Preparation of aqueous silica sols free of alkali metal oxides

A process for the preparation of an aqueous silica sol containing less than 200 ppm of an alkali metal having a SiO.sub.2 concentration of from 5-55% SiO.sub.2 and a surface area of less than 800 M.sup.2 /gram said process comprising the steps of:

• A. providing a 0.1-3.0% aqueous solution of a lower alkanol amine;
• B. heating the aqueous solution of the lower alkanol amine to its boiling point;
• C. adding to the boiling aqueous solution of the lower alkanol amine a 2 to 10% by weight aqueous solution of silicic acid, the mole ratio of SiO.sub.2 to alkanol amine being from 1:1 to 100:1;
• D. removing water by distillation so as to keep a constant volume as the silicic acid solution is added;
• E. recovering an aqueous colloidal silica sol containing 5-55% by weight SiO.sub.2 having a pH of 8-10;
• F. passing the aqueous silica sol of Step E above through an ion exchange resin or resins;
• and then,
• G. recovering a deionized acidic aqueous silica sol containing less than 200 ppm of an alkali metal and having a pH of 2 to 5.

A process for the preparation of an aqueous silica sol containing less than 200 ppm of an alkali metal having a SiO.sub.2 concentration of from 5-55% SiO.sub.2 and a surface area of less than 800M.sup.2 /gram said process comprising the steps of:

• A. providing a 0.1-3.0% aqueous solution of a lower alkanol amine;
• B. heating the aqueous solution of the lower alkanol amine to its boiling point;
• C. adding to the boiling aqueous solution of the lower alkanol amine a 2 to 10% by weight aqueous solution of silicic acid, the mole ratio of SiO.sub.2 to lower alkanol amine being from 1:1 to 100:1;
• D. removing water by distillation so as to keep a constant volume as the silicic acid solution is added;
• E. recovering an aqueous colloidal silica sol containing 5-55% by weight SiO.sub.2 having a pH of 8-10;
• F. passing the aqueous silica sol of Step E above through an ion exchange resin or resins;
• G. recovering a deionized acidic aqueous silica sol containing less than 200 ppm of an alkali metal and having a pH of 2 to 5;
• H. adding to the acidic aqueous silica sol of Step G an aqueous solution of ammonia so as to raise the pH of said silica sol to from 9-10;
• I. recovering a deionized alkaline silica sol containing less than 200 ppm of an alkali metal.