JPH09155363A - Treatment of selenium-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable development of effect even with respect to SeO4 <2-> , extremely lower the finally reachable concn. of selenium, economically perform treatment by simple operation and clear general waste water standards. SOLUTION: Waste water containing at least SeO4 <2-> is brought into contact with a selenium alloy generating hydrogen selenide in the presence of water and, thereafter, a solid component is removed by solid-liquid separation. After a ferrous salt is added to the obtained liquid component, alkali is added thereto to neutralize the liquid component to adjust the pH thereof to 6-8 and air is blown into the liquid component to form a precipitate which is, in turn, subjected to solid-liquid separation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention removes an Se component from a waste water containing at least SeO ₄ ²⁻ (the selenium oxidation number is + VI), which is considered to be difficult to remove by a conventional method, and has an extremely low selenium content. The present invention relates to a method for treating selenium-containing wastewater that reaches a concentration.

[0002]

2. Description of the Related Art According to the water quality standard based on the Water Supply Act promulgated as a ministerial ordinance in 1992, the selenium content in drinking water was restricted to 0.01 mg / L or less, As a general drainage standard, 0.1 mg / L or less will be applied.

Conventionally, as a method for treating selenium wastewater, (A) a method mainly for reduction / precipitation / removal to elemental Se and the like, (B) a method for precipitating / removing as a metal selenide,
(C) a method comprising a process of precipitating as a sulfide,
(D) Coprecipitation / aggregation method with iron salt or other compound,
Many methods are known such as (E) a method using an adsorbent and a filtering agent, (F) a method using a chelate resin, an ion-exchange resin, (G) a reverse osmotic pressure method, and (H) a biological method.

However, most of them are effective in removing SeO ₃ ^2- , but SeO ₄ ^2- (selenium oxidation number is + VI)
Has little or no effect on the removal of selenium, and the selenium concentration that can be finally reached cannot be sufficiently reduced.

However, among the above methods (A), the method of reducing selenium-containing ions in waste water with a metal such as iron has some effect on SeO ₄ ²⁻ . However, there is a limit to the selenium concentration that can be finally reached by that method, and it is hard to say that it is a sufficient wastewater treatment method to meet the above criteria.

[0006]

[Problems to be Solved by the Invention]
O ₄ ²⁻ is reduced by iron to give red selenium (Se
It has been known for a long time that O ₃ ²⁻ ) is produced, but this reaction is said to be difficult to proceed sufficiently (Gmelins Ha
ndbuch der Anorg. Chemie 10 Se [B] S.97 (1949)). This was also confirmed in the additional test by the inventors.

Further, if ferrous sulfate and NaOH, which is a method of removing SeO ₃ ^2- , is added to this method and coprecipitated with iron oxide by a method of blowing air, the removal rate of selenium can be increased. I was able to clarify. However, the selenium concentration after removal could not be reduced to 3 ppm or less.

It is also known that when SeO ₄ ²⁻ is heated with Se powder in a sealed tube, it is reduced to SeO ₃ ²⁻ according to the following reaction formula (Gmelins Handbuch der Anorg. Chem.
ie 10 Se [B] S.97 (1949)). 2H ₂ SeO ₄ + Se + xH ₂ O = 3H ₂ SeO ₃ + (x−1) H ₂ O According to this document, this reaction is 300 ° C., NaOH 50
It is said to be complete at g / L.

However, according to the experiments by the present inventors, the pH
Is higher, the reaction speed tends to be slightly higher, but
The reaction gradually proceeds in a wide range of pH 2 to 12, and the reaction mechanism cannot be clarified, but reduction to SeO ₃ ²⁻ occurs with some generation of red selenium.

Subsequently, it is clarified that selenium is removed by adding ferrous sulfate and NaOH, which is a method of removing SeO ₃ ^2- , and coprecipitating with iron oxide by a method of blowing air. However, similarly to the above, the selenium concentration after removal could not be reduced to 3 ppm or less.

In order to solve the above problems, the object of the present invention is to exert an effect even on SeO ₄ ^2- , which has been difficult to process by the conventional technique, and further, the selenium concentration that can be finally reached is It is an object of the present invention to provide a method for treating selenium-containing wastewater which is extremely low and can be economically implemented by a simple operation.

[0012]

Based on the results of the additional experiment as described above, the inventors of the present invention have thought of using an alloy of iron and selenium, and the waste water containing at least SeO ₄ ^2- is converted to ferroselen. It was discovered that the selenium component can be highly removed by bringing it into contact and filtering and removing the precipitate containing red selenium produced by the reduction, and further earnestly researched to reach the present invention. In addition, subsequently SeO ₃ ^2-
By adding ferrous sulfate and NaOH, which is a method of removing selenium, and coprecipitating with iron oxide by blowing air, a slight amount of remaining selenium component is removed, and more advanced selenium wastewater treatment is achieved. I was able to make clear what was done.

That is, the gist of the present invention is (1) after contacting a wastewater containing at least SeO ₄ ^2- with a selenium alloy which produces hydrogen selenide in the presence of water, solid-liquid separation is performed to remove solid components. A method for treating selenium-containing wastewater, characterized by removing (2) a selenium alloy that produces hydrogen selenide in the presence of water is ferroselene [Fe _x Se _y ,
x: y = 3 to 0.3 (molar ratio)], the treatment method according to (1) above, (3) the contact between the waste water and the selenium alloy is p
The treatment method according to (1) or (2) above, which is carried out under a condition of H6 or lower, (4) The liquid component obtained by the treatment method according to any one of (1) to (3) above, and a ferrous salt. And then adding an alkali to neutralize the solution to pH 6 to 8 and blowing air, and solid-liquid separation of the deposited precipitate, (5) Wastewater and selenium alloy After the contact, the ferrous salt is added, an alkali is added to neutralize the solution to pH 6 to 8 and air is blown into it, and then solid components are removed by solid-liquid separation. To (3) any one of the processing methods.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The wastewater to be treated according to the present invention is not particularly limited as long as it contains at least SeO ₄ ^2- , and in addition to the wastewater containing SeO ₃ ^2- , It may contain inorganic acids such as nitric acid, sulfuric acid and hydrochloric acid, and sodium salts such as sodium nitrate, sodium sulfate and sodium chloride.

In some cases, it is advisable to apply the method of the present invention to the treatment of waste water in which the concentration of selenium ions is reduced as much as possible by other known methods, and to perform advanced treatment.

In the method for treating selenium-containing wastewater of the present invention, the wastewater as described above is contacted with a selenium alloy that produces hydrogen selenide in the presence of water, and then solid components are removed by solid-liquid separation. It is characterized by. In addition, to produce hydrogen selenide in the presence of water means to produce hydrogen selenide by contact with water at room temperature or under acidic conditions, that is, contact with an acidic aqueous solution.

The selenium alloy used can obtain the effects of the present invention as long as it produces hydrogen selenide in the presence of water. However, from the viewpoint of the effectiveness of the reduction reaction in a liquid, ferroselen [! Fe _x Se _y , x: y = 3 to 0.3
(Molar ratio), preferably x: y = 2.5 to 0.5] is suitably used. In addition, Al ₂ Se ₃ , MgSe, Z
The effects of the present invention can be obtained with nSe, Na ₂ Se _{4 and the} like, but it has been found that ZnSe and the like are not as good as ferrocele.

On the other hand, copper selenide and nickel selenide, which do not easily generate hydrogen selenide in the presence of water, show almost no effect of the present invention. These facts indicate that in the process of the present invention, SeO ₄ ²⁻ is reduced to give red selenium, which is the fact that the selenium alloy produces what is called generator hydrogen selenide in water, which reacts with SeO ₄ ²⁻ ions. It proves that it does.

The shape of the selenium alloy may be any shape such as powder, lump, or molded product, but it is advisable to determine it in consideration of the relationship with the contact method with drainage. Further, the kind of alloy may be any of solid solution alloy, compound alloy, mixture alloy and the like.

The amount of selenium alloy used depends on the selenium ion to be treated in order to make the treatment reaction rate as short as possible.
It needs to be excessive. For example, as the Se of the selenium-containing ion to be removed, 1 g (the atomic weight of Se is 78.96).
On the other hand, it is preferable to use 50 g or more of the selenium alloy, and 100 to 150 g is more preferable. Therefore, it is advantageous to apply this method after removing SeO ₃ ^2- that can be removed by other methods in advance.

The method of contacting the waste water with the selenium alloy is not particularly limited and can be appropriately selected in consideration of the contact efficiency. For example, a method in which powder of selenium alloy is added to waste water and stirred, a method in which waste water is passed through a column filled with selenium alloy, and the like are adopted.

The higher the processing temperature is, the shorter the processing time can be. However, even at room temperature, the purpose is usually reached within 5 to 6 hours, so that the processing at room temperature is economical.

In the present invention, the contact between the waste water and the selenium alloy can be carried out in a wide pH range, but from the viewpoint of the reaction rate, it is preferably carried out under the condition of pH 6 or less, most preferably the waste water. Is carried out after or while adjusting pH to around pH 2.

Here, as a method of adjusting the pH, there is a method of adding an acid such as hydrochloric acid, sulfuric acid or nitric acid, or an alkali such as sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate or calcium hydroxide. Can be mentioned.

In the present invention, solid components (residual selenium alloy, red selenium, iron oxide, etc.) are removed by solid-liquid separation after contact between the waste water and the selenium alloy. The solid-liquid separation method is not particularly limited, and examples thereof include filtration and centrifugation.

In the above-mentioned method of the present invention, since a large amount of coprecipitant, adsorbent, etc. are not used, it is not necessary to consider the amount of the precipitate filtered and recovered, and it should be recycled as a raw material of selenium. Is possible. Also, when the cement solidification / disposal method is adopted, the amount is small, which is economical.

The primary-treated wastewater obtained by the above-mentioned method, that is, contact between wastewater and selenium alloy, filtration, etc., still contains a small amount of selenium, and a new regulation value of wastewater of 0.1
To satisfy mg / L, it may be necessary to dilute with a large amount of water.

In this case, subsequently, ferrous salt is added to the liquid component obtained by the above-mentioned treatment method, and then alkali is added to neutralize the solution to pH 6 to 8 and air is blown in to precipitate it. By separating the precipitate by solid-liquid separation, selenium remaining slightly is removed, and a more advanced selenium wastewater treatment is achieved.

The above-mentioned method is known as a method for removing SeO ₃ ^2- , and known reagents and treatment conditions may be appropriately used. For example, as the ferrous salt, sulfate,
Mineral salts such as hydrochloride are preferably used, and as the alkali, sodium hydroxide, sodium carbonate, calcium hydroxide and the like are preferably used. In addition, the method of solid-liquid separation,
Same as above. In addition, the above-mentioned method is such that after the contact between the waste water and the selenium alloy, the ferrous salt is added, the alkali is added to neutralize the pH to 6 to 8 and air is blown, and then solid components are separated by solid-liquid separation. Can also be carried out by a method of removing.

[0030]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples. A similar prior art is given as a comparative example.

Example 1 Waste water 2 containing SeO ₄ ²⁻ as Se in an amount of 71.7 ppm 2
After adjusting the pH to about 2 with hydrochloric acid at 20 ° C. in a beaker, ferroselen powder [Fe _x Se _y , x: y =
1.40 (molar ratio)] 20 g was added and stirred. A sample was taken after a predetermined time, filtered, and the Se content of the filtrate was analyzed. The progress is shown in Table 1.

[0032]

[Table 1]

Example 2 In Example 1, the adjusted pH at the start with hydrochloric acid was set to about 4. The same measurement process is shown in Table 2.

[0034]

[Table 2]

Example 3 In Example 1, the adjusted pH at the start with hydrochloric acid was set to about 7. The same measurement process is shown in Table 3.

[0036]

[Table 3]

Example 4 In Example 1, the pH at the start was adjusted to about 9 with NaOH. The same measurement process is shown in Table 4.

[0038]

[Table 4]

Example 5 In Example 1, ferrocelenium powder [Fe _x Se _y ,
Ferroselene powder [Fe _x Se _y , x: y = 2.40 (molar ratio)] was used instead of x: y = 1.40 (molar ratio). The Se concentration after 5 hours was 0.3 ppm, and the Se removal rate was 99.58%.

Example 6 In Example 1, ferrocelenium powder [Fe _x Se _y ,
x: y = 1.40 Feroseren powder [Fe _x Se _y in place of (molar ratio)], x: using y = 0.80 (molar ratio)]. The Se concentration after 5 hours was 0.4 ppm, and the Se removal rate was 99.44%.

Example 7 Table 5 shows the results obtained by changing the amount of ferrocelenium used in Example 1.

[0042]

[Table 5]

Example 8 SeO ₄ ²⁻ treated in Example 1 is used as Se.
SeO instead of 2 liters of wastewater containing 1.7 ppm
N ² at 20 ° C. using waste water containing 75.5 ppm of ₄ ²⁻ as Se and 10.2 ppm of SeO ₃ ²⁻ as Se.
After adjusting to pH2.0 with NaOH, Feroseren powder _{[Fe x Se y, x: y} = 1.40 ( molar ratio)] 20g
Was added and stirred. A sample was taken after a predetermined time and analyzed for Se content. Se concentration is 0.4p after 5 hours
The removal rate of pm and Se was 99.53%.

Example 9 Instead of performing the treatment in Example 1 by stirring in a beaker, the treatment was performed by circulating waste water through a column filled with ferrocelenium. That is, 2 liters of waste water containing 71.7 ppm of SeO ₄ ²⁻ as Se was adjusted to pH 2.0 with hydrochloric acid at 20 ° C. in a beaker, and then ferroselene [Fe _x Se _y , x: y = 1.40 (mol Ratio)] 3 in a glass column filled with 50 g of lumps (diameter 3 to 20 mm).
It was passed and circulated at a flow rate of 00 ml / min. The pH of the liquid was constantly maintained at 2 to 4, samples were taken at predetermined time intervals, and the Se content was analyzed. The progress is shown in Table 6.

[0045]

[Table 6]

Example 10 The 60-hour-treated wastewater obtained in Example 1 was further treated by a coprecipitation method. That is, 1.6 g of ferrous sulfate heptahydrate was added to 200 ml of the treated wastewater containing 0.12 ppm of Se, pH was adjusted to 7 with NaOH, and then air was blown for 20 hours. The pH was adjusted to 6.5 and filtered. Se concentration in the filtrate is 0.013ppm, Se
The removal rate was 99.99%.

Comparative Example 1 2 liters of waste water containing 100 ppm of SeO ₄ ^2- as Se was adjusted to a predetermined pH with hydrochloric acid or NaOH at 20 ° C. in a beaker, 40 g of reduced iron powder was added, and the mixture was stirred for 24 hours. . After filtration, adjust the liquid volume to 3 liters and add S
e concentration was measured. Table 7 shows the relationship between the pH at the start of stirring and the Se concentration of the filtrate.

[0048]

[Table 7]

Comparative Example 2 150 g of iron sulfate heptahydrate was added to 1 liter of each of the filtrates of Experiment Nos. 1, 2 and 3 of Comparative Example 1 and p was added with NaOH.
After adjusting to H7, air was blown in for 20 hours. pH
It was adjusted to 6.5 and filtered. The Se concentration in the filtrate is shown in Table 8.

[0050]

[Table 8]

Comparative Example 3 2 liters of waste water containing 100 ppm of SeO ₄ ^2- as Se was adjusted to a predetermined pH with hydrochloric acid or NaOH at 20 ° C. in a beaker, and then selenium powder (purity 99.99%).
40 g was added and stirred for 42 hours. After filtration, the liquid amount was adjusted to 4 liters and the Se concentration was measured. Table 9 shows the relationship between the pH at the start of stirring and the Se concentration of the filtrate.

[0052]

[Table 9]

Comparative Example 4 150 g of iron sulfate heptahydrate was added to each 2 liters of the filtrates of Experiment Nos. 1 ', 2', 3'and 4'of Comparative Example 3,
After adjusting the pH to 7 with NaOH, air was blown in for 20 hours. The pH was adjusted to 6.5 and filtered. The Se concentration in the filtrate is shown in Table 10.

[0054]

[Table 10]

Comparative Example 5 Wastewater 3 containing SeO ₄ ²⁻ as Se as 71.4 ppm
In beaker in 100 ml, copper selenide powder [Cu _x Se
_y , x: y≈1 (molar ratio)] 3.0 g, and 20 ° C.
The pH was adjusted to 2.0 with hydrochloric acid and the mixture was stirred for 24 hours.
When the filtrate was filtered and analyzed, the Se concentration was 66.5 pp
The m and Se removal rates were 6.86%. 200m of this filtrate
1.5 g of ferrous sulfate heptahydrate was added to 1 l and p was added with NaOH.
Adjust to H7, blow in air for 4 hours, then filter,
The filtrate was analyzed. The Se concentration was 29.3 ppm, and the total Se removal rate was 59.0%.

Comparative Example 6 Wastewater 3 containing SeO ₄ ²⁻ as Se as 71.4 ppm
In a beaker to 00 ml, nickel selenide powder [Ni
_x Se _y , x: y≈1 (molar ratio)] 3.0 g,
After adjusting the pH to 2.0 with hydrochloric acid at 20 ° C., the mixture was stirred for 24 hours. When the filtrate was filtered and analyzed, the Se concentration was 69.
The removal rate was 0 ppm and the Se removal rate was 3.40%. This filtrate 2
1.5 g of ferrous sulfate heptahydrate was added to 00 ml, and NaO was added.
The pH was adjusted to 7 with H, air was bubbled in for 4 hours, then filtered and the filtrate was analyzed. The Se concentration was 23.6 ppm, and the total Se removal rate was 67.0%.

Example 11 Wastewater 3 containing SeO ₄ ^2- as Se of 67.8 ppm
Zinc selenide powder [Zn _x S
e _y , x: y ≈ 1 (molar ratio)] 5.0 g, and
After adjusting the pH to 2.0 with hydrochloric acid at ℃, it was stirred for 24 hours. When the filtrate was filtered and analyzed, the Se concentration was 28.9.
The ppm and Se removal rate were 57.4%. This filtrate 20
To 0 ml, add 1.5 g of ferrous sulfate heptahydrate, add NaOH
The pH was adjusted to 7, and air was blown in for 4 hours, followed by filtration, and the filtrate was analyzed. Se concentration 10.3ppm, total S
e Removal rate was 84.8%.

Example 12 Waste water 2 containing SeO ₄ ²⁻ as Se of 71.7 ppm
After adjusting the pH to about 2 with hydrochloric acid at 20 ° C. in a beaker, ferroselen powder [Fe _x Se _y , x: y =
1.40 (molar ratio)] 20 g was added and stirred for 60 hours. Thereafter, 16 g of ferrous sulfate heptahydrate was added to this liquid, pH was adjusted to 7 with NaOH, and air was blown therein for 20 hours. After adjusting this to pH 6.5, it filtered and analyzed the filtrate. The Se concentration was 0.012 ppm, and the total Se removal rate was 99.9%.

[0059]

The method for treating selenium-containing wastewater of the present invention comprises:
A method for treating selenium-containing wastewater that is effective even for SeO ₄ ^2- , which was difficult to treat with conventional technology, and has a very low selenium concentration that can be finally reached, and that can be economically implemented with a simple operation. Is. As a result, it has become possible to meet the general wastewater standards after February 1995, and the utility value is extremely high in industry.

Claims (5)

[Claims] 1. A selenium characterized by removing solid components by solid-liquid separation after contacting a wastewater containing at least SeO ₄ ²⁻ with a selenium alloy that produces hydrogen selenide in the presence of water. Treatment method of contained wastewater. 2. A selenium alloy which produces hydrogen selenide in the presence of water is ferroselene [Fe _x Se _y , x: y =
3 to 0.3 (molar ratio)]. 3. The treatment method according to claim 1, wherein the contact between the waste water and the selenium alloy is performed under the condition of pH 6 or less. 4. A ferrous salt is added to the liquid component obtained by the treatment method according to any one of claims 1 to 3 and then an alkali is added to neutralize the pH to 6 to 8 to blow air, A method for treating selenium-containing wastewater, which comprises solid-liquid separating the deposited precipitate. 5. After contact between the waste water and the selenium alloy, a ferrous salt is added, an alkali is added to neutralize the pH to 6 to 8 and air is blown, and then solid components are removed by solid-liquid separation. The processing method according to claim 1, wherein