JP2006263699A - Heavy metal-containing water treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment system for efficiently and economically removing heavy metals from heavy metal-containing water. <P>SOLUTION: A treatment method for removing heavy metals by adding a reducing iron compound to the heavy metal-containing water to precipitate the heavy metals, and performing the solid-liquid separation of the precipitate comprises a process for adding the reducing iron compound to the heavy metal-containing water [an iron compound addition process], a process for introducing the heavy metal-containing water to which the reducing iron compound has been added to a reaction tank to generate a precipitate [a precipitation process], a process for performing the solid-liquid separation of the generated precipitate (sludge) [a solid-liquid separation process] and a process for making the whole of or a part of the separated sludge alkaline and then returning it to the reaction tank [a sludge return process]. In the precipitation process, the wastewater to which the reducing iron compound has been added and alkaline sludge are mixed, and reacted under a nonoxidizing atmosphere and an alkaline condition to generate the precipitate of the reducing iron compound, and the heavy metals are incorporated into the precipitate to be removed to the outside of a system. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 heavy metal-containing water treatment system that is simple in process, excellent in practicality, and efficient in removing heavy metals contained in wastewater efficiently 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) Add reducible iron compound to water containing heavy metals in a treatment method that adds heavy irons to water containing heavy metals to precipitate heavy metals, and separates this precipitate into solid and liquid to remove heavy metals. Step of adding [iron compound adding step], step of introducing precipitate containing heavy metal containing water containing reducing iron compound into the reaction vessel [precipitation step], step of solid-liquid separation of the generated precipitate (sludge) [ Solid-liquid separation step], a step of converting all or part of the separated sludge to alkalinity and returning it to the reaction tank (sludge return step), and in the precipitation step, heavy metal-containing water added with a reducing iron compound A method of treating heavy metal-containing water by mixing a mixture with alkaline sludge and reacting in a non-oxidizing atmosphere and under alkaline conditions to form a reducible iron compound precipitate, and taking the heavy metal into the precipitate and removing it from the system .
(2) 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), wherein the precipitate is formed so as to be 0.4 to 0.8.
(3) 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 (1) or (2) above, wherein an iron compound precipitate is formed.
(4) Any one of (1) to (3) above, wherein a ferrous compound is used as the reducing iron compound and a precipitate is produced in a non-oxidizing atmosphere at a liquid temperature of 10 ° C. to 30 ° C. in a closed reaction tank. The processing method described in.
(5) In the above treatment method, before the iron compound addition step, an iron compound or an aluminum compound is added to the heavy metal-containing water, and an iron or aluminum hydroxide is precipitated under alkalinity, whereby silicate ions, Precipitating step for 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 (1) to (4), wherein each treatment of the precipitation step, the solid-liquid separation step, and the sludge return step is performed.
(6) The solid formed by adding the iron compound or aluminum compound to the heavy metal-containing water and then separating the solid, and then adding the ferrous compound to the heavy metal-containing water, and adding the ferrous compound to the heavy metal Water is introduced into the reaction tank, while alkali is added to a part or all of the sludge extracted from the reaction tank and separated into solid and liquid to adjust the sludge pH to 11-13, and this alkaline sludge is returned to the reaction tank. In the reaction tank, the reaction was carried out for 30 minutes to 3 hours under a non-oxidizing atmosphere in which the air was shut off, at a temperature of 10 ° C. to 30 ° C., and at a pH of 8.5 to 11 for 30 minutes to 3 hours. While solid-liquid separation is repeated, a part or all of the precipitate is alkalized and returned to the reaction tank repeatedly to reduce the heavy metal concentration of the solid-liquid separated heavy metal-containing water to 0.01 mg / L or less ( Heavy metal as described in any of 1) to (5) Method for treating genus-containing water.
(7) Contained heavy metals are selenium, cadmium, hexavalent chromium, lead, zinc, copper, nickel, arsenic and antimony, one or more, and these concentrations are 0.01 mg / L or less. The method for treating heavy metal-containing water according to any one of (1) to (6), wherein
(8) 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 (7), wherein force contained in the waste water or the like is decomposed using force.

Moreover, this invention relates to the processing apparatus of the following heavy metal containing water.
(9) 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 2. A means for separating, a tank for adding alkali to the separated sludge, a pipe for returning the alkaline sludge to the reaction tank, and a pipe for communicating each of these tanks and the solid-liquid separation means. An apparatus for treating water containing heavy metals.
(10) In the treatment apparatus of (9), 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 is a treatment method in which a reducing iron compound is added to heavy metal-containing water to precipitate heavy metals, and the precipitate is solid-liquid separated to remove heavy metals, and reduced to the heavy metal-containing water. A step of adding a ferrous iron compound [iron compound addition step], a step of introducing a heavy metal-containing water to which a reducing iron compound has been added to a reaction vessel to generate a precipitate [precipitation step], and the generated precipitate (sludge) to be solidified. It has a step of liquid separation [solid-liquid separation step], a step of converting all or part of the separated sludge to alkalinity and returning it to the reaction tank [sludge return step]. In the precipitation step, a reducing iron compound is added. Heavy metal containing water and alkaline sludge are mixed and reacted in a non-oxidizing atmosphere under alkali to produce a reduced iron compound precipitate, and the heavy metal is taken out of the system by taking the heavy metal into the precipitate Contains water It is a management method.

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, a tank 20 for adding alkali to the separated sludge, a conduit for returning the alkaline sludge to the reaction tank 30, and a pipe for communicating these tanks and the solid-liquid separation means It has a road. 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 FeI II 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 ° C. 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.

By repeating the return of alkaline sludge to the reaction tank 30 and repeating the reaction with the heavy metal-containing water to which the reducing iron compound is added, the green rust is oxidized and iron ferrite is formed. Gradually 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, the reducing sludge (iron compound precipitation) is separated, and a part or all of the reduced sludge is alkalinized and returned to the reaction tank, reacted in a non-oxidizing atmosphere, and the reducing sludge is precipitated again. By repeating this process, iron ferrite is formed while maintaining the reducibility of the sludge (precipitation), so that the consolidation of the precipitation proceeds and the concentration of the starch is remarkably increased, thereby improving the effect of removing heavy metals. 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 can be solid-liquid separated 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. 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, and in a closed reaction tank in which air contamination was blocked, at a temperature of 10 ° C. to 30 ° C., pH 9.0 to 9. 3 for 30 minutes to 3 hours, the resulting precipitate is separated into solid and liquid, alkali is added to a part of the precipitate, returned to the reaction vessel, and repeatedly used, so that the selenium concentration in the waste water is 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. 3, before the iron compound addition step, the iron compound or 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 still has a reducing power, and the 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 concentration of heavy metals contained in waste water or the like can be reduced to 0.01 mg / L or less of the waste water reference value. Furthermore, this treatment method does not require heating, can be ferritized at room temperature, forms a compact compact starch, and has a very good dehydration, high removal effect of heavy metals, and economic efficiency. In addition, it is a processing method with excellent handleability.

Hereinafter, the present invention will be specifically described by examples and comparative examples. In each example, the ferrite of the starch was determined by magnetism, and the compactness of the starch was determined by bulkiness and sedimentation.

[Example 1]
According to the treatment flow of the present invention shown in FIG. 1, wastewater containing heavy metals was treated in a batch manner as follows. First, 2.0 L of heavy metal-containing water (concentration of each heavy metal: 2 mg / L each) was introduced into the addition tank 10 and ferrous sulfate was added as Fe (II) to 600 mg / L. On the other hand, the total amount of the solid-liquid separated precipitate was returned to the alkali addition tank 20 and 1.5 g of slaked lime was added to adjust to a strong alkali of pH 12. This strong alkali precipitate was returned to the reaction vessel, mixed with waste water to which ferrous sulfate was added, and reacted for 2 hours. Next, the slurry extracted from the reaction vessel was allowed to stand for 20 hours with a thickener to settle the precipitate, and solid-liquid separation was performed. The total amount of the precipitate was adjusted to strong alkalinity as described above and returned to the reaction vessel, and the precipitate was separated and produced 30 times. The processing results together with the processing conditions are shown in Table 1.

[Examples 2-3, Comparative Examples 1-2]
Except for the treatment conditions shown in Table 1, wastewater containing heavy metals was treated in the same manner as in Example 1. The results are shown in Table 1. Moreover, about the selenium among heavy metals, the selenium density | concentration in the waste_water | drain according to the processing frequency of Example 1 and Example 2 was shown on the graph of FIG.

As shown in the results of Table 1, by repeating the wastewater treatment by this treatment method, the precipitates are ferritized at room temperature to form highly compacted precipitates, and the concentration of heavy metals in the wastewater is set at an environmental standard of 0. It can be reduced to 01 mg / L or less.

Example 4
Add ferric chloride solution to 1.0 ml / L to 2 L of simulated waste water containing 100 ppm each of silicate ions and aluminum ions, and further containing 2 ppm selenium, and further add alkali to adjust the pH of the waste water to 8- Adjusted to 8.5 to produce a precipitate. After the precipitate was separated by filtration, the filtrate was treated in the same manner as in Example 1. On the other hand, Table 2 shows a comparison of results obtained by performing the same processing as in Example 1 without performing this pretreatment. As shown in Table 2, wastewater in which aluminum ions and silicate ions have been reduced to 1 ppm and 15 ppm by pretreatment has been reduced to a selenium concentration of less than 0.01 ppm by the ferritization treatment, so that ferritization is sufficient. The removal effect has been achieved because of the progress. On the other hand, the selenium concentration of the wastewater not subjected to pretreatment is 0.07 ppm after treatment, and the removal effect is lower than that of the pretreatment.

Example 5
Ferric chloride solution is added to 2 mL of simulated waste water containing 50 ppm of trace organic matter (TOC) and 2 ppm of selenium to 1.0 ml / L, and further alkali is added to adjust the pH of the waste water to 8 to 8.5. To produce a precipitate, which was filtered and separated to reduce the TOC concentration of the wastewater to 20 ppm or less. The filtrate was treated in the same manner as in Example 1. On the other hand, Table 3 shows a comparison of results obtained by performing the same processing as in Example 1 without performing this pretreatment. As shown in Table 3, the pretreated wastewater had a low selenium concentration and a concentrated sludge volume ratio of 20, a strong magnetic property, and sufficiently ferritized. On the other hand, wastewater without pretreatment had a slightly high selenium concentration and a concentrated sludge volume ratio of 25, was weak in magnetism, and was not sufficiently ferritized. The volume ratio of concentrated sludge is the ratio of the slurry volume that settled and settled to the total volume of the slurry before standing [concentrated sludge volume ratio% = (slurry volume that settled and settled) / (total volume of slurry before standing)]. It is.

Example 6
According to the treatment flow of the present invention shown in FIG. 3, wastewater containing heavy metals was treated in a batch manner as follows. First, 2.0 L of heavy metal-containing water (concentration of each heavy metal: 2 mg / L each) was introduced into the addition tank 10 and ferrous sulfate was added as Fe (II) to 600 mg / L. On the other hand, the total amount of the solid-liquid separated precipitate was returned to the alkali addition tank 20 and 1.5 g of slaked lime was added to adjust to a strong alkali of pH 12. This strong alkali precipitate was returned to the reaction vessel, mixed with waste water to which ferrous sulfate was added, and reacted for 2 hours. Next, the slurry extracted from the reaction vessel was allowed to stand for 20 hours with a thickener to settle the precipitate, and solid-liquid separation was performed. The total amount of the precipitate was adjusted to strong alkalinity and returned to the reaction vessel, and the precipitate was separated 60 times. The resulting excess residue was filtered with a filter press to obtain 790 g (wet amount) of residue. When 2.0 L of heavy metal-containing wastewater, which is different from the above-mentioned heavy metal-containing wastewater, was adjusted to pH 9 and passed through the residue, the concentration of heavy metals in the wastewater was 1/10 as shown in Table 4. Reduced to: Table 4 shows the concentrations of heavy metals before passing through the filter cake (before treatment) and after passing through the water (after treatment).

Example 7
In accordance with the treatment flow of the present invention shown in FIG. 1, groundwater containing heavy metals was treated in a batch manner as follows. First, 2.0 L of ground water containing Se concentration of 0.5 mg / L, As concentration of 0.2 mg / L and Cr (VI) of 0.3 mg / L is introduced into the addition tank 10 and ferrous sulfate is added to Fe (II). As 600 mg / L. On the other hand, the total amount of the solid-liquid separated precipitate was returned to the alkali addition tank 20 and 1.5 g of slaked lime was added to adjust to a strong alkali of pH 12. This strong alkali precipitate was returned to the reaction vessel, mixed with waste water to which ferrous sulfate was added, and reacted for 2 hours. Next, the slurry extracted from the reaction vessel was allowed to stand for 20 hours with a thickener to settle the precipitate, and solid-liquid separation was performed. The total amount of the precipitate was adjusted to strong alkalinity and returned to the reaction vessel, and the precipitate was separated and produced 30 times. As a result, the Se concentration in the groundwater after treatment was reduced to 0.002 mg / L, the As concentration was 0.001 mg / L, and the Cr (VI) concentration was 0.005 mg / L.

Example 8
In accordance with the treatment flow of the present invention shown in FIG. 1, river water containing heavy metals was treated in a batch manner as follows. First, 2.0 L of river water containing Se concentration of 0.05 mg / L, Zn concentration of 0.3 mg / L and Cu of 0.1 mg / L is introduced into the addition tank 10 and ferrous sulfate is converted to Fe (II) to 600 mg / L. L was added. On the other hand, the total amount of the solid-liquid separated precipitate was returned to the alkali addition tank 20 and 1.5 g of slaked lime was added to adjust to a strong alkali of pH 12. This strong alkali precipitate was returned to the reaction vessel, mixed with waste water to which ferrous sulfate was added, and reacted for 2 hours. Next, the slurry extracted from the reaction vessel was allowed to stand for 20 hours with a thickener to settle the precipitate, and solid-liquid separation was performed. The total amount of the precipitate was adjusted to strong alkalinity and returned to the reaction vessel, and the precipitate was separated and produced 30 times. As a result, the Se concentration contained in the river water after treatment was reduced to <0.001 mg / L, the Zn concentration was 0.003 mg / L, and the Cu concentration was 0.002 mg / L.

Process diagram of this treatment method The graph which shows the processing effect of Example 1 and 2 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 (10)

A step of adding a reducing iron compound to water containing heavy metals in a processing method of adding heavy irons to water containing heavy metals to precipitate heavy metals, and separating the precipitate by solid-liquid separation to remove heavy metals. Iron compound addition step], a step of producing precipitates by introducing heavy metal-containing water added with a reducing iron compound to a reaction tank (precipitation step), a step of solid-liquid separation of the generated precipitate (sludge) [solid-liquid separation Step), a step (sludge return step) for making all or part of the separated sludge alkaline and returning it to the reaction tank, and in the precipitation step, heavy metal-containing water and alkaline sludge added with a reducing iron compound And a reaction in a non-oxidizing atmosphere and under alkali to form a reducible iron compound precipitate, which takes heavy metals into the precipitate and removes them outside the system.
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, 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 according to claim 1 or 2, wherein:
The processing method according to any one of claims 1 to 3, 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 10 ° C to 30 ° C.
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 1-4 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 the reaction tank, and alkali is added to a part or all of the sludge separated and solid-liquid separated to adjust the pH of the sludge to 11-13, and the alkaline sludge is returned to the reaction tank, and the reaction is performed. In a tank, the reaction was carried out for 30 minutes to 3 hours under a non-oxidizing atmosphere in which air was shut off, at a temperature of 10 ° C. to 30 ° C., and at a pH of 8.5 to 11 for 30 minutes to 3 hours. 6. While separating, repeating a part or all of the precipitate alkalinized and returning to the reaction tank is repeated to reduce the heavy metal concentration of the solid-liquid separated heavy metal-containing water to 0.01 mg / L or less. Heavy metals described in any of the above Processing method of Arimizu.
Contained heavy metals are selenium, cadmium, hexavalent chromium, lead, zinc, copper, nickel, arsenic, antimony, one or more, and these concentrations are all reduced to 0.01 mg / L or less The processing method of the heavy metal containing water in any one of Claims 1-6.
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 A tank for adding alkali to the separated sludge, a pipe for returning the alkaline sludge to the reaction tank, and a pipe for communicating each of these tanks and the solid-liquid separation means. A water treatment apparatus containing heavy metals.
10. The treatment apparatus according to claim 9, 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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