JP2014223579A - Method for processing cyan-containing drain water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing cyan-containing drain water, capable of effectively removing cyanide compounds from cyan-containing drain water which contains cyanide compounds complexed with metal ions and organic compounds besides cyan ions, so that the cyan concentration can be sufficiently reduced.SOLUTION: A ferric salt is added to cyan-containing drain water. The pH of the mixture is adjusted to 6 or more and 8 or less. Subsequently, a ferrous salt is added to the mixture. The addition amount of the ferrous salt is 8 mass% or more and 25 mass% or less relative to the addition amount of the ferric salt.

Description

  The present invention relates to a treatment method for efficiently removing cyanide from wastewater containing cyanide (hereinafter referred to as cyanine-containing wastewater).

An alkali chlorine method is generally known as a method for treating cyanide-containing wastewater discharged from a coke production factory or the like (see, for example, Patent Document 1). However, the alkali chlorine method has low processability for the hardly decomposable cyanide compound complexed with metal ions, and it has been difficult to sufficiently decompose and remove the cyanide compound in the waste water.
As a method for treating waste water containing a hardly decomposable cyanide compound complexed with a metal ion, a divalent copper salt and a reducing agent are added to the waste water to form a hardly soluble salt (CuCN, CuFe (CN) _6, etc. ) Is generated, and this is separated / removed (refer to Patent Document 2, for example).

Japanese Patent Laid-Open No. 2001-269664 Japanese Unexamined Patent Publication No. 63-039693

The Water Pollution Control Law stipulates that the cyan concentration in the treated waste water is 1.0 mg / L or less.
In addition to cyanide ions, wastewater containing cyanide compounds complexed with metal ions, for example, cyanine-containing wastewater discharged from coke production plants, etc., the cyan concentration in the wastewater is 0.1 mg using the all cyan method. / L or less, but if organic substances are mixed in the waste water, the cyan concentration may not be lowered to 1.0 mg / L or less. In this case, the cyan density is lowered by repeating the processing using the all-cyan method, but there is a problem that it takes time and cost.

  Therefore, the present invention solves the problems of the prior art as described above, and efficiently removes cyanide compounds from cyanide containing wastewater containing cyanide and organic compounds complexed with metal ions in addition to cyanide ions. It is an object of the present invention to provide a method for treating cyanide-containing wastewater that can be sufficiently reduced in cyan density.

In order to solve the above-described problems, an aspect of the present invention has the following configuration. That is, the method for treating cyanide-containing wastewater according to one aspect of the present invention is a treatment method for removing cyanide from cyanide-containing wastewater containing cyanide, and adding ferric salt to the cyanide-containing wastewater. After adjusting the pH to 6 or more and 8 or less, ferrous salt is added, and the addition amount of the ferrous salt is set to 8 mass% or more and 25 mass% or less of the addition amount of the ferric salt. Features.
In this method for treating cyanide-containing wastewater, the cyanine-containing wastewater may contain a cyanide compound and an organic substance complexed with metal ions.

  The method for treating cyan-containing wastewater according to the present invention can efficiently remove cyanide from cyanide-containing wastewater containing cyanide, and can sufficiently reduce the cyan concentration.

  Embodiments of the method for treating cyan-containing wastewater according to the present invention will be described in detail below. The cyan-containing wastewater to be treated in the present embodiment is not particularly limited as long as it is a wastewater containing a cyanide compound, but cyan-containing wastewater discharged from a coke manufacturing plant or a smelter is an example. In particular, cyan-containing wastewater generated by cooling or washing of the cyan-containing gas is suitable.

  Such cyanide-containing wastewater often contains not only cyan but also metals, and as a result, cyanide-containing wastewater contains many types including cyanide compounds complexed with metal ions such as iron and copper. There is a cyanide compound. Furthermore, organic substances such as aromatic compounds such as phenol and pyridine may be mixed in such cyanide-containing wastewater. Even when cyanide-containing wastewater containing a cyanide compound and an organic substance complexed with metal ions as described above is treated using the all-cyan method, the cyan concentration in the cyanide-containing wastewater is reduced to 1.0 mg / L or less. It is difficult.

Therefore, in the present embodiment, first, ferric salt is added to the cyanate-containing wastewater and the pH is adjusted to 6 or more and 8 or less. At this time, the addition amount of the ferric salt is determined as follows. That is, the amount of cyanide in the wastewater containing cyanide is measured, and the amount of ferric salt added sufficient to precipitate the cyanide is calculated.
The type of ferric salt is not particularly limited as long as it is a compound that is soluble in water and can form trivalent iron ions in water. For example, ferric chloride, ferric sulfate, Iron alum.

Further, the method for adjusting the pH to 6 or more and 8 or less is not particularly limited, and examples thereof include addition of an alkali compound. The kind of alkali compound is not particularly limited, and examples thereof include sodium hydroxide and calcium hydroxide.
Subsequently, ferrous salt is added to the cyanate-containing wastewater. As a result, a hardly soluble salt is produced, and the cyanide compound can be removed from the cyanate-containing wastewater by solid-liquid separation using a conventional separation means such as filtration.

The addition amount of the ferrous salt needs to be 8% by mass or more and 25% by mass or less of the addition amount of the ferric salt. If it is less than 8% by mass, the production of a hardly soluble salt is insufficient, and there is a risk that the cyan density will not be sufficiently reduced. On the other hand, if it exceeds 25% by mass, there is a possibility that the production of solids becomes excessive and the piping is blocked.
The type of ferrous salt is not particularly limited as long as it is a compound that is soluble in water and can form divalent iron ions in water. For example, ferrous chloride, ferrous sulfate Iron can be given.

In addition, it is preferable to add a ferrous salt so that the density | concentration of the ferrous salt in cyanate containing waste_water | drain will be 50 ppm or more and 100 ppm or less.
The present invention will be described more specifically with reference to the following examples and comparative examples. In this example and comparative example, wastewater generated mainly at a coke production plant was used as cyanide-containing wastewater. The cyan concentration of this cyanine-containing wastewater is 13.6 mg / L, but it contains many kinds of cyanide compounds including cyanide compounds complexed with metal ions in addition to cyanide ions, and also contains organic matter.

(Example 1)
First, ferric chloride was added to the cyanate-containing wastewater, and at the same time, sodium hydroxide was added to adjust the pH to 6.8. Next, ferrous sulfate was added to carry out the treatment. The amount of ferrous sulfate added was 15% by mass of the amount of ferric chloride added. It was 0.5 mg / L when the cyan density | concentration of the cyanate containing waste water after a process was measured.

(Comparative Example 1)
First, the same amount of ferric salt of the same kind as in Example 1 was added to the cyanate-containing wastewater, and at the same time an alkali was added to adjust the pH to 6.8. And the ferrous salt was not added and the process was complete | finished. It was 1.0 mg / L when the cyan density | concentration of the cyanate containing waste water after a process was measured.

(Comparative Example 2)
First, the same amount of ferric salt of the same kind as in Example 1 was added to the cyanate-containing wastewater, and at the same time an alkali was added to adjust the pH to 6.8. Next, the same kind of ferrous salt as in Example 1 was added for treatment. The amount of ferrous salt added was 30% by mass of the amount of ferric salt added. It was 0.8 mg / L when the cyan density | concentration of the cyanate containing wastewater after a process was measured (however, the fluctuation | variation was 0.4-1.4 mg / L was large).

  Thus, it can be seen that Example 1 is more effective in removing cyanide than Comparative Examples 1 and 2. Moreover, the cyan concentration of the treated cyan-containing wastewater is 0.5 mg / L. In addition to cyanide ions, cyanide containing wastewater containing cyanide and organic substances complexed with metal ions is also efficient. It can be seen that the cyan density can be sufficiently reduced.

Claims (2)

  A treatment method for removing cyanide from wastewater containing cyanide, adding ferric salt to the wastewater containing cyanide and adjusting the pH to between 6 and 8, and then adding ferrous salt And the addition amount of this ferrous salt shall be 8 mass% or more and 25 mass% or less of the addition amount of said ferric salt, The processing method of the cyanogen containing waste water characterized by the above-mentioned.   The method for treating cyan-containing wastewater according to claim 1, wherein the cyanide-containing wastewater contains a cyanide compound and an organic substance complexed with metal ions.