JPH10216740A - Treatment of fluorine-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sufficient amount of treated water while preventing the clogging in a reaction tower. SOLUTION: Raw water is allowed to flow in the bottom part of a reaction tower 16 and passed through a packed bed 18 as ascending flow and treated water is discharged to a treated water storage tank 20 from the upper part of the reaction tower 16. The treated water in the treated water storage tank 20 can be circulated to the reaction tower 16. The treated water is circulated to the reaction tower 16 at a high linear speed at every predetermined time to fluidize the packed bed 18 in the reaction tower 16 to prevent the clogging of the packed bed 18. When raw water is treated, treated water is passed through the packed bed 18 at a low linear speed to prevent the deterioration of treated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating fluorine-containing wastewater by removing the fluorine by flowing the fluorine-containing wastewater through a reaction tower filled with a solid filler of a calcium compound.

[0002]

2. Description of the Related Art In the electronics industry for manufacturing LSIs and the like, various chemicals are used in the manufacturing process. Therefore, in the wastewater treatment, wastewater containing these various chemicals must be removed.

For example, since hydrofluoric acid is often used as an etching agent for silicon wafers, wastewater often contains fluorine. Therefore, this fluorine must be removed. Although the standard for releasing fluorine is 15 mg / L or less, many municipalities have stricter additional standards, and most of the standard values are 1 to 8 mg / L or less.

In the treatment of fluorine, a calcium compound that generates calcium ions, such as calcium chloride or slaked lime, is added to crystallize calcium fluoride. And, in the usual case, after crystallizing calcium fluoride, this is subjected to coagulation sedimentation treatment with an inorganic coagulant such as an aluminum-based coagulant to ensure solid-liquid separation and further remove residual fluorine. .
However, this method has a problem that sludge having a high moisture content is generated.

[0005] Therefore, granular calcium carbonate (filler)
A method for removing fluorine using a reaction tower filled with is described in JP-A-5-170435 and the like. In this method, the fluoride ions replace the carbonate groups on the filled calcium carbonate particles, and the particles together become calcium fluoride. Therefore, there is an advantage that granular calcium fluoride is obtained by the treatment and sludge is not generated. further,
Since the obtained calcium fluoride has high purity, it can be diverted to other uses.

Japanese Patent Application Laid-Open No. 60-206485 discloses that after adding a soluble calcium compound to raw water, the raw water is passed upward through a reaction tower filled with granular calcium fluoride, and treated water is treated. Is circulated to the raw water side to increase the flow rate in the reaction tower to fluidize the filler. In this method, calcium fluoride generated by the reaction between fluorine in raw water and calcium ions generated from the added calcium compound precipitates and grows on the surface of the calcium fluoride filler in the tower, thereby removing fluorine. .

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No.
The device described in Japanese Patent No. 70435 has a problem that clogging is likely to occur because the filler is substantially fixed. In particular, since a large amount of calcium fluoride was precipitated on the raw water inflow side, the fillers were likely to adhere to each other in this portion. Further, there is a problem that carbon dioxide gas generated by the treatment accumulates in the packed bed and causes channeling when the gas escapes.

In the apparatus described in Japanese Patent Application Laid-Open No. 60-206485, the filler is constantly flowed and treated, so that it is possible to prevent the filler from sticking to each other. The surface of the packing material is shaved, thereby increasing the concentration of SS (suspended solids) in the treated water, and the need to constantly fluidize the packing material, thereby increasing the energy consumption required for processing. There was a point.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a method for treating a fluorine-containing wastewater capable of performing a sufficient treatment while preventing clogging due to sticking of fillers. The purpose is to do.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a treatment of fluorine-containing wastewater by removing the fluorine in the wastewater by passing the fluorine-containing wastewater in an upward flow through a reaction tower filled with a solid filler of a calcium compound. A method comprising flowing a fluorine-containing wastewater into the lower part of the reaction tower and flowing the inside of the reaction tower in an upward flow to obtain treated water from the upper part of the reaction tower; And a circulation step of flowing the reaction water upward in the reaction tower.These steps are repeated alternately, and the upward linear velocity of the treated water in the circulation step in the reaction tower is changed to the raw water flow rate in the raw water flow step. In the raw water flow process, the solid filler in the reaction tower is substantially fixed in the raw water flow step, and the solid filler in the reaction tower is fluidized as a whole in the circulation step. I do.

As described above, according to the present invention, the upward linear velocity in the reaction tower of the treated water in the circulation step is made higher than the upward linear velocity in the reaction tower of the raw water in the raw water flow step. The solid filler in the reactor is substantially fixed, and the solid filler in the reaction tower is fluidized as a whole in the circulation step. Therefore, in the raw water flow process, the filler layer functions substantially as a fixed bed, and the deterioration of the treated water quality that occurs when the filler layer is a fluidized bed can be prevented. Further, in the circulation process that is periodically performed, the sticking of the filler and the occurrence of clogging can be prevented. Therefore, stable processing can be performed over a long period of time.

The filler used in the present invention is, for example, calcium carbonate, calcium fluoride, or calcium fluoride particles used for removing fluorine, in which almost all carbonate groups of calcium carbonate are replaced by fluoride ions. Can be mentioned.

When calcium carbonate is used as the filler, the raw water containing fluorine can be passed as it is without adding calcium ions from the outside, or after the pH is adjusted to the acidic side, so that the water is passed over the calcium carbonate particles. Fluoride ions are removed by replacing the carbonate groups of calcium carbonate.

On the other hand, when calcium fluoride is used as the filler, fluorine cannot be removed even if the raw water is passed through as it is, and it can be brought into contact with calcium fluoride in the presence of calcium ions. is necessary. Therefore, when there is no calcium ion necessary for removing fluorine in the raw water, a soluble calcium compound such as calcium chloride or slaked lime is added from the outside, and then water is passed through the reaction tower. In addition, the raw water flowing through the reaction tower is subjected to a coagulation treatment by adding a soluble calcium compound to the fluorine-containing raw wastewater in advance of the reaction tower,
Then, when the coagulation treatment water obtained by solid-liquid separation,
Usually, a considerable amount of calcium ions remains in the coagulation treatment water, so that fluorine remaining in the coagulation treatment water can be removed by passing the coagulation treatment water through the reaction tower as it is.

When calcium carbonate is used as the filler, calcium ions do not need to be basically present in the raw water passing through the reaction tower as described above.
Even in the case of using calcium carbonate, as in the case of using the above-mentioned calcium fluoride as a filler, calcium ions are added to raw water and then water is passed through, or coagulation treatment by adding a soluble calcium compound in the former stage is performed. The coagulated water may be passed through, and when the raw water is brought into contact with the calcium carbonate particles in the presence of calcium ions, the raw water remains almost neutral without pH adjustment to the acidic side. To remove fluorine.

The method of the present invention is effective when applied to any of the above embodiments.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a diagram showing a configuration of a processing apparatus according to a first embodiment. Raw water, which is fluorine-containing wastewater, flows into the raw water storage tank 10 and is stored therein.
The raw water storage tank 10 is connected to a suction side of a raw water pump 12, and the discharge side of the raw water pump 12 is connected to a valve 1.
The reaction tower 16 is connected via 4.

The inside of the reaction tower 16 has a particle size of 0.2 to 0.1.
A filler made of granular calcium carbonate of about 3 mm is filled, thereby forming a filling layer 18. The raw water in the raw water storage tank 10 is supplied by the raw water pump 12.
The water flows into the bottom of the reaction tower 16 and the treated water is discharged from the top of the reaction tower 16. Therefore, the raw water passes through the packed bed 18 in an upward flow.

The treated water from the reaction tower 16 is supplied to the treated water storage tank 2
0, temporarily stored here and released. On the other hand, a suction side of a circulation pump 22 is connected to the treated water storage tank 20, and a discharge side of the circulation pump 22 is connected to the bottom of the reaction tower 16 via a valve 24. Therefore, by driving the circulation pump 22, the treated water storage tank 20
Is supplied to the lower part of the reaction tower 16,
Is returned upward to the treated water storage tank 20. The raw water can be supplied to the reaction tower 16 by opening the valve 14 and closing the valve 24, and the treated water can be circulated to the reaction tower 16 by closing the valve 14 and opening the valve 24.

Here, when processing is performed in the apparatus of the present embodiment, a raw water flow step of supplying raw water to the reaction tower 16 to obtain treated water, and stopping supply of the raw water to circulate the treated water to the reaction tower 16. The circulation process is repeated alternately.

That is, in the raw water flow process, the valve 14
Is opened, the valve 24 is closed, the raw water pump 12 is driven to supply the raw water to the reaction tower 16, and the treated water is stored in the treated water storage tank 20.
Release from The LV (linear velocity) at this time varies depending on the type and particle size of the filler to be used.
In the case of calcium carbonate of about 2 to 0.3 mm, 1 to 10
m / h. Thereby, the packed bed 18 becomes a substantially fixed bed, and in this state, the raw water passes through the packed bed 18. Then, by flowing the raw water through the packed bed 18, the fluorine in the raw water is replaced by the carbonate group of calcium carbonate, calcium fluoride is generated and precipitated, and the fluorine is removed from the raw water.

As described above, in this raw water flow process, L
V is not very high and packed bed 18 is substantially a fixed bed. Therefore, with a sufficient contact time, a short circuit can be prevented, reliable processing can be performed, and outflow of SS can be minimized. This raw water flow step is continued for about 10 minutes to 5 hours, depending on the raw water quality and the like.

Next, when the raw water flow process is completed,
The supply of the raw water to the reaction tower 16 is stopped, and the circulation process is performed. In this circulation step, the valve 14 is closed and the valve 24 is opened, and the circulation pump 22 is driven to drive the treated water storage tank 20.
The treated water inside is circulated to the reaction tower 16 in an upward flow. At this time, the LV (linear velocity) is set to about 10 to 50 m / h, more preferably about 20 to 50 m / h. As a result, the packed bed 18 is in a fluid state, and the filler material flows. Therefore, clogging in the filling layer 18 and fixation of the fillers are eliminated.

That is, in the raw water flow process, the packed bed 18
Is a substantially fixed bed, and since the raw water is supplied to the lower part of the packed bed 18, the fluorine concentration therein is high. Therefore, precipitation of calcium fluoride is likely to occur in this portion, and sticking between the fillers is likely to occur. In the present embodiment, in the circulation step, the filler is caused to flow by circulating the treatment water, so that the fixation of the filler can be effectively eliminated. In this circulation step, the filler may be sufficiently fluidized,
It may be about 0.5 to 5 minutes.

In such a short circulation step, there is no adverse effect on the treatment, and the capacity of the raw water tank 10 does not need to be so large. In addition, the energy consumed for circulation is small and the processing costs are not significantly different.

In the raw water flow process, the treatment water may be partially circulated in order to maintain a constant water flow rate. In this case, the raw water pump 12 and the circulation pump 22 may be driven by opening the valve 14 and the valve 24.
The amount of circulation can be easily adjusted by adjusting the opening of the valve 24 or the like.

In the above description, calcium carbonate is used as the filler, but calcium fluoride can be used as the filler. When calcium fluoride is filled, it is essential that calcium ions be present in the raw water as described above. In this case, fluorine generated in the raw water reacts with calcium ions also contained in the raw water. Calcium fluoride precipitates and grows on the surface of the calcium fluoride filler, thereby removing fluorine.

"Addition of calcium ion" Even when calcium carbonate is used as the filler, if the fluorine concentration in the raw water is as low as about 20 to 30 mg / L, calcium ion is added in advance. It is preferable to pass the water through the reaction tower after the addition into water, for the following reason. That is, in the case of performing fluorine removal by passing wastewater containing almost no calcium ions such as fluorine-containing wastewater discharged from a semiconductor manufacturing plant through, for example, a reaction tower filled with granular calcium carbonate, as described below. Fluorine cannot be efficiently removed unless water is passed after the pH of the raw water is adjusted to the acidic side of about pH = 3. However, when water is passed through the acidic raw water, the dissolution of calcium carbonate as a filler is promoted and the treatment is performed. There is a risk that the water will be discharged unnecessarily into the water. However, the dissolution and outflow of calcium carbonate causes an increase in the frequency of replacement of the filler, so that it is desirable to reduce the amount as much as possible.

Therefore, when passing raw water containing calcium ions as described above, calcium fluoride originally contained in the raw water is used to deposit calcium fluoride on the surface of the filler. As a result, even if the pH of the raw water is neutral, fluorine is efficiently removed. Therefore, in this case, the dissolution of calcium carbonate is hardly a problem, and the filler can be used for a long time. In order to add calcium ions, a soluble calcium compound may be added. For example, it is preferable to add calcium chloride or slaked lime. In this case, the addition amount of the soluble calcium compound is preferably about several hundred mg / L as calcium. This makes it possible to efficiently remove fluorine while minimizing the dissolution of calcium carbonate.

"Adjustment of pH" When treating raw water in the absence of calcium ions using calcium carbonate as a filler, it is also preferable to adjust the pH of the raw water as described above. For example, when the pH is set to the acidic side, the dissolution of calcium carbonate is promoted. For this reason, the calcium ion concentration in the treated water is increased, and the fluorine removal rate can be increased. In particular, when the fluorine concentration is 100 mg / L
In the case of the above raw water treatment, an acid is added to the raw water and p
It is preferable to adjust H to about 3. by this,
Elution of calcium ions from the filler is promoted, and the ability to remove fluorine can be increased. If the pH is too low, such as 2 or less, the dissolution of the filler will proceed too much. Therefore, it is preferable to adjust the pH by adding an alkali.

Note that there is a certain relationship between the calcium ion concentration in the treated water from the reaction tower 16 and the fluorine concentration, and the fluorine concentration can be reduced by increasing the calcium ion concentration in the treated water. Therefore, the calcium ion concentration in the treated water was monitored,
By controlling the amount of calcium chloride added to the raw water and the amount of the pH adjuster to be about g / L, the fluorine concentration in the treated water can be maintained at 10 mg / L or less.

[Structure of Inflow into Reaction Tower] Inflow of raw water into the bottom of the reaction tower 16 in the raw water flow process is performed by the reaction tower 16.
It is preferred that the raw water is evenly diffused over the entire bottom of the base. For this purpose, as shown in FIG. 1, the bottom of the reaction tower 16 is formed into an inverted truncated cone as a whole by a hopper-shaped slope 26 and a flat plate-shaped bottom 27, and the opening of the raw water introduction pipe 28 is inverted. It is preferable that the raw water is provided so as to face down at the trapezoidal bottom, and the raw water is caused to flow out so as to collide with the flat bottom surface 27. In this case, when the raw water flows obliquely toward the vicinity of the boundary between the slope 26 and the bottom surface 27 as shown in the figure, the raw water flows toward the entire bottom rather than flowing the raw water vertically toward the center of the flat bottom surface 27. As a result, irregular supply of raw water to the packed bed 18 can be achieved. In this case, the direction of the opening of the outlet of the raw water is preferably inclined at about 5 to 30 ° with respect to the center of the cone, and the distance from the bottom is preferably about 5 to 50 cm.

[Second Embodiment] FIG. 2 shows the configuration of the second embodiment. In the second embodiment, a coagulation tank 30 and a sedimentation tank 32 are provided before the raw water storage tank 10. Then, the fluorine-containing wastewater first undergoes coagulation sedimentation treatment, and the treated water flows into the raw water storage tank 10 as raw water.

In other words, the coagulation tank 30 adjusts the pH to, for example, near neutrality by adding and mixing a soluble calcium compound such as calcium chloride, and adding a pH adjuster as necessary, so that the fluorine in the wastewater is fluorinated. It precipitates and solidifies as calcium iodide. Then, the solidified calcium fluoride is precipitated and separated in the precipitation tank 32. Therefore, the raw water flowing into the raw water storage tank 10 has a part or most of the fluorine removed in advance, has a substantially neutral pH, and contains calcium ions. For example, the addition amount of calcium chloride in the flocculation tank 30 is adjusted to the concentration of calcium ion 10 in the supernatant of the precipitation tank 32.
If the concentration is controlled to be about 0 mg / L, the fluorine concentration of the supernatant of the precipitation tank 32 will be about several tens mg / L.

Therefore, calcium fluoride can be effectively deposited and removed in the reaction tower 16 by passing the raw water through the reaction tower 16 as it is without adjusting the pH to an acidic side and further processing the raw water. Thus, the fluorine concentration of the treated water discharged from the reaction tower 16 can be effectively reduced to several mg / L or less.

Instead of the precipitation tank 32, various solid-liquid separation means such as a filtration tank and a membrane filtration device can be adopted. Further, it is also preferable to add a coagulation treatment using an aluminum-based or iron-based inorganic coagulant after the coagulation treatment with calcium ions, as is performed in a usual fluorine treatment facility. Thereby, the fluorine concentration of the water flowing into the raw water storage tank 10 can be further reduced, and the fluorine load on the reaction tower 16 can be reduced. In addition, by adding the reaction tower 16 to an existing facility already having the above-described coagulation treatment facility, the facility as shown in FIG. 2 can be constructed, and the existing facility can be effectively used. .

[0038]

【Example】

"Example 1" SV (water flow / packed bed volume) = 5 h ^-1 (LV = 1.2 m) in a column (2.6 cm inside diameter, packed height 25 cm) packed with granular calcium carbonate having a particle diameter of 0.3 mm.
/ H), while alternately repeating a water passage step of 2 hours in which raw water is passed through and a circulation step of 2 minutes (LV = 20 m / h) in which the passage of raw water is interrupted to fluidize the packed bed by circulating treated water. Using a raw water having a fluorine concentration of 20 mg / L, a fluorine treatment experiment was performed for two months under the condition of an addition amount of calcium of 250 mg / L (adding calcium chloride). Table 1 shows the results.

Table 1 shows, as a comparative example, a processing result obtained by conducting an experiment under the same conditions as in the present embodiment, in which raw water was constantly flowed upward at a constant flow rate and the other conditions were the same.

[0040]

[Table 1] Fluorine concentration of treated water Treated water SS Operating conditions (mg / L) (mg / L) Example 144 No trouble Comparative example 1 (LV1.2) 43 Clogging in one week Comparative example 2 (LV20) 1225 No trouble Here, in Comparative Example 2 (LV20), the LV was adjusted by constantly circulating the treated water. The operation was performed at a pH of about 5 to 6 at the column inlet.

As can be seen from Table 1, treated water is constantly circulated while maintaining the same flow rate of raw water, and LV = 20 m /
h (Comparative Example 2), there was no trouble due to sticking, but the fluorine concentration of the treated water was 12 mg / L and SS was 25
It deteriorates considerably with mg / L. On the other hand, always LV = 1.2m
/ H (Comparative Example 1), the quality of the treated water was sufficient, but a trouble due to clogging occurred, and the treatment could not be continued. The clogging occurred at the entrance of the reaction tower, and the filler was fixed.

Example 2 In the same apparatus as in Example 1 described above, a raw water having a fluorine concentration of 100 mg / L was used, and HCl was added to the raw water (pH ≒ 7) to add calcium ions to the treated water. The amount of HCl added was controlled so that the concentration became about 100 mg / L. In this case, the pH of the raw water at the column inlet was about 2.8. Also,
The operation was carried out with the raw water passing process for 15 minutes and the circulation process for 1 minute. Other conditions were the same as in Example 1. Also,
No calcium ions were added to the raw water. Table 2 shows the processing results.

Table 2 shows, as a comparative example, a processing result obtained by conducting an experiment under the same conditions as in the present embodiment, in which raw water was constantly flowed upward at a constant flow rate and the other conditions were the same.

[0044]

[Table 2] Fluorine concentration of treated water Treated water SS Operating condition (mg / L) (mg / L) Example 2 6 12 No trouble Comparative example 3 (LV1.2) 615 Clogging in one week Comparative example 4 (LV20) 20 80 No trouble As described above, also in this embodiment, it is understood that by providing the circulation step, occurrence of trouble can be eliminated and sufficient processing can be performed. The clogging in Comparative Example 3 (LV = 1.2 m / h) was different from Comparative Example 1 and occurred over the entire packed bed.

[0045]

As described above, according to the present invention,
In the circulation step, the filler in the reaction tower is fluidized by the circulation of the treated water. Therefore, by performing the circulation step every predetermined period, it is possible to prevent the clogging of the packed bed. In the raw water flow process, since the packed bed functions as a fixed bed, there is no problem such as deterioration of treated water.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first embodiment.

FIG. 2 is a block diagram illustrating a configuration of a second embodiment.

[Explanation of symbols]

10 raw water storage tank, 12 raw water pump, 14, 24 valve, 16 reaction tower, 18 packed bed, 20 treated water storage tank,
22 circulation pump, 30 coagulation tank, 32 sedimentation tank.

Claims (1)

[Claims] 1. A method for treating fluorine-containing wastewater, wherein fluorine in the wastewater is removed by flowing the fluorine-containing wastewater through a reaction tower filled with a solid filler of a calcium compound in an upward flow. Into the lower part of the reaction tower, circulate the inside of the reaction tower in an upward flow and obtain treated water from the upper part of the reaction tower, and return the treated water to the lower part of the reaction tower, A circulating step of circulating in an upward flow, and repeating these steps alternately, and the upward linear velocity in the reaction tower of the treated water in the circulating step is made smaller than the upward linear velocity in the reaction tower of the raw water in the raw water passing step A method for treating fluorine-containing wastewater, characterized in that in the raw water flow step, the solid filler in the reaction tower is substantially fixed in the raw water flow step, and the solid filler in the reaction tower is fluidized as a whole in the circulation step.