JPS6231994B2 - - Google Patents

Description

[Detailed description of the invention] Fluorine compounds such as hydrofluoric acid are used in the electronic industry,
It is widely used in large quantities both industrially and in laboratories, including the metal industry.

Incidentally, fluorine and fluorine compounds are substances that are extremely harmful to the human body, and require sufficient consideration in their processing and handling in terms of pollution prevention, safety and health. In wastewater treatment, it is a duty to remove fluorine, and currently the wastewater standard for fluorine is 15%.
mg/. Conventionally, as a method for treating fluorine, it is known to use calcium salts such as slaked lime or calcium chloride, and to precipitate and separate the calcium fluoride, which has a relatively low solubility.

However, calcium fluoride is soluble in water, easily affected by coexisting ions, and fluorine tends to form complex ions, so in practice it is very difficult to treat it below the wastewater standard value. It is difficult to For this reason, the current situation is that the regulation value is only maintained through various improvements in the treatment process, and the development of more reliable treatment technology is desired.

On the other hand, the regulatory value for fluorine is being pushed down to an even lower value due to additions, etc., and advanced treatment methods using special adsorbents such as activated alumina and adsorption-precipitation methods by adding chemicals have been proposed as a way to respond to this. Attempts have been made to implement these methods, but these methods also have many practical problems in terms of selectivity, increased sludge volume, increased processing costs, etc.

In view of this situation, the present invention provides a completely new method for highly treating fluorine in wastewater. That is, the present invention is completely different from the conventional concept of separating fluorine by neutralization or adsorption, and the present invention generates volatile fluorine compounds with almost no solubility in water in the waste liquid and extracts them from the liquid. The feature is that fluorine can be easily separated and removed.

The principle of the present invention will be explained below.

Under acidic conditions, for example, hexamethyldisiloxane reacts with fluorine ions to form the low-boiling compound fluorotrimethylsilane. Chlorotrimethylsilane, another low boiling point compound of silicon, is Fluorotrimethylsilane is produced by the following reaction.

Although fluorotrimethylsilane easily evaporates at room temperature, it can be more easily evaporated from the liquid by introducing a gas such as air. The higher the acidity of the liquid, the greater the amount of hydrophobic fluorotrimethylsilane produced, which is convenient for processing.

Note that the evaporated fluorotrimethylsilane reacts with a weakly alkaline aqueous solution to liberate fluorine.

The present invention removes fluorine from wastewater by artificially creating a situation corresponding to the above principle in wastewater containing fluorine and fluorine compounds.

In particular, wastewater is generally acidic, and the fact that one of the conditions necessary for removing fluorine using the above-mentioned principle is satisfied also suggests the usefulness of this method.

Examples of the present invention will be described below.

Example 1 Fe5ppm, Mn0.5ppm, Zn5.6ppm,
Add 10 ml of sulfuric acid (1:1) and 74.2 mg of hexamethyldisiloxane (mole ratio Si/F =
Add 1.9) and blow in 800ml of air per minute after stirring.
After 12 hours, the concentration of fluorine ions remaining in the solution was determined.
It was analyzed according to the method of JIS K-0102.28. The result was 0.2 ppm. When the same waste liquid was neutralized and precipitated by adding calcium hydroxide, the fluorine concentration in the supernatant liquid was 15 ppm. Such processability could not be achieved at all using conventional methods.

Example 2 25 ml of sulfuric acid (1:1) and 525 mg of chlorotrimethylsilane (molar ratio Si/F = 2.3) were added to 400 ml of a liquid containing 22 ppm of Al, 39 ppm of Si, and 100 ppm of fluorine, and after stirring, air was blown in at 400 ml/min for 2 hours. I blew time. The remaining fluorine concentration of this liquid was analyzed according to the same JIS method as in Example 1. The result was 2.5ppm.

Conventional method using calcium hydroxide: 40ppm
of fluorine remained.

Example 3 Al102ppm, Si105ppm, B41ppm, Fluorine
3 ml of sulfuric acid (1:1), 0.2 g of activated carbon, and 512 mg of hexamethyldisiloxane (molar ratio Si/F = 4) were added to 30 ml of a solution containing 1000 ppm, stirred for 15 hours, and then aerated with air for 20 minutes. The fluorine concentration remaining in this solution was 8 ppm.

As shown in this example, the effect of this method is remarkable even in the presence of silicon, aluminum, and boron, which form complexes with fluorine that are difficult to remove, and even when the fluorine concentration is as high as 1000 ppm.

Incidentally, when the liquid of this example was treated by the conventional method, the residual fluorine concentration was about 60 ppm in a good case.

Example 4 Using the same solution as in Example 1, only the amount of hexamethyldisiloxane added to this solution was changed to 0.5, 1.1, and 5 in terms of Si/F molar ratio, and the residual fluorine concentration was determined according to the JIS method. When measurements were subsequently taken, they were 15 ppm, 1 ppm, and 0.2 ppm, respectively.

This result shows that the addition and amount of hexamethyldisiloxane should be selected so that silicon is added in an amount equal to or more than the fluorine in the liquid.

According to the present invention as shown in the above embodiments,
Even in the presence of heavy metals and aluminum and silicon, which tend to form complexes, the residual concentration of fluorine in the liquid can be significantly reduced. In this way, the method of the present invention has not only been proven to be far below the current regulation value for fluorine in wastewater, but also capable of fully responding to future tightening regulations. It is clear that this is a method for treating fluorine and its compounds.

Although sulfuric acid was used in the above embodiments to make the liquid acidic, similar effects can be obtained by using other acids such as nitric acid or hydrochloric acid. Further, as the silicon compound to be added, in addition to hexamethyldisiloxane and chlorotrimethylsilane shown in the examples, a low boiling point silicon compound bonded to an alkyl group may be used. Furthermore, although air is aerated in the embodiments of the present invention, other non-reactive gases such as nitrogen may also be used. In addition,
The amount of ventilation affects the length of transpiration time. Furthermore, when the reaction is carried out in a container having a sufficiently large area, it is sufficient to simply stir and shake. It is also effective to use heat of reaction or artificial heating to promote evaporation of low-boiling compounds.

As described above, the present invention creates reaction conditions for producing low boiling point compounds of fluorine in waste liquid containing fluorine and fluorine compounds, and simply adds a silicon compound bonded to an alkyl group. Since low-boiling compounds naturally evaporate at room temperature or under heating, no special process is required to remove the fluorine-boiling compounds generated in the liquid, simplifying the treatment process and increasing treatment efficiency. Moreover, advanced processing can be performed with simple operations. In particular, since the waste liquid is generally kept acidic, workability can be further improved compared to conventional methods. Note that it is also extremely easy to recover and reuse the low boiling point compound of fluorine produced. Therefore, according to the present invention, it is possible to treat fluorine to a low concentration below the current wastewater standards, and it is possible to solve various problems in the treatment of fluorine and fluorine compounds in wastewater, which have been considered troublesome in the past. This has the effect of solving problems all at once.

Claims (1)

[Claims] 1. When removing fluorine and fluorine compounds contained in waste liquid, a low boiling point compound of silicon bonded to an alkyl group is added to the waste liquid in an acidic liquid state,
A waste liquid treatment characterized by evaporating and removing from the liquid a low boiling point compound of fluorine produced by the reaction of fluorine ions and fluorine compounds in the waste liquid with a silicon compound bonded to an alkyl group. Method. 2. A patent claim characterized in that the amount of a low-boiling silicon compound bonded to an alkyl group added to the wastewater is set to a molar ratio of silicon to fluorine relative to fluorine contained in the wastewater of 1 or more. A method for treating waste liquid according to item 1. 3. The method for treating waste liquid according to claim 1, characterized in that activated carbon is allowed to coexist in the waste liquid to which a low-boiling compound of silicon bonded to an alkyl group is added.