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Sodium cyanide

physical science Maturity 11-13 Next article →

Sodium cyanide is a chemical compound with the formula NaCN. It appears as a white, water-soluble solid. This substance is a moderately strong base in chemical terms. It is also known for having a very high affinity for metals. This means it has a powerful attraction to metallic elements. Because of this reactivity, it is used widely in many industrial processes. However, this same chemical nature makes it one of the most rapidly acting poisons known.

The way sodium cyanide works inside a living body is quite specific. It acts as a potent inhibitor of cellular respiration. This means it interferes with how cells breathe and create energy. Specifically, it targets a part of the cell called mitochondrial cytochrome oxidase. By acting on this enzyme, it blocks the process of electron transport. This blockage causes a decrease in oxidative metabolism and oxygen utilization. As a result, the body undergoes lactic acidosis due to anaerobic metabolism. An oral dose as small as 200 to 300 mg can be fatal.

In industry, sodium cyanide is used to extract precious metals through a process called cyanidation. This is the dominant technique for extracting gold from low-grade ore. The process exploits the high affinity of gold(I) for cyanide. When gold is placed in a mixture of water, air, and cyanide, it undergoes oxidation. This causes the solid metal to dissolve into a liquid salt called sodium dicyanoaurate. Once the gold is in this soluble form, it can be converted back into solid metal through electrolysis. This single method accounts for more than 70% of global cyanide consumption.

Beyond mining, sodium cyanide is essential for the field of electroplating. Electroplating is a process used to coat one metal with a layer of another. Cyanide baths, which are solutions of metal ions, are used to plate metals like platinum, gold, and silver. It is also used to create cadmium plating, which provides excellent corrosion resistance. In some cases, it helps create copper "strikes." These are thin, high-quality layers that allow metals like chromium and aluminum to adhere to one another.

The production of sodium cyanide has changed over time. In the past, it was prepared using the Castner process. This method involved reacting sodium amide with carbon at elevated temperatures. Today, the standard method is to treat hydrogen cyanide with sodium hydroxide. This chemical process creates the white solid used by industries today. In the year 2006, worldwide production was estimated at approximately 500,000 tons. The crystal structure of solid NaCN is actually related to the structure of sodium chloride, which is common table salt.

Because of its high toxicity, the disposal of cyanide is subject to very stringent regulations. Industrial waste containing cyanide, known as effluent, must be destroyed carefully. One efficient way to detoxify it is through oxidation using hydrogen peroxide. This reaction produces water and sodium cyanate. Other industrial methods include the "Inco process," which uses sulfur dioxide and copper salts. Another option is the "Combiox Process," which uses a combination of peroxysulfuric acid, hydrogen peroxide, and sulfur dioxide.

Sodium cyanide also serves as a chemical feedstock for many other important substances. It is used to produce chemicals like cyanuric chloride, cyanogen chloride, and cyanogen. It can also be used to make specialty nitriles through a process called alkylation. In some niche areas, it is used by entomologists to stun or kill insects for collection. While it was once used as an insecticide and a rodenticide, the EPA cancelled those uses in 1987. This highlights the delicate balance between using powerful chemicals for industry and protecting the environment.

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