JP2006159042A - Method and apparatus for treating fluorine ion-containing waste solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating a waste solution which recover fluorine in a waste solution containing fluorine ions as precipitates having high purity. <P>SOLUTION: A fluorine ion-containing waste solution transported from a raw water tank 1 to a precipitator 7 is supplied with a calcium chloride solution. Calcium chloride and fluorine ions are reacted using a line mixer 3 and a magnetic field applicator 4 provided at a transport passage for a waste solution to thereby promote the production of calcium fluoride, and, before the waste solution reaches the precipitator 7, caustic soda is supplied, and the PH of the waste solution is adjusted. In the precipitator 7, precipitated calcium fluoride and a supernatant waste solution are separated to recover the precipitated calcium fluoride. The remaining supernatant waste solution is transported to an electrolyzer 8, the fluorine ions are fixed using the electrolyzer 8, the supernatant waste solution from which the fluorine ions are removed is transported to a filtering device 9, and solid matter suspended in the supernatant waste solution is separated with a filter 21 made of a fluorine resin subjected to hydrophilic treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a processing method and a processing apparatus for waste liquid containing fluorine ions. In particular, the present invention relates to a processing method and processing apparatus for an etching solution used for etching Si.

  There are many water treatment technologies in wastewater treatment, such as purification of drinking water, domestic wastewater, and factory wastewater. The feature of these technologies is that there is no same waste liquid, and it is necessary to deal with each according to the purpose and the content of the waste liquid, and a treatment method must be developed according to the situation.

  Patent Document 1 is an invention relating to a wafer processing process wastewater treatment method. Semiconductor wafer processing is mainly classified into (1) ammonia hydrogen peroxide wastewater, (2) silicon sludge-containing surfactant wastewater, and (3) nitric acid hydrofluoric acid wastewater. Patent Document 1 discloses that, among the semiconductor wafer processing process wastewater, PH is adjusted with a strongly acidic waste liquid discharged from another system in the presence of ferrous salt in the persistent organic wastewater, and another system Comprehensive treatment such as oxidative decomposition of the hardly decomposable organic matter with hydrogen peroxide from the hydrogen peroxide-containing wastewater discharged from the wastewater. In this way, the water quality can be discharged into the river at a lower cost than before. In this invention, hydrofluoric acid is reacted with slaked lime or lime carbonate to precipitate calcium fluoride, and the precipitated calcium fluoride is removed by coagulation precipitation.

  Patent Document 2 relates to a method for treating fluorine-containing wastewater after PFC (perfluorocompound) gas detoxification. This treatment method includes an electrodialysis step for desalting and concentrating the fluorine-containing wastewater, regenerating the desalination treatment liquid as makeup water to the source of the fluorine-containing wastewater, and using the hydrofluoric acid concentrate Electrodialyze to the extent that it is regenerated as a concentrated hydrofluoric acid solution. According to this method, concentrated water and demineralized water having a target hydrofluoric acid concentration can be obtained by treating the fluorine-containing wastewater in an electrodialysis step while keeping the hydrofluoric acid acidic.

JP 2001-334275 A JP 2004-174439 A

  On the other hand, the waste liquid generated in the etching process of the silicon wafer mainly contains nitric acid and hydrofluoric acid, and contains ammonia, a surfactant and the like. Of these, hydrofluoric acid is particularly toxic, so the regulation of the allowable content in wastewater is strict. Furthermore, recently, the concentration of hydrofluoric acid used to increase the etching rate tends to increase. However, since an efficient treatment technique for waste liquid containing hydrofluoric acid has not been established, the storage amount of such waste liquid is gradually increasing. Therefore, the development of a fluorine fixing technique and a technique for recovering the fixed fluorine that reduce the fluorine concentration in the waste liquid to a level that can be discarded in a river has become particularly necessary.

  Fluorine constituting hydrofluoric acid is obtained from fluorite. However, fluorite is ubiquitous on the earth and is gradually becoming a scarce resource. Therefore, there is an increasing need to recover and reuse fluorine in hydrofluoric acid.

  Specifically, the technology of Patent Document 1 uses fine powdered calcium carbonate or slaked lime that is hardly soluble in water in order to remove hydrofluoric acid. However, industrially, it only reacts with hydrofluoric acid at the surface portion of calcium carbonate or slaked lime powder, and does not contribute to the reaction up to the inside of the powder. Therefore, according to the technique of Patent Document 1, the purity of recovered calcium fluoride is low, and the recovery cost of fluorine is high.

  On the other hand, in the technique of Patent Document 2, this air is washed with water in order to prevent the air containing fluorine, hydrofluoric acid and the like generated in the process using hydrofluoric acid from diffusing. In this case, the present invention relates to the treatment of cleaning water that is extremely diluted and discharged in large quantities. Since this waste liquid is dilute, electrodialysis is used to divide it into a liquid with a higher concentration of hydrofluoric acid and a desalted liquid. The liquid having a higher concentration of hydrofluoric acid is regenerated as a hydrofluoric acid solution having an available concentration. On the other hand, the desalted liquid is regenerated as makeup water to the source of fluorine-containing wastewater. Therefore, nothing is disclosed about the technology for discarding the hydrofluoric acid-containing liquid.

  Accordingly, a main object of the present invention is to provide a treatment method and a treatment apparatus for a fluorine ion-containing waste liquid that efficiently reacts hydrofluoric acid in the waste liquid to precipitate it as a high-purity fluorine compound. It is another object of the present invention to provide a fluorine ion-containing waste liquid treatment method and a compact treatment device that can collect different types of fluorine compounds generated in the process separately by the same dehydrator.

  Another object of the present invention is to provide a treatment method and a treatment apparatus for a fluorine ion-containing waste liquid that lowers the fluorine ion concentration of the waste liquid to below the discharge standard and contains almost no solid matter in the waste liquid.

The present invention (A) achieves the above object by accelerating the production of calcium fluoride by the reaction of calcium chloride and fluorine ions by applying a magnetic field to the waste liquid containing fluorine ions.
In the present invention (B), calcium chloride and fluorine ions are reacted to precipitate calcium fluoride as a reactant, and then the supernatant is electrolyzed to fix a small amount of fluorine ions to a solid substance. The above object is achieved by removing the solid matter by filtration through a filter.

The fluorine ion-containing waste liquid treatment method of the present invention (A) is characterized by comprising the following steps.
A step of mixing a calcium chloride solution with a waste liquid containing fluoride ions.
Applying a magnetic field to the mixture to react calcium chloride and fluoride ions to promote the production of calcium fluoride;
A process of adjusting the pH of the mixed solution by mixing caustic soda with the mixed solution to which a magnetic field is applied.
Separating the pH-adjusted liquid into calcium fluoride and supernatant waste liquid.

In addition, a fluorine ion-containing waste liquid treatment apparatus for performing the treatment method of the present invention (A) has the following configuration.
Raw water tank in which waste liquid containing fluoride ions is stored.
Calcium chloride supply means for supplying calcium chloride to the waste liquid conveyed from the raw water tank.
A magnetic field applying device that applies a magnetic field to the waste liquid after supplying calcium chloride.
Caustic soda supply means for supplying caustic soda solution to the waste liquid after applying a magnetic field and adjusting the pH of the waste liquid.
A precipitation device for precipitating calcium fluoride produced by the reaction between calcium chloride and fluoride ions and separating it from a supernatant waste liquid.

  In the above processing method and processing apparatus, an oscillating magnetic field is applied to the water molecules in the waste liquid to activate the breakage or the bond between fluorine and hydrogen (hydrogen bond). Thus, it is considered that the time during which fluorine is not bonded to hydrogen can be lengthened, and fluorine ions and calcium ions are efficiently reacted to generate calcium fluoride, so that calcium fluoride can be recovered with high efficiency.

The fluorine ion-containing waste liquid treatment method of the present invention (B) is characterized by comprising the following steps.
A step of mixing a calcium chloride solution with a waste liquid containing fluoride ions.
A step of mixing the mixed solution with caustic soda to adjust the pH of the mixed solution.
Separating the pH-adjusted liquid into calcium fluoride and supernatant waste liquid.
A step of reducing the fluorine ion concentration in the supernatant waste liquid by subjecting the supernatant waste liquid to electrolytic treatment and converting the fluoride ion in the supernatant waste liquid to a solid.
The step of filtering the supernatant waste liquid that has been subjected to electrolytic treatment, and separating the solid matter in the supernatant waste liquid with a fluororesin filter.

In addition, a fluorine ion-containing waste liquid treatment apparatus for performing the treatment method of the present invention (B) has the following configuration.
Raw water tank in which waste liquid containing fluoride ions is stored.
Calcium chloride supply means for supplying calcium chloride to the waste liquid conveyed from the raw water tank.
Caustic soda supply means for supplying caustic soda solution to the waste liquid after supplying calcium chloride and adjusting the pH of the waste liquid.
A precipitation apparatus for precipitating calcium fluoride produced by the reaction between calcium chloride and fluoride ions and separating it from a supernatant waste liquid.
An electrolyzer that electrolyzes the supernatant waste liquid and uses the fluorine ions in the supernatant waste liquid as a solid.
A filtration device for filtering solid matter in the supernatant waste liquid after the electrolytic treatment with a filter made of fluororesin.

  In the treatment method and treatment apparatus of the present invention (B), the waste liquid and the calcium fluoride solution are mixed, the pH is adjusted, the calcium fluoride and the supernatant waste liquid are separated, and then the fluoride ions in the supernatant waste liquid are electrolyzed to form a solid material And fixate is removed by filtration. By doing so, the fluorine ion concentration in the waste liquid can be reduced below the discharge standard, and waste water containing almost no solid matter can be obtained. In the present invention (B), if the fluorine ion concentration of the supernatant waste liquid before electrolytic treatment is lowered to some extent, the fluorine ion concentration can be reduced by electrolytic treatment.

  In the method of the present invention (B), after the step of mixing the calcium chloride solution with the waste liquid containing fluorine ions, a magnetic field is applied to the mixed liquid to react calcium chloride and fluorine ions to promote the formation of calcium fluoride. It is preferable to have the process to do. Moreover, it is preferable that the apparatus which performs the method of this invention (B) has a magnetic field application apparatus which applies a magnetic field to the waste liquid after supplying calcium chloride after a calcium chloride supply means.

Hereinafter, the waste liquid containing hydrofluoric acid as an example of the fluorine ion-containing waste liquid will be described in detail with a focus on the present invention (A).
In the present invention, the waste liquid containing hydrofluoric acid is treated using a calcium chloride solution and a caustic soda solution. The apparatus for performing this treatment includes, as main components, a raw water tank, calcium chloride supply means, a magnetic field application apparatus, caustic soda supply means, and a precipitation apparatus. Furthermore, it is preferable to combine a cooling device, an electrolysis device, and a filtration device as necessary.

  The waste liquid to be treated in the present invention is a waste liquid containing fluorine ions. An example of such a waste liquid is a waste liquid containing hydrofluoric acid used when, for example, etching Si. Waste liquid containing hydrofluoric acid is stored, for example, in a raw water tank. The waste liquid may be supplied from the raw water tank to a downstream processing step through a transport channel using a pump. The calcium chloride solution and the caustic soda solution are each made into an aqueous solution having a predetermined concentration, and are supplied from the calcium chloride supply means and the caustic soda supply means.

  When processing the waste liquid, first, a calcium chloride solution is mixed with the waste liquid containing hydrofluoric acid. The calcium chloride solution reacts with fluorine ions in the waste liquid to produce calcium fluoride. The calcium chloride supply means includes, for example, a calcium chloride tank for storing a calcium chloride solution, a stirrer for stirring the solution, and a pump for supplying the calcium chloride solution to the conveyance channel. In order to mix the amount of hydrofluoric acid contained in the waste liquid and the amount of calcium chloride in an equivalent amount, it is desirable to use a metering pump as the waste liquid transport pump and the calcium chloride solution transport pump.

  The calcium chloride solution is supplied before reaching the magnetic field application device provided in the conveyance flow path from the raw water tank to the precipitation device. With this configuration, when the mixed solution of hydrofluoric acid and calcium chloride passes through the magnetic field applying device, the generation reaction of calcium fluoride is efficiently performed by applying the magnetic field.

  The magnetic field applying device is a device that generates an oscillating magnetic field in the waste liquid, and is configured to wind a coil around the mixed liquid transport flow path and to pass a predetermined alternating current through the coil. By generating a magnetic field in the mixed waste liquid of hydrofluoric acid and calcium chloride, an oscillating magnetic field is applied to the water molecules in the mixed liquid, and the bond between hydrogen and hydrogen (hydrogen bond) is actively broken or combined. Turn into. Thus, it is considered that the time during which fluorine is not bonded to hydrogen can be lengthened, and fluorine ions and calcium ions are efficiently reacted to generate calcium fluoride. Therefore, there is an effect of reducing the amount of calcium chloride used.

In the present invention, calcium chloride and hydrofluoric acid react as shown in Formula (1). If PH is greater than 5.5, CaF ₂ precipitates and the reaction proceeds to the right. In particular, HF becomes almost CaF ₂ by adding a calcium chloride solution more than the equivalent of HF contained in the waste liquid. In addition, since the reaction is promoted using a magnetic field application device, the reaction speed is fast. Among the components on the right side of the formula (1), hydrogen chloride HCl remains in the waste liquid and proceeds to the next step. The reason why this method has not been used frequently is that chlorine ions had to be further treated after the calcium fluoride recovery.
2HF + CaCl ₂ ⇔ CaF ₂ ↓ + 2HCl (1)

On the other hand, in the reaction of solid matter such as slaked lime (Ca (OH) ₂ ) and hydrofluoric acid, which is a conventional technique, the following formula 2 is obtained, and there are precipitates on both the left side and the right side. The reaction proceeds to the right when fluorine diffuses into the slaked lime, which is a precipitate, but the reaction rate is slow because diffusion takes time. Further, when trying to increase the reaction rate, only the surface of the Ca (OH) ₂ powder is reacted, so the amount of Ca (OH) ₂ powder used is increased.
2HF + Ca (OH) ₂ ↓ ⇔ CaF ₂ ↓ + 2H ₂ O （2）

  Subsequently, calcium fluoride is rapidly precipitated by mixing caustic soda with the mixed solution to which a magnetic field is applied and adjusting the PH of the mixed solution to 5.5 or more. The caustic soda supply means includes, for example, a caustic soda tank for storing caustic soda, a stirrer for stirring the solution, and a pump for supplying the caustic soda solution. When supplying caustic soda quantitatively, it is desirable to use a metering pump.

  Caustic soda is mixed with a liquid mixture to which a magnetic field is applied in advance by a magnetic field application device, and prepared to have a pH of 5.5 or more. The pH-adjusted liquid is separated into calcium fluoride that precipitates in the precipitation device and supernatant waste liquid. Here, it is important to add caustic soda after the calcium chloride and hydrofluoric acid have sufficiently reacted. This is because calcium chloride reacts with caustic soda to form calcium hydroxide, and calcium ions are not effectively used.

Below, a more preferable aspect is demonstrated in detail. In the present invention, it is further preferable to reduce the concentration of fluorine ions in the supernatant waste liquid by subjecting the supernatant waste liquid obtained by the precipitation apparatus to an electrolytic treatment and converting the fluorine ions in the supernatant waste liquid to a solid. Since the solubility of calcium fluoride in water is 0.016 g / dm ³ (16 ppm), the supernatant waste liquid contains about 16 ppm of calcium fluoride (in fact, calcium is not contained up to 16 ppm). However, the drainage standard for hydrofluoric acid is usually 5 to 7 ppm or less. By electrolyzing the supernatant waste liquid, it cannot be discharged unless the contained fluorine is further reduced. Another content is chlorine, which is also removed by an electrolysis apparatus on the same principle as fluorine.

  An electrolytic device is used for this electrolytic treatment. This electrolysis apparatus has a metal electrode. More specifically, fluorine ions are taken into a compound such as a hydroxide produced by a metal anode by electrolysis to fix the fluorine ions. These compounds float or precipitate in the supernatant waste liquid. The metal used for the electrode can be copper, nickel, zinc, aluminum or the like. Since the electrodes are used by alternately switching the poles of the anode and the cathode, it is desirable that the anode and the cathode are the same metal.

  In the present invention, it is preferable that the supernatant waste liquid subjected to the electrolytic treatment is filtered with a filter made of a fluororesin to separate the solid matter in the supernatant waste liquid from the waste liquid. By this filtration, the solid substance floating in the supernatant waste liquid is separated from the waste liquid by a filter made of fluororesin. The filtered water can be discharged as wastewater because the fluorine concentration is below the emission standard.

  A filter made of a fluororesin is used for the filtration device. PTFE (tetrafluoroethylene resin), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene-6fluoropropylene copolymer resin), PCTFE (trifluoroethylene chloride resin), PVDF ( And ETFE (ethylene-tetrafluoroethylene copolymer resin).

  Hydrofluoric acid, which is a representative example of a fluorine ion-containing waste liquid, is an extremely corrosive acid. Fluororesin is suitable as a filter because it does not corrode with hydrofluoric acid. Further, since the fluororesin is a non-adhesive material, the filtered solid matter is easily peeled off and is suitable for the filter of the present invention. Among them, a PTFE (tetrafluoroethylene resin) filter having the greatest non-adhesiveness is desirable because it can easily remove solid matter attached to the filter. In addition, PTFE can be used for a long time because it is chemically stable and has high strength.

  The present invention preferably further includes a step of cooling the pH-adjusted liquid before the step of separating calcium fluoride and supernatant waste liquid. PH adjustment of the mixed solution of waste liquid and calcium chloride is a neutralization reaction accompanied by heat generation, and the neutralized liquid becomes high temperature. Moreover, since calcium fluoride precipitates rapidly when the pH is 5.5 or more, adding caustic soda in the middle of the transport channel may clog the channel. Therefore, it is preferable to adjust the pH by adding caustic soda to the mixed solution in the cooling device, and cool it. The cooling device includes, for example, a cooling tank that stores a mixed liquid of calcium fluoride, calcium chloride, and caustic soda, and a stirrer for mixing these liquids.

  The present invention further dehydrates the separated calcium fluoride. A dehydrator is used for dehydration. For example, the dehydrator is separated into a separation member such as a paper filter that receives the precipitate from the precipitation device and separates the precipitate into moisture, and a recovery container that collects the precipitate separated by the separation member. A liquid reservoir for storing the liquid is used. The water separated from the precipitate is preferably refluxed to a precipitation apparatus, that is, a step of separating calcium fluoride and supernatant waste liquid. This is to prevent discharge of waste liquid that does not satisfy the discharge standard.

  Further, the present invention preferably further dehydrates the precipitated solid in the electrolytically treated supernatant waste liquid and refluxes the separated water to a step of separating calcium fluoride and supernatant waste liquid. By this dehydration and reflux, the water separated from the solid can be prevented from being discharged as waste water. For the dehydration, it is preferable to use the dehydrator described above. By sharing the dehydration device with the solid matter dehydration of the precipitation device, the configuration of the processing device can be simplified.

  Furthermore, in the present invention, it is desirable that the solid matter separated by the filter is dehydrated, and the separated water is refluxed to a step of separating calcium fluoride and supernatant waste liquid. This dehydration and reflux can prevent the water separated from the solid matter from being discharged as waste water. For the dehydration, it is preferable to use the dehydrator described above. By sharing the dehydration device with the solid matter dehydration of the precipitation device, the configuration of the processing device can be simplified. Whether the object to be supplied to the dehydrator is a solid matter precipitated by the precipitation device, a solid matter generated by the electrolysis device, or a solid matter separated by a filter, is determined by these transport channels. Is preferably switched by a valve.

  In the present invention, it is further preferable that the electrolysis apparatus has positive and negative electrodes made of an Al plate. When electrolysis is performed, Al is dissolved from the anode, so that the anode gradually becomes smaller. In order to make both electrodes equally small, it is desirable to exchange the anode and the cathode at regular intervals. The precipitate obtained here is sent to a dehydrator and treated as solid waste. However, the precipitate in the precipitation device was a solid with a lot of calcium fluoride, but the precipitate obtained with the electrolysis device was a precipitate with a lot of aluminum and could be treated separately from the above-mentioned precipitate. desirable.

  The filter of the present invention preferably further has pores having a pore diameter of 0.05 to 10 μm and is hydrophilically treated. This is because most of the solids contained in the supernatant waste liquid have a size larger than the above. In addition, since the fluororesin is water repellent, it is desirable to perform a hydrophilic treatment in order to improve wettability with the waste liquid.

  The filter may be a bundle of many tube-like ones, a sheet-like one in the form of a plate together with a support, and a stacked arrangement thereof, or a sheet pleated and housed in a housing. Of these, a tube-like one and a sheet-like one arranged in a stacked manner are desirable. Of these, the tube-shaped one is preferable because a large filtration area per volume can be obtained.

  The filtration device of the present invention preferably further includes a backwash device for backwashing. When a filtration device is used for the treatment of waste liquid, the solid matter adheres to the filter and becomes clogged, so the permeability decreases. Therefore, it is preferable to remove the solid with a backwashing device and restore the permeability. In backwashing, a fluid such as air, water, alcohol or the like is flowed in a direction opposite to the traveling direction of the waste liquid when the fluid is filtered, and solid matter adhering to the filter is collected into the filter. By doing so, the filter clogging is recovered by approximately 85% or more. If necessary, in addition to the above-described backwash device, water or air can be sprayed from the outside of the tube to drop solids.

According to the method or the device of the present invention, the following effects can be obtained.
(1) By applying a magnetic field when reacting a waste liquid containing fluorine ions with calcium chloride, calcium fluoride can be efficiently generated and high-purity calcium fluoride can be recovered.

  (2) By electrolyzing the separated supernatant waste liquid, the fluorine contained in the supernatant waste liquid can be reduced to below the emission standard for the environment, and the treated waste liquid can be discharged to the river.

  (3) By filtering the supernatant waste liquid after the electrolytic treatment, the solid matter in the supernatant waste liquid can be removed, and the waste water can be drained with a lower waste content.

  (4) It is possible to simplify the processing equipment by sharing the dehydrating equipment that dehydrates calcium fluoride, dehydrates the solids in the supernatant waste liquid that has been subjected to electrolytic treatment, and dehydrates the solids separated by the filter. it can.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic conceptual diagram of the device of the present invention. This device is a raw water tank 1 that stores waste liquid, a cooling device 6 that cools a mixed liquid such as waste liquid, calcium chloride, and caustic soda, a precipitation device 7 that precipitates calcium fluoride, and an electrolytic treatment of the supernatant waste liquid of the precipitation device 7 The main configuration is an electrolysis apparatus 8, a filtration apparatus 9 that filters the supernatant waste liquid after the electrolytic treatment, and a dehydration apparatus 10 that dehydrates the recovered calcium fluoride and the solid matter taken out by the electrolysis apparatus 8 or the filtration apparatus 9.

  A waste liquid containing 10% by weight of hydrofluoric acid discharged from the etching apparatus is stored in the raw water tank 1. The waste liquid is transported to the downstream process via the transport channel 11A. An amount of calcium chloride solution corresponding to the hydrofluoric acid concentration in the waste liquid is supplied from the calcium chloride tank 2 by the transfer pump P in the middle of the transfer channel 11A. The waste liquid supplied with the calcium chloride solution in the waste liquid is mixed by the line mixer 3 and further conveyed to the cooling device 6 via the magnetic field applying device 4. The cooling device 6 measures the pH of the mixed solution of the waste liquid and calcium chloride, and the caustic soda is transported from the caustic soda tank 5 to the cooling device 6 by the transport pump P based on the result. Stir with a stirrer M if necessary in both the calcium chloride tank and the caustic soda tank.

  The magnetic field applying device 4 is configured such that a coil is wound around the outer periphery of the transport channel, and AC can be supplied to the coil from an AC power source (not shown). This coil is preferably loaded with 25-40 W of power. In this example, the inner diameter D of the oscillating magnetic field tube (portion where the coil is wound in the transport channel) is 8 mm, the length L is 20 cm, and the number of coil turns N is 100 times. However, this value is closely related to the amount of waste liquid to be treated. As a guideline, this value is about 0.1 to 1 ton per hour. If the amount of waste liquid transported varies, the amount of power used may be changed accordingly.

  The suitable ranges are preferably the coil current I = 20 to 50 mA and the coil voltage V = 1000 to 1700V. In particular, in the present invention, a rapid voltage fluctuation such as a rectangular wave is preferable to a smooth voltage fluctuation such as a sine curve. The rapid voltage fluctuation has a strong effect of breaking the bond between hydrogen and fluorine, and it is considered that the time in which fluorine is not bonded to hydrogen is longer than the state in which fluorine is bonded to hydrogen. In order to further increase this effect, it is preferable that the rectangular wave includes a high-frequency component.

  After the calcium chloride solution is added to the waste liquid, the waste liquid passes through the line mixer 3 and the magnetic field application device 4, so that the hydrofluoric acid and calcium chloride in the waste liquid react well to produce hydrogen chloride and calcium fluoride. In the cooling device 6, caustic soda is further mixed with this mixed solution to adjust the PH to 5.5 or more, and the mixture is thoroughly stirred with a stirring motor M (M in a circle in the figure). Since this neutralization reaction is exothermic, it is cooled in a cooling bath. The waste liquid thus treated is sent to the precipitation device 7 via the transport channel 11B, and calcium fluoride is precipitated as the sludge 31.

  The purpose of the line mixer is to disturb the flow of the waste liquid and to mix the hydrofluoric acid and the calcium chloride solution well. Specifically, a line mixer can be obtained by disposing a filler that obstructs the flow in the middle of the conveyance flow path. In addition, a line mixer can be formed by using a structure that generates a vortex in the flow path or a structure that reverses the direction of the vortex in a short cycle.

  The sedimented sludge 31 is sent from the sedimentation device 7 to the dehydration device 10 via the transport flow path 11D by the transport pump P, where moisture is removed by the paper filter 24. The sludge from which moisture has been removed is treated as solid waste 32. The sludge collected by the settling device 7 has a higher calcium fluoride content than sludge generated in other parts. On the other hand, since the waste water collected by the dehydrating apparatus 10 contains hydrofluoric acid as described below, it is recirculated to the precipitation apparatus 7 via the transport channel 11E by the transport pump P.

  By the treatment up to the precipitation device 7, most of the fluorine in the hydrofluoric acid is precipitated and recovered as calcium fluoride. However, since the solubility of calcium fluoride in water is 16 mg / liter, about 16 ppm of fluorine is contained in the supernatant waste liquid as hydrofluoric acid. Since hydrofluoric acid is highly toxic, the emission standard is generally set at about 6 ppm. Therefore, the supernatant waste liquid is further processed to reduce the content of hydrofluoric acid.

  An electrolysis apparatus 8 is used to reduce the content of hydrofluoric acid. That is, the supernatant waste liquid of the precipitation device 7 is transported to the electrolysis device 8 by the transport pump P via the transport channel 11C. Fluorine in the supernatant waste liquid is fixed to the metal compound generated in the electrolysis device 8. The electrolyzer 8 includes an anode 22A, a cathode 22B, and a power source 23. As the electrodes 22A and 22B, both electrodes were made of Al, and a plate having a size of 300 mm × 100 mm × 8 mm was used.

The anode and cathode of the electrolyzer are preferably made of Al metal. This is because, among various metal ions eluted from the anode by electrolysis, trivalent Al ³⁺ ions are more active than divalent metal ions, and the aggregating power of aluminum hydroxide is superior. Examples of the anion in the waste liquid include a hydroxyl group and a fluorine group. When these react with aluminum and become mostly aluminum hydroxide Al (OH) ₃ which is a precipitate, fluorine is trapped in it, for example, AlFO, AlF (OH) ₂ etc., and fluorine is fixed Conceivable. The specific electrolytic treatment conditions are preferably electrolysis using a constant current power source having a voltage of 6 to 18V. Chlorine is removed by forming a compound in which the fluorine atom is replaced with a chlorine atom.

  In the electrolyzer 8, the aluminum hydroxide containing fluorine precipitates in the waste liquid, and the supernatant waste liquid from which the fluorine has been removed remains. The precipitate generated by the electrolyzer 8 is sent to the dehydrator 10 via the transport channel 11F, dehydrated by the paper filter 24, and discarded as a solid waste 32. On the other hand, the supernatant waste liquid from which the fluorine has been removed is conveyed to the filtration device 9.

  In the filtering device 9, the solid material and the waste water in the supernatant waste liquid from which the fluorine transported from the electrolysis device 8 has been removed are separated by the filter 21. The supernatant waste liquid from which the solid matter passed through the filter was removed contained only 5 ppm of fluorine and can be discharged out of the system as water. Solid matter adheres to the outer periphery of the filter as sludge 31. The sludge 31 peeled off from the filter by backwashing is transported to the dehydrator 10 by the transport pump P via the transport channel 11G, dehydrated by the paper filter 24, and then discarded as solid waste 32.

  Solids that reach the filtration device 9 include solids that have not been precipitated by the precipitation device 7 and those that have been generated by the electrolysis device 8. Since any solid matter is fine, the pore size of the filter 21 is desirably in the range of 0.05 to 10 μm. In the present invention, PTFE made of PTFE having a pore diameter of about 1 μm (registered trademark of Sumitomo Electric Industries, Ltd.) was used. The optimum pore diameter can be selected depending on the waste liquid.

  In FIG. 1, the filter is schematically shown as one tube. In practice, a cartridge filter as shown in FIG. 2 is used. This cartridge filter has a structure in which a disk-shaped top plate 42 and a bottom plate 41 are held with a support rod at an interval, and a number of tubes (filters 21) having ridges between the top plate 42 and the bottom plate 41 are held. It is. The upper end side of the tube is sealed with a top plate 42 so that the waste liquid does not flow out of the tube. Further, the bottom plate 41 is provided with a discharge port 43 so that the inner peripheral sides of all the tubes are collectively connected to the discharge port 43.

  This cartridge is used in the filtration device 9 shown in FIG. The discharge port 43 is connected from the transfer pump P to the transfer channel 11H. As an example of the filter 21, 500 porous tubes made of tetrafluoroethylene having an outer diameter of 2 mm and a wall thickness of 0.5 mm and having a pore diameter of 1 μm can be assembled into a cartridge filter.

  Further, in order to allow the sludge to adhere to the outside of the tube, the waste liquid is passed under pressure from the outer periphery of the tube toward the inside. On the other hand, when pressure is fed from the inner diameter side of the tube, if a solid matter having a volume equal to the diameter of the tube is accumulated, it cannot be used. Further, the tube needs to have a strength that can withstand at least the working pressure. When the wall thickness is increased, the strength is increased, but the transmittance is decreased. Therefore, it is desirable to select an appropriate thickness. Further, when backwashing is performed by applying pressure from the inner diameter side, the ridges are elongated and the sludge is easily peeled off.

  The filter has pores with a pore diameter of 0.05 to 10 μm, and is preferably tube-shaped. This is because most of the solids contained in the supernatant waste liquid contain solids having the above size. In particular, the pore diameter is preferably 0.45 to 2 μm. Most of the solid matter that could not pass through the filter is removed by backwashing, for example, by a backwashing device described later.

  The filter is preferably subjected to a hydrophilic treatment. Fluorine resin is water repellent, so it is difficult for water to pass through. Therefore, it is preferable to perform a hydrophilic treatment so that the waste liquid containing water as a main component can easily pass through the filter. Specifically, the filter can be hydrophilized by pre-immersing the filter in a liquid such as IPA (isopropyl alcohol). When hydrophilized using IPA, hydrophilicity is maintained when backwashed with water. When backwashing with air, IPA is expelled from the pores of the filter, dries, and returns to its original water repellency.

  Moreover, a hydrophilic polymer can be combined with the surface of the hole of a fluororesin to make it hydrophilic. As a hydrophilic method, a porous PTFE porous membrane is first impregnated with IPA, and then impregnated with, for example, 0.5 wt% of a polyvinyl alcohol aqueous solution, and then 0.5 wt% of glutaraldehyde as a crosslinking agent is mixed with 1% hydrochloric acid. Soak in the solution and chemically cross-link. Thereafter, the PVA cross-linked polymer can be stably fixed to the PTFE membrane by rinsing with water to remove unnecessary residues. According to this treatment, the hydrophilic polymer PVA is firmly fixed and integrated on the surface without substantially changing the porous structure of the PTFE membrane. As a result, rapid permeability of the aqueous solution is exhibited, and even after the membrane is dried by backwashing with air, rapid filtration can be continued because the membrane is easily wetted with waste water.

  In order to confirm the effect of the present invention (B), the magnetic field application device 4 was stopped in FIG. 1, and the waste liquid containing 5 wt% hydrofluoric acid was treated under the same conditions as in the previous example. In the filtering device 9, the fluorine concentration of the supernatant waste liquid filtered by the filter was such that it could be discharged.

  The apparatus and method of the present invention can treat not only the wastewater treatment of an etching solution used for etching a silicon wafer, but also the waste solution containing hydrofluoric acid used for removing the scale of steel. In the case of a waste liquid containing hydrofluoric acid and nitrate groups, the concentration of hydrofluoric acid can be reduced by first proceeding to the step of separating the waste liquid into calcium fluoride and supernatant waste liquid, and further nitrate groups can be treated by treating microorganisms such as bacteria. . Since microorganisms such as bacteria are killed by hydrofluoric acid, the hydrofluoric acid is first removed and then biological treatment is performed.

It is a schematic conceptual diagram of the processing apparatus of the fluorine ion containing waste liquid of this invention. It is a perspective view of the cartridge filter used by this invention.

Explanation of symbols

1 Raw water tank 2 Calcium chloride tank
3 Line mixer 4 Magnetic field applying device
5 Caustic soda tank 6 Cooling device
7 Precipitator 8 Electrolyzer
9 Filtration equipment 10 Dehydration equipment
11A, B, C, D, E, F, G, H
21 Filter 22A anode
22B Cathode 23 Power supply
24 Paper filter
31 Sludge 32 Solid waste
41 Bottom plate 42 Top plate
43 outlet
M Stirrer P Transfer pump

Claims (23)

Mixing a calcium chloride solution with a waste liquid containing fluoride ions;
Applying a magnetic field to the mixture to react calcium chloride and fluoride ions to promote the production of calcium fluoride;
A step of mixing caustic soda with the liquid mixture to which a magnetic field is applied, and adjusting the pH of the liquid mixture;
A process for treating a fluorine ion-containing waste liquid, comprising a step of separating the PH-adjusted liquid into calcium fluoride and a supernatant waste liquid.   2. The fluorine ion-containing waste liquid according to claim 1, further comprising a step of reducing the fluorine ion concentration in the supernatant waste liquid by subjecting the supernatant waste liquid to an electrolytic treatment and converting the fluorine ions in the supernatant waste liquid to a solid. Processing method.   The method for treating a fluorine ion-containing waste liquid according to claim 2, further comprising a step of filtering the supernatant waste liquid that has been subjected to electrolytic treatment, and separating solids in the supernatant waste liquid from the waste liquid using a fluororesin filter. . Mixing a calcium chloride solution with a waste liquid containing fluoride ions;
Mixing caustic soda with the mixture and adjusting the pH of the mixture;
Separating the PH-adjusted liquid into calcium fluoride and supernatant waste liquid;
A step of reducing the fluorine ion concentration in the supernatant waste liquid by subjecting the supernatant waste liquid to electrolytic treatment and converting the fluorine ions in the supernatant waste liquid into a solid matter;
A method for treating a fluorine ion-containing waste liquid, comprising a step of filtering a supernatant waste liquid that has been subjected to electrolytic treatment and separating a solid in the supernatant waste liquid with a filter made of a fluororesin.   Between the step of mixing the calcium chloride solution with the waste liquid containing fluorine ions and the step of adjusting the pH, a step of applying a magnetic field to the mixed solution to react calcium chloride and fluoride ions to promote the formation of calcium fluoride. 5. The method for treating a fluorine ion-containing waste liquid according to claim 4, wherein:   6. The method for treating a fluorine ion-containing waste liquid according to any one of claims 1 to 5, further comprising a step of cooling the pH-adjusted liquid before the step of separating calcium fluoride and supernatant waste liquid.   The fluoride ion-containing waste liquid according to any one of claims 1 to 6, wherein the separated calcium fluoride is dehydrated, and the separated water is refluxed to a step of separating calcium fluoride and a supernatant waste liquid. Processing method.   The precipitated solid in the electrolytically treated supernatant waste liquid is dehydrated, and the separated water is refluxed to the step of separating calcium fluoride and the supernatant waste liquid. Treatment method for fluorine ion-containing waste liquid.   9. The fluoride ion-containing waste liquid according to claim 3, wherein the solid matter separated by the filter is dehydrated and refluxed to the step of separating the separated water into calcium fluoride and a supernatant waste liquid. Processing method. A raw water tank in which waste liquid containing fluoride ions is stored;
Calcium chloride supply means for supplying calcium chloride to the waste liquid conveyed from the raw water tank;
A magnetic field application device for applying a magnetic field to the waste liquid after supplying calcium chloride;
A caustic soda supply means for supplying a caustic soda solution to the waste liquid after application of the magnetic field and adjusting the pH of the waste liquid;
An apparatus for treating a fluorine ion-containing waste liquid, comprising: a precipitation device for precipitating calcium fluoride produced by the reaction between calcium chloride and fluoride ions and separating the calcium fluoride from a supernatant waste liquid.   11. The apparatus for treating a fluorine ion-containing waste liquid according to claim 10, further comprising an electrolytic device that electrolyzes the supernatant waste liquid and uses the fluorine ions in the supernatant waste liquid as a solid.   12. The fluorine ion-containing waste liquid treatment apparatus according to claim 11, further comprising a filtration device for filtering solid matter in the supernatant waste liquid after the electrolytic treatment with a filter made of a fluororesin. A raw water tank in which waste liquid containing fluoride ions is stored;
Calcium chloride supply means for supplying calcium chloride to the waste liquid conveyed from the raw water tank;
A caustic soda supply means for adjusting the pH of the waste liquid by supplying a caustic soda solution to the waste liquid after the supply of calcium chloride;
A precipitation device for precipitating calcium fluoride produced by the reaction of calcium chloride and fluoride ions;
An electrolytic device for subjecting the supernatant waste liquid to an electrolytic treatment, and using the fluorine ions in the supernatant waste liquid as a solid;
A fluorine ion-containing waste liquid treatment apparatus, comprising: a filtration device for filtering solid matter in the supernatant waste liquid after the electrolytic treatment with a filter made of a fluororesin.   14. The fluorine ion-containing waste liquid treatment apparatus according to claim 13, further comprising a magnetic field application device that applies a magnetic field to the waste liquid between the calcium chloride supply means and the caustic soda supply means.   15. The fluorine ion-containing waste liquid treatment apparatus according to claim 10, further comprising a cooling device that cools the waste liquid, calcium chloride, and caustic soda between the magnetic field application device and the precipitation device.   16. The apparatus for treating a waste liquid containing fluorine ions according to claim 10, further comprising a dehydrating apparatus for dehydrating calcium fluoride precipitated in the precipitating apparatus.   17. The fluorine ion-containing waste liquid treatment apparatus according to claim 11, further comprising a dehydration apparatus for dehydrating a solid material generated by the electrolytic treatment of the electrolysis apparatus.   18. The apparatus for treating a fluorine ion-containing waste liquid according to claim 12, further comprising a dehydrator that dehydrates the solid separated by the filter.   19. The fluorine ion-containing waste liquid treatment apparatus according to claim 11, wherein the electrolysis apparatus has positive and negative electrodes made of an Al plate.   20. The fluorine ion-containing waste liquid treatment apparatus according to claim 12, wherein the filter has pores having a pore diameter of 0.05 to 10 μm and is hydrophilically treated.   21. The fluorine ion-containing waste liquid treatment apparatus according to claim 12, wherein the filter includes a plurality of tubes.   21. The fluorine ion-containing waste liquid treatment apparatus according to claim 12, wherein the filter is composed of one or more sheets.   23. The apparatus for treating a waste liquid containing fluorine ions according to claim 12, further comprising a backwashing device for backwashing the filter.

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