JPH05169071A - Treatment of cyanide containing waste water - Google Patents

Abstract

PURPOSE:To improve treating efficiency by oxidation-treating cyanide containing waste water with Fenton's reagent, next adding copper salt to decompose excess hydrogen peroxide and further adding a reducing agent to make cyanide compounds hard to dissolve, permitting them to be separated. CONSTITUTION:Fenton's reagent which is formed by combining hydrogen peroxide and ferrous salt is added to cyanide containing waste water under acidic conditions of pH2-6 to give it oxidation treatment. In this case, the added quantity of the reagent is determined by previously giving sampling treatment to the waste water so that treating time may be about 0.5-5hr. After the oxidation treatment, sodium hydroxide, etc., are added to make it alkaline, pH8-10, and copper salt, such as copper sulfate is added by such amount that treating time may be about 10min-3hr to decompose excess hydrogen peroxide. Next, a reducing agent, such as sodium sulfite is added under conditions of pH2-10 by such amount that treating time may be 5min-1hr to make cyanide compounds hard to dissolve. Next, the precipitate is removed in a precipitator, etc.

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 cyanide-containing wastewater. More specifically, the present invention relates to a method for treating cyanide-containing wastewater that can effectively remove cyanogen precursors that cannot be removed by conventional treatment methods.

[0002]

2. Description of the Related Art Heretofore, various methods have been known as methods for treating cyanide-containing wastewater. For example, waste water containing free cyan and various cyan complex salts is usually treated by the alkali chlorine method. However, in this alkali chlorine method, free cyan and cyan complex salts such as zinc, copper and cadmium can be decomposed, but cyan complex salts such as iron, nickel, cobalt or gold and silver are difficult to decompose. .. Therefore, for wastewater containing such a hardly decomposable cyan complex salt, a dark blue method, a method of forming a hardly soluble salt using zinc, or a copper salt / reducing agent method of simultaneously making free cyan and various cyan complex salts difficult to dissolve (Tokuhei 2-4
No. 8315) is applied. However, it is known that some of the cyanide-containing wastewater cannot be treated even if such a treatment method is applied. On the other hand, regarding the case where cyanide is detected from factory wastewater that does not use cyan at all. The number of reports has been increasing recently [Chiba Prefectural Mizuhoken Annual Report (1985)] 37-41
Page, "Tokyo Metropolitan Institute of Environmental Science, Annual Report 1990", "Environment and Measurement Technology" Volume 17, No. 1, No. 2, No. 3 (1
990)]. It is presumed that these causes are due to the presence of substances that interfere with the cyanide treatment and cyanogen precursors that produce cyan during the distillation operation of cyanogen analysis in the wastewater. The details are not always clear. Examples of such wastewater that is difficult to perform cyan treatment include coke manufacturing wastewater, non-cyan plating factory wastewater, and steel manufacturing wastewater.
Since there is no fundamental treatment method, the actual situation is that measures such as a dilution treatment method are taken.

[0003]

Under these circumstances, the present invention is applied to wastewater containing a cyanogen-treating interfering substance, a cyan precursor, etc., which cannot be removed by a conventional treating method. The object of the present invention is to provide a method for treating cyanide-containing wastewater capable of decomposing substances and effectively removing cyanide.

[0004]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that first, a Fenton's reagent is added to cyanide-containing wastewater and subjected to an oxidation treatment to effect the interfering substance or the cyanogen precursor. It was found that the objective can be achieved by decomposing bisphenol, then decomposing excess hydrogen peroxide by adding a copper salt, and then adding a reducing agent to make the cyanide compound insoluble and separate. Based on this, the present invention has been completed. That is, according to the present invention, cyanide-containing wastewater is subjected to oxidation treatment by adding Fenton's reagent, and then copper salt is added to decompose excess hydrogen peroxide, and then a reducing agent is added to remove cyanide compounds. The present invention provides a method for treating cyanide-containing wastewater, which is characterized in that it is made insoluble and separated. Hereinafter, the present invention will be described in detail.

The method of the present invention comprises (A) an oxidation treatment step with a Fenton reagent, (B) a decomposition treatment step of excess hydrogen peroxide with a copper salt, (C) a step of making a cyanide compound insoluble by a reducing agent, and (D). It is composed of a step of separating the sparingly soluble cyanide compound. In the step (A), the Fenton's reagent is added to the wastewater containing cyanide, and the oxidation treatment is performed.
The Fenton's reagent is an oxidizing agent that combines hydrogen peroxide and a ferrous salt. The treatment with the Fenton's reagent is usually performed under acidic conditions of pH 2-6. About the action in this oxidation treatment step, although it is not always clear, decomposition of cyanogen-interfering substances contained in the wastewater,
The conversion action of the cyan precursor to the cyan compound is considered. In particular, as shown in the comparative example, an increase in cyanide due to a cyanide oxidation treatment method such as chlorine and ozone shows the complexity of the reaction.

The amount of Fenton's reagent added is not particularly limited as long as it is sufficient to oxidize and decompose the cyanide-treating substance or cyanogen precursor present in the wastewater, but other amounts are not included in the wastewater. It often contains a substance that consumes the Fenton reagent, and therefore it is desirable to sample the wastewater to be treated in advance and determine the addition amount of the Fenton reagent. The processing time is usually 0.5 to 5
Time is enough. In the step (B), the excess hydrogen peroxide is decomposed by adding a copper salt to the wastewater subjected to the oxidation treatment in the step (A). The residual hydrogen peroxide not only serves as a COD source,
Oxygen generated from hydrogen peroxide in the subsequent precipitation step undesirably brings about a situation such as floating the generated precipitate, so it is necessary to decompose it.

Catalytic decomposition of hydrogen peroxide by a copper salt is economically advantageous because it does not require a chemical agent such as a reducing agent or an enzyme such as catalase which is usually used for decomposition of hydrogen peroxide. It contributes to the insolubility of the cyanide compound in the next step (C). It is desirable to perform the hydrogen peroxide decomposition treatment with this copper salt under alkaline conditions of pH 8 to 10. Therefore, since the wastewater subjected to the oxidation treatment in the step (A) is usually acidic, sodium hydroxide and carbonic acid are used. An alkali such as sodium, sodium hydrogen carbonate or calcium hydroxide is added to adjust the pH within the above range, and hydrogen peroxide is decomposed by a copper salt. At this time, as the copper salt, for example, a water-soluble divalent copper salt such as divalent copper sulfate, copper chloride or copper nitrate is preferably used. Further, the amount of the copper salt added is not particularly limited as long as it is a sufficient amount to decompose excess hydrogen peroxide and is equal to or more than the reaction equivalent of cyanide in the wastewater. A treatment time of 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 process for making the cyanide compound insoluble is performed. Examples of the reducing agent used at this time include those capable of monovalent reduction of divalent copper ions, such as sulfite, divalent iron salt, and hydrazine. Among them, reduction of sludge generation amount and Sulfite is preferable from the viewpoint of easy availability. As the sulfite, for example, sodium sulfite, sodium hydrogen sulfite, etc. are preferably used. Generally, even if various reducing agents such as sulfite, divalent iron salt and hydrazine are added to divalent copper salt such as copper sulfate and the pH is set to 2 to 11, no apparent formation of monovalent copper ion is observed. Although the reduction rate is slow, the presence of a cyanide compound causes the cyanide compound of monovalent copper to form a sparingly soluble salt and precipitate. This is because the monovalent copper ion generated by the reducing agent reacts with the cyanide compound and precipitates, creating an atmosphere in which monovalent copper ion cannot exist in the system, so the apparent redox potential changes and the reduction occurs. Is presumed to have progressed. The reaction is a reaction formula ^{Cu + + CN - → CuCN ↓} ··· [1] 4Cu + + Zn (CN) 4 2- → 4CuCN ↓ + Zn 2+ ··· [2] Cu + + Ag (CN) 2 - → CuAg (CN) ₂ ↓ ・ ・ ・ Represented by three types represented by [3].

The above formula [1] is a reaction of free cyan, the formula [2] is a reaction of a readily decomposable cyan complex salt, and the formula [3] is a reaction of a hardly decomposable cyan complex salt. Produces a sparingly soluble precipitate and is processed in batches. The amount of the reducing agent added is not particularly limited as long as it is equal to or more 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 about a liter. The pH of the hardly soluble treatment of the cyan compound with the reducing agent is usually 2 to 10, preferably 5
It is selected in the range of ~ 9.5. In addition, Cd ²⁺ , Ni ²⁺ , M
When there are many coexisting heavy metal ions such as n ²⁺ that do not completely precipitate at pH 9.5 or lower, a two-stage precipitation is performed 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. Adopting the law is advantageous.
The treatment time with the reducing agent is usually 5 minutes to 1 hour.

In step (D), the wastewater treated in this manner is subjected to solid-liquid separation treatment by adding a polymer flocculant or the like to form flocs having a good sedimentation property. This solid-liquid separation treatment may be carried out using a settling tank such as a thickener, or may be carried out using a filter or the like if it contains a surfactant or dispersant and the aggregation and sedimentation properties are poor. ..
The treated wastewater from which the solid content has been separated in this manner contains almost no heavy metals such as cyanide and copper, and therefore can be discharged as it is. According to the processing method of the present invention, cyan which could not be processed by the conventional method can be processed to 0.1 mg / liter or less.

[0011]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. As cyanide-containing wastewater, COD _Mn
1,350 mg / liter, COD _Cr 2,300 mg / liter, BOD 2,000 mg / liter, phenol 408 m
g / liter, SCN403 mg / liter, T-CN1
Anhydrous water containing 6.5 mg / liter was used for COD _Mn loading 0.4-
COD _Mn 6 obtained by biological treatment at 0.5 kg / m ³ · day
6.3 mg / liter, COD _Cr 2,300 mg / liter,
BOD 11.8 mg / liter, phenol 0.1 mg / liter or less, SCN 9.5 mg / liter, T-CN 1.30
The treated water containing mg / liter was used for cyanide treatment. Example 1 Hydrogen peroxide (500 mg / Fenton reagent) was added to treated water.
Lithium and ferrous sulfate heptahydrate 200 mg / liter were added, oxidation treatment was carried out at pH 3 for 2 hours, cupric sulfate 20 mg / liter in terms of copper was added, and the mixture was stirred at pH 9 for 1 hour to remove residual excess. Hydrogen oxide was decomposed. Next, add 200 mg / liter of sodium sulfite, and add 3 at pH 7.
The mixture was stirred for 0 minutes, and a treatment for making cyan less soluble was performed. The analysis results are shown below.

Raw water Fenton treatment Insoluble treatment pH 8.5 9.0 7.0 COD _Mn (mg / liter) 66.3 31.0 29.0 T-CN (mg / liter) 1.3 6.13 .04 Cu (mg / liter) -1.7

Comparative Example 1 Alkali Chlorine Treatment To treated water, sodium hypochlorite was added at 200 mg / liter (as Cl ₂ ) which was more than the decomposition equivalent of cyan, and the pH was adjusted.
It was treated with 7.5 for 15 minutes and pH 10.5 for 20 minutes. The cyan analysis results are shown in Table 1.

COMPARATIVE EXAMPLE 2 Ozone Treatment Treated water with 100 m of ozone having a decomposition equivalent or more at pH 11.0.
Ozone treatment was performed by blowing in g / liter and 600 mg / liter (as O ₃ ) respectively. The concentration of the ozonized air was blown at this time 10 mg-O ₃ / l - is air. The cyan analysis results are shown in Table 1.

COMPARATIVE EXAMPLE 3 Treatment with deep blue blue Assuming that the remaining cyan in the treated water is an iron-cyan complex of Fe (CN) ₆ ³⁻ , a reaction equivalent of ferrous sulfate 20 or more is obtained.
After adding 0 mg / liter and 600 mg / liter respectively and treating at pH 5.5 for 20 minutes, the filtrate was analyzed for cyanide. The results are shown in Table 1.

Comparative Example 4 Insoluble treatment with Cu / Na ₂ SO ₃ 20 mg / liter of cupric sulfate (as Cu) in treated water
And sodium sulfite 200 mg / liter are added to adjust the pH.
After treatment with 6 for 20 minutes, the filtrate was analyzed for cyan.
The results are shown in Table 1.

Comparative Example 5 Combination Treatment of Comparative Example 2/4 600 mg / l of ozone (as O ₃ ) was blown into the treated water to carry out ozone treatment, and then the same treatment as in Comparative Example 4 was conducted. The cyan analysis results are shown in Table 1.

[0018]

[Table 1]

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

[0020]

EFFECTS OF THE INVENTION According to the method of the present invention, cyan processing interfering substances and cyan precursors, which cannot be removed by the conventional processing methods, are oxidized and decomposed by the Fenton reagent, and cyan can be efficiently removed. Further, since no chlorine-based oxidizing agent is used, there is no danger of producing an organic chlorine compound, and since COF is treated with a Fenton reagent, a reduction in COD can be expected.

Claims (1)

[Claims] 1. A cyan-containing wastewater is added with a Fenton's reagent to be oxidized, and then a copper salt is added to decompose excess hydrogen peroxide, and then a reducing agent is added to make a cyanide compound difficult. A method for treating cyanide-containing wastewater, which comprises solubilizing and separating.