JPH1057972A - Treatment of iron-cyanide complex containing cyanic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat a cyanide in a waste water to low concn. by irradiating the waste water with UV rays to visible rays after adding sulfuric acid, a soluble sulfate and an oxidizing agent to execute a decomposition and oxidation treatment of an iron-cyanide complex at the time of treating a cyanic waste water containing the iron-cyanide complex. SOLUTION: The cyanic waste water is irradiated with UV rays-visible rays in a reactor 16 provided with a light source 15 after adding sulfuric acid or sulfuric acid and the soluble sulfate and the oxidizing agent to the cyanic waste water containing the iron-cyanide complex from a feed device 12. In this way, a decomposition and oxidation treatment of the iron-cyanide complex is allowed to progress by a two step reaction. That is, at the first step reaction, the iron-cyanide complex is excited by light energy to be decomposed to a free cyanide and iron ion. At the second step reaction, the free cyanide is oxidized with the oxidizing agent supplied from an oxidizing agent feed device 13 to convert it into a carbonate and nitrogen. The waste water with cyanide compd. decomposed and oxidized is discharged from a discharge pipe 17 as a treated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater containing a hardly decomposable iron cyanide complex compound generated in a plating factory for performing surface processing, photographic development and the like. The present invention is also applicable to the treatment of leaked water from industrial waste treatment or iron cyanide complex compounds contained in contaminated water.

[0002]

2. Description of the Related Art Wastewater containing cyanide (cyanide wastewater) generated in plating factories that perform metal surface treatment and in the chemical, petroleum, and gas industries, etc., has a strong adverse effect on ecosystems because cyanide has a strong adverse effect on ecosystems. It cannot be released. Therefore, it is necessary to remove the cyanide from the cyanide wastewater, make it below the national standard for environmental emissions, detoxify the wastewater, and discharge it to sewage. Generally, free cyanide or a cyan compound which easily produces it is easily oxidized. As a method for treating such cyan wastewater, an alkali chlorine method of performing an oxidation treatment using a chlorine-based oxidizing agent such as sodium hypochlorite after adjusting to alkali has been put to practical use as a general treatment method. . However, unlike the free cyanide and the like, in the treatment of cyanide wastewater containing an iron cyanide complex compound having a chemically stable structure, the oxidizing power of the oxidizing agent is weak in the above-mentioned alkali chlorine method, and the oxidation treatment is usually difficult. is there. As a method of treating cyan waste water containing such a hardly decomposable iron cyan complex compound, the cyan waste water is irradiated with ultraviolet to visible light to decompose the iron cyan complex compound into free cyanide and iron ions which are easily oxidized. A method of oxidizing the free cyanide with an oxidizing agent has been used.

FIG. 1 shows a conventional apparatus for decomposing and oxidizing an iron cyanide complex by irradiating ultraviolet to visible light in the presence of an oxidizing agent. (Hereinafter referred to as the conventional method). 3 is an oxidant supply device, 6 is a reaction vessel equipped with a light source 5 for ultraviolet to visible light, 1
Is a supply pipe for cyan wastewater, and 7 is a discharge pipe for treated water. The cyan wastewater sent through the supply pipe of cyan wastewater 1 is sent to the reaction tank 6 together with the oxidant supplied from the oxidant supply device 3 and irradiated with ultraviolet to visible light. The decomposition and oxidation treatment of the iron cyanide complex compound generally proceeds in a two-stage reaction. That is, in the first-stage reaction, the iron-cyan complex compound is excited by the irradiated light energy and decomposed into free cyanide and iron ions, which are easily oxidized. In the second stage reaction, the free cyanide thus generated by the decomposition is oxidized by the oxidizing agent supplied from the oxidizing agent supply device 3 and converted into carbonate and nitrogen. The wastewater obtained by decomposing and oxidizing the cyanide is discharged to a discharge line for treated water 7. If the oxidizing agent remains in the treated water, it is separately treated as required by a treatment method used industrially.

However, according to the study by the present inventors, in the above-mentioned method of decomposing and oxidizing an iron cyanide complex compound in the conventional method, iron ions dissociated from the iron cyanide complex in a one-step reaction are soluble. Form fine precipitates such as low hydroxides. The fine precipitate absorbs a wide range of wavelengths of light energy. It was found that when the amount of fine precipitates increased with the progress of the first-stage reaction, the amount of light energy absorbed increased, and the light energy consumed for the production of free cyan decreased. Therefore, as the treatment proceeds, the decomposition of the iron cyanide complex compound into free cyan in the first-stage reaction is delayed. For example, the comparative example shown in [Table 1] is a result obtained by adding hydrogen peroxide to cyan wastewater containing an iron cyanide complex compound and performing the treatment by the conventional treatment method. It can be seen that the decomposition rate of the cyanide compound becomes extremely slow as the decomposition of the cyanide compound proceeds. Further, under these conditions, treating the concentration of cyanide in wastewater to 1 mg / L or less, which is equal to or less than the environmental emission standard value, is not an economical treatment method because the cost of light energy is greatly increased.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the cyanide concentration in wastewater to a low concentration while maintaining the effective utilization of light energy used for the decomposition of the iron cyanide complex compound at a high level. It is an object of the present invention to provide a new treatment technology of cyan wastewater containing an iron cyanide complex compound.

[0006]

SUMMARY OF THE INVENTION The present inventors have found that iron ions dissociated from an iron cyanide complex compound in the conventional method form fine precipitates such as hydroxides, and the precipitates absorb light energy. As a result, the present invention described below has been made from novel findings such as Comparative Examples in which the decomposition treatment of the cyanide is delayed.

That is, the present invention relates to (1) a method for treating cyanide wastewater containing an iron cyanide complex compound, wherein sulfuric acid or sulfuric acid and a soluble sulfate and an oxidizing agent are added in advance, and then ultraviolet to visible light. A wastewater treatment method comprising irradiating a light beam to decompose and oxidize an iron cyanide complex compound; (2) sulfuric acid or an amount of sulfuric acid and soluble sulfate added to the iron cyanide contained in cyan wastewater. (1) The method according to (1), wherein the amount is at least equal to the total amount of iron ions of the complex compound, (3) Use of a gas containing ozone or an aqueous solution containing hydrogen peroxide as an oxidizing agent. The method according to (1), which is characterized in that:

The iron ion dissociated in the first-stage reaction by irradiation of ultraviolet light to visible light is converted into a compound having a stable structure in which light energy is hardly absorbed and a compound having high solubility in water, thereby forming a precipitate. In order to prevent the formation, sulfuric acid or
Sulfuric acid and soluble sulfates and oxidizing agents are added. Thus, the iron ion dissociated from the iron cyanide complex in the first reaction once forms a single salt of sulfuric acid and iron sulfate,
Since this simple salt is unstable, it immediately forms a double salt with another sulfate formed in addition to iron or added soluble sulfate in wastewater. This double salt of iron sulfate has a stable structure and is a compound having high solubility in water, so that it cannot precipitate and does not hinder light transmission. By forming a double salt of iron sulfate, the treatment can be performed without impairing the effective use of light energy from ultraviolet to visible light in the first-stage reaction, and the concentration of the cyanide compound in the wastewater can be reduced to a low concentration. It is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 12 is a sulfuric acid and soluble sulfate supply device, 13 is an oxidant supply device, 1
4 is a line mixer, 16 is a light source for ultraviolet to visible light 1
A reaction tank equipped with 5, a supply pipe 11 for cyan wastewater, 17
Is a treated water discharge pipe. In the cyan waste water containing the iron cyan complex compound sent in through the supply pipe of cyan waste water of No. 11, the sulfuric acid or the sulfur of sulfuric acid and the soluble sulfate are contained in the cyan waste water in advance. After the addition of an oxidizing agent and preferably an equimolar amount or more of the total amount of ions, the cyan wastewater is irradiated with ultraviolet to visible light. The decomposition and oxidation treatment of the iron cyanide complex compound proceeds in a two-stage reaction. Here, as the soluble sulfate,
Sulfates containing alkali metals, alkaline earth metals, and ammonium are exemplified. Examples of the oxidizing agent include a gas containing ozone, an aqueous solution containing hydrogen peroxide, and a chlorine-based oxidizing agent such as sodium hypochlorite and sodium perchlorate. An aqueous solution containing hydrogen is preferred. In the first-stage reaction, the iron-cyan complex compound is excited by the irradiated light energy and decomposed into free cyanide and iron ions, which are easily oxidized. In the second-stage reaction, free cyanide generated by decomposition is 13
Is oxidized by the oxidizing agent supplied from the oxidizing agent supply device, and is converted into carbonate (carbon dioxide) and nitrogen. The wastewater thus decomposed and oxidized by the cyanide is 1
The treated water is discharged to the discharge pipe of No. 7. When the oxidizing agent remains in the treated water, it is separately treated as necessary by a known treatment method used industrially.

Although the above-mentioned processing method is of a continuous type, the present invention is not limited to this method, but may be of course a batch type or the like. That is, FIG. 3 shows a schematic view of an apparatus embodying the embodiment of the present invention and the comparative example. Examples 1 and 2 and Comparative Example of the present invention shown in Table 1 are the results of tests performed using this batch apparatus. In a reaction tank 26 equipped with a light source 25 (1 kW medium-pressure mercury lamp), cyan wastewater containing an iron cyanide complex compound is supplied to a cyan wastewater supply pipe 2.
1 and sulfuric acid or sulfuric acid and soluble sulfuric acid are added from a salt sulfuric acid and soluble sulfate supply device 22 and an oxidizing agent is added from an oxidizing agent supply device 23. Irradiation was performed to decompose and oxidize the iron cyanide complex compound. In the comparative example, the light source 25 was used without adding sulfuric acid or sulfuric acid and a soluble sulfate.
(1 kW medium-pressure mercury lamp)
After feeding the cyan wastewater containing the iron cyan complex compound and adding the oxidizing agent, the mixture was irradiated with ultraviolet rays while stirring to decompose and oxidize the iron cyan complex compound.

[0011]

【Example】

(Example 1) Sulfuric acid was added to cyanide wastewater containing potassium ferrocyanide having a cyan concentration of 102 mg / L.
00 mg / L and hydrogen peroxide were added at a concentration of 1000 mg / L, and irradiation with ultraviolet light was performed to decompose and oxidize the iron cyanide complex compound. The residual cyan concentration with respect to the reaction time was sampled from the sampling port 28 and measured. The results are shown in [Table 1].

Example 2 100 mg as cyan concentration
/ L 1000 mg / L sulfuric acid and 1000 mg sodium sulfate in cyanide wastewater containing potassium ferrocyanide
mg / L and hydrogen peroxide were added so as to be 1000 mg / L, and irradiation with ultraviolet rays was performed to decompose and oxidize the iron cyanide complex compound.

(Comparative Example) A cyan concentration of 102 mg /
L: Add hydrogen peroxide to cyan wastewater containing potassium ferrocyanide at a concentration of 1000 mg / L;
Irradiation with ultraviolet light was performed to decompose and oxidize the iron cyanide complex compound.

[0014]

[Table 1]

A comparison between Examples 1 and 2, which are the processing method of the present invention, and Comparative Examples, which is a conventional processing method, shows that by using the present invention, it is possible to decompose a cyan compound without impairing the effective use of light energy. It can be seen that the processing speed of the oxidation treatment is significantly improved. Further, the residual concentration of the cyanide compound can be easily processed up to 0.5 mg / L.

[0016]

The present invention provides a new technology for treating cyanide wastewater containing an iron cyanide complex compound, wherein iron ions dissociated during the treatment of the cyanide complex compound are converted into a double salt of iron sulfate. Thus, the effective use of light energy for decomposing the iron cyanide complex compound into free cyanide and iron ions was not impaired, and the cyanide concentration in the wastewater could be efficiently reduced to a low concentration.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an apparatus for implementing a conventional method.

FIG. 2 is an explanatory diagram showing an apparatus for performing the method of the present invention.

FIG. 3 is an explanatory view showing an apparatus in which an example and a comparative example are implemented.

[Description of Signs] 1 Supply pipe for cyan wastewater 3 Oxidant supply device 5 Light source 6 Reaction tank equipped with ultraviolet to visible light source 7 Discharge pipe for treated water 11 Supply pipe for cyan wastewater 12 Sulfuric acid and soluble sulfate supply Apparatus 13 Oxidant supply device 14 Line mixer 15 Light source 16 Reaction tank equipped with ultraviolet to visible light source 17 Discharge pipe of treated water 21 Supply pipe of cyan wastewater 22 Sulfuric acid and soluble sulfate supply apparatus 23 Oxidant supply apparatus 25 Light source 26 Reaction tank provided with a light source of ultraviolet to visible light 27 Discharge pipe of treated water 28 Sampling port 29 Stirrer 30 Stirrer blade

Continued on the front page (72) Inventor Hiroharu Miyagawa 1190 Kasama-cho, Sakae-ku, Yokohama City, Kanagawa Prefecture Mitsui Toatsu Chemicals Co., Ltd.

Claims (3)

[Claims] 1. A method for treating cyanide wastewater containing an iron cyanide complex compound, comprising adding sulfuric acid or sulfuric acid and a soluble sulfate and an oxidizing agent in advance, and irradiating ultraviolet light to visible light with iron. A wastewater treatment method, comprising decomposing and oxidizing a cyan complex compound. 2. The amount of sulfuric acid or the amount of sulfuric acid and soluble sulfate added is at least equal to the total amount of iron ions of the iron cyanide complex compound contained in the cyanide wastewater. The described method. 3. The method according to claim 1, wherein a gas containing ozone or an aqueous solution containing hydrogen peroxide is used as the oxidizing agent.