Process for producing crystalline sodium silicates having a layered structure

摘要

For producing crystalline sodium silicates having a layer structure, an SiO2/Na2O molar ratio of (1.9 to 2.1):1 and a water content of less than 0.3% by weight from a waterglass solution containing at least 20% by weight of solids, the waterglass solution is obtained by reacting quartz sand with sodium hydroxide solution at an SiO2/Na2O molar ratio of (2.0 to 2.3):1 at temperatures of 180 DEG to 240 DEG C. and pressures of 10 to 30 bar. This waterglass solution is treated in a spray-drying zone with hot air at 200 DEG to 300 DEG C. for a residence time of 10 to 25 seconds and at a temperature of the exit gas leaving the spray-drying zone of 90 DEG to 130 DEG C., to form a pulverulent amorphous sodium silicate having a water content (determined as the 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 introduced into an obliquely arranged rotary kiln fitted with devices for moving solids and treated therein with flue gas in countercurrent at temperatures from more than 500 DEG up to 850 DEG C. for 1 to 60 minutes to form crystalline soidium silicate. The rotary kiln is here insulated in such a way that its outside wall temperature is less than 60 DEG C. Finally, the crystalline sodium silicate emerging from the rotary kiln is comminuted by means of a mechanical crusher to grain sizes of 0.1 to 12 mm.