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

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

fertilizer A fertilizer or fertiliser 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 liming materials or other non-nutrient soil amendments. Man ...

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 an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

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, ...

and

calcium nitrate Calcium nitrate are inorganic compounds 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 anhydrous and hydrated forms are colourless salts. Hydrated ...

. :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 chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

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 sa ...

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, prov ...

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 (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

nor producing

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, 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, drywall and blackboard or sidewalk ...

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, particularly phosphoric acid, from phosphate rock. It is mainly composed of gypsum (). Although gypsum is a widely used material in the cons ...

). 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 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, but does not form hydrates. It is predominantly us ...

and

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

using

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 Norsk Hydro ASA (often referred to as just ''Hydro'') is a Norway, 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 th ...

BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...

, Hoechst, 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 (Norsk Hydro),

Acron Acron (), son of Zeno of Elea, was a Medicine in ancient Greece, Greek physician born at Agrigentum (Gk. Acragas) in Magna Graecia. Life The exact dates of Acron is not known; but, as he is mentioned as being contemporary with Empedocles, who di ...

, EuroChem, 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 technol ...

, 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