JP2005177669A - Treatment method for fluorine-containing wastewater - Google Patents

Abstract

Treatment of fluorine-containing wastewater that can remove fluorine from fluorine-containing wastewater with a high removal rate and that can precipitate fluorine as calcium fluoride with good filterability and reduce the amount of sludge Provide a method.
SOLUTION: Fluorine-containing wastewater is reacted with 1.5-3 times equivalent of calcium chloride with respect to the amount of fluorine contained in the fluorine-containing wastewater under the condition of pH 1.5-4. Next, after adjusting the pH of the reaction solution obtained to preferably 5 or more and less than 8 by adding calcium hydroxide, the precipitate containing calcium fluoride as a main component is separated from the reaction solution.
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Description

  The present invention relates to a novel treatment method for removing fluorine from wastewater containing fluorine. More specifically, the present invention provides a method for treating fluorine-containing wastewater that enables fluorine contained in fluorine-containing wastewater to be removed as calcium fluoride while suppressing the amount of sludge generated very efficiently.

  Fluorine-containing wastewater discharged from various factories such as an electronic material manufacturing factory needs to remove fluorine contained in the wastewater amount regulation.

  Conventionally, as a method for removing fluorine from fluorine-containing wastewater, a method is known in which calcium salt or calcium hydroxide is added to the wastewater, and fluorine is precipitated as hardly soluble calcium fluoride for separation.

  Moreover, in the said method, after adding calcium salt to the fluorine-containing wastewater whose pH is 1-7 as a method of removing the fluorine contained highly while suppressing the production | generation of sludge by addition of calcium salt, A method has been proposed in which calcium oxide (slaked lime) is added to adjust the pH of wastewater to 8 to 11 and the generated precipitate is removed (see Patent Document 1).

  In addition, the above-mentioned document describes that a high fluorine removal rate can be maintained while reducing the generation of sludge by making the addition amount of calcium salt approximately equivalent to the expected fluorine amount in wastewater. Has been.

  However, although the above method can reduce the amount of sludge generated, calcium hydroxide added to adjust the wastewater pH leads to an increase in the amount of sludge, and thus further reduction of the amount of sludge is desired. Moreover, the particle size of the calcium fluoride produced is small, and there is room for improvement in filterability.

JP 54-7761 A

  Accordingly, an object of the present invention is to remove fluorine from a fluorine-containing wastewater at a high removal rate, and to precipitate the fluorine as calcium fluoride having good filterability, thereby further reducing the amount of sludge as compared with the conventional method. It aims at providing the processing method of the fluorine-containing wastewater which can be reduced.

  The present inventors have intensively studied to achieve the above object. As a result, in order to increase the particle size of calcium fluoride produced by the addition of calcium salt, it is necessary to use a water-soluble calcium salt and add it in an excessive and limited amount. At this time, it was found that the effect of increasing the particle diameter is remarkably exhibited by maintaining the pH within a specific range. In addition, by increasing the pH of the solution after the reaction to a specific value (reachable pH), the dissolved fluorine is precipitated, and as a result, it is possible to obtain treated wastewater in which the fluorine concentration is drastically reduced. The headline and the present invention were completed.

  That is, the present invention reacts a fluorine-containing wastewater with a water-soluble calcium salt equivalent to 1.5 to 3 times the amount of fluorine contained in the fluorine-containing wastewater under the conditions of pH 1.5 to 4. Fluorine-containing wastewater characterized in that calcium fluoride is produced, and then the pH of the resulting reaction solution is adjusted to 5 or more and less than 8, and then a precipitate containing calcium fluoride as a main component is separated from the reaction solution. It is a processing method.

  According to the present invention characterized by the combination of the addition of excess calcium salt at the specific pH and the ultimate pH, the generated calcium fluoride has a large particle size, and the filtration rate and separation of the precipitate mainly composed thereof As a result, the efficiency can be remarkably improved and the moisture content is lowered. As a result, the amount of sludge produced can be reduced. Moreover, when using calcium hydroxide for the alkali for pH adjustment, it is possible to keep sludge generation amount low. Furthermore, it is possible to obtain treated wastewater in which the fluorine concentration is reduced to an extremely low fluorine concentration, for example, about 2 to 5 ppm, at the ultimate pH by adding an excessive amount of water-soluble calcium salt as compared with the conventional method. .

  In the present invention, the fluorine-containing wastewater to be treated is not particularly limited, and the wastewater discharged from various factories and containing fluorine is targeted. In general, the fluorine-containing wastewater has a pH in a wide range of 0.1 to 12, and a fluorine ion amount of 50 to 2000 ppm. There are also those containing other coexisting ions.

  In the present invention, it can be applied to any of these fluorine-containing wastewaters. Particularly, the pH is 1 to 9, and the amount of fluorine ions is 300 to 1000 ppm. It is suitable for fluorine-containing wastewater of 50% or less, particularly 30% or less, based on fluorine ions.

  Typical examples of such fluorine-containing wastewater include wastewater from factories such as fluorine compound manufacturing industry, semiconductor manufacturing industry, steel manufacturing industry, glass manufacturing industry, and fertilizer manufacturing industry.

  In the present invention, the condition for adding the water-soluble calcium salt to the fluorine-containing wastewater is 1.5 to 3 times equivalent, preferably 1.5 to 2 times equivalent to the amount of fluorine in the fluorine-containing wastewater. In such an amount that the pH is 1.5 to 4, preferably 1.5 to 2.5 (first pH adjustment step).

  That is, calcium fluoride crystals having an increased particle size can be precipitated by a combination of the amount of the specific water-soluble calcium salt added and the pH value. Therefore, when each condition is out of the above range, the calcium fluoride particles to be produced are remarkably miniaturized, and the amount of solid sludge is increased due to a decrease in separability such as filterability and an increase in water content. In addition, even when the ultimate pH described later is satisfied, the above-mentioned micronized calcium fluoride particles are mixed into the treatment wastewater to increase the SS concentration, and thus the object of the present invention cannot be achieved.

  In the present invention, as the water-soluble calcium salt, calcium chloride, calcium bromide, calcium iodide, calcium nitrite, calcium nitrate, calcium thiosulfate, calcium thiocyanate, or the like is used. Of these, calcium chloride is preferred.

  In the present invention, the fluorine content in the fluorine-containing wastewater can be measured by lanthanum-alizarin complexone absorptiometry, ion electrode method, ion chromatograph method, and water-soluble calcium salt based on this measurement value. Is added.

  In general, the alkali is adjusted when the pH of the fluorine-containing wastewater is low relative to the pH range, and the acid is added when the pH is high. Examples of the alkali include sodium hydroxide and calcium hydroxide, and examples of the acid include hydrochloric acid, nitric acid, sulfuric acid and the like. Of these, calcium hydroxide is preferred as the alkali, and hydrochloric acid is preferred as the acid.

  The above reaction is preferably carried out in a reaction vessel with stirring. The reaction temperature is suitably 0 to 40 ° C., and the reaction time is suitably 2 to 5 minutes.

  By the above reaction, calcium fluoride having a particle size of 5 times or more with respect to the crystal particle size of calcium fluoride generated by the conventional reaction can be generated.

  In the present invention, the reaction solution in which calcium fluoride is generated has a pH of 5 or more and less than 8, preferably 6.5 to 7.5. This is a very important operation for reducing the fluorine concentration (second pH adjustment step). That is, when the ultimate pH is lower than 5, calcium fluoride precipitates are not sufficiently generated, and the fluorine removal rate in the resulting treated wastewater decreases. In addition, when the ultimate pH is 8 or more, there is almost no change in the fluorine removal rate in the treated wastewater obtained, and when lime milk is used for pH adjustment, not only the amount of sludge increases, but also the wastewater is discharged. When sulfuric acid is used for the neutralization treatment, the amount of sludge is further increased because calcium sulfate is newly precipitated, and the object of the present invention cannot be achieved. In addition, the cost for the drug is increased due to the neutralization treatment.

  The alkali, particularly calcium hydroxide, is used for the adjustment to the ultimate pH.

  In addition, it is preferable that the temperature at the time of the said pH adjustment is adjusted to 0-40 degreeC. Moreover, it is preferable to hold | maintain the said reaction liquid at this pH for 1 minute or more. It is sufficient to hold the holding time for 1 hour.

  In the present invention, the reaction liquid adjusted to the ultimate pH is separated from the precipitate by a known method to obtain treated wastewater from which fluorine has been removed.

  A known solid-liquid separator is used for separating the precipitate. For example, a filter press type filter, a centrifuge, and an oliver filter can be used. Among these, a filter press type filter is preferably used. In the filtration, a known filter aid or a flocculant can be used.

  EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

  In the examples, the fluorine concentration was measured by an ion chromatograph (manufactured by DIONEX, DX-AQ).

Examples 1 to 3, Comparative Examples 1 and 2
In the reaction tank, after adjusting pH by adding hydrochloric acid to fluorine-containing wastewater having a fluorine content of 500 ppm and pH 6.8, the first pH adjustment step of Table 1 is performed with respect to the fluorine content contained in the fluorine-containing wastewater. The indicated calcium chloride was added with stirring, and the reaction was carried out at the reaction pH shown in Table 1. In this case, the temperature of the liquid was adjusted to 20 ° C. and held for 5 minutes.

  Next, calcium hydroxide was added to the resulting reaction solution to adjust the pH of the solution to the pH value shown in the second pH adjustment step of Table 1, and kept at a temperature of 20 ° C. for 2 minutes.

  Finally, the produced precipitate was filtered under reduced pressure with a 0.1 μm membrane filter, and the filtration time was measured. Further, the fluorine concentration and water content of the treated wastewater obtained after filtration were measured.

  The results are also shown in Table 1. As is clear from Examples 1 to 3 and Comparative Examples 1 and 2, it is understood that by satisfying the conditions of the present invention, the filterability of the produced calcium fluoride is good and the amount of sludge is reduced. .

  Moreover, the microscope picture which shows the particle structure of the precipitation obtained by Example 1 is shown in FIG. 1, and the microscope picture which shows the particle structure of the precipitation obtained by Comparative Example 1 is shown in FIG. As is apparent from the figure, it is understood that the particle diameter of the calcium fluoride produced is significantly increased by satisfying the conditions of the present invention.

Photomicrograph showing the particle structure of the precipitate obtained in Example 1 Micrograph showing the particle structure of the precipitate obtained in Comparative Example 1

Claims (2)

  Fluorine-containing wastewater is reacted with 1.5 to 3 equivalents of calcium chloride with respect to the amount of fluorine contained in the fluorine-containing wastewater under the conditions of pH 1.5 to 4 to produce calcium fluoride, A method for treating fluorine-containing wastewater, wherein the pH of the reaction solution obtained is adjusted to 5 or more and less than 8, and then the precipitate containing calcium fluoride as a main component is separated from the reaction solution. The method for treating fluorine-containing wastewater according to claim 1, wherein the reaction liquid whose pH is adjusted to 5 or more and less than 8 is held for at least 1 minute.

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