JPH0757348B2 - Method for treating fluorine in wastewater - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating fluorine in waste water.

[0002]

2. Description of the Related Art Conventionally, as a method of treating fluorine in waste water of this type, a mixed solution of aluminum and sodium soluble salts, which has been mixed in advance, is added to a waste water containing fluorine in a reaction equivalent amount and iced. Orylite: N
a ₃ AlF ₆ ), the cryolite is separated and removed, and calcium fluoride (cal) is added in the waste water containing residual fluorine.
There is known a method for producing oium fluoride: CaF ₂ (see Japanese Patent Application Nos. 3-35004 and 3-35005).

In the above-mentioned conventional example, the addition amount of the soluble salt mixture of aluminum and sodium to be added is
The concentration of fluorine in the wastewater was measured by the neutralization titration method, and the result was used for determination (hereinafter, this method is called cryolite method).

[0004]

[Problems to be Solved by the Invention] In the conventional cryolite method,
The addition amount of the chemical agent necessary for the production of cryolite was determined based on the result of measuring the fluorine concentration in the waste water, and thus the operation of determining the addition amount of the chemical agent was complicated.

An object of the present invention is to provide a method for fluorine treatment by producing cryolite, which facilitates the operation of determining the amount of added chemicals.

[0006]

In order to achieve the above object, in the method for treating fluorine in waste water according to the present invention, a mixed solution of aluminum and sodium soluble salts in the waste water containing fluorine in a reaction equivalent amount. Is a method of treating fluorine in wastewater to form separable cryolite in the wastewater, wherein the reaction equivalence of the mixed solution necessary for the production of cryolite is determined by It is performed while detecting the change in conductivity.

Further, a mixed solution of soluble salts of aluminum and sodium is gradually added, and the addition of the mixed solution is terminated when the minimum point of electric conductivity is detected.

[0008]

[Function] When producing cryolite in waste water containing fluorine, aluminum and sodium to be added must be in a reaction equivalent amount. When the mixed solution of aluminum and sodium-soluble salts was gradually added while measuring the electrical conductivity of waste water containing fluorine with a pH meter, the pH of the solution gradually increased with the formation of cryolite. The pH becomes minimal and the pH becomes a minimum when the reaction solution of the mixed solution of soluble salts is added. In addition, the residual fluorine ion concentration also changes, and p
It is the lowest at the point where H becomes a minimum. That is, the amount of addition of the mixed solution of aluminum and sodium-soluble salts is determined by measuring the change in the electric conductivity in the reaction tank using a pH meter and detecting the point where the pH becomes a minimum.

[0009]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is an overall flow chart of the present invention, and FIG. 2 is a diagram showing a relationship between a drug addition amount and pH.

In this embodiment, the concentration of fluorine ion containing ammonium fluoride and hydrofluoric acid is 50,000 mg.
/ L, fluorine-containing wastewater 1 having a pH of 6.3 is injected into the reaction tank 2 of 1000 ml, and the fluorine-containing wastewater 1 is gently stirred in the reaction tank 2 while the Na / Al mixed solution supply device 3 supplies polyaluminum chloride Al ₂ O ₃ 10%) and sodium chloride solution (98.3 g / l as Na) for 30
While the solution mixed at a ratio of 0: 480 was gradually added to the fluorine-containing wastewater 1, the electrical conductivity of the fluorine-containing wastewater 1 was measured with a pH meter 4. The pH of the mixed solution was 3.5. With the addition of the mixed solution, the pH of the fluorine-containing wastewater 1 in the reaction tank 1 gradually decreased, and became the minimum at pH 3.7. P in the fluorine-containing wastewater 1 in the reaction tank 2
The peak detector 5 is used to detect that h is minimized, and the controller 6 controls the Na and Al based on the detection signal.
The driving of the mixed solution supply device 3 is stopped, and the mixed solution waste water 1
Was stopped. The amount of the mixed solution added when the pH becomes the minimum is the reaction equivalent amount for producing cryolite with respect to the fluorine contained in the wastewater 1. The precipitated cryolite was separated and removed, and the concentration of fluorine remaining in the solution in the reaction tank 2 was adjusted to J
It was measured according to IS K0102. As a result of the measurement, the residual fluorine concentration was 150 mg / l.

[0011]

As described above, according to the present invention, a mixture of aluminum and sodium soluble salts in a reaction equivalent amount is added to the fluorine-containing wastewater by utilizing the change in electric conductivity in the treatment reactor. Since the cryolite is produced by the above method, it is very easy to determine the amount of the drug at the stage of producing the cryolite, and there is an advantage that a complicated control device is not required.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall flow of the present invention.

FIG. 2 is a diagram showing a relationship between a drug addition amount and pH.

[Explanation of symbols]

 1 Fluorine-containing wastewater 2 Reaction tank 3 Na / Al mixed solution supply device 4 pH meter 5 Peak detector 6 Controller

Claims (2)

[Claims] 1. A method of treating fluorine in waste water, which comprises adding a mixture of soluble salts of aluminum and sodium in a reaction equivalent amount to waste water containing fluorine, and producing separable cryolite in the waste water. Therefore, the determination of the reaction equivalent of the mixed solution necessary for the production of cryolite is
A method for treating fluorine in wastewater, which is performed while detecting a change in electrical conductivity in the wastewater. 2. The method according to claim 1, wherein a mixed solution of soluble salts of aluminum and sodium is gradually added, and the addition of the mixed solution is terminated when the minimum point of electrical conductivity is detected. Method for treating fluorine in wastewater.