JPH10310411A - Treatment of selenium-containing solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the soln. almost neutral to prevent the precipitation of iron oxide and to efficiently lower the selenium concn. in the soln. by bringing the soln. contg. selenium into contact with a ferrous metal in the presence of a chelating compd. and/or a chelating resin. SOLUTION: One part by volume of a ferrous metal such as steel wool is mixed with 0.01-100 parts of a chelating compd. such as EDTA and/or 0.1-10 parts of an iminodiacetic acid-type chelating resin or a phosphoric acid-type chelating resin, and the mixture is packed in a treating tower to form a packed bed. A soln. contg. 0.2-5 ppm selenium and kept at pH2-10, preferably pH4-8, is brought into contact with the packed bed at room temp. to 90 deg.C in an oxygen- contg. atmosphere to deposit selenium on the metal surface. The metal deposited with selenium is incinerated to recover metallic selenium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating a solution containing selenium to efficiently reduce the selenium concentration in the solution or to recover selenium.

[0002]

2. Description of the Related Art Selenium and selenium compounds are used in various manufacturing industries such as a decolorizing agent for glass, a photoreceptor for a copying machine, a rectifier, a semiconductor material, a battery material, and an electrolytic coloring agent for metals such as aluminum. Wastewater discharged from these manufacturing processes often contains a relatively high concentration of selenium. It has also been found that wastewater discharged from thermal power plants also contains selenium. Since selenium is a very toxic environmental pollutant, its amount in the effluent is strictly regulated, especially in recent years, the allowable amount has been set more strictly, and the effluent standard has been set at 0.1 to 0.01 mg / l. I have.

[0003] As a method for recovering selenium, generally, a neutralization coagulation precipitation method, an iron hydroxide precipitation method, a ferrite precipitation method, an ion exchange membrane method, an activated carbon adsorption method and the like are known.
However, these methods require special equipment and equipment for using a plurality of treatment methods in order to efficiently remove selenium, which increases equipment costs and operation costs, and is economically disadvantageous. is there. Further, a method of adding iron or an iron-based metal to wastewater to precipitate selenium on the surface of the iron or iron-based metal (Japanese Patent Laid-Open No. 7-2502), or adding a reducing iron compound to a selenium-containing solution, For recovering selenium by adjusting the temperature and adding a metal collecting agent (JP-A-9-59)
007) are also known. However, in the former method of depositing selenium on the surface of iron metal, it takes not only a long time to reduce a large amount of wastewater to a very low standard concentration, but also it is difficult to handle heavy iron metal. Met. Also, in the latter method, p
Since H adjustment is required, the operation is complicated and is not suitable as a method for treating a large amount of wastewater.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have made intensive studies to solve the above problems and to provide a method for efficiently removing and recovering selenium from selenium-containing effluent water. , Fe (II) and Fe (I) generated by oxidation-reduction reaction when selenium is deposited on the surface of iron metal
By capturing II) with a chelate compound or chelate resin, the pH value of the solution can be maintained in a nearly neutral region, and precipitation of iron hydroxide is also prevented, effectively reducing the selenium concentration in the solution. The inventors have found that the present invention can be performed, and arrived at the present invention based on this finding.

[0005]

That is, the gist of the present invention is as follows.
Contacting a solution containing selenium with an iron-based metal to precipitate selenium on the surface of the iron-based metal, and contacting the solution with the iron-based metal in the presence of a chelate compound and / or a chelate resin; The method for treating the contained solution is as follows.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The selenium-containing solution to be treated in the present invention is mainly intended for the wastewater of various manufacturing plants or the wastewater of a thermal power plant, and the selenium contained therein is various selenium compounds depending on the source of the wastewater. As, for example, selenic acid, selenium dioxide, selenium trioxide, selenous acid,
Selenium compounds such as selenium tetrachloride, sodium selenide, potassium selenide, ferrocene, copper selenide, nickel selenide, selenites such as sodium selenite, potassium selenite, barium selenite, sodium selenite And selenates such as potassium selenate and barium selenate. The selenium concentration in the solution also differs depending on the type of the wastewater. For example, the wastewater from a thermal power plant usually contains 0.2 to 5 ppm (in terms of selenium).

[0007] These wastewaters usually contain inorganic salts of other metals in addition to selenium.
Metal salts such as chromium and nickel, and further sodium sulfate,
Alkali metal or alkaline earth metal sulfates and chlorides such as magnesium sulfate, sodium chloride and magnesium chloride are contained, but a solution containing these salts can also be applied to the treatment method of the present invention.

The pH value of the selenium-containing solution to be treated by the method of the present invention is usually adjusted to a range of 2 to 10, preferably around neutral, that is, a pH range of 4 to 8. If the pH value is lower than 2, the elution of iron becomes unnecessarily remarkable and, in addition, the amount of acid added for pH adjustment is large, which is not practical. On the other hand, when the pH value exceeds 10, the reactivity decreases, and the effect of the present invention is not achieved, which is not preferable. Adjustment of the pH is performed using an acid or an alkali.As the acid, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are used.
Examples of the alkali include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

In the present invention, an iron-based metal is used to precipitate selenium, where the iron-based metal includes pure metal iron and ferromagnetic iron containing other metals such as chromium and manganese. Things. Specifically, electrolytic iron, low carbon steel, medium carbon steel, high carbon steel, extreme mild steel, mild steel, alloy steel, pig iron, cast iron, rimmed steel, capped steel, semi-killed steel, killed steel, clad steel, crude steel, Steel ingot and the like. In the present invention, these ferrous metals can be used as molded products formed into a desired shape, but they are hot-rolled products, cold-rolled products, compressed products, extruded products, drawn products, plastic products. Any of processed products, forged products, cast steel products, etc. may be used.

Although the shape of the iron-based metal used in the present invention is not particularly limited, in the treatment method of the present invention, selenium in the solution is transferred to the surface of the iron-based metal by a catalytic reduction reaction with the selenium-containing solution to be treated. A shape having as large a contact surface area as possible is desirable because of precipitation, and a shape capable of easily forming a uniform packed layer when packed in a treatment tower and used in a column system is preferred. Specific examples include thin fibrous wire rods such as steel wool, plate-like strips, porous bodies, powdery bodies, granular bodies, and fine-grained chips.Steel wool is preferable, and in the case of a column method, Preferably, powdery or granular iron that can be uniformly mixed with the chelating resin is preferable.

Other shapes include steel bars, round bars, square bars, and 6 bars.
Square steel, deformed bar, bar-in-coil, shaped steel, angle steel, H-shaped steel, I-shaped steel, T-shaped steel, channel steel, flat steel, sheet pile, anti-frame steel, lightweight steel, flat steel, deformed flat Steel, thick steel plate, thin steel plate, strip steel plate, round steel tube, square steel tube, billet, plate, flat, rod, band, tubular, linear, granular, sand, powder, block, chip, Examples include rivet-shaped, crude shaped slabs, slabs, blooms, sheet bars, billets, cast steel castings, cast steel castings, cast steel castings, and waste materials such as cutting scraps and processing scraps.

In the method of the present invention, when a metal such as iron is brought into contact with a selenium-containing solution, it is necessary to coexist a chelate compound. As the chelate compound, a compound having a function of selectively adsorbing Fe (II) and Fe (III) in a solution having a pH value suitable for the oxidation-reduction reaction conditions between the iron-based metal and selenium is preferable. Include EDTA and the like. Also, considering the economics of wastewater treatment, Fe (I
It is preferable to use a chelate resin that has a function of selectively adsorbing and separating I) and Fe (III) and can be used in a column method. The chelate resin is not particularly limited as long as it can selectively adsorb Fe (II) and Fe (III) .In terms of selectivity to iron ions, iminodiacetic acid type chelate resin or phosphate type chelate resin is particularly preferable. Preferably, the resin matrix is of a macroporous type, from the viewpoints of adsorption speed and adsorption capacity.

Such a resin can be appropriately selected from commercially available chelate resins, and for example, Diaion CR-10, CR-11, CRP-200.
(Manufactured by Mitsubishi Chemical Corporation), Eporus MX-10, MX-2 (manufactured by Miyoshi Yushi Co., Ltd.), Dowex A-1 (Dow Chemica)
l), Amberlite IRC-718 (Rohm Ant Haas) and the like. When these chelate resins are used after being adjusted to the H-form, protons are released together with the capture of iron, and a rise in pH can be prevented, which is advantageous in reaction. Therefore, it is preferable to use the H type. But,
It can be used even when used in a salt form such as sodium.

The amount of the chelate compound used is usually 0.01 to 100 times the volume of the iron-based metal, and the amount of the chelate resin used depends on its exchange capacity. 0.1 to 10 times the volume is used. In the treatment method of the present invention, selenium in a solution is reduced on the surface of the iron-based metal, and selenium is deposited on the surface.The pH suitable for the oxidation-reduction reaction between the iron metal and selenium is in an acidic range. . However, as this contact reaction progresses,
The pH value in the solution gradually increases. For example, when the pH at the beginning of the reaction is 3, it becomes about 4 to 5. On the other hand, a part of the oxidized iron is eluted in the solution as Fe (II) or Fe (III). Therefore, when the pH value in the treatment solution increases, the iron ions, particularly Fe (III), are hydroxylated. It is easy to precipitate as iron.
When the precipitation of iron hydroxide occurs, it is not preferable to treat the selenium-containing solution by the column method, because it causes operation troubles such as pressure increase and blockage. In the present invention, at the time of this contact treatment, by coexisting a chelate compound or a chelate resin, the eluted iron ions are captured by the chelate compound and the chelate resin, and at the same time, the formation of a precipitate of iron hydroxide is prevented.
This makes it possible to keep the pH value in the liquid almost constant.
As a result, the selenium removal rate in a wide pH range including the neutral range can be increased.

In the method of the present invention, a selenium-containing treatment solution is contact-treated with an iron-based metal in the presence of a chelate compound or a chelate resin to precipitate selenium on the metal surface. Any method may be used as long as the iron-based metal is sufficiently contacted, for example, a method in which the iron metal and the chelate resin are immersed in the solution to be treated and agitated or vibrated, or the mixed filling layer of the iron metal and the chelate resin is treated. A method of bringing the solution into contact with water is exemplified. Further, a chelate compound may be added to the solution to be treated, and the ferrous metal may be immersed in the solution. In the method of the present invention, the contact treatment temperature when selenium is deposited on the surface of a metal such as iron is not particularly limited, and is usually from room temperature to about 90 ° C. Further, in the method of the present invention, since the removal of selenium by the catalytic reduction reaction of selenium with iron is promoted by oxygen dissolved in the liquid to be treated, the contact treatment between the metal such as iron and the liquid to be treated is carried out by air. It is preferably performed in an oxygen-containing atmosphere such as

Selenium deposited on the surface of a metal such as iron by the method of the present invention can be recovered as metal selenium by incineration. This incineration method is not particularly limited, and any type of selenium can be used as long as selenium can be easily recovered from incineration residues such as a rotary incinerator such as a rotary kiln and a crucible-type incinerator. Can be. Further, a method in which a dilute acid is brought into contact with a metal surface on which selenium has been deposited, and selenium which has come off is recovered as a solid can also be employed. In this case, 0.01 to 6N hydrochloric acid may be passed through the column to separate solid selenium that is separated with the dissolution of iron from the column. In addition, there is a method of separating selenium that separates by subjecting selenium-precipitated metal to ultrasonic treatment, and a method of separating selenium that separates by passing hot water through the selenium-precipitated metal. No. Since selenium does not have a strong adsorption force on the metal surface, a method of removing selenium by some physical action is also used without limitation. Further, the iron-based metal and the chelate resin can be separated by utilizing a difference in specific gravity or the like. The treatment method of the present invention includes a conventional neutralization precipitation method for recovering selenium, an iron hydroxide precipitation method,
The method can be carried out in combination with a method such as a ferrite precipitation method, an ion-exchange membrane treatment method, or an activated carbon adsorption method, if necessary.

[0017]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

Example 1 A steel wool (trade name: Bonstar; manufactured by Nippon Steel Wool Co., Ltd.) 0.0
35 g, 5 ml of iminodiacetic acid type chelate resin (trade name: Diaion CR11: manufactured by Mitsubishi Chemical Corporation) adjusted to H-type
, And then 50 m of a solution of 10 ppm of sodium selenate (in terms of selenium) adjusted to an initial pH value of 4 with HCl.
After adding 1 l, the mixture was reacted at 25 ° C. for 8 hours while shaking with a shaker. After the reaction, the selenium concentration in the solution was quantified by ICP emission. As a result, the selenium concentration in the solution was 0.1 p
pm.

Comparative Example 1 A steel wool (trade name: Bonstar; manufactured by Nippon Steel Wool Co., Ltd.) 0.0
Only 35 g was added, and then 10 ppm of sodium selenate (in terms of selenium) adjusted to an initial pH value of 4 with HCl.
After adding 50 ml of the solution, the mixture was reacted at 25 ° C. for 8 hours while shaking with a shaker. After the reaction, the selenium concentration in the solution was adjusted to I
It was quantified by CP emission. As a result, the selenium concentration in the solution was 6.0 ppm.

Comparative Example 2 In an Erlenmeyer flask having an internal volume of 100 ml, an iminodiacetic acid type chelate resin (trade name: Diaion CR1) adjusted to H-form was placed.
1: Mitsubishi Chemical Co., Ltd.) 5 ml, then 10 ppm of sodium selenate adjusted to an initial pH value of 4 with HCl
After adding 50 ml (in terms of selenium) of the solution, the mixture was reacted at 25 ° C. for 8 hours while shaking with a shaker. After the reaction, the selenium concentration in the solution was quantified by ICP emission. As a result, the selenium concentration in the solution was 10.0 ppm.

Example 2 Iminodiacetic acid type chelate resin DIAION CR11
5 ml of trademark (Na type, manufactured by Mitsubishi Chemical Corporation) and 1.65 g of steel wool (trade name: Bonstar, manufactured by Nippon Steel Wool Co., Ltd., fiber diameter 0.04 mm) were mixed, and a jacketed column (inner diameter 11 mm) was mixed. , Height 120mm, column volume 1
2 ml). In this column, 0.2 ppm selenate ion, 2000 ppm sulfate ion, 6000 ppm
Of selenium waste liquid (pH = 4) containing chloride ions was passed upward at SV = 2. During the passage, the temperature of the jacket was maintained at 50 ° C. The selenium concentration in the liquid at the outlet of the column was quantified by ICP emission analysis. The selenium concentration when passing 10 B.V. was 0.08 ppm, and no suspension was found in the solution.

Comparative Example 3 1.65 g of steel wool (trade name: Bonstar, manufactured by Nippon Steel Wool Co., Ltd., fiber diameter: 0.04 mm) was charged into a jacketed column (inner diameter: 11 mm, height: 120 mm, column volume: 12 ml)
Stuffed. A selenium waste liquid (pH = 4) containing 0.2 ppm of selenate ion, 2000 ppm of sulfate ion, and 6000 ppm of chloride ion is applied to the column in an upward direction.
The solution was passed at V = 2. During the flow, the jacket temperature should be 50
C. was maintained. The concentration of selenium in the liquid at the outlet of the column is determined by IC
It was quantified by P emission analysis. The selenium concentration at the time of passing 10 BV was 0.10 ppm, and a brown suspension was formed in the solution.

[0023]

According to the method of the present invention, when a metal such as iron is brought into contact with a selenium-containing liquid to be treated, a chelate compound or a chelate resin is allowed to coexist. Can prevent the pH of the processing solution from becoming more alkaline, and at the same time, prevent precipitation of iron hydroxide derived from iron ions generated by the reaction. Selenium concentration can be reduced.

Continuing on the front page (72) Inventor Koji Kubebe 1-2, Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Kawasaki Chemical Industry Co., Ltd. (72) Inventor Tatsuya Sakurai 1-2-2, Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Kawasaki Chemical Industry Co., Ltd.

Claims (4)

[Claims] When a selenium-containing solution is brought into contact with an iron-based metal to precipitate selenium on the surface of the iron-based metal, the solution is brought into contact with the iron-based metal in the presence of a chelate compound and / or a chelate resin. A method for treating a selenium-containing solution. 2. The method for treating a selenium-containing solution according to claim 1, wherein the chelate compound and / or the chelate resin has a function of selectively adsorbing and separating Fe (II) and Fe (III). 3. The method for treating a selenium-containing solution according to claim 1, wherein the chelate resin is an iminodiacetic acid type or phosphoric acid type resin. 4. The pH value of the solution containing selenium is 4-8.
The method for treating a selenium-containing solution according to claim 1, wherein the selenium-containing solution is adjusted.