Removal of aluminum contamination during production of phosphoric acid

A process for acidulating phosphate rock to produce phosphoric acid having reduced aluminum content comprising the steps of:

• a. feeding phosphate rock, sulfuric acid, recycle phosphoric acid, and acid soluble silica into a set of attack tanks, thereby acidulating said phosphate rock and effecting the dissolution of its phosphate content;
• b. maintaining the molar ratio of non-fluosilicate fluoride to aluminum in the liquid phase of the acidulation slurry formed in step (a.) between 2.5 and 5.0, thereby precipitating aluminum from the liquid phosphoric acid phase during the acidulation of phosphate rock;
• c. subjecting the acidulation slurry from step (b.) to filtration;
• d. recovering a liquid phosphoric acid phase from filtration step (c.);
• e. washing the filter cake from step (c.) with water to generate recycle phosphoric acid for return to step (a.), and
• f. recycling said recycle phosphoric acid to the attack tanks in step (a.).