Abstract:The direct carbothermic reduction of marmatite in the presence of lime was studied by thermogravimetric method to determine the technical feasibility to produce Zn(g) without polluting with SO₂(g). X-ray diffraction analysis of partially reacted samples indicated that the reduction occurred through the formation of ZnCaOS and Ca₂Fe₂O₅ as intermediate products to yield Zn(g), and solid Fe and CaS as the final products. Temperature had the major effect on the rate of reduction. Complete conversion of marmatite was obtained at 1100 °C in about 10 min using 300 mg samples with molar ratio of (Zn,Fe)S:CaO:C equal to 1:1:1. The kinetics of the overall reduction reaction was analyzed by the model ln(1-X)=-kt, which represented the data well up to a fractional conversion of 0.95 in the temperature range of 1000-1150 °C. The determined activation energy in this temperature range was 257 kJ/mol. The results demonstrated the technical feasibility to produce Zn(g) by this method without producing noxious SO₂(g) emissions.

Key words: kinetics; marmatite; high-iron sphalerite; carbothermic reduction; direct reduction; ZnCaOS