Method of recovering non-ferrous metal values

Claim 1

IN A METHOD OF METAL RECOVERY INVOLVING ROASTING A METAL-SULFIDE-CONTAINING ORE, SUBJECTING THE CALCINE TO OXIDATION-LEACHING WITH AN AQUEOUS SULFURIC ACID-LIQUOR IN THE PRESENCE OF OXYGEN AND RECOVERING METAL FROM THE LEACH LIQUOR, THE IMPROVED METHOD OF PRECONCENTRATING THE NONFERROUS METAL VALUES FROM A HIGH-SULFUR-CONTENT METAL-SULFIDE ORE, CONTAINING FERROUS AND NON-FERROUS METAL VALUES, WHICH COMPRISES: DETERMINING, FROM THE SULFUR AND NON-FERROUS AND FERROUS CONTENTS AND RATIOS, THE SULFUR CONTENT FOR A CONCENTRATE OF THE ORE LOWER THAN ITS INITIAL CONTENT WHICH WILL FURNISH ON OXIDATION TO SULFATE SUFFICIENT HEAT TO MAINTAIN THE OXIDATION-LEACHING REACTION RATE AND WILL, WITH ANY AVAILABLE SULFUR IN THE LEACH LIQUOR, PROVIDE AT LEAST STOICHIOMETRIC EQUIVALENTS OF SULFUR TO METAL SULFATES OF THE NON-FERROUS METAL VALUES; ROASTING AT LEAST A PART OF THE ORE UNDER TEMPERATURE AND RATE CONDITIONS OPTIMUM FOR EFFICIENT SULFUR REMOVAL; STOPPING THE ROASTING AT A RESIDUAL SULFUR CONTENT OF FROM ABOUT 70% OF SAID STOICHIOMETRIC REQUIREMENTS TO NOT MORE THAN THAT WHICH WILL PRODUCE ABOUT 10% FREE SULFURIC ACID IN THE LIQUOR AFTER LEACHING; LEACHING THE SO-TREATED MATERIAL AT FROM ABOUT 250* TO ABOUT 650* F. UNDER AN O2 PARTIAL PRESSURE OF 50-300 POUNDS PER SQUARE INCH GAUGE OF OXYGEN, WHEREBY SUBSTANTIALLY ALL THE OXIDIZABLE SULFUR IS CONVERTED TO SULFATE IONS IN A LOW IRON-CONTENT LIQUOR CONTAINING SULFURIC ACID AND A DISSOLVED PRECONCENTRATE OF NONFERROUS METAL VALUES AS SULFATES.