Process for producing amorphous sodium silicate

Claim 1

A process for producing amorphous sodium silicates having a water content of 0.3 to 6% by weight and an SiO 2 /Na 2 O molar ratio of (1.9 to 2.8) : 1 from a waterglass solution containing at least 20% by weight of solids, which comprises a) obtaining the waterglass solution by reacting quartz sand with sodium hydroxide solution in an SiO 2 /Na 2 O molar ratio of (2.0 to 2.8) : 1 at temperatures from 180° to 240° C. and pressures from 10 to 30 bar, b) treating the waterglass solution in a spray-drying zone with hot air at 200° to 300° 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° to 130° C., to form a pulverulent amorphous sodium silicate having a water content (determined as the loss on ignition at 700° C.) of 15 to 23% by weight and a bulk density of more than 300 g/l, c) introducing the pulverulent sodium silicate according to b) into an obliquely arranged rotary kiln being fitted with devices for moving solids, said rotary kiln showing a low heat transfer through its wall because of its good insulation causing an outside wall temperature of the rotary kiln of less than 60° C. with the resultant counteraction to the sticking tendency of the sodium silicate, and treating said pulverulent sodium silicate in said rotary kiln with flue gas in counter-current at temperatures from 250° to 500° C. for 1 to 60 minutes, d) exhausting the exit gas from the rotary kiln in the central region thereof and in the region of the end where the pulverulent amorphous sodium silicate having a water content of 15 to 23% by weight is introduced, purifying said exit gas by means of a dry dust filter, and admixing the sodium silicate taken from the dry dust filter, and admixing the sodium silicate taken from the dry dust filter to the pulverulent amorphous sodium silicate destined to be introduced into the rotary kiln with the resultant increase of the throughput of sodium silicate. through the rotary kiln per unit of time, e) communiting the amorphous sodium silicate emerging from the rotary kiln by means of a mechanical crusher to grain sizes of 0.1 to 12 mm, and f) grinding the comminuted sodium silicate by means of a mill to grain sizes of 2 to 400 μm.