JP5794422B2 - Treatment method and treatment apparatus for removing fluorine and harmful substances - Google Patents

Description

In the present invention, fluorine is discharged from wastewater with high fluorine concentration to a level below the drainage standard [8 mg / L (public water areas other than sea areas), 15 mg / L (sea area)] or environmental standards (0.8 mg / L or less) in a short time. The present invention relates to a processing method and a processing apparatus that can be removed at low cost. More particularly, the present invention relates to a treatment method and a treatment apparatus that can remove fluorine at a low cost to a wastewater standard value or lower or an environmental standard value, and can simultaneously remove harmful substances such as heavy metals.

For example, Japanese Patent Application Laid-Open No. 2003-285076 (Patent Document 1) discloses that a layered double hydroxide is generated by adding a divalent metal ion and a trivalent metal ion to a wastewater containing fluorine to form the layered double hydroxide. A treatment method for incorporating fluorine between the two layers is described.

In International Publication WO2005-087664 (Patent Document 2), an acidic solution containing aluminum ions and magnesium ions and an alkaline solution containing alkali are mixed, and after mixing of the acidic solution and the alkaline solution is completed, no time is left. By immediately removing or neutralizing water, the general formula: Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O (A ⁿ⁻ is an anion) The hydrotalcite-like substance is formed, and a treatment method is described in which fluorine or the like is taken into the substance and fixed.

JP 2003-285076 A International Publication WO2005-087664

The conventional treatment method described above is a method of removing fluorine by producing a layered double hydroxide such as hydrotalcite, but has a problem that the treatment time is prolonged due to poor sedimentation of the produced sludge. Further, the treatment method of Patent Document 2 is troublesome to adjust the treatment conditions from the addition of chemicals to dehydration / neutralization, and when the fluorine concentration is high, the burden of chemical costs is greatly increased and sludge is generated. There is a problem that the amount increases.

The present invention solves the above-mentioned problems in the conventional treatment method, is excellent in the adsorption effect on fluorine and the sedimentation property of the generated sludge, and is easy to treat sludge and has a high fluorine concentration. Provided is a treatment method capable of reducing fluorine to a wastewater standard value or lower or an environmental standard value at a low cost and simultaneously removing harmful substances such as heavy metals.

The present invention relates to a processing method having the following configuration.
[1] A primary treatment step in which calcium salt is added to raw water containing fluorine to form a calcium fluoride precipitate at pH 4 to 9, and the precipitate is solid-liquid separated to remove fluorine , treated water after this primary treatment (Primary treated water), a hardly soluble metal oxide and a soluble metal compound are added to adjust the pH to 7 to 11, and the surface of the hardly soluble metal oxide is dissolved and the others are undissolved parts. The sludge in which layered double hydroxide is formed on the surface of the undissolved part of the hardly soluble metal oxide is generated by the reaction between the product and the soluble metal compound, and residual fluorine and harmful substances are taken into the layered double hydroxide. , processing method for removing fluorine and harmful substances and having a secondary treatment process for solid-liquid separation by settling the sludge.
[2] The hardly soluble metal oxide is magnesium oxide, the soluble metal compound is a soluble aluminum salt, and magnesium oxide and a soluble aluminum salt are added to the treated water after the primary treatment and reacted under alkaline conditions. The hydrotalcite is formed on the surface of the liquid, and sludge in which fluorine and harmful substances are taken into the hydrotalcite is generated, and the sludge is solid-liquid separated to remove fluorine and harmful substances. Treatment method to remove fluorine and harmful substances.
[3] For raw water having a fluorine concentration of 30 mg / L or more, the primary treatment reduces the fluorine concentration to 10 to 20 mg / L and the secondary treatment reduces the fluorine concentration to 8 mg / L or less [1] or [2 The processing method which removes the fluorine and harmful substance described in].
[4] For raw water with a fluorine concentration of 30 mg / L or more, the primary treatment reduces the fluorine concentration to 10-20 mg / L and the secondary treatment reduces the fluorine concentration to 0.8 mg / L or less [1] or above The processing method for removing fluorine and harmful substances according to [2].
[5] The treatment method for removing fluorine and harmful substances according to any one of [1] to [4] above, wherein the sludge slurry produced in the secondary treatment has a stable volume after standing for 30 minutes of 40% or less .
[6] The processing method for removing fluorine and harmful substances according to any one of [1] to [5] above, wherein fluorine is recovered from a calcium fluoride precipitate separated in solid and liquid in the primary treatment.
[7] Part or all of the sludge separated and solid-liquid separated in the secondary treatment is returned to the reaction step of the secondary treatment, and the returned sludge is used for forming the layered double hydroxide. ] The processing method which removes the fluorine and harmful substance described in any one of.
[8] The treatment method for removing fluorine and harmful substances according to any one of [1] to [7] above, wherein surplus sludge not returned to the reaction step is used as a cement raw material, a purification material, or a primary treatment pH adjuster. .

Moreover, this invention relates to the processing apparatus which removes the fluorine which consists of the following structures.
[9] Reaction tank A in which calcium fluoride is added to raw water containing fluorine to adjust the pH to 4 to 9, and calcium fluoride is precipitated, separation tank B for solid-liquid separation of the precipitate, primary treated water extracted from separation tank B Addition tank C for adding a soluble metal compound to the water, adding a hardly soluble metal oxide to primary treated water to which a soluble metal compound has been added to adjust the pH to 7-11, and dissolving the surface of the hardly soluble metal oxide while others are undissolved parts And forming a sludge in which a layered double hydroxide is formed on the surface of the undissolved portion of the hardly soluble metal oxide by a reaction between the dissolved poorly soluble metal oxide and the soluble metal compound to form the layered double hydroxide. reactor D to incorporate residual fluorine and hazardous substances, means E for supplying a pH adjusting agent to the reaction vessel D, it means F for supplying coagulant withdrawn slurry from the reaction tank D, a slurry prepared by adding an aggregating agent Processing apparatus for removing fluorine and harmful substances, characterized in that it comprises a separation vessel G for liquid separation.
[10] The second addition tank H is provided in the pipeline for returning the sludge from the separation tank G to the reaction tank D, and the poorly soluble metal oxide is added to the sludge in the second addition tank H. The processing apparatus for removing fluorine and harmful substances according to [9] above , wherein the sludge to which the product is added is supplied to the reaction tank D.

Since the treatment system (treatment method and treatment apparatus) of the present invention generates a calcium fluoride precipitate in the primary treatment step and separates the precipitate out of the system, even in raw water with a high fluorine concentration, the fluorine concentration in the primary treatment step is reduced. In the secondary treatment, the fluorine concentration can be easily reduced below the drainage standard. Furthermore, by returning the separated sludge to the reaction step, the effect of removing fluorine can be enhanced, and the fluorine concentration in the waste water can be easily reduced to the environmental standard.

As the calcium salt used in the primary treatment, an inexpensive material such as slaked lime, calcium carbonate, calcium chloride, calcium oxide, and carbide can be used, so that the fluorine concentration can be reduced at a low cost.

Moreover, the sludge produced | generated by a secondary treatment process is excellent in sedimentation property, for example, the stable volume after standing for 30 minutes is 40% or less, and settles in a short time, Therefore Solid-liquid separation is carried out in a short time The solid-liquid separation tank can be downsized.

Furthermore, since the sludge in the secondary treatment process takes in harmful substances at the same time as fluorine, it can remove harmful substances together with fluorine, for example, take in and remove harmful substances such as heavy metals, boron, nitrogen compounds, and phosphorus. Can do.

Process drawing showing the processing method of the present invention Process drawing provided with the second addition tank in the treatment method of the present invention Process drawing using surplus sludge from secondary treatment for primary treatment in the treatment method of the present invention SEM photograph of sludge generated in the secondary treatment process of the present invention Component analysis diagram inside the sludge of Fig. 3 (Fig. 4a) Fig. 3 Component analysis diagram near the sludge surface (Fig. 4 b) A photograph showing the state after standing for 30 minutes for the sludge of FIG. 4 and the sludge of the conventional treatment method XRD analysis chart of sludge generated in the secondary treatment process of the present invention

Hereinafter, the present invention will be specifically described based on embodiments.
The treatment method of the present invention comprises a primary treatment step in which calcium salt is added to raw water containing fluorine , adjusted to pH 4 to 9 to produce a calcium fluoride precipitate, and the precipitate is solid-liquid separated to remove fluorine. To the treated water after the primary treatment (primary treated water), a hardly soluble metal oxide and a soluble metal compound are added to adjust the pH to 7 to 11, the surface of the hardly soluble metal oxide is dissolved, and the others are undissolved parts. Sludge in which a layered double hydroxide is formed on the surface of the undissolved portion of the hardly soluble metal oxide by the reaction between the hardly soluble metal oxide and the soluble metal compound is generated, and residual fluorine is left in the layered double hydroxide. And a treatment method for removing fluorine and harmful substances, characterized by having a secondary treatment step of taking in harmful substances and allowing the sludge to settle and solid-liquid separation. 1, 2, and 3 show the processing steps of the present invention.

The treatment method of the present invention can be widely applied to various types of wastewater and wastewater generated naturally and artificially and containing fluorine (referred to as raw water containing fluorine). For example, industrial effluent and sewage, seawater, river water, lake and pond water, surface pool water, river dam water, underground running water and pool water, culvert water, etc. with high fluorine concentration Can be applied to things. Furthermore, wastewater with high salt concentration, such as purified wastewater from soil contaminated with harmful substances, seawater and leachate from the final disposal site, is converted into clear water (fresh water) and concentrated water using reverse osmosis membranes and electrodialysis. Concentrated water after separation (desalting treatment) can also be applied to those having a high fluorine concentration.

In the treatment method of the present invention, harmful substances are substances other than fluorine, for example, heavy metals, boron, nitrogen, phosphorus and the like. Heavy metals include cadmium, lead, copper, zinc, iron, nickel, selenium, hexavalent chromium, arsenic, manganese, and antimony. Further, harmful substances include halide ions, various halogen acids (such as halogen acids, perhalogen acids, halous acids, hypohalous acids), hexafluorophosphate ions (PF ₆ ⁻ ), borofluoride ions (BF ₄ ^-), silicofluoride fluoride ions (SiF ₆ ^2-), organic acids, and the like suspended solids (SS) and organic. According to the treatment system of the present invention, raw water containing harmful substances other than fluorine together with fluorine has an excellent removal effect.

[Primary treatment process]
A calcium salt is added to raw water containing fluorine to form a calcium fluoride precipitate, and the precipitate is separated into solid and liquid. As the calcium salt, inexpensive materials such as slaked lime, calcium carbonate, calcium chloride, calcium oxide, and carbide can be used. What is necessary is just to determine the addition amount of a calcium salt according to the fluorine concentration of raw | natural water.

In the processing flow of FIG. 1 and FIG. 2, raw water is supplied to the reaction tank A, the calcium salt is added while stirring the raw water, the pH is adjusted, and the reaction is performed for several minutes to cause calcium fluoride precipitation (CaF ₂ precipitation). Generate. Next, a flocculant is added and gently stirred to form a floc of precipitate, introduced into the separation tank B in a state containing the floc, and solid-liquid separated to take out the CaF ₂ precipitate out of the system.

The reaction tank A is adjusted to pH 4-9, preferably pH 5.5-7. As a pH adjuster, an acid such as sulfuric acid, hydrochloric acid or nitric acid, or an alkali such as slaked lime, quicklime or sodium hydroxide can be used. Moreover, you may utilize the excess sludge extracted from the separation tank G of a secondary process (refer FIG. 3). Sedimentation may be promoted by adding an inorganic flocculant (aluminum sulfate, polyaluminum chloride, ferric chloride, etc.) or a polymer flocculant to the resulting slurry.

According to this primary treatment, the fluorine concentration after the primary treatment can be reduced to 10 to 20 mg / L for raw water having a high fluorine concentration (for example, a fluorine concentration of 30 mg / L or more). The separated precipitate is mainly CaF ₂ and can be disposed of after dehydration. Those having a CaF ₂ purity of 85 wt% or more can be reused as a substitute for fluorite. In addition, harmful substances other than fluorine may be reduced by the primary treatment by generating a hydroxide precipitate by adjusting the pH and separating the precipitate.

[Secondary treatment process]
Sludge having a layered double hydroxide formed on the surface of the hardly soluble metal oxide by adding a hardly soluble metal oxide and a soluble metal compound to the treated water after the primary treatment and reacting under alkaline conditions. The sludge is allowed to settle and solid-liquid separation is performed.

In the processing flow of FIGS. 1, 2, and 3, the primary treated water is introduced into the addition tank C, and a soluble metal compound is added thereto, and then introduced into the reaction tank D. A hardly soluble metal oxide is added to the reaction vessel D. As shown in the flow of FIG. 2, the hardly soluble metal oxide may be added to the returned sludge, and this sludge may be supplied to the reaction tank D. Note that a hardly soluble metal oxide and a soluble metal compound may be added to the addition tank C or the reaction tank D. Moreover, when a soluble metal compound is added to the addition tank C, it may not completely dissolve. In that case, a pH adjusting agent may be added to completely dissolve the soluble metal compound, or it may be introduced into the reaction vessel D as it is. Moreover, you may add a pH adjuster to the reaction tank D as needed.

The hardly soluble metal oxide partially dissolves on its surface and becomes a component source of the layered double hydroxide, and most of it remains as an undissolved part, and the dissolved hardly soluble metal oxide reacts with the soluble metal compound. A layered double hydroxide is formed on the surface of the hardly soluble metal oxide. Further, the dissolved hardly soluble metal oxide serves as a component source of the layered double hydroxide and serves as an alkali agent.

Examples of the hardly soluble metal oxide include magnesium oxide and calcium oxide. In addition, magnesium oxide is preferable for forming the hydrotalcite of the layered double hydroxide. This magnesium oxide may be one containing magnesium oxide as a part of the component, such as a baked product of dolomite [CaMg (CO ₃ ) ₂ ], or one containing magnesium oxide together with other components, not limited to Ca. it can.

A soluble aluminum salt, a soluble iron salt, etc. can be used as a soluble metal compound. Among these, a soluble aluminum salt is preferable for forming hydrotalcite. Specifically, polyaluminum chloride, aluminum sulfate (sulfuric acid band), aluminum chloride, aluminum nitrate and the like are preferable. In addition, as a soluble aluminum salt, a waste liquid containing a high concentration of aluminum (a recovery waste liquid of a noble metal catalyst, a liquid in which metal aluminum is dissolved, or the like) can be used.

The amount of the soluble aluminum salt added is suitably such that the aluminum concentration in the water is 10 to 1000 mg / L with respect to 1 L of the primary treated water with a fluorine concentration of 1 to 50 mg / L. The amount of magnesium oxide added is suitably 0.05 to 10 g / L with respect to 1 L of primary treated water with a fluorine concentration of 1 to 50 mg / L.

For example, when magnesium oxide is used as the hardly soluble metal oxide, soluble aluminum salt is used as the soluble metal compound, and these are added to the primary treated water and reacted under alkaline conditions (preferably pH 7 to 11), the magnesium oxide is dissolved. Since it is difficult, most remains as an undissolved portion, but the surface is partially dissolved, and the eluted magnesium reacts with aluminum to form a layered double hydroxide on the surface of magnesium oxide. Specifically, magnesium and aluminum react with the magnesium oxide surface to form hydrotalcite [general formula: Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O ( ^An- is an anion)].

The sludge in this state is shown in FIG. FIG. 5 shows an EDX analysis chart inside the sludge (A) in FIG. As shown in the figure, the magnesium component is overwhelmingly large and indicates magnesium oxide. On the other hand, FIG. 6 shows an EDX analysis chart in the vicinity (b) of the sludge surface in FIG. As shown in the figure, the peaks of magnesium and aluminum are detected, and it can be seen that hydrotalcite is formed.

The layered double hydroxide has a layered structure containing water molecules between layers, and has the property of taking in anions between layers in order to maintain electrical neutrality. The fluorine remaining in the primary treated water is Captured between layers. In addition to fluorine, anions such as organic acid, oxyanionic boron, nitrogen, phosphorus, selenium, hexavalent chromium, arsenic, and antimony are also taken in between the layers. Furthermore, cadmium, lead, copper, zinc, a part of divalent metals (such as magnesium) and trivalent metals (such as aluminum) forming the layered double hydroxide are replaced with cationic heavy metals. Harmful heavy metals such as iron, nickel and manganese are taken in. The suspended matter (SS) is aggregated and taken in with the sludge containing the layered double hydroxide, and the organic matter is adsorbed and taken in the surface of the sludge containing the layered double hydroxide. In this way, fluorine and harmful substances are taken into the layered double hydroxide, and sludge containing the layered double hydroxide settles, and the solid and liquid can separate the fluorine and harmful substances at the same time.

A pH adjuster can be added to the reaction vessel D as necessary. As the pH adjuster, an alkali such as sodium hydroxide, calcium hydroxide or calcium oxide, or an acid such as sulfuric acid or hydrochloric acid can be used. The reaction tank D may be adjusted to pH 7-11. The pH may be adjusted before the reaction, during the reaction, or after the reaction, but preferably during or after the reaction in order to promote the formation of the layered double hydroxide.

The slurry containing the generated sludge is guided to the separation tank G to be settled and solid-liquid separated. The sludge produced by the treatment method of the present invention has a structure in which a layered double hydroxide is formed on the surface of an undissolved hardly soluble metal oxide (magnesium oxide or the like), and thus has good sedimentation.

For example, as shown in FIG. 7, when the sludge slurry produced by the treatment method of the present invention is placed in a graduated cylinder and allowed to stand for 30 minutes, the sludge slurry volume at the start of standing is 2300 mL. The volume of the later sludge slurry portion is about 550 mL, and the stable volume is 40% or less, preferably 25% or less in a short time. Here, the stable volume is an index calculated by the following equation [1]. A smaller stable volume indicates that sludge can be solid-liquid separated in a short time.
(Sludge slurry volume after a certain period of time) / (initial sludge slurry volume) × 100 ... [1]

On the other hand, instead of sparingly soluble magnesium oxide, a soluble magnesium salt (magnesium chloride, etc.) is used, and this is added to toxic substance-containing water together with a soluble aluminum salt, and further sodium hydroxide is added to adjust to alkalinity. When the sludge slurry generated by the treatment method is placed in a graduated cylinder and allowed to stand for 30 minutes, as shown in FIG. 7, for example, the initial sludge slurry volume at the start of standing is 2300 mL. The sludge slurry volume after standing is about 2200 mL, and hardly settles in about 30 minutes.

Since the treatment method of the present invention can solid-liquid separate sludge in a short time, the separation tank G can be downsized. If a flocculant is added before the sludge slurry is introduced into the separation tank G, solid-liquid separation can be performed in a shorter time. As the flocculant, inorganic flocculants and anionic, cationic, nonionic and amphoteric polymer flocculants can be used.

In the treatment method of the present invention, preferably, part or all of the solid-liquid separated sludge is returned to the reaction tank D, and the returned sludge is used for the formation of the layered double hydroxide. By returning part or all of the sludge to the reaction process, the formation of layered double hydroxides is promoted, and fluorine and heavy metals, as well as toxic substances such as boron, nitrogen compounds, phosphorus, etc., are often incorporated into the sludge. Thus, these removal effects are improved.

In addition, about the sludge isolate | separated into solid and liquid, it is good to return the sludge concentrated to the thing with much amount of a hardly soluble metal oxide using the difference in a weight, specific gravity, or sedimentation speed to a reaction process. For example, since sludge with a large amount of hardly soluble metal oxides is heavier than other sludges and settles quickly, it is possible to collect sludge at the initial stage of sedimentation and concentrate it to sludge with a large amount of hardly soluble metal oxides. By returning the sludge having a large amount of the hardly soluble metal oxide to the reaction step, the generation of the layered double hydroxide can be promoted. For example, when magnesium oxide is used as the hardly soluble metal oxide, the formation of hydrotalcite can be promoted by concentrating sludge having a large amount of magnesium oxide and returning it to the reaction step.

On the other hand, surplus sludge that is not returned to the reaction process can be recovered and recycled as a cement raw material. Moreover, surplus sludge can be utilized as a purification material for soil contamination or wastewater treatment. Or surplus sludge can be introduce | transduced into the reaction tank A as a pH adjuster of a primary process. FIG. 3 shows a process diagram in which surplus sludge from the secondary treatment is used for the primary treatment.

The processing method of this invention can provide the process of post-processing the liquid component (secondary process water) which isolate | separated sludge. Since organic substances, suspended solids, and nitrogen compounds may remain in the secondary treated water, or the pH of the treated water may be 9 or higher, the secondary treated water may be post-treated.

Organic substances contained in the secondary treated water can be removed by a biological treatment method (such as an activated sludge method) or an accelerated oxidation method (such as an ultraviolet oxidation or a photocatalyst). The suspended substance (SS) may be precipitated and separated by adding an inorganic flocculant or a polymer flocculant. Nitrogen compounds can be reduced by biological treatment (such as nitrification and denitrification). If the pH is high, neutralization may be performed by adding sulfuric acid or hydrochloric acid.

[Processing equipment]
The processing apparatus (processing system) of this invention is shown in FIG.1, FIG2 and FIG.3.
In the treatment apparatus shown in FIG. 1, a reaction tank A in which calcium fluoride is added to raw water containing fluorine to precipitate calcium fluoride, a separation tank B for solid-liquid separation of the precipitate, and a primary treatment extracted from the separation tank B. Addition tank C for adding soluble metal compounds to water, reaction tank D for reacting by adding a hardly soluble metal oxide to primary treated water to which soluble metal compounds have been added, and generating sludge incorporating fluorine and heavy metals, reaction A means E for supplying a pH adjusting agent to the tank D, a means F for supplying a flocculant to the slurry extracted from the reaction tank D, and a separation tank G for solid-liquid separation of the slurry added with the flocculant are installed.

The reaction tank A, the separation tank B, the addition tank C, the reaction tank D, and the separation tank G are connected by a pipe 50, and the secondary treated water is drained outside the system through the pipe 51. The sludge in the separation tank G is extracted through the pipe line 52, and part or all of the sludge is returned to the reaction tank D through the pipe line 53.

In the processing apparatus shown in FIG. 2, a second addition tank H is provided in the pipe line 53. The return sludge is introduced into the second addition tank H, the hardly soluble metal oxide is added thereto, and the sludge to which the hardly soluble metal oxide is added is supplied to the reaction tank D.

The processing apparatus shown in FIG. 3 is provided with a return pipeline 54 that supplies surplus sludge from the secondary treatment to the reaction tank A as a pH adjuster for the primary treatment.

The reaction tank D has a concern that absorption of carbon dioxide may affect the uptake of harmful substances. Therefore, a structure that hardly absorbs carbon dioxide is preferable, and a closed reaction tank is preferable. You may abbreviate | omit the addition tank C and add a soluble metal compound to raw | natural water within a pipe line.

The said processing apparatus can be used as the portable apparatus which made it possible to mount in-vehicle or made separation into units, such as an addition tank, a reaction tank, and a solid-liquid separation tank, for example.

Examples of the present invention are shown below together with comparative examples. The fluorine concentration was measured by an ion electrode method. The concentrations of Cr, iron and Ni were measured by ICP emission spectroscopy.

[Example 1]
<Primary treatment process>
According to the treatment process shown in FIG. 2, the fluorine-containing water was treated as follows. First, fluorine-containing water (fluorine concentration 80 mg / L, pH 2.9) was supplied to the reaction tank A, and calcium hydroxide was added while stirring to adjust the pH to 7.0. After reacting for 30 minutes, 2 mg / L of anionic polymer flocculant was added and gently stirred to form a floc of precipitate. This was introduced into separation tank B and separated by settling. At this time, the fluorine concentration of the primary treated water was 20 mg / L.

<Secondary treatment process>
Primary treated water was introduced into the addition tank C, and polyaluminum chloride was added to the reaction tank D after the aluminum concentration was added to 200 mg / L. On the other hand, the entire amount of sludge extracted from the separation tank G was introduced into the second addition tank H, where 0.9 mg / L of magnesium oxide was added. This sludge was added to reaction tank D and mixed with primary treated water to which polyaluminum chloride was added, stirred for 30 minutes, and reacted at a temperature of 20 ° C. for 30 minutes. After the reaction, sodium hydroxide was added as a pH adjuster to adjust the pH to 8.5 to 9.5, and then the generated sludge was placed in the separation tank G and allowed to stand for 20 hours to settle the sludge. Before being introduced into the separation tank G, 2 mg / L of an anionic polymer flocculant was added. The settled sludge was extracted from the separation tank G, the entire amount of sludge was introduced into the second addition tank H, magnesium oxide was added and returned to the reaction layer D, and the generation of sludge was repeated 17 times.
The results are shown in Tables 1 and 2. Further, an X-ray analysis chart of sludge is shown in FIG. In FIG. 8, 1st to 10th is the number of repetitions.

As shown in Tables 1 and 2, the primary treatment reduced the fluorine concentration of raw water from 80 mg / L to 20 mg / L, and in the secondary treatment, 6.7 mg / L below the wastewater standard value in the first treatment. The fluorine concentration decreases as the number of treatments is repeated. Furthermore, when the number of repetitions is increased, the fluorine concentration is reduced to 0.6 mg / L and can be processed to the environmental standard value. Iron, Cr, and Ni contained in the raw water are also removed.

Moreover, as shown in the X-ray analysis chart of sludge, the peak of hydrotalcite appears with magnesium oxide, and it turns out that the hydrotalcite is formed on the magnesium oxide surface. When the number of repetitions is 1, the hydrotalcite peak is small, but when the number of repetitions is 5 or more, the hydrotalcite peak increases and grows in proportion to the number of repetitions.

A-reaction tank, B-separation tank, C-addition tank, D-reaction tank, G-separation tank, H-second addition tank, 50-pipe, 51, 52-discharge pipe, 53-return pipe , 54-return line.

Claims (10)

Calcium salt is added to the raw water containing fluorine, pH is adjusted to 4-9 to produce a calcium fluoride precipitate, the precipitate is solid-liquid separated to remove fluorine, and the treated water after this primary treatment (primary treatment) Water) is added with a hardly soluble metal oxide and a soluble metal compound to adjust the pH to 7 to 11, so that the surface of the hardly soluble metal oxide is dissolved and the others are undissolved parts. A sludge having a layered double hydroxide formed on the surface of the undissolved part of the hardly soluble metal oxide by reaction with a metal compound is generated, and residual fluorine and harmful substances are taken into the layered double hydroxide. A treatment method for removing fluorine and harmful substances, comprising a secondary treatment step of causing solids and liquids to settle.
The hardly soluble metal oxide is magnesium oxide, the soluble metal compound is a soluble aluminum salt, and magnesium oxide and a soluble aluminum salt are added to the treated water after the primary treatment and reacted under alkalinity on the surface of the magnesium oxide. The fluorine and harmful substances according to claim 1, wherein hydrotalcite is formed, sludge in which fluorine and harmful substances are taken into hydrotalcite is generated, and the sludge is solid-liquid separated to remove fluorine and harmful substances. Treatment method to remove material. Fluorine according to claim 1 or 2, wherein the raw water having a fluorine concentration of 30 mg / L or more is reduced to 10 to 20 mg / L by primary treatment and reduced to 8 mg / L or less by secondary treatment. And processing methods to remove harmful substances. The raw water having a fluorine concentration of 30 mg / L or more is reduced to 10 to 20 mg / L by primary treatment, and the fluorine concentration is reduced to 0.8 mg / L or less by secondary treatment. Treatment method to remove fluorine and harmful substances. The treatment method for removing fluorine and harmful substances according to any one of claims 1 to 4, wherein a stable volume of the sludge slurry produced in the secondary treatment after standing for 30 minutes is 40% or less. 6. The treatment method for removing fluorine and harmful substances according to any one of claims 1 to 5, wherein fluorine is recovered from a calcium fluoride precipitate that has been solid-liquid separated in a primary treatment. A part or all of the sludge separated and solid-liquid separated in the secondary treatment is returned to the reaction step of the secondary treatment, and the returned sludge is used for the formation of the layered double hydroxide. Treatment method to remove fluorine and harmful substances to be described. The treatment method for removing fluorine and harmful substances according to any one of claims 1 to 7, wherein surplus sludge not returned to the reaction step is used as a cement raw material, a purification material, or a pH adjuster for primary treatment. A reaction tank A in which calcium fluoride is added to raw water containing fluorine to adjust the pH to 4-9 to precipitate calcium fluoride, a separation tank B in which the precipitate is separated into solid and liquid, a soluble metal in the primary treated water extracted from the separation tank B Addition tank C to which the compound is added, the hardly treated metal oxide is added to the primary treated water to which the soluble metal compound has been added to adjust the pH to 7 to 11, the surface of the hardly soluble metal oxide is dissolved, and the other is dissolved as an undissolved part By reacting the hardly soluble metal oxide with the soluble metal compound, sludge having a layered double hydroxide formed on the surface of the undissolved portion of the hardly soluble metal oxide is generated, and residual fluorine and reactor D to incorporate toxic substances, means E for supplying a pH adjusting agent to the reaction vessel D, means F for supplying coagulant withdrawn slurry from the reactor D, solid-liquid separation of the slurry was added flocculant Processing apparatus for removing fluorine and harmful substances, characterized in that it comprises a separation vessel G to.
A second addition tank H is provided in the pipeline for returning the sludge from the separation tank G to the reaction tank D, and the hardly soluble metal oxide is added to the sludge in the second addition tank H. The processing apparatus for removing fluorine and harmful substances according to claim 9 , wherein the treated sludge is supplied to the reaction tank D.