| abstract |
To prepare crystalline sodium disilicates having a laminar structure, a molar ratio of SiO2 to Na2O of (1.9 to 2.1) 1 and a water content of less than 0.3% by weight, a water glass solution is first obtained by reacting sand with sodium hydroxide solution in a molar ratio of SiO2 to Na2O of (2.0 to 2.3) : 1 at temperatures of 180 DEG to 240 DEG C. and pressures of 10 to 30 bar. This water glass solution having at least 20% by weight of solids is treated in a spray drier with hot air at 200 DEG to 300 DEG C. with the formation of a pulverulent amorphous sodium disilicate having a water content (determined as loss on heating at 700 DEG C.) of 15 to 23% by weight and a bulk density of at least 300 g/l. The spray-dried pulverulent, amorphous sodium disilicate is ground. The ground sodium disilicate is introduced into a rotary kiln equipped with devices for moving solids, externally heated via the wall and having in its interior a plurality of different temperature zones, and is treated therein at temperatures of 400 DEG to 800 DEG C. for 1 to 60 minutes with formation of crystalline sodium disilicate. |