JP4771284B2 - Method and apparatus for treating selenium-containing wastewater - Google Patents

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 with a very small amount of metal elution, particularly by reducing wastewater containing hexavalent selenium using two or more metals. The present invention relates to a treatment method and a treatment apparatus for selenium-containing wastewater in which generated sludge is white and can be easily treated.

  Coal-fired power plant flue gas desulfurization effluent, copper smelter effluent, oil refinery effluent, etc. may contain selenium. Further, since selenium is used as an industrial raw material in the production of glass decolorizers and colorants, and photosensitive drums for dry copying machines, selenium may also be contained in these industrial wastewaters. Furthermore, selenium-containing wastewater is discharged from factories that produce selenium compounds by extracting selenium from scraps or sludge containing selenium by roasting or alkali melting. Although selenium is rarely contained at high concentrations in wastewater, selenium is regulated for environmental conservation, and the uniform wastewater standard based on the Water Pollution Control Law is set at 0.1 mg / L. ing. However, since stable treatment technology for selenium-containing wastewater is still under development and it is difficult to achieve uniform wastewater standards immediately, the selenium compound manufacturing industry has a provisional wastewater standard of 0.3 mg / L. Is scheduled to be extended until 2009.

In many cases, selenium in wastewater usually exists as colloidal selenium, tetravalent selenite ion (SeO ₃ ²⁻ ) or hexavalent selenate ion (SeO ₄ ²⁻ ). As a method for treating such selenium-containing wastewater, many coagulation precipitation methods have been proposed. For example, as a method for treating selenium-containing wastewater that removes both SeO ₃ ^2- and SeO ₄ ^2- in wastewater and reduces the amount of sediment concentrate discarded outside the system, SeO ₃ ^2- and SeO ₄ ^{2 are used. -} a primary process of coprecipitating removing a mixture of copper hydroxide was added a neutralizing agent containing a hydroxyl group suspended solids in wastewater containing Cu ²⁺ and suspended solids, and an acid to the primary treated water After adding a salt with Fe ²⁺ , the neutralizing agent is added again, and secondary precipitation is carried out by coprecipitation removal of SeO ₃ ^2- and SeO ₄ ^2- remaining in the primary treated water as a mixture of selenium and iron hydroxide. A method for treating selenium-containing wastewater for treatment has been proposed (Patent Document 1). However, in this method, the amount of divalent iron salt required is large, and the generated sludge is colored, so that the treatment is not easy.

  In addition, these harmful substances can be effectively removed simultaneously from the flue gas desulfurization waste water containing harmful substances such as selenium, fluorine, peroxide and heavy metals, and the deterioration of the COD adsorption resin due to the peroxide is also possible. As a treatment method of flue gas desulfurization wastewater that can obtain treated water of good water quality for a long time by preventing the flue gas, after adjusting the pH of the flue gas desulfurization wastewater to 5 or less and contacting with iron, A flue gas desulfurization method in which solid-liquid separation is performed and further contacted with a COD adsorption resin has been proposed (Patent Document 2). However, even in this method, since iron such as fine particles is used for the treatment, the generated sludge is colored, and the treatment is difficult.

Furthermore, as a method for removing selenium that can easily reduce the selenium concentration of wastewater including not only tetravalent selenium but also hexavalent selenium to 0.1 mg / L or less, the pH of selenium-containing wastewater is set to 6 A hydroxide obtained by adding divalent iron ions while adjusting the following, then adding a reducing agent such as aluminum, and adjusting the pH to 8 to 10 by adding an alkali agent. A method for removing selenium in the effluent has been proposed comprising a second step of solid-liquid separation (Patent Document 3). However, in this method, the sludge is colored by the iron component, and even if the pH of the waste water is adjusted to acidity and brought into contact with metal aluminum, the elution of aluminum is not easy and the expected reduction effect is obtained. I can't.
JP-A-6-79286 JP-A-9-187778 JP-A-8-224585

  The present invention reduces the wastewater containing hexavalent selenium, and can effectively remove selenium with a very small amount of metal elution, and the selenium-containing wastewater that is easily treated when the sludge generated at that time is white The present invention was made for the purpose of providing a processing method and a processing apparatus.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors brought the selenium-containing wastewater into contact with an alloy or mixture of two or more metals having different ionization tendencies, and eluted a part of the metal. By reducing hexavalent selenium, selenium can be effectively removed with an extremely small amount of metal elution, and metal is selected so that the sludge generated at that time becomes white sludge that can be easily treated. Based on this finding, the present invention has been completed.

That is, the present invention
(1) A selenium-containing wastewater containing hexavalent selenium is brought into contact with metal aluminum and an alloy or mixture of a metal having a relatively lower ionization tendency than the metal aluminum, and an acid is added to the wastewater to form the metal. A reduced treated water obtained by reducing hexavalent selenium to tetravalent to zero-valent selenium by eluting a part of aluminum is obtained, and an alkali is added to the reduced treated water to precipitate the eluted aluminum metal as a metal hydroxide. And co-precipitating tetravalent selenium remaining in the reduction treated water with a metal hydroxide to obtain an agglomerated reaction treated water in which the metal hydroxide is precipitated, and subjecting the agglomerated reaction treated water to solid-liquid separation. A method for treating selenium-containing wastewater, characterized by obtaining treated water having a reduced concentration ;
( 2 ) The method for treating selenium-containing wastewater according to (1), wherein the selenium-containing wastewater is flue gas desulfurization wastewater, and
( 3 ) There is an alloy or mixture of metallic aluminum and a metal that is relatively less ionized than the metallic aluminum, and wastewater in which acid is added to selenium-containing wastewater containing hexavalent selenium is introduced into the wastewater. A reduction reactor for reducing hexavalent selenium, an agglomeration reaction tank into which reduction-treated water flowing out from the reduction reactor is introduced, and an alkali as a pH adjuster added to the agglomeration reaction tank to adjust the pH to be alkaline. a selenium-containing wastewater treatment apparatus, comprising: a pH adjuster addition means; and a solid-liquid separation apparatus for solid-liquid separation of the aggregation reaction treated water sent from the aggregation reaction tank ,
Is to provide.

  According to the method and apparatus for treating selenium-containing wastewater of the present invention, selenium can be reduced with an extremely small amount of metal elution, and is particularly effective for treating wastewater containing hexavalent selenium. In addition, since sludge generated by selecting metal can be white, sludge treatment is easy, and in workplaces where flue gas desulfurization is performed by the lime gypsum method, sludge is collected by mixing with recovered gypsum. be able to. Furthermore, in some cases, flue gas desulfurization wastewater contains fluorine and boron in addition to selenium, but according to the method and apparatus of the present invention, not only selenium but also fluorine and boron can be removed simultaneously.

  In the selenium-containing wastewater treatment method of the present invention, selenium-containing wastewater is brought into contact with an alloy or mixture of two or more metals having different ionization tendencies, and selenium is reduced by eluting part of the metal. The method of the present invention contains selenium such as flue gas desulfurization effluent from a coal-fired power plant, copper smelter effluent, oil refining plant effluent, glass manufacturing plant effluent, photosensitive drum manufacturing effluent from a dry copying machine, and selenium compound manufacturing effluent. The present invention can be applied to the treatment of wastewater discharged, and can be particularly suitably applied to the treatment of flue gas desulfurization wastewater containing hexavalent selenium.

In the method of the present invention, selenium-containing wastewater is brought into contact with an alloy or mixture of two or more metals having different ionization tendencies. The ionization tendency is a tendency of metal to come into contact with water to become an ion. Quantitatively, it is expressed by the standard electrode potential E ⁰ of the metal (M) / metal cation (M ^{z +} ) system in water. The order is determined, and the smaller the standard electrode potential E ^{0, the} greater the ionization tendency. There are no particular limitations on the metal used in the method of the present invention. For example, aluminum (Al → Al ³⁺ + 3e, −1.66 V (E ^{0 at} 25 ° C., the same shall apply hereinafter)), zinc (Zn → Zn ²⁺ + 2e, − 0.763V), chromium (Cr → Cr ³⁺ + 3e, −0.74V)), cadmium (Cd → Cd ²⁺ + 2e, −0.40V), nickel (Ni → Ni ²⁺ + 2e, −0.25V) , Tin (Sn → Sn ²⁺ + 2e, −0.136V), lead (Pb → Pb ²⁺ + 2e, −0.126V), copper (Cu → Cu ²⁺ + 2e, 0.337V), and the like. . Among these, aluminum, zinc, tin, and copper can be suitably used because of their relatively low toxicity. When using hazardous substances such as chromium, cadmium, lead, etc., care must be taken so that these metals do not remain in the treated water.

  The metal used in the method of the present invention is preferably a metal in which sludge composed of hydroxide generated by pH adjustment after elution exhibits a white color. When the sludge is white, it is easier to treat the sludge than when it is colored brown or the like. As a metal which white sludge produces | generates, the alloy or mixture of aluminum and tin and the alloy or mixture of zinc and tin can be used especially suitably.

In the method of the present invention, the difference between the maximum value and the minimum value of the standard electrode potential E ⁰ at 25 ° C. of two or more metals is preferably 0.5 V or more, more preferably 1 V or more. More preferably, it is 5 V or more. If the difference between the maximum value and the minimum value of the standard electrode potential E ⁰ is less than 0.5 V, the reduction of selenium may not proceed sufficiently. When an alloy or a mixture of two or more metals having different ionization tendencies is brought into contact with water, the metal having a large ionization tend to elute first. For this reason, in an alloy or a mixture of two kinds of metals having different ionization tendencies, it is preferable that the metal having a large ionization tendency is 2 to 1,000 mol with respect to 1 mol of the metal having a small ionization tendency. More preferably, it is 100 moles.

In the method of the present invention, since metal elution requires a long time when neutral, it is preferable to add metal to selenium-containing wastewater to promote metal elution. Examples of the acid to be added include hydrochloric acid and sulfuric acid. The amount of acid added is preferably set according to the amount of metal to be eluted. The metal elution amount is generally proportional to the acid addition amount, and the acid addition amount can be determined by a relational expression obtained in advance by experiments. Further, the elution amount of the metal can be set according to the hexavalent selenium concentration to be reduced. It is considered that aluminum and zinc eluted in the selenium-containing wastewater react with selenate ions as shown in the following formulas to reduce selenium.
2Al ⁰ + SeO ₄ ²⁻ + 8H ⁺ → 2Al ³⁺ + Se ⁰ + 4H ₂ O
3Zn ⁰ + SeO ₄ ²⁻ + 8H ⁺ → 3Zn ²⁺ + Se ⁰ + 4H ₂ O

  In the method of the present invention, the shape of the alloy or mixture of two or more metals is preferably one having a large surface area. Examples of the shape having a large surface area include powdery and granular materials having a particle size of about 10 μm to 5 mm, fibrous materials, and fine thin films. In the method of the present invention, there is no particular limitation on the method of bringing the selenium-containing wastewater into contact with two or more kinds of metal alloys or mixtures. For example, a reaction in which a metal powder is added and reacted after the wastewater is introduced into the reaction vessel. Examples include a tank system, a packed tower system in which a packed tower is filled with metal particulates, metal fibers, and the like, and drainage is passed through the packed bed.

  There are no particular limitations on the alloy of two or more metals used in the method of the present invention, and any of solid solutions, intermetallic compounds, and eutectic gold can be used. As a method for producing an alloy of two or more kinds of metals, for example, a method utilizing a difference in metal ionization tendency, an electrolytic method, a melting method, and the like can be given. In the method of the present invention, the details of the mechanism in which the performance of selenium reduction treatment is greatly improved by contacting the selenium-containing wastewater with an alloy or mixture of two or more metals having different ionization tendencies as compared with the case of contacting with a single metal. Although it is not clear, a metal with a high ionization tendency elutes, electrons move through the metal with a low ionization tendency, and selenium is reduced on the surface of the metal with a low ionization tendency. It is done.

  In the method of the present invention, a selenium-containing wastewater is passed through a reaction tower filled with a granular alloy or mixture of two or more kinds of metals or a reaction tank to which an alloy or mixture of two or more kinds of metal powders is added. When reducing selenium, the temperature and the water flow rate are not particularly limited, but the higher the temperature and the slower the water flow rate, the lower the selenium concentration in the treated water. Selenium reduced to zero-valent selenium adheres to and is removed from the alloy or metal mixture in the reaction tower or reaction vessel, but tetravalent selenium elutes the pH of the reduced treated water in the reaction tower or reaction vessel. By adjusting the pH to produce hydroxide, it is coprecipitated with the precipitated metal hydroxide and removed. When the selenium-containing wastewater is wastewater in which fluorine and boron coexist, such as flue gas desulfurization wastewater, fluorine and boron can be simultaneously removed by coprecipitation by using aluminum as the eluted metal. In addition, when the metal to be eluted is aluminum, the sludge generated by solid-liquid separation is white, so it can be recovered by mixing with gypsum generated in the flue gas desulfurization device, and the sludge treatment load is reduced. .

  The apparatus for treating selenium-containing wastewater of the present invention includes a reduction reactor in which an alloy or a mixture of two or more metals having different ionization tendency is present, and selenium-containing wastewater is introduced to reduce selenium in the wastewater, and the reduction reactor It has an agglomeration reaction tank into which reduced treated water flowing out from the reactor is introduced, a pH adjusting agent adding means for adjusting the pH of the agglomeration reaction tank, and a solid-liquid separation device for separating the agglomerated reaction treated water into solid and liquid.

  FIG. 1 is a process flow diagram of one aspect of the apparatus of the present invention. The apparatus of this aspect includes a reduction reactor 1, an agglomeration reaction tank 2, and a solid-liquid separation device 3. An acid is added to the selenium-containing wastewater according to the amount of metal to be eluted, and water is passed through the reduction reactor 1 filled with an alloy or mixture of two or more metals having different ionization tendencies. By passing the selenium-containing wastewater to which acid is added, a metal having a higher ionization tendency elutes than a metal having a lower ionization tendency, and hexavalent selenium is reduced to tetravalent to zero-valent selenium. The reduction treated water flowing out from the reduction reactor 1 is guided to the agglomeration reaction tank 2, to which alkali is added by the pH adjuster adding means, and the metal eluted and ionized as water precipitates as hydroxide. At this time, the reduced selenium present in the water is coprecipitated with the metal hydroxide and removed. The agglomeration reaction-treated water on which the metal hydroxide is precipitated is added with a polymer flocculant if necessary, sent from the agglomeration reaction tank 2 to the solid-liquid separation device 3, and sludge is drawn from the bottom of the solid-liquid separation device. Then, treated water having a reduced selenium concentration is obtained as supernatant water.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, Se (VI) prepared by dissolving 2.39 mg of sodium selenate (Na ₂ SeO ₄ ) and 1.48 g of anhydrous sodium sulfate (Na ₂ SO ₄ ) per liter of ultrapure water. A synthetic waste water containing 1 mg / L and SO ₄ 1,000 mg / L was used.

Example 1
A solution prepared by dissolving 21.6 g of tin chloride (SnCl ₂ .2H ₂ O) in a solution of 0.5 mL of concentrated hydrochloric acid in 100 mL of ultrapure water was added to 50 mL of metal aluminum having a particle diameter of 1 to 2 mm and a purity of 99.5% (86 .3 g) was passed through a glass column at 60 ° C. with SV 2.5 h ⁻¹ to prepare an Al—Sn alloy. The molar ratio of Al to Sn used is 33: 1.
Hydrochloric acid 35 mg / L (concentrated hydrochloric acid 0.42 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. The raw water was passed through the glass column filled with the Al—Sn alloy at a flow rate of SV5h ⁻¹ while heating to 60 ° C.
The aluminum concentration of the reduced treated water flowing out from the glass column was 1.8 mg / L, and the tin concentration was 1.2 mg / L. The pH of the reduced treated water flowing out from the glass column was adjusted to 7 with an aqueous sodium hydroxide solution, reacted for 10 minutes, and then filtered using No. 5C filter paper. The solid on the filter paper was white. The selenium concentration in the filtered water was 0.33 mg / L. The ratio of the amount of selenium removed to the total amount of eluted aluminum and tin is 0.18.

Example 2
The same operation as in Example 1 was repeated to prepare a glass column filled with an Al—Sn alloy.
Hydrochloric acid 100 mg / L (concentrated hydrochloric acid 1.2 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. In the same manner as in Example 1, the raw water was passed through a glass column filled with an Al—Sn alloy, the concentration of aluminum and tin in the reduced treated water flowing out, and the neutralized filtration with an aqueous sodium hydroxide solution. The selenium concentration of water was measured.
The aluminum concentration was 19.0 mg / L, the tin concentration was 1.1 mg / L, and the selenium concentration was 0.046 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed to the total amount of aluminum and tin eluted is 0.041.

Example 3
A solution prepared by dissolving 80.0 g of copper sulfate (CuSO ₄ .5H ₂ O) in 400 mL of ultrapure water was placed on a glass column packed with 50 mL (86.6 g) of metallic aluminum having a particle diameter of 1 to 2 mm and a purity of 99.5%. Then, water was passed at SV 1.7h ⁻¹ at 60 ° C. to prepare an Al—Cu alloy. The molar ratio of Al to Cu used is 10: 1.
Hydrochloric acid 100 mg / L (concentrated hydrochloric acid 1.2 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. In the same manner as in Example 1, this raw water was passed through a glass column filled with an Al—Cu alloy, the concentration of aluminum and copper in the reduced treated water flowing out, and the filtration after neutralization with an aqueous sodium hydroxide solution The selenium concentration of water was measured.
The aluminum concentration was 17.8 mg / L, the copper concentration was 0.1 mg / L or less, and the selenium concentration was 0.55 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed and the total amount of eluted aluminum and copper is 0.023.

Reference example 4
250 mL of a solution obtained by dissolving 25.8 g of tin chloride (SnCl ₂ .2H ₂ O) in a solution of 400 mL of ultrapure water and 3 mL of concentrated hydrochloric acid is charged with 20 mL (74.9 g) of metallic zinc having a particle diameter of 1 to 2 mm. Then, water was passed through the glass column at SV 5 h ⁻¹ at 60 ° C. to prepare a Zn—Sn alloy. The molar ratio of Sn in the solution passed through with Zn used is about 16: 1.
Hydrochloric acid 35 mg / L (concentrated hydrochloric acid 0.42 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. The raw water was passed through the glass column filled with the above Zn—Sn alloy at a flow rate of SV5h ⁻¹ while heating to 60 ° C.
The zinc concentration of the reduced treated water flowing out from the glass column was 13.8 mg / L, and the tin concentration was 0.29 mg / L. The pH of the reduced treated water flowing out from the glass column was adjusted to 10 with an aqueous sodium hydroxide solution, reacted for 10 minutes, and then filtered using No. 5C filter paper. The solid on the filter paper was white. The selenium concentration in the filtered water was 0.41 mg / L. The ratio of the amount of selenium removed to the total amount of zinc and tin eluted is 0.041.

Reference Example 5
A glass column was filled with 15 mL of metallic zinc having a particle diameter of 1 to 2 mm and 5 mL of metallic copper having a particle size of 12 to 16 mesh and a purity of 99.99% or more.
The same raw water as in Reference Example 4 was passed through a glass column filled with a Zn-Cu mixture in the same manner as in Reference Example 4, and the concentration of zinc and copper in the reduced treated water flowing out was measured, and an aqueous sodium hydroxide solution was used. The selenium concentration of filtered water after pH adjustment was measured.
The zinc concentration was 24.4 mg / L, the copper concentration was 0.1 mg / L or less, and the selenium concentration was 0.27 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed to the total amount of zinc and copper eluted is 0.030.

Comparative Example 1
A glass column was filled with 50 mL of metallic aluminum having a particle size of 1 to 2 mm and a purity of 99.5%.
Hydrochloric acid 500 mg / L (concentrated hydrochloric acid 6.05 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. The raw water was passed through the glass column filled with the above metallic aluminum at a flow rate of SV5h ^-1 while heating to 60 ° C.
The aluminum concentration of the reduced treated water flowing out from the glass column was 123 mg / L. The pH of the reduced treated water flowing out from the glass column was adjusted to 7 with an aqueous sodium hydroxide solution, reacted for 10 minutes, and then filtered using No. 5C filter paper. The solid on the filter paper was white. The selenium concentration in the filtered water was 0.88 mg / L. The ratio of the amount of selenium removed to the amount of aluminum eluted is 0.0073.

Comparative Example 2
The same operation as in Comparative Example 1 was repeated except that 2,000 mg / L of hydrochloric acid (concentrated hydrochloric acid 24.2 mL / 5 L-drainage) was added to the synthetic waste water to obtain raw water.
The aluminum concentration of the reduced treated water flowing out from the glass column was 344 mg / L, and the selenium concentration of the filtered water was 0.79 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed to the amount of aluminum eluted is 0.00052.

Comparative Example 3
20 mL of metallic zinc having a particle diameter of 1 to 2 mm was packed in a glass column.
Hydrochloric acid 500 mg / L (concentrated hydrochloric acid 6.05 mL / 5 L-drainage) was added to the synthetic wastewater to obtain raw water. The raw water was passed through the glass column filled with the metal zinc at a flow rate of SV5h ^-1 while heating to 60 ° C.
The zinc concentration of the reduced treated water flowing out from the glass column was 440 mg / L. The pH of the reduced treated water flowing out from the glass column was adjusted to 10 with an aqueous sodium hydroxide solution, reacted for 10 minutes, and then filtered using No. 5C filter paper. The solid on the filter paper was white. The selenium concentration in the filtered water was 0.21 mg / L. The ratio of the amount of selenium removed to the amount of zinc eluted is 0.0019.

Comparative Example 4
A glass column was packed with 50 mL of metallic tin having a particle size of 12 to 32 mesh and a purity of 99.99% or more.
Hydrochloric acid 100 mg / L (concentrated hydrochloric acid 1.2 mL / 5 L-drainage) was added to the synthetic waste water to obtain raw water, which was passed in the same manner as in Comparative Example 3, and the concentration of tin in the reduced treated water flowing out was measured. The selenium concentration of the filtrate after pH adjustment with an aqueous sodium solution was measured.
The tin concentration was 30.7 mg / L and the selenium concentration was 0.58 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed to the amount of tin eluted is 0.014.

Comparative Example 5
A glass column was filled with 50 mL of metallic copper having a particle size of 12 to 16 mesh and a purity of 99.99% or more.
Hydrochloric acid 500 mg / L (concentrated hydrochloric acid 6.05 mL / 5 L-drainage) is added to the synthetic waste water to obtain raw water, which is passed in the same manner as in Comparative Example 3 to measure the concentration of copper in the reduced treated water flowing out, The selenium concentration of the filtrate after pH adjustment with an aqueous sodium solution was measured.
The copper concentration was 42.2 mg / L and the selenium concentration was 0.91 mg / L. The solid on the filter paper was white. The ratio of the amount of selenium removed to the total amount of zinc and copper eluted is 0.0021.
The results of Examples 1 to 3, Reference Examples 4 to 5, and Comparative Examples 1 to 5 are shown in Table 1.

  As can be seen in Table 1, in Examples 1-5, in which synthetic wastewater containing hexavalent selenium was contacted with an aluminum-tin alloy, aluminum-copper alloy, zinc-tin alloy or zinc-copper mixture, a small amount Treated water with a low selenium concentration is obtained with the amount of metal elution. On the other hand, in Comparative Examples 1 to 5 in which the synthetic waste water containing hexavalent selenium was brought into contact with a single metal of aluminum, zinc, tin or copper, elution of a large amount of metal was required for removing selenium. Yes.

Example 6
The same operation as in Example 1 was repeated to prepare a glass column filled with an Al—Sn alloy.
Glass filled with Al-Sn alloy under the same conditions as in Example 1 by adding hydrochloric acid to flue gas desulfurization waste water containing 0.46 mg / L of selenium and 54 mg / L of fluorine to make hydrogen chloride concentration 2,000 mg / L Water was passed through the column.
The aluminum concentration of the reduced treated water flowing out from the glass column was 382 mg / L, and the tin concentration was 2.1 mg / L. The pH of the reduced treated water flowing out from the glass column was adjusted to 6.8 with an aqueous sodium hydroxide solution, reacted for 10 minutes, and then filtered using No. 5C filter paper. The sludge (SS) on the filter paper was white and had the same color as the gypsum generated in the flue gas desulfurizer. The selenium concentration of the filtered water was 0.01 mg / L or less, and the fluorine concentration was 4.7 mg / L. The ratio of the amount of selenium removed to the total amount of eluted aluminum and tin is 0.0002 or more.
As a result, according to the method of the present invention, selenium in the flue gas desulfurization effluent can be removed to a sufficiently low concentration, and at the same time, the fluorine in the flue gas desulfurization effluent can be removed below a regulation value that can be discharged, and It was revealed that the sludge produced was white and could be recovered by mixing with gypsum.

  According to the method and apparatus for treating selenium-containing wastewater of the present invention, selenium can be reduced with an extremely small amount of metal elution, and is particularly effective for treating wastewater containing hexavalent selenium. In addition, since sludge generated by selecting metal can be white, sludge treatment is easy, and in workplaces where flue gas desulfurization is performed by the lime gypsum method, sludge is collected by mixing with recovered gypsum. be able to. Furthermore, in some cases, flue gas desulfurization wastewater contains fluorine and boron in addition to selenium, but according to the method and apparatus of the present invention, not only selenium but also fluorine and boron can be removed simultaneously.

It is a process flow diagram of one mode of the present invention device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reduction reactor 2 Aggregation reaction tank 3 Solid-liquid separator

Claims (3)

The selenium-containing wastewater containing hexavalent selenium is brought into contact with metal aluminum and an alloy or mixture of a metal having a relatively low ionization tendency than that of the metal aluminum, and an acid is added to the wastewater so that one of the metal aluminum is added. A reduced treated water obtained by reducing hexavalent selenium to tetravalent to zero-valent selenium by eluting the portion, adding alkali to the reduced treated water to precipitate the eluted metallic aluminum as a metal hydroxide, The tetravalent selenium remaining in the reduction treated water is coprecipitated with a metal hydroxide to obtain a coagulation reaction treated water in which the metal hydroxide is precipitated, and the selenium concentration is reduced by solid-liquid separation of the coagulation reaction treated water. A method for treating selenium-containing wastewater, characterized by obtaining treated water .   The method for treating selenium-containing wastewater according to claim 1, wherein the selenium-containing wastewater is flue gas desulfurization wastewater. And metallic aluminum, alloy or mixture of metal having a low higher ionization tendency than said metallic aluminum is present, hexavalent selenium wastewater acid was added to the selenium-containing wastewater in the waste water is introduced containing hexavalent selenium A reduction reactor for reducing the pH , an agglomeration reaction tank into which reduction-treated water flowing out of the reduction reactor is introduced, and a pH adjuster for adjusting the pH to alkalinity by adding alkali as a pH adjuster to the agglomeration reaction tank An apparatus for treating selenium-containing wastewater, comprising addition means and a solid-liquid separation device for solid-liquid separation of the agglomeration reaction treated water sent from the agglomeration reaction tank .

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