JP2003251367A - Treatment method for selenic acid-containing waste water and treating agent used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently removing selenic acid contained in water, and a chemical agent used therefor. <P>SOLUTION: In this method for removing selenic acid contained in water to be treated, an aluminum compound, an iron compound, and an oxidizing agent are made to exist together, and pH of the water to be treated is adjusted in a range of 4-8, thereby insolubilizing selenic acid and removing it. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing selenate contained in water and a drug used therefor.

[0002]

2. Description of the Related Art Conventionally, a coprecipitation treatment method has been adopted as the simplest method for treating wastewater containing selenium discharged from a non-ferrous smelter or factory. However,
Although the selenium in the waste water can be removed to some extent by the conventional method, the degree thereof is not sufficient. The reason is that for soluble selenium, selenite [SeO
₃ ^{2 -} (IV)] and selenate [SeO ₄ ^2- (VI)] and has,
Although coprecipitation treatment with iron (III) hydroxide is effective for selenious acid, the efficiency of selenoic acid is low and the removal rate is limited to 10% or less. ) ”Ministry of International Trade and Industry Bureau, Environmental Location Bureau). Further, there is an aluminum salt as a typical coprecipitant, but even if an aluminum salt is used, selenate cannot be effectively removed. Therefore, in order to remove selenate, after the selenate is reduced to selenious acid,
It was necessary to perform coprecipitation treatment. As a method for reducing selenate, for example, JP-A-10-99874 discloses
A technique for reducing hexavalent selenium with ferrous chloride is disclosed. However, this method is problematic in that it requires the use of a large amount of drug and the reaction must be performed at a high temperature for a long time. As described above, selenium acid cannot be treated unless it is reduced to selenious acid, but since the reduction is not easy, it has been extremely difficult to effectively remove selenium. In recent years, the importance of solving the problem of environmental pollution due to industrial wastewater and the like has led to strong demand for an effective method for removing harmful substances such as selenium.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for removing selenate in water with a small amount of sludge, and a chemical agent used therefor.

[0004]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. Even if an iron compound is added to the selenate-containing wastewater to be treated and an alkali is added to remove selenate by coprecipitation with the produced iron hydroxide, the removal rate is low (10% or less). There is a method of reducing selenate with a ferrous salt, but it requires a large amount of chemicals and requires a long-term reaction at high temperature. Further, even in this case, the concentration of the treated water cannot be reduced to 0.1 mg / l or less of the wastewater standard. The present inventors have made it possible to improve the efficiency of selenic acid from water by coexisting an aluminum compound, an iron compound and an oxidizing agent in the water to be treated containing selenate and adjusting the pH of the water to be treated to 4-8. It was found that they are often removed (0.1 mg / l or less of the wastewater standard). Under these conditions, iron oxide is produced rather than iron hydroxide. Selenium is effectively incorporated into the iron oxide-containing precipitate. As shown in Example 1 (wastewater containing aluminum) described below, the selenium concentration of the treated water was 0.21 mg / l even if ferrous sulfate was used, unless the oxidizing agent was present. It cannot be made lower than the standard value of 0.1 mg / l. On the other hand, the addition of a chemical containing an oxidizing agent enables treatment far below the wastewater standard. Then, iron hydroxide was produced when the oxidizing agent was not present, and iron oxide was produced when the oxidizing agent was present. That is, according to the present invention, the following method for removing selenate and agents used for the method are provided. (1) An aluminum compound, an iron compound and an oxidizing agent are allowed to coexist in the water to be treated containing selenate, and the water to be treated is p
A method for removing selenate, which comprises adjusting H to 4 to 8 to insolubilize selenate contained in water to be treated. (2) The method for removing selenate according to item (1), wherein the iron compound is ferrous sulfate or ferrous chloride. (3) The method for removing selenate according to item (1), wherein the oxidizing agent is a chlorine-based oxidizing agent having an effective chlorine amount of 0.1 to 25%. (4) The method for removing selenate according to any one of (1) to (3), wherein selenate is insolubilized in a state where carbonate ions are present in the water to be treated. (5) The method for removing selenate according to any one of (1) to (4), wherein the carbonate ion is obtained by adding a carbonate ion generator to waste water. (6) The method for removing selenate according to any of (1) to (5), wherein the carbonate ion generating agent is selected from sodium carbonate and potassium carbonate. (7) Add a flocculant to the water to be treated (1) to
The method according to any one of (6). (8) A drug comprising a mixture of (i) a chlorine-based oxidizing agent having an effective chlorine amount of 0.1 to 25% and (ii) a water-soluble carbonate compound, which is used in the method described in (4). . (9) From a mixture of (i) a chlorine-based oxidizing agent having an effective chlorine content of 0.1 to 25%, (ii) a water-soluble carbonate compound, and (iii) sodium hydroxide, which is used in the method described in the item (4). A drug characterized by:

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a drug used for removing selenate of the present invention (hereinafter, also simply referred to as drug A) is
(I) A chlorine-based oxidizer having an effective chlorine amount of 0.1 to 25% and (i
i) It is composed of a mixture with a water-soluble carbonate compound. Another aspect of the drug of the present invention (hereinafter, also simply referred to as drug B) is (i) the amount of available chlorine is 0.1 to 25%.
Chlorine-based oxidizers of (ii) water-soluble carbonate compounds and (iii)
It is a drug characterized by comprising a mixture with sodium hydroxide.

The time of adding the oxidizing agent to the water to be treated is not particularly limited, but may be before the addition of the aluminum compound or the iron compound or at the same time or after the addition thereof. After that, the pH is adjusted.

The aluminum compound used in the present invention includes
Examples thereof include aluminum chloride, aluminum sulfate, polyaluminum chloride, sodium aluminate, and aluminum hydroxide. These iron compounds can be used alone or in the form of a mixture.

The iron compound used in the present invention includes the first chloride.
Examples thereof include iron, ferric chloride, ferrous sulfate, ferric sulfate, polyiron chloride and polyiron sulfate. These iron compounds are
It can be used alone or in the form of a mixture.

As the alkali used for adjusting the pH for making selenate in the water to be treated insoluble, conventionally known ones are used. Such alkalis include sodium hydroxide, calcium hydroxide, magnesium hydroxide,
Included are potassium hydroxide, sodium carbonate, ammonium hydroxide and the like. In the present invention, particularly from the viewpoint of economy,
For alkali, sodium hydroxide, calcium hydroxide,
Is preferably used.

The amount of alkali to be added to the water to be treated may be such that selenate in the water becomes an insolubilized product. Generally, the pH of the treated water is 4 to 8, preferably 5.
The amount may be such that it is controlled within the range of 5 to 6.0.

The presence of the oxidizing agent and carbonate ion is as follows.

In the present invention, the oxidizing agent is added to the wastewater to be treated. This oxidant is capable of converting selenate into an insolubilized product. Specific examples of such an oxidant include hypochlorous acid, chlorous acid, perchloric acid, and their water-soluble substances. Examples include chlorine-based oxidizers such as salts, hydrogen peroxide, and ozone. Among these, the amount of available chlorine (in terms of Cl, hereinafter the same) is 0.
It is convenient and preferable to use a chlorine-based oxidizer of 1 to 25%, more preferably 1 to 20%, particularly preferably 1 to 13%. As the chlorine-based oxidizing agent, agents such as the above hypochlorous acid, chlorous acid, chloric acid, perchloric acid and their water-soluble salts may be used, but chlorine gas is introduced into the sodium hydroxide solution. What was prepared by this may be used.

When the oxidant is reacted with selenate in water according to the invention, it is preferred that carbonate ions be present. The presence of this carbonate ion makes it possible to lower the concentration of selenium in the treated water as compared with the case of using the oxidant alone, and to accelerate the formation of flocs. It is possible to obtain effects such as obtaining good flock.

As the compound that generates carbonate ions (carbonate ion generator), any compound can be used as long as it is a compound that generates carbonate ions in water. Such substances include water-soluble carbonates such as sodium carbonate and sodium hydrogen carbonate, carbon dioxide gas and the like. The amount of carbonate ion in the water to be treated is 0.00
0005 to 0.1 mol / L, preferably 0.00005
It is a ratio such that it is about 0.01 mol / L.

The time of adding the carbonate ion generating agent is not particularly limited, and may be before, during or after the addition of the oxidizing agent.
It is preferably immediately before or at the same time as the addition of the oxidizing agent.

The amount of the aluminum compound added is 1 to 5000 mol, preferably 1 to 40 mol, per 1 mol of selenic acid.
The amount is 00 mol, more preferably 1 to 3000 mol.

The amount of the iron compound added is 0.1 to 10000 mol, preferably 0.2 to 10 mol, per 1 mol of selenic acid.
The amount is 000 mol, more preferably 1 to 10000 mol.

One embodiment (drug A) of the drug used for the removal of selenate of the present invention is (i) an effective chlorine amount of 0.1 to 25.
% Chlorine-based oxidant and (ii) a mixture of a water-soluble carbonate compound such as sodium carbonate. Another aspect of the drug of the present invention (drug B) is (i) a chlorine-based oxidizing agent having an effective chlorine amount of 0.1 to 25%, and (ii) a water-soluble carbonate compound such as sodium carbonate (iii). ) A drug characterized by comprising a mixture with sodium hydroxide.

In the case of producing the above-mentioned drug A, a chlorine-based oxidizer having an effective chlorine amount of 0.1 to 25% (such as an aqueous solution)
Then, carbonate is added and dissolved. In this case, the proportion of carbonate is 0.001-1 mol, preferably 0.01-0.5 mol, per mol of available chlorine. In this case,
Since no alkali is added, crystal precipitation may occur.

In order to preferably produce the drug B of the present invention,
Do the following: First, the available chlorine amount (concentration) is 0.1
Sodium hydroxide is dissolved in a 25% chlorine-based oxidizing agent (such as an aqueous solution), and a carbonate is added to this to dissolve it. In this case, the proportion of sodium hydroxide is 0.01 to 1 mol, preferably 0.1 to 1 mol, per 1 mol of available chlorine. The ratio of carbonate is
The amount is 0.001 to 1 mol, preferably 0.01 to 0.5 mol.

When the treatment water concentration of selenate is reduced by the agent of the present invention, either an agent containing sodium hydroxide or an agent not containing sodium hydroxide may be used, but it does not contain sodium hydroxide. When a drug is used, if the pH drops after the drug is added, the alkali may be added again. In order to reduce the concentration of selenate treated water with the agent of the present invention, an aluminum compound, an iron compound and an agent are added to the water to be treated, and then an alkali is added to adjust the pH to 4 to 8, preferably 5 to 7. , And more preferably adjusted to 5.5 to 6.0.

The addition amount of the chemical agent is the number of moles of available chlorine of the oxidizing agent, and is 0.1 to 3000 moles per 1 mole of selenic acid.
Preferably 0.2 to 3000 mol, more preferably 0.1.
It is 5 to 3000 mol.

In the present invention, it is preferable to use a coagulant together. The aggregating agent in this case may be any agent used for floc aggregating, and examples thereof include cation-modified polyacrylamide, polyacrylic acid dimethylaminoethyl ester, and polymethacrylic acid dimethylaminoethyl. Cationic organic flocculants such as ester, polyethyleneimine and chitosan, nonionic organic flocculants such as polyacrylamide, anionic organic flocculants such as polyacrylic acid, copolymers of acrylamide and acrylic acid and salts thereof. Is included. The coagulant may be usually added to the water to be treated after the chemical is added.

The water to be treated containing the flocs after the treatment of the present invention is subjected to solid-liquid separation treatment. Examples of the solid-liquid separation method in this case include conventional methods such as filtration separation, centrifugation and sedimentation separation.

The water to be treated used in the present invention is a liquid containing selenate, and various industrial wastewaters are used. The concentration of selenate in the water to be treated is not particularly limited, and it is possible to treat wastewater containing high to low concentrations of selenate up to the wastewater standard or lower.

[0026]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Reference Example 1 Sodium hypochlorite aqueous solution (for industrial use) (effective chlorine amount: 12
%) 1 liter, 36 g of sodium carbonate was added and dissolved. This solution is designated as drug A.

Reference Example 2 Sodium hypochlorite aqueous solution (for industrial use) (effective chlorine amount: 12
%) 1 g of 43 g of sodium hydroxide was dissolved in 36 g of sodium carbonate. This solution is designated as drug B.

Reference Example 3 Sodium hypochlorite aqueous solution (for industrial use) (effective chlorine amount: 12
%) 1 liter, 43 g of sodium hydroxide was added and dissolved. This solution is designated as drug C.

Example 1 10% of actual wastewater containing selenium acid (0.28 mg / l as selenium) (aluminum concentration 200 mg / l)
40 ml / l of ferrous sulfate solution was added, the pH was adjusted to 3 with an aqueous sodium hydroxide solution, then a predetermined amount of the drug B was added, and then the pH was adjusted to 5.5 with an aqueous sodium hydroxide solution.
After adjusting to 6.5, 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. The selenium concentration of the supernatant water was measured with an ICP emission spectrometer. The results are shown in Table 1.

[0031]

[Table 1]

Example 2 To the same actual wastewater as in Example 1, 1 ml / l of the chemical B was added, 10 wt% ferrous sulfate solution was added in the same amount as in Example 1, and then the aqueous sodium hydroxide solution was added. Adjust the pH to 5.5-6.
After adjusting to 5, polymer coagulant 3 mg / l was added to cause coagulation and precipitation. Regarding the results, similar to Example 1, the addition of the drug B gave good results.

Example 3 To the same actual wastewater as in Example 1, a predetermined amount of 10 wt% ferrous sulfate solution was added, the pH was adjusted to 3 with an aqueous sodium hydroxide solution, and then the drug B was added at 1 ml / ml. Then, the pH was adjusted to 5.5 to 6.5 with an aqueous sodium hydroxide solution, and then 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. The results are shown in Table 2.

[0034]

[Table 2]

Example 4 Actual drainage having a pH of 2.5 containing 0.387 mg / l of selenium acid as selenium and 169 mg / l of aluminum,
0.6 ml / l of a 5% by weight solution of aluminum sulfate and 33 ml / l of a 10% by weight ferrous chloride solution were added, and the pH was adjusted to 3 with an aqueous sodium hydroxide solution.
ml / l, then add pH with aqueous sodium hydroxide
Was adjusted to 5.5, and 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. When the selenium concentration of the supernatant water was measured, it was 0.000 mg / l.

Example 5 2.1 ml / l of a 5% by weight aluminum sulfate solution and 10 ml of ferrous chloride were added to actual wastewater containing 0.330 mg / l of selenium acid as selenium and 89 mg / l of aluminum and having a pH of 2.7. Add 33 ml / l of the wt% solution, adjust the pH to 3 with aqueous sodium hydroxide, and then add the drug B to 1 m.
Then, the pH was adjusted to 5.5 with an aqueous sodium hydroxide solution, and then 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. When the selenium concentration of the supernatant water was measured, it was 0.000 mg / l.

Example 6 To a wastewater having a pH of 2.3 containing 1.18 mg / l of selenium as selenium and 191 mg / l of aluminum, 0.6 ml / l of a 10% by weight aluminum sulfate solution and 10 parts of ferrous chloride were used. Add 33 ml / l of the wt% solution, adjust the pH to 3 with aqueous sodium hydroxide solution, then add 1 part of drug B.
ml / l, then add pH with aqueous sodium hydroxide
Was adjusted to 5.5, and 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. When the selenium concentration of the supernatant water was measured, it was 0.000 mg / l.

Example 7 In an actual waste water of pH 2.7 containing 0.63 mg / l of selenium acid as selenium and 115 mg / l of aluminum, 2.1 ml / l of a 10 wt% aluminum sulfate solution and 10 parts of ferrous chloride were used. Add 33 ml / l of the wt% solution, adjust the pH to 3 with aqueous sodium hydroxide solution, then add 1 part of drug B.
ml / l, then add pH with aqueous sodium hydroxide
Was adjusted to 5.5, and 3 mg / l of a polymer flocculant was added to cause flocculation and precipitation. When the selenium concentration of the supernatant water was measured, it was 0.000 mg / l.

Example 8 In place of the drug B, 1 ml of the drug C was added to the actual waste water of Example 6.
As a result of the same treatment as in Example 6 except that the amount of selenium added was 1 / l, the selenium concentration in the supernatant water was 0.116 mg / l. With the chemical C, the model drainage can treat up to near the drainage standard, but with the actual drainage, it is difficult to constantly keep the drainage standard or below.

Example 9 In place of the drug B, 1 ml of the drug A was added to the actual waste water of Example 6.
As a result of the same treatment as in Example 6 except that the amount of selenium added was 1 / l, the selenium concentration in the supernatant water was 0.035 mg / l.

[0041]

According to the method of the present invention, selenate in water to be treated can be efficiently removed as an insolubilized product.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinji Wada             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             Inside the Tsukuba Center, National Institute of Advanced Industrial Science and Technology (72) Inventor, Yasuhiro Yukawa             2-1-6 Sengen, Tsukuba-shi, Ibaraki Mitsubishi Corporation             Environment & Development Project Co., Ltd.             Sakai / Infrastructure Unit, Institute for Environmental Resources F-term (reference) 4D015 BA19 BB05 CA20 DA40 DB03                       DB07 DB12 DB15 DB19 DB32                       DC06 DC07 DC08 EA32 EA35                       EA39 FA01 FA24 FA28                 4D038 AA08 AB70 AB82 BB13 BB16                       BB18                 4D050 AA13 AB55 BB06 BB07 CA13                       CA16

Claims (9)

[Claims] 1. An aluminum compound, an iron compound and an oxidizing agent are allowed to coexist in treated water containing selenate to adjust the pH of the treated water to 4 to 8 so that the selenate contained in the treated water is removed. A method for removing selenate, which comprises insolubilizing. 2. The method for removing selenate according to claim 1, wherein the iron compound is ferrous sulfate or ferrous chloride. 3. The oxidizing agent has an effective chlorine amount of 0.1 to 2
The method for removing selenate according to claim 1, wherein the selenate is removed with 5% chlorine-based oxidant. 4. The method for removing selenate according to claim 1, wherein selenate is insolubilized in a state where carbonate ions are present in the water to be treated. 5. The method for removing selenate according to claim 1, wherein the carbonate ion is obtained by adding a carbonate ion generating agent to waste water. 6. The method for removing selenic acid according to claim 1, wherein the carbonate ion generating agent is selected from sodium carbonate and potassium carbonate. 7. The method according to claim 1, wherein a coagulant is added to the water to be treated. 8. (i) a chlorine-based oxidant having an effective chlorine content of 0.1 to 25%, which is used in the method according to claim 4;
i) A drug characterized by comprising a mixture with a water-soluble carbonate compound. 9. A chlorine-based oxidizer having an effective chlorine content of 0.1 to 25%, which is used in the method according to claim 4, and (i)
A drug characterized by comprising a mixture of i) a water-soluble carbonate compound and (iii) sodium hydroxide.