Nitric acid leaching process

Claim 1

IN A PROCESS FOR PRODUCTION OF FERRIC OXIDE FROM NON-SULFIDE IRON BEARING MATERIAL WHICH CONTAINS A SMALLER AMOUNT OF NON-FERROUS METAL VALUES IN WHICH THE IRON BEARING MATERIAL IS LEACHED WITH NITRIC ACID LEACH SOLUTION AT A TEMPERATURE BELOW ABOUT 250*C., UNDISSOLVED RESIDUE IS SEPARATED FROM THE LEACH SOLUTION, CLARIFIED LEACH SOLUTION IS HEATED AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 50*C. TO ABOUT 230*C. TO PRECIPITATE DISSOLVED IRON VALUED AS FERRIC OXIDE, AND PRECIPITATED FERRIC OXIDE IS SEPARATED FROM THE SOLUTION, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF HEATING THE CLARIFIED IRON BEARING LEACH SOLUTION AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 50*C. TO ABOUT 250*C. UNDER A PARTIAL PRESSURE OF OXYGEN ABOVE ABOUT 50 POUNDS PER SQUARE INCH TO PRECIPITATE FROM THESOLUTION DISSOLVED IRON VALUES AS FERRIC OXIDE, TERMINATING THE HEATING STEP AT A MOL RATIO OF DISSOLVED IRON VALUES TO DISSOLVED NONFERROUS METAL VALUES GREATER THAN ABOUT 1:1 WHEREBY FERFIC OXIDE SUBSTANTIALLY FREE FROM IMPURITIES IS PRECIPITATED FROM THE SOLUTION, SEPARATING PRECIPITATED FERRIC OXIDE FROM THE SOLUTION SUBSTANTIALLY FREE FROM NON-FERROUS METAL VALUES, AND RECYCLING AT LEAST A PORTION OF THE RESIDUAL IRON BEARING SOLUTION TO THE LEACHING STEP OF THE PROCESS.