Phosphorus occurs in natural geological deposits of phosphate rock, which is mined from the earth’s crust. The largest deposits of phosphate rock are located in North Africa, China, India, the United States, Brazil, Australia and Russia.
Most phosphate ores require a treatment referred to as “beneficiation,” which entails washing, crushing, sizing and flotation before the material is pure enough to be used as phosphate rock raw material for further chemical processing.
Phosphate ore deposits are not evenly distributed in the earth’s crust; some countries and areas are endowed with enormous resources. Major mining today occurs only on deposits where grade, geometry and logistics are most favorable for low-cost production. In 2002, 11 countries were responsible for 83 percent of the world’s aggregate production of approximately 143 million tons of phosphate rock. As of 1999, the total known reserves of phosphate rock (defined as mineral deposits of established extension that are, or could be, profitably mined under prevailing conditions of costs, market prices and technologies) amounted to 56 billion tons, with 60 percent of this located in Morocco.
To make the phosphorus in phosphate rock soluble and available to plants, the rock is digested with sulfuric or nitric acid to manufacture phosphoric acid, an intermediate product that is further processed to make many different kinds of phosphate-containing fertilizers.
The principal phosphate-based fertilizer products are:
Monammonium phosphate (MAP) (containing 52 percent phosphate as P2O5) and diammonium phosphate (DAP) (containing 46 percent phosphate as P2O5) – referred to as ammoniated phosphates because phosphoric acid is treated with ammonia to form these products, both of which also contain nitrogen. Both are widely produced in granular form for use as such or for blending with other types of fertilizers, and are also produced in non-granular forms for use in liquid fertilizers.
Nitrophosphate products – in which part of the nitrogen content is in nitrate form (as opposed to the purely ammonium form found in the MAP and DAP products). Nitrophosphate products are produced when the phosphate rock is dissolved in nitric acid rather than sulfuric acid.
Single superphosphate – produced by treating phosphate rock with sulfuric acid, single superphosphate contains 16-20 percent phosphate as P2O5.
Triple superphosphate, produced by treating phosphate rock with phosphoric acid, is a highly concentrated form of phosphate fertilizer (containing roughly 46 percent phosphate as P2O5) and is produced in both granular and non-granular forms.