JPH10314797A - Method for treating water containing fluoride ion and cod component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating water containing fluoride ions and COD components wherein water can be recovered so as to be utilized and fluoride ions and COD components can be removed efficiently at a high rate using a small amount of chemicals. SOLUTION: In a preliminary reaction tank 1, Ca salts and/or Al salts 7 are added to water 6 containing fluoride ions and COD components to adjust pH to 5-8 to effect sedimentation and solid-liquid separation is effected at a solid-liquid separation tank 2 to discharge sludge 11 and flowing out liquid 12 is evaporated at an evaporating device 3 to recover water 13 and concentrated liquid 14 is introduced into a coagulating reaction tank 4, where polyvalent metal salts 15 are added to the liquid 14 to adjust pH so that solids are produced and solid-liquid separation is effected in a solid-liquid separation tank 5 and sludge 20 is returned to the tank 1, while separated liquid is subjected to an ion-exchange treatment at an ion-exchange tank 22 filled with weak-base anion-exchange resins 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fluoride ions and COD from water containing fluoride ions and COD components.
A treatment method for removing the D component, in particular, recovering water in a state where it can be used, and using fluoride ions and COD
Fluoride ion and C for efficient removal of components
The present invention relates to a method for treating OD component-containing water.

[0002]

2. Description of the Related Art Water containing fluoride ions and COD components such as flue gas desulfurization effluent discharged from a thermal power plant or the like cannot be reused as it is because it contains fluoride ions and COD components. Conventionally, as a method of treating fluoride ion-containing water, there is known a treatment method in which calcium ions or aluminum ions of about twice the amount of fluoride ions are added, a precipitate is formed, and the precipitate is removed.
This method generates a large amount of sludge due to the large amount of added chemicals,
In addition, since the fluoride ion concentration of the resulting treated water is high,
It was not a perfect treatment.

[0003] In order to improve such a point, a high-grade treatment is further performed by forming and separating a precipitate in the presence of magnesium ions, and a magnesium circulation method capable of recycling magnesium is combined. A method for treating fluoride ion-containing water has been proposed (Japanese Patent Publication No. 58-13230). However, with the above method,
The amount of the alkali agent used to generate the magnesium precipitate is large, and the treated water cannot be reused as it is, but is wastefully discharged as effluent.

[0004] In addition, flue gas desulfurization wastewater contains fluoride ions and COD components, which cannot be removed by the above treatment. As a method for removing the COD component, treatment with a weakly basic anion exchange resin is known.
When fluoride ions coexist, there is a problem that the removal efficiency of the COD component is reduced.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is possible to recover water in a usable state, and to use a small amount of chemicals efficiently and highly. An object of the present invention is to propose a method for treating fluoride ion and COD component-containing water that can remove fluoride ions and COD components.

[0006]

The present invention is the following method for treating water containing fluoride ions and COD components. (1) An evaporation step of evaporating fluoride ion and COD component-containing water to recover water and concentrating the fluoride and COD components, and converting the concentrated solution obtained in the evaporation step to a pH value in the presence of polyvalent metal ions. Adjusting, forming a precipitate, and performing a solid-liquid separation, and an ion exchange step of removing the COD component by treating the separated liquid obtained in the aggregation and separation step with an anion exchange resin. Of water containing fluoride ions and COD components. (2) Before the evaporating step, a pre-separation step of adjusting the pH of the water containing the fluoride ion and the COD component to pH 5 to 8.5 in the presence of calcium ions and / or aluminum ions to precipitate and separate the insoluble compound is included. The method according to the above (1).

In the present invention, water is recovered in a usable state by the evaporation step, and the concentration of fluoride ions is increased to promote the precipitation of calcium fluoride, thereby reducing the amount of the pH adjuster used in the coagulation separation step. This is a method in which fluoride ions are efficiently removed with a small amount, whereby COD components are efficiently removed by anion exchange.

The water containing fluoride ions and COD components to be treated in the present invention may contain other components as long as they contain fluoride ions and COD components. Examples include wastewater discharged from a flue gas desulfurization step in a place or the like. The flue gas desulfurization wastewater contains COD such as dithionic acid in addition to fluoride ions.
Some contain components.

[0009] The characteristics of the flue gas desulfurization wastewater vary depending on the flue gas desulfurization method such as the suit separation method and the suit mixing method. The suit separation method is a method in which exhaust gas is sequentially passed through a dust removing tower and an absorption tower to treat the waste water, and the waste water is discharged from the dust removing tower. In this case, the waste water has a low pH and contains a large amount of fluoride ions. The suit mixing method is a method in which exhaust gas treatment is performed only by an absorption tower. In this case, the pH of the wastewater is neutral and the amount of fluoride ions is small. Therefore, when the mixture is neutral and has a small amount of fluoride ions as in the case of the suit mixing method, it can be directly evaporated and concentrated in the evaporation step. It is preferable to provide a preliminary separation step which combines neutralization and removal of fluoride ions before the step.

In the pre-separation step, calcium ions and / or aluminum ions are present in the fluoride ions containing a large amount of fluoride ions and the COD component-containing water, and if necessary, a pH adjuster is added to adjust the pH to 5-8. 5
By doing so, the fluoride ions are separated into solid and liquid as a precipitate, and the sludge is removed out of the system. This precipitate is presumed to be CaF ₂ in the case of calcium ions and Al (OH) _{3 in} the case of aluminum ions in which fluoride is embraced.

In the pre-separation, if calcium ions and / or aluminum ions are sufficiently present in the water containing the fluoride ions and the COD component, a precipitate can be formed by adjusting the pH as it is. Can be added. As such an agent, a calcium salt is desirable, for example, calcium chloride, calcium carbonate, calcium hydroxide and the like.

The necessary amount of calcium ion may be at least equivalent to the amount of fluoride ion, but it is desirably 1.2 to 3 times equivalent, preferably 1.5 to 2.5 times equivalent. However, when a sufficient amount of aluminum ions is contained, such as in flue gas desulfurization and / or denitrification wastewater, the amount of calcium ions added can be reduced or made zero. The required amount of aluminum ions varies depending on the amount of fluoride ions, but as a guide, the weight ratio to fluoride ions is 1: 0.5 to 2, preferably 1: 0.7 to 1.5. Is desirable. However, when calcium ions are contained, the amount is reduced by a corresponding amount. The amount of calcium ion and / or aluminum ion added can be confirmed experimentally.

When the raw water is acidic, sodium hydroxide, sodium carbonate, calcium hydroxide and the like can be used as the pH adjuster used in the preliminary separation step. Of these, calcium hydroxide can also be used as a calcium ion source and is preferable. . If the raw water is alkaline, sulfuric acid,
Hydrochloric acid or the like can be used. The pH range in the pre-separation step is a range in which the solubility of precipitation products such as calcium fluoride and aluminum hydroxide is small, and the precipitation generation of magnesium hydroxide returned in the coagulation separation step described below is small,
That is, the pH is 5 to 8.5, particularly preferably 6 to 7. In this pre-separation step, the concentration of fluoride ions in the effluent is preferably several tens mg / l or less in order to prevent corrosion or the like of the apparatus used for evaporation in the next evaporation step due to fluorine.

[0014] In the evaporation step of the present invention, the effluent from which the sediment has been removed in the pre-separation step or the effluent of the fluoride ion, as in the suit separation method, for the water to be treated containing a large amount of fluoride ions as in the suit mixing method. A small amount of water to be treated is evaporated to recover water, and the remaining fluoride ions and calcium ions are concentrated to precipitate calcium fluoride. In the case of the water to be treated having a small amount of fluoride ions, if necessary, a pH adjuster is added to adjust the pH to 5 to 8.5, preferably to 6 to 7, and then evaporation is performed.

In the evaporation step, water is recovered in a usable state by evaporation, and the concentration is reduced by reducing the amount of water guided to the next aggregation / separation step, thereby obtaining a concentrated solution having a high fluoride concentration. In the concentrated solution, the concentration of the fluoride ion and the calcium ion increases and precipitates as calcium fluoride, so that the amount of the alkali agent added in the coagulation separation step is reduced. In addition, when calcium fluoride is deposited, if a seed crystal is present in the concentrated solution due to a seed addition method or the like, calcium fluoride is deposited around the seed crystal, and scaling does not occur.

The concentration ratio in the evaporation step is not particularly limited. However, for example, when the concentration is performed until crystallization, water-soluble crystals such as sodium fluoride are discharged to make the treatment difficult and the concentration of coexisting salts increases. In addition, the cohesiveness of the precipitate generated in the coagulation separation step is deteriorated. For this reason, it is preferable to concentrate at the concentration ratio immediately before the precipitation of crystals. Generally, the concentration ratio can be several tens of times, whereby the amount of concentrated water used for the following treatment is several tenths of the amount of raw water.
Becomes

In the coagulation / separation step of the present invention, a precipitate is formed by adding a pH adjuster to the concentrate obtained in the evaporating step in the presence of polyvalent metal ions to adjust the pH, and forming a precipitate. Separate by liquid separation. As the polyvalent metal ion, those which generate a precipitate by adding a pH adjuster, such as magnesium ion, aluminum ion and iron ion, can be used. The pH range to be adjusted depends on the type of polyvalent metal ion, and the optimum pH at which a precipitate is formed is determined.
H range. For example, p in the presence of magnesium ions
By adjusting the pH to 9.5 or more by adding an H adjuster, a precipitate of Mg (OH) ₂ is generated, and the fluoride in the liquid is also embraced by the precipitate to precipitate. In the case of aluminum ions, the pH is adjusted to 5 to 8.5. 3 for iron ions
The pH is adjusted to 4 or more for divalent and 6 or more for divalent.

When a polyvalent metal ion such as a magnesium ion is present in the concentrated solution in the coagulation separation step, a precipitate is formed by adding the pH adjuster as it is. Add the metal salt. Magnesium chloride can be used as the magnesium salt, and aluminum chloride and aluminum sulfate can be used as the aluminum salt. By setting the amount of polyvalent metal ions to be present in the reaction solution to 20 times or more, preferably 20 to 25 times, the weight ratio of fluoride ions, the amount of residual fluoride ions can be reduced to 1 mg / l or less. . Sodium hydroxide, sodium carbonate, calcium hydroxide and the like can be used as the pH adjuster.

The reaction liquid in which the precipitate is formed is separated into sludge by solid-liquid separation and discharged out of the system.
When performing preliminary separation, this sludge is returned to the preliminary separation step, and the sludge is dissolved to release fluoride ions to the preliminary separation step. In this case, when the raw water in the pre-separation step is acidic, the precipitate may be directly mixed and dissolved in the raw water, but when the raw water is alkaline or neutral, it is preferable to return after dissolving with the acid. The fluoride ions thus released are subjected to the above-mentioned preliminary separation process together with the fluoride ions in the raw water.

When magnesium ions are used in the coagulation / separation step, the magnesium ions returned from the coagulation / separation step and dissolved in the preparatory separation step are directly discharged to the evaporation step and recycled. Therefore, the amount of magnesium ion added in the coagulation separation step may be an amount corresponding to the magnesium precipitate discharged from the preliminary separation step.
At this time, when the pH is adjusted to 7 or less in the preliminary separation step, magnesium hardly precipitates, so that the amount of the magnesium salt added in the aggregation separation step is small except for the first time. When aluminum ions are used in the coagulation separation step, the aluminum ions that have become precipitates are used for precipitation of fluoride ions in the preliminary separation step.

In the above treatment, if the concentration ratio in the evaporation step is high, the cohesiveness of magnesium hydroxide generated in the coagulation separation step becomes poor due to an increase in the coexisting salt concentration, and solid-liquid separation becomes difficult. In such a case, when returning the sludge mainly composed of magnesium hydroxide generated in the coagulation separation step,
It is preferable to circulate a part of the sludge in the coagulation separation step, because the sedimentation of the sludge is improved. In this case, the amount of sludge circulated in the coagulation / separation step is preferably 0.1 to 30 times the amount of new SS generated in the coagulation / separation step (as SS), and the sedimentation of the generated sludge is within this range. Determine the amount of circulation to be the highest. All remaining sludge is returned to the pre-separation process. Since only a certain amount of sludge is circulated to the coagulation / separation step, the entire amount of sludge generated in the coagulation / separation step is returned to the preliminary separation step.

Since COD components such as dithionic acid present in the raw water are not removed in the preliminary separation step or the coagulation separation step, they are concentrated in the evaporation step and become more difficult to remove. In such a case, in the ion exchange step, the separated liquid in the aggregation separation step is ion-exchanged with an anion exchange resin to remove the COD component. The ion exchange resin is preferably a weakly basic anion exchange resin, but may be a strongly basic anion exchange resin.

In this case, it is preferable that SS is removed by a filtration step prior to the ion exchange step, and organic substances and other TOC components are removed by an activated carbon treatment step. The filtration step may be filtration by a packed bed of a granular filter material such as sand or anthracite, or fine filtration. Activated carbon treatment includes treatment with a packed bed of granular activated carbon or treatment with powdered activated carbon.

In the ion exchange step, if necessary, the separated solution filtered or activated carbon-treated is passed through an ion exchange resin layer such as a weak or strong basic anion exchange resin to perform ion exchange.
Dithionate ion and other COD components are removed. After ion exchange, regenerate by passing acid or alkaline solution,
COD components such as dithionate ions adsorbed on the resin elute in the regenerated effluent. The dithionate ions in the regenerated effluent can be detoxified by oxidation to sulfate ions.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing a treatment apparatus for treating water containing fluoride ions and COD components according to a preferred embodiment.
An example is shown in which H is applied to the treatment of water to be treated, which is rich in fluoride ions. In FIG. 1, 1 is a preliminary reaction tank, 2 is a solid-liquid separation tank, 3 is an evaporator, 4 is an agglutination reaction tank, 5 is a solid-liquid separation tank,
22 is an ion exchange tank.

First, in the preparatory separation step, raw water is introduced from the raw water pipe 6 into the preliminary reaction tank 1, and calcium salts and / or aluminum salts are added from the chemical injection pipe 7,
Further, a pH adjusting agent is injected from the chemical injection tube 8. Then, the mixture is stirred by the stirrer 9 to adjust the pH to 5-8.5 in the presence of calcium ions and / or aluminum ions,
Form a precipitate. The reaction liquid in the preliminary reaction tank 1 is sent from the flow path 10 to the solid-liquid separation tank 2 to perform solid-liquid separation, and the precipitate is discharged as sludge from the sludge pipe 11 to the outside of the system. From 12, it is discharged to the evaporator 3 in the evaporating step.

Next, in the evaporation step, the pre-separated liquid from the flow channel 12 is evaporated in the evaporator 3 to recover available water from the water recovery channel 13 and to concentrate the fluoride in the effluent. At this time, fluoride ions and calcium ions are concentrated and precipitated as calcium fluoride, and no scaling occurs. The concentrate of the evaporator 3 is sent from the flow path 14 to the coagulation reaction tank 4.

In the aggregating / separating step, a polyvalent metal salt is added to the concentrate from the evaporating step into the aggregating reaction tank 4 through the chemical injection pipe 15, and a pH adjuster is added from the chemical injection pipe 16 to the agitator 17.
And adjust the pH in the presence of polyvalent metal ions to form a precipitate. At this time, since the concentration of the concentrated solution is small, the amount of the pH adjuster may be small. The reaction liquid in the coagulation reaction tank 4 is sent from the flow path 18 to the solid-liquid separation tank 5 to perform solid-liquid separation, and the separated liquid is sent from the flow path 19 to the ion exchange tank 22.

The sludge solid-liquid separated in the coagulation separation step is returned to the preliminary reaction tank 1 from the return pipe 20. When the raw water in the pre-separation step is acidic, the sludge may be directly mixed and dissolved in the raw water. However, when the raw water is alkaline or neutral, it is desirable that the sludge is dissolved in the dissolving tank 21 and then returned. . Also, the concentration ratio in the evaporator 3 is high,
When the concentration of the coexisting salts in the concentrated liquid is high, the coagulation property of the sludge in the solid-liquid separation tank 5 is poor. Therefore, when returning the sludge from the return pipe 20 to the preliminary reaction tank 1, a part of the sludge is coagulated from the return pipe 20a. By circulating in the reaction tank 4, the sedimentability of the sludge is improved.

Thus, fluoride ion and CO
When the D-containing water is treated, the water recovered from the evaporator 3 can be used as clean water. Further, since calcium ions and fluoride ions remaining in the effluent from the solid-liquid separation tank 2 are concentrated and precipitated as calcium fluoride, the amount of the alkali agent added in the coagulation reaction tank 4 is reduced.

In the ion exchange step, the separated liquid is introduced into the ion exchange tank 22 from the flow path 19 and passed through a resin layer 23 such as a weakly basic anion exchange resin to carry out ion exchange, thereby obtaining COD such as dithionate ions. The components are removed by exchanging and adsorbing the resin, and the treated water is discharged from the treated water pipe 24 to the outside of the system. In this case, since the fluoride ions are removed in the preliminary separation step and the coagulation separation step, the load of the fluoride ions in the ion exchange step can be reduced, whereby the COD component is efficiently removed in the ion exchange tank. can do.

The regeneration is performed by injecting a regenerant such as an acid or an alkali solution from a chemical tube 25 and discharging the regenerated waste liquid from a drain tube 26. The dithionic acid in the regenerated effluent can be converted to a sulfate by oxidation.

FIG. 2 is a system diagram showing a processing apparatus according to another embodiment.
Shows an example in which the present invention is applied to water to be treated which is near neutral and has a small amount of fluoride ions. In FIG. 2, 31 is a filtration tank and 32 is an activated carbon treatment tank.

This processing method does not have a preparatory separation step, and starts with an evaporation step. In the evaporating step, raw water is introduced from the raw water pipe 6 into the evaporator 3 and processed in the same manner as in FIG. Subsequently, the coagulation separation step is also performed in the coagulation reaction tank 4 and the solid-liquid separation tank 5 in the same manner as described above. A part of the separated sludge in the solid-liquid separation tank 5 is returned from the return pipe 20 to the coagulation reaction tank 4, and the remaining part is discharged from the sludge discharge pipe 33.

The separated liquid in the solid-liquid separation tank 5 is used as a filtration step.
The liquid is introduced into the filtration tank 31 from the flow path 19, and is filtered through the filtration layer 34. The filter layer 34 is made of a packed layer of a granular filter material such as sand and anthracite, where SS is removed. Filter layer 3
After blockage of block 4, backwashing is performed to regenerate the filter layer.

As the activated carbon treatment step, the filtrate in the filtration tank 31 is introduced into the activated carbon treatment tank 32 from the flow path 35 and is passed through the activated carbon layer 36 to perform activated carbon treatment to adsorb and remove TOC components. As the activated carbon layer 36, a packed bed of granular activated carbon can be used. When the adsorption power is reduced, the activated carbon layer 36 can be replaced or regenerated by a heating / regeneration furnace and reused. The activated carbon treatment tank 31 may be provided after the ion exchange tank 22. Further, as the activated carbon treatment, a treatment can be performed using powdered activated carbon instead of the activated carbon layer 36, but in this case, it is preferable to add the activated carbon layer to the coagulation reaction tank 4.

The activated carbon treatment liquid that has been treated in the activated carbon treatment tank 32 is introduced into the ion exchange tank 22 through a flow path 37.
The ion exchange is performed as described above. Since the SS is removed in the filtration tank 31, sludge and blockage of the resin layer 23 are prevented. Further, since the TOC component is removed in the activated carbon treatment tank 32, the load on the resin layer 23 can be reduced, and the TOC value of the treated water can be reduced.

The filtration tank 31 and the activated carbon treatment tank 32 described above can be provided between the solid-liquid separation tank 5 and the ion exchange tank 22 in the apparatus shown in FIG. 1 and can be treated in the same manner as described above. .

[0039]

Next, the present invention will be described with reference to test examples. Example 1 F500-1100 mg / l, Mg 400-700 mg
As a preliminary separation step, return sludge is mixed and dissolved in a flue gas desulfurization wastewater of a suit separation system having a pH of 1.4 to 2.5 and containing Ca (OH) ₂ in an amount of 4000 to 6000 mg.
/ L was added and reacted for 30 minutes, followed by solid-liquid separation to obtain an effluent of the preliminary separation step. This effluent is used as an evaporation step in a forced circulation type evaporator (1.7 m ^{3 of} retained water) in an amount of 1.1 m ^3.
/ Hr and evaporated at a concentration factor of 10x.
This concentrated liquid is used as a coagulation separation step by adding 1 part of sodium hydroxide.
6000 mg / l (1600 mg / l-raw water) was added for coagulation, separated into solid and liquid, and the separated sludge was returned to the preliminary step. After filtering the separated liquid, 100 l
Activated carbon treatment was performed in the filled activated carbon treatment tank, and thereafter, ion exchange was performed in an ion exchange tank filled with 200 liters of a weakly basic anion exchange resin. Regeneration of the ion exchange resin was performed with sodium hydroxide and sulfuric acid. Table 1 shows the water quality at each stage. All heavy metals in the treated water were below the drainage standard.

[0040]

[Table 1]

[0041]

According to the present invention, fluoride ion and CO
Since the water containing the D component was evaporated to recover the water, and the concentrated solution was subjected to coagulation separation and then ion exchange,
Water can be recovered in a usable state, and fluoride ions and COD components can be efficiently and highly removed.

When calcium ions and / or aluminum ions are present in the water containing fluoride ions and COD components to form precipitates, and the precipitate is solid-liquid separated, the effluent is evaporated. Fluoride ions and COD components can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a system diagram of an apparatus for treating water containing fluoride ions and COD components according to an embodiment.

FIG. 2 shows fluoride ion and CO according to another embodiment.
FIG. 2 is a system diagram of a treatment device for D-component-containing water.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Preliminary reaction tank 2, 5 Solid-liquid separation tank 3 Evaporator 4 Coagulation reaction tank 6 Raw water pipe 7, 8, 15, 16 Chemical injection pipe 9, 17 Stirrer 10, 12, 14, 18, 19, 35, 37 Flow Paths 11, 33 Drainage pipe 13 Water recovery path 20, 20a Return pipe 21 Dissolution tank 22 Ion exchange tank 23 Resin layer 24 Treatment water pipe 25 Chemical liquid pipe 26 Drainage pipe 31 Filtration tank 32 Activated carbon treatment tank 34 Filter layer 36 Activated carbon layer

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 9/00 504 C02F 9/00 504E 1/04 1/04 C 1/42 ZAB 1/42 ZABE 1/52 CDG 1/52 CDGJ 1/58 1/58 M (72) Inventor Koji Toyama 3-3-22 Nakanoshima, Kita-ku, Osaka-shi, Osaka Inside Kansai Electric Power Co., Inc. (72) Ryoichi Yamada 3-4-1 Nishishinjuku, Shinjuku-ku, Tokyo No. 7 Inside Kurita Kogyo Co., Ltd. (72) Yoshihiro Endo 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd. (72) Hiroyuki Asada 3-4-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Kurita Industrial Co., Ltd.

Claims (2)

[Claims] 1. A method for recovering water by evaporating water containing a fluoride ion and a COD component, and for removing fluoride and COD.
An evaporating step of concentrating the D component; an aggregating / separating step of adjusting the pH of the concentrated solution obtained in the evaporating step in the presence of polyvalent metal ions to generate a precipitate and solid-liquid separating; An ion exchange step of treating the separated solution with an anion exchange resin to remove a COD component. 2. Prior to the evaporation step, fluoride ions and C
The method according to claim 1, further comprising a preliminary separation step of adjusting the pH of the OD component-containing water to pH 5 to 8.5 in the presence of calcium ions and / or aluminum ions to precipitate out and separate insoluble compounds.