JPS5834082A - Treatment of cyanide waste water - Google Patents

Abstract

PURPOSE:To decompose cyanoferate complex salt, etc. which have been difficult to decompose so far, by adding NaOH or H2SO4 together with a catalyst to cyanide waste water, reacting it with ozone to decompose it, and then reducing it with Na2SO3. CONSTITUTION:Cyanide waste water having cyanide content below 10ppm is introduced into a pretreating vessel 1 provided with an agitator, where it is made alkaline by reaction with NaOH or H2SO4 and mixed with manganese as a catalyst. In this case, calcium as a co-catalyst may be added at needs to enhance the catalytic effect. The waste water is then decomposed by reaction with ozone in a decomposing vessel 2, introduced into a reducing vessel 3, provided with an agitator, to which Na2SO3 is added, and reduced. Thereafter, the waste water is coagulated in a coagulating vessel 4, provided with an agitator, to which a flocculant is added together with NaOH or H2SO4, and the resulting supernatant liquid is drained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating cyanide wastewater using an ozone oxidation method.

The wastewater discharged from plating factories, etc. contains a large amount of cyanide, and must be treated in some way to reduce the wastewater to 1.0pp, which is the wastewater standard value stipulated in the Water Pollution Control Law.
Unless m+ is cleared, this wastewater cannot be discharged into rivers, etc. outside the factory.

Conventionally, cyanide wastewater has been generally treated by an alkali chlorine method. This method makes the wastewater alkaline (−
Secondary decomposition PHI 0 or more, secondary decomposition P) 17.5~aO)
The reaction formula is shown below for a method in which cyanide is decomposed into nitrogen and carbon dioxide by adding hypochlorous acid.

Addition of nczowo (PH7.5~ao), 2CNo −
+50CZ-+H1O→2COs+N@+3C1-+2
0H-(8)''i;Q This method is very effective for cyanide compounds which are relatively easy to decompose, but it is effective against cyanide complexes, iron cyano complexes, etc.
Cyanide compounds such as cyanocobalt complex salts are difficult to decompose and pose a pollution problem. This method also has the disadvantage that good decomposition is difficult unless the amount of yen and hypochlorous acid added is strictly controlled.

The present invention has been made in consideration of these drawbacks of the alkali chlorine method, and provides a method for treating cyanide wastewater that can clear the wastewater standard value even for cyanide compounds such as cyanoiron complex salts and cyanocobalt complex salts that are difficult to decompose. It provides:

The treatment method according to the present invention is characterized by the use of ozone, and is a method of converting cyanide compounds into harmless nitrogen and carbonate ions in the same reaction as the alkali chlorine method. The reaction formula is as follows.

CN-+OB -m-CN0-+OB ・・・””
= 1412ONO-+301+H,O→2HCOi+
) is430m...tls1 Figure is an explanatory diagram for explaining the wastewater treatment method of the present invention. Cyanide wastewater (cyanide content less than 10pcy) is first introduced into a pretreatment tank 1 equipped with an agitator, where the wastewater is sNa0
It is made alkaline by reacting with a or a=eo=. In addition to )ra (H or H2BO3), manganese, for example, is added to this pretreatment tank 1 in order to perform a catalytic action. Calcium is added as a cocatalyst for 6-i.

Next, in the decomposition tank 2, decomposition is performed by reacting with ozone. Here, since ozone alone causes gas-liquid contact, equation (4),
Decomposition is difficult unless the reaction shown by formula (6) is instantaneously carried out. In the present invention, manganese having a catalytic action is added in the pretreatment tank 1 to increase contact efficiency and complete decomposition. K t, I'm trying to do it.

Next, a reduced species 3 with a stirrer and Na2804 added.
, followed by a stirrer, a flocculating agent, and N
A0tI or H,804 is aggregated in the aggregate tank 4, and the supernatant liquid is discharged.

An example of the experimental results according to the method of the present invention is shown below. First, the results of experiments using the two-way configuration method regarding circles and the amount of catalyst added were as follows: pH 12, manganese used as a catalyst, and the amount added was 100 pp pm. , 5pp-ferricyanide ion was decomposed by 741 (i7ppm). Note that 2B'l will not decompose unless a catalyst is added. The reaction formula in this case is estimated as follows.

Mn + 20 "Mn(OH)1 -- t8)
Mll(OH)1+03--1---→Mn104+0
1...-171Mn! 04+OI
Mn10g+01...
...(8) Mn01+01 M
n01+01 ・・・・・・(9) MnO1+
01+NaOHNa2804・”
”' Q(1Mn04+Fe(CN)/-6CN
O+N1+M+sO1+++ +++ allMn O
4+ CNO+H2O-m--→ HCO7+N1+M
n01 - ...121Next, regarding the amount of ozone, it was determined from the experiment that the amount of ferricyanion ions in the sample was
It turned out that I needed twice as much. Note that for cyanide compounds that are easily decomposed, it is sufficient to use twice the amount of the cyanide compound.

From these experiments, the conditions for the treatment method according to the present invention are as follows: when the cyanide content is 5 ppm, pn12, catalyst (
Manganese) addition amount 1100pp, ozone amount 10000
p.

It is. When wastewater containing cyanide compounds was treated under such treatment conditions, it was possible to clear the wastewater standard value of lppm even if it contained cyano compounds such as cyano iron complexes that were difficult to decompose. Further, when 1100 pp or more of calcium, for example, is added as a co-catalyst, activation of the catalyst can be increased and cyanide decomposition efficiency can be improved. According to experiments, when 1100pp or more of co-catalyst is added, ferricyanion ions are reduced to 100%.Furthermore, when alkaline earth metals are added as co-catalysts, they also have an excellent coprecipitation effect, which reduces the amount of harmful heavy metals. Processing can also be done in one go. Note that the decomposition rate when no promoter is added is around 90-.

In addition, in the above explanation, the case where manganese is used as a catalyst is illustrated, but silver may be used instead of manganese.
In addition to calcium, co-catalysts include barium, magnesium, copper, and silver.

It is also possible to use aluminum, molybdenum, nickel, zinc, etc.

As explained above, according to the method of the present invention, cyanide compounds such as cyano iron complex salts and cyano cobalt complex salts, which have been difficult to decompose up to now, can be decomposed without causing any pollution problems.

[Brief explanation of the drawing]

The figure is an explanatory diagram for explaining the present invention in detail. 1... Pretreatment tank, 2... Decomposition tank, 6... Reduction tank,
4...6 collection tanks.

Claims (1)

[Claims] (1) Each step of pretreating cyanide wastewater K by adding NaOH or Hs804 and a catalyst, reacting it with ozone to decompose it, and reducing the decomposed wastewater with Na1aO@. A method for treating cyanide wastewater, characterized in that the cyanide wastewater is treated after the treatment. (2) The pressure of cyanide wastewater is 12f1 or more, and the amount of catalyst added is 100. , - The method for treating cyanide wastewater according to claim 1, wherein the amount of ozone is 2000 times that of cyanide. 13) The method for treating cyanide wastewater according to claim 1, wherein a co-catalyst is added in the pre-treatment step. (4) The method for treating cyanide wastewater according to claim 3, wherein the amount of co-catalyst added is 1100 pp or more.