JP4546764B2 - Calcium fluoride manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a method for producing calcium fluoride, a method for treating fluorine-containing wastewater using the same, a device for producing calcium fluoride, and a device for treating fluorine-containing wastewater using the same.

  In etching processes and cleaning processes such as the production of liquid crystals, semiconductors, and solar cells, wastewater containing fluorine is generated, and its treatment becomes a problem. Recently, the drainage standards for fluorine have become increasingly strict considering the impact on the environment. Therefore, it is extremely important to perform treatment before disposal and to adjust the fluorine concentration in the wastewater to meet the drainage standards. Need to be low.

Conventionally, in order to reduce the fluorine concentration in fluorine-containing wastewater, an aqueous calcium compound is added to the wastewater to produce sludge-like calcium fluoride (CaF ₂ ), and the sludge is separated into solid and liquid as fluoride. A method of recovery is used. Thus, since fluorine is removed from the waste water as CaF ₂ , the fluorine concentration in the treated waste water can be reduced. In addition, as a method for increasing the fluorine recovery rate as CaF ₂ , for example, the amount of fluorine ions contained in the wastewater to be treated and the amount of ions that form calcium and a hardly soluble salt are measured, and the total amount of ions is measured. A method of adjusting the amount of aqueous calcium compound added so as to add an aqueous calcium compound is known (for example, see Patent Document 1). Further, there is also known a method of reducing the fluorine concentration in the treated fluorine-containing waste water by partially returning the concentrated sludge containing CaF ₂ to the reaction tank and circulating the sludge (see, for example, Patent Document 2). ).

The sludge-like CaF ₂ collected in this way is being recycled as a cement material or the like. However, sludge-like CaF ₂ obtained by wastewater treatment often contains many impurities such as chlorine, calcium carbonate, calcium hydroxide, calcium phosphate, gypsum, and precious metals other than CaF _2. It is inappropriate as a material. Further, since the allowable concentration of fluorine (including CaF ₂ ) and chlorine that may be contained in the entire cement is low, the use of recovered sludge-like CaF ₂ as a cement material has also been limited. On the other hand, sludge-like CaF ₂ is being recycled as a fluorine raw material such as hydrogen fluoride gas. However, high purity CaF ₂ is required as the fluorine raw material. In order to satisfy this requirement, that is, to increase the CaF ₂ purity in the sludge-like CaF ₂ , if the amount of the aqueous calcium compound added to the fluorine-containing waste water is decreased, the fluorine recovery rate is lowered. Reduction of fluorine concentration in the waste water becomes insufficient. Accordingly, it has been desired to develop a method capable of producing high-purity CaF ₂ from fluorine-containing wastewater and reducing the fluorine concentration in the wastewater.
JP 2001-212574 A JP-A-6-114382

The present invention is applicable to the processing of waste water containing fluorine, and an object of the invention to provide a method and apparatus which can be manufactured with high purity CaF ₂ from fluorine-containing waste water.

In order to achieve the above object, the production method of the present invention is a method for producing calcium fluoride from fluorine-containing wastewater, and is a production method having the following steps (a) to (d).
(A) Calcium source addition step of adding a calcium compound as a calcium source to the fluorine-containing wastewater (b) Solid content separation step (c) for separating the solid content generated in the step (a) In the step (b) Acid washing step for washing the resulting solid content with acid (d) Separation step for separating the solid content after acid washing in the step (c) as a calcium fluoride-containing material. Is an apparatus for producing calcium fluoride from the following (e) to (h).
(E) Calcium source addition means for adding a calcium compound as a calcium source to the fluorine-containing wastewater (f) Solid content separation means (g) for separating the solid content generated by the means (e) means (f) means Acid cleaning means for cleaning the generated solid content with acid (h) Separation means for separating the solid content after acid cleaning of the means (g) as a calcium fluoride-containing material

  In the production method and production apparatus of the present invention, components other than calcium fluoride (such as calcium salts) are solubilized and removed by washing the solid content generated by adding a calcium source to fluorine-containing wastewater with an acid. . For this reason, in the manufacturing method and manufacturing apparatus of this invention, highly purified calcium fluoride is obtained. Therefore, if the fluorine-containing wastewater is treated according to the present invention, high-purity calcium fluoride is obtained, which can be preferably used as a fluorine material, and a sufficient amount of calcium source can be input, so that the fluorine concentration in the wastewater is effective. Can be reduced.

In the present invention, as the calcium source, for example, a calcium compound can be used. Examples of the calcium compound include CaCl ₂ , Ca (OH) ₂ , CaCO ₃ , CaO and Ca (NO ₃ ) _{2, which} may be used alone or in combination of two or more. Among these, CaCl ₂ , Ca (OH) ₂ and CaCO ₃ are preferable, and CaCl ₂ and Ca (OH) ₂ are more preferable.

  In the production method of the present invention, it is preferable to use calcium ions in waste water generated when the solid content in the step (d) is separated as a calcium fluoride-containing material as a calcium source. Similarly, in the production apparatus of the present invention, it is preferable to use calcium ions in waste water generated when the solid content is separated as calcium fluoride-containing material in the means (h) as a calcium source. This is because the calcium source can be saved by doing so.

  In the present invention, for example, hydrochloric acid or nitric acid can be used as the acid in the acid cleaning in the step (c) or the means (g), and these may be used alone or in combination. In the step (c) or the means (g), it is preferable to carry out acid cleaning under the condition of pH 2-4.

  In the production method of the present invention, the step (d) preferably includes at least one of a water washing step after acid washing and a neutralization step after acid washing, and the (h) means of the production apparatus of the present invention. It is preferable to have at least one of water washing means after acid washing and neutralization means after acid washing.

  In the production method of the present invention, the step (d) includes the aggregation step of the separated calcium fluoride-containing material, the dehydration step of the separated calcium fluoride-containing material, and the separated calcium fluoride-containing material. It is preferable to have at least one step selected from the group consisting of a drying step and a pulverization step of the separated calcium fluoride-containing material. Further, the means (h) of the production method of the present invention includes the aggregating means for the separated calcium fluoride-containing material, the dehydrating means for the separated calcium fluoride-containing material, and the separated calcium fluoride-containing material. It is preferable to have at least one means selected from the group consisting of a drying means and a means for grinding the separated calcium fluoride-containing material.

  In the step (d) of the production method of the present invention and the means (h) of the production apparatus of the present invention, the calcium fluoride concentration in the separated calcium fluoride-containing material is in the range of 90 to 100% by weight. It is preferable to adjust, More preferably, it is the range of 92-100 weight%, More preferably, it is the range of 95-100 weight%.

  Since the said calcium fluoride containing material obtained by the manufacturing method of this invention is suitable as a fluorine material, what satisfy | fills the following specifications is preferable.

  The treatment method of the present invention is a treatment method of fluorine-containing wastewater in which a calcium source is added to fluorine-containing wastewater to separate solids and moisture, and wastewater is produced while producing calcium fluoride by the production method of the present invention. This is a processing method for processing.

  The treatment apparatus of the present invention is a treatment apparatus for fluorine-containing wastewater that adds a calcium source to fluorine-containing wastewater and separates solids and moisture, and wastewater while producing calcium fluoride by the production apparatus of the present invention. A processing device for processing.

  Next, an example of the method for producing calcium fluoride of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram of the manufacturing method of the above example. As shown in the figure, in the example of this production method, first, a step of adding a calcium source to fluorine-containing wastewater, and a solid-liquid separation step (solid content separation step) for separating the solid content and liquid content generated in the above-mentioned step And an acid washing step for washing the solid content with an acid and a separation step for separating the calcium fluoride-containing material, and calcium fluoride is obtained through these steps.

  First, the calcium source addition process will be described. In the production method of the present invention, the fluorine-containing wastewater is, for example, a semiconductor production process such as a silicon wafer, a liquid crystal production process such as a liquid crystal panel, a solar cell production process, a printed circuit board production process, a stainless steel sheet production process, a hook. Fluorine-containing wastewater discharged in connection with the acid production process. In particular, the production method of the present invention can be preferably applied to fluorine-containing wastewater generated in a liquid crystal production process, a solar cell production process, and a semiconductor production process. Specifically, the fluorine-containing wastewater generated in the semiconductor manufacturing process is a thick fluorine-containing wastewater, a wastewater discharged from an etching or cleaning process, a dilute fluorine-containing wastewater, a film-forming process in a semiconductor manufacturing process, etc. Examples thereof include fluorine-containing wastewater generated in a step of removing various gases (deposit gas, cleaning gas, dry etching gas, etc.) containing fluorine used by thermal decomposition or the like. The fluorine concentration of the fluorine-containing wastewater before application of the present invention is, for example, 200 to 30,000 mg / L, preferably 300 to 30,000 mg / L, more preferably 1,000 to 30,000 mg / L.

In the production method of the present invention, the calcium source is not limited as long as it supplies calcium ions (Ca ²⁺ ). The amount of the calcium source added is preferably 1 equivalent or more with respect to the anion in the fluorine-containing wastewater, more preferably 2 equivalents or more with respect to the fluorine ion in the fluorine-containing wastewater, more preferably fluorine in the fluorine-containing wastewater. 3 equivalents or more with respect to ions. Examples of the anions include silicon ions, sulfate ions (SO ₄ ²⁻ ), carbonate ions (CO ₃ ²⁻ ), phosphate ions (PO ₄ ³⁻ ) and the like in addition to fluorine ions. Such ions react with calcium ions to form calcium poorly soluble salts (for example, CaF ₂ , CaSO ₄ , CaCO ₃ , Ca (OH) _2, etc.), which precipitate, aggregate, precipitate, Minute (solid component). In addition, since the addition amount of the calcium source may be excessive with respect to the anion in the fluorine-containing wastewater that forms a sparingly soluble salt with calcium ions, the addition amount of the calcium source in the production method of the present invention. Is easy, and by administering the calcium source in an excessive amount, most of the fluorine in the wastewater can be converted to calcium fluoride, and as a result, the fluorine concentration in the wastewater can be effectively reduced.

The calcium source is as described above. When CaCl ₂ is used as a calcium source in the conventional method, the resulting CaF ₂ contains chlorine derived from CaCl _{2, and} thus is inappropriate for use as a cement material. Therefore, CaCl ₂ could not be used as a calcium source. However, according to the present invention, not only the chlorine component in the CaF ₂ -containing solid content but also other impurities can be reduced, and high-purity CaF ₂ can be obtained. Can do. Therefore, in the present invention, CaCl ₂ can be used as the calcium compound. The calcium compound used as the calcium source can be added to the fluorine-containing wastewater in the form of powder, solution, slurry, etc., but is preferably added in the form of slurry or solution because the dissolution rate is fast. For preparing the slurry and solution, for example, water can be used as a solvent.

Next, the solid (solid content) thus produced is separated (solid-liquid separation step). This solid-liquid separation step can be performed by a conventionally known solid and liquid separation method, and can be performed using, for example, a clarifier, a thickener, or the like. The liquid separated here is subjected to further wastewater treatment as a separated wastewater as needed, and discarded. In the addition step, since the fluorine ions in the fluorine-containing wastewater produce CaF ₂ , the fluorine ions in the separated liquid are significantly reduced. May be discharged as is to the outside water system as it is.

  In addition, it is preferable that the said addition process of the manufacturing method of this invention further includes an aggregation process. This is because the solid-liquid separation process can be efficiently performed because the solids aggregate when the aggregation process is performed. Aggregation can be performed by adding an aggregating agent to the solid. Examples of the flocculant include polyaluminum chloride (PAC), sulfuric acid band, polymer flocculant, and ferric chloride.

Next, the solid (solid content) separated in the solid-liquid separation step is washed with an acid (acid washing step). The acid washing is performed to dissolve calcium-insoluble salts (for example, CaCl ₂ , Ca (OH) ₂ , CaCO ₃ , CaO, Ca (NO ₃ ) _2, etc.) other than CaF ₂ contained in the solid. . Examples of the acid used for the acid cleaning include hydrochloric acid and nitric acid. By this acid cleaning step, the purity of calcium fluoride can be improved.

  The acid washing step is performed, for example, under conditions of pH 2-4, preferably under conditions of pH 2-3.

By the acid washing step, a calcium poorly soluble salt other than CaF ₂ in the solid (in the solid content) is dissolved. Therefore, the wastewater generated in the separation step of calcium fluoride-containing substances after the acid washing contains calcium ions and ions that form a sparingly soluble salt with calcium ions, that is, sulfate ions (SO ₄ ²⁻ ), carbonate ions (CO ² ). ₃ ^2- ), phosphate ion (PO ₄ ^3- ), and the like. In addition, the calcium ion contained in this washing waste water can be used as the calcium source. In this way, if calcium ions contained in the washing wastewater are reused in the production method of the present invention, effective utilization of calcium can be realized and costs can be reduced.

Next, the solid (solid content) washed in the acid washing step is separated to obtain a calcium fluoride (CaF ₂ ) -containing material (separation step). The separation step preferably includes at least one of a water washing step for washing the solid content after acid washing and a neutralization step for neutralizing the solid content from the viewpoint of safety. The water washing step can be performed by passing washing water through the solid content after acid cleaning, and the neutralization step can be performed by adding a neutralizing agent (alkali agent) to the solid content after acid cleaning. The pH after neutralization is preferably 6.5 to 8.5, and more preferably pH 7 to 8. As the alkali agent, for example, sodium hydroxide, potassium hydroxide and the like can be used, and among these, sodium hydroxide is preferable.

The separation step preferably includes a dehydration step. By the dehydration step, CaF ₂ can be obtained, for example, as a slurry (water content exceeding about 80% by weight). Dehydration can be performed using a conventionally known dehydration method. Examples of such a dehydration method include centrifugation and filtration, and among these, centrifugation is preferable. The centrifugation is preferably performed by a continuous dehydrator with a water washing function. By this water washing, impurities derived from the calcium compound (for example, chloride derived from calcium chloride) remaining in CaF ₂ can be removed. The dehydrated wastewater obtained by the dehydration step contains calcium ions, sulfate ions (SO ₄ ²⁻ ), carbonate ions (CO ₃ ²⁻ ), phosphate ions (PO ₄ ³⁻ ), and the like. In addition, as mentioned above, it is preferable to use the calcium ion contained in this dehydrated waste water as the calcium source. Further, this dewatered waste water may be subjected to further waste water treatment and discarded as necessary. The CaF ₂ content in the solid content of the slurry-like CaF ₂ is, for example, 92% by weight or more, preferably 95% by weight or more. In the dehydration step, the moisture content can be adjusted to obtain a CaF ₂ cake (moisture content exceeding about 50 wt% and not more than 80 wt%).

  In the production method of the present invention, the separation step preferably includes an aggregation step. This is because when the aggregation process is performed, the solid content is aggregated, so that the dehydration process can be performed efficiently. Aggregation can be performed by adding an aggregating agent (for example, the aforementioned aggregating agent) to the solid content. Among these, as the flocculant, a polymer flocculant is preferable.

In the production method of the present invention, the separation step preferably includes a drying step. By the drying step, the water content can be further reduced, and the quality as calcium fluoride (CaF ₂ ) is improved. The degree of drying is not particularly limited. For example, the water content is 20% by weight or less, preferably the water content is 18% by weight or less, and more preferably the water content is 15% by weight or less. The drying can be performed by a drying means such as a hot air drying method or a conductive heating drying method. Examples of the hot air drying include multi-stage disk drying, air flow drying, rotary drying, and the like. Examples of the conductive heat drying include groove type stirring drying. Examples of other drying methods include fluidized bed drying, spray drying, vacuum drying, freeze drying, infrared drying, and high frequency drying. In this drying step, the moisture content of the CaF ₂ obtained can be adjusted by adjusting the drying time and temperature.

  In the production method of the present invention, the separation step preferably includes a pulverization step because it is granulated into granules when drying such as rotary drying is performed. If the calcium fluoride-containing material having a reduced water content is pulverized, it becomes a small particle and is easy to use. The pulverization can be performed by, for example, an airflow pulverizer, a mechanical pulverizer, or the like, and is preferably performed by an airflow pulverizer.

  Next, an example of the calcium fluoride production apparatus of the present invention is shown in FIG. FIG. 2 is a block diagram of the apparatus of this example. As shown, this apparatus includes a fluorine-containing drainage storage tank 10, a calcium compound storage tank 11, a reaction tank 50, a solid-liquid separation tank 51, an acid cleaning tank 52, an acid storage tank 12, a dehydrator 54, a dryer 62 and The crusher 82 is a main component. In the figure, V indicates a valve and P indicates a pump.

  As illustrated, in this apparatus, first, calcium fluoride is formed by means of adding a calcium source to fluorine-containing wastewater. That is, the fluorine-containing wastewater storage tank 10 and the calcium compound storage tank 11 are connected to the reaction tank 50 by pipes, and valves and pumps are arranged in the respective pipes. Fluorine-containing wastewater is introduced into the reaction tank 50, and a calcium compound is added thereto. Further, as will be described later, the waste water generated by the acid cleaning is also connected to the cleaning waste water storage tank 53 and the reaction tank 50 so as to be introduced into the reaction tank 50 in order to effectively use calcium ions therein. In this pipe, a valve and a pump are arranged.

  Next, in this apparatus, the solid content (solid content) generated by the calcium source addition means and the liquid content are separated by the solid content separation means. That is, the reaction liquid generated in the reaction tank 50 is introduced into the solid-liquid separation tank 51 through a pipe equipped with a valve and a pump, where the solid content containing calcium fluoride is precipitated and solid-liquid separated. The supernatant liquid generated at this time is sent to the waste water treatment step.

  Next, in this apparatus, the precipitated solid content is washed with an acid by an acid washing means. That is, the precipitate in the solid-liquid separation tank 51 is introduced into the acid cleaning tank 52 through a pipe by a pump. The acid cleaning tank 52 is connected to the acid cleaning tank 52 by a pipe having a valve and a pump. The acid cleaning tank 52 has a stirring blade, which is connected to a drive motor (indicated by M in the figure). Acid (for example, hydrochloric acid or nitric acid) is added from the acid storage tank 12 to the solid content introduced into the acid cleaning tank 52, and acid cleaning is performed while stirring with the stirring blade. Thereby, the hardly soluble calcium salt in the solid content is solubilized, and this is transferred into the waste liquid. This waste liquid is transferred to the dehydrating means together with the solid content.

  Next, in this apparatus, the solid content after the acid cleaning is dehydrated by a dehydrating means. That is, the solid content (calcium fluoride-containing material) in the acid cleaning tank 52 and the waste liquid are introduced into the dehydrator 54 through a pipe having a valve and a pump. In the present invention, the type of dehydrator is not particularly limited, and various dehydrators can be used. In this apparatus, a cylindrical screw decanter is used as a centrifugal dehydrator. This cylindrical screw decanter is preferable because it is small in size, can be continuously processed, and can be dehydrated to a desired water content. In this cylindrical screw decanter, the sedimentation speed of the particles is proportional to the difference in density between centrifugal force and solid-liquid and the square of the particle diameter, and inversely proportional to the concentration of the mother liquor. , The centrifugal force can be adjusted and dehydrated to a desired water content. For example, when dehydration is performed in batch processing, continuous processing is possible with this dehydrator 54 (decanter method). At the time of dehydration, the solid content can be washed in advance with a large amount of washing water, and the impurities can be transferred to the washing waste water storage tank 53 as washing waste water. Thereafter, for example, by adding a neutralizing agent (alkali agent) to the dehydrator 54 (decanter method), dehydration can be performed while washing and neutralization. The degree of washing and neutralization can be set as appropriate by adjusting the residence time of the dehydrator 54, for example. Even if a filter press type dehydrator is used instead of the dehydrator 54 (decanter type), for example, washing water and a neutralizing agent can be added in stages, and the process can be similarly performed until dehydration.

  Next, an example of an apparatus capable of performing washing and neutralization at the front stage of the dehydrating means will be described. FIG. 2 is a configuration diagram of a part of an example of the calcium fluoride production apparatus of the present invention (instead of the acid washing tank 52 to the dehydrator 54 in FIG. 2, the acid washing tank 52 to the dehydrator 59 of the apparatus is used). As shown in FIG. First, the solid content of the acid cleaning tank 52 and the waste liquid are introduced into, for example, the acid cleaning drainage storage tank 55 by a pipe having a valve and a pump. The solid content and the waste liquid are allowed to pass through the UF membrane (ceramic separation membrane) 56 from the acid cleaning drainage storage tank 55 by a pipe provided with a valve and a pump. When transferring from the acid cleaning / drainage tank 55 to the UF membrane 56, for example, cleaning water is passed in advance to the solid content and the waste liquid in the pipe, and then a neutralizing agent (alkali agent) is added. Also good. After passing through the UF membrane 56, the permeated liquid content of the cleaning wastewater is transferred to the cleaning wastewater storage tank 53 through the pipe. On the other hand, after passing through the UF membrane 56, the solid content is returned to the acid cleaning drainage storage tank 55 through a pipe. For example, a pH meter 57 and a conductivity meter 58 are provided in the pipe between the UF membrane 56 and the acid cleaning drainage storage tank 55, and the pH and conductivity of the solid content passing through the pipe are monitored. Can do. The solid content returned to the acid cleaning drainage storage tank 55 is allowed to pass through the UF membrane 56 again from the acid cleaning drainage storage tank 55 by a pipe provided with a valve and a pump. Such a pH and conductivity monitored by the pH meter 57 and the conductivity meter 58 in the circulation line between the acid washing drainage storage tank 55 and the UF membrane 56 reach, for example, a predetermined pH and conductivity. Can be continued. In addition, while continuing the circulation line of the said acid cleaning waste water storage tank 55 and the UF membrane 56, new solid content and waste liquid should not be introduce | transduced from the acid cleaning tank 52 by adjusting a valve and a pump. Can do. When the pH and conductivity of the solid content monitored by the pH meter 57 and the conductivity meter 58 reach a predetermined value, for example, the solid content in the acid wash drainage storage tank 55 is reduced by a pipe equipped with a valve and a pump. The dehydrator 59 may be introduced into a dehydrator 59 (regardless of a method, for example, a filter press type). Although the UF membrane is made of ceramic, it is not limited to this as long as there is no problem in use such as chemical resistance and separation performance.

  Next, in this apparatus, the dehydrated solid content is dried by a drying means. That is, the dehydrated solid content is introduced from the dehydrator 54 (or dehydrator 59) into the hopper 61 through a pipe provided with a valve and a pump, and is then introduced into the dryer 62. In the present invention, the type of the dryer is not limited, and various dryers can be used. In this apparatus, an external jacket type agitating dryer 62 is used. The dryer 62 has a box-shaped container 62a and a jacket 64 for conductive heating provided around the box-shaped container 62a. Inside the box-shaped container 62a is a drive motor (indicated by M in the figure). A stirring blade 66 connected to is disposed. Further, the dryer 62 has a gas discharge port, and the gas discharge port is connected to the condenser 72 by a pipe. In the dryer 62, the dehydrated solid content (calcium fluoride-containing material) is heated and dried while being stirred, and the vapor generated at this time is introduced into the condenser 72 and condensed with cooling water. Become liquid. This liquid is conveyed to the waste water treatment process, while the gas that has passed through the condenser 72 is exhausted to the outside.

  Next, in this apparatus, the agitation dryer has a granulation effect, and as a result, the solid content becomes a large granular material. Make things. That is, the solid content (calcium fluoride-containing material) dried by the dryer 62 is put into the hopper 74 and thereby introduced into the pulverizer 82. In the present invention, the type of pulverizer is not particularly limited, and various pulverizers can be used. In this apparatus, an airflow pulverizer 82 is used. This airflow type pulverizer 82 has a box-shaped container 82a having a rotor 84 in which a plurality of impellers 83 are arranged along the flow direction of the airflow. The box-shaped container 82a has a raw material introduction port. And a pulverized material discharge port. The crusher 82 has a hopper 76 from which the solid content is fed into the raw material inlet. Note that the transportation of the solid content from the hopper 74 to the hopper 76 is gas transportation, and both the hoppers are connected by a pipe, and the solid content is gas transported by suction from the hopper 76 side. At this time, a filter for collecting dust is preferably disposed on the exhaust side of the hopper 76. The exhaust that collects the dust with the filter is discharged to the outside. In this airflow type pulverizer, air is allowed to flow from the inlet to the outlet, and the raw material is introduced into the rotor 84 inside the pulverizer by the airflow, where the raw material is pulverized by the impeller 83. The degree of pulverization can be appropriately set by adjusting the distance between the inner wall portion of the box-shaped container 82a and the blades and adjusting the passage time (speed). According to the airflow type pulverizer 82, the solid content can be pulverized efficiently, and the generated particulate matter is discharged from the discharge port. And a granular material is conveyed to the granular material storage tank 92 by gas transport. Therefore, the dryer 82 and the storage tank 92 are connected by a pipe for gas transportation, and the gas is transported by suction from the storage tank 92 side. Moreover, it is preferable to arrange a filter for collecting dust on the exhaust side of the storage tank 92. The exhaust that collects the dust with the filter is discharged to the outside. And the granular material of the calcium fluoride stored by the storage tank 92 is shipped suitably for recycling. The quality of the calcium fluoride granules is as described above.

  Next, this apparatus may be operated manually, or may be operated by automatic control by a computer. For example, each valve, pump, device and motor can be connected to a computer and operated under predetermined conditions.

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Each property of the resultant calcium fluoride (CaF ₂₎ was evaluated by the following methods.

(SS (suspended substance) concentration)
The suspended solids concentration was measured using an infrared moisture meter (FD-600 (trade name), Kett Science Laboratory Co., Ltd.).

(Median size and particle size distribution)
For the median diameter and particle size distribution, a laser diffraction / scattering particle size distribution measuring device (LA-920 (trade name), Horiba, Ltd.) is used in accordance with the laser diffraction / scattering particle size distribution measuring method (measuring principle: Mie scattering theory). And measured.

  In this example, calcium fluoride was produced from fluorine-containing wastewater as shown below using the apparatus shown in FIG.

In the reaction tank 50, a calcium compound (Ca (OH) ₂ ) was added to fluorine-containing wastewater (fluorine concentration 300 mg / L). The addition ratio of this calcium compound is 3 equivalents with respect to the fluorine concentration. In this reaction, the pH of the reaction solution was pH 11.5, and the reaction time was about 20 minutes. The reaction solution was neutralized with sulfuric acid to a pH of about 8. And this reaction liquid was separated into solid and liquid. The solid-liquid separation was performed by leaving it in the solid-liquid separation tank 51 for about 4 hours and separating it into a precipitate and a supernatant. The precipitate obtained at this time had a solid concentration of about 5% and a water content of 95%. The precipitate was transferred to the acid washing tank 52, hydrochloric acid was added, and the mixture was stirred for about 10 minutes under the condition of pH 2 to 3 and washed with acid. This was introduced into a centrifugal dehydrator 54 (TOMOE decanter TSM-0050 type (trade name), Sakai Kogyo Co., Ltd.) while putting washing water therein, followed by washing with water. After washing with water, a neutralizing agent (NaOH) was introduced into the dehydrator 54 to neutralize, and dehydrated until the water content became 60% (SS concentration 40%). By adjusting this centrifugal dehydrator, it was possible to carry out the steps of water washing, neutralization and dehydration in the separation means. The dehydrated slurry is dried with a vertical steam indirect heating dryer (Okadora (trade name), Okadora Co., Ltd.) at a drying temperature of 120 ° C. and a drying time of 20 minutes until the water content becomes 15%. It was. This agitation dryer tends to granulate solids by rotating during drying. For this reason, the dried granular calcium fluoride containing material was pulverized by an airflow type pulverizer (Selenium Mirror (trade name), Masuko Sangyo Co., Ltd.) to obtain a granular calcium fluoride containing material. In this granular calcium fluoride-containing material, the median diameter was 70 μm, 20 to 300 μm particles were 100% of the entire granular material, and the concentration of calcium fluoride was 95%. In addition, when the various treated water which arose in the said series of processes was investigated, all the treated water was less than 8 mg / L which is a fluorine drainage standard. Therefore, according to the present invention, it can be said that high-purity calcium fluoride can be produced from fluorine-containing wastewater, and the fluorine concentration in the wastewater can be effectively reduced. In addition, in the conventional calcium fluoride recovery method, calcium fluoride can be easily recovered by adding an aqueous calcium compound only to concentrated fluorine-containing wastewater. However, according to the present invention, it is possible to produce high-purity calcium fluoride by returning the acid-washed wastewater containing impurities generated in the acid washing to the reaction tank even in the diluted fluorine-containing wastewater, and A calcium source can be used effectively. Therefore, according to the present invention, the range of applicable fluorine-containing wastewater has been expanded. In the present invention, when the drying step and the pulverization step are further performed, the moisture content and the particle size are easy to handle as the fluorine raw material such as hydrogen fluoride by adjusting the degree of drying and the pulverization particle size. Of calcium fluoride can be obtained.

  According to the present invention, for example, high-quality calcium fluoride can be efficiently produced from fluorine-containing wastewater generated in a production process of liquid crystals, solar cells, semiconductors, and the like, and the fluorine concentration in the wastewater is sufficient. Can be reduced.

It is a flowchart which shows an example of the manufacturing method of this invention. It is a schematic diagram which shows an example of the apparatus of this invention. It is a schematic diagram which shows another example (only a part) of the apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fluorine containing waste water storage tank 11 Calcium compound storage tank 12 Acid storage tank 50 Reaction tank 51 Solid-liquid separation tank 52 Acid washing tank 53 Washing waste water storage tank 54 Dehydrator 55 Acid washing waste water storage tank 56 UF membrane 59 Dehydrator 61 Hopper 62 Dryer 62a Box-shaped container 64 Jacket 66 Stirrer blade 72 Condenser 74 Hopper 82 Airflow type pulverizer 83 Impeller 84 Rotor 82a Box-shaped container 76 Hopper 92 Granular substance storage tank
V Valve P Pump M Motor

Claims (14)

A method for producing calcium fluoride from fluorine-containing wastewater, comprising the following steps (a) to (d) :
(A) a calcium source addition step of adding a calcium compound as a calcium source to the fluorine-containing waste water ;
(B) a solid content separation step for separating the solid content generated in the step (a) ,
(C) the (b) acid washing step to wash the solids produced in step with an acid, and (d) is a separation step of separating the solids after acid washing step (c) as a calcium fluoride-containing compounds Have
The manufacturing method including using further the calcium ion in the waste_water | drain produced at the said (d) process as a calcium source . As the acid in the acid washing of the step (c), the manufacturing method of claim 1 wherein using at least one of hydrochloric acid and nitric acid. The manufacturing method according to claim 1 or 2, wherein in the step (c), acid cleaning is performed under conditions of pH 2 to 4 . The manufacturing method according to claim 1, wherein the step (d) includes a water washing step after acid washing. The manufacturing method according to claim 1, wherein the step (d) includes a neutralization step after acid cleaning. In the step (d), the separated calcium fluoride-containing material is aggregated, the separated calcium fluoride-containing material is dehydrated, the separated calcium fluoride-containing material is dried, and the separated calcium fluoride-containing material is dried. The manufacturing method according to any one of claims 1 to 5, further comprising at least one step selected from the group consisting of a step of grinding the calcium fluoride-containing material. A method for treating fluorine-containing wastewater by adding a calcium source to fluorine-containing wastewater and separating solids and moisture, wherein the wastewater is produced while producing calcium fluoride by the production method according to claim 1. Processing method to perform processing. An apparatus for producing calcium fluoride from fluorine-containing wastewater, the following means (e) to (h) :
(E) Calcium source addition means for adding a calcium compound as a calcium source to the fluorine-containing waste water ,
(F) Solid content separation means for separating the solid content generated by the means (e) ,
(G) the (f) acid cleaning means for cleaning the solids generated in the unit with an acid, and (h) separating means for separating the solids after acid washing of the (g) means as a calcium fluoride-containing compounds And a manufacturing apparatus that further uses calcium ions in the wastewater generated by the means (h) as a calcium source . The production measure according to claim 8 , wherein at least one of hydrochloric acid and nitric acid is used as the acid in the acid cleaning of the means (g). The manufacturing apparatus according to claim 8 or 9, wherein in the means (g), acid cleaning is performed under conditions of pH 2 to 4. The manufacturing apparatus according to any one of claims 8 to 10, wherein the means (h) has a water washing means after acid washing. The manufacturing apparatus according to claim 8 , wherein the means (h) has a neutralizing means after acid cleaning. The (h) means includes aggregating means for separating the calcium fluoride-containing material, a dehydrating means for separating the calcium fluoride-containing material, a drying means for separating the calcium fluoride-containing material, and the separated The manufacturing apparatus according to any one of claims 8 to 12, comprising at least one means selected from the group consisting of means for grinding calcium fluoride-containing material. A treatment apparatus for fluorine-containing wastewater that adds a calcium source to fluorine-containing wastewater and separates solids and moisture, wherein the wastewater is produced while producing calcium fluoride by the production apparatus according to claim 8. A processing device that performs processing.

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