METHOD FOR PREPARATION OF SODIUM SILICATES

In order to prepare amorphous sodium silicates having a water content of 0.3 to 6% by weight and an SiO2 to Na2O molar ratio of (1.9 to 2.8):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 2.8):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 20 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 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 250 to up to 500 DEG C for 1 to 60 minutes. 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 amorphous sodium silicate leaving the rotary kiln is comminuted by means of a mechanical crusher to particle sizes of 0.1 to 12 mm.