JP3191372B2 - Treatment of wastewater containing cyanide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for treating wastewater containing cyanide. More specifically, the present invention relates to a method for treating cyan-containing wastewater that can effectively remove cyan precursors and the like that cannot be removed by conventional treatment methods.

[0002]

2. Description of the Related Art Conventionally, various methods have been known as methods for treating cyanide-containing wastewater. For example, wastewater containing free cyanide and various cyanate complex salts is usually treated by an alkali chlorine method. However, in this alkali chlorine method, free cyanide, cyanide complex salts such as zinc, copper, and cadmium can be decomposed, but iron, nickel, cobalt, or cyanide complex salts such as gold and silver are difficult to decompose. . Therefore, for wastewater containing such a hardly decomposable cyan complex, a navy blue method, a method for producing a hardly soluble salt using zinc, or a copper salt / reducing agent method for simultaneously insolubilizing free cyanide and various cyan complex salts are used. (2-4
No. 8315) is applied. However, among cyanide-containing wastewaters, there is known the presence of wastewater which cannot be treated even by applying such a treatment method, while the case where cyanide is detected from factory wastewater not using cyanide at all is known. Reports have increased recently [Chiba Prefectural Mizuhoken Annual Report (Showa 60), pp. 37-41]
Page, "Tokyo Metropolitan Institute of Environmental Science Annual Report 1990", "Environment and Measurement Technology", Vol. 17, No. 1, No. 2, No. 3 (1
990)]. These causes are presumed to be due to the presence in the wastewater of substances that interfere with the cyanide treatment and that generate cyanide during the distillation operation of the cyan analysis. Is not always clear. Examples of such wastewater for which cyan treatment is difficult include coke production wastewater, non-cyan plating plant wastewater, steel production wastewater, and the like.
Since there is no fundamental treatment method, it is a fact that measures such as a dilution treatment method are taken.

[0003]

SUMMARY OF THE INVENTION Under such circumstances, the present invention is applied to wastewater containing a cyanide disturbing substance or a cyan precursor which cannot be removed by a conventional treatment method. An object of the present invention is to provide a method for treating a wastewater containing cyanide, which can decompose substances and remove cyanide effectively.

[0004]

Means for Solving the Problems As a result of intensive studies conducted by the present inventor to achieve the above object, the present inventors first added a Fenton's reagent to cyanide-containing wastewater and oxidized it to remove the interfering substance and cyanogen precursor. After decomposition, it was found that the purpose could be achieved by adding a copper salt to decompose excess hydrogen peroxide and then adding a reducing agent to make the cyanide compound hardly soluble and separated. Based on this, the present invention has been completed. That is, the present invention, after adding the Fenton reagent to the cyanide-containing wastewater and performing oxidation treatment,
An object of the present invention is to provide a method for treating wastewater containing cyanide, which comprises adding a copper salt to decompose excess hydrogen peroxide, and then adding a reducing agent to make a cyanide compound hardly soluble to separate it. Hereinafter, the present invention will be described in detail.

The method of the present invention comprises (A) an oxidation treatment step using a Fenton's reagent, (B) a decomposition treatment step of excess hydrogen peroxide using a copper salt, (C) a step of making a cyanide compound hardly soluble with a reducing agent, and (D) It comprises a separation step of a hardly soluble cyanide compound. In the step (A), an oxidation treatment is performed by adding a Fenton reagent to the wastewater containing cyanide.
Note that the Fenton's reagent is an oxidizing agent combining hydrogen peroxide and a ferrous salt. The treatment with the Fenton's reagent is usually performed under acidic conditions of pH 2 to 6. Although it is not always clear about the action in this oxidation treatment step, decomposition of cyanide interfering substances contained in wastewater,
The effect of converting the cyan precursor into a cyan compound is considered. In particular, as shown in the comparative examples, the increase in cyanide in the cyanidation treatment method such as chlorine or ozone indicates the complexity of the reaction.

[0006] The amount of the Fenton's reagent added is not particularly limited as long as it is an amount sufficient to oxidatively decompose the cyanide-interfering substance and the cyanogen precursor present in the wastewater. In many cases, a substance that consumes the Fenton's reagent is contained. Therefore, it is desirable to sample the wastewater to be treated in advance to determine the amount of the Fenton's reagent added. The processing time is usually 0.5 to 5
About an hour is enough. In the step (B), an excess hydrogen peroxide is decomposed by adding a copper salt to the wastewater subjected to the oxidation treatment in the step (A). Residual hydrogen peroxide is not only a source of COD,
Oxygen generated from hydrogen peroxide in the subsequent precipitation step causes undesired situations such as floating of the generated precipitate, so that it is necessary to decompose it.

[0007] The catalytic decomposition of hydrogen peroxide with a copper salt does not require a drug such as a reducing agent or an enzyme such as catalase which is usually used for decomposing hydrogen peroxide, and is economically advantageous. It contributes to making the cyanide hardly soluble in the next step (C). This decomposition treatment of hydrogen peroxide with a copper salt is desirably performed under alkaline conditions of pH 8 to 10. Therefore, since the wastewater subjected to the oxidation treatment in step (A) is usually acidic, sodium hydroxide, carbonate The pH is adjusted to the above range by adding an alkali such as sodium, sodium hydrogen carbonate, calcium hydroxide, etc., and the decomposition treatment of hydrogen peroxide with a copper salt is performed. At this time, as the copper salt, for example, a water-soluble divalent copper salt such as copper sulfate, copper chloride, or copper nitrate is preferably used. The amount of the copper salt to be added is not particularly limited as long as it is an amount sufficient to decompose excess hydrogen peroxide and is equal to or more than the reaction equivalent to cyanide in the wastewater. Processing time of about 10 minutes to 3 hours is usually sufficient.

In the step (C), a reducing agent is added to the wastewater treated in the step (B),
A treatment for insolubilizing the cyanide is performed. As the reducing agent used at this time, those capable of monovalently reducing divalent copper ions, for example, sulfites, divalent iron salts, hydrazine and the like, among which reduction in the amount of generated sludge and Sulfite is preferred from the viewpoint of easy availability. As the sulfite, for example, sodium sulfite or sodium hydrogen sulfite is preferably used. In general, even when various reducing agents such as sulfite, divalent iron salt, and hydrazine are added to divalent copper salts such as copper sulfate and the pH is adjusted to pH 2 to 11, no apparent formation of monovalent copper ions is observed. Although the reduction rate is much slower, when a cyanide compound is present, the monovalent copper cyanide compound becomes a poorly soluble salt and precipitates. This is because the monovalent copper ion generated by the reducing agent reacts with the cyanide to precipitate and the atmosphere in which the monovalent copper ion does not exist in the system. It is presumed that has progressed. The above reaction is carried out by the reaction formula Cu ⁺ + CN ⁻ → CuCN ↓... [1] 4Cu ⁺ + Zn (CN) ₄ ^2- → 4CuCN ↓ + Zn 2 ⁺ ... [2] Cu ⁺ + Ag (CN) ₂ ⁻ → CuAg (CN) ₂ ↓ ··· [3] This is represented by three types.

The above formula [1] is a reaction of free cyanide, formula [2] is a reaction of readily decomposable cyan complex, and formula [3] is a reaction of hardly decomposable cyan complex. , Produces a sparingly soluble precipitate and is processed in batch. The amount of the reducing agent added is not particularly limited as long as it is not less than the total amount of the theoretical amount for reducing divalent copper ions to monovalent and the amount consumed by the substance to be reduced such as dissolved oxygen. , Usually 50-500 mg / NaHSO ₃
It is on the order of liters. The pH in the treatment for making the cyanide hardly soluble with the reducing agent is usually 2 to 10, preferably 5 to 5.
~ 9.5. Cd ²⁺ , Ni ²⁺ , M
When there are many coexisting heavy metal ions, such as n ²⁺ , which do not completely precipitate at pH 9.5 or lower, a two-step precipitation in which the cyanide compound is once precipitated at pH 5 to 9.5 and then the heavy metal is further precipitated at pH 10 to 11 Advantageously, a law is adopted.
Further, the treatment time with the reducing agent is usually about 5 minutes to 1 hour.

The wastewater thus treated is subjected to a solid-liquid separation treatment in step (D) by adding a polymer flocculant or the like to form flocs or the like having good sedimentation properties. This solid-liquid separation treatment may be performed using a sedimentation tank such as a thickener, or may include a surfactant or a dispersant, and when the coagulation sedimentation property is poor, may be performed using a filter or the like. .
The treated wastewater from which solids are separated in this manner can be discharged as it is because it contains almost no heavy metals such as cyan and copper. According to the processing method of the present invention, cyan which cannot be processed by the conventional method can be processed to 0.1 mg / liter or less.

[0011]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. In addition, COD _Mn
1,350mg / L, COD _Cr 2,300mg / L, BOD 2,000mg / L, Phenol 408m
g / liter, SCN 403 mg / liter, T-CN1
The cheap water containing 6.5 mg / l is supplied with COD _Mn load of 0.4 ~
COD _Mn 6 obtained by biological treatment at 0.5 kg / m ³ · day
6.3 mg / l, COD _Cr 2,300 mg / l,
BOD 11.8 mg / L, phenol 0.1 mg / L or less, SCN 9.5 mg / L, T-CN 1.30
Cyan treatment was performed using treated water containing mg / liter. Example 1 500 mg / hydrogen peroxide as a Fenton's reagent in treated water
Liter and 200 mg / liter of ferrous sulfate heptahydrate were added, and the mixture was oxidized at pH 3 for 2 hours. Then, cupric sulfate was added at 20 mg / liter in terms of copper, and the mixture was stirred at pH 9 for 1 hour. Hydrogen oxide was decomposed. Then, 200 mg / liter of sodium sulfite was added,
The mixture was stirred for 0 minutes to perform a hardly solubilizing treatment of cyan. The results of the analysis are shown below.

Raw water Fenton treatment Resolubilization treatment pH 8.5 9.0 7.0 COD _Mn (mg / l) 66.3 31.0 29.0 T-CN (mg / l) 1.3 6.130 .04 Cu (mg / liter) --1.7

Comparative Example 1 Alkali Chlorine Treatment To treated water, sodium hypochlorite was added in an amount of 200 mg / liter (as Cl ₂ ), which was equal to or more than the decomposition equivalent of cyanide, and pH was adjusted.
The mixture was treated at 7.5 for 15 minutes and at pH 10.5 for 20 minutes. Table 1 shows the analysis results of cyan.

Comparative Example 2 Ozone Treatment 100 m of ozone having a decomposition equivalent or more at pH 11.0 was added to treated water.
g / liter and 600 mg / liter (as O ₃ ) were respectively blown to perform ozone treatment. The concentration of the ozonized air was blown at this time 10 mg-O ₃ / l - is air. Table 1 shows the analysis results of cyan.

[0015] Comparative Example 3 in Prussian process treated water, cyan Fe (CN) ₆ on the assumption that the iron cyanide complex reaction equivalent or more ferrous sulfate is a ^3-remaining 20
After adding 0 mg / liter and 600 mg / liter, respectively, and treating at pH 5.5 for 20 minutes, the filtrate was analyzed for cyan. Table 1 shows the results.

Comparative Example 4 Refractory treatment with Cu / Na ₂ SO _{3 In} treated water, cupric sulfate 20 mg / liter (as Cu)
And 200 mg / liter of sodium sulfite
After treatment with No. 6 for 20 minutes, the filtrate was analyzed for cyan.
Table 1 shows the results.

Comparative Example 5 Combination Treatment of Comparative Example 2/4 Ozone was blown into treated water at 600 mg / liter (as O ₃ ) to perform ozone treatment, and then the same treatment as in Comparative Example 4 was performed. Table 1 shows the analysis results of cyan.

[0018]

[Table 1]

From the above results, the cyan content cannot be reduced to 0.1 mg / l or less even in the combination treatment of ozone treatment and Cu / NaSO ₃ treatment which is the most effective among the conventional methods. According to the method, the content of cyan can be easily reduced to 0.1 mg / liter or less.

[0020]

According to the method of the present invention, the cyanide disturbing substance and the cyan precursor which cannot be removed by the conventional treatment method are oxidatively decomposed by the Fenton's reagent, and the cyanide can be removed efficiently. Further, since no chlorine-based oxidizing agent is used, there is no danger of producing an organic chlorine compound, and COD can be expected to be reduced because the treatment with the Fenton reagent is performed.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C02F 9/00 504 C02F 9/00 504B 504E

Claims (1)

(57) [Claims] 1. An oxidation treatment by adding a Fenton's reagent to wastewater containing cyanide, adding a copper salt to decompose excess hydrogen peroxide, and then adding a reducing agent to make the cyanide difficult. A method for treating cyanide-containing wastewater, comprising the steps of solubilizing and separating.