JPH10323676A - Method for treating solution containing selenium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove and collect selenium contained in a selenium-containing waste water effectively by removing a bivalent cation constituent and/or a bivalent anion constituent from a solution containing selenium and then bringing the solution in contact with an iron metal for removing the selenium. SOLUTION: When a solution discharged from fields of manufacture industry and containing selenium is treated, a bivalent cation constituent and/or a bivalent anion constituent is removed in a first step. As the bivalent cation constituent, magnesium ion and calcium ion are cited and removal thereof is carried out by bringing them into contact with a cation exchange resin or a chelate resin. As the anion constituent, especially in sulfuric acid ion, its removal carried out by bringing it into contact with an anion exchange resin. Then, an iron metal is used to deposit metallic selenium from selenium oxide and/or selenic acid, and as the iron metal electrolytic iron and the like are cited and are used in the form of fibrous wire, plate-shaped thin pieces and the like.

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. Especially,
The present invention relates to the treatment of selenium-containing wastewater in water and wastewater belonging to the environmental conservation fields such as the chemical industry, metallurgy industry, and electric and electronic work.

[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. The wastewater discharged from these production processes usually 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] Therefore, there is a demand for a resource-saving, energy-saving and efficient selenium separation system to achieve these standards. The selenium compound exists in water mainly in the form of selenous acid, which is tetravalent selenium, and selenic acid, which is hexavalent selenium. Generally, in the treatment of wastewater containing a selenium compound, it is required to remove a trace amount of a selenium compound in the presence of a large amount of coexisting salts, and selenium removal in such a situation often involves difficulties.

[0004] As a method for removing such a selenium compound, first, removal by an adsorbent such as an anion exchange resin can be considered. However, the anion exchange resin is selenic acid,
Although selenous acid itself has adsorptive properties, it has no selectivity with other coexisting ions, and thus is not suitable for a system having a large amount of coexisting ions. In addition, for selective removal of metal ions, removal by a chelating resin is generally considered. A chelate resin is often used for removal of a specific metal in the presence of a high concentration of coexisting salt because it specifically interacts with, and adsorbs and removes a specific metal ion due to its chemical properties. At present, chelating resins such as Eporus K-6 (manufactured by Miyoshi Oil & Fats Co., Ltd.) are known as resins adsorbing selenium, but these resins do not have high selectivity for selenium, and selenium concentration is low and coexisting salt with high concentration Has no effect on the removal of selenium from industrial effluents containing selenium. In addition, it has been reported that resins carrying bismuthiol II or azothiophyllin disulfonic acid on the anion exchange resin selectively adsorb tetravalent selenium (selenous acid). Unsuitable for industrial use in processing. Thus, selenium removal by a chelate resin is also difficult at present.

[0005] The difficulty in removing selenium with such chelating resins stems from the chemical structure of selenium.
Usually, selenium is present in an aqueous solution in the form of selenic acid, selenious acid or a salt thereof in the form of an anion in which oxygen is bonded to a selenium atom. In general, various chelating resins are used for removing a trace amount of heavy metal ions, and the chelating resin is useful for selectively removing cationic heavy metal ions such as iron and copper. It is not suitable for removing a metal present as an anion bonded with a suitable oxygen. This is because selenium atoms have a structure in which selenic acid and selenous acid are bonded to oxygen, so that selenium atoms are less likely to directly interact with other ligands.

It is also conceivable to reduce the selenium compound in the aqueous solution to metal selenium by chemical reduction, electrical reduction, or the like, and to remove the metal selenium by solid-liquid separation. However, this method also has difficulty with selenium compounds. This is because the structural property that selenium exists as an oxyanion reduces the chemical reactivity of the selenium compound, that is, the reduction reactivity. In general, compared to a metal ion to which oxygen is not bonded, reduction of a metal ion to which oxygen is bonded is difficult to proceed because a reduction reaction involves a structural change of a compound. That is, the reduction of oxyanions such as selenium hardly progresses, while the reduction to metals such as iron ions and copper ions easily progresses. For this reason, it is generally difficult to apply a reduction method that has been effective for reducing metal ions such as iron and copper to selenium.

As a method for removing a selenium compound by chemical reduction or electrical reduction, Japanese Patent Application Laid-Open Nos.
Although the method described in JP-A-224585 can be mentioned, a process for recovering reduced metal selenium by coagulation precipitation or the like is required, so that the process becomes complicated. Another disadvantage is that a large amount of the used reducing agent is not recovered. However, since it is extremely difficult to remove a selenium compound by an ion exchange method or a chelate method, it is certain that a method of removing a selenium compound by reduction to a metal is one of the effective methods.

As a method for removing a selenium compound by reduction to metal, JP-A-7-2502 describes a method in which iron or an iron-based metal is added to wastewater and selenium is deposited on the surface of the iron or iron-based metal. Have been. However, with respect to such a method of removing selenium with an iron-based metal, it is known that the presence of coexisting salts other than selenium deteriorates the efficiency of selenium removal and causes corrosion by iron surface oxidation. Was.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied a method for solving the above problems and efficiently removing and recovering selenium from selenium-containing effluent water. The present inventors have found that the selenium concentration can be effectively reduced in a short time by reducing the divalent cation component and / or the divalent anion component among the coexisting salts contained therein. Reached.

[0010]

That is, the gist of the present invention is a first step of removing a divalent cation component and / or a divalent anion component from a selenium-containing solution, and the first step obtained from the first step. A method for treating a selenium-containing solution, comprising a second step of removing selenium by bringing the solution into contact with an iron-based metal; the selenium-containing solution in which the divalent cation component is a magnesium ion and / or a calcium ion. A method for treating the selenium-containing solution in which the divalent anion component is a sulfate ion; a method for treating the selenium-containing solution in which the divalent cation component is removed using a cation exchange resin or a chelate resin; A method for treating the selenium-containing solution in which the anion component is removed with an anion exchange resin; the iron-based metal may be in a fibrous form, a porous body, a fine plate-like form,
A method for treating the selenium-containing solution, which is in the form of granules or powder; a first step of removing a divalent cation component and / or a divalent anion component from the selenium-containing solution, and a second step Contacting the solution obtained from the first step with an iron-based metal, and reducing the selenite compound and / or selenite compound to metal selenium to precipitate on the metal surface, the treatment of the selenium-containing solution. And removing the divalent cation component and / or the divalent anion component from the selenium-containing solution in the first step, and contacting the solution obtained from the first step with an iron-based metal in the second step. Reducing the selenite compound and / or selenite compound to metal selenium and depositing it on the metal surface, and then burning off the iron-based metal obtained by depositing the metal selenium obtained in the second step on the surface or Subjected to processing, resides in method of treating the selenium-containing solution, characterized in that the metallic selenium separated and recovered.

[0011]

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 generally a solution containing selenous acid, selenic acid or a salt thereof, and is mainly intended for wastewater from various manufacturing factories or thermal power plants. In such cases, it contains high concentrations of other salts (alkaline metal ions, alkaline earth metal ions, chloride ions, sulfate ions, etc.) along with selenium,
Solutions with dilute selenium concentrations can also be of interest.

Although the type of selenium varies depending on the source of the wastewater, examples of selenous acid and salts of selenic acid include sodium salts, potassium salts, magnesium salts, calcium salts and the like. The selenium concentration in the solution also varies depending on the type of the effluent. For example, effluent from a thermal power plant usually contains 0.2 to 5 ppm (in terms of selenium).

In the method of the present invention, the divalent cation component and / or the divalent anion component are removed in the first step. Hereinafter, the removal of the divalent cation component will be described.
As the divalent cation component, in particular, by removing magnesium ions and calcium ions, or by converting these ions to monovalent cations such as sodium, and then contacting with a ferrous metal in the second step, Selenium can be removed efficiently. Here, when a divalent cation is present, the selenium removal property is deteriorated at the time of contact with the iron-based metal in the second step. The lower the divalent cation concentration after the removal is, the better, but for efficient operation of the process, it is sufficient to reduce the divalent cation concentration to about 100 ppm or less. As a method for lowering the divalent cation concentration to about 100 ppm or less, for example, a selenium-containing solution containing a divalent cation may be brought into contact with a cation exchange resin or a chelate resin. As the cation exchange resin and the chelate resin used here, any of the cation exchange resin and the chelate resin used for ordinary water treatment can be used.

The contact of the selenium-containing solution with the cation exchange resin or the chelate resin may be carried out by a commonly used method, and may be carried out at room temperature under column conditions such as SV1-20. In addition, in order to reduce the load on the cation exchange resin, in order to maintain a certain level of divalent cation concentration, the outlet solution and the undiluted solution passed through a column packed with an excess of cation resin capable of removing the cation concentration to near 0 ppm May be subjected to the second step.

The method for reducing the concentration of divalent cations may be carried out by an operation such as coagulation sedimentation, and is not limited to contact with a cation resin and a chelate resin.
Next, the removal of the divalent anion component will be described. As the divalent anion component, particularly, sulfate ion is removed or
Alternatively, selenium can be efficiently removed by converting these ions into monovalent anions such as chloride ions and bringing them into contact with an iron-based metal in the subsequent second step. Here, if a divalent anion is present, selenium removal will be poor at the time of contact with an iron-based metal. The lower the concentration of divalent anions after removal, the better, but for efficient operation of the process,
It is sufficient to reduce the divalent anion concentration to about 500 ppm or less. As a method for lowering the divalent anion concentration to about 500 ppm or less, for example, a selenium-containing solution containing a divalent anion may be contacted with an anion exchange resin. As the anion exchange resin used here, any of the anion exchange resins used for ordinary water treatment can be used.

The contact between the selenium-containing solution and the anion exchange resin may be carried out by a commonly used method.
Conditions such as SV 1 to 20 can be adopted in the column method. In addition, in order to reduce the load on the anion exchange resin, in order to maintain a certain level of divalent anion concentration, an outlet liquid passed through a column packed with an excess of anion exchange resin capable of removing the anion concentration to near 0 ppm is used. The mixture with the undiluted solution may be subjected to the second step.

Here, selenate ions can also be removed by setting conditions for removing all the coexisting salts with an anion exchange resin. However, considering such a process, the amount of the required anion exchange resin becomes very large, and the practical Not. Therefore,
In the first step, there is a method in which the divalent anion component is removed to the extent that the removability of the selenate ion by the iron-based metal in the subsequent second step is not impaired, and the selenate ion is removed by the iron-based metal in the second step. Efficient and economical.

The method for reducing the concentration of divalent anions may be carried out by an operation such as coagulation and precipitation, and is not limited to contact with an anion exchange resin. In the present invention, the removal of the divalent cation component and the removal of the divalent anion component are both effective if performed alone, but are most effective when both are performed. As a method for performing both, a method combining the above-described divalent cation component removal methods and divalent anion component removal methods may be used.

In the method of the present invention, in the second step, an iron-based metal is used to precipitate metal selenium from the selenite compound and / or selenic acid. It also includes iron containing other metals such as iron alloys. Specific examples of iron-based metals include electrolytic iron, low-carbon steel, medium-carbon steel, high-carbon steel, extremely 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 can be mentioned.

In the present invention, these iron-based metals can be used as molded articles formed into a desired shape.
They may be any of hot rolled products, cold rolled products, compressed products, extruded products, drawn products, plastic processed products, forged products, cast steel products and the like. The shape of the iron-based metal used in the present invention is not particularly limited, but in the treatment method of the present invention, selenium in the solution is precipitated on the surface of the iron-based metal by a catalytic reduction reaction with the selenium-containing solution to be treated. It is desirable to have a shape having as large a contact surface area as possible, and in the case of using it by filling it in a treatment tower, a shape capable of easily forming a uniform packed layer is preferable. Specific examples include thin fibrous wires such as steel and wool, plate-like strips, porous bodies, powdery bodies, granular bodies, and fine-grained chips.
Wool is preferred, but not limited thereto.

Other shapes include bar steel, round steel, square steel,
Square steel, deformed bar, bar-in-coil, shaped steel, angle steel, H-shaped steel, I-shaped steel, T-shaped steel, flat steel, sheet pile, steel frame, lightweight steel, flat steel, deformed flat steel, heavy steel plate , Thin steel plate, strip steel plate, round steel pipe, square steel pipe, billet, plate, flat, rod, strip, tubular,
Linear, granular, sandy, powdery, block, chip, rivet, coarse billet, slab, bloom, sheet bar,
Examples include billets, cast steel pouring, cast steel as-cast, cast steel as-cast, and waste materials in the form of cutting waste and processed waste.

In the second step, the solution treated in the first step is brought into contact with the iron-based metal as described above. The method of contacting the solution treated in the first step with the iron-based metal may be any method as long as the solution and the iron-based metal are sufficiently contacted, for example, immersing the iron-based metal in the solution to be treated, stirring or A method of giving vibration, a method of bringing the solution to be treated into contact with the packed bed of the iron-based metal through water, and the like can be mentioned.

In the method of the present invention, the contact treatment temperature for depositing selenium on the surface of a metal such as iron is not particularly limited, and is usually performed at room temperature to about 90 ° C., but more preferably at 30 ° C. or more. preferable. The pH value of the selenium-containing solution to be treated by the method of the present invention is usually preferably adjusted to a range of 2 to 10, particularly preferably a pH of 3 to 7. If the pH value is lower than 2, the elution of iron becomes unnecessarily significant,
A large amount of acid is added for pH adjustment, 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.

In the method of the present invention, the removal of selenium by the catalytic reduction reaction of selenium with iron is promoted by oxygen dissolved in the liquid to be treated. It is preferably performed in an oxygen-containing atmosphere such as air. Selenium deposited on the surface of a metal such as iron by the method of the present invention can be recovered as metallic selenium by burning it. 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 coming off by ultrasonic treatment of the metal on which selenium is deposited, and a method of separating selenium coming off by passing hot water through the metal on which selenium is deposited. 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.

It is most economically preferable to carry out the method of the present invention by directly connecting the first step and the second step by a column method. In the present invention, in order to reduce the load on the iron-based metal, it is preferable to perform the first step and the second step separately, for example, a cation exchange resin, a chelate resin used in the first step A method in which a selenium-containing solution is brought into contact with a system in which an anion exchange resin and an iron-based metal used in the second step are mixed and coexistent to remove selenium in one step can also be adopted.

Between the first step and the second step, if necessary, the pH of the solution to be treated containing selenium can be adjusted. Further, the treatment method of the present invention may be used in combination with conventional methods such as a neutralization precipitation method for recovering selenium, an iron hydroxide precipitation method, a ferrite precipitation method, an ion exchange membrane treatment method, and an activated carbon adsorption method, if necessary. Can be implemented.

[0027]

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. In the following Examples and Comparative Examples, the selenium concentration was quantified by ICP emission analysis. Example 1 10 ppm sodium selenate solution (in terms of selenium), 1000 ppm magnesium sulfate solution (1000 ppm sulfate ion, 250 pp magnesium ion) in a 100 ml Erlenmeyer flask
cation exchange resin Diaion SK1B (Mitsubishi Chemical Corporation) 1
0 ml and shaken at 25 ° C for 2 hours to convert magnesium ions into sodium ions,
Reduced to 10 ppm or less. After filtering the cation exchange resin from this solution, 0.35 g of steel wool (inner diameter 0.4 mm) made by Nippon Steel Wool was added and shaken at 25 ° C for 2 hours. After filtering the steel wool, the selenium concentration in the solution was quantified to be 8.5 ppm. [Comparative Example 1] 10 ppm sodium selenate solution (in terms of selenium), 1000 ppm magnesium sulfate solution (1000 ppm sulfate ion, 250 pp magnesium ion) in a 100 ml Erlenmeyer flask
To 50 ml of the solution containing m), 0.35 g of steel wool (0.4 mm in inner diameter) made by Nippon Steel Wool was added and shaken at 25 ° C for 2 hours. After the steel wool was filtered, the selenium concentration in the solution was quantified to be 9.2 ppm. Example 2 10 ppm sodium selenate solution (in terms of selenium), 1000 ppm magnesium sulfate solution (sulfate ion 1000
ppm, 250 ppm of magnesium ion), 30 ml of this was added to a 100 ml Erlenmeyer flask, and 2 ml of anion exchange resin Diaion SA10A (manufactured by Mitsubishi Chemical Corporation) adjusted to Cl form was added. At ゜ C
Shake for 2 hours to convert sulfate ions to chloride ions,
Sulfate ions were reduced to 10 ppm or less, and selenate ions were removed to 0.1 ppm or less. After filtering the anion exchange resin from this solution, the remaining 20 ml of selenium solution was added. At this point, the selenium concentration is 4 ppm and the sulfate ion concentration is
It is 400 ppm. To 50 ml of this solution was added 0.35 g of steel wool (inner diameter 0.4 mm) made by Nippon Steel Wool, and 25 ゜
Shake at C for 2 hours. After filtering the steel wool, when the selenium concentration in the solution was determined, the selenium concentration was 2.9 ppm
Met. Example 3 10 ppm sodium selenate solution (in terms of selenium), 1000 ppm magnesium sulfate solution (1000 ppm sulfate ion, 250 pp magnesium ion) in a 100 ml Erlenmeyer flask
50 ml of the solution containing m) and the cation exchange resin Diaion SK1B (manufactured by Mitsubishi Chemical Corporation) adjusted to the Na form.
The mixture was shaken at 25 ° C. for 2 hours to convert magnesium ions into sodium ions and reduce magnesium ions to 10 ppm or less. From this solution, the cation exchange resin was filtered. Of the filtrate, 30 ml was added to a 100 ml Erlenmeyer flask, 2 ml of anion exchange resin Diaion SA10A (manufactured by Mitsubishi Chemical Corporation) adjusted to Cl form was added, and the mixture was shaken at 25 ° C for 2 hours to remove sulfate ions from chloride ions. To reduce sulfate ions to 10 ppm or less and remove selenate ions to 0.1 ppm or less. After filtering the anion exchange resin from this solution, the remaining
20 ml of selenium solution was added. At this point, the selenium concentration
4 ppm, sulfate ion concentration is 400 ppm, and magnesium ion concentration is 10 ppm or less. To 50 ml of this solution, 0.35 g of steel wool (inner diameter 0.4 mm) made by Nippon Steel Wool was added and shaken at 25 ° C for 2 hours. After filtering the steel wool, the selenium concentration in the solution was quantified to be 1.9 ppm. [Comparative Example 2] 4 ppm sodium selenate solution (in terms of selenium), 1000 ppm magnesium sulfate solution (1000 ppm sulfate ion, 250 pp magnesium ion) in a 100 ml Erlenmeyer flask
To 50 ml of the solution containing m), 0.35 g of steel wool (0.4 mm in inner diameter) made by Nippon Steel Wool was added and shaken at 25 ° C for 2 hours. After filtering the steel wool, the selenium concentration in the solution was determined, and the selenium concentration was 3.8 ppm.

[0028]

According to the method of the present invention, the divalent cation component and / or the divalent anion component are reduced in the coexisting salt contained in the selenium-containing wastewater, so that the salt can be effectively treated in a short time. It is possible to reduce the selenium concentration.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Kusabe 1-2, Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Kawasaki Chemical Industry Co., Ltd. (72) Tatsuya Sakurai 1 Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture No. 2 Kawasaki Chemical Industry Co., Ltd.

Claims (8)

[Claims] 1. A first step of removing a divalent cation component and / or a divalent anion component from a selenium-containing solution, and contacting the solution obtained from the first step with an iron-based metal to remove selenium. A method for treating a selenium-containing solution, comprising a second step of removing. 2. The method for treating a selenium-containing solution according to claim 1, wherein the divalent cation component is a magnesium ion and / or a calcium ion. 3. The method for treating a selenium-containing solution according to claim 1, wherein the divalent anion component is a sulfate ion. 4. The method for treating a selenium-containing solution according to claim 1, wherein the divalent cation component is removed using a cation exchange resin or a chelate resin. 5. The method for treating a selenium-containing solution according to claim 1, wherein the divalent anion component is removed with an anion exchange resin. 6. The method according to claim 1, wherein the iron-based metal is in a fibrous form, a porous body, a fine plate-like form, a granular form, or a powdery form.
6. The method for treating a selenium-containing solution according to any one of claims 1 to 5. 7. The method according to claim 1, wherein in the first step, 2
In the second step, the solution obtained from the first step is brought into contact with an iron-based metal, and the selenite compound and / or the selenate compound are converted to metal selenium. The method for treating a selenium-containing solution according to any one of claims 1 to 6, wherein the selenium-containing solution is reduced and deposited on a metal surface. 8. The method according to claim 1, wherein in the first step, a solution containing
In the second step, the solution obtained from the first step is brought into contact with an iron-based metal, and the selenite compound and / or the selenate compound are converted to metal selenium. Reducing and depositing on the metal surface, and then subjecting the iron-based metal deposited on the surface to the metal selenium obtained in the second step by incineration or acid treatment to separate and recover the metal selenium. A method for treating a selenium-containing solution according to claim 1.