Ammonium Nitrate Fertilisers: Benefits, Challenges and Solutions: The 32nd Francis New Memorial Lecture

Keywords: ammonium nitrate, nitrogen fertilisers, safety, hazards.

Ammonium nitrate (AN) has been with us for more than a hundred years as an important industrial product. Virtually all ammonium nitrate is chemically produced from ammonia and nitric acid. Its commercial production in a significant way started around the beginning of the last century, when the Haber Bosch process for making ammonia from the atmospheric air came on the scene. The world annual production reached close to 50 million tonnes in the period around 2020.

Its two main uses are as a nitrogen fertiliser and as a basic raw material for making commercial explosives. In addition, it is used in a variety of industries, for example, the production of nitrous oxide gas and cool packs.

Ammonium nitrate is a very efficient nitrogen fertiliser, particularly for regions with temperate climatic conditions, as it provides both types of nitrogen: nitrate (NO₃^–) and ammonium (NH₄⁺). It can provide nitrogen over a long period. Consequently, AN continues to be the preferred nitrogen source in comparison with urea in most parts of Europe, despite its safety and security issues. The early fertiliser products were a double salt of ammonium nitrate and ammonium sulphate, called the OPPAU salt, and CAN, a chemical mixture of AN and limestone. The current range includes their upgraded versions and, in addition, straight-AN, compound fertiliser and liquid fertiliser.

Ammonium nitrate and AN-based fertilisers possess potential chemical hazards in industrial operations, namely fire, decomposition and explosion. However it also has several properties which enable it to be handled safely when treated appropriately. In addition, safe treatment systems, processes and procedures have been developed to carry out various operations safely.

The ammonium nitrate industry has faced a number of major challenges in the areas of safety, environmental impacts and security. It has addressed these successfully and effectively. It will continue to face further ones in the future. The Beirut explosion accident has raised new challenges. In addition, major concerns relating to climate change have raised the stakes. They have the potential to open new opportunities in the wider chemical industry, including a shift from chemical to biochemical processing.