KR19990080957A - Fluoride Removal Solution in Wastewater and Fluoride Removal Method Using the Same - Google Patents

Abstract

The present invention relates to a fluorine removal solution in wastewater and a fluorine removal method using the same, wherein 10% (w / v) cerium sulfate solution, 20% (w / v) ferrous sulfate solution and concentrated sulfuric acid are 100: 25 to 30: 1.5. A fluorine removal solution formed by mixing at a volume ratio of ˜2.5 and

Reacting the fluorine removal solution with waste water to produce cerium fluoride;

Adding a coagulant and sodium hydroxide to the cerium fluoride-containing wastewater and neutralizing the solution to pH 6.5-7.5 to co-precipitate to a slurry state;

Agglomerating co-precipitates using a flocculant to the slurry co-precipitates; And

Separating the precipitated slurry and the supernatant and draining the final treated water is provided.

According to the above, the fluorine ions contained in the waste water can be removed in a short time, the fluorine removal solution is not solidified, there is no fear of clogging the transfer pipe, and the pH is adjusted to 6.5-7.5, so there is no need to reverse neutralization. In addition to shortening the treatment process, the amount of sludge generated during wastewater treatment is reduced, and the calcium hardness of the treated water can be reused due to the low water treatment.

Description

Fluoride Removal Solution in Wastewater and Fluoride Removal Method Using the Same

The present invention relates to a method for removing fluorine contained in a fluorine removal solution and waste water. More specifically, the present invention relates to fluorine which is an environmental pollutant contained in waste water such as cooling water and dust collection in a manufacturing process using fluorite, hydrofluoric acid and fluorine compounds. It is related with the method of removing using cerium ion.

Conventionally, a large amount of fluorine ions are contained in cooling water, dust collection, and other waste water generated in the steel industry, chemical industry, semiconductor industry, etc. using fluorite, hydrofluoric acid, and fluorine compounds. Particularly, in the steel manufacturing industry, fluorine is contained in the casting powder (Mold Power) used for thermal insulation and lubrication purposes and iron powder (Iron Power) used for slab cutting in the continuous casting equipment of the steelmaking process, and is generated during cooling of the dust collector and the slab. As a large amount of fluorine ions are mixed in steelmaking wastewater, the fluorine contained in the wastewater must be removed and discharged to less than 15 ppm, which is regulated by the Water Quality Preservation Act.

As described above with reference to Fig. 1, the conventional neutralization treatment for removing fluorine ions contained in the wastewater is performed by adjusting the pH to 2-3 using sulfuric acid (1) in the adjusting tank (7). Then send to the neutralization tank 8. Lime milk (2) is added to the neutralization tank to adjust the pH to 9.5-10.5 to make the alkali slightly weak to precipitate fluorine ions contained in the waste water in the form of calcium fluoride. This calcium fluoride precipitate is very fine and unstable, so a certain amount of coagulant (polyaluminum chloride) 4 is added and then sent to the coagulation bath 9. A flocculant (polyacrylamide) 5 is put in this flocculation tank, the sludge is settled, it is sent to the precipitation tank 10, and the supernatant liquid and sludge are separated, and the fluorine contained in wastewater is removed.

In the neutralization treatment method, the slaked lime (3), which is a neutralizing agent used, has low solubility, so that excess water is used to make the slaked lime solution, so that the slaked lime is generally used in a milk state (Lime Milk).

However, if the hydrated lime in such a milk state is not continuously stirred, undissolved hydrated lime in the slaked lime solution tank 2 will solidify in the lower part of the tank. To prevent this, install a stirring device inside the slaked lime solution tank 2. Continuous stirring, the neutralization tank (7) due to the rise of the pH of the solution and repair of the neutralization tank delayed the transfer of the lime solution or when the waste water treatment for a while, the lime is solidified inside the transfer pipe clogging the transfer pipe problem There is this.

In addition, as shown in Table 3, the reaction rate of fluorine ions contained in the wastewater and the slaked lime is slow to react for 2 hours or more, while the fluorine removal rate is low and the slaked lime solution may be excessively added.

In addition, as shown in Tables 5 and 6, the treated water of the neutralization method using slaked lime has a high calcium hardness and cannot be reused, which is a problem in terms of waste resources, waste water treatment time, and sludge generation. Has

Accordingly, an object of the present invention is to provide a fluorine removal liquid capable of effectively removing fluorine ions in wastewater without using slaked lime.

Another object of the present invention is to provide a fluorine removal method capable of removing fluorine in a short time while shortening the treatment step using the fluorine removal solution.

1 is a view showing a conventional fluorine removal treatment process in wastewater.

2 is a view showing a fluorine removal treatment process in wastewater of the present invention,

3 is a graph showing the amount of fluorine removal according to the reduction time of the fluorine removal solution and the amount of ferrous sulfate solution used;

4 is a graph showing the amount of fluorine removal according to the amount of fluorine removal solution added;

5 is a graph showing the amount of fluorine removal by reaction time using a conventional slaked lime and

6 is a graph showing the amount of fluorine removal by reaction time of a fluorine removal solution.

* Description of the simple symbols for the main parts of the drawings *

1 ... sulfuric acid tank 2 ... slaked lime solution storage tank (Lime Milk)

3 ... slaked lime storage tank 4 ... aluminum polychloride tank (PAC)

5 ... polyacrylamide tank (PAA) 6 ... wastewater collection tank

7 ... adjustment tank 8 ... neutralization tank

9 ... flocculation tank 10 ... precipitation tank

11 ... Neutralization Tank 12 ... Sand Filter

13 ... Filtrate Collector 14 ... Filter Presser

15 ... sludge cake collection tank 16 ... 10% cerium sulfate solution tank

17 ... 20% ferrous sulfate solution tank 18 ... fluorine removal solution tank

19 ... 20% caustic soda solution tank 20 ... reactor

According to one aspect of the present invention, a waste water obtained by mixing 10% (w / v) cerium sulfate solution, 20% (w / v) ferrous sulfate solution and concentrated sulfuric acid in a volume ratio of 100: 25 to 30: 1.5 to 2.5 Fluoride removal solution is provided.

According to the second aspect of the present invention,

Reacting the wastewater with the fluorine removal solution of the first aspect to produce cerium fluoride;

Neutralizing the cerium fluoride product with a coagulant and sodium hydroxide to pH 6.5-7.5 to co-precipitate in a slurry state;

Agglomerating co-precipitates using a flocculant to the slurry co-precipitates; And

Separation of the precipitated slurry and the supernatant to discharge the final treated water is provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, a diluent containing 10% (w / v) cerium sulfate solution, 20% (w / v) ferrous sulfate solution and concentrated sulfuric acid in a volume ratio of 100: 25 to 30: 1.5 to 2.5 is used as a fluorine removal solution. .

Here, the cerium sulfate and ferrous sulfate acid mixed solution react quantitatively with the fluorine ions contained in the waste water and have a short reaction time, and once the reacted cerium fluoride precipitate has low solubility, it is almost insoluble in water.

Since fluorine ions contained in the waste water react with trivalent cerium ions to react as precipitates of cerium fluoride, it is believed to be due to the addition of cerium sulfate and ferrous sulfate solution to form cerium trivalent cerium sulfate (III). As follows.

2Ce (SO ₄ ) ₂ + 2FeSO ₄ → Ce ₂ (SO ₄ ) ₃ + Fe ₂ (SO ₄ ) ₃

In addition, since the reduction reaction is fast in acidity, sulfuric acid is added to make the liquid acid, and the cation bound with fluorine ions contained in the waste water is replaced with hydrogen ions to improve reactivity with cerium ions. The reaction formula is the following formula (2);

2NaF + H ₂ SO ₄ → 2HF + Na ₂ SO ₄

In addition, in the formula (1), the cerium sulfate in which Ce ions are reduced from tetravalent to trivalent is reacted with fluorine ions in wastewater to form precipitates of poorly soluble cerium fluoride to remove fluorine ions. ;

Ce ₂ (SO ₄ ) ₃ + 6HF → 2CeF ₃ ↓ + 3H ₂ SO ₄

The sulfuric acid produced in the formula (3) is neutralized by reacting with NaOH in a subsequent step to be discharged into dissolved water such as Na ₂ SO ₄ as a product in the formula (2).

The volume ratio of the 10% (w / v) cerium sulfate solution, 20% (w / v) ferrous sulfate solution and concentrated sulfuric acid is preferably 100: 25 to 30: 1.5 to 2.5, which is the volume of ferrous sulfate to cerium sulfate. If less than 25%, as shown in the graph of Figure 3 is not effective because of poor reactivity, when the ferrous sulfate exceeds 30% is not economical in terms of cost.

When the dilution solution thus prepared is used as a fluorine removal solution, it is preferable to use the dilution solution for 20 minutes or more, and the amount of the dilution solution is about 3.5-5.0 ml, considering that 45 L of fluorine is usually contained in 1 L of steelmaking wastewater. desirable. Even if the reduction time is less than 10 minutes, there is no significant difference in fluorine removal, but if it is 20 minutes or more, the fluoride ions and cerium ions contained in the waste water are almost reacted to form cerium fluoride to keep the data of fluorine ions contained in the filtrate constant. It is more preferable because it can be obtained.

In addition, if the amount is less than 3.5ml, the fluorine concentration in the treated water can not be removed to less than 15ppm, if the amount is more than 5.0ml fluorine removal effect is excellent but not economical.

In order to prevent the risk of some fine cerium fluoride from escaping into the treatment liquid without agglomeration, a coagulant is added and caustic soda is added to neutralize the pH to 6.5-7.5 to co-precipitate fine cerium fluoride in a sludge state.

Coagulants useful herein use polyaluminum chloride (PAC).

In addition, caustic soda is used to neutralize the pH to 6.5-7.5, thereby precipitating unaggregated cerium fluoride under acidity, and at the same time shortening the deneutralization step required when using conventional slaked lime.

The sludge is then precipitated using polyacrylamide (PAA) as the flocculant.

After the sludge is settled, the supernatant is passed through a sand filter to filter out fine cerium fluoride deposits to obtain treated water which is significantly lower than 15 ppm, which is the fluoride regulation value of the water conservation method. Since this treated water does not use slaked lime, its calcium hardness is low and can be reused if necessary.

In addition, the precipitated sludge collects the sludge cake through the dehydration device and the filtered water is discharged or recycled to the wastewater collection tank.

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

<Example 1>

Example of fluorine removal using fluorine removal solution of the present invention

First, a 10% (w / v) cerium sulfate solution 16 and a 20% (w / v) ferrous sulfate solution were mixed at a ratio of 100: 25, and 20 ml of sulfuric acid was added per 1250 ml of the mixed solution to prepare a fluorine removal solution. This fluorine removal solution was placed in the reactor 20 shown in FIG. 2 and reacted with the fluorine ions contained in the waste water for about 20 minutes or more in an amount of 6 ml per liter of steelmaking wastewater (73 ppm of fluorine ions), and then sent to the neutralization tank 8.

About 100 ppm of polyaluminum chloride (PAC) (4) was added to the neutralization tank (8), 20% caustic soda solution (19) was added, neutralized to pH 6.5-7.5, and then sent to the coagulation tank (9).

In the flocculation tank 9, about 5 ppm of polyacrylamide (5) was added to coagulate the sludge and sent to the precipitation tank (10).

The sludge and the supernatant are separated from the sedimentation tank 10 and the clear solution of the supernatant is passed through a sand filter 12 to be microfiltered and reused when necessary, and the sludge is dewatered in a filter presser 14. After the sludge cake (15) was made and landfilled, the filtered water was sent back to the reactor 20 for reprocessing.

<Example 2>

Effect of Fluoride Removal by Reduction Time of Fluoride Removal Solution and Concentration of Ferrous Sulfate Solution

In order to examine the reduction reaction of the cerium sulfate solution and the ferrous sulfate solution in the fluorine removal solution of the present invention, 100 ml of 10% (w / v) cerium sulfate solution was collected several times, and 20% (w / v) sulfuric acid was added to the solution. The ferrous iron solution was added in an amount as described in Table 1 and concentrated sulfuric acid was added in 2 ml to prepare a fluorine removal solution. 0.4 ml of steelmaking wastewater (containing 73 ppm of fluorine ions) generated in the steelmaking process was added to 0.4 ml each of the vessels, and the amount of fluoride removed according to the amount of ferrous sulfate and reduction time was investigated. 3 is shown.

Ferrous sulfate solution addition amount (ml) Reduction reaction time (min) 5 10 15 20 25 30 35 40 10 57.3 41.2 30.4 22.7 16.8 16.2 15.4 15.6 20 55.6 41.3 29.5 21.2 15.9 15.2 15.8 15.4 30 54.7 40.8 30.1 19.7 15.3 15.3 14.8 15.2 40 54.9 40.0 28.6 19.7 15.6 15.2 15.7 15.0

(Fluorine ion content: ppm)

As shown in Table 1, when 100 ml of 10% cerium sulfate solution is added to 25 ml of 20% ferrous sulfate solution and reacted for 20 minutes or more, Ce ⁴⁺ of cerium sulfate is completely reduced to Ce ³⁺ ions to optimally remove fluorine. Able to know.

Therefore, a dilution ratio of 10% (w / v) cerium sulfate solution to 20% (w / v) ferric sulfate solution to concentrated sulfuric acid of the fluorine removal solution of the present invention is suitable for a volume ratio of 100: 25 to 30: 2. It can be seen that the time is more than 20 minutes.

<Example 3>

Fluoride Removal Effect According to the Addition of Fluoride Removal Solution

In order to derive the optimal addition amount of the cerium sulfate and ferrous sulfate mixed solution, the mixed solution of cerium sulfate and ferrous sulfate acid was added stepwise to 1000 ml of steelmaking wastewater (73 ppm) produced in the steelmaking process as shown in Table 2 below. Next, the amount of fluorine removal was examined, and the result is shown in FIG.

Fluoride removal solution added amount (ml) 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Fluorine concentration in the treated water (ppm) 25.2 19.4 15.8 12.4 10.3 8.5 6.3 4.7 Fluoride Removal Rate (%) 65.5 73.4 78.4 83.0 85.9 88.4 91.4 93.6

As shown in the table above, when the maximum amount of fluorine ions in steelmaking wastewater is 73ppm, it is preferable to add about 4.5 to 6.0ml of fluorine removal solution per liter of steelmaking wastewater. Therefore, in general steelmaking wastewater, about 45-50 ppm In consideration of the fact that it is effective to add about 3.5-5.0 ml of fluorine removal solution.

Therefore, the content of fluorine ions in the filtered filtrate by adding more than 4.5ml of cerium sulfate and ferrous sulfate acidic mixed solution to 1000ml (73ppm) of steelmaking wastewater was able to remove fluorine ions below 15ppm which is the regulation of water quality preservation method. When 6.0 ml or more of the mixed solution was added, fluorine ions were remarkably removed.

Comparative Example 1

Fluorine ion removal by reaction time using slaked lime

100 ml of re-wastewater was added several times, and sulfuric acid was added to the pH of the wastewater to pH 2.0 by the conventional treatment method, and then neutralized to weak alkaline to pH 9.5-10.5 using slaked lime and the reaction time is shown in Table 3 below. The treatment was carried out in stages.

The fluorine ions contained in the filtrate were analyzed to investigate the fluorine removal rate according to the reaction time, and the results are shown in Table 3 and FIG. 5.

Reaction time 10 minutes 30 minutes 50 minutes 70 minutes 90 minutes 110 minutes 130 minutes 150 minutes Fluorine concentration in the treated water (ppm) 23.3 16.3 14.7 13.2 12.5 10.8 8.6 8.8 Fluoride Removal Rate (%) 68.1 77.7 79.9 81.9 82.9 85.2 88.2 87.9

As shown in the table, the fluorine removal rate was found to be less than 90% even if the fluorine removal rate was 150 minutes or more.

<Example 4>

Reaction Rate of Fluoride Removal Solution

In order to investigate the reaction rate of the fluorine removal solution, 0.7 ml of cerium sulfate and ferrous sulfate acid mixed solution were added to 100 ml of steelmaking wastewater (73 ppm of fluoride ions) generated in the steelmaking process, and the reaction time was stepwise as shown in Table 4 below. The amount of fluorine removal according to the reaction time was investigated and the results are shown in Table 4 and FIG. 6.

Reaction time 5 minutes 10 minutes 20 minutes 30 minutes 40 minutes 50 minutes 60 minutes 70 minutes Fluorine concentration in the treated water (ppm) 9.4 6.2 5.3 4.8 4.7 3.0 3.4 3.5 Fluoride Removal Rate (%) 87.1 91.5 92.7 93.4 93.6 95.9 95.3 95.2

As a result, the fluorine removal rate was 91% or more even when only 10 minutes were reacted.

Example 5

Sludge Generation

In order to investigate the amount of sludge produced in the neutralization tank, take 1000 ml of steelmaking wastewater twice, add fluorine removal solution (18) and polyaluminum chloride (4), and add 20% caustic soda solution (19) to pH. Table 5 shows the results of comparing the amount of sludge generated in each of the examples in which the fine cerium fluoride was co-precipitated in the sludge state and the comparative example in which the wastewater was treated by the conventional removal method using slaked lime was neutralized to 6.5-7.5. .

Conventional processing method Treatment method of the present invention Reduction rate (%) Sludge generation amount in steel treatment 1000ml 0.4032 0.3215 20.3

As shown in the above table, it can be seen that the amount of sludge generated by the treatment method of the present invention is generated by about 20% less than the amount of sludge generated by the treatment method using the conventional slaked lime. This is believed to be due to the unreacted calcium that was released to the sludge by not using slaked lime.

<Example 6>

Calcium hardness

In comparison with the removal method according to the present invention and the conventional removal method using slaked lime, the calcium hardness contained in the wastewater treated water was compared and tested, and the results are shown in Table 6 below.

Steelmaking Wastewater (Before Treatment) Filtrate of the Conventional Method Filtrate of the Invention Calcium hardness 174 683 97

As a result, it can be seen that when the fluorine ions are removed according to the present invention, the calcium hardness is significantly lower than that of the conventional removal method, and there is also an effect of reducing the calcium hardness contained in the wastewater before treatment.

According to the above, the fluorine ions contained in the waste water can be removed in a short time, and since the fluorine removal solution is not solidified by not using slaked lime, there is no fear of clogging the transfer pipe, and caustic soda is used to adjust the pH to 6.5-7.5. Because it does not need to reverse neutralization, the treatment process is not only shortened. Furthermore, the amount of sludge generated and the calcium hardness of the treated water can be reused.

Claims (5)

10% (w / v) cerium sulfate solution, 20% (w / v) ferrous sulfate solution and concentrated sulfuric acid in a volume ratio of 100: 25-30: 1.5-2.5 To remove large amounts of fluoride ions in cooling water, dust collection, and other generated wastewater generated using fluorspar, hydrofluoric acid, and fluorine compounds, Reacting the fluorine removal solution of claim 1 with wastewater to produce cerium fluoride; Adding a coagulant and sodium hydroxide to the cerium fluoride product to neutralize it to pH 6.5-7.5 and coprecipiting it into a slurry state; Agglomerating co-precipitates using a flocculant to the slurry co-precipitates; And And separating the precipitated sludge and the supernatant to discharge the final treated water. The method of claim 2, wherein the hydrofluoric acid removal solution is used after reducing for at least 20 minutes before use. The method of claim 2, wherein the hydrofluoric acid removal solution is characterized in that 3.5 to 5.0 ml per 1000 ml steelmaking wastewater is used. The method of claim 2, wherein the time for reacting the fluorine removal solution with the wastewater is 10 minutes or more.