Nitrophosphate process

Lore & Background

Erling Johnson created the nitrophosphate process while working for the Odda Smelteverk, but his company never employed it. Instead, it licensed the process to Norsk Hydro, BASF, Hoechst, and DSM. Each of these companies used the process, introduced variations, and licensed it to other companies. The process involves acidifying phosphate rock with dilute nitric acid to produce a mixture of phosphoric acid and calcium nitrate. The mixture is cooled to below 0 °C, where the calcium nitrate crystallizes and can be separated from the phosphoric acid. The resulting calcium nitrate produces nitrogen fertilizer, while the filtrate is neutralized with ammonia to produce a compound fertilizer. If potassium chloride or potassium sulfate is added, the result will be NPK fertilizer.

Reader's Guide

The nitrophosphate process represents a significant innovation in fertilizer manufacturing because it avoids the use of expensive sulfuric acid and eliminates the production of phosphogypsum waste, a common byproduct of traditional phosphate processing. Although invented by Erling Johnson around 1927, the process was commercialized and refined by major chemical companies such as Norsk Hydro, BASF, Hoechst, and DSM. These companies introduced variations and licensed the technology further, leading to the process being generally referred to as the nitrophosphate process rather than the Odda process. Today, only a few companies—including Yara (Norsk Hydro), Acron, EuroChem, Borealis Agrolinz Melamine GmbH, Omnia, and GNFC—still use the Odda process. The process remains relevant for producing nitrogen and compound fertilizers without the environmental burden of gypsum waste.

Did You Know?

• The process requires neither expensive sulfuric acid nor produces gypsum waste (phosphogypsum).
• Johnson's employer, Odda Smelteverk, never used the process but licensed it to Norsk Hydro, BASF, Hoechst, and DSM.
• The calcium nitrate produced can be converted into ammonium nitrate and calcium carbonate using carbon dioxide and ammonia.