| 摘要 |
The present invention provides a basic method for producing high purity silica and ammonium fluoride from silicon tetrafluoride-containing gas, particularly the gas generated by acidulation. The basic method comprises recovering silicon tetrafluoride-containing gas from the acidulation of a fluorine-containing phosphorus source, separating liquid entrainment from the gas, converting the gas recovered to an ammonium fluosilicate solution, and ammoniating said ammonium fluosilicate solution to produce high purity silica and ammonium fluoride. The present invention goes beyond this basic method with an improved stripper design for removing impure silicon tetrafluoride from the wet phosphoric acid process, the use of demisting equipment on the anhydrous ammonia vaporizer to reduce contamination in the gas stream, the use of ion-exchange to remove impurities from the ammonium fluosilicate or fluosilicic acid solutions, seeding an ammonium fluosilicate/ammonia reactor with silica crystals to permit continuous reactor operation, and the operation of an ammonium fluoride evaporator in a manner to reduce the N/F mole ratio below about 1 which prevents premature precipitation of silica when the ammonium fluoride is introduced in an absorber.
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