JP2565110B2 - Method and apparatus for treating fluorine-containing water - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating fluorine-containing water, and more particularly to treating raw water by passing the fluorine-containing water through a calcium carbonate packed column filled with calcium carbonate granules. The present invention relates to a method and apparatus for appropriately controlling the amount of acid or alkali added to prevent the filter material from collapsing in a packed column and stably treating fluorine with high removal efficiency.

[0002]

2. Description of the Related Art Hydrogen fluoride (HF) and ammonium fluoride (NH ₄ ) are used in the field of semiconductor manufacturing and related fields, in the field of surface treatments of various metal materials, single crystal materials, optical materials, etc.
Since a large amount of the etching agent containing F) as a main component is used, waste water containing fluorine is discharged.

Such fluorine-containing wastewater is generally treated as a separate wastewater by a separation treatment or together with other wastewater, and its treatment method is generally calcium hydroxide (Ca (OH) ₂ ). To produce insoluble matter of calcium fluoride (CaF ₂ ),
We perform processing such as coagulation sedimentation. However, this method
There is a problem that a large amount of sludge with poor sedimentation is generated, and reduction of this sludge generation amount has been a problem.

Conventionally, as a measure for reducing the amount of sludge generation, there has been a method in which fluorine-containing water is passed through a calcium carbonate packed column to convert fluorine into calcium fluoride (CaF ₂ ) having good crystallinity, and removing and recovering it. Proposed. Further, in such a method, when sulfuric acid or nitric acid other than hydrofluoric acid is contained in the raw water, as a pretreatment of the raw water, other than hydrofluoric acid in the raw water, in order to prevent the filter medium (calcium carbonate) from collapsing. A method of adding an alkaline agent (ammonia, ammonium fluoride, etc.) in an amount equal to or more than the equivalent of an acid has been proposed (Japanese Patent Application No. 1-1).
21374). However, in this case, excessive addition of alkali causes a decrease in the fluorine removal rate, and there is a problem that the fluorine concentration of the final treated water becomes high. Further, from such a fact, if the raw water has a high alkalinity, the fluorine removal rate may be inferior. Therefore, in this case,
It becomes necessary to add an acid to the raw water to reduce the alkalinity.

However, addition of an alkali or an acid to the raw water is effective in preventing the filter medium from collapsing and maintaining the fluorine removal rate.
It is necessary to control to an appropriate value, but since the fluorine-containing wastewater discharged from semiconductor factories, etc. generally has a drastic change in the composition of its components, properly control the addition of alkali or acid to raw water. It wasn't easy.

Conventionally, the addition of acid or alkali to the raw water is controlled so that the pH of the raw water will be constant.

[0007]

However, when the control method of adding an alkali or an acid so that the pH of the raw water is kept constant is applied to the treatment of the fluorine-containing water, the composition fluctuation of the raw water is sufficiently dealt with. Therefore, it is difficult to perform proper control from both aspects of preventing the filter medium from collapsing and maintaining the fluorine removal rate. Since the material of the pH sensor is generally weak to fluorine, it is difficult to measure the pH of the raw water. There is such a problem.

Moreover, in the treatment of fluorine-containing wastewater,
The set pH of the raw water is not fixed depending on the type and composition of the fluorine-containing wastewater, and it is extremely difficult to perform steady control.

From the above, when the fluorine-containing wastewater is passed through the calcium carbonate packed column for treatment, the amount of alkali or acid added to the raw water is adjusted to prevent the filter medium from collapsing and the fluorine removal rate to be increased. New water quality indicators were needed for proper control to maintain high levels.

The present invention has been made in view of the above conventional circumstances, and when the fluorine-containing water is passed through a calcium carbonate packed column for treatment, an alkali or acid to the raw water is added according to a new water quality index. It is possible to provide a method and a device therefor, which can respond to fluctuations in the water quality of raw water sufficiently by preventing the filter medium from collapsing and stably treat fluorine with high removal efficiency by automatically controlling the addition amount of To aim.

[0011]

A method for treating fluorine-containing water according to claim 1, wherein fluorine-containing water is passed through a calcium carbonate packed column filled with calcium carbonate particles to remove fluorine. In the method, the concentration of fluorine and the concentration of acid in the fluorine-containing water are measured, the α value is determined from the measured value by the following formula (I), and the calculated α value is compared with a predetermined reference range to obtain the α value. When the value is out of the reference range, a predetermined amount of acid or alkali is added to the fluorine-containing water, and then water is passed through the calcium carbonate packed tower.

[0012]

(Equation 3)

The treatment apparatus for fluorine-containing water according to claim 2 is a raw water tank for storing fluorine-containing water, a calcium carbonate packed tower filled with calcium carbonate granules, and the raw water in the raw water tank is fed to the calcium carbonate packed tower. In the apparatus for treating fluorine-containing water, which comprises means for discharging treated water from a calcium carbonate packed tower, measuring means for sampling raw water in the raw water tank to measure fluorine concentration and acid concentration in the water, An operation comparing means for receiving a signal from the measuring means to calculate an α value by the above formula (I) and comparing it with a predetermined reference range, and an acid or raw water in response to the signal from the operation comparing means. It is characterized in that a chemical injection means for adding a predetermined amount of alkali is provided.

[0014]

[Function] As described above, when the fluorine-containing water is treated with the calcium carbonate packed tower, the properties of the raw water (acid and alkalinity)
Is known not only to affect the quality of treated water, but also to affect the collapse loss of the packed filter medium depending on the state of raw water, but quantitative studies on such a phenomenon have not been conducted so far.

The present inventors have examined the relationship between the raw water quality in the treatment of fluorine-containing water, the quality of the treated water and the collapse of the filter medium, and have various fluorine-containing wastewater (fluorine concentration 10 g / l) discharged from a certain factory. Alkali (NaO
When H) is added, as shown in FIG. 3, the fluorine concentration of the treated water deteriorates as the amount of alkali added increases, and conversely, the SS concentration of the treated water indicating the amount of collapse of the filter medium decreases as the amount of alkali added decreases. It was found that there was an optimum point in the amount of alkali added, for both the fluorine concentration and the SS concentration of the treated water.

As a result of examination using various drainage water, the pH at the optimum point varies depending on the raw water condition.
It has been found that it is inappropriate to use the pH value as an index, and the optimum point can be indicated by using the α value calculated by the formula (I) as an index.

The α value calculated by the above formula (I) is the most excellent treated water quality in terms of fluorine concentration when adjusted to α = 0 for any wastewater. . Therefore, when it is desired to reduce the fluorine concentration in the treated water as much as possible, it is preferable to set α = 0 to 0.05 as the reference range. However, when the α value is excessively low, the calcium carbonate filter medium tends to be collapsed. Therefore, when it is desired to improve the quality of treated water in general, α = 0.3 to 0.5, particularly α =
It is preferable to set the reference range to about 0.25 to 0.40. Such a reference range can be obtained by conducting an experiment in advance.

In the present invention, such α
By calculating the value and adding acid or alkali to the raw water so that this value falls within the preset reference range, the raw water can be easily and reliably adjusted to the optimum properties for treatment in the calcium carbonate packed tower. it can.

Incidentally, general fluorine-containing wastewater contains hydrofluoric acid (HF) and ammonium fluoride (NH ₄ F) as main components, but α = 0 for HF alone and α = for NH ₄ F alone.
It becomes 1. When nitric acid or acetic acid is mixed, the α value becomes negative.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing a method of treating fluorine-containing water according to an embodiment of the present invention.

In the method of this embodiment, three calcium carbonate packed towers are installed in series and treated in an upward flow.
In the figure, 1, 2 and 3 are calcium carbonate packed towers, 4 is a raw water tank, 5 is a raw water pump, 6, 7, and 8 are circulating water tanks, and 9.1 and 1
Reference numerals 0 and 11 indicate circulation pumps. 21 to 31 indicate pipes.

In this embodiment, the raw water in the raw water tank 4 of such a treatment apparatus is withdrawn from the pipe 13 equipped with the sample pump 12, the total acid concentration and the fluorine concentration are measured, and the formula (I) is used from the measured values. Α value is calculated by
A chemical injection control device 14 is provided which compares the value with a predetermined reference range and outputs a signal for adding a predetermined amount of acid or alkali to the raw water tank 4 when the α value is out of the reference range. 1
5, 16 and 17 are a H ₂ SO ₄ storage tank for adding sulfuric acid (H ₂ SO ₄ ) as an acid, a chemical pump and a pipe, and 18, 19 and 20 are sodium hydroxide (NaOH) as an alkali. A NaOH storage tank, a chemical injection pump, and piping for adding.

In this embodiment, the raw water tank 4 is connected to the pipe 21.
A part of the raw water (fluorine-containing water) introduced in (1) is sampled from the pipe 13, the total acid concentration is measured by the chemical injection control device 14, and then the fluorine concentration is measured.

Here, the total acid concentration is preferably measured by a neutralization titration method. Since the water to be detected is water containing fluorine, the method for detecting the color development after the addition of the indicator by an optical sensor is preferable. desirable. Further, it is preferable to measure the fluorine concentration by an ion meter method because it is simple.

In the chemical injection control device 14, the α value is calculated from the above formula (I) from the total acid concentration measured value and the fluorine concentration measured value. Then, the calculated α value is compared with a preset reference range (for example, α = 0.25 to 0.40), and when the calculated α value is outside this reference range, the α value falls within this reference range. In this way, a signal for adding acid or alkali is output.

That is, for example, when the calculated α value is larger than 0.40, H ₂ S is adjusted so that the α value becomes 0.40 or less.
An operation signal of the O ₄ chemical injection pump 16 is output for a predetermined time. On the contrary, when the calculated α value is smaller than 0.25, the operation signal of the NaOH chemical injection pump 19 is output for a predetermined time so that the α value becomes 0.25 or more.

In this way, the raw water in the raw water tank 4 is adjusted so that the calculated α value becomes 0.25 to 0.40, and then introduced into the circulating water tank 6 through the pipe 22 equipped with the pump 5. Then, together with the outflow water of the calcium carbonate packed tower 1 from the pipe 24, it is introduced into the calcium carbonate packed tower 1 through the pipe 23 provided with the pump 9. The outflow water of the calcium carbonate packed tower 1 is returned to the circulating water tank 6 through the pipe 24, and the circulating water tank 6
The overflow water is introduced into the circulating water tank 7 through the pipe 25. Then, the calcium carbonate packed tower 2 from the pipe 27
Is introduced into the calcium carbonate packed tower 2 through the pipe 26 equipped with the pump 10. The effluent of the calcium carbonate packed tower 2 is returned to the circulating water tank 7 through a pipe 27. The overflow water of the circulating water tank 7 is introduced into the circulating water tank 8 through the pipe 28, and is introduced into the calcium carbonate packed tower 3 through the pipe 29 equipped with the pump 11 together with the outflow water of the calcium carbonate packed tower 3 through the pipe 30. The effluent of the calcium carbonate packed tower 3 is returned to the circulating water tank 8 from the pipe 30, and the overflow water in the circulating water tank 8 is discharged from the pipe 31 as treated water to the outside of the system.

Each calcium carbonate packed tower 1, 2, 3
The flow velocity of the inflowing water to the filter varies depending on the particle size of the calcium carbonate filter medium filled, etc., and is appropriately determined within a range in which the filter medium is in a fluidized state and the filter medium does not flow out of the tower. Normally, if the filter media particle size is about 0.3 mm, it is about 10 m /
It is set to be not less than hr, especially about 20 to 30 m / hr.

The amount of raw water supplied by the raw water pump is
Depending on the fluorine concentration and the form of fluorine in the raw water,
For normal, substantially 1 to 5 m ³ relative to the filter medium of calcium carbonate packed column 1 - preferably made to be about filter media · hr - raw / m ^3.

In such a treatment, when there is no difference in the fluorine concentration of the inflow water of the calcium carbonate packed tower and the fluorine concentration of the outflow water, the filter medium in the tower is converted to calcium fluoride and saturated. Has been reached. In this case, the filter medium is withdrawn and replaced with a new calcium carbonate filter medium.

When raw water is treated in series through a plurality of calcium carbonate packed towers in accordance with such a method, the inflow water of the calcium carbonate packed tower on the most upstream side has the highest fluorine concentration. Since the calcium fluoride conversion rate of the tower is the highest, the filter material of the calcium carbonate packed tower on the most upstream side is exchanged, and the calcium carbonate packed tower after this exchange is moved to the most downstream side, and the carbon dioxide on the lower side is sequentially Raise the calcium packed column to the upper side.
As a result, it is possible to efficiently recover high-purity calcium fluoride from the most upstream calcium carbonate packed tower, and the most downstream calcium carbonate packed tower always has a calcium fluoride conversion rate of the filter medium. Since it is low, it is possible to obtain high quality treated water as the final treated water.

The apparatus shown in FIG. 1 is an embodiment of the present invention, and the present invention is not limited to the illustrated apparatus as long as the gist thereof is not exceeded.

For example, in the illustrated embodiment, the α value is calculated by receiving the signals from the measuring means for sampling the raw water in the raw water tank and measuring the fluorine concentration and the acid concentration in the water, and the α value, which is predetermined. The calculation comparing means for comparing with the reference range and the means for outputting the signal from the calculation comparing means are incorporated in one drug injection control device, but they may be independent devices. In addition, the chemical injection control of acid or alkali can be performed by opening and closing the valve as well as operating and stopping the pump. In addition, as the alkali added to the raw water,
Besides NaOH, ammonium hydroxide (NH ₄ OH), ammonium fluoride (NH ₄ F), or the like can be used. In addition to H ₂ SO ₄ , HCl, HNO
₃ etc. can be used.

In the illustrated embodiment, the calcium carbonate packed column is installed in three stages, but in the present invention, the calcium carbonate packed column may be provided in two stages, or four or more stages. May be provided in multiple stages. Also, as shown in the figure, the effluent of the calcium carbonate packed tower is returned to the circulating water tank,
Not only the circulation form in which a part of the water is circulated as the inflow water of the calcium carbonate packed tower and the rest is sent to the calcium carbonate packed tower of the subsequent stage, but a part of the outflow water of the calcium carbonate packed tower is packed with the calcium carbonate. It may be returned to the lower part of the tower as the inflow water of the tower, and the rest may be sent as the inflow water of the latter calcium carbonate packed tower. In any case, by providing a circulating water tank as in the present embodiment, it is extremely advantageous to obtain the effect of releasing the gas generated in the calcium carbonate packed tower.

Although it is possible to dispose the calcium carbonate packed tower in one stage for the treatment, a plurality of calcium carbonate packed towers are provided in series as shown in the drawing, and a part of the outflow water is supplied to the calcium carbonate packed tower. By circulating and passing water,
Fluorine removal rate can be improved, and the purity of recovered calcium fluoride can be improved, which is extremely advantageous industrially.

As shown in FIG. 2, the raw water α value is adjusted by providing two or more raw water tanks 4A and 4B (two tanks in FIG. 2), and one of the raw water tanks 4A has an α value. When performing the adjustment, the α value adjustment and the feed of the raw water are alternately performed in a batch method so that the α water adjusted raw water of the other raw water tank 4B is fed to the calcium carbonate packed tower. As a result, more stable control can be performed. In FIG. 2, 12A and 12B are sample pumps,
13A and 13B are sample pipes, 16A, 16B and 19
A and 19B are chemical injection pumps, 17A, 17B, 20A and 2
Reference numeral 0B is a chemical injection pipe, 22A and 22B are raw water pipes, and other members having the same functions as those shown in FIG. 1 are denoted by the same reference numerals.

The present invention will be described in more detail below with reference to specific examples and comparative examples.

Example 1 90 kg of calcium carbonate particles having a diameter of 0.3 mm were packed in a column having an inner diameter of 315 mm and a height of 1780 mm, and three columns were used to form hydrofluoric acid in a three-column series system as shown in FIG. The treatment was performed by passing the contained water.

Raw water (waste water discharged from the semiconductor manufacturing process: fluorine concentration 2000 mg / l) is stored in a raw water tank (capacity 6 m ³ ) 4
Then, 90 ml of the sample was sampled and the fluorine concentration was measured by a fluorine ion meter (manufactured by Nikkaki Co., Ltd.), while the total acid concentration was determined by the neutralization titration method using phenolphthalein as an indicator.

When the α value was calculated from the obtained numerical value by the above formula (I), α = 0.6.

Then, a predetermined amount of H ₂ SO ₄ was added by automatic control so that the α value became 0. After the adjustment, the water quality was measured again, and α = 0.01 was obtained. Therefore, the water was sent to the calcium carbonate packed column 1 at a flow rate of 0.20 m ³ / hr.

In the treatment, in the calcium carbonate packed tower 1, the effluent water was 1400 liters / hr (LV = 20 m / h).
It was circulated in the same packed tower 1 at the flow rate of r), a part of the circulating water was transferred to the calcium carbonate packed tower 2, and the water was circulated and circulated under the same conditions as the calcium carbonate packed tower 1. Further, a part of the circulating water of the calcium carbonate packed tower 2 was transferred to the calcium carbonate packed tower 3, and the water was circulated and circulated under the same conditions as the calcium carbonate packed tower 1, and a part thereof was discharged as treated water.

Each circulating water tank (capacity 1 m ³ ) 6, 7, 8
A fluorine ion meter was installed in the above to monitor the water quality, and when the concentration of fluorine ions in the final treated water was measured, the removal rate of fluorine ions was 99.4%.

Comparative Example 1 The procedure of Example 1 was repeated except that the α value was not adjusted, and the fluorine ion removal rate was 87.9%.
It was considerably inferior to that of Example 1.

[0046]

As described above in detail, according to the method and apparatus for treating fluorine-containing water of the present invention, the α value of the raw water can be continuously and automatically controlled by measuring only the total acid concentration and the fluorine concentration. It is possible to obtain a high-quality treated water by sufficiently responding to fluctuations in raw water quality and performing stable and efficient treatment without causing problems such as filter media collapse of the calcium carbonate packed tower and reduction of fluorine removal rate. Made possible.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example method of a method for treating fluorine-containing water according to the present invention.

FIG. 2 is a system diagram showing another embodiment method of the present invention.

FIG. 3 is a graph showing the relationship between the amount of added HaOH to raw water and the fluorine concentration of treated water and the SS concentration of treated water.

[Explanation of symbols]

1,2,3 Calcium carbonate packed tower 4 Raw water tank 5 Raw water pump 6,7,8 Circulating water tank 9.10,11 Circulating pump 12 Sample pump 14 Chemical injection control device 15 H ₂ SO ₄ storage tank 16,19 Chemical injection pump 18 NaOH storage tank

Claims (2)

(57) [Claims] 1. A method for treating fluorine-containing water, which comprises passing the fluorine-containing water through a calcium carbonate packed column filled with calcium carbonate granules to remove fluorine, and measuring the fluorine concentration and the acid concentration in the fluorine-containing water. The α value is calculated from the measured value by the following formula (I), the calculated α value is compared with a predetermined reference range, and when the α value is out of the reference range, a predetermined amount of acid or alkali is determined. A method for treating fluorine-containing water, which comprises adding water to the fluorine-containing water and then passing the water through the calcium carbonate packed tower. [Equation 1] 2. A raw water tank for storing fluorine-containing water, a calcium carbonate packed tower filled with calcium carbonate granules, means for feeding the raw water in the raw water tank to the calcium carbonate packed tower, and treated water from the calcium carbonate packed tower. In a treatment apparatus for fluorine-containing water, which comprises a means for discharging water, a measuring means for sampling the raw water in the raw water tank to measure the fluorine concentration and the acid concentration in the water; Computation comparing means for computing the α value by the formula (I) and comparing it with a predetermined reference range, and chemical injection means for receiving a signal from the computing comparison means and adding a predetermined amount of acid or alkali to the raw water. A treatment device for fluorine-containing water, which is characterized by being provided. [Equation 2]