KR960002260B1 - Treatment method for waste water including fluorine - Google Patents

Abstract

The waste water treatment is performed by (A) adding to waste water a soluble rare earth compound in an amount 2-10 times the chemical equivalent which is needed to combine with fluorine and adjusting the pH at 5-10 ; (B) separating solid and liquid portions, while discharging fluorine-free water and obtaining the sludge of rare earth fluoride and rare earth hydroxide ; (C) adding inorganic acid to the sludge to adjust the pH at 2.5-5.5 and dissolving rare earth hydroxide selectively ; and (D) recovering rare earth-containing liquid, which is recycled to the process, and rare earth fluoride in a solid form after solid-liquid separation.

Description

Treatment method of waste water containing fluorine

1 is a process chart of wastewater containing fluorine groups.

2 is a peak of the X-ray diffraction analysis results before and after the PH adjustment process, which is a selective dissolution process, wherein (a) is a state diagram before the selective dissolution process, and (b) is a state diagram after the selective dissolution process.

The present invention relates to the treatment of wastewater containing fluorine, and more particularly, by adding soluble rare earth compounds to wastewater containing dissolved fluorine ions to remove fluorine ions to low concentrations with high efficiency and to recover and reuse rare earths used at this time. The present invention relates to a method for treating wastewater having economic feasibility.

It is emitted from all factories that use fluorine compounds such as semiconductor manufacturing plant, metal surface treatment plant, ceramics manufacturing plant, etc. of wastewater containing F (fluorine), which can effectively remove fluorine at low concentrations as environmental regulations are gradually strengthened. Development of a method is required.

In this regard, the most common method for removing fluorine has been proposed in Japanese Patent Laid-Open No. 60-117 and Japanese Patent Laid-Open No. 62-125894 by adding a Ca compound or an Al compound to waste water to insolubilize fluorine ions. This method is not suitable for removing fluorine at low concentration because the amount of chemicals used and the amount of sludge generated are high, and fluorine ions of up to 8mg / l are theoretically retained in the solution when fluoride is removed as a Ca compound.

Recently, as a method of removing dissolved fluorine using rare earth, Japanese Patent Application Laid-Open No. 3-186393 discloses a method of insoluble fluorine ion by adding a water-soluble composition such as rare earth compound, alkaline earth metal compound, and alkali metal compound to waste water containing fluorine. After the solid-liquid separation is characterized in that.

However, this method also has various problems. The addition of alkaline earth metals and alkali metals increases the amount of residues after treatment, and the high solubility of BaF2, LiF, MgF2, NaF compounds that can be formed by combining with fluorine causes waste treatment plants. For example, wastewater containing fluorine may leak from waste landfills, and it may be economically disadvantageous as the amount of fluorine is added. Also, this method cannot remove fluorine at low concentrations.

Therefore, there is a need for a method for more efficiently removing fluorine without artificially adding alkali metal compounds or alkaline earth metal compounds.

In addition, the method of removing fluorine by adsorption method other than the above precipitation method has been proposed in Korean Patent 89-3882. However, this adsorption removal method is expensive because the adsorbent used is an insoluble rare earth compound. The amount is excessive, and the ion exchange action is performed only in an acidic solution, and the reaction rate is slow because it has to rely on the ion exchange reaction when desorbed.

In addition, this method does not use the existing equipment, it is cumbersome to intermittently work in a number of vessels containing a large amount of adsorbent, and when treating the generated alkali fluoride with Ca (OH) ₂ CaF2 residue occurs, and when treated with Ca (OH) ₂ , there is a disadvantage that F remaining in the solution is always present at a concentration of about 8 mg / l or more.

Therefore, the present invention is drawn to solve the conventional problems, and by adding a solution of soluble rare earth salt to the dissolved fluorine waste water to remove fluorine ions with high efficiency, and to treat wastewater economically advantageous by reusing the rare earth elements used at this time. The purpose is to provide a method.

Hereinafter, the present invention will be described.

The present invention relates to a first step of adding 2-10 times the stoichiometric reaction equivalent of soluble rare earth salt solution to fluorine-containing wastewater and adding a PH regulator so that the pH is 5-10. The second step is to discharge the liquid after the process is solid-liquid, to discharge the liquid containing low concentration of fluorine, and to make the rare earth fluoride and the rare earth hydroxide into sludge, and to add the inorganic acid to the sludge separated from the rare earth fluoride and the rare earth hydroxide. The pH is adjusted to selectively dissolve the rare earth hydroxide, and then the solid-liquid separation is performed to recover the liquid containing the rare earth and reuse it, and to recover the rare earth fluoride as a solid.

The rare earth fluoride recovered as a solid is used after reprocessing.

1 is a process chart of the present invention for treating wastewater containing fluorine, which will be described in detail accordingly.

To the fluorine-containing wastewater, a rare earth chloride, a soluble rare earth compound, is added 2-10 times the chemical reaction equivalent of fluorine, preferably 3 times or more, so that the fluorine in the solution is 1 mg / l or less.

Caustic rare earth salts include, for example, CeCl ₃ , LaCl ₃ , NdCl ₃ , PrCl ₃ , but are not limited thereto. Chlorides, sulfides and nitrides, including rare earths belonging to the lanthanide series of the chemical periodic rate, are limited to the above chlorides. I never do that.

In this way, after adding rare earth chloride, the pH is formed by using a stirring apparatus. In this case, the pH of the wastewater is adjusted to 5-10, preferably 6-8, in case of strong acidity or strong alkalinity.

At this time, the pH adjustment is adjusted with inorganic reagent caustic soda, ammonia, calcium hydroxide, sulfuric acid, hydrochloric acid, nitric acid and the like.

After performing the above process, the solid and fluorine of rare earth fluoride and rare earth hydroxide are separated into a liquid in which concentrations of fluorine and rare earth hydroxide are removed at a concentration of 1 mg / l or less through a conventional technique such as filtration, decantation, centrifugation, or dehydration. And the liquid is discharged.

As such, the rare earth hydroxide is selectively dissolved in a mixture of the rare earth fluoride and the rare earth hydroxide, which is the solid-liquid separation process, to recover and reuse the rare earth ions. The recovery process suspends the sludge of the solid in water and stirs the rare earth fluoride by stirring. After the rare earth hydroxide is uniformly released, the rare earth hydroxide is selectively dissolved by adjusting the pH using inorganic acids (hydrochloric acid, sulfuric acid, nitric acid).

At this time, the pH adjustment is 2.5-5.5, preferably 3.5-4.5.

When the pH is 2.5 or less, the fluorine in the fluoride may be dissolved in the solution again, and when the pH is 5.5 or more, the hydroxide may not be easily dissolved in the solution.

As such, the rare earth solution recovered as a liquid by solid-liquid separation of the rare earth fluoride and the rare earth dissolved therein may be used again for fluorine removal, and the rare earth fluoride separated as a solid may be reprocessed.

The following is described according to the embodiment.

Example 1

Soluble rare earth chloride, a soluble rare earth compound, was added 1-10 times the chemical reaction amount to 500 ml of wastewater discharged from a plant using a fluorine compound (fluorine concentration 25.0 mg / l, PH = 2.0).

Which is added to the rare earth compound is a rare earth chloride solution, the composition of the main component is the _{CeCl 3 183.5g / ℓ, LaCl 3} 86.4g / ℓ, NdCl 3 54.1g / ℓ, PrCl becomes consists of ₃ 12.0g / ℓ small amount of NH ₄ It is composed of Cl, CaCl ₂ and BaCl ₂ .

After the rare earth solution was added, the mixture was stirred using a general stirring apparatus, and an alkaline solution, preferably caustic soda, was added so that the pH of the solution was 6.5.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separator.

At this time, the concentration of dissolved fluorine ion in the filtrate (liquid discharged) of the solid-liquid separation was measured using an ionic meter, SRANDARD METHODS for the examination of water & waste water APHA (American public health association), AWWA (American water works association), WPCF (water pollution control fedcratio), measured using a 16th edition.

The result by the addition of each equivalent is shown in [Table 1].

TABLE 1

Concentration of Fluoride Ion According to Addition Amount

Looking at the results of Table 1 it can be seen that between 1 and 2 times the equivalent of fluorine is present in the solution at a concentration of about 6-13 mg / L, and the concentration of fluorine ion is drastically reduced at the added amount of 2 or more times.

According to the above results, it is a feature of the present invention that at least two times, preferably three times or more, of chemical equivalents are added when fluorine is removed at low concentrations.

Example 2

Soluble rare earth chloride, a soluble rare earth compound, was added 2-4 times the chemical reaction amount to 500 ml of wastewater discharged from the plant using fluorine compounds (fluorine concentration 25.0 mg / l, PH = 4.5).

Rare earth compounds that are participating is a rare-earth chloride solution, the composition of the main component is the _{CeCl 3 135.0g / ℓ, LaCl 3} 64.0g / ℓ, NdCl 3 40.0g / ℓ, PrCl becomes consists of ₃ 8.3g / ℓ small amount of NH ₄ It is composed of Cl, CaCl ₂ and BaCl ₂ .

After the rare earth solution was added, the mixture was stirred using a general stirring apparatus, and an alkaline solution, preferably caustic soda, was added so that the pH of the solution was 6.5-10.5.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separator.

At this time, the concentration of dissolved fluorine ions of the filtrate separated from the solid-liquid solution was analyzed in the same manner as in Example 1 and the rare earth ions in the solution was analyzed using ICP (ion xpupled plasma).

The concentrations of fluorine and rare earth ions in the effluent after removing the dissolved fluorine while changing the pH by equivalent weight are shown in (Table 2).

TABLE 2

Elimination Effect by Equivalent and PH Control

Looking at the results of Table 2, Ln (lanthanide) ions are precipitated with rare earth hydroxides, such as rare earth fluorides in the PH range, and are 0.3-0.7 mg / l in solution, whereas PH = 8.5 in the case of dissolved fluorine. In this case, since the considerable amount remains in the liquid, the pH should not be raised above 8.5 after the addition of the rare earth solution.

According to the above results, in order to remove fluorine at low concentration, the rare earth compound is added at least two times, preferably at least three times the equivalent of the chemical reaction, and then the pH is adjusted when adjusting the pH with alkali in the pH adjustment step. Up to 10, preferably adjusted to PH6-8 characterized in that the filtrate is discharged by solid-liquid separation.

Example 3

The composition and concentration of the wastewater containing dissolved fluorine and the rare earth compound added are the same as in Example 2.

To 1,000 ml of wastewater, a rare earth chloride, a soluble rare earth compound, is added four times the reaction equivalent weight, and a rare earth solution is added, followed by stirring using a general stirring apparatus, and an alkaline solution, preferably caustic soda, to bring the pH of the solution to 7.0. It was.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separation device.

At this time, the concentrations of fluorine and rare earth ions of the filtrate separated from the solid-liquid solution were F 0.5 mg / l and 0.7 mg / l, respectively, and the removal efficiency of fluorine ion was 99.5%. The rare earth ions added were rare reactions of rare earth fluoride and rare earth hydroxide. Will be present in the mixture.

The reaction product was subjected to the above step without suspending the drying step and suspended in 100 ml of water, followed by stirring to uniformly dissolve the rare earth fluoride and rare earth hydroxides, and then adjusted the pH using diluted hydrochloric acid to selectively dissolve the rare earth hydroxides. After the solid-liquid separation, the concentration of rare earth ions and fluorine ions in the filtrate was measured in the same manner as in Example 2.

In this case, the inorganic acid added for selective dissolution may be hydrochloric acid, nitric acid, sulfuric acid, etc. The selection of the inorganic acid may be selected according to the type of rare earth compound to be added, and the acidity of the inorganic acid is not critical in the present process and is uniform. It is thought that it is preferable to use dilute acid for the reaction in achieving the object of this process.

The ratio of water and reaction product when the reaction product is suspended in water in the process is not important in the present invention and is related to the concentration of the rare earth solution, which may be adjusted according to the conditions of the concentration control process.

According to the method described above, the results of measuring the concentration of rare earth ions and fluorine ions by adjusting the pH control range at the time of selective dissolution to 3.0-5.0 are shown in (Table 3).

TABLE 3

Changes in Ln & F Ions According to PH Change in Selective Dissolution of Reactant

As a result, the absolute amount of rare earth ions initially added is 466.3 mg, the amount of which is bound by rare earth fluoride and the amount of which is bound by rare earth hydroxide is 116.6 mg and 349.7 mg, respectively. It recovers about 20% of the amount of rare earths bound to it, and recovers 97.6%, 91.2%, and 90.7% at pH 3.6, 4.0, and 4.2, respectively.When pH is 3.0, it combines with rare earth fluoride as well as rare earths that are combined with rare earth hydroxides. Some rare earths are also eluted and at the same time the F ions dissociate, which makes them unsuitable for recovery and reuse.

According to the above results, the pH of the selective dissolution process of the present invention for removing dissolved fluorine at low concentration and at the same time minimizing the rare earth consumption is characterized in that it is adjusted to the range of 2.5-5.5, preferably PH 3.5-4.5.

Example 4

The wastewater containing dissolved fluorine is the same as in Example 2, and the composition of the rare earth compound added is composed of CeCl ₃ 54.7g / L, LaCl ₃ 54.7g / L.

When the rare earth compound is added, 2%, 5%, and 10% of Ca ions and Mg ions are added in the form of CaCl ₂ and MgCl ₂ as weight ratios to Ln (lanthanide ions) to the rare earth compound. By comparing the elimination effect of these, we examined the effects of artificial addition of alkaline earth metals.

Each composition is added three times the reaction equivalent weight and then stirred using a general stirrer and an alkaline solution, preferably caustic soda, is added so that the pH of the solution is 7.0.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides are separated using a conventional solid-liquid separation device.

At this time, the concentration of fluoride ions in the filtrate separated from the solid-liquid solution is shown in Table 4.

TABLE 4

Effect of Alkaline Metal Addition

The results in Table 4 show that the fluoride removal effects of the Ca and Mg additions and non-additions are almost the same, so that the addition of artificial alkali metals other than those contained in the ore or intermediates of the rare earth compounds is not necessary.

Example 5

The wastewater containing dissolved fluorine was the same as in Example 2, and the rare earth compound added was a rare earth nitrate solution, and its composition and concentration were 350.7 g / L of La (NO ₃ ) ₃ .

When the rare earth nitrate was added and the rare earth chloride mentioned in Example 1, the effect of removing fluorine was compared.

The rare earth nitrate was added 1-4 times the chemical reaction equivalent weight, followed by stirring using a general stirring apparatus, and an alkaline solution, preferably caustic soda, was added so that the pH of the solution was 6.5.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separation device.

At this time, the concentration of fluorine ions of the filtrate separated from the solid-liquid separation and the concentration of fluorine ions in Example 1 are shown in Table 5.

TABLE 5

Comparison of Addition Effects of Rare Earth Nitrate and Rare Earth Chloride

The results of Table 5 show that the removal effect of fluorine is almost the same when rare earth nitrate is added and rare earth chloride is added.Therefore, there is no effect of anion group in the use of rare earth compounds. Can be used selectively depending on the nature of the.

Example 6

Soluble earth chloride, a soluble rare earth compound, is added to 1,000 ml of wastewater discharged from the plant using fluorine compounds (Fluorine concentration of 100.0 mg / l, PH = 2.5) by adding four times the reaction equivalent to fluorine as an insoluble compound. The composition and concentration of the losing rare earth chloride solution are the same as in Example 2.

After the rare earth solution was added, the mixture was stirred using a general stirring apparatus and an alkaline solution, preferably caustic soda, was added so that the pH of the solution was 7.0.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separation device.

At this time, the concentrations of fluorine and rare earth ions of the solid-liquid separated solution were F 0.5 mg / l and Ln 1.4 mg / l, respectively, and the removal efficiency of fluorine ion was 99.5%, and the added rare earth ions were mostly present as reaction products.

The reaction product passed through the above step is suspended in 100 ml of water without performing a drying step, stirred to uniformly freeze the rare earth fluoride and the rare earth hydroxide, and the pH is adjusted to 4.2 using diluted hydrochloric acid.

At this time, rare earth fluoride is present as a stable compound in the PH, but excess rare earth hydroxide is recovered in the solution.

After the pH adjustment process, the solid-liquid separation using the conventional solid-liquid separation method recovers 91% of the excess of 3 equivalents of rare earth compounds into the solution, and the concentration of F ions becomes 0.1 mg / l, which is used again for wastewater treatment. Can be done.

Figure 2 shows the results of X-ray gray matter analysis before and after the PH, which is the selective dissolution process.

As a result, the mixture of rare earth fluoride and rare earth hydroxide was used before the pH adjustment process. However, the rare earth hydroxide rarely disappears and the peak of rare earth fluoride is formed after the pH adjustment process.

Example 7

To 300 ml of wastewater discharged from the plant using the fluorine compound (fluorine concentration 50.0 mg / l, PH = 2.5), a rare earth chloride solution, a soluble rare earth compound, was added three times the chemical reaction equivalent weight.

At this time, the concentration and composition of the rare earth chloride solution added are the same as in Example 6.

After the rare earth solution was added, the mixture was stirred using a general stirring apparatus, and an alkaline solution, preferably caustic soda, was added so that the pH of the solution was 6.5.

After adjusting the pH, the rare earth fluoride and rare earth hydroxides were separated using a conventional solid-liquid separation device.

At this time, the concentrations of fluorine and rare earth ions of the filtrate separated from the solid-liquid solution were F 0.4 mg / l and 0.6 mg / l of Ln, respectively, and the removal efficiency of fluorine ions was 99.2%.

The reaction product which passed through this process is suspended in 25 ml of water without performing a drying process, stirring is carried out, the rare earth fluoride and a rare earth hydroxide are uniformly solved, and pH is adjusted to 4 using diluted hydrochloric acid.

At this time, rare earth fluoride is present as a stable compound in the PH, but excess rare earth hydroxide is recovered in the solution.

After the pH adjustment process, the solid-liquid separation is carried out using a conventional solid-liquid separation method, and 90% of the excess of 3 equivalents of rare earth compounds are recovered into the solution, and the concentration of F ions becomes 0.1 mg / l, which is used again for wastewater treatment. Can be done.

As mentioned above, rare earth elements form rare earth fluoride, which is a very stable compound with fluorine, and the rare earth fluoride formed is poorly soluble, so it is excellent in fluorine removal effect and uses less rare earth as fluorine remover. It is quite advantageous, but the biggest problem is that the cost of chemicals becomes expensive by using rare earth elements. Especially, when fluoride is removed to a low concentration, it is possible to add several times the equivalent amount when it is discharged. Rare earths in excess of equivalents are present in hydroxides or solutions and have been considered economically inexpensive for industrial use.

However, the present invention removes fluorine at low concentrations with high efficiency, but the rare earths actually used are equivalent to the reaction equivalents, and the rare earths above the equivalents are recovered again to participate in the fluorine removal reaction, thereby having an excellent treatment method in terms of economic efficiency.

Claims (6)

The fluorine-free wastewater is added to the fluorine-containing waste water by adding 2-10 times the equivalent of a chemical reaction equivalent to fluorine, and controlling the pH, followed by the first step to solid-liquid separation to remove fluorine. The rare earth fluoride and rare earth hydroxide are sludge, and the inorganic acid is added to the sludge through the second step to adjust the pH, selectively dissolve the rare earth hydroxide, and then liquid-separate the liquid containing rare earth. A method for treating fluorine-containing wastewater, wherein the effluent is recovered and reused and the rare earth fluoride is recovered as a solid. The method of treating fluorine-containing wastewater according to claim 1, wherein the soluble rare earth compound is a solution selected from chloride, sulfide and nitride as a soluble rare earth salt. The method for treating fluorine-containing wastewater according to claim 1, wherein the fluorine-containing wastewater is formed in a first process having a pH of 5-10. The method for treating fluorine-containing wastewater according to claim 1 or 3, wherein the rare earth hydroxide is dissolved to have a pH of 2.5-5.5 after the second process. The method of treating wastewater containing fluorine according to claim 4, wherein the alkali used for pH adjustment is selected from caustic soda, potassium hydroxide and ammonia water. The method of treating wastewater containing fluorine according to claim 4, wherein the acid used for pH adjustment is selected from hydrochloric acid, nitric acid and sulfuric acid.