JPH0714513B2 - Treatment method of cyanide waste liquid containing iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively treating cyan waste liquid.

Since cyanide is a highly poisonous waste liquid containing cyanide such as a pre-plating treatment solution, it is essential to completely decompose cyanide into harmless carbon dioxide gas and nitrogen gas in order to prevent pollution.

Conventionally, the oxidative decomposition treatment method has been widely used for the treatment of this cyan waste liquid.

For example, the oxidative decomposition method using hypochlorous acid (HOCl), which is the most general method, first converts cyan to cyanic acid at pH 10 or higher by the formula (1), and then lowers the pH to 7.5 to 8 to produce cyanic acid. Is a method of decomposing CO ₂ and N ₂ as in formula (2).

^{CN - + HOCl → Cl - +} HCNO ...... (1) 2CNO - + 3OCl - + H 2 O → 2CO 2 + N 2 + 3Cl - + 2OH - ...... (2) , however the iron when iron is present in the cyan liquid waste mainly Hue Russian ions [Fe (CN) ▲ ^4- ₆ ▼] such waste for hard to be very oxidized even has a form the ions by oxidation agents are those which can not be treated just oxidative decomposition method.

For this reason, as a treatment method of a cyan waste liquid containing iron, a method of adding ferrous sulfate to the liquid after oxidative decomposition treatment and precipitating iron as ferrous cyan ferrous salt according to the formula (3) is adopted.

Fe (CN) ▲ ^4- ₆ ▼ + 2 Fe ²⁺ → Fe ₂ [Fe (CN) ₆ ] ↓ …… (3) However, the precipitate generated by the formula (3) is oxidized by oxygen in the air, or the action of ultraviolet rays. Therefore, there is a risk that the soluble salt tends to change, and there is a risk that the cyan concentration in the waste liquid will increase again after the treatment. It is difficult to sufficiently reduce the cyan concentration of the cyan waste liquid even by this two-stage treatment. is there.

In the present invention, in consideration of such a situation, the cyan concentration after treatment of the cyan waste liquid is 1 mg / m even when it contains iron as a result of various studies.
We have developed a treatment method capable of reducing the amount of iron to less than 1. In the method of oxidative decomposition treatment of a cyan waste liquid containing iron, free cyan contained in the waste liquid, a ferrocyan complex and a cyan complex having a stable number smaller than that of the ferrocyan complex are treated with copper. A copper cyanide containing iron, which is characterized in that ferrocyan complex is converted to a copper cyan complex by adding copper ions in an amount equal to or more than the amount required to convert to a cyan complex, and then oxidative decomposition treatment is performed. or iron that is the addition of copper ions and Hue Russian ions by copper solution (4) copper and substituted copper cyanide ion [Cu (CN) ▲ _^2-4 ▼] is produced by expression, the iron and a hydroxyl group They combine to form hydroxides and precipitate. Copper cyanide can be completely treated by a conventional oxidative decomposition treatment.

_{^{2Fe (CN) ▲ 4- 6 ▼}} + 3Cu 2+ → 3Cu (CN) ▲ 2- 4 ▼ + 2Fe 2+ ...
... (4) In addition, iron has a full collar cyanide ion [Fe (CN) ▲ ^3- ₆ ▼] can be stability constant of the ion is replaced with larger for copper than copper cyanide ions But not
Since the ferricyan ion is oxidized and decomposed by the usual method like the copper cyan ion, there is no problem.

The reason why the amount of copper ions added before the oxidation treatment is limited as described above is as follows.

When copper ions are added to a cyan waste liquid containing a metal that forms a cyan complex having a smaller stability constant than copper cyan complexes such as free cyan, cadmium, zinc, and ferrous iron, copper ions have a small stability constant. sequentially replaced with the metal forming the (5) (6) (7 ) (8) 4CN forming copper cyanide complexes by formula ^{- + Cu 2+ → Cu (CN} ) ▲ 2- 4 ▼ ...... (5 _{^{) Cd (CN) ▲ 2- 4}} ▼ + Cu 2+ → Cu (CN) ▲ 2- 4 ▼ ...... (6) Zn (CN) ▲ 2- 4 ▼ + Cu 2+ → Cu (CN) ▲ 2- 4 ▼ ...... (7) 2Fe (CN) ▲ 4- 6 ▼ + 3Cu 2+ → 3Cu (CN) ▲ 2- 4 ▼ ......
(8) Therefore, after the reaction according to the equations (5), (6) and (7) is completed, the reaction according to the equation (4) (or the equation (8)) is completed, so that the ferrous iron is completely replaced with copper. In order to convert the free cyan, the ferrocyan complex, and the cyan complex having a stable number smaller than that of the ferrocyan complex into the copper cyan complex, copper ions must be added in an amount equal to or more than the equivalent amount. Most of the iron in the cyanogen effluent is present as ferrous iron, so it is difficult to separate and analyze ferrous and ferric iron in actual operation, so copper should be used in an amount equivalent to the total iron. There is no problem in determining the amount of added ions.

In addition, if the copper ion is added in excess of the minimum amount of copper ion determined in this way, the excess copper ion becomes green copper hydroxide and precipitates.Therefore, the composition of the cyanogen waste solution and the copper concentration of the added copper solution are unknown. In some cases, it is convenient in practical operation to use the point at which copper hydroxide precipitates as the end point of copper ion addition.

Examples of the present invention will be described below.

Example 1 Iron 3 g / l, free cyanide 800 mg / l copper sulfate solution to the waste liquid 5 m ³ comprising (Cu25g / l) 1.25m ³ (free cyanide, copper to iron 1.1
After adding 1 equivalent) sodium hypochlorite solution (10W / V
%) 0.7 m ² was added and then the pH was lowered to 8 for decomposition. Cyan concentration in the waste liquid after this treatment is 0.8m
It was g / l.

Example 2 Copper sulphate solution (Cu25g / l) 1.35m in 5m ³ of the same waste liquid as in Example 1
³ (free cyan, 1.20 equivalents of copper relative to iron) was added, and then 0.7 m ³ of sodium hypochlorite solution (10 W / V%) was added, and after the oxidation treatment, the pH was lowered to 8 for decomposition treatment. The cyanide concentration in the waste liquid after this treatment was 0.5 mg / l.

Example 3 A waste solution containing copper (copper concentration unknown) was added to 7 m ³ of waste solution of iron 5 g / l and free cyan 600 mg / l until copper hydroxide was formed, and then sodium hypochlorite solution (10 W / V% ) 0.7m ³ was added for oxidation and then pH was lowered to 8 for decomposition. The cyanide concentration of the waste liquid after this treatment was 0.4 mg / l.

Comparative Example Copper sulfate solution (Cu25g / l) 1.0m ^{3 in the} same waste liquid 5m ³ as in Example 1
(Free cyan, Cu 0.89 equivalent to iron) was added, and then sodium hypochlorite solution (10 W / V%) 0.7 m ³ was added for oxidation treatment, and then the pH was lowered to 8 for decomposition treatment. The cyanide concentration of the waste liquid after this treatment was 30.2 mg / l.

Conventional example 4m ³ of cyanogen waste solution containing 3g / l of iron and 800mg / l of free cyan was added with 2m ³ of sodium hypochlorite solution (10W / V%), and then the pH was lowered to 8 for decomposition treatment. The cyanide concentration of the waste liquid after the treatment was 45 mg / l. Ferrous sulfate was further added to the waste liquid after this treatment to form a precipitate, and the cyan concentration of the waste liquid was 5.3 mg / l.

As described above, the method of the present invention can treat cyanide waste liquid containing iron more easily and effectively than the conventional method.
It has a remarkable effect on pollution prevention.

Claims (1)

[Claims] 1. In a method for oxidative decomposition treatment of a cyan waste liquid containing iron, it is necessary to convert a free cyan, a ferrocyan complex and a cyan complex having a stable number smaller than the ferrocyan complex contained in the waste liquid into a copper cyan complex. A method for treating a cyan waste liquid containing iron, which comprises adding a copper ion in an equivalent amount or more to convert a ferrocyan complex into a copper cyan complex, and then performing an oxidative decomposition treatment.