Carbothermic reduction of zinc sulfide in the presence of sodium carbonate

The carbothermic reduction of zinc sulfide in the presence of sodium carbonate has been studied using X-ray diffractometry (XRD), thermogravimetric analysis system (TGA), atomic absorption spectrometry (AAS), inductively coupled plasma-mass spectrometry (ICP-MS), elemental analyzer (EA) and scanning electron microscopy (SEM). Experimental results of AAS indicated that the reduction in the presence of sodium carbonate proceeded significantly faster than in the presence of calcium carbonate and its sulfur fixation efficiency was acceptable. The results of XRD revealed that zinc sulfide was first transformed from β-type to α-type, then reduced to zinc vapor. The sequence of the variation of sodium containing material was found to be

. A reaction mechanism is proposed to interpret the overall reaction. Results of kinetic study indicated that the rate of reduction could be increased by increasing the reaction temperature, the initial molar ratio of C/ZnS, or the initial molar ratio of Na₂CO₃/ZnS. The rate was also found to be increased with a decrease in sample height, size of C aggregate, size of Na₂CO₃ aggregate or the initial bulk density. The reduction rate, however, was found not to be influenced by the argon flow rate. An empirical expression of the initial rate of zinc yield has been determined.