The nitrophosphate process (also known as the Odda process) is a method for the industrial production of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

s invented by Erling Johnson in the municipality of Odda, Norway around 1927. The process involves acidifying

phosphate rock Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxi ...

with dilute

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

to produce a mixture of phosphoric acid and calcium nitrate. :Ca₅(PO₄)₃OH + 10 HNO₃ → 3 H₃PO₄ + 5 Ca(NO₃)₂ + H₂O The mixture is cooled to below 0 °C, where the calcium nitrate crystallizes and can be separated from the phosphoric acid. :2 H₃PO₄ + 3 Ca(NO₃)₂ + 12 H₂O → 2 H₃PO₄ + 3 Ca(NO₃)₂·4H₂O The resulting calcium nitrate produces nitrogen fertilizer. The filtrate is composed mainly of phosphoric acid with some nitric acid and traces of calcium nitrate, and this is neutralized with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

to produce a compound fertilizer. :Ca(NO₃)₂ + 4 H₃PO₄ + 8 NH₃ → CaHPO₄ + 2 NH₄NO₃ + 3(NH₄)₂HPO₄ If

potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...

or potassium sulfate is added, the result will be NPK fertilizer. The process was an innovation for requiring neither the expensive

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

nor producing

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...

waste (known in the context of phosphate production as phosphogypsum). The calcium nitrate mentioned before, can as said be worked up as calcium nitrate fertilizer but often it is converted into ammonium nitrate and calcium carbonate using

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

and ammonia. :Ca(NO₃)₂ + 2 NH₃ + CO₂ + H₂O → 2 NH₄NO₃ + CaCO₃ Both products can be worked up together as straight nitrogen fertilizer. Although Johnson created the process while working for the Odda Smelteverk, his company never employed it. Instead, it licensed the process to Norsk Hydro, BASF,

Hoechst Hoechst, Hochst, or Höchst may refer to: * Hoechst AG, a former German life-sciences company * Hoechst stain, one of a family of fluorescent DNA-binding compounds * Höchst (Frankfurt am Main), a city district of Frankfurt am Main, Germany ** Fra ...

, and DSM. Each of these companies used the process, introduced variations, and licensed it to other companies. Today, only a few companies (e.g.

Yara Yara may refer to: People * YARA (girl group), a Filipino girl group * Yara (given name) * Yara (surname), a Japanese surname * Yara (singer) (born 1983), Lebanese pop singer * Yara (footballer) (born 1964), Brazilian footballer Locations * Y ...

(Norsk Hydro), Acron, EuroChem, Borealis Agrolinz Melamine GmbH, Omnia,

GNFC Gujarat Narmada Valley Fertilizers & Chemicals (GNFC) is an Indian manufacturer of fertilizers and chemicals. GNFC was founded in 1976, jointly promoted by the Government of Gujarat and the Gujarat State Fertilizers and Chemicals (GSFC). Locat ...

) still use the Odda process. Due to the alterations of the process by the various companies who employed it, the process is now generally referred to as the nitrophosphate process.

References

* {{cite book , editor = Nielsson, F.T. , title=Manual of fertilizer processing , publisher=

CRC Press The CRC Press, LLC is an American publishing group that specializes in producing technical books. Many of their books relate to engineering, science and mathematics. Their scope also includes books on business, forensics and information tec ...

, year=1986 , pages = 393–420, isbn=0-8247-7522-8 , chapter = 15. The Norsk Hydro Nitrophosphate Process , author1=J. Steen , author2=H. Aasum , author3=T. Heggeboe Chemical processes Norwegian inventions