PROCESS FOR THE PRODUCTION OF AMORPHOUS SODIUM SILICATE

In order to prepare crystalline sodium silicates having a layered structure, a water content of less than 0.3% by weight and an SiO2 to Na2O molar ratio of (1.9 to 2.1):1 from a water glass solution containing at least 20% by weight of solid, the water glass solution is obtained by reaction of silica sand with sodium hydroxide solution in an SiO2 to Na2O molar ratio of (2.0 to 2.3):1 at temperatures of 180 to 240 DEG C and pressures of 10 to 30 bar. This water glass solution is treated in a spray-drying zone with hot air of 200 to 300 DEG C at a residence time of 10 to 25 s and a temperature of the waste gas leaving the spray-drying zone of 90 to 130 DEG C with formation of a pulverulent amorphous sodium silicate having a water content (determined as loss on ignition at 700 DEG C) of 15 to 23% by weight and a bulk density of more than 300 g/l. The pulverulent, amorphous, water-containing sodium silicate is placed in a tilted rotary kiln equipped with means for moving solids and treated therein counter-currently with flue gas at temperatures of more than 500 DEG C to 850 DEG C for 1 to 60 minutes with formation of crystalline sodium silicate. The rotary kiln is insulated here in such a manner that the temperature of its outer wall is less than 60 DEG C. Finally, the crystalline sodium silicate leaving the rotary kiln is comminuted by means of a mechanical crusher to particle sizes of 0.1 to 12 mm.