KR940011221B1 - Method for treatment of waste-water having fluorine - Google Patents

Abstract

The fluorine-containing industrial waste water is produced generally from the semiconductor manufacturing process and the stainless steel manufacturing process, and the waste water is treated generally with calcium chloride as a fluorine treatment agent. But the treatment of fluorine-containing waste water(I) which contains multivalent cation such as AlCl3 was not developed. The treatment of (I) is processed in three steps. The slaked lime and alum are input to the waste water I to adjust it to pH < 5.8 and then metallic hydride is input to adjust it to pH 5.8-8.6, the floating material is coagulated polyacrylamide to be removed.

Description

Treatment of fluorine-containing industrial wastewater containing water-soluble chlorides

1 is a process chart showing a fluorine treatment process in industrial wastewater according to a conventional method.

2 is a graph showing the change in solubility (F ion concentration) of CaF ₂ according to the amount of water-soluble chloride in the fluorine treatment according to the conventional method.

3 is a graph showing the concentration of fluorine treatment when calcium salt is added according to the conventional method.

4 is a process chart showing a fluorine treatment process according to the present invention.

The present invention relates to a method for treating fluorine-containing industrial wastewater, and more particularly, to a method for treating fluorine-containing industrial wastewater containing a water-soluble chloride containing a polyvalent cation such as AlCl ₃ .

In general, fluorine-containing industrial wastewater is mainly generated in the semiconductor manufacturing process, stainless steel manufacturing process, etc. As a method for treating such fluorine-containing industrial wastewater, calcium salt is mainly used as a fluorine treatment agent.

However, a method of treating fluorine-containing wastewater (hereinafter, referred to as "playing wastewater") in which polyvalent cations such as AlCl ₃ are mainly produced in steelmaking processes and the like has not been published until now. The treatment of fluorine-containing industrial wastewater is urgently needed.

On the other hand, in the conventional method for treating fluorine-containing industrial wastewater using calcium salt, as shown in FIG. 1, calcium salts such as slaked lime [Ca (OH) ₂ ] are added to the fluorine-containing wastewater to leach fluorine with CaF ₂ . It consists of a fluorine treatment process, a flocculant administration process to sludge the suspended solids generated in this process, and a wastewater treatment process in which strong acid (sulfuric acid) is added in order to set the pH as a legal emission standard (pH: 5.8 to 8.6).

However, when treating a fluorine-containing industrial wastewater in which a polyvalent water-soluble chloride such as AlCl ₃ is present using such a conventional method, there are the following problems.

In other words, if AlCl ₃ is present in the wastewater, it is difficult to remove fluorine due to the increased solubility of CaF ₂ by Al ³⁺ (see Encyclopedia of chemical technology, Vol 10, (1980) p 709).

This can be explained by the following equation.

Ca ²⁺ + 2F ⁻ → CaF ₂ (S)... … … … … … … … … … … … … … … … … … … … (One)

_{^{3CaF 2 + 2Al 3+ + 6Cl -}} → 3Ca 2+ + 6Cl - + 2Al 3+ + 6F - ... … … … … … … … (2)

Equation (1) shows that the fluorine is removed in accordance with the addition of calcium salt when fluorine treatment with calcium salt in a general industrial wastewater.

Equation (2) shows the case in which AlCl ₃ is present, such as wastewater, and when calcium salt is added, some of CaF ₂ generated through the reaction as in Equation (1) is redissolved by water-soluble chloride such as AlCl ₃ . It is to be shown.

The CaF ₂ is redissolved in more detail with reference to the drawings. As shown in FIG. _2, the solubility (fluorine ion concentration) of CaF ₂ increases as the concentration of various water-soluble chlorides in the fluorine-containing wastewater increases. Appeared.

That is, polyvalent ions Al ³⁺ and Fe ³⁺ were found to increase CaF ₂ solubility when present as water-soluble chlorides than monovalent ions Na ⁺ and K ⁺ . In particular, when AlCl ₃ contained about 100 mg / l of industrial wastewater, the fluorine ion increased by about 370% or more compared with the case where it did not contain.

As described above, it is very difficult to treat fluorine in the recyclable wastewater to 15 ppm or less, which is the legal reference value according to the conventional method, due to the phenomenon that CaF ₂ is re-dissolved.

That is, FIG. 3 shows the effect of fluorine treatment in the wastewater when adding calcium salts of Ca (OH) ₂ and CaCl ₂ according to the conventional method, and accordingly, Ca (OH) ₂ is used as the fluorine treatment agent. In this case, it can be seen that fluorine can be treated to 15 ppm or less only when an excess amount of Ca (OH) ₂ is added (2000 ppm or more), and when CaCl ₂ is used, it is difficult to treat fluorine to 15 ppm or less.

In addition, in order to reduce the fluorine concentration to 15 ppm or less, an excessive amount of calcium salt, which is an alkaline substance, needs to be added. It must go through.

Accordingly, an object of the present invention is to solve the above problems by adding hydrated lime and alum in the first step to make it acidic, injecting the metal hydroxide in the second step and adding the flocculant in the third step, The present invention aims to provide a method for treating fluorine-containing industrial wastewater containing a polyhydric water-soluble chloride that treats the concentration to be less than or equal to the legal standard of 15 ppm.

In order to achieve the above object, the treatment method of the present invention comprises alum so that the fluorine-containing industrial wastewater containing a water-soluble chloride containing polyvalent cations (Ca (OH) ₂ ) and the pH is less than 5.8 acid. 1st process which throws in; A second step of introducing metal hydroxide (M (OH) x) such that the pH of the wastewater treated in the first step is equal to or less than a legal reference value (pH; 5.8 to 8.6); And a third step of adding PAA (Poly Acryl Amide), which is a flocculant, to remove suspended matters generated in the first and second processes.

Hereinafter, the present invention will be described in detail with reference to the drawings.

As shown in FIG. 4, the first step of the present invention is a fluorine treatment step for firstly removing fluorine, and includes hydrated lime (Ca (OH) ₂ ) and alum (e.g. Al ₂ (SO ₄ ) ₃ .14H ₂ O. ) To react with fluorine-containing wastewater.

At this time, the alum is added to the acid pH of 5.8 or less, when the pH is 5.8 or more, the slaked lime is more than the amount of acidic alum, the fluorine treatment efficiency is lowered and the slaked lime is expensive compared to alum, so the pH is lowered. It is preferable to add so that it may be 5.8 or less.

In the present step, by adding slaked lime and alum as described above, chemical treatment and adsorption treatment of fluorine proceed simultaneously to remove fluorine.

That is, when the slaked lime and alum are added, fluorine chemically reacts with Ca ²⁺ ions generated from the slaked lime to form a CaF ₂ compound, and at the same time, Al (OH) ₃ generated by the acid and alkali reactions of the slaked lime and alum. And CaSO ₄ will adsorb fluorine.

In more detail, Ca (OH) ₂ is poorly soluble in water but readily soluble in acid. Therefore, Ca (OH) ₂ is easily dissolved and becomes Ca ²⁺ by adding alum to pH 5.8 or less, and then reacts with F ^- to remove high concentrations of fluorine ions as CaF ₂ and at the same time the acid of calcined lime and alum , Al (OH) ₃ and CaSO ₄ produced by alkali reaction are treated with fluorine.

In the second step, a metal hydroxide (M (OH) x, M: metal ion, and X: integer) is added to treat the untreated fluorine in the first step so that the pH becomes a legal reference value. If the reference value is 5.8-8.6, the unreacted Al ³⁺ ions in the first process become Al (OH) ₃ to adsorb untreated fluorine. At this time, it is preferable to use NaOH, Ba (OH) ₂ and Ca (OH) ₂ as the metal hydroxide.

The third step is to precipitate and remove the suspended matter produced in the first and second processes by using a flocculant (polyacrylamide). Through this process, suspended matter such as CaSO ₄ , Al (OH) _3, and CaF ₂ is removed. This is finally precipitated into sludge and removed.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Containing a water-soluble chloride containing a polyvalent cation which is generated in the playing step fluorine (concentration: 120.0F ^- ㎎ / ℓ) of calcium hydroxide according to the conventional method shown in FIG. 1 in industrial waste water (Ca (OH) ₂₎ and After adding 500ppm of alum and adding polyacrylamide (PAA) as a flocculant, and then adding sulfuric acid, a fluorine removal experiment was performed to adjust pH, and the results are shown in Table 1 below.

TABLE 1

Example 2

In the first fluorine-containing industrial wastewater as in Example 1, 500 ppm of slaked lime and alum were added in the first step, respectively, and the following Table 2 and NaOH, Ba (OH) ₂ and Ca (OH) ₂ were used in the _{second step} . Each 500ppm was added to adjust the pH within the range of 7.0 ~ 7.5, and then the flocculant (PAA) was added in the third step to conduct the experiment to precipitate and remove the suspended solids and the results are shown in Table 2 below.

TABLE 2

As shown in Tables 1 and 2, the present invention methods (1, 2, 3), unlike the conventional methods (a, b), can treat the concentration of fluorine in industrial wastewater to 15 ppm or less, which is the legal standard, as well as the second. In the process, metal hydroxides are added with a pH of 5.8-8.6 to leach out untreated fluorine, eliminating the need for a separate wastewater treatment process (adjusting the pH of the fluorinated wastewater to the legal emission standard).

In addition, since the solubility of slaked lime is relatively low at 1.26 g / l at 20 ° C, the conventional method (a) not only takes a lot of time to dissolve during fluorine treatment, but also removes enough fluorine according to the amount of slaked lime because the slaked lime is not sufficiently dissolved. In the present invention method (12, 3), the alkali calcined lime and the acidic alum were added to the same process, and it was confirmed that the calcined lime was sufficiently utilized for fluorine removal in a short time through an acid and alkali reaction.

As described above, the present invention can control the pH of the fluorine-containing industrial wastewater containing water-soluble chloride (120F ^- mg / L) to a legal emission standard of 5.8 to 8.6 without using a separate wastewater treatment process. Of course, there is an effect that the fluorine content can be easily processed to less than the legal threshold (15F ^- mg / l) within a short time.

Claims (1)

In the method for treating fluorine-containing industrial wastewater containing a water-soluble chloride containing a polyvalent cation, alum is added to the industrial wastewater so that the calcium (Ca (OH) ₂ ) and the pH is less than 5.8 acid. First process; A second step of introducing a metal hydroxide such that the pH of the wastewater treated in the first step is in a range of pH: 5.8 to 8.6, which is a legal reference value; And a third process of adding polyacryl amide (PAA), which is a flocculant, to remove suspended matters generated in the first and second processes.