JP2000140863A - Treatment of fluorine-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the decreasing effect of fluorine concn. in treated water at the calcium treating process of fluorine-containing waste water. SOLUTION: In the reactor 1, calcium fluoride is formed by mixing the waste water (fluorine-containing waste water) 8, a calcium soln. 9 and gel-like aluminum hydroxide previously formed by neutralizing an aluminum sulfate soln. (aluminum salt aq.soln.) 10 with NaOH (NaOH aq.soln.) 11 in a neutralization tank 4. Moreover, after adsorption of the calcium fluoride to the gel-like aluminum hydroxide, a polymer 12 being a high molecular flocculating agent is mixed in a flocculation tank 2, and the flocculated matter is lastly separated from treated water 13 in a precipitation tank 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fluorine-containing wastewater,
For example, the present invention relates to a method for treating fluorine-containing wastewater discharged from a semiconductor manufacturing plant, a metal surface treatment plant, a stainless steel manufacturing plant, a ceramics manufacturing plant, and the like.

[0002]

2. Description of the Related Art Conventionally, as a method for treating fluorine-containing wastewater, there has been known a method in which a calcium compound is added to fluorine-containing wastewater, and fluorine is solid-liquid separated as hardly soluble calcium fluoride. In the calcium treatment step, it is necessary to add a flocculant for the purpose of flocculating the colloid of calcium fluoride and increasing the floc size. The coagulant is roughly classified into two types: an inorganic coagulant such as an aluminum salt and an iron salt; and a polymer coagulant. Usually, in order to obtain good coagulability, an inorganic coagulant and a polymer coagulant are used. Agents are often used in combination. In addition, an aluminum salt is often used as the inorganic coagulant.

In the calcium treatment step, when an aluminum salt is used as an inorganic coagulant, aluminum ions are zwitterions and are acidic or alkaline and are dissolved in water. Therefore, an acidic or alkaline aqueous solution of an aluminum salt is usually used. When an aqueous solution of an aluminum salt is added to the fluorine-containing wastewater, the pH of the fluorine-containing wastewater to which the aqueous solution of the aluminum salt has been added is adjusted to near neutrality by adding an acidic or alkaline pH adjuster. As a result, the aluminum ions in the fluorine-containing waste water become gelled aluminum hydroxide. The gelled aluminum hydroxide adsorbs the calcium fluoride colloid in the fluorine-containing wastewater, and exhibits an effect as a fluorine coagulant.

[0004]

However, in the above-mentioned calcium treatment step using an aqueous solution of a calcium compound and an aluminum salt, there is a problem that aluminum does not sufficiently contribute to the fluorine treatment reaction. For this reason, the limit of the fluorine concentration of the treated water is about 20 mg / L only in the calcium treatment step. Therefore, if it is necessary to further improve the processability, it is common to install a treatment system that utilizes the ability to adsorb fluorine such as aluminum salts in a separate step after the calcium treatment step, which makes the process complicated. There was a problem of becoming.

Accordingly, it is an object of the present invention to provide a method for treating fluorine-containing wastewater that can reduce the fluorine concentration of the fluorine-containing wastewater with as few processing steps as possible. Another object of the present invention is to provide a method for treating fluorine-containing wastewater, which further enhances the effect of reducing the concentration of fluorine in treated water in the calcium treatment step. Still another object of the present invention is to provide a method for treating fluorine-containing wastewater, which can improve the action of aluminum in the calcium treatment step.

[0006]

According to the present invention, there is provided a gelled aluminum hydroxide producing step of producing a gelled aluminum hydroxide by neutralizing an aqueous solution of an acidic or alkaline aluminum salt. And adding a calcium compound and the gelled aluminum hydroxide to the fluorine-containing wastewater to generate calcium fluoride and include an adsorption step of adsorbing the calcium fluoride to the gelled aluminum hydroxide. We propose a method for treating fluorine-containing wastewater. Further, in the adsorption step, after a calcium compound is added to the fluorine-containing wastewater to generate calcium fluoride, a gelled aluminum hydroxide is added, and the calcium fluoride is adsorbed on the gelled aluminum hydroxide. Is preferred. Further, it is preferable that the pH at the time of neutralization in the step of producing a gelled aluminum hydroxide is 4 to 9. Further, it is preferable to perform a step of adding a polymer flocculant after the adsorption step.

[0007]

FIG. 1 is an explanatory view showing a first example of a continuous treatment apparatus for treating fluorine-containing waste water according to the present invention. First, waste water (fluorine-containing waste water) 8 is supplied to a reaction tank. 1 continuously. The wastewater 8 is obtained by adjusting the pH of the wastewater containing fluorine discharged from a semiconductor factory or the like to 4 to 9, preferably 7, using NaOH or the like.
At the same time, a calcium solution 9, which is an aqueous solution of a calcium compound, is continuously flowed into the reaction tank 1. Examples of the calcium compound include calcium chloride, calcium hydroxide, calcium carbonate, calcium sulfate and the like.

On the other hand, an aluminum sulfate solution 10 in which an aluminum sulfate salt is dissolved in water is supplied to the neutralization tank 4. In this example, the aluminum sulfate solution 10 is used, but other examples of the aluminum salt include polyaluminum chloride and sodium aluminate. Further, depending on the type of aluminum salt, the pH of the aqueous solution becomes acidic or alkaline. Then, NaOH (aqueous NaOH solution) 11 was added to the aluminum sulfate solution 10 in the neutralization tank 4 while intermixing with the stirrer 7 in conjunction with the measured value of the pH meter 14, and the p was added.
H is adjusted to 4 to 9 to generate gelled aluminum hydroxide (gelled aluminum hydroxide generation step). In this example, NaOH is used as a neutralizing agent, but the present invention is not limited to this. When the aqueous solution of the aluminum salt is alkaline, neutralization is performed using a neutralizing agent that exhibits acidity.

By adjusting the pH to 4 to 9 in this manner, a sufficient amount of gelled aluminum hydroxide can be generated from the ionic aluminum in the aluminum sulfate solution 10. When the pH is outside the range of 4 to 9, gelled aluminum hydroxide is generated, but the proportion of dissolved ionic aluminum increases, so that the effect of adsorbing calcium fluoride may decrease.

Next, the gelled aluminum hydroxide generated in the neutralization tank 4 is supplied to the reaction tank 1 by overflowing. Then, the gelled aluminum hydroxide is mixed by the stirrer 5 with the above-described wastewater 8 and calcium solution 9 supplied at the same time. Then, calcium fluoride generated by mixing the wastewater 8 and the calcium solution 9 is adsorbed on the gelled aluminum hydroxide (adsorption step).

Thereafter, the mixture is caused to flow into the coagulation tank 2. At the same time, the polymer 12 which is a polymer coagulant is supplied to the coagulation tank 2. The polymer 12 is not particularly limited, and for example, an aqueous solution of a polymer flocculant AP-120 manufactured by Diafloc is used.
Then, in flocculation tank 2, floc containing gelled sodium hydroxide to which calcium fluoride is adsorbed grows and coarsens by the action of polymer 12 by gentle stirring by stirrer 6. And finally sedimentation tank 3
Floc, that is, sludge is settled and treated water 1
3. Separate from the supernatant water. In this first example, the gelled aluminum hydroxide generated in the neutralization tank 4 was supplied to the reaction tank 1. However, the same applies when the gelled aluminum hydroxide was supplied to the coagulation tank 2. The effect of is obtained.

FIG. 2 is an explanatory view showing a second example of a continuous treatment apparatus for treating a fluorine-containing wastewater of the present invention,
The difference from the first example shown in FIG. 1 is that the reaction tank 15 for mixing the wastewater 24 and the calcium solution 25 and the reaction tank 16 for mixing the mixture of the wastewater 24 and the calcium solution 25 with the gelled aluminum hydroxide are independent. This is the point provided. Thereby, after sufficient generation of calcium fluoride, it can be adsorbed on the gelled aluminum hydroxide.

That is, the wastewater 24 and the calcium solution 25
Are mixed in the reaction tank 15 by the action of the stirrer 20 to generate calcium fluoride.
Introduce to 6. On the other hand, in the neutralization tank 19, the pH meter 30
The operation of mixing the aluminum sulfate solution 26 and NaOH 27 with the stirrer 23 to produce a gelled aluminum hydroxide while being linked to the measurement value of the above is the same as in the first example described above (the production of the gelled aluminum hydroxide). Process).

Next, the gelled aluminum hydroxide is supplied to the reaction tank 16 from the neutralization tank 19 by overflowing.
Is mixed with the mixture containing calcium fluoride supplied from the above by the action of the stirrer 21, and the calcium fluoride is adsorbed on the gelled aluminum hydroxide (adsorption step). Further, when the mixture is allowed to flow into the coagulation tank 17 and the polymer 28 is supplied in the same manner as in the first example, and the mixture is gently stirred by the stirrer 22, the flocs grow and become coarse. Then, the floc (sludge) is settled in the settling tank 18 and separated from the supernatant water as the treated water 29.

As described above, in the above-mentioned first and second examples, the aqueous solution of the aluminum salt is neutralized into gelled aluminum hydroxide and then added to the fluorine-containing wastewater, thereby adsorbing calcium fluoride. You can improve your ability.

[0016]

The present invention will be described below in more detail with reference to examples. (Example 1) The wastewater containing fluorine was treated using the continuous treatment apparatus shown in FIG. That is, the drainage 8 was continuously flown into the reaction tank 1 having a capacity of 0.8 L at 1 L / hr. The drainage 8 is obtained by adjusting the pH of a semiconductor factory wastewater having the properties shown in Table 1 to 7 with NaOH. Also, calcium chloride is dissolved in city water to increase the calcium concentration to 20,000.
The calcium solution 9 adjusted to 0 mg / L was continuously flowed into the reaction tank 1 at 30 mL / hr. On the other hand, the aluminum sulfate solution 10 whose aluminum concentration was adjusted to 800 mg / L was supplied to the neutralization tank 4 at 40 mL / hr,
Further, NaOH11 was added to adjust the pH to 7, thereby producing gelled aluminum hydroxide.

Next, the gelled aluminum hydroxide generated in the neutralization tank 4 is supplied to the reaction tank 1 by overflowing, mixed with the above-mentioned waste water 8 and the calcium solution 9, and then the mixture is added in a volume of 0.2 L. Into the coagulation tank 2 of Then, a polymer flocculant AP-120 manufactured by Diafloc was dissolved in city water, and the polymer 12 adjusted to 100 mg / L was treated for 30 m.
The mixture was continuously flown at L / hr into the coagulation tank 2 and mixed with the mixture. And finally, in the sedimentation tank 3, the treated water 13 and the floc (sludge) were separated. This treated water 1
No. 3 was collected. After filtration through 5C filter paper, the fluorine concentration and pH were measured. The results are shown in Table 2.

(Example 2) The fluorine-containing wastewater was treated using the continuous treatment apparatus shown in FIG. That is, the waste water 24 whose semiconductor factory waste water was adjusted to pH 7 in the same manner as in Example 1 was continuously flown at 1 L / hr into the reaction tank 15 having a volume of 0.8 L. Further, a calcium solution 25 prepared in the same manner as in Example 1 was added to the reaction tank 15 at a rate of 30 mL / hr.
To mix continuously with the waste water 24. Then, this mixture was allowed to flow into a reaction tank 16 having a volume of 0.5 L. On the other hand, in the same manner as in Example 1, the aluminum sulfate solution 26 was neutralized to produce gelled aluminum hydroxide, and this gelled aluminum hydroxide was supplied to the reaction tank 16 and mixed with the mixture. And this is the volume 0.2
L into the coagulation tank 17.
The polymer 28 prepared in the same manner as in Example 1 was added to 3
After continuously supplying and mixing at 0 mL / hr, the sedimentation tank 1
At 8, the treated water 29 and floc (sludge) were separated. The fluorine concentration and pH of the treated water 29 were measured in the same manner as in Example 1, and the results are shown in Table 2.

Example 3 An experiment was performed in the same manner as in Example 1 except that the gelled aluminum hydroxide produced in the neutralization tank 4 was supplied to the flocculation tank 2 after flowing over. Table 2 shows the results
It was shown to.

(Comparative Example 1) A pH meter was installed in the reaction tank 1,
The experiment was performed in the same manner as in Example 1 except that the aluminum sulfate solution was directly added to the reaction tank 1 while adding the NaOH solution so that the pH in the tank was maintained at 7.
The results are shown in Table 2. (Comparative Example 2) A pH meter was installed in the reaction tank 16, and the pH in the tank was adjusted.
While adding the NaOH solution so that is maintained at 7.
An experiment was performed in the same manner as in Example 2 except that the aluminum sulfate solution was directly added to the reaction tank 16. The results are shown in Table 2. (Comparative Example 3) A pH meter was installed in the coagulation tank 2 and an aluminum sulfate solution was directly added to the coagulation tank 2 while adding a NaOH solution so that the pH in the tank was maintained at 7. The experiment was performed in the same manner as in Example 3. The results are shown in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

From the results shown in Table 2, it is clear that the effect of lowering the fluorine concentration is greater in the examples according to the present invention than in the comparative example in which an aqueous solution of an aluminum salt was directly added to the fluorine-containing wastewater. Was.

[0024]

As described above, in the present invention, the effect of aluminum can be effectively exerted by using gelled aluminum hydroxide instead of an aqueous solution of an acidic or alkaline aluminum salt as an inorganic coagulant. In addition, the ability to adsorb fluorine can be improved. As a result, in the calcium treatment step, the fluorine concentration can be reduced as compared with the conventional case, and another treatment step can be simplified or omitted.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a first example of a continuous treatment apparatus for treating a fluorine-containing wastewater of the present invention.

FIG. 2 is an explanatory view showing a second example of the continuous treatment apparatus for treating the fluorine-containing wastewater of the present invention.

[Explanation of symbols]

1, 15, 16: reaction tank, 2, 17: coagulation tank, 3, 18
... sedimentation tank, 4, 19 ... neutralization tank, 8, 24 ... wastewater (fluorine-containing wastewater), 9, 25 ... calcium solution (calcium compound), 10, 26 ... aluminum sulfate solution (aqueous solution of aluminum salt), 11, 27 ... NaOH, 12, 28
... Polymer (polymer coagulant), 13,29 ... Treated water.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D024 AA04 AA09 AB11 BA11 BA13 BA17 BC04 CA01 CA06 DA01 DA04 DB12 DB21 DB30 4D038 AA08 AB41 BA04 BB06 BB13 BB18 4D062 BA05 BA19 BA23 BA26 BB06 CA17 DA02 DA22 DA39 DB02 DC02 DC10 EA EA14 EA15 EA16 EA19 EA32 FA01 FA11 FA22 FA28

Claims (4)

[Claims] 1. A gelled aluminum hydroxide producing step of producing a gelled aluminum hydroxide by neutralizing an aqueous solution of an acidic or alkaline aluminum salt, and a calcium compound and the gelled aluminum hydroxide in a fluorine-containing wastewater. A method for treating fluorine-containing wastewater, comprising an adsorption step of adding calcium fluoride to the gelled aluminum hydroxide to generate calcium fluoride by adding the calcium fluoride. 2. In the adsorption step, a calcium compound is added to a fluorine-containing wastewater to generate calcium fluoride, and then gelled aluminum hydroxide is added, and the calcium fluoride is added to the gelled aluminum hydroxide. The method for treating a fluorine-containing wastewater according to claim 1, wherein the fluorine-containing wastewater is adsorbed. 3. The method for treating a fluorine-containing wastewater according to claim 1, wherein the pH at the time of neutralization in the step of producing a gel aluminum hydroxide is 4 to 9. 4. The method for treating fluorine-containing wastewater according to claim 1, further comprising a step of adding a polymer flocculant after the adsorption step.