing the precipitation of calcium, for example, acrylic acid-based, phosphonic acid-based, and polyphosphoric acid-based (polymerized phosphoric acid)-based chelating agents. An acrylic acid-based chelating agent, which is an organic carboxylic acid-based chelating agent, is preferred because it is more effective in suppressing calcium deposition.

The amount ^of the dispersant contained in the water to be treated is not particularly limited. It is preferably in the range of L or more and 400 mg/L or less, more preferably in the range of 40 mg/L or more and 150 mg/L or less. If the amount of the dispersant contained in the water to be treated is less than 300 times the weight milligram of the square of the molar concentration of fluorine as a solid content concentration, the effect of promoting crystallization of fluorine becomes small, and the recovery rate of fluorine may decrease. However, if it exceeds 400 mg/L, crystallization may be adversely affected, and the treated water may flow out to the latter stage, which may adversely affect the coagulation and sedimentation of the latter stage. If the water to be treated contains a dispersant and the amount of the dispersant contained in the water to be treated is 300 times the weight milligram of the square of the molar concentration of fluorine as a solid content concentration, the dispersant is not added separately. If the amount of the dispersant contained in the water to be treated is less than 300 times the square of the molar concentration of fluorine in weight milligrams as a solid concentration, the dispersant may be added through the dispersant supply pipe 30 .

As the calcium agent, calcium chloride, slaked lime (calcium hydroxide), calcium carbonate and the like are used, and slaked lime is particularly preferably used from the viewpoint of chemical cost and the like. The calcium agent may be added in the form of a powder, an aqueous solution, or a slurry such as water. A preferred mode of adding the calcium agent is to add it as a calcium agent slurry.

When added as a calcium agent slurry, the concentration of the calcium agent slurry is not particularly limited, and may be, for example, a generally used range of 1% by mass to 20% by mass.

The amount of the calcium agent to be injected into the crystallization reaction tank 10 may be, for example, 0.8 to 2 times the chemical equivalent of fluorine, more preferably 1 to 2 times, more preferably 1 to 1 times the chemical equivalent of calcium. A .2-fold range is more preferred. If the chemical equivalent of calcium is more than twice the chemical equivalent of fluorine in the water to be treated, calcium fluoride and the like are likely to form as fine particles without precipitating on the seed crystals, resulting in contamination of the crystallization treated water with calcium fluoride and the like. If it is less than 0.8 times, the proportion of fluorine in the water to be treated that does not become calcium fluoride or the like increases, and fluorine may be mixed in the crystallization treated water.

Before the water to be treated and the calcium agent are added to the crystallization reaction tank 10, seed crystals may exist in advance in the crystallization reaction tank 10, or the water to be treated and the calcium agent may be added to the crystallization reaction tank 10. A seed crystal may be supplied into the crystallization reaction tank 10 while adding to the crystallization reaction tank 10 . In order to perform stable treatment, it is preferable that 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 crystallization reactor 1 may include a seed crystal tank, and the seed crystal inlet of the crystallization reaction tank 10 and the seed crystal tank outlet may be connected by a seed crystal addition pipe.

The seed crystal may be any material as long as it can precipitate crystals of the sparingly soluble calcium salt formed on its surface, and any material can be selected. Particles containing oxides of metal elements such as Random (trade name, manufactured by Nihon Cartrit Co., Ltd.), and particles containing sparingly soluble salts, which are precipitates due to crystallization reaction, may be mentioned. , but not limited to these. From the viewpoint of obtaining a more pure sparingly soluble salt in the form of pellets or the like, particles containing a sparingly soluble salt that is a precipitate produced by a crystallization reaction (for example, fluorite in the case of calcium fluoride) are preferable.

The crystallization reaction tank 10 is equipped with a stirring device having a stirring blade or the like, and the fluorine in the water to be treated reacts with the calcium agent to precipitate crystals of the sparingly soluble calcium salt, thereby producing treated water with reduced fluorine content. The length, inner diameter, shape, etc. of the reactor may be arbitrary, and are not particularly limited.

The crystallization reaction tank 10 includes a stirring type crystallization reaction tank in which a stirring device having a stirring blade or the like is installed and the inside of the crystallization reaction tank 10 is stirred by the stirring device to flow the pellets. The stirring blades are not particularly limited as long as they can stir the contents in the crystallization reaction tank 10, and the manner of installation of the stirring blades, the size of the stirring blades, and the like are not particularly limited.

The addition (injection point) of the calcium agent to the crystallization reaction tank 10 is preferably performed near the stirring blades of the stirring device 20 . By adding the calcium agent near the stirring blade, the calcium agent is diffused immediately after being injected into the crystallization reaction tank 10, and its concentration quickly decreases. As a result, the formed salt is less likely to precipitate directly into the liquid, and the fluorine in the liquid can be taken in over time as sparingly soluble salt crystals on the granular seed crystals in the crystallization reaction tank 10. can. In addition, the calcium agent becomes more soluble, and rapid reaction between the undissolved calcium agent and fluorine can be suppressed. As a result, it is possible to produce calcium fluoride with high particle uniformity and low moisture content.

The addition (injection point) of the water to be treated to the crystallization reaction tank 10 is also preferably performed near the stirring blades of the stirring device 20 . By adding the water to be treated in the vicinity of the stirring blade, the water to be treated is diffused immediately after being injected into the crystallization reaction tank 10, and the concentration of fluorine quickly decreases. For this reason, the fluorine in the liquid can be incorporated over time as the sparingly soluble salt crystals on the granular seed crystals in the crystallization reaction tank 10 . As a result, it is possible to produce calcium fluoride with higher particle uniformity and lower water content.

A pH adjuster such as an acid is added to the crystallization reaction tank 10 to adjust the pH of the crystallization reaction solution in the crystallization reaction tank 10 to a range of 4 or more and 9 or less, preferably 4.5 to 8. , 5 to 8. The concentration of fluorine in the crystallization-treated water can be reduced even when the crystallization reaction tank 10 is operated under near-neutral conditions in which the pH is in the range of 4 or more and 9 or less. The reason for this is thought to be that the chelating effect of the dispersant works more by operating at a pH in the range of pH 4 or more and 9 or less, and there is an effect that fine crystals are less likely to precipitate.

Examples of the pH adjuster include acids such as hydrochloric acid and sulfuric acid, and alkaline agents such as aqueous sodium hydroxide solution.

The liquid temperature in the crystallization reaction step is not particularly limited, and is, for example, in the range of 15 to 35°C. Since the separability changes depending on the viscosity and the like, it is desirable to adjust the liquid temperature so as to be as constant as possible.

Under the water surface of the crystallization reaction tank 10, a cylindrical draft tube having open upper and lower surfaces may be installed such that the stirring blades of the stirring device 20 are positioned in the cylinder. At this time, it is preferable that the stirring impeller forms a descending flow. When the draft tube is installed in this way, a downward flow is generated toward the lower part of the tube, forming a zone of relatively high diffusion velocity. For this reason, the water to be treated, the calcium agent, etc. can be diffused more quickly, and it is possible to prevent the direct generation of calcium fluoride particles due to the contact between regions with locally high concentrations of the water to be treated and the calcium agent. It is possible to suppress it as much as possible.

When the draft tube and the stirring blades are installed as described above, an upward flow zone with gentle flow is formed on the outer circumference of the draft tube. In this zone, particles are classified and small particles rise along the outer surface of the tube, enter the inside of the tube again from the upper end of the tube and descend, near the injection point of the water to be treated, calcium agents, etc. Recirculate to the agitation zone below it. These small grain size crystals act as nuclei to promote the crystallization reaction. Therefore, it is possible to stably form calcium fluoride crystals having a large particle size, and the recovery rate can be improved.

Furthermore, the crystals that have grown in size due to the progress of the crystallization reaction do not rise due to the upward flow around the outer circumference of the tube, but rather sink down and are less likely to enter the draft tube again. It is possible to suppress destruction by collision with. Such an advantage also contributes to stably obtaining calcium fluoride crystals having a large particle size, and can contribute to an improvement in recovery rate.

In order to form a zone with a relatively high agitation flow velocity in the lower part of the draft tube and to form a stable upward flow around the outer periphery of the tube, the agitation impeller should be positioned somewhere in the lower half of the tube. is preferred. More preferably, the position is slightly above the lower end of the tube. With such an arrangement, a zone of high agitation flow velocity is formed near the lower end of the tube like a vortex, and an upward flow is stably formed from there along the outer circumference of the tube. Therefore, it is possible to effectively promote the diffusion of the water to be treated, the calcium agent, etc., and the classification of the calcium fluoride particles.

When a draft tube is provided, the injection points of the water to be treated and the calcium agent are preferably placed inside the draft tube so that they can be quickly and effectively diffused by the downward flow in the draft tube. A more preferable position is inside the draft tube and above the stirring blades.

In the stirring-type crystallization reaction tank 10, an inner peripheral wall is arranged so as to face the peripheral wall of the crystallization reaction tank 10, and a treated water discharge passage is provided between the inner and outer peripheral walls, and the calcium fluoride particles and the crystallization treated water are discharged. It may have a separation zone that improves the separation ability of the crystallization treatment water and suppresses the outflow of calcium fluoride particles into the crystallization treated water. In this aspect, it is preferable that a crystallization treated water outlet is provided above the treated water discharge path and a pipe for discharging the crystallization treated water is connected to the crystallization treated water outlet. In addition, in order to improve the pellet separation performance, the treated water discharge channel has a baffle plate composed of a plurality of baffle plates and a baffle plate composed of a plurality of rectifying plates at the entrance portion of the treated water discharge channel. may be positioned. Details of this aspect are described in JP-A-2005-230735 and JP-A-2005-296888, and the crystallization reactors described in these patent documents can also be used in the present embodiment.

The amount of fluorine contained in the treated water in which fluorine has been reduced by the crystallization reaction in the crystallization reaction tank 10 is not particularly limited, but is, for example, 2000 mg/L or less, particularly in the range of 100 to 1000 mg/L. is. Most of the dispersant is incorporated into crystals of calcium fluoride, and the amount of the dispersant contained in the treated water is not particularly limited, but is, for example, 50 mg/L or less, particularly 1 to 30 mg/L. Range.

Calcium fluoride produced by the crystallization reaction in the crystallization reaction tank 10 is withdrawn from the crystal discharge pipe 28 and discharged out of the system. The method for drawing out calcium fluoride is not particularly limited, but it may be a method of drawing out calcium fluoride from the crystallization reaction tank 10 using a slurry pump such as a tube pump, or a method in which a valve is installed in the crystal discharge pipe 28 . may be attached, and calcium fluoride may be withdrawn from the crystallization reaction tank 10 simply by gravity.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Fluorine-containing water was prepared by adding hydrofluoric acid to purified water so that the fluorine concentration was 5500 mg-F/L and the fluorine concentration was 10000 mg-F/L. Furthermore, an acrylic acid-based chelating agent (Orpersion G600, manufactured by Organo Co., Ltd.) as a dispersant was used at a fluorine concentration of 5500 mg-F / L, and the solid content concentration was 0 mg / L (Comparative Example 1), 40 mg / L (Example 1), added to 120 mg/L (Example 2), and when the fluorine concentration was 10000 mg-F/L, the solid content concentration was 80 mg/L (Comparative Example 2) and 200 mg/L (Example 3). The water to be treated was obtained by adding and stirring so that A pH adjuster (hydrochloric acid or aqueous sodium hydroxide solution) was added to the water to be treated and stirred to adjust the pH of the reaction solution in the crystallization reaction tank to 4 or more and 9 or less.

Here, when the fluorine concentration of the water to be treated is 5500 mg / L, 300 times the weight milligram of the square of the molar concentration of fluorine is
F = 5500 mg / L = 0.29 mol / L → squared → 0.084 × 300 → 25 mg / L,
When the fluorine concentration of the water to be treated is 10000 mg / L, 300 times the weight milligram of the square of the molar concentration of fluorine is
F = 10000 mg/L = 0.53 mol/L → squared → 0.28 x 300 → 84 mg/L.

As the crystallization reaction tank, an acrylic reaction tank with a capacity of 10 L was used, and 5000 g of calcium fluoride (fluorite) seed crystals were filled in the tank as seed crystals and flowed by a stirrer having a stirring blade. A 5% by mass calcium hydroxide aqueous solution was supplied to the crystallization reactor as a calcium agent so that the residual calcium concentration in the treated water was 500 to 1000 mg-Ca/L.

<Example 1>
Hydrofluoric acid was added to purified water so that the fluorine concentration was 5500 mg-F/L to prepare fluorine-containing water, and an acrylic acid-based chelating agent (Orpersion G600) was added as a dispersant to a solid concentration of 40 mg/L. The water to be treated was obtained by adding and stirring so that Fluoride ion concentrations in the water to be treated and the resulting treated water were measured by lanthanum alizarin complexon spectrophotometry. The F recovery rate was 84% to 99%, averaging 95%, based on the mass balance of the F concentrations in the water to be treated and the treated water.

<Example 2>
Hydrofluoric acid was added to purified water so that the fluorine concentration was 5500 mg-F/L to prepare fluorine-containing water, and an acrylic acid-based chelating agent (Orpersion G600) was added as a dispersant to a solid concentration of 120 mg/L. The water to be treated was obtained by adding and stirring so that The F recovery rate was 79 to 95%, with an average of 90%, based on the mass balance of the F concentrations in the water to be treated and the treated water.

<Example 3>
Hydrofluoric acid was added to purified water so that the fluorine concentration was 10000 mg-F/L to prepare fluorine-containing water, and an acrylic acid-based chelating agent (Orpersion G600) was added as a dispersant to a solid concentration of 200 mg/L. The water to be treated was obtained by adding and stirring so that The F recovery rate was 91 to 99%, with an average of 96%, based on the mass balance of the F concentrations in the water to be treated and the treated water.

<Comparative Example 1>
Hydrofluoric acid was added to purified water so that the fluorine concentration was 5500 mg-F/L to prepare fluorine-containing water. The F recovery rate was 33 to 63%, with an average of 47%, based on the mass balance of the F concentrations in the water to be treated and the treated water.

<Comparative Example 2>
Hydrofluoric acid was added to purified water so that the fluorine concentration was 10000 mg-F/L to prepare fluorine-containing water, and an acrylic acid-based chelating agent (Orpersion G600) was added as a dispersant to a solid concentration of 80 mg/L. The water to be treated was obtained by adding and stirring so that From the mass balance of the F concentrations in the water to be treated and the treated water, the F recovery rate was 0 to 43%, with an average of 21%.

Thus, according to the method of the example, in the crystallization reaction using a stirred crystallization reaction tank, fluorine could be recovered at a high recovery rate even under near-neutral conditions.

[Confirmation of crystallization effect by type of dispersant]
Pure water and a dispersant shown in Table 1 were added to a 1 L beaker. Sodium fluoride and calcium chloride solutions were added with stirring to the predetermined concentrations shown in Table 1, and the pH was adjusted to 7 with hydrochloric acid or sodium hydroxide aqueous solution. After 24 hours, the sample was filtered through a 0.2 μm filter, and the fluorine concentration and calcium concentration were measured by an ion chromatograph device Dionex Integrion (manufactured by Thermo Fisher) and atomic absorption spectrophotometry. If the fluorine concentration and calcium concentration did not decrease (10% or more) compared to the raw water concentration, it was judged that no precipitate was formed (judgment: ◯), and the fluorine concentration and calcium concentration compared to the raw water concentration was judged to have formed precipitates (judgment: ×). Table 1 shows the results.

It is preferable that the dispersant be effective in suppressing precipitation of calcium. The effect of suppressing calcium deposition varies depending on conditions such as fluorine concentration, calcium concentration, and pH, but the results of the above test showed that the acrylic acid system was the most effective in the high calcium concentration range (No. 4 to 6). The effect of increasing the recovery rate of calcium fluoride was obtained by adding a dispersant at a solid concentration of 40 mg/L or more.

1 Crystallization reactor 10 Crystallization reaction tank 12 Water tank to be treated 14 Calcium agent tank 16, 18 Pump 20 Stirrer 22 Water to be treated supply pipe 24 Calcium agent supply pipe 26 Treated water discharge pipe 28 crystal discharge pipe, 30 dispersant supply pipe, 32 pH adjuster supply pipe.

Claims (8)

A crystallization reaction method in which a calcium agent is added to fluorine-containing water to be treated to generate calcium fluoride crystals, and the calcium fluoride crystals are recovered,
A crystallization reaction method comprising adding a dispersant to the water to be treated and carrying out the crystallization reaction under conditions of pH 4 or more and 9 or less using a crystallization reaction tank equipped with stirring means having a stirring blade. The crystallization reaction method according to claim 1,
The crystallization reaction method, wherein the fluorine concentration in the water to be treated is in the range of 5000 to 50000 mg/L. The crystallization reaction method according to claim 1 or 2,
The crystallization reaction method, wherein the concentration of the dispersant in the water to be treated is 300 times the weight milligram of the square of the molar concentration of fluorine as a solid content concentration. The crystallization reaction method according to any one of claims 1 to 3,
The crystallization reaction method, wherein the dispersant contains an acrylic acid-based chelating agent. A crystallization reactor for adding a calcium agent to water to be treated containing fluorine to generate calcium fluoride crystals and recovering the calcium fluoride crystals,
a crystallization reactor equipped with stirring means having stirring blades;
dispersant addition means for adding a dispersant to the water to be treated;
with
A crystallization reaction apparatus characterized in that the crystallization reaction is carried out under the condition of pH 4 or more and 9 or less in the crystallization reaction tank. A crystallization reactor according to claim 5,
The crystallization reactor, wherein the fluorine concentration in the water to be treated is in the range of 5000 to 50000 mg/L. The crystallization reactor according to claim 5 or 6,
The crystallization reaction apparatus, wherein the concentration of the dispersant in the water to be treated is 300 times the weight milligram of the square of the molar concentration of fluorine as a solid content concentration. The crystallization reactor according to any one of claims 5 to 7,
The crystallization reactor, wherein the dispersant contains an acrylic acid-based chelating agent.