Production of gases containing sulfur dioxide

Claim 1

IN A FLUIDIZED BED PROCESS FOR ROASTING SULFIDIC IRON ORE CONTAINING LEAD AND AT LEAST ONE OF THE ELEMENTS ARSENIC AND ANTIMONY WITH A GAS CONTAINING FREE OXYGEN TO PRODUCE SULFUR DIOXIDE BY CARRYING OUT THE ROASTING IN THREE SUCCESSIVE SEPARATE FLUIDIZED BED ROASTING STAGES, THE GAS CONTAINING FREE OXYGEN BEING SUPPLIED AS FRESH GAS TO SAID STAGES SEPARATELY TO EACH STAGE AND THE ROASTER GAS FORMED IN SAID STAGES BEING WITHDRAWN SEPARATELY FROM EACH STAGE AND THE SOLID PARTICLES IN EACH STAGE BEING PREVENTED FROM ENTERING A PRECEDING STAGE, THE IMPROVEMENT FOR PRODUCING COMPLETELY ROASTED SOLID RESIDUE SUBSTANTIALLY FREE OF SAID LEAD, ARESENIC AND ANTIMONY WHICH COMPRISES; SUPPLYING TO EACH OF SAID STAGES APPROXIMATELY ONE THIRD OF THE TOTAL AMOUNT OF SAID GAS CONTAINING FREE OXYGEN BEING SUPPLIED FOR THE ROASTING, THE AMOUNT OF FREE OXYGEN SUPPLIED TO THE THIRD FLUIDIZED BED BEING IN AN EXCESS OF 10% UP TO 50% OF THE AMOUNT THEORETICALLY REQUIRED FOR COMPLETE ROASTING, MAINTAINING A SULFIDE SULFUR CONTENT OF 38 TO 26% BY WEIGHT IN THE FIRST STAGE AND A SULFIDE SULFUR CONTENT OF 19 TO 10% BY WEIGHT IN THE SECOND STAGE AND MAINTAINING A TEMPERATURE OF ABOUT 550* TO 800*C. IN THE FIRST STAGE, A TEMPERATURE OF AT LEAST 800* UP TO 1,000*C. IN THE SECOND STAGE AND A TEMPERATURE OF ABOUT 550* TO 800*C. IN THE THIRD STAGE.