Production of finely divided calcium carbonate

Claim 1

IN A PROCESS FOR PRODUCING FINELY DIVIDED CALCIUM CARBONATE IN WHICH A MIXTURE IS FORMED CONSISTING OF AT LEAST ONE ALKALI-METAL CARBONATE AND AT LEAST ONE CALCIUMCARBONATE-CONTAINING MATERIAL; SAID MIXTURE IS MAINTAINED IN THE MOLTEN STATE AT A TEMPERATURE BELOW 900*C. AND ABOVE THE MELTING POINT OF THE MIXTURE FOR A TIME SUFFICIENT FOR THE MELT TO BECOME HOMOGENEOUS; AND THEN THE MELT IS DECANTED INTO AN AQUEOUS QUENCHING MEDIUM IN WHICH THE AMOUNT OF WATER IS INSUFFICIENT TO DISSOLVE AN APPRECIABLE PROPORTION OF THE CALCIUM CARBONATE IN THE MELT BUT IS AT LEAST SUFFICIENT TO DISSOLVE THE ALKALI METAL COMPOUNDS PRESENT; THE IMPROVEMENT WHICH COMPRISES: INCORPORATING IN THE MELT A SILICEOUS MATERIAL OF THE GROUP CONSISTING OF SILICA AND ALKALI-METAL SILICATES IN AN AMOUNT BETWEEN 2% TO 20% BY WEIGHT, BASED ON THE WEIGHT OF THE CALCIUM-CARBONATE-CONTAINING MATERIAL IN THE MIXTURE, BY ADDITION OF SAID SILICEOUS MATERIAL TO THE OTHER MELT-FORMING CONSTITUENTS; WHEREBY THE PARTICLE SIZE OF THE CALCIUM CARBONATE PRECIPITATED BY DECANTING THE MELT INTO THE AQUEOUS QUENCHING MEDIUM IS SUBSTANTIALLY SMALLER THAN THE SIZE OF THE PARTICLES OBTAINED BY CARRYING OUT THE PROCESS WITHOUT THE INTENTIONAL ADDITION OF SILICEOUS MATERIAL IN THE AMOUNTS STATED.