JP2002316176A - Catalytic reduction material for wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalytic treatment material for wastewater which can efficiently separate/remove harmful substances such as dissolved selenium and oxidizing substances from the wastewater in the selenium removing treatment of the selenium-containing wastewater, can keep a stable selenium removing ratio over a long time, and can minimize the amount of a iron family metal to be used and the amount of generated sludge to reduce a load in the operation of wastewater treatment. SOLUTION: The catalytic reduction material which is contacted with the wastewater containing the harmful substances comprising the dissolved selenium, or the dissolved selenium and the oxidizing substances to reduce the harmful substances is formed from a metal fiber molding obtained by molding the fibers of a iron family metal. The decrease of the selenium removing ratio is 10% or below until a residual percentage Y defined by the formula of Y(%)= [A-B)/A]/t}×100 [A is the initial weight of the reduction treatment material; B is the weight of the reduction treatment material after the passage of time of t hours; t is a treatment time (h)] reaches 30%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to harmful substances such as selenate ion (SeO ₄ ^2- ) and selenite ion (Se
O ₃ ^2- ) and other wastewater containing various oxidizing substances such as selenium (dissolved selenium) and sulfur oxides,
The present invention relates to a catalytic reducing agent used for separating and removing harmful substances in wastewater.

[0002]

2. Description of the Related Art Selenium and selenium compounds are used in glass products, ceramic products, semiconductor materials, solar cells and movie films,
Infrared polarizers, pigments, sensitizers, dehydrogenating agents, foaming agents, etc., are widely used in the production of various industrial products, and from industrial factories that use such selenium and selenium compounds. Inevitably, selenium-containing wastewater containing dissolved selenium is discharged.

[0003] Regarding this selenium-containing wastewater,
Environmental standard is selenium concentration (as Se) 0.01mg / L
Torr or less is also triggered,
Various methods have been proposed for separating and removing dissolved selenium.
ing. For example, in U.S. Pat.No. 4,405,464,
Hexavalent selenium ion [for example, selenate ion (Se
O_Four ^{Two -})] And metallic iron at pH 6 or less.
And convert the hexavalent selenium ion to a tetravalent selenium ion [eg
If selenite ion (SeO_Three ^2-)] And money
The iron oxide is oxidized and dissolved, and the dissolved iron oxide is dissolved in water.
Precipitated in the form of iron oxide and solid-liquid separation of the precipitated iron hydroxide
Water that has reduced hexavalent and lower selenium ions
A method for collecting a solution is described. Also, JP-A-7-
No. 2,502 discloses selenium and / or selenium-containing waste liquid.
Contact with metallic iron in the pH range of 0 to 6
Precipitating selenium to reduce selenium concentration in waste liquid and
Methods for removal are described. Further, JP-A-11-207,3
No. 64 discloses that a selenium-containing solution is woven at a temperature of 30 ° C. or more.
Contact with a filler layer of iron-based metal such as fiber
A method for depositing selenium on the surface is described.

[0004] In these methods, since dissolved selenium precipitates on the surface of the iron-based metal (metallic iron) in contact with the wastewater, the iron-based metal used is, for example, disclosed in Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 7-2,502 describes that a shape having a large surface area, that is, a shape having a large specific surface area is preferable compared to the entire volume of a thin wire, a small plate piece, a powder, a fine chip, and the like. Japanese Patent Application Laid-Open No. 11-207,364 describes that preferable shapes are fibrous, porous, fine plate-like, granular, powdery, and the like.

However, selenium-containing wastewater generally contains various oxidizing substances such as sulfur oxides and nitrogen oxides in addition to dissolved selenium, and also contains dissolved oxygen. In order to reduce the selenium concentration to 0.1 mg / liter or less, which is specified as a standard, a large amount of selenium in the wastewater in the reaction zone where the wastewater is brought into contact with iron-based metal is several thousand to several tens of thousands times higher than the selenium concentration in the wastewater. It is necessary to generate iron ions. For this reason, the iron-based metal used in this reaction zone is severely consumed, and the removal efficiency of dissolved selenium is poor, so that an unnecessarily large amount of sludge (such as iron hydroxide) is generated, and a large amount of iron is formed in the reaction zone. There is also a need to frequently supply system metals and to treat sludge generated in large quantities, and these have become a great burden on the operation of de-selenium treatment of selenium-containing wastewater.

The problem of the mass use of iron-based metals and the problem of the large amount of sludge associated therewith are caused, for example, by a flue gas desulfurization system installed in a facility such as a coal-fired power plant and mainly for removing sulfurous acid gas in flue gas. From flue gas desulfurization wastewater containing a relatively large amount of oxidizing substances such as sulfur oxides that can be determined by the diethyl-p-phenylenediamine colorimetric method (industrial wastewater test method) 1
If two processes try to remove them at the same time,
Combined with the large amount of processing, it has become a more serious problem.

[0007]

Accordingly, the present inventors have been able to efficiently separate and remove dissolved selenium and oxidizing substances from selenium-containing wastewater, and to reduce the amount of ferrous metal used and the amount of sludge generated as much as possible. As a result of intensive studies on means that can reduce the load on the operation of wastewater treatment, it is possible to form iron-based metal fibers into a predetermined shape as a contact reducing agent for selenium-containing wastewater. It has been found that the use of the obtained metal fiber molded body can maintain a stable selenium removal rate over a long period of time, and completed the present invention.

Accordingly, an object of the present invention is to provide a selenium-containing wastewater that can be efficiently separated and removed from effluents such as dissolved selenium and oxidizing substances at the time of selenium removal, and that the selenium removal rate is stable over a long period of time. And the amount of ferrous metal used and the amount of sludge generated can be reduced as much as possible, thereby greatly reducing the operational burden of wastewater treatment. It is to provide a contact treatment material.

[0009]

That is, the present invention relates to a contact reducing material for reducing harmful substances by contacting wastewater containing dissolved selenium or toxic substances consisting of dissolved selenium and oxidizing substances. Yes, it is made of a metal fiber molded body formed by molding a metal fiber of an iron-based metal into a predetermined shape, and the following relational expression Residual rate Y (%) = [(AB) / A] × 100 (where A : The initial weight of the reduced material, and B: the weight of the reduced material after a predetermined time has passed.
%, The reduction of the selenium removal rate in the waste water is 10% or less.

The catalytic reducing agent of the present invention comprises Fe, Mn, Ni,
Forming a metal fiber made of at least one iron-based metal selected from the group consisting of Cu into a cubic, spherical, cylindrical, disk-like, or other shape that can be filled in the reaction zone of a contact reactor. a metal fiber molding obtained Te, preferably its volume 0.002～0.2M ^3, more preferably a 0.02～0.04M ^3, the bulk density of 50
100 kg / m ^3, preferably 50~70kg / m ^3. Note that, as the shape of the metal fiber form, a too flat shape or an elongated shape is not preferable.

The volume of the metal fiber molded body is 0.002 m
^If it is smaller than ^3, the liquid circulation inside the obtained catalytic reduction material will be too high, the consumption will be fast, the selenium removal rate will decrease quickly, and frequent addition of the catalytic reduction material will be required, and the operation of wastewater treatment will be difficult. And the overflow of the contact reducing material of the catalytic reactor may cause a problem such as breakage or blockage of the downstream equipment, and conversely, if it is larger than 0.2 m ³ , In addition to the case where the liquid flowability into the obtained catalytic reduction material becomes too low, the reactivity decreases and the desired selenium removal rate cannot be achieved, and ferrite is generated due to lack of oxygen inside the catalytic reduction material. As a result, the catalytic reducing agent may be deactivated, and the weight of the catalytic reducing agent may increase, and the handling property of the catalytic reducing agent may decrease.

Further, the bulk density of the molded metal fiber is 50 kg.
/ M ^3, the liquid circulation inside the obtained catalytic reduction material becomes too high, the consumption is fast, the selenium removal rate decreases quickly, and the frequent addition of the catalytic reduction material is required, so that the wastewater treatment becomes difficult. On the other hand, when the load on the operation is increased, when it is higher than 100 kg / m ³ , the liquid flowability into the obtained catalytic reduction material becomes too low, the reactivity is lowered, and the desired selenium removal rate can be achieved. In some cases, sludge deposits become noticeable, and the reaction rate decreases.

The metal fibers used for forming the catalytic reduction material of the present invention are preferably those produced by a cutting method or the like that does not use oils and fats.
The average fiber diameter is preferably 25 to 70 μm, more preferably 50 to 70 μm, and the average fiber length is preferably 100 mm or more, more preferably 100 to 200 μm.
mm. When the average fiber diameter of the metal fibers is smaller than 25 μm, the formed contact reducing material is easily broken, and conversely,
If the thickness is larger than 70 μm, problems such as poor molding and an increase in filling amount occur. The average fiber length is 100mm
If the length is shorter, it may be difficult to maintain the shape after forming the metal fiber molded body, and there may be a problem that the broken metal fiber overflows to the wake, and the average fiber length exceeds 200 mm. If the length is too long, molding failure may occur.

[0014] The method for producing such a metal fiber molded article to be used as the catalytic reduction material of the present invention by molding such a metal fiber comprises the steps of using a metal fiber having a predetermined average fiber diameter and an average fiber length to obtain a predetermined volume. There is no particular limitation as long as a metal fiber molded body having a bulk density can be produced.For example, a metal mold having a desired shape and volume is filled with metal fibers having a weight necessary to achieve a desired bulk density. It can be easily manufactured by compression.

In order to remove selenium from wastewater containing selenium using the catalytic reducing agent of the present invention and to reduce dissolved selenium in the wastewater to a selenium concentration of 0.1 mg / liter or less, which is specified as a wastewater standard, Although it depends on the selenium concentration in the wastewater to be treated, the selenium removal rate is usually 95% or more, preferably 92% or more. Therefore, the operation of de-selenium treatment reduces the selenium removal rate by 10% or less. , Preferably in a range of 3% or less.

The catalytic reducing agent used in the de-selenium treatment is consumed over time because it becomes a reactant during the operation. The reduction needs to be within the above range of 10% or less. In order to reduce the number of times of supplying the contact reducing agent during the operation of the de-selenium treatment as much as possible, the supplied contact reducing agent is efficiently used. Since it is necessary to use it, in the present invention, the following relational expression: Residual rate Y (%) = [(AB) / A] × 100 (where A: initial weight of the reduced material, and B: The residual rate defined by the weight of the reduced material after a predetermined time has passed is 30.
%, Preferably up to 20%, the reduction of the selenium removal rate in the wastewater must be maintained at 10% or less.

The remaining rate at which the reduction of the selenium removal rate in the wastewater can be maintained at 10% or less depends on the volume and bulk density of the catalytic reducing agent if the used metal fibers are the same. For example, some of the catalytic reduction materials having different volumes and bulk densities were prototyped, and the residual ratio when the reduction of the selenium removal rate in each catalytic reduction material reached 3% was measured. By determining the relationship between the change and the change in the residual ratio, it is possible to design the volume and bulk density of the catalytic reduction agent that achieves the desired residual ratio.

Further, the method for treating wastewater using the catalytic reducing agent of the present invention is not particularly different from the conventional method, and the catalytic reducing agent of the present invention has been proposed and disclosed. In the method for treating selenium-containing wastewater using a systemic metal, it can be used in place of various forms of iron-based metal used therein, but it is preferably carried out under the following treatment conditions.

That is, the ratio (V ₂ / V ₁ ) of the volume V ₁ of the catalytic reaction zone filled with the catalytic reducing agent of the present invention to the total volume V ₂ of the catalytic reducing agent filled in the catalytic reaction zone. Is 0.
15 to 0.4, preferably 0.2 to 0.3, and the flow rate (liquid space velocity: SV) of the wastewater passing through this catalytic reaction zone is 0.03 to 0.5 hr ^-1 , preferably Is 0.0
5 to 0.1 hr ^-1 , and the average passage speed of the wastewater passing through the catalytic reaction zone is 0.5 to 2.5 m / min, preferably 0.2 to 0.5 m / min. Good. By adopting such processing conditions, a stable and high selenium removal rate can be achieved over a long period of time.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a preferred embodiment of the present invention will be specifically described. As shown in FIG. 1, it is manufactured by a cutting method without using oil and fat, and has an average fiber diameter of 25 to 7
The steel wool 2a is pulled out from the raw roll 3 of the steel wool 2a having a thickness of 0 μm and cut by a cutting machine 4 to prepare a cut steel wool 2b having an average fiber length of 100 mm or more. Length 100
mm or more of the cut steel wool 2b is filled into a mold 5 having a predetermined shape such as a cubic shape and a volume of 0.002 to 0.2 m ³ by a weight necessary to achieve a desired bulk density, Cut steel wool 2b filled in this mold 5
To a desired shape such as a cubic shape, volume 0.002 to
An iron fiber molded body 1 having 0.2 m ³ and a bulk density of 50 to 100 kg / m ³ is manufactured and used as a contact reducing agent for wastewater.

[0021]

The present invention will now be described more specifically based on examples and comparative examples. Example 1 Using a steel wool having an average fiber diameter of 70 μm (manufactured by Nippon Steel Wool Co., Ltd.) manufactured by a cutting method without using oil and fat, and using a cutting machine, an average fiber length of 150 m
m cut steel wool was prepared, and a predetermined amount of the obtained cut steel wool was 100 mm × 100 mm × 100 m
m is filled in a cube-shaped mold having a size of m, and the filled cut steel wool is compressed to the size of the mold to have a volume of 0.01 m ³ (1 liter) and a bulk density of 7 m.
An iron fiber molded body 1 of 0 kg / m ³ was produced.

As shown in FIG. 2, a contact type reaction device R having a contact reaction zone 7 having a volume of 30 liters and divided by a liquid-permeable partition member 6 is used as the contact reaction device. The reaction zone 7 was filled with 20 pieces of the iron fiber molded body 1 as a catalytic reducing agent.

Further, the liquid-flow type contact reactor R is provided with a total selenium concentration (Se) obtained by treating coal-fired exhaust gas from below to above by a wet flue gas desulfurization apparatus using limestone as an absorbent. About 1.0 mg / liter of flue gas desulfurization wastewater is introduced at a rate of 8 liter / hr, residence time in the reactor R is 15 hours, temperature is 40 ± 5 ° C., pH is 6 to
A test operation of de-selenium treatment was conducted under the conditions of 7, and the reactor R
A method of measuring the selenium concentration in the wastewater extracted from the outlet 10 of the reactor over time, and arranging a sample of a catalytic reducing agent having a known volume in the reactor R and measuring the volume loss thereof, The volume change of the iron fiber molded body 1 filled in the contact reaction zone 7 of the reactor R was examined.

The selenium concentration of the flue gas desulfurization wastewater introduced into the reactor R and the selenium concentration of the treated wastewater extracted from the reactor R are used to determine the selenium removal rate. The residual rate of the catalytic reducing agent was determined from the change in the physical volume, and the relationship between the elapsed time (days) and the selenium removal rate or the residual rate of the catalytic reducing material was examined with the elapsed time (days) as the horizontal axis. The results are shown in FIG.

After the start of the test operation for de-selenium treatment,
Five days later, when the iron fiber compacts 1 filled in the contact reaction zone 7 of the reactor R and consumed were examined, the volume of each iron fiber compact 1 was about 20% of the original volume (the residual rate was about 20%). %)
The selenium removal rate at this time decreased from about 95% at the beginning of the operation to about 92%, and drainage was continued until 15 days after the start of the test operation. The standard selenium concentration of 0.1 mg / liter or less was achieved.

Comparative Example 1 Deselenium treatment was performed in the same manner as in Example 1 except that the bulk density of the manufactured iron fiber molded body 1 was 35 kg / m ³ , and the elapsed time (days) and selenium removal were The relationship with the rate was examined. The results are shown in the graph of FIG. 3 showing the relationship between elapsed time (days) and selenium removal rate. In the case of Comparative Example 1, the selenium removal rate decreased from about 98% at the beginning of the test operation to about 90% after 5 days from the start of the test operation for the selenium removal treatment. Concentrations of 0.1 mg / l or less could be achieved, but not thereafter.

Comparative Example 2 Deselenium treatment was performed in the same manner as in Example 1 except that the bulk density of the manufactured iron fiber molded body 1 was 140 kg / m ³ , and the elapsed time (days) and selenium removal were changed. The relationship with the rate was examined. As a result, the selenium removal rate did not increase to 90% or more from the beginning of the test operation of the de-selenium treatment, and the selenium concentration of the drainage standard of 0.
Less than 1 mg / liter could not be achieved.

[0028]

According to the contact treatment material of the present invention, harmful substances such as dissolved selenium and oxidizing substances can be efficiently separated and removed from the selenium-containing waste water during the de-selenium treatment, and stable for a long time. Selenium removal rate can be maintained, and the amount of ferrous metal used and the amount of sludge generated can be reduced as much as possible, thereby greatly reducing the operational burden of wastewater treatment. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an example of a process for producing a catalytic reduction material of the present invention.

FIG. 2 is an explanatory view showing a flow-type contact reaction apparatus for performing a de-selenium treatment of selenium-containing wastewater using an iron fiber formed body (contact reducing material) according to Example 1 of the present invention.

FIG. 3 is a graph showing elapsed time (days) obtained in Example 1.
It is a graph which shows the relationship of-the selenium removal rate, and the relationship of elapsed time (day)-residual rate of a catalytic reduction material, respectively.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Iron fiber molded object (contact reducing material), 2a ... Steel wool, 2b ... Cut steel wool, 3 ... Raw roll, 4 ... Cutting machine, 5 ... Mold, 6 ... Partition material, 7 ... Contact reaction zone,
R: Flow type contact reactor.

Claims (4)

[Claims] 1. A contact reducing agent for contacting wastewater containing dissolved selenium or a harmful substance comprising dissolved selenium and an oxidizing substance to reduce the harmful substance. And the following relational expression: Residual rate Y (%) = [(AB) / A] × 100 (where A: initial weight of reduction-treated material, and B : The weight of the reduced material after the lapse of a predetermined time) is 30.
%, Wherein the reduction of the selenium removal rate in the wastewater is 10% or less. 2. The metal fiber molded body has a volume of 0.00
A 2~0.2m ^3, the bulk density of 50~100k
The contact reducing material for wastewater according to claim 1, wherein the amount is g / m ³ . 3. The contact reducing material for waste water according to claim 1, wherein the metal fiber molded body is formed into a cubic shape, a spherical shape, a columnar shape, or a disk shape. 4. The metal fiber has an average fiber diameter of 25-7.
The contact reducing material for wastewater according to any one of claims 1 to 3, wherein the contact reducing material has a fiber length of 0 µm and an average fiber length of 100 mm or more.