Production of silica-free alumina

Claim 1

THE PROCESS OF PRODUCING SILICA-FREE ALUMINA FROM AN ALUMINIFEROUS RAW MATERIAL CONTAINING IRON AND ONLY A VERY SMALL AMOUNT OF SILICA RELATIVE TO THE AMOUNT OF ALUMINA WHICH COMPRISES PREPARING A MIXTURE OF THE ALUMINIFEROUS MATERIAL AND SUFFICIENT SODIUM CARBONATE TO FORM SODIUM ALUMINATE WITH THE ALUMINA THEREIN, INCORPORATING IN SAID MIXTURE AN AMOUNT OF LIME GREATLY IN EXCESS OF THE AMOUNT REQUIRED TO FORM DICALCIUM SILICATE WITH THE SILICA THEREIN, SINTERING THE MIXTURE AT A TEMPERATURE ABOVE ABOUT 1700*F., THEREBY CONVERTING ALL THE SILICA AND AN EQUIVALENT PORTION OF THE ALUMINUM CALCIUM ALUMINUM SILICATE WHICH IS SUBSTANTIALLY COMPLETELY INSOLUBLE IN AN ALKALINE AQUEOUS LEACH SOLUTION AND CONVERTING ESSENTIALLY ALL THE REMAINDER OF THE ALUMINA TO SODIUM ALUMINATE, LEACHING THE SINTERED MIXTURE WITH AN AQUEOUS ALKALINE MEDIUM TO FORM A SODIUM ALUMINATE SOLUTION FREE FROM SILICA AND IRON, AND RECOVERING ALUMINA FROM THE RESULTING LEACH SOLUTION.