JP5162210B2 - Crystallization reactor and crystallization reaction method - Google Patents

Description

  The present invention relates to a crystallization reaction apparatus and a crystallization reaction method in which a crystallization agent is added to a crystallization target substance in a liquid to crystallize a hardly soluble salt, which is treated and recovered as a crystal. For example, substances to be crystallized such that fluorine in hydrofluoric acid-containing raw water reacts with calcium agent to recover calcium fluoride, or phosphoric acid in calcium-containing raw water reacts with calcium agent to recover calcium phosphate. The present invention relates to a recovery technique for recovering a hardly soluble salt using a crystallization method in which a crystallization agent is reacted with a crystallization agent.

Conventionally, a technique has been proposed in which a crystallization agent such as calcium agent is added to the crystallization target substances such as fluorine and phosphorus in the liquid to crystallize insoluble salts such as calcium fluoride and calcium phosphate, and then treated and recovered as crystals. Has been. For example, in order to recover and reuse calcium fluoride by adding a calcium agent to raw water containing fluorine as a crystallization target substance, the fluorine-containing raw water and the crystallizer are contained in a crystallization reaction tank filled with seed crystals. A method of obtaining calcium fluoride crystals by injecting a calcium agent and depositing calcium fluoride on the seed crystal surface has been proposed.
2HF + CaCl ₂ → CaF ₂ ↓ + 2HCl

  For example, a fluidized bed crystallizer (Patent Document 1) or the like has been proposed in which a liquid is supplied to a crystallization reaction tank in an upward flow, and a crystal of a hardly soluble salt in the crystallization reaction tank is flowed. Yes.

  In such an apparatus, when the crystals in the crystallization reaction tank grow to a certain extent, a drawing operation for drawing a part of the crystals from the crystallization reaction tank and a seed crystal having a smaller particle diameter than the drawn crystals are newly made. A method of continuously obtaining crystals by repeatedly performing a replenishment operation for replenishment is employed. As the seed crystal used at this time, it is common to use particles of a hardly soluble salt to be obtained. For example, as a seed crystal of calcium fluoride, a mineral fluorite, and as a seed crystal of calcium phosphate, In general, a pulverized mineral ore is used. The seed crystal is directly added to the crystallization reaction tank by a seed crystal addition apparatus, or mixed with water and added to the crystallization reaction tank as a slurry.

  FIG. 4 shows a schematic configuration diagram of an example of a conventional crystallization reaction apparatus. The crystallization reaction apparatus 60 includes a crystallization agent storage tank 62, a raw water storage tank 64, a crystallization reaction tank 66, and a seed crystal addition apparatus 68. In the crystallization reaction apparatus 60, a crystallization agent such as a calcium agent is added from a crystallization agent storage tank 62, and raw water containing a crystallization target substance such as a fluorine-containing raw water is added from a raw water storage tank 64 to a crystallization reaction tank 66. Crystals are added directly from the seed crystal addition device 68 into the crystallization reaction tank 66 to form crystals of a hardly soluble salt.

JP 2003-225680 A

  When minerals such as fluorite and phosphate ore are used as the seed crystals, seed crystals with a small particle size contained in the seed crystals flow out into the treated water when the seed crystals are introduced into the crystallization reaction tank. There is a problem that it deteriorates or floats on the liquid surface of the crystallization reaction tank and separates.

  The present invention is a crystallization reaction apparatus and a crystallization reaction method capable of obtaining treated water with good water quality.

The present invention relates to a crystallization reactor to produce crystals of calcium fluoride by adding calcium agent to raw water containing fluorine, in order to produce crystals of calcium fluoride was added to the calcium agent to the raw water A crystallization reaction tank, a treatment means for treating the compound containing calcium fluoride as a main component in a slurry state with an acid treatment at a pH of 3 or less or an alkali treatment with a pH of 12 or more, and the treatment compound treated with the acid treatment or alkali as a seed crystal And a seed crystal addition means for adding to the crystallization reaction tank.

The present invention is also a crystallization reaction method in which a calcium agent is added to raw water containing fluorine to produce calcium fluoride crystals, and the compound containing calcium fluoride as a main component is in a slurry state at a pH of 3 or less. An acid treatment or a treatment step of alkali treatment at pH 12 or higher, a seed crystal addition step of adding the acid treatment or alkali treatment treatment compound as a seed crystal to the crystallization reaction tank, and adding the calcium agent to the raw water And a crystallization reaction step of generating calcium fluoride crystals.

  In the present invention, in a crystallization reaction apparatus and a crystallization reaction method for adding a crystallization agent to raw water containing a substance to be crystallized to produce crystals of a hardly soluble salt, a compound containing the hardly soluble salt as a main component is in a slurry state. By treating with acid or alkali and adding the treated compound as a seed crystal to the crystallization reaction tank, 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 of FIG. 1 includes a crystallization agent storage tank 10, a raw water storage tank 12, a crystallization reaction tank 14, and a treatment tank 16.

  In the crystallization reaction apparatus 1 of FIG. 1, a crystallization agent addition pipe 28 from the crystallization agent storage tank 10 is connected to the crystallization reaction tank 14 via a pump 22 as a crystallization agent addition means. A raw water addition pipe 30 from the storage tank 12 is connected via a pump 24 as raw water addition means. Further, a seed crystal addition pipe 32 from the treatment tank 16 is connected to the crystallization reaction tank 14 via a pump 26 as a seed crystal addition means, and a treated water discharge pipe 36 is connected to the outlet. . The crystallization reaction tank 14 is connected with a pH adjusting agent addition pipe 34 and is provided with a stirring device 42 such as a stirring blade which is a stirring means equipped with a motor. A processing agent addition pipe 46 such as acid or alkali, and a solvent addition pipe 50 such as water are connected to the processing tank 16 as a processing means, and a stirring device 40 such as a stirring blade, which is a stirring means equipped with a motor, pH A pH meter 38 as a measuring means is installed. In addition, a compound addition pipe 48 from the compound storage tank 18 is connected to the treatment tank 16 via a compound supply device 20. The compound supply device 20 includes a motor 44.

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

  A solvent such as water is added to the treatment tank 16 through the solvent addition pipe 50. Further, a compound 52 such as a mineral mainly composed of a hardly soluble salt such as calcium fluoride or calcium phosphate is added to the treatment tank 16 from the compound storage tank 18 through the compound addition pipe 48 by the compound supply device 20 driven by the motor 44. . In the treatment tank 16, a treatment agent such as acid or alkali is added through the treatment agent addition pipe 46 while the contents are stirred by the stirring device 40, and the compound is subjected to acid treatment or alkali treatment in a slurry state (treatment step). In the treatment tank 16, the amount of acid or alkali added may be controlled by the pH meter 38.

  On the other hand, the crystallization target substance-containing raw water containing the crystallization target substance such as fluorine and phosphorus (hereinafter sometimes simply referred to as “raw water”) is crystallized by the pump 24 from the raw water storage tank 12 through the raw water addition pipe 30. Added to tank 14. Further, a crystallization agent such as a calcium agent is added from the crystallization agent storage tank 10 to the crystallization reaction tank 14 through the crystallization agent addition pipe 28 by the pump 22. At this time, the processing compound processed in the processing tank 16 is added to the crystallization reaction tank 14 through the seed crystal addition piping 32 by the pump 26 as a seed crystal (seed crystal addition process). In the crystallization reaction tank 14, the crystallization target substance contained in the raw water and the crystallization agent react with the seed crystal as a nucleus to produce a hardly soluble salt crystal (crystallization reaction step). In the crystallization reaction tank 14, the pH adjusting agent may be added from the pH adjusting agent addition pipe 34 as necessary to adjust the pH of the crystallization reaction solution, and the crystallization reaction solution is stirred by the stirring device 42. May be. The seed crystal may be added to the raw water before the crystallization agent is added, may be added to the raw water after the crystallization agent is added, or may be added to the raw water together with the crystallization agent. Good. The seed crystal may be added to the crystallization reaction tank 14 continuously or intermittently.

  The addition of the raw water to the crystallization reaction tank 14 and the addition of the crystallization agent to the crystallization reaction tank 14 can take any form as long as the raw water and the crystallization agent can be added to the crystallization reaction tank 14. . The raw water storage tank 12 and the crystallization agent storage tank 10 may be provided with a stirring device.

  In this embodiment, a compound containing a sparingly soluble salt as a main component is acid-treated or alkali-treated in a slurry state, and the treated compound is added as a seed crystal to the crystallization reaction tank 14 to obtain treated water with good water quality. Can be obtained.

  For example, when obtaining calcium fluoride crystals from raw fluorine-containing water and a calcium agent, fluorite containing calcium fluoride as a main component is used as a seed crystal, but when this is directly charged into the crystallization reaction tank 14 The cause of deterioration of the quality of the treated water and the cause of the improved quality of the treated water when treated with an acid or alkali as described above are not clear, but the surface of the fluorite particles is dissolved by an acid or alkali. This is considered to be because the crystallized more easily by activation, or the particles aggregated and coarsened and dispersed in an acid and alkali state. It is considered that the finely dispersed particles are likely to capture ultrafine particles and are unlikely to flow out into the treated water. It is also considered that the finely dispersed particles are likely to adhere to the coarse crystals in the crystallization reaction tank 14.

  In this embodiment, before adding the raw water and the crystallization agent to the crystallization reaction tank 14, seed crystals may exist in the crystallization reaction tank 14 in advance, or in the crystallization reaction tank 14 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 14 in advance. The amount of seed crystals filled in the crystallization reaction tank 14 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, the crystallization agent The concentration is appropriately set according to the operating conditions of the crystallization reaction apparatus 1 and the like.

  When the crystallization reaction tank 14 is filled with seed crystals in advance, for example, a crystallization agent is added to the raw water in the crystallization reaction tank 14, and the hardly soluble salt is added on the seed crystals in the crystallization reaction tank 14. Precipitated to form pellets, resulting in treated water with reduced crystallization target substances. On the other hand, when seed crystals are not present in the crystallization reaction tank 14 in advance, a hardly soluble salt precipitated in the crystallization reaction tank 14 forms pellets by adding a crystallization agent to the raw water. Will grow. In any case, when the crystals in the crystallization reaction tank 14 grow to a certain extent, a drawing operation for drawing a part of the crystals from the crystallization reaction tank 14 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 pH of the treatment solution in the treatment tank 16 is 3 or less when fluorite is treated with an acid, and 12 or more when treated with an alkali, in view of obtaining a seed crystal having high reaction activity. In view of obtaining a seed crystal having higher reaction activity, it is more preferable to treat with an acid.

  The acid to be added is not particularly limited, but hydrochloric acid is preferable from the viewpoint of preventing unintended reactions other than pH adjustment.

  The alkali to be added is not particularly limited, but sodium hydroxide is preferable from the viewpoint of preventing unintended reactions other than pH adjustment.

  The amount of acid or alkali to be added is appropriately adjusted so as to obtain a desired pH.

  Examples of the solvent used for the acid treatment or the alkali treatment include water and organic solvents such as ethanol, and usually water. The amount of solvent used is preferably in the range of 10% to 60% by weight with respect to the amount of compound used. If the amount is less than 10% by weight, it may be difficult to form a slurry. If the amount is more than 60% by weight, the amount of the treatment liquid may increase.

  The treatment time in the treatment tank 16 is not particularly limited as long as a seed crystal having a desired particle diameter can be obtained, but is preferably 30 minutes or more, and more preferably 2 hours or more.

  The seed crystal addition means is not particularly limited as long as the slurry can be transferred, but a tube pump, a slurry pump or the like is preferable.

  The seed crystal may be a particle that is capable of precipitating crystals of a hardly soluble salt generated on the surface thereof and includes a hardly soluble salt that is a precipitate by a crystallization reaction. Examples of the compound mainly composed of a hardly soluble salt that is a precipitate by a crystallization reaction include fluorite when the hardly soluble salt is calcium fluoride, and minerals such as phosphate ore when the hardly soluble salt is calcium phosphate. Minerals based on sparingly soluble salts are readily available as pellets or the like with purer sparingly soluble salts. The shape and particle size of the seed crystal are appropriately set according to the flow rate in the crystallization reaction tank 14, the crystallization target substance, the concentration of the crystallization agent, and the like, and are not particularly limited.

  The particle diameter of the seed crystal produced in the treatment tank 16 is preferably in the range of 1 μm to 50 μm, more preferably in the range of 5 μm to 20 μm, in terms of the volume average particle diameter calculated from the volume frequency. If the volume average particle size of the seed crystal is smaller than 1 μm, it may flow into the treated water and cause deterioration of the quality of the treated water. If the seed crystal is larger than 50 μm, not only the seed crystal effect but also the inside of the crystallization reaction tank 14 In some cases, the crystal of the crystal may be prevented from crystallizing and growing. Further, the uniformity coefficient, which is an index of the particle size distribution, is preferably 5 or less, and if the uniformity coefficient is 1, it is ideal.

  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 may be two or more kinds. 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 V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Cd, Hg, Sn, Pb, and Te, but are not limited thereto. . 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 ionized state of the crystallization target substance include those in which atoms such as F ⁻ and Cu ²⁺ are ionized, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, tetraphosphoric acid, and phosphorous acid. Examples thereof include compounds obtained by ionizing a compound containing a substance to be crystallized such as, etc., and complex ions such as heavy metals, but are not limited thereto.

  Raw water containing fluorine is also discharged from the aluminum electrolytic refining process, steelmaking process, etc., but in particular, it is discharged in large quantities at semiconductor factories. Concentrated hydrofluoric acid is used for cleaning a semiconductor silicon wafer, etc., and discharged as a 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 thus may become wastewater containing them. 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. . This method 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, and for phosphorus, 500 mg / L to The range is 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 crystallizing agent to recover calcium carbonate, sodium carbonate or the like is used as the crystallizing agent.

  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 obtained by adding an arbitrary compound such as an acid, an alkali, or a salt thereof to the water can be used. In addition, “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. It does not specifically limit as an acid used for preparation of a calcium solution, Arbitrary acids can be used. Preferably, it is an arbitrary acid that does not contain a component that forms a sparingly soluble salt with calcium, and examples thereof include hydrochloric acid, but are 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 amount of 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 various 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 existence of the optimum pH does not completely dissolve slaked lime fine particles by making the pH within a certain range, 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 component 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 produced by reacting raw phosphorus-containing water with a calcium agent, hydroxyapatite, etc., fluorine In addition, fluoroapatite and the like produced by reacting raw phosphorus-containing water with a calcium agent are also included.

  The crystallization reaction tank 14 is a reaction tank in which a crystallizing target substance and a crystallizing agent in the raw water react to precipitate crystals of a hardly soluble salt, thereby generating treated water in which the target crystallizing substance is reduced. The length, the inner diameter, the shape, and the like may be arbitrary, and are not particularly limited.

  As the crystallization reaction tank, as shown in FIG. 1, a stirring device 42 such as a stirring blade is installed in the crystallization reaction tank 14, and the inside of the crystallization reaction tank 14 is stirred by the stirring device 42 to flow the pellets. A stirring type crystallization reaction tank may be mentioned. The stirring blade is not particularly limited as long as the content can be stirred in the crystallization reaction tank 14 and the installation mode of the stirring blade, the size of the stirring blade, and the like are not particularly limited.

  Further, as the stirring type crystallization reaction tank 14, an inner peripheral wall is disposed so as to face the peripheral wall of the crystallization reaction tank 14, and a treatment water discharge path is formed between the inner and outer peripheral walls. It may have a separation zone that improves the separation ability and prevents the insoluble salt particles from flowing out into the treated water. In this aspect, an aspect in which the treated water discharge pipe 36 is connected to the upper part of the treated water discharge path is preferable. In addition, in this treated water discharge path, a buffer plate made up of a plurality of baffle plates and a buffer plate made up of a plurality of rectifying plates at the inlet of the treated water discharge path in order to improve the separation performance of the pellets May be located. Details of this aspect are described in JP-A-2005-230735 and JP-A-2005-296888, and the crystallization reaction tank described in these patent documents can also be used in this embodiment.

  Examples of the crystallization reaction tank include a fluidized bed type crystallization reaction tank in which an upward flow is formed in the crystallization reaction tank, and pellets flow through the upward flow.

  The concentration of the crystallization agent such as calcium agent in the crystallization agent solution such as 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 14 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 1 to 2 times that of fluorine as a chemical equivalent, but more preferably 1 to 1.2 times. If the chemical equivalent of calcium is more than twice the chemical equivalent of fluorine in 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, the total amount of fluorine in the raw water will not be calcium fluoride, and fluorine may be mixed into the treated water. Similarly, when the substance to be crystallized is phosphorus and calcium phosphate is produced, the amount of calcium injection is preferably 1 to 2 times that of phosphorus as a chemical equivalent, but more preferably 1 to 1.2 times.

  In the present embodiment, it is preferable to deposit a hardly soluble salt in the crystallization reaction tank 14 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 11, preferably from pH 2 to 3, from the viewpoint of suppressing fine particle formation. In the case where the pH changes with the formation reaction of calcium fluoride, it is desirable that a pH adjusting agent can be appropriately added to the crystallization reaction tank 14. 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 14 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 14 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 precipitating calcium phosphate, it is preferable to precipitate calcium phosphate under conditions of pH 6 to 8 from the viewpoint of pH 6 to 13 and suppression of fine particle formation.

  The pH adjusting agent adding means for adding the pH adjusting agent to the crystallization reaction tank 14 can be in any form as long as the pH adjusting agent can be added to the crystallization reaction tank 14. The pH adjusting agent may be added to the crystallization reaction tank 14 from the pH adjusting agent storage tank via the pH adjusting agent addition pipe. As a pH adjuster addition means, a mode in which a pH adjuster addition pipe is connected to an arbitrary part of the crystallization reaction tank 14 and the pH adjuster is directly added to an arbitrary part of the crystallization reaction tank 14 through the pipe. It may be a mode in which a pH adjuster is added to at least one of the raw water addition pipe or the crystallization agent addition pipe.

  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 addition pipe 30, the crystallization agent addition pipe 28, and the pH adjuster addition pipe 34 can be connected to any part of the crystallization reaction tank 14. In the case of a stirring type crystallization reaction tank as shown in FIG. 1, the raw water addition pipe 30, the crystallization agent addition pipe 28, and the pH adjuster addition pipe 34 are crystallized from the viewpoint of separation of precipitates and pellets and treated water. It is preferably connected to the upper part of the deposition reaction tank 14. Moreover, in FIG. 1, although the raw | natural water addition piping 30, the crystallization agent addition piping 28, and the pH adjuster addition piping 34 are each one, it is not limited to this, Even if these are provided with two or more good. In the case of a fluidized bed crystallization reaction tank, the raw water addition pipe, the crystallization agent addition pipe, and the pH from the viewpoint that the crystallization reaction can be efficiently performed by forming an upward flow in the crystallization reaction tank. It is preferable that the adjusting agent addition pipe is connected to the lower part of the crystallization reaction tank, particularly to the bottom part.

  In this embodiment, the crystallization reaction tank is provided with a stirring device equipped with a stirring blade or the like for stirring the fluid in the reaction tank, and in the region where the stirring flow can quickly diffuse into the reaction tank, the raw water and the crystallization agent Preferably at least one is injected. 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 or the like is large, or provided in the vicinity of the stirring blade or the like. In particular, the height of at least one injection point of the raw water and the crystallization agent in the rotation axis direction of the stirring blade is preferably a distance within twice the rotation radius of the stirring blade from the rotation center of the stirring blade. . Moreover, it is preferable that the position of the rotation direction of the stirring blade is a distance within twice the rotation radius of the stirring blade from the rotation center of the stirring blade. Furthermore, it is preferable that the center is provided in a spherical region whose center is the rotation center of the stirring blade and whose radius is twice the rotation radius of the stirring blade. As a result, the crystallization target substance and the crystallization agent are immediately diffused when injected into the crystallization reaction tank, and the concentration thereof quickly decreases. For this reason, the formed salt is less likely to be precipitated directly in the liquid, and the substance to be crystallized in the liquid can be taken in carefully as crystals of a hardly soluble salt on the granular seed crystal. Therefore, the amount of the hardly soluble salt particles mixed in the treated water can be extremely reduced, the hardly soluble salt particles having a large particle diameter can be stably obtained, and the recovery rate of the substance to be crystallized can be greatly improved. .

  Moreover, it is preferable that the injection point of the pH adjusting agent is also provided in a region where it can be quickly diffused into the reaction vessel by the stirring flow by a stirring blade or the like. When a pH adjusting agent is injected into a region where the stirring flow rate is low, such as when a pH adjusting agent is dropped on the surface of the water, a region with a high pH is generated locally. In this region, it is possible to directly generate slightly soluble salt fine particles such as calcium fluoride. Easy to encourage. However, if the pH adjusting agent is allowed to diffuse quickly after injection, a region having a high pH is extremely unlikely to be generated, and direct generation of hardly soluble salt fine particles not due to the crystallization reaction can be suppressed. Therefore, the recovery rate of the crystallization target substance can be further improved by discharging the pH adjuster to a region where the stirring flow rate is large.

  It is also preferable to install a draft tube below the water surface of the crystallization reaction tank so that the stirring blades of the stirring device and the like are located in the cylinder. FIG. 2 shows a schematic configuration of another example of the crystallization reaction apparatus. FIG. 3 shows a schematic configuration diagram of the crystallization reaction tank 14 provided with the draft tube 54. The crystallization reaction apparatus 3 of FIG. 2 includes a draft tube 54 in the crystallization reaction tank 14 in addition to the configuration of FIG. The stirring blade of the stirring device 42 is rotated by the rotational force generated by the stirrer motor transmitted through the stirring shaft.

  At this time, it is preferable that the stirring blades and the like form a downward flow. When the draft tube 54 is installed in this manner, 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, crystallization agent, etc. can be diffused more quickly, and the generation of poorly soluble salt particles is suppressed as much as possible by bringing the regions where the concentrations of raw water and crystallization agent are locally deep into contact with each other. It becomes possible to do.

  Further, when the draft tube 54 and the stirring blade 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, the particles are classified so that small-sized 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, near the injection point of raw water, crystallization agent, etc. Recirculate to lower stirring zone. These small-sized crystals serve as nuclei to promote the crystallization reaction. For this reason, it becomes possible to stably form crystals of a hardly soluble salt having a large particle size, and the recovery rate of the crystallization target substance can be improved.

  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, sinks down and does not enter the draft tube 54 again. It can be prevented from being destroyed by collision with a blade 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 stably form an upward flow at the outer periphery of the tube, stirring blades, etc. must be located somewhere in the lower half of the tube in the tube. preferable. 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., and particle classification can be effectively advanced.

  When the draft tube 54 is provided, the injection points of the raw water, the crystallization agent, and the pH adjusting agent are placed in the cylinder of the draft tube 54 in order to quickly and effectively diffuse them on the downflow in the draft tube 54. It is preferable to arrange in A more preferable position is in the cylinder of the draft tube 54 and above the stirring blade 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 14 or in the treated water, the means for measuring the concentration of the substance to be crystallized such as a fluorine concentration meter is used to discharge the crystallization reaction tank 14 or the treated water You may install in the piping 36. FIG. Further, in order to measure the concentration of the crystallization agent such as soluble calcium in the crystallization reaction tank 14 or in the treated water, a crystallization agent concentration measuring means such as a calcium concentration meter is used as the crystallization reaction tank 14 or the treated water discharge pipe 36. You may install in. The installation position of the fluorine concentration meter, calcium concentration meter and the like in the crystallization reaction tank 14 is not particularly limited. For example, when measuring the concentration in the treated water, the vicinity of the exit of the crystallization reaction tank 14 Can be installed.

  The treated water in which the crystallization target substance generated by the crystallization reaction in the crystallization reaction tank 14 is reduced is discharged to the outside of the crystallization reaction tank 14. The treated water can be discharged from any part according to the liquid flow in the crystallization reaction tank 14. In FIG. 1, the treated water discharged from the upper part of the crystallization reaction tank 14 is finally discharged out of the system through the treated water discharge pipe 36. Further, when an upward flow is formed in the fluidized bed type crystallization reaction tank, treated water is discharged from the upper part of the crystallization reaction tank. A treated water storage tank may be installed in the subsequent stage of the crystallization reaction tank 14.

  In the treated water to be obtained, for example, the fluorine concentration is usually about 500 mg-F / L or less as total fluorine including insoluble fluorine such as calcium fluoride, and usually about 50 mg-F / L or less as soluble fluorine ions. The concentration is usually about 50 mg-P / L or less as total phosphorus including insoluble phosphorus such as calcium phosphate, and 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 supernatant water can be obtained. For example, when the substance to be crystallized 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 supernatant water with further reduced phosphorus concentration. be able to.

  By crystallization of a hardly soluble salt in the crystallization reaction tank 14 by the crystallization reaction apparatus and the crystallization reaction method according to this embodiment, the crystallization target substance in the raw water is recovered as a hardly soluble salt crystal. As a result, treated water with reduced crystallization target substances is produced. In the present embodiment, the recovery rate of the crystallization target substance element (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%. As described above, even more preferably, 90% or more can be achieved.

  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.

  Under the following conditions, fluorite as a seed crystal was dissolved in industrial water to form a slurry, and experiments were conducted with and without fluorite acid treatment or alkali treatment in a treatment tank. ). The particle sizes of the fluorite used in the experiment and the seed crystals produced in the treatment tank were measured with a laser diffraction particle size distribution meter (LS230, manufactured by Beckman Coulter, Inc.).

(Examples 1 to 4, Comparative Examples 2 and 3 )
Raw water: Hydrofluoric acid-containing waste water Crystallizer: Calcium chloride Crystallization reaction tank Specifications: 150 L (500 mmφ × 1200 mmH)
Crystallization reactor pH: 2.5 ± 0.5
pH adjuster: Sodium hydroxide and hydrochloric acid Seed slurry tank Specification: 15 L (250 mmφ × 300 mmH)
Seed crystal addition amount: 30 g / H
Fluorine concentration of hydrofluoric acid-containing raw water: 10000 mg / L
Hydrofluoric acid-containing raw water flow rate: 30 L / H

  The experiment was carried out by changing the pH of the treatment tank to 1, 3, 5, 9, 12, 14 ± 0.2, respectively. The injection points of the raw water addition pipe and the crystallization agent addition pipe were set at a position 100 mm higher than the stirring blade. Further, the used draft tube had a diameter of 250 mm, and was installed so that the upper end was located 150 mm from the water surface and the lower end was located 150 mm below the stirring blade. The particle size of fluorite used in the experiment was 5 to 40 μm (volume average particle size = 19 μm), and the particle size of the seed crystals produced in the treatment tank was 3 μm to 20 μm (volume average particle size = 9 μm). The seed crystal was continuously supplied to the crystallization reaction tank. The results are shown in Table 1. The treated water fluorine concentration referred to here is the total fluorine concentration including SS-type fluorine (= calcium fluoride) and soluble fluorine.

(Comparative Example 1)
Experiments were performed in the same manner as in Example 1 except that no acid treatment or alkali treatment seed crystals were used (treatment tank pH was about 7.2). The results are shown in Table 1.

As can be seen from Table 1, as in Examples 1 to 4 , a compound containing a sparingly soluble salt as a main component was subjected to acid treatment at a pH of 3 or less or an alkali treatment at a pH of 12 or more in a slurry state, and the treated compound was crystallized as a seed crystal. By adding to the deposition reaction tank, treated water with good water quality could be obtained.

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 the other 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 crystallization reaction apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,3 Crystallization reactor, 10 Crystallizer storage tank, 12 Raw water storage tank, 14 Crystallization reaction tank, 16 Treatment tank, 18 Compound storage tank, 20 Compound replenishment apparatus, 22, 24, 26 Pump, 28 Crystallizer addition piping , 30 Raw water addition pipe, 32 seed crystal addition pipe, 34 pH adjuster addition pipe, 36 treated water discharge pipe, 38 pH meter, 40, 42 stirrer, 44 motor, 46 treatment agent addition pipe, 48 compound addition pipe, 50 Solvent addition piping, 52 compounds, 54 draft tube, 60 crystallization reaction apparatus, 62 crystallization agent storage tank, 64 raw water storage tank, 66 crystallization reaction tank, 68 seed crystal addition apparatus.

Claims (2)

A crystallization reaction apparatus for generating calcium fluoride crystals by adding a calcium agent to raw water containing fluorine ,
A crystallization reaction tank for generating calcium fluoride crystals by adding the calcium agent to the raw water;
Treatment means for treating the compound containing calcium fluoride as a main component in a slurry state with an acid treatment at pH 3 or lower or an alkali treatment at pH 12 or higher ;
Seed crystal addition means for adding the acid-treated or alkali-treated treatment compound as a seed crystal to the crystallization reaction tank;
A crystallization reaction apparatus characterized by comprising: By adding calcium agent to raw water containing fluorine and a crystallization reaction method to produce crystals of calcium fluoride,
A treatment step of treating the compound containing calcium fluoride as a main component in a slurry state with an acid treatment at pH 3 or lower or an alkali treatment at pH 12 or higher ;
A seed crystal addition step of adding the acid-treated or alkali-treated treatment compound as a seed crystal to the crystallization reaction tank;
A crystallization reaction step of generating calcium fluoride crystals by adding the calcium agent to the raw water;
A crystallization reaction method comprising:

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