Zinc Sulfide concentration contains 50%Zn, 13%Fe, 32%S & 5%SiO2. When 100kg is roasted with air, 85kg of Calcine with 54.4%Zn, 14.1%Fe, 2.7%S & 5.4% SiO2 is obtained. Remaining percentages are assumed to be Oxygen and the flue dust is assumed to have the same composition as the Calcine. The roast gas contains 8 vol. % SO2. Hint: Air may be regarded as containing 21 vol. % of O2 and 79 vol. % of N2