Production of Phosphoric acid includes three routes - the Thermal Process, the Wet Process and the dry Kiln Process.
Firstly let us introduce thermal phosphoric acid
This very pure phosphoric acid is obtained by burning elemental phosphorus to produce phosphorus pentoxide and dissolving the product in dilute phosphoric acid. Because most impurities present in the rock have been removed when extracting phosphorus from the rock in a furnace, this produces a very pure phosphoric acid. The end result is food-grade, thermal phosphoric acid; however, for critical applications, additional processing to remove arsenic compounds may be needed.
Secondly let us introduce wet phosphoric acid
See also: Nitrophosphate process
Wet process phosphoric acid process: add sulfuric acid to tricalcium phosphate rock, typically found in nature as apatite.
The reaction is: Ca5(PO4)3X + 5 H2SO4 + 2 H2O → 3 H3PO4 + 5 CaSO4 · 2 H2O + HX
where X may include OH, F, Cl, and Br
The initial phosphoric acid solution may contain 23-33% P2O5, but can be concentrated by the evaporation of water to produce commercial- or merchant-grade phosphoric acid, which contains about 54% P2O5. Further evaporation of water yields superphosphoric acid with a P2O5 concentration above 70%.
Digestion of the phosphate ore using sulfuric acid yields the insoluble calcium sulfate (gypsum), which is filtered and removed as phosphogypsum. Wet-process acid can be furthered purified by removing fluorine to produce animal-grade phosphoric acid, or by solvent extraction and arsenic removal to produce food-grade phosphoric acid.
Finally let us introduce Kiln Phosphoric Acid
Kiln phosphoric acid (KPA) process technology is the most recent technology which will both make low grade phosphate rock reserves commercially viable and will increase the P2O5 recovery from existing phosphate reserves. This may significantly extend the commercial viability of phosphate reserves.