JP2912934B2 - Method for treating wastewater containing borofluoride ions - 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 boron-containing fluoride wastewater discharged from a plating plant or discharged from an exhaust gas cleaning apparatus for producing boron trifluoride.

[0002]

2. Description of the Related Art As a method for treating wastewater containing borofluoride ions, JP-A-52-58253 discloses a method of decomposing borofluoride ions by adding an aluminum compound and then adding calcium hydroxide to adjust the pH. A method of adjusting to alkali has been proposed. However, this method can remove fluorine but does not consider boron at all.

In Japanese Patent Publication No. Sho 60-117, calcium hydroxide is added to a solution which has been treated with aluminum, and then the solid is separated from the solution. Aluminum is added again to the filtrate, followed by addition of alkali. After adjusting the pH to 10 or more, the solid-liquid is separated again to remove fluorine. This method has a drawback of poor workability such as treating wastewater of flue gas desulfurization, that is, wastewater containing low concentrations of fluorine and boron, separating solid and liquid on the way, and adding an aluminum compound again. Further, since a large amount of aluminum compound is used, there is a disadvantage that the amount of solid waste is increased.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior art described above, and treats wastewater containing high concentrations of fluorine and boron in a relatively simple and easily implementable manner. To develop a method for defluorination and deboronation.

[0005]

Means for Solving the Problems First, aluminum sulfate is added to waste water containing borofluoride ions and reacted at a temperature of 50 ° C. or more to decompose borofluoride ions.
A step of adding calcium carbonate to the solution of the first step to fix fluorine as calcium fluoride; and adding calcium hydroxide or (and) calcium chloride to the slurry solution of the second step. a third step of aging calcium fluoride at a pH of 4 or less, and adding calcium hydroxide to the slurry of the third step at a temperature of 50 ° C. or less to adjust the pH to 9 or more and convert boron and fluorine into insoluble compounds. The above problem is solved by employing a method for treating wastewater containing borofluoride ions, which comprises a fourth step of solid-liquid separation.

[0006]

In the present invention, wastewater containing borofluoride ions is treated, but high-concentration wastewater having a fluorine concentration of 1% or more and a boron concentration of 500 ppm or more is treated by the present invention. It is preferable to perform the following pretreatment before performing the above treatment.

That is, with respect to the high-concentration wastewater, potassium salts are added in advance to separate and remove fluorine and boron as potassium borofluoride, so that the fluorine concentration in the wastewater is 1% or less and the boron concentration is 500 ppm or less. The potassium borofluoride is recovered in the treatment step, and the filtrate is sent to the defluorination and deboronation step of the present invention. Examples of the potassium salt used in this case include potassium salts such as potassium hydroxide, potassium chloride, and potassium fluoride. The amount of the potassium salt is appropriately adjusted according to the fluorine concentration and the boron concentration of the wastewater. It is used in an amount below the concentration.

[0008] Fluorine and in waste water containing boron, most of the fluorine and boron fluoroboric acid ion BF ₄ ^-
And a portion of which is hydroxyborate ion B
F ₃ (OH) ^- present as, fluorine and boron present in excess in addition to the molar ratios are present as fluoride ions and boric acid. The BF ₄ ^- ion is decomposed when reacted with aluminum sulfate at a pH of 3 or less and a reaction temperature of 50 ° C. or more for 30 to 60 minutes. The decomposition reaction is considered to be based on the following estimation formula.

2Al ₂ (SO ₄ ) ₃ + HBF ₄ + 2H ₂ O =
4AlF (SO ₄ ) + 2H ₂ SO ₄ + H ₃ BO ₃

[0010] The amount of aluminum sulfate used in the first step is at least 4.5 times the amount of fluorine of the existing BF ₄ ^- ion,
That is, Al / F needs to be 1.1 or more, preferably 1.2 or more. This corresponds to generation of AlF (SO ₄ ) instead of generation of AlF ₃ in the above equation.

Fluorine bound to aluminum formed by the decomposition in the first step is converted to calcium fluoride by treating at a pH of 4 or less for 30 to 60 minutes in a second step of adding an equivalent of calcium carbonate to the fluorine. You. But,
Under this acidity condition, the solubility of calcium fluoride is large, and considerable calcium fluoride remains dissolved.
The reason for using calcium carbonate in the second step is to convert only fluorine into calcium fluoride while keeping the pH acidic. Here, when calcium hydroxide is used, the pH rises, and a part of calcium ions reacts with sulfuric acid to form gypsum, so that fixation of fluorine becomes insufficient. When the generation of calcium fluoride is insufficient, the removal of fluorine and boron in the final step becomes insufficient. Here, fixing only fluorine with calcium carbonate is one of the features of this method. In the second step, the pH needs to be 4 or less. If the pH is higher than 4, sulfate ions are consumed by calcium ions and aluminum ions also become aluminum hydroxide, and boron ions are fixed in a later step. I cannot do it.

In the third step, the generated calcium fluoride is adjusted to pH 4 with calcium hydroxide and treated for 60 to 90 minutes to be completely precipitated . If the pH is less than 4, the calcium hydroxide will not yet react with the sulphate. When the wastewater contains salts such as magnesium fluoride and sodium fluoride in an amount of about 1000 ppm or more, the pH may be higher than 4 when calcium hydroxide is used. In this case, it is preferable to use calcium chloride instead of calcium hydroxide.
Due to the use of calcium chloride, even if the above-mentioned salts coexist in the wastewater, the pH does not become higher than 4;
Can be kept to 4 or less. The reason for this is that even if the salts are defluorinated, they will not be hydroxides but chlorides.
This is because H is not changed.

[0013] Calcium chloride can be used in place of calcium hydroxide even when the above-mentioned salts do not coexist in the wastewater. However, when calcium chloride is used, hydrochloric acid is by-produced, and calcium hydroxide in the subsequent step is not used. If the pH does not rise above 4, it is more preferable to use calcium hydroxide because it tends to increase the amount used.

As long as the pH can be maintained at 4 or less, calcium chloride and calcium hydroxide may be used in combination.
Since it is necessary to adjust the mixing ratio of the two while adjusting the pH control, it is preferable to use each of them alone.

When the pH of the solution becomes about 3 during the treatment in the second step, it can be determined in advance that there is a possibility that the pH may become higher than 4. Therefore, use of calcium chloride or water in the third step The decision to use calcium oxide can be easily determined.

In the fourth step, calcium hydroxide is further added to the slurry of the third step to adjust the pH to 9 or more, and the mixture is sufficiently reacted until boron becomes an insoluble solid, followed by solid-liquid separation.
It is considered that when the pH is higher than 9, calcium hydroxide reacts with sulphate at the same time as free boric acid to form an insoluble ettringite-type solid containing boron. This product has the feature of good dehydration.

When treated under these conditions, both fluorine and boron in the waste water are reduced to 10 ppm or less. There is no need for heating after the second step. Particularly, in the fourth step, the reaction temperature is set to 50 ° C.
Hereafter, it is necessary to process at preferably 40 ° C. or lower. 5
If the treatment is performed at a temperature higher than 0 ° C., boron cannot be removed. At a temperature higher than 50 ° C., it is considered that the formation of an insoluble ettringite-type compound containing boron is inhibited, the compound becomes another compound, and boron is dissolved. Fluorine also precipitates as calcium fluoride, but the concentration of fluorine contained in wastewater is lower than that in normal fluoride wastewater treatment, probably because it is absorbed by this insoluble solid containing boron. doing.

When the pretreatment step is performed, that is, in the case of wastewater containing high concentrations of fluorine and boron, the wastewater is treated with a potassium salt such as potassium chloride, and those having a solubility higher than that of potassium borofluoride are solidified. When separated, the filtrate contains about 1 to 4% of chloride ions. In the method of the present invention, the amount of calcium hydroxide used in the fourth step increases.
Does not affect defluorination and deboronation.

[0019]

Example 1 159 g of aluminum sulfate was added to 2000 g of wastewater containing 3020 ppm of fluorine and 430 ppm of boron, and reacted at 65 ° C. for 1 hour at pH = 1.6. Next, 20 g of calcium carbonate was added and stirred for 30 minutes. At this time, heating was stopped. The pH was 2.9.
21.6 g of calcium hydroxide was added to this solution, and pH =
The mixture was stirred and reacted at 3.6 for 90 minutes to completely fix fluorine as calcium fluoride. 88 g of calcium hydroxide was further added to the slurry solution, and the reaction was stirred at a reaction temperature of 40 ° C. or lower for 1 hour. The pH at this time was 9.7.
The filtrate in which the solid and liquid were separated contained 10 ppm of fluorine and 0.1 ppm of boron. 500 g of a solid with a water content of 60% were separated.

[0020]

Example 2 120 g of aluminum sulfate was added to 2000 g of waste water containing 3020 ppm of fluorine, 430 ppm of boron and 1% of chlorine, and reacted at 75 ° C. for 1 hour at pH = 0.7. Next, 20 g of calcium carbonate was added and stirred for 30 minutes. At this time, heating was stopped. The pH was 1.0. 21.6 calcium hydroxide was added to this solution.
g was added, and the mixture was stirred and reacted at pH = 2.9 for 90 minutes to completely fix fluorine as calcium fluoride. 116 g of calcium hydroxide was further added to this slurry solution, and a reaction was carried out with stirring at a reaction temperature of 40 ° C. or lower for 1 hour. At this time
pH was 9.7. The filtrate from which the solid and liquid were separated contained 6 ppm of fluorine and 1.2 ppm of boron. 700 g of a solid with a water content of 60% were separated.

[0021]

Example 3 190 g of potassium chloride was added to 2300 g of waste water containing 6.9% of fluorine and 1% of boron to cause a reaction.
263 g of the precipitated KBF ₄ were separated by filtration. The composition of the filtrate is 1900 ppm of fluorine, 340 ppm of boron and 3.
4%. To 1000 g of this solution, 40 g of sulphate was added and reacted at 60 ° C. for 1 hour. The heating was stopped and 6 g of calcium carbonate was added to fix the fluorine. Further, calcium hydroxide was added, and stirring was continued at pH = 4 for 1 hour.
Subsequently, 100 g of calcium hydroxide was added to adjust the pH to 9 or more, and the mixture was treated for 1 hour. The filtrate from which the solid and liquid were separated contained only 9 ppm of fluorine and 1.0 ppm of boron.

[0022]

Example 4 120 g of aluminum sulfate was added to 2000 g of waste water containing 3020 ppm of fluorine and 430 ppm of boron, and reacted at 60 ° C. for 1 hour at pH = 0.7. Next, 20 g of calcium carbonate was added and stirred for 30 minutes. At this time, heating was stopped. The pH was 3.0. To this solution was added 32 g of calcium chloride, and pH =
The mixture was stirred and reacted at 2.9 for 90 minutes to completely fix fluorine as calcium fluoride. 116 g of calcium hydroxide was further added to this slurry solution, and a reaction was carried out with stirring at a reaction temperature of 40 ° C. or lower for 1 hour. The pH at this time was 9.7. The filtrate in which the solid and liquid were separated contained 8 ppm of fluorine and 2.2 ppm of boron. 700 g of a solid with a water content of 60% were separated.

[0023]

Comparative Example 1 120 g of aluminum sulfate was added to 2000 g of waste water containing 3020 ppm of fluorine, 430 ppm of boron and 1% of chlorine, and reacted at pH = 0.7 and 65 ° C. for 1 hour. Then add 20 g of calcium carbonate and add 30 g
The mixture was stirred for minutes. The pH was 1.0. To this solution, 21.6 g of calcium hydroxide was added, and at pH = 2.9, 90
The mixture was stirred and reacted for a minute to completely fix the fluorine as calcium fluoride. Calcium hydroxide 1 is added to this slurry solution.
16 g was added, and a stirring reaction was performed for 1 hour. PH at this time
Was 9.7. The reaction temperature was 65 ° C. until the end. The filtrate from the solid-liquid separation contained 16 ppm of fluorine and 100 ppm of boron.

[0024]

Comparative Example 2 120 g of aluminum sulfate was added to 2000 g of waste water containing 3020 ppm of fluorine and 430 ppm of boron, and reacted at 65 ° C. for 1 hour at pH = 0.7. Next, 20 g of calcium carbonate was added and stirred for 30 minutes. Also p
H was 3.0. When calcium hydroxide was added to this solution, the pH became 4 or more when 21.6 g was added. The mixture was stirred and reacted for 90 minutes. 116 g of calcium hydroxide was further added to this slurry solution, and a stirring reaction was performed for 1 hour. The pH at this time was 9.7. The filtrate from which the solid and liquid were separated contained 55 ppm of fluorine and 80 ppm of boron.

[0025]

According to the present invention, the treatment of wastewater containing borofluoride ions, which has been regarded as difficult, has been performed by decomposing borofluoride ions, fixing fluorine ions and fixing boron in order. Boron can be efficiently used. It has become possible to treat wastewater after reaction using BF ₃ gas as a catalyst and wastewater treatment for plating using a borofluoride solution.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 1/58

Claims (2)

(57) [Claims] 1. A first step in which aluminum sulfate is added to waste water containing borofluoride ions and reacted at a temperature of 50 ° C. or higher to decompose borofluoride ions, and calcium carbonate is added to the solution in the first step. A second step of fixing fluorine as calcium fluoride at a pH of 4 or less;
A third step of adding calcium hydroxide or (and) calcium chloride to the slurry solution of the step to ripen the calcium fluoride at a pH of 4 or less;
Wastewater containing borofluoride ions, comprising a fourth step of converting boron and fluorine to insoluble compounds by adding calcium hydroxide at a temperature of not more than 9 to convert the boron and fluorine into insoluble compounds, Processing method. 2. A wastewater containing borofluoride ions having a fluorine concentration of 1% or more and a boron concentration of 500 ppm or more is added to a potassium salt to separate fluorine and boron as potassium borofluoride. Removed, the concentration of fluorine in wastewater is 1% or less and the concentration of boron is 500p
2. The processing method according to claim 1, wherein the processing is performed in a pre-processing step of not more than pm.