JP5139376B2 - Crystallization reaction method, crystallization reaction apparatus and calcium agent - Google Patents

Description

  The present invention relates to a crystallization reaction method, a crystallization reaction apparatus, and a calcium agent for treating and recovering a crystallization target substance containing raw material for crystallization, such as fluorine and phosphorus, as a hardly soluble calcium salt.

  Conventionally, in order to treat raw water containing crystallization target substances such as fluorine and phosphorus, a coagulation precipitation method in which a calcium agent and a coagulant are added is generally used. However, since calcium fluoride and calcium phosphate sludge produced by this method have low purity, they cannot be recovered as raw materials.

  As a method for recovering and reusing the product, the raw material water containing the crystallization target and the calcium agent are injected into the reaction tank filled with the seed crystal, and a hardly soluble salt is precipitated on the seed crystal surface to obtain a crystal product. Methods have been proposed.

  For example, in the patent document 1, the present inventors have proposed a device for allowing crystallization target substance-containing raw water to flow upward by a fluidized bed type crystallizer and crystallizing at pH 3 to 11 ( As shown in FIG.

  In addition, for example, in Patent Document 2, when the crystallization target component in the raw water has a high concentration, the present inventors set up an apparatus for crystallization at pH 2 to 3 in a crystallization reaction tank equipped with a draft tube and a stirrer. Proposed (shown in FIG. 8).

JP 2003-225680 A JP 2008-86840 A

  Examples of calcium agents used in the above method include calcium chloride and slaked lime. Although slaked lime is very cheap compared to calcium chloride, when commercially available slaked lime is used as a calcium agent as it is, there is a problem that the crystallization reaction is not stable and the recovery rate of the hardly soluble calcium salt is varied. .

  Thus, as a result of intensive studies, the present inventors have found that the sulfur content contained in slaked lime and the particle size distribution of slaked lime affect the crystallization reactivity and the recovery rate of poorly soluble calcium salts.

  Then, the objective of this invention is providing the crystallization reaction method and the crystallization reaction apparatus which can ensure the stable collection | recovery rate of a hardly soluble calcium salt, even if it uses slaked lime as a calcium agent.

The present invention is a crystallization reaction method in which slaked lime is added to raw water containing a substance to be crystallized to produce crystals of a hardly soluble calcium salt, and the sulfur content in the slaked lime is 0.003 in terms of SO ₃ . A washing step of washing the slaked lime so as to be 1% or less, and a crystallization reaction step of mixing the washed slaked lime with raw water to form crystals of a hardly soluble calcium salt.

  Further, the crystallization reaction method preferably includes a pH adjustment step of adjusting the pH of the treated water by mixing the washing waste water from which the slaked lime has been washed and the treated water discharged by the crystallization reaction step.

In the crystallization reaction method, in the washing step, the sulfur content in slaked lime is measured, and based on the measured content, the sulfur content in the slaked lime is 0.1% or less in terms of SO _3. It is preferable that the slaked lime is washed.

  The crystallization reaction method preferably includes a classification step of classifying the slaked lime so that the particle size distribution of the slaked lime is 90% or more before or after the washing step.

Further, the present invention is a crystallization reaction apparatus for adding a slaked lime to raw water containing a substance to be crystallized to produce crystals of a hardly soluble calcium salt, wherein the raw water and the slaked lime are mixed and hardly soluble. A crystallization reaction tank for generating calcium salt crystals, a washing means for washing the slaked lime so that the sulfur content in the slaked lime is 0.1% or less in terms of SO ₃ , and the washed slaked lime Slaked lime addition means for adding to the crystallization reaction tank.

  Further, the crystallization reaction apparatus preferably includes a pH adjusting means for adjusting the pH of the treated water by adding the washing waste water from which the slaked lime has been washed to the treated water discharged from the crystallization reaction tank.

  The crystallization reaction apparatus further includes classification means for classifying the slaked lime added to the crystallization reaction tank so that the particle size distribution of 53 μm or less is 90% or more before or after the washing means.

The present invention is also a calcium agent for reacting with raw water containing a substance to be crystallized to form a hardly soluble calcium salt crystal, and the calcium agent has a sulfur content of 0 in terms of SO _3. 0.1% or less slaked lime.

  According to the present invention, even when slaked lime is used as the calcium agent, a stable recovery rate of the hardly soluble calcium salt can be ensured.

It is a schematic diagram which shows an example of the crystallization reaction apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows an example of the crystallization reaction apparatus which concerns on other embodiment of this invention. It shows the relationship between the sulfur content in the slaked lime and (SO ₃ conversion) and the fluorine concentration in the treated water. The relationship between the particle | grain ratio (%) of 53 micrometers or more in slaked lime and the fluorine concentration in treated water is shown. Sulfur content in lime showing the relationship between the (SO ₃ conversion) processing the phosphorus concentration in the water. The relationship between the particle | grain ratio (%) of 53 micrometers or more in slaked lime and the phosphorus concentration in a treated water is shown. It is a schematic diagram which shows an example of the conventional crystallization reaction apparatus. It is a schematic diagram which shows an example of the conventional crystallization reaction apparatus.

  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 showing an example of a crystallization reaction apparatus according to an embodiment of the present invention. As shown in FIG. 1, the crystallization reaction apparatus 1 includes a slaked lime silo 10, a cleaning tank 12 that is a cleaning means, a dissolution tank 14, a crystallization reaction tank 16, a seed crystal silo 18, and a neutralization tank 20.

  A slaked lime first addition pipe 22 is connected between the slaked lime silo 10 and the cleaning tank 12, and a slaked lime second addition pipe 26 is connected between the cleaning tank 12 and the dissolution tank 14 via a pump 23. In addition, a slaked lime third addition pipe 28 is connected between the dissolution tank 14 and the crystallization reaction tank 16 via a pump 24 which is a slaked lime addition means. In addition, a raw water addition pipe 30 from a raw water storage tank (not shown) is connected to the crystallization reaction tank 16, and a seed crystal addition pipe 32 from a seed crystal silo 18 is connected. A treated water discharge pipe 34 is connected to the treated water outlet of the crystallization reaction tank 16, and a hardly soluble salt discharge pipe 36 is connected to the hardly soluble salt discharge port of the crystallization reaction tank 16.

  Further, a cleaning water addition pipe 38 is connected to the cleaning tank 12. A cleaning water discharge pipe 40 serving as a pH adjusting means is connected to the cleaning water outlet of the cleaning tank 12. Note that a pump may be interposed in the cleaning water discharge pipe 40. Moreover, the return piping 43 is connected to the slaked lime 3rd addition piping 28, and a part of slaked lime which passes along the slaked lime 3rd addition piping 28 can be returned to the dissolution tank 14. FIG. The neutralization tank 20 is connected to a treated water discharge pipe 34 from the crystallization reaction tank 16 and is connected to a wash water discharge pipe 40 from the cleaning tank 12.

  The cleaning means in the present embodiment is not limited to a tank type like the cleaning tank 12 as long as it can be cleaned so that the sulfur content in the slaked lime falls within the range described below. For example, a pipe having a predetermined length may be used as a cleaning means, and water and slaked lime may be mixed and cleaned in the pipe.

  The crystallization reaction tank 16 includes a stirring device 44 and a draft tube 46 which are stirring means including a motor and a stirring blade 42 for stirring the fluid in the crystallization reaction tank 16. The stirring blade 42 of the stirring device 44 is disposed in the draft tube 46 and is rotated by a rotational force generated by a motor transmitted through the stirring shaft. A similar stirring device 44 is also provided in the dissolution tank 14 and the neutralization tank 20.

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

  Raw water containing a substance to be crystallized such as fluorine or phosphorus (hereinafter sometimes simply referred to as “raw water”) is added to the crystallization reaction tank 16 through the raw water addition pipe 30.

Further, slaked lime in the slaked lime silo 10 is added to the cleaning tank 12 by the motor 48 through the first slaked lime addition pipe 22, and cleaning water such as pure water or ultrapure water is supplied to the cleaning tank 12 through the cleaning water addition pipe 38. Added. Then, in the cleaning tank 12, slaked lime is washed, sulfur content in the slaked lime is 0.1% or less converted to SO _3. Here, it is preferable to measure the sulfur content of slaked lime in the washing tank 12 and wash the slaked lime based on the measured value. However, when the sulfur content in the slaked lime is specified in advance, the relationship between the sulfur content in the slaked lime and the washing time is measured in advance, and the washing time of the slaked lime is determined based on the measurement data. Cleaning may be performed.

  Next, the washed slaked lime is added to the dissolution tank 14 through the slaked lime second addition pipe 26 by the pump 23. The slaked lime is stirred by the stirring device 44 of the dissolution tank 14 and becomes a uniform slaked lime slurry. Then, slaked lime (slurry) is added to the crystallization reaction apparatus 1 through the slaked lime third addition pipe 28 by the pump 24. The slaked lime is preferably added in the vicinity of the stirring blade 42 of the crystallization reaction tank 16. In order to obtain a more uniform slaked lime slurry, a part of the slaked lime slurry passing through the slaked lime third addition pipe 28 may be returned from the return pipe 43 to the dissolution tank 14. In the present embodiment, the dissolution tank 14 is not always necessary.

  Moreover, it is preferable that the seed crystal in the seed crystal silo 18 is added to the crystallization reaction tank 16 through the seed crystal addition pipe 32 by the motor 50.

  In the crystallization reaction tank 16, the crystallization target substances such as fluorine and phosphorus contained in the raw water react with slaked lime to generate calcium fluoride and calcium phosphate (slightly soluble calcium salt), which are deposited on the seed crystal surface. A crystal of a poorly soluble calcium salt is produced.

As in this embodiment, fine calcium fluoride and calcium phosphate are produced by reacting slaked lime with a sulfur content of 0.1% or less, preferably 0.01% or less in terms of SO ₃ , with fluorine, phosphorus or the like. Therefore, it is possible to suppress the generation of the sparingly soluble calcium salt and the like to the outside of the crystallization reaction tank 16 together with the treated water, thereby improving the recovery rate of the sparingly soluble calcium salt. Further, by 0.1% or less of sulfur content of slaked lime converted to SO _3, it is possible to suppress the generation of multiple products such as calcium sulfate, calcium fluoride, sparingly soluble calcium salts such as calcium phosphate The recovery rate can be improved.

  The treated water in which the crystallization target substance such as fluorine and phosphorus is reduced by the crystallization reaction in the crystallization reaction tank 16 is supplied to the neutralization tank 20 through the treated water discharge pipe 34. Since the pH of the treated water obtained by the crystallization reaction is acidic (approximately pH 1.5 to 3), it is preferably neutralized (pH adjusted) by the neutralization tank 20. Here, when neutralizing the treated water, an alkaline agent such as sodium hydroxide may be added to the neutralization tank 20 to neutralize the treated water, but the washing water discharged from the washing tank 12 is washed. It is preferable to add to the neutralization tank 20 from a water pipe to neutralize the treated water. Thereby, processing cost can be reduced.

  Slightly soluble calcium salts such as calcium fluoride and calcium phosphate generated in the crystallization reaction tank 16 are extracted from the hardly soluble salt discharge pipe 36 and discharged out of the system. The method for pulling out the hardly soluble calcium salt is not particularly limited, but may be a method for pulling out the hardly soluble calcium salt from the crystallization reaction tank 16 using a slurry pump such as a tube pump, as shown in FIG. Thus, a method may be used in which a valve is attached to the hardly soluble salt discharge pipe 36 and the hardly soluble calcium salt is simply pulled out of the crystallization reaction tank 16 by gravity.

  FIG. 2 is a schematic view showing an example of a crystallization reaction apparatus according to another embodiment of the present invention. In the crystallization reaction apparatus 2 shown in FIG. 2, the same code | symbol is attached | subjected about the structure similar to the crystallization reaction apparatus 1 shown in FIG. 1, and the description is abbreviate | omitted. In the crystallization reaction apparatus 2 of FIG. 2, a classification device 52 as a classification means is provided. In the present embodiment, the classification device 52 is installed in the previous stage of the cleaning tank 12, but the classification apparatus 52 may be installed in the subsequent stage of the cleaning tank 12.

  Although it does not restrict | limit especially as the classification apparatus 52, For example, the cylindrical container which allows slaked lime to flow by an upward flow may be sufficient, and the apparatus classified by mechanical means, such as a cyclone, may be sufficient. . A small particle size discharge pipe 53 is connected between the classification device 52 and the cleaning tank 12. Further, a large particle size discharge pipe 54 is connected between the classifier 52 and the washing water discharge pipe 40 (or between the neutralization tank 20).

  In the present embodiment, slaked lime is classified by the classification device 52. Specifically, the particle size distribution of slaked lime passing through the small particle size discharge pipe 53 by the classifier 52, that is, the particle size distribution of slaked lime supplied to the washing tank 12 (crystallization reaction tank 16 side) is 53 μm or less. It is classified so that it becomes more than%. Therefore, in this embodiment, slaked lime having a small particle size is added to the crystallization reaction tank 16 (in this embodiment, it is added to the crystallization reaction tank 16 via the cleaning tank 12). And since slaked lime becomes easy to melt | dissolve by adding slaked lime with a fine particle diameter to the crystallization reaction tank 16 in this way, rapid reaction with crystallization target substances, such as an undissolved slaked lime and fluorine, phosphorus, etc. The production | generation of the fine hardly soluble calcium salt by can be suppressed. As a result, the hardly soluble calcium salt can be prevented from being discharged out of the crystallization reaction tank 16 together with the treated water, and the recovery rate of the hardly soluble calcium salt can be improved.

  In the present embodiment, slaked lime classified by the classifier 52 and having a particle size distribution outside the above range (that is, slaked lime having a large particle size) is washed from the large particle size discharge pipe 54 (functioning as pH adjusting means). It is preferably used for neutralization (pH adjustment) of the treated water supplied to the neutralization tank 20 through the discharge pipe 40 and discharged from the crystallization reaction tank 16. Thereby, processing cost can be reduced. The slaked lime having a large particle size may be supplied directly to the neutralization tank 20 from the large particle size discharge pipe 54.

  Moreover, in FIG. 1 and 2, although the raw | natural water addition piping 30 and the slaked lime 3rd addition piping 28 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 slaked lime to the crystallization reaction tank 16 is preferably performed in the vicinity of the stirring blade 42. By adding slaked lime in the vicinity of the stirring blade 42, the slaked lime is immediately diffused when injected into the crystallization reaction tank 16, and its concentration quickly decreases. For this reason, the formed salt is less likely to be precipitated directly in the liquid, and the crystallization target substance (fluorine, phosphorus, etc.) in the liquid as a hardly soluble salt crystal on the granular seed crystal in the crystallization reaction tank 16. Can be captured carefully. Moreover, it becomes easy to melt | dissolve a calcium agent and it can also suppress the rapid reaction with an undissolved calcium agent and a fluorine. As a result, it is possible to produce calcium fluoride with high particle uniformity and low water content. In the present embodiment, addition of raw water to the crystallization reaction tank 16 (injection point) is also preferably performed in the vicinity of the stirring blade 42. By adding the raw water in the vicinity of the stirring blade 42, the raw water is immediately diffused when injected into the crystallization reaction tank 16, and the concentration of substances to be crystallized such as fluorine and phosphorus is quickly reduced. For this reason, the crystallization target substance in the liquid can be more carefully taken in as the hardly soluble salt crystals on the granular seed crystals in the crystallization reaction tank 16. As a result, it is possible to produce calcium fluoride with higher particle uniformity and lower moisture content.

  In this embodiment, acid addition means for adding an acid to raw water, slaked lime, or the crystallization reaction tank 16 is provided, and the pH of the crystallization reaction solution in the crystallization reaction tank 16 is in the range of 0.8 to 3. It is preferable that the range is 1 to 1.5. By adding an acid and operating the pH of the crystallization reaction tank 16 in the range of 0.8 to 3, the concentration of the substance to be crystallized such as fluorine and phosphorus in the treated water can be reduced. The reason for this is considered to be that slaked lime is easily dissolved by operating at a low pH in the range of 0.8 to 3, and that there is an effect of suppressing a rapid reaction between undissolved slaked lime and the substance to be crystallized.

  In the present embodiment, as shown in FIGS. 1 and 2, it is preferable to install a draft tube 46 below the water surface of the crystallization reaction tank 16 so that the stirring blade 42 of the stirring device 44 is positioned in the cylinder. At this time, the stirring blade 42 preferably forms a downward flow. When the draft tube 46 is installed in this manner, a downward flow is generated toward the lower portion of the tube, and a zone having a relatively large diffusion flow rate is formed. For this reason, raw water, 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 sparingly soluble salt particles occurs. It becomes.

  Moreover, when the draft tube 46 and the stirring blade 42 are installed as described above, an upward flow zone having a gentle flow is formed on the outer periphery of the tube. In this zone, the particles are classified and the small particles rise along the outer surface of the tube and re-enter the tube from the upper end of the tube and descend.Then, near the injection point of raw water, slaked lime, etc. Recirculate to the agitation zone. These small-sized crystals serve as nuclei to promote the crystallization reaction. For this reason, it becomes possible to form stably the crystal | crystallization of a slightly soluble salt with a large particle size, and can improve a recovery rate.

  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 46 again. It can be prevented from being destroyed by the collision with the wing 42. Such an advantage also contributes to stably obtaining crystals of a hardly soluble salt having a large particle size, and can contribute to an improvement in the recovery rate.

  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 42 should 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, calcium agent, etc. and particle classification can be effectively advanced.

  When the draft tube 46 is provided, the injection points of the raw water and slaked lime are preferably arranged in the cylinder of the draft tube 46 in order to quickly and effectively diffuse them on the downward flow in the draft tube 46. A more preferable position is in the cylinder of the draft tube 46 and above the stirring blade 42.

  The raw water containing crystallization target substances such as fluorine and phosphorus in the present embodiment may be raw water of any origin as long as it contains fluorine and phosphorus removed by crystallization treatment. Examples include, but are not limited to, raw water discharged from the electronics industry, power plant, aluminum industry and the like.

  Fluorine, phosphorus, and the like that are crystallization target substances can be present in the raw water in an arbitrary state as long as they are 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.

  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 fluorine or phosphorus contained in the raw water is not particularly limited, but is, for example, 1000 mg / L or more, particularly 5000 mg / L or more.

  In the present embodiment, slaked lime is used as the calcium agent, but the form in which slaked lime is added may be a powder state or a slurry state. The preferable aspect of addition of slaked lime is an aspect added as slaked lime slurry.

  In this embodiment, since slaked lime is washed and classified before adding slaked lime to the crystallization reaction tank 16, even when any grade of slaked lime is used, a stable recovery rate of hardly soluble calcium salt is ensured. Can do. The density | concentration of slaked lime slurry is not specifically limited, The range of 1 to 20 weight% generally used may be sufficient.

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

  In the present embodiment, before adding raw water and calcium agent to the crystallization reaction tank 16, seed crystals may exist in the crystallization reaction tank 16 in advance, or in the crystallization reaction tank 16 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 16 in advance.

  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 crystallization reaction tank 16 may be any reaction tank that can generate treated water in which fluorine or phosphorus in raw water reacts with slaked lime to precipitate crystals of sparingly soluble calcium salt, thereby reducing fluorine and phosphorus. The length, the inner diameter, the shape, and the like can be arbitrarily selected and are not particularly limited.

  The crystallization reaction tank 16 includes a stirring type crystallization reaction tank 16 in which a stirring device 44 including a stirring blade 42 and the like is installed, and the inside of the crystallization reaction tank 16 is stirred by the stirring device 44 to flow pellets. It is done. The stirring blade 42 may be anything as long as the contents can be stirred in the crystallization reaction tank 16, and the installation mode of the stirring blade 42, the size of the stirring blade 42, and the like are not particularly limited.

  Further, as the stirring type crystallization reaction tank 16, an inner peripheral wall is disposed so as to face the peripheral wall of the crystallization reaction tank 16, and the treated water discharge path 56 is formed between the inner and outer peripheral walls, and the hardly soluble salt particles and the treated water are disposed. 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 34 is connected to the upper part of the treated water discharge path 56 is preferable. In addition, in order to improve the separation performance of the pellet, the treated water discharge channel 56 is configured by a baffle plate formed by a plurality of baffle plates and a plurality of rectifying plates at the inlet portion of the treated water discharge channel 56. A baffle plate may be positioned. 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.

  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, the crystallization reaction apparatus shown in FIG. 1 was used, and calcium fluoride was recovered from the fluorine-containing raw water under the following conditions. In Example 1, what washed the slaked lime of the industrial special name A until the sulfur content rate was set to 0.1% in terms of SO ₃ was used as a calcium agent. The slaked lime was washed by a batch method. Four times the weight of pure water was poured into slaked lime, stirred for 5 minutes, allowed to settle for 30 minutes, and the supernatant water was discarded.

<Experimental conditions>
Fluorine concentration of raw water containing fluorine: 10000 mg / L
Fluorine-containing raw water flow rate: 25 L / h
Slaked lime slurry concentration: 5% by weight
Acid: hydrochloric acid (5% by weight)
Crystallization reaction tank: 100 L (440 mmφ × 1000 mmH)
Stirring blade diameter: 160mm

(Example 2)
In Example 2, the test was performed under the same conditions as in Example 1 except that slaked lime of industrial special name B was washed until the sulfur content was 0.01% in terms of SO ₃ and used as a calcium agent. Went.

(Comparative Examples 1 and 2)
In Comparative Example 1, the slaked lime of industrial special name A having a sulfur content of 0.5% in terms of SO ₃ was used as a calcium agent without washing, and in Comparative Example 2, the sulfur content was 0.00 in terms of SO ₃ . The test was performed under the same conditions as in Example 1 except that 2% of the industrial slaked lime slaked lime was used as a calcium agent without washing.

Table 1 summarizes the results of the fluorine concentration in the treated water obtained in Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 3 shows the relationship between the sulfur content in slaked lime (in terms of SO ₃ ) and the fluorine concentration in the treated water.

As can be seen from Table 1, when Example 1 and Comparative Example 1 using the same industrial special name A slaked lime are compared with Example 2 and Comparative Example 2 using the same industrial special name B slaked lime, In Examples 1 and 2 in which the sample was washed, the fluorine concentration in the treated water decreased and the recovery rate of calcium fluoride was higher than those in Comparative Examples 1 and 2. Further, as can be seen from FIG. 3, as the slaked lime was washed and the sulfur content in the slaked lime decreased, the fluorine concentration in the treated water also decreased. From these results, it is necessary to wash at least slaked lime until the sulfur content becomes 0.1% or less in terms of SO ₃ , and it is preferable to wash until the slaked lime becomes 0.01% or less. It was.

(Examples 3 to 5)
In Examples 3 to 5, calcium fluoride was recovered from fluorine-containing raw water using the crystallization reaction apparatus shown in FIG. 1 or 2. In Example 3, the industrial special number C washed until the sulfur content was 0.01% in terms of SO ₃ was classified, and the particle size distribution was classified so that 53 μm or more was 10%. It was. In Example 4, the slaked lime of industrial special name C washed until the sulfur content was 0.01% in terms of SO ₃ was used without classification. The particle size distribution of Industrial Special C was 18% at 53 μm or more. In Example 5, the slaked lime of industrial special name D washed until the sulfur content was 0.01% in terms of SO ₃ was used without classification. The particle size distribution of the industrial special code D was 13% at 53 μm or more.

  Table 2 summarizes the results of the fluorine concentration in the treated water obtained in Examples 3 to 5. Moreover, FIG. 4 shows the relationship between the particle | grain ratio (%) of 53 micrometers or more in slaked lime, and the fluorine concentration in treated water.

  As can be seen from Table 2 and FIG. 4, if the sulfur content in the slaked lime is the same, the smaller the particle size, the lower the fluorine concentration in the treated water and the higher the calcium fluoride recovery rate. From this result, it was found that a stable recovery rate of calcium fluoride can be obtained by classifying the slaked lime particle size distribution so that 53 μm or less is 90% or more.

(Example 6)
In Example 6, the crystallization reaction apparatus shown in FIG. 1 was used, and calcium phosphate was recovered from phosphorus-containing raw water under the following conditions. In Example 6, the slaked lime of Industrial Special A was washed until the sulfur content was 0.1% in terms of SO ₃ , and used as a calcium agent.

<Experimental conditions>
Phosphorus concentration of raw water containing phosphorus: 4000 mg / L
Phosphorus-containing raw water flow rate: 25 L / h
Slaked lime slurry concentration: 5% by weight
Acid: hydrochloric acid (5% by weight)
Crystallization reaction tank: 100 L (440 mmφ × 1000 mmH)
Stirring blade diameter: 160mm

(Example 7)
In Example 7, the test was carried out under the same conditions as in Example 6 except that the slaked lime of Industrial Special Number B was washed until the sulfur content was 0.01% in terms of SO ₃ and used as a calcium agent. Went.

(Comparative Examples 3 and 4)
In Comparative Example 3, the slaked lime of industrial special name A having a sulfur content of 0.5% in terms of SO ₃ was used as a calcium agent without washing, and in Comparative Example 4, the sulfur content was 0.00 in terms of SO ₃ . The test was carried out under the same conditions as in Example 6 except that 2% of the industrial special B slaked lime was used as a calcium agent without washing.

Table 3 summarizes the results of the phosphorus concentration in the treated water obtained in Examples 6 and 7 and Comparative Examples 3 and 4. FIG. 5 shows the relationship between the sulfur content in slaked lime (in terms of SO ₃ ) and the phosphorus concentration in the treated water.

As can be seen from Table 3, when Example 6 and Comparative Example 3 using the same industrial special name A slaked lime are compared with Example 7 and Comparative Example 4 using the same industrial special name B slaked lime, In Examples 6 and 7 in which the sample was washed, the phosphorus concentration in the treated water was decreased and the recovery rate of calcium phosphate was higher than those in Comparative Examples 3 and 4. Further, as can be seen from FIG. 5, the slaked lime was washed, and as the sulfur content in the slaked lime decreased, the phosphorus concentration in the treated water also decreased. From these results, in the case of phosphorus recovery treatment as well, it is necessary to wash at least slaked lime until the sulfur content is 0.1% or less in terms of SO ₃ , and 0.01% or less It was found preferable to wash until

(Examples 8 to 10)
In Examples 8 to 10, calcium phosphate was recovered from phosphorus-containing raw water using the crystallization reaction apparatus shown in FIG. 1 or 2. In Example 8, the special industrial grade C washed until the sulfur content was 0.01% in terms of SO ₃ was classified, and the particle size distribution was classified so that 53 μm or more was 10%. It was. In Example 9, the special slaked lime slaked until the sulfur content was 0.01% in terms of SO ₃ was used without classification. The particle size distribution of Industrial Special C was 18% at 53 μm or more. In Example 10, the slaked lime of industrial special name D washed until the sulfur content was 0.01% in terms of SO ₃ was used without classification. The particle size distribution of the industrial special code D was 13% at 53 μm or more.

  Table 4 summarizes the results of phosphorus concentration in the treated water obtained in Examples 8 to 10. Moreover, FIG. 6 shows the relationship between the particle | grain ratio (%) of 53 micrometers or more in slaked lime, and the phosphorus concentration in treated water.

  As can be seen from Table 4 and FIG. 6, if the sulfur content in the slaked lime is the same, the smaller the particle size, the lower the phosphorus concentration in the treated water and the higher the calcium phosphate recovery rate. From this result, it was found that a stable recovery rate of calcium phosphate can be obtained by classifying the slaked lime particle size distribution such that 53 μm or less is 90% or more.

  1, 2 Crystallization reactor, 10 Slaked lime silo, 12 Washing tank, 14 Dissolution tank, 16 Crystallization reaction tank, 18 Seed silo, 20 Neutralization tank, 22 Slaked lime first addition pipe, 23, 24 Pump, 26 Slaked lime 2nd addition piping, 28 Slaked lime 3rd addition piping, 30 Raw water addition piping, 32 Seed addition piping, 34 Treated water discharge piping, 36 Insoluble salt discharge piping, 38 Washing water addition piping, 40 Washing water discharge piping, 42 Stirring Wings, 43 Return piping, 44 Stirrer, 46 Draft tube, 48, 50 Motor, 52 classifier, 53 Small particle size discharge piping, 54 Large particle size discharge piping, 56 Treated water discharge channel.

Claims (8)

A crystallization reaction method in which slaked lime is added to raw water containing a substance to be crystallized to produce crystals of a hardly soluble calcium salt,
A washing step of washing the slaked lime so that the sulfur content in the slaked lime is 0.1% or less in terms of SO ₃ ;
And a crystallization reaction step of mixing the washed slaked lime with raw water to produce a hardly soluble calcium salt crystal.   It is a crystallization reaction method of Claim 1, Comprising: The pH adjustment process which mixes the washing | cleaning waste water which wash | cleaned the said slaked lime, and the treated water discharged | emitted by the said crystallization reaction process is provided. A crystallization reaction method characterized by 2. The crystallization reaction method according to claim 1, wherein in the washing step, the sulfur content in slaked lime is measured, and based on the measured content, the sulfur content in the slaked lime is 0.003 in terms of SO ₃ . A crystallization reaction method, wherein the slaked lime is washed so as to be 1% or less.   The crystallization reaction method according to claim 1, further comprising a classification step of classifying the slaked lime so that the particle size distribution of the slaked lime is not less than 53% and not less than 90% before or after the washing step. Reaction method. A crystallization reaction apparatus for adding slaked lime to raw water containing a substance to be crystallized to produce crystals of a hardly soluble calcium salt,
A crystallization reaction tank for mixing the raw water and the slaked lime to produce crystals of a sparingly soluble calcium salt;
A cleaning means for cleaning the slaked lime so that the sulfur content in the slaked lime is 0.1% or less in terms of SO ₃ ;
Slaked lime addition means for adding the washed slaked lime to the crystallization reaction tank;
A crystallization reaction apparatus comprising:   6. The crystallization reaction apparatus according to claim 5, further comprising pH adjusting means for adjusting the pH of the treated water by adding the washing waste water from which the slaked lime has been washed to the treated water discharged from the crystallization reaction tank. A crystallization reaction apparatus characterized by   6. The crystallization reaction apparatus according to claim 5, further comprising a classifying unit that classifies the slaked lime so that the particle size distribution of the slaked lime is 90% or more at a stage before or after the cleaning unit. Crystallization reactor. A calcium agent for reacting with raw water containing a substance to be crystallized to produce crystals of sparingly soluble calcium salt,
The calcium agent is a slaked lime having a sulfur content of 0.1% or less in terms of SO ₃ .

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