Process for producing amorphous aluminosilicates

A process for producing an amorphous aluminosilicate having an average particle size of no larger 0.5 .mu.m and a specific surface area of at least 5 m.sup.2 /g having the formula:

• xNA.sub.2 O.Al.sub.2 O.sub.3.YSiO.sub.2
• wherein x is a number between 0.6 and 1.8 inclusive;
• and y is a number between 1.3 and 7 inclusive;
• which comprises:
• maintaining an alkali solution (Solution-C), the alkalinity of which is within the range of 1.2-3.5 N under stirring;
• adding a sodium aluminate solution (Solution-A), containing free alkali, and sodium silicate solution or collodial silica solution (Solution-B) containing free alkali, to the Solution-C, separately to prepare a slurry which contains an amorphous sodium aluminosilicate in the form of finely divided particles which are only slightly soluble in water;
• and
• aging the slurry after completing said addition at 55.degree. C. or lower for at least one hour until ripe, wherein the addition of Solution-A and Solution-B into Solution-C is carried out so that the Si/Al ratio in the resultant mixture is kept within the range of 0.7 to 7.6 during and after the addition, and mixing effected at 55.degree. C. or lower, and Solution-A and Solution-B are prepared so that the alkalinity of the aqueous solution phase during the formation of the slurry and during the aging is kept within .+-.0.30 N of the alkalinity of Solution-C.