Production of finely divided amorphous alumino-silicate pigments from kaolin

Claim 1

The method in accordance with claim 1 wherein the alkaline earth metal hydroxide is selected from the group consisting of calcium hydroxide, strontium hydroxide, barium hydroxide, and radium hydroxide, said method further comprising conducting said hydrothermal treatment at a temperature in the range of from about 100*C to about 180*C for a reaction period of not less than one hour.

Claim 2

A method for producing finely divided, amorphous alumino silicate pigment having increased brightness from a refined kaolin clay pigment produced by the air-flotation process, said method comprising the steps of: forming an aqueous dispersion of a refined kaolin clay pigment having a GE brightness of about 78-80, a particle size range where about 60-70 percent by weight are less than 2 microns and about 10-15 percent by weight are greater than 5 microns and a moisture content of less than about 27 percent, said refined kaolin clay being produced by the dry or air-flotation process; contacting said aqueous dispersion with a hydroxide of a metal having an atomic number greater than 19 and being selected from Group II-a of the Periodic Table; introducing said alkaline earth metal hydroxide into said aqueous dispersion of said refined pigment such that the molar ratio of the said hydroxide to said pigment is at least 1:1; subjecting said dispersion to hydrothermal treatment at a temperature in the range of from about 100*C to 200*C for a period of not less than one hour whereby said refined kaolin clay pigment is converted into an alumino-silicate pigment having a brightness of at least 10 to 12 points higher than that of said refined kaolin clay pigment employed as the starting material, and recovering the resulting product.