JP2006007010A - Crystallization treatment method of fluorine-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine crystallization treatment method which enables the supply of phosphate ions and sulfate ions to a crystallization reaction tank. <P>SOLUTION: The fluorine crystallization treatment method yields treated water of reduced fluorine by supplying fluorine-containing water to be treated, a crystallization agent, and the phosphate ions and the sulfate ions to the crystallization reaction tank and precipitating fluorine compounds onto seed crystals in the crystallization reaction tank to form pellets. This method can prevent the generation of white turbidity in the treated water, and enables stable and efficient crystallization and removal of fluorine even when the water to be treated contains high concentration of fluorine. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fluorine crystallization treatment method for crystallizing and removing fluorine from water to be treated containing fluorine. In particular, the present invention relates to a fluorine crystallization treatment method in which phosphate ions and sulfate ions are supplied to a crystallization reaction tank.

  In the electronics industry that manufactures semiconductors and liquid crystals, fluorine is often contained in wastewater because fluorine is used in the manufacturing process. In Japan, the emission standard value for fluorine was strengthened from 15 mg / L to 8 mg / L in July 2001, and the need for fluorine removal is increasing. As a method for removing fluorine, calcium salt is added to water to be treated to precipitate calcium fluoride fine particles, and these fine particles are agglomerated with an Al or Fe inorganic flocculant or organic polymer flocculant. Thus, a method of sedimentation and separation is mainly employed. In addition, as one of the methods for precipitating and separating fluorine in wastewater by insolubilization, a method of adding a calcium compound and adding sulfate ions to fluorine-containing wastewater is also disclosed (Patent Document 1: Japanese Patent Application Laid-Open No. 2000-200027). -334470).

  Also, wastewater from the electronics industry often contains phosphorus as well as fluorine in the wastewater, and it is necessary to remove phosphorus from the viewpoint of preventing eutrophication in closed waters. It is the target of. In the removal of phosphorus, as in the case of fluorine, in addition to adding calcium salt and coagulating and precipitating as calcium phosphate, it is coagulating and precipitating as aluminum phosphate or iron phosphate using Al or Fe inorganic coagulant. Yes.

  The sludge produced by adding Al or Fe-based flocculant in the above coagulation sedimentation method incorporates water molecules inside the floc, so the sludge is poorly dewatered and the amount of sludge generated is extremely high, resulting in sludge disposal. There is a problem that it is expensive.

  On the other hand, a fluorine or phosphorus-containing waste water and a metal that serves as a crystallization agent are supplied to a reaction tank that holds the crystallized product in a fluid state, and a metal fluoride or a phosphate compound is supplied to the surface of the crystallized product. There is a method called a crystallization method for precipitating on a film (Patent Document 2: JP-A-60-206485). In the crystallization method, in general, water to be treated is introduced from the lower part of the reaction tank, and water is flowed upward while fluidizing the solid particles that are crystallized, and the reaction tank flows out as necessary. Water is circulated to the reaction vessel. As a crystallization agent capable of crystallizing fluorine and phosphoric acid, a water-soluble compound containing at least one kind of metal element of Ca, Mg, rare earth metal, Ti, Zr, Hf, V, Nb, and Ta is known. (Patent Document 3: Japanese Patent Application Laid-Open No. 2004-97861). Metal fluoride or phosphoric acid compound particles generated by reaction with metal elements contained in the crystallizer have low water content and high purity, so that fluorine and phosphorus can be recovered and reused, and the equipment installation area can be reduced. Advantages such as low sludge generation are mentioned.

JP 2000-334470 A JP 60-206485 A Japanese Patent Application Laid-Open No. 2004-97861

However, in order to perform a favorable process in the fluorine crystallization removal process, it is necessary to control the reaction conditions between fluorine and the crystallization reaction element added as a crystallization agent so that the crystallization reaction easily occurs.
In the crystallization process of fluorine, for example, in the calcium fluoride crystallization method in which calcium (Ca) is used as a crystallization reaction element to produce calcium fluoride (CaF ₂ ) crystals, crystal growth of calcium fluoride occurs. It is necessary to control the reaction conditions to a supersaturated state called a metastable region. In general, the reaction conditions are controlled by adjusting the amount of calcium agent, which is a crystallization agent. However, when the fluorine concentration in the wastewater rises rapidly, the relationship between fluorine and calcium is unstable. Enter the area. Since the crystal formation reaction rate of calcium fluoride is fast in the unstable region, crystal growth does not occur on the solid particles, and fine particles are generated and the treated water becomes cloudy. Moreover, in order to control the relationship between fluorine and calcium to a supersaturated state, the higher the fluorine concentration in the wastewater, the narrower the allowable range of the amount of calcium added, so that the control becomes difficult, and white turbidity of the treated water is likely to occur. Furthermore, if the amount of calcium added is reduced to prevent white turbidity, the residual fluorine concentration in the treated water increases and the water quality deteriorates. From the above, in order to perform a stable treatment, there are restrictions on the fluorine concentration in the waste water and the fluorine load that can be introduced into the crystallization reaction tank.

  The present invention has been made in view of such circumstances, and in a crystallization reaction system that crystallizes and removes fluorine from water to be treated using a crystallization reaction element, the crystallization reaction system includes the crystallization reaction system. By adding phosphate ions and sulfate ions, it is possible to suppress the occurrence of white turbidity in the treated water in the crystallization treatment, and even if the treated water contains a high concentration of fluorine, stable and efficient crystallization of fluorine is possible. An object of the present invention is to provide a fluorine crystallization treatment method that can be removed by precipitation.

In the first aspect of the present invention, fluorine-containing water to be treated, a crystallization reaction element, phosphate ions and sulfate ions are supplied to a crystallization reaction tank, and a fluorine compound is deposited on the seed crystal in the crystallization reaction tank. Provided is a fluorine crystallization treatment method for producing treated water with reduced fluorine by forming pellets by precipitation.
As a second aspect of the present invention, the amount of phosphate ions supplied to the crystallization reaction tank is 0.2 to 0.6 times the amount of fluorine supplied to the crystallization reaction tank (PO ₄ ³⁻ Weight / F weight), the fluorine crystallization treatment method of the first aspect is provided.
In the third aspect of the present invention, the amount of sulfate ions supplied to the crystallization reaction tank is 1.5 to 10 times the amount of fluorine supplied to the crystallization reaction tank (SO ₄ ^2- weight / F The fluorine crystallization treatment method of the first or second aspect is provided.

  The present invention relates to a crystallization treatment method in which phosphoric acid ions and sulfate ions are supplied to a crystallization reaction tank in a fluorine crystallization treatment method for producing treated water with reduced fluorine from treated water containing fluorine. Generation of white turbidity can be suppressed, and even if the water to be treated contains a high concentration of fluorine, the fluorine can be crystallized and removed stably and efficiently. Moreover, in the fluorine crystallization treatment method, the above advantageous effect when both phosphate ions and sulfate ions are supplied to the crystallization reaction tank is that each of phosphate ions or sulfate ions is added to the crystallization reaction tank alone. Compared to the case, it was a synergistic effect exceeding a simple additive effect.

The treated water containing fluorine in the present invention may be treated water of any origin as long as it contains fluorine. For example, from the electronics industry including the semiconductor-related industry, the power plant, the aluminum industry, etc. Examples include, but are not limited to, discharged wastewater. The fluorine contained in the water to be treated can be present in the water to be treated in any state 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. Examples of the ionized state include, but are not limited to, fluorine ions (F ⁻ ) or those in which a compound containing a fluorine element is ionized. The fluorine contained in the water to be treated is preferably present in the form of fluorine ions. Further, since hydrofluoric acid is a weak acid, it may exist in the form of molecular hydrogen fluoride (HF) depending on the pH.
The amount of fluorine contained in the water to be treated containing fluorine is not particularly limited, but is preferably 10,000 mg · F / L or less, more preferably 1000 mg · F / L or less.
Moreover, the water to be treated containing fluorine in the present invention may contain any other component other than fluorine in any amount, and may contain phosphate ions and sulfate ions.

  The crystallization reaction element in the method of the present invention refers to an element that can react with fluorine contained in water to be treated to crystallize and remove fluorine. Preferably, the crystallization reaction element includes Ca, Mg, rare earth elements, Ti, Zr, Hf, V, Nb, and Ta. More preferably, the crystallization reaction element is Ca or Mg, and more preferably Ca. In the present invention, when supplying the crystallization reaction element to the crystallization reaction tank, a crystallization agent that is an arbitrary compound containing one or more of the crystallization reaction elements is used. Preferably, the crystallizing agent is a compound containing at least one element of Ca, Mg, rare earth elements, Ti, Zr, Hf, V, Nb, and Ta, and a mixture of two or more of the compounds. More preferably, the crystallization agent is a compound containing Ca and Mg, and even more preferably a compound containing Ca. For example, when Ca and Mg are used, chlorides, hydroxides, carbonate compounds and the like can be mentioned. Examples of rare earth elements include Sc, Y, and lanthanoids La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Examples of the agent include chlorides, sulfates and nitrates. Further, Ti, Zr, Hf, V, Nb, Ta chlorides, sulfates, nitrates, chlorides, and sulfates can also be used as a crystallization agent. As described above, the crystallization agent is exemplified, but is not limited thereto, and phosphate, sulfate, etc. that can be a source of phosphate ions and sulfate ions, as long as the object of the present invention is not violated. Any compound may be used.

  The crystallization agent is preferably supplied to the crystallization reaction tank as a crystallization agent-containing liquid containing a crystallization agent, and may be supplied to the crystallization reaction tank in a solution state dissolved in a liquid medium. Alternatively, all or a part of the slurry may be supplied in the form of a slurry that remains as a solid in the liquid medium. The liquid medium is not particularly limited, but is preferably water. The concentration of the crystallization agent contained in the crystallization agent-containing liquid is appropriately set according to the solubility of the crystallization agent, the fluorine concentration in the water to be treated, the treatment capacity of the crystallization reaction tank, the amount of the treated water to be circulated, and the like. .

  The amount of the crystallization reaction element supplied to the crystallization reaction tank can also be set as appropriate. For example, when calcium is used as the crystallization reaction element, that is, when calcium fluoride is crystallized, the supply amount of calcium is at least a molar ratio of fluorine to fluorine supplied to the crystallization reaction tank: It is desirable that calcium = 2: 1, ie, fluorine: calcium = 1: (20/19) by weight ratio. In order to crystallize calcium fluoride, it is preferable that calcium is present excessively with respect to the amount of calcium required by the weight ratio of the above formula. On the other hand, it is more preferable to supply calcium so that the concentration in the crystallization reaction tank is 200 to 600 mg · Ca / L excess. The amount of calcium supply can be controlled using the calcium concentration in the treated water generated by the fluorine crystallization treatment as an index, that is, the calcium concentration remaining in the treated water is controlled to be 200 to 600 mg · Ca / L. It is preferable.

In the present invention, phosphate ions and sulfate ions are supplied to a crystallization reaction tank in which fluorine crystallization treatment is performed. The phosphate ion in the present invention is not only PO ₄ ^3- which is an anion in which phosphoric acid (H ₃ PO ₄ ) is completely ionized, but also an ion in which phosphoric acid is partially ionized, or an ionic form Some salts thereof are also included, such as H ₂ PO ₄ ⁻ , HPO ₄ ²⁻ , NaPO ₄ ²⁻ , KPO ₄ ²⁻ , Na ₂ PO ₄ ⁻ , K ₂ PO ₄ ⁻ , NaHPO ₄ ⁻ , KHPO ₄ ^{− and the} like. This ion form also corresponds to the phosphate ion in the present invention. However, when the supply amount of phosphate ions to the crystallization reaction tank is shown, the weight and concentration in terms of PO ₄ ³⁻ are used as the supply amount of phosphate ions. In this case, (PO ₄ ^{3 −} ) It is clearly indicated that
In addition, the sulfate ion in the present invention is not only SO ₄ ^2- which is an anion of a form in which sulfuric acid (H ₂ SO ₄ ) is completely ionized, but also an ion or an ion form in which sulfuric acid is partially ionized. Also includes salts. However, when the supply amount of sulfate ion to the crystallization reaction tank is shown, the weight and concentration in terms of SO ₄ ²⁻ are used as the supply amount of sulfate ion. In this case, (SO ₄ ²⁻ ) It is clearly shown that

The amount of phosphate ions and sulfate ions supplied to the crystallization reaction tank depends on the inflow concentration of fluorine supplied to the crystallization reaction tank, the type and amount of coexisting substances in the treated water, and the type of crystallization reaction elements used. However, if the amount of phosphate ion and sulfate ion is small, it will not be possible to effectively prevent white turbidity in the treated water. When an insoluble compound derived from sulfate ion itself, for example, a calcium compound is used as a crystallization agent, white turbidity occurs due to calcium phosphate or calcium sulfate, which is not economically preferable. Regarding phosphate ions, preferably, the amount of phosphate ions (PO ₄ ³⁻ ) supplied to the crystallization reaction tank is 0.1 to 1 of the amount of fluorine (F) supplied to the crystallization reaction tank. The amount is 0.0 times (PO ₄ ^3- weight / F weight), more preferably 0.2 to 0.6 times (PO ₄ ^3- weight / F weight). For sulfate ions (SO ₄ ²⁻ ), preferably, the amount of sulfate ions supplied to the crystallization reaction tank is 1.0 to 15 of the amount of fluorine (F) supplied to the crystallization reaction tank. Double amount (SO ₄ ^2- weight / F weight), more preferably 1.5 to 10 times (SO ₄ ^2- weight / F weight). The preferred weight ratio described above is based on the total amount of phosphate ions or sulfate ions supplied to the crystallization reaction tank.

  As an aspect of supplying phosphate ions and sulfate ions to the crystallization reaction tank, it is supplied to the crystallization reaction tank where the crystallization treatment is performed, and the present invention of suppressing the white turbidity of the treated water and reducing the total fluorine concentration in the treated water Any method and means can be adopted as long as the above effect can be achieved, and there is no particular limitation. For example, by adding phosphate ions and sulfate ions to one or more of the water to be treated, the crystallization agent, and the circulated treated water supplied to the crystallization reaction tank, the crystallization reaction can be performed via these treated water. A mode of supplying to the tank is possible. An embodiment in which phosphate ions and sulfate ions are directly supplied to the crystallization reaction tank is also possible. For example, when a crystallization reaction apparatus as shown in FIG. 1 is used, it may be supplied directly to the crystallization reaction tank 1, the treated water supply line 3, the treated water storage tank 4, the crystal It can be supplied from any one of the depositing agent supply line 5, the crystallizing agent storage tank 10, the treated water storage tank 7, and the treated water circulation line 8. In addition, phosphate ions and sulfate ions may be supplied at the same point of the apparatus, or may be supplied separately at different points of the apparatus. Further, phosphate ions and sulfate ions may be supplied at a plurality of points.

  The supply substance that is a source of phosphate ions supplied to the crystallization reaction tank is not particularly limited. However, in consideration of ease of supply, phosphoric acid or a phosphate having high solubility in water, For example, alkali metal (sodium, potassium, etc.) salts of phosphoric acid are preferable. In addition, the compound serving as a source of sulfate ions supplied to the crystallization reaction tank is not particularly limited, but considering the ease of supply, sulfuric acid, sulfate having high solubility in water, for example, sulfuric acid Alkali metal (sodium, potassium, etc.) salts are preferred.

  In the present invention, when the pH in the crystallization reaction field where the crystallization reaction is performed in the crystallization reaction tank is in the alkaline range, it is derived from phosphate ions supplied to the crystallization reaction tank, for example, calcium phosphate. Therefore, it is preferable to maintain the pH of the treated water discharged from the crystallization reaction tank in the range of 3 to 7. The pH can be adjusted by any known method. For example, the pH of the treated water discharged from the crystallization reaction tank outlet or the seed crystal filling part of the crystallization reaction tank can be adjusted by any known apparatus such as a pH meter. It is possible to adjust by supplying any acid or alkali to the crystallization reaction tank by any route according to the measured value.

  FIG. 1 is a schematic view showing an example of a crystallization reaction apparatus that can be used in the fluorine crystallization treatment method of the present invention, and the present invention will be described in detail based on this. The crystallization reaction apparatus includes a crystallization reaction tank 1 that discharges treated water in which a crystallization reaction is performed and fluorine is reduced, and a water to be treated supply unit that supplies treated water containing fluorine to the crystallization reaction tank 1. And a crystallization agent supply means for supplying the crystallization agent to the crystallization reaction tank 1, and optionally returning at least a part of the treated water discharged from the crystallization reaction tank to the crystallization reaction tank 1. Treated water circulation means. The seed crystal filling section 2 of the crystallization reaction tank 1 is filled with seed crystals, and the reaction between fluorine contained in the water to be treated and the crystallization reaction elements in the crystallizer on the surface of the seed crystals. By precipitating a fluorine compound as a product to form a pellet, treated water with reduced fluorine is discharged. In the present invention, the phrase “precipitate the fluorine compound on the seed crystal” not only means that the fluorine compound is deposited directly on the seed crystal but also a fluorine compound further deposited on the fluorine compound precipitated on the seed crystal. It also includes precipitation. As long as the crystallization reaction tank 1 has the above-mentioned functions, the length, the inner diameter, the shape and the like can be in any form and are not particularly limited.

  The amount of seed crystals filled in the crystallization reaction tank 1 is not particularly limited as long as fluorine can be removed by a crystallization reaction. The concentration of fluorine in the water to be treated, the concentration of the crystallization agent, It is set as appropriate according to the operating conditions of the crystallization reaction apparatus. In the crystallization reaction apparatus, the crystallization reaction tank 1 is preferably a fluidized bed in which an upward flow is formed in the crystallization reaction tank 1 and the pellets are flowed by the upward flow. The crystallization reaction tank 1 is preferably filled in an amount.

  As long as the seed crystal is not contrary to the object of the present invention, any material can be used. For example, filtered sand, activated carbon, zircon sand, garnet sand, and sac random (trade name, manufactured by Nippon Carlit Co., Ltd.) And particles composed of oxides of metal elements such as, and particles composed of fluorine compounds that are precipitates by a crystallization reaction, including calcium fluoride, but are not limited thereto. . From the viewpoint that a purer fluorine compound can be obtained as pellets, particles made of a fluorine compound that is a precipitate by a crystallization reaction are preferable. For example, when a calcium compound is used as a crystallizing agent, it is possible to obtain a crystallization reaction on the seed crystal and from the viewpoint that more pure calcium fluoride can be recovered from the pellets produced. Calcium fodder (fluorite) is preferably used as a seed crystal. The shape and particle size of the seed crystal are appropriately set according to the flow rate in the crystallization reaction tank 1, the fluorine concentration and the concentration of the crystallization agent, the concentration of the supplied phosphate ion and sulfate ion, and the like. There is no particular limitation as long as it does not contradict the purpose.

The treated water supply means can be in any form as long as it can supply treated water containing fluorine to the crystallization reaction tank 1. In the embodiment of FIG. 1, to-be-treated water containing fluorine is supplied to the crystallization reaction tank 1 from the to-be-treated water supply line 3 connected to the crystallization reaction tank 1. In order to make the fluorine concentration in the treated water constant, the treated water supply line 3 may be connected to a treated water storage tank 4 that can temporarily store the treated water.
The crystallization agent supply means can be in any form as long as the crystallization agent can be supplied to the crystallization reaction tank 1. In the embodiment of FIG. 1, the crystallization agent is supplied from the crystallization agent storage tank 10 to the crystallization reaction tank 1 through the crystallization agent supply line 5.

  The treated water supply line 3 and the crystallization agent supply line 5 can be connected to any part of the crystallization reaction tank 1. In the crystallization reaction apparatus that can be used in the present invention, from the viewpoint that when the upward flow is formed in the crystallization reaction tank 1, the crystallization reaction can be efficiently performed, the treated water supply line 3 and the crystallization reaction are performed. The agent supply line 5 is preferably connected to the lower part of the crystallization reaction tank 1, particularly to the bottom part. Moreover, in the aspect of FIG. 1, although the to-be-processed water supply line 3 and the crystallization agent supply line 5 are each one, it is not limited to this, These may be provided with two or more.

  The crystallization reaction tank 1 discharges treated water in which fluorine generated by the crystallization reaction is reduced to the outside of the crystallization reaction tank 1. The treated water is discharged from an arbitrary part according to the liquid flow in the crystallization reaction tank 1. When an upward flow is formed in the crystallization reaction tank 1, treated water is discharged from the upper part of the crystallization reaction tank 1. In the embodiment of FIG. 1, the treated water discharged from the upper part of the crystallization reaction tank 1 is finally discharged out of the system through the treated water discharge line 6. In the embodiment of FIG. 1, a treated water storage tank 7 is interposed in the treated water discharge line 6, but this installation is optional. It is also possible to provide other means such as a pH measuring means such as a pH meter used in ordinary water treatment, and a pH adjusting means for supplying acid and alkali. In the embodiment of FIG. 1, a pH meter is provided in the upper part of the crystallization reaction tank 1.

The crystallization treatment apparatus of FIG. 1 has treated water circulation means for returning at least a part of the treated water discharged from the crystallization reaction tank 1 to the crystallization reaction tank 1. The treatment water circulation means can be any mode as long as at least a part of the treatment water can be returned to the crystallization reaction tank 1, and is not particularly limited. In the embodiment of FIG. 1, a treated water circulation line 8 connecting the treated water storage tank 7 and the crystallization reaction tank 1 is provided as treated water circulation means, and the treated water circulation line 8 has a pump for transferring treated water. Is intervening. The treated water circulation means dilutes the treated water supplied into the crystallization reaction tank 1 by circulating the treated water to the crystallization reaction tank 1, mixes the crystallization agent and the treated water, A predetermined flow, preferably an upward flow, can be formed in the crystallization reaction tank 1. Therefore, when an upward flow is formed in the crystallization reaction tank 1, an embodiment in which the treated water circulation line 8 is connected to the lower part of the crystallization reaction tank 1, particularly the bottom part as shown in FIG. 1 is preferable. .
Further, in the embodiment of FIG. 1, the treated water storage tank 7 functions as a means for branching the treated water to be circulated and the treated water discharged out of the system, and forms treated water circulating means. The formation of the treated water circulation means is not limited to this form, and any form such as a form in which the treated water circulation line 8 branches directly from the treated water discharge line 6 is possible.

  In the method of the present invention, phosphate ions and sulfate ions are supplied to a crystallization reaction tank in which fluorine crystallization reaction is performed. Although this supply mode has already been described, for example, a supply line 9 is connected to the treated water storage tank 4, and phosphate ions and / or sulfate ions are supplied from the supply line 9 to the treated water storage tank 4. By this, the aspect by which the to-be-processed water containing a fluorine and the phosphate ion and / or a sulfate ion in the to-be-processed water storage tank 4 may be mixed. Moreover, the supply line 9a may be connected to the to-be-processed water supply line 3, and the to-be-processed water containing a fluorine and the phosphate ion and / or a sulfate ion may be mixed in the to-be-processed water supply line 3.

Further, as another embodiment, a mode in which a supply line 9b is directly connected to the crystallization reaction tank 1 and phosphate ions and / or sulfate ions are directly supplied into the crystallization reaction tank 1 from the supply line 9b. Is possible. Furthermore, as another embodiment, phosphate ions and / or sulfate ions are added to the treated water circulated in the crystallization reaction tank 1, and phosphate ions and / or sulfate ions are crystallized together with the circulated treated water. A mode of supplying to the reaction tank 1 is also possible. In this case, for example, a supply line 9 c is connected to the treated water circulation line 8, and treated water and phosphate ions and / or sulfate ions are mixed in the treated water circulation line 8 and supplied to the crystallization reaction tank 1. Also good. Further, a supply line 9d is connected to the treated water storage tank 7, and phosphate ions and / or sulfate ions are supplied to the treated water storage tank 7 from the supply line 9d, so that the treated water is stored in the treated water storage tank 7. A mode in which phosphate ions and / or sulfate ions are mixed and treated water containing phosphate ions and / or sulfate ions is supplied to the crystallization reaction tank 1 may be employed. Further, a supply line 9e is connected to the crystallization agent supply line 5, or a supply line 9f is provided in the crystallization agent storage tank 10, and phosphate ions and / or sulfate ions are supplied from these supply lines 9e or 9f. In this case, phosphate ions and / or sulfate ions may be supplied to the crystallization reaction tank 1 together with the crystallization agent.
EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

Sodium fluoride is dissolved in purified water so as to have a fluorine concentration of 1000 mg · F / L. Further, an aqueous solution of phosphoric acid and an aqueous solution of sulfuric acid are mixed with a phosphate ion concentration of 0 to 700 mg · PO ₄ ³⁻ / L and sulfate ions. A fluorine crystallization test was performed by the flow of the embodiment shown in FIG. 1, with water to be treated added and stirred so that the concentration was 0 to 11000 mg · SO ₄ ²⁻ / L. In addition, the pH of the water to be treated is adjusted so that the pH of the crystallization water at the outlet of the crystallization reaction tank becomes 4 to 5 by adding and stirring a pH adjuster (NaOH) to the water tank to be treated. It was. As described above, the supply of phosphate ions and sulfate ions to the crystallization reaction tank in the present invention is performed by mixing the treated water, phosphoric acid and sulfuric acid in the treated water storage tank, and supplying this to the crystallization reaction tank. Done by feeding.

As the crystallization reaction tank, a cylindrical acrylic column having an inner diameter of 20 mmφ, a height of 2.5 m, and a capacity of 0.8 L, filled with 150 mL of a natural calcium fluoride (fluorite) seed crystal having a particle size of about 0.1 mm was used. . The treated water storage tank had a capacity of 100 L, the treated water storage tank had a capacity of 500 mL, and the crystallizer storage tank had a capacity of 10 L. Water flow to the crystallization reaction tank is such that fluorine load = 3 kg · F / m ² / h and treated water is circulated to the crystallization reaction tank so that LV = 40 m / h, and the treated water is crystallized. Feeded to the tank. The seed crystals and pellets in the crystallization reaction tank were in a fluidized bed when water was passed. A 10% calcium chloride aqueous solution was supplied as a crystallization agent to the crystallization reaction tank so that the residual calcium concentration in the treated water was 300 to 500 mg · Ca / L.

  About the treated water 3 hours after the start of liquid flow, the total fluorine concentration (total F concentration) and the soluble fluorine concentration (soluble F concentration) in the treated water, and the turbidity of the treated water were measured. The total fluorine concentration is the total concentration of fluorine present in a dissolved state in the treated water and fluorine present as an insoluble substance (white turbid substance). The insoluble substance (white turbid substance) in the treated water is dissolved and the treated water is separated into insoluble substances. It is obtained by measuring. The soluble fluorine concentration is a fluorine concentration existing in a state of being dissolved in the treated water, and can be obtained by measuring the treated water after removing insoluble substances (white cloudy substances) by membrane filtration. The fluorine concentration is measured by ion chromatography, and the turbidity is the result of measuring the integrating sphere turbidity. The results are shown in Table 1.

Comparative Examples 1-3
In Comparative Example 1 in which neither phosphate ion nor sulfate ion was supplied, the soluble fluorine concentration in the treated water was reduced to 8 mg · F / L, but the total fluorine concentration was 100 mg · F / L and the turbidity was Under this condition, white turbidity of the treated water due to the hardly soluble fluorine compound was observed.
Further, in Comparative Example 2 in which phosphate ion 200 mg · PO ₄ ³⁻ / L is supplied but sulfate ion is not supplied, the total fluorine concentration is 80 mg · F / L and the turbidity is 80. Although slight suppression of white turbidity was observed as compared with Comparative Example 1 in which no ions were supplied, the degree of suppression was insufficient. The soluble fluorine concentration in the treated water was 10 mg / L.
Further, in Comparative Example 3 in which 1500 mg · SO ₄ ²⁻ / L of sulfate ion is supplied but phosphate ion is not supplied, the total fluorine concentration is 90 mg · F / L and the turbidity is 90. Although slight suppression of white turbidity was observed as compared with Comparative Example 1 in which no ions were supplied, the degree of suppression was insufficient. The soluble fluorine concentration in the treated water was 10 mg · F / L.

Example 1
In Example 1 in which 200 mg · PO ₄ ³⁻ / L of phosphate ion and 1500 mg · SO ₄ ²⁻ / L of sulfate ion are supplied, the soluble fluorine concentration is 10 mg · F / L, and the total fluorine concentration is 18 mg · F / L. L and turbidity were 5, and the remarkable suppression of the white turbidity of the treated water and the improvement of the treated water were observed as compared with Comparative Examples 1 to 3. The degree of suppression of the white turbidity of the treated water was found to be synergistic beyond the additive degree in the case where phosphate ions and sulfate ions were supplied alone.

Example 2
In Example 2 in which 400 mg · PO ₄ ³⁻ / L of phosphate ion and 3000 mg · SO ₄ ²⁻ / L of sulfate ion are supplied, the soluble fluorine concentration is 10 mg · F / L and the total fluorine concentration is 15 mg · F / L. L and turbidity were 3, and the remarkable suppression of the white turbidity of the treated water and the improvement of the treated water were observed as compared with Comparative Examples 1 to 3.

Example 3
In Example 3 supplying 600 mg · PO ₄ ³⁻ / L of phosphate ion and 10000 mg · SO ₄ ²⁻ / L of sulfate ion, the soluble fluorine concentration was 10 mg · F / L and the total fluorine concentration was 18 mg · F / L. L and turbidity were 5, and the remarkable suppression of the white turbidity of the treated water and the improvement of the treated water were observed as compared with Comparative Examples 1 to 3.

Example 4
In Example 4 which supplies 700 mg · PO ₄ ³⁻ / L of phosphate ion and 11000 mg · SO ₄ ²⁻ / L of sulfate ion, the soluble fluorine concentration is 10 mg · F / L and the total fluorine concentration is 30 mg · F / L. L and turbidity are 30, and the suppression of the white turbidity of the treated water and the improvement of the quality of the treated water were recognized compared with Comparative Examples 1 to 3, but the white turbidity of the treated water was suppressed as compared with Examples 1 to 3. The degree of was low. This is presumably because the supply amount of phosphate ions and sulfate ions became excessive, and not only calcium fluoride but also insoluble fine particles such as calcium phosphate and calcium sulfate were generated. This suggests that there is an optimum range for the amount of phosphate ions and sulfate ions supplied to the crystallization reaction tank.

FIG. 1 is a schematic view showing one embodiment of a crystallization treatment apparatus that can be used in the crystallization treatment method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystallization reaction tank 2 Seed crystal filling part 3 Treated water supply line 4 Treated water storage tank 5 Crystallizer supply line 6 Treated water discharge line 7 Treated water storage tank 8 Treated water circulation lines 9, 9a, 9b, 9c, 9d, 9e, 9f Supply line 10 Crystallizer storage tank

Claims (3)

  By supplying water to be treated containing fluorine, crystallization reaction elements, phosphate ions and sulfate ions to a crystallization reaction tank, and depositing a fluorine compound on the seed crystals in the crystallization reaction tank to form pellets Fluorine crystallization treatment method for producing treated water with reduced fluorine. The amount of phosphate ions supplied to the crystallization reaction tank is 0.2 to 0.6 times the amount of fluorine supplied to the crystallization reaction tank (PO ₄ ^3- weight / F weight). Item 2. A crystallization method for fluorine according to Item 1. The amount of sulfate ions supplied to the crystallization reaction tank is 1.5 to 10 times the amount of fluorine supplied to the crystallization reaction tank (SO ₄ ^2- weight / F weight). 2. The fluorine crystallization treatment method according to 2.

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