DFFLURINATION OF WET-PROCESS PHOSPHORIC ACID FOR PRODUCTION OF DICALCIUM PHOSPHATE

摘要

In Egypt, concentrated wet-process phosphoric acid is produced from Nile Valley phosphate concentrate by the conventional Dihydrate process. It contains 48% P_2O_5 and 0.8% F. For production of dicalcium phosphate (animal feed supplement), F content in concentrated phosphoric acid should be < 0.17%. Decreasing fluorine content to this level was achieved by reaction of merchant-grade phosphoric acid with silica dust followed by sodium hydroxide addition. The following optimal reaction conditions were determined: 80 deg C reaction temperature, 3 h reaction time, 1.3 stoichiometric ratio of SiO_2:F and 0.9 stoichiometric ratio of Na_2O:F. These conditions lead to removal of about 81% F from the acid. Dicalcium phosphate was prepared from the produced defluorinated phosphoric acid.