Nitrophosphate process

The "Odda process" refers to the industrial process to produce fertilizers. It was invented by Erling Johnson at the town Odda in Norway around 1927. In this process phosphate rock is acidulated with nitric acid to produce a mixture of phosphoric acid and calcium nitrate. By cooling down the solotion to a temperature less than 0 ° celcius the calcium nitrate crystalises and can be separated from the phosphoric acid. The separated calcium nitrate can be worked up as nitrogen fertilizer. The filtrate mainly phosphoric acid with reste of nitric acid and traces of calcium nitrate is neutralised with ammonia to produce a compound fertilizer. An addition of pottash wil result in the famous NPK fertilizer. Reasons why this proces became popular are that there is no need for expensive sulphuric acid to acidulate and that there is no gypsum waste. Allthow the proces was invented by Erling Johnson in the company "Odda Smelteverk" the company itself never used the process. It did gave licences to the company's Norsk Hydro, BASF, Hoechst and DSM. They all used the process but with some differences in details. Today Only Yara (Norsk Hydro), BASF, AgroLinz and GNFC are still producing by the "Odda process".