JPH11156355A - Method for treating fluorine-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover fluorine efficiently as high purity calcium fluoride by a method in which fluorine-containing water of low concentration is passed through an ion exchange device, and the regeneration waste liquid of the ion exchange device and fluorine-containing water of high concentration are combined and passed through a column filled with calcium carbonate for fluorine recovery treatment. SOLUTION: When fluorine containing water of low concentration and fluorine- containing water of high concentration are treated, the water of low concentration, after being stored in a low concentration fluorine-containing water storage tank 1, is passed through an ion exchange device 2 to remove fluorine ions. A regenerating liquid is passed appropriately through the anion exchange resin in the device 2 for regeneration, and regeneration waste liquid, after being stored in a regeneration waste liquid storage tank 5, is sent to a high concentration fluorine-containing water storage tank 6 to be mixed with the water of high concentration. The water of high concentration mixed with the regeneration waste liquid is passed through a column 7 filled with calcium carbonate and circulated by an intermediate tank 8 and a circulating pump 9 to reduce impurities in calcium fluoride, obtaining high purity calcium fluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating fluorine-containing water. More specifically, the present invention treats low-concentration fluorine-containing water and high-concentration fluorine-containing water discharged from semiconductor factories and liquid crystal factories, etc., and can efficiently recover fluorine as recyclable calcium fluoride. The present invention relates to a method for treating fluorine-containing water.

[0002]

2. Description of the Related Art In semiconductor factories and liquid crystal factories,
Large amounts of hydrofluoric acid (HF), ammonium fluoride (N
H ₄ F) aqueous solution, ammonium acid fluoride (NH ₄ H)
F ₂ ) Etching of silicon wafers and the like is performed using a chemical solution such as an aqueous solution. As a process, after etching with a chemical solution, cleaning with ultrapure water is performed, so that wastewater containing a high concentration of fluorine is generated in the etching process, and fluorine is reduced to a low concentration in the cleaning process with ultrapure water. Contains wastewater. Various studies have conventionally been made to efficiently treat such high-concentration fluorine-containing water and low-concentration fluorine-containing water. For example, Clean Technology, Vol. 6, No. 1, 35-
On page 37 (1996), the fluorine-containing wastewater is separated into a concentrated system and a diluted system, and the concentrated fluorine-containing wastewater is subjected to fluorine recovery treatment. And a method of treating by a coagulation sedimentation method. However, depending on this method, the fluorine in the concentrated fluorine-containing wastewater can be recovered by the fluorine recovery treatment, but the diluted fluorine-containing wastewater needs to be treated by the coagulation sedimentation method, which generates a large amount of sludge, Fluorine in the contained wastewater could not be recovered in the form of recyclable calcium fluoride or the like. Japanese Patent Application Laid-Open No. 5-92187 discloses a system in which low-concentration fluorine-containing water and high-concentration fluorine-containing water are discharged. There has been proposed a method for treating fluorine-containing water in which a resin waste solution is combined with high-concentration fluorine-containing water, a calcium compound is added thereto, and coagulation treatment is performed to separate solid-liquid. According to this method, efficient treatment of fluorine-containing water can be performed, but high-concentration fluorine-containing sludge is generated. For this purpose, two or more systems of fluorine-containing water consisting of low-concentration fluorine-containing water and high-concentration fluorine-containing water discharged from semiconductor factories and liquid crystal factories are rationally treated to recycle fluorine. There has been a demand for a method of treating fluorine-containing water that can be efficiently recovered by the method.

[0003]

SUMMARY OF THE INVENTION The present invention treats low-concentration fluorine-containing water and high-concentration fluorine-containing water discharged from a semiconductor factory, a liquid crystal factory, and the like, so that high-purity fluorine that can easily recycle fluorine can be obtained. An object of the present invention is to provide a method for treating fluorine-containing water that can be efficiently recovered as calcium iodide.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor separated the discharged fluorine-containing water into a concentrated system and a dilute system, and separated the low-concentration fluorine-containing water. By passing the water through the ion exchange device and mixing the high-concentration fluorine-containing water with the regenerated wastewater containing high concentration of fluorine discharged when regenerating the ion exchange device, and passing the water through the calcium carbonate packed column, The inventors have found that fluorine can be easily and easily recovered as high-purity calcium fluoride, and have completed the present invention based on this finding. That is, the present invention relates to a method for treating low-concentration fluorine-containing water and high-concentration fluorine-containing water, wherein the low-concentration fluorine-containing water is passed through an ion exchange device, and the regenerated waste liquid of the ion exchange device and the high-concentration fluorine-containing water are treated. In addition, the present invention provides a method for treating fluorine-containing water, characterized in that a fluorine recovery treatment is carried out by passing water through a calcium carbonate packed tower.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The method for treating fluorine-containing water according to the present invention is a method for treating low-concentration fluorine-containing water and high-concentration fluorine-containing water, wherein the low-concentration fluorine-containing water is passed through an ion exchange device. The recycle waste liquid of the ion exchange device and the high-concentration fluorine-containing water are combined, and the mixture is passed through a calcium carbonate packed tower to perform a fluorine recovery treatment. In a semiconductor factory or the like, a silicon wafer or the like is etched using a large amount of a chemical solution such as hydrofluoric acid (HF), ammonium fluoride (NH ₄ F), or ammonium acid fluoride (NH ₄ HF ₂ ). As a process, after etching with a chemical solution, cleaning with ultrapure water is performed, so that the drainage liquid can be divided into high-concentration fluorine-containing water generated in the etching process and low-concentration fluorine-containing water generated in the cleaning process. it can.

FIG. 1 is a process flow chart of one embodiment of the method for treating fluorine-containing water of the present invention. The fluorine concentration of the low-concentration fluorine-containing water is usually about 100 mg / liter or less, and nitric acid or acetic acid may be contained as a substance other than the above-mentioned fluorine compound, but the mixture of other ions is small. In the method of the present invention, low-concentration fluorine-containing water is stored in a low-concentration fluorine-containing water storage tank 1 as necessary, and then passed through an ion exchange device 2 by a pump to remove fluorine ions. The ion exchange device used is preferably an ion exchange column filled with an anion exchange resin. The treated water obtained by passing the water through the ion exchange device contains few fluorine ions and other ions, and has a low electric conductivity. Therefore, the treated water is stored in the treated water storage tank 3 as necessary, and low-purity water or the like is used. Can be reused as In the method of the present invention, since an ion exchange device is used,
It can remove ions other than fluorine and is useful when reusing treated water. The ion exchange treatment of the anion exchange resin is appropriately stopped, and a regeneration solution such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is passed from the regeneration solution tank 4 by a pump to be periodically regenerated. The regeneration waste liquid generated at this time contains fluorine at a high concentration, and a solution containing concentrated fluorine is obtained. The regenerated waste liquid containing fluorine at a high concentration is stored in a regenerated waste liquid storage tank 5 and then sent to a high-concentration fluorine-containing water storage tank 6 by a pump to be mixed with the high-concentration fluorine-containing water.

[0007] In the method of the present invention, a mixture of high-concentration fluorine-containing water and the above-mentioned regenerated waste liquid from the ion exchange device is subjected to a fluorine recovery treatment by passing the mixture through a column packed with calcium carbonate. The calcium carbonate packed in the calcium carbonate packed tower is preferably granular calcium carbonate having a particle size of 0.1 to 0.5 mm. The high-concentration fluorine-containing water mixed with the regeneration waste liquid of the ion exchange device flows from the high-concentration fluorine-containing water storage tank 6 to a calcium carbonate packed tower 7 by a pump. There is no particular limitation on the direction of water flow in the calcium carbonate packed tower, and it can be either an upward flow or a downward flow. Is preferred. In addition, the water flow rate (L
V) is preferably 20 m / h or more. For this purpose, an intermediate tank 8 and a circulating pump 9 can be provided for circulating water. Since the fluorine concentration in the treated water obtained by passing the water through the calcium carbonate packed tower is usually reduced to about several tens of mg / liter, it is stored in the treated water storage tank 10 and subjected to higher-order treatment as necessary. Can be reused. When the calcium carbonate packed tower is used for the fluorine recovery treatment, the amount of impurities such as silica contained in the calcium fluoride subjected to the coagulation treatment can be reduced, and calcium fluoride with higher purity can be obtained.

[0008] It is preferable that two or more calcium carbonate packed columns are provided, connected in series, and water is sequentially passed from the first column to the last column. Water is passed from the first column until the calcium carbonate in the first column reacts with fluorine to become completely calcium fluoride. When the calcium carbonate in the first column is completely converted to calcium fluoride, high-purity is obtained by performing so-called merry-go-round operation in which the calcium fluoride in the first column is extracted, filled with new calcium carbonate, and installed as the final column. Can be recovered. According to the method of the present invention, calcium fluoride having a purity of 90 to 98% or more can be recovered by reacting calcium carbonate with fluorine ions in fluorine-containing water in a calcium carbonate packed tower. Calcium fluoride with high utility value can be obtained.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 Low-concentration fluorine-containing water and high-concentration fluorine-containing water discharged from a semiconductor factory were treated. The fluorine concentration of the low-concentration fluorine-containing water was 100 mg / liter, and the fluorine concentration of the high-concentration fluorine-containing water was 5,000 mg / liter.
Low-concentration fluorine-containing water is converted to an anion exchange resin [Kurita Industries
EX-AG]
After passing water at a flow rate of 5 L / h for 40 hours, the anion exchange resin was regenerated using an aqueous sodium hydroxide solution. The amount of the generated regeneration waste liquid was 25 liters, and the fluorine concentration was 2,000 mg / liter. 25 liters of this reclaimed waste liquid was mixed with 75 liters of high-concentration fluorine-concentrated water, and 0.1 liter / kg was added to a calcium carbonate packed column having three columns connected in series with 50 g of calcium carbonate having a particle size of 0.32 mm. h. After flowing water continuously for 4 days, the obtained 9.6 liter of treated water was analyzed for fluorine concentration.
It was 30 mg / liter. After the packing of the first column was dried and subjected to chemical analysis, the purity was 98.
It was 0% by weight calcium fluoride. Comparative Example 1 The low-concentration fluorine-containing water used in Example 1 was passed through a column packed with 5 liters of a fluorine-adsorbing resin [Asahi Glass Co., Ltd., READ-F] at a flow rate of 25 liters / h for 40 hours. Thereafter, the fluorine-adsorbing resin was regenerated using an aqueous sodium hydroxide solution. The amount of the generated regeneration waste liquid was 25 liters, and the fluorine concentration was 2,000 mg / liter. 25 liters of this reclaimed waste liquid and 75 liters of high-concentration fluorine-concentrated water were placed in a reaction vessel and mixed, and 2,400 g of calcium hydroxide was added and stirred for 1 hour. The obtained white suspension was transferred to a precipitation tank to perform solid-liquid separation. The fluorine concentration of the supernatant water was 30 mg / liter, and the dried sludge was calcium fluoride having a purity of 70.0% by weight. Table 1 shows the results of Example 1 and Comparative Example 1.

[0010]

[Table 1]

From the results shown in Table 1, it is found that low-concentration fluorine-containing water is passed through the ion exchange apparatus, and the regenerated wastewater of the ion exchange apparatus and the high-concentration fluorine-containing water are combined and passed through a calcium carbonate packed column. According to the method of the present invention, a calcium compound is added to a mixture of a regeneration waste liquid and high-concentration fluorine-containing water to cause coagulation, and treated water having water quality equivalent to that of a conventional method of solid-liquid separation, and calcium fluoride having a higher purity Is obtained.

[0012]

According to the method of the present invention, low-concentration fluorine-containing water and high-concentration fluorine-containing water discharged from semiconductor factories and liquid crystal factories are treated, and high-purity fluorinated fluorine can be easily recycled. It can be efficiently recovered as calcium.

[Brief description of the drawings]

FIG. 1 is a process flow chart of one embodiment of the method for treating fluorine-containing water of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Low concentration fluorine-containing water storage tank 2 Ion exchange device 3 Treated water storage tank 4 Regeneration liquid tank 5 Regeneration waste liquid storage tank 6 High concentration fluorine-containing water storage tank 7 Calcium carbonate filling tower 8 Intermediate tank 9 Circulation pump 10 Treated water storage tank

Claims (1)

[Claims] 1. A method for treating low-concentration fluorine-containing water and high-concentration fluorine-containing water, wherein the low-concentration fluorine-containing water is passed through an ion exchange device, and the regenerated waste liquid of the ion exchange device and the high-concentration fluorine-containing water are mixed with each other. A fluorine recovery treatment by passing water through a calcium carbonate packed tower.