| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 93 === Carbothermic reduction of zinc sulfide in the presence of lithium carbonate and calcium oxide was carried out in a thermogravimetic analysis system (TGA). Solid sample before and after reaction were analyzed by an X-ray diffractometer (XRD), an atomic absorption spectrometer (AAS), a carbon and sulfur determinator (CSD), an elemental analyzer (EA), a scanning electron microscope (SEM) and a surface area analyzer (SAA).
Experimental results revealed that reaction rate was enhanced about four times in the Li2CO3 catalyzed system. The results of TGA, AAS, CSD and EA were found to be close to each other. The results of SEM indicated that zinc containing grains, carbon grains and the calcium containing grains were covered by a layer of liquid film of lithium carbonate. The results of SAA indicated that the pore surface area and average pore diameter of a solid sample reduced drastically and the pore volume increased rapidly in the initial stage. When the reaction time elapsed, the changes of the pore surface and average pore diameter become mild and the pore volume reduced drastically and then remain unchanged. The effects of reaction temperature on the variations of pore surface area, pore diameter and average pore diameter were similar to that of reaction times.
A mechanism and a model were proposed to interpret this reaction.
The study on the kinetics of the carbothermic reduction was based on the data of the TGA. Experimental results indicated that the reduction rate could not be changed by the variation of argon flow rate. However, it could be increased by the reaction temperature, the initial molar ratio of C/ZnS, the initial molar ratio of CaO/ZnS, or the initial molar ratio of Li2CO3/ZnS and decreasing the sample height, the size of carbon aggregate, or initial bulk density. The effects of the operating variables, excluding the initial molar ratio of Li2CO3/ZnS, on the reaction rate in Li2CO3 catalyzed system were found to be close to those of uncatalyzed system.
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