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

Abstract: 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/H.sub.2 SiF.sub.6 /H.sub.2 O, into two regions. Anhydrous hydrogen fluoride is recovered from the resulting composition by distillation.

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Inventors: Nagasubramanian, Krishnamurthy (Parsippany, NJ, US)
Chlanda, Frederick P. (Rockaway, NJ, US)
Liu, Kang-Jen (Bridgewater, NJ, US)

Application Number: 851234
Filing Date: 1977-11-14
Publication_date: 1979-03-13
Assignee: Allied Chemical Corporation (Morris Township, Morris Country, NJ)
Primary Class(es): 204/517 204/531, 423/240R, 423/337, 423/484
Other Classes:
US Patent Ref:

3787304	Jan, 1974	Chlanda et al.	204/180.
3907653	Sep, 1975	Horn	204/180.

Other Refs: 174610

Dec, 1965	SU

Primary Examiner: Prescott, Arthur C.
Assistant Examiner:
Attorney: North; Robert J., Harman; Robert A.