JP2009226232A - Crystallization reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallization reactor capable of recovering a substance to be crystallized from raw water containing a substance to be crystallized in a high recovery ratio and capable of obtaining treated water good in quality. <P>SOLUTION: The crystallization reactor is used for adding a crystallizing agent to a raw water containing the substance to be crystallized to produce crystals of a hardly soluble salt, and includes: a crystallizing reaction tank for adding the crystallizing agent to the raw water to produce the crystals of the hardly soluble salt; a solid-liquid separation tank for forming an upward flow and solid-liquid separating while subjecting the reaction liquid sent from the crystallizing reaction tank to flow; a reaction liquid sending means for sending the reaction liquid to the solid-liquid separation tank from the crystallizing reaction tank; and a returning means for returning at least a part of the crystals of the hardly soluble salt subjected to solid-liquid separation to the crystallizing reaction tank from the solid-liquid separation tank. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystallization reaction apparatus that crystallizes a hardly soluble salt by adding a crystallization agent to a crystallization target substance in raw water, and treats and collects it as a crystal. For example, fluoridation-containing raw water reacts with calcium agent to recover calcium fluoride, and phosphoric acid-containing raw water reacts with phosphoric acid and calcium agent to recover calcium phosphate. The present invention relates to a recovery technique for recovering a hardly soluble salt by using a crystallization method in which a substance and a crystallization agent are reacted.

  Conventionally, in order to treat raw water containing a crystallization target substance such as fluorine and phosphorus, a coagulation precipitation method in which a crystallization agent such as a calcium agent and a coagulant are added is generally used. However, in sludge containing hardly soluble salts such as calcium fluoride and calcium phosphate produced by this method, it is difficult to recover and reuse the hardly soluble salt because the purity of the hardly soluble salt is low.

On the other hand, a crystallization method is used to recover and reuse the hardly soluble salt. For example, when fluorine in hydrofluoric acid wastewater is recovered as calcium fluoride, wastewater and crystals containing fluorine, which is a crystallization target substance, are retained in the crystallization reaction tank while the granular calcium fluoride is retained as a seed crystal. A method of obtaining calcium fluoride crystals by injecting and reacting with a calcium agent as a depositing agent to precipitate calcium fluoride on the seed crystal surface is employed.
2HF + CaCl ₂ → CaF ₂ ↓ + 2HCl

  For example, when the concentration of the crystallization target substance in the raw water is low, the inventors of the present invention will crystallize at pH 3 to 11 (see Patent Document 1) using a fluidized bed type crystallization reaction apparatus (see FIG. 3). is suggesting.

  In addition, when the crystallization target substance in the raw water has a high concentration, a stirring crystallization reaction apparatus is used (see FIG. 4). The present inventors injected the raw water containing the crystallization target substance, the crystallization agent, and the pH adjuster into the vicinity of the stirring blade of the stirring crystallization reaction tank provided with the draft tube. It has been proposed that the recovery rate is high (see Patent Document 2).

  In the crystallization reaction apparatus 100 of FIG. 4, the raw water containing the crystallization target substance, the crystallization agent, and the pH adjusting agent are, for example, of the stirring blade 108 of the crystallization reaction tank 102 with the draft tube 106 provided with the stirring apparatus 104. It is injected in the vicinity and processed for crystallization reaction. Thereafter, the treated water is integrated in direct communication with the lower part of the crystallization reaction tank 102, separated into solid and liquid at the precipitation part 110 where an upward flow is formed, and discharged from the upper part of the precipitation part. On the other hand, the generated crystals of the hardly soluble salt form an interface 112 at the precipitation part 110 and are extracted from the lower part of the crystallization reaction tank 102 and recovered and reused. The crystallization reaction apparatus 100 has an advantage that the crystallization reaction tank 102 and the precipitation unit 110 are integrated and compact.

JP 2003-225680 A Japanese Patent Application No. 2006-254065

  In the crystallization reaction apparatus 100 that directly communicates with the lower part of the crystallization reaction tank 102 and performs solid-liquid separation in the precipitation part 110 in which an upward flow is formed, the hardly soluble salt generated in the crystallization reaction tank 102. In some cases, some of the fine particles are mixed into the treated water discharged from the upper part of the precipitation unit 110, the quality of the treated water is deteriorated, and the recovery rate of the crystallization target substance is lowered.

  The reason for this is that crystals in the crystallization reaction tank 102 are vigorously flowing by the stirring force of the stirring device 104, but the crystallization reaction tank 102 and the precipitation unit 110 communicate with each other at the lower part of the crystallization reaction tank 102. Therefore, since the crystals in the crystallization reaction tank 102 repeatedly collide with the crystals below the precipitation portion 110 to cause the crystals in the precipitation portion 110 to flow, turbulent flow is generated in the precipitation portion 110 and fine particles are generated. It is conceivable to let it flow into treated water.

  In addition, in the precipitation part 110 of the crystallization reaction apparatus 100, crystals of the hardly soluble salt are separated into solid and liquid, and relatively large particles return from the lower part of the precipitation part 110 into the crystallization reaction tank 102. Since an interface of fine particles is formed in the upper part and relatively fine particles are likely to accumulate in the sedimentation part 110, the fine particles are more likely to flow out into the treated water due to the generation of the turbulent flow. It may be easy.

  The present invention is a crystallization reaction apparatus capable of recovering a crystallization target substance at a high recovery rate from raw water containing the crystallization target substance and obtaining treated water with good water quality.

  The present invention is a crystallization reaction apparatus for generating a crystal of a hardly soluble salt by adding a crystallization agent to raw water containing a substance to be crystallized, wherein the crystallization agent is added to the raw water to form a hardly soluble salt. A crystallization reaction tank for generating crystals, a solid-liquid separation tank for forming an upward flow and separating the liquid and liquid while flowing the reaction liquid sent from the crystallization reaction tank, and the crystal A reaction liquid feeding means for feeding the reaction liquid from the precipitation tank to the solid-liquid separation tank, and at least a part of the crystals of the hardly soluble salt separated from the solid-liquid separation tank to the crystallization reaction tank. A crystallization reaction apparatus comprising: a return means for returning.

  In the crystallization reaction apparatus, it is preferable that the reaction solution feeding unit sends the reaction solution from an upper part of the crystallization reaction tank to a lower part of the solid-liquid separation tank.

  In the crystallization reaction apparatus, the return means includes at least a part of the crystals of the hardly soluble salt separated into the crystallization reaction tank from at least one of the lower part and the intermediate part of the solid-liquid separation tank. Is preferably returned.

  In the present invention, a crystallization reaction tank, a solid-liquid separation tank for forming an upward flow, and separating the liquid and liquid while flowing the reaction liquid sent from the crystallization reaction tank, and the crystallization reaction tank A reaction liquid feeding means for feeding the reaction liquid to the solid-liquid separation tank, and a return means for returning at least part of the crystals of the hardly soluble salt separated from the solid-liquid separation tank to the crystallization reaction tank. Thus, the crystallization target substance can be recovered at a high recovery rate from the crystallization target substance-containing raw water, and treated water with good water quality can be obtained.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  An outline of an example of a crystallization reaction apparatus according to an embodiment of the present invention is shown in FIG. The crystallization reaction apparatus 1 in FIG. 1 includes a crystallization reaction tank 10 and a solid-liquid separation tank 12.

  In the crystallization reaction apparatus 1 of FIG. 1, a raw water addition pipe 14, a crystallization agent addition pipe 16, and a pH adjuster addition pipe 18 are connected to the crystallization reaction tank 10. Further, the crystallization reaction tank 10 is provided with a stirring device 30 that is a stirring means including a motor and a stirring blade 32 that stirs the fluid in the crystallization reaction tank 10, and a pH meter 36 that is a pH measurement means. A draft tube 34 is provided. Connected to the lower part of the solid-liquid separation tank 12 is a reaction liquid feed pipe 20 which is a reaction liquid feed means for feeding the reaction liquid from the crystallization reaction tank 10 to the solid-liquid separation tank 12. A treated water discharge pipe 22 is connected to the upper part of the solid-liquid separation tank 12. A return pipe 48 is connected to the intermediate part of the solid-liquid separation tank 12 via a valve 46, the return pipe 48 is branched, and one of the return pipes 24 is connected to the upper part of the crystallization reaction tank 10 via a pump 38. It is connected. The other return pipe 26 through the valve 44 and the pipe 50 through the valve 56 are connected to the bottom of the solid-liquid separation tank 12. In addition, a drawing pipe 28 connected to the bottom of the crystallization reaction tank 10 and connected to a connection point between the return pipe 26 and the pipe 50 through the valve 40 is connected to the drawing pipe 54. Yes.

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

  Raw water containing crystallization target substances containing crystallization target substances such as fluorine and phosphorus (hereinafter sometimes simply referred to as “raw water”) is added to the crystallization reaction tank 10 from the raw water storage tank through the raw water addition pipe 14. Is done. In addition, a crystallization agent such as a calcium agent is supplied to the crystallization reaction tank 10 from the crystallization agent storage tank or the like through the crystallization agent addition pipe 16, and a pH adjustment agent is supplied from the pH adjustment agent storage tank or the like through the pH adjustment agent addition pipe 18. Added. In the crystallization reaction tank 10, the crystallization target substance contained in the raw water reacts with the crystallization agent to produce crystals of a hardly soluble salt (crystallization reaction step). The reaction solution in the crystallization reaction tank 10 is stirred by the stirring device 30. The reaction liquid containing the hardly soluble salt crystals generated by the crystallization reaction in the crystallization reaction tank 10 is sent to the solid-liquid separation tank 12 through the reaction liquid sending pipe 20.

  In the solid-liquid separation tank 12, an upward flow is formed by the reaction liquid fed from the reaction liquid feeding pipe 20 connected to the lower part of the solid-liquid separation tank 12, and the solid-liquid separation is performed while the reaction liquid flows. (Solid-liquid separation process). The supernatant water that has been subjected to solid-liquid separation and reduced in the crystallization target substance is discharged out of the system through the treated water discharge pipe 22 as treated water.

  It is preferable that the reaction liquid feeding pipe 20 for connecting the crystallization reaction tank 10 and the lower part of the solid-liquid separation tank 12 is connected to the upper part of the crystallization reaction tank 10. By sending the reaction liquid from the top of the crystallization reaction tank 10 toward the bottom of the solid-liquid separation tank 12, an upward flow can be satisfactorily formed in the solid-liquid separation tank 12.

  At least a part of the crystals of the hardly soluble salt separated in the solid-liquid separation tank 12 is solidified by the pump 38 through the return pipes 48 and 24 with the valve 46 opened and the valve 44 closed. The liquid separation tank 12 may be returned to the crystallization reaction tank 10, the valves 56 and 44 are opened, the valves 42 and 46 are closed, and the pipe 50 and the return pipes 26 and 24 are closed. And may be returned from the bottom of the solid-liquid separation tank 12 (returning step). In this case, the return pipes 48, 24, 26, the pipe 50, and the pump 38 function as return means.

  Either one of the return from the intermediate part of the solid-liquid separation tank 12 and the return from the bottom may be used, or they may be used in combination. For example, in the normal operation, as fine particles as possible are returned from the middle part of the solid-liquid separation tank 12 so that the fine particles do not flow into the treated water, and the crystals do not solidify in the solid-liquid separation tank 12 during the operation stop. Thus, it is better to switch between the return of the intermediate part and the return from the bottom depending on the operation state, such as returning from the bottom of the solid-liquid separation tank 12.

  In the present specification, the “intermediate portion” of the solid-liquid separation tank 12 refers to a portion between the connection portion of the treated water discharge pipe 22 and the bottom portion, that is, the connection portion of the pipe 50, and is not particularly limited. In order to return as fine particles as possible from the intermediate part of the solid-liquid separation tank 12, the supernatant liquid separated into solid and liquid is provided in the vicinity of the connection part of the return pipe 48 provided in the intermediate part of the solid-liquid separation tank 12. The amount of reaction liquid sent from the crystallization reaction tank 10 to the solid-liquid separation tank 12, the amount returned from the solid-liquid separation tank 12 to the crystallization reaction tank 10, and the solid-liquid separation tank 12 so that the interface with the crystal comes. It is preferable to operate by adjusting the amount of extraction from the pipe.

  The interface between the supernatant and the crystal in the solid-liquid separation tank 12 can be detected by, for example, an interface detector such as an interface meter (not shown) installed in the solid-liquid separation tank 12.

  When the interface between the solid-liquid separated supernatant and crystal fluctuates during operation, for example, the minimum level of the fluctuation may be adjusted so as to match the vicinity of the connection portion of the return pipe 48.

  In the case of pulling out the crystal of the hardly soluble salt for recovery, either the drawing from the bottom of the solid-liquid separation tank 12 or the drawing from the bottom of the crystallization reaction tank 10 may be used, or a desired drawing concentration You may use together according to.

  For example, at least part of the crystals of the hardly soluble salt separated in the solid-liquid separation tank 12 are opened in the valves 56, 42 and closed in the valves 46, 44, 40, the pipe 50, It may be drawn through the drawing pipes 52 and 54 (drawing step). Further, at least a part of the crystals of the hardly soluble salt in the crystallization reaction tank 10 is drawn through the drawing pipes 28 and 54 with the valve 40 opened and the valve 42 closed as necessary. Also good. In this case, the pipe 50, the drawing pipes 28, 52, and 54 and the valves 40, 56, and 42 function as a drawing means for drawing out the crystal.

  The drawn crystal is dehydrated, washed, and dried as necessary, recovered as a recovered crystal, and reused as necessary.

  Examples of the extracting means include a method of extracting from the crystallization reaction tank 10 and the solid-liquid separation tank 12 by gravity by opening and closing valves 40, 56 and 42, and a method of extracting by a pump or the like.

  The shape of the solid-liquid separation tank 12 that forms the upward flow is not particularly limited, such as a cylindrical shape or a cone shape whose cross section expands upward, but in order to prevent the deposition of crystals at the bottom of the solid-liquid separation tank 12 Further, a cone shape is preferable in order to achieve good solid-liquid separation by gradually lowering the linear velocity (LV) and allowing large particles to settle in the lower part.

  As a flow rate in the solid-liquid separation tank 12, the upper linear velocity (LV) is preferably in the range of 0.1 to 1 m / hr, and more preferably in the range of 0.1 to 0.5 m / hr. As the upper linear velocity (LV) is smaller, the fine particles tend not to flow out into the treated water. If the upper linear velocity (LV) is less than 0.1 m / hr, the process may slow down and the solid-liquid separation tank 12 may become larger. If it exceeds 1 m / hr, the outflow of fine particles will increase significantly. There is a case.

  The raw material water containing the target substance for crystallization in the present embodiment may be any source water as long as it contains the target substance for crystallization to be removed by the crystallization process. Examples include, but are not limited to, raw water discharged from industries, power plants, aluminum industries, and the like.

  The crystallization target substance in the raw water includes any element that can be crystallized by crystallization reaction and removed from the raw water, and is not particularly limited. Moreover, the kind of element used as a crystallization target substance may be one, and two or more kinds may be sufficient as it. In particular, from the viewpoint that existence in raw water becomes a problem, examples of the crystallization target substance in the present embodiment include fluorine, phosphorus, heavy metal elements, calcium, and mixtures thereof. Examples of heavy metal elements include, but are not limited to, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Cd, Hg, Sn, Pb, and Te. Preferably, the substance to be crystallized is fluorine.

The element to be crystallized can be present in the raw water in any state as long as it is crystallized by a crystallization reaction. From the viewpoint that it is dissolved in the raw water, the crystallization target substance is preferably in an ionized state. Examples of the state in which the crystallization target substance is ionized include those in which atoms such as F ⁻ and Cu ²⁺ are ionized, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, tetraphosphoric acid, phosphorous acid, and the like. Examples thereof include compounds obtained by ionizing a compound containing a substance to be crystallized such as, and complex ions such as heavy metals, but are not limited thereto.

  Raw water containing fluorine is also discharged from aluminum electrolytic refining process, steelmaking process, etc., but it is discharged in large quantities especially in 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 of the order of%. At this time, ammonia, hydrogen peroxide, phosphoric acid, and the like are also used as cleaning agents, and therefore, wastewater containing them may be produced. In addition, a large amount of water is used for cleaning hydrofluoric acid remaining on the semiconductor silicon wafer, cleaning HF contained in the gas after decomposition of perfluoro compounds (PFCs), etc., and is also discharged as dilute fluorine-containing raw water. . The crystallization reaction apparatus according to the present embodiment can be particularly suitably applied to remove fluorine from raw water containing hydrofluoric acid (hydrogen fluoride).

  The amount of the crystallization target substance contained in the raw water is not particularly limited. For example, when the crystallization target substance is fluorine, a range of 5000 mg / L to 100,000 mg / L, particularly 5000 mg / L to 20000 mg / L. In the case of phosphorus, the range is 500 mg / L to 5000 mg / L.

  The substance to be crystallized is fluorine in hydrofluoric acid-containing raw water, and when calcium fluoride is recovered by reacting with a calcium agent that is a crystallizing agent, or the substance to be crystallized is phosphorus in phosphoric acid-containing raw water, In the case of recovering calcium phosphate by reacting with a calcium agent that is a crystallizing agent, calcium chloride, slaked lime, or the like is used as the crystallizing agent.

  When the substance to be crystallized is a heavy metal in water and reacts with a crystallizing agent to recover a hardly soluble salt, sodium sulfide, sodium carbonate, or the like is used as the crystallizing agent. When the substance to be crystallized is calcium in water and is reacted with a crystallizer to recover calcium carbonate, sodium carbonate or the like is used as the crystallizer.

  In the present embodiment, a calcium solution in which slaked lime and an acid are mixed may be used as the crystallization chemical solution. The “calcium solution” in the present specification is a liquid obtained by adding an acid to slaked lime (calcium hydroxide) and having a certain range of pH. The “calcium solution” may be in a solution state in which slaked lime is completely dissolved, or may contain solid particles of slaked lime. The acid can be added to the slaked lime by any known method as long as the acid is added to the slaked lime. For example, the acid is added to the slaked lime slurry, and the acid is added to the dried slaked lime solid. Embodiments, or combinations thereof, but are not limited thereto. The preferable aspect of addition of the acid to slaked lime is an aspect which adds an acid to slaked lime slurry.

  In this specification, “slaked lime slurry” refers to a slurry formed by adding water or an aqueous solution to dry solids of slaked lime, and the water used is any source such as distilled water, purified water, tap water, etc. As the aqueous solution, an aqueous solution in which an arbitrary compound such as an acid, an alkali, or a salt thereof is added to the water can be used. In addition, the “dry slaked lime solid” in the present specification indicates a concept for the slaked lime slurry, and may be any solid, such as powder, granule, or lump, that does not form a slurry. It does not mean the anhydride.

  As the slaked lime used for preparing the calcium solution, any grade of slaked lime can be used, and it is not particularly limited. The acid used for preparing the calcium solution is not particularly limited, and any acid can be used. Preferably, it is an arbitrary acid that does not contain a component that forms a sparingly soluble salt with calcium, such as hydrochloric acid, but is not limited thereto. More preferably, the acid is hydrochloric acid. One type of acid may be used, or a plurality of types of acids may be used. The concentration and addition amount of the acid used are appropriately set so that the calcium solution has a desired pH. For example, it is convenient to use slaked lime slurry that is mixed with water and circulated in the factory for the purpose of neutralization in facilities in the factory.

  In this embodiment, the pH range of the calcium solution is preferably pH 9 or less, more preferably pH 8 or less, still more preferably pH 8 to 4, and particularly preferably pH 7 to 5. . By adjusting the pH of the calcium solution to the above range, slaked lime can be dissolved to some extent. Here, it is considered that conditions under which slaked lime slurry is completely dissolved, that is, a lower pH is better in the crystallization treatment. However, the present inventors have found that it is effective to set the pH of the calcium solution within a predetermined range in order to further reduce the concentration of the crystallization target component in the treated water obtained by the crystallization treatment. It was. That is, rather than lowering the pH of the calcium solution to less than pH 4, the concentration of the crystallization target component in the treated water is remarkably increased by adjusting the pH to the range of 8 to 4 as described above, and further to the range of pH 7 to 5. Can be reduced. The presence of the suitable pH range does not completely dissolve the slaked lime fine particles by making the pH constant, but by leaving a certain amount of slaked lime fine particles in the calcium solution, This is probably because the fine particles increase the reaction area of the crystallization reaction to improve the crystallization reaction efficiency and reduce the concentration of the crystallization target substance in the treated water.

  As the hardly soluble salt to be produced, in addition to calcium fluoride produced by reacting raw fluorine-containing water with a calcium agent, for example, calcium phosphate, hydroxyapatite produced by reacting raw phosphorus-containing water with a calcium agent, fluorine Also included are fluoroapatite and the like produced by reacting raw phosphorus-containing water with a calcium agent.

  In this embodiment, before adding raw water and a crystallization agent to the crystallization reaction tank 10, seed crystals may exist in advance in the crystallization reaction tank 10, or in the crystallization reaction tank 10 in advance. The seed crystal may not exist. In order to perform a stable treatment, it is preferable that seed crystals exist in the crystallization reaction tank 10 in advance. The amount of seed crystals charged in the crystallization reaction tank 10 is not particularly limited as long as the crystallization target substance can be removed by the crystallization reaction. The concentration of the crystallization target substance in the raw water, crystallization The concentration is appropriately set according to the concentration of the agent and the operating conditions of the crystallization reaction apparatus 1.

  The seed crystal may be any material as long as it can precipitate a hardly soluble salt crystal formed on the surface, and any material can be selected. For example, filtered sand, activated carbon, zircon sand, garnet sand, Particles composed of oxides of metal elements including random (trade name, manufactured by Nippon Carlit Co., Ltd.), and particles composed of hardly soluble salts that are precipitates by crystallization reaction However, it is not limited to these. From the viewpoint that a purer hardly soluble salt can be obtained as a pellet or the like, particles composed of a hardly soluble salt that is a precipitate by a crystallization reaction (for example, fluorite in the case of calcium fluoride) are preferable. The shape and particle size of the seed crystal are appropriately set according to the flow rate in the crystallization reaction tank 10, the crystallization target substance, the concentration of the crystallization agent, and the like, and are not particularly limited.

  In the case where the seed crystal is filled in the crystallization reaction tank 10 in advance, for example, a crystallization agent is added to the raw water in the crystallization reaction tank 10, and the hardly soluble salt is formed on the seed crystal in the crystallization reaction tank 10. Precipitate to form pellets. On the other hand, when seed crystals are not present in the crystallization reaction tank 10 in advance, the hardly soluble salt precipitated in the crystallization reaction tank 10 forms pellets by adding a crystallization agent to the raw water. Will grow. In any case, when the crystals in the crystallization reaction tank 10 grow to a certain extent, a drawing operation for drawing a part of the crystals from the crystallization reaction tank 10 and a seed crystal having a smaller particle diameter than the drawn crystals are newly added. A method is adopted in which crystals are continuously obtained by repeatedly performing a replenishment operation for replenishing.

  The crystallization reaction tank 10 may be any reaction tank that can cause the crystallization target substance in the raw water to react with the crystallization agent to precipitate a hardly soluble salt crystal, and the length, inner diameter, shape, etc. are arbitrary. Embodiments are possible and are not particularly limited.

  As the crystallization reaction tank, as shown in FIG. 1, a stirring device 30 having a stirring blade is installed in the crystallization reaction tank 10, and the reaction solution in the crystallization reaction tank 10 is stirred by the stirring device 30 to pellets. And a stirring type crystallization reaction tank in which the water is fluidized. The stirring blade is not particularly limited as long as the contents can be stirred in the crystallization reaction tank 10 and the installation mode of the stirring blade, the size of the stirring blade, and the like are not particularly limited.

  The concentration of the crystallization agent such as the calcium agent in the crystallization agent solution such as the calcium solution is appropriately set according to the concentration of the crystallization target substance of the raw water, the treatment capacity of the crystallization reaction tank 10 and the like, and is particularly limited. is not. When the crystallization target substance is fluorine and produces calcium fluoride, the amount of calcium injection is preferably in the range of 1 to 2 times that of fluorine as the chemical equivalent, but more preferably in the range of 1 to 1.2 times. If the chemical equivalent of calcium is more than twice the chemical equivalent of fluorine in the raw water, calcium fluoride does not precipitate on the seed crystal and is easily formed as fine particles, and calcium fluoride may be mixed into the treated water. If it is less than twice, the total amount of fluorine in the raw water does not become calcium fluoride, and fluorine may be mixed into the treated water. Similarly, when the crystallization target substance is phosphorus and produces calcium phosphate, the amount of calcium injection is preferably in the range of 1 to 2 times that of phosphorus as the chemical equivalent, but more preferably in the range of 1 to 1.2 times.

  In this embodiment, it is preferable to deposit a hardly soluble salt in the crystallization reaction tank 10 under the conditions of pH 2 to 11 using a calcium agent. When precipitating calcium fluoride, it is preferable to precipitate calcium fluoride under conditions of pH 2 to 3 and preferably pH 2 to 3 from the viewpoint of suppressing fine particle production. In the case where the pH changes with the calcium fluoride production reaction, it is desirable that the pH adjusting agent can be appropriately added to the crystallization reaction tank 10. The pH at the time of precipitation of calcium fluoride is determined by measuring the pH of the reaction field in the crystallization reaction tank 10 using a pH measuring means such as a pH meter, and depending on the measured pH, the pH of acid or alkali or the like. The pH can be controlled by adding a regulator to the tank. The pH meter may be installed in any part of the crystallization reaction tank 10 as long as the pH of the reaction field of the calcium fluoride precipitation reaction can be monitored. There are no particular limitations on the vicinity of the outlet of the treated water. Similarly, when calcium phosphate is precipitated, it is preferable to precipitate calcium phosphate under the conditions of pH 6 to 8 from the viewpoints of pH 6 to 13 and suppression of fine particle formation.

  As the pH adjuster, an acid such as hydrochloric acid or sulfuric acid or an alkali such as sodium hydroxide can be used.

  The raw water, the crystallization agent, and the pH adjusting agent can be added to the crystallization reaction tank 10 as long as the raw water, the crystallization agent, and the pH adjusting agent can be added to the crystallization reaction tank 10. . The raw water addition pipe 14, the crystallization agent addition pipe 16, and the pH adjuster addition pipe 18 can be connected to any part of the crystallization reaction tank 10. In FIG. 1, the raw water addition pipe 14, the crystallization agent addition pipe 16, and the pH adjuster addition pipe 18 are each one, but the present invention is not limited to this, and a plurality of these may be provided. The aspect which connects the pH adjuster addition piping 18 to the arbitrary site | parts of the crystallization reaction tank 10, and adds a pH adjuster directly to the arbitrary site | parts of the crystallization reaction tank 10 through the said piping may be sufficient, The aspect which adds a pH adjuster to at least 1 of the raw | natural water addition piping 14 or the crystallization agent addition piping 16 may be sufficient.

  In the present embodiment, the crystallization reaction tank 10 is provided with a stirring device 30 including a stirring blade 32 for stirring the reaction liquid in the reaction tank, and the crystallization reaction tank is provided in the vicinity of the stirring blade 32, that is, by the stirring flow of the stirring blade 32. It is preferable to inject at least one of raw water and a crystallization agent into a region where the ten reaction liquids can diffuse quickly. For example, it is preferable that at least one injection point of the raw water and the crystallization agent is provided in a region where the stirring flow velocity by the stirring blade 32 or the like is large, or provided in the vicinity of the stirring blade 32 or the like. In particular, the height in the rotational axis direction of the stirring blade 32 of at least one injection point of the raw water and the crystallization agent is a distance within twice the rotation radius of the stirring blade 32 from the rotation center of the stirring blade 32. It is preferable. In addition, the position of the stirring blade 32 in the direction of the rotation diameter is preferably a distance within twice the rotation radius of the stirring blade 32 from the rotation center of the stirring blade 32. Furthermore, it is preferable that the center is provided in a spherical region whose center is the rotation center of the stirring blade 32 and whose radius is twice the rotation radius of the stirring blade 32. As a result, the crystallization target substance and the crystallization agent are immediately diffused when injected into the crystallization reaction tank 10, and the concentration thereof quickly decreases. For this reason, the formed hardly soluble salt is less likely to be directly deposited in the liquid, and the substance to be crystallized in the liquid can be taken in carefully as crystals of the hardly soluble salt on the granular seed crystal. Therefore, it is possible to extremely reduce the amount of fine particles of the hardly soluble salt mixed in the treated water, stably obtain the hardly soluble salt particles having a large particle size, and greatly improve the recovery rate of the target substance for crystallization. Can do.

  The injection point of the pH adjusting agent is also preferably provided in a region where it can be quickly diffused into the reaction vessel by the stirring flow by the stirring blade 32 or the like. When a pH adjusting agent is injected into a region where the stirring flow rate is low, such as when the pH adjusting agent is dropped onto the water surface, a region having a high pH is locally generated. In this region, fine particles of a sparingly soluble salt such as calcium fluoride are directly formed. Easy to promote generation. However, if the pH adjuster is allowed to diffuse quickly after injection, it is extremely unlikely that a region having a high pH will be generated locally, and the direct formation of fine particles of a hardly soluble salt that does not depend on the crystallization reaction can be suppressed. it can. Therefore, the recovery rate of the crystallization target substance can be further improved by injecting the pH adjuster into the region where the stirring flow rate is large.

  It is also preferable to install the draft tube 34 below the water surface of the crystallization reaction tank 10 so that the stirring blade 32 of the stirring device 30 and the like are positioned in the cylinder. FIG. 2 shows a schematic configuration diagram of the crystallization reaction tank 10 including the draft tube 34. The stirring blade 32 of the stirring device 30 is rotated by the rotational force generated by the motor transmitted through the stirring shaft.

  At this time, it is preferable that the stirring blades 32 and the like form a downward flow inside the draft tube 34. When the draft tube 34 is thus installed, a downward flow is generated toward the lower portion of the tube, and a zone having a relatively large diffusion flow rate is formed. For this reason, raw water and crystallization agents can be diffused more quickly, and the regions where the concentrations of raw water and crystallization agents are locally concentrated are in contact with each other to produce fine particles of sparingly soluble salt as much as possible. It becomes possible to suppress.

  Moreover, when the draft tube 34 and the stirring blade 32 are installed as described above, an upward flow zone with a gentle flow is formed on the outer periphery of the tube. In this zone, particles are classified so that small particles rise along the outer surface of the tube, and re-enter from the upper end of the tube to the inside of the tube and descend. Recirculate to lower stirring zone. These small-sized crystals serve as nuclei to promote the crystallization reaction. For this reason, it becomes possible to form stably the crystal | crystallization of a slightly soluble salt with a big particle size, and can improve the recovery rate of the crystallization target substance.

  Further, the crystal having a larger particle size due to the progress of the crystallization reaction does not rise due to the upward flow at the outer periphery of the tube but sinks down, but it is difficult to enter the draft tube 34 again. It is possible to prevent destruction due to collision with the stirring blade 32 or the like. Such an advantage also contributes to stably obtaining a crystal of a hardly soluble salt having a large particle size, which in turn can contribute to an improvement in the recovery rate of the crystallization target substance.

  In order to form a zone with a relatively large stirring flow velocity at the bottom of the tube and to form an upward flow stably on the outer periphery of the tube, the stirring blade 32 or the like must be located in one of the lower half of the tube in the tube. Is preferred. More preferably, a position slightly above the lower end of the tube is good. With such an arrangement, a zone with a high stirring flow rate is formed like a vortex near the lower end of the tube, and an upward flow is stably formed along the outer periphery of the tube. Therefore, diffusion of raw water, a crystallization agent, etc. can be advanced effectively.

  When the draft tube 34 is provided, the injection points of the raw water, the crystallization agent, and further the pH adjusting agent are placed in the cylinder of the draft tube 34 in order to quickly and effectively diffuse them on the downward flow in the draft tube 34. It is preferable to arrange in. A more preferable position is in the cylinder of the draft tube 34 and above the stirring blade 32 and the like.

  In order to measure the concentration of the substance to be crystallized such as the soluble fluorine concentration in the crystallization reaction tank 10, the solid-liquid separation tank 12, or in the treated water, a crystallization target substance concentration measuring means such as a fluorine concentration meter is crystallized. You may install in the reaction tank 10, the solid-liquid separation tank 12, or the treated water discharge piping 22. FIG. Further, in order to measure the concentration of the crystallization agent such as soluble calcium in the crystallization reaction tank 10, the solid-liquid separation tank 12, or the treated water, a crystallization agent concentration measuring means such as a calcium concentration meter is used as the crystallization reaction tank. 10 may be installed in the solid-liquid separation tank 12 or the treated water discharge pipe 22. The installation position of the fluorine concentration meter, the calcium concentration meter, etc. in the crystallization reaction tank 10 and the solid-liquid separation tank 12 is not particularly limited. For example, when measuring the concentration in the treated water, It can be installed near the outlet of the liquid separation tank 12.

  The treated water in which the crystallization target substance is reduced in the solid-liquid separation tank 12 is discharged to the outside of the solid-liquid separation tank 12. The treated water can be discharged from any part according to the liquid flow in the solid-liquid separation tank 12. In FIG. 1, the treated water discharged from the upper part of the solid-liquid separation tank 12 is finally discharged out of the system through the treated water discharge pipe 22. You may install a treated water storage tank in the back | latter stage of the solid-liquid separation tank 12. FIG.

  In the treated water obtained, for example, the fluorine concentration is usually about 500 mg-F / L or less as total fluorine containing insoluble fluorine such as calcium fluoride, and usually about 50 mg-F / L or less as soluble fluorine ions, The phosphorus concentration is generally about 50 mg-P / L or less as total phosphorus including insoluble phosphorus such as calcium phosphate, and is usually about 5 mg-P / L or less as soluble phosphate ions. The calcium concentration is pH 2 to 3 when the crystallization target substance is fluorine, and is usually about 50 mg-Ca / L as soluble calcium ion, and is pH 6 to 8 when the crystallization target substance is phosphorus and is soluble. The calcium ion is usually about 10 mg-Ca / L, but is not limited thereto.

  The treated water obtained by treating the raw water may be further treated in a precipitation tank. In the precipitation tank, for example, when the substance to be crystallized is fluorine, by adjusting the pH to 3 to 12, preferably 4 to 11, calcium fluoride is generated and the fluorine is precipitated and removed, thereby further increasing the fluorine concentration. Reduced treated water can be obtained. For example, when the crystallization target substance is phosphorus, the pH is adjusted to 8 to 13, preferably 9 to 12, calcium phosphate is generated, and phosphorus is precipitated and removed to obtain treated water with further reduced phosphorus concentration. be able to.

  In the crystallization reaction apparatus according to the present embodiment, the crystallization reaction tank and the solid-liquid separation tank are separated, and crystals of hardly soluble salts are precipitated in the crystallization reaction tank 10, and are solidified in the solid-liquid separation tank 12. By performing liquid separation, the crystallization target substance in the raw water is recovered as a hardly soluble salt crystal, and treated water in which the crystallization target substance is reduced is obtained. In the present embodiment, the recovery rate of the crystallization target substance (1- (amount of crystallization target substance in treated water / amount of crystallization target substance in raw water)) is preferably 80% or more, more preferably 85% or more. Even more preferably, 90% or more can be achieved.

  In the treatment of raw water containing the substance to be crystallized, there are cases where a coagulation reaction tank and a precipitation tank are installed, and the sludge in the precipitation tank is circulated to the coagulation reaction tank. In the meantime, at least one of an inorganic flocculant and a polymer flocculant is added, the generated particles are coarsened and separated by precipitation, and the purity of the resulting crystals is low, making recovery and reuse difficult. This is different from the crystallization reaction apparatus according to this embodiment.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Examples 1-4)
Using the experimental apparatus as shown in Fig. 1, the experiment was conducted by changing the specifications of the solid-liquid separation tank and the installation position of the return pipe in the solid-liquid separation tank under the conditions shown in Table 1, and the fluorine concentration of the treated water and the fluorine recovery rate Compared. The experimental results are shown in Table 1. The crystallization reaction tank has a common specification. In Examples 1 and 2, a solid-liquid separation tank having a straight barrel diameter of 25 cmφ, a cone shape with a bottom of 60 °, and a horizontal cross-sectional area of 491 cm ² was used. In No. 4, a solid-liquid separation tank having a straight body diameter of 50 cmφ, a cone shape with a lower portion of 60 °, and a horizontal cross-sectional area of 1963 cm ² was used. In Examples 1 and 3, the crystals are returned to the crystallization reaction tank from the return pipe at the bottom of the solid-liquid separation tank. In Examples 2 and 4, the intermediate part of the solid-liquid separation tank (the height of the solid-liquid separation tank is The crystal was returned to the crystallization reaction tank from the return pipe at about half the position. In Examples 2 and 4, the operation was performed by adjusting the minimum level of fluctuation at the interface between the supernatant and the crystal so as to match the vicinity of the connection portion of the return pipe.

  The injection point of the raw water addition pipe, the crystallization agent addition pipe and the pH adjuster addition pipe is near the stirring blade of the crystallization reaction tank (rotated from the rotation center of the stirring blade at a position 100 mm higher than the rotation center of the stirring blade). In the direction of 100 mm (the distance from the rotation center of the stirring blade is 1.25 times the rotation radius). The used draft tube was 200 mm in diameter, installed so that the upper end was 150 mm from the water surface and the lower end was located 160 mm below the stirring blade. The treated water fluorine concentration referred to here is the total fluorine concentration including SS-type fluorine (= calcium fluoride) and soluble fluorine.

<Experimental conditions>
Raw water: Hydrofluoric acid-containing wastewater Crystallizer: Calcium chloride solution pH adjuster: Sodium hydroxide aqueous solution Crystallization reactor pH: 2.0 to 2.5
Fluorine concentration in hydrofluoric acid-containing wastewater: 10,000 mg / L
Hydrofluoric acid-containing wastewater flow rate: 30 L / hr
Treated water flow rate: 45L / hr
Crystal return flow rate: 4.5 L / hr
Crystal withdrawal amount: 15 L / times, once every 17 hours, drawn from the bottom of the crystallization reaction tank Crystallization reaction tank crystal concentration: When the crystal withdrawal was performed in the above amount, it was about 50 to 75 wt / wt%.

  In addition, since a crystallizer and a pH adjuster are added, the treated water flow rate increases compared to the hydrofluoric acid-containing wastewater flow rate.

  The crystal concentration in the crystallization reaction tank was controlled by the height of the interface between the supernatant and the crystal in the solid-liquid separation tank. When the height of the interface was increased, the crystal was pulled out to lower the interface height (crystal concentration was reduced). As the crystallization reaction progresses and the crystal grows, the interface increases with the passage of time (the crystal concentration increases).

(Comparative Examples 1 and 2)
Using an experimental apparatus in which the crystallization reaction tank and the precipitation part as shown in FIG. 4 are integrated, the experiment is performed by changing the specifications of the precipitation part under the conditions shown in Table 1, and the fluorine concentration of the treated water and the fluorine recovery rate Compared. The experimental results are shown in Table 1. The crystallization reaction tank has the same specifications as those of the Examples. In Comparative Example 1, a precipitation section having a horizontal sectional area of 500 cm ² is used. In Comparative Example 2, a precipitation section having a horizontal sectional area of 2000 cm ² is used. Using.

  As described above, in Examples 1 to 4, the fluorine concentration of the treated water was reduced as compared with Comparative Examples 1 and 2, and the fluorine recovery rate was improved. Further, in comparison with Examples 1 and 3 in which crystals were returned to the crystallization reaction tank from the bottom of the solid-liquid separation tank, Example 2 in which crystals were returned to the crystallization reaction tank from the vicinity of the interface in the middle part of the solid-liquid separation tank. , 4, the fluorine concentration of the treated water further decreased and the fluorine recovery rate improved.

It is a schematic block diagram which shows an example of the crystallization reaction apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows an example of the crystallization reaction tank in the crystallization reaction apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows an example of the conventional fluidized bed type crystallization reaction apparatus. It is a schematic block diagram which shows an example of the conventional stirring type crystallization reaction apparatus.

Explanation of symbols

  1,100 crystallization reaction apparatus, 10,102 crystallization reaction tank, 12 solid-liquid separation tank, 14 raw water addition pipe, 16 crystallization agent addition pipe, 18 pH adjuster addition pipe, 20 reaction liquid feed pipe, 22 treatment Water discharge pipe, 24, 26, 48 Return pipe, 28, 52, 54 Pull-out pipe, 30, 104 Stirrer, 32, 108 Stirrer blade, 34, 106 Draft tube, 36 pH meter, 38 Pump, 40, 42, 44 46,56 Valve, 50 piping, 110 sedimentation section, 112 interface.

Claims (3)

A crystallization reaction apparatus that generates a crystal of a hardly soluble salt by adding a crystallization agent to raw water containing a substance to be crystallized,
A crystallization reaction tank for adding the crystallization agent to the raw water to form crystals of a hardly soluble salt;
A solid-liquid separation tank for forming an upward flow and separating the liquid and liquid while flowing the reaction liquid sent from the crystallization reaction tank;
A reaction liquid feeding means for feeding the reaction liquid from the crystallization reaction tank to the solid-liquid separation tank;
A return means for returning at least a part of the solid-liquid separated crystals of the hardly soluble salt from the solid-liquid separation tank to the crystallization reaction tank;
A crystallization reaction apparatus comprising: The crystallization reaction apparatus according to claim 1,
The crystallization reaction apparatus, wherein the reaction solution feeding means sends the reaction solution from an upper part of the crystallization reaction tank to a lower part of the solid-liquid separation tank. The crystallization reaction apparatus according to claim 1 or 2,
The return means returns at least a part of the crystals of the hardly soluble salt separated into the solid-liquid separation from at least one of the lower part and the intermediate part of the solid-liquid separation tank to the crystallization reaction tank. Analysis reaction equipment.

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