JP6797632B2 - Fluorine-containing water treatment method and treatment equipment - Google Patents

Description

The present invention is a fluoride ion (F ^-) and silicofluoride ions; relates to a method and apparatus for processing and concentrating the treated liquid containing at least one of (SiF ₆ ^2-also called hexafluorosilicate ions).

In order to recover and reuse the aqueous waste liquid containing fluoride ions such as hydrofluoric acid waste liquid and siliceous hydrofluoric acid waste liquid and siliceous fluoride ion, or to reduce the volume for disposal treatment, the waste liquid is concentrated. In Patent Document 1, as a method for efficiently recovering the fluorine component contained in the hydrofluoric acid-containing waste liquid in the form of fluoride ions, water is flash-evaporated by a heated evaporative can to concentrate the fluorine component, and the fluorine component is concentrated with the water. It is disclosed that the hydrogen fluoride (HF) gas appearing on the gas phase side is absorbed by water or an alkali in the subsequent stage and removed.

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

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

Japanese Unexamined Patent Publication No. 2004-188411

As described above, when concentrating the fluorine component in the liquid to be treated containing fluoride ions and silica fluoride ions, sufficient consideration must be given to safety when using a heated evaporation can, and the equipment must be downsized. There is a problem that it is difficult. When the fluorine component is concentrated using alkali, there are problems of cost and precipitation due to the use of alkali.

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

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

The fluorine-containing water treatment apparatus for treating the liquid to be treated containing at least one of the fluoride ion and the siliceous fluoride ion of the present invention is a concentration provided in contact with one surface of the hydrophobic porous membrane and 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 the vaporized vapor permeated into the decompression chamber through the hydrophobic porous membrane are cooled to generate condensed water. A condensing means for depressurizing and a depressurizing means for depressurizing the decompression chamber are provided. Increases the concentration of fluorine components in the liquid.

In the present invention, by using membrane distillation, the water content of the liquid to be treated is used as water vapor to permeate the hydrophobic porous membrane, 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 ions and siliceous fluoride ions does not pass through the hydrophobic porous membrane by membrane distillation as long as it is dissociated into ions, and is hydrophobic. It will remain on the supply side of the porous membrane. In addition, since hydrofluoric acid is classified as a weak acid, hydrogen fluoride molecules may be present in the liquid to be treated depending on the liquid property, but hydrogen fluoride molecules are strong polar molecules and are compared with water molecules. However, it does not easily pass through the hydrophobic porous film. Therefore, by using the hydrophobic porous membrane, the fluorine component in the liquid to be treated can be efficiently concentrated.

However, hydrogen fluoride molecules are not completely opaque to the hydrophobic porous membrane, and some of them permeate the hydrophobic porous membrane together with water vapor. Since the permeated hydrogen fluoride can cause corrosion in decompression means such as a blower or a vacuum pump, in the present invention, it permeates to the other side of the hydrophobic porous film in order to reduce the risk of corrosion. Moreover, the evaporated steam containing a fluorine compound is cooled to obtain condensed water. When the evaporated steam is cooled to obtain condensed water, it is preferable that the hydrogen fluoride concentration in the gas portion after obtaining the condensed water is 10% by volume ppm or less, and preferably 1 volume ppm or less. It is more preferable to do so.

In order to sufficiently generate condensed water by cooling the evaporated vapor, the amount of heat required for condensation is sufficiently transferred by lowering the temperature of the refrigerant used for cooling and reducing the thickness of the heat transfer surface. It is important to determine the cooling conditions to heat. Cold water is generally used as the refrigerant, but the lower the temperature, the better, and the temperature is preferably 25 ° C. or lower. As the cooling method, any method that can transfer the required amount of heat can be used, 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). Generally, non-corrosive materials have a lower heat transfer coefficient than metals, but the required amount of heat can be transferred by taking measures such as making the heat transfer surface thinner 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 treatment conditions of the conventional treatment method using alkali will be approached, and the same problems as those of the conventional treatment method will occur. In particular, the precipitates can cause clogging of the hydrophobic porous membrane. On the other hand, when the pH is lower than 1 and the condition is strongly acidic, a large amount of hydrogen fluoride molecules permeate the hydrophobic porous membrane, and 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 the hydrophobic porous membrane becomes excessive. Considering that the conventional method by heat concentration 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, one made of a fluororesin can be used, and a polytetrafluoroethylene (PTFE) membrane or a polyvinylidene fluoride (PVDF) membrane can be preferably used. The hydrophobic porous membrane is used, for example, by being incorporated in a membrane distillation module. 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. The liquid to be treated containing at least one of fluoride ions and silica fluoride ions is supplied to the concentration chamber. In the membrane distillation module, in order to reduce the risk of corrosion, it is preferable to form the wall surface in contact with the liquid to be treated in the concentration chamber and the wall surface in contact with the evaporated vapor in the decompression chamber with a resin. Further, the wall surface of the decompression chamber itself may be cooled to cool the evaporated steam to generate condensed water.

In the present invention, the liquid is concentrated using a membrane distillation apparatus. The use of membrane distillation for concentrating a liquid is described in, for example, Japanese Patent Application Laid-Open No. 2016-68006, but the use of membrane distillation for concentrating a liquid to be treated containing a fluorine compound has not been studied, and is hydrophobic. No description is made of the conditions for the means for cooling the vapor that has passed through the porous membrane.

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

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 an 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 treatment apparatus shown in FIG. 1 uses an aqueous waste liquid containing fluoride ions and siliceous fluoride ions as a liquid to be treated, and concentrates a fluorine component in the liquid to be treated. 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, and the membrane distillation module 10 is provided in contact with one surface of the hydrophobic porous membrane 11 and 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 treated 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 pipe 21 supplies the liquid to be treated to the concentration chamber 12. A supply pump 22 for this purpose is provided. The liquid to be treated discharged from various processes is supplied to the storage tank 20 via 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 steam that has permeated into the decompression chamber 13 through the hydrophobic porous film 11 with cooling water, and the evaporated steam is cooled by the heat exchanger 32 to generate condensed water. The heat exchanger 32 functions as a condensing means. The condensed water passes through the pipe 31 and collects in the condensed water tank 33. Further, a decompression blower 34 is connected to the condensed water tank 33, and by operating the decompression blower 34, the inside of the decompression chamber 13 is depressurized to a predetermined pressure via the condensing water tank 33 and the pipe 31. It has become. Further, the storage tank 20 is also connected to the inlet side of the pressure reducing blower 34 by a pipe 50 provided with a pressure adjusting valve 51. By reducing the pressure in the storage tank 20, the concentration chamber 12 of the membrane distillation module 10 is also reduced in pressure, so that the boiling point of the liquid to be treated can be lowered and the membrane distillation can be performed at a lower temperature.

In the membrane distillation module 10, the hydrophobic porous membrane 11 is, for example, a porous membrane made of a fluororesin, and a polytetrafluoroethylene (PTFE) membrane or a polyvinylidene fluoride (PVDF) membrane is preferably used. Further, 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, a concentration treatment of water to be treated, such as a hydrofluoric acid waste liquid, using the treatment apparatus shown in FIG. 1 will be described. The pressure reducing blower 34 is driven to reduce the pressure inside the pressure reducing chamber 13 to a predetermined pressure, and this reduced pressure state is maintained. After driving the pump 25 and the heater 26 to heat the water to be treated in the storage tank 20 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 occurs in the membrane distillation module 10 via the hydrophobic porous membrane 11, and the water content in the liquid to be treated permeates into the decompression chamber 13 in the form of water vapor as shown by the wavy arrow 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, which means that the fluorine component is concentrated. The liquid to be treated having an increased fluorine component concentration is discharged from the concentration chamber 12 as a concentrated liquid. By returning the concentrated water to the storage tank 20 and circulating it, the fluorine component concentration can be further increased.

The evaporated vapor that has passed through the hydrophobic porous film 11 and reached the decompression chamber 13 is mainly composed of water vapor, but contains some molecular fluorine compounds such as hydrogen fluoride and silane tetrafluoride, which are corrosive. It is not preferable to release it into the environment as it is as it causes it. Therefore, the heat exchanger 32 cools the evaporated steam to generate condensed water so that hydrogen fluoride and silane tetrafluoride are dissolved in the condensed water. Since the generated condensed water is collected in the condensed water tank 33, appropriate wastewater 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 volume ppm 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, the decompression blower 34 is protected from a fluorine-containing gas such as hydrogen fluoride, but 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 to generate condensed water on this cooling surface. You can also do it. Compared to the processing device of FIG. 1, the processing device shown in FIG. 2 is not provided with the pipe 31, the heat exchanger 32, and the condensed water tank 33, 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 high thermal conductivity, and cooling water circulates inside the cooling module 40. 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 is a cooling surface facing the inside of the decompression chamber 13, and is cooled by the cooling module 40 on the other side of the resin film. The evaporated steam in the decompression chamber 13 touches the cooling surface cooled by the cooling module 40 and condenses into condensed water. Since the condensed water collects at the bottom of the decompression chamber 13, when the amount of the accumulated water exceeds a certain value, the operation of the membrane distillation module 10 may be stopped and the condensed water may be discharged from the decompression chamber 13.

Next, the present invention will be described in more detail by way of examples. In the embodiment, 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, but is shown in FIG. 1 in that the concentrated liquid discharged from the concentration chamber 12 is circulated to the storage tank 20 as it is. Is different. In the pipe 21, a regulating valve 27 is provided between the supply pump 22 and the concentrating chamber 12, and a return pipe 28 that returns to the storage tank 20 from the front of the adjusting valve 27 is provided. By adjusting the opening degree of the adjusting valve 27, the flow rate of the liquid to be treated to the concentrating chamber 12 can be controlled. The liquid to be treated is stored in advance in the storage tank. Further, in order to measure the hydrogen fluoride concentration in the evaporated vapor before condensing, the sampling pipe 36 branches 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 size 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 ) manufactured by Hisaka Works, which is made of a corrosion-resistant alloy SUS316L, was used. Water at 25 ° C. was supplied to the heat exchanger 32 as cooling water.

Two types of wastewater, supply liquid 1 and supply liquid 2 shown in Table 1, were used as the liquid to be treated, and experiments were conducted for each of them. The supply liquid 1 is waste water from the lead electrorefining step, and contains a large amount of lead hexafluorosilicate (PbSiF ₆ ). The supply liquid 2 is hydrofluoric acid wastewater and contains hydrogen fluoride. In Table 1, "fluorine compound" indicates the mass-based concentration of only fluorine atoms for F ^- ion and SiF ₆ ^2- ion. “Ionic silica” refers to the mass-based concentration of only silicon atoms for 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 set to −95 kPa. At this time, the permeation flux in the hydrophobic porous membrane 10 was about 60 to 110 kg / m ² / hour.

The operation of the processing apparatus is continued under these conditions, and at 1 hour after the start of operation, the hydrogen fluoride concentration in the gas collected through the sampling valve 37, that is, the gas before cooling from the decompression chamber 13 and the decompression Gas detection of the hydrogen fluoride concentration in the gas at the outlet of the blower 34, that is, the gas after exiting the decompression chamber 13 and being cooled to generate condensed water (at this time, the contribution of the gas from the storage tank 20 can be ignored). It was measured using a tube. The results are shown in Table 2.

As shown in Table 2, even when the hydrogen fluoride concentration in the evaporated steam in the decompression chamber 13 exceeds 10 ppm, the remaining after the condensed water is generated by cooling the evaporated steam to generate condensed water. It was found that the hydrogen fluoride concentration in the vapor can be less than 1 ppm, and sufficient detoxification can be quickly achieved.

10 Membrane Distillation Module 11 Hydrophobic Porous Membrane 12 Concentration Room 13 Decompression Room 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 siliceous fluoride ions.
Under the condition that the pH of the liquid to be treated is 1 or more and 6 or less, the liquid to be treated is supplied to one side of the hydrophobic porous membrane, membrane distillation is performed by the hydrophobic porous membrane, and a fluorine component in the liquid to be treated is performed. Increase the concentration,
As the hydrogen fluoride concentration in the gas portion of the after obtaining the condensed water becomes less than 10 vol ppm, the condensed water to cool the evaporated vapor containing transmitted on the other side of the hydrophobic porous membrane and a fluorine compound A method for treating fluorine-containing water. The method for treating fluorine-containing water according to claim 1, wherein the evaporated steam is cooled so that the hydrogen fluoride concentration in the gas portion after obtaining the condensed water is 1 volume ppm or less. The method for treating fluorine-containing water according to claim 1 or 2, wherein the hydrophobic porous membrane is a polytetrafluoroethylene membrane or a polyvinylidene fluoride membrane. A fluorine-containing water treatment device that treats a liquid to be treated containing at least one of fluoride ions and silica fluoride 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 that cools the evaporated vapor that has permeated into the decompression chamber through the hydrophobic porous membrane to generate condensed water.
A decompression means for decompressing the decompression chamber and
With
The liquid to be treated having a pH of 1 or more and 6 or less is supplied to the concentration chamber and membrane distillation is performed by the hydrophobic porous membrane to increase the concentration of fluorine components in the liquid to be treated in the concentration chamber .
The condensing means is such that said concentration of hydrogen fluoride in the gas portion of the after obtaining the condensed water is less than 10 volume ppm, you cool the evaporative vapor processing apparatus of the fluorine-containing water. The device for treating fluorine-containing water according to claim 4, wherein the decompression means decompresses the decompression chamber via the condensing means. The fluorine-containing water treatment apparatus according to claim 4, wherein the condensing means is composed of cooling means for cooling the wall surface of the decompression chamber. The treatment of fluorine-containing water according to any one of claims 4 to 6, wherein 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. apparatus. The fluorine-containing water treatment apparatus according to any one of claims 4 to 7, wherein the hydrophobic porous membrane is a polytetrafluoroethylene membrane or a polyvinylidene fluoride membrane.

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