Production of alumina

Claim 2

IN A PROCESS FOR THE OF SILICA-CONTAINING ALUMINOUS RAW MATERIAL TO PRODUCE ALUMINA, INCLUDING THE STEPS OF EXTRACTING THE RAW MATERIAL WITH NITRIC ACID TO PROVIDE AN ACID EXTRACT CONTAINING ALUMINUM NITRATE, THEN RECOVERING AND DECOMPOSING THE ALUMINUM NITRATE TO FORM ALUMNA, THE IMPORVEMENT WHICH COMPRISES CALCINING THE ALUMINOUS RAW MATERIAL IN THE TEMPERATURE RANGE FORM ABOUT 650*C. TO ABOUT 850*C.; EXTRACTING THE CALCINED MATERIAL WITH ABOUT THE STOICHIOMETRICAL AMOUNT OF NITRIC ACID NEEDED TO DISSOLVE THE ALUMINA PRESENT IN SAID MATERIAL, AT TEMPERATURE CORRESPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SAID ACID HAVING A CONCENTRATION BETWEEN ABOUT 46% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE EXTRACTION OF SILICA FROM THE MATERIAL; SEPARATING THE ACID EXTRACT CONTAINING ALUMINA AS ALUMINUM NITRATE FROM THE ACID INSOLUBLE RESIDUE, WASHING SAID RESIDUE WITH WATER, CONCENTRATING THE WATER WASHINGS TO A CONCENTRATION ABOUT EQUAL TO THAT OF THE NITRIC ACID USED FOR EXTRACTION, AND RECYCLING THIS CONCENTRATE TO THE ORIGINAL EXTRACTION STEP.

Claim 3

PROCESS FOR THE PRODUCTION OF ALUMINA HAVING A SILICA CONTENT NO GREATER THAN 0.02% SILICA BY WEIGHT AND AN IRON CONTENT NO GREATER THAN 0.03% FE2O3 BY WEIGHT FROM A SILICA-AND IRON-CONTAINING ALUMINOUS RAW MATERIAL, COMPRISING THE STEPS OF PELLETIZING SAID RAW MATERIAL AND CALCINING THE PELLETS IN THE TEMPERATURE RANGE FROM ABOUT 650* TO ABOUT 850*C., EXTRACTING THE CALCINED MATERIAL WITH ABOUT THE STOICHIOMETRICAL AMOUNT OF NITRIC ACID NEEDED TO DISSOLVE THE ALUMINA PRESENT IN SAID MATERIAL, AT A TEMPERATURE CORREPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SAID ACID HAVING A CONCENTRATION BETWEEN 46% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE EXTRACTION OF SILICA FROM THE MATERIAL, SEPARATING THE ACID EXTRACT CONCENTRATING THE WATER WASHINGS TO A CONCENTRATION ABOUT EQUAL TO THAT OF THE NITRIC ACID USED FOR EXTRACTION AND RECYCLING THIS CONCENTRATE TO THE ORIGINAL EXTRACTION STEP, EXTRACTING SAID NITRIC ACID SOLUTION WITH AN ORGANIC EXTRACTANT COMPRISING A SOLUTION IN AN ALIPHATIC HYDROCARBON SOLVENT OF A DI-LOWER-ALKYL ESTER OF ORTHOPHOSPHORIC ACID CAPABLE OF FORMING A COMPLEX WITH THE IRON PRESENT, SEPARATING THE RESULTING IRON COMPLEX SOLUTION, RECOVERING THE ALUMINUM NITRATE IN THE EXTRACTED ALUMINUM NITRATE SOLUTION, AND DECOMPOSING THE ALUMINUM NITRATE TO FORM ALUMINA.

Claim 4

PROCESS FOR THE PRODUCTION OF ALUMINA HAVING A SILICA CONTENT NO GREATER THAN 0.02% SILICA BY WEIGHT AND AN IRON CONTENT NO GREATER THAN 0.03% FE2O3 BY WEIGHT FROM A SILICA-AND IRON-CONTAINING ALUMINOUS RAW MATERIAL, COMPRISING THE STEPS OF PELLETIZING SAID RAW MATERIAL AND CALCINING THE PELLETS IN THE TEMPERATURE RANGE FROM ABOUT 650* TO ABOUT 850*C., EXTRACTING THE CALCINED MATERIAL WITH ABOUT THE STOICHIOMETRICAL AMOUNT OF NITRIC ACID NEEDED TO DISSOLVE THE ALUMINA PRESENT IN SAID MATERIAL, AT A TEMPERATURE CORREPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SAID ACID HAVING A CONCENTRATION BETWEEN 46% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE EXTRACTION OF SILICA FROM THE MATERIAL, SEPARATING THE ACID EXTRACT CONCENTRATING THE WATER WASHINGS TO A CONCENTRATION ABOUT EQUAL TO THAT OF THE NITRIC ACID USED FOR EXTRACTION AND RECYCLING THIS CONCENTRATE TO THE ORIGINAL EXTRACTION STEP, EXTRACTING SAID NITRIC ACID SOLUTION WITH AN ORGANIC EXTRACTANT COMPRISING A SOLUTION IN AN ALIPHATIC HYDROCARBON SOLVENT OF A DI-LOWER-ALKYL ESTER OF ORTHOPHOSPHORIC ACID CAPABLE OF FORMING A COMPLEX WITH THE IRON PRESENT, SEPARATING THE RESULTING IRON COMPLEX SOLUTION, RECOVERING THE ALUMINUM NITRATE IN THE EXTRACTED ALUMINUM NITRATE SOLUTION, AND DECOMPOSING THE ALUMINUM NITRATE TO FORM ALUMINA.