JPS5931397B2 - Treatment method for cyanide-containing wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating cyanide-containing wastewater, and more specifically, to remove cyanide from wastewater by bringing the cyanide-containing wastewater into contact with oxygen in the presence of a Raney copper catalyst to oxidize and decompose the cyanide. It's about how to do it.

Cyanide here means cyanides such as cyanide ions (including hydrogen cyanide) and cyanide complex ions.

Currently, the methods for removing cyanide from wastewater include the alkaline chlorine method, which makes the wastewater alkaline and injects chlorine to oxidize and decompose the cyanide, the ozone oxidation method, which applies the strong oxidizing power of ozone to decompose cyanide compounds, and the non-alkaline method. Electrolytic oxidation method, which uses a soluble electrode to electrolyze wastewater and perform an oxidation reaction; Prussian method, which adds ferrous sulfate to wastewater and precipitates and removes it as ferriferrocyanide; and biological methods that decompose and remove cyanide through the action of microorganisms. There are various processing methods.

However, all of these methods have the following drawbacks.

In other words, the alkali chlorine method is the most common treatment method, but the treatment is carried out in two stages, and the p
H value (first stage pH 10 or more, second stage pH 7.5-8
．． 0), and the amount of oxidizing agent added, amount of residual chlorine, etc. must be constantly monitored.

The ozone oxidation method has advantages such as the product after the reaction does not contain any harmful substances and the reduced form of ozone (02) is completely harmless, but because the reaction must be carried out in a gas-liquid state, , We have devised equipment to make 100% of the ozone react (for example, we have two oxidation towers, put a packing inside the tower, and bring the wastewater and ozone into contact with each other in a countercurrent manner at a high rate, so that the ozone reacts 100% with the first oxidation tower. (e.g., using the exhaust gas from the second oxidation tower to fully utilize the residual ozone) is necessary.

Furthermore, it is necessary to perform coagulation and precipitation treatment of metal hydroxides produced as a result of cyanide decomposition.

. In addition, the high cost of ozone is also a problem. The electrolytic oxidation method is characterized by the efficient and economical treatment of concentrated waste liquid, but when treating the residual cyanide concentration to 11,000 pp or less, it consumes a large amount of electricity and the treatment cost increases. It is necessary to switch to another treatment method from this stage.

The Prussian method is suitable for the treatment of cyanide-containing wastewater that contains iron and produces stable iron-cyanide complex salts that are difficult to oxidize and decompose even with other cyanide treatment methods, and the treatment cost is extremely low. If the amount of ferrous sulfate added is small, the resulting complex salt remains in a soluble state, resulting in a high degree of coloration of the treated water.

Moreover, when the pH is high, the residual ferrocystic acid residue in the P solution increases.

Furthermore, since it is easily oxidized by oxygen in the air and becomes ferriferrotype and dissolves, it is difficult to reduce the cyanide concentration of treated water to several ppm or less.

In addition, the biological treatment method has the disadvantages peculiar to microbial reactions, such as maintaining a pH suitable for microbial treatment and adding nutrients (nitrogen, nitrogen, etc.).
In addition to requiring complicated operations such as adjusting the activated sludge concentration (MLSS), and treating surplus sludge (phosphorus content, etc.), if the cyanide concentration is high, it must be diluted due to toxicity problems, and it is necessary for microbial decomposition. It has disadvantages such as long contact time.

In order to overcome these drawbacks of conventional cyanide treatment technology and effectively treat cyanide-containing wastewater in a short period of time, the present inventors have repeatedly searched and researched catalysts for wastewater treatment. They discovered that Raney copper is effective in the oxidation treatment of metals, and completed the present invention.

The effluent water quality standard for cyanide-containing wastewater is "not detected (tolerable value of 0.01■/or less)", which is an extremely strict value of 75@
It is marked with an S.

In general, equipment for treating wastewater containing toxic substances such as cyanide is strongly required to be reliable, safe, easy to operate and maintain, and the like.

The present invention is characterized in that cyanide-containing wastewater is brought into contact with one or more selected from the group consisting of pure oxygen, oxygen-containing scum, and oxygen-generating substances in the presence of a Raney copper catalyst. The present invention provides a method for treating cyanide-containing wastewater.

The Raney copper catalyst used in the present invention refers to copper and one or two metals (magnesium, aluminum, zinc, iron, nickel, tin, lead, silica, titanium, boron, etc.) that are attacked by water, alkalis, acids, etc. This refers to the product obtained by applying an alkaline aqueous solution such as IJum (hydroxide) or an acid aqueous solution such as hydrochloric acid to an alloy with a metal or more, and the amount of metal eluted outside the copper plate by the alkali or acid is particularly limited. Not done.

Also, the weight ratio of copper and metal outside the copper plate is usually 1:
1 is used, but it is not limited to this ratio.

An example of a Raney copper catalyst preparation method is 1:1 by weight.
When a sodium hydroxide aqueous solution is applied to the copper-aluminum alloy, an elution reaction occurs rapidly, and a Raney copper catalyst in which more than 90% of the aluminum in the alloy is eluted is obtained.

In this way, the Raney copper catalyst becomes porous due to the elution of metal outside the copper plate.

The Raney copper catalyst obtained as described above is usually adjusted to have a particle size of about 200 mesh from the viewpoint of strength.
It is desirable to select an appropriate particle size depending on the method of contact reaction with cyanide-containing wastewater, and it is not necessary to select this particle size.

Next, the method of contacting the cyanide-containing wastewater with the Raney copper catalyst is not particularly limited, and any method such as a completely mixed type, fixed bed, fluidized bed, or moving bed may be used.

Further, the oxygen necessary for oxidative decomposition may be dissolved in the raw cyanide-containing wastewater in advance, or may be supplied in a reaction tank.

Further, oxygen may be pure oxygen gas, liquid oxygen, air, oxygen-containing waste gas, oxygen-generating substances such as hydrogen peroxide, etc., and may be used alone or in combination.

Regarding the amount of oxygen supplied, it is sufficient to supply about 1.2 times the theoretical amount of oxygen required to oxidize cyanide.

However, if the concentration of cyanide to be treated is low and the amount of oxygen required for its oxidation is already contained in the wastewater to be treated, it is natural that pure oxygen, oxygen-containing gases, and oxygen-generating substances will be used. There is no need for contact with either.

Further, the reaction temperature and reaction pressure may be normal temperature or normal pressure, and there is no need to particularly raise the temperature or apply pressure.

However, if it is desired to increase the reaction efficiency, this can be achieved by increasing the temperature or applying pressure.

According to the present invention, cyanide in cyanide-containing wastewater can be easily removed by oxidative decomposition using oxygen in the presence of a Raney copper catalyst at room temperature and pressure, which requires less complicated operations than conventional treatment methods. It has the advantage of being able to be oxidized and decomposed in a short period of time.

Furthermore, the reaction equipment is also smaller compared to microbial treatment.

Furthermore, when the Raney copper catalyst contains aluminum, iron, etc., these are oxidized and eluted as hydroxides, which have the effect of coagulating suspended substances in wastewater.

The present invention will be explained in detail below using examples.

Example 1 Two types of cyanide-containing wastewater with different concentrations were placed in two 2-ton beakers with 1.5 liters of each type and mixed with a Raney copper catalyst (particle size 200 mesh, copper content 96.2 wt%, aluminum content 3.8 wt%). , Yoken Fine Chemical■
An experiment of oxidative decomposition of cyanide was carried out on a sample containing 30 cc of Cyanide (manufactured by J.D. Co., Ltd.) and a sample without a catalyst, while blowing air and stirring.

The results are shown in Table-1.

As is clear from Table 1, no oxidative decomposition of cyanide is observed in the non-catalyzed product when the contact time is less than 1 hour.
It can be seen that oxidative decomposition is easily carried out with the addition of Raney copper catalyst.

Example 2 Cyan Raney copper catalyst wet oxidation treatment method, alkali chlorine method, electrolytic oxidation method, and microbial treatment method (sprinkling bed)
We conducted a comparative experiment with

The results are shown in Table-2.

Experimental conditions (1) Wet oxidation method using Raney copper catalyst (batch method) Catalyst amount 30 cc Pressure Normal pressure Temperature 25°C Air amount 60 t/Hr Wastewater treatment amount 1.5 t (Alkali chlorine method (batch method) % formula % Sodium used) Temperature: 26°C pH: 8,95 Waste water treatment amount: 1 t (3) Electrolytic oxidation method (batch method) Electrode: 70 cm long x 25 cm wide x 3 cage electrode spacing: 2
5mm Current 4A Power consumption 192W, Hr Wastewater treatment amount 2t (4) Microbial treatment method (sprinkling fluidized bed) batch type % type % Filler Grid wastewater treatment amount 10t As is clear from Table 2, the alkali chlorine method was used. However, since a large amount of oxidizing agent is used relative to the amount of cyanide to be treated, the processing cost becomes high.

Furthermore, the electrolytic oxidation method consumes a large amount of power and has high processing costs.

On the other hand, microbial treatment methods have very slow reaction rates.

In contrast, it can be seen that in the wet oxidation method using a Perranay copper catalyst, the reaction rate is fast and the oxidation can be carried out to the permissible amount (0.01/1) or less in a short time.

Claims (1)

[Claims] 1. Cyanide-containing wastewater, which is characterized by contacting cyanide-containing wastewater with one or more selected from the group consisting of pure oxygen, oxygen-containing gas, and oxygen-generating substances in the presence of a Raney copper catalyst. Wastewater treatment methods.