|The majority of the phosphoric acid in fertilizer phosphates is produced from sulfuric acid and phosphate rock. This phosphoric acid, known as "wet-process" acid, is then used in the manufacture of triple superphosphate, ammonium phosphates and other high analysis fertilizer products.
Phosphoric acid production by the wet process consists of three main operations: reaction between the phosphate rock and sulfuric acid, separation of the gypsum from the phosphoric acid and concentration of the phosphoric acid to the desired P2O5 level.
The primary chemical reaction in the production of the wet process is between the calcium phosphate constituent of the phosphate rock and sulfuric acid to form diluted phosphoric acid (26-28% P2O5) and calcium sulfate, which precipitates as dihydrate (gypsum). The gypsum is pumped into settling ponds or conveyed to dry disposal. The diluted acid is concentrated, with the highest concentration normally being 52-54% P2O5, and used for fertilizers production in situ or shipped for fertilizer usages