JP2009148750A - Heavy metal-containing water treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating method with superior economic performance, and efficiently removing heavy metals from drainage containing heavy metals like cadmium even under a low temperature environment. <P>SOLUTION: The treating method includes steps of: adding a reducing iron compound to heavy metal-containing water; forming precipitation by leading the heavy metal-containing water added with the reducing iron compound to a reaction vessel; separating the formed precipitation (sludge) into solid matter and liquid; and returning all or part of the separated sludge to the reaction vessel by turning it to alkalinity. The returned sludge is adjusted to pH of 11-13, the reaction vessel is adjusted to pH of 8.5 or more, and the reducing iron compound precipitation having green rust and iron ferrite as a main component is made to take in heavy metals in a sealed non-oxidation environment for precipitation. A seed crystal containing magnetite is added to the reactor vessel in advance prior to the adding step of the iron compound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an economical treatment system that efficiently removes heavy metals from waste water containing heavy metals even in a low temperature environment. 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 even in a low temperature environment.

  A processing method is known in which divalent iron ions are added to wastewater containing heavy metals, and then the temperature of the liquid is maintained at 30 ° C. or higher, in an air-blocking environment, and alkali is added to generate and remove starch. (Patent Document 1). In addition, alkali is added to wastewater containing heavy metals to precipitate heavy metal hydroxides, inert gas is introduced into this treatment liquid to remove dissolved oxygen, and then ferrous salt is added in the alkaline region. There is known a processing method for precipitating heavy metals and then blowing air into the iron-containing precipitate to precipitate the heavy metals remaining in the liquid (Patent Document 2). In addition, ferrous hydroxide and alkali are added to the wastewater to precipitate heavy metals, while a part of the sludge is circulated to the reaction tank after alkali addition to increase the processing efficiency. (Patent Document 3).

  However, it is difficult to reduce the concentration of heavy metals in the waste water to an environmental standard value of 0.01 mg / L or less in any of the above conventional treatment methods. Further, in the method of simply adding ferrous hydroxide, oxygen in the wastewater 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, 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 treatment 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.

Furthermore, in the wastewater treatment method of adding sludge by adding alkali to water containing heavy metals, separating the sludge, adding alkali to a part of the separated sludge and returning this alkali sludge to the reaction tank Methods are 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) Japanese Patent No. 395978

  A treatment method for heavy metal-containing water that solves the above problems by improving a treatment method based on a conventional ferrite method is known (Patent Document 7: Japanese Patent No. 395978). In this treatment method, a precipitate containing green rust and iron ferrite is formed, so the precipitate is consolidated, solid-liquid separation is good, and ferrite treatment is possible at room temperature, and the concentration of heavy metals is the environmental standard value. It has the advantage that it can be reduced to 0.01 mg / L or less.

  In the treatment method for forming a precipitate containing green last and iron ferrite, for example, magnetite formation tends to be slow in a low temperature environment at a water temperature of 10 ° C. or less, and sedimentation and compaction tend to be low. The present invention improves this point, and provides a treatment method in which the effect of removing heavy metals is maintained even in a low temperature environment, the solid concentration of the precipitate is high, and the sedimentation property is excellent.

The present invention relates to a method for treating heavy metal-containing water that solves the above-described problems by the constitution shown in the following [1] to [5].
[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 into 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). The sludge to be returned is adjusted to pH 11 to 13, the reaction tank in the precipitation step is adjusted to alkaline of pH 8.5 or more, and a reducing iron compound mainly composed of green last and iron ferrite in a sealed non-oxidizing atmosphere. In the processing method of generating a precipitate, incorporating heavy metals into the iron compound precipitate to cause precipitation, and separating the precipitate into solid and liquid to remove heavy metals, seed crystals containing magnetite are added to the reaction tank in advance. This Processing method of heavy metal containing water, wherein.
[2] The method for treating heavy metal-containing water as described in [1] above, wherein the seed crystal is a mixed precipitate of green last and iron ferrite.
[3] The method for treating heavy metal-containing water according to [1] or [2] above, wherein the reduced iron compound precipitate generated in the series of treatment steps from the iron compound addition step to the sludge return step is used as a seed crystal. .
[4] When performing a series of treatments from the iron compound addition step to the sludge return step in a low temperature environment with a water temperature of 10 ° C. or lower, a reductive iron compound precipitate is generated in advance in a reaction vessel at a temperature of room temperature or higher. The method for treating heavy metal-containing water according to any one of [1] to [3] above, wherein the treatment is performed as a seed crystal in a low-temperature environment.
[5] The method for treating heavy metal-containing water according to any one of [1] to [4] above, wherein seed crystals are added to a solid-liquid separation tank.

  In the treatment method of the present invention, seed crystals mainly composed of magnetite are added in advance to the reaction tank, so that a reductive iron compound precipitate is easily generated, and the treatment effect under a low temperature environment is excellent. Specifically, the solid concentration of the generated precipitate is remarkably high, the compactness is excellent, and the sedimentation rate is fast. Therefore, in the drainage with a low water temperature and the winter treatment, the initial treatment effect is excellent, and a stable treatment effect can be obtained.

Hereinafter, the processing method of the present invention will be specifically described based on embodiments.
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 a step (sludge return step) of returning all of the separated sludge to alkalinity and returning it to the reaction tank The sludge to be returned to the reaction tank is adjusted to pH 11 to 13, the reaction tank in the precipitation step is adjusted to alkaline of pH 8.5 or higher, and the reduction mainly consists of green last and iron ferrite in a sealed non-oxidizing atmosphere. In a treatment method in which a heavy iron compound precipitate is formed, heavy metals are taken into the iron compound precipitate and precipitated, and the precipitate is solid-liquid separated to remove heavy metals. It is a method of treating heavy metals containing water, characterized in that to keep pressure.

  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.

  In the present invention, the pH may be measured by the pH measurement method based on the glass electrode method of JIS standard (JIS K0102 12.1).

  The outline of this processing system is shown in FIG. As shown in the figure, this treatment system includes a tank 10 for adding a reducing iron compound to heavy metal-containing water, a sealed reaction tank 20 in a non-oxidizing atmosphere for reacting heavy metal-containing water to which a reducing iron compound is added, and the reaction. Means 30 for solid-liquid separation of the slurry extracted from the tank 20, a tank 40 for adding alkali to the separated sludge, a conduit for returning the alkaline sludge to the reaction tank 20, 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, two or more reaction tanks 20 may be installed in series, and these may be sealed in a sealed structure purged with nitrogen so that the ferritization treatment is performed 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 20.

  The alkaline sludge is returned to the reaction tank 20 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 alkaline sludge, the pH of the reaction tank 20 is adjusted to 8.5 to 11, preferably 9.0 to 10.

  In the reaction vessel 20, 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)

Further, iron ferrite is a Fe ^II ferrate and is mainly composed of magnetite (Fe ^II Fe ^III ₃ O ₄ ), but may also contain a heavy metal ferrate in 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.

  In the treatment method of the present invention, seed crystals containing magnetite are added to the reaction vessel 20 in advance. For this seed crystal, a mixed precipitation of green last and iron ferrite can be used. Specifically, for example, the reducible iron compound precipitate generated in the series of treatment steps from the iron compound addition step to the sludge return step can be used as a seed crystal. As described above, since this reducible iron compound precipitate contains magnetite, it can be used as the seed crystal. A solution prepared by adding an alkali to the seed crystal to have a pH of 11 to 13 is added to the reaction vessel 20. Alternatively, the seed crystal is added to the solid-liquid separation tank 30 as it is. Preferably, it may be added to the solid-liquid separation tank 30.

  When the treatment method of the present invention is carried out in a low-temperature environment with a water temperature of 10 ° C. or lower, a reducing iron compound precipitate is generated in advance in a reaction vessel at a temperature of room temperature or higher, and this is used as a seed crystal. It is good to perform the process in.

  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 reductive iron compound precipitate in the reaction tank 20, and has a pH of 8.5 to 11, preferably pH 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 the divalent iron ions to the 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.

As for the above [Fe ²⁺ / T-Fe] measurement, the [T-Fe] concentration was measured by “1,10 phenanthroline absorptiometry” of JIS standard (JIS K0102 57.1) after acid precipitation of iron compound precipitate. Similarly, the [Fe ²⁺ ] concentration may be measured by the phenanthroline spectrophotometry method without adding a reducing agent. [Fe ²⁺ / T-Fe] is calculated from the ratio of the absorbances of the two.

By repeating the return of the alkaline sludge to the reaction tank 20 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 20 is guided to a solid-liquid separation means such as a thickener, for example, and the sludge is settled on the tank bottom and 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 some or all of the sludge to adjust to pH 11 to 13 and returned to the reaction tank 20, and the precipitation generation reaction is repeated in the reaction tank 20. The ratio of 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 20 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.

  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.

  About the heavy metal-containing water from which silicate ions and aluminum ions that affect ferritization or trace organic substances have been removed in advance by the pretreatment, 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 this 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. Regarding heavy metal measurement methods, Cd is JIS standard (JIS K0102 55.3), Pb is JIS standard (JIS K0102 54.3), Cu is JIS standard (JIS K0102 52.4), Zn is JIS standard (JIS K0102 53.3), Ni JIS standard (JIS K0102 59.3), Cr (VI) JIS standard (JIS K0102 65.2.4), Mn was measured by JIS standard (JIS K0102 56.4) ICP emission spectroscopy. As was measured by the hydrogen compound generation atomic absorption method of JIS standard (JIS K0102 61.2).

[Example 1]
According to the treatment flow of the present invention shown in FIG. 1, wastewater containing heavy metals with a water temperature of 10 ° C. was treated in a batch manner as follows. First, 2.0 L of the above heavy metal-containing water (concentration of Cd, Pb, Cu, Zn, Ni, Cr (VI), As, Mn: 2 mg / L each) is introduced into the addition tank 10 to introduce ferrous sulfate. Fe (II) was added so as to be 300 mg / L. On the other hand, a mixed precipitate of green last and iron ferrite produced by the previous treatment was used as a seed crystal, and 5 ml of 12.5 wt% NaOH was added to make it strongly alkaline (pH 13) in the reaction tank 20 in advance. Added. Waste water added with ferrous sulfate was introduced into the reaction vessel 20 and mixed for reaction for 15 minutes. 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. This precipitation was performed in a refrigerator (4 ° C.). The total amount of the solid-liquid separated precipitate was introduced into the alkali addition tank 40, and slaked lime was added to adjust the pH to 11-13, and the reaction product was returned to the reaction tank 20 to repeat the formation and separation of the precipitate. The processing results together with the processing conditions are shown in Tables 1 to 3 and FIG. The X-ray diffraction pattern of the product is shown in FIG.

[Comparative Example 1]
Exhaust water containing the above heavy metals was treated in the same manner as in Example 1 except that seed crystals were not added. The results are shown in Tables 1 to 3 and FIG. The X-ray diffraction pattern of the product is shown in FIG.

  As shown in the results of Table 1, according to this treatment method, the concentrations of Cd, Pb, Cu, Zn, Ni, Cr (VI), and As contained in the waste water are all reduced to less than 0.01 mg / L. The concentration of Mn can be reduced to 0.04 mg / L. Further, according to the treatment method of the present invention, the precipitate produced is strong in magnetism, so the compaction of the precipitate is high, and the concentration of the precipitate (sludge) is about 14 to 32 times that of the comparative example in which no seed crystal is used. . Moreover, as shown in FIG. 1, the sedimentation rate of precipitation is also four times or more high.

  As shown in the structural analysis result by the X-ray diffraction pattern of FIG. 3, when the seed crystal is present, a crystal structure in which green last and ferromagnetic magnetite (iron ferrite) coexist is confirmed. On the other hand, it was confirmed that without seed crystals, there was no clear diffraction image and it was amorphous.

Process chart of the present invention The graph which shows the processing effect of Example 1 and Comparative Example 1 of the present invention Graph showing the X-ray diffraction pattern of the product

Explanation of symbols

10-addition tank, 20-reaction tank, 30-solid-liquid separation tank, 40-alkali addition tank.

Claims (5)

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], Sludge that has a step of solid-liquid separation of the precipitate (sludge) (solid-liquid separation step), a step of returning all of the separated sludge to alkalinity and returning it to the reaction vessel (sludge return step), and returning it to the reaction vessel Is adjusted to pH 11-13, the reaction tank in the precipitation step is adjusted to alkaline of pH 8.5 or higher, and a reductive iron compound precipitate mainly composed of green last and iron ferrite is produced in a sealed non-oxidizing atmosphere. In the treatment method in which heavy metal is incorporated into the iron compound precipitate to be precipitated, and this precipitate is solid-liquid separated to remove heavy metal, a seed crystal containing magnetite is previously added to the reaction vessel. Processing method of heavy metal containing water to.
The method for treating heavy metal-containing water according to claim 1, wherein the seed crystal is a mixed precipitate of green last and iron ferrite.
The method for treating heavy metal-containing water according to claim 1 or 2, wherein the reducing iron compound precipitate generated in the series of treatment steps from the iron compound addition step to the sludge return step is used as a seed crystal.
When performing a series of treatments from the iron compound addition process to the sludge return process in a low temperature environment with a water temperature of 10 ° C. or less, a reducing iron compound precipitate is generated at a temperature higher than room temperature in a reaction tank in advance, and this is used as a seed crystal The method for treating heavy metal-containing water according to any one of claims 1 to 3, wherein the treatment is performed in the low temperature environment.
The method for treating heavy metal-containing water according to any one of claims 1 to 4, wherein seed crystals are added to the solid-liquid separation tank.

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