JPS58193788A - Treatment of waste water of complex iron cyanide - Google Patents

Abstract

PURPOSE:To treat complex iron cyanide to a low concn. by making effective use of light, by adding an oxidizing agent to waste cyanide water contg. complex iron cyanide, etc. coexisting with a reductive material so as to oxidize the same prior to oxidative decomposition of said waste water by combination use of light and ozone. CONSTITUTION:An oxidizing aget of hydrogen peroxide or hypochlorite is added from an storage tank 10 for oxidizing agent to the water cyanide water which contains the complex iron cyanide coexisting with a reductive material and/or in the form of ferrocyanide and is pumped up from a raw water tank 12. The waste water is then fed into a reaction vessel 9. The reductive material contained in the waste cyanide water is oxidized in said vessel to oxidize the ferrocyanide to ferricyanide. The waste water subjected to such oxidation treatment is conducted into an ozone reaction vessel 2 where the waste water is subjected to an ozone oxidation treatment under irradiation of light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing persistent iron complex cyanide.

In general, cyanide-containing wastewater (hereinafter referred to as cyanide wastewater) generated in industrial processes is required to be treated strictly because cyanide compounds have strong toxicity.

Oxidation methods are usually used to treat this cyanide wastewater. An example of an oxidation method is an alkali-chlorine method in which cyanide wastewater is treated with a chlorine-based oxidizing agent under highly alkaline conditions. However, iron complex cyanide compounds have a very stable structure and cannot be easily oxidized and decomposed by the above-mentioned alkali-chlorine method. Based on this background, a method is used to treat waste liquid containing iron-complexed cyanide by irradiating it with ultraviolet or visible light to convert the iron-complexed cyanide into a form that can be easily oxidized and decomposed, followed by oxidation treatment. ing.

Figure 1 shows a method for treating wastewater containing iron-complex cyanide such as ferrocyanate and ferricyanide using a combination of light and ozone. In FIG. 1, 1 is a waste water feed pump, 2 is an ozone reactive species, and a light source 3 is installed inside this ozone reactive species 2. 4 is an ozone generator for making ozone, 5
is an ozone decomposer that decomposes unreacted ozone discharged from the ozone reaction species 2; 6 is a raw water inlet; 7 is a treated water outlet; and 8 is a diffuser plate provided at the bottom of the ozone reaction tank 2.

In order to treat iron-complexed cyanide wastewater using the apparatus shown in FIG. The complex cyanide is irradiated with ultraviolet rays or visible light from a light source 3 to cause intramolecular excitation. There are many excited states of iron-complexed cyanide, and an example is the excitation of the ligand field between a gold m atom and a cyanide molecule. As a result, a substitution reaction occurs between water molecules as a solvent and cyan molecules fixed as ligands. Therefore, cyan molecules are liberated and become cyan ions, and the iron complex becomes an aco complex containing water molecules. Further, this aco complex is sequentially photoexcited, and the cyan molecules of the ligands are replaced with water molecules, and finally become iron ions. Therefore, the liberated cyanide ions are usually called free cyanide, and are easily converted into cyanic acid and cyanide by oxidizing agents.
Furthermore, carbon dioxide and nitrogen are also oxidized. In the apparatus shown in FIG. 1, ozone as an oxidizing agent enters the ozone reaction tank 2 through an ozone generator 4 and a diffuser 8 in the lower part of the ozone reaction tank 2, forming fine bubbles in the form of ozone-containing gas. Free cyanide is oxidized. Wastewater in which cyanide compounds have been oxidized and decomposed is discharged from the lower treated water outlet as treated water. ``In addition, the above ozone reaction tank 2
The gas discharged from the upper part of the ozone contains unreacted ozone, and this ozone is completely decomposed in the ozone decomposer 5 and then discharged to the outside of the system.

Cyanide, which becomes free cyanide due to light illumination, can be oxidized and decomposed using chlorine-based oxidizing agents, but in order to efficiently treat it down to low concentrations, it is economically advantageous to use ozone, which has strong oxidizing power. It is said that

However, when the conventional treatment method of light, ozone, and iron-complexed cyanide as described above is applied to water to be treated where a reducing agent coexists or ferrocyanate and ferricyantoca coexist, the treatment takes an extremely long time. It also has the disadvantage that cyan processing up to low density cannot be performed. Curve (a) in Figure 2 is the result of light irradiation and ozone treatment using a ferrocyan aqueous solution containing 200 ppm of cyanide.
Even if the reaction was carried out for 3 hours, the cyanide treatment was carried out to only about 10 ppm, and even if the reaction time was extended.

The residual cyanide concentration did not decrease below 11 tons. Furthermore, when sodium thiosulfate 100/l is present as a reducing agent in the ferrocyan aqueous solution, t
As shown in the curve in Figure 2, tc shows that even in the early stages of the reaction, the cyanide concentration decreases drastically, and the treatment time increases as the ozone supplied is consumed in the oxidation of sodium thiosulfate. Furthermore, the cyanide concentration reached was around 15 ppm. In any of the above cases, if the amount of irradiated light is significantly increased by 1.

Therefore, the inventor of this invention proposed that if the light irradiation effect in the conventional processing power method described above decreases, the cyanide concentration in the final treatment agglomerate should be increased to 1Iiii 1 degree. I did not bother to consider the reason why the limit exists. As a result, three causes became clear. (′
The first point is that Ferrin Anne has a lower light absorption rate than Ferrin Anne, so even if the vehicle ahead is irradiated by 10 inches, the
One of the reasons is that the efficiency of generating free cyan from armor cyan is low. The second point is that some iron-complexed cyanide sequentially releases cyanide molecules as ligands and becomes trivalent iron ions. This Prussian blue is a poorly soluble and stable cyanide complex salt, and at the same time has the property of easily absorbing ultraviolet rays and visible light. Therefore, most of the irradiated light is absorbed by the Glucian blue and becomes ineffective. Thirdly, the coexistence of reducing substances preferentially consumes ozone, and during this time cyanide ions liberated by light are incorporated into the rehydration complex by a reverse reaction, reducing the effect of light irradiation. will not be kept alive.

This invention solves the drawback that the conventional treatment method for iron-complex cyanide using a combination of light and ozone, as described above, cannot economically process down to low concentrations. The purpose of the present invention is to provide a processing method that can process iron-complex cyanogen to a lower concentration than conventional processing methods using a light source.

To achieve this objective, the method for treating iron-complexed cyanide wastewater according to the present invention comprises treating cyanide wastewater containing iron-complexed cyanide coexisting with reducing substances and/or in the form of ferrocyanate using a combination of light and ozone. Prior to the treatment of oxidizing and decomposing cyanide, an oxidizing agent is added to the raw cyanide wastewater to oxidize coexisting reducing substances and/or to oxidize ferrocyan, which is a reduced form of iron-complexed cyanide, to ferricyan. This is a sign.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows an apparatus for carrying out the method for treating iron complex cyanide wastewater according to the present invention. In FIG. 3, 1 to 5.7.8 are the same parts as the conventional apparatus shown in FIG.

9 is a reaction tank for oxidizing reducing substances in the raw cyanide wastewater as a pretreatment and oxidizing the coexisting 7 Elysian to 7 Elysian, IO is an oxidizing agent storage tank, and 11 is an oxidizing agent injected into the raw cyanide wastewater. 12 is the raw water tank,
13 is a pump for guiding the cyanide wastewater from the reaction tank 9 to the ozone reaction tank 2; K is a pump for treating the iron-complex cyanide wastewater with the device shown in FIG. 3;
First, the raw cyanide wastewater pumped up from the raw water tank 12 by the pump 1 is added to the oxidizer storage tank 10 using the pump 7''11.
An oxidizing agent is added thereto and the mixture is fed into the reaction tank 9. In this reaction tank 9, ferrocyan is oxidized to ferricyan simultaneously with the oxidation of the reducing substance contained in the raw cyanide wastewater. In this way, the raw cyanide wastewater whose iron complex salt form has been completely converted to ferricyanide is guided into the ozone reaction tank 2 by the pump f13, and is subjected to ozone oxidation treatment while being irradiated with light. Note that the ozone reaction tank 2 and its subsequent operations are the same as those in the conventional treatment method, so a description thereof will be omitted.

Next, the effects of this invention will be explained. As mentioned above and as follows, the drawbacks of conventional processing methods can be easily overcome by oxidizing the reducing substance and oxidizing ferrocyan to ferricyan. In other words, by converting ferrocyan to ferricyan in advance, the problem of low absorbance of ferrocyan can be solved, and trivalent iron ions and ferrocyan do not coexist. The generation of Prussian blue can be prevented. Furthermore, since the reducing substance is oxidized in advance, the cyanide ions liberated in the initial stages of light irradiation and ozone treatment do not form a re-complex, and are therefore quickly oxidized by ozone.

The processing result using the above-mentioned processing method of the present invention is lc as shown by the curve (e) in FIG. This song! (C) with 200 ppm ferrocyan as the initial seapon;
To a mixed solution of 100 ppm sodium thiosulfate, 1100 ppm of hydrogen peroxide was added as an oxidizing agent in advance,
Thereafter, a treatment similar to the conventional treatment method described above using both light and ozone was performed.

As is clear from the song &1 (cJ in Figure 3), iron-complex cyanide treatment was possible down to a low concentration within a short time.

In addition, in this invention, the same effect as described above can be obtained by using a hypochlorite-removing salt such as VC bleaching powder (1 g of VC bleaching powder) in place of the above-mentioned hydrogen peroxide as an oxidizing agent. . In this invention, the amount of the oxidizing agent used is sufficient to oxidize the ferrocyanide complex salt to the ferricyanide complex salt and to oxidize the coexisting reducing substance. Excessive oxidizing agent causes ozone consumption during ozone treatment, resulting in a decrease in ozone utilization efficiency, which is undesirable.

Examples and Comparative Examples Fe(CN) - In wastewater with a CN concentration of 200 ppm, 100 ppm of NILtStOs and 100 ppm of Le
pp! ml was added, stirred and reacted for 30 minutes, and then subjected to photo-ozone treatment under the following conditions (Example).

High pressure mercury lamp 100W Ozone injection 2047 minutes Semi-batch treatment (Continuous ozonated gas injection) For comparison, in the above example, Na, S, α and ) & Ot were not added (Comparative Example 1), and H202 was not added. The same procedure was carried out for (2).

Changes in the residual *CN# degree of these wastewaters over time were determined and the results are shown in the table below.

As with the soil surface, the CN concentration was reduced on the order of several hundred minutes after 10 hours due to the present invention.

As explained above, by using the method for treating iron-complexed cyanide wastewater according to the present invention, the irradiated light can be used efficiently, and even with a small capacity light source, it is possible to treat iron-complexed cyanide to a low degree of conversion in a short period of time. Effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an apparatus used in a conventional iron-complex cyanide wastewater treatment method, and FIG. 2 is a reaction time-cyanide concentration relationship diagram showing the results of treatment with the conventional treatment method and the treatment method of the present invention.
FIG. 3 is a schematic diagram showing an example of an apparatus used in the method for treating iron-complex cyanide wastewater according to the present invention. 2... Ozone reaction tank, 3... Light source, 4... Ozone generator, 9... Reaction tank, 10... Shunting agent storage hinoki. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Makoto Kuzuno - Figure 1 Figure 2 (a) Fe (CN) knee: CN・200ppm+No
zSzO3・100p100pp Fe(CN):'-
CN・200ppm reaction reaction (H")

Claims (2)

[Claims] (1) An oxidizing agent is added to the raw cyanide wastewater prior to treatment of cyanide wastewater containing ffi-elementary physical substances and/or iron-complex cyanide in the form of ferrocyane to oxidize and decompose the contained cyanide using a combination of light and ozone. 1. A method for treating iron-complexed cyanide wastewater, the method comprising: adding a coexisting reducing substance, and/or oxidizing ferrocyane, which is a reduced form of iron-complexed cyanide, to ferricyanide. (2) The method for treating iron-complexed wastewater according to claim 1, which uses hydrogen peroxide or a hypochlorite-based oxidizing agent as the oxidizing agent.