Ammonium nitrate

Ammonium nitrate (NH₄NO₃) is a straight nitrogenous fertiliser produced by neutralising nitric acid with ammonia. The exothermic reaction yields a concentrated solution which, following evaporation, is solidified into prills or granules. The commercial product contains 33 to 34.5% nitrogen, split equally between ammoniacal and nitric forms^[1][2]. Its high water solubility and acidifying effect on soil make it agronomically effective though demanding in terms of management.

Manufacturing and industrial chain

Production sits within the nitrogenous fertiliser stream, downstream of the Haber-Bosch process and the Ostwald process. Nitric acid, obtained through catalytic oxidation of ammonia, is neutralised by additional ammonia gas to form ammonium nitrate^[3]. Plants manufacturing both ammonium nitrate and calcium ammonium nitrate typically operate at rates ranging from a few hundred to 3,600 tonnes per day^[4]. ANS — aqueous ammonium nitrate solution — represents an intermediate commercial form with annual worldwide volumes in the region of 40 to 45 million tonnes^[4]. The solid product generally receives an anti-caking coating to maintain its handling characteristics in storage^[1].

Agronomic and environmental properties

From a nutritional standpoint, ammonium nitrate provides nitrogen in two forms: the ammonium ion (NH₄⁺), adsorbed onto clay colloids and thus relatively immobile, and the nitrate ion (NO₃⁻), immediately available for root uptake^[5]. This instant availability of nitrate distinguishes it from prilled urea, which must undergo hydrolysis then nitrification dependent on soil temperature and pH^[5]. Nitric fertilisers, defined as containing at least 50% of their nitrogen in nitric form, offer better control of volatilisation losses and a lower carbon footprint than urea-based products under European conditions^[6][7]. For granular ammonium nitrate, manufacturing-related emissions amount to 3.42 kg CO₂ equivalent per kilogramme of nitrogen in the European Union, compared with 8.61 kg for a Chinese gas-fired site and 3.78 kg for a US producer^[7][8].

Markets and non-agricultural uses

Whilst the fertiliser market predominates, technical ammonium nitrate supplies the civil explosives industry, notably as ANFO (Ammonium Nitrate Fuel Oil), the most widespread mining explosive owing to its low unit energy cost and handling safety^[9][10]. The main segments encompass civil explosives companies, opencast coal and iron ore extraction. In explosive emulsions, calcium nitrate is added as a supplementary nitric source, which extends shelf life, increases ammonium nitrate solubility, and boosts overall energy content^[9][10].

Regulation and safety

The oxidising character and detonation risk of ammonium nitrate have prompted stringent controls within the European Union. Fertiliser product legislation distinguishes high-nitrogen fertilisers (at least 28% N), subject to specific requirements: detonation resistance, combustible matter limited to 0.2-0.4% carbon depending on nitrogen concentration, minimum pH of 4.5, and mandatory packaging in tamper-evident bags^[11][12][11]. These provisions aim to prevent diversion towards explosive uses. Transport additionally falls under UN regulations for classification of oxidising substances^[4].