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Kinetic Studies on Evaporation of Liquid Vanadium Oxide, VOx (Where x = 4 or 5)
YANG YANG, LIDONG TENG, and SESHADRI SEETHARAMAN
As part of the Swedish National Eco-steel project, the present work was carried out with a view to study the evaporation of vanadium as V2O5 with a focus on the health hazards. The evaporation rate was followed by monitoring the mass loss from liquid V2O5 melts by thermogravimetric analysis (TGA) in the temperature range 1723 K to 1873 K (1450 C to 1600 C). The studies were carried out under three dierent oxygen partial pressures, viz, oxygen, air, or CO2. The experiments were carried out in the isothermal mode. The Arrhenius activation energies for the evaporation reaction in dierent atmospheres were calculated from the results.
A mathematical model was developed in order to describe the kinetics of the evaporation process. Good agreement could be achieved between the mathematical model and the experimental results. Evaporation coecients and enthalpies in dierent atmospheres were also estimated. The present results may also have implications in recovering vanadium values from dierent vanadium sources.
DOI: 10.1007/s11663-012-9742-3 The Minerals, Metals & Materials Society and ASM International 2012
I. INTRODUCTION
VANADIUM occurs as V2O5 in dierent minerals containing up to nearly 30 pct of this oxide. It is also associated with the Swedish magnetite ores containing up to 1.4 wt pct V2O5. The literature[1] shows that V2O5 has a relatively low melting point, 943 K (670 C). This would imply that there may be a risk of vaporization of V2O5 while roasting the ores, with consequent impact on the biosphere. Wang et al.[2] observed, in their thermogravimetric studies of the oxidation of Fe-V alloys, an incubation period at the start of the oxidation reaction, which these authors attributed to the evaporation of vanadium oxide. To the knowledge of the present authors, no systematic investigation of the volatilization of the oxide of vanadium has been carried out so far.
The V-O phase diagram[3] presents the dierent valence states of vanadium exhibited in its oxides. The stability of these as a function of oxygen partial pressure is presented in Figure 1. As can be seen, pure V2O5 is
stable at higher oxygen pressures. In silicate melts, vanadium has been reported to exhibit dierent...