CS270486B1 - The way of removing cyanides from wastewater - Google Patents

Abstract

The solution relates to a method for removing cyanides from wastewater, also containing complex iron cyanides, by alkaline chlorination. The essence of the solution consists in adding a water-soluble copper compound, preferably copper sulfate, to the wastewater before alkaline chlorination, preferably in the form of an aqueous solution, in such an amount that for one molar part of iron present in the wastewater, there are at least two molar parts of copper, after which the precipitate formed is separated from the wastewater.

Description

The invention relates to a process for removing cyanides from wastewater, also containing complex iron cyanides, by alkaline chlorination.

The cyanides contained in wastewater, both from the galvanic and engineering industries and from the chemical treatment of ores, are either free cyanides or complex cyanides, which are formed by the reactions of simple cyanides with heavy metal ions.

Disposal of said cyanides present in the wastewater is usually carried out by oxidation with strong oxidizing agents. In practice, sodium hypochlorite or chlorine gas is often used and this method is called alkaline chlorination. This chlorination mainly decomposes the free cyanides and only then does the decomposition of more diazolated complex cyanides take place, depending on the stability constant of the individual complex cyanides present. Alkaline chlorination of ee removes complex copper, zinc and cadmium cyanides from wastewater without difficulty, and the decomposition of these compounds is primarily a function of time.

However, if the waste water also contains complex iron cyanide in the form

Fe / (CN) _6: _7 ³ and Fe / 7 (CN) g ^ ² having a high stability constant, is achieved by alkaline chlorination decomposition of said iron complex cyanides only to a slight extent, whereby the degree of degradation of cyanides would increase significantly even using excess of oxidizing agent, nor by prolonging the oxidation time.

The above-mentioned drawbacks are largely eliminated by a process for removing cyanides from waste water, also containing complex iron cyanides, by alkaline chlorination, the essence of which consists in adding a water-soluble copper compound, preferably copper sulphate, preferably copper sulphate, preferably copper sulphate, to the waste water before alkaline chlorination. in the form of an aqueous solution, in such an amount that for one molar part of iron present in the waste water, there are at least two molar parts of copper, after which the precipitate formed is separated from the waste water.

From výěe follows that the degradation of cyanides in waste water is carried out in two stages, the first stage is first removed by precipitation of an iron cyanide complex as cugFe / '(CN) ₆ J7. By adding HgO with a water-soluble copper compound, the precipitate formed can be deposited as an insoluble compound on the sludge field after separation from the waste water, for example by filtration. In the subsequent second step, the remaining cyanides, including complex cyanides of other metals, are degraded by alkaline chlorination.

The advantage of the method for removing cyanides from wastewater according to the invention is that this method increases the degree of cyanide removal compared to alkaline chlorination alone, while it is possible to remove soluble iron compounds (soluble iron ion) from wastewater at the same time. The resulting precipitate is insoluble and can therefore be deposited on the sludge pond.

The method for removing cyanides from wastewater according to the invention can be used, for example, in the disposal of cyanides from wastewater arising from electroplating in the engineering industry, metallurgical industry, in the treatment of precious metals, i.e. wherever cyanides are handled and formed in wastewater. complex cyanides with iron.

In the following part of the description, the method according to the invention will be elucidated on the basis of a specific exemplary embodiment. This example also documents the feasibility according to the invention and the higher effect which the method according to the invention achieves in comparison with the prior art.

Example

In the oxidation of wastewater with input composition:

CN _ce ik 329 mg / dm ³ , Cu 121 mg / dm ³ , Fe 116 mg / dm ³ , Zn 209 mg / dm ³ were the method of two-stage alkaline chlorination with the consumption of active chlorine 16 g / g CN_ „,. complex cyanides were removed to a _total CN value> 200 mg / d 2 and Fe 70 mg / d 2. In the process according to the invention, complex cyanides are first precipitated from the waste water by metering into the waste water a 10% aqueous solution of copper sulphate in an amount corresponding to 10.0 g of this flow per 1 dm ^{3 of} said waste water and the precipitate formed. separates, a pot with two-stage alkaline chlorination at the same chlorine consumption degrades complex cyanides to a value of 30 mg / dm ³ . Said pretreatment cyanide wastewater increase the degree of removal CN _Cel 85%.

Claims (1)

OBJECT OF THE INVENTION Process for removing cyanides from waste water, also containing complex iron cyanides, by alkaline chlorination, characterized in that a water-soluble copper compound, preferably copper sulphate, preferably in the form of an aqueous solution, is added to the waste water before alkaline chlorination in such an amount that for one molar part of iron present in the waste water, there are at least two molar parts of copper, after which the precipitate formed is separated from the waste water.