| 摘要 |
In the present invention, there is disclosed a process to obtain a colloidal silica suspension in a concentration above its gel point wherein the process consists in the steps of: - preparing a stable suspension by causing an aqueous solution of an alkaline metal silicate to pass, at room temperature, through a strong cationic ion exchange column to obtain unstable silicic acid at a final pH of 2 to 3.5; - stabilizing the acid sol at room temperature by vigorous stirring and rapidly adding an alkaline silicate, abruptly to bring the pH final value to 9 to 11; - feeding the stabilized suspension to evaporators and concentrate said suspension at a temperature ranging from approximately 90 degC to 98 degC under vacuum until obtaining a final concentration of SiOi2 of approximately 5 to 15 percent by weight; - cooling the suspension to room temperature and subjecting it to cold ultrafiltration, wherein amount of cations and anions in so treated suspension is adjusted so as to be compatible with suspension concentration and silica particle size. So obtained suspension, containing silica particles with size less than 10 nm and with concentration exceeding 50 percent by weight, has concentration above its gel point and is suitable for use as flocculation agent, plastics additive or in paper manufacture. |
