Example of phosphoric acid production Wet process phosphoric acid is prepared by adding sulfuric acid H 2 SO 4 to apatite or tricalcium phosphate rock resulting in the following reaction 3 H 2 SO 4 Ca 3 PO 4 2 6 H 2 O ↔ 2 H 3 PO 4 3 CaSO 4 2H 2 O Wet process acid has to be purified by removing fluorine and other undesirable elements to produce feed grade phosphoric acid