JP5110013B2 - Method and apparatus for treating fluorine-containing wastewater - Google Patents

Description

  The present invention relates to a method and apparatus for treating fluorine-containing wastewater, and more particularly, to a method and apparatus for treating fluorine-containing wastewater for treating fluorine-containing wastewater discharged from a semiconductor manufacturing factory or the like.

  In semiconductor manufacturing factories and related factories, a large amount of an etchant mainly composed of hydrogen fluoride or ammonium fluoride is used. For this reason, mineral acid etc. which coexist with hydrogen fluoride and ammonium fluoride as a main component coexist in factory wastewater, and the process which removes fluorine from this fluorine-containing wastewater is needed.

  Conventionally, treatment of fluorine-containing wastewater has been carried out by coagulation sedimentation, etc., and calcium salts such as calcium hydroxide are added to fluorine-containing wastewater to form poorly soluble calcium fluoride, and this calcium fluoride is agglomerated. By doing so, the fluorine component is removed. However, this method has a problem that a large amount of sludge with poor sedimentation is generated, and it is necessary to reduce the amount of sludge generated.

  Therefore, a method using a calcium carbonate packed tower has been proposed as a method for reducing the amount of sludge generated. In this method, fluorine-containing waste water is passed through a calcium carbonate packed tower to convert fluorine into granular calcium fluoride and remove it. Furthermore, it has been proposed to use the obtained granular calcium fluoride as a filter medium for a filtering device (Patent Document 1).

JP 2000-070962 A

  By the way, when using granular calcium fluoride obtained from a packed tower, its purity is low, so there is a problem that it cannot be reused as a raw material for industrial products and disposed as industrial waste. There was a need for pure calcium fluoride.

  However, the method described in Patent Document 1 has been difficult to increase the purity of calcium fluoride.

  This invention is made | formed in view of such a situation, and it aims at providing the processing method and processing apparatus of the fluorine-containing waste water which can obtain high purity calcium fluoride.

  In order to achieve the object, the method for treating fluorine-containing wastewater of the present invention comprises a step of concentrating fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L to a fluorine concentration of 1000 mg / L or more, A step of adjusting the pH value to 3 or less, and passing the pH-adjusted fluorine-containing wastewater through a calcium carbonate packed tower to remove fluorine from the fluorine-containing wastewater by converting fluorine to calcium fluoride, And at least a step of discharging as water.

  In order to achieve the above object, the fluorine-containing wastewater treatment apparatus of the present invention is disposed downstream of the concentrating device for concentrating fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L to a fluorine concentration of 1000 mg / L or more. And a pH adjusting tank for adjusting the pH value of the concentrated fluorine-containing wastewater to 3 or less, and a downstream of the pH adjusting tank, and converting fluorine into calcium fluoride to convert fluorine into the fluorine-containing wastewater. And a calcium carbonate packed tower that is removed and discharged as treated water.

  The inventor carefully observed the treatment of fluorine-containing wastewater using a calcium carbonate packed tower. As a result, (1) because the calcium carbonate particle size is 0.3-0.5 (mm), the internal osmotic force varies depending on the fluorine concentration in the water. The purity of the calcium fluoride is reduced, and (2) if the pH value of the fluorine-containing wastewater flowing into the calcium carbonate packed tower is close to the neutral region, the solubility of the calcium carbonate surface is low, so It was found that the purity of calcium deteriorates.

  As a result of intensive studies, the fluorine-containing wastewater was concentrated to a fluorine concentration of 1000 mg / L or more, adjusted to a pH value of 3 or less, and then passed through a calcium carbonate packed tower to obtain high-purity calcium fluoride. The inventor found out that it was obtained and reached the present invention.

  In the method for treating fluorine-containing wastewater and the apparatus for treating fluorine-containing wastewater of the present invention, the concentration of the fluorine-containing wastewater is preferably performed by a reverse osmosis device.

  According to the present invention, since the reverse osmosis device is used as the concentrating device, the ratio of permeated water to concentrated water (concentration ratio) can be easily adjusted by pressure operation.

  In the invention, the fluorine-containing wastewater treatment method and the fluorine-containing wastewater treatment apparatus of the present invention are preferably performed by a plurality of reverse osmosis devices connected in series.

  According to the present invention, even if the concentration of fluorine contained in the fluorine-containing waste water is 200 to 500 mg / L, which is relatively low, the fluorine concentration can be concentrated to 1000 mg / L or more.

  In the method for treating fluorine-containing waste water according to the present invention, it is preferable that the permeated water taken out from the reverse osmosis device is reused. According to the present invention, the reuse rate of water can be improved to 80% by reusing the permeated water from the reverse osmosis device.

  In the method for treating fluorine-containing wastewater according to the present invention, the recovered calcium fluoride is preferably reused as a raw material for hydrofluoric acid chemicals. In the method for treating fluorine-containing wastewater according to the present invention, in the invention, the purity of the calcium fluoride is preferably 85% or more.

  According to the present invention, since calcium fluoride formed when fluorine is removed from fluorine-containing wastewater is reused, resources can be effectively used. In particular, since the calcium fluoride taken out from the calcium carbonate packed tower can be discharged in a granular form, sludge concentration equipment and dehydration equipment are not required and the purity is high, and it can be reused as a hydrofluoric acid chemical raw material. Moreover, the utility value as a raw material of a hydrofluoric acid chemical | medical agent can be raised by the purity of calcium fluoride being 85% or more.

  In the above invention, the fluorine-containing wastewater treatment apparatus of the present invention preferably further includes a fluorine monitor before and after the concentration apparatus. According to the present invention, the fluorine concentration state in the concentration device can be managed by providing the fluorine monitor before and after the concentration device.

  According to the method and apparatus for treating fluorine-containing wastewater of the present invention, high-purity granular calcium fluoride can be obtained.

The schematic block diagram of the processing apparatus of the fluorine-containing waste_water | drain which concerns on this invention. The schematic block diagram of the processing apparatus of other fluorine-containing waste_water | drain. The graph which shows the relationship between the fluorine concentration of fluorine-containing wastewater, and the purity of calcium fluoride. The graph which shows the relationship between the pH value of fluorine-containing wastewater, and the purity of calcium fluoride.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described with reference to the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment can be used. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to”.

  The present invention is characterized by concentrating the fluorine concentration of fluorine-containing wastewater to 1000 mg / L or more and adjusting its pH value to 3 or less, and then passing the water through a calcium carbonate packed tower. Calcium can be obtained.

  Preferred embodiments of a method and apparatus for treating fluorine-containing wastewater according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows the configuration of the waste water treatment apparatus of the present embodiment. As shown in the figure, the waste water treatment apparatus 100 includes a raw water tank 10, a reverse osmosis device 12, a pH adjustment tank 14, a calcium carbonate packed tower 16, and a coagulation sedimentation device 18.

  Piping is connected to the raw water tank 10, and fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L from the semiconductor manufacturing factory flows into the raw water tank 10 and is stored therein. A pump 11 is connected to the raw water tank 10. By driving the pump 11, fluorine-containing wastewater is supplied from the raw water tank 10 to the reverse osmosis device 12 through the pipe 20.

  The reverse osmosis device 12 includes a reverse osmosis membrane 13. The fluorine-containing wastewater permeates through the reverse osmosis membrane 13 to be separated into concentrated water and permeated water. A fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L, for example, a fluorine concentration of 500 mg / L is concentrated by the reverse osmosis device 12 into a fluorine-containing wastewater having a fluorine concentration of 1000 mg / L or more. Since the concentrated fluorine-containing wastewater has a pH value of 3 to 4, the fluorine-containing wastewater is sent to the downstream pH adjusting tank 14 via the pipe 21 in order to make the pH value 3 or less. By providing the fluorine monitors 15 on the inflow side and the outflow side of the reverse osmosis device 12, the concentration state of fluorine can be managed.

  On the other hand, the permeated water is reused via the pipe 23 because the fluorine concentration becomes 20 mg / L, for example. Conventionally, fluorine-containing wastewater in a semiconductor factory has been discharged outside the factory after being treated with a water treatment facility, and the reuse rate of the wastewater was as low as 50 to 60%. However, since the permeated water of the reverse osmosis device 12 can be recycled by applying the present invention, the water reuse rate can be improved to 80%.

  FIG. 2 shows a plurality of reverse osmosis devices 12a, 12b connected in series. As shown in FIG. 2, the reverse osmosis devices 12a and 12b include reverse osmosis membranes 13a and 13b, respectively. By connecting reverse osmosis devices 12a and 12b in series in multiple stages, even if the fluorine concentration of the fluorine-containing wastewater from the semiconductor factory is relatively low, such as 200 to 500 mg / L, the fluorine concentration is concentrated to 1000 mg / L or more. can do. Moreover, as shown in FIG. 2, the fluorine concentration state can be managed by providing the fluorine monitor 15 on the inflow side of the reverse osmosis device 12a and the outflow side of the reverse osmosis device 12b. In FIG. 2, the example of two stages has been described, but the fluorine concentration can be further increased in multiple stages.

  Next, as shown in FIG. 1, fluorine-containing wastewater whose fluorine concentration is concentrated to 1000 mg / L or more by the reverse osmosis device 12 is flowed into the pH adjustment tank 14 through a pipe 21. In the pH adjustment tank 14, the pH value of the fluorine-containing wastewater supplied to the calcium carbonate packed tower 16 is adjusted. The fluorine-containing wastewater sent from the pH adjusting tank 14 to the calcium carbonate packed tower 16 is adjusted so that its pH value is 3 or less. This is because, if the pH value of the fluorine-containing wastewater that passes through the calcium carbonate packed tower 16 is close to the neutral region, the solubility of the calcium carbonate surface becomes low, and the purity of calcium fluoride deteriorates.

  The pH adjustment tank 14 is provided with a pH meter 22 for measuring the pH value of the fluorine-containing wastewater in the pH adjustment tank 14. The pH adjustment tank 14 is connected to the acid storage tank 28 via the pipe 26 and is connected to the alkali storage tank 32 via the pipe 30. The acid storage tank 28 is a storage tank for storing acid as a solution for shifting the pH value of the fluorine-containing wastewater stored in the pH adjustment tank 14 to the acidic side. By driving the pump 34, the acid (for example, hydrochloric acid) stored in the acid storage tank 28 is supplied to the pH adjustment tank 14. The alkali storage tank 32 is a storage tank that stores an alkaline liquid as a solution for shifting the pH value of the fluorine-containing wastewater stored in the pH adjustment tank 14 to the alkaline side. By driving the pump 36, the alkaline liquid (for example, sodium hydroxide) stored in the alkaline storage tank 32 is supplied to the pH adjustment tank 14. A pH meter 22 and pumps 34 and 36 are connected to the control device 24. Based on the pH value of the fluorine-containing wastewater measured by the pH meter 22, the pumps 34 and 36 are driven, and the fluorine-containing wastewater is adjusted so that its pH value is 3 or less. The pH adjusting tank 14 may be provided with stirring means 29 in order to stabilize the pH value.

  A piping 40 is connected to the pH adjustment tank 14 and is connected to the calcium carbonate packed tower 16 through the piping 40. A pump 42 is provided in the pipe 40, and by driving the pump 42, fluorine-containing wastewater whose pH value is adjusted is sent to the calcium carbonate packed tower 16.

The calcium carbonate packed tower 16 is packed with granular calcium carbonate having a particle size of 0.3 to 0.5 mm. When the pH-adjusted fluorine-containing wastewater comes into contact with calcium carbonate, a substitution reaction of fluorine and carbonic acid occurs, and fluorine is removed from the fluorine-containing wastewater. The substitution reaction of fluorine and carbonic acid proceeds from the surface of granular calcium carbonate and transitions to the inside. For this reason, the calcium carbonate is converted into calcium fluoride with the passage of water passing through the calcium carbonate packed tower 16. This reaction is represented by the following chemical formula.
CaCO ₃ + 2HF → CaF ₂ + H ₂ O + CO ₂
In particular, in the present invention, since the fluorine concentration of the fluorine-containing wastewater that comes into contact with calcium carbonate is set to 1000 mg / L or more, the fluorine-containing wastewater can be sufficiently permeated into the calcium carbonate. That is, as the fluorine concentration of the fluorine-containing wastewater is higher, the unreacted calcium carbonate can be reduced, and calcium fluoride with high purity can be obtained.

  As the calcium carbonate packed column 16, an upward flow type is used. That is, the pipe 40 is connected to the lower part of the calcium carbonate packed tower 16, and the treated water pipe 44 is connected to the upper part of the calcium carbonate packed tower 16. Therefore, the waste water that flows in from the lower part of the calcium carbonate packed tower 16 forms an upward flow, is treated by the calcium carbonate inside, and is discharged from the treated water from the upper part of the calcium carbonate packed tower 16.

Further, according to the above reaction scheme, since the hydrogen fluoride (HF) is converted to calcium fluoride (CaF ₂₎ and water _(H 2 O), pH value of the treated water is increased. However, when the reaction with calcium carbonate approaches the end, the pH value of the treated water gradually decreases.

  When the pH value of the treated water is 5 or less, the treatment is terminated as the reaction is completed. Calcium fluoride is taken out from the calcium carbonate packed tower 16 and reused as a raw material for hydrofluoric acid chemicals. In this invention, since the purity of calcium fluoride is 85% or more, it can be effectively used as a raw material for hydrofluoric acid chemicals. Fluorine removal The calcium carbonate in the calcium carbonate packed tower 16 is renewed with new calcium carbonate.

  A circulation line 46 is connected to the calcium carbonate packed tower 16. The circulation line 46 is connected to the upper and lower parts of the calcium carbonate packed tower 16, and the treated water is drawn from the upper part of the calcium carbonate packed tower 16 by driving a pump 48 provided in the circulation line, and the calcium carbonate packed tower 16 The liquid is fed to the lower part of 16.

  The treated water pipe 44 is connected to the coagulation sedimentation device 18, and the treated water treated in the calcium carbonate packed tower 16 is sent to the coagulation sedimentation device 18. The coagulation sedimentation apparatus 18 is an apparatus for coagulating and precipitating turbid components by adding a coagulant such as PAC or a polymer coagulant. A pipe 52 and a pump 54 for feeding the coagulant in 50 to the coagulation sedimentation apparatus 18 are provided. By this coagulating sedimentation apparatus 18, the fluorine contained in the fluorine-containing wastewater is coagulated and removed by precipitation.

  FIG. 3 is a graph showing the relationship between the fluorine concentration of fluorine-containing wastewater and the purity of calcium fluoride when fluorine-containing wastewater having a pH value of 3 is passed through calcium carbonate. As is clear from this graph, it can be understood that the purity of calcium fluoride is 85% or more when the fluorine concentration is 1000 mg / L or more. Here, the purity of calcium fluoride refers to a value calculated using the total weight of calcium carbonate with the surface taken out from the calcium carbonate packed tower converted to calcium fluoride as the denominator and the weight of calcium fluoride as the numerator.

  FIG. 4 is a graph showing the relationship between the pH value of fluorine-containing wastewater and the purity of calcium fluoride when fluorine-containing wastewater having a fluorine concentration of 1050 mg / L is passed through calcium carbonate. As is apparent from this graph, it can be understood that when the pH value is 3 or less, the purity of calcium fluoride is 85% or more.

  In order to obtain calcium fluoride having a purity of 85% or more, it is important that water is passed through calcium carbonate in a state where the fluorine concentration of the fluorine-containing wastewater is 1000 mg / L or more and the pH value is 3 or less. Understandable.

  DESCRIPTION OF SYMBOLS 100 ... Waste water treatment apparatus, 10 ... Raw water tank, 11 ... Pump, 12 ... Reverse osmosis apparatus, 13 ... Reverse osmosis membrane, 14 ... pH adjustment tank, 15 ... Fluorine monitor, 16 ... Calcium carbonate packed tower, 18 ... Collection apparatus 20, 21 and 23 ... piping, 22 ... pH meter, 24 ... control device, 28 ... acid storage tank, 32 ... alkali storage tank, 34, 36, 42 ... pump, 44 ... treated water piping, 46 ... circulation line, 48 ... Pump

Claims (4)

Concentrating fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L with a reverse osmosis membrane device to a fluorine concentration of 1000 mg / L or more;
Managing the concentration of fluorine in the reverse osmosis membrane device by means of a fluorine monitor provided before and after the reverse osmosis membrane device;
Adjusting the pH value of the concentrated fluorine-containing wastewater to 3 or less;
The fluorine- containing wastewater concentrated to a fluorine concentration of 1000 mg / L or more and adjusted in pH is passed through a calcium carbonate packed tower to convert fluorine into calcium fluoride having a purity of 85% or more. Removing fluorine and discharging as treated water;
A method for treating fluorine-containing wastewater.   2. The method for treating fluorine-containing wastewater according to claim 1, wherein the concentration of the fluorine-containing wastewater is performed by a plurality of reverse osmosis devices connected in series. A reverse osmosis membrane device that concentrates fluorine-containing wastewater having a fluorine concentration of less than 1000 mg / L to a fluorine concentration of 1000 mg / L or more;
A fluorine monitor provided before and after the reverse osmosis membrane device in order to manage the concentration of fluorine in the reverse osmosis membrane device;
A pH adjusting tank that is arranged downstream of the reverse osmosis membrane device and adjusts the pH value of the concentrated fluorine-containing wastewater to 3 or less;
The fluorine-containing wastewater is disposed downstream of the pH adjusting tank, is converted to calcium fluoride having a purity of 85% or more from the fluorine- containing wastewater that is concentrated to a fluorine concentration of 1000 mg / L or more and adjusted in pH. A calcium carbonate packed tower that removes fluorine from the water and discharges it as treated water;
An apparatus for treating fluorine-containing wastewater. The fluorine-containing wastewater treatment apparatus according to claim 3 , wherein the reverse osmosis membrane device is constituted by a plurality of reverse osmosis devices connected in series.

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