Method for producing high grade hematite from nickeliferous iron sulfide ore

Claim 1

A PROCESS FOR PRODUCING HIGH-GRADE HEMATITE OR IRON OXIDE FROM SULFIDE MINERAL MATERIAL CONTAINING NICKELIFEROUS PYRRHOTITE AND A SMALL AMOUNT OF AT LEAST ONE OTHER METAL-SULFIDE MINERAL, WITH NICKEL CONSTITUTING AT LEAST ABOUT 1% OF THE TOTAL SULFIDE CONTENT OF THE MINERAL MATERIAL, THE BALANCE OF THE MINERAL MATERIAL BEING MAINLY SILICEOUS GANGUE, WHICH COMPRISES SUBJECTING SAID SULFIDE ORE TO A SERIES OF COMMINUTION AND CONCENTRATION OPERATIONS TO OBTAIN A FINELY-DIVIDED, CLEAN, NICKELIFEROUS PYRRHOTITE CONCENTRATE CONTAINING NOT MORE THAN ABOUT 0.85% NICKEL, NOT MORE THAN ABOUT 0.1% COPPER, LESS THAN ABOUT 2.5% SILICA AND LESS THAN ABOUT 2.5% TOTAL ALUMINA, LIME AND MAGNESIA; SUSPENSION ROASTING SAID PYRRHOTITE CONCENTRATE IN AN OXIDIZING ATMOSPHERE AT A TEMPERATURRE NOT LESS THAN ABOVE 1200* F. AND BELOW ABOUT 1400* F. TO PRODUCE AN ACTIVE, PERMEABLE, LOW-SULFUR CALCINE; MIXING SAID CALCINE WITH MORE THAN ABOUT 2% AND LESS THAN ABOUT 8% BY WEIGHT OF SODIUM SULFATE; SUBJECT ING THE MIXTURE OF CALCINE AND SODIUM SULFATE TO A SUL-