JP3157347B2 - Treatment of wastewater containing fluorine compounds - 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 compound-containing wastewater discharged from the electronics industry and the like, and more particularly to a method for treating fluorine compound-containing wastewater utilizing a calcium fluoride precipitation reaction and its treatment equipment. It is.

[0002]

2. Description of the Related Art Fluorine compound-containing wastewater discharged from the process of manufacturing electronic parts such as semiconductor wafers and liquid crystal substrates and metal surface treatment processes, or fluorine compound-containing wastewater discharged from a flue gas desulfurization unit of a thermal power plant As a method for removing the fluorine compound therein, the following method is generally employed.

That is, as shown in FIG. 2, wastewater containing fluorine compounds (hereinafter simply referred to as wastewater containing F) is supplied to an inflow pipe (2).
Enters the reactor via 1) (11), with the addition of ^{Ca ++} here via Ca ⁺⁺ solution added tube (22), p
By adding a pH adjuster via an H adjuster addition pipe (23) to adjust the pH to near neutrality, fluorine ions in the F-containing wastewater are reacted with calcium ions to produce CaF
_Two compounds are formed and precipitated, and this reaction solution is directly used as a tube (2
After flowing into the coagulation tank (13) through 4), the coagulant is added through the coagulant addition tube (26), and the pH is adjusted by adding the pH adjuster through the pH adjustment tube (27). after coagulation the CaF ₂ precipitate is solid-liquid separated sludge (28) and the treated water (29) in the settling tank through a pipe (25) (14). The coagulation tank (13) is not always necessary and may be omitted. Generally, CaCl ₂ , Ca (OH) ₂ , CaCO _{3 and the} like are used as the above Ca ⁺⁺ .

In the coagulation tank (13), P is used as a coagulant.
AC (polyaluminum chloride) or sulfuric acid bands are often used, and in many cases, an organic polymer flocculant is used in combination as a flocculant for effective solid-liquid separation. Recently, there has been a movement to use a membrane separation device instead of a settling tank. Furthermore, the intended use of the PAC or aluminum sulfate not only promote solid-liquid separation, F by coprecipitation effect ^- is also intended achieve further removal.

[0005] Here, the formation reaction of CaF ₂ is Where the solubility product K at 20 ° C. is K = [Ca ⁺⁺ ]
[F ^-] a ² = 3.45 × 10 ^-11. However, in actual wastewater, CaF _2, a reaction product of Ca ⁺⁺ and F ⁻ , does not precipitate according to the solubility product and always exists in the solution as a metastable supersaturated state. Therefore, the supersaturated state of CaF ₂ is destroyed by adding excessive calcium ions,
It is a common practice to accelerate the precipitation reaction of ₂ .
If satisfactory results are still not obtained, methods such as adding an excessive amount of an inorganic coagulant or adding another treatment process as shown in FIG. 2 are taken.

[0006] However, the above-mentioned methods have satisfactory treatment effects, but have problems such as waste of chemicals, an increase in sludge treatment amount, a high concentration of calcium ions remaining in treated water or an increase in equipment investment. I have. In addition, Ca ⁺⁺
And F ^- as can be seen from the reaction formula of, F ^- the more it decreases the concentration, the amount of Ca ⁺⁺ to be introduced in order to destroy the supersaturation of CaF ₂ is increased by the square of the relationship. Therefore low concentrations of F ^- (e.g. 20~30mgF ^- / liter) to remove very high Ca ⁺⁺ concentration in the reaction vessel (e.g., 1000
When mgCa ⁺⁺ / l or more), and not, F ^- is CaF ₂
It is not removed as a precipitate.

[0007]

SUMMARY OF THE INVENTION The present invention has the above-mentioned problems associated with the conventional removal of fluorine compounds, that is, the treatment of wastewater containing low concentrations of fluorine compounds containing high concentrations of residual Ca ^{++ in the} treated water is unstable. effect is significant when the content level to process the waste water 20 to 100 mg / l ^- which has been made to solve the problem etc., especially F, which is thought to normally difficult to process.

[0008]

The gist of the present invention is as follows.
When adding Ca salt to a fluorine compound-containing wastewater having a F ^- content concentration of 20 to 100 mg / liter and removing the fluorine compound contained in the wastewater as calcium fluoride, the amount of the fluorine compound-containing wastewater is reduced to 10 to 30%. Adding and reacting the entire amount of Ca salt to be added, adding and reacting the reaction solution to most of the remaining fluorine-containing wastewater, and then performing solid-liquid separation. Treatment method, and F ^- containing concentration of 20 to 100 mg / liter
A first reaction tank for adding the entire amount of Ca salt to be added to the total amount of fluorine-containing wastewater to 10 to 30% of a certain amount of fluorine-containing wastewater to cause a reaction; A second reaction tank for merging and reacting the reaction liquid from the tank with a reaction device for treating wastewater containing fluorine compounds, which is provided at the preceding stage of the solid-liquid separator. The purpose of the period has been reached. Up
In the above description, the dispensing rate of wastewater to the first reaction tank is 10 to 30%.
The amount is appropriately determined within the range of the amount.

[0009]

According to the present invention, the raw water of the wastewater containing F is dispensed into a first reaction tank for injecting a part of the raw water and a second reaction tank for injecting most of the raw water, and the total amount of the raw water is supplied to the first reaction tank. The total amount of Ca ⁺⁺ to be added to
allowed promote CaF ₂ precipitation reaction to enhance a ⁺⁺ concentration, is introduced directly into the second reaction vessel without further agglomeration process the reaction solution containing the resultant CaF ₂ product in the first reaction vessel. In the second reaction tank, most of the F ^{− in} the raw water sent directly to the second reaction tank and the C − remaining after the reaction in the first reaction tank.
The precipitation reaction with a ⁺⁺ is promoted by the CaF ₂ product sent from the first reaction vessel, so that F
^- it will be removed.

[0010] effluent also containing fluorine as seen in JP-A-51-86069 in conventional, reaction products of fluorine and calcium compounds, or precipitation grout product obtained by processing the waste liquid containing fluorine A method of treating a fluorine-containing waste liquid by adding and treating as a seed is known. In this case, Ca ⁺⁺ is added to a solid such as calcium fluoride or a waste liquid containing fluorine to a waste liquid containing fluorine, and coagulation treatment is performed. the resulting precipitated sediment was one in which each addition. On the other hand, the present invention divides the raw water of the F-containing waste water into two parts, one part and most parts, and adds the whole amount of Ca ⁺⁺ to one part of the raw water system to increase the Ca ⁺⁺ concentration to carry out the CaF ₂ precipitation reaction. The reaction solution containing the precipitated CaF ₂ product is allowed to flow into the other majority of the raw water system without coagulation, and the remaining Ca ⁺⁺ and the latter are mixed by the CaF ₂ product from the former system. In this method, a stable fluorine treatment is performed by accelerating the precipitation reaction with F ^{− in the} system, and then solid-liquid separation is performed. The structure and effects are different from those of the above-described conventional method.

That is, according to the present invention, the entire amount of Ca ⁺⁺ corresponding to the whole raw water is added to one part of the raw water system, and the freshly produced CaF _2, ie, the sol-like CaF _2, is kept in its entirety as it is. Sol-like Ca
F were stable to perform the crystallization in the surface of the F ₂ ^- process a feature be performed, thereby especially treatment is difficult low concentration F ^- remaining in the treated water showed excellent removal effect of containing wastewater treatment The Ca ⁺⁺ concentration can also be reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to FIG.
The F-containing wastewater is not entirely flown into the first reaction tank (11) as in the prior art, but is branched into inflow pipes (21) and (21 '), and each of them is branched into the first reaction tank (11) and the second reaction tank. (12). The ratio of drainage flowing into the inflow pipes (21) and (21 ') is 0.05 to 0.5: 0.5 to 0.95, preferably 0.1 to 0.3.
: 0.7 to 0.9. In the first reaction tank, a part of the wastewater and the total amount of Ca ⁺⁺ to be added enter, so that the Ca ⁺⁺ concentration in the solution becomes extremely high, so that CaF ₂ precipitates quickly. In the CaF ₂ generation reaction, if the pH becomes 4 or more, the pH hardly affects the CaF ₂ precipitation reaction. Therefore, the pH of the first reaction tank may be adjusted to 5 to 12 as necessary. Further, the pH of the second reaction tank may be adjusted by adding an excessive amount of a pH adjuster in the first reaction tank in advance so that the pH in the second reaction tank becomes substantially neutral.
Alternatively, the pH may be newly adjusted by adding a pH adjuster to the second reaction tank, either of which may be used.
What is necessary is just to determine suitably according to the problem of equipment or the chemical used. Since the formation of CaF ₂ is a chemical reaction, it reacts essentially instantaneously.

Therefore, the residence time in the first reaction tank is 2 to 10
And the residence time in the second reaction tank is preferably about 20 to 40 minutes from the viewpoint of performing the precipitation reaction completely. The coagulation tank and the sedimentation separation tank after the second reaction tank are the same as those in FIG. The coagulated sedimentation portion may be replaced with another solid-liquid separation means, for example, a combination of a coagulation treatment and a membrane separation device or a membrane separation device without the coagulation treatment, if necessary.

[0014]

Table 1 shows the effects of the present invention. First
In the conventional treatment method in which the inflow rate of wastewater into the reaction tank is 1, that is, only one stage, when the raw water F ^- is 50 mg / liter, the CaF ₂ precipitation reaction does not occur even if 150 mg / liter of Ca ⁺⁺ is present. When the initial Ca ⁺⁺ concentration is increased to 500 mg / liter, F
^- was reduced to 9 mg / liter, but the residual Ca ⁺⁺ concentration
Since there is about 450 mg / liter, there is a scale problem due to the treated water. In addition, since it is actually impossible to adjust the Ca ⁺⁺ concentration accurately, in order to obtain stable treated water quality,
Generally, there is no other choice but to further increase the Ca ⁺⁺ concentration or to add an inorganic coagulant in excess. On the other hand, when the two-stage treatment method of the present invention is used, the Ca ⁺⁺ concentration
At the same amount of CaCl ₂ as in the case of mg / liter,
In both cases where the inflow rate of wastewater into the first reaction tank was 0.1 or 0.3, a very good treatment effect was obtained at a low concentration of residual Ca ⁺⁺ of about 110 mg / liter.

[0015]

[Table 1]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a flow showing an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional flow.

[Explanation of symbols] 11 First reaction tank 12 Second reaction tank 13 Coagulation tank 14 Sedimentation separation tank 21 F ^- containing wastewater

Claims (4)

(57) [Claims] 1. An F ^- containing concentration of 20 to 100 mg / litre.
The total amount of Ca ⁺⁺ to be added to 10 to 30% of the fluorine compound-containing wastewater when Ca ⁺⁺ is added to the fluorine compound-containing wastewater to remove the fluorine compounds contained in the wastewater as calcium fluoride , And reacting the solution with most of the remaining fluorine compound-containing wastewater, followed by solid-liquid separation, followed by solid-liquid separation. 2. An F ^- containing concentration of 20 to 100 mg / litre.
When Ca ⁺⁺ is added to the fluorine compound-containing wastewater and the fluorine compound contained in the wastewater is removed as calcium fluoride, 10 to 30% of the fluorine compound-containing wastewater should be branched and added to this. Adding and reacting the entire amount of Ca ⁺⁺ , reacting the reaction solution as it is with most of the remaining fluorine compound-containing wastewater, and then performing solid-liquid separation. Wastewater treatment method. 3. An F ^- containing concentration of 20 to 100 mg / litre.
A first reaction tank for adding 10% to 30% of the fluorine-containing wastewater, which is to be added, to the total amount of Ca ⁺⁺ to be added to the total amount of the fluorine-containing wastewater, and causing the reaction to proceed. A facility for treating fluorine compound-containing wastewater, comprising a second reaction tank for combining and reacting a reaction solution from a first reaction tank with a solid-liquid separator. 4. An F ^- containing concentration of 20 to 100 mg / litre.
A first reaction tank for adding 10% to 30% of the fluorine-containing wastewater, which is to be added, to the total amount of Ca ⁺⁺ to be added to the total amount of the fluorine-containing wastewater, and causing the reaction to proceed. A second reaction tank for joining and reacting the reaction liquid from the first reaction tank, an aggregation tank for adding an aggregating agent to the reaction liquid from the second reaction tank to cause an aggregation reaction, A facility for treating fluorine compound-containing wastewater, which is provided with a solid-liquid separation device comprising a tank or a membrane separation device.