JP2006095519A - Treating method and treating apparatus for heavy metals-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating system with which heavy metals are efficiently and economically removed from heavy metals-containing water. <P>SOLUTION: The treating method for the heavy metals-containing water has an iron compound addition step of adding a reducing iron compound to the heavy metals-containing water, a precipitation step of leading the heavy metals-containing water to which the reducing iron compound is added to a reaction tank and forming a precipitate, a solid-liquid separation step of separating the formed precipitate (sludge) by solid-liquid separation and a sludge return step of alkalinizing all or a portion of the separated sludge to form alkaline sludge and returning it to the reaction tank. In the precipitation step, a sealed reaction tank is used, and an open type alkali addition tank is used in the sludge return step, and the return sludge to which alkali is added under open conditions is introduced into the sealed reaction tank and is blended with the heavy metals-containing water to which the reducing iron compound is added, and the obtained alkaline mixture is allowed to react in a non-oxidizing atmosphere under an alkaline condition to form a reducing iron compound precipitate, thereby incorporating heavy metals in the precipitate to remove them out of the system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an economical treatment system that efficiently removes heavy metals from water containing heavy metals. More specifically, the present invention relates to a system for treating heavy metal-containing water that is simple and excellent in practicality, has a compact sludge, and can efficiently remove heavy metals in waste water at room temperature. .

Selenium is known as an example of heavy metals contained in waste water and the like. Usually, selenium contained in waste water or the like exists in the form of selenite ion [SeO ₃ ^2- ] (tetravalent selenium) or selenate ion [SeO ₄ ^2- ] (hexavalent selenium). This selenium is a pollutant and its emission standards are strictly regulated. Conventionally, as a method for removing selenium contained in wastewater, (i) a method in which a trivalent iron compound such as ferric hydroxide is added and selenium is adsorbed to the precipitate by coagulation, and (b) barium There are known a method of forming a poorly soluble selenate precipitate by adding lead or lead, (c) a method of adsorbing and removing selenium using an ion exchange resin, and (d) a biological treatment method.

However, since precipitation with barium or lead is easily affected by coexisting ions, a large amount of addition is required, and since barium and lead are also heavy metals, a burden of post-treatment arises. Further, the method using an ion exchange resin has a problem that the removal effect is drastically reduced if sulfate ions or the like are present. Furthermore, the biological treatment method takes a long time. On the other hand, the method using a trivalent iron compound has little effect on hexavalent selenium. Therefore, a method using ferrous salt (divalent iron) has been proposed.

In this method, precipitation of selenium is promoted by reducing hexavalent selenium to tetravalent selenium by utilizing the reducing power of ferrous iron. For example, divalent iron ions are added to selenium-containing wastewater, and then There is known a treatment method in which a liquid temperature is maintained at 30 ° C. or higher while maintaining an air-blocking environment, and alkali is added to produce selenium starch (Patent Document 1). In addition, the first step of adding alkali to the selenium-containing wastewater to precipitate heavy metal hydroxides, and introducing an inert gas into the treatment liquid to remove dissolved oxygen, and then adding ferrous salt in the alkaline region And a second step of adding and reducing selenium and precipitating, and a third step of blowing air into the treatment liquid and taking in heavy metals remaining in the liquid into the iron-containing precipitate and precipitating. Known (Patent Document 2). Besides this, ferrous hydroxide is added to the selenium-containing wastewater, and further alkali is added to produce a selenium-containing precipitate, while a part of the sludge is circulated to the reaction tank after the addition of alkali to increase the processing efficiency. A processing method is known (Patent Document 3).

However, it is difficult to reduce the selenium concentration in the waste water to an environmental standard value of 0.01 mg / L or less in any of the above-described conventional treatment methods. Further, in the method of simply adding ferrous hydroxide, oxygen in the wastewater competes with selenium and reacts with ferrous ions, so it is necessary to remove dissolved oxygen in the wastewater in advance, and the treatment process is troublesome. Furthermore, since precipitation of ferrous hydroxide has a large water content and becomes bulky, the burden on slurry processing is large as it is. In addition, a method is known in which a part of the generated precipitate is circulated to the reaction vessel. However, even if the generated precipitate is simply circulated, the precipitation compaction effect is low, and the post-treatment is burdened. Moreover, many of the conventional treatment methods have the problem that ferrous hydroxide is heat-treated to form iron ferrite, and the treatment process is complicated and the heating cost increases.

In addition, ferrous ions etc. are added to heavy metal wastewater, adjusted to pH 5 or higher to produce iron ferrite or pseudo iron ferrite, and the generated ferrite sludge is separated into solid and liquid, and part of it is returned to the reaction tank And the processing method which removes heavy metals from waste water by circulating sludge is known (patent document 4). This method pays attention to the fact that ferrite sludge (FeO · Fe ₂ O ₃ ) contains ferrous iron and ferric iron. Ferrite sludge is easier to form with ferrous iron and ferric iron than ferrous alone. However, the ferrite sludge of this method has a weak reducing power, and even if this sludge is returned to the reaction tank, the effect of removing heavy metals is limited.

On the other hand, in the wastewater treatment method of adding sludge by adding alkali to water containing heavy metals and separating this sludge, alkali is not added directly to the heavy metal wastewater, but alkali is added to a part of the separated sludge. A processing method for returning the alkaline sludge to the reaction tank is known (Patent Documents 5 and 6). However, it is difficult to reduce heavy metals below the environmental standard value with alkaline sludge alone.
Japanese Patent Laid-Open No. 08-267076 JP 2002-326090 A JP 2001-9467 A Japanese Patent Laid-Open No. 2001-321781 Japanese Patent Publication No. 61-156 Japanese Patent Laid-Open No. 05-57292 (Japanese Patent No. 2910346)

The present invention improves the treatment method based on the conventional ferrite method using a ferrous salt and solves the above problems. The precipitate is consolidated, the solid-liquid separability is good, and the ferrite treatment is performed at room temperature. Therefore, the present invention provides a treatment method that is excellent in economic efficiency and treatment effect, and that can reduce the concentration of heavy metals to an environmental standard value of 0.01 mg / L or less.

The present invention relates to the following methods for treating heavy metal-containing water.
(1) A step of adding a reducing iron compound to heavy metal-containing water [iron compound addition step], a step of introducing a heavy metal-containing water added with a reducing iron compound to a reaction vessel to generate a precipitate [precipitation step] A process for solid-liquid separation of the generated precipitate (sludge) (solid-liquid separation process), a process for converting all or part of the separated sludge to alkalinity and returning it to the reaction tank (sludge return process) In addition, a closed reaction vessel is used in the precipitation step, an open type alkali addition vessel is used in the sludge return step, and the return sludge to which alkali has been added in the open state is introduced into the reaction vessel in the closed state, and the reducing iron compound is introduced. It is mixed with the added heavy metal-containing water and reacted in a non-oxidizing atmosphere and under alkaline conditions to form a reduced iron compound precipitate, and the heavy metal is taken into the precipitate and removed out of the system. How to process .
(2) By adjusting the opening area of the alkali addition tank, the oxidation of the iron compound caused by contact with the air interface is controlled, and the precipitation generation of the sealed reaction tank in which the alkaline return sludge containing this iron compound is introduced is adjusted. Processing method of (1).
(3) The reducing iron compound precipitate produced in the reaction tank is a mixture of green last and iron ferrite, and the ratio of the divalent iron ions to total iron ions in the precipitate [Fe ²⁺ / Fe (T)] The processing method according to the above (1) or (2), wherein the precipitate is formed so as to be 0.4 to 0.8.
(4) The pH of the alkaline sludge to be returned to the reaction tank is adjusted to 11 to 13, the pH in the reaction tank in which the alkaline sludge is mixed is adjusted to 8.5 to 11, and the reducing property is reduced in a non-oxidizing atmosphere. The processing method according to any one of (1) to (3) above, wherein an iron compound precipitate is formed.
(5) The ferrous compound is used as the reducing iron compound, and a precipitate is produced in a closed reaction tank under a non-oxidizing atmosphere at a liquid temperature of 30 ° C. or lower. Processing method.
(6) In the above treatment method, before the iron compound addition step, by adding an iron compound or an aluminum compound to heavy metal-containing water and precipitating iron or aluminum hydroxide under alkalinity, silicate ions, Precipitating step of precipitating at least one of aluminum ions and trace organic substances together with the hydroxide, and removing the precipitate by filtration. About the heavy metal-containing water from which the precipitate has been removed, the reducing iron compound adding step, The method for treating heavy metal-containing water according to any one of the above (1) to (5), wherein each treatment of the precipitation step, the solid-liquid separation step, and the sludge return step is performed.
(7) After solid-liquid separation of a precipitate formed by adding an iron compound or an aluminum compound to heavy metal-containing water, a ferrous compound is added to the heavy metal-containing water, and the heavy metal to which the ferrous compound is added Water is introduced into a closed reaction tank, while alkali is added to a part or all of the sludge that has been extracted from the reaction tank and separated into solid and liquid to open the sludge to a pH of 11-13. It returned to the said reaction tank, and it was made to react for 30 minutes-3 hours under the non-oxidizing atmosphere which interrupted | blocked air, the temperature of 30 degrees C or less, and the liquidity of pH 8.5-11, and produced | generated. While solid-liquid separation of the precipitate (sludge), part or all of the precipitate is alkalized and returned to the above reaction tank, and the heavy metal concentration of the heavy metal-containing water separated by solid-liquid separation is 0.01 mg / L or less (1) to (6) what to reduce to Processing method of heavy metal containing water described crab.
(8) The method for treating heavy metal-containing water according to any one of the above (1) to (7), wherein the concentration of the contained heavy metal is reduced to 0.01 mg / L or less.
(9) For sludge separated in the solid-liquid separation means, sludge that is not returned to the reaction tank is filtered and dehydrated, and water is discharged out of the system. The method for treating heavy metal-containing water according to any one of the above (1) to (8), wherein force is used to decompose pollution contained in the drainage or the like.

Moreover, this invention relates to the processing apparatus of the following heavy metal containing water.
(10) A tank for adding ferrous compounds to heavy metal containing water, a non-oxidizing atmosphere sealed reaction tank for reacting heavy metals containing water added with ferrous compounds, and a slurry extracted from the reaction tank A means for separating, an open type alkali addition tank for adding alkali to the separated sludge, a pipe for returning the alkaline sludge to the reaction tank, a pipe for communicating each of these tanks and the solid-liquid separation means, An apparatus for treating heavy metal-containing water, wherein the treatment system of 1) is formed.
(11) In the processing apparatus of (10), before the tank for adding the reducing iron compound to the heavy metal-containing water, the tank for adding the iron compound or the aluminum compound to the heavy metal-containing water, and the generated precipitate An apparatus for treating heavy metal-containing water having solid-liquid separation means.

[Specific description]
The treatment method of the present invention includes a step of adding a reductive iron compound to heavy metal-containing water [iron compound addition step], a step of introducing a heavy metal-containing water to which the reductive iron compound has been added to a reaction vessel to generate a precipitate [ (Precipitation step), solid-liquid separation of the generated precipitate (sludge) (solid-liquid separation step), and treatment (sludge return step) in which all or part of the separated sludge is made alkaline and returned to the reaction tank In this method, a closed reaction tank is used in the precipitation step, an open type alkali addition tank is used in the sludge return step, and the return sludge to which alkali has been added in the open state is introduced into the closed reaction tank for reduction. Mixed with water containing heavy metals to which a ferrous iron compound has been added and reacted in a non-oxidizing atmosphere and under alkaline conditions to form a reduced iron compound precipitate, which is then taken out of the system by incorporating heavy metals into the precipitate. Special Is a processing method to be.

In the present invention, heavy metal-containing water broadly means water containing heavy metals, and includes various wastewater and wastewater generated naturally and artificially, such as factory wastewater and sewage, seawater, river water, This refers to water from marshes and lakes, surface pools, rivers and other dams, underground running water and pools, underdrains, etc. that contain heavy metals. In the following description, these waters may be referred to as waste water, and the heavy metal containing water may be referred to as waste water containing heavy metals.

In the present invention, heavy metals refer to heavy metal elements such as selenium, cadmium, hexavalent chromium, lead, zinc, copper, nickel, arsenic, and antimony, and metal elements. The treatment system of the present invention has an excellent removal effect with respect to any one or more of the heavy metals that are the sources of contamination contained in the waste water and the like.

The outline of this processing system is shown in FIG. As shown in the figure, the present processing system includes a tank 10 for adding a reducing iron compound to heavy metal-containing water, a sealed reaction tank 30 in a non-oxidizing atmosphere for reacting heavy metal-containing water added with a reducing iron compound, and the reaction. Means 40 for solid-liquid separation of the slurry extracted from the tank 30, an open-type alkali tank 20 for adding alkali to the separated sludge, pipes for returning the alkaline sludge to the reaction tank 30, each of these tanks and solid-liquid separation means It has a pipe line that communicates. In the treatment system shown in FIG. 1, it is preferable to install two or more reaction tanks 30 in series, to form a sealed structure purged with nitrogen, and to perform the ferritization treatment in a reducing atmosphere.

In the treatment system of the present invention, the heavy metal-containing water is guided to the addition tank 10 and the reducing iron compound is added. As the reducing iron compound, ferrous compounds such as ferrous sulfate (FeSO ₄ ) and ferrous chloride (FeCl ₂ ) can be used. The addition amount of the ferrous compound is appropriate such that the Fe ²⁺ ion concentration is 400 to 600 mg / L. Heavy metal-containing water to which the reducing iron compound is added is introduced into the reaction tank 30.

Alkaline sludge is returned to the reaction tank 30 from the solid-liquid separation step together with the heavy metal-containing water to which the reducing iron compound is added, and mixed with the heavy metal-containing water. This alkaline sludge is adjusted to pH 11 to 13 by adding alkali to a part or all of the precipitate (sludge) separated into solid and liquid in the subsequent step. As the alkaline substance to be added, slaked lime, quick lime, sodium hydroxide or the like can be used. By mixing the alkaline sludge, the pH of the reaction tank 30 is adjusted to 8.5 to 11, preferably pH 9.0 to 10.

In the reaction tank 30, heavy metal-containing water to which a reducing iron compound is added and alkaline return sludge are mixed and reacted in a non-oxidizing atmosphere to generate a reducing iron compound precipitate. This iron compound precipitate is a mixture of green last and iron ferrite and is a reductive precipitate.

Green last is a blue-green substance in which a hydroxide of ferrous iron and ferric iron forms a layer, and has a structure in which an anion of heavy metals is incorporated between layers, and is represented by, for example, the following formula (1).
_{^{[Fe II (6-x) Fe}} III x (OH) 12 ] ^{x +} [A _x / n · yH ₂ O] ^x- ... (1)
(0.9 <x <4.2, Fe ²⁺ / total Fe = 0.3 to 0.85).

Moreover, iron ferrites are Fe ^II iron (III) salt, but mainly of magnetite _{^{(Fe II Fe III 3 O 4}} ), or those containing ferrate heavy metals in a part. In the reducing iron compound precipitate of the present invention, for example, heavy metal ions in water containing heavy metals are taken in between the layers of the green last, and iron ferrite is formed in a state in which the heavy metals are partially included. Specifically, for example, hexavalent selenium (SeO ₄ ^2- ) contained in waste water and the like is reduced by ferrous compounds to tetravalent selenium (SeO ₃ ^2- ) and elemental selenium, which are It precipitates in the state of being taken in between the layers.

The treatment method of the present invention uses a closed reaction tank in which the inflow of air is blocked in order to produce the reduced iron compound precipitate in the reaction tank 30, and has a pH of 8.5 to 11 and preferably a pH of 9 in a non-oxidizing atmosphere. The reaction is carried out under alkaline conditions of 0.0 to 10. The liquid temperature may be about 10 to 30 ° C. and does not need to be heated. The reaction time may be about 30 minutes to 3 hours.

Even in a treatment method in which ferrous compound and alkali are added to heavy metal-containing water to produce an iron compound precipitate, the reaction vessel is not sealed as in the conventional case, and the reaction is performed in a non-oxidizing atmosphere. Those having a low alkali level do not produce precipitates having the above reducing power, and the same effects as those of the present invention cannot be obtained.

In the treatment method of the present invention, the ratio of divalent iron ions to total iron ions of the precipitate [Fe ²⁺ / Fe (T )] Is preferably 0.4 to 0.8, and the iron ion ratio is more preferably controlled to 0.55 to 0.65. When this ratio is out of the above range, the reduction of heavy metals becomes insufficient, or the sedimentation property of starch deteriorates, which is not preferable. By producing the reducible iron compound precipitate, the contained heavy metals are reduced and easily incorporated into the precipitate.

When the alkaline sludge is repeatedly returned to the reaction tank 30 and the reaction with the heavy metal-containing water to which the reducing iron compound is added is repeated, the green rust is oxidized to iron ferrite, and the precipitate which was initially deep blue-green gradually It turns black. Since the reducibility is lost when most of the green rust becomes iron ferrite, in the treatment method of the present invention, the ratio [Fe ²⁺ / Fe (T)] of the divalent iron ions to the total iron ions in the iron compound precipitate is set as described above. Control within the range to produce a reducing precipitate.

In the treatment method of the present invention, a part or all of the reducing sludge (iron compound precipitation) is separated, alkali is added to the separated sludge, the alkalinized sludge is returned to the reaction tank, and a non-oxidizing atmosphere is obtained. Repeat the reaction below to precipitate reducing sludge again. When making sludge alkaline, an open tank (alkali addition tank) is used, and alkali is added to the sludge under open conditions. By adding alkali to the sludge in an open state, the sludge comes into contact with air, and the iron compound contained in the sludge is partially oxidized. By introducing the alkaline sludge containing the oxidized iron compound into the sealed reaction tank and mixing with the heavy metal-containing water in a non-oxidizing atmosphere, the generation of the reducing iron compound precipitate proceeds well.

In addition, when adding alkali to the return sludge, the oxidation reaction of the iron compound generated by contact with the air interface is controlled by adjusting the opening area of the alkali addition tank, and the sealed reaction that introduces the alkaline return sludge containing this iron compound The precipitation of the tank can be adjusted. An open-type buffer tank that uses a sealed-type alkali addition tank instead of an open-type alkali addition tank, and accumulates sludge between any path from the sealed reaction tank to the alkali-added tank via the solid-liquid separation means. Here, the sludge may be in contact with air. Such a configuration is also included in the scope of the present invention as an application example using an open type alkali addition tank.

In the treatment method of the present invention, iron ferritization proceeds while maintaining the reducibility of sludge (precipitation), so that the consolidation of the precipitation proceeds and the concentration of the starch is remarkably increased, so that the effect of removing heavy metals is improved. Incidentally, precipitation (sludge) mainly composed of iron hydroxide is bulky and has a heavy dehydration burden. Further, in the treatment method of the present invention, the iron ferrite forming the precipitate is magnetized because it is mainly composed of magnetite, and the separated precipitate can be adsorbed to a magnet for treatment.

The slurry discharged from the reaction tank 30 is guided to a solid-liquid separation means such as a thickener, for example, and sludge is settled on the tank bottom to be separated. This starch (sludge) can be subjected to solid-liquid separation to remove heavy metals out of the system. Moreover, as already stated, an alkali is added to part or all of sludge, it adjusts to pH 11-13, and it returns to the reaction tank 30, The precipitation production | generation reaction is repeated in the reaction tank 30. The ratio of the sludge to be returned (circulation ratio of the returned sludge) is determined so that the ratio [Fe ²⁺ / Fe (T)] of the divalent iron ions and total iron ions in the precipitate generated in the reaction tank 30 is within the above range. Just do it. The treatment method of the present invention can be carried out in either a batch type or a continuous type.

As a specific example of this treatment method, a ferrous compound is added to and dissolved in wastewater having an initial selenium concentration of 2 mg / L so that the Fe ²⁺ ion concentration becomes 400 to 600 mg / L. In a closed reaction tank in which the waste slurry to which the iron compound was added was mixed with a precipitate slurry adjusted to pH 11 to 13 by adding alkali to prevent air contamination, at a temperature of 30 ° C. or less, at a pH of 9.0 to 9.3. By reacting for 30 minutes to 3 hours, the produced precipitate is solid-liquid separated, a part of the precipitate is introduced into an open-type alkali addition tank, the sludge added with alkali is returned to the reaction tank, and repeatedly used. The selenium concentration in the waste water can be reduced to 0.01 mg / L or less.

If the heavy metal-containing water contains silicate ions, aluminum ions, or trace amounts of organic substances, ferritization is affected by these ions, and the removal effect of heavy metals may be reduced. For such heavy metal-containing water, as shown in FIG. 2, before the iron compound addition step, an iron compound or an aluminum compound is added to the heavy metal-containing water to precipitate these ions. It is preferable to provide a pretreatment step for removing silicate ions and the like by filtration.

In the pretreatment step, an iron compound is added to the heavy metal-containing water, an alkali is added, and an iron hydroxide is generated under alkalinity, whereby at least one of silicate ions, aluminum ions, and a trace amount of organic substances is added to the iron water. It precipitates together with the oxide precipitate, and this precipitate is separated from the system by solid-liquid separation. A ferric compound such as ferric chloride is preferred as the iron compound. An aluminum compound may be used in place of the iron compound. An aluminum compound is added to heavy metal-containing water, an alkali is added, and an aluminum hydroxide is precipitated under alkalinity. Since silicate ions and trace organic substances are taken into this precipitate and precipitate, it is separated from the system by solid-liquid separation.

By this pretreatment, silicate ions and aluminum ions that affect ferritization, or heavy metal-containing water from which trace organic substances have been removed in advance, the reducing iron compound addition step, the precipitation step, the solid-liquid separation step, If each process of the said sludge return process is performed, the said ferritization will not be inhibited and the removal effect of heavy metals can be heightened.

In the pretreatment step, a tank for adding an iron compound or an aluminum compound to heavy metal-containing water and a solid-liquid separation means for the generated precipitate are provided before the tank for adding the reducing iron compound to the heavy metal-containing water. It ’s fine.

Further, as described above, all or part of the sludge separated in the solid-liquid separation means is made alkaline and returned to the reaction tank, but the sludge not returned to the reaction tank is filtered and dehydrated by a filter press or the like, Drains out of the system. On the other hand, the filter residue has a reducing power, and this filter residue has good water permeability. Therefore, as shown in FIG. The contamination contained in the drainage can be decomposed and removed from the drainage by utilizing the reducing power remaining in the residue.

According to the treatment method of the present invention, the alkali is added to the return sludge in an open state to make the sludge alkaline and the iron compound contained in the sludge is partially oxidized, and this is introduced into the sealed reaction tank. Then, mixing with heavy metal-containing water and repeating the operation of precipitating the reducing iron compound in a non-oxidizing atmosphere, iron ferritization proceeds smoothly while maintaining sludge reducibility, and sludge consolidation is achieved. As the starch concentration increases significantly, the removal effect of heavy metals is improved.

Since the partial oxidation of the iron compound contained in the sludge at the time of alkali addition can be controlled by adjusting the opening area of the alkali addition tank, depending on the state of precipitation generated by repeated sludge return, What is necessary is just to set the opening area of an alkali tank, or to adjust the said opening area suitably, and can obtain the outstanding process effect according to process conditions. Incidentally, according to the treatment method of the present invention, the concentration of heavy metals contained in the waste water or the like can be reduced to an environmental standard value of 0.01 mg / L or less.

The treatment method of the present invention does not require heating, can proceed to iron ferritization at room temperature, and forms a compact compact starch so that the dehydration is remarkably good, and the effect of removing heavy metals is high, It is a processing method with excellent economy and handling.

Hereinafter, the present invention will be specifically described by examples and comparative examples. Table 1 shows the processing conditions and processing results of each example.

[Example 1]
In accordance with the treatment flow of the present invention shown in FIG. 1, heavy metal-containing water (drainage containing selenium and arsenic, selenium and arsenic concentrations: 2 mg / L each) was treated in a batch manner as follows. First, 2.0 L of this heavy metal-containing water was introduced into the addition tank 10 and ferrous sulfate was added as Fe (II) to 600 mg / L. On the other hand, the entire amount of the solid-liquid separated precipitate was returned to the open addition tank 20, and 1.5 g of slaked lime was added to the precipitate under the open condition to adjust to a strong alkali of pH 12. This strong alkali precipitate was introduced into the sealed reaction tank 30 and mixed with waste water to which ferrous sulfate was added, and reacted for 2 hours. Next, the slurry extracted from the reaction vessel 30 was allowed to stand for 20 hours with a thickener to settle the precipitate, and solid-liquid separation was performed. The total amount of this precipitate was adjusted to strong alkalinity by adding slaked lime while being open as described above, and returned to the reaction vessel 30, and the precipitate formation and separation were repeated 30 times.

[Comparative Examples 1 and 2]
Heavy metal-containing water was treated in the same manner as in Example 1 except that open tanks were used for both the reaction tank and the alkali addition tank (Comparative Example 1). Moreover, the closed type tank was used for both the reaction tank and the alkali addition tank, and the heavy metal containing water was processed like Example 1 except that (comparative example 2).

As shown in Table 1, in Example 1 of the present invention using a closed type reaction vessel and an open type addition vessel, a starch composed of a mixture of green last and iron ferrite is formed. On the other hand, in Comparative Example 1 using an open type tank for both the reaction tank and the addition tank, the oxidation of the iron compound proceeds greatly, so that the starch as in the present invention is not formed, and the starch mainly composed of FeOOH. Formed. Further, in Comparative Example 2 in which the closed tank was used for both the reaction tank and the addition tank, the ferritization of the iron compound hardly progressed, and a starch mainly composed of iron hydroxide Fe (OH) ₂ was formed. .

In Example 1 of the present invention, the sedimented sludge has a large solid content, the reduction potential (ORP) is large, and the removal rate of both selenium and arsenic is as high as 100%. In Comparative Example 1, although the sedimented sludge has a large solid content, it does not have reducing properties, so the reduction potential is low, and the removal rate of both selenium and arsenic is low. On the other hand, in Comparative Example 2, the solid content contained in the settled sludge is small, and the water content is remarkably large. For this reason, the burden of a dehydration process is large. Further, since the properties of the formed starch are different from those of the present invention, the selenium removal rate is high, but the arsenic removal rate is only about half.

Process chart of the present invention Process diagram of the present invention including pretreatment process

Explanation of symbols

10-reducing iron compound addition tank, 20-alkali addition tank, 30-reaction tank, 40-solid-liquid separation means.

Claims (11)

A step of adding a reducing iron compound to heavy metal-containing water [iron compound addition step], a step of introducing heavy metal-containing water added with a reducing iron compound into a reaction vessel to generate a precipitate [precipitation step], A treatment method comprising a step of solid-liquid separation of precipitate (sludge) (solid-liquid separation step), a step of returning all of the separated sludge to alkalinity and returning it to the reaction tank (sludge return step), and precipitation Heavy metal with a reducing iron compound added by using a closed reaction tank in the process and using an open-type alkali addition tank in the sludge return process, introducing the return sludge to which alkali has been added under the open condition into the sealed reaction tank A treatment method characterized by mixing with water containing water and reacting in a non-oxidizing atmosphere and under alkali to form a reducible iron compound precipitate, taking heavy metals into the precipitate and removing it from the system.
The oxidation of the iron compound generated by contact with the air interface is controlled by adjusting the opening area of the alkali addition tank, and the precipitation generation of the sealed reaction tank in which the alkaline return sludge containing the iron compound is introduced is adjusted. Processing method.
The reducing iron compound precipitate produced in the reaction vessel is a mixture of green last and iron ferrite, and the ratio of the divalent iron ion to the total iron ion [Fe ²⁺ / Fe (T)] of the precipitate is 0.4. The processing method according to claim 1 or 2, wherein the precipitate is formed so as to be -0.8.
The pH of the alkaline sludge to be returned to the reaction tank is adjusted to 11 to 13, the pH in the reaction tank mixed with the alkaline sludge is adjusted to 8.5 to 11, and the reducing iron compound precipitates in a non-oxidizing atmosphere. The processing method in any one of Claims 1-3 which produce | generate.
The processing method according to any one of claims 1 to 4, wherein a ferrous compound is used as the reducing iron compound, and a precipitate is produced in a closed reaction tank in a non-oxidizing atmosphere at a liquid temperature of 30 ° C or lower.
In the treatment method, before the iron compound addition step, an iron compound or an aluminum compound is added to heavy metal-containing water, and iron or aluminum hydroxide is precipitated under alkalinity, whereby silicate ions, aluminum ions, A pretreatment step for precipitating at least one of the trace organic substances together with the hydroxide and removing the precipitate by filtration is provided, and for the heavy metal-containing water from which the precipitate has been removed, the reducing iron compound addition step, the precipitation The processing method of the heavy metal containing water in any one of Claims 1-5 which performs each process of a process, the said solid-liquid separation process, and the said sludge return process.
After solid-liquid separation of the precipitate formed by adding an iron compound or aluminum compound to heavy metal-containing water, the ferrous compound is added to the heavy metal-containing water, and the heavy metal-containing water to which the ferrous compound is added Is added to a part or all of the sludge that has been extracted from the reaction tank and separated into solid and liquid, and the pH of the sludge is adjusted to 11 to 13 by opening the sludge to 11-13. In the reaction tank, the reaction was performed for 30 minutes to 3 hours under a non-oxidizing atmosphere in which air was blocked, at a temperature of 30 ° C. or less, and at a pH of 8.5 to 11 for 30 minutes to 3 hours. ) Is solid-liquid separated, while part or all of the precipitate is alkalized and returned to the reaction vessel, and the heavy metal concentration of the solid-liquid separated heavy metal-containing water is reduced to 0.01 mg / L or less. Any one of claims 1-6 Processing method of heavy metal containing water described.
The method for treating heavy metal-containing water according to any one of claims 1 to 7, wherein the concentration of the heavy metal is reduced to 0.01 mg / L or less.
For sludge separated in the solid-liquid separation means, sludge that is not returned to the reaction tank is filtered and dehydrated, and water is discharged out of the system. On the other hand, drainage from another system is passed through the filter residue and the remaining reducing power is used. And the processing method of the heavy metal containing water in any one of Claims 1-7 which decomposes | disassembles the contamination contained in the said waste_water | drain etc.
A tank for adding ferrous compounds to heavy metal-containing water, a non-oxidizing atmosphere sealed reaction tank for reacting heavy metals-containing water added with ferrous compounds, and a means for solid-liquid separation of the slurry extracted from the reaction tank 2. An open type alkali addition tank for adding alkali to the separated sludge, a pipe for returning the alkaline sludge to the reaction tank, and a pipe for communicating the tank and the solid-liquid separation means. An apparatus for treating heavy metal-containing water, characterized in that a system is formed.
11. The treatment apparatus according to claim 10, wherein a tank for adding an iron compound or an aluminum compound to the heavy metal-containing water is added before the tank for adding the reducing iron compound to the heavy metal-containing water, and a solid-liquid separation means for the generated precipitate. An apparatus for treating water containing heavy metals.

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