JP2001300553A - Method for treating cyanide-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating cyanide-containing wastewater, by which cyanide can be safely removed by simple operation at a low cost. SOLUTION: This method for treating cyanide-containing wastewater comprises adding a hypochlorite of the amount enough to remove the cyanide contained in the wastewater and a manganese compound to the cyanide- containing wastewater and removing the produced water insoluble manganese salt from the wastewater to remove the cyanide in the wastewater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention provides a simple operation,
The present invention relates to a method for treating cyanide-containing wastewater that can remove cyanide safely and at low cost. More specifically, the present invention relates to a metal cyanide compound (hydrogen cyanide salt), a cyan ion (free cyan or cyanide ion), a cyano complex salt discharged from a chemical plant, a plating plant, a coke production plant, a metal surface treatment plant, and the like. The present invention relates to a method for treating cyan-containing wastewater containing cyano complex ions and the like.

[0002]

2. Description of the Related Art Since cyan has a strong adverse effect on ecosystems, it is not possible to directly discharge cyanide-containing wastewater (hereinafter referred to as "cyan wastewater") to nature. Wastewater standards have been established for cyanide, and these standards (1 mg /
l or less), the cyanide removal treatment is performed, and the wastewater cannot be discharged to sewage or the like unless it is detoxified wastewater.

[0003] As a method for removing cyan from cyan waste water, an alkali chlorine method in which cyan waste water is adjusted to alkalinity and then chlorine is injected to oxidize and decompose cyan, and cyano is converted into nitrogen gas by strong ozone oxidizing power. An ozone oxidation method that oxidizes and decomposes into bicarbonate, an electrolytic oxidation method in which cyanide is electrolyzed using an insoluble electrode to perform an oxidation reaction, and a ferrous ion supply compound such as ferrous sulfate in cyanide wastewater To form a hardly soluble ferriferrocyanide and remove it by sedimentation, and a biological treatment method of decomposing cyanide into microorganisms acclimated to cyanide (cyanase-decomposing bacteria) (for example, "Basic Chemistry and Wastewater Treatment Technology", Information Research Institute, Ltd., pp. 152-158).

However, each of the above methods has the following disadvantages. The alkali chlorine method is the most common cyanide removal treatment method, but this method is a two-step treatment, and a pH value (first reaction:
It is necessary to maintain the pH at 10 or more and the second reaction: pH 7.5 to 8.0), and the amount of the oxidizing agent added, the amount of residual chlorine, and the like must be constantly monitored.

[0005] The ozone oxidation method has such advantages that no harmful compounds are produced by this treatment and that only harmless oxygen is produced even if the ozone used itself is decomposed. However, since this treatment is a gas-liquid reaction, Requires complex and extensive equipment. Also, because the production cost of ozone is high,
It is necessary to devise a device for effectively reacting ozone. For example, two oxidation towers are provided, a filler is put in the first oxidation tower, and the cyan wastewater and the ozone are efficiently brought in countercurrent contact with each other, and the exhaust gas from the first oxidation tower is discharged to the second oxidation tower. Used in oxidation tower to make full use of residual ozone. Further, it is necessary to perform a coagulation precipitation treatment of the metal hydroxide generated by the decomposition of cyan.

[0006] The electrolytic oxidation method has an advantage that a concentrated waste liquid of cyan can be efficiently and economically treated, but a large amount of electric power is required and the treatment cost is increased. Also,
There is also a method of removing cyan by using an electrolytic oxidation method and another processing method together, but in any case, the processing becomes complicated and the processing cost increases.

[0007] The navy blue method is suitable for the treatment of cyan wastewater in which it is difficult to oxidize and decompose cyan by other treatment methods. However, if there is little iron ion, the produced complex salt remains in a soluble state in the cyanide wastewater, resulting in a treatment. When the water is colored or the pH of the treated water is high, the amount of residual ferrocyanin in the filtrate increases. In addition, since the formed complex salt is easily oxidized by oxygen in the air and becomes a ferriferro type and redissolved, it is difficult to reduce the cyanide concentration of the treated water to the effluent standard by the navy blue method.

[0008] Biological treatment methods include the maintenance of pH suitable for the treatment of microorganisms, the addition of nutrients (nitrogen, phosphorus, etc.), the adjustment of activated sludge concentration (MLSS), the treatment of excess sludge, etc. Complicated operations are required, and
When the treatment time (the contact time between cyan and microorganisms) is long and the cyan concentration in the cyan wastewater is high, there are disadvantages such that the wastewater to be treated must be diluted in advance.

The applicant of the present invention has proposed a method for treating cyanide wastewater by a simple operation and a treatment agent used therefor, which adjusts iron cyanide complex ion-containing wastewater to a pH of 6.0 or more, and adds a manganese compound to this. A method of producing a water-insoluble manganese salt of an iron cyanide complex compound and removing the same from a wastewater system (Japanese Patent No. 1418529), and a method in which a cuprous halide solution contains a reducing substance capable of reducing Fehling's solution. And a treatment agent for wastewater containing cyan and / or thiocyan having improved stability and treatment efficiency (Japanese Patent No. 1456722).

[0010] Also, JP-A-2-35991 discloses that
The first-stage reaction is performed by adding 1.4 mol or more of formaldehyde of cyan amount to the cyanide wastewater, and the hydrogen peroxide of 3.0 mol or more of cyan amount is further added to the second-stage reaction at pH 7 or more. A method for detoxifying cyan wastewater by doing so is disclosed.

Recently, an alkali agent and an oxidizing agent (ozone, hydrogen peroxide, sodium hypochlorite, etc.) have been added to cyan wastewater containing an iron cyanide complex compound in advance.
Is adjusted to alkaline and then irradiated with ultraviolet to visible light to oxidize free cyanide while separating and removing precipitates such as hydroxides generated from iron ions dissociated by decomposition of the iron cyanide complex compound from wastewater as needed. A wastewater treatment method for performing treatment has been proposed (JP-A-10-057974).

However, in the above prior arts, complicated operations and steps such as pH adjustment of cyan wastewater are required in any case, and a method of treating cyan wastewater capable of removing cyan by a simple operation has been desired. . Further, there has been a demand for a safe and inexpensive method for treating cyanide wastewater, which can remove cyanogen by using an inexpensive compound instead of a carcinogen such as formaldehyde.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for treating cyan wastewater, which can remove cyan cyanide safely and inexpensively with a simple operation.

[0014]

Means for Solving the Problems The inventors of the present invention provide:
In light of this situation, as a result of diligent research, normal pH
A water-insoluble manganese salt formed by adding hypochlorite and a manganese compound as oxidizing agents to a cyan wastewater (6.0 to less than 10.0) without pH adjustment. The present inventors have found that free cyanide, a cyanide compound producing the same, a cyano complex ion, a cyano complex salt producing the same, and the like can be removed by removing from the cyan wastewater, thereby completing the present invention.

Thus, according to the present invention, an amount of hypochlorite and a manganese compound capable of removing cyan contained in the wastewater is added to the wastewater, and the produced water-insoluble manganese salt is removed from the wastewater. Thus, there is provided a method for treating cyan wastewater, which comprises removing cyan from the wastewater.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The cyan wastewater to be treated in the present invention includes metal cyanide, cyanide ion, cyano complex salt, cyano complex metal discharged from a chemical plant, a plating plant, a coke production plant, a metal surface treatment plant and the like. Cyan wastewater containing complex ions and the like can be mentioned.

The hypochlorite used in the present invention includes sodium hypochlorite, potassium hypochlorite and the like. The manganese compound used in the present invention may be any compound that is soluble in water and can form manganese ions in water, and specific examples thereof include manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate. Is mentioned. Of these, manganese chloride and manganese sulfate are particularly preferred in terms of the effect of removing the cyanide compound, and manganese chloride is particularly preferred in terms of the cost of treating cyanide wastewater.

According to the method of the present invention, hypochlorite and a manganese compound in an amount capable of removing cyan contained in cyan wastewater are added to the cyan wastewater simultaneously or separately. The hypochlorite and the manganese compound are each preferably added in the form of an aqueous solution. The concentration of each aqueous solution may be determined in consideration of workability when adding them to cyan wastewater, reactivity between cyanide and the added compound, and specifically, hypochlorite is 10 to 10%. About 7000 mg / l and the manganese compound is about 10 to 5500 mg / l.

The amounts of the hypochlorite and the manganese compound added are affected by the type and concentration of other metal ions contained in the cyan wastewater, in addition to the type and concentration of cyan contained in the cyan wastewater. Therefore, these addition amounts may be appropriately determined according to the conditions. In particular,
The cyan concentration and the like of the cyan wastewater before treatment may be measured in advance, and the amount of each additive to be added may be determined based on the measured value.

The content of cyan in the waste water to be treated in the present invention is not particularly limited, but the above-mentioned cyan waste water generally has a total cyan concentration of 10 to 500.
It is about mg / l. When treating such cyan wastewater, hypochlorite is added to the cyan wastewater so as to have an effective chloride ion concentration of 50 to 7000 mg / l, preferably 50 to 2000 mg / l, and a manganese compound. Is 40 to 2000 mg as manganese ion concentration
/ L, preferably 40 to 1000 mg / l, to the cyan wastewater.

As described above, the cyan concentration (total cyan content (mg / l)) before the treatment is significantly reduced to a value equal to or lower than the wastewater reference value by performing the cyan removal treatment on the cyan wastewater by the method of the present invention. Can be done. In the method of the present invention, when the treated wastewater is discharged as it is, hypochlorite and a manganese compound may be added in an amount required to reduce the total cyanide concentration to the wastewater standard value or less. When diluting treated wastewater with other wastewater and discharging it,
Hypochlorite and a manganese compound may be added so that the waste water after dilution is equal to or less than the above waste water standard value.

Usually, in a factory or the like, treated wastewater is often diluted with other wastewater and discharged, and it is preferable to control the amount of each active ingredient in consideration of the effect on cost. Therefore, the total cyan density after processing is 1 mg
It is understood that the processing not included in the present invention is also included in the present invention even when it does not fall below 5 mg / l.

When the hypochlorite and manganese compounds are added, and when these added compounds react with cyanide, it is preferable to stir the mixed solution from the viewpoint of cyanide removal effect. The mixed solution is preferably heated to a certain degree in order to promote the reaction at the time of stirring.
About 0 to 60 ° C. is sufficient. The time required for the reaction varies depending on the amount of cyan wastewater, the type and concentration of cyan, the form and scale of the treatment apparatus, and the like, but may be determined so that cyan and the added compound are sufficiently contacted.

The water-insoluble manganese salt formed in the treated water is removed from the wastewater by a known method. In the case of an apparatus provided with a reaction tank and a thickener described later, the time required for the reaction and the removal of the manganese salt is about 10 to 60 minutes.

The method for treating cyan wastewater of the present invention will be specifically described with reference to a schematic diagram (FIG. 1) showing an example of a cyan wastewater treatment apparatus, but this description does not limit the present invention. . The cyan wastewater to be treated (indicated by an arrow in the figure) has a cyan concentration measured at point A, is sent to the reaction treatment tank 1, and is measured based on the measured value of the cyan concentration and the like.
A hypochlorite aqueous solution and a manganese salt aqueous solution are respectively added from the additive first tank 2 and the additive second tank 3.
After stirring the cyan wastewater in the reaction tank 1 for a predetermined time, the generated cyan wastewater containing a water-insoluble manganese salt is sent to the thickener 4 from below the reaction tank 1. In the thickener 4, the formation reaction of the water-insoluble manganese salt is advanced, and the solid content is recovered from below the thickener 4. On the other hand, the supernatant liquid is discharged from above the thickener 4, the cyan concentration of the supernatant liquid is measured at point B, and after confirming that the measured value is equal to or lower than the drainage standard value, the supernatant liquid is drained. When the measured value of the cyan concentration is equal to or higher than the wastewater reference value, the supernatant is sent to an upstream process (for example, the reaction tank 1) and treated again, or mixed with another wastewater and discharged. Reusing the above treated wastewater is
No problem.

That is, a treatment apparatus for cyan wastewater which can be used in the treatment method of the present invention basically comprises an additive tank for adding an aqueous solution of hypochlorite and an aqueous solution of manganese salt, and a water-insoluble manganese salt. It consists of a reaction tank for producing, a sedimentation tank for collecting the manganese salt, a pipe connecting these, a stirring means, a pump and the like.
The reaction tank and the precipitation tank can be used in combination, and in such a case, a device such as a thickener can be used.

The feature of the treatment method of the present invention is that it is not necessary to make the pH of the cyan wastewater to be treated 10 or more highly alkaline, whereby the cyan wastewater can be treated more easily than the conventional method. And an excellent cyan removal effect can be obtained.

Although the formation mechanism of the water-insoluble manganese salt in the present invention is not clear, the manganese ions generated in the cyanide wastewater accelerate the decomposition reaction of the cyanide compound by hypochlorite, and further, the unreacted cyanide. And water-insoluble cyanogen manganese salts.

[0029]

EXAMPLES The present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Preparation of Sample Water 1 (Cyanide Wastewater Containing Zinc) 0.11 g / l potassium ferricyanide solution, 0.30 g / l potassium cyanide solution and 5.4 g / zinc chloride
Using l, sample water 1 (pH 8) containing a cyano complex and a cyanide ion was prepared. Table 1 shows the water quality of the obtained sample water 1.

[0031]

[Table 1]

The obtained sample water 1 was dispensed into a beaker having a capacity of 500 ml, and sodium hypochlorite and / or manganese chloride were added so that the concentrations shown in Table 2 were obtained. Stirred for 10 minutes. The water-insoluble product in the test water was filtered off, and the total cyanide concentration and cyanide ion concentration in the filtrate were measured in accordance with JIS K0102, and the effect of removing the cyanide in each test water was evaluated.

With respect to Comparative Examples 1 and 2, test water was treated by the alkali chlorine method. In this alkali chlorine method, the pH of test water is adjusted to pH 10 in the first reaction and p
Adjusted to H8. In this test, a blank test (Comparative Example 5) in which sodium hypochlorite and manganese chloride were not added was simultaneously performed. The obtained results are shown in Table 2 together with the added concentrations of sodium hypochlorite and manganese chloride.

[0034]

[Table 2]

Sample water 2 (cyan waste water containing no zinc)
Preparation of sample water 1 except that zinc chloride is not used,
Sample water 2 (pH 8) was prepared. Table 3 shows the water quality of the obtained sample water 2.

[0036]

[Table 3]

The obtained sample water 2 was dispensed into a beaker having a capacity of 500 ml, and a compound selected from sodium hypochlorite, manganese chloride and formaldehyde was added so that the concentration shown in Table 4 was obtained. Each of the test waters was stirred for 10 minutes. The water-insoluble product in the test water was filtered off, and the total cyanide concentration and cyanide ion concentration in the filtrate were measured in accordance with JIS K0102, and the effect of removing the cyanide in each test water was evaluated. In addition, formaldehyde is a known chemical for treating wastewater of cyanide.

In this test, a blank test (Comparative Example 20) in which sodium hypochlorite, manganese chloride and formaldehyde were not added was simultaneously performed. The results obtained are shown in Table 4 together with the concentrations of sodium hypochlorite, manganese chloride and formaldehyde.

[0039]

[Table 4]

[0040]

According to the method for treating cyan waste water of the present invention,
It is not necessary to adjust the pH of the wastewater before the treatment reaction, and the wastewater can be treated in a one-step reaction. Further, since a carcinogenic substance such as formaldehyde is not used, cyan wastewater can be safely treated, and an inexpensive compound such as manganese chloride can be used. It is advantageous. Therefore, according to the present invention, it is possible to provide a method for treating cyan wastewater, which can remove cyan cyanide safely and inexpensively with a simple operation.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a cyan wastewater treatment apparatus used in a cyan wastewater treatment method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction processing tank 2 Additive first tank 3 Additive second tank 4 Thickener

Claims (3)

[Claims] Claims: 1. An amount of hypochlorite and a manganese compound capable of removing cyan contained in waste water is added to the waste water containing cyanide, and the produced water-insoluble manganese salt is removed from the waste water. A method for treating cyan-containing wastewater, comprising: removing cyan. 2. The treatment method according to claim 1, wherein the hypochlorite is sodium hypochlorite or potassium hypochlorite. 3. The treatment method according to claim 1, wherein the manganese compound is manganese chloride or manganese sulfate.