Abstract: In a process for the reaction of phosphate rock and sulfuric acid in the presence of potassium ion to form a mixture of phosphoric acid and a precipitated gypsum wherein the presence of the potassium ion causes precipitation of fluorides from the phosphate rock as potassium silicofluoride as a coprecipitate with the gypsum, and the phosphoric acid is separated from the gypsum slurry, the potassium silicofluoride is separated from the gypsum by extraction with phosphoric acid which may contain from 0-25 weight percent of sulfuric acid based on the amount of gypsum to be extracted or such phosphoric acid which may contain some fluorine. This extraction procedure provides a substantially fluoride-free gypsum product and an extraction solution containing recoverable potassium silicofluoride.

Abstract: 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.