JP3249749B2 - Treatment method for wastewater containing selenium - Google Patents

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, and more particularly to an improvement in the efficiency of removing selenium from wastewater. They try to use it.

[0002]

2. Description of the Related Art Since selenium is dissolved at a relatively high concentration in wastewater generated in a process of treating electrolytic deposits of metal (anode mud), it is necessary to remove selenium from the wastewater. is there. As a method for removing selenium of this waste water, for example, in the case of JP-B-48-30558, the addition of Fe ²⁺ to wastewater containing selenium, then pH: the Cu ²⁺ in the range of 3-5 A method is disclosed in which the addition promotes the oxidation and hydrolysis of Fe ²⁺ and coprecipitates and recovers selenium together with the hydroxide of Fe ^{3+ in} the pH range of 5 to 6. In addition, a method is known in which one or two of water-soluble ions such as Ag ⁺ , Cu ²⁺ , and Fe ³⁺ or Fe powder are added to selenium-containing wastewater and fixed as insoluble selenide.

[0003]

Selenium in the wastewater [SUMMARY OF THE INVENTION] is usually dissolved in the form of SeO ₃ ^2- (4-valent selenium). However, it is known that when an oxidizing agent is present, this SeO ₃ ^2- changes to SeO ₄ ^2- (hexavalent selenium). As a result, in the waste water, in a state where SeO ₃ ^2-with SeO ₄ ^2-has dissolved. However, the above prior art is effective for SeO ₃ ^2-removal, SeO ₄ ^2-removal is difficult. Therefore, in the conventional technique, the removal of SeO ₄ ^2- is not sufficiently performed, and therefore, the improvement of the selenium removal efficiency cannot be expected. Further, in the conventional wastewater treatment, a large amount of iron hydroxide is generated due to the addition of iron, and reduction of the amount has been strongly desired. The main object of the present invention is to
Selenium is dissolved in SeO ₃ ^2-form to the selenium-containing wastewater, of course, is to propose wastewater treatment method capable also the recovery of selenium dissolved in SeO ₄ ^2-form. Another object of the present invention is to recover the iron content in the sediment accompanying this wastewater treatment,
The goal is to make effective use of it.

[0004]

The basic idea of the present invention is to provide a method for adding a reducing agent and a neutralizing agent to waste water containing selenium to reduce and remove selenium. This is a method for treating selenium-containing wastewater in which ferrous iron and a neutralizing agent are added and mixed, and the mixed solution is heated to a temperature of 40 to 80 ° C. in an air atmosphere to reduce selenium and remove it as a thickener precipitate. .

[0005] The present invention, in order to achieve the above objects, by adding a reducing agent and a neutralizing agent to the waste water in the containing selenium in a method for reducing and removing selenium, preliminary treatment
Process (A) after the process (B)
A selenium-containing wastewater.
First, in the pretreatment tank for de-selenium reaction,
Heat to a temperature of 40-80 ° C under
Contains selenium and ferrous iron generated in this treatment step (A)
By adding thickener sediment and neutralizing agent,
Preliminary reduction of ren, addition of sedimentation agent
After filtration, the filtration residue (Se) is separated and removed.
On the other hand, the filtrate generated at this time is
To the main processing step (A)
In step (A), the filtrate and the thickener supernatant are used.
The mixture, in the process tank for removing selenium reaction, the atmosphere, both heated to a temperature of 40 to 80 ° C., the mixture
It was added and mixed ferrous and neutralizer sulfate in the liquid to reduce the selenium, and thickening After addition of subsequent settling agent, this
Selenium and ferrous-containing thickener precipitate generated by thickening in the pretreatment step (B)
It is added to the pretreatment tank for de-selenium reaction and
And Turkey to remove the emissions proposes a processing method of the selenium-containing wastewater according to claim.

Hereinafter, a basic method for treating selenium-containing wastewater of the present invention will be described in detail. First, selenium-containing wastewater, namely the wastewater SeO ₄ ^2-was dissolved in addition to SeO ₃ ^2-, heated to a temperature range of 40 to 80 ° C. in a heater in air atmosphere. At this time, ferrous sulfate as a reducing agent and an amount equivalent to 0.5 to 3.0 g / l in terms of Fe ²⁺ ion amount and a neutralizing agent such as caustic soda and slaked lime were added to the wastewater source liquid. To adjust the pH to a range of 8 to 10. Thereafter, the mixture after the pH adjustment is stirred for 10 to 30 minutes. In the process of this step is Fe ²⁺ in the mixture is oxidized to Fe ^3+, SeO ₃ ^2- and SeO ₄ ^2-reducing is accelerated selenium generates, on the selenium Fe (OH) ₂ As it is absorbed and fixed, selenium will become
It co-precipitates with Fe (OH) ₂ to form a precipitate. What is important in the treatment at this stage is that the wastewater temperature is always heated to 40 to 80 ° C. by a heater under an air atmosphere.

FIG. 1 shows the effect of the atmosphere and the temperature of the wastewater on the Se removal efficiency.
4 is a graph showing a relationship with an addition amount (g / l). As shown in this figure, when the temperature of the wastewater source liquid is low, the nitrogen atmosphere
Good Se removal efficiency. However, at a temperature of 60 ° C., there is no difference in atmosphere. Then, in the atmosphere, when the temperature of the wastewater source liquid is set to 50 ° C. or higher, the Se removal efficiency is improved.
From this, in order to increase the Se removal efficiency, the wastewater treatment is performed in the atmosphere, and the temperature of the wastewater is 55 to 65.
It can be seen that it is effective to keep the temperature at ° C. further,
By setting the temperature of the wastewater to 55 to 80 ° C., SO ₄ ^2-
Of course, it has been newly found that it is easy to reduce SO ₄ ^2- which is hardly reducible. The reason is that the [FeOH] ⁺ layer formed on the surface of Fe (OH) ₂ or green rust particles is increased by increasing the temperature, and the reduction reaction of SO ₄ ²⁻ is promoted.

FIG. 2 shows that in a treatment in which a reducing agent and a neutralizing agent are added to selenium-containing wastewater and stirred to coprecipitate selenium with iron hydroxide, the atmosphere and the temperature of the wastewater source liquid are
4 is a graph showing the effect of selenium and iron hydroxide on the sedimentation rate. As shown in this figure, while the influence of the atmosphere is not so significant, the temperature of the wastewater
It can be seen that the sedimentation distance is significantly increased when the temperature is set to 60 ° C. That is, the temperature of the wastewater source liquid is 60 to 80 ° C in the atmosphere.
, The sedimentation velocity is significantly improved. The preferred temperature of the wastewater source solution is in the range of 55 to 65 ° C. In FIG. 2, an increase in the sedimentation speed means that the amount of fine particles that escape from the thickener as a suspension decreases, and the amount of heavy metal discharged as SS can be reduced.

In the present invention, the reason why ferrous sulfate is added in an amount corresponding to 0.5 to 3.0 g / l in terms of the amount of Fe ²⁺ ions is that F
This is because if the amount of e ²⁺ ions is small, the removal of Se will be poor, and if the amount of Fe ²⁺ ions added is increased, the cost of chemicals will be increased and the amount of generated residues will also increase. The reason for adjusting the pH of the mixture to a range of 8.0 to 10.0 by adding a neutralizing agent is as follows.
This is because the Se removal efficiency is deteriorated even when H8 or less and pH10 or more. Preferred pH levels are between 8.5 and 9.5. Next, a sedimentation agent such as a polymer flocculant is added to the mixed solution that has undergone the above treatment, and aggregation, concentration, and sedimentation of the selenium-containing substance generated in the mixed solution are measured. Separately discharge. On the other hand, the thickener precipitate after concentration is refluxed into the original liquid of the wastewater and reused.

Next, the basic processing of the present invention will be specifically described with reference to FIG. Selenium-containing wastewater 1 is supplied to a heating and mixing tank 2. The wastewater source liquid 3 in the heating and mixing tank 2 is heated and maintained at 55 to 65 ° C., and ferrous sulfate 4 as a reducing agent is added. Next, the wastewater source liquid 3 is transferred to the main treatment tank 5 for de-selenium reaction , a neutralizing agent 6 such as NaOH is added, and the mixture is stirred and mixed for about 30 minutes to adjust the pH to 8.5 to 9.5. Reduce selenium.

Next, the mixed solution in the main treatment tank 5 for the de-selenium reaction is transferred to a settling agent addition tank 7 where a settling agent 8 is added and then transferred to a thickener 9. Selenium and Fe (OH) ₂ are co-precipitated by the thickening treatment in the thickener 9 and collected as a thickener precipitate 12. On the other hand, the supernatant liquid 10 is discharged into the liquid storage tank 11. The heating of the waste liquid is preferably carried out by an electric heater, steam injection, or the like. In addition, the main treatment tank 5 for the de-selenium reaction is used.
Can be used in plural as needed.

Next, the thickener precipitate 12 is collected in a recovery tank.
Transfer to 13 where sulfuric acid 14 is added and the solution is filtered 15
The selenium is removed while remaining in the residue, while the Fe ²⁺ solution is recovered. That is, the obtained filtrate 16 is temporarily stored in the adjustment tank 17, and ferrous sulfate is added to the filtrate transferred into the adjustment tank as needed to adjust the Fe ²⁺ concentration. The adjusted ferrous sulfate solution is supplied to the heating and mixing tank 2 described above.
Is reused as ferrous sulfate 4 to be added to the iron.

[0013] Under this concept, the present invention is to reuse the form of thickener precipitate, which for the preliminary treatment to preliminarily reduce the selenium concentration in the waste water is added to the selenium-containing wastewater It is a method to reuse. That is,
Since the thickener precipitate 12 in the thickener 9 is a coprecipitated selenium and iron (Fe (OH) ₂ ), ferrous iron is present in the thickener precipitate 12 together with selenium.
Therefore, when the thickener precipitate 12 is supplied into the selenium-containing wastewater, the thickener precipitate can act as a reducing agent. This is because, as shown in the following reaction formula, SeO ₃ ^2- and SeO ₄ ^2- in selenium-containing wastewater are reduced by ferrous iron (Fe ²⁺ ) in the thickener precipitate to produce selenium. Then, selenium is removed. H ₂
SeO ₄ + 9Fe (OH) ₂ → Se + 3Fe ₃ O ₄ + 10H ₂ O

Then, the thickener supernatant liquid generated in the pretreatment step (B) is supplied to the main treatment tank 5 for the selenium removal in the selenium original wastewater treatment (selenium reduction removal treatment) step (A). When such preliminary treatment (B) is performed, the concentration of selenium during wastewater treatment is reduced in advance in this treatment (B) , so that the subsequent treatment in the original wastewater treatment step (A) is efficiently performed. This is also preferable in reducing the amount of ferrous sulfate used.

A method for treating selenium-containing wastewater comprising the preliminary treatment (B) and the main treatment (A) will be described with reference to FIG. In the pretreatment step (B) , the selenium-containing wastewater 1 is first
It is introduced into the pretreatment tank 2B for de-selenium reaction . In addition, the de
In the selenium reaction pretreatment tank 2B , while adding the ferrous-containing thickener precipitate 12 generated in the present treatment step (A) ,
Neutralizing agent 6 such as NaOH was also added, wherein the pH of the mixture was adjusted to about 9, and mixed with heating and stirring for about 30 minutes. Next, the mixed solution is transferred to a settling agent addition tank 7B, where a settling agent 8 is added, and then transferred to a thickener 9B. In the thickener 9B, a liquid phase and a solid phase are separated and concentrated.

[0016] When the above pre-treatment (B) is completed, the supernatant liquid 10B for the thickener. 9B, hot mix and de selenium reaction
It is transferred to the main treatment tank 5 for deselenization reaction which functions as a tank . On the other hand, the sediment 12B generated in this thickener 9B is:
The filtrate 16B is filtered into a filter 15B, and the filtrate 16B is mixed with the supernatant 10B and then charged into the main treatment tank 5 for de-selenium reaction . The filtration residue (Se) is discarded. Then, in the main treatment tank 5 for de-selenium reaction, the liquid temperature is heated and maintained at 60 ° C., and ferrous sulfate 4 is added as a reducing agent. Further, a neutralizing agent 6 is added, the pH is adjusted to about 9, and the mixture is mixed by stirring for about 30 minutes. The mixed solution is transferred to a sedimentation agent addition tank 7, where a sedimentation agent 8 is added, and then a thickening treatment is performed in a thickener 9 to perform solid-liquid separation. The supernatant liquid 10 generated at the time of this thickening treatment is discharged to a liquid storage tank 11, while the thickener precipitate 12 is sent to a pretreatment tank 2B for a de-selenium reaction . By repeating the above steps, the selenium concentration is removed to an extremely low level while recycling the precipitate.

REFERENCE EXAMPLE The selenium-containing wastewater was treated by the method shown in FIG. In other words, selenium-containing wastewater is
Wastewater source solution obtained by heating to a temperature range of to 60 ° C., ferrous sulfate, with respect to the dissolved selenium amount as Fe ²⁺ ion content 0.5
~ 2.0 g / l, and NaOH as a neutralizing agent.
Was added to adjust the pH of the mixture to 9. Then, the mixture is stirred for 30 minutes, and Cliffloc is used as a precipitant.
After adding (trademark), selenium is converted to Fe (OH)
_By coprecipitation with ₂ , a thickener precipitate was obtained. On the other hand, the components of the supernatant liquid in this thickener were measured. The results are shown in Table 1 together with the component analysis results of the wastewater source liquid.

[0018]

[Table 1]

Further, according to the method shown in FIG. 3, the above-mentioned thickener precipitate was reused as a reducing agent. That is, sulfuric acid was added to the precipitate obtained from the thickener to adjust the pH to 5, and then this solution was filtered to separate and remove selenium, and further, ferrous sulfate was appropriately added to the filtrate. , The Fe ²⁺ concentration was adjusted to 12.5 g / l.
Then, the solution after the adjustment was led to the heating and mixing tank 2 and was added to the wastewater source solution to try reuse. We investigated the recovery rate of iron by reuse when the above operations were repeated. Table 2 shows the results together with the liquid compositions before and after the treatment.

[0020]

[Table 2]

[0021] Table According to the method as shown in 2, SeO ₄ at only heating and pH adjustment of the waste water source fluid, which has been conventionally difficult
^{Since 2-} can be recovered, the selenium removal rate of selenium-containing wastewater can be improved. Further, in the present method, the sediment generated accompanying the selenium removal treatment is effectively reused without being discarded, so that the amount of waste can be reduced and resources can be saved.

EXAMPLE A two-stage treatment of wastewater containing selenium was performed according to the present method shown in FIG. In this method, ferrous sulfate is added to a wastewater source liquid obtained by heating selenium-containing wastewater to a temperature range of 60 ° C. in an air atmosphere, and then pH is adjusted to 9 by adding NaOH, and then mixed. The solution was stirred for 30 minutes, and selenium was co-precipitated with Fe (OH) _{2 using} a thickener to obtain a thickener precipitate. Then, as shown in FIG. 4, the thickener precipitate obtained in this treatment is introduced into a pretreatment tank for a selenium removal reaction, and a pretreatment for reducing the selenium concentration of the selenium-containing wastewater is performed. Thereafter, the mixture was led to the main treatment tank for the de-selenium reaction , and the above-described steps were repeated. Table 3 shows the results of measurements of the components of the liquid after treatment and the components of the wastewater source liquid obtained under this method. As shown in Table 3, it was possible to recover SeO ₄ ^2- , which was conventionally difficult, and at the same time, it was possible to improve the selenium removal rate of selenium-containing wastewater.
In addition, the sediment produced during the selenium removal treatment can be effectively reused without being discarded, so that the amount of waste can be reduced and resources can be saved.

[0023]

[Table 3]

[0024]

As described above, according to the present invention, it is possible to effectively recover SeO ₄ ^2- , which has been difficult in the past, and to improve the selenium removal rate of selenium-containing wastewater. it can. In addition, the sediment generated during the selenium removal treatment can be effectively reused without being discarded, which leads to reduction of waste and realization of resource saving.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the atmosphere, the temperature of a wastewater source liquid and the amount of Fe added on selenium removal.

FIG. 2 is a graph showing the effect of the atmosphere and the temperature of the wastewater source liquid on the sedimentation rates of selenium and iron hydroxide.

FIG. 3 is a schematic view showing a processing step according to the present invention.

FIG. 4 is a schematic view showing another processing step according to the present invention.

[Explanation of symbols]

 1 Wastewater containing selenium 2 Heat treatment tank 2BFor de-selenium reactionPretreatment tank 3 Wastewater source solution 4 Ferrous sulfate 5 Deselenium reactionBookbindingTank 6 Neutralizing agent 7,7B Precipitant addition tank 8 Precipitant 9,9B thickener 10,10B Supernatant 11 Storage tank 12,12B Thickener precipitate 13 Recovery tank 14 Sulfuric acid 15 Filtrate 15B Filter 16 Filtrate 17 Adjustment tank A main processingProcess  B Preliminary processingProcess

Claims (3)

(57) [Claims] A method for reducing and removing selenium by adding a reducing agent and a neutralizing agent to wastewater containing selenium,
After the processing in the preliminary processing step (B), the processing in the main processing step (A)
In the pretreatment step, selenium-containing
First, waste water is removed from the atmosphere in a pretreatment tank for de-selenium reaction.
While heating to a temperature of 40-80 ° C in an atmosphere, this waste
In the water, selenium generated in this treatment step (A) and
The addition of the ferrous thickener precipitate and the neutralizing agent
Selenium is preliminarily reduced, and a sedimentation agent is added.
After filtration, the residue (Se) is filtered.
While separating and removing, the filtrate generated at this time is thickened.
It is sent to this treatment step (A) together with the supernatant, and then the
In the present treatment step (A), the filtrate and the thickener
Place the mixture of the supernatant in the main treatment tank for de-selenium reaction.
Then, the mixture was heated to a temperature of 40 to 80 ° C. in the atmosphere , and at the same time, ferrous sulfate and a neutralizing agent were added to and mixed with this mixture to reduce selenium, and then the sedimentation agent was removed. After the addition, the selenium and the ferrous-containing thickener precipitate generated by the thickening are subjected to the pretreatment process.
Extent the processing method of the selenium-containing wastewater, wherein by the Turkey to remove selenium in waste water by adding to the pretreatment tank for removal of selenium reaction of (B). 2. A pre-treatment tank for de-selenium reaction and a de-selling reaction
The treatment method according to claim 1, wherein the pH of the liquid to be treated is adjusted in the range of 8 to 10 when the neutralizing agent is added to the main treatment tank for the reaction . Wherein the addition amount of the ferrous sulfate to de selenium reaction the process tank is in claim 1, characterized in that in the range of 0.5 to 3.0 g / l as Fe ²⁺ ion content The processing method described.