Defluorination of wet-process phosphoric acid for production of dicalcium phosphate

In Egypt, concentrated wet-process phosphoric acid is produced from Nile Va lley phosphate concentrate by the conventional Dihydrate process. It contai ns 48% P2O5 and 0.8% F. For production of dicalcium phosphate (animal feed supplement), F content in concentrated phosphoric acid should be < 0.17%. D ecreasing fluorine content to this level was achieved by reaction of mercha nt-grade phosphoric acid with silica dust followed by sodium hydroxide addi tion. The following optimal reaction conditions were determined: 80 degrees C reaction temperature, 3 h reaction time, 1.3 stoichiometric ratio of SiO 2:F and 0.9 stoichiometric ratio of Na2O:F. These conditions lead to remova l of about 81% F from the acid. Dicalcium phosphate was prepared from the p roduced defluorinated phosphoric acid.