JP2009011915A - Selenium-containing wastewater treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a selenium-containing wastewater treatment method and apparatus which can perform the reduction treatment of hexavalent selenium-containing wastewater to effectively remove selenium with a small elution amount of metal, and preferably, generate easily disposable sludge whose color is white. <P>SOLUTION: The selenium-containing wastewater treatment method comprises the wastewater treatment process where selenium-containing wastewater is brought into contact with an alloy or mixture of metallic titanium and other metals, and a part of the other metals is eluted to reduce selenium, and the acid washing process where an acid-containing aqueous solution whose acid concentration is 0.03 N or more is brought into contact with the alloy or mixture. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for treating selenium-containing wastewater, and more specifically, selenium-containing wastewater is reduced using an alloy or a mixture of metal titanium and another metal to effectively remove selenium. 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 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, the pH is adjusted to 8.5 to 10 and the mixture is reacted (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 metal aluminum, the pH is adjusted to 6 or less in selenium-containing waste water, and then copper or iron ions are dissolved, then metal such as metal iron or metal aluminum is added to bring ORP to −350 mV or less, and then to pH 8 to 10 Solid-liquid separation is performed by adjusting (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.
JP-A-6-79286 JP-A-9-187778 JP-A-8-224585

  The present invention provides a method for treating selenium-containing wastewater that can obtain a necessary amount of metal elution when reducing selenium using a metal, and thereby stably and reliably reduce and remove selenium. An object is to provide a processing apparatus. Moreover, this invention aims at providing the processing method and processing apparatus of the selenium containing waste water which can make sludge white when sludge generate | occur | produces in the one aspect | mode.

  In the method for treating selenium-containing wastewater according to the present invention (claim 1), the selenium-containing wastewater is brought into contact with an alloy or a mixture of titanium metal and another metal, and part of the other metal is eluted. It has a waste water treatment process to reduce, and an acid washing process which makes acid containing aqueous solution of acid concentration 0.03N or more contact this alloy or a mixture.

  The selenium-containing wastewater treatment method according to claim 2 is the acid-containing aqueous solution according to claim 1, wherein in the acid cleaning step, the supply of the selenium-containing wastewater to the alloy or mixture is stopped, and the acid concentration is 0.03N or more. In contact with the alloy or mixture.

  The selenium-containing wastewater treatment method according to claim 3 is the acid-containing aqueous solution having an acid concentration of 0.03 N or more obtained by adding an acid to the selenium-containing wastewater in the acid cleaning step according to claim 1. An aqueous solution is contacted with the alloy or mixture.

  A method for treating selenium-containing wastewater according to a fourth aspect is characterized in that, in any one of the first to third aspects, the acid cleaning step is performed first.

  The method for treating selenium-containing wastewater according to claim 5 is the acid cleaning method according to any one of claims 1 to 3, wherein the wastewater treatment step is performed and the selenium reduction treatment performance of the alloy or mixture is lowered. A process is performed.

  The method for treating selenium-containing wastewater according to claim 6 is the method according to any one of claims 1 to 5, wherein, in the wastewater treatment step, the selenium-containing wastewater is brought into contact with an alloy or a mixture of titanium metal and another metal. An acid is added to the selenium-containing wastewater.

  The method for treating selenium-containing wastewater according to claim 7 is the method for treating selenium-containing wastewater according to any one of claims 1 to 6, wherein in the drainage step, after reducing selenium, the eluted metal is adjusted by pH adjustment and precipitated. It is characterized by solid-liquid separation.

  The method for treating selenium-containing wastewater according to claim 8 is characterized in that, in any one of claims 1 to 7, the other metal is at least one selected from aluminum, zinc and tin.

  The method for treating selenium-containing wastewater according to claim 9 is characterized in that, in any one of claims 1 to 8, at least a part of selenium is hexavalent selenium.

  The method for treating selenium-containing wastewater according to claim 10 is characterized in that, in any one of claims 1 to 9, the selenium-containing wastewater is flue gas desulfurization wastewater.

  The method for treating selenium-containing wastewater according to claim 11 is characterized in that, in any one of claims 1 to 10, the selenium-containing wastewater contains fluorine or / and boron, and the other metal is aluminum. To do.

  The selenium-containing wastewater treatment method of the present invention (Claim 12) includes a reduction reactor in which an alloy or a mixture of titanium metal and another metal exists, and selenium-containing wastewater is introduced to reduce selenium in the wastewater. A coagulation reaction tank into which the reduction treated water flowing out from the reduction reactor is introduced, a pH adjusting agent adding 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. A selenium-containing wastewater treatment apparatus comprising: means for supplying an acid-containing aqueous solution to the reduction reactor; and means for adding acid to the selenium-containing wastewater to the reduction reactor or upstream thereof It has the means.

  According to the method and apparatus for treating selenium-containing wastewater of the present invention, since the wastewater is contacted with an alloy or mixture of metal titanium and other metals other than metal titanium, compared to the case of other metal alone or metal titanium alone. Thus, the reducing ability is improved, and selenium can be reduced with a small amount of metal elution. In particular, it is effective for treatment of wastewater containing hexavalent selenium, and selenium is reduced to zero valence and deposited on the metal surface of the alloy or mixture, or reduced to tetravalent or lower selenium and easily deposited. become.

  In addition, according to the method and apparatus for treating selenium-containing wastewater of the present invention, the reducing ability of the alloy or mixture can be improved or recovered by bringing acid into contact with the alloy or mixture.

  That is, the surface of the alloy or mixture may be passivated by an oxide film or the like before being used for wastewater treatment. Moreover, the surface of an alloy or a mixture may be passivated by an oxide film or the like due to the suspension of wastewater treatment for a long time. Furthermore, in the process of wastewater treatment, the reduction performance of the alloy or mixture may be deteriorated due to the contamination of the metal or hydroxide on the surface of the alloy or mixture.

  In such a case, the reducing ability of the alloy or mixture is improved or recovered by removing the passive film or dirt of the alloy or mixture by acid cleaning.

  According to the second aspect, by using an acid-containing aqueous solution containing little selenium and other impurities, the alloy and the mixture can be suitably subjected to acid cleaning.

  According to the third aspect, the acid cleaning of the alloy or the mixture and the reduction treatment of the selenium-containing waste water can be performed together.

  According to the fourth aspect, since the acid cleaning step is first performed, the reduction treatment of the selenium-containing wastewater can be performed with high efficiency in the wastewater treatment step that is subsequently performed.

  According to the fifth aspect, since the acid cleaning step is performed when the reducing performance of the alloy or the mixture is lowered, the reducing performance of the alloy or the mixture can be maintained.

  According to the sixth aspect, the addition of the acid promotes the elution of other metals coexisting with the metal titanium, and the metal elution amount necessary for selenium reduction can be obtained.

  According to claim 7, the pH of the reduced treated water is adjusted so that the eluted metal is precipitated, and then solid-liquid separation is performed, whereby a part of the low-valent selenium remaining in the reduced treated water when the metal is precipitated. Can be precipitated by coprecipitation with the metal and separated from the treated water by solid-liquid separation to obtain treated water from which selenium and metal have been removed.

  According to the eighth aspect, since aluminum, zinc, or tin is used as a metal that coexists with titanium metal, a desired metal elution amount can be obtained. In addition, sludge produced by pH adjustment after elution is not colored sludge in the case of iron, but is white, and in workplaces where flue gas desulfurization is performed by the lime gypsum method, sludge is collected by mixing with recovered gypsum. it can.

  According to claim 9, although hexavalent selenium is contained as selenium in the selenium-containing wastewater, a sufficient amount of metal elution 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 10, the treatment of the flue gas desulfurization waste water can be effectively performed by the present invention. The flue gas desulfurization effluent contains selenium, which is reduced and removed by the present invention. And, if aluminum, zinc or tin is used as another metal as in claim 8, the sludge produced is white and mixed with a large amount of gypsum generated in the flue gas desulfurization apparatus where flue gas desulfurization waste water is generated. And sludge treatment can be reduced.

  According to the eleventh aspect, when fluorine and / or boron coexists in the selenium-containing wastewater, selenium can be reduced with the eluted aluminum, and selenium, fluorine, and boron can be insolubilized simultaneously with the precipitation of the eluted aluminum. Therefore, it is not necessary to provide a separate water treatment device for removing fluorine and boron.

  According to the selenium-containing wastewater treatment apparatus of the present invention (claim 12), the wastewater is brought into contact with an alloy or a mixture of metal titanium and another metal other than metal titanium, so that other metal alone or metal titanium alone Compared with the above case, the reducing ability is improved, and selenium can be reduced with a small amount of metal elution. In particular, it is effective for treatment of wastewater containing hexavalent selenium, and selenium is reduced to zero valence and deposited on the metal surface of the alloy or mixture, or reduced to tetravalent or lower selenium and easily deposited. become. Then, the pH of the reduced treated water is adjusted so that the eluted metal precipitates, and then solid-liquid separation is performed, so that when the metal is precipitated, a part of the low-valent selenium remaining in the reduced treated water is coprecipitated with the metal. It is possible to obtain treated water from which selenium and metal have been removed by being precipitated by the phenomenon and separated from the treated water by solid-liquid separation.

  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 contains selenium as hexavalent selenium such as selenic acid and tetravalent selenium such as selenious acid, for example, smelting effluent from a nonferrous metal refining process, Examples include flue gas desulfurization effluent from coal flue gas desulfurization process, various factory effluents from factories using selenium as a raw material and additive.

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

  The selenium wastewater treatment method according to the present embodiment includes a wastewater treatment step and an acid cleaning step.

  In the wastewater treatment step, selenium-containing wastewater is brought into contact with an alloy or mixture of titanium metal and another metal, and selenium is reduced by eluting a part of the other metal. Since most of the reduced selenium precipitates on the metal surface, the treated water can be treated water. However, if necessary, after the reduction treatment, the pH is adjusted to precipitate the eluted metal, which is separated by solid-liquid separation. Remove the metal to make treated water.

  On the other hand, in the acid cleaning step, an acid-containing aqueous solution having an acid concentration of 0.03 N or more is brought into contact with the alloy or the mixture. This acid-containing aqueous solution removes the passive film and dirt on the surface of the alloy or mixture.

  As this acid-containing aqueous solution, an acid added to selenium-containing wastewater to have an acid concentration of 0.03 N or more may be used. In this case, the selenium-containing waste water can be reduced simultaneously with the acid cleaning of the alloy or the mixture. As the acid-containing aqueous solution, an acid concentration of 0.03 N or more may be used by adding an acid to industrial water or clean water instead of the selenium-containing waste water. In this case, since the content of impurities such as selenium is small in the acid-containing aqueous solution, it is possible to suitably perform acid cleaning of the alloy or the mixture. This acid washing step may be performed before the wastewater treatment step is performed, after the wastewater treatment step is performed, or both. When the acid cleaning step is performed after the wastewater treatment step, the acid cleaning step is preferably performed every time the selenium reduction performance of the alloy or the mixture is lowered in the wastewater treatment step.

  In this reduction treatment, an alloy or a mixture of titanium metal and another metal other than titanium metal is used. Various metals can be used as the metal to be alloyed with or mixed with titanium metal, but it is preferable that the sludge composed of hydroxide generated by pH adjustment after metal elution exhibits a white color. When the sludge is white, it is easier to dispose of the sludge than when it is colored brown or the like. Examples of metals that generate white sludge include aluminum, zinc, tin, and copper, which can be used. In particular, aluminum, zinc, and tin are excellent in terms of solubility, and can be suitably used in the present invention. As the metal other than metal titanium, only one kind of metal may be used, but a mixture or alloy of two or more kinds of metals may be used.

  As an alloy of titanium metal and another metal used in the present invention, any of a solid solution, an intermetallic compound, and a covalent alloy can be used. As an alloying method, for example, a method using a difference in ionization tendency of metal, an electrolytic method, a melting method, or the like can be employed.

  Moreover, in this invention, metal titanium and another metal can also be used as a mixture, without alloying. Metal titanium in the form of powder, granule, fiber, etc. and other metal in the form of powder, granule, fiber, etc., mixed in the same form or different Forms can be mixed into a mixture.

  The shape of the alloy or mixture of titanium and another metal is preferably one having a large surface area. For example, it is used as a powdery material, a granular material, a fibrous material, a fine thin film, or the like having a particle size of about 10 μm to 5 mm.

  There is no restriction | limiting in the method of contacting a selenium containing waste_water | drain with the alloy or mixture of titanium and another metal, It can contact with arbitrary types of reduction reactors. The reduction reactor may be, for example, a reduction reaction tank in which selenium-containing wastewater is introduced into the reaction tank and a powdered, fine-grained alloy or mixture is added. It is also possible to use a packed tower in which waste water is passed through the packed bed.

  When the selenium-containing wastewater is brought into contact with an alloy or mixture of titanium metal and another metal, the other metal is eluted and dissolved in the wastewater. When the metal elutes into ions, a strong reducing action occurs, and selenium in the wastewater is reduced. Since this metal elution is neutral and takes a long time, it is preferable to promote acid elution by adding an acid to the selenium-containing wastewater. 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.

  The acid added to the selenium-containing wastewater also has an action of removing the passive film on the surface of the alloy or mixture. In particular, when the selenium concentration in the selenium-containing wastewater is high and the treatment conditions are such that the acid concentration in the selenium-containing wastewater is 0.03 N or more, the acid cleaning effect on the surface of the alloy or mixture is high.

  Metals other than selenium eluted in the selenium-containing wastewater, such as aluminum and zinc, are considered to react with selenate ions as shown below 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 present invention, when contact is made with wastewater under the coexistence state by alloying or mixing of metal titanium and another metal, the selenium reduction treatment performance is greatly improved as compared with the treatment by single contact of metal titanium or other metal. The reason for this is that metals other than titanium such as aluminum and zinc dissolve, electrons move through titanium that hardly dissolves even in the presence of an acid, and selenium is reduced on the titanium surface. At that time, there is a possibility that some electrical effect is manifested.

  The ratio T / M between the volume T of the metal titanium and the volume M of the other metal is preferably 1/3 or more, particularly preferably 1/2 or more. When the ratio T / M is 1/3 or more, the selenium reduction performance is improved. The reason for this is that since the proportion of titanium metal is high, the amount of electrons generated during the dissolution of other metals moves to the surface of the titanium metal, and the amount of selenium reduced on the surface of the metallic titanium increases. It is thought that it is to do. On the other hand, when the ratio T / M is less than 1/3, the ratio of titanium metal is low, and thus electrons generated during dissolution of other metals are emitted from the surface of the other metals. It is considered that the performance of selenium reduction treatment decreases because the amount of electrons that increase and the amount of electrons that move to the metal titanium surface and contribute to the reduction of selenium decreases.

  When the filling capacity of other metals is constant and the ratio T / M is increased, a good reduction treatment performance is maintained, but a large amount of titanium metal is required, and these other metals and metals The volume of the titanium filling device needs to be increased. For this reason, this ratio T / M is preferably 3/1 or less, particularly 1/1 or less. More preferably, this ratio T / M is 1/3 to 3/1, in particular 1/2 to 1/1.

  In the present invention, the other metal is preferably aluminum. Further, when the volume of titanium metal is T and the volume of aluminum is A, when T / A is 1/3 to 3/1, particularly 1/2 to 2/1, selenium is removed very efficiently. Can do.

  Reduced selenium, for example hexavalent selenium, becomes mostly zero-valent selenium, which is deposited on the titanium surface of the alloy or mixture and removed from the waste water. Residual selenium is reduced from hexavalent to low valent selenium, for example, tetravalent selenium, and is easily precipitated by agglomeration.

  In the present invention, it is preferable to subject the selenium-containing wastewater to a reduction treatment and then a reduction treatment of the reduction-treated water. The agglomeration treatment is performed by adjusting the pH of the reduction treatment water, precipitating the eluted metal as an insoluble compound such as hydroxide, and solid-liquid separation of the precipitated metal compound.

  The pH of the reduced water is usually adjusted by adding an alkali such as sodium hydroxide, potassium hydroxide or slaked lime. When the metal used with the metal titanium is aluminum, an alkali is added to the reduction-treated water, and the 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. When the metal used together with titanium metal is zinc, the pH is adjusted to 9 to 10, and when it is tin, it is precipitated as a hydroxide by adjusting the pH to around 8.

  When the metal compound is precipitated by adjusting the pH, an organic flocculant and an inorganic flocculant can be added to improve solid-liquid separation.

  In order to separate the precipitated metal compound from water, a solid-liquid separation operation is performed. For solid-liquid separation, any commonly used method can be adopted, and separation into treated water and sludge composed of an insoluble metal compound is performed by precipitation, filtration, centrifugation, membrane separation, or the like.

  The metal eluted during the reduction treatment is insolubilized by pH adjustment and solid-liquid separation of the reduced treated water, separated from the water, and discharged as treated water containing no metal. Further, when the eluted metal is precipitated as an insoluble compound, for example, aluminum hydroxide, reduced low-valent selenium remaining in the water is also adsorbed on the aluminum hydroxide flocs and is precipitated by a coprecipitation phenomenon.

  In addition, when fluorine and / or boron coexist in the selenium-containing wastewater, when aluminum is used as the metal to be used with the metal titanium, when aluminum hydroxide is precipitated by pH adjustment after the reduction treatment, fluorine and / or boron is also present. Precipitated by coprecipitation phenomenon.

  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
Selenium removal by coprecipitation with calcium aluminate has a better selenium removal effect than aluminum hydroxide. 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.

  In the present invention, after the steps of reduction treatment, metal precipitation by pH adjustment, and solid-liquid separation, it is separated into treated water and sludge containing precipitated metal compound, selenium, and optionally fluorine and boron. By selecting the metal to be used together with titanium metal, the sludge generated by solid-liquid separation is white, so it can be collected and mixed with gypsum generated in the flue gas desulfurization equipment, reducing sludge disposal. Is done.

  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. 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 device, and 6 is pH adjustment. It is an agent addition means.

  The reduction reactor 1 is a packed tower filled with an alloy or mixture of titanium metal and another metal inside, and a support plate is arranged in the lower part of the tower, and particles of the alloy or mixture are packed on the support plate. Thus, the metal filling layer 11 is formed. The support plate has a structure that allows water to flow but prevents the passage of metal particles, and a perforated plate or a strainer is used. As described above, preferably, the other metal is aluminum, and the volume ratio T / A between titanium metal and aluminum is 1/3 to 3/1, particularly 1/2 to 2/1.

  Below the support plate is a drainage inflow chamber 12, and a drainage supply pipe 4 is opened in the drainage inflow chamber 12. Above the metal packed bed 11 is a reduction treatment water chamber, and a conduit 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 waste water supply pipe 4 so that acid can be injected into the selenium-containing waste water. The acid addition device 5 can also inject the acid-containing aqueous solution into the reduction reactor 1 through the drainage supply pipe 4 in a state where the supply of the selenium-containing drainage to the drainage supply pipe 4 is stopped. It has become. The acid addition device may be provided so as to add the acid or the acid-containing aqueous solution to the drainage inflow chamber 12 instead of the drainage supply pipe 4.

  The reduction reactor 1 is preferably a reaction vessel that can be shut off to the atmosphere so that the reduction reaction occurring in the reactor can be performed in a reducing atmosphere.

  The reduction reactor 1 is provided with a metal alloy or mixture inlet that can be opened and closed at an arbitrary position, for example, on the upper wall of the reactor, so that the metal can be filled into the reactor at any time.

  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 aggregation reaction tank 2 may be a commonly used aggregation reaction tank. The agglomeration reaction tank 2 communicates with a pipe line for introducing the reduction treated water flowing out from the reduction reactor 1 and a pH adjusting agent adding means 6 for introducing a pH adjusting agent. A stirring device is provided in the reaction tank 2 so that a uniform agglomeration reaction occurs. The reaction tank 2 is connected to a conduit for transferring the flocculated water to the solid-liquid separator 3.

  The solid-liquid separator 3 is connected to a treated water pipe for discharging treated water generated by solid-liquid separation and a sludge discharge path for discharging separated sludge. The solid-liquid separator 3 shown in FIG. 1 is a precipitation tank, but other solid-liquid separators such as a membrane separator may be used.

  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.

  Next, a method for treating selenium-containing wastewater by the treatment apparatus of FIG. 1 configured as described above will be described. In this description, it is assumed that the metal packed bed 11 is filled with a mixture of granular metal titanium and granular metal aluminum in the reduction reactor 1.

<Wastewater treatment process>
The selenium-containing wastewater is introduced into the reduction reactor 1 through the wastewater supply pipe 4 after the acid is injected and mixed from the acid addition device 5. When the selenium-containing wastewater contains turbidity, contaminants such as heavy metals other than selenium, organic matter, etc., before being introduced into the reduction reactor, the wastewater is preliminarily treated, for example, a coagulation device, a filtration device, a membrane separation device, It is desirable to remove coexisting contaminants by passing water through a pretreatment device (not shown) such as an activated carbon adsorption device.

  The wastewater introduced into the wastewater inflow chamber 12 of the reduction reactor 1 flows in an upward flow in the reactor 1 and contacts the metal packed bed 11. At this time, the acid injected into the waste water promotes dissolution of the metal aluminum. Metal aluminum is smoothly eluted according to the amount of acid present, and reducing power is generated during the dissolution. Selenium in waste water, particularly hexavalent selenium, is reduced by the reducing power when aluminum is eluted. Reduced selenium is reduced from tetravalent to zero. It is estimated that most of the reduced zero-valent selenium is deposited on the surface of the titanium metal of the metal filling layer 11.

  The reaction temperature and water flow rate are not particularly limited, but the selenium concentration in the treated water decreases as the temperature increases and the water flow rate decreases. For this reason, it is desirable to heat the temperature of waste water to about 50-70 degreeC, and it is preferable that a water flow rate shall be SV1-30 (1 / h). Also in the acid cleaning step described later, the higher the temperature, the higher the rate at which the alloy or mixture is activated by the acid cleaning. For example, when acid cleaning is performed by heating the acid-containing aqueous solution to 50 ° C. or higher, the alloy or mixture can be activated at a water flow rate of SV15 (l / h) and a water flow time of 3 hours or less. .

  The reduced treated water containing a part of the reduced selenium is transferred from the reduced treated water chamber in the upper part of the reduction reactor 1 to the agglomeration reaction tank 2 through a pipeline. Alkali is supplied from the pH adjuster adding means 6 to the reduction treated water introduced into the agglomeration reaction tank 2 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.

  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. In the precipitation tank which is the solid-liquid separator 3, the selenium that has been insolubilized and co-precipitated with the precipitated aluminum compound is precipitated and discharged as sludge from the sludge discharge path at the bottom of the precipitation tank 3, and the supernatant water at the top of the precipitation tank is treated. It is taken out from the treated water pipe as water. The treated water is subjected to post-treatment such as pH adjustment, removal of residual suspension, removal of residual COD as necessary, and then discharged or recovered.

  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 when aluminum, zinc, tin or the like is used as another metal, and the gypsum slurry generated in the flue gas desulfurization device generated in the flue gas desulfurization device, and the separated sludge Can be recovered by mixing and dewatering with a dehydrator, and sludge disposal is reduced.

<Acid cleaning process>
Supply of selenium-containing wastewater from the wastewater supply pipe 4 to the reduction reactor 1 is stopped, and an acid-containing aqueous solution having an acid concentration of 0.03 N or more is supplied from the acid addition device 5 into the reduction reactor 1 through the wastewater supply pipe 4 To do. With this acid-containing aqueous solution, the mixture in the reduction reactor 1 is acid-washed, and the passive film and dirt on the surface of the mixture are removed. Thereafter, the acid-containing aqueous solution is taken out from the reduction reactor 1.

  In the acid washing step, the supply of the selenium-containing wastewater to the reduction reactor 1 was stopped, and an acid-containing aqueous solution having an acid concentration of 0.03 N or more was supplied from the acid addition device 5 to the reduction reactor 1. In the waste water treatment step, the acid addition amount from the acid addition device 5 to the selenium-containing waste water is increased so that the acid concentration in the selenium-containing waste water is 0.03 N or more, and this may be the acid cleaning step.

  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
A column having an inner diameter of 25 mm is prepared by mixing 10 ml (14.4 g) of metal titanium having a particle diameter of 2 to 5 mm and a purity of 99% or more and 20 ml (34.8 g) of metal aluminum having a particle diameter of 1 to 2 mm and a purity of 99.5%. Filled.

  Hydrochloric acid was added to flue gas desulfurization effluent containing 1.3 mg / l of selenium to a concentration of 0.03 N, and water was passed through this column at a flow rate of SV15 (l / h) while heating to 60 ° C. Caustic soda was added to the column outlet water to adjust the pH to around 7, and after reaction for 10 minutes, NO. Filtered with 5C filter paper. The selenium concentration and aluminum concentration in the column outlet water and the selenium concentration in the treated water were measured.

  The selenium concentration in the treated water is stable from 0.01 mg / l or less to 0.06 mg / l (average 0.027 mg / l) until 100 hours have passed since the start of water flow, and the treatment performance is completely degraded. I did not. The aluminum concentration in the column outlet water was 156 to 172 mg / l, and no decrease in the aluminum concentration was observed.

Example 2
Under the same conditions as in Example 1, a column was filled with a mixture of metallic titanium and metallic aluminum. Hydrochloric acid was added to flue gas desulfurization waste water containing 1.2 mg / l of selenium so as to have a concentration of 0.03 N, and water was passed for 3 hours under the same conditions as in Example 1.

  Thereafter, the amount of hydrochloric acid added was reduced so that the concentration of hydrochloric acid in the flue gas desulfurization effluent became 0.008 N, and water flow was continued. The selenium concentration and aluminum concentration in the column outlet water and the selenium concentration in the treated water were measured.

  The selenium concentration in the treated water was stable at 0.33 to 0.42 mg / l (average 0.36 mg / l) until 20 hours passed after the hydrochloric acid concentration was reduced to 0.008N, and the treatment performance was It did not drop at all. The aluminum concentration in the column outlet water was 68 to 76 mg / l, and no decrease in the aluminum concentration was observed.

Example 3
The test and measurement were performed under the same conditions as in Example 2 except that the concentration of hydrochloric acid in the flue gas desulfurization effluent after passing water for 3 hours was set to 0.016N instead of 0.008N.

  The selenium concentration in the treated water is stable at 0.09 to 0.13 mg / l (average 0.11 mg / l) until 20 hours have passed since the hydrochloric acid concentration was reduced to 0.016 N, and the treatment performance was It did not drop at all. The aluminum concentration in the column outlet water was 150 to 155 mg / l, and no decrease in the aluminum concentration was observed.

Comparative Example 1
Tests and measurements were performed under the same conditions as in Example 2 except that the concentration of hydrochloric acid in the flue gas desulfurization effluent was 0.008 N from the beginning of water flow.

  The selenium concentration in the treated water after 5 hours from the start of water flow was 0.36 mg / l, but the selenium concentration gradually increased, and the selenium concentration in the treated water after 20 hours from the start of water flow was 0.00. It was 78 mg / l. The aluminum concentration in the column outlet water was 68 to 71 mg / l.

Comparative Example 2
Tests and measurements were performed under the same conditions as in Example 3 except that the concentration of hydrochloric acid in the flue gas desulfurization effluent was 0.016 N from the beginning of water flow.

  The selenium concentration in the treated water after 5 hours from the start of water flow was 0.09 mg / l, but the selenium concentration gradually increased, and the selenium concentration in the treated water after 20 hours from the start of water flow was 0.00. 27 mg / l. The aluminum concentration in the column outlet water was 137 to 150 mg / l.

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 separation apparatus 4 Drainage supply pipe 5 Acid addition apparatus 6 pH adjuster addition means 11 Metal packed bed 12 Drainage inflow chamber

Claims (12)

A wastewater treatment step of reducing the selenium by bringing the selenium-containing wastewater into contact with an alloy or mixture of titanium metal and another metal and eluting a part of the other metal;
A method for treating selenium-containing wastewater, comprising: an acid cleaning step of bringing an acid-containing aqueous solution having an acid concentration of 0.03 N or more into contact with the alloy or the mixture.   2. The acid washing step according to claim 1, wherein the supply of the selenium-containing wastewater to the alloy or mixture is stopped, and the acid-containing aqueous solution having an acid concentration of 0.03 N or more is brought into contact with the alloy or mixture. To treat selenium-containing wastewater.   2. The acid cleaning step according to claim 1, wherein an acid is added to the selenium-containing wastewater to form an acid-containing aqueous solution having an acid concentration of 0.03 N or more, and the acid-containing aqueous solution is brought into contact with the alloy or the mixture. A method for treating selenium-containing wastewater.   The method for treating selenium-containing wastewater according to any one of claims 1 to 3, wherein the acid cleaning step is first performed.   The selenium-containing wastewater according to any one of claims 1 to 3, wherein the wastewater treatment step is carried out, and the acid washing step is carried out when the selenium reduction treatment performance of the alloy or mixture is lowered. Processing method.   In any 1 item | term of the Claims 1 thru | or 5, in the said waste water treatment process, when making a selenium containing waste water contact with the alloy or mixture of metal titanium and another metal, an acid is added to a selenium containing waste water, It is characterized by the above-mentioned. A method for treating selenium-containing wastewater.   The selenium-containing wastewater according to any one of claims 1 to 6, wherein, in the drainage step, after reducing selenium, the eluted metal is pH-adjusted and precipitated, and the precipitated metal is solid-liquid separated. Processing method.   The method for treating selenium-containing wastewater according to any one of claims 1 to 7, wherein the other metal is at least one selected from aluminum, zinc, and tin.   The method for treating selenium-containing wastewater according to any one of claims 1 to 8, wherein at least a part of selenium is hexavalent selenium.   The method for treating selenium-containing wastewater according to any one of claims 1 to 9, wherein the selenium-containing wastewater is flue gas desulfurization wastewater.   The method for treating selenium-containing wastewater according to any one of claims 1 to 10, wherein the selenium-containing wastewater contains fluorine and / or boron, and the other metal is aluminum. There is an alloy or mixture of titanium metal and another metal, a selenium-containing wastewater is introduced, a reduction reactor for reducing selenium in the wastewater, and agglomeration in which the reduction-treated water flowing out from the reduction reactor is introduced A selenium-containing wastewater treatment apparatus having a reaction tank, a pH adjuster addition means for adjusting the pH of the aggregation reaction tank, and a solid-liquid separation apparatus for solid-liquid separation of the aggregation reaction treated water,
A selenium-containing wastewater characterized by comprising at least one of a means for supplying an acid-containing aqueous solution to the reduction reactor and a means for adding an acid to the selenium-containing wastewater at or upstream of the reduction reactor. Processing equipment.

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