Kinetics and mechanism of oxidation of a concentrate of spfalerite

The oxidation of sphalerite (ZnS) concentrate by gaseous oxygen was carried out by means of thermogravimetric analysis (TGA). The products of oxidation were analyzed by X-ray diffractometry and microscopy electronic scanning (MEV/EDS) and the formation of zinc sulphate was detected during the oxidation process. The pyrite present on concentrate was roasted at lower temperature than sphalerite and the mechanism of oxidation was in agreement with the mechanism proposed by Dunn J. G. et. al. (1989). The kinetics of sphalerite oxidation was evaluated by mean of Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) and nonlinear (MNL) isoconversional method and the results suggest that the oxidation process follow a complex mechanism. The values of activation energy founded were higher than 40kJ/mol at full range of conversion and suggest that the controlling step takes place via chemical reaction. (author)