Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1990-12-31
1992-11-24
Chaudhuri, Olik
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
423335, 423470, 423471, C01B 3312, C01C 0116
Patent
active
051659077
ABSTRACT:
A method for producing high purity silica and ammonium fluoride from silicon tetrafluoride-containing gas wherein silicon tetrafluoride-containing gas from the acidulation of phosphorus-containing rock is recovered and the liquid entrainment is separated from the gas. The recovered gas is converted to an ammonium fluosilicate solution and is ammoniated to produce high purity silica and ammonium fluoride. The recovered gas can be converted to an ammonium fluosilicate solution either by absorbing the gas directly in a solution of ammonium fluoride or by first absorbing the gas in water to produce fluosilicic acid and then reacting the fluosilicic acid with ammonia or ammonium fluoride. In a second aspect, the invention provides a method of separately recovering high purity silica and ammonium fluoride from an impure aqueous fluosilicic acid solution by reacting the fluosilicic acid solution with ammonia or ammonium fluoride for a time and at a temperature sufficient to form ammonium fluosilicate solution, recovering solid ammonium fluosilicate from the solution, purifying the solid ammonium fluosilicate by dissolving the solid in high purity water or ammonium fluosilicate solution, recrystallizing solid ammonium fluosilicate, and recovering purified ammonium fluosilicate crystals from the solution, forming an aqueous solution of the purified ammonium fluosilicate crystals and ammoniating the solution for a time and at a temperature sufficient to precipitate silica, and separately recovering high purity silica and ammonium fluoride.
REFERENCES:
patent: 2780522 (1957-02-01), Gloss et al.
patent: 4981664 (1991-01-01), Chieng
Perry et al., "Perry's Chemical Engineers' Handbook", 6th Ed., pp. 19-28-19-29.
Slack, Phosphoric Acid, Marcel Dekker, Inc. N.Y., N.Y., (1968), pp. 163-169.
Weast, Handbook of Chemistry and Physics, CRC Press, Cleveland, Ohio (195), p. F-7.
Chaudhuri Olik
Farquer Thomas L.
Fisher William J.
Guffey Wendell Ray
Horton Ken
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