Phosphoric acid by wet process
1. H2SO4 leaching
Reaction:
Process: Phosphate rock is ground and fed to chute where a recycle stream of weak phosphoric acid washes into reaction tank. Strong sulfuric acid is fed to the reactor. Around 98% conversion takes in 4-6 hours. Heat of reaction is controlled by using cooling air. Gypsum –Acid slurry is fed to travelling pan filter where 40% acid is removed and cake is washed with water. Filtrate is return to the reactor. The gypsum obtained is dried and send for paint or cement manufacturing. Dilute acid obtained can be concentrated in single effect evaporator.
OR
2. HCL leaching
Phosphate rock is ground and HCl is added in it. Fumes of CO2, HF and HCl are scrubbed for acid recovery. The mixture is fed to series of decanter and settlers and then to counter current solvent extraction operations. The solids underflow goes to 2-3 washing thickeners. Extraction of phosphoric acid and some free HCl is done in an battery of mixer –settlers with CaCl2 retain in aqueous phase. The extract is passed through several more mixer settlers. Phosphoric acid is recovered in triple effect evaporator and CaCl2 is separated from final settler.