Sulfuric Acid → Phosphoric Acid

Participants

Reaction Steps

A method of producing wet process phosphoric acid comprises reacting, in a reactor system, calcium phosphate rock particles with a mixture of recycled phosphoric and sulfuric acids, preferably supplemented with added fresh sulfuric acid, to form additional phosphoric acid and calcium sulfate dihydrate (gypsum). The reactor environment is controlled so as to avoid appreciable coating of the rock particles with calcium sulfate. A gypsum slurry is withdrawn and product phosphoric acid is separated therefrom and withdrawn from the process. The gypsum may be washed with a dilute sulfuric acid wash solution which is then added to the reactor. The gypsum is passed to a first recrystallizer wherein sulfuric acid is introduced, and the gypsum is recrystallized to hemihydrate. A slurry of the hemihydrate is passed to a second recrystallizer, wherein water obtained as described below is added and the hemihydrate is recrystallized to gypsum. The liquid component of the recrystallized gypsum slurry is separated therefrom and is employed as the above mentioned dilute sulfuric acid wash solution with, preferably, a portion being diverted to the first recrystallizer to control the solids content thereof. The recrystallized gypsum is washed with water, which is then added to the second recrystallizer as described above, and the washed gypsum is removed from the process as by-product.

Provenance & Evidence