JP2013202521A - Treatment method of selenium-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly efficiently remove selenium in a shorter time compared to addition of a reducing agent in a solution state when reducing the selenium.SOLUTION: In a treatment method of selenium-containing waste water, for introducing the selenium-containing waste water to a reaction tank, adding a reducing agent into the reaction tank, and coprecipitating/removing selenium together with the reducing agent, powder of ferrous salt is used as the reducing agent.

Description

  The present invention relates to a method for treating wastewater containing selenium, and more particularly, to a method for continuously and efficiently removing selenium contained in wastewater generated during the treatment of electrolytic precipitates and the like in non-ferrous smelting. This is a proposal.

  In non-ferrous smelting, especially in the electrolytic smelting process of copper, a precipitate containing selenium is generated as a smelting intermediate. Conventional smelting processes usually have a step of recovering selenium from this selenium-containing precipitate. However, the selenium generated in this selenium recovery step contains selenium that has been dissolved in an aqueous solution and cannot be recovered at a relatively high concentration as selenous acid or selenic acid. Therefore, since such waste water cannot be discharged as it is outside the factory, it is necessary to collect selenium from the waste water.

As a technology to recover selenium from selenium-containing wastewater,
(1) By introducing selenium-containing wastewater into a batch-type reaction tank and adding ferrous salt to the wastewater, selenium in the wastewater reacts with the ferrous salt to coprecipitate selenium and iron. A method of collecting as a product,
(2) The ferrous salt equivalent to twice the molar amount of the selenium content is added to the selenium-containing wastewater, and then the pH of the selenium-containing wastewater is adjusted to 3 to 5, corresponding to 0.5 to 1 times the molar amount. Method of promoting oxidation and hydrolysis of ferrous salt by adding an amount of copper salt, and further maintaining the pH of selenium wastewater at 5 to 6 and recovering the selenium by coprecipitation with ferric hydroxide (See Japanese Patent Publication No. 48-030558),
(3) In the method of (2), the treatment of selenium-containing wastewater is performed in multiple stages, and a reducing agent is added in each stage (see JP 09-249922 A).
Etc. are known.

Japanese Patent Publication No. 48-030558 JP 09-249922 A

  The prior art (1) in which ferrous salt is added to remove selenium has a slow reaction rate, and it takes too much time to reduce the selenium concentration to the waste water discharge allowance standard. There was a problem of increasing the size.

  In addition, the prior art (2) disclosed in Patent Document 1 relates to a technique for improving the treatment method using the ferrous salt, and can reduce the selenium concentration in wastewater relatively quickly. It is technically difficult to continuously adjust the pH and the copper addition with high efficiency and high efficiency after adding the iron salt, and this is a technique that can be carried out only in a batch system. Accordingly, the amount of selenium-containing wastewater to be treated is limited, and it has not been possible to solve the desire to continuously treat selenium-containing wastewater that is continuously discharged.

The prior art (3) disclosed in Patent Document 2 is an improved technique of the prior art (2), and continuously and efficiently removes selenium contained in waste water. In a more preferred embodiment, the pH in each stage of reaction is controlled to the alkali side to stabilize the FeOH ⁺ layer that contributes to the reduction of selenium, thereby increasing the reaction rate of selenium in wastewater and removing selenium. Techniques for improving the rate are disclosed. However, there remains room for improvement in that selenium reduction still takes time.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and the object is to remove selenium contained in wastewater with high efficiency in a short time.

  As a result of intensive studies on the problem of removing selenium contained in wastewater with high efficiency in a shorter time, the present inventor did not make the ferrous salt added as a reducing agent into a solution, but a powder. By making it into a state, it has been found that selenium contained in the waste liquid can be performed in a shorter time and with higher efficiency, and the present invention has been completed.

Therefore, the present invention is as follows.
(1) In a method for treating selenium-containing wastewater in which wastewater containing selenium is introduced into a reaction vessel, a reducing agent is added to the reaction vessel, and selenium is coprecipitated and removed together with the reducing agent, ferrous iron as the reducing agent A method for treating selenium-containing wastewater, wherein a salt powder is used.
(2) The method according to (1), wherein the reducing agent is ferrous sulfate.
(3) The method according to (1) or (2), wherein the particle size measured with a sieve of the reducing agent is 1 mm to 150 μm.
(4) The reducing agent is added at an iron content addition ratio of 765 to 1529 times the content of selenium in the selenium-containing wastewater. the method of.
(5) The method according to any one of (1) to (4), wherein the selenium concentration in the selenium-containing wastewater is 5 to 10 mg / l.
(6) The method according to any one of (1) to (5), wherein an oxidation-reduction potential during the reduction reaction is −700 mV vs Ag | AgCl (70 ° C.) or less.
(7) The method according to (6), wherein the pH of the reaction solution during the reduction reaction is 6.9 to 7.2.

  According to the method for treating selenium-containing wastewater according to the present invention, when reducing selenium, selenium can be removed with high efficiency in a shorter time than when a reducing agent is added in a solution state.

It is a flowchart which shows the processing method which concerns on embodiment of this invention. It is a graph which shows the relationship between reaction time and Se density | concentration in a reaction liquid about Experimental example 1-4 and 6. FIG.

Hereinafter, the embodiment of the processing method of the selenium content drainage concerning the present invention is described.
FIG. 1 is a flowchart showing a procedure of a method for treating selenium-containing wastewater according to this embodiment. First, pH of the selenium (Se) -containing wastewater is adjusted (step (S1)), followed by addition of a reducing agent (step (S2)), a reduction reaction (step (S3)), and filtration of the post-reaction solution. (Step (S4)), selenium (Se) metal is removed, and a post-treatment liquid is obtained as a filtrate.

  The selenium-containing wastewater applied to the treatment method of this embodiment is obtained, for example, in the process of filtration discharged in the carbonation treatment of lead soot. For example, selenium has a concentration of 5 to 10 mg / l, or 0.0008. It is contained in an amount of mass%.

Moreover, in this embodiment, in step (S2), ferrous salt is introduced as a reducing agent in a powder state.
As the ferrous salt, ferrous sulfate can be preferably used.
Further, the particle size of the particles constituting the powder can be represented by a 0.5 mm particle size, preferably 1 mm to 150 μm, more preferably 1 mm to 250 μm, and even more preferably a particle size smaller than 250 μm from the viewpoint of easy solubility.

Hereinafter, a preferred embodiment will be described with reference to FIG.
In step (S1), the pH is adjusted to near neutral, for example, 6.9 to 7.2, preferably 7.0 to 7.1, using an appropriate pH adjuster for the Se-containing waste liquid described above. Here, as a pH adjuster, an alkali and an acid can be used as appropriate. Examples of the alkali include an aqueous sodium hydroxide solution. Here, the reason for adjusting the pH to the above-described range is a pH range necessary for adjusting the potential to −700 mV as described later.

In step (S2), the reducing agent powder described above is added to the Se-containing waste liquid whose pH has been adjusted in step (S1).
If the amount of the reducing agent powder added is too small at this time, depending on the conditions of the reduction reaction in step (S3), it may take time to reduce Se, which is sufficient from the viewpoint of reducing selenium in a short time. However, if it is too large, the solubility will be poor.
The amount of iron is preferably 765 to 1529 times that of the selenium contained in the selenium-containing wastewater, and more preferably 1147 to 1529 times the amount of iron.

In step (S3), a reduction reaction is performed. The conditions for this reduction reaction are the pH adjusted in step (S1), preferably 70 ° C. or higher, and more preferably 70 to 75 ° C.
At this time, the oxidation-reduction potential (ORP) of the solution with respect to the Ag | AgCl standard electrode is −700 mV or less, preferably −760 mV or less.

  In step (S4), the post-reaction liquid obtained in step (S3) is subjected to solid-liquid separation by suction filtration using a filter paper having a diameter of 1.0 μm. Selenium is removed as a solid.

Hereinafter, a description will be given based on examples.
(Experimental Examples 1-4)
The selenium-containing wastewater to be treated was as follows.
-PH: 1.01
-ORP: 112 mV
-Se content: 1.7 mg (concentration: 8.3 mg / l)

The selenium-containing wastewater was adjusted to each pH shown in Table 1 by adding a sodium hydroxide aqueous solution having a concentration of 100 g / l at 70 ° C.
Thereafter, with respect to 200 ml of the selenium-containing waste water having the pH, the sulfuric acid solution was adjusted so as to be 0.75 g, 1.3 g, 1.95 g, 2.6 g in terms of divalent iron ion concentration while maintaining the liquid temperature. Ferrous and heptahydrate (molecular weight 278.05) powders were added, respectively, and the reduction reaction was performed for 120 minutes.

Immediately after the start of the reaction, 15 minutes, 30 minutes, 60 minutes, and 120 minutes later, a small amount (0.45 μm) was taken out and filtered through a 1.0 μm membrane filter, and the selenium concentration in the filtrate was measured.
After completion of the reaction, the post-reaction solution was filtered through a 1.0 μm membrane filter, and the selenium concentration of the filtrate was measured.
The results are shown in Table 1.

(Experimental Examples 5-8)
Except that the ferrous sulfate solution having a divalent iron ion concentration of 64.3 g / l was added in an amount of 20 ml, 40 ml, 60 ml, and 80 ml, respectively, to the selenium-containing waste water described above, and the reduction reaction was performed. In the same manner as in Experimental Examples 1 to 4, the selenium concentration in the solution component of a small sample immediately after, 15 minutes, 30 minutes, 60 minutes, and 120 minutes after the reduction reaction, and selenium in the solution component after completion of the reaction Concentration was measured. The results are shown in Table 1.

FIG. 2 shows the relationship between the reaction time and the Se concentration in the reaction solution for Experimental Examples 1 to 6 in Table 1.
According to Table 1 and FIG. 2, in Experimental Example 4 and Experimental Example 6, although the reducing agent addition amount was equal, the Se concentration became zero in a short time after the start of the reduction reaction. This suggests that Se reduction proceeded in a short time. Furthermore, it can be seen that in Experimental Example 3, Se reduction proceeded in a shorter time than Experimental Example 4 although the amount of reducing agent used was smaller than in Experimental Example 4.
In comparison between Experimental Example 2 and Experimental Example 5, there was no significant difference in se concentration change with time even when the reducing agent was introduced in the solution state or in the powder state.
In view of the above, when the reducing agent is introduced in the powder state, the result is that a remarkable effect equal to or higher than that in the case where the reducing agent is introduced in the solution state is obtained with respect to the time required for Se reduction.

Claims (7)

  In the method for treating selenium-containing wastewater, in which wastewater containing selenium is introduced into a reaction vessel, a reducing agent is added to the reaction vessel, and selenium is coprecipitated and removed together with the reducing agent. Ferrous salt powder as the reducing agent A method for treating selenium-containing wastewater, wherein   The method according to claim 1, wherein the reducing agent is ferrous sulfate.   3. The method according to claim 1, wherein the particle size measured with a sieve of the reducing agent is 1 mm to 150 μm.   The method according to any one of claims 1 to 3, wherein the reducing agent is added at an iron content addition ratio of 765 to 1529 times the mass of selenium in the selenium-containing wastewater.   The selenium concentration in the said selenium containing waste water is 5-10 mg / l, The method as described in any one of Claims 1-4 characterized by the above-mentioned.   6. The method according to claim 1, wherein an oxidation-reduction potential at the time of the reduction reaction is −700 mV vs Ag | AgCl (70 ° C.) or less.   The method according to claim 6, wherein the pH of the reaction solution during the reduction reaction is 6.9 to 7.2.

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