JP2006218343A - Method and apparatus for treating selenium-containing waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating selenium-containing waste water, in each of which the amount of aluminum to be required to reduce selenium by using metallic aluminum can be eluted, consequently selenium can be stabilized, reduced and removed surely and the fluorine and boron coexisting in selenium-containing waste water can be removed together with selenium. <P>SOLUTION: The method for treating selenium-containing waste water comprises a step of bringing selenium-containing waste water into contact with oxidized film-removed metallic aluminum in the presence of an acid to reduce selenium in waste water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method and an apparatus for treating selenium-containing wastewater. More specifically, the present invention can reduce selenium effectively by reducing selenium, particularly wastewater containing hexavalent selenium, using metallic aluminum. The present invention relates to a method and apparatus for treating selenium-containing wastewater.

Smoke desulfurization effluent from coal-fired power plants and non-ferrous metal refining plant effluent may contain selenium. Although it is rare that selenium is contained in wastewater at a high concentration, it is necessary to remove selenium from wastewater for environmental conservation even at a selenium concentration of about several mg / L.

Conventionally, as a method for removing selenium from selenium-containing wastewater, a method using divalent iron, a method using metallic iron, a method using aluminum salt or metallic aluminum, and the like are known.

In the method using divalent iron, a salt of acid and divalent iron is added to selenium-containing wastewater, and the pH is adjusted to 8.5 to 8.5.
After adjusting to 10 and reacting, solid-liquid separation is performed (for example, Patent Document 1).

In the method using metallic iron, the selenium-containing wastewater is adjusted to pH 5 or lower and brought into contact with metallic iron to reduce selenium, and then agglomeration treatment and solid-liquid separation are performed (Patent Document 2).

In the method using metallic aluminum, the pH is adjusted to 6 or less in selenium-containing wastewater, and then copper ions or iron ions are dissolved. Then, metal such as metallic iron or metallic aluminum is added to make ORP −
350 mV or less, and then adjusted to pH 8 to 10 for solid-liquid separation (Patent Document 3).

However, in the method using divalent iron or metal iron, the separated sludge is colored, so there is a limit to the disposal of sludge. In the method using metal aluminum, the waste water is adjusted to acidity and contacted with metal aluminum. Even if it is made to elute, the elution of aluminum is not easy and the reduction effect is not obtained as expected. In addition, in any method, in the case of wastewater containing fluorine and / or boron together with selenium, it is difficult to remove fluorine and / or boron even if selenium can be removed, and removal of fluorine and / or boron. Needed to be treated separately.
JP-A-6-79286 JP-A-9-187778 JP-A-8-224585

The present invention is a method for treating selenium-containing wastewater, which can obtain the required amount of aluminum elution when reducing selenium using metallic aluminum, thereby stably reducing and removing selenium. And a treatment apparatus, and a treatment method and a treatment apparatus for selenium-containing wastewater capable of removing fluorine and boron coexisting in the wastewater together with selenium.

The method for treating selenium-containing wastewater of the present invention (Claim 1) is to treat selenium-containing wastewater in the presence of an acid.
It is characterized in that it is brought into contact with metallic aluminum from which the oxide film has been removed to dissolve aluminum in the wastewater and to reduce selenium in the wastewater.

The method for treating selenium-containing wastewater according to claim 2 is characterized in that, in claim 1, after reducing selenium in the wastewater, the pH is adjusted to precipitate an aluminum compound, and the precipitated aluminum compound is solid-liquid separated. To do.

The selenium-containing wastewater treatment method according to claim 3 is characterized in that, in claim 2, the pH is adjusted to 5-8.

The selenium-containing wastewater treatment method according to claim 4 is characterized in that, in claim 2, the pH is adjusted to 9 or more in the presence of a calcium compound.

The method for treating selenium-containing wastewater according to claim 5 is characterized in that in any one of claims 1 to 4, the selenium-containing wastewater contains hexavalent selenium.

The method for treating selenium-containing wastewater according to claim 6 is characterized in that, in claim 3, fluorine coexists in the selenium-containing wastewater.

The method for treating selenium-containing wastewater according to claim 7 is characterized in that, in claim 4, selenium-containing wastewater coexists with fluorine and / or boron.

The method for treating selenium-containing wastewater according to claim 8 is characterized in that in any one of claims 1 to 7, the selenium-containing wastewater is flue gas desulfurization wastewater.

The selenium-containing wastewater treatment method according to claim 9 is characterized in that, in claim 1, the metal aluminum from which the oxide film has been removed is obtained by surface treatment of untreated metal aluminum with an acid or an alkaline aqueous solution. And

The apparatus for treating selenium-containing wastewater according to claim 10 includes metal aluminum from which an oxide film has been removed, a reduction reactor for introducing selenium-containing wastewater to reduce selenium in the wastewater, and acid to the selenium-containing wastewater. Solid-liquid separation of the acid addition means to be added, the aggregation reaction tank into which the reduction treated water flowing out from the reduction reactor is introduced, the pH adjusting agent addition means for adjusting the pH of the aggregation reaction tank, and the aggregation reaction treated water And a solid-liquid separator.

The selenium-containing wastewater treatment apparatus according to claim 11 is characterized in that, in claim 10, calcium compound addition means for supplying calcium compounds to the agglomeration reaction tank is provided.

According to the selenium-containing wastewater treatment method of the present invention (Claim 1), since the wastewater is brought into contact with the metal aluminum from which the oxide film has been removed in the presence of an acid, the required amount of the selenium-containing wastewater is not disturbed by the oxide film. Aluminum can be eluted, and selenium in the waste water can be stably reduced to low-value selenium that is easy to precipitate and can be reliably reduced. Even if metal aluminum that is usually available is brought into contact with acidic wastewater without treatment, the amount of aluminum eluted is small, the reducing power accompanying aluminum elution is poor, and the reducing power that can stably reduce selenium is obtained. Absent. According to the present invention, since aluminum can be eluted according to the amount of acid present in the wastewater, selenium can be reduced stably.

According to claim 2 and claim 10, the pH of the reduced treated water is adjusted so that aluminum is precipitated, and then solid-liquid separation is performed, so that when dissolved aluminum is precipitated, the reduced selenium is aluminum. It is possible to obtain treated water from which selenium has been removed by being separated from the treated water by solid-liquid separation. The separated sludge is white, unlike the colored sludge produced by the conventional selenium removal method using iron salt or metallic iron.

According to the third aspect, when aluminum is precipitated by adjusting the pH to 5 to 8, aluminum is precipitated as aluminum hydroxide, and selenium is adsorbed and co-precipitated on the aluminum hydroxide and can be separated from water. Since this pH adjustment may be almost neutral, the addition amount of the pH adjusting agent may be small, and the pH can be discharged.

According to Claims 4 and 11, since the reduced water is adjusted to pH 9 or higher in the presence of the calcium compound, aluminum is precipitated as calcium aluminate, and selenium is adsorbed and precipitated by coprecipitation. Treated water from which selenium has been removed can be obtained. This selenium removal by coprecipitation with calcium aluminate has a very high selenium removal rate, and the selenium concentration of the treated water can be reduced to 0.1 mg / L or less.

According to claim 5, although hexavalent selenium is contained as the selenium of the selenium-containing wastewater, a sufficient amount of eluted aluminum can be obtained and the reducing power is high, so that hexavalent selenium can be reduced. Hexavalent selenium cannot be easily reduced to low-valent selenium with a normal reducing agent such as a divalent iron salt or hydrazine, but according to the present invention, hexavalent selenium can also be reduced.

According to claim 6, when fluorine coexists in the selenium-containing wastewater, selenium and fluorine can be insolubilized simultaneously with the precipitation of aluminum.

According to claim 7, when fluorine and boron coexist in the selenium-containing wastewater, selenium, fluorine and boron can be insolubilized simultaneously with the precipitation of aluminum. Therefore, it is not necessary to provide a separate water treatment device for removing fluorine and boron.

According to the eighth aspect, the treatment of the flue gas desulfurization waste water can be effectively performed by the present invention.
Smoke desulfurization effluent contains selenium and, in some cases, fluorine and boron,
Not only can selenium be removed, it can also remove fluorine and boron. Further, even when the flue gas desulfurization waste water contains an oxidizing substance such as persulfate or iodate, the oxidizing substance can be removed.

According to the ninth aspect, the oxide film on the surface of the metal aluminum can be removed by surface-treating the metal aluminum with an acidic aqueous solution or an alkaline aqueous solution. By using metal aluminum from which the oxide film has been removed, the required amount of aluminum can be eluted without being disturbed by the oxide film, and selenium in the waste water can be stably reduced.

Embodiments of the method and apparatus for treating selenium-containing wastewater of the present invention will be described in detail below.

The selenium-containing wastewater to be treated in the present invention includes hexavalent selenium such as selenic acid and tetravalent selenium such as selenious acid as selenium, for example, refining wastewater from a nonferrous metal refining process, Flue gas desulfurization wastewater from coal combustion gas flue gas desulfurization process, raw material of selenium,
Various factory effluents from factories used as additives.

Moreover, the selenium-containing wastewater may contain fluorine and / or boron, and examples of such wastewater include flue gas desulfurization wastewater.

In the present invention, selenium-containing wastewater is brought into contact with metallic aluminum from which an oxide film has been removed in the presence of an acid to dissolve aluminum in the wastewater and reduce selenium in the wastewater. The metallic aluminum used in this reduction treatment is powder, granular, fibrous, crushed,
Although arbitrary shapes, such as rod shape and plate shape, may be sufficient, in order to enlarge a contact area with waste_water | drain, a powder, a granular form, a fibrous form, and a crushed form are preferable. Moreover, it may be unused aluminum as an aluminum material or waste aluminum used for an arbitrary use.

In general, metallic aluminum is difficult to dissolve the required amount of aluminum even when it is brought into contact with acidic waste water. This is because an oxide film is formed on the surface of the metal aluminum if it is not treated, whether it is unused aluminum or waste aluminum. A surface treatment is performed to remove the oxide film before contacting with waste water. It is important to keep it. The surface treatment of the metal aluminum is performed by immersing the metal aluminum in the surface treatment liquid using a surface treatment liquid of an alkaline aqueous solution or an acidic aqueous solution, or bringing the surface treatment liquid into contact with the surface of the metal aluminum by flowing or spraying.

When surface treatment is performed using an alkaline aqueous solution, sodium hydroxide, potassium hydroxide,
The oxide film on the surface of the metal aluminum can be removed by bringing an alkaline aqueous solution containing 0.1 to 5% of an alkaline substance such as ammonia into contact with metal aluminum at room temperature for 10 to 60 minutes.

When surface treatment is performed using an acidic aqueous solution, an acidic substance such as hydrochloric acid, sulfuric acid or nitric acid is added in an amount of 0.1 to 1
An acidic aqueous solution containing 0% concentration and metallic aluminum are 40 ° C. or higher, preferably 50 to 90 ° C.
The oxide film on the surface of the metal aluminum can be removed by bringing it into contact for 1 to 10 hours under heating at 0 ° C.

The surface treatment of the metal aluminum can be performed at an arbitrary place, and the surface-treated metal aluminum can be transferred to a non-oxidizing atmosphere and supplied to a reduction reactor that performs a reduction reaction of the selenium-containing waste water. Alternatively, the surface treatment of metallic aluminum may be performed in a reduction reactor, and the waste water may be supplied to the reduction reactor after the surface treatment. The surface treatment in the latter reduction reactor
The possibility that an oxide film is formed again after the surface treatment is small and preferable.

The contact between the selenium-containing wastewater and the metal aluminum that has been surface-treated to remove the oxide film is carried out in a reduction reactor, but the reduction reactor may be a packed tower filled with metal aluminum of any shape, in powder form, It may be a reaction vessel in which fine granular metal aluminum is added.

When selenium-containing wastewater is brought into contact with metallic aluminum from which an oxide film has been removed in the presence of an acid, aluminum is easily eluted and dissolved in the wastewater. When metallic aluminum elutes into aluminum ions, a strong reducing action occurs, and selenium in the waste water is reduced. For example, hexavalent selenium becomes low-valent or zero-valent selenium, and is easily precipitated by aggregation treatment.

  The following reaction formula is assumed as the reduction reaction of selenic acid.

2Al ⁰ + SeO ₄ ²⁻ + 8H ⁺ → 2Al ³⁺ + Se ⁰ + 4H ₂ O
Since the amount of aluminum eluted depends on the amount of acid present, the amount of aluminum eluted can be increased by increasing the amount of acid added. By reducing the amount of eluted aluminum, the reducing action becomes stronger, hexavalent selenium can be reliably reduced to a lower value, and the amount of selenium removed can be increased. As the acid to be added, any acid such as hydrochloric acid, sulfuric acid, nitric acid can be used. The amount of acid added is set according to the wastewater selenium concentration and treated water selenium concentration.

After reducing the selenium, the reduction-treated water is agglomerated. In the aggregation treatment, aluminum dissolved in the reduction-treated water is precipitated as an insoluble aluminum compound. For example, an alkali is added to reduction-treated water, and dissolved aluminum is precipitated as aluminum hydroxide. It is preferable to adjust the pH to 5 to 8 by adding an alkali, and aluminum hydroxide dissolves at pH 4 or lower or pH 9 or higher, which is not suitable. As alkali, sodium hydroxide,
Potassium hydroxide can be used. When aluminum hydroxide is precipitated, reduced low-valent selenium in water is also adsorbed on the aluminum hydroxide flocs and is precipitated by a coprecipitation phenomenon.

  In this coagulation precipitation, it is assumed that the following reaction is performed.

^{Al 3+ + Se 0 + 3OH -} → Al (OH) 3 · Se 0 ↓
Moreover, when fluorine coexists in selenium-containing wastewater, when aluminum hydroxide is precipitated,
Fluorine also precipitates due to the coprecipitation phenomenon. The phenomenon in which fluorine is precipitated together with selenium is a characteristic effect when aluminum is used, which cannot be expected by removing selenium with metallic iron or divalent iron.

In the present invention, another preferred method for precipitating dissolved aluminum is a method of precipitating as calcium aluminate. A calcium compound is added to the reduction-treated water, and the pH is adjusted to 9 or more and the coagulation treatment is performed. Examples of calcium compounds to be added include calcium hydroxide, calcium oxide, and calcium chloride. Use of calcium hydroxide is preferable because it serves as a calcium source and also acts as an alkali for pH adjustment. When using another calcium compound, an arbitrary alkali is added to adjust the pH. The pH is adjusted to 9 or more, preferably 9-12. When the pH is lower than 9, it is difficult to produce calcium aluminate.

In this way, when dissolved aluminum precipitates as calcium aluminate, reduced low-valent selenium in water is also adsorbed on the calcium aluminate flocs and precipitates due to the coprecipitation phenomenon.

  In this coagulation precipitation, it is assumed that the following reaction is performed.

2Al (OH) ₃ + Ca (OH) ₂ + Se ⁰ → CaAl ₂ O ₄ .Se ⁰ ↓ + 4H ₂ O
The selenium removal by coprecipitation with calcium aluminate has a better selenium removal effect than the case of aluminum hydroxide, as shown in the examples described later. The reason for this is not clear, but it is presumed that selenium, which is insufficiently reduced, is also removed by calcium aluminate.

In addition, when fluorine or boron is contained in the selenium-containing wastewater, when calcium aluminate is precipitated, fluorine and boron are simultaneously deposited. For this reason, it is extremely preferable to apply the precipitation method using calcium aluminate to wastewater containing fluorine and boron together with selenium, for example, flue gas desulfurization wastewater.

Next, the agglomerated water on which the aluminum compound is precipitated is subjected to solid-liquid separation. By solid-liquid separation, it is separated into treated water and sludge containing precipitated aluminum compound, selenium, and optionally fluorine and boron.

As the solid-liquid separation means, known solid-liquid separation means such as precipitation separation, flotation separation, centrifugation, membrane separation can be used.

Prior to the solid-liquid separation, for example, a polymer flocculant is added to the reaction tank provided in the above-described flocculation process or in the subsequent stage of the flocculation process, so that the flocs of aluminum hydroxide and calcium aluminate are coarsened and solidified. Liquid separation may be improved.

The sludge generated by solid-liquid separation is mainly aluminum and is white, so it can be recovered by mixing with gypsum generated in the flue gas desulfurization apparatus, and sludge disposal is reduced.

  Below, the processing apparatus of the selenium containing waste_water | drain of this invention is demonstrated.

In FIG. 1, an example of embodiment of the processing apparatus of the selenium containing waste_water | drain of this invention is shown. In the figure,
Reference numeral 1 is a reduction reactor, 2 is an agglomeration reaction tank, 3 is a solid-liquid separator, 4 is a drainage supply pipe for introducing selenium-containing wastewater into the reduction reactor, 5 is an acid addition means, and 6 is an agglutination reaction. This is a drug supply pipe for adding a drug to the tank.

In FIG. 1, a reduction reactor 1 is a packed tower filled with metallic aluminum inside, a supporting plate is arranged in the lower part of the tower, and particles of metallic aluminum 11 are packed on the supporting plate to form a packed bed. Has been. The support plate can flow water, but has a structure that prevents the passage of metal aluminum particles, and a perforated plate or a strainer is used. Below the support plate is a drainage inflow chamber 12, and a drainage supply pipe 4 is opened in the drainage inflow chamber 12. On the other hand, the upper part of the packed bed of metal aluminum 11 is a reduction treatment water chamber, and a pipe line for transferring the reduction treatment water to the next stage is opened. An upper support plate may be provided near the upper surface of the packed bed.

The acid addition device 5 is connected to the drainage supply pipe 4 so that acid can be injected into the drainage. The acid addition device 5 may be opened to the drainage inflow chamber 12 instead of connecting to the drainage supply pipe.

The reduction reactor 1 is preferably a reaction vessel that can be shut off to the atmosphere, and the reduction reaction that occurs in the reactor can be performed in a reducing atmosphere. In addition, the reduction reactor 1 is provided with a metal aluminum inlet that can be opened and closed at an arbitrary position, for example, on the upper wall of the reactor, so that the metal aluminum can be filled into the reactor at any time. Furthermore, it is preferable to arrange a heating means for heating the waste water from the reduction reactor 1 or the waste water supply pipe 4. For example, a steam injection pipe, a heating jacket or a heater can be provided at an arbitrary position, or a heat exchanger can be provided in the drainage supply pipe.

The agglomeration reaction tank 2 may be a commonly used agglomeration reaction tank. The agglomeration reaction tank 2 is necessary for an agglutination reaction such as a conduit for introducing reduction reaction water flowing out from the reduction reactor 1, a pH adjuster, a calcium compound, or the like. A drug supply pipe 6 for introducing a drug communicates. In addition, a stirring device is provided in the reaction tank 2 so as to cause a uniform agglomeration reaction, and a pipe line for transferring the agglomerated water to the solid-liquid separation device 3 communicates therewith.

The solid-liquid separator 3 is provided with a treated water pipe for discharging treated water generated by solid-liquid separation and a sludge discharge passage for discharging separated sludge. The solid-liquid separator 3 shown in FIG. 1 is a precipitation tank,
Any solid-liquid separator such as a membrane separator can be provided.

Although not shown, a second agglomeration reaction tank is provided between the reaction tank 2 and the solid-liquid separator, and a polymer flocculant is added to the second agglomeration reaction tank to produce the agglomeration reaction tank 2. You may coarsen a fine aggregation floc.

An embodiment of the present invention will be described below based on the processing apparatus of FIG. First, before passing selenium-containing wastewater, untreated metallic aluminum is supplied into the reduction reactor 1 from the inlet, and a packed layer of metallic aluminum 11 is formed in the reactor. Next, a surface treatment liquid, for example, the alkaline aqueous solution or the acidic aqueous solution described above is supplied to the metal aluminum filled layer through the acid addition means 5 to remove the oxide film on the surface of the metal aluminum. After surface treatment for a predetermined time,
Move to wastewater treatment. In addition, when the surface treatment of the metal aluminum is performed outside the reduction reactor 1, after the metal aluminum from which the oxide film has been removed is filled in the reduction reactor 1, the process immediately shifts to the waste water treatment.

The selenium-containing wastewater is introduced and mixed with acid from the acid addition means 5 and introduced into the reduction reactor 1 through the wastewater supply pipe 4. If the selenium-containing wastewater contains turbidity, pollutants such as heavy metals other than selenium, organic matter, etc., before introducing it into the reduction reactor,
It is desirable to remove coexisting contaminants by passing water through a pretreatment device (not shown) such as a coagulation device, a filtration device, a membrane separation device, or an activated carbon adsorption device.

The wastewater introduced into the wastewater inflow chamber of the reduction reactor 1 flows in contact with the packed bed of metal aluminum 11 in an upward flow in the reactor. At this time, the acid injected into the wastewater dissolves the metal aluminum. Since the aluminum oxide film on the surface of the metal aluminum is removed, the aluminum is smoothly eluted according to the amount of acid present, and reducing power is generated at the time of this elution. Selenium in waste water, particularly hexavalent selenium, is reduced by the reducing power when aluminum is eluted. The reduced selenium is reduced from tetravalent to zero valence, and it is estimated that a part of the reduced zero-valent selenium is deposited on the metal aluminum.

Reduction treatment water containing most of the reduced selenium is transferred from the reduction treatment water chamber above the reduction reactor to the agglomeration reaction tank 2 via a pipe line. The reducing water introduced into the agglomeration reaction tank 2 is supplied with a chemical, for example, alkali, for depositing dissolved aluminum from the chemical supply pipe 6 and mixed with stirring. When the drainage pH is adjusted to 5 to 8 by supplying alkali, the dissolved aluminum is precipitated as aluminum hydroxide. At this time, selenium in the drainage is adsorbed and coprecipitated to make selenium insoluble. In addition, when fluorine coexists in the selenium-containing wastewater, the dissolved aluminum also reacts with fluorine, insolubilizes the fluorine, and precipitates together with the hydroxylated floc.

Further, a pH adjuster and a calcium compound are supplied from the drug supply pipe 6 to the agglomeration reaction tank 2,
When the pH in the tank is adjusted to 9 or more, dissolved aluminum produces calcium aluminate and precipitates. At this time, selenium is adsorbed and selenium is also insolubilized by coprecipitation. If fluorine coexists in the selenium-containing wastewater, fluorine is insolubilized together with selenium, if boron is coexisted, boron is also insolubilized, and if fluorine and boron coexist, fluorine and boron are insolubilized together with selenium.

The agglomerated water that has been agglomerated in the agglomeration reaction tank 2 is preferably transferred from the pipe to the solid-liquid separator 3 after the flocs are coarsened by the polymer aggregating agent. The selenium that is insolubilized in the precipitation tank as the solid-liquid separator 3 and coprecipitated with the precipitated aluminum compound is precipitated and discharged as sludge from the sludge discharge passage at the bottom of the precipitation tank 3, and the supernatant water at the top of the precipitation tank is treated water. Is taken out from the treated water pipe. Treated water is adjusted to pH if necessary, removal of residual suspension, residual COD
It is discharged or recovered after undergoing post-treatment such as removal.

On the other hand, the separated sludge is disposed of after being subjected to a dehydration treatment by a dehydrator. The sludge generated in the present invention is white because it is a sludge mainly composed of aluminum, and is mixed with the gypsum slurry generated in the flue gas desulfurization device generated in the flue gas desulfurization device and the separated aluminum-containing sludge. And it can collect | recover by dehydrating with a dehydrator and sludge disposal is reduced.

Hereinafter, the present invention will be described with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
Surface treatment of metallic aluminum was performed by passing a hydrochloric acid aqueous solution having a hydrochloric acid concentration of 4000 mg / L through a glass column packed with 50 mL of metallic aluminum particles having a particle diameter of 1 to 2 mm at a flow rate of 250 mL / h while heating to 60 ° C. It was. At the stage where the dissolution of aluminum becomes steady, flue gas desulfurization effluent (hexavalent selenium concentration 1.2 mg / L, fluorine concentration 96 mg / L, boron 110 mg
/ L) hydrochloric acid to a concentration of 4000 mg / L, temperature 60 ° C., 250 mL / h
Was passed through the column. Reduced treated water flowing out from the column (dissolved aluminum concentration 950 mg
/ L) was added sodium hydroxide to adjust the pH to 6.7, which seems to be optimal for the production of insoluble aluminum hydroxide, and allowed to react for 10 minutes. Then, no. Solid-liquid separation was performed with 5C filter paper, and the water quality in the filtered water was measured.

As a result, the water quality of the filtered water was selenium concentration 0.51 mg / L, fluorine concentration 1.2 mg / L,
The boron concentration was 62 mg / L.

Example 2
It implemented like Example 1 except having added pH to 11.9 by adding slaked lime to reduced treated water instead of sodium hydroxide added to reduced treated water in Example 1.

As a result, the quality of filtered water was as follows: selenium concentration 0.052 mg / L, fluorine concentration 2.1 mg / L
The boron concentration was 1.2 mg / L.

Comparative Example 1
To a glass column packed with 50 mL of metallic iron having an average particle diameter of 0.6 mm, hydrochloric acid was added to the same waste water as in Example 1 to 1250 mg / L, and water was passed through the column at a temperature of 60 ° C. and 250 mL / h. PH of sodium hydroxide to the effluent from the column (dissolved iron concentration 952mg / L)
The mixture was adjusted to 9.5 and allowed to react for 10 minutes. Then, no. Solid-liquid separation was performed with 5C filter paper, and the water quality in the filtered water was measured.

As a result, the quality of the filtered water was as follows: selenium concentration 0.051 mg / L, fluorine concentration 86 mg / L,
The boron concentration was 101 mg / L.

Comparative Example 2
Water was passed through a column packed with 50 mL of the same metal aluminum particles as in Example 1 under the same conditions as in the wastewater treatment of Example 1 without surface treatment. The aluminum concentration of the column effluent after 0.5 hours was 55 mg / L, and the desired amount of aluminum dissolution was not obtained.

As is apparent from the above examples, it is understood that selenium in the waste water is reduced with metallic aluminum and removed by subsequent precipitation of aluminum. Further, in the conventional selenium removal using metallic iron, fluorine and boron coexisting in the waste water are hardly removed, but in the present invention, fluorine is also removed together with selenium. Above all, add calcium compound to the treated water
When H is adjusted, not only boron can be removed, but also the selenium removal rate is remarkably improved to 95.7%, and the selenium concentration of the treated water can be reduced to 0.1 mg / L or less. In addition, even if it performs a waste water treatment with untreated metal aluminum, the amount of required aluminum does not melt | dissolve and a selenium removal effect cannot be expected.

It is a systematic diagram which shows embodiment of the processing apparatus of the selenium containing waste_water | drain of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reduction reactor 2 Aggregation reaction tank 3 Solid-liquid separator 4 Drain supply pipe 5 Acid addition means 6 Chemical supply pipe 11 Metal aluminum 12 Drain inflow chamber

Claims (11)

The selenium-containing wastewater is contacted with metal aluminum from which the oxide film has been removed in the presence of an acid,
A method for treating selenium-containing wastewater, wherein aluminum is dissolved in wastewater and selenium in the wastewater is reduced. 2. The method for treating selenium-containing wastewater according to claim 1, wherein after reducing selenium in the wastewater, p
A method for treating selenium-containing wastewater, wherein an aluminum compound is precipitated by adjusting H, and the precipitated aluminum compound is subjected to solid-liquid separation. The method for treating selenium-containing wastewater according to claim 2, wherein the pH is adjusted to 5 to 8. The method for treating selenium-containing wastewater according to claim 2, wherein the pH is 9 in the presence of a calcium compound.
A method for treating selenium-containing wastewater, which is adjusted as described above. 5. The method for treating selenium-containing wastewater according to any one of claims 1 to 4, wherein the selenium-containing wastewater contains hexavalent selenium. 4. The method for treating selenium-containing wastewater according to claim 3, wherein fluorine is present in the selenium-containing wastewater. 5. The method for treating selenium-containing wastewater according to claim 4, wherein fluorine and / or boron coexists in the selenium-containing wastewater. The method for treating selenium-containing wastewater according to any one of claims 1 to 7, wherein the selenium-containing wastewater is flue gas desulfurization wastewater. 2. The method for treating selenium-containing wastewater according to claim 1, wherein the metallic aluminum from which the oxide film has been removed is obtained by surface-treating untreated metallic aluminum with an acid or an alkaline aqueous solution. Processing method. There is metal aluminum from which the oxide film has been removed, a selenium-containing wastewater is introduced, a reduction reactor for reducing selenium in the wastewater, an acid addition means for adding acid to the selenium-containing wastewater, and the reduction reactor It has a coagulation reaction tank into which the reduced treated water flowing out is introduced, a pH adjuster addition means for adjusting the pH of the coagulation reaction tank, and a solid-liquid separation device for solid-liquid separation of the coagulation reaction treated water. Selenium-containing wastewater treatment equipment. The apparatus for treating selenium-containing wastewater according to claim 10, further comprising calcium compound addition means for supplying calcium compounds to the agglomeration reaction tank.

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