Method of producing phosphoric acid and potassium dihydrogen phosphate from phosphate rock in the substantial absence of fluorine evolution

摘要

Substantially fluoride-free phosphoric acid is produced by the acidulation of phosphate rock with sulfuric acid wherein the acidulation reaction is conducted in the presence of added potassium as K.sub.2 O bearing compounds, e.g. KHSO.sub.4, K.sub.2 SO.sub.4, KH.sub.2 PO.sub.4 or KOH, and additional silica, to precipitate fluorides and silica as potassium silicofluoride and then removed on separation of the gypsum formed. Optionally, additional silica may be added to the phosphoric acid solution recovered after precipitation and removal of the gypsum, to precipitate additional fluoride as potassium silicofluoride to further purify the phosphoric acid. In a further embodiment sufficient potassium may be added along with additional silica in the acidulation step to produce potassium dihydrogen phosphate and phosphoric acid as additional products. The phosphoric acid and potassium dihydrogen phosphate are recovered substantially free from fluoride contamination and the reaction is carried out in the substantial absence of fluorine evolution into the atmosphere. Also disclosed is a process for conducting aconventional phosphoric acid facility to produce phosphoric acid and gypsum wherein defluorination of the phosphoric acid recovered is achieved by silicon dioxide and K.sub.2 O addition and the fluorides are removed from the system, the process including steps for production of pure phosphoric acid and potassium dihydrogen phosphate.