TWI588097B - Method for treating fluoride containing waste water - Google Patents

Description

Fluorine-containing wastewater treatment method

The present invention relates to a wastewater treatment method, and more particularly to a fluorine-containing wastewater treatment method.

With the improvement of living standards and industrialization, under the rapid development of the consumer electronics industry, high-tech industry, semiconductor industry and electronics industry, Taiwan's economic development has also been relatively enhanced, accompanied by environmental pollution.

Among the above industries, fluorine-based wastewater is one of the major wastewater discharges in the semiconductor industry. The main sources of waste water are, for example, waste water produced by using hydrofluoric acid during wafer cleaning and wet etching, or waste water produced by recycling recycled resin in a water system, or a local exhaust gas treatment facility at the machine end (Local Scrubber) and wastewater discharged from the Center Scrubber. In the Basel Convention, fluorine-containing wastewater and sludge are classified as hazardous waste and must be disposed of properly in the country and must not be transported out of the country. It can be seen that the fluorine-containing wastewater treatment method and technology research department is an important issue in the field of environmental protection.

The invention provides a fluorine-containing wastewater treatment method, which can obtain a high-purity cryolite crystal body, thereby improving the recovery value.

The invention provides a method for treating fluorine-containing wastewater, comprising the following steps. A water inflow step is performed to a mixing tank, wherein a water to be treated enters the mixing tank in a batch operation, and the water to be treated in the mixing tank contains a high concentration fluorine-containing wastewater and a low concentration fluorine-containing wastewater. The fluorine ion detecting unit controls the fluoride ion concentration of the water to be treated in the mixing tank, wherein when the fluoride ion concentration of the water to be treated reaches a predetermined concentration, the high-concentration fluorine-containing wastewater is stopped from entering the mixing tank. When the water level of the water to be treated reaches a predetermined liquid level, the low-concentration fluorine-containing wastewater is stopped from entering the mixing tank. The water to be treated and an aluminum salt solution are introduced into a fluidized bed crystallization tank and mixed to obtain a cryolite crystal.

In one embodiment of the invention, the ratio of aluminum to fluorine in the fluidized bed crystallization tank is between 0.8:6 and 1.2:6.

In an embodiment of the invention, the fluoride ion detecting unit comprises a fluoride ion selective electrode and a fluorine ion detecting groove. In the step of controlling the fluoride ion concentration of the water to be treated in the mixing tank by the fluorine ion detecting unit, the following steps are further included. Introduce high concentration fluorine-containing wastewater and an ionic liquid to the fluoride ion detection tank. Next, the fluorine ion selective electrode is used to detect the fluoride ion concentration in the fluoride ion detecting bath.

In an embodiment of the present invention, in the step of introducing the water to be treated and the aluminum salt solution to the fluidized bed crystallization tank and mixing to obtain the cryolite crystal, the following steps are further included. A separation step is performed to obtain a low concentration fluorine-containing wastewater and a sludge. Next, a reflux pump is controlled by the fluoride ion detecting unit to introduce the low concentration fluorine-containing wastewater into the mixing tank.

In an embodiment of the present invention, in the step of introducing the water to be treated and the aluminum salt solution to the fluidized bed crystallization tank and mixing to obtain the cryolite crystal, the following steps are further included. A pH controller is used to control the pH in the fluidized bed crystallization tank to a predetermined pH. Then, when the flow When the pH in the crystallization tank of the bed is not within a predetermined pH range, an alkali solution is introduced to bring the pH in the fluidized bed crystallization tank to a predetermined pH.

In one embodiment of the invention, the predetermined pH range is between 5.0 and 5.5.

Based on the above, the fluorine-containing wastewater treatment method of the present invention allows the water to be treated to enter the mixing tank in a batch type rather than a continuous manner, thereby avoiding the subsequent crystallization failure due to excessive change of the influent water quality. Further, the fluoride ion detecting unit controls the fluorine ion concentration within a certain range to maintain the cryolite crystal in a high-purity cryolite crystal.

The above described features and advantages of the present invention will be more apparent from the following description.

20‧‧‧Regulation tank

22‧‧‧Level gauge

24‧‧‧ pump

30‧‧‧Fluoride detection unit

32‧‧‧Fluoride ion selective electrode

34‧‧‧Fluoride detection tank

36‧‧‧Reflow pump

40‧‧‧ Fluidized bed crystallization tank

60‧‧‧pH controller

62‧‧‧pH electrode

64‧‧‧Separate pump

80‧‧‧Sedimentation tank

90‧‧‧Three-phase separator

AL‧‧‧Aluminium salt solution

ALF‧‧‧Crylite crystal

L.1‧‧‧Predetermined liquid level

ND‧‧‧ lye

S100‧‧‧Fluorine wastewater treatment method

S110~S150‧‧‧Steps

S122~S124‧‧‧Steps

S132~S134‧‧‧Steps

SF‧‧‧ ionic liquid

SL‧‧‧Sludge

WA‧‧‧ water to be treated

WF‧‧‧high concentration fluorine-containing wastewater

WR‧‧‧Low concentration fluorine-containing wastewater

Fig. 1 is a schematic flow chart showing the method for treating fluorine-containing wastewater according to the present invention.

Fig. 2 is a schematic view showing the system of the fluorine-containing wastewater treatment method of the present invention.

Fig. 3 is a schematic flow chart showing the detection mode of the fluoride ion detecting unit of Fig. 1.

Figure 4 is a schematic flow chart for controlling the pH in the fluidized bed crystallization tank.

Fig. 5 is a schematic flow chart showing a further flow of the fluorine-containing wastewater treatment method of Fig. 1.

The technical means and efficacy of the present invention for achieving the object will be described below with reference to the accompanying drawings, and the embodiments listed in the following drawings are only for the purpose of explanation, and are to be understood by the reviewing committee, but the technical means of the present invention are not Limited to the listed figures.

Please refer to FIG. 1 and FIG. 2 , wherein FIG. 1 is the fluorine containing the present invention. Schematic diagram of the process of wastewater treatment. Fig. 2 is a schematic view showing the system of the fluorine-containing wastewater treatment method of the present invention. The fluorine-containing wastewater treatment method S100 of the present embodiment forms an ice crystal (Cryolite, Na3AlF6) crystal by adding an aluminum salt solution and fluoride ions to achieve the effect of treating the fluorine-containing wastewater and the waste liquid. The fluorine-containing wastewater treatment method S100 includes at least the following steps S110 to S130.

In step S110, the water inflow step is performed to the mixing tank 20, wherein the water inflow step is to enter a water to be treated WA into the mixing tank 20 in a batch operation, and the water to be treated WA in the mixing tank 20 contains a high concentration. Fluorine-containing wastewater WF and a low concentration fluorine-containing wastewater WR. It should be noted that the source of the low-concentration fluorine-containing wastewater WR is, for example, the recovered treated water obtained by a subsequent process.

Next, in step S120, the fluorine ion detecting unit 30 controls the fluoride ion concentration of the water to be treated WA in the mixing tank 20, wherein when the fluoride ion concentration of the water to be treated WA reaches a predetermined concentration, the high concentration is stopped. The fluorine-containing wastewater WF enters the mixing tank 20, and when the water level of the water to be treated WA reaches a predetermined liquid level L1, the low-concentration fluorine-containing wastewater WR is stopped from entering the mixing tank 20.

In addition, the embodiment further includes a liquid level gauge 22 connected to the fluorine ion detecting unit 30. The level gauge 22 is capable of displaying the water level in the tempering tank 20 and providing the water level information to the fluorine ion detecting unit 30.

Further, in step S130, the water to be treated WA and the aluminum salt solution AL are introduced into a fluidized crystallization bed 40, and mixed to obtain a cryolite crystallization 40.

Under the above method, the fluorine-containing wastewater treatment method of the present invention, the step of operating the water to be treated WA into the mixing tank 20 by batch operation, in detail, the first batch of high-concentration fluorine-containing wastewater WF and The low-concentration fluorine-containing wastewater WR is introduced into the mixing tank 20, and the high-concentration fluorine-containing wastewater WF is mixed with the low-concentration fluorine-containing wastewater WR to form the water to be treated WA. When the water of the water to be treated WA of the tank 20 is adjusted When the predetermined liquid level L1 is reached, the low-concentration fluorine-containing wastewater WR is stopped from entering the mixing tank 20, and at the same time, the water to be treated WA is continuously introduced into the fluidized bed crystallization tank 40 until the water to be treated of the mixing tank 20 is treated. The water level is not up to the predetermined liquid level L1, and then the water inflow step is performed, that is, the second batch of the high-concentration fluorine-containing wastewater WF and the low-concentration fluorine-containing wastewater WR are introduced into the mixing tank 20, so that the water to be treated WA is The batch operation enters the step of the tempering tank 20 instead of continuously operating the water to be treated WA into the tempering tank 20. In addition, when the fluoride ion concentration of the water to be treated WA reaches a predetermined concentration, the high-concentration fluorine-containing wastewater WF is also stopped from entering the mixing tank 20, so that the embodiment is In a batch manner, the water to be treated WA is introduced into the mixing tank 20 to maintain the fluoride ion concentration of the water in the mixing tank 20 within a predetermined concentration, so as to prevent the water to be treated WA from entering the mixing tank 20 in a continuous operation manner. When the fluoride ion concentration of the water is changed too much, the subsequent crystallization efficiency is not good.

The detection method of the fluorine ion detecting unit 30 in the fluorine-containing wastewater treatment method S100 of the present embodiment will be further described below. It should be noted that the fluorine ion detecting unit 30 is executed by, for example, a Programmable Logic Controller (PLC), but the invention is not limited thereto.

Fig. 3 is a schematic flow chart showing the detection mode of the fluoride ion detecting unit of Fig. 1. Please refer to Figure 3 and Figure 2. The fluoride ion detecting unit 30 includes a fluorine ion selective electrode 32 and a fluorine ion detecting groove 34. In the step S120 of controlling the fluoride ion concentration of the water to be treated WA in the mixing tank 20 by the fluorine ion detecting unit 30, the fluorine-containing wastewater processing method S100 further includes the following steps S122 to S124.

Step S122 is performed to introduce high-concentration fluorine-containing wastewater WF and an ionic liquid SF to the fluorine ion detecting tank 34. Next, proceeding to step S124, the fluoride ion selective electrode 32 is used to detect the fluoride ion. The concentration of fluoride ions in the tank 34 is detected.

After the above steps, the step of controlling the ratio of the high-concentration fluorine-containing wastewater WF to the ionic liquid SF is 1:100. Further, in the present embodiment, the high-concentration fluorine-containing wastewater WF is, for example, a fluorine-containing wastewater containing 20%, but the present invention is not limited thereto, and it depends on the actual situation. Since the fluoride ion selective electrode 32 itself cannot withstand such a high concentration (or medium or higher concentration) of fluorine-containing wastewater, during the control and detection period, for example, the pump 24 is used to quantitatively select the high concentration in the homogenization tank 20 at a constant rate. Fluorine wastewater WF, and ensure that the ratio of high concentration fluorine-containing wastewater WF to ionic liquid SF is 1:100. In other words, this embodiment is to detect high concentration in the homogenization tank 20 by diluting high-concentration fluorine-containing wastewater WF. Fluoride ion concentration of fluorine-containing wastewater WF. In this way, not only the detection and ensuring that the concentration of the fluoride ion is within a certain range, but also the life of the fluoride ion selective electrode 32 can be prolonged, thereby saving cost.

Further, in the present embodiment, the ratio of aluminum to fluorine in the fluidized bed crystallization tank 40 is in the range of 0.8:6 to 1.2:6. Due to the excessive addition of the aluminum salt solution AL and the improper pH environment, the purity of the recovered cryolite crystal ALF is lowered. In detail, when an excessive amount of the aluminum salt solution AL is added, the excess aluminum salt solution AL precipitates, so that the purity of the cryolite crystal ALF is lowered. When the added aluminum salt solution AL is insufficient, the formed precipitate will be dominated by cryolite crystal ALF. Further, when the pH is more than 7, even if the added aluminum salt solution AL is insufficient, the formed precipitate is mainly composed of aluminum hydroxide. It can be seen that how to maintain the ratio of aluminum to fluorine in the fluidized bed crystallization tank 40 between 0.8 and 1.2:6, and an appropriate pH environment, the purity of the cryolite crystal ALF and the fluoride ion removal efficiency are very high. Great impact.

Regarding the control of the addition of the aluminum salt solution AL, the embodiment further includes: controlling the fluoride ion concentration of the high-concentration fluorine-containing wastewater WF in the mixing tank 20 to be 3000±500 mg/L, thus introducing the high-concentration fluorine-containing wastewater WF into the fluidization. After the bed crystallization tank 40, it can ensure and precisely control the fluidized bed crystallization The stable concentration ratio of aluminum to fluorine in the tank 40 is to obtain a high purity cryolite crystal ALF. It should be noted that the present embodiment further includes the following steps: the ratio of aluminum to fluorine in the fluidized bed crystallization tank 40 is in the range of 0.8:6 to 1.2:6.

Figure 4 is a schematic flow chart for controlling the pH in the fluidized bed crystallization tank. Please refer to Figure 4 and Figure 2. In this embodiment, with respect to the control method of the pH value, the step S130 is performed by introducing the water to be treated WA and the aluminum salt solution AL to the fluidized bed crystallization tank 40 to obtain the cryolite crystal ALF, which further includes the following step S132. Step S134.

Step S132 is performed to control the pH value in the fluidized bed crystallization tank 40 to a predetermined pH value by a pH controller 60, wherein the predetermined pH value ranges, for example, between 5.0 and 5.5. Next, in step S134, when the pH value in the fluidized bed crystallization tank 40 is not within the range of the predetermined pH value, an alkali solution ND is introduced to bring the pH value in the fluidized bed crystallization tank 40 to a predetermined pH value. The lye ND used in the examples is, for example, sodium hydroxide (NAOH), but the invention is not limited thereto, and is employed depending on the actual use.

In this embodiment, the water quality change (such as pH value) in the fluidized bed crystallization tank 40 can be immediately detected by a pH electrode 62, and the switch of the diaphragm type pump 64 is controlled via the pH controller 60 to control The flow rate of the lye ND to the fluidized bed crystallization tank 40 is controlled to control the pH in the fluidized bed crystallization tank 40 to be between 5.0 and 5.5.

Fig. 5 is a schematic flow chart showing a further flow of the fluorine-containing wastewater treatment method of Fig. 1. Please refer to Figure 5 and Figure 2. In the present embodiment, in the step S130, in the step of introducing the water to be treated WA and the aluminum salt solution AL to the fluidized bed crystallization tank 40 and mixing to obtain the cryolite crystal ALF, the fluorine-containing wastewater treatment unit S100 further includes The following steps S140 to S150.

Then proceeding to step S140, performing a separation step to obtain a low concentration fluorine Waste water WR and sludge SL. In the present embodiment, the separated sludge SL is discharged. Further, in the above step S140, as shown in Fig. 2, the present embodiment further includes a three-phase separator 90 disposed above the fluidized bed crystallization tank 40 to prevent bubbles from entering the sedimentation tank 80. It should be noted that, in actual operation, since the coagulant is not required to be added, the sludge produced in the present embodiment is very small. Accordingly, in addition to the purpose of treating the fluorine-containing wastewater WF, the obtained cryolite crystal ALF has a moisture content of 10% or less. Moreover, since it is not necessary to add a coagulant, the amount of sludge SL generated by the discharge can be greatly reduced, and the cost of the sludge SL can be reduced.

Further, in step S150, a reflux pump 36 is controlled by the fluoride ion detecting unit 30 to introduce the low-concentration fluorine-containing wastewater WR into the mixing tank 20. In other words, the recovered treated water obtained by the above steps can be used as the low-concentration fluorine-containing wastewater WR in the sedimentation tank 80, and if the water level of the water to be treated WA in the mixing tank 20 does not reach the predetermined liquid level L1, the low concentration includes The fluorine wastewater WR can be introduced into the mixing tank 20.

In summary, the fluorine-containing wastewater treatment method of the present invention introduces a high-concentration fluorine-containing wastewater and a low-concentration fluorine-containing wastewater into a mixing tank. When the water level of the water to be treated in the mixing tank reaches a predetermined liquid level, the low-concentration fluorine-containing wastewater is stopped from entering the mixing tank, and at the same time, the water to be treated is continuously introduced into the fluidized bed crystallization tank until the mixing tank is to be treated. The above water inflow step is performed again if the water level of the water does not reach the predetermined level. In addition, when the fluorine ion concentration of the water to be treated reaches a predetermined concentration by the fluorine ion detecting unit, the high-concentration fluorine-containing wastewater is also stopped from entering the mixing tank, and thus the present invention is in a batch manner. The water to be treated is introduced into the mixing tank to control the fluoride ion concentration of the water in the mixing tank to be maintained at a predetermined concentration, so as to avoid excessive change of the fluoride ion concentration of the water in the water inlet step, resulting in poor subsequent crystallization efficiency.

Although the present invention has been disclosed above by way of example, it is not intended to limit the present invention. It is to be understood that the scope of the invention is defined by the scope of the appended claims. quasi.

S100‧‧‧Fluorine wastewater treatment method

S110~S130‧‧‧Steps

Claims (5)

A method for treating a fluorine-containing wastewater, comprising: performing a water inflow step to a mixing tank, wherein a water to be treated enters the mixing tank in a batch operation, and the water to be treated in the mixing tank contains a high concentration fluorine Waste water and a low concentration fluorine-containing waste water; the fluorine ion detecting unit comprises a fluorine ion selective electrode and a fluoride ion detecting unit by controlling a fluorine ion concentration of the water to be treated in the mixing tank by a fluorine ion detecting unit The measuring tank further comprises: introducing the high concentration fluorine-containing wastewater and an ionic liquid to the fluoride ion detecting step by the fluorine ion detecting unit to control the fluoride ion concentration of the water to be treated in the mixing tank; And detecting the fluoride ion concentration in the fluoride ion detecting tank by using the fluorine ion selective electrode, wherein when the fluoride ion concentration of the water to be treated reaches a predetermined concentration, stopping the high concentration fluorine-containing wastewater from entering a smelting tank, when the water level of the water to be treated reaches a predetermined liquid level, stopping the supply of the low-concentration fluorine-containing wastewater into the tempering tank; and introducing the water to be treated and an aluminum salt solution into a fluidized bed crystallization tank, mixing and And the step of introducing the water to be treated and the aluminum salt solution into the fluidized bed crystallization tank to obtain the cryolite crystal, further comprising controlling the fluidized bed by a pH controller The pH value in the crystallization tank reaches a predetermined pH value, wherein the batch operation is to introduce the high concentration fluorine-containing wastewater and the low concentration fluorine-containing wastewater into the tempering tank, the high concentration fluorine-containing wastewater and the low concentration The fluorine-containing wastewater is mixed into the water to be treated, and the water to be treated is continuously introduced into the fluidized bed crystallization tank until the water level of the water to be treated in the tempering tank does not reach the predetermined liquid level, and the high-concentration fluorine is further The wastewater and the low-concentration fluorine-containing wastewater are introduced into the mixing tank. The fluorine-containing wastewater treatment method according to claim 1, wherein a ratio of aluminum to fluorine in the fluidized bed crystallization tank is in a range of from 0.8:6 to 1.2:6. The method for treating fluorine-containing wastewater according to claim 1, wherein the water to be treated is introduced And the step of mixing the aluminum salt solution into the fluidized bed crystallization tank to obtain the crystal of the cryolite, further comprising: performing a separation step to obtain the low concentration fluorine-containing wastewater and a sludge; and using the fluorine The ion detecting unit controls a reflux pump to introduce the low concentration fluorine-containing wastewater into the mixing tank. The method for treating a fluorine-containing wastewater according to the above aspect of the invention, wherein the step of introducing the water to be treated and the aluminum salt solution into the fluidized bed crystallization tank to obtain the cryolite crystal further comprises: When the pH in the fluidized bed crystallization tank is not within the predetermined pH range, an alkali solution is introduced to bring the pH in the fluidized bed crystallization tank to the predetermined pH value. The method for treating fluorine-containing wastewater according to claim 4, wherein the predetermined pH range is between 5.0 and 5.5.