JP2002172395A - Method for iron hydroxide flocculation and sedimentation treatment of thick inorganic component- containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly treat wastewater containing an inorganic component in high concentration. SOLUTION: A first process - a third process are successively performed. The first process is process for adding a water soluble ferric salt aqueous solution to wastewater containing a thick inorganic component and, if ferric ions are mixed with wastewater in the first process, the pH of wastewater is lowered by a water soluble ferric salt showing weak acidity. The second process is a process for neutralizing the ferric salt added to wastewater by alkali and ferric ions are reacted with hydroxyl ions in the second process to form an iron hydroxide precipitate. Further, heavy metal components in wastewater are also precipitate as hydroxide. The third process is a process for succeedingly repeating the first and second processes once or more. By successively performing these processes, an iron hydroxide flocculated precipitate excellent in sedimentation properties, filterability and dehydration properties is obtained in wastewater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating wastewater which contains a high concentration of inorganic harmful substances such as heavy metals and arsenic contained in the wastewater.

[0002]

2. Description of the Related Art As a technique for removing inorganic harmful substances such as heavy metals and arsenic contained in wastewater, an iron hydroxide coagulation precipitation method has been well known. In this method, an aqueous solution of 10 to several hundred ppm, and in some cases, several thousand ppm, of a ferric salt is added to the wastewater in advance, and then p
Neutralize to H7.0 or more to form a precipitate of iron hydroxide, coagulate and precipitate inorganic harmful substances such as heavy metals and arsenic contained in the wastewater together with the precipitate of iron hydroxide, A sedimentation accelerator is added, gravity sedimentation is separated, and sediment components are separated and dehydrated using a method such as filtration with a filter press, and inorganic harmful substances such as heavy metals and arsenic in wastewater are transferred to solid sludge. is there.

According to the iron hydroxide precipitation method, the treatment cost is low and the inorganic harmful substances such as heavy metals and arsenic in the wastewater can be relatively efficiently removed. Has been put to practical use.

[0004]

However, in the actual operation of wastewater treatment equipment, the gravitational sedimentation and sedimentation and sediment filtration / dewatering properties of the formed iron hydroxide precipitate often deteriorate significantly. This is a major obstacle to smooth driving.

[0005] However, when the gravity sedimentation property and the filterability of such iron hydroxide precipitate are deteriorated, as a symptomatic treatment, the amount of iron to be added or the amount of polymer aggregation promoter to be added are increased. In some cases, the problem can be avoided by taking the above measures. However, there are many cases where such a measure still does not solve the problem.

That is, if it is considered that the cause of such trouble in the smooth operation of the equipment is a high concentration of water-soluble inorganic components contained in the waste water, the growth of the iron hydroxide precipitate is inhibited by the high concentration of ions in the liquid. However, gravity sedimentation will be poor because the precipitate size remains very small. In this case, it is possible to improve the sedimentation by gravity by increasing the amount of the polymer coagulation promoter added, but in order to improve the sedimentation, a large amount of the polymer coagulation promoter must be added. Not
Due to factors such as cost and increased viscosity of waste water, the amount of addition is naturally limited.

[0007] Even if gravity sedimentation can be sufficiently performed, the performance at the time of filtration and dehydration by a filter press or the like is hindered. In other words, filtration and dewatering operations using a filter press are technically classified as cake filtration,
It is known that this filtration rate is extremely low because the filtration resistance increases due to the small size of the precipitated particles forming the cake.

Further, even if the size of the agglomerated particles by the agglomeration accelerator is large, in cake filtration, if the opening of the filter cloth is larger than the size of the precipitated particles, a fatal effect such that the sediment easily passes through the filter cloth can be obtained. There are drawbacks. If a filter cloth having a smaller mesh size is used to prevent the precipitate from passing through the filter cloth, a defect that the filtration resistance is further increased and the filtration speed is reduced becomes remarkable.

[0009] The inventors have studied various causes of the occurrence of such problems in a wastewater treatment facility that employs an iron hydroxide coagulation sedimentation method. As a result, in many cases, it was confirmed that the concentration of water-soluble inorganic components other than the harmful substances to be treated, such as sulfate ions, phosphate ions, aluminum ions, and silica ions, had increased. They also found that the presence of these high concentrations of water-soluble inorganic components seemed to inhibit the growth of iron hydroxide precipitated particles.

[0010] In recent years, the inventors have particularly experienced such phenomena. This is because, as a result of social demands for water environmental conservation and the increasing public awareness, the voluntary environmental regulations of wastewater discharge companies have been strengthened, and as a result of efforts to reduce the amount of wastewater as much as possible, the concentration of components in wastewater has increased. It is presumed that the effect is that wastewater from each system, which had been introduced into wastewater treatment facilities without separation in the past, is now separated by concentration. Under these circumstances, the emergence of an iron hydroxide coagulation sedimentation method capable of treating thick wastewater as it has been awaited.

On the other hand, the calcium precipitation method is widely applied as a method for treating wastewater containing harmful substances such as heavy metals and arsenic by a method other than the iron hydroxide coagulation precipitation method. However, the method using calcium as a precipitant often cannot be applied to wastewater containing concentrated inorganic components. The reason is that wastewater containing concentrated inorganic components often contains high concentrations of sulfate ions that are not harmful components.
This is because the formation of the calcium sulfate precipitate causes a fatal defect that the consumption of the precipitant increases and the amount of sludge increases.

[0012] For such wastewater containing a concentrated inorganic component,
It is also conceivable to apply an evaporation to dryness method or an adsorbent treatment method. However, because of the increase in operating costs, wastewater discharge companies do not treat wastewater containing toxic substances such as heavy metals and arsenic containing rich inorganic components on their own. In many cases, such methods as outsourcing to a contractor are taken.

[0013] The inventors of the present invention have frequently encountered problems in the operation of the iron hydroxide coagulation and sedimentation facility, and found that the cause was the concentration of water-soluble inorganic components such as sulfate ion, phosphate ion, aluminum ion and silica ion. As a result of intensive research, we have found a new treatment method to which the coagulation and precipitation method of iron hydroxide can be applied. According to this treatment method, it is applied to wastewater treatment in which the concentration of water-soluble inorganic components such as sulfate ion, phosphate ion, aluminum ion, and silica ion is extremely high, and generates a precipitate having excellent gravity sedimentation properties and filtration / dehydration properties. be able to.

It is an object of the present invention to provide a method for treating wastewater containing a high concentration of inorganic components to a high degree, in particular, even if a high concentration of inorganic components is contained, by adequately controlling the conditions for precipitation to sufficiently grow. It is an object of the present invention to provide a method for forming a precipitate.

[0015]

In order to achieve the above object, in the first method of the present invention, there is provided a method for coagulating and precipitating an aqueous solution containing a concentrated inorganic component, the method comprising the steps of: A first step of adding an aqueous solution of iron salt;
A second step of neutralizing the added ferric salt with an alkali;
And a third step of continuously repeating the first and second steps one or more times.

In the second method, a first step of preliminarily neutralizing the concentrated inorganic component-containing wastewater and a second step of adding a water-soluble ferric salt aqueous solution to the neutralized wastewater are added. A third step of neutralizing the ferric salt with an alkali; and a fourth step of continuously repeating the second and third steps one or more times.
And the step of

A third step of adding the neutralized wastewater obtained in the first step to the wastewater mixture to which the first step has been added, and a fourth step of continuously repeating the second and third steps one or more times. It is a thing.

In the second or third method of the present invention, the first step is a step of introducing acidic or alkaline waste water and neutralizing the mixture in a pH range of 6.0 to 8.0 while stirring. , The second step is 0.2 to 0.5 of the total amount of iron.
Is a step of adding an amount of an aqueous ferric salt solution to the wastewater,
The third step is to re-neutralize the wastewater and raise the pH to between 6.0 and 8.
This is the step of adjusting to zero.

The neutralizing agent is an alkali metal hydrate or a mineral acid other than phosphoric acid.

In the first, second or third method, chloride or nitrate / sulfate is added as a ferric salt to the wastewater in a total amount of 20 to 5000 ppm Fe, and the ferric salt is added. After the addition, the mixture is stirred for 5 to 10 minutes to maintain the reaction time.

[0021]

Embodiments of the present invention will be described below. The present invention relates to a method for coagulating and precipitating iron hydroxide from wastewater containing a concentrated inorganic component, and comprises a high concentration of sulfate ion, phosphate ion, aluminum ion, silica, which inhibits sedimentation, filtration, and dehydration of the precipitate. Even if ions are present in the wastewater, a proper precipitate can be formed.

That is, in the present invention, the following steps are sequentially performed to remove high concentrations of sulfate, phosphate, aluminum, and silica ions that inhibit the sedimentation, filtration, and dehydration of the precipitate. A proper precipitate is formed even if it is present therein, and there are three methods as described below. The first method is a method in which iron hydroxide is dividedly added without neutralizing the wastewater and the neutralization treatment is repeated, and is realized by sequentially performing the first to third steps.

The first step is a step of adding (mixing) an aqueous solution of a water-soluble ferric salt to wastewater containing a concentrated inorganic component. In the first step, when the ferric ions are mixed in the wastewater, the pH of the liquid is lowered by the weakly acidic water-soluble ferric salt. The second step is a step of neutralizing the ferric salt added to the wastewater with an alkali. In the second step, ferric ions and hydroxide ions react to form iron hydroxide precipitate. Heavy metal components in the wastewater also precipitate as hydroxides.

Fe ⁺⁺⁺ + 3OH ⁻ → Fe (OH) ₃ ↓ (1) M ^{n +} + nOH ⁻ → M (OH) _n ↓ (2) In addition, neutralization pH is weak acidity. If the wastewater contains a large amount of phosphoric acid when neutral, iron phosphate also precipitates. Fe ⁺⁺⁺ + PO ₄ ^--- → FePO ₄ ↓ (3) The color of iron hydroxide generally shows reddish brown to brown, and the color of iron phosphate generally shows yellowish white. However, the color of the precipitate formed in the wastewater to which the ferric salt has been added cannot be clearly described by the ratio of the precipitate component in the wastewater.

According to the first method, the color of the precipitate formed in the wastewater is generally dominated by the brown color of iron hydroxide. The third step is a step of continuously repeating the first and second steps one or more times. FIG. 1 shows a flow of the first method.

The second method is a method in which the wastewater is neutralized in advance, and then the treatment of neutralization is repeated by adding iron hydroxide in portions, which is realized by sequentially performing the first to fourth steps. Is done. The first step is a step of preliminarily neutralizing the concentrated inorganic component-containing wastewater, in which acidic or alkaline wastewater is introduced, and the wastewater is neutralized within a pH range of 6.0 to 8.0 while stirring. The first step makes the pH of the wastewater neutral.

When the wastewater is acidic, H ⁺ + OH ⁻ → H ₂ O (4) When the waste water is alkaline OH ⁻ + H ⁺ → H ₂ O (5) The components contained in the wastewater are Precipitation may occur due to neutralization, or may not occur. Also, the SS content in the wastewater usually does not usually change. The component precipitated by the neutralization of the wastewater is, for example, aluminum ion.

When the wastewater is acidic, Al ⁺⁺⁺ + 3OH ⁻ → Al (OH) ₃ ↓ (6) When the wastewater is alkaline: AlO ₂ ⁻ + H ⁺ + H ₂ O → Al (OH) ₃ ↓ (7) Whether or not a precipitate is formed by the first step is not important for the present invention.

The second step is a step of adding (mixing) an aqueous solution of a water-soluble ferric salt to the neutralized waste water. In the second step, an aqueous ferric salt solution in an amount of 0.2 to 0.5 based on the total amount of iron is added in order to provide sufficient processability. Second
In the step (2), the added iron ions partially react with the components in the wastewater to form a precipitate. In this case, for example, the formation of an iron phosphate precipitate occurs preferentially.

The excess iron ions formed by the precipitation of iron phosphate react with the hydroxide ions in the waste water to form iron hydroxide precipitates, which usually have a colloidal gel form. The reaction formula is as shown in the above (1) to (3). The third step is a step of neutralizing the added ferric salt with an alkali, and adjusting the pH from 6.0 to 8.0. By the third step, the size of the iron hydroxide precipitate in the form of a colloidal gel can be increased. Then, as a fourth step,
The second and third steps are repeated one or more times. FIG. 2 shows a flowchart of the second method.

The third method is a method in which the neutralized wastewater and iron hydroxide are separately neutralized, respectively, and finally subjected to a neutralization treatment, and the first to fourth steps are sequentially performed. Is achieved. That is, the first step is a step of neutralizing the concentrated inorganic component-containing wastewater in advance, and the second step is a step of adding (mixing) a water-soluble ferric salt aqueous solution to the wastewater. The first step and the second step are basically the same as the second method. Next, as a third step, the neutralized wastewater of the first step is added again to the wastewater mixture to which the ferric salt has been added, and the pH is 6.0 to 8.0, preferably,
Adjust the pH to 7 or higher.

It is presumed that the pH of the mixture slightly shifts to the neutral side by the third step, and the surface condition of the formed precipitate changes. It is also presumed that phenomena such as adsorption of components in the wastewater that have already formed a precipitate on the precipitate occur. It is impossible to completely describe such a microscopic state change due to the fluctuation of the pH of the sediment in the wastewater (see, for example, "Handbook for Wastewater and Wastewater Revised 2nd Edition", 1984, Maruzen, p. 399).

Thereafter, as a fourth step, the above-mentioned second and third steps are continuously repeated one or more times. Above, the first
In the third to third methods, chloride or nitrate / sulfate can be used as the water-soluble ferric salt to be added to the wastewater, and the total amount of iron salt added to the wastewater is 20 to 500.
0 ppm Fe is an appropriate amount. After the addition of the ferric salt to the waste water, stirring is continued for 5 to 10 minutes to maintain the reaction time.

The neutralizing agent added to the wastewater may be an alkali metal hydroxide or a mineral acid (excluding phosphoric acid) such as hydrochloric acid, sulfuric acid and nitric acid. FIG. 3 shows a flowchart of the third method.

The method of the present invention is completely different in principle from the well-known “seed precipitation circulation method” in principle. That is, the seed precipitation circulation method is a method in which a precipitate that has already grown to a sufficiently large size is transferred from equipment other than the iron hydroxide coagulation sedimentation tank, and is mixed with the wastewater beforehand to form a new precipitate. In contrast, according to the present invention, the transfer of such precipitates is not required, and iron and precipitates are alternately added in the presence of iron hydroxide precipitates of very small size, which are in principle conventional methods. It is clear that this is a completely new invention.

If the present invention is further described,
In the above method, it is important to neutralize the acidic or alkaline wastewater in advance. Depending on the type of wastewater containing high-concentration inorganic components, sufficient treatment may be provided by simply alternately adding iron salts and neutralizing agents without performing a neutralization operation in advance, but sufficient treatment may not always be possible. In some cases, sex is not given.

However, after neutralizing the wastewater in advance,
By alternately adding the iron salt and the neutralizing agent, the treatability of all wastewaters is improved as compared to the conventional method.

In addition, wastewater which has been neutralized in advance (whether neutral wastewater as it is, or neutral wastewater neutralized with an alkali metal or alkaline earth metal hydroxide excluding calcium, or alkaline wastewater) For example, according to the method of alternately adding the wastewater neutralized with a mineral acid except phosphoric acid) and the iron salt, a precipitate having more excellent processability can be obtained.

When the wastewater is strongly acidic or alkaline, the microprecipitation reaction field between the iron salt and the neutralizing agent is exposed to a remarkable alkali condition, so that the condition is easily affected by a high concentration of inorganic components. It is presumed that mild precipitation conditions are adjusted by neutralizing the wastewater in advance.

In the present invention, calcium is excluded as a neutralizing agent, because, as described above, calcium sulfate precipitates not to be treated are formed. In addition, the reason why phosphoric acid is excluded as a neutralizing agent is that the pH range in which iron phosphate precipitates is different from the pH range in which iron hydroxide precipitates. This is to make the sex worse.

In the present invention, the pH in the waste water by the neutralization treatment is:
It should be between 6.0 and 8.0, preferably between 6.5 and 7.0. If the pH of the neutralization is too high, p
H adjustment is required.

The type of ferric salt may be any of chloride, sulfate and nitrate. Further, the amount of addition is selected to be an optimum amount that can sufficiently treat harmful substances such as heavy metals and arsenic. Usually, the amount of iron salt added to the wastewater is preferably 20 to 5000 ppm Fe.

According to the method of the present invention, sedimentation, filtration,
An iron hydroxide coagulated sediment having excellent dehydration properties is obtained. In some cases, this precipitation does not require the addition of a polymer coagulation promoter, and may exhibit sufficient gravity sedimentation. In general, the amount of the polymer coagulation promoter added is small. Further, when a filter press type filtration / dehydrator is used as a means for separating the precipitate, it is recognized that the filterability is remarkably improved as compared with the ordinary method.

The method of the present invention can be carried out in either batch processing or continuous processing, but the first method and the second method are advantageously batch processing. That is, in any of the first to third methods, the total amount of the repeatedly added water-soluble ferric salt and the neutralizing agent does not change so much. However, in the first method and the second method, Since the operation of adjusting the pH is required each time the re-neutralization is repeated, it can be said that the method is more suitable for batch processing than continuous processing.

Of course, this does not mean that continuous processing is impossible. When performing the second method by continuous processing, a plurality of stirring tanks, for example, using six stirring tanks,
The first tank is a storage tank that sends the neutralized wastewater to the second tank, the third tank, and the fifth tank, the second tank, and the fourth tank are reaction tanks that mix an aqueous ferric salt solution, and the third tank is The fifth tank is a reaction tank for adding neutral wastewater to the wastewater to which iron salt has been added, the sixth tank is a tank for adjusting the final pH, and the wastewater is sequentially discharged from the first tank to the second tank and the third tank.
Are fed in the order of tanks,..., A predetermined reaction is performed in the second to fifth tanks, and the pH is adjusted in the sixth tank.

Similarly, in the first method, continuous processing can be performed according to the above example. In the third method, batch processing is of course possible, but rather continuous processing is suitable. FIG. 4 shows a process flow of a continuous process according to the third method. In this example, a total of seven tanks are used. First tank 3
And the seventh tank 10 are a neutralization tank, the second tank 5, the fourth tank 6, and the sixth tank 9
Is a ferric salt mixing tank, and the third tank 6 and the fifth tank 8 are neutralization wastewater mixing tanks.

The concentrated inorganic component-containing wastewater 2 is supplied to the first tank 3, and is sent from the first tank 3 to the second tank 5, the third tank 6,... The neutralizing agent 1 is supplied to the first tank 3, the seventh tank
The ferric salt aqueous solution 4 added to the tank 10 is added to the second tank 5, the fourth tank 7, and the sixth tank 9, and the neutralized waste water discharged from the first tank 3 is added to the third tank 6. , The precipitate in the treated water 11 discharged from the seventh tank 10 can be sufficiently grown to a separable level.

[0048]

Examples of the present invention will be described below. (Example 1) Table 1 Drainage Characteristics pH 0.9 As 10ppm P 370ppm SO ₄ 530ppm SS 33ppm

Embodiment 1 is an application example of the second method.
15 liters of waste water having the properties shown in Table 1 were placed in a 20 liter container, and stirred with a stirrer, and 25
The solution was neutralized to pH 6.7 with an aqueous sodium hydroxide solution.

No special precipitate was formed by the neutralization.
While stirring the neutralized waste water, 87 cc of an aqueous ferric chloride solution (38%) was added as a second step. Addition of the iron salt lowered the pH of the liquor to 4.2 and produced a white-brown colloidal precipitate. As a third step, the solution was re-neutralized with alkali to adjust the pH to 6.7. Although there was no significant change in the state of the white precipitate, a brown precipitate of iron hydroxide was formed in a part of the container for a short time when the alkali was added, and disappeared immediately. Next, as a fourth step, when 87 cc of the second aqueous ferric chloride solution was added, the pH of the solution dropped to 4.1,
The color of the precipitate became slightly clear white.

Then, after neutralization again and the pH was adjusted to 6.7, it was observed that the color of the precipitate was very slightly brownish. To this solution was added a third aqueous ferric chloride solution
When 7 cc was added, the pH became 4.1 and the precipitate was dominated by brown. Further, when the pH was adjusted to 6.7, the size of the precipitate became large enough to be confirmed with the naked eye.

When the slurry containing the precipitate was subjected to vacuum filtration with a No. 5C filter paper, the filtration speed was extremely high as shown in FIG. Table 2 shows the properties of the treated water after removing the precipitate.

Table 2 Aqueous treatment pH 6.7 AS <0.05 ppm SS 0.1 ppm

(Embodiment 2) Embodiment 2 is an application example of the third method. 15 liters of the same waste water as in Example 1 was placed in a 20 liter container, and neutralized to pH 6.7 with a 25% aqueous sodium hydroxide solution as a first step while stirring with a stirrer. No special precipitate was formed by the neutralization. Transfer 5 liters of this neutralized wastewater to another 20 liter container,
While stirring, an aqueous ferric chloride solution (3
8%) was added.

The addition of the iron salt lowered the pH of the liquor to 3.6 and produced a white-brown colloidal precipitate. In this liquid,
As a third step, when 5 liters of newly neutralized waste water was added, the pH of the solution became 5.5, but the state of the white colloid precipitate did not change.

Next, when 55 cc of the aqueous ferric chloride solution was added again, the pH dropped to 3.4, and the color of the colloidal precipitate became slightly yellow. After stirring for 5 minutes in this state,
As a fourth step, when 5 liters of new neutralized wastewater and 55 cc of an aqueous ferric chloride solution were added, the pH changed to 5.4 and 3.3. The color of the precipitate formed is light yellow,
Its size was large enough to be recognized by the naked eye.

Finally, after adjusting the pH of the solution to 6.7, the stirring was stopped and the solution was allowed to stand. After 10 minutes, it was observed that the sediment volume was settled and concentrated to 15% of the whole solution volume. . When the slurry containing the precipitate was subjected to vacuum filtration in the same manner as in Example 1, the filtration speed showed the value shown in FIG. Table 3 shows the properties of the treated water after removing the precipitate.

Table 3 Treatment aqueous state pH 6.7 As <0.05 ppm SS 0.1 ppm

(Embodiment 3) Embodiment 3 is an application example of the first method. 15 liters of the same waste water as in Example 1 was placed in a 20 liter container, and 87 cc of an aqueous ferric chloride solution was added as a first step while stirring with a stirrer. The pH changed slightly to 0.8. As a second step, the solution was neutralized to pH 6.7 with a 25% aqueous sodium hydroxide solution.

By this operation, a brown precipitate began to form when the pH of the solution was around 3. When the pH reached 6.8, neutralization was stopped and stirring was continued for 5 minutes. At this time, the precipitate was very fine and its color was slightly light brown. In the third step, when 87 cc of ferric chloride was added, the pH of the solution dropped to 4.2, but no change was observed in the color of the precipitate in each step.

When this was re-neutralized, the brown color of the precipitate became slightly darker. When this third step (iron re-neutralization) was repeated a total of three times, the brown color of the precipitate became dark, and the size of the precipitate became large enough to be seen with the naked eye. The sedimentation reached 13% after 10 minutes. Regarding the filterability of the precipitate, an intermediate filtration rate between Example 1 and Comparative Example 2 shown below was obtained as shown in FIG. 4, and was slightly lower than that of Example 1.

[0062]

[Comparative Example 1] A part of the initial colloid solution produced by the first addition of the iron salt in Example 1 was taken out, the pH was adjusted to 6.7, and its sedimentation property was observed. Was not found. When the filtration rate of the liquid containing the colloidal precipitate was measured by the same method as in Example 1, the filtration rate was extremely small as shown in FIG.

[0063]

Comparative Example 2 15 liters of the same waste water used in Example 1 was taken, 165 cc of an aqueous ferric chloride solution (38%) was added with stirring, and then the pH was adjusted to 6.5 with a 25% aqueous sodium hydroxide solution. Adjusted to 7. It was recognized that a brown-brown precipitate was formed in the tank as the pH increased. After stirring was continued for about 30 minutes, the stirring was stopped, and about half of the liquid was allowed to stand for 60 minutes. As a result, the solid-liquid interface had an extremely slow sedimentation speed of less than 5% of the liquid volume.

On the other hand, about the remaining half, a polymer flocculant was added, and the mixture was stirred for about 5 minutes and allowed to stand. After about 5 minutes, the sedimentation interface reached 70% of the total liquid volume. No coagulant added
The filtration rate was measured for both of the additions in the same manner as in Example 1, but the filtration rate was extremely low as shown in FIG.

[0065]

As described above, according to the present invention, even if the wastewater has a very high concentration of water-soluble inorganic components such as sulfate ions, phosphate ions, aluminum ions, and silica ions, the treatment for purifying iron hydroxide precipitates the wastewater. Applying the method to produce an appropriate precipitate, the precipitate can be separated from the wastewater by gravity sedimentation or filtration, and the separated precipitate is
It has an excellent dewatering property, and has an effect that a slurry containing a precipitate can be easily dewatered using a vacuum filtration method or the like.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a first method according to the present invention.

FIG. 2 is a flowchart showing a second method according to the present invention.

FIG. 3 is a flow chart showing a third method according to the present invention.

FIG. 4 is a graph showing a comparison of filtration speed between Examples 1, 2, and 3 and Comparative Examples 1 and 2 for a slurry containing a precipitate treated by the method of the present invention.

FIG. 5 is a view showing a flow of a continuous processing step according to a third method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Neutralizing agent 2 Drainage containing a concentrated inorganic component 3 First tank (neutralization tank) 4 Ferric salt aqueous solution 5 Second tank (ferric salt mixing tank) 6 Third tank (neutralization drainage mixing tank) 7th 4 tanks (ferric salt mixing tank) 8 5th tank (neutralization wastewater mixing tank) 9 6th tank (ferric salt mixing tank) 10 7th tank (neutralization tank) 11 treated water

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Nakamura 1933-10 Shimonumabe, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Within Nippon Electric Environmental Engineering Co., Ltd. (72) Yoshihiro Oguchi 1-1-107 Satsukicho, Ebina-shi, Kanagawa Prefecture F term (reference) 4D015 BA19 BB01 CA17 CA20 FA03 FA12 4D038 AA08 AB63 AB70 AB85 BA04 BB18 4D062 BA19 BB01 CA17 CA20 FA03 FA12

Claims (6)

[Claims] 1. A first step of adding an aqueous solution of a water-soluble ferric salt to a wastewater containing a concentrated inorganic component, a second step of neutralizing the added ferric salt with an alkali, and the first and second steps. And a third step of continuously repeating the step of repeating the step one or more times. 2. A first step of preliminarily neutralizing a wastewater containing a concentrated inorganic component, a second step of adding a water-soluble ferric salt aqueous solution to the neutralized wastewater, and adding the added ferric salt to an alkali. A process for coagulating and precipitating waste water containing concentrated inorganic components, the method comprising a third step of neutralizing with water and a fourth step of continuously repeating the second and third steps one or more times. . 3. A first step of preliminarily neutralizing a concentrated inorganic component-containing wastewater, a second step of adding a water-soluble ferric salt aqueous solution to the wastewater, and a wastewater mixture to which a ferric salt is added. A third step of adding the neutralized wastewater obtained in the first step,
And a fourth step of continuously repeating the second and third steps one or more times. 4. The method for coagulating and precipitating iron hydroxide containing concentrated inorganic components as set forth in claim 2 or 3, wherein the first step comprises introducing acidic or alkaline waste water and stirring the solution to a pH of 6.0 to 8 while stirring. The second step is a step of adding an aqueous ferric salt solution in an amount of 0.2 to 0.5 of the total amount of iron to the wastewater, and the third step is a third step. Is a step of re-neutralizing the waste water and adjusting the pH from 6.0 to 8.0, wherein the concentrated inorganic component-containing waste water is subjected to coagulation and precipitation of iron hydroxide. 5. The method for coagulating and precipitating iron hydroxide of concentrated inorganic component wastewater according to claim 1, 2 or 3, wherein the neutralizing agent is an alkali metal hydrate or a mineral acid excluding phosphoric acid. A method for coagulating and precipitating iron hydroxide from wastewater containing a concentrated inorganic component, comprising: 6. The method for coagulating and precipitating iron hydroxide in a wastewater containing a concentrated inorganic component according to claim 1, 2, or 3, wherein chloride or nitrate / sulfate is added as a ferric salt to the wastewater. A method for coagulating and precipitating iron hydroxide from a wastewater containing a concentrated inorganic component, comprising adding 20 to 5000 ppm Fe, stirring the mixture for 5 to 10 minutes after adding the ferric salt, and maintaining the reaction time.