JPH1057974A - 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 an alkali agent and an oxidizing agent to a cyanic waste water containing an iron-cyanide complex, adjusting pH alkaline and oxidizing a free cyanide while separating and removing a precipitate from the waste water. SOLUTION: The cyanic waste water is irradiated with UV rays to visible rays in a reactor 16 provided with a light source 15 after adding the alkali agent to the cyanic waste water containing the iron-cyanide complex from an alkali agent feed device 12 to adjust pH adding the oxidizing agent from an oxidizing agent feed device 13. 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 executed 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 the 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, etc., but leaked from industrial waste treatment. A method for treating iron cyanide complex compounds contained in leaked water or contaminated water is also possible.

[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 cyanide complex compound is excited by the irradiated light energy and is 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. Wastewater that has undergone decomposition and oxidation treatment of cyanide
The treated water is discharged to the discharge pipe of No. 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-described method of decomposing and oxidizing an iron cyanide compound by 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. The decomposition rate of cyanide is
It can be seen that the progress has been extremely slow with the progress of the decomposition treatment of the cyanide compound. Further, under this condition, the concentration of the cyanide in the wastewater is adjusted to 1 mg / L which is equal to or less than the environmental emission standard value.
Processing below is not an economical processing 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. Thus, 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 provides (1) an alkali agent and an oxidizing agent which are added in advance to an iron-cyan complex compound-containing cyanine wastewater, and the pH is adjusted to alkali;
Wastewater treatment characterized by oxidizing free cyanide while irradiating visible light and separating and removing precipitates such as hydroxides generated from iron ions dissociated by decomposition of the iron cyanide complex compound from wastewater as needed. Method (2) The method according to (1), wherein the pH of the cyanide wastewater containing the iron cyanide complex compound is 7.5 or more and 12 or less, (3)
The method according to (1), wherein a gas containing ozone, an aqueous solution containing hydrogen peroxide, or a chlorine-based oxidizing agent is used as the oxidizing agent.

[0007] In order to oxidize free cyanide while separating and removing precipitates such as hydroxides generated from iron ions dissociated in the first stage reaction from wastewater as needed, a cyanide containing an iron cyanide complex compound must be prepared in advance. An alkaline agent and an oxidizing agent are added to the wastewater to adjust the pH to alkaline. The iron ions dissociated from the iron cyanide complex in the first-stage reaction by irradiation of ultraviolet light to visible light thus form a precipitate such as a hydroxide. By performing treatment while separating and removing precipitates such as hydroxides from wastewater as needed, the treatment can be performed without impairing the effective use of light energy from ultraviolet to visible light in the first-stage reaction, and It is possible to process the cyanide in the medium down to a low concentration.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the present invention. 12
Is an alkali agent supply device, 13 is an oxidant supply device, 14 is a line mixer, 16 is a reaction tank provided with a light source 15 for ultraviolet to visible light, 18 is a filtration device, 11 is a supply pipe for cyan wastewater, and 17 is treated water. Discharge pipe. The pH of the cyan waste water containing the iron cyan complex compound fed through the supply pipe of the cyan waste water of No. 11 is preferably adjusted to 7.5 or more and 12 or less in advance with the alkali agent supply device of 12 to adjust the oxidizing agent. After the addition, 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. 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. Precipitates such as hydroxides formed from iron ions are 18
Is optionally filtered off. The filtration device may be a device used industrially, such as a filter press or sand filtration, and the pore size of the filter cloth or the like may be several microns to several tens microns. In the second-stage reaction, free cyan generated by the decomposition is oxidized by the oxidizing agent supplied from the 13 oxidizing agent supply devices, and is converted into carbonate (carbon dioxide) and nitrogen. The wastewater in which the cyanide has been decomposed and oxidized is discharged to the discharge pipe for the 17 treated water. Here, as the oxidizing agent, a gas containing ozone, an aqueous solution containing hydrogen peroxide, sodium hypochlorite,
A chlorine-based oxidizing agent such as sodium peroxide may be mentioned, and a gas containing ozone and an aqueous solution containing hydrogen peroxide are particularly preferable. 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 a continuous method, it is not limited to this method, but may be a batch method 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 of the present invention shown in Table 1
And Comparative Examples are the results of tests performed in a batch system. Hereinafter, cyan wastewater containing an iron cyan complex compound is fed into a reaction tank 26 equipped with a light source 25 (1 kW medium-pressure mercury lamp) from a supply pipe 21 of cyan wastewater, and an alkali agent is supplied from an alkali agent supply device 22. To adjust the pH,
After the oxidizing agent was added from the oxidizing agent supply device 23, the mixture was irradiated with ultraviolet rays while being stirred by the stirring device 30. Also, during the treatment, the precipitate of hydroxide precipitates in the wastewater, so that the wastewater during the treatment is circulated by a pump, and is filtered and removed by a filtration device 28 as needed. went. As the alkali agent, a known alkali agent containing an alkali metal, an alkaline earth metal, and ammonium is used. A filter cartridge (pore size: 10 microns) manufactured by Pall Corporation was used as a filter medium for removal by filtration. In the comparative example, the cyan wastewater containing the iron cyan complex compound was placed in a reaction tank 26 equipped with a light source 25 (1 kW medium-pressure mercury lamp) without performing the filtration and removal operation of the precipitates such as hydroxides. , An oxidizing agent was added thereto, and then ultraviolet irradiation was performed with stirring to decompose and oxidize the iron cyanide complex compound.

[0010]

【Example】

(Example 1) A sodium hydroxide solution was added to cyan wastewater containing potassium ferrocyanide having a cyan concentration of 120 mg / L, the pH was adjusted to 9, hydrogen peroxide was added to 1000 mg / L, and ultraviolet light was added. 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 29 and measured. The results are shown in [Table 1].

(Embodiment 2) Cyan concentration of 120 mg
/ L: Add sodium hydroxide solution to cyan wastewater containing potassium ferrocyanide, adjust pH to 11, add sodium hypochlorite to 1000 mg / L, irradiate ultraviolet rays Compound decomposition and oxidation treatment steps were performed.

(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.

[0013]

[Table 1]

A comparison between Examples 1 and 2, which are the processing method of the present invention, and a Comparative Example, which is a conventional processing method, shows that the use of the present invention makes it possible to decompose the cyan compound without impairing the effective use of light energy. It can be seen that the processing speed of the oxidation treatment is remarkably improved. In addition, the residual concentration of the cyanide can be easily reduced to 0.1 mg / L.

[0015]

Industrial Applicability The present invention provides a new technology for treating cyanide wastewater containing an iron cyanide complex compound. The precipitate such as a hydroxide formed during the treatment of the iron cyanide complex compound is optionally filtered off. By removing it, the effective use of light energy for decomposing the iron cyanide complex compound into free cyanide and iron ions is not impaired, and the cyanide concentration in the wastewater can be efficiently treated 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.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 supply pipe for cyan wastewater 3 oxidant supply apparatus 5 light source 6 reaction tank provided with a light source for ultraviolet to visible light 7 discharge pipe for treated water 11 supply pipe for cyan wastewater 12 alkali agent supply apparatus 13 oxidant supply apparatus 14 line mixer Reference Signs List 15 light source 16 reaction tank provided with ultraviolet to visible light source 17 treated water discharge pipe 18 filtration device 21 cyan wastewater supply pipe 22 alkaline agent supply device 23 oxidant supply device 25 light source 26 equipped with ultraviolet to visible light source Reaction tank 27 treated water discharge pipe 28 filtration device 29 sampling port 30 stirring device 31 stirring blade

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C02F 1/78 ZAB C02F 1/78 ZAB (72) Inventor Hiroharu Miyagawa Kasama-cho, Sakae-ku, Yokohama, Kanagawa Prefecture 1190 Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. An iron and cyanide complex-containing cyanide wastewater is added with an alkali agent and an oxidizing agent in advance to adjust the pH to alkali, and then irradiated with ultraviolet to visible light to dissociate iron by decomposition of the iron cyanide complex compound. A wastewater treatment method comprising oxidizing free cyanide while separating and removing precipitates such as hydroxides generated from ions from wastewater as needed. 2. A p-cyanide wastewater containing an iron-cyan complex compound
2. The method according to claim 1, wherein H is not less than 7.5 and not more than 12. 3. The method according to claim 1, wherein a gas containing ozone, an aqueous solution containing hydrogen peroxide or a chlorine-based oxidizing agent is used as the oxidizing agent.