Method of recovering alumina from alumina-bearing ores

Claim 1

THE PROCESS OF TREATING ALUMINA BEARING ORES AND THE LIKE WHICH COMPRISES THE STEPS OF CRUSHING, GRINDING AND SCREENING THE ORE AND PASSING IT TO A KILN, CALCINING THE SCREENED ORE AT TEMPERATURES BETWEEN 300* C. TO 900* C., ADDING SULPHURIC ACID OF A CONCENTRATION OF AT LEAST 30% TO DIGEST THE CALCINED MATERIAL TO CHANGE AL2O3 TO SOLUBLE AL2(SO4)3, AND THE IRON OR TITAMIUM OXIDES TO SOLUBLE SULPHATES, PASSING THE DIGESTED PRODUCT TO A SECOND CALCINING KILN, TREATING IT AT A TEMPERATURE OF FROM 480* C. TO 770* C. TO DRIVE OFF EXCESS H2SO4 AND SO3 TO CHANGE FE2(SO4)3 TO INSOLUBLE FE2O3, ADDING WATER AND HEATING TO DISSOLVE ALL AL2(SO4)3, K2SO4 AND NA2SO4, REMOVING THE INSOLUBLE RESIDUE, EVAPORATING THE SOLUBLE PARTS TO A SOLID MASS AS CRYSTALS OR POWDER, PASSING THE SOLUBLE PARTS TO A THIRD KILN, HEATING IT TO A TEMPERATURE ABOVE 770* C. TO DRIVE OFF ALL SO3 TO CHANGE AL2(SO4)3 TO INSOLUBLE AL2O3, ADDING WATER TO LEACH OUT K2SO4, NA2SO4 AND TI2(SO4)3 IF PRESENT, AND REMOVING THE INSOLUBLE AL2O3.