Ammonium nitrate

The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical formula NH₄NO₃, is a white crystalline solid at room temperature and standard pressure. It is commonly used in agriculture as a high-nitrogen fertilizer, and it has also been used as an oxidizing agent in explosives, including improvised explosive devices.

Ammonium nitrate is used in cold packs, as hydrating the salt is an endothermic process.

Production

The processes involved in the production of ammonium nitrate in industry, although chemically simple, are technologically challenging. The acid-base reaction of ammonia with nitric acid gives a solution of ammonium nitrate:^[3] HNO₃(aq) + NH₃(g) → NH₄NO₃(aq). For industrial production, this is done using anhydrous ammonia gas and concentrated nitric acid. This reaction is violent and very exothermic. After the solution is formed, typically at about 83% concentration, the excess water is evaporated to an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in a spray tower, or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.

The Haber process combines nitrogen and hydrogen to produce ammonia, part of which can be oxidised to nitric acid and combined with the remaining ammonia to produce the nitrate. Another production method is used in the so-called Odda process.