2Raw Materials for Phosphoric Acid Production •Phosphate ores are of two major geological origins:–•Igneous –found in Kola, South Africa, Brazil, etc. •Sedimentary –found in Morocco, Algeria, Jordan, U.S.A., etc. •The phosphate minerals in both types of ore are of the apatite group, of which the most commonly encountered is the Fluorapatite –CaF2.3Ca3(PO4)2•Most phosphate ores have to be concentrated or beneficiated before they can be used.
3Principles of the Di-Hydrate Process•The tricalcium phosphate in the phosphate rock is converted by reaction with concentratedsulphuric acid into phosphoric acid and the insoluble salt calcium sulphate.Ca3(PO4)2+ 3H2SO42H3PO4+ 3CaSO4•The insoluble calcium sulphate is then separated from the phosphoric acid, most usually byfiltration.•The reaction between phosphate rock and sulphuric acid is self-limiting because an insoluble layerof calcium sulphate forms on the surface of the particles of the rock. This problem is kept to a