JP2018065101A - Method and apparatus for treating fluorine-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for concentrated and separated liquid to be treated containing at least one of fluoride ions and silicofluoride ions with a compact and inexpensive facility and to treat fluorine-containing water which promptly enables the generated hydrogen fluoride gas or silicon tetrafluoride gas to render harmless.SOLUTION: A liquid to be treated is supplied to one side of the hydrophobic porous membrane under conditions where the pH of the liquid to be treated is 1 or more and 6 or less to perform membrane distillation with the hydrophobic porous membrane to increase the fluorine component concentration in the liquid to be treated. The evaporated vapor which permeates the other side of the hydrophobic porous membrane and contains the fluorine compound is cooled to obtain condensed water.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and an apparatus for concentrating and treating a liquid to be treated containing at least one of fluoride ions (F ⁻ ) and silicofluoride ions (SiF ₆ ²⁻ ; also called hexafluorosilicate ions).

  In order to collect and reuse aqueous waste liquids containing fluoride ions and silicofluoride ions such as hydrofluoric acid waste liquid and silicic acid waste liquid, or reducing the volume for waste treatment, the waste liquid is concentrated. In Patent Document 1, as a method of efficiently recovering the fluorine component contained in the hydrofluoric acid-containing waste liquid in the form of fluoride ions, the moisture is flash evaporated by a heating evaporator, and the fluorine component is concentrated. It is disclosed that hydrogen fluoride (HF) gas appearing on the gas phase side is absorbed and removed by water or alkali at a later stage.

By the way, when waste liquid containing a fluorine compound is heated and concentrated acidic, hydrogen fluoride gas and silicon tetrafluoride (SiF ₄ ) gas harmful to human bodies are generated. Since the heating evaporator has a large space for gas-liquid separation, it is very dangerous if the evaporator portion of the heating evaporator is filled with these gases and leaks. In addition, since these gases corrode the apparatus, it is necessary to use expensive metal equipment having a corrosion resistance or lining equipment. When an evaporator is manufactured from an inexpensive resin in order to solve the corrosion problem, there is a problem in terms of durability because the structure has a large space as described above. Furthermore, since the blower or vacuum pump for reducing the pressure of the evaporator corrodes when an acidic gas is sucked, it is necessary to remove most of the hydrogen fluoride gas or silicon tetrafluoride gas generated from the evaporator. For this purpose, as described in Patent Document 1, it is necessary not only to simply contact the generated gas with water, but also to contact alkali, or to contact water in multiple stages. It will be a big one.

  As a method of concentrating the fluorine component from the waste liquid containing fluoride ions and silicofluoride ions, there is a method of making the waste liquid alkaline, but it is costly to make the waste liquid alkaline, and sodium fluoride ( This causes a problem that precipitates such as NaF) are generated.

JP 2004-188411 A

  As mentioned above, when concentrating fluorine components in the liquid to be treated containing fluoride ions and silicofluoride ions, when using a heating evaporator, sufficient safety considerations are necessary, and downsizing of equipment is required. There is a problem that is difficult. When the fluorine component is concentrated using an alkali, there are a problem of cost and a precipitate due to the use of the alkali.

  An object of the present invention is to provide a treatment method capable of concentrating and separating a liquid to be treated containing fluoride ions and silicofluoride ions with a small and inexpensive facility and quickly detoxifying the generated hydrogen fluoride gas or silicon tetrafluoride gas. And providing a processing apparatus.

  In the method for treating fluorine-containing water for treating a treatment liquid containing at least one of fluoride ions and silicofluoride ions according to the present invention, the pH of the treatment liquid is 1 or more and 6 or less. The liquid to be treated is supplied to the side and membrane distillation is performed by the hydrophobic porous membrane to increase the concentration of fluorine components in the liquid to be treated, and the vapor vapor that permeates the other side of the hydrophobic porous membrane and contains the fluorine compound is cooled. To obtain condensed water.

  The apparatus for treating fluorine-containing water for treating a liquid to be treated containing at least one of fluoride ions and silicofluoride ions according to the present invention includes a hydrophobic porous membrane and a concentration provided in contact with one surface of the hydrophobic porous membrane. A membrane distillation module having a chamber and a decompression chamber provided in contact with the other surface of the hydrophobic porous membrane, and condensate water is generated by cooling the vapor evaporated through the hydrophobic porous membrane into the decompression chamber A condensing means for depressurizing and a depressurizing means for depressurizing the interior of the decompression chamber, supplying a liquid to be treated having a pH of 1 or more and 6 or less to the concentrating chamber, performing membrane distillation with a hydrophobic porous membrane, and treating the concentrating chamber Increase the concentration of fluorine components in the liquid.

  In the present invention, by using membrane distillation, water in the liquid to be treated is permeated through the hydrophobic porous membrane using water vapor, thereby concentrating the fluorine component in the liquid to be treated. The fluorine component or fluorine compound contained in the liquid to be treated containing at least one of fluoride ion and silicofluoride ion does not pass through the hydrophobic porous membrane by membrane distillation as long as it is dissociated into ions. It remains on the supply side of the porous porous membrane. In addition, hydrofluoric acid is classified as a weak acid, so depending on the liquidity, hydrogen fluoride molecules exist in the liquid to be treated. However, hydrogen fluoride molecules are strongly polar molecules, and compared with water molecules. However, it is difficult to pass through the hydrophobic porous membrane. Therefore, the use of the hydrophobic porous membrane can efficiently concentrate the fluorine component in the liquid to be treated.

  However, hydrogen fluoride molecules are not completely impermeable to the hydrophobic porous membrane, and some of it penetrates the hydrophobic porous membrane together with water vapor. Since the permeated hydrogen fluoride can cause corrosion in a decompression means such as a blower or a vacuum pump, the present invention permeates the other side of the hydrophobic porous membrane in order to reduce the risk of corrosion. The vaporized vapor containing the fluorine compound is cooled to obtain condensed water. When condensate is obtained by cooling the evaporated vapor, it is preferable that the hydrogen fluoride concentration in the gas part after obtaining the condensate is 10 ppm by volume or less, so that 1 ppm by volume or less. More preferably.

  In order to sufficiently generate condensed water by cooling the evaporating vapor, the amount of heat necessary for condensation is sufficiently transferred by lowering the temperature of the refrigerant used for cooling or reducing the thickness of the heat transfer surface. It is important to determine the cooling conditions so as to heat. Although cold water is generally used as the refrigerant, the lower the temperature, the better. The temperature is preferably 25 ° C. or lower. Any cooling method may be used as long as a necessary amount of heat can be transmitted, and a general method such as a heat exchanger can be used. However, in order to reduce the concern about corrosion due to hydrogen fluoride or the like, it is preferable to perform heat exchange using a non-corrosive material (such as a resin heat transfer surface or a thin film). In general, non-corrosive materials have a lower heat transfer coefficient than metals, but the necessary amount of heat can be transferred by devising measures such as thinning the heat transfer surface and increasing the heat transfer area.

  In the present invention, the pH of the liquid to be treated is 1 or more and 6 or less, preferably 1 or more and 4 or less. If the pH of the liquid to be treated exceeds 6, the processing conditions in the conventional processing method using alkali will be approached, and the same problem as in the conventional processing method will occur. In particular, the deposits can cause clogging of the hydrophobic porous membrane. On the other hand, when the pH is lower than 1 and a strong acidic condition is reached, a large amount of hydrogen fluoride molecules permeate the hydrophobic porous membrane, so that the fluorine component on the supply side of the hydrophobic porous membrane is sufficiently concentrated. In addition to this, the burden required for the treatment of hydrogen fluoride that has permeated through the hydrophobic porous membrane becomes excessive. Considering that the conventional heat concentration method has a big problem in the treatment when the pH is 4 or less, the present invention achieves a remarkable effect when the pH of the liquid to be treated is 1 or more and 4 or less.

  As the hydrophobic porous membrane used for membrane distillation, for example, a fluororesin film can be used, and a polytetrafluoroethylene (PTFE) membrane or a polyvinylidene fluoride (PVDF) membrane can be preferably used. The hydrophobic porous membrane is used by being incorporated into a membrane distillation module, for example. The membrane distillation module is composed of a hydrophobic porous membrane, a concentration chamber provided in contact with one surface of the hydrophobic porous membrane, and a decompression chamber provided in contact with the other surface of the hydrophobic porous membrane, A liquid to be treated containing at least one of fluoride ions and silicofluoride ions is supplied to the concentration chamber. In the membrane distillation module, in order to reduce the risk of corrosion, it is preferable that the wall surface in contact with the liquid to be treated in the concentration chamber and the wall surface in contact with the vaporized vapor in the decompression chamber are formed of resin. Further, the evaporated vapor may be cooled to generate condensed water by cooling the wall surface of the decompression chamber itself.

  In the present invention, the liquid is concentrated using a membrane distillation apparatus. The use of membrane distillation for concentration of liquid is described in, for example, JP-A-2006-68006, but the use of membrane distillation for concentration of a liquid to be treated containing a fluorine compound has not been studied, and hydrophobic There is no description of the conditions of the means for cooling the vapor that has passed through the porous porous membrane.

  According to the present invention, the fluorine component in the liquid to be treated containing fluoride ions and silicofluoride ions can be concentrated and separated by an inexpensive facility, the space on the evaporation side is reduced, and the generated gas such as hydrogen fluoride is reduced. Since it can be quickly dissolved in condensed water and recovered, hydrogen fluoride gas can be easily rendered harmless. Therefore, the fluorine-containing water treatment method and apparatus of the present invention are superior in safety and equipment cost compared to other methods.

It is a figure which shows the structure of the processing apparatus of one Embodiment of this invention. It is a figure which shows the structure of the processing apparatus of another embodiment of this invention. It is a figure which shows the structure of the processing apparatus used in the Example.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a processing apparatus according to an embodiment of the present invention.

  The processing apparatus shown in FIG. 1 uses an aqueous waste liquid containing fluoride ions and silicofluoride ions as a liquid to be processed, and concentrates a fluorine component in the liquid to be processed. The pH of the liquid to be treated is 1 or more and 6 or less. The processing apparatus includes a membrane distillation module 10 for performing membrane distillation. The membrane distillation module 10 includes a hydrophobic porous membrane 11 and a concentration chamber 12 provided in contact with one surface of the hydrophobic porous membrane 11. And a decompression chamber 13 provided in contact with the other surface of the hydrophobic porous membrane 11. A storage tank 20 for temporarily storing the liquid to be processed is provided, the storage tank 20 and the concentration chamber 12 of the membrane distillation module 10 are connected by a pipe 21, and the liquid to be processed is fed to the pipe 21 to the concentration chamber 12. A supply pump 22 is provided. The liquid to be treated discharged from various processes is supplied to the storage tank 20 through the pipe 23. A circulation pipe 24 is connected to the storage tank 20, and a pump 25 and a heater 26 are provided in the circulation pipe 24 so that the liquid to be treated in the storage tank 20 can be heated to a temperature suitable for membrane distillation.

  A pipe 31 is connected to the decompression chamber 13, and a heat exchanger 32 is provided in the middle of the pipe 31. The heat exchanger 32 cools the evaporated vapor that has permeated into the decompression chamber 13 through the hydrophobic porous membrane 11 with cooling water, and the evaporated vapor is cooled by the heat exchanger 32 to generate condensed water. The heat exchanger 32 functions as a condensing means. Condensed water is accumulated in the condensed water tank 33 through the pipe 31. Further, a decompression blower 34 is connected to the condensed water tank 33, and by operating the decompression blower 34, the interior of the decompression chamber 13 is decompressed to a predetermined pressure via the condensed water tank 33 and the piping 31. It has become. The storage tank 20 is also connected to the inlet side of the decompression blower 34 by a pipe 50 having a pressure regulating valve 51. By depressurizing the inside of the storage tank 20, the concentration chamber 12 of the membrane distillation module 10 is also depressurized, so that the boiling point of the liquid to be treated can be lowered and membrane distillation can be performed at a lower temperature.

  In the membrane distillation module 10, the hydrophobic porous membrane 11 is a porous membrane made of, for example, a fluororesin, and a polytetrafluoroethylene (PTFE) membrane or a polyvinylidene fluoride (PVDF) membrane is preferably used. In order to prevent corrosion of the membrane distillation module 10, the membrane module 10 is made of, for example, a resin or a corrosion resistant alloy. For example, the wall surface in contact with the liquid to be treated in the concentration chamber 12 and the wall surface in contact with the evaporated vapor in the decompression chamber 13 are formed of a resin having resistance to hydrogen fluoride or the like.

  Next, the concentration process of the to-be-processed water which is a hydrofluoric acid waste liquid etc. using the processing apparatus shown in FIG. 1 is demonstrated. The decompression blower 34 is driven to decompress the interior of the decompression chamber 13 to a predetermined pressure, and this decompressed state is maintained. After the pump 25 and the heater 26 are driven to heat the water to be treated in the storage tank 10 to a predetermined temperature (for example, 60 ° C.), the supply pump 22 is driven to supply the water to be treated to the concentration chamber 12. As a result, membrane distillation through the hydrophobic porous membrane 11 occurs in the membrane distillation module 10, and moisture in the liquid to be treated permeates into the decompression chamber 13 in the form of water vapor as shown by an arrow in the wavy line in the figure. Since the fluorine component in the liquid to be treated remains in the concentration chamber 12 as it is, the concentration of the fluorine component in the liquid to be treated in the concentration chamber 12 increases and the fluorine component is concentrated. The liquid to be treated with the increased fluorine component concentration is discharged from the concentration chamber 12 as a concentrated liquid. Note that the concentration of the fluorine component can be further increased by returning the concentrated water to the storage tank 20 and circulating it.

  The evaporated vapor that has passed through the hydrophobic porous membrane 11 and reached the decompression chamber 13 is mainly composed of water vapor, but contains some molecular fluorine compounds such as hydrogen fluoride and tetrafluorosilane, which are corrosive. In addition to being a cause, it is not preferable to release it into the environment as it is. Therefore, the vaporized vapor is cooled by the heat exchanger 32 to generate condensed water, and hydrogen fluoride or tetrafluorosilane is dissolved in the condensed water. Since the generated condensed water accumulates in the condensed water tank 33, an appropriate drainage treatment may be performed on the condensed water. At this time, it is preferable to set the cooling conditions in the heat exchanger 32 so that the hydrogen fluoride concentration in the gas portion after obtaining the condensed water, that is, the exhaust of the decompression blower 34 is 10 ppm by volume or less. For example, the temperature of the cooling water supplied to the heat exchanger 32 is set to 25 ° C. or lower.

  In the processing apparatus shown in FIG. 1, although the vacuum blower 34 is protected from a fluorine-containing gas such as hydrogen fluoride, the heat exchanger 32 comes into contact with hydrogen fluoride or the like. Therefore, as shown in FIG. 2, instead of providing a heat exchanger in the pipe extending from the decompression chamber 13, a part of the wall surface of the decompression chamber 13 is used as a cooling surface so that condensed water is generated on this cooling surface. You can also The processing apparatus shown in FIG. 2 is not provided with the piping 31, the heat exchanger 32, and the condensed water tank 33 as compared with the processing apparatus of FIG. 1, and instead cools a part of the wall surface of the decompression chamber 13. A cooling module 40 is provided. The decompression blower 34 is directly connected to the decompression chamber 13. The cooling module 40 is made of a material having a high thermal conductivity, and cooling water is circulated therein. A resin film having corrosion resistance is stretched on the surface of the cooling module 40, and this resin film is a part of the wall surface of the decompression chamber 13. That is, one side of the resin film faces the inside of the decompression chamber 13 and becomes a cooling surface, and is cooled by the cooling module 40 on the other side of the resin film. The evaporated vapor in the decompression chamber 13 is condensed by touching the cooling surface cooled by the cooling module 40 to become condensed water. Since the condensed water accumulates at the bottom of the decompression chamber 13, when the amount of the accumulated condensed water exceeds a certain value, the operation of the membrane distillation module 10 is stopped and the condensed water is discharged from the decompression chamber 13.

  Next, the present invention will be described in more detail with reference to examples. In the example, the processing apparatus shown in FIG. 3 was used. The processing apparatus shown in FIG. 3 is the same as that shown in FIG. 1, except that the concentrated liquid discharged from the concentration chamber 12 is circulated as it is to the storage tank 20 as shown in FIG. Is different. A regulating valve 27 is provided between the piping 21 and the concentration chamber 12 of the supply pump 22, and a return piping 28 is provided from the front of the regulating valve 27 to the storage tank 20. The flow rate of the liquid to be processed into the concentration chamber 12 can be controlled by adjusting the opening of the adjustment valve 27. The liquid to be processed is stored in advance in the storage tank. In order to measure the concentration of hydrogen fluoride in the evaporated vapor before condensation, a sampling pipe 36 is branched from the front of the heat exchanger 32 in the pipe 31, and the pipe 36 is provided with a sampling valve.

In the membrane distillation module 10, a polytetrafluoroethylene membrane having a diameter of 75 mm and a membrane area of 44 cm ² was used as the hydrophobic porous membrane 11. This membrane is a porous membrane having a nominal pore diameter of 0.2 μm. The portion of the membrane distillation module 10 excluding the hydrophobic porous membrane 11 was made of polyethylene (PE). As the heat exchanger 32, BHE-005 (heat transfer area: 0.135 m < ² >) made from a corrosion resistant alloy SUS316L manufactured by Nisaka Manufacturing Co., Ltd. was used. The heat exchanger 32 was supplied with 25 ° C. water as cooling water.

As the liquid to be treated, two types of wastewaters of the supply liquid 1 and the supply liquid 2 shown in Table 1 were used, and an experiment was conducted for each. The supply liquid 1 is the waste water from the electrolytic refining process of lead, and contains a large amount of lead hexafluorosilicate (PbSiF ₆ ). The supply liquid 2 is hydrofluoric acid waste water and contains hydrogen fluoride. In Table 1, “fluorine compound” indicates the concentration based on the mass of only fluorine atoms for F ⁻ ions and SiF ₆ ²⁻ ions. “Ionic silica” refers to the concentration based on the mass of only the silicon atoms for the SiF ₆ ²⁻ ions.

The liquid to be treated was heated to 60 ° C. by the heater 26 and supplied to the membrane distillation module 10 at a flow rate of 1 L / min. The suction pressure by the decompression blower 34 was -95 kPa. At this time, the permeation flux in the hydrophobic porous membrane 10 was about 60 to 110 kg / m ² / hour.

  Under this condition, the operation of the treatment apparatus is continued, and at one hour after the start of operation, the concentration of hydrogen fluoride in the gas collected through the sampling valve 37, that is, the gas before cooling from the decompression chamber 13, and the decompression The gas at the outlet of the blower 34, that is, the hydrogen fluoride concentration in the gas that has been cooled after exiting the decompression chamber 13 and produced condensed water (at this time, the contribution of the gas from the storage tank 20 can be ignored) is detected. Measurement was performed using a tube. The results are shown in Table 2.

  As shown in Table 2, even when the concentration of hydrogen fluoride in the vaporized vapor in the decompression chamber 13 exceeds 10 ppm, the vaporized vapor is cooled to generate condensed water, thereby remaining after the condensed water is generated. It was found that the hydrogen fluoride concentration in the gas was less than 1 ppm, and sufficient detoxification could be achieved quickly.

DESCRIPTION OF SYMBOLS 10 Membrane distillation module 11 Hydrophobic porous membrane 12 Concentration chamber 13 Decompression chamber 20 Storage tank 22 Supply pump 32 Heat exchanger 33 Condensed water tank 34 Decompression blower 40 Cooling module

Claims (8)

A method for treating fluorine-containing water for treating a liquid to be treated containing at least one of fluoride ions and silicofluoride ions,
Fluorine component in the liquid to be treated by supplying the liquid to be treated to one side of the hydrophobic porous membrane and performing film distillation with the hydrophobic porous membrane under the condition that the pH of the liquid to be treated is 1 or more and 6 or less Increase the concentration,
A method for treating fluorine-containing water, wherein condensed water is obtained by cooling evaporating vapor that permeates the other side of the hydrophobic porous membrane and contains a fluorine compound.   The method for treating fluorine-containing water according to claim 1, wherein the vaporized vapor is cooled so that the hydrogen fluoride concentration in the gas portion after obtaining the condensed water is 10 ppm by volume or less.   The method for treating fluorine-containing water according to claim 1 or 2, wherein the hydrophobic porous film is a polytetrafluoroethylene film or a polyvinylidene fluoride film. A treatment apparatus for fluorine-containing water that treats a liquid to be treated containing at least one of fluoride ions and silicofluoride ions,
A membrane distillation module having a hydrophobic porous membrane, a concentration chamber provided in contact with one surface of the hydrophobic porous membrane, and a decompression chamber provided in contact with the other surface of the hydrophobic porous membrane; ,
A condensing means for cooling the evaporated vapor that has permeated through the hydrophobic porous membrane into the decompression chamber to generate condensed water;
Decompression means for decompressing the decompression chamber;
With
supplying the liquid to be treated having a pH of 1 to 6 to the concentration chamber, performing membrane distillation with the hydrophobic porous membrane, and increasing a fluorine component concentration in the liquid to be treated in the concentration chamber; Processing equipment.   The apparatus for treating fluorine-containing water according to claim 4, wherein the decompression means decompresses the decompression chamber via the condensation means.   The apparatus for treating fluorine-containing water according to claim 4, wherein the condensing unit is configured by a cooling unit that cools a wall surface of the decompression chamber.   The treatment of fluorine-containing water according to any one of claims 4 to 6, wherein a wall surface in contact with the liquid to be treated in the concentration chamber and a wall surface in contact with the vaporized vapor in the decompression chamber are formed of resin. apparatus.   The treatment apparatus for fluorine-containing water according to any one of claims 4 to 7, wherein the hydrophobic porous film is a polytetrafluoroethylene film or a polyvinylidene fluoride film.

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