JP2003181467A - Treatment method for wastewater containing selenium - Google Patents

Abstract

(57) Abstract: SeO ₃ ^2-and SeO ₄ ^2-and can be processed in the waste water with high efficiency of dissolved and moreover of be performed using relatively handleability What better for drug Provided is a method for treating selenium-containing wastewater. The process wastewater A SeO ₃ ^2-and SeO ₄ ^2-and is dissolved with the addition of metal ions to react to form insoluble salts and SO ₄ ^2-, in the treated waste water SO ₄ ^2- (A first step) in which sulfate is precipitated as a hardly soluble salt, and after the sulfate ion removing step, Fe powder is added to the treated wastewater after removing the hardly soluble salt to reduce each Se salt, Reduction step of separating water from treated wastewater as a hardly soluble substance (fifth step)
A method for treating selenium-containing wastewater, comprising:

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating selenium-containing wastewater, particularly Se which is difficult to remove by a conventional method.
The present invention relates to a method for treating selenium-containing wastewater, which is effective in treating wastewater containing O ₄ ^2- .

[0002]

2. Description of the Related Art In the process of treating electrolytic deposits of metals such as copper, selenium (Se) may be dissolved in a relatively high concentration in discharged wastewater. In such a case, in order to pass this as general wastewater, it is naturally necessary to perform a treatment to satisfy the drainage standard and remove selenium in the wastewater.

Selenium is generally dissolved in waste water in the form of SeO ₃ ^2- (tetravalent selenium). As a treatment method for such a form of tetravalent selenium, for example, Japanese Patent Publication No.
There is a method disclosed in JP-A-8-30558. However, when SeO ₄ ²⁻ (hexavalent selenium) coexists in the waste water, it is known that the treatment by the above method is less effective.

Therefore, when SeO ₄ ²⁻ (hexavalent selenium) coexists in this way, for example, in a weakly acidic region, SeO ₄ ²⁻ is treated with a strong reducing agent such as SO ₂ or an organic acid salt. The method of fixing as metal selenium is adopted.

[0005]

However, in such a method of treating with a strong reducing agent such as SO ₂ or organic acid salt, the treatment efficiency is low due to insufficient reduction of SeO ₄ ^2- There were complaints that the recovery rate was also low. In addition, there is also a complaint that a treatment (reducing agent) such as SO ₂ and an organic acid salt having poor handling property is used, and therefore the treatment needs to be performed with sufficient caution.

The present invention has been made in view of the above circumstances, and an object thereof is SeO ₃ ²⁻ and SeO ₄ ^2−.
It is an object of the present invention to provide a method for treating selenium-containing wastewater, which can treat wastewater having dissolved thereinto with high efficiency, and can be carried out using a medicine which has relatively good handleability.

[0007]

The present inventor has obtained the following findings as a result of intensive studies to achieve the above object.
SeO ₃ ^2- (tetravalent selenium) and SeO ₄ ^2- (hexavalent selenium)
For wastewater bets is dissolved, the as removal processing method of each Se salt, neutralization reaction product precipitate FeCl ₃ (Fe
Adsorption reaction with (OH) ₃ ) and reduction reaction with iron powder in a weakly acidic region are known as effective means. However, although these methods are effective in reducing the Se concentration, the wastewater is treated, for example, at an environmental standard value of 0.0
Insufficient to reduce to 1 mg / l (0.01 ppm). Therefore, in carrying out the above treatment method, as a result of an examination to establish better treatment conditions, it was found that SO ₄ ²⁻ present in the wastewater hinders the removal treatment of the Se salt. It was As a result of further research based on such knowledge, the present invention has been completed.

That is, in the method for treating selenium-containing wastewater of the present invention, the treated wastewater in which SeO ₃ ²⁻ and SeO ₄ ²⁻ are dissolved is treated with metal ions which react with SO ₄ ²⁻ to form a sparingly soluble salt. In addition, a sulfate ion removing step of removing SO ₄ ^2- in the treated wastewater by precipitation as a sparingly soluble salt, and a sulfate powder removing step, and then adding Fe powder to the treated wastewater after removing the sparingly soluble salt. A Se reducing step of reducing each of the Se acid salts and separating Se as a hardly soluble substance from the treated wastewater was taken as a means for solving the above problems.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
In the method for treating selenium-containing wastewater of the present invention, first, as a first step that is a sulfate ion removal step in the present invention, raw water (treated wastewater in which SeO ₃ ²⁻ and SeO ₄ ²⁻ are dissolved as shown in FIG. ), A metal ion that reacts with SO ₄ ²⁻ to form a sparingly soluble salt and fixes SO ₄ ²⁻ is added.

Examples of such metal salts include Ba salt and Ca.
Although a salt or the like is used, BaCl ₂ is particularly preferably used, and in that case, a dihydrate (BaCl ₂ · 2H ₂ O) is more preferably used. In addition, such a metal salt is used in a molar ratio of 1.5 to about the total amount of SO ₄ ^2- present in the raw water.
An amount that doubles, that is, an excessive amount is added. Also,
In this step, the sparingly soluble salt such as BaSO _{4 is used.}
It is necessary to adjust the pH of the wastewater to about 4 to 5 in advance in order to generate the above, and therefore, for example, HCl having an appropriate concentration is added as an acid. In this way, when the first step is performed as shown in FIG. 1, SO ₄ ²⁻ becomes a sparingly soluble salt due to the metal salt, and as a result, it is fixed and precipitated.

Next, prior to the Se reduction step of the present invention, as a second step of the Se salt adsorption step of the present invention, ferric ion is added, and alkali is added to reach a weakly acidic region. Process the sum. As the ferric ion, although not particularly limited, FeCl ₃ is preferably used, and in that case, it is added to the treated wastewater (raw water) so as to have a concentration of about 0.5 g / l to 1 g / l. . Also, as alkali, NaOH or Ca (OH)
₂ or the like is used, and NaOH is particularly preferable because it has a fast reaction and facilitates pH adjustment. Regarding the neutralization treatment by the addition of alkali, the pH is 4 to 6,
It is preferable to adjust it to about 4.5 to 5.5 in order to precipitate the ferric ion.

When ferric ion is added in this way,
When both are neutralized, ferric ions will become weakly acidic.
By being set, Fe, which is a precipitate formed by the neutralization reaction,
(OH)₃Becomes At this time, dissolve in raw water (treatment wastewater)
Each existing Se salt (SeO ₃ ^2-, SeO_Four ^2-) No
Most of SeO₃ ^2-And some SeO_Four ^2-Is the above F
e (OH)₃Is adsorbed on.

Therefore, as a third step, Fe (OH) ₃
A high-molecular flocculant is added to the treated wastewater (raw water) in which the Fe salt is produced, and Fe (OH) ₃ adsorbing the Se salt and further the sparingly soluble salt such as BaSO ₄ previously precipitated are aggregated and settled. . Then, at a predetermined time, when aggregation and sedimentation are sufficiently performed, the sediment is separated into concentrated sediment and clear overflow water.
The polymer coagulant is not particularly limited, and conventionally known ones are appropriately used.

The precipitate obtained in the third step is further subjected to solid-liquid separation as a fourth step, and solid-liquid separation is carried out into cake which is a solid content and filtered water. For solid-liquid separation, a known solid-liquid separation device can be used. Since the cake thus obtained contains the Se salt,
Do not treat it as general waste, but treat it with an appropriate treatment method based on regulations. On the other hand, the drained water is returned to the third step and reused.

Regarding the overflow water obtained in the third step, as a fifth step which is the Se reduction step in the present invention, Fe powder (iron powder) is added to this overflow water (treatment wastewater), and it is appropriately added. By stirring, each of the Se acid salts is reduced. At this time, in order to promote the reduction reaction smoothly, HCl of a proper concentration is added to the overflow water (treatment wastewater) in advance,
Adjust the pH to about 3.5-4.5. F to add
The e powder is not particularly limited, but has an average particle size of about 5 to 300 μm and a particle size range of 10 to
Those having a thickness of about 100 μm are preferably used. Regarding the addition of the Fe powder, a molar amount that is an excess amount with respect to the dissolved Se concentration is added. In addition, when the Fe powder is added, it is preferable to add the Fe powder not in a single amount but in a plurality of times. This is F during the reduction process.
This is because the surface of the e-powder changes and the ability as a reducing agent deteriorates, so that the fresh Fe powder is always present in the treated wastewater by adding it in multiple times.

When the Fe powder is added in this way and the reduction treatment is performed by stirring, each of the Se salts is reduced and the metal S is reduced.
It becomes a complex such as e or FeSe, which becomes insoluble and is suspended, aggregated, or settled in the treated wastewater.

Then, as a sixth step, a magnetic separation treatment is carried out in which the unreacted Fe powder is separated and collected by adsorption and separation by a magnet. Then, unreacted F separated from the treated wastewater
The e powder is washed with diluted HCl, and then, as a seventh step, a sedimentation treatment is performed to separate the Fe powder and the washing water. The Fe powder thus obtained is returned to the fifth step and reused. As for the washing water, Fe ions (Fe ₂ ) mixed with hydrogen peroxide water (H ₂ O ₂ ) are added.
²⁺ ) is oxidized and then sent back to the first step for reuse.

On the other hand, regarding the treated wastewater remaining after the magnetic separation treatment, as the eighth step which is the ion removal step in the present invention, the Fe ions generated in the Se reduction step (fifth step) are oxidized to form a hardly soluble substance. At the same time, the residual portion of the metal ion (for example, Ba ²⁺ ) added in the sulfate ion removing step (first step) is made difficult to be a poorly soluble material. That is, in order to oxidize Fe ions, H ₂ O ₂ is added so that (H ₂ O ₂ /2Fe)=0.6 to 1 times the molar amount of Fe ions, and metal ions (for example, Ba ^{2 +} )
In order to make the residual component of the insoluble matter into a hardly soluble substance, for example, Ba ²⁺
If (SO ₄ ^2- / Ba ²⁺ ) = 1.2 to 1.5 times mol, and Na ₂ SO ₄ is added.

Subsequently, NaOH is added to treat the treated wastewater with p
A weak coagulant was added to this treated wastewater while neutralizing to a weakly acidic region of about H 5.5 to 5.8, and a sparingly soluble product, that is, Fe (OH) ₃ and a sulfate (for example, BaSO ₄ ) is further aggregated and precipitated. And
After a predetermined period of time, when aggregation and sedimentation have been sufficiently performed, a concentrated precipitate is separated into clear overflow water. The polymer flocculant is not particularly limited, as in the case of the third step above, and conventionally known ones are appropriately used.

The precipitate obtained in the eighth step (ion removing step) is further subjected to solid-liquid separation as a ninth step, and solid-liquid separation is performed into a cake which is a solid content and filtered water. For solid-liquid separation, a known solid-liquid separation device can be used. Since the cake thus obtained contains Se as in the case of the fourth step, the cake is treated by an appropriate treatment method based on regulations without being treated as general waste. On the other hand, the drained water is returned to the eighth step and reused.

The overflow water obtained in the eighth step was neutralized by adding NaOH so that the pH was in the range of 5.8 to 8.6. As the wastewater that has been removed and treated in the same way, it is drained in the same way as general wastewater.

In such a method for treating selenium-containing wastewater, SO ₄ ²⁻ in the treated wastewater is precipitated and removed in advance as a sparingly soluble salt in the sulfate ion removing step. Se salt adsorption step by addition,
It is possible to efficiently remove the Se salt in the Se reduction step by adding Fe powder, and therefore it is difficult to remove the Se salt from the waste water containing SeO ₄ ²⁻ which was difficult to remove by the conventional method.
It can be processed so that the e concentration is equal to or lower than the environmental standard value. Also, the drug used is barium chloride (BaC).
l ₂ ), iron chloride (FeCl ₃ ), Fe powder, etc., are easy to handle, and are therefore a good processing method in terms of workability and the like.

Further, after the Se reduction step, metal ions such as Fe ions and Ba are separated as refractory substances by an ion removal step, so that the obtained overflow water is simply subjected to a very general treatment such as pH adjustment. The selenium-containing wastewater can be treated efficiently and easily so that it can be discharged as general wastewater simply by performing it.

In the above embodiment, after the sulfate ion removing step, the Se acid salt adsorbing step, the Se reducing step, and the ion removing step are carried out. However, the present invention is not limited to this, After the removal step, only the Se reduction step may be performed, and even in that case, a sufficiently high effect on the removal of the Se salt can be obtained.

[0025]

EXAMPLES The present invention will be described more specifically by way of examples. (Example 1) Samples 1-1 to 1-4 were prepared as shown in Table 1 as waste water containing Se salt. However, Sample 1-2 and Sample 1-4 were the same raw water (waste water). These samples 1-1 to 1-4 are the same as those of sample 1-3.
Examination of ⁴⁺ (tetravalent selenium) revealed that it ^contained Se ⁶⁺ (hexavalent selenium) because it was less than the total concentration of Se. In addition, SO ₄ ^{2- in} these samples The concentration was investigated, and the obtained results are shown in Table 1.

[0026]

[Table 1]

First, to each of these samples 1-1 to 1-4, BaCl ₂ .2H ₂ O was added in an amount shown in Table 1, and hydrochloric acid was added in an appropriate amount to adjust its pH to a value shown in Table 1. Adjusted to. In addition, “BaCl ₂ · 2H ₂
In the column of “O”, the value in parentheses on the right side of the value is (SO ₄ ^2- ) To the addition mole multiple, that is, (B
a ²⁺ / SO ₄ ^2- ) Is shown. In this way SO ₄ ^2- Is BaSO _4, and after being made insoluble,
A sedimentation process was performed. As the sample to be subjected to the subsequent Se reduction step, the suspensions obtained in Sample 1-1, Sample 1-3, and Sample 1-4 and the filtered water obtained in Sample 1-2 were used.

Then, in the Se reduction step, the amounts of HCl shown in Table 1 were added to each of the above-mentioned samples, and the pH was adjusted to the range shown in the lower side of Table 1, and then Fe powder was added. The added Fe powder had an average particle size of 42 μm and a particle size range of 10 to 100 μm, and 87% by weight of 45 μm or less. Regarding the addition of Fe powder, in Samples 1-1 and 1-2, 1.0 g was added twice at a time of 1.0 g, and a total of 2.0 g was added. On the other hand, in Samples 1-3 and 1-4, 0.5 g was added four times, for a total of 2.0 g. Regarding the reaction time at this time, Sample 1-1, Sample 1
In No. 2, the Fe powder was added and stirred for 60 minutes to cause the reaction, and in Samples 1-3 and 1-4, the Fe powder was added and stirred for 30 minutes to react each. The Se concentration in the supernatant of the treated water thus obtained was examined, and the obtained results are shown in Table 1. From the results shown in Table 1, it was confirmed that the Se concentration was lower than that of the wastewater before treatment.

(Example 2) As waste water containing Se salt,
As shown in Table 2, samples 2-1 to 2-4 were prepared.
However, Sample 2-1 is the same raw water (waste water) as Sample 1-3 above, and Sample 2-2, Sample 2-3, and Sample 2-4 are the same raw water as Sample 1-2 and Sample 1-4 above. (Waste water).

[0030]

[Table 2]

Firstly, respectively the samples 2-1 to 2-4, as with the previous case of Embodiment 1 BaCl ₂ · 2
H ₂ O was added in the amount shown in Table 2, and hydrochloric acid was added in an appropriate amount to adjust the pH to the value shown in Table 2, and SO ₄ ^2- Was used as BaSO ₄ to make it insoluble.

Next, FeCl ₃ was added to each of these samples.
And NaOH were added in the amounts shown in Table 2, respectively, and adjusted to a weakly acidic region to form FCl ₃ which is a precipitation product of the neutralization reaction of FCl _3.
e (OH) ₃ was generated, and Se was adsorbed on it. Then, each sample after the reaction was subjected to sedimentation treatment. Samples 2-1, 2-2, and 2-2 were used as samples for the subsequent Se reduction step.
The filtered water obtained in -4 was used, and the suspension obtained in sample 2-3 was used. In addition, when the dissolved Se concentrations of the filtered water of Sample 2-1 and the filtered water of Sample 2-4 were examined here, as shown in Table 2, all were significantly lower than the Se concentration of the sample before treatment. Was.

Then, in the Se reduction step, the amounts of HCl shown in Table 2 were added to each of the above-mentioned specimens to adjust the pH to the range shown in the lower side of Table 2, and then the same Fe as in Example 1 was used. The flour was added. Regarding the addition of Fe powder, 0.5 g was added four times to all the samples, and a total of 2.0 g was added. Regarding the reaction time at this time, Sample 2-1 and
Samples 2-2 and 2-3 each had 30 after adding Fe powder.
The reaction was carried out by stirring for 15 minutes, and in sample 2-4, the reaction was carried out by stirring for 15 minutes after each addition of Fe powder.

After reacting in this way, unreacted F
The e powder was subjected to magnetic separation separation treatment, and the Se concentration (treated water Se) of the sample (treated water) after the separation treatment was examined, and the obtained results are shown in Table 2. Further, the Ba concentration (treated water Ba) of the sample (treated water) after the separation treatment was also investigated, and the obtained results are shown in Table 2. From the results shown in Table 2, compared to the wastewater before treatment,
It was found that the Se concentration was lowered. Further, it was found that in Samples 2-1 and 2-4, the Se concentration was further reduced as compared with the case where the examination was performed after the treatment with FeCl _{3 described} above.

Then, as a treatment for flowing the obtained samples (treated water) as general waste water, H ₂ O ₂ was added to each sample to oxidize the Fe ions generated in the Se reduction step described above, thereby refractory substances. At the same time, Na ₂ SO ₄ was added and the residual portion of Ba ²⁺ added in the sulfate ion removing step was used as a hardly soluble substance. Subsequently, NaOH was added to each sample to neutralize it,
Further, solid-liquid separation was performed. Se concentration (treated water Se) and Ba concentration (treated water B) of treated water (overflow water) after solid-liquid separation
A) was examined again, and the obtained results are shown in Table 2.

From the results shown in Table 2, it was found that in the treatment here, there was no great change in the Se concentration, while the Ba concentration was significantly decreased. In addition,
The Se concentration of the sample 2-3 is increased by the treatment here because the Se salt adsorbed on the hardly soluble substance (precipitate) caused a secondary reaction by the addition of Na ₂ SO ₄ . It is considered that a part was eluted.

(Example 3) As waste water containing Se salt,
As shown in Table 3, samples 3-1 to 3-4 were prepared.
These samples had significantly lower Se concentrations than the samples used in Examples 1 and 2 above.

[0038]

[Table 3]

Samples 3-1 to 3-4 were treated in the same manner as in Example 2. From the results shown in Table 3, the Se concentration (treated water Se) of the treatment liquid obtained in the Se reduction step using Fe powder is significantly lower than the environmental standard value of 0.01 mg / l, and The effect of the method was confirmed. It was also confirmed that the Ba concentration (treated water Ba) of the sample (treated water) after the separation treatment after adding H ₂ O ₂ and Na ₂ SO ₄ was also significantly reduced.

(Comparative Example 1) For comparison, the Se salt adsorption step was directly carried out without removing sulfate ions. Samples 4-1 to 4-6, as shown in Table 4, were used as samples containing the Se salt.
Prepared. However, Samples 4-1 to 4-4 are assumed to contain sulfate ions (SO ₄ ²⁻ ), and Samples 4-5 and 4-6
Was prepared using pure water so as not to contain sulfate ions. Sample 4-2 was the same raw water (waste water) as Sample 1-3 above, and Sample 4-4 was the same raw water (waste water) as Samples 3-1 and 3-2 above.

[0041]

[Table 4]

By adding FeCl ₃ and NaOH as in Examples 2 and 3 to these samples without removing the sulfate ions as in Examples 1 to ₃ , the S
An e-acid salt adsorption step was performed. The Se concentration in the supernatant of the treated water thus obtained was examined, and the obtained results are shown in Table 4.
It was shown to. From the results shown in Table 4, samples 4-1 to 4-4
Then, the Se removal rate was about 50 to 75%, and the residual Se concentration in the treated water was 0.2 to 0.38 mg / l.
Further, in Samples 4-5 and 4-6, the Se removal rate is higher than in the cases of Samples 4-1 to 4-4. Therefore, the absence of sulfate ions is effective in the removal of Se. It was confirmed.

(Comparative Example 2) For comparison, the Se reduction step was directly carried out without removing sulfate ions. Samples 5-1 to 5-6 were prepared as shown in Table 5 as samples containing the Se salt. However, Samples 5-1 to 5-4 were assumed to contain sulfate ions (SO ₄ ²⁻ ), and Samples 5-5 and 5-6 were prepared using pure water so as not to contain sulfate ions. Samples 5-1 and 5-2 are the same raw water (waste water) as the previous sample 1-1, sample 5-3 is the same raw water (waste water) as the previous sample 4-3, and sample 5-5 is the same. The same raw water (waste water) as Sample 4-5 was used, and Sample 5-6 was the same raw water (waste water) as Sample 5-6.

[0044]

[Table 5]

For these samples, the sulfate ions were not removed as in Examples 1 to 3 above, and Examples 1, 2, and 3 were used.
Then, the Se reduction step was performed by adding the Fe powder (the same as that in Example 1) performed in step 3. The Se concentration in the supernatant of the treated water thus obtained was examined, and the obtained results are shown in Table 5. From the results shown in Table 5, sample 5-1
In 5-3, the removal rate of Se is about 40-65%,
The residual Se concentration in the treated water was 0.4 to 0.5 mg / l. Further, in Samples 5-5 and 5-6, Samples 5-1 to 5
-4, the removal rate of Se is higher than that in the case of -4.
It was confirmed to be effective in removing e.

Comparative Example 3 For comparison, after removing sulfate ions, only the Se salt adsorption step was performed. As the sample containing the Se salt, as shown in Table 6, samples 6-1 to 6-
Prepared up to 5. However, sample 6-1 is the same as sample 1-
The same raw water (wastewater) as 3 was used, and sample 6-2 was sample 1-
The same raw water (wastewater) as 2 was used, and samples 6-3, 6-4, 6-
No. 5 was the same raw water (waste water) as Samples 3-1, 3-2 above.

[0047]

[Table 6]

Sulfate ion removal was performed on these samples in the same manner as in Examples 1 to 3 above, and then FeCl ₃ and NaOH as in Examples 2 and ₃ were added.
The Se salt adsorption step was performed. The Se concentration in the supernatant of the treated water thus obtained was examined, and the obtained results are shown in Table 6. From the results shown in Table 6, it was confirmed that the Se concentration was lower than that of the wastewater before treatment. In addition, as compared with Comparative Example 1 in which sulfate ion removal is not performed, S
It was found that the concentration of e was lowered, and it was confirmed that the absence of sulfate ion is effective for the removal of Se.

[0049]

As described above, the selenium-containing wastewater treatment method of the present invention is a treatment method in which SO ₄ ^2- in the treatment wastewater is precipitated and removed in advance as a sparingly soluble salt in the sulfate ion removing step. After that, the Se salt can be efficiently removed by performing the Se reduction step by adding the Fe powder, and therefore the Se concentration of the waste water containing SeO ₄ ² -which was difficult to remove by the conventional method, can be improved. Can be sufficiently reduced. Moreover, since the chemicals used are barium chloride (BaCl ₂ ) and Fe powder, the chemicals are easy to handle, and the workability is good.

If a Se salt adsorption step is provided between the sulfate ion removal step and the Se reduction step, S
By further reducing the e concentration, it is possible to process the Se concentration of the treated wastewater to an environmental standard value or less.

If an ion removing step is provided after the Se reducing step, the treated wastewater obtained by separating metal ions such as Fe ions and Ba as hardly soluble substances is simply subjected to pH adjustment or the like. The wastewater containing selenium can be treated efficiently and easily so that it can be discharged as general wastewater by performing only a very general treatment.

[Brief description of drawings]

FIG. 1 is a process flow chart for explaining an example of an embodiment of a method for treating selenium-containing wastewater according to the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoki Yamaguchi             1-297 Kitabukuro-cho, Saitama City, Saitama Prefecture             Terial Co., Ltd. (72) Inventor Kazuya Koyama             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             National Institute of Advanced Industrial Science and Technology Tsukuba Center F-term (reference) 4D038 AA08 AB36 AB70 AB81 BB06                       BB11 BB13 BB15 BB16 BB18                 4D050 AA13 AB41 AB59 BA02 BB09                       CA06 CA11 CA13 CA16

Claims (3)

[Claims] To 1. A SeO ₃ ^2- and SeO ₄ process ^{wastewater 2} and is dissolved with the addition of metal ions which react with the SO ₄ ^2- to produce a sparingly soluble salt, SO ₄ of the treatment in the wastewater Sulfate ion removal step of precipitating ^2- as a sparingly soluble salt, and after the sulfate ion removal step, Fe powder is added to the treated wastewater after removal of the sparingly soluble salt to reduce each Se acid salt, and S
and a Se reduction step of separating e as a hardly soluble substance from the treated wastewater, the method for treating selenium-containing wastewater. 2. Between the sulfate ion removing step and the Se reducing step, a ferric ion is added to the treated wastewater after SO ₄ ^2- is precipitated as a sparingly soluble salt, and an alkali is added to weakly acidize the treated wastewater. Se acid for performing neutralization treatment up to the region, adsorbing each of the Se salts to the iron salt neutralization reaction product precipitate, and further separating the Se salt adsorbed iron salt neutralization reaction product precipitate from the treatment wastewater The method for treating selenium-containing wastewater according to claim 1, further comprising a salt adsorption step. 3. After the Se reduction step, the Fe ions generated in the Se reduction step are oxidized to form a sparingly soluble substance, and SO ₄ ^2- remaining in the waste water is added to form a sparingly soluble salt. 3. The treatment of selenium-containing wastewater according to claim 1 or 2, further comprising: an ion removing step of making the hardly-dissolved metal ions into a hardly-soluble substance and separating the hardly-soluble substance from the treated wastewater. Method.