GB848933A - Alkaline earth metal silicates and method for their treatment - Google Patents

Abstract

A finely-divided amorphous alkaline earth metal silicate e.g calcium silicate having a surface area of 20-70 sq.m/g. may be obtained in the form of non-dusting water dispersable pellets, having a bulk density of at least 16 lbs./cu.ft. suitable for use in pigmenting paper, by tumbling in a container e.g. a rotatable cylindrical drum, at least half full, preferably 50-75% full, of said silicate. Tumbling may alternatively be obtained by a rocking or gentle shaking motion. The bulk density of the initial material is normally from 9-14 lbs./cu.ft., and it may be prepared by reacting sodium silicate and 5-30% in excess of the stoichiometric amount of an alkaline earth metal chloride with gentle agitation under such conditions that the solutions are distributed throughout the reaction medium: in an example calcium silicate was prepared by admitting a plurality of streams of sodium silicate solution on to the surface of the reaction mixture in a tank into which the calcium silicate was introduced from below. Air was passed into the tank to provide the desired agitation. The so-formed slurry was removed, washed, filtered and dried to produce a calcium silicate of surface area 32-36 sq.m/g. and having a formula CaO.(SiO2)x where x = 3.1-4.75 depending on reaction conditions. This material was charged into a rotary drum containing baffles parallel to the axis to facilitate tumbling, and rotated. Pellets were formed and increased in bulk density as the rotation was continued until a final bulk density of 23.4 lbs./cu.ft was attained: in another example a bulk density of 26.3 lbs./cu.ft. was obtained.