JP2010207755A - Apparatus for treating fluorine-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for treating fluorine-containing water, by which calcium fluoride having high particle-size uniformity and a low water content can be obtained, and a high recovery rate of calcium fluoride can be achieved. <P>SOLUTION: The apparatus for treating fluorine-containing water includes: a crystallization reaction tank provided with a stirring means having a stirring blade, for adding a calcium agent to fluorine-containing raw water to form calcium fluoride crystals; a flocculation tank for adding a flocculant to the treated water discharged from the crystallization reaction tank to flocculate the calcium fluoride in the treated water; and a solid-liquid separation tank for subjecting the treated water discharged from the flocculation tank to solid-liquid separation into sludge containing the flocculated calcium fluoride, and separated water. In addition, the apparatus includes a calcium-agent addition means for adding the calcium agent to the vicinity of the stirring blade in the crystallization reaction tank, and a return means for returning the sludge containing the calcium fluoride to the crystallization reaction tank. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fluorine-containing water treatment apparatus for treating and recovering fluorine of raw fluorine-containing water such as a semiconductor factory as calcium fluoride.

  Conventionally, as a method for recovering calcium fluoride by adding a calcium agent to fluorine-containing raw water, the fluorine-containing raw water and the calcium agent are injected into a crystallization reaction tank filled with seed crystals, and the surface of the seed crystals is filtered. A crystallization method or the like for precipitating calcium fluoride to obtain calcium fluoride crystals has been proposed.

  When the fluorine content of the fluorine-containing raw water is low, it is crystallized at a pH of 3 to 11 with a fluidized bed type crystallizer (fluidized bed type, see FIG. 3, Patent Document 1). The inventors have proposed that crystallization is performed at a pH of 2 to 3 in a crystallization reaction tank equipped with a tube and a stirrer (stirring crystallization apparatus, see FIG. 4, Patent Document 2).

  When such a crystallizer is used, the treated water obtained by the crystallizer contains a certain amount of fluorine, depending on the fluorine concentration of the raw water. For example, when the fluorine concentration of raw water is 10,000 mg / L, the total fluorine concentration of the treated water is several hundred mg / L. The total fluorine concentration includes not only dissolved fluorine ions but also fluorine compounds such as fine particles of calcium fluoride generated in the crystallization reaction tank.

  Therefore, in order to further reduce the total fluorine concentration of the treated water obtained by the crystallizer, an inorganic flocculant or a polymer flocculant is added to the treated water to aggregate fine particles of calcium fluoride, It is common to perform a coagulation sedimentation process in which the aggregated calcium fluoride is precipitated as sludge (see FIG. 5 and Patent Document 3). In addition, for example, a system in which a fluidized bed type crystallizer and an aggregator are combined has been proposed (see FIG. 6 and Patent Document 1). Also, for example, while reducing the fluorine of the treated water in a two-stage reaction tank and a coagulation sedimentation treatment tank, the calcium fluoride sludge that has been precipitated is returned to the reaction tank to grow to a particle size capable of recovering calcium fluoride. In addition, a technique for recovering and collecting them has also been proposed (see FIG. 7 and Patent Document 4).

Japanese Patent No. 4139600 JP 2008-73589 A JP 2006-167633 A JP 2008-104946 A

  However, in the conventional method described above, when the high concentration fluorine-containing raw water is treated, the seed crystals previously added to the crystallization reaction tank flow out, or the fluorination produced in the crystallization reaction tank. It came to know that the fine particle | grains of calcium flowed out, and subsequent solid-liquid separation became difficult and there existed a problem that a recovery rate fell.

  Further, in the method of returning and growing the calcium fluoride sludge separated into solid and liquid as in the method of Patent Document 4, since the extracted calcium fluoride sludge contains a large amount of fine particles, the dehydrating property In addition, there is a problem that the uniformity of the particle size is deteriorated.

  Accordingly, an object of the present invention is to provide a treatment apparatus for raw fluorine-containing water that can obtain calcium fluoride having a uniform particle size and a low water content, and that enables a high recovery rate of calcium fluoride. It is in.

  The present invention comprises a stirring means having a stirring blade, a crystallization reaction tank for generating calcium fluoride crystals by adding a calcium agent to raw water containing fluorine, and a treatment discharged from the crystallization reaction tank Solid liquid into a coagulation tank for adding a flocculant to water and coagulating calcium fluoride in the treated water; sludge containing calcium fluoride obtained by coagulating the treated water discharged from the coagulation tank; and separated water A fluorine-containing water treatment apparatus comprising: a solid-liquid separation tank for separating; a calcium agent addition means for adding the calcium agent in the vicinity of a stirring blade of the crystallization reaction tank; and the calcium fluoride. Returning means for returning the sludge containing it to the crystallization reaction tank.

  In the fluorine-containing water treatment apparatus, the crystallization reaction tank preferably has a pH in the range of 0.8 to 3.

  In the fluorine-containing water treatment apparatus, the injection point of the calcium agent added in the vicinity of the stirring blade is within twice the rotation radius of the stirring blade in the rotation axis direction and the rotation radial direction of the stirring blade. It is preferable to be installed at a distance.

  Further, in the fluorine-containing water treatment apparatus, a draft tube is provided in the crystallization reaction tank, and the stirring blade is installed in the draft tube and injected with a calcium agent to be added in the vicinity of the stirring blade. The point is preferably placed in the draft tube.

  According to the fluorine-containing water treatment apparatus of the present invention, calcium fluoride having a high particle size uniformity and a low water content can be obtained, and a high recovery rate of calcium fluoride can be achieved.

It is a schematic diagram which shows an example of the processing apparatus of fluorine-containing water which concerns on embodiment of this invention. It is a schematic diagram which shows an example of the processing apparatus of fluorine-containing water which concerns on other embodiment of this invention. It is a schematic diagram which shows an example of the conventional fluidized bed type crystallization reaction apparatus. It is a schematic diagram which shows an example of the conventional stirring type crystallization reaction apparatus. It is a schematic diagram which shows an example of the processing apparatus of the conventional fluorine-containing water. It is a schematic diagram which shows an example of the processing apparatus of the conventional fluorine-containing water. It is a schematic diagram which shows an example of the processing apparatus of the conventional fluorine-containing water.

  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.

  FIG. 1 is a schematic diagram illustrating an example of a treatment apparatus for fluorine-containing water according to an embodiment of the present invention. As shown in FIG. 1, the treatment apparatus for fluorine-containing raw water includes a crystallization reaction tank 10, a coagulation tank 12, and a solid-liquid separation tank 14.

  A raw water addition pipe 16 is connected to the crystallization reaction tank 10 of FIG. 1, and a calcium agent addition pipe 18 is connected via a pump 20 which is a calcium agent addition means. A calcium fluoride discharge pipe 22 is connected to the calcium fluoride discharge port of the crystallization reaction tank 10, and a first treated water discharge pipe 24 is connected to the treated water outlet of the crystallization reaction tank 10. . The crystallization reaction tank 10 is provided with a stirring device 28 and a draft tube 30 which are stirring means including a motor and a stirring blade 26 for stirring the fluid in the crystallization reaction tank 10. The stirring blade 26 of the stirring device 28 is disposed in the draft tube 30 and is rotated by a rotational force generated by a motor transmitted through the stirring shaft.

  A first treated water discharge pipe 24 is connected to the coagulation tank 12 in FIG. 1, a coagulant addition pipe 32 is connected via a pump 34 which is a coagulant addition means, and a pH adjuster addition pipe 36. Are connected via a pump 38 which is a pH adjuster addition means. A second treated water discharge pipe 40 is connected to the treated water outlet of the coagulation tank 12. The agglomeration tank 12 is provided with an agitation device 44 that is an agitation means including a motor and an agitation blade 42 for agitating the fluid in the agglomeration tank 12.

  The aggregating agent supplied to the aggregating tank 12 is not particularly limited as long as it can agglomerate calcium fluoride. For example, inorganic aggregating agents such as PAC and sulfuric acid band, anionic polymer organic aggregating Agents, nonionic polymer organic flocculants, and polymer organic flocculants having a cationic group.

  A second treated water discharge pipe 40 is connected to the solid-liquid separation tank 14 of FIG. A third treated water discharge pipe 46 is connected to the treated water outlet of the solid-liquid separation tank 14. The sludge discharge port of the solid-liquid separation tank 14 and the sludge inlet of the crystallization reaction tank 10 are connected via a pump 50 that is a sludge return pipe 48 as sludge return means. Further, the solid-liquid separation tank 14 is provided with a scraper 54 including a scraper 52 that scrapes sludge at the bottom of the motor and the solid-liquid separation tank 14.

  Operation | movement of the processing apparatus 1 of the fluorine-containing water which concerns on this embodiment is demonstrated.

  Fluorine-containing raw water containing fluorine (hereinafter sometimes simply referred to as “raw water”) is added to the crystallization reaction tank 10 through the raw water addition pipe 16. Next, the calcium agent is added to the vicinity of the stirring blade 26 of the crystallization reaction tank 10 through the calcium agent addition pipe 18 by the pump 20. In the crystallization reaction tank 10, the fluorine contained in the raw water reacts with the calcium agent to produce calcium fluoride crystals. The crystallization reaction liquid is stirred by the stirring device 28.

  In the present embodiment, the raw water addition pipe 16 and the calcium agent addition pipe 18 can be connected to any part of the crystallization reaction tank 10. In the case of the stirring type crystallization reaction tank 10 as shown in FIG. 1, it is preferably connected to the upper part of the crystallization reaction tank 10 from the viewpoint of separation of precipitates, pellets and treated water. Moreover, in FIG. 1, although the raw | natural water addition piping 16 and the calcium-agent addition piping 18 are each one, it is not limited to this, These may be provided with two or more.

  In the present embodiment, the addition (injection point) of the calcium agent to the crystallization reaction tank 10 is performed in the vicinity of the stirring blade 26. By adding the calcium agent in the vicinity of the stirring blade 26, the calcium agent is immediately diffused when injected into the crystallization reaction tank 10, and the concentration thereof quickly decreases. For this reason, the formed salt is less likely to precipitate directly in the liquid, and the crystallization target substance in the liquid (calcium fluoride) as a crystal of a hardly soluble salt (calcium fluoride) on the granular seed crystal in the crystallization reaction tank 10 ( Fluorine) can be taken in carefully. Moreover, a calcium agent becomes easy to melt | dissolve and it can also suppress the rapid reaction of the calcium agent and fluorine which are not dissolved. As a result, it is possible to produce calcium fluoride with high particle uniformity and low water content. In the present embodiment, addition (injection point) of the fluorine-containing raw water to the crystallization reaction tank 10 is also preferably performed in the vicinity of the stirring blade 26. By adding the fluorine-containing raw water in the vicinity of the stirring blade 26, the fluorine-containing raw water is immediately diffused when injected into the crystallization reaction tank 10, and the fluorine concentration quickly decreases. For this reason, the substance to be crystallized (fluorine) in the liquid can be taken in more carefully as crystals of the hardly soluble salt (calcium fluoride) on the granular seed crystals in the crystallization reaction tank 10. As a result, it is possible to produce calcium fluoride with higher particle uniformity and lower moisture content.

  The first treated water in which fluorine generated by the crystallization reaction is reduced in the crystallization reaction tank 10 is supplied to the aggregation tank 12 through the first treated water discharge pipe 24. Next, the flocculant is added to the flocculant tank 12 through the flocculant addition pipe 32 by the pump 34. As described above, the first treated water obtained by the crystallization reaction tank 10 includes not only dissolved fluorine ions but also calcium fluoride fine particles generated in the crystallization reaction tank 10. Therefore, in the flocculation tank 12, the calcium fluoride in the first treated water is flocculated by the flocculating agent. Further, a pH adjusting agent may be added to the aggregation tank 12 from the pH adjusting agent adding pipe 36 by the pump 38. For example, in the coagulation tank 12, the pH is set to 3 to 12, preferably 4 to 11, so that calcium fluoride is generated to remove dissolved fluorine ions in the first treated water, and the fluorine concentration is further reduced. Treated water can be obtained. Arbitrary acid and alkali can be used for a pH adjuster, For example, a sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide etc. can be used.

  The second treated water containing calcium fluoride aggregated in the aggregation tank 12 is supplied to the solid-liquid separation tank 14 through the second treated water discharge pipe 40. In the solid-liquid separation tank 14, solid-liquid separation is performed on the aggregated calcium fluoride sludge and separated water. The solid-liquid separation tank 14 is not particularly limited as long as it can be solid-liquid separated into sludge containing agglomerated calcium fluoride and separated water. For example, sedimentation separation, membrane separation, and pressure levitation Separation and the like. The solid-liquid separation tank 14 shown in FIG. 1 is exemplified by sedimentation separation. The separated water in the solid-liquid separation tank 14 is discharged from the third treated water discharge pipe 46 to obtain a final treated water having a reduced fluorine concentration. Aggregated calcium fluoride is present at the bottom of the solid-liquid separation tank 14. Accumulate as sludge.

  Next, the accumulated calcium fluoride sludge is scraped by a scraper 54, and returned to the crystallization reaction tank 10 through the sludge return pipe 48 by the pump 50. Thus, by returning the calcium fluoride sludge to the crystallization reaction tank 10, the calcium fluoride sludge becomes a nucleus and calcium fluoride is likely to be deposited on the surface thereof. The generation of calcium fluoride is suppressed, and at the same time, the calcium fluoride particles grow greatly. As a result, a high calcium fluoride recovery rate can be obtained stably. The return position of calcium fluoride is not particularly limited as long as it is in the crystallization reaction tank 10, but is preferably the upper part of the crystallization reaction tank 10.

  In addition, as in this embodiment, calcium fluoride sludge may be directly returned from the sludge return pipe 48 to the crystallization reaction tank 10 by the pump 50, or a storage tank is interposed in the sludge return pipe 48, and the After receiving calcium fluoride sludge in the storage tank and adjusting the pH, it may be returned to the crystallization reaction tank 10 through the sludge return pipe 48. The amount of calcium fluoride sludge returned is preferably 0.003 to 0.5 times, more preferably 0.005 to 0.01 times the flow rate of the fluorine-containing raw water.

  Calcium fluoride generated in the crystallization reaction tank 10 is extracted from the calcium fluoride discharge pipe 22 and supplied to the dehydrator 56. The extracted calcium fluoride is in a slurry state and has a water content of about 40 to 70%. From the viewpoint of collecting and transporting calcium fluoride, it is preferable to dehydrate the calcium fluoride to a moisture content of about 10% by a dehydrator 56. As a means for dehydration by a dehydrator, it may be dehydrated naturally from a flexible container bag of a mesh suitable for the particle size of calcium fluoride, dehydrated by a filter press, or centrifugal dehydration. You may dehydrate by a machine.

  In the present embodiment, the calcium fluoride deposited on the bottom of the crystallization reaction tank 10 is drawn out and supplied to the dehydrator 56, but is not necessarily limited to this, and the calcium fluoride passing through the sludge return pipe 48. A part of the above may be extracted and supplied to the dehydrator 56. The method of extracting the calcium fluoride is not particularly limited, but may be a method of extracting the calcium fluoride from the crystallization reaction tank 10 (or the sludge return pipe 48) using a slurry pump such as a tube pump. Alternatively, a method may be used in which a valve is attached to the calcium fluoride discharge pipe 22 and the like, and calcium fluoride is simply pulled out of the crystallization reaction tank 10 (or sludge return pipe 48) by gravity.

  In addition, a classifier is provided in the sludge return pipe 48, and calcium fluoride sludge passing through the sludge return pipe 48 is returned to the crystallization reaction tank 10 with a relatively small particle size calcium fluoride. Calcium fluoride may be extracted from the sludge return pipe 48 and supplied to the dehydrator 56. Thereby, calcium fluoride can be efficiently recovered. The classifying device is not particularly limited, but may be, for example, a cylindrical container that allows calcium fluoride sludge to flow in an upward flow, or a device that performs classification by mechanical means such as a cyclone. Also good. The classifier may be attached to the bottom of the crystallization reaction tank 10 without being interposed in the sludge return pipe 48.

  As described above, in this embodiment, by adding the calcium agent in the vicinity of the stirring blade 26 of the crystallization reaction tank 10, the rapid reaction between the undissolved calcium agent and fluorine is suppressed, and the uniformity of the particles. Calcium fluoride having a high water content and a low water content can be generated, and the calcium fluoride sludge obtained by agglomeration and precipitation treatment is returned to the crystallization reaction tank 10, thereby generating the fluoride generated in the crystallization reaction tank 10. It becomes possible to grow calcium fluoride particles greatly and to obtain a high calcium fluoride recovery rate stably. In the present embodiment, since most of the fluorine in the raw water can be recovered in the crystallization reaction tank 10, the amount of calcium fluoride sludge in the solid-liquid separation tank 14 can be reduced. Operation with a small amount of returned sludge is possible.

  FIG. 2 is a schematic view showing an example of a treatment apparatus for fluorine-containing water according to another embodiment of the present invention. In the fluorine-containing water treatment apparatus 2 shown in FIG. 2, the same components as those in the fluorine-containing water treatment apparatus 1 shown in FIG. In the fluorine-containing water treatment apparatus 2 of FIG. 2, a pH adjusting agent addition pipe 58 is connected to the crystallization reaction tank 10 via a pump 60 that is a pH adjusting agent addition means.

  In the present embodiment, when the fluorine contained in the raw water and the calcium agent are reacted in the crystallization reaction tank 10, the pH adjuster is added to the crystallization reaction tank 10 through the pH adjuster addition pipe 58 by the pump 60. Is done. The pH adjuster to be added is not particularly limited, but is preferably any acid or alkali that does not contain a component that forms a sparingly soluble salt with calcium, such as hydrochloric acid, sulfuric acid, sodium hydroxide, and the like. Can be mentioned.

  In the present embodiment, the pH of the crystallization reaction solution in the crystallization reaction tank 10 is preferably 3 or less. By adding a pH adjuster and operating the crystallization reaction tank 10 at a pH of 3 or less, the calcium agent is more easily dissolved, and there is an effect of further suppressing a rapid reaction between undissolved slaked lime and fluorine. . When the pH of the crystallization reaction solution in the crystallization reaction tank 10 exceeds 3, the calcium agent is difficult to dissolve, and fine calcium fluoride may be generated due to a rapid reaction between the undissolved calcium agent and fluorine. is there. However, the lower limit of the operating pH of the crystallization reaction tank 10 may be slightly different depending on the calcium agent used. For example, when calcium chloride is used as the calcium agent, an alkali such as calcium hydroxide is used as the pH adjuster. It is preferable to operate by adjusting the pH of the crystallization reaction tank 10 to 2 to 3. Details of this embodiment using calcium chloride are described in JP-A-2008-73589.

  In the present embodiment, the pH adjuster is added directly to the crystallization reaction solution in the crystallization reaction tank 10 through the pH adjuster addition pipe 58, but is not limited to this, for example, the pH adjuster. The addition pipe 58 may be connected to the calcium agent addition pipe 18, and the pH adjuster may be supplied to the crystallization reaction tank 10 together with the calcium agent before being added to the crystallization reaction tank 10. You may connect to the raw | natural water addition piping 16, and you may supply the crystallization reaction tank 10 with the fluorine-containing raw | natural water before adding a pH adjuster to the crystallization reaction tank 10. FIG. It is preferable to add the pH adjusting agent in the vicinity of the stirring blade 26 in that the pH adjusting agent can be quickly diffused after injection and the calcium agent can be easily dissolved. Thereby, the recovery rate of fluorine can be further improved.

  The pH at the time of calcium fluoride precipitation is determined by measuring the pH of the reaction field in the crystallization reaction tank 10 using a pH measuring means such as a pH meter, and adding a pH adjuster in the tank according to the measured pH. It is preferable to control the pH by adding to. The pH meter may be installed in any part of the crystallization reaction tank 10 as long as the pH of the reaction field of the calcium fluoride precipitation reaction can be monitored. There are no particular limitations on the vicinity of the outlet of the treated water.

  In the present embodiment, the pH adjuster addition pipe 58 can be connected to any part of the crystallization reaction tank 10. In the case of the stirring type crystallization reaction tank 10 as shown in FIG. 2, it is preferably connected to the upper part of the crystallization reaction tank 10 from the viewpoint of separation of precipitates, pellets and treated water. In FIG. 2, the number of pH adjusting agent addition pipes 58 is one, but is not limited to this, and a plurality of pipes may be provided.

  In this specification, “near” the stirring blade 26 means a region where the crystallization reaction liquid in the crystallization reaction tank 10 can quickly diffuse by the stirring flow of the stirring blade 26. For example, the injection point of the calcium agent, the fluorine-containing raw water, and the pH adjuster is preferably provided in a region where the stirring flow rate by the stirring blade 26 is large. In particular, the height of the injection point of the calcium agent, the fluorine-containing raw water and the pH adjuster in the direction of the rotation axis of the stirring blade 26 is within a distance within twice the rotation radius of the stirring blade 26 from the rotation center of the stirring blade 26. Preferably there is. Further, the position of the stirring blade 26 in the direction of the rotation diameter is preferably a distance within twice the rotation radius of the stirring blade 26 from the rotation center of the stirring blade 26. Furthermore, it is preferable that the center is provided in a spherical region whose center is the rotation center of the stirring blade 26 and whose radius is twice the rotation radius of the stirring blade 26. As a result, the calcium agent, the fluorine-containing raw water, and the pH adjuster are immediately diffused when injected into the crystallization reaction tank 10, and their concentrations are quickly reduced. For this reason, the formed salt is less likely to precipitate directly in the liquid, and the crystallization target substance in the liquid (calcium fluoride) as a crystal of a hardly soluble salt (calcium fluoride) on the granular seed crystal in the crystallization reaction tank 10 ( Fluorine) can be taken in carefully. Moreover, a calcium agent becomes easy to melt | dissolve and it can also suppress the rapid reaction of the calcium agent and fluorine which are not dissolved. As a result, it is possible to produce calcium fluoride with high particle uniformity and low water content.

  In this embodiment, as shown in FIGS. 1 and 2, it is preferable to install a draft tube 30 below the water surface of the crystallization reaction tank 10 so that the stirring blade 26 of the stirring device 28 is positioned in the cylinder. At this time, the stirring blade 26 preferably forms a downward flow. When the draft tube 30 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, slaked lime, etc. can be diffused more quickly, and it is possible to suppress as much as possible that the regions where the concentrations of raw water and slaked lime are locally concentrated contact each other and direct generation of hardly soluble salt particles occurs It becomes.

  Further, when the draft tube 30 and the stirring blade 26 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 and small particles rise along the outer surface of the tube, and re-enter from the upper end of the tube to the inside of the tube. Recirculate to the 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 fluorine 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 30 again. It can be prevented from being destroyed by the collision with the wing 26. Such an advantage also contributes to stably obtaining crystals of a hardly soluble salt having a large particle size, which in turn can contribute to an improvement in the recovery rate of fluorine.

  In order to form a zone with a relatively large stirring flow velocity at the lower part of the tube and to stably form an upward flow at the outer periphery of the tube, the stirring blade 26 may 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 large 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, calcium agent, etc. and particle classification can be effectively advanced.

  When the draft tube 30 is provided, the injection points of raw water, calcium agent, and acid are placed in the cylinder of the draft tube 30 in order to quickly and effectively diffuse them on the downflow in the draft tube 30. It is preferable. A more preferable position is in the cylinder of the draft tube 30 and above the stirring blade 26.

  The fluorine-containing raw water in the present embodiment may be raw water of any origin as long as it contains fluorine removed by crystallization treatment, for example, electronic industries including semiconductor-related industries, power plants, aluminum Examples include raw water discharged from industry and the like, but are not limited thereto.

Fluorine serving as a crystallization target substance can be present in the raw water in any state as long as it is crystallized by a crystallization reaction. From the viewpoint that it is dissolved in the raw water, the crystallization target substance is preferably in an ionized state. Examples of the state in which the substance to be crystallized is ionized include, but are not limited to, those in which atoms such as F ⁻ are ionized and those in which a compound containing fluorine is ionized.

  Raw water containing fluorine is also discharged from aluminum electrolytic refining process, steelmaking process, etc., but in particular at semiconductor factories, it is discharged in large quantities. 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 fluorine contained in the raw water is not particularly limited, but is, for example, 1000 mg / L or more, particularly 5000 mg / L or more.

  The injection amount of the calcium agent is preferably 0.8 to 2 times and 1 to 2 times that of fluorine as the chemical equivalent of calcium, but more preferably 1 to 1.2 times. If the chemical equivalent of calcium is more than twice the chemical equivalent of fluorine in the raw water, calcium fluoride does not precipitate on the seed crystal and is easily formed as fine particles, and calcium fluoride may be mixed in the treated water. If it is less than 8 times, the proportion of fluorine in the raw water that does not become calcium fluoride increases, and fluorine may be mixed into the treated water.

  In this embodiment, before adding raw water and a calcium agent to the crystallization reaction tank 10, a seed crystal may exist in advance in the crystallization reaction tank 10, or in the crystallization reaction tank 10 in advance. There may be no seed crystals. 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 fluorine can be removed by a crystallization reaction. The concentration of fluorine in raw water, the concentration of calcium agent, It is set as appropriate according to the operating conditions.

  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 including 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 purer 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 concentrations of fluorine and calcium agent, etc., and are not particularly limited.

  In the present embodiment, when calcium fluoride in the crystallization reaction tank 10 is pulled out from the calcium fluoride discharge pipe 22, a replenishment operation for newly replenishing a seed crystal having a smaller particle diameter than the extracted calcium fluoride crystal is performed. A method of continuously obtaining crystals by repeatedly performing is employed.

  The crystallization reaction tank 10 may be any reaction tank that can react with fluorine in the raw water and the calcium agent to precipitate calcium fluoride crystals of a poorly soluble salt to produce treated water with reduced fluorine. The length, the inner diameter, the shape, and the like can be arbitrarily selected and are not particularly limited.

  As the crystallization reaction tank 10, a stirring type crystallization reaction tank 10 in which a stirring device 28 equipped with a stirring blade 26 and the like is installed, and the inside of the crystallization reaction tank 10 is stirred by the stirring device 28 to flow the pellets. It is done. The stirring blade 26 may be anything as long as the contents can be stirred in the crystallization reaction tank 10, and the installation mode of the stirring blade 26, the size of the stirring blade 26, 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 of the first treatment water and prevents the hardly soluble salt particles from flowing out into the first treated water. In this aspect, an aspect in which the first 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 10 described in these patent documents can also be used in this embodiment.

  In order to measure the soluble fluorine concentration in the crystallization reaction tank 10 or in the first treated water, a fluorine concentration measuring means such as a fluorine concentration meter is installed in the crystallization reaction tank 10 or the first treated water discharge pipe 24. Also good. Further, in order to measure the calcium concentration such as soluble calcium in the crystallization reaction tank 10 or in the treated water, a calcium concentration measuring means such as a calcium concentration meter is installed in the crystallization reaction tank 10 or the first treated water discharge pipe 24. May be. 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.

  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.

Example 1
In Example 1, using the treatment apparatus for fluorine-containing raw water shown in FIG. 2, calcium fluoride was recovered from the fluorine-containing raw water under the following conditions. The amount of sludge returned from the settling tank to the crystallization reaction tank was visually confirmed so that the sludge leak in the settling tank was minimized, and the amount returned was adjusted.

In addition, the fluorine recovery rate was calculated by measuring the total fluorine concentration of treated water once a day (total 30 days). Table 1 summarizes the average values for 30 days as the fluorine recovery rate. Table 1 summarizes the purity, water content, and uniformity coefficient of CaF ₂ collected on the 30th day. The uniformity coefficient is the same as the particle size (effective diameter) D10 having a mass passage percentage of 10% based on the particle size distribution data measured by a laser diffraction particle size distribution analyzer (LS230 type, manufactured by Beckman Coulter, Inc.). % Particle diameter (effective diameter) The ratio (D60 / D10) with D60 was calculated.

<Experimental conditions>
Fluorine concentration in fluorine-containing raw water: 10000 mg / L
Calcium agent: Calcium hydroxide pH adjuster: Hydrochloric acid Crystallization reaction tank: 150 L (500 mmφ × 1200 mmH)
Fluorine-containing raw water flow rate: 30L / hr
Crystallization reactor pH: 2 ± 0.5

(Example 2)
In Example 2, the test was performed under the same conditions as in Example 1 except that the pH of the crystallization reaction tank was adjusted to a range of 4 ± 0.5. Table 1 summarizes the fluorine recovery rate (average value for 30 days), the purity, moisture content, and uniformity coefficient of CaF ₂ recovered on the 30th day.

(Comparative Examples 1-3)
In Comparative Example 1, the test was performed under the same conditions as in Example 1 except that calcium fluoride in the solid-liquid separation tank was not returned to the crystallization reaction tank. In Comparative Example 2, the test was performed under the same conditions as in Example 1 except that the calcium agent was added not to the vicinity of the stirring blade but to the crystallization reaction liquid surface in the crystallization reaction tank. In Comparative Example 3, the test was performed under the same conditions as in Example 2 except that the calcium agent was added not to the vicinity of the stirring blade but to the crystallization reaction liquid surface in the crystallization reaction tank. Table 1 summarizes the fluorine recovery rates (average values for 30 days) of Comparative Examples 1 to 3, the purity, water content, and uniformity coefficient of CaF ₂ recovered on the 30th day.

As can be seen from Table 1, in Examples 1 and 2, the fluorine recovery rate of 90% or more, CaF ₂ in a purity of 90% or higher, 10% moisture content or less, uniformity coefficient 3 below, was a sludge return amount 0.4 or less . In particular, in Example 1 in which the pH of the crystallization reaction tank was adjusted to 3 or less (range of 2 ± 0.5), the pH of the crystallization reaction tank was adjusted to 3 or more (range of 4 ± 0.5). From Example 2, the fluorine recovery rate, the purity of CaF ₂ , the moisture content, the uniformity coefficient, and the sludge return amount were all improved. On the other hand, although the calcium agent was added in the vicinity of the stirring blade, the comparative example 1 in which the sludge was not returned was worse than the examples 1 and 2 in the fluorine recovery rate. In Comparative Example 2, since the sludge is returned, the fluorine recovery rate is improved as compared with Comparative Example 1. However, the fluorine recovery rate, the purity of CaF ₂ , the moisture content, the uniformity coefficient, and the sludge return amount are all in Example 1. And worse than 2. In Comparative Example 3 in which the pH of the crystallization reaction tank is 3 or more (in the range of 4 ± 0.5), the fluorine recovery rate, the purity of CaF ₂ , the moisture content, the uniformity coefficient, and the sludge return amount are all included in the crystallization reaction. The result was worse than Comparative Example 2 in which the pH of the tank was adjusted to 3 or less (range of 2 ± 0.5).

  1, 2 Fluorine-containing water treatment apparatus, 10 crystallization reaction tank, 12 coagulation tank, 14 solid-liquid separation tank, 16 raw water addition pipe, 18 calcium agent addition pipe, 20, 34, 38, 50, 60 pump, 22 foot Calcium fluoride discharge pipe, 24 First treated water discharge pipe, 26, 42 Stirrer blades, 28, 44 Stirrer, 30 Draft tube, 32 Flocculant added pipe, 36, 58 pH adjuster added pipe, 40 Second treated water discharged Piping, 46 Third treated water discharge piping, 48 sludge return piping, 52 scraper, 54 scraper, 56 dehydrator.

Claims (4)

A crystallization reaction tank comprising a stirring means having a stirring blade, for adding calcium agent to raw water containing fluorine to generate calcium fluoride crystals,
A flocculant for aggregating calcium fluoride in the treated water by adding a flocculant to the treated water discharged from the crystallization reaction tank;
A solid-liquid separation tank for solid-liquid separation into sludge containing calcium fluoride and separated water, which is agglomerated treated water discharged from the coagulation tank, and a fluorine-containing water treatment apparatus comprising:
Calcium agent addition means for adding the calcium agent in the vicinity of the stirring blade of the crystallization reaction tank;
Returning means for returning the sludge containing calcium fluoride to the crystallization reaction tank, and a treatment apparatus for fluorine-containing water. The apparatus for treating fluorine-containing water according to claim 1,
The apparatus for treating fluorine-containing water, wherein the pH of the crystallization reaction tank is in the range of 0.8-3.   2. The apparatus for treating fluorine-containing water according to claim 1, wherein the injection point of the calcium agent added in the vicinity of the stirring blade is the rotation radius of the stirring blade in the rotation axis direction and the rotation radial direction of the stirring blade The apparatus for treating fluorine-containing water, characterized in that it is installed at a distance within twice the distance. The fluorine-containing water treatment apparatus according to claim 1, wherein a draft tube is provided in the crystallization reaction tank,
The stirring blade is installed in the draft tube,
An apparatus for treating fluorine-containing water, wherein an injection point of a calcium agent to be added in the vicinity of the stirring blade is installed in the draft tube.

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