| 摘要 |
PURPOSE:To produce high-purity silica at a low cost, by dissolving a low-purity silica source in a mixture of hydrofluoric acid and sulfuric acid, distilling the solution and adding ammonia water to the resultant silicon fluoride to form a silica gel. CONSTITUTION:A compound or mixture utilizable as a silica source (e.g. white carbon) is dissolved in a liquid mixture of hydrofluoric acid and sulfuric acid. The hydrofluoric acid is preferably the one having a concentration of about 45% and its amount is selected to be sufficient to convert silicon in the raw material to fluoride. The sulfuric acid is preferably the one having a concentration of about 60% and its amount is selected to be sufficient to convert the ingredient metals in the raw material to sulfides. The solution produced by the above method is distilled at about 120 deg.C to recover a fraction composed of high-purity silicon fluoride and water. The fraction is added with ammonia water of about 25% concentration and the formed silica gel is separated by filtration, washed with water, dried and calcined to obtain silica having a purity of higher than five-nines.
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