JP2002011482A - Method of treating water containing selenium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating water containing selenium, by which the selenium is efficiently removed with a small amount of a reagent used and a small elution amount of iron. SOLUTION: In a method of treating water containing selenium, where an operation of adding an acid to the water containing the selenium and bringing the acid-added water into contact with iron metal is repeated twice or more times and a method of treating water containing selenium, where the water containing the selenium is acidified to be passed through a layer filled with iron metal, the acid is poured into at least one part on the way of the flow passage in the layer filled with the iron metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating selenium-containing water. More specifically, the present invention relates to a method for treating selenium-containing water that can efficiently remove selenium with a small amount of drug used and a small amount of iron eluted.

[0002]

2. Description of the Related Art In some cases, flue gas desulfurization effluent from coal-fired power plants and effluent from petroleum refineries contain selenium. In addition, selenium is used as an industrial raw material as a decolorizing agent and coloring agent for glass, as a high-grade pigment, as an additive to steel and copper, and as a catalyst for the synthesis of urethane and urea. May also contain selenium. It is rare that selenium is contained in wastewater at high concentrations, but as selenium is regulated for environmental protection,
It is necessary to treat selenium in wastewater, and the selenium wastewater standard based on the Water Pollution Control Law is set to 0.1 mg / L. Selenium in the wastewater is usually present as colloidal selenium, tetravalent selenite ion (SeO ₃ ²⁻ ) or hexavalent selenite ion (SeO ₄ ²⁻ ) in many cases. As a method for treating such selenium-containing water, many coagulation sedimentation methods have been proposed. For example, Japanese Patent Laid-Open No. 6-79286, both removed SeO ₃ ^2-and SeO ₄ ^2-a in the wastewater treatment method of the selenium-containing wastewater to reduce the amount of precipitated concentrate is dropped out and system As SeO ₃ ^2- , SeO ₄
^2- , a neutralization agent containing a hydroxyl group is added to the wastewater containing Cu ²⁺ and the suspended matter to coprecipitate and remove the mixture of copper hydroxide and the suspended matter, and the acid is added to the primary treated water. and after the addition salts with Fe ^2+, again added the neutralizing agent, coprecipitated removed primary process remains in the water SeO ₃ ^2-and SeO ₄ ^2-a as a mixture of selenium and iron hydroxide 2 A selenium-containing wastewater treatment method for performing the next treatment has been proposed. However, in this method, the required amount of iron salt to be added is large, and the selenium concentration in the final treated water is reduced to only 0.2 to 0.4 mg / L, and 0.1 mg / L.
Wastewater standards cannot be achieved. Japanese Patent Application Laid-Open No. 10-128343 discloses a method for treating selenium-containing water that can reduce the consumption of iron metal and the amount of settled sludge and efficiently remove selenium by injecting hydrochloric acid or sulfuric acid into wastewater. A method for treating selenium-containing water has been proposed in which the pH is adjusted to 4 to 5 to remove the alkalinity component, and then hydrochloric acid or sulfuric acid is further injected into the wastewater and then passed through the iron metal packed bed. Further, JP-A-11-28475 discloses a method of treating selenium-containing water for removing selenium efficiently by contacting selenium-containing water with iron metal under acidic conditions, and treating the pH of the treated water. And then contacting with peroxide after adjusting the selenium concentration to be approximately neutral. According to these methods, the selenium concentration in the treated water can be reduced to 0.1 mg / L or less with a smaller iron elution amount than the coagulation sedimentation treatment method.
There has been a demand for a method capable of treating with a smaller iron elution amount.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for treating selenium-containing water that can efficiently remove selenium with a small amount of drug used and an elution amount of iron. .

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the removal rate of selenium from selenium-containing water has been determined to be irrespective of the selenium concentration in raw water. ^It is determined by the ratio of ²⁺ elution amount to selenium concentration in raw water.Therefore, adding acid in two or more portions to selenium-containing water reduces the amount of acid used and the amount of iron eluted, That can be efficiently removed,
Based on this finding, the present invention has been completed. That is, the present invention provides (1) a method for treating selenium-containing water, wherein the operation of adding an acid to water containing selenium and bringing the same into contact with iron metal is performed twice or more, and (2) selenium-containing water. A method for treating selenium-containing water in which the contained water is acidified and passed through the iron-metal-filled layer, wherein a method for treating selenium-containing water characterized by injecting an acid into at least one portion of the iron-metal-filled layer in the middle of the flow. To provide.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the first embodiment of the method for treating selenium-containing water of the present invention, the operation of adding an acid to selenium-containing water and bringing the same into contact with iron metal is performed twice or more. In the second embodiment of the method for treating selenium-containing water of the present invention,
In the method for treating selenium-containing water in which the selenium-containing water is acidified and circulated through the iron metal packed bed, the acid is injected into at least one portion of the iron metal packed bed that is flowing. The method of the present invention can be effectively applied to selenium-containing water, particularly wastewater containing hexavalent selenium. Examples of such selenium-containing water include selenium-containing water having a selenium concentration of about 1 mg / liter, which is obtained by subjecting wastewater from a thermal power plant containing several mg / liter of selenium to coagulation sedimentation and biological denitrification. be able to. The reaction of bringing selenium-containing water into contact with iron metal under acidic conditions to reduce hexavalent selenium is represented by the following equation. _{^{SeO 4 2+ 3Fe 0 + 8H +}} → Se 0 + 3Fe 2+
+ 4H ₂ O However, in actuality, the amount of selenium to be reduced is very small compared to the elution amount of Fe ²⁺ ions, and to reduce hexavalent selenium, it is required to be 1,000 equivalent times as much as selenium. It is necessary to elute a large excess of Fe ²⁺ ions.

[0006] FIG.²⁺Elution amount and hexavalent in raw water
Shows the relationship between selenium concentration and weight ratio and selenium removal rate
It is a graph. From this graph, for example, hexavalent selenium
Remove 90% of selenium in raw water containing 1mg / L
In order to obtain treated water having a selenium concentration of 0.1 mg / L,
About 700mg / L Fe²⁺I need to elute ions
You can see that. The data in this graph show that the selenium concentration is
7-5 mg / L selenium-containing water at 70 ° C., space velocity
15h^-1Treated water obtained by passing water through the
Measured. Selenium concentration 0.7-5mg / L
In the range of, regardless of the selenium concentration in the raw water, Fe²⁺Dissolution
Relationship between output / Se concentration (weight ratio) in raw water and Se removal rate
Is constant as seen in FIG. Therefore,
The acid is added in two portions to the water containing ren, for example,
The first addition of acid to raw water with a concentration of 1 mg / L
250 mg / L Fe ²⁺To elute ions
With this, 70% of selenium is removed and the selenium concentration is 0.3 m
g / L of treated water, and a second acid was added to the treated water.
0.3 × 250 = 75 mg / L of F
e²⁺By eluting further 70% of selenium
Removal to obtain final treated water with a selenium concentration of 0.09 mg / L
be able to. Thus, raw water with a selenium concentration of 1 mg / L
To remove 90% of selenium by one treatment
Contains 700 mg / L of Fe²⁺Requires elution of ions
Divides the acid addition into two, giving 250 + 7
5 = 325 mg / L Fe²⁺90% selection by ion elution
Can be removed. That is, according to the method of the present invention,
The iron dissolution required to remove selenium from selenium-containing water
Output and at the same time Fe²⁺To elute ions
The required amount of acid to be added can be reduced.

[0007] The acid used in the method of the present invention is not particularly limited, but inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid can be suitably used, and hydrochloric acid and sulfuric acid can be particularly preferably used. In the method of the present invention, the iron metal used is not particularly limited, and examples thereof include pure iron, crude steel, alloy steel, and other iron alloys. Iron metal is iron fine particles,
It is preferable to use a shape having a large surface area such as a wire mesh wire or granular iron, and the particle size is more preferably 0.1 to 3 mm, particularly preferably 1 mm or less. There is no particular limitation on the method of bringing selenium-containing water into contact with iron metal.For example, selenium-containing water can be passed through a column filled with iron fine particles, iron wire, granular iron, or in a reaction vessel. The contact can also be made by adding iron fine particles, iron mesh wire, granular iron, etc. to the selenium-containing water. If it passed through selenium-containing water to ferrous metal packed column, preferably at a space velocity 0.5～500H ^-1, and more preferably 10~100h ^-1. The contact between the selenium-containing water and the iron metal is preferably performed at 40 to 90 ° C, more preferably at 50 to 70 ° C. FIG. 2 is a process flow chart of an embodiment of the method of the present invention. In this embodiment, the operation of adding an acid to the selenium-containing water and bringing the same into contact with the iron metal is performed twice by installing two iron metal packed towers in series and continuously treating the selenium-containing water. The selenium-containing water is supplied to the first ferrous metal packed tower 1
The first acid is injected into the raw water inlet pipe via the valve 2 and comes into contact with the ferrous metal in the first ferrous metal packed tower to reduce hexavalent selenium. Selenium alone. A second acid is injected into the water having a reduced concentration of hexavalent selenium flowing out of the first ferrous metal packed tower via the valve 3, and flows into the second ferrous metal packed tower 4 in an upward flow. Water is passed. The treated water from which selenium has been removed flows out from the top of the second iron metal packed tower.

FIG. 3 is a flow chart of another embodiment of the method of the present invention. In this embodiment, raw water containing hexavalent selenium is continuously passed through the iron metal packed tower 5 in an upward flow, and acid is injected into the raw water inlet pipe via the valve 6;
It is injected into the intermediate portion of the iron metal packed bed via the valve 7. The selenium-containing water receives the addition of the acid divided into two times, and comes into contact with the iron metal to reduce hexavalent selenium to form selenium alone and adhere to or be adsorbed on the surface of the iron metal. The treated water from which selenium has been removed flows out from the top of the tower. In the method of the present invention, when a certain amount of selenium-containing water is passed through an iron metal packed tower, by washing the inside of the tower, it is possible to remove selenium adhering to or adsorbed to iron metal. preferable. There is no particular limitation on the method of washing the inside of the iron metal packed tower, and for example, washing can be performed by a method of supplying a mixed flow of water and air in an upward flow. The selenium alone removed by washing is discharged as a suspended substance together with other insoluble components in the washing waste liquid, so that it can be separated into solid and liquid and discarded. According to the method of the present invention, in the method of removing selenium by bringing selenium-containing water into contact with iron metal under acidic conditions, the amount of acid used and the amount of elution of iron are reduced, and selenium in water is effectively reduced. It can be removed to a concentration.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 (Relationship between ratio of iron elution amount / selenium concentration in raw water and selenium removal rate) Using an apparatus shown in FIG. 4, ratio of Fe ²⁺ elution amount / selenium concentration in raw water and selenium removal rate The relationship was investigated. The iron metal packed tower used had 15 L of iron particles having a diameter of 0.6 mm (75 k).
g) was charged. The flue gas desulfurization effluent containing all 0.69 mg / L of selenium as hexavalent selenium is passed through a ferrous metal packed tower at a temperature of 70 ° C and a flow rate of 225 L / h (SV 15 h ^-1 ), and the test water inlet pipe , The amount of Fe ²⁺ eluted was 93
Hydrochloric acid was injected so as to be mg / L. The selenium concentration in the treated water flowing out of the iron metal packed tower was 0.31 mg / L, and the selenium removal rate was 55%. When the injection amount of hydrochloric acid was increased so that the elution amount of Fe ²⁺ became 199 mg / L and 317 mg / L, the removal rate of selenium was 7
3% and 82%. Furthermore, the content of hexavalent selenium in the flue gas desulfurization effluent is 1.59 mg / L and 5.10 mg / L.
About the test water which added sodium selenate so that it might be set to L, the water penetration test to the iron metal packed tower was performed similarly. The obtained results are summarized in Table 1 and FIG.

[0010]

[Table 1]

From the results shown in Table 1 and FIG. 1, it can be seen that the selenium removal rate is determined by the ratio of the amount of Fe ²⁺ eluted / the selenium concentration in the raw water, regardless of the selenium concentration in the raw water. Example 2 (Treatment of selenium-containing flue gas desulfurization effluent) The test water obtained by adding sodium selenate to selenium 1.59 mg / L to the flue gas desulfurization effluent used in Example 1 was used by using the apparatus shown in FIG. Processed. The iron metal packed tower used was
It is filled with 15 L (75 kg) of iron particles having a diameter of 0.6 mm, and has an acid injection port in the middle of the raw water inlet pipe and the iron metal packed bed. Test water at a temperature of 70 ° C and a flow rate of 225L
/ H (SV 15 h ^-1 ), water was passed through the tower packed with iron metal, and hydrochloric acid equivalent to 430 mg / L of HCl concentration in the raw water inlet pipe and 210 mg / L of HCl concentration in the middle of the iron metal packed bed was injected. The elution amount of Fe ²⁺ was 450 mg / L,
The selenium concentration in the treated water flowing out of the ferrous metal packed tower is 0.1.
08 mg / L, and the selenium removal rate was 95%. Comparative Example 1 Test water was passed through the iron metal packed tower under the same conditions as in Example 2 except that hydrochloric acid corresponding to an HCl concentration of 650 mg / L was injected only into the raw water inlet pipe. The amount of Fe ²⁺ eluted was 450 mg / L, the ratio of the amount of Fe ²⁺ eluted to the concentration of selenium in the raw water was 283 weight times, and the concentration of selenium in the treated water flowing out of the iron metal packed column was 0.48 mg / L. Yes, the selenium removal rate was 70%. Comparative Example 2 The injection amount of hydrochloric acid in the raw water inlet pipe was adjusted to an HCl concentration of 1,
Test water was passed through the iron metal packed tower under the same conditions as in Comparative Example 1 except that the amount was equivalent to 570 mg / L. The amount of Fe ²⁺ eluted was 1,100 mg / L, the ratio of the amount of Fe ²⁺ eluted to the concentration of selenium in the raw water was 692 times by weight, and the concentration of selenium in the treated water flowing out of the iron metal packed tower was 0%. .2
The amount was 3 mg / L, and the selenium removal rate was 86%. The results of Example 2 and Comparative Examples 1 and 2 are shown in Table 2, and the results of Comparative Examples 1 and 2 are shown in FIG.

[0012]

[Table 2]

As can be seen from Table 2, in Example 2 in which hydrochloric acid was divided and added to two portions, that is, a raw water inlet pipe and an intermediate portion of a ferrous metal packed bed, the selenium concentration in the treated water was 0.0.
It has dropped to 8 mg / L. On the other hand, Comparative Example 1 in which almost the same amount of hydrochloric acid was added at one time in the raw water inlet pipe.
Although the same amount of Fe ²⁺ was eluted as in Example 2, the selenium concentration in the treated water was 0.48 mg / L, which is 6 times higher than that of Example 2. Further, in Comparative Example 2 in which the injection amount of hydrochloric acid in the raw water inlet pipe was about 2.4 times, the elution amount of Fe ²⁺ was also about 2.4 times, but the selenium concentration in the treated water was 0.4. It has only dropped to 23 mg / L. From these results, in the step of treating the selenium-containing water in contact with iron metal under acidic conditions,
It can be seen that by adding hydrochloric acid in two portions, the amount of hydrochloric acid used and the amount of iron eluted can be reduced, and selenium in water can be effectively removed. Also in Comparative Examples 1 and 2, the amount of Fe ²⁺ eluted / Se concentration in raw water and S shown in FIG.
It can be seen that the relationship of the e removal rate is suitable.

[0014]

According to the method of the present invention, in a method of removing selenium by contacting selenium-containing water with iron metal under acidic conditions, the amount of acid used and the amount of iron eluted are reduced, and the method is more effective. Selenium in water can be removed to a low concentration.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of Fe ²⁺ elution amount / selenium concentration in raw water and the selenium removal rate.

FIG. 2 is a process flow chart of one embodiment of the method of the present invention.

FIG. 3 is a process flow chart of another embodiment of the method of the present invention.

FIG. 4 is an explanatory diagram of an apparatus used in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First iron metal packed tower 2 Valve 3 Valve 4 Second iron metal packed tower 5 Iron metal packed tower 6 Valve 7 Valve

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D038 AA08 AB70 AB82 BA02 BA04 BA06 BB13 BB15 BB18 BB19 4D050 AA13 AB59 BA02 BD03 BD06 BD08 CA13 CA16 CA17

Claims (2)

[Claims] 1. A method for treating selenium-containing water, wherein the operation of adding an acid to selenium-containing water and bringing the same into contact with iron metal is performed twice or more. 2. A method for treating selenium-containing water in which selenium-containing water is acidified and passed through an iron metal-filled layer, wherein the acid is injected into at least one portion of the iron metal-filled layer in the middle of the flow. Water treatment method.