4. A zinc concentrate analyzing 60% ZnS, 10% PbS, 2% CdS, 6% FeS, 2% FeS2, 10% SiO2, and 10% H2O is roasted in a fluid-bed roaster. The roasted product contains CdO, Fe2O3, PbO, PbSO4, SiO2, ZnO, and ZnO-Fe2O3. Assuming lead is evenly distributed between PbO and PbSO4, find: a) The theoretical air requirement. b) The volume (in m³ at STP) and composition of the off-gases when air 15% (by volume) in excess of the theoretical requirement is used. c) The volume (in m³ at STP) and composition of the off-gases when oxygen- enriched (28% O2 by volume) air 10% (by volume) in excess of the theoretical requirement is used. Hint: This problem is probably easiest to complete using an Excel spreadsheet.