Sodium nitrate is used as an ingredient in fertilizers, pyrotechnics, as a food preservative, and as a solid rocket propellants, as well as in glass and pottery enamels; the compound has been mined extensively for those purposes.
The mining of 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).
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. The former Chilean saltpeter mining communities of Humberstone and Santa Laura were declared Unesco World Heritage sites in 2005.
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. 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. In about 1970, it was found that the addition of ascorbic acid inhibited nitrosamine production. U.S. manufacturing of cured meats now requires the addition of 500 ppm of ascorbic acid or erythorbic acid, a cheaper isomer. The nitrate compound itself is not harmful, however, and is among the antioxidants found in fresh vegetables.
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. Hobbyist gold refiners use sodium nitrate to make a hybrid aqua regia that dissolves gold and other metals.