JP2000301153A - Method for electrolysis of water containing oxidizable pollutant and electrode for electrolysis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To oxidize/decompose oxidizable pollutants efficiently and to extend the life of electrodes by using an electrode having a liquid-contact part comprising a mixed layer of platinum and iridium as an anode. SOLUTION: A specimen water tank 1 and an electrolytic bath 2 are installed adjacently, and an anode 3 and a cathode 4 are formed in the electrolytic bath 2. Water containing oxidizable pollutants and an inorganic chloride is electrolyzed by using an electrode having a liquid-contact part comprising a mixed layer of platinum and iridium as the cathode 3. The electrode for electrolyzing the pollutants-containing water has the liquid-contact part comprising platinum and iridium. The form of the mixed layer is not restricted in particular, and for example, the layer comprises a platinum-iridium alloy, or platinum portions and iridium portions are dispersed in the layer. As the oxidation-reactive pollutants, organic compounds in general and inorganic compounds such as ammonia and hydrazine can be named.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic treatment method for water containing oxidizable pollutants and an electrode for electrolytic treatment. More specifically, the present invention electrolyzes water containing oxidizable pollutants at normal temperature and normal pressure, and oxidizes and decomposes oxidizable pollutants in water with high efficiency to reduce the chemical oxygen consumption (COD). Electrolytic treatment method of water containing oxidizable pollutants that can be reduced, and high oxidizing agent generation efficiency during the electrolytic treatment,
The present invention relates to a long-life electrode for electrolytic treatment.

[0002]

2. Description of the Related Art When released into water, organic compounds, ammonia and the like cause eutrophication. Emission sources of organic compounds and ammonia include chemical factories, petrochemicals, petroleum refining, and semiconductor factories. As a typical method for treating organic compounds and ammonia in wastewater, an activated carbon adsorption method, a biological treatment method, and the like are known. According to the activated carbon adsorption method, it is necessary to regenerate the activated carbon when the adsorption equilibrium is reached, and there is a problem that a regenerated effluent concentrated to a high concentration is generated along with the regeneration, and further treatment is required.
In the case of biological treatment of organic compound-containing wastewater, there is a problem that the reaction time is long due to a low reaction rate, a large-capacity biological reaction tank is required, and a large amount of excess sludge is generated. The present inventors have previously described Japanese Patent Application Laid-Open No. 9-1177.
No. 81 proposes a method of adding an oxidizing agent to wastewater containing an organic compound and oxidatively decomposing the organic compound in the presence of a metal catalyst under heating conditions. According to this method, an organic compound can be efficiently oxidatively decomposed, but further improvements such as a need to add an oxidizing agent and a heat treatment at a temperature of 100 ° C. or more are expected. Was rare. Further, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 10-174976 a method of oxidatively decomposing and removing a nitrogen compound in water without using an oxidizing agent. After decomposition, a method of contacting with a metal peroxide catalyst was proposed. At this time, in the electrolysis, a platinum-plated titanium electrode was used. However, since platinum plating was worn out and needed to be renewed in a relatively short period of time, an electrode having a longer life was required.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a method for electrolyzing oxidizable contaminant-containing water at ordinary temperature and normal pressure without using an oxidizing agent to oxidize oxidizable contaminants in water with high efficiency. Electrolytic treatment method for water containing oxidizable pollutants capable of decomposing and reducing chemical oxygen consumption (COD), and an electrode for electrolytic treatment having high generation efficiency of oxidizing agent and long life in electrolytic treatment The purpose of this is to provide.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, water containing oxidizable pollutants and inorganic chloride has been removed from the electrode contacting part with platinum. By conducting an electrolytic treatment using an electrode consisting of a mixed layer of iridium and iridium as the anode, it was possible to oxidize and decompose oxidizable contaminants with high efficiency, and found that the electrode maintained a long life. The invention has been completed.
That is, the present invention provides (1) an electrolytic treatment method for electrolyzing water containing an oxidizable pollutant and an inorganic chloride, wherein the electrode contact portion is a mixed layer of platinum and iridium. (2) The oxidizable pollutant according to (1), wherein the oxidizable pollutant is an organic compound. (3) The method for electrolyzing water containing oxidizable pollutants according to (1), wherein the oxidizable pollutant is ammonia or hydrazine; (4) The method for containing oxidizable pollutants An electrode for electrolytically treating water, wherein the electrode contact part is composed of a mixed layer of platinum and iridium; and (5) platinum is plated and supported on the electrode base part. And a mixed layer of platinum and iridium on the surface The electrode for electrolytic treatment according to the above (4), wherein the electrode is subjected to plating support treatment. Further, as a preferred embodiment of the present invention, (6) the electrode serving as the anode is obtained by plating platinum on an electrode base portion and further plating and supporting a mixed layer of platinum and iridium on the surface thereof. (1) The method for electrolyzing water containing oxidizable pollutants according to (1), (7) The water after electrolysis is further contacted with a metal peroxide catalyst, containing the oxidizable pollutants according to (1). A method for electrolyzing water, and (8) a method wherein the metal peroxide catalyst is nickel peroxide or cobalt peroxide.
(7) The method for electrolyzing water containing oxidizable pollutants according to item (7),
Can be mentioned.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, water containing an oxidizable pollutant and an inorganic chloride is subjected to electrolytic treatment using an electrode whose liquid contact part is a mixed layer of platinum and iridium as an anode. The electrode of the present invention is an electrode for electrolytically treating oxidizable contaminant-containing water, wherein the liquid contact part of the electrode is made of a mixed layer of platinum and iridium. The oxidizable pollutants that can be treated by the method of the present invention include general organic compounds contained in water and inorganic compounds such as ammonia and hydrazine. When applying the method of the present invention, if the oxidizable pollutant-containing water also contains an inorganic chloride, the oxidizable pollutant-containing water contains a sufficient amount of the inorganic chloride when the oxidizable pollutant-containing water contains an inorganic chloride. Otherwise, electrolytic treatment can be performed after adding inorganic chloride. The inorganic chloride to be added is not particularly limited as long as it has water solubility, and examples thereof include sodium chloride and potassium chloride. Electrode for electrolytic treatment of the present invention, the electrode contact part is an electrode composed of a mixed layer of platinum and iridium, in the method of the present invention,
Water containing an oxidizable pollutant and inorganic chloride is subjected to electrolytic treatment using an electrode whose liquid contact part is a mixed layer of platinum and iridium as an anode. There is no particular limitation on the form of the mixed layer of platinum and iridium, and for example, it may be an alloy layer of platinum and iridium, or a mixed layer in which a portion of platinum and a portion of iridium are dispersed and scattered. Can also.
The electrode can be formed not only of the liquid contact part but also of the entire electrode from platinum and iridium. However, from the viewpoint of processing and cost, the base part of the electrode is preferably formed of another material. As a material constituting the electrode base portion, for example, a material usually used as an electrode material such as titanium, stainless steel, or carbon can be used. In this case, a mixed layer of platinum and iridium can be formed in a thin film shape so as to cover the surface of the electrode matrix.

In the electrode of the present invention, it is preferable to provide an intermediate layer made of platinum between the electrode base and the electrode contact part. By providing an intermediate layer made of platinum,
The electrode wetted part consisting of a mixed layer of platinum and iridium is easily retained, and after the electrode has been used for a long time, the mixed layer of platinum and iridium in the wetted part of the electrode has been depleted for a certain period of time. Electrolytic treatment of oxidizing pollutants can be continued. There is no particular limitation on the thickness of the electrode of the present invention, for example,
The thickness of the electrode base part is several mm, the thickness of the intermediate layer made of platinum is 1 to 3 μm, and the electrode contact part made of a mixed layer of platinum and iridium is 0.01 to 1 μm, preferably 0.1 to 0.1 μm. 5 μm
It can be. If the thickness of the mixed layer of platinum and iridium is less than 0.01 μm, the durability of the electrode is low, and the frequency of electrode replacement may be excessive. If the thickness of the mixed layer of platinum and iridium exceeds 1 μm, the unit price of the electrode increases, and the economic efficiency may be impaired. The method for producing the electrode of the present invention is not particularly limited, but an electrode produced by plating is preferable because of its excellent durability. The plating may be either electrolytic plating or electroless plating. For example, when manufacturing by electroplating titanium as the electrode base part,
Immerse the electrode matrix in a phosphate bath in which platinum chloride is dissolved,
An intermediate layer made of platinum is formed by carrying out plating treatment at a temperature of 50 to 70 ° C. and a current density of 0.5 to 1 A / dm ² , and further, phosphoric acid in which a hydrate of platinum chloride and iridium chloride is dissolved Continue the plating support process using a salt bath,
An electrode liquid contact portion made of a mixed layer of platinum and iridium can be formed. In the method of the present invention, the cathode used is not particularly limited, and for example, a known electrode such as stainless steel, carbon steel, or carbon can be used.

In the method of the present invention, the inorganic chloride is dissolved in water to generate chloride ions, and the chlorine ions are converted into hypochlorite ions by the electrolytic treatment as shown in the following formula. Cl ⁻ + 2OH ⁻ → ClO ⁻ + H ₂ O + 2e ^{− When the} oxidizable contaminant is an organic compound, hypochlorite ion reacts with the organic compound to form harmless carbon dioxide,
It is converted to water or the like to reduce the total organic carbon content and chemical oxygen consumption (COD) of the treated water. When the oxidizable pollutant is an inorganic compound such as ammonia or hydrazine, hypochlorite ion reacts with these and converts it into harmless nitrogen gas and water. In the electrode for electrolytic treatment of the present invention, the liquid contact portion also has a catalytic action, so that these reactions proceed rapidly. For example, the reaction of hypochlorite ion with methanol, methyl ethyl ketone, ethanolamine, toluene, phenol, aniline, urea, ammonia, and hydrazine proceeds as in the following equation. ^{_{CH 3 OH + 3ClO - → CO}} 2 + 2H 2 O + 3Cl - CH 3 COC 2 H 5 + 11ClO - → 4CO 2 + 4H 2 O + 11Cl - 2H 2 NCH 2 CH 2 OH + 13ClO - → N 2 + 4CO ^{_{2 + 7H 2 O + 13Cl -}} C 6 H 5 CH 3 + 18ClO - → 7CO 2 + 4H 2 O + 18Cl - C 6 H 5 OH + 14ClO - → 6CO 2 + 3H 2 O + 14Cl - 2C 6 H 5 NH _{^{2 + 31ClO - → N 2 +}} 12CO 2 + 7H 2 O + 31Cl - CO (NH 2) 2 + 3ClO - → N 2 + CO 2 + 2H 2 O + 3Cl - 2NH 3 + 3ClO - → N 2 + 3H 2 _{^{O + 3Cl - N 2 H 4}} + 2ClO - → N 2 + 2H 2 O + 2Cl -

In the method of the present invention, chloride ions generated by dissolving inorganic chloride in water are converted into hypochlorite ions by electrolysis to oxidize oxidizable contaminants to form chloride ions, which are again electrolyzed. It circulates between the form of chloride ion and the form of hypochlorite ion so that it becomes hypochlorite ion, and one chlorine ion participates in the reaction multiple times. Therefore, the amount of the inorganic chloride coexisting with the oxidizable pollutant is usually less than the stoichiometric value shown in the above formula. In processes where electrolytic treatment is performed while circulating water containing oxidizable pollutants and inorganic chlorides between the storage tank and the electrolytic reaction tank, the type and concentration of oxidizable pollutants contained in the water and The optimum amount of the inorganic chloride can be determined in consideration of conditions such as the circulation speed to the electrolytic reaction tank. In the method of the present invention, the electrolytic treatment conditions are not particularly limited, but the distance between the electrodes is 2 to 10 m.
m, and the current density is preferably 10 to 30 A / dm ² .
If the distance between the electrodes is less than 2 mm, bubbles and scale may be generated, which may cause a voltage rise or a current short circuit. If the distance between the electrodes exceeds 10 mm, the required voltage increases, which may lead to an increase in power consumption. If the current density is less than 10 A / dm ² , the device may be too large. If the current density exceeds 30 A / dm ² , the life of the electrode may be shortened. In the method of the present invention,
Electrolytic treatment is performed using an electrode in which the electrode contact part is made of a mixed layer of platinum and iridium as an anode. The amount generated is large, and oxidizable pollutants can be effectively oxidatively decomposed. Also, the electrode whose liquid contact part is made of a mixed layer of platinum and iridium hardly loses its surface during electrolytic treatment, and its surface depletion rate is 1/30 as compared with an electrode whose liquid contact part is made of platinum.
In addition, the electrolytic treatment can be continued for a long period of time without replacing the electrode for a long period of time.

In the method of the present invention, the water after the electrolytic treatment can be further contacted with a metal oxide catalyst.
By contacting the water after the electrolytic treatment with the metal oxide,
The oxidizable pollutants remaining in the water after the electrolytic treatment react with hypochlorite ions to completely decompose and remove the same, and decompose excess hypochlorite ions present in the water after the electrolytic treatment, The quality of the treated water can be improved. When the oxidizable pollutant and water containing hypochlorite ion come into contact with the metal peroxide catalyst, the decomposition reaction of the oxidizable pollutant represented by the above reaction formula and the like is rapid at normal temperature and normal pressure. And the oxidizable pollutants are decomposed and removed. Examples of the metal peroxide catalyst used in the method of the present invention include nickel peroxide, cobalt peroxide, copper peroxide, silver peroxide and the like. Among them, nickel peroxide and cobalt peroxide can be particularly preferably used. These metal peroxide catalysts include X-type, Y-type or A-type synthetic zeolites, clinoptilolite-type or mordenite-type natural zeolites, titania, α-alumina, γ
-It is preferable to use it supported on alumina or the like.
There is no particular limitation on the method of bringing the electrolyzed water into contact with the metal peroxide catalyst. For example, water can be passed through a packed tower filled with the metal peroxide catalyst. According to the method of the present invention, water containing oxidizable contaminants is treated at normal temperature and normal pressure without using an oxidizing agent, so that chemical oxygen consumption (C
OD) and can be treated water of good water quality.
The excessively generated hypochlorite ion is easily decomposed by the metal peroxide catalyst and does not remain in the treated water. Also,
Since the electrode of the present invention keeps a much longer life than the conventionally used platinum-plated titanium electrode, it is possible to reduce the frequency of electrode replacement and economically treat oxidizable pollutant-containing water. Can be.

[0010]

The present invention will be described in more detail with reference to the following examples.
The present invention is not limited to these examples.
It is not specified. Example 1 FIG. 1 is a schematic diagram of an electrolytic treatment apparatus used in this example.
You. A sample water tank 1 and an electrolytic tank 2 are provided adjacent to each other,
Is the distance between the anode 3 and the cathode 4 with a width of 4 cm and a height of 25 cm.
Is set as 3 mm. The anode is 3mm thick titanium
A 1.8 μm thick platinum layer is plated on the
Mixed with platinum and iridium with a thickness of 0.2 μm
The layer is provided by carrying a plating treatment. The cathode is thick
It is a SUS316L plate of 3 mm in length. Current density is 10A
/ Dm^TwoIt is. The sample water is supplied to the electrolytic cell by the circulation pump 5.
The water that has been sent and electrolyzed
It is returned to the water tank and circulated. The water in the sample tank is
The mixture is stirred by the stirrer 6. Butanol 4,000mg / liter
Toul (COD_Mn2500mg / l) and sodium chloride
Thorium 33,000mg / l (chloride ion 20,
PH of water containing 2,000 mg / liter)
The sample water was adjusted to 10 using lithium. This sample
Put 1 liter of water into the sample tank and circulate at 110 ml per minute.
Electrolytic treatment. COD of sample water after 5 hours treatment
_MnIs 50 mg / liter and COD _Mn98% removal rate
Met. Also, the concentration of sodium hypochlorite in the sample water
The degree was 11,000 mg / liter. After electrolytic treatment
Sample water was mixed with 50 ml of nickel peroxide catalyst and cobalt peroxide.
The column packed with 50 ml of the catalyst in two layers is SV2h^-1,
When passing water at 30 ° C, treated water flowing out of the column
COD_MnIs 1 mg / liter or less, sodium hypochlorite
The concentration was 1 mg / liter. Water pump for sample tank
And a sampling pump, and switched to continuous processing.
Trial containing butanol and sodium chloride, pH adjusted
Supply water at 200 ml / h to the sample tank and
Drain the sample water electrolyzed from the water tank at 200ml / h
And drained through a column packed with catalyst. Platinum layer of anode and white
The total thickness of the mixed layer of gold and iridium is 1.
96 μm, 1.94 μm after 6 months, 1.87 μ after 12 months
m, 1.80 μm after 18 months, 1.24 μm after 24 months
there were. During this time, COD of the sample water after electrolytic treatment_MnIs 50
mg / l, concentration of sodium hypochlorite is 11.0
00 mg / liter, and treated water after passing through the catalyst column.
COD_MnIs 1 mg / liter or less, sodium hypochlorite
Was stable at 1 mg / liter. Comparative Example 1 A 2 μm thick platinum layer was formed on a 3 mm thick titanium plate as an anode.
Of platinum and iridium coated by plating
Same as Example 1 except that an electrode having no mixed layer was used
The operation was performed. COD of sample water after 5 hours treatment_MnIs 10
0 mg / liter and COD_MnThe removal rate is 96%
Was. The concentration of sodium hypochlorite in the sample water is
It was 9,000 mg / liter. After this electrolytic treatment
The feed water was passed through the catalyst column in the same manner as in Example 1.
At this time, COD of treated water flowing out of the column_MnIs 1mg / l
The concentration of sodium and sodium hypochlorite is 1 mg / liter.
there were. Switching to continuous processing in the same manner as in the first embodiment
Was. The thickness of the platinum layer of the anode becomes 1.13 μm after two months.
3 months later, it became 0.62 μm.
Cut off. From the results of Example 1 and Comparative Example 1, the electrode liquid contact part
Using an anode composed of a mixed layer of platinum and iridium
Therefore, when the anode part made of platinum is used
In comparison, the amount of generated hypochlorite ion is large,
OD_MnIs removed to a lower level, and
The anode whose liquid part consists of a mixed layer of platinum and iridium
Longer lifespan than anode with wetted parts made of platinum
You can see that. In addition, the sample water after electrolytic treatment is
COD by passing water through a column filled with a medium_MnSuccess
Is almost completely removed and excess sodium hypochlorite
Is also decomposed and removed. Example 2 1,800 mg / liter of ammoniacal nitrogen and sodium chloride
PH of water containing 12,000 mg / l of lithium
Adjust to 11 using sodium hydroxide to obtain sample water
Was. Using the same apparatus as in Example 1, 1 liter of this sample water
Into a raw water tank and circulate at 110 ml / min.
Processed. Ammonia in sample water after 1.5 hours treatment
The concentration of nitrogen is 1 mg / l, ammonia nitrogen
Was 100%. Also, nitrous acid in sample water
Total of nitrogen and nitrate is 30mg / l or less
The concentration of sodium hypochlorite is 3,000 mg / liter.
Torr. The sample water after the electrolytic treatment is
50 ml of catalyst and 50 ml of cobalt peroxide catalyst are filled in two layers.
SV2h^-1When water is passed at 30 ° C,
Ammonia nitrogen concentration of treated water flowing out of ram is 1mg
/ Liter or less, the total of nitrite nitrogen and nitrate nitrogen is 3
mg / liter or less, and the sodium hypochlorite concentration
It was 1 mg / liter. From the results of Example 2,
Sample water containing near
Electrolytic treatment using an anode consisting of a mixed layer of
The ammonia in the water is effectively decomposed and removed,
The electrolyzed sample water is mixed with a peroxide catalyst-filled color
Ammonia and excess hypochlorite
It can be seen that the sodium acid is almost completely removed.

[0011]

According to the method of the present invention, water containing oxidizable contaminants is treated at normal temperature and normal pressure without using an oxidizing agent to easily reduce the chemical oxygen consumption (COD). It can be treated water of low good quality. The excessively generated hypochlorite ion is easily decomposed by the metal peroxide catalyst and does not remain in the treated water. Further, the electrode of the present invention has a much longer life than a conventionally used platinum-plated titanium electrode.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electrolytic treatment apparatus used in Examples and Comparative Examples.

[Explanation of symbols]

 Reference Signs List 1 sample water tank 2 electrolysis tank 3 anode 4 cathode 5 circulation pump 6 stirrer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D050 AA13 AB07 AB14 AB15 AB17 AB35 AB36 BB06 BC06 BC10 BD02 BD04 BD08 CA10 CA13 4D061 DA08 DB10 DB19 DC06 DC09 DC15 EA03 EB14 EB30 EB39 ED13 ED20 GC12 GC20 4K011 AA21 AA21A 4K021 AB07 DA09 DA13 DC11

Claims (5)

[Claims] A method for electrolyzing water containing an oxidizable pollutant and electrolyzing water containing an oxidizable pollutant and an inorganic chloride, wherein the electrode contact part is formed of a mixed layer of platinum and iridium. An electrolytic treatment method for water containing oxidizable pollutants, comprising an anode. 2. The method according to claim 1, wherein the oxidizable pollutant is an organic compound. 3. The method according to claim 1, wherein the oxidizable pollutant is ammonia or hydrazine. 4. An electrode for electrolytically treating water containing an oxidizable pollutant, wherein an electrode contact part is made of a mixed layer of platinum and iridium. 5. The electrode for electrolytic treatment according to claim 4, wherein the electrode base is plated with platinum and the surface thereof is plated with a mixed layer of platinum and iridium.