Phosphate's value has long been recognized by farmers who once applied ground phosphate rock directly to acidic soils. However, due to the limited effectiveness of this method, very little ground phosphate rock is currently being directly applied in agriculture.
Phosphate ore from mineral deposits is now mostly processed into the chemical fertilizers that are commonly used by farmers around the world. (See below for information on downstream fertilizer products.)
Phosphate from mineral deposits is the only source of phosphate used in the manufacture of fertilizers.
Approximately 90% of all phosphate rock is consumed annually in the production of fertilizers. The manufacturing process varies depending on the type being produced and can involve the conversion to phosphoric acid as an intermediate step, mainly for the production of ammonium phosphate fertilizers.
Types of phosphate fertilizers include:
- Single superphosphate (SSP)
- Triple superphosphate (TSP)
- Diammonium phosphate (DAP)
- Monoammonium phosphate (MAP)
- Ground phosphate rock
The remaining 10% of phosphate rock is used in livestock and poultry feed supplements, pesticides, detergents, water treatment chemicals, food additives and metal surface treatments.
Fertilizer manufacturers usually require that the phosphate rock concentrate (also known as phosphate rock or phosrock) they are using to make fertilizers has a P2O5 grade of about 28% or more. Since most phosphate deposits have a grade below that level, the ore that is extracted from the deposits typically needs to be upgraded into a phosphate rock concentrate before it is shipped to fertilizer producers. The upgrading process (sometimes referred to as "beneficiation") usually involves washing, separation, flotation and concentration.
Phosphate rock grades are customarily expressed as percent P2O5 (Phosphorus Pentoxide), but also may be referred to as percent BLP (Bone Phosphate of Lime). The conversion factor is:
%P2O5 x 2.185 = %BLP
For example, a range of 30 to 32% P2O5 equals a range of 65 to 70% BLP.