Hydrogen Fluoride and Pyrogenic Silica from Fluosilicic Acid

Fluosilicic acid is obtained in large quantities as a byproduct when manufacturing wet process phosphoric acid and superphosphate. Only a minor part of the acid is utilized. It is therefore not surprising that many attempts have been made to produce hydrogen fluoride using fluosilicic acid as a raw material. Some methods suggested in the literature are briefly described.

For many years AB Nynas-Petroleum, Sweden, has manufactured pyrogenic silica by means of flame hydrolysis of silicon tetrafluoride which has been manufactured by means of reacting fluosilicic acid and sulphuric acid. In the flame are formed not only silica but also hydrogen fluoride. Together with Unie van Kunstmestfabrieken bv., Holland, a method of separating anhydrous hydrogen fluoride has been worked out. The process and the products obtained are described.