| 摘要 |
PURPOSE:To obtain a high-purity silica having an impurity content of lower than a specific level, in a short time at a low cost, by pouring an aqueous solution of an alkali silicate adjusted to a specific viscosity into a mineral acid to extract the impurities into the mineral acid solution and washing the precipitated silica with a mineral acid. CONSTITUTION:Viscosity of an aqueous solution of an alkali silicate (e.g. water glass) is adjusted to 10-10,000 poise e.g. by polymerization with dehydrative concentration process. The adjusted aqueous solution of alkali silicate is directly poured into a mineral acid (e.g. dilute sulfuric acid) to extract the impurities in the alkali silicate into the mineral acid solution and, at the same time, to produce precipitate of silica. The precipitate is separated by filtration, washed with a mineral acid and then with water. The resultant water-containing silica is dried and calcined to completely remove the water. A high-purity silica having a total impurity content of <=5ppm can be produced by this process. The silica is suitable as optical material, electronic material, etc.
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