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 pentox ...

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 Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...

and

calcium nitrate Calcium nitrate, also called ''Norgessalpeter'' (Norwegian salpeter), is an inorganic compound with the formula Ca(NO3)2(H2O)x. The anhydrous compound, which is rarely encountered, absorbs moisture from the air to give the tetrahydrate. Both anhyd ...

. :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 or

potassium sulfate Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the inorganic compound with formula K2SO4, a white water-soluble solid. It is commonly used in fertilizers, pro ...

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 Phosphogypsum (PG) is the calcium sulfate hydrate formed as a by-product of the production of fertilizer from phosphate rock. It is mainly composed of gypsum (CaSO4·2H2O). Although gypsum is a widely used material in the construction industry, p ...

). The calcium nitrate mentioned before, can as said be worked up as calcium nitrate fertilizer but often it is converted into

ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...

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 Odda () is a former municipality in the old Hordaland county, Norway. The municipality existed from 1913 until its dissolution in 2020 when it was merged into Ullensvang Municipality in Vestland county. It was located in southeastern Hordaland c ...

, his company never employed it. Instead, it licensed the process to

Norsk Hydro Norsk Hydro ASA (often referred to as just ''Hydro'') is a Norwegian aluminium and renewable energy company, headquartered in Oslo. It is one of the largest aluminium companies worldwide. It has operations in some 50 countries around the world a ...

BASF BASF Societas Europaea, SE () is a German multinational corporation, multinational chemical company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters is located in Ludwigshafen, Germany. The ...

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 EuroChem Group AG is a Swiss fertilizer producer. It is a fertilizer manufacturer with its own capacity in all three primary nutrients – nitrogen, phosphates and potash. It is headquartered in Zug, Switzerland. It manufactures and markets ag ...

, Borealis Agrolinz Melamine GmbH, Omnia, GNFC) 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