Study of the Reduction of Industrial Grade MoO 3 Powders with CO or CO-CO 2 Gases to Prepare MoO 2
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INTRODUCTION
MOLYBDENUM dioxide (MoO2), a potential Mo source for the direct alloying steelmaking or production of ferromolybdenum processes, has a higher density (6.47 g/cm3) than that of molybdenum trioxide (4.692 g/ cm3);[1,2] the melting point of MoO2 (>2773 K) (> 2500 C)[3] is much higher than that of MoO3 (1068 K) (795 C),[4–7] and it will not sublime at the normal steelmaking temperature (1773 K) (1500 C) and thus will reduce the loss of metal Mo. Additionally, the amount of reducing agent (aluminum, silicon, ferrosilicon, carbon, etc) required to reduce the same amount of Mo into steel is decreased by 1/3 as a result of its reduced oxygen content. The use of MoO2 rather than MoO3 in the production of molybdenum steel would appear to be advantageous.[2] At present, many methods have been proposed for the preparation of MoO2. For example, H2 can be used as a reducing agent for the reduction of MoO3 powders.[8–12] The oxidation of molybdenum sulfide concentrate with water vapor to produce MoO2 has also been proposed.[13–15] A different approach to produce MoO2 involves the mixing stoichiometric amount of powdered
LU WANG, GUO-HUA ZHANG, JING-SONG WANG, and KUO-CHIH CHOU are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, P.R. China. Contact e-mail: [email protected] CHUN-YANG BU is with Jinduicheng Molybdenum Co. Ltd., Xi’an, 710077, P.R. China. Manuscript submitted January 20, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
or pelletized MoS2 and MoO3 in the temperature range of 873 K to 973 K (600 C to 700 C).[2,16] Very recently, the looping sulfide oxidation process was also reported by Lessard et al.[17] In the present study, a new method of producing industrial grade MoO2 powders is developed. Herein, CO or the mixed gases of CO and CO2 are used as the reducing agent. In addition, the phase transitions and morphology evolutions during the reduction processes are also investigated. II.
MATERIALS AND EXPERIMENTAL PROCEDURES
A. Materials Industrial grade molybdenum trioxide powders from Jinduicheng Molybdenum Co. Ltd., which were generated by the oxidation roasting of molybdenite concentrates in air, were used for the experiments. The corresponding chemical compositions are given in Table I. From Table I, it can be seen that the principal component is MoO3, which accounts for about 92.5 mass pct. The other impurities include SiO2 and Fe2O3. Figure 1 shows the XRD pattern and scanning electron micrograph of the industrial grade MoO3. It can be clearly seen that the main peaks are well defined to be MoO3 and the particle morphology is layer or platelet-shaped.[18] B. Experimental Procedures In order to monitor the weight loss continuously during the reduction process, a thermal analysis system
Table I. Chemical Compositions of Industrial Grade Molybdenum Trioxide Powders Obtained by X-ray Fluorescence Analysis (XRF) Compositions
MoO3
SiO2
Fe2O3
Al2O3
CaO
K2O
Mass (pct)
92.47
3.24
2.03
0.7
0.4
0.35
Compositions
MgO
PbO
CuO
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