Structural change of mechanically activated molybdenite and the effect of mechanical activation on molybdenite
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IPING HU, Associate Professor, QIYUAN CHEN, Vice President of Central South University, and Professor, ZHOULAN YIN and PINGMIN ZHANG, Professors, and GUANHUA GUO, Undergraduate Student, are with the Institute of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, People’s Republic of China. Contact e-mail: [email protected] GÜNTER Gottstein, Professor, is with the Institute of Physical Metallurgy and Metal Physics, RWTH Aachen, Germany. Manuscript submitted September 25, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
X-ray diffraction profiles from the milled powders, the degree of structural disorder, the specific granulometric surface area (SG), the measurements pertaining to thermogravimetry, and the elemental sulfur contents of mechanically activated molybdenites were determined as in Reference 16. The morphology analysis of nonactivated and mechanically activated molybdenites was performed using scanning electron microscopy (SEM) with a JSM-5600LV scanning electron microscope (JEOL, Tokyo). The thermogravimetric anaysis (TGA) curves for nonactivated and mechanically activated molybdenites were obtained (shown in Figure 1). The mass loss ratio at 610 K in the TGA curves for different molybdenites is also presented in Table II. Table II shows that the mass loss ratio at 610 K in the TGA curves for different molybdenites occurs less apparently with the increased grinding time than that of our previously studied sphalerite[15] and galena.[16] The mechanical activation of the samples in this experiment was performed under inert atmosphere, and almost no elemental sulfur was produced during the mechanical activation of molybdenite. So the chemical reaction of sulfide ores with air during mechanical activation can be neglected. The specific granulometric surface area (SG) of mechanically activated molybdenites (shown in Figure 2) indicates that SG of mechanically activated molybdenite increases gradually with the increased grinding time. X-ray diffraction peaks (002) and (008) for different molybdenites are listed in Figures 3(a) and (b). By analyzing XRD peaks (002) and (008) of nonactivated and mechanically activated molybdenites, the D and values, compared with previously reported results,[14–16] are obtained (Table III), which shows that the decrease of the crystallite sizes (D) and the increase of lattice deformations () for mechanically activated molybdenite occur much less apparently than that for pyrite,[14] sphalerite,[15] and galena[16] at the same grinding time interval. All these results indicate that the mass loss of mechanically activated molybdenite at 610 K in the TGA curves is mainly caused by the increase of surface area with the increased grinding time, which is distinct from our previous investigation of the oxidation behavior of mechanically activated sphalerite[15] and galena.[16] Therefore, nonactivated molybdenite undergoes much less structural distortion during the mechanical activation in inert atmosphere than nonactivated pyrite, sphalerite, and galena
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