JP5414169B2 - 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 substance such as fluorine and phosphorus in the liquid to crystallize insoluble salts such as calcium fluoride and calcium phosphate, and are 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.

  FIG. 8 shows a schematic configuration diagram of an example of a conventional crystallization reaction apparatus. The crystallization reaction apparatus 100 includes a crystallization reaction tank 102, a seed crystal addition apparatus 104, and a crystal slurry tank 106. In the crystallization reaction apparatus 100, raw water containing a crystallization target substance such as fluorine-containing raw water, a crystallization agent such as a calcium agent, and a pH adjuster are added to the crystallization reaction tank 102, and a seed crystal is added to the seed crystal addition apparatus. From 104, it is added into the crystallization reaction tank 102 to produce crystals of a hardly soluble salt. When the crystal in the crystallization reaction tank 102 grows to some extent, a part of the crystal is extracted from the crystallization reaction tank 102. The drawn crystal is in the form of a slurry and is stored in the crystal slurry tank 106. Thereafter, the slurry containing the crystal is dehydrated by a dehydrating apparatus such as a filter press type or a centrifugal dehydration type to obtain a recovered crystal.

  Usually, when the crystals in the crystallization reaction tank 102 become larger, the crystal interface 112 in the precipitation area 110 communicating with the reaction area 108 in the crystallization reaction tank 102 rises. A method is used in which the interface 112 is detected by an interface meter or the like installed on the crystallization reaction tank 102 and is extracted from the valve 114 below the crystallization reaction tank 102.

  The seed crystal may be replenished at any time, but is usually intermittently replenished. For example, the seed crystal having an average of about 20 μm is supplemented, and the seed crystal is grown to an average of about 70 to 80 μm.

  Even if seed crystals are not replenished, some crystals grow with fine crystal particles that naturally occur in the crystallization reaction tank 102 as nuclei, but the amount of naturally occurring crystal particles is the same as the amount of crystallization in the raw water. Since it varies depending on various reaction conditions such as the concentration of the target substance, pH, and coexisting ions, it is difficult to obtain crystals with a certain particle size. In particular, when there are few fine crystals that are generated naturally and become the core of the crystal, there is a problem that the crystallization reaction does not occur sufficiently and the recovery rate is lowered. It is common to do.

  It is desirable that the crystal grain size distribution in the crystallization reaction tank 102 be within a certain range. When the particle size becomes coarse, the reactivity becomes poor and the recovery rate deteriorates. When the particle size becomes fine, the amount of seed crystals to be replenished increases, which is disadvantageous in terms of cost.

  In addition, since the crystal grain size distribution is always drawn within a certain range, the drawn crystal can be easily reused. For example, when recovering calcium fluoride as a raw material for hydrofluoric acid production, if the particle size is large, there is a problem that it is difficult to dissolve in sulfuric acid, and if it is fine, hydrofluoric acid production is likely to be scattered and difficult to handle. Due to the above problems, calcium fluoride crystals having the same particle size as the mineral raw material fluorite are required.

JP 2003-225680 A

  In the above crystallization reactor, even if the seed crystal is replenished, if the concentration of the crystallization target substance fluctuates or the concentration of coexisting ions fluctuates, the quality of the treated water changes and the recovered crystals that are crystallized and recovered This also causes a problem that the grain size of the recovered crystals is not constant. In addition, the replenished seed crystals often have a wide particle size distribution, and it is difficult to obtain a recovered crystal with the optimum particle size by operating with the optimum particle size distribution by the method of constantly replenishing a constant weight of seed crystals. It is.

  The present invention relates to a crystallization reaction apparatus and a crystallization reaction method capable of controlling the particle size, particle size distribution, and the like of the recovered hardly soluble salt crystals.

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 stirring-type crystallization reaction tank for generating crystals, seed crystal addition means for adding seed crystals to the crystallization reaction tank, and drawing means for extracting at least part of the crystals generated in the crystallization reaction tank And at least one of the volume average particle size, number average particle size and particle size distribution of the drawn crystal, and volume average particle size, number average particle size and particle size distribution of the crystal in the crystallization reaction tank. It is a crystallization reaction apparatus having a particle diameter measuring means for measuring and a crystal amount adjusting means for adjusting the amount of the seed crystal to be added based on the measured value.

The present invention also relates to a crystallization reaction method in which a crystallizing agent is added to raw water containing a substance to be crystallized to form a hardly soluble salt crystal , wherein the raw water is mixed with the raw water in the crystallization reaction tank. At least a part of the crystals generated in the crystallization reaction step, a crystallization reaction step of adding a crystallization agent to form crystals of a hardly soluble salt, a seed crystal addition step of adding seed crystals to the raw water, and the crystallization reaction step. Of the drawing step, the volume average particle size, number average particle size and particle size distribution of the drawn crystal, and the volume average particle size, number average particle size and particle size distribution of the crystal produced in the crystallization reaction step It is a crystallization reaction method including a particle size measuring step for measuring at least one and a crystal amount adjusting step for adjusting the amount of the seed crystal to be added based on the measured value.

  In the present invention, in a crystallization reaction apparatus and a crystallization reaction method in which a crystallizer is added to raw water containing a substance to be crystallized to form a hardly soluble salt crystal, at least a part of the crystal generated in the crystallization reaction step. And at least one of a value related to the particle size of the extracted crystal and a value related to the particle size of the crystal formed in the crystallization reaction step is measured, and based on the measured value, the amount of seed crystals to be added and By adjusting at least one of the amount of crystals to be drawn, the particle size, particle size distribution, etc. of the recovered hardly soluble salt crystals can be controlled.

  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 reaction tank 10, a seed crystal storage tank 12, and a crystal slurry tank 14.

  In the crystallization reaction apparatus 1 of FIG. 1, a raw water addition pipe 18, a crystallization agent addition pipe 16, a pH adjuster addition pipe 22, and a treated water discharge pipe 24 are connected to the crystallization reaction tank 10. A stirring device 30 such as a stirring blade, which is a stirring means, is provided. In addition, a seed crystal addition pipe 20 from the seed crystal storage tank 12 is connected to the crystallization reaction tank 10 via a seed crystal supply device 42 as a seed crystal addition means. The seed crystal replenishing device 42 includes a motor 40 as crystal amount adjusting means. A slurry discharge pipe 26 from the crystallization reaction tank 10 is connected to the crystal slurry tank 14 via a valve 34 as a drawing means, and a stirring device 32 is installed. A slurry discharge pipe 28 is connected to the crystal slurry tank 14 via a pump 36. The slurry discharge pipe 28 is connected to the dehydrating device, but is branched halfway and connected to the crystal slurry tank 14. Further, a particle size measuring device 38 as a particle size measuring means is connected to the crystal slurry tank 14 side downstream of the branch point of the slurry discharge pipe 28. The particle size measuring device 38 also has a function as a control unit, and is electrically connected to the motor 40. The control unit may be provided separately from the particle size measuring device 38.

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

  Raw material 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 18. The Further, a crystallization agent such as a calcium agent is added to the crystallization reaction tank 10 through the crystallization agent addition pipe 16 from the crystallization agent storage tank or the like. Further, the seed crystal 44 is added from the seed crystal storage tank 12 to the crystallization reaction tank 10 through the seed crystal addition pipe 20 by the seed crystal supply device 42 driven by the motor 40 (seed crystal addition process). In the crystallization reaction tank 10, 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 10, the pH adjusting agent may be added from the pH adjusting agent addition pipe 22 as necessary to adjust the pH of the crystallization reaction solution, and the crystallization reaction solution is stirred by the stirring device 30. May be.

  When the hardly soluble salt crystal in the crystallization reaction tank 10 grows to a certain extent, the valve 34 is opened, and at least a part of the hardly soluble salt crystal is drawn from the crystallization reaction tank 10 through the slurry discharge pipe 26. (Drawing process). The drawn crystal is in a slurry form and is stored in the crystal slurry tank 14. In the crystal slurry tank 14, the drawn slurry may be stirred by the stirring device 32. Thereafter, the drawn slurry containing the crystals is sent to the dehydrator through the slurry discharge pipe 28 by the pump 36, and dehydrated in the dehydrator (dehydration step). The dehydrated crystal is washed with a solvent such as water as necessary (washing step), and dehydrated again as necessary to obtain a recovered crystal.

  At this time, in the slurry discharge pipe 28, a value relating to the particle size of the crystal in the drawn slurry is measured by the particle size measuring device 38. Based on the measured value, the control unit adjusts the amount of the seed crystal added to the crystallization reaction tank 10 by the seed crystal replenishing device 42 driven by the motor 40 (crystal amount adjusting step).

  The outline of the other example of the crystallization reaction apparatus which concerns on embodiment of this invention is shown in FIGS. In the crystallization reaction device 3 of FIG. 2, a particle size measuring device 38 is connected to the crystal slurry tank 14 side downstream of the branch point of the slurry discharge pipe 28. The particle size measuring device 38 also has a function as a control unit, and is electrically connected to a valve 34 as crystal amount adjusting means. The control unit may be provided separately from the particle size measuring device 38.

  In the crystallization reaction device 3, a value related to the particle size of the crystal in the drawn slurry is measured by the particle size measuring device 38 in the slurry discharge pipe 28. Based on the measured value, the control unit adjusts the amount of crystals drawn from the crystallization reaction tank 10 to the crystal slurry tank 14 by the valve 34 (crystal amount adjustment step).

  In the crystallization reaction apparatus 5 of FIG. 3, the slurry discharge pipe 28 is connected to a dehydrator. A reaction solution discharge pipe 52 is connected to the lower part of the crystallization reaction tank 10 via the pump 54 and to the upper part of the crystallization reaction tank 10. The particle size measuring device 38 is connected in the middle of the reaction liquid discharge pipe 52. The particle size measuring device 38 also has a function as a control unit, and is electrically connected to a motor 40 as crystal amount adjusting means. The control unit may be provided separately from the particle size measuring device 38.

  In the crystallization reaction device 5, a value related to the particle size of crystals in the reaction solution is measured by the particle size measurement device 38 in the reaction solution discharge pipe 52. Based on the measured value, the control unit adjusts the amount of the seed crystal added to the crystallization reaction tank 10 by the seed crystal replenishing device 42 driven by the motor 40 (crystal amount adjusting step).

  In the crystallization reaction apparatus 7 of FIG. 4, the slurry discharge pipe 28 is connected to a dehydrator. A reaction solution discharge pipe 52 is connected to the lower part of the crystallization reaction tank 10 via the pump 54 and to the upper part of the crystallization reaction tank 10. The particle size measuring device 38 is connected in the middle of the reaction liquid discharge pipe 52. The particle size measuring device 38 also has a function as a control unit, and is electrically connected to a valve 34 as crystal amount adjusting means. The control unit may be provided separately from the particle size measuring device 38.

  In the crystallization reaction device 7, a value related to the particle size of crystals in the reaction solution is measured by the particle size measurement device 38 in the reaction solution discharge pipe 52. Based on the measured value, the control unit adjusts the amount of crystals drawn from the crystallization reaction tank 10 to the crystal slurry tank 14 by the valve 34 (crystal amount adjustment step).

  Usually, when the crystal in the crystallization reaction tank 10 becomes larger, the crystal drawing of the crystal 50 in the precipitation area 48 communicating with the reaction area 46 of the crystallization reaction tank 10 rises. A method is used in which the interface 50 is detected by an interface meter or the like installed on the crystallization reaction tank 10 and is extracted from the valve 34 at the bottom of the crystallization reaction tank 10.

  In the present embodiment, at least a part of the crystal generated in the crystallization reaction step is drawn, and at least one of a value relating to the particle size of the drawn crystal and a value relating to the particle size of the crystal generated in the crystallization reaction step is measured. Then, based on the measured value, the particle size, particle size distribution, etc. of the recovered hardly soluble salt crystals are controlled by adjusting at least one of the amount of seed crystals to be added and the amount of crystals to be extracted. can do.

  In the present specification, “value relating to particle size” refers to volume average particle size, number average particle size, particle size distribution, and the like. As the particle size measuring device 38, a particle size measuring device for measuring particle size and particle size distribution such as laser diffraction type, light scattering type, image analysis type, and electric resistance type is adopted. Usually, either a value relating to the particle size of the drawn crystal or a value relating to the particle size of the crystal in the crystallization reaction tank 10 may be measured. Both the crystal grain size values may be measured, and at least one of the amount of seed crystals to be added and the amount of crystals to be drawn may be adjusted based on the measured values.

  Examples of the seed crystal replenishing device 42 as seed crystal addition means include, but are not limited to, a powder feeder that transfers the seed crystal as a powder and a pump that transfers the seed crystal as a slurry.

  As the crystal amount adjusting means, there are a crystal amount adjusting means for continuously adding seed crystals to increase or decrease the amount of seed crystals added, or a crystal amount adjusting means for intermittently adding seed crystals to change the amount of seed crystals added. Examples include but are not limited to these.

  Examples of the drawing means include a method of drawing from the crystallization reaction tank 10 by gravity by opening and closing the valve 34 and a method of drawing by a pump.

  Examples of the crystal amount adjusting means include, but are not limited to, a crystal amount adjusting means for changing the drawing amount according to the opening / closing time of the valve 34 and the operating time of the pump.

  As a method for controlling the amount of seed crystal added or the amount of drawn crystal drawn, if the measured value is smaller than the required particle size, particle size distribution, etc., the amount of seed crystal added and the drawn crystal drawn by the crystal amount adjusting means Decrease at least one of the amounts, and if the measured value is larger than the required particle size, particle size distribution, etc., increase at least one of the added amount of seed crystals and the drawn amount of drawn crystals by the crystal amount adjusting means By making it, the crystal | crystallization which has a desired particle size, a particle size distribution, etc. can be obtained.

  Addition of raw water, crystallization agent and pH adjusting agent to the crystallization reaction tank 10 and addition of the drawing slurry to the crystal slurry tank 14 are performed by adding the raw water, the crystallization agent, the pH adjusting agent and the drawing slurry to the crystallization reaction tank 10, Any mode that can be added to the crystal slurry tank 12 is possible.

  Filter press type, centrifugal dehydration type, etc. are adopted as the dehydration device, but the generated crystal particles have a large particle size of several tens of μm and good dehydration. Therefore, filtration using gravity in addition to centrifugal force, pressure, etc. A type dehydrator (such as non-woven fabric) is also employed. The dehydrated crystals may be washed with washing water or the like. Further, the drawing slurry may be neutralized before the dehydration step (neutralization step).

  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 10 is a reaction tank capable of producing a treated water in which the crystallization target substance in the raw water reacts with the crystallization agent to precipitate crystals of a hardly soluble salt, thereby reducing the crystallization target substance. The length, the inner diameter, the shape, and the like may be arbitrary, and are not particularly limited.

  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 filled 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, the crystallization agent The concentration is appropriately set according to the operating conditions of the crystallization reaction apparatus 1 and the like.

  The seed crystal may be any material as long as it can precipitate a hardly soluble salt crystal formed on the surface thereof, and any material can be selected. For example, filtered sand, activated carbon, zircon sand, garnet sand, Particles composed of oxides of metal elements such as random (trade name, manufactured by Nihon Cartrit 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 more pure hardly soluble salt can be obtained as a pellet or the like, particles (for example, fluorite in the case of calcium fluoride) including a hardly soluble salt that is a precipitate by a crystallization reaction 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. 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 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.

  As the crystallization reaction tank, as shown in FIG. 1, a stirring device 30 such as a stirring blade is installed in the crystallization reaction tank 10, and the inside of the crystallization reaction tank 10 is stirred by the stirring device 30 to flow the pellets. A stirring type crystallization reaction tank may be mentioned. 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.

  In addition, as the stirring type crystallization reaction tank 10, an inner peripheral wall is disposed so as to face the peripheral wall of the crystallization reaction tank 10, and a space between the inner and outer peripheral walls is used as a treated water discharge path. 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 24 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 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 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 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 11, preferably from pH 2 to 3, from the viewpoint of suppressing fine particle formation. 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 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 it can monitor the pH of the reaction field of the calcium fluoride precipitation reaction. 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 10 can be in any form as long as the pH adjusting agent can be added to the crystallization reaction tank 10. The pH adjuster may be added to the crystallization reaction tank 10 from the pH adjuster storage tank via the pH adjuster 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 10 and a pH adjuster is directly added to an arbitrary part of the crystallization reaction tank 10 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 18, the crystallization agent addition pipe 16, and the pH adjuster addition pipe 22 can be connected to any part of the crystallization reaction tank 10. In the case of a stirring type crystallization reaction tank as shown in FIG. 1, the raw water addition pipe 18, the crystallization agent addition pipe 16 and the pH adjuster addition pipe 22 are crystallized from the viewpoint of separation of precipitates and pellets and treated water. It is preferable to be connected to the upper part of the deposition reaction tank 10. Moreover, in FIG. 1, although the raw | natural water addition piping 18, the crystallization agent addition piping 16, and the pH adjuster addition piping 22 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, instead of supplying a seed crystal from the seed crystal storage tank 12, a seed crystal generation tank is provided to cause a part of raw water and a part of a crystallization agent to react to generate a seed crystal. By adding to the crystallization reaction tank 10, treated water with good water quality can be obtained.

  FIG. 5 shows a schematic configuration of another example of the crystallization reaction apparatus according to the embodiment of the present invention. The crystallization reaction device 9 includes a crystallization agent storage tank 56, a raw water storage tank 58, a crystallization reaction tank 10, and a seed crystal for generating a seed crystal by reacting a part of raw water and a part of the crystallization agent. A generation tank 60 and a crystal slurry tank 14 are provided.

  In the crystallization reaction apparatus 9 of FIG. 5, the crystallization reaction tank 10 is connected to a crystallization agent addition pipe 16 from the crystallization agent storage tank 56 via a pump 70 as a crystallization agent addition means. The raw water addition pipe 18 from the storage tank 58 is connected via a pump 74 as raw water addition means. A crystallization agent addition pipe 62 from the crystallization agent storage tank 56 is connected to the seed crystal generation tank 60 via a pump 68, and a raw water addition pipe 64 from the raw water storage tank 58 is connected via a pump 72. Yes. Further, in the crystallization reaction tank 10, a seed crystal addition pipe 66 from the seed crystal generation tank 60 is a valve 80, a seed crystal addition means for adding the generated seed crystal to the crystallization reaction tank, and a pump as a crystal amount adjustment means. The treated water discharge pipe 24 is connected to the outlet. The seed crystal production tank 60 and the crystallization reaction tank 10 are connected to pH adjusting agent addition pipes 78 and 22, respectively, and are equipped with stirring devices 76 and 30 such as stirring blades which are stirring means equipped with a motor. ing. A slurry discharge pipe 26 from the crystallization reaction tank 10 is connected to the crystal slurry tank 14 via a valve 34 as a drawing means, and a stirring device 32 is installed. A slurry discharge pipe 28 is connected to the crystal slurry tank 14 via a pump 36. The slurry discharge pipe 28 is connected to the dehydrating device, but is branched halfway and connected to the crystal slurry tank 14. Further, a particle size measuring device 38 as a particle size measuring means is connected to the crystal slurry tank 14 side downstream of the branch point of the slurry discharge pipe 28. The particle size measuring device 38 also has a function as a control unit, and is electrically connected to the pump 82. The control unit may be provided separately from the particle size measuring device 38.

  A part of the raw water containing the substance to be crystallized is added from the raw water storage tank 58 to the seed crystal generation tank 60 through the raw water addition pipe 64 by the pump 72. A part of the crystallization agent is added from the crystallization agent storage tank 56 to the seed crystal generation tank 60 through the crystallization agent addition pipe 62 by the pump 68. In the seed crystal generation tank 60, the crystallization target substance contained in the raw water reacts with the crystallization agent to generate a seed crystal (seed crystal generation step). In the seed crystal production tank 60, a pH adjuster may be added from the pH adjuster addition pipe 78 as necessary to adjust the pH of the reaction solution, or the reaction solution may be stirred by the stirring device 76. .

  On the other hand, the remaining raw water is added from the raw water storage tank 58 to the crystallization reaction tank 10 through the raw water addition pipe 18 by the pump 74. The remainder of the crystallization agent is added from the crystallization agent storage tank 56 to the crystallization reaction tank 10 through the crystallization agent addition pipe 16 by the pump 70. At this time, the seed crystals generated in the seed crystal generation tank 60 are added to the crystallization reaction tank 10 through the seed crystal addition pipe 66 by the pump 82 (seed crystal addition step). In the crystallization reaction tank 10, 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 10, the pH adjusting agent may be added from the pH adjusting agent addition pipe 22 as necessary to adjust the pH of the crystallization reaction solution, and the crystallization reaction solution is stirred by the stirring device 30. May be. The seed crystals added to the crystallization reaction tank 10 for adjusting the amount of crystals may be added to the raw water before the crystallization agent is added, or added to the raw water after the crystallization agent is added. It may be added to the raw water together with the crystallizing agent. The seed crystal may be added to the crystallization reaction tank 10 continuously or intermittently.

  When the hardly soluble salt crystal in the crystallization reaction tank 10 grows to a certain extent, the valve 34 is opened, and at least a part of the hardly soluble salt crystal is drawn from the crystallization reaction tank 10 through the slurry discharge pipe 26. (Drawing process). The drawn crystal is in a slurry form and is stored in the crystal slurry tank 14. In the crystal slurry tank 14, the drawn slurry may be stirred by the stirring device 32. Thereafter, the drawn slurry containing the crystals is sent to the dehydrator through the slurry discharge pipe 28 by the pump 36, and dehydrated in the dehydrator (dehydration step). The dehydrated crystal is washed with a solvent such as water as necessary (washing step), and dehydrated again as necessary to obtain a recovered crystal.

  At this time, in the slurry discharge pipe 28, a value relating to the particle size of the crystal in the drawn slurry is measured by the particle size measuring device 38. Then, based on the measured value, the control unit adjusts the amount of seed crystals added to the crystallization reaction tank 10 by the pump 82 (crystal amount adjusting step). In the crystal amount adjustment step, the value related to the particle size of the crystal in the crystallization reaction tank 10 may be measured, or the value related to the particle size of the drawn crystal and the value related to the particle size of the crystal in the crystallization reaction tank 10. Both may be measured. Based on these measured values, at least one of the amount of seed crystals to be added and the amount of crystals to be extracted may be adjusted. This makes it possible to obtain treated water with good water quality and to adjust the replenishment amount of seed crystals to the optimum range, thereby reducing the amount of seed crystals and crystallizer used and reducing the cost. The effect that it becomes dominant is obtained.

  The addition of the raw water to the seed crystal production tank 60 and the addition of the crystallization agent to the seed crystal production tank 60 can be in any form as long as the raw water and the crystallization agent can be added to the seed crystal production tank 60. . The raw water storage tank 58 and the crystallization agent storage tank 56 may be provided with a stirring device.

  The seed crystal generated in the seed crystal generation tank 60 usually grows to about 5 μm to 50 μm, but even if it has a small particle size compared to a seed crystal using minerals, it does not flow into the treated water and has good water quality. can get. The reason for this is not clear, but the seed crystals produced in the seed crystal production tank 60 are more active than the seed crystals using minerals, and are added to the seed crystals in the crystallization reaction tank 10 and the crystallization reaction tank 10. It is considered that a crystal having a large particle size can be obtained because it is easy to crystallize with at least one of the hardly soluble salt crystals produced by the reaction between the crystallization target substance and the crystallization agent. Further, it is considered that the seed crystal generated in the seed crystal generation tank 60 has fewer fine crystals than the seed crystal using the mineral.

  The amount of raw water added to the seed crystal production tank 60 is preferably in the range of 0.1% by weight to 5% by weight of the amount of raw water added to the crystallization reaction tank 10, and is in the range of 0.3% by weight to 3% by weight. More preferred. If the amount is less than 0.1% by weight, the function as a seed crystal is not sufficient, and the quality of the treated water may be deteriorated, and if it is more than 5% by weight, the quality of the treated water may be deteriorated.

  The reaction time of the crystallization target substance and the crystallization agent in the seed crystal production tank 60 is not particularly limited as long as a seed crystal having a desired particle diameter can be obtained, but is preferably 3 hours or more, and more preferably 6 hours or more.

  The pH of the reaction solution of the crystallization target substance and the crystallization agent in the seed crystal production tank 60 is not particularly limited as long as a desired seed crystal can be obtained, but is preferably in the range of pH 1 to 4, more preferably in the range of pH 1 to 2. More preferred. A lower pH tends to yield a seed crystal with higher reaction activity.

  The seed crystal should just be what can precipitate the crystal | crystallization of the hardly soluble salt produced | generated on the surface. 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.

  The particle diameter of the seed crystal generated in the seed crystal generation tank 60 is preferably in the range of 1 μm to 50 μm, more preferably in the range of 5 μm to 20 μm, as a volume average particle diameter calculated from the volume frequency. If the volume average particle diameter 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 10 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 amount of the crystallization agent added to the seed crystal production tank 60 is preferably the same as the chemical equivalent of the crystallization target substance contained in the raw water added to the seed crystal production tank 60, and the crystallization agent is added in excess. Then, the seed crystal particles become finer, and when this is added to the crystallization reaction tank 10, the treated water may be deteriorated. Therefore, as the chemical equivalent of the crystallization target substance added to the seed crystal generation tank 60 1.2 times or less is preferable.

  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. 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. 6 shows a schematic configuration diagram of the crystallization reaction tank 10 including the draft tube 84. The stirring blades of the stirring device 30 are 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 84 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, 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.

  Moreover, when the draft tube 84 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 by the upward flow at the outer periphery of the tube, sinks down and does not enter the draft tube 84 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 84 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 84 in order to quickly and effectively diffuse them on the downward flow in the draft tube 84. It is preferable to arrange in A more preferable position is in the cylinder of the draft tube 84 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 10 or in the treated water, the means for measuring the concentration of the substance to be crystallized, such as a fluorine concentration meter, is discharged from the crystallization reaction tank 10 or the treated water. You may install in the piping 24. FIG. Further, in order to measure the concentration of the crystallization agent such as soluble calcium in the crystallization reaction tank 10 or in the treated water, a crystallization agent concentration measuring means such as a calcium concentration meter is used as the crystallization reaction tank 10 or the treated water discharge pipe 24. You may install in. The installation position of the fluorine concentration meter, the calcium concentration meter, etc. in the crystallization reaction tank 10 is not particularly limited. For example, when measuring the concentration in the treated water, the vicinity of the exit of the crystallization reaction tank 10 Can be installed.

  The treated water in which the crystallization target substance generated by the crystallization reaction in the crystallization reaction tank 10 is reduced is discharged to the outside of the crystallization reaction tank 10. The treated water can be discharged from any part according to the liquid flow in the crystallization reaction tank 10. In FIG. 1, the treated water discharged from the upper part of the crystallization reaction tank 10 is finally discharged out of the system through the treated water discharge pipe 24. 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. You may install a treated water storage tank in the back | latter stage of the crystallization reaction tank 10. FIG.

  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 10 by the crystallization reaction apparatus and the crystallization reaction method according to the present embodiment, the crystallization target substance in the raw water is recovered as the 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.

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

Example 1
Raw water: Hydrofluoric acid-containing waste water Crystallizer: Calcium chloride Crystallization reactor diameter: 440 mmφ
Crystallization reactor height: 620 mmH
Crystallization reactor pH: 2.5 ± 0.5
pH adjuster: Sodium hydroxide Fluorine concentration of hydrofluoric acid-containing raw water: 5000-20000 mg / L
Hydrofluoric acid-containing raw water flow rate: 25 L / H
Target particle size: 70 μm

  The experiment was performed using the crystallization reaction apparatus shown in FIG. For the measurement of the particle size, an in-line monitoring system LASENTEC D600L manufactured by LASENTEC was used. As shown in Table 1, it was varied at 0, 300, 600, 900, 1200 g / day according to the measured volume average particle diameter. The particle size distribution of the produced pellets after 600 hours of water flow is shown in FIG.

(Comparative Example 1)
The experiment was performed in the same manner as in Example 1 except that the seed crystal replenishment amount was a fixed amount of 600 g / day and the fluorine concentration of hydrofluoric acid-containing raw water was 20000 to 90000 mg / L. The results are shown in FIG.

(Comparative Example 2)
The experiment was conducted in the same manner as in Example 1 except that the seed crystal replenishment amount was a fixed amount of 600 g / day and the fluorine concentration of hydrofluoric acid-containing raw water was 5000 to 20000 mg / L. The results are shown in FIG.

  As can be seen from FIG. 7, at least a part of the crystal formed in the crystallization reaction step is drawn, the volume average particle size of the drawn crystal is measured, and the amount of seed crystal to be added based on the measured particle size It was possible to control the particle size distribution of the recovered sparingly soluble salt crystals to be small and the particle size distribution to be narrowed.

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 the other 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 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 figure which shows the particle size distribution of the production | generation pellet after 600-hour water flow in the Example of this invention. It is a schematic block diagram which shows an example of the conventional crystallization reaction apparatus.

Explanation of symbols

  1,3,5,7,9,100 Crystallization reactor 10,102 Crystallization reaction tank, 12 seed crystal storage tank, 14,106 Crystal slurry tank, 16,62 Crystallizer addition pipe, 18,64 Raw water addition Pipe, 20, 66 Seed addition pipe, 22, 78 pH adjuster addition pipe, 24 treated water discharge pipe, 26, 28 slurry discharge pipe, 30, 32, 76 stirring device, 34, 80, 114 valve, 36, 54 , 68, 70, 72, 74, 82 Pump, 38 Particle size measuring device, 40 Motor, 42 Seed crystal replenishment device, 44 Seed crystal, 46, 108 Reaction zone, 48, 110 Precipitation zone, 50, 112 interface, 52 reaction Liquid discharge piping, 56 crystallizer storage tank, 58 raw water storage tank, 60 seed crystal generation tank, 84 draft tube, 104 seed crystal addition apparatus.

Claims (2)

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 stirring crystallization reaction tank for adding the crystallization agent to the raw water to form crystals of a hardly soluble salt;
Seed crystal addition means for adding seed crystals to the crystallization reaction tank;
A drawing means for drawing at least part of the crystals generated in the crystallization reaction tank;
Measure at least one of the volume average particle size, number average particle size and particle size distribution of the drawn crystal, and volume average particle size, number average particle size and particle size distribution of the crystal in the crystallization reaction tank. Particle size measuring means;
Crystal amount adjusting means for adjusting the amount of the seed crystal to be added based on the measured value;
A crystallization reaction apparatus characterized by comprising: A crystallization reaction method in which a crystal of a hardly soluble salt is formed by adding a crystallization agent to raw water containing a crystallization target substance,
In a stirring-type crystallization reaction tank, a crystallization reaction step in which the crystallizer is added to the raw water to form crystals of a hardly soluble salt;
A seed crystal addition step of adding seed crystals to the raw water;
A drawing step of drawing at least a part of the crystals generated in the crystallization reaction step;
Measure at least one of the volume average particle size, number average particle size and particle size distribution of the drawn crystal, and volume average particle size, number average particle size and particle size distribution of the crystal produced in the crystallization reaction step. A particle size measuring step to perform,
Based on the measured value, a crystal amount adjusting step for adjusting the amount of the seed crystal to be added,
A crystallization reaction method comprising:

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