GB855014A - Method of forming alkaline earth metal silicates - Google Patents

Abstract

Hydrated alkaline earth metal silicates are prepared by reacting a water-soluble alkaline earth metal salt and a water-soluble alkali metal silicate in an aqueous medium whilst maintaining in the reaction medium substantially throughout the reaction, an amount of the alkaline earth metal salt 0.4-5% mole in excess of that required to neutralise the alkali metal oxide content of the alkali metal silicate. The products have a surface area of 5-20 sq.m./g. and are in the form of flocs of size 0.5-10 microns made up of particles of size below 1 micron, usually 0.1-0.3 microns; they are amorphous and have a bulk density of 10-18 lbs./cu.ft.; free and bound water are each present to the extent of 2-10% wt. Specified alkaline earth metal salts are calcium, barium and strontium chlorides and strontium nitrate; specified alkali metal silicates are sodium and potassium silicates and generally contain at least 2 mols, e.g. 2.5-4.5 mols, SiO2 per mol of Na2O. In the examples, a solution containing 100 g./l. of calcium chloride was introduced into the bottom of a rubber-lined tank and a solution containing 100 g./l. of silica as sodium silicate was introduced through a horizontal multiple stream distributer spanning the top of the tank, and agitation was performed by aeration. Product slurry was continuously removed, calcium chloride added thereto to facilitate settling (as described and claimed in Specification 855,015), and the slurry washed with water at 105 DEG C., filtered, dried and milled.