JP4608868B2 - Treatment method for fluorine-containing wastewater - Google Patents

Description

  The present invention relates to a method for treating fluorine-containing wastewater, and more particularly, to a method for treating high-quality treated wastewater having a low fluorine concentration by treating fluorine contained in the wastewater.

  Fluorine-containing wastewater is discharged from various industrial fields such as the metal surface treatment industry, the glass industry, the phosphorus fertilizer manufacturing industry, and the semiconductor manufacturing industry, as well as from cleaning plants that incinerate various types of garbage. Currently, the water pollution control law sets the emission standard for fluorine at 8 mg / liter, but for the purpose of further reducing the environmental impact, local governments and others are 3 mg / liter or less, or 0.8 mg / liter (equal to tap water). (Environmental standards) Some of the following are being studied, and advanced treatment methods for fluorine are being studied.

Conventionally, as a method for treating fluorine-containing wastewater, there is a coagulation sedimentation method in which a calcium compound is added to fluorine-containing wastewater, and fluorine in the fluorine-containing wastewater is precipitated as calcium fluoride (CaF ₂ ) and solid-liquid separated. This method is a method proposed by Scott et al. In 1937 (see Non-Patent Document 1). However, the amount of generated sludge is large, and the solubility of calcium fluoride (CaF ₂ ) is relatively high. There is a drawback that it is extremely difficult to reduce the concentration to 10 ppm or less. In order to reduce the wastewater standard value to 8 mg / liter using this method, it is necessary to add a calcium compound that is 10 to 100 times the theoretical reaction amount. As another method, as described in 1934 C.I. S. A method of adding an aluminum salt proposed by Boruff (see Non-Patent Document 2) is known. However, this method also has a poor sedimentation property of the generated suspension, and since the solubility of aluminum fluoride (AlF ₃ ) is relatively high like calcium fluoride (CaF ₂ ), the fluorine concentration is reduced to 10 ppm or less. Has the disadvantage of being extremely difficult. Even if this method is used, in order to reduce the wastewater standard value to 8 mg / liter, it is necessary to add an aluminum compound that is 10 to 100 times the theoretical reaction amount.

As a method for solving these problems, a method is proposed in which a water-soluble zirconium salt is added to fluorine-containing wastewater, and after stirring, an alkaline agent is added to react with calcium ions under conditions of pH 6-8 to remove them. (For example, refer to Patent Document 1). Compared with the coagulation sedimentation method as calcium fluoride (CaF ₂ ) or aluminum fluoride (AlF ₃ ), this method can improve the sedimentation of the suspension and can obtain treated wastewater with a low fluorine concentration. The reduction value is only about a few ppm, and it is very difficult to treat it to 3 mg / liter or less as studied by local governments or 0.8 mg / liter (environmental standard) or less that is equivalent to tap water. .

Japanese Patent Laid-Open No. 58-196887

R. D. Scott, two others, OhioConf. Water Purification, 16th. Ann. Rept. 1963, 26-30 (1937) C. S. Boruff, Ind. Eng. Chem. 26, 69-71 (1934)

  As described above, in the conventional coagulation-precipitation treatment method for fluorine-containing wastewater, a method for obtaining high-quality wastewater with a low fluorine concentration has not yet been developed, and fluorine treatment technology for reducing future environmental impacts. The biggest problem is that is not established.

  An object of the present invention is to provide a method for obtaining a high-quality treated wastewater from which fluorine has been removed by treating fluorine-containing wastewater.

In order to achieve the above object, the present invention maintains the pH of fluorine-containing wastewater at more than 4 and less than 6, while the alkaline earth metal salt is 0.5 to 2 times the fluorine content contained in the wastewater. Mol, zirconium salt is added in an amount corresponding to 0.1 to 4 g / liter when the zirconium salt is zirconium oxychloride with respect to a fluorine content of 50 mg / liter contained in the waste water. is there.

  The present invention is described in detail below.

  In the treatment of the present invention, pH control is extremely important. It is necessary to maintain the pH at more than 4 and less than 6, and therefore, an acid or an alkali is added as necessary to adjust the pH. When the pH is 4 or less, a suspension formed by the reaction of fluorine with an alkaline earth metal salt and a zirconium salt is not sufficiently formed, and sedimentation separation is impossible. On the other hand, when the pH is 6 or more, a part of the zirconium salt does not react with fluorine and precipitates itself as zirconium hydroxide, so that the zirconium salt does not work effectively in the reaction with fluorine.

  Moreover, although it is unclear why the treatment is carried out while maintaining the pH at more than 4 and less than 6, the amount of fluorine in the wastewater after the treatment is drastically reduced, and high-quality treated wastewater can be obtained. This phenomenon is extremely specific, and the alkaline earth metal salt and zirconium salt and fluorine act synergistically only in a limited pH region to form a special suspension, and the sedimentation separation is also marked. Estimated as an improved result. The pH maintenance range is more preferably in the range of 4.5 to 5.5.

In the present invention, when the pH of the fluorine-containing wastewater itself is 4 or less, or 6 or more, an inorganic alkali such as sulfuric acid, hydrochloric acid, nitric acid or sodium hydroxide, potassium hydroxide, calcium hydroxide is added to increase the pH to more than 4 It is necessary to adjust to less than 6. Of these, it is particularly preferable to adjust using calcium hydroxide. This is because calcium hydroxide not only acts as an alkali agent but also reacts with fluorine ions to form calcium fluoride (CaF ₂ ), thereby contributing to insolubilization and removal of fluorine.

Examples of the alkaline earth metal salt used in the present invention include calcium, magnesium, barium, and strontium chlorides, sulfates, nitrates, carbonates, and acetates, and these may be used singly or in combination. Of these, calcium chloride and magnesium chloride are particularly preferred. This is because the solubility is high and, as described above, it reacts with fluorine ions to form calcium fluoride (CaF ₂ ) and magnesium fluoride (MgF ₂ ), thereby contributing to insolubilization and removal of fluorine. The addition amount of the alkaline earth metal salt is 0.5 to 2 times the fluorine content contained in the waste water . If the amount is less than 0.5 times mol, the effect of reducing fluorine is inferior. On the other hand, even if an amount exceeding 2 times mol is added, not only calcium and magnesium are added to the solution, but also the fluorine is not effectively reduced .

  Examples of the zirconium salt used in the present invention include zirconium sulfate, zirconium nitrate, zirconium chloride, zirconium oxychloride, and zirconium hydroxide, and these may be used singly or in combination. Among them, zirconium oxychloride having high solubility is particularly preferable, and when zirconium oxychloride is used, it can be supplied as a high concentration solution. In use, it is preferable to use it as a liquid dissolved in water because it is easy to handle in operation, but it can also be used as a solid.

The addition amount of the zirconium salt used in the present invention, when the fluorine content in the exhaust water is 50 mg / liter, in the case of adding zirconium oxychloride, for example a zirconium oxychloride with respect to drainage 0. Add to 1 to 4 g / liter .

  In order to treat the fluorine-containing wastewater in the present invention, acid or alkali is added to the fluorine-containing wastewater as necessary to adjust the pH to more than 4 and less than 6. And it is essential to add the alkaline earth metal salt and the zirconium salt to insolubilize the fluorine ions in the waste water while maintaining the pH at more than 4 and less than 6.

  For that purpose, it is very important to maintain and adjust the pH. When the alkaline earth metal salt used for addition is chloride, sulfate, nitrate, carbonate, acetate, the pH does not fluctuate very much, but when adding hydroxide, hydrochloric acid, sulfuric acid, etc. It is good to adjust to the above-mentioned pH range by adding acidic chemicals. Zirconium salts are generally acidic salts, and when adding a zirconium salt, the pH is generally lowered, so an alkaline chemical such as calcium hydroxide or sodium hydroxide may be added to adjust the pH range.

  Addition of the alkaline earth metal salt and the zirconium salt is usually performed by adding the alkaline earth metal salt with stirring, and then adding the zirconium salt to insolubilize fluorine ions in the waste water. Even if the alkaline earth metal salt and the zirconium salt are added simultaneously, or the order of addition is reversed, the object of the present invention can be achieved. If the initial fluorine content is very high, adding an alkaline earth metal salt first, reducing the fluorine concentration to a certain level, and then adding the zirconium salt minimizes the amount of zirconium salt added. This is a more preferable method as an embodiment.

  Furthermore, as a temperature which processes waste_water | drain, 5-60 degreeC is suitable, for example.

  Next, solid-liquid separation of the insolubilized product generated above is usually performed. For this purpose, for example, precipitation, levitation, dehydration, filtration and the like may be performed. At this time, the suspension obtained by the treatment method of the present invention is agglomerated to form a floc and is easy to separate into solid and liquid. A method of solid-liquid separation using an inorganic flocculant or a polymer flocculant such as an acrylic polymer in combination is appropriately employed.

  Further, in the present invention, a method of solid-liquid separation in combination with other lime aggregation methods, sulfate band aggregation methods, fluoroapatite aggregation methods, ion exchange resin adsorption methods, chelating agent aggregation methods, etc. is also performed by performing the treatment of the present invention. It is possible to adopt as appropriate.

  As is clear from the above description, according to the method for treating fluorine-containing wastewater of the present invention, it is possible to obtain high-quality treated wastewater from which fluorine is highly removed.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples.

Examples 1-5, Comparative Examples 1-8
A 1 liter aqueous solution with a pH of 1.5 containing 20 mg / liter as fluorine was used as a sample. Calcium chloride is added as an alkaline earth metal salt in an amount of 1 times the amount of fluorine while adding calcium hydroxide to maintain a constant pH in the range of 2 to 11, and 14% concentration as a zirconium salt. After adding 2 g of zirconium oxychloride and stirring for 20 minutes, the suspension was filtered, and fluorine in the filtrate was analyzed. The water temperature is 22-24 ° C. The results are shown in Table 1 and FIG.

  Under the processing conditions in which the pH is maintained at more than 4 and less than 6, the fluorine concentration in the filtrate is 0.8 mg / liter (environmental standard) or less, indicating that high quality water treatment is possible.

Examples 6 to 17 and Comparative Example 9
A 1 liter aqueous solution with a pH of 1.5 containing 20 mg / liter as fluorine was used as a sample. To this, sodium hydroxide is added and the pH is maintained at 5, while calcium chloride and / or magnesium chloride is added as an alkaline earth metal salt in an amount of 0 to 4 times the amount of fluorine. After adding 2 g of zirconium oxychloride and stirring for 20 minutes, the suspension was filtered, and fluorine and calcium or magnesium in the filtrate were analyzed. The water temperature is 22-24 ° C. The results are shown in Table 2.

  When calcium chloride and / or magnesium chloride is added in an amount of 0.5 mol or more of the fluorine amount, the fluorine concentration in the filtrate becomes 0.8 mg / liter (environmental standard) or less, indicating that high quality water treatment is possible. The However, under the treatment conditions added in excess of 2 moles, calcium and magnesium ions in the solution only increased, and the result was that it did not work effectively to reduce fluorine.

Example 18 and Comparative Example 10
One liter of industrial fluorine-containing wastewater containing pH 3 containing 100 mg / liter as fluorine was used as a sample. Calcium chloride was added as an alkaline earth metal salt in an amount of 1 times the amount of fluorine while maintaining the pH at 5 by adding calcium hydroxide, and 14% concentration zirconium oxychloride was not added as a zirconium salt and 10 g. After addition and stirring for 20 minutes, the suspension was filtered and analyzed for fluorine in the filtrate. The water temperature is 22-24 ° C. The results are shown in Table 3.

  When the zirconium oxychloride is added, the fluorine concentration in the filtrate is 0.8 mg / liter (environmental standard) or less, and it can be seen that high water quality treatment is possible. However, it can be seen that fluorine insolubilization treatment cannot be performed without addition of zirconium oxychloride.

It is a graph which shows the experimental result of Examples 1-5 / comparative examples 1-8.

Claims (4)

In the method for treating fluorine-containing wastewater, the alkaline earth metal salt is 0.5 to 2 times the fluorine content contained in the wastewater, zirconium oxychloride , while maintaining the pH of the wastewater at more than 4 and less than 6 Is added in an amount of 0.1 to 4 g / liter with respect to a fluorine content of 50 mg / liter contained in the wastewater. The method for treating fluorine-containing wastewater according to claim 1, wherein the pH is 4.5 to 5.5. The method for treating fluorine-containing wastewater according to claim 1 or 2, wherein the alkaline earth metal salt is a calcium salt and / or a magnesium salt. The method for treating fluorine-containing wastewater according to any one of claims 1 to 3 , wherein the pH is adjusted with calcium hydroxide.

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