The Commercial Wet Process

The commercial wet process consists essentially of grinding the apatite phosphate rock, reacting it with acid, and then separating the insoluble calcium sulphate by filtration (5.7). In practice, the 

Relative Importance of Phosphoric Acid Production in the United States 1994 

Efficient separation of the precipitated calcium sulphate, which is crucial to a successful commercial process, depends on its crystallisation behaviour and the acid viscosity. These factors are influenced by the acid concentration, the temperature and the impurities in the phosphate rock which can themselves be precipitated. 

Several variations of the basic process have been evolved, one of the options being to precipitate the calcium sulphate as dihydrate (x = 2), hanihydrate (x= 1/2) or anhydrite (x = 0). In the most used dihydrate process, the acid is usually obtained at a concentration of about 32% P2O5. Evaporation is used to increase the concentration to 40-42% P2O5 (as required for ammonium phosphate manufacture) or 52-54% P2O5 - merchant grade (as required for superphosphate production). During 

Typical Impurity Levels in Commercial Phosphoric Acid (wt%) 

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