JP3175445B2 - Fluorine-containing water treatment method - 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 for treating fluorine-containing water, and more particularly to a method for removing and recovering fluorine as calcium fluoride by passing fluorine-containing water in series through a plurality of calcium carbonate packed towers. The present invention relates to a method for obtaining high-quality treated water by preventing the collapse of a calcium carbonate filter medium and reducing the amount of an alkali agent added for preventing the filter medium from collapsing.

[0002]

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

[0003] Such a fluorine-containing wastewater is generally treated as a separate wastewater or as a general wastewater together with other wastewater. The method of treating the wastewater includes calcium hydroxide such as calcium hydroxide (Ca (OH) ₂ ). A method of adding a salt to generate an insoluble calcium fluoride (CaF ₂ ) and performing solid-liquid separation is generally used. However, in this method, since a large amount of sludge containing fluorine is generated, reduction of the amount of generated sludge has been a problem.

Conventionally, as a measure for reducing fluorine-containing sludge, a method has been proposed in which a fluorine-containing waste liquid is passed through a plurality of calcium carbonate packed towers, and fluorine is converted to calcium fluoride having good crystallinity and removed and recovered. ing. In addition, in such a method, when the raw water is a fluorine-containing acidic wastewater, an alkali agent (ammonia, ammonium fluoride, or the like) is added to the raw water for the purpose of preventing filter medium (calcium carbonate) from disintegrating. There has also been proposed a method of circulating a part of treated water of a packed tower to a raw water tank to reduce the amount of an alkali agent added.

However, in the method of circulating a part of the treated water in the final packed tower to the raw water tank, the circulating water changes the ion form in the raw water from HF type to NH ₄ F and NH ₄ HCO ₃ type. Accordingly, the reaction rate with calcium carbonate, which is a filter medium, decreases. For this reason, problems such as a decrease in the fluorine removal rate and a deterioration in the quality of the final treated water (that is, an increase in the fluorine concentration) or a decrease in the purity of the recovered calcium fluoride occur. I do. As a countermeasure for this, it is conceivable to further increase the number of packed columns of calcium carbonate. However, further addition of packed columns of calcium carbonate causes an increase in equipment size and an increase in equipment cost, which is industrially disadvantageous.

The present inventors have solved the above conventional problems,
In the method of removing and recovering fluorine as calcium fluoride by passing fluorine-containing water through a plurality of calcium carbonate packed towers, it is possible to increase the fluorine removal rate without increasing the number of calcium carbonate packed towers and increase the quality of the treated water. As a method of recovering high-purity calcium fluoride, in a method of treating fluorine-containing water by passing it through a plurality of calcium carbonate packed towers in series, a part of the effluent of each calcium carbonate packed tower is treated. A method of passing water through the same calcium carbonate packed column again was proposed, and a patent application was filed earlier (Japanese Patent Application No. Hei 5
-48018. Hereinafter, it is referred to as “first application”. ).

[0007] According to the method of the prior application, the effluent of the calcium carbonate packed tower is circulated to the inflow side of the calcium carbonate packed tower to dilute the inflow water, thereby reducing the fluorine concentration of the inflow water. Since the fluorine removal efficiency in the calcium carbonate packed tower is increased, the size of the apparatus can be reduced, the fluorine removal rate can be improved, and the purity of the recovered calcium fluoride can be improved.

Further, carbon dioxide gas generated by the reaction between fluorine and calcium carbonate in the calcium carbonate packed tower causes a part of the filter medium to flow out of the tower. This is prevented by a decrease in the amount of generated gas due to a decrease in the concentration and a decrease in the fluorine concentration.

[0009]

By the way, in such treatment of fluorine-containing water, an increase in the amount of cations in the treated water is minimized in order to reuse the treated water obtained as raw water for producing pure water. Is needed. Therefore, it is important to prevent the filter material from collapsing and to reduce the amount of the alkali agent added to prevent the filter material from collapsing. However, the amount of the alkaline agent (NH ₃ ) added, the filter material collapse rate, and the treatment shown in FIG. Relationship with water fluorine concentration (raw water fluorine concentration 85
As is clear from the above, when the added amount of the alkali agent is reduced, the filter material collapse rate is increased, which is not desirable as raw water for producing pure water from the viewpoint of the amount of treated water cation and the turbidity. There is.

According to the present invention, in the method of the above-mentioned prior application, the amount of an alkali agent added and the amount of cations in the treated water required for preventing the filter material from collapsing are reduced, so that the raw water for producing purified water of the treated water is reduced. It is an object of the present invention to provide a method for treating fluorine-containing water, which enables reuse of water.

[0011]

The method for treating fluorine-containing water according to the present invention is a method for treating fluorine-containing water by passing it through a plurality of calcium carbonate packed towers in series. After aeration, a part thereof is again passed through the same calcium carbonate packed column.

[0012]

[Function] It is known that calcium carbonate (CaCO ₃ ) filter medium is dissolved by mineral acids other than hydrofluoric acid (HF). However, since the following reaction with hydrofluoric acid proceeds in the filter medium, it is theoretically possible. If there is no mineral acid other than hydrofluoric acid in raw water,
Filter media does not dissolve.

CaCO ₃ (filter material) + 2HF → CaF ₂ (filter material) + H ₂ O + CO ₂ ↑ (1) However, even if mineral acids other than hydrofluoric acid do not actually exist in the raw water, some of the filter media Collapses. We have:
As a result of examining the cause of the collapse of the filter medium even when mineral acids other than hydrofluoric acid were not present in the raw water, the following facts were found.

That is, during the reaction according to the above formula (1), C
Although O ₂ gas is generated, the concentration of H ₂ CO _{3 in} water is actually increased by the reaction of the following formula (2). This H ₂ CO
₃ , Ca ²⁺ of the filter medium reacts according to the following formula (3),
Experiments have shown that the filter media dissolves.

CaCO ₃ + 2HF → CaF ₂ + H ₂ CO ₃ (2) CaCO ₃ + H ₂ CO ₃ → Ca ²⁺ +2 (HCO ₃ ) ^- (3) In the method for treating fluorine-containing water of the present invention, By aerating the effluent of each calcium carbonate packed tower, H ₂ CO ₃ in the effluent is released as CO ₂ gas, and then the water is again passed through the same calcium carbonate packed tower, whereby the calcium carbonate packed tower is filled. The amount of H ₂ CO ₃ flowing into the tower is reduced as much as possible. As a result, the filter medium is prevented from collapsing due to H ₂ CO ₃ and the amount of cations in the treated water and the amount of the alkali agent added for preventing the filter medium from collapsing are reduced.

[0016]

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

FIG. 1 is a system diagram showing an embodiment of a method for treating fluorine-containing water according to 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 are provided with diffuser pipes 6A, 7A and 8A, respectively. . 9,
Reference numerals 10 and 11 indicate circulation pumps. Reference numerals 20 to 31 indicate pipes.

In this embodiment, raw water, for example, high-concentration fluorine-containing water containing hydrofluoric acid, ammonium fluoride, etc., is first introduced into the raw water tank 4 through the pipe 20 and then into the raw water tank 21.
Further, an alkali agent for preventing the filter material from collapsing is added. Next, the calcium carbonate is introduced into the circulating water tank 6 through the pipe 22 having the pump 5, and is aerated with the outflow water of the calcium carbonate packed tower 1 from the pipe 24 by the diffuser 6 </ b> A. It is introduced into the packed tower 1. The effluent of the calcium carbonate packed tower 1 is returned to the circulating water tank 6 from the pipe 24, and the overflow water in the circulating water tank 6 is introduced to the circulating water tank 7 from the pipe 25. After being aerated with the diffuser 7A together with the outflow water of the calcium carbonate packed tower 2 from the pipe 27, the pump 10
Is introduced into the calcium carbonate packed tower 2 from a pipe 26 having The effluent of the calcium carbonate packed tower 2 is
7 returns to the circulating water tank 7. The overflow water in the circulating water tank 7 is introduced into the circulating water tank 8 through a pipe 28,
After being aerated with the air diffuser 8A together with the outflow water of the calcium carbonate packed tower 3 from 0, it is introduced into the calcium carbonate packed tower 3 from a pipe 29 provided with the pump 11. The effluent from 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.

In such a method for treating fluorine-containing water, the raw water may be various kinds of fluorine-containing water, each of which may be treated separately, or may be mixed and treated. If it is done, it will react with the filter medium calcium carbonate in the calcium carbonate packed tower and cause gelation,
Preferably, the phosphorus is removed in advance.

Ammonia (NH ₄ OH) or the like is added to the raw water as an alkaline agent in order to prevent the filter medium from collapsing. According to the present invention, the amount of the alkaline agent required to prevent the filter medium from collapsing is reduced. H ₂ CO _{3 in} the calcium carbonate packed tower effluent by aeration and the circulation of the calcium carbonate packed tower effluent are greatly reduced.

The amount of the alkaline agent to be added varies depending on the quality of the raw water and the degree of aeration, but it is usually preferable to set the concentration to about 0 to 0.6 equivalent times the fluorine concentration in the raw water.

The flow rate of the inflow water into each of the calcium carbonate packed towers varies depending on the particle size of the calcium carbonate filter medium filled therein, and is appropriately determined within a range in which the filter medium is in a fluid state and the filter medium does not flow out of the tower. In a normal case, if the filter medium particle size is about 0.3 mm, it is about 10 m / hr or more, especially 2 m / hr.
It is about 0 to 30 m / hr.

The raw water supply by the raw water pump is as follows:
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.

When the difference between the fluorine concentration of the influent water and the fluorine concentration of the effluent water of the column packed with calcium carbonate disappears, conversion of the filter medium in the column to calcium fluoride is completed.
It has reached saturation. In this case, the filter medium is withdrawn and replaced with a new calcium carbonate filter medium.

According to the present invention, when raw water is passed through a plurality of calcium carbonate packed towers in series, the fluorine concentration of the inflow water of the most upstream calcium carbonate packed tower is the highest, and this calcium carbonate packed tower has Since the conversion rate of calcium fluoride is the highest, the filter material of the calcium carbonate packed tower on the most upstream side is replaced, and the calcium carbonate packed tower on which this replacement has been performed is moved to the most downstream side, and the calcium carbonate packed on the lower side is sequentially filled. Raise the tower to the upper side. This makes it possible to efficiently recover high-purity calcium fluoride from the most upstream calcium carbonate packed tower,
Moreover, since the calcium carbonate conversion ratio of the filter medium in the most downstream calcium carbonate packed tower is always low, it is possible to obtain high quality treated water as the final treated water.

The method shown in FIG. 1 is an embodiment of the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist. For example, the aeration of the effluent from the calcium carbonate packed tower is preferably performed by a diffuser provided in a circulating water tank as shown in the figure.
Any method can be adopted as long as it can obtain the same aeration effect as diffused aeration, such as stirring the surface of the circulating water tank or hitting the water surface with a pump.

Further, two or more circulating water tanks may be provided for each calcium carbonate packed tower in order to prevent a short circuit of water.

In the illustrated embodiment, an example is shown in which the calcium carbonate packed tower is provided in three stages. However, in the present invention, the calcium carbonate packed tower may be provided in two stages, or a plurality of columns of four or more stages may be provided. A step may be provided.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

EXAMPLE 1 100 ml of calcium carbonate particles having a diameter of 0.3 mm were packed in a column having an inner diameter of 3 cm, and three such columns (columns,...) Were used in a three-column series as shown in FIG. The treatment was performed by passing the contained water through. Raw water is obtained by diluting the reagent hydrogen fluoride to 500 mg-F / l with water, and adding NH ₄ O
H was added at 60 mg / l. The feed rate of the raw water pump 5 was 200 ml / hr.

In the treatment, in the column (calcium carbonate packed column 1), the effluent is circulated to the circulating water tank 6 at a flow rate of 230 ml / hr, and a part of the circulating water is circulated in the circulating water tank 7 of the column.
And subjected to water flow and circulation treatment under the same conditions as the column. Further, a part of the circulating water of the column was transferred to the circulating water tank 8 of the column, subjected to water passage and circulation treatment under the same conditions as the column, and a part thereof was discharged as treated water. In each of the circulating water tanks 6, 7, and 8, the air in the circulating water is aerated at 500 ml / min by air diffusers 6A, 7A, and 8A, respectively.
O ₂ gas was released into the air.

After passing water for one week, the fluorine concentration, calcium concentration and turbidity of the treated water were examined. The results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that air aeration was not performed in each of the circulating water tanks 6, 7, and 8. When water was passed for one week, the fluorine concentration of the treated water was measured. , Calcium concentration and turbidity were examined, and the results are shown in Table 1.

[0035]

[Table 1]

The following is clear from Table 1.

That is, the treated water of Example 1 in which the aeration of the circulating water tank was performed was the same as that of Comparative Example 1 in which the aeration of the circulating water tank was not performed.
The treated water has substantially the same treatment effect as the fluorine concentration, but the calcium concentration (dissolved amount of calcium) and the turbidity (dissolved Ca ²⁺ and F ^{− in the} water indicating that the filter medium has collapsed) are CaF ₂ sludge, which is measured as turbidity.) For Comparative Example 1 according to the method of Example 1.
A remarkably good result is obtained as compared with the method of (1). Example 1
By aerating the circulating water tank with air and dispersing CO ₂ gas in the method of the above, Ca ²⁺ elution from the filter medium due to filter medium collapse and CaF ₂ sludge outflow can be prevented.
High-quality treated water that can be directly passed to a pure water production apparatus using an ion exchange resin was obtained.

[0038]

As described in detail above, according to the method for treating fluorine-containing water of the present invention, fluorine-containing water is passed in series through a plurality of calcium carbonate packed towers to remove and recover fluorine as calcium fluoride. In this method, the collapse of the calcium carbonate filter medium can be prevented, and the amount of the alkali agent added for preventing the filter medium from collapsing can be reduced. For this reason, the amount of cations and turbidity in the obtained treated water are reduced, and high-quality treated water is obtained, so that the treated water can be effectively reused as raw water for producing pure water.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between the amount of an alkaline agent (NH ₃ ) added, the filter material collapse rate, and the concentration of treated water fluorine.

[Explanation of symbols]

 1,2,3 Calcium carbonate packed tower 4 Raw water tank 5 Raw water pump 6,7,8 Circulating water tank 6A, 7A, 8A Air diffuser 9.10,11 Circulating pump

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-254571 (JP, A) JP-A-5-293475 (JP, A) JP-A-5-301092 (JP, A) 10798 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 1/58 C01F 11/22

Claims (1)

(57) [Claims] 1. A method for treating fluorine-containing water by passing water through a plurality of calcium carbonate packed towers in series, comprising aerating the effluent of each calcium carbonate packed tower and partially refilling the same calcium carbonate packed tower. A method for treating fluorine-containing water, comprising passing water through a tower.