GB805491A - Improved process for the manufacture of finely divided silica - Google Patents

Abstract

Finely divided silica of a particle size of 20-50 mm is produced by adding an aqueous solution of an alkali metal silicate, e.g. sodium silicate, containing at least 160 gm./l of SiO2 to an aqueous solution of an ammonium salt, e.g. ammonium chloride, at a temperature above 60 DEG C., preferably 85-95 DEG C. A 20 per cent excess of either reactant may be employed. The time of mixing may be 3 min.-2 hr. Small amounts of impurities such as iron oxide and alumina may be present. A surface-active agent, e.g. a salt of octadecyl amine, may also be present. The alkali metal silicate solution may contain 160-270 gm./l. of silica. The ratio Na2O/SiO2 may be 1 to 2-4. When using ammonium chloride solution, the solution may contain 80-130 gm./l. of this salt. The ammonium chloride solution may contain free ammonia and other chlorides, and may be obtained from the ammonia-soda process. The product as filtered, washed, and dried, e.g. at 125 DEG or 140 DEG C. According to the examples, a cold solution of sodium silicate is slowly introduced into the vortex of a rapidly stirred hot solution of ammonium chloride.