Process for the production of alumina

Claim 2

PROCESS FOR THE TREATMENT OF SILICA-CONTAINING ALUMINOUS RAW MATERIAL TO PRODUCE ALUMINA HAVING A SILICA CONTENT NO GREATER THAN ABOUT 0.02% BY WEIGHT, COMPRISING THE STEPS OF CALCINING AN ALUMINOUS RAW MATERIAL AT A TEMPERATURE BETWEEN ABOUT 650*C. AND ABOUT 850*C., EXTRACTING THE CALCINED MATERIAL WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 46% AND ABOUT 70% HNO3 BY WEIGHT, TO MINIMIZE EXTRACTION OF SILICA THEREFROM AT A TEMPERATURE CORRESPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SEPARATING THE ACID EXTRACT CONTAINING THE ALUMINA AS ALUMNINUM NITRATE FROM THE ACID INSOLUBLE RESIDUE, WASHING SAID RESIDUE WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 50% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE SOLUTION OF SILICA THEREFROM, COMBINING THE ACID WASHINGS WITH THE ORIGINAL ACID EXTRACT, RECOVERING THE ALUMINUM NITRATE IN THE ACIDIC COMBINED EXTRACT AND WASHINGS, AND DECOMPOSING THE ALUMINUM NITRATE TO FORM ALUMINA.

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-CONTAINING ALUMINOUS RAW MATERIAL, COMPRISING THE STEPS OF PELLETIZING SAID RAW MATERIAL AND CALCINING THE PELLETS AT A TEMPERATURE BETWEEN ABOUT 650* AND 850*C., EXTRACTING THE CALCINED MATERIAL WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 46% AND ABOUT 70% HNO3 BY WEIGHT, TO MINIMIZE EXTRACTION OF SILICA THEREFROM AT A TEMPERATURE CORRESPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SEPARATING THE ACID EXTRACT CONTAINING THE ALUMINA AS ALUMINUM NITRATE FROM THE ACID INSOLUBLE RESIDUE, WASHING SAID RESIDUE WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 50% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE SOLUTION OF SILICA THERFROM, COMBINING THE ACID WASHINGS WITH THE ORIGINAL ACID EXTRACT, EXTRACTING SAID ACIDIC COMBINED WASHINGS AND NITRIC ACID SOLUTION WITH A SOLUTION IN AN ORGANIC SOLVENT OF A LOW DIALKYL ESTER OF ORTHOPHOSPHORIC ACID CAPABLE OF FORMING A COMPLEX WITH THE IRON PRESENT, SEPARATING THE 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-CONTAINING ALUMINOUS RAW MATERIAL, COMPRISING THE STEPS OF PELLETIZING SAID RAW MATERIAL AND CALCINING THE PELLETS AT A TEMPERATURE BETWEEN ABOUT 650* AND 850*C., EXTRACTING THE CALCINED MATERIAL WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 46% AND ABOUT 70% HNO3 BY WEIGHT, TO MINIMIZE EXTRACTION OF SILICA THEREFROM AT A TEMPERATURE CORRESPONDING TO THE BOILING RANGE OF THE NITRIC ACID AT THE PRESSURE USED FOR DIGESTION, SEPARATING THE ACID EXTRACT CONTAINING THE ALUMINA AS ALUMINUM NITRATE FROM THE ACID INSOLUBLE RESIDUE, WASHING SAID RESIDUE WITH NITRIC ACID HAVING A CONCENTRATION BETWEEN ABOUT 50% AND ABOUT 70% HNO3 BY WEIGHT TO MINIMIZE SOLUTION OF SILICA THERFROM, COMBINING THE ACID WASHINGS WITH THE ORIGINAL ACID EXTRACT, EXTRACTING SAID ACIDIC COMBINED WASHINGS AND NITRIC ACID SOLUTION WITH A SOLUTION IN AN ORGANIC SOLVENT OF A LOW DIALKYL ESTER OF ORTHOPHOSPHORIC ACID CAPABLE OF FORMING A COMPLEX WITH THE IRON PRESENT, SEPARATING THE IRON COMPLEX SOLUTION, RECOVERING THE ALUMINUM NITRATE IN THE EXTRACTED ALUMINUM NITRATE SOLUTION, AND DECOMPOSING THE ALUMINUM NITRATE TO FORM ALUMINA.