Dorr
Dorr : One of the two wet processes for making phosphoric acid by the acidulation of phosphate rock; the other is the Haifa process. The Dorr process uses sulfuric acid. Phosphate rock is primarily apatite, Ca5(PO4)3F. The calcium phosphate portion generates orthophosphoric acid and calcium sulfate: Ca3(PO4)2 + 3H2SO4 + 3CaSO4 + 2H3PO4 The fluoride portion is either removed as gaseous silicon tetrafluoride, if silica is added, or as the sparingly soluble sodium hexafluorosilicate, which remains with the calcium sulfate. There are several variants of the Dorr process which differ according to the treatment of the calcium sulfate. Some variants produce the dihydrate, gypsum, others produce the hemihydrate. The variants also differ in the concentration of the phosphoric acid produced, but it is never more than 43 percent. (Check source for accuracy of chemical formula)
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