Sodium nitrate

Sodium nitrate is the chemical compound with the formula NaNO₃. This salt, also known as saltpeter, is a white solid which is very soluble in water. Sodium nitrate is used as an ingredient in fertilizers, explosives, and in solid rocket propellants, as well as in glass and pottery enamels; the compound has been mined extensively for those purposes.

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The mining of so-called "Chile saltpeter" was such a profitable business that three nations, Chile, Peru, and Bolivia fought over the richest deposits in the War of the Pacific. The world's largest natural deposits of caliche ore were in the Atacama desert of Chile, and many deposits were mined for over a century, until the 1940s, when its value declined dramatically in the first decades of the twentieth century (see Haber Process). The former Chilean saltpeter mining communities of Humberstone and Santa Laura were declared Unesco World Heritage sites in 2005.

Chile still has the largest reserves of caliche, with active mines in such locations as Pedro de Valdivia, Maria Elena and Pampa Blanca. Sodium nitrate, potassium nitrate, sodium sulfate and iodine are all obtained by the processing of caliche.

Sodium nitrate is also synthesized industrially by neutralizing nitric acid with soda ash.

Applications

Sodium nitrate was used extensively as a fertilizer and a raw material for the manufacture of gunpowder in the late nineteenth century.

Sodium nitrate has antimicrobial properties when used as a food preservative. It is found naturally in leafy green vegetables.

Sodium nitrate should not be confused with the related compound, sodium nitrite. The presence of sodium nitrite in food is controversial due to the development of nitrosamines when the food, primarily bacon, is cooked at high temperatures. The nitrate compound itself is not harmful, however, and is among the antioxidants found in fresh vegetables. ^[1] Its usage is carefully regulated in the production of cured products; in the United States, the concentration in finished products is limited to 200 ppm, and is usually lower.

It can be used in the production of nitric acid by combining it with sulfuric acid and subsequent separation through fractional distillation of the nitric acid, leaving behind a residue of sodium bisulfate.

Less common applications include its use as a substitute oxidizer used in fireworks as a replacement for potassium nitrate commonly found in black powder. The first paragraph of this article where it names sodium nitrate as salt peter is in error. Salt peter is potassium nitrate KNO3. The confusion comes from the use of the term Chile saltpeter for sodium nitrate. The two are not interchangable.

Because sodium nitrate can be used as a Phase Change Material it may be used for heat transfer in solar power plants.^[2]

Notes and references