Introduction of Cyanide Containing Wastewater

Cyanide containing wastewater mainly comes from processing such as electroplating, gas, coking, metallurgy, metal processing, chemical fiber, plastics, pesticide, and chemical industry.

Cyanides are divided into two categories:

• Inorganic cyanide, such as hydrocyanic acid and its salts.
• Organic cyanide or nitrile, such as acrylonitrile, acetonitrile, and other cyanide ions, which are characterized by their easy formation of complexes with certain metals.

Nitrile is a compound that connects carbon atoms of hydrocarbon and cyano groups, and has a special odor. In the coal coking process, hydrogen cyanide (ECN) is used for the production of polyacrylonitrile fibers, sodium cyanide is used for metal electroplating, ore flotation, and the production of dyes, pharmaceuticals, and plastics, potassium cyanide is used for the electrolytic refining of platinum, and production processes such as metal coloring, electroplating, and pharmaceuticals all generate cyanide containing wastewater.

For example, the cyanide content in the condensate water of the coking plant (calculated by HCN) is about 55mg/L, and the content in the ammonia water is 200~2000mg/L; In the production of acrylonitrile, about 110~120kg of acetonitrile and 50~100kg of HCN are discharged per 1t of acrylonitrile production. The concentration of cyanide ions in electroplating wastewater is about 20~70mg/L. Electroplating water containing cyanic acid is generally treated by alkaline chlorination or electrolysis.

Cyanide containing wastewater is a highly toxic industrial wastewater, which is unstable in water and easy to decompose. Inorganic and organic cyanide are highly toxic substances, and can cause acute poisoning if ingested by humans. The lethal dose of cyanide to humans is 0.18, and potassium cyanide is 0.12g. The mass concentration of cyanide to fish in water is 0.04-0.1mg/L.

The main treatment measures for cyanide containing wastewater include:

Reform the process to reduce or eliminate the discharge of cyanide containing wastewater, such as the use of cyanide free electroplating method can eliminate industrial wastewater from electroplating workshops.

Wastewater with high cyanide content should be recycled, and wastewater with low cyanide content should be purified before being discharged. The recovery methods include acidification aeration alkali liquor absorption method, steam desorption method, etc.

Other treatment methods include alkaline chlorination method, electrolytic oxidation method, pressurized hydrolysis method, biochemical method, biological iron method, ferrous sulfate method, air stripping method, etc.

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