JPH1094789A - Treatment of selenium-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the solenium concentration in waste water by adding aluminum ion in the waste water containing 4-valent selenium ion, further adding a metal removing agent having chelating ability and neutralizing the mixed solution thereby coagulating them. SOLUTION: The waste water to be treated is supplied to a pH adjusting tank 3 from a waste water storage tank 1 by a waste water supply pump 2 after an aluminum ion solution and the metal removing agent are added. The metal removing agent is added as standard by 0.1-0.5ml/l in the case of having only dithicarbamic acid group as the chelating group, 0.05-0.1ml/l in the case of having thiol group (-S group), 40-200mg/l in the case of having a compound having dithiocarbamic acid and 50-300mg/l in the case of having xanthates. As the aluminum ion source, polyaluminum chloride, aluminum sulfate and the like are exemplified and the adding quantity is controlled to >=100mg/l in terms of aluminum in the waste water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating selenium-containing waste liquid for reducing the selenium concentration in selenium-containing waste liquid such as wastewater from a coal-fired power plant.

[0002]

2. Description of the Related Art A method for treating selenium contained in wastewater is disclosed.
The coprecipitation method using divalent or trivalent iron ions is known
Metals such as Ba that form hardly soluble salts with selenium
Salt and then a soluble iron salt (trivalent) to adjust the pH.
Selenium as Fe 4-5.5 _Two(SeO_Three)_ThreeAs
A method of fixing (Japanese Patent Laid-Open No. 5-78105)
SO_FourTo fix selenium, dilute sulfuric acid and iron powder
, And the mixture is filtered, and sludge containing selenium and FeSO_Four
Separate the solution and add FeSO_FourMethod for reuse of
-79286).

[0003]

Since the regulation on selenium in wastewater was promulgated in 1993, the treatment method has not been studied yet, but it is the most widely studied among the few studied cases and the literature is also available. The most common is the coagulation precipitation method using iron ions. In this method, FIG. 5 (Kametani Hiroshita one example of examination result of the processing conditions; Study on wastewater treatment by suspending electrolyte; NRIM report collection, 9
As shown in (1988) p207), the treatment performance varied greatly depending on the concentration of the coprecipitated salt, and the treatability was unstable, and the selenium regulation value of 0.1 mg / liter was not always satisfied in some cases.

For the time being, the wastewater to be treated with selenium is wastewater from a coal-fired power plant. Since this wastewater often contains high-concentration salts, it is stable against wastewater of any salt concentration. There has been a demand for a processing method that can clear the regulation value.

[0005] In view of the above prior art, an object of the present invention is to provide a method for treating a selenium-containing waste liquid capable of stably reducing the selenium concentration even under the condition that a high concentration of salt coexists.

[0006]

The present invention adopts the following constitutions (1) to (4) as means for solving the above-mentioned problems. (1) An aluminum ion is added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ), a metal collecting agent having a chelate-forming group is further added, and the mixture is neutralized and coagulated. A method for treating a selenium-containing waste liquid, wherein the Se concentration in the liquid is reduced. (2) The addition amount of aluminum ions is 50 to 1000 m
The method for treating a selenium-containing waste liquid according to the above (1), wherein g-Al / liter is used.

(3) An aluminum ion is added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ) so as to have a concentration of 50 mg-Al / liter or more, and a dithiocarbamic acid group and a thiol group having a chelate-forming group. Selenium characterized by adding a molecular metal scavenger so as to have a concentration of 0.02 to 0.2 ml / liter, neutralizing the mixed solution and subjecting it to a coagulation treatment to reduce the Se concentration in the solution. How to treat contained waste liquid.

(4) An aluminum ion is added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ) so as to have a concentration of 50 mg-Al / liter or more, and a polymer metal having only a dithiocarbamic acid group as a chelate-forming group. A selenium-containing waste liquid characterized by reducing the Se concentration in a liquid by adding a collecting agent to a concentration of 0.05 to 0.7 ml / liter and neutralizing and aggregating the mixed liquid. Processing method.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an apparatus configuration for performing the method of the present invention. In the process of FIG. 1, wastewater to be treated is supplied from a waste liquid storage tank 1 to a pH adjustment tank 3 by a waste liquid supply pump 2, and an aluminum ion solution and a metal collecting agent are added before entering the pH adjustment tank 3.

In the present invention, a dithiocarbamic acid group, a thiocarbamic acid group, a thiol group, an amino group, an imino group, an aminocarboxylic acid group, an iminocarboxylic acid group, an iminodicarboxylic acid group, which are chelating groups, are used as metal-collecting agents. , Xanthate, aminoalkylphosphate, iminoalkylphosphate, phosphate, carboxyl, sulfonic, thioureido, amidoxime, imidoxime, acid hydrazine, thiourea, etc. Agents can be used.

Preferred examples of these metal scavengers are high molecular metal scavengers having a dithiocarbamic acid group represented by the following formula (1) or a dithiocarbamic acid group and a thiol group (-S group), dithiocarbamic acid compounds Metal collectors, xanthates (-OCS ₂ group-containing metal collectors) and the like. Among them, a polymer metal collecting agent having a dithiocarbamic acid group or a dithiocarbamic acid group and a thiol group has good cohesion after treatment due to a polymer effect,
It has good operability and is a suitable metal collecting agent for the purpose of the present invention.

Embedded image

The amount of the metal scavenger added varies depending on the concentration of selenium present in the waste liquid and the type of the metal scavenger, and may be appropriately set according to the treatment conditions. Is 0.05 to 0.7 ml / liter, preferably 0.1 to 0.5 ml / liter in the case of a polymer metal collector having only a dithiocarbamic acid group as In addition, in the case of a polymer metal collector having a thiol group (-S group), 0.02 to 0.2 ml / liter, preferably 0.05 to 0.1 ml / liter is added. In the case of a compound having a dithiocarbamic acid group as a chelating group,
200mg / l, 50 ~ 3 for xanthates
It is about 00 mg / liter. These metal scavengers may be used alone or in combination of two or more.

Representative examples of the polymeric metal scavenger having a dithiocarbamic acid group include Epofloc L-1 and Epofloc L-2 (trade names, manufactured by Miyoshi Oil & Fats Co., Ltd.).
1 has a dithiocarbamic acid group and a thiol group, whereas L-2 has only a dithiocarbamic acid group. It is considered that the difference between the two is due to the difference in selectivity for the ion and the difference in the reducing action between the dithiocarbamic acid group and the thiol group.

In the present invention, an inorganic sulfide agent such as sodium hydrogen sulfide, sodium monosulfide, sodium disulfide, sodium trisulfide, sodium tetrasulfide, sodium pentasulfide, and the like, together with the above metal-collecting agent, One or more potassium sulfides such as potassium hydrogen, potassium disulfide, potassium trisulfide, potassium tetrasulfide, and potassium pentasulfide may be used in combination. The addition of these sulfurizing agents has the effect of improving Se removal performance.
When a complex is formed with Se only by a sulfurizing agent, it may be water-soluble, but when used in combination with a metal collecting agent, it becomes water-insoluble and Se can be removed efficiently. It is also effective to use a water-soluble polymer drug such as a polymer flocculant in combination.

Preferable examples of the aluminum ion source include polyaluminum chloride and aluminum sulfate. The concentration of the aluminum ion source in the waste liquid is 50 mg / liter or more, preferably 100 mg / liter, as aluminum (Al).
To be at least liters. In addition, since it is not economical to add more than necessary, a preferable range is 50 to 10.
00 mg / l, especially 50-500 mg / l.

The waste liquid to which the aluminum ions and the metal trapping agent have been added is sent to a pH adjusting tank 3 and neutralized by adding a neutralizing agent (acid or alkali) while stirring with a stirrer 4. A polymer coagulant is added to the liquid overflowing from the pH adjusting tank 3 and sent to the coagulating sedimentation tank 5 for solid-liquid separation. By this operation, the Se concentration in the waste liquid to be treated is 2 at Se ^{+ 4} .
If it is 0 mg / liter or less, the Se concentration in the supernatant water of the coagulation sedimentation tank 5 will be 0.1 mg / liter or less, which is the regulated value, and it will be possible to discharge.

The purpose of the coagulation / sedimentation tank 5 in FIG. 1 is to perform solid-liquid separation, and it is also possible to combine other solid-liquid separation methods such as separation by a filter and a high-speed coagulation / sedimentation method. In this example, a polymer flocculant is added as a flocculation treatment to perform coagulation precipitation. However, a polymer flocculant is not required when solid-liquid separation can be easily performed by separation with a filter or the like.

[0018]

EXAMPLE Se is present in the waste liquid in the form of selenic acid (SeO ₄ ²⁻ ) and selenous acid (SeO ₃ ²⁻ ). For example, in coal-fired wastewater, Se exists almost in the form of selenous acid. By removing selenic acid, it is possible to make all Se below the regulation value. Here, a treatment test was performed using simulated water (hereinafter simply referred to as waste liquid) of coal-fired power plant wastewater having the composition shown in Table 1.

[0019]

[Table 1]

(Reference Example) An aluminum ion solution was added stepwise to the waste liquid having the above composition, and a flocculation operation was performed under the condition of pH 7, and Se in the supernatant water was measured. In addition, poly aluminum chloride (PAC) was used as an aluminum ion source. FIG. 2 shows the measurement results. As shown in FIG. 2, the Se concentration in the treated water also decreased with an increase in the amount of added aluminum, but could not be reduced to the regulated value of 0.1 mg / liter or less.

(Example 1) A metal collecting agent having a chelate functional group added to a polymer was added to a waste liquid having the above composition together with PAC (addition amount: 100 mg / liter as Al ion), and the effect was confirmed. Representative examples of the high-molecular metal collecting agent are Epofloc L-1 (having dithiocarbamic acid group and thiol group) and Epofloc L-2 (having only dithiocarbamic acid group) manufactured by Miyoshi Oil & Fats Co., Ltd.
And the amount of polymer metal scavenger added and the Se in the treated water
The relationship with concentration was investigated. FIG. 3 shows the result of measuring the Se concentration in the treated water while changing the added concentration of L-1 and L-2.

As is apparent from FIG.
At the added amount of 02 to 0.2 ml / l, the Se concentration in the treated water becomes 0.1 mg / l or less, which is the regulated value, and for L-2, the added amount of 0.05 to 0.7 ml / l is used. The Se concentration in the treated water becomes equal to or lower than the regulated value of 0.1 mg / liter.

(Example 2) Al ion (PAC) and a polymer metal scavenger (Epofloc L-1) were added to wastewater having the above composition.
Was added at a different concentration to adjust the pH to 7, and then the Se concentration of the supernatant was measured. As a result, as shown in FIG.
When the addition amount of -1 is 0.05 and 0.1 milliliter / liter, the addition amount of Al ion is 50 mg / liter or more, the Se concentration in the treated water becomes 0.1 mg / liter or less, and further the addition of Al ion Increase the amount to 100mg
/ L or more, the Se concentration in the treated water became steady.
Further, when the addition amount of L-1 is less than 0.02 ml / liter and when it exceeds 0.2 ml / liter, the Se concentration in the treated water is 0.1 even if the addition amount of Al ions is increased. It did not fall below 1 mg / l.

Example 3 Aluminum sulphate was used as the source of Al ions in the wastewater of the above composition, and 20% of sodium diethyldithiocarbamate [(C ₂ H ₅ ) ₂ NCSSSNa] was used instead of the high-molecular metal scavenger. A Se treatment test was performed using an aqueous solution. Al ion addition amount is 100
Under the condition of mg / liter and pH 7, 0.4 ml / liter of the aqueous solution of the metal collecting agent was added.
The Se concentration of the supernatant water was 0.1 mg / liter or less.

Example 4 PAC was used as the source of Al ions in the wastewater having the above composition, and sodium dibutyldithiocarbamate [(C ₄ H ₉ ) ₂ NC was used as the metal-collecting agent.
A treatment test of Se was performed using a 40% aqueous solution of [SSNa]. Al ion addition amount is 100mg / L, pH
Under the condition of 7, as a result of adding 0.3 ml / l of the aqueous solution of the metal collecting agent, the Se concentration of the supernatant water became 0.1 mg / l or less.

Example 5 A wastewater having the above composition was subjected to a Se treatment test using PAC as an Al ion source and a 40% aqueous solution of ethyl xanthate (C ₂ H ₅ OCSSNa) as a metal collector. went. Al ion addition amount is 1
Under the conditions of 20 mg / liter and pH 7, 0.3 ml / liter of the aqueous solution of the metal collecting agent was added, and as a result, the Se concentration of the supernatant water became 0.1 mg / liter or less.

Example 6 PAC was used as the source of Al ions in the wastewater of the above composition, and diethylene triamine (dipotassium salt of 1,3-dithiocarboxydiethylene triamine) having an imino group and a dithiocarbamic acid group was used as a metal collecting agent. A Se treatment test was performed using a 40% aqueous solution. Al ion addition amount is 105mg / L,
Under the condition of pH 6.5, the aqueous solution of the metal-collecting agent was added at a pH of 0.1.
As a result of adding 2 ml / liter, the supernatant water Se
The concentration became 0.1 mg / liter or less.

(Example 7) In the composition of the simulated water of the coal-fired power plant effluent shown in Table 1, the concentration of Se ⁴⁺ was 18 mg /
Liter, PAC was used as an Al ion source, and a treatment test for Se was performed using Epofloc L-1 as a metal metal collecting agent as a metal collecting agent. Al ion addition amount is 7
Under the conditions of 00 mg / liter and pH 7, 0.4 ml / liter of the metal collecting agent was added, and as a result, the Se concentration of the supernatant water became 0.1 mg / liter or less.

As described above, the Se in the waste liquid in which the salt coexists is used.
In the treatment, Al ions and a metal collecting agent are used in combination, and the concentration thereof is limited to an appropriate range.
The e-concentration can be lower than the regulation value.

[0030]

According to the method of the present invention, the Se concentration in a waste liquid in which a high concentration of salt coexists, such as the wastewater of a coal-fired power plant, is stably reduced to a regulated value of 0.1 mg / liter or less. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus configuration for performing a method of the present invention.

FIG. 2 is a graph showing the relationship between the amount of Al ions added and the Se concentration in treated water.

FIG. 3 is a graph showing the relationship between the amount of polymer metal scavenger added and the Se concentration in treated water when the amount of Al ions added is constant.

FIG. 4 is a diagram showing a change in Se concentration in treated water when the addition amount of Al ions and the addition amount of a polymer metal collector are changed.

FIG. 5: pH and Na ₂ SO for the Fe co-precipitation method of Se
_The figure which shows the influence of ₄ .

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaaki Negoro 2-1-1 Shinama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Naoyuki Uejima Machiichi Wadasaki, Hyogo-ku, Kobe-shi Chome 1-1 Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Ryoichi Asano 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Iwao Nakayasu Hyogo Prefecture 2-8-19 Shinhama, Arai-machi, Takasago-shi Takaishi Engineering Co., Ltd. (72) Inventor Kazuo Hosoda 4-66-1, Horikiri, Katsushika-ku, Tokyo Miyoshi Oil & Fat Co., Ltd. (72) Inventor Masafumi Moriya Katsushika-ku, Tokyo 4-66-1, Horikiri Miyoshi Oil & Fat Co., Ltd.

Claims (4)

[Claims] 1. An aluminum ion is added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ), and a metal collecting agent having a chelate-forming group is added. A method for treating a selenium-containing waste liquid, characterized by reducing the Se concentration in the liquid. 2. The addition amount of aluminum ions is 50 to 1
000 mg-Al / liter.
2. The method for treating a selenium-containing waste liquid according to item 1. 3. A polymer having aluminum ion added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ) at a concentration of 50 mg-Al / liter or more, and further having a dithiocarbamic acid group and a thiol group as chelating groups. A selenium-containing material characterized by adding a metal-collecting agent to a concentration of 0.02 to 0.2 ml / liter, neutralizing the mixture and subjecting it to a coagulation treatment to reduce the Se concentration in the solution. Waste liquid treatment method. 4. An aluminum ion is added to a waste liquid containing tetravalent selenium ion (Se ⁴⁺ ) so as to have a concentration of 50 mg-Al / liter or more, and a polymer metal trap having only a dithiocarbamic acid group as a chelate-forming group. 0.
A method for treating a selenium-containing waste liquid, wherein the selenium-containing waste liquid is added to the mixture so as to have a concentration of 0.5 to 0.7 milliliter / liter, and the mixture is neutralized and coagulated to reduce the Se concentration in the liquid.