JP2503806B2 - Fluoride-containing water treatment method - 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 fluoride-containing water, which is particularly easy to operate and has no problem of scale deposition, and is capable of obtaining stable, efficient and inexpensive treated water of high quality. The present invention relates to a method of treating fluoride-containing water capable of producing.

[0002]

2. Description of the Related Art The slaked lime method and the sulfuric acid band method have hitherto been known as methods for treating fluoride-containing water such as flue gas desulfurization wastewater. Among these, as the slaked lime method, after the fluoride-containing water is adjusted to pH 10 to 12, a water-soluble calcium compound is added, the generated precipitate is separated, and then the pH is adjusted to 4 to 7 to perform reverse osmotic pressure treatment for further advanced treatment. A method of attaching is proposed (Japanese Patent Publication No. 59-9236).

[0003]

Among the above-mentioned conventional methods, the slaked lime method disclosed in Japanese Examined Patent Publication No. 59-9236 requires a settling tank and uses a reverse osmosis membrane so that the scale component (calcium concentration) is reduced. However, there is a drawback in that it often increases and often causes problems due to scale precipitation such as gypsum. Also,
Since the injection of the calcium hydroxide compound is carried out by pH control and only corresponds to the acidity of the fluoride-containing water that is the raw water, it cannot cope with the fluctuation of the fluoride ion of the raw water and the treated water quality There is also the drawback that deterioration often occurs. For this reason, it is considerably difficult to manage operation by the slaked lime method in order to stably recover high-quality treated water.

On the other hand, even in the treatment by the sulfuric acid band method, calcium hydroxide (Ca (OH)) is used as a pH adjusting agent.
_{When 2} ) is used, problems similar to the above occur. When caustic soda (NaOH) is used as a pH adjuster, scale hindrance does not occur, but since the injection of the sulfuric acid band is a quantitative injection, it is still not possible to deal with fluctuations in the water quality (fluoride ion concentration) of the raw water. There is. Therefore, in the sulfuric acid band method, it is necessary to inject an excessive amount of the sulfuric acid band in order to prevent the deterioration of the treated water quality due to the fluctuation of the raw water quality. In this case, the running cost of the sulfuric acid band method was very high.

The present invention solves the above-mentioned conventional problems, is easy to operate and manage, does not have the problem of scale deposition, and contains a fluoride containing stable, efficient and inexpensive processed water of high quality. It is intended to provide a method for treating water.

[0006]

The method for treating fluoride-containing water according to claim 1 is a suspension obtained by adjusting the pH to 6 to 8 by adding a calcium compound to water containing fluoride and sulfate ions. The reaction step of introducing the turbid liquid into the circulation tank, the membrane separation step of separating the liquid introduced from the circulation tank into the permeate and the concentrated liquid, and the concentrated liquid discharged from the membrane separation step into the circulation tank. circulating step circulating in, and the adsorption step to obtain a treated water permeate adsorption treatment to a method of treating a fluoride-containing water by, characterized that you adding sulfuric acid to the reaction step.

[0007]

[Function] By adding a calcium compound to fluoride and sulfate ion- containing water, the fluoride ion becomes CaF ₂
Is deposited as.

By the way, in such a treatment using a calcium compound, the concentration of dissolved calcium in the reaction step becomes very high, and a calcium-based scale is easily generated. Further, since the dissolved calcium concentration is high, a large amount of expensive softening agent such as sodium carbonate is required in the subsequent softening step of the treated water. As described above, the treatment method using the calcium compound has problems that scales are likely to occur and the cost of the medicine is high.

[0009] In contrast, in the method of the present invention, order to add sulfuric acid to the reaction step, scale formation due to the high calcium concentration, drug costs rise problems are solved.
That is, due to the increase of sulfate ion in the system, due to the common ion effect
The solubility of calcium sulfate is significantly reduced,
As a result of the precipitation of calcium ions as calcium sulfate, dissolved ions
Decrease in lucium concentration. Incidentally, sulfuric <br/> acid that is used in the present invention because it is inexpensive chemicals, there is no problem of rising costs by this.

When the suspension in the reaction step is directly subjected to the membrane separation treatment, scale is generated on the surface of the separation membrane due to unreacted calcium components and the like. That is, since gypsum, which is a scale component, takes time to generate a reaction, in many cases, gypsum is generated and scales on the surface of the separation membrane after the completion of the reaction step. On the other hand, in the present invention, since a circulation tank is provided and the suspension of the reaction step is not directly passed through the membrane separation step but is temporarily stored in the circulation tank and then supplied to the membrane separation step, the separation membrane is used. Surface scaling is prevented. Further, by supplying the concentrated water of the membrane separation process to this circulation tank, S
S acts as a seed crystal, the crystallization effect reduces the calcium concentration, and the scale generation in the circulation tank is prevented.

In the membrane separation step, fluoride-containing deposits and other fine SS deposited in the reaction step are highly removed.

Then, the permeated water in the membrane separation step is further subjected to adsorption treatment to obtain treated water of higher quality.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing a method for carrying out the method for treating fluoride-containing water according to the present invention.

[0015] In the illustrated method, first, a water containing fluoride and sulfate ions is the raw water fed to the reaction vessel 1 equipped with a stirrer 1A from the pipe 10, sulfuric acid from line 11 <br/> and pipe 12 A calcium compound and, if necessary, a pH adjusting agent are added and stirred to adjust the pH to 6-8.

Examples of the calcium compound added to the reaction tank 1 include calcium hydroxide (Ca (OH) ₂ ) and calcium oxide (CaO).

[0017] In reaction vessel 1, since the sulfate ions increases in the system by the addition of sulfuric acid, by a common ion effect, significantly reduced the solubility of calcium sulfate. Therefore, calcium ions are easily precipitated as calcium sulfate, and the dissolved calcium concentration becomes low.

In the reaction step, the pH of the reaction solution is adjusted to 6 to
In order to adjust the pH to 8, preferably 6 to 7, a pH adjuster is added as needed. That is, when the addition of Ca (OH) ₂ or the like, in order to Ca (OH) ₂ itself acts as a pH adjusting agent, there is no need to use a separate pH adjusting agent, a pH drop due to the addition of sulfuric acid PH to adjust
An alkali such as NaOH or Ca (OH) ₂ is added as a regulator. In the present invention, the problem of scale disorder has been solved, and there is no fear of scale disorder occurring as in the conventional sulfuric acid band method, so Ca (O 2) is used as a pH adjuster.
It is advantageous to use H) ₂ .

PH by adding calcium compound and sulfuric acid
By adjusting to 6-8, the fluoride ion in the raw water is solidified. That is, fluoride ions are precipitated as CaF ₂ by the calcium compound. At this time, since sulfuric acid is added to the reaction tank 1, the concentration of dissolved calcium in the reaction tank 1 becomes low, and scale failure is prevented.

In the usual case, the addition amount of the calcium compound in the reaction vessel 1 is preferably about 0.5 to 3 times the equivalent of the fluoride ion in the raw water. Usually, the flue gas desulfurization wastewater contains a calcium compound, and the above range may be included including these.

The amount of sulfuric acid added also depends on the quality of the raw water and the amount of calcium compound added. Therefore, sulfur
The injection amount of the acid may be fixed amount injection, but it is preferable to measure the calcium concentration of the treated water obtained from the pipe 21 described later and set the injection amount based on the measured value. In this case, sulfuric acid is used. In the case of automatic injection of
It suffices to measure with a CP, an ion meter or the like and input the numerical value into a sequencer, a personal computer or the like to operate the chemical injection pump. By adopting such an automatic injection method, it is possible to respond favorably to changes in calcium concentration, and it is possible to always perform stable treatment.

The reaction time in this reaction tank 1 is
Normally, it should be 30 minutes or longer. That is, since it takes about 30 minutes to sufficiently form the precipitate from the reaction solution in the reaction tank 1, particularly for the gypsum-forming reaction, the reaction in the reaction tank 1 is prevented from the viewpoint of preventing scale failure. The time is preferably 30 minutes or more.

The suspension obtained in the reaction tank 1 is then introduced into the circulation tank 2 via the pipe 13.

Concentrated water discharged from the membrane separator 3 at the subsequent stage through the pipe 15 is introduced into the circulation tank 2 through the pipe 16. The suspension from the reaction tank 1 and the concentrated liquid of the membrane separation device 3 in the circulation tank 2 are introduced into the membrane separation device 3 via a pipe 14 equipped with a pump 6, and separated by a separation membrane 3A. To process.

The sludge retention time in the circulation tank 2 is 1 to 20.
It is preferable to set it so that it is about time. Further, since SS is concentrated and accumulated in the circulation tank 2 over time, sludge containing this SS is discharged from the lower part of the tank to the outside of the system through the pipe 17 as needed.

As the separation membrane 3A of the membrane separation device 3, it is preferable to use a microfiltration (MF) membrane or an ultrafiltration (UF) membrane. When the MF membrane is used, if the pore size is large and 1 μm or more, the precipitate containing fluoride may permeate. Therefore, it is preferable to use an MF film having a pore size of 0.5 μm or less. In such a membrane separator 3, the unreacted calcium compound in the liquid is not permeated through the membrane, remains in the concentrated water, and is returned to the circulation tank 2. Since it exerts the immobilization function of, it is extremely advantageous.

The reverse osmosis (RO) membrane is composed of Ca ²⁺ , F ^〜 ,
It has the ability to remove SO ₄ ²⁻ , and scale is generated by concentration polarization of the film surface, which is not preferable in the present invention.

The concentrated water of the membrane separator 3 is circulated to the circulation tank 2 via the pipes 15 and 16 as described above. In the present invention, a part of this concentrated water may be sent back to the reaction tank 1 (pipe 18). By sending a part of the concentrated water back to the reaction tank 1, the calcium concentration in the reaction tank 1 is further reduced by the crystallization effect that SS in the concentrated water becomes a seed crystal.
The formation of scale is prevented more reliably. Further, since sludge such as Ca (OH) ₂ is sent back to the concentrated water without being permeated through the membrane, these exert the adsorbing ability of fluoride ions. With such an effect, the processing efficiency is further improved, and stable processing is possible. In addition, when returning a part of concentrated water to the reaction tank 1, it is important to inject | pouring into the site | part away from the addition site of sulfuric acid .

On the other hand, the permeated water of the membrane separation device 3 is the pipe 19
More, and if necessary, pH of NaOH, HCl, etc.
After the adjusting agent is added from the pipe 20 to adjust the pH, the adjusting agent is introduced into the adsorption tower 4 filled with the adsorbent 4A for adsorption treatment.

As the adsorbent 4A of the adsorption tower 4, a fluorine adsorbent for adsorbing and removing fluoride ions still remaining in the permeated water of the membrane separator 3 or a COD adsorbent for adsorbing and removing COD components is used. be able to. Therefore, the pH adjustment by the pH adjusting agent from the pipe 20 needs to be adjusted to the optimum pH according to the type of the adsorbent 4A of the adsorption tower 4, and for example, the adsorbent 4A of the adsorption tower 4 is a fluoride. The pH is preferably adjusted to about 3 to 7 for the ion adsorbent and about 2 to 9 for the COD adsorbent.

As the fluoride ion adsorbent, tritium, zirconium, titanium or hafnium type cation exchange resin, strong or weakly acidic cation exchange resin, haloalkylsilane adsorbent resin, weakly basic anion exchange resin, rare earth metal hydration. Examples thereof include adsorption resins such as oxide type chelate resins and Al salt type chelate resins, as well as activated alumina and magnesia type adsorbents. Examples of the COD adsorbent include gel-type or MR-type weak, medium and strong basic anion exchange resins and other COD adsorption resins, and activated carbon.

The treated water obtained by the adsorption treatment with the adsorbent 4A is discharged from the system through the pipe 21.

In the present invention, raw water fluoride and sulfuric acid
There are no particular limitations on the water containing ions, e.g., flue gas desulfurization and / or denitrification wastewater, aluminum electrolytic refining process wastewater, the manufacturing process wastewater phosphate fertilizer, the process of cleaning the electrical components such as silicon, uranium refining process, Surface treatment cleaning process drainage etc. are mentioned.

The example shown in FIG. 1 is an embodiment of the present invention, and the present invention is not limited to the illustrated method. In the method of this embodiment, sulfuric acid is injected into the reaction tank 1, which is an inlet pipe for raw water (pipe 1 in FIG. 1).
0) may be directly injected. Also, the adsorption tower 4
Needless to say, the adsorption treatment may be performed in an upward flow or a downward flow, but in general, fluoride ion adsorption and COD adsorption are performed in a downward flow.
Fluoride ion adsorption treatment may be further performed after the COD adsorption treatment.

Specific examples and comparative examples will be described below. Example 1 A synthetic flue gas desulfurization wastewater having the following water quality was treated according to the method shown in FIG. Raw water quality pH: 1.4 Ca: 450 mg / l Al: 240 mg / l Fe: 50 mg / l F: 210 mg / l SO ₄ ^2- : 5700 mg / l Cl: 4000 mg / l Raw water in the reaction tank 1 8.5 l / is introduced at a rate of hr, it was added Ca (OH) ₂及beauty H ₂ SO ₄ at the following ratio, to adjust the pH to 7, followed by reaction under stirring for 30 minutes.
The suspension obtained by the reaction was introduced into the circulation tank 2 and was supplied to the membrane separation device 3 having the following specifications together with the circulating content of concentrated water (SS concentration: 4% by weight) for membrane separation treatment.

Reaction tank 10% by weight Ca (OH) ₂ addition amount: 0.5 l / hr 5% by weight H ₂ SO ₄ addition amount: 0.2 l / hr pH: 7 Circulation tank concentrated water circulation amount: 60 times amount of raw water Residence time: 10 hours Membrane separation device Separation membrane: Microfiltration membrane (polysulfone membrane) Nominal pore size 0.2 μm Permeate obtained by membrane separation treatment with H ₂ SO ₄ at pH 3.0
After the adjustment, the water was passed through the adsorption tower 4 filled with the hydrated cerium oxide type chelate resin with SV of 20 hr ⁻¹ in a downward flow for adsorption treatment.

When operated for 200 hours under such conditions, the concentration of fluoride in the treated water (adsorbed treated water) was always 1 m.
In addition to being stable at g / l or less, generation of foreign matters such as precipitates in the adsorption tower was not observed at all. By the way, the calcium ion concentration in the effluent of the reaction tank 1 is 1100 to
It was 1200 mg / l.

Comparative Example 1 Following the operation described in Example 1, H ₂ SO was added to reaction vessel 1.
_When operated without adding ₄ , white precipitates began to be observed at the treated water inlet (upper side) of the chelate resin-filled adsorption tower 4 in about 10 hours, and after a further 20 hours, the difference in the adsorption tower 4 was increased. The pressure rose abnormally, making it virtually impossible to run water.

During this period, the concentration of fluoride in the treated water was 1 mg.
/ L or less was maintained, but the calcium ion concentration in the effluent of the reaction tank 1 was 1400 to 1600 mg / l.

[0040]

As described in detail above, according to the method for treating fluoride-containing water of the present invention, the concentration of dissolved calcium in the reaction tank is reduced, so that scale failure is prevented. Further, since the calcium concentration of the treated water is also reduced at the same time, the addition amount of the softening agent used in the softening treatment or the like in the subsequent step can be significantly reduced. Therefore, the drug cost can be reduced.

Therefore, according to the method of the present invention, it is possible to stably and efficiently obtain treated water of high water quality at low cost.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a treatment method of a fluoride-containing water treatment method of the present invention.

[Explanation of symbols]

 1 Reaction tank 2 Circulation tank 3 Membrane separation device 4 Adsorption tower

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C02F 5/08 C02F 5/08 9/00 502 9/00 502E 502H 503 503G 504 504B (56) Reference Reference JP-A-3-118897 (JP, A) JP-A-51-81789 (JP, A) JP-A-62-168508 (JP, A) JP-A-63-31505 (JP, A)

Claims (1)

(57) [Claims] 1. A reaction step in which a calcium compound is added to water containing a fluoride and a sulfate ion to adjust the pH to 6 to 8 and a suspension obtained is introduced into a circulation tank, which is introduced from the circulation tank. Membrane separation process for separating the liquid into a permeate and a concentrated liquid by a membrane separation process, a circulation process for circulating the concentrated liquid discharged from the membrane separation process to the circulation tank, and a treated water by absorbing the permeated liquid. adsorption process obtaining a method of processing a fluoride-containing water, the method of treating a fluoride-containing water, characterized that you adding sulfuric acid to the reaction step.