Management of Fluorine in Phosphoric Acid Production

Keywords: Phosphate rock, fluorine recovery, fluosilicic acid, defluorination, Praysepâ„¢ separator.

During the production of phosphoric acid, part of the fluoride salts contained in phosphate rock is transformed into volatile fluorinated compounds and escapes from the gypsum slurry. The proportion of fluorine going to the gaseous effluents, in dihydrate reaction conditions, is in the order of 5-10% compared to the initial quantity in the rock. This proportion increases with the phosphoric acid strength and can increase up to 50-60% at a concentration of 45-50% P₂O₅.

Therefore, for both environmental and economic reasons, there is an obvious interest in managing this issue and recovering the fluorine. Fluorine is a potential atmospheric pollutant and pollutant of waste water, but it is possible to recover it as fluosilicic acid and to valorise this latter.

This paper describes the processes for the recovery of fluorine in the form of fluosilicic acid at commercial strength and of a considerable proportion of the fluorine leaving the flash chamber of the phosphoric acid concentration unit.

Benoît Van Massenhove, Marc Collin and Tibaut Theys, Prayon Technologies s.a. Rue Joseph Wauters 144, B-4480 Engis, Belgium.

15 pages, 11 figures, 2 tables, 9 references.