JP4348116B2 - Fluorine or phosphorus-containing water treatment equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for removing fluorine or phosphorus.
[0002]
[Prior art]
In the electronics industry that manufactures semiconductors, liquid crystals, and the like, fluorine is often contained in the wastewater from the electronics industry because fluorine is used in the manufacturing process. As a method for removing fluorine from this fluorine-containing water, calcium agent is added to raw water to precipitate fine particles of calcium fluoride, and these fine particles are agglomerated with Al, Fe inorganic flocculant or organic polymer. A method of aggregating with an agent and separating by precipitation is employed. According to this method, the treated water fluorine can be reduced to 10 to 20 mg / l. However, in Japan, the emission standard value for fluorine was strengthened from 15 mg / l to 8 mg / l in July 2001, and it became necessary to treat fluorine more highly.
[0003]
As a method for highly treating fluorine, a method of increasing the amount of the flocculant added in the coagulation sedimentation treatment or performing the coagulation sedimentation treatment once again after the coagulation sedimentation treatment is employed. The amount of the flocculant used in such treatment is 2000 to 5000 mg / l, and fluorine is adsorbed on Al or Fe hydroxide to improve the fluorine removal rate. By this method, the treated water fluorine concentration can be reduced to 2 to 8 mg / l.
[0004]
As another method, it has been proposed to improve the fluorine removal rate by supporting a hydrous oxide of Zr or Ce on a resin or using a fluorine adsorbent granulated with a polymer substance (Patent Document 1). (Japanese Patent Publication No. 6-79665), Patent Document 2 (Japanese Patent Publication No. Sho 61-47134)). It is said that these methods can reduce the fluorine concentration of treated water to 0 to 1 mg / l.
[0005]
Here, the adsorbent is a hydrous oxide MO _n · XH ₂ O (≈M (OH) _m ) generated by hydrolysis by adding an alkali to a rare earth element or a salt of Ti, Zr or heating. A substance as represented utilizes the property of anion exchange on the acidic side with anions such as PO ₄ ³⁻ , F ⁻ , SO ₄ ²⁻ , and cation exchange on the alkali side (Patent Document 3). JP-B-2-17220), Patent Document 4 (Japanese Patent Laid-Open No. 60-172353)). M is a metal, and X, m, and n are arbitrary numbers.
[0006]
In addition, as a method for improving and stabilizing the quality of treated water, reducing the amount of coagulant used, and reducing sludge volume, there are sludge circulation methods (Patent Document 5 (Patent Document No. 2912226) and Patent Document 6 (Japanese Patent Laid-Open Publication No. Hei 9) -276875), Patent Document 7 (Japanese Patent Laid-Open No. 2000-84570)). This is because sludge containing Al-based or Fe-based inorganic flocculant is solid-liquid separated and then returned through a circulation line, and the sludge is returned as it is or after being subjected to acid or alkali treatment (sludge regeneration treatment). Is. It has been reported that by returning this sludge, the sludge becomes a seed crystal, the crystallization reaction proceeds easily, and the solid-liquid separation property is improved. It has also been reported that the total amount of the inorganic flocculant can be reduced by reusing the inorganic flocculant obtained by treating the sludge with acid or alkali before returning it to liberate fluorine or phosphorus.
[0007]
Electronic industry wastewater often contains phosphorus, and phosphorus is also contained in household wastewater. It is necessary to remove phosphorus from the viewpoint of preventing eutrophication in closed waters, and in many areas phosphorus is subject to additional regulations. In the removal of phosphorus, as in the case of fluorine, in addition to the treatment of adding calcium agent to agglomerate and precipitate as calcium phosphate, Al or Fe inorganic aggregating agent is used to agglomerate as aluminum phosphate or iron phosphate. Precipitation has been processed. Furthermore, the adsorbent described above can treat not only fluorine ions (F ⁻ ) but also phosphate ions (PO ₄ ³⁻ ). Therefore, these adsorbents can also be used for phosphorus removal.
[0008]
[Patent Document 1]
Japanese Patent Publication No. 6-79665 [Patent Document 2]
Japanese Patent Publication No. 61-47134 [Patent Document 3]
Japanese Patent Publication No. 2-17220 [Patent Document 4]
JP-A-60-172353 [Patent Document 5]
Japanese Patent No. 2912226 [Patent Document 6]
Japanese Patent Laid-Open No. 9-276875 [Patent Document 7]
JP 2000-84570 A [0009]
[Problems to be solved by the invention]
In the coagulation sedimentation method, several thousand mg / l of an Al or Fe type coagulant is added in order to reduce fluorine. Such agglomerated sludge incorporates water molecules inside the floc, so that the dewaterability of the sludge is poor and the amount of flocculant added is large, resulting in a very large amount of sludge generated. Therefore, there is a problem that the sludge disposal cost increases. In addition, such a process for generating a large amount of waste is a technology that goes against social demands for reducing the amount of waste.
[0010]
On the other hand, although the fluorine adsorbent does not increase sludge, the adsorption rate is slow and the amount of adsorbent used is large. For this reason, there exists a problem that processing cost is very high. Another problem is that the adsorbent deteriorates due to an oxidizing agent such as hydrogen peroxide contained in the wastewater from the electronics industry or hydrofluoric acid in the raw water, causing the base material to collapse and flow out.
[0011]
In the sludge circulation method, sludge is treated with either acid or alkali. However, in many cases, sludge cannot be completely dissolved by acid treatment. If it does so, at least one part of sludge will remain in the state couple | bonded with the fluorine or phosphorus, it will not melt | dissolve completely, but the reuse efficiency of a metal compound will deteriorate easily. On the other hand, in the alkali treatment, the sludge is excessively densified by the dehydration condensation reaction while the sludge circulation is repeated. Such excessively densified sludge is difficult to react because the physical contact efficiency with fluorine and / or phosphorus is reduced. As a result, the recycling efficiency of the metal compound may deteriorate.
[0012]
This invention is made | formed in view of the said subject, and it aims at providing the fluorine or phosphorus removal agent or removal method which can remove fluorine and / or phosphorus efficiently from fluorine and / or phosphorus containing water.
[0013]
[Means for Solving the Problems]
The present invention relates to a calcium reaction means for adding a calcium agent to fluorine or phosphorus-containing water and reacting with calcium in a fluorine or phosphorus-containing water treatment apparatus for removing fluorine or phosphorus from fluorine or phosphorus-containing water, and the calcium reaction means. Metal salt addition means for adding a water- soluble metal compound to the treated water containing the reaction product generated by the above, and solid-liquid separation means for separating and removing the fluorine or phosphorus insolubilized product produced by the metal salt addition means as a solid matter And an alkali treatment means for alkali treatment by adding an alkali to a part of the solid separated by the solid-liquid separation means, and an acid treatment for acid treatment by adding an acid to the solid after the alkali treatment And a return means for returning the solid material after the acid treatment to the upstream side of the solid-liquid separation means, That.
[0014]
In the sludge circulation method of the present invention, first, solid or liquid-separated solid is subjected to alkali treatment to release fluorine or phosphorus from the metal compound in the solid. In this way, the metal compound is converted into a hydroxide. Metal compounds converted to hydroxides are easily soluble in acids. By treating the metal compound that is easily dissolved in the acid, the solid can be reliably dissolved even during the acid treatment, and the reuse efficiency of the metal compound can be improved. Moreover, it can prevent that a solid substance densifies by the dehydration condensation reaction by an alkali treatment by acid-treating before return.
[0015]
The water-soluble metal compound is preferably at least one metal compound selected from Al, Fe, Ti, Zr, Hf, V, Nb, Ta, and rare earth metals.
[0016]
Moreover, when adding or adding an acid or alkali to the solid material, it is preferable to add calcium to insolubilize the eluted fluorine and / or phosphorus. Thereby, fluorine or phosphorus liberated from the metal compound by acid or alkali can be insolubilized with the calcium compound. When insolubilized with a calcium compound, solid-liquid separation can be improved.
[0017]
Moreover, it is preferable that the return destination of the solid is a metal salt addition means.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiment, the fluorine-containing wastewater is used as raw water, and the water-soluble metal compound to be added is described using zirconyl chloride as the Zr metal compound. The water-soluble metal compound to be added may be a metal salt compound of Al, Fe, Ti, Hf, V, Nb, Ta, rare earth metal (Ce, La, etc.). Moreover, as a form of a metal compound, nitrates, sulfates, chlorides, chloride oxides, sulfate oxides, and the like can be considered, but are not limited thereto. Preferably, zirconyl chloride, zirconyl sulfate, zirconyl nitrate, titanyl sulfate, titanium tetrachloride, lanthanum chloride, lanthanum sulfate, cerium chloride, cerium sulfate and the like are used.
[0019]
“First Embodiment”
FIG. 1 is a diagram showing a processing apparatus according to the first embodiment of the present invention. Raw water containing fluorine such as hydrofluoric acid is first introduced into a calcium reaction tank 18 where it is mixed with a calcium agent. In addition, it is necessary to maintain pH of this calcium reaction tank 18 at about 4-11, and when it is not in this range, pH is adjusted in this range with an acid or an alkali. The calcium reaction tank 18 is provided with a stirrer and the like, and is rapidly stirred (rotation speed is, for example, 150 rpm), whereby zirconyl chloride and raw water are stirred and mixed. The stirring may be performed by aeration.
[0020]
And in this calcium reaction tank 18, the fluorine in raw | natural water reacts with a calcium ion, and insoluble calcium fluoride is produced | generated. Then, the treated water in the calcium reaction tank 18 containing calcium fluoride is introduced into the metal reaction tank 10 and insolubilized by zirconyl chloride to which fluorine still remaining in the treated water is added. The metal reaction tank 10 is supplied with an aqueous solution of zirconyl chloride and a pH adjuster such as hydrochloric acid or sodium hydroxide (acid for lowering the pH of raw water, alkali for higher). The metal reaction vessel 10 is also rapidly stirred. The reaction shown in the following formula is caused by the metal reaction layer 10,
[Chemical 1]
ZrOCl ₂ + 2F ⁻ → ZrOF ₂ + 2Cl ⁻
Fluorine is insolubilized. Moreover, the pH in the metal reaction tank 10 is adjusted to 4 to 7, more preferably pH 5 to 6 with sodium hydroxide or the like. As a result, the above reaction proceeds promptly.
[0021]
The addition amount of zirconyl chloride added in the metal reaction vessel 10 is preferably added as a reaction equivalent or more as Zr to the raw water fluorine (F). That is, the molar ratio is preferably Zr / F = 1/2 or more. The fluorine concentration of the raw water is preferably applied to raw water of 20 mg / l or less from the economical viewpoint, and the Zr concentration is preferably 200 mg / l or less. The pH of the reaction may be 4 to 7, but more preferably 5.0 to 6.0.
[0022]
The treated water in the metal reaction tank 10 is supplied to the aggregation tank 12. The coagulation tank 12 is supplied with a polymer coagulant, and the inside is slowly stirred (for example, 40 rpm) by a stirrer or the like. The insolubilized fluorine produced in the metal reaction vessel 10 is agglomerated and coarsened. The polymer flocculant may be any of cationic, anionic and nonionic, and those having a good aggregation effect are appropriately employed. Furthermore, instead of the polymer flocculant, an aluminum-based or iron-based inorganic flocculant may be employed, or both may be used in combination.
[0023]
Moreover, it is also suitable to use an inorganic flocculant in combination according to the properties of the water to be treated. The kind of the inorganic flocculant is not particularly limited, and examples thereof include aluminum (PAC, sulfate band) and iron (iron chloride, polyiron sulfate). The addition method may be directly added to the metal reaction tank 10 or an inorganic flocculant reaction tank may be provided separately. When an inorganic flocculant reaction tank is newly provided, it may be either before or after the metal reaction tank 10 (between the polymer flocculant tank 12).
[0024]
The agglomerated water from the agglomeration tank 12 is introduced into the precipitation tank 14 where the solid matter is precipitated and separated. That is, the above-mentioned ZrOF ₂ aggregate is precipitated and separated, and treated water having a low fluorine concentration is obtained as a supernatant. The solid-liquid separation means is not limited to the precipitation tank 14, and various devices such as a membrane separation device can be used. In particular, when a membrane separator is employed, the aggregating treatment with the polymer flocculant can be omitted.
[0025]
Part of the precipitated sludge that has been precipitated and separated in the settling tank 14 is charged into the alkaline reaction tank 16. Although the alkaline agent is not particularly limited, for example, slaked lime (calcium agent) is charged into the alkaline reaction tank 16 to adjust the pH to be alkaline (pH 8 to 11). The alkaline reaction tank 16 is also rapidly stirred by a stirrer or the like. A part of the sludge is an aggregate of ZrOF ₂ . This aggregate is substituted in the alkaline solution by fluorine (F) with a hydroxyl group (OH), thereby liberating fluorine ions. In addition, the metal hydroxide produced | generated in this way is high compared with fluoride. On the other hand, the liberated fluorine ions react with slaked lime and become insoluble as calcium fluoride. Thus, even if alkaline, calcium fluoride is insolubilized, so fluorine forms calcium fluoride with the injected calcium agent. The treatment time in the alkaline reaction tank 16 is 30 minutes to 60 minutes, but it may be longer.
[0026]
Next, the treated sludge treated in the alkaline reaction tank 16 is put into the acid reaction tank 17. Hydrochloric acid or the like is added to the acid reaction tank 17 to adjust the acidity (<pH 3). The acid reaction tank 17 is also rapidly stirred by a stirrer or the like. Since the aggregate of ZrO (OH) ₂ in which fluorine is substituted with a hydroxyl group in the alkaline reaction tank 16 is easily dissolved in an acid, it is easily dissolved in the acid reaction tank 17. The treatment time in the acid reaction tank 17 is 30 to 60 minutes, but it may be longer. Here, a calcium agent such as calcium chloride may be added to insolubilize the liberated fluorine ions. In addition, although hydrochloric acid is suitable as an acid added to the acid reaction tank 17, other acids, such as a sulfuric acid and nitric acid, may be sufficient.
[0027]
As described above, in this embodiment, first, the aggregate of ZrOF ₂ precipitated in the precipitation tank 14 is alkali-treated in the alkali reaction tank 16 to release fluorine to form a metal hydroxide. By doing so, it can be dissolved reliably during the acid treatment, and the reuse efficiency of the metal compound can be improved. Further, by subjecting the alkali-treated aggregated precipitate to acid treatment in the acid reaction tank 17, it is possible to prevent the aggregated precipitate from being excessively densified due to a dehydration condensation reaction only by alkali treatment.
[0028]
“Second Embodiment”
FIG. 2 is a diagram showing the configuration of the second embodiment, and sludge treated in the alkali reaction tank 16 and the acid reaction tank 17 is returned to the metal reaction tank 10. And a calcium agent is also added to this metal reaction tank 10.
[0029]
As a result, fluorine liberated from the metal compound (zirconyl compound) in the alkali reaction tank 16 and the acid reaction tank 17 reacts with the calcium agent added here to generate calcium fluoride.
[0030]
For example, when the sludge is returned to the calcium reaction tank 18 when the pH of the calcium reaction tank 18 is 4 to 7, a part of the zirconyl compound that has become fluorine-free in the alkali reaction tank 16 and the acid reaction tank 17 is part of the calcium reaction tank 18. It reacts with the fluorine in the influent water and becomes a competitive reaction with the calcium agent, which may consume a part of the zirconyl compound. By making the sludge return into the metal reaction tank 10, such a competitive reaction can be avoided and the amount of zirconyl chloride added can be further reduced. At this time, the calcium agent is preferably added to both the sludge reaction tank 16 and the calcium reaction tank 18, and is preferably injected separately into the metal reaction tank 10.
[0031]
"Other"
Further, in the above description, only the treatment of fluorine-containing water is targeted. However, in this embodiment, the same insolubilization reaction as that of fluorine occurs with respect to phosphorus. Therefore, the above treatment can be applied to phosphorus-containing water as it is. In addition, since phosphorus can be removed as calcium phosphate, treatment with a calcium agent can be applied to phosphorus-containing water as it is. Phosphorus is insolubilized by the following reaction. In addition, the form of phosphorus changes with pH etc.
[0032]
[Chemical formula 2]
ZrOCl ₂ + 2H ₂ PO ₄ ⁻ → ZrO (H ₂ PO ₄ ) ₂ + 2Cl ⁻
ZrOCl ₂ + HPO ₄ ²⁻ → ZrOHPO ₄ + 2Cl ⁻
【Example】
A processing experiment was performed using the processing apparatus (Example) of the first embodiment shown in FIG. 1 and the processing apparatus 1 (Comparative Example 1) and the processing apparatus 2 (Comparative Example 2) shown in FIGS. . 3 and 4 are treatment apparatuses that do not have the alkali reaction tank 16 or the acid reaction tank 17. The process is the same as the apparatus of the first embodiment shown in FIG. 1 except that only one of the alkali reaction tank 16 or the acid reaction tank 17 is provided.
[0033]
Items common to these processes are as follows.
[0034]
Raw water flow rate: 100 L / h, calcium reaction tank 18, metal reaction tank 10 and coagulation tank 12 capacity: 30L, alkali reaction tank 16, acid reaction tank 17: 8L, precipitation tank 14 capacity: about 100L. In addition, raw water: synthetic waste water was prepared by dissolving sodium fluoride in pure water to a concentration of 100 mg / L. The pH was 6.5-7.0. Insolubilizer: Zirconyl chloride octahydrate (ZrOCl ₂ .8H ₂ O) dissolved in pure water so as to be 10% as Zr was used. Calcium agent: 10% slaked lime slurry or 35% calcium chloride solution was used. pH adjuster: The pH of each reactor was adjusted with hydrochloric acid or 10% sodium hydroxide solution. Calcium reaction tank 18: 500 mg / L of Ca was added by slaked lime slurry, and the pH was adjusted to 10 with hydrochloric acid. Metal reaction vessel 10: An insolubilizing agent was added as Zr to 15 mg / L, and the pH was adjusted to 5 with hydrochloric acid. Coagulation tank 12: Polymer flocculant Olflock OA-23 was added to 2 mg / L. The sedimentation sludge in the sedimentation tank 14 was extracted as needed. Part of the sedimentation tank sludge (flow rate of 5% based on the raw water) was returned to the calcium reaction tank 18 or the metal reaction tank 10 through at least one of the alkaline reaction tank 16 and the acid reaction tank 17 through the circulation line. This treatment step was continued for one week and for another month, and the amount of total contained fluorine and SS in the treated water was measured. The total fluorine content in the treated water indicates the total fluorine concentration in the treated water including the fluorine contained in the SS in the treated water.
[0035]
"Comparative Example 1"
The experiment was performed according to the following equation according to the flow shown in FIG. A part of the sludge was alkali-treated only in the alkali reaction tank 16 to release fluorine, and then returned to the calcium reaction tank 18. That is, the alkaline reaction tank 16 was provided and adjusted to pH 10 by adding slaked lime. The treated water after treatment for about 1 week was 4.5 mg / L of total fluorine and 3 mg / L of SS. As it is, the treated water after one month treatment is 5.3 mg / L of total fluorine and SS is 3 mg / L, and although the amount of SS is the same as after one week, the amount of total fluorine is It was increasing.
[0036]
"Comparative Example 2"
The experiment was performed according to the following equation according to the flow shown in FIG. A part of the sludge was acid-treated only in the acid reaction tank 17 to release fluorine, and then returned to the calcium reaction tank 18. That is, an acid reaction tank 17 was provided and adjusted to pH 2.5 by adding hydrochloric acid. The treated water after the treatment for about 1 week was 6.2 mg / L of total fluorine and 3 mg / L of SS. The treated water after one month treatment was 6.2 mg / L of total fluorine and 3 mg / L of SS, and both the amount of fluorine contained and the amount of SS were not changed compared to one week later.
[0037]
"Example"
The experiment was performed according to the following equation according to the flow shown in FIG. A portion of the sludge is alkali-treated in an alkali reaction tank 16 (pH 10), alkali-treated, then acid-treated in an acid reaction tank 17 (pH 2.5) to liberate fluorine, and then returned to the calcium reaction tank 18 did. The treated water after the treatment for about one week was 3.2 mg / L of total fluorine and 3 mg / L of SS. The treated water after one month treatment was 3.2 mg / L of total fluorine and 3 mg / L of SS, and both the amount of fluorine contained and the amount of SS did not change compared to one week later.
[0038]
"Evaluation"
Comparative Example 1:
In Comparative Example 1, the total fluorine content after one month was increased as compared with the total fluorine content after one week, but by repeating the alkali treatment many times, the dehydration condensation reaction of sludge proceeds, This is thought to be due to the increased density of sludge. It is considered that the concentration of fluorine dissolved in the treated water increased because the physical contact between fluorine and the zirconyl compound decreased due to the densification of the sludge and the recycling efficiency of the zirconyl compound deteriorated. This is because the amount of SS has not increased.
[0039]
Comparative Example 2:
In Comparative Example 2, the total fluorine content after one month did not change compared with the total fluorine content after one week. This is thought to be because sludge densification hardly occurs. Moreover, the density | concentration of all the containing fluorine is large compared with the comparative example 1 (alkali treatment). This is thought to be because sludge could only be dissolved incompletely by acid treatment, and the recycle efficiency of the zirconyl compound was poor and fluorine dissolved in the treated water could not be removed. This is because the amount of SS is the same as in Comparative Example 1.
[0040]
Example:
In the examples, the amount of total fluorine contained was smaller than in Comparative Examples 1 and 2. This is considered to be because the zirconyl compound can be efficiently regenerated by the combined use of alkali treatment and acid treatment, and the contained fluorine can be further insolubilized by the zirconyl compound. Furthermore, the amount of total fluorine contained did not change after one week or one month. This is thought to be because the recycling efficiency of the zirconyl compound was maintained over a long period of time as a result of preventing the sludge from being excessively densified by acid treatment after alkali treatment.
[0041]
【The invention's effect】
As described above, according to the present invention, the addition of the water-soluble metal compound insolubilizes fluorine or phosphorus to form a solid. A part of the separated solid is acid-treated after alkali treatment and mixed with fluorine and / or phosphorus-containing water upstream of the solid-liquid separation means. By doing so, fluorine or phosphorus can be removed with high efficiency over a long period of time, and the efficiency can be maintained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an apparatus according to a first embodiment.
FIG. 2 is a diagram illustrating a configuration of an apparatus according to a second embodiment.
FIG. 3 is a diagram showing a configuration of a conventional apparatus (alkali treatment).
FIG. 4 is a diagram showing a configuration of a conventional apparatus (acid treatment).
(Explanation of symbols)
10 Metal reaction tank, 12 Coagulation tank, 14 Precipitation tank, 16 Alkaline reaction tank, 17 Acid reaction tank, 18 Calcium reaction tank.

Claims (4)

In a fluorine or phosphorus-containing water treatment apparatus that removes fluorine or phosphorus from fluorine or phosphorus-containing water,
A calcium reaction means for adding a calcium agent to fluorine- or phosphorus-containing water and reacting with calcium;
A metal salt addition means for adding a water- soluble metal compound to the treated water containing the reactant produced by the calcium reaction means ;
A solid-liquid separation means for separating and removing the insoluble matter of fluorine or phosphorus produced by the metal salt addition means as a solid,
Alkaline treatment means for adding alkali to alkali treatment for a part of the solid separated by the solid-liquid separation means,
An acid treatment means for adding an acid to the solid after the alkali treatment to perform acid treatment;
A return means for returning the solid after the acid treatment to the upstream side of the solid-liquid separation means;
A fluorine or phosphorus-containing water treatment device having The apparatus of claim 1.
The water-soluble metal compound is a fluorine or phosphorus-containing water treatment apparatus in which the water-soluble metal compound is at least one of Al, Fe, Ti, Zr, Hf, V, Nb, Ta, and a rare earth metal. The apparatus according to claim 1 or 2,
A fluorine or phosphorus-containing water treatment apparatus for adding a calcium compound to insolubilize eluted fluorine or phosphorus when an acid or an alkali is added to the solid matter or after the addition. The device according to any one of claims 1 to 3,
The return means is a fluorine or phosphorus-containing water treatment device for returning a part of solid matter to the metal salt addition means.

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