Process for manufacture of anhydrous hydrogen fluoride and finely divided silica from fluosilicic acid

摘要

An improved process is described for converting aqueous fluosilicic acid waste product into anhydrous hydrogen fluoride and finely divided silica in which aqueous fluosilicic acid is pyrolyzed to produce silica and a dilute aqueous solution of hydrogen fluoride and fluosilic acid. The resulting dilute solution is subjected to electrodialysis, thereby obtaining a hydrogen fluoride concentration greater than that which characterizes the boiling point ridge which divides the phase diagram of the system hydrogen fluoride/fluosilicic acid/water, i.e. HF/H2SiF6/H2O, into two regions. Anhydrous hydrogen fluoride is recovered from the resulting composition by distillation.