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Concept
Ammonium nitrate
Summary
Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer.
Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction. It is the major constituent of ANFO, a popular industrial explosive which accounts for 80% of explosives used in North America; similar formulations have been used in improvised explosive devices.
Many countries are phasing out its use in consumer applications due to concerns over its potential for misuse. Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century. Global production was estimated at 21.6 million tonnes in 2017. By 2021, global production of ammonium nitrate was down to 16.7 million tonnes.
Ammonium nitrate is found as the natural mineral gwihabaite (formerly known as nitrammite) – the ammonium analogue of saltpetre (mineralogical name: niter) – in the driest regions of the Atacama Desert in Chile, often as a crust on the ground or in conjunction with other nitrate, iodate, and halide minerals. Ammonium nitrate was mined there until the Haber–Bosch process made it possible to synthesize nitrates from atmospheric nitrogen, thus rendering nitrate mining obsolete.
The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid:
HNO3 + NH3 → NH4NO3
The ammonia required for this process is obtained by the Haber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidized to nitric acid by the Ostwald process. Ammonia is used in its anhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highly exothermic nature. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate (AN) content of 95% to 99.
Official source
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