WO2007080686A1

WO2007080686A1 - Process for the disposal of selenium-containing wastewater

Info

Publication number: WO2007080686A1
Application number: PCT/JP2006/321244
Authority: WO
Inventors: Yasuto Kashiwagi
Original assignee: University Of Tsukuba
Priority date: 2006-01-12
Filing date: 2006-10-25
Publication date: 2007-07-19
Also published as: JP5211320B2; JPWO2007080686A1

Abstract

A process for removing effectively selenium and selenium compounds from wastewater containing selenium and selenium compounds in a short time under ordinary temperature conditions at a low cost and collecting vaporized selenium and selenium compounds. This process comprises the step (a) of adding an inorganic acid to wastewater to adjust the pH of the wastewater to 3 or below, the step (b) of throwing iron powder into the resulting wastewater, the step (c) of agitating the wastewater at ordinary temperature, the step (d) of passing air containing the gas generated in the step (c) through a potassium permanganate solution acidified with sulfuric acid, the step (e) of reducing residual potassium permanganate contained in the solution and then adding the resulting solution to the wastewater, and the step (f) of conducting the steps (a), (b) and (c).

Description

Specification

Selenium-containing wastewater treatment method

Technical field

The present invention relates to a wastewater treatment method for removing selenium and a selenium compound from wastewater containing selenium and a selenium compound efficiently and at low cost in consideration of safety in the work environment.

Background art

[0002] Selenium is used as a raw material, a secondary ingredient in various manufacturing processes such as semiconductors, glass, batteries including solar cells, red pigments, metal surface colorants, pharmaceuticals, flue gas desulfurization processes, and petroleum refining processes. It is handled as a product or a substance to be removed. However, since selenium and selenium compounds are harmful substances, selenium and selenium compounds have been revised on December 27, 1993 by the partial amendment of the Water Pollution Control Act (Decree No. 401 of 1993). Were added to the drainage standard health items, and the drainage standard value was set at 0.1 mgZ liter.

[0003] Currently, the drainage power treatment methods for removing selenium and selenium compounds include neutralization coagulation precipitation method, iron hydroxide precipitation method, coagulation precipitation method such as ferrite precipitation method, ion exchange membrane method, activated charcoal. Adsorption methods and the like are known. By the way, selenium in waste water is usually colloidal selenium, oxidation number 4 valent selenite ion (SeO ² ) or oxidation number 6 valent selenate ion (SeO ² ").

It often exists as 3 4. As a treatment method for such selenium-containing wastewater, a coagulation sedimentation method and an ion exchange method are often employed. Among these, as an example of the coagulation sedimentation method, Japanese Patent Application Laid-Open No. 2000-167572 discloses a method of evaporating and concentrating selenium-containing wastewater, adjusting the pH of the concentrated water to 6 or less, and warming it to 60 ° C or higher to form a metal. Disclosed is a method for treating selenium-containing water by contact with iron or by adding iron (Π) salt. As another example of the coagulation precipitation method, Japanese Patent Application Laid-Open No. 10-218611 discloses a reduction in which sulfuric acid is added so that the concentration of sulfuric acid in the selenium-containing solution is 3.5 to 6N, and metal powder or metal ion power is also obtained. A method for treating a selenium-containing solution in which selenium is precipitated as a selenide of a reducing agent metal by adding an agent and treating at a temperature of 80 ° C. or higher is disclosed.

[0004] As an example of the ion exchange method, Japanese Patent Application Laid-Open No. 09-239377 discloses selenate ions. Selenium containing wastewater containing selenium is irradiated with light in the presence of a semiconductor photocatalyst and an organic cyclic agent to reduce the selenate ion to solid selenium and Z or gaseous selenium-hydrogen. We propose a method for removing acid ions.

Patent Document 1: Japanese Unexamined Patent Publication No. 2000-167572

Patent Document 2: Japanese Patent Laid-Open No. 10-218611

Patent Document 3: Japanese Patent Laid-Open No. 09-239377

Disclosure of the invention

Problems to be solved by the invention

[0005] However, although the above-described conventional coagulation-precipitation treatment method can effectively treat selenium and a selenium compound by using the activated carbon treatment method in combination, it involves a large amount of expense for wastewater treatment facilities and treatment work. There are problems such as large economic burden.

In addition, since the treatment method using the ion exchange method requires irradiation with light in the presence of a semiconductor photocatalyst and an organic cyclizing agent, it requires a long time for wastewater treatment and the above-described coagulation precipitation treatment method. Similar to, a large amount of expenditure is required for wastewater treatment facilities and treatment work.

[0006] Therefore, an object of the present invention is to provide a treatment method that effectively removes selenium and selenium compounds containing selenium and selenium compounds in a short time and at low cost. Furthermore, the present invention effectively collects selenium and a selenium compound vaporized during the treatment of the waste water and returns them to the waste water, so that the selenium and selenium can also be contained in the atmosphere and working environment air. Means for solving the problems aimed at providing a wastewater treatment method that does not release compounds

[0007] Therefore, the present invention provides a wastewater treatment method for treating wastewater containing selenious acid and selenic acid, and (a) the inorganic waste acid is added to make the wastewater acidic at a pH of 3 or less. (B) a step of introducing iron powder into the waste water; (c) a step of stirring the waste water at room temperature; and (d) air containing gas generated in the stirring step (c) is sulfuric acid. (E) reducing the remaining potassium permanganate in the sulfuric acid acidic potassium permanganate solution and adding the solution to the waste water; and (f) passing the acidic permanganate solution through the acidic potassium permanganate solution; Above The present invention provides a method for treating selenium-containing wastewater characterized by comprising the steps of performing the treatments described in steps (a) to (c).

[0008] Thereby, selenium and selenium compounds vaporized during waste water treatment are effectively collected and returned to the waste water, so that selenium and selenium compounds are also released into the air in the atmosphere and working environment. I did it.

Here, the inorganic acid used in the step (a) is hydrochloric acid or sulfuric acid, and the molar concentration of the inorganic acid with respect to the waste water is 0.03 M or more.

[0010] Further, in the step (b), 3 to 5 grams of iron powder is injected per liter of the waste water. Further, for the stirring in the step (c), strong stirring for about 10 minutes is sufficient.

[0011] Further, the sulfuric acid potassium permanganate solution used in the step (d) is 0.3 to 0.5% by weight / volume permanganese in dilute sulfuric acid having a mol concentration of 1 to 2M. Use one that contains acid potassium. In the step (d), when the red fading of the sulfuric acid potassium permanganate solution is lower than a predetermined level, the step (d) is performed.

Then, the treatment is performed by passing through a plurality of air selenium removing means connected in series.

[0012] Then, the waste water after the step (c) is subjected to coagulation sedimentation by adding an alkaline agent to pHIO or more, and the resulting precipitate is separated and concentrated in a sedimentation tank, and the concentrated precipitate is further dehydrated. . The invention's effect

[0013] The wastewater treatment method for treating wastewater containing selenious acid and selenate according to the present invention includes a facility, a semiconductor photocatalyst, and an organic cyclic agent used together with an activated carbon treatment method as in the conventional treatment method. Since there is no need to irradiate light in the presence of existing equipment and the existing wastewater treatment facility can be used as it is, it can be treated at a low cost and by simply stirring the wastewater for about 10 minutes at room temperature. This made it possible to treat wastewater containing selenious acid and selenic acid.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to the drawings, the details of the wastewater treatment method for treating wastewater containing selenious acid and selenic acid according to the present invention will be described.

[0015] FIG. 1 shows an overview of the steps of a wastewater treatment method for treating wastewater containing selenious acid and selenic acid according to the present invention. In Figure 1, industrial wastewater containing selenium is often colloidal selenium, tetravalent oxide selenite ion (SeO ² or less, referred to as `` Se (IV) '' where appropriate) and

3 Z or Oxide number Hexavalent selenate ion (SeO ² or less, expressed as “Se (VI)” where appropriate)

Four

To do.

[0016] As shown in FIG. 1, in the method for treating selenium-containing wastewater according to the present invention, the pH of the wastewater is adjusted to 3 or less by first adding hydrochloric acid or an inorganic acid of sulfuric acid to the selenium-containing wastewater. (Step (a)). Here, when the inorganic acid is hydrochloric acid, the molar concentration of hydrochloric acid with respect to the wastewater is 0.03M or more. Next, iron powder is put into the wastewater adjusted to pH 3 or less (step (b)). The amount of iron powder input is 3 to 5 grams per liter of wastewater, but about 5 grams is desirable. And the waste water after iron powder injection | throwing-in is stirred strongly (process (c)). The stirring time is about 8 to 10 minutes. Due to this strong stirring, the selenite ion having a tetravalent acid number changes to red selenium Se (0) in a very short time (a few seconds after the start of stirring). It was confirmed that the selenate ion began to turn reddish brown after depositing red selenium after about 90 seconds. From the observation of the reduction behavior of selenite and selenate, the selenate ion with an oxidation number of 6 is first reduced to a selenite ion with an oxidation number of 4 and then reduced to red selenium as a simple selenium. Was confirmed.

[0017] The method for treating selenium-containing wastewater according to the present invention includes a step of recovering selenium and a selenium compound transferred to the gas phase in the above-described strong stirring step. That is, air containing selenium and a selenium compound that have been transferred to the gas phase through the stirring step is passed through the potassium sulfate permanganate solution (step (d)). As a result, the selenium and the selenium compound transferred to the gas phase are collected in the sulfuric acid potassium permanganate solution. The acidic permanganate solution is reduced to the remaining potassium permanganate with a general-purpose reducing agent, returned to the selenium-containing wastewater, and reliably recovered through the above steps (a) to (c). It is. Here, the sulfuric acid potassium permanganate solution used in the above step (d) contains 0.3 to 0.5% potassium permanganate by weight to volume% in dilute sulfuric acid having a molar concentration of 1 to 2M. Contains.

[0018] By the way, redness of the sulfuric acid potassium permanganate solution produced by the step (d) is obtained. When the color fading is lower than a predetermined level, it may be processed by passing it through a plurality of air selenium removal means connected in series. However, as will be described later, a single pass process is usually sufficient.

[0019] In addition, the waste water after the step (c) is released into sewage or the like by a coagulating sedimentation treatment by adding a known alkali agent, separation and concentration of the precipitate, and dehydration treatment, and solid matter is sludge. Will be processed.

FIG. 2 schematically shows the steps constituting the selenium-containing wastewater treatment method according to the present invention shown in FIG. The process illustrated in FIG. 2 is a force that describes the process that should be added as necessary in addition to the essential process of the present treatment method. The description regarding the process is as described above. In addition, when wastewater contains harmful substances related to wastewater regulations such as arsenic, mercury, cyanide, and fluorine other than selenium that is subject to removal by the present invention, these harmful substances constitute the present invention. Needless to say, it can also be removed simultaneously by adding iron powder and intensive stirring.

[0021] As shown in Fig. 2, in the wastewater treatment of the present invention, the wastewater containing selenious acid and selenic acid is passed through the chemical reaction inlet from the chemical solution inlet to the sealed reaction tank having an intake pipe and an exhaust pipe. Put it into a pH of 3 or less, add force iron powder from the iron powder feeder, and immediately stir the selenium-containing wastewater in the reaction tank with a stirrer. Immediately after the start of the iron powder reaction by vigorous stirring, hydrochloric acid and iron powder react to generate hydrogen in the active stage, and selenite and selenic acid are reduced to room temperature by chemical conversion to single selenium. . Further, a part of the produced single selenium is vaporized by chemical reduction at room temperature to hydrogen selenide. In addition, foaming associated with the iron powder reaction and strong stirring of the selenium-containing wastewater in the reaction tank generate mist containing selenious acid and selenic acid. With the start of the iron powder reaction, the selenium-hydrogen and selenium-containing mist move to the upper air phase in the iron powder reactor.

[0022] And, by the normal temperature chemical reduction action of this iron powder reaction, most of the selenite and selenate in the selenium-containing wastewater are reduced to the precipitation of simple selenium, and as a subsequent treatment in an alkali agglomeration reaction tank. Most selenite and selenate in the selenium-containing wastewater collected in the iron hydroxide precipitate produced by the addition of alkali undergo floc formation in the polymer flocculant tank. In the settling tank, the precipitate is separated.

[0023] Furthermore, as the iron powder reaction starts, hydrogen selenide gas and selenium-containing mist generated from the selenium-containing wastewater move to the upper air phase in the iron powder reaction tank. Air containing hydrogen selenide gas and selenium-containing mist at the top is always exhausted from the exhaust pipe to the air washing tank using the exhaust pump, and the air containing the selenium-hydrogen gas and selenium-containing mist is exhausted to produce low-concentration sulfuric acid permanganate. It is blown into an air cleaning solution consisting of potassium acid, purifying the air by absorbing hydrogen selenide gas and collecting selenium-containing mist. Further, the air purified in the air cleaning tank is further purified in the water cleaning tank and safely released to the atmosphere or working environment.

[0024] Further, since the cleaning liquid in the air cleaning tank containing hydrogen selenide gas and selenium-containing mist has an oxidizing power and uses a sulfuric acid potassium permanganate liquid that changes color according to the oxidizing power, A small amount of selenium-hydrogen gas will be absorbed by acid, and the exhaust air will be washed with water and safely discharged into the atmosphere or working environment. Under long-term use conditions or conditions that treat wastewater containing high concentrations of selenium, it is better to detect the cleaning ability easily by using the sulfuric acid potassium permanganate solution based on the degree of red fading of the cleaning solution.

[0025] Then, in order to safely ensure the treatment under the long-term use conditions and the wastewater treatment conditions containing high-concentration selenium, the washing tanks are arranged in parallel, and the degree of red fading of the potassium permanganate liquid as the washing liquid Depending on the situation, by switching the introduction of exhaust air to another air cleaning tank containing unused cleaning liquid, it is possible to deal with the treatment of wastewater containing low concentration, high concentration selenium. In addition, the used cleaning solution containing selenium whose fading color has faded and whose collection performance has deteriorated is returned to the reaction tank, and the remaining potassium permanganate is reduced for general water treatment such as sodium sulfite. It also has the ability to remove vaporized selenium by chemical reduction action at room temperature by the iron powder treatment method after reduction with an agent.

FIG. 3 is a graph showing the total residual selenium concentration in the wastewater when the above-described method for treating selenium-containing wastewater according to the present invention is carried out. The unit of the horizontal axis of the graph indicates the concentration of selenium in the wastewater [Se (IV) and Se (VI) concentrations, mgZ liters], and the vertical axis of the graph shows the treatment method for this selenium-containing wastewater. The total residual selenium concentration in the treated water (Se ( IV) and Se (VI) are summed, and mgZ liter) is determined. The treatment conditions in the graph shown in Fig. 3 are as follows. Hydrochloric acid was added to the selenium-containing wastewater to make it pHO.4 (step (a)), and 5 grams of iron powder was added per liter of wastewater ( Step (b)). Then, it was vigorously stirred for 10 minutes (step (c)).

[0027] As shown in FIG. 3, when the undiluted solution before treatment contains 1 to 100 (mgZ liters, ppm) of selenite and selenate, the method for treating selenium-containing wastewater of the present invention is carried out. After that, after the treatment of the present invention, the wastewater standard value of 0.1 mgZ liter, which was established based on the amendment of the 1993 Water Pollution Control Law Enforcement Order, was completely cleared.

[0028] Fig. 4 shows the residual concentration of selenic acid after wastewater treatment and the reaction liquid concentration due to the concentration of inorganic acid (hydrochloric acid) in the wastewater acidification treatment (step (a)) that constitutes the treatment method of this selenium-containing wastewater. It is a graph which shows the influence degree to pH. Other conditions are the same as those described in FIG.

The conditions of the graph shown in FIG. 4 were that hydrochloric acid was used as the inorganic acid, and the concentration of selenic acid (hexavalent selenium) in the stock solution was 50 (mgZ liter). The horizontal axis of the graph shows the molar concentration of hydrochloric acid in the stock solution, and the left vertical axis of the graph shows the residual concentration of selenic acid (hexavalent selenium) in the treated water after the treatment method for this selenium-containing wastewater (mgZ liters) The right vertical axis of the graph indicates the pH value of the reaction solution.

[0030] As shown in FIG. 4, by setting the molar concentration of hydrochloric acid in the effluent to about 0.03M, the pH value of the effluent is reduced to 3 or less. It is important to clear 0. lmgZ liters, which is the standard value for drainage established based on the revision of the enforcement order.

[0031] Fig. 5 shows that in the present method for treating selenium-containing wastewater, when iron powder is introduced into the selenium-containing wastewater and vigorously stirred (step (c)), selenite and selenate in the wastewater are vapor-phased. It shows the percentage (%) to shift to. Other conditions are the same as those described in FIG.

[0032] FIG. 5 shows that 0.3 to 4% of the tetravalent selenium and the hexavalent selenium migrate to the gas phase. The stirring time was 10 minutes. In this case, the higher the selenium content in the stock solution, the lower the percentage (%) of selenium transferred to the gas phase. However, the average selenium concentration in the gas phase is 0.59 to 23.2 mgZm ³ , and the exposure limit of selenium to humans is 0. It exceeded 2 mg / m ³ . In addition, the proportion of tetravalent selenium and hexavalent selenium transferred to the gas phase is never negligible, indicating the need to collect this.

[0033] As described above, the method for treating selenium-containing wastewater according to the present invention further recovers tetravalent selenium and hexavalent selenium transferred to the gas phase through the iron powder charging step and the strong stirring step. Process (step (d)). That is, air containing a gaseous substance is passed through the sulfuric acid potassium permanganate solution in the stirring step. As a result, the tetravalent selenium and hexavalent selenium transferred to the gas phase are collected in the sulfuric acid potassium permanganate solution. Then, the acidic permanganate sulfate solution containing the tetravalent selenium and the hexavalent selenium thus collected is reduced to the remaining potassium permanganate and then returned to the selenium-containing waste water to be reliably recovered. It is. Here, the sulfuric acid acidic potassium permanganate solution used in the step (d) is prepared by adding 0.3 to 0.5% potassium permanganate by weight to volume% in dilute sulfuric acid having a molar concentration of 1 to 2M. It contains.

FIG. 6 is a graph showing the collection rate of tetravalent selenium and hexavalent selenium transferred to the gas phase by the treatment step (d). As shown in Fig. 6, it is possible to collect 98% or more of both tetravalent selenium and hexavalent selenium. In the treatment step (d), red fading of the sulfuric acid-acid potassium permanganate solution is achieved by one-step passage of air containing tetravalent selenium and hexavalent selenium that has been transferred to the gas phase into the potassium acid permanganate solution. If the degree of slag is significant, it may be treated by passing it through a plurality of stages of air selenium removal means connected in a plurality of stages in series. The processing conditions in FIG. 6 are the same as those described in FIG.

By the way, in the method for treating selenium-containing wastewater according to the present invention, not only batch treatment using a batch reaction tank but also continuous flow treatment using a continuous flow reaction tank is possible. In addition, existing wastewater treatment facilities, especially alkali coagulation sedimentation treatment in the latter stage, coagulation treatment with high molecular coagulant-added water, solid-liquid separation in a sedimentation tank, pressure filtration and dewatering treatment of concentrated sludge (precipitation), etc. It can be diverted and is extremely advantageous. The iron powder reaction tank is sufficient to have a structure that can reliably intake and exhaust air into and from the reaction tank by the intake and exhaust facilities, and the practicality of the present invention can be said to be very high.

Industrial applicability

[0036] The present invention relates to selenium and selenium compounds from waste water containing selenium and selenium compounds. It is related to a wastewater treatment method that removes water efficiently and at low cost in consideration of the safety of the work environment, and has industrial applicability.

Brief Description of Drawings

FIG. 1 shows an outline of the steps of a wastewater treatment method for treating wastewater containing selenious acid and selenic acid according to the present invention.

FIG. 2 schematically shows the steps constituting the selenium-containing wastewater treatment method according to the present invention shown in FIG.

FIG. 3 is a graph showing the total residual selenium concentration in wastewater when the above-described method for treating selenium-containing wastewater according to the present invention is carried out.

[Fig. 4] A graph showing the effect of inorganic acid (hydrochloric acid) concentration on the residual concentration of selenic acid after wastewater treatment and the pH of the reaction solution in the acidity treatment of wastewater that constitutes the treatment method for wastewater containing selenium. is there.

[Fig. 5] In this selenium-containing wastewater treatment method, when iron powder is introduced into selenite and selenate-containing wastewater and stirred vigorously, selenite and selenate in the wastewater are transferred to the gas phase. It shows the result.

FIG. 6 is a graph showing the collection rate of selenic acid transferred to the gas phase in the present invention. Explanation of symbols

[0038] (a): Acidification process

(b): Iron powder charging process

(c): Stirring process

(d): Collection process of selenite and selenate transferred to the gas phase

Claims

The scope of the claims

[1] A waste water treatment method for treating waste water containing selenious acid and selenic acid,

(a) adding an inorganic acid to make the waste water acidic at pH 3 or less;

(b) introducing iron powder into the waste water;

(c) stirring the waste water at room temperature;

(d) passing the air containing the gas generated in the stirring step (c) through a sulfuric acid permanganate solution;

(e) reducing the remaining potassium permanganate in the sulfuric acid potassium permanganate solution, and then adding the solution to the waste water;

(f) performing the process described in the steps (a), (b) and (c);

A method for treating selenium-containing wastewater, comprising the steps of:

[2] The selenium-containing wastewater according to claim 1, wherein the inorganic acid used in the step (a) is hydrochloric acid or sulfuric acid, and the molar concentration of the inorganic acid with respect to the wastewater is 0.03 M or more. Processing method.

[3] The method for treating selenium-containing wastewater according to claim 1, wherein in the step (b), 3 to 5 grams of iron powder is introduced per liter of the wastewater.

[4] The method for treating selenium-containing wastewater according to claim 1, wherein the stirring time in the step (c) is 8 to 10 minutes.

[5] The sulfuric acid potassium permanganate solution used in the step (d) contains 0.3 to 0.5% potassium permanganate by weight to volume% with respect to 1 to 2 M dilute sulfuric acid. The method for treating selenium-containing wastewater according to claim 1, wherein the selenium-containing wastewater is contained.

[6] In the step (d), when the red color fading is lower than a predetermined level as the acidity of the sulfuric acid potassium permanganate solution decreases, the step (d) is performed. 6. The method for treating selenium-containing wastewater according to claim 5, wherein the treatment is performed by passing through a plurality of air selenium removal means connected in series.

[7] The waste water after the step (c) is characterized in that an alkaline agent is added to cause a pHIO or more to coagulate and precipitate, the generated precipitate is separated and concentrated in a sedimentation tank, and the concentrated precipitate is further dehydrated. The method for treating selenium-containing wastewater according to claim 1.