JP4382556B2 - Treatment method of wastewater containing cyanide - Google Patents

Description

  The present invention relates to a method for treating cyan-containing wastewater containing cyanide-containing wastewater discharged from various factories or cyanide-containing sludge, which can more reliably remove cyanide compounds by a simple operation.

  Since cyanide has a strong negative impact on the ecosystem, cyanide-containing wastewater cannot be released to nature as it is. Cyanide drainage standards are established for cyanide compounds. Cyan removal treatment is performed so as to satisfy this standard (1 mg / L or less), and wastewater that has been rendered harmless can be discharged into sewage and the like.

As a method for removing cyanide from wastewater containing cyanide,
(1) An alkali chlorine method in which after cyanide-containing wastewater is adjusted to be alkaline, chlorine is injected to oxidatively decompose cyanide,
(2) Ozone oxidation method in which cyanide is oxidatively decomposed into nitrogen gas and bicarbonate with strong ozone oxidizing power,
(3) An electrolytic oxidation method in which a cyanide compound is electrolyzed using an insoluble electrode and an oxidation reaction is performed.
(4) A bitumen method in which, for example, ferrous sulfate is added as a supply compound of iron ions to cyanide-containing wastewater to form a hardly soluble ferriferrocyanide, and this is precipitated and removed.
(5) Biological treatment methods in which cyanide is decomposed by microorganisms (cyanolytic bacteria) acclimatized to cyanide (for example, Yasuhiko Miyoshi, “Chemical Basics and Wastewater Treatment Technology”, Information of Co., Ltd.) (Research Institute, November 10, 1996, second edition issued, p. 152-158: see Non-Patent Document 1).

However, each of the above methods has the following drawbacks.
The alkali chlorine method of method (1) is the most common cyan compound removal treatment method, but the removal of the cyano complex salt is insufficient.

  The ozone oxidation method of method (2) has advantages such as that no harmful compounds are generated by this treatment and that only harmful oxygen is produced even when the ozone itself is decomposed, but this treatment is a gas-liquid reaction. Therefore, complicated and large-scale equipment is required. Moreover, since the manufacturing cost of ozone is high, the device on the apparatus for making ozone react effectively is required. For example, two oxidation towers are provided, a packing is placed in the first oxidation tower, the cyanide-containing wastewater and ozone are contacted efficiently countercurrently, and the exhaust from the first oxidation tower is discharged to the second. To fully utilize residual ozone. Furthermore, it is necessary to perform a coagulation precipitation treatment of the metal hydroxide generated by the decomposition of the cyanide compound.

  The electrolytic oxidation method of the method (3) has an advantage that the concentrated waste water of cyanide can be treated efficiently and economically, but requires a large amount of electric power and the treatment cost is increased. In addition, there is a method of removing a cyanide compound using an electrolytic oxidation method and another treatment method in combination, but in any case, the treatment becomes complicated and the treatment cost increases.

  The bitumen method of method (4) is suitable for the treatment of cyanide-containing wastewater, which is difficult to oxidatively decompose cyanide compounds by other treatment methods. If the treated water is colored or the pH of the treated water is high, the amount of residual ferrocyan in the filtrate increases. In addition, since the complex salt formed is easily oxidized with oxygen in the air to become a ferriferro type and redissolved, it is difficult to make the cyan concentration of the treated water below the drainage standard by the bitumen method.

  The biological treatment method of method (5) is the maintenance of pH suitable for microbial treatment, which is a disadvantage inherent to microbial reactions, addition of nutrient substances (nitrogen, phosphorus, etc.), adjustment of activated sludge concentration (MLSS), treatment of excess sludge In addition, if the treatment time (contact time between cyanide and microorganisms) is long and the cyan concentration in the cyan-containing wastewater is high, the wastewater to be treated must be diluted in advance. It has disadvantages such as must.

The applicant of the present invention is a method for treating cyanide-containing wastewater by a simple operation and a treating agent used therefor,
(1) A method in which waste water containing iron cyanide complex ions is adjusted to pH 6.0 or more, a manganese compound is added thereto to form a manganese salt of a water-insoluble iron cyanide complex, and the waste water is removed from the waste water system (Japanese Patent Publication No. 62) No. 24157 (see Patent Document 1),
(2) A treatment agent for wastewater containing cyanide and / or thiocyanate having improved stability and treatment efficiency, which contains a reducing substance capable of reducing the failing solution in the cuprous halide solution (Japanese Examined Patent Publication No. 63- 1919 publication: see Patent Document 2),
(3) Add cyanide-containing wastewater to formaldehyde with a cyan content of 1.4 mol or more to perform the first stage reaction, and further add hydrogen with a cyan content of 3.0 mol or more to a pH of 7 or more. A method of detoxifying cyanogen-containing wastewater by performing a second-stage reaction (see JP-A-2-35991: Patent Document 3), and (4) removing cyanide compounds contained in the wastewater from cyanide-containing wastewater A treatment method for cyanogen-containing wastewater, in which a hypochlorite and a manganese compound are added in an amount capable of being removed, and the produced water-insoluble manganese salt is removed from the wastewater (see Japanese Patent Application Laid-Open No. 2001-300553: Patent Document 4)
Has been proposed.

  Furthermore, after adding an alkali agent and an oxidizing agent (such as ozone, hydrogen peroxide, sodium hypochlorite) to the cyanide-containing wastewater containing the iron cyanide complex compound to adjust the pH to alkaline, ultraviolet to visible A wastewater treatment method has been proposed in which free cyanide oxidation treatment is carried out while separating and removing precipitates such as hydroxides generated from iron ions dissociated by decomposition of iron cyanide complex compounds by irradiation with light. (See JP-A-10-57974: Patent Document 5).

  However, in the above prior art, the cyan removal effect may not be sufficient depending on the type of wastewater, and a method with a higher treatment effect has been desired.

Japanese Examined Patent Publication No. 62-24157 Japanese Patent Publication No. 63-1919 JP-A-2-35991 JP 2001-300553 A Japanese Patent Laid-Open No. 10-57974 Yasuhiko Miyoshi, “Chemical Fundamentals and Wastewater Treatment Technology”, Information Research Laboratory, Inc., November 10, 1996, second edition, p. 152-158

  According to the present invention, cyanide which can remove all cyanide compounds such as metal cyanide (hydrogen cyanide salt), cyanide ion (free cyanide or cyanide ion), cyano complex salt, cyano complex ion more reliably by simple operation. An object of the present invention is to provide a treatment method for cyanogen-containing wastewater that can suppress elution of cyanide compounds from sludge separated from the wastewater, particularly in cyanide-containing wastewater containing cyanide-containing sludge.

  The inventors of the present invention, as a result of diligent research in view of this situation, found that the first stage treatment with chlorine gas or hypochlorite, and formaldehyde, a manganese compound and / or a copper compound, and chlorine gas Alternatively, the second stage treatment with a ternary system of hypochlorite can remove free cyanide in cyanide-containing wastewater, cyan compounds that produce it, cyano complex ions or cyano complex salts that produce it, etc. In the cyan-containing wastewater containing cyanide-containing sludge, it was found that elution of cyanide compounds from the sludge separated from the wastewater can be suppressed, and the present invention has been completed.

  Thus, according to the first aspect of the present invention, the first stage treatment for oxidatively decomposing the cyanide compound is performed by introducing chlorine gas into the cyan-containing wastewater in advance under alkaline conditions or adding hypochlorite. Next, the cyanide remaining in the wastewater is treated with a ternary system of formaldehyde, a manganese compound and / or a copper compound, and chlorine gas or hypochlorite, so that the cyanide is decomposed and / or a water-insoluble salt. A process for treating cyanide-containing wastewater is provided, characterized in that the second stage treatment is removed as follows.

  In addition, according to the second invention, the cyan-containing wastewater contains cyanide-containing sludge, and the cyanide-containing wastewater treatment method described above, wherein elution of cyanide compounds from the sludge separated from the wastewater in the second stage treatment is suppressed. Is provided.

  Further, according to the third invention, in the first stage treatment, the above-mentioned cyanide-containing wastewater treatment method is provided in which hypochlorite is added in an amount of 50 to 500 mg / L in terms of effective chlorine ion concentration with respect to the wastewater. Is done.

  Moreover, according to 4th invention, the processing method of said cyan containing wastewater which adjusts pH of wastewater to 10 or more before the 1st stage process or during the 1st stage process is provided.

  According to the fifth invention, in the second stage treatment, formaldehyde, a manganese compound and / or a copper compound, and hypochlorite are 30 to 60 mg / L, 25 to 75 mg / Provided is a method for treating the above-mentioned cyanide-containing wastewater, wherein 50 to 300 mg / L is added in terms of L and effective chloride ion concentration.

  According to a sixth aspect of the invention, there is provided the above-described method for treating cyanide-containing wastewater, wherein the pH of the wastewater is adjusted to 7 to 8.5 after the first stage treatment and before the second stage treatment or during the second stage treatment. Provided.

  Moreover, according to 7th invention, the processing method of said cyanogen containing wastewater whose hypochlorite is sodium hypochlorite or potassium hypochlorite is provided.

  Moreover, according to 8th invention, the processing method of said wastewater containing cyanide whose manganese compound is manganese chloride or manganese sulfate and whose copper compound is cupric chloride is provided.

  According to the present invention, all cyan compounds such as metal cyanide (hydrogen cyanide salt), cyan ion (free cyanide or cyanide ion), cyano complex salt, and cyano complex ion can be more reliably removed by a simple operation. Cyanide-containing wastewater treatment method, particularly cyanide-containing wastewater containing cyanide-containing sludge, can provide a cyanide-containing wastewater treatment method that can suppress elution of cyanide compounds from sludge separated from wastewater. Very useful.

In the method for treating cyanide-containing wastewater according to the present invention, a first stage treatment is performed in which chlorine gas is introduced into the cyanide-containing wastewater in advance under alkaline conditions or hypochlorite is added to oxidatively decompose the cyanide. Then, the cyanide remaining in the wastewater is treated with a ternary system of formaldehyde, a manganese compound and / or a copper compound, and chlorine gas or hypochlorite, so that the cyanide is decomposed and / or insoluble in water. It is characterized by performing a second stage treatment to remove as salt.
In the present invention, metal cyanide (hydrogen cyanide salt), cyan ion (free cyanide or cyanide ion), cyano complex salt, cyano complex ion and the like are collectively referred to as cyanide compounds.

  Cyan-containing wastewater to be treated in the present invention (hereinafter referred to as “cyan wastewater”) includes metal cyanide compounds, cyanide discharged from steel mills, chemical factories, plating factories, coke factories, metal surface treatment factories, and the like. Examples include cyan waste water containing ions, cyanide complex salts, and cyano complex ions. In particular, the present invention can be suitably used for treating cyan wastewater containing cyanogen-containing sludge. The cyan-containing sludge contains the above-described cyan components and elutes them into the waste water. In the present invention, when the cyan waste water contains cyan-containing sludge, the cyan compound from the sludge separated from the waste water in the second stage treatment Elution is suppressed.

In this invention, chlorine gas which can be obtained industrially can be used suitably.
Moreover, as hypochlorite, sodium hypochlorite, potassium hypochlorite, etc. are mentioned, These can also use what can be obtained industrially suitably.

  Although the form is not specifically limited as formaldehyde used in this invention, About 40-50% formaldehyde aqueous solution (formalin aqueous solution) which can be obtained industrially is especially preferable.

  The manganese compound used in the present invention may be any compound that is soluble in water and can form manganese ions in water. Specific examples thereof include manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate. It is done. Among these, manganese chloride and manganese sulfate are particularly preferable from the viewpoint of the removal effect of the cyanide compound, and manganese chloride is particularly preferable from the viewpoint of the treatment cost of the cyan waste water.

  The copper compound used in the present invention may be any compound that is soluble in water and can form copper ions in water. Specific examples thereof include cupric chloride, cupric sulfate, and cupric nitrate. And cupric acetate. Among these, cupric chloride is particularly preferable from the viewpoint of the effect of removing cyanide and the processing cost.

According to the method of the present invention, as a first-stage treatment, first, chlorine gas is introduced into cyan waste water in advance under alkaline conditions, or hypochlorite is added to oxidatively decompose the cyanide compound.
Chlorine gas introduced into cyan wastewater generates hypochlorous acid by reaction with water, and exhibits the same function as hypochlorite added to cyanine wastewater. That is, hypochlorous acid oxidizes and decomposes a cyanide compound, and generates cyanic acid via chlorocyanide.
Specifically, hypochlorite is added to cyan waste water in an amount of 50 to 500 mg / L, preferably 150 to 500 mg / L in terms of effective chlorine ion concentration.

At this time, it is preferable to stir the cyan waste water in terms of the effect of removing the cyanide compound and the effect of suppressing the elution of cyan from the sludge separated from the waste water. In addition, it is preferable to heat the cyan waste water to some extent in order to promote the reaction during stirring, but a liquid temperature of about 20 to 60 ° C. is sufficient.
The stirring time varies depending on the amount of cyanide wastewater, the type and concentration of cyanide contained, the form of the treatment apparatus and its scale, etc., but usually it may be 10 minutes or more, preferably 20 to 30 minutes. .

  Further, it is preferable to adjust the pH of the cyan waste water to 10 or more in terms of the effect of removing the cyan compound and the effect of suppressing the elution of cyan from the sludge separated from the waste water. For pH adjustment, a known method such as alkali addition such as sodium hydroxide can be used.

Next, as a second stage treatment, the cyanide compound remaining in the wastewater is treated with a ternary system of formaldehyde, a manganese compound and / or a copper compound, and chlorine gas or hypochlorite, and the cyanide compound is decomposed. And / or removed as a water-insoluble salt.
Formaldehyde reacts with cyanide to produce non-toxic glycolonitrile (formaldehyde cyanohydrin).
Further, the manganese compound and / or the copper compound reacts with the cyan complex to produce a water-insoluble manganese salt and / or copper salt.
Hypochlorous acid oxidizes and decomposes a cyanide compound in the same way as the first stage treatment, and generates cyanic acid via chlorocyanide.

Formaldehyde, a manganese compound and / or a copper compound, and hypochlorite are each preferably added in the form of an aqueous solution. The concentration of each aqueous solution may be determined in consideration of the workability when adding them to cyan waste water, the reactivity between the cyan compound and the added compound, and the like.
Since the addition amount of each component of the ternary system is affected by the type and concentration of the cyanide compound contained in the cyan waste water, these addition amounts may be appropriately determined according to the conditions. Specifically, the cyan concentration of the cyan waste water before treatment is measured in advance, and the addition amount of each component may be determined based on the measured value.

  Although the content of the cyanide compound in the cyan wastewater to be treated in the present invention is not particularly limited, the above cyan wastewater is generally about 10 to 500 mg / L in terms of the total cyan concentration. In the case of treating such cyan wastewater, formaldehyde, manganese compound and / or copper compound, and hypochlorite are 30 to 60 mg / L, preferably 30 to 50 mg / L, respectively, with respect to the wastewater. 25 to 75 mg / L, preferably 30 to 50 mg / L, and 50 to 300 mg / L, preferably 150 to 300 mg / L in terms of effective chloride ion concentration can be added.

At this time, it is preferable to stir the cyan waste water in terms of the effect of removing the cyanide compound and the effect of suppressing the elution of cyan from the sludge separated from the waste water. In addition, it is preferable to heat the cyan waste water to some extent in order to promote the reaction during stirring, but a liquid temperature of about 20 to 60 ° C. is sufficient.
The stirring time varies depending on the amount of cyanide wastewater, the type and concentration of cyanide contained, the form of the treatment apparatus and its scale, etc., but usually it may be 10 minutes or more, preferably 20 to 30 minutes. .

  Further, in terms of the effect of removing cyanide and the effect of suppressing the elution of cyanide from sludge separated from the wastewater, the pH of the cyanine wastewater is preferably 7 to 8.5, preferably in terms of preventing the generation of cyanogen gas (hydrogen cyanide). Is preferably adjusted to 8 to 8.5. For pH adjustment, a known method such as acid addition such as dilute sulfuric acid can be used.

  As described above, by treating cyan wastewater with the method of the present invention, it is possible to more reliably reduce the cyan concentration (total cyan content (mg / L)) of the wastewater before treatment to a drainage standard value or less. it can. In particular, when cyanide wastewater containing cyanogen-containing sludge is treated, the cyanide in the wastewater is removed and the elution of the cyanide from the sludge separated from the wastewater is suppressed, so that the cyanide wastewater before treatment is treated. The density (total cyan content (mg / L)) can be more reliably reduced below the drainage standard value.

In the method of the present invention, when the treated wastewater is discharged as it is, after the first stage treatment, it may be treated with a ternary system in an amount necessary to reduce the total cyan concentration below the drainage standard value.
Usually, in factories and the like, the treated wastewater is often diluted with other wastewater and discharged, and it is preferable to control the amount of each component added in consideration of the cost effect.
Therefore, it is understood that the processing included in the present invention is when the total cyan density after processing does not become 1 mg / L or less, and when it becomes approximately 5 mg / L or less.

Decomposition products and / or water-insoluble salts generated in the treated wastewater can be removed from the wastewater by a known method.
In the case of the apparatus provided with the reaction processing tank and thickener which are mentioned later, the time required for reaction and precipitation removal of a water-insoluble salt is about 10 to 60 minutes.

The cyan wastewater treatment method of the present invention will be specifically described with reference to a schematic diagram (FIG. 1) showing an example of the wastewater treatment apparatus, but this description does not limit the present invention.
First, before measuring the cyan concentration of cyanide wastewater containing cyanide-containing sludge to be treated (the flow is indicated by an arrow in the figure) before the primary reaction treatment tank, the cyan wastewater is sent to the primary reaction treatment tank. . Based on the measured value such as the cyan concentration, sodium hypochlorite and sodium hydroxide for pH adjustment are added from the additive first tank (1) and additive second tank (2), respectively. Next, after confirming that the pH of the cyan waste water is adjusted to 10 or more with a pH meter, the cyan waste water in the primary reaction treatment tank is retained while stirring for a predetermined time. Subsequently, the cyan waste water is fed to the secondary reaction treatment tank, and the additive first tank (1), additive third tank (3), additive fourth tank (4) and additive fifth tank (5). To each of sodium hypochlorite, dilute sulfuric acid for adjusting pH, formaldehyde and manganese compounds. Then, after confirming that the pH of the cyan waste water is adjusted to 7 to 8.5 with a pH meter, the cyan waste water in the secondary reaction treatment tank is retained while stirring for a predetermined time.

  Next, the cyan wastewater containing the produced water-insoluble manganese salt is sent to the thickener from the lower side of the secondary reaction treatment tank to further promote the formation of the water-insoluble manganese salt and perform the SS coagulation treatment. Let it stay for a predetermined time. Thereafter, the supernatant is sent from above the thickener to the turbidity sedimentation basin, and the sedimented sludge is collected from below the thickener. After further aggregating SS in the turbidity sedimentation basin to stabilize the water quality, the cyan concentration of the supernatant liquid in the turbidity sedimentation basin was measured, and the measured value was confirmed to be below the drainage standard value. Thereafter, the supernatant is discharged. If the measured value of the cyan concentration is equal to or greater than the drainage standard value, the supernatant liquid in the turbidity sedimentation basin is sent to the upstream process (for example, primary reaction treatment tank) and treated again or mixed with other wastewater. Dilute and discharge. The discharged water can be reused.

  The present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Test Example 1 (Cyan removal effect confirmation test of prepared slurry)
Sludge collected from the Sakai Steel Factory was mixed with Osaka city water to prepare a 15% test slurry solution (pH 11). To this sample slurry, the reagent agents shown in Table 1 were added as the first stage treatment, and the mixture was stirred and mixed at a rotation speed of 200 rpm for 30 minutes. Next, as the second stage treatment, the pH of each slurry slurry was adjusted to 8 with 5% sulfuric acid, then the reagent agents shown in Table 1 were added, and the mixture was stirred and mixed at a rotation speed of 200 rpm for 30 minutes.
The obtained treated slurry was diluted with Osaka city water and left for 60 minutes. The mixture was filtered through 5C filter paper, and the total cyan concentration (T-CN), cyanide ion concentration (CN) and cyano complex salt concentration (complex salt) in the filtrate were measured according to JIS K0102.
The obtained results are shown in Table 1 together with the amount of reagent reagent added. In the table, (a), (b), and (c) indicate sodium hypochlorite, formaldehyde 20% aqueous solution, and manganese chloride, respectively, and the added amount of (a) indicates an effective chloride ion concentration conversion value.

  From the results of Table 1, in Examples 1-4, the total cyan concentration (T-CN), cyanide ion concentration (CN), and cyano complex salt concentration (complex salt) are comprehensively compared with Comparative Examples 1-10. It turns out that it is low. That is, after adding and mixing sodium hypochlorite as the first stage treatment, and adding and mixing formaldehyde, sodium hypochlorite and manganese chloride as the second stage treatment, the cyanide compound is more reliably obtained from the cyan waste water. It can be seen that it can be removed.

Test example 2 (confirmation effect for inhibiting the re-elution of cyanide from sludge separated from wastewater after treatment)
In Test Example 1, water was added to the sludge separated when the treated slurry liquids of Example 3 and Example 4 were filtered, so that a test slurry liquid was prepared. After stirring this test slurry at 200 rpm for 6 hours, The mixture was filtered through 5C filter paper, and the total cyan concentration (TC), cyanide ion concentration (CN) and cyano complex salt concentration (complex salt) in the filtrate were measured according to JIS K0102.
The obtained results are shown in Table 2.

  From the results in Table 2, it can be seen that there is almost no elution of cyanide from the sludge separated from the waste water, and re-elution of cyanide from the sludge is remarkably suppressed.

It is a schematic diagram which shows an example of the processing apparatus of the cyan waste water used for the processing method of the cyan waste water of this invention.

Explanation of symbols

1 Additive 1st tank (sodium hypochlorite)
2 Additive second tank (sodium hydroxide)
3 Additive third tank (dilute sulfuric acid)
4 Additive 4th tank (formaldehyde)
5 Additive 5th tank (Mn component)

Claims (5)

Measured in advance cyan density of the cyan-containing waste water containing cyanide-containing sludge, and the cyan-containing waste water was water in the primary reaction treatment tank, based on the cyan density, the alkali for pH adjustment to the cyan-containing waste water, It was added and mixed with chlorine gas or hypochlorite, wherein the cyan-containing waste water pH was stirred while adjusting to 10 or more of the cyan-containing first stage oxidative decomposition of the cyanide contained in the waste water performs processing, then water pre Symbol cyan-containing waste water in the second reaction treatment tank, before Symbol acid for pH adjustment cyan-containing waste water, formaldehyde, manganese compound and / or a copper compound, and a chlorine gas or hypochlorous and adding and mixing the three components of chlorate, said stirring while adjusting the pH of the cyanide-containing waste water to 7-8.5, cyanide remaining in the cyan-containing waste water Processing method cyan-containing waste water and performing a second-stage process of removing the decomposition product and water insoluble salt. 2. The method for treating cyan-containing wastewater according to claim 1, wherein in the first-stage treatment, 50 to 500 mg / L of the hypochlorite is added to the cyanide-containing wastewater in terms of effective chlorine ion concentration. In the second stage treatment, the formaldehyde, manganese compound and / or copper compound, and hypochlorite are 30 to 60 mg / L, 25 to 75 mg / L and effective chlorine ions, respectively, with respect to the cyanide-containing wastewater. The method for treating cyanide-containing wastewater according to claim 1 or 2 , wherein 50 to 300 mg / L is added in terms of concentration. The method for treating cyanogen-containing wastewater according to any one of claims 1 to 3 , wherein the hypochlorite is sodium hypochlorite or potassium hypochlorite. The method for treating cyanogen-containing wastewater according to any one of claims 1 to 4 , wherein the manganese compound is manganese chloride or manganese sulfate, and the copper compound is cupric chloride.

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