Influences of Different Components on Agglomeration Behavior of MoS 2 During Oxidation Roasting Process in Air
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MOLYBDENITE concentrate (mainly MoS2) is the essential ore mineral of the molybdenum industry for the production of technical-grade molybdenum trioxide (MoO3), molybdenum dioxide (MoO2), molybdenum, ferromolybdenum (FeMo) alloy, and other pure molybdenum compounds.[1,2] At present, the oxidation roasting of molybdenite concentrate has been commercially carried out in multiple hearth furnaces or fluidized bed furnaces. Many chemical reactions take place in the roasting processes. However, the main reaction is shown as follows: MoS2 þ 3:5O2 ¼ MoO3 þ 2SO2
½1
[3–10]
Much research has been done to investigate the mechanisms and kinetics of the oxidation roasting process of molybdenite concentrate. Wilkomirsky et al.[5] studied the reaction of oxygen with molybdenite in a recirculating fluidized bed under batch conditions and found that the growth of MoO3 crystals seemed to be a vaporization–condensation mechanism. Reza et al.[6] did a lot of research on the mechanochemical effects on the molybdenite roasting kinetics by conducting nonisothermal thermogravimetry–differential thermal analysis (TG–DTA) experiments, the results of which showed that the reaction mechanism for
LU WANG, Doctoral Student, GUO-HUA ZHANG, Associate Professor, and JING-SONG WANG and KUO-CHIH CHOU, Professors, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 12, 2015. Article published online May 26, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
nonactivated molybdenite concentrate was determined to be a chemical reaction control, whereas for the activated molybdenite concentrate, the reaction mechanism changed to diffusion control. Utigard[8] conducted a large number of experiments about the oxidation roasting of molybdenite concentrate by using a thermal gravimetric (TG) unit on a small scale both in air and in the oxygen atmosphere. The solid-state reaction between MoS2 and MoO3 to form MoO2 was found to take place. Marin et al.[9] carried out molybdenite concentrate roasting by using small MgO disks with a thin layer of sample in a muffle furnace in air to simulate the reactions taking place in the multiple hearth furnace. A two-step reaction mechanism involving the intermediate phase of MoO2 was proposed ðMoS2 ! MoO2 ! MoO3 Þ. However, some investigators[8–10] found that the agglomeration phenomenon will occur when the roasting temperature is higher, which has led to the agglomerate/melting/glazing of samples. Many difficulties have been experienced in removing the samples from the crucible bottom after reaction. In fact, the agglomeration phenomenon also occurred in the actual multiple hearth furnace or fluidize bed furnace.[11] There are a lot of disadvantages due to the occurrence of agglomeration during the roasting process of molybdenite concentrate in multiple hearth furnace roasters. The molybdenite concentrate cannot be oxidized completely to MoO3, which will lead to the increase of resi
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